GB2206870A

GB2206870A - Sheet feeding device

Info

Publication number: GB2206870A
Application number: GB08814887A
Authority: GB
Inventors: Lionel Augustine Wilson
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1987-06-26
Filing date: 1988-06-22
Publication date: 1989-01-18
Anticipated expiration: 2008-06-22
Also published as: GB2206870B; GB8814887D0; GB8715015D0

Abstract

An automatic document feeder for use in a photocopying machine comprises a sheet feed roll 1 and a retard pad (5) engaging the roll (1) to prevent multi-feeds. The roll and pad are each provided at their adjoining surfaces with corresponding grooves (11, 12) extending in the direction of sheet feed in order to improve misfeed and multi-feed prevention over an extended lifetime. <IMAGE>

Description

Sheet Feeder This invention relates to apparatus for feeding and separating individual sheets from a stack of sheets.

Photocopying machines are known which have automatic document feeders comprising a sheet feed roll, and a fixed retard pad engaging the sheet feed roll in order to prevent multi-feeds. For a given normal force between the pad and the feed roll the following friction balance must be maintained for effective operation of the feeder: the coefficient of friction between one sheet and another is less than the coefficient of friction between the retard pad and the sheet, which in turn is less than the coefficient of friction between the feed roll and a sheet.

In practice, the contact area between the retard pad and the feed roll tends to become contaminated quite rapidly due to loose print, fuser oils, paper fibres, and dust on the documents being fed, which can alter the frictional balance and consequently impair the document drive and retard functions leading to spasmodic multi-feeds and misfeeds.

It has been proposed to provide grooves in the surface of the retard pad adjacent the roller which act as resilient gates to block second and subsequent sheets from passing through the feed means. The relatively high friction between the first sheet and the feed roll overcomes the gating effect enabling the first sheet to be separated and fed individually. The grooves have the added advantage that they collect contamination which can subsequently be cleaned out for example by blowing or scraping.

According to the present invention apparatus for feeding and separating individual sheets from a stack of sheets, comprising a sheet feed roll, and a retard pad engaging said sheet feed roll, the retard pad being provided with grooves in its surface adjacent the roller, is characterised in that the grooves in the retard pad extend in the direction of sheet feed, and in that the sheet feed roll is provided with grooves corresponding with the grooves in the retard pad.

By providing corresponding grooves in the retard pad and feed roll surfaces, the normal force per unit area at the nip in the solid areas is increased slightly and hence friction to paper is increased and so too is the surface wear at the pad and roll surface. This wear tends to prevent contamination build-up so that the desired frictional balance is maintained, and therefore the apparatus is less prone to multi-feeds and misfeeds.

Moreover, not only do the grooves collect contamination, but because they extend in the direction of sheet feed the apparatus tends to be self-cleaning since the contamination tends to fall out of the grooves unaided.

Also, it has been found in practice, that a sheet apparatus in accordance with the invention has the advantage that it gives better multi-feed and misfeed prevention over an extended lifetime and that the cleaning intervals due to contamination are lengthened.

The grooves in the feed roll preferably extend around the full circumference thereof and have the same width as the grooves in the retard pad. Also, the depth of the grooves may be the same in the feed roll and the retard pad. In one embodiment the depth of the grooves is the same as the groove width in both the feed roll and the retard pad. Suitably the crosssection of the grooves in the feed roll and the retard pad is square. The spacing between adjacent grooves is preferably greater than, e.g. twice, their width.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing in which: Figure 1 is a sectional view of the sheet feeding apparatus in accordance with the invention, and Figure 2 is a front elevation of the apparatus in Figure 1.

The apparatus shown in the Figures is intended for use as an automatic document feeder in a photocopying machine for feeding and separating individual original documents from a stack and advancing them towards a copying station. The apparatus comprises a resilient feed roll 1 mounted for rotation on a drive shaft 2. The roll 1 protrudes through an aperture 4 on a support and guide platform 3. Bearing against the upper surface of the feed roll 1 is a concave resilient retard pad 5. The retard pad 5 is fastened to a support 6 which is pivoted about axis 7 to the main assembly of the copier (not shown). The retard pad 5 is loaded in known manner in the direction of the arrow, e.g. by spring biasing, to apply a normal force to the roll 1 to promote feeding.

A stack of up to, say 50 original documents to be copied may be placed on the support and guide plate 3 within the recess 8 formed beneath the retard pad 5 on the upstream side of feed roll 1. The apparatus acts to feed the bottom sheet 10 and to retard a second or subsequent sheets 9 so that the sheets are fed one at a time from the bottom to the top of the stack in correct sequence.

In accordance with the invention the retard pad 5 and the feed roll 1 are provided with several, for example six, corresponding grooves symmetrically distributed. In this particular embodiment the grooves 11 in the feed roll 1 and the grooves 12 in the retard pad 5 are square in cross section and are 1 mm wide and 1 mm deep and are spaced apart by 2 mm.

The grooves 11 extend the full length of the surface of the retard pad 5 adjacent the feed roll 1 in the direction of sheet feed, as shown in Figure 1 and the grooves 12 in the feed roll 1 extend around the full circumference thereof.

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the present invention. For example, more or less than six grooves may be provided, and their cross sections need not be square, but may for example be rectangular, triangular, or semi-circular. Also, the grooves need not be distributed across the whole of the retard pad and feed roll surfaces, but may for example be restricted to a central portion thereof.

Claims

Claims:

1. Apparatus for feeding and separating individual sheets from a stack of sheets, comprising a sheet feed roll, and a retard pad engaging said sheet feed roll, the retard pad being provided with grooves in its surface adjacent the roller, characterised in that the grooves in the retard pad extend in the direction of sheet feed, and in that the sheet feed roll is provided with grooves corresponding with the grooves in the retard pad.

2. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in claim 1, wherein the grooves in the feed roll extend around the full circumference thereof.

3. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in claim 1 or claim 2, wherein the width of the grooves in the feed roll is substantially the same as the width of the grooves in the retard pad.

4. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in any of the preceding claims, wherein the depth of the grooves in the feed roll is substantially the same as the depth of the grooves in the retard pad.

5. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in any of the preceding claims wherein the depth of the grooves in the feed roll is substantially the same as the width of the grooves in the feed roll.

6. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in claim 5, wherein the grooves in the feed roll are substantially square in crosssection.

7. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in any preceding claim, wherein the depth of the grooves in the retard pad is substantially the same as the width of the grooves in the retard pad.

8. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in claim 7, wherein the grooves in the retard pad are substantially square in crosssection.

9. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in any of the preceding claims, wherein the grooves in the feed roll and the retard pad are spaced apart by a distance greater than their width.

10. Apparatus for feeding and separating individual sheets from a stack of sheets as claimed in claim 9, wherein the grooves in the feed roll and the retard pad are spaced apart by a distance substantially twice their width.

11. Apparatus for feeding and separating individual sheets from a stack of sheets substantially as herein described with reference to Figures 1 and 2 of the accompanying drawing.