JP5407729B2 - Transfer device and image forming apparatus - Google Patents

Description

  The present invention relates to a transfer device that transfers an image formed on an image carrier to a recording medium, and an image forming apparatus equipped with the device.

  In the field of image forming technology for forming an image on a recording material such as paper, a secondary transfer roller is brought into contact with an image carrier such as an intermediate transfer belt for temporarily carrying an image to form a transfer nip. Some are configured to transfer an image onto a recording material by passing the recording material through a transfer nip. For example, in a liquid developing type image forming apparatus described in Patent Document 1, a backup roller is brought into contact with a drum-shaped intermediate transfer medium under a certain load, and a sheet is passed through a nip formed in this manner to perform intermediate transfer. The toner image on the medium is pressure-transferred to the paper.

JP 2002-156839 A (for example, FIG. 1) JP 2000-238400 A (for example, FIG. 1) Japanese Unexamined Patent Publication No. 2000-33686 (for example, FIG. 1)

  When the contact pressure applied to the recording material at the nip increases, a problem that the recording material sticks to the image carrier tends to occur. In order to prevent this, it has been proposed to use a transfer device used in a stencil printing apparatus. The reason is as follows.

  In the stencil printing apparatus, an impression cylinder provided with a paper clamper that holds the leading edge of the paper is provided as a transfer device. In other words, the impression cylinder (corresponding to the “transfer roller” of the present invention) is positioned at a fixed position with respect to the plate cylinder around which the master made from the plate is wound. The impression cylinder is rotated by a driving force applied from a driving unit such as a motor while the leading end of the sheet is held by a sheet clamper, and ink printing is performed (for example, see Patent Document 2). For this reason, the printed paper is satisfactorily peeled from the plate cylinder on the downstream side of the pressing position without sticking to the plate cylinder, despite using high viscosity ink. Therefore, it is conceivable to configure the secondary transfer roller in the same manner as the above-described impression cylinder, that is, to provide a gripping portion for gripping the recording medium with respect to the secondary transfer roller. In the apparatus configured as described above, the recording medium that has passed through the nip is peeled off from the intermediate transfer belt by driving the secondary transfer roller while gripping the leading end portion (non-image portion) of the recording medium with the gripping portion. It becomes possible to do.

  However, in this type of image forming apparatus, in order to transfer an image onto a recording medium having various thicknesses, for example, the secondary transfer roller is pressed toward the intermediate transfer belt and the intermediate transfer belt is interposed via the recording medium. Is transferred with a constant load. Therefore, it is necessary to adopt the constant load method even when the transfer device described in Patent Document 2 is diverted. Further, it is necessary to provide a concave portion on the outer peripheral surface of the secondary transfer roller and to arrange a gripping portion in the concave portion. In other words, while the concave portion faces the intermediate transfer belt, it is necessary to hold the recording medium in a state where the outer peripheral surface of the secondary transfer roller is separated from the surface of the intermediate transfer belt.

Thus, for example, it has been proposed to provide a bearer described in Patent Document 3 (corresponding to the “first support portion” of the present invention). More specifically, by providing the bearer at a position corresponding to the concave portion with respect to the rotation shaft end portion of the secondary transfer roller, the secondary transfer roller is excellent while the concave portion faces the intermediate transfer belt. It becomes possible to support. In addition, the contact period and the separation period are as follows by installing the bearer so that the peripheral end of the bearer partially overlaps the peripheral surface of the secondary transfer roller when viewed from the direction of the rotation axis. Switch to That is, during switching from the separation period to the contact period,
(A) The support state of the secondary transfer roller only by the bearer,
(B) A state where the support of the secondary transfer roller by the bearer and the contact of the secondary transfer roller with the intermediate transfer belt coexist.
(C) The support release state in which the support of the secondary transfer roller by the bearer is released switches in order. Further, when the separation period is switched to the contact period, the recording medium is conveyed toward the nip, and the leading end of the recording medium enters between the intermediate transfer belt and the secondary transfer roller.

  By the way, in the image forming apparatus, since the image is transferred to the recording medium having various thicknesses as described above, the peripheral surface of the secondary transfer roller comes into contact with the intermediate transfer belt via the recording medium according to the thickness of the recording medium. The timing is different. For example, when a relatively thick recording medium is conveyed, the contact timing is earlier than when a relatively thin recording medium is conveyed. Further, the contact timing differs even when the case where the recording medium is conveyed and the case where the recording medium is not conveyed are compared. Then, as will be described later with reference to FIG. 10, when the secondary transfer roller is supported by a contact member such as a bearer at each contact timing, the secondary transfer roller becomes an image carrier. The load fluctuation at the time of abutting on is different. Therefore, the speed fluctuation of the secondary transfer roller varies depending on the presence or absence and the thickness of the recording medium, which may impede stable image transfer to the recording medium.

  Some embodiments according to the present invention include a transfer device that transfers an image formed on an image carrier to a recording medium using a transfer roller having a recess on a part of the peripheral surface, and an image forming apparatus equipped with the device. In the apparatus, to solve the above-described problem, to obtain a stable transfer image by suppressing variation in load fluctuation when the peripheral surface of the transfer roller contacts the image carrier regardless of the presence and thickness of the recording medium. Provide technology.

  One aspect of the transfer device according to the present invention is an image carrier that carries an image, a concave portion provided on a peripheral surface, and a peripheral surface different from the concave portion and an image carrier and a recording medium that are in contact with each other while rotating. A transfer roller for transferring the image carried on the carrier to the recording medium, a pressing part for pressing the transfer roller against the image carrier, and a position corresponding to the recess in the axial direction of the transfer roller and rotating together with the transfer roller A first support portion and a second support portion that contacts the first support portion when the concave portion faces the image carrier and when a peripheral surface different from the concave portion of the transfer roller and the image carrier abut via the recording medium And a first support portion that contacts the second support member from a position where the concave portion faces the image carrier to a position where the peripheral surface different from the concave portion of the transfer roller and the image carrier contacts via the recording medium The shape of the contact surface is the rotation of the first support The amount of change in the distance to the abutment surface of the first supporting portion from the center of rotation of the transfer roller in the unit rotation angle per direction is characterized in that it is configured so as to be constant or approximately constant.

  According to another aspect of the image forming apparatus of the present invention, an image forming unit that forms an image, an image carrier that carries an image formed by the image forming unit, and a concave portion are provided on the peripheral surface, which are different from the concave portion. A transfer roller that contacts the peripheral surface, the image carrier, and the recording medium while rotating through the recording medium and transfers the image carried on the image carrier to the recording medium, a pressing unit that presses the transfer roller against the image carrier, and a transfer A first support portion that is provided at a position corresponding to the concave portion in the axial direction of the roller and rotates together with the transfer roller, and a recording device that records the peripheral surface and the image carrier different from the concave portion of the transfer roller when the concave portion faces the image carrier. A second support portion that contacts the first support portion when contacting through the medium, and the peripheral surface different from the recess portion of the transfer roller and the image carrier from the position where the recess faces the image carrier. 2nd support to the position where it abuts via The shape of the abutment surface of the first support portion that abuts the material is the amount of change in the distance from the rotation center of the transfer roller to the abutment surface of the first support portion per unit rotation angle in the rotation direction of the first support portion. Is configured to be constant or substantially constant.

  In the invention thus configured (transfer device and image forming device), the transfer roller having a concave portion on the peripheral surface rotates while being pressed toward the image carrier by the pressing portion. Further, a first support portion is provided at a position corresponding to the concave portion in the axial direction of the transfer roller and rotates together with the transfer roller. A part of the peripheral surface of the first support part is the second support part when the concave part faces the image carrier and when the peripheral surface different from the concave part of the transfer roller and the image carrier abut via the recording medium. To support the transfer roller. In addition, the contact of the first support portion that contacts the second support member from the position where the recess faces the image carrier to the position where the peripheral surface different from the recess of the transfer roller and the image carrier contacts via the recording medium. The shape of the surface is configured such that the amount of change in the distance from the rotation center of the transfer roller to the contact surface of the first support portion per unit rotation angle in the rotation direction of the first support portion is constant or substantially constant. ing. Therefore, even if the contact timing between the peripheral surface of the transfer roller and the image carrier (including the case of contact via the recording medium) slightly varies depending on the presence or absence of the recording medium and the thickness thereof, the first support to the second support portion is performed. The support state of the transfer roller by the contact of the support portion is constant or substantially constant, and the load fluctuation when the transfer roller contacts the image carrier is constant. As a result, it is possible to stabilize the image transfer from the image carrier to the recording medium by suppressing variations in the speed fluctuation of the transfer roller.

  Here, the first elastic layer may be provided on a peripheral surface different from the concave portion of the transfer roller, whereby the transferability of the image formed on the image carrier to the recording medium can be enhanced.

  In addition, a second elastic layer may be disposed on the contact surface of the first support portion, and an impact generated when the first support portion contacts the second support portion due to the elastic force of the second elastic layer. It is absorbed by the elastic force of the second elastic layer. Further, when the first elastic layer is provided on a peripheral surface different from the concave portion of the transfer roller, it is preferable to provide the second elastic layer on the contact surface of the first support portion. The reason is as follows. While the transfer roller provided with the first elastic layer abuts the image carrier, a load is applied to the image carrier by the first elastic layer, while the load is eliminated while the concave portion faces the image carrier. However, when the second elastic layer is provided on the contact surface of the first support portion, the second elastic layer contacts the second support portion and another load is applied to the image carrier while the concave portion faces the image support member. Given to. Thus, the difference between the load applied to the image carrier during the period in which the concave portion faces the image carrier (opposite period) and the period in which the concave portion does not face (non-opposition period) can be suppressed, and the load generated during transfer The fluctuation can be further suppressed.

  Furthermore, the distance from the rotation center when the concave portion faces the image carrier to the contact surface of the first support is arbitrary, but for example, the first from the rotation center when the transfer roller contacts the image carrier. You may comprise so that it may become shorter than the distance to the contact surface of a support part.

1 is a diagram showing an 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 perspective view which shows the whole structure of a secondary transfer roller. FIG. 2 is a first diagram schematically showing the operation of the image forming apparatus in FIG. 1. FIG. 3 is a second diagram schematically showing the operation of the image forming apparatus in FIG. 1. The figure which shows the shape of the outer peripheral surface of the contact member (1st support part) in this embodiment. FIG. 4 is a diagram illustrating a distance between a rotation center of a secondary transfer roller and an intermediate transfer belt. The figure which shows the change aspect of the distance of the rotation center of a secondary transfer roller, and an intermediate transfer belt. The figure which shows typically the nip start state according to the presence or absence and thickness of a recording medium. The figure which shows typically the nip start state in a comparative example. FIG. 6 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 5 is a diagram showing another embodiment of the image forming apparatus according to the present invention.

  FIG. 1 is a diagram showing an 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 medium RM such as paper, transfer paper, paper, and an OHP transparent sheet. As described above, in this embodiment, the image forming stations 2Y, 2M, 2C, and 2K correspond to the “image forming unit” of the present invention.

  Each of the image forming stations 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. The photosensitive drums 21 are arranged such that the rotation axis thereof is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 1), and a predetermined speed is indicated in the direction of arrow D21 in FIG. Is driven to rotate.

  Around each 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 by exposing the surface of the photosensitive drum 21 according to an image signal. An exposure unit 23 that forms an image, a developing unit (developing unit) 24 that visualizes the electrostatic latent image as a toner image, a first squeeze unit 25, a second squeeze unit 26, and a transfer of the toner image A primary transfer portion 27 that performs primary transfer onto the intermediate transfer belt 31 of the unit 3, a cleaning unit that cleans the surface of the photosensitive drum 21 after transfer, and a cleaner blade are each in the order of rotation D 21 of the photosensitive drum 21. (Clockwise in FIG. 1).

  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 positive 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 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 embodiment, it is not a volatile liquid developer that is generally used in the past and has a low concentration (1-2 wt%) and low viscosity at room temperature using Isopar (trademark: Exon) as a carrier liquid. A solid particle 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, is placed in a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. A liquid developer having a high viscosity (about 30 to 10,000 mPa · s) which is added together with a dispersant and has a toner solid content concentration of about 20% is used.

  A first squeeze portion 25 is disposed on the downstream side of the developing position in the rotation direction D 21 of the photosensitive drum 21, and a second squeeze portion 26 is disposed on the downstream side of the first squeeze portion 25. The squeeze rollers 25 and 26 are respectively provided with squeeze rollers. 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 images that have passed through the squeeze portions 25 and 26 are primarily transferred to the intermediate transfer belt 31 by the primary transfer portion 27. 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 stretched around a plurality of rollers 32 and 33. 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 embodiment, a driver 11 is provided to drive the belt drive motor M3. The driver 11 sends a drive signal corresponding to a command pulse given from the controller 10 to the belt drive motor M3. Output. As a result, the belt driving roller 32 rotates at a rotational speed corresponding to the command pulse, and the surface of the intermediate transfer belt 31 moves in the direction D31 at a constant speed V3. 2 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 and 33 around which the intermediate transfer belt 31 is stretched, only the belt drive roller 32 described above is driven by the motor, and the other rollers 33 are driven not having a drive source. It is a roller. The driven roller 33 is a tension roller that adjusts the tension of the intermediate transfer belt 31 with its rotating shaft elastically supported by a spring 331. 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. Note that the number of rollers that are stretched over the intermediate transfer belt 31 is not limited to “2”, and the intermediate transfer belt 31 may be stretched over three or more rollers. The rollers other than the driving roller 32 are driven rollers.

  The primary transfer unit 27 includes a backup roller 271 and a winding roller 272. The backup roller 271 is disposed at the primary transfer position TR 1 so as to face the photosensitive drum 21 with the intermediate transfer belt 31 interposed therebetween, and is in contact with the photosensitive drum 21 via the intermediate transfer belt 31. Further, a winding roller 272 is provided on the downstream side of the contact position in the belt moving direction D31, and the intermediate transfer belt 31 is pushed toward the photosensitive drum 21 to form a winding portion on the downstream side of the backup roller 271. doing. Further, a primary transfer bias applying unit (not shown) is electrically connected to the backup roller 271, and a predetermined primary transfer bias is applied to transfer the toner image on the photosensitive drum 21 to the intermediate transfer belt 31. To do. Then, the toner image is transferred by the primary transfer portion 27 of each color, whereby the toner images of each color on the photosensitive drum 21 are sequentially superimposed on the intermediate transfer belt 31 to form a full color toner image. Thus, in this embodiment, the intermediate transfer belt 31 configured as described above corresponds to the “image carrier” of the present invention.

  The toner image thus transferred to the intermediate transfer belt 31 is conveyed to the secondary transfer position TR2 as shown in FIG. At the secondary transfer position TR2, the transfer device according to the present invention is arranged. That is, the secondary transfer roller 4 of the transfer device (corresponding to the “transfer portion” of the present invention) is disposed opposite to the intermediate transfer belt 31 wound around the drive roller 32 of the transfer unit 3. Further, the rotation shaft 421 of the secondary transfer roller 4 is supported elastically by a pressing portion 45 that is an elastic member such as a coil spring, and can be moved toward and away from the intermediate transfer belt 31.

  Then, at the secondary transfer position TR2, a single-color or multiple-color toner image formed on the intermediate transfer belt 31 is transferred from the pair of gate rollers 51, 51 to the recording medium RM that is transported along the transport path PT. The 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, a secondary transfer roller 4 having a grip portion is used as will be described in detail later. ing.

  The recording medium RM on which the toner image is secondarily transferred is sent from the secondary transfer roller 4 to the transport mechanism 6 along the transport path PT. In the transport mechanism 6, the first suction unit 61, the transfer material transport unit 62, and the second suction unit 63 are sequentially arranged along the transport path PT, and these cooperate to transport the recording medium RM to the fixing unit 7. To do.

  In addition, when the recording medium RM on which the toner image is secondarily transferred is sent to the transport mechanism 6, in order to surely send the recording medium RM to the first suction unit 61 and to prevent image staining, Then, the blower unit 9 is arranged so as to face the secondary transfer roller 4 between the secondary transfer position TR2 and the first suction part 61. In the blower unit 9, the secondary transfer roller 4 (a gripping to be described later) is performed by discharging air from the opening 93 of the housing 92 generated in accordance with the operation of the airflow generating unit 91 as indicated by a white arrow. Air is blown to the leading end of the recording medium RM released from the gripping by the portion 44), and the leading end is pushed out and pressed away from the secondary transfer roller 4 by a claw (not shown). Thus, the leading end portion of the recording medium RM is fed toward the first suction portion 61. Further, when air is blown onto the recording medium RM, when the rear end of the recording medium RM is discharged from the secondary transfer position TR2, the rear end of the recording medium RM touches the intermediate transfer belt 31 and the like, and the image is stained. Can be prevented. In the case of the recording medium RM having a small elastic restoring force and a weak waist, the air blowing by the blower unit 9 can be omitted.

  Further, a fixing unit 7 is disposed on the downstream side of the transport path PT, that is, on the side opposite to the secondary transfer roller 4 with respect to the transport mechanism 6 (left hand side in FIG. 1), and is transferred to the recording medium RM. The toner image is fixed to the recording medium RM by applying heat, pressure, or the like to the single color or multiple color toner images.

  FIG. 3 is a perspective view showing the overall configuration of the secondary transfer roller. As shown in FIGS. 1 and 3, 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 a cylinder. In this roller base material 42, the rotation shaft 421 that is rotatable in the direction D 4 is arranged at the rotation center 4210 of the rotation shaft 421 so as to be parallel or substantially parallel to the rotation shaft of the drive roller 32 and driven by the pressing portion 45. A predetermined load (60 kgf in this embodiment) is applied by being biased toward the roller 32 side. Further, side plates 422 and 422 are attached to both ends of the rotation 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 recess 41 extending in parallel or substantially in parallel with the rotation 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 drive roller 32.

  In addition, a grip 44 for gripping the recording medium 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 medium RM is prepared for gripping or 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 medium RM. In addition, about the structure of the holding part 44, it is not limited to this embodiment, A conventionally well-known holding | grip mechanism can be employ | adopted.

  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 47 is attached to the flat area 461, respectively. In the abutting member 47, the base part 471 is attached to the support member 46, and the abutting part 472 extends from the base part 471 in the normal direction of the planar region 461, and the distal end portion of the abutting part 472 Extends to the opening side end of the recess 41. That is, when the contact member 47 is viewed from the direction of the rotation shaft 421, the contact member 47 closes the recess 41, and the peripheral end of the contact portion 472 is the peripheral surface of the secondary transfer roller 4 (elastic layer 43. The contact member 47 is rotatably provided with the axis of the rotation shaft 421 as the rotation center 4210 so as to partially overlap with the rotation center 4210.

  Further, as will be described later, bearings 322 that are coaxial with the drive roller 32 and rotatable independently of the drive roller 32 are provided at both ends of the drive roller 32 around which the intermediate transfer belt 31 is wound (see FIGS. 6 and 7). ) Is provided. In this embodiment, the diameter of each bearing 322 is set to {(diameter of the drive roller 32) + (thickness of the intermediate transfer belt 31) × 2}. As shown in FIG. 6, the intermediate transfer belt 31 wound around the drive roller 32 overlaps the bearing 322. When the contact member 47 of the secondary transfer roller 4 faces the drive roller 32, the outer peripheral surface of the contact member 47 and the outer peripheral surface of the bearing 322 are in contact with each other, so Against this, the distance R1 between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 is defined. Thus, in this embodiment, the contact member 47 functions as the “first support portion” of the present invention, and the bearing 322 functions as the “second support portion” of the present invention.

In this embodiment, the opening length (opening width) W41 of the recess 41 along the rotation direction D4 of the roller base material 42 is about 105 mm. When the elastic layer 43 formed in the region excluding the concave portion 41 on the outer peripheral surface of the secondary transfer roller 4 is in a position facing the intermediate transfer belt 31, the elastic layer 43 is pressed against the intermediate transfer belt 31 and the transfer nip NP. Is formed. The length (transfer nip width) Wnp of the transfer nip NP along the rotation direction D4 of the roller base material 42 is about 11 mm,
(Opening width W41 of the recess 41)> (transfer nip width Wnp at the transfer 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.

  The length of the elastic layer 43 along the rotation direction D4 of the roller base material 42 is set to about 495 mm, and this is the largest size of the recording medium RM that can be used in the apparatus 1 is wound. It is something that can be done. That is, the length of the elastic layer 43 is determined to be longer than the length of the usable recording paper whose length along the rotation direction D4 of the roller base material 42 is the maximum.

  A transfer roller drive motor M4 is mechanically connected to the rotation shaft 421 of the secondary transfer roller 4. In this embodiment, a driver 12 is provided to drive the transfer roller drive motor M4 as shown in FIG. 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. Further, the contact member 47 together with the secondary transfer roller 4 also rotates about the rotation center 4210 in the rotation direction D4.

  In the present embodiment, the driver 12 outputs a drive signal corresponding to the command pulse given from the controller 10 to the motor M4. As a result, the transfer roller rotates at a rotation speed corresponding to the command pulse.

  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. The controller 10 passes the recording medium RM through the transfer nip NP based on the output of the phase detection sensor 8. It is possible to grasp the timing.

  4 and 5 are diagrams schematically showing the operation of the image forming apparatus shown in FIG. The operation of the image forming apparatus 1 configured as described above will be described with reference to FIGS. 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.

  Then, the phase detection sensor 8 (FIG. 2) provided on the secondary transfer roller 4 has a cylindrical circumference 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 the surface is switched to the recess 41 and when the recess 41 is switched to the elastic layer 43. That is, in the phase detection sensor 8, as shown in FIGS. 4 and 5, the disk-shaped slit plate 81 is connected to the rotation shaft 421 of the secondary transfer roller 4 and rotates together with the rotation shaft 421. The slit plate 81 has slits 811 and 812 formed at two locations. Among these, the slit 811 is for detecting the nip elimination position, that is, the position where the elastic layer 43 is separated from the intermediate transfer belt 31, whereas the slit 812 is the nip start position, that is, the elastic layer 43 is located at the intermediate transfer belt 31. This is for detecting the position where the transfer nip NP is formed by starting to abut. Further, in the phase detection sensor 8, a sensor element 82 for detecting these slits 811 and 812 is fixedly arranged, and each time the slits 811 and 812 are located in the detection range of the sensor element 82, the controller 82 controls the controller 82. The level of the signal output to 10 changes from the L level to the H level, and the nip release position and the nip start position can be detected. Therefore, the start of passage of the recording medium RM to the transfer nip NP is detected when the slit 812 is positioned within the detection range of the sensor element 82.

  When the output of the phase detection sensor 8 changes at a predetermined timing and the secondary transfer roller 4 changes from the concave portion 41 to the elastic layer 43 at the secondary transfer position TR2, the transfer nip NP is formed, and this timing is used as an exposure start start point. Then, 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, when a predetermined time has elapsed from the above timing, 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. In addition, magenta exposure is started after yellow exposure is started, cyan exposure is started after magenta exposure is started, and black exposure is started after cyan 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 in the rotation direction D4, and the transfer nip NP that has been once eliminated is formed again. When a predetermined time has elapsed from this timing, 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. As a result, conveyance of the recording medium RM to the secondary transfer position TR2 is started (FIG. 4A).

  When the secondary transfer roller 4 changes to the concave portion 41 at the secondary transfer position TR2 and the transfer nip is eliminated, the slit 811 is positioned in the detection range of the sensor element 82 and is output from the sensor element 82 to the controller 10. The signal level changes from L level to H level. In response to this signal, the controller 10 gives a command pulse to the driver 12. As a result, the secondary transfer roller 4 rotates in the rotation direction D4 and moves to a predetermined recording paper gripping position (FIG. 4B). 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 medium RM is completed. Then, the leading end of the recording medium RM sent by the gate roller 51 enters between the gripper member 442 and the gripper support member 441, and a paper holding operation is started.

  The controller 10 gives a grip command to a gripper driving unit (not shown). 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 edge of the recording medium RM is gripped, and the “paper holding operation” is completed (FIG. 4C). 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.

  In this way, the recording medium RM is conveyed in the rotational direction D4 together with the secondary transfer roller 4 while the leading end is gripped by the gripping portion 44. At the timing when the elastic layer 43 on the surface of the secondary transfer roller 4 reaches the secondary transfer position TR2 and the transfer nip NP starts to be formed, a slit is formed in the detection range of the sensor element 82 as shown in FIG. The level of a signal output from the sensor element 82 to the controller 10 when 812 is positioned changes from L level to H level.

  Then, the leading end portion of the recording medium RM is sandwiched between the transfer nip NP formed by the secondary transfer roller 4 and the intermediate transfer belt 31, and is conveyed along with the rotation thereof. Thereby, the secondary transfer of the toner image TI formed on the intermediate transfer belt 31 to the lower surface (front surface) of the recording medium RM is started (FIG. 4D).

  Further, the secondary transfer roller 4 rotates in the rotation direction D4, and accordingly, the recording medium RM passes between the transfer nips NP while the front end is held by the grip portion 44, and the secondary transfer of the toner image TI is performed. Progresses (FIG. 5A). When the grip 44 moves to a position near the transport mechanism 6, the leading end of the recording paper held by the grip 44 is sufficiently separated from the intermediate transfer belt 31 and reaches the transport entrance of the transport mechanism 6. Has been transported. As shown in FIG. 5B, the controller 10 gives a release command to the gripper drive unit at the timing when the gripping part 44 has moved to the vicinity of the upstream end of the transport mechanism 6, and the tip of the gripper member 442 is moved to the gripper. The holding of the recording medium RM is released away from the tip of the support member 441. As a result, the leading end of the recording medium RM is reliably fed into the transport mechanism 6 without sticking to the surface of the intermediate transfer belt 31. Then, the color toner image TI is fixed onto the recording medium RM by the fixing unit 7 disposed behind the transport mechanism 6. After the release, the leading end side of the recording medium RM is conveyed to the fixing unit side along the conveying path PT, and the trailing end side of the recording medium RM is the transfer nip NP at the elastic layer 43 of the secondary transfer roller 4. And the intermediate transfer belt 31, and the secondary transfer process is executed.

  In the image forming apparatus 1 that performs the above-described operation, since the secondary transfer roller 4 has a shape in which a part of its peripheral surface is cut out, the transfer nip NP is periodically formed with the rotation thereof. Or temporarily resolved. More specifically, when the recess 41 faces the drive roller 32 and the nip NP is not formed, the outer peripheral surface of the contact member 47 contacts the outer peripheral surface of the bearing 322 to support the secondary transfer roller 4. The distance between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 is defined. As described above, the front end of the recording medium RM is gripped while the nip NP is not formed, and the secondary transfer roller 4 and the contact member 47 are integrally rotated to move the front end of the recording medium RM. It is sandwiched between the elastic layer 43 on the circumferential surface of the secondary transfer roller 4 and the intermediate transfer belt 31 and enters the transfer nip NP. As described above, the leading end of the recording medium RM enters between the elastic layer 43 and the intermediate transfer belt 31, and the timing at which the two come into contact with each other via the recording medium RM depends on the thickness of the recording medium RM. Further, the contact timing of the recording medium RM when the recording medium RM is not conveyed, that is, the formation timing of the transfer nip NP is also different from that when the recording medium RM is conveyed. Therefore, the same problem as described in the section “Problems to be solved by the invention” can also occur in this embodiment. In other words, when no special consideration is given to the configuration of the contact member 47, particularly the shape of the peripheral end of the contact portion 472, the secondary transfer roller 4 is moved by the intermediate transfer belt depending on the presence or absence of the recording medium RM and the thickness. As a result, the variation in the speed of the secondary transfer roller 4 may hinder stable image transfer to the recording medium.

  Therefore, in this embodiment, the variation in the speed variation of the secondary transfer roller 4 is suppressed by devising the shape of the peripheral surface of the contact member 47 depending on the presence / absence and thickness of the recording medium RM. Hereinafter, the peripheral shape of the abutting member 47 and the effects obtained by adopting the peripheral surface shape will be described in detail with reference to FIGS. 6 to 10.

  FIG. 6 is a view showing the shape of the outer peripheral surface of the contact member in this embodiment. For the purpose of simply keeping the distance between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 when the recess 41 faces the drive roller 32, as shown by the broken line in FIG. What is necessary is just to make the outer peripheral surface of the contact member 47 make the circular arc centering on the rotation center 4210 of the secondary transfer roller 4. In contrast, in the present embodiment, the central portion 47a of the outer peripheral surface of the contact member 47 has an arc shape centered on the rotation center 4210 of the secondary transfer roller 4, while the end portions 47b and 47c thereof are the following. It is formed in a shape that satisfies the relationship. That is, with respect to the outer peripheral surface end 47b positioned on the upstream side in the rotation direction D4 of the contact member 47 and the secondary transfer roller 4, the periphery of the contact member 47 from the rotation center 4210 per unit rotation angle in the rotation direction D4. The amount of change in the distance R1 to the surface (= dR1 / dθ) is finished to be a constant value a1. Further, the peripheral surface end portion 47c located on the downstream side is finished so that the amount of change in the distance R1 (= dR1 / dθ) becomes a constant value a2. In order to facilitate understanding, FIG. 6 exaggerates the amount of change (= dR1 / dθ) so as to be clear. The reason for this shape will be described below.

  FIG. 7 is a diagram illustrating the distance between the rotation center of the secondary transfer roller and the intermediate transfer belt. Further, FIG. 8 is a diagram showing how the distance between the rotation center of the secondary transfer roller and the intermediate transfer belt changes. In this embodiment, since the rotating shaft 421 of the secondary transfer roller 4 is supported by the pressing portion 45 so as to be able to come into contact with and separate from the intermediate transfer belt 31, the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 are supported. Is not constant, and varies periodically according to the rotation of the secondary transfer roller 4. First, when the elastic layer 43 of the secondary transfer roller 4 is pressed against the intermediate transfer belt 31 to form the transfer nip NP, as shown in FIG. 7A, the rotation center 4210 of the secondary transfer roller 4 and The distance R 0 with the intermediate transfer belt 31 is substantially equal to the original radius Rr of the secondary transfer roller 4, that is, the distance Rs from the rotation center 4210 to the surface of the elastic layer 43. In this embodiment, the radius Rr of the secondary transfer roller 4 is set to 95 mm, and the distance Rs from the rotation center 4210 of the secondary transfer roller 4 to the elastic layer 43 is a concave portion 41 as shown by a thick solid line in FIG. Except for the radius Rr (= 95 mm), which is abruptly shortened at both ends of the recess 41 (θ = 5 (deg), 68 (deg)). Here, in the transfer nip NP, since the elastic layer 43 is crushed by an amount corresponding to the pressing force to reduce the thickness, the distance R0 is slightly shorter than the radius Rr, but from the rotation center 4210 to the intermediate transfer belt 31. In this specification, the distance R0 is equal to the distance Rr.

  On the other hand, in a state where the concave portion 41 faces the driving roller 32 and the transfer nip NP is eliminated, the contact member 47 attached to the secondary transfer roller 4 and the bearing 322 attached to the driving roller 32 are respectively connected. Abutting each other on the outer peripheral surface, the distance between the rotation center 4210 of the secondary transfer roller 4 and the intermediate transfer belt 31 is defined. The distance at this time is determined by the shape of the contact member 47 and the bearing 322. However, since the bearing 322 has a disk shape, the rotation center 4210 of the secondary transfer roller 4 is substantially determined by the outer peripheral shape of the contact member 47. And the intermediate transfer belt 31 are determined.

  Here, as shown in FIG. 7B, the contact member 47 is on an imaginary straight line (two-dot chain line in the figure) connecting the rotation center 4210 of the secondary transfer roller 4 and the rotation shaft 321 of the drive roller 32. The rotation angle of the secondary transfer roller 4 when the downstream end is positioned at zero (deg). When the secondary transfer roller 4 and the contact member 47 are integrally rotated by 73 (deg), the upstream end of the contact member 47 is positioned on the virtual straight line. Of this rotation angle range (0 to 73 (deg)), the angle range AR1 of the angle 0 to θ1 corresponds to the downstream outer peripheral surface end portion 47c of the contact member 47, and the angle range AR2 of the angles θ1 to θ2. Corresponds to the central portion 47a of the outer peripheral surface of the contact member 47, and the angle range AR3 of the angle θ2 to 73 (deg) corresponds to the upstream outer peripheral surface end portion 47b of the contact member 47. In each of the angle ranges AR1 to AR3, the secondary transfer roller 4 comes into contact with the intermediate transfer belt 31 as follows. The outer peripheral surface of the contact member 47 is formed so that the distance R1 from the rotation center 4210 of the secondary transfer roller 4 to the outer peripheral surface of the contact member 47 changes according to the angle θ as will be described below. However, in FIG. 8, the change of the distance R1 with respect to the angle θ is indicated by a one-dot chain line.

Angle range AR1
At angle = 0 (deg), the distance R1 from the rotation center 4210 to the peripheral surface of the contact member 47 is shorter than the radius Rr (95 mm in this embodiment) of the secondary transfer roller 4. Accordingly, the elastic layer 43 of the secondary transfer roller 4 contacts the intermediate transfer belt 31 to form the transfer nip NP, whereas the downstream outer peripheral surface end 47 c of the contact member 47 is separated from the bearing 322. ing. As the angle θ increases, the proportional constant a2 becomes longer, and coincides with the radius Rr of the secondary transfer roller 4 at a predetermined angle (4 (deg) in the present embodiment). At this time, the downstream outer peripheral surface end 47 c of the contact member 47 contacts the bearing 322. Further, when the secondary transfer roller 4 and the contact member 47 are rotated in the rotation direction D4, the recess 41 is opposed to the intermediate transfer belt 31, and the distance R1 is proportionally increased as the angle θ increases. At the time when θa is reached, the distance R1 is longer than the radius Rr of the secondary transfer roller 4 by about 0.4 mm, and the secondary transfer roller 4 is 0.4 mm from the intermediate transfer belt 31 while being supported by the contact member 47. Only apart upwards. Thus, in the present embodiment, the shape of the downstream outer peripheral surface end 47c of the contact member 47 is the distance R1 from the rotation center 4210 to the peripheral surface of the contact member 47 per unit rotation angle in the rotation direction D4. The amount of change (= dR1 / dθ) is a constant value a2.

Angle range AR2
In the angle range AR2, as shown in FIG. 8, the distance R1 is maintained at a constant value (95.4 mm). That is, in this embodiment, the shape of the outer peripheral surface central portion 47a of the contact member 47 is the amount of change in the distance R1 from the rotation center 4210 to the peripheral surface of the contact member 47 per unit rotation angle in the rotation direction D4 (= dR1 / dθ) is zero. Therefore, in the angle range AR2, the secondary transfer roller 4 is supported by the contact member 47 and floats upward by 0.4 mm from the intermediate transfer belt 31. It is rotated as a rotation center 4210.

Angle range AR3
When the rotation angle θ of the secondary transfer roller 4 reaches the predetermined angle θb, the distance R1 decreases with the proportionality constant a1 as the angle θ increases. That is, at the angle θ = θb, as shown in FIG. 8, the distance R 1 is 0.4 mm longer than the radius Rr of the secondary transfer roller 4, and the upstream outer peripheral surface end 47 b of the contact member 47 contacts the bearing 322. The secondary transfer roller 4 is in contact with and supports the secondary transfer roller 4, and the secondary transfer roller 4 is separated from the intermediate transfer belt 31 by 0.4 mm upward. When the secondary transfer roller 4 and the contact member 47 rotate in the rotation direction D4, the distance R1 decreases as the angle θ increases, and the secondary transfer is performed at a predetermined angle (about 69 (deg) in the present embodiment). It coincides with the radius Rr of the roller 4. At this time, the upstream outer peripheral surface end 47 b of the contact member 47 starts to contact the bearing 322. Further, when the secondary transfer roller 4 and the contact member 47 are rotated in the rotation direction D4, the concave portion 41 is separated from the intermediate transfer belt 31 and the distance R1 is proportionally shortened as the angle θ is increased. The elastic layer 43 comes into contact with the intermediate transfer belt 31 and starts to form the transfer nip NP. On the other hand, the distance R 1 is shorter than the radius Rr of the secondary transfer roller 4, and the contact member 47 is separated from the bearing 322. Thus, in this embodiment, the shape of the upstream outer peripheral surface end 47b of the contact member 47 is the distance R1 from the rotation center 4210 to the peripheral surface of the contact member 47 per unit rotation angle in the rotation direction D4. The amount of change (= dR1 / dθ) is a constant value a1. In this state where the recording medium RM is not conveyed (when no paper is present), in this embodiment, the secondary transfer roller 4 starts to contact the intermediate transfer belt 31 at the contact timing of the angle θ = 69 (deg). The amount of change in the distance R1 (= dR1 / dθ) at about −0.20.

  By the way, when the recording medium RM is conveyed and enters the transfer nip NP between the secondary transfer roller 4 and the intermediate transfer belt 31, the contact timing is when the recording medium RM is not conveyed (when no paper is present). ) Will be faster. The contact timing also varies depending on the thickness of the recording medium RM. For example, as shown in FIG. 9, when the contact timing is examined under the conditions of (a) no paper, (b) thin paper (about 0.05 mm thick), and (c) thick paper (about 0.15 mm thick), The angle θ = 69 (deg) is the contact timing, the angle θ = about 68.7 (deg) is the contact timing for thin paper, and the angle θ = about 68.2 (deg) is the contact timing for thick paper. Yes. As described above, although the contact timing varies depending on the presence or absence and the thickness of the recording medium RM, in this embodiment, the amount of change in the distance R1 from the rotation center 4210 to the peripheral surface of the contact member 47 per unit rotation angle in the rotation direction D4. (= DR1 / dθ) is a constant value a1. Therefore, even if the contact timing is different, the amount of change in the distance R1 (= dR1 / dθ) at each contact timing is approximately −0.20, and the speed of the secondary transfer roller 4 at the time of contact. Variation in fluctuation can be suppressed.

  Here, in order to clarify the operational effects of the present embodiment, a comparative example will be exemplified and described. FIG. 10 is a diagram schematically showing a nip start state in the comparative example. In the figure, the broken line shows an example of the shape of the upstream outer peripheral surface end 47b of the contact member 47, and the change amount (= dR1 / dθ) of the distance R1 continuously changes. When the contact member 47 having such a shape is used, the contact timing is as follows: (a) no paper, (b) thin paper (about 0.05 mm thick), and (c) thick paper (about 0.15 mm thick). When the paper is not used, the angle θ = about 70.1 (deg) is the contact timing, when the paper is thin, the angle θ = about 69.9 (deg) is the contact timing, and when the paper is thick, the angle θ = about 69.5. (deg) is the contact timing. As described above, the contact timing varies depending on the presence / absence and thickness of the recording medium RM, and the amount of change in the distance R1 from the rotation center 4210 to the peripheral surface of the contact member 47 per unit rotation angle in the rotation direction D4 (= dR1 // dθ) is also different from “−0.26”, “−0.22”, and “−0.18”, respectively. Therefore, the speed fluctuation of the secondary transfer roller 4 at each contact time varies, and it is difficult to perform stable transfer processing.

  As described above, according to the present embodiment, the recording medium RM is formed when the concave portion 41 faces the intermediate transfer belt (image carrier) 31 and between the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31. The outer peripheral surface of the contact member 47 is in contact with the bearing 322 to support the secondary transfer roller 4 when the front end portion of the toner enters, but the upstream outer peripheral surface end portion 47b is finished in the above shape. Therefore, even if the contact timing of the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 (including the case of contact via the recording medium RM) slightly varies depending on the presence or absence of the recording medium RM and the thickness thereof, The amount of change in the distance R1 at the contact timing (= dR1 / dθ) is the same value, and the load fluctuation when the secondary transfer roller 4 contacts the intermediate transfer belt 31 is constant. As a result, it is possible to satisfactorily transfer the toner image TI on the intermediate transfer belt 31 to the recording medium RM while suppressing variations in speed variation of the secondary transfer roller 4.

  Thus, in this embodiment, the upstream outer peripheral surface end 47b of the contact member 47 corresponds to the “contact surface” of the present invention. The elastic layer 43 provided on the peripheral surface of the secondary transfer roller 4 corresponds to the “first elastic layer” 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 the above-described embodiment, the shape of the central portion 47a of the outer peripheral surface of the contact member 47 is formed so that the distance R1 is longer than the radius Rr of the secondary transfer roller 4 between the angle range AR2, that is, the angles θa to θb. However, the shape is not limited to this, and for example, as shown in FIG. 11, the contact member such that the distance R1 is shorter than the radius Rr of the secondary transfer roller 4 between the angles θa to θb. The shape of the outer peripheral surface central portion 47a of 47 may be formed. In this case, the distance between the axes of the secondary transfer roller 4 and the drive roller 32 in the angle range AR2 is smaller than that in the other angle ranges, and the concave portion 41 faces the intermediate transfer belt 31. A part of the intermediate transfer belt 31 passes through the opening of the recess 41.

  In addition, as shown in FIG. 12, an elastic layer 473 may be provided on the outer peripheral surface of the contact member 47. By providing the elastic layer 473 in this manner, an impact generated when the contact member 47 contacts the bearing 322 by the elastic force of the elastic layer 473 can be absorbed by the elastic force of the elastic layer 473. In the above embodiment, since the elastic layer 43 is provided on the peripheral surface of the secondary transfer roller 4, a load is applied to the intermediate transfer belt 31 by the elastic layer 43 while the secondary transfer roller 4 is in contact with the intermediate transfer belt 31. In contrast, the load is eliminated while the recess 41 faces the intermediate transfer belt 31. However, when the elastic layer 473 is provided on the outer peripheral surface of the contact member 47, the elastic layer 473 contacts the bearing 322 and another load is applied to the intermediate transfer belt 31 while the concave portion 41 faces the intermediate transfer belt 31. It is done. Thus, the difference between the load applied to the intermediate transfer belt 31 during the period in which the concave portion 41 faces the intermediate transfer belt 31 (opposite period) and the period in which the recess 41 does not face (non-opposite period) can be suppressed. The load fluctuation that occurs when the toner image TI formed on the recording medium RM is transferred to the recording medium RM can be further suppressed. Thus, in this embodiment, the elastic layer 473 corresponds to the “second elastic layer” of the present invention.

  Further, for example, in the above embodiment, 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 to this. For example, the present invention can be applied to an image forming apparatus including only one image forming station.

  In the above-described embodiment, 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, an image forming apparatus having a structure in which the secondary transfer roller 4 having a surface shape with a part of the cylindrical peripheral surface cut out is brought into contact with the intermediate transfer belt. The present invention can be applied to all transfer apparatuses.

  Furthermore, the present invention can be applied to an apparatus including the secondary transfer roller 4 that does not have a grip portion. For example, in an apparatus in which the surface layer is formed by winding a sheet-like elastic body around the surface of the secondary transfer roller 4, it is necessary to provide the recess 41 on the outer peripheral surface of the secondary transfer roller 4 in order to fix the end of the sheet. However, the present invention can also be applied to an apparatus having such a configuration (concave portion 41) but not having a gripping portion.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2Y, 2M, 2C, 2K ... Image forming station (image forming part), 4 ... Secondary transfer roller, 31 ... Intermediate transfer belt (image carrier), 41 ... Concave part, 43 ... (first) DESCRIPTION OF SYMBOLS 1) Elastic layer, 45 ... Press part, 47 ... Contact member, 47b ... Upstream outer peripheral surface edge part (contact surface), 421 ... Rotating shaft, 4210 ... Center of rotation, 473 ... (2nd) elastic layer, D4 ... Rotation direction, RM ... Recording medium, TI ... Toner image

Claims (5)

An image carrier for carrying an image;
A transfer roller provided with a concave portion on the peripheral surface and contacting the peripheral surface different from the concave portion while rotating through the image carrier and the recording medium and transferring the image carried on the image carrier to the recording medium When,
A pressing portion for pressing the transfer roller against the image carrier;
A first support that is provided at a position corresponding to the recess in the axial direction of the transfer roller and rotates together with the transfer roller;
A second support that comes into contact with the first support portion when the concave portion faces the image carrier and when the peripheral surface different from the concave portion of the transfer roller and the image carrier abut via the recording medium. And comprising
The second contact member contacts the second support member from a position where the concave portion faces the image carrier to a position where the peripheral surface different from the concave portion of the transfer roller contacts the image carrier. The shape of the abutment surface of one support portion is a constant amount of change in the distance from the rotation center of the transfer roller to the abutment surface of the first support portion per unit rotation angle in the rotation direction of the first support portion. Alternatively, a transfer device configured to be substantially constant.   The transfer device according to claim 1, wherein a first elastic layer is disposed on a peripheral surface different from the concave portion of the transfer roller.   The transfer device according to claim 1, wherein a second elastic layer is disposed on a contact surface of the first support portion.   The distance from the rotation center of the transfer roller to the contact surface of the first support portion when the concave portion faces the image carrier is the distance of the transfer roller when the transfer roller contacts the image carrier. The transfer device according to claim 1, wherein the transfer device is shorter than a distance from a rotation center to a contact surface of the first support portion. An image forming unit for forming an image;
An image carrier that carries the image formed by the image forming unit;
A transfer roller provided with a concave portion on the peripheral surface and contacting the peripheral surface different from the concave portion while rotating through the image carrier and the recording medium and transferring the image carried on the image carrier to the recording medium When,
A pressing portion for pressing the transfer roller against the image carrier;
A first support that is provided at a position corresponding to the recess in the axial direction of the transfer roller and rotates together with the transfer roller;
A second support that comes into contact with the first support portion when the concave portion faces the image carrier and when the peripheral surface different from the concave portion of the transfer roller and the image carrier abut via the recording medium. And comprising
The second contact member contacts the second support member from a position where the concave portion faces the image carrier to a position where the peripheral surface different from the concave portion of the transfer roller contacts the image carrier. The shape of the abutment surface of one support portion is a constant amount of change in the distance from the rotation center of the transfer roller to the abutment surface of the first support portion per unit rotation angle in the rotation direction of the first support portion. Alternatively, an image forming apparatus configured to be substantially constant.

Images