JP2011128180A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can stably run a belt member in a state having small amount of deviation by promptly offsetting the amount of deviation when the deviation occurs in the belt member. <P>SOLUTION: The image forming apparatus is composed to be able to brake/release brake by a brake mechanism 55 by arranging a slip roller 25 on an upstream side of a steering roller 22. Responsiveness for a tilting angle is improved by carrying out skew control using the steering roller 22 with an intermediate transfer belt 20 in a sliding state by locking rotation of the slip roller 25 in a stage when the amount of deviation is great in a process for correcting the deviation in the intermediate transfer belt 20. Then, in the stage when the amount of deviation is converged to a prescribed value, braking of the intermediate transfer belt 20 by the slip roller 25 is released and the slip roller 25 is made to follow rotation of the intermediate transfer belt 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that tilts a steering roller to correct a running deviation of a belt member, and more particularly, to a control that quickly converges the deviation amount of a belt member.

  A tandem full-color image forming apparatus in which a plurality of image forming units having different development colors are arranged along an intermediate transfer belt or a recording material conveying belt is widely used. A monochrome high-speed printer that transfers a toner image from a photosensitive member to a recording material carried on a transfer belt is also widely used. An image forming apparatus equipped with a fixing device for forming a heating nip of a recording material carrying a toner image by a combination of a fixing roller / pressure belt, a fixing belt / pressure roller, or a fixing belt / pressure belt is also put into practical use. Has been.

  These belt members are supported across a plurality of support rotating bodies, and in order to avoid adverse effects on the formed image, the belt members rotate stably at a fixed position in the longitudinal direction of the support rotating body. It is hoped that this will continue. However, the belt member of the image forming apparatus may move and be biased in the longitudinal direction of the support rotator due to a placement error of the support rotator, a change in a contact state during operation, or the like. For this reason, an image forming apparatus including a steering mechanism that actively cancels the deviation of the travel of the belt member by tilting the steering roller according to the detected deviation amount has been put into practical use (Patent Documents 1 and 2).

  Patent Document 1 discloses an intermediate transfer belt provided with a steering mechanism. Here, a support rotating body (25: FIG. 1) is disposed between the steering roller and the image forming unit so that the inclination of the belt member due to the tilting of the steering roller does not affect the image forming unit. Then, by removing the output fluctuation of the belt edge sensor and operating the steering mechanism, even the belt member whose belt edge is disturbed can be converged stably.

  Patent Document 2 shows an intermediate transfer belt provided with a steering mechanism. Here, by replacing the support rotating body (25: FIG. 1) of Patent Document 1 with “a support member that does not restrain the rotation direction of the belt member”, the response of movement of the belt member to the tilting of the steering roller is disclosed in Patent Document 1. Higher than.

Japanese Patent Laid-Open No. 11-295948 JP 2004-359438 A

  As described above, the belt member of the image forming apparatus moves in the longitudinal direction of the support rotating body due to the start / stop / speed switching and the change of the contact state of the other members during operation, and the running bias occurs. In such a case, a tilt amount corresponding to the detected deviation amount of the belt member is set in the steering roller, and the belt member is moved in a direction to cancel the deviation.

  However, at this time, in the steering mechanism disclosed in Patent Document 1, the support rotating body (25: FIG. 1) disposed between the steering roller and the image forming unit reduces the responsiveness of the movement of the belt member. It has been found.

  On the other hand, in the steering mechanism disclosed in Patent Document 2, since the support member disposed between the steering roller and the image forming unit does not restrain the moving direction of the belt member, the responsiveness of the movement of the belt member is enhanced. However, it has been found that as the response increases, the belt member reacts excessively to the steering operation and the control tends to diverge, and the running stability in the steady state is also lacking.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of quickly canceling out the amount of deviation when the belt member is biased and allowing the belt member to travel stably in a state where the amount of bias is small. Yes.

  The image forming apparatus according to the present invention is based on a belt member, a detection unit that detects a deviation of the rotating belt member, a steering roller that can be tilted to correct the deviation of the belt member, and an output of the detection unit. Steering roller control means for controlling tilting of the steering roller. In the process of supporting the belt member in parallel with the steering roller and changing the circumferential speed difference with the belt member, and the steering roller control means converge the deviation of the belt member. Slip roller control means for controlling the slip roller so as to reduce the peripheral speed difference.

  In the image forming apparatus of the present invention, when the amount of deviation is large in the process of correcting the deviation of the belt member, the restraint of the rotation direction of the belt member by the slip roller is reduced, and the response of the movement of the belt member to the tilting of the steering roller Increase sex. Therefore, even if the amount of tilting of the steering roller is small, the large amount of deviation can be quickly reduced.

  Then, when the amount of deviation becomes small, the restraint in the rotational direction of the belt member by the slip roller is increased, and the responsiveness of the movement of the belt member to the tilting of the steering roller is lowered. As shown in FIG. 10, the fluctuation of the bias becomes longer due to the restraint of the rotation direction of the belt member by the slip roller, and the convergence state of the bias amount is stably maintained.

  Therefore, when a deviation occurs in the belt member, the deviation amount can be quickly canceled, and the belt member can be stably driven in a state where the deviation amount is small.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of an image formation part and a secondary transfer part. It is an explanatory view of a steering control mechanism of the intermediate transfer belt. It is explanatory drawing of operation | movement of a steering roller. It is explanatory drawing of operation | movement of an edge sensor. It is explanatory drawing of control of a steering motor. It is a comparison figure of the shift speed when the slip roller is stopped and rotated. It is a comparison figure of the amount of meandering when a slip roller is stopped and rotated. It is explanatory drawing of the braking mechanism used in Example 1. FIG. 3 is a flowchart of control according to the first embodiment. It is explanatory drawing of the steering control of Example 1. FIG. It is explanatory drawing of the change of deviation | shift amount. It is explanatory drawing of the braking mechanism used in Example 2. FIG. FIG. 9 is an explanatory diagram of a configuration of an image forming apparatus according to a third embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be implemented in another embodiment in which a part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the support roller having a variable rotation speed is disposed in the vicinity of the steering roller.

  Therefore, any image forming apparatus that forms an image using a belt member can be implemented as a steering mechanism for these intermediate transfer belts, recording material transport belts, transfer belts, and fixing belts without being distinguished. Further, an image forming apparatus using a belt member that is controlled by steering can be implemented without distinction between a tandem type / 1 drum type, an intermediate transfer type / a recording material conveyance type. In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter of the image forming apparatus shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. FIG. 2 is an explanatory diagram of the configuration of the image forming unit and the secondary transfer unit.

  As shown in FIG. 1A, an image forming apparatus 100 includes a tandem intermediate transfer system in which yellow, magenta, cyan, and black image forming units 10Y, 10M, 10C, and 10Bk are arranged along an intermediate transfer belt 20. This is a full color printer.

  In the image forming unit 10Y, a yellow toner image is formed on the photosensitive drum 11Y and is primarily transferred to the intermediate transfer belt 20. In the image forming unit 10M, a magenta toner image is formed on the photosensitive drum 11M, and is primarily transferred onto the yellow toner image on the intermediate transfer belt 20. In the image forming units 10C and 10Bk, a cyan toner image and a black toner image are formed on the photosensitive drums 11C and 11Bk, respectively, and are sequentially transferred onto the intermediate transfer belt 20 in order to be primarily transferred.

  The four color toner images carried on the intermediate transfer belt 20 are conveyed to the secondary transfer portion T2 and are collectively secondary transferred to the recording material P. The recording material P on which the four-color full-color toner image has been secondarily transferred is separated from the intermediate transfer belt 20 by the curvature, is transferred to the conveying belt 43, is conveyed to the conveying belt 43, and is sent to the fixing device 44. The fixing device 44 heats and presses the recording material P to fix the toner image on the surface. Thereafter, the recording material P is discharged to the discharge tray 45.

  The image forming units 10Y, 10M, 10C, and 10Bk are configured substantially the same except that the color of toner used in the developing devices 14Y, 14M, 14C, and 14K is different from yellow, magenta, cyan, and black. In the following, the yellow image forming unit 10Y will be described, and the other image forming units 10M, 10C, and 10Bk will be described by replacing Y at the end of the reference numerals attached to the constituent members being described with M, C, and Bk. Shall be.

  As shown in FIG. 2A, the image forming unit 10Y includes a corona charger 13Y, an exposure device 12Y, a developing device 14Y, a primary transfer roller 17Y, and a drum cleaning device 15Y around the photosensitive drum 11Y. Yes.

  The photosensitive drum 11Y has a negatively charged photosensitive layer formed on the surface of an aluminum cylinder and rotates in the direction of arrow R1 at a predetermined process speed. The corona charger 13Y irradiates charged particles associated with corona discharge to charge the surface of the photosensitive drum 11Y to the negative dark portion potential VD. The exposure device 12Y scans, with a rotating mirror, a laser beam obtained by ON-OFF modulation of scanning line image data obtained by developing a yellow separation color image, and writes an electrostatic image of the image on the surface of the photosensitive drum 11Y.

  The developing device 14Y charges a developer containing toner and a carrier, carries the developer on a rotating developing sleeve 14s, conveys it to a portion facing the photosensitive drum 11Y, and slides the electrostatic image of the photosensitive drum 11Y in a magnetic brush state. Rub. By applying an oscillating voltage in which an AC voltage is superimposed on a DC voltage to the developing sleeve, the negatively charged toner is transferred to the surface portion of the photosensitive drum 11Y having a relatively positive polarity, and the electrostatic image is reversed and developed. Is done.

  The primary transfer roller 17 </ b> Y presses the inner surface of the intermediate transfer belt 20 to form a primary transfer portion TY between the photosensitive drum 11 </ b> Y and the intermediate transfer belt 20. By applying a positive voltage to the primary transfer roller 17Y, the toner image carried on the photosensitive drum 11Y is primarily transferred to the intermediate transfer belt 20.

  The drum cleaning device 15Y slides a cleaning blade on the photosensitive drum 11Y to collect the transfer residual toner remaining on the photosensitive drum 11Y by escaping from the primary transfer to the intermediate transfer belt 20.

  As shown in FIG. 2B, the secondary transfer roller 30 contacts the intermediate transfer belt 20 whose inner surface is supported by the opposing roller 23 to form a secondary transfer portion T2. As shown in FIG. 1, the recording material P drawn from the recording material cassette 40 by the pickup roller 41 is separated one by one by the separation roller 46 and sent to the registration roller 42. The registration roller 42 receives and waits for the recording material P in a stopped state, and sends the recording material P to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 20.

  A full color toner image is recorded from the intermediate transfer belt 20 by applying a positive DC voltage to the secondary transfer roller 30 while the recording material P is nipped and conveyed by the secondary transfer portion T2 while being superimposed on the toner image. Secondary transfer to the material P is performed. The transfer residual toner that is not transferred and remains on the surface of the intermediate transfer belt 20 is collected by the belt cleaning device 26.

<Intermediate transfer belt>
The intermediate transfer belt 20 is formed in an endless shape, and is supported by being driven over a driving roller 21, a counter roller 23, a steering roller 22, a tension roller 24, and a slip roller (stretching roller) 25 in the direction of arrow R2. Rotate. The intermediate transfer belt 20 is made of polyimide resin, and is formed endlessly by welding both ends of a thin film film sheet having a thickness of 60 to 90 μm.

  As shown in FIG. 2B, the secondary transfer roller 30 is configured to be able to contact and separate from the intermediate transfer belt 20, and is retracted away from the operating position (solid line position) in contact with the intermediate transfer belt 20. The position (broken line position) can be taken. While the rotation of the intermediate transfer belt 20 is stopped, the secondary transfer roller 30 is moved to the retracted position to avoid permanent deformation of the elastic layer 30b of the secondary transfer roller 30. After the rotation of the intermediate transfer belt 20 is started, the secondary transfer roller 30 comes into contact with the intermediate transfer belt 20 to form the secondary transfer portion T2.

  As shown in FIG. 2A, the primary transfer roller 17 </ b> Y (17 </ b> M, 17 </ b> C) is configured to be able to contact and separate from the intermediate transfer belt 20. The primary transfer roller 17Y is moved upward to move the intermediate transfer belt 20 into contact with the photosensitive drum 11Y (solid line position), and moved down to move the intermediate transfer belt 20 away from the photosensitive drum 11Y (broken line position). Can take.

  As shown in FIG. 1B, the image forming apparatus 100 can execute a black monochrome mode in which only the image forming unit 10Bk is operated to output a monochrome image in addition to the above-described full color mode. In the black monochromatic mode, the contact / separation mechanism 18 retracts the primary transfer rollers 17Y, 17M, and 17C from the intermediate transfer belt 20 during a print job to avoid unnecessary power consumption and wear of the photosensitive drums 11Y, 11M, and 11C. ing.

  Even in the print standby state in which the main power of the image forming apparatus 100 is turned on and waiting for the start of the print job, the contact / separation mechanism 18 moves the primary transfer rollers 17Y, 17M, and 17C to the retracted position so as to correspond to the black monochrome mode. Has been moved to. The rotation of the intermediate transfer belt 20 is stopped, and the primary transfer rollers 17Y, 17M, and 17C are moved to the retracted position so as to be separated from the intermediate transfer belt 20.

  When a full color mode print job is started, the primary transfer rollers 17Y, 17M, and 17C are lifted from the retracted position and moved to the operating position. Since the full color mode requires more time for image processing than the black single color mode, the waiting time for starting the print job is not noticeable by raising the primary transfer rollers 17Y, 17M, and 17C using the processing time. In the full color mode, first, after the rotation of the intermediate transfer belt 20 is started, the secondary transfer roller 30 that has been moved to the retracted position is moved to the contact position. Subsequently, the primary transfer rollers 17Y, 17M, and 17C that have moved to the retracted position move to the contact position, and all the primary transfer rollers including the black primary transfer roller 17Bk are exposed to the photosensitive drums 11Y, 11M, 11C, and 11Bk. The intermediate transfer belt 20 is sandwiched between the two.

  On the other hand, the primary transfer roller 17Bk of the black image forming unit 10Bk does not move up and down, and is always in contact with the intermediate transfer belt 20, so that a black single color mode print job can be started immediately. Only the image forming unit 10Bk is in a state where the toner image can be primarily transferred to the intermediate transfer belt 20, and in the black monochrome mode, the print job is executed with the primary transfer rollers 17Y, 17M, and 17C in the retracted position. In the black monochrome mode, first, after the rotation of the intermediate transfer belt 20 is started, the secondary transfer roller 30 that has been lowered to the retracted position is raised and returned to the operating position.

<Steering mechanism>
In an image forming apparatus that forms a full-color image, it is necessary to superimpose and transfer yellow, magenta, cyan, and black toner images formed on an image carrier in accordance with image information on a recording material. The As a method of superimposing the toner images of each color on the recording material, the recording material is electrostatically adsorbed on an endless recording material conveyance belt, and the image is carried on the recording material conveyed as the recording material conveyance belt rotates. Some toner images are sequentially transferred from the body. In addition, there is also a type in which each color toner image is not directly transferred from the image carrier to the recording material but is primarily transferred to an endless intermediate transfer belt and then secondarily transferred to the recording material.

  In the latter method using the intermediate transfer belt, the toner images of the respective colors are superimposed on the intermediate transfer belt, so that the toner images of a plurality of colors can be superimposed without being affected by a change in the resistance value of the recording material accompanying a change in humidity. . Also, for the recording material, compared to the former case, it becomes easier to control the transfer conditions of the toner image when forming a color image, and the conveyance of the recording material is also simplified. The occurrence of jam can be prevented as much as possible.

  When a recording material conveyance belt or an intermediate transfer belt is used, in order to form a high-quality color recording image without color misregistration, the recording material conveyance belt or the intermediate transfer belt rotates at a certain position and is not biased in the width direction. This is very important. However, there are molding errors in the diameters of the belt member and the conveyance roller, and there are also assembly errors in a plurality of conveyance rollers and the like over which the belt member is stretched. For this reason, generally, when an endless belt member is wound around a plurality of conveying rollers including a driving roller and a driven roller and rotated, a biasing force acts on the belt member in one longitudinal direction of the conveying roller. Then, the belt member seeks a stable rotational position and moves in the longitudinal direction of the conveying roller, that is, the width direction of the belt member, thereby causing a bias.

  For this reason, a steering system in which one of the conveying rollers around the belt member is configured as a steering roller that can be freely tilted and the deviation of the belt member is suppressed by controlling the tilting amount of the steering roller has been put into practical use. Yes.

  The simplest configuration of the steering system is to set the amount of tilting of the steering roller at a fixed value so as to cancel the bias due to the fixed factors described above when the image forming apparatus is assembled or installed. If the steering roller is given a fixed amount of tilting, and a shifting force in the opposite direction to the shifting force due to a fixed factor is applied to achieve a balanced state, the belt member will be biased thereafter unless a new shifting force is generated. Rotates stably without any problems.

  However, since the transfer member, the cleaning member, the recording material, and the like change the contact state with the belt member during the image forming process, a new offset force is generated on the recording material conveyance belt and the intermediate transfer belt. Will be biased. For this reason, the movement of the belt member in the width direction cannot be suppressed with a fixed tilt amount.

  Therefore, an active steering system has been put into practical use in which the deviation of the belt member is constantly detected and the amount of tilting of the steering roller is converted momentarily based on the detection result. Specifically, a belt edge sensor is provided to detect the amount of movement of the belt member in the width direction, and the tilt amount of the steering roller is set based on the detection result. This suppresses and corrects the movement of the rotating belt member in the width direction, and continuously rotates the belt member at a predetermined reference position in the width direction (Patent Document 1).

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a belt conveyance device that includes one of a plurality of conveyance rollers and a steering roller that can arbitrarily change the arrangement angle with respect to the other conveyance rollers. And the conveyance roller adjacent to the upstream or downstream side of a steering roller regarding the rotation direction of a belt member is comprised as an omnidirectional conveyance member. By configuring the conveying roller as an omnidirectional conveying member, the meandering amount of the belt member can be made to react sensitively to the amount of tilt applied to the steering roller. The omnidirectional conveying member does not guide the belt member in a specific conveying direction. Even when the omnidirectional conveying member is close to the steering roller, the shifting force exerted on the belt member by the steering roller is not reduced. Therefore, the meandering amount of the belt member can be made to react sensitively to the tilting amount given to the steering roller, and as a result, the control performance regarding the displacement of the belt member in the width direction is improved. Thereby, the control performance regarding the displacement to the width direction of a belt member can be improved.

  FIG. 3 is an explanatory diagram of the steering control mechanism of the intermediate transfer belt. FIG. 4 is an explanatory view of the operation of the steering roller. FIG. 5 is an explanatory diagram of the operation of the edge sensor. FIG. 6 is an explanatory diagram of control of the steering motor. FIG. 7 is a comparison diagram of the shifting speed when the slip roller is stopped and rotated. FIG. 8 is a comparison view of the meandering amount when the slip roller is stopped and rotated.

  As shown in FIG. 3A, since the image forming apparatus 100 superimposes each color toner image on the intermediate transfer belt 20 with high accuracy, the deviation of the running state of the intermediate transfer belt 20 is corrected by a so-called active steering system. Suppressed. The edge of the rotating intermediate transfer belt 20 is detected by the edge sensor 1, the rotation angle of the steering motor 54 is set based on the detection result, and the steering roller 22 is tilted. By tilting the steering roller 22, as shown in FIGS. 4B and 4C, a correction external force acting in the width direction is applied to the intermediate transfer belt 20.

  One end of the rotating shaft of the steering roller 22 is rotatably supported by a bearing portion fixedly provided on the apparatus frame 50, and the other end is rotatably supported on one end of the swing arm 51. The swing arm 51 is swingably provided around the rotation shaft 52, and the opposite swing end supporting the steering roller 22 is in pressure contact with the eccentric cam 53. The eccentric cam 53 is connected to the steering motor 54. When the steering motor 54 is rotated, the eccentric cam 53 rotates, and thereby, one end side of the swing arm 51 that supports the steering roller 22 swings up and down. Move. As the steering motor 54, a stepping motor capable of controlling the rotation angle to be positioned and stopped with high accuracy according to the number of input pulses is used.

  As shown in FIG. 3B, the control unit 2 constituted by a microcomputer system sets the travel position so that the travel position of the intermediate transfer belt 20 is positioned at a predetermined reference position in the longitudinal direction of the steering roller 22. Correct it.

  The control unit 2, which is an example of a steering roller control unit, detects a position change in the width direction of the intermediate transfer belt 20 by the edge sensor 1, and rotates the steering motor 54 in a direction to cancel the position change to thereby turn the steering roller 22. Change the amount of tilt. As a result, the movement of the intermediate transfer belt 20 in the width direction can be suppressed, and the position in the width direction on the steering roller 22 can be corrected. As a result, the intermediate transfer belt 20 can be stably stabilized in a fixed path without meandering. Let it run.

  The amount of tilt given to the steering roller 22 is calculated by the control unit 2 and given to the steering motor 54. The control unit 2 captures the detection result of the edge sensor 1 and compares the detection result, that is, the actual position in the width direction of the intermediate transfer belt 20 with a predetermined reference position, and calculates the amount of tilt to be given to the steering roller 22. .

  As shown in FIG. 4A, it is assumed that the eccentric cam 53 stops at a predetermined angle, and the steering roller 22 is held substantially horizontal (tilt is almost zero) corresponding to the stop angle. . In this state, if the running intermediate transfer belt 20 is biased in the y1 direction, the steering roller 22 is tilted as shown in FIG. 4B, and if it is biased in the y2 direction, as shown in FIG. The steering roller 22 is tilted. A tilting force in the axial direction is applied to the intermediate transfer belt 20 by tilting the steering roller 22. Due to this shifting force, the movement of the intermediate transfer belt 20 in the longitudinal direction of the steering roller 22 is suppressed, or the amount of deviation is canceled and the intermediate transfer belt 20 is pushed back to a predetermined position.

  As shown in FIG. 4B, when the steering motor 54 is operated to rotate the eccentric cam 53 clockwise by a predetermined angle corresponding to the amount of deviation, the swing arm 51 is moved according to the amount of eccentricity of the eccentric cam 53. Swings in the θ1 direction. Thereby, since one end of the steering roller 22 is lifted by the swing arm 51, the steering roller 22 is inclined according to the lift amount. At this time, the intermediate transfer belt 20 wound around the steering roller 22 moves to the side lifted by the swing arm 51.

  As shown in FIG. 4C, when the steering motor 54 is operated and the eccentric cam 53 is rotated counterclockwise by a predetermined angle corresponding to the amount of deviation, the swing arm 51 is changed according to the amount of eccentricity of the eccentric cam 53. Swings in the θ2 direction. As a result, one end of the steering roller 22 is pushed down by the swing arm 51, so that the steering roller 22 is inclined according to the amount of the push-down. At this time, the intermediate transfer belt 20 wound around the steering roller 22 moves to the opposite side pushed down by the swing arm 51.

  As shown in FIG. 5A, the light receiving portion 91 is provided with a slit 91a. A predetermined voltage is output by detecting the amount of light that has passed through the slit 91a out of the light emitted from the light emitting unit (90: FIG. 3). When the amount of change in the width direction y changes with the edge portion 20a of the intermediate transfer belt 20 positioned at the slit 91a, the output voltage of the belt edge sensor 1 changes as shown in FIG. 5B. Considering the case where the edge portion 20a has moved from the predetermined position X0 and moved to X1, the amount by which the edge portion 20a blocks the slit 91a decreases, and as a result, the amount of light detected by the light receiving portion 91 increases.

  At this time, the belt edge sensor 1 outputs a voltage V1. Based on the information of the output voltage V1, the number of driving pulses of the steering motor 54 is determined by the control unit 2 shown in FIG.

  As shown in FIG. 6, the number of drive pulses output to the steering motor 54 is set according to the output voltage of the belt edge sensor 1. When the voltage V <b> 1 is output from the belt edge sensor 1, the control unit 2 determines P <b> 1 as the number of drive pulses for the steering motor 54. The drive pulse signal P1 is sent to the steering motor 54, and the steering motor 54 rotates in the direction of the arrow M1 by the number of pulses P1.

  By the way, when the steering roller 22 is tilted, the conveyance direction of the intermediate transfer belt 20 by the steering roller 22 is inclined with respect to the original rotation direction, and as a result, a shifting force acts on the intermediate transfer belt 20. As the tilting amount (steering amount) applied to the steering roller 22 is increased, the lateral force acting on the intermediate transfer belt 20 is increased. As the steering amount is increased, the moving amount of the intermediate transfer belt 20 per one rotation of the steering roller 22 is increased, and as a result, the moving speed in the width direction of the intermediate transfer belt 20 is also increased.

  FIG. 7 shows the relationship between the steering angle of the steering roller 22 and the axial shift speed of the steering roller 22 of the intermediate transfer belt 20. Regarding the steering angle, an angle θ1 shown in FIG. 4B is a positive direction, and an angle θ2 shown in FIG. 4C is a negative direction. FIG. 8 is a diagram in which the locus of the belt edge detected by the belt edge sensor 1 is plotted.

  As shown in FIG. 7, the moving speed (shifting speed) in the width direction of the intermediate transfer belt 20 indicated by the solid line increases as the steering amount increases. As shown in FIG. 8, the meandering amount of the intermediate transfer belt 20 represented by the curve of the solid line 1 is gradually biased to zero by controlling the steering amount so as to decrease the steering amount as the bias amount decreases. It converges to the state of.

<Slip roller>
As shown in FIG. 1, image forming portions 10Y, 10M, 10C, and 10Bk are arranged on the transfer plane of the intermediate transfer belt 20 supported by the driving roller 21 and the slip roller, and the toner images of the respective colors are transferred to the intermediate transfer belt 20. Primary transfer. The slip roller 25 is arranged adjacent to the upstream side of the steering roller 22 with respect to the rotation direction of the intermediate transfer belt 20, and is driven to rotate by the intermediate transfer belt 20 to constrain the rotation direction of the intermediate transfer belt 20 to a specific direction. Guide in the transport direction.

  Here, a similar experiment was performed by rotating the intermediate transfer belt 20 with the slip roller 25 forcedly stopped. By stopping the rotation of the slip roller 25, the slip roller 25 becomes non-directional with respect to the intermediate transfer belt 20 in the same manner as that disclosed in Patent Document 2. The result is shown by a broken line 2 in FIG. 8 in comparison with the case where the rotation is driven (solid line 1).

  As shown in FIG. 8, the movement speed in the width direction of the intermediate transfer belt 20 when the rotation of the slip roller 25 indicated by the broken line 2 is stopped is more responsive to the steering amount than during the driven rotation indicated by the solid line. is doing. The meandering amount of the intermediate transfer belt 20 when the rotation of the slip roller 25 indicated by the broken line 2 is stopped is the time from the start of the steering control until the convergence amount returns to 0 compared to the time of the driven rotation indicated by the solid line 1. Has been shortened.

  However, when the rotation of the slip roller 25 is stopped, the sensitivity of movement in the width direction of the intermediate transfer belt 20 with respect to the tilt amount of the steering roller 22 is good. 20 responds. For this reason, the intermediate transfer belt 20 cannot converge to the zero bias state, and vibration in the direction along the steering roller 22 is generated. As a result, the amount of meandering during the stable running of the intermediate transfer belt 20 increases, and the running stability is increased. Sex has declined. As a result, the overlay error of each color toner image increases. That is, when the intermediate transfer belt 20 is desired to travel stably in the direction of the steering roller 22, the good control sensitivity with respect to the control amount of the steering roller 22 has an adverse effect.

  Therefore, in the following embodiment, the rotation state of the rotatable slip roller is controlled by supporting the belt member in parallel with the steering roller on the upstream side or the downstream side in the rotation direction of the steering roller. The slip roller control means controls the slip roller so as to reduce a difference in peripheral speed between the slip roller and the belt member in the process of correcting the deviation of the belt member. The correction of the bias of the belt member is started in a state where the peripheral speed of the slip roller is lower than the rotational speed of the belt member, and then, the peripheral speed of the slip roller is matched with the rotational speed of the belt member. Finish correcting the bias. A braking mechanism is provided to brake the rotation of the slip roller to switch between the slip state and the driven rotation state. The correction of the bias of the belt member is started in a state where the slip roller is stopped by the braking mechanism, and then the correction of the bias of the belt member is finished in a state where the braking is gradually released and the slip roller is driven by the belt member. .

<Example 1>
FIG. 9 is an explanatory diagram of a braking mechanism used in the first embodiment. FIG. 10 is a flowchart of control according to the first embodiment. FIG. 11 is an explanatory diagram of the steering control according to the first embodiment. FIG. 12 is an explanatory diagram of changes in the bias amount.

  As shown in FIG. 3B, the control unit 2 controls the braking mechanism 55, which is an example of the slip roller control means, so that the slip roller (slip roller 25) has the first peripheral speed and the second peripheral speed. At least two peripheral speeds can be set. The first circumferential speed is set to be equal to the traveling speed of the belt member, and no slip occurs between the slip roller and the belt member. Therefore, a force is applied to suppress the position variation in the width direction of the belt member by the steering roller. be able to. On the other hand, the second circumferential speed is different from the traveling speed of the belt member, and by generating slip between the slip roller (slip roller 25) and the belt member, the width of the belt member by the steering roller is increased. Does not act to suppress position fluctuations.

  When the controller 2 determines that the position of the belt member in the width direction is within a predetermined range and is in a stable running state, the control unit 2 sets the slip roller to the first peripheral speed and sets the driven rotation state. On the other hand, when the belt member starts running and the position in the width direction fluctuates outside the predetermined allowable deviation range due to external factors, the width direction of the belt member by the steering roller with the slip roller set to the second peripheral speed is set. The position control is performed.

  As shown in FIG. 9, the braking mechanism 55 according to the first embodiment controls the rotation and stop of the slip roller 25 by engaging the engagement cam 61 with the engagement portion 63 of the slip roller 25. The steering roller 22 has a diameter of 30 mm and a length of 400 mm. The slip roller 25 is formed of a cylindrical member made of aluminum having a diameter of 20 mm and a length of 400 mm, and the surface is mirror-finished and then blasted with glass beads.

  The engaging portion 63 is fixed to the shaft end portion of the slip roller 25 and rotates integrally. The braking mechanism 55 stops the rotation of the slip roller 25 by operating the braking motor 62 to rotationally drive the engagement cam 61 to change the protruding amount up and down.

  When the engagement cam 61 is positioned below, the slip roller 25 rotates following the intermediate transfer belt 20 because it does not interfere with the engagement portion 63. When the engagement cam 61 is positioned above, the engagement portion 63 interferes with the engagement cam 61 and the slip roller 25 is braked.

  As shown in FIG. 12 with reference to FIG. 3, the controller 2 starts meandering control by the steering roller 22 at the same time as the running of the intermediate transfer belt 20 is started (S11). The correction of the bias of the belt member (20) is started in a state where the peripheral speed of the slip roller (25) is lower than the rotational speed of the belt member (20). Then, the correction of the bias of the belt member (20) is finished in a state where the peripheral speed of the slip roller (25) is matched with the rotational speed of the belt member (20).

  At the start of the meandering control, the rotation of the slip roller 25 is stopped (S12). Next, the control unit 2 determines whether or not the meandering amount of the intermediate transfer belt 20 detected by the belt edge sensor 1 is equal to or less than a predetermined value (S13). While the meandering amount exceeds the predetermined value (NO in S13), the meandering control is continued, and when the meandering amount becomes equal to or less than the predetermined value (YES in S12), the driven rotation of the slip roller 25 is started ( S14).

  Next, the control unit 2 determines whether or not the meandering amount is below a predetermined value (S15). If the meandering amount exceeds the predetermined value (NO in S15), the slip roller 25 is rotated again. Stop (S12).

  Then, in a state where the meandering amount is in a predetermined range (YES in S15), image formation is performed while the intermediate transfer belt 20 is controlled to be shifted (S16). Then, when the image formation is completed (YES in S17), the intermediate transfer belt 20 is stopped while performing the deviation control.

  In this way, by controlling the braking / braking of the slip roller 25, as shown in FIG. 8, the amount of meandering during stable running after T2 indicated by the solid line 1 is kept within a predetermined range, while the broken line 2 It is possible to shorten the time until the stable running shown by T2 from T2 to T1. As a result, meandering control of the intermediate transfer belt 20 that can maintain a stable running against the disturbance after the convergence can be performed despite the rapid convergence as shown in FIG.

  As shown in FIG. 12B, when the slip roller 25 rotates in accordance with the running of the intermediate transfer belt 20, a static frictional force acts between the intermediate transfer belt 20 and the slip roller 25. . On the other hand, as shown in FIG. 12A, when the slip roller 25 is stopped, the intermediate transfer belt 20 always slides on the surface of the slip roller 25, so that a dynamic friction force works. . Therefore, when the slip roller 25 is stopped, the shifting speed becomes faster even at the same steering angle. For this reason, as shown in FIG. 7, in the case of the solid line 1 in which the slip roller 25 is rotated in accordance with the travel of the intermediate transfer belt 20, the shift speed with respect to the steering angle is smaller than in the case of the broken line 2 in which the rotation is stopped. Get smaller.

  As shown in FIG. 10, immediately after the control of the meandering direction of the intermediate transfer belt 20 is started, it is in a transitional state and the amount of meandering is large, so that the shifting speed needs to be increased. Therefore, the control unit 2 stops the rotation of the slip roller 25 so that a dynamic frictional force is exerted between the control unit 2 and the intermediate transfer belt 20. Thereby, the response of the intermediate transfer belt 20 to the steering angle of the steering roller 22 is improved, so that the intermediate transfer belt 20 can be quickly moved to the target position.

  Next, when the meandering amount of the intermediate transfer belt 20 has converged within a predetermined range, the intermediate transfer belt 20 is in a stable state, and it is necessary to slow the shifting speed in order to minimize the meandering amount. Therefore, the control unit 2 causes the slip roller 25 to rotate following the travel of the intermediate transfer belt 20 so that a static frictional force acts between the slip roller 25 and the intermediate transfer belt 20. As a result, the response of the intermediate transfer belt 20 to the steering angle of the steering roller 22 is deteriorated, so that the intermediate transfer belt 20 is less likely to move in the roller axial direction, and more stable running can be performed.

  According to the control of the first embodiment, the restraining force between the intermediate transfer belt 20 and the conveying member is reduced in a transient state where the steering control is started or in a transient state in which the intermediate transfer belt 20 varies greatly in the width direction due to external factors. Accordingly, the response speed of the movement of the intermediate transfer belt 20 in the width direction with respect to the tilt amount of the steering roller 22 is increased, and the control sensitivity with respect to the tilt amount of the steering roller 22 is increased.

  However, when the running state of the intermediate transfer belt 20 is stable with respect to the axial direction of the steering roller 22 and the control is performed in a steady state, the restraining force between the intermediate transfer belt 20 and the conveying member is increased. Thereby, the sensitivity to the steering control amount and the axial movement of the steering roller 22 of the intermediate transfer belt 20 is lowered.

  With such a configuration, by changing the sensitivity of the intermediate transfer belt 20 with respect to the axial direction of the steering roller 22, the intermediate transfer belt 20 can be quickly and stably moved. In the stable state, the intermediate transfer belt 20 can be kept running with high stability.

  The method of changing the axial restraint force due to the static friction of the intermediate transfer belt 20 by the slip roller 25 is not limited to braking / braking of the slip roller 25. For example, the pressing pressure of the slip roller 25 against the intermediate transfer belt 20 may be changed. Two types of members having different restraining forces may be switched. However, since the mechanism is complicated and the movement of the intermediate transfer belt 20 in the width direction is disturbed, braking / braking is preferable.

<Example 2>
FIG. 13 is an explanatory diagram of a braking mechanism used in the second embodiment. The second embodiment is configured in the same manner as the first embodiment except that the braking mechanism 55 shown in FIG. 9 is replaced with a stepping motor 65 shown in FIG. Therefore, the description will be made with reference to FIGS. 1 to 8 and FIGS.

  As shown in FIG. 13, the slip roller 25 is connected to a stepping motor 65, which is an example of a pulse motor that can arbitrarily set the rotational speed of the slip roller (25). By controlling the stepping motor 65 as a braking mechanism, an arbitrary peripheral speed and a peripheral speed change can be set in the slip roller 25.

  In the second embodiment, the stepping motor 65 is energized to apply a braking force to the slip roller 25 so that a dynamic friction force can be exerted between the intermediate transfer belt 20 and the slip roller 25. Further, by turning off the excitation of the stepping motor 65, the slip roller 25 can be idled and driven and rotated by the intermediate transfer belt 20, and a static frictional force can be exerted between the intermediate transfer belt 20 and the slip roller 25.

  Further, the stepping motor 65 can be controlled not only in braking but also in the acceleration direction to generate slip between the slip roller 25 and the intermediate transfer belt 20 to exert a dynamic friction force.

  Further, the drive roller 21 and the slip roller 25 are configured to be equal and driven by different stepping motors, and the two stepping motors 65 are synchronized and rotated at the same rotational speed to drive the intermediate transfer belt 20. Also good.

  In addition, when the slip roller 25 is switched between stopped and driven rotation, the peripheral speed is continuously adjusted so that the speed difference between the slip roller 25 and the intermediate transfer belt 20 gradually increases or gradually converges to a constant speed. Control may be performed. As a result, the switching between the dynamic friction and the static friction is smooth, and the running state of the intermediate transfer belt 20 is not shocked.

<Example 3>
FIG. 14 is an explanatory diagram of a configuration of the image forming apparatus according to the third embodiment. In the third embodiment, the slip roller 25 disposed on the upstream side of the steering roller 22 in the first embodiment is disposed on the downstream side of the steering roller 22. The rest of the configuration is the same as that of the first embodiment, and the peripheral speed control of the slip roller 25 and the switching between static friction and dynamic friction are performed in the same manner as in the first embodiment.

  As shown in FIG. 14, in the image forming apparatus 200 according to the second embodiment, the slip roller 25 is disposed downstream of the steering roller 22 with respect to the travel of the intermediate transfer belt 20. In such a configuration, the moving direction of the belt member with respect to the steering angle described in FIGS. 4B and 4C is reversed, but the control sequence of the slip roller 25 described with reference to FIG. The same effect can be obtained by the same control as described in 1.

DESCRIPTION OF SYMBOLS 1 Belt edge sensor, 2 Control part 11Y, 11M, 11C, 11K Photosensitive drum 17Y, 17M, 17C, 17K Primary transfer roller 20 Intermediate transfer belt, 21 Drive roller, 22 Steering roller 25 Slip roller, 30 Secondary transfer roller 50 Apparatus Frame, 51 Swing arm, 52 Rotating shaft, 53 Eccentric cam 54 Steering motor, 57 Braking mechanism 61 Engaging cam, 63 Engaging portion, 65 Stepping motor 66 Spring, 67 Support member, 90 Light emitting portion, 91 Light receiving portion

Claims (6)

A belt member; detection means for detecting the bias of the rotating belt member; a steering roller capable of correcting the bias of the belt member by tilting; and tilting of the steering roller based on an output of the detection means. In an image forming apparatus comprising a steering roller control means,
A slip roller that supports the belt member in parallel with the steering roller and can change a peripheral speed difference with the belt member;
An image forming apparatus comprising: a slip roller control unit that controls the slip roller so as to reduce the peripheral speed difference in a process in which the steering roller control unit converges the bias of the belt member.   The slip roller control means starts correction of the bias of the belt member in a state where the peripheral speed of the slip roller is lower than the rotational speed of the belt member, and the peripheral speed of the slip roller is set to rotate the belt member. The image forming apparatus according to claim 1, wherein the correction of the bias of the belt member is terminated in a state where the speed matches the speed.   The slip roller control means has a braking mechanism for braking the rotation of the slip roller, starts correction of the bias of the belt member in a state where the slip roller is stopped by the braking mechanism, releases the brake, and 3. The image forming apparatus according to claim 2, wherein the correction of the deviation of the belt member is finished in a state where the slip roller is driven to rotate by the belt member.   The slip roller control means releases the braking of the slip roller when the deviation amount of the belt member converges within a predetermined range, and then brakes the slip roller when the deviation amount of the belt member exceeds the predetermined range. The image forming apparatus according to claim 3, wherein the image forming apparatus is stopped.   5. The image forming apparatus according to claim 3, wherein image formation is performed while the slip roller is braked and image formation is performed in a state in which braking of the slip roller is released.   The image forming apparatus according to claim 1, wherein the slip roller control unit is a pulse motor capable of arbitrarily setting a rotation speed of the slip roller.

Images