JP2011248056A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing a deformation of a belt due to foreign matters adhered to a support member, and extending the durability life of the belt.SOLUTION: The image forming apparatus including a belt 7 for carrying a toner image, and a plurality of rotation support members 8a, 8b, 8c and 8d for rotatably supporting the belt comprises: a detection member 30 for detecting a position of the belt in a longitudinal direction orthogonal to the rotation direction; and a displacement member 41 for displacing the predetermined rotation support member 8b so as to move the belt to a predetermined target position in the longitudinal direction orthogonal to the rotation direction of the belt. When a rotation time period of the belt reaches a set time length for preventing a belt deformation due to foreign matters adhered to the outside surface of the rotation support member contacting with the belt, the predetermined rotation support member 8b is displaced by the displacement member to change a predetermined target position of the belt.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  In image forming apparatuses such as electrophotographic copying machines and printers, the following direct transfer type and intermediate transfer type image forming apparatuses are known as color image forming apparatuses capable of forming full-color images. In a direct transfer type image forming apparatus, a toner image formed on one or a plurality of photosensitive drums is recorded on a transfer sheet or the like that is carried on a peripheral surface (surface) of a transfer belt that is suspended by a plurality of rollers and can be moved around. Transfer to material. In an intermediate transfer type image forming apparatus, a toner image formed on one or a plurality of photosensitive drums is transferred (primary transfer) to an outer peripheral surface (surface) of an intermediate transfer belt that is suspended by a plurality of rollers and can be moved around. . The toner image transferred to the surface of the intermediate transfer belt is transferred (secondary transfer) to a recording material such as transfer paper. The intermediate transfer type image forming apparatus can easily form an image on a variety of recording materials and can increase the selectivity of the recording material, as compared with the direct transfer type image forming apparatus.

  In the above-described image forming apparatus, during the circular movement of the intermediate transfer belt, foreign matter such as paper dust of the recording material is formed on the outer peripheral surface (surface) of the suspension roller that is in contact with the inner peripheral surface (inner surface) of the intermediate transfer belt. May adhere. When foreign matter adheres to the surface of the suspension roller, the foreign matter travels along the surface of the suspension roller for a long time and forms an indentation streak of about 1 μm on the inner surface of the intermediate transfer belt. This streak causes the intermediate transfer belt itself to deform. May end up. This deformation of the intermediate transfer belt causes unevenness in transfer of a toner image from the photosensitive drum to the surface of the intermediate transfer belt, causes streak-like image defects, and shortens the durable life of the intermediate transfer belt. It is one. In Patent Document 1, the intermediate transfer belt is deformed by an indentation of the foreign matter on the inner surface of the intermediate transfer belt by removing the foreign matter adhering to the surface of the suspension roller by a cleaning member brought into contact with the surface of the suspension roller or the inner surface of the intermediate transfer belt. It is reduced.

JP 2004-184602 A

  If a method of removing foreign matter adhering to the surface of the suspension roller with a cleaning member is used, it is expected that a certain endurance life of the intermediate transfer belt will be achieved. In order to further extend the durability of the intermediate transfer belt, it is necessary to remove foreign matter of several μm attached to the surface of the suspension roller with a cleaning member. However, it is difficult to remove foreign matters of about several μm with a cleaning member. Therefore, it is desired to reduce the deformation of the intermediate transfer belt due to the foreign matter without removing the foreign matter and extend the durability life of the intermediate transfer belt.

  An object of the present invention is to provide an image forming apparatus capable of reducing deformation of a belt due to foreign matter adhering to a support member and extending the durable life of the belt.

  To achieve the above object, a typical configuration of an image forming apparatus according to the present invention is an image forming apparatus having a belt for carrying a toner image and a plurality of rotation support members for rotatably supporting the belt. A detection member that detects a position in a longitudinal direction orthogonal to the rotation direction of the belt, and a predetermined rotation support member that moves the belt to a predetermined target position in a longitudinal direction orthogonal to the rotation direction of the belt. A displacement member to be displaced, and when the rotation time of the belt reaches a set time for preventing belt deformation due to foreign matter attached to the outer surface of the rotation support member that contacts the belt, the displacement member A predetermined target position of the belt is changed by displacing the predetermined rotation support member.

  According to the present invention, it is possible to provide an image forming apparatus capable of reducing the deformation of the belt due to the foreign matter adhering to the support member and extending the durable life of the belt.

1 is a schematic configuration schematic diagram of an example of an image forming apparatus according to Embodiment 1. FIG. FIG. 5A is a diagram illustrating a positional relationship among an intermediate transfer belt, a driving roller, a steering roller, a belt end sensor, and a roller end displacement mechanism of the image forming apparatus according to the first exemplary embodiment. (B) is a schematic diagram of a schematic configuration of an example of a roller end displacement mechanism. (C) is a diagram showing a temporal change in the end position (belt end position) in the longitudinal direction of the intermediate transfer belt when the longitudinal end of the steering roller is displaced. (A) is a schematic diagram of a schematic configuration of an example of a belt end sensor, and (b) is a block diagram of a hardware configuration that controls the shift position of the intermediate transfer belt. 6 is a flowchart of intermediate transfer belt shift control initialization of the image forming apparatus according to the first exemplary embodiment. 3 is an explanatory diagram of a shift movement range of an intermediate transfer belt of the image forming apparatus according to Embodiment 1. FIG. FIG. 6 is an explanatory diagram of the intermediate transfer belt shift control of the image forming apparatus according to the first embodiment, and is a flowchart of an intermediate transfer belt shift target value change sequence according to the endurance time of the intermediate transfer belt. FIG. 10 is an explanatory diagram of the intermediate transfer belt shift control of the image forming apparatus according to the second embodiment, and is a flowchart of an intermediate transfer belt shift target value changing sequence based on the durable number of intermediate transfer belts.

  [Example 1] Example of image forming apparatus: Fig. 1 is a schematic diagram of a schematic configuration of an example of an image forming apparatus according to this example. This image forming apparatus is a full-color laser printer that forms an image on a recording material such as transfer paper using electrophotographic technology. In the image forming apparatus shown in the present embodiment, the control unit 100 executes a predetermined image forming control sequence in response to a print command output from an external apparatus (not shown) such as a host computer, a terminal on a network, or an external scanner. To do. The control unit 100 includes a CPU and a memory such as a RAM and a ROM. The memory stores an image formation control sequence, an intermediate transfer belt shift control initialization sequence, an intermediate transfer belt shift target value change sequence, and various data necessary for image formation. Has been.

  The image forming apparatus according to the present exemplary embodiment includes first to fourth image forming units YS, MS, CS, and KS that form images using toners (developers) of yellow, magenta, cyan, and black. It is an in-line type apparatus arranged in a line along the transport direction. Each of the image forming units YS, MS, CS, and KS has a cylindrical electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 basically has a cylindrical conductive substrate such as aluminum and a photoconductive layer formed on the outer peripheral surface of the conductive substrate. In each of the image forming units YS, MS, CS, and KS, a charging roller 2 as a charging unit and a scanning exposure device 3 as an exposure unit are provided around the outer peripheral surface (surface) of the photosensitive drum 1. Further, a developing device 4 as a developing unit and a drum cleaner 6 are provided around the surface of the photosensitive drum 1. An intermediate transfer belt 7 is provided as a belt so as to straddle the photosensitive drums 1 of the image forming units YS, MS, CS, and KS. The intermediate transfer belt 7 is suspended over a drive roller 8a, a steering roller 8b, a secondary transfer counter roller 8c, and a tension roller 8d. The driving roller 8a, the steering roller 8b, the secondary transfer counter roller 8c, and the tension roller 8d are a plurality of rotation support members that rotatably support the intermediate transfer belt 7, respectively. On the inner peripheral surface (inner surface) side of the intermediate transfer belt 7, a primary transfer roller 5 as a first transfer member is provided so as to sandwich each photosensitive drum 1 and the intermediate transfer belt 7. On the outer peripheral surface (front surface) side of the intermediate transfer belt 7, a secondary transfer roller 9 as a second transfer member is provided so as to sandwich the secondary transfer counter roller 8 c and the intermediate transfer belt 7. A belt cleaner 10 is provided on the surface side of the intermediate transfer belt 7 so as to sandwich the drive roller 8 a and the intermediate transfer belt 7.

  An image forming operation of the image forming apparatus according to the present exemplary embodiment will be described. When the image forming control sequence is executed, the image forming units YS, MS, CS, and KS are sequentially driven. That is, in each of the image forming units YS, MS, CS, and KS, the photosensitive drum 1 is rotated in the arrow direction at a predetermined peripheral speed (process speed). The intermediate transfer belt 7 is rotated in the direction of the arrow by a driving roller 8a at a predetermined peripheral speed (process speed) corresponding to the rotational peripheral speed of each photosensitive drum 1. First, in the first color yellow image forming portion YS, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2 to a predetermined polarity and potential. Next, the scanning exposure device 3 scans and exposes the charged surface of the photosensitive drum 1 with laser light L corresponding to image data (image information) output from the external device. As a result, an electrostatic latent image (electrostatic image) corresponding to the image data is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed by the developing device 4 using yellow toner (developer). As a result, a yellow toner image (development image) is formed on the surface of the photosensitive drum 1. The same steps of charging, exposure, and development are also performed in the second color magenta image forming unit MS, the third color cyan image forming unit CS, and the fourth color black image forming unit KS. Each color toner image formed on the surface of each photosensitive drum 1 is sequentially transferred onto the surface of the intermediate transfer belt 7 by the primary transfer roller 5 at the primary transfer nip portion between the surface of the photosensitive drum 1 and the surface of the intermediate transfer belt 7. The As a result, a full-color toner image is carried on the surface of the intermediate transfer belt 7. The transfer residual toner remaining on the surface of the photosensitive drum 1 is removed by the cleaner 6 on the surface of the photosensitive drum 1 after the toner image is transferred, and is used for the next image formation.

  On the other hand, the recording material fed one by one from the paper feeding cassette 11 by the feeding roller 12 is conveyed to the registration roller 14 by the conveying roller 13. Next, the recording material P is conveyed by the registration roller 14 to the secondary transfer nip portion between the intermediate transfer belt 7 and the secondary transfer roller 9. In this conveyance process, the toner image on the surface of the intermediate transfer belt 7 is transferred to the recording material P by the secondary transfer roller 9. As a result, the recording material P carries an unfixed full-color toner image. The transfer residual toner remaining on the surface of the intermediate transfer belt 7 on the surface of the intermediate transfer belt 7 after the toner image transfer is removed by the belt cleaner 10.

  The recording material P carrying a full-color toner image is separated from the surface of the intermediate transfer belt 7 and is provided with a fixing film (fixing rotator) 16 and a pressure roller (pressure rotator) 17 provided in a fixing device (fixer) 15. It is introduced into the fixing nip portion between them. The recording material P is nipped at the fixing nip portion by the fixing film 16 heated by the ceramic heater (heating body) 18 and the pressure roller 17 and conveyed in that state. As a result, the unfixed toner image is heated and fixed to the recording material P by receiving heat and pressure. The recording material P exiting the fixing nip portion of the fixing device 15 is discharged to a discharge tray (not shown).

  [Description of Belt End Sensor and Roller End Displacement Mechanism]: In the image forming apparatus of this embodiment, the recording material P is nipped and conveyed by the intermediate transfer belt 7 and the secondary transfer roller 9 from the surface of the intermediate transfer belt 7. A toner image is transferred to the recording material P. For this reason, foreign matters such as paper dust of the recording material P and toner of the toner image may wrap around the inner peripheral surface (inner surface) of the intermediate transfer belt 7 from the end in the longitudinal direction orthogonal to the recording material conveyance direction of the intermediate transfer belt 7. is there. When the foreign matter goes around the inner surface of the intermediate transfer belt 7, the foreign matter may adhere to the outer peripheral surfaces (surfaces, outer surfaces) of the rollers 8a, 8b, 8c, and 8d that are in contact with the inner surface of the intermediate transfer belt 7. In the image forming apparatus of this embodiment, the intermediate transfer belt 7 is displaced by displacing the steering roller 8b in order to reduce the deformation due to the foreign matter of the intermediate transfer belt 7 and to extend the durable life of the intermediate transfer belt 7 without removing the foreign matter. 7 was moved and moved. The position of the intermediate transfer belt 7 is detected by a belt end sensor 30 as a detection member, and the steering roller 8b is displaced by a cam 41 as a displacement member of the roller end displacement mechanism 40.

  2A is a view showing the positional relationship among the intermediate transfer belt 7, the driving roller 8a, the steering roller 8b, the belt end sensor 30, and the roller end displacement mechanism 40. FIG. FIG. 2B is a schematic configuration schematic diagram of an example of a roller end portion displacement mechanism 40. 3A is a schematic configuration diagram of an example of the belt end sensor 30, and FIG. 3B is a block diagram of a hardware configuration that controls the shift position of the intermediate transfer belt 7.

  The belt end sensor 30 includes an image forming unit KS that is most downstream in the rotation direction of the intermediate transfer belt 7 among the image forming units YS, MS, CS, and KS, and the rotation of the intermediate transfer belt relative to the image forming unit. It is provided between the steering roller 8b on the downstream side in the direction. In this embodiment, an angle sensor is used as the belt end sensor 30. The belt end sensor 30 is disposed between the image forming unit KS and the tension roller 8b at a position outside the longitudinal end of the intermediate transfer belt 7 so as to be orthogonal to the longitudinal end of the intermediate transfer belt 7. Has been. The belt end sensor 30 is rotatably supported by a bracket 31 via a shaft 32 at a substantially vertical center perpendicular to the longitudinal end of the intermediate transfer belt 7 of the belt end sensor 30. The lower part of the belt end sensor 30 is urged from the intermediate transfer belt 7 side to the outer side of the intermediate transfer belt 7 by a compression spring (pressure member) 33 with a pressure of about 0.3 N (300 g · f). . As a result, the upper portion of the belt end sensor 30 can be pressed against the longitudinal end of the intermediate transfer belt 7 in a pressurized state, and the belt end sensor 30 can detect the longitudinal end position of the intermediate transfer belt 7 with high accuracy. Improvements can be made. The length from the upper end surface to the lower end surface of the belt end sensor 30 is 2 cm. When the intermediate transfer belt 7 approaches the longitudinal end portion (right side in the drawing) of the intermediate transfer belt as shown by a one-dot chain line in FIG. 3A, a belt end sensor is detected at the longitudinal end portion of the intermediate transfer belt. When the upper portion is pushed, the inclination angle θ of the belt end sensor 30 with respect to the intermediate transfer belt surface changes. The belt end sensor 30 outputs a signal corresponding to the inclination angle θ. That is, the position of the intermediate transfer belt 7 in the longitudinal direction of the steering roller 8b is grasped from the inclination angle θ of the belt end sensor 30. The control unit 100 takes in an output signal from the belt end sensor 30 and obtains a shift position of the intermediate transfer belt 7 based on the output signal. In this embodiment, the inclination angle θ of the belt end sensor 30 is sampled every 10 ms, and the average value of the 20 sampled sampling data is set as the position near the intermediate transfer belt 7 at that time. The offset position of the intermediate transfer belt 7 can be obtained using a predetermined arithmetic expression or using a predetermined table. As shown in the figure, when the inclination angle of the belt end sensor 30 with respect to the longitudinal end portion of the intermediate transfer belt 7 is θ, the shift position of the intermediate transfer belt 7 is a predetermined arithmetic expression using a trigonometric function sin θ. Can be sought.

  Of the longitudinal end portions 8b1 and 8b2 of the steering roller 8b, the longitudinal end portion 8b1 on the back side of the main body of the image forming apparatus is rotatable on a support plate (not shown) via a bearing (not shown). Is supported so that the angle can be freely changed. The longitudinal end 8b2 on the front side of the image forming apparatus main body is rotatable on a support plate (not shown) via a bearing 81 (see FIG. 2B) and moved by a predetermined amount in the horizontal direction with respect to the support plate. Supported to be able to. The roller end displacement mechanism 40 is provided at a position outside the longitudinal end of the intermediate transfer belt 7 on the longitudinal end 8b2 side of the steering roller 8b (see FIG. 2A). The roller end displacement mechanism 40 includes a plate-like cam 41 for displacing the longitudinal end 8b2 of the steering roller 8b in the horizontal direction (moving direction). The cam 41 is supported by a rotatable cam shaft 42 disposed in parallel with the drive roller 8a. When the cam shaft 42 is rotated by a cam motor (drive source) M, the cam 41 rotates in the CW direction or the CCW direction indicated by an arrow. The bearing 81 of the steering roller 8b is urged by the compression spring 43 from the outside to the inside of the intermediate transfer belt 7, and is in contact with the outer peripheral surface (cam surface) of the cam 41 in a pressurized state. A compression spring support member 44 supports the compression spring 43. A cam surface of the cam 41 is provided with a first cam portion 41a, a second cam portion 41b, and a third cam portion 41c. The second cam portion 41b is a cam portion for displacing the steering roller 8b via a bearing 81 so that the intermediate transfer belt 7 is supported at a predetermined reference position by the steering roller 8b. The dimension b to the cam shaft 42 of the second cam part 41b is smaller than the dimension a to the cam shaft 42 of the first cam part 41a (a <b), and the dimension c to the cam shaft 42 of the third cam part 41c. Greater than (a> c). That is, the size relationship among the dimensions a, b, c of the first cam portion 41a, the second cam portion 41b, and the third cam portion 41c is a> b> c.

  The cam 41 is rotated in the CW direction from the position shown in FIG. 2 (b), and the rotation of the cam 41 is stopped at a position where the first cam portion 41 a contacts the bearing 81. Then, the longitudinal end 8b2 of the steering roller 8b is displaced in the rotational direction of the intermediate transfer belt 7 shown in FIG. As a result, the winding angle of the intermediate transfer belt 7 around the steering roller 8b changes, and the intermediate transfer belt 7 moves in the displacement direction of the steering roller 8b. On the contrary, the cam 41 is rotated in the CCW direction from the position shown in FIG. 2B, and the rotation of the cam 41 is stopped at the position where the third cam portion 41 c contacts the bearing 81. Then, the longitudinal end 8b2 of the steering roller 8b is displaced in the direction opposite to the rotation direction of the intermediate transfer belt 7 shown in FIG. As a result, the winding angle of the intermediate transfer belt 7 around the steering roller 8b changes, and the intermediate transfer belt 7 moves in the displacement direction of the steering roller 8b. FIG. 2C shows a temporal change in the end position (belt end position) in the longitudinal direction of the intermediate transfer belt 7 when the longitudinal end 8b2 of the steering roller 8b is displaced. As shown in FIG. 2A, an angle formed by the steering roller 8b before displacement shown by a solid line and the steering roller 8b after displacement shown by a one-dot chain line is a steering roller angle θr. As shown in FIG. 2C, when the steering roller angle θr is changed from negative to positive (−3 ° to + 6 °), the shifting speed of the intermediate transfer belt 7, that is, the belt becomes larger as the steering roller angle θr increases. It can be seen that the changing speed of the end position increases. In the image forming apparatus of this embodiment, when the steering roller angle θr is ± 3 degrees, the shifting speed of the intermediate transfer belt 7 is ± 70 to ± 130 μm / second. This shift speed of ± 70 to ± 130 μm / sec is an optimal shift speed from the viewpoint of controlling the color shift of the toner image transferred to the surface of the intermediate transfer belt 7 and the meandering while the intermediate transfer belt 7 is rotating. Therefore, in this embodiment, the shift position of the intermediate transfer belt 7 is controlled at the steering roller angle θr in the vicinity of ± 3 degrees corresponding to the shift speed ± 70 to ± 130 μm / second (hereinafter referred to as the shift reference speed). I made it. That is, when the intermediate transfer belt 7 moves from the predetermined belt end reference position to the rear side and the front side in the longitudinal direction of the steering roller 8b, the position of the intermediate transfer belt 7 close to the steering roller angle ± 3 degrees. Control was performed. In this embodiment, for example, the longitudinal position of the intermediate transfer belt when the angle θ (see FIG. 3A) formed by the longitudinal end of the intermediate transfer belt 7 and the belt end sensor 30 is 45 ° is defined as the belt. It is set as the end reference position (target position). The belt end reference position is not limited to the above angle, and the longitudinal position of the intermediate transfer belt at a desired angle may be set as the belt reference position. The steering roller angle corresponding to the shifting speed ± 70 to ± 130 μm / sec of the intermediate transfer belt 7 is not limited to ± 3 degrees, and the shape of the intermediate transfer belt 7 or the rollers 8 a to 8 d and the intermediate transfer belt 7 are moving around. It varies depending on the frictional force.

  [Description of Intermediate Transfer Belt Shift Control Initialization]: The intermediate transfer belt shift control initialization performed before the control unit 100 executes an intermediate transfer belt shift target value changing sequence described later will be described. FIG. 4 is a flowchart of the intermediate transfer belt shift control initialization.

  In S1, the cam motor M is rotationally driven by a predetermined amount, the cam 41 is rotated in the CCW direction, the steering roller 8b is displaced, and θr = −10 degrees is fixed. As a result, the intermediate transfer belt 8 starts to move toward the front side of the steering roller 8b and stops at a predetermined position when the steering roller 8b is fixed at θr = −10 degrees.

  In S2, the cam motor M is rotationally driven by a predetermined amount, the cam 41 is rotated in the CW direction, the steering roller 8b is displaced, and fixed at θr = + 5 degrees (= B). As a result, the intermediate transfer belt 8 starts to move toward the back side of the steering roller 8b and stops at a predetermined position when the steering roller 8b is fixed at θr = B.

  In S3, the intermediate transfer belt 8 shifts by a shift distance from the stop position when the steering roller 8b is fixed at θr = −10 degrees to the stop position when the steering roller 8b is fixed at θr = B. The time difference C required for the measurement is measured with a timer.

  In S <b> 4, the shift speed A is obtained from the shift time C and the shift movement distance D of the intermediate transfer belt 8.

  In S5, it is determined whether or not the shifting speed A obtained in S4 is in the range of the shifting reference speed ± 70 to ± 130 μm / sec (± 130 μm / sec <A <± 70 μm / sec). If the shift speed A is within the shift reference speed range (YES), the process proceeds to S6, and if the shift speed A is not within the shift reference speed range (NO), the process proceeds to S7.

  In S6, θr is determined to be B, and the steering roller 8b is displaced within the range of +5 degrees and −5 degrees, and the shift control of the intermediate transfer belt 7 is performed.

  In S7, it is determined whether or not the shifting speed A is greater than the maximum allowable speed of the shifting reference speed ± 130 μm / second. If the shift speed A is greater than the maximum allowable speed of the shift reference speed ± 130 μm / sec (YES), the process proceeds to S8. If the shift speed A is smaller than the maximum allowable speed of the shift reference speed ± 130 μm / sec (YES), the process proceeds to S9.

  In S8, an angle smaller than B (B = B-1), for example, +4 degrees is used as θr, and the processes from S1 to S4 are repeated to determine whether the shifting speed A is within the range of the shifting reference speed (S5). ). When the shifting speed A is not within the range of the shifting reference speed and is greater than the maximum allowable speed ± 130 μm / sec, the process from S1 to S7 is repeated using an angle smaller than +4 degrees as θr.

  In S9, an angle larger than B (B = B + 1), for example, +6 degrees, is used as θr, and the processes from S1 to S4 are repeated to determine whether the shifting speed A is within the range of the shifting reference speed (S5). If the shifting speed A is not within the range of the shifting reference speed and is smaller than the maximum allowable speed ± 130 μm / second, the process from S1 to S7 is repeated using an angle larger than +6 degrees as θr.

  In this way, in the intermediate transfer belt shift control initialization, the process of obtaining θr is performed so that the shift speed A of the intermediate transfer belt 7 is within the shift reference speed range.

  [Explanation of the intermediate transfer belt shift target value change sequence by endurance time]: As the endurance time (rotation drive time) of the intermediate transfer belt increases, it is caused by indentation streaks on the inner surface of the intermediate transfer belt due to foreign matter adhering to the roller surface The plastic deformation of the belt is promoted. Therefore, in this embodiment, every time the accumulated rotation time D of the intermediate transfer belt reaches a set time for preventing deformation of the belt due to foreign matter, for example, 30 hours, the target value of the intermediate transfer belt shift control is changed to thereby change the intermediate transfer belt. The indentation streaks were not concentrated in one place in the longitudinal direction of the belt.

  FIG. 5 is an explanatory diagram of the shift movement range when the shift control of the intermediate transfer belt 7 is performed. In this embodiment, as shown in FIG. 5, the movable range of the intermediate transfer belt 7 on the back side and the near side in the longitudinal direction is set to 2 cm. Within this 2 cm shift possible range, the shift target value of the intermediate transfer belt 7 is gradually changed. This shiftable range is not limited to 2 cm and may be set to a desired value.

  An intermediate transfer belt shift target value changing sequence executed by the control unit 100 in accordance with the accumulated rotation time of the intermediate transfer belt 7 will be described. FIG. 6 is a flowchart of an intermediate transfer belt shift target value changing sequence.

  In S11, the rotation driving time of the intermediate transfer belt 7 is obtained based on an output signal from a predetermined rotation speed sensor (not shown) that detects the rotation speed of the intermediate transfer belt 7. Then, it is determined whether or not an accumulated rotation time (belt rotation time) D obtained by integrating the rotation driving time of the intermediate transfer belt 7 has reached 30 hours. When the accumulated rotation time D of the intermediate transfer belt 7 reaches 30 hours, the process proceeds to S12.

  In S 12 and S 14, the current shift target position of the intermediate transfer belt 7 is determined based on the output signal of the belt end sensor 30. Then, based on the current near target position of the intermediate transfer belt 7, it is determined whether the change direction of the near target value is set to the front side in the longitudinal direction of the steering roller 8b or the far side in the longitudinal direction of the steering roller 8b. In the initial S12 of S12 and S14, the changing direction of the shift target value of the intermediate transfer belt 7 is set to the front side in the longitudinal direction of the steering roller 8b. However, the longitudinal position of the intermediate transfer belt 7 is changed by displacing the steering roller 8b, and when the steering roller 8b is at the limit position of the movable range described above, the direction of change of the target value is set in the opposite direction. To do. In S12, when the target shift position of the intermediate transfer belt 7 reaches the innermost position (the settable innermost position) that is the limit of the movable range on the inner side in the longitudinal direction (YES), the process proceeds to S13, and the inner side in the longitudinal direction. If the innermost position that is the limit of the movable range is not reached (NO), the process proceeds to S14. In S13, the changing direction of the shift target value is set to the front side in the longitudinal direction. In S14, when the target shift position of the intermediate transfer belt 7 reaches the innermost position (the settable innermost position) that is the limit of the movable range on the front side in the longitudinal direction (YES), the process proceeds to S15 and the inner side in the longitudinal direction. If the innermost position that is the limit of the movable range is not reached (NO), the process proceeds to S16. In S15, the changing direction of the shift target value is set on the far side in the longitudinal direction. That is, by performing the processing in S12 and S14, the deviation target value of the intermediate transfer belt 7 is prevented from exceeding the movable range.

  In S16, the deviation target value of the intermediate transfer belt 7 is set to a predetermined value smaller than the movable range in the change direction, for example, 3 mm.

  In S17, θr (steering roller angle) corresponding to the target deviation value of the intermediate transfer belt 7 set in S16 is obtained from a predetermined deviation target value-θr conversion table. Then, θr is gradually changed by performing the above-described shift control initialization so as to displace the steering roller 8b based on this θr. As a result, the intermediate transfer belt 7 can be reciprocated within a movable range with respect to the belt end reference position, and indentation streaks can be prevented from being concentrated at one place in the longitudinal direction of the intermediate transfer belt 7.

  In S18, the accumulated rotation time D is cleared (= 0 hours). As a result, a series of processes of the intermediate transfer belt shift target value changing sequence based on the durability time is completed.

  In the image forming apparatus of this embodiment, when the accumulated rotation time of the intermediate transfer belt 7 reaches a set time (30 hours) for preventing deformation of the belt due to foreign matters, the cam 41 displaces the steering roller 8b and the intermediate transfer belt 7 is moved. Change the target position. Thereby, it is possible to prevent the indentation streaks from being concentrated at one place in the longitudinal direction of the intermediate transfer belt 7. As a result, deformation of the intermediate transfer belt 7 due to foreign matter adhering to the surfaces of the rollers 8a, 8b, 8c, and 8d can be reduced, and the endurance life of the intermediate transfer belt 7 can be extended.

[Example 2]
Another example of the image forming apparatus will be described. In the image forming apparatus according to the present exemplary embodiment, the control unit executes the intermediate transfer belt shift target value change sequence based on the number of durable sheets instead of the intermediate transfer belt shift target value change sequence based on the accumulated rotation time of the image forming apparatus according to the first exemplary embodiment. It is comprised as follows. Except for this point, the configuration is the same as that of the image forming apparatus of the first embodiment. In this embodiment, the same members and portions as those of the image forming apparatus of Embodiment 1 are denoted by the same reference numerals.

  [Explanation of the target value change sequence for the intermediate transfer belt depending on the endurance number]: As the endurance number of the intermediate transfer belt (recording material transport number) increases, foreign matter adhering to the roller surface causes indentation streaks on the inner surface of the intermediate transfer belt. The plastic deformation of the resulting belt is promoted. Therefore, in this embodiment, every time the cumulative number of recording material transports E of the intermediate transfer belt reaches a set number for preventing deformation of the belt due to foreign matter, for example, 50,000, the target value of the intermediate transfer belt shift control is changed. As a result, the indentation streaks are not concentrated at one place in the longitudinal direction of the intermediate transfer belt. As in Example 1, the movable range of the intermediate transfer belt in the longitudinal direction on the back side and the near side was set to 2 cm.

  An intermediate transfer belt shift target value changing sequence executed by the control unit 100 in accordance with the cumulative number of recording material transported sheets of the intermediate transfer belt 7 will be described. FIG. 7 is a flowchart of the intermediate transfer belt shift target value changing sequence.

  In S21, the number of recording material transported sheets of the intermediate transfer belt 7 is obtained based on an output signal from a predetermined recording material sensor (not shown) that detects the recording material transported by the intermediate transfer belt 7. Then, it is determined whether or not the total recording material transport number E obtained by integrating the recording material transport number of the intermediate transfer belt 7 has reached 50,000. When the accumulated recording material transport number E of the intermediate transfer belt 7 reaches 50,000, the process proceeds to S22.

  In S 22 and S 24, the current shift target position of the intermediate transfer belt 7 is determined based on the output signal of the belt end sensor 30. Based on the current shift target position of the intermediate transfer belt 7, it is determined whether the shift target value change direction is set to the front side in the longitudinal direction of the steering roller 8b or to the rear side in the longitudinal direction of the steering roller 8b. In the initial S22 out of S22 and S24, the changing direction of the shift target value of the intermediate transfer belt 7 is set to the front side in the longitudinal direction of the steering roller 8b. However, the longitudinal position of the intermediate transfer belt 7 is changed by displacing the steering roller 8b, and when the steering roller 8b is at the limit position of the movable range described above, the direction of change of the target value is set in the opposite direction. To do. In S22, when the target shift position of the intermediate transfer belt 7 becomes the innermost position (the settable innermost) that is the limit of the movable range on the inner side in the longitudinal direction (YES), the process proceeds to S23, and the inner side in the longitudinal direction. If the innermost position that is the limit of the movable range is not reached (NO), the process proceeds to S24. In S23, the changing direction of the shift target value is set to the front side in the longitudinal direction. In S24, when the target position of the intermediate transfer belt 7 shifts to the innermost position (settable innermost) which is the limit of the movable range on the front side in the longitudinal direction (YES), the process proceeds to S25, and the inner side in the longitudinal direction. If the innermost position that is the limit of the movable range is not reached (NO), the process proceeds to S26. In S25, the changing direction of the shift target value is set on the far side in the longitudinal direction. That is, by performing the processing in S22 and S24, the deviation target value of the intermediate transfer belt 7 is prevented from exceeding the movable range.

  In S26, the deviation target value of the intermediate transfer belt 7 is set to a predetermined value that is smaller than the movable range in the change direction, for example, 3 mm.

  In S27, θr (steering roller angle) corresponding to the target deviation value of the intermediate transfer belt 7 set in S26 is obtained from a predetermined deviation target value-θr conversion table. Then, θr is gradually changed by performing the above-described shift control initialization so as to displace the steering roller 8b based on this θr. As a result, the intermediate transfer belt 7 can be reciprocated within a movable range with respect to the belt end reference position, and indentation streaks can be prevented from being concentrated at one place in the longitudinal direction of the intermediate transfer belt 7.

  In S28, the accumulated recording material conveyance number E is cleared (= 0). Thereby, a series of processes of the target value changing sequence for the intermediate transfer belt shift by the durable number is completed.

  The image forming apparatus of this embodiment displaces the steering roller 8b by the cam 41 when the cumulative number of recording material transported sheets of the intermediate transfer belt 7 reaches a set number (50,000 sheets) for preventing belt deformation due to foreign matter. The shift target position of the intermediate transfer belt 7 is changed. Thereby, it is possible to prevent the indentation streaks from being concentrated at one place in the longitudinal direction of the intermediate transfer belt 7. As a result, deformation of the intermediate transfer belt 7 due to foreign matter adhering to the surfaces of the rollers 8a, 8b, 8c, and 8d can be reduced, and the endurance life of the intermediate transfer belt 7 can be extended.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

7: Intermediate transfer belt, 8a: Driving roller, 8b: Steering roller, 8c: Secondary transfer counter roller, 8d: Tension roller, 30: Belt end sensor, 41: Cam

Claims (2)

In an image forming apparatus comprising: a belt that carries a toner image; and a plurality of rotation support members that rotatably support the belt.
A detection member that detects a position in a longitudinal direction orthogonal to the rotation direction of the belt, and a predetermined rotation support member that displaces the belt to a predetermined target position in a longitudinal direction orthogonal to the rotation direction of the belt. A displacement member, and when the rotation time of the belt reaches a set time for preventing belt deformation due to foreign matter adhering to an outer surface of the rotation support member that contacts the belt, a predetermined value is set by the displacement member. An image forming apparatus characterized in that the predetermined support position of the belt is changed by displacing the rotation support member. A belt that carries a toner image; a plurality of rotation support members that rotatably support the belt; and a transfer member that forms a transfer portion with the belt. In the image forming apparatus for transferring the toner image carried by the belt to a recording material,
A detection member that detects a position in a longitudinal direction orthogonal to the rotation direction of the belt, and a predetermined rotation support member that displaces the belt to a predetermined target position in a longitudinal direction orthogonal to the rotation direction of the belt. A displacement member to be moved, and when the number of recording material transports of the belt reaches a set number for preventing belt deformation due to foreign matter adhering to an outer surface of the rotation support member in contact with the belt, the displacement member And a predetermined target position of the belt is changed by displacing the predetermined rotation support member.