JP4784218B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that is used in a printer, a copying machine, a facsimile, or the like and forms an image on a recording medium through an intermediate transfer member by an electrophotographic method.

In an electrophotographic image forming apparatus used for a printer, a copying machine, a facsimile, etc., an electrostatic latent image formed on the surface of a photosensitive drum as an image carrier is visualized (toner image) by toner development, Further, this toner image is transferred to a recording medium such as recording paper to obtain an image.
In recent years, a plurality of color toner images sequentially formed on a photosensitive drum are superimposed on an endless belt-like intermediate transfer belt as an intermediate transfer member, and then transferred to a recording medium and fixed for full color printing. An image forming apparatus that outputs an image is also widespread (see, for example, Patent Document 1).

A color image forming apparatus using an intermediate transfer belt includes a four-cycle method for sequentially forming toner images of different colors using a single photosensitive drum, and a tandem method having a photosensitive drum for forming toner images of different colors. There is. In either method, the basic arrangement and function of the intermediate transfer belt are the same.
The intermediate transfer belt is stretched around a plurality of rollers, contacts a photosensitive drum as an image carrier, and a toner image is transferred to the intermediate transfer belt. It is provided so as to rotate around a path around the secondary transfer portion to be transferred. Then, the toner images of different colors formed on the photosensitive drum are sequentially superimposed and transferred in the primary transfer portion, and the toner images are secondarily transferred to the recording paper in the secondary transfer portion.

  As described above, in an image forming apparatus including an intermediate transfer belt to which toner images of a plurality of colors are transferred in a multiple manner, in order to obtain a high-quality image with no color misregistration, a route defined by the intermediate transfer belt is high. It is necessary to go around with high accuracy. On the other hand, the intermediate transfer belt expands and contracts due to environmental changes such as temperature and humidity. For this reason, a tension stabilizing mechanism that absorbs expansion and contraction of the intermediate transfer belt and maintains the tension constant is provided.

FIG. 5 is a conceptual configuration diagram of an example of a color image forming apparatus provided with a tension stabilizing mechanism using an intermediate transfer belt and a tension roll. FIG. 6 is an enlarged view of a portion where the tension stabilizing mechanism is disposed.
The color image forming apparatus 80 shown in the figure is a four-cycle system (developing apparatus is not shown) that sequentially forms toner images of different colors using a single photosensitive drum 81.
In this configuration, a primary transfer roll 83A (primary transfer unit 83), an idle roll 84, a tension roll 85A (tension stabilization mechanism 85), and a secondary transfer backup roll 86B are rotated clockwise from the drive roll 82 located at the right end in the drawing. A (secondary transfer portion 86) is disposed, and the intermediate transfer belt 87 is stretched around these rolls.
The drive roll 82 is connected to a drive motor (not shown). Then, it is driven to rotate by a drive motor, thereby driving the intermediate transfer belt 87 to rotate clockwise in the figure.

The primary transfer roll 83 </ b> A is opposed to the photosensitive drum 81 with the intermediate transfer belt 87 interposed therebetween, and this is the primary transfer unit 83. Further, a secondary transfer roll 86A is disposed opposite to the secondary transfer backup roll 86B across the intermediate transfer belt 87, and this is the secondary transfer portion 86. The secondary transfer unit 86 is supplied with a recording sheet guided and conveyed by a recording sheet conveyance guide 88.
The idle roll 84 is disposed downstream of the primary transfer portion 83 in the moving direction of the intermediate transfer belt 87. Thus, the path of the intermediate transfer belt 87 from the drive roll 82 to the idle roll 84 through the primary transfer portion 83 is defined.

  The tension stabilizing mechanism 85 rotatably supports the tension roll 85A by a tension arm 85B that is urged to swing counterclockwise in the drawing by a tension spring 85C. The tension roll 85A is positioned between the idle roll 84 and the secondary transfer portion 86, and presses the intermediate transfer belt 87 between the two from the inner peripheral side to the outside with a predetermined force. Maintain a constant tension. In this way, by providing the tension stabilizing mechanism 85 between the idle roll 84 and the secondary transfer unit 86, when the secondary transfer unit 86 bites the recording paper or discharges the recording paper, It is possible to prevent image disturbance caused by a change in tension caused by a change in conditions being transmitted to the primary transfer portion 83.

The tension arm 85B is formed in an L shape in which the support arm portion 85Ba and the operation arm portion 85Bb are substantially orthogonal, and is pivotally attached to the chassis fixed to the frame of the color image forming apparatus 80 at the corner portion by the swing shaft 85D. Has been. The tension roll 85A is rotatably supported by the tip of the support arm portion 85Ba, and the operation arm portion 85Bb is pressed by the elastic return force of the tension spring 85C, and is oscillated and biased counterclockwise in the drawing.
Here, the swing shaft 85 </ b> D around which the tension arm 85 </ b> B is pivotally attached to the chassis is set at a position adjacent to the path between the idle roll 84 and the intermediate transfer belt 87. The support arm portion 85Ba is provided along the path of the intermediate transfer belt 87 from the idle roll 84 to the tension roll 85A.

In such a tension stabilizing mechanism 85, the tension arm 85B is urged to swing counterclockwise in the drawing by the tension spring 85C. Then, the tension roller 85A presses the intermediate transfer belt 87 by the swinging urging force, and acts to keep the tension of the intermediate transfer belt 87 constant. For example, when the intermediate transfer belt 87 is extended from the standard state shown by the solid line in FIG. 6, the tension arm 85B swings counterclockwise in the drawing as shown by the two-dot chain line in the drawing, and the tension Is granted.
The tension roll 85A is substantially orthogonal to the orbit of the intermediate transfer belt 87 that connects the idle roll 84 and the secondary transfer portion 86 by the swing of the tension arm 85B, as indicated by the one-dot chain line and the two-dot chain line in FIG. Move in the direction you want. For this reason, the pressing force of the tension spring 85C acts to efficiently press the intermediate transfer belt 87, and the rotation path of the intermediate transfer belt 87 can be greatly changed by the small swing angle of the tension arm 85B.

JP 2002-91185 A

  However, in the tension stabilizing mechanism 85 configured as described above, the approach angle of the intermediate transfer belt 87 to the secondary transfer portion 86 is greatly changed by the movement of the tension roll 85A for tension adjustment. On the other hand, the path of the recording paper supplied to the secondary transfer unit 86 is defined by the recording paper conveyance guide 88 and does not change. As a result, the wrap angle at the secondary transfer portion 86 of the intermediate transfer belt 87 in the secondary transfer portion 86 changes, and the relative supply angle of the recording paper to the intermediate transfer belt 87 also changes. Cause problems.

That is, due to a change in the wrap angle of the intermediate transfer belt 87 to the secondary transfer portion 86, the image quality deteriorates due to gap discharge or the like.
In addition, the recording paper supplied to the secondary transfer unit 86 first comes into contact with the intermediate transfer belt 87 and is then sandwiched between the intermediate transfer belt 87 and the secondary transfer roll 86A. Thereafter, the recording paper and the intermediate transfer belt 87 are bitten between the secondary transfer roll 86A and the secondary transfer backup roll 86B, and the intermediate transfer belt 87 is applied by the action of the transfer bias applied to the secondary transfer roll 86A. The toner image is transferred from the toner image. However, since the approaching angle of the intermediate transfer belt 87 to the secondary transfer portion 86 changes due to the action of the tension stabilizing mechanism 85, the contact position of the recording paper to the intermediate transfer belt 87 is not constant. . As a result, when the contact angle of the recording paper to the intermediate transfer belt 87 is increased, streak-like disturbances and color shifts occur in the image due to the impact at the time of contact.

Further, the distance of the intermediate transfer belt 87 to the recording paper conveyance guide 88 also changes due to the change in the angle of entry of the intermediate transfer belt 87 into the secondary transfer portion 86 by the action of the tension stabilizing mechanism 85. For this reason, when the distance increases, the trailing edge of the recording sheet jumps as soon as it is released from the recording sheet conveyance guide 88, and the impact and the impact of the intermediate transfer belt 87 cause toner scattering, thereby disturbing the image. Arise.
If an idle roll is added between the tension roll 85 </ b> A of the tension stabilizing mechanism 85 and the secondary transfer unit 86, the approach angle of the intermediate transfer belt 87 to the secondary transfer unit 86 can be changed. It can be configured to be constant regardless. By doing so, the above-mentioned problems are solved, but in that case, the cost is increased and the size of the apparatus is increased.

  The present invention has been made to solve the technical problems as described above, and the object of the present invention is to adjust the tension of the intermediate transfer member without changing the entry angle to the secondary transfer portion. It is an object of the present invention to provide an image forming apparatus that can be performed and that can prevent problems caused by changes in the angle of entry of an intermediate transfer member into a secondary transfer portion.

  For this purpose, the image forming apparatus according to the present invention includes an image carrier that carries a toner image, a primary transfer portion that contacts the image carrier and the toner image is transferred from the image carrier, and the toner image as a recording medium. An intermediate transfer member that rotates in a path through a secondary transfer portion that transfers to the intermediate transfer member, and a tension adjustment member that is positioned on the inner peripheral side of the intermediate transfer member upstream of the secondary transfer portion in the movement direction of the intermediate transfer member. And a tension adjusting mechanism that adjusts the tension of the intermediate transfer member by moving the tension adjusting member substantially parallel to the path of the intermediate transfer member entering the secondary transfer portion.

  Here, for example, the tension adjusting mechanism supports the tension adjusting member by a swingable arm member, and the tension adjusting member is substantially parallel to the entry path of the intermediate transfer member to the secondary transfer portion by the swing of the arm member. Configured to move. The arm member may further include an urging unit that urges the arm member to swing toward the side where the tension adjusting member is separated from the secondary transfer portion. Furthermore, the tension adjusting member is a roll member, and is rotatably supported by the arm member.

  In addition, another image forming apparatus of the present invention includes an image carrier that carries a toner image, a primary transfer portion that contacts the image carrier and the toner image is transferred from the image carrier, and transfers the toner image to a recording medium. An intermediate transfer member that rotates around a path that passes through the secondary transfer portion, a tension adjustment member that is positioned on the inner peripheral side of the intermediate transfer member upstream of the secondary transfer portion in the movement direction of the intermediate transfer member, and a tension adjustment member And a straight line that passes through the tension adjusting member and the swing fulcrum of the arm member is substantially orthogonal to the entry path of the intermediate transfer member to the secondary transfer portion. It is characterized by being set.

  According to the image forming apparatus of the present invention, it is possible to suppress a change in the approach angle of the intermediate transfer member to the secondary transfer portion due to the adjustment of the tension of the intermediate transfer member, and the intermediate transfer member enters the secondary transfer portion. Problems caused by changes in angle can be suppressed.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a diagram conceptually illustrating the overall configuration of an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in the figure is a digital color printer using a rotary (rotary) developing device.
An image forming apparatus 10 is formed on a photosensitive drum 11 that is rotatably arranged in a clockwise direction in the figure and a photosensitive drum 11 that is rotatable in a clockwise direction in the figure. Further, an intermediate transfer belt 30 as an intermediate transfer member to which each color component toner image is sequentially transferred (primary transfer) by the primary transfer unit 20 is provided. The intermediate transfer belt 30 includes a tension stabilizing mechanism 70 on the inner side of the circulation track. In addition, the image forming apparatus 10 includes a secondary transfer unit 40 that batch-transfers (secondary transfer) the toner image transferred onto the intermediate transfer belt 30 to the recording paper P, and the secondary transferred image on the recording paper. And a fixing device 50 for fixing the toner image on P. Further, a recording paper transport mechanism 60 that transports the recording paper P via the secondary transfer unit 40 and the fixing device 50 is provided.

Although not shown, around the photosensitive drum 11, along with its rotating direction, a charging device that charges the photosensitive drum 11 to a predetermined potential, and the photosensitive drum 11 charged by the charging device is electrostatically exposed by exposure. And a laser exposure device for writing a latent image.
A rotary developing device 12 is provided downstream of the laser exposure device in the rotation direction of the photosensitive drum 11. The rotary developing device 12 includes developing devices 12Y, 12M, 12C, and 12K that respectively store yellow, magenta, cyan, and black color component toners. The developing units 12Y, 12M, 12C, and 12K visualize the electrostatic latent image on the photosensitive drum 11 with each toner (toner image).

A primary transfer roll 21 is provided on the downstream side in the rotation direction of the photosensitive drum 11 from the rotary developing device 12 so as to face the photosensitive drum 11 with the intermediate transfer belt 30 interposed therebetween. The primary transfer roll 21 is given a predetermined primary transfer bias and transfers the toner image carried on the photosensitive drum 11 to the intermediate transfer belt 30. This is the primary transfer unit 20.
A cleaning device (not shown) for removing residual toner on the photosensitive drum 11 after the primary transfer is provided on the downstream side of the primary transfer roll 21 in the rotation direction of the photosensitive drum 11.

  The intermediate transfer belt 30 is formed into an endless belt having a thickness of, for example, 0.1 mm and a predetermined width by using a material that contains carbon black as a conductive agent in resin, rubber, or the like and has an appropriate volume resistivity. Has been. Then, the primary transfer roll 21, the idle roll 32, the tension adjusting member of the tension stabilizing mechanism 70, the tension roll 71 as the roll member, the secondary transfer, which are arranged clockwise from the drive roll 31 located at the right end in the figure. It is stretched around the backup roll 42.

The drive roll 31 is connected to a drive motor (not shown). Then, it is driven to rotate by a drive motor, thereby driving the intermediate transfer belt 30 to rotate in the clockwise direction in the drawing.
The idle roll 32 is disposed downstream of the primary transfer unit 20 in the moving direction of the intermediate transfer belt 30. Thus, the path of the intermediate transfer belt 30 from the drive roll 31 to the idle roll 32 through the primary transfer unit 20 is always defined to be constant.

  The tension stabilizing mechanism 70 rotatably supports a tension roll 71 with a tension arm 72 as an arm member that is oscillated and biased by a tension spring 73 as a biasing means. The tension roll 71 is located between the idle roll 32 and the secondary transfer unit 40, and presses the intermediate transfer belt 30 between the two from the inner peripheral side to the outside with a predetermined force, and the tension is kept constant. maintain. The tension stabilizing mechanism 70 will be described later in detail.

  A secondary transfer roll 41 is provided at a position facing the secondary transfer backup roll 42 across the intermediate transfer belt 30. This is the secondary transfer unit 40 that transfers the toner image carried by the intermediate transfer belt 30 onto the recording paper P. A predetermined potential difference is required between the secondary transfer backup roll 42 and the secondary transfer roll 41 in order to transfer the toner image carried by the intermediate transfer belt 30 onto the recording paper P. For example, one secondary transfer When the roll 41 is connected to a high voltage, the other opposing secondary transfer backup roll 42 is grounded. The secondary transfer unit 40 is supplied with a recording sheet P that is transported along a path defined by a recording sheet transport guide 64.

Further, a belt cleaner (not shown) is provided facing the intermediate transfer belt 30 in the vicinity of the drive roll 31. The belt cleaner scrapes off and removes residual toner on the intermediate transfer belt 30 after the secondary transfer.
The secondary transfer roll 41 and the belt cleaner are provided so as to be able to contact and separate from the intermediate transfer belt 30. When forming a color (multiple color) image, the secondary transfer roll 41 and the belt cleaner are separated from the intermediate transfer belt 30 until the toner image before the final color passes.

  The fixing device 50 includes a heat roll 51 that heats the toner image formed on the recording paper P, and a pressure roll 52 provided to face the heat roll 51. The pressure roll 52 presses the recording paper P against the heated heat roll 51 and fixes the toner image on the recording paper P by heating and pressing.

  The recording paper transport mechanism 60 includes a paper feed cassette 61 that stores the recording paper P, a feed roll 62 that feeds the recording paper P from the paper feed cassette 61, and a registration roll that transports the recording paper P at a timing for transfer. 63. Further, a recording paper conveyance guide 64 that forms a conveyance path is provided. Further, a discharge roll 65 for driving to discharge the recording paper P after being fixed by the fixing device 50 is provided.

Then, the image forming apparatus 10 configured as described above forms an image by the following process.
First, the photosensitive drum 11 and the intermediate transfer belt 30 start rotating, and an electrostatic latent image is written on the surface of the photosensitive drum 11 charged to a predetermined potential by the charging device by the laser exposure device. Thereafter, the electrostatic latent image is developed by any one of the corresponding developing devices 12Y, 12M, 12C, and 12K. The toner image formed on the photosensitive drum 11 is transferred to the intermediate transfer belt 30 by the primary transfer bias applied to the primary transfer roll 21 in the primary transfer unit 20.
When a color image is formed by superimposing a plurality of color toner images, the toner image formation and primary transfer steps are repeated for the number of colors. On the other hand, the intermediate transfer belt 30 rotates with the same period as the photosensitive drum 11 while holding the primary transferred toner image, and holds the toner images of the respective colors in an overlapping manner.

  The toner image primarily transferred to the intermediate transfer belt 30 in this way is conveyed to the secondary transfer unit 40 as the intermediate transfer belt 30 rotates. In synchronization with this, the recording paper P is fed from the paper feed cassette 61 by the feed roll 62 and is supplied to the secondary transfer section 40 by the registration roll 63 at a predetermined timing. In the secondary transfer unit 40, the secondary transfer roll 41 nips the recording paper P with respect to the intermediate transfer belt 30 (secondary transfer backup roll 42). The toner image carried on the intermediate transfer belt 30 is electrostatically transferred (secondary transfer) to the recording paper P by the action of the secondary transfer electric field formed between the secondary transfer roll 41 and the secondary transfer backup roll 42. Transcribed). The recording paper P on which the toner image is transferred is discharged after the toner image is fixed by the fixing device 50. The toner remaining on the intermediate transfer belt 30 that has passed through the secondary transfer portion 40 is removed by a belt cleaner.

Next, the tension stabilizing mechanism 70 which is a main part of the present embodiment will be described in detail.
FIG. 2 is an enlarged view showing the tension stabilizing mechanism 70, and FIG. FIG. 4 is a diagram for explaining the concept of adjusting the tension without changing the approach path of the intermediate transfer belt 30 to the secondary transfer unit 40.
As described above, the tension stabilizing mechanism 70 is a tension roll 71 as a roll member, a tension arm 72 as an arm member that supports the tension roll 71, and an urging means that urges the tension arm 72 to swing. A tension spring 73 is used.

The tension arm 72 is formed in an L shape in which the support arm portion 72A and the operation arm portion 72B are substantially orthogonal, and a pivot shaft is attached to a chassis (not shown) fixed to the frame of the image forming apparatus 10 at the corner portion. It is pivotally attached at 74. A tension roll 71 is rotatably mounted on the tip of the support arm portion 72A. Further, the operation arm portion 72B is pressed and urged by the elastic return force of the tension spring 73, and is oscillated and urged counterclockwise in the drawing.
The tension roll 71 is set to a position where a path directly connecting the idle roll 32 and the secondary transfer backup roll 42 is bent outward by a predetermined amount when the intermediate transfer belt 30 is in a set reference length (hereinafter referred to as a standard state). Has been. Thereby, the position of the tension roll 71 defines the entry path of the intermediate transfer belt 30 to the secondary transfer unit 40.
In the standard state indicated by the solid line in FIG. 2, the operation arm portion 72 </ b> B has a substantially vertical posture, and the tip thereof is pressed by the elastic return force of the tension spring 73.

Here, the pivot point (swinging shaft 74) of the tension arm 72 is such that the tension arm 72 swings around the swinging shaft 74, so that the supporting tension roll 71 performs intermediate transfer to the secondary transfer unit 40. The belt 30 is set to move substantially along the approach path of the belt 30.
That is, the tension arm 72 has a straight line (indicated by a long and short dashed line in FIG. 3) connecting the rotation center of the tension roll 71 and the center of the swing shaft 74 and the intermediate transfer belt 30 to the secondary transfer unit 40. The angle θ formed with the approach path is set so that the tension roll 71 in FIG. 3 has a substantially right angle (θ≈90 °) in a standard state indicated by a solid line. The length of the support arm portion 72A (the distance from the rotation center of the tension roll 71 to the swing shaft 74) is set as large as possible. As a result, the tension roller 71 moves along a path closer to a straight line along the approach path of the intermediate transfer belt 30 to the secondary transfer unit 40 by the swing of the tension arm 72 about the swing shaft 74. It is like that.

That is, ideally, as shown in FIG. 4, if the tension roll 71 is linearly moved in the direction along the entry path 30S of the intermediate transfer belt 30 to the secondary transfer unit 40, the secondary transfer unit The change in the length of the intermediate transfer belt 30 can be absorbed and the tension can be kept constant without changing the entry path 30S of the intermediate transfer belt 30 to 40 at all. The positions of the tension arm 72 and the swing shaft 74 are set so that the tension roll 71 moves along a locus approximate to this as much as possible.
Needless to say, the tension roll 71 may be configured to move linearly as shown in FIG. 4 without using the swinging tension arm 72.

In the tension stabilizing mechanism 70 configured as described above, when the intermediate transfer belt 30 expands and contracts due to the influence of temperature and humidity, the tension arm 72 swings due to the pressing biasing force of the tension spring 73, and the intermediate transfer belt 30. It acts to absorb changes in length and maintain a constant tension.
That is, when the intermediate transfer belt 30 is extended from the standard state shown by the solid line in FIG. 2, the tension arm 72 swings counterclockwise in the figure by the pressing biasing force of the tension spring 73, and the two-dot chain line in FIG. As shown in FIG. 8, the tension roll 71 is separated from the secondary transfer portion 40. As a result, the stretch path of the intermediate transfer belt 30 that has become longer is absorbed, and the tension is maintained constant.

On the other hand, when the intermediate transfer belt 30 contracts from the standard state, the tension arm 72 swings clockwise in the figure against the pressing biasing force of the tension spring 73, and the tension roll 72 as shown by the one-dot chain line in the figure. 71 is close to the secondary transfer unit 40. The tension path of the intermediate transfer belt 30 shortened thereby is absorbed, and the tension is kept constant.
As described above, regardless of whether the intermediate transfer belt 30 is extended or contracted, the tension roll 71 moves substantially along the entry path of the intermediate transfer belt 30 from the standard state to the secondary transfer unit 40, and the intermediate transfer belt 30 Absorb 30 length changes to keep the tension constant. For this reason, the change in the angle of entry of the intermediate transfer belt 30 to the secondary transfer unit 40 can be suppressed to an extremely small level.

Accordingly, it is possible to prevent problems caused by changes in the wrap angle at the secondary transfer portion 40 of the intermediate transfer belt 30 and changes in the supply angle of the recording paper P with respect to the intermediate transfer belt 30.
That is, there is no deterioration in image quality due to gap discharge or the like due to a change in the wrap angle at the secondary transfer portion 40 of the intermediate transfer belt 30. Further, since the change in the approach angle of the intermediate transfer belt 30 to the secondary transfer portion 40 is small, the contact position of the recording paper P with the intermediate transfer belt 30 can be maintained substantially constant. Accordingly, there is no image streaking or color deviation caused by the increase in the contact angle of the recording paper P to the intermediate transfer belt 30, toner scattering or image distortion due to the trailing edge of the recording paper jumping up. Is. In addition, an idle roll is added between the tension roll 71 of the tension stabilizing mechanism 70 and the secondary transfer unit 40, and the angle of entry of the intermediate transfer belt 30 into the secondary transfer unit 40 acts on the tension stabilizing mechanism 70. However, as in the case where it is constant, there is no increase in cost and size of the apparatus.

  By the way, in the tension stabilizing mechanism 70 of this configuration, the swing angle of the tension arm 72 necessary to absorb the change in the length of the intermediate transfer belt 30 is slightly increased, and the elastic return force of the tension spring 73 is intermediate. The conversion efficiency into the pressing force of the transfer belt 30 decreases. However, this can be solved by increasing the pressing force of the tension spring 73.

  In this embodiment, the present invention is applied to a color image forming apparatus using a rotary developing device. However, the target image forming apparatus is not limited to this, and includes an intermediate transfer belt. Needless to say, the present invention may be applied to, for example, a monochrome copying machine.

1 is a diagram conceptually illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is an enlarged view which shows a tension stabilization mechanism. It is operation | movement explanatory drawing of a tension stabilization mechanism. FIG. 5 is a diagram for explaining a concept of adjusting tension without changing an approach path of an intermediate transfer belt to a secondary transfer unit. It is a conceptual block diagram of an example of the color image forming apparatus provided with the tension | tensile_strength stabilization mechanism by the tension roll as a prior art example. It is an enlarged view of the arrangement | positioning site | part of the tension roll as a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 11 ... Photosensitive drum (image carrier), 20 ... Primary transfer part, 30 ... Intermediate transfer belt (intermediate transfer member), 40 ... Secondary transfer part, 70 ... Tension stabilization mechanism, 71 ... Tension roll (tension adjusting member: roll member), 72 ... tension arm (arm member), 73 ... tension spring (biasing means)

Claims (5)

An image carrier for carrying a toner image;
A first roll member that forms a primary transfer portion to which a toner image is transferred from the image carrier, and a second roll member that forms a secondary transfer portion that transfers the toner image to a recording medium, and is rotatable An intermediate transfer belt that is stretched around a third roll member and rotates so as to pass through the first roll member, the third roll member, and the second roll member in this order;
An arm member provided so as to be swingable about a swing fulcrum, and supporting the third roll member so that the intermediate transfer belt bends toward the outer peripheral side of the intermediate transfer belt ;
A straight line connecting the rotation center of the third roll member and the swing fulcrum of the arm member and a surface of the intermediate transfer belt passing through the third roll member and before contacting the second roll member. The angle is less than 90 degrees when the length of the intermediate transfer belt is the first length, and the length of the intermediate transfer belt is the second length shorter than the first length. And an urging unit that urges the third roll member against the intermediate transfer belt via the arm member so that the angle is greater than 90 degrees . The intermediate transfer belt contacts the intermediate transfer belt from the inside of the intermediate transfer belt on the downstream side in the movement direction of the intermediate transfer belt from the first roll member and on the upstream side in the movement direction of the intermediate transfer belt from the third roll member. The image forming apparatus according to claim 1, further comprising a fourth roll member that spans the intermediate transfer belt together with the first roll member, the second roll member, and the third roll member. apparatus. The surface of the intermediate transfer belt before passing through the fourth roll member and in contact with the third roll member, and the intermediate transfer belt before passing through the third roll member and in contact with the second roll member The image forming apparatus according to claim 2, wherein an angle formed by the surface is an obtuse angle. Opposite the outer peripheral surface of the intermediate transfer belt before passing through the third roll member and coming into contact with the second roll member, the distance from the intermediate transfer belt becomes shorter as the secondary transfer portion is approached. The image forming apparatus according to claim 1, further comprising a guide member provided to guide the recording material to the secondary transfer unit. The image forming apparatus according to claim 1, wherein the swing fulcrum of the arm member is located on an inner peripheral side of the intermediate transfer belt.

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