GB2041887A

GB2041887A - Feeding Sheets from a Stack

Info

Publication number: GB2041887A
Application number: GB7905071A
Authority: GB
Original assignee: Simon Container Machinery Ltd
Current assignee: Simon Container Machinery Ltd
Priority date: 1979-02-13
Filing date: 1979-02-13
Publication date: 1980-09-17
Also published as: IT1141198B; IT8019783A0; DE2947709A1; JPS55111336A; FR2449055A1

Abstract

A system for feeding sheets from a stack (5) thereof in timed sequence to match the operation of a subsequent work station such as a printing cylinder (21) to which the sheets are fed, comprises an intermittently driven belt (15) having alternate perforated and plain surface portions passing across a suction chamber (18) thus intermittently to capture and convey the sheets one at a time from the stack, the drive means for the conveying member operating in one direction only and being controlled to feed the sheets one at a time at a predetermined rate of acceleration up to a predetermined speed and to convey them in fixed spaced relationship at that speed towards the said work station. <IMAGE>

Description

SPECIFICATION A System for Feeding Sheets from a Stack This invention relates to a system for feeding sheets from a stack thereof in timed sequence to match the operation of a subsequent work station to which the sheets are fed. In connection with, for example, a rotary printing machine where sheets of paper or board are fed to a printing plate or cylinder from a stack of such sheets, the speed at which the paper travels must be equal to the surface speed of the printing plate or cylinder.

Also it is necessary in such systems to deliver successive sheets from the stack in synchronism with rotation of the printing cylinder so as to ensure correct print register. Therefore, each sheet must be accelerated from standstill to the correct paper speed in a controlled manner such that it will coincide at its leading edge with the "zero" or "start" position on the printing cylinder.

In conventional systems, the sheets are usually fed by means of reciprocating devices which engage the sheets either mechanically or by suction, deliver them into a pair of pull rolls for final cceleration up to paper speed, and then return to pick up the next sheet, all within one revolution of the printing cylinder.

An object of the present invention is to provide a sheet feeding system of the kind generally referred to above and wherein the aforementioned requirements are met, but where a single feeding device travelling in one direction only, accelerates the sheets up to paper speed and continues to feed same at that speed.

According to the present invention there is provided a system for feeding sheets from a stack thereof in timed sequence to match the operation of a subsequent work station to which the sheets are fed, the system comprising an intermittently driven endless conveying member having means for capturing the sheets one at a time and feeding them from the stack, the member moving only in the direction of sheet feed, a gate associated with the conveying member to permit passage of one sheet at a time, drive means for the conveying member adapted to cause successive sheets to be fed thereby at a predetermined rate of acceleration up to a predetermined speed and conveyed at that speed towards the said work station, and control means for operating drive means and said capturing means in accordance with said timed sequence.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a view showing a sheet feeding system made in accordance with the invention, associated with a rotary printing machine; and Figs. 2 to 6 are schematic illustrations showing the timed interrelation of the feed mechanism and the printing cylinder.

For the purpose of this description the diameter of the printing plate or cylinder will be referred to as the paper speed diameter, and the circumference of the cylinder as the paper speed circumference.

Referring now to the drawings, this embodiment is applied to a rotary printing machine used in the manufacture of corrugated cardboard boxes where box blanks are fed through one or more printing units prior to being folded and glued to produce formed but collapsed boxes.

A stack of sheets or blanks is fed on to a roller carriage 10 which, in this case, may be elevated within machine frames 11 with the boards being fed from the top of the stack by means of an endless conveying member generally indicated at 12. The member 12 feeds the sheets one at a time into a printing unit 13 including a printing cylinder 14.

The conveying member 12 comprises a flexible toothed belt 1 5 wrapped around a pair of driven toothed pulleys 1 6 and 1 7. The belt 1 5 comprises six equal length portions with alternate portions having high friction perforated and low friction plain surfaces, respectively.

With reference to Figs. 2 to 6 it will be seen that the diameter of each of the pulleys 16 and 17 is equal to half the paper of speed diameter. The centres of the pulleys 16 and 1 7 are spaced apart by a distance a equal to half of the paper speed circumference, and the length of the belt is one and a half times the paper speed circumference.

The dimensions b and c in Fig. 2 represent respectively one eighth and one quarter of the paper speed circumference.

A suction chamber 1 8 lies between pulleys 1 6 and 1 7 and is exposed to the surface of the belt 1 5 remote from the stack. The chamber 1 8 which is capable of connection selectively to a source of suction and to atmosphere, extends in the direction of travel of the belt 1 5, by a distance equal to three eighths of the paper speed circumference. The chamber 1 8 is divided into two substantially equal sections d and e with a dividing wall 1 9 between them.

A gate 30 provided at the top of the front wall of the stack S is positioned one eighth of the paper speed circumference rearwardly of the axis of rotation of the pulley 16, and a gap between the gate 30 and the belt 1 5 is sufficient to allow one sheet only to pass at a time.

As will be seen from Figs. 2 to 6, sheets are fed from the stack S by the belt 1 5 in the direction of arrow 20 towards the printing cylinder 21 which rotates in an anti-clockwise direction as indicated by arrow 22. The cylinder 21 carries on its surface, a printing plate having a leading edge which, at the start of each printing cycle, is located at the position of top dead centre as indicated by the zero mark in Fig. 2. With the printing cylinder in that position, a first perforated section of the belt 1 5 is located with its leading edge at the position of the gate 30 at the front of the stack S, the other end of the same perforated section being disposed at the rear end of the suction chamber, that is at the extremity of section e thereof.The stack must have a minimum length equivalent to one quarter of the paper speed circumference so that the top sheet covers the perforations formed in the belt 1 5 and provides an effective seal against the latter so that when the chamber 1 8 is under suction, the sheet is held against the belt.

Drive to the pulleys 16 and 17 is intermittent and is effected in timed relationship with rotation of the printing cylinder 21 which is continuous.

In operation therefore, when the zero mark passes top dead centre, drive to the pulleys 1 6 and 1 7 commences. When the printing cylinder has rotated through 900 to the position indicated in Fig. 3, the belt 1 5 has been accelerated from standstill to normal paper speed, thus advancing the top sheet of the stack to the position indicated in Fig. 3. That is to say, whilst the printing cylinder has advanced one quarter of the paper speed circumference, the top sheet of the stack has advanced one eighth of the paper speed circumference in its acceleration up to paper speed. It will be noted that as the perforated section of the belt with the sheet held thereto advances across the suction chamber 18, the following plain section of the belt seals the area of the suction chamber behind the sheet.After a further 450 of rotation of the pnnting cylinder 21 to the position indicated in Fig. 4, the sheet has advanced by a further one eighth of the paper speed circumference which is equivalent to the latest increment of movement of the printing cylinder itself. Thus, the speeds of the printing cylinder and the advancing sheet are now synchronised. At this point in the cycle, the following perforated section of belt is about to pass over the chamber 18, and so the section e thereof is opened to atmosphere thus to prevent the next sheet in the stack from being prematurely drawn upwardly into contact with the belt.

With a further 450 of rotation of the printing cylinder to the position indicated in Fig. 5, the belt and the first sheet continue to advance at constant paper speed by a further one eighth of the paper speed circumference. At this point, the first sheet leaves the traction effect of the belt 1 5 and continues to be driven at constant speed by further means forming part of the mechanism associated with the printing unit.

Section d of suction chamber 1 8 is vented to atmosphere after the first sheet has left the confines of the belt and so the whole of chamber 1 8 is then open to atmosphere.

During the next 900 of rotation of the printing cylinder to the position indicated in Fig. 6, the drive to the belt 1 5 is decelerated and stops at the position illustrated in Fig. 6 with the next perforated section of the belt located over the stack. Thus the belt 1 5 is correctly located for feeding the next sheet. As the belt slows to a standstill, the first sheet continues to move forwardly and travels a distance equivalent to one quarter of the paper speed circumference in synchronism with the 900 of rotation of the cylinder 21, to the position shown in Fig. 6.

The final 900 of rotation of the printing cylinder to bring the zero mark to top dead centre, produces no related movement of the belt 15 but suction is recreated in the chamber 1 8 and the first sheet travels a further distance equivalent to one quarter of the paper speed circumference.

When the zero mark on the printing cylinder reaches top dead centre, the suction in the chamber 18 is at a maximum and the first sheet has travelled a total distance of seven eighths of the paper speed circumference.

During the next revolution of the printing cylinder 21, the feeding sequence is repeated on the second sheet in the stack. When the cylinder again reaches the position illustrated in Fig. 3 the second sheet will have advanced one eighth of the paper speed circumference, whilst the first sheet which is still moving at full paper speed, will have advanced a further one quarter of the paper speed circumference, and this relationship maintains a distance equivalent to the paper speed circumference, between the leading edges of consecutive sheets.

It is not intended to limit the invention to the above example only, many variations such as might readily occur to one skilled in the art being possible without departing from the scope of the invention as defined by the appended claims.

For example, it is envisaged that the system can operate such that the sheets are fed sequentially from the bottom of the stack or from the end of a row of sheets of board where the sheets are disposed verticaily.

Claims

1. A system for feeding sheets from a stack thereof in timed sequence to match the operation of a subsequent work station to which the sheets are fed, the system comprising an intermittently driven endless conveying member having means for capturing the sheets one at a time and feeding them from the stack, the member moving only in the direction of sheet feed, a gate associated with the conveying member to permit passage of one sheet at a time, drive means for the conveying member adapted to cause successive sheets to be fed thereby at a predetermined rate of acceleration up to a predetermined speed and conveyed at that speed towards the said work station, and control means for operating said drive means and said capturing means in accordance with said timed sequence.

2. A system according to claim 1 in which said conveying member comprises a flexible belt having a plurality of equal length portions therein with alternate portions having perforated and plain surfaces respectively, the means for capturing and feeding the sheets from the stack comprising a suction chamber exposed to the inner surface of the belt thus to cause the sheets to be drawn into contact with the perforated portions of the outer surface thereof.

3. A system according to claim 2, in which said suction chamber comprises a pair of sections having a divided wall between them, each section of the chamber being connected selectively to a source of suction and to atmosphere.

4. A system according to claim 2, wherein said flexible belt is a toothed belt and wraps a pair of toothed pulleys at least one of which is connected to said drive means.

5. A system according to any one of the preceding calims wherein the drive means provides constant acceleration from standstill to a predetermined constant speed.

6. A system according to any one of the preceding claims, wherein the conveying member is located at the top of the stack, and said gate forms a gap between its upper limit and the surface of the belt sufficient to allow the passage of single sheets.

7. A system according to claim 2, wherein the drive means for the flexible belt is adapted for operation such that during acceleration thereof from standstill to said predetermined speed the belt is advanced by a distance equal to half of the length of a perforated portion thereof.

8. A system according to claim 4, wherein the belt comprises six equal length portions, the pulleys around which the belt is wrapped having their axes of rotation spaced apart by a distance equal to two belt portions.

9. A system for feeding sheets from a stack thereof in timed sequence to match the operation of a subsequent work station to which the sheets are fed, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.