Abstract:
A belt apparatus including a belt configured to rotate around a plurality of belt rollers, a belt speed detection system configured to detect a speed of the belt, and a contact roller configured to contact the belt. A control device is configured to control the contact roller based on a detected speed of the belt. An image forming apparatus includes an image forming part configured to form an image, a first image transfer device, a transfer belt configured to rotate around a plurality of belt rollers and to hold the image transferred by the first image transfer device, a transfer belt speed detection system configured to detect a speed of the transfer belt, and a second transfer roller configured to transfer the image held on the transfer belt to a paper. A control device configured to control the second transfer roller based on a detected speed of the transfer belt.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to Japanese Patent Application No. 2002-103028 filed in the Japanese Patent Office on Apr. 4, 2002, Japanese Patent Application No. 2002-103032 filed in the Japanese Patent Office on Apr. 4, 2002, and Japanese Patent Application No. 2003-47623 filed in the Japanese Patent Office on Feb. 25, 2003, the disclosures of which are incorporated by reference herein in their entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a belt apparatus and an image forming apparatus such as a copier, a facsimile machine, a printer, or other similar image forming apparatus. 
   2. Description of the Related Art 
   Recently, the market is demanding color printers and color copiers. Such color printers and copiers are conventionally either a one drum type, which includes plural developing devices positioned around a photo conductor, or a tandem type having each developing device positioned around each photo conductor. The one drum type has an advantage in that it is comparatively smaller than the tandem type and has a reduced cost. On the other hand, the tandem type has an advantage that it can provide increased copying or printing speed. 
   In the field of a color electronography, the tandem type device is recently used because a speed demand of the color electronography is required to be the same as with monochoromatic electronography. An example of the conventional tandem type device is explained by reference to  FIGS. 9-11 .  FIG. 9  is a perspective view of an image forming apparatus of a direct transfer type, and  FIG. 10  is a side view of the device shown in  FIG. 9 , while  FIG. 11  is a side view of an image forming apparatus of an indirect transfer type. 
   As shown in  FIGS. 9 and 10 , photo conductors  100 K,  100 Y,  100 C and  100 M of the direct transfer type device are disposed in a straight line along a conveyance belt  500  that conveys a paper  400 . Each motor  100   a  drives a respective photo conductor  100 K,  100 Y,  100 C, and  100 M. The conveyance belt  500  is stretched between a driven roller  501  that is driven by motor  501  a, and a roller  502 . As seen in  FIG. 10 , the direct transfer type device includes a feed device  700  and a fixing device  800 . The paper  400  is moved by the feed device  700  to the belt  500 , where color toner images are formed on the paper  400  by each of the photo conductors  100 K,  100 Y,  100 C and  100 M. The paper with the toner image is then moved by the belt  500  to the fixing device  800 , where the toner image is fixed to the paper. 
   As shown in  FIG. 11 , photo conductors  100 K,  100 Y,  100 C and  100 M of the indirect transfer type are disposed in a straight line along an intermediate transfer belt  600 . The intermediate belt  600  is stretched around a driven roller  201 , and rollers  202  and  203 . Color toner images are superimposed over one another onto the intermediate transfer belt  600 . A multicolor toner image on the intermediate transfer belt  600  is then transferred to a paper by way of a second transfer device  300 . As with the direct transfer device, the device of  FIG. 11  includes a feed device  900  and a fixing device  1000 . A paper is moved by the feed device  900  to a transfer part  1100  at a nip between the roller  203  and the second fixing device  300 , where the multicolor toner image is formed on the paper. The paper with the toner image is then moved to the fixing device  1000 , where the toner image is fixed to the paper. 
   Comparing the direct transfer type with the indirect transfer type, the size of conveyance distance of the direct transfer type device is bigger than the size of the conveyance distance of the indirect transfer type device. Specifically, as seen in  FIG. 10 , a paper feed part  700  and a fix part  800  of the direct transfer type is required to be positioned beside the conveyance belt  500 . On the other hand, the indirect transfer type device shown in  FIG. 11  allows the paper feed part  900  and the fixing part  1000  to be disposed under the intermediate transfer belt  600 . This positioning under the intermediate transfer belt  600  allows the conveyance distance from the feed device to the fixing device of the indirect device to be smaller than that of a direct transfer device. 
   Further, in order to minimize the conveyance distance of the direct transfer type device in  FIGS. 9 and 10 , the fixing part  800  is located very close to the conveyance belt  500 . This configuration causes the fixing device  800  to influence the image formed on the paper  400  by the photo conductor  100 K. On the other hand, the fixing device  1000  of the indirect transfer type device does not influence the image formation because a relatively large space is provided between the fixing part  1000  and a transfer part  1100 . Therefore, the indirect transfer type device is generally preferred over the direct transfer device in terms of image quality. 
   In addition, both the direct and indirect transfer devices have a problem in that it is difficult to superimpose color toner images over one another in a multicolor image because the speed of the belt of these devices changes. Therefore, Japanese Registered Patent No.3186610 bulletin discloses a device that can control the speed of a photo conductor and a conveyance belt based on data obtained from detecting a pattern formed on the belt. However, when a second transfer device of the disclosed device has a change of speed, the change affects the first and the second transfers. Further, if the change is too big, speed of the intermediate transfer belt becomes out of control. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to reduce or solve any or all of the above-described problems. 
   A more specific object of the present invention is to provide an indirect transfer belt apparatus or image forming apparatus that can control the change of speed of a second transfer device. 
   These and other objects of the present invention are provided by a belt apparatus including a belt configured to rotate around a plurality of belt rollers, a belt speed detection system configured to detect a speed of the belt, a contact roller configured to contact the belt, and a control device configured to control the contact roller based on a detected speed of the belt. 
   In another aspect of the present invention, an image forming apparatus includes an image forming part configured to form an image, a first image transfer device, a transfer belt configured to rotate around a plurality of belt rollers and to hold the image transferred by the first image transfer device, a transfer belt speed detection system configured to detect a speed of the transfer belt, a second transfer roller configured to transfer the image held on the transfer belt to a paper, and a control device configured to control the second transfer roller based on a detected speed of the transfer belt. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
       FIG. 1  is a perspective view of an image forming apparatus in accordance with a first embodiment of the present invention; 
       FIG. 2  is a side view of the image forming device of  FIG. 1 ; 
       FIG. 3  is a diagram showing the relationship between the intermediate transfer belt and a detect device in accordance with the first embodiment of the present invention; 
       FIG. 4  is a diagram showing a speed detection pattern on the intermediate transfer belt in accordance with the first embodiment of the present invention; 
       FIG. 5  is a block diagram showing a control system in accordance with the first embodiment of the invention; 
       FIG. 6  is a perspective view of an image forming apparatus in accordance with a second embodiment of the present invention; 
       FIG. 7  is a side view of the device shown in  FIG. 6 ; 
       FIG. 8  is a block diagram showing a control system in accordance with the second embodiment of the present invention; 
       FIG. 9  is a perspective view of an image forming apparatus of a direct transfer type device; 
       FIG. 10  is a side view of the device shown in  FIG. 9 ; and 
       FIG. 11  is a side view of an image forming apparatus of an indirect transfer type. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  is a perspective view of an image forming apparatus in accordance with a first embodiment of the present invention, and  FIG. 2  is a side view of the image forming device of FIG.  1 . As seen in these figures, the image forming apparatus of this embodiment includes photo conductors  100 K,  100 Y,  100 C, and  100 M positioned along an image transfer belt  200 . The photoconductors carry latent images formed by the image forming part  10 . Each of the motors  100   a  drives a respective photo conductor. The photo conductors  100 K,  100 Y,  100 C and  100 M contain black, yellow, cyan and magenta toner, respectively. When the intermediate transfer belt  200  rotates in direction of arrow A, each black, yellow, cyan, magenta toners are transferred to the intermediate transfer belt  200  such that each color is overlapped to form a multicolor image. The intermediate transfer belt  200  is stretched around driven roller  201 , roller  202  and pressure roller  203 . The driven roller  201  is driven by motor  201  a. A second transfer roller  300  is positioned opposing the pressure roller  203  with the intermediate transfer belt  200  interposed therebetween. The second transfer roller  300  is controlled by a motor  300   a  based on a speed of the intermediate transfer belt  200  as will be described below. 
   As best seen in  FIG. 2 , the driven roller  201 , roller  202 , and pressure roller  203  stretch the intermediate transfer belt  200  to form three plane parts  204 ,  205 ,  206 . The photo conductors  100 K,  100 Y,  100 C,  100 M are located along the plane part  204 , between the roller  201  and the roller  202 . A detect sensor  211  located in the plane part  206  in a downstream position of the pressing roller  203  reads a speed detective pattern  210  formed on the intermediate transfer belt  200  for detecting the speed of the intermediate transfer belt  200 . The speed detecting sensor  211  is disposed downstream of the pressure roller  203  in a direction of rotation of the intermediate transfer belt  200 . Because the location of the sensor  211  is near the second transfer roller  300 , the sensor  211  can detect the speed of the belt  200  near the second transfer roller  300 , and a linear control becomes possible. The present inventors have determined that if a sensor is disposed near the plane part  205  close to the driven roller  201 , the tension of the intermediate transfer belt  200  is not constant in this area and the sensor  211  cannot precisely detect a speed of the belt. On the other hand, the tension is constant in the plane part  206 , which is the reason why the sensor  211  is located near the plane part  206 . Further, the speed of the second transfer roller  300  can be controlled precisely because the sensor  211  is located near the second transfer roller  300 . 
   As also seen in  FIGS. 1 and 2 , a sensor  212  is positioned adjacent to the roller  300  to detect a speed of the roller. In one embodiment, the sensor  212  is part of an encoder system provided on the second transfer roller  300 . The encoder system may include an encoder pattern (not shown) provided on an edge of the second transfer roller, which the sensor  212  detects to determine a speed of the second transfer roller  300 . Thus, the image forming device of the first embodiment includes a sensor  211  for detecting a speed of the intermediate transfer belt  200 , and a sensor  212  for detecting the speed of the roller  300 . Therefore, a difference of speed between the intermediate transfer belt  200  and the second transfer roller  300  can be determined and controlled to be substantially constant, or near zero. As a consequence, the effect of the rotation of the second transfer roller  300  on the intermediate transfer belt  200  is reduced by the present invention. 
     FIG. 3  is a diagram showing the relationship between the intermediate transfer belt  200  and the speed detect sensor  211  according to the first embodiment of the present invention. As seen in this figure, a reading mask of the speed detect sensor  211  is downward facing in a direction of gravity. Therefore, substances such as dirt or trash are prevented from attaching to the reading mask and the sensor  211  can detect the speed precisely. Furthermore, as shown in  FIG. 1 , because the speed detective pattern  210  is disposed on the backside, or inside, surface of the intermediate transfer belt  200 , substances such as toner or paper powder are prevented from attaching to the speed detective pattern  210  and the sensor can detect the speed precisely. 
     FIG. 4  is a diagram showing a speed detection pattern on the intermediate transfer belt according to an embodiment of the invention. As shown in  FIG. 4 , the speed detection pattern  210  includes two patterns each disposed a distance L apart from the center of the intermediate transfer belt  200 . In a preferred embodiment, each pattern is detected by a sensor and a speed of the intermediate transfer belt  200  is determined for each pattern. A difference between the detected speed of the two patterns is caused by meandering of the intermediate transfer belt  200 . When this difference is too large, the image forming device determines which of the detected speeds corresponds to a normal speed of the intermediate transfer belt, and disregards the other detected speed as an error output. Therefore, the sensor  211  can detect the speed precisely by utilizing two different speed detection patterns on the intermediate transfer belt  200 . 
     FIG. 5  is a block diagram showing a control system of the image forming device in accordance with the first embodiment of the present invention. As seen in this figure, the control device includes a CPU, a first motor driver  271 , and a second motor driver  272 . The first motor driver  271  controls a first drive motor  201   a , which drives the driven roller  201  for rotating the intermediate transfer belt  200 , as previously described. The speed detect sensor  211  detects the detect pattern  210  on the intermediate transfer belt  200  and provides a detected output to CPU  270 . The CPU  270  calculates the speed of the intermediate transfer belt  200  and commands the motor driver  271  to drive the drive motor  201   a  in the regulation speed. Similarly, the second motor driver  272  controls a second drive motor  300   a , which drives the second transfer roller  300  while the sensor  212  detects an encoder pattern on the roller  300 . 
   Upon receiving the input signals from the sensors  211  and  212 , the CPU  270  compares a input signal of the sensor  212  with a input signal of the sensor  211  and calculates the difference of speed between the intermediate transfer belt  200  and the second transfer roller  300 . The CPU  270  then commands the motor driver  272  to eliminate this difference. Therefore, the speed of the intermediate transfer belt  200  corresponds to the speed of the second transfer roller  300  by repeating a feedback control. As a consequence, the irregular rotation of the second transfer belt  200  can be controlled. 
     FIG. 6  is a perspective view of an image forming apparatus in accordance with a second embodiment of the present invention, and  FIG. 7  is a side view of the image forming device of FIG.  6 . As seen in these Figures, the image forming apparatus of this embodiment includes photo conductors  150 K,  150 Y,  150 C, and  150 M positioned along an image transfer belt  251 . The photoconductors carry latent images formed by the image forming part  10 . Each of the motors  150   a  drives a respective photo conductor. The photo conductors  150 K,  150 Y,  150 C and  150 M contain black, yellow, cyan and magenta toner, respectively. When the intermediate transfer belt  250  rotates in direction of arrow B, each black, yellow, cyan, magenta toners are transferred to the intermediate transfer belt  250  such that each color is overlapped to form a multicolor image that is transferred to paper  450 . The intermediate transfer belt  250  is stretched around driven roller  251 , roller  252  and pressure roller  253 . The driven roller  251  is driven by motor  251   a . A second transfer roller  350  is positioned opposing the pressure roller  253  with the intermediate transfer belt  250  interposed therebetween. The second transfer roller  350  is controlled by a motor  350   a  based on a speed of the intermediate transfer belt  250  as will be described below. 
   As also seen in  FIGS. 6 and 7 , a sensor  261  is positioned adjacent to the pressing roller  253  to detect a speed of the roller  253 , and a sensor  262  is positioned adjacent to the roller  350  to detect a speed of this roller. In one embodiment, an encoder pattern  260  is disposed on the outer circumference of the pressing roller  253  and the second transfer roller  350  and the sensors  261  and  262  detect the encoder patterns. In another embodiment, the encoder pattern may be formed on an edge of the rollers  253 . Thus, the image forming device of the second embodiment detects a speed of the pressing roller  253  and the second transfer roller  350 . Therefore, a difference of speed between the pressing roller  253  and the second transfer roller  350  can be determined and controlled to be substantially constant, or near zero. As a consequence, the effect of the rotation of the second transfer roller  350  on the intermediate transfer belt  250  is reduced by the present invention. 
     FIG. 8  is a block diagram showing a control system of the image forming device in accordance with the second embodiment of the present invention. As seen in this figure, the control device includes a CPU  280 , a first motor driver  281 , and a second motor driver  282 . The first motor driver  281  controls a first drive motor  251   a , which drives the driven roller  251  for rotating the intermediate transfer belt  250 , as previously described. When the intermediate transfer belt  250  rotates, the pressure roller  253  also rotates. The speed detect sensor  261  detects the detect pattern on the pressure roller  253  and provides a detected output to CPU  280 . The CPU  280  calculates the speed of the intermediate transfer belt  250  by way of the roller  253 , and commands the motor driver  251  to drive the drive motor  251   a  in the regulation speed. Similarly, the second motor driver  282  controls the second drive motor  350   a , which drives the second transfer roller  350  while the sensor  262  detects an encoder pattern on the roller  350 . 
   Upon receiving the input signals from the sensors  261  and  262 , the CPU  280  compares a input signal of the sensor  262  with an input signal of the sensor  261  and calculates the difference of speed between the intermediate transfer belt  250  and the second transfer roller  350 . The CPU  280  then commands the motor driver  282  to eliminate this difference. Therefore, the speed of the intermediate transfer belt  250  corresponds to the speed of the second transfer roller  350  by repeating a feedback control. As a consequence, the irregular rotation of the second transfer belt  250  can be controlled. Further, instead of the position of the outer circumference of the roller, a speed detect pattern can be disposed the edge of the pressure roller instead of on the circumference of the pressure roller. 
   Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.