JP2019020499A - Image formation device - Google Patents

Abstract

To provide an image formation device that can cause paper to pass through an image formation unit a plurality of times without reversing a front and back sides of the paper.SOLUTION: An image formation device comprises: an image formation unit 10 that forms images on paper P; an image formation route R1 that conveys the paper P to the image formation unit 10; a reverse route R3 that has a switchback part R31 branching from the image formation route R1 more downstream in a paper conveyance direction than the image formation unit 10, and causing the paper P to reversely run after passing forward the paper P until a rear end of the paper P reaches a prescribed position, and a paper re-feeding part R32 causing the paper P to be reversely run by the switchback part R31 to be jointed to the image formation route R1 more upstream in the paper conveyance direction than the image formation unit 10; and a shortcut route R4 that branches from the switchback part R31 more upstream in the paper conveyance direction than the prescribed position when passing forward the paper P, and conveys the paper P to the paper re-feeding part R32 without causing the paper P to reversely run.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

Conventionally, an image forming unit for transferring a toner image formed on a photosensitive drum onto a sheet via an intermediate transfer belt, and heating and pressurizing the sheet to fix the toner image on the sheet, thereby forming an image on the sheet. An image forming apparatus including the image forming apparatus is known.
In such an apparatus, a configuration is generally provided with a reversing path that can reverse the front and back of the paper on which the image is formed on one side, pass the image forming unit again, and perform image formation on both sides of the paper. (For example, see Patent Document 1).

JP 2006-298605 A

In recent years, in such an image forming apparatus, there is a demand to perform a process of passing the image forming unit a plurality of times without reversing the front and back of the paper with the aim of further improving the image quality. For example, it is necessary to form an image on the same surface of the paper.
However, in order to pass the image forming unit a plurality of times without inverting the front and back of the paper, it is necessary to set the paper that has passed the image forming unit in the apparatus again.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can pass through an image forming unit a plurality of times without reversing the front and back of a sheet.

In order to solve the above-mentioned problem, the invention according to claim 1 is an image forming apparatus comprising:
An image forming unit for forming an image on paper;
An image forming path for conveying paper to the image forming unit;
A switchback unit that branches off from the image forming path downstream of the image forming unit in the paper conveyance direction, and forwards until the trailing edge of the paper reaches a predetermined position, and reversely feeds by the switchback unit. A reversing path having a refeeding section that joins the sheet to be fed to the image forming path upstream of the image forming section in the sheet conveying direction;
A shortcut path for branching from the switchback unit upstream of the predetermined position in the paper transport direction at the time of forward feeding of the paper, and transporting the paper to the refeeding unit without reverse feeding;
It is characterized by providing.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect,
A first switching unit that switches a sheet transport destination on the image forming path to the switchback unit;
A second switching unit and a third switching unit that are provided from the upstream side to the downstream side in the paper conveyance direction during the progressive feeding of the paper in the switchback unit;
With
The second switching unit switches a transport destination of paper sequentially fed on the switchback unit to the shortcut path,
The third switching unit switches a transport destination of a sheet to be reversely fed on the switchback unit to the refeed unit.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
A control unit configured to perform a process of causing the sheet to pass through the image forming unit a plurality of times by conveying the sheet to the re-feeding unit via the shortcut path so that the image forming surface is the same surface; It is characterized by that.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect,
The switchback unit is continuously provided from the downstream end in the sheet conveyance direction during the progressive feeding of the sheet, and the sheet on the switchback unit is upstream of the image forming unit without being fed backward. A second refeeding unit that joins the image forming path in
When the control unit executes the process, the control unit conveys the sheet to the refeed unit via the shortcut path or the sheet to the second refeed unit according to the length in the conveyance direction of the sheet. It is characterized by selecting whether to carry.

According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect,
The second re-feeding unit is provided so that the sheet travels in the vicinity of the bottom surface of the image forming apparatus.

  According to the present invention, it is possible to pass through the image forming unit a plurality of times without inverting the front and back of the paper.

1 is a configuration diagram schematically illustrating an image forming apparatus according to an exemplary embodiment. FIG. 2 is a block diagram schematically showing a configuration of a control system of the image forming apparatus in FIG. 1. 3 is a flowchart showing image forming processing executed in the image forming apparatus of FIG. 1. It is a block diagram which shows the modification of an image forming apparatus typically. 5 is a flowchart showing an image forming process executed in the image forming apparatus of FIG.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[Configuration of Image Forming Apparatus 100]
First, the configuration of the image forming apparatus 100 in the present embodiment will be described.
FIG. 1 is a configuration diagram schematically illustrating an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 is an electrophotographic image forming apparatus 100 such as a copying machine, and forms a full-color image by arranging a plurality of photoconductors facing one intermediate transfer belt in the vertical direction. This is a so-called tandem color image forming apparatus.

  The image forming apparatus 100 is mainly composed of a document reading device SC, an image forming unit 10, a sheet conveying unit 20, and a control unit 11, and these are housed in one casing.

  The document reader SC scans and exposes an image of the document with the optical system of the scanning exposure device, reads the reflected light with a line image sensor, and obtains an image signal. This image signal is subjected to processing such as A / D conversion, shading correction, and compression, and then input to the control unit 11 as image data. Note that the image data input to the control unit 11 is not limited to the data read by the document reading device SC. For example, the image data is received from a personal computer connected to the image forming device 100 or another image forming device by the communication unit 13. It may be what you did.

The image forming unit 10 includes four sets of normal color image forming units 10Y, 10M, 10C, and 10K, one set of special color image forming units 10W, an intermediate transfer belt 6, a secondary transfer roller 8, a fixing device 9, and the like. Configured.
The image forming units 10Y, 10M, 10C, and 10K are an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and an image that forms a cyan (C) image. The forming unit 10C includes an image forming unit 10K that forms a black (K) image.
The image forming unit 10W includes an image forming unit 10W that forms a white (W) image.

  The image forming unit 10Y includes a photosensitive drum 1Y and a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a drum cleaner 5Y arranged around the photosensitive drum 1Y. Similarly, the image forming units 10M, 10C, 10K, and 10W include photosensitive drums 1M, 1C, 1K, and 1W and charging units 2M, 2C, 2K, and 2W, optical writing units 3M, 3C, and the like disposed around the photosensitive drums 1M, 1C, 1K, and 1W. 3K, 3W, developing devices 4M, 4C, 4K, 4W and drum cleaners 5M, 5C, 5K, 5W.

  The surfaces of the photosensitive drums 1Y to 1W are uniformly charged by the charging units 2Y to 2W, and latent images are formed on the photosensitive drums 1Y to 1W by scanning exposure by the optical writing units 3Y to 3W. Is done. Further, the developing devices 4Y to 4W develop the latent images on the photosensitive drums 1Y to 1W by developing with toner. As a result, a toner image of a predetermined color corresponding to any one of yellow, magenta, cyan, black and white is formed on the photosensitive drums 1Y to 1W. The toner images formed on the photosensitive drums 1Y to 1W are sequentially transferred to predetermined positions on the rotating intermediate transfer belt 6 by the primary transfer rollers 7Y, 7M, 7C, 7K, and 7W.

  The toner images composed of the respective colors transferred onto the intermediate transfer belt 6 are transferred by the secondary transfer roller 8 to the paper P that is conveyed at a predetermined timing by a paper conveying unit 20 described later. The secondary transfer roller 8 is a pressure contact member that forms a nip portion (hereinafter referred to as “transfer nip portion”) by being disposed in pressure contact with the intermediate transfer belt 6.

  The fixing device 9 is a device that performs a fixing process on the paper P on which the toner image is transferred, that is, the paper P sent out from the transfer nip portion. For example, the fixing device 9 includes a pair of fixing members (for example, a pair of rollers) and the fixing device. It is comprised with the heater which heats one or both of the members. The fixing device 9 fixes the toner image on the paper P through the action of the pressure applied by the pair of fixing members and the heat of the fixing member in the conveyance process of the paper P.

The paper transport unit 20 transports the paper P along the transport path of the paper P.
The paper transport unit 20 includes an image forming path R1 for transporting the paper P to the image forming unit 10, a paper discharge path R2 for discharging the paper P after image formation to the outside, a reversing path R3 for reversing the front and back of the paper P, And a shortcut path R4 used to circulate the paper P without inverting it.
Further, a switching gate G1 (first switching unit) is provided on the downstream side of the fixing device 9 in the sheet conveyance direction in the image forming path R1, and a switching gate G2 is provided in a switchback unit R31 (described later) of the reversing path R3. (Second switching unit) and a switching gate G3 (third switching unit) are provided.

Each transport path is provided with a plurality of transport means for transporting the paper P. Each of the conveying means is composed of a pair of pressure-contacted rollers, and conveys the paper P when at least one of the rollers is rotationally driven through a driving mechanism mainly composed of an electric motor.
In addition, the pair of rollers constituting the individual conveying means is configured so that the state between the rollers can be switched between a pressure contact state and a separated state.
In addition to the configuration of the pair of rollers, the conveyance unit can widely employ a configuration including a pair of rotating members such as a combination of belts or a combination of a belt and a roller.

The image forming path R1 is a path for transporting the paper P from the paper feed tray to the switching gate G1.
The paper P is accommodated in a paper feed tray 21 located at the lower part of the image forming apparatus 100, and the paper P accommodated in the paper feed tray 21 is taken in by the paper feed unit 22 and enters the image forming path R1. Sent out.
Alternatively, the paper P is stored in a paper feed tray included in a paper feed device (not shown) connected to the image forming apparatus 100, and the paper P held by the paper feed device forms an image from the paper feed device. It is supplied to the apparatus 100 and sent out to the image forming path R1.
The paper P may be placed on a manual feed tray provided in the image forming apparatus 100 and sent out to the image forming path R1.

  An image forming unit 10 is provided on the image forming path R1. Further, in the image forming path R1, an intermediate conveyance roller 23, a loop roller 24, and a registration roller 25 are provided as conveyance means from the upstream side to the downstream side in the paper conveyance direction.

The sheet P is sequentially transported by the intermediate transport roller 23 and the loop roller 24 and travels through the image forming path R1. When the leading edge of the paper P approaches the registration roller 25, the paper P conveyed by the loop roller 24 or the like is abutted against the registration roller 25 in a rotation stop state, and the loop roller 24 continues to rotate for a predetermined time. As a result, a loop is formed on the paper P. By this loop forming action, the bending of the leading edge of the paper P is corrected (skew correction).
Next, when the registration roller 25 starts rotating at a predetermined timing so as to synchronize with the toner image carried by the intermediate transfer belt 6, the intermediate conveyance roller 23 and the loop roller 24 are switched from the pressure contact state to the separated state, The paper P is transported to the transfer nip portion of the image forming unit 10 only by the registration rollers 25, and then transported to the fixing device 9 by the secondary transfer roller 8. The paper P on which the fixing process has been performed in the fixing device 9 is conveyed to the switching gate G1, and proceeds to the paper discharge route R2 or the reversing route R3 according to the guidance of the switching gate G1.

  The paper discharge path R2 is a conveyance path for discharging the paper P that has been subjected to the fixing process by the fixing device 9 to a paper discharge tray 26 attached to the outer side surface of the housing.

The reversing path R3 is a conveyance path for reversing the front and back of the paper P on which the fixing process has been performed by the fixing device 9 to the image forming path R1.
The reversing path R3 includes a switchback unit R31 for reversing the front and back of the paper P, and a refeeding unit R32 for transporting the paper P reversed by the switchback unit R31 to the image forming path R1.

The switchback portion R31 is arranged to branch from the position of the switching gate G1 in the image forming path R1 and extend downward.
The switchback portion R31 is provided with a switching gate G2, a switching gate G3, and a reversing roller 27 from the upstream side to the downstream side in the paper conveyance direction when sequentially feeding the paper P (from the top to the bottom of the apparatus). Yes.
When reversing the front and back of the sheet P and returning the sheet P to the image forming path R1, the sheet P conveyed from the image forming path R1 until the trailing edge reaches the reversing roller 27 (predetermined position). Reverse feed is started when the reverse roller 27 reverses at the timing when the reverse roller 27 pinches the trailing edge of the paper P. The reversely fed paper P advances from its rear end to the paper refeed unit R32 according to the guidance of the switching gate G3.
For example, when it is assumed that the paper P is a long paper having a longer length in the paper conveyance direction than the standard paper, the switchback portion R31 is indicated by a chain line L in FIG. It is also preferable to provide a position that reaches the vicinity of the bottom surface of the image forming apparatus 100.

The re-feeding unit R32 is arranged so as to branch from the position of the switching gate G3 in the switchback unit R31 and reach a junction 51 provided in the middle of the image forming path R1.
In the refeed unit R32, an intermediate transport roller 28 is provided as a transport unit from the upstream side to the downstream side in the paper transport direction. Note that the intermediate transport rollers 28 are arranged so as to have an interval shorter than the length of the smallest paper P passing through in the paper transport direction.
Then, the paper P that has been reversely fed by the switchback unit R31 is transported from the rear end thereof by the refeed unit R32, and a confluence 51 provided upstream of the image forming unit 10 in the paper transport direction in the image forming path R1. To reach. The paper P that has reached the confluence 51 is sent out again to the image forming path R1.

The shortcut path R4 is a transport path used for returning the paper P, which has been subjected to the fixing process by the fixing device 9, to the image forming path R1 without inverting the front and back (without changing the image forming surface). is there.
The shortcut route R4 is arranged so as to branch from the position of the switching gate G2 in the switchback portion R31 of the reversing route R3 and reach the refeeding portion R32.
When the paper P is returned to the image forming path R1 without reversing the front and back of the paper P, the paper P conveyed from the image forming path R1 is switched without reaching the switching gate G3 or the reversing roller 27. In accordance with the guidance of the gate G2, it proceeds to the shortcut route R4 and is conveyed to the refeed unit R32 by the shortcut route R4.
The paper P that has reached the paper re-feed unit R32 via the shortcut path R4 is transported by the paper re-feed unit R32, and is sent out again to the image formation path R1 via the junction 51 provided in the image formation path R1. It becomes.

The switching gate G1 is provided on the downstream side of the fixing device 9 in the paper conveyance direction in the image forming path R1, and switches the conveyance destination of the paper P that has passed through the fixing device 9. Specifically, the switching gate G1 guides the paper P downward when the paper P that has passed through the fixing device 9 is conveyed to the reversing path R3. The switching gate G1 moves the paper P straight when transporting the paper P to the paper discharge path R2.
Note that the switching gate G1 is normally in a state of feeding the paper P to the paper discharge path R2. When the paper P is sent to the reversing path R3, the paper P is driven by a driving unit (not shown) to transport the paper P downward, and then returns to the original state.

The switching gate G2 is provided in the switchback portion R31 of the reversing path R3, and switches the transport destination of the paper P guided downward by the switching gate G1. Specifically, the switching gate G2 guides the paper P downward when the paper P is turned upside down. Further, the switching gate G2 guides the paper P diagonally downward to the right in FIG. 1 when the front and back of the paper P are not reversed, that is, when transported to the shortcut route R4.
Note that the switching gate G2 is normally in a state of guiding the paper P downward. When the paper P is sent to the shortcut path R4, the paper P is driven by a drive unit (not shown) to convey the paper P diagonally downward to the right, and then returns to the original state.

The switching gate G3 is provided downstream of the switching gate G2 in the paper transport direction during the forward feeding of the paper P in the switchback unit R31, and switches the transport destination of the paper P that is reversely fed by the switchback unit R31. Specifically, the switching gate G3 guides the paper P obliquely upward to the right in FIG. 1 when transporting the paper P that is fed back through the switchback portion R31 to the paper refeeding portion R32. The switching gate G3 guides the paper P downward when the paper P conveyed from the image forming path R1 is sequentially fed.
Note that the switching gate G3 is normally in a state in which the paper P is guided downward (a state in which the paper P is sequentially fed). When the paper P is transported (reversely fed) to the re-feeding unit R32, the paper P is driven by a driving unit (not shown), transports the paper P diagonally upward to the right, and then returns to the original state.

FIG. 2 is a block diagram schematically showing the configuration of the control system of the image forming apparatus 100 according to the present embodiment.
As shown in FIG. 2, the control unit 11 is connected to the storage unit 12, the communication unit 13, the operation unit 14, the document reading device SC, the image forming unit 10, and the paper transport unit 20.

The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The CPU of the control unit 11 reads the system program and various processing programs stored in the storage unit 12 and expands them in the RAM, and centrally controls the operations of the respective units of the image forming apparatus 100 according to the expanded programs.
For example, when a job execution command is input from the operation unit 14, the control unit 11 executes a job and forms a toner image on the paper P based on image data input by the document reading device SC or the communication unit 13. Take control.
In the present embodiment, the control unit 11 circulates the paper P on which the image is formed by the image forming unit 10 without inverting the front and back, and forms an image on the image forming surface by the image forming unit 10. It is possible to execute an overwriting process.

  The storage unit 12 is configured by a nonvolatile semiconductor memory, an HDD (Hard Disk Drive), or the like, and stores various programs executed by the control unit 11 as well as parameters and data necessary for each unit.

  The communication unit 13 includes various interfaces such as a NIC (Network Interface Card), a MODEM (Modulator-DEModulator), and a USB (Universal Serial Bus), and connects to an external device.

  The operation unit 14 outputs various information set by the user to the control unit 11. As the operation unit 14, for example, a touch panel capable of performing an input operation according to information displayed on the display can be used. Through the operation unit 14, the user sets image forming conditions, that is, the type of paper P (for example, basis weight, size, paper quality, etc.), paper feed tray to be used, image density, magnification, image forming mode, and the like. be able to. Further, the user can input job execution commands and operation instructions in various modes through the operation unit 14. The control unit 11 can display various messages to the user via the operation unit 14 by controlling the operation unit 14.

[Operation of Image Forming Apparatus 100]
Next, the operation of the image forming apparatus 100 in the present embodiment will be described.
FIG. 3 is a flowchart showing an image forming process executed by the image forming apparatus 100. The processing shown in this flowchart is executed in cooperation with the program stored in the control unit 11 and the storage unit 12 in accordance with a job execution command from the user.

First, the control unit 11 acquires job information transmitted from an external device via the communication unit 13 (step S1).
The job information includes various types of information relating to image forming processing, such as mode information and image data of an image to be formed.
As the mode information, for example, any one of a normal mode, a duplex mode, and an overwriting mode is set. The normal mode is a mode in which image formation is performed once on one side of the paper P. The duplex mode is a mode in which image formation is performed on both sides of the paper P. The overwriting mode is a mode in which image formation is performed a plurality of times on one side of the paper P.
The image data includes one or a plurality of image data corresponding to the image forming mode, and information such as on which side of the sheet P is formed, how many times it is formed is added.

Next, the control unit 11 causes the image forming unit 10 to perform the highest priority image formation among the unprocessed image formations (step S2).
For example, in the normal mode, the control unit 11 forms an image on one surface (front surface) of the paper P.
In addition, for example, in the overwriting mode, the control unit 11 executes this when the first image formation is not processed, completes the first image formation, and does not process the second image formation. In this case, the second image formation is executed.
Further, for example, in the double-sided mode, the control unit 11 executes this when the front surface image formation is not processed, and when the front surface image formation is completed and the back surface image formation is not processed, the rear surface is formed. The image formation is executed.

  Next, the control unit 11 determines whether or not the overwriting mode or the double-sided mode is set (step S3). If the setting is not made (normal mode) (step S3: NO), this process is performed. finish.

  On the other hand, when the overwriting mode or the duplex mode is set (step S3: YES), the control unit 11 determines whether or not there is an unprocessed image formation (step S4). (S4: NO), this process is terminated.

  On the other hand, when there is unprocessed image formation (step S4: YES), the control unit 11 switches the switching gate G1 and conveys the paper P to the switchback unit R31 of the reverse path R3 (step S5).

Next, the control unit 11 determines whether or not the overwriting mode is set (step S6), and when the overwriting mode is set (step S6: YES), the control unit 11 switches the switching gate G2 (step S6). S7) Thereafter, the process proceeds to step S2, and the subsequent processing is repeated.
As a result, the paper P is transported to the refeed unit R32 via the shortcut path R4, and returns to the image forming path R1 by the refeed unit R32 and reaches the image forming unit 10.

On the other hand, when the overwriting mode is not set (step S6: NO), the control unit 11 determines whether or not the trailing edge of the paper P has reached the reversing roller 27 (step S8), and has not reached it. If so (step S8: NO), the process of step S8 is repeated.
On the other hand, when the trailing edge of the paper P reaches the reversing roller 27 (step S8: YES), the control unit 11 switches the switching gate G3 (step S9), and then proceeds to the above step S2 and thereafter Repeat the process.
As a result, the paper P is reversely fed and conveyed to the refeed unit R32, and the refeed unit R32 returns to the image forming path R1 and reaches the image forming unit 10.

As described above, according to the present embodiment, the image forming unit 10 that forms an image on the paper P, the image forming path R1 that transports the paper P to the image forming unit 10, and the paper transport more than the image forming unit 10 A switchback portion R31 that branches off from the image forming path R1 downstream in the direction and forwardly feeds until the trailing edge of the paper P reaches a predetermined position, and the paper P that is reversely fed by the switchback portion R31. A reversing path R3 having a paper refeeding section R32 that merges with the image forming path R1 upstream of the image forming section 10 and a switchback section R31 upstream of the predetermined position with respect to a predetermined position when sequentially feeding the paper P. And a shortcut path R4 that transports the paper P to the paper refeed unit R32 without being reversely fed.
For this reason, the paper P that has progressed to the switchback unit R31 is advanced to the refeed unit R32 via the shortcut path R4, so that it can be returned to the image forming unit 10 without reversing the front and back of the paper P. It becomes possible.
That is, it is possible to pass through the image forming unit 10 a plurality of times without inverting the front and back of the paper P.

Further, according to the present embodiment, the switching gate G1 that switches the transport destination of the paper P on the image forming path R1 to the switchback unit R31, and the upstream in the paper transport direction when the paper P is sequentially fed in the switchback unit R31. A switching gate G2 and a switching gate G3 provided from the downstream side to the downstream side. The switching gate G2 switches the transport destination of the paper P sequentially fed on the switchback portion R31 to the shortcut path R4, and the switching gate G3 Then, the transport destination of the paper P that is fed back on the switchback unit R31 is switched to the refeed unit R32.
For this reason, before the paper P which has advanced to the switchback unit R31 is reversed, it can be advanced to the refeed unit R32 via the shortcut path R4.

Further, according to the present embodiment, the image forming unit 10 is moved a plurality of times so that the image forming surface of the paper P becomes the same surface by transporting the paper P to the refeed unit R32 via the shortcut path R4. The control part 11 which performs the process to let it pass is provided.
Therefore, for example, processing such as forming an image on the same surface of the paper P can be performed.

[Modification]
Next, a modification of the image forming apparatus 100 of the above embodiment will be described.
FIG. 4 is a configuration diagram schematically illustrating a modified image forming apparatus 100A. Note that the same components as those of the image forming apparatus 100 of FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
As shown in FIG. 4, in the image forming apparatus 100A, the reversing path R3 includes a second refeeding unit R33 in addition to the switchback unit R31 and the refeeding unit R32.
The second re-feeding unit R33 is provided continuously from the downstream end in the paper transport direction when the paper P is sequentially fed in the switchback unit R31, and reaches the junction 52 provided in the middle of the image forming path R1. Is arranged.
In addition, the second refeed unit R33 is provided so that the sheet P travels below the sheet feed tray 21, that is, near the bottom surface of the image forming apparatus 100A.
The second refeed unit R33 can be used, for example, when the paper P is circulated when the paper P is a long paper having a longer length in the paper transport direction than the standard paper.
When the paper P is a long paper, the paper P is image-formed by, for example, a paper feed device (not shown) connected to the image forming apparatus 100A or a manual tray provided in the image forming apparatus 100A. It can be sent out to the route R1.

Hereinafter, the operation of the image forming apparatus 100A will be described.
FIG. 5 is a flowchart showing an image forming process executed by the image forming apparatus 100A. Note that the same processing as the image forming processing of FIG. 3 is given the same reference numerals and description thereof is omitted.

As shown in FIG. 5, the control unit 11 executes the same processing as the image forming processing in FIG. 3 from step S <b> 1 to step S <b> 6.
If the overwriting mode is set in step S6 (step S6: YES), the control unit 11 determines whether or not the paper P is a long paper (step S10), and the long paper is used. (Step S10: YES), the process proceeds to Step S2.
That is, in the case of a long sheet, the switching gate G2 is not switched, and the sheet P is forwarded as it is by the switchback unit R31, reaches the second refeed unit R33, and is conveyed by the second refeed unit R33. Thus, the image forming path R1 is reached.

  On the other hand, when the paper is not long (step S10: NO), the control unit 11 switches the switching gate G2 (step S7), and then returns to step S2 to repeat the subsequent processing.

As described above, according to the present modification, the reversing path R3 is continuously provided from the downstream end portion in the paper transport direction when the paper P is sequentially fed in the switchback portion R31, and is on the switchback portion R31. When the control unit 11 executes the overwriting process, the control unit 11 includes a second refeed unit R33 that joins the paper P to the image forming path R1 upstream of the image forming unit 10 without being reversely fed. Depending on the length in the transport direction of the paper P, the paper P is transported to the refeed unit R32 via the shortcut path R4, or the paper P is transported to the second refeed unit R33 via the switchback unit R31. Select what to do.
For this reason, an appropriate conveyance path can be selected according to the length of the sheet P in the sheet conveyance direction.

Further, according to the present modification, the second refeed unit R33 is provided so that the paper P travels in the vicinity of the bottom surface of the image forming apparatus 100A.
For this reason, since the straight line portion of the second refeed unit R33 can be lengthened, jamming of the paper P can be suppressed.

  Further, as a method of using the second refeed unit R33, in addition to the above, processing such as changing the transport order of a plurality of sheets P by retaining the sheets P in the second refeed unit R33 It can also be used.

  In addition, according to the said embodiment and modification, although the overwrite process which performs image formation in multiple times with respect to the same surface of the paper P was illustrated and demonstrated as a process which the control part 11 performs, an overwrite process is demonstrated. In addition to this, for example, processing for controlling gloss by passing the sheet P on which the image has been formed and passing through the fixing device 9 without forming an image at the second time or later can be executed.

Further, in the above-described embodiment and modification, the configuration including the image forming unit 10 </ b> W that forms a white (W) toner image as a special color has been described as an example, but the special color is not limited to white. In addition, for example, clear (transparent) or the like may be used.
Further, although there is one image forming unit that forms a spot color, a configuration including two or more sets of image forming units that form two or more spot colors may be employed.
Of course, the image forming unit for forming the spot color may not be provided.

  Further, in the above-described embodiments and modifications, examples have been disclosed in which a nonvolatile memory, a hard disk, or the like is used as a computer-readable medium for the program according to the present invention, but the present invention is not limited to this example. As another computer-readable medium, a portable recording medium such as a CD-ROM can be applied. A carrier wave is also applied as a medium for providing program data according to the present invention via a communication line.

  In the above-described embodiments and modifications, the electrophotographic image forming apparatus has been described as an example, but the present invention can also be applied to other image forming methods such as an ink jet method. Also, the transfer method is not limited to those in the above-described embodiments and modifications.

  In addition, the detailed configuration and detailed operation of the image forming apparatus can be changed as appropriate without departing from the spirit of the present invention.

100, 100A Image forming apparatus SC Original document reading apparatus 10 Image forming units 10Y, 10M, 10C, 10K, 10W Image forming units 1Y, 1M, 1C, 1K, 1W Photosensitive drums 2Y, 2M, 2C, 2K, 2W Charging unit 3Y, 3M, 3C, 3K, 3W Optical writing unit 4Y, 4M, 4C, 4K, 4W Developing device 5Y, 5M, 5C, 5K, 5W Drum cleaner 6 Intermediate transfer belt 7Y, 7M, 7C, 7K, 7W Primary transfer Roller 8 Secondary transfer roller 9 Fixing device 20 Paper transport unit 21 Paper feed tray 22 Paper feed unit 23 Intermediate transport roller 24 Loop roller 25 Registration roller 26 Paper discharge tray 27 Reverse roller 28 Intermediate transport roller 51 Junction point R1 Image formation path R2 Paper discharge path R3 Reverse path R31 Switchback section R32 Refeed section R33 Second refeed section R4 Route G1 switching gate (first switching unit)
G2 switching gate (second switching part)
G3 switching gate (third switching unit)
11 Control Unit 12 Storage Unit 13 Communication Unit 14 Operation Unit P Paper

Claims (5)

An image forming unit for forming an image on paper;
An image forming path for conveying paper to the image forming unit;
A switchback unit that branches off from the image forming path downstream of the image forming unit in the paper conveyance direction, and forwards until the trailing edge of the paper reaches a predetermined position, and reversely feeds by the switchback unit. A reversing path having a refeeding section that joins the sheet to be fed to the image forming path upstream of the image forming section in the sheet conveying direction;
A shortcut path for branching from the switchback unit upstream of the predetermined position in the paper transport direction at the time of forward feeding of the paper, and transporting the paper to the refeeding unit without reverse feeding;
An image forming apparatus comprising: A first switching unit that switches a sheet transport destination on the image forming path to the switchback unit;
A second switching unit and a third switching unit that are provided from the upstream side to the downstream side in the paper conveyance direction during the progressive feeding of the paper in the switchback unit;
With
The second switching unit switches a transport destination of paper sequentially fed on the switchback unit to the shortcut path,
The image forming apparatus according to claim 1, wherein the third switching unit switches a transport destination of a sheet that is reversely fed on the switchback unit to the refeed unit.   A control unit configured to perform a process of causing the sheet to pass through the image forming unit a plurality of times by conveying the sheet to the re-feeding unit via the shortcut path so that the image forming surface is the same surface; The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The switchback unit is continuously provided from the downstream end in the sheet conveyance direction during the progressive feeding of the sheet, and the sheet on the switchback unit is upstream of the image forming unit without being fed backward. A second refeeding unit that joins the image forming path in
When the control unit executes the process, the control unit conveys the sheet to the refeed unit via the shortcut path or the sheet to the second refeed unit according to the length in the conveyance direction of the sheet. The image forming apparatus according to claim 3, wherein whether or not to convey the image is selected.   5. The image forming apparatus according to claim 4, wherein the second re-feed unit is provided so that a sheet travels in the vicinity of a bottom surface of the image forming apparatus.

Images