JP2006259483A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing variation in speed of an intermediate transfer belt due to influence of the thickness of transfer paper. <P>SOLUTION: The image forming apparatus is equipped with an image formation unit including a photoreceptor having a toner image formed on its surface, the intermediate transfer belt 31 which is wound around a plurality of rollers 30 etc., including a driving roller 27 and to which the toner image formed on the photoreceptor is primarily transferred, and a secondary transfer roller 36 which is arranged while being brought into press-contact with the intermediate transfer belt 31 and secondarily transfers the toner image on the intermediate transfer belt 31 to transfer paper S passing through a press-contact section formed with the intermediate transfer belt 31. Further, the image forming apparatus is equipped with a paper thickness measurement section 46 which measures the thickness of the transfer paper S upstream from the press-contact section in the conveying direction of the transfer paper and a control section which controls the rotation of a cam 47 on the basis of the measurement result of the paper thickness measurement section 46 to make press-contact force of a transfer roller 36 at the press-contact section nearly constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer.

  An electrophotographic image forming apparatus generally includes a plurality of image forming units for speeding up, and transferring images by sequentially superimposing different color images on an intermediate transfer belt or the like.

  In such an image forming apparatus, as shown in FIG. 5, an endless intermediate transfer belt 5 is wound around the driving roller 1 and the rollers 2 to 4, and the intermediate transfer belt 5 is disposed below the intermediate transfer belt 5. The image forming units 6 to 9 are arranged at regular intervals along the conveyance direction (arrow a direction). The image forming units 6 to 9 primarily transfer yellow, cyan, magenta, and black toner images to the intermediate transfer belt 5, respectively. Further, a secondary transfer roller 10 is disposed on the side of the drive roller 1 with the intermediate transfer belt 5 interposed therebetween, and a pressure contact portion between the intermediate transfer belt 5 and the secondary transfer roller 10 is provided on the intermediate transfer belt 5. The toner image is secondarily transferred to the transfer paper S. A pair of registration rollers 11 is provided below the secondary transfer roller 10 (see Patent Document 1).

  In the image forming apparatus having the above configuration, the conveyance speed of the intermediate transfer belt 5 is required to be constant. When the conveyance speed of the intermediate transfer belt 5 fluctuates, color misregistration occurs when a toner image is transferred from the image forming units 6 to 9 to the intermediate transfer belt 5, and an image defect called so-called “color misregistration” occurs. appear.

  By the way, in recent image forming apparatuses, the number of “vertical conveyance” apparatuses in which the transfer path of the transfer sheet S is in the vertical direction is increasing due to the miniaturization / space saving of the apparatus.

  FIG. 6 is an enlarged view of the image forming process unit (near the secondary transfer roller 10) of FIG. The secondary transfer roller 10 is pressed against the intermediate transfer belt 5 by a spring 12. The transfer sheet S is conveyed from below by the registration rollers 11 and the conveyance guide plate 13. At this time, when the transfer sheet S is thin, as shown in FIG. 6A, even if the transfer sheet S enters the nip portion between the intermediate transfer belt 5 and the secondary transfer roller 10, the secondary transfer is performed. Since the roller 10 does not move so much and the contraction amount of the spring 12 is small, the pressure contact force F at the pressure contact portion is weak.

  However, when the transfer sheet S is thick, as shown in FIG. 6B, when the transfer sheet S enters the nip portion between the intermediate transfer belt 5 and the secondary transfer roller 10, the secondary transfer roller 10 moves greatly. Since the amount of contraction of the spring 12 is large, the pressure contact force F at the pressure contact portion is increased. For this reason, when the transfer sheet S is passing through the press contact portion and when it is not passing (that is, after one transfer sheet passes through the press contact portion, the next transfer paper enters the press contact portion. In the meantime, the conveyance speed of the intermediate transfer belt 5 is not constant but varies greatly.

  FIG. 7 shows actual measurement values when the conveyance speed of the intermediate transfer belt 5 is measured. In the figure, A indicates the transfer speed of the transfer paper, and B indicates whether or not the transfer paper is passing through the press-contact portion (section 1 is passing and section 2 is not passing). As shown in the figure, when there is no transfer paper at the press contact portion (that is, section 2), the conveyance speed of the intermediate transfer belt 5 is substantially constant without increasing, but when the thick transfer paper S enters the press contact portion. In other words (in section 1), the conveyance speed of the intermediate transfer belt 5 increases rapidly.

As a method for solving such a speed fluctuation of the intermediate transfer belt, for example, by providing a belt extension absorbing mechanism on the downstream side of the position where the developing unit contacts the intermediate transfer belt, and a belt rotation preventing member on the upstream side, There has been proposed an image forming apparatus which prevents the occurrence of deflection in a part of the intermediate transfer belt, thereby suppressing the speed fluctuation of the intermediate transfer belt (see Patent Document 2).
JP 2001-194923 A JP-A-9-160437

  However, when the developing unit comes into contact, the deflection may occur not only in a part of the intermediate transfer belt but also in the entire circumference. In such a case, the conventional technology cannot cope with the intermediate transfer belt. There is a problem that the speed becomes faster all around.

  An object of the present invention is to provide an image forming apparatus capable of suppressing the speed fluctuation of the intermediate transfer belt due to the influence of the thickness of the transfer paper.

  In order to solve the above-mentioned problem, the invention according to claim 1 is wound around an image forming unit including a photoconductor on which a toner image is formed and a plurality of rollers including a driving roller. An intermediate transfer belt on which the formed toner image is primarily transferred, and the intermediate transfer belt are disposed in pressure contact with the intermediate transfer belt, and the toner image on the intermediate transfer belt is transferred to the transfer paper passing through the pressure contact portion between the intermediate transfer belt and the intermediate transfer belt. An image forming apparatus comprising a transfer member for secondary transfer, the measuring means for measuring the thickness of the transfer paper on the upstream side of the pressure contact portion along the transfer paper transport direction, and the measurement means And a control means for controlling the pressure contact force of the transfer member at the pressure contact portion to be substantially constant based on the measurement result at 1.

  According to the above configuration, the control means controls the pressure contact force of the transfer member at the pressure contact portion to be substantially constant based on the measurement result of the measurement means, so that the speed of the intermediate transfer belt becomes substantially constant and the speed fluctuation is suppressed. can do.

  According to a second aspect of the present invention, in the first aspect, the measuring unit has a contact, and the contact contacts the transfer paper surface from a direction perpendicular to the transfer paper transport direction, and the contact The thickness of the transfer paper is measured by detecting the distance that the contact moves. With this configuration, the thickness of the transfer paper can be directly detected with high accuracy.

  A third aspect of the invention is characterized in that, in the first aspect, the measuring means is formed integrally with the transfer member. With this configuration, the mechanism for moving the transfer member can be simplified, contributing to cost reduction of the image forming apparatus.

  According to a fourth aspect of the present invention, in the first aspect, the measuring unit includes an optical distance sensor, and the thickness of the transfer paper is measured without contact with the surface of the transfer paper. If configured in this manner, it is possible to detect the paper thickness without increasing the load on the transfer paper because it is not in contact with the surface of the transfer paper.

  According to the present invention, it is possible to suppress the speed fluctuation of the intermediate transfer belt due to the influence of the thickness of the transfer paper, and as a result, it is possible to form a high-quality image.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram of an image forming apparatus according to the present invention. As shown in FIG. 1, the image forming apparatus 20 includes an image reader unit 21 that reads a document image and a printer unit 22 that reproduces a document image read by the image reader unit 21.

  The image reader unit 21 includes a document table 23 on which a document is placed, a scanner 24 that performs exposure scanning while moving the document placed on the document table 23 in the direction of the arrow b, and a plurality of reflected lights due to exposure by the scanner 24. The CCD sensor 25 that is incident through an optical system including a mirror and a lens and photoelectrically converts the reflected light into R, G, and B color multi-value electric signals for each pixel, and the multi-value electric signal is reflected. And an image signal processing unit 26 inputted as analog data of the rate.

  An endless intermediate transfer belt 31 that is wound around the drive roller 27 and rollers 28 to 30 and is driven to rotate in the direction of the arrow c is disposed at the approximate center of the printer unit 22. Below the intermediate transfer belt 31, image forming units 32 to 35 are arranged at regular intervals in order along the conveyance direction (arrow c direction). The image forming units 32 to 35 primarily transfer yellow, cyan, magenta, and black toner images to the intermediate transfer belt 31, respectively.

  Although not shown in the figure, the image forming units 32 to 35 include a photoconductor, a charging charger that uniformly charges the surface of the photoconductor, an exposure device that exposes the surface of the photoconductor to form an electrostatic latent image, A developing device or the like is provided that develops the electrostatic latent image formed on the photosensitive member into a toner image.

  Further, a secondary transfer roller 36 is disposed so as to sandwich the intermediate transfer belt 31 between the drive roller 27. The secondary transfer roller 36 constitutes a transfer member, and at least the outer peripheral portion is made of a conductive elastic material. A fixing unit 38 having a fixing roller 37 is provided above the secondary transfer roller 36.

  A pair of registration rollers 39 is provided below the secondary transfer roller 36, and a conveyance guide plate 40 that guides the conveyance of the transfer sheet S between the registration roller 39 and the secondary transfer roller 36 is substantially up and down. In the direction.

  In FIG. 1, reference numeral 41 denotes a paper feed tray, 42 denotes a paper feed roller, and 43 denotes a paper discharge tray.

  FIG. 2 is a detailed configuration diagram in the vicinity of the secondary transfer roller 36. As shown in the figure, the secondary transfer roller 36 is fixed to a movable wall 45 via a spring 44, and this movable wall 45 is attached to the main body frame of the image forming apparatus via an elastic member (not shown). ing. Therefore, the movable wall 45 can reciprocate in the direction of the arrow d.

  In the present embodiment, a paper thickness measuring unit 46 that measures the thickness of the transfer paper S is provided. The paper thickness measuring unit 46 is fixed to the main body frame of the image forming apparatus. The paper thickness measuring unit 46 has a contact 46A on the side close to the conveyance guide plate 40, and the contact 46A comes into contact with the surface of the transfer paper S to measure the thickness of the transfer paper S. it can.

  An elliptical cam 47 is provided in contact with the surface of the movable wall 45 so as to be rotatable about a shaft 47A. The shaft 47A is fixed to the main body frame of the image forming apparatus. The cam 47 is rotationally driven by a motor (not shown), and a microcomputer is built in the paper thickness measuring unit 46, and the rotation of the motor is controlled by the microcomputer in the paper thickness measuring unit 46.

  In the above configuration, the contact 46A constitutes a measuring means for measuring the thickness of the transfer paper S, and the microcomputer and the cam 47 in the paper thickness measuring section 46 constitute a control means.

  Next, the operation of the image forming apparatus having the above configuration will be described.

  First, as shown in FIG. 2A, when the transfer sheet S is thin, the secondary transfer is performed even if the transfer sheet S enters the nip portion between the intermediate transfer belt 5 and the secondary transfer roller 36. Since the roller 36 does not move so much and the amount of contraction of the spring 44 is small, the pressure contact force F (see FIG. 6A) by the spring 44 is also relatively small. At this time, the microcomputer in the paper thickness measuring unit 46 performs control so that the elliptical cam 47 is directed in the vertical direction, and as a result, the movable wall 45 does not move.

  Next, when the transfer sheet S is thick as shown in FIG. 2B, when the transfer sheet S enters the nip portion between the intermediate transfer belt 31 and the secondary transfer roller 36, the secondary transfer roller 36 moves to the right in the figure and the amount of contraction of the spring 44 increases, so that the pressure F (see FIG. 6B) by the spring 44 tends to increase. However, at this time, the microcomputer in the paper thickness measuring unit 46 controls the elliptical cam 47 to face in the lateral direction, and as a result, the movable wall 45 moves in the right direction in the figure, so that the amount of contraction of the spring 44 is reduced. Thus, an increase in the pressure contact force F by the spring 44 is suppressed.

  According to the present embodiment, the pressure contact force F by the spring 44 can be made substantially equal between the case of FIG. 2A and the case of FIG. It is possible to suppress the speed fluctuation. As a result, a high quality image can be formed.

  In place of the cam 47, an electrical actuator may be provided, and the operation of this actuator may be controlled by a microcomputer in the paper thickness measuring unit 46.

  FIG. 3 is a detailed configuration diagram in the vicinity of the secondary transfer roller 36 according to the second embodiment. In the present embodiment, a paper thickness measuring unit 50 that measures the thickness of the transfer paper S is integrally fixed to the movable wall 45. A roller 50A is rotatably attached to the leading end of the paper thickness measuring unit 50, and the roller 50A rotates while contacting the surface of the transfer paper S. Other configurations are the same as those in the first embodiment.

  In the above configuration, when the thick transfer paper S is conveyed from below, the entire paper thickness measuring unit 50 is pushed by the transfer paper S and moves rightward in the figure. Since the paper thickness measuring unit 50 is integrally fixed to the movable wall 45, when the entire paper thickness measuring unit 50 moves in the right direction in the figure, the movable wall 45 also moves in the same direction.

  When the transfer sheet S enters the nip portion between the intermediate transfer belt 31 and the secondary transfer roller 36, the secondary transfer roller 36 moves greatly in the right direction in the figure, and the contraction amount of the spring 44 increases. Although the pressing force F by the spring 44 tends to increase, the movable wall 45 moves in the right direction in the figure, so that the amount of contraction of the spring 44 is reduced and the increase of the pressing force F by the spring 44 is suppressed.

  According to the present embodiment, the pressing force F by the spring 44 can be made substantially constant regardless of the thickness of the transfer paper S, and as a result, a high-quality image can be formed. In addition, since the paper thickness measuring unit 50 is simply formed integrally with the movable wall 45, the configuration is very simple.

  FIG. 4 is a detailed configuration diagram in the vicinity of the secondary transfer roller 36 according to the third embodiment. In this embodiment, the thickness of the transfer sheet S is measured by an optical displacement sensor (not shown). The displacement sensor is provided in the paper thickness measuring unit 55, and the paper thickness measuring unit 55 is fixed to the main body frame of the image forming apparatus. As in the case of the first embodiment, an elliptical cam 47 is provided in contact with the surface of the movable wall 45 so as to be rotatable about a shaft 47A.

  The cam 47 is rotationally driven by a motor (not shown), and a microcomputer is built in the paper thickness measuring unit 55, and the rotation of the motor is controlled by the microcomputer in the paper thickness measuring unit 55.

  In the above configuration, when the thick transfer paper S is conveyed from below, the paper thickness measurement unit 55 irradiates the transfer paper S with light from the displacement sensor and receives the reflected light to receive the transfer paper S. Detect that the thickness of the is thick. Then, the microcomputer in the paper thickness measurement unit 55 controls the elliptical cam 47 to face in the horizontal direction based on the detection result (thickness data of the transfer paper S) by the displacement sensor, so that the movable wall 45 Is moved to the right in the figure.

  When the transfer sheet S enters the nip portion between the intermediate transfer belt 31 and the secondary transfer roller 36, the secondary transfer roller 36 moves greatly in the right direction in the figure, and the contraction amount of the spring 44 increases. Although the pressing force F by the spring 44 tends to increase, the movable wall 45 moves in the right direction in the figure, so that the amount of contraction of the spring 44 is reduced and the increase of the pressing force F by the spring 44 is suppressed.

  According to the present embodiment, the pressing force F by the spring 44 can be made substantially constant regardless of the thickness of the transfer paper S, and as a result, a high-quality image can be formed. Further, since the transfer paper S is not contacted when the thickness of the transfer paper S is measured, the load on the drive source for transporting the transfer paper S can be reduced.

  Instead of the optical displacement sensor, the paper thickness measuring unit 55 may be provided with a sensor that detects the paper thickness by eddy current.

  In each of the above embodiments, a copying machine has been described as an example of the image forming apparatus. However, the present invention can also be applied to a printer.

1 is an overall configuration diagram of an image forming apparatus according to the present invention. 2A and 2B show a detailed configuration in the vicinity of a secondary transfer roller according to the first embodiment, in which FIG. 4A shows a state in which a thin transfer paper passes through a nip portion, and FIG. FIG. 6 is a detailed configuration diagram in the vicinity of a secondary transfer roller according to Embodiment 2. FIG. FIG. 6 is a detailed configuration diagram in the vicinity of a secondary transfer roller according to Embodiment 3. 1 is a configuration diagram of a main part of an image forming apparatus. The detailed structure of the secondary transfer roller vicinity by a prior art is shown, (a) is a figure which shows a mode that a thin transfer paper passes a nip part, (b) shows a mode that a thick transfer paper passes a nip part. FIG. FIG. 6 is a diagram illustrating that the pressure contact force of the secondary transfer roller varies depending on the presence or absence of transfer paper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Image forming apparatus 27 Drive roller 28-30 Roller 31 Intermediate transfer belt 32-35 Image forming unit 36 Secondary transfer roller 44 Spring 45 Movable wall 46, 50, 55 Paper thickness measuring part 46A Contact 47 Cam S Transfer paper

Claims (4)

An image forming unit including a photoconductor on which a toner image is formed;
An intermediate transfer belt that is wound around a plurality of rollers including a driving roller and to which a toner image formed on the photoconductor is primarily transferred;
An image forming apparatus comprising: a transfer member that is disposed in pressure contact with the intermediate transfer belt and that secondarily transfers a toner image on the intermediate transfer belt onto a transfer sheet that passes through a pressure contact portion between the intermediate transfer belt. And
Measuring means for measuring the thickness of the transfer paper on the upstream side of the pressure contact portion along the transfer paper transport direction;
An image forming apparatus comprising: a control unit configured to control the pressure contact force of the transfer member at the pressure contact portion to be substantially constant based on a measurement result of the measurement unit.   The measuring means has a contact, and the contact is in contact with the transfer paper surface from the direction perpendicular to the transfer direction of the transfer paper, and by detecting the distance that the contact moves at the time of the contact, The image forming apparatus according to claim 1, wherein the thickness of the transfer paper is measured.   The image forming apparatus according to claim 1, wherein the measuring unit is formed integrally with the transfer member. The image forming apparatus according to claim 1, wherein the measuring unit includes an optical distance sensor, and measures the thickness of the transfer paper without contacting the surface of the transfer paper.

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