JP5601574B2 - Belt unit, belt driving device, and image forming apparatus - Google Patents

Description

  The present invention corrects a belt shift of an endless belt member that is stretched by a plurality of stretching rollers disposed inside the belt loop by an inclination of a shift correction roller that is one of the plurality of stretching rollers. It relates to the belt unit. The present invention also relates to a belt driving device and an image forming apparatus using such a belt unit.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. FIG. 1 is a schematic configuration diagram illustrating a main part of an image forming apparatus described in Patent Document 1. This image forming apparatus includes a belt unit that moves an endless intermediate transfer belt 901 endlessly in a counterclockwise direction while being stretched by a plurality of stretching rollers, and four photoconductors (902Y, M, C, K). ) Etc. Y, M, C, and K toner images are formed on the surfaces of the photoreceptors 902Y, M, C, and K by a known electrophotographic process. These toner images are superimposed on the surface of the intermediate transfer belt 901 in the primary transfer nip for Y, M, C, and K where the photoreceptors 902Y, M, C, and K abut against the intermediate transfer belt 901. Primary transfer is performed. After that, the secondary transfer nip where the intermediate transfer belt 901 and the secondary transfer roller 905 are in contact with each other is batch-transferred onto a recording sheet (not shown) from the belt.

  When the intermediate transfer belt 901 repeats the circular movement, the position in the axial direction on the roller circumferential surface is inevitably shifted to one end side due to the eccentricity of the stretching rollers, errors in parallelism, and the like. If the deviation is left unattended, the intermediate transfer belt 901 will eventually detach from the roller peripheral surface. In view of this, the image forming apparatus described in Patent Document 1 includes a deviation correction roller 903 for correcting the deviation of the intermediate transfer belt 901. The deviation correcting roller 903 is one of a plurality of stretching rollers that stretch the intermediate transfer belt 901, and can swing around a swing axis that is located in the center in the roller axis direction. Is held by a bracket 904. By swinging the bracket 904, the intermediate transfer belt 901 that has been offset is moved toward the opposite side by taking an inclined posture with respect to a plurality of other stretching rollers arranged in parallel to each other. Can be corrected.

  In the old days, it is common to use a method that temporarily interrupts a print job and corrects the belt offset at the stage when the belt offset becomes large to some extent, or always corrects the belt offset at the start of a print job. there were. On the other hand, in the image forming apparatus described in Patent Document 1, the belt deviation is corrected during a normal print job. With such a configuration, it is possible to eliminate the downtime of the apparatus for correcting the belt misalignment. However, if an attempt is made to correct a large belt shift, the intermediate transfer belt 901 is largely moved in the roller axis direction, thereby causing a toner image registration error at each primary transfer nip. For this reason, it is necessary to slightly adjust the belt offset little by little.

  As a result of performing a print test using a printer tester that corrects belt misalignment during a print job as in the image forming apparatus described in Patent Document 1, the present inventors have found the following problems. It was. That is, when the misalignment correction roller 903 is tilted, the intermediate transfer belt 901 is greatly moved in the roller axial direction, and accordingly, the registration shift of the toner image in the roller axial direction is promoted at each primary transfer nip. It is. Specifically, as shown in FIG. 2, the misalignment correcting roller 903 is a bracket (not shown) that swings around a swing axis 910 extending orthogonal to the axis near the center in the axial direction. 904) in FIG. Assume that the shift correction roller 903 that is not tilted as shown by the dotted line in the figure is rotated by a predetermined angle around the swing axis 910 as shown by the solid line in the figure. Then, the position in the roller axial direction of the surface portion around which the belt of the misalignment correction roller 903 is wound changes greatly. In the example shown in the drawing, the surface portion of the roller around which the belt is hung is greatly moved in the left direction in the figure due to the inclination of the roller. As a result, the position of the intermediate transfer belt 901 on the roller surface also moves greatly in the left direction in the figure. Then, in the primary transfer nip of each color, a force that causes the belt to slip in the roller axis direction works. In particular, as shown in FIG. 1, in the primary transfer nip for K located closest to the misalignment correction roller 903, the above-described force acts so that the belt is slightly slipped in the roller axis direction. Then, the slip causes the transfer position of the toner image to the belt in each primary transfer nip to vary in the roller axial direction, thereby causing image quality deterioration due to overlay deviation.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a belt unit and a belt drive capable of suppressing a registration error of a toner image in the roller axial direction caused by tilting a shift correction roller. An apparatus and an image forming apparatus are provided.

In order to achieve the above-mentioned object, the invention of claim 1 is characterized in that an endless belt member and the belt member are hung around a part of its peripheral surface in a state of being arranged inside the loop of the belt member. A plurality of stretching rollers that stretch the belt member, and an oscillation axis that is one of the plurality of stretching rollers and extends in a direction perpendicular to the roller axis at the center in the roller axis direction The belt member is held so as to be able to swing around the swing axis, and by tilting around the swing axis, its own roller axis is inclined with respect to the roller axis of another stretching roller. A belt unit comprising a deviation correction roller for correcting a belt deviation, and a holding means for holding the deviation correction roller in a swingable manner about the swing axis, wherein the holding means is the deviation correction roller. Of the circumference of In serial state where along the tangent to the point that wrapped around the belt member extending the swing axis, it is characterized in that the closer modified roller is to swingably hold.
Further, the invention of claim 2 is the belt unit of claim 1, wherein the tension unit is different from a tension roller that is biased toward the belt member and applies tension to the belt member. The gantry roller is made to function as the misalignment correction roller.
According to a third aspect of the present invention, there is provided a belt unit that hangs an endless belt member around each of the plurality of stretching rollers disposed inside the loop, and the plurality of the belt units in the belt unit. It is one of the stretch rollers, and its own roller axis line is moved by swinging around the swing axis line extending in the belt moving direction at a position between one end and the other end in its own roller axis direction . A posture control means for controlling a swing stop position of a shift correction roller that corrects a belt shift of the belt member by taking a posture inclined with respect to the roller axis of another stretch roller, and among the plurality of stretch rollers A belt driving device having driving means for rotationally driving a driving roller that moves the belt member endlessly in accordance with its own rotational driving, wherein the belt unit includes: It is characterized in that using a belt unit.
According to a fourth aspect of the present invention, there is provided a belt driving device for moving an endless belt member stretched by a plurality of stretching rollers endlessly, and the surface of the belt member or the surface of the belt member. In an image forming apparatus including a visible image forming unit that forms a visible image on a recording sheet, the belt driving device according to claim 3 is used as the belt driving device.
The invention according to claim 5 is the image forming apparatus according to claim 1, wherein the belt member is an intermediate transfer belt.

  In these inventions, as shown in FIG. 3, the swing axis 910 of the shift correction roller 903 extends along the tangent to the portion of the peripheral surface of the shift correction roller 903 around which the belt member 909 is wound. I am letting. In the configuration in which the tilt is made about the swing axis 910 as described above, the belt member accompanying the tilt of the misalignment correction roller 903 is compared with the configuration in which the tilt is centered on the swing axis positioned on the rotation axis as in the prior art. The amount of movement of 909 in the roller axis direction is reduced. When the conventional example shown in FIG. 2 is compared with the present invention shown in FIG. 3, it can be seen that the amount of movement of the belt is greatly reduced. In particular, in the roller axis direction, the position of the belt does not change at the position of the swing axis 910 at all. As described above, according to the present invention, the amount of movement of the belt member 909 in the roller axial direction along with the inclination of the deviation correction roller 903 is reduced, so that the toner images are superimposed in the roller axis direction by inclining the deviation correction roller. Deviation can be suppressed.

FIG. 2 is a schematic configuration diagram illustrating a main part of an image forming apparatus described in Patent Document 1. Explanatory drawing for demonstrating the tilting operation | movement of the conventional deviation correction roller. Explanatory drawing for demonstrating the tilting operation | movement of the shift correction roller in this invention. 1 is a main part configuration diagram showing a printer according to an embodiment. FIG. 3 is a perspective view illustrating a shift correction roller of the printer and a swing bracket as a holding unit that holds the shift roller in a swingable manner. The enlarged block diagram which shows the rocking | fluctuation bracket of the printer, and the surrounding part of a near-end correction roller. Explanatory drawing for demonstrating the tilting operation | movement of a closeness correction roller. FIG. 3 is an enlarged configuration diagram illustrating a first belt end position detection unit of the printer. The top view and side view which show the belt unit of the transfer unit of the printer. The block diagram which shows the belt unit and attitude | position control means.

Hereinafter, an embodiment of an electrophotographic printer will be described as an image forming apparatus to which the present invention is applied.
First, the basic configuration of the printer will be described. FIG. 4 is a block diagram showing the main part of the printer. In the figure, the printer includes four image forming units 2Y, 2M, 2C, and 2K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. Yes. In addition, a sheet conveyance path 21 including a plurality of guide plates for conveying the recording sheet P in the apparatus, a registration roller pair 37, a fixing unit 150, an optical writing unit (not shown), a transfer unit 60, and the like are also provided. Have

  An optical writing unit (not shown) includes a laser diode, a polygon mirror, various lenses, and the like, and drives the laser diode based on image information sent from an external personal computer or the like. Then, the photoconductors 3Y, M, C, and K of the image forming units 2Y, M, C, and K are optically scanned. Specifically, the photoconductors 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 performs optical scanning processing by irradiating the driven photosensitive members 3Y, 3M, 3C, and 3K while deflecting the laser light L in the rotation axis direction. As a result, electrostatic latent images based on Y, M, C, and K image information are formed on the photoreceptors 3Y, 3M, 3C, and 3K that are latent image carriers.

  This printer 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 described later. The image forming units 2Y, 2M, 2C, and 2K of the respective colors have a common support as a single unit including the photoreceptors 3Y, 3M, 3C, and 3K that are latent image carriers and various devices disposed around the photoreceptors. They are supported by the body, and are integrally detachable from the printer unit main body. The configuration is the same except that the colors of the toners used are different. Taking the image forming unit 2Y for Y as an example, this includes, in addition to the photoreceptor 3Y, a developing device 4Y for developing an electrostatic latent image formed on the surface thereof into a Y toner image, and a drum-shaped photoreceptor. A charging device 16Y for uniformly charging 3Y, a drum cleaning device 18Y, and the like are provided.

  The charging device 16Y uniformly charges the peripheral surface of the rotationally driven photoreceptor 3Y to the same polarity as the toner charging polarity. An electrostatic latent image is formed on the circumferential surface of the photoreceptor 3Y that is uniformly charged in this way by optical scanning by the optical writing device described above. 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 the electrostatic latent image on the photoreceptor 3Y using a two-component developer (hereinafter simply referred to as developer) containing a magnetic carrier (not shown) and non-magnetic Y toner. Instead of the two-component developer, a type in which development is performed with a one-component developer not containing a magnetic carrier may be used.

  The Y toner image formed on the photoreceptor 3Y by development is transferred to the front surface of the intermediate transfer belt 61 at a Y primary transfer nip described later. The transfer residual toner adhering to the photoreceptor 3Y after transferring the Y toner image in this way is removed from the surface of the photoreceptor 3Y by the drum cleaning device 18Y. Prior to this cleaning, the surface of the photoreceptor 3Y is discharged by receiving light from a discharge lamp (not shown).

  Although the Y image forming unit 2Y has been described, M, C, and K toner images are similarly formed on the surfaces of the photoreceptors 3M, C, and K in the M, C, and K image forming units.

  Below the four image forming units 2Y, 2M, 2C, and 2K, a transfer unit 60 is disposed. This transfer unit 60 is driven by a rotational drive of a drive roller 67 while an intermediate transfer belt 61, which is an image carrier stretched by a plurality of stretch rollers, is brought into contact with the photoreceptors 3Y, 3M, 3C, and 3K. Move endlessly counterclockwise. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 3Y, 3M, 3C, and 3K contact the intermediate transfer belt 61 are formed.

  In the vicinity of the primary transfer nips for Y, M, C, and K, the intermediate transfer belt 61 is moved to the photoreceptors 3Y, M, C, and K by primary transfer rollers 62Y, 62M, 62C, and 62K disposed inside the belt loop. Pressing toward K. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, 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. Has been.

  In the drawing, a toner image is formed on each of the primary transfer nips on the front surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for Y, M, C, and K with endless movement in the clockwise direction. Are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 61.

  A secondary transfer roller 74 is disposed below the intermediate transfer belt 61 in the drawing, and a secondary transfer nip is brought into contact with the transfer surface of the intermediate transfer belt 61 with respect to the transfer counter roller 69 from the belt front surface. Is forming. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 61 and the secondary transfer roller 74 abut is formed.

  A secondary transfer bias having the same polarity as the toner is applied to the transfer counter roller 69 in the belt loop by a power source (not shown). On the other hand, the secondary transfer roller 74 outside the belt loop is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A pair of registration rollers 37 is disposed on the left side of the secondary transfer nip in the drawing, and the secondary transfer nip 37 is arranged at a timing at which the recording sheet P sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 61. Send to transfer nip. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 61 are secondarily transferred onto the recording sheet under the influence of the secondary transfer electric field and the nip pressure, and become a full color image combined with the white color of the recording sheet.

  The transfer residual toner that has not been transferred to the recording sheet P at the secondary transfer nip is attached to the front 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 73 that contacts the intermediate transfer belt 61.

  The recording sheet P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and fed toward the fixing unit 150. The fixing unit 150 forms a fixing nip by bringing a pressure roller 4152 and a fixing roller 151 containing a heat source into contact with each other. The recording sheet P received by the fixing unit 150 is pressed or heated in the fixing nip, whereby the full color image on the surface is fixed.

  The secondary transfer roller 74, which is in contact with the intermediate transfer belt 61 and forms a secondary transfer nip, includes a metal cored bar and an elastic member such as rubber coated on the peripheral surface thereof. In the secondary transfer nip, the portion of the intermediate transfer belt 61 that is wound around the transfer counter roller 69 bites into the elastic member on the surface of the secondary transfer roller 74. Thereby, a wide secondary transfer nip is formed.

  The rotation shaft of the secondary transfer roller 74 is rotatably received by a bearing fixed to a swing arm 76 as a holding body. The swing arm 76 is supported so as to swing about the swing shaft 84, and the rotation shaft of the secondary transfer roller 74 and the rotation of the transfer counter roller 69 along with the swing of the swing arm 76. Change the distance to the axis (distance between axes). By changing the distance according to the thickness of the recording sheet P, the secondary transfer nip pressure can be made constant regardless of the sheet thickness.

  The transfer unit 60 includes an intermediate transfer belt 61 as a belt member, and a plurality of stretching rollers that stretch the intermediate transfer belt 61 while looping the intermediate transfer belt 61 around a part of its surface inside the loop. A belt unit is provided. Specifically, the plurality of stretching rollers in this belt unit include Y, M, C, and K primary transfer rollers 62Y, M, C, and K, a misalignment correction roller 64, a primary transfer nip upstream roller 65, A driving upstream roller 66, a driving roller 67, a secondary transfer nip upstream roller 68, a transfer counter roller 69, and a cleaning backup roller 70. Among these stretching rollers, the belt winding angle with respect to the misalignment correction roller 64, the driving roller 67, and the transfer counter roller 69 is particularly large. That is, in this printer, the misalignment correction roller 64, the drive roller 67, and the transfer counter roller 69 each function as a large winding angle roller. The intermediate transfer belt 61 is mainly stretched by these three rollers, and the stretching rollers other than the three rollers back up the intermediate transfer belt 61 as an auxiliary. The winding angle is an angle formed by a line segment connecting the roller center and the belt contact start point on the roller circumferential surface and a line segment connecting the roller center and the belt contact end point on the roller circumferential surface.

  On the outer side of the belt loop, a tension roller 71 that presses against the front surface of the intermediate transfer belt 61 and applies a predetermined tension to the intermediate transfer belt 61 while being urged toward the loop inner side of the intermediate transfer belt 61 by a spring. It is arranged.

  In the transfer unit 60, a belt shift occurs in the intermediate transfer belt 61 due to a shape error of each stretching roller that stretches the intermediate transfer belt 61, a tilt due to an assembly error, a circumferential length difference in the belt width direction, and the like. . A virtual center line extending in the circumferential direction at the center in the width direction of the stretched intermediate transfer belt 61 if the axes of all the stretch rollers are parallel to each other and all the stretch rollers are completely cylindrical. Takes a posture that extends straight. However, such a situation is not possible in reality. Since the axis of any of the stretching rollers is slightly inclined or not completely cylindrical, the virtual center line is not a straight line but is in a complicated bent posture. For this reason, the belt is inevitably generated. If a large belt shift occurs, the belt end may come into contact with the surrounding parts of the transfer unit 60 and be damaged or the surrounding parts may be damaged. Moreover, it becomes a factor of image position shift. In particular, in the case where a tandem system such as this printer is used, when the respective color toner images are superimposed on the intermediate transfer belt 61, it becomes a factor that causes a misalignment.

  Therefore, in this printer, the belt deviation is corrected by tilting a deviation correction roller 64 described later.

Next, a characteristic configuration of the printer according to the embodiment will be described.
FIG. 5 is a perspective view showing the misalignment correction roller 64 and a swing bracket 211 as a holding means for holding the shift roller 64 so as to be swingable. In the figure, the offset correcting roller 64 is held by a swing bracket 211 so as to be swingable about a swing axis 910 extending at the center position in the roller axis direction of the roller. Then, by taking a posture in which its own roller axis is inclined with respect to the roller axis of the other stretching roller, the belt shift of the intermediate transfer belt (61 in FIG. 4) is corrected.

  In the swing bracket 211, the rotary shaft member 212 projecting from the bracket body is driven to rotate while rotatably receiving the roller shafts respectively present at both ends of the misalignment correction roller 64 in the axial direction. The rotation center of the rotary shaft member 212 is a swing axis 910. That is, as the rotation shaft member 212 rotates, the rotation correction member 64 swings about the swing axis 910 and swings.

  FIG. 6 is an enlarged configuration diagram showing the swing bracket 202 and the peripheral portion of the misalignment correction roller 64 in the belt unit. In the drawing, the intermediate transfer belt 61 is moved endlessly in the counterclockwise direction in the figure so as to sequentially pass through the place where the intermediate transfer belt 61 is wound around the deviation correcting roller 64 and the place where the intermediate transfer belt 61 is wound around the primary transfer nip upstream roller 65. ing. The swing bracket 211 is not illustrated in such a posture that its swing axis 910 is perfectly positioned on the extended line of the extension portion between the misalignment correction roller 64 and the primary transfer nip upstream roller 65 in the intermediate transfer belt 61. It is supported by the support means. In other words, the swing bracket 211 as the holding means swings the shift correction roller 64 in a state where the swing axis 910 extends at a position tangent to the belt wrapping position on the peripheral surface of the shift correction roller 64. Hold it possible.

  As shown in FIG. 7, the deviation correction roller 64 swung in such a state has a center position (swinging in the roller axis direction) on the contact surface with the belt even if it is inclined by the swinging. The position of the movement axis 910) is not changed at all. In addition, although the positions of the one end and the other end in the roller axial direction are slightly changed, they are changed in opposite directions toward the center in the axial direction. For this reason, the force that changes the belt toward the center in the axial direction due to the position change on one end side cancels out the force that changes the belt toward the center due to the position change on the other end side. . As a result, even if the deviation correction roller 64 is tilted as shown in the drawing, the belt extending portion between the deviation correction roller 64 and the primary transfer nip upstream roller 65 shown in FIG. Almost no force to move is applied. Therefore, it is possible to suppress the misalignment of the toner image in the axial direction due to the inclination correction roller 64 being inclined.

  FIG. 8 is an enlarged configuration diagram showing the first belt end position detecting means 200. The support body 201 having an L-shaped cross-sectional shape is supported so as to be rotatable about a rotation shaft 201a provided at an L-shaped bent portion. One end of the support 201 is abutted against one end in the width direction of the intermediate transfer belt 61 by being pulled by a spring 203. When the intermediate transfer belt 61 moves from the left side to the right side in the figure, the support 201 rotates in the clockwise direction in the figure at an angle corresponding to the belt movement amount around the rotation shaft 201a against the force of the spring 203. To do. Further, when the intermediate transfer belt 61 moves from the right side to the left side in the figure, the support 201 is rotated in the counterclockwise direction in the figure at an angle corresponding to the belt movement amount around the rotation shaft 201a according to the force of the spring 203. Rotate. Due to these rotations, the distance between the other end of the support and the displacement sensor 202 changes. Based on the distance change detected by the displacement sensor 202, the position of the intermediate transfer belt 61 on the roller in the belt width direction is grasped. Although a reflection type displacement sensor is used, another type of displacement sensor may be used, or a linear position sensor in which a light emitting unit and a light receiving unit are arranged above and below the belt may be used. According to the output of the belt position detecting means, the first adjusting means is controlled and the inclination angle of the position correcting roller is adjusted to correct the belt position and adjust so that the belt is at an appropriate position in the width direction. can do.

  FIG. 9 is a plan view and a side view showing the belt unit of the transfer unit. As shown in the figure, the first belt end position detecting means 200 is arranged to detect the belt end position at a position in the vicinity of the primary transfer nip upstream roller 65. Further, the second belt end position detecting means 250 is disposed so as to detect the belt end position in the vicinity of the drive roller 67. The second belt end detection means 250 detects the belt end position by the same configuration as the first belt end position detection means 200. By calculating by combining the respective output values, the inclination of the belt due to the difference in the amount of belt deviation at each position can be detected. Hereinafter, the belt region from the position passing through the primary transfer nip upstream roller 65 through the primary transfer nip to the drive upstream roller 66 is referred to as a primary transfer surface. On the primary transfer surface of the intermediate transfer belt 61, belt position detecting means are provided upstream of the most upstream photosensitive drum and downstream of the most downstream photosensitive drum, so that the primary transfer surface of the intermediate transfer belt 61 It is possible to detect the inclination of the belt.

  FIG. 10 is a configuration diagram illustrating a belt unit and a posture control unit in the printer according to the embodiment. The detection result of the belt deviation amount by the first belt end position detection unit 200 and the detection result of the belt deviation amount by the second belt end position detection unit 250 are sent to the attitude control unit. This posture control means includes a belt inclination calculation means 300, a deviation correction control unit 301, a steering motor 302, and the like. The belt inclination calculating unit 300 calculates a relative belt shift amount of the primary transfer surface based on signals sent from the first belt end position detecting unit 200 and the second belt end position detecting unit 250. . Then, the result is output to the shift correction control unit 301. The shift correction control unit 301 determines the belt shift amount based on the relative belt shift amount of the primary transfer surface. This belt shift amount is an amount by which the belt is intentionally moved in the direction opposite to the direction in which the belt is moving. The shift correction control unit 301 that has determined the belt shift amount tilts the shift correction roller 64 by rotating the steering motor 302 in a direction (forward or reverse) according to the shift direction for a predetermined time.

Hereinafter, in order to explain the behavior of the intermediate transfer belt 61 in detail, terms are defined as follows.
Steering An operation of tilting the correction roller 64 from the same horizontal direction as the axial direction of the other stretching postures is shown.
-Tilt angle of the misalignment correction roller The tilt angle of the misalignment correction roller in a posture in which the rotation axis extends in the horizontal direction is defined as 0 [°]. In a state of being tilted from the posture, the difference between the rotation axis of the misalignment correction roller and the horizontal line is the tilt angle.

  The stretching roller that stretches the intermediate transfer belt 61 hangs the belt around its circumferential surface with a certain length in the belt moving direction. Such a tension roller has a force (belt deviation coefficient) that generates belt deviation due to differences in parallelism with other tension rollers, eccentricity, axial diameter error, surface friction error, contact area with the belt, etc. ) Is different for each roller. The sum of the belt slip coefficients (the signs differ depending on the slip direction) of each stretch roller works as the overall belt slip coefficient, and finally the belt is moved to one end or the other end in the roller axis direction. Bring

  When the deviation correction control unit 301 detects a certain amount of belt deviation, the deviation correction control unit 301 inclines the deviation correction roller 64 in a direction that can generate a belt deviation opposite to the deviation direction. As a result, the belt movement in the roller axis direction accompanying the endless movement is changed in the opposite direction, and the belt shift is corrected little by little. Then, when the deviation correction control unit 301 detects that the belt has almost returned to the center, it returns the deviation correction roller 64 to a horizontal posture.

Hereinafter, the belt behavior when the following conditions are satisfied will be described.
-Perimeter of the intermediate transfer belt 61: 2 [m]
-Width of intermediate transfer belt 61: 36 [cm]
-Length of the primary transfer surface in the belt moving direction: 75 [cm]

An experiment was conducted using a conventional configuration in which the swing axis of the shift correction roller was positioned on the roller rotation axis. When the shift correction roller was tilted at an inclination angle of 0.1 °, the intermediate transfer belt was moved in the circumferential direction. Each time 1 [mm] is moved, 0.05 × 10 ⁻³ [mm] is moved in the roller axial direction. The movement in the roller axis direction at this time is a movement in the opposite direction to that when the roller is not tilted. At this time, the center line of the belt was tilted at a rate of 0.035 × 10 ⁻³ [mm] per 1 [mm] in the direction opposite to the belt moving direction in the roller axis direction (belt tilt). Under such conditions, when the belt in a state of being shifted by 0.5 [mm] from the center in the axial direction on the roller peripheral surface as a whole is returned to the center, it is necessary to move the belt endlessly about five times. At that time, the following overlay deviation occurs on the primary transfer surface. In other words, in the period from the start of steering to the time when the belt travels 75 [cm] (hereinafter referred to as the initial stage of steering), an overlay deviation of about 75 [μm] at maximum occurs. Further, in the period of 1 to 2 rounds thereafter, a maximum of 30-40 [μm] misalignment occurs, and thereafter, a misalignment of approximately 11 [μm] occurs on the primary transfer surface. .

  In the conventional configuration, the initial misalignment of 75 [μm] is caused by a force acting to move the belt in the axial direction by moving the roller peripheral surface in the axial direction when steering is started. Is. On the other hand, in the printer according to the embodiment, as described above, when the steering is started, the force does not work at all, so that the overlay deviation at the initial stage of steering hardly occurs. Subsequent misalignment of 30 to 40 [μm] in 1 to 2 rounds and further overlay misalignment of 11 [μm] occur in the same manner as in the conventional configuration, but 75 μm in the initial stage of steering. In order to improve the image quality, it is very large that the maximum overlay error does not occur at all.

  Note that the overlay deviation can be further suppressed by further reducing the tilt angle. For example, in the printer according to the embodiment, when the inclination angle is set to 0.05 [°], when the belt is rotated 10 times, the belt shift of approximately 0.5 [mm] can be eliminated. At this time, the amount of misalignment is very small.

Up to this point, a description has been given of a printer having a configuration in which a toner image formed on each color photoreceptor is transferred onto the intermediate transfer belt 61 and then transferred to a recording sheet, but the toner image formed on each color photoreceptor is described. The present invention can also be applied to an image forming apparatus configured to superimpose and transfer the image on a recording sheet conveyed by a conveying belt.

  In the printer according to the embodiment, among the plurality of stretching rollers, a stretching roller that is different from the tension roller that is biased toward the intermediate transfer belt 61 and applies tension to the belt is used as the misalignment correction roller 64. It is functioning. With such a configuration, it is possible to avoid applying an unstable force to the belt during steering due to an urging force of a spring or the like for applying a tension.

2Y, M, C, K: Image forming unit (visible image forming means)
60: Transfer unit (belt unit, belt driving device)
61: Intermediate transfer belt 64: Shift correction roller 201: Swing bracket (holding means)
300: Shift correction control unit (attitude control means)

JP 2000-266139 A

Claims (5)

An endless belt member;
A plurality of stretching rollers that stretch the belt member by winding the belt member around a part of its peripheral surface in a state of being disposed inside the loop of the belt member;
One of the plurality of stretching rollers, and is held so as to be swingable around a swing axis extending in a direction perpendicular to the roller axis at the center in the roller axis direction of the roller, A swing correction roller that corrects the belt shift of the belt member by tilting its own roller axis with respect to the roller axis of another stretching roller by swinging about the axis, and the swing axis A belt unit comprising holding means for swingably holding the misalignment correction roller around the center,
The holding means can swing the shift correcting roller in a state where the swing axis extends along a tangent to a portion of the peripheral surface of the shift correcting roller around which the belt member is wound. A belt unit characterized by being held. The belt unit according to claim 1, wherein
Of the plurality of tension rollers, a tension roller that is biased toward the belt member and is different from a tension roller that applies tension to the belt member functions as the misalignment correction roller. Belt unit. A belt unit that hangs an endless belt member around each circumferential surface of a plurality of stretching rollers disposed inside the loop; and
Swing about one of the plurality of stretching rollers in the belt unit, centering on a swinging axis extending in the belt moving direction at a position between one end and the other end in the roller axial direction The attitude control means for controlling the oscillation stop position of the deviation correction roller for correcting the belt deviation of the belt member by taking the attitude of inclining its own roller axis with respect to the roller axis of the other stretching roller,
In the belt driving device having driving means for rotationally driving a driving roller that moves the belt member endlessly with its own rotational driving among the plurality of stretching rollers,
A belt driving device using the belt unit according to claim 1 or 2 as the belt unit. A visible image is formed on a belt driving device that moves an endless belt member stretched by a plurality of stretching rollers endlessly, and on the surface of the belt member or a recording sheet held on the surface of the belt member. In an image forming apparatus provided with visible image forming means
An image forming apparatus using the belt driving device according to claim 3 as the belt driving device. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the belt member is an intermediate transfer belt.

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