JP2011090179A - Image forming device and transfer device - Google Patents

Abstract

In an image forming apparatus and a transfer apparatus having a belt-like image carrier and a transfer roller having a concave portion on a peripheral surface, image disturbance such as displacement of an image transfer position on a recording material is prevented.
In a configuration in which tension rollers (33, 35) are provided at positions sandwiching a secondary transfer position (TR2) where a secondary transfer roller (4) having a recess (41) and an intermediate transfer belt (31) contact each other, a secondary transfer backup roller (34) is provided. A blade-like contact body 347 is brought into contact with the surface. Even when the concave portion 41 is located at the secondary transfer position TR2 and the pressure on the intermediate transfer belt 31 is released, the blade-like contact body 347 acts to brake the rotation of the secondary transfer backup roller 34. The swinging of the tension rollers 33 and 35 can be converged in a short time.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus and a transfer apparatus having a belt-shaped image carrier and a transfer roller having a recess on a peripheral surface.

  Examples of an image forming apparatus that transfers an image formed on an image carrier onto a recording material include those described in Patent Documents 1 and 2. These apparatuses are so-called liquid development type image forming apparatuses that develop an electrostatic latent image with a liquid developer containing toner particles and a carrier liquid. In these apparatuses, a recording material is gripped by a gripper (gripping part) provided on a part of the peripheral surface of a pressing roller (corresponding to a transfer roller), and the recording material is wound around the pressing roller to form a drum-shaped intermediate transfer. The image is transferred onto the recording material by passing through a nip with the body (image carrier).

  In these conventional techniques, the image formed on the photosensitive drum is primarily transferred to the intermediate transfer member, and then sent to a nip (transfer nip) formed by the contact between the pressure roller and the intermediate transfer member. Secondary transfer onto the recording material. As described above, in the structure in which the photosensitive member and the pressure roller (transfer roller) are in contact with the drum-shaped intermediate transfer member, the transfer nip is not changed when the recording material enters the transfer nip or during the passage of the transfer nip. There is a possibility that the vibration and the speed fluctuation generated in the process will be transmitted to the photoconductor to disturb the image formation and the image quality will deteriorate. In particular, when a concave portion is provided on the transfer roller peripheral surface to dispose the grip portion, the surface of the transfer roller facing the intermediate transfer body is alternately switched between the concave portion and the other peripheral surface. The problem is remarkable.

  On the other hand, in the techniques described in Patent Documents 3 and 4, the intermediate transfer belt, which is a belt-like image carrier, is used, and the intermediate transfer belt is wound around an elastically supported tension roller, thereby causing impact generated in the transfer nip. It is configured to mitigate.

Japanese translation of PCT publication No. 2000-508280 (for example, FIG. 1 and FIG. 2A) Japanese translation of PCT publication No. 2002-530722 (for example, FIG. 4) Japanese Patent Laid-Open No. 10-268595 (for example, FIG. 2) JP-A-5-224572 (for example, FIG. 1)

  It is conceivable to combine a transfer roller having a recess described in Patent Documents 1 and 2 and a belt-shaped image carrier using a tension roller described in Patent Documents 3 and 4. However, in the configuration in which the concave portion is provided on the peripheral surface of the transfer roller, the pressure on the image carrier by the transfer roller is temporarily released when the concave portion faces the image carrier. Takes time to converge. In addition to disturbing the image, the tension roller vibrations also fluctuate the tension path of the belt-like image carrier, causing the image transport path length to fluctuate, resulting in misalignment of the image transfer position on the recording material. Will be allowed to.

  Some embodiments according to the present invention provide an image forming apparatus and a transfer apparatus having a belt-shaped image carrier and a transfer roller having a concave portion on a peripheral surface. The present invention provides a technique capable of preventing image disturbance such as displacement of the transfer position.

  In order to solve the above problems, an image forming apparatus according to the present invention has a belt-like image carrier that carries an image, a first image forming unit that transfers a first image to the image carrier, and the first image forming unit. A second image forming unit for transferring a second image and the image carrier to which the first image and the second image are transferred are wound around the image carrier to which the first image is transferred. And a driving roller for driving the image carrier around, a first roller for winding the image carrier driven by the driving roller, and a concave portion in a part of the peripheral surface. A transfer roller that is in contact with the image carrier wound around the first roller via a recording material; a gripping portion that is disposed in the recess and grips the recording material; and a driving unit that rotationally drives the transfer roller And applying a tension to the image carrier by winding the image carrier. And rollers, is characterized by comprising a braking unit for braking at least one of the first roller and the second roller.

  In this specification, the phrase “the peripheral surface of the transfer roller and the image carrier abut” means that the transfer roller is formed by the peripheral surface of the transfer roller and the image carrier in addition to the case where they are in direct contact with each other. This includes the case where the recording material fed to the nip is interposed between them, that is, the peripheral surface of the transfer roller is in contact with the image carrier via the recording material.

  In the invention configured as described above, the second roller has a function as a tension roller that relieves the impact generated on the image carrier described above. Then, by providing a braking unit that brakes at least one roller different from the driving roller among the plurality of rollers around which the belt-shaped image carrier is wound, when the pressure on the image carrier by the transfer roller is released The vibration generated in is converged in a short time. As a result, image formation such as disorder of image formation in each image forming unit, displacement of the image transfer position on the image carrier between each image forming unit, image transfer position shift from the image carrier to the recording material, etc. Disturbance can be prevented.

  For example, the second roller is disposed at a position where the image carrier wound around the driving roller is wound, and the first roller is disposed at a position where the image carrier wound around the second roller is wound. The braking unit may be a squeeze roller that contacts the second roller via the image carrier. In the configuration in which the squeeze roller that contacts the image carrier wound around the second roller is provided, the squeeze roller acts as a load on the second roller and the image carrier wound around the second roller and exerts a braking action.

  Further, for example, the braking unit may be a cleaning member that abuts the second roller disposed at the position where the image carrier wound around the first roller is wound via the image carrier. In the configuration in which the cleaning member that comes into contact with the image carrier wound around the second roller is provided, the cleaning member acts as a load on the second roller and the image carrier wound around the second roller and exerts a braking action.

  For example, the braking unit may be a regulating member that regulates the rotation of the first roller. By restricting the rotation of the first roller, it is possible to avoid a sudden change in the rotation speed of the first roller even when the pressure on the image carrier by the transfer roller is released. If the rotation speed of the first roller does not fluctuate, speed fluctuations and vibrations of the image carrier wound around the first roller can be suppressed.

  More specifically, for example, the regulating member may be in contact with the first roller. As the regulating member to be brought into contact with the first roller, a blade-shaped member or a roller-shaped member can be used. Further, for example, the regulating member may be a torque limiter on the rotation shaft of the first roller. In any of these configurations, it is possible to prevent the rotation speed of the first roller from fluctuating when the pressure applied to the image carrier by the transfer roller is released, and the speed of the image carrier wound around this can be suppressed. Variation and vibration are also suppressed.

  In addition, in order to solve the above-described problems, the transfer device according to the present invention winds the belt-shaped image carrier to which an image is transferred and the image carrier to which the image has been transferred. A driving roller that is driven to rotate, a first roller that winds the image carrier driven by the driving roller, a concave portion in a part of the peripheral surface, and the peripheral surface is wound around the first roller A transfer roller that contacts and drives the image carrier via a recording material; a grip portion that is disposed in the concave portion and grips the recording material to which the image is transferred; and winds the image carrier. A second roller that applies tension to the image carrier, and a braking unit that brakes at least one of the first roller and the second roller. In the invention configured as described above, similarly to the above-described invention of the image forming apparatus, the vibration generated in the image carrier can be converged in a short time to prevent image disturbance.

1 is a diagram illustrating a first embodiment of an image forming apparatus according to the present invention. The block diagram which shows the electric constitution of the apparatus of FIG. The figure which shows the structure of a secondary transfer roller. The figure explaining the effect | action of the contact member in this embodiment. 2 is a timing chart illustrating an operation example of the image forming apparatus in FIG. 1. FIG. 2 is a diagram schematically illustrating the operation of the image forming apparatus in FIG. 1. The figure which shows the principal part of 2nd Embodiment of the image forming apparatus concerning this invention. FIG. 5 is a diagram illustrating a third embodiment of an image forming apparatus according to the present invention. FIG. 9 is a diagram illustrating an image forming apparatus according to a fourth embodiment of the invention.

  FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. The image forming apparatus 1 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan), and 2K (for black) that form images of different colors. The image forming apparatus 1 includes a color mode in which four color toners of yellow (Y), magenta (M), cyan (C), and black (K) are overlapped to form a color image, and black (K). A monochrome mode in which a monochrome image is formed using only toner can be selectively executed. In this image forming apparatus, when an image forming instruction is given from an external device such as a host computer to a controller 10 having a CPU, a memory, etc., the controller 10 controls each part of the apparatus to execute a predetermined image forming operation, and copy An image corresponding to the image formation command is formed on a sheet-like recording material RM such as paper, transfer paper, paper, and an OHP transparent sheet.

  Each of the image forming stations 2Y, 2M, 2C, and 2K has the same structure and function except for the toner color. Therefore, in FIG. 1, in order to make the drawing easier to see, reference numerals are given only to the components constituting the image forming station 2 </ b> C, and description of reference numerals to be attached to the other image forming stations 2 </ b> Y, 2 </ b> M, and 2 </ b> K is omitted. In the following description, the structure and operation of the image forming station 2C will be described with reference to the reference numerals in FIG. 1, but the structure and operation of the other image forming stations 2Y, 2M, and 2K also differ in toner color. It is the same except that.

  The image forming station 2C is provided with a photosensitive drum 21 on which a cyan toner image is formed. The photosensitive drum 21 is arranged such that its rotation axis is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 1), and at a predetermined speed in the direction of arrow D21 in FIG. Driven by rotation.

  Around the photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential, and an electrostatic latent image is formed by exposing the surface of the photosensitive drum 21 according to an image signal. An exposure unit 23 for forming the electrostatic latent image, a developing unit 24 for developing the electrostatic latent image as a toner image, a first squeeze unit 25, a second squeeze unit 26, and an intermediate transfer of the toner image to the transfer unit 3. A primary transfer unit for primary transfer to the belt 31, a cleaning unit for cleaning the surface of the photosensitive drum 21 after transfer, and a cleaner blade are arranged in the order of rotation D21 of the photosensitive drum 21 (in FIG. Around).

  The charger 22 does not come into contact with the surface of the photosensitive drum 21, and a conventionally well-known and commonly used corona charger can be used as the charger 22. When a scorotron charger is used as the corona charger, a negative wire current flows through the charge wire of the scorotron charger and a direct current (DC) grid charging bias is applied to the grid. When the photosensitive drum 21 is charged by corona discharge by the charger 22, the surface potential of the photosensitive drum 21 is set to a substantially uniform potential.

  The exposure unit 23 exposes the surface of the photosensitive drum 21 with a light beam in accordance with an image signal given from an external device to form an electrostatic latent image corresponding to the image signal. The exposure unit 23 can be constituted by a light beam from a semiconductor laser that is scanned in the main scanning direction by a polygon mirror, or a line head in which light emitting elements are arranged in the main scanning direction.

  Toner is applied from the developing unit 24 to the electrostatic latent image thus formed, and the electrostatic latent image is developed with the toner. In the developing unit 24 of the image forming apparatus 1, toner development is performed using a liquid developer in which toner is dispersed in a carrier liquid in an approximate weight ratio of about 20%. In this image forming apparatus 1, a volatile liquid developer having a low concentration (1 to 2 wt%) and a low viscosity at room temperature, which is generally used conventionally, is Isopar (trademark: exon) as a carrier liquid. Rather, solid particles having an average particle diameter of 1 μm, in which a colorant such as a pigment is dispersed in a non-volatile resin having a high concentration and high viscosity at room temperature, liquid such as organic solvent, silicon oil, mineral oil, or edible oil A liquid developer having a high viscosity (about 30 to 10,000 mPa · s) added to the solvent together with the dispersant and having a toner solid content concentration of about 20% is used.

  The first squeeze unit 25 and the second squeeze unit 26 are provided with squeeze rollers, respectively. Each squeeze roller comes into contact with the surface of the photosensitive drum 21 to remove excess carrier liquid and fog toner from the toner image. In the present embodiment, the excess carrier liquid and fog toner are removed by the two squeeze portions 25 and 26. However, the number and arrangement of the squeeze portions are not limited to this, for example, one squeeze portion. May be arranged.

  The toner image that has passed through the squeeze portions 25 and 26 is primarily transferred to the intermediate transfer belt 31 by the primary transfer unit. The intermediate transfer belt 31 is an endless belt as an image carrier that can temporarily carry a toner image on its surface, more specifically, on its outer peripheral surface, and is laid over a plurality of rollers 32, 33, 34 and 35. Has been. Of these, the roller 32 is mechanically connected to the belt drive motor M3, and functions as a belt drive roller for driving the intermediate transfer belt 31 in the direction of the arrow D31 in FIG. As shown in FIG. 2, in this image forming apparatus, a driver 11 is provided to drive a belt drive motor M3. The driver 11 outputs a drive signal corresponding to a command pulse supplied from the controller 10 to the belt drive motor M3. Output to. As a result, the belt driving roller 32 rotates at a peripheral speed corresponding to the command pulse, and the surface of the intermediate transfer belt 31 rotates in the direction D31 at a constant speed. Reference numeral E3 in the figure is an encoder attached to the belt drive motor M3, and a signal corresponding to the rotation of the belt drive motor M3 is given to the driver 11, and the driver 11 receiving the signal drives the belt based on the signal. The motor M3 is feedback-controlled.

  As will be described in detail later, among the rollers 32 to 35 around which the intermediate transfer belt 31 is stretched, only the belt driving roller 32 is driven by the motor, and the other rollers 33, 34 and 35 are driving sources. The driven roller does not have

  The primary transfer unit has a primary transfer backup roller 271, and the primary transfer backup roller 271 is disposed to face the photosensitive drum 21 with the intermediate transfer belt 31 interposed therebetween. At the primary transfer position TR1 where the photosensitive member 21 and the intermediate transfer belt 31 are in contact, the toner image on the photosensitive drum 21 is transferred to the outer peripheral surface of the intermediate transfer belt 31 (the lower surface at the primary transfer position TR1). Thus, the cyan toner image formed by the image forming station 2 </ b> C is transferred to the intermediate transfer belt 31. Similarly, the toner images are transferred at the other image forming stations 2Y, 2M, and 2K, so that the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 31 to form a full-color toner image. On the other hand, when a monochrome toner image is formed, the toner image is transferred to the intermediate transfer belt 31 only in the image forming station 2K corresponding to the black color.

  The toner image thus transferred to the intermediate transfer belt 31 is conveyed to the secondary transfer position TR2. At the secondary transfer position TR2, the secondary transfer roller 4 is disposed opposite to the roller 34 around which the intermediate transfer belt 31 is wound, with the intermediate transfer belt 31 interposed therebetween, and the surface of the intermediate transfer belt 31 and the transfer roller 4 are disposed. The surface is in contact with each other to form a transfer nip NP. That is, the roller 34 functions as a secondary transfer backup roller. A blade-like contact body 347 is in contact with the surface of the secondary transfer backup roller 34. The function will be described in detail later.

  At the secondary transfer position TR2, the single-color or multi-color toner images formed on the intermediate transfer belt 31 are transferred from the pair of gate rollers 51 to the recording material RM conveyed along the conveyance path PT. In this embodiment, since the toner image is formed by a wet development method in which a toner image is formed using a liquid developer, in order to obtain good transfer characteristics, the intermediate transfer belt 31 is used in the transfer nip. It is desired that the recording material RM is pressed with a high pressing force. Further, since the liquid developer is interposed, there is a high possibility that the recording material RM sticks to the intermediate transfer belt 31 and is jammed. In view of this, the image forming apparatus 1 uses a secondary transfer roller 4 having a grip portion as will be described in detail later.

  The recording material RM on which the toner image is secondarily transferred is sent from the secondary transfer roller 4 to the fixing unit 7 provided on the transport path PT. In the fixing unit 7, heat or pressure is applied to the toner image transferred to the recording material RM to fix the toner image on the recording material RM.

  FIG. 3 is a diagram showing the configuration of the secondary transfer roller. More specifically, FIG. 3A is a perspective view showing the entire configuration of the secondary transfer roller 4, and FIG. 3B is a diagram for explaining the shape of the contact member 47. As shown in FIG. 1 and FIG. 3A, the secondary transfer roller 4 has a roller base 42 provided with a recess 41 formed by cutting out a part of the outer peripheral surface of the cylinder. In the roller base material 42, a rotating shaft 421 that is rotatable in the direction D 4 is arranged around the rotating shaft 4210 in parallel or substantially parallel to the rotating shaft of the secondary transfer backup roller 34.

  Further, side plates 422 and 422 are attached to both ends of the rotating shaft 421, respectively. More specifically, each of these side plates 422 and 422 has a shape in which a notch 422a is provided on a disk-shaped metal plate. As shown in FIG. 3, the notches 422 a and 422 a are attached to the rotating shaft 421 while facing each other and separated by a distance slightly longer than the width of the intermediate transfer belt 31. In this way, the roller base material 42 is formed, which has a drum shape as a whole but has a concave portion 41 extending in parallel or substantially parallel to the rotating shaft 421 on a part of the outer peripheral surface thereof.

  Further, an elastic layer 43 such as rubber or resin is formed on the outer peripheral surface of the roller base material 42, that is, on the surface region of the metal plate surface excluding the region corresponding to the inside of the recess 41. The elastic layer 43 forms a transfer nip NP so as to face the intermediate transfer belt 31 wound around the backup roller 34. In the transfer nip NP, a predetermined load (60 kgf in this embodiment) is applied between the secondary transfer roller 4 and the intermediate transfer belt 31 wound around the backup roller 34.

  In addition, a grip 44 for gripping the recording material RM is disposed inside the recess 41. The gripping portion 44 includes a gripper support member 441 erected on the outer peripheral surface of the roller base 42 from the inner bottom portion of the recess 41, and a gripper member 442 that is supported so as to be able to come into contact with and separate from the distal end portion of the gripper support member 441. And have. The gripper member 442 is connected to a gripper driving unit (not shown). In response to the ungrip command from the controller 10, the gripper driving unit is actuated so that the leading end of the gripper member 442 is separated from the leading end of the gripper support member 441, and the recording material RM is gripped and released. On the other hand, when the gripper driving unit is operated in response to a grip command from the controller 10, the leading end of the gripper member 442 moves to the leading end of the gripper support member 441 and grips the recording material RM. In addition, about the structure of the holding part 44, it is not limited to this embodiment, You may employ | adopt other conventionally well-known holding mechanisms.

  At both ends of the secondary transfer roller 4, support members 46 are attached to the outer surfaces of the side plates 422 so that they can rotate integrally with the roller base material 42. Further, the support member 46 is formed with a planar region 461 corresponding to the recess 41. The transfer roller side contact member 470 is attached to the flat area 461, respectively. In the contact member 470, the base part 471 is attached to the support member 46, and the contact part 472 extends from the base part 471 in the normal direction of the planar region 461, and the distal end portion of the contact part 472 Extends to the vicinity of the opening side end of the recess 41. That is, when the roller base material 42 is viewed from the end of the rotating shaft 421, the contact member 470 is disposed so as to close the recess 41. Therefore, when the concave portion 41 reaches a position facing the intermediate transfer belt 31 by the rotation of the secondary transfer roller 4, the contact member 470 comes into contact with the end surface of the secondary transfer backup roller 34.

  Further, as shown in FIG. 3B, the tip peripheral surface of the contact portion 472 is formed such that the curvature Rct of the central portion of the peripheral surface on the tip side is larger than the curvatures Rrs and Rls of both ends. . For example, in this embodiment, the roller outer diameter of the roller base material 42 including the elastic layer 43 is set to about 191 mm, whereas the curvature Rct is set to 88.2 mm, and the curvatures Rrs and Rls at both ends are both. It is set to 22.4 mm. The center of curvature CC of the center portion of the contact portion 47 is disposed on the rotation axis of the roller base material 42, that is, the center axis 4210 of the rotation shaft 421, and the angle range α of the center portion is the opening range (60 ° of the recess 41). ) Is set to 63 °, which is slightly wider than). For this reason, when the secondary transfer roller 4 rotates, the concave portion 41 faces the intermediate transfer belt 31 wound around the drive roller 32 over the angular range α.

In addition, the opening length (opening width) W41 of the recess 41 along the rotation direction D4 of the roller base material 42 is:
191 × π × (60/360) ≈100 mm
It is. On the other hand, in the angle range β (= 360 ° -60 °), the elastic sheet 43 faces the intermediate transfer belt 31 to form a nip NP as described below, and follows the rotation direction D4 of the roller base material 42. The length of the elastic layer 43 is
191 × π × {(300/360} ≈500 mm
Is set to This is so that the largest size of the recording material RM usable in the apparatus 1 can be wound. That is, the length of the elastic layer 43 is determined to be longer than the length of the usable recording material having the maximum length along the rotation direction D4 of the roller base material 42.

In this embodiment, the length (nip width) Wnp of the nip NP along the rotation direction D4 of the roller base material 42 is about 11 mm,
(Opening width W41 of recess 41)> (nip width Wnp at nip NP)
Have the relationship. Therefore, when the concave portion 41 of the secondary transfer roller 4 faces the intermediate transfer belt 31, the transfer nip temporarily disappears.

  In this state, and the secondary transfer backup roller 34 is configured to be movable toward and away from the secondary transfer roller 4, the recess 41 of the secondary transfer roller 4 faces the intermediate transfer belt 31. Then, there is a possibility that the secondary transfer roller 34 is displaced to the secondary transfer roller 4 side. The contact member 47 has a function of restricting such displacement of the secondary transfer roller 34.

  FIG. 4 is a view for explaining the operation of the contact member in this embodiment. More specifically, FIG. 4A is a view of the contact member 47 viewed from the axial direction when the concave portion 41 faces the secondary transfer position TR2, and FIG. 4B shows this in the axial direction. It is the figure seen from the orthogonal direction. As shown in FIG. 4A, the shape of the outer peripheral surface of the contact member 47 is a substantially arc shape centered on the rotation center 4210 of the secondary transfer roller 4 in the region facing the recess 41 of the secondary transfer roller 4. It has become. On the other hand, the end of the secondary transfer backup roller 34 has an outer diameter larger than the diameter of the secondary transfer backup roller 34, is coaxial with the secondary transfer backup roller 34, and is rotatable independently of this. The bearing 342 is provided. When the contact member 47 of the secondary transfer roller 34 faces the secondary transfer roller 34, the outer peripheral surface of the contact member 47 and the outer peripheral surface of the bearing 342 come into contact with each other, so that the secondary transfer roller 4 defines the distance between the rotation center 4210 of the fourth roller and the surface of the intermediate transfer belt 31.

  The elastic layer 43 forms an interval R0 from the rotation center 4210 of the secondary transfer roller 4 to the intermediate transfer belt 31 when the recess 41 is located at the secondary transfer position TR2 and the contact member 47 is in contact with the bearing 342. The radius Rr of the secondary transfer roller 4 is set to be slightly smaller. More precisely, the interval R0 is set to be the same as the interval between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 in a state where the transfer nip NP is formed at the secondary transfer position TR2. . When the transfer nip NP is formed, the elastic layer 43 is pressed against the intermediate transfer belt 31 and elastically deforms. Therefore, a pressing force is applied to the interval between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31. It is slightly smaller than the radius Rr of the secondary transfer roller 4 in a state where it is not. In this state, that is, in a state where the transfer nip NP is formed, the interval between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 is R0. Therefore, in this embodiment, the interval between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 is maintained at a substantially constant value R0 regardless of the rotation phase of the secondary transfer roller 4.

  A transfer roller drive motor M4 is mechanically connected to the rotation shaft 421 of the secondary transfer roller 4. In the present embodiment, a driver 12 is provided to drive the transfer roller drive motor M4. The driver 12 drives the motor M4 in accordance with a command given from the controller 10 to rotate the secondary transfer roller 4 in the clockwise direction D4 in FIG. 1, that is, in the width direction with respect to the belt moving direction D31. The secondary transfer backup roller 34 is a driven roller having no drive source. By using the secondary transfer backup roller 34 facing the secondary transfer roller 4 driven by the motor as a driven roller, between the secondary transfer roller 4 and the intermediate transfer belt 31 in the transfer nip NP, or with the intermediate transfer belt 31. Slip with the secondary transfer backup roller 34 can be prevented.

  In the present embodiment, an AC servomotor is used as the motor M4, and the position of the AC servomotor can be controlled by the driver 12 or the torque can be controlled. That is, the driver 12 has a position control circuit and a torque control circuit, and can selectively execute position control and torque control. The controller 10 can input a command pulse related to position information, a command torque related to torque information, and a control switching signal to the driver 12.

  2 is an encoder attached to the transfer roller drive motor M4, and a signal corresponding to the rotation of the transfer roller drive motor M4 is given to the driver 12, and the driver 12 that has received the signal is based on the above signal. The motor M4 is feedback-controlled. Reference numeral 8 denotes a phase detection sensor connected to one end of the rotation shaft 421 of the secondary transfer roller 4, and the controller 10 grasps the rotation phase of the secondary transfer roller 4 from the output of the phase detection sensor 8. can do.

  Returning to FIG. 1, the description of the device configuration will be continued. Among the rollers around which the intermediate transfer belt 31 is stretched, the rollers 33 and 35 provided at positions sandwiching the transfer nip NP are elastically supported by springs 331 and 351, respectively, of the rotation shafts of the intermediate transfer belt 31. It is a tension roller that adjusts the tension. More specifically, the rotation shaft of the tension roller 33 is elastically supported by a spring 331 that can expand and contract in a substantially horizontal direction, so that the tension roller 33 is substantially in a state where the intermediate transfer belt 31 is wound. A predetermined amount can be moved in the horizontal direction.

  In addition, the rotation shaft of the tension roller 35 is elastically supported by a spring 351 that can expand and contract in a direction substantially perpendicular to a virtual plane that is in contact with both the outer peripheral surface of the drive roller 32 and the outer peripheral surface of the secondary transfer backup roller 34. As a result, the tension roller 35 is movable by a predetermined amount in the same direction while the intermediate transfer belt 31 is wound around. In a steady state, the tension roller 35 is urged by a spring 351 so as to push the intermediate transfer belt 31 stretched between the belt driving roller 32 and the secondary transfer backup roller 34 outward. Yes.

  At the secondary transfer position TR2, when the surface of the secondary transfer roller 4 facing the intermediate transfer belt 31 is switched from the elastic layer 43 to the recess 41 with the rotation of the secondary transfer roller 4, the recess is reversed. When switching from 41 to the elastic layer 43, the load torque of the belt drive motor M3 that drives the belt drive roller 32 varies greatly. The fluctuation is particularly large when a high pressing force is applied between the elastic layer 43 and the intermediate transfer belt 31. Due to this, it is conceivable that the speed fluctuation and vibration of the intermediate transfer belt 31 occur, and the tension of the belt 31 changes temporarily.

  However, in this embodiment, the tension roller 35 provided between the belt driving roller winding position and the secondary transfer position TR2 along the tension direction of the intermediate transfer belt 31 and the primary transfer downstream of the secondary transfer position TR2. The tension roller 33 provided on the upstream side of the transfer position TR1y acts so as to cancel the variation in tension by moving the rotation shaft thereof. For this reason, the speed fluctuation and vibration of the intermediate transfer belt 31 at the secondary transfer position TR2 are prevented from reaching the primary transfer position TR1 corresponding to each image forming station 2Y, 2M, 2C and 2K. The speed fluctuation or vibration of the intermediate transfer belt 31 at the primary transfer position TR1 disturbs the toner image transferred from the image forming station and deteriorates the image quality. It is prevented beforehand.

  Both of the tension rollers 33 and 35 are in contact with the intermediate transfer belt 31 from the inner side of the intermediate transfer belt 31, that is, from the back side opposite to the surface that is the image carrying surface of the intermediate transfer belt 31. The reason is as follows. First, the contact with the opposite side of the image carrying surface causes the tension rollers 33 and 35 to disturb the toner image carried on the intermediate transfer belt 31, or conversely, it is soiled by toner remaining on the intermediate transfer belt 31. There is nothing. In order to increase the tension adjustment effect by the tension roller, it is effective to increase the winding angle of the intermediate transfer belt 31, but the tension roller is brought into contact with the image carrying surface and the winding angle is increased. If it is going to be, it is necessary to give the surface of the intermediate transfer belt 31 a large negative curvature, there is a concern about the influence on the toner image, and there is a structural problem. For these reasons, the tension rollers 33 and 35 are in contact with the back surface of the intermediate transfer belt 31.

  Further, in this apparatus 1, the belt driving roller 32 and the tension roller are arranged so that the surface of the intermediate transfer belt 31 is substantially horizontal between the downstream of the tension roller 33 and the upstream of the belt driving roller 32 in the belt moving direction D31. 33 is arranged. The primary transfer position TR1 for each image forming station is arranged on the same plane formed by the surface of the intermediate transfer belt 31 (more specifically, the lower surface to which the toner image is transferred). Furthermore, the moving direction of the rotation shaft of the tension roller 33 is also set to be substantially horizontal. For this reason, even if the tension roller 33 moves in order to absorb speed fluctuations and vibrations, the surface of the intermediate transfer belt 31 is kept horizontal, and the influence on image formation can be minimized. Although it is not essential that the surface of the intermediate transfer belt 31 is horizontal in the vicinity of the image forming station, it is desirable that at least the moving direction of the surface of the belt 31 and the moving direction of the tension roller 33 are the same or substantially the same.

  As for the tension roller 35, the belt driving roller 32 is interposed between the tension transfer roller 35 and the primary transfer position TR1, so that the moving direction is not restricted in image formation. Therefore, the intermediate transfer belt 31 is most subject to speed fluctuations and vibrations by moving in a direction substantially perpendicular to a virtual plane that contacts both the outer peripheral surface of the drive roller 32 and the outer peripheral surface of the secondary transfer backup roller 34. It can be effectively reduced.

  In addition, a cleaner unit 39 is provided in the vicinity of the intermediate transfer belt 31 wound around the tension roller 33 so as to be able to come into contact with and separate from the surface of the intermediate transfer belt 31. The cleaner unit 39 cleans the intermediate transfer belt 31 by scraping off the toner remaining on the surface of the intermediate transfer belt 31. The cleaner unit 39 is supported integrally with the rotation shaft of the tension roller 33 supported by the spring 331, and is displaced according to the displacement of the tension roller 33. For this reason, the relative position between the cleaner unit 39 and the intermediate transfer belt 31 does not change. As such a structure, for example, the structure described in Japanese Patent Application Laid-Open No. 2009-169354 previously disclosed by the applicant of the present application can be applied.

  Next, the operation of the image forming apparatus 1 configured as described above will be described with reference to FIGS. FIG. 5 is a timing chart showing an operation example of the image forming apparatus of FIG. FIG. 6 is a diagram schematically showing the operation of the image forming apparatus of FIG. In this image forming apparatus 1, when an image formation command for forming a color image is given to the controller 10 from an external device such as a host computer, the controller 10 follows a program stored in a memory (not shown). Control each part of the device. First, the belt drive motor M3 and the transfer roller drive motor M4 are operated to drive the intermediate transfer belt 31 and the secondary transfer roller 4, respectively.

  The phase detection sensor 8 (FIG. 2) provided on the secondary transfer roller 4 is formed from a cylindrical peripheral surface in which the surface of the secondary transfer roller 4 facing the intermediate transfer belt 31 at the secondary transfer position TR2 has an elastic layer 43. An H level signal is temporarily output each time when switching to the recess 41 and when switching from the recess 41 to the elastic layer 43. The controller 10 alternately switches the drive control mode of the secondary transfer roller 4 by the driver 12 between position control and torque control based on the change in the signal level. More specifically, the position control is performed when the concave portion 41 of the secondary transfer roller 4 faces the intermediate transfer belt 31, and the torque is generated when the elastic layer 43 faces the intermediate transfer belt 31 and the transfer nip NP is formed. Control is performed. Note that the position of the belt drive motor M3 is always controlled, and the surface of the intermediate transfer belt 31 rotates at a predetermined moving speed.

  When the output of the phase detection sensor 8 changes at the timing tA0 and the secondary transfer roller 4 facing the secondary transfer position TR2 changes from the recess 41 to the elastic layer 43 to form the transfer nip NP, the controller 10 switches the control. The drive control mode by the driver 12 is switched to torque control according to the signal, and the command torque is applied to the driver 12 to torque control the secondary transfer roller 4. Further, with the timing tA0 as an exposure start point, a toner image is formed at each of the image forming stations 2Y, 2M, 2C, and 2K, and the toner image is primarily transferred onto the surface of the intermediate transfer belt 31.

  That is, as shown in FIG. 5, when the time Ta elapses from the timing tA0, latent image formation by the exposure unit 23 is started in the image forming station 2Y based on various signals from the controller 10, and a toner image is formed with yellow toner. The Further, when the time Tb elapses from the start of the yellow exposure, the magenta exposure is started. When the time Tc elapses from the start of the magenta exposure, the cyan exposure is started, and the time Td from the start of the cyan exposure is started. When elapses, black exposure is started. Thus, the toner images of the respective colors are formed and are sequentially superimposed on the intermediate transfer belt 31 to form a full color toner image TI on the surface of the intermediate transfer belt 31.

  While the toner images of the respective colors are formed in this way, the secondary transfer roller 4 further rotates one turn in the rotation direction D4, and the transfer nip NP that has been once eliminated is formed again. When a predetermined time Te elapses from this timing tA1, the controller 10 inputs a command pulse to a driver (not shown) that controls a gate roller drive motor (not shown) connected to the gate roller 51 to operate the gate roller drive motor. Let Thereby, the conveyance of the recording material RM to the secondary transfer position TR2 is started (FIG. 6A).

  Further, when the secondary transfer roller 4 facing the secondary transfer position TR2 changes to the concave portion 41 and the transfer nip is eliminated, the controller 10 changes the drive control mode by the driver 12 from the torque control by the control switching signal at the timing tB2. While switching to position control, a command pulse is given to the driver 12. As a result, the secondary transfer roller 4 rotates in the rotation direction D4 and moves to a predetermined recording material gripping position (FIG. 6B). Further, the leading end of the gripper member 442 is separated from the leading end of the gripper support member 441, and the preparation for gripping the recording material RM is completed. Then, the leading end of the recording material RM fed by the gate roller 51 enters between the gripper member 442 and the gripper support member 441, and a paper gripping operation is started (FIG. 6B). Here, for convenience of explanation, it is referred to as “paper holding operation”, but as described above, the recording material RM is not limited to paper.

  The controller 10 gives a grip command to the gripper driving unit (not shown) at the same time or slightly delayed from the timing tB2. In response to this gripping command, the gripper drive unit operates to move the tip of the gripper member 442 to the tip of the gripper support member 441. As a result, the leading end of the recording material RM is gripped, and the “paper holding operation” is completed (FIG. 6C). At the time when the “paper holding operation” is completed, the toner image TI is located upstream of the secondary transfer position TR2 in the moving direction D31 of the surface of the intermediate transfer belt 31, as shown in FIG. 6C.

  In this way, the recording material RM is conveyed in the rotational direction D4 together with the secondary transfer roller 4 with its leading end held by the holding portion 44. At the timing tA2 when the elastic layer 43 on the surface of the secondary transfer roller 4 reaches the secondary transfer position TR2 and the formation of the transfer nip NP is started, the recording material RM includes the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt. 31 is nipped in a transfer nip NP between the surface 31 and conveyed along with these rotations. Thereby, secondary transfer of the toner image TI formed on the intermediate transfer belt 31 to the lower surface (front surface) of the recording material RM is started (FIG. 6D). Further, at this timing tA2, the controller 10 switches the drive control mode by the driver 12 to torque control by the control switching signal and gives the command torque to the driver 12 to control the torque of the secondary transfer roller 4.

  The secondary transfer roller 4 rotates in the rotational direction D4 while being torque controlled in this way, and accordingly, the recording material RM passes between the transfer nips NP while the leading end portion is held by the grip portion 44, and the toner image TI. Secondary transfer proceeds. When the grip 44 moves to a position near the upstream end (the right end in FIG. 1) of the transport roller 7, the leading end of the recording material held by the grip 44 is an intermediate transfer belt. It has been sufficiently separated from 31 and conveyed to the conveyance entrance of the conveyance roller 7. As shown in FIG. 6 (e), the controller 10 gives a release command to the gripper drive unit at the timing when the grip 44 moves to the vicinity of the upstream end of the transport roller 7, and the tip of the gripper member 442 is moved to the gripper. The recording material RM is released from being separated from the distal end portion of the support member 441. As a result, the leading end portion of the recording material RM is surely sent to the fixing unit 7 without being attached to the surface of the intermediate transfer belt 31 (FIG. 6F). Then, the fixing unit 7 fixes the color toner image TI to the recording material RM. After the release, the leading end side of the recording material is conveyed to the fixing unit side along the conveying path PT, and the trailing end side of the recording material RM is connected to the elastic layer 43 of the secondary transfer roller 4 at the transfer nip NP. The secondary transfer process is executed while being nipped and conveyed by the intermediate transfer belt 31.

  As described above, in this embodiment, the images formed by the plurality of image forming stations 2Y, 2M, 2C, and 2K are primarily transferred and superimposed on the intermediate transfer belt 31 that is stretched around the plurality of rollers 32 to 35. The recording material RM is passed through a transfer nip NP formed by bringing the secondary transfer roller 4 into contact with the intermediate transfer belt 31 at a position different from the image forming position (that is, the primary transfer position TR1) by these image forming stations. Thus, the image is secondarily transferred to the recording material RM.

  During this time, the distance between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 is maintained at a substantially constant value R0. However, the timing at which the surface of the secondary transfer roller 4 located at the intermediate transfer position TR2 is switched from the concave portion 41 to the elastic layer 43, and the timing at which the surface is switched from the elastic layer 43 to the concave portion 41, and the rear end portion of the recording material RM are Regarding the timing of passing through the transfer nip NP, the object with which the secondary transfer roller 4 abuts changes. Further, when the surface of the secondary transfer roller 4 located at the intermediate transfer position TR2 is switched from the recess 41 to the elastic layer 43, torque for elastically deforming the elastic layer 43 in addition to torque for rotating the secondary transfer roller 4 Is required. On the other hand, when switching from the elastic layer 43 to the recess 41, torque for deforming the elastic layer 43 is not necessary. Due to these factors, it is inevitable that the load torque of the secondary transfer roller drive motor M4 varies.

  Further, when viewed from the intermediate transfer belt 31, while the elastic layer 43 of the secondary transfer roller 4 is in contact with the surface of the intermediate transfer belt 31, the driving force of the secondary transfer roller driving motor M <b> 4 is indirectly passed through the secondary transfer roller 4. On the other hand, when the concave portion 41 of the secondary transfer roller 4 faces, the transmission of the force is interrupted. Due to these, at each timing described above, vibration may occur in the intermediate transfer belt 31 that is stretched over the plurality of rollers 32 to 35. If such vibration is transmitted to the primary transfer position TR1, image formation at the primary transfer position TR1 may be disturbed.

  In particular, when the secondary transfer backup roller 34 facing the secondary transfer roller 4 is used as a driving roller for driving the intermediate transfer belt 32 to rotate, the secondary transfer roller 4 and the secondary transfer backup roller 34 Even a slight speed difference (more precisely, a difference in the peripheral speed of the surface between the secondary transfer roller 4 and the intermediate transfer belt 31) can cause slippage and vibration of the intermediate transfer belt 31. Since the elastic layer 43 provided on the surface of the secondary transfer roller 4 and the intermediate transfer belt 31 are elastically deformed, it is extremely difficult to completely eliminate the peripheral speed difference between the secondary transfer roller 4 and the intermediate transfer belt 31. .

  If the secondary transfer roller and the backup roller facing each other are driven independently, they may interfere with each other or slip between the secondary transfer roller and the intermediate transfer belt. Further, speed unevenness due to a difference in friction coefficient may occur between when the recording material RM is present in the transfer nip NP and when it is not. On the other hand, if a roller other than the backup roller is a belt drive roller, such a problem can be avoided. Therefore, in this embodiment, the secondary transfer backup roller 34 is a driven roller, and a different roller 32 is a belt driving roller.

  Further, the intermediate transfer belt 31 is wound around the belt driving roller 32 between the primary transfer position TR1 and the secondary transfer position TR2, so that the vibration of the intermediate transfer belt 31 generated at the secondary transfer position TR2 is transmitted to the belt driving roller 32. It is possible to prevent the signal from being transferred to the primary transfer position TR1. That is, the belt driving roller 32 driven by the motor M3 also has a function of blocking the vibration generated at the secondary transfer position TR2.

  Further, in this embodiment, the fluctuation in the tension of the intermediate transfer belt 31 generated at the secondary transfer position TR2 is absorbed by the tension rollers 33 and 35 around which the intermediate transfer belt 31 is wound. At this time, since the fluctuation is absorbed by the swing of the tension rollers 33 and 35 supported by the spring, the position of the tension rollers 33 and 35 is changed by the swing, and the tension path of the intermediate transfer belt 31 is Will fluctuate. In particular, the change in the stretching path from the primary transfer position TR1 to the secondary transfer position TR2, that is, the swing of the tension roller 35, causes the toner image transferred at each image forming station to be conveyed to the secondary transfer position TR2. This leads to a change in the length of the transport path until the end. This can be a problem in the alignment of the recording material RM sent to the secondary transfer position TR2 and the toner image TI in the image forming operation described above.

  That is, in order for the toner image TI to be correctly transferred to a predetermined position of the recording material RM, the toner is determined by the timing at which the recording material RM is gripped by the gripping portion 44 and sent to the transfer nip NP and the rotation of the intermediate transfer belt 31. It is necessary to synchronize with a certain correlation with the timing at which the image TI is sent to the transfer nip NP. However, if the transport path length of the toner image up to the transfer nip NP fluctuates, this synchronization cannot be achieved, and as a result, the image transfer position on the recording material RM varies. In particular, in a configuration in which gripping of the recording material RM is started when the concave portion 41 of the secondary transfer roller 4 is positioned at the secondary transfer position TR2 and the transfer nip NP is eliminated, the intermediate transfer belt 31 is configured to be the secondary transfer roller 31. 4, the tension roller 35 takes a long time to converge, and the intermediate transfer belt 31 at the secondary transfer position TR2 is likely to cause speed fluctuations and vibrations. Therefore, the above-described transfer position deviation is likely to occur.

  Therefore, in this embodiment, the blade-like contact body 347 is brought into contact with the surface of the secondary transfer backup roller 34 which is a driven roller and is not originally restricted in rotation. Since the blade-like contact body 347 acts as a load with respect to the rotation of the secondary transfer backup roller 34, the rotation of the secondary transfer backup roller 34 is braked compared to the case where the corresponding contact body 34 is not provided. It will be. Therefore, the secondary transfer backup roller 34 is free to rotate even when the recess 41 is located at the secondary transfer position TR2 and the intermediate transfer belt 31 is released from the pressure by the secondary transfer roller 4. In addition, the speed fluctuation of the intermediate transfer belt 31 wound around the roller 34 is also suppressed.

  That is, since the movement of the intermediate transfer belt 31 is restrained by braking the rotation of the secondary transfer backup roller 34, the kinetic energy when the tension roller 35 swings is consumed and the swing converges in a short time. It will be. If the position of the tension roller 35 has returned to the position in the steady state before the secondary transfer process is started, there will be a problem of displacement of the transfer position on the recording material due to fluctuations in the transport path length of the toner image. Absent. Thus, the effect of converging the swing extends to the other tension roller 33 as well.

  As described above, in this embodiment, among the plurality of rollers 32 to 35 that span the intermediate transfer belt 31, a roller 32 that is different from the secondary transfer backup roller 34 that faces the secondary transfer roller 4 is used as a belt drive roller. By doing so, the intermediate transfer belt 31 is prevented from slipping or vibrating due to the peripheral speed difference between the secondary transfer roller 4 and the intermediate transfer belt 31. In addition, a blade-like contact body 347 that absorbs fluctuations and vibrations in tension caused by the difference in peripheral speed by the tension rollers 33 and 35 and brakes the rotation of the secondary transfer backup roller 34 is provided. By doing so, the intermediate transfer belt 31 acts as a load against the swinging of the tension rollers 33 and 35 even when released from the pressure by the secondary transfer roller 4. For this reason, the swinging of the tension rollers 33 and 35 can be converged in a short time, and image disturbance at the primary transfer position TR1 and displacement of the toner image onto the recording material RM at the secondary transfer position TR2 can be prevented. This can be prevented beforehand.

  In the above configuration in which the blade-like contact body 347 is in contact with the secondary transfer backup roller 34, the displacement itself of the tension rollers 33 and 35 is not regulated, so the effect of suppressing the tension variation of the tension roller is sacrificed. Will not do. Note that the contact body that brakes the rotation of the secondary transfer backup roller 34 is not limited to the blade-shaped member described above, and may be a roller-shaped contact body.

  Next, a second embodiment of the image forming apparatus according to the present invention will be described. In the apparatus 1 of the first embodiment described above, the rotation of the secondary transfer backup roller 34 is braked by bringing the blade-like contact body 347 into contact with the surface of the secondary transfer backup roller 34. On the other hand, in the apparatus 1a of the second embodiment described below, a torque limiter is provided on the rotating shaft 341 of the secondary transfer backup roller 34 instead of the contact body to the secondary transfer backup roller 34.

  FIG. 7 is a view showing a main part of a second embodiment of the image forming apparatus according to the present invention. As shown in FIG. 7, in the image forming apparatus 1 a of this embodiment, a contact body that contacts the secondary transfer backup roller 34 is not provided. Instead, torque is applied to the rotating shaft 341 of the secondary transfer backup roller 34. A limiter 348 is installed. The torque limiter 348 has a function of regulating the rotation of the secondary transfer backup roller 34 when a large rotational torque exceeding a predetermined torque is applied to the rotary shaft 341. Various products are commercially available as torque limiters to be mounted on such a rotating shaft, and the structures thereof are well-known. Such well-known structures can be applied to this embodiment as well, so a detailed description will be given here. Is omitted.

  Further, the configuration and operation of the device 1a of the second embodiment excluding the above points are basically the same as those of the device 1 of the first embodiment. Therefore, the same components are denoted by the same reference numerals and description thereof is omitted. Moreover, the effect which 1st Embodiment described above show | plays is obtained similarly also in the apparatus 1a of 2nd Embodiment. However, in this embodiment, the secondary transfer backup roller 34 to which the torque limiter 348 is attached acts as a load for the swinging of the tension rollers 33 and 35 and consumes kinetic energy to converge the swinging. . As a result, in this embodiment, it is possible to effectively prevent image distortion at the primary transfer position TR1 and transfer position shift to the recording material at the secondary transfer position TR2.

  Next, a third embodiment of the image forming apparatus according to the present invention will be described. In the apparatus 1 of the first embodiment and the apparatus 1a of the second embodiment described above, the kinetic energy of the tension roller is consumed and the oscillation is converged by braking the rotation of the secondary transfer backup roller 34. On the other hand, in the third embodiment described below, the swinging of the tension rollers 33 and 35 is not restricted, but the rotation is braked to converge the swinging in a short time.

  FIG. 8 is a view showing a third embodiment of the image forming apparatus according to the present invention. An image forming apparatus 1b according to the third embodiment also has the same basic configuration and operation as those of the first embodiment. Therefore, in the following description, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted, and description will be made focusing on differences from the first embodiment. This also applies to the description of the image forming apparatus 1c of the fourth embodiment described later.

  In this embodiment, the contact body to the secondary transfer backup roller 34 is omitted. On the other hand, a squeeze roller 357 is brought into contact with the intermediate transfer belt 31 wound around the tension roller 35. The squeeze roller 357 is applied with a positive potential (about +200 to 600 V) that is the same polarity as the charging polarity of the toner, and the squeeze roller 357 causes the squeeze roller 357 to transfer the positively charged toner constituting the toner image to the intermediate transfer belt 31. The fog toner and the carrier liquid charged to the opposite polarity while being left on are removed from the intermediate transfer belt 31.

  The rotation shaft of the squeeze roller 357 is configured to be displaced integrally with the rotation shaft of the tension roller 35 and is always in contact with the surface of the intermediate transfer belt 31, but does not restrict the displacement of the tension roller 35. Absent. On the other hand, when the squeeze roller 357 is pressed and becomes a load, the rotation of the tension roller 35 that is a driven roller is restricted. For this reason, after the tension roller 35 is displaced due to temporary fluctuations in the tension of the intermediate transfer belt 31, the squeeze roller 357 is loaded and consumes kinetic energy when the tension roller 35 swings due to the elasticity of the spring 351. In addition, the swing can be converged in a short time.

  On the other hand, a cleaner unit 39 having a cleaning blade 391 that comes into contact with the intermediate transfer belt 31 wound around the roller 33 is provided for the other tension roller 33, and the cleaner unit 39 serves as a load. An effect of converging the swing of the tension roller 33 is achieved.

  As described above, in the image forming apparatus 1b according to the third embodiment, by swinging the rotation of the two tension rollers 33 and 35, the swing can be converged in a short time. As a result, in this embodiment, it is possible to effectively prevent image distortion at the primary transfer position TR1 and transfer position shift to the recording material at the secondary transfer position TR2.

  Note that such a member for braking may be disposed on only one of the two tension rollers. Further, the tension roller 33 provided on the downstream side of the secondary transfer position TR2 may be made to act as a load by contacting the roller in addition to or instead of the blade 391. In this embodiment, the members (the cleaning blade 391 and the squeeze roller 357) that are originally brought into contact with the intermediate transfer belt 31 wound around the tension rollers 33 and 35 for other purposes also function as a swing load. However, it may be in direct contact with the surface of the tension roller.

  FIG. 9 shows a fourth embodiment of the image forming apparatus according to the present invention. In the image forming apparatus 1 c according to this embodiment, the spring constant is different between the spring 331 that supports the tension roller 33 and the spring 351 that supports the tension roller 35. Therefore, the natural frequency is different between the two tension rollers 33 and 35. For example, when the spring constant of the spring 351 that supports the tension roller 35 is 1 N / mm, the spring constant of the spring 331 that supports the other tension roller 33 can be set to a larger 6 N / mm. The ratio may not be a simple integer ratio.

  When the spring constants of the two springs 331 and 351 are the same, it may take a long time for the two tension rollers to be alternately displaced and the oscillation to converge. On the other hand, by making the spring constants of the springs supporting the tension roller different from each other, the other tension roller acts as a load with respect to the swing of one tension roller. Thereby, the oscillation converges in a short time.

  From the viewpoint of effectively absorbing the tension fluctuation of the intermediate transfer belt 31 generated at the secondary transfer position TR2 and suppressing the change in the transport path length of the toner image due to the swing of the tension roller. As described above, the tension roller provided on the toner image conveyance path, that is, the spring that supports the other tension roller 33 provided outside the conveyance path is larger than the spring constant of the spring 351 that supports the tension roller 35. It is preferable that the constant is larger. This is because it is preferable to reduce the spring constant of the spring 351 in order to absorb the tension fluctuation of the intermediate transfer belt 31, but it is on the toner image conveyance path by increasing the spring constant of the spring 331. This is because the load on the tension roller 35 is increased to make it easier to converge the oscillation.

  As described above, in the image forming apparatus 1c according to the fourth embodiment, the spring constants of the springs 331 and 351 that support the two tension rollers 33 and 35 are set to different values, so that one is a load with respect to the other swing. It is possible to act and converge the oscillation in a short time. As a result, in this embodiment, it is possible to effectively prevent image distortion at the primary transfer position TR1 and transfer position shift to the recording material at the secondary transfer position TR2. Further, since the rotation of any roller is not restricted, it is not necessary to increase the driving torque for driving the intermediate transfer belt 31 in a steady state.

  As described above, in each of the above embodiments, the intermediate transfer belt 31 functions as the “image carrier” of the present invention, while the image forming stations 2Y, 2M, 2C, and 2K are the “first image forming device” of the present invention. Part "and" second image forming part ". In each of the above embodiments, the belt drive roller 32 functions as the “drive roller” of the present invention, while the secondary transfer backup roller 34 functions as the “first roller” of the present invention. The secondary transfer roller 4 functions as the “transfer roller” of the present invention, and the transfer roller drive motor M4 that drives the secondary transfer roller 4 functions as the “drive unit” of the present invention. In addition, the grip portion 44 functions as a “grip portion” of the present invention.

  In addition, the blade-like contact body 347 in the first embodiment functions as the “restricting member” of the present invention, while the torque limiter 348 in the second embodiment functions as the “torque limiter” and “restricting member” of the present invention. ing. These all function as the “braking part” of the present invention.

  In the first and second embodiments, the tension rollers 33 and 35 function as the “second roller” of the present invention. The squeeze roller 357 in the third embodiment functions as the “squeeze roller” of the present invention when the tension roller 35 is the “second roller” of the present invention, while the cleaner unit in the same embodiment No. 39 functions as the “cleaning member” of the present invention when the tension roller 33 is the “second roller” of the present invention. All of these functions as the “braking part” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, two tension rollers are provided with the secondary transfer position TR2 interposed therebetween, but in the first to third embodiments, one tension roller may be provided.

  Further, for example, in each of the above embodiments, four image forming stations are arranged in a line along the stretching direction of the intermediate transfer belt 31, but the number and arrangement of the image forming stations are not limited thereto. The present invention can be applied to all image forming apparatuses including two or more image forming stations.

  In each of the above embodiments, the intermediate transfer belt 31, the belt driving roller 32, the secondary transfer backup roller 34, the secondary transfer roller 4, the tension rollers 33 and 35, and the like are integrated as a transfer unit of the present invention. 3 is constituted. In this case, it is not essential for the transfer unit to include a drive source for driving the transfer roller or the drive roller. For example, when the transfer unit is mounted, a motor fixed to the apparatus main body side is connected to the transfer roller or the drive roller. You may be comprised so that it may function as a drive source by engaging with a roller.

  Further, in each of the above-described embodiments, the image forming apparatus is a so-called liquid development type that uses a developer in which toner is dispersed in a liquid carrier. However, the application target of the present invention is not limited to that type. That is, regardless of the development method, as illustrated in FIG. 1, for an image forming apparatus in general having a structure in which a transfer roller having a surface shape in which a part of a cylindrical peripheral surface is notched is brought into contact with an intermediate transfer belt. Thus, the present invention can be applied.

  2Y, 2M, 2C, 2K ... image forming station (first image forming unit, second image forming unit), 4 ... secondary transfer roller (transfer roller), 31 ... intermediate transfer belt (image carrier), 32 ... belt drive roller (drive roller), 34 ... secondary transfer backup roller (first roller), 33 ... tension roller (second roller, braking part), 44 ... gripping part, 35 ... tension roller (second roller) Roller), 39 ... cleaner unit (cleaning member, braking part), 347 ... blade-like contact body (regulating member, braking part), 348 ... torque limiter (regulating member, braking part), 357 ... squeeze roller (braking part) M3 ... Belt drive motor, M4 ... Transfer roller drive motor (drive unit), NP ... Transfer nip, RM ... Recording material, TR1 ... Next transfer position, TR2 ... secondary transfer position

Claims (7)

A belt-like image carrier for carrying an image;
A first image forming unit that transfers a first image to the image carrier;
A second image forming unit that transfers a second image to the image carrier onto which the first image has been transferred;
A driving roller that wraps around the image carrier onto which the first image and the second image have been transferred, and drives the image carrier to go around;
A first roller for winding the image carrier driven by the driving roller;
A transfer roller that has a recess in a part of the peripheral surface, and the peripheral surface contacts the image carrier wound around the first roller via a recording material;
A gripping part disposed in the recess for gripping the recording material;
A drive unit that rotationally drives the transfer roller;
A second roller that winds the image carrier and applies tension to the image carrier;
An image forming apparatus comprising: a braking unit that brakes at least one of the first roller and the second roller. The second roller is disposed at a position where the image carrier wound around the driving roller is wound, and the first roller winds the image carrier wound around the second roller. Is located at a position,
The image forming apparatus according to claim 1, wherein the braking unit is a squeeze roller that contacts the second roller via the image carrier.   2. The cleaning unit is a cleaning member that comes into contact with the second roller disposed at a position where the image carrier wound around the first roller is wound via the image carrier. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the braking unit is a regulating member that regulates rotation of the first roller.   The image forming apparatus according to claim 4, wherein the regulating member is in contact with the first roller.   The image forming apparatus according to claim 4, wherein the restriction member is a torque limiter disposed on a rotation shaft of the first roller. A belt-like image carrier onto which an image is transferred;
A drive roller that wraps around the image carrier to which the image has been transferred and drives the image carrier to go around;
A first roller for winding the image carrier driven by the driving roller;
A transfer roller that has a recess in a part of the peripheral surface, and the peripheral surface contacts and drives the image bearing member wound around the first roller via a recording material;
A gripping part disposed in the recess for gripping the recording material onto which the image is transferred;
A second roller that winds the image carrier and applies tension to the image carrier;
A transfer device comprising: a braking unit that brakes at least one of the first roller and the second roller.

Images