JP2007079017A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus where a toner image on an image carrier is primarily transferred to an intermediate transfer belt wound and laid on a driving roller and a counter roller and driven, the toner image is secondarily transferred to a transfer fixing roller and also the toner image on the transfer fixing roller is heated and tertiarily transferred to a recording medium fed to space between the transfer fixing roller and a pressure roller, and which prevents the image quality of the toner image secondarily transferred from the intermediate transfer belt to the transfer fixing roller from being deteriorated by the sudden speed variation of the transfer fixing roller. <P>SOLUTION: The transfer fixing roller 21 is driven and rotated by a motor 51, and also the rotation of the transfer fixing roller 21 is transmitted to the counter roller 6 by driving transmission gears 53 and 54 fixed on the transfer fixing roller 21 and passive gears 55 and 56 fixed on the counter roller 6 and meshed with the driving transmission gears 53 and 54. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  According to the present invention, at least one image carrier on which a toner image is formed and at least two support rollers including a driving roller and a counter roller are wound around, and the toner image formed on the image carrier is primarily transferred. An intermediate transfer belt, a transfer fixing member that is opposed to the opposing roller via the intermediate transfer belt, to which the toner image on the intermediate transfer belt is secondarily transferred, and the toner image transferred to the transfer fixing member is heated And a pressure member pressed against the transfer fixing member. The recording medium that passes between the transfer fixing member and the pressure member is secondarily transferred to the transfer fixing member and heated. The present invention relates to an image forming apparatus that tertiary-transfers the toner image and fixes the toner image on a recording medium.

  An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile, or a complex machine of these is well known (see Patent Document 1). This type of image forming apparatus is configured to pass a recording medium between a transfer fixing member and a pressure member, and at this time, the toner image on the transfer fixing member is thirdarily transferred to the recording medium. When the leading edge of the medium enters between the transfer fixing member and the pressure member, and when the trailing edge of the recording medium comes out between the transfer fixing member and the pressure member, the rotational speed of the transfer fixing member increases rapidly. Fluctuates. As a result, a large difference occurs in the surface speed between the intermediate transfer belt and the transfer fixing member in the secondary transfer portion where the toner image is secondarily transferred, and the toner image on the intermediate transfer belt is shear transferred to the transfer fixing member. As a result, image quality deterioration called shock jitter occurs.

JP 2004-145260 A

  The present invention has been made on the basis of the above-described new recognition, and its object is to effectively suppress the occurrence of shock jitter and improve the image quality as compared with the prior art. An image forming apparatus is provided.

  According to the present invention, in the image forming apparatus of the type described at the beginning to achieve the above object, a drive source for rotationally driving the transfer fixing member is provided, and a transfer fixing member in a secondary transfer portion where the secondary transfer is performed An image forming apparatus comprising drive transmission means for transmitting the rotation of the transfer fixing member to the counter roller so that the surface speed of the intermediate transfer belt in the secondary transfer portion follows the surface speed of Proposed (claim 1).

  The image forming apparatus according to claim 1, wherein the drive transmission unit includes a drive transmission gear provided on the transfer fixing member and a passive gear provided on the counter roller and meshing with the drive transmission gear. (Claim 2).

  The image forming apparatus according to claim 1, wherein the drive transmission unit is provided on a drive transmission friction member provided on the transfer fixing member and on the opposing roller, and is pressed against the drive transmission friction member. It is advantageous if a passive friction member is provided (claim 3).

  The image forming apparatus according to any one of claims 1 to 3, further comprising a clutch that switches whether to transmit the rotation of the transfer fixing member to the counter roller via the drive transmission unit. It is advantageous (claim 4).

  The image forming apparatus according to claim 4, wherein the clutch includes a front end portion of the recording medium that protrudes between the transfer-fixing member and a pressure member, and a rear end portion of the recording medium. Turned on when the transfer fixing member and the pressure member come out, and transmits the rotation of the transfer fixing member to the opposing roller via the drive transmission means, and the leading end portion and the trailing end portion of the recording medium Is turned off when the recording medium portion in between passes between the transfer fixing member and the pressure member, and the rotation of the transfer fixing member is not transmitted to the counter roller via the drive transmission means. It is advantageous if it is constituted in this way (claim 5).

  6. The image forming apparatus according to claim 1, wherein an intermediate transfer belt portion on the upstream side in the movement direction of the intermediate transfer belt and a downstream side in the movement direction of the intermediate transfer belt with respect to the secondary transfer portion. It is advantageous to provide a tension applying member for applying tension to the intermediate transfer belt portion.

  Furthermore, in the image forming apparatus according to any one of claims 1 to 6, a friction coefficient between the facing roller and the intermediate transfer belt is larger than a friction coefficient between the transfer fixing member and the intermediate transfer belt. It is advantageous if the counter roller, the intermediate transfer belt, and the transfer fixing member are configured to be large.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing the occurrence of shock jitter and improving the image quality.

  FIG. 1 is a partial sectional schematic view showing an example of an image forming apparatus according to the present invention. The image forming apparatus shown here has first to fourth image carriers 3Y, 3C, 3M, 3BK configured as drum-shaped photoconductors, and a yellow toner image and cyan on each of the image carriers. A toner image, a magenta toner image, and a black toner image are formed. An intermediate transfer belt 4 made of an endless belt is disposed opposite to the first to fourth image carriers 3Y to 3BK. The intermediate transfer belt 4 is driven by a driving roller 5 and an intermediate transfer belt 4 to be described later. The roller is wound around a counter roller 6 disposed opposite to the fixing roller 21, tension rollers 22 and 23, and a guide roller 7. The intermediate transfer belt 4 is made of, for example, a resin material such as polyimide or PVDF. The drive roller 5 is rotationally driven in the clockwise direction in FIG. 1 by a drive motor (not shown), so that the intermediate transfer belt 4 is rotationally driven in the arrow A direction. At this time, the other rollers 6, 7, 22, and 23 also rotate clockwise.

  The first image carrier 3Y is driven to rotate counterclockwise in FIG. 1. At this time, the image carrier 3Y is charged to a predetermined polarity by the charging roller 8, and then is emitted from the laser writing unit 9 to the charged surface. The light-modulated laser beam L is irradiated. As a result, an electrostatic latent image is formed on the image carrier 3Y, and the electrostatic latent image is visualized by the developing device 10 as a yellow toner image.

  A primary transfer roller 12 is disposed on the side opposite to the image carrier 3Y with the intermediate transfer belt 4 interposed therebetween, and a transfer voltage is applied to the primary transfer roller 12 so that the toner image on the image carrier 3Y is changed to an arrow. Primary transfer is performed on the intermediate transfer belt 4 running in the A direction. The transfer residual toner adhering to the image carrier 3Y after the transfer of the toner image is removed by the cleaning device 13, and the surface of the image carrier after the transfer of the toner image is irradiated with a charge eliminating light (not shown). The potential on the surface of the carrier is initialized. In exactly the same manner, a cyan toner image, a magenta toner image, and a black toner image are respectively formed on the second to fourth image carriers 3C, 3M, and 3BK shown in FIG. 1, and these toner images are converted into yellow toner images. The toner images are transferred onto the intermediate transfer belt 4 and transferred to the primary transfer, and a toner image is formed on the intermediate transfer belt 4.

  In the illustrated image forming apparatus, a plurality of image carriers 3Y to 3BK are provided, but one image carrier is provided, and a toner image formed on the image carrier is primarily transferred to the intermediate transfer belt 4. It can also be configured to. Further, the intermediate transfer belt 4 shown in FIG. 1 is wound around five support rollers, that is, a drive roller 5, a counter roller 6, tension rollers 22 and 23, and a guide roller 7. Other support rollers can be omitted. As described above, the image forming apparatus has at least one image carrier on which a toner image is formed, and is wound around at least two support rollers, that is, a driving roller and a counter roller, to be formed on the image carrier. And an intermediate transfer belt on which the toner image is primarily transferred.

  Further, as shown in FIG. 2, the image forming apparatus of this example also includes a transfer fixing roller 21 that is an example of a transfer fixing member that is opposed to the opposing roller 6 via the intermediate transfer belt 4, and the transfer fixing roller 21. And a pressure roller 24 that is an example of a pressure member that is in pressure contact with the pressure member. The transfer fixing roller 21 rotates in the direction of arrow B at a surface speed substantially the same as the surface speed of the intermediate transfer belt 4, and the pressure roller 24 rotates in the direction of arrow C following the rotation of the transfer fixing roller 21. Further, a heater 25 which is an example of a heating unit is disposed facing the transfer fixing roller 21. For example, a halogen heater can be used as the heater 25. A heating unit may be provided in the transfer fixing roller 21 or the transfer fixing roller itself may generate heat, and the transfer fixing roller itself may have a heating unit.

  As illustrated in FIG. 3, the transfer fixing roller 21 includes a cored bar 26, a heat insulating layer 27 provided on the cored bar 26, an elastic layer 28 made of, for example, rubber laminated on the surface thereof, and a periphery thereof. The surface is composed of a release layer 29 made of, for example, PFA coated on the surface. As shown in FIG. 2, the shaft portions 30 and 31 at each end in the axial direction of the transfer and fixing roller 21 are composed of the core metal 26 alone. Yes. A heat generating layer made of a metal such as SUS or Ni may be provided between the heat insulating layer 27 and the elastic layer 28 so that the transfer fixing roller itself generates heat. Further, the transfer fixing roller 21 can also be constituted by a metal pipe such as aluminum and a release layer coated on the surface thereof.

  Further, as illustrated in FIG. 3, the pressure roller 24 includes a cored bar 32 and an elastic layer 33 made of rubber or the like laminated on the surface thereof. As shown in FIG. The shaft portions 34 and 35 at the respective end portions in the axial direction are composed of the core metal 32 alone.

  Further, as shown in FIG. 3, the opposing roller 6 is composed of a roller in which an elastic layer 37 made of rubber or the like is laminated on a core metal 36. As shown in FIG. The shaft portions 38 and 39 at the end portions are constituted by the core metal 36 alone.

  As shown in FIGS. 1 and 2, the shaft portions 30 and 31 of the transfer and fixing roller 21 are supported by a support side plate (not shown) through bearings 40 and 41, but are rotatably supported. . Further, the shaft portions 34 and 35 of the pressure roller 24 are supported by the support side plates via the bearings 42 and 43 so as to be movable in a direction approaching or separating from the transfer fixing roller 21. The bearings 42 and 43 are pressed by the springs 44 and 45, so that the pressure roller 24 is in pressure contact with the transfer fixing roller 21. Further, the shaft portions 38 and 39 of the facing roller 6 are also supported by the support side plate via the bearings 46 and 47 so as to be movable in the direction approaching or separating from the transfer fixing roller 21. The bearings 46 and 47 are pressed by the springs 48 and 49, so that the opposing roller 6 is pressed against the transfer fixing roller 21 via the intermediate transfer belt 4.

  Further, the tension rollers 22 and 23 are also supported so as to be movable in the direction approaching or separating from the intermediate transfer belt 4, although the shaft portions of the tension rollers 22 and 23 are rotatable on the support side plate via the bearings. The tension rollers 22 and 23 are pressed against the back surface of the intermediate transfer belt 4 by applying pressure to the intermediate transfer belt 4, whereby tension is applied to the intermediate transfer belt 4.

  A transfer voltage (including superposition of AC, pulses, etc.) is applied to the opposing roller 6 by a bias applying means (not shown), and thereby the intermediate transfer belt 4 driven to travel in the direction of arrow A as described above. The toner image primarily transferred above is electrostatically secondarily transferred to the transfer fixing roller 21 rotating in the direction of arrow B. The toner image transferred to the transfer fixing roller 21 in this way is heated by the heater 25, and the toner is softened. On the other hand, the transfer residual toner adhering to the intermediate transfer belt 4 after the toner image transfer is removed by the cleaning device 20.

  A sheet feeding device (not shown) that stores a recording medium made of, for example, transfer paper is disposed below the intermediate transfer belt 4, and the recording medium P sent out from the sheet feeding device is indicated by an arrow E in FIG. As described above, the toner image on the transfer and fixing roller 21 is pressed against the transfer and fixing roller 21 by being sent between the transfer and fixing roller 21 and the pressing roller 24 that rotate in the directions of arrows B and C, respectively, at a predetermined timing. Pressurized by the roller 24, and is thirdarily transferred and fixed on the recording medium. Next, the recording medium P is discharged to a paper discharge unit (not shown). In this way, the toner image that is secondarily transferred to the transfer fixing member and heated by the heating means is transferred to the recording medium passing between the transfer fixing member and the pressure member, and the toner image is recorded. It is fixed on the medium.

  By thinly forming the elastic layer 28 of the transfer fixing roller 21 and the elastic layer 33 of the pressure roller 24 shown in FIG. 3, the width of the nip between the transfer fixing roller 21 and the pressure roller 24 is reduced. Moreover, although the pressure in the nip can be increased, the toner image that is thirdarily transferred to the recording medium made of cardboard can be reduced by reducing the heat transfer to the recording medium by making the pressure high in the narrow nip. It can be fixed on the recording medium with the same power consumption as that of the toner image thirdarily transferred onto the recording medium made of thin paper. In this way, heat can be used efficiently and energy can be easily achieved. In addition, by increasing the pressure at the nip between the transfer fixing roller 21 and the pressure roller 24, an effect of increasing the glossiness of the image fixed on the recording medium and reducing the uneven gloss can be expected.

  4A shows a state in which the leading end of the recording medium P has entered the nip between the transfer fixing roller 21 and the pressure roller 24. At this time, the transfer fixing roller 21 is shown in FIG. The surface speed of the transfer and fixing roller 21 is decelerated momentarily. When the recording medium P passes between the transfer and fixing roller 21 and the pressure roller 24, the transfer and fixing roller 21 returns to the steady rotation, but as shown in FIG. When the rear end portion passes between the transfer fixing roller 21 and the pressure roller 24, the load on the transfer fixing roller 21 is reduced in an impulse manner. As a result, the surface speed of the transfer fixing roller 21 is increased momentarily, and then steady. Return to rotation. As described above, when the front end portion of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24 and then the rear end portion thereof comes out, the surface speed of the transfer fixing roller 21 fluctuates rapidly. This appears more prominently as the recording medium P is thicker. As described above, since the surface speed of the transfer and fixing roller 21 fluctuates, in the conventional image forming apparatus of this type, when the toner image is secondarily transferred from the intermediate transfer belt 4 to the transfer and fixing roller 21, A large speed difference is generated between the surface speed of the intermediate transfer belt 4 and the surface speed of the transfer fixing roller 21, and the toner image is largely sheared and transferred. If the toner image transferred in such a large amount is, for example, a round dot shape, the image quality deteriorates due to the shape or pitch extending or shrinking in the rotation direction of the transfer and fixing roller 21. Since this shear transfer occurs only for a moment, the image that has been shear-transferred has a density different from that of the other parts. If this image is a halftone solid image, it will be visually recognized as a horizontal streak, resulting in an image with shock jitter. .

  Therefore, in the image forming apparatus of this example, as shown in FIG. 2, a drive gear 50 is fixed to one shaft portion 30 of the transfer fixing roller 21, and the drive gear 50 includes a drive source including a motor 51. The motor gear 52 is engaged with each other, and the rotation of the motor 51 is transmitted to the transfer fixing roller 21 via the gears 52 and 50, whereby the transfer fixing roller 21 is rotationally driven in the direction indicated by the arrow B in FIG. As described above, the image forming apparatus of the present example is provided with the drive source including the motor 51 that rotationally drives the transfer fixing member including the transfer fixing roller 21.

  On the other hand, as shown in FIG. 2, drive transmission gears 53 and 54 are fixed to the shaft portions 30 and 31 of the transfer fixing roller 21, respectively, and the drive portions are respectively connected to the shaft portions 38 and 39 of the opposing roller 6. Passive gears 55 and 56 meshing with the transmission gears 53 and 54 are fixed, respectively. With this configuration, the rotation of the transfer fixing roller 21 is transmitted to the opposing roller 6 via the drive transmission gears 53 and 54 and the passive gears 55 and 56. At this time, the rotation of the transfer fixing roller 21 is transmitted to the opposing roller 6 so that the surface speed of the intermediate transfer belt 4 wound around the opposing roller 6 is substantially equal to the surface speed of the transfer fixing roller 21. In FIG. 1, the drive transmission gear 54 and the passive gear 56 are not shown.

  As described above, the transfer and fixing roller 21 is actively driven to rotate by the motor 51 and the rotation is transmitted to the opposing roller 6 via the gears 53 and 54; 55 and 56. The intermediate transfer belt 4 rotates following the rotation of the opposing roller 6 along with the rotation of the fixing roller 21. For this reason, as described above with reference to FIGS. 4A and 4B, the leading end of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24, or the recording thereof. Even if the speed fluctuation of the transfer fixing roller 21 occurs when the rear end portion of the medium P passes between the transfer fixing roller 21 and the pressure roller 24, the opposing roller 6 and the intermediate transfer belt 4 are not affected by the transfer fixing roller. Therefore, a large amount of shear transfer does not occur in the secondary transfer portion between the intermediate transfer belt 4 and the transfer fixing roller 21, and thus thick paper is used as a recording medium. Even in this case, the occurrence of shock jitter can be effectively suppressed.

  The transfer speed of the toner image can be improved by providing a slight speed difference between the surface speeds of the intermediate transfer belt 4 and the transfer fixing roller 21, but the leading edge and the trailing edge of the recording medium are added to the transfer fixing roller 21. The speed fluctuation of the transfer and fixing roller 21 when entering or exiting from the pressure roller 24 is considerably larger than the above-described speed difference.

  In the above-described example, since the two drive transmission gears 53 and 54 and the passive gears 55 and 56 meshing with the respective gears are provided, the rotation of the transfer fixing roller 21 is caused to rotate without causing the counter roller 6 to twist. However, the number of gear pairs of the drive transmission gear and the passive gear meshing with the drive transmission gear may be one or three or more.

  The drive transmission gears 53 and 54 and the passive gears 55 and 56 described above are arranged so that the surface speed of the transfer fixing roller 21 in the secondary transfer portion where the secondary transfer of the toner image is performed, and the intermediate transfer belt 4 in the secondary transfer portion. In order to follow the surface speed, an example of a drive transmission means for transmitting the rotation of the transfer fixing roller 21 to the opposing roller 6 is configured. That is, the drive transmission means of this example includes drive transmission gears 53 and 54 provided on the transfer fixing roller 21 and passive gears 55 and 56 provided on the opposing roller and meshing with the drive transmission gears 53 and 54. It has.

  On the other hand, in the image forming apparatus shown in FIG. 5, instead of the drive transmission gears 53 and 54 shown in FIG. 2, ring-shaped drive transmission members 53A and 54A are respectively connected to the shaft portions 30 and 30 of the transfer fixing roller 21, respectively. In place of the passive gears 55 and 56 shown in FIG. 2, ring-shaped passive friction members 55A and 56A are fixed to the shaft portions 38 and 39 of the opposing roller 6, respectively. 53A and 54A are in pressure contact with each passive friction member 55A and 56A. The surface portions of the friction members 53A to 56A are made of, for example, a material having a high friction coefficient such as rubber, and the rotation of the transfer fixing roller 21 is transferred to the opposing roller 6 via the friction members 53A, 54A; 55A, 56A. Thus, the same operation as that of the image forming apparatus shown in FIG. 2 can be achieved. Other configurations of the image forming apparatus shown in FIG. 5 are the same as those shown in FIGS.

  As described above, in the image forming apparatus shown in FIG. 5, the drive transmission means is provided on the drive transmission friction members 53 </ b> A and 54 </ b> A provided on the transfer fixing roller 21 and the opposing roller 6. Passive friction members 55A and 56A are in pressure contact with the members 53A and 54A. As described above, when the rotation of the transfer fixing roller 21 is transmitted to the opposing roller 6 by the frictional force of the friction member, the rotation transmission when the surface speed of the transfer fixing roller 21 follows the opposing roller 6 is affected. Is less likely to occur, and the occurrence of shock jitter due to rattling can be prevented.

  In the image forming apparatus shown in FIG. 2, the drive transmission gears 53 and 54 fixed to the transfer and fixing roller 21 and the passive gears 55 and 56 fixed to the opposing roller 6 are always meshed with each other. The rotation is always transmitted to the facing roller 6. The same applies to the image forming apparatus shown in FIG. According to this configuration, the following problem may occur.

  In general, it is inevitable that the diameters of the opposing roller 6 and the transfer fixing roller 21 vary somewhat. Due to such variations, a difference occurs between the surface speed of the intermediate transfer belt 4 and the surface speed of the transfer fixing roller 21 in the secondary transfer portion. At this time, it is assumed that the intermediate transfer belt 4 adheres to the surface of the transfer fixing roller 21 due to frictional force, and the intermediate transfer belt 4 is forcibly rotated at the same speed as the transfer fixing roller 21. The surface of the intermediate transfer belt 4 and the surface of the transfer fixing roller 21 try to rotate at different speeds due to variations in the diameters of the opposing roller 6 and the transfer fixing roller 21. It adheres and forcibly rotates at the same speed as the transfer and fixing roller 21. When such a phenomenon occurs, the intermediate transfer belt 4 rotates at the same speed as that of the transfer fixing roller 21 for a short period of time. As a result, distortion is accumulated in the intermediate transfer belt 4, and suddenly at a certain time. The intermediate transfer belt 4 slides with respect to the transfer fixing roller 21. Such a phenomenon is generally called stick-slip, but such stick-slip is repeated. As a result, the image quality of the toner image secondarily transferred to the transfer fixing roller 21 is deteriorated.

  Therefore, in the image forming apparatus shown in FIG. 6, the shaft 57 of the transfer fixing roller 21 is provided with the clutch 57, and the drive transmission friction member 54 </ b> A provided on the shaft 31 is provided with the shaft 31. Is supported so as to be freely rotatable. The drive transmission friction member 54A is in pressure contact with the passive friction member 56A fixed to the shaft portion 39 of the counter roller 6. The other configuration of the image forming apparatus shown in FIG. 6 is the same as that of the image forming apparatus shown in FIG.

  When the clutch 57 shown in FIG. 6 is turned off, the drive transmission friction member 54A can freely rotate with respect to the shaft portion 31 of the transfer fixing roller 21, so that the rotation is driven by the rotation of the passive friction member 56A. To do. The intermediate transfer belt 4 is rotationally driven by the rotation of the driving roller 5, and the counter roller 6 rotates in the clockwise direction in FIG. 1, and the rotation of the passive friction member 56A at this time is transmitted to the drive transmission friction member 54A. The friction member 54A rotates freely. Accordingly, at this time, the rotation of the transfer fixing roller 21 is not transmitted to the counter roller 6.

  When the clutch 57 is turned on, the drive transmission friction member 54A is fixed to the shaft portion 31 of the transfer fixing roller 21 via the clutch 57, so that the rotation of the transfer fixing roller 21 is coupled with the drive transmission friction member 54A. It is transmitted to the opposing roller 6 through a drive transmission means comprising a passive friction member 56A.

  As described above, the image forming apparatus shown in FIG. 6 includes the clutch 57 that switches whether or not to transmit the rotation of the transfer and fixing roller 21 to the opposing roller 6 via the drive transmission unit. As shown in FIG. 4, when the leading end of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24, and the trailing end of the recording medium P is the transfer fixing roller 21 and the pressure roller 24. By turning off the clutch 57 and rotating the opposing roller 6 along with the intermediate transfer belt 4 at appropriate times except when coming out of the gap, the distortion caused by the speed difference between the intermediate transfer belt 4 and the transfer fixing roller 21 can be released. The occurrence of stick-slip can be prevented.

  At that time, when the leading end portion of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24, the trailing end portion of the recording medium P is between the transfer fixing roller 21 and the pressure roller 24. When the clutch 57 comes out, the clutch 57 is turned on to transmit the rotation of the transfer and fixing roller to the opposing roller 6 via the drive transmission means, and the recording medium portion between the leading end and the trailing end of the recording medium P is transferred to the fixing roller. And the pressure roller 24, the clutch 57 is turned off so that the rotation of the transfer and fixing roller 21 is not transmitted to the counter roller 6 via the drive transmission means. Is preferred. More specifically, as shown in FIGS. 2 and 4, a paper detection sensor 58 made of, for example, a photo interrupter is provided upstream of the nip between the transfer fixing roller 21 and the pressure roller 24 in the recording medium conveyance direction. The clutch 57 is turned off during normal operation. As a result, the drive transmission friction member 54 </ b> A shown in FIG. 6 rotates freely with respect to the shaft portion 31 of the transfer fixing roller 21. When the recording medium P is fed and its leading end is detected by the paper detection sensor 58, the clutch 57 is turned on and remains on until the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24. While the state continues and the recording medium P passes between the transfer fixing roller 21 and the pressure roller 24, the clutch 57 is turned off. Thereafter, the time after the leading end of the recording medium is detected by the paper detection sensor 58 is counted by a control unit (not shown), and the trailing end of the recording medium passes between the transfer fixing roller 21 and the pressure roller 24. The clutch 57 is kept on from just before it is released to the moment it is released, and then turned off. In the case of continuous paper passing, the clutch 57 is turned off when the recording medium passes between the recording medium and between the transfer fixing roller 21 and the pressure roller 24, and the leading end of the recording medium enters and exits. The clutch is repeatedly turned on at the timing.

  According to the above-described configuration, when the leading end of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24 and when the leading end of the recording medium comes out between the rollers 21 and 24. The occurrence of shear transfer based on the speed fluctuation of the transfer fixing roller 21 can be prevented, and the speeds of the intermediate transfer belt 4 and the transfer fixing roller 21 can be different based on the diameter variation of the transfer fixing roller 21 and the opposing roller 6. Time can be shortened.

  The clutch 57 described above is provided on the counter roller 6, the passive friction member 56 A is rotatably supported on the shaft portion 39 of the counter roller 6, and the drive transmission friction member 54 A is fixed to the shaft portion 31 of the transfer fixing roller 21. However, the same effect as described above can be achieved.

  Further, each configuration related to the clutch 57 described above can also be applied when the drive transmission means is composed of a drive transmission gear and a passive gear meshing therewith as shown in FIG. Further, as shown in FIGS. 2 and 5, when a plurality of pairs of drive transmission gears and passive gears meshing with the drive transmission gears are provided, or when a plurality of pairs of drive transmission friction members and passive friction members that are pressed against the drive transmission friction members are provided. However, by providing a clutch corresponding to each gear pair or each friction member pair, the same action as described above can be achieved.

  In each of the image forming apparatuses described above, an intermediate transfer belt portion on the upstream side in the moving direction of the intermediate transfer belt 4 relative to the secondary transfer portion of the toner image between the intermediate transfer belt 4 and the transfer fixing roller 21; A tension applying member including tension rollers 22 and 23 for applying tension to the intermediate transfer belt 4 is provided on the intermediate transfer belt portion on the downstream side in the moving direction of the intermediate transfer belt 4. By providing the tension rollers 22 and 23, the following operation can be achieved.

  As described above, when the leading end portion of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24, the speed of the transfer fixing roller 21 decreases at that moment, and the counter roller 6 follows the speed. The speed of the portion of the intermediate transfer belt 4 that is wound also decreases. In addition, since the intermediate transfer belt 4 is driven by the driving roller 5 so as to have a constant speed, the intermediate transfer belt portion on the downstream side in the moving direction of the intermediate transfer belt with respect to the opposing roller 6 is located between the opposing roller 6 and the driving roller 5. The intermediate transfer belt portion on the upstream side is pulled between the counter roller 6 and the driving roller 5 and tries to sag. If such a phenomenon occurs, the speed of the entire intermediate transfer belt 4 may fluctuate, and the toner image may be misaligned at the primary transfer portion of the toner image from the image carriers 3Y to 3BK to the intermediate transfer belt 4. There is.

  On the other hand, if tension rollers 22 and 23 are provided as in the image forming apparatus of this example, the speed fluctuation of the intermediate transfer belt 4 is absorbed here, and the speed fluctuation of the intermediate transfer belt in the primary transfer portion is absorbed. It is possible to suppress the load fluctuation on the drive roller 5. The broken line in FIG. 4A indicates the steady state of the intermediate transfer belt 4 and the tension rollers 22 and 23, and the intermediate transfer is performed at the moment when the leading end of the recording medium P enters between the transfer fixing roller 21 and the pressure roller 24. The belt 4 and the tension rollers 22 and 23 move as indicated by a solid line in FIG. 4A to prevent propagation of speed fluctuations of the intermediate transfer belt 4 to the primary transfer unit or the drive roller 5.

  When the rear end portion of the recording medium P passes between the transfer fixing roller 21 and the pressure roller 24, the speed of the transfer fixing roller 21 increases at that moment, and is wound around the opposing roller 6 accordingly. The speed of the intermediate transfer belt portion is increased. In this case, sagging occurs in the intermediate transfer belt portion on the downstream side in the moving direction of the intermediate transfer belt with respect to the opposing roller 6, and the intermediate transfer belt portion on the upstream side is pulled. The broken line in FIG. 4B shows the steady state of the intermediate transfer belt 4 and the tension rollers 22 and 23, and the moment when the rear end of the recording medium passes between the transfer fixing roller 21 and the pressure roller 24 is intermediate. The transfer belt 4 and the tension rollers 22 and 23 are moved to the positions indicated by solid lines to prevent propagation of speed fluctuations of the intermediate transfer belt 4.

Here, in the image forming apparatus of this example, the friction coefficient μ ₁ between the facing roller 6 and the intermediate transfer belt 4 is larger than the friction coefficient μ ₂ between the transfer fixing roller 21 and the intermediate transfer belt 4. The counter roller 6, the intermediate transfer belt 4, and the transfer fixing roller 21 are configured so as to be. For example, the transfer fixing roller 21 and the opposing roller 6 are configured as described above with reference to FIG. 3 and the intermediate transfer belt 4 is formed of a resin material such as polyimide or PVDF, so that μ ₁ > μ _2. It can be.

As described above, by setting the friction coefficient μ ₁ between the opposing roller 6 and the intermediate transfer belt 4 to be large, it is possible to prevent slippage between the opposing roller 6 and the intermediate transfer belt 4. Therefore, as described above, when the rotation of the transfer fixing roller 21 is transmitted to the counter roller 6 via the drive transmission means, the speed of the intermediate transfer belt 4 can surely follow the speed of the transfer fixing roller 21. it can. In addition, by reducing the friction coefficient μ ₂ between the intermediate transfer belt 4 and the transfer fixing roller 21, the surface of the transfer fixing roller 21 becomes slippery with respect to the surface of the intermediate transfer belt 4. Even if there is, the above-mentioned stick slip hardly occurs, and a high-quality image can be formed.

1 is a partial cross-sectional schematic diagram illustrating an example of an image forming apparatus. FIG. 2 is an enlarged plan view of a part of the image forming apparatus illustrated in FIG. 1. It is the III-III sectional view taken on the line of FIG. The speed of the transfer fixing roller fluctuates when the leading end of the recording medium enters between the transfer fixing roller and the pressure roller, or when the trailing end of the recording medium exits between the transfer fixing roller and the pressure roller. FIG. FIG. 4 is a plan view similar to FIG. 2 showing another example of the image forming apparatus. FIG. 10 is a plan view similar to FIG. 2, showing still another example of the image forming apparatus.

Explanation of symbols

3Y, 3C, 3M, 3BK Image carrier 4 Intermediate transfer belt 5 Drive roller 6 Opposing roller 53, 54 Drive transmission gear 53A, 54A Drive transmission friction member 55, 56 Passive gear 55A, 56A Passive friction member

Claims (7)

At least one image carrier on which a toner image is formed, and an intermediate transfer belt on which at least two support rollers, a driving roller and a counter roller, are wound and the toner image formed on the image carrier is primarily transferred A transfer fixing member that is opposed to the opposing roller via the intermediate transfer belt and to which the toner image on the intermediate transfer belt is secondarily transferred; and a heating unit that heats the toner image transferred to the transfer fixing member. A toner image that is secondarily transferred to the transfer fixing member and heated on a recording medium that passes between the transfer fixing member and the pressure member. In an image forming apparatus that performs tertiary transfer and fixes the toner image on a recording medium.
A drive source for rotationally driving the transfer fixing member is provided, and the surface speed of the intermediate transfer belt in the secondary transfer portion is made to follow the surface speed of the transfer fixing member in the secondary transfer portion where the secondary transfer is performed. In addition, the image forming apparatus further comprises drive transmission means for transmitting the rotation of the transfer fixing member to the opposing roller. The image forming apparatus according to claim 1, wherein the drive transmission unit includes a drive transmission gear provided on the transfer fixing member, and a passive gear provided on the counter roller and meshing with the drive transmission gear. The drive transmission means includes a drive transmission friction member provided on the transfer fixing member, and a passive friction member provided on the counter roller and in pressure contact with the drive transmission friction member. Image forming apparatus. 4. The image forming apparatus according to claim 1, further comprising a clutch that switches whether to transmit the rotation of the transfer fixing member to the opposing roller via the drive transmission unit. 5. The clutch is configured such that when the leading end of the recording medium enters between the transfer fixing member and the pressure member, and when the trailing end of the recording medium exits between the transfer fixing member and the pressure member. And the rotation of the transfer and fixing member is transmitted to the counter roller via the drive transmission means, and the recording medium portion between the front end portion and the rear end portion of the recording medium is transferred to the transfer fixing member and the pressure member. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus is turned off when passing between and the rotation of the transfer fixing member so as not to be transmitted to the counter roller via the drive transmission unit. apparatus. A tension applying member that applies tension to the intermediate transfer belt portion on the upstream side in the movement direction of the intermediate transfer belt and the intermediate transfer belt portion on the downstream side in the movement direction of the intermediate transfer belt with respect to the secondary transfer portion. Item 6. The image forming apparatus according to any one of Items 1 to 5. The counter roller, the intermediate transfer belt, and the transfer fixing member are configured such that a friction coefficient between the counter roller and the intermediate transfer belt is larger than a friction coefficient between the transfer fixing member and the intermediate transfer belt. Item 7. The image forming apparatus according to any one of Items 1 to 6.

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