JP2006282349A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plurality of branch carrying passages of sheets as recording paper sheets, for responding to a trouble occurring in one of the branch carrying passages by using the other branch carrying passage so as not to halt the device and maintain its processing capability, and for allocating a branch carrying passage suitable for a thick or thin paper sheet to implement highly accurate image formation so as to print in high quality and improve its reliability. <P>SOLUTION: A sheet S is fed from a paper feeding cassette 209 of a sheet feeding part. Switching between a first branch carrying passage 208 and a second branch carrying passage 209 is performed by operation of a branch carrying passage switch flapper 235 to guide the sheet S to either the first branch carrying passage 208 or the second branch carrying passage 209, and then the sheet S is carried to a photoreceptor drum 13 of the image forming part. The branch carrying passages are alternately switched, for example, the sheet S is carried by the first branch carrying passage 208, and then the next sheet S is carried by the second branch carrying passage 209. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a laser beam printer, a copying machine, and a facsimile machine.

  In general, an image forming apparatus is provided with a sheet conveyance path for feeding a sheet, which is a recording medium, from a sheet storage unit such as a paper feed cassette and conveying the sheet to the image forming unit via a registration roller.

  In such a sheet conveyance path, when a paper jam (jam) occurs in the sheet being conveyed, the operation of the image forming apparatus main body is temporarily stopped, and during that time, the user performs jam processing, finishes the processing, and restarts. However, the next print job is not started until the fixing device reaches a predetermined temperature, and there is a problem that time is wasted.

  In addition, the surface of various types of feed rollers may wear due to use over time, or slippage will occur if paper dust adheres to the roller surface, so periodic roller cleaning is necessary, and the operation of the image forming apparatus main body during that time must be temporarily stopped. There is a problem of not getting.

  In particular, when a sheet is transferred to a photosensitive drum, which is an image carrier, in an image forming unit, it is necessary to distinguish between a thin sheet and a thick sheet and consider the drum entry direction. For example, it shows a behavior in which the rear end jumps up when it passes through the registration roller, which propagates to the transfer portion and causes image blurring. For this reason, for thick sheets, there is a restriction that the sheet conveyance path from the registration roller to the transfer unit is required to be as straight as possible, and it is mechanically difficult to cope with a thin sheet with one branch conveyance path. There is a problem with it.

  Further, in order to synchronize with the image formation on the photosensitive drum, a registration roller is disposed on the upstream side of the drum to correct skewing and meandering of the sheet, and then the sheet is fed to the drum. In that case, an appropriate interval, that is, a distance between the sheets, is provided between the preceding sheet and the succeeding sheet that enter the nip portion of the registration roller in the stopped state. Thereby, the corresponding position between the sheet and the image formed thereon can be maintained with high accuracy. The minimum required sheet-to-sheet distance must be set to be larger than the sheet interval (hereinafter referred to as “process sheet interval”) in the image forming section such as a photosensitive drum. It has become an obstacle to improvement of ability.

  Previously, many image forming apparatuses have been proposed for solving the conventional problems that occur in such a sheet conveyance path. The sheet conveyance path is composed of a plurality of branch conveyance paths, and a sheet is provided in each branch conveyance path. Some of the above-mentioned problems have been overcome by arranging a feeding unit and registration rollers, and alternately feeding out sheets from each sheet feeding unit to substantially increase the distance between the sheets in the registration rollers (for example, Patent Document 1).

JP-A-8-217340

  However, each branch conveyance path constituting the conveyance path has a restriction that the sheet feeding unit must be loaded with exactly the same size sheet, and there is a problem that the user needs trouble in handling and operation. In addition, when a sheet of a different size is set in the sheet sheet feeding section of each branch conveyance path due to a user's misjudgment or misoperation, there is no means for judging it and no warning means. There is a risk of jamming on the way.

  Accordingly, an object of the present invention is to configure the sheet conveyance path with a plurality of branch conveyance paths, so that even if a trouble occurs in one branch conveyance path, the apparatus is temporarily stopped in response to another one of the branch conveyance paths. And maintain the required processing capacity, and realize high-precision image formation by assigning branch conveyance paths corresponding to thick and thin sheets, enabling high-quality printing and high reliability An object is to provide an image forming apparatus.

  In order to achieve the above object, an image forming apparatus of the present invention includes a sheet feeding unit that feeds a stored sheet to a sheet conveying path, and an image forming unit that forms an image on the sheet conveyed by the sheet conveying path. And a plurality of branch conveyance paths that diverge a sheet conveyance path between the sheet feeding unit and the image forming unit on the downstream side of the sheet feeding unit and merge on the upstream side of the image forming unit. And a switching means provided in the branch portion for selecting any of the plurality of branch conveyance paths and guiding the sheet.

  According to the image forming apparatus of the present invention, the sheet conveyance path from the sheet feeding unit to the image forming unit is configured by a plurality of branch conveyance paths, and the sheet is selected by any switching unit and is arranged on any of the branch conveyance paths. Can be guided and conveyed, for example, one of the branch conveyance paths and the other one can be switched alternately and used alternately, or even if one of the branch conveyance paths becomes unusable, another branch conveyance path Since the operation of the main body of the image forming apparatus can be continued as it is without being temporarily stopped, it is possible to obtain an effect that the processing capacity is not lowered.

  Hereinafter, a preferred embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the laser beam printer 1 in this case, which is an embodiment of the image forming apparatus, includes a sheet feeding unit 200. The sheet feeding unit 200 includes a sheet feeding cassette 209 that stores a plurality of sheets S, and a pickup roller 201 that picks up and feeds out the uppermost one of the stacked sheets S. Further, a feed roller 203a and a retard roller 203b for separating and carrying out the fed sheet S are disposed on the downstream side of the pickup roller 201, and a sheet detection sensor 207 and a drawing roller 206 are sequentially disposed on the downstream side.

  Further, the first branch conveyance path 208 that forms two sheet conveyance paths in this example is assumed to branch from immediately after the downstream side of the drawing roller 206 to constitute the sheet conveyance path that is the gist of the present invention. The second branch conveyance path 209 is arranged substantially in parallel in the printer main body 9. A switching flapper (switching means) 235 for selecting and switching between the first branch transport path 208 and the second branch transport path 209 and guiding the sheet S to the switched branch transport path is provided at the branch portion. Is provided. The switching flapper 235 is driven by an electromagnetic switching solenoid 114 so that the switching flapper 235 is switched to a position indicated by a solid line in the figure when off and to a position indicated by a broken line in the figure when on. In this embodiment, the sheet S is guided to the first branch conveyance path 208 when the flapper is turned off, and the sheet S is guided to the second branch conveyance path 209 when the flapper is turned on.

  In the first branch conveyance path 208, feed rollers 210, 211, and 212 for conveying the sheet S to the downstream side in the conveyance direction are arranged in pairs, respectively. In the second branch conveyance path 209, the feed rollers 214, 215 and 216 are provided as opposed pairs. Each feed roller is provided with an electromagnetic clutch, which receives rotational driving from a main drive motor (not shown) and performs on / off control of rotational driving by these electromagnetic clutches. Further, first and second registration rollers 213 and 217 are provided in the first and second branch conveyance paths 208 and 209, respectively.

  On the other hand, the printer main body 9 is provided with a multi-manual paper feed unit 300, and is picked up by a paper feed tray 306 for stacking sheets S, a pickup roller 305 for picking up sheets S in the paper feed tray 306, and a pickup roller 305. A feed roller 301a, a retard roller 301b, and a drawing roller 303 for separating and conveying the sheet S are provided, and a sheet detection sensor 308 is disposed between these rollers.

  A sheet conveyance path 309 that conveys the sheet S fed from the multi-manual sheet feeder 300 crosses the first branch conveyance path 208 and joins the second separation conveyance path 209. A manual feed switching flapper 307 is disposed at the junction 304 with the first branch conveyance path 208. The manual feed switching flapper 307 is driven by an electromagnetic switching solenoid (not shown), and in this example, the position of the solid line in the figure is switched when the solenoid is off, and the position indicated by the broken line in the figure when the solenoid is on. Yes. When the manual feed switching flapper 307 is switched to the ON position indicated by the solid line in the figure, the sheet is guided to the first branch conveyance path 208, and when the manual feed switching flapper 307 is switched to the OFF position indicated by the broken line in the figure, A sheet is guided to the two-branch conveyance path 209.

  By the way, the sheet S fed from the paper feed cassette 209 or the multi-manual paper feed unit 300 during printing is conveyed in a state where the rotation of the first and second registration rollers 213 and 217 is stopped, The front end is pressed against the nip portion of each of the first and second registration rollers 213 and 217 by 216 to form a loop, thereby correcting the skew and positioning. Thereafter, the first and second registration rollers 213 and 217 are rotated in synchronization with an image vertical synchronization signal output from a personal computer or a host computer (not shown) that supplies image information, and sent images are sent. The data and the sheet S are synchronized, and an image is printed at a predetermined position on the sheet S.

  Optical first and second registration roller front sensors 218 and 219, such as photocouplers, are provided correspondingly in the vicinity of the upstream side in the conveying direction of the first and second registration rollers 213 and 217, respectively. Control for forming a loop on the sheet S, and jam monitoring is performed by detecting the occurrence of a jam in the first branch conveyance path 208 and the second branch conveyance path 209. Further, downstream of the first and second registration rollers 213 and 217, an image forming unit 3 including a photosensitive drum that forms an image by laser light from the laser scanner unit 10 is disposed, and the first and second registration rollers are arranged. The sheet S sent out from the rollers 213 and 217 passes through the first branch conveyance path horizontal path 230 and the second branch conveyance path oblique path 231 and is conveyed to the photosensitive drum 13 of the image forming unit 3.

  A fixing device 4 is disposed on the downstream side of the image forming unit 3, and paper discharge rollers 5, 6, 7, and 8 are disposed on the downstream side of the fixing device 4. The sheet S on which an image is formed and fixed by the image forming unit 3 and the fixing device 4 by these paper discharge rollers 5, 6, 7, and 8 is conveyed to the paper discharge tray 9.

  On the other hand, as shown in FIG. 1, the printer main body 9 includes a main control device (control means) 101, and controls the operation of the printer main body 9 and the paper feeding operation of the paper feeding device 200. And a gate element (both not shown), and the main part of the control is realized by software written in the ROM.

  In FIG. 2, which shows a functional block diagram constituting the main control device 101, it has a paper feed control means 111, and this paper feed control means 111 comprises a paper feed motor control means 110, a pickup control means 111 and a flapper control means 112. ing. From these three control means, drive signals are sent to the paper feed motor drive circuit 106, the pickup solenoid drive circuit 105, and the flapper switching solenoid drive circuit 113, respectively. From these three drive circuits, operation on / off signals are sent to the paper feed motor 109, the flapper switching solenoid, the pickup solenoid 108a and the flapper switching solenoid 114. On the other hand, the main controller 101 has a main motor drive circuit 104 along with the drive circuits. The main motor drive circuit 104 sends an operation on / off signal to the main motor 107.

  When the cassette feeding mechanism composed of the pickup roller 201, the feed / retard roller pair 203a, 203b, and the transport roller 206 is driven by the control by the main controller 101 and the rotation of the main motor 107, the switching operation by the switching flapper 235 causes the first change. One of the first branch transport path 208 and the second branch transport path 209 is selected, and the sheet S set in the paper feed cassette 209 is sent to either the first or second registration rollers 213, 217. Yes. The paper feed control timer 103 is for managing timing for the paper feed control means 102 to sequentially control the paper feed device 200.

  In FIG. 1, in the case of the laser beam printer 1, the cassette paper feeding form presses the pickup roller 201 against the sheet S to rotate it, and sends the sheet S to the feed / retard roller pair 203a, 203b. Here, the pickup roller 201 starts an operation of moving the pickup roller 201 up and down by a pickup solenoid 108 driven by a drive signal from the pickup solenoid drive circuit 105 based on a signal from the paper feed control unit 102. It has become. That is, when the pickup solenoid 108 is turned on, the pickup roller 201 is lowered by the driving force.

  The pickup roller 201 is rotated by a paper feed motor 109 driven by a drive signal from the paper feed motor drive circuit 106. The paper feed motor 109, which is a driving device for rotating the pickup roller 201, is a feed / retard roller pair. 203a and 203b are also rotated and stepping motors are used. The feed roller 203 a rotates in the direction in which the sheet S is conveyed to the drawing roller 206 at the same rotational speed as the pickup roller 201. The retard roller 203b rotates in the opposite direction to the feed roller 203a and applies a smaller torque to the lower surface of the sheet S in the opposite direction to the feed roller 203a than the feed roller 203a.

  Since the frictional force acting between the sheets is weaker than the frictional force between the roller surface of the retard roller 203b and the sheet S, it is conveyed to the feed roller pair 203a in a state where two or more sheets S overlap. In this case, only the uppermost sheet is fed toward the registration roller by the feed roller 203a, and the lower sheet S is sequentially separated by the retard roller 203b and pushed back to the cassette 209 side. Further, when only one sheet S is sandwiched between the feed roller 203a and the retard roller 203b, the retard roller 203b has a lower torque than the feed roller 203a, and therefore rotates together with the feed roller 203a. .

  From the above, when feeding, when the pickup solenoid 108 is in the OFF state, as shown in FIG. 1, the pickup roller 201 maintains the position of the broken line in the drawing and is separated from the uppermost sheet S of the stacked sheet bundle. It has become.

  When a paper feed start signal is transmitted from the main controller 101, first, the pickup solenoid 108 is turned on at a predetermined timing, and the pickup roller 201 contacts the uppermost sheet S as indicated by a solid line in the drawing. Subsequently, based on a paper feed motor rotation start signal transmitted from the main controller 101 at a predetermined timing, a paper feed motor ON signal is transmitted from the paper feed motor control means 110, and the paper feed motor 109 starts rotating. Accordingly, the pickup roller 201, the feed roller 203a, and the retard roller 203b start to rotate, and the uppermost first sheet S is fed from the stacked sheet bundle. When the leading edge of the first sheet S reaches the sheet detection sensor 207 and the sheet detection sensor detects the presence of the sheet, the pickup solenoid 108 is turned off and the pickup roller 201 is retracted again to the broken line position in the figure. To do. The leading edge of the sheet S is nipped by the drawing roller 206 and conveyed downstream, and the leading edge of the sheet S is guided to the first branch conveying path 208 by the switching flapper 235 and sequentially conveyed by the conveying rollers 210, 211, and 212. The leading edge of the paper is detected by the sensor before the first registration, and after a predetermined time, the driving of the conveying rollers 210, 211, 212 is stopped, the leading edge of the paper hits the first registration roller 213, and a loop is formed. In the state, stop and correct skew. Then, at a predetermined timing synchronized with the toner image on the image carrier, the driving of the transport rollers 210, 211, 212 and the first registration roller 213 is resumed and transported to the image forming unit 3.

  Next, when a paper feed start signal is transmitted from the main control device 101 in order to feed and feed the subsequent second sheet S, the pickup is picked up from the paper feed control means 102 in the same manner as the first sheet S. An ON signal for operating the solenoid 108 is transmitted, and the pickup roller 201 comes into contact with the uppermost sheet S as indicated by a solid line in the drawing. Then, similarly to the first sheet, based on a sheet feeding motor rotation start signal transmitted by the main controller 101 at a predetermined timing, a sheet feeding motor operation on signal is transmitted again, and the sheet feeding motor 109 starts to rotate. The sheet S feeding operation is started. Similarly to the first sheet, when the leading edge of the second sheet arrives at the sheet detection sensor 207 and the leading edge detects the presence of paper, the pickup solenoid 201 is turned off, and the pickup roller 201 again returns to the broken line in FIG. Retreat to the position.

  Further, based on the sheet leading edge detection signal from the sheet detection sensor 207, the flapper solenoid 114 is turned on, and the switching flapper 235 is switched to the broken line position in the figure. As a result, the sheet S sandwiched between the drawing rollers 206 is then guided to the second branch conveyance path 209 and sequentially conveyed by the conveyance rollers 214, 215, and 216, and the leading edge of the paper is detected by the sensor 219 before the second registration. Then, after a predetermined time, the driving of the conveying rollers 214, 215, and 216 is stopped, and once the paper leading edge hits the second registration roller 217 and a loop is formed, the driving is temporarily stopped and skew correction is performed. Then, at a predetermined timing to synchronize with the toner image on the photosensitive drum 13 which is an image carrier, the driving of the conveying rollers 214, 215, 216 and the second registration roller 217 is resumed, and the photosensitive member of the image forming unit 3 is exposed. It is conveyed to the body drum 13.

  Further, the feeding of the third sheet S subsequent to the second sheet is switched again to the position of the solid line in the drawing based on the detection signal of the sheet detection sensor 207 as in the case of feeding the first sheet. In the same manner as the first sheet, the first branch conveyance path 208 is selected. In this way, the first branch conveyance path 208 and the second branch conveyance path 209 are alternately used every time one sheet S is conveyed.

  As is clear from the above, in the present embodiment, the first branch conveyance path 208 and the second branch conveyance path 209 are alternately used, so that the sheet S is substantially not provided on the first and second registration rollers 213 and 217. Rushes into every other piece. As a result, the distance between the sheets at the first and second registration rollers 213 and 217 can be sufficiently secured, and the jam margin time can be set large. Further, since the distance between the sheets at the registration rollers 213 and 217 is not limited, the total processing capability in the printer main body 9 can be improved. In addition, since the registration rollers 213 and 217 and the conveyance rollers are provided in the first branch conveyance path 208 and the second branch conveyance path 209 and used alternately, the wear of each roller such as the registration roller is also halved. In addition, since the amount of paper dust generated is halved, the durability life can be doubled compared to the conventional one, and the maintenance and maintenance such as roller cleaning can be greatly reduced.

  On the other hand, in the present embodiment, the handling process and operation when a jam occurs in either the first branch transport path 208 or the second branch transport path 209 are as follows.

  During operation of the printer main body 9, when a sheet S is jammed in the first branch conveyance path 208 during sheet feeding using the first branch conveyance path 208 and the second branch conveyance path 209 alternately, for example, the switching flapper 235. Is switched to the position of the broken line in the figure, and the feeding operation is continued using only the second branch conveyance path 209. As a result, even if a jam occurs in the conveyance section between the sheet feeding unit and the first and second registration rollers 213 and 217, it is not necessary to temporarily stop the operation of the printer body 9, and the total processing capacity is reduced. I won't let you. Even if the printer main body 9 is in operation, the first branch is notified by notifying the user that a jam has occurred in the first branch conveyance path 208 on the monitor screen or display display section provided in the printer main body 9. When the jammed sheet S can be removed in the transport path 208 and the jam processing is completed, the first branch transport path 208 and the second branch transport path 209 are alternately used again as described above. That's fine.

  Further, when it is desired to perform maintenance (for example, cleaning of rollers or removal of paper dust on the sheet conveyance path) in one of the first branch conveyance path 208 and the second branch conveyance path 209, not shown. Only one of the first and second branch conveyance paths 208 and 209 is used by operating a selection switch provided in the operation unit. As a result, only one of the branch conveyance paths is used, and maintenance of the unused branch conveyance path can be performed in the meantime, so that the operation of the printer main body 9 is temporarily stopped for maintenance without being brought down. That's it.

  In addition, even if the transportation system parts such as the rollers provided in the first branch transport path 208 and the second branch transport path 209 are damaged, the repair staff has to be repaired. If the branch conveyance path on the other side is input from the operation unit or the like, the printer main body 9 can be operated for the time until the repair specialist arrives at the site and completes the repair, so productivity is not lowered. .

(Second Embodiment)
In the second embodiment, the positions of the transfer unit 3 and the first registration roller 213 are such that the final path 218 of the first branch conveyance path in the section from the first registration roller 213 to the transfer unit 3 is substantially horizontal. Is selected. In addition, the final path 231 of the second branch conveyance path from the second registration roller 217 to the transfer unit 3 is aligned with the photosensitive drum 13 so that the sheet enters the photosensitive drum 13 of the image forming unit 3 obliquely upward. The position of the second registration roller 217 is set.

  As shown in FIG. 3, in the present embodiment, a material input unit (input unit) 115 is provided in an operation unit (not shown), and the user can input the material type of the sheet S inserted in the paper feed cassette 200. By acquiring such sheet information, the main control apparatus 101 determines in advance whether the sheets stored in the sheet feeding cassette 200 are thick or thin.

  For example, when the user inputs and designates a thick sheet S with the material input unit 115, the flapper switching solenoid 114 is turned off prior to the start of feeding, and the switching flapper 235 is set to the position of the solid line in the figure. The thick sheet S is set to be guided to the first branch conveyance path 208. At the same time, the manual feed switching flapper 307 is also switched to the position indicated by the solid line in the drawing so that the sheet S is guided to the first registration roller 213. In advance, the thick sheet S is conveyed through the first branch conveyance path 208 and passes through the horizontal path 213 of the first branch conveyance path provided substantially horizontally by such an operation to obtain a good image without transfer blur. Can do. Further, by selecting the first branch conveyance path 208, the conveyance resistance in the sheet conveyance path having a small curvature (1 / R) (large R) is small, and good and stable conveyance can be obtained.

  On the other hand, when the user inputs and designates a thin sheet S with the material input unit 115, the flapper switching solenoid 114 is activated prior to the start of feeding, and the switching flapper 235 is moved to the position of the broken line in the figure. Switch. Accordingly, the thin sheet S is guided to the second branch conveyance path 209, conveyed, and sent to the second registration roller 217. As a result, the thin sheet S enters the photosensitive drum 13 of the image forming unit 3 from the oblique path 231 of the second branch conveyance path in an obliquely downward direction, and the thin sheet S is exposed to light before entering the transfer region. It can be made to wrap around the body drum 13, and a good image without a defective transfer image such as scattering can be obtained. A good transfer image free from image blurring and scattering can be obtained for both thick paper and thin paper.

  However, the present invention is not limited to the case of paper feeding from the paper feeding cassette 200 as described above, and even when the paper is fed from the multi-manual paper feeding unit 300, By switching the manual feed switching flapper 307, a good image can be obtained without changing both the thick and thin sheets S in the same manner as the feeding from the paper feeding cassette 200.

  As described above, the sheet conveyance path from the sheet feeding unit to the registration roller is configured by the two parallel first branch conveyance paths 208 and second branch conveyance paths 209, so that a jam occurs in one of the branch conveyance paths. Even so, the operation of the printer main body 9 can be continued without stopping the apparatus, and downtime can be minimized. In addition, even when any branch conveyance path is maintained, the operation of the apparatus can be continued in the same manner.

  Further, by alternately using the first branch conveyance path 208 and the second branch conveyance path 209, the distance between sheets can be minimized, productivity can be increased, and the durability life can be doubled. Can be several times longer. Further, by alternately using the first and second branch conveyance paths 208 and 209, it is possible to save the trouble of setting the same sheet S as in the conventional two sheet feeding units, thereby improving the operability and work by the user. It is effective in greatly reducing labor. Further, even when the same sheet is not set in the two sheet feeding units due to an erroneous operation or erroneous determination by the user, the occurrence of a jam can be prevented. In addition, by forming the branch conveyance path in the section from the registration roller to the transfer section (image forming section) in two types, a substantially horizontal path and an inclined path, a good image can be obtained regardless of whether the sheet S is a thick letter or a thin thin paper. In addition, the transport performance of thick letters can be greatly improved.

  As described above, the first and second embodiments have been described for the image forming apparatus of the present invention. However, other embodiments and combinations thereof, application examples, and modifications may be used without departing from the gist of the present invention. Examples are also possible.

  For example, in the present embodiment, the structure in which the sheet conveyance path is configured by the first branch conveyance path 208 and the second branch conveyance path 209 has been described. However, the number of the branch conveyance paths is not limited to the above. Further, the number of branch conveyance paths can be increased, and not only the sheet feeding unit 200 including one sheet feeding cassette 209 but also a structure provided in a plurality of stages is possible.

  Further, the embodiment has been described in which the feeding of the succeeding sheet S is started after the preceding sheet S arrives at the registration roller, but when the trailing end of the preceding sheet passes the leading end of the switching flapper 235, Since the feeding of the succeeding sheet can be started, the preceding sheet is looped by the registration roller, and is waiting for the start in order to synchronize with the toner image on the photosensitive drum 13 of the image forming unit 3 which is an image carrier. Even in this state, the succeeding sheet can be rushed into the other registration roller.

  Of course, the first sheet of the sheet S is not limited to the first branch conveyance path 208 but can be started from the second branch conveyance path 209. Further, a memory means is provided to store which of the first branch transport path 208 and the second branch transport path 209 was used last by the previous print job, and when the next job starts, the other branch transport path is stored. If used, the frequency of use of the first and second branch conveyance paths 208 and 209 is further averaged, which is effective in further increasing the service life. Further, not only the first and second pre-registration sensors 218 and 217 but also more sheet detection sensors installed in each branch conveyance path may be installed. Further, not only the sheet feeding operation from the sheet feeding cassette 209 but also the sheet feeding from the multi-manual sheet feeding unit 300, the manual switching flapper 307 is alternately switched every time one sheet S is conveyed to improve productivity. It can be improved and the durable life can be doubled or longer.

1 is a schematic diagram showing a configuration of a laser beam printer as an embodiment of an image forming apparatus of the present invention. The functional block diagram by 1st Embodiment. The functional block diagram by 2nd Embodiment.

Explanation of symbols

1 Laser beam printer (image forming device)
9 Printer body 13 Photosensitive drum (image forming unit)
101 Main controller (control means)
200 Sheet feeding unit (sheet feeding unit)
209 Paper feed cassette 208 First branch conveyance path (sheet conveyance path)
209 Second branch conveyance path (sheet conveyance path)
235 Branch conveyance path switching flapper (branch conveyance path switching means)
213 First registration roller 217 Second registration roller 307 Manual branch conveyance path switching flapper

Claims (7)

A sheet feeding unit that feeds the stored sheets to the sheet conveyance path;
An image forming unit that forms an image on a sheet conveyed by the sheet conveying path;
A plurality of branch conveyance paths that diverge a sheet conveyance path between the sheet feeding unit and the image forming unit on the downstream side of the sheet feeding unit and merge on the upstream side of the image forming unit;
Switching means provided in the branching section for selecting one of the plurality of branching conveyance paths and guiding the sheet;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein a registration roller for correcting the skew of the sheet is disposed in each of the branch conveyance paths. 5. A control unit that controls to sequentially switch to another branch conveyance path every time the switching unit is operated to guide one sheet to one of the branch conveyance paths. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, further comprising a control unit that transmits a switching signal to the switching unit in accordance with sheet type information. Each of the plurality of branch conveyance paths includes curved paths having different curvatures, the sheet type information is the sheet thickness, and when the sheet is thick, the sheet is guided to the branch conveyance path having a small curvature path. The image forming apparatus according to claim 4, wherein the control unit controls the switching unit. One branch conveyance path among the plurality of branch conveyance paths is formed substantially horizontally along a path between the image forming unit and the registration roller disposed on the downstream side, and information on the sheet type is provided. 5. When the sheet is thick, the control means controls the switching means so as to guide the sheet to a branch conveyance path having a path formed substantially horizontally. The image forming apparatus described in 1. The image forming apparatus according to claim 4, further comprising an operation unit having an input unit for inputting various pieces of information on the sheet.

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