Abstract:
A belt-driving apparatus has a belt in the shape of an endless loop. The belt has an outside surface and inside surface, and a guide belt that is formed on the inside surface. The belt is entrained about a roller with the inside surface in contact with the roller. A pulley is mounted at least on one axial end of the roller, the pulley having a circumferential groove formed therein that receives the guide belt therein. A resilient member that urges the first surface of the belt in such a direction that the guide belt enters the groove. The roller may have a circumferential groove formed therein to receive the guide belt, thereby eliminating the pulley.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a belt-driving apparatus that drives a belt such as a transfer belt incorporated in an electrophotographic recording apparatus.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 13 is a perspective view of a conventional belt-driving apparatus for use in an electrophotographic printer.  
           [0005]    Referring to FIG. 13, a belt  1  is in the form of an endless belt and has a width greater than a maximum length of a printed line of an electrophotographic printer, not shown. The belt  1  is entrained about idle rollers  3 ,  4 , and  5 , and a drive roller  6 , and runs at a constant speed in a direction shown by arrow C. A spring, not shown, maintains moderate tension in the belt  1  at all times. The belt  1  has an endless guide belt  2  that is attached to the inside surface of the belt  1 . The guide belt  2  extends along the lateral ends portion of the belt  1  to describe a loop. The drive roller  6  has a surface made of a highly frictional material.  
           [0006]    The idler roller  4  rotates about a shaft, not shown, on which pulleys  8  rotate freely. The pulley  8  is formed with a circumferential groove  26  therein having depth and width that are sufficient to receive the guide belt  2  therein. The groove  26  is tapered such that the groove  26  is wider at its opening than at its bottom. When the guide belt  2  is received in the groove  26 , the belt  1  is ready to run properly.  
           [0007]    The operation of the conventional belt-driving apparatus will now be described. When the drive roller  6  is driven in rotation by a drive source, not shown, the frictional force and the angle of contact between the belt  1  and the drive roller  6  cause the belt  1  to run in the direction shown by arrow C. When the belt  1  becomes skewed due to mechanical distortions of the system and variations of length of the belt  1  across the width of the belt  1 , the guide belt  2  received in the groove  26  effectively alleviates the influence of the skewing problem to some extent.  
           [0008]    However, too large an amount of skewing causes the guide belt  2  to exert a large force on the side wall of the groove  26 , so that the guide belt  2  will climb the tapered side wall of the groove  26  to move out of the groove  26 .  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is to provide a belt-driving apparatus in which the guide belt attached to an endless belt such as a transport belt is prevented from coming off the guide groove.  
           [0010]    An object of the present invention is to provide a belt-driving apparatus in which the belt is prevented from becoming skewed.  
           [0011]    A belt-driving apparatus has a belt in the shape of an endless loop. The belt has an outside surface and inside surface, and a guide belt that is formed on the inside surface. The belt is entrained about a roller with the inside surface in contact with the roller. The belt is entrained about the roller with a certain angle of contact. A pulley has a circumferential groove formed therein that receives the guide belt therein, and is mounted on a shaft of the roller. The pulley rotates independently of the roller. A resilient member that urges the first surface of the belt in such a direction as to increase the angle of contact. The roller may have a circumferential groove formed therein to receive the guide belt, thereby eliminating the pulley with a groove.  
           [0012]    The resilient member is in pressure contact with the outside surface at a position between a first position and a second position to urge the outside surface of the belt toward the inside surface the belt. The first position is such that the guide belt is about to run into the groove of the pulleys and the second position is such that the guide belt has been completely received in the groove.  
           [0013]    The resilient member may be in the shape of a plate that extends substantially parallel to an axial direction of the roller over a distance longer than a width of the belt.  
           [0014]    The resilient member may be a cleaning blade that cleans the outside surface of the belt.  
           [0015]    The roller, pulley, and resilient member are supported on a supporting member that may be urged by an urging member in such a direction as to maintain tension in the belt.  
           [0016]    Instead of incorporating the pulley, the apparatus may have a groove formed in the roller. The groove may have a depth greater than a height of the guide belt such that there is a clearance between a bottom of said groove and a top of the guide belt.  
           [0017]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limiting the present invention, and wherein:  
         [0019]    [0019]FIG. 1 is a perspective view of a belt driving apparatus according to a first embodiment;  
         [0020]    [0020]FIG. 2 is a side view of the belt-driving apparatus according to the first embodiment;  
         [0021]    [0021]FIG. 3 is a cross-sectional view taken along lines VII-VII lines of FIG. 2;  
         [0022]    [0022]FIG. 4 is an enlarged view of the spring and guide members  15   a  and  15   b.    
         [0023]    FIGS.  5 - 7  are cross-sectional views illustrating the relation among the belt  11 , guide belt  12 , and cleaning blade  18  according to the first embodiment;  
         [0024]    [0024]FIG. 8 illustrates a cleaning blade having a much narrower width than the belt;  
         [0025]    [0025]FIG. 9 illustrates a blade disposed near the drive roller;  
         [0026]    [0026]FIG. 10 illustrates a modification to the first embodiment;  
         [0027]    [0027]FIG. 11 is a cross-sectional view of a belt driving apparatus according to a second embodiment, taken along lines VII-VII of FIG. 2;  
         [0028]    [0028]FIG. 12 illustrates the relationship between the gap G and the cleaning failure rate of the belt surface that is cleaned with the cleaning blade, and the relationship between the gap G and the frictional load developed between belt and idler roller; and  
         [0029]    [0029]FIG. 13 is a perspective view of a conventional belt-driving apparatus for an electrophotographic printer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    The present invention will be described in detail with reference to the accompanying drawings.  
         [0031]    First Embodiment  
         [0032]    [0032]FIG. 1 is a perspective view of a belt-driving apparatus according to a first embodiment.  
         [0033]    [0033]FIG. 2 is a side view of the belt-driving apparatus according to the first embodiment.  
         [0034]    A belt-driving apparatus  20  is incorporated in an electrophotographic printer, not shown.  
         [0035]    Referring to FIGS. 1 and 2, there are structural elements of a print engine including a photoconductive drum, not shown, above a belt  11 . The belt  11  describes a loop and has a width greater than a maximum length of a printed line of an electrophotographic printer, not shown. The belt  11  is entrained about idle rollers  13  and a drive roller  14  and runs at a constant speed. The idler roller is made of a metal material such as aluminum. The drive roller  14  is mounted on a shaft  19  that is rotatably supported on a frame of the printer, not shown. Compressed springs  16  (only one spring is shown in FIG. 1) urge supporting members  15   a  and  15   b  in a direction shown by arrow E to maintain moderate tension in the belt at all times. The belt  11  has guide belts  12  that are attached to the inner surface of the belt  11 . The guide belts  12  run along the lateral end portions of the looped belt  11  to describe a loop. FIG. 1 shows only one of two guide belts. The drive roller  14  has a surface made of a highly frictional material. The drive roller  14  is slightly shorter than the width of the belt  11  such that the drive roller  14  does not interfere with the guide belt  12 .  
         [0036]    A cleaning blade  18  is mounted at its one end  18   a  to the supporting members  15   a  and  15   b  and contacts the belt  11  at its other end, i.e., free end  18   b.  The cleaning blade removes foreign material deposited on the belt  11 . The cleaning belt  18  has a width the same as or slightly greater than that of the belt  11  and extends across the width of the belt  11 . The cleaning belt  18  is a plate of a resilient material such as urethane and resiliently abuts the belt  11 .  
         [0037]    [0037]FIG. 3 is a cross-sectional view taken along lines D-D of FIG. 2.  
         [0038]    The idle roller  13  is mounted on a shaft  21  that is rotatably supported by the supporting members  15   a  and  15   b.    
         [0039]    Pulleys  17  are rotatably mounted on the shaft  21  with the roller sandwiched therebetween and rotate freely independently of the idle roller  13 . The pulley  17  is formed with a circumferential groove  24  therein. The depth and width are sufficient to loosely receive the guide belt  2  therein. The groove  24  is tapered such that the groove  24  is wider at toward the opening and narrower toward the bottom. When the guide belt  2  is received in the groove  24 , the belt  1  is ready to run properly.  
         [0040]    [0040]FIG. 4 is an enlarged view of the spring and guide members  15   a  and  15   b.    
         [0041]    The supporting members  15   a  and  15   b  are movably supported on the frame of the printer, not shown. Each of the springs  16  is loosely received in a cylindrical hole  23   a  formed in a frame  23  so that the spring can be compressed and stretched. The spring  16  has one end that engages bottom of the hole  23   a,  and the other end that engages the supporting member  15   a  or  15   b  so that the supporting members  15   a  and  15   b  are urged in the direction shown by arrow E to apply tension to the belt  11 . Thus, the belt  11  can run without slack therein.  
         [0042]    FIGS.  5 - 7  are cross-sectional views illustrating the relation among the belt  11 , guide belt  12 , and cleaning blade  18  according to the first embodiment.  
         [0043]    The belt  11  wraps around the pulley  7  by an angle of contact of θ1. As shown in FIGS. 5 and 6, the free end  18   b  is brought into contact with the belt  11  somewhere between a position A depicted by arrow A and a position B depicted by arrow B. The position A is a position where the guide belt  12  is about to enter the groove  24  of the pulley  17  and the position B is a position where the guide belt  12  is completely received in the groove  24 .  
         [0044]    The aforementioned structural elements form a belt-driving apparatus  20 . There is no pulley provided on the shaft  19  and the drive roller  14  is shorter than the width of the belt  11  so that the drive roller  14  does not interfere with the guide belt  12 .  
         [0045]    The operation of the belt-driving apparatus according to the first embodiment will now be described with reference to FIGS.  5 - 7 .  
         [0046]    Referring back to FIG. 1, when the drive roller  14  is driven in rotation by a drive source, not shown, the angle of contact and the frictional force between the drive roller  14  and the belt  11  cause the belt  11  to run in the direction shown by arrow C. The guide belt  12  received in the groove  24  also runs and therefore the belt  11  continues to rotate with stability. The skew problem of the belt  11  results from the mechanical distortions of the system and the variation of circumferential length of the belt  11  across the width of the belt  11 . When the belt  11  becomes skewed, the guide belt  12  received in the groove  24  moves in the direction of the skewing until it presses the tapered side wall of the groove  24 . A further force exerted on the tapered side wall will produce a force that causes the guide belt  12  to climb the tapered side wall.  
         [0047]    The force that causes the guide belt  12  to climb the tapered side wall acts on a portion where the belt  11  is about to contact the idle roller  13 . The springs  16  exert a tensile force on the belt  11 , the tensile force resulting in a force that tends to suppress the force that causes the guide belt  12  to climb the side wall of the groove  24 . However, the suppressing force created by the urging force of the springs  16  is not large enough to completely overcome the climbing force resulting from the skewing problem.  
         [0048]    In the present embodiment, the cleaning blade  18  is disposed such that the free end  18   b  of the blade  18  contacts the belt  11  at a portion where the guide belt  12  is about to enter the groove  24 . The cleaning blade  18  tends to push the guide belt  12  into the groove  24 , thereby preventing the guide belt  12  from overriding the side wall of the groove  24 . Thus, the cleaning blade  18  allows for proper engagement of the guide belt  12  with the grooves  24  of the pulleys  17 .  
         [0049]    If the free end  18   a  of the cleaning blade  18  is in contact with the belt  11  at a position downstream of the position B (FIG. 5) with respect to the direction in which the belt  11  runs, the guide belt  12  cannot be properly pulled into the groove  24 .  
         [0050]    If the free end  18   a  of the cleaning blade  18  is in contact with the belt  11  at a position upstream of the position A (FIG. 6), the guide belt  12  may not be properly pulled into the groove  24 .  
         [0051]    Referring to FIG. 7, the cleaning blade  18  pushes the belt  11  in such a direction as to increase an angle of contact θ2 by which the belt  11  contacts the pulley  7 . If the force that cleaning blade  18  pushes the belt  11  and guide belt  12  changes, then the cleaning blade  18  may press the belt  11  at somewhat shifted positions. Thus, the cleaning blade  18  should be disposed such that even if the cleaning blade may press the belt  11  at somewhat shifted positions, the free end  18   a  is still between the position A and position B.  
         [0052]    [0052]FIG. 8 illustrates a cleaning blade having a much narrower width than the belt.  
         [0053]    If the cleaning blade  18  has a width that is the same as or slightly larger than the thickness of the pulley  17  as shown in FIG. 8, then the cleaning blade  18  presses only a part of the belt  11  against the pulley. As a result, the belt  11  will have slack S 1  therein that extends across its width and results in unstable running of the belt  11 . Therefore, the cleaning blade should have a dimension such that the cleaning blade  18  presses the belt  11  evenly all across the width of the belt  11 .  
         [0054]    [0054]FIG. 9 illustrates a blade disposed near the drive roller.  
         [0055]    The groove  24  should preferably be formed in a member other than the drive roller  14 . As shown in FIG. 9, if the groove  24  is formed in the drive roller  14  and the cleaning blade  18  is pressed against the drive roller  14 , then the force exerted by the cleaning blade  18  on the belt  11  causes the belt  11  to have slack S 2  therein around the drive roller  14 . This slack S 2  prevents the belt  11  from firmly holding the driver roller  14 , resulting in slippage of the belt  11  around the drive roller  14 .  
         [0056]    In the first embodiment, the cleaning blade  18  applies a uniform pressing force across the width of the belt  11 , thereby minimizing the chance of the belt  11  becoming wavy in the running direction so that the skewing force is not concentrated at one location. The cleaning blade  18  plays two roles: a cleaning member for cleaning the surface of the belt  11  and a pressing member for pressing the guide belt  12  toward the groove  24 . Thus, providing the cleaning blade  18  eliminates the need for providing a member that presses the guide belt  12  against the groove  24 .  
         [0057]    [0057]FIG. 10 illustrates a modification to the first embodiment.  
         [0058]    Referring to FIG. 10, there is no pulley provided. The guide belt  12  is attached to the inner surface of the belt  11  at opposing end portions of the width such that the roller  13  extends between the endless guide belts. The guide belt  12  serves to limit the width-wise position of the belt  13  relative to the roller  13 .  
         [0059]    Second Embodiment  
         [0060]    In the first embodiment, the pulleys  17  are rotatably mounted on the shaft  21  of the idle roller  13  and rotate independently of the idle roller  13 . The groove  24  has a depth substantially equal to the height of the guide belt  12 .  
         [0061]    The belt  11  is guided by the guide belt  12  received in the groove  25 .  
         [0062]    When the drive roller  14  is driven in rotation by a drive source, not shown, the angle of contact of the belt  11  and the frictional force between the belt  11  and the drive roller  14  cause the belt  11  to run in the direction shown by arrow C. Because the depth of the groove  24  is substantially the same as the height of the guide belt  12 , the guide belt  12  runs with its upper surface in contact with the bottom of the groove  24 .  
         [0063]    Therefore, the circumferential velocity of the bottom of the groove  24  is the same as that of the guide belt  12  in contact with the bottom of the groove  24 , provided that the guide belt  12  and groove  24  are very accurately dimensioned. However, if the groove  24  is little shallow compared to the height of the guide belt  12 , the bottom of the groove  24  pushes up the guide belt  12 . In this case, the circumferential velocity of the bottom of the groove  24  is slightly higher than that of the surface of the guide belt  12  in contact with the bottom of the groove  24 . Thus, if the pulley  17  is secured to the roller  13  and rotates together with the roller  13 , the guide belt  12  and the bottom of the groove  24  rub each other due to the difference in circumferential velocity. The difference in circumferential velocity exerts an undesired load on the guide belt  12 . In order to avoid such a load, the pulleys  17  in the first embodiment are constructed to rotate independently of the idle roller  13 .  
         [0064]    [0064]FIG. 11 is a cross-sectional view of a belt-driving apparatus according to a second embodiment, taken along lines VII-VII of FIG. 2.  
         [0065]    However, as is clear from FIG. 11, the second embodiment differs from the first embodiment in that a pulley is not used but an idle roller  22  made of aluminum has a groove  25  formed therein. The depth of the groove  25  is greater than the height of the guide belt  12 . The groove  25  is tapered from its bottom  25   a  to its open end. The bottom  25   a  is a slightly larger width than the guide belt  12 . In order to accommodate the dimensional errors of the structural elements, there is provided a gap G between the upper surface  12   a  of the guide belt  12  and the bottom  25   a  of the groove  25 .  
         [0066]    The gap G prevents the upper surface  12   a  of the guide belt  12  from contacting the bottom  25   a  of the groove  25 . This structure eliminates the problem of the difference in circumferential velocity between the bottom  25   a  and the surface of the guide roller  22 . Thus, pulley and idle roller can be of an integral construction.  
         [0067]    [0067]FIG. 12 illustrates the relationship between the gap G and the cleaning failure rate of the belt surface that is cleaned with the cleaning blade, and the relationship between the gap G and the frictional load developed between belt and idler roller.  
         [0068]    Too large a value of the gap G allows the guide belt  12  to enter deep into groove  25 , the guide belt  12  and belt  11  not resisting sufficiently to the pressing force of the cleaning blade  18 . This will not create a sufficient frictional force between the cleaning blade  18  and the belt  11 , causing poor cleaning result. The optimum value of the gap G varies depending on the rigidity of the belt  11  and cleaning blade  18  and smoothness of their contact surfaces. The gap G is preferably such that the cleaning failure rate of the surface of the belt  11  and the frictional force between the guide belt  12  and the groove  25  in the idle roller  22  are minimized. Referring to FIG. 12, the cleaning failure rate of the belt surface increases gradually for the gap G=0 to 0.6 mm and rapidly for the gap G greater than 0.6 mm. The frictional load developed between the belt and the idler roller gradually increases for the gap G greater than 0.1 mm and abruptly increases for the H smaller than 0.1 mm. Thus, the value of the gap G should be in the range of 0.1 to 0.6 mm, and preferably about 0.2 mm.  
         [0069]    The arrangement, construction, and operation of the cleaning blade, belt, and guide belt are the same as those of the first embodiment and the description thereof is omitted.  
         [0070]    The second embodiment eliminates the need for providing a pulley. This leads to reduction of manufacturing costs.  
         [0071]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art intended to be included within the scope of the following claims.