JP2005326532A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for preventing conveyance inferiority of a cardboard without enlarging deformation of a transfer outer roller by suppressing abnormal images generated in a secondary transfer when forming images on thin paper. <P>SOLUTION: The representative configuration of the image forming apparatus comprises an intermediate transfer belt 3 comprising an endless belt member, a transfer outer roller 5 for transferring toner images on the intermediate transfer belt 3 on a sheet, a transfer inner roller 4 arranged inside the intermediate transfer belt 3 and opposed to the transfer outer roller 5, and a moving roller 51 arranged in an upstream side of a rotation direction of the intermediate transfer belt 3 more than the inside of the intermediate transfer belt 3 and the transfer inner roller 4. The nip of the transfer outer roller 5 and the transfer inner roller 4 can modify an orbit of the intermediate transfer belt 3 of the upstream side more than the nip by moving the moving roller 51. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer, and more particularly to an image forming apparatus provided with an intermediate transfer belt made of an endless belt member.

  Conventionally, in an image forming apparatus such as a color copying machine or a color laser beam printer, an intermediate transfer belt made of an endless belt member has been used as disclosed in Japanese Patent Application Laid-Open No. 8-328348 (Patent Document 1). There is something.

  FIG. 4 is a cross-sectional view of a conventional image forming apparatus. In the image forming apparatus 100 shown in FIG. 4, a latent image is formed on the photosensitive drum 101 by the laser unit 102. The latent image is developed by the developing unit 103, and a toner image of each color is formed. Each time a toner image of each color is formed, it is primarily transferred onto the intermediate transfer belt 104 in a superimposed manner. The intermediate transfer belt 104 is stretched around a driving roller 105, a transfer inner roller 106, and a tension roller 107. An outer transfer roller 108 is disposed at a position facing the inner transfer roller 106 with the intermediate transfer belt 104 interposed therebetween. A transfer bias is applied to the outer transfer roller 108, and the toner images on the intermediate transfer belt 104 are secondarily transferred collectively to the sheet S fed by the pair of conveying rollers 109.

JP-A-8-328348

  As a problem in the conventional image forming apparatus, there is an abnormal image generated in the secondary transfer unit. FIG. 5 is an enlarged explanatory view of a conventional secondary transfer portion.

  The first problem is that before the toner image on the intermediate transfer belt 104 is transferred to the sheet at the secondary transfer portion T2 (nip portion between the transfer inner roller 106 and the transfer outer roller 108), the charge of the toner image is transferred outside the transfer. This is a phenomenon in which air discharges toward the roller 108. As a result, white portions are formed in the transferred image.

  This phenomenon varies depending on the rigidity of the sheet. As shown in FIG. 5A, when a sheet is sandwiched between the transfer inner roller 106 and the transfer outer roller 108 in a highly rigid paper (thick paper S1), the rigidity of the sheet causes a nip line D (secondary transfer). (Tangent at portion T2). Accordingly, since the thick paper S1 is close to the intermediate transfer belt 104 immediately before the secondary transfer portion T2, it is difficult to discharge in the air and occurrence of image defects can be suppressed.

  On the other hand, as shown in FIG. 5B, in the case of paper with a low rigidity (thin paper S2), the sheet is conveyed so as to follow a line E connecting the secondary transfer portion T2 and the nip of the conveying roller pair 109. The For this reason, the gap between the sheet and the intermediate transfer belt 104 is increased immediately before the secondary transfer portion T2. Accordingly, the charge on the intermediate transfer belt 104 is easily discharged in the air, and the transferred image is whitened.

  As a countermeasure against the image defect, for example, a configuration as shown in FIG. FIG. 5C shows a configuration in which the sheet is conveyed to the secondary transfer unit from the lower part in the drawing toward the upper part in the drawing. The intermediate transfer belt 104 is suspended by an inner transfer roller 106, a driven roller 110, and a driving roller (not shown) disposed on the inner side. The outer transfer roller 108 made of an elastic member is pressed toward the inner transfer roller 106 by a pressing spring 111. Then, the driven roller 110 is arranged so as to protrude from the nip line D to the outer transfer roller 108 side so that the intermediate transfer belt surface 104a before entering the secondary transfer portion T2 is on the outer transfer roller 108 side. It is composed. As a result, since the sheet comes into contact with the intermediate transfer belt surface 104a in advance and then enters the secondary transfer portion T2, it is possible to prevent image defects due to aerial discharge immediately before the secondary transfer portion T2.

  However, in the configuration shown in FIG. 5C, the intermediate transfer belt surface 104 a is positioned on the transfer outer roller 108 side with respect to the nip line D. The problem that becomes smaller will occur. When the pressure of the outer transfer roller 108 is reduced, there is no particular problem with paper with a low rigidity (thin paper S2), but with paper with a high rigidity (thick paper S1), there is a possibility that the conveyance force is insufficient and a conveyance failure occurs.

  Therefore, it is conceivable to strengthen the pressing spring 111 so that the thick paper S1 can be conveyed. However, since the outer transfer roller 108 is made of an elastic member, a high pressure is always applied to the outer transfer roller 108, and the position in contact with the inner transfer roller 106 at the time of stoppage is crushed and deformed. If secondary transfer is performed with the outer transfer roller 108 deformed, an image defect or a conveyance defect occurs. Therefore, strengthening the pressing spring 111 is not preferable because it leads to a large deformation of the outer transfer roller 108.

  Accordingly, the present invention provides an image forming apparatus capable of suppressing abnormal images generated in the secondary transfer unit when forming an image on thin paper and preventing a conveyance failure of thick paper without increasing the deformation of the outer transfer roller. The purpose is to do.

  In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an intermediate transfer belt formed of an endless belt member, and an outer transfer roller that transfers a toner image on the intermediate transfer belt to a sheet. A transfer inner roller disposed on the inner side of the intermediate transfer belt and facing the outer transfer roller, and a movement disposed on the inner side of the intermediate transfer belt and on the upstream side of the inner transfer roller in the rotational direction of the intermediate transfer belt. A roller, and by moving the moving roller, the trajectory of the intermediate transfer belt upstream of the nip portion can be changed at the nip portion between the outer transfer roller and the inner transfer roller. To do.

  According to the present invention, the trajectory of the intermediate transfer belt immediately before the secondary transfer portion is variable with respect to the nip line formed by the inner transfer roller and the outer transfer roller. Thereby, it is possible to suppress a transfer failure when an image is formed on thin paper. Further, it is possible to suppress the conveyance failure of the thick paper without increasing the transfer pressure.

  Embodiments of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating the overall configuration of the image forming apparatus according to the present embodiment, FIG. 2 is a diagram illustrating a state of a secondary transfer unit when transporting thin paper, and FIG. 3 is a secondary when transporting thick paper. It is a figure explaining the state of a transfer part. In this embodiment, the image forming apparatus is a copying machine using an electrophotographic system, and includes a reader unit A above the printer unit B.

  Image information read by the reader unit A is converted into an electronic signal and sent to the printer unit B. The printer unit B includes an intermediate transfer belt 3 made of an endless belt member that travels in the direction of arrow X.

  The intermediate transfer belt 3 is suspended by a driving roller 62, an inner transfer roller 4, a driven roller 55, and a tension roller 51. Although the operation of the tension roller 51 will be described later, the solid line position in the figure indicates the position when the sheet is thin paper S2 (see FIG. 2), and the one-dot chain line position indicates the position when the sheet is thick paper S1. (See FIG. 3).

  Four image forming portions Pa, Pb, Pc, and Pd having substantially the same configuration are arranged on the upper portion of the intermediate transfer belt 3, and each forms a toner image of each color of yellow, magenta, cyan, and black. . The configuration of the image forming unit Pa will be described as an example.

  The image forming portion Pa includes a photosensitive drum 1a that is rotatably arranged. A primary charger 42a, a developing device 43a, and a cleaning device 41a are arranged around the photosensitive drum 1a. The photosensitive drum 1a is uniformly charged by the primary charger 42a, and based on the electronic signal from the reader unit A, the light emitting elements such as Y, M, C, and Bk lasers and LEDs emit light. An electrostatic latent image is formed on the body drum 1a. Subsequently, yellow toner is supplied from the developing device 43a, and the electrostatic latent image is developed as a yellow toner image.

  When the toner image arrives at the primary transfer portion T1 where the photosensitive drum 1a and the intermediate transfer belt 3 come into contact with the rotation of the photosensitive drum 1a, a transfer bias is applied from the primary transfer roller 44a, and yellow The toner image is transferred to the intermediate transfer belt 3. The intermediate transfer belt 3 carrying the yellow toner image is conveyed to the next image forming unit Pb. By this time, the magenta toner image has been formed on the photosensitive drum 1b in the image forming unit Pb by the same method as described above. The magenta toner image is primarily transferred so as to overlap the yellow toner image.

  Similarly, as the intermediate transfer belt 3 advances to the image forming portions Pc and Pd along the arrow X direction, the cyan toner image and the black toner image are superimposed and transferred onto the above-described toner images in the respective transfer portions T1. On the other hand, the sheet S sent out from the feeding cassette 27 is conveyed to the secondary transfer portion T2. By applying a transfer bias to the outer transfer roller 5, the above-described four color toner images are transferred onto the sheet S. A fixing device 22 is arranged on the downstream side of the secondary transfer portion T2 in the sheet conveying direction, and heat and pressure are applied to fix the toner image on the sheet S as a permanent image. The sheet S on which the toner image is fixed is discharged to the discharge unit 25 by the discharge roller pair 24.

  In this embodiment, an image forming apparatus having four image forming units is described. However, as long as the intermediate transfer belt is used, the present invention can be applied to an image forming apparatus including a single photosensitive drum using a rotary developing device as in the conventional example shown in FIG. it can.

  The present embodiment aims to prevent abnormal images of thin paper and poor conveyance of thick paper by changing the trajectory of the intermediate transfer belt 3 at the secondary transfer portion. Below, this characteristic part is demonstrated. FIG. 2 is an explanatory diagram of the secondary transfer unit when transporting thin paper, and FIG. 3 is an explanatory diagram of the secondary transfer unit when transporting thick paper.

  The sheet S is conveyed by registration rollers 7 and 8 that are driven by a driving source (not shown), passes between the first pre-secondary transfer guide 11 and the second pre-secondary transfer guide 12, and is subjected to the secondary transfer. To the department. In the secondary transfer portion, the toner image on the intermediate transfer belt 3 is transferred to the sheet S by the transfer inner roller 4 and the transfer outer roller 5. The outer transfer roller 5 is pressed against the inner transfer roller 4 by a pressure spring 10.

  A tension roller 51 as an example of a moving roller is rotatably attached to a bearing 56. The bearing 56 is urged toward the intermediate transfer belt 3 by a tension spring 53 as an example of urging means, and applies a predetermined tension via the tension roller 51. The lever 52 as an example of the guide member supports the bearing 56 of the tension roller 51 so as to be movable in the urging direction, and is supported so as to be rotatable about the shaft 52a. The lever 52 is rotatable to two positions using a motor 54 as an example of a driving means as a driving source.

  Accordingly, when the motor 54 is driven to rotate the lever, the tension roller 51 moves, and the trajectory of the intermediate transfer belt 3 can be moved within that range. Even if the position of the tension roller 51 is changed, the tension applied to the intermediate transfer belt 3 is constant, so the length of the intermediate transfer belt 3 is also constant. Accordingly, the lever 52 rotates about the shaft 52a, but the movement locus of the tension roller 51 draws a part of an ellipse focusing on the inner transfer roller 4 and the driving roller 62 (see FIG. 1). Become.

  The image forming apparatus having the above configuration has two switching modes in this embodiment. One is a thick paper transport mode, and the other is a thin paper transport mode. The switching between the two may be designated by the user, or it may be determined whether the sheet is thick paper or thin paper by automatic detection means for automatically detecting the sheet during the conveyance pass.

  In the thin paper transport mode, as shown in FIG. 2, the lever 52 is rotated by rotating the motor 54 by a predetermined amount, and the tension roller 51 is moved toward the outer transfer roller 5 for positioning. As a result, the trajectory of the intermediate transfer belt 3 is changed toward the outer side of the intermediate transfer belt 3 with respect to the nip line D (tangent to the nip portion) between the outer transfer roller 5 and the inner transfer roller 4. That is, the position of the intermediate transfer belt surface 3 a is on the transfer outer roller 5 side with respect to the nip line D.

  In this way, by changing the path of the intermediate transfer belt so as to be close to the sheet conveyance path, the thin paper S2 conveyed by the registration rollers 7 and 8 comes into contact with the intermediate transfer belt surface 3a in advance before the secondary transfer unit. You will enter T2. Accordingly, there is no gap between the intermediate transfer belt 3 and the thin paper S2 immediately before the nip portion, and the charge on the intermediate transfer belt 3 is not discharged in the air, so that it is possible to suppress an image defect in which the transferred image is white.

  In the thick paper transport mode, as shown in FIG. 3, the lever 54 is rotated by rotating the motor 54 by a predetermined amount in the reverse direction, and the tension roller 51 is moved inward of the belt for positioning. Accordingly, the track of the intermediate transfer belt 3 is moved toward the transfer inner roller 4 with respect to the nip line D. That is, the position of the intermediate transfer belt surface 3 a is on the transfer inner roller 4 side with respect to the nip line D.

  Here, in the thin paper conveyance mode, the intermediate transfer belt 3 is slightly wound around the outer transfer roller 5, and the contact length is long. Since the biasing force of the pressure spring 10 is supported by the reaction force of the transfer inner roller 4 and the elasticity of the intermediate transfer belt 3, the load is dispersed and the pressure is reduced. On the other hand, in the thick paper transport mode, the intermediate transfer belt 3 is wound only on the inner transfer roller 4, so that the contact length between the outer transfer roller 5 and the intermediate transfer belt 3 is shortened. The contact length is the length of the nip where the outer transfer roller 5 made of an elastic member is deformed by the urging force of the pressure spring 10. Since the urging force of the pressure spring 10 is supported only by the reaction force from the transfer inner roller 4, the pressure does not decrease.

  In this manner, by shortening the contact length of the outer transfer roller 5 with respect to the intermediate transfer belt 3, it is possible to secure the pressure to be held without increasing the urging force of the pressure spring 10, so that the thick paper S1 is reliably conveyed. It becomes possible to do. Further, since the biasing force of the pressure spring 10 is not increased, the deformation of the outer transfer roller 5 is not increased.

  In the above embodiment, the tension roller 51 is used as the moving roller. However, the present invention is not limited to this, and a tension roller only for tensioning the intermediate transfer belt may be provided, and a moving roller for changing the belt trajectory may be provided separately.

  The present invention can be used as an image forming apparatus using an intermediate transfer belt.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure explaining the state of the secondary transfer part at the time of conveying thin paper. It is a figure explaining the state of the secondary transfer part at the time of conveying a thick paper. It is sectional drawing of the conventional image forming apparatus. It is an enlarged explanatory view of a conventional secondary transfer portion.

Explanation of symbols

Pa to Pd Image forming section S Sheet S1 Thick paper S2 Thin paper T1 Primary transfer section T2 Secondary transfer section 1a Photosensitive drum 3 Intermediate transfer belt 3a Intermediate transfer belt surface 4 Transfer inner roller 5 ... Outside transfer roller 7 ... Registration roller 8 ... Registration roller
10… Pressure spring
51… Tension roller
52… Lever
52a axis
53… Tension spring
54… Motor
55… driven roller
56… Bearings
62… Drive roller

Claims (5)

An intermediate transfer belt made of an endless belt member;
An outer transfer roller for transferring the toner image on the intermediate transfer belt to a sheet;
An inner transfer roller disposed inside the intermediate transfer belt and facing the outer transfer roller;
A moving roller disposed inside the intermediate transfer belt and on the upstream side in the rotation direction of the intermediate transfer belt with respect to the inner transfer roller,
An image forming apparatus characterized in that, by moving the moving roller, an orbit of the intermediate transfer belt upstream of the nip portion can be changed at a nip portion between the outer transfer roller and the inner transfer roller. By moving the moving roller, the trajectory of the intermediate transfer belt can be changed to the outer transfer roller direction or the inner transfer roller direction with respect to the tangent line of the nip portion between the outer transfer roller and the inner transfer roller. The image forming apparatus according to claim 1, wherein: When the sheet to be conveyed is thick paper, the moving roller is moved to move the track of the intermediate transfer belt toward the inner transfer roller with respect to the tangent line of the nip portion between the outer transfer roller and the inner transfer roller. The image forming apparatus according to claim 2, wherein: When the sheet to be conveyed is thin paper, by moving the moving roller, the track of the intermediate transfer belt moves in the direction of the outer transfer roller with respect to the tangent line of the nip portion between the outer transfer roller and the inner transfer roller. The image forming apparatus according to claim 2, wherein: Biasing means for biasing the moving roller toward the intermediate transfer belt;
A guide member that supports the moving roller so as to be movable in an urging direction;
Drive means for rotating the guide member,
2. The trajectory of the intermediate transfer belt is changed without changing the tension of the intermediate transfer belt by moving the moving roller by driving the driving means and rotating the guide member. The image forming apparatus described.

Images