Retard roll enhancement

Abstract: An apparatus (60) for feeding individual sheets from the bottom of a sheet stack (100). The sheet stack (100) is placed in the paper tray (102) with the lead edge (104) abutting the sheet feeding apparatus (60). The face of the stack rests against the main fang (90). As the feed roll (70) forwards the sheets from the bottom of the stack to a position under the main fang (90), further sheet separation occurs as the lead edges (104) of the sheets strike a substantially arcuate member (92) located between the main fang (90) and the retard roll (80). The curved portion of the member (92) which has a larger radius of curvature than the retard member (80) causes the sheets to be shingled out permitting a single sheet to pass under the retard roll (80) and to be advanced by the feed roll (70).

Description: This invention relates generally to a bottom feed sheet feeding system, and more particularly concerns an improved sheet separator for preventing multi-sheet feeding from the bottom of a stack of sheets in a feeder for original documents and/or copy sheets for use in an electrophotographic printing machine. In a commercial printing machine of the type employing an electrophotographic printing process, a sheet misfeed or multi-fed sheets can seriously impair the operation of the machine. It is advantageous in many of today's machines to provide for the in seriatim feeding of sheets from the bottom of the stack. This is useful in both recirculating document handlers for original sheets and to enable replenishment of copy sheets without interrupting machine operation for copy sheets. Due to the inherent problems of feeding from the bottom of the paper stack, many devices have been developed to attempt to alleviate the problems and prevent multi-fed sheets. Three typical problems encountered in bottom feeding sheets from a stack include (1) separating a sheet or sheets from the stack; (2) queuing the separated sheets into an order corresponding to their order in the stack; and (3) advancing the queued sheets into the sheet processing system served by the feeding device. It is also desirous to provide a retard feed device that is self-adjusting, requires little or no set-up for tight tolerances and does not allow sheets to ride up on or stub on the retard surface. The present invention improves over past systems by separating multi-feeds simply, quickly and effectively. The other problems noted with retard feed devices are also solved by the present invention. US-A-4,327,904 discloses an apparatus for selectively increasing the effective frictional force between a retard member and a feed member by making both members from conductive elastomers and providing a source of electrical potential to produce electrical potential between them. A sensor located downstream of the retard member will sense a multi-feed between the pad and retard member and effect the production of electrical potential to increase the friction between the two members. WO-A-91/02690 discloses a sheet feeder device including a support for a stack of sheets. A stationary gate forming member is positioned to define a nip for permitting the lowermost sheet of the stack to pass forwardly from the stack through the nip. The gate forming member is a cylindrical roll defining a central axis and having a plurality of annular grooves extending about the circumference thereof and concentric about a second axis which is eccentric to the central ais. An elastomeric ring is disposed in each of the grooves, and the rings have a coefficient of friction which is higher than that of the material of the roll. US-A-3,937,455 discloses an apparatus for feeding individual sheets from a hopper, including a rotating prefeed member positioned near the exit end of the hopper and having projections for repeatedly beating the next sheet to be fed from the stack of sheets, to help separate the sheets. Further, the apparatus comprises means for queuing sheets advanced from the stack and comprising a substantially planar member adapted to engage the lead edge of one portion of the sheets of the stack so as to initially separate a plurality of sheets from one side of the stack. In accordance with one aspect of the present invention, there is provided a sheet feeding apparatus adapted to advance sheets from a stack of sheets, comprising: means for supporting the stack of sheets; means, mounted adjacent said support means, for advancing sheets from the stack; a retard member having a substantially arcuate surface in engagement with a portion of said advancing means, said retard member comprising a ribbed elastomeric roll in circumferential contact with a portion of said advancing means so as to form a nip therebetween; and means for queuing and separating sheets being advanced by said advancing means from the stack, said queuing and separating means comprising a substantially planar member adapted to engage a lead edge of one portion of the sheets of the stack so as to initially separate a plurality of sheets from one side of the stack, and a ring having a radius of curvature greater than the arcuate surface of said retard member, said ring having an interior diameter greater than the diameter of said ribbed elastomeric roll disposed so that said ring encircles said elastomeric roll and is adapted to engage said separated portion of sheets of the stack. Pursuant to another aspect of the present invention, there is provided an electrophotographic printing machine according to claim 6 of the appended claims, and a module sheet feeding machine according to claim 7. Pursuant to still another aspect of the present invention, there is provided a module sheet feeding machine according to claim 9 of the appended claims. Other features of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which: Fig. 1 is a plan view of the sheet separating device of the present invention; and Figure 2 is an elevational view taken along the line A-A of Figure 1 in the direction of the arrows; and Figure 3 is an end view of the sheet separating device of the present invention. For a general understanding of an electrophotographic printing machine in which the features of the present invention may be incorporated, reference is first made to Figure 4 of US-A-5 211 388 (published on 18.05.1993) which depicts schematically the various components thereof. Hereinafter, like reference numerals will be employed throughout to designate identical elements. Although the sheet feeding apparatus is particularly well adapted for use in the electrophotographic printing machine of Figure 4 of US-A-5 211 388, it should become evident from the following discussion that it is equally well suited for use in a wide variety of devices and is not necessarily limited in this application to the particular embodiment shown herein. Since the practice of electrophotographic printing is well known in the art, the description of various processing stations for producing a copy of an original document represented in Figure 4 of US-A-5 211 388 has been omitted from the present disclosure. Figure 1 illustrates a plan view of the paper tray 102 and sheet feeding apparatus indicated generally by the reference numeral 60. A sheet stack 100 to be fed into the machine is initially placed in the support tray 102. The lead edge 104 of the sheet stack 100 rests against the main fang 90 of the sheet feeding apparatus 60. In the preferred embodiment the main fang 90 is a substantially planar element approximately 70 mm square. There is a small finger 91 located at the bottom center of the main fang 90, which is an integral part of the main fang, which finger 91 is approximately 10 mm wide by 5 mm high. The main fang 90 is mounted so that there is a space of approximately 5 mm between the bottom of the fang finger 91 and the top surface of the sheet support tray 102. A nudger 74 is located in the bottom of the support tray 102 and in combination with the feed roll 70 (Fig. 2), provides a transport means between the support tray 102 and the input portion of the electrophotographic printing machine generally indicated by the reference numeral 30. The nudger 74 is a substantially square cornered roll which rotates and contacts the bottom of the sheet stack 100. A ribbed, frictional retard roll 80 is located between the support tray 102 and the machine input 30. The retard roll 80 is mounted so that it rests upon the feed roll 70. In operation, the retard roll 80 rotates so that its tangential direction is in the opposite direction of that of the feed roll 70. When a single sheet enters the nip 82 (Fig. 2) between the feed roll 70 and the retard roll 80, the frictional force exerted on the sheet by the feed roll 70 is greater than the tangential frictional force exerted by the retard roll 80 so the sheet is forwarded to the machine input 30. If multiple sheets enter the nip 82 between the retard roll 80 and feed roll 70, the frictional force between the sheets is less than that exerted by the retard roll 80 and only the bottommost sheet, which is driven by the greater frictional force of the feed roll 70 is forwarded to the machine input 30. Any other sheets are held back by the retard roll 80 until they are driven toward the machine input 30 by the greater force of the feed roll 70. The retard enhancement ring 92 of the present invention encircles the retard roll 80 at the ribbed portion 83, with the enhancement ring 92 having an inside diameter larger than the outside diameter of the ribbed portion 83 of the retard roll 80 to allow for some movement. The retard enhancement ring 92 encircles the retard roll 80 and extends to the main fang 90. The operation of the retard enhancement ring 92 can best be illustrated by reference to Figure 2. In Figure 2, as the nudger roll 74 is driven in the direction of arrow 72, the entire sheet stack 100 initially has the lead edge 104 of the sheets come into contact with the main fang 90. The main fang 90 acts as a queuing device and allows only a small number of sheets 200 from the bottom of the stack 100 to be forwarded toward the machine input 30. As the sheets 200 continue in the direction of arrow A, the lead edges 204, 206, 208, 210 in turn contact the arcuate surface of the retard enhancement ring 92, further separating and shingling the group of sheets 200. The retard enhancement ring 92 is free to move upward to a limited extent due to the inside diameter of the ring being greater than that of the ribbed portion 83 of the retard roll 80 to avoid wedging of the sheets 200. A stop 98 prevents the enhancement ring 92 from moving in the direction of paper travel (arrow A). Also, as the enhancement ring 92 is free to rotate about the rib of the retard roll 80 there is no stubbing caused by the sheets 200 contacting the ring arcuate surface 93. If multiple sheets enter the nip area, the enhancement ring 92 is free to lift to a certain extent to allow more of the retard surface to be exposed to the sheets to separate and prevent misfeeding of the sheets. Final sheet separation occurs as sheets 202, 204 reach the retard roll 80 which, as is explained previously, due to the higher coefficient of friction of the retard roll 80 to a sheet than a sheet to a sheet, prevents all but a single sheet 202 from being forwarded between the retard roll 80 and nudger roll 70 to the machine input 30. Each subsequent sheet is separated in a like manner and individually fed to the machine input 30. The configuration of the main fang 90 can be seen most clearly in Fig. 3. The small finger 91 located at the bottom center of the main fang 90 and the resulting clearance between the bottom of the small finger 91 and the sheet support tray 102 is clearly illustrated. The enhancement ring 92 is shown encircling the ribbed portion 83 of the retard roll 80. The retard enhancement ring 92 is preferably constructed of a non-elastomer, low-coefficient of friction material such as an acetal resin, to prevent stubbing of, and damage to, the lead edges of the sheets and to allow each sheet to be forwarded in seriatim as it is advanced. The enhancement ring 92 also prevents sheets from riding up the retard surface and being damaged thereby. Although not illustrated, it is also apparent that the separating device can be utilized to feed from the bottom of the stack in a recirculating document handler. It is further evident that the device can be adapted to separate the topmost sheet from a stack in a like manner so as to be adaptable to top feeding devices. In recapitulation, there is provided a device for feeding individual sheets from the bottom of a sheet stack. The sheet stack is placed in the paper tray with the lead edge abutting the sheet feeding device. The face of the stack rests against the main fang which acts as an initial queuing device. As the nudger roll forwards the sheets from the bottom of the stack under the main fang, further sheet separation occurs as the lead edges of the sheets strike the arcuate surface of the retard enhancement ring located between the main fang and the retard roll. The arcuate surface presents the same or similar curvature to the sheet stack face as the retard roll and causes the sheets to be shingled out individually and only a single sheet is allowed to pass under the retard roll and to be fed by the feed roll into the machine processor. It is, therefore, apparent that there has been provided in accordance with the present invention, a sheet separator for a bottom feed or a top feed sheet feeder that fully satisfies the aims and advantages hereinbefore set forth.

Claims: A sheet feeding apparatus adapted to advance sheets from a stack of sheets, comprising: means (102) for supporting the stack (100) of sheets; means (74,70), mounted adjacent said support means, for advancing sheets from the stack; a retard member (80) having a substantially arcuate surface in engagement with a portion of said advancing means, said retard member (80) comprising a ribbed elastomeric roll in circumferential contact with a portion of said advancing means (70) so as to form a nip (82) therebetween; and means for queuing and separating sheets being advanced by said advancing means from the stack, said queuing and separating means comprising a substantially planar member (90) adapted to engage a lead edge (204-210) of one portion of the sheets of the stack so as to initially separate a plurality of sheets (200) from one side of the stack, and a ring (92) having a radius of curvature greater than the arcuate surface of said retard member, said ring having an interior diameter greater than the diameter of said ribbed elastomeric roll disposed so that said ring encircles said elastomeric roll and is adapted to engage said separated plurality of sheets of the stack. The apparatus according to any of Claim 1, wherein said advancing means (74,70) advances successive bottommost sheets from the stack being supported by said support means. An apparatus according to any of the preceding Claims, wherein said sheet advancing means (74,70) comprises: a nudger (74) adapted to engage successive bottommost sheets of the stack being supported on said support means; and a feed roll (70) in circumferential frictional contact with said ribbed elastomeric roll so as to form a drive nip therebetween to drive successive bottommost sheets of the stack. The apparatus of any of the preceding Claims, wherein the sheet being advanced is a copy sheet. The apparatus of any of the preceding Claims, wherein the sheet being advanced is an original document. An electrophotographic printing machine of the type in which a sheet is advanced from a sheet stack, incorporating an apparatus according to any of the preceding claims. A module sheet feeding machine adapted to be removably positioned adjacent a sheet inlet of a printing machine, comprising: an apparatus according to any of claims 1 to 5; wherein the advancing means (74,70) is adapted for advancing sheets from the stack to the sheet inlet of the printing machine.

Inventors: WALLUK EDWARD L, WALLUK, EDWARD L.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1993
Main classification: B65H3
IPC codes: B65H3, G03G15