Patent Publication Number: US-7896332-B2

Title: Belt driving mechanism, image forming apparatus including the same, and method for driving belt

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from U.S. provisional application 60/982102, filed on Oct. 23, 2007, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a belt driving mechanism, an image forming apparatus including the same, and a method for driving the belt, and more in particular to a belt driving mechanism for carrying papers by a reciprocating motion in a finisher of an image forming apparatus, an image forming apparatus including the same, and a method for driving the belt. 
     BACKGROUND 
     Recently, an image forming apparatus of an electrophotographic scheme such as a laser printer, a digital copier, or a laser facsimile is equipped with a post-processing device (finisher) which staples or sorts a bunch of papers, as disclosed in, for example, JP-A 2007-76893. 
     In the finisher, a reciprocating motion of an assist arm (an ejector) is carried out by, for example, a reciprocal motion of a belt (hereinafter, referred to as “an eject belt”) to which the ejector is fixed, as shown in JP-A 2007-76893. 
     In order to increase a throughput of a stapling processing or sorting processing performed repeatedly, it is required to increase a moving speed of the ejector in the returning path as well as in the going path. In addition, the ejector is required to stop at the home position accurately and further surely. In order to satisfy these requirements, a torsional coil spring with a large elastic force it is require is used for the movement of the returning path. 
     Meanwhile, a protrusion is provided on a predetermined position of the eject belt. The protrusion collides with a belt stopper fixed outside the eject belt, thereby stopping the movement of the eject belt in the returning direction. The stop position of the eject belt is adjusted such that the ejector stops at the home position. 
     Due to the large elastic force of the torsional coil spring, the eject belt accelerates considerably right before the protrusions thereof collide with the belt stopper. 
     As a result, conventionally, the protrusions on the eject belt collide with the belt stopper for stopping in an impact manner, thereby generating an impact sound. When the stapling processing or the sorting processing is performed repeatedly, the impact sound is also generated repeatedly. 
     SUMMARY 
     The present invention is designed in consideration of such situation, an object of which is to provide a belt driving mechanism, an image forming apparatus including the same and a method for driving a belt, capable of preventing an impact sound using a very simple configuration without decreasing a movement speed of the belt, in the belt driving mechanism to perform a reciprocating motion. 
     In order to accomplish the above object, a belt driving mechanism related to one aspect of the present invention includes: a toothed drive pulley; a toothed driven pulley; a toothed belt to engage with the toothed pulleys by tooth on an inner circumference thereof; and an elastic member to move the toothed belt in a returning direction by an elastic force accumulated while the toothed drive pulley moves the toothed belt in a going direction. At least one of the toothed belt, the toothed drive pulley, and the toothed driven pulley is formed such that at least one of tooth bottoms is shallower than at least other one of the tooth bottoms. 
     An image forming apparatus related to another aspect of the present invention comprises: a printer to print images on a plurality of papers; a processing tray to stack papers to match end portions of the papers; a stapler to staple the papers; and the above belt driving mechanism. 
     In addition, relating to another aspect of the invention, a method for driving a belt that has the above belt driving mechanism includes: moving the toothed belt in a going direction to move the hook from a first position to a second position, by a driving force of a motor; and moving the toothed belt in a returning direction to return the hook from the second position to the first position, by an elastic force accumulated in an elastic member while the toothed drive pulley moves the toothed belt in a going direction. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view to illustrate an example of an appearance of an image forming apparatus related to the present embodiment; 
         FIG. 2  is a diagram to in detail illustrate an exemplary configuration of a finisher of the image forming apparatus related to the present embodiment; 
         FIG. 3  is a diagram to schematically illustrate a configuration of the finisher; 
         FIG. 4  is a first perspective view to illustrate a configuration of a main part of the finisher; 
         FIG. 5  is a second perspective view to illustrate the configuration of the main part of the finisher; 
         FIG. 6  is a first perspective view to illustrate an exemplary configuration of a processing tray unit; 
         FIG. 7  is a perspective view to illustrate an exemplary configuration of a processing tray unit related to another embodiment; 
         FIG. 8  is a second perspective view to illustrate the exemplary configuration of the processing tray unit; 
         FIG. 9  is a plan view to schematically illustrate a configuration of a belt driving mechanism related to the present embodiment; 
         FIG. 10  is a side view to schematically illustrate a configuration of the belt driving mechanism related to the present embodiment; 
         FIG. 11  is a view to illustrate a first operation of the belt driving mechanism; 
         FIG. 12  is a view to illustrate a second operation of the belt driving mechanism; 
         FIG. 13  is a view to illustrate a third operation of the belt driving mechanism; 
         FIG. 14  is a view to illustrate the fourth operation of the belt driving mechanism; 
         FIG. 15  is a perspective view to illustrate an example of an appearance of a toothed pulley; 
         FIG. 16  is a diagram to illustrate the first Example to increase a tension of an eject belt for braking in the belt driving mechanism related to the present embodiment; 
         FIG. 17  is a diagram to illustrate the second Example to increase a tension of the eject belt for braking in the belt driving mechanism related to the present embodiment; 
         FIG. 18  is a diagram to illustrate the third Example to increase a tension of the eject belt for braking in the belt driving mechanism related to the present embodiment; and 
         FIG. 19  is a diagram to illustrate the fourth Example to increase a tension of the eject belt for braking in the belt driving mechanism related to the present embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of a belt driving mechanism, an image forming apparatus including the same and a belt driving method related to the present invention will be described with reference to the accompanying drawings. 
     (1) Image Forming Apparatus 
       FIG. 1  is a diagram to illustrate an exemplary appearance of a copier (or an MFP) as a model of an image forming apparatus  100  related to the present embodiment. 
     The image forming apparatus  100  includes a printer  2  and a finisher  1 . The printer  2  includes a read-out unit  3 , an image forming unit  4  and a paper supply unit  5  and the like. 
     The read-out unit  3  optically reads out an original document mounted on a document plate or an original document inputted in an ADF (Auto Document Feeder) to generate image data. 
     The image forming unit  4  prints the image data on a paper supplied from the paper supply unit  5  by use of an electrophotographic scheme. The image forming unit  4  is provided with a control panel  6  where a user performs a variety of operations and a display panel  7  for displaying a variety of information. 
     The finisher  1  is a device for performing post-processing such as a sorting processing of, or a stapling processing of a paper P printed in the printer  2 . 
       FIG. 2  is a diagram to in detail illustrate an exemplary configuration of specially the finisher  1  of the image forming apparatus  100  related to the present embodiment. Further,  FIG. 3  is a diagram to schematically illustrate a configuration of the finisher  1 . 
     Entrance rollers  11   a  and  11   b  configured of a pair of rollers are provided on the lateral side of the finisher  1  adjacent to the printer  2 . The entrance rollers  11   a  and  11   b  receive a print-finished paper supplied from the printer  2 . The entrance rollers  11   a  and  11   b  carry the received paper P to exit rollers  12   a  and  12   b.    
     A stand-by tray  13  is provided in front of the exit rollers  12   a  and  12   b  and temporarily keeps the paper P carried from the exit rollers  12   a  and  12   b.    
     If a predetermined keeping period elapses, the stand-by tray  13  opens and drops the temporarily kept paper P on a processing tray  14 . A bunch of papers B which are a stack of the papers P are mounted on the processing tray  14 . 
     The processing tray  14  is disposed on a slant in a vertical direction as shown in  FIG. 2 . A stapler  19  for stapling the bunch of papers B with staples is provided in front of the lower end of the processing tray  14 . A loading tray  23  for loading the stapled bunch of papers B is also provided in front of the upper end of the processing tray  14 . 
     A paper guide  18  is provided over the lower end of the processing tray  14  and guides the rear ends of the bunch of the papers B supplied to the processing tray  14  toward the stapler  19 . 
     A transverse matching plate  16  is provided on both sides of the processing tray  14 . The transverse matching plate  16  transversely matches the papers P on the processing tray  14 . In addition, a longitudinal matching roller  17  is provided on the rear end of the processing tray  14  and a paddle  15  is provided thereover. The paddle  15  and the longitudinal matching roller  17  enable the rear ends of the papers P on the processing tray  14  to collide with a rear stopper  26  to be matched longitudinally. 
     The papers P are guided to the processing tray  14  via the stand-by tray  13  sequentially and a plurality of papers P are guided to the stapler  19  as a bunch of papers B. If a last paper P of the bunch of papers B is guided to the stapler  19 , the stapler  19  staples the vicinity of the rear ends of the bunch of papers B with staples. 
     The stapled bunch of papers B are hooked in the rear ends thereof by an ejector  20  (hook member) fixed to an eject belt  30  (toothed belt) or a bunch claw  21   a  (carrying hook member) fixed to a bunch claw belt  21  (carrying belt), and are carried toward the loading tray  23  by driving of the eject belt  30  or the bunch claw belt  21 . A protruding rod  25  (rod-shaped member) is fixed to the eject belt  30  at an opposite of the ejector  20 , and the bunch of papers B are supported by the protruding rod  25  in the bottom thereof and are protruded toward the loading tray  23  and further are discharged to the loading tray  23  by a discharge roller  22 . A belt driving mechanism or a belt driving method of the eject belt  30  and the bunch claw belt  21  will be described in detail later. 
     The loading tray  23  can load many bunches of papers B, and the loading tray  23  moves down gradually as the number of the bunch of papers B loaded thereon increases. 
       FIGS. 4 and 5  are perspective views to illustrate a main part of the finisher  1 .  FIGS. 4 and 5  illustrate an appearance where the stand-by tray  13  and components thereon are removed. 
       FIG. 6  is a perspective view to illustrate a structure of a processing tray unit  50 . The processing tray unit  50  has the processing tray  14  on which the bunch of papers B is mounted as described above. The transverse matching plate  16  is provided on the both sides of the processing tray  14 , and transverse matching plate  16  moves in the left and right direction, thereby matching lateral ends of the bunch of papers B before stapling. In addition, two longitudinal matching rollers  17  bring the rear ends of the bunch of papers B on the processing tray  14  into contact with the rear stopper  26  to be matched longitudinally. 
     As the post-processing performed by the finisher  1 , there is a sorting in addition to the stapling. In the sorting process, a predetermined number of papers are matched transversely and longitudinally as one unit of sorting and are alternately shifted for each unit of sorting in a transverse direction (left and right) to discharge to the loading tray  23 . The shift in the transverse direction is performed by use of the transverse matching plate  16 . 
     The bunch of papers B for which the post-processing (the stapling or the sorting) is performed are discharged to the loading tray  23  from the processing tray  14  by a belt driving mechanism  60  (refer to  FIGS. 9 and 10 ) or four discharge rollers  22 . The belt driving mechanism  60  may include the bunch claw belt  21 , the bunch claw  21   a  fixed to the bunch claw belt  21 , two eject belts  30  disposed on both sides of the bunch claw belt  21  in parallel, and the ejector  20  or the protruding rod  25  fixed to the eject belt  30 . 
     Moreover, an embodiment including four protruding rods  25  may be possible like a processing tray unit  50   a  shown in  FIG. 7 . Each one of the same protruding rods  25  may be provided on both outsides of two protruding rods  25  fixed to the eject belt  30 . Two outside protruding rods  25  and two inside protruding rod  25  are configured to move mutually synchronously. Since the processing tray unit  50   a  can support the bunch of papers B in a wide range in the transverse direction for protrusion toward the loading tray  23 , mismatch of a position is less, thereby carrying them stably. 
       FIG. 8  is a perspective view of the processing tray unit  50  seen from an angle different from the  FIG. 6 . On the lower portion of the processing tray unit  50 , a motor  51  which is a driving source of the bunch claw belt  21  and the eject belt  30 , and an electromagnetic clutch  52  for connecting and disconnecting a transmission of driving force to the eject belt  30  are positioned. The motor  51  and the electromagnetic clutch  52  are components of the belt driving mechanism  60  as well. 
     (2) Belt Driving Mechanism and Belt Driving Method 
       FIG. 9  is a plan view to schematically illustrate an exemplary configuration of the belt driving mechanism  60  mainly, and  FIG. 10  is a side view to schematically illustrate the exemplary configuration of the belt driving mechanism  60 . 
     The belt driving mechanism  60  related to the present embodiment includes the bunch claw belt  21  disposed at the near center of the processing tray  14  and two eject belts  30  disposed on both sides of the bunch claw belt  21 , as shown in  FIG. 9 . 
     The bunch claw belt  21  hangs on a pair of conveyance pulleys  61  and  62  and continuously rotates in a counterclockwise direction indicative of the arrow B (refer to  FIG. 10 ). The bunch claw  21   a  is fixed to a specific position of the outer circumference of the bunch claw belt  21 . The bunch claw  21   a  also continuously rotates in a counterclockwise direction accompanied by the rotation of the bunch claw belt  21 . 
     The bunch claw belt  21  is driven by the rotation of the motor  51 . The rotational force of the motor  51  is transmitted to the electromagnetic clutch  52  by a transmission belt  64  and further is transmitted to the conveyance pulley  61  (driving pulley) by a transmission belt  63 . 
     The rotation of the motor  51  is always transmitted to the conveyance pulley  61  without the electromagnetic clutch  52  turning on and off, as to driving transmission to the bunch claw belt  21 . 
     Two eject belts  30  hang between a toothed drive pulley  31  and a toothed driven pulley  32 , respectively, and are configured to go and return as indicated by the arrow A (refer to  FIG. 10 ) 
     The ejector  20  for hooking end portions of the rear side of the bunch of papers B and the protruding rods  25  for supporting and protruding lower portions of the front side of the bunch of papers B are fixed to the outer circumference of the eject belt  30 . 
     The ejector  20  is formed by, for example, bending a head portion of a ribbon-shaped metal plate into a U-shape and can hook the rear end portion of the bunch of papers B stably. 
     The head portion of the protruding rod  25  is slightly bent downwardly and a resin such as rubber for increasing a frictional force on its surface is attached thereto. Thereby, a stable support of the lower portion of the front side of the bunch of papers B without sliding, and a sure push of the bunch of papers B toward the loading tray  23  are achieved. 
     Teeth for engaging with the teeth of the toothed pulleys  31  and  32  are formed on the entire inner circumference of the eject belt  30 , and thus, even if a sudden force is applied to the toothed pulleys  31  and  32  or the eject belt  30 , no sliding occurs. 
     A belt protrusion  33  (protrusion for stop) is fixed to a specific position of the inner circumference of the eject belt  30 . The belt protrusion  33  is position-adjusted in the home position of the eject belt  30  (this home position is also a home position of the ejector  20  or the protruding rod  25 ) in order to contact to a stopper  200  fixed to an outside of the belt driving mechanism  60  (for example, a suitable structure member of the processing tray unit  50 ). 
     A pulley gear  68  which is axial-bonded to the shaft of the toothed drive pulley  31  engages with a middle gear  65 , and the middle gear  65  engages with a clutch gear  67  which is axial-bonded to the shaft of the electromagnetic clutch  52 . The electromagnetic clutch  52  turns on to transmit the rotation of the motor  51  to the toothed drive pulley  31  to rotate in a counterclockwise direction. The electromagnetic clutch  52  turns off to disengage the rotation of the toothed drive pulley  31  from the motor  51 . 
     On the other hand, one end of a pulley shaft  31   a  of the toothed drive pulley  31  lies within a torsional coil spring  66  (elastic member) as shown in  FIG. 9 . One end of the torsional coil spring  66  is fixed to the pulley shaft  31   a  and the other end thereof is fixed to the outside of the belt driving mechanism  60  (for example, a suitable structure member of the processing tray unit  50 ) via a spring fix member  66   a.    
     When the electromagnetic clutch  52  turns on, the torsional coil spring  66  is tortured in a counterclockwise direction by the rotation of the motor  51  and thus an elastic force is accumulated on the torsional coil spring  66 . When the electromagnetic clutch  52  turns off, the pulley shaft  31   a  separates from the rotation of the motor  51  to be in a free state, and the toothed drive pulley  31  strongly begins to rotate in a reverse direction (clockwise direction) by releasing the elastic force accumulated in the torsional coil spring  66 . The eject belt  30  also begins to move in the reverse direction by the rotation in the reverse direction, and finally stops at a position where the belt protrusion  33  and the stopper  200  are contacted. As above, the eject belt  30  can perform a reciprocating motion by turning on and turning off of the electromagnetic clutch  52 . 
     A series of operations of the belt driving mechanism  60  configured as described above will be described with reference to  FIGS. 11 to 14 . 
       FIG. 11  illustrates a state where the eject belt  30  (and the ejector  20  or the protruding rod  25  fixed to the eject belt  30 ) lies in the home position (first position). The ejector  20  is stopped, hooking the rear end of the bunch of papers B, at nearly the same position as the rear stopper  26 . 
     When the ejector  20  and the like lie in the home position, the transverse matching or the longitudinal matching is performed for the bunch of papers B by the transverse matching plate  16  or the longitudinal matching roller  17 , and then the stapling is performed therefor by the stapler  19 . 
     When the eject belt  30  lies in the home position, the electromagnetic clutch  52  is turned off and the toothed drive pulley  31  is separated from the rotation of the motor  51 . The eject belt  30  stops with the belt protrusion  33  being in contact with the stopper  200 . 
     Even when the ejector  20  or the like lies in the home position, the bunch claw belt  21  continuously keeps rotating in a counterclockwise direction. Right before the ejector  20  and the like begin to move from the home position, the bunch claw  21   a  on the bunch claw belt  21  is moving, for example, the vicinity under the toothed driven pulley  32  located on the right hand side or the eject belt  30 . 
       FIG. 12  illustrates a case where time elapses for a moment after the electromagnetic clutch  52  turns on in the state of  FIG. 11 . When the electromagnetic clutch  52  turns on in the state of  FIG. 11  (the state where the eject belt  30  lies in the home position and the bunch claw  21   a  is moving the vicinity under the toothed driven pulley  32 ), the toothed drive pulley  31  begins to rotate in a counterclockwise direction. The eject belt  30  (and the ejector  20  or the protruding rod  25 ) begins to move in the left direction of the figure (going direction), and the belt protrusion  33  and the stopper  200  depart from each other. The bunch of papers B is hooked in the rear end thereof by the ejector  20 , supported in the front end side by the protruding rods  25 , and carried to the loading tray  23  from the processing tray  14 . 
     Concurrently, the torsional coil spring  66  is coiled up by the rotation of the toothed drive pulley  31  to accumulate an elastic force gradually. 
     Meanwhile, the bunch claw belt  21  keeps rotating, and the bunch claw  21   a  approaches the ejector  20  from the rear side thereof in a state shown in  FIG. 12 . 
     When the ejector  20  reaches a predetermined second position, the electromagnetic clutch  52  is turned off. Before the ejector  20  reaches the second position (i.e., before the electromagnetic clutch  52  is turned off), the bunch claw  21   a  outruns the ejector  20 , and the hooking of the rear end of the bunch of papers B is relayed to the bunch claw  21   a  from the ejector  20 . After that, the bunch of papers B are carried by the bunch claw  21   a , as shown in  FIG. 13 . 
     When the electromagnetic clutch  52  turns off, as shown in  FIG. 14 , the toothed drive pulley  31  begins to rotate in an opposite direction (clockwise direction) by the elastic force accumulated in the torsional coil spring  66  and the ejector  20  goes toward the home position in a returning direction while increasing a velocity. 
     In order to stop the eject belt  30  at the home position, the existing art only depends on a contact between the belt protrusion  33  and the stopper  200 . As a result, the accelerated belt protrusion  33  collides with the stopper  200  fiercely to generate an unpleasant impact sound. 
     In contrast, the belt driving mechanism  60  related to the embodiment brakes the eject belt  30  right before the belt protrusion  33  collides with the stopper  200  to reduce a velocity of the eject belt  30 , thereby preventing generation of an impact sound. 
     Specifically, the eject belt  30  is braked by increasing a tension of the eject belt  30  right before the belt protrusion  33  collides with the stopper  200 . 
     The increase of the tension of the eject belt  30  is carried out by forming a shallower tooth bottom of the tooth of at least one of the eject belt (toothed belt)  30 , the toothed drive pulley  31 , and the toothed driven pulley  32 , than a normal tooth bottom. 
       FIG. 15  is a perspective view of an appearance of an exemplary shape of the toothed pulleys  31  and  32 . Teeth are formed on the outer circumference of the toothed pulleys  31  and  32  such as those shown in  FIG. 15 . 
     In the conventional eject belt, the teeth with a typical depth are formed on the entire inner circumference thereof, and the teeth of the toothed drive pulley (or the toothed driven pulley) and the teeth of the eject belt rotate engaging with each other. In the conventional eject belt and the toothed drive pulley (or the toothed driven pulley), the eject belt is applied with almost uniform tension at any rotational positions and thus a smooth rotation is possible. 
     In contrast, in the eject belt  30  related to the present embodiment, as shown in  FIGS. 16 to 19  as Examples, the tooth bottom of the eject belt  30  is made shallow at a position right before collision of the belt protrusion  33  and the stopper  200  (at a position right before the ejector  20  returns to the home position (the first position)), thereby increasing a tension of the eject belt  30 . 
     More in detail, a shape where the saw tooth bottom becomes shallower is formed on the vicinity of a position where the toothed drive pulley  31  and the eject belt  30  begin to engage with each other. 
     By making the tooth bottom of the eject belt  30  shallow on the driving side, vibration of the eject belt  30  does not easily occur, and therefore, a stable and accurate braking performance is obtained. 
     On the driven side where the toothed driven pulley  32  and the eject belt  30  engage with each other, a shallow tooth bottom of the eject belt  30  can increase a tension of the eject belt  30 . 
     If a moving distance (a distance of the going path or the returning path) of the eject belt  30  is shorter than a circumference length of the toothed drive pulley  31 , a shallow tooth bottom of the toothed drive pulley  31  can increase a tension, too. 
       FIG. 16  illustrates an example to realize a shape where the tooth bottom becomes shallow by attaching a cushion member  80  having a lower elastic modulus than that of material (for example, rubber) of the eject belt  30  to the normal tooth bottom of the eject belt  30 . 
     A tension of the eject belt  30  increases when the tooth of the toothed drive pulley  31  contacts to the cushion member  80 , and the increase of the tension brakes the eject belt  30 . 
       FIG. 17  illustrates an example to form the tooth bottoms such that a plurality of continuous tooth bottoms  80   a ,  80   b  and  80   c  become shallow gradually. The tooth bottoms become shallow gradually, and thereby a smooth braking of the eject belt  30  is possible. 
       FIG. 18  illustrates an example to obtain a shape where the tooth bottom is shallow by filling one or a plurality of continuous saw tooth bottoms completely to make a predetermined region identical to a height of the saw tooth top. The saw tooth of the toothed drive pulley  31  contacts to the shape  80   d  with no tooth bottom to increase a tension of the eject belt  30 , thereby braking the eject belt  30 . 
       FIG. 19  illustrates an example to implement a shape where the saw tooth bottom is shallow by a first region  81  where the saw tooth bottom is shallow, a second region  82  where the saw tooth bottom has a normal depth, adjacent to the first region  81 , and a third region  83  where the saw tooth bottom is shallow, adjacent to the second region. The eject belt  30  is braked preliminarily at the first region  81  and again braked at the third region  83 . As such, the eject belt  30  is braked at two stages, and thereby smoother and more accurate braking and stop can be realized. 
     As described above, according to the belt driving mechanism, the image forming apparatus including the same and the belt driving method of the embodiments, a tension of the belt increases using a very simple configuration right before the belt stops and thereby the belt can stop smoothly without generating an impact sound, in the belt driving mechanism to perform a reciprocating motion. 
     The present invention is not limited to the embodiments as they are but can modify the elements to be embodied in a range of not departing from a gist thereof. In addition, a variety of embodiments of the invention can be made by a proper combination of a plurality of elements disclosed in the respective embodiments. For example, several elements may be removed from the overall elements shown in the embodiments. Further, elements extending over other embodiments may be combined properly.