US3645527A

US3645527A - Sheet-feeding devices

Info

Publication number: US3645527A
Application number: US39977A
Authority: US
Inventors: Albert George Ronald Gates
Original assignee: NRG Manufacturing Ltd
Current assignee: NRG Manufacturing Ltd
Priority date: 1969-06-12
Filing date: 1970-05-25
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28
Also published as: DE2026848B2; DE2065252C3; YU150270A; DK126173B; AT312411B; DE2065252B2; DE2065252A1; FR2049177A1; FR2049177B1; AR211218A1; GB1271526A; YU34584B; AT302806B; DE2026848C3; JPS4932834B1; DE2026848A1

Abstract

The specification discloses a sheet feeder in which the sheets are driven by one-way rotatable friction rollers mounted on a lever freely pivotably mounted on a reciprocable support, the height of the pivot of the lever being adjustable to vary the angle of inclination of said lever to the horizontal to adapt the sheet feeder for feeding different weight sheets. The pivot of the lever may also be adjustable forwards and backwards to adapt the feeder for different sheet sizes and thicknesses of paper.

Description

United States Patent Gates 51 Feb.29,1972

[54] SHEET-FEEDING DEVICES 21 Appl. No.: 39,971

2,126,5l4 8/1938 Storck et al ..27 l /42 3,379,433 4/l968 Gates 27l/42 2,062,643 l2/l936 Edmunds ..27 I /42 2,197,036 4/l940 Ford ...27l/42 UX 768,979 8/]904 Dexter et al. ..27 l I42 Primary Examiner-Joseph Wegbreit Assistant Examiner-Bruce H. Stoner. Jr. Attorney-Spencer & Kaye [S 7] ABSTRACT [30} Foreign Application Priority Data The specification discloses a sheet feeder in which the sheets June l2, I969 Great Britain ..29,957I69 are dfiven by onemay rotatable friction rollers mourned on a lever freely pivotably mounted on a reciprocable support, the U.S. Cl. ..271/42, 271/21 height the pivm of the lever being adjustable to vary the angle of inclination of said lever to the horizontal to adapt the [58] ndddsemh 36 sheet feeder for feeding different weight sheets. The pivot of I the lever may also be adjustable forwards and backwards to [56] Cited adapt the feeder for different sheet sizes and thicknesses of UNITED STATES PATENTS P P"- 2,759,4l5 8/ 1956 Harris et al. ..27 1 I42 X H Clalms,6 Drawing Figures Patented Feb. 29, 1972 3,645,527

5 Sheets-Sheet 1 Q FIG] 13 FIG 2.

\ lnvenlor Albert George Ronald Gates A Home 34.

Patented Feb. 29, 1972 3,645,527

3 Shee cs-Sheet 2 Inventor Albert George Ronald Gates A Home 4.

Patented Feb. 29, 1972 3 Sheets-Sheet 5 lnotnlor Albert George Ronald Gates Attorney.

SHEET-FEEDING DEVICES The present invention relates to an improvement in sheetfeeding devices, and more particularly to an improved feed unit for use with a sheet feeder in which the top sheet of a stack of sheets is to be fed horizontally.

In the past it has been known to provide a sheet feeder comprising a feedboard which supports a stack of sheets to be fed and which advances the stack upwardly so that the top sheet of the stack arrives at a feeding level at which it is engageable by a sheet-feeding member. It has been discovered that in such a mechanism it is necessary either to provide a complicated compensating mechanism on the feedboard raising device which ensures that, after each individual sheet is fed, the remainder of the stack is indexed upwardly to bring the next successive sheet to the feeding level, or alternatively to pro vide a complicated compensating mechanism on the sheet feed member in order to ensure that a constant feeding force is exerted on whichever sheet happens to be at the top of the stack so that only the top sheet is fed. Clearly, the compensating mechanism must be capable of ensuring that the frictional force is sufficient to entrain the top sheet and yet the downward force exerted on the stack by the feed member should not be so great as to result in frictional binding of the top sheet with successive sheets therebelow and thus cause multiple feeding. Hitherto such compensating mechanisms have been provided, but their incorporation has necessitated considerable complication and thus increase in cost of construction and maintenance of the sheet feeder.

It is an object of the present invention to provide a feed unit for a sheet feeder which includes a simple yet reliable compensating mechanism in the feed unit.

According to the present invention there is provided a sheet feeder including a feed table for supporting a stack of sheets to be fed, two feed rollers for frictional engagement with the top sheet of a stack on said table, a one-way clutch mechanism associated with each roller to prevent rotation of the roller during movement of the roller in a feeding direction and to permit the roller to roll back along the stack of sheets during movement in a return direction, a reciprocable feed member carrying a freely pivotable lever to which said rollers are connected by means of the one-way clutch devices, a gimballing structure for connecting the two feed rollers to said feeding member and permitting independent up and down movement of the feed rollers with respect to one another and means for adjusting the height of the pivot axis of the said freely pivotable lever.

Advantageously the sheet feeder may include a front stop to hold the leading edge of the top sheets of said stack during the early part of the movement of the rollers in a feed direction to cause the sheets to undergo bowing to release the top most sheet from the contacting sheet, and means for adjusting the horizontal positioning of the said pivot axis whereby the range of movement of the rollers can be moved towards and away from said front stop. In such an arrangement the rollers may be adjusted to a position closer to the front stop when feeding sheets having a low resistance to bowing so that the extent of the region of bowing may be reduced, making the bowing more acute and thus separating the top sheets more effective- Iy.

Preferably the rollers are each provided with a rubber tire to increase the friction between the roller and a sheet being fed. Advantageously the means for adjusting the vertical positioning of the pivot axis may comprise a vertically extending slot arrangement fonned on the reciprocable feed member, and a pivot shaft of the lever engageable in the slot for vertical movement therealong between indents at spaced positions along the slot. Suitably spring biased abutment means may be provided for urging the pivot shah into the indents. Conveniently the abutment means may comprise a pair of plates spring biased in a direction parallel to the direction of return movement of the reed rollers, each plate having a vertically extending slot.

The gimballing structure may conveniently comprise a common spindle the ends of which carry the rollers, and a spindle support pivotally connecting the midpoint of the spindle to the freely pivotable lever.

More preferably the sheet feeder may include a feedboardraising mechanism for automatically adjusting the level of the top of the stack once a noticeable departure from the desired level has been sensed. The departure from the desired level may be sensed by a set of stack height stop fingers pivotable between a first position in which they contact the top sheet of a stack to be fed, and a second position in which the top sheet is free to advance, means being provided for sensing the precise orientation of the fingers when in said first position whereby lowering of the stack height will vary said first position and will trip the feedboard-raising mechanism for raising movement.

In order that the present invention may more readily be understood the following description is given, merely by way of example, reference being made to the accompanying drawings in which:

FIG. 1 is a side elevational, partly sectional view of one embodiment of sheet-feeding device according to this invention, the device being shown in the process of entraining the top sheet of a stack;

FIG. 2 is a view, corresponding to FIG. I, and showing the sheet in a subsequent position in the feeding cycle;

FIG. 3 is a further view similar to FIGS. I and 2 and showing the device returning to its starting position prior to feeding the subsequent sheet;

FIG. 4 is an end elevational view of the feed unit of FIGS. 1 to 3;

FIG. 5 is a side elevational view showing the feed unit of FIG. 4 but with one feeding roller removed for purposes of clarity; and

FIG. 6 is a further side elevational view depicting the geometry of the feed unit and illustrating the self-compensating nature of the feed unit.

Referring now to the drawings, FIG. 1 shows a sheet feeder in which a stack of paper sheets is supported on a feed board 14 between a front paper fence II and a backstop 12, a paperweight 13 being slidably mounted on the backstop to bear downwardly against the upper sheets of the stack adjacent their rear edges. A paper height stop 8 at the top of the sheet fence comprises a plurality of finger-shaped cams fixedly mounted on a rotatable spindle I0 which is carried by bearings in side frames of the sheet feeder.

The top sheet of the stack is caused to move forwards, i.e., to the right as viewed in FIGS. I to 3, by means ofa feed unit 5 carrying a pair of rubber-tired rollers provided with a one-way clutching arrangement arranged so mat the feed unit may roll freely along the stack of paper in a leftward direction but upon rightward movement of the feed unit, the rollers I frictionally entrain the top sheet for feeding movement towards the right. The feed unit 5 is carried by a feed unit support bar 7 driven for purely horizontal reciprocating movement from left to right as shown by the arrows in FIGS. 1 and 3.

Just to the right of the paper fence II are two secondary feed rollers 15 and I6 which, in die FIG. I position, are vertically spaced to provide an open passage through which the right-hand or leading edge of a sheet may pass.

FIG. I shows that the top sheet of the stack has been entrained during rightward motion of the feed unit and is caused to bow near its right-hand edge which is caught in a recess 9b behind the finger 9a of the cam 9.

In the FIG. 2 condition the feed unit 5 has moved further rightwardly and the finger cams 9 have been rotated in the clockwise sense by rotation of the common spindle 10. This rotation of the cams has released the right-hand edge of the top sheet of the stack and permitted it to flick forwards into the gap between the two secondary feed rollers 15 and I6. Simultaneously, the secondary feed rollers have moved together to define a closed nip therebetween through which y the sheet is driven by rotation of the rollers in the appropriate sense, i.e., clockwise in the case of the lower roller I5 and anticlockwise in the case of the upper roller 16. Upper and lower sheet guides I7 and 18 have also moved together along with the rollers to define a narrow passage through which the leading edge of the driven sheet may pass. In the FIG. 2 position, the feed unit has arrived at its rightward limit of motion and the one-way clutch devices of the rollers 1 permit the rollers to freewheel in the anticlockwise direction during withdrawal of the top sheet, by frictional engagement with the secondary feed rollers and 16. During this feeding action on the top sheet, rubber pads [30 of the paper weight 13 bear downwardly on the rear edge of the next successive sheet to reduce the powbility of more than one sheet being fed at a time. However, even allowing for the action of the paper weight 13, it is possible for the top few sheets to become dragged through a small distance towards the right, and particularly so when the sheet feeder is being used for high-speed operation. In order to restore the stack to its original configuration, the finger cams 9 are provided with raised cam surface portions 90 which, during anticlockwise rotation of the cams between the FIG. 2 position and the FIG. 3 position, push the top sheets back into their starting position. This action is clearly visible from a study of FIG. 3 in which the finger cams 9 are partially returned to their starting position and the raised cam surface portions 9c can be seen to urge the top few sheets leftwardly into contact with the back stop 12. In order to en sure that the returning action of the finger cams 9 is not resisted by the presence of the paperweight 13, the weight is constructed and balanced so that it can rock backwards and forwards on the support part comprising the back stop 12.

In P16. 3 the

secondary feed rollers

15 and 16 have once again separated, and the feed unit 5 is shown as moving leftwardly to return to its starting position prior to feed of the next sheet. The rollers 1 are freewheeling as they roll along the top surface of the stack of sheets.

Although the above-described arrangement of feed unit 5 and paperweight 13 is intended at least partly to avoid double feeding, the feed unit 5 is carefully constructed to provide a simple yet effective self-compensating arrangement which adjusts the normal reaction exerted by the roller 1 on the top of the stack so that the frictional force with which the rollers urge the top sheet rightwardly is of sufficient magnitude to drive the top sheet rightwardly. However. the normal reaction is prevented from being so great as to cause the top sheet and the second sheet to undergo mutual frictional engagement which might otherwise result in double feeding.

The self-compensating arrangement of the feed unit 5 is illustrated particularly clearly in FIGS. 4 and 5 which show the arrangement by means of which the two rollers l are mounted on stub spindles 2c of a swivel block 2 by means of a pin I9 secured to the free end of a swinging arm 3. The opposite end of the swinging arm is secured to a shaft 4 which in turn is freely rotatable with respect to its mount, formed by the casing of the horizontally reciprocable feed unit 5, and thus permits pivoting of the swinging arm 3. Clearly therefore the two rollers 1 will be independently movable vertically by virtue of the two pivoting joints formed by the pin 19 and the shaft 4. Thus, any irregularities in the thickness across the stack of sheets can be taken up by the independent movement of the rollers I. The degrees of freedom of the pivotable block are indicated by the

arrows

20 and 21 in FIGS. 4 and 5 respectively.

The stub spindles 2c are each provided with a shoulder 20 which, together with a circlip 2b, define axial constraints on the rollers l which are nevertheless freely rotatable in one direction of rotation only, since reverse rotation is prevented by the one-way clutch devices associated therewith. Each roller 1 has an axially extending spacer collar la integrally formed therewith and thus by arranging the rollers l with the spacer portions la facing axially outwardly, i.e., adjacent the associated circlip 2b, the spacing between the roller tires can be reduced. However since each roller has a built-in one-way clutch it will also be necessary to transpose the rollers from one side of the swivel block to the other when reversing the spacer locations if the one-way clutch device is not to be upset.

The sides of the frame of the feed unit 5 are provided with similarly shaped U slots 22 which are of a width sufficient to accommodate a central narrow diameter portion 23 of the shaft 4. Each of the slots 22 is provided with leftwardly extending portions or

indents

24 and 25 positioned at the tops of the left-hand and right-hand limbs of the U respectively. A further leftwardly extending portion or indent 26 is provided at the base of the left hand limb of the U. The small diameter portion 24 of the shaft 4 is thus able to be located in any one of the three

indents

24, 25 and 26. and is held in position in the associated indent by means of spring-loaded plates 6 having a vertical slot 27 of a length equal to the height of the two limbs of the U-shaped slots 22. The plates 6 are positioned one on each side of the feed unit (as shown in FIG. 5) and are spring loaded towards the left by means of tension springs 30 mounted between studs 31 fixed to the feed unit frame and suitable mountings 32 on the right-hand ends of the plates 6. The purpose ofthe U slot 22 and the

indents

24, 25 and 26 will be described later.

Turning now to FIG. 6, the length of the swinging arm 3 is designated y and the center of gravity of the assembly comprising swinging arm 3, pin I9, swivel block 2, stub spindles 2c and rollers l is positioned a distance 1 away from the axis of the shaft 4, the weight of the assembly being designated W, and the swinging arm 3 being inclined at a normally constant angle a to the horizontal. The frictional contact between the rubber covered rollers l and the top sheet of the stack is such that a frictional force F in the leftward direction is exerted on the rollers as a result of a normal reaction R acting on the rollers in the upward direction by virtue of the contact between the rollers and the paper stack. The coefiicient of static friction between the rollers I and the top sheet of paper is assumed to be u, and the coefficient of static friction between the top sheet of paper and the second sheet is assumed to be At the start of rightward purely horizontal movement of the feed unit 5 causing the then nonrotatable rollers l to entrain the top sheet of paper by frictional contact, F=p.,,R.

Now, considering the moments acting on the swinging arm 3 and taken about the axis of the shaft 4, the anticlockwise moment will be R-y cosa and will balance the clockwise moment comprising the sum of W2 cosa and F(a-+y sin a) where a is the radius of the rollers 1.

u R (a't-ysin a)+Wz cos a=Ry cos a.

W: cos ct=Ry cos ar -m ff (a+y sin or) =R(y cos au,,un,.y sin ul Wz cos a y 005 ap. a-u,,y Sin a Differentiating with respect to or gives a positive slope from which it can be seen that within the operating range of a, an increase in a will be accompanied by an increase in R.

Clearly, by moving the axis of the shafts 4 between the upper and

lower indents

24 and 26, the angle a can be selected at either of two fixed valves. More than two such values may be provided for if necessary.

The need for varying a arises because it is essential that there be imparted some minimum downward force upon the paper stack, to induce sufficiently high reaction R to ensure that slipping does not occur between the rollers l and the top sheet. If this force and reaction are too low, then the horizontal force imparted by the rollers to the surface of the stack will be too low to:

a. overcome the static frictional forces between first and second sheets b. overcome at the same time the resistance of the top sheet to buckling (insofar that its leading edge is held at this time by the Paper Height Stop 9).

in the case of very lightweight papers it is usually undesirable to increase the value of R to a value much higher than this minimum, since this can tend to induce "creep" of the upper sheelsof the paper stack, to an extent which cannot be counteracted by the action of the Paper Height Stop. Thus, for lightweight papers, (1 and therefore R, must be suitable low and this is provided for by the lowest position for the axis 4.

However, where heavier papers are involved this value of R would be inadequate to induce the frictional force needed to move the top sheet, for reasons already indicated in (a) and (b) above, especially since heavier papers usually have a greater resistance to buckling. in these cases the vertical force component and its reaction R, must be increase by increasing a, i.e., choosing a higher position for the shaft 4.

It has been found that in the case of heavier papers this can be achieved without inducing excessive creep, such as would occur with lighter papers.

One reasonforthetwoupperindentsflandzsisthatthe rightmost or forward indent 25 can be used when feeding short sheets such as cards, where the distance between the rightmost position of the rollers I and the secondary feed rollers is to be at a minimum. Clearly, wherever possible it will be desirable to use the

leftmost indents

24 and 26 since this will allow the maximum length of sheet between the rollers 1 and the sheet fence 1] and will thus permit the desired bowing of the right hsnd part of the sheet. However, when feeding papers which have a low longitudinal resilience in which case a sheet may be reluctant to release itself after forward rotation of the Paper Height Stop positioning the roller nearer to the Paper Height Stop causes the buckling to be distributed over a shorter span, and therefore become more acute. This in turn affords greater resilience to the buckled part of the sheet and assists sheet release.

Because of the desirability of varying both the vertical and horizontal positioning of the shaft 4 it may be preferred to construct the slots 22 to have both upper and lower forward indents, or even a choice of three or more vertical and/r horizontal adjustment settings.

During normal operation of the sheet feeder, the vertical spacing x between the axis of shaft 4 and the top sheet of paper will be maintained constant since the feedboard raising mechanism will always maintain the stack of sheets at the appropriate height governed by contact of the finger cams 9 of the paper height stop contacting the top sheet of the stack. In practice several sheets may be fed in succession from the top of the stack without any upward movement of the feedboard, and then when the feedboard-raising mechanism senses that the top of the stack has dropped, the raising mechanism will index the feedboard upwardly to bring the top sheets once again into the correct position. During the slight descent of the top of the stack before an upward adjusting movement of the feedboard, the normal operation of the feed unit is unaffected since the swinging arm 3 is able to drop into contact with the top sheet of the stack and, provided the resulting variations in the angle a are only slight, a constant sheet-feeding force will be applied to the top sheet during each cycle, regardless of the slight variations in stack height. Without this compensating feature provided by the swinging arm 3, the sheet feeder might othenlvise exert a reduced sheet-feeding force with a pomible result that the sheet-feeding member (in this case the pair of rollers i) would exert insufficient frictional force on the top sheet for feed to occur. Hence the illustrated feed unit incorporates a particularly simple yet reliable self-compensating mechanism and also includes a manual compensating device to allow for different grades of sheet smoothness.

The sheet-feeding operation described above is only possi ble provided is in excess of u, so that the top sheet is gripped by the rollers but permitted to slide with respect to the next successive sheet during application of a given value of R. This relationship between s, and p, is assured by using rubber tired rollers 1, preferably provided with a roughened high-grip periphery. Once sliding of the top sheet relative to the next sheet commences, the coefficient of friction between the top two sheets will reduce from p, to p, the sliding friction value, and the feed cycle will continue satisfactorily since the value of intersheet friction will fall to -R. The value of roller to sheet friction F will also reduce to F= r,,-R and since ;r.,, the sheets will continue to slide while the rollers l grip the top sheet.

Although the secondary feed rollers clearly contribute to the effectiveness of the illustrated arrangement the essential sheet-feeding components of the feeder include the novel feed unit 5, a paper height stop 8 and littable feed board 14. The secondary feed rollers may be eliminated and the device be used to feed directto some part ofa printing machine or other device to which sheets are to be fed. The particular paper height stop mechanism 8 described is not essential but may be replaced by any other mechanically equivalent device which restrains the leading edge of the top sheets yet permits the very top sheet to be advanced from the stack at the appropriate part of the feed cycle.

The stack-raising mechanism driving the feedboard is not illustrated in the drawings but in this embodiment is in the form of a reciprocating pawl which engages a ratchet wheel. When the paper stack is at the correct height the pawl reciprocates but remains clear of the ratchet wheel. 111e pawl only engages the ratchet wheel when the stack height falls and causes an angular displacement of the extreme anticlockwise position of the paper height stop spindle 10, in which case the pawl will engage the ratchet wheel causing the feedboard to rise to its correct position. Clearly, such a device will not advance after each individual sheet is fed unless the sheets are of considerable thickness. With a normal paper sheet feeder it is envisaged that several sheets will be fed between successive indexing raising movements of the feedboard. This feed stack raising mechanism is particularly simple and is thus convenient for use with the low-cost, self-compensating, reliable sheet feed unit illustrated. However, any other suitable feedboard-raising mechanism may be employed.

Further advantages of the sheet feed unit described include:

a. the simple nature of the feed unit makes it possible to employ less moving parts than in conventional sheet-feeding devices and this produces a saving in production and maintenance costs;

. the swinging arm 3 carrying the one-way clutched rollers provides a feed unit which executes a simple reciprocating movement in a horizontal plane and thus the operating noise is considerably reduced with respect to the operating noise normally experienced when using a sheet feeder employing vertical and horizontal movements of the sheet feed members;

. the more compact arrangement afforded by the simple construction enables a more aesthetically pleasing design to be obtained and the resulting feed unit is unobtrusive both from the point of view of design appearance and of mechanical accessibility.

The limits of up-and-down movement of the gimballing mechanism are defined by the upper and

lower end

33 and 34 of a slot 35 formed in each plate 6 and engageable with the stub spindles 2c, as shown in FIG. 5.

We claim:

I. A sheet feeder comprising:

a. a feed table for supporting a stack of sheets to be fed;

b. two feed rollers for frictional engagement with the top sheet of a stack on said table;

c. reciprocably driven feed means movable along said stack in a purely horizontal feed direction and an opposite purely horizontal return direction;

d. a lever carried by said feed means;

e. means mounting said lever on said feed means for pivotal motion about an axis;

t. gimballing means connecting said lever with said two feed rollers for allowing independent up and down movement of the feed rollers relative to one another;

g. one-way clutch means connecting said rollers to said gimballirtg means for preventing rotation of said rollers during movement of the feed means in said feed direction but allowing roller rotation during movement of said feed means in said return direction; and

h. means for adjusting the height of the said pivot axis of the lever.

2. A sheet feeder as set forth in claim 1. including means for adjusting the horizontal positioning of said pivot axis with to said feed means.

3. A sheet feeder as set forth 'in claim 1, wherein said height adjusting meani comprises vertically extending slot means on said feed means for slidably receiving said pivot means, and vertically spaced indents in said slot means for locating said pivot iii alternative vertically spaced positions.

4. A sheet feeder as set forth in claim 3, and including means resiliently biasing said pivot means into engagement with saidjndents 5. A sheet feeder according to claim 4, wherein said resilient biasing means includes plate means, resiliently biased for urging said pivot means towards said indents, first vertically extending further slot means formed in said plate means means, second further slot rtieans for for receiving said gimballing means, and means on further slot means for defining upper and lower limits of up and down movement of said rollers.

6. A sheet feeder as set forth in claim 3, and including horizontally extending slot means communicating with said vertically extending slot means, and at least one further indent communicating with said horizontally extending slot means and horizontally displaced from the first-mentioned indents.

7. A sheet feeder as set forth in claim 1, and including an integrally formed coaxially extending spacer collar on each said roller, and means permitting reversal of the orientation of each said roller.

8. A sheet feeder as set forth in claim I, wherein said gimballing means comprises spindle means for supporting both said rollers, and spindle support means pivotally connected to said lever.

9. A street feeder according to claim I. and including a rubber tire on each said roller for gripping engagement with sheets being fed.

10. A feeder including: o

a. a fecd table for supporting a stack of sheets to be fed and having a pair of opposed edges;

b. sheet feed means for engaging thetop sheet of such a stack and urging the said top sheet along a given direction parallel'to said table over one of said opposed edges;

c. drivemeansoperablyconnectedtosaid sheet feed means for driving movement following a path along said given n and a reverse direction, said path extending between predetermined limits of movement of said feed means; 7

releasable street stop meanspositioned above said one edge for obstructing movement of said top sheet along said given direction during movement of said drive m sheet stop release means for releaing said sheet stop means after a predetermined part of said drive means movementzand V l f. adjustable connecting means operably' associated with saiddrive mean and saidsheet feed means for-varying simultaneously the horizontal positioning of the'limits of said path with respect to said releasable sheet stop means.

II. A sheet feeder according to claim [0, and including friction means disposed above the other of said opposed edges for resisting movement of said stack of sheets along said given direction.

Claims

1. A sheet feeder comprising: a. a feed table for supporting a stack of sheets to be fed; b. two feed rollers for frictional engagement with the top sheet of a stack on said table; c. reciprocably driven feed means movable along said stack in a purely horizontal feed direction and an opposite purely horizontal return direction; d. a lever carried by said feed means; e. means mounting said lever on said feed means for pivotal motion about an axis; f. gimballing means connecting said lever with said two feed rollers for allowing independent up and down movement of the feed rollers relative to one another; g. one-way clutch means connecting said rollers to said gimballing means for preventing rotation of said rollers during movement of the feed means in said feed direction but allowing roller rotation during movement of said feed means in said return direction; and h. means for adjusting the height of the said pivot axis of the lever.

2. A sheet feeder as set forth in claim 1, including means for adjusting the horizontal positioning of said pivot axis with respect to said feed means.

3. A sheet feeder as set forth in claim 1, wherein said height adjusting means comprises vertically extending slot means on said feed means for slidably receiving said pivot means, and vertically spaced indents in said slot means for locating said pivot means in alternative vertically spaced positions.

4. A sheet feeder as set forth in claim 3, and including means resiliently biasing said pivot means into engagement with said indents.

5. A sheet feeder according to claim 4, wherein said resilient biasing means includes plate means, resiliently biased for urging said pivot means towards said indents, first vertically extending further slot means formed in said plate means for receiving said pivot means, second further slot means for receiving said gimballing means, and means on said further slot means for defining upper and lower limits of up and down movement of said rollers.

8. A sheet feeder as set forth in claim 1, wherein said gimballing means comprises spindle means for supporting both said rollers, and spindle support means pivotally connected to said lever.

9. A sheet feeder according to claim 1, and including a rubber tire on each said roller for gripping engagement with sheets being fed.

10. A sheet feeder including: a. a feed table for supporting a stack of sheets to be fed and having a pair of opposed edges; b. sheet feed means for engaging the top sheet of such a stack and urging the said top sheet along a given direction parallel to said table over one of said opposed edges; c. drive means operably connected to said sheet feed means for driving movement following a path along said given direction and a reverse direction, said path extending between predetermined limits of movement of said feed means; d. releasable sheet stop means positioned above said one edge for obstructing movement of said top sheet along said given direction during movement of said drive means; e. sheet stop release means for releasing said sheet stop means after a predetermined part of said drive means movement; and f. adjustable connecting means operably associated with said drive means and said sheet feed means for varying simultaneously the horizontal positioning of the limits of said path with respect to said releasable sheet stop means.

11. A sheet feeder according to claim 10, and including friction means disposed above the other of said opposed edges for resisting movement of said stack of sheets along said given direction.