GB2369112A

GB2369112A - Feeding and registering sheets from a pile

Info

Publication number: GB2369112A
Application number: GB0028338A
Authority: GB
Inventors: John Anthony Sullivan
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-11-21
Filing date: 2000-11-21
Publication date: 2002-05-22
Anticipated expiration: 2020-11-21
Also published as: GB0028338D0; GB2369112B

Abstract

A sheet feeder 10 has a feeder arrangement 18 below a pile of sheets, a gate 14 permitting the passage of the lowermost sheet LS and a datum position means. The feeder arrangement comprises a reciprocating support mounting means, for contacting the bottom sheet, wherein the contacting means 22 is locked against movement in one direction (figure 2), when moving the sheet forward, and freely movable in the opposite direction (figure 3). A means is provided for moving the next sheet NS into registration with the datum means so that it is maintained in registration in preparation for feeding. The feeder arrangement may comprise rollers 22 and a suction chamber 20. The registration means may comprise a suction chamber 26, the gate 14 or a rearward stop (40 figure 6).

Description

METHOD AND APPARATUS FOR FEEDING SHEETS This invention relates to methods and apparatus for feeding discrete sheets of material from a stack thereof to a means for processing the sheet. Such means typically comprise a sheet take-up mechanism, e. g. a roll set or gripper bars. having a nip zone into which the sheets are feed, the roll set carrying sheet treatment tooling such as die cutting tooling.

Our prior GB Patent No. 2274276 discloses methods and apparatus for this purpose. One embodiment disclosed involves the use of roller means mounted in a reciprocating support and so arranged that the roller means are locked during the forward stroke of the support but are able to free wheel during the reverse stroke.

Although this form of reciprocating sheet feeder was attractive in terms of its cost of manufacture, difficulties were encountered with securing adequate registration between the sheets and the sheet processing means. At the time, no solution to this problem was evident which allowed the reciprocating drive arrangement to be retained.

As a result, the roller means were instead mounted on a non-reciprocating support and were driven using a servo-motor drive. The servo drive approach provides a relatively expensive solution to the problem.

The present invention allows a reciprocating drive to be employed whilst achieving adequate sheet registration.

According to the present invention there is provided a method for feeding from a stack thereof individual sheets of material, said method comprising:

stacking the sheets above a feeding arrangement upstream of a gate which holds back sheets other than the lowermost sheet, the feeding arrangement comprising a reciprocating support mounting sheet-contacting means for contact with the lowermost sheet ; during a forward stroke of the support, feeding the lowermost sheet forwardly beyond the gate for take-up by sheet processing means downstream of the gate, the sheet contacting means means being locked during such forward feed of sheet; and during the return stroke of the support, allowing the sheet contacting means to free wheel while in contact with the next sheet; characterised by using the sheet contacting means to register the next sheet with a predetermined datum position during each cycle of reciprocation in such a way that that sheet is registered with the datum position at the beginning of forward feed thereof during the next cycle of reciprocation.

The sheet contacting means may comprise roller means arranged to lock against rotation in one direction but being capable of freewheeling in the opposite direction. Although the invention is conveniently implemented by means of such roller means, we do not exclude the possibility of the sheet contacting means being implemented by other arrangements having the capability of locking in one direction but freewheeling in the opposite direction, e. g. an endless belt or belts which lock against movement relative to the support during the return stroke. While the invention is defined and described hereinafter with reference to roller means, it will be appreciated that references to roller means may, where the context admits, be equally applicable to other forms of sheet contacting means such as an endless belt or belts.

In one embodiment of the invention, such registration of the next sheet is secured by exerting a forward drag force thereon by the moving lowermost sheet during said forward stroke so that the leading edge of the next sheet to be fed contacts forward stop means defining the datum position and restraining rearward movement of the next sheet by the roller means during said return stroke. In this manner, it is possible to ensure that the next sheet to be fed is, at the beginning of the next forward stroke, in a welldefined position for registration with the downstream processing means.

Restraint of rearward movement of the next sheet to be fed may be achieved by the application of suction to said next sheet thereby holding it with its leading edge in contact with the forward stop means.

In a second embodiment of the invention, such registration of the next sheet to be fed is secured by using the free-wheeling roller means to exert a rearward drag force on the next sheet so that the trailing edge of the next sheet is displaced by the roller means during the return stroke into contact with rearward stop means defining the datum position.

The rearward drag force may be secured by limiting the rotational speed of the roller means during return stroke of the support. This may be effected by the application of a braking force to the roller means so that the peripheral speed at the point of contact with the next sheet is lower than the speed of the return stroke, over at least a sufficient part of the return stroke to ensure contact of the trailing edge of the next sheet with the rearward stop means.

According to another aspect of the present invention there is provided a sheet feeder comprising stack forming means, a gate for permitting passage of the lowermost sheet of the stack to the nip of a sheet take-up mechanism downstream of the

gate, a feeder arrangement located beneath the stack for feeding the lowermost sheet beyond the gate, and datum position means, the feeder arrangement comprising a reciprocating support mounting means, e. g. roller or equivalent means, for contact with the lowermost sheet, the sheet contacting means being locked against movement in one direction so as to impart forward drive to the lowermost sheet during the forward stroke of the support and being movable in the opposite direction by contact with the next sheet during the return stroke of the support, characterised in that means is provided for moving the next sheet into registration with the datum position means during each cycle of reciprocation in such a way that the next sheet is maintained registered in preparation for the next cycle of operation.

The forward stroke of the support may be greater than the distance between the gate and nip of the take-up mechanism.

The reciprocating support may be driven through a crank drive so that the speed of travel of the support varies in sinusoidal fashion between the extremities of its stroke and the arrangement may be such that transfer of the sheet from the sheet feeder to the take-up mechanism occurs when the forward motion of the support and hence the roller means is at or substantially at its peak speed. The peak speed may be substantially matched with the sheet feed speed of the take-up mechanism or it may be slightly slower than the take-up mechanism.

The sheets may be held against the roller or equivalent means by differential pressure.

The sheets may be held against the roller or equivalent means by suction.

For example, the support may comprise a suction chamber.

The invention will now be described by way of example only with reference I w to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a first embodiment employing leading edge registration of the sheet with a forward datum position, the sheet feeder being shown with the reciprocating support/roller drive at its rearward extremity ; Figure 2 is a view similar to that of Figure 1 showing the reciprocating support/roller drive at an intermediate position during its forward stroke; Figure 3 is a view similar to that of Figure 1 after transfer of the lowermost sheet to the take-up mechanism, the reciprocating support/roller drive being shown at an intermediate position during its return stroke; and Figures 4,5 and 6 are is a diagrammatic views similar to those of Figures 1 to 3 of a second embodiment employing trailing edge registration of the sheet with a rearward datum position, the sheet feeder being shown with the reciprocating support/roller drive at its rearward extremity, an intermediate position during its forward stroke and partway through its return stroke respectively; and Figure 7 is a view showing the arrangement of a braking device controlling freewheeling of the rollers during the return stroke.

Referring to Figures 1 to 3, the feeder 10 illustrated comprises a stacking table 12 on which a stack of discrete sheets (e. g. corrugated board) are stacked. At the front of the stacking table, a gate 14 is provided which with the table 12 defines a gap for

passage of the sheets one at a time to the nip of a sheet take-up mechanism 16 which may, for example, comprise a roll set 16A, 16B carrying tooling, e. g. die-cutters. for processing the sheets. On entry into the nip, feed of the sheets is transferred from the feeder 10 to the roll set 16.

The feeder comprises a set of rollers 18 mounted in a box 20 which is driven in reciprocating fashion by a crank drive (not shown) towards and away from the gate. The crank drive may be linked to a conventional kicker bar feed whose operation is coordinated with the tooling carried by the roll set 16. The rollers 18 are located for engagement with the underside of the lowermost sheet LS in the stack. The box 20 is connected to means, e. g. a suction fan (not shown), for evacuating the interior of the box 20 so as to draw sheets downwardly against the rollers 18. The rollers 18 are locked against rotation about their axes 22 in a clockwise direction as seen in Figure 1 so that, during the forward stroke of the box 20 (to the left in Figure 1), the rollers 18 drive the lowermost sheet F forwardly beyond the gate 14 and into the nip of the mechanism 16 (Figure 2). Such locking action may be achieved by means of sprag clutches as disclosed in GB Patent No. 2274276. The rollers 18 may be provided with rings of polyurethane to provide good surface frictional contact with the sheets. After transfer of the lowermost sheet LS to the mechanism 16, the sheet is rapidly withdrawn from the feeder 10 and the next sheet NS comes into contact with the table 12 and the rollers 18.

It will be appreciated that, while the rollers may be locked against rotation in the clockwise direction, they need not be locked throughout the forward stroke of the box 20/rollers 18; they need only be locked against rotation during that part of the forward stroke in which they are effective to drive the sheet. Once the sheet is transferred to the nip of the mechanism 18, the rollers 18 no longer need to be locked against clockwise rotation.

At the end of its forward stroke, the box 20 reverses direction and. during the return stroke of the box 20, the rollers 18 are free to rotate counterclockwise as they travel beneath and in contact with the next sheet NS (now the lowermost sheet), see Figure 3.

The reciprocating motion imparted to the box 20 may be of a sinusoidal nature so that, during the forward stroke, the box initial starts from rest and progressively

speeds up to a peak speed before progressively decelerating and reversing back to the 9 rearward starting position. The arrangement is desirably such that the sheet is released to the sheet take-up mechanism in the vicinity of the peak speed of the reciprocating motion of the box 20 such that the departing sheet speed resulting from engagement with the nip of the sheet take-up mechanism is slightly greater than the speed of the roller box 20 at the point of transfer.

In the embodiment of Figures 1 to 3. the rear face of the gate 14 serves to define a forward datum position F for contact by the leading edges of the sheets in order to secure correct registration of the sheets. During forward feed of the lowermost sheet LS, the next sheet NS is dragged forwardly by frictional force until its leading edge abuts the rear face of the gate 14 (see Figure 2). At this point, the leading edge of the next sheet NS is in registry with the datum position. As the rollers 18 return following transfer of the lowermost sheet LS to the mechanism 16, it has now been recognised that despite the intended freewheeling action of the rollers 18 on the return stroke, there is some tendency for the next sheet to be displaced in the rearward direction with the consequence that, if the gate is relied on as a datum position, the registration achieved on the forward stroke is rendered unreliable depending on the extent to which the next sheet is disturbed on the return stroke.

To secure reliable registration in this embodiment of the invention, a feature of the embodiment of Figures 1 to 3 is the provision of a braking means for preventing the next sheet being disturbed during the return stroke of the rollers 18. Such braking means may be implemented for example by the creation of differential pressure sufficient to hold the next sheet stationary and thereby maintain its leading edge in contact with the gate 14 throughout the return movement of the rollers 18. As illustrated diagrammatically in Figures 1 to 3, suction is applied to the next sheet NS, at least during the time that it may otherwise be disturbed, by means of a suction chamber 26 located at or adjacent the trailing portion of the sheet. Thus, the suction chamber 26 is operative during the return stroke of the box 20 and rollers 18 to maintain the next sheet firmly against the forward datum position and thereby zero it in readiness for the next feed cycle.

Figures 4 to 7 illustrate a modification in which the same reference numerals are used to depict like parts. In this embodiment, the drive arrangement for the roller box is the same as that described in relation to Figure 3 but the datum position is defined by a rearward stop 40. As shown in Figures 1 and 2. the forward movement of the rollers 18 serves to drive the lowermost sheet into the nip between the roll set 16. In this case, the rearward movement of the rollers 18 drives the next sheet NS rearwardly until its trailing edge contacts the rearward stop 40. This is achieved by braking the freewheeling rollers 18 during the return stroke so that, while they freewheel, they do so at a reduced speed compared with the linear speed of the reciprocating box 20 thereyb causing them to drag the next sheet NS rearwardly during the return stroke. Such braking may be secured by means of a bar brake 42 (see Figure 7) bearing against the shafts 44 of the rollers 18, the braking bars 42 bearing against sections of the shafts lying between the drive rings 46 which may be of for example polyurethane. The shafts 44, particularly those sections which are engaged by the braking bars 42, may have a coating of low friction material applied thereto so that the braking action allows the rollers 18 to rotate during the return stroke.

It will be seen that in the arrangement of Figure 7 the bar brakes bear down on the rollers 18 and, while freewheeling is permitted, the extent of such freewheeling is restricted. By appropriate design, the braking bars 42 (which may be adjustable) may offer just enough resistance to ensure that the sheet is taken against the rearward stop 40 in such a way the rollers 18 continue to freewheel once the trailing edge of the sheet contacts the datum defining stop 40. In this way, each sheet to be fed forwardly next is zeroed individually against the rearward datum position when the next forward feed stroke commences. Braking of the rollers (or equivalent locking/freewheeling elements) is not of course limited to the particular arrangement shown; the critical feature is that the rollers (or equivalents) should be controlled so that they drive the next sheet into contact with the stop 40 during the return stroke.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features disclosed herein and/or shown in the drawings whether or not particular emphasis has been placed on such feature or features.

Claims

1. A method for feeding from a stack thereof individual sheets of material, said method comprising: stacking the sheets above a feeding arrangement upstream of a gate which holds back sheets other than the lowermost sheet, the feeding arrangement comprising a reciprocating support mounting sheet-contacting means for contact with the lowermost sheet; during a forward stroke of the support, feeding the lowermost sheet forwardly beyond the gate for take-up by sheet processing means downstream of the gate, the sheet contacting means means being locked during such forward feed of sheet; and during the return stroke of the support, allowing the sheet contacting means to free wheel while in contact with the next sheet ; characterised by using the sheet contacting means to register the next sheet with a predetermined datum position during each cycle of reciprocation in such a way that that sheet is registered with the datum position at the beginning of forward feed thereof during the next cycle of reciprocation.

2. A method as claimed in Claim 1 in which the sheet contacting means comprises roller or equivalent means arranged to lock against rotation in one direction but being capable of freewheeling in the opposite direction.

3. A method as claimed in Claim I or 2 in which such registration of the next sheet is secured by exerting a forward drag force thereon by the moving lowermost sheet during said forward stroke so that the leading edge of the next sheet to be fed contacts forward stop means defining the datum position and restraining rearward movement of the next sheet by the roller means during said return stroke.

4. A method as claimed in Claim 3 in which restraint of rearward movement of the next sheet to be fed is achieved by the application of suction to said next sheet thereby holding it with its leading edge in contact with the forward stop means.

5. A method as claimed in Claim 1 or 2 in which such registration of the next sheet to be fed is secured by using the free-wheeling roller means to exert a rearward drag force on the next sheet so that the trailing edge of the next sheet is displaced by the roller means during the return stroke into contact with rearward stop means defining the datum position.

6. A method as claimed in Claim 5 in which the rearward drag force is secured by limiting the rotational speed of the roller means during return stroke of the support.

7. A method as claimed in Claim 6 in which the rotational speed of the roller means during return stroke of the support is effected by the application of a braking force to the roller means so that the peripheral speed at the point of contact with the next sheet is lower than the speed of the return stroke, over at least a sufficient part of the return stroke to ensure contact of the trailing edge of the next sheet with the rearward stop means.

8. A sheet feeder comprising stack forming means, a gate for permitting passage of the lowermost sheet of the stack to the nip of a sheet take-up mechanism downstream of the gate, a feeder arrangement located beneath the stack for feeding the lowermost sheet

beyond the gate, and datum position means, the feeder arrangement comprising a reciprocating support mounting means, e. g. roller or equivalent means, for contact with the lowermost sheet, the sheet contacting means being locked against movement in one direction so as to impart forward drive to the lowermost sheet during the forward stroke of the support and being movable in the opposite direction by contact with the next sheet during the return stroke of the support, characterised in that means is provided for moving the next sheet into registration with the datum position means during each cycle of reciprocation in such a way that the next sheet is maintained registered in preparation for the next cycle of operation.

9. A feeder as claimed in Claim 8 in which the forward stroke of the support is greater than the distance between the gate and nip of the take-up mechanism.

10. A feeder as claimed in Claim 8 or 9 in which the reciprocating support is driven in such a way that the speed of travel of the support varies in sinusoidal fashion between the extremities of its stroke.

11. A feeder as claimed in Claim 10 in which the arrangement is such that transfer of the sheet from the sheet feeder to the take-up mechanism occurs when the forward motion of the support and hence the roller means is at or substantially at its peak speed.

12. A feeder as claimed in Claim 11 in which the peak speed is substantially matched with the sheet feed speed of the take-up mechanism.

13. A feeder as claimed in Claim 11 in which the peak speed is slightly slower than the take-up mechanism.

14. A feeder as claimed in any one of Claims 8 to 13 in which the sheets are held against the roller or equivalent means by differential pressure.

15. A feeder as claimed in any one of Claims 8 to 13 in which the sheets are held against the roller or equivalent means by suction applied by means of a suction chamber.

16. A method for feeding from a stack thereof individual sheets of material, said method being substantially as hereinbefore described with reference to any one of the embodiments illustrated in the accompanying drawings.

17. A sheet feeder substantially as hereinbefore described with reference to, and as shown in, any one of the embodiments illustrated in the accompanying drawings.