GB2166419A

GB2166419A - Sheet registration device and method

Info

Publication number: GB2166419A
Application number: GB08524014A
Authority: GB
Inventors: Alan Keith Mccombie
Original assignee: ROTAPRINT PLC
Current assignee: ROTAPRINT PLC
Priority date: 1984-09-28
Filing date: 1985-09-30
Publication date: 1986-05-08
Also published as: GB8524014D0; GB2166419B

Abstract

A sheet registering device for a sheet handling apparatus, the device comprising a rotatable cylinder 2 provided on its circumferential surface with stop means (11, see Fig 2) to determine the location of the head of a sheet and stop means 7 to determine the location of a side edge of the sheet, means such as belts 12 for moving a sheet on the surface of the cylinder in a circumferential direction and means such as belts 3 for moving a sheet on the surface of the cylinder in an axial direction. <IMAGE>

Description

SPECIFICATION Sheet registration device and method This invention relates to a device for effecting proper positioning of a sheet, for use in any machine, such for example as a printing, cutting or folding machine in which successive paper sheets or board blanks are to be processed in precise relation to one or more of their edges. In particular, but not exclusively, it relates to the registration of paper sheets in high-speed printing presses so that the printed image is produced in a precise and repeatable relationship to the head and side edges of the paper. The principal function of such registration is to allow successive images to be precisely superimposed in multi-colour work.

Hitherto, the registration has, typically, been accomplished as follows: the sheet is advanced into the machine by a feeder which by its timing gives a first approximation to head register, and by its sideways position aims the paper to within 2-3 millimetres of the desired side register. The drive rollers then decelerate and bring the sheet to a halt. A ball-bar or similar device is applied to keep the sheet flat while it is driven by stroker bars against the front and side stops. The front stop or "headlay" is then withdrawn by a cam and the sheet is seized and advanced by grippers mounted on the receiving cylinder.

The disadvantages of this method are numerous.

Its speed of operation is limited by the intermittent motions involved and by the need to stop and start the sheet without marking, damage or loss of position due to mis-timing, excessive acceleration or inadequate grip. The mechanisms involved are intricate and often inaccessible. There is a basic contradiction between the need to squeeze the sheet flat so that it does not buckle when pushed, and the need for minimal resistance to pushing. Pushing, in turn, can only be accomplished by developing frictional drive forces which increase the resistance still further. Also, present-day registration systems have a limited range of correcting movement, which is inadequate to deal with the greater inaccuracies expected with future highspeed feeders.

It is therefore an object of the invention to be able, if desired, to perform the registration process while the sheet is moving at its full processing speed, by means of mechanisms which move continuously rather than intermittently, and which positively confine the sheet in a curved shape which is inherently resistant to buckling. Under such conditions, the drawbacks mentioned above are eliminated and there is, within reason, no limit to the operating speed.

According to the present invention, there is provided a sheet registering device for a sheet handling apparatus, the device comprising a rotatable cylinder provided on its circumferential surface with stop means to determine the location of the head of a sheet and stop means to determine the location of a side edge of the sheet, means for moving a sheet on the surface of the cylinder in a circumferential direction and means for moving a sheet on the surface of the cylinder in an axial direction.

Advantageously, the means for moving the sheet in a circumferential direction comprises at least one endless belt. Also, advantageously, the means for moving the sheet in an axial direction comprises at least one endless belt, the line of contact of which with the surface of the cylinder is at a small angle, preferably 1' to 5 , to a circumferential line perpendicular to the axis of the cylinder.

Although the same means, for example, an endless belt or belts, may be used to effect axial and circumferential movement, advantageously, the means for moving the sheet in a circumferential direction is a means distinct from that for moving the sheet in an axial direction. Preferably, in such a case, the means for moving the sheet in a circumferential direction allows motion of the sheet in an axial direction. This may readily be achieved, for example, if the means for moving the sheet in a circumferential direction comprises at least one endless belt of round, for example, circular, crosssection.

The present invention also provides a method for effecting sheet registration, which comprises feeding a sheet onto the circumferential surface of a rotating cylinder, moving the sheet along the surface of the cylinder in an axial direction until a side edge of the sheet lies in a desired position, and moving the sheet along the surface of the cylinder in a circumferential direction until the head of the sheet lies in a desired position. Advantageously, the axial movement is at least commenced before the circumferential movement is commenced.

Advantageously, the axial movement is effected by at least one endless belt urging the sheet against at least a portion of the circumference of the cylinder, the coefficient of friction between the belt and the sheet, for movement in the axial direction at least, being greater than that between the sheet and the cylinder.

Advantageously, the circumferential movement is effected by at least one endless belt urging the sheet against at least a portion of the circumference of the cylinder, the coefficient of friction between the belt and the sheet, for movement in the circumferential direction at least, being greater than that between the sheet and the cylinder.

Where the sheet is subject to simultaneous circumferential and axial movement, the coefficient of friction between the belt or belts effecting circumferential movement and the sheet is advantageously less, in the axial direction, than is the coefficient of friction between the belt or belts effecting axial movement and the sheet.

In other, though less preferred, embodiments of the invention, registration of one edge only, either the head or the side edge, may be effected by the device or method of the present invention, the other edge registration being effected by other means.

According to a preferred aspect of the present invention, the registration process is carried out on a revolving drum timed with a printing cylinder.

The sheet is accelerated to full speed by the feeder and it then passes to the registration drum, on which it rides while being registered against preset stops fixed to the drum. The drum diameter may be equal to the printing cylinder diameter, in which case the sheet will perform a complete revolution and wind off the drum at approximately the same point that it wound on; in this case there must be a sizeable gap between the sheets. (Alternatively the drum diameter may be some multiple of the printing cylinder diameter, in which case the winding-on and winding-off paths of the sheet will not cross and the sheets can be closely spaced.

This, however, necessitates a bulkier machine.) According to this aspect of the invention, the sheet is confined and held against the drum by independently driven endless belts which are wrapped round a substantial part of the drum surface. They are of higher friction than the drum surface, so that if a speed differential is applied the paper will move with the belts until it encounters a stop on the drum, after which the belts will slip on the paper. Because the belts pass over the stops, which are only as high as the paper is thick, the sheet is totally confined and cannot buckle. Thus the sheet always reaches precisely the same position relative to the rest of the machine regardless of its position on entering the drum.Head registration may thus be obtained from belts travelling in the paper direction but slightly faster, and side registration from belts travelling in a direction slightly angled to that of the paper. The two processes may be simultaneous, in which case the head registration belts may be of circular section so that they do not restrict sideways movement but merely roll. Alternatively, the side registration belts (only) may be of circular section, to restrict their side thrust without breaking their frictional grip.

Either set of belts may be varied in speed, to restrict its action to certain parts of the cycle. Either process may instead be effected by an array of elastomeric rollers, provided that belts are also provided to confine the sheet against the curved cylinder face and prevent its riding over the stops.

Such rollers may promote sideways movement of the sheet, either by having their axes slightly angled to that of the drum, or by being shifted axially at a suitable moment in the cycle. The rollers may be of thin cross-section so that their sideways thrust is limited by bending.

An embodiment of the invention will now be described with reference to the accompanying drawings.

Figures 1 and 1A are schematic diagrams of a drum and belt arrangement adapted for head and side registration. This is only one example of many possible groupings, of belts around the drum, which may be selected to suit particular machines or conditions.

Figure 2 is an enlarged section of part flf Figure 1 showing constructional details of the head lay system.

In Figure 1, each sheet 1 from a stack 1A is fed in turn by a suction feeder (not shown) which places the head of the sheet between the revolving drum 2 and the flat belts 3 where they pass around the pulley 4. The sheet thus trapped is drawn on to the drum and is wrapped closely around it by the pressure of belts 3, a number of which are deployed across the full width of the sheet as shown in the plan view Figure 1A. It will be seen that each belt is at a slight angle (1 -5 ) to the direction of motion of the drum surface. The belts are driven by the pulleys 5 by way of the cantilevered drive shaft 6. In this particular embodiment their speed is identical to the surface speed of the drum 2. This drum carries a number of adjustable side stops 7 which protrude to a height approximately equal to the paper thickness, e.g. about 50 microns.All these protruding stops pass under the outermost belt 5A. Because of the angle of the belts to the drum axis, there is relative motion. Consequently, if a sheet of paper is trapped between the belts and the drum it will move sideways with the belts until it is prevented by the stops. It will not ride over the stops, partly because it is enclosed by the belt 5A and partly because of the forced curvature of the paper.

Thus, by the time the head of the sheet reaches rollers 5 it will have been drawn against the appropriate side stop 7. If allowed to, the sheet will move bodily sideways without turning. It is preferable however that the head moves first, turning the sheet slightly. This is accomplished by means of a vertical side guide 8 placed against the stack 1A, which prevents the tail of the sheet moving across until it is clear of the guide. This yawing of the sheet towards the side stops is a necessary precaution against yaw in the other direction, which might cause the tail of the sheet to be trapped between the belts 3 and the tops of the stops 7. The amount of yaw will not exceed about 2mm.

The suction feeder is timed to deliver each sheet so that its initial position on the drum is short of its desired final position. This means there is always a gap 9 (Figure 2), of indeterminate length, between the head of the paper 10 and the head stop 11. This stop, like the side stops 7, is only as high as the paper is thick.

In Figure 2 the belts 3 are for sideways movement as described above, and they do not cause gap 9 to close. It is clear however that if they were running a little faster than the drum surface they would draw the paper forward until it reached stop 11, after which the belts would slip over the paper, holding it in place.

This is precisely the function of the belts 12 running between pulleys 13 and 14.

Before the head of the paper reaches the belts 12, it has to cross the gap between pulley 5 and pulley 13, i.e. the gap through which it will eventually be transferred to the receiving cylinder 15. For this reason, suction holes 16 are provided. These are connected via conventional kidney ports (not shown) to a vacuum source. The ports are arranged so that the suction is only applied while the paper head is crossing the gap, and serves to prevent the head of the paper from lifting away from the cylinder surface unless it is peeled off by grip pers mounted on cylinder 15.

The belts are sufficiently long to deal with comparatively large gaps 9 should these arise through inaccurate feeding. By the time the head reaches the pulley 14 the gap 9 will have been closed, and the tail of the sheet meanwhile will have been drawn against stops 7 by belts 3. The yaw of the paper will thus have been removed and it will be in the correct sideways position as well as the correct longitudinal position against stop 11.

The paper will then pass a second time under belts 3 which will apply any further side corrections that may be required in exceptional cases such as an undersized sheet.

An important feature of the invention is that stops 7 act along the full length of the paper and thus give the most accurate possible register to a sheet fed lengthwise.

Belts 3 are synchronous with drum 2 (rather than faster) because with some papers it is not possible to produce sideways motion while simultaneously urging the head of the paper against the head stop 11. Thus if belts 3 ran faster, gap 9 might be closed prematurely and further sideways motion would be prevented.

Because of this disparity of speeds, it is desirable but not essential that belts 12 have a higher coefficient of friction than belts 3. Failing this, belts 12 will take over from belts 3 as soon as the length of paper under belts 12 exceeds that under belts 3.

The disparity of speeds will also cause a slight loop to form, as more paper is fed out from under pulley 14 than is taken in under pulley 4. In many cases this is unobjectionable, but it may be corrected by slowing down belts 12 during this part of the cycle. This slowing-down will be by known means such as a variable speed motor, a timing belt drive with oscillating jockey pulley, or non-circular gears.

While the sheet is under belts 3 and 12 simultaneously, it is desirable that belts 12 should not inhibit any sideways motion imparted by belts 3. For this reason, belts 12 may be of circular section so that they will roll upon the paper, offering little resistance to sideways motion while maintaining a static frictional contact for forward motion.

The head stop 11 is at one side of the paper only, corresponding to belt 5A, which passes over it. This is to avoid a conflict of head registers with sheets that are cut out-of-square. In a printing press an alternative head stop and side stops will also be provided at the other side of the paper but will not be deployed unless the sheet is to be registered to that side. Likewise the supports and drives of belts will be adaptable to incline these belts to the other side.

Claims

1. A sheet registering device for a sheet handling apparatus, the device comprising a rotatable cylinder provided on its circumferential surface with stop means to determine the location of the head of a sheet and stop means to determine the location of a side edge of the sheet, means for moving a sheet on the surface of the cylinder in a circumferential direction and means for moving a sheet on the surface of the cylinder in an axial direction.

2. A device as claimed in claim 1, wherein the means for moving the sheet in a circumferential direction comprises at least one endless belt.

3. A device as claimed in claim 1 or claim 2, wherein the means for moving the sheet in an axial direction comprises at least one endless belt, the line of contact of which with the surface of the cylinder is at a small angle to a circumferential line perpendicular to the axis of the cylinder.

4. A device as claimed in claim 3, wherein the angle is within the range of from 1" to 5 .

5. A device as claimed in any one of claims 1 to 4, wherein the means for moving the sheet in a circumferential direction is a means distinct from that for moving the sheet in an axial direction.

6. A device as claimed in claim 5, wherein the means for moving the sheet in a circumferential direction allows motion of the sheet in an axial direction.

7. A device as claimed in claim 6, wherein the means for moving the sheet in a circumferential direction comprises at least one endless belt of round cross-section.

8. A sheet registering device substantially as hereinbefore described with reference to and as illustrated by any one or more of the accompanying drawings.

9. A method for effecting sheet registration, which comprises feeding a sheet onto the circumferential surface of a rotating cylinder, moving the sheet along the surface of the cylinder in an axial direction until a side edge of the sheet lies in a desired position, and moving the sheet along the surface of the cylinder in a circumferential direction until the head of the sheet lies in a desired position.

10. A method as claimed in claim 9, wherein the axial movement is at least commenced before the circumferential movement is commenced.

11. A method as claimed in claim 9, wherein the axial movement is effected by means effecting no circumferential movement.

12. A method as claimed in claim 9, wherein the axial movement is effected by at least one endless belt urging the sheet against at least a portion of the circumference of the cylinder, the coefficient of friction between the belt and the sheet, for movement in the axial direction at least, being greater than that between the sheet and the cylinder.

13. A method as claimed in claim 9 or claim 12, wherein the circumferential movement is effected by at least one endless belt urging the sheet against at least a portion of the circumference of the cylinder, the coefficient of friction between the belt and the sheet, for movement in the circumferential direction at least, being greater than that between the sheet and the cylinder.

14. A method as claimed in claim 13 as dependent on claim 12, wherein the sheet is subject to simultaneous circumferential and axial move ment, the coefficient of friction between the belt or belts effecting circumferential movement and the sheet is less, in the axial direction, than is the coefficient of friction between the belt or belts effecting axial movement and the sheet.

15. A method of effecting sheet registration, substantially as hereinbefore described with reference to and as illustrated by any one or more of the accompanying drawings.

16. A method as claimed in claim 9, carried out using a device as specified in any one of claims 1 to 8.

17. A sheet handling apparatus, incorporating a device as claimed in any one of claims 1 to 8.

18. Apparatus as claimed in claim 17, which is a printing machine.

19. Any new feature herein before described or any new combination of herein before described features.