Abstract:
A belt conveyor includes a driving roller, a driven roller, a conveyor belt wound around the driving roller and driven roller to run endlessly by rotation of the driving roller, and a pair of regulation members arranged adjacent to both the ends of the axial direction of the driving roller to regulate movement of the conveyor belt in the axial direction of the driving roller. The conveyor belt has a conveying portion which conveys an image receiving medium and a returning portion which returns from an ending position of the conveying portion to a starting position of the conveying portion. The pair of regulation members each have a regulating surface that is arranged at a position able to contact a side edge of the conveyor belt at only the returning portion side of the conveyor belt below a middle position between the conveying portion and the returning position where the conveyor belt winds around the driving roller.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a belt conveyor that conveys an image receiving medium held on a conveying belt to a developed image formed on an image carrier, and an image forming apparatus that transfers the developed image onto the image receiving medium conveyed by the belt conveyor and thereby forms an image onto the image receiving medium. 
     2. Description of the Related Art 
     In these years, demands for color printing has been increasing in offices, and accordingly color copiers are spreading widely. As one of these color copiers, for example, well known is a 4-drum tandem type color copier. In this type of color copier, toner images of respective colors are formed on 4 tandem photosensitive drums, and toner images of respective colors are transferred and lapped one after another onto a image receiving medium that is transferred via a conveyor belt, and transferred toner images of respective colors are melted and fixed, thereby a color image is output on the image receiving medium. 
     In more details, toner images of yellow, magenta, cyan, and black are formed on the surface of 4 photosensitive drums. The image receiving medium is electro statically sucked onto the conveyor belt that is rolled over the surface of respective photosensitive drums and run endlessly, and thereby conveyed, and transfer electric fields are formed by transfer means including transferring rollers and transfer brushes and so forth that are arranged to surfaces of the respective photosensitive drums. By these transfer electric fields, toner images of respective colors are piled one after another and transferred onto the image receiving medium, thereby a color image is output onto the image receiving medium. 
     However, in the prior art, as mentioned above, it was extremely difficult to transfer toner images of 4 colors, i.e., yellow, magenta, cyan and black onto a image receiving medium with their respective transfer positions arranged accurately, accordingly it was hard to output a quality image without color displacement, which has been a problem in the prior art. 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide a belt conveyor that may make a conveyor belt to convey a image receiving medium stably run at a specified position, and an image forming apparatus that is equipped with the belt conveyor, and may remove image displacement output on the image receiving medium that is conveyed via the belt conveyor, and form quality images. 
     According to the present invention, there is provided a belt conveyor comprising a driving roller; a driven roller arranged roughly in parallel with, and away from the driving roller; a conveyor belt wound around the driving roller and driven roller, to run endlessly by rotation of the driving roller; and a regulation member arranged adjacent to at least one end of the axial direction of the driving roller, to regulate the moving of the conveyor belt in the axial direction of the driving roller; wherein the regulation member has a regulating surface that may slide on and contact to a lower part portion in a range where the conveyor belt contacts the driving roller. 
     Further, according to the present invention, there is provided an image forming apparatus comprising a driving roller; a driven roller arranged roughly in parallel with, and away from the driving roller; a conveyor belt wound around the driving roller and driven roller, and has a transfer surface to hold an image receiving medium, to run endlessly by rotation of the driving roller; regulation members arranged adjacent to both the ends of the axial direction of the driving roller, to regulate the moving of the conveyor belt in the axial direction of the driving roller; plural image carriers arranged to the conveying surface of the conveyor belt and along the running direction; image forming means for forming a developed image on each of the image carriers; and transfer means for transferring the developed image onto the image receiving medium that is held by the conveying surface and made to go through the plural image carriers; wherein the regulation members have regulating surfaces that may slide on and contact to lower parts in ranges where the conveyor belt contacts the driving roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing a structure of an important portion of an image forming apparatus according to a preferred, embodiment under the present invention; 
     FIG. 2 is a schematic diagonal view showing a laser optical system for yellow built in the image forming apparatus shown in FIG. 1; 
     FIG. 3 Is a diagonal view showing a transfer mechanism according to the above first preferred embodiment built in the image forming apparatus shown in FIG. 1; 
     FIG. 4 is a diagram to show an experiment to investigate appropriate positions of the regulating surface of the regulation member by the transfer mechanism shown in FIG. 3; 
     FIG. 5 is a diagonal view showing a structure according to a second preferred embodiment under the present invention; 
     FIG. 6 is a cross sectional view showing details of the important portion of FIG. 5; 
     FIG. 7 is a diagonal view showing a structure according to a third preferred embodiment under the present invention; 
     FIG. 8 is a view to explain an experiment to investigate appropriate positions of the regulating surface of the regulation member by the transfer mechanism shown in FIG. 7; 
     FIG. 9 is a diagonal view showing a structure according to a fourth preferred embodiment under the present invention; 
     FIG. 10 is a schematic top view showing the relation between the regulation member at the driving roller side and that at th driven roller side; 
     FIG. 11 is a diagonal view showing the relation between the regulation member at the driving roller side and that at the driven roller side; 
     FIG. 12 is a top view showing the transfer mechanism shown in FIG. 11; and 
     FIG. 13 is a graph showing the results of experiment to investigate the distance margin between the regulating surface of the regulation member at the driving roller side and the regulating surface of the regulation member at the driven roller side. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is illustrated in more details by reference to the following referential examples and preferred embodiments wherein. 
     In FIG. 1, shown as an image forming apparatus under a preferred embodiment of the present invention is a structure of an important portion of a 4 tandem type full color copier. 
     This color copier has 4 photosensitive drums (image carriers)  1 Y,  1 M,  1 C and  1 Bk that are arranged along a roughly horizontal direction with specific intervals. Around the respective photosensitive drums  1 Y,  1 M,  1 C and  1 Bk, arranged are plural image forming units (image forming means)  10 Y,  10 M,  10 C and  10 Bk that form images of corresponding colors on the respective photosensitive drums  1 Y,  1 M,  1 C and  1 Bk. And under the respective photosensitive drums  1 Y,  1 M,  1 C and  1 Bk, arranged are a conveying mechanism  20  as a belt conveyor under the present invention for conveying a image receiving medium P along the surface of each photosensitive drum. 
     The conveying mechanism  20  has a driving roller  22  and a driven roller  24  that are away from each other in roughly horizontal direction, and between this pair of rollers  22  and  24 , arranged is an endless conveyor belt  21 . Inside of the conveyor belt  21 , arranged are 4 transferring rollers (transfer means)  5 Y,  5 M,  5 C and  5 Bk to the respective photosensitive drums  1 Y,  1 M,  1 C and  1 Bk. 
     Each of the respective image forming units  10 Y,  10 M,  10 C and  10 Bk is equipped with main chargers  2 Y,  2 M,  2 C and  2 Bk, laser systems  3 Y,  3 M,  3 C and  3 Bk, developing devices  4 Y,  4 M,  4 C and  4 Bk, cleaners  6 Y,  6 M,  6 C and  6 Bk, charge removers  7 Y,  7 M,  7 C and  7 Bk. 
     Herein, as one example, the yellow image forming unit  10 Y is described in details. 
     As shown in FIG. 2, in the yellow laser optical system  3 Y, on the basis of image data coming in from external devices and so forth, a semiconductor laser generator  32  is driven by a printing signal that is sent from a printing control portion not illustrated herein, and laser beam  31  is output. This output beam light  31  is shaped by a beam shaping optical system comprising for instance a cylindrical lens  33  or so, and is polarized by a polygon mirror  34  as a rotating polygon mirror that is rotated by a high speed motor not illustrated herein. 
     The polarized beam light  31  goes through an fθ lens  35 , and is reflected by a reflection mirror  36 , and thereby forms a spot having a necessary resolution at a specified exposure position on the photosensitive drum  1 Y, and then scanned and exposed, thereby forms a electrostatic latent image on the photosensitive drum  1 Y. And the polarized beam light  31  is detected by a beam detector  37  comprising a photo diode, and thereby synchronization of main scanning direction (horizontal direction). 
     Now back to FIG. 1, around the photosensitive drum  1 Y, arranged are a main charger  2 Y that charges the surface of the photosensitive drum  1 Y, the above mentioned laser optical system  3 Y, a developing device  4 Y, a transferring roller  5 Y, a cleaner  6 Y and a charge remover  7 Y. 
     The photosensitive drum  1 Y is rotated at external circumferential speed Vo by a driving motor not illustrated herein. The surface of this photosensitive drum  1 Y is charged by a main charger  2 Y comprising a charging roller having electric conductivity that is arranged to the surface concerned. By the way, this charging roller rotates, by contacting the surface of the photosensitive drum  1 Y. 
     The surface of the photosensitive drum  1 Y is formed with organic system photo conductive material. This photo conductive material is normally at high resistance, but once light is radiated onto it, the specific resistance of its light radiation portion will change. Therefore, by irradiating light corresponding to yellow printing pattern via the laser optical system  3 Y onto the surface of the charged yellow photosensitive drum  1 Y, the electrostatic latent image of yellow printing pattern is formed on the surface of the photosensitive drum  1 Y. 
     An electrostatic latent image is one that is formed on the surface of the photosensitive drum  1 Y by charging. Namely, by light radiation from the laser optical system  3 Y, the specific resistance of the radiated portion of photo conductive material decreases, charged electric charge of the surface of the photosensitive drum  1 Y flows, and electric charge remains at the portion which was not light radiated by the laser optical system  3 Y, thereby, an electrostatic latent image is formed. This is what is called a negative latent image. 
     In this manner, the photosensitive drum  1 Y where an electrostatic latent image has been formed rotates to the specific developing position at circumferential speed Vo. And at this developing position, the electrostatic latent image on the photosensitive drum  1 Y is toner imaged as a visible image by the developing device  4 Y. 
     Contained in the developing device  4 Y is a yellow toner that contains yellow dye and is formed by resin. The yellow toner is abrasion charged by being stirred by a developing roller  40 Y in the developing device  4 Y, and thereby has electric charge of the same polarity as charged electric charge on the photosensitive drum  1 Y. As the surface of the photosensitive drum  1 Y goes through the developing device  4 Y, yellow toner attaches in electrostatic manner only to the latent image portion where electric charge has been removed, and a electrostatic latent image is developed by yellow toner (in reverse development). 
     The photosensitive drum  1 Y where a yellow toner image has been formed continuously rotates at circumferential speed Vo, by the transferring roller  5 Y at a specified transfer position, a toner image is transferred onto an image receiving medium P that is supplied timingly by paper supply system described later herein. The image receiving medium P, being held on the conveyor belt  21  of the conveying mechanism  20 , is sent to the transfer position. 
     The paper supply system  40  for supplying the image receiving medium P has a paper supply cassette  41 , a pickup roller  42 , a feed roller  43 , a paper supply guide  44 , and an aligning roller  45 . 
     Only one sheet of the image receiving medium P that is taken out of the paper supply cassette  41  by the pickup roller  42  is conveyed by the feed roller  43  along the paper supply guide  44  to the aligning roller  45 . The aligning roller  45  positions the image receiving medium P correctly, then sends the image receiving medium P to a suction roller  25  on the conveyor belt  21 . The external circumferential speed of the aligning roller  45  and the circumferential speed of the conveyor belt  21  are set so as to be equal to the circumferential speed Vo of the photosensitive drum  1 Y. The image receiving medium P, whose part being held by the aligning roller  45 , is conveyed to between the suction roller  25  and the conveyor belt  21 . At that position, the image receiving medium P is charged by electric charge, and thereby is statically sucked onto the conveyor belt  21  in electro static manner, and is sent along with the conveyor belt  21  that runs at the same speed Vo of that of the photosensitive drum  1 Y to the transfer position of the photosensitive drum  1 Y. 
     At the transfer position, the yellow toner image on the photosensitive drum  1 Y that contacts the image receiving medium P is released from the photosensitive drum  1 Y and transferred to the image receiving medium P by the transferring roller  5 Y. As the result, a yellow toner image of printing pattern based on yellow printing signal is formed on the image receiving medium P. 
     The transferring roller  5 Y comprises raw material having electric conductivity. From the back side of the conveyor  21 , this transferring roller  5 Y supplies an electric field having polarity opposite to the electric charge of yellow toner statically attaching onto the photosensitive drum  1 Y. This electric field works through the conveyor belt  21  and the image receiving medium P to the yellow toner image on the photosensitive drum  1 Y, consequently, the electric field transfers the toner image from the photosensitive drum  1 Y to the image receiving medium P. 
     In this manner, the image receiving medium P that has transferred the yellow toner image is made to pass a magenta image forming unit  10 M, cyan image forming unit  10 C and black image forming unit  10 Bk in order. The magenta image forming unit  10 M, cyan image forming unit  10 C and black image forming unit  10 Bk respectively comprise of same structure components and workings with only replacement of yellow (Y) in the above-mentioned yellow image forming unit  10 Y by magenta (M), cyan (C) and black (Bk), therefore, detailed explanations about these image forming units are omitted herein. 
     Now, the image receiving medium P that passed the yellow transfer position, magenta transfer position, cyan transfer position and black transfer position in this order, is then sent into a fixing device  50 . 
     The fixing device  50  has a heat roller  51  incorporating a heater not illustrated herein and a pressing roller  52 , and heats up the toner image that is only positioned on the image receiving medium P by electric charge, thereby melts color lapped toner image, and permanently fixes the toner image onto the image receiving medium P. The image receiving medium P after completion of fixation is carried out to a receiving tray  56  by an exit roller  54 . 
     On the other hand, the respective photosensitive drums  1 Y,  1 M,  1 C and  1 Bk that have passed the transfer position, are rotated and driven at circumferential speed Vo as well as before, and remaining toner and paper powder are cleaned off them by the cleaners  6 Y,  6 M,  6 C and  6 Bk. And further, the electric charge on the surface is made uniform by charge remover lamps of charge removers  7 Y,  7 M,  7 C and  7 Bk, and at necessity, a series of processes from the main chargers  2 Y,  2 M,  2 C and  2 Bk is carried out. 
     While, as for the conveyor belt  21 , after sending out the image receiving medium P to the fixing device  50 , remaining toner and paper powder attaching onto the belt surface are cleaned off by a belt cleaner  27 , and at necessity a next image receiving medium P is conveyed. 
     By the way, in the case of single color printing, image forming is carried out by the above-mentioned optional single color image forming unit. In this case, other image forming units than selected do not carry out their actions. 
     In the next place, the above mentioned conveying mechanism  20  is explained in detail hereinafter. 
     As shown in FIG. 3, the conveying mechanism  20  has a driving roller  22  and a driven roller  24  that are away from each other in roughly horizontal direction. And between this pair of rollers  22  and  24 , arranged is an endless conveyor belt  21 . 
     Each end at the front side and the rear side of the rotating shafts of the respective rollers  22  and  24  is rotatably arranged to a pair of belt frames  23 F and  23 R which are of roughly rectangular shape respectively. At the portion where the rotating shaft of the driven roller  24  of the belt frames  23 F and  23 R, formed are slide holes  231 F and  231 R wherein bearings  241 F and  241 F arranged at both ends of the rotating shaft are engaged so as to move in roughly horizontal direction, namely along the running direction of the conveyor belt  21 . Respective bearings  241 F and  241 F are equipped with springs  242 F and  242 R, and a driven roller  24  is energized in the direction away from the driving roller  22 . Thereby, a specified tension is given to the conveyor belt  21  arranged between the respective rollers  22  and  24 . 
     In the above conveying mechanism  20 , to make the conveyor belt  21  run precisely on specified position, and for the conveyor belt  21  to keep the conveyor surface to the respective photosensitive drums  1 Y,  1 M,  1 C and  1 Bk roughly in horizontal manner, is important so as to obtain quality transfer of toner image to image receiving medium. 
     However, the conveyor belt  21  generally has unevenness in the thickness thereof, and the length at both the ends along the running direction thereof is slightly different, so the conveyor belt  21  is displaced to one side in the direction crossing the running direction during running, that is, in the shaft direction of the respective rollers  22  and  24 , which is known by those skilled in the art. As for the direction where the conveyor belt  21  displaces (front side or rear side), there is difference among conveyor belts  21 , and the arrangement direction of the conveyor belt  21  between rollers  22  and  24  also makes difference. 
     In any way, when the conveyor belt  21  is run displaced to one side in shaft direction, the image receiving medium that is sucked to the conveyor surface of the conveyor belt  21  is conveyed displaced to one side in shaft direction, and in case of large displacement degree, color displacement is caused. 
     Therefore, in the present invention, so as to make the conveyor belt  21  run at specified position in stable manner, arranged is a structure that is explained in detail hereinafter. 
     According to a first preferred embodiment of the present invention, regulation members  60 F and  60 R are arranged adjacent to both the ends of the rotating shaft of the driving roller  22  so as to regulate the movement of the conveyor belt  21  to the shaft direction of the driving roller  22 . The respective regulation members  60 F and  60 R are fixed to the insides of the belt frames  23 F and  23 R at the position adjacent to both the ends of the driving roller  22 , and have regulating surfaces  62 F and  62 R so as to regulate the movement of the conveyor belt  21  to the belt frame side at end corresponding by sliding both ends along the conveyor direction. 
     The distance between the regulating surfaces  62 F and  62 R of the respective regulation members  60 F and  60 R is set so as to be slightly wider than the width along the shaft direction of the conveyor belt  21 . And the regulating surfaces  62 F and  62 R of the respective regulation members  60 F and  60 R is set at the position where the conveyor belt  21  slides and contacts the corresponding end of the conveyor belt  21  at downstream side than the central position along the running direction in the range where the conveyor belt  21  contacts the external circumferential surface of the driving roller  22 . Namely, the respective regulating surfaces  62 F and  62 R is set so as to slide and contact both the ends of the conveyor belt  21  at the lower portion of the conveyor belt  21  that is run from the driving roller  22  toward the driven roller  24 . 
     In this manner, the respective regulation members  60 F and  60 R are arranged adjacent to both the ends of the driving roller  22 , thereby when the conveyor-belt  21  starts displacing to one side in axial direction during running, the end of the displaced side of the conveyor belt  21  is slid and contacted to the regulating surface of the corresponding regulation member, and at this position, the movement of the conveyor belt  21  to the axial direction of the driving roller  22  is regulated, as a consequence, the running position of the conveyor belt  21  is stabilized. 
     It is known that, however, regulation members are slid and contacted to end of the conveyor belt  21 , its stress is transmitted to position away from the end of the conveyor belt  21 , and a concave is caused at the position. For example, when there is a concave caused at the portion (upper portion) of the conveyor belt  21  at the side wherein contact is made to the respective photosensitive drums running from the driven roller  24  toward the driving roller  22  (image receiving medium conveyance side), waving is caused on-the conveyance surface at upper portion where this concave is made, waving is also caused on image receiving medium that is conveyed on the transfer surface with the original waving, and surface position of image receiving medium changes, causing color displacement. Namely, so as to form a quality image, it is indispensable not to make a concave on the upper portion of the conveyor belt  21 . 
     The position of a concave arising on the conveyor belt  21  when regulation members are slid and contacted to end of the conveyor belt  21  changes with the position where the regulating surface of regulation member slides and contacts to the end of the upper conveyor belt  21 . For instance, when regulation member is slid and contacted to the end of the conveyor belt  21 , as mentioned above, a concave is made at the upper portion of the conveyor belt  21 . That is because the pressing pressure by regulation member used at the end of the upper portion of the conveyor belt  21  is transmitted more to the upper portion of the conveyor belt  21 , than to the lower portion of the conveyor belt  21  at the side where image receiving medium is not conveyed from the driving roller  22  toward the driven roller  24 . Herein, so as to investigate the position of regulating surface where there should be no concave on the upper portion of the conveyor belt  21 , an experiment has been conducted as described hereinafter. 
     In this experiment, prepared are  11  kinds of regulation members  60  as shown in the table in FIG. 4, and the positions of concave on the conveyor belt  21  were investigated when respective regulation members  60  were arranged at both the ends of the driving roller. At this moment, the regulating surface of the respective regulation members  60  were set as of the shape shown in slash lines in FIG. 4, and the regulating surface was set so as to slide and contact to the end of the conveyor belt  21  in the position relations shown in the table. Namely, the position where the conveyor belt  21  starts sliding and contacting to the regulating surface was changed by  15  degrees to the downstream side-along the running direction of the conveyor belt  21  from the top position where the conveyor belt  21  starts contacting to the driving roller  22 . 
     As a result, it was found that there will be a concave or waving on the upper portion (upper surface) when the conveyor belt  21  is at the upstream side along the running direction of the conveyor belt  21  than the central position along the running direction of the semi circular range where the conveyor belt  21  contacts the driving roller  22  and the end of the conveyor belt  21  slides and contacts to the regulating surface of the regulation members. While there occurs a concave on the lower portion (under surface) of the conveyor belt  21  when the conveyor belt  21  is at the downstream side along the running direction of the conveyor belt  21  than the central position of the contact range between the conveyor belt  21  and the driving roller  22  and the regulating surface slides and contacts to the end of the :conveyor belt  21 . 
     On the basis of the experiment results, in the present preferred embodiment, the respective regulating surfaces  62 F and  62 R were set so that the conveyor belt  21  should on the downstream side than the central position along the running direction in the range where the conveyor belt  21  contacts the driving roller  22 , and the respective regulating surfaces  62 F and  62 R of the respective regulation members  60 F and  60 R should slide and contact to the end of the conveyor belt  21 . Thereby, the pressing pressure working on the end of the conveyor belt  21  by the respective regulating surfaces  62 F and  62 R prevents a concave from occurring on the upper portion of the conveyor belt  21 , and enables to make the conveyor belt  21  run precisely on specified position. And further, it is possible to keep the transfer surface in a roughly horizontal status at the upper portion of the conveyor belt  21 , and to output a precise and preferable image onto the image receiving medium that is held and conveyed on the conveyor surface. 
     By the way, as mentioned above, in the structure wherein the regulating-surfaces  62 F and  62 R of the respective regulation members  60 F and  60 R are slid and contacted to the end of the conveyor belt  21 , and thereby the movement of the conveyor belt  21 , to the shaft direction is regulated, when the twisting force of the conveyor belt  21  to the shaft direction is unexpectedly large, there may be a case where the end of the conveyor belt  21  flips up and goes over the regulating surface. If the end of the conveyor belt  21  goes over the regulating surface as in this case, the movement of the conveyor belt  21  to the shaft direction of the driving roller  22  cannot be regulated, and there will be deformation on the conveyor belt  21  itself, and in worst case, the conveyor belt  21  will be broken. 
     To prevent such cases, in a second preferred embodiment under the present invention, as shown in FIG.  5  and FIG. 6, projections  74 F and  74 R that protruding in eaves share are arranged along the conveyance surface of the conveyor belt  21  from the regulating surfaces  12 F and  72 R of the regulation members  70 F and  70 R. Thereby, even if abnormal twisting forth of the conveyor belt  21  is to make flipping of the end of the conveyor belt  21  large, the conveyor belt  21  will not go over the eaves shaped protrusions  74 F and  74 R. Consequently, it is possible to keep the sliding and contacting status between the regulating surface and the end of the conveyor belt. At the same time, it is possible to prevent the end of the conveyor belt  21  from going over the regulating surface, therefore, there will be no fear of the conveyor belt  21  being broken. 
     In FIG. 7, shown is a structure according to a third preferred embodiment under the present invention. In this preferred embodiment, regulation members  80 F and  80 R similar to the regulation members  60 F and  60 R in the above first preferred embodiment are arranged adjacent to both the ends of the driven roller  24 . 
     As shown in FIG. 3, in a structure wherein the regulation members  60 F and  60 R are arranged only at the driving roller  22  side, if twisting force of the conveyor belt  21  to shaft direction is abnormally large, even it is possible to regulate the twisting of the conveyor belt  21  at the driving roller  22  side, it may not be possible to regulate the twisting of the conveyor belt  21  at the driven roller  24  side. In this case, the conveyor belt  21  is forcibly twisted by the regulation members  60 F and  60 R at the driving roller  22  side. If this status continues, in worst case, the conveyor belt  21  is broken. 
     For this reason, in this preferred embodiment, the regulation members  60 F and  60 R of the first preferred embodiment are arranged, and further regulation members  80 F and  80 R for regulating the movement of the conveyor belt  21  to the shaft direction of the driven roller  24  are arranged adjacent to both the ends of the driven roller  24 . The respective regulation members  80 F and  80 R are fixed to the inside of the belt frames  23 F and  23 R at the position adjacent to the both ends of the driven roller  24  respectively. The attachment positions of the respective regulation members  80 F and  80 R may be adjusted in running direction to respectively corresponding belt frames  23 F and  23 R. And the respective regulation members  80 F and  80 R have regulating surfaces  82 F and  82 R for making both the ends along the conveyance direction of the conveyor belt  21  slide and contact and regulating the movement of the conveyor belt to the belt frame side of corresponding end. 
     The distance between the regulating surfaces  82 F and  82 R of the respective regulation members  80 F and  80 R is set so as to be slightly wider than the width along the shaft direction of the conveyor belt  21 . And the regulating surfaces  82 F and  82 R of the respective regulation members  80 F and  80 R are set at the position where the conveyor belt  21  slides and contacts the corresponding end of the conveyor belt  21  at upstream side than the central position along the running direction in the range where the conveyor belt  21  contacts the external circumferential surface of the driven roller  21 . Namely, the respective regulating surfaces  82 F and  82 R is set so as to slide and contact both the ends of the conveyor belt  21  at the lower portion of the conveyor belt  21  that is run from the driving roller  22  toward the driven roller  24 . 
     In this manner, the respective regulation members  60 F and  60 R are arranged adjacent to both the ends of the driving roller  22 , and further the respective regulation members  80 F and  80 R are adjacent to both the ends of the driven roller  24 , it is possible to regulate the twisting of the conveyor belt  21  along the shaft direction of the driving roller  22  and the driven roller  24  at the driving roller  22  side and the driven roller  24  side, and it is possible to stabilize the running position of the conveyor belt  21 . 
     In this preferred embodiment too, as same as in the aforementioned first preferred embodiment, so as to investigate the position of regulating surface where there should be no concave on the upper portion of the conveyor belt  21  owing to the arrangement of the regulation members  80 F and  80 R, and so as to find the appropriate positions of the regulating surfaces  82 F and  82 R, an experiment has been conducted as described hereinafter. 
     In this experiment, prepared are  11  kinds of regulation members  80 R as shown in the table in FIG. 8, and the positions of concave on the conveyor belt  21  were investigated when respective regulation members  80 R were arranged at both the ends of the driving roller  24 . At this moment, the regulating surface of the respective regulation members  80 R were set as of the shape shown in slash lines in FIG. 8, and the regulating surface was set so as to slide and contact to the end of the conveyor belt  21  in the position relations shown in the table. Namely, the position where the conveyor belt  21  finishes sliding and contacting to the regulating surface was changed by 15 degrees to the upstream side in the opposite direction to the running direction of the conveyor belt  21  from the end of the range where the conveyor belt  21  contacts the driven roller  24 . 
     As a result, it was found that there will be a concave on the upper portion (upper surface) when the conveyor belt  21  is at the downstream side along the running direction of the conveyor belt  21  than the central position along the running direction of the semi circular range where the conveyor belt  21  contacts the driven roller  24  and the end of the conveyor belt  21  slides and contacts to the regulating surface of the regulation members. While there occurs a concave on the lower portion (under surface) of the conveyor belt  21  when the conveyor belt  21  is at the upstream side along the running direction of the conveyor belt  21  than the central position of the contact range between the conveyor belt  21  and the driven roller  24  and the regulating surface slides and contacts to the end of the conveyor belt  21 . 
     On the basis of the experiment results, in the present preferred embodiment, the respective regulating surfaces  82 F and  82 R were set so that the conveyor belt  21  should on the upstream side than the central position along the running direction in the range where the conveyor belt  21  contacts the driven roller  24 , and the respective regulating surfaces  82 F and  82 R of the respective regulation members  80 F and  80 R should slide and contact to the end of the conveyor belt  21 . Thereby, the pressing pressure working on the end of the conveyor belt  21  by the respective regulating surfaces  82 F and  82 R prevents a concave from occurring on the upper portion of the conveyor belt  21 . 
     As mentioned so far, according to this preferred embodiment under the present invention, four regulation members  60 F,  60 R,  80 F and  80 R are arranged adjacent to both the ends of the driving roller  22  and the driven roller  24 , it is possible to prevent a concave from occurring on the upper portion of the conveyor belt  21 , and further it is possible to prevent unwanted twisting of the conveyor belt  21 . 
     By the way, in such a structure as the third preferred embodiment shown in FIG. 7, when the twisting force of the conveyor belt  21  to the shaft direction of the driving roller  22  and the driven roller  24  is unexpectedly large, there may be a case where the end of the conveyor belt  21  flips up and goes over the regulating surface  62  and  82  of the respective regulation members  60  and  80 . If the end of the conveyor belt  21  goes over the regulating surfaces as in this case, the movement of the conveyor belt  21  to the shaft direction cannot be regulated, and there will be deformation on the conveyor belt  21  itself, and in worst case, the conveyor belt  21  will be broken. 
     To prevent such cases, in a fourth preferred embodiment under the present invention, as shown in FIG. 9, projections  74 F,  74 R,  94 F and  94 R that protruding in eaves shape are arranged along the conveyance surface of the conveyor belt  21  from the respective regulating surfaces  72 F,  72 R,  92 F and  92 R of the respective regulation members  70 F,  70 R,  90 F and  90 R. Thereby, even if abnormal twisting forth of the conveyor belt  21  is to make flipping of the end of the conveyor belt  21  large, the conveyor belt  21  will not go over the eaves shaped protrusions  74 F,  74 R,  94 F and  94 R, consequently, it is possible to keep the sliding and contacting status between the regulating surface and the end of the conveyor belt. At the same time, it is possible to prevent the end of the conveyor belt  21  from going over the regulating surfaces, therefore, there will be no fear of the conveyor belt  21  being broken. 
     While, in the case where regulation members are arranged respectively on both the ends of the driving roller  22  and the driven roller  24 , like in the above-mentioned third and fourth preferred embodiments under the present invention, for example, when the distance along shaft direction between the regulating surface  72 R of the regulation member  70 R arranged adjacent to the rear side end of the driving roller  22  and the regulating surface  92 R of the regulation member  90 R arranged adjacent to the rear side end of the driven roller  24  is too large, it leads to the same status where the end of the conveyor belt  21  is regulated by the regulation member of only one roller side, therefore, sufficient effects are not obtained. Further, if the distance between the respective regulating surfaces  72 R and  92 R is widely open, in worst case, the conveyor belt  21  may be broken. This is same to the regulation members  70 F and  90 F arranged at the front sides of the respective rollers  22  and  24 . In short, ideally, it is preferable to place the regulating surfaces of facing two regulation members along the running direction of the conveyor belt  21  at the same position along shaft direction. 
     Through this, so as to investigate the distance margin between the above-mentioned regulating surfaces  72 R and  92 R (hereinafter, only the rear side is described), carried out was the experiment explained hereinafter. In this experiment, the breaking conditions of the conveyor belt  21  were studied by changing the positions of the respective regulating surfaces  72 F,  72 R,  92 F and  92 R of the regulation members  70 F and  70 R at the driving roller  22  side and the regulation members  90 F and  90 R at the driven roller  24  side, with the thickness of the conveyor belt  21  as parameter. 
     As the conditions for the experiment, as shown in FIG. 10, the distance L [mm] along shaft direction between the regulating surface  72 R of the regulation member  70 R at the driving roller  22  side and the regulating surface  92 R of the regulation member  90 R at the driven roller  24  side was changed gradually from 0.5 [mm] to 3.0 [mm], while the thickness t [mm] of the belt  21  was changed gradually from 0.08 [mm] to 1.4 [mm]. At this moment, the twisting force of the conveyor belt  21  to the rear side was set 1 [kg], and the conveyance speed of the conveyor belt  21  was set 200 [mm/s], but under these conditions it would take much time, therefore, an acceleration test was carried out. FIG. 13 shows the results of the acceleration test which was converted into the original conditions. By the way, in this experiment, in all the cases, it was made as completion at the stage when the running distance of the conveyor belt  21  exceeded one million rounds. 
     In the graph in FIG. 13, the horizontal axis is shown as L, while the vertical axis is shown as breakage conveyance number N. Herein, the service life (breakage life) of the conveyor belt  21  is set 200 thousand rounds, while the exchange interval of the-conveyor belt  21  is set 180 thousand rounds. When the service life (breakage life) of the conveyor belt  21  is set 200 thousand rounds as in this experiment, settings may be L≦1.6 in the case where the thickness of conveyor belt  21  t=0.08, while L≦2.0 in the case t=0.10, L≦2.4, in the case t=0.12, L≦2.8 in the case t=0.14, which may be read from the graph. 
     In other words, so as to meet the relation L≦20t including all the results mentioned above, by setting the distance L between the regulating surface  72 R of the regulation member  70 R at the driving roller  22  side and the regulating surface  92 R of the regulation member  90 R at the driven roller  24  side, it is possible to create conditions wherein the conveyor belt  21  will not break within the exchange interval of the conveyor belt  21 . 
     As mentioned so far, so as to meet the relation L≦20t, setting of the distance L between the regulating surface of the regulation member at the driving roller  22  side and the regulating surface of the regulation member at the driven roller  24  side enables to provide a highly reliable conveying mechanism  20  where the belt thereof will never break within belt exchange interval. 
     By the way, in the fourth preferred embodiment explained with FIG. 9, for example, when the conveyor belt  21  slides with and contacts to the regulation member  70 R at the rear side of the driving roller  22 , the twisting force of the conveyor belt  21  to the regulation member  70 R becomes largest at the position where the lower portion of the conveyor belt  21  gets away from the driving roller  22 . When the twisting force is concentrated at this position, the conveyor belt  21  will be rolled downward as the direction to let the reaction force from the regulation member  70 R. 
     Originally, it is ideal that the twisting force of the conveyor belt  21  works vertically onto the regulating surface  72 R of the regulation member  70 R, and as reaction thereto, a force to push back the conveyor belt  21  vertically occurs from the regulation member  70 R, however, in the case of large twisting force, the conveyor belt  21  that has combustible nature will cause deformation, as a result it will be rolled up. As one of the reasons for this, it is pointed out that the conveyor belt  21  has free degrees downward to the regulation member  70 R. Namely, the conveyor belt  21  has spatial free degree in the direction where it rolls up, therefore it will be rolled up. 
     Therefore, in this preferred embodiment under the present invention, the regulation member  70 R is configures as shown in FIG. 9, thereby the rolling up of the conveyor belt  21  is prevented. In more details, the regulation member  70 R has a regulating surface  72 R that makes the end of the conveyor belt  21  slide and contact thereto, and at the lower end side of this regulating surface  72 R, formed is a roughly circular protrusion  74 R. This protrusion  74 R of the regulation member  70 R is away from and faces to the external circumferential surface of the driving roller  22 , and the protrusion length thereof is L, and the distance between the external circumferential surface of the driving roller  22  and the protrusion  74 R is S. 
     As the conveyor belt  21  under twisting force is being rolled up along the regulating surface  72 R of the regulation member  70 R, the end of the conveyor belt  21  contacts the protrusion  74 R, and receives reaction force in the vertical direction to the twisting force, thereby rolling up is prevented. And rolling up of the conveyor belt  21  is also regulated by this protrusion  74 R, it is possible to prevent breakage owing to bending fatigue of rolling root portion that has been caused by rolling up of the conveyor belt  21 . 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 1.0 
                 1.2 
                 1.4 
                 1.6 
                 1.8 
                 2.0 
                 2.2 
                 2.4 
                 2.6 
                 2.8 
                 3.0 
                 3.2 
                 3.4 
                 3.6 
                 3.8 
                 4.0 
                 4.2 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 0.06 
                 X 
                 X 
                 ◯ 
                 ◯ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 0.08 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
                 ◯ 
               
               
                 0.10 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
               
               
                 0.12 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
                 ◯ 
               
               
                 0.14 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
                 ◯ 
               
               
                 0.16 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
                 ◯ 
               
               
                 0.18 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
                 ◯ 
               
               
                 0.20 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 X 
                 ◯ 
               
               
                   
               
             
          
         
       
     
     Table 1 shows the results of the experiment with the conveyor belt having a practically upper limit Young&#39;s modulus 7×10 4  [kg/cm 2 ] in the present regulation member system, and the thickness T of practical conveyor belt  21  at 0.06 [mm]−0.20 [mm] as parameter. 
     In this experiment, twisting force was uniformly set to practical lower limit 0.1 [kg], the length L of the projection  74 R of the regulation member  70 R was fixed to 1.4 [mm], and the conveyor belt  21  was run, and the distance S between the external circumferential surface of the driving roller  22  to the protrusion  74 R of the regulation member  70 R was charged, thereby studied was whether or not there was breakage owing to rolling up the conveyor belt  21  up to 120 thousand rounds that was the exchange standard interval of the conveyor belt  21 . 
     The experiment results are shown with ◯ in the case wherein the conveyor belt  21  did not break up to the 120 thousand rounds running as the exchange target of the conveyor belt  21 , while with × in the case wherein the conveyor belt  21  broke before that. As the distance S between the external circumferential surface of the driving roller  22  to the protrusion  74 R of the regulation member  70 R becomes larger, the conveyor belt  21  will roll up more. 
     In the experiment, tests were carried out per belt thickness, and when specifications were attained, for confirmation, tests were carried out further with one step higher distance S. As the results, it has found that the following relational equation stands to the practically upper limit Young&#39;s modulus 7×10 4  [kg/cm 2 ] in the regulating plate method, and the practical lower limit twisting force 0.1 [kg]. 
     
       
           S[mm] &lt;15 T[mm]   
       
     
     The above relational equation is based on the conveyor belt  21  of the practically upper limit Young&#39;s modulus and the practical lower limit twisting force, so it is effective to the cases with the conveyor belt  21  having lower Young&#39;s modulus, and with larger twisting force too. 
     For example, in the case wherein Young&#39;s modulus of the conveyor belt  21  is low, the conveyor belt  21  is apt to roll up, therefore, it is necessary to make the distance S small. And in the case wherein twisting force is large, the conveyor belt  21  is apt to roll up, therefore, it is necessary to make the distance S small. Accordingly, the above relational equation has the meaning to regulate the upper limits of the distance S and the belt thickness T, thus it shows all the relations. 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 0.4 
                 0.6 
                 0.8 
                 1.0 
                 1.2 
                 1.4 
                 1.6 
                 1.8 
                 2.0 
                 2.2 
                 2.4 
                 2.6 
                 2.8 
                 3.0 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 0.06 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 0.08 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                 0.10 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                 0.12 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                 0.14 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                 0.16 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                 0.18 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                 0.20 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
               
               
                   
               
             
          
         
       
     
     Table 2 shows the results of the experiment wherein the influence of the length L of the protrusion  74 R of the regulation member  70 R was studied, and the conveyor belt having a practically upper limit Young&#39;s modulus 7×10 4  [kg/cm 2 ], and the thickness T of practical conveyor belt  21  at 0.06 [mm]−0.20 [mm] as parameter were employed. 
     In this experiment, twisting force was uniformly set to practical lower limit 0.1 [kg], the length L of the projection  74  R of the regulation member  70 R was fixed to the minimum distance to the belt thickness T obtained in the foregoing experiment, and the conveyor belt  21  was run, and the distance L between the regulating surface  72 R of the regulation member  70 R to the protruded end of the protrusion  74 R of the regulation member  70 R was changed, thereby studied was whether or not there was breakage owing to rolling up the conveyor belt  21  up to 120 thousand rounds that was the exchange standard interval of the conveyor belt  21 . 
     The experiment results are shown with ◯ in the case wherein the conveyor belt  21  did not break up to the 120 thousand rounds running as the exchange target of the conveyor belt, while with × in the case wherein the conveyor belt  21  broke before that. As the distance L to the protruded end of the protrusion  74 R, there may be rolling up at the outside of the protrusion  74 R, accordingly the conveyor belt  21  will roll up more. 
     In the experiment, tests were carried out per belt thickness, and when specifications were attained, for confirmation, tests were carried out further with one step higher distance L. As the results, it has found that the following relational equation stands to the practically upper limit Young&#39;s modulus 7×10 4  [kg/cm 2 ] in the regulating plate method, and the practical lower limit twisting force 0.1 [kg]. 
     
       
           L[mm] &lt;20 T[mm]   
       
     
     The above relational equation is based on the conveyor belt  21  of the practically upper limit Young&#39;s modulus and the practical lower limit twisting force, so it is effective to the cases with the conveyor belt  21  having lower Young&#39;s modulus, and with larger twisting force too. 
     For example, in the case wherein Young&#39;s modulus of the conveyor belt  21  is low, the conveyor belt  21  is apt to roll up, therefore, it is necessary to make the protruded length L of the protrusion  74 R large. And in the case wherein twisting force is large, the conveyor belt  21  is apt to roll up, therefore, it is necessary to make the protruded length L of the protrusion  74 R large. 
     Accordingly, the above relational equation has the meaning to regulate the protruded length L of the protrusion  74 R of the regulation member  70 R and the lower limit of the belt thickness T, thus it shows all the relations. And further, the above explanations have been made mainly on the regulation member  70 R as a representative, however the explanations are same to other regulation members  70 F,  90 R and  90 F. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     As mentioned so far herein, the belt conveyor and the image forming apparatus equipped therewith have the structures and functions mentioned above, therefore, it is possible to make the conveyor belt for transferring a image receiving medium at a specified position in stable manners, and to remove displacement of an image to be output onto the image receiving medium that is conveyed via the conveyor belt, thereby to form quality images.