JP2012098363A - Belt unit and image forming apparatus equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt unit able to prevent damage to a belt while correcting meander and to provide an image forming apparatus equipped with the same.SOLUTION: The belt unit comprises: an endless belt (14) stretched such that the back is engaged with a plurality of rollers; a short roller (16) which is at least one of the plurality of rollers and formed such that the roller length is shorter than the belt width on the back; a meandering force generation mechanism (40) which axially displaces the axis (92) of at least the one of the rollers so that the axis (92) tilts; a detecting means (35) for detecting the edge the belt in its width direction; and a control means (92) for obtaining a target belt position for meander correction based on the detected edge of the belt in its width direction, and running the endless belt by use of the target belt position for the meander correction with respect to the meandering force generation mechanism, thereby correcting the displacement of the endless belt in its width direction. In order to change the position of the contact between the edge portion of the short roller and the back of the belt, the target belt position for meander correction is altered according to the running time of the endless belt.

Description

  The present invention relates to a belt unit that forms an image using a seamless belt and an image forming apparatus equipped with the belt unit.

  In this type of image forming apparatus, an electrophotographic system is used. When the charger precharges the photosensitive drum and the exposure device irradiates light on the surface of the photosensitive drum, the surface of the photosensitive drum is statically exposed. An electrostatic latent image is formed. Further, the developing device carries toner, and when a developing bias voltage is applied, the toner charged in advance adheres to the electrostatic latent image, and a toner image is formed.

Then, the recording material is conveyed to the transfer nip by a pair of rollers arranged on the upstream side of the transfer nip, and the visualized toner image is transferred to the recording material via a seamless belt.
Here, since the meandering of the belt affects the image quality, a technique for correcting the meandering has been proposed (for example, see Patent Documents 1 and 2).

  Specifically, in Document 1, a guide rib is bonded to the back surface of the belt to correct meandering, and in Document 2, at least one of the rollers that stretch the belt is tilted so that the axis of the roller is inclined. Thus, a meandering force in the reverse direction that cancels the meandering force of the belt is generated to prevent meandering of the belt.

JP 2006-251131 A JP 2007-65692 A

By the way, according to the technique of the above-mentioned document 2, even if a strong stress is generated at the end of the guide rib of the above-mentioned document 1, it is possible to prevent peeling due to insufficient adhesive strength, surface cracks caused by using a laminated belt, and the like. .
However, even if the meandering is corrected by changing the axis of the roller shaft, if the belt width is longer than the roller length, the back surface of the belt is scratched at the portion in contact with the edge portion of the roller. There is a problem of entering.

This is because, in the above technique, the belt is driven at a fixed position, in other words, the target belt position for meandering correction is always a constant value, and the belt stress is always in the same place. It is.
In particular, when the belt has a laminated structure using a resin layer having a large Young's modulus on the back surface, an elastic layer having a low Young's modulus in the middle, and a release layer having a thin film and a large Young's modulus as the surface layer In this case, cracks also occur on the surface of the belt, which causes new problems such as a starting point of peeling of the release layer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a belt unit and an image forming apparatus equipped with the belt unit that can solve the above-described problems and prevent the belt from being damaged while performing meandering correction.

  According to a first aspect of the present invention for achieving the above object, an endless belt whose back surface is stretched by being engaged with a plurality of rollers and travels along a predetermined circulation path, and at least one of the plurality of rollers. A short roller whose length is shorter than the belt width on the back surface, a meandering force generating mechanism for changing the axis so that at least one of the plurality of rollers is inclined, and an end in the belt width direction are detected. The endless belt is obtained by obtaining the meandering correction target belt position based on the detecting means and the detected end in the belt width direction, and causing the meandering force generating mechanism to run the endless belt at the meandering correction target belt position. And a control means for correcting the positional deviation in the width direction of the belt, and this control means eliminates the meandering correction target belt position in order to change the contact position between the edge portion of the short roller and the back surface. To change in accordance with the running time of Jo belt.

  According to the first aspect of the invention, the endless belt is stretched with its back surface engaged with the plurality of rollers, and travels along a predetermined circulation path. This belt meandering affects the image quality. Therefore, when meandering can occur, the control means obtains the target belt position for meander correction based on the end of the belt width direction by the detecting means, and outputs a signal to the meandering force generation mechanism. The belt is driven at the target belt position for meander correction. Thereby, the shaft is changed so that the roller shaft is inclined, and the positional deviation in the width direction of the belt can be corrected.

  Here, even when the meandering of the running belt is corrected by changing the axis of the roller, the belt and the roller even if the meandering force generating mechanism is used because the belt width is formed longer than the roller length. If the relative position of the belt always remains constant, the back surface of the belt will be scratched at the point of contact with the edge portion of the roller, while the end of the belt protruding from the edge portion will be slightly drooped. Therefore, since a tensile force is generated at a portion of the surface of the belt opposite to the contact portion with the edge portion, there is a concern that the portion of the surface of the belt is cracked.

  However, the control means of the present invention does not use the unchanged meandering correction target belt position, but changes the meandering correction target belt position in accordance with the travel time of the endless belt. Therefore, the contact position between the edge portion of the roller and the back surface of the belt continues to change, and the location where the stress is concentrated is always changed. As a result, it is possible to prevent damage to the back and front surfaces of the belt.

According to a second aspect of the present invention, in the configuration of the first aspect, the endless belt is provided on the resin layer forming the back surface, the elastic intermediate layer provided on the resin layer, and the intermediate layer. It is characterized by comprising a release layer.
According to the second invention, in addition to the action of the first invention, a resin layer having a large Young's modulus can be obtained by using a belt in which an elastic body is further laminated on a resin film and a release layer is further laminated on the surface layer. In addition, an elastic body having a low Young's modulus and a release layer having a high Young's modulus are stacked, and there is a concern that cracks are particularly likely to enter the surface of the belt, which becomes a starting point for peeling of the release layer. However, if the target belt position for variable meander correction described above is used, cracks on the surface of the belt can be prevented by meander correction.

A third invention is characterized in that, in the configuration of the first invention, the endless belt is a photosensitive belt that develops a latent image on the surface thereof with toner and forms a toner image.
According to the third aspect of the invention, in addition to the action of the first aspect, in the case of the photosensitive belt for forming a toner image, if the above-described variable meander correction target belt position is used, the belt by meander correction is used. Can prevent damage to the back and front of the.

According to a fourth aspect of the invention, in the configurations of the first to third aspects of the invention, the apparatus further comprises bias cleaning means for cleaning the endless belt using electrostatic force.
According to the fourth invention, in addition to the effects of the first to third inventions, the roller length is formed shorter than the belt width, and the bias cleaning means uses electrostatic force around the roller. Even when the endless belt is cleaned, compared to the case where the roller length and the belt width are substantially equal, the current applied from the bias cleaning means is less likely to escape from the edge portion of the roller, and the belt can be reliably cleaned.

The fifth invention is an image forming apparatus equipped with the belt unit of the first to fourth inventions.
According to the fifth aspect of the invention, in addition to the effects of the first to fourth aspects of the invention, a stable image can be obtained over a long period of time by the long-life belt, which contributes to improving the reliability of the image forming apparatus. .

  According to the present invention, it is possible to provide a belt unit capable of preventing the belt from being damaged even when the stress concentration portion of the belt is constantly changed and performing meandering correction, and an image forming apparatus equipped with the belt unit.

1 is a schematic configuration diagram of a printer according to an embodiment. It is a block diagram of the printer of FIG. 1 including a controller. It is a perspective view of the belt unit of FIG. It is explanatory drawing of the edge part of the belt width of FIG. 3, and the edge of a driven roller. It is explanatory drawing of the target belt position of the meander correction | amendment by the target belt position adjustment part of FIG. It is a perspective view which shows an example of a meandering force generation mechanism.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a tandem color printer according to the present embodiment. The right direction in FIG. 1 corresponds to the front of the printer 1 and the left direction corresponds to the back.
As shown in FIG. 1, a sheet (recording material) cassette 3 is arranged at the lower part of the apparatus main body 2, and sheets P before image formation are accommodated in the cassette 3 in a stacked state. Are separated one by one and sent from the cassette 3 toward the front of the printer 1.

  The paper P sent out from the cassette 3 is conveyed toward the back of the printer 1 through the paper conveyance path 4. Inside the apparatus main body 2, a registration roller 5, an image forming unit 6, a secondary transfer unit 17, and a fixing unit 18 are arranged in order on the downstream side when viewed in the paper conveyance direction, and are sent from the fixing unit 18. The paper P is discharged to the paper discharge tray 22 through the paper conveyance path 20.

  The image forming unit 6 and the like described above are electrically connected to a controller (main ECU) 90 (FIG. 2). The controller 90 is an element that functions as a computer, and has hardware resources such as a CPU and a memory. The input port 91 is configured so that image data to be printed can be received from the outside, and this image data is data in which various images such as characters, signs, figures, symbols, diagrams, and patterns are converted into data. is there. Based on this data, the controller 90 executes a predetermined program using hardware resources.

Returning again to FIG. 1, the image forming section 6 of this embodiment includes four image forming units 6 </ b> M, 6 </ b> C, 6 </ b> Y, and 6 </ b> B, and includes a belt unit 30.
These image forming units 6M, 6C, 6Y, and 6B are arranged in order from the back side to the front side of the printer 1, and are provided corresponding to images of four different colors (magenta, cyan, yellow, and black). Magenta, cyan, yellow, and black images are sequentially formed through charging, exposure, development, and transfer processes.

Specifically, each of the image forming units 6M, 6C, 6Y, and 6B is provided with a photosensitive drum 7 that carries a visible image (toner image) of each corresponding color. Each photosensitive drum 7 is rotatably installed with respect to the apparatus main body 2 and is driven counterclockwise in FIG. 1 by a drum motor.
Corresponding chargers 8, exposure units (LED print head units, etc.) 9, developing units 10, primary transfer rollers 12, and rubbing rollers 13 are provided at appropriate positions around the respective photosensitive drums 7. ing.

The charger 8 is disposed on the opposite side of the intermediate transfer roller 12 and uniformly charges the surface of each corresponding photosensitive drum 7. The exposure unit 9 is disposed on the downstream side of the charger 8 as viewed in the rotation direction of the photosensitive drum 7 and irradiates light toward the surface of the corresponding photosensitive drum 7.
The developing device 10 is arranged on the downstream side of the exposure unit 9 when viewed in the rotational direction of the photosensitive drum 7, and magenta, cyan, yellow, and black toners are supplied from the toner containers 11M, 11C, 11Y, and 11B, respectively. The toner of each color is electrostatically attached to the surface of the photosensitive drum 7.

As a result, a toner image corresponding to the electrostatic latent image by the exposure unit 9 is developed on the surface of each photosensitive drum 7. The belt unit 30 has an intermediate transfer belt (endless belt) 14.
The intermediate transfer belt 14 of this embodiment is a seamless belt having no seam, and includes a driving roller 15, a driven roller (short roller) 16, each primary transfer roller 12, and a roller of the secondary transfer unit 17. 1 is run around a plurality of rollers, and the belt motor runs clockwise in FIG.

The intermediate transfer belt 14 is laminated in the order of a resin layer 50, an intermediate layer 51, and a release layer 52, as shown in FIG.
The resin layer 50 forms the back surface 14b of the intermediate transfer belt 14 and is in contact with the driving roller 15 and the driven roller 16 and has a large Young's modulus E with a thickness of about 100 μm (1 μm = 1 × 10 ⁻⁶ m). Consists of resin.

  An elastic intermediate layer 51 having a thickness of about 300 μm and a small Young's modulus E is provided on the resin layer 50. On this intermediate layer 51, for example, urethane having a large Young's modulus E or urethane mixed with PTFE. A release layer 52 having a thickness of about 2 μm is provided. The release layer 52 forms the surface 14 a of the intermediate transfer belt 14 and faces the photosensitive drums 7.

When a voltage having a polarity opposite to that of the toner adhering to the electrostatic latent image on the photosensitive drum 7 is applied to the intermediate transfer roller 12, the toner on the photosensitive drum 7 is separated from the photosensitive drum 7, and the intermediate transfer belt 14. The images are sequentially transferred to the surface 14a and synthesized as a toner image for one page.
Thereafter, when a voltage having a polarity opposite to that of the toner adhering to the electrostatic latent image is applied to the secondary transfer unit 17, the toner image on the intermediate transfer belt 14 is separated from the surface 14 a and is fed from the registration roller 5. The sheet is secondarily transferred to P, and the sheet is sent to the fixing unit 18.

  The rubbing roller 13 in FIG. 1 is disposed on the upstream side of the charger 8 when viewed in the rotational direction of the photosensitive drum 7. The rubbing roller 13 is configured to be able to contact the surface of each corresponding photosensitive drum 7, and is driven counterclockwise in FIG. 1 by a drive motor to polish the surface of the photosensitive drum 7. Yes. The toner remaining on each photosensitive drum 7 is removed by a cleaning unit (not shown).

  1 is a bias cleaning unit (bias cleaning means). The bias cleaning unit 60 is downstream of the secondary transfer position as viewed in the traveling direction of the intermediate transfer belt 14 and upstream of the primary transfer position of each photosensitive drum 7, in this embodiment, the driven roller 16. The remaining toner on the surface 14a after the secondary transfer is performed by contact with the rotationally driven brush-like member 61, which is disposed oppositely, is adsorbed by electrostatic force to clean the surface 14a. . In FIG. 3, the structure of the belt unit 30 is simplified and the primary transfer roller 12 and the rollers of the secondary transfer unit 17 are omitted.

  Since a bias for generating an electrostatic force is applied to the bias cleaning unit 60, the driven roller 16 is driven in the thrust direction of the driven roller 16 (rotation of the roller shaft 42) as shown in FIGS. The roller length, which is the surface length in the axial direction), is shorter than the belt width of the back surface 14b of the intermediate transfer belt 14 (the length of the roller shaft 42 in the rotational axis direction).

  In this embodiment, the meandering force generating mechanism 40 shown in FIG. 2 applies a meandering force to the driven roller 16. The meandering force generating mechanism 40 has various modes, and an example is shown in FIG. The meandering force generating mechanism 40 has a swing arm 43 installed at one end of the roller shaft 42 of the driven roller 16. One end of the roller shaft 42 may be an end portion facing the right side surface of the printer 1 visible in FIG. 3 or an end portion facing the left side surface of the printer 1 on the opposite side.

  The swing arm 43 is composed of a plate-like member, and moves the roller shaft 42 in the vertical direction (substantially orthogonal to the rotation axis direction of the roller shaft 42) indicated by an arrow in FIG. One end of the plate-like swing arm 43 rotatably supports the roller shaft 42, and one end of the bias cleaning unit 60 is also fixed to the swing arm 43. On the other hand, the other end side extends toward the driving roller 15 and is configured to be able to contact the outer peripheral surface of the three-dimensional cam 44 disposed in the vicinity of the driven roller 16. The three-dimensional cam 44 has a cam portion integrally formed on one side surface (the back surface in FIG. 6) of the gear 44a.

Further, an intermediate portion between the one end side and the other end side of the swing arm 43 is pivotally supported on the frame of the belt unit 30, and the swing arm 43 swings around the pivot support portion.
The three-dimensional cam 44 described above is rotated by a motor 45 disposed on the frame. A worm gear 45 a is formed on the output shaft of the motor 45, and the worm gear 45 a meshes with the wheel gear 46. The wheel gear 46 meshes with the idle gear 47, and the idle gear 47 and the gear 44a of the three-dimensional cam 44 mesh with each other. The idle gear 47 is integrally formed with a slit plate 47a, and an optical sensor 48 for detecting the rotation of the slit plate 47a is provided. The slit holes 47b are formed at equal intervals in the circumferential direction of the slit plate 47a, but the interval between the slit holes 47b is different from the other only at one place, and when the motor 45 is rotated in a predetermined direction, the optical sensor It is possible to detect the position from the detection interval of 48 and set the rotation angle of the three-dimensional cam 46 to an arbitrary position using that position as a reference position. When the solid cam 46 rotates, for example, clockwise, the other end side of the swing arm 43 is lowered. As a result, the one end side of the swing arm 43 raises the roller shaft 42.

On the other hand, when the three-dimensional cam 46 rotates counterclockwise, for example, the other end side of the swing arm 43 rises, so that one end side of the swing arm 43 lowers the roller shaft 42.
The meandering force generating mechanism 40 moves one end of the roller shaft 42 up and down by an instruction signal from the controller 90, can change the axis so as to twist the roller shaft 42, and can apply a meandering force to the intermediate transfer belt 14.

The position of the intermediate transfer belt 14 is detected by a belt position detection sensor (detection means) 35.
As shown in FIG. 3, the belt position detection sensor 35 of this embodiment is disposed at one end of the intermediate transfer belt 14 so as to sandwich the front surface 14a and the back surface 14b. The belt position detection sensor 35 has, for example, a light emitting portion and a light receiving portion, and based on the location where the measurement light from the light emitting portion is blocked by the intermediate transfer belt 14 and the location detected by the light receiving portion without being blocked, The position of the end of the intermediate transfer belt 14 is detected.

The detection result of the belt position detection sensor 35 is input to the controller 90, and the target belt position adjustment unit (control unit) 92 in FIG. 2 changes the twist angle of the driven roller 16 so that the intermediate transfer belt 14 is always turned on. Correction can be made to maintain the center.
Specifically, the target belt position adjustment unit 92 outputs a drive signal to the meandering force generation mechanism 40 to cause the intermediate transfer belt 14 to travel at the target belt position for meander correction.

More specifically, in consideration of the detection range of the belt position detection sensor 35, it is assumed that the distance L from the end of the intermediate transfer belt 14 to the edge of the driven roller 16 can be changed within a range of 2 mm to 4 mm ( FIG. 4).
Assuming that the distance L is 3 mm as the target belt position for meandering correction, if the current distance L is 2 mm, the target belt position adjusting unit 92 performs the width direction of the intermediate transfer belt 14. It is determined that a positional deviation of (-1 mm) has occurred.

Here, when it is desired to eliminate the positional deviation of the intermediate transfer belt 14 of −1 mm, the target belt position adjusting unit 92 is set to the target belt position (3 mm) for the meander correction for the meandering force generating mechanism 40. Then, a signal that causes the current distance L to meander in a direction that increases at a stroke by 1 mm is output.
On the other hand, if the current distance L is 4 mm, the target belt position adjustment unit 92 determines that a positional deviation (+1 mm positional deviation) in the width direction of the intermediate transfer belt 14 has occurred.

When it is desired to eliminate the positional deviation of the +1 mm intermediate transfer belt 14, the current distance L is reduced by 1 mm at a stroke so that the meandering force generation mechanism 40 reaches the specified meandering correction target belt position (3 mm). To meander.
Thus, the intermediate transfer belt 14 can travel at the meandering correction target belt position where the distance L from the end of the intermediate transfer belt 14 to the edge of the driven roller 16 is always 3 mm.

As a result, there is no positional shift in the width direction of the intermediate transfer belt 14, and the meandering of the intermediate transfer belt 14 affecting the image quality can be corrected.
However, in this embodiment, the meandering of the intermediate transfer belt 14 is not simply corrected, but the meandering time of the intermediate transfer belt 14 is also provided in order to change the location of the intermediate transfer belt 14 where stress occurs.

Specifically, the target belt position adjusting unit 92 of the present embodiment changes the above-described meandering correction target belt position according to the running time of the intermediate transfer belt 14, and the edge portion of the driven roller 16 and the intermediate transfer The contact position with the back surface 14b of the belt 14 is changed.
In other words, according to the variable meander correction target belt position, a period for meandering the intermediate transfer belt 14 as well as a period for eliminating the meandering of the intermediate transfer belt 14 is positively provided.

  More specifically, if the current distance L is 2 mm, the target belt position adjustment unit 92 determines that a positional deviation of −1 mm has occurred, and causes the meandering force generation mechanism 40 to detect the current distance. Although meandering is performed in the direction of increasing L, the current distance L is not increased at a stroke so that the target belt position for fixed meander correction (3 mm above) is reached, but the target belt position for meander correction is increased by 1000 sheets. Each time it is increased by 0.1 mm.

  That is, since the target belt position for meander correction gradually increases by 0.1 mm, the current distance L until the passage of 1000 sheets is 2.0 mm and the current distance until the passage of 2000 sheets, as shown in FIG. L is 2.1 mm, the current distance L up to 3000 sheets is 2.2 mm, and the increase in the target belt position of the meander correction exceeds the 3 mm position, and the current distance L is 4 mm. Until the number of printed sheets reaches 21,000, it is continued.

  Next, when the current distance L reaches 4 mm, the target belt position adjusting unit 92 determines that a positional deviation of +1 mm has occurred, and causes the meandering force generation mechanism 40 to meander in a direction to reduce the current distance L. However, instead of reducing the current distance L at a stretch so that the target belt position for fixed meander correction (3 mm above) is reached, the target belt position for meander correction is reduced by 0.1 mm every time 1000 sheets have been printed. ing.

  That is, in this case, the target belt position for meander correction gradually decreases by 0.1 mm, so the current distance L up to 21000 sheets is 4.0 mm, the current distance L up to 22000 sheets is 3.9 mm, The current distance L until 23,000 sheets has elapsed is 3.8 mm, and the decrease in the target belt position of the meander correction exceeds the 3 mm position until the current distance L reaches 2 mm. This is continued until the number of printed sheets reaches 41,000.

Thereafter, the increase and decrease of the target belt position for meandering correction are repeated, and the contact position between the edge portion of the driven roller 16 and the back surface 14b of the intermediate transfer belt 14 is changed.
As described above, the target belt position adjusting unit 92 of this embodiment prompts the meandering force generation mechanism 40 to cancel the meandering as the current distance L approaches the position of 3.0 mm, and the intermediate transfer belt. 14 is eliminated. However, as the current distance L moves away from the position of 3.0 mm, the meandering force generation mechanism 40 is urged to meander, and a positional deviation occurs in the width direction of the intermediate transfer belt 14.

  In the printer 1 equipped with the belt unit 30 described above, the paper P is separated and sent from the cassette 3 one by one, and the paper P reaches the registration roller 5. The registration roller 5 corrects the oblique feeding of the paper P and feeds the paper P toward the secondary transfer unit 17 while measuring the timing of the image transfer operation by each of the photosensitive drums 7 and the intermediate transfer roller 12. .

In the printer 1, the laser beam irradiation by the exposure unit 9 is controlled. As a result, an electrostatic latent image of a document image is created on each photoconductive drum 7 in the image forming unit 6, and then a toner image is formed on each photoconductive drum 7 from this latent image.
Subsequently, the toner images on the photosensitive drum 7 are superimposed on the intermediate transfer belt 12 (primary transfer), and are secondarily transferred to the paper P by the secondary transfer unit 17. The sheet P is fed toward the fixing unit 18 with an unfixed toner image carried thereon, and after a desired image is formed, the sheet P is discharged to the sheet discharge tray 22 through the sheet conveyance path 20.

In the above-described embodiment, the intermediate transfer belt 14 has been described. However, the endless belt of the present invention may be applied to a photosensitive belt.
Specifically, the photosensitive belt has an organic photosensitive layer on the surface thereof, and a charger, an exposure unit, a developing device, and the like are provided at appropriate positions around the photosensitive belt. The toner image synthesized on the photosensitive layer of the photosensitive belt is transferred to a sheet via a drum-shaped intermediate transfer member.

Even in the case of the photosensitive belt for forming the toner image, damage to the back surface or the surface of the photosensitive belt can be prevented by using the above-described variable meandering correction target belt position.
As described above, according to this embodiment, the intermediate transfer belt 14 is stretched with the back surface 14b engaged with the surfaces of a plurality of rollers including the driving roller 15, the driven roller 16, and the like. The toner image is primarily transferred, and then secondarily transferred onto the paper P. The meandering of the intermediate transfer belt 14 affects the image quality.

  Therefore, if meandering can occur, the target belt position adjusting unit 92 obtains the target belt position for meander correction based on the end of the belt position detection sensor 35 in the belt width direction, and sends a signal to the meandering force generation mechanism 40. When output, the meandering force generating mechanism 40 causes the intermediate transfer belt 14 to travel at the meandering correction target belt position. As a result, the axis of the driven roller 16 is changed so that the roller shaft 42 is inclined, and the positional deviation in the width direction of the intermediate transfer belt 14 can be corrected.

  Here, even when the meandering of the intermediate transfer belt 14 is corrected by changing the axis of the roller shaft 42, since the belt width is formed longer than the roller length of the driven roller 16, the meandering force is generated. Even if the mechanism 40 is used, if the relative position between the intermediate transfer belt 14 and the driven roller 16 is always constant, the back surface 14b of the intermediate transfer belt 14 is damaged at a position in contact with the edge portion of the driven roller 16. There is a concern. Further, the end portion of the intermediate transfer belt 14 protruding from the edge portion of the driven roller 16 hangs down slightly, and a tensile force is generated in a portion of the surface 14 a opposite to the contact portion with the edge portion of the driven roller 16. Therefore, there is also a concern that a crack will enter the surface 14a.

  However, the target belt position adjusting unit 92 of the present embodiment does not use the unchanged meandering correction target belt position, but changes the meandering correction target belt position according to the running time of the intermediate transfer belt 14. Therefore, the contact position between the edge portion of the driven roller 16 and the back surface 14b of the intermediate transfer belt 14 is continuously changed, and the location where the stress is concentrated is always changed. As a result, damage to the back surface 14b and the front surface 14a of the intermediate transfer belt 14 can be prevented, and a long-life intermediate transfer belt 14 can be provided.

  Further, when the intermediate transfer belt 14 in which the elastic intermediate layer 51 is laminated on the resin layer 50 of the resin film and the release layer 52 is further laminated on the surface layer is used, the resin layer 50 having a large Young's modulus, A low elastic intermediate layer 51 and a thin film release layer 52 having a large Young's modulus are stacked, and the surface 14a of the intermediate transfer belt 14 is particularly susceptible to cracks, and the release layer 52 is peeled off. There are concerns such as starting point. This is because tension is generated on the surface 14a of the intermediate transfer belt 14 from the inside of the intermediate transfer belt 14, and a larger tensile force can be generated on the surface 14a. However, if the above-described variable meander correction target belt position is used, cracks on the surface 14a of the intermediate transfer belt 14 can be prevented by meander correction.

  Furthermore, the roller length of the driven roller 16 is shorter than the belt width. Even if the bias cleaning unit 60 cleans the intermediate transfer belt 14 using electrostatic force around the driven roller 16, the roller length Compared to the case where the belt width is substantially equal, the current applied from the bias cleaning unit 60 is less likely to escape from the edge portion of the driven roller 16, and the intermediate transfer belt 14 can be reliably cleaned.

Furthermore, since a stable image can be obtained over a long period of time by the long-life belt, it contributes to improving the reliability of the printer 1.
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. For example, a part of the configuration of the above embodiment can be omitted or arbitrarily combined so as to be different from the above.

  For example, in the above embodiment, the length of the driven roller 16 is shortened. However, the length of the driven roller 16 is not necessarily limited to this form, and when the driving roller 15 and the tension roller are provided according to the installation position of the bias cleaning unit, The length of the tension roller or the like may be shortened. The meandering force generating mechanism 40 may also change the axis of a roller shaft such as the drive roller 15 in addition to changing the axis so that the roller shaft 42 of the driven roller 16 is twisted.

Further, in the above embodiment, an example in which the image forming apparatus is embodied in a printer is shown. However, the image forming apparatus of the present invention is naturally applicable to a multifunction machine, a copier, a facsimile machine, and the like.
In either case, the belt can be prevented from being damaged while the meandering correction is performed in the same manner as described above.

1 Printer (image forming device)
14 Intermediate transfer belt (endless belt)
16 Followed roller (short roller)
30 Belt unit 35 Belt position detection sensor (detection means)
40 Meandering force generation mechanism 42 Roller shaft 50 Resin layer 51 Intermediate layer 52 Release layer 60 Bias cleaning unit (bias cleaning means)
90 controller 92 target belt position adjustment unit (control means)

Claims (5)

An endless belt whose back surface is stretched by engaging with a plurality of rollers and travels along a predetermined circulation path;
A short roller in which at least one of the plurality of rollers has a length shorter than a belt width of the back surface;
A meandering force generating mechanism for changing the axis so that at least one of the plurality of rollers is inclined;
Detecting means for detecting an end in the belt width direction;
A meandering correction target belt position is obtained based on the detected end in the belt width direction, and the endless belt is caused to travel at the meandering correction target belt position with respect to the meandering force generating mechanism. A control means for correcting a positional deviation in the width direction of the belt,
This control means changes the meandering correction target belt position according to the travel time of the endless belt so as to change the contact position between the edge portion of the short roller and the back surface. . The belt unit according to claim 1,
The endless belt is composed of a resin layer forming the back surface, an intermediate layer of an elastic body provided on the resin layer, and a release layer provided on the intermediate layer. Belt unit to be used. The belt unit according to claim 1,
The endless belt is a belt unit that develops a latent image on a surface thereof with toner and forms a toner image. The belt unit according to any one of claims 1 to 3,
A belt unit further comprising bias cleaning means for cleaning the endless belt using electrostatic force.   An image forming apparatus comprising the belt unit according to claim 1.

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