JP5991588B2 - Belt device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a belt device capable of correcting displacement in the belt width direction of an endless belt that runs while being stretched on a plurality of support members, and an image forming apparatus including the belt device.

  As this type of image forming apparatus, an image forming apparatus disclosed in Patent Document 1 is known. This image forming apparatus is configured to change the position of the intermediate transfer belt in the width direction when an intermediate transfer belt (endless belt) on which toner images are transferred from a plurality of photosensitive members is driven by a driving roller, and to change the inclination of the steering roller. The belt displacement correction control to be adjusted in (1) is performed. In this image forming apparatus, a speed detection mark is provided on the inner peripheral surface of the intermediate transfer belt, and a belt speed detection sensor is disposed so as to face a passage path through which the speed detection mark passes. In addition, a sensor cleaning member is fixed to the inner peripheral surface of the intermediate transfer belt at a location that passes the position opposed to the belt speed detection sensor when the intermediate transfer belt is forcibly displaced in the belt width direction by a predetermined amount. Has been. In addition, a mark cleaning member is disposed at a location facing the passage path through which the speed detection mark passes when the intermediate transfer belt is forcibly displaced by a predetermined amount.

  In the image forming apparatus disclosed in Patent Document 1, at a predetermined cleaning timing, the steering roller is controlled to forcibly displace the intermediate transfer belt in the width direction by a predetermined amount. Thus, the sensor cleaning member passes through the position facing the belt speed detection sensor to clean the belt speed detection sensor, and the speed detection mark passes through the position facing the mark cleaning member to clean the speed detection mark. The

  When correcting the position of the endless belt in the belt width direction, generally, the belt displacement amount detecting means detects a belt displacement amount in which the endless belt is displaced in the belt width direction, and the belt width of the endless belt is determined based on the detected belt displacement amount. Correct the displacement in the direction. In order to appropriately correct the endless belt displacement in the belt width direction, it is important to detect the amount of displacement of the endless belt in the belt width direction with high resolution. However, in the belt displacement amount detection means, the required detection range (belt displacement amount detection range) and the required detection resolution are in a trade-off relationship, and it is difficult to achieve both.

  For example, consider a belt displacement amount detection unit configured such that a moving member that moves in conjunction with a displacement of an endless belt in the belt width direction crosses an optical path from a light emitting unit to a light receiving unit of the optical sensor member. In this belt displacement amount detection means, an output level is output from the light receiving portion according to the ratio of the light shielding portion that is neither a notch nor transparent of the moving member blocking the optical path of the optical sensor member. Detect the belt displacement. If the optical sensor member is composed of a single optical sensor (single light receiving surface), when the endless belt is displaced from the lower limit to the upper limit of the belt displacement detection range of the endless belt, The maximum detection resolution can be obtained by configuring so that the light shielding unit moves from a position where the light path is not blocked at all to a position where the light path is completely blocked.

  In order to suppress the belt displacement within a range in which color misregistration and color unevenness when forming a color image can be sufficiently suppressed, the belt displacement is detected in units of about 0.005 mm as the detection resolution of the belt displacement detection means. Is required to be detected. When a detection range of the belt displacement amount of the endless belt is required, for example, a range of ± 1 mm, a detection resolution of about 400 times the detection range (± 1 mm) is required. Under this condition, if it is configured to obtain the maximum detection resolution as described above, the optical sensor member of the belt displacement amount detecting means is an inexpensive light with an analog output of 0 to 5 V, for example. Even if a sensor is used, it is only necessary to detect a voltage (sensor output) in units of 12.5 mV, so that it can be realized at a relatively low cost.

On the other hand, when a range of ± 5 mm, for example, is required as the detection range of the displacement amount of the endless belt, a detection resolution of about 2000 times is required for this detection range (± 5 mm). At this time, when the above-described inexpensive optical sensor is used as the optical sensor member of the belt displacement amount detecting means, and the detection resolution of 2000 times is obtained, the maximum detection resolution is obtained as described above. Even with this configuration, it is necessary to detect a voltage (sensor output) in units of 2.5 mV. Considering the noise in the device and the performance of the A / D conversion circuit (analog / digital conversion circuit) on the controller side, it is difficult to stably perform appropriate detection for a voltage of 2.5 mV.
As described above, in the belt displacement detection means, the required detection range (belt displacement detection range) and the required detection resolution are in a trade-off relationship, and it is difficult to achieve both. is there.

  In the image forming apparatus disclosed in Patent Document 1, at a predetermined cleaning timing, the passage of the speed detection mark and the sensor cleaning member is from a position in the belt width direction that does not pass through the opposing position of the belt speed detection sensor and the mark cleaning member. The intermediate transfer belt is forcibly displaced to a position in the belt width direction that does not pass through the facing position. The displacement amount in the belt width direction (forced belt displacement amount) at this time is an amount greater than the length in the belt width direction of the speed detection mark, the sensor cleaning member, etc. This is the detection of the displacement amount of a normal endless belt. It greatly exceeds the range (for example, a range of ± 1 mm, a range of ± 2 to 3 mm at most).

  Patent Document 1 does not specifically describe belt displacement amount detection means for detecting the belt width direction displacement amount of the intermediate transfer belt (endless belt). However, in the image forming apparatus disclosed in Patent Document 1, not only during normal image formation (a state in which forced displacement in the belt width direction is not performed) but also in cleaning (forced displacement in the belt width direction). It is necessary to carry out belt displacement correction control of the intermediate transfer belt also after the execution. This is because if the belt displacement correction control of the intermediate transfer belt is not performed at the time of cleaning, the width direction of the intermediate transfer belt deviates from the target position during the cleaning, and the belt speed detection sensor or speed detection mark is detected by the sensor cleaning member or mark cleaning member. It is because it becomes impossible to clean properly. Further, if the belt displacement correction control of the intermediate transfer belt is not performed at the time of cleaning, the position of the intermediate transfer belt in the width direction may be greatly deviated from the target position, and the intermediate transfer belt may be removed.

  In the image forming apparatus disclosed in Patent Document 1, the amount of displacement of the intermediate transfer belt is detected by the belt displacement amount detecting means using one inexpensive optical sensor member during belt displacement correction control during both normal image formation and cleaning. When detecting the belt displacement amount detecting means, the belt displacement amount detecting means is configured to obtain the maximum detection resolution as described above with respect to a wide detection range including all detection ranges required at the time of individual belt displacement correction control. It is possible. However, in such a configuration, the detection resolution of the belt displacement amount detection means has to be lowered, and the width direction position of the intermediate transfer belt at the time of each belt displacement correction control is controlled to each target position with high accuracy. The problem of not being able to occur.

  On the other hand, when installing individual belt displacement amount detection means corresponding to each belt displacement amount detection range at the time of individual belt displacement correction control, the belt at the time of each belt displacement correction control without lowering the detection resolution. The amount of displacement can be detected. However, since the number of installed belt displacement amount detecting means increases, there arises a problem that the cost increases.

  These problems are not limited to the purpose of cleaning the speed detection mark and the belt speed detection sensor for detecting the speed detection mark as in the image forming apparatus described in Patent Document 1, and a plurality of controls with different target positions in the belt width direction are used. In the configuration in which the belt displacement correction control of the endless belt is performed in the mode, the same problem occurs.

  The present invention has been made in view of the above problems, and an object thereof is to provide a belt for an endless belt in each control mode in a configuration in which belt displacement correction control is performed in a plurality of control modes having different target positions. To provide a belt device capable of detecting the amount of displacement by a single optical sensor member without lowering the detection resolution, and an image forming apparatus including the belt device.

In order to achieve the above object, the present invention provides an endless belt that travels in a state of being stretched on a plurality of support members, and a belt displacement amount detecting unit that detects a belt displacement amount in which the endless belt is displaced in the belt width direction. And a belt width direction position correcting means for correcting the belt width direction position of the endless belt, and the belt width direction position of the endless belt becomes the target position based on the belt displacement amount detected by the belt displacement amount detecting means. Control means for controlling the belt width direction position correcting means, and the control means controls the belt width direction position of the endless belt to be a predetermined first target position; A belt device having a second control mode for controlling the endless belt in a belt width direction position to be a second target position different from the first target position. The means includes a moving member that moves in conjunction with the displacement of the endless belt in the belt width direction, and an optical sensor that outputs a signal having an output level corresponding to a rate at which the moving member blocks an optical path from the light emitting unit to the light receiving unit. The moving member is a first light-shielding portion in which a shielding amount that blocks an optical path of the optical sensor member changes in conjunction with displacement of the endless belt in the belt width direction in the first control mode. And a second light-shielding portion that does not overlap with the first light-shielding portion in which the shielding amount that blocks the optical path of the photosensor member changes in conjunction with the displacement of the endless belt in the belt width direction in the second control mode. And an optical detection mark provided on an outer peripheral surface or an inner peripheral surface of the endless belt, and a position facing a mark passing path through which the optical detection mark passes during traveling of the endless belt in the second control mode. In It is location, characterized by chromatic and cleaning member mark for cleaning the mark optical detection by the position mark optical detection passes.

  In the present invention, in the first control mode, the proportion of the first light-shielding portion of the moving member in the optical path of the optical sensor member changes in conjunction with the displacement in the belt width direction of the endless belt, and the output level corresponding to this proportion Is output from the optical sensor member. Therefore, in the first control mode, the belt displacement amount of the endless belt is detected according to the ratio of the first light shielding portion of the moving member to the optical path of the optical sensor member. On the other hand, when operating in the second control mode in which the target position is different from the first control mode, up to the control range of the second control mode (the range in which the position in the width direction of the endless belt can be corrected to the second target position), The endless belt is forcibly moved (displaced) in the belt width direction. Then, the moving member moves in conjunction with this forced movement, whereby the portion of the moving member that blocks the optical path of the photosensor member is switched from the first light shielding portion to the second light shielding portion. Thereafter, in the second control mode, the proportion of the second light-shielding portion of the moving member in the optical path of the optical sensor member changes in conjunction with the displacement in the belt width direction of the endless belt, and an output level signal corresponding to this proportion. Is output from the optical sensor member. Therefore, in the second control mode, the belt displacement amount of the endless belt is detected in accordance with the ratio of the second light shielding portion different from the first light shielding portion in the moving member in the optical path of the optical sensor member. With such a configuration, in the present invention, each belt displacement amount detection range corresponding to each control mode is individually corresponded to each control mode by the belt displacement amount detection means using one optical sensor member. A detection resolution comparable to that in the case of installing a belt displacement amount detection means (using one optical sensor member) can be obtained.

  Belt displacement amount detection using one optical sensor member so as to obtain the maximum detection resolution as described above for a wide detection range including any belt displacement amount detection range required in each control mode. When configuring the means, the detection range is expanded and the detection resolution is lowered as the forcible movement amount of the endless belt is increased. On the other hand, according to the present invention, no matter how large the forcible movement amount of the endless belt is, the detection resolution is not affected, and the distance between the first light-shielding portion and the second light-shielding portion according to the movement amount ( The distance in the moving direction of the moving member may be set apart.

  According to the present invention, in a configuration in which belt displacement correction control is performed in a plurality of control modes with different target positions, one optical sensor member can detect the belt displacement amount of an endless belt in each control mode without reducing the detection resolution. As a result, an excellent effect of being detectable is obtained.

1 is a schematic configuration diagram illustrating an example of a printer according to an embodiment. FIG. 2 is an explanatory diagram illustrating a schematic configuration of a transfer belt unit in the printer. FIG. 4 is a perspective view showing a part of a tilt mechanism provided on one end side (drive end side) in the roller axial direction of a steering roller mounted on the transfer belt unit, obliquely from above. It is a block diagram which shows a part of electric circuit of the printer. It is a front view showing an edge sensor in the printer. It is a side view which shows the edge sensor. FIG. 3 is an enlarged perspective view partially showing the transfer belt unit. (A), (b), (c) is the change of the relative position of the 1st opening or 2nd opening of the light-shielding part formed in the arm member of the edge sensor, and the 1st light-receiving part and the 2nd light-receiving part. It is an enlarged plan view for demonstrating. (A) is a graph which shows the relationship between the 1st output voltage Va, the 2nd output voltage Vb, and a belt displacement, (b) shows the relationship between a difference signal (Va-Vb) and a belt displacement. It is a graph and (c) is a graph which shows the relationship between a sum signal (Va + Vb) and a belt displacement amount. 4 is a flowchart showing a flow of steering control of a steering roller in Control Example 1; 6 is a flowchart showing a flow of control mode switching processing in Control Example 1; FIG. 6 is an explanatory diagram showing an arrangement of a belt scale and a mark sensor used for belt running control of an intermediate transfer belt. It is explanatory drawing for demonstrating the detection method of the mark for optical detection on the belt scale by the mark sensor. It is a graph which shows the waveform of the appropriate output signal output from the mark sensor. It is a graph which shows the waveform of the improper output signal output from the mark sensor. It is explanatory drawing which shows arrangement | positioning of the cleaning member for cleaning the dirt adhering to a belt scale or a mark sensor at the time of 1st control mode. 6 is a flowchart showing a control flow in a control example 2; It is explanatory drawing which shows arrangement | positioning of the cleaning member for cleaning the dirt adhering to a belt scale or a mark sensor at the time of 2nd control mode. FIG. 6 is an explanatory diagram illustrating a configuration example in which a cleaning end detection mark is arranged on an outer peripheral surface portion of an intermediate transfer belt on a cleaning member passage path through which a sensor cleaning member passes during traveling of the intermediate transfer belt. It is explanatory drawing which shows the structural example which grasps | ascertains a 1st control mode or a 2nd control mode using a transmissive | pervious optical sensor. It is explanatory drawing which shows the structural example which grasps | ascertains a 1st control mode or a 2nd control mode using the arm member from which the opening area of a 1st opening and a 2nd opening differs. In the same structural example, it is a graph which shows the difference in the output voltage of an edge sensor by the 1st control mode and the 2nd control mode. An example of a configuration for grasping the first control mode or the second control mode by using an arm member whose second opening is longer than the first opening so that only the second opening reaches the third light receiving unit is shown. It is explanatory drawing. It is explanatory drawing which shows the structure of the edge sensor in the example of a structure. In the same structural example, it is a graph which shows the output voltage output from an edge sensor at each control mode. FIG. 11 is an explanatory diagram illustrating a configuration of a modification applied to the fixing belt. It is explanatory drawing which shows the structure of the other modification applied to the paper conveyance belt.

Hereinafter, an embodiment in which the present invention is applied to a printer as an image forming apparatus that forms an image by electrophotography will be described.
First, a basic configuration of the printer according to the embodiment will be described.
FIG. 1 is a schematic configuration diagram illustrating an example of a printer according to an embodiment.
This printer includes two optical writing units 1YM and 1CK and four image forming units 2Y, 2M, 2C, and 2K for forming Y, M, C, and K toner images. Further, the sheet feeding path 30, the pre-transfer conveying path 31, the manual sheet feeding path 32, the manual feed tray 33, the registration roller pair 34, the conveying belt unit 35, the fixing device 40, the conveyance switching device 50, the sheet discharging path 51, and the sheet discharging roller. A pair 52, a paper discharge tray 53, a first paper feed cassette 101, a second paper feed cassette 102, a retransmission device, and the like are also provided.

  Each of the first paper feed cassette 101 and the second paper feed cassette 102 accommodates a bundle of recording papers P as recording materials. Then, the uppermost recording paper P in the paper bundle is sent out toward the paper feed path 30 by the rotational drive of the paper feed rollers 101a and 102a. The feeding path 30 is followed by a pre-transfer conveyance path 31 for conveying the recording paper immediately before a secondary transfer nip described later. The recording paper P sent out from the paper feed cassettes 101 and 102 enters the pre-transfer conveyance path 31 through the paper feed path 30.

  A manual feed tray 33 is disposed on the side surface of the printer housing so as to be openable and closable with respect to the housing, and a bundle of paper is manually fed to the upper surface of the tray in an open state with respect to the housing. The uppermost recording paper P in the manually fed paper bundle is sent out toward the pre-transfer conveyance path 31 by the feed roller of the manual feed tray 33.

  Each of the two optical writing units 1YM and 1CK has a laser diode, a polygon mirror, various lenses, and the like, and is used for image information read by a scanner outside the printer or image information sent from a personal computer. Based on this, the laser diode is driven. Then, the photoconductors 3Y, 3M, 3C, and 3K of the image forming units 2Y, 2M, 2C, and 2K are optically scanned. Specifically, the photoreceptors 3Y, 3M, 3C, and 3K of the image forming units 2Y, 2M, 2C, and 2K are rotationally driven in the counterclockwise direction in the drawing by driving means (not shown). The optical writing unit 1YM performs an optical scanning process by irradiating the driven photoconductors 3Y and 3M while deflecting the laser light in the rotation axis direction. Thereby, electrostatic latent images based on the Y image information and the M image information are formed on the photoreceptors 3Y and 3M, respectively. Further, the optical writing unit 1CK performs an optical scanning process by irradiating the driven photoconductors 3C and 3K while deflecting the laser light in the rotation axis direction. Thereby, electrostatic latent images based on the C image information and the K image information are formed on the photoreceptors 3C and 3K, respectively.

  Each of the image forming units 2Y, 2M, 2C, and 2K includes drum-shaped photoconductors 3Y, 3M, 3C, and 3K as latent image carriers. The image forming units 2Y, 2M, 2C, and 2K support various devices arranged around the photoreceptors 3Y, 3M, 3C, and 3K as a single unit on a common support. Can be attached to and detached from the printer unit main body. The image forming units 2Y, 2M, 2C, and 2K have the same configuration except that the colors of the toners used are different from each other. Taking the image forming unit 2Y for Y as an example, this has a developing device 4Y for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image in addition to the photoreceptor 3Y. In addition, the charging device 5Y that uniformly charges the surface of the photoconductor 3Y that is driven to rotate, or the transfer residue that has adhered to the surface of the photoconductor 3Y after passing through the primary transfer nip for Y described later. A drum cleaning device 6Y for cleaning toner is also provided.

  The printer according to this embodiment has a so-called tandem configuration in which four image forming units 2Y, 2M, 2C, and 2K are arranged along an endless movement direction with respect to an intermediate transfer belt 61 that is an endless belt described later. It has become.

  As the photoreceptor 3 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a base tube made of aluminum or the like. However, an endless belt may be used.

  The developing device 4Y develops a latent image using a two-component developer (hereinafter simply referred to as “developer”) containing a magnetic carrier (not shown) and non-magnetic Y toner. As the developing device 4Y, a type that performs development with a one-component developer not including a magnetic carrier may be used instead of the two-component developer. The developing device 4Y is appropriately replenished with Y toner in the Y toner bottle 103Y by a Y toner replenishing device (not shown).

  As the drum cleaning device 6Y, a system in which a polyurethane rubber cleaning blade as a cleaning member is pressed against the photoreceptor 3Y is used, but another system may be used. In order to improve the cleaning property, this printer employs a system in which a rotatable fur brush is brought into contact with the photoreceptor 3Y. This fur brush also serves to apply the lubricant to the surface of the photoreceptor 3Y while scraping the lubricant from a solid lubricant (not shown) into a fine powder.

  A neutralizing lamp (not shown) is disposed above the photoreceptor 3Y, and this neutralizing lamp is also a part of the image forming unit 2Y. The neutralization lamp neutralizes the surface of the photoreceptor 3Y after passing through the drum cleaning device 6Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging device 5Y, and then optically scanned by the optical writing unit 1YM described above. The charging device 5Y is rotationally driven while receiving a charging bias from a power source (not shown). Instead of this method, a scorotron charger method in which the photosensitive member 3Y is charged without contact may be employed.

  The image forming unit 2Y for Y has been described above, but the image forming units 2M, 2C, and 2K for M, C, and K have the same configuration as that for Y.

  A transfer belt unit 60 is disposed below the four image forming units 2Y, 2M, 2C, and 2K. The transfer belt unit 60 rotates the rotation of any one of the support rollers while bringing the intermediate transfer belt 61, which is an endless belt stretched by a plurality of support rollers, into contact with the photoreceptors 3Y, 3M, 3C, 3K. Drive (run endlessly) in the clockwise direction in the figure by driving. Thereby, primary transfer nips for Y, M, C, and K in which the photoreceptors 3Y, 3M, 3C, and 3K and the intermediate transfer belt 61 abut are formed.

  In the vicinity of the primary transfer nips for Y, M, C, K, primary transfer rollers 62Y, 62M, serving as primary transfer members disposed in a belt loop that is a space surrounded by the inner peripheral surface of the intermediate transfer belt. The intermediate transfer belt 61 is pressed toward the photoreceptors 3Y, 3M, 3C, and 3K by 62C and 62K. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, and 62K by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. .

  In the drawing, toner images are sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement in the clockwise direction. The primary transfer. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as “four-color toner image”) is formed on the outer peripheral surface of the intermediate transfer belt 61.

  A secondary transfer roller 72 is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer roller 72 abuts from the outer peripheral surface of the intermediate transfer belt 61 around the secondary transfer backup roller 68 to form a secondary transfer nip. Thus, a secondary transfer nip is formed in which the outer peripheral surface of the intermediate transfer belt 61 and the secondary transfer roller 72 are in contact with each other.

  A secondary transfer bias is applied to the secondary transfer roller 72 by a power source (not shown). On the other hand, the secondary transfer backup roller 68 in the belt loop is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  The registration roller pair 34 is disposed on the right side of the secondary transfer nip in the figure, and the recording paper P sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 61. Send to the secondary transfer nip. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 61 are collectively transferred to the recording paper P due to the influence of the secondary transfer electric field and the nip pressure, and combined with the white color of the recording paper P, becomes a full color image.

  The transfer residual toner that has not been transferred to the recording paper P at the secondary transfer nip adheres to the outer peripheral surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This transfer residual toner is cleaned by a belt cleaning device 75 in contact with the intermediate transfer belt 61.

  The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and transferred to the transport belt unit 35. The transport belt unit 35 endlessly moves the endless belt-shaped transport belt 36 endlessly in the counterclockwise direction in the figure by the rotational drive of the drive roller 37 while being stretched by the drive roller 37 and the driven roller 38. Then, the recording paper P delivered from the secondary transfer nip is conveyed with the endless movement of the conveying belt 36 while being held on the stretched surface of the outer circumferential surface of the conveying belt, and is delivered to the fixing device 40 as a fixing unit. .

  In this printer, the transfer switching device 50, the retransmission path 54, the switchback path 55, the post-switchback transfer path 56, and the like constitute a retransmission means. Specifically, the conveyance switching device 50 switches the subsequent conveyance destination of the recording paper P received from the fixing device 40 between the paper discharge path 51 and the retransmission path 54. When executing a single-side mode print job for forming an image only on the first side of the recording paper P, the conveyance destination of the recording paper P is set to the paper discharge path 51. As a result, the recording paper P on which the image is formed only on the first surface is sent to the paper discharge roller pair 52 via the paper discharge path 51 and discharged onto the paper discharge tray 53 outside the apparatus. In addition, when executing a print job in a duplex mode in which images are formed on both sides of the recording paper P, when the recording paper P having images fixed on both sides is received from the fixing device 40, the recording paper P Is set to the paper discharge path 51. As a result, the recording paper P having images formed on both sides is discharged onto a discharge tray 53 outside the apparatus. On the other hand, when the recording paper P having an image fixed only on the first side is received from the fixing device 40 during execution of the double-side mode print job, the transport destination of the recording paper P is set to the retransmission path 54.

  A switchback path 55 is connected to the retransmission path 54, and the recording paper P sent to the retransmission path 54 enters the switchback path 55. When the entire area in the conveyance direction of the recording paper P enters the switchback path 55, the conveyance direction of the recording paper P is reversed and the recording paper P is switched back. In addition to the retransmission path 54, a post-switchback transport path 56 is connected to the switchback path 55, and the recording paper P that has been switched back enters the post-switchback transport path 56. At this time, the upper and lower sides of the recording paper P are reversed. The recording paper P that is turned upside down is retransmitted to the secondary transfer nip via the post-switchback transport path 56 and the paper feed path 30. The recording paper P on which the toner image is also transferred to the second surface at the secondary transfer nip is fixed on the second surface via the fixing device 40, and then the conveyance switching device 50, the paper discharge path 51, and the like. The paper is discharged onto a paper discharge tray 53 via a pair of paper discharge rollers 52.

FIG. 2 is an explanatory diagram showing a schematic configuration of the transfer belt unit 60 in the printer.
The transfer belt unit 60 has an intermediate transfer belt 61 stretched and supported by a plurality of support rollers 63, 67, 68, 69, 71 and the like including a steering roller 63 for correcting a belt width direction position. Further, a tilt mechanism that performs an operation for tilting the steering roller 63 by a driving force from the steering motor 23 that is a driving source, and a belt displacement amount detecting unit that detects a belt displacement amount in which the intermediate transfer belt 61 is displaced in the belt width direction. The edge sensor 24 is also included. Further, the steering control for driving the steering motor 23 so as to determine the tilt amount of the steering roller 63 based on the belt displacement detected by the edge sensor 24 and to tilt the steering roller 63 by the determined tilt amount. It also has a device 21. The position of the intermediate transfer belt 61 in the belt width direction is corrected by changing the amount of inclination of the steering roller 63. In this printer, the support roller 67 is a drive roller, but another support roller may be a drive roller.

  The steering control device 21 may be a dedicated microcomputer or a controller built in the printer. The steering control device 21 adjusts the inclination amount of the steering roller 63 based on the belt displacement amount detected by the edge sensor 24, and performs feedback control so that the belt width direction position of the intermediate transfer belt 61 is stabilized at the target position. .

FIG. 3 is a perspective view showing a part of the tilt mechanism provided on the other end side (drive end side) of the steering roller 63 in the roller axis direction from obliquely above.
In this printer, as the tilt mechanism that performs the operation for tilting the steering roller 63, a cantilever wire system is adopted as shown in FIG.

  The steering motor 23 has a drive pulley 86 on its output shaft. The drive pulley 86 stretches a timing belt 88 together with the take-up pulley 87. The take-up pulley 87 is formed by coaxially forming a belt pulley portion around which the timing belt 88 is wound and a wire pulley portion to which one end of the wire 80 (hereinafter referred to as “drive end”) is fixed. . When the steering motor 23 is driven to rotate and the drive pulley 86 rotates, the take-up pulley 87 rotates via the timing belt 88, and the drive end side of the wire 80 is taken up by the wire pulley portion. Since the winding pulley 87 of this printer is formed so that the diameter of the wire pulley portion is smaller than the diameter of the belt pulley portion, the winding pulley 87 constitutes a speed reducing means.

  The drive end side of the wire 80 is fixed to the take-up pulley 87. On the other hand, the other end side of the wire 80 is wound around the movable pulley 83, and the end thereof is fixed to the wire holding member 84. The movable pulley 83 is rotatably supported by one end portion of the long roller holder 81. The driving end of the steering roller 63 is rotatably supported at the end opposite to the end of the roller holder 81 on which the movable pulley 83 is supported. The roller holder 81 is supported by a support shaft 82 so that a middle portion in the longitudinal direction can rotate. The roller holder 81 is applied with an urging force that urges the roller holder 81 in the clockwise direction in FIG. The tension spring 85 applies a biasing force that displaces the movable pulley 83 around which the wire 80 is wound in the upward direction in FIG. Functions as tension applying means.

  The wire portion 80 a is pulled by a tension spring 89. As a result, a biasing force that rotates counterclockwise in FIG. 2 is applied to the take-up pulley 87. The wire portion 80 a and the tension spring 89 are for reducing the driving torque of the steering motor 23. That is, when the steering motor 23 is rotationally driven in a direction against the urging force of the tension spring 85, a driving load is applied to the steering motor 23 due to the urging force of the tension spring 85. Since the urging force is applied, the driving addition is reduced.

  In the tilting mechanism having the above configuration, the steering motor 23 is driven to rotate, and the wire 80 is wound up or taken out by the take-up pulley 87, whereby the moving pulley 83 is displaced, whereby the roller holder 81 moves the support shaft 82. Rotate to the center. As a result, the driving end of the steering roller 63 is displaced relative to the other end, and the steering roller 63 tilts. According to the wire system in which the wire 80 is wound around the take-up pulley 87 as in this printer, the movable amount of the wire 80 can be increased, so that the tilting range of the steering roller 63, that is, the controllable tilt amount range is set. Can be taken widely. However, if the tilting range of the steering roller 63 is too wide and the roller holder 81 may interfere with surrounding parts, a restricting means for restricting the rotation range of the roller holder 81 to a predetermined range may be provided. . In this printer, a stopper 95 is provided as the restricting means as shown in FIG.

  In the present printer, since the movable amount of the wire 80 can be increased, the tilting range of the steering roller 63 can be sufficiently ensured even if the speed reduction means is interposed. Therefore, it is possible to employ a configuration in which the amount of inclination of the steering roller 63 is controlled with high accuracy by interposing a speed reduction means. Therefore, in this printer, the diameter ratio between the belt pulley portion and the wire pulley portion in the winding pulley 87 described above, the use of the movable pulley 83, the length ratio from the support shaft 82 to each end portion in the roller holder 81 (the lever lever) (Principle) employs a configuration in which the rotational drive of the steering motor 23 is decelerated and transmitted to the roller holder 81, thereby increasing the resolution of the amount of inclination of the steering roller 63 and enabling highly accurate inclination control.

  In addition, since the printer employs a wire system, the steering motor 23 can be disposed at a position farther from the steering roller 63 than a cam system that does not use a wire. Therefore, the degree of freedom in layout around the steering roller 63 is high.

FIG. 4 is a block diagram showing a part of the electric circuit of the printer.
The steering control device 21 controls the driving state of the steering motor 23 and outputs a motor control signal (motor drive signal) for that purpose to the steering motor 23. As the steering motor 23, a stepping motor, a linear motor, or the like capable of controlling the rotation angle and rotation speed with high accuracy is used. In the present embodiment, a stepping motor is used as the steering motor 23. Further, an edge sensor 24 is connected to the steering control device 21, and belt position information from the edge sensor 24 is input.

FIG. 5 is a front view showing the edge sensor 24 in the printer.
FIG. 6 is a side view showing the edge sensor 24.
The edge sensor 24 is fixed so as to rise in the axial direction of the support shaft 24c from an L-shaped arm member as a moving member that is supported rotatably about the support shaft 24c, or from the surface of one end of the arm member. The contact pin 24k is provided. In addition, it also includes a light emitting unit 24h, a first light receiving unit 24e that receives light emitted from the light emitting unit 24h, a second light receiving unit 24f, and the like.

  The other end of the L-shaped arm member is interposed between the light emitting unit 24h and the first light receiving unit 24e or the second light receiving unit 24f, and serves as a light shielding unit 24d that blocks light from the light emitting unit 24h. ing. The light-shielding portion 24d is formed with two openings 24i and 24j through which light from the light-emitting portion 24h is transmitted and received by the first light-receiving portion 24e and the second light-receiving portion 24f.

  The contact pin 24k fixed to one end portion of the L-shaped arm member is pressed against the side portion (belt width direction end surface) of the intermediate transfer belt 61 by the force of the spring 24a as shown in FIG. . When the belt displacement amount of the intermediate transfer belt 61 changes in this state, the arm member rotates around the support shaft 24c accordingly. Then, as shown in FIGS. 8A to 8C, the relative position between the first opening 24i or the second opening 24j and the first light receiving unit 24e or the second light receiving unit 24f changes, and the first light receiving The amount of light received by the part 24e and the second light receiving part 24f changes.

FIG. 9A is a graph showing the relationship between the first output voltage Va from the first light receiving unit 24e, the second output voltage Vb from the second light receiving unit 24f, and the belt displacement.
FIG. 9B is a graph showing the relationship between the difference signal (Va−Vb), which is the first output voltage Va−the second output voltage Vb, and the belt displacement amount.
FIG. 9C is a graph showing the relationship between the sum signal (Va + Vb) that is the first output voltage Va + the second output voltage Vb and the belt displacement.
The vertical axis of these graphs indicates the output voltage value [V]. The horizontal axis indicates the position in the belt width direction of the intermediate transfer belt 61 (belt displacement from the reference position 0). The reference position 0 on the horizontal axis is the roller center position (first target position). The steering control device 21 controls the tilting operation of the steering roller 63 so that the belt displacement amount becomes the reference position 0, whereby the belt displacement amount is appropriately controlled in the region C.

  When the belt displacement amount of the intermediate transfer belt 61 is within the region C, the output voltage Va and the output voltage Vb are both in accordance with the displacement in the width direction of the intermediate transfer belt 61 as shown in the graph of FIG. The output change range where the output level is changing. That is, as shown in FIG. 8B, the light that has passed through the first opening 24i or the second opening 24j while part of the light is shielded by the light-shielding part 24d is the first light-receiving part 24e and the second light-receiving part. The light is received by both of the parts 24f. That is, the ratio of the light shielding part 24d in the optical path from the light emitting part 24h to the first light receiving part 24e and the second light receiving part 24f changes. In this state, the value of the difference signal (Va−Vb) is smaller than + Vmax as shown in the graph of FIG. When the belt displacement is completely at the first target position (roller center position), the value of the difference signal (Va−Vb) is zero.

  If the belt width direction position of the intermediate transfer belt 61 is slightly shifted to the minus side from the first target position (the center of the region C), the value of the difference signal (Va−Vb) becomes larger than zero. When the belt displacement further shifts to the minus side, as shown in FIG. 8C, only the first light receiving unit 24e receives light, and the value of the difference signal (Va−Vb) is the output voltage. It becomes almost the same value as + Vmax which is the maximum value of Va (area E). When the belt displacement further shifts to the minus side, the light that has passed through the first opening 24i or the second opening 24j while the part of the light is shielded by the light shielding part 24d is now transmitted to the first light receiving part. Only 24e receives light (region E). That is, the ratio of the light shielding part 24d in the optical path from the light emitting part 24h to the first light receiving part 24e changes. In this case, the value of the difference signal (Va−Vb) is smaller than + Vmax as shown in the graph of FIG. 9B.

  In the present embodiment, when the value of the difference signal (Va−Vb) obtained from the optical sensor member configured by the light emitting unit 24h, the first light receiving unit 24e, and the second light receiving unit 24f is a positive value (belt displacement amount). Is negative), the steering control device 21 performs control so that the steering roller 63 is tilted in the direction in which the belt displacement amount is toward the positive side. In this control, control is performed so that the amount of inclination of the steering roller 63 increases as the absolute value of the belt displacement amount increases. At this time, as shown in FIG. 9B, the value of the difference signal (Va−Vb) is the same between the belt displacement amount in the region C and the belt displacement amount in the region E. Since it can take a value, it is necessary to distinguish this. In this embodiment, in the case where the region C and the region E can take the same value, when the belt displacement amount is within the region C, the value of the sum signal (Va + Vb) is a threshold value as shown in FIG. While the value is larger than Vth, when the belt displacement is in the region E, the value of the sum signal (Va + Vb) is lower than the threshold value Vth as shown in FIG. Therefore, the two can be distinguished by referring to the value of the sum signal (Va + Vb).

  On the other hand, when the belt width direction position of the intermediate transfer belt 61 is slightly shifted to the plus side from the first target position (the center of the region C), the value of the difference signal (Va−Vb) becomes a value smaller than zero. When the belt displacement further shifts to the plus side, as shown in FIG. 8A, only the second light receiving unit 24f receives light, and the value of the difference signal (Va−Vb) is the output voltage. It becomes almost the same value as −Vmax obtained by inverting the sign of the maximum value of Vb (region D). When the belt displacement amount further shifts to the plus side, the light that has passed through the first opening 24i or the second opening 24j while the part of the light is shielded by the light-shielding part 24d is transmitted to the second light-receiving part. The light is received only by 24f (area D). That is, the ratio of the light shielding part 24d in the optical path from the light emitting part 24h to the second light receiving part 24f changes. In this case, the value of the difference signal (Va−Vb) is larger than −Vmax as shown in the graph of FIG.

  In the present embodiment, when the value of the differential signal (Va−Vb) obtained from the optical sensor member configured by the light emitting unit 24h, the first light receiving unit 24e, and the second light receiving unit 24f is a negative value (belt displacement amount). Is positive), the steering control device 21 performs control so that the steering roller 63 is tilted in the direction in which the belt displacement amount is toward the negative side. In this control, control is performed so that the amount of inclination of the steering roller 63 increases as the absolute value of the belt displacement amount increases. At this time, as shown in FIG. 9B, the value of the difference signal (Va−Vb) is the same between the belt displacement amount in the region C and the belt displacement amount in the region D. Since it can take a value, it is necessary to distinguish this. As described above, this distinction is made by referring to the value of the sum signal (Va + Vb).

  In the present embodiment, in the region C, the change rate of the differential signal (Va−Vb) (the change rate of the signal voltage value with respect to the belt displacement amount) is the individual output voltage in the first light receiving unit 24e and the second light receiving unit 24f. It is larger than the rate of change of Va and Vb, and the detection resolution is high. Therefore, in the region C, it is possible to detect the belt displacement amount with higher accuracy and to perform finer belt displacement correction control.

[Control example 1]
Next, a control example of the steering roller in the present embodiment (hereinafter, this control example is referred to as “control example 1”) will be described.
FIG. 10 is a flowchart showing the flow of control in the present control example 1.
When a print job is input (S1), driving of the intermediate transfer belt 61 is started (S2), and an image forming operation according to the print job is performed (S3). During this image forming operation, the edge sensor 24 detects the displacement amount (belt displacement amount) of the intermediate transfer belt 61 in the width direction (S4). Specifically, the first output voltage Va of the first light receiving unit 24e and the second output voltage Vb of the second light receiving unit 24f output from the edge sensor 24 are acquired. The steering motor 23 necessary for correcting the position in the width direction of the intermediate transfer belt 61 to the target position based on the belt displacement amounts (first output voltage Va and second output voltage Vb) detected in this way. The control amount (target rotation angle) is calculated, and belt displacement correction control is performed in which the rotation angle of the steering motor 23 is controlled so that the rotation angle of the steering motor 23 becomes the target rotation angle based on the calculation result.

  Specifically, the steering control device 21 acquires the output voltages Va and Vb output from the light receiving units 24e and 24f, and uses a difference signal (Va−Vb) between these output voltages Va and Vb. The steering motor 23 is controlled as follows.

  First, when the difference signal (Va−Vb) is in a range larger than −Vmax and smaller than + Vmax (Yes in S5), the difference signal (Va−Vb) is used by using the difference signal (Va−Vb). The steering motor 23 is controlled (S6) to correct the position in the width direction of the intermediate transfer belt 61 so that is zero (that is, the belt displacement is zero). Specifically, when the output shaft of the steering motor 23 is rotated counterclockwise in FIG. 2 from a state where the steering roller 63 is horizontal, the wire 80 is taken up by the take-up pulley 87 and the roller holder 81 is moved in the θ1 direction. Rotate. As a result, the driving end of the steering roller 63 is lifted by the roller holder 81, and the steering roller 63 is inclined according to the lift amount. At this time, the belt width direction position of the intermediate transfer belt 61 wound around the steering roller 63 is displaced to the side opposite to the driving end of the steering roller 63. On the other hand, when the output shaft of the steering motor 23 is rotated clockwise in FIG. 2 from the state where the steering roller 63 is horizontal, the wire 80 is fed out from the take-up pulley 87 and the roller holder 81 is moved in the θ2 direction. Rotate. As a result, the driving end of the steering roller 63 is pushed down by the roller holder 81, and the steering roller 63 is inclined according to the amount of the pushing down. At this time, the position in the belt width direction of the intermediate transfer belt 61 wound around the steering roller 63 is displaced toward the driving end of the steering roller 63. Therefore, the displacement (position fluctuation) of the intermediate transfer belt 61 in the belt width direction is detected by the edge sensor 24 described above, and the steering motor 23 is driven based on the detected belt displacement amount to appropriately control the inclination of the steering roller 63. As a result, the displacement of the intermediate transfer belt 61 can be corrected.

  When the difference signal (Va−Vb) is −Vmax or less (Yes in S7), the belt displacement amount of the intermediate transfer belt 61 is a region D that exceeds the region C of the edge sensor 24 on the plus side. . Therefore, in this case, the steering motor 23 is controlled by a predetermined control amount so that the intermediate transfer belt 61 is displaced to the minus side of the belt displacement direction (S8). Thereby, the position in the width direction of the intermediate transfer belt 61 can be returned to a position where the detailed steering control is possible (a position where the belt displacement amount is in the region C). As a result, if the position in the width direction of the intermediate transfer belt 61 is corrected to a position corresponding to the region C, the steering motor 23 can be controlled in accordance with the value (belt displacement) of the difference signal (Va−Vb). Become.

  When the difference signal (Va−Vb) is equal to or greater than + Vmax (Yes in S9), the belt displacement amount of the intermediate transfer belt 61 is a region E that exceeds the region C of the edge sensor 24 on the minus side. Therefore, in this case, the steering motor 23 is controlled by a predetermined control amount so that the intermediate transfer belt 61 is displaced toward the plus side of the belt displacement direction (S10). Thereby, the position in the width direction of the intermediate transfer belt 61 can be returned to a position where the detailed steering control is possible (a position where the belt displacement amount is in the region C). As a result, if the position in the width direction of the intermediate transfer belt 61 is corrected to a position corresponding to the region C, the steering motor 23 can be controlled in accordance with the value (belt displacement) of the difference signal (Va−Vb). Become.

  In this embodiment, when the intermediate transfer belt 61 is greatly displaced by a belt displacement amount exceeding the region C, the accurate width direction position of the intermediate transfer belt 61 can be grasped from the detection results Va and Vb by the edge sensor 24. Can not. Therefore, detailed steering control according to the value of the difference signal (Va−Vb) obtained from the detection result of the edge sensor 24 cannot be performed. However, in the present embodiment, when the intermediate transfer belt 61 is largely displaced in this way, the direction in which the intermediate transfer belt 61 is largely displaced is separated from the light receiving units 24e and 24f as described above. It is possible to grasp from the output voltages Va and Vb of these light receiving portions 24e and 24f without using the sensor. Therefore, even when the intermediate transfer belt 61 is greatly displaced beyond the region C, it is not necessary to immediately stop the traveling of the intermediate transfer belt 61 to request a maintenance operation, and the frequency of the maintenance operation can be reduced.

  The control from the above-described processing steps S4 to S10 is repeated until the image forming operation is completed (S11). When the image forming operation is completed, in the present control example 1, the steering control device 21 determines that the count value of the number of prints for control mode switching that has been counted up every time one sheet is printed is equal to or greater than a predetermined value. It is determined whether or not (S12). In this determination, if the number of prints for control mode switching has not yet reached the specified value (No in S12), the image forming operation is terminated as it is. On the other hand, if the number of prints for control mode switching is equal to or greater than the specified value (Yes in S12), it is determined that the control mode switching condition is satisfied, and the control mode switching process described below is executed. After that, the count value of the number of prints for control mode switching is reset (S13).

Next, the control mode switching process in the present control example 1 will be described.
The steering control device 21 selects one of two control modes having different target positions in the width direction position of the intermediate transfer belt 61 and moves the intermediate transfer belt 61 in the width direction toward the target position corresponding to the selected control mode. Perform control to correct the position. The reason why such two control modes are provided in the present control example 1 is to extend the life of the intermediate transfer belt 61.

  Specifically, when the recording paper P enters the secondary transfer nip, the corner of the leading edge of the recording paper P hits the outer peripheral surface of the intermediate transfer belt 61. Since the position in the belt width direction where the leading edge of the recording paper P abuts is substantially the same position, when the number of prints increases, the corner of the leading edge of the recording paper P repeatedly strikes the same portion of the intermediate transfer belt 61, and the middle The outer peripheral surface of the transfer belt 61 is damaged, causing image quality deterioration. Therefore, in this control example 1, when the number of printed sheets exceeds a certain amount (specified value), the control is switched to another control mode in which the correction target position in the width direction position of the intermediate transfer belt 61 is different, and the leading end corner of the recording paper P is moved. Change the position of the belt in the width direction.

FIG. 11 is a flowchart showing the flow of the control mode switching process.
In the control mode switching process, first, it is determined whether the current control mode of the steering control device 21 is the first control mode or the second control mode (S21). If it is determined in this determination that the control mode is the first control mode (Yes in S21), the second control is performed from the first target position corresponding to the first control mode in order to switch from the first control mode to the second control mode. The position in the width direction of the intermediate transfer belt 61 is forcibly moved toward the second target position corresponding to the mode. In the present embodiment, the first target position corresponding to the first control mode is set on the belt displacement direction plus side with respect to the second target position corresponding to the second control mode. Therefore, when switching from the first control mode to the second control mode, the steering motor 23 is controlled by a predetermined constant control amount so that the intermediate transfer belt 61 is displaced to the minus side of the belt displacement direction (S22). ). When the intermediate transfer belt 61 is displaced to the minus side in the belt displacement direction by this control, the belt displacement amount finally changes from the region C to the region E to the region G as shown in FIG.

  The steering control device 21 detects the displacement in the width direction (belt displacement) of the intermediate transfer belt 61 by the edge sensor 24 (S23), and determines whether or not the value of the first output voltage Va has become zero (S24). ). When the value of the first output voltage Va becomes zero, it means that the belt displacement amount with respect to the first target position is in the region G in the first control mode. Thereafter, when the intermediate transfer belt 61 is further displaced toward the minus side in the belt displacement direction, as shown in FIG. 5, the arm member rotates about the support shaft 24c. Thus, until then (during the first control mode), the first opening 24i formed in the light shielding portion 24d of the arm member has reached the first light receiving portion 24e and the second light receiving portion 24f. The second opening 24j formed in the light shielding portion 24d reaches the first light receiving portion 24e and the second light receiving portion 24f.

  Specifically, when the intermediate transfer belt 61 is further displaced toward the minus side in the belt displacement direction, the second opening 24j reaches the second light receiving unit 24f. As a result, the value of the second output voltage Vb gradually increases from zero according to the displacement of the intermediate transfer belt 61, and eventually reaches the maximum value Vmax. At this time, it means that the belt displacement amount is in the region D with respect to the second target position in the second control mode. Therefore, the steering control device 21 determines whether or not the value of the second output voltage Vb has reached the maximum value Vmax (S25).

  When the intermediate transfer belt 61 is further displaced toward the minus side of the belt displacement direction, the second opening 24j also reaches the first light receiving portion 24e, and the position in the width direction of the intermediate transfer belt 61 is displaced to the second target position. When the difference signal (Va−Vb) becomes zero. Therefore, the steering control device 21 determines whether or not the difference signal (Va−Vb) has become zero (S26), and when the difference signal (Va−Vb) has become zero, the belt displacement amount in the second control mode. As a result, the driving of the intermediate transfer belt 61 is stopped. Thereafter, the steering control device 21 operates in the second control mode, and controls the steering motor 23 so that the belt displacement becomes zero, thereby correcting the position in the width direction of the intermediate transfer belt 61 to the second target position. Control will be performed.

  On the other hand, when it is determined in the processing step S21 that the control mode is the second control mode (No in S21), the second control mode is switched from the second control mode to the first control mode. The position in the width direction of the intermediate transfer belt 61 is forcibly moved toward the first target position corresponding to the one control mode. At this time, the steering motor 23 is controlled by a predetermined control amount so that the intermediate transfer belt 61 is displaced toward the plus side in the belt displacement direction (S27). When the intermediate transfer belt 61 is displaced toward the plus side in the belt displacement direction by this control, the belt displacement amount finally becomes the region F from the region C through the region D as shown in FIG.

  The steering control device 21 detects the width direction displacement amount (belt displacement amount) of the intermediate transfer belt 61 by the edge sensor 24 (S28), and determines whether or not the value of the second output voltage Vb has become zero (S29). ). When the value of the second output voltage Vb becomes zero, it means that the belt displacement amount with respect to the second target position is in the region F in the second control mode. Thereafter, when the intermediate transfer belt 61 is further displaced toward the minus side in the belt displacement direction, as shown in FIG. 5, the arm member rotates about the support shaft 24c. Thus, until then (during the second control mode), the second opening 24j formed in the light shielding portion 24d of the arm member has reached the first light receiving portion 24e and the second light receiving portion 24f. The first opening 24i formed in the light shielding portion 24d reaches the first light receiving portion 24e and the second light receiving portion 24f.

  Specifically, when the intermediate transfer belt 61 is further displaced toward the plus side in the belt displacement direction, the first opening 24i reaches the first light receiving unit 24e. As a result, the value of the first output voltage Va gradually increases from zero according to the displacement of the intermediate transfer belt 61, and eventually reaches the maximum value Vmax. At this time, the belt displacement amount means that the region E is in the first target position in the first control mode. Therefore, the steering control device 21 determines whether or not the value of the first output voltage Va has reached the maximum value Vmax (S30).

  When the intermediate transfer belt 61 is further displaced toward the plus side in the belt displacement direction, the first opening 24i also reaches the second light receiving portion 24f, and the width direction position of the intermediate transfer belt 61 is displaced to the first target position. When the difference signal (Va−Vb) becomes zero. Therefore, the steering control device 21 determines whether or not the difference signal (Va−Vb) has become zero (S26), and when the difference signal (Va−Vb) has become zero, the amount of belt displacement in the first control mode. As a result, the driving of the intermediate transfer belt 61 is stopped. Thereafter, the steering control device 21 operates in the first control mode and controls the steering motor 23 so that the belt displacement becomes zero, thereby correcting the position in the width direction of the intermediate transfer belt 61 to the first target position. Control will be performed.

  According to this control example 1, every time the number of prints for control mode switching reaches a specified value, the control mode switching process can be executed to switch the correction target position in the width direction position of the intermediate transfer belt 61. Thereby, compared with the case where the width direction position of the intermediate transfer belt 61 is always corrected to the same target position, the locations on the outer peripheral surface of the intermediate transfer belt 61 where the leading edge of the recording paper P abuts can be dispersed. . As a result, scratches due to repeated cornering of the leading edge of the recording paper P are less likely to occur, and the life of the intermediate transfer belt 61 can be extended.

[Control example 2]
Next, another control example of the steering roller in the present embodiment (hereinafter, this control example is referred to as “control example 2”) will be described.
In the present embodiment, as shown in FIG. 12, a belt scale 73 made up of a large number of optical detection marks is formed in the belt width direction end region on the outer peripheral surface of the intermediate transfer belt 61. The belt scale 73 is formed by arranging a large number of optical detection marks having the same dimensions along the belt traveling direction at a predetermined interval. Further, as a mark detection means for optically detecting the optical detection mark at a position facing the belt scale 73 (position facing the mark passing path through which the optical detection mark passes while the intermediate transfer belt 61 is traveling). Mark sensor 74 is arranged.

  As shown in FIG. 13, the mark sensor 74 is a reflection type optical sensor, and reflects the mark reflected light when the optical detection mark 73a passes through the irradiation region (sensor region) of the light irradiated from the light emitting portion 74a. Light is received by the light receiving unit 74b and an output signal corresponding to the amount of light received is output. This output signal is sent to a main body control unit (not shown), and is fed back to the motor input voltage or motor input current of the driving motor that transmits the driving force to the driving roller 67 that drives the intermediate transfer belt 61. Thereby, feedback control is performed so that the traveling speed of the intermediate transfer belt 61 becomes the target traveling speed. By performing such control, the running of the intermediate transfer belt 61 is reduced so as to reduce the influence of disturbance on the image quality, such as the thickness deviation of the intermediate transfer belt 61, the vibration of the driving roller 67, and the load fluctuation due to the presence or absence of recording paper. The speed can be controlled. The output motor of the mark sensor 74 may be used to feedforward control the drive motor for the intermediate transfer belt 61.

  In order to appropriately perform such belt running control, it is necessary to appropriately detect each optical detection mark 73 a on the belt scale 73 by the mark sensor 74. However, since dirt such as a small amount of toner is floating inside the printer, the dirt adheres to the optical detection mark 73a on the belt scale 73, or adheres to the light emitting surface and the light receiving surface of the mark sensor 74. There are things to do. In the state where there is no dirt, an appropriate output signal for continuously receiving the reflected light from all the optical detection marks 73a on the belt scale 73 is obtained as shown in FIG. However, as the adhesion of dirt gradually increases, the dirt accumulates and, for example, as shown in FIG. 15, an inappropriate output signal that cannot detect reflected light from some of the optical detection marks 73a is obtained. . As a result, the traveling speed of the intermediate transfer belt 61 cannot be detected properly, and proper belt traveling control cannot be realized.

  The dirt adhering to the belt scale 73 and the mark sensor 74 can be removed by a worker performing a cleaning operation during regular maintenance, and appropriate belt running control can be maintained. However, such maintenance is very costly, and it is difficult to properly predict when the dirt that needs to be cleaned accumulates. Is often difficult to maintain. Therefore, in the present embodiment, a cleaning member for cleaning dirt adhering to the belt scale 73 and the mark sensor 74 is provided in order to eliminate the cleaning work by the worker.

FIG. 16 is an explanatory diagram for explaining a cleaning member for cleaning dirt adhered to the belt scale 73 and the mark sensor 74.
In this embodiment, the sensor cleaning member 76 as a detection member cleaning member for cleaning dirt adhering to the light emitting surface and the light receiving surface of the mark sensor 74 and the optical detection mark 73 a on the belt scale 73 are attached. The mark cleaning member 77 is provided to clean the dirt, but only one of the cleaning members may be provided.

  The sensor cleaning member 76 is composed of an elastic member, a brush member, or the like, and is disposed on the outer peripheral surface of the intermediate transfer belt 61. When the sensor cleaning member 76 passes through the region facing the mark sensor 74 when the intermediate transfer belt is running, the sensor cleaning member 76 rubs the light emitting surface and the light receiving surface of the mark sensor 74, and the light emitting surface and the light receiving surface are rubbed. Remove the dirt attached to the.

  Further, the mark cleaning member 77 is composed of an elastic member, a brush member, or the like, and is attached to the mark sensor 74 so as to face the outer peripheral surface of the intermediate transfer belt 61 as shown in FIG. . When the intermediate transfer belt travels, the optical detection mark 73a on the belt scale 73 passes through a region facing the mark cleaning member 77, so that the optical detection mark 73a is rubbed by the mark cleaning member 77, and the optical detection mark 73a is rubbed. Dirt adhering to the mark 73a is removed.

FIG. 17 is a flowchart showing a control flow in the present control example 2.
In this control example 2, it is determined whether or not the cleaning conditions of the belt scale 73 and the mark sensor 74 are satisfied at a predetermined timing such as when the power is turned on or when the print job is finished. 73 and the mark sensor 74 are cleaned. Specifically, when the cleaning process is not performed (during a normal image forming operation), the steering control device 21 operates in the first control mode, and the position in the width direction of the intermediate transfer belt 61 is the first target. Belt displacement correction control is performed so that the position becomes the same. The steering control device 21 causes the intermediate transfer belt 61 to travel while the belt displacement correction control is being performed in the first control mode, and acquires an output signal output from the mark sensor 74. Thereafter, the number of pulses of the output signal in a certain period is counted, and the number of missing pulses is calculated by subtracting the counted number of pulses from the appropriate number of pulses that should be included in the certain period. Then, it is determined whether or not the number of missing pulses exceeds a predetermined number (S42). If the number of missing pulses does not exceed the predetermined number in this determination, the control is terminated as it is.

  On the other hand, if it is determined that the number of missing pulses exceeds the predetermined number (Yes in S42), the steering control device 21 performs a process of switching from the first control mode to the second control mode, assuming that the cleaning condition is satisfied. . Specifically, as indicated by an arrow H in FIG. 16, the position in the width direction of the intermediate transfer belt 61 from the first target position corresponding to the first control mode to the second target position corresponding to the second control mode. Force to move. The contents of the process for switching from the first control mode to the second control mode (S43 to S46) are the same as the contents of the process (S22 to S26) in the control example 1 shown in FIG.

  The steering control device 21 controls the steering motor 23 with a predetermined constant control amount so that the intermediate transfer belt 61 is displaced in the belt displacement direction minus side (S43), and finally the difference signal (Va−Vb). ) Until the intermediate transfer belt 61 is forcibly displaced until it becomes zero (S44 to S46), then, it operates in the second control mode and controls the steering motor 23 so that the belt displacement amount becomes zero. Thus, control for correcting the position in the width direction of the intermediate transfer belt 61 to the second target position is performed. At this time, the position of the intermediate transfer belt 61 in the width direction is as shown in FIG. As a result, the sensor cleaning member 76 on the intermediate transfer belt passes through the position opposed to the mark sensor 74 as the intermediate transfer belt 61 travels, and the mark sensor 74 is cleaned. Further, the optical detection mark 73a on the intermediate transfer belt passes through the position facing the mark cleaning member 77 as the intermediate transfer belt 61 travels, and the optical detection mark 73a is cleaned.

  Thereafter, when the cleaning end condition such as the elapse of a predetermined time is satisfied (Yes in S47), the steering control device 21 performs a process of switching from the second control mode to the first control mode. Specifically, as indicated by an arrow I in FIG. 18, the position in the width direction of the intermediate transfer belt 61 from the second target position corresponding to the second control mode to the first target position corresponding to the first control mode. Force to move. The contents of the process for switching from the second control mode to the first control mode (S48 to S51) are the same as the contents of the process (S27 to S31) in the control example 1 shown in FIG.

  The steering control device 21 controls the steering motor 23 with a predetermined control amount so that the intermediate transfer belt 61 is displaced in the belt displacement direction plus side (S48), and finally the difference signal (Va-Vb). ) Is forcibly displaced until it becomes zero (S49 to S51), and then operates in the first control mode to control the steering motor 23 so that the belt displacement becomes zero. Thus, control for correcting the position in the width direction of the intermediate transfer belt 61 to the first target position is performed. At this time, the position in the width direction of the intermediate transfer belt 61 is the position shown in FIG. As a result, the optical detection mark 73 a on the intermediate transfer belt passes through the position opposed to the mark sensor 74 as the intermediate transfer belt 61 travels. As a result, the mark sensor 74 with the dirt removed can detect the optical detection mark 73a with the dirt removed, and appropriate belt running control can be performed.

  According to this control example 2, appropriate belt displacement correction control is performed not only during the image forming operation (in the first control mode) but also during the cleaning process of the belt scale 73 and the mark sensor 74 (in the second control mode). It can be carried out. Therefore, it is possible to suppress a situation in which the intermediate transfer belt 61 meanders during the cleaning process (second control mode) to prevent an appropriate cleaning process or the intermediate transfer belt 61 is removed.

  In the present control example 2, a configuration as shown in FIG. 19 may be adopted as a determination as to whether or not the cleaning end condition has been satisfied after switching to the second control mode. In this configuration, the cleaning end detection mark 78 is disposed on the outer peripheral surface portion of the intermediate transfer belt on the cleaning member passage path through which the sensor cleaning member 76 passes while the intermediate transfer belt 61 is traveling. At this time, the steering control device 21 functions as a cleaning end timing determination unit, and after switching to the second control mode (Yes in S46), according to the timing at which the mark sensor 74 detects the cleaning end detection mark 78. The cleaning end timing is determined. For example, when the mark sensor 74 detects the cleaning end detection mark 78 at least twice, it is determined that the cleaning end condition is satisfied.

  In the second control example, the main body control unit that performs the belt traveling control is configured such that the traveling speed of the intermediate transfer belt is higher in the second control mode in which the cleaning process is performed than in the first control mode in which the image forming operation is performed. In addition, the traveling speed of the intermediate transfer belt may be switched. Thereby, the frequency | count that the cleaning members 76 and 77 contact the mark sensor 54 or the optical detection mark 73a per unit time can be increased, and the cleaning efficiency can be improved. As a result, the cleaning process time can be shortened.

  In the second control example, the main body control unit performs the cleaning process on the belt contact member such as the belt cleaning device 75 that contacts the intermediate transfer belt 61 in the first control mode in which the image forming operation is performed. Sometimes, it may be separated from the intermediate transfer belt 61. In this case, it is necessary to provide a contact / separation mechanism on the belt abutting member and to control it by the main body control unit. Can be suppressed. In addition, since the driving load of the intermediate transfer belt 61 during the cleaning process is reduced, it is possible to realize the cleaning process with low power.

  The belt cleaning device 75 of the present embodiment includes a cleaning blade as a contact blade that contacts the intermediate transfer belt 61 from the counter direction in the first control mode in which an image forming operation is performed. The cleaning blade is in contact with the outer peripheral surface of the intermediate transfer belt 61 with a relatively high contact pressure in order to scrape unnecessary toner or the like adhering to the outer peripheral surface of the intermediate transfer belt 61. Therefore, a high driving load is applied to the intermediate transfer belt 61. When it is desired to reduce the driving load of the intermediate transfer belt 61 during the cleaning process, the intermediate transfer belt 61 is caused to travel in the opposite direction to the first control mode in which the image forming operation is performed in the second control mode in which the cleaning process is performed. May be. In this case, while the intermediate transfer belt 61 is driven during the cleaning process, the cleaning blade comes into contact with the intermediate transfer belt 61 from the trailing direction, and the intermediate pressure is reduced by reducing the contact pressure as compared with the case of contacting from the counter direction. The driving load of the transfer belt 61 can be reduced.

  In the present embodiment, from the output signals Va and Vb of the edge sensor 24, whether the current control mode is the first control mode or the second control mode, in other words, the first light receiving unit 24e and the second light receiving unit of the edge sensor 24. It is impossible to grasp whether the first opening 24i or the second opening 24j of the arm member is approaching the portion 24f. Therefore, the detecting means for detecting whether the first light receiving portion 24e and the second light receiving portion 24f of the edge sensor 24 are the first opening 24i or the second opening 24j of the arm member. Is preferably provided.

  As this detection means, for example, a sensor configuration using a transmissive optical sensor 79 as shown in FIG. 20 can be adopted. In this case, in the first control mode, the position in the width direction of the intermediate transfer belt 61 is positioned at the first target position as shown in FIG. 20, thereby blocking the optical path of the optical sensor 79 by the intermediate transfer belt 61. On the other hand, in the second control mode, the position of the intermediate transfer belt 61 in the width direction is displaced in the direction of the arrow H in FIG. 20 and is positioned at the second target position, whereby the intermediate transfer belt 61 is retracted from the optical path of the optical sensor 79. To do. Therefore, based on the output signal of the optical sensor 79, it can be determined whether the current control mode is the first control mode or the second control mode. The member that blocks the optical path of the optical sensor 79 may not be the belt itself of the intermediate transfer belt 61, and may be, for example, the arm member or the contact pin 24k described above.

  Further, as another detection means, for example, an arm member as shown in FIG. 21 is used, and means for detecting whether the current control mode is the first control mode or the second control mode from the output signal of the edge sensor 24. It can also be adopted. Specifically, in the first control mode, the first opening 24i, which is a first light transmitting slit that reaches the first light receiving unit 24e and the second light receiving unit 24f of the edge sensor 24, is provided in the edge sensor 24 in the second control mode. It is formed so that the maximum amount of transmitted light is different from the second opening 24j ′ as the second light transmitting slit that reaches the first light receiving unit 24e and the second light receiving unit 24f. In the example of FIG. 21, the opening area of the second opening 24j 'is formed larger than the opening area of the first opening 24i.

  Thus, in the first control mode in which the first opening 24i is approaching the first light receiving unit 24e and the second light receiving unit 24f of the edge sensor 24, the output voltages Va and Vb are indicated by solid lines in FIG. Such a waveform is shown. On the other hand, in the second control mode in which the second opening 24j ′ reaches the first light receiving unit 24e and the second light receiving unit 24f of the edge sensor 24, the output voltages Va ′ and Vb ′ are broken lines in FIG. A waveform as shown in FIG. This difference in waveform can be recognized by the difference in the maximum values of the output voltages Va and Vb. At this time, in order to further improve the recognition accuracy, it is preferable to recognize the sum signal (Va + Vb). Therefore, as shown in FIG. 22B, when the sum signal (Va + Vb) is less than or equal to the threshold value Vth ′, it is determined that the control mode is the first control mode, and when the sum signal (Va + Vb) is greater than the threshold value Vth ′, It is determined that the control mode is set.

  As another detection means, for example, an edge sensor 24 ′ using an arm member as shown in FIG. 23 and two light receiving portions as shown in FIG. 24 is used. It is also possible to adopt means for detecting whether the current control mode is the first control mode or the second control mode from the output signal of '. Specifically, in the second control mode, the second opening 24j '' approaching the first light receiving part 24e and the second light receiving part 24f of the edge sensor 24 is enlarged, and the second opening 24j '' is in the second control mode. Sometimes, it approaches the third light receiving part 24g of the edge sensor 24 '. However, the third light receiving portion 24g of the edge sensor 24 'is disposed at a position where the first opening 24i does not reach even in the first control mode.

  Thus, in the first control mode in which the first opening 24i is approaching the first light receiving unit 24e and the second light receiving unit 24f of the edge sensor 24, the first output voltage Va and the second output voltage Vb are shown by solid lines in FIG. The second output voltage Vc at this time is zero. On the other hand, in the second control mode in which the second opening 24j ″ reaches the first light receiving unit 24e, the second light receiving unit 24f, and the third light receiving unit 24g of the edge sensor 24, the output voltages Va ″ and Vb ″. , Vc indicate waveforms as indicated by broken lines in FIG. Therefore, when the third output voltage Vc indicates near zero, it is determined that the control mode is the first control mode, and when the third output voltage Vc indicates a certain value or more, it is determined that the control mode is the second control mode. Can do.

  In the description so far, the case where the intermediate transfer belt 561 is the target has been described. However, as illustrated in FIG. 26, the fixing belt 41 of the fixing device 40 may be the target. That is, in the fixing device 40, the fixing belt 41 stretched between the two support rollers 42 and 43 forms a fixing nip with the pressure roller 44, and a recording in which an unfixed toner image is placed on the fixing nip. The paper P is allowed to enter and a fixing process using heat and pressure is performed. The fixing belt 41 is also subjected to belt displacement correction control in the same manner as in the control example 1 described above, and the position in the width direction of the fixing belt 41 is corrected. Further, by performing the same control mode switching process as in the control example 1 described above, the life of the fixing belt 41 can be extended as in the case of the intermediate transfer belt 61 in the control example 1.

  In addition, as shown in FIG. 27, the recording material on which the toner images on the photoreceptors 3Y, 3M, 3C, and 3K are carried and conveyed on the outer peripheral surface of a paper conveying belt 36 ′ as a recording material conveying member that is an endless belt. In the direct transfer type tandem image forming apparatus that directly transfers to P, the paper transport belt 36 ′ may be the target. That is, with respect to the paper transport belt 36 ', belt displacement correction control is performed in the same manner as in the control example 1 described above, and the position in the width direction of the paper transport belt 36' is corrected. At this time, by performing the same control mode switching process as in the control example 1 described above, it is possible to extend the life of the paper transport belt 36 ′ as in the case of the intermediate transfer belt 61 in the control example 1. When the control mode switching process similar to that in the control example 2 described above is performed, as in the case of the intermediate transfer belt 61 in the control example 2, the belt scale 73 and the mark sensor 74 are cleaned (second control). Also in the mode), proper belt displacement correction control can be performed, and during the cleaning process, the paper transport belt 36 'meanders to prevent proper cleaning processing, or the paper transport belt 36' may be removed. The situation can be suppressed.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
[Aspect A]
An endless belt such as an intermediate transfer belt 61 that travels while being stretched between a plurality of support members 63, 67, 68, 69, 71, and a belt displacement that detects a belt displacement amount in which the endless belt is displaced in the belt width direction. The belt width of the endless belt based on the amount of belt detection, the belt width direction position correcting means such as a tilting mechanism for correcting the belt width direction position of the endless belt, and the belt displacement detected by the belt displacement amount detecting means; And a control means such as a steering control device 21 for controlling the belt width direction position correcting means so that the direction position becomes a target position. The control means has a predetermined first width position of the endless belt. A first control mode for controlling to be a target position, and a second control for controlling the position in the belt width direction of the endless belt to be a second target position different from the first target position. The belt displacement amount detecting means includes a moving member such as an arm member that moves in conjunction with the displacement of the endless belt in the belt width direction, and the light emitting unit 24h to the light receiving units 24e and 24f. And an optical sensor member such as an edge sensor 24 that outputs a signal having an output level corresponding to a ratio of the moving member blocking the optical path toward the optical path, and the moving member is configured to move the endless belt in the first control mode. The first light-shielding portion (the first opening 24i reaches the optical path to the first light-receiving part 24e and the second light-receiving part 24f) in which the shielding amount that blocks the optical path of the optical sensor member changes in conjunction with the displacement in the belt width direction. A part of the light shielding portion 24d that blocks the optical path when the optical sensor member is in the middle), and a shielding amount that blocks the optical path of the optical sensor member in conjunction with the displacement of the endless belt in the belt width direction in the second control mode. The second light-shielding part that does not overlap with the changing first light-shielding part (the other light-shielding part 24d that shields the optical path when the second opening 24j reaches the optical path to the first light-receiving part 24e and the second light-receiving part 24f) Part).
According to this, it is possible to detect the amount of displacement in the belt width direction of the endless belt in each control mode by one optical sensor member (edge sensor 24) without reducing the detection resolution.

[Aspect B]
In the aspect A, the optical detection mark 73a provided on the outer peripheral surface or the inner peripheral surface of the endless belt, and the mark passage through which the optical detection mark 73a passes during traveling of the endless belt in the second control mode. And a mark cleaning member 77 for cleaning the optical detection mark by passing the optical detection mark through the position.
According to this, the detection resolution is also lowered when switching to the second control mode and performing the cleaning process for cleaning the optical detection mark 73a with the mark cleaning member 77 and maintaining proper detection of the optical detection mark. Therefore, the belt displacement correction control can be appropriately performed. Therefore, during the cleaning process (in the second control mode), it is possible to suppress a situation in which the endless belt meanders to prevent an appropriate cleaning process or the endless belt is removed.

[Aspect C]
In the aspect B, the control means switches to the second control mode when it is determined that the optical detection mark 73a satisfies a predetermined cleaning condition.
Accordingly, the cleaning process can be performed at an appropriate timing that requires cleaning of the optical detection mark 73a.

[Aspect D]
In any one of the aspects A to C, the optical detection mark 73a provided on the outer peripheral surface or the inner peripheral surface of the endless belt, and the optical detection mark during traveling of the endless belt in the second control mode. The mark 73a is disposed on the outer peripheral surface or the inner peripheral surface of the endless belt so as to pass through a position facing a mark detection means such as a mark sensor 74 that optically detects the mark 73a, and the mark detection is performed by passing through the position. And a cleaning member for detection means such as a sensor cleaning member 76 for cleaning the means.
According to this, even when switching to the second control mode and performing the cleaning process for cleaning the mark detection means with the detection means cleaning member and maintaining proper detection of the optical detection mark, the detection resolution is not lowered. Belt displacement correction control can be appropriately performed. Therefore, during the cleaning process (in the second control mode), it is possible to suppress a situation in which the endless belt meanders to prevent an appropriate cleaning process or the endless belt is removed.

[Aspect E]
In the above aspect D, the control means switches to the second control mode when it is determined that the mark detection means satisfies a predetermined cleaning condition.
Thereby, the cleaning process can be performed at an appropriate timing that requires cleaning of the mark detection means.

[Aspect F]
In the above aspect D or E, a cleaning end detection mark 78 disposed on the outer peripheral surface or inner peripheral surface of the endless belt on the cleaning member passage path through which the detection member cleaning member passes during traveling of the endless belt; Cleaning end timing determining means such as a steering control device 21 for determining the cleaning end timing according to the detection timing of the cleaning end detection mark by the mark detecting means, and the control means includes the cleaning end timing. When the cleaning end timing determined by the determining means arrives, the mode is switched to the first control mode.
According to this, it is possible to return to the first control mode at an appropriate cleaning end timing.

[Aspect G]
In any one of the above aspects B to F, the control means is configured such that the running speed of the endless belt is higher in the second control mode than in the first control mode. It is characterized by switching.
According to this, the cleaning efficiency in the cleaning process described above can be improved, and the time required for the cleaning process can be shortened.

[Aspect H]
In any one of the above aspects B to G, the control means separates the belt contact member that contacts the endless belt in the first control mode in the second control mode.
According to this, there is an advantage that the driving load of the endless belt at the time of the cleaning process described above can be reduced, and the power can be reduced.

[Aspect I]
In any one of the above aspects B to G, a contact blade that contacts the endless belt from the counter direction in the first control mode is provided, and the control means is configured to The endless belt is caused to travel in the opposite direction to that in the first control mode.
According to this, since the contact blade is in contact with the traveling direction of the endless belt from the trailing direction during the cleaning process described above, the driving load of the endless belt during the cleaning process can be reduced, and low power consumption is achieved. There is a merit that it can be realized.

[Aspect J]
In any one of the above aspects A to I, the optical sensor 79 detects whether the part of the moving member blocking the optical path of the optical sensor member is the first light shielding part or the second light shielding part. It has the light-shielding part detection means, such as.
According to this, it becomes possible to accurately grasp whether the control means is operating in the first control mode or the second control mode.

[Aspect K]
In the aspect J, the moving member includes a first light transmission slit such as a first opening 24i that approaches the optical path of the optical sensor member in the first control mode, and an optical path of the optical sensor member in the second control mode. And a second light transmission slit such as a second opening 24j ′ having a maximum transmitted light amount different from that of the first light slit, and the light-shielding portion detection means is configured to output the light sensor member with an output level Va, Based on the difference in the maximum value of Vb, it is detected whether the portion of the moving member blocking the optical path of the optical sensor member is the first light shielding portion or the second light shielding portion. .
According to this, it can be grasped with a simple configuration whether the control means is operating in the first control mode or the second control mode.

[Aspect L]
In the aspect J, the light-shielding part detection means determines whether the third light-receiving part 24g detects a light-shielding part detection mark or a light-shielding part detection slit such as the second opening 24J ″ formed in the moving member. Thus, it is characterized in that it is detected whether the part of the moving member blocking the optical path of the optical sensor member is the first light shielding part or the second light shielding part.
According to this, it can be grasped with a simple configuration whether the control means is operating in the first control mode or the second control mode.

[Aspect M]
An image forming apparatus that forms an image on a recording material such as recording paper P using an endless belt such as an intermediate transfer belt 61, a fixing belt 41, and a paper conveying belt 36 'that runs while being stretched on a plurality of support members The belt device according to any one of the above embodiments A to L is used as the belt device including the endless belt.
According to this, it is possible to detect the amount of displacement in the belt width direction of the endless belt in each control mode by one optical sensor member (edge sensor 24) without reducing the detection resolution.

2 Image forming unit 3 Photoconductor 21 Steering control device 23 Steering motor 24 Edge sensor 24c Support shaft 24d Light shielding portion 24e First light receiving portion 24f Second light receiving portion 24g Third light receiving portion 24h Light emitting portion 24i First opening 24j Second opening 24k Contact pin 40 Fixing device 41 Fixing belt 60 Transfer belt unit 61 Intermediate transfer belt 62 Primary transfer roller 63 Steering roller 67 Driving roller 73 Belt scale 73a Optical detection mark 74 Mark sensor 74a Light emitting part 74b Light receiving part 75 Belt cleaning device 76 For sensor Cleaning member 77 Mark cleaning member 78 Cleaning end detection mark 79 Optical sensor

JP 2009-300701 A

Claims (12)

An endless belt that travels in a stretched state on a plurality of support members;
Belt displacement amount detecting means for detecting a belt displacement amount in which the endless belt is displaced in the belt width direction;
Belt width direction position correcting means for correcting the belt width direction position of the endless belt;
Control means for controlling the belt width direction position correcting means based on the belt displacement amount detected by the belt displacement amount detecting means so that the belt width direction position of the endless belt becomes a target position;
The control means includes a first control mode for controlling the endless belt in a belt width direction position to be a predetermined first target position, and the endless belt in a belt width direction position different from the first target position. In the belt device having the second control mode for controlling to be the second target position,
The belt displacement amount detecting means includes a moving member that moves in conjunction with the displacement of the endless belt in the belt width direction, and an output level signal corresponding to a ratio that the moving member blocks an optical path from the light emitting unit to the light receiving unit. And an optical sensor member that outputs
The moving member includes a first light-shielding portion in which a shielding amount that blocks an optical path of the optical sensor member changes in conjunction with a displacement of the endless belt in the belt width direction during the first control mode, and a time during the second control mode. in conjunction with the displacement of the belt width direction of the endless belt to have a second light-shielding portion that does not overlap with the first light shielding portion shielding amount changes to block the optical path of the light sensor element,
An optical detection mark provided on the outer peripheral surface or inner peripheral surface of the endless belt;
In the second control mode, the optical detection mark is disposed at a position facing a mark passage path through which the optical detection mark passes during travel of the endless belt, and the optical detection mark passes through the position. belt device characterized in that it have a mark for cleaning member for cleaning the mark. The belt device according to claim 1 ,
The belt device according to claim 1, wherein the control means switches to the second control mode when it is determined that the optical detection mark satisfies a predetermined cleaning condition. The belt device according to claim 1 or 2 ,
Arranged on the outer peripheral surface or inner peripheral surface of the endless belt so as to pass through a position opposed to the mark detecting means for optically detecting the optical detection mark during traveling of the endless belt in the second control mode. by belt apparatus characterized by having the mark to clean the detection means detecting means for cleaning member by passing through the position. The belt device according to claim 3 .
The belt device according to claim 1, wherein the control means switches to the second control mode when it is determined that the mark detection means satisfies a predetermined cleaning condition. The belt device according to claim 3 or 4 ,
A cleaning end detection mark disposed on an outer peripheral surface or an inner peripheral surface of the endless belt on a cleaning member passage path through which the cleaning member for the detection unit passes during travel of the endless belt;
Cleaning end timing determining means for determining the cleaning end timing according to the detection timing of the cleaning end detection mark by the mark detection means,
The control device switches to the first control mode when the cleaning end timing determined by the cleaning end timing determination unit arrives. The belt device according to any one of claims 1 to 5 ,
The belt device characterized in that the control means switches the travel speed of the endless belt in the second control mode so that the travel speed of the endless belt is faster than in the first control mode. The belt device according to any one of claims 1 to 6 ,
The belt device characterized in that the control means separates a belt contact member that contacts the endless belt in the first control mode in the second control mode. The belt device according to any one of claims 1 to 6 ,
A contact blade that contacts the endless belt from the counter direction in the first control mode;
In the second control mode, the control means causes the endless belt to travel in a direction opposite to that in the first control mode. The belt device according to any one of claims 1 to 8 ,
A belt device comprising: a light shielding portion detecting means for detecting whether a portion of the moving member blocking an optical path of the optical sensor member is the first light shielding portion or the second light shielding portion. The belt device according to claim 9 , wherein
The moving member includes a first light transmission slit that reaches the optical path of the optical sensor member during the first control mode, and an optical path of the optical sensor member that corresponds to the first optical slit during the second control mode. Has a second light transmission slit with different maximum transmitted light amount,
The light-shielding part detection means determines whether the part of the moving member that is blocking the optical path of the optical sensor member is the first light-shielding part based on the difference in the maximum value of the output level of the optical sensor member. A belt device characterized by detecting whether it is a light shielding portion. The belt device according to claim 9 , wherein
The light-shielding part detection means detects whether the light-shielding part detection mark or the light-shielding part detection slit formed on the moving member detects the part of the moving member that blocks the optical path of the optical sensor member. A belt device that detects whether the light shielding portion is the first light shielding portion or the second light shielding portion. In an image forming apparatus that forms an image on a recording material using an endless belt that travels while being stretched on a plurality of support members,
As a belt device including the endless belt, the image forming apparatus, which comprises using a belt device according to any one of claims 1 to 11.

Images