Patent Publication Number: US-7711301-B2

Title: Image transfer device for image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus such as a copier, printer, facsimile device, printing press or composite machines thereof, and more particularly to an image transfer device of a type for forming an electrostatic latent image on an image carrier and performing a primary transfer of a toner image obtained by developing this electrostatic latent image onto an endless belt serving as an intermediate transfer member at a primary transfer portion, that is to say, a primary transfer nip position, and performing a secondary transfer of the toner image that has been primary transferred onto the endless belt onto a recording medium, such as a sheet, carried to a secondary transfer portion, that is to say, a secondary transfer nip position. 
   2. Description of the Related Art 
   While a seamless, endless belt is preferably employed as the intermediate transfer member in the image transfer device employed in this kind of image forming apparatus, for reasons of cost a seamed, endless belt is commonly employed. However, because the seam of a seamed, endless belt protrudes therefrom, undesirable load and torque fluctuations attributable to this protruding section are generated as the belt is moved when the seam passes the primary transfer nip position and the secondary transfer nip position. These fluctuations affect the movement of the belt and cause a change in the moving speed that leads to unstable belt movement. 
   On the other hand, when the front-end portion of the sheet serving as the recording medium P (particularly in the case of a thick sheet (extra thick paper)) goes into the secondary transfer nip position and the rear-end portion thereof comes out of the secondary transfer nip position, load and torque fluctuations attributable to the thickness of the recording medium P that which cause unstable belt movement occur. Because these fluctuations are transferred by way of the endless belt to the primary transfer portion, that is to say, the primary transfer nip portion, fluctuations in the correct transfer position are produced at the primary transfer nip position resulting in generation of a so-called shock jitter. Accordingly, warp leading to unsatisfactory image production is generated in the toner image transferred onto the sheet. 
   The fluctuations affecting the stable movement of the endless belt are attributable to several other factors apart from the protruding seam of the endless belt and the employment of a thick recording medium P such as extra thick paper. These include, for example, minute belt slip caused by load and torque fluctuations, belt stretching, deflection during rotation at the joint mechanism or gear portion serving as the decelerator mechanism of the transmission system and, furthermore, inability of the retention force of the drive motor to withstand the load and torque fluctuations. 
   Increasing the output of the drive sources for driving the endless belt and improving the drive transmission rigidity of the decelerator for transmitting the drive force of the drive sources have been considered as means to obviate the various problems inherent to the prior art described above. Turning of an endless belt around a tension roller urged by a spring or the like of a conventional image forming apparatus and movement of the position of the tension roller to absorb torque fluctuation so as to alleviate shock has been proposed (for example, Japanese Patent No. 3,294,342 and Japanese Laid-open Patent Application No. H06-115752). 
   However, concerns exist regarding the increased size and weight and so on of the apparatus and associated increase in costs that results from increasing the output of the drive force and improving the drive transmission rigidity of the decelerator. In addition, in apparatus in which the endless belt is turned around a tension roller, when the mass of the member for absorbing shock is increased a drop in responsivity and inability to withstand high-frequency sudden load fluctuation occurs and, accordingly, the desired improvement cannot be achieved. 
   On the other hand, image forming apparatuses that utilize a system based on integrated configuring of a section from a secondary transfer portion to a fixing portion have been proposed in recent years with a compacting of the apparatuses and improved reliability of the sheet carry thereof being achieved as a result (for example, Japanese Laid-open Patent Application Nos. H10-63121 and 2004-145260). 
   However, there is a problem inherent to these image forming apparatuses in that, because the load fluctuation that occurs when the front-end portion and rear-end portion of the extra thick paper serving as the recording medium P pass through the fixing nip portion is transferred by way of the intermediate transfer belt to the primary transfer nip position, the shock jitter described above which leads to generation of warp in the transfer image occurs. 
   Technologies relating to the present invention are disclosed in, for example: 
   Japanese Patent No. 3,042,414, 
   Japanese Patent No. 3,514,134, 
   Japanese Laid-open Patent Application. No. S63-189878, 
   Japanese Laid-open Patent Application. No. H04-360179, 
   Japanese Laid-open Patent Application. No. H06-308839, 
   Japanese Laid-open Patent Application. No. H10-268595, 
   Japanese Laid-open Patent Application. No. H11-231677, 
   Japanese Laid-open Patent Application. No. 2000-089601 
   Japanese Laid-open Patent Application. No. 2001-092274, 
   Japanese Laid-open Patent Application. No. 2001-296764, 
   Japanese Laid-open Patent Application. No. 2002-268325, 
   Japanese Laid-open Patent Application. No. 2002-278311, 
   Japanese Laid-open Patent Application. No. 2002-304080 and 
   Japanese Laid-open Patent Application. No. 2005-309227. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an image transfer device for an image forming apparatus of a type performing image transfer at nip positions of a primary transfer portion and secondary transfer portion employing an intermediate transfer member such as an endless belt, wherein transfer of fluctuations in load and torque of an endless belt generated at the nip position of one transfer portion to the nip position of the other transfer portion whereby the generation of warp in the transferred image can be effectively prevented. 
   In an aspect of the present invention, an image transfer device is provided in which an image carried on image carrier is primary transferred at a first transfer nip onto an endless belt configured from endless belt device and supported by a support member and in which the image primary transferred onto the endless belt is secondary transferred at a second transfer nip by secondary transfer device. Deflection is generated in the endless belt between the first transfer nip and the second transfer nip, and the endless belt is driven at the first transfer nip and the second transfer nip individually. 
   In another aspect of the present invention, an image transfer device is provided in which an image carried on image carrier is primary transferred at a first transfer nip onto an endless belt configured from endless belt device and supported by a support member and in which the image primary transferred onto the endless belt is secondary transferred at a second transfer nip by secondary transfer device. Deflection is generated in the endless belt between the first transfer nip and the second transfer nip to prevent torque fluctuation generated at one transfer nip when the endless belt is moved from affecting the other transfer nip. 
   In another aspect of then present invention, an image transfer device is provided in which an image carried on image carrier is primary transferred at a first transfer nip onto an endless belt configured from endless belt device and supported by a support member, and in which the image primary transferred onto the endless belt is secondary transferred at a second transfer nip by secondary transfer device. Deflection is generated in the endless belt between the first transfer nip and the second transfer nip to an extent that torque fluctuation generated at one transfer nip when the endless belt is moved can be absorbed. 
   In another aspect of the present invention, an image transfer device is provided in which an image carried on image carrier is primary transferred at a first transfer nip onto an endless belt configured from endless belt device and supported by a support member, and in which the image primary transferred onto the endless belt is secondary transferred at a second transfer nip by secondary transfer device. Belt length of the endless belt between one transfer nip and the other transfer nip is varied at the upstream side and downstream side of the transfer nips in the direction of movement of the endless belt to an extent that torque fluctuation generated at one transfer nip when the endless belt is moved can be absorbed. 
   In another aspect of the present invention, an image forming apparatus has an image transfer device in which an image carried on image carrier is primary transferred at a first transfer nip onto an endless belt configured from endless belt device and supported by a support member and in which the image primary transferred onto the endless belt is secondary transferred at a second transfer nip by secondary transfer device. Deflection is generated in the endless belt between the first transfer nip and the second transfer nip, and the endless belt is driven at the first transfer nip and the second transfer nip individually. 
   In another aspect of the present invention, a method of image transfer comprises the steps of: forming a first transfer nip by endless belt device comprising an endless belt and image carrier; forming a second transfer nip by the endless belt device and other device; driving a roller serving as a belt support member for turning the endless belt by a drive source dedicated for the endless belt device to move the endless belt at each of the first transfer nip and the second transfer nip individually; varying the speed at which the endless belt is moved at the first transfer nip and the speed at which the endless belt is moved at the second transfer nip to generate deflection in the endless belt between the first transfer nip and the second transfer nip; performing primary transfer, at the first transfer nip, of an image carried by the image carrier onto the endless belt of the endless belt device; and performing secondary transfer, at the second transfer nip, of the image carried by the endless belt. 
   In another aspect of the present invention, a method of image transfer comprises the steps of: forming a first transfer nip by endless belt device comprising an endless belt and image carrier; forming a second transfer nip by the endless belt device and other device; driving a roller serving as a belt support member for turning the endless belt of the endless belt device by a drive source dedicated for the endless belt device to move the endless belt at either the first transfer nip or the second transfer nip; transmitting a drive force from the exterior by an external drive source for the endless belt device to move the endless belt at either the first transfer nip or the second transfer nip so as to vary the speed at which the endless belt is moved at the first transfer nip and the speed at which the endless belt is moved at the second transfer nip, and generate deflection in the endless belt between the first transfer nip and the second transfer nip; performing primary transfer, at the first transfer nip, of an image carried by the image carrier onto the endless belt of the endless belt device; and performing secondary transfer, at the second transfer nip position, of the image carried by the endless belt. 
   In another aspect of the present invention, a method of image transfer comprises the steps of: forming a first transfer nip by endless belt device comprising an endless belt and image carrier; forming a second transfer nip by the endless belt device and other device; transmitting a drive force from the exterior by an external drive source for the endless belt device to move the endless belt of the endless belt device at each of the first transfer nip and the second transfer nip individually; varying the speed at which the endless belt is moved at the first transfer nip and the speed at which the endless belt is moved at the second transfer nip to generate deflection in the endless belt between the first transfer nip and the second transfer nip; performing primary transfer, at the first transfer nip, of an image carried by the image carrier onto the endless belt of the endless belt device; and performing secondary transfer of the image carried by the endless belt at a secondary transfer nip position. 
   In another aspect of the present invention, a method of forming deflection is provided in which deflection is formed in an endless belt of endless belt device supported by a support member between a primary transfer nip position and a secondary transfer nip position of an image transfer device. The speed at which the endless belt is moved at the first transfer nip and the speed at which the endless belt is moved at the second transfer nip are different from each other. 
   In another aspect of the present invention, a transfer device comprises an image carrier on which a toner image is carried: an opposing member provided opposite to the image carrier to form a nip portion; and a rotating member that abuts the image carrier at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the image carrier in the same direction, whereby the toner image is transferred onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, a transfer fixing device comprises a transfer fixing member onto which a toner image is transferred: an opposing member provided opposite to the transfer fixing member to form a nip portion; and a rotating member that abuts the transfer fixing member at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the transfer fixing member in the same direction, whereby the toner image is fixed onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, an image forming apparatus is provided with a transfer device. The transfer device comprises an image carrier on which a toner image is carried: an opposing member provided opposite to the image carrier to form a nip portion; and a rotating member that abuts the image carrier at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the image carrier in the same direction, whereby the toner image is transferred onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, an image forming apparatus is provided with a transfer fixing device. The transfer fixing device comprises a transfer fixing member onto which a toner image is transferred: an opposing member provided opposite to the transfer fixing member to form a nip portion; and a rotating member that abuts the transfer fixing member at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the transfer fixing member in the same direction, whereby the toner image is fixed onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, a transfer method uses a transfer device. The transfer device comprises an image carrier on which a toner image is carried: an opposing member provided opposite to the image carrier to form a nip portion; and a rotating member that abuts the image carrier at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the image carrier in the same direction, whereby the toner image is transferred onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, a transfer fixing method uses a transfer fixing device. The transfer fixing device comprises a transfer fixing member onto which a toner image is transferred: an opposing member provided opposite to the transfer fixing member to form a nip portion; and a rotating member that abuts the transfer fixing member at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the transfer fixing member in the same direction, whereby the toner image is fixed onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, an image forming method has a latent image forming step for forming a latent image on an image carrier and an image developing step for developing the latent image on the image carrier, and uses a transfer device. The transfer device comprises an image carrier on which a toner image is carried: an opposing member provided opposite to the image carrier to form a nip portion; and a rotating member that abuts the image carrier at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the image carrier in the same direction, whereby the toner image is transferred onto a recording medium passing through the nip portion. 
   In another aspect of the present invention, an image forming method has a latent image forming step for forming a latent image on an image carrier and an image developing step for developing the latent image on the image carrier, and uses a transfer fixing device. The transfer fixing device comprises a transfer fixing member onto which a toner image is transferred: an opposing member provided opposite to the transfer fixing member to form a nip portion; and a rotating member that abuts the transfer fixing member at a downstream side of the nip portion and rotates at a speed higher than the drive speed of the transfer fixing member in the same direction, whereby the toner image is fixed onto a recording medium passing through the nip portion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: 
       FIG. 1  is a diagram showing schematically the configuration of an image transfer device of a conventional image forming apparatus; 
       FIG. 2  is a diagram showing schematically the configuration of a main part of an image forming apparatus pertaining to a first embodiment of the present invention; 
       FIG. 3  is a diagram showing the configuration of an image transfer device provided in this image forming apparatus; 
       FIGS. 4A to 4C  are diagrams each showing the configuration of modifications of this image transfer device; 
       FIG. 5  is a diagram showing the configuration of a further modification of this image transfer device; 
       FIG. 6  is a diagram showing the configuration of another example of an image transfer device; 
       FIG. 7  is a diagram showing the configuration of another further example of an image transfer device; 
       FIG. 8  is a diagram showing the configuration of another further example of an image transfer device; 
       FIG. 9  is a diagram showing the configuration of a first modification of the image transfer device shown in  FIG. 8 ; 
       FIG. 10  is a diagram showing the configuration of another further example of an image transfer device; 
       FIG. 11  is a diagram showing the configuration of another further example of an image transfer device; 
       FIG. 12  is a diagram showing the configuration of another further example of an image transfer device; 
       FIG. 13  is a diagram for explaining image transfer onto extra thick paper in an image transfer device of an image forming apparatus comprising photoconductive drums arranged in a tandem configuration; 
       FIGS. 14A and 14B  are diagrams for explaining measurement of speed fluctuation of the extra thick paper in this image transfer onto extra thick paper; 
       FIG. 15  is a diagram for explaining the measurement results of speed fluctuation; 
       FIG. 16  is a diagram showing a configuration of a tandem-type color copier as an image forming apparatus pertaining to a second embodiment of the present invention; 
       FIG. 17  is a diagram showing an example configuration of this color copier that eliminates shock jitter arising when the blank paper is advanced into a nip portion; 
       FIG. 18  is a diagram showing an example configuration of this color copier in which a cleaning roller serves as a cooling roller; 
       FIG. 19  is a diagram showing the configuration of a discharge roller of this color copier; 
       FIG. 20  is a diagram of the state that exists when the rear end of the blank paper passes through a register sensor; 
       FIG. 21  is a diagram of the rear end of the blank paper passing through a fixing nip portion; and 
       FIG. 22  is a diagram of the secondary transfer fixing performed in this embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described hereinafter. It is to be noted that the reference numbers used in each embodiment are independent of the reference numerals of other embodiments, i.e., the same reference numerals do not always designate the same structural elements. 
   First Embodiment 
   The description of this embodiment is based on a description of the prior art pertaining to this embodiment as given hereinafter with reference to the drawings. 
   In modern electrophotographic-type image forming apparatuses an electrostatic latent image is formed on a photoconductive drum or photoconductive belt, the electrostatic latent image is visualized and formed as a toner image by fixing of toner by a developing device, the toner image is primary transferred onto an endless belt-like intermediate transfer member, and the toner image primary transferred onto this intermediate transfer member is secondary transferred onto a recording medium P such as blank paper or an OHP film or the like. For example, as shown in  FIG. 1 , an image is transferred from a photoconductive belt  1  to a recording medium P by primary transfer of a toner image carried on the photoconductive belt  1  of an image carrier device A onto an endless belt (intermediate transfer member)  2  of an intermediate transfer device B at a primary transfer nip position a, and secondary transfer of the image supported on the endless belt  2  by a secondary transfer device C onto a recording medium P such as a sheet carried in the direction shown by the arrow at a secondary transfer nip position b. 
   The use of a seamless-type endless belt  2  in an image forming apparatus such as this is very expensive and, accordingly, from the viewpoint of cost reduction, the use of an endless belt  2  with a seam  4  is preferred. However, an problem inherent to the use of an endless belt  2  with seam  4  pertains to the protrusion formed by the seam  4  and the generation of load fluctuation which cause the moving speed of the endless belt  2  to change and inhibit the stable movement of the endless belt  2  as the seam  4  passes through the primary transfer nip position a and secondary transfer nip position b. 
   In addition, load fluctuation that cause the moving speed of the endless belt  2  to change and inhibit the stable movement of the endless belt  2  is similarly generated when the front end of the recording medium P goes into the secondary transfer nip position b and the rear end thereof comes out of the secondary transfer nip position b. An additional problem pertains to transfer of this disturbance to the stable movement to the primary transfer position a by way of the endless belt  2  which results in an image transfer disturbance and the generation of image warp such as the so-called shock jitter. 
   Although absorption of torque fluctuation to alleviate this shock based on increasing the output of the drive sources for driving the intermediate transfer device B, improving the drive transmission rigidity of the decelerator for decelerating the drive force of the drive sources, and turning the endless belt  2  around a tension roller urged by a spring or the like and moving the position of the tension roller have been hitherto implemented with a view to resolving these problems, a satisfactory resolution to the problems described above has not been achieved with these methods. 
   A first embodiment for resolving the problems described above will be described in detail hereinafter with reference to the drawings. 
     FIG. 2  shows a main part configuration of the internal mechanism of an image forming apparatus such as a copier, printer, facsimile device or combination copier-printer-fax device. 
   In the image forming apparatus shown in the diagram, toner images imaged on photoconductive drums  10   b ,  10   c ,  10   m ,  10   y  by a plurality of imaging devices  100   b ,  100   c ,  100   m ,  100   y  are transferred onto an intermediate transfer member  20  of an intermediate transfer device  200 , the toner images on the intermediate transfer member  20  are transferred onto an endless belt  30  of an endless belt device  300 , and the toner images on the endless belt  30  are transferred onto a recording medium p such as blank paper or OHP film by a secondary transfer device  400 . 
   The imaging device  100  comprises four imaging devices  100   b ,  100   c ,  100   m ,  100   y  of colors black, cyan, magenta and yellow juxtaposedly provided in a tandem-type horizontal arrangement along the direction in which the intermediate transfer member  20  of the intermediate transfer device  200  extends. The photoconductive drums  10   b ,  10   c ,  10   m ,  10   y  are juxtaposedly provided in parallel with the imaging devices  100   b ,  100   c ,  100   m ,  100   y  and are similarly rotatable in the anticlockwise direction. 
   In addition, charging devices  11   b ,  11   c ,  11   m ,  11   y , developing devices  12   b ,  12   c ,  12   m ,  12   y , transfer devices  13   b ,  13   c ,  13   m ,  13   y  and photoconductive drum cleaning devices  14   b ,  14   c ,  14   m ,  14   y  are arranged around the photoconductive drums  10   b ,  10   c ,  10   m ,  10   y . An exposure device  15  is provided above the four imaging devices  100 . 
   As illustrated in the diagram, the endless belt-like intermediate transfer member  20  of the intermediate transfer device  200  is movable in the clockwise direction in the diagram turning between a drive roller  22  and driven roller  23 . The roller-shaped transfer devices  13   b ,  13   c ,  13   m ,  13   y  are provided on the inner side of the intermediate transfer member  20  sandwiching the intermediate transfer member  20  together with the photoconductive drums  10   b ,  10   c ,  10   m ,  10   y . In addition, as illustrated in the diagram, a transfer member cleaning device  25  for removing the residual toner remaining on the intermediate transfer member  20  following transfer is provided around the intermediate transfer member  20  on the left of the intermediate drive roller  22 , and the endless belt device  300  is arranged to the lower right of the driven roller  23 . 
   The endless belt device  300  is configured so that the endless belt  30  is turned between a large roller  31  and small  32  serving as belt support members. In addition, the large roller  31  is pushed against the driven roller  23  by way of the endless belt  30  and intermediate transfer member  20  forming a first transfer nip position n 1  together with the intermediate transfer device  200  serving as the image carrier device. On the other hand, a pressure roller  40  of the secondary transfer device  400  is pushed from the exterior by way of the endless belt  30  against the small roller  32  forming a second transfer nip position n 2  between the endless belt device  300  and secondary transfer device  400 . 
   A recording material tray  50  in which a recording material p is housed in a ream, a supply roller  51  that upon contact with the front end of the uppermost recording material of the recording material p provided in a ream in the recording material tray  50  separates and pays out single sheets of the recording material p in sequence from the top, a guide member  52  for guiding the recording material p paid out by the supply roller  51 , and a resist roller  53  that feeds the recording material p being guided by the guide member  52  to the second transfer nip position n 2  at a set timing are provided below the intermediate transfer device  200  and endless belt device  300  described above. 
   In addition, for recording of a color image on the recording material p employing this image forming apparatus, each of the photoconductive drums  10  of the imaging devices  100 , the intermediate transfer member  20  of the intermediate transfer device  200 , the endless belt  30  of the endless belt device  300 , and the supply roller  51  and so on are rotatably driven at an appropriate timing by, in the case of a copier, operation of a start switch not shown in the diagram, in the case of a printer in accordance with an image signal from a host, and in the case of a facsimile in accordance with an image signal sent by way of a telephone line. 
   In addition, accompanying the rotation of the photoconductive drums  10  the surface of the photoconductive drums  10  is uniformly decharged by a decharging device  11  whereupon, in accordance with a read signal from an original document read device or an image signal from a host or an image signal by way of a telephone line, writing is executed as a result of exposure of a writing light by the exposure device  15 , electrostatic images are formed on the photoconductive drums  10 , toner is individually affixed by the developer devices  12  to visualize the electrostatic latent images, and single color toner images of each of black, cyan, magenta and yellow are formed on the individual photoconductive drums  10 . 
   The single color toner images on the photoconductive drums  10  are overlappingly transferred in sequence onto the intermediate transfer member  20  forming a synthesized color image on the intermediate transfer member  20  as a result of a predetermined transfer bias being imparted to each of the transfer devices  13 . The original state of the photoconductive drums  10  is restored in preparation for subsequent image formation by removal of the residual toner remaining thereon following image transfer by photoconductive drum cleaning devices  14 , and decharging by a decharging device not shown in the diagram. 
   A transfer electric field is formed in the transfer nip position n 1  by imparting of a transfer bias that affords the electrostatic primary transfer of the synthesized color image on the intermediate transfer member  20  onto the endless belt  30 . If overlap of the alternating component and pulse component of the transfer bias occurs at this time the electrostatic force acting on the toner oscillates and, as a result of this oscillation, the adhesive force of the toner weakens and the toner can be easily moved. The intermediate transfer member  20  is restored to its initial state in preparation for subsequent image transfer by removal of residual toner on the surface thereof following image transfer by a transfer member cleaning device  25 . 
   Accompanying the rotation of the supply roller  51 , the uppermost recording material p of the recording material p provided in a ream in the recording material tray  50  is separated and paid out in single sheets, and is then guided and carried by the guide member  52  and led to the second transfer nip position n 2  by the resist roller  53  at a predetermined timing. A transfer bias is imparted to the pressure roller  40  of the secondary transfer device  400  at the second transfer nip position n 2  and, as a result, the toner image carried on the endless belt  30  described above is transferred onto the recording material p passing through the second transfer nip position n 2  and the color image is recorded on the recording material p. 
   While the description given above describes recording of a color image recorded on the recording material p, a color image or monochrome image can be arbitrarily formed by selective use of the imaging devices  100  of the image forming apparatus described above in accordance with a selected single color mode or plurality of colors mode. 
     FIG. 3  shows an image transfer device  500  in which a toner image carried by the intermediate transfer member  20  of the intermediate transfer device  200  serving as the image carrier device is transferred onto the recording material p by way of the endless belt  30  of the endless belt device  300 . 
   With cost reduction in mind, the image transfer device  500  in this diagram uses an endless belt  30  with seam  33  provided to turn between the large roller  31  and small roller  32  with deflection. The endless belt  30  is configured from a 3-layered structure of a polyimide base layer, a silicon rubber layer provided on this base layer, and a fluorine resin upper layer. Replacing the polyimide as the base layer, a metal such as nickel may be employed. In addition, a first drive source  34  and second drive source  35  serving as specialist drive sources for the endless belt device  300  are provided, the large roller  31  being rotationally driven by the first drive source  34  by way of a decelerator  36  and the small roller  32  being rotationally driven by the second drive source  35  by way of a decelerator  37 , and the moving speed at the first transfer nip position n 1  and the moving speed at the second transfer nip position n 2  of the endless belt  30  being set as appropriate. 
   For example, the moving speed at which the endless belt  30  is moved at the second transfer nip position n 2  is set slightly faster than the moving speed at which the endless belt  30  is moved at the first transfer nip position n 1 . 
   The torque fluctuation of the endless belt  30  when the recording material p goes into the second transfer nip position n 2  is absorbed by the deflection t of the endless belt  30  at the downstream position of the second transfer nip position n 2 , and the torque fluctuation of the endless belt  30  when the recording material p comes out of the second transfer nip position n 2  is absorbed by the deflection t of the endless belt  30  at the upstream position of the second transfer nip position n 2 . In addition, because the absorption of the deflection t is greater at the downstream position than the upstream position of the second transfer nip position n 2 , gradual decrease of the deflection t of the endless belt  30  at the downstream position is gradually corrected by making the moving speed at which the endless belt  30  is moved at the second transfer nip position n 2  faster than the moving speed at which the endless belt  30  is moved at the first transfer nip position n 1 . 
   Accordingly, by the simple turning of the endless belt  30  between the large roller  31  and small roller  32  with deflection between the first transfer nip position n 1  and second transfer nip position n 2  and, in addition, the setting of the moving speed at the first transfer nip position n 1  and the moving speed at the second transfer nip position n 2  as appropriate, the effect of a torque fluctuation generated at one transfer nip position on the other transfer nip position can be prevented and, as a result, the need to increase the output of the drive sources of the image transfer device  500  and to improve the drive transmission rigidity of the decelerators  36 ,  37  and so on for relaying the drive force of the drive sources is eliminated and, in turn, concerns regarding the increased size and weight of the apparatus and the associated increased costs are alleviated. 
   In addition, the torque fluctuations of the endless belt  30  generated when the protruding seam  33  of the endless belt  30  passes through the nip positions n 1  and n 2  and when the recording material p goes into the second transfer nip position n 2  and comes out of the second transfer nip position n 2  and so on are absorbed by the deflection t generated in the endless belt  30 , whereupon change in the moving speed of the endless belt  30  caused by these torque fluctuations and the effect of this change on the other transfer nip position can be effectively prevented to ensure elimination of the generation of image warp such as the so-called shock jitter. 
   In this example a third drive source  26  is provided in the intermediate transfer device  200  serving as the image carrier device, and a drive roller  22  is driven by the third drive source  26  by way of the decelerator  27  to move the intermediate transfer member  20 . No drive source is provided in the secondary transfer device  400  and the pressure roller  40  is driven and rotated by the movement of the endless belt  30 . 
   In the example shown in  FIG. 3  specialist drive sources  34 ,  35  are provided in the endless belt  300 , the large roller  31  and small roller  32  being individually driven to move the endless belt  30  by the drive sources  34 ,  35 . As shown in  FIG. 4A , the first drive source  34  is dispensed with and drive force is transmitted to the endless belt  30  as a result of frictional contact thereof with the intermediate transfer member  20  moved by the third drive source  26 , that is to say, drive force is able to be transmitted from the exterior to move the endless belt  30  at the first transfer nip position n 1  employing the third drive source  26  provided in the exterior of the endless belt  300 . 
   In addition, conversely, as shown in  FIG. 4B , the second drive source  35  is dispensed with and a separate fourth drive source  41  for driving the pressure roller  40  of the secondary transfer device  400  is provided, the pressure roller  40  being rotationally driven by the fourth drive source  41  by way of a decelerator  42  with the drive force thereof being transmitted to the endless belt  30  by frictional contact therewith, that is to say, drive force is able to be transmitted from the exterior to move the endless belt  30  at the second transfer nip position n 2  employing the fourth drive source  41  provided in the exterior of the endless belt  300 . 
   Furthermore, as shown in  FIG. 4C , the two specialist drive sources  34 ,  35  of the endless belt  300  are dispensed with and drive force is able to be transmitted from the exterior to move the endless belt  30  at the first transfer nip position n 1  employing the third drive source  26  provided in the exterior of the endless belt  300  and, in addition, drive force is able to be transmitted from the exterior to move the endless belt  30  at the second transfer nip position n 2  employing the fourth drive source  41  provided in the exterior of the endless belt  300 . 
   Here, as shown in  FIG. 5 , when specialist drive sources  34 ,  35  are not employed to rotationally drive the large roller  31  and small roller  32 , a fixedly-provided non-rotating nip forming member  38  for forming the second transfer nip position n 2  may be employed as a belt support member replacing the rotating roller. 
     FIG. 6  shows another example of a configuration of the image transfer device  500 . 
   In this example, the drive sources for moving the endless belt  30  are controlled so that the moving speed at which the endless belt  30  is moved at the second transfer nip position n 2  is faster than the moving speed at which the endless belt  30  is moved at the first transfer nip position n 1  and deflection is continuously generated in the endless belt  30  at the downstream position of the second transfer nip position n 2 . 
   Deflection is reliably generated in the endless belt  30  at the downstream position of the second transfer nip position n 2  in this way and, as a result of the absorption of the torque fluctuation of the endless belt  30  by this deflection when, in particular, the recording material p goes into the second transfer nip position n 2 , the effect on the first transfer nip position n 1  of change in moving speed of the endless belt  30  caused by this torque fluctuation can be effectively prevented. 
   In the image transfer device  500  of this example the effect on the first transfer nip position n 1  of the torque fluctuation of the endless belt  30  when the recording material p comes out of the second transfer nip position n 2  cannot be prevented. However, because the torque fluctuation of the endless belt  30  when the recording material p goes into the second transfer nip position n 2  is greater than when the recording material p comes out of the second transfer nip position n 2 , the adoption of the configuration of this example is especially effective where the torque fluctuation of the former can be largely ignored by comparison to the latter. 
     FIG. 7  is a further example of a configuration of the image transfer device  500 . 
   In addition to the image transfer device  500  of the configuration shown in  FIG. 3 , the image transfer device  500  of this example comprises a microswitch  60  in the downstream position of the second transfer nip position n 2  and a microswitch  61  in the upstream position thereof provided as deflection amount detection means for detecting the deflection amount of the endless belt  30 , and drive control means  62  for performing feedback control of, for example, the first drive source  34  and fourth drive source  41  serving as the drive sources in accordance with an output signal of these microswitches  60 ,  61 . 
   The deflection amount of the endless belt  30  is detected by the microswitches  60 ,  61  and the output signal of the microswitches  60 ,  61  is input into drive control means  62 , and the endless belt  30  is moved as a result of a feedback control performed by drive control means  62  on the first drive source  34  or fourth drive source  41  in accordance with the output signal thereof and rotation of the large roller  31  and pressure roller  40  by way of the decelerators  36 ,  42 , the moving speed of the endless belt  30  at the first transfer nip position n 1  being varied slightly from the moving speed of the endless belt  30  at the second transfer nip position n 2  so as to generate a continuous fixed deflection in the endless belt  30  between the first transfer nip position n 1  and the second transfer nip position n 2 . 
   As a result, the torque fluctuation generated in the endless belt  30  is absorbed by the deflection generated in the endless belt  30 , and decrease in the deflection amount of the endless belt  30  as a result of absorption of the torque fluctuation is detected by the microswitches  60 ,  61  serving as deflection amount detections means. In addition, when the moving speed of the endless belt  30  is destabilized when the recording material p passes through the second transfer nip position n 2  resulting in a disturbance of the deflection amount, this disturbance is detected by the microswitches  60 ,  61 . The deflection amount is gradually restored to the original deflection amount by feedback control performed on the first drive source  34  or fourth drive source  41  by drive control means  62  so that when a subsequent torque fluctuation is generated it can be reliably absorbed, and so that when torque fluctuations are generated continuously in the endless belt  30  the effect of the torque fluctuation of the endless belt  30  generated at one transfer nip position on another transfer nip position can be constantly and effectively obstructed. 
   While in the example illustrated in the diagram the microswitches  60 ,  61  serving as deflection amount detections means are provided in the upstream position and downstream position of the second transfer nip position n 2 , there are no restrictions thereto and one or three or more microswitches may be provided. 
   The example described above describes an image transfer device  500  in which a toner image carried by a intermediate transfer device  200  serving as an image carrier devices is primary transferred onto an endless belt  30  of an endless belt  300  at the first transfer nip position n 1 , and the toner image carried on the endless belt  30  is secondary transferred onto the recording material p at the second transfer nip position n 2 . 
     FIG. 8  shows another example of a configuration of the image transfer device  500 . 
   In this example of the image transfer device  500  toner images are formed by imaging devices  100   b ,  100   c ,  100   m ,  100   y  serving as image carrier devices, the toner images carried by respective photoconductive drums  10   b ,  10   c ,  10   m ,  10   y  are primary transferred onto the intermediate transfer member  20  of the intermediate transfer member  200  serving as the endless belt of the endless belt devices by transfer devices  13   b ,  13   c ,  13   m ,  13   y  at the first transfer nip position n 1 , and the toner images carried by the intermediate transfer member  20  are secondary transferred onto the recording material p by the pressure roller  40  of the secondary transfer device  400  at the second transfer nip position n 2 . 
   Next, to ensure the deflection t is continuously generated in the intermediate transfer member  20  between the first transfer nip position n 1  and second transfer nip position n 2 , the intermediate transfer member  20  is turned by the drive roller  22  and driven roller  23  serving as belt support members, the third drive source  26  and fifth drive source  65  are driven to rotationally drive the drive roller  22  by way of the decelerator  27  and to rotationally drive the pressure roller  40  by way of the decelerator  66 , and the intermediate transfer member  20  is driven at the first transfer nip position n 1  and the second transfer nip position n 2  individually to maintain the deflection t. 
   Accordingly, in particular in the image transfer device  500  of a type comprising imaging devices  100   b ,  100   c ,  100   m ,  100   y  for forming images on the photoconductive drums  10   b ,  10   c ,  10   m ,  10   y  serving as image carrier devices, the torque fluctuation of the intermediate transfer member  20  generated when the seam of the intermediate transfer member  20  serving as the endless belt passes through one of the transfer nip positions and when the recording material goes into the second transfer nip position n 2  and comes out of the second transfer nip position n 2  and so on are absorbed by the deflection t generated in the intermediate transfer member  20 , and change in the moving speed of the intermediate transfer member  20  due to torque fluctuation and the effect thereof on the other transfer nip position can be effectively prevented. 
   The symbol  67  in the diagram schematically denotes toner affixed to the intermediate transfer member  20  from which the toner image carried on the intermediate transfer member  20  is formed. 
   In the image transfer device  500  as shown in  FIG. 8 , because the deflection amount of the intermediate transfer member  20  decreases each time the recording material p passes though the second transfer nip position n 2 , the fifth drive source  65  is driven to rotate the pressure roller  40  of the secondary transfer device  400  and restore and maintain the deflection amount at the original amount when the recording material p is not passing through the second transfer nip position n 2 . The intermediate transfer member  20  can be reliably moved without slip to restore the deflection amount to the original amount while the recording material p is not at the second transfer nip position n 2 . 
     FIG. 9  shows one modification of the image transfer device  500  shown in  FIG. 8 . 
   In this example, a pair of rollers  68  are provided between the second transfer nip position n 2  and the first transfer nip position n 1  of the photoconductive drum  10   y  of the image transfer device  500  of the configuration shown in  FIG. 8  sandwiching the intermediate transfer member  20  and restricting the range across which the deflection t is formed. 
     FIG. 10  shows another modification of the image transfer device  500 . 
   In the image transfer device  500  of this example, toner images carried by each of the photoconductive drums  10   b ,  10   c ,  10   m ,  10   y  as a result of formation thereon by the imaging devices  100   b ,  100   c ,  100   m ,  100   y  are transferred onto the intermediate transfer member  20  of the intermediate transfer device  200  serving as the image carry device, the toner images carried by the intermediate transfer member  20  are primary transferred at the first transfer nip position n 1  onto a transfer fixing belt  70  of a transfer fixing device  700  serving as the endless belt of an endless belt device, and the toner images carried on the transfer fixing belt  70  are secondary transferred at the second transfer nip position n 2  onto the recording material p by the pressure roller  40  of the secondary transfer device  400 . 
   In this transfer fixing device  700  the transfer fixing belt  70  is turned with a deflection t between a small roller  71  and a large roller  72  and, while on the one hand the small roller  71  is pushed against the drive roller  22  of the intermediate transfer device  200  by way of the transfer fixing belt  70  and intermediate transfer member  20 , the large roller  72  is pushed against the pressure roller  40  of the secondary transfer device  400  by way of the transfer fixing belt  70 . 
   In addition, heating means  73  for heating the toner image carried by the transfer fixing belt  70  is provided around the transfer fixing device  700  serving as the endless belt device, the toner  67  being heated by heating means  73  and the heated toner image being transferred and simultaneously fixed to the recording material p by the pressure roller  40  of the secondary transfer device  400 . Heating means  73  is configured from, for example, a halogen heater  74  for heating the toner image and a reflecting plate  75  for reflecting the heat of the halogen heater  74  toward the transfer fixing belt  70 . 
   In addition, in this example, the drive force of a sixth drive source  76  is transferred to the drive roller  22  by way of a decelerator  77  to move the intermediate transfer member  20  turned between the driven roller  23  in the direction shown by the arrow and, in addition, while on the one hand the transfer fixing belt  70  is moved at the first transfer nip position n 1  as a result of frictional contact with the intermediate transfer member  20 , the drive force of a seventh drive source  78  is transmitted to the large roller  72  by way of a decelerator  79  to move the transfer fixing belt  70  at the second transfer nip position n 2  in the direction shown by the arrow, and the pressure roller  40  is driven and rotated in the direction shown by the arrow at the second transfer nip position n 2  as a result of frictional contact with the transfer fixing belt  70 . In addition, at normal operation the moving speed at which the transfer fixing belt  70  moves at the second transfer nip position n 2  is made faster than the moving speed at which the transfer fixing belt  70  moves at the first transfer nip position n 1  to generate deflection t at the downstream position of the second transfer nip position n 2 . 
   Recording material detection means  80  such as a photosensor for detecting the recording material p passing through the second transfer nip position n 2  is provided in the upstream position of the second transfer nip position n 2  in the direction in which the recording material p is carried. Drive control means  81  into which the output signal of recording material detection means  80  is input and which, in accordance with the output signal thereof, performs a feedback control of the sixth drive source  76  and seventh drive source  78  is also provided. More specifically, when the recording material p is detected by recording material detection means  80 , the moving speed at which the transfer fixing belt  70  is moved at the second transfer nip position n 2  is made equal with the moving speed at which the transfer fixing belt  70  moves at the first transfer nip position n 1 , or the latter is made slower than the former, by drive control means  81 . 
   Accordingly, deflection is generated in the transfer fixing belt  70  at the downstream position of the second transfer nip position n 2  prior to the recording material p advancing into the second transfer nip position n 2  whereupon the torque fluctuation of the transfer fixing belt  70  when the recording material p goes into the second transfer nip position n 2  is absorbed. On the other hand, when the recording material p passing through the second transfer nip position n 2  is detected, a feedback control of the sixth drive source  76  and drive source  78  is performed to generate deflection in the transfer fixing belt  70  at the upstream position of the second transfer nip position n 2  whereupon the torque fluctuation of the transfer fixing belt  70  when the recording material p comes out of the second transfer nip position n 2  is absorbed and change in the moving speed of the transfer fixing belt  70  due to the torque fluctuation and the effect of this change on the first transfer nip position n 1  can be effectively prevented. 
   That is to say, when the recording material p goes into the second transfer nip position n 2 , the moving speed of the transfer fixing belt  70  is slowed to generate a speed fluctuation. Because of the deflection of the transfer fixing belt  70  at the downstream position of the second transfer nip position n 2  at this time, the slowing of the moving speed of the transfer fixing belt  70  has no effect at all on the moving speed of the transfer fixing belt  70  at the first transfer nip position n 1  due to a change in the deflection amount. 
   In addition, deflection is generated in the transfer fixing belt  70  at the upstream position of the second transfer nip position n 2  by slowing the moving speed of the transfer fixing belt  70  at timings prior to and subsequent to the recording material p advancing into the second transfer nip position n 2 . While in this state the moving speed of the recording material p increases and a speed fluctuation is generated when the rear end of the recording material p comes out of the second transfer nip position n 2 , because of the deflection of the transfer fixing belt  70  at the upstream position of the second transfer nip position n 2 , the increase of the moving speed of the transfer fixing belt  70  has no effect at all on the moving speed of the transfer fixing belt  70  at the first transfer nip position n 1  due to a change in the deflection amount. 
   In addition, while the example above describes a case in which images carried by all image carrier devices are primary transferred onto the endless belt of the endless belt device at the first transfer nip position n 1  and the images carried on the endless belt are secondary transferred onto the recording material p at the second transfer nip position n 2 , the images carried on the endless belt may be secondary transferred onto a transfer image carrier device for carrying transfer images rather than onto a recording material. 
     FIG. 11  shows another example of the configuration of the image transfer device  500 . 
   In this image transfer device  500  toner images on the photoconductive drums  10   b ,  10   c ,  10   m ,  10   y  of the imaging devices  100   b ,  100   c ,  100   m ,  100   y  are primary transferred onto the intermediate transfer member  20  of the intermediate transfer device  200 , the toner images carried by the intermediate transfer member  20  are secondary transferred onto a transfer fixing roller  84  in which a heater  83  is housed, and the toner images carried by the transfer fixing roller  84  are transferred onto the recording material p and simultaneously fixed by a transfer roller  85 . 
   The recording material p is paid out from the recording material tray  50  by the supply roller  51  and, while being guided by the guide member  52 , is carried by the carry roller  54  and fed out to a third transfer nip position n 3  by the resist roller  53  at a predetermined timing. 
   In addition, the moving speed of the intermediate transfer member  20  serving as the endless belt at the first transfer nip position n 1  and the moving speed of the intermediate transfer member  20  at the second transfer nip position n 2  where the intermediate transfer member  20  is secondary transferred onto the transfer fixing roller  84  serving as the image carrier devices are set as appropriate to generate deflection continuously in the intermediate transfer member  20  between the first transfer nip position n 1  and the second transfer nip position n 2 . 
   In the image transfer device  500  of a type that performs secondary transfer onto the transfer fixing roller  84  serving as the transfer image carrier device at the second transfer nip position n 2  in particular in this way, the torque fluctuation of the intermediate transfer member  20  generated when the seam of the intermediate transfer member  20  serving as the endless belt passes through the transfer nip position and so on are absorbed by the deflection generated in the intermediate transfer member  20  whereupon change in the moving speed of the intermediate transfer member  20  due to torque fluctuations and the effect of this change on the other transfer nip position can be effectively prevented. 
     FIG. 12  shows another example of the configuration of the image transfer device  500 . 
   In this image transfer device  500 , a toner image on a photoconductive drum  10  of a color imaging device  800  is primary transferred onto the transfer fixing belt  70  of the transfer fixing device  700  at the first transfer nip position n 1 , and the toner image carried by the transfer fixing belt  70  is secondary transferred at the second transfer nip position n 2  onto the recording material p by the pressure roller  40  of the secondary transfer device  400  and simultaneously fixed. 
   While a belt may be employed as the color imaging device  800  serving as the image carrying device, in the example shown in this diagram, four developer devices  12   y ,  12   c ,  12   m ,  12   b  of yellow, cyan, magenta and black are provided around a photoconductive drum  10 . In addition, when a full color image is recorded on the recording material p, accompanying rotation of the photoconductive drum  10  in the direction shown by the arrow in the diagram, first, a first color electrostatic latent image is formed on the photoconductive drum  10  by charging thereof by a charging device not shown in the diagram and writing by means of an exposure device whereupon, following development thereof by a first color developer device, a first color toner image is formed on the photoconductive drum  10 . 
   Next, following this first transfer, a second color electrostatic image is formed on the photoconductive drum  10  by a similar charging thereof by a charging device not shown in the diagram and writing by means of an exposure device whereupon, following development by a second color developer device, a second color toner image is overlappingly formed on the first color toner image on the photoconductive drum  10 . A full color image is formed on the photoconductive drum  10  by forming third color and fourth color toner images in the same way. The symbol  86  in the diagram shows schematically the toner used to form the full color image. 
   In the transfer fixing device  700  serving as the endless belt device, the transfer fixing belt  70  comprising an induction exothermic layer is turned between the large roller  31  and small roller  32  serving as belt support members, and an induction heating device  87  comprising an induction coil is provided therearound. In addition, the induction exothermic layer of the transfer fixing belt  70  rotating in the direction shown by the arrow in the diagram is caused to emit heat by the induction coil of the induction heating device  87  whereupon the full color image primary transferred onto the transfer fixing belt  70  of the transfer fixing device  700  is heated at the first transfer nip position n 1 . 
   While not shown in the diagram, the recording material p is similarly paid out by the supply roller from the recording material tray and delivered to the second transfer nip position n 2  by a resistant roller at a predetermined timing. The heated full color image is secondary transferred and pressured by the pressure roller  40  of the secondary transfer device  400  at the second transfer nip position n 2  onto the recording material p, and is simultaneously fixed as it is transferred. 
   In this image transfer device  500  as well, the moving speed of the transfer fixing belt  70  serving as the endless belt at the first transfer nip position n 1  and the moving speed of the transfer fixing belt  70  at the second transfer nip position n 2  are set as appropriate to generate deflection continuously in the intermediate transfer member  20  between the first transfer nip position n 1  and the second transfer nip position n 2 . 
   In an image transfer device  500  of a type in which the image carried on the photoconductive drum  10  of, in particular, the color imaging device  800  serving as the image carrier device is primary transferred at the first transfer nip position n 1  onto the transfer fixing belt  70  of the transfer fixing device  700  serving as the endless belt of the endless belt device and the image carried on the transfer fixing belt  70  is secondary transferred onto the recording material p at the second transfer nip position n 2  in this way, the torque fluctuation of the transfer fixing belt  70  generated when the seam of the transfer fixing belt  70  passes through the transfer nip position are absorbed by the deflection generated by the transfer fixing belt  70  whereupon change in the moving speed of the transfer fixing belt  70  due to this torque fluctuation and the effect of this change on the other transfer nip position can be effectively prevented. 
   The following effects are afforded by the first embodiment described above.
     (1) Because the effect of a torque fluctuation generated at one transfer nip position on the other transfer nip position is prevented by simply turning of an endless belt between belt support members with deflection between a primary transfer nip position and secondary transfer nip position and setting of the moving speed at the primary transfer nip position and the moving speed at the secondary transfer nip position as appropriate, the need to increase output of the drive source of the image transfer device and to improve the drive transmission rigidity of the decelerator relaying the drive force of the drive sources is eliminated and, in turn, concerns regarding the size and width and so on of the apparatus and the associated increased costs can be eliminated.   (2) The torque fluctuation of the endless belt generated when the seam of the endless belt passes through the transfer nip position and when the recording material goes into the secondary transfer nip position and comes out of the secondary transfer nip position are absorbed by deflection generated in the endless belt whereupon change in the moving speed of the endless belt due to this torque fluctuation and the effect of this change on the other transfer position can be effectively prevented and, in turn, the generation of image warp such as so-called shock jitter can be eliminated.   

   Second Embodiment 
   The description of this embodiment is based on a description of the prior art pertaining to this embodiment as given hereinafter with reference to the drawings. 
     FIG. 13  shows a configuration of a primary transfer portion and secondary transfer portion of a conventional color image forming apparatus. The symbol D in the diagram denotes the primary transfer portion and the symbol E denotes the secondary transfer portion. Furthermore, the symbol  2  denotes an endless belt serving as an intermediate transfer member,  9  denotes a drive roller,  18  denotes a resist roller,  21   a  denotes a secondary transfer roller,  21   b  denotes an opposing roller, P denotes a recording material, M denotes a DC motor or pulse motor serving as a drive source, and b denotes a nip portion formed between the secondary transfer roller  21   a  and opposing roller  21   b.    
   In a color image forming apparatus such as this, when the recording material P being carried in the direction shown by the arrow in the diagram is an extra thick paper, load fluctuation generated when the front end portion thereof goes into the nip portion b or the rear end portion comes out of the nip portion b is transferred from the secondary transfer portion E to the drive roller  9  by way of the endless belt  2  serving as the intermediate transfer member. A drive shaft of the drive roller  9  is coupled to the drive motor M by way of a rotating joint mechanism or decelerator mechanism. The intermediate transfer belt  2  winds around the drive roller  9 , minute movement amounts thereof being controlled by friction drive force. When load fluctuation at the secondary transfer portion E cannot be controlled by the drive roller  9  small movement speed errors of the intermediate transfer belt  2  are transferred to the primary transfer portion D upstream thereof which result in the generation of fluctuation, that is to say, shock jitter, in the transfer position which in turn causes defects in the transferred image. 
   Measurement of the speed fluctuation of the intermediate transfer belt  2  will be described in detail hereinafter with reference to  FIGS. 14A and 14B .  FIG. 14A  shows the state of the front end portion of the blank paper P going into a measurement roller  50 , and  FIG. 14B  shows a state of the rear end portion coming out therefrom. The actual measurement results of speed fluctuation in the measurement roller  50  of a blank paper P carried by two pairs of rollers indicate that the generation of speed fluctuation is largest when the front end portion of the blank paper P goes into the measurement roller  50  and when the rear end portion comes out therefrom. 
     FIG. 15  shows one example of the measurement results of this load fluctuation. The symbols ( 14 A) and ( 14 B) in the diagram denote the speed fluctuation in the state shown in  FIGS. 14A and 14B . It is clear from the diagram that speed fluctuation increases significantly when the recording medium P is an extra thick paper. 
   The second embodiment for resolving the problems of the prior art described above will be hereinafter described in detail with reference to the diagrams. 
     FIG. 16  shows a configuration of a tandem-type electrophotographic-type color copier as a color image forming apparatus pertaining to this embodiment. 
   The symbol  1  in the drawing denotes a color copier,  2  denotes an intermediate transfer belt,  3  denotes photoconductive drums,  4  denotes charging devices,  5  denotes a writing device,  6  denotes developer devices,  7  denotes primary transfer devices,  8  denotes cleaning devices,  9  denotes a drive roller,  10  denotes a driven roller (serving as a secondary transfer roller),  11  denotes a cleaning device,  12  denotes a fixing device,  13  denotes a transfer fixing device,  14  denotes a pressure roller,  15  denotes a halogen heater,  16  denotes a paper supply tray,  17  denotes a paper supply roller,  18  denotes a register roller pair,  19  denotes a register sensor,  21  denotes a secondary transfer roller,  22  denotes a transfer fixing roller,  23  denotes a cleaning roller,  25  denotes a scraper,  26  denotes a discharge roller pair,  27  denotes a pressure roller,  30  denotes a reflecting plate,  1 A denotes an image forming portion,  11  denotes a paper supply portion, A denotes an upstream region from a nip portion, B denotes a downstream region of the nip portion, n denotes a secondary transfer nip portion, N denotes a fixing nip portion, and P denotes a recording medium P. 
   The configuration and actuation of this color copier will be described in detail hereinafter. 
   The color copier  1  comprises the image forming portion  1 A located in the middle portion of the apparatus main body, the paper supply portion  1 B located below the image forming portion  1 A, and an image read portion not shown in the diagram located above the image forming portion  1 A. A configuration in which the intermediate transfer belt  2  serving as the intermediate transfer member is arranged with its transfer surface extending in the horizontal direction is provided in the image forming portion  1 A, an image of a color-separated colors and complementary colors being formed on the upper surface of the intermediate transfer belt  2 . That is to say, photoconductive drums  3 Y,  3 M,  3 C,  3 B serving as image carriers able to carry images of complementary color toners (yellow, magenta, cyan, black) are juxtaposedly arranged along the transfer surface of the intermediate transfer belt  2 . The photoconductive drums  3 Y,  3 M,  3 C,  3 B are configured from drums rotatable in the same direction (anticlockwise direction) around which are arranged charging devices  4 , writing device  5  as the optical write means, developer devices  6 , primary transfer devices  7  and cleaning devices  8  for executing image forming processing as the rotation is performed. 
   The alphabetical letters assigned to each symbol denote, as in the case of the photoconductive drum  3 , the different toner colors. The respective color toners are housed in the developer devices  6 . The intermediate transfer belt  2  comprises a configuration that is turned between the drive roller  9  and the driven roller  10 , and which is movable in the same direction therewith in an opposing position to the photoconductive drums  3 Y,  3 M,  3 C,  3 B. The cleaning device  11  for cleaning the surface of the intermediate transfer belt  2  is provided in a position opposing the drive roller  9 . 
   The surface of the photoconductive drum  3 Y is uniformly charged by the charging device  4  and, in accordance with image information from an image read portion, an electrostatic latent image is formed on the photoconductive drum  3 Y. The electrostatic latent image is visualized as a toner image by the developer device  6 Y in which a yellow toner is housed, and the toner image is primary transferred onto the intermediate transfer belt  2  by the primary transfer device  7 Y to which a predetermined bias is imparted. Image formation is similarly performed with the different toner colors of the other photoconductive drums  3 M,  3 C,  3 B to transfer and overlap toner images of each color in sequence on the intermediate transfer belt  2 . The toner remaining on the photoconductive drum  3  following transfer is removed by the cleaning device  8  and, in addition, the electric potential of the photoconductive drum  3  is restored to its original state following transfer in preparation for the next imaging step by a decharging lamp not shown in the diagram. 
   The fixing device  12  is provided in a position opposing the driven roller  10 . The fixing device  12  comprises a transfer fixing belt  13  serving as a transfer fixing member to which a non-fixed toner image as the image on the intermediate transfer belt  2  is transferred, the secondary transfer roller pairs  10 ,  21  for forming the secondary transfer nip portion n with the intermediate transfer belt  2 , the transfer fixing roller  22  for rotationally driving the transfer fixing belt  13 , and the pressure roller  14  serving as a pressure member or opposing member for forming the fixing nip portion N with the transfer fixing belt  13 . The transfer fixing belt  13  comprises an elastic layer of silicon rubber or the like on an approximately 100 μm base material of polyimide or the like, a release layer of a PFA coating or the like being coated thereon as the upper layer. In addition, the halogen heater  15  as heating means for heating the image on the transfer fixing belt  13  and reflecting plate  30  are provided in proximity of the transfer fixing belt  13  in the exterior or inner part thereof. The pressure roller  14  comprises a core metal  14   a  and an elastic layer  14   b  of rubber or the like. 
   The paper supply part  1 B comprises the paper supply tray  16  in which the recording medium P (hereinafter referred to simply as blank paper P) is housed in a ream, the paper supply roller  17  for separating and supplying the blank paper P of the paper supply tray  16  in single sheets in order from the top, and the resist roller  18  which, following temporary stoppage of the supplied blank paper P and correction of diagonal displacement, feeds the blank paper out toward the fixing nip portion N at a timing at which the front end of the image on the transfer fixing belt  13  coincides with a predetermined position in the direction of carry. The timing at which the blank paper is fed out is established in accordance with the register sensor  19  provided in the upstream side of the resist roller pair. A discharge roller for pinching the blank paper and feeding it out in the direction of discharge from the main body is provided in the downstream side of the fixing nip portion N. 
   The toner image T (hereinafter referred to simply as toner) primary transferred onto the intermediate transfer belt  2  from the photoconductive drums  3 Y,  3 M,  3 C,  3 B is secondary transferred by means of an electrostatic force onto the transfer fixing belt  13  by a bias (containing overlaid AC, pulse and so on) imparted to the secondary transfer roller (driven roller)  10  by bias imparting means not shown in the diagram. In order to improve the secondary transfer characteristics, that is to say, the close adhesion between the intermediate transfer belt and the transfer fixing belt  13 , the secondary transfer roller  10  is pressured in the center direction of the transfer fixing belt  13  by a spring by way of a bearing provided in both ends thereof not shown in the diagram. 
   The toner image T transferred from the intermediate transfer belt  2  to the transfer fixing belt  13  is independently heated on the transfer fixing belt  13  until it is fixed on the blank paper P at the fixing nip portion N. Because the process for heating the toner T alone is able to be achieved satisfactorily in advance, the heating temperature can be kept comparatively lower than in conventional methods in which the toner T and blank paper P are simultaneously heated. It was confirmed through actual testing that satisfactory image quality could be produced even at low temperatures of the transfer fixing belt  13  of 110 to 120° C. With consideration of the drop in temperature produced by the blank paper, a heat amount of the order of 1.5 times that used for monochrome image forming apparatuses is adopted in conventional color image forming apparatuses to produce satisfactory gloss. Accordingly, the blank paper is heated to a temperature above what is required and the close adhesion of the toner and blank paper is increased above what is required. 
   Because the temperature for producing satisfactory gloss can be independently set in this embodiment without need for consideration of the blank paper P, the temperature of the transfer fixing belt  13  (fixing set temperature) can be reduced. In addition, because the blank paper P is heated at the secondary nip portion N only, overheating and increase of the close adhesion between the toner T and blank paper beyond what is required is prevented. This embodiment facilitates fixing at low temperature that allows for shortening of the warp-up time and improved energy saving characteristics. In addition, because thermal motion to the intermediate transfer member can be controlled, the durability thereof can be improved. In addition, the temperature of the intermediate transfer can be lowered and thermal deterioration at the intermediate transfer member side can be suppressed. As is described above, the fixing device  12  itself of this embodiment comprises a function for transferring the non-fixed toner image and, compared with conventional fixing devices which simple heat and pressurize the blank paper in which a non-fixed toner image is supported, constitutes a “transfer-type fixing device”. 
     FIG. 17  shows an example configuration for alleviating shock jitter when the blank paper is advanced into a nip portion. The symbols in this diagram correspond to those used in  FIG. 16 . 
   The suspended transfer fixing belt  13  is rotationally driven in the anticlockwise direction in the diagram by the transfer fixing roller  22  rotated by a drive motor not shown in the diagram. The cleaning roller  23  and pressure roller  27  are provided in a space (B region in  FIG. 16 ) from the fixing nip portion N to the secondary transfer nip portion n in the direction of rotation of the belt. The cleaning roller  23  is driven in the same direction as the direction of movement of the belt at a belt contact part thereof, the speed thereof being set by the transfer fixing roller  22  to a speed: V′ higher than a drive line speed: V of transfer fixing belt  13 . The pressure roller  27  is provided to generate a suitable pressure force for dealing with frictional force toward the downstream side in the movement direction produced as a result of the line speed difference of the transfer fixing belt  13  with the transfer fixing roller  23 , and revolves accompanying the movement of the transfer fixing belt  13 . While not shown in the diagram, in accordance with need a member such as a spring can be employed to generate this pressure force. In addition, replacing the pressure roller  27 , elastic pushing by means of a fixed contact member (for example, plate spring) of sufficiently small frictional force is also possible. The residual toner on transfer fixing belt  13  is transferred to the cleaning roller  23  and is scraped off and recovered by the scraper  25 . The circumferential length of the transfer fixing belt  13  is set slightly longer than the length of a inner side connecting line of the two roller pairs. 
   Based on this configuration, the transfer fixing belt  13 , while being rotationally driven, is paid out faster at the position of the cleaning roller  23  than anywhere else and, as a result, a slight sag is formed in the section B between the cleaning roller  23  and the secondary transfer roller  21 . When the blank paper P is advanced into the fixing nip portion N an increase in the load for opening up the fixing roller pair under high pressure occurs and, momentarily, the rotational speed of the transfer fixing roller  22  is slowed. Accordingly, a speed difference with the secondary transfer roller  21  is generated and shock jitter is produced. 
   In this embodiment, even if the rotational speed of the transfer fixing roller  22  slows due to the motion forward of the blank paper, the sag between the cleaning roller  23  and the secondary transfer roller  21  absorbs the difference in belt pay out amount with the secondary transfer roller  21 . As a result, diffusion of shock jitter to the secondary transfer portion the primary transfer portion by way of the intermediate transfer belt can be prevented. In this embodiment the secondary transfer roller  21  may be revolved by the driven transfer fixing roller  22  by way of a belt, and an overrun clutch may be provided in the secondary transfer roller  21  driven at substantially the same speed. 
     FIG. 18  shows an example configuration in which the cleaning roller serves as a cooler roller. The symbol  31  in the diagram denotes a motor gear,  32  denotes a driven gear,  33  denotes a cooling fan,  34  denotes a cooling fin, and Mc denotes a cleaning motor. 
   In this transfer fixing method the heat of the heated transfer fixing belt diffuses through secondary transfer to the intermediate transfer belt  13  and further diffuses to the photoconductive drum resulting in an increase in the temperature of the photoconductive drum  3  to a temperature above that of a conventional method which, in turn, leads to a deterioration in development and transfer of the toner image. To prevent this problem the diffusion of heat must be prevented and, in this present invention, a configuration in which a cooling roller serving jointly as the cleaning roller  23  is provided beyond the transfer fixing nip portion N is adopted. 
   The driving gear  32  is fixed to a shaft end portion of the cleaning roller  23  and, engaging with the motor gear  31 , the drive force of the cleaning motor Mc is transferred to rotate the cooling roller. In a configuration in which the cooling roller serves jointly as the cleaning roller  23 , the scraper  25  is provided to scrape and recover the residual toner transferred from the transfer fixing belt  13 . The cooling roller is configured from a metal of good heat transfer characteristics such as copper or aluminium, the cooling fin  34  being provided in the other end portion of the roller shaft and the heat thereof being radiated by the cooling fan  33 . 
     FIG. 19  shows the configuration of the discharge rollers. The symbol  35  in the diagram denotes a spring,  36  denotes a coupling, and  37  denotes an electromagnetic brake. A discharge roller  26   b  is pressured at both ends toward the discharge roller  26   a  by springs  35  by way of a bearing (not shown in the diagram). The discharge roller comprises a surface layer of high friction coefficient such as a rubber material surface layer of urethane, EPDM or silicon or the like or a metal to which a metal powder or ceramic or the like has been adhered or fused or the surface has been roughened. The electromagnetic brake  37  is coupled by way of the coupling  36  to the shaft end of the discharge roller  26   a  and applies a brake torque action in response to an input voltage. Subsequent to voltage being imparted to the electromagnetic brake when the blank paper P goes into the discharge roller pair  26  and the discharge roller pair  26  are caused to revolve by the carry force of the blank paper P, a brake torque action is applied to slow the carry speed of the blank paper. 
   A description of the blank paper passing through the fixing nip portion N will be given with reference to  FIG. 20  and  FIG. 21 . 
     FIG. 20  shows the rear end of the blank paper passing through the register sensor. The symbol  38  in the diagrams denotes a paper thickness sensor. 
   The diagram shows the front end of the paper passing though the fixing nip portion N and the discharge roller and the rear end passing through the resist sensor. The paper thickness sensor  38  is provided in the pressure-side roller of the resist roller pair  18 . The paper thickness sensor  38  comprises a laser displacement gauge, eddy current displacement gauge and contact displacement gauge, and the paper thickness is measured by calculation of the pressure-side roller displacement amount when the blank paper P goes into the register roller pair  18 . When the blank paper P is carried, the rear end of the blank paper is detected by the resist sensor  19 , and the paper thickness of the blank paper P is detected as is passes though the resist roller  18 . At this time, after passing through the fixing nip portion N, the blank paper P is pinched and carried by the discharge roller pair  26 . At this time the electromagnetic brake  37  coupled to the discharge roller pair  26  is in the voltage OFF state, and the discharge roller pair  26  is revolved by the carry force of the blank paper P. The carry force of the blank paper P is produced from the drive force of the transfer fixing roller  22  of the fixing nip portion N. 
     FIG. 21  shows the rear end of the blank paper passing through the fixing nip portion. 
   The timing of the passing of the rear end of the blank paper P is measured from the detected timing of the resist sensor  19 , and voltage is imparted to the electromagnetic brake  37  at this timing resulting in the action of a brake torque on the discharge roller pair  26  and a slowing of the carry speed of the blank paper P. When the rear end of the blank paper comes out of the fixing nip portion N where it is subjected to a high surface pressure, the load for pinching and carrying the blank paper P is released from the drive force of the transfer fixing roller  32  and, accordingly, the speed of the transfer fixing belt  13  temporarily increases. By slowing the blank paper P at this timing, the speed fluctuation of the transfer fixing belt  13  due to the resiliency of the blank paper P can be suppressed as the blank paper comes out of the nip portion. Accordingly, the diffusion of speed fluctuation from the A region of the upstream side of the transfer fixing belt  13  to the secondary transfer portion and the primary transfer portion by way of the intermediate transfer belt  2  resulting in the generation of shock jitter in the toner image can be prevented. 
   Furthermore, the voltage imparted to the electromagnetic brake  37  is altered in response to the thickness of the blank paper P detected by the paper thickness sensor  38 . In other words, the thicker the paper the greater the voltage imparted to increase the brake torque on the t discharge roller pair  26  whereupon, accordingly, large speed fluctuation that occurs with extra thick paper can be precisely suppressed. 
   When the method of controlling the imparted voltage is digitally controlled by a simple ON/OFF means it is difficult to ensure coincidence between the timing at which the rear end of the blank paper comes out from the transfer nip portion N and the timing at which the voltage is imparted to the electromagnetic brake  37  and, when lag between the timings occurs, speed fluctuation cannot be suppressed. Thereupon, an analog method of control is adopted in which, even through the control itself is a digital control, prior to the timing at which the blank paper comes out the imparted voltage is gradually increased to gradually decrease the rotation of the discharge roller pair and, beyond a calculated timing at which the blank paper would be expected to have come out, the imparted voltage is gradually decreased to gradually increase the rotation of the discharge roller pair. By adopting this method the need for precise synchronization of the timings is eliminated and speed fluctuation can be suppressed even when lag between these timings occurs. 
   Replacing an electromagnetic brake, the rotation control of this discharge roller pair  26  may be based on connection with a drive source such as a motor. 
     FIG. 22  shows one example of a secondary transfer fixing device. The symbol  102  in the diagram denotes a transfer fixing belt,  112  denotes a transfer fixing roller,  114  denotes a pressure roller, and  123  denotes a cleaning roller. 
   The toner image primary transferred onto the transfer fixing belt  102  is heated by the halogen heater  15  and secondary transferred and fixed onto the recording medium P at a transfer fixing portion formed by the transfer fixing roller  112  and pressure roller  114 . The recording medium P is discharged to the exterior of the apparatus by the discharge roller pair  26 . 
   While the description given hitherto with reference to the diagrams pertains to an embodiment for tertiary transfer fixing, as shown in  FIG. 22 , application of the present invention in secondary transfer fixing is also possible. In a word, because the present invention is applicable to transfer nip portions where, in the end, the transfer is performed onto the recording medium P, this transfer is possible irrespective of whether a secondary transfer fixing or a tertiary transfer fixing is being performed. 
   While the transfer onto the recording medium P described above is in all cases described with reference to a transfer fixing configuration, the method of fixing is not restricted to the method outlined in the embodiments above and, accordingly, the use of a discharge roller paper serving additionally as a fixing roller without employing the halogen heater  15  is also possible. 
   Based on the second embodiment as described above, even if a speed fluctuation (temporary slowing of speed of the belt) occurs when the blank paper (particularly extra thick paper) advances into and is held in the fixing nip portion, because a section of deflection is produced in the belt by a roller rotated at high speed in the downstream side of the fixing nip portion, transfer of the speed fluctuation to the section where the image on the image carrier is transferred is absorbed by the belt defection on the upstream side thereof and, accordingly, shock jitter when the front end of the blank paper advances into the transfer nip portion can be satisfactorily avoided. Furthermore, by controlling the rotational speed of the discharge roller for pinching the blank paper beyond the transfer nip part portion, speed fluctuation (temporary slowing of the belt speed) that occurs when the rear end of the blank paper comes out of the nip portion can be suppressed and, in turn, shock jitter can be avoided. 
   Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.