JP5594072B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus. More specifically, as a fixing device for fixing a toner image on a sheet, the sheet is heated and pressurized by a heating member and a pressure member, and has a fixing device using a pressure belt as the pressure member. The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, a fixing device that simultaneously performs heating and pressurization is used to fix a toner image formed on a sheet. For example, a sheet is sandwiched between a heating roller and a pressure roller, and fixing is performed while the sheet is conveyed. Conventionally, in order to properly separate the paper after the fixing process from the fixing device, there is a paper provided with a separation claw at the exit of the nip.

  However, when the separation claw is arranged in a non-contact manner with respect to the fixing roller, there is a problem that separation property is not so good particularly in thin paper. On the other hand, when it is arranged in a contact type, there are problems that the surface of the fixing roller is damaged, or that the claw is soiled and the stain is transferred to the paper. Therefore, Patent Document 1 discloses an image forming apparatus having means for denting a heating roller near the exit of the fixing nip instead of providing a separation claw. As a result, a convex portion having a small radius of curvature is formed on the fixing nip side of the recess, and the paper is peeled off from the heating roller with its own rigidity by passing through that portion. In this document, as a means for denting the heating roller, a configuration in which the heating roller is pushed by a lever from its outer peripheral side is disclosed. By doing so, it is said that the paper can be easily separated without using a separation claw.

Japanese Patent Application Laid-Open No. 07-092937

  However, if the configuration in which the roller is recessed like the conventional image forming apparatus described above is provided outside the heating roller, there is a problem that the apparatus becomes large. In addition, repeated indentation of the heating roller for each fixing process, regardless of the type of paper, could lead to a shortened life of the fixing device.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus capable of appropriately separating sheets after fixing without using a separation claw, and suppressing the enlargement of the apparatus and the shortening of the fixing apparatus. There is to do.

In order to solve this problem, an image forming apparatus according to an aspect of the present invention includes a toner image forming unit that forms a toner image on a sheet, and a sheet on which the toner image is formed by the toner image forming unit. An image forming apparatus having a fixing unit for fixing a toner image on a sheet by applying pressure and heating, wherein the fixing unit includes a cylindrical fixing belt and a pressure member disposed on the outer peripheral side of the fixing belt. And a fixing roller that is disposed in contact with the inner peripheral surface of the fixing belt and not facing the pressure member, has a heat source therein, and rotates together with the fixing belt, and pressurizes on the inner peripheral side of the fixing belt. It is disposed in a position facing the member, by pressing toward the fixing belt pressing member, a fixing pad which forms a fixing nip between the fixing belt and the pressure member, the fixing nip in the fixing pad A movable part that is movably mounted at the mouth side, and by moving the movable part, a strong separation arrangement in which a part of the fixing belt is pushed out toward the pressure member and a normal arrangement in which no extrusion is carried out are provided. If the arrangement moving unit to be selectively taken and the sheet fixed by the fixing unit are thinner than a predetermined thickness, the arrangement moving unit takes a strong separation arrangement; otherwise, the arrangement moving unit takes a normal arrangement. A control unit.

In the image forming apparatus of the above aspect , a fixing nip is formed between the fixing belt and the pressure member, and a fixing roller and a fixing pad are arranged on the inner peripheral side of the fixing belt. Further, on the inner peripheral side of the fixing belt, a moving portion is provided at a position on the outlet side of the fixing nip in the fixing pad . Therefore, when the moving part is moved, the shape of the fixing belt on the exit side of the fixing nip can be changed. In the strong separation arrangement, by moving the moving portion, a part of the fixing belt is pushed out toward the pressure member, so that a convex shape having a small curvature radius can be formed at that location. Furthermore, in the present invention, since the strong separation arrangement is used only when printing on thin paper, the time during which the fixing roller is deformed is made shorter than the conventional one, and the life of the roller is suppressed. As a result, it is possible to appropriately separate the paper after fixing without using a separation claw, and suppressing the enlargement of the device and the shortening of the life of the fixing device.

Further in the present invention of the above aspect, the control unit may be thinner than the thickness of the sheet for fixing is predetermined by the fixing unit, and the smaller than the value coverage ratio in the predetermined range of the sheet leading end is predetermined Ikoto When one or both of the cases where there is no print data within a predetermined range at the front end of the sheet are satisfied , it is desirable that the arrangement movement unit is allowed to take the normal arrangement.
If the image thickness is moderate and does not have much toner attached to the leading edge of the paper, or if the image data is easy to separate such that there is a sufficient blank at the leading edge of the paper, it will be reliably separated even in the normal layout. be able to. In this way, shortening of the life of the fixing device can be further suppressed. Note that the predetermined range of the leading edge of the sheet may be the same range or may be different in the determination of the coverage ratio value and the determination of the presence or absence of print data at the leading edge of the sheet.

Furthermore , an image forming apparatus according to an aspect of the present invention includes a toner image forming unit that forms a toner image on a sheet, and pressurizing and heating the sheet on which the toner image is formed by the toner image forming unit at a fixing nip, An image forming apparatus having a fixing unit for fixing a toner image on a sheet, wherein the fixing unit includes a cylindrical fixing belt, a pressure member disposed on an outer peripheral side of the fixing belt, and an inner peripheral surface of the fixing belt It is disposed in contact with a position that does not face the pressure member, has a heat source inside, and is disposed at a position facing the pressure member on the inner peripheral side of the fixing belt, and a fixing roller that rotates together with the fixing belt. , By pressing the fixing belt toward the pressure member, the fixing pad that forms the fixing nip between the fixing belt and the pressure member, and the inner side of the fixing belt move to the position on the outlet side of the fixing nip Possible An arrangement movement unit that selectively moves between a strong separation arrangement in which a part of the fixing belt is pushed out toward the pressure member and a normal arrangement in which the extrusion belt is not pushed out by moving the movement part. And a control unit that causes the arrangement moving unit to take a strong separation arrangement when the sheet fixed by the fixing unit is thinner than a predetermined thickness, and otherwise causes the arrangement movement unit to take a normal arrangement , Even if the sheet fixed by the fixing unit is thinner than a predetermined thickness , the control unit has a coverage ratio within a predetermined range at the leading end of the sheet that is smaller than a predetermined value and is within a predetermined range at the leading end of the sheet. if it meets one or both of the no print data, along with those that assume a normally arranged in the arrangement moving part, the paper to be fixed by the fixing portion is thinner than the thickness decided in advance, predetermined If the second thinner than the thickness are each a Ikoto smaller than the value coverage ratio was predetermined for predetermined range of the paper leading end, and that there is no print data in the predetermined range of the paper leading edge of even if it meets one or both or, Ru der which assume a strong separation arranged in the arrangement moving part.
By being like this, even tend to separate image data, since a strong separation arrangement in the case of particularly thin sheet, can be reliably separated.

Furthermore, in the present invention, the moving part is rotatably provided on the exit side of the fixing nip of the fixing pad. In the normal arrangement, the tip part is arranged in a direction not facing the pressure member, and in the strong separation arrangement, It is desirable that the front end portion be disposed in a direction facing the pressure member across the fixing belt.
In such a case, switching between the normal arrangement and the strong separation arrangement is easy.

  According to the image forming apparatus of the present invention, it is possible to appropriately separate the paper after fixing without using a separation claw and suppressing the enlargement of the apparatus and the shortening of the life of the fixing apparatus.

1 is a schematic configuration diagram illustrating a color printer according to an embodiment. FIG. 2 is an explanatory diagram illustrating a schematic configuration of a fixing unit according to the present embodiment. FIG. 3 is a cross-sectional view showing the vicinity of a fixing nip. It is sectional drawing which expands and shows a protrusion member. It is explanatory drawing which shows the protrusion member after rotation. It is a flowchart figure which shows the printing treatment of this form. It is explanatory drawing which shows another example of a fixing | fixed part. It is a fragmentary perspective view which shows another example of a fixing | fixed part.

"First form"
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a so-called tandem type electrophotographic color printer.

  The color printer 1 of this embodiment is a so-called tandem type image forming apparatus capable of forming a color image, as shown in FIG. In the middle of the figure, four color image forming portions are arranged along the intermediate transfer belt 11 in the order of yellow 10Y, magenta 10M, cyan 10C, and black 10K from left to right in the figure. Above the intermediate transfer belt 11, toner storage portions 12 (12Y, 12M, 12C, and 12K) that store toner of each color are provided.

  A detachable paper feed cassette 13 is mounted on the lower portion of the color printer 1 in FIG. Further, on the right side in the figure, a paper transport path 14 is provided from the bottom upward. A paper feed roller 15, a secondary transfer unit 16, a fixing unit 17, and a paper discharge roller 18 are provided in order from the bottom along the paper conveyance path 14. A discharge tray 19 is provided on the upper surface of the color printer 1. Note that a registration roller 20 is provided in the paper transport path 14 in order to adjust the paper entry timing to the secondary transfer unit 16. Further, the fixing unit 17 of the present embodiment includes a fixing member 31 on the left side in the drawing and a pressure member 32 on the right side in the drawing. The detailed configuration of the fixing unit 17 will be described later.

  The image forming units 10Y, 10M, 10C, and 10K for the respective colors include a charging unit 22, an exposing unit 23, a developing unit 24, a primary transfer unit 25, and a cleaner 26 in the clockwise direction in FIG. Have. The exposure unit 23 is provided below the image forming unit for each color, and is common to each color. A belt cleaner 27 is provided in contact with the left end of the intermediate transfer belt 11 in the figure.

  Next, the operation of each part when a color image is formed by the color printer 1 will be briefly described. At the time of image formation, the intermediate transfer belt 11 and the photosensitive members 21 of the respective colors are rotated as indicated by arrows in FIG. The photoreceptor 21 is uniformly charged by the charging unit 22 and then exposed by the exposure unit 23. As a result, an electrostatic latent image based on the image data is formed on the surface of the photoreceptor 21.

  Subsequently, toner is supplied to the electrostatic latent image by the developing unit 24, and a toner image is formed on the photoreceptor 21. The toner images of the respective colors are transferred onto the intermediate transfer belt 11 by the primary transfer unit 25 and superimposed. The toner remaining on the photoreceptor 21 even after passing through the primary transfer area is scraped off by the cleaner 26.

  On the other hand, the sheets stored in the sheet feeding cassette 13 are pulled out one by one by the sheet feeding roller 15. Then, the toner image superimposed on the intermediate transfer belt 11 is transferred by the secondary transfer unit 16 to the sheet conveyed through the sheet conveyance path 14. The sheet on which the toner image is transferred is further conveyed upward and reaches the fixing unit 17.

  In the fixing unit 17, the toner is fixed to the sheet by being heated and pressurized. In this embodiment, the toner image is formed on the left side of the sheet in FIG. 1, and the surface of the sheet carrying the toner image is in contact with the heating member 31 and the back side thereof is in contact with the pressure member 32. . Further, the paper on which the toner is fixed is discharged to a paper discharge tray 19 by a paper discharge roller 18. Note that the toner remaining on the intermediate transfer belt 11 after the sheet has passed through the secondary transfer area is scraped off by the belt cleaner 27.

  As shown in FIG. 2, the fixing unit 17 according to the present embodiment includes a fixing roller 34 having a heat source 33 and a pad 35 as a heating member 31, and a heat belt 36 spanning them. The fixing roller 34 is for heating and rotating the heat belt 36 by the heat of the heat source 33. The right side surface of the pad 35 is formed in a concave shape along the outer peripheral surface of the pressing member 32 in the drawing. The pad 35 is pressed against the pressure member 32 with an appropriate pressure by sandwiching the heat belt 36 between the concave portion and the pressure member 32.

  The pressure member 32 is an elastic roller having appropriate elasticity. As shown in FIG. 2, a fixing nip N is formed between the heat belt 36 and the pressure member 32 by the pressure contact of the pad 35. The sheet is conveyed through the fixing nip N upward from the bottom in the drawing. The pad 35 is fixedly arranged in the machine by a support 37.

  As shown in FIGS. 2 and 3, a protruding member 41 for changing the separability is attached to the upper right corner in the drawing of the pad 35. This position is on the exit side of the fixing nip N. Further, the protruding member 41 is attached to the pad 35 so as to be rotatable. And in this form, as shown in FIG. 3, it has the rotation drive part 45 which rotates the protrusion member 41, and the control part 46 which controls the rotation position. The rotation driving unit 45 corresponds to the arrangement moving unit.

  The projecting member 41 has support portions 42 at both ends in the axial direction (in the depth direction in the drawing) and projecting portions 43 between them as shown in FIG. The support portion 42 is rotatably attached to both end portions of the pad 35 in the axial direction. The protrusion 43 is an axially long plate-like member disposed outside the outer peripheral surface of the pad 35, and moves outside the pad 35 by the rotation of the support portion 42.

  When the projecting member 41 is rotated about 90 ° in the clockwise direction in the drawing from the arrangement of FIG. 4, the solid line is shown in FIG. 5. In this arrangement, the protrusion 43 pushes the heat belt 36 toward the pressure member 32 from the inner peripheral side thereof. Therefore, a convex shape E having a small curvature radius is formed on the outer peripheral surface of the heat belt 36 at the exit of the fixing nip N. The convex shape E formed at the exit of the fixing nip N allows the sheet to be easily separated by curvature, so that the separation performance is higher than that of the shape without the convex shape E (the state shown in FIG. 4). Hereinafter, the state in which the convex shape E is not formed (FIG. 4) is referred to as normal arrangement, and the state in which the convex shape E is formed (FIG. 5) is referred to as strong separation arrangement. In the normal arrangement, the projecting member 41 does not contribute to the separability, and may not be in contact with the heat belt 36.

In this embodiment, in the normal arrangement (FIG. 4), the size of each part is determined so that the curvature can be separated only by the rigidity of the paper if it is a relatively thick paper having a basis weight of about 80 g / m ² or more. . At the exit of the fixing nip in the normal arrangement, the radius of curvature of the heat belt 36 is about 4 to 8 mm.

On the other hand, in the strong separation arrangement, at the exit of the fixing nip N, the outer shape of the heat belt 36 is a convex shape E having a radius of curvature of about 1 mm. That is, in the strong separation arrangement, the radius of curvature of the outer shape of the heat belt 36 at the outlet of the fixing nip N is smaller than in the normal arrangement, and the separation force of the fixing unit 17 is strong. Therefore, in the present embodiment, the strong separation arrangement (FIG. 5) is adopted only when a sheet thinner than the basis weight of about 80 g / m ² is used. In this way, even if the paper is a fairly thin paper having a basis weight of 60 g / m ² or less, it can be reliably separated.

  That is, in this embodiment, it is determined whether or not the strong separation arrangement is used according to the thickness of the paper. In the strong separation arrangement, a greater stress is applied to the heat belt 36 than in the normal arrangement. Therefore, the life of the heat belt 36 may be shortened if it is continuously separated for a long time or repeated many times. Therefore, in this embodiment, a strong separation arrangement is adopted only when necessary. That is, a strong separation arrangement is used only during printing using thin paper. This is because in the case of printing on relatively thick paper, it is possible to reliably separate even in the normal arrangement, so that it is not necessary to use a strong separation arrangement.

  Therefore, in this embodiment, the control unit 46 determines whether or not the sheet to be used for printing is a thin sheet. Only when it is determined that the sheet is a thin sheet, the strong separation arrangement is used. In this way, the influence on the life of the heat belt 36 can be minimized.

  Therefore, in this embodiment, it is stored for each paper feed cassette 13 whether or not the paper stored therein is thin paper. Then, it is possible to determine whether the paper is thin or not by the paper feed cassette 13 selected at the time of printing. For this purpose, for example, when the paper is stored in the paper feed cassette 13, whether or not the paper to be stored is thin paper may be registered in advance by the user. Alternatively, a sensor for detecting the paper thickness may be disposed in the paper transport path so that the thickness of the paper to be printed is detected each time.

  If it is determined that a strong separation arrangement is necessary, the position of the sheet is determined using, for example, the registration roller 20 (see FIG. 1). In this embodiment, the entry timing to the fixing nip N can be known from the elapsed time from the timing when the leading edge of the sheet is discharged from the registration roller 20. Then, before the sheet enters the fixing nip N, the protruding member 41 is rotated. As a result, when the sheet after the secondary transfer enters the fixing nip N, a strong separation arrangement is made.

  In this way, since the shape of the fixing nip N can be changed before the leading edge of the sheet reaches the fixing nip N, even thin paper can be reliably separated. If only the leading edge is separated, the back side of the sheet can be separated. However, if the arrangement is changed in the middle of fixing one sheet, the image quality may be affected. Therefore, it is preferable not to change the arrangement in the middle. When the end of the paper passes, the normal arrangement is restored. By doing so, it is possible to achieve a strong separation arrangement only for a necessary period without affecting the image quality.

  In the color printer 1 of the present embodiment, processing when receiving a print instruction will be described based on the flowchart shown in FIG. In this embodiment, this process is executed when a print job is received. In this embodiment, the normal arrangement is used while the print job is not being executed. Therefore, at the start of this flowchart, the fixing unit 17 is in a normal arrangement.

  When the execution of the print job is started, first, it is determined whether or not the paper to be printed is thin paper (S101). This determination may be made as described above. If it is determined that the paper is not thin (S101: No), the printing process is executed as it is (S102). In this case, the fixing unit 17 remains in the normal arrangement. Since it is not thin paper, it can be reliably separated even in normal placement. When printing is finished, the processing of this job is finished.

  On the other hand, when it is determined that the paper is thin (S101: Yes), the fixing unit 17 is changed to the strong separation arrangement. For this purpose, the timing for entering the fixing nip N is acquired based on the timing at which the leading edge of the first sheet of the job comes out of the registration roller 20, and the protruding member 41 is rotated in time (S103). This results in a strong separation arrangement. By performing the fixing process while maintaining the position of the protruding member 41, it is possible to reliably separate even thin paper. Thus, printing on thin paper (S104) is performed.

  If the job being executed is for printing a plurality of sheets, the plurality of sheets are printed with the fixing unit 17 in a strongly separated arrangement (S105: No → S104). When the trailing edge of the last sheet of the job passes through the fixing nip N (S105: Yes), the printing of this job is completed. Therefore, the protruding member 41 is rotated in the opposite direction to S103, the fixing unit 17 is returned to the normal arrangement (S106), and this process is terminated. This is the end of the description of this process.

  As described above in detail, according to the color printer 1 of the present embodiment, only when printing on thin paper, the protruding member 41 is rotated to be in a strong separation arrangement. In the strong separation arrangement, the protruding portion 43 of the protruding member 41 protrudes toward the pressure member 32 at the exit of the fixing nip N, so that a convex shape E having a small curvature radius is formed on the heat belt 36. Therefore, the paper is easily separated at this location. Further, in this embodiment, it is determined whether or not the paper is thin paper, and the strong separation is arranged only when the paper is thin paper, so that the life of the heat belt 36 is suppressed.

In the above embodiment, the separability is selected only according to the thickness of the paper. However, in addition to the thickness of the paper, the image data to be printed also affects the separation of the paper after fixing. Even if the sheet is not so thin, it tends to be harder to be separated when the coverage at the leading edge is large or when the blank at the leading edge of the sheet is small than when it is not. Conversely, if the coverage at the leading edge is small and there is sufficient space at the leading edge of the paper, even if it is a medium thickness paper with a basis weight of about 60 to 80 g / m ² , for example, it is usually placed Can be separated sufficiently. Therefore, in such a case, the strong separation arrangement is not necessarily required.

For example, when printing using a medium thickness paper having a basis weight of 60 to 80 g / m ² , the printing area ratio (coverage ratio) within a range of 10 mm from the front edge of the paper is 20% or less, and the paper When there is no print data within a range of 3 to 6 mm from the tip, the normal arrangement may be used. In addition, both the coverage ratio at the leading edge and the blank amount at the leading edge of the paper, which are these conditions, may be considered, or only one of them may be considered. When only a part of paper in the job satisfies this condition, the normal arrangement may be made only while fixing the corresponding paper in the job, or the strong arrangement may be given for all of the jobs.

  Further, instead of attaching the protruding member 41 to the outside of the pad 35, a part of the pad 35 may be a rotatable protruding portion 51 as shown in FIG. Then, the heat belt 36 can be pushed out toward the pressure member 32 by rotating the protruding portion 51 around the rotation shaft 52. Then, the normal arrangement shown by the solid line in the figure can be changed to the strong separation arrangement shown by the two-dot chain line in the figure. In this case, the entire pad 35 may not necessarily be rotated in the axial direction. The protruding portions 51 may be formed at several locations in the axial direction.

  Alternatively, as shown in FIG. 8, a protruding member 55 may be arranged on the inner peripheral side of the heat belt 36 separately from the pad 35. This figure shows a strong separation arrangement. Thus, if the convex-shaped part 55a of the protrusion member 55 is protruded toward the pressurization member 32, the convex part with a small curvature radius will be formed there. If the projecting member 55 is rotated about 90 ° counterclockwise in the figure by the rotation shaft 56 from the arrangement shown in this figure, the normal arrangement can be obtained. Even in this case, even the thin paper can be reliably separated without much deterioration of the heat belt 36.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, in this embodiment, the projecting portion 43 of the projecting member 41 is formed over the entire axial direction, but only the support portions 42 without the projecting portion 43 may be provided at both end portions in the axial direction. Good. Or you may make it provide the thing similar to the support part 42 in the several location of an axial direction, and make it rotate simultaneously and protrude.

DESCRIPTION OF SYMBOLS 1 Color printer 10Y, 10M, 10C, 10K Image formation part 17 Fixing part 32 Pressure member 33 Heat source 34 Fixing roller 35 Pad 36 Heat belt 41 Projection member 43 Projection part 45 Rotation drive part 46 Control part

Claims (4)

A toner image forming unit for forming a toner image on the paper, and a fixing unit for fixing the toner image on the paper by pressurizing and heating the paper on which the toner image is formed by the toner image forming unit in a fixing nip. In an image forming apparatus,
The fixing unit is
A cylindrical fixing belt;
A pressure member disposed on the outer peripheral side of the fixing belt;
A fixing roller which is disposed in contact with a position which is an inner peripheral surface of the fixing belt and does not face the pressure member, has a heat source therein, and rotates together with the fixing belt;
The fixing belt is disposed at a position facing the pressure member on the inner peripheral side of the fixing belt, and the fixing belt is pressed between the fixing belt and the pressure member by pressing the fixing belt toward the pressure member. A fixing pad forming a nip;
A moving part movably mounted at a position on the outlet side of the fixing nip in the fixing pad ;
An arrangement moving unit for selectively taking a strong separation arrangement in which a part of the fixing belt is pushed out toward the pressure member and a normal arrangement in which the pushing unit is not pushed out by moving the moving unit;
A control unit that causes the arrangement movement unit to take the strong separation arrangement when a sheet fixed by the fixing unit is thinner than a predetermined thickness, and otherwise causes the arrangement movement unit to take the normal arrangement. An image forming apparatus comprising: The image forming apparatus according to claim 1 , wherein the control unit includes:
The even paper to be fixed by the fixing portion is thinner than the thickness of said predetermined, printing and Ikoto smaller than the value coverage ratio was predetermined for predetermined range of the paper leading end, in the predetermined range of the paper tip An image forming apparatus characterized in that, when either or both of the absence of data is satisfied , the arrangement moving unit takes the normal arrangement. A toner image forming unit for forming a toner image on the paper, and a fixing unit for fixing the toner image on the paper by pressurizing and heating the paper on which the toner image is formed by the toner image forming unit in a fixing nip. In an image forming apparatus,
The fixing unit is
A cylindrical fixing belt;
A pressure member disposed on the outer peripheral side of the fixing belt;
A fixing roller which is disposed in contact with a position which is an inner peripheral surface of the fixing belt and does not face the pressure member, has a heat source therein, and rotates together with the fixing belt;
The fixing belt is disposed at a position facing the pressure member on the inner peripheral side of the fixing belt, and the fixing belt is pressed between the fixing belt and the pressure member by pressing the fixing belt toward the pressure member. A fixing pad forming a nip;
A moving part movably attached to a position on the outlet side of the fixing nip on the inner peripheral side of the fixing belt,
An arrangement moving unit for selectively taking a strong separation arrangement in which a part of the fixing belt is pushed out toward the pressure member and a normal arrangement in which the pushing unit is not pushed out by moving the moving unit;
A control unit that causes the arrangement movement unit to take the strong separation arrangement when a sheet fixed by the fixing unit is thinner than a predetermined thickness, and otherwise causes the arrangement movement unit to take the normal arrangement. Have
The controller is
Even if the paper fixed by the fixing unit is thinner than the predetermined thickness, the coverage ratio within the predetermined range at the front end of the paper is smaller than the predetermined value and the print data within the predetermined range at the front end of the paper. If either or both of the above are satisfied, the arrangement moving unit is allowed to take the normal arrangement,
Paper to be fixed by the fixing unit, the less than predetermined thickness is, when the second thinner than the thickness decided in advance, not smaller than the value coverage ratio is predetermined in the predetermined range of the paper tip And the fact that there is no print data within a predetermined range at the front end of the paper, or both of them satisfy the strong separation arrangement. An image forming apparatus. In the image forming apparatus according to any one of claims 1 to 3 ,
The moving part is
The fixing pad is rotatably provided on the outlet side of the fixing nip,
In the normal arrangement, the tip is arranged in a direction not facing the pressure member,
In the strong separation arrangement, the image forming apparatus is characterized in that a front end portion thereof is arranged to face the pressure member with the fixing belt interposed therebetween.

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