Patent Publication Number: US-6712350-B2

Title: Sheet feeding apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a sheet feeding apparatus for separating and feeding sheets such as stacked originals and recording mediums one by one, and an image forming apparatus provided with the sheet feeding apparatus. 
     2. Description of Related Art 
     There are known an image forming apparatus of the ink jet type for discharging ink to a recording medium such as recording paper to thereby form an image thereon, and an image forming apparatus of the electrophotographic type for forming an image on a recording medium by the use of a developer (toner), and these image forming apparatuses are provided with a sheet feeding apparatus for supplying the recording medium to an image forming portion. 
     Now, in some printers, as a sheet feeding apparatus for supplying a recording medium (hereinafter referred to as the sheet) to image forming means, provision is made of a multisheet feeding apparatus of a construction in which sheets set on a tray by a user are fed out, besides a sheet feeding apparatus of a construction in which sheets are fed out from a sheet feeding cassette containing the sheets therein. The multisheet feeding apparatus can set and feed sheets of various sizes and sheets of various kinds, and is efficient for the feeding of a small quantity of sheets, and the feeding of spatial paper such as thick paper or film paper. 
     An example of the conventional multisheet feeding apparatus will hereinafter be described with reference to FIGS. 6 to  8  of the accompanying drawings. FIG. 6 is a longitudinal cross-sectional view of the multisheet feeding apparatus, FIG. 7 is a perspective view of a separating pad, and FIG. 8 is an enlarged view showing a state in which a sheet is being separated by a sheet feeding roller and the separating pad. 
     The multisheet feeding apparatus  50  is provided with an intermediate plate  54  on which a plurality of sheets P are stacked, a side regulating plate  82  for regulating the widthwise position of the sheets P stacked on the intermediate plate  54 , and an intermediate plate spring  56  for upwardly biasing the leading edge side end portion of the intermediate plate  54  in the sheet feeding direction. Above the intermediate plate spring  56 , there is disposed a sheet feeding roller  58  for contacting with the sheets P stacked on the intermediate plate  54  to thereby feed out the sheets P one by one in the sheet feeding direction (the direction indicated by the arrow C). 
     Downstream of the sheet feeding roller  58  in the sheet feeding direction, there is disposed a sheet feeding guide  60  for guiding the sheet P fed out by the sheet feeding roller  58  to a pair of registration rollers  38  disposed on the downstream side in the sheet feeding direction. A pair of U-shaped grooves  62  (shown in FIG. 8) are formed at the right and left of the sheet feeding guide  60  as viewed in a direction orthogonal to the sheet feeding direction on the upstream side in the sheet feeding direction, and the opening  62   a  of each groove  62  faces downwardly. 
     A separating pad  70  is disposed adjacent to and upstream of the sheet feeding guide  60  in the sheet feeding direction. The separating pad  70  is comprised of a plate-shaped separating pad holder  70   a  provided with two pivot shafts  72  orthogonal to the sheet feeding direction on the downstream side in the sheet feeding direction, and a rectangular separating pad member  74  stuck on the upstream side surface of the separating pad holder  70   a  in the sheet feeding direction and formed of urethane rubber containing cork or the like. The two pivot shafts  72  of the separating pad holder  70   a  fit into the grooves  62 , whereby the separating pad  70  is supported for pivotal movement. 
     Below the separating pad holder  70   a,  there is disposed a separating spring  76  comprising a coil spring for upwardly biasing the separating pad holder  70   a.  Since the separating spring  76  pushes up that portion of the separating pad holder  70   a  which is opposite to the pivot shaft  72  from below it, the separating pad holder  70   a  is pivotally moved about the pivot shaft  72 . As the result, the separating pad member  74  is urged against the sheet feeding roller  58 . Accordingly, the sheet feeding roller  58  is rotated in the direction indicated by the arrow D, whereby the stacked sheet is fed out from the intermediate plate  54 , and when two or more sheets are fed out, they are separated one by one between the separating pad member  74  and the sheet feeding roller  58 . 
     Now, to feed the sheet P smoothly in the sheet feeding direction, it is necessary that the surface of the separating pad member  74  be urged against the outer peripheral surface of the sheet feeding roller  58  with uniform contact pressure, and if the contact pressure is non-uniform, the sheet P may not be fed smoothly. When for example, greater contact pressure acts on one of the portions of the separating pad member  74  in the left to right direction thereof (the direction orthogonal to the direction indicated by the arrow C) than on the other portion, the sheet P being separated may be skew-fed or the sheet P may not be separated but may be jammed near the separating pad member  74 . 
     In order that as described above, the surface of the separating pad member  74  may be urged against the outer peripheral surface of the sheet feeding roller  58  with uniform contact pressure, it is necessary that the line of contact  74   a  (shown in FIG. 7) when the separating pad member  74  contacts with the sheet feeding roller  58  and the center line of pivotal movement  72   a  (shown in FIG. 7) of the pivot shafts  72  of the separating pad holder  70   a  be parallel to each other. However, the accuracy of the position at which the sheet feeding guide  60  is fixed to the main body of the printer  10  or the accuracy of the shape thereof is sometimes bad due to the deformation or the like of the separating pad holder  70   a  and therefore, the line of contact  74   a  and the center line of pivotal movement  72   a  sometimes do not become parallel to each other. 
     Accordingly, when the pivot shafts  72  are fitted into the grooves  62  without any gap to such a degree that the pivot shafts  72  can freely pivotally move in the grooves  62 , it is difficult due to the above-mentioned accuracy for the line of contact  74   a  and the center line of pivotal movement  72   a  to become parallel to each other. So, the grooves  62  are formed relatively larger than the outer diameter of the pivot shafts  72  so that irrespective of the above-mentioned accuracy, the line of contact  74   a  and the center line of pivotal movement  72   a  may become parallel to each other. By so constructing, the surface of the separating pad member  74  is urged against the outer peripheral surface of the sheet feeding roller  58  with uniform contact pressure. 
     Now, the coefficient of friction of the sheet feeding roller  58  and the coefficient of friction of the separating pad member  74  with respect to the sheet P differ from each other. Also, as described above, the grooves  62  are larger than the outer diameter of the pivot shafts  72  and therefore, there is more or less play or slop between these two. Therefore, when the sheet P nipped by and between the separating pad member  74  and the sheet feeding roller  58  is fed, the sheet P and the separating pad member  74  may rub against each other to thereby cause stick-slip motion. Due to the stick-slip motion, there occurs vibration and occurs an abnormal sound called pad chatter (squeak). 
     So, as techniques for preventing the pad chatter, the following techniques (1) to (4) are under consideration: 
     (1) The technique of disposing a member for contacting with the front side or the backside of the sheet P on the downstream side of the position, in which the sheet feeding roller  58  and the separating pad member  74  nip the sheet P therebetween, in the sheet feeding direction, and stopping the vibration of the sheet P; 
     (2) The technique of weakening the force with which the separating pad member  74  urges the sheet feeding roller  58  and preventing the stick-slip motion to thereby prevent the pad chatter; 
     (3) The technique of contriving the weight and shape of the separating pad holder  70   a  to change the resonance point of the separating pad holder  70   a  and decrease the vibration of the separating pad holder  70   a;  and 
     (4) The technique of fitting the pivot shafts  72  into the grooves  62  without any gap to thereby prevent the vibration of the separating pad holder  70   a.    
     However, according to the technique (1), the vibration of the sheet P can be stopped, but the vibration of the separating pad holder  70   a  cannot be stopped and therefore, the pad chatter cannot be completely prevented. 
     According to the technique (2), the possibility of the separation of the sheet P becoming incomplete is great and therefore, the sheets P may be double-fed, and the sheet feeding performance is reduced. 
     According to the technique (3), the vibration of the separating pad holder  70   a  can be mitigated, but depending on the thickness, density and stiffness of the sheet P, the pad chatter occurs and cannot be sufficiently coped with. 
     According to the technique (4), the contact pressure with which the separating pad member  74  contacts with the sheet feeding roller  58  becomes non-uniform, and the sheet P is not fed smoothly and skew feed or jam or the like is liable to occur and the sheet feeding performance may be reduced. 
     SUMMARY OF THE INVENTION 
     In view of the above-noted circumstances, the present invention has as its object to provide a sheet feeding apparatus in which pad chatter is prevented without the sheet feeding performance being reduced. 
     The sheet feeding apparatus of the prevent invention for achieving the above object is a sheet feeding apparatus provided with a sheet feeding rotary member rotatable in a direction for feeding sheets, and a separating pad biased toward the sheet feeding rotary member, and for separating the sheets one by one between the sheet feeding rotary member and the separating pad and feeding the sheets, wherein a vibration absorbing member for absorbing the vibration of the separating pad is interposed between the separating pad and a pad supporting portion for pivotally supporting the separating pad. 
     Also, the sheet feeding apparatus of the present invention is provided with a sheet feeding rotary member rotatable in a direction for feeding sheets, and a separating pad biased toward the sheet feeding rotary member, and for separating the sheets one by one between the sheet feeding rotary member and the separating pad and feeding the sheets, wherein the space between the separating pad and a pad supporting portion for pivotally supporting the separating pad is filled with an elastic adhesive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view showing the essential portions of a first embodiment of the sheet feeding apparatus of the present invention. 
     FIG. 2 is a front view of the sheet feeding apparatus of FIG. 1 as viewed in the sheet feeding direction. 
     FIGS. 3A and 3B are enlarged views showing a pivot shaft fitted in a groove. 
     FIG. 4 is a longitudinal cross-sectional view showing an example of an image forming apparatus provided with the sheet feeding apparatus of the present invention. 
     FIG. 5 is an exploded perspective view showing another example of the groove into which the pivot shaft of a separating pad is fitted. 
     FIG. 6 is a longitudinal cross-sectional view showing an example of a conventional sheet feeding apparatus. 
     FIG. 7 is a perspective view of a conventional separating pad. 
     FIG. 8 is an enlarged view of a conventional sheet feeding roller and the conventional separating pad. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some embodiments of the present invention will hereinafter be described with reference to the accompanying drawings. FIG. 1 is a longitudinal cross-sectional view showing a first embodiment of the sheet feeding apparatus of the present invention, FIG. 2 is a front view of the sheet feeding apparatus of FIG. 1 as viewed in the sheet feeding direction, FIGS. 3A and 3B are enlarged views showing a pivot shaft fitted in a groove, and FIG. 4 is a longitudinal cross-sectional view of an image forming apparatus (printer) on which the sheet feeding apparatus of the present embodiment is mounted. In these figures, the same constituents as the conventional constituents shown in FIGS. 6 to  8  are given the same reference characters. 
     As example of the printer provided with the sheet feeding apparatus of the present invention will first be described with reference to FIG.  4 . 
     The printer  10  contains therein a laser optical system  14  emitting a laser beam  12  on the basis of image information. The laser beam  12  emitted from the laser optical system  14  is applied to a photosensitive drum  16 , whereby an electrostatic latent image is formed thereon. A charger  18  for uniformly charging the surface of the photosensitive drum  16 , a developing device  20  for supplying a developer (toner) to the electrostatic latent image to thereby form a developed image, a transferring roller  22  for transferring the developed image to a sheet, etc. are successively disposed around the photosensitive drum  16  along the direction of rotation thereof (the direction indicated by the arrow A). 
     A fixing device  24  for fixing the developed image on the sheet is disposed in above the photosensitive drum  16 . In the fixing device  24 , there are disposed a fixing roller  24   a  containing a heater therein, and a pressure roller  24   b  which is in pressure contact with the fixing roller  24   a.  When the transferred image is to be fixed on the sheet, the sheet is nipped between the fixing roller  24   a  and the pressure roller  24   b  and the transferred image is heated at a predetermined fixing temperature and at the same time, is pressurized. By the heating and pressurization, the transferred image is fixed on the sheet. 
     Below the photosensitive drum  16 , a sheet feeding cassette  26  for containing therein sheets by each same size is detachably mounted in the directions indicated by the double-headed arrow B. An intermediate plate  28  on which the sheets are stacked is disposed in the sheet feeding cassette  26 . One end portion of the intermediate plate  28  is upwardly biased by a separating spring  30 . In the outlet of the sheet feeding cassette  26  (above the separating spring  30 ), there is disposed a sheet feeding roller  32  for feeding out the sheets contained in the sheet feeding cassette  26 . 
     The sheet fed out by the sheet feeding roller  32  is conveyed toward the photosensitive drum  16  while being guided by a guide roller  34 . In FIG. 4, the alternate long and two short dashes line  36  indicates the conveying route of the sheet. Downstream of the guide roller  34  in the conveying direction, there are disposed a set of registration rollers  38  rotated in synchronism with the rotative driving of the photosensitive drum  16 , and the registration rollers  38  correct the skew feed of the sheet, and adjust the feed timing of the sheet so as to positionally accord with the developed image formed on the photosensitive drum  16 . 
     When an image is to be formed on the sheet by the printer  10 , the laser beam  12  emitted from the laser optical system  14  is applied to the photosensitive drum  16 , whereby an electrostatic latent image is formed thereon. The electrostatic latent image is developed by the toner supplied from the developing device  20 , whereby a developed image is formed. The developed image moves toward the transferring roller  22  with the rotation of the photosensitive drum  16 . 
     On the other hand, the sheet fed out of the sheet feeding cassette  26  is guided to the registration rollers  38  by the guide roller  34 . The sheet is conveyed from the registration rollers  38  toward the transferring roller  22  at a predetermined timing. The thus conveyed sheet is charged to the opposite polarity to the developer forming the developed image and therefore, the developer is attracted to the sheet and a transferred image is formed. The sheet on which the transferred image has been formed is sent into the fixing device  24 , whereby the transferred image is fixed on the sheet, whereafter the sheet is discharged onto a sheet discharge tray  42  by sheet discharging rollers  40 . Below the laser optical system  14 , there is disposed a case  44  containing therein electrical parts such as a power source and a printed substrate, a control device for effecting various kinds of control, a controller board and so on. 
     A multisheet feeding apparatus  50  is disposed on the front side of the printer  10 , and the multisheet feeding apparatus  50  will hereinafter be described with reference to FIGS. 1,  2 ,  3 A and  3 B. 
     Sheets of various sizes or various kinds can be set on the multisheet feeding apparatus  50 . The multisheet feeding apparatus  50  is provided with an intermediate plate  54  on which a plurality of sheets P are stacked, and an intermediate plate spring  56  for upwardly biasing the leading edge side end portion of the intermediate plate  54  in the sheet feeding direction. Above the intermediate plate spring  56 , there is disposed a sheet feeding roller  58  as the sheet feeding rotary member of the present invention for feeding the sheets stacked on the intermediate plate  54  one by one in the sheet feeding direction (the direction indicated by the arrow C). Also, the multisheet feeding apparatus  50  is provided with a side regulating plate  82  for regulating and jogging the widthwise opposite end portions of the sheets P stacked on the intermediate plate  54 . 
     The construction of a separating pad  70  which is an essential portion of the present invention will now be described in detail. Two pivot shafts  72  are formed on the separating pad holder  70   a  of the separating pad  70  provided in the multisheet feeding apparatus  50 . Also, a separating pad member  74  is stuck on the separating pad holder  70   a.  This structure is the same structure as that of the conventional multisheet feeding apparatus  50 . Also, a sheet feeding guide  60  is formed of grooves  62  of U-shaped cross-section as the recess of the present invention into which two pivot shafts  72  are fitted. 
     A feature of the multisheet feeding apparatus  50  of the present invention is that a silicone adhesive  84  which is an elastic adhesive material as the vibration absorbing member of the present invention is interposed in the portion of contact wherein the two pivot shafts  72  are in contact with the inner wall surfaces  63  of the grooves  62 . Since the silicone adhesive  84  is thus interposed between the pivot shafts  72  and the inner wall surfaces  63  of the grooves  62 , the pivot shafts  72 , even if vibrated, do not contact with the inner wall surfaces  63  (except vertexes  63   a ). Also, as shown in FIG. 3A, the silicone adhesive  84  is not interposed between the vertex  63   a  of the inner wall surface  63  and the pivot shaft  72 , whereas the silicone adhesive  84  having a thickness  84   a  is interposed between the side  63   b  of the inner wall surface  63  and the pivot shaft  72 . 
     Also, as shown in FIG. 3B, the silicone adhesive  84  is interposed between the inner wall surface  63  and the pivot shaft  72  even at a location whereat the pivot shaft  72  is off the vertex  63   a  of the inner wall surface  63  of the groove  62  and therefore, in whatever state, the space between the inner wall surface  63  and the pivot shaft  72  can be filled with the silicone adhesive  84 . 
     Further, the pivot shaft  72  of the separating pad holder  70   a  is fitted into the U-shaped groove  62  and the separating pad holder  70   a  is biased by the separating spring  76 , whereby the separating pad holder  70   a  is moved in the groove  62 , and the line of contact  74   a  when the separating pad member  74  contacts with the sheet feeding roller  58  and the center line of pivotal movement  72   a  of the pivot shafts  72  of the separating pad holder  70   a  can be automatically made parallel to each other. 
     In interposing the silicone adhesive  84  as described above, a liquid silicone adhesive  84  is poured into between the pivot shaft  72  and the inner wall surface  63 . When a predetermined time elapses, the silicone adhesive  84  cures and has elasticity. Also, the pivot shaft  72  is biased against the vertex  63   a  of the U-shaped groove  62  by the separating spring  76 . Accordingly, the separating pad holder  70   a  is forced into coincidence with the position of the U-shaped groove  62  and therefore, the positional relationship between the separating pad member  74  and the sheet feeding roller  58  is kept proper, and the sheet P is fed smoothly without such a trouble as double feed. Also, the pivot shaft  72  is elastically secured in the interior of the groove  62  by the adhesive and is free to move and therefore, the separating pad holder  70   a  can also be freely pivotally moved about the pivot shaft  72  by the separating spring  76 . 
     Also, by using the silicone adhesive, it is easy to bring the silicone adhesive into between the pivot shaft  72  and the groove  62 . Also, the silicone adhesive cures and becomes rubber-like and therefore, after it has cured, it does not protrude and can be easily interposed as a vibration absorbing material. 
     Here, description will be made of the action of the silicone adhesive  84  when the multisheet feeding apparatus  50  feeds the sheet P in the direction indicated by the arrow C. 
     The separating pad member  74  is biased against the sheet feeding roller  58  by the separating spring  76 . Therefore, the sheets P nipped by and between the separating pad member  74  and the sheet feeding roller  58  are fed one by one in the sheet feeding direction by the sheet feeding roller  58  being rotated in the direction indicated by the arrow D. Here, the coefficient of friction of the sheet feeding roller  58  and the coefficient of friction of the separating pad member  74  with respect to the sheet P differ from each other. Also, in the multisheet feeding apparatus  50 , the grooves  62  are larger than the outer diameter of the pivot shafts  72 , and the silicone adhesive  84  is interposed between the two. 
     Accordingly, when the sheet P nipped by and between the separating pad member  74  and the sheet feeding roller  58  is fed, even if the sheet P and the separating pad member  74  rub against each other to thereby cause a stick-slip motion and the separating pad holder  70   a  tends to vibrate in the sheet feeding direction and the direction opposite thereto, the vibration is absorbed by the silicone adhesive  84 . Also, depending on the thickness, density and stiffness of the sheet P, a vehement stick-slip motion is caused and the separating pad holder  70   a  tends to vibrate greatly in the sheet feeding direction and the direction opposite thereto. Such vibration, however, is absorbed by the silicone adhesive  84 . Thus, even if the separating pad holder  70   a  tends to vibrate, the vibration is suppressed by the silicone adhesive  84  and therefore, the pad chatter can be reliably prevented. 
     Thus, the use of the elastic adhesive leads to the adhesively securing function of pivotally supporting the separating pad and the vibration absorbing function of absorbing the vibration of the separating pad, and the pad chatter can be prevented by a simple construction. 
     Reference is now had to FIG. 5 to describe another example of the groove into which the pivot shaft  72  is fitted. FIG. 5 is a perspective view showing a sheet feeding guide  90  from which the separating pad holder  70   a  has been detached. In FIG. 5, the same constituents as the constituents shown in FIG. 7 are given the same reference characters. 
     The shaft feeding guide  90  is formed with a groove  92  into which the pivot shaft  72  is fitted. As in FIG.  3 A, a silicone adhesive  84  is interposed between the pivot shaft  72  fitted in the groove  92  and the groove  92 . The feature of the sheet feeding guide  90  is that a groove  94  deeper than the groove  92  is formed in the inner side adjacent to the groove  92 . 
     As described above, in interposing the silicone adhesive  84 , a liquid silicone adhesive  84  is poured into between the pivot shaft  72  and the inner wall surface  63 . If in this case, the quantity of the liquid silicone adhesive  84  is too great, the excess quantity will flow into the groove  94 . Accordingly, the silicone adhesive  84  will not leak to the surface (the surface contacted by the sheet P) of the sheet feeding guide  90  and the separating pad  70  side, and bad conveyance and bad separation by the separating pad  70  can be prevented. 
     The present invention is not restricted to the above-described embodiments, and while in the above-described embodiments, the silicone adhesive has been described as an example of the vibration absorbing member, other elastic adhesive may be used as the vibration absorbing member. 
     Also, the pivot shaft of the separating pad may be designed to be inserted not into a U-shaped groove but into a circular hole, which may be filled with an elastic adhesive. Also, a groove or a hole may be formed in the separating pad holder side of the separating pad and a pivot shaft may be provided on a member (the sheet feeding guide  60  in the present embodiment) supporting the separating pad, and the separating pad may be fitted onto the pivot shaft so as to pivotally support the separating pad. 
     Further, while in the present embodiment, description has been made of an example in which the present invention is applied to a sheet feeding apparatus for a recording medium to be supplied to effect image formation, the present invention may also be applied to a sheet feeding apparatus for supporting an original to image reading means, i.e., a so-called auto original feeder.