JP4385714B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming apparatus capable of recording an image on both sides of an image recording sheet, and particularly, when the image recording areas respectively formed on both sides of the sheet are viewed from a direction perpendicular to the sheet surface. The present invention relates to an image forming apparatus that can be easily made.
The present invention can be applied to an image forming apparatus such as an electrophotographic copying machine, a FAX (facsimile), a printer, or an ink jet type image forming apparatus.

There are various sizes of sheets for image recording. The image recordable range when an image is recorded on the surface of the sheet is different for each sheet size, and is different for each type of image forming apparatus.
Further, in a general image forming apparatus capable of recording images on both sides of a sheet, the image recorded on the first side is reversed and then the image is recorded on the second side.

As a general image forming apparatus capable of recording images on both sides of the sheet, an electrophotographic image forming apparatus is conventionally known. Conventionally known electrophotographic image forming apparatuses having the following structural requirements (B01) to (B06) are known.
(B01) A sheet feeding device for feeding a sheet stored in a sheet feeding tray to a registration roller,
(B02) The registration roller that temporarily stops the conveyed sheet front end portion to form a loop at the sheet front end portion and then conveys the sheet to an image recording position (transfer position);
(B03) a toner image forming apparatus for forming a toner image in an image recording area having a predetermined width in the width direction of the surface of the rotating image carrier disposed at the image recording position (sheet transfer position);
(B04) a transfer device for transferring a toner image formed on the surface of the image carrier to a sheet passing through the sheet transfer position;
(B05) a fixing device having a pair of fixing rotating members that heat-fix the toner image transferred onto the sheet when the sheet onto which the toner image has been transferred passes through the fixing region;
(B06) In the case of having a sheet reversing path for reversing a sheet that has been image-recorded on the first surface and passed through the fixing area in a direction perpendicular to the normal sheet conveying direction, and performing image recording on both sides of the sheet, A sheet conveying apparatus capable of double-sided recording for retransmitting a sheet reversed on the sheet reversing path to the registration roll.

  In the image forming apparatus for double-sided recording, an image is formed on a first side image recording area having a first side set image recording width in the sheet width direction and a first side set image recording length in the sheet conveying direction on the first side of the sheet, When forming an image on the second side image recording area having the second side set image recording width and the second side set image recording length on the second side of the sheet, the first side image recording area when viewed from the direction perpendicular to the sheet surface In some cases, it may be desirable to arrange the second image recording area and the second image recording area.

  FIG. 9 is an explanatory diagram in the case of recording an image so that the image recording areas on both sides of the sheet overlap. FIG. 9A is an A3SEF sheet (short edge feed, that is, a sheet conveyed with the short side of the A3 sheet as the leading edge) 9B is a diagram illustrating a state in which image recording is performed while passing the transfer area on the A3SEF sheet, and FIG. 9C is a diagram illustrating a state in which image recording is performed on the image recording area on the first surface of the A3SEF sheet. 9D is a diagram showing a state in which the sheet of FIG. 9C is turned upside down, FIG. 9E is a diagram showing a state in which image recording is performed on the second surface while passing the transfer region through the sheet of FIG. 9D, and FIG. FIG. 9G is a diagram illustrating a state in which image recording is performed on the second surface of the sheet in FIG. 9D, and FIG. 9G illustrates that the image recording region S1 on the first surface of the sheet S and the image recording region S2 on the second surface are perpendicular to the paper surface of the sheet S. FIG. 9H is a diagram illustrating a state in which the sheet is displaced in the sheet conveyance direction when viewed from any direction, and FIG. 9H is a diagram illustrating the sheet S on which the first image recording area S1 and the second image recording area S2 of the sheet S are arranged. FIG. 6 is a diagram showing a state where the sheet is displaced in the sheet width direction when viewed from a direction perpendicular to the sheet.

When double-sided image recording is performed using the A3SEF sheet S shown in FIG. 9A, the sheet S is first conveyed to the sheet transfer area (image recording position) Q4 in FIG. 9B in order to record an image on the first side. .
In FIG. 9B, a transfer roller (not shown) is in pressure contact with the lower surface of the cylindrical image carrier PR on which the toner image is formed, and a transfer area Q4 is formed by the pressure contact area. When the sheet S passes through the transfer area Q4, the image on the first surface is recorded within the image recording area S1 having the set image recording width S1a on the first surface of the sheet S.
In FIG. 9C, an image is recorded in the first image recording area S1 (set image recording width S1a, set image recording length S1b) of the sheet S that has passed through the transfer area Q4.

9D, the first surface of the sheet S obtained by inverting the sheet S of FIG. 9C is on the lower side, and the second surface is on the upper side.
In FIG. 9E, the second image (toner image) formed on the surface of the image carrier PR is the second surface of the sheet S when the reverse sheet S whose upper surface is the upper surface passes through the transfer region (image recording position) Q4. Are transferred to the image recording area S2. The image recording width S2a and the image recording length S2b of the image recording area S2 on the second surface are set to the same size as the set image recording width S1a and the image recording length S1b on the first surface.
In FIG. 9F showing a state in which the sheet S has passed the transfer area Q4 (image recording position) and an image is recorded on the second surface, the first image recording area S1 and the second image recording area S2 are the sheets. When viewed from the direction perpendicular to the sheet of S, they are arranged at overlapping positions.

In the case of FIGS. 9G and 9H, when a frame-like image is recorded along the outer periphery of the image recording areas S1 and S2 of the sheet S, the first side and The position of the frame on the second side may appear slightly shifted. Further, when a plurality of sheets on which double-sided images are recorded are bound, the position of the image frame may be shifted in the vertical direction on the left and right pages of the spread page.
In the description of FIG. 9, the case where the toner image formed on the surface of the cylindrical image carrier PR is transferred to the sheet has been described. However, the intermediate transfer belt is formed on the side surface opposite to the side on which the backup roll contacts. The same can be said for the case where the toner image is transferred to the sheet by the secondary transfer roll disposed so as to face the backup roll, and the case where the image is recorded on the sheet by the ink jet recording head.

  FIG. 10 uses an actual image recording apparatus, controls the direction of one end edge in the width direction of the sheet to be constant at the image recording position, and inverts the sheet so that the front and rear ends of the sheet are interchanged, and on both sides of the sheet. FIG. 10A is a diagram illustrating a conventional technique when recording an image, FIG. 10A is a diagram illustrating a sheet stored in a sheet feed tray, and FIG. 10B is a diagram illustrating a state in the middle of conveying a sheet taken out from the sheet feed tray. 10C is a diagram illustrating a state of the sheet passing through the sheet guide and the registration roller, and FIG. 10D is a diagram illustrating a state of the sheet passing through the transfer region (image recording position on the sheet) while the toner image is transferred to the first surface of the sheet. FIG. 10E is a diagram illustrating a state in which the sheet having the toner image on the first surface transferred thereon passes through the fixing region, and FIG. 10F illustrates the sheet having the toner image on the first surface transferred and fixed in the sheet conveyance direction. FIG. 10G is a diagram illustrating a state in which the front and rear ends are reversed, FIG. 10G is a diagram illustrating a state in which the reversed sheet passes through a sheet guide and a registration roller, and FIG. FIG. 10I is a diagram illustrating a state in which a toner image is transferred to both sides of a sheet.

In FIG. 10A showing the sheet S accommodated in a sheet feed tray (not shown), the size of the actual sheet S (refer to the solid line in FIG. 10A) of A3SEF accommodated in the sheet feed tray accommodating the A3SEF sheet is There is an error compared to the size of an ideal A3SEF sheet S ′ (see the dashed line in FIG. 10A). That is, in the case of FIG. 10A, compared to the sheet width (width in the direction perpendicular to the sheet conveyance direction) and sheet length (length in the sheet conveyance direction) of the ideal A3SEF sheet S ′ (see the one-dot chain line) The sheet width and the sheet length of the actual sheet S (see solid line) of A3SEF accommodated in the sheet feeding tray are large. Further, the ideal A3SEF sheet S ′ (see the one-dot chain line) is rectangular, but the actual A3SEF sheet S (see the solid line) accommodated in the paper feed tray is not necessarily rectangular. In the actual sheet S (see solid line) of A3SEF shown in FIG. 10A, the front edge in the sheet conveying direction is inclined.
That is, in the image forming apparatus, the sheet size of the A3SEF sheet stores (recognizes) the ideal sheet size of the A3SEF sheet S ′ (see the one-dot chain line), but the A3SEF sheet that is actually used. The size of S (see solid line) is different from the sheet size recognized by the image forming apparatus (has an error).

When the actual sheet S (see the solid line) of the A3SEF is taken out from the position shown in FIG. 10A (position accommodated in the paper feed tray) and conveyed, it may be conveyed in an inclined manner as shown in FIG. 10B. Many.
When the actual sheet S (refer to the solid line) of the A3SEF passes through the positioning guide SG of FIG. 10C, one of the end edges parallel to the conveying direction of the sheet S is the guide surface of the positioning guide SG. (Refer to the two-dot chain line in FIG. 10C) and positioning. The registration roller Rr that conveys the positioned sheet S to the downstream side as shown by a two-dot chain line in FIG. 10C is configured to be movable in its axial direction. The registration roller Rr moves in the sheet width direction (the axial direction of the registration roller Rr) when conveying the sheet S indicated by the two-dot chain line in FIG. The sheet is conveyed in the sheet width direction by a certain distance from the position of the chain line.
That is, when the leading edge of the sheet S reaches the position of the lead registration sensor SN1 (lead registration position), the sheet S has moved to the solid line position shown in FIG. 10C in the sheet width direction. The moving distance d0 in the sheet width direction when the sheet S in FIG. 10C moves from the two-dot chain line position (the position where one end edge of the sheet contacts the sheet guide SG) to the solid line position is a set value, and image formation Stored in the device. The reason why the sheet S is moved away from the position in contact with the sheet guide SG by the moving distance d0 is that when the sheet S is transported in the transport direction at the position in contact with the sheet guide SG, the sheet S is used for duplex recording. This is to prevent the sheet guide SG from colliding with the end of the guide wall when it is retransmitted after being reversed.

The sheet S in FIG. 10C temporarily stops in a state where the leading edge is detected by the lead registration sensor SN1, and is conveyed downstream in the sheet conveying direction at a predetermined timing. The sheet S conveyed downstream from the position of the solid line in FIG. 10C in the sheet conveying direction is a roll-shaped image carrier PR (see FIG. 10D) on which a toner image is formed, and a transfer roller (see FIG. To the transfer area Q4, which is a pressure contact area.
In FIG. 10D, when the sheet S passes through the transfer area Q4, the image on the first surface is recorded within the range of the image recording area S1 having the set image recording width S1a on the first surface of the sheet S. In FIG. 10D, the actual sheet S is indicated by a solid line, and the ideal sheet S ′ is indicated by a one-dot chain line. The distance d1 between the image recording area S1 on the first surface of the sheet S and the one end edge of the sheet S in FIG. 10D is a set value and is stored in the image forming apparatus. As can be seen from FIGS. 10C and 10D, the distance between the sheet guide SG and the image recording area S1 on the first surface of the sheet S is (d0 + d1). The distance (d0 + d1) is recognized by the image forming apparatus.

In FIG. 10E, the distance from the front edge of the sheet S to the image recording area S1 is e1, and the distance e1 is a set value. When the size of the actual sheet S (see solid line) of A3SEF is an ideal sheet size, the distance between the trailing edge of the sheet S in FIG. 10E and the image recording area S1 is also set to e1. Yes. However, since the actual sheet S (see the solid line) of the A3SEF in FIG. 10E is longer than the ideal sheet S ′ (see the one-dot chain line) in the sheet conveyance direction, the trailing edge of the sheet S in FIG. The distance e1 'between the image recording area S1 and the image recording area S1 is longer than e1.
In FIG. 10E, the toner image (image) transferred to the first surface of the sheet S has a fixing area which is a pressure contact area of a heating roll Fh of the fixing device and a pressure roll (not shown) pressed under the heating roll Fh. It is heat-fixed when passing.
The sheet S heat-fixed by the heating roll Fh in FIG. 10E is inverted so that the front end edge and the rear end edge in the sheet conveying direction are interchanged to be in the state of FIG. 10F. In the state of FIG. 10F, the image area S1 of the first surface of the sheet S is disposed on the lower side and is indicated by a dotted line.

The sheet (first image-recorded sheet) S shown in FIG. 10F is parallel to the conveyance direction of the sheet S when passing through the positioning guide SG of FIG. 10G, as described in FIG. 10C. One end edge of the both end edges comes into contact with the guide surface of the positioning guide SG (see the two-dot chain line in FIG. 10G) for positioning. The registration roller Rr that conveys the sheet S positioned downstream as indicated by a two-dot chain line in FIG. 10G is conveyed in the sheet width direction (axial direction of the registration roller Rr) when conveyed to the downstream lead registration sensor SN1. The sheet S is moved and conveyed in the sheet width direction by a predetermined distance from the position of the two-dot chain line.
That is, the sheet S has moved to the position of the solid line shown in FIG. 10G when the leading edge thereof reaches the position of the lead registration sensor SN1 (lead registration position). The sheet S of FIG. 10G moves in the sheet width direction when the two-dot chain line position (the position where one end edge (the same edge as the first surface) of the sheet S abuts the sheet guide SG) moves to the solid line position. d0 is a set value and is stored in the image forming apparatus.

The sheet S transported downstream from the position of the solid line in FIG. 10G in the sheet transport direction is a roll-shaped image carrier PR (see FIG. 10H) on which a toner image is formed, and a transfer roller (see FIG. 10H). To the transfer area Q4, which is a pressure contact area.
In FIG. 10H, when the sheet S passes through the transfer area Q4, the image on the second side is recorded within the range of the image recording area S2 having the set image recording width S2a on the second side of the sheet S. A distance d2 between the image recording area S2 on the second surface of the sheet S in FIG. 10H and one end edge of the sheet S is a set value and is stored in the image forming apparatus. As can be seen from FIGS. 10G and 10H, the distance between the sheet guide SG and the image recording area S2 on the second surface of the sheet S is (d0 + d2). The distance (d0 + d2) is recognized by the image forming apparatus.

In the case of FIG. 10, one end edge of the sheet S guided by the sheet guide SG at the time of image recording on the first side and the second side is the same end edge, and the same one end edge of the sheet S is the moving distance from the sheet guide SG. It has moved to a position separated by d0. Further, since d1 and d2 are set to the same value (d1 = d2), the distance (d0 + d2) between the one end edge of the sheet S and the second image recording area S2 is the one end edge of the sheet S. Is equal to the distance (d0 + d1) between the first image recording area S1 and the first image recording area S1. That is, (d0 + d2) = (d0 + d1).
Therefore, as shown in FIG. 10I, the first and second image recording areas S1 and S2 of the actual sheet S of A3SEF coincide with each other in the sheet width direction when viewed from the direction perpendicular to the sheet surface.

In FIG. 10I, the distance from the front edge of the sheet S to the image recording area S2 is e2, and the distance e2 is a set value. The distance e2 is set to the same value as the distance e1. That is, e2 = e1. When the size of the actual sheet S (see the solid line) of A3SEF is an ideal sheet size, the distance e2 ′ between the trailing edge of the sheet S and the image recording area S2 in FIG. 10I is also e2 ′ (= e1 = e2). However, since the actual sheet S (see the solid line) of the A3SEF in FIG. 10I is longer than the ideal sheet S ′ (see the one-dot chain line in FIG. 10E) in the sheet conveyance direction, the sheet S in FIG. The distance e2 ′ between the rear end edge and the image recording area S2 is longer than e2 (= e1). That is, since e2 ′> e2, e2 <e1 ′ (see FIG. 10H).
Therefore, as shown in FIG. 10I, the first and second image recording areas S1 and S2 of the actual sheet S of A3SEF do not coincide with each other in the sheet conveying direction when viewed from the direction perpendicular to the sheet surface. is doing.

As can be seen from the description of FIG. 10, when there is an error in the dimensions of the actual sheet S of A3SEF (see the solid line in FIG. 10A) and the ideal sheet S ′ of A3SEF (see the dashed line in FIG. 10A), In the sheet reversing method of FIG. 10 in which the front end and the rear end of the sheet S are switched, the first image recording area S1 and the second image recording area S2 are displaced in the sheet conveying direction.
In the description of FIG. 10, the case where the toner image formed on the surface of the cylindrical image carrier PR is transferred to the sheet has been described. However, the intermediate transfer belt is formed on the side surface opposite to the side on which the backup roll contacts. The same applies to the case where the transferred toner image is transferred onto the sheet by the secondary transfer roll disposed opposite to the backup roll, or when the image is recorded on the sheet by the ink jet recording head.

  FIG. 11 uses an actual image recording apparatus, and inverts the sheet so that the direction of the front end edge of the sheet passing through the image recording position is constant and the front and rear ends of the sheet are reversed, and images are formed on both sides of the sheet. 11A and 11B are explanatory diagrams of the prior art in the case of recording, in which FIG. 11A shows a sheet stored in a paper feed tray, FIG. 11B shows a state in the middle of conveying a sheet taken out from the paper feed tray, and FIG. FIG. 11D is a diagram showing a state in which the sheet is temporarily stopped by the registration roller and the front edge of the sheet is aligned in the registration roller axis direction and then moved in the registration roller axis direction. FIG. FIG. 11E is a diagram illustrating a state of the sheet passing through the image recording position). FIG. 11E is a diagram illustrating a state in which the sheet having the first toner image transferred passes through the fixing region. FIG. 11G is a diagram showing a state in which the toner image on the first surface is transferred and fixed and reversed so that the front and rear ends in the sheet conveyance direction are interchanged. FIG. 11G shows the direction of the front edge of the sheet after the reversed sheet is temporarily stopped by a registration roller FIG. 11H is a diagram illustrating a state in which the reversal sheet is moved in the registration roller axial direction and then moved in the registration roller axial direction, and FIG. 11H illustrates a state in which the toner image is transferred to the second surface while passing through the transfer region (image recording position on the sheet). FIG. 11I is a diagram illustrating a state in which the toner image is transferred to both sides of the sheet.

In FIG. 11A showing the sheets stored in the paper feed tray, the same sheet S ′ as in FIG. 10 is stored in the paper feed tray.
When the actual sheet S (refer to the solid line) of the A3SEF is taken out from the position shown in FIG. 11A (position accommodated in the paper feed tray) and conveyed, it may be conveyed with an inclination as shown in FIG. 11B. Many.

  The actual sheet S of the A3SEF (see the solid line) is temporarily stopped with the front end of the sheet in contact with the registration roller Rr in FIG. 11C, and the front end of the sheet is in the axial direction of the registration roller Rr as indicated by the two-dot chain line in FIG. 11C. Aligned (skew that is the inclination of the front edge of the sheet is corrected). The registration roller Rr that conveys the sheet S in the state indicated by the two-dot chain line in FIG. 11C to the downstream side is configured to be movable in the axial direction thereof. The registration roller Rr moves in the sheet width direction (the axial direction of the registration roller Rr) when the sheet S indicated by the two-dot chain line in FIG. The sheet is conveyed in the sheet width direction from the position of the dotted line to the position where the one end edge of the sheet is detected by the side registration sensor SN2 (the position indicated by the solid line).

  The sheet S indicated by a solid line in FIG. 11C is conveyed while the position in the sheet width direction is controlled in a state where one end edge of the sheet S is detected by the side registration sensor SN2. The leading edge of the sheet S reaches the position (lead registration position) of the lead registration sensor SN1. That is, when the leading edge of the sheet S reaches the position (lead registration position) of the lead registration sensor SN1, one end edge of the sheet S is detected by the side registration sensor SN2.

After the leading edge of the sheet S reaches the position of the lead registration sensor SN1 (lead registration position), the registration roller Rr does not move in the sheet width direction and only rotates for conveying the sheet S. The sheet S conveyed by the registration roller Rr that does not move in the sheet width direction and performs only rotation for conveying the sheet is in an inclined state (attitude) when the front end of the sheet S is inclined, It is transported downstream in the transport direction.
The sheet S conveyed by the registration roller Rr in the inclined state is a roll-shaped image carrier PR (see FIG. 11D) on which the first-side toner image is formed, and a transfer roller (not shown) in pressure contact with the lower surface thereof. To the transfer area Q4 which is the pressure contact area.

  In FIG. 11D, when the inclined sheet S passes through the transfer area Q4, the first image is recorded in the range of the image recording area S1 having the set image recording width S1a for the first surface of the sheet S. In FIG. 11D, the actual sheet S is indicated by a solid line, and the ideal sheet S ′ is indicated by a one-dot chain line. The front end of the first image recording area S1 of the sheet S conveyed in an inclined state in FIG. 11D is parallel to the transfer area Q4, and both ends in the sheet width direction of the image recording area S1 are perpendicular to the transfer area Q4. is there.

In FIG. 11E, the distance from the front edge of the sheet S to the image recording area S1 is e1, and the distance e1 is a set value. When the size of the actual sheet S (see the solid line) of A3SEF is an ideal sheet size, the distance e1 ′ between the trailing edge of the sheet S and the image recording area S1 in FIG. 11E is e1 ′ = e1. Is set to However, the actual sheet S (refer to the solid line) of the A3SEF in FIG. 11E is longer than the ideal sheet S ′ (refer to the alternate long and short dash line) in the sheet conveying direction, and therefore the trailing edge of the sheet S in FIG. The distance e1 'between the image recording area S1 and the image recording area S1 is longer than e1. That is, e1 ′> e1.
Further, as can be seen from FIG. 11E, the actual sheet width of the sheet S is larger than the ideal sheet width of the sheet S ′, so that it is compared with the distance d1 between one edge of the sheet S and the first image recording area S1. Thus, the distance d1 ′ between the other end edge of the sheet S and the image recording area S1 on the first surface is large.

In FIG. 11E, the toner image (image) transferred to the first surface of the sheet S has a fixing area which is a pressure contact area of the heating roll Fh of the fixing device and a pressure roll (not shown) pressed underneath. It is heat-fixed when passing.
The sheet S heat-fixed by the heating roll Fh in FIG. 11E is inverted so that the front edge and the rear edge in the sheet conveyance direction are interchanged, and the state shown in FIG. In the state of FIG. 11F, the image area S1 on the first surface of the sheet S is arranged on the lower side and is indicated by a dotted line.
The sheet (first image-recorded sheet) S shown in FIG. 11F is conveyed to the registration roller Rr in FIG. 11G.

In FIG. 11G, the sheet S (see the two-dot chain line) conveyed to the registration roller Rr is temporarily stopped with its front end in contact with the registration roller Rr, and the direction of the sheet front end is aligned with the axial direction of the registration roller Rr ( The skew that is the inclination of the front edge of the sheet is corrected). The registration roller Rr that conveys the sheet S in the state indicated by the two-dot chain line in FIG. 11G to the downstream side, when conveying the sheet S indicated by the two-dot chain line in FIG. 11G to the lead registration sensor SN1 on the downstream side. The sheet S is transported in the sheet width direction from the position of the two-dot chain line to the position where the one end edge of the sheet is detected by the side registration sensor SN2 (position indicated by the solid line).
The sheet S indicated by a solid line in FIG. 11G is conveyed while its position in the sheet width direction is controlled in a state where one end edge in the width direction of the sheet S is detected by the side registration sensor SN2. Then, the leading edge of the sheet S reaches the position (lead registration position) of the lead registration sensor SN1. That is, when the leading edge of the sheet S reaches the position (lead registration position) of the lead registration sensor SN1, one end edge of the sheet S is detected by the side registration sensor SN2.

After the leading edge of the sheet S reaches the position of the lead registration sensor SN1 (lead registration position), the registration roller Rr does not move in the sheet width direction and only rotates for conveying the sheet S. The sheet S conveyed by the registration roller Rr that does not move in the sheet width direction and performs only rotation for conveying the sheet is in an inclined state (attitude) when the front end of the sheet S is inclined, It is transported downstream in the transport direction.
The sheet S conveyed by the registration roller Rr in the inclined state is a roll-shaped image carrier PR (see FIG. 11H) on which a second-side toner image is formed, and a transfer roller (not shown) that presses the lower surface thereof. To the transfer area Q4 which is the pressure contact area.

In FIG. 11H, when the inclined sheet S passes through the transfer area Q4, the image on the second side is recorded within the range of the image recording area S2 having the set image recording width S2a on the second side of the sheet S. The front end of the second image recording area S2 of the sheet S conveyed in an inclined state in FIG. 11H is parallel to the transfer area Q4, and both ends in the sheet width direction of the image recording area S2 are perpendicular to the transfer area Q4. is there.
The sheet S on which the second image is recorded is heat-fixed as described with reference to FIG. 11E.

In FIG. 11I showing the sheet S on which the image on the second surface is recorded, the distance from the front edge of the sheet S to the image recording area S2 on the second surface is e2, and the distance e2 is a value set to e2 = e1. It is. When the size of the actual sheet S of A3SEF (see the solid line) is an ideal sheet size, the distance between the trailing edge of the sheet S in FIG. 11I and the second image recording area S2 is also e2. Is set. However, since the actual sheet S (see the solid line) of the A3SEF in FIG. 11I is longer than the ideal sheet S ′ (see the one-dot chain line in FIG. 11A) in the sheet conveyance direction, the sheet S in FIG. The distance e2 ′ between the trailing edge and the second image recording area S2 is e2 ′> e2.
11A and 11E, the actual sheet width of the sheet S is larger than the ideal sheet width of the sheet S ′, and therefore, the one edge of the sheet S and the image recording area S2 on the second surface are separated. Compared to the distance d2, the distance d2 'between the other end edge of the sheet S and the image recording area S2 on the second surface is larger.

In FIG. 11I, the distance from the front edge of the sheet S to the image recording area S2 is e2, and e2 = e1. When the size of the actual sheet S of A3SEF (see the solid line) is an ideal sheet size, the distance e2 ′ between the trailing edge of the sheet S in FIG. 11I and the image recording area S2 is e2 ′ (= e2 = e1). However, the actual sheet S (see the solid line) of the A3SEF in FIG. 11I is more than the sheet length (the length in the sheet conveying direction) of the ideal sheet S ′ (see the one-dot chain line in FIGS. 11A and 11E). Since it is long, the distance e2 ′ between the trailing edge of the sheet S in FIG. 11I and the image recording area S2 is e2 ′> e2. Further, as described above, e1 ′> e1.
In FIG. 11I, the positions of e1 ′ and e1 are illustrated as being shifted downward from the positions of e2 and e2 ′, but in fact, e1 ′ (see FIG. 11F) is e2 (see FIG. 11F). 11 (see 11I) and e1 (see FIG. 11F) overlaps e2 ′ (see FIG. 11I).
Therefore, as shown in FIG. 11I, the first and second image recording areas S1 and S2 of the actual sheet S of A3SEF do not coincide with each other in the sheet conveying direction when viewed from the direction perpendicular to the sheet surface. is doing.
As shown in FIG. 11, when the sheet S is not rectangular and the front edge of the sheet is inclined, the image recording areas S1 and S2 on the first and second surfaces of the actual sheet S of A3SEF are on the sheet surface. They are inclined so as to cross each other when viewed from the vertical direction.

As can be seen from the description of FIG. 11, in the case of FIG. 11 (the sheet is reversed so that the direction of the front edge of the sheet conveyance direction is constant at the image recording position and the front and rear edges of the sheet are switched, so that both sides of the sheet are reversed. When recording an image), the image recording areas S1 and S2 on both sides of the sheet do not match when viewed from the direction perpendicular to the sheet surface.
In the description of FIG. 11, the case where the toner image formed on the surface of the cylindrical image carrier PR is transferred to the sheet has been described. However, the intermediate transfer belt is formed on the side surface opposite to the side on which the backup roll abuts. The same applies to the case where the transferred toner image is transferred onto the sheet by the secondary transfer roll disposed opposite to the backup roll, or when the image is recorded on the sheet by the ink jet recording head.

As can be seen from the description of FIGS. 9 to 11, the side edge reference method (in the case of FIG. 10) for adjusting the sheet position with reference to the side edge of the sheet, or the sheet position with reference to the front edge of the sheet. In the front end reference method (in the case of FIG. 11) and the conventional sheet reversal method in which the front and rear ends of the sheet are exchanged, the front and back of the sheet are changed due to actual sheet size variation and shape variation (squareness variation). It was difficult to align the image recording area.
In view of the above-described circumstances, the present invention has the following description (O01) as a problem.
(O01) The image recording area on the first surface and the image recording area on the second surface when images are recorded on both sides of the sheet are overlapped when viewed from the direction perpendicular to the sheet surface.

  Next, the present invention that solves the above-described problems will be described. In order to facilitate the correspondence with the elements of the embodiments described later, the elements of the present invention are shown by enclosing the reference numerals of the elements of the embodiments in parentheses. Appendices. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described later is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(Invention)
In order to solve the above-described problems, an image forming apparatus according to the present invention includes the following structural requirements (A01) to (A05).
(A01) A sheet feeding device (SH1 + Rp + Rs + Ra) for conveying the sheet (S) stored in the sheet feeding trays (TR1 to TR3) to the registration roller (Rr) and the conveyed sheet front end are temporarily stopped to stop the sheet. After the loop is formed at the front end, the registration roller (Rr) that conveys the sheet (S) to the image recording position (Q4) and the sheet (S) on which the image is recorded on the first surface are perpendicular to the normal sheet conveying direction. A sheet reversing path (SH3) that is conveyed and reversed in the direction, and when image recording is performed on both sides of the sheet (S), the sheet (S) that has been reversed by the sheet reversing path (SH3) is transferred to the registration roller ( Sheet transport device (SH) to be retransmitted to Rr),
(A02) A set image recording width (S1a, S2a) set in the sheet width direction on the sheet (S) passing through the image recording position (Q4) and a set image recording length set in the sheet conveyance direction ( An image recording device (UY to UK + BM + T2) for recording an image in a set image area (S1, S2) having S1b, S2b),
(A03) It is arranged between the registration roller (Rr) and the image recording position (Q4), and when the image is recorded on the first surface of the sheet (S), it is located at both end edges in the width direction of the sheet (S). A first-side side registration sensor (SN2) that detects the position of one end edge, and an end edge that is the same as the one end edge in the width direction of the sheet (S) reversed when recording an image on the second side of the sheet (S) Side registration sensor (SN2 + SN3) having a second side registration register (SN3) for detecting the position
(A04) First-side side registration position detection for detecting a first-side side registration position, which is the position of the one edge at the time of image recording on the first side of the sheet (S), according to a detection signal of the first-side side registration sensor (SN2). And a second-side side registration position that is the same edge as the one-end edge during image recording on the second-side image of the sheet (S) reversed according to the detection signal of the second-side side registration sensor (SN3) Side register position detecting means having second side side register position detecting means for performing,
(A05) At the time of image recording of the first surface of the sheet (S), the first image is set in the set image area (S1) at a position separated from the first surface side registration position by the first surface setting distance d1 to the center side of the sheet (S). While recording an image, at the time of recording an image on the second side of the sheet (S), a position separated from the second side side registration position by a second side set distance d2 equal to the first side set distance d1 on the center side of the sheet (S). The image recording apparatus (UY to UK + BM + T2) that records the second image in the set image area (S2).

(Operation of the present invention)
In the image forming apparatus of the present invention having the above-described configuration requirements, the sheet conveying device (SH1 + Rp + Rs + Ra) of the sheet conveying device (SH) receives the sheets (S) accommodated in the sheet feeding trays (TR1 to TR3) as registration rollers. Transport to. The registration roller (Rr) temporarily stops the front end of the sheet conveyed to the lead registration position to form a loop at the front end of the sheet, and then conveys the sheet (S) to the image recording position (transfer position) (Q4). .
The image recording devices (UY to UK + BM + T2) are set in the set image recording width (S1a, S2a) set in the sheet width direction on the sheet (S) passing through the image recording position (Q4) and in the sheet conveying direction. The image is recorded in the set image area (S1, S2) having the set image recording length (S1b, S2b).
The sheet conveying device (SH) has a sheet reversing path (SH3) for conveying and reversing the sheet (S) image-recorded on the first surface in a direction perpendicular to the normal sheet conveying direction, and both sides of the sheet (S). When image recording is performed, the sheet (S) reversed by the sheet reversing path (SH3) is retransmitted to the registration roller (Rr). In the sheet (S) reversed by the sheet reversing path (SH3), the positions of both end edges in the sheet width direction are exchanged (replaced).
The side registration sensor (SN2 + SN3) has a first-side side registration sensor (SN2) and a second-side side registration sensor (SN3) disposed between the registration roller (Rr) and the image recording position (Q4). The first-side side registration sensor (SN2) detects the position of one end edge of both end edges in the width direction of the sheet (S) when an image is recorded on the first surface of the sheet (S). The second side registration sensor (SN3) detects the position of the same edge as the one edge in the width direction of the inverted sheet (S) when an image is recorded on the second surface of the sheet (S).
The side registration position detection means includes a first-side side registration position detection means and a second-side side registration position detection means, and the first-side side registration position detection means has the one end edge at the time of image recording on the first side of the sheet (S). Is detected in accordance with a detection signal of the first-side side registration sensor (SN2). The second-side side registration position detection means uses the second-side side registration position, which is the same edge position as the one edge when recording the second-side image of the sheet (S), as a detection signal of the second-side side registration sensor (SN3). Detect accordingly.
The image recording device (UY to UK + BM + T2) is configured to transfer the sheet (S) from the first side registration position (position of one edge of the sheet (S) at the time of image recording on the first surface) during image recording on the first surface of the sheet (S). ) Is recorded on the set image area (S1) at a position separated by the first surface set distance d1 at the center side of the sheet (S), and the second-side side register position ( The set image area (S2) at a position separated from the center side of the sheet (S) by the second surface setting distance d2 equal to the first surface setting distance d1 from the position of the same edge as the one edge when the second surface image is recorded. ) To record the second image.

Accordingly, the first set image area (S1) and the second set image area (S2) on the sheet (S) are formed from the same edge in the sheet width direction of the sheet (S). Is arranged at a position separated by the set distance (d1, d2, where d1 = d2). For this reason, when viewed from the direction perpendicular to the sheet of the sheet (S), the setting image region (S1) on the first surface and the setting image region (S2) on the second surface are arranged at positions overlapping in the sheet width direction. The
Further, the sheet (S) is conveyed so as to be conveyed in a direction perpendicular to the normal sheet conveying direction, so that both end edges in the width direction of the sheet (S) are reversed (replaced). At the time of image recording, the distance e1 between the front edge of the first image recording area (S1) and the front edge of the sheet and the distance e2 between the front edge of the second image recording area (S2) and the front edge of the sheet are set to the same value (e2 = e1). Accordingly, the setting image region (S1) on the first surface and the setting image region (S2) on the second surface can be formed at the same position from the front edge of the sheet in the sheet conveyance direction, and therefore perpendicular to the paper surface of the sheet (S). When viewed from one direction, the setting image area (S1) on the first side and the setting image area (S2) on the second side can be arranged at positions overlapping in the sheet conveyance direction.
Therefore, for example, when a frame along the outer peripheral edge of the set image area (S2) on the first and second surfaces is recorded as an image, when viewed from a direction perpendicular to the paper surface of the sheet (S), the first surface It can be formed at a position where the frame image and the frame image on the second surface overlap.

(Embodiment 1 of the present invention)
The image forming apparatus according to the first exemplary embodiment of the present invention can include the following configuration requirement (A06) in the image forming apparatus of the present invention.
(A06) The first surface side registration sensor (SN2) and the first surface side registration position set at the same position in the sheet width direction so that one end edge of the sheet (S) passes through the first surface side registration sensor. The sheet conveying device (SH) for conveying a sheet (S) during image recording.
(Operation of Form 1 of the Present Invention)
In the image forming apparatus according to the first exemplary embodiment of the present invention having the configuration requirement (A06), the sheet conveying device (SH) is set at the same position in the sheet width direction as the arrangement position of the first-side side registration sensor (SN2). The sheet (S) at the time of image recording on the first surface is conveyed so that one end edge of the sheet (S) passes through the position registration position on the first surface.
In this case, the set image area (S1) that is separated from the first-side side registration position by the first-side set distance d1 to the center side of the sheet (S) at the time of recording the first-side image of the sheet (S) is the first-side side. It is arranged at a position separated from the position of the registration sensor (SN2) by the first surface set distance d1 on the center side of the sheet (S).
Therefore, the image recording devices (UY to UK + BM + T2) are separated from the first-side side registration sensor (SN2) by the first-side set distance d1 from the first-side side registration sensor (SN2) when recording the first-side image of the sheet (S). The first image is recorded so that the set image area (S1) is arranged at the position.

(Embodiment 2 of the present invention)
An image forming apparatus according to Embodiment 2 of the present invention is characterized in that the image forming apparatus of the present invention has the following structural requirements (A07).
(A07) One end edge of the sheet (S) passes through the first-side side registration position set at a position separated by a distance d0 in the sheet width direction from the arrangement position of the first-side side registration sensor (SN2). The sheet conveying device (SH) for conveying the sheet (S) at the time of image recording on the first surface.
(Operation of Embodiment 2 of the present invention)
In the image forming apparatus according to the second embodiment of the present invention having the configuration requirement (A07), the sheet conveying device (SH) is separated from the arrangement position of the first-side side registration sensor (SN2) by a distance d0 in the sheet width direction. The sheet (S) at the time of image recording on the first side is conveyed so that one end edge of the sheet (S) passes through the side registration position on the first side set at a predetermined position.
In this case, the set image area (S1) separated from the first-side side registration position by the first-side set distance d1 from the first-side side registration position at the time of recording the first-side image of the sheet (S) is the first-side side. The registration sensor (SN2) is disposed at a position separated from the position of the registration sensor (SN2) by a distance (d0 + d1) toward the center of the sheet (S).
Therefore, the image recording devices (UY to UK + BM + T2) are separated from the first-side side registration sensor (SN2) by the distance (d0 + d1) from the first-side side registration sensor (SN2) when recording the first-side image of the sheet (S). The first image is recorded so that the set image area (S1) is arranged at the position.

(Embodiment 3 of the present invention)
The image forming apparatus according to the third embodiment of the present invention is characterized in that the above-described present invention or the image forming apparatus according to the first or second embodiment of the present invention includes the following constituent elements (A08).
(A08) The second surface side registration sensor (SN3) and the second surface side registration position set at the same position in the sheet width direction so that one end edge of the sheet (S) passes through the second surface side registration position. The sheet conveying device (SH) for conveying a sheet (S) during image recording.
(Operation of Form 3 of the Present Invention)
In the image forming apparatus according to the third embodiment of the present invention having the configuration requirement (A08), the sheet conveying device (SH) is set at the same position in the sheet width direction as the arrangement position of the second side registration sensor (SN3). The sheet (S) at the time of image recording on the second side is conveyed so that one end edge of the sheet (S) passes through the second side registration position on the second side.
In this case, when the image of the second side of the sheet (S) is recorded, the set image area (S2) that is separated from the second side side registration position by the second side set distance d2 to the center side of the sheet (S) is the second side It is arranged at a position separated from the position of the registration sensor (SN3) by the second surface set distance d2 on the center side of the sheet (S).
Therefore, the image recording apparatus (UY to UK + BM + T2) is separated from the second side registration sensor (SN3) by the second surface set distance d2 toward the center side of the sheet (S) when recording the second surface image of the sheet (S). The image on the second side is recorded so that the set image area (S2) is arranged at the predetermined position.
By setting the second surface setting distance d2 to d2 = d1 with respect to the first surface setting distance d1, the second surface setting image region (S2) and the first surface setting image region (S1) are set on the sheet surface. It can be overlapped in the sheet width direction when viewed from the vertical direction.

(Embodiment 4)
The image forming apparatus according to Embodiment 4 of the present invention is characterized in that the image forming apparatus according to the present invention or Embodiment 1 or 2 of the present invention has the following structural requirements (A09).
(A09) The one end edge of the sheet (S) passes through the second side registration position set at a position separated by a distance d0 in the sheet width direction from the arrangement position of the second side registration register (SN3). The sheet conveying device (SH) for conveying the sheet (S) at the time of image recording on the second surface.
(Operation of Form 4 of the Present Invention)
In the image forming apparatus according to the fourth embodiment of the present invention having the configuration requirement (A09), the sheet conveying device (SH) is separated from the arrangement position of the second side registration sensor (SN3) by a distance d0 in the sheet width direction. The sheet (S) at the time of image recording on the second side is conveyed so that one end edge of the sheet (S) passes through the side registration position on the second side set at the position.
In this case, when the image of the second side of the sheet (S) is recorded, the set image area (S2) that is separated from the first side side registration position by the second side set distance d2 to the center side of the sheet (S) is the second side The registration sensor (SN3) is disposed at a position separated from the position of the registration sensor (SN3) by a distance (d0 + d2) toward the center of the sheet (S).
Therefore, the image recording devices (UY to UK + BM + T2) are separated from the second side registration sensor (SN3) by the distance (d0 + d2) from the second side registration sensor (SN3) when recording the second side image of the sheet (S). The second image is recorded so that the setting image area (S2) is arranged at the position.
By setting the second surface setting distance d2 to d2 = d1 with respect to the first surface setting distance d1, the second surface setting image region (S2) and the first surface setting image region (S1) are set on the sheet surface. The sheets can be stacked in the sheet (S) width direction as viewed from the vertical direction.

(Embodiment 5)
An image forming apparatus according to a fifth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first and fourth aspects of the present invention includes the following structural requirements (A010) and (A011).
(A010) Sheet width for conveying the sheet (S) in the sheet width direction so that one end edge of the sheet (S) is detected by the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3) Direction conveying member,
(A011) A direction in which the setting image region (S1) on the first surface of the sheet (S) and the setting image region (S2) on the second surface are perpendicular to the paper surface by controlling the operation of the conveying member in the sheet width direction. Sheet width direction position control means for controlling the position of the sheet (S) in the sheet width direction so as to coincide with each other.
(Operation of Form 5 of the Present Invention)
In the image forming apparatus according to the fifth embodiment of the present invention having the structural requirements (A010) and (A011), the sheet width direction conveying member is formed by the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). The sheet (S) is conveyed in the sheet width direction so that one end edge of the sheet (S) is detected.
The sheet width direction position control means controls the operation of the sheet width direction conveying member so that the setting image area (S1) on the first surface of the sheet (S) and the setting image area (S2) on the second surface are located. The position of the sheet (S) in the sheet width direction is controlled so as to match when viewed from the direction perpendicular to the paper surface.

(Embodiment 6 of the present invention)
The image forming apparatus of Embodiment 6 of the present invention is characterized in that the image forming apparatus of Embodiment 5 of the present invention is provided with the following structural requirements (A010 ′) and (A011 ′).
(A010 ′) A registration roller moving device that moves the registration roller (Rr) during sheet conveyance in the sheet width direction in order to adjust the position in the width direction of the sheet (S) at the image recording position (Q4). The sheet width direction conveying member,
(A011 ′) The registration roller (Rr) is placed on the sheet so that the set image area (S1) on the first side of the sheet (S) and the set image area (S2) on the second side match when viewed from the direction perpendicular to the paper. The sheet width direction position control means comprising registration roller movement control means for adjusting the position of the sheet (S) in the width direction at the image recording position (Q4) by moving in the width direction.
(Operation of Embodiment 6 of the present invention)
In the image forming apparatus according to the sixth embodiment of the present invention having the structural requirements (A010 ′) and (A011 ′), the sheet width direction conveying member formed by the registration roller moving device is the image recording position (Q4). In order to adjust the position in the width direction of the sheet (S), the registration roller (Rr) during sheet conveyance is moved in the sheet width direction.
The sheet width direction position control means constituted by the registration roller movement control means is configured so that the first set image area (S1) and the second set image area (S2) of the sheet (S) are viewed from a direction perpendicular to the paper surface. The registration roller (Rr) is moved in the sheet width direction so as to match, thereby adjusting the position in the width direction of the sheet (S) at the image recording position (Q4).

(Embodiment 7 of the present invention)
An image forming apparatus according to a seventh aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first and fourth aspects of the present invention includes the following constituent elements (A012).
(A012) The setting image area (S1) on the first side of the sheet (S) and the setting image area (S2) on the second side match in the sheet width direction of the first side so that they match when viewed from the direction perpendicular to the page. The image recording apparatus (UY to UK + BM + T2) for shifting the set image area recording position in the sheet width direction on the second surface in the sheet width direction with respect to the set image area recording position.
(Operation of Embodiment 7 of the present invention)
In the image forming apparatus according to the seventh embodiment of the present invention having the configuration requirement (A012), the image recording apparatuses (UY to UK + BM + T2) have the setting image area (S1) on the first surface and the setting image on the second surface of the sheet (S). The set image in the sheet width direction on the second side with respect to the recording position of the set image area (S1) in the sheet width direction on the first side so that the area (S2) matches with the direction perpendicular to the page. The recording position of the area (S2) is shifted in the sheet width direction.

(Embodiment 8)
An image forming apparatus according to an eighth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first and seventh aspects of the present invention includes the following structural requirements (A013) to (A015).
(A013) Standard size sheet width storage means for storing the sheet width of the standard size sheet (S) used for the image recording,
(A014) Used sheet fixed size detecting means for detecting a fixed size of the used sheet (S) when the sheet (S) used for the image recording is a fixed size sheet (S);
(A015) The first-side side registration sensor (SN2) and the second-side side registration sensor (SN3) that are spaced apart in the sheet width direction by the sheet width of the standard size to be used.

(Operation of Embodiment 8 of the present invention)
In the image forming apparatus according to the eighth embodiment of the present invention having the configuration requirements (A013) to (A015), the standard size sheet width storage unit stores the sheet width of the standard size sheet (S) used for the image recording. To do.
The used sheet fixed size detecting means detects the fixed size of the used sheet (S) when the sheet (S) used for the image recording is the fixed size sheet (S).
The first-side side registration sensor (SN2) and the second-side side registration sensor (SN3) are arranged apart from each other in the sheet width direction by the sheet width of the standard size to be used. In this case, the sheet width of the standard size to be used is equal to or less than the distance between the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). Therefore, the image of the first or second surface is transferred to the sheet (S) while the sheet (S) is conveyed in a state of being disposed between the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). Can be formed. In this case, the position adjustment in the sheet width direction of the sheet (S) and the position adjustment in the sheet width direction of the set image area (S1, S2) in which image recording is performed are performed on the first side side registration sensor (SN2) and the second side. It can be adjusted with the register sensor (SN3).

(Embodiment 9)
The image forming apparatus of the ninth embodiment of the present invention is characterized in that the image forming apparatus of the present invention or the eighth embodiment of the present invention has the following configuration requirement (A016).
(A016) The first-side side registration sensor (SN2) and the second-side side registration sensor (SN3) that are arranged apart from each other in the sheet width direction by the sheet width of the standard size to be used.
(Operation of Embodiment 9 of the present invention)
In the image forming apparatus according to the ninth embodiment of the present invention having the configuration requirement (A016), the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3) have the sheet width of the standard size to be used. They are arranged apart in the sheet width direction.
In this case, the first and second sheet conveying methods and the positioning of the set image areas (S1, S2) in the sheet width direction are performed as in the following (1) and (2), whereby the first and second sheets are aligned. The setting image area (S2) can be easily arranged at a position overlapping in the sheet width direction.
(1) The sheet (S) is conveyed so that the position of the first side side registration sensor (SN2) and the first side side registration position at the image recording position (Q4) are the same in the sheet width direction, and the sheet ( The image on the first surface is arranged so that the set image area (S1) is arranged at a position separated by the first surface set distance d1 from the side registration position on the first surface at the center side of the sheet (S) during the image recording on the first surface in S). Record.
(2) The sheet (S) is conveyed so that the position of the second-side side registration sensor (SN3) and the second-side side registration position at the image recording position (Q4) are the same in the sheet width direction, and the sheet ( The image on the second side is arranged so that the set image area (S2) is arranged at a position separated by the second side set distance d2 from the side registration position on the second side at the center side of the sheet (S) during the image recording on the second side of S). Record.

(Embodiment 10)
An image forming apparatus according to a tenth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention includes the following constituent elements (A017).
(A017) It is arranged to be movable between the first-side side register position and the second-side side register position, and operates as the first-side side register sensor (SN2) when moved to the first-side side register position. One said side registration sensor which operate | moves as said 2nd surface side registration sensor (SN3) in the state which moved to the said 2nd surface side registration position.
(Operation of Form 10 of the Present Invention)
In the image forming apparatus according to the tenth embodiment of the present invention having the configuration requirement (A017), one side registration sensor is disposed so as to be movable between the first side registration position and the second side registration position. The one side registration sensor operates as the first-side side registration sensor (SN2) when moved to the first-side side registration position, and the second-side side registration sensor (SN2) when moved to the second-side side registration position. SN3). In this case, one side registration sensor is used. However, by using the one side registration sensor, sheet edges of various sizes having different sizes can be detected at appropriate positions. Further, since one side register sensor is used, the number of side register sensors to be used can be reduced.

(Embodiment 11)
An image forming apparatus according to an eleventh aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention includes the following configuration requirement (A018).
(A018) One first-side side registration sensor (SN2) fixedly arranged, and the first-side side registration sensor (SN2) arranged to be movable to a plurality of positions according to a plurality of standard-size sheet widths to be used. ) One side registration sensor (SN3) different from the second side.
(Operation of Form 11 of the Present Invention)
In the image forming apparatus according to the eleventh aspect of the present invention having the configuration requirement (A018), according to the fixed-placed first-side side registration sensor (SN2) and a plurality of standard-size sheet widths to be used. One second-side side registration sensor (SN3) different from the first-side side registration sensor (SN2) arranged to be movable at a plurality of positions is used. In this case, two side registration sensors are used. However, by using the two side registration sensors, sheet edges of various sizes having different sizes can be detected at appropriate positions.

(Embodiment 12)
The image forming apparatus according to the twelfth aspect of the present invention can include the following constituent element (A019) in the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention.
(A019) One of the first-side side registration sensors (SN2) fixedly arranged and a plurality of the second-side side registration sensors (SN3) fixedly arranged according to the sheet widths of a plurality of standard sizes to be used.
(Operation of Form 12 of the Present Invention)
In the image forming apparatus according to the twelfth aspect of the present invention having the above-described configuration requirement (A019), each of the first-side first-side side registration sensor (SN2) that is fixedly arranged and a plurality of standard-size sheet widths to be used. A plurality of second-side side registration sensors (SN3) fixedly arranged are used. In this case, there is no need to provide a mechanism for moving the side registration sensor (SN3) on the second surface.

(Embodiment 13)
An image forming apparatus according to a thirteenth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention includes the following constituent elements (A020).
(A020) The first side registration sensor (SN2) fixedly arranged and the same edge as the one edge of all the sheets (S) of a plurality of fixed sizes used are fixedly arranged so as to be detectable. The second-side side registration sensor (SN3) configured by one line sensor having a plurality of light receiving elements.
(Operation of Form 13 of the Present Invention)
In the image forming apparatus according to the thirteenth aspect of the present invention having the structural element (A020), one first-side side registration sensor (SN2) that is fixedly arranged and all the sheets (S) having a plurality of fixed sizes to be used. A second-side side registration sensor (SN3) configured by a single line sensor having a plurality of light receiving elements fixedly arranged so that the same end edge as the one end edge can be detected is used. The second-side side registration sensor (SN3) configured by one line sensor having the plurality of light receiving elements detects the same edge as the one end edge of all the sheets (S) having a plurality of fixed sizes to be used. be able to.

(Embodiment 14 of the present invention)
An image forming apparatus according to a fourteenth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to thirteenth aspects of the present invention includes the following structural requirements (A021) to (A023).
(A021) A toner image is formed at a predetermined set image recording width (S1a, S1b) in the width direction of the surface of the rotating image carrier (Py, Pm, Pc, Pk) disposed at the image recording position (Q4). The toner image formed on the surface of the image carrier (Py, Pm, Pc, Pk) is transferred to the toner image forming apparatus (UY to UK) and the sheet (S) passing through the image recording position (Q4). The image recording device (UY to UK + BM + T2) constituted by a transfer device (BM + T2),
(A022) Heating the toner image on the sheet (S) having a pair of fixing rotation members (Fh, Fp) that form a fixing area (Q5) by the area where they are pressed against each other and passing through the fixing area (Q5). Fixing device (F) for fixing,
(A023) The sheet conveying device (SH) that conveys the sheet (S) on which the toner image is transferred to the fixing region (Q5).

(Operation of Form 14 of the Present Invention)
In the image forming apparatus according to the fourteenth aspect of the present invention having the structural requirements (A021) to (A023), the toner image forming apparatuses (UY to UK) of the image recording apparatuses (UY to UK + BM + T2) have the image recording positions (UY to UK). A toner image is formed in a predetermined set image recording width (S1a, S2a) in the width direction of the surface of the rotating image carrier (Py, Pm, Pc, Pk) arranged in Q4). The transfer device (BM + T2) transfers the toner image formed on the surface of the image carrier (Py, Pm, Pc, Pk) to the sheet (S) that passes through the image recording position (Q4).
A fixing device (F) having a pair of fixing rotation members (Fh, Fp) that form a fixing region (Q5) by an area that is in pressure contact with each other includes a toner image on a sheet (S) that passes through the fixing region (Q5). Is fixed by heating. The sheet conveying device (SH) conveys the sheet (S) on which the toner image has been transferred to the fixing region (Q5).
That is, in the image forming apparatus according to the fourteenth aspect of the present invention, the toner image transferred and fixed on both surfaces (first and second surfaces) of the sheet (S) can be formed, and the first and second surfaces can be fixed. The image recording areas (S1, S2) of the toner images can be overlapped when viewed from the direction perpendicular to the sheet surface.

(Embodiment 15 of the present invention)
An image forming apparatus according to a fifteenth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention includes the following constituent elements (A024).
(A024) The one-side edge registration sensor (SN2) configured by one line sensor having a plurality of light receiving elements fixedly arranged, and the one end edge of all the sheets (S) having a plurality of fixed sizes to be used The second-side side registration sensor (SN3) configured by one line sensor having a plurality of light receiving elements fixedly arranged so that the same edge can be detected.
(Operation of Form 15 of the Present Invention)
In the image forming apparatus according to the fifteenth aspect of the present invention having the above-described configuration requirement (A024), the first-side side registration sensor (SN2) configured by one line sensor having a plurality of light receiving elements fixedly arranged is used. The second-side side register sensor (SN3) configured by one line sensor having a plurality of light receiving elements fixedly arranged so that the same edge as the one edge of all the sheets (S) of a plurality of fixed sizes can be detected. ) And are used.
The first-side side registration sensor (SN2) constituted by one line sensor having the plurality of light receiving elements can accurately detect the position of one end edge of the sheet (S) to be used. The second side registration sensor (SN3) composed of one line sensor having the plurality of light receiving elements has the same edge as the one edge of all the sheets (S) having a plurality of fixed sizes to be used. The position can be detected accurately.

(Embodiment 16 of the present invention)
An image forming apparatus according to a sixteenth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention includes the following constituent elements (A025).
(A025) The first-side side registration sensor (SN2) and the second-side side registration sensor (SN2) that are configured by two side registration sensors (SN2, SN3) that are fixedly arranged apart from the maximum sheet width of a standard size that can be used. SN3).
(Operation of Form 16 of the Present Invention)
In the image forming apparatus according to the sixteenth aspect of the present invention having the structural element (A025), two side registration sensors (SN2, SN2) constituting the first side registration sensor (SN2) and the second side registration sensor (SN3). SN3) is fixedly arranged apart from the maximum sheet width of the standard size that can be used. In this case, the sheet widths of all the sheets (S) to be used are equal to or less than the distance between the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). Therefore, the image of the first or second surface is transferred to the sheet (S) while the sheet (S) is conveyed in a state of being disposed between the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). Can be formed. In this case, the position adjustment in the sheet width direction of the sheet (S) and the position adjustment in the sheet width direction of the set image area (S1, S2) in which image recording is performed are performed on the first side side registration sensor (SN2) and the second side. It can be adjusted with the register sensor (SN3).

(Embodiment 17 of the present invention)
An image forming apparatus according to a seventeenth aspect of the present invention is characterized in that the image forming apparatus according to the present invention or any one of the first to ninth aspects of the present invention includes the following constituent elements (A026).
(A026) The first-side side registration sensor (SN2) and the second-side side registration sensor (SN2) configured by two side registration sensors (SN2, SN3) fixedly spaced apart by the maximum sheet width of a standard size that can be used. SN3).
(Operation of Form 17 of the Present Invention)
In the image forming apparatus according to the seventeenth aspect of the present invention having the configuration requirement (A026), the two side registration sensors constituting the first side registration sensor (SN2) and the second side registration sensor (SN3) are used. They are fixedly spaced apart by the maximum sheet width of the standard size possible. In this case, the sheet widths of all the sheets (S) to be used are equal to or less than the distance between the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). Therefore, the image of the first or second surface is transferred to the sheet (S) while the sheet (S) is conveyed in a state of being disposed between the first-side side registration sensor (SN2) and the second-side side registration sensor (SN3). Can be formed. In this case, the position adjustment in the sheet width direction of the sheet (S) and the position adjustment in the sheet width direction of the set image area (S1, S2) in which image recording is performed are performed on the first side side registration sensor (SN2) and the second side. It can be adjusted with the register sensor (SN3).

When image recording is performed on both sides of the sheet (S) having the maximum sheet width, the sheet conveying method for the first side and the second side and the positioning of the set image areas (S1, S2) in the sheet width direction are as follows ( By performing steps 1) and (2), the setting image regions (S2) on the first and second surfaces can be easily arranged at positions overlapping in the sheet width direction.
(1) The sheet (S) is conveyed so that the position of the first side side registration sensor (SN2) and the first side side registration position at the image recording position (Q4) are the same in the sheet width direction, and the sheet ( The image on the first surface is arranged so that the set image area (S1) is arranged at a position separated by the first surface set distance d1 from the side registration position on the first surface at the center side of the sheet (S) during the image recording on the first surface in S). Record.
(2) The sheet (S) is conveyed so that the position of the second-side side registration sensor (SN3) and the second-side side registration position at the image recording position (Q4) are the same in the sheet width direction, and the sheet ( The image on the second side is arranged so that the set image area (S2) is arranged at a position separated by the second side set distance d2 from the side registration position on the second side at the center side of the sheet (S) during the image recording on the second side of S). Record.

The above-described image forming apparatus of the present invention has the following effect (E01).
(E01) When images are recorded on both sides of a sheet, the first image recording area and the second image recording area of the sheet can be overlapped when viewed from a direction perpendicular to the sheet surface.

  Next, specific examples (examples) of the embodiments of the image forming apparatus of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples.

FIG. 1 is an explanatory diagram of Embodiment 1 of the image forming apparatus of the present invention.
In FIG. 1, an image forming apparatus (digital copying machine) U according to the first embodiment includes a printer (image forming apparatus main body) U1, an image scanner U2, and an automatic document feeder U3.
The automatic document feeder U3 is supported on a platen glass PG on the upper surface of the image scanner U2.

The automatic document feeder U3 has a document feed tray TG1 on which a plurality of documents Gi to be copied are stacked. Each of the plurality of documents Gi placed on the document feed tray TG1 sequentially passes through the copy position on the platen glass PG (the press contact position of the platen roll GR1) and is discharged from the document discharge roll GR2 to the document discharge tray TG2. It is comprised so that.
The automatic document feeder U3 can be rotated with respect to the upper surface of the platen glass PG by a hinge shaft (not shown) provided at the rear end thereof and extending in the left-right direction. When placed on the PG, it is rotated upward.

The image scanner U2 has a UI (user interface) through which a user inputs an operation command signal such as a copy start.
An exposure optical system A for reading a document image is disposed below the transparent platen glass PG.
Reflected light from a document which is transported to the upper surface of the platen glass PG by the automatic document feeder U3 and passes through the copy position or a document (not shown) manually placed on the platen glass PG is reflected by the exposure optical system A. Then, it is converted into an electrical signal by a CCD (solid-state imaging device).
The IPS (image processing system) converts R, G, B (red, green, blue) electrical signals input from the CCD into Y, M, C, K (yellow, magenta, cyan, black) image data (digital). Data) and temporarily stored, and the image data is output to the laser drive circuit DL as image data for forming a latent image at a predetermined timing.
The laser drive circuit DL outputs a laser drive signal to a laser diode (not shown) of a ROS (latent image forming apparatus) in accordance with the input image data. The operations of the UI (user interface), the IPS and the laser drive circuit DL, the power supply circuit E for applying a bias voltage to the developing roll R0, the transfer roll T1, the secondary transfer roll (sheet transfer member) T2b, etc., which will be described later. Is controlled by the controller C.

  The laser drive circuit DL to which the four-color image data (laser drive data) of YMCK output from the IPS is input, the laser drive signal of each color corresponding to the input image data of each color at a predetermined timing for each color. Output to a ROS (latent image forming apparatus).

  Each image bearing member (photosensitive member) Py, Pm, Pc, Pk is uniformly charged by a respective charging roll (charging member) CR, and then the light output from each color ROSy to ROSk (latent image forming device). An electrostatic latent image is formed on the surface by the beam. The electrostatic latent images on the surfaces of the image carriers Py, Pm, Pc, and Pk are developed into toner images of the respective colors YMCK in the developing areas that face the developing units Gy, Gm, Gc, and Gk, respectively. Each of the developing units Gy, Gm, Gc, and Gk includes a developing container that stores toner of each color, an electrostatic image on the surface of the image carrier Py, Pm, Pc, and Pk that is rotatably supported by the developing container. A developing roll R0 is provided for conveying toner to the latent image and developing the toner image. The developing containers Gy, Gm, Gc, and Gk of the respective colors are configured to be supplied with toner of each color from the toner cartridges Ty to Tk.

  The developed toner images of the respective colors YMCK are conveyed to a primary transfer position Q3 where the image carriers Py, Pm, Pc, Pk and the endless intermediate transfer belt (image carrier) B are in contact with each other. The primary transfer roll T1 disposed on the back side of the intermediate transfer belt B at each primary transfer position Q3 has a polarity opposite to the developer charging polarity at a predetermined timing from the power supply circuit E controlled by the controller C. A primary transfer voltage is applied. The toner images on the image carriers Py to Pk are primarily transferred to the intermediate transfer belt B at the primary transfer position Q3 facing the primary transfer rolls T1. Residual toner on the surface of the image carrier Py, Pm, Pc, Pk after the primary transfer is removed by the image carrier cleaner CLp.

  Each color toner that forms a toner image of each color on each image carrier Py-Pk by each image carrier Py-Pk, each color ROSy-ROSK (latent image forming device), and each color developer Gy-Gk An image forming apparatus UY (Py + ROSy + Gy), UM (Pm + ROSm + Gm), UC (Pc + ROSc + Gc), and UK (Pk + ROSK + Gk) are configured.

Below the image carriers Py, Pm, Pc, and Pk of the respective colors, a slide frame F1 is slidable in the front-rear direction (direction perpendicular to the paper surface, that is, the X-axis direction) by a pair of left and right slide rails SR, SR. It is supported. The slide frame F1 includes an operating position where the belt frame F2 of the belt module BM is raised (a position where the belt frame F2 is in contact with the image carriers Py to Pk) and a maintenance position where the belt frame BM is moved downward (a position away from the image carriers Py to Pk). It is supported so that it can move up and down. In a state where the belt module BM is lowered to the belt maintenance position, the slide frame F1 and the belt module BM supported by the slide frame F1 are not brought into frictional contact with the image carrier PR, and the image forming apparatus main body U1. It is configured to be able to enter and exit.
The configuration for moving the slide frame F1 back and forth and the configuration for moving the belt module BM up and down are conventionally known (see, for example, JP-A-8-171248), and various conventionally known configurations can be employed. .

  The belt module BM includes a belt support roll (Rd, Rt, Rw) including the intermediate transfer belt B, a belt drive roll Rd, a tension roll Rt, a walking roll Rw, a plurality of idler rolls (free rolls) Rf, and a backup roll T2a. , Rf, T2a) and the four primary transfer rolls T1. The intermediate transfer belt B is supported by the belt support rolls (Rd, Rt, Rw, Rf, T2a) so as to be rotatable in the arrow Ya direction.

A secondary transfer roll (sheet transfer member) T2b is disposed opposite to the surface of the intermediate transfer belt B in contact with the backup roll T2a, and the secondary transfer is performed depending on the contact position between the intermediate transfer belt B and the secondary transfer roll T2b. A position (a sheet transfer position at which the toner image is transferred to the sheet S, that is, an image recording position at which an image is recorded on the sheet S) Q4 is formed. A secondary transfer voltage having a polarity opposite to the charging polarity of the developer is applied to the secondary transfer roll T2b from the power supply circuit E controlled by the controller C at a predetermined timing. The backup roll T2a disposed opposite to the secondary transfer roll T2b is grounded, and when a secondary transfer voltage is applied to the secondary transfer roll T2b, the secondary transfer roll T2b and A secondary transfer electric field is formed between the backup rolls T2a. The backup roll T2a and the secondary transfer roll T2b constitute a secondary transfer device T2.
Surfaces of image carriers Py to Pk of toner image forming apparatuses (UY, UM, UC, UK) by a belt module BM including the four primary transfer rolls T1 and the intermediate transfer belt B, a secondary transfer unit T2, and the like. The transfer device (BM + T2) for transferring the toner image formed on the recording sheet S is configured.
An image recording device (UY to UK + BM + T2) for recording an image (toner image) on the sheet S is constituted by the toner image forming devices UY to UK and a transfer device (BM + T2).
The image recording devices (UY to UK + BM + T2) are arranged in the axial positions of electrostatic latent images (laser beams for writing electrostatic latent images) when forming electrostatic latent images on the surfaces of the image carriers Py to Pk. The position of the toner image formed on the intermediate transfer belt B can be controlled in the belt width direction (shifted in the sheet width direction).

Under the printer (image forming apparatus main body) U1, cassette trays (sheet feeding trays) TR1 to TR3 that store sheets S and a sheet feeding path SH1 for sheet feeding are provided. The sheet size of the sheet S accommodated in the cassette trays TR1 to TR3 is detected by a sheet size sensor provided in the cassette tray, and the detected sheet size is stored in the memory of the control part of the image forming apparatus.
The sheet feeding path SH1 is configured to be fed from a manual feed tray (sheet feeding tray) TR4. The sheets S accommodated in the cassette trays (sheet feeding trays) TR1 to TR3 are taken out by the pick-up roll Rp at a predetermined timing, separated one by one by the separating roll Rs, and then transferred to the registration roller Rr by the plurality of conveying rolls Ra. Be transported. Further, the sheet fed from the manual feed tray (paper feed tray) TR4 is transported to the registration roller Rr by the transport roll Ra. The recording sheet S conveyed to the registration roller Rr is subjected to the secondary transfer at the timing when the multiple toner image or the single color toner image primarily transferred to the intermediate transfer belt B moves to the secondary transfer position Q4. Transported to position Q4.
A sheet feeding apparatus (SH1 + Rp + Rs + Ra) for feeding a sheet to the registration roller Rr is configured by the elements SH1, Rp, Rs, Ra and the like.
When the recording sheet S passes through the secondary transfer position Q4, the secondary transfer voltage is applied to the secondary transfer roll T2b, so that the color toner image primarily transferred over the intermediate transfer belt B is Secondary transfer is performed on the recording sheet S at a time at the secondary transfer position Q4.
The residual toner is removed from the intermediate transfer belt B after the secondary transfer by the belt cleaner CLb.

The recording sheet S on which the toner image is secondarily transferred is conveyed to the fixing device F by the post-transfer sheet guide SG and the sheet conveying belt HB. The fixing device F has a pair of pressure rolls Fh and pressure rolls Fp (see FIG. 2) that are in pressure contact with each other, and a fixing area Q5 is formed by the pressure contact areas of the heat rolls Fh and pressure rolls Fp. The toner image on the recording sheet S is heat-fixed when passing through the fixing area Q5. The recording sheet S on which the toner image is fixed is conveyed to the discharge sheet conveyance path SH2 or the duplex recording sheet conveyance path SH3 by the conveyance path switching gate GT. The sheet conveyed to the discharge sheet conveyance path SH2 is discharged to the sheet discharge tray TRh, and the sheet conveyed to the double-sided recording sheet conveyance path SH3 is turned upside down and retransmitted to the registration roller Rr.
A sheet conveying device SH is constituted by the elements indicated by the symbols Rp, Rs, Ra, Rr, SG, HB, SH1, SH2, SH3 and the like.
A sheet conveying path (SH1 to SH3) is configured by the elements indicated by the symbols SH1, SH2, and SH3. Further, a sheet conveying member (Rp, Rs, Ra, Rr, HB) is constituted by the elements indicated by the symbols Rp, Rs, Ra, Rr, HB and the like.

2A and 2B are explanatory views of the double-sided sheet conveying apparatus. FIG. 2A is a schematic cross-sectional view taken along the line IIA-IIA in FIG. 1, and FIG.
1 and 2, the double-sided recording sheet conveyance path SH3 includes a double-sided recording upper sheet conveyance path SH3a disposed on the upper side of the paper feed tray TR1 and a double-sided recording lower sheet conveyance path SH3b disposed on the lower side. And have. When performing double-sided recording, the sheet on which the image is recorded on the first side is fixed on both sides of the sheet conveyance path SH3 for double-sided recording by the switching gate GT after the toner image recorded on the first side of the sheet is fixed when passing through the fixing device F. It is conveyed to the upper recording sheet conveyance path SH3a. In the double-sided recording sheet conveyance path SH3, a plurality of normal sheet conveyance rollers Ra and a width direction conveyance roller Rb are arranged.
The sheet conveying roller Ra and the width direction conveying roller Rb are constituted by a pair of upper and lower rollers (a driving roller and a driven roller), and the pair of upper and lower rollers of the sheet conveying roller Ra are in pressure contact with each other at normal times. The pair of upper and lower rollers of the width direction conveying roller Rb are separated from each other.

The first image-recorded sheet S conveyed to the double-sided recording upper sheet conveyance path SH3a is conveyed by a conveyance roller Ra disposed in the double-sided recording upper sheet conveyance path SH3a. At this time, the pair of upper and lower rollers of the width direction conveying roller Rb are separated. A sheet sensor SN4 (see FIG. 1) is disposed on the downstream side of the double-sided recording upper sheet conveyance path SH3a, and the sheet conveyance roller Ra is stopped when the front end of the sheet S is detected by the sheet sensor SN4. The pair of upper and lower rollers of the stopped sheet conveying roller Ra are separated in the vertical direction, and the pair of rollers of the plurality of widthwise conveying rollers Rb separated in the vertical direction are pressed against each other with the sheet S interposed therebetween.
A pair of upper and lower rollers of a plurality of width direction conveying rollers Rb sandwiching the sheet S rotate to convey the sheet S in the width direction. At this time, the sheet S in the upper sheet conveying path SH3a for double-sided recording is conveyed in the sheet width direction, and the lower sheet for double-sided recording is conveyed through the sheet conveying through hole TR1a formed in the sheet feeding tray TR1 shown in FIG. 2A. It is conveyed to the path SH3b.

In FIG. 2, a sheet sensor SN5 (see FIG. 2A) is disposed in the lower sheet conveyance path SH3b for double-sided recording. When the front end of the first image-recorded sheet S conveyed to the double-sided recording lower sheet conveyance path SH3b is detected by the sheet sensor SN5, the rotation of the plurality of width-direction conveyance rollers Rb stops, A pair of upper and lower rollers of the width direction conveyance roller Rb are separated in the vertical direction, and a pair of normal sheet conveyance rollers Ra separated in the vertical direction are pressed against each other with the sheet S interposed therebetween.
As shown in FIG. 1, the sheet S on which the first-side image has been recorded conveyed to the double-side recording lower sheet conveyance path SH3b is transferred from the double-side recording lower sheet conveyance path SH3b to the sheet feeding sheet conveyance path SH1. Then, it is retransmitted to the registration roller Rr.

The registration roller Rr according to the first exemplary embodiment is movable in the sheet conveyance direction (in the axial direction) during rotation (described later with reference to FIG. 3), and simultaneously conveys the sheet in the sheet conveyance direction. It is possible. As described above, a sheet conveying roller capable of conveying a sheet in the sheet conveying direction and the sheet width direction is conventionally known (see JP-A-8-208098).
A device for moving the registration roller Rr in the axial direction constitutes a registration roller moving device (not shown), and means for controlling the movement of the registration roller Rr in the axial direction by controlling the operation of the registration roller moving device ( The registration roller movement control means) constitutes means for controlling the position in the sheet width direction (sheet width direction position control means, not shown).

In the first embodiment, as shown in FIG. 1 and FIGS. 3 and 4 to be described later, a lead registration sensor SN1 and a first-side side registration for detecting both edges of the sheet in the sheet width direction on the downstream side of the registration roller Rr. Sensor SN2 and second-side side registration sensor SN3 are arranged.
4A, which will be described later, the first-side side registration sensor SN2 that detects the position of one end edge in the sheet width direction of the sheet S when the first-side image recording of the sheet S is performed is fixedly arranged and the second-side image recording is performed. The second-side side registration sensor SN3 that detects the position of the same edge as the one edge in the sheet width direction of the sheet S at the time is disposed so as to be adjustable in the sheet width direction. When image recording is performed, the second-side side registration sensor SN3 moves to a position away from the first-side side registration sensor SN2 by the sheet width of the sheet used for image recording (the sheet width recognized by the image forming apparatus). Stop in state.
The toner image forming area (image recording area) S1a on the intermediate transfer belt B is set at a position separated from the side registration sensors SN2 and SN3 by a set distance d1 (= d2).
The position in the sheet width direction at the time of image recording on the first surface of the sheet S is controlled by a detection signal of the first surface side registration sensor SN2 that detects one edge of the sheet, and the sheet at the time of image recording on the second surface of the sheet S. The position in the width direction is controlled by a detection signal of the second side side registration sensor SN3 that detects the same edge as the one edge of the sheet.

(Operation of Example 1)
FIG. 3 uses the image forming apparatus of the first embodiment, and inverts the sheet so that the direction of the front edge in the conveyance direction of the sheet passing through the image recording position is constant and the both edges of the sheet in the sheet width direction are switched. FIG. 3A is a diagram illustrating a sheet stored in the sheet feed tray, and FIG. 3B is a diagram illustrating a state in the middle of conveying the sheet taken out from the sheet feed tray. FIG. 3C is a diagram showing a state in which the sheet is temporarily stopped by the registration roller and the front edge of the sheet is aligned in the registration roller axial direction and then moved in the registration roller axial direction. FIG. FIG. 3E is a diagram showing a state of the sheet passing through the transfer region (image recording position on the sheet), FIG. 3E is a diagram showing a state where the sheet on which the first-side toner image is transferred passes through the fixing region, and FIG. FIG. 3G is a diagram showing a reversal sheet obtained by reversing the sheet on which the toner image of the front surface is transferred and fixed so that both end edges in the sheet width direction are interchanged. FIG. FIG. 3H is a diagram illustrating a state in which the reversal sheet passes through a transfer region (image recording position on the sheet) while the toner image is transferred onto the second surface. 3I is a diagram illustrating a state in which the toner image is transferred to both surfaces of the sheet.

In FIG. 3A showing the sheets stored in the sheet feeding tray, the size of the actual sheet S (refer to the solid line in FIG. 3A) of the A3 SEF stored in the sheet feeding tray storing the A3 SEF sheet is the ideal A3 SEF sheet. There is an error compared to the size of S ′ (see the dashed line in FIG. 3A). That is, in the case of FIG. 3A, the sheet width (width in the direction perpendicular to the sheet conveyance direction) and sheet length (length in the sheet conveyance direction) of the actual sheet S (see solid line) of A3SEF accommodated in the sheet feed tray are as follows. It is larger than the sheet width and sheet length of an ideal A3SEF sheet S ′ (see the two-dot chain line). Further, the ideal A3SEF sheet S ′ (see the one-dot chain line) is rectangular, but the actual A3SEF sheet S (see the solid line) accommodated in the paper feed tray is not necessarily rectangular. In the actual sheet S (see solid line) of A3SEF shown in FIG. 3A, the front edge in the sheet conveying direction is inclined.
That is, the image forming apparatus stores (recognizes) the ideal sheet size of the A3SEF sheet S ′ (see the two-dot chain line) as the sheet size of the A3SEF sheet. The size of the sheet S (see the solid line) is different from the sheet size recognized by the image forming apparatus (has an error).

When the actual sheet S (see solid line) of the A3SEF is taken out from the position shown in FIG. 3A (position accommodated in the paper feed tray) and conveyed, it may be conveyed in an inclined manner as shown in FIG. 3B. Many.
The actual sheet S of the A3SEF (refer to the solid line) is temporarily stopped in a state where the front end of the sheet is in contact with the registration roller Rr in FIG. It is aligned in the axial direction of Rr (skew which is the inclination of the front edge of the sheet is corrected). The registration roller Rr that conveys the sheet S in the state indicated by the two-dot chain line in FIG. 3C to the downstream side is movable in the axial direction.
Means (registration roller movement control) for moving the registration roller Rr in the axial direction (sheet width direction) when the registration roller Rr conveys the sheet S indicated by the two-dot chain line in FIG. 3C to the downstream lead registration sensor SN1. Means) moves the registration roller Rr in the sheet width direction (the axial direction of the registration roller Rr). At this time, the sheet S is conveyed in the sheet width direction from the position of the two-dot chain line to the position where the one end edge of the sheet is detected by the first side side registration sensor SN2 (the position indicated by the solid line).

  The sheet S indicated by a solid line in FIG. 3C is conveyed while the position in the sheet width direction is controlled in a state where one end edge of the sheet S is detected by the first-side side registration sensor SN2. The leading edge of the sheet S reaches the position (lead registration position) of the lead registration sensor SN1. That is, when the leading edge of the sheet S reaches the position (lead registration position) of the lead registration sensor SN1, one end edge of the sheet S is detected by the first-side side registration sensor SN2.

After the leading edge of the sheet S reaches the position of the lead registration sensor SN1 (lead registration position), the registration roller Rr does not move in the sheet width direction and only rotates for conveying the sheet S. When the front end of the sheet S is inclined, the sheet S conveyed by the registration roller Rr that performs only the rotation for conveying the sheet is conveyed downstream in the conveying direction in an inclined state (posture).
The sheet S conveyed by the registration roller Rr in the inclined state is formed with an intermediate transfer belt B (see FIG. 1 and FIG. 3D) on which a first-side toner image is formed and a backup roll T2a (see FIG. 3D) abuts the upper surface. (Not shown) and a secondary transfer roller T2b (see FIG. 1; not shown in FIG. 3) that is in pressure contact with the lower surface thereof, the sheet is conveyed to a transfer area Q4.

  In FIG. 3D, when the inclined sheet S passes through the transfer area Q4, the image on the first surface is recorded in the range of the image recording area S1 having the set image recording width S1a on the first surface of the sheet S. In FIG. 3D, the actual sheet S is indicated by a solid line, and the ideally shaped sheet S ′ is indicated by a one-dot chain line. The front end of the first image recording area S1 of the sheet S conveyed in an inclined state in FIG. 3D is parallel to the transfer area Q4, and both ends in the sheet width direction of the image recording area S1 are perpendicular to the transfer area Q4. In addition, the sheet S is inclined with respect to the edge in the width direction.

  In FIG. 3E, the distance from the front edge of the sheet S to the image recording area S1 is e1, and the distance e1 is a set value. When the size of the actual sheet S (see the solid line) of A3SEF is an ideal sheet size, the distance e1 ′ between the trailing edge of the sheet S in FIG. 3E and the image recording area S1 is also e1 ′ = e1. Is set to However, the actual sheet S (see the solid line) of the A3SEF in FIG. 3E is longer than the ideal sheet S ′ (see the one-dot chain line) in the sheet conveyance direction, so the trailing edge of the sheet S in FIG. 3E The distance e1 'between the image recording area S1 and the image recording area S1 is longer than e1. That is, e1 ′> e1.

In FIG. 3C, in the first embodiment, the first-side side registration sensor SN2 is fixedly arranged, and the second-side side registration sensor SN3 is arranged so that its position can be adjusted in the sheet width direction. The second-side side registration sensor SN3 is stopped in a state where it has moved to a position away from the first-side side registration sensor SN2 by the sheet width of the standard sheet size to be used. For example, when the A3SEF sheet S is used, the second-side side registration sensor SN3 is connected to the ideal A3SEF sheet S (see the one-dot chain line in FIG. 3A) from the fixed-side first-side side registration sensor SN2. Move to a position separated by the width and stop. Further, for example, when the A4SEF sheet S is used, the second-side side registration sensor SN3 is an ideal A4SEF sheet S from the first-side side registration sensor SN2 that is fixedly arranged (see the one-dot chain line in FIG. 5A). And move to a position (see SN3 ′ in FIG. 5A) separated by a width of.
The first and second image recording areas S1 and S2 in the width direction on the intermediate transfer belt B are arranged between the side registration sensors SN2 and SN3 and are set by a set distance d1 from the side registration sensors SN2 and SN3. It is arranged at a position away from the inside.

As can be seen from FIG. 3E, when the sheet width of the actual sheet S is larger than the ideal sheet width of the sheet S ′, it is compared with the distance d1 between one edge of the sheet S and the front edge of the first image recording area S1. Thus, the distance d1 ′ between the other end edge of the sheet S and the front end of the first image recording area S1 is large.
In FIG. 3E, the toner image (image) transferred to the first surface of the sheet S has a fixing area which is a pressure contact area of a heating roll Fh of the fixing device and a pressure roll (not shown) pressed under the heating roll Fh. It is heat-fixed when passing.
The sheet S heat-fixed by the heating roll Fh in FIG. 3E is inverted so that the one end edge and the other end edge in the sheet width direction are interchanged, and the state shown in FIG. 3F is obtained. In the state of FIG. 3F, the image area S1 of the first surface of the reversing sheet S is arranged on the lower side and is indicated by a dotted line.
The reversal sheet (first image-recorded sheet) S shown in FIG. 3F is conveyed to the registration roller Rr in FIG. 3G.

In FIG. 3G, the reverse sheet S (see the two-dot chain line) conveyed to the registration roller Rr is temporarily stopped with its front end in contact with the registration roller Rr, and the direction of the front end of the sheet S is aligned with the axial direction of the registration roller Rr. (Skew which is the inclination of the front edge of the sheet is corrected). The registration roller Rr that conveys the reverse sheet S in the state indicated by the two-dot chain line in FIG. 3G to the downstream side, when conveying the reverse sheet S indicated by the two-dot chain line in FIG. 3G to the downstream lead registration sensor SN1. The sheet is moved in the sheet width direction (the axial direction of the registration roller Rr) and the reversing sheet S is moved from the position of the two-dot chain line to one end edge of the reversing sheet S (one end position replaced with the other end edge after the toner image transfer on the first surface) Edge) is conveyed in the sheet width direction to a position (position indicated by a solid line) detected by the second side side registration sensor SN3.
The reversal sheet S indicated by a solid line in FIG. 3G is conveyed while the position in the sheet width direction is controlled in a state where the one end edge of the reversal sheet S is detected by the second-side side registration sensor SN3. Then, the leading edge of the reversing sheet S reaches the position of the lead registration sensor SN1 (lead registration position). That is, when the leading edge of the reversing sheet S reaches the position of the lead registration sensor SN1 (lead registration position), the one end edge of the reversing sheet S is detected by the second side registration sensor SN3.

After the leading edge of the reversal sheet S reaches the position of the lead registration sensor SN1 (lead registration position), the registration roller Rr does not move in the sheet width direction and only rotates for transporting the reversal sheet S. The reverse sheet S transported by the registration roller Rr that performs only the rotation for transporting the sheet is transported downstream in the transport direction in an inclined state (posture) when the front end of the reverse sheet S is tilted. .
The reversal sheet S conveyed by the registration roller Rr in the inclined state has an intermediate transfer belt B (see FIG. 1 and FIG. Is not shown) and a secondary transfer roller T2b (see FIG. 1, not shown in FIG. 3) that is in pressure contact with the lower surface thereof is conveyed to a transfer region Q4 that is a pressure contact region.

In FIG. 3H, when the inclined sheet S passes through the transfer region Q4, the image on the second surface is recorded within the range of the image recording region S2 having the set image recording width S2a on the second surface of the sheet S. The front end of the second image recording area S2 of the sheet S conveyed in an inclined state in FIG. 3H is parallel to the transfer area Q4, and both ends in the sheet width direction of the image recording area S2 are perpendicular to the transfer area Q4. is there.
The sheet S on which the second image is recorded is heat-fixed as described with reference to FIG. 3E.

In FIG. 3I showing the sheet S on which the image on the second surface is recorded, the distance from the front edge of the sheet S to the image recording area S2 on the second surface is e2, and the distance e2 is the same as the distance e1 on the first surface. It is the value set in the value. When the size of the actual sheet S of A3SEF (see the solid line) is an ideal sheet size, the distance between the trailing edge of the sheet S in FIG. 3I and the image recording area S2 on the second surface is also the same value as e2. It is set to become. However, since the actual sheet S (see the solid line) of the A3SEF in FIG. 3I is longer than the ideal sheet S ′ (see the one-dot chain line in FIG. 3A) in the sheet conveyance direction, the actual sheet S in FIG. The distance e2 ′ between the rear edge and the second image recording area S2 is longer than e2. That is, e2 ′> e2.
In the first embodiment, since the positions of the edges in the width direction of the sheet S are reversed, the front edge of the sheet during image recording on the first and second surfaces is not replaced and is the same edge. .

In FIG. 3I, the positions of e1 ′ and e1 are illustrated as positions shifted downward from the positions of e2 and e2 ′. E1 ′ (see FIG. 3F) and e2 ′ (see FIG. 3I) overlap. As can be seen from FIGS. 3F and 3H, e2 = e1 and e1 ′ = e2 ′.
Therefore, the position of the image recording area S1 on the first surface of the sheet S and the image recording area S2 on the second surface overlap each other when viewed from the direction perpendicular to the sheet S.

3A and 3E, the actual sheet width of the sheet S is larger than the ideal sheet width of the sheet S ′, so that the one edge of the sheet S and the image recording area S2 on the second surface are separated. Compared to the distance d2, the distance d2 'between the other end edge of the sheet S and the image recording area S2 on the second surface is larger.
As described above, the first and second image recording areas S1 and S2 in the width direction on the intermediate transfer belt B are arranged between the side registration sensors SN2 and SN3 and set from the side registration sensors SN2 and SN3. It is arranged at a position separated inward by a distance d1.
The distance d2 between the one end edge of the sheet S and the image recording area S2 on the second surface is set to the same value as d1 (d2 = d1).
Accordingly, the positions in the sheet width direction of the image recording area S1 on the first surface and the image recording area S2 on the second surface of the sheet S overlap as viewed from the direction perpendicular to the sheet S.

Therefore, in the first exemplary embodiment, the position in the sheet width direction and the sheet conveyance direction of the first image recording area S1 and the second image recording area S2 of the sheet S overlap when viewed from the direction perpendicular to the sheet S.
In the description of FIG. 3, the toner image formed on the side opposite to the side where the backup roll T2a contacts the intermediate transfer belt B is transferred to the sheet S by the secondary transfer roll T2b disposed opposite to the backup roll T2a. However, the same applies to the case where the toner image formed on the surface of the cylindrical image carrier is transferred to the sheet or the case where the image is recorded on the sheet by the ink jet recording head. The same applies when the paper is smaller than ideal.

(Description of the relationship between the toner image forming position on the intermediate transfer belt B and the position of the sheet in the sheet width direction at the image recording position when image recording is performed on both sides of a rectangular A3SEF sheet)
FIG. 4 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus of the first embodiment, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. 4A is the image forming apparatus. FIG. 4B shows the positional relationship between the A3SEF sheet size S ′ recognized by the image forming area, the image recording area S1, and the side registration sensors SN2 and SN3. FIG. 4B shows the A3SEF sheet size S ′ recognized by the image forming apparatus and actual FIG. 4C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface. FIG. 4C is a diagram illustrating the sheet of FIG. The figure which shows the state which moved the edge to the position detected by the 2nd surface side registration sensor SN3, FIG. 4D is image recording area S2 of the 2nd surface on the inversion sheet | seat of the said FIG. It illustrates.

Referring to FIG. 4, the image forming apparatus of the first embodiment is used to record an image on both sides of an actual rectangular sheet S having a slightly larger sheet width and length than the ideal rectangular A3SEF sheet S ′. The relationship between the toner image forming position on the intermediate transfer belt B and the position of the sheet in the sheet width direction at the image recording position will be described.
In FIG. 4, the position of the first-side side registration sensor SN2 is fixed, and the second-side side registration sensor SN3 is movable in the sheet width direction. When image recording is performed on both sides of the rectangular A3SEF sheet S, the distance between the second side registration sensor SN3 and the first side registration sensor SN2 is the SE of the A3 sheet recognized by the image forming apparatus (short of the A3 sheet). It is set to the same distance as the edge).

In FIG. 4A, the set distance in the sheet conveyance direction between the outer edge of the sheet size S ′ of A3SEF recognized by the image forming apparatus and the outer edge of the image recording area S1 is e1, and the set distance in the sheet width direction. Is d1. The set image recording width in the sheet width direction of the image recording area S1 is S1a, and the set image recording length in the sheet conveyance direction is S1b.
In Embodiment 1, the toner image formed on the intermediate transfer belt B is formed in the area of the set image recording width S1a in the sheet width direction at a position d1 from the side registration sensors SN2 and SN3. Is done.

In FIG. 4B, the actual size of the sheet S used in the image forming apparatus is a rectangle in which the length in the sheet conveying direction and the length in the sheet width direction are slightly larger than the ideal sheet size S ′. To do. In the first embodiment, when image recording on the first surface is performed on an actual sheet S, image recording is performed without moving the sheet S in the sheet width direction in a state where one end edge of the sheet S is detected by the first surface side registration sensor SN2. Transport to position Q4. That is, the position in the width direction of the one edge of the sheet S at the image recording position Q4 (the edge detected by the first surface side registration sensor SN2) (the first surface side registration position at the image recording position of the sheet S) is the first surface side register. It is the same as the position where the sensor SN2 is arranged.
When the actual sheet S passes through the image recording position Q4, the distance e1 from the front end of the sheet S, the first-side side registration position of the sheet S (one edge of the sheet S detected by the first-side side registration sensor SN2). The image is recorded in the image recording area S1 on the first surface at a distance d1 from the position at the image recording position Q4, that is, the position of the first surface side registration sensor SN2 in the sheet width direction. The image recording area S1 on the first side has the set image recording width S1a and the set recording length S1b, and the distance between the image recording area S1 on the first side and the other edge of the sheet is d1 ′ (> d1). The distance between the image recording area S1 and the rear end of the sheet is e1 ′ (e1 ′> e1).

4C, the sheet S of FIG. 4B is inverted so that both end edges in the sheet width direction are interchanged, and one end edge of the sheet (detected by the first-side side registration sensor SN2 shown in FIG. 4B during image recording on the first side) The sheet edge) is moved to a position detected by the second-side side registration sensor SN3.
When the second side image is recorded on the actual sheet S in Example 1, the sheet S is not moved in the sheet width direction in a state where the one end edge of the sheet S is detected by the second side side registration sensor SN3. It is conveyed to the image recording position Q4. That is, the position in the width direction of the one edge of the sheet S at the image recording position Q4 (the edge detected by the first and second side registration sensors SN2 and SN3) (the second side registration position at the image recording position of the sheet S) is It is the same as the position where the second side side registration sensor SN3 is arranged.
The position in the sheet width direction of the first image recording area S1 of the sheet S in the state of FIG. 4C is the same position as in FIG. 4B.

As described above, the toner image formed on the intermediate transfer belt B is formed in the area of the set image recording width S1a in the sheet width direction at a position d1 from the side registration sensors SN2 and SN3. The
4D shows a state in which the image on the second side is recorded on the sheet S in FIG. 4C, and the image recording area S2 on the second side is separated from the one edge of the sheet S by the second plane set distance d2. Placed in position. The second surface setting distance d2 and the first surface setting distance d1 are set to d2 = d1. The set image recording width S2a on the second side and the set image recording width S1a on the first side are set to S2a = S1a. Therefore, the positions in the sheet width direction of the image recording areas S1 and S2 on the first surface and the second surface of the sheet S coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.
The image recording area S2 on the second surface of the sheet S is disposed at a distance e2 from the front end of the sheet S, and e2 = e1 is set. Therefore, the positions of the first and second image recording areas S1 and S2 in the sheet conveyance direction coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.
Accordingly, the positions of the image recording areas S1 and S2 in the sheet conveyance direction and the sheet width direction coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.

(Description of the relationship between the toner image forming position on the intermediate transfer belt B and the position of the sheet in the sheet width direction at the image recording position when image recording is performed on both sides of the B4SEF sheet)
FIG. 5 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the first embodiment, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. FIG. 5B is a diagram showing the positional relationship between the B4SEF sheet size S ′ and the image recording area S1 and the side registration sensors SN2 and SN3 recognized by FIG. 5, and FIG. 5B shows the B4SEF sheet size S ′ recognized by the image forming apparatus and the actual FIG. 5C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface, and FIG. 5C shows the sheet of FIG. The figure which shows the state which moved the edge to the position detected by the 2nd surface side registration sensor SN3, FIG. 5D shows image recording area S2 of the 2nd surface of the said inversion sheet | seat of FIG. 5C. It is to figure.

Referring to FIG. 5, the image forming apparatus of the first embodiment is used to record an image on both sides of an actual rectangular sheet S having a slightly larger sheet width and length than the ideal rectangular B4SEF sheet S ′. The relationship between the toner image forming position on the intermediate transfer belt B and the position of the sheet in the sheet width direction at the image recording position will be described.
5, when image recording is performed on both sides of the sheet S of B4SEF, the position of the second side side registration sensor SN3 is moved in the sheet width direction from the position in FIG. 4 (the position indicated by the two-dot chain line in FIG. 5). Move to the position indicated by the solid line. The distance between the side registration sensors SN2 and SN3 in this state is the length of the SE (short edge of the B4 sheet) of the B4 sheet recognized by the image forming apparatus. D0 is the difference between the length of SE (A3 short edge) of the A3 sheet and the length of SE (B4 short edge) of the B4 sheet.

In FIG. 5A, the set distance in the sheet conveyance direction between the outer edge of the sheet size S ′ of B4SEF recognized by the image forming apparatus and the outer edge of the image recording area S1 is e1, and the set distance in the sheet width direction. Is d1. The set image recording width in the sheet width direction of the image recording area S1 is S1a, and the set image recording length in the sheet conveyance direction is S1b.
In Embodiment 1, the toner image formed on the intermediate transfer belt B is formed in the area of the set image recording width S1a in the sheet width direction at a position d1 from the side registration sensors SN2 and SN3. Is done.

In FIG. 5B, the actual size of the sheet S used in the image forming apparatus is a rectangle in which the length in the sheet conveying direction and the length in the sheet width direction are slightly larger than the ideal sheet size S ′. To do. 1 of the set image recording width S1a and the set recording length S1b at the position of the distance e1 from the front end of the actual sheet S and the distance d1 from the one end edge of the sheet S detected by the first-side side registration sensor SN2. When an image is recorded in the first image recording area S1, the distance between the image recording area S1 and the other edge of the sheet is d1 ′ (> d1), and the distance between the image recording area S1 and the trailing edge of the sheet is e1 ′ (e1). '> E1).
5C, the sheet S of FIG. 5B is inverted so that both end edges in the sheet width direction are replaced, and one end edge of the sheet (detected by the first-side side registration sensor SN2 shown in FIG. 5B during image recording on the first side) The sheet edge) is moved to a position detected by the second-side side registration sensor SN3. The position in the sheet width direction of the first image recording area S1 of the sheet S in the state of FIG. 5C is the same position as in FIG. 5B.

As described above, the toner image formed on the intermediate transfer belt B is formed in the area of the set image recording width S1a in the sheet width direction at a position d1 from the side registration sensors SN2 and SN3. The
FIG. 5D shows a state in which the second image is recorded on the sheet S of FIG. 5C, and the image recording width S2a of the second image in the sheet width direction overlaps the set image recording width S1a. Therefore, the positions in the sheet width direction of the image recording areas S1 and S2 on the first surface and the second surface of the sheet S coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.
The image recording area S2 on the second surface of the sheet S is disposed at a distance e2 from the front end of the sheet S, and e2 = e1 is set. Therefore, the positions of the first and second image recording areas S1 and S2 in the sheet conveyance direction coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.
Accordingly, the positions of the image recording areas S1 and S2 in the sheet conveyance direction and the sheet width direction coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.

In the image forming apparatus according to the first exemplary embodiment, each time the sheet size to be used is different, the second side surface is located at a position separated from the first side side registration sensor SN2 by the same distance as the sheet width recognized by the image forming apparatus. The position of the registration sensor SN3 is moved. The image recording area S1 on the first surface and the image recording area S2 on the second surface are set at positions separated from the side registration sensors SN2 and SN3 by a set distance d1.
The position of the sheet S in the sheet width direction at the time of image recording is determined by positioning one edge of the sheet by the first surface side registration sensor SN2, and the position of the sheet S in the sheet width direction at the time of image recording is When the edge of the sheet is positioned by the second-side side registration sensor SN3, the positions of the image recording areas S1 and S2 in the sheet conveyance direction and the sheet width direction are viewed from the direction perpendicular to the sheet surface of the sheet S. Can be matched.

FIG. 6 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the second embodiment of the present invention, the position of the image recording area in the sheet width direction at the image recording position, and the position of the sheet S. FIG. FIG. 6B is a diagram showing the positional relationship between the B4SEF sheet size S ′ recognized by the forming apparatus and the image recording area S1 and the side registration sensors SN2 and SN3. FIG. 6B shows the B4SEF sheet size S ′ recognized by the image forming apparatus. FIG. 6C is a diagram showing the positional relationship between the actual sheet size S, the side registration sensors SN2 and SN3, and the first image recording area S1, FIG. 6C is a diagram in which the sheet of FIG. The figure which shows the state which moved the edge of the sheet | seat to the position detected by the 2nd surface side registration sensor SN3, FIG. 6D is the image recording area of the 2nd surface of the said inversion sheet | seat of the said FIG. 6C It shows a 2 and an image recording area S1 of the first side which is formed on the back surface, Figure 6E is a diagram showing an image recording area S2 of the second surface of the reversed sheet of FIG 6D.
FIG. 6 of the second embodiment corresponds to FIG. 5 of the first embodiment. The image forming apparatus of the second embodiment is different from the first embodiment in which the second-side side registration sensor SN3 is movably arranged in that the second-side side registration sensor SN3 is fixedly arranged. In the second embodiment, the second sheet when the double-sided image is recorded on a sheet having a sheet width smaller than the length of A3SE (short edge of A3 sheet) or the length of A4LE (long edge of A4 sheet). Example 1 is the same as Example 1 except that the transport method is slightly different from Example 1.

  In FIG. 6, the position of the second-side side registration sensor SN3 indicated by the solid line is separated from the first-side side registration sensor SN2 by the length of A3SE (A3 short edge) of the A3 sheet recognized by the image forming apparatus. In the second embodiment shown in FIG. 6, the positions of the side registration sensors SN2 and SN3 are fixedly arranged. That is, the second-side side registration sensor SN3 is moved from the position shown by the solid line in FIG. 6 (the A3SE (A3 short edge) of the A3 sheet recognized by the image forming apparatus from the first-side side registration sensor SN2). Accordingly, the second-side side registration sensor SN3 of the second embodiment does not move to the position of the two-dot chain line in FIG. 6 (position separated by the length of B4SE (B4 short edge) of the B4 sheet). .

However, in FIG. 6, the difference d0 between the length of A3SE and the length of B4SE, that is, the distance d0 between the solid line position and the two-dot chain line position of the second-side side registration sensor SN3 is stored (recognized). It can be calculated from the sheet size. In FIG. 6, only the difference d0 between the length of A3SE (A4LE length) and the length of B4SE (B5LE length) is shown, but in reality, the length of A3SE (A4LE) The difference from the lengths such as A4 short edge) and B5SE (B5 short edge) can also be calculated from the sheet size stored (recognized) by the image forming apparatus.
In the second embodiment, image recording on the A3SEF sheet is performed in the same manner as in the case described with reference to FIG.
In Example 2, image recording on a B4SEF sheet is performed as shown in FIG.

In FIG. 6A, the set distance in the sheet conveyance direction between the outer edge of the B4SEF sheet size S ′ recognized by the image forming apparatus and the outer edge of the image recording area S1 is e1, and the set distance in the sheet width direction. Is d1. The set image recording width in the sheet width direction of the image recording area S1 on the sheet S is S1a, and the set image recording length in the sheet conveyance direction is S1b.
In the second exemplary embodiment, the toner image formed on the intermediate transfer belt B is positioned inward by the distance d1 from the first-side side registration sensor SN2 (to the second-side side registration sensor SN3 side) and the second-side side registration. It is formed within the area of the set image recording width S1a in the sheet width direction at a position (d0 + d1) inside (on the first side side registration sensor SN2 side) from the sensor SN3.

In FIG. 6B, the actual size of the sheet S used in the image forming apparatus is a rectangle in which the length in the sheet conveying direction and the length in the sheet width direction are slightly larger than the ideal sheet size S ′. To do. 1 of the set image recording width S1a and the set recording length S1b at the position of the distance e1 from the front end of the actual sheet S and the distance d1 from the one end edge of the sheet S detected by the first-side side registration sensor SN2. When an image is recorded in the first image recording area S1, the distance between the image recording area S1 and the other edge of the sheet is d1 ′ (> d1), and the distance between the image recording area S1 and the trailing edge of the sheet is e1 ′ (e1). '> E1).
6C, the sheet S of FIG. 6B is inverted so that both end edges in the sheet width direction are interchanged, and one end edge of the sheet (detected by the first-side side registration sensor SN2 shown in FIG. 6B during image recording on the first side) The sheet edge) is moved to a position detected by the second-side side registration sensor SN3. The position in the sheet width direction of the first image recording area S1 on the sheet S in the state of FIG. 6C is a position moved from the position of FIG. 6B by the distance d0 toward the second side registration sensor SN3.
Therefore, when the sheet S is moved from the position of FIG. 6C to the first side side registration sensor SN2 side by the distance d0, the position of the first image recording area S1 on the sheet S in the sheet width direction is the first side. The position is the same as the image recording area on the intermediate transfer belt B. In order to move the sheet S from the position of FIG. 6C toward the first-side side registration sensor SN2 by the distance d0, the registration roller Rr may be moved in the axial direction (sheet width direction) by the distance d0.

As described above, the toner image formed on the intermediate transfer belt B is d1 from the first-side side registration sensor SN2 (the second-side side registration sensor SN3 side) and from the second-side side registration sensor SN3 (d0 + d1). Only at the position on the inner side (first side side registration sensor SN2 side), it is formed in the area of the set image recording width S1a in the sheet width direction.
FIG. 6D shows a state in which the second image is recorded on the sheet S of FIG. 6C. The image recording width S2a in the sheet width direction of the second image overlaps the set image recording width S1a. Therefore, the positions in the sheet width direction of the image recording areas S1 and S2 on the first surface and the second surface of the sheet S coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.
The image recording area S2 on the second surface of the sheet S is disposed at a distance e2 from the front end of the sheet S, and e2 = e1 is set. Therefore, the positions of the first and second image recording areas S1 and S2 in the sheet conveyance direction coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.
Accordingly, the positions of the image recording areas S1 and S2 in the sheet conveyance direction and the sheet width direction coincide with each other when viewed from a direction perpendicular to the sheet surface of the sheet S.

In the image forming apparatus according to the second embodiment, the first image recording area S1 and the second image recording area S2 on the intermediate transfer belt B are separated from the first side registration sensor SN2 by a set distance d1. And set to a position separated from the second side side registration sensor SN3 by a set distance (d0 + d1).
And the position of the sheet width direction at the time of image recording of the 1st surface of the sheet | seat S positions the edge of a sheet | seat by 1st surface side registration sensor SN2.
Further, the position in the sheet width direction at the time of image recording on the second surface of the sheet S is determined by the size in the sheet width direction of the sheet to be used when moving from the state of FIG. 6C to the state of FIG. The sheet S is moved to the first side side registration sensor SN2 side by the difference d0 from the size of the A3SEF sheet in the sheet width direction. By doing so, the positions of the image recording areas S1 and S2 in the sheet conveying direction and the sheet width direction can be matched when viewed from the direction perpendicular to the sheet surface of the sheet S.

FIG. 7 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the third embodiment, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. FIG. 7B is a diagram showing the positional relationship between the recognized B4SEF sheet size S ′, the image recording area S1, and the side registration sensors SN2 and SN3. FIG. 7B shows the B4SEF sheet size S ′ recognized by the image forming apparatus and the actual FIG. 7C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface, and FIG. FIG. 7D shows the image recording area S2 on the second surface of the reversal sheet in FIG. 7C. It is.
FIG. 7 of the third embodiment corresponds to FIG. 5 of the first embodiment. In the image forming apparatus according to the third embodiment, the second-side side registration sensor SN3 includes a line sensor having a plurality of light receiving elements, and is fixedly arranged with respect to the side sensor SN2. One edge in the sheet width direction when image recording is performed on the second surface of the sheet having a sheet width smaller than the length of A3SE (short edge of A3 sheet) or A4LE (long edge of A4 sheet) by the image forming apparatus In the first embodiment, the second-side side registration sensor SN3 is configured to be movable. However, the second-side side registration sensor SN3 configured by the line sensor of the third embodiment is fixedly arranged. In this state, the position of one edge in the sheet width direction when image recording is performed on the second surface is detected.
In other respects, the image forming apparatus of the third embodiment is the same as that of the first embodiment.

FIG. 8 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the fourth embodiment, the position of the image recording area in the sheet width direction at the image recording position, and the position of the sheet S. FIG. FIG. 8B is a diagram showing the positional relationship between the recognized B4SEF sheet size S ′, the image recording area S1, and the side registration sensors SN2 and SN3. FIG. 8B shows the B4SEF sheet size S ′ recognized by the image forming apparatus and the actual size. FIG. 8C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface. FIG. 8C shows the sheet of FIG. FIG. 8D shows the image recording area S2 on the second surface of the reversal sheet of FIG. 8C. FIG. 8D shows a state where the image is moved to the position detected by the second surface side registration sensor SN3. It is.
FIG. 8 of the fourth embodiment corresponds to FIG. 6 of the second embodiment. The image forming apparatus according to the fourth embodiment has a second side when recording a double-sided image on a sheet having a sheet width smaller than the length of A3SE (short edge of A3 sheet) or the length of A4LE (long edge of A4 sheet). The second embodiment is the same as the second embodiment except that the sheet conveying method and the position of the image recording area on the intermediate transfer belt B in the sheet width direction are different from those of the first embodiment.
In Example 4, image recording on a B4SEF sheet (sheet having a sheet width smaller than A3SEF) is performed as shown in FIG.

In FIG. 8, B4SEF image recording is performed on the first side of the sheet S, the sheet is inverted so that both end edges in the sheet width direction are interchanged, and one end edge of the inverted sheet S is detected by the second-side side registration sensor SN3. The operation until the inverted sheet S is moved in the sheet width direction to the position shown in FIG. 8C is the same as that in the second embodiment in which the state shown in FIG. 6C is set.
In Example 2, the sheet S in the state shown in FIG. 6C is moved in the sheet width direction so as to be in the state shown in FIG. 6D, and then the second image is recorded on the sheet S. The image on the second side is recorded on the sheet S without moving the sheet S in the 8C state in the sheet width direction.

That is, in the image forming apparatus of Embodiment 4, when the difference between the length of A3SE and the length of B4SE is d0, the first image recording area S1 on the intermediate transfer belt B is from the first-side side registration sensor SN2. It is formed at a position separated by a set distance d1 inside and at a position separated by a set distance (d0 + d1) from the second side side registration sensor SN3.
The position in the sheet width direction at the time of image recording on the first surface of the sheet S is 1 which is a set distance d1 away from one end edge of the sheet S in a state where the one end edge of the sheet S is positioned by the first surface side registration sensor SN2. An image is recorded in the image recording area S1 of the surface. The sheet S on which the first image has been recorded is inverted so that both end edges in the sheet width direction are interchanged, and the one end edge of the inverted sheet S is positioned by the second surface side registration sensor SN3 (state shown in FIG. 8C) ), Image recording is performed in the image recording area S2 on the second side.

When performing image recording on the second surface, the position of the image recording area S1 on the first surface is a position away from the second-side side registration sensor SN3 by a set distance d1. That is, the image recording area S1 on the first surface on the sheet S is moved by (d0 + d1) −d1 = d0 to the second side registration sensor SN3 side when recording the second image, compared to when recording the first image. Yes.
Accordingly, the two image recording areas on the intermediate transfer belt B are separated from the first image recording area on the intermediate transfer belt B by a distance d0 closer to the second side registration sensor SN3 in the sheet width direction. Formed at the position.
In the fourth embodiment, the position in the sheet width direction at the time of image recording on the second surface of the sheet S is controlled to a position at which one end edge of the sheet is detected by the second surface side registration sensor SN3. By moving the image recording area of the first surface by d0 from the position of the first surface to the second side registration sensor SN3 side, the positions of the image recording areas S1 and S2 on the sheet S in the sheet conveying direction and the sheet width direction are changed. This can be matched when viewed from a direction perpendicular to the sheet surface of S.

(Example of change)
As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various change is performed within the range of the summary of this invention described in the claim. It is possible. Examples of modifications of the present invention are illustrated below.
(H01) In the first to fourth embodiments, the first-side side registration sensor SN2 and the second-side side registration sensor SN3 are configured by separate side registration sensors, but a plurality of 2 corresponding to the first-side side registration position and the sheet size to be used are used. It can be constituted by one side register sensor that can move between the side register positions.
(H02) It is also possible to use a line sensor as the first side registration sensor SN2 that is fixedly arranged.
(H03) The present invention can also be applied to an inkjet recording type image forming apparatus other than an electrophotographic image forming apparatus, a thermal transfer type image forming apparatus, and the like.

FIG. 1 is an explanatory diagram of Embodiment 1 of the image forming apparatus of the present invention. 2A and 2B are explanatory views of the double-sided sheet conveying apparatus. FIG. 2A is a schematic sectional view taken along the line IIA-IIA in FIG. 1, and FIG. 2B is a sectional view taken along the line IIB-IIB in FIG. FIG. 3 uses the image forming apparatus of the first embodiment, and inverts the sheet so that the direction of the front edge in the conveyance direction of the sheet passing through the image recording position is constant and the both edges of the sheet in the sheet width direction are switched. FIG. 3A is a diagram illustrating a conventional technique when images are recorded on both sides of a sheet. FIG. 3A is a diagram illustrating a sheet stored in a sheet feeding tray, and FIG. 3B is a state in the middle of conveying a sheet taken out from the sheet feeding tray. FIG. 3C is a diagram illustrating a state in which the sheet is temporarily stopped by the registration roller and the front edge of the sheet is aligned in the registration roller axial direction and then moved in the registration roller axial direction. FIG. 3D is a diagram illustrating a toner image on the first surface of the sheet. FIG. 3E is a diagram illustrating a state of a sheet passing through a transfer region (image recording position on the sheet) while being transferred, and FIG. 3E is a diagram illustrating a state in which the sheet on which the first toner image is transferred passes through the fixing region. FIG. 3F is a view showing a reversal sheet obtained by reversing the sheet on which the toner image on the first surface is transferred and fixed so that both edges in the sheet width direction are interchanged. FIG. 3G is a front end edge of the sheet after the reversal sheet is temporarily stopped by a registration roller. FIG. 3H is a diagram illustrating a state in which the toner image is moved on the second side while the toner image is transferred to the second surface while the toner image is transferred to the second surface. FIG. 3I is a diagram illustrating a state in which the toner image is transferred to both sides of the sheet. FIG. 4 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus of the first embodiment, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. 4A is the image forming apparatus. FIG. 4B is a diagram showing the positional relationship between the A3SEF sheet size S ′ recognized by the image forming area, the image recording area S1, and the side registration sensors SN2 and SN3. FIG. 4B shows the A3SEF sheet size S ′ recognized by the image forming apparatus and actual FIG. 4C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface. FIG. 4C is a diagram illustrating the sheet of FIG. The figure which shows the state which moved the edge to the position detected by the 2nd surface side registration sensor SN3, FIG. 4D is image recording area S2 of the 2nd surface on the inversion sheet | seat of the said FIG. 4C. It illustrates. FIG. 5 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the first embodiment, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. FIG. 5B is a diagram showing the positional relationship between the B4SEF sheet size S ′ and the image recording area S1 and the side registration sensors SN2 and SN3 recognized by FIG. 5, and FIG. 5B shows the B4SEF sheet size S ′ recognized by the image forming apparatus and the actual FIG. 5C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface, and FIG. 5C shows the sheet of FIG. The figure which shows the state which moved the edge to the position detected by the 2nd surface side registration sensor SN3, FIG. 5D shows image recording area S2 of the 2nd surface of the said inversion sheet of FIG. 5C. It is to figure. FIG. 6 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the second embodiment of the present invention, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. FIG. 6B is a diagram showing the positional relationship between the B4SEF sheet size S ′ recognized by the forming apparatus and the image recording area S1 and the side registration sensors SN2 and SN3. FIG. 6B shows the B4SEF sheet size S ′ recognized by the image forming apparatus. FIG. 6C is a diagram showing the positional relationship between the actual sheet size S, the side registration sensors SN2 and SN3, and the first image recording area S1, FIG. 6C is the sheet of FIG. The figure which shows the state which moved the edge of the sheet | seat to the position detected by the 2nd surface side registration sensor SN3, FIG. 6D is the image recording area | region of the 2nd surface of the said inversion sheet | seat of the said FIG. 6C It shows a 2 and an image recording area S1 of the first side which is formed on the back surface, Figure 6E is a diagram showing an image recording area S2 of the second surface of the reversed sheet of FIG 6D. FIG. 7 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the third embodiment, the position of the image recording area in the sheet width direction and the position of the sheet S at the image recording position, and FIG. FIG. 7B is a diagram showing the positional relationship between the recognized B4SEF sheet size S ′, the image recording area S1, and the side registration sensors SN2 and SN3. FIG. 7B shows the B4SEF sheet size S ′ recognized by the image forming apparatus and the actual size. FIG. 7C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface, and FIG. 7C shows the sheet of FIG. FIG. 7D shows the image recording area S2 on the second surface of the reversal sheet of FIG. 7C. FIG. 7D shows a state where the image is moved to the position detected by the second surface side registration sensor SN3. It is. FIG. 8 is an explanatory diagram of the side registration sensors SN2 and SN3 of the image forming apparatus according to the fourth embodiment, the position of the image recording area in the sheet width direction at the image recording position, and the position of the sheet S. FIG. FIG. 8B is a diagram showing the positional relationship between the recognized B4SEF sheet size S ′, the image recording area S1, and the side registration sensors SN2 and SN3. FIG. 8B shows the B4SEF sheet size S ′ recognized by the image forming apparatus and the actual size. FIG. 8C is a diagram showing the positional relationship between the sheet size S, the side registration sensors SN2 and SN3, and the image recording area S1 on the first surface. FIG. 8C shows the sheet of FIG. FIG. 8D shows the image recording area S2 on the second surface of the reversal sheet of FIG. 8C. FIG. 8D shows a state where the image is moved to the position detected by the second surface side registration sensor SN3. It is. FIG. 9 is an explanatory diagram in the case of recording an image so that the image recording areas on both sides of the sheet overlap. FIG. 9A is an A3SEF sheet (short edge feed, that is, a sheet conveyed with the short side of the A3 sheet as the leading edge) 9B is a diagram illustrating a state in which image recording is performed while passing the transfer area on the A3SEF sheet, and FIG. 9C is a diagram illustrating a state in which image recording is performed on the image recording area on the first surface of the A3SEF sheet. 9D is a diagram showing a state in which the sheet of FIG. 9C is turned upside down, FIG. 9E is a diagram showing a state in which image recording is performed on the second surface while passing the transfer region through the sheet of FIG. 9D, and FIG. FIG. 9G is a diagram illustrating a state in which image recording is performed on the second surface of the sheet in FIG. 9D, and FIG. 9G illustrates that the image recording region S1 on the first surface of the sheet S and the image recording region S2 on the second surface are perpendicular to the paper surface of the sheet S. FIG. 9H is a diagram illustrating a state in which the sheet is displaced in the sheet conveyance direction when viewed from any direction, and FIG. 9H is a diagram illustrating the sheet S on which the first image recording area S1 and the second image recording area S2 of the sheet S are arranged. FIG. 6 is a diagram showing a state where the sheet is displaced in the sheet width direction when viewed from a direction perpendicular to the sheet. FIG. 10 uses an actual image recording apparatus, controls the direction of one end edge in the width direction of the sheet to be constant at the image recording position, and inverts the sheet so that the front and rear ends of the sheet are interchanged, and on both sides of the sheet. FIG. 10A is a diagram illustrating a conventional technique when recording an image, FIG. 10A is a diagram illustrating a sheet stored in a sheet feed tray, and FIG. 10B is a diagram illustrating a state in the middle of conveying a sheet taken out from the sheet feed tray. 10C is a diagram illustrating a state of the sheet passing through the sheet guide and the registration roller, and FIG. 10D is a diagram illustrating a state of the sheet passing through the transfer region (image recording position on the sheet) while the toner image is transferred to the first surface of the sheet. FIG. 10E is a diagram illustrating a state in which the sheet having the toner image on the first surface passed through the fixing region, and FIG. FIG. 10G is a diagram showing a state in which the edge is reversed so as to be replaced, FIG. 10G is a diagram showing a state in which the reversed sheet passes through the sheet guide and the registration roller, and FIG. FIG. 10I is a diagram illustrating a state in which a toner image is transferred to both sides of a sheet. FIG. 11 uses an actual image recording apparatus, and inverts the sheet so that the direction of the front end edge of the sheet passing through the image recording position is constant and the front and rear ends of the sheet are reversed, and images are formed on both sides of the sheet. 11A and 11B are explanatory diagrams of the prior art in the case of recording, in which FIG. 11A shows a sheet stored in a paper feed tray, FIG. 11B shows a state in the middle of conveying a sheet taken out from the paper feed tray, and FIG. FIG. 11D is a diagram showing a state in which the sheet is temporarily stopped by the registration roller and the front edge of the sheet is aligned in the registration roller axis direction and then moved in the registration roller axis direction. FIG. FIG. 11E is a diagram illustrating a state of the sheet passing through the image recording position). FIG. 11E is a diagram illustrating a state in which the sheet having the first toner image transferred passes through the fixing region. FIG. 11G is a diagram showing a state in which the toner image on the first surface is transferred and fixed and reversed so that both edges in the sheet width direction are interchanged. FIG. 11G shows the direction of the front edge of the sheet after the reversed sheet is temporarily stopped by a registration roller. FIG. 11H is a diagram illustrating a state in which the reversal sheet is moved in the registration roller axial direction and then moved in the registration roller axial direction, and FIG. 11H illustrates a state in which the toner image is transferred to the second surface while passing through the transfer region (image recording position on the sheet). FIG. 11I is a diagram illustrating a state in which the toner image is transferred to both sides of the sheet.

Explanation of symbols

d1 ... First surface set distance,
d2 ... second surface set distance,
F: Fixing device,
Py, Pm, Pc, Pk ... image carrier,
Q4: Image recording position (transfer position),
Q5 ... Fixing area,
Rr ... Register Roller
S ... Sheet
S1, S2 ... setting image area,
S1 ... first side setting image area,
S1a, S2a ... set image recording width,
S1b, S2b ... set image recording length,
S2 ... second side setting image area,
SH: Sheet conveying device,
SH3: sheet inversion path,
SN2 ... first side side register sensor,
SN3 ... second side side register sensor,
TR1 to TR3 ... paper feed tray,
UY to UK: toner image forming apparatus,
(BM + T2) ... transfer device,
(Fh, Fp) ... a pair of fixing rotating members,
(SH1 + Rp + Rs + Ra)... Sheet feeding device for feeding,
(SN2 + SN3) ... Side register sensor,
(UY to UK + BM + T2) ... image recording device,

Claims (8)

An image forming apparatus comprising the following structural requirements (A01) to (A05):
(A01) A sheet feeding device for feeding a sheet stored in a sheet feeding tray to a registration roller, and temporarily stopping the conveyed sheet front end portion to form a loop at the sheet front end portion, and then returning to the image recording position. In the case of carrying out image recording on both sides of the sheet, the registration roller for conveying the sheet, and a sheet reversing path for conveying and reversing the sheet image-recorded on the first surface in a direction perpendicular to the normal sheet conveying direction, A sheet conveying device that resends the sheet reversed in the sheet reversing path to the registration roller;
(A02) An image for recording an image in a set image area having a set image recording width set in the sheet width direction on the sheet passing through the image recording position and a set image recording length set in the sheet conveyance direction Recording device,
(A03) A first-side side registration sensor that is arranged between the registration roller and the image recording position and detects the position of one end edge of both end edges in the width direction of the sheet when an image is recorded on the first surface of the sheet And a side registration sensor having a second side side registration sensor for detecting a position of the same edge as the one end edge in the width direction of the sheet reversed when recording an image on the second surface of the sheet,
(A04) First-side side registration position detection means for detecting a first-side side registration position, which is a position of the one end edge at the time of recording an image on the first side of the sheet, in accordance with a detection signal of the first-side side registration sensor; Side registration position detecting means having second side side registration position detection means for detecting a second side side registration position, which is the same edge position as the one end edge during image recording on the second side, in accordance with a detection signal of the second side registration register sensor ,
(A05) At the time of recording an image on the first surface of the sheet, an image on the first surface is recorded in the set image area at a position separated by a first surface set distance d1 from the side registration position on the first surface to the center side of the sheet. The image recording for recording the second side image in the set image area at a position away from the second side side register position by the second side set distance d2 equal to the first side set distance d1 from the second side side register position at the time of recording the second side image apparatus. The image forming apparatus according to claim 1, comprising the following constituent elements (A06):
(A06) The sheet at the time of image recording on the first side is set so that one end edge of the sheet passes through the first side side registration position set at the same position as the arrangement position of the first side side registration sensor in the sheet width direction. The sheet conveying apparatus for conveying. The image forming apparatus according to claim 1, comprising the following constituent elements (A07):
(A07) Image recording on the first side so that one end edge of the sheet passes through the first side side registration position set at a distance d0 away from the arrangement position of the first side side registration sensor in the sheet width direction. The sheet conveying apparatus that conveys a sheet of time. The image forming apparatus according to any one of claims 1 to 3, comprising the following constituent elements (A08):
(A08) The sheet at the time of recording the image on the second side is set so that one end edge of the sheet passes through the second side side registration position set at the same position as the arrangement position of the second side side registration sensor in the sheet width direction. The sheet conveying apparatus for conveying. The image forming apparatus according to any one of claims 1 to 3, comprising the following constituent elements (A09):
(A09) Image recording on the second side so that one end edge of the sheet passes through the second side side registration position set at a position d0 away from the arrangement position of the second side side registration sensor in the sheet width direction. The sheet conveying apparatus that conveys a sheet of time. The image forming apparatus according to any one of claims 1 to 5, comprising the following constituent elements (A010) and (A011):
(A010) a sheet width direction conveying member that conveys the sheet in the sheet width direction so that one end edge of the sheet is detected by the first side registration register and the second side registration sensor;
(A011) The operation of the sheet width direction conveying member is controlled so that the set image area on the first surface of the sheet coincides with the set image area on the second surface when viewed from a direction perpendicular to the paper surface. Sheet width direction position control means for controlling the position of the sheet in the sheet width direction. The image forming apparatus according to claim 6, comprising the following constituent elements (A010 ') and (A011'):
(A010 ′) the sheet width direction conveying member configured by a registration roller moving device that moves the registration roller in the sheet width direction in order to adjust the position in the width direction of the sheet at the image recording position;
(A011 ′) The registration roller is moved in the sheet width direction so that the setting image area on the first side of the sheet matches the setting image area on the second side when viewed from the direction perpendicular to the paper surface. The sheet width direction position control means configured by registration roller movement control means for adjusting the position of the sheet in the width direction. The image forming apparatus according to any one of claims 1 to 5, comprising the following constituent elements (A012):
(A012) With respect to the set image area recording position in the sheet width direction on the first side, the set image area on the first side of the sheet and the set image area on the second side match when viewed from the direction perpendicular to the page. The image recording apparatus that shifts the set image area recording position in the sheet width direction on the second surface in the sheet width direction.

Images