Image forming apparatus, belt adjustment method, and belt adjustment program

Abstract

To facilitate position adjustment of an endless belt.SOLUTION: An image forming apparatus comprises: a plurality of rollers; an endless intermediate transfer belt 30 that is laid on the outside of the plurality of rollers; developing units that form toner images on the intermediate transfer belt 30; a driving unit 33B that rotates at least one drive roller 33 of the plurality of rollers; a position adjustment mechanism 80 that changes the relative positions of the plurality of rollers; and a position adjustment control unit that controls the position adjustment mechanism to change the relative positions of the intermediate transfer belt 30 and the drive roller 33, with a tension applied to the intermediate transfer belt 30 adjusted to a second tension that is smaller than a first tension in a development state in which the toner images are formed by the developing units on the intermediate transfer belt 30.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, a belt adjustment method, and a belt adjustment program, and in particular to an image forming apparatus that fixes toner to a recording medium by applying pressure and heat to the recording medium, a belt adjustment method executed in the image forming apparatus, and a belt adjustment program for causing a computer that controls the image forming apparatus to execute the belt adjustment method. [Background technology]

[0002] In image forming devices such as copiers, printers, and facsimile machines, a toner image formed by developing an electrostatic latent image with toner is transferred onto a transfer belt, and the toner image carried by the transfer belt is transferred onto a recording medium such as paper. The transfer belt rotates while being stretched over multiple rollers arranged in parallel. For this reason, the transfer belt may become biased or meander with respect to a reference track.

[0003] For example, Japanese Patent Application Laid-Open No. 2017-111203 describes a belt drive device including: an endless belt; a tension roller that is one of a plurality of tension rollers that tension the endless belt and rotate it; a frame member that is disposed at both axial ends of the tension roller; an arm member that is disposed at at least one axial end of a rotation shaft of the tension roller, the arm member having a first end rotatably supported by the axial end and a second end rotatably supported by the frame member, and that supports the axial end so as to be freely reciprocating in a predetermined direction perpendicular to the axial direction; an elastic member that is disposed between the first end and the second end and biases the axial end in a direction that increases the tension of the endless belt; a meandering correction mechanism that tilts the rotation shaft in the one direction in accordance with the amount of displacement of the endless belt in the axial direction; and a regulating member that regulates the movement of the axial end in the one direction within a range in which the center of rotation of the second end is disposed in the one direction with respect to the resultant force direction of the tension of the endless belt from the axial end.

[0004] In the image forming apparatus described in JP 2017-111203 A, the rotating shaft is tilted in a predetermined direction perpendicular to the axial direction according to the amount of displacement of the endless belt in the axial direction, so that the tension of the endless belt varies in the axial direction. However, the shaft end portion of the rotating shaft that is not supported by the arm member does not move, so the tension of the shaft end portion of the belt that is not supported by the arm member remains the same as before the rotating shaft is tilted in one direction. Therefore, the frictional force between the endless belt and the tension roller is maintained, so that the movement of the endless belt in the axial direction is hindered by the tilt of the tension roller, and there is a problem that it takes time to move the endless belt in the axial direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-111203 A Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus in which the position of an endless belt can be easily adjusted.

[0007] Another object of the present invention is to provide a belt adjustment method that facilitates the position adjustment of an endless belt.

[0008] It is still another object of the present invention to provide a belt adjustment program that facilitates the position adjustment of an endless belt. [Means for solving the problem]

[0009] According to one aspect of the present invention, an image forming apparatus includes a plurality of rollers, an endless belt that is stretched around the outside of the plurality of rollers, a developing unit that forms a toner image on the belt, and a drive unit that rotates at least one drive roller of the plurality of rollers. By changing the distance between the rotation axis of at least one position adjustment roller among the plurality of rollers and the rotation axis of the drive roller,The device includes a position adjustment mechanism that changes the relative positions of the rollers, and a position adjustment control unit that controls the position adjustment mechanism to change the relative position between the belt and the drive roller in a state in which tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by a developing device. The position adjustment control unit controls the position adjustment mechanism to set the belt tension to a second tension while making the movement amounts of both ends of the rotation shaft of the position adjustment roller different from each other. do.

[0010] According to this aspect, the belt, which is stretched over a plurality of rollers, rotates with the rotation of the drive roller. When the tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by a developing device, the frictional force between the drive roller and the belt is reduced. This makes it easier to change the relative positions of the drive roller and the belt. As a result, it is possible to provide an image forming apparatus in which the position of the belt can be easily adjusted. In addition, the tension of the belt can be easily adjusted, and the relative position between the belt and the drive roller can be easily changed.

[0014] According to this aspect, the relative positions of the belt and the drive roller can be easily changed.

[0015] Preferably, the device further includes a position detection unit that detects the relative position of a reference line parallel to the rotation direction of the belt with respect to the drive roller, and the position adjustment control unit changes the relative position of the belt and the drive roller based on the relative position detected by the position detection unit.

[0016] According to this aspect, when the relative position between the belt and the drive roller changes, the relative position is changed, so that the belt can be adjusted to a predetermined position with respect to the drive roller.

[0017] Preferably, the multiple rollers are configured to suspend the belt such that the relative position between the belt and the drive roller changes in a first direction from a reference position toward a first relative position, and the position adjustment control unit adjusts the relative position between the belt and the drive roller such that the relative position between the belt and the drive roller changes in a second direction toward a second relative position opposite the first relative position with respect to the reference position.

[0018] According to this aspect, when the relative position between the belt and the drive roller is not adjusted, the relative position changes in the first direction, and when the relative position between the belt and the drive roller is adjusted, the relative position changes in the second direction, so that the belt can be positioned between the first relative position and the second relative position with respect to the drive roller.

[0019] Preferably, the position adjustment control section changes the relative position between the belt and the drive roller in a direction opposite to a direction in which the relative position between the belt and the drive roller was previously changed.

[0020] According to this aspect, the direction of change is reversed every time the relative position between the belt and the drive roller is changed, so that the belt can be adjusted to a predetermined position with respect to the drive roller.

[0021] Preferably, the device further comprises a timing determination unit which determines the timing for changing the relative position between the belt and the drive roller based on an amount of variation in the relative position between the belt and the drive roller.

[0022] According to this aspect, when the relative position between the belt and the drive roller deviates by a predetermined amount from the reference position, the relative position between the belt and the drive roller is changed, so that the relative position between the belt and the drive roller can be adjusted at an appropriate timing.

[0023] Preferably, the device further comprises a timing determination unit which determines the timing for changing the relative position between the belt and the drive roller based on the distance that the belt has rotated.

[0024] According to this aspect, the relative position between the belt and the drive roller is changed every time the belt rotates a predetermined distance, so that the relative position between the belt and the drive roller can be adjusted at an appropriate timing.

[0025] Preferably, the drive section rotates the drive roller at a second rotation speed faster than the first rotation speed in the developing state while the relative position between the belt and the drive roller is being adjusted by the position adjustment control section.

[0026] According to this aspect, the relative position between the belt and the drive roller is adjusted while rotating the drive roller at a second rotation speed that is faster than the first rotation speed in the developing state, thereby making it possible to shorten the time required to adjust the relative position between the belt and the drive roller.

[0027] According to another aspect of the present invention, an image forming apparatus includes a plurality of rollers, an endless belt stretched around the outside of the plurality of rollers, a developing unit that forms a toner image on the belt, a driving unit that rotates at least one driving roller among the plurality of rollers, a position adjustment mechanism that changes a relative position of the plurality of rollers, and a position adjustment control unit that controls the position adjustment mechanism to change the relative position of the belt and the driving roller in a state in which a tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by the developing unit, and the driving unit rotates the driving roller at a second rotation speed that is faster than the first rotation speed in the developing state while the relative position between the belt and the driving roller is adjusted by the position adjustment control unit, The second rotational speed is a maximum speed corresponding to the upper limit speed at which the belt can rotate.

[0028] According to this aspect, the time required to adjust the relative positions of the belt and the drive roller can be shortened.

[0029] According to another aspect of the present invention, a belt adjustment method is a belt adjustment method for adjusting an image forming apparatus, the image forming apparatus including a plurality of rollers, an endless belt stretched around the plurality of rollers, a developing device that forms a toner image on the belt, and a drive unit that rotates at least one drive roller of the plurality of rollers. By changing the distance between the rotation axis of at least one position adjustment roller among the plurality of rollers and the rotation axis of the drive roller, and a position adjustment mechanism for changing the relative positions of the plurality of rollers, and the image forming apparatus is caused to execute a position adjustment step of changing the relative position between the belt and the drive roller in a state in which the tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by a developing device by controlling the position adjustment mechanism. The position adjustment step includes a step of controlling the position adjustment mechanism to set the belt tension to a second tension while making the movement amounts of both ends of the rotation shaft of the position adjustment roller different from each other. .

[0030] According to this aspect, it is possible to provide a belt adjustment method that makes it easy to adjust the position of an endless belt.

[0031] According to another aspect of the present invention, the belt adjustment program is executed by a computer that controls an image forming apparatus, the image forming apparatus including a plurality of rollers, an endless belt that is stretched around the plurality of rollers, a developing device that forms a toner image on the belt, a driving unit that rotates at least one driving roller among the plurality of rollers, and By changing the distance between the rotation axis of at least one position adjustment roller among the plurality of rollers and the rotation axis of the drive roller,and a position adjustment mechanism for changing the relative positions of the plurality of rollers, and a position adjustment step for controlling the position adjustment mechanism to change the relative position between the belt and the drive roller in a state in which the tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by a developing device, is performed by a computer. The position adjustment step includes a step of controlling the position adjustment mechanism to set the belt tension to a second tension while making the movement amounts of both ends of the rotation shaft of the position adjustment roller different from each other. .

[0032] According to this aspect, it is possible to provide a belt adjustment program that makes it easy to adjust the position of an endless belt. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a perspective view illustrating the appearance of a printer according to an embodiment of the invention. [Diagram 2] FIG. 2 is a block diagram illustrating an example of a hardware configuration of a printer. [Diagram 3] FIG. 2 is a cross-sectional view illustrating an example of the internal configuration of a printer. [Figure 4] FIG. 4 is a diagram illustrating an example of a suspension state of an intermediate transfer belt. [Diagram 5] FIG. 2 is a first diagram showing an example of a position adjustment mechanism. [Figure 6] FIG. 13 is a second diagram showing an example of a position adjustment mechanism. [Figure 7] 6A and 6B are diagrams illustrating an example of positions of a driven roller and a cam at an image forming position. [Figure 8] 11 is a diagram showing an example of positions of a driven roller and a cam in a first standby position. FIG. [Figure 9] 13 is a diagram showing an example of positions of a driven roller and a cam in a second standby position. FIG. [Figure 10] 5A and 5B are schematic diagrams for explaining the relative positions of a drive roller and a driven roller and the moving direction of an intermediate transfer belt. [Figure 11] 2 is a block diagram showing an example of functions of a CPU included in the printer according to the embodiment. FIG. [Figure 12] 6 is a flowchart showing an example of the flow of a belt adjustment process in the present embodiment. [Figure 13] 13A and 13B are schematic diagrams for explaining the relative positions of a drive roller and a driven roller and the moving direction of an intermediate transfer belt in a first modified example. [Figure 14] 13A and 13B are schematic diagrams for explaining the relative positions of a drive roller and a driven roller and the moving direction of an intermediate transfer belt in a second modified example. [Figure 15] 13 is a block diagram showing an example of functions of a CPU included in a printer according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[0035] <First embodiment> Fig. 1 is a perspective view showing the appearance of a printer according to one embodiment of the present invention. Fig. 2 is a block diagram showing an example of a hardware configuration of the printer. With reference to Figs. 1 and 2, printer 100 is an example of an image forming device, and includes a main circuit 110, an image forming unit 140 for forming an image on paper or the like based on image data, a paper feed unit 150 for supplying paper to image forming unit 140, and an operation panel 160 as a user interface.

[0036] The main circuit 110 includes a CPU (Central Processing Unit) 111 that controls the entire printer 100, a communication interface (I / F) unit 112, a ROM (Read Only Memory) 113, a RAM (Random Access Memory) 114, a hard disk drive (HDD) 115 as a large-capacity storage device, and an external storage device 117. The CPU 111 is connected to an image forming unit 140, a paper feeding unit 150, and an operation panel 160, and controls the entire printer 100.

[0037] Paper feed unit 150 transports the paper stored in a paper feed cassette to image forming unit 140. Image forming unit 140 is controlled by CPU 111 and forms an image by a well-known electrophotographic method, forming an image on the paper transported by paper feed unit 150 based on image data input from CPU 111, and discharging the paper on which the image has been formed to paper discharge tray 39 (see FIG. 3). The image data output by CPU 111 to image forming unit 140 includes image data such as print data received from an external personal computer or the like.

[0038] The ROM 113 stores the programs executed by the CPU 111 or data necessary for executing the programs. The RAM 114 is used as a work area when the CPU 111 executes the programs.

[0039] Operation panel 160 is provided on the top surface of printer 100. Operation panel 160 includes a display unit 161 and an operation unit 163. Display unit 161 is, for example, a liquid crystal display (LCD), and displays an instruction menu for the user, information related to acquired image data, and the like. Note that instead of an LCD, for example, an organic EL (electroluminescence) display can be used as long as it is a device that displays images.

[0040] Operation unit 163 includes touch panel 165 and hard key unit 167. Hard key unit 167 includes a plurality of hard keys. The hard keys are, for example, contact switches. Touch panel 165 detects a position on the display surface of display unit 161 that is designated by the user.

[0041] The communication I / F unit 112 is an interface for connecting the printer 100 to a network. The communication I / F unit 112 communicates with other computers connected to the network using a communication protocol such as TCP (Transmission Control Protocol) or UDP (User Datagram Protocol). The network to which the communication I / F unit 112 is connected is a local area network (LAN), and the connection form may be either wired or wireless. The network is not limited to a LAN, and may be a wide area network (WAN), a public switched telephone network (PSTN), the Internet, or the like.

[0042] External storage device 117 is controlled by CPU 111, and is equipped with CD-ROM (Compact Disk Read Only Memory) 118 or a semiconductor memory. In this embodiment, an example in which CPU 111 executes a program stored in ROM 113 will be described, but CPU 111 may control external storage device 117 to read a program to be executed by CPU 111 from CD-ROM 118, store the read program in RAM 114, and execute it.

[0043] The recording medium for storing the program executed by CPU 111 is not limited to CD-ROM 118, but may be a medium such as a flexible disk, a cassette tape, an optical disk (MO (Magnetic Optical Disc) / MD (Mini Disc) / DVD (Digital Versatile Disc)), an IC card, an optical card, a semiconductor memory such as a mask ROM, or an EPROM (Erasable Programmable ROM). Furthermore, CPU 111 may download a program from a computer connected to the network and store it in HDD 115, or a computer connected to the network may write a program to HDD 115, and the program stored in HDD 115 may be loaded into RAM 114 and executed by CPU 111. The program here includes not only a program that can be directly executed by CPU 111, but also a source program, a compressed program, an encrypted program, and the like.

[0044] Figure 3 is a cross-sectional view that shows a schematic example of the internal configuration of a printer. For the sake of explanation, the left-right direction in Figure 3 is referred to as the left-right direction, and the front-to-back direction is referred to as the depth direction. The direction from left to right in the left-to-right direction is referred to as the right side direction, and the direction from right to left is referred to as the left side direction. The direction from the front to the back in the depth direction is referred to as the back direction, and the direction from the back to the front is referred to as the front direction.

[0045] The printer 100 includes image forming units 20Y, 20M, 20C, and 20K for yellow, magenta, cyan, and black, respectively. Here, "Y", "M", "C", and "K" represent yellow, magenta, cyan, and black, respectively. An image is formed by driving at least one of the image forming units 20Y, 20M, 20C, and 20K. When all of the image forming units 20Y, 20M, 20C, and 20K are driven, a full-color image is formed. Print data for yellow, magenta, cyan, and black is input to the image forming units 20Y, 20M, 20C, and 20K, respectively. The image forming units 20Y, 20M, 20C, and 20K differ only in the color of the toner they handle, so here, the image forming unit 20Y for forming a yellow image will be described.

[0046] The image forming unit 20Y includes an exposure device 21Y to which yellow printing data is input, a photoconductor drum 23Y which is an image carrier, a charging roller 22Y for uniformly charging the surface of the photoconductor drum 23Y, a developing device 24Y, a primary transfer roller 25Y for transferring the toner image formed on the photoconductor drum 23Y onto the intermediate transfer belt 30 which is an image carrier by the action of an electric field force, a drum cleaning blade 27Y for removing residual toner on the photoconductor drum 23Y, a toner bottle 41Y, and a toner hopper 42Y.

[0047] The toner bottle 41Y contains yellow toner. The toner bottle 41Y rotates using a toner bottle motor as a drive source, and discharges toner to the outside. The toner discharged from the toner bottle 41Y is supplied to a toner hopper 42Y. The toner hopper 42Y supplies toner to the developing device 24Y when the remaining amount of toner contained in the developing device 24Y falls below a predetermined lower limit.

[0048] Around the photoconductor drum 23Y, a charging roller 22Y, an exposure device 21Y, a developing device 24Y, a primary transfer roller 25Y, and a drum cleaning blade 27Y are arranged in this order along the rotation direction of the photoconductor drum 23Y.

[0049] After being charged by the charging roller 22Y, the photoconductor drum 23Y is irradiated with a laser beam emitted by the exposure device 21Y. The exposure device 21Y exposes the image corresponding portion of the surface of the photoconductor drum 23Y to form an electrostatic latent image. As a result, the electrostatic latent image is formed on the photoconductor drum 23Y. Then, the developing device 24Y develops the electrostatic latent image formed on the photoconductor drum 23Y with the charged toner. Specifically, the toner is placed on the electrostatic latent image formed on the photoconductor drum 23Y by the action of the electric field force, so that a toner image is formed on the photoconductor drum 23Y. The toner image formed on the photoconductor drum 23Y is transferred onto the intermediate transfer belt 30, which is an image carrier, by the action of the electric field force by the primary transfer roller 25Y. The toner remaining on the photoconductor drum 23Y without being transferred is removed from the photoconductor drum 23Y by the drum cleaning blade 27Y.

[0050] Meanwhile, the intermediate transfer belt 30 is suspended by a driving roller 33 and a driven roller 34 so as not to slacken. When the driving roller 33 rotates counterclockwise in FIG. 2, the intermediate transfer belt 30 rotates counterclockwise in the figure at a predetermined speed. In conjunction with the rotation of the intermediate transfer belt 30, the driven roller 34 rotates counterclockwise.

[0051] As a result, the image forming units 20Y, 20M, 20C, and 20K sequentially transfer the toner images onto the intermediate transfer belt 30. The timing at which each of the image forming units 20Y, 20M, 20C, and 20K transfers a toner image onto the intermediate transfer belt 30 is adjusted by detecting a reference mark provided on the intermediate transfer belt 30. As a result, the yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30.

[0052] The toner image formed on the intermediate transfer belt 30 is transferred to paper by the action of an electric field force by the secondary transfer roller 26, which is a transfer member. The paper is transported by timing roller 31 to a nip portion where the intermediate transfer belt 30 and the secondary transfer roller 26 come into contact. The paper with the toner image transferred thereto is transported to the fixing device 50, where it is heated and pressurized. This melts the toner and fixes it to the paper. The paper is then discharged to the paper output tray 39.

[0053] A belt cleaning blade 28 is provided upstream of the image forming unit 20Y of the intermediate transfer belt 30. The belt cleaning blade 28 removes toner remaining on the intermediate transfer belt 30 that has not been transferred to paper.

[0054] When forming a full-color image, the printer 100 drives all of the image forming units 20Y, 20M, 20C, and 20K, but when forming a monochrome image, it drives any one of the image forming units 20Y, 20M, 20C, and 20K. In addition, an image can be formed by combining two or more of the image forming units 20Y, 20M, 20C, and 20K. Note that, here, an example is described in which the printer 100 employs a tandem system equipped with image forming units 20Y, 20M, 20C, and 20K that form four color toners on paper, but a four-cycle system in which four color toners are transferred to paper in sequence using one photosensitive drum may also be employed.

[0055] A plurality of sheets of paper are set in paper feed cassette 35. The sheets of paper stored in paper feed cassette 35 are supplied one by one to the transport path by take-out rollers 36 attached to paper feed cassette 35, and sent to timing rollers 31 by paper feed rollers 37. When one or more sheets of paper are set in manual feed cassette 35A, the one or more sheets of paper set in manual feed cassette 35A are supplied one by one to the transport path by take-out rollers 36A attached to manual feed cassette 35A, and sent to timing rollers 31 by paper feed rollers 37.

[0056] The paper transport path includes an image forming path 45, a first transport path 46, a second transport path 47, and a front / back inversion path 48. The image forming path 45 is a path from the timing roller 31 to the path switching gate 49, and the secondary transfer roller 26 and the fixing device 50 are arranged in this order from the timing roller 31. The timing roller 31 sends the paper transported from the paper feed cassette 35 or the manual feed cassette 35A to the image forming path 45. The timing roller 31 starts transporting the paper so that the paper reaches the secondary transfer roller 26 at the timing when the toner image formed on the intermediate transfer belt 30 reaches the secondary transfer roller 26. The paper transported by the timing roller 31 is pressed against the intermediate transfer belt 30 by the secondary transfer roller 26, and the yellow, magenta, cyan, and black toner images formed on the intermediate transfer belt 30 in a superimposed manner are transferred to the paper.

[0057] The paper conveyed from the secondary transfer roller 26 is conveyed to the fixing device 50. The fixing device 50 heats and presses the paper, thereby fixing the toner to the paper. The paper is then conveyed to either the first conveying path 46 or the second conveying path 47 by the path switching gate 49.

[0058] The first transport path 46 is a path from the path switching gate 49 to the paper discharge rollers 43. The paper transported to the first transport path 46 is discharged to the paper discharge tray 39 by the paper discharge rollers 43.

[0059] The second transport path 47 is a path from the path switching gate 49 to the reversing roller 44. The second transport path 47 is connected to the image forming path 45 and the front / back reversing path 48 at the path switching gate 49. The paper entering the second transport path 47 from the path switching gate 49 is transported to the reversing roller 44. The reversing roller 44 performs three operations: a standby operation, a reversing operation, and a paper ejection operation. When performing the standby operation, the reversing roller 44 rotates forward and stops a predetermined time after the timing roller 31 is driven. As a result, the reversing roller 44 holds the paper entering from the path switching gate 49 in a state where the back end of the paper has passed through the path switching gate 49. The reversing roller 44 performs the reversing operation after the standby operation. When performing the reversing operation, the reversing roller 44 rotates backward and transports the held paper to the path switching gate 49 side. As a result, the paper is transported along the second transport path 47 by the reversing rollers 44, and is guided to the front / back reversing path 48 by the path switching gate 49. When performing a discharge operation, the reversing rollers 44 rotate forward to discharge the paper onto the paper discharge tray 39.

[0060] The front / back inversion path 48 is a path that connects the path switching gate 49 and the timing roller 31 in the image formation path 45. The paper that enters the front / back inversion path 48 from the path switching gate 49 is transported to the timing roller 31 by the transport roller 38. Therefore, an image is formed on the front side of the paper while the paper is passing through the image formation path 45 for the first time, and an image is formed on the back side of the paper while the paper passes through the image formation path 45 again via the front / back inversion path 48. The paper with the image formed on the back side is guided to the first transport path 46 by the path switching gate 49 and discharged to the paper discharge tray 39.

[0061] FIG. 4 is a diagram showing an example of a suspension state of the intermediate transfer belt. FIG. 4 is a diagram showing the intermediate transfer belt 30 as viewed from the front to the back. Referring to FIG. 4, the intermediate transfer belt 30 is an endless belt. The intermediate transfer belt 30 is stretched over a driving roller 33, a driven roller 34, and two tension rollers 61 and 63, which are arranged on the inner circumference of the intermediate transfer belt 30. The driving roller 33 and the tension rollers 61 and 63 each have a rotation shaft supported by the main body frame. Note that the rotation shafts of the tension rollers 61 and 63 may be movable relative to the main body frame when adjusting the tension of the intermediate transfer belt 30. After the adjustment of the tension of the intermediate transfer belt 30 is completed, the rotation shafts of the tension rollers 61 and 63 are fixed to the main body frame.

[0062] Support plate 81A and support plate 81B (see FIG. 6) are arranged in the front and rear directions with intermediate transfer belt 30 in between. Support plate 81A is arranged at a predetermined distance on the front side of intermediate transfer belt 30, and support plate 81B is arranged at a predetermined distance on the rear side of intermediate transfer belt 30. Support plate 81A and support plate 81B are part of the main body frame.

[0063] The drive roller 33 has a rotating shaft 33A rotatably supported at both ends by a support plate 81A and a support plate 81B. One end of the rotating shaft 33A is connected to a drive motor 33B. When the drive motor 33B is driven, the driving force is transmitted to the rotating shaft 33A, causing the drive roller 33 to rotate.

[0064] Both ends of the rotating shaft 34A of the driven roller 34 are inserted into slide holes 83 formed in the support plates 81A and 81B, respectively. The slide hole 83 is rectangular, with a vertical length slightly larger than the diameter of the rotating shaft 33A and a horizontal length larger than the diameter of the rotating shaft 33A. Therefore, the rotating shaft 34A of the driven roller 34 can slide horizontally through the slide hole 83. Hereinafter, of both ends of the rotating shaft 34A of the driven roller 34, the end supported by the support plate 81A is referred to as the front end, and the end supported by the support plate 81B is referred to as the back end.

[0065] The printer 100 includes a position adjustment mechanism that changes the relative positions of the driven roller 34 and the drive roller 33. The position adjustment mechanism moves both ends of the rotation shaft 34A of the driven roller 34 along the slide hole 83.

[0066] FIG. 5 is a first diagram showing an example of a position adjustment mechanism. FIG. 5 is a front view of the driven roller 34 seen from the front to the back direction. FIG. 6 is a second diagram showing an example of a position adjustment mechanism. FIG. 6 is a plan view of the driven roller 34 seen from above. With reference to FIGS. 5 and 6, the position adjustment mechanism 80 includes a cam 77, a support base 81, an elastic member 73, and a sliding hole 83. The cam 77 and the support base 81 are attached to each of the support plates 81A and 81B. The cam 77 has a rotating shaft 77A arranged at the center of gravity, and the rotating shaft 77A is rotatably supported by each of the support plates 81A and 81B. The rotating shaft 77A is supported by each of the support plates 81A and 81B on the left side surface direction from the sliding hole 83. The support base 81 is fixed to each of the support plates 81A and 81B on the right side surface direction from the sliding hole 83. Therefore, a slide hole 83 is located between the rotation shaft 77A of the cam 77 and the support base 81.

[0067] One end of the elastic member 73 is fixed to a side surface of the support base 81 facing the cam 77. A contact portion 75 is fixed to the other end of the elastic member 73. The contact portion 75 abuts against the rotation shaft 34A of the driven roller 34 and holds the rotation shaft 34A in a slidable state. The elastic member 73 biases the contact portion 75 toward the rotation shaft 77A of the cam 77. Therefore, the rotation shaft 34A is biased in a direction toward the rotation shaft 77A of the cam 77 by the elastic member 73. The contact portion 75 may be a bearing that supports the rotation shaft 34A of the driven roller 34.

[0068] The cam 77 is supported by the support plates 81A and 81B so as to be rotatable about the rotation shaft 77A. The cam 77 is disposed at a position where it contacts the rotation shaft 34A of the driven roller 34, and is rotated by a motor (not shown). The outer circumference of the cam 77 is elliptical. Therefore, the distance between the rotation shaft 77A and the part where it contacts the rotation shaft 34A of the driven roller 34 varies depending on the rotation angle of the cam 77. Therefore, when the cam 77 rotates, both ends of the rotation shaft 34A slide in the sliding hole 83. In this embodiment, an example will be described in which both ends of the rotation shaft 34A are moved to three different positions. The three different positions include an image forming position during a period in a developing state in which the image forming unit 140 forms an image, and a first standby position and a second standby position during a period in which the image forming unit 140 is not in a developing state. The distance between the first standby position and the rotation shaft 77A of the cam 77 is longer than the distance between the second standby position and the rotation shaft 77A of the cam 77.

[0069] The cam 77 supported by the support plate 81A and the cam 77 supported by the support plate 81B can rotate independently. Therefore, both ends of the rotation shaft 34A of the driven roller 34 can be in either a state where both are in the image forming position or a state where one is in the first standby position and the other is in the second standby position.

[0070] The length of the intermediate transfer belt 30 in the front-rear direction, in other words the width, is shorter than the lengths of the drive roller 33 and the driven roller 34 in the front-rear direction. Therefore, the intermediate transfer belt 30 is movable in a direction parallel to the rotation axis 33A of the drive roller 33. The driven roller 34 is a position adjustment roller for changing the relative positions of the intermediate transfer belt 30 and the drive roller 33.

[0071] As shown in FIG. 6, the sensor 71 is fixed to the side surface on the rear side of the support plate 81A. The sensor 71 is a photoelectric sensor having a light source and a light receiving unit that receives light emitted from the light source. The light receiving unit has a light receiving surface extending in the front-rear direction. The sensor 71 is disposed at a position where the end of the intermediate transfer belt 30 on the front side intersects with the light receiving surface in the vertical direction. A plurality of photoelectric conversion elements are arranged in the front-rear direction on the light receiving surface. The sensor 71 detects the amount of light received by each of the plurality of photoelectric conversion elements and outputs the amount of light received to the CPU 111. The sensor 71 may be a transmission type photoelectric sensor instead of a reflection type photoelectric sensor. Furthermore, an ultrasonic sensor, a magnetic sensor, or the like may be used instead of the photoelectric sensor as long as it can detect the intermediate transfer belt 30.

[0072] FIG. 7 is a diagram showing an example of the positions of the driven roller and the cam at the image forming position. FIG. 7 shows the positional relationship between the cam 77 provided on the support plate 81A and the driven roller 34. Referring to FIG. 7, when the front end of the rotation shaft 34A of the driven roller 34 is located at the image forming position, the cam 77 is at a position where the distance between the rotation shaft 77A and the rotation shaft 34A of the driven roller 34 is the shortest. The rotation angle of the cam 77 when the rotation shaft 34A of the driven roller 34 is located at the image forming position is set to 0 degrees. Hereinafter, the position of the cam 77 is indicated by the rotation angle, and the position of the cam 77 shown in FIG. 7 is referred to as the position of the rotation angle of 0 degrees. When each of the two cams 77 is located at the position of the rotation angle of 0 degrees, both ends of the rotation shaft 34A of the driven roller 34 are located at the image forming position. When the cam 77 is at a position where the rotation angle is 0 degrees, the distance L1 between the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 is maximum, and therefore the tension of the intermediate transfer belt 30 is maximum. The tension of the intermediate transfer belt 30 when each of the two cams 77 is at a position where the rotation angle is 0 degrees is defined as a first tension.

[0073] FIG. 8 is a diagram showing an example of the positions of the driven roller and the cam at the first standby position. FIG. 8 shows the positional relationship between the cam 77 provided on the support plate 81A and the driven roller 34. Referring to FIG. 8, when the rotation shaft 34A of the driven roller 34 is located at the first standby position, the cam 77 is at a position where the distance between the rotation shaft 77A and the rotation shaft 34A of the driven roller 34 is the longest. The rotation angle of the cam 77 when the rotation shaft 34A of the driven roller 34 is located at the first standby position is 90 degrees. Hereinafter, the position of the cam 77 shown in FIG. 8 is referred to as a position of a rotation angle of 90 degrees. When the cam 77 provided on the support plate 81A is located at a position of a rotation angle of 90 degrees, the front end of the rotation shaft 34A of the driven roller 34 is located at the first standby position. When the cam 77 provided on the support plate 81B is located at a position of a rotation angle of 90 degrees, the back end of the rotation shaft 34A of the driven roller 34 is located at the first standby position. When the cam 77 provided on the support plate 81A is at a position where the rotation angle is 90 degrees, the distance L2 between the front end of the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 is shortest, and therefore the tension of the intermediate transfer belt 30 is minimum.

[0074] FIG. 9 is a diagram showing an example of the positions of the driven roller and the cam at the second standby position. FIG. 9 shows the positional relationship between the cam 77 provided on the support plate 81B and the driven roller 34. When the rotational axis 34A of the driven roller 34 is located at the second standby position, the cam 77 is located between the position of the rotational angle of 0 degrees and the position of the rotational angle of 90 degrees. Therefore, the second standby position is located between the image forming position and the first standby position. Here, when the rotational axis 34A of the driven roller 34 is located at the second standby position, the rotational angle of the cam 77 is set to 45 degrees. Hereinafter, the position of the cam 77 shown in FIG. 9 is referred to as the position of the rotational angle of 45 degrees. When the cam 77 provided on the support plate 81A is located at the position of the rotational angle of 45 degrees, the front end of the rotational axis 34A of the driven roller 34 is located at the second standby position. When the cam 77 provided on the support plate 81B is located at the position of the rotational angle of 45 degrees, the back end of the rotational axis 34A of the driven roller 34 is located at the second standby position. When the cam 77 provided on the support plate 81A is at a rotation angle of 45 degrees, the distance L3 between the front end of the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 is a length between the distance L1 when the front end is at the image forming position and the distance L2 when the front end is at the first standby position. Therefore, when each of the two cams 77 is at a rotation angle of 45 degrees, the tension of the intermediate transfer belt 30 is intermediate. The tension of the intermediate transfer belt 30 when each of the two cams 77 is at a rotation angle of 45 degrees is defined as the second tension. The second tension is smaller than the first tension.

[0075] When the front and rear ends of the rotation shaft 34A of the driven roller 34 are positioned at the image forming position, in other words, when each of the two cams 77 is at a rotation angle of 0 degrees, the two cams 77 are adjusted so that the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are parallel to each other.

[0076] When the front end and rear end of the rotation shaft 34A of the driven roller 34 are located at the second standby position, in other words, when each of the two cams 77 is at a position where the rotation angle is 45 degrees, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are parallel to each other. In this case, the distance L3 between the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 is shorter than the distance L1 when the front end and rear end of the rotation shaft 34A of the driven roller 34 are located at the image forming position. Therefore, the second tension applied to the intermediate transfer belt 30 when the front end and rear end of the rotation shaft 34A of the driven roller 34 are located at the second standby position is smaller than the first tension applied to the intermediate transfer belt 30 when the front end and rear end of the rotation shaft 34A of the driven roller 34 are located at the image forming position.

[0077] When one of the front end and the rear end of the rotation shaft 34A of the driven roller 34 is located at the second standby position and the other is located at the first standby position, in other words, when one of the two cams 77 is at a position of 45 degrees rotation angle and the other is at a position of 90 degrees rotation angle, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted relationship and are not parallel. Even in this case, the movement amount of the front end and the rear end of the rotation shaft 34A of the driven roller 34 is adjusted so that the intermediate transfer belt 30 receives tension from the drive roller 33, the driven roller 34, and the tension rollers 61 and 63. In other words, the size of the cam 77 is determined based on the movement amount of the front end and the rear end of the rotation shaft 34A of the driven roller 34.

[0078] Fig. 10 is a schematic diagram for explaining the relative positions of the drive roller and the driven roller and the moving direction of the intermediate transfer belt. Referring to Fig. 10, the front end of the rotation shaft 34A of the driven roller 34 is located at the first standby position and the rear end is located at the second standby position. In this case, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Also, the tension of the intermediate transfer belt 30 is smaller on the front side than on the rear side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the rear direction.

[0079] 10, when the front end of the rotation shaft 34A of the driven roller 34 is located at the second standby position and the rear end is located at the first standby position, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Also, the tension of the intermediate transfer belt 30 is greater on the front side than on the rear side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the front direction.

[0080] In this manner, when both ends of the rotation shaft 34A of the driven roller 34 move, the intermediate transfer belt 30 moves in the front direction or the rear direction.

[0081] Fig. 11 is a block diagram showing an example of functions of a CPU included in a printer according to the present embodiment. The functions shown in Fig. 11 are realized by CPU 111 included in printer 100 as CPU 111 executes a belt adjustment program stored in ROM 113, HDD 115, or CD-ROM 118. Referring to Fig. 11, CPU 111 included in printer 100 includes a position adjustment control unit 251 and a timing determination unit 253. Position adjustment control unit 251 changes the relative position of intermediate transfer belt 30 with respect to drive roller 33. Timing determination unit 253 determines the timing for causing position adjustment control unit 251 to adjust the position of rotation shaft 34A.

[0082] The timing determination unit 253 causes the position adjustment control unit 251 to adjust the position of the rotation shaft 34A when the image forming unit 140 is not in a developing state where an image is formed. The developing state is a state in which at least one of the image forming units 20Y, 20M, 20C, and 20K, each including the developing devices 24Y, 24M, 24C, and 24K, is transferring a toner image onto the intermediate transfer belt 30.

[0083] The developing state includes a case where at least one of the image forming units 20Y, 20M, 20C, and 20K transfers a toner image onto the intermediate transfer belt 30. Therefore, the period of the developing state includes, for example, a period where only the image forming unit 20K transfers a toner image onto the intermediate transfer belt 30, and the image forming units 20Y, 20M, and 20C do not transfer a toner image onto the intermediate transfer belt 30. In this case, the primary transfer rollers 25Y, 25M, and 25C of the image forming units 20Y, 20M, and 20C may be separated from the intermediate transfer belt 30.

[0084] The timing determination unit 253 determines the timing for causing the position adjustment control unit 251 to adjust the position of the rotation shaft 34A based on the relative position of the intermediate transfer belt 30 with respect to the drive roller 33. The timing determination unit 253 detects the relative position of the intermediate transfer belt 30 with respect to the drive roller 33 based on the output of the sensor 71. Specifically, the timing determination unit 253 determines the deviation between a reference line parallel to the rotation direction of the intermediate transfer belt 30 and the reference position based on the output of the sensor 71.

[0085] In this embodiment, the reference line is the end of the intermediate transfer belt 30 on the front side. The reference position is the position of the reference line when the center of the intermediate transfer belt 30 overlaps with the center of the drive roller 33 in a direction parallel to the rotation axis 33A of the drive roller 33. Therefore, the deviation between the reference line and the reference position is indicated by the distance between the reference line and the reference position in either the front or rear direction of the reference line. Specifically, the deviation between the reference line and the reference position includes the direction in which the reference line deviates from the reference position and the amount of deviation. The amount of deviation is the distance between the reference line and the reference position.

[0086] The timing determination unit 253 detects the deviation between the reference line and the reference position based on the output of the sensor 71. As described above, the sensor 71 outputs the amount of received light indicating the amount of light received by each of the multiple photoelectric conversion elements arranged in the front-rear direction. The timing determination unit 253 identifies the photoelectric conversion elements that receive light reflected by the intermediate transfer belt 30 and the photoelectric conversion elements that do not receive light reflected by the intermediate transfer belt 30 based on the output of the sensor 71, thereby identifying the position of the reference line.

[0087] The timing determination unit 253 determines the deviation between the reference line and the reference position based on the amount of received light input from the sensor 71 at any time during the non-developed period. The timing determination unit 253 determines the time when the distance between the reference line and the reference position becomes equal to or greater than the threshold value TH as the timing to cause the position adjustment control unit 251 to adjust the position of the rotation shaft 34A. When the distance between the reference line and the reference position becomes equal to or greater than the threshold value TH, the timing determination unit 253 outputs an adjustment instruction to the position adjustment control unit 251. The adjustment instruction includes the direction in which the reference line deviates from the reference position.

[0088] The position adjustment control unit 251 changes the relative position of the intermediate transfer belt 30 with respect to the drive roller 33 in response to an adjustment instruction input from the timing determination unit 253. The position adjustment control unit 251 includes a tension control unit 261 and a relative position adjustment unit 263. In response to an adjustment instruction input from the timing determination unit 253, the tension control unit 261 reduces the tension of the intermediate transfer belt 30 from a first tension to a second tension. Specifically, the tension control unit 261 rotates each of the cams 77 journaled on the support plate 81A and the cams 77 journaled on the support plate 81B to positions with a rotation angle of 45 degrees. As a result, both ends of the rotation shaft 34A of the driven roller 34 move from the image forming position to the second standby position.

[0089] The relative position adjustment unit 263 changes the relative position between the intermediate transfer belt 30 and the rotation shaft 33A of the drive roller 33 in response to an adjustment instruction input from the timing determination unit 253. Specifically, the relative position adjustment unit 263 rotates either the cam 77 axially supported by the support plate 81A or the cam 77 axially supported by the support plate 81B to a position where the rotation angle is 90 degrees. The relative position adjustment unit 263 determines either the cam 77 axially supported by the support plate 81A or the cam 77 axially supported by the support plate 81B based on the direction of deviation included in the adjustment instruction.

[0090] When the direction of deviation is the front direction, the relative position adjustment unit 263 rotates the cam 77 journaled on the support plate 81A on the front direction side to a position where the rotation angle is 90 degrees. As a result, the tension on the rear direction side of the intermediate transfer belt 30 becomes greater than the tension on the front direction side, so that the intermediate transfer belt 30 moves toward the rear direction side while rotating by receiving power from the drive roller 33. When the direction of deviation is the rear direction, the relative position adjustment unit 263 rotates the cam 77 journaled on the support plate 81A on the rear direction side to a position where the rotation angle is 90 degrees. As a result, the tension on the front direction side of the intermediate transfer belt 30 becomes greater than the tension on the rear direction side.

[0091] After changing the relative position between the intermediate transfer belt 30 and the rotation shaft 33A of the drive roller 33, the relative position adjustment unit 263 drives the drive motor 33B to rotate the drive roller 33. This rotates the intermediate transfer belt 30. The intermediate transfer belt 30 receives power from the drive roller 33 and rotates while moving toward the front side or the rear side.

[0092] The relative position adjustment unit 263 rotates the driving roller 33 at a second rotation speed that is higher than the first rotation speed of the driving roller 33 in the developing state. As a result, the speed at which the intermediate transfer belt 30 moves becomes faster than the speed in the developing state, so that the time required to move the intermediate transfer belt 30 to the reference position can be shortened. The second rotation speed is preferably set to a rotation speed corresponding to the upper limit speed at which the intermediate transfer belt 30 can rotate around the driving roller 33, the driven roller 34, and the tension rollers 61 and 63. As a result, the time required to move the intermediate transfer belt 30 to the reference position can be minimized. The maximum rotation speed allowed for the driving roller 33 is determined by experiment or simulation, and is stored in the HDD 115.

[0093] In addition, the timing for driving the drive motor 33B is not limited to after the relative position between the intermediate transfer belt 30 and the rotating shaft 33A of the drive roller 33 is changed, but may be before the relative position between the intermediate transfer belt 30 and the rotating shaft 33A of the drive roller 33 is changed.

[0094] The timing determination unit 253 determines the deviation between the reference line and the reference position based on the amount of received light input from the sensor 71 after outputting the adjustment instruction. The timing determination unit 253 determines the time when the distance between the reference line and the reference position becomes equal to or smaller than the threshold value TL as the timing to stop adjusting the position of the rotation shaft 34A by the position adjustment control unit 251. The timing determination unit 253 outputs a stop instruction to the position adjustment control unit 251 in response to the distance between the reference line and the reference position becoming equal to or smaller than the threshold value TL.

[0095] In response to the input of the stop command, the position adjustment control unit 251 stops the drive motor 34B. Furthermore, the position adjustment control unit 251 changes the relative position of the intermediate transfer belt 30 with respect to the drive roller 33 and the tension of the intermediate transfer belt 30 to a first tension. Specifically, the position adjustment control unit 251 rotates each of the cams 77 journaled on the support plate 81A and the cams 77 journaled on the support plate 81B to a position where the rotation angle is 0 degrees. As a result, both ends of the rotation shaft 34A of the driven roller 34 are in the image forming position, and the tension of the intermediate transfer belt 30 becomes the first tension.

[0096] Fig. 12 is a flow chart showing an example of the flow of the belt adjustment process in this embodiment. The process shown in Fig. 12 is a function realized by CPU 111 included in printer 100 by CPU 111 executing a belt adjustment program stored in ROM 113, HDD 115, or CD-ROM 118. Referring to Fig. 12, CPU 111 included in printer 100 determines whether the development state has ended (step S01). The printer is in a standby state until the image forming operation by image forming unit 140 ends (NO in step S01), and when the image forming operation by image forming unit 140 ends (YES in step S01), the process proceeds to step S02.

[0097] In step S02, the position of the intermediate transfer belt 30 is detected, and the process proceeds to step S03. The position of the reference line is detected based on the amount of received light output from the sensor 71. The reference line is the end of the intermediate transfer belt 30 on the front direction side.

[0098] In step S03, it is determined whether the deviation is equal to or greater than a threshold value TH. The deviation is the distance between the reference line and the reference position. If the deviation is equal to or greater than the threshold value TH, the process proceeds to step S04. If not, the belt adjustment process ends. In step S04, both ends of the rotating shaft 34A of the driven roller 34 are moved to a second standby position, and the process proceeds to step S05. The cam 77 supported by the support plate 81A and the cam 77 supported by the support plate 81B are each rotated to a position where the rotation angle is 45 degrees. This reduces the tension of the intermediate transfer belt 30 from the first tension to the second tension.

[0099] In step S05, the process branches depending on the direction of the deviation of the intermediate transfer belt 30. If the deviation is in the front direction, the process proceeds to step S06, and if the deviation is in the rear direction, the process proceeds to step S07. In step S06, the front end of the rotating shaft 34A of the driven roller 34 is moved to a first standby position, and the process proceeds to step S08. The cam 77 supported by the support plate 81A on the front side is rotated to a position where the rotation angle is 90 degrees. On the other hand, in step S07, the rear end of the rotating shaft 34A of the driven roller 34 is moved to the first standby position, and the process proceeds to step S08. The cam 77 supported by the support plate 81B on the rear side is rotated to a position where the rotation angle is 90 degrees.

[0100] In step S08, the driving motor 33B is rotated at the maximum rotation speed, and the process proceeds to step S09. The maximum rotation speed of the driving motor 33B corresponds to the maximum rotation speed at which the intermediate transfer belt 30 can rotate. In step S09, similar to step S02, the position of the intermediate transfer belt 30 is detected, and the process proceeds to step S10.

[0101] In step S10, it is determined whether the amount of deviation is equal to or less than the threshold value TL. If the amount of deviation is equal to or less than the threshold value TL, the process proceeds to step S12, but if not, the process returns to step S10. In step S12, the driving motor 33B stops, and the process ends. The driving motor 33B rotates until the amount of deviation becomes equal to or less than the threshold value TL.

[0102] In the embodiment described above, in order to change the relative position between the intermediate transfer belt 30 and the driven roller 34, the distance between one of the ends of the driven roller 34 and the rotation shaft 33A of the drive roller 33 is made shorter than the distance between the other end and the rotation shaft 33A of the drive roller 33. For this reason, the distances by which both ends of the driven roller 34 are moved in the horizontal direction are made different from each other. The direction in which both ends of the driven roller 34 are moved does not have to be the horizontal direction.

[0103] <First Modification> In the first modified example, the direction in which both ends of the driven roller 34 are moved in order to change the relative positions of the intermediate transfer belt 30 and the driven roller 34 is the vertical direction.

[0104] 13 is a schematic diagram for explaining the relative positions of the drive roller and the driven roller and the movement direction of the intermediate transfer belt in the first modified example. Referring to FIG. 13, a state in which both ends of the rotation shaft 34A of the driven roller 34 are located at the second standby position is shown. Both ends of the rotation shaft 34A of the driven roller 34 are guided by the slide hole 83 so as to be vertically movable. In the first modified example, the first standby position is lower than the second standby position.

[0105] When the front end of the rotation shaft 34A of the driven roller 34 is located at the first standby position and the rear end is located at the second standby position, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Therefore, the tension of the intermediate transfer belt 30 is greater on the front side than on the rear side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the front direction.

[0106] 13, when the front end of the rotation shaft 34A of the driven roller 34 is located at the second standby position and the rear end is located at the first standby position, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Therefore, the tension of the intermediate transfer belt 30 is greater on the rear side than on the front side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the rear direction.

[0107] In the first modified example, the first standby position is lower than the second standby position, but the first standby position may be higher than the second standby position. In the first modified example, in order to reduce the tension of the intermediate transfer belt 30 from the first tension to the second tension, both ends of the rotation shaft 34A of the driven roller 34 need to be moved from the image forming position to the second standby position. The configuration for moving both ends of the rotation shaft 34A of the driven roller 34 from the image forming position to the second standby position is the same as that in the above-described embodiment.

[0108] <Second Modification> In the second modified example, the direction in which both ends of the driven roller 34 are moved in an oblique direction between the vertical direction and the horizontal direction in order to change the relative position between the intermediate transfer belt 30 and the driven roller 34.

[0109] 14 is a schematic diagram for explaining the relative positions of the drive roller and the driven roller and the moving direction of the intermediate transfer belt in the second modified example. Referring to FIG. 14, a state in which both ends of the rotation shaft 34A of the driven roller 34 are located at the second standby position is shown. Both ends of the rotation shaft 34A of the driven roller 34 are guided by the slide hole 83 so as to be movable obliquely upward. In the second modified example, the first standby position is higher than the second standby position and the distance between the rotation shaft 33A of the drive roller 33 and the first standby position is shorter.

[0110] When the front end of the rotation shaft 34A of the driven roller 34 is located at the first standby position and the rear end is located at the second standby position, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Therefore, the tension of the intermediate transfer belt 30 is greater on the rear side than on the front side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the rear direction.

[0111] 14, when the front end of the rotation shaft 34A of the driven roller 34 is located at the second standby position and the rear end is located at the first standby position, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Therefore, the tension of the intermediate transfer belt 30 is greater on the front side than on the rear side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the front direction.

[0112] In the second modified example, the first standby position is lower than the second standby position, but the first standby position may be higher than the second standby position. In the second modified example, in order to reduce the tension of the intermediate transfer belt 30 from the first tension to the second tension, both ends of the rotation shaft 34A of the driven roller 34 need to be moved from the image forming position to the second standby position. The configuration for moving both ends of the rotation shaft 34A of the driven roller 34 from the image forming position to the second standby position is the same as that in the above-described embodiment.

[0113] <Third Modification> In the embodiment described above, the timing determination unit 253 determines the timing for causing the position adjustment control unit 251 to adjust the position of the rotating shaft 34A based on the relative position of the intermediate transfer belt 30 with respect to the drive roller 33. In the third modified example, the timing determination unit 253 determines the timing for causing the position adjustment control unit 251 to adjust the position of the rotating shaft 34A based on the distance by which the intermediate transfer belt 30 has rotated.

[0114] The timing determination unit 253 measures the amount of rotation of the drive motor 33B and calculates the distance rotated by the intermediate transfer belt 30 from the amount of rotation. When the distance rotated by the intermediate transfer belt 30 is equal to or greater than a predetermined distance threshold, the timing determination unit 253 determines the timing to cause the position adjustment control unit 251 to adjust the position of the rotation shaft 34A. In this case, the threshold TH is not required. Also, it is not necessary for the sensor 71 to detect the relative position of the intermediate transfer belt 30 with respect to the drive roller 33.

[0115] The distance threshold is determined in advance by experiment or simulation. The distance threshold is determined based on the relationship between the distance the intermediate transfer belt 30 rotates and the amount of misalignment. The distance threshold may be different depending on the distance the intermediate transfer belt 30 rotates. For example, the distance threshold is set to a relatively large value at the first rotation since the degree of deterioration of the intermediate transfer belt 30 is small. From the second rotation onwards, the degree of deterioration of the intermediate transfer belt 30 progresses, so the distance threshold is set to a gradually smaller value as the number of rotations increases.

[0116] <Fourth modified example> The sensor 71 has a light receiving surface extending in the front-rear direction. photoelectric The sensor 71 may be a sensor having a conversion element. The larger the area where the light receiving section of the sensor 71 and the intermediate transfer belt 30 overlap in the vertical direction, the more light is reflected by the intermediate transfer belt, and the larger the amount of light received by the light receiving section becomes, and the smaller the overlapping area becomes, the smaller the amount of light received becomes. The sensor 71 outputs the detected amount of received light to the CPU 111. There is a predetermined relationship between the area where the light receiving section of the sensor 71 and the intermediate transfer belt 30 overlap in the vertical direction and the amount of light received by the light receiving section of the sensor 71. Here, a case where the area and the amount of received light are proportional will be described as an example. Here, the relationship between the area and the amount of received light is obtained by experimental measurement or simulation, and is stored in the HDD 115 as a table or a formula that defines the relationship between the area and the amount of received light.

[0117] The timing determination unit 253 determines the deviation between the reference line and the reference position based on the amount of received light input from the sensor 71 at any point in time, using a table or a formula that defines the relationship between the area and the amount of received light. The timing determination unit 253 determines the point in time when the distance between the reference line and the reference position becomes equal to or greater than the threshold value TH as the timing for causing the position adjustment control unit 251 to adjust the position of the rotation shaft 34A. The timing determination unit 253 outputs an adjustment instruction to the position adjustment control unit 251 in response to the distance between the reference line and the reference position becoming equal to or greater than the threshold value TH.

[0118] The timing determination unit 253 may store in the HDD 115 a reference amount of received light, which is a measurement of the amount of received light when the intermediate transfer belt 30 is at the reference position. In this case, a table or a formula that defines the relationship between the area and the amount of received light is not necessary. The timing determination unit 253 determines the time when the absolute value of the difference between the amount of received light input from the sensor 71 at any time and the reference amount of received light becomes equal to or greater than the upper threshold as the timing to cause the position adjustment control unit 251 to adjust the position of the rotating shaft 34A. The timing determination unit 253 also determines the time when the absolute value of the difference between the amount of received light input from the sensor 71 thereafter and the reference amount of received light becomes equal to or less than the lower threshold as the timing to cause the position adjustment control unit 251 to end adjustment of the position of the rotating shaft 34A. The upper threshold is greater than the lower threshold.

[0119] <Fifth modified example> In addition, an elastic member 73 and a cam 77 are used to move the rotation shaft 34A of the driven roller 34, but instead of these, a direct-acting stepping motor consisting of a ball screw and a stepping motor, or a piston driven by air or hydraulic pressure may be used.

[0120] As described above, the printer 100 in this embodiment functions as an image forming apparatus, and includes the drive roller 33, the driven roller 34, and the tension rollers 61 and 63, the endless intermediate transfer belt 30 that is stretched around the outside of the drive roller 33, the driven roller 34, and the tension rollers 61 and 63, the developers 24Y, 24M, 24C, and 24K that form toner images on the intermediate transfer belt, the drive motor 33B that rotates the drive roller 33, and the position adjustment mechanism 80 that changes the relative position between the driven roller 34 and the drive roller 33. The CPU 111 includes a position adjustment control unit 251 that controls the position adjustment mechanism 80 to change the relative position between the intermediate transfer belt 30 and the drive roller 33 in a state in which the tension applied to the intermediate transfer belt 30 is set to a second tension that is smaller than the first tension in the development state. Therefore, when the tension applied to the intermediate transfer belt 30 is set to a second tension that is smaller than the first tension in the developing state, the frictional force between the drive roller 33 and the intermediate transfer belt 30 is reduced. This makes it easier to change the relative position between the drive roller 33 and the intermediate transfer belt 30, and shortens the time required to change the relative position. This makes it easier to adjust the position of the intermediate transfer belt 30.

[0121] Moreover, the position adjustment mechanism 80 includes a movement mechanism that changes the distance between the rotation shaft 34A of the driven roller 34, which is a position adjustment roller, and the rotation shaft 33A of the drive roller 33, and the position adjustment control unit 251 includes a tension control unit 261 that controls the position adjustment mechanism 80 to set the tension of the intermediate transfer belt 30 to the second tension. This makes it easy to adjust the tension of the intermediate transfer belt 30.

[0122] Furthermore, the position adjustment control unit 251 controls the position adjustment mechanism 80 to cause both ends of the rotation shaft 34A of the driven roller 34 to move by different amounts. This makes it easy to change the relative positions of the intermediate transfer belt 30 and the drive roller 33.

[0123] The printer 100 also includes a sensor 71 that detects the relative position of the intermediate transfer belt 30 with respect to the drive roller 33 of a reference line parallel to the rotation direction of the intermediate transfer belt 30, and the position adjustment control unit 251 changes the relative position between the intermediate transfer belt 30 and the drive roller 33 based on the relative position detected by the sensor 71. Therefore, when the relative position between the intermediate transfer belt 30 and the drive roller 33 changes, the relative position is changed. Therefore, the intermediate transfer belt 30 can be adjusted to a predetermined position with respect to the drive roller 33.

[0124] Furthermore, the timing determination unit 253 included in the CPU 111 determines the timing for changing the relative position between the intermediate transfer belt 30 and the drive roller 33 based on the amount of variation in the relative position between the intermediate transfer belt 30 and the drive roller 33. Therefore, when the relative position between the intermediate transfer belt 30 and the drive roller 33 deviates by a predetermined amount from the reference position, the relative position between the intermediate transfer belt 30 and the drive roller 33 is changed. Therefore, the relative position between the intermediate transfer belt 30 and the drive roller 33 can be adjusted at an appropriate timing.

[0125] Furthermore, while the relative position between the intermediate transfer belt 30 and the drive roller 33 is being adjusted by the position adjustment control unit 251, the drive motor 33B rotates the drive roller 33 at a second rotation speed that is faster than the first rotation speed in the developing state. The relative position between the intermediate transfer belt 30 and the drive roller 33 is adjusted while rotating the drive roller 33 at the second rotation speed that is faster than the first rotation speed in the developing state. This makes it possible to shorten the time required to adjust the relative position between the intermediate transfer belt 30 and the drive roller 33.

[0126] In particular, the second rotation speed may be set to a rotation speed corresponding to the maximum rotation speed at which the intermediate transfer belt 30 can rotate. In this case, the time required to adjust the relative positions of the intermediate transfer belt 30 and the drive roller 33 can be shortened.

[0127] Furthermore, in the third modified example, the timing determination unit 253 determines the timing for changing the relative position between the intermediate transfer belt 30 and the drive roller 33 based on the distance that the intermediate transfer belt 30 has rotated. Every time the intermediate transfer belt 30 rotates a predetermined distance, the relative position between the intermediate transfer belt 30 and the drive roller 33 is changed. Therefore, the relative position between the intermediate transfer belt 30 and the drive roller 33 can be adjusted at an appropriate timing.

[0128] <Second embodiment> The printer 100 in the second embodiment is configured so that the intermediate transfer belt 30 moves in either the front or rear direction in the developing state, and moves the intermediate transfer belt in the other direction in the adjustment state when not in the developing state. Below, differences from the printer 100 in the first embodiment will be mainly described. Here, the printer 100 in the second embodiment is configured so that the intermediate transfer belt 30 moves in the front direction in the developing state, and moves the intermediate transfer belt 30 in the rear direction in the adjustment state when not in the developing state. In addition, the printer 100 in the second embodiment does not include a sensor 71.

[0129] In the printer 100 in the second embodiment, the driven roller 34 is shaped like a truncated cone. In a cross section perpendicular to the rotation axis 34A of the driven roller 34, the radius of the cross section in the front direction is greater than the radius of the cross section in the rear direction. Therefore, the tension of the intermediate transfer belt 30 in the front direction is greater than the tension in the rear direction. The rotation axis 34A of the driven roller 34 is parallel to the rotation axis 33A of the drive roller 33. In addition, the drive roller 33 is shaped like a cylinder. Therefore, the intermediate transfer belt 30 moves in the front direction in the developing state.

[0130] Fig. 15 is a block diagram showing an example of functions of a CPU included in a printer in the second embodiment. The functions shown in Fig. 15 differ from those shown in Fig. 11 in that the relative position adjustment unit 263 and the timing determination unit 253 are changed to a relative position adjustment unit 263A and a timing determination unit 253A, respectively. The other functions are the same as those shown in Fig. 11, and therefore will not be described again here.

[0131] The timing determination unit 253A determines the timing for causing the position adjustment control unit 251 to adjust the position of the rotating shaft 34A based on the distance rotated by the intermediate transfer belt 30. The timing determination unit 253A measures the amount of rotation of the drive motor 33B and calculates the distance rotated by the intermediate transfer belt 30 from the amount of rotation. When the distance rotated by the intermediate transfer belt 30 is equal to or greater than a predetermined distance threshold, the timing determination unit 253A determines the timing for causing the position adjustment control unit 251 to adjust the position of the rotating shaft 34A.

[0132] The distance threshold is determined in advance by experiment or simulation. The distance threshold is determined based on the relationship between the distance the intermediate transfer belt 30 rotates and the amount of misalignment. The distance threshold may be different depending on the distance the intermediate transfer belt 30 rotates. For example, the first time, the intermediate transfer belt 30 is not deteriorated with time, so the distance threshold is set to a relatively large value. From the second time onwards, the intermediate transfer belt 30 deteriorates with time, so the distance threshold is set to a gradually smaller value as the number of times increases.

[0133] In response to an adjustment instruction input from a timing determination unit 253A, the position adjustment control unit 251 changes the relative position of the intermediate transfer belt 30 with respect to the drive roller 33. The position adjustment control unit 251 includes a tension control unit 261 and a relative position adjustment unit 263A.

[0134] The relative position adjustment unit 263A changes the relative position between the intermediate transfer belt 30 and the rotation shaft 33A of the drive roller 33 in response to an adjustment instruction input from the timing determination unit 253A. Specifically, the relative position adjustment unit 263A rotates either the cam 77 axially supported by the support plate 81A or the cam 77 axially supported by the support plate 81B to a position where the rotation angle is 90 degrees. The relative position adjustment unit 263A determines either the cam 77 axially supported by the support plate 81A or the cam 77 axially supported by the support plate 81B based on the direction of deviation included in the adjustment instruction. Here, since the intermediate transfer belt 30 is configured to move in the front direction in the developing state, the relative position adjustment unit 263A determines the cam 77 axially supported by the support plate 81A.

[0135] The relative position adjustment unit 263A rotates the cam 77, which is supported by the support plate 81A on the front side, to a position where the rotation angle is 90 degrees. As a result, the tension on the rear side of the intermediate transfer belt 30 becomes greater than the tension on the front side, so that the intermediate transfer belt 30 moves to the rear side while being rotated by the drive roller 33.

[0136] After changing the relative position between the intermediate transfer belt 30 and the rotation shaft 33A of the drive roller 33, the relative position adjustment unit 263A drives the drive motor 33B for a predetermined time, and stops the drive motor 33B when the predetermined time has elapsed. This rotates the intermediate transfer belt 30 for a predetermined time. The predetermined time is a time required to move the intermediate transfer belt 30 a predetermined distance in the rear direction. The predetermined time is a period determined in advance by an experiment or a simulation. The predetermined time is stored in the HDD 115. The intermediate transfer belt 30 moves toward the rear direction while being rotated by the power transmitted from the drive roller 33.

[0137] The relative position adjustment unit 263A rotates the drive roller 33 at a second rotation speed that is higher than the first rotation speed of the drive roller 33 in the developing state. This increases the speed at which the intermediate transfer belt 30 moves, thereby shortening the time required to move the intermediate transfer belt 30 a predetermined distance in the rear direction. The second rotation speed is preferably set to a rotation speed that corresponds to the maximum rotation speed at which the intermediate transfer belt 30 can rotate. This minimizes the time required to move the intermediate transfer belt 30 in the rear direction. The maximum rotation speed allowed for rotating the intermediate transfer belt 30 is determined by experiment or simulation, and is stored in the HDD 115.

[0138] In addition, the timing for driving the drive motor 33B is not limited to after the relative position between the intermediate transfer belt 30 and the rotating shaft 33A of the drive roller 33 is changed, but may be before the relative position between the intermediate transfer belt 30 and the rotating shaft 33A of the drive roller 33 is changed.

[0139] 10, in the printer 100 in the second embodiment, the front end of the rotation shaft 34A of the driven roller 34 is located at the first standby position and the rear end is located at the second standby position. In this case, the rotation shaft 34A of the driven roller 34 and the rotation shaft 33A of the drive roller 33 are in a twisted positional relationship. Also, the tension of the intermediate transfer belt 30 is smaller on the front side than on the rear side. In this state, when the drive roller 33 rotates, the intermediate transfer belt 30 moves in the rear direction.

[0140] The printer 100 in the second embodiment may be provided with a sensor 71 to detect the direction and amount of deviation of the reference line of the intermediate transfer belt 30 from the reference position. In this case, the relative position between the intermediate transfer belt 30 and the drive roller 33 may be changed when the amount of deviation becomes equal to or greater than a threshold value TH. Also, the change in the relative position between the intermediate transfer belt 30 and the drive roller 33 may be stopped when the amount of deviation becomes equal to or less than a threshold value TL.

[0141] The printer 100 in the second embodiment is configured such that the driven roller 34 suspends the intermediate transfer belt 30 so that the relative position between the intermediate transfer belt 30 and the drive roller 33 changes in a first direction (one of the front direction and the rear direction) from a reference position toward a first relative position, and the position adjustment control unit 251 adjusts the relative position between the intermediate transfer belt 30 and the drive roller 33 so that the relative position between the intermediate transfer belt 30 and the drive roller 33 changes in a second direction (the other of the front direction and the rear direction) toward a second relative position opposite to the first relative position with respect to the reference position. Therefore, when the relative position between the intermediate transfer belt 30 and the drive roller 33 is not adjusted, the relative position changes in the first direction, and when the relative position between the intermediate transfer belt 30 and the drive roller 33 is adjusted, the relative position changes in the second direction. Therefore, the intermediate transfer belt 30 can be positioned between the first relative position and the second relative position with respect to the drive roller 33.

[0142] <Third embodiment> When the rotation axis 34A of the driven roller 34 and the rotation axis 33A of the drive roller 33 are parallel, the probability that the intermediate transfer belt 30 moves in the front direction and the rear direction in the developing state are both 50%. The printer 100 in the third embodiment moves the intermediate transfer belt alternately in either the front direction or the rear direction for the movement time each time the switching time elapses. The printer 100 in the third embodiment does not include the sensor 71.

[0143] The switching time is the cumulative time that the intermediate transfer belt 30 rotates in the developing state, and is a predetermined time. The movement time is the time required to move the intermediate transfer belt 30, and is a predetermined time. The movement amount of the intermediate transfer belt 30 during the switching time is smaller than the movement amount of the intermediate transfer belt 30 during the movement time. In this way, the printer 100 in the third embodiment is adjusted so that the reference line of the intermediate transfer belt 30 approaches the reference position.

[0144] The printer 100 in the third embodiment may be provided with a sensor 71 to detect the direction and amount of deviation of the reference line of the intermediate transfer belt 30 from the reference position. In this case, the relative position between the intermediate transfer belt 30 and the drive roller 33 may be changed when the amount of deviation becomes equal to or greater than the threshold value TH. In this case, no switching time is required. Also, the change in the relative position between the intermediate transfer belt 30 and the drive roller 33 may be stopped when the amount of deviation becomes equal to or less than the threshold value TL. In this case, no movement time is required.

[0145] In the printer 100 according to the third embodiment, the position adjustment control unit 251 changes the relative position between the intermediate transfer belt 30 and the drive roller 33 in the direction opposite to the direction in which the relative position between the intermediate transfer belt 30 and the drive roller 33 was changed previously. Therefore, the direction of change is reversed every time the relative position between the intermediate transfer belt 30 and the drive roller 33 is changed. Therefore, the intermediate transfer belt 30 can be adjusted to a predetermined position with respect to the drive roller 33.

[0146] In this embodiment, the printer 100 has been described as an example of an image forming apparatus, but the image forming apparatus may also be a copier, a laser beam printer, a facsimile machine, or a multifunction peripheral (multifunction peripheral) that combines these.

[0147] In addition, in the present embodiment, the printer 100 that forms a tandem type color image has been described as an example of an image forming apparatus, but the present invention is not limited to this, and may be an image forming apparatus that forms a monochrome image. The configurations and arrangements of the image forming units 20Y, 20M, 20C, and 20K, the exposure devices 21Y, 21M, 21C, and 21K, the charging rollers 22Y, 22M, 22C, and 22K, the photoconductor drums 23Y, 23M, 23C, and 23K, the developing devices 24Y, 24M, 24C, and 24K, the primary transfer rollers 25Y, 25M, 25C, and 25K, the secondary transfer roller 26, and the fixing device 50 are not limited to those in the present embodiment, and may be other configurations and arrangements.

[0148] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0149] 100 printer, 111 CPU, 140 image forming section, 150 paper feed section, 20Y, 20M, 20C, 20K image forming unit, 24Y, 24M, 24C, 24K developing device, 25Y, 25M, 25C, 25K primary transfer roller, 30 intermediate transfer belt, 33 drive roller, 33A rotating shaft, 33B drive motor, 34 driven roller, 34A rotating shaft, 34B drive motor, 50 fixing device, 61, 63 tension roller, 71 sensor, 73 elastic member, 75 contact section, 77 cam, 77A rotating shaft, 80 position adjustment mechanism, 81 support base, 81A, 81B support plate, 83 sliding hole, 251 position adjustment control section, 253, 253A timing determination section, 261 Tension control section, 263,263A Relative position adjustment section.

Claims

1. A number of rollers; an endless belt that is stretched around the outer sides of the rollers; a developer for forming a toner image on the belt; A drive unit that rotates at least one drive roller among the plurality of rollers; a position adjustment mechanism that changes a distance between a rotation axis of at least one position adjustment roller among the plurality of rollers and a rotation axis of the drive roller to change a relative position of the plurality of rollers; a position adjustment control unit that controls the position adjustment mechanism to change a relative position between the belt and the drive roller in a state in which a tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by the developing device, The position adjustment control unit controls the position adjustment mechanism to set the tension of the belt to the second tension while making the movement amounts of both ends of the rotation shaft of the position adjustment roller different from each other.

2. A position detector detects a relative position of a reference line parallel to a rotation direction of the belt with respect to the driving roller, The image forming apparatus according to claim 1 , wherein the position adjustment control unit changes the relative position between the belt and the drive roller based on the relative position detected by the position detection unit.

3. the plurality of rollers are configured to suspend the belt such that a relative position between the belt and the drive roller changes in a first direction from a reference position toward a first relative position; 2. The image forming apparatus according to claim 1, wherein the position adjustment control unit adjusts the relative position between the belt and the drive roller so that the relative position between the belt and the drive roller changes in a second direction toward a second relative position opposite to the first relative position with respect to the reference position.

4. 4. The image forming apparatus according to claim 1, wherein the position adjustment control unit changes the relative position between the belt and the drive roller in a direction opposite to a direction in which the relative position between the belt and the drive roller was changed previously.

5. 5. The image forming apparatus according to claim 1, further comprising a timing determination unit that determines a timing for changing the relative position between the belt and the drive roller based on an amount of fluctuation in the relative position between the belt and the drive roller.

6. 5. The image forming apparatus according to claim 1, further comprising a timing determination unit that determines a timing for changing a relative position between the belt and the drive roller based on a distance that the belt has rotated.

7. The image forming apparatus according to any one of claims 1 to 6, wherein the drive unit rotates the drive roller at a second rotation speed faster than a first rotation speed in the developing state while the relative position between the belt and the drive roller is being adjusted by the position adjustment control unit.

8. A plurality of rollers; an endless belt that is stretched around the outer sides of the rollers; a developer for forming a toner image on the belt; A drive unit that rotates at least one drive roller among the plurality of rollers; a position adjustment mechanism for changing a relative position of the plurality of rollers; a position adjustment control unit that controls the position adjustment mechanism to change a relative position between the belt and the drive roller in a state in which a tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by the developing device, the drive unit rotates the drive roller at a second rotation speed that is faster than a first rotation speed in the developing state while the relative position between the belt and the drive roller is being adjusted by the position adjustment control unit; The second rotation speed is a maximum speed corresponding to an upper limit speed at which the belt can rotate.

9. A belt adjustment method for adjusting an image forming apparatus, comprising the steps of: The image forming apparatus includes a plurality of rollers; an endless belt stretched over the rollers; a developer for forming a toner image on the belt; A drive unit that rotates at least one drive roller among the plurality of rollers; a position adjustment mechanism that changes a distance between a rotation axis of at least one position adjustment roller among the plurality of rollers and a rotation axis of the drive roller to change a relative position of the plurality of rollers; a position adjustment step of controlling the position adjustment mechanism to change a relative position between the belt and the drive roller in a state in which a tension applied to the belt is set to a second tension smaller than a first tension in a developing state in which a toner image is formed on the belt by the developing device, in the image forming apparatus; The belt adjustment method includes a step of controlling the position adjustment mechanism to set the tension of the belt to the second tension while making the movement amounts of both ends of the rotation shaft of the position adjustment roller different from each other.

10. A belt adjustment program executed by a computer that controls an image forming apparatus, The image forming apparatus includes a plurality of rollers; an endless belt stretched over the rollers; a developer for forming a toner image on the belt; A drive unit that rotates at least one drive roller among the plurality of rollers; a position adjustment mechanism that changes a distance between a rotation axis of at least one position adjustment roller among the plurality of rollers and a rotation axis of the drive roller to change a relative position of the plurality of rollers; a position adjustment step of controlling the position adjustment mechanism to change a relative position between the belt and the drive roller in a state in which a tension applied to the belt is set to a second tension that is smaller than a first tension in a developing state in which a toner image is formed on the belt by the developing device, and The position adjustment step includes a step of controlling the position adjustment mechanism to set the tension of the belt to the second tension while making the movement amounts of both ends of the rotation shaft of the position adjustment roller different from each other.

Images