JP2015049471A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to prevent reduction in image quality when an image side of a sheet is rubbed in a conveyance roller section located upstream of a registration roller section during duplex image formation.SOLUTION: An image forming apparatus includes a transfer roller section for transferring a toner image to a sheet; a registration roller section for conveying the sheet to the transfer roller section; a conveyance roller section having a driving roller fixed on an inner periphery of a bent path where the sheet passes during duplex image formation and a driven roller to be brought into pressure contact with the drive roller or to be separated therefrom, to convey the sheet to the registration roller section; and a control section which controls rotation of the driving roller in the conveyance roller section and pressure-contact/separation operation of the driven roller. The control section separates the driven roller from the driving roller until the sheet passes through the conveyance roller section when the sheet is conveyed by the transfer roller section or the registration roller section in duplex image formation, and rotates the driving roller.

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In general, in an image forming apparatus (printer, copying machine, facsimile, etc.) using an electrophotographic process technology, a laser beam based on image data is irradiated (exposed) to a uniformly charged photoconductor (for example, a photoconductive drum). ), An electrostatic latent image is formed on the surface of the photoreceptor. Then, toner is supplied to the photoconductor on which the electrostatic latent image is formed, so that the electrostatic latent image is visualized and a toner image is formed. The toner image is transferred directly or indirectly to the sheet via an intermediate transfer member, and then heated and pressed by a fixing device, whereby an image is formed on the sheet.

  The image forming apparatus described above includes a paper transport unit that transports paper supplied from a paper feed unit (a paper feed tray, an external paper feed device, etc.) to the image forming unit. A configuration of a general paper transport unit is shown in FIG. As shown in FIG. 1, the paper transport unit reverses the paper on which the image is formed by the first transport unit 53 that transports the paper to the image forming unit, and delivers the paper to the first transport unit 53. A second transport unit 54 is provided.

  The first transport unit 53 includes a plurality of transport roller units such as an intermediate transport roller unit 531, a loop roller unit 532, and a registration roller unit 533, and narrows the sheet with at least one of the plurality of transport roller units. Hold and transport. The second transport unit 54 includes a plurality of transport roller units including a pre-registration roller unit 543, and transports the paper while sandwiching at least one of the plurality of transport roller units.

In the first transport unit 53, the paper supplied from the paper feed unit is transported by the intermediate transport roller unit 531 and transferred to the loop roller unit 532. Similarly, the paper is sequentially transferred from the loop roller unit 532 to the registration roller unit 533 and conveyed. The registration roller unit 533 corrects the inclination of the sheet and adjusts the conveyance timing, and then conveys the sheet to the image forming unit 40 (toner image transfer unit).
In addition, when forming a double-sided image in which an image is also formed on the back side of the paper, the paper on which the image is formed by the image forming unit 40 is fixed by the fixing unit 60 and then reversed by the second transport unit 54. Then, the pre-registration roller unit 543 delivers the first transfer unit 53 (loop roller unit 532).

Here, the loop roller unit 532 and the pre-registration roller unit 543 are a portion where the second conveyance unit 54 joins the first conveyance unit 53, that is, in the vicinity of a bent conveyance path 544 (referred to as a “bend path 544”). Placed in. At the time of double-sided image formation, the loop roller unit 532 and the pre-registration roller unit 543 are positioned on the upstream side of the registration roller unit 533 in the sheet conveyance direction.
In order to prevent the inclination of the paper corrected in the registration roller unit 533 from returning to the original, and to smoothly correct the deviation in the width direction of the paper by the swinging operation of the registration roller unit 533, the loop roller unit 532 and the pre-registration roller portion 543 are configured to be capable of being separated from each other by pressure (for example, Patent Document 1). That is, at the time of double-sided image formation, after the leading edge of the sheet reversely conveyed by the second conveyance unit 54 reaches the registration roller unit 533 and the conveyance of the sheet by the registration roller unit 533 is started, the loop roller unit 532 and The press-bonded state in the pre-registration roller unit 543 is released, and the sheet is conveyed by the registration roller unit 533.

Specifically, as shown in FIG. 2, the loop roller unit 532 includes a driving roller 532A and a driven roller 532B. In the loop roller portion 532, a drive roller 532A having gears and pulleys is disposed on the inner peripheral side of the bending path 544 in order to save space. Further, when the pressing and separating operation is performed with the driving roller 532A movable, it is necessary to use a coupling member and a positioning member in order to ensure the accuracy of the gear backlash and the roller pressing force, which increases the apparatus cost. Therefore, normally, the driving roller 532A is fixed, and the driven roller 532B is configured to be crimped or separated from the driving roller 532A.
Similarly, in the pre-registration roller portion 543, the driving roller 543A is fixed to the inner peripheral side of the bending path 544, and the driven roller 543B is pressure-bonded or separated from the driving roller 543A.

JP 2004-123377 A

  In the loop roller unit 532 and the pre-registration roller unit 543 that are positioned upstream of the registration roller unit 533 when the double-sided image is formed, the driven rollers 532B and 543B move when the conveyance of the paper by the registration roller unit 533 is started. Then, they are separated from the driving rollers 532A and 543A (see FIG. 2). On the other hand, the rotation of the driving rollers 532A and 543A is temporarily stopped. This is because if the drive rollers 532A and 543A are rotated when the driven rollers 532B and 543B are pressed against the drive rollers 532A and 543A again, the motor will step out due to torque fluctuation.

  As described above, in the conventional image forming apparatus, when the paper is transported by the registration roller unit 533, the rotation of the driving rollers 532A and 543A is stopped, so that the image surface of the paper (the image is formed). The surface) is rubbed against the drive rollers 532A and 543A, and the image quality of the image surface may deteriorate. Further, when the image surface is rubbed and toner adheres to the driving rollers 532A and 543A, the toner may be transferred to the succeeding paper and the paper may be soiled, which also deteriorates the image quality.

  An object of the present invention is to provide an image forming apparatus capable of preventing a reduction in image quality due to the rubbing of the image surface of a sheet in a transport roller unit positioned upstream of a registration roller unit during double-sided image formation. .

An image forming apparatus according to the present invention includes a transfer roller unit that transfers a toner image to paper,
A registration roller unit that conveys the sheet to the transfer roller unit;
A conveyance roller unit having a driving roller fixed on the inner peripheral side of a bending path through which a sheet is passed during double-sided image formation and a driven roller that is pressed against or separated from the driving roller and conveys the sheet to the registration roller unit When,
A control unit for controlling the rotation operation of the driving roller and the pressure-separation separation operation of the driven roller in the transport roller unit,
In the double-sided image formation, the control unit separates the driven roller from the driving roller until the sheet is removed from the conveyance roller unit when the sheet is conveyed by the transfer roller unit or the registration roller unit. The drive roller is rotated.

  According to the image forming apparatus of the present invention, since the image surface of the paper is not rubbed against the driving roller of the transport roller unit, the image quality of the image surface is maintained, and the toner does not adhere to the driving roller due to the rub. Therefore, it is possible to prevent the image quality from being deteriorated due to the image surface of the paper being rubbed at the transport roller portion located on the upstream side of the registration roller portion during the double-sided image formation.

FIG. 3 is a diagram illustrating a configuration of a general paper transport unit. It is a figure which shows the conveyance state of the paper in the conventional paper conveyance part. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the embodiment. It is a figure which shows a 1st conveyance part and a 2nd conveyance part in detail. 6 is a flowchart illustrating an example of a paper conveyance control process in double-sided image formation. It is a timing chart which shows an example of operation | movement of the registration roller part in a double-sided image formation, a loop roller part, and a pre-registration roller part.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 is a diagram showing an overall configuration of the image forming apparatus 1 according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a main part of a control system of the image forming apparatus 1 according to the embodiment.
An image forming apparatus 1 shown in FIGS. 3 and 4 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. In the image forming apparatus 1, photosensitive drums 413 corresponding to four colors of CMYK are arranged in series in the running direction (vertical direction) of the intermediate transfer belt 421, and each color toner image is sequentially transferred to the intermediate transfer belt 421 in one procedure. The vertical tandem system is adopted.
That is, the image forming apparatus 1 primarily transfers Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421, After the four color toner images are superimposed on the transfer belt 421, the image is formed by secondary transfer onto the paper.

  As shown in FIGS. 3 and 4, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100. .

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads out a program corresponding to the processing content from the ROM 102 or the storage unit 72, develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program.

  The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive. The storage unit 72 stores a lookup table LUT that is referred to when, for example, controlling the operation of each block.

  The control unit 100 also exchanges various data with an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Send and receive. For example, the control unit 100 receives a page description language (PDL) transmitted from an external device, and forms an image on a sheet based on image data (input image data) included in the PDL. The communication unit 71 includes various interfaces such as a NIC (Network Interface Card), a MODEM (MODulator-DEModulator), and a USB (Universal Serial Bus).

The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.
The automatic document feeder 11 conveys the document placed on the document tray by the conveyance mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents placed on the document tray.
The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.
The user can operate the operation display unit 20 to perform settings relating to image formation such as document setting, image quality setting, magnification setting, application setting, output setting, single-sided / double-sided setting, paper setting, and swing amount adjustment. .

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs tone correction based on tone correction data (tone correction table) under the control of the control unit 100 (image density control). Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, compression process, and the like on the input image data. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 includes an image forming unit 41 and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component based on input image data. Here, the writing range of the image formed by the image forming unit 40 is set in advance.

  The image forming unit 41 includes four image forming units 41Y, 41M, 41C, and 41K for Y component, M component, C component, and K component. Since the image forming units 41Y, 41M, 41C, and 41K have the same configuration, for convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and when distinguished from each other, the reference numerals Y, M, and C are used. Or K. In FIG. 4, reference numerals are given only to the components of the image forming unit 41Y for the Y component, and reference numerals of the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

The photosensitive drum 413 includes, for example, an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). : A negatively charged organic photoconductor (OPC) in which Charge Transport Layers are sequentially stacked.
The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges upon exposure by the exposure device 411. The charge transport layer consists of a hole transport material (electron donating nitrogen-containing compound) dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The charging device 414 is constituted by a corona discharge generator such as a scorotron charging device or a corotron charging device. The charging device 414 uniformly charges the surface of the photosensitive drum 413 to a negative polarity by corona discharge.

  The exposure apparatus 411 is composed of, for example, a semiconductor laser. The exposure device 411 irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. The positive charge generated in the charge generation layer of the photosensitive drum 413 is transported to the surface of the charge transport layer, so that the surface charge (negative charge) of the photosensitive drum 413 is neutralized. Thereby, an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 contains a developer of each color component (a two-component developer composed of a toner having a small particle diameter and a magnetic carrier), and electrostatically adheres the toner of each color component to the surface of the photosensitive drum 413. The latent image is visualized to form a toner image. Specifically, a developing bias voltage is applied to the developer carrying member (developing roller), and the charged toner on the developer carrying member is applied to the surface of the photosensitive drum 413 by the potential difference between the surface of the photosensitive drum 413 and the developer carrying member. Move to and adhere to exposed areas.

  The drum cleaning device 415 includes a drum cleaning blade that is in sliding contact with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, whereby a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421 is formed.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face a roller 423B (referred to as “backup roller 423B”) disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the sheet. The secondary transfer roller 424 and the intermediate transfer belt 421 constitute a secondary transfer unit 425 that performs secondary transfer of the toner image while transporting the paper.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photosensitive drum 413 are primarily transferred to the intermediate transfer belt 421 in order. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet. Specifically, by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper (the side in contact with the secondary transfer roller 424), the toner image becomes It is electrostatically transferred to the paper. The sheet on which the toner image has been transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

  In the intermediate transfer unit 42, instead of the secondary transfer roller 424, a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller (so-called belt-type secondary transfer). Unit) may be adopted.

The fixing unit 60 is arranged on the upper fixing unit 60A having a fixing surface side member arranged on the fixing surface (surface on which the toner image is formed) side of the paper, and on the back surface (surface opposite to the fixing surface) side of the paper. A lower fixing unit 60B having a back-side support member and a heating source 60C.
When the upper fixing unit 60A is a belt heating system (see FIG. 3), the fixing belt is a fixing surface side member, and when it is a roller heating system, the fixing roller is a fixing surface side member. Further, when the lower fixing unit 60B is a roller pressurization method (see FIG. 3), the pressure roller is a back side support member, and when it is a belt pressurization method, the pressure belt is a back side support member. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the sheet is formed.

  The fixing unit 60 fixes the toner image on the sheet by secondarily transferring the toner image and heating and pressurizing the conveyed sheet at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F may be provided with an air separation unit that separates the sheet from the fixing surface side member or the back surface side support member by blowing air.

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a first transport unit 53, a second transport unit 54, and the like.
In the three paper feed tray units 511 to 513 constituting the paper feed unit 51, paper (standard paper, special paper) identified based on basis weight, size, etc. is stored for each preset paper type. .

The first transport unit 53 includes a plurality of transport roller units including an intermediate transport roller unit 531, a loop roller unit 532, and a registration roller unit 533. The first transport unit 53 transports paper fed from the paper feed unit 51 or an external paper feed device (not shown) to the image forming unit 40 (secondary transfer unit).
The second transport unit 54 includes a switchback path 541 and a back surface transport path 542 in which a plurality of transport roller units including the pre-registration roller unit 543 are arranged. The second transport unit 54 once transports the paper to the switchback path 541, switches back and transports the paper to the back-side transport path 542, thereby reversing the paper, and the first transport unit 53 (loop roller unit 532). Upstream).

  A sheet fed from the sheet feeding unit 51 or an external sheet feeding device (not shown) is conveyed to the image forming unit 40 by the first conveying unit 53. At this time, even after the leading edge of the paper reaches the registration roller unit 533, the conveyance by the loop roller unit 532 is continued while the rotation operation of the registration roller unit 533 (drive roller 533A) is stopped. As a result, the leading edge of the paper comes into contact with the registration nip, and the paper is bent at the loop forming portion. The inclination of the paper is corrected by the stress generated in the paper.

  After the inclination of the sheet is corrected, sheet conveyance (rotation operation of the driving roller 533A) by the registration roller unit 533 is started, and the sheet is conveyed toward the secondary transfer unit 425 of the image forming unit 40. At this time, if the deviation detection sensor 85 detects the deviation of the sheet, the position in the width direction of the sheet is corrected in the process of being conveyed by the registration roller unit 533 (registration swing).

  Then, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to one side (front surface) of the sheet at a time, and a fixing process is performed in the fixing unit 60. The paper on which the image is formed is discharged out of the apparatus by a paper discharge unit 52 having a paper discharge roller 52a. When images are formed on both sides of the paper, the paper on which the image is formed on the front surface is sent to the second transport unit 54, and after being inverted, an image is formed on the back surface.

FIG. 5 is a diagram illustrating the first transport unit 53 and the second transport unit 54 in detail.
As shown in FIG. 5, in the first transport unit 53, the loop roller unit 532 is a junction with the first transport unit 53 in the second transport unit 54, that is, on the downstream side in the paper transport direction of the bent path 544. Be placed. The loop roller unit 532 includes a driving roller 532A and a driven roller 532B. The driving roller 532A is fixed to the inner peripheral side of the bending path 544, and the driven roller 532B is pressed against or separated from the driving roller 532A.

  A driving motor 81 is connected to the driving roller 532A (see FIG. 4). The drive motor 81 is arranged by effectively using the space formed on the inner peripheral side of the bending path 544. A crimping separation portion 82 is connected to the driven roller 532B (see FIG. 4). When the control unit 100 controls the driving motor 81 and the pressure-bonding / separating unit 82, the rotation operation of the driving roller 532A and the pressure-bonding / separating operation of the driven roller 532B are controlled. The loop roller unit 532 is in a pressure-bonded state when the paper is conveyed, and is in a separated state after the paper is transferred to the registration roller unit 533.

  The registration roller unit 533 is disposed on the upstream side of the image forming unit 40 (secondary transfer unit 425) and on the downstream side of the loop roller unit 532. The registration roller unit 533 includes a driving roller 533A and a driven roller 533B. The driven roller 533B is pressed against or separated from the driving roller 533A. Specifically, the registration roller unit 533 is in a pressure-bonded state when the paper is conveyed, and is in a separated state after the paper is transferred to the secondary transfer unit 425.

  A drive motor 83 and a swing motor 84 are connected to the drive roller 533A (see FIG. 4). When the control unit 100 controls the driving motor 83 and the swinging motor 84, the rotation operation of the driving roller 533A and the swinging operation of the registration roller unit 533 are controlled.

  In the second transport unit 54, the pre-registration roller unit 543 is disposed on the upstream side of the bending path 544 in the paper transport direction. A paper detection sensor 88 that detects the conveyed paper is disposed on the upstream side of the pre-registration roller unit 543 in the paper conveyance direction. The pre-registration roller unit 543 includes a driving roller 543A and a driven roller 543B. The driving roller 543A is fixed to the inner peripheral side of the bending path 544, and the driven roller 543B is pressed against or separated from the driving roller 543A.

  A driving motor 86 is connected to the driving roller 543A (see FIG. 4). The drive motor 86 is disposed by effectively using the space formed on the inner peripheral side of the bending path 544. A crimping separation portion 87 is connected to the driven roller 543B (see FIG. 4). When the control unit 100 controls the driving motor 86 and the pressure separating / separating part 87, the rotation operation of the driving roller 543A and the pressure separating / separating operation of the driven roller 543B are controlled. The pre-registration roller unit 543 is in a pressure-bonding state when the paper is conveyed, and is in a separated state after the paper is transferred to the registration roller unit 533.

As described above, the image forming apparatus 1 includes the secondary transfer unit 425 (transfer roller unit) that transfers the toner image to the paper, the registration roller unit 533 that transports the paper to the secondary transfer unit 425, and the paper when the double-sided image is formed. Drive rollers 532A, 543A and driven rollers 532B, 543B that are pressed against or separated from the drive rollers 532A, 543A are fixed to the inner peripheral side of the bending path 544 through which the paper passes, and convey the paper to the registration roller portion 533. Control the rotation operation of the driving rollers 532A and 543B and the pressure-separation operation of the driven rollers 532B and 543B in the loop roller unit 532 and the pre-registration roller unit 543 (conveyance roller unit). And a control unit 100.
When the double-sided image is formed in the image forming apparatus 1, the image surface of the paper (the surface on which the image is formed) comes into contact with the loop roller portion 532 and the driving rollers 532 A and 543 A of the pre-registration roller portion 543.

FIG. 6 is a flowchart illustrating an example of a sheet conveyance control process in double-sided image formation. FIG. 7 is a timing chart illustrating an example of operations of the registration roller unit 533, the loop roller unit 532, and the pre-registration roller unit 543 in double-sided image formation. During double-sided image formation, the rotation operation of the drive rollers 533A, 532A, and 543A and the pressure-separation operation of the driven rollers 533B, 532B, and 543B are controlled according to the flowchart shown in FIG.
The flowchart shown in FIG. 6 is realized when the CPU 101 executes a predetermined program stored in the ROM 102 in response to an instruction to form a double-sided image.

  Note that the registration roller unit 533, the loop roller unit 532, and the pre-registration roller unit 543 are normally in a pressure-bonded state. A case where image formation is performed on a sheet having a sheet length longer than the conveyance path length from the pre-registration roller unit 543 to the secondary transfer unit 425 will be described.

  In step S101 in FIG. 6, the control unit 100 determines whether or not a sheet is detected by the sheet detection sensor 85 disposed upstream of the pre-registration roller unit 543 in the sheet conveyance direction. When a sheet is detected by the sheet detection sensor 85 (“YES” in step S101, tying T1 in FIG. 7), the process proceeds to step S102.

In step S102, the control unit 100 rotates the driving roller 543A of the pre-registration roller unit 543 and the driving roller 532A of the loop roller unit 532 (timing T2 in FIG. 7). The paper is conveyed by the pre-registration roller unit 543 and, after reaching the loop roller unit 532, is conveyed by the pre-registration roller unit 543 and the loop roller unit 532.
The driving roller 532 </ b> A of the loop roller unit 532 may be driven before the paper reaches the loop roller unit 532.

  In step S <b> 103, the control unit 100 determines whether the sheet has reached the registration roller unit 533. Whether or not the sheet has reached the registration roller unit 533 is determined based on, for example, the time from when the sheet is detected by the sheet detection sensor 85 (timing T1 in FIG. 7). When the sheet reaches the registration roller unit 533 (“YES” in step S103, timing T3 in FIG. 7), the process proceeds to step S104.

  In step S104, the control unit 100 rotates the driving roller 533A of the registration roller unit 533 after a predetermined time has elapsed after the sheet reaches the registration roller unit 533 (timing T4 in FIG. 7). During a predetermined time after the paper arrives at the registration roller unit 533 (timing T3 to T4 in FIG. 7), the paper is conveyed by the pre-registration roller unit 543 and the loop roller unit 532. Thereby, a bend is formed in the loop forming portion, and the inclination of the paper is corrected.

  In step S105, the control unit 100 separates the driven roller 543B of the pre-registration roller unit 543 from the driving roller 543A and also separates the driven roller 532B of the loop roller unit 532 from the driving roller 532A (timing T4 in FIG. 7). By setting the pre-registration roller unit 543 and the loop roller unit 532 apart, it is possible to prevent the inclination of the paper corrected in the registration roller unit 533 from returning to the original state, and the swinging operation of the registration roller unit 533 causes the paper to be The deviation in the width direction can be smoothly corrected.

  After the sheet is delivered to the registration roller unit 533, the sheet is conveyed only by the registration roller unit 533. When the pre-registration roller unit 543 and the driving rollers 543A and 533A of the loop roller unit 533 are stopped as in the prior art, the image surface is rubbed in the paper conveyance direction. In addition, when the registration roller unit 533 corrects the position in the width direction of the sheet by swinging in the sheet width direction while conveying the sheet, the image surface is also rubbed in the sheet width direction.

  In the present embodiment, when the sheet is conveyed by the registration roller unit 533, the rotation of the driving rollers 543A and 532A of the pre-registration roller unit 543 and the loop roller unit 532 is continued, so that the image surface of the sheet is driven. Although it contacts with the rollers 543A and 532A, it is not rubbed.

  Further, when the sheet is conveyed by the registration roller unit 533, the rotational speeds of the driving rollers 543A and 532A of the pre-registration roller unit 543 and the loop roller unit 532 are specifically based on the conveyance speed in the registration roller unit. It is preferable that the rotational speed of the driving roller 533A of the roller portion 533 is set to be the same. Thus, the conveyance of the paper and the rotation of the drive rollers 543A and 532A are synchronized, so that it is possible to reliably prevent the image surface from being rubbed.

  In step S106, the control unit 100 determines whether the sheet has reached the secondary transfer unit 425 (transfer roller unit). Whether or not the sheet has reached the secondary transfer unit 425 is determined based on, for example, the time from when the driving of the registration roller unit 533 is started (timing T4 in FIG. 7). When the sheet reaches the secondary transfer unit 425 (“YES” in step S106, timing T5 in FIG. 7), the process proceeds to step S107.

In step S107, the control unit 100 stops the rotation of the driving roller 533A of the registration roller unit 533 and separates the driven roller 533B (timing T6 in FIG. 7). The sheet is conveyed by the secondary transfer unit 425.
At this time, the rotation speeds of the driving rollers 543A and 532A of the pre-registration roller unit 543 and the loop roller unit 532 are based on the conveyance speed in the secondary transfer unit 425, specifically, the secondary transfer roller of the secondary transfer unit 425. It is preferably set to be the same as the rotational speed of 424. Thereby, even after the sheet is delivered to the secondary transfer unit 425, the conveyance of the sheet and the rotation of the drive rollers 543A and 532A are synchronized, so that the image surface can be prevented from being rubbed.

  In step S <b> 108, the control unit 100 determines whether the sheet has passed through the pre-registration roller unit 543. Whether or not the sheet has passed through the pre-registration roller unit 543 is determined based on, for example, the time from when the trailing edge of the sheet is detected by the sheet detection sensor 85 (timing T7 in FIG. 7). When the sheet passes through the pre-registration roller unit 543 (“YES” in step S108), the process proceeds to step S109.

  In step S109, the control unit 100 stops the rotation of the driving roller 543A of the pre-registration roller unit 543 (timing T8 in FIG. 7). Thereby, when the driven roller 543B is pressure-bonded with the drive roller 543A, it is possible to prevent the motor from being stepped out due to torque fluctuation.

  In step S <b> 110, the control unit 100 determines whether the sheet has passed through the loop roller unit 532. Whether or not the sheet has passed through the loop roller portion 532 is determined based on, for example, the time from when the sheet detection sensor 85 detects the trailing end of the sheet (timing T7 in FIG. 7). When the sheet passes through the loop roller unit 532 (“YES” in step S110), the process proceeds to step S111.

  In step S111, the control unit 100 stops the rotation of the driving roller 532A of the loop roller unit 532 (timing T9 in FIG. 7). Thereby, when the driven roller 532B is pressure-bonded to the driving roller 532A, it is possible to prevent the motor from stepping out due to torque fluctuation.

  In step S112, the control unit 100 brings the pre-registration roller unit 543, the loop roller unit 532, and the registration roller unit 533 into a press-bonded state at a predetermined timing (timing T10 in FIG. 7). There is no particular limitation on the timing of the press-bonding state, and it is sufficient that the pre-registration roller unit 543, the loop roller unit 532, and the registration roller unit 533 are in the press-bonding state before the paper is conveyed.

  In this way, the control unit 100 performs the pre-registration roller unit 543 and the loop roller unit 533 (conveyance) when the sheet is conveyed by the secondary transfer unit 425 (transfer roller unit) or the registration roller unit 533 in double-sided image formation. The driven rollers 543B and 532B are separated from the driving rollers 543A and 532A and the driving rollers 543A and 532A are rotated until the trailing edge of the sheet passes through the roller section.

  As a result, the image surface of the paper is not rubbed against the pre-registration roller unit 543 and the driving rollers 543A and 532A of the loop roller unit 533, so that the image quality of the image surface is maintained, and the toner adheres to the driving roller by rubbing. Absent. Accordingly, it is possible to prevent the image quality from being deteriorated due to the image surface of the paper being rubbed at the transport roller portion located on the upstream side of the registration roller portion when the double-sided image is formed.

As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.
For example, the drive rollers 543A and 532A may be rotated for a while after the pre-registration roller portion 543 and the loop roller portion 533 are brought into the press-bonded state. Thus, even if a small amount of toner is transferred to the driving rollers 543A and 532A by contacting the image surface of the paper with the driving rollers 543A and 532A, the toner can be adapted to the driving rollers 543A and 532A. It is possible to prevent the retransfer of the toner to the paper.

  Further, for example, in the embodiment, when the sheet is conveyed by the secondary transfer unit 425 or the registration roller unit 533, the rotation of the driving rollers 543A and 532A is continued, but the pre-registration roller unit 543, the loop The drive rollers 543A and 532A do not always need to be rotated after the roller portion 532 is in the separated state, and may be rotated intermittently.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 30 Image processing part 40 Image forming part 50 Paper conveyance part 53 1st conveyance part 54 2nd conveyance part 60 Fixing part 100 Control part 425 Secondary transfer part 532 Loop roller (Conveyance roller)
532A, 533A, 543A Drive roller 532B, 533B, 543B Driven roller 533 Registration roller part 543 Pre-registration roller part (conveyance roller part)
544 Conveyance path (bending path)

Claims (5)

A transfer roller section for transferring a toner image to paper,
A registration roller unit that conveys the sheet to the transfer roller unit;
A conveyance roller unit having a driving roller fixed on the inner peripheral side of a bending path through which a sheet is passed during double-sided image formation and a driven roller that is pressed against or separated from the driving roller and conveys the sheet to the registration roller unit When,
A control unit for controlling the rotation operation of the driving roller and the pressure-separation separation operation of the driven roller in the transport roller unit,
In the double-sided image formation, the control unit separates the driven roller from the driving roller until the sheet is removed from the conveyance roller unit when the sheet is conveyed by the transfer roller unit or the registration roller unit. An image forming apparatus that rotates a driving roller.   2. The image formation according to claim 1, wherein the control unit stops the rotation of the driving roller after the sheet has passed through the conveyance roller unit, and presses the driven roller against the driving roller. apparatus.   The said control part sets the rotational speed of the said driving roller based on the conveyance speed in the said registration roller part, when a paper is conveyed by the said registration roller part, The Claim 1 or 2 characterized by the above-mentioned. Image forming apparatus. The registration roller unit is in a separated state when the sheet is conveyed by the transfer roller unit,
The said control part sets the rotational speed of the said drive roller based on the conveyance speed in the said transfer roller part, when a sheet | seat is conveyed by the said transfer roller part, Any one of Claim 1 to 3 characterized by the above-mentioned. The image forming apparatus according to claim 1.   5. The registration roller unit according to claim 1, wherein the registration roller unit corrects the position in the width direction of the sheet by conveying the sheet while swinging in the sheet width direction orthogonal to the sheet conveyance direction. The image forming apparatus described in 1.

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