Patent Abstract:
A driving force transmitting apparatus includes a driving source; a drive pulley rotatable by a driving force supplied from the driving source; a follower pulley rotatable with a member to be rotated; a belt member extending around a cylindrical surface of the driving pulley and a cylindrical surface of the follower pulley; and an intermediate transmission member disposed between the driving pulley and the follower pulley, the intermediate transmission member having a rigidity higher than that of the belt member and contacted to the pulleys or opposed to the pulleys with the belt member therebetween.

Full Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a driving force transmitting device using a pulley and a belt member and relates to an electrophotographic image forming apparatus, including such a driving force transmitting device, such as a copying machine, a facsimile machine, a printer or a multi-function machine. 
         [0002]    In the image forming apparatus such as the copying machine or a printer, the driving force transmitting device for rotationally driving a photosensitive drum which is an image bearing member or rotationally driving an intermediary transfer belt is required to have a high-precision rotation performance with less rotation non-uniformity. For example, in a color image forming apparatus of a four-drum type in which four drums for yellow (Y), magenta (M), cyan (C) and black (K) are used, belt or color misregistration occurs due to the rotation non-uniformity of the photosensitive drum or the intermediary transfer belt, so that an image quality is impaired. Incidentally, the belt is such a phenomenon that sparseness/denseness of writing intervals by a laser on the photosensitive drum surface occurs with respect to a sub-scan direction due to the rotation non-uniformity of, e.g., the photosensitive drum and thus density non-uniformity occurs no a print. 
         [0003]    As a countermeasure against the belt and the color misregistration, an encoder for monitoring the rotation non-uniformity was provided on a rotational axis of a driving roller for the photosensitive drum or the intermediary transfer belt and on the basis of a signal of the encoder, rotation of the driving source has been controlled. Thus, the rotation non-uniformity of the driving roller for the photosensitive drum or the intermediary transfer belt is suppressed, so that the belt and the color misregistration are prevented. Incidentally, as the driving source used in such a driving device, a DC motor or a stepping motor may be used. 
         [0004]    Further, as a structure for transmitting a driving force from the driving source, a reduction gear train is generally used. That is, a rotational driving force of the driving source is transmitted to the driving roller for the photosensitive drum or the intermediary transfer belt through the reduction gear train in a speed reduction manner. However, in the case where such a reduction gear train is used, the rotation non-uniformity occurs even at an engaging portion between gears due to a manufacturing error of the gears, so that there arises a problem that the belt occurs and thus the image quality is lowered. As a countermeasure against the belt with respect to the reduction gear train, such an attempt that processing accuracy or rigidity of the respective gears was enhanced or that inertial mass (flywheel) was attached on the rotational axis of the driving roller for the photosensitive drum or the intermediary transfer belt has been made. 
         [0005]    However, even when the processing accuracy or rigidity of each of the gears of the reduction gear train is enhanced or the inertial mass (flywheel) is provided, there is a limit to a suppressing effect on the rotation non-uniformity of the photosensitive drum or the intermediary transfer belt. Particularly, in recent years, with high-definition image forming process by formation of toner particles in a small particle size or formation of minute exposure spots, a demand for alleviating the rotation non-uniformity becomes increasingly severe, so that a conventional method is being in a state in which it cannot meet the demand. 
         [0006]    For this reason, a proposal such that a driving force transmitting device using an endless non-toothed belt of steel and a pulley, not a toothed drive transmission means such as a gear or a timing belt was applied to the image forming apparatus has been proposed. That is, a driving device including a driving device for being rotationally driven by a driving source, a driven pulley rotated together with a member to be rotated such as the driving roller for the photosensitive drum or the intermediary transfer belt, and the non-toothed belt member stretched on a cylindrical surface of the driving pulley and the cylindrical surface of the driven pulley has been known. Such a driving device has no tooth at a power transmitting portion, so that it has an advantage that the rotation non-uniformity or belt due to an engaging portion does not occur in principle (e.g., Japanese Laid-Open Patent Application No. Hei 7-36346). 
         [0007]    However, in the conventional driving force transmitting device using the belt member and the pulley, the following problems arise. First, there is a problem of responsiveness of the driving pulley and the driven pulley. For example, similarly as in the above-described case, in the case of the structure in which the encoder for monitoring the rotation non-uniformity is provided on the rotational axis of the driven pulley and the rotation of the driving source is controlled on the basis of the signal of the encoder, there is a need to increase the responsiveness of the driving pulley and the driven pulley. However, e.g., when the belt member is been ton its tension side (where a tension pulley is not provided) by a change in tension of the belt member due to a driven pulley-side load variation, a restrictive property at a phase relation between the driving pulley and the driven pulley is eliminated. That is, to the belt member to be stretched between the driving pulley and the driven pulley, a predetermined tension is applied by the tension pulley. However, when the load variation as described above occurs, the tension of the belt member is changed and thus a position of the tension pulley is also changed, so that the bending occurs on the side where the tension pulley is not provided. As a result, the responsiveness of the driving pulley and the driven pulley is lowered. 
         [0008]    Such lowering in responsiveness occurs when the load on the driven pulley side is abruptly reduced or changed into a reverse load. Specifically, in the case where a cleaner, such as a blade or a brush, of a belt cleaning device for removing residual toner on the intermediary transfer belt is moved toward and away from the intermediary transfer belt, the decrease in load occurs when the cleaner is moved away from the intermediary transfer belt. 
         [0009]    Further, in the case where a difference in rotational speed is provided between the photosensitive drum and the intermediary transfer belt, the reverse load as described below can occur. That is, in the case where a peripheral speed of the intermediary transfer belt is set at a value which is higher than that of the photosensitive drum at a primary transfer portion where a toner image is transferred from the photosensitive drum onto the intermediary transfer belt, when an electrostatic attraction force is generated at the primary transfer portion by application of a high voltage, a force from the intermediary transfer belt acts on the photosensitive drum. In this case, the photosensitive drum is in a state in which it receives the driving force from two members of the intermediary transfer belt and the driving device for the photosensitive drum. In the case where the above-described electrostatic attraction force exceeds, e.g., a brake force of the cleaner of the cleaning device for removing the residual toner on the photosensitive drum, the photosensitive drum is driven by the intermediary transfer belt. That is, the reverse load by which a driving force transmission path in a normal operation is reversed occurs. Further, such a reverse load state is abruptly generated, in the conventional belt driving device, control is lost and thus the color misregistration occurs. 
         [0010]    Further, in the case of the conventional belt driving device, there is a problem such that a lifetime of the device is reduced by a slip (sliding) generated between the pulley and the belt. As described above, the non-toothed driving system is advantageous for belt prevention but is less liable to obtain a power transmitting ability as obtained by engagement by gear teeth. Further, in the case where the slip occurs, the belt is abraded and is liable to be bent, so that the lifetime of the driving device is shortened. Particularly, in the case of a speed reduction mechanism including the driven pulley having an outer diameter larger than that of the driving pulley, a length of winding of the belt about the driving pulley having the smaller outer diameter is short, i.e., a contact area between the driving pulley and the belt is small, so that the slip is liable to occur. 
         [0011]    Further, during actuation of the device, not only frictional loads of the respective members are applied but also inertial load is added, so that the slid is liable to occur particularly. For this reason, as a countermeasure against the slip during the actuation, it would be considered that, e.g., a method in which a motor actuation profile is slowly raised is adopted. However, the method in which the motor actuation profile is slowly raised is effective as the countermeasure against the inertial load but cannot meet such a phenomenon (load) that the friction load is temporarily increased. 
         [0012]    A specific example of the load may include those of the cleaner for the photosensitive drum and a transfer cleaner after these cleaners are left standing. That is, a cleaner blade which is a rubber member of such cleaners closely contacts the photosensitive drum or the intermediary transfer belt by being left standing and thus the load is increased when compared with the case of the normal operation. Further, at a nip of the cleaner blade, collected transfer residual toner is fixedly deposited to increase the load in some cases. Further, also at a seal portion where scattering toner is prevented from entering a portion for supporting an end portion of the photosensitive drum, a similar toner deposition (sticking) phenomenon occurs. Further, in the case of, e.g., a structure for supporting a roller such as a primary transfer roller disposed in the intermediary transfer belt by a sliding bearing, the scattering toner enters and is deposited on a sliding portion of the bearing and can cause the load phenomenon due to a similar a toner deposition. With respect to such a friction load increasing phenomenon, it is effective that the change in state (close contact state or deposition or sticking state) is accelerated by an impulse force (impact force) through instantaneous rising rather than the slow rising. This is contradictory to the slow rising as the counter measure against the inertial load. 
         [0013]    On the other hand, it would also be considered that a method of increasing the drive transmitting force by increasing the tension of the belt is employed but this method causes a decrease in lifetime of the belt by an increase in stress of the belt accompanying the increased tension. Further, radial load acting on each of the pulleys is increased, so that such a problem that the lifetimes of the parts such as the bearings for supporting the respective pulleys are shortened occurs. 
       SUMMARY OF THE INVENTION 
       [0014]    A principal object of the present invention is to provide a driving force transmitting device, using a pulley and a belt member, capable of enhancing rotation stability of the belt member. 
         [0015]    Another object of the present invention is to provide an image forming apparatus including the driving force transmitting device. 
         [0016]    According to an aspect of the present invention, there is provided 
         [0017]    According to an aspect of the present invention, there is provided a driving force transmitting apparatus comprising a driving source; a drive pulley rotatable by a driving force supplied from said driving source; a follower pulley rotatable with a member to be rotated; a belt member extending around a cylindrical surface of said driving pulley and a cylindrical surface of said follower pulley; and an intermediate transmission member disposed between said driving pulley and said follower pulley, said intermediate transmission member having a rigidity higher than that of said belt member and contacted to said pulley or opposed to said pulley with said belt member therebetween. 
         [0018]    These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic view for illustrating an image forming apparatus including a driving device in First Embodiment according to the present invention. 
           [0020]      FIG. 2  is a partly cutaway view for illustrating the driving device in First Embodiment. 
           [0021]      FIG. 3  is a sectional view taken along A-A line indicated in  FIG. 2 . 
           [0022]      FIG. 4  is a schematic view showing a state in which a load variation occurs in a conventional structure. 
           [0023]      FIG. 5  is a graph showing a relationship between the load variation and positional deviation amount in the conventional structure. 
           [0024]      FIG. 6  is a graph showing a relationship between the load variation and the positional deviation amount in First Embodiment. 
           [0025]      FIG. 7  is a schematic view of a driving device in Second Embodiment. 
           [0026]      FIG. 8  is a sectional view taken along B-B line indicated in  FIG. 7 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0027]    Next, referring to  FIGS. 1-6 , the first preferred embodiment of the present invention will be described. First, the image forming apparatus in this embodiment will be described with reference to  FIG. 1 . The image forming apparatus in this embodiment is a full-color laser beam printer of the intermediary transfer type, and also, of the tandem type. That is, it has four image formation stations, more specifically, yellow (Y), magenta (M), cyan (c), and black (K) image formation stations, which are in parallel to each other. An image forming apparatus of this type has a printer portion P and a reader portion R. Generally speaking, the printer portion P is made up of an image forming portion  11 , a recording medium (paper) feeder unit  12 , an intermediary transfer unit  13 , a fixation unit  14 , and a control unit (unshown). The image forming portion  11  has four image formation stations which are the same in structure. 
         [0028]    The structure of the image forming portion  11  is as follows: The image forming portion  11  has multiple (four) photosensitive drums  15 , which are image bearing members. Each photosensitive drum  15  is supported at the lengthwise ends of its shaft (drum shaft  15   a ). It is rotated in the counterclockwise direction indicated by an arrow mark in  FIG. 1 , by a driving apparatus  50  which is actually a driving force transmitting apparatus. The driving apparatus  50  will be described later. Each image formation station has a charging device  16 , a developing device  17 , and a cleaning apparatus  18 , which are sequentially positioned in the adjacencies of the peripheral surface of the photosensitive drum  15 , in the listed order. The image forming operation of this image forming apparatus is as follows. First, the peripheral surface of the photosensitive drum  15  is uniformly charged to preset polarity and potential level by the charging device  16 , such as a charging device of the corona type. Next, a beam of light, for example, a beam of laser light, is projected, while being modulated with the image formation signals obtained by the reader portion R, upon the charged area of the peripheral surface of the photosensitive drum  15 , by an optical system apparatus  19  provided with a light source, etc. In other words, the charged area of the peripheral surface of the photosensitive drum  15  is exposed to form an electrostatic latent image on the peripheral surface of the photosensitive drum  15 . Then, the electrostatic latent image is developed by the developing device  17 , which contains toner (developer) which is Y, M, C, or K in color, into a visible image formed of the toner (which hereafter will be referred to simply as toner image); the toner is adhered to the electrostatic latent image on the peripheral surface of the photosensitive drum  15  by the developing device  17 . This toner image is transferred (first transfer) onto an intermediary transfer belt  21 , in the first transfer portion T 1 ; four toner images, different in color, are sequentially transferred onto the intermediary transfer belt  21 , in the four first transfer portions T 1 , one for one. The toner remaining on the peripheral surface of the photosensitive drum  15  after the first transfer is removed by the cleaning apparatus  18 . 
         [0029]    The recording medium feeder unit  12  is made up of the recording medium feeder cassette  22 , a recording medium feeder tray  23 , a pickup roller  24 , a recording medium conveyance path  25 , a pair of registration rollers  26 , etc. The sheets of recording mediums S in the recording medium feeder cassette  22  or recording medium feeder tray  23  are send one by one into the recording medium conveyance path  25  by the corresponding pickup roller  24 , and are conveyed through the recording medium conveyance path  25  to the pair of registration rollers  26 . Then, each sheet of recording medium S (which hereafter will be referred to simply as recording medium S) is sent to the second transfer portion T 2  by the pair of registration rollers  26  in synchronism with the progression of the image formation. 
         [0030]    The intermediary transfer unit  13  has the intermediary transfer belt  21 , which is an endless image bearing member which is supported and kept stretched in such a manner that it can be circularly moved. More specifically, the intermediary transfer belt  21  is supported, and kept stretched, by a driver roller  27 , a tension roller  28 , and a belt backing roller  29  (which hereafter may be referred to simply as backup roller  29 ) which backs up the intermediary transfer belt  21  against a second transfer roller. Among the three rollers  27 ,  28 , and  29 , the driver roller  27  is driven by the aforementioned driving apparatus  50 , which will be described later. The tension roller  28  provides the intermediary transfer belt  21  with a preset amount of tension, in coordination with an unshown pressure applying means. The backup roller  29  opposes the second transfer roller, with the presence of the intermediary transfer belt  21  between the two rollers, forming thereby the second transfer portion T 2 . The backup roller  29  is rotated by the movement of the intermediary transfer belt  21 ; it is rotated by utilizing the friction between the intermediary transfer belt  21  and backup roller  29 . The portion of the intermediary transfer belt  21 , which is moving between the driver roller  27  and tension roller  28 , opposes each of the four photosensitive drums  15 . There are four charging blades  30  for the first transfer, which oppose the four photosensitive drums  15 , one for one, in such a manner that the intermediary transfer belt  21  is pinched between the peripheral surface of each photosensitive drum  15  and each of the four charging blades  30 . There is also a belt cleaning apparatus  31 , which opposes the driver roller  27  with the presence of the intermediary transfer belt  21  between the belt cleaning apparatus  31  and driver roller  27 . 
         [0031]    The four toner images formed on the four photosensitive drums  15 , one for one, are sequentially transferred (first transfer) onto the intermediary transfer belt  21  in the first transfer portion T 1 , by applying a preset voltage to the intermediary transfer belt  21  by the charge blades  30 . After being transferred onto the intermediary transfer belt  21 , the toner images on the intermediary transfer belt  21  are conveyed to the second transfer portion T 2 , in which they are transferred from the intermediary transfer belt  21  onto the recording medium S which is delivered to the second transfer portion T 2  by the registration rollers  26  in synchronism with the arrival of the toner images on the intermediary transfer belt  21  at the second transfer portion T 2 . The toner on the intermediary transfer belt  21 , which was not transferred in the second transfer portion T 2 , that is, the toner remaining on the intermediary transfer belt  21  after the second transfer, is removed by the belt cleaning apparatus  31 , and conveyed to an unshown waste toner box. 
         [0032]    The fixation unit  14  is provided with a fixation roller  33  and a pressure roller  34 , which have an internal heat source  32 , such as a halogen heater. It fixes the toner images (unfixed toner images), which have just been transferred onto the recording medium S in the second transfer portion T 2 , to the recording medium S. After the fixation of the toner images to the recording medium S, the recording medium S is discharged into a delivery tray  36  by a pair of discharge rollers  35 . The operation of each of the mechanical or electro-mechanical portions described above is controlled by an unshown control unit. The image forming apparatus may be designed so that this control unit integrally controls the entirety of the operation of the image forming apparatus, including the aforementioned driving apparatus  50 , which will be described next. 
         [0033]    Next, referring to  FIGS. 2 and 3 , the driving apparatus  50  will be described. The driving apparatus  50  is a driving force transmitting apparatus which transmits driving force to the photosensitive drums  15  and the driver roller  27  of the intermediary transfer unit  13 . Incidentally, the apparatus for driving the driver roller  27  of the intermediary transfer unit  13  is the same as the apparatus  50  for driving the photosensitive drum  15 . Thus, only the driving apparatus for the photosensitive drum  15  will be described. The driving apparatus  50  is an apparatus which transmits the rotational force of a DC motor  51 , which is the mechanical power source, to the photosensitive drum  15 , while reducing the force in velocity. Thus, the driving apparatus  50  has: a driver pulley  52  which is rotationally driven by the DC motor  51 ; a follower pulley  53  with which the photosensitive drum  15  rotates; a toothless belt  54  stretched around the cylindrical peripheral surface  52   a  of the driver pulley  52  and the cylindrical surface  53   a  of the follower pulley  53 . The driving force is transmitted from the pulley  52  to the pulley  53  by utilizing the friction between the belt  54  and the two pulleys  52  and  53 . The belt  54  in this embodiment is toothless. However, the belt  54  may be in such a form that its cross section has multiple indentations, or is wavy. Further, it may be toothed. In other words, the present invention is applicable to any driving force transmitting apparatus, as long as it is structured so that driving force is transmitted between the two pulleys  52  and  53  by the utilization of the friction between the belt  54  and the two pulleys  52  and  53 . 
         [0034]    More specifically, the driver pulley  52 , which is cylindrical, is in connection to the output shaft  51   a  of the DC motor  51 . The driver pulley  51  is made of a metallic substance, and is roughly cylindrical. It has a circumferential groove  52   b , which is in the middle of the driver pulley  51  in terms of the axial direction of the driver pulley  52 . The bottom surface  52   a  of the circumferential groove  52   b  is toothless. The depth of the groove  52   b  is greater than the thickness of the aforementioned belt  54 , which will be described later. Both of the lengthwise end portions  52   c , relative to the groove  52   b , of the driver pulley  52  are cylindrical, and engage with a driving force transmitting intermediary member  56  of the apparatus  50 ; the peripheral surface of each of the lengthwise end portions  52   c  engages with the peripheral surface of the driving force transmitting intermediary member  56  (which hereafter will be referred to simply as intermediary transmitting member  56 , which will be will be described later. Hereafter, the lengthwise end portions  52   c , which engage with the intermediary transmitting member  56 , may be referred to as engaging portions  52   c.    
         [0035]    The aforementioned follower pulley  53  is in connection with the drum shaft  15   a  of the photosensitive drum  15 . The follower pulley  53  also is made of a metallic substance, and is roughly cylindrical, like the driver pulley  52 . It has a circumferential groove  53   b , which is in the middle of the follower pulley  53 , n terms of the axial direction of the follower pulley  53 . The bottom surface  53   a  of the circumferential groove  53   b  is toothless. The depth of the groove  53   b  is also greater than the thickness of the belt  54 . Both of the lengthwise end portions  53   c , relative to the groove  53   b , of the follower pulley  53  are cylindrical, and engage with the intermediary transmitting member  56  of the apparatus  50 ; the peripheral surface of each of the lengthwise end portions  53   c  engages with the peripheral surface of the intermediary transmitting member  56 . Hereafter, the lengthwise end portion  53   c , which engage with the intermediary transmitting member  56 , may be referred to as engaging portions  53   c . The follower pulley  53  is greater in diameter than the driver pulley  52 . The dimension of the follower pulley  53  in terms of its axial direction is roughly the same as the dimension of the driver pulley  52  in terms of its axial direction. The material for the driver pulley  52  and follower pulley  53  is desired to be a hard metallic substance, such as stainless steel. 
         [0036]    The toothless belt  54  is made of a ferric material such as stainless steel, and is wrapped around, being thereby kept stretched, by the driver pulley  52  and follower puller  53 , bridging thereby between the bottom surface  52   a  of the groove  52   c  of the driver pulley  52 , and the bottom surface  53   a  of the groove  53   b  of the follower pulley  53 . The depth of the grooves  52   b  and  53   b , which correspond to the bottom surfaces  52   a  and  53   a , respectively, is greater than the thickness of the belt  54 . Therefore, after the fitting of the belt  54  into the grooves  52   b  and  53   b , the belt  54  does not protrude above the peripheral surface of engaging portion  52   c  and that of the engaging portion  53   c . Further, the belt  54  is wrapped around a tension pulley  55 , which is on the downstream side of the driver pulley  52  in terms of the moving direction of the belt  54 . The tension pulley  55  is under the pressure from springs  56 , and provides the belt  54  with a proper amount of tension. 
         [0037]    Further, there is an intermediary transmission member  57  between the driver pulley  52  and follower pulley  53 . The intermediary member  57  is also cylindrical. The belt  54  is wrapped around also the peripheral surface  57   a  of the intermediary transmitting member  57 . The intermediary transmitting member  57  is a piece of a hollow cylinder (having through hole  58 ) made of a very hard and rigid metallic substance, such as stainless steel. It has a circumferential groove  57   b , which is in the middle in terms of the axial direction of the intermediary transmitting member  57 . The bottom surface  57   a  of the groove  57   b  is toothless. The depth of the groove  57   b  is also greater than the thickness of the belt  54 . The intermediary transmitting member  57  is formed of a substance which is higher in rigidity than the material for the belt  54 . 
         [0038]    The lengthwise end portions of the intermediary transmitting member  57  are cylindrical, and function as engaging portions  57   c , which engage with the engaging portion  52   c  of the driver pulley  52 , and the engaging portion  53   c  of the follower pulley  53 , one for one. The external diameter of each of the engaging portions  57   c  of the intermediary transmitting member  57  is greater than the distance between the engaging portion  52   c  of the driver pulley  52  and the engaging portion  53   c  of the follower pulley  53 . The relationship in terms of external diameter among the engaging portions  57   c ,  52   c , and  53   c  is to be set in consideration of the relationship between the efficiency with which the driving force is transmittable by the belt  54  and the reduction ratio (between driver pulley  52  and follower pulley  53  in terms of peripheral velocity), and the transmission efficiency of the intermediary transmitting member  57 . For example, it is set so that external diameter of engaging portion  52   c :external diameter of engaging portion  57   c :external diameter of engaging portion  53   c= 1:2:8. In terms of axial direction, the dimension of the intermediary transmitting member  57  is roughly the same as the dimension of the driver pulley  52  and the dimension of the follower pulley  53 . The peripheral surface of the engaging portions  57   c  of the intermediary transmitting member  57  is also minimized in coefficient of friction. 
         [0039]    The intermediary transmitting member  57  is supported by a supporting shaft  59 , which is put through the through hole  58  of the intermediary transmitting member  57 . The supporting shaft  59  is rotatably supported by a pair of bearings  60 , which are plane bearings, roller bearings, ball bearings, or the like. The lengthwise end portions of the supporting shaft  59  are loosely fitted in the cylindrical holes of the unshown frame of the apparatus; the diameter of the cylindrical holes is slightly larger than the external diameter of the supporting shaft  59 . Further, the supporting shaft  59  is under the pressure applied to its lengthwise end portions by a pair of springs  61 . More specifically, the base portion of each of the springs  61  is anchored to a part of the frame, and the opposite end of the spring  61  from the base portion is attached to the corresponding lengthwise end of the supporting shaft  59 . Therefore, the intermediary transmitting member  57  supported by the supporting shaft  59  is also kept pressured in the preset direction by this pair of springs  61 . The direction in which the intermediary transmitting member  57  is kept pressed by the pair of springs  61  is such direction that causes the intermediary transmitting member  57  to move into the gap between the driver pulley  52  and follower pulley  53 , that is, toward where the gap between the driver pulley  52  and follower pulley  35  is narrowest. In the case of the structural setup shown in the drawing, however, the intermediary transmitting member  57  is on the tension pulley side (left side in  FIG. 2 ) of the theoretical line L (dotted line) which connects the center of the driver pulley  52  and the center of the follower pulley  53 . Therefore, the pressure applied to the intermediary transmitting member  57  by the pair of springs  61  works in the direction to increase the distance between the intermediary transmitting member  57  and tension pulley  55 . Since the driving apparatus  50  is structured as described above, the intermediary transmitting member  57  is afforded a certain amount of positional latitude, and is properly positioned by being kept in contact with the driver pulley  52  and follower pulley  53 . In comparison, the driver pulley  52  and follower pulley  53  are rotatably supported with the presence of no play relative to the frames, and therefore, they are stable in the position of their rotational axis. 
         [0040]    The belt  54  is stretched in such a manner that it wraps the tension pulley side of the peripheral surface  57   a  of the intermediary transmitting member  57 . Thus, the intermediary transmitting member  57  is kept wedged between the driver pulley  52  and follower pulley  53  by the tension of the belt  54 . That is, the intermediary transmitting member  57  is on the tension pulley side of the aforementioned theoretical line L, as described above. Further, the belt  54  is stretched so that it wraps around the tension pulley side of the intermediary transmitting member  57  to keep the intermediary transmitting member  57  pressed by the tension of the belt  54 , toward where the gaps between the driver pulley  52  and follower pulley  53  is narrowest. Therefore, it is ensured that the engaging portions  57   c  of the intermediary transmitting member  57  are kept in contact with the engaging portions  52   a  of the driver pulley  52 , and the engaging portions  53   a  of the follower pulley  53 , by the coordination of the tension of the intermediary transmitting member  57  and the pressure from the above described pair of springs  61 , providing thereby a proper amount of contact pressure between the intermediary transmitting member  57  and driver pulley  52 , and between the intermediary transmitting member  57  and follower pulley  53 . Incidentally, as long as the proper amount of contact pressure can be provided between the engaging portions  57   c  of the intermediary transmitting member  57  and the engaging portions  52   a  of the driver pulley  52 , and between the engaging portions  57   c  of the intermediary transmitting member  57  and the engaging portions  53   a  of the follower pulley  53 , by the belt tension alone, the pair springs  61  may be eliminated. 
         [0041]    Referring to  FIG. 2 , since the driving apparatus  50  is structured so that the intermediary transmitting member  57  is between the driver pulley  52  and follower pulley  53 , and the belt  54  is wrapped around the tension pulley side of the intermediary transmitting member  57 . Therefore, the belt  54  is wrapped around the driver pulley  52  and follower pulley  53  by a sufficient angle. In other words, the area of contact between the belt  54  and peripheral surface  52   a  of the driver pulley  52 , and the area of contact between the belt  54  and the peripheral surface  53   a  of the follower pulley  53 , are substantial in size. Therefore, it is ensured that the driving force is reliably transmitted from the driver pulley  52  to the follower pulley  53  by the belt  54 . Incidentally, the intermediary transmitting member  57  may be positioned on the opposite side (right side in  FIG. 2 ) of the theoretical line L from the tension pulley  55 . In such a case, however, the intermediary transmitting member  57  is kept pressed by the tension of the belt  54 , in the direction to increase the distance between the intermediary transmitting member  57  and driver pulley  52 , and the distance between the intermediary transmitting member  57  and follower pulley  53 . Therefore, the pair of springs  61  have to be made large enough in resiliency to keep the intermediary transmitting member  57  wedged between the two pulleys  52  and  53 . 
         [0042]    Further, the driving apparatus  50  has an encoder wheel  62 , which is solidly attached to the shaft  15   a  of the photosensitive drum  15 . It has also at least one detecting portion  63 , which is in the adjacencies of the peripheral surface of the encoder wheel  62 . The encoder wheel  62  and detecting portion  63  make up a rotational speed detecting means  64 , making it possible to detect the rotational speed of the photosensitive drum  15 . The signals outputted as the detecting portion  63  detects the rotational speed of the photosensitive drum  15  are sent to a control portion  65  as a controlling means. The control portion  65  controls the DC motor  51  in response to the signals sent from the detecting portion  63 , controlling thereby the driver pulley  52  in rotational speed. Incidentally, the control portion  64  may be a part of the control unit described above, or independent from the control unit. 
         [0043]    The driving apparatus  50  structured as described above rotates the photosensitive drums  15  by transmitting driving force from the DC motor  51  to the photosensitive drums  15  by transmitting the driving force from the driver pulley  52  to the follower pulley  53  through the belt  54  and intermediary transmitting member  57 . As long as the image forming apparatus is normally operating, that is, as long as the load resulting from the driving of the image forming portions does not substantially change, the driving force from the DC motor  51  is satisfactorily transmitted by way of the belt  54 . However, if the load to which the follower pulley  53  is subjected suddenly reduce in amount, or reverses in direction, that is, if the load to which the follower pulley  53  is subjected changes in amount, the belt  54  is allowed to slacken, failing thereby to transmit the diving force by a satisfactorily amount. In this embodiment, however, when the image forming apparatus is in the above described condition, the driving force from the DC motor  51  is transmitted from the driver pulley  52  to the follower pulley  53  by the intermediary transmitting member  57 , and therefore, the driving force is reliably transmitted to the follower pulley  53 . To describe in more detail, the intermediary transmitting member  57  is higher in rigidity than the belt  54 . Therefore, even if the load to which the follower pulley  53  is subjected changes in amount and/or direction, the intermediary transmitting member  57  does not deform like the belt  54 . Therefore, it is ensured that the driving force from the DC motor  51  is satisfactorily transmitted to the follower pulley  53  by being transmitted by way of the intermediary transmitting member  57 . Therefore, it does not occur that the image forming portions reduces in responsiveness. Next, referring to  FIGS. 4 to 6 , this feature of the driving apparatus  50  in this embodiment will be described in detail. 
         [0044]      FIG. 4  is a schematic sectional view of a driving force transmitting apparatus which does not have the intermediary transmitting member  57 . The inventors of the present invention performed the following experiments to compare, in structure, the driving force transmitting apparatus in  FIG. 4  with the driving apparatus  50 , or the driving force transmitting apparatus in this embodiment. That is, the distance between the drum shaft  15   a  and output shaft  51   a  was measured while the amount of torque (load) to which the follower pulleys  53  and  53 A are subjected was varied by controlling the rotational speed of the photosensitive drum  15 .  FIGS. 5 and 6  show the results of this experiment. In  FIGS. 5 and 6 , the vertical axis stands for the amount of torque (load) to which the follower pulleys  53  and  53   a  were subjected, and the amount of the positional deviation of the follower pulleys  53  and  53   a , and rotational axis (output shaft  51   a ) of the driver pulleys  52  and  52 A, whereas the horizontal axis stands for the elapsed time.  FIG. 5  shows the test results of the driving force transmitting apparatus shown in  FIG. 4 , that is, a driving force transmitting apparatus which does not have the intermediary transmitting member  57 .  FIG. 6  shows the test results of the driving apparatus  50 , that is, the driving force transmitting apparatus in this embodiment, which is structured as shown in  FIGS. 2 and 3 . The amounts of positional deviation shown in  FIGS. 5 and 6  are represented by the values equivalent to the positional deviation of the peripheral surface of the photosensitive drum  15 . These experiments were performed under the following conditions. 
         [0045]    The photosensitive drum  15  was 30 mm in diameter, and the driver pulley  52  was 12.06 mm in diameter. The follower pulley  53  was 96.48 mm in diameter, and the intermediary transmitting member  57  was 24.12 mm in diameter. Further, the tension pulley  55  was 23.96 mm in diameter. Further, the driver pulley  52 A and follower pulley  53 A were 11.96 mm and 95.96 mm, respectively, in diameter. Incidentally, the abovementioned diameters of the driver pulley  52 , follower pulley  53 , and intermediary transmitting member  57  are the diameters of the engaging portions  52   c ,  53   c , and  57   c , respectively. The depths of the grooves  52   b ,  53   b , and  57   b  are 0.05 mm, 0.26 mm, and 0.08 mm, respectively. As the material for each pulley and intermediary transmitting member, stainless steel was used. The belt  54  was 0.04 mm in thickness, 12 mm in width, and 420 mm in length. It was made of stainless steel. The revolution of the DC motor (hence, revolution of driver pulleys  52  and  52 A) was 1,068 rpm, and the target revolution for the follower pulleys  53  and  53 A and the photosensitive drum  15  was 133.5 rpm. Each of the pair of springs  56  by which the tension pulley  55  was kept pressed was 31 N in resiliency, providing thereby the belt  54  with 46 N of tension when the belt  54  is under no load (when driving force is not transmitted). 
         [0046]    Referring to  FIGS. 5 and 6 , in both the case of the structural arrangement, the test results of which are shown in  FIG. 5 , and the case of the structural arrangement, the test results of which are given in  FIG. 6 , the drum shaft  15   a  slightly shifted relative to the output shaft  51   a  in the direction in which the belt  54  was moved, that is, the positive direction in the graphs ( FIGS. 5 and 6 ), even if there is no change in the amount of the load. On the other hand, as the amount of the load changed in the positive direction, the drum shafts  15   a  gradually shifted in the negative direction. In either case, however, the positional deviation (shifting) was slight. In comparison, in the case where the load reversed in direction, that is, the sign of the value which shows the amount of the load changed from plus to minus, the amount by which the positional deviation occurred to the drive shaft  15   a  (photosensitive drum  15 ) of the driving force transmitting apparatus which does not have the intermediary transmitting member  57  was very large, as shown in  FIG. 5 . Consequently, a certain amount of play (slackening) occurred to the portion of the belt  54 , which was between the upstream side of the driver pulley  52 A and the downstream side of the follower pulley  53 A in terms of the belt movement direction, as depicted by the solid line in  FIG. 4 . Thus, the follower pulley  53 A becomes unsynchronized relative to the driver pulley  52 A by a rotational angle of θ. 
         [0047]    To describe this subject in more detail, in more detail, if the load to which the follower pulley  53 A is subjected suddenly reduces, the torque stored in the driving system is instantly released, whereby the follower pulley  53 A is made to temporarily overrun in the moving direction of the belt  54  (this phenomenon is similar in nature to the temporary vibrations which occurs as the right hand is moved away from an object which is being dragged by the left hand, with the presence of a piece of rubber band between the left hand and the object, while securing the object with the right hand). In particular, as the load becomes negative (reverse in direction), the follower pulley  53 A is driven by the downstream portions of the image forming apparatus in terms of the direction in which the driving force is normally transmitted, the follower pulley  53 A becomes large in the amount of its overrun. In the case of the driving force transmitting apparatus which is not provided with the intermediary transmitting member  57 , the relationship, in terms of rotational phase, between the driver pulley  52 A and follower pulley  53 A cannot be precisely regulated. Therefore, the amount of the overrun such as the above-described one, is large. Therefore, the amount of the positional deviation of the drum shaft  15   a  (photosensitive drum  15 ) is substantial. Thus, in the case of a driving force transmitting apparatus structured as shown in  FIG. 4 , it is difficult to keep the speed of the follower pulley  53 A at a preset value by controlling the drum shaft  15   a  in rotational speed. 
         [0048]    In comparison, in this embodiment, the follower pulley  53  is driven by utilizing the friction between the driver pulley  52  and intermediary transmitting member  37 , and the friction between the intermediary transmitting member  57  and follower pulley  53 , by placing the intermediary transmitting member  57  in contact with the driver pulley  52  and follower pulley  53 . Therefore, the relationship, in angle of rotation, between the driver pulley  52  and follower pulley  53  can be more strictly controlled than in the case of the conventional driving force transmitting apparatuses. Being able to more strictly controlling the relationship, in rotational angle, between the driver pulley and follower pulley can more effectively control the transmission of driving force, based on the detected rotational speed of the photosensitive drum  15 . As will be evident from the comparison between the results given in  FIG. 5  and those in  FIG. 6 , in the case of the driving force transmitting apparatus, the test results of which are given in  FIG. 5 , the positional deviation (shifting) of the drive shaft  15   a  (photosensitive drum  15 ) was roughly 40 μm, whereas in the case of the driving apparatus  50 , that is, the driving force transmitting apparatus in this embodiment, the test results of which are given in  FIG. 6 , the positional deviation (shifting) of the drive shaft  15   a  (photosensitive drum  15 ) was roughly 10 μm. In other words, the experiments confirmed that the driving apparatus  50 , that is, the driving force transmitting apparatus in accordance with the present invention, was a substantial improvement over the conventional ones. That is, if an image forming apparatus of the tandem type, such as the one shown in  FIG. 1 , can be reduced in the amount of the positional deviation of its photosensitive drum  15 , it is possible to prevent the misalignment among the monochromatic images, which occurs in the image forming portions. Therefore, it is possible to prevent a full-color image forming apparatus of the tandem type from outputting multicolor images (which are obtained by layering multiple monochromatic images different in color) which suffer from color deviation. 
         [0049]    Also in the case of this embodiment, even if the image forming apparatus is in the condition in which the belt  54  might slip at the time of startup, the driving force is transmitted by the intermediary transmitting member  57 , and therefore, the driving force transmission failure, which might have occurred, due to the slippage, in the case of conventional driving force transmitting apparatuses, does not occur. Thus, the driving apparatus  50 , that is, the driving force transmitting apparatus in this embodiment, last substantially longer than any of the conventional driving force transmitting apparatuses for an image forming apparatus. To describe this subject in more detail, the length by which the belt  54  is wrapped around the driver pulley  52  is less than the length by which the belt  54  is wrapped around the follower pulley  53 . Thus, it is between the driver pulley  52  and belt  54  that slipping is likely to occur as the DC motor  51  is started up. In this embodiment, however, the driving force from the DC motor  51  can be transmitted from the driver pulley  52  to the follower pulley  53  by way of the intermediary transmitting member  57 . That is, the driving force can be transmitted through the engaging portions  52   c ,  53   c , and  57   c . Thus, as the DC motor  51  is started up, the intermediary transmitting member  57  is initially driven directly by the driver pulley  52 , whereby the follower pulley  53  is driven by the rotationally driven by the intermediary transmitting member  57 . Then, the follower pulley  53  is rotationally driven by the belt  54 , with no slipping. In other words, even if the image forming apparatus is in the condition in which the belt  54  might slip, the driving force is transmitted to the follower pulley  53  by way of the intermediary transmitting member  57 . Therefore, the belt  54  does not slip. Incidentally, in order to make it easier to understand the mechanism of the transmission of the driving force from the DC motor  51 , the mechanism was described in steps. In reality, however, the movement of these components virtually instantly (simultaneously) occurs. 
         [0050]    In this embodiment, the intermediary transmitting member  57  is positioned on the tension roller side (opposite side from side from which belt  54  is wrapped around intermediary transmitting member  57 ) of the theoretical line L which connects the center of the driver pulley  52  and the center of the follower pulley  53 . Therefore, as the DC motor  51  is started, the intermediary transmitting member  57  is pressed by the tension of the belt  54  in the direction to wedge into the gap between the driver pulley  52  and follower pulley  53 , whereby friction is increased across the areas of contact between the engaging portions  52   a ,  53   a , and  57   a  and the belt  54 , ensuring thereby further that the belt  54  is unlikely to slip. As long as the belt  54  can be prevented from slipping, it is possible to prevent the belt  54  from being prematurely worn and/or breaking. In other words, the present invention can makes a driving force transmitting apparatus ( 50 ) more durable. 
         [0051]    Also in this embodiment, not only is the driving force transmitted by the belt  54 , but also, by the intermediary transmitting member  57 . Therefore, the amount of the tension with which the belt  54  needs to be provided to prevent the positional deviation of the photosensitive drum  15  does not need to be as large as that in the case of conventional driving force transmitting apparatuses. Therefore, the amount of the load which is applied to the driver pulley  52  and follower pulley  53  by the tension of the belt  54  in their radial direction of the pulleys is smaller than that in the case of the conventional driving force transmitting apparatuses. Therefore, the driving apparatus  50 , that is, the driving force transmitting apparatus in this embodiment, is significantly less likely to collapse, and also, is significantly smaller in the amount of the frictional wear of the driver pulley  52  and follower pulley  53 , than the conventional driving force transmitting apparatuses. In other words, the present invention can provide a driving force transmitting apparatus which is substantially more durable than the conventional ones. 
         [0052]    Further, because the driving force transmitting apparatus in this embodiment is provided with the intermediary transmitting member  57 , it is substantially greater in the angle by which the belt  54  is wrapped around the driver pulley  52  and follower pulley  53 , than the conventional ones, as described above. Therefore, it is substantially greater than conventional ones, in the efficiency with which the driving force is transmitted by the belt  54 . That is, as long as a driving force transmitting apparatus can be improved in the efficiency with which the driving force is transmitted by the belt  54 , it is unnecessary to increase the apparatus in the efficiency with which the driving force is transmitted by the intermediary transmitting member  57 , and therefore, it is unnecessary to increase the apparatus in the amount of contact pressure among the engaging portions  52   c ,  53   c , and  57   c , and the belt  54 . Thus, the driving force transmitting apparatus in this embodiment is substantially smaller in the amount of the frictional wear of these engaging portions  52   c ,  53   c , and  57   c , and therefore, the driving force transmitting apparatus in this embodiment is significantly more durable than the conventional ones. For example, in the case of a driving force transmitting apparatus which transmits driving force only by the intermediary transmitting member  57 , that is, without employing the belt  54 , the apparatus has be greater in the amount of the contact pressure across the areas of contact among the engaging portions  52   c ,  53   c , and  57   c  than a driving force transmitting apparatus having the intermediary transmitting member  57 . In the case of the driving force transmitting apparatus in this embodiment, both the belt  54  and intermediary transmitting member  57  are used for driving force transmission. Therefore, the contact pressure among the engaging portions  52   c ,  53   c , and  57   c  of the apparatus in this embodiment does not need to be as high as that in the conventional ones. Thus, the driving force transmitting apparatus in this embodiment is significantly more durable than the conventional ones. 
       Embodiment 2 
       [0053]    Next, referring to  FIGS. 7 and 8 , the second preferred embodiment of the present invention will be described. In this embodiment, the intermediary transmitting member  57 A is not directly in contact with the driver pulley  52 B and follower pulley  53 B because of the presence of the belt  54  between the intermediary transmitting member  57  and driver pulley  52 , and also, between the intermediary transmitting member  57  and follower pulley  53 B. That is, the belt  57  remains pinched by the peripheral surface of the driver pulley  52 B and the peripheral surface of the intermediary transmitting member  57 , and also, by the peripheral surface of the follower pulley  53 B and the peripheral surface of the intermediary transmitting member  57  (forming thereby nips  66   a  and  66   b ). That is, in this embodiment, the two pulleys  52 B and  53 B, and the intermediary transmitting member  57 , are in the form of a plane cylindrical member; the peripheral surface of the driver pulley  52 B, peripheral surface of the  53 B, and peripheral surface of the intermediary transmitting member  57 , do not have a groove. Otherwise, the driving force transmitting apparatus in this embodiment is the same in structure as the driving force transmitting apparatus in the first embodiment. Therefore, the structural components, members, etc., of the apparatus in this embodiment, are given the same referential codes as those given to their counterparts of the apparatus in the first embodiment, and will not described here. 
         [0054]    In this embodiment, the intermediary transmitting member  57 A is kept wedged between the two pulleys  52 B and  53 B by a pair of springs  61 . Therefore, the driving force transmitting apparatus in this embodiment is higher in the amount of force with which the belt  54  is pinched in the nips  66   a  and  66   b  than the conventional ones. Further, in the case of the driving force transmitting apparatus in this embodiment, the belt  54  is wrapped around the tension pulley side of the intermediary transmitting member  57 A, and the intermediary transmitting member  57 A is kept under the pressure which works in the direction to wedge the intermediary transmitting member  57 A into the gap between the two pulleys  52 B and  53 B. Therefore, not only is the belt  54  of the driving force transmitting apparatus in this embodiment less likely to slacken than that of the conventional ones, but also, the driving force transmitting apparatus in this embodiment is greater than the conventional ones, in the amount of force with which the belt  57  is pinched in the nips  66   a  and  66   b . Thus, in this embodiment, the relationship, in terms of rotational phase, between the driver pulley  52 B and follower pulley  53 B is more strictly regulated, being therefore more desirable in terms of the response to a control command. In other words, this embodiment of the present invention also proved that the present invention can prevent the photosensitive drum  15  from deviating in position, and therefore, can prevent an image forming apparatus from outputting multicolor images, that is, images made up of layered monochromatic images, different in color, which suffer from chromatic deviation. 
         [0055]    Further, the driver pulley wrapping portion of the belt  54 , which is in the nip  66   a , that is, the nip resulting from the pinching of the belt  54  by the driver pulley  52 B and intermediary transmitting member  57 A, is different in the distribution of the normal force from the comparable portion of the belt  54  of any of the conventional driving force transmitting apparatuses. Ordinarily, the distribution of the normal force across the pulley wrapping portion of the belt  54  is such that the normal force is higher across the center of the pulley wrapping portion of the belt  54  than across the end portions of the pulley wrapping portion of the belt  54 , and is zero at the ends. In this embodiment, however, one of the ends of the pulley wrapping portion of the belt  54  coincides with the nip  66   a  in which the belt  54  is pinched by the driver pulley  52  and intermediary transmitting member  57 A, being therefore greater in the normal force. Therefore, the total amount of the normal force in this embodiment is greater than that of any of the conventional driving force transmitting apparatuses. Therefore, the amount of torque transmitted between the driver pulley  52 B and intermediary transmitting is greater; the belt  54  is prevented from slipping. 
         [0056]    Further, the intermediary transmitting member  57 A is positioned on the tension roller side of the theoretical line L which connects the center of the driver pulley  52 B and the center of the follower pulley  53 B. Therefore, as the DC motor  51  is started, the intermediary transmitting member  57  is subjected to such a force that works in direction to cause the intermediary transmitting member  57  to wedge into the gap between the driver pulley  52 B and follower pulley  53 B, whereby the normal force is increased, which in turn makes it unlikely for the belt  54  to slip. 
         [0057]    The embodiments described above are effective even if the driving force transmitting apparatus is not controlled in response to the detected rotational speed of the photosensitive drum  15 . That is, the structural arrangements, in the first and second embodiments, for the driving force transmitting apparatus is for strictly regulating the relationship in terms of rotational phase between the driver pulley  52  ( 52 B) and follower pulley  53  ( 53 B) (for improving driving force transmitting apparatus in responsiveness). Therefore, the structural arrangements make it easier for the changes in the load to which the follower pulley  53  and  53 B are subjected, to be transmitted to the drive shaft of the DC motor. Ordinarily, a motor is under its own internal control so that it remains stable in rotational speed. Therefore, the faster the speed with which the changes in the rotation of the follower pulleys  53  and  53 B are transmitted, the faster, the recovery, and therefore, the smaller the position deviation of the photosensitive drum  15 . Further, even if the motor D is not controlled by its own control system so that it remains stable in rotational speed, the inertia of the drive shaft of the motor D (rotor inertia) functions as a force which counters the changes in the load to which the follower pulleys  53  and  53 A are subjected. The amount of this force equals the square of the reduction ratio. Therefore, the driving force transmitting apparatus in this embodiment is smaller in the amount of the positional deviation of the drum shaft  15   a  than any of the conventional ones, even if the motor D is not controlled in rotation speed. 
         [0058]    Further, the driver pulleys  52  and  52 B, follower pulleys  53  and  53 B, intermediary transferring members  56  and  56 A, and tension pulley  55 , may be shaped, as necessary, so that in terms of the cross-sectional view, their peripheral portions (peripheral surfaces  52   a  and  53   a ) arc outward. The employment of this structural arrangement can easily prevent the belt  54  from shifting in the direction perpendicular to the direction in which the belt  54  is driven. Further, the materials for the pulleys  52 ,  52 B,  53 ,  53 B, and intermediary transferring members  56  and  56 A are desired to be a highly rigid metallic substance. However, a substance other than the highly rigid metallic substance may be employed as the material for these components, provided that these components are for a driving force transmitting apparatus which is relatively low in the changes in the amount of the load, or according to the target amount of color deviation. When a substance other than the rigid metallic substance is used as the material for these components, the material for the belt  54  should be a substance which is lower in hardness than the material for the metallic belt. For example, it should be rubber. 
         [0059]    According to the present invention, even if the load to which the follower pulley is subjected changes, the driving force is transmitted by the intermediary transmitting member, which is higher in rigidity than the belt  54 . Therefore, it is ensured that the driver pulley and follower pulley quickly and accurately respond to each other in terms of rotation. Further, if an image forming apparatus is used under the condition in which the belt of its driving force transmitting apparatus may slip, the driving force is transmitted by the intermediary transmitting member, preventing thereby the belt from slipping. In other words, the present invention can provide a driving force transmitting apparatus which is substantially more durable than any of the conventional driving force transmitting apparatuses. 
         [0060]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
         [0061]    This application claims priority from Japanese Patent Application No. 185128/2009 filed Aug. 7, 2009 which is hereby incorporated by reference.

Technology Classification (CPC): 6