JP2019026430A - Image forming apparatus and control method - Google Patents

Abstract

To provide an image forming apparatus that improves the position accuracy of an image to be transferred to a sheet refed from a reversion path.SOLUTION: An image forming apparatus 100 comprises a second position detection sensor 63 that is arranged on a reversion path R2 and detects a position of a side end part of a sheet P. A control section 11 performs oscillation control of a register roller 27 when transporting toward a secondary transfer roller 9 a sheet P refed from the reversion path R2, based on a detection result by the second position detection sensor 63.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus and a control method.

  In recent years, multifunctional image forming apparatuses having functions such as printers, scanners, copiers, and fax machines have been widely used. In an image forming apparatus, paper is transported from a paper feed unit or a reverse path to a transfer unit during image formation. (There is also a case of direction). When the printing process is performed in such a state where the paper is misaligned, there is a problem that the image forming position on the paper is deviated from the original proper position.

Therefore, in order to accurately align the image and the paper in consideration of the deviation of the paper, the registration rocking that corrects the deviation of the paper by sandwiching the paper with the registration roller and swinging in the paper width direction is performed. Dynamic correction is performed.
For example, in Patent Document 1, a registration roller is disposed on the upstream side of the secondary transfer roller, and a line sensor is disposed on the downstream side of the registration roller and on the upstream side of the secondary transfer roller. An image forming apparatus that corrects a deviation of a sheet by swinging the sheet in the sheet width direction based on the position of the side edge of the sheet is disclosed.

JP 2013-91563 A

  By the way, when performing double-sided printing, the paper on which image formation on the first surface has been completed is conveyed to the reversing path, the front and back sides are reversed, re-fed, conveyed again to the transfer unit via the registration rollers, An image is transferred to the two surfaces. However, in conventional techniques such as Japanese Patent Application Laid-Open No. H10-228707, the variation in conveyance in the reversing path is not taken into account in the resist swing when the sheet re-feeded from the reversing path is conveyed to the transfer unit. For this reason, the position of the image transferred to the second surface of the paper cannot be accurately aligned with the paper.

  An object of the present invention is to improve the positional accuracy of an image to be transferred onto a sheet re-feeded from a reversing path.

In order to solve the above-described problem, an image forming apparatus according to a first aspect of the present invention provides:
A transfer section for transferring an image to paper;
A fixing unit for fixing the image transferred by the transfer unit to the paper;
An image forming path for conveying the sheet to the transfer unit and the fixing unit;
A swing roller that is disposed in the image forming path and includes a pair of rollers that convey the paper toward the transfer unit;
The image forming path is branched from the image forming path downstream of the fixing unit, and the front and back sides of the paper on which image formation on the first surface has been completed by the transfer unit and the fixing unit are reversed and re-entered in the image forming path. Reversing path to feed paper,
A detection unit that is disposed in the reversing path and detects a position of a side edge of the paper;
A control unit that performs swing control of the swing roller when transporting the sheet re-feeded from the reversing path toward the transfer unit based on a detection result by the detection unit;
Is provided.

The invention according to claim 2 is the invention according to claim 1,
The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A second path that is provided on the downstream side of the first path in the sheet conveyance direction after the conveyance direction is changed by the reversing roller, and that reverses the front and back of the sheet and refeeds the image forming path. ,
With
The detection unit is disposed on the downstream side of the reverse roller in the paper transport direction after the transport direction is changed by the reverse roller.

The invention according to claim 3 is the invention according to claim 1,
The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A second path that is provided on the downstream side of the first path in the sheet conveyance direction after the conveyance direction is changed by the reversing roller, and that reverses the front and back of the sheet and refeeds the image forming path. ,
A conveyance roller that is provided in the second path, temporarily stops before the sheet is re-fed to the image forming path, and then conveys the sheet to the image forming path;
With
The detection unit is disposed on the downstream side of the transport roller.

The invention according to claim 4 is the invention according to claim 1,
The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A bent portion is provided on the downstream side of the first path in the conveyance direction of the paper after the conveyance direction is changed by the reversing roller, and the paper is reversed by the bending portion. A second path for reversing the front and back of the paper and refeeding the image forming path,
With
The detection unit is provided on the bent part, on the downstream side of the bent part, or before and after the bent part.

The invention according to claim 5 is the invention according to claim 1,
The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A second path that is provided on the downstream side of the first path in the sheet conveyance direction after the conveyance direction is changed by the reversing roller, and that reverses the front and back of the sheet and refeeds the image forming path. ,
A merging path for rejoining the first path branched from the image forming path to the image forming path;
With
The detection unit is provided in the merge path.

The invention according to claim 6 is the invention according to claim 1,
A plurality of the detection units are provided,
The control unit performs swing control of the swing roller when transporting the sheet re-feeded from the reversing path toward the transfer unit, based on detection results by the plurality of detection units.

The invention according to claim 7 is the invention according to any one of claims 1 to 6,
The control unit determines swing control information of the swing roller based on a detection result by the detection unit, and performs swing control of the swing roller based on the determined swing control information.

The invention according to claim 8 is the invention according to claim 7,
The detection unit is disposed on the side of the sheet on which the image is transferred, detects the position of the side edge of the sheet and the position of the image on the sheet,
The control unit determines the swing control information based on the position of the side edge of the sheet detected by the detection unit and the position of the image on the sheet.

The invention according to claim 9 is the invention according to claim 7 or 8,
The control unit further determines the swing control information according to a condition related to paper conveyance.

The invention according to claim 10 is the invention according to any one of claims 7 to 9,
The control unit determines the swing control information for each of a plurality of timings at which the swing roller is swung based on a detection result by the detection unit.

The invention according to claim 11 is the invention according to any one of claims 1 to 10,
The swing roller swings in a direction orthogonal to the paper transport direction.

The invention according to claim 12
A transfer section for transferring an image to paper;
A fixing unit for fixing the image transferred by the transfer unit to the paper;
An image forming path for conveying the sheet to the transfer unit and the fixing unit;
A swing roller that is disposed in the image forming path and includes a pair of rollers that convey the paper toward the transfer unit;
The image forming path is branched from the image forming path downstream of the fixing unit, and the front and back sides of the paper on which image formation on the first surface has been completed by the transfer unit and the fixing unit are reversed and re-entered in the image forming path. Reversing path to feed paper,
A control method of a swing roller in an image forming apparatus comprising:
Based on a detection result by a detection unit that detects a position of a side end portion of the paper disposed in the reversing path, the paper that is re-fed from the reversing path is transported toward the transfer unit. Performs swing control of the swing roller.

  According to the present invention, it is possible to improve the positional accuracy of an image to be transferred to a sheet that has been re-fed from the reversing path.

1 is a configuration diagram schematically illustrating an image forming apparatus according to an embodiment. FIG. 6 is a diagram for explaining a paper swing process by a registration roller. FIG. 2 is a block diagram schematically showing a configuration of a control system of the image forming apparatus in FIG. 1. It is a flowchart which shows the rocking | swiveling control process performed by the control part of FIG. It is a figure which shows the example of arrangement | positioning of the 2nd position detection sensor in the modification 1. FIG. It is a figure which shows the example of arrangement | positioning of the 2nd position detection sensor in the modification 2. FIG. It is a figure which shows the example of arrangement | positioning of the 2nd position detection sensor in the modification 3. It is a figure which shows an example of a sub scanning curve.

  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 fixing device 50, 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 image forming units 10Y, 10M, 10C, and 10K, an intermediate transfer belt 6, a secondary transfer roller 9, and the like. 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 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, and 10K include the photosensitive drums 1M, 1C, and 1K and charging units 2M, 2C, and 2K, optical writing units 3M, 3C, and 3K, and developing devices 4M, arranged around the photosensitive drums 1M, 1C, and 1K. 4C, 4K and drum cleaners 5M, 5C, 5K.

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

  The toner image composed of each color transferred onto the intermediate transfer belt 6 is transferred to a sheet P conveyed at a predetermined timing by a sheet conveying unit 20 described later by a secondary transfer roller 9 as a transfer unit. The secondary transfer roller 9 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 paper transport unit 20 transports the paper P along the transport path of the paper P. The transport path is configured by an image forming path R1 and a reverse path R2. The image forming path R <b> 1 is a transport path for transporting the paper P to the secondary transfer roller 9 and the fixing device 50. The reversing path R2 is branched from the image forming path R1 downstream of the fixing device 50, and reverses the front and back of the sheet P on which the image formation on the first surface (front surface) has been completed and re-feeds the image forming path R1. It is a transport route. In FIG. 1, the image forming path R1 is indicated by a thin line, and the inversion path R2 is indicated by a thick line.

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 paper P is accommodated in the paper feed tray 21, and the paper P accommodated in the paper feed tray 21 is taken in by the paper feed unit 22 and sent out to the image forming path R1. Alternatively, the paper P is stored in a paper feed tray included in an external paper feed device (not shown) connected to the image forming apparatus 100 via the external paper feed ports 81 and 82 and the like. The held paper P is supplied from the paper supply device to the image forming apparatus 100 via the external paper supply port 81 or 82, and is sent out to the image forming path R1. For example, the long paper is supplied from the external paper feeder to the image forming apparatus 100 via the external paper feed port 81 or 82.

  In the image forming path R <b> 1, the paper P fed from the paper feed tray 21 or the paper feed tray of the paper feed device is sequentially supplied by a plurality of intermediate transport rollers 23 to 25 and a loop roller 26 provided from the upstream side to the downstream side. It is conveyed and proceeds on the image forming path R1. When the leading edge of the paper P approaches the registration roller 27, the paper P conveyed by the loop roller 26 and the like is abutted against the registration roller 27 in a rotation stopped state, and the loop roller 26 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 27 starts rotating at a predetermined timing so as to synchronize with the toner image carried by the intermediate transfer belt 6, the intermediate transport rollers 23 to 25 and the loop roller 26 are switched from the pressure contact state to the separated state. It is done. That is, after the loop roller 26 transitions to the separated state, the paper P is conveyed only by the registration roller 27. The registration roller 27 performs a swinging process, which will be described later, while transporting the paper P as a swinging roller, and transfers the paper P to the transfer nip portion of the intermediate transfer belt 6 and the secondary transfer roller 9 as an image carrier. Transport.

  As shown in FIG. 2, the registration roller 27 is configured to be swingable in the sheet width direction CD (direction perpendicular to the sheet conveyance direction (sub-scanning direction) FD). A driving mechanism 34 mainly composed of an electric motor (for example, a stepping motor) is coupled to the registration roller 27, and is driven by the driving mechanism 34, whereby the sheet width direction CD starts from a predetermined home position. Can be moved to.

  The registration rollers 27 move the conveyed paper P along the paper width direction CD by moving along the paper width direction CD in accordance with the passage period during which the paper P passes through the registration roller 27 (oscillation process). Thereby, the registration roller 27 adjusts the transport position of the paper P in the paper width direction CD so as to be aligned with the position of the transferred toner image.

  A registration sensor 61 is disposed between the registration roller 27 and the loop roller 26 in the image forming path R1. The registration sensor 61 detects the arrival of the leading edge of the paper P at the detection position of the registration sensor 61 (a position that is a predetermined distance before the registration roller 27). The detection result of the registration sensor 61 is used for detection of the rotation start timing of the registration roller 27 and the like.

  A first position detection sensor 62 is provided between the registration roller 27 and the secondary transfer roller 9. The first position detection sensor 62 includes, for example, a linear image sensor (for example, a CCD line sensor) in which a plurality of light receiving elements are linearly arranged along the paper width direction CD, an optical system, a light source, and the like. . The first position detection sensor 62 detects the position of the side edge of the paper P in the paper width direction CD. The detection result of the first position detection sensor 62 is output to the control unit 11 and is used for determining the swing control information of the registration roller 27 in the swing process during image formation on the first surface.

The inversion route R2 includes a first route R21, a second route R22, and a merging route R23.
The first path R21 is a path branched from the image forming path R1, and includes a reversing roller 31, and after the sheet P fed from the image forming path R1 is conveyed by the reversing roller 31 in a certain direction (forward direction) as it is. This is a path that changes the conveyance direction of the paper P to the direction of the second path R22 by the reverse rotation of the reversing roller 31.
The second path R22 has two bent portions 35 and 36, and is a path for refeeding the image P in the image forming path R1 with the front and back sides of the paper P reversed and the second surface facing upward.
The joining path R23 is a path for joining the first path R21 again to the image forming path R1.

When image formation is performed also on the second surface of the paper P, the paper P that has completed image formation (transfer and fixing) on the first surface is sent to the first route R21 of the reversal route R2 by the switching gate 30, and It is conveyed to the reverse roller 31 along one path R21. The reverse roller 31 conveys the sheet P in a certain direction (forward direction) as it is, holds the rear end of the sheet P, and then reversely rotates to change the conveyance direction of the sheet P to the direction of the second path R22. It sends out to 2nd path | route R22. When the length of the first path R21 is insufficient, such as when the sheet P is a long sheet, the leading edge of the sheet P is advanced to the image forming path R1 via the merging path R23. It becomes possible to send out to 2nd path | route R22.
The sheet P sent out to the second path R22 passes through the bent portion 35, so that the first surface once turns upward from the state where the second surface faces upward, and is temporarily stopped by the transport roller 32. After that, the sheet is fed again to the image forming path R1 at a predetermined timing. At this time, the sheet P passes through the bent portion 36 and is re-fed to the image forming path R1 with the front and back sides reversed and the second surface facing upward, and passes through the registration roller 27 to the transfer nip portion. Be transported. It should be noted that transporting means for refeeding such as the paper discharge roller 28, the switching gate 30, the reversing roller 31, and the transport roller 32 also constitute the paper transport unit 20 described above.

  A second position detection sensor 63 is provided on the downstream side of the reverse roller 31 in the paper conveyance direction after the reverse rotation of the reverse roller 31 is started. The second position detection sensor 63 includes, for example, a linear image sensor (for example, a CCD line sensor) in which a plurality of light receiving elements are linearly arranged along the paper width direction CD, an optical system, a light source, and the like. . The second position detection sensor 63 is a detection unit that detects the position of the side edge of the paper P in the paper width direction CD. Further, by arranging the second position detection sensor 63 on the image surface side of the paper P, it is possible to detect the image position of the toner image transferred to the paper P. The detection result of the second position detection sensor 63 is output to the control unit 11 and used for determining the swing control information of the registration roller 27 in the swing process when the paper P is re-feeded.

  The fixing device 50 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 50 includes a pair of fixing members (eg, a pair of rollers) It is comprised with the heater which heats one or both of the members. The fixing device 50 fixes the toner image onto 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 P subjected to the fixing process by the fixing device 50 is discharged by a paper discharge roller 28 to a paper discharge tray 29 attached to the outer side surface of the housing. When image formation is also performed on the second surface of the paper P, the paper P on which image formation on the first surface has been completed is sent out by the switching gate 30 to the reversing path R2.

  As shown in FIG. 3, the control unit 11 includes a storage unit 12, a communication unit 13, an operation unit 14, a document reading device SC, an image forming unit 10, a sheet conveying unit 20, a fixing device 50, a registration sensor 61, a first sensor. It is connected to the position detection sensor 62, the second position detection sensor 63, the environment sensor 64, and the like. 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. Further, when a command for executing a double-sided printing job is input from the operation unit 14, the control unit 11 executes a swing control process to be described later, and performs swing control of the registration roller 27 during job execution.

  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 can set the printing conditions, that is, the paper type, basis weight, size, paper feed tray to be used, image density, magnification, presence / absence of duplex printing, and the like. Further, the user can input a job execution command or the like 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.

  The environment sensor 64 includes, for example, a temperature sensor, a humidity sensor, and the like, detects the temperature and humidity in the housing of the image forming apparatus 100, and outputs the detection result to the control unit 11.

[Operation of Image Forming Apparatus 100]
Next, the operation of the image forming apparatus 100 in the first embodiment will be described.
FIG. 4 is a flowchart showing a swing control process for controlling the swing operation of the registration roller 27. The processing shown in this flowchart is executed in cooperation with a program stored in the control unit 11 and the storage unit 12 in accordance with a double-sided print job execution command from the user. In the present embodiment, as an example, a case where image formation on the second surface of the paper P is continuously performed after the image formation on the first surface of the paper P will be described.

  When the job is started, the control unit 11 waits for the first position detection sensor 62 to detect the leading edge of the paper P (step S1).

  When the leading edge of the paper P is detected by the first position detection sensor 62 (step S1; YES), the control unit 11 is based on the detection result of the position of the side edge of the paper P by the first position detection sensor 62. Then, the registration roller 27 is swung by the drive mechanism 34 (step S2). For example, the control unit 11 calculates a deviation amount between the position of the paper side edge detected by the first position detection sensor 62 and the target position, and based on the calculated deviation amount, the swing control information (swing amount). , Swing direction, swing speed). If the side edge of the paper P passes through that position, the target position of the toner image with respect to the paper P is the optimum image position (for example, the center of the paper P in the width direction matches the center of the toner image in the width direction). This position is expected to be transferred to the position. Based on the determined swing control information, the registration roller 27 is swung by the drive mechanism 34.

Next, the control unit 11 waits for the second position detection sensor 63 to detect the leading edge of the paper P after the reverse rotation of the reversing roller 31 is started (step S3).
When the leading edge of the paper P is detected by the second position detection sensor 63 (step S3; YES), the control unit 11 causes the paper side edge at a plurality of positions in the sub-scanning direction of the paper P by the second position detection sensor 63. The detection result of the position of the part is acquired (step S4).

  Next, the control unit 11 determines the swing control information of the registration roller 27 at each predetermined swing timing based on the detection result by the second position detection sensor 63 (step S5). Here, the swing timing is a timing at which the registration roller 27 is swung. In the present embodiment, for example, a plurality of swing timings (for example, approximately equidistant intervals) such as t1 seconds after the timing when the second position detection sensor 63 detects the leading edge of the paper P, t2 seconds later,. N) predetermined.

  In step S <b> 5, for example, the control unit 11 acquires the detection result of the position (X <b> 1, X <b> 2) of the sheet side end by the second position detection sensor 63 at two points in the sub-scanning direction on the leading end side of the sheet P. Then, the inclination of the paper P is calculated based on the acquired detection result. Then, based on the calculated inclination, the amount of deviation from the target position of the sheet side edge at each swing timing is calculated, and based on the calculated shift amount, swing control information (swing amount, Determine the rocking direction and rocking speed.

The inclination of the paper P can be calculated by the following equation, for example.
Inclination of paper P = (difference in the paper width direction between X1 and X2) / (transport distance between X1 and X2)
Further, the swing amount can be calculated by the following equation, for example.
Swing amount = Deviation amount from the target position at the paper side edge x α
Here, α is a coefficient. The transport state of the paper P differs depending on the paper transport conditions, for example, the paper type, basis weight, environment (temperature, humidity, etc.), paper size (paper width, paper length), etc. of the paper P. It is preferable that the value varies depending on the conditions related to the sheet conveyance and the swing timing (that is, the position in the sub-scanning direction to be swung). Further, it is preferable to increase the swing speed as the swing amount increases.

  The second position detection sensor 63 may be disposed on either the image surface side or the non-image surface side. However, when the second position detection sensor 63 is disposed on the image surface side, the image information of the toner image can be acquired. The swing control information of the registration roller 27 may be determined based on the detection result of the position of the sheet side edge and the position of the toner image by the position detection sensor 63. For example, based on the detection result of the position of the paper side edge and the position of the toner image at the plurality of points detected by the second position detection sensor 63, the distance and inclination of the paper side edge and the toner image at the plurality of points are calculated. Then, based on the calculated distance and inclination, the distance between the sheet side edge and the toner image at each swing timing is calculated. Then, the difference (deviation amount) between the calculated distance and the distance between the sheet side edge when the toner image is placed at the optimum image position and the toner image is calculated, and each swing is calculated based on the calculated deviation amount. The swing control information at the timing is determined. Thereby, the toner image can be aligned with the optimum image position with higher accuracy.

  Next, the control unit 11 waits for the swing timing of the registration roller 27 to come (step S6). When it is determined that the swing timing has arrived (step S6; YES), the control unit 11 causes the drive mechanism 34 to move the registration roller 27 based on the swing control information determined in step S5 according to the swing timing. Swing is performed (step S7).

  Next, the control unit 11 determines whether or not the swing at the final swing timing is finished (step S8). For example, whether or not the swing at the final swing timing is finished based on the paper size of the paper P, the elapsed time since the second position detection sensor 63 detected the leading edge of the paper P, and the conveyance speed. Judging.

  When it is determined that the swing at the final swing timing is not completed (step S8; NO), the control unit 11 returns to step S6, waits for the next swing timing, and the swing timing arrives. Then, the process of swinging the registration roller 27 is repeated.

When it is determined that the swing at the final swing timing has been completed (step S8; YES), the control unit 11 determines whether the transfer to the final page has been completed (step S9).
When it is determined that the transfer to the last page has not been completed (step S9; NO), the control unit 11 returns to step S1.
When it is determined that the transfer to the last page has been completed (step S9; YES), the control unit 11 ends the swing control process.

As described above, according to the image forming apparatus 100 of the present embodiment, the second position detection sensor 63 is provided in the reversing path R2, and the detection result of the second position detection sensor 63 (the position of the edge on the paper side and / or Based on the position of the toner image, the swing of the registration roller 27 when the paper P re-feeded from the reversing path R2 is conveyed toward the secondary transfer roller 9 is controlled. Therefore, since the conveyance variation of the paper P in the reversing path R2 can be absorbed, it is possible to improve the positional accuracy of the image transferred to the second surface of the paper P re-fed from the reversing path R2. In particular, as in the present embodiment, the second position detection sensor 63 is provided on the downstream side of the reverse roller 31 in the paper conveyance direction after the reverse rotation of the reverse roller 31 is started, and the detection result is used to swing the registration roller 27. By feeding back, the paper bending caused by the switching of the conveyance direction of the paper P by the reversing roller 31 can be corrected, and the positional accuracy of the image transferred to the second surface of the paper P re-fed from the reversing path R2 is improved. Can be improved.
Further, in the present embodiment, the control unit 11 controls the paper side at each position in the sub-scanning direction corresponding to a plurality of swing timings for swinging the registration roller 27 based on the detection result of the second position detection sensor 63. The shift amount of the end portion is calculated, and based on the calculated shift amount, swing control information at each swing timing is determined, and swing control of the registration roller 27 is performed. Accordingly, since different swing control can be performed on the front end side and the rear end side of the paper P, it is possible to suppress the displacement of the image position due to the sub-scanning bending (see FIG. 8) in which the paper P is bent in the middle with high accuracy. it can. In particular, it is more effective when the paper is long in the paper conveyance direction, such as long paper.

(Modification 1)
In the above embodiment, the case where the second position detection sensor 63 is provided on the downstream side of the reversing roller 31 in the paper conveyance direction after the reverse rotation of the reversing roller 31 is described as an example, but as shown in FIG. It is good also as a structure provided with the 2nd position detection sensor 63 in the downstream of the conveyance roller 32 in 2nd path | route R22. Then, the control unit 11 executes a process similar to the swing control process shown in FIG. 4, and based on the detection result of the second position detection sensor 63, the sheet P that has been re-feeded from the reversing path R <b> 2 It is also possible to control the swinging of the registration roller 27 when transported toward the next transfer roller 9. This absorbs variations in conveyance due to the temporary stop and refeeding of the paper P by the conveyance roller 32, and improves the positional accuracy of the image transferred to the second surface of the paper P re-fed from the reversing path R2. it can.

(Modification 2)
In the above embodiment, the case where the second position detection sensor 63 is provided on the downstream side of the reversing roller 31 in the paper conveyance direction after the reverse rotation of the reversing roller 31 is described as an example, but as shown in FIG. It is good also as a structure provided with the 2nd position detection sensor 63 in the bending part 35 (or the downstream of the bending part 35) in 2nd path | route R22. Then, the control unit 11 executes a process similar to the swing control process shown in FIG. 4, and based on the detection result of the second position detection sensor 63, the sheet P that has been re-feeded from the reversing path R <b> 2 It is also possible to control the swinging of the registration roller 27 when transported toward the next transfer roller 9. Thereby, it is possible to absorb the conveyance variation due to the passage of the bent portion 35 of the paper P, and to improve the positional accuracy of the image transferred to the second surface of the paper P that is re-fed from the reversing path R2.
In addition, since the paper P follows substantially the same position along the guide in the bent portion, by providing the second position detection sensor 63 in the bent portion 35, fluctuation of the detection result can be suppressed and the paper side edge portion can be detected with high accuracy. Can be performed. In addition, by providing the second position detection sensor 63 on the downstream side of the bent portion 35, after the bending of the paper P due to the passage of the bent portion 35 is determined, the paper side edge is detected, and the registration roller 27 is swung. It is possible to feed back to dynamic control.

  Further, in the compact image forming apparatus 100 having a large curvature of the bent portion, the second position detection sensor 63 is disposed before and after the bent portion 35, so that the side of the sheet P when passing through the bent portion 35 is provided. It becomes possible to grasp the shift amount of the end portion more accurately. For example, since the difference between the deviation amount on the upstream side and the deviation amount on the downstream side with respect to the bent portion 35 becomes an error received when passing through the bent portion 35, the control unit 11 swings so as to cancel this amount. Control information is determined and the registration roller 27 is swung.

(Modification 3)
In the above embodiment, the case where the second position detection sensor 63 is provided on the downstream side of the reversing roller 31 in the paper conveyance direction after the reverse rotation of the reversing roller 31 is described as an example, but as shown in FIG. It is good also as a structure provided with the 2nd position detection sensor 63 in merge path | route R23. Then, the control unit 11 executes a process similar to the swing control process shown in FIG. 4, and based on the detection result of the second position detection sensor 63, the sheet P that has been re-feeded from the reversing path R <b> 2 It is also possible to control the swinging of the registration roller 27 when transported toward the next transfer roller 9. Thereby, when the paper P is a long paper, it is possible to absorb the conveyance variation of the rear end side when the paper P is re-feeded in the reversing path R2, so that the paper P is re-feeded from the reversing path R2. The positional accuracy of the image transferred to the second surface of the paper P can be improved.

  Further, when the paper P is a long paper, when the paper P is conveyed in the forward direction along the first path R21, the leading end of the paper P may reach the registration roller 27 via the merging path R23. Therefore, in such a case, the control unit 11 causes the sheet P to pass through the merge path R23 based on the detection result of the side edge portion at the leading edge of the sheet P by the second position detection sensor 63 arranged in the merge path R23. The swing control information of the registration roller 27 when it reaches the registration roller 27 is determined, and the registration is performed when the paper P reaches the registration roller 27 via the merge path R23 based on the determined swing control information. The roller 27 may be controlled to swing. Accordingly, it is possible to correct the transport variation on the leading end side (the rear end side after the change of the transport direction) of the paper P generated before the change of the transport direction.

(Modification 4)
The second position detection sensor 63 is provided at any of the plurality of positions described in the embodiment and the first to third modifications, and the control unit 11 is based on the detection results of the plurality of second position detection sensors 63. The swinging of the registration roller 27 at the time of refeeding for image formation on the second surface of the paper P may be controlled. For example, each of the second position detection sensors 63 detects the side edge of the sheet P at the timing at which the sheets P simultaneously pass through the positions of the plurality of second position detection sensors 63, and the control unit 11 detects the detection result. The inclination of the paper P is calculated based on the above, and based on the calculated inclination, the deviation amount from the target position of the paper side edge at the position corresponding to each swing timing of the paper P is calculated. Then, based on the calculated deviation amount, the swing control information is determined in the same manner as in the above embodiment, and based on the determined swing control information, an image is formed on the second surface of the sheet P at each swing timing. The swing of the registration roller 27 at the time of re-feeding may be controlled. As a result, variations in the conveyance of the paper P in the reversing path R2 can be absorbed, so that the positional accuracy of the image transferred to the second surface of the paper P re-fed from the reversing path R2 can be improved. In particular, as shown in FIG. 8, for the long paper, the paper itself may be deformed (bent) at the leading end side and the trailing end side, so that the method according to the modification example 4 is effective. Note that the first position detection sensor 62 may be used instead of one of the plurality of second position detection sensors 63.

(Modification 5)
In the embodiment and the first to fourth modifications, the registration roller 27 is swung at the time of refeeding for image formation on the second surface of the paper P based on the detection result by the second position detection sensor 63. The control is performed to correct the image writing position by the image forming units 10Y, 10M, 10C, and 10K (image writing position to the photosensitive drums 1Y to 1K by the optical writing units 3Y to 3K) and the registration roller 27. These swing controls may be combined.
For example, by performing control for correcting the image writing position by the image forming units 10Y, 10M, 10C, and 10K, the absolute position of the image with respect to the paper is corrected, and then control for swinging the registration roller 27 is performed. Thus, the variation in the side edge of the paper P may be reduced.

  Although it is conceivable to perform only control for correcting the image writing position by the image forming units 10Y, 10M, 10C, and 10K based on the detection result by the second position detection sensor 63, the positions of the paper P and the toner image are considered. In consideration of the accuracy of deviation suppression, it is preferable that only the swing control of the registration roller 27 or the swing control of the registration roller 27 and the correction of the image writing position be combined. In the correction of the image writing position, the entire image can be shifted in the scanning direction, but it cannot be handled when the paper is bent in the middle. On the other hand, in the swing control of the registration roller 27, the swing amount can be changed at each position in the sub-scanning direction (for example, at the front end side and the rear end side). The position of the edge can be corrected, and even when the paper is bent in the middle, the positional deviation of the image with respect to the paper P can be more accurately suppressed. Further, when the second position detection sensor 63 is provided on the downstream side of the position of the second position detection sensor 63 shown in FIG. 1, feedback of the detection result is an image by the image forming units 10Y, 10M, 10C, and 10K. Since the writing timing is not in time, the position of the second position detection sensor 63 is limited to the position shown in FIG. 1 or upstream thereof when the image position deviation with respect to the paper P is suppressed only by correcting the image writing position. However, when swing control of the registration roller 27 is performed, since there is no such restriction, the second position detection sensor 63 is disposed closer to the registration roller 27 and the detection result is swung. Feedback can be given to the control.

  Although the embodiment of the present invention and the modification thereof have been described above, the description in the above embodiment and the modification shows a preferable example of the image forming apparatus according to the present invention, and is not limited to this. Absent.

  For example, in the above embodiment, a color image forming apparatus that primarily transfers an image formed on a photosensitive drum to an intermediate transfer roller and transfers the image from the intermediate transfer roller to a sheet by a secondary transfer roller has been described as an example. However, the present invention is also applicable to a monochrome image forming apparatus that directly transfers an image from a photosensitive drum to a sheet by a transfer roller.

  In the above-described embodiment, the registration roller 27 is described as swinging in a direction orthogonal to the paper transport direction. However, the swing direction is not necessarily a direction orthogonal to the paper transport direction. You can change

  In the above embodiment, the case where the swing roller is the registration roller 27 has been described as an example. However, the present invention is not limited to this, and may be a separate body from the registration roller 27, for example.

  In the above description, an example in which a non-volatile memory, a hard disk, or the like is used as a computer-readable medium for the program according to the present invention is disclosed, 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 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.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 11 Control part 12 Storage part 13 Communication part 14 Operation part SC Document reading apparatus 10 Image forming part 9 Secondary transfer roller 20 Paper conveyance part 27 Registration roller 31 Reverse roller 32 Conveyance rollers 35 and 36 Bending part 50 Fixing device 61 registration sensor 62 first position detection sensor 63 second position detection sensor 64 environmental sensor R1 image formation path R2 reverse path R21 first path R22 second path R23 merging path

Claims (12)

A transfer section for transferring an image to paper;
A fixing unit for fixing the image transferred by the transfer unit to the paper;
An image forming path for conveying the sheet to the transfer unit and the fixing unit;
A swing roller that is disposed in the image forming path and includes a pair of rollers that convey the paper toward the transfer unit;
The image forming path is branched from the image forming path downstream of the fixing unit, and the front and back sides of the paper on which image formation on the first surface has been completed by the transfer unit and the fixing unit are reversed and re-entered in the image forming path. Reversing path to feed paper,
A detection unit that is disposed in the reversing path and detects a position of a side edge of the paper;
A control unit that performs swing control of the swing roller when transporting the sheet re-feeded from the reversing path toward the transfer unit based on a detection result by the detection unit;
An image forming apparatus comprising: The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A second path that is provided on the downstream side of the first path in the sheet conveyance direction after the conveyance direction is changed by the reversing roller, and that reverses the front and back of the sheet and refeeds the image forming path. ,
With
The image forming apparatus according to claim 1, wherein the detection unit is disposed on the downstream side of the reversing roller in the transport direction of the paper after the transport direction is changed by the reversing roller. The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A second path that is provided on the downstream side of the first path in the sheet conveyance direction after the conveyance direction is changed by the reversing roller, and that reverses the front and back of the sheet and refeeds the image forming path. ,
A conveyance roller that is provided in the second path, temporarily stops before the sheet is re-fed to the image forming path, and then conveys the sheet to the image forming path;
With
The image forming apparatus according to claim 1, wherein the detection unit is disposed on a downstream side of the transport roller. The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A bent portion is provided on the downstream side of the first path in the conveyance direction of the paper after the conveyance direction is changed by the reversing roller, and the paper is reversed by the bending portion. A second path for reversing the front and back of the paper and refeeding the image forming path,
With
The image forming apparatus according to claim 1, wherein the detection unit is provided on the bent portion, on the downstream side of the bent portion, or before and after the bent portion. The inversion path is
A first path that includes a reversing roller that diverts from the image forming path and changes the transport direction of the paper by rotating in reverse after transporting the paper in a certain direction;
A second path that is provided on the downstream side of the first path in the sheet conveyance direction after the conveyance direction is changed by the reversing roller, and that reverses the front and back of the sheet and refeeds the image forming path. ,
A merging path for rejoining the first path branched from the image forming path to the image forming path;
With
The image forming apparatus according to claim 1, wherein the detection unit is provided in the merge path. A plurality of the detection units are provided,
The control unit performs swing control of the swing roller when transporting the sheet re-feeded from the reversing path toward the transfer unit based on detection results by a plurality of the detection units. Item 2. The image forming apparatus according to Item 1.   The said control part determines the rocking | swiveling control information of the said rocking | swiveling roller based on the detection result by the said detection part, and performs rocking | fluctuation control of the said rocking | swiveling roller based on the determined rocking | fluctuation control information. The image forming apparatus according to any one of 1 to 6. The detection unit is disposed on the side of the sheet on which the image is transferred, detects the position of the side edge of the sheet and the position of the image on the sheet,
The image forming apparatus according to claim 7, wherein the control unit determines the swing control information based on a position of a side edge portion of the sheet detected by the detection unit and a position of the image on the sheet.   The image forming apparatus according to claim 7, wherein the control unit further determines the swing control information according to a condition related to sheet conveyance.   The said control part determines the said rocking | swiveling control information for every some timing which rocks the said rocking | fluctuating roller based on the detection result by the said detection part, respectively. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the swing roller swings in a direction orthogonal to a conveyance direction of the paper. A transfer section for transferring an image to paper;
A fixing unit for fixing the image transferred by the transfer unit to the paper;
An image forming path for conveying the sheet to the transfer unit and the fixing unit;
A swing roller that is disposed in the image forming path and includes a pair of rollers that convey the paper toward the transfer unit;
The image forming path is branched from the image forming path downstream of the fixing unit, and the front and back sides of the paper on which image formation on the first surface has been completed by the transfer unit and the fixing unit are reversed and re-entered in the image forming path. Reversing path to feed paper,
A control method of a swing roller in an image forming apparatus comprising:
Based on a detection result by a detection unit that detects a position of a side end portion of the paper disposed in the reversing path, the paper that is re-fed from the reversing path is transported toward the transfer unit. A control method for performing swing control of the swing roller.

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