GB2214495A

GB2214495A - Sheet separation; preventing double feed

Info

Publication number: GB2214495A
Application number: GB8800865A
Authority: GB
Inventors: Peter Jamieson Troup
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1988-01-15
Filing date: 1988-01-15
Publication date: 1989-09-06
Anticipated expiration: 2008-01-15
Also published as: GB2214495B; GB8800865D0

Abstract

Apparatus for extracting sheets singly from the bottom of a stack 2 and feeding them to a sheet-using apparatus, prevents mis-feed of the sheets by means of at least one closed loop 26 of elastomeric material the bight of which is positioned to be contacted by any second other sheet blown down and fed with the bottom (first) sheet, the contact stopping longitudinal movement of the 'shingled' sheet unit after the first sheet has been completely extracted. The apparatus includes a vacuum corrugation feeder having an air chamber 10, perforated belts 16 and an air knife 22. <IMAGE>

Description

SHEET-FEEDERS This invention relates to sheet-feeders, and particularly to feeders incorporating means for preventing more than one sheet at a time being extracted from a stack of sheets and fed to a downstream sheet-using device, such as a xerographic copier.

it is known to extract sheets seriatim from the bottom of a stack of cut paper or other sheets by means of an air knife and a so-called 'vacuum corrugation feeder'. To permit this to happen, the stack is supported on the surface which leaves a significant area of the bottom sheet unsupported, particularly in the vicinity of what is to be the lead edge of the sheet when it is being fed. The pocket formed by the surface below the bottom sheet has a blast of air directed into it by the air knife so as to riffle the edges of the bottom-most few sheets. The pocket is designed to have air sucked through its perforated surface spaced from the bottom sheet, and movable over the surface is at least one belt of rubber or like highfriction material. Each belt is preferably perforated so that air can be sucked through it even when it is moving.

The air sucked through the perforated surface of the pocket passes into a plenum chamber from which it is extracted by a vacuum pump exhausting to the atmosphere, and/or supplying compressed air to the air knife.

When a sheet is to be fed from the stack, the vacuum pump is coupled to the plenum chamber; each friction belt is driven, and air is blown from the air knife. The lead edge of the bottom sheet is blown into contact with the belt(s) and the pocket surface, and remains held against the belt by suction. Air then tends to be blown between the captured sheet and the one(s) above it, to keep them longitudinally immobile while the bottom sheet is pulled from underneath the stack by virtue of the force by which it is held against the belts being greater than the friction applied to the rest of the sheet by the weight of the stack.

However, despite the air knife, it sometimes happens that the second sheet from the bottom can move with the first sheet, and fail to be separated from it completely, so that it becomes partially pulled from beneath the stack as the first sheet is extracted. This sheetfeeder defect is known as 'shingling', and leads to a mis-feed of the second sheet when it becomes the bottom sheet.

The present invention aims at overcoming this defect by providing a mechanical detent for preventing any substantial longitudinal movement of the second and higher sheets in the stack as the bottom sheet is being extracted.

Accordingly, the present invention provides a sheet-feeder which is as claimed in the appended claims.

The present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic side view of a sheet-feeder of the present invention, and Figure 2 is a view, to a larger scale than Figure 1, of the front face of the stack showing the vacuum plenum in section.

In Figure 1, a stack 2 of sheets of cut paper has its weight carried by a tray 4 associated with which is a front wall 6 intended to provide a preliminary registration edge.

The surface 4 is formed at one end with a D-shaped depression 8 to provide a pocket below the respective edge and the adjoining area of the bottom sheet. The pocket 8 ends in a substantially-flat surface which is contiguous with, or forms the upper surface of, a plenum chamber 10 from which air is able to be extracted by a vacuum pump (not shown) to which it is connected by a port 12 (see Figure 2).

In one version of a sheet-feeder of the present invention, the upper surface of the chamber 10 is formed with a rib 14 extending in parallel with the direction in which sheets are to be extracted from the bottom of the stack. The function of the rib is to cause the bottom sheet, after it has been captured1 to assume a lazy-W shape to give the sheet significant beam strength, for reasons which will be discussed more fully below.

The chamber 10 is positioned within a volume bounded by four (in this case) rubber belts 16 which are entrained over a pair of rollers 18, of which one is intended to be rotated, in the direction shown by the respective arrow, by means of a suitably-energised motor (not shown). As can be seen from Figure 2 (in which only the upper runs of the belts are shown in section) the belts are themselves perforated at intervals along their length so as to give them the necessary surface area of high-frictional grip, while at the same time permitting air to flow through the aligned openings in the belts 16 and the lower surface 20 of the pocket.

Extending across the width of the respective front face of the stack 2 is an air knife 22, which is arranged to be supplied with air under pressure, either from the outlet of the vacuum pump extracting air from chamber 10, or from a separate source. A ribbon-sectioned blast of air issues from the outlet nozzle 24 of the air knife, being directed at the centre of the lead edge of the bottom sheet, and therefore into the mouth of pocket 8.

Intercepting the blast, but virtually unaffected by it, are two spaced-apart closed loops of resilient, high-friction, material, such as synthetic rubber, which are secured by any appropriate means to the registration wall 6. The loops 26 are carefully dimensioned and positioned such that the lower-most bights of the loops lie either in the plane of the top surfaces of the belts 16 or close thereto.

The dimensions are chosen so that when the sheet-feeder is working, the blast of air from air knife 22 riffles at least the bottom sheet in stack 2 and deflects it sufficiently for it to come into contact with the belt 16, to be held there by suction. This suctional force is sufficient to ensure that the centre of the lead edge of the bottom sheet comes into contact with rib 14, to induce a longitudinal fold in the lead edge and the contiguous regions of the sheet, so as to increase the stiffness of the sheet.If a second sheet of paper tends to be displaced downwardly by the air knife, it might come into contact with the top of the fold produced in the bottom sheet by rib 14, but as there are no suction forces acting on it, and as the air knife continues to blow air into the space between the two sheets, the second sheet will continue to be spaced by an appreciable distance from the bottom sheet, and it is on this fact that the present invention is based.

After the bottom sheet has been captured by suction1 with the pressure differential across the respective area of the sheet being sufficient to hold the sheet in contact with the upper surface of the belts, so that when they are driven the whole of the bottom sheet is pulled out from beneath the rest of the stack, against the friction imposed on that sheet by the weight of the stack, it could be that the second sheet is in sufficient frictional engagement with the bottom sheet so start to move with it as the feed belts move in order to extract the bottom sheet from the stack. As soon as the second sheet moves more than a slight distance, it comes into contact with the two loops 26.The resilience of the material forming these loops is such that they provide such a resistance to further movement of the second sheet that it comes to a standstill, despite the drag applied to it by the continuing movement of the bottom sheet.

It is a significant feature of the present invention that the surface of the loops contacted by such a mis-fed second sheet slopes downwardly and away from the stack. The importance of this is that when the bottom sheet has been completely removed from beneath the stack, the halted second sheet is quickly captured by the feed belts, the sloping surface of the loops very quickly ceasing to have any effect on the movement of the second sheet as it is blown by the air blast, and sucked by the air flow into the plenum chamber, into contact with the feed belts.

Although the loops 26 are shown as being secured directly to the outside face of wall 6, they could be mounted in other ways. The natural resilience of the rubber of like material forming the loops tends to cause them to assume a symmetrical shape of 'teardrop' cross-section. The desired angle which the loops present to sheets other than the first sheet contacting them can be controlled by mounting the loops on an ancillary support attached to wall 6, with the ancillary support being at such an angle that the 'contact' parts of the loops lie at the desired angle of about 15 to the vertical.

The loops 26 themselves may be made of any suitable material, of either monolithic or layered construction, and the frictional properties of the contact surfaces of the loops may be controlled by suitable texturing of the outside surface of the loops, or by the application of small patches of suitable material to the loops themselves.

As mentioned above, the lower-most parts of the bights of the loops may be intended either to just brush the surface of the bottom sheet when captured, or to be spaced slightly above it so as to be contacted by any sheet which does not follow the shape of the captured sheet slavishly, for whatever reason.

It will thus be seen that the present invention provides a simple and low-cost feature for use in sheet-feeders, and which may be even retro-fitted to existing sheet-feeders, enabling the shingling or similar mis-feed of sheets from the stack to be reduced significantly, if not eliminated.

Claims

Claims:

1. A sheet-feeder including means for extracting sheets seriatim from the bottom of a stack of sheets and feeding them to a downstream sheet-using station, the extracting means including a down-curved perforated surface into contact with which the bottom sheet is intended to be sucked, the device including a mis-feed preventer in the form of at least one closed loop of elastomeric, high-friction, material fixed to a member above the path of the sheets; lying in an upright plane substantially parallel with the direction of sheet travel, and having its bight positioned in, or slightly above1 the path of the bottom sheet so as to intercept and stop any sheet(s) tending to be dragged along with the bottom sheet.

2. A sheet-feeder as claimed in claim 1, in which there are two such loops positioned on that face of an upright wall forming a registration surface for the stack, which opposes an air knife directing its blast at the lower front edge of the stack, the loops being mounted so that the portions thereof extend at an acute angle to the vertical at the level of the bottom face of the stack.

3. A sheet-feeder as claimed in claim 1 or 2, in which the stack is supported on a surface having a dished portion adjacent its front edge so as to form a pocket extending below the centre line of the bottom sheet, at least part of the bottom surface of the pocket being perforated to enable air to be extracted from the interior of the pocket.

4. A sheet-feeder as claimed in claim 3, in which the perforated surface of the pocket either forms, or is secured to, the ceiling of a plenum chamber of which the interior is adapted to be placed in communication with the inlet of a suction pump, so as to enable the interior of the plenum to be reduced to a sub-atmospheric pressure.

5. A sheet-feeder as claimed in claim 3 or 4, in which the lower surface of the pocket has formed in it a rib which extends parallel with the direction in which sheets are extracted from the stack.

6. A sheet-feeder as claimed in any preceding claim, in which at least one perforated belt of friction material travels over the perforated surface of the pocket so as to enable a sheet to be pulled from beneath a stack of sheets after it has been held in contact with the belt by suction.