JP5868742B2 - Belt drive device and image forming apparatus - Google Patents

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 endless belt causes meandering due to variations in the outer diameter of the tension roller due to manufacturing errors, deviations in parallelism between the tension rollers due to mounting errors, and the like. 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, in the electric control system, a sensor, an electric circuit, a drive motor, and the like are necessary, and the configuration becomes complicated due to an increase in the number of parts, and the cost increases.

  Therefore, a technique is known that attempts to suppress meandering of the endless belt by adjusting the tension of the endless belt using a mechanical mechanism (see, for example, Patent Documents 1 and 2).

  In the conventional belt driving device 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.

  Further, in the conventional belt driving device described in Patent Document 2, a pair of fixing flanges are disposed on both sides of the roller body around which the transfer belt is wound. One fixed flange is formed with a flange portion protruding from the outer peripheral surface of the roller body. The other fixed flange is slidably configured to be a slidable flange having a flange portion protruding from the outer peripheral surface of the roller body, and is biased by a spring. Accordingly, it is intended to prevent meandering of the transfer belt by restricting both end portions of the transfer belt by both flange portions of the one fixed flange and the sliding flange.

JP-A-2005-162466 JP 2003-149951 A

  However, in the conventional belt driving device 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, and therefore the amount of deviation of the endless belt is large. When the friction force received by the belt contact portion increases, the endless belt traveling force causes the arm member to fall over the top and fall downstream in the traveling direction of the endless belt, and the tension applied to the endless belt by the tension roller is extreme. 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.

  Further, in the conventional belt driving device of Patent Document 2, the sliding flange is urged by a spring, one end of the transfer belt is pressed against the flange of the sliding flange, and the sliding flange rotates the roller body. Since a load in the direction of braking is generated, the roller body may not be able to rotate smoothly. Also, the other end of the transfer belt is easily damaged by contact with the fixed flange.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a belt drive device that can smoothly and stably correct meandering of an endless belt with a simple mechanism, and an image forming apparatus including the belt drive device.

  The belt driving device according to the present invention includes an endless belt, a plurality of stretching rollers, a shaft member, a long hole holding member, an abutting member, an offset 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. The long hole retaining member has a long hole that penetrates in the axial direction of the tension roller and is long in a predetermined direction that is not parallel to the inner peripheral surface of the portion of the endless belt that contacts the tension roller. Both end portions are guided independently of each other so as to be movable in a predetermined direction. The contact member is disposed on the inner surface of the long hole, and has a rib extending in a predetermined direction and having a smaller dimension in the axial direction than that of the long hole holding member. The offset transmission member is externally inserted into the shaft member so as to be adjacent to both ends of the tension roller in the axial direction, and is inserted through the long hole. The offset transmission member arranged at least downstream in the offset direction along the axial direction of the endless belt 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 working end portion is pivotally supported by the offset transmission member, and the base end portion is the working end in the axial direction. Except for the same position as the part, it is pivotally supported at a predetermined position on either the same side or the opposite side of the tension roller with respect to the working end.

  In this configuration, both end portions of the shaft member move independently of each other in the long hole, whereby the tension of the endless belt in each portion in the axial direction of the tension roller is changed.

  When the endless belt does not have elasticity, both the base end portions of the urging members are pivotally supported at a predetermined position on the opposite side of the tension roller with respect to the working end portion in the axial direction of the tension roller. For this reason, the urging member is inclined 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 of the tension roller, at least the downstream transmission member in the offset direction moves along the axial direction of the tension roller. As a result, the inclination angle of the biasing member on the downstream side in the offset direction approaches perpendicular to the axial direction of the tension roller, 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.

  On the other hand, when the endless belt has elasticity, both the base end portions of the urging members are pivotally supported at predetermined positions on the same side as the tension roller with respect to the working end portion in the axial direction of the tension roller. For this reason, the urging member inclines in a direction approaching the offset transmission member as it goes from the center side to the end side in the axial direction of the tension roller. When the endless belt meanders and shifts to one side in the axial direction of the tension roller, at least the downstream transmission member in the offset direction moves along the axial direction of the tension roller. As a result, the inclination angle of the biasing member on the downstream side in the offset direction approaches parallel to the axial direction of the tension roller, and the degree of contraction of the biasing member is reduced. 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 reduced, and the tension of the endless belt is reduced. Since the endless belt having elasticity has a property of moving from a weaker tension to a stronger one, 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.

  Even in a configuration in which the base end portion of the urging member is pivotally supported on the same side as the tension roller or the opposite side of the working end in the axial direction of the tension roller, the long hole through which the offset transmission member is inserted A contact member is disposed on the inner surface. The contact member has a rib, and the offset transmission member contacts the rib in the long hole. The rib extends in the length direction of the long hole, and the dimension of the rib in the axial direction of the tension roller is smaller than the dimension of the long hole holding member. For this reason, the static friction coefficient of the offset transmission member in the axial direction of the tension roller is smaller than when the offset transmission member is in contact with the long hole holding member. Thus, even when the speed of the endless belt is low, the offset transmitting member reacts sensitively to the offset of the endless belt and moves smoothly along the axial direction of the tension roller. Therefore, the meandering of the endless belt can be corrected smoothly.

  In the above-described configuration, it is preferable that the ribs are disposed on both inner surfaces facing in a direction orthogonal to the predetermined direction. The offset transmission member is sandwiched between ribs on both sides in a direction orthogonal to the length direction of the long hole. For this reason, compared to the case where only one side abuts on the rib and the other side abuts on the long hole holding member in the direction perpendicular to the length direction of the long hole, the displacement transmission member in the axial direction of the tension roller is stationary. The coefficient of friction is reduced. As a result, the offset transmission member reacts more sensitively to the offset of the endless belt and moves smoothly along the axial direction of the tension roller.

  The top surface of the rib can be configured to be a flat surface. If the outer cross-sectional shape of the offset transmission member is circular, the offset transmission member is in line contact with the top surface of the rib in the elongated hole in the axial direction of the tension roller. For this reason, the static friction coefficient of the offset transmission member in the axial direction of the tension roller is smaller than in the case of surface contact.

  Furthermore, it is preferable that the top surface of the rib has a cylindrical shape with the predetermined direction as an axis. If the outer cross-sectional shape of the offset transmission member is circular, the offset transmission member makes point contact with the top surface of the rib within the long hole. For this reason, the static friction coefficient of the offset transmission member in the axial direction of the tension roller becomes smaller.

  Further, the base end portion of the urging member can be configured to be pivotally supported by the long hole holding member. In this configuration, it is not necessary to provide a member that supports the base end portion of the biasing member separately from the long hole holding member that guides the shaft member in the direction in which the tension of the endless belt is changed, thereby reducing the number of parts. be able to.

  The image forming apparatus according to the present invention includes the belt driving device having any one of the above-described configurations. In this configuration, the contact member is arranged on the inner surface of the long hole through which the offset transmission member is inserted. The contact member has a rib, and the offset transmission member contacts the rib in the long hole. The rib extends in the length direction of the long hole, and the dimension of the rib in the axial direction of the tension roller is smaller than the dimension of the long hole holding member. For this reason, the static friction coefficient of the offset transmission member in the axial direction of the tension roller is smaller than when the offset transmission member is in contact with the long hole holding member. Thus, even when the speed of the endless belt is low, the offset transmitting member reacts sensitively to the offset of the endless belt and moves smoothly along the axial direction of the tension roller. Therefore, the meandering of the endless belt can be corrected smoothly.

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

1 is a front view illustrating a schematic configuration of an image forming apparatus including an intermediate transfer unit according to a first 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 a part of the 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. It is a front view of a contact member. It is a top view of a contact member. It is a top view of the contact member concerning a modification. FIG. 6 is a side sectional view of a part of a secondary transfer unit according to a second embodiment of the belt driving device of the present invention.

  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, the black image forming station 31 disposed on the most downstream side of the image forming stations 31 to 34 in the traveling direction of the intermediate transfer belt 51 in the region facing the image forming stations 31 to 34. A pre-transfer charger (PTC) 56 is disposed between the intermediate transfer belt driving roller 52 and the transfer roller. 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 FIGS. 3 to 5, the intermediate transfer belt tension roller 54 that stretches the intermediate transfer belt 51 is rotatable about the shaft member 21 and slidable along the shaft member 21 in the axial direction 101. The shaft member 21 is supported. The shaft member 21 is restricted from rotating. The shaft member 21 has a uniform perfect circular cross-sectional shape in the axial direction 101. The shaft member 21 is formed of a drawn material of SUS (stainless steel), and the arithmetic average roughness Ra of the peripheral surface of the shaft member 21 is 0.5 μm or less. Also when the shaft member 21 is a SUM (free-cutting steel) drawn material having a thickness of 3 μm plated, the arithmetic average roughness Ra of the peripheral surface of the shaft member 21 can be reduced.

  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. Each of the diameter-expanding members 23A and 23B has a diameter-expanded portion whose diameter is larger than that of the intermediate transfer belt tension roller 54 at the end far from the intermediate transfer belt tension roller 54 in the axial direction 101. Yes. The portions other than the enlarged diameter portion in the axial direction 101 of each of the enlarged diameter members 23A and 23B are formed to have the same diameter as the intermediate transfer belt tension roller 54. The diameter-expanding members 23A and 23B are extrapolated by the shaft member 21 and are movable in the axial direction 101, and are supported by the shaft member 21 so as to be rotatable.

  In the axial direction 101, a sliding member 24A is disposed on the opposite side of the intermediate transfer belt tension roller 54 with respect to the diameter expanding member 23A. A sliding member 24B is disposed on the opposite side of the intermediate transfer belt tension roller 54 with respect to the diameter expanding member 23B in the axial direction 101. The sliding members 24A and 24B are passed through the shaft member 21 so as to be adjacent to the diameter-expanding members 23A and 23B in the axial direction 101, and are movable 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 sliding member 24A is inserted through the long hole 221A of the apparatus frame 22A and the long hole 271A of the long hole holding member 27A. The long hole holding member 27A is disposed on the opposite side of the intermediate transfer belt tension roller 54 with respect to the apparatus frame 22A, and is supported by the apparatus frame 22A.

  The sliding member 24B is inserted through the long hole 221B of the device frame 22B and the long hole 271B of the long hole holding member 27B. The long hole holding member 27B is disposed on the opposite side of the intermediate transfer belt tension roller 54 with respect to the apparatus frame 22B, and is supported by the apparatus frame 22B.

  The long holes 271A and 271B of the long hole holding members 27A and 27B penetrate in the axial direction 101 and are long in a predetermined direction that is not parallel to the inner peripheral surface of the intermediate transfer belt 51 where the intermediate transfer belt tension roller 54 contacts. . As an example, the long holes 271A and 271B are long in the direction perpendicular to the inner peripheral surface of the portion of the intermediate transfer belt 51 that contacts the intermediate transfer belt tension roller 54, that is, the vertical direction in FIG.

  As shown in FIGS. 6 and 7, the long holes 221A and 221B of the device frames 22A and 22B penetrate in the axial direction 101 and are long in the same direction as the long holes 271A and 271B. The long hole 221A is formed in a larger size than the long hole 271A so that all of the long holes 271A can be seen from the intermediate transfer belt tension roller 54. Similarly, the long hole 221B is formed in a larger size than the long hole 271B so as to face all the long holes 271B from the intermediate transfer belt tension roller 54.

  The contact members 28A and 28B are fixedly arranged on the inner surfaces of the long holes 271A and 271B of the long hole holding members 27A and 27B, respectively. The contact member 28A has ribs 281A and 282A (282A is not shown). The ribs 281A and 282A are respectively disposed on the inner surfaces of the long holes 271A that face each other in the direction orthogonal to the length direction of the long holes 271A. The rib 281A extends in the length direction of the long hole 271A. In the axial direction 101, the dimension of the rib 281A is smaller than the dimension of the long hole holding member 271A. As an example, the top surface of the rib 281A in contact with the sliding member 24A is a flat surface. The rib 282A is configured similarly to the rib 281A.

  The contact member 28B has ribs 281B and 282B. The ribs 281B and 282B are configured similarly to the ribs 281A and 282A.

  The sliding member 24A is sandwiched between the top surfaces of the ribs 281A and 282A of the abutting member 28A in the long hole 271A, and movement in the direction perpendicular to the length direction of the long hole 271A is restricted. Thus, the sliding member 24A is supported by the long hole holding member 27A so as to be movable along the top surfaces of the ribs 281A and 282A in the length direction of the long hole 271A, that is, the direction in which the tension of the intermediate transfer belt 51 is changed. ing. Further, as described above, the sliding member 24A is also movable in the axial direction 101 while being in contact with the top surfaces of the ribs 281A and 282A.

  Similarly, the sliding member 24B is sandwiched between the top surfaces of the ribs 281B and 282B of the abutting member 28B in the long hole 271B, and is restricted from moving in a direction perpendicular to the length direction of the long hole 271B. Accordingly, the sliding member 24B is supported by the long hole holding member 27B so as to be movable along the top surfaces of the ribs 281B and 282B in the length direction of the long hole 271B, that is, the direction in which the tension of the intermediate transfer belt 51 is changed. ing. Further, as described above, the sliding member 24B is also movable in the axial direction 101 while being in contact with the top surfaces of the ribs 281B and 282B.

  By being configured as described above, the shaft member 21 can move independently at both ends in the direction in which the tension of the intermediate transfer belt 51 is changed, that is, in the vertical direction in FIG. 3 in this embodiment.

  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 long hole holding member 27A at a predetermined position opposite to the intermediate transfer belt tension roller 54 with respect to the pivot point of the first bracket 261A. That is, the base end portion of the urging member 26A is pivotally supported by the long hole holding member 27A at a predetermined position on the opposite side of the intermediate transfer belt tension roller 54 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 long hole holding member 27B at a predetermined position opposite to the intermediate transfer belt tension roller 54 with respect to the pivot point of the first bracket 261B.

  In other words, the shaft fulcrum of the second brackets 262A and 262B is disposed closer to the end of the shaft member 21 than the shaft fulcrum of the first brackets 261A and 261B in the axial direction 101.

  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 shaft fulcrums of the second brackets 262A and 262B are disposed on the opposite side of the intermediate transfer belt 51 with respect to the shaft member 21. Therefore, the urging members 26 </ b> A and 26 </ b> B 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 perpendicular to the axial direction 101, 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. Thereby, the inclination angle of the biasing member 26A on the upstream side in the offset direction with respect to the axial direction 101 approaches parallel to the axial direction 101, and the degree of contraction of the biasing member 26A becomes small. 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.

  Further, since the working end portions of the urging members 26A and 26B are pivotally supported by the sliding members 24A and 24B whose rotation about the shaft member 21 is restricted, there is a certain amount of deviation of the intermediate transfer belt 51. In this case, the arrangement and the degree of contraction of the urging members 26A and 26B are stabilized, and the accuracy of the meandering correction of the intermediate transfer belt 51 is further improved.

  Further, as described above, the contact members 28A and 28B are arranged on the inner surfaces of the long holes 271A and 271B through which the sliding members 24A and 24B are inserted. The abutting members 28A, 28B have ribs 281A, 282A, 281B, 282B, and the sliding members 24A, 24B abut against the ribs 281A, 282A, 281B, 282B in the long holes 271A, 271B. The ribs 281A, 282A, 281B, 282B extend in the length direction of the long holes 271A, 271B.

  Each dimension of the ribs 281A and 282A in the axial direction 101 is smaller than the dimension of the long hole holding member 27A. Each dimension of the ribs 281B and 282B in the axial direction 101 is smaller than the dimension of the long hole holding member 27B. For this reason, the static friction coefficient of the sliding members 24A and 24B in the axial direction 101 is smaller than when the sliding members 24A and 24B are in contact with the long hole holding members 27A and 27B. As a result, even when the speed at which the intermediate transfer belt 51 is shifted is low, the sliding members 24 </ b> A and 24 </ b> B react sensitively to the shift of the intermediate transfer belt 51 and move smoothly along the axial direction 101. Therefore, the meandering of the intermediate transfer belt 51 can be corrected smoothly. Therefore, the meandering of the intermediate transfer belt 51 in the intermediate transfer unit 50 can be corrected smoothly and stably with a simple mechanism.

  Further, the sliding member 24A is sandwiched between the ribs 281A and 282A in the direction perpendicular to the length direction of the long hole 271A. The sliding member 24B is sandwiched between the ribs 281B and 282B in the direction perpendicular to the length direction of the long hole 271B. For this reason, in comparison with the case where only one side is in contact with the ribs 281A, 282A, 281B, 282B and the other side is in contact with the long hole holding members 27A, 27B in the direction perpendicular to the length direction of the long holes 271A, 271B. The static friction coefficient of the sliding members 24A and 24B in the axial direction 101 becomes small. As a result, the sliding members 24 </ b> A and 24 </ b> B react more sensitively to the offset of the intermediate transfer belt 51 and move smoothly along the axial direction 101. For this reason, the meandering of the intermediate transfer belt 51 can be corrected more smoothly.

  Further, since the top surfaces of the ribs 281A, 282A, 281B, and 282B are flat and the outer shape of the sliding members 24A and 24B has a circumferential shape, the sliding members 24A and 24B are ribbed in the long holes 271A and 271B. Line contact is made in the axial direction 101 with the top surfaces of 281A, 282A, 281B, and 282B. For this reason, the static friction coefficient of the sliding members 24 </ b> A and 24 </ b> B in the axial direction 101 is smaller than in the case of surface contact.

  Further, since the arithmetic average roughness Ra of the peripheral surface of the shaft member 21 is 0.5 μm or less, the shafts of the intermediate transfer belt tension roller 54, the diameter-expanding members 23A and 23B, and the sliding members 24A and 24B in the axial direction 101 are used. The coefficient of static friction with respect to the member 21 is also reduced. For this reason, the sliding members 24 </ b> A and 24 </ b> B react more sensitively to the offset of the intermediate transfer belt 51 and move more smoothly along the axial direction 101. As a result, the meandering of the intermediate transfer belt 51 can be corrected more smoothly.

  Further, since the base end portions of the urging members 26A and 26B are pivotally supported by the long hole holding members 27A and 27B, the long hole holding member 27A that guides the shaft member 21 in the direction in which the tension of the intermediate transfer belt 51 is changed. 27B, it is not necessary to provide a member that pivotally supports the base ends of the urging members 26A, 26B, so that the number of parts can be reduced.

  As shown in FIG. 8, it is preferable that the top surfaces of the ribs 281A, 282A, 281B, and 282B are configured so as to exhibit a circumferential surface shape of a cylindrical body whose axis is the length direction of the long holes 271A and 271B. Since the outer shape of the sliding members 24A and 24B has a circumferential shape and is disposed in a direction perpendicular to the ribs 281A, 282A, 281B and 282B, the sliding members 24A and 24B are disposed in the long holes 271A and 271B. Point contact is made with the top surfaces of the ribs 281A, 282A, 281B, and 282B. For this reason, the static friction coefficients of 24A and 24B in the axial direction 101 become smaller.

  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.

  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 present invention can also be applied to a belt drive device for an endless belt having elasticity, and the meandering of the endless belt can be corrected smoothly and stably with a simple mechanism. As an example, the present invention can also be applied to the secondary transfer unit 60. In FIG. 9 showing the embodiment when the present invention is applied to the secondary transfer unit 60, the same reference numerals are used for the same configurations as those of the intermediate transfer unit 50 for convenience of explanation.

  As shown in FIG. 9, the secondary transfer belt 61 has elasticity, and the base end portions of the urging members 26 </ b> A and 26 </ b> B are both secondary to the working end portion in the axial direction 101 of the secondary transfer belt tension roller 65. It is pivotally supported at a predetermined position on the same side as the next transfer belt tension roller 65. For this reason, the urging member 26 </ b> A is inclined in a direction approaching the sliding member 24 </ b> A as it goes from the center side to the end side in the axial direction 101. The urging member 26B is inclined in a direction approaching the sliding member 24B as it goes from the center side to the end side in the axial direction 101. When the secondary transfer belt 61 meanders and shifts to one side in the axial direction 101, at least the downstream sliding members 24 </ b> A and 24 </ b> B in the offset direction move along the axial direction 101. As a result, the inclination angles of the biasing members 26A and 26B on the downstream side in the offset direction approach parallel to the axial direction 101, and the degree of contraction of the biasing members 26A and 26B on the downstream side becomes small. For this reason, on the downstream side of the secondary transfer belt 61 in the axial direction 101, the pressing force of the urging members 26A and 26B against the sliding members 24A and 24B becomes small, and the tension of the secondary transfer belt 61 becomes weak. . Since the secondary transfer belt 61 having elasticity has a property of moving from a weaker tension to a stronger tension, the meandering of the secondary transfer belt 61 can be corrected.

  The sliding member 24A contacts the ribs 281A and 282A in the long hole 271A. The sliding member 24B contacts the ribs 281B and 282B in the long hole 271B. Each dimension of the ribs 281A and 282A in the axial direction 101 is smaller than the dimension of the long hole holding member 27A. Each dimension of the ribs 281B and 282B in the axial direction 101 is smaller than the dimension of the long hole holding member 27B. For this reason, the static friction coefficient of the sliding members 24A and 24B in the axial direction 101 is smaller than when the sliding members 24A and 24B are in contact with the long hole holding members 27A and 27B. As a result, even when the speed on the side of the secondary transfer belt 61 is low, the sliding members 24A and 24B react sensitively to the side of the secondary transfer belt 61 and move smoothly along the axial direction 101. . For this reason, the meandering of the secondary transfer belt 61 can be corrected smoothly. Therefore, the meandering of the secondary transfer belt 61 in the secondary transfer unit 60 can be corrected smoothly and stably with a simple mechanism.

  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 27A, 27B Long hole holding member 271A, 271B Long hole 28A, 28B Abutting member 281A, 282A, 281B, 282B Rib 50 Intermediate transfer unit (belt driving device)
51 Intermediate transfer belt 54 Intermediate transfer belt tension roller 60 Secondary transfer unit (belt drive 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,
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;
The front Symbol tension roller together when extending in the axial direction of the tension roller has a long elongated hole in a predetermined direction to change the tension of the endless belt, independently both ends of the shaft member to each other in the long hole A long hole holding member that is movably guided in the predetermined direction;
An abutting member disposed on an inner surface of the elongated hole and extending in the predetermined direction and having a rib whose dimension in the axial direction is smaller than the dimension of the elongated hole holding member;
A displacement transmission member that is externally inserted into the shaft member so as to be adjacent to both end portions of the tension roller in the axial direction and that is inserted through the elongated hole, and the displacement of the endless belt along the axial direction A displacement transmission member disposed at least on the downstream side in the direction, and a displacement transmission member that moves in the displacement direction along with the displacement of the endless belt;
The shaft member has an elastic force that urges the endless belt in a direction in which the tension of the endless belt is increased, the working end portion is pivotally supported by the offset transmission member, and the base end portion is both in the axial direction in the working end. An urging member pivotally supported at a predetermined position on either the same side or the opposite side of the tension roller with respect to the working end except for the same position as the part,
The biasing member includes a mandrel, a bracket, and an elastic member, and the mandrel is arranged with one end on one of the working end and the base end, and the bracket includes the working end and the The base end is disposed at least on the other side, the mandrel is inserted through the bracket disposed on the other end, and the elastic member includes the one end and the working end and the base end. A belt driving device arranged to extend and contract along the mandrel between the bracket arranged on the other side .   The belt driving device according to claim 1, wherein the ribs are arranged on both inner surfaces facing in a direction orthogonal to the predetermined direction.   The belt driving device according to claim 1, wherein a top surface of the rib is a flat surface.   3. The belt drive device according to claim 1, wherein a top surface of the rib has a cylindrical peripheral surface shape having the predetermined direction as an axis.   The belt drive device according to claim 1, wherein the base end portion is pivotally supported by the long hole holding member. The endless belt has elasticity,
6. The belt driving device according to claim 1, wherein both of the base end portions are pivotally supported at a predetermined position on the same side as the tension roller with respect to the working end portion in the axial direction. An image forming apparatus having a belt driving device according to any one of claims 1 6.

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