Sheet feeding apparatus and image forming apparatus

Abstract

A sheet feeding apparatus includes an endless attraction member ( 200 ) attracting a sheet and rotating, and the attraction member ( 200 ) includes a plurality of electrode pattern areas. Each of the electrode pattern areas includes first and second electrodes ( 510 and 511 ) supplied the voltages from a power feed portion respectively. The electrode pattern areas are arrayed in the circumferential direction in such a manner that the electrode pattern areas are electrically insulated each other, and each circumferential direction length of the electrode pattern areas is set shorter than a circumferential direction length, between the power feed portion and the discharge portion, of the attraction member.

1 . A sheet feeding apparatus comprising:
 a support portion supporting a sheet;   a first rotator disposed above the support portion;   a second rotator disposed downstream, in a sheet feeding direction, of the first rotator;   an endless attraction member, whose inner surface is supported at least by the first and second rotators, rotating in a circumferential direction, the attraction member configured to feed the sheet by attracting the sheet by its outer surface opposing to the sheet supported by the support portion;   a power feed portion feeding positive and negative voltages to the attraction member such that electrostatic attraction force is generated when the attraction member contacts the sheet on the support portion; and   a discharge portion discharging an electric charge on the attraction member by being in contact with the attraction member,   wherein the attraction member comprises a plurality of electrode pattern areas extending along the circumferential direction, each of the electrode pattern areas comprising first and second electrodes supplied the voltages from the power feed portion respectively, and   the electrode pattern areas are arrayed in the circumferential direction in such a manner that the electrode pattern areas are electrically insulated each other, and each circumferential direction length of the electrode pattern areas is set shorter than a circumferential direction length, between the power feed portion and the discharge portion, of the attraction member.   
     
     
         2 . The sheet feeding apparatus according to  claim 1 , further comprising a rotator pair nipping the sheet having been attracted and fed by the attraction member from the support portion and conveying the sheet downstream,
 wherein each circumferential direction length of the electrode pattern areas is set such that a rear end side of the electrode pattern area is in contact with the power feed portion at a point of time when a front end portion of a sheet, having a size capable of being attracted and fed by one electrode pattern area, is nipped by the rotator pair.   
     
     
         3 . The sheet feeding apparatus according to  claim 1 , wherein the attraction member is formed such that a front end of one of the electrode pattern areas attracting an uppermost sheet is positioned adjacent to the front end of the uppermost sheet when an attraction area of the attraction member with respect to the uppermost sheet is maximized and before the uppermost sheet among sheets supported in the support portion is separated from a subsequent sheet. 
     
     
         4 . The sheet feeding apparatus according to  claim 1 , wherein the power feed portion comprises only one power feed rotator disposed at one location in a circumferential direction of the attraction member, and each circumferential direction length of the electrode pattern areas is set shorter than a circumferential direction length, between the power feed rotator and the discharge portion, of the attraction member. 
     
     
         5 . The sheet feeding apparatus according to  claim 4 , wherein each electrode pattern area comprises comb teeth-shaped electrodes formed in a comb teeth-shape by protruding alternately from the first and second electrodes in a width direction orthogonal to the circumferential direction. 
     
     
         6 . The sheet feeding apparatus according to  claim 5 , wherein the comb teeth-shaped electrodes are configured such that positive and negative polarities are positioned alternately in the circumferential direction. 
     
     
         7 . The sheet feeding apparatus according to  claim 1 , wherein the power feed portion comprises a first power feed rotator and a second power feed rotator as the second rotator, the first and second power feed rotators being disposed such that a first position where the outer surface, opposing to the sheet supported by the support portion, of the attraction member attracts the sheet is placed between the first and second power feed rotators, and
 each circumferential direction length of the electrode pattern areas is set shorter than a circumferential direction length, between the first power feed rotator and the discharge portion, of the attraction member, and set shorter than a circumferential direction length, between the second power feed rotator and the discharge portion, of the attraction member.   
     
     
         8 . The sheet feeding apparatus according to  claim 7 , wherein a circumferential direction length, between the first power feed rotator and the second power feed rotator, of the attraction member is set shorter than each circumferential direction length of the electrode pattern areas. 
     
     
         9 . The sheet feeding apparatus according to  claim 7 , wherein each electrode pattern area comprises comb teeth-shaped electrodes formed in a comb teeth shape by protruding alternately from the first and second electrodes in a width direction orthogonal to the circumferential direction. 
     
     
         10 . The sheet feeding apparatus according to  claim 9 , wherein a distance amoung the plurality of electrode pattern areas is set to a same dimension as a pitch of the comb teeth-shaped electrodes in each electrode pattern area. 
     
     
         11 . The sheet feeding apparatus according to  claim 9 , wherein the comb teeth-shaped electrodes are configured such that a positive polarity and a negative polarity are positioned alternately in the circumferential direction. 
     
     
         12 . The sheet feeding apparatus according to  claim 1 , wherein the power feed portion comprises a driving rotator, the sheet feeding apparatus further comprising:
 a first nipping member nipping the attraction member together with the driving rotator;   a second nipping member nipping the attraction member together with the second rotator;   first and second driving sources driving the driving rotator and the second rotator respectively; and   a control portion configured to control the first and second driving sources such that rotational speeds of the driving rotator and the second rotator differ, increases a downward sagging quantity of the attraction member to attract the sheet on the support portion, and reducing the downward sagging quantity of the attraction member while feeding the sheet attracted to the attraction member.   
     
     
         13 . An image forming apparatus comprising:
 an image forming portion forming an image on a sheet; and   the sheet feeding apparatus according to  claim 1  feeding the sheet to the image forming portion.   
     
     
         14 . A sheet feeding apparatus comprising:
 an endless attraction member configured to have its outer surface attract the sheet and rotate;   a power feed portion configured to feed voltage to the attraction member at a power feed position; and   a discharge portion configured to discharge the attraction member at a discharging position,   wherein the attraction member comprises a first electrode pattern area comprising an electrode, to which the voltage is fed from the power feed portion, extending along a circumference direction of the attraction member and a second electrode pattern area arrayed in the circumference direction with the first electrode pattern area, the second electrode pattern area comprising an electrode, to which the voltage is fed from the power feed portion, extending along the circumference direction of the attraction member, and   each circumferential direction length of the first and second electrode pattern areas is set shorter than a circumferential direction length, between the power feed position and the discharging position, of the attraction member.