JP2013061532A - Belt driving device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably correct the meandering of an endless belt by a simple mechanism.SOLUTION: An intermediate transfer unit 50 includes: an intermediate transfer belt 51 which does not have elasticity; an intermediate transfer belt tension roller 54; a shaft member 21; deviation transmitting members 25A and 25B; and energizing members 26A and 26B. The deviation transmitting members 25A and 25B are inserted in the shaft member 21 so as to be respectively adjacent to both end portions in an axial direction 101 of the intermediate transfer belt tension roller 54. The deviation transfer member disposed at least on a downstream side in a deviation direction along the axial direction 101 of the deviation transmitting member 25A and 25B, moves along the shaft member 21 with the intermediate transfer belt 51. The energizing members 26A and 26B are journaled by the deviation transmitting members 25A and 25B at action end portions, and journaled by device frames 22A and 22B at base end portions at predetermined positions on the end portion side in the axial direction 101 rather than the action end portions.

Description

  The present invention relates to a belt driving device that rotates an endless belt stretched around a plurality of stretch rollers, and an image forming apparatus including the belt drive device.

  For example, some electrophotographic image forming apparatuses include an endless belt such as an intermediate transfer belt, a secondary transfer belt, and a fixing belt. As a belt driving device for rotating such an endless belt, a plurality of stretching rollers arranged in parallel to each other for stretching the endless belt are provided, and the driving roller of the stretching rollers is driven to rotate the endless belt. What is to be known is known. The belt driving device has a problem that the endless belt meanders due to a variation in the outer diameter of the tension roller due to a manufacturing error or a deviation in parallelism between the tension rollers due to an installation error. Particularly in an image forming apparatus, meandering of an endless belt adversely affects image quality, so it is important to suppress the meandering of an endless belt as much as possible.

  As a technique for suppressing the meandering of the endless belt, an electric control system is known in which a deviation amount of the endless belt is detected by a sensor and a meandering correction roller is moved in accordance with a detection signal. However, the electrical control system has a problem that the number of components is increased, the configuration is complicated, and the cost is increased by including a sensor, an electrical circuit, a drive motor, and the like.

  Therefore, a technique is known in which meandering of the endless belt is suppressed by adjusting the tension of the endless belt using a mechanical mechanism without using a sensor (see, for example, Patent Document 1). In the prior art described in Patent Document 1, the tension roller is pivotally supported by the arm member. The arm member is rotatable along the traveling direction of the endless belt, and is biased to the downstream side in the traveling direction of the endless belt by a spring. Belt contact portions are provided on both ends of the tension roller. When the endless belt meanders, the endless belt comes into contact with the belt contact portion. As the contact width between the endless belt and the belt contact portion increases, the frictional force received by the belt contact portion increases. Therefore, the tension roller rotates by this frictional force and the biasing force of the spring, and the tension of the endless belt is increased. Is intended to increase.

JP-A-2005-162466

  However, in the prior art described in Patent Document 1, the rotational direction of the arm member for increasing the tension of the endless belt is the same as the traveling direction of the endless belt. When the frictional force received by the contact portion increases, the arm member falls over the top due to the running force of the endless belt and falls downstream in the running direction of the endless belt, and the tension applied to the endless belt by the tension roller becomes extremely weak. The tension of the endless belt may not be adjusted. In order to prevent the arm member from exceeding the top, various settings such as the strength of the spring, the length and the mass of the arm member are difficult, and it is difficult to stably correct the meandering of the endless belt.

  An object of the present invention is to provide a belt driving device capable of stably correcting meandering of an endless belt with a simple mechanism, and an image forming apparatus including the belt driving device.

  The belt driving device of the present invention includes an endless belt that does not have elasticity, a plurality of stretching rollers, a shaft member, a displacement transmission member, and an urging member. The tension roller stretches the endless belt. The tension roller includes a drive roller that rotates the endless belt and a tension roller that can freely change the tension of the endless belt. The shaft member rotatably supports the tension roller, and both end portions thereof can move independently in a direction in which the tension of the endless belt is changed. The offset transmission member is inserted into the shaft member so as to be adjacent to both end portions in the axial direction of the tension roller. The offset transmission member disposed at least downstream in the offset direction along the axial direction of the endless belt among the offset transmission members moves in the offset direction along with the offset of the endless belt. The urging member has an elastic force that urges the shaft member in a direction in which the tension of the endless belt is increased. The urging member is pivotally supported by the offset transmission member at the working end, and is pivotally supported by the apparatus frame at a predetermined position on the end side in the axial direction from the working end.

  In this configuration, the urging member is inclined and arranged in a direction approaching the offset transmission member as it goes from the end side to the center side in the axial direction of the tension roller. When the endless belt meanders and shifts to one side in the axial direction, the offset transmission member on the downstream side in the offset direction moves along the axial direction. As a result, the inclination angle of the biasing member on the downstream side in the offset direction with respect to the axial direction of the tension roller approaches perpendicular, and the degree of contraction of the biasing member increases. For this reason, on the downstream side of the endless belt in the axial direction of the tension roller, the pressing force of the urging member against the offset transmission member is increased, and the tension of the endless belt is increased. Since the endless belt that does not have stretchability has a property of moving from a stronger tension to a weaker tension, the meandering of the endless belt is corrected.

  Further, a meandering amount of the endless belt is corrected by a simple mechanism without requiring a sensor or an electric circuit for detecting a deviation amount of the endless belt.

  Further, since the rotation direction around the base end portion of the urging member is different from the traveling direction of the endless belt, the urging member is rotated by the running force of the endless belt even if the deviation amount of the endless belt is increased. There is nothing. Therefore, the tension applied to the endless belt by the tension roller does not become extremely weak against the intention. For this reason, the meandering of the endless belt can be corrected stably.

  In the above-described configuration, it is preferable that the offset transmission member disposed on the upstream side in the offset direction moves in the offset direction along with the offset of the endless belt. As a result, the inclination angle of the upstream biasing member in the offset direction approaches the axial direction of the tension roller, and the degree of contraction of the biasing member is reduced. For this reason, on the upstream side in the offset direction of the endless belt in the axial direction of the tension roller, the pressing force of the urging member against the offset transmission member becomes small, and the tension of the endless belt becomes weak. Since the endless belt that does not have stretchability has a property of moving from a stronger tension to a weaker tension, the effect of correcting the meandering of the endless belt becomes larger.

  Further, it is preferable that the offset transmission member includes a diameter-expanding member whose diameter is larger than that of the tension roller, and the diameter-expanding member is rotatably supported by the shaft member. Since the diameter-expanding member is rotatable, friction with the diameter-expanding member of the endless belt is reduced, and wear at both ends of the endless belt is reduced.

  Furthermore, the offset transmission member further includes a sliding member whose rotation about the shaft member is restricted on the end side of the diameter-expanding member in the axial direction, and the working end portion of the biasing member is slid It can comprise so that it may be supported by the member. The working end is pivotally supported by the sliding member whose rotation is restricted, so that the biasing member's arrangement and contraction degree are stable when the offset amount of the endless belt is a certain value, and the tension of the endless belt Is stable.

  Further, it is preferable that the surface including the rotation locus centering on the base end portion of the urging member and the traveling direction of the endless belt at the portion in pressure contact with the tension roller are orthogonal to each other. Thereby, even if the deviation amount of the endless belt increases, the biasing member is more reliably prevented from rotating by the running force of the endless belt. Therefore, the tension applied to the endless belt by the tension roller does not become extremely weak against the intention. For this reason, the meandering of the endless belt can be corrected stably.

  The biasing member has one end fixed to one of the first bracket pivotally supported by the offset transmission member, the second bracket pivotally supported by the apparatus frame, the first bracket, and the second bracket. It is preferable to have a mandrel inserted through the other bracket so as to be displaceable, and an elastic member disposed between the first bracket and the second bracket. Since the elastic member contracts along the mandrel, the direction of the elastic force does not distort even when the degree of contraction increases. For this reason, the meandering of the endless belt can be corrected stably.

  The image forming apparatus according to the present invention includes the belt driving device having any one of the above-described configurations. On the downstream side of the endless belt in the axial direction of the tension roller, the pressing force of the urging member against the offset transmission member is increased and the tension of the endless belt is increased, so that the meandering of the endless belt is corrected. Further, a meandering amount of the endless belt is corrected by a simple mechanism without requiring a sensor or an electric circuit for detecting a deviation amount of the endless belt. Further, since the rotation direction around the base end portion of the urging member is different from the traveling direction of the endless belt, the urging member is rotated by the running force of the endless belt even if the deviation amount of the endless belt is increased. There is nothing. For this reason, the meandering of the endless belt can be corrected stably.

  According to the present invention, meandering of the endless belt in the belt driving device can be corrected stably with a simple mechanism.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including an intermediate transfer unit according to an embodiment of a belt driving device of the present invention. 2 is an enlarged view of a part of the image forming apparatus. FIG. FIG. 3 is a side sectional view of an intermediate transfer unit. FIG. 4 is a diagram illustrating a state where an intermediate transfer belt is offset toward the back side. FIG. 4 is a diagram illustrating a state where an intermediate transfer belt is offset toward the front side.

  Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the image forming apparatus 100 forms a single-color or multicolor image on a sheet based on image data generated from a document or image data input from the outside. Examples of the paper include recording media such as plain paper, photographic paper, and OHP film.

  The image forming apparatus 100 includes an image reading unit 120, an image forming unit 110, a paper feed unit 80, and a paper discharge unit 90.

  The image reading unit 120 reads an image of a document, generates image data, and supplies the image data to the image forming unit 110.

  The image forming unit 110 includes an exposure unit 3, four image forming stations 31, 32, 33, 34, an intermediate transfer unit 50, a secondary transfer unit 60, and a fixing device 70, and performs image forming processing on a sheet.

  The intermediate transfer unit 50 includes an intermediate transfer belt 51, an intermediate transfer belt drive roller 52, an intermediate transfer belt driven roller 53, and an intermediate transfer belt tension roller 54. The intermediate transfer belt drive roller 52, the intermediate transfer belt driven roller 53, and the intermediate transfer belt tension roller 54 are arranged in parallel to each other. As the intermediate transfer belt 51, a resin film having no stretchability such as polyimide is used. The intermediate transfer belt 51 is an endless belt, and is stretched between the intermediate transfer belt driving roller 52 and the intermediate transfer belt driven roller 53 to form a loop-shaped movement path. The tension of the intermediate transfer belt 51 can be changed by the intermediate transfer belt tension roller 54. Each of the intermediate transfer belt driving roller 52, the intermediate transfer belt driven roller 53, and the intermediate transfer belt tension roller 54 is a tension roller that stretches the intermediate transfer belt 51.

  Based on the image data, the image forming unit 110 forms an image of black and toner images of four hues of cyan, magenta, and yellow, which are three subtractive primary colors obtained by color separation of a color image. Formed at stations 31-34. The image forming stations 31 to 34 are arranged in a line along the movement path of the intermediate transfer belt 51. The image forming stations 32 to 34 are configured in substantially the same manner as the image forming station 31.

  The black image forming station 31 includes a photosensitive drum 1, a charger 2, a developing device 4, an intermediate transfer roller 5, and a cleaner unit 6.

  The photosensitive drum 1 is an electrostatic latent image carrier, and rotates in a predetermined direction when a driving force is transmitted from a driving source (not shown). The charger 2 charges the peripheral surface of the photosensitive drum 1 to a predetermined potential.

  The exposure unit 3 irradiates the respective photosensitive drums 1 of the image forming stations 31 to 34 with laser beams modulated by image data of hues of black, cyan, magenta, and yellow. On the peripheral surfaces of the four photosensitive drums 1, electrostatic latent images based on image data of each hue of black, cyan, magenta, and yellow are formed.

  The developing device 4 supplies black toner, which is the hue of the image forming station 31, to the peripheral surface of the photosensitive drum 1, and visualizes the electrostatic latent image into a toner image.

  The outer peripheral surface of the intermediate transfer belt 51 faces the four photosensitive drums 1 in order. An intermediate transfer roller 5 is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 51 interposed therebetween. Each of the positions where the intermediate transfer belt 51 and the photosensitive drum 1 face each other is a primary transfer position.

  A primary transfer bias is applied to the intermediate transfer roller 5 by constant voltage control with a toner charging polarity (for example, minus) and a reverse polarity (for example, plus). The same applies to the image forming stations 32-34. As a result, the toner images of the respective colors formed on the respective photosensitive drums 1 are sequentially transferred to the outer peripheral surface of the intermediate transfer belt 51 so as to be primarily transferred, and a full-color toner image is formed on the outer peripheral surface of the intermediate transfer belt 51. .

  However, when image data of only a part of the hues of black, cyan, magenta, and yellow is input, only the part of the four photosensitive drums 1 corresponding to the hue of the input image data is static. An electrostatic latent image and a toner image are formed, and only a partial toner image is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 51.

  The cleaner unit 6 collects the toner remaining on the peripheral surface of the photosensitive drum 1 after the primary transfer.

  The toner image primarily transferred to the outer peripheral surface of the intermediate transfer belt 51 at each primary transfer position is rotated by the intermediate transfer belt 51 and the secondary transfer belt 61 provided in the secondary transfer unit 60 and the intermediate transfer belt 51. Is conveyed to a secondary transfer position which is a position opposite to.

  The paper feed unit 80 includes a paper feed cassette 81, a manual feed tray 82, a first paper transport path 83, and a second paper transport path 84. Paper is stored in each of the paper feed cassette 81 and the manual feed tray 82. The first paper transport path 83 is formed so as to reach the paper discharge unit 90 from each of the paper feed cassette 81 and the manual feed tray 82 via the secondary transfer position and the fixing device 70. The second paper conveyance path 84 is a paper conveyance path for double-sided printing, and is formed so that the paper on which an image is formed on one side is conveyed again to the secondary transfer position with the front and back sides reversed. Yes.

  The secondary transfer unit 60 includes a secondary transfer roller 62 in addition to the secondary transfer belt 61. The secondary transfer roller 62 is in pressure contact with the intermediate transfer belt driving roller 52 with a predetermined nip pressure across the secondary transfer belt 61 and the intermediate transfer belt 51. In order to maintain the nip pressure between the secondary transfer roller 62 and the intermediate transfer belt 51 at a predetermined value, either the secondary transfer roller 62 or the intermediate transfer belt drive roller 52 is made of a hard material (for example, metal or resin). The other is made of a soft material (for example, elastic rubber or foamable resin).

  When the sheet passes through the secondary transfer position, a secondary transfer bias having a toner charging polarity (for example, minus) and a reverse polarity (for example, plus) is applied to the secondary transfer roller 62 by constant voltage control. Thus, the toner image carried on the outer peripheral surface of the intermediate transfer belt 51 is secondarily transferred to the paper.

  The toner remaining on the intermediate transfer belt 51 after the toner image is transferred to the paper is collected by the intermediate transfer belt cleaning unit 55.

  The sheet on which the toner image is transferred is sent to the fixing device 70. The fixing device 70 includes a fixing roller 71 and a pressure roller 72. The fixing device 70 performs a fixing process for firmly fixing the toner image on the paper by heating and pressurizing the paper by rotating the paper between the fixing roller 71 and the pressure roller 72.

  The paper discharge unit 90 includes a paper discharge tray 91 and a paper discharge roller 92. The sheet on which the toner image has been fixed is discharged to a discharge tray 91 by a discharge roller 92. The paper is stored in the paper discharge tray 91 with the surface on which the toner image is fixed facing down.

  As shown in FIG. 2, in the traveling direction of the intermediate transfer belt 51, between the black image forming station 31 and the intermediate transfer belt driving roller 52 arranged on the most downstream side among the image forming stations 31 to 34, A pre-transfer charger (PTC) 56 is disposed. The pre-transfer charger 56 faces the outer peripheral surface of the intermediate transfer belt 51. A counter roller 57 is disposed so as to face the pre-transfer charger 56 with the intermediate transfer belt 51 interposed therebetween. The pre-transfer charger 56 adjusts the charge amount of the toner constituting the toner image carried on the outer peripheral surface of the intermediate transfer belt 51 before the secondary transfer. This improves the image quality of the toner image transferred to the paper.

  The secondary transfer unit 60 includes a secondary transfer belt driving roller 63, a secondary transfer belt driven roller 64, and a secondary transfer belt tension roller 65 in addition to the secondary transfer belt 61 and the secondary transfer roller 62. The secondary transfer belt 61 is an endless belt. As the secondary transfer belt 61, a rubber material having elasticity is used.

  Each of the secondary transfer roller 62, the secondary transfer belt drive roller 63, the secondary transfer belt driven roller 64, and the secondary transfer belt tension roller 65 is a tension roller that stretches the secondary transfer belt 61. The tension of the secondary transfer belt 61 can be changed by the secondary transfer belt tension roller 65.

  As shown in FIG. 3, the intermediate transfer belt tension roller 54 that stretches the intermediate transfer belt 51 is supported by the shaft member 21 so as to be rotatable about the shaft member 21 and slidable along the shaft member 21. ing. The shaft member 21 is supported by the apparatus frames 22A and 22B so that both ends can be independently moved in the direction in which the tension of the intermediate transfer belt 51 is changed, that is, in the vertical direction in FIG. The shaft member 21 is restricted from rotating. As an example, in FIG. 3, the left side is the front surface F side of the image forming apparatus 100, and the right side is the back surface R side of the image forming apparatus 100.

  In the axial direction 101 of the intermediate transfer belt tension roller 54, diameter expanding members 23A and 23B are arranged so as to be adjacent to both ends of the intermediate transfer belt tension roller 54, respectively. In the axial direction 101, the end of each of the enlarged diameter members 23A and 23B farther from the intermediate transfer belt tension roller 54 is larger in diameter than the intermediate transfer belt tension roller 54, and the other parts are The diameter is the same as that of the intermediate transfer belt tension roller 54. The diameter-expanding members 23 </ b> A and 23 </ b> B are inserted into the shaft member 21, are slidable in the axial direction 101, and are rotatably supported by the shaft member 21.

  Sliding members 24A and 24B are disposed on the end sides of the diameter-expanding members 23A and 23B in the axial direction 101, respectively. The sliding members 24A and 24B are inserted into the shaft member 21 so as to be adjacent to the diameter-expanding members 23A and 23B, respectively, and are slidable in the axial direction 101. The sliding members 24A and 24B are restricted from rotating around the shaft member 21. The enlarged diameter member 23A and the sliding member 24A constitute one offset transmission member 25A, and the enlarged diameter member 23B and the sliding member 24B constitute the other offset transmission member 25B.

  The intermediate transfer unit 50 further includes urging members 26A and 26B. The biasing member 26A includes a first bracket 261A, a second bracket 262A, a mandrel 263A, and an elastic member 264A. The first bracket 261A is pivotally supported by the sliding member 24A. The second bracket 262A is pivotally supported by the apparatus frame 22A at a predetermined position on the end side in the axial direction 101 with respect to the pivot point of the first bracket 261A. That is, the base end portion of the biasing member 26A is pivotally supported by the apparatus frame 22A at a predetermined position on the end side in the axial direction 101 with respect to the working end portion.

  The mandrel 263A has one end fixed to one of the first bracket 261A and the second bracket 262A, and is inserted through the other bracket so as to be displaceable. As an example, the mandrel 263A has one end fixed to the second bracket 262A and is inserted through the first bracket 261A so as to be displaceable. The elastic member 264A is disposed between the first bracket 261A and the second bracket 262A. Since the elastic member 264A expands and contracts along the mandrel 263A, the direction of the elastic force does not distort even if the degree of contraction increases.

  The urging member 26B includes a first bracket 261B, a second bracket 262B, a mandrel 263B, and an elastic member 264B, and is configured in the same manner as the urging member 26A. The first bracket 261B is pivotally supported by the sliding member 24B. The second bracket 262B is pivotally supported by the device frame 22B at a predetermined position on the end side in the axial direction 101 with respect to the pivot point of the first bracket 261B.

  As described above, the urging member 26A is disposed so as to be inclined toward the sliding member 24A in the axial direction 101 of the intermediate transfer belt tension roller 54 from the end side toward the center side. The urging member 26 </ b> B is disposed so as to be inclined toward the sliding member 24 </ b> B as it goes from the end side to the center side in the axial direction 101 of the intermediate transfer belt tension roller 54. The urging members 26A and 26B urge the shaft member 21 in a direction in which the tension of the intermediate transfer belt 51 is increased.

  FIG. 4 shows a state in which the intermediate transfer belt 51 is displaced from the ideal position in the width direction to be traveled, that is, a meander is caused. When the intermediate transfer belt 51 meanders and shifts to one side in the axial direction 101, for example, the back surface R side, the end in the width direction of the intermediate transfer belt 51 pushes the enlarged diameter portion of the enlarged diameter member 23B. The offset transmission member 25 </ b> B on the downstream side in the offset direction moves along the shaft member 21 to the back surface R side.

  As a result, the inclination angle of the biasing member 26B on the downstream side in the offset direction with respect to the axial direction 101 approaches perpendicularly, and the degree of contraction of the biasing member 26B increases. For this reason, the pressing force of the urging member 26B against the shaft member 21 is increased on the downstream side of the intermediate transfer belt 51 in the axial direction 101 in the axial direction 101 of the intermediate transfer belt tension roller 54, that is, the back surface R side. Tension increases.

  Further, the offset transmission member 25 </ b> A arranged on the upstream side in the offset direction moves downstream in the offset direction by the elastic force of the biasing member 26 </ b> A along with the offset of the intermediate transfer belt 51. Accordingly, the inclination angle of the biasing member 26A on the upstream side in the offset direction with respect to the axial direction 101 approaches the axial direction 101, and the degree of contraction of the biasing member 26A is reduced. For this reason, on the upstream side in the offset direction of the intermediate transfer belt 51 in the axial direction 101, the pressing force of the biasing member 26A against the offset transmission member 25A becomes small, and the tension of the intermediate transfer belt 51 becomes weak.

  Since the endless belt that does not have elasticity has a property of moving from a stronger tension to a weaker tension, the intermediate transfer belt 51 moves to the front surface F side. As a result, meandering of the intermediate transfer belt 51 toward the back surface R is corrected.

  FIG. 5 shows a state where the intermediate transfer belt 51 meanders to the front surface F side. Also in this case, as in the case shown in FIG. 4, when the intermediate transfer belt 51 meanders and shifts to the front surface F side, the end in the width direction of the intermediate transfer belt 51 pushes the enlarged diameter portion of the enlarged diameter member 23A. Accordingly, the offset transmission member 25A on the downstream side in the offset direction, that is, on the front surface F side, moves along the shaft member 21 to the front surface F side. Accordingly, the degree of contraction of the biasing member 26A on the downstream side in the offset direction is increased, and the tension of the intermediate transfer belt 51 on the front surface F side is increased. Further, the tension of the intermediate transfer belt 51 becomes weak on the upstream side in the offset direction, that is, on the back surface R side. Therefore, the intermediate transfer belt 51 moves to the back surface R side. As a result, meandering of the intermediate transfer belt 51 toward the front surface F is corrected.

  In this way, the intermediate transfer belt 51 meanders and pushes the enlarged diameter portions of the enlarged diameter members 23A and 23B, so that the tension of the intermediate transfer belt 51 on the downstream side in the offset direction increases and the upstream tension decreases. Therefore, the position in the width direction of the intermediate transfer belt 51 is maintained at a position where the balance between the force to move to the front surface F side and the force to move to the rear surface R side of the intermediate transfer belt 51 is balanced.

  Further, a meandering amount of the intermediate transfer belt 51 is corrected by a simple mechanism without requiring a sensor or an electric circuit for detecting the amount of deviation of the intermediate transfer belt 51.

  Further, the urging member 26A is in pressure contact with the intermediate transfer belt tension roller 54 and the rotation direction of the urging member 26A around the shaft fulcrum of the second bracket 262A and the rotation direction of the urging member 26B around the fulcrum of the second bracket 262B. Since the traveling direction of the partial intermediate transfer belt 51 is different, the urging members 26 </ b> A and 26 </ b> B are not rotated by the traveling force of the intermediate transfer belt 51 even when the amount of deviation of the intermediate transfer belt 51 increases. Therefore, the tension applied to the intermediate transfer belt 51 by the intermediate transfer belt tension roller 54 does not become excessively weak. For this reason, the meandering of the intermediate transfer belt 51 can be corrected stably.

  The surface including the locus of rotation around the base end of each of the urging members 26A and 26B and the traveling direction of the intermediate transfer belt 51 at the portion in pressure contact with the intermediate transfer belt tension roller 54 are orthogonal to each other. Is preferred. As a result, even if the deviation amount of the intermediate transfer belt 51 is increased, the biasing members 26A and 26B are more reliably prevented from rotating by the running force of the intermediate transfer belt 51. For this reason, the meandering of the intermediate transfer belt 51 can be corrected more stably.

  Further, since the diameter expanding members 23A and 23B are rotatable, friction between the intermediate transfer belt 51 and the diameter expanding members 23A and 23B is reduced, and wear at both ends of the intermediate transfer belt 51 is reduced.

  The offset transmission member disposed at least on the downstream side in the offset direction along the axial direction 101 of the intermediate transfer belt 51 among the offset transmission members 25A and 25B moves along the axial direction 101 together with the intermediate transfer belt 51. Then, the meandering correction effect of the intermediate transfer belt 51 is exhibited. The offset transmission member arranged on the upstream side in the offset direction also moves along the axial direction 101 together with the intermediate transfer belt 51, so that the meandering correction effect of the intermediate transfer belt 51 is further increased.

  Further, the diameter-expanding members 23A and 23B can be configured integrally with the intermediate transfer belt tension roller 54.

  Furthermore, the present invention can be applied to devices other than the intermediate transfer unit 50 as long as it is a belt drive device for an endless belt that does not have elasticity, and can correct meandering of the endless belt.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

21 Shaft member 22A, 22B Device frame 23A, 23B Expanding member 24A, 24B Sliding member 25A, 25B Offset transmission member 26A, 26B Biasing member 261A, 261B First bracket 262A, 262B Second bracket 263A, 263B Mandrel 264A , 264B elastic member 50 intermediate transfer unit 51 intermediate transfer belt 54 tension roller 60 secondary transfer unit 61 secondary transfer belt 62 secondary transfer roller 65 secondary transfer belt tension roller 100 image forming apparatus 101 axial direction

Claims (7)

An endless belt having no elasticity,
A plurality of stretching rollers including a tension roller that stretches the endless belt, a driving roller that rotates the endless belt, and a tension roller that can freely change the tension of the endless belt;
A shaft member that rotatably supports the tension roller and whose end portions are independently movable in a direction to change the tension of the endless belt;
A shift transmission member inserted through the shaft member so as to be adjacent to both ends in the axial direction of the tension roller, and disposed at least downstream in the shift direction along the axial direction of the endless belt. The offset transmission member moves in the offset direction along with the offset of the endless belt; and
An urging member having an elastic force that urges the shaft member in a direction in which the tension of the endless belt is increased. A biasing member that is pivotally supported by the device frame at a predetermined position on the end side in the axial direction.   The belt drive device according to claim 1, wherein the offset transmission member disposed on the upstream side in the offset direction moves in the offset direction along with the offset of the endless belt.   3. The belt drive device according to claim 1, wherein the offset transmission member includes a diameter-expanding member whose diameter is larger than that of the tension roller, and the diameter-expanding member is rotatably supported by the shaft member. The offset transmission member further includes a sliding member whose rotation about the shaft member is restricted on an end side of the diameter-expanding member in the axial direction,
The belt driving device according to claim 3, wherein the working end portion is pivotally supported by each of the sliding members.   The surface of the urging member including a rotation trajectory centered on the base end portion and a traveling direction of the endless belt at a portion in pressure contact with the tension roller are orthogonal to each other. A belt driving device according to claim 1.   The biasing member has one end portion on one of the first bracket pivotally supported by the offset transmission member, the second bracket pivotally supported by the device frame, the first bracket, and the second bracket. The belt driving device according to claim 1, further comprising: a mandrel that is fixedly inserted into the other bracket so as to be displaceable, and an elastic member that is disposed between the first bracket and the second bracket. .   An image forming apparatus comprising the belt driving device according to claim 1.

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