JP2011059460A - Medium conveying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a medium conveying device configured to accurately detect the conveying position of a medium to be conveyed, and to provide an image forming apparatus. <P>SOLUTION: In the image forming apparatus 1, a registration part 25 is disposed on this side of a secondary transfer roller part 26 in the paper conveying direction. In the registration part 25, a lower registration roller 25a and an upper registration roller 25b configured to convey the paper P while sandwiching the paper P therebetween are disposed facing each other. The upper registration roller 25b is divided into two roller parts 25ba and 25bb with a prescribed interval therebetween in the axial direction, and a registration sensor 25h, whose detecting position is the vicinity on the paper P sandwiching line formed by the roller part 25aa of the lower registration roller 25a and the roller parts 25ba and 25bb, is disposed between the roller part 25ba and the roller part 25bb. The registration sensor 25h is configured to detect the leading end of the paper P sandwiched and conveyed by the roller part 25aa and the roller parts 25ba and 25bb. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a medium conveying apparatus and an image forming apparatus, and more particularly to a medium conveying apparatus and an image forming apparatus that accurately detect a conveyance position of a medium to be conveyed.

  In an electrophotographic image forming apparatus, a toner image on an image carrier such as an intermediate transfer belt or a photosensitive member is transferred to a transfer position with a position opposed to the image carrier as a transfer position. The image is formed by transferring to a recording medium. In this case, it is necessary to match the toner image on the image carrier and the entry timing of the recording medium conveyed to the transfer position to the transfer position.

  Therefore, a timing adjustment roller pair that controls the conveyance of the recording medium by sandwiching the recording medium such as a pair of registration rollers and a transfer timing roller is disposed in front of the recording medium conveyance direction to the transfer position. An image carrier is provided with a medium sensor disposed either before or after the pair of timing adjustment rollers in the medium conveyance direction, and the rotation of the timing adjustment roller is controlled based on the detection result of the leading edge of the recording medium by the medium sensor. The position of the upper toner image and the recording medium is adjusted, and the recording medium is conveyed to a transfer position by a timing adjustment roller (see Patent Document 1). In this prior art, the tip of the recording medium is detected using an optical sensor as a medium sensor.

  However, in the above prior art, the front end of the recording medium is detected by the medium sensor at any position before or after the timing adjustment roller, and the target is detected based on the detection result of the front end of the recording medium by the medium sensor. Since the conveyance control of the recording medium is performed, the accurate conveyance position of the recording medium cannot be detected, and it is necessary to improve the conveyance performance.

  That is, in the prior art, for example, a resist unit 100 as shown in FIG. 6 which is a view taken along the line A-A in FIG. 5 and FIG. The registration unit 100 is provided with a pair of upper and lower registration rollers 101 and 102, a support frame 103, an arm 104, a registration sensor 105, and the like. The lower registration roller 101 is rotationally driven by a registration motor 106 connected to a rotation shaft 101a. The lower registration roller 101 and the upper registration roller 102 are the rotation shaft 101a of the lower registration roller 101 and the rotation shaft of the upper registration roller 102, respectively. The gears 101b and 102b fixed to the gear 102a mesh with each other, and the rotation of the lower registration roller 101 is transmitted to the upper registration roller 102, thereby rotating in synchronization. The rotation shaft 101a of the lower registration roller 101 and the rotation shaft 102a of the upper registration roller 102 are rotatably supported by a support frame 103, and the support frame 103 is supported by registration rollers 101 and 102 as shown in FIG. Also, the arm 104 is attached to the downstream side in the paper transport direction in a state extending in the paper transport direction. A resist sensor 105 using a reflective photosensor is attached to the tip of the arm 104.

  The registration sensor 105 is arranged on a paper conveyance path by the lower registration roller 101 and the upper registration roller 102 so as to detect the leading edge of the paper conveyed by the lower registration roller 101 and the upper registration roller 102.

  However, when the sheet P conveyed by the lower registration roller 101 and the upper registration roller 102 passes through the lower registration roller 101 and the upper registration roller 102, the leading end of the sheet flutters in the vertical direction (perpendicular to the sheet surface). For example, as shown by the broken line in FIG. 6, the registration sensor 105 is detected even though the leading end of the sheet is actually conveyed to the position of the solid line. As a measurement error (for example, about 200 μm), as shown by a double-headed arrow, a position delayed from the actual paper front end position is detected as the paper front end position. That is, in this state, the front end of the paper viewed from the registration sensor 105 appears to be in a state in which the front end of the paper is located on the rear side in the transport direction with respect to the actual front end position of the paper because the front end of the paper fluctuates. In this state, since the registration sensor 105 detects the leading edge of the paper, the registration sensor 105 cannot accurately detect the leading edge of the paper. As a result, it is not possible to appropriately control the sheet conveyance timing, and there is a possibility that the image transfer timing is deviated to deteriorate the image quality.

  The above problem is the same even when the registration sensor 105 is disposed in front of the registration rollers 101 and 102 in the conveyance direction, and a detection error is caused by flapping of the leading edge of the paper conveyed to the registration rollers 101 and 102. appear.

  The problem that occurs in the detection of the passage timing for such a conveyance medium such as a sheet is not limited to the case where the timing at which the sheet passes the registration roller pair is detected. This is a problem that generally occurs when passing is detected.

  SUMMARY An advantage of some aspects of the invention is that it provides a medium conveyance device and an image forming apparatus that accurately detect the passage of a conveyance medium that is nipped and conveyed between a pair of conveyance rollers.

In order to achieve the above object, according to the present invention, among a pair of transport rollers that sandwich and transport a sheet-shaped transport medium, the medium sandwiching portion of at least one transport roller has a predetermined interval in the axial direction. It is divided into a plurality of divided medium sandwiching portions in a space, and between the plurality of divided medium sandwiching portions adjacent in the axial direction, the vicinity of the sandwiched line of the transport medium by the pair of transport rollers is set as a detection position. It is characterized in that at least one medium detecting means for detecting the transport medium that is sandwiched and transported by a pair of transport rollers is provided.

  Further, the present invention may be characterized in that the driving of the transport roller is controlled based on a detection result of the medium detection unit.

  According to the present invention, it is possible to accurately detect the passage of a transport medium that is transported between a pair of transport rollers.

1 is a schematic front view of an image forming apparatus to which an embodiment of the present invention is applied. FIG. 2 is a schematic configuration diagram of a main part of an image forming unit. The front view seen from the paper conveyance direction downstream of the registration part. FIG. 4 is an AA arrow view of FIG. 3. The front view seen from the paper conveyance direction downstream side of the conventional registration part. FIG. 6 is an AA arrow view of FIG. 5.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, since the Example described below is a suitable Example of this invention, various technically preferable restrictions are attached | subjected, However, The range of this invention is unduly limited by the following description. However, not all the configurations described in the present embodiment are essential constituent elements of the present invention.

  1 to 4 are diagrams showing an embodiment of a medium conveying apparatus and an image forming apparatus according to the present invention, and FIG. 1 is an image forming system to which the embodiment of the medium conveying apparatus and the image forming apparatus according to the present invention is applied. 2 is a schematic front view of the apparatus 1. FIG.

  In FIG. 1, the image forming apparatus 1 has a configuration in which a sheet feeding unit 10, an image forming unit 20, a scanner unit 30, and the like are sequentially stacked in a main body housing 2. An automatic document feeder (hereinafter referred to as ADF) 40 and an operation display unit (not shown) are provided. A paper discharge tray 3 and a manual feed tray 4 are provided on the side surface of the main body housing 2.

  A plurality of documents are set in the ADF 40, and the ADF 40 feeds the set documents one by one to the document reading position of the scanner unit 30.

  As the scanner unit 30, for example, a line image scanner using a CCD (Charge Coupled Device) is used. The scanner unit 30 irradiates the original conveyed from the ADF 40 with light, photoelectrically converts the light reflected by the original with the CCD, and reads an image of the original with a predetermined resolution.

  A plurality of (two in FIG. 1) paper feed trays 11a to 11d, feed rollers 12a to 12d, feed rollers 13a to 13d, a paper transport path 14, and a paper transport path 14 are provided in plural. The paper feed trays 11a to 11d can store a plurality of sheets of paper P (see FIG. 4) that are transport media of different paper sizes.

  The paper feed unit 10 feeds the paper P stored in each of the paper feed trays 11a to 11d one by one from the uppermost paper P by feed rollers 12a to 12d. The paper is fed to the paper transport path 14 by the feed rollers 13a to 13d. The paper feed unit 10 conveys the paper P sent to the paper conveyance path 14 to the image forming unit 20 by a plurality of conveyance rollers 15 provided along the paper conveyance path 14. Further, although not shown, the paper supply unit 10 is provided with a paper presence / absence sensor that detects the presence / absence of the paper P in each of the paper supply trays 11a to 11d.

  An image forming unit (image forming unit) 20 includes an intermediate transfer belt 22 stretched between a plurality of rollers 21, and Y (yellow), M (magenta), and C (cyan) arranged side by side along the transfer belt 22. ) And K (black) four image forming units 23Y, 23M, 23C, and 23K, an optical writing unit 24, a registration unit 25, a secondary transfer roller unit 26, a paper transport unit 27, a fixing unit 28, and a paper discharge control reverse transport. The image forming units 23Y, 23M, 23C, and 23K include a charging unit, an exposure unit, and a developing unit around the photoconductors 23Ya, 23Ma, 23Ca, and 23Ka of the respective colors as illustrated in FIG. , A primary transfer unit (primary transfer roller), a charge eliminating unit, a cleaning unit, and the like.

  The optical writing unit 24 appropriately scans color image data of a document read by the scanner unit 30 or color image data sent from an external device such as a computer connected to the image forming apparatus 1. The laser beam bundle sent after being subjected to image processing such as conversion, image separation, gradation correction processing, etc. and modulated based on the image data is converted into image forming units 23Y, 23M, 23C, and 23K for each color. The surface of each of the photoconductors 23Ya, 23Ma, 23Ca, and 23Ka is irradiated to form an electrostatic latent image of each color image on the photoconductors 23Ya, 23Ma, 23Ca, and 23Ka.

  The image forming units 23Y, 23M, 23C, and 23K uniformly charge the surfaces of the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka at the charging unit, and the surfaces of the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka that have been subjected to the charging process. Then, a laser beam bundle modulated and deflected based on the image data of each color is irradiated from the optical writing unit 24, and electrostatic latent images for the respective colors are formed on the surfaces of the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka. Form. The image forming units 23Y, 23M, 23C, and 23K supply each color toner from the developing unit to each color photoconductor 23Ya, 23Ma, 23Ca, and 23Ka on which the electrostatic latent image is formed, and develop the electrostatic latent image. Then, a toner image of each color is formed.

  The image forming units 23Y, 23M, 23C, and 23K transfer the toner images formed on the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka to the intermediate transfer belt 22 and transfer the photoreceptors 23Ya, 23Ma, 23Ca, and The transfer residual toner remaining on the surface of 23 Ka is cleaned by the cleaning unit. In the image forming units 23Y, 23M, 23C, and 23K, the photoconductors 23Ya, 23Ma, 23Ca, and 23Ka cleaned by the cleaning unit are neutralized by the neutralizing unit, uniformly charged by the charging unit, and image formation is performed again.

  In the image forming units 23Y, 23M, 23C, and 23K, an endless belt-like intermediate transfer belt 22 is stretched around a plurality of rollers 21, and the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka are sandwiched between the intermediate transfer belts 22. A primary transfer roller (number omitted) is disposed at a position facing each other. The intermediate transfer belt 22 is endlessly rotated in a clockwise direction indicated by an arrow in FIGS. 1 and 2 by driving at least one roller 21 by a belt drive motor (not shown) that is driven and controlled. The image forming units 23Y, 23M, 23C, and 23K are each applied with a primary transfer bias from a power source (not shown) to the respective primary transfer rollers, whereby the photoconductors 23Ya, 23Ma, and 23K of the image forming units 23Y, 23M, 23C, and 23K, respectively. The toner images of the respective colors on 23Ca and 23Ka are sequentially superimposed and transferred onto the intermediate transfer belt 22, and a color toner image is formed on the intermediate transfer belt 22.

  The image forming unit 20 transfers the color toner image superimposed and transferred on the intermediate transfer belt 22 onto the sheet P conveyed from the sheet feeding unit 10 by a secondary transfer roller unit 26 which is a secondary transfer nip described later. The transfer residual toner remaining on the surface of the intermediate transfer belt 22 after passing through the secondary transfer roller section 26 is cleaned by a belt cleaning section (not shown).

  The image forming unit 20 conveys the paper P on which the toner image has been transferred to the fixing unit 28 by the paper conveying unit 27, and conveys the toner image on the paper P by heating and pressurizing the paper P by the fixing unit 28. To settle.

  The image forming unit 20 determines a paper conveyance destination by the paper discharge control reverse conveyance unit 29 and discharges the fixed paper P onto the paper discharge tray 3 as it is. Alternatively, the image forming unit 20 reverses the paper P on which image formation has been performed on one side by the paper discharge control reversing conveyance unit 29 and sends it again to the secondary transfer roller unit 26 through the registration unit 25. At 26, the toner image is transferred to the back surface of the paper P, and the paper P on which the image is formed on the back surface of the paper P is discharged onto the paper discharge tray 3.

  The secondary transfer roller section 26 is disposed in a state where the secondary transfer roller 26a and the roller 21 are in contact with each other with a predetermined pressure across the intermediate transfer belt 22, and the sheet P conveyed from the registration section 25 is disposed. A secondary transfer voltage is applied to the secondary transfer roller 26a at the timing when it passes through the nip portion (nipping portion) between the secondary transfer roller 26a and the intermediate transfer belt 22, and the toner image on the intermediate transfer belt 22 is transferred onto the paper P. Let them transcribe.

The registration unit (medium conveying device, medium conveying means) 25 is arranged in a direction perpendicular to the conveying path H (sheet) with the conveying path H of the sheet P interposed therebetween, as shown in FIGS. A lower registration roller 25a and an upper registration roller 25b are disposed in a state where they are in contact with each other at a predetermined pressure. The lower registration roller 25a has a roller portion (medium holding portion) 25aa formed longer than the maximum sheet width that is an image forming target of the image forming apparatus 1, and the roller portion 25aa has a rotation shaft (axis). It is fixed at 25ab. In the upper registration roller 25b, roller portions (medium holding portions) 25ba and 25bb which are divided into two in the axial direction are fixed to a rotation shaft (shaft) 25bc.
As shown in FIG. 3, which is a front view of the registration unit 25 as viewed from the downstream side in the sheet conveyance direction, the upper registration roller 25b is fixed to the rotating shaft 25bc with a predetermined interval between the roller unit 25ba and the roller unit 25bb. The rotation shaft 25ab of the lower registration roller 25a and the rotation shaft 25bc of the upper registration roller 25b are rotatably supported by the support frame 25c. Gears 25d and 25e having the same number of teeth are fixed to the respective rotation shafts 25ab and 25bc, and the rotation shaft 25ab and the rotation shaft 25bc rotate synchronously when the gear 25d and the gear 25e are engaged with each other. The rotation shaft 25ab of the lower registration roller 25a is connected to the drive shaft of the registration motor 25f, and the rotation shaft 25ab of the lower registration roller 25a is rotationally driven by the registration motor 25f.

  The registration unit 25 is configured such that the rotation shaft 25ab is rotated by a registration motor 25f, the lower registration roller 25a and the gear 25d fixed to the rotation shaft 25ab are rotated, and the gear 25d is rotated to The gear 25e meshing with 25d rotates synchronously. As the gear 25e rotates, the rotation shaft 25bc to which the gear 25e is fixed rotates, and the roller portions 25ba and 25bb of the upper registration roller 25 fixed to the rotation shaft 25bc are driven to rotate.

  The registration portion 25 is a space between the support frame 25c and the roller portions 25ba and 25bb of the upper registration roller 25b, and a nip portion between the roller portion 25aa of the lower registration roller 25a and the roller portions 25ba and 25bb. The L-shaped sensor mounting arm 25g is mounted on the support frame 25c in a state of extending to a nearby position, and is located at the tip position of the sensor mounting arm 25g, that is, a position directly below the rotating shaft 25bc. At a position near the nip portion between the roller portion 25aa of the registration roller 25a and the roller portions 25ba and 25bb of the upper registration roller 25b, as shown in FIG. It is attached.

  The registration sensor 25h is a reflection type optical sensor. The registration sensor 25h emits detection light from the light emitting element in the direction of the rotation axis 25bc of the lower registration roller 25a, and the roller portion 25aa of the lower registration roller 25a and the upper registration roller. When the detection light is reflected by the paper P that is nipped and conveyed by the roller portions 25ba and 25bb of the 25b, the leading edge of the paper P is detected by photoelectrically converting the reflected light by the light receiving element. In other words, the registration sensor 25h is arranged on the line connecting the nip portion between the roller portion 25aa of the lower registration roller 25a and the roller portions 25ba and bb of the upper registration roller 25b (on the pinching line) and the roller portion 25aa of the lower registration roller 25a and the upper registration roller. The leading end of the paper P conveyed while being nipped by the roller portions 25ba and bb of the roller 25b is detected.

  In the image forming apparatus 1, although not shown, the control unit controls the driving of the registration motor 25 f based on the detection result of the registration sensor 25 h to adjust the rotation of the lower registration roller 25 a and the upper registration roller 25 b. The sheet P is transported to the nip portion in accordance with the timing at which the toner image on the intermediate transfer belt 22 is transported to the nip portion of the transfer roller portion 26 between the secondary transfer roller 26a and the intermediate transfer belt 22. Therefore, the control unit and the registration motor 25f function as a conveyance roller drive control unit and a conveyance control unit as a whole.

  Next, the operation of this embodiment will be described. The image forming apparatus 1 according to the present exemplary embodiment detects the leading edge of the paper P conveyed to the image transfer position with high accuracy and accurately adjusts the conveyance timing.

  That is, when the image forming apparatus 1 is instructed to start the copying operation or the printing operation, the image forming units 23Y, 23M, 23C, and 23K of the image forming unit 20 perform the image regardless of the sheet detecting operation of the registration sensor 25h. The forming operation is started, and the sheet supply timing is adjusted by the registration unit 25 in accordance with the toner image formed on the intermediate transfer belt 22.

  Accordingly, when the start of the copying operation or the printing operation is instructed, the image forming apparatus 1 rotationally drives the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka of the image forming units 23Y, 23M, 23C, and 23K, and the charging unit. The uniformly charged photoconductors 23Ya, 23Ma, 23Ca, and 23Ka are irradiated with a laser beam modulated with image data by the optical writing unit 24 in accordance with the writing timing of each of the image forming units 23Y, 23M, 23C, and 23K. Then, an electrostatic latent image is formed. Each of the image forming units 23Y, 23M, 23C, and 23K supplies toner of each color to the photoreceptors 23Ya, 23Ma, 23Ca, and 23Ka on which the electrostatic latent image is written to form a toner image. A color toner image is formed on the intermediate transfer belt 22 that is driven to rotate by being accurately and sequentially superimposed.

  On the other hand, the image forming apparatus 1 conveys the paper P from the paper supply unit 10 in accordance with the image formation by the image forming unit 20. That is, among the paper feed trays 11a to 11d, the paper P in the designated paper feed trays 11a to 11d is fed one by one from the uppermost paper P by the feed rollers 12a to 12d, and the fed paper is sent out. P is fed to the paper transport path 14 by the feed rollers 13a to 13d. The paper feeding unit 10 conveys the paper P sent out to the paper conveyance path 14 to the registration unit 25 of the image forming unit 20 by a plurality of conveyance rollers 15 along the paper conveyance path 14.

  The registration unit 25 detects the leading edge of the paper P conveyed from the paper supply unit 10 by the registration sensor 25h.

  As shown in FIGS. 2, 3, and 4, the registration unit 25 is a lower registration roller that extends in a direction (paper width direction) perpendicular to the conveyance path H across the conveyance path H of the sheet P. 25a and the upper registration roller 25b are arranged so as to face each other, and the roller part 25aa of the lower registration roller 25 and the roller parts 25ba and 25bb of the upper registration roller 25b divided into two are arranged to face each other. The lower registration roller 25a and the upper registration roller 25b have gears 25d and 25e fixed to the respective rotation shafts 25ab and 25bc by the rotation of the registration motor 25f connected to the rotation shaft of the lower registration roller 25a. Rotate synchronously.

  The registration unit 25 is provided with a registration sensor 25h between the roller unit 25ba and the roller unit 25bb of the upper registration roller 25b divided into two via a support frame 25c and a sensor mounting arm 25g. The sensor 25h emits detection light from the light emitting element toward a line connecting the nip portion between the roller portion 25aa of the lower registration roller 25a and the divided roller portions 25ba and 25bb of the upper registration roller 25b, and the lower registration roller The light receiving element photoelectrically converts the reflected light reflected by the paper P conveyed while being held between the roller portion 25aa of 25a and the roller portions 25ba and 25bb of the upper registration roller 25b, thereby changing the amount of reflected light. Based on this, the leading edge of the paper P is detected.

  Accordingly, the registration sensor 25h includes a nip portion between the roller portion 25aa of the lower registration roller 25a and the roller portion 25ba of the upper registration roller 25b and a nip portion between the roller portion 25aa of the lower registration roller 25a and the roller portion 25bb of the upper registration roller 25b. Is a detection position, and both sides in the width direction orthogonal to the conveying direction are the roller portion 25aa of the lower registration roller 25a, the roller portion 25ba of the upper registration roller 25b, and the roller portion 25aa of the lower registration roller 25a and the upper registration roller. The leading edge of the paper P that is sandwiched between the roller portions 25bb of 25b and transported in a state where the flapping is suppressed is detected, and the leading edge of the conveyed paper P can be accurately detected.

  When the registration sensor 25h detects that the sheet P is conveyed to the registration unit 25, the control unit of the image forming apparatus 1 controls the driving of the registration motor 25f to rotate the lower registration roller 25a and the upper registration roller 25b. The sheet P is fed to the nip portion in accordance with the timing at which the toner image on the intermediate transfer belt 22 is conveyed to the nip portion between the secondary transfer roller 26a of the secondary transfer roller portion 26 and the intermediate transfer belt 22. Transport. When the sheet P is conveyed to the nip portion of the secondary transfer roller unit 26, the control unit applies a secondary transfer voltage to the secondary transfer roller 26a so that the toner image on the intermediate transfer belt 22 is applied onto the sheet P. The paper P to which the toner image has been transferred is conveyed to the fixing unit 28 by the paper conveying unit 27, and the paper P is conveyed while being heated and pressurized by the fixing unit 28, and the toner image on the paper P is transferred to the paper P Let it settle. The image forming apparatus 1 discharges the fixed sheet P onto the sheet discharge tray 3 as it is, or reverses the sheet P by the sheet discharge control reversing conveyance unit 29 and again passes through the registration unit 25 to the secondary transfer roller unit. The toner image is transferred onto the back surface of the paper P by the secondary transfer roller unit 26, and the paper P on which the image is formed on the back surface of the paper P is discharged onto the paper discharge tray 3.

  In the present embodiment, the upper registration roller is divided into two roller portions 25ba and 25bb in the axial direction (the direction perpendicular to the paper transport direction). Between the divided roller portion 25ba and roller portion 25bb, a registration sensor 25h of a reflection type photosensor is provided. However, the arrangement state of the registration sensor 25h is not limited to the above arrangement state. Alternatively, the roller portion 25aa of the lower registration roller 25a may be divided into two or more and a registration sensor of a reflection type optical sensor may be disposed between the divided lower registration rollers 25a in the same manner as described above. Good. Further, the lower registration roller and the upper registration roller may be divided into two or more, respectively, and a registration sensor of a reflective optical sensor may be disposed on either or both of the divided lower registration roller and upper registration roller, Each of the lower registration roller and the upper registration roller may be divided at the same position, and a transmission type optical sensor in which a light emitting element and a light receiving element are arranged between the divided registration rollers may be provided as a registration sensor.

  As described above, the image forming apparatus 1 according to the present exemplary embodiment includes the upper registration roller 25b that is at least one of the lower registration roller 25a and the upper registration roller 25b that sandwich and convey the sheet P that is a sheet-shaped conveyance medium. Is divided into a plurality of (two in the present embodiment) roller portions 25ba and 25bb at predetermined intervals in the axial direction, and the roller portions 25ba and 25bb Between the roller portion 25aa of the lower registration roller 25a and the roller portion 25aa of the lower registration roller 25a and the upper registration roller 25b and the roller portions 25ba and 25bb of the upper registration roller 25b, the roller portion 25aa of the lower registration roller 25a and the upper registration roller are detected near the pinching line. There are few registration sensors 25h that detect the paper P that is nipped and conveyed by the roller portions 25ba and 25bb of the 25b. Both are one disposed.

  Therefore, the leading edge of the paper P can be detected in a state where the flapping of the paper P that is the transport medium is suppressed, and the leading edge of the paper P can be detected with high accuracy.

  In addition, the image forming apparatus 1 according to the present exemplary embodiment includes, as the registration sensor 25h, a reflective optical sensor including a light emitting element that emits detection light and a light receiving element that receives reflected light from the paper P and performs photoelectric conversion. Is used.

  Therefore, it is possible to detect the paper accurately and inexpensively with a simple configuration.

  Furthermore, in the image forming apparatus 1 of the present embodiment, the pair of registration rollers are divided by a predetermined interval at the positions where the roller portions (medium sandwiching portions) face each other. A light emitting element disposed between the roller parts divided in the roller part of the registration roller and emitting light for detection, and a light emitting element arranged between the roller parts divided in the roller part of the other registration roller from the light emitting element A transmissive optical sensor including a light receiving element that receives the detected light and performs photoelectric conversion.

  In this way, it is possible to accurately detect a transport medium that is difficult to detect by reflection of light, with or without transmitted light.

  Further, the image forming apparatus 1 of the present embodiment conveys a plurality of types of paper P having different lengths (widths) in the axial direction, and the registration sensor 25h is disposed at a position where all types of paper P can be detected. Has been.

  Therefore, the image forming apparatus 1 can accurately detect the leading ends of all the papers P having different paper sizes to be image-formed, and the image quality can be improved.

  Further, in the image forming apparatus 1 of the present embodiment, the control unit controls the driving of the registration motor 25f based on the detection result of the registration sensor 25h, and controls the driving of the lower registration roller 25a and the upper registration roller 25b. Yes.

  Accordingly, the conveyance timing of the paper P is conveyed in accordance with the transfer timing from the intermediate transfer belt 22 to the paper P in the image forming units 23Y, 23M, 23C, and 23K based on the detection result of the accurate paper leading edge by the registration sensor 25h. Image quality can be improved.

  In the above-described embodiment, the case where the front end of the sheet P to be conveyed is detected has been described. However, the present invention is not limited to the sheet P, and other general conveyance media conveyed by rollers in general. On the other hand, it can be applied to the case where the tip is accurately detected.

  Although the invention made by the present inventor has been specifically described based on the preferred embodiments, the present invention is not limited to that described in the above embodiments, and various modifications can be made without departing from the scope of the invention. It goes without saying that it is possible.

  The present invention can be used for a medium conveying apparatus such as a composite apparatus, a copying apparatus, and a printer apparatus for conveying a conveying medium such as paper, and an image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Main body housing | casing 3 Paper discharge tray 4 Manual feed tray 10 Paper feed part 11a-11d Paper feed tray 12a-12d Feeding roller 13a-13d Feeding roller 14 Paper conveyance path 15 Conveyance roller 20 Image formation part 21 Roller 22 Intermediate transfer belt 23Y, 23M, 23C, 23K Image forming unit 23Ya, 23Ma, 23Ca, 23Ka Photoconductor 24 Optical writing unit 25 Registration unit 25a Lower registration roller 25aa Roller unit 25ab Rotating shaft 25b Upper registration roller 25ba, 25bb Roller unit 25bc Rotation Shaft 25c Support frame 25d, 25e Gear 25f Registration motor 25g Sensor mounting arm 25h Registration sensor 26 Secondary transfer roller section 26a Secondary transfer roller 27 Paper transport section 28 Fixing section 29 Paper discharge control Reverse transport 30 scanner unit 40 an automatic document feeder (ADF)
P paper

JP 2008-139777 A

Claims (6)

A direction perpendicular to the conveyance direction of the sheet-shaped conveyance medium is defined as an axial direction, and the conveyance medium is nipped and conveyed by a pair of conveyance rollers that are arranged to face each other over a predetermined length in the axial direction and are driven to rotate. In the medium transport device
Each of the pair of transport rollers includes a shaft and a medium holding portion fixed to the shaft.
Of the pair of transport rollers, the medium sandwiching portion of at least one transport roller is divided into a plurality of divided medium sandwiching portions at a predetermined interval in the axial direction.
Between the plurality of divided medium nipping parts adjacent in the axial direction, the vicinity of the nipping line of the conveying medium by the pair of conveying rollers is set as a detection position and is nipped by the pair of conveying rollers and conveyed. At least one medium detection unit for detecting the conveyance medium is provided.   The said medium detection means is a reflection type optical sensor provided with the light emitting element which radiate | emits detection light, and the light receiving element which light-receives the reflected light from the said conveyance medium, and photoelectrically converts it. The medium conveying apparatus as described. The medium conveying device is:
The pair of transport rollers is divided into divided transport rollers at predetermined intervals at opposite positions, respectively.
The medium detecting means is disposed between the divided conveying roller of one of the conveying rollers and the divided conveying roller and emits detection light, and the divided conveying roller of the other conveying roller and the divided The medium transporting apparatus according to claim 1, wherein the medium transporting apparatus includes a light-receiving element that is disposed between transporting rollers and that receives a detection light from the light-emitting element and performs photoelectric conversion. The medium transport device transports a plurality of types of the transport media having different lengths in the axial direction,
The medium conveying apparatus according to claim 1, wherein the medium detecting unit is disposed at a position where all types of the conveying medium can be detected. The medium transport device includes a transport roller drive control unit that controls driving of the transport roller,
5. The medium conveying apparatus according to claim 1, wherein the conveying roller driving control unit controls driving of the conveying roller based on a detection result of the medium detecting unit. Image forming means for forming an image on a transport medium at a predetermined image forming timing;
Medium conveying means for conveying the conveying medium to the image forming means;
Transport control means for controlling transport of the transport medium by the medium transport means;
An image forming apparatus in which the conveyance control unit controls the conveyance of the conveyance medium by the medium conveyance unit in accordance with the image formation timing on the conveyance medium in the image forming unit.
An image forming apparatus comprising the medium conveying device according to claim 1 as the medium conveying unit.

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