Abstract:
A web driving device including a web, a winding axis connected to a first end of the web and configured to rotate and wind the web about the winding axis in a winding direction, and a supplying axis connected to a second end of the web and configured to rotate. The web driving device further includes a driving device configured to drive the winding axis in the winding direction. The driving device is configured to prevent rotation of the winding axis when the driving device is in an inactive condition. The web driving device further advantageously includes an intermediate gear device engaged to the winding axis and configured to restrict rotation of the supplying axis when the winding axis stops rotating.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present document incorporates by reference the entire contents of Japanese priority document 10-303048 filed in Japan on Oct. 23, 1998 and Japanese priority document 10-342841 filed in Japan on Dec. 2, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates a to web driving device for cleaning an object or for applying liquid such as oil to an object by the action of contact. The web driving device is equipped in a device such as an image forming apparatus (e.g., a copier, a facsimile, or a printer). More specifically, the web driving device is equipped in a fixing device or a photosensitive device in the image forming apparatus. 
     2. Discussion of the Background 
     A conventional web driving device, as depicted in FIG. 1, is equipped in a fixing device. The fixing device generally includes a fixing roller  1  that has a heater  3  inside such that a surface of the fixing roller  1  is heated and controlled at prescribed temperature. A press roller  2  presses the fixing roller  1  and makes a nip portion between them. When a sheet of paper  5  having unfixed toner image thereon is fed through the nip portion, the toner image is fixed to the paper  5 . The fixing device further includes a web device having a web  44  made of an unwoven wiper that is constructed of aramid fiber mixed with PET (polyethylene terephthalate) fiber. The web  44  contains oil as required. One edge of the web  44  is fixed to a winding axis  42  and another edge of the web is fixed to a supplying axis  43 . Most of the web  44  is wound in the supplying axis  43  in initial condition. A pressing roller  45  is located between the winding axis  42  and supplying axis  43  for pressing the web  44  to the fixing roller  1 . The web  44  is moved step by step and then the web  44  removes a residual quantity on the fixing roller  1  or supplies oil to the fixing roller  1 . A motor  72  drives the winding axis  42  for winding the web  44  at a constant angle in one action via a transferring mechanism  71  such as a gear or a timing pulley. The pressing roller  45  has a layer made of a silicon rubber or a forming rubber on a core metal. 
     Construction of the web driving device and amount of sending (or unwinding) of the web has numerous variations depending upon the manner in which the image forming apparatus is going to be utilized. The amount of sending is generally limited to a small amount because the web  44  is restricted in length or setting space. More specifically, the amount of sending is generally limited to between 0.5 mm/hour and 2 mm/hour. 
     In this conventional web driving device, there is a problem that when the web is pulled unexpectedly (for example during a paper jam) and the fixing roller is manually rotated via a handling knob, then the winding axis is rotated in conjunction with the fixing roller. The reason why the problem comes up is the winding axis is usually put only under light load for helping the supplying axis for taking up the web. More specifically, when a paper  5  is jammed, as depicted in FIG.  2 ( a ), and the paper  5  is taken out along a normal feeding direction (indicated by an arrow), the web  44  may not be drawn by a torque of the fixing roller  1  as the winding axis  42  is locked by the motor  72  in an undriving condition. However, when a paper  5 , as depicted in FIG.  2 ( b ), is taken out along a counter direction of the normal feeding direction (indicated by an arrow), the web  44  is drawn by a torque of the fixing roller  1  (as shown using a dotted lines) because the supplying axis  43  is not locked. Accordingly, cleaning ability of the web  44  is reduced. Furthermore, the web  44  may be caught in the nip portion by the slack when the printing action restarts. 
     To solve the above problem, a device is disclosed in a Laid-Open Japanese Patent Application No. 08-185074. The device has a locking mechanism for preventing the looseness of the web. The device has a supplying axis including a ratchet gear at the edge thereof, a winding axis for taking up the web, a solenoid actuated in response to winding action of the winding axis. 
     The solenoid has a ratchet hook that is engaged with the ratchet gear only when the winding axis rotates. However, as a controller must control the action of the solenoid and the action of the winding axis accurately, controlling by the controller becomes difficult. Furthermore, the device must have a ratchet hook and a solenoid of increased rigidity in order to insure that the rotation of the supplying axis is properly stopped. Therefore the device must be upsized. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a novel web driving device that overcomes the above-mentioned limitations of existing methods and systems. 
     Another object of the present invention is to provide a novel web driving device that actuates with reliability. 
     The present invention provides a web driving device including a web, a winding axis connected to a first end of the web and configured to rotate and wind the web about the winding axis in a winding direction, and a supplying axis connected to a second end of the web and configured to rotate. The web driving device further includes a driving device configured to drive the winding axis in the winding direction. The driving device is configured to prevent rotation of the winding axis when the driving device is in an inactive condition. The invention further advantageously provides an intermediate gear device engaged to the winding axis and configured to restrict rotation of the supplying axis when the winding axis stops rotating. 
     The present invention advantageously includes a first embodiment where the supplying axis includes a first protrusion fixed thereto, and the intermediate gear device includes a second protrusion fixed thereto. In this embodiment the second protrusion is configured to engage the first protrusion to prevent the supplying axis from rotating in at least one direction when the driving device is in the inactive condition. The first protrusion and the second protrusion are preferably configured to allow relative rotation between the supplying axis and the intermediate gear device in a first direction but prevent relative rotation between the supplying axis and the intermediate gear device in a direction opposite to the first direction. The first protrusion is incorporated in a cam surface attached to the supplying axis and the supplying axis is biased towards the intermediate gear device to maintain contact between the second protrusion and the cam surface during rotation of the supplying axis and the intermediate gear device. 
     The present invention advantageously includes a second embodiment where the supplying axis includes a one-way gear assembly having a one-way clutch configured to engage the supplying axis with the intermediate gear device and prevent the supplying axis from rotating in at least one direction when the driving device is in the inactive condition. 
     The present invention further advantageously includes a third embodiment where the intermediate gear device includes a first portion engaged to the supplying axis and having a first tooth and a second portion engaged to the winding axis and having a second tooth. The second tooth is configured to engage the first tooth to prevent the supplying axis from rotating in at least one direction when the driving device is in the inactive condition. The first tooth and the second tooth are preferably configured to allow relative rotation between the first portion and the second portion in a first direction but prevent relative rotation between the first portion and the second portion in a direction opposite to the first direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 illustrates a conventional fixing device including a web driving device; 
     FIG.  2 ( a ) illustrates the conventional fixing device of FIG. 1, where a paper jam is dislodged in a direction towards the left side of the figure; 
     FIG.  2 ( b ) illustrates the conventional fixing device of FIG. 1, where a paper jam is dislodged in a direction towards the right side of the figure; 
     FIG.  3 ( a ) illustrates a first embodiment of a web driving device according to the present invention; 
     FIG.  3 ( b ) illustrates an interaction between a restricting part and a stopper of the first embodiment; 
     FIG.  3 ( c ) illustrates an interaction between the restricting part and the stopper in relation to a supplying axis and a web; 
     FIG. 4 illustrates a motor and gear system according to the present invention; 
     FIG. 5 illustrates a second embodiment of a web driving device according to the present invention; 
     FIG. 6 is a graphical representation of the rotational speed of the supplying axis and of the winding axis; 
     FIG. 7 illustrates a third embodiment of a web driving device according to the present invention; 
     FIG. 8 illustrates a relationship between a small gear and a large gear of the third embodiment; 
     FIG. 9 is a graphical representation of the rotational speed of various gears of the third embodiment; 
     FIGS.  10 ( a ) and  10 ( b ) illustrate a relationship between lugs of the small gear and lugs of the large gear of the third embodiment when the small gear is rotating faster than the large gear; and 
     FIGS. 11 ( a ) and  11  ( b ) illustrate a relationship between lugs of the small gear and lugs of the large gear of the third embodiment when the small gear is stationary. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, where like reference numerals identify the same or corresponding parts throughout the several views, FIGS.  3 ( a )- 3 ( c ) depict a first embodiment of the present invention which is adopted in a fixing device of an image forming apparatus. 
     The embodiment of the web driving device depicted in FIG.  3 ( a ) has a web  44 , a winding axis  42 , a supplying axis  43 , a motor  72 , a transferring gear  81  for transferring torque of the motor  72  to the winding axis  42 , and an intermediate gear  82  having a restricting part  83 . Since the motor  72  is configured to rotate in only one direction, the winding axis  42  can rotate in only one direction, called the winding direction (depicted as a clockwise direction), as shown by an arrow A. The winding axis  42  cannot rotate while the motor  72  is stopped. The transferring gear  81  rotates in the same direction as the winding direction. 
     The intermediate gear  82  is placed between the winding axis  42  and the supplying axis  43 . As the intermediate gear  82  is engaged with the transferring gear  81 , when the winding axis  42  winds the web  44  the intermediate gear rotates in a direction opposite that of the winding direction, as shown by an arrow B. The restricting part  83  is concentrically connected with the intermediate gear  82 . The supplying axis  43  has a stopper  84  in an end of the supplying axis  43 . The stopper  84  has a cam body that is generally helical in shape and that is engaged with the restricting part  83 . The stopper  84  is movably pushed towards the restricting part  83  by a spring  85  in normal condition. 
     As depicted in FIG.  3 ( b ), when the restricting part  83  is stopped due to the restricting part  83  being meshed with the stopper  84 , the supplying axis  43  cannot rotate and a new part of the web  44  is prevented from unwinding from the supplying axis. When the motor  72  starts to drive the winding axis  42 , the restricting part  83  also rotates, as depicted in FIG.  3 ( c ), thereby freeing the restriction of the stopper  84  and allowing the supplying axis  43  to rotate. To insure that the rotational speed of the restricting part  83  is always faster than the rotational speed the stopper  84 , the stopper  84  does not collide with the restricting part  83  when the motor  72  drives the winding axis  42 . When the restricting part  83  overtakes and passes the stopper  84 , the stopper  84  moves away along helical shape thereof against the spring  85 . 
     It is favorable that the stopper  84  moves around a contact point of the fixing roller  1  and the web  44 . Then the web  44  is not loose and unstable. 
     In this embodiment, the restricting part  83  includes four projections and the cam body includes one projection of the cam body, however the number of projections on the restricting part and on the cam body can be varied depending upon the desired amount of sending of the web  44 . 
     The restricting part  83  is stopped by providing a motor that has a breaking function. An embodiment of such a motor and a gear system is depicted in FIG.  4 . The motor  72  has a gear GI. The motor  72  drives the winding axis  42  via reduction gears G 2  to G 9  and transferring gear  81 . The intermediate gear  82  engages with the transferring gear  81  that is nearest to the winding axis  42  among the reduction gears. In this configuration, as the breaking function made from the gear ratio of the reduction gears is added to the breaking function of the motor  72 , the rotational stop of the restricting part  83  becomes sure. 
     FIG. 5 depicts a second embodiment of the present invention. In the second embodiment a transferring gear  81  is set at an end of a winding axis  42 , and a one-way gear  101  including a one-way clutch  100  is set at an end of a supplying axis  43 . The transferring gear  81  is meshed with an intermediate gear  102 , and the intermediate gear  102  is meshed with the one-way gear  101 . In this embodiment, the intermediate gear  102  is constructed as a two-step gear whose teeth are different from each other. However, alternatively, it is possible to use a normal gear instead of the two-step gear. 
     An outer ring of the one-way clutch  100  is rotated in conjunction with the one-way gear  101  and an inner ring of the one-way clutch  100  is rotated in conjunction with the supplying axis  43  at all times. When the winding axis  42  rotates, the one-way gear  101  is always rotated by the intermediate gear  102  at a constant rotational speed. However, when the rotational speed of the one way-gear  101  is faster than the rotational speed of the supplying gear  43 , it is constituted so that the inner ring races for the outer ring. When the inner ring and the outer ring rotate such that the rotational speed of the outer ring is greater than or equal to the rotational speed of the inner ring, then the one-way clutch  100  goes into a freewheeling condition. On the other hand, when the inner ring and the outer ring are rotating such that the rotational speed of the outer ring is less than the rotational speed of the inner ring, then the one-way clutch  100  is locked. 
     FIG. 6 is a graphical representation of how the rotational speed of the supplying axis  43  and of the winding axis  42  change over time. Point A indicates when the web driving action starts, point B indicates when the rotational speed of the supplying axis  43  becomes the same as that of the winding axis  42 , and point C indicates when the supplying axis  43  becomes empty of the web  44 . This graph shows that the winding axis  42  is rotated always at a constant level by the driving motor  72 , but the supplying axis  43  increases speed as a diameter of the winding axis  42  gradually becomes bigger. Accordingly, when designing a reduction ratio of the transferring gear  81 , the one-way gear  101 , and the intermediate gear  102 , it is important to take into account that the rotational speed of the one-way gear  101  is faster than the rotational speed of the supplying axis  43  at the point C. A torque of the oneway clutch is commonly low so that it is desirable to include a plate spring to load a tension against the supplying axis  43  within a level that winding action runs easily. 
     FIGS. 7 and 8 depict a third embodiment of the present invention. The third embodiment includes an intermediate gear  204  that has a small gear  200  and a large gear  202 , whose diameter is larger than the small gear  200 . The small gear  200  and the large gear  202  each have at least one lug as depicted in FIG.  8 . The small gear  200  is engaged with a transferring gear  81 , and the large gear  202  is engaged with a driving gear  201  set at an end of a supplying axis  43 . The large gear  202  has a spring  203  for pressing the large gear  202  to the small gear  200  in a normal condition. When winding a web  44 , the large gear  202  and the small gear  200  are rotated in same direction (in a clockwise direction in FIG.  7 ). As mentioned above, the outer diameter of the winding axis  42  increases as the web  44  is wound onto the winding axis which increases a rotational speed of the supplying axis  43 . Accordingly, the larger gear  202  is also rotated faster with time. The small gear  200  is, of course, rotated at a constant level. In this embodiment, a reduction ratio of the transferring gear  81  and the small gear  200  and a reduction ratio of the driving gear  201  and the large gear  202  always satisfy the following relationship: the number of revolutions of the small gear  200  are greater than or equal to the number of revolutions of the large gear  202 , as depicted in FIG. 9, when the web  44  is wound. 
     FIGS.  10 ( a ),  10 ( b ),  11 ( a ), and  11  ( b ) depict a relationship of the lugs of the large gear  202  and the lugs of the small gear  200 . When the web  44  is wound, as the small gear  200  rotates faster than the large gear  202 , the small gear  200  passes the large gear  202 . When passing, the slopes of the small gear&#39;s lug (or tooth)  200   a  pushes the slopes of the large gear&#39; lug (or tooth)  202   a  and the large gear  202  is moved away against the spring  203  in the axis&#39; direction, as depicted in FIG.  10 ( b ). When the winding action is stopped (the motor  72  is at rest), then the small gear  200  is fastened. So the web  44  is not pulled, even if the fixing roller is manually rotated in a normal fixing direction by a knob, which is not shown but that is usually set at an end of a pursuer roller  2 , when a paper jam occurs. More specifically, as depicted in FIGS. 11 ( a ) and  11  ( b ), vertical portions of the small gear&#39;s lug  200   a  are engaged with vertical portions of the large gear&#39;s lugs  202   a  so that the large gear  202  is restricted from moving. In this embodiment, as the large gear  202  is moved for the axis&#39;s direction of the large gear  202 , we need not consider web&#39;s looseness caused by the moving action of the large gear  202 . 
     In above-mentioned embodiments, as the device has mechanically restrictive parts, the web is not pulled unnecessarily with stability in spite of very simplified structure. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.