JP2015165279A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveying device and an image forming apparatus that can correct inclination of sheets without damaging the sheets.SOLUTION: A sheet conveying device includes: a first conveyance roller part that holds and conveys a sheet; a second conveyance roller part that is configured to rotate in a regular and reverse directions and arranged on the downstream side in the conveyance direction of the sheet of the first conveyance roller part; a control part that causes the second conveyance roller part to rotate in the reverse direction while the leading end of the sheet abuts against a nip of the second conveyance roller part, and causes the first conveyance roller part to continue the conveyance to form deflection of the sheet, and thereby correcting inclination of the sheet; and an inclination detection part that detects inclination of the sheet having passed through the second conveyance roller part. The control part controls a reverse mode in rotating the second conveyance roller part in the reverse direction according to the current inclination correction ability based on a result of the detection by the inclination detection part.

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus capable of correcting sheet inclination.

  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. The paper transport unit includes a plurality of transport roller units such as a loop roller unit and a registration roller unit. In the paper transport unit, the paper is transported in a tilted state due to a slight inclination of the transport roller axis or a difference in nip pressure (hereinafter referred to as “transport nip pressure”) of a plurality of roller pairs constituting the transport roller unit. Is known (the so-called skew).

  The inclination of the paper with respect to the paper conveyance direction is eliminated by, for example, continuing the paper conveyance with the leading edge of the paper abutting against the nip (hereinafter referred to as “registration nip”) of the registration roller portion, and forming a deflection in the paper. Is done. At this time, if the leading edge of the paper bites into the registration nip, even if the paper is bent, the inclination of the paper is not sufficiently corrected. For this reason, it has been proposed to rotate a roller (hereinafter referred to as “registration roller”) constituting the registration roller unit in a direction opposite to that during paper conveyance to push the paper back and re-enter (for example, Patent Documents 1 and 2). As the reversing speed of the registration roller is faster or the reversing time is longer, the energy for pushing back the paper by the reversal of the registration roller becomes larger, so that the tilt correction capability becomes higher.

JP 2013-56734 A Japanese Patent No. 4016621

  However, if the speed of reversing the registration rollers is too fast or if the time is too long, the possibility that the leading edge of the paper will be damaged (drooped) increases. This phenomenon becomes more prominent as the cardboard has higher rigidity.

  An object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus that can correct the inclination of the sheet without damaging the sheet.

A sheet conveying apparatus according to the present invention includes a first conveying roller unit that nipped and conveys a sheet,
A second conveyance roller unit configured to be capable of normal rotation and reverse rotation, and disposed on the downstream side in the sheet conveyance direction of the first conveyance roller unit;
With the leading edge of the paper abutting against the nip of the second conveyance roller section, the second conveyance roller section is reversed and the conveyance by the first conveyance roller section is continued to form a bend in the sheet. A control unit for correcting the tilt of the paper,
An inclination detection unit that detects an inclination of the sheet that has passed through the second transport roller unit,
The control unit controls a reverse rotation mode when the second transport roller unit is reversely rotated according to a current tilt correction capability based on a detection result of the tilt detection unit.

An image forming apparatus according to the present invention includes the above-described sheet conveying apparatus and an image forming unit that forms an image on a sheet conveyed by the sheet conveying apparatus.

  According to the present invention, since the reverse mode of the second transport roller unit at the time of tilt correction is appropriately controlled according to the current tilt correction capability, the tilt of the sheet can be efficiently adjusted without damaging the sheet. It can be corrected.

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 the structure of a 1st conveyance part in detail. It is a timing chart which shows an example of the drive condition of the intermediate conveyance roller part in a 1st conveyance part, a loop roller part, and a registration roller part. It is a flowchart which shows an example of the reverse rotation speed control process of a registration roller part. It is a flowchart which shows an example of the reverse rotation speed control process of a registration roller part. It is a flowchart which shows an example of the reverse rotation speed control process of a registration roller part. It is a figure which shows the attitude | position of the paper which passes a registration roller part.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 1 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 1 according to the embodiment.
An image forming apparatus 1 shown in FIGS. 1 and 2 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. 1 and 2, 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, for example, a look-up table that is referred to when 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 image data (input image data) in a page description language (PDL) transmitted from an external device, and forms an image on a sheet based on the received image data. The communication unit 71 has various interfaces such as a network interface card (NIC), a modem-demodulator (MODEM), and a universal serial bus (USB).

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, and paper setting.

  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.

  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. 1, 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, 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 for each color component (for example, a two-component developer composed of toner and a magnetic carrier), and an electrostatic latent image is formed by attaching the toner for each color component to the surface of the photosensitive drum 413. Visualize 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 support roller 423 disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. As the driving roller 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 one of the plurality of support rollers 423. The support roller 423 arranged to face the intermediate transfer belt 421 is called a backup roller. The secondary transfer roller 424 is pressed against the backup roller 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.

  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 disposed on the upper fixing unit 61 having a fixing surface side member disposed 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 62 having a back surface side support member, a heating source 63 for heating the fixing surface side member, and the like.

  When the upper fixing unit 61 is a belt heating method (see FIG. 1), the fixing belt is a fixing surface side member, and when the upper fixing unit 61 is a roller heating method, the fixing roller is a fixing surface side member. When the lower fixing unit 62 is a roller pressurization method (see FIG. 1), the pressure roller is a back surface side support member, and when the lower fixing unit 62 is a belt pressure method, the pressure belt is a back surface 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 sheet onto which the toner image has been secondarily transferred and conveyed is heated and pressurized when passing through the fixing nip. As a result, the toner image is fixed on the paper. Further, the fixing unit 60 may include a separation air blowing unit that blows air to the fixing surface side member or the back surface side support member and separates the sheet from the fixing surface side member or the back surface side support member.

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a first transport unit 53 to a fourth transport unit 56, a transport path switching unit 57, 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 (see FIG. 3). 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 transports the paper on which the image is formed on the first surface (front surface) in the image forming unit 40 to the third transport unit 55. Further, the second transport unit 54 transports the paper that is switched back and sent out by the third transport unit 55 to the paper discharge unit 52.

  The third transport unit 55 temporarily stops the paper sent from the second transport unit 54 and reverses the transport direction (switchback). The third transport unit 55 transports the switched back sheet to the second transport unit 54 or the fourth transport unit 56.

  The fourth transport unit 56 is a circulation path that transports the paper that is switched back and sent out by the third transport unit 55 to the first transport unit 53 (upstream of the loop roller unit 532). A sheet having the second surface (back surface) as an upper surface is passed through the first transport unit 53.

  The conveyance path switching unit 57 switches the conveyance path depending on whether the sheet delivered from the fixing unit 60 is discharged as it is or reversed and discharged. Specifically, the control unit 100 controls the operation of the transport path switching unit 57 based on the processing content of the image forming process (single-sided / double-sided printing, face-up discharge, face-down discharge, etc.).

  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. Then, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred onto the first surface (fixing surface) of the sheet at once and subjected to fixing processing 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 and the like. When images are formed on both sides of a sheet, the sheet on which the image is formed on the first side is sent to the second conveyance unit 54 and is reversed by the third conveyance unit 55 and the fourth conveyance unit 56 and then the second one. Images are formed on two sides.

  FIG. 3 is a diagram showing the configuration of the first transport unit 53 in detail. As shown in FIG. 3, the first transport unit 53 includes a plurality of transport roller units including the intermediate transport roller unit 531, the loop roller unit 532, and the registration roller unit 533 described above, and a sheet detection sensor 534, and An inclination detection sensor 535 is provided.

  The intermediate conveyance roller unit 531 includes a driving roller 531A and a driven roller 531B. The control unit 100 controls the driving motor 81 and the pressure separating / separating unit 82 (see FIG. 2), thereby controlling the rotation operation of the driving roller 531A and the pressure separating / separating operation of the driven roller 531B. The intermediate conveyance roller unit 531 is in a pressure-bonded state when the sheet is conveyed, and is in a separated state after the sheet is transferred to the registration roller unit 533.

  The loop roller unit 532 is disposed on the downstream side of the intermediate conveyance roller unit 531 in the sheet conveyance direction. The loop roller unit 532 includes a driving roller 532A and a driven roller 532B. The controller 100 controls the driving motor 83 and the pressure separating / separating part 84 (see FIG. 2), whereby the rotation operation of the driving roller 532A and the pressure separating / separating operation of the driven roller 532B are controlled. Similar to the intermediate transport roller unit 531, the loop roller unit 532 is in a pressure-bonded state when transporting paper, 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) in the sheet conveyance direction 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 controller 100 controls the driving motor 85 (see FIG. 2), whereby the rotation operation of the driving roller 533A is controlled. The driving roller 533A (driving motor 85) is configured to be able to reversely rotate. For example, the driving roller 533A (driving motor 85) reverses when the registration roller unit 533 corrects the sheet inclination. The driven roller 533B may be always in a pressure-bonded state with respect to the driving roller, or may be capable of being pressed and separated.

  A paper detection sensor 534 (paper detection unit) that detects the conveyed paper is disposed upstream of the registration roller unit 533 in the paper conveyance direction. The paper detection sensor 534 is configured by, for example, a reflective or transmissive optical sensor. After the paper is detected by the paper detection sensor 534 and a predetermined time has elapsed, the driving of the registration roller unit 533 is started.

  On the downstream side of the registration roller unit 533 in the sheet conveyance direction, an inclination detection sensor 535 (an inclination detection unit) that detects the inclination of the sheet that has passed the registration roller unit 533 is disposed. The inclination detection sensor 535 is constituted by a line sensor arranged in parallel with the registration roller unit 533, for example.

  The inclination of the sheet that has passed through the registration roller unit 533 is corrected to such an extent that high image quality is maintained, but a slight inclination (for example, 0.5 ° or less) remains. In particular, when the inclination correction is not sufficiently performed due to the paper biting into the registration nip, the inclination of the paper becomes large. Such an inclination of the sheet is detected by an inclination detection sensor 535.

  Based on the detection result by the inclination detection sensor 535, the current degree of inclination correction capability, that is, the suitability of the reverse rotation mode of the registration roller unit 533 can be determined. For example, when the inclination of the sheet detected by the inclination detection sensor 535 is large, the current inclination correction capability is low, so that it is possible to determine that the reverse rotation mode of the registration roller unit 533 is inappropriate.

  FIG. 4 is a timing chart illustrating an example of the driving status of the intermediate conveyance roller unit 531, the loop roller unit 532, and the registration roller unit 533 in the first conveyance unit 53. The registration roller unit 533, the loop roller unit 532, and the intermediate transport roller unit 531 are normally in a pressure-bonded state, and are separated as necessary.

  First, when the image forming apparatus 1 receives information (for example, a print job) for forming an image, and a sheet is fed from the sheet feeding unit 51 or an external sheet feeding device (not shown), the intermediate conveyance roller unit 531. And the drive of the loop roller part 532 is started (timing T1). The fed paper is transported by the intermediate transport roller unit 531 and the loop roller unit 532.

  When the leading edge of the paper reaches the detection area of the paper detection sensor 534, the paper detection sensor 534 detects the paper (timing T2). After a predetermined time has elapsed since the paper was detected by the paper detection sensor 534, the registration roller unit 533 (drive roller 533A) reverses (timing T3). The paper that has reached the registration roller unit 531 is pushed back by the reverse rotation of the registration roller unit 533. On the other hand, since the conveyance of the sheet by the loop roller unit 532 is continued, the sheet re-enters toward the registration roller unit 533 (registration nip), and the sheet is bent. As a result, the leading edge of the sheet comes into contact with the registration nip uniformly, and the inclination of the sheet is corrected. However, when the reverse rotation mode of the registration roller unit 533 is not appropriate (for example, when the reverse rotation speed is insufficient), the tilt is not sufficiently corrected.

  After the bend is formed on the sheet and the inclination is corrected, the registration roller unit 533 is switched to the normal rotation driving, and the sheet is conveyed toward the image forming unit 40 (secondary transfer unit) (timing T4). It is also possible to temporarily stop the resist roller 533 after it is reversed and to rotate it forward after a predetermined amount of bending is formed.

  After the sheet is transferred to the registration roller unit 533, the intermediate conveyance roller unit 531 and the loop roller unit 532 are separated from each other, and the sheet is conveyed only by the registration roller unit 533. The driving of the intermediate transport roller unit 531 and the loop roller unit 532 is stopped after, for example, the trailing edge of the sheet is completely pulled out.

  When the sheet is transferred to the secondary transfer unit and the trailing end of the sheet completely comes out of the registration roller unit 533, the driving of the registration roller unit 533 is stopped (timing T5), and the intermediate conveyance roller unit 531 and the loop roller unit are soon completed. 532 is brought into a crimped state (timing T6).

  Thus, the first transport unit 53 (paper transport device) is configured to be able to rotate forward and reverse with the loop roller unit 532 (first transport roller unit) that sandwiches and transports the paper, and the loop roller unit. The registration roller unit 533 (second conveyance roller unit) disposed on the downstream side in the sheet conveyance direction of 532 and the registration roller unit 533 are reversed in a state where the leading edge of the sheet is in contact with the registration nip of the registration roller unit 533. A control unit 100 that corrects the inclination of the sheet by forming a bend in the sheet by continuing the conveyance by the loop roller unit 532, and an inclination detection sensor 535 (an inclination detection unit) that detects the inclination of the sheet that has passed through the registration roller unit 533. And). As a result, the leading edge of the paper re-enters the registration nip during tilt correction, and the paper bite into the registration nip is eliminated, so that the correction efficiency is improved.

  Furthermore, in the present embodiment, the control unit 100 increases the inclination correction efficiency in a range where no leading edge bending occurs based on the detection result of the inclination detection sensor 535 disposed on the downstream side of the registration roller unit 533 in the sheet conveyance direction. In this manner, the reverse rotation mode (for example, the reverse rotation speed and the reverse rotation time) of the registration roller unit 533 is appropriately controlled. As a result, the inclination of the paper can be corrected without damaging the paper.

Here, the reverse rotation speed is controlled as one of the reverse rotation modes of the registration roller unit 533. Specifically, the reverse rotation speed in the registration roller unit 533 is controlled in five stages of V1 to V5 (V1 <V2 <V3 <V4 <V5).
The reverse speed control range V1 to V5 is preferably set according to the type of paper used for image formation. This is because the reverse rotation speed at which the leading edge of the paper is bent and the reverse rotation speed at which tilt correction can be performed efficiently differ depending on the paper type. In other words, the reverse speed control range V1 to V5 is set according to the paper type of the paper used for image formation, so that the leading edge of the paper can be prevented and the inclination can be corrected efficiently. It is also possible to easily cope with the case where a highly rigid sheet that tends to bend the tip, such as a thick sheet, is used.

  Specifically, when priority is given to preventing paper curling (curling prevention priority mode), the reverse rotation speed of the registration roller unit 533 is controlled in three stages V1 to V3, and priority is given to tilt correction capability (tilt correction). In the priority mode), the reverse rotation speed of the registration roller unit 533 is controlled in three stages V3 to V5. The higher the reverse rotation speed of the registration roller unit 533, the greater the energy for pushing back the paper and the higher the inclination correction capability, but the higher the risk that the leading edge of the paper will curl.

  By setting the reverse rotation speed V3 to a value at which the leading edge of the paper cannot be curled, the leading edge of the paper can be reliably prevented in the curling prevention priority mode. In the case of the reverse rotation speeds V4 and V5, the possibility of leading edge curling of the paper increases, but leading edge curling does not necessarily occur. That is, in the tilt correction priority mode, tilt correction is performed so that the leading edge of the sheet is not bent as much as possible.

  5 to 7 are flowcharts illustrating an example of the reverse rotation speed control process of the registration roller unit 533. This process is realized, for example, when the CPU 101 executes a predetermined program stored in the ROM 102 when the image forming process is started in the image forming apparatus 1. It is assumed that the priority mode in the reverse rotation speed control process (prevention priority mode or tilt correction priority mode) is set in advance. For example, the user can select and set a desired priority mode by operating the operation display unit 20.

In step S11 of FIG. 5, the control unit 100 determines the set priority mode. If the drooling prevention priority mode is set, the process proceeds to step S12. If the tilt correction priority mode is set, the process proceeds to step S13.
In step S12, the control unit 100 sets the reverse rotation speed of the registration roller unit 533 to V2. The process proceeds to step S101 in FIG.
In step S13, the control unit 100 sets the reverse rotation speed of the registration roller unit 533 to V4. The process proceeds to step S201 in FIG.

When the dripping prevention priority mode is set, the flowchart of FIG. 6 is executed.
In step S101 of FIG. 6, the control unit 100 reverses the registration roller unit 533 at a predetermined timing (timing T3 in FIG. 4). At this time, the reverse rotation speed set in step S12 (see FIG. 5) or any of steps S107 to S109 described later is applied to the reverse rotation speed of the registration roller unit 533.

In step S <b> 102, the control unit 100 acquires the posture of the sheet (tilt amount Δ, total sheet length L) after passing through the registration roller unit 533 based on the detection result of the tilt detection sensor 535.
FIG. 8 shows the inclination amount Δ of the sheet after passing through the registration roller portion 533 and the total length L of the sheet (hereinafter “measured length L”). FIG. 8 shows a case where the sheet is inclined in the + direction. As shown in FIG. 8, the inclination angle theta, when the standard length of the paper and L _0, the inclination amount Δ is represented by L ₀ sin [theta, measured length L is expressed by L ₀ cos [theta].

In step S <b> 103, the control unit 100 calculates a criterion for determining whether or not the tilt correction is properly performed, that is, a correction index A indicating the current tilt correction capability. As the correction index A, for example, a value calculated by the following equation (1) can be applied.
Correction index A = slope rate / reference slope rate (1)
Here, the “inclination rate” is calculated by the following equation (2) using the inclination amount Δ (= L ₀ sin θ) detected by the inclination detection sensor 535 and the measurement length L (= L ₀ cos θ). Value.
Inclination rate = inclination amount Δ / measurement length L (2)
The “reference inclination rate” is a value calculated by the following equation (3) using an allowable inclination amount Δ ₀ (hereinafter referred to as “allowable inclination amount Δ ₀ ”) and a standard length L ₀ . Allowable tilt amount delta ₀ varies depending on the size and the paper type or the like of the paper.
Reference inclination rate = allowable inclination amount Δ ₀ / standard length L ₀ (3)

For example, when A4 size plain paper is used, if the allowable inclination amount Δ ₀ is 1.5 mm, the standard length L ₀ is 297 mm, so the reference inclination rate is 0.5% (constant). The smaller the actual sheet inclination amount Δ, the smaller the correction index A. That is, the smaller the correction index A, the higher the inclination correction capability. In the drooling prevention priority mode, for example, when the correction index A is “1” or less, it is determined that the inclination correction has been properly performed.

In step S104, the control unit 100 determines whether the inclination of the paper is stable. If the paper inclination is stable, the process proceeds to step S106. If the paper inclination is unstable, the process proceeds to step S105.
For example, when the direction of the sheet inclination is constant (for example, the + direction), specifically, 75% or more of the most recent N sheets (for example, 10 sheets) that have passed through the registration roller unit 533. When the sheet inclination is the same direction, it is determined that the sheet inclination is stable.
For example, when the correction index A is within an assumed range (for example, A ≦ 1.0), it is determined that the inclination of the sheet is stable.

  In step S105, the control unit 100 averages the correction index A calculated for the latest N sheets, and sets the result (ΣA / N) as the correction index A. This is because if the tilt correction ability of the registration roller unit 533 is determined using the pinpoint correction index A when the tilt of the paper is unstable, there is a high risk of erroneous determination. That is, by averaging the correction index A, the current inclination correction capability of the registration roller unit 533 can be appropriately determined.

  In step S <b> 106, the control unit 100 determines the current inclination correction capability of the registration roller unit 533 based on the calculated correction index A. Here, “0.9” and “1.0” are used as threshold values for determining the inclination correction capability. When the correction index A is 0.9 or less, it is determined that the current inclination correction capability is extremely high (the reverse rotation speed is sufficiently high), and when the correction index A is greater than 1.0, the current inclination correction capability is Judged to be low (insufficient reverse speed).

  When the correction index A is 0.9 or less, the process proceeds to step S107, and the control unit 100 sets the reverse rotation speed to the one-step low speed side. For example, when the current reverse rotation speed is V3, it is set to V2, and when the current reverse rotation speed is V2, it is set to V1. Further, when the current reverse speed V1 is the slowest, it is maintained as it is. Since the current tilt correction capability is extremely high, the tilt correction capability is maintained even if the reverse rotation speed is slowed down, and the possibility that the leading edge of the paper will curl is further reduced.

  When the correction index A is greater than 0.9 and less than or equal to 1.0, it can be determined that the current inclination correction capability is high (the reverse rotation speed is appropriate). In this case, the process proceeds to step S108, and the control unit 100 maintains the reverse rotation speed V at the current reverse rotation speed.

  If the correction index A is greater than 1.0, the process proceeds to step S109, and the control unit 100 sets the reverse rotation speed V to the one-step high speed side. For example, when the current reverse speed is V1, it is set to V2, and when the current reverse speed is V2, it is set to V3. Further, when V3 has the fastest reverse speed, it is maintained as it is. There is a high possibility that the leading edge of the paper will be bent, but the tilt correction capability will also be high.

  In step S110, the control unit 100 determines whether a series of image forming processes has been completed. A series of image forming processes is a process for forming an image set by a signal (for example, a print job) instructing image formation. When the series of image forming processes is finished, the reverse rotation speed control process is finished. When the series of image forming processes is not finished, the processes after step S101 are repeated.

  As described above, in the priority prevention mode, when the tilt correction capability is insufficient (when 1.0 <correction index A), the reverse rotation speed is set to the high speed side so that the energy for pushing back the paper becomes large. Is done. On the other hand, when the tilt correction capability is excessive (when the correction index A ≦ 0.9), the reverse rotation speed is set to the low speed side so that the energy for pushing back the paper becomes small. Accordingly, it is possible to efficiently correct the inclination of the sheet while preventing the leading edge of the sheet from being bent as much as possible.

  When the tilt correction priority mode is set, the flowchart of FIG. 7 is executed. The flowchart in FIG. 7 is almost the same as the flowchart in FIG.

  In the tilt correction priority mode, the reverse rotation speed of the registration roller unit 533 is controlled in the range of V3 to V5. Here, in the anti-dripping priority mode, the threshold values for determining the tilt correction capability are set to “0.9” and “1.0”, whereas in the tilt correction priority mode, the tilt correction capability is The threshold values for determination are set to “0.8” and “0.9”. In other words, in the tilt correction priority mode, the reverse rotation speed is set faster than in the drought prevention priority mode, and the tilt correction capability is high. Therefore, the threshold value for determining the suitability of the tilt correction capability is set more severely than in the droop prevention priority mode. .

  As described above, in the tilt correction priority mode, when the tilt correction capability is insufficient (in the case of 0.9 <correction index A), the reverse rotation speed is set to the high speed side so that the energy for pushing back the paper is increased. When the tilt correction capability is excessive (when the correction index A ≦ 0.8), the reverse rotation speed is set to the low speed side so that the energy for pushing back the paper becomes small. Accordingly, it is possible to efficiently correct the inclination of the sheet while preventing the leading edge of the sheet from being bent as much as possible.

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, in the embodiment, the case where the reverse rotation speed is controlled as one of the reverse rotation modes of the registration roller unit 533 has been described, but the reverse rotation time may be controlled (reverse rotation time control processing). The relationship between the reverse rotation time and the energy for pushing back the paper can be considered in the same way as the relationship between the reverse rotation speed and the energy for pushing back the paper. Thus, the reverse rotation time control process can be easily realized.
Furthermore, if both the reverse rotation speed and the reverse rotation time of the registration roller unit 533 are controlled, and the reverse rotation mode control table is set in detail, the reverse rotation mode can be controlled more appropriately.

  In the embodiment, the correction index A is calculated from the detection result (inclination amount) of the inclination detection sensor 535 to determine the current inclination correction capability. However, the detection result (inclination amount) of the inclination detection sensor 535 is used. ) May be used as they are to determine the current tilt correction capability.

  When performing double-sided image formation in the image forming apparatus 1, reverse rotation speed control processing (or reverse rotation time control processing) is performed for each image formation on one sheet, and image formation is performed on the front and back surfaces. The reversal mode of may be the same. If the inclination correction capability differs between when the image is formed on the front side of the paper and when the image is formed on the back side, the image quality between the front and back sides is different. Therefore, when it is important that the front surface and the back surface have the same image quality, it is preferable that the reverse rotation mode of the registration roller unit 533 is controlled to be the same so that the same inclination correction is performed. .

  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 (paper conveyance apparatus)
531 Intermediate Conveying Roller Unit 532 Loop Roller Unit (First Conveying Roller Unit)
533 Registration roller section (second transport roller section)
534 Paper detection sensor 535 Tilt detection sensor (tilt detection unit)
60 Fixing unit 100 Control unit

Claims (10)

A first transport roller unit that sandwiches and transports the paper;
A second conveyance roller unit configured to be capable of normal rotation and reverse rotation, and disposed on the downstream side in the sheet conveyance direction of the first conveyance roller unit;
With the leading edge of the paper abutting against the nip of the second conveyance roller section, the second conveyance roller section is reversed and the conveyance by the first conveyance roller section is continued to form a bend in the sheet. A control unit for correcting the tilt of the paper,
An inclination detection unit that detects an inclination of the sheet that has passed through the second transport roller unit,
The control unit controls a reverse mode when the second transport roller unit is rotated in reverse according to a current tilt correction capability based on a detection result of the tilt detection unit.   When the tilt correction capability is insufficient, the control unit controls the reverse rotation mode within a predetermined control range so that energy for pushing back the paper is increased, and when the tilt correction capability is excessive. 2. The paper conveying apparatus according to claim 1, wherein the reverse rotation mode is controlled within a predetermined control range so that energy for pushing back the paper becomes small.   The sheet conveying apparatus according to claim 2, wherein the control range is set according to a paper type. A first priority mode that prioritizes leading edge blur prevention and a second priority mode that prioritizes tilt correction;
4. The sheet conveying apparatus according to claim 2, wherein the control range is set for each of the first priority mode and the second priority mode. 5.   The sheet conveying apparatus according to claim 4, further comprising an operation unit configured to set one of the first priority mode and the second priority mode.   The said control part controls the reverse rotation mode of the said 2nd conveyance roller part according to the said inclination correction capability based on the average value of the detection result of the said inclination detection part, The any one of Claim 1 to 5 characterized by the above-mentioned. A paper conveying apparatus according to claim 1.   The paper transport device according to claim 1, wherein the control unit controls a reverse speed of the second transport roller unit as one of the reverse modes.   The paper transport apparatus according to claim 1, wherein the control unit controls a reverse rotation time of the second transport roller unit as one of the reverse rotation modes. An image forming apparatus comprising: the sheet conveying apparatus according to claim 1; and an image forming unit that forms an image on a sheet conveyed by the sheet conveying apparatus. It has a configuration that can form images on both sides of the paper,
The control unit makes the reverse mode of the second transport roller unit when forming an image on the back surface of the paper the same as the reverse mode when forming an image on the front surface of the paper. The image forming apparatus according to 9.

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