WO1995035253A1

WO1995035253A1 - Transfer device for sheet material

Info

Publication number: WO1995035253A1
Application number: PCT/AU1995/000370
Authority: WO
Inventors: Michael Austin; Kieran Barr
Original assignee: M.T. Graphics Pty. Limited
Priority date: 1994-06-22
Filing date: 1995-06-22
Publication date: 1995-12-28
Also published as: AUPM651894A0

Abstract

Apparatus, system and method for transferring sheet material of a finite length between two processing stages (4, 5) that operate independently and at varying processing rates is disclosed. Apparatus, system and method disclose a transfer means (2) that controls the force applied to the sheet material as it is transferred from one stage to the other so that said material is not forcibly removed from the first processing stage. The preferred embodiment discloses a carriage (2) that translates along guide rails (3) when transferring the sheet material from one stage to the other. The drive motor (6) of the carriage (2) is torque controlled by a microprocessor so that excessive force can not be applied to the sheet material. The carriage contains two opposed rollers (11, 12) that operate as feed rollers. The feed rollers may be separated on an intermittent basis as the sheet material is fed through them. Separating the rollers in the manner disclosed ensures that the film tracks correctly through the rollers.

Description

TRANSFER DEVICE FOR SHEET MATERIAL

FIELD OF INVENTION

This invention relates to devices which transfer between different apparatus sheet or film products, such as rolls of paper, thin film plastics and light sensitive film, such products being particularly though not exclusively used in the printing industry. It is particularly directed to the transfer of these products between pieces of apparatus where the processing rates of the apparatus are non-synchronous, intermittently variable or continuously changing at differing rates.

PRIOR ART

Automated type setting in the printing industry uses a laser printing technique, similar to plain paper laser printing, to expose film used in the production of printing plates. This process is referred to as imagesetting. After the film is exposed by the imagesetter, it is transferred to a second machine where it is developed.

Imagesetters typically have the capacity to expose film which is the width of a standard newspaper. They can expose many pages at a time, resulting in continuous lengths of exposed film exceeding ten meters or more. This process is widely practised and understood, within the printing industry.

The imagesetter and the film processor operate independently and depending on the resolution requirements of the particular page their processing rates may be intermittently variable. Such variability in speed is non-predictable where resolution requirements vary from page to page and within each page due to the placement of photographs and changing font requirements.

It is therefore impractical to have one portion of the film exposed at one speed in the imagesetter at the same time as a previously exposed portion of the film is developed at a different speed in a film processor.

EP 0 639 521 A1 discloses a mechanism for feeding sheet material between apparatus that process sheet material at different rates. It uses a pair of feed rollers positioned within a buffer that is intermediate the two processing stages. These feed rollers are adapted to operate at the processing rate of the first processing stage until the sheet material is fed out of the first stage. The rollers then operate at the processing rate of the second processing stage as they feed the sheet material into this stage.

The rollers operate in this manner so that the sheet material is not dragged from the first stage thereby causing mis-registration of the image.

However to achieve this, complex control of the roller speed is required. This control is dependant on the instantaneous processing rate of the first stage.

Hence communication between the buffer and processing stages is required.

The use of this system is therefore restricted to proprietary equipment. It is believed that similar problems arise in other industries that process continuous sheet material, for example the thin film plastics processing industry, the textile processing industry and other paper processing industries.

It is an object of the present invention to provide an arrangement allowing for effective transfer of film or sheet materials between different processes which operate at different rates.

Summary of Invention

According to one aspect the present invention provides apparatus adapted to transfer sheet material of a finite length between first and second processing stages; said apparatus operating as a buffer so that said stages process said material independently; said first stage having a minimum retention force before slipping of said material; said apparatus characterised in that; a sheet transfer means is adapted to receive said sheet material as it emerges from said first stage and to position said material so that it can be received by said second stage; and a control means limits the force exerted by said transfer means on said sheet material to be less than said minimum retention force.

Limiting the force exerted by the transfer means on the sheet material ensures that mis-registration does not occur due to the sheet being dragged prematurely from the first stage. Preferably the transfer means is adapted to translate from a first position where it receives said sheet material from said first stage to a second position where said second stage can receive said sheet material. Preferably the transfer means is adapted to operate asynchronously to the processing rate of the first stage.

Preferably the transfer means is adapted so that said sheet material is received by said second stage without relative movement between said transfer means and said sheet material.

Preferably the transfer means is adapted to move along guide rails between said first and second positions.

Preferably the control means is a torque controlled motor providing motive force to said transfer means. Preferably the transfer means is adapted to eject said material after being received by said second stage so that said transfer means can receive further sheet material from said first stage before said second stage has completed processing of previous sheet material.

Preferably the transfer means includes at least one pair of opposed rollers adapted to receive said material as it emerges from said first stage; said rollers contacting each other along a plane parallel with their axes and said rollers mutually rotating in response to at least one of said rollers being rotated by a motive force; said material thereby translated through said rollers so as to eject it from said transfer means. Preferably the rollers are adapted to periodically separate when said material is being translated for ejection with at least one of said rollers remaining in contact with said material and continuing to be driven so as to maintain said sheet material in alignment with said second stage. Brief Description of the Drawings Figure 1 is a perspective view of the preferred film transfer apparatus.

Figure 2 is a cross sectional view of the apparatus as adapted for use in developing the film for automated typesetting;

Figure 3 is a front view of the moveable carriage;

Figure 4 is a top view of the moveable carriage; Figure 5 is a side view of the moveable carriage;

Figure 6 is a flow chart of the steps involved in transferring the film from the imagesetter to the processor; Figure 6 is view of the moveable carriage in transit from the imagesetter to the processor;

Figure 8 is a view of the moveable carriage adjacent the processor;

Figure 9 is a view of the film being fed through the moveable carriage after the processor has begun processing the film.

Figure 10 is a view of the moveable carriage when it has returned to its home position adjacent the imagesetter.

Figure 1 1 is a view of the moveable carriage after it has received a second film and is awaiting the processor to complete processing of the first film. Figures 12 through 15 demonstrate the realignment process of film misaligned in the between the opposed rollers. Description of the preferred embodiment

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings. It will be appreciated that while the present invention is described with particular reference to a particular application in the printing industry, the inventive concept is of broader application, where similar problems arise in other industries.

The buffer mechanism 1 of figure 1 and figure 6 comprises a film transfer apparatus which in the preferred embodiment is a moveable carriage 2. The film transfer apparatus operates to receive a leading edge of sheet material as it emerges from a first processing stage. The transfer apparatus then transfers the leading edge to a position where it can be taken up by the second processing stage. Typically, the second processing stage will wait until the first stage has completed processing the sheet material before it commences processing. In some embodiments, the second stage may receive the leading edge and hold it in a queue. In this way, the transfer apparatus can then eject the film and return to receive the leading edge of a further sheet as it emerges from the first stage.

The moveable carriage 2 of the preferred embodiment is guided by rails 3 between the film dispenser port 4 of the imagesetter and the film receiving port 5 of the processing apparatus. The moveable carriage 2 moves along the rails 3 to position the received portion of the film 20 adjacent the receiving port 5 so that the film can be taken up by the processing apparatus. The moveable carriage 2 will preferably move along the rails 3 at a speed that is equal to the maximum speed that the film can emerge from the imagesetter. The motor propelling the transfer apparatus along the rails is preferably torque controlled so that the force exerted by the transfer apparatus on the film does not exceed the minimum force exerted by the imagesetter on the film. This force is called the minimum retention force of the imagesetter. If this force was exceeded by the transfer apparatus, then the film would be dragged from the imagesetter before processing was completed.

With the arrangement of the preferred embodiment, the moveable carriage 2 can only move along the rails 3 at the instantaneous processing speed of the imagesetter. When the instantaneous speed of the imagesetter is less than its maximum, the excess speed of the transfer apparatus will be absorbed by the torque control allowing the motor to slip.

Such an arrangement can be achieved by other means. The film transfer apparatus may take the form of a belt drive or feed rollers that may be driven at the maximum rate of the imagesetter by a torque controlled motor. In such an arrangement, the frictional force between the roller and the film or the belt drive and the film would have to exceed the force required to drag the film from the imagesetter so that slipping of the motor would occur before slipping of the film relative to the rollers or belt occurs.

Alternatively, a clutch mechanism could operate to control the force exerted by the transfer apparatus on the film. The clutch could be affixed to, for example, feed rollers, a belt drive mechanism or to a moveable carriage that translates across the buffer. The clutch will operate to so that it slips when force exerted by the transfer apparatus on the film is equal to or preferably less than the minimum force required to drag the film from the imagesetter.

By controlling the force exerted by the transfer apparatus on the imagesetter, the buffer can operate asynchronously to both the imagesetter and the processing stage. Asynchronous operation means that the transfer apparatus operates without accounting for the instantaneous processing rate of the imagesetter or the processing stage. This reduces the need for communication between the buffer and the imagesetter. It also reduces the complexity of control algorithms and circuitry required by the buffer.

Some communication between the imagesetter and the buffer and the film processing apparatus and the buffer may be required. In this embodiment, the imagesetter and film processing apparatus communicate to the buffer whether or not they are busy. These signals can be readily accessed from the signal bus of most machines.

The moveable carriage 2 of the preferred embodiment contains two opposed rollers 11 and 12. Roller 11 is driven by an electric motor and roller 12 rotates in sympathy with roller 11. Roller 12 is mounted on a pivot bar 14.

Solenoid 13 acts to either engage the rollers or to separate them. The carriage also contains a film out switch 15 which detects when the leading edge of the film has translated through the rollers.

When film 20 is received by the moveable carriage 2 , through the film dispenser port 4, the film-in switch 8, located on the buffer, is activated. This signals to the solenoid 13 that film 20 has been detected entering the transfer apparatus through the film dispenser port 4 from the imagesetter. This signal causes the solenoid 13 to be activated. The solenoid 13 lifts the pivot bar 14 which in turn separates the opposed rollers 11 and 12 of the moveable carriage. The drive roller 11 then begins to turn and the film 20 is fed by the imagesetter through the separated rollers. When the film 20 has fed through the roller a sufficient distance the film-out switch 16 is activated. This causes the drive roller 11 to cease turning and the solenoid 13 to release the pivot bar 14 so that the opposed rollers 11 and 12 are brought back into contact. The opposed rollers now act as gripping means that hold the film 20 firmly in place so that the film 20 is not displaced from between the opposed rollers during transfer of the film from the dispensing port 4 to the receiving port 5 of the apparatus 1.

At this time the drive motor 6 of carriage 2 is activated. This causes the carriage drive belt 7 to rotate about rollers 20 and 21. The belt places motive force on the moveable carriage 2 which subsequently moves across the guide rails 3 towards the film receiving port 5 (See figure 6). As the carriage 2 translates across the guide rails 3, relative movement between the leading edge of the film 20 and the carriage 2 does not occur. This reduces the need for controlling rotating rollers and motors.

The drive motor 6 is torque controlled so that the torque generated by the motor never imparts a motive force to the film that will cause it to be dragged out of the imagesetter at a rate faster than which the imagesetter processes the film. This ensures the quality of the print. In some embodiments the imagesetter may process faster than the speed at which the moveable carriage 2 is traversing the guide rails 3. In this case, the excess film 20 simply falls in behind the moveable carriage 2 and the film transfer apparatus 1 acts as a buffer mechanism that stores the excess film 20 until the moveable carriage reaches the film receiving port 5.

In some applications, the film will be light sensitive, in which case the buffer mechanism should be light proof box. To control the torque of the motor supplying motive force to the film transfer apparatus, motor control chip L293E from SGS THOMPSON is preferably used in conjunction with a 12V DC motor. When the buffer is installed, the duty cycle of the control signals to the motor control chip are calibrated so that the motor operates at the maximum speed of the imagesetter and with a torque equal to the minimum film retention force of the imagesetter.

When the moveable carriage 2 reaches the film receiving port 5 (see figure 7) the carriage limit switch 9 is activated and the drive motor 6 ceases to operate. The moveable carriage waits in this position adjacent the film receiving port 5 while the film 20 from the imagesetter continues to be stored in the film transfer apparatus. When the imagesetter signals that it is no longer processing film, and the film processing apparatus, which receives the film through the film receiving port 5, signals that it is not busy, the drive roller 11 is activated and the film 20 is fed to the processor through the receiving port 5. When the film processing apparatus signals that it is busy, the film transfer apparatus deactivates the drive roller and the solenoid 13 will be activated and the idler roller 12 separated from the drive roller 1 1. The carriage drive motor 6 is now activated and the moveable carriage moves to midway the guide rails 3 (see figure 8). At this point the solenoid 13 lowers the idler roller 12 so that the opposed rollers 11 and 12 are engaged. The drive roller 1 1 is now activated and the film is ejected from the carriage by being fed from one side of the opposed rollers to the other side of the opposed rollers. As is often the case with feeding film through opposed rollers of this nature, the film may mis-track across the rollers (see figure 11 ). This is seen as kinking or twisting in the film adjacent the opposed rollers. To prevent this from happening or to rectify its occurrence the solenoid 13 separates the opposed rollers while the drive roller 12 is activated (see figure 12). The twisting forces in the film 20 naturally operate to return the film to it's state of minimum stress. This is the point where the film 20 is in alignment with the drive roller 1 1 (see figure 13). After a period sufficient for realignment the solenoid causes re-engagement of the opposed rollers 1 1 and 12 and the film continues to be fed out through the opposed rollers (see figure 14). This process is repeated for example at 10 second intervals, until the film 20 is completely fed through the rollers. The absence of film between the opposed rollers deactivates the film-out switch 16 and the drive roller 11 ceases from being driven.

Deactivation of the film-out switch 16 is the signal that the film has been ejected from the carriage 2. once this has happened the moveable carriage 2 returns to it's home position adjacent the film dispenser port 4. When the moveable carriage reaches the home position it activates the carriage home switch 10. This causes the carriage drive motor to cease driving. At this point the moveable carriage is ready to again receive film 20 from the imagesetter (see figure 9). Should the imagesetter commence exposing film again and the moveable carriage receive this newly exposed film 23 whilst previously exposed film 20 remains in the apparatus 1 (see figure 10), the process of transporting the newly exposed film 23 to the film receiving port 5 may be repeated as described above. When the moveable carriage 2 arrives at the film receiving port 5, it waits until the processor has finished processing the first film 20 before it transfers the newly exposed film 20 to the processor. In some applications it is possible for the film receiving port 5 to hold a plurality of such exposed films 20, 23 in queue like manner, feeding each to the processor through the receiving port 5 as it becomes available.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. Apparatus adapted to transfer sheet material of a finite length between first and second processing stages; said apparatus operating as a buffer so that said stages process said material independently; said first stage having a minimum retention force before slipping of said material; said apparatus characterised in that; a sheet transfer means is adapted to receive said sheet material as it emerges from said first stage and to position said material so that it can be received by said second stage; and a control means limits the force exerted by said transfer means on said sheet material to be less than said minimum retention force.

2. Apparatus as claimed in claim 1 characterised in that said transfer means is adapted to translate from a first position where it receives said sheet material from said first stage to a second position where said second stage can receive said sheet material.

3. Apparatus as claimed in claim 1 or claim 2 characterised in that said transfer means is adapted so that said sheet material is received by said second stage without relative movement between said transfer means and said sheet material

4. Apparatus as claimed in claim 3 characterised in that said transfer means is adapted to move along guide rails between said first and second positions.

5. Apparatus as claimed in any preceding claim characterised in that said transfer means is adapted to operate asynchronously to the processing rate of said first stage.

6. Apparatus as claimed in claim 5 characterised in that said control means is a torque controlled motor providing motive force to said transfer means.

7. Apparatus as claimed in any preceding claim characterised in that said transfer means is adapted to eject said material after being received by said second stage so that said transfer means can receive further sheet material from said first stage before said second stage has completed processing of previous sheet material.

8. Apparatus as claimed in claim 7 characterised in that said transfer means includes at least one pair of opposed rollers adapted to receive said material as it emerges from said first stage; said rollers contacting each other along a plane parallel with their axes and said rollers mutually rotating in response to at least one of said rollers being rotated by a motive force; said material thereby translated through said rollers so as to eject it from said transfer means.

9. Apparatus as claimed in claim 8 characterised in that said rollers are adapted to periodically separate when said material is being translated for ejection with at least one of said rollers remaining in contact with said material and continuing to be driven so as to maintain said sheet material in alignment with said second stage.

10. System for processing sheet material of a finite length; said system including first and second processing stages and a buffer stage located intermediate said processing stages; said buffer operating so that said stages process said material independently; said first stage having a minimum retention force before slipping of said material said system characterised in that; a sheet transfer means is adapted to receive said sheet material as it emerges from said first stage and to position said material so that it can be received by said second stage; and a control means limits the force exerted by said transfer means on said sheet material to a force less than said minimum retention force.

11. System as claimed in claim 10 characterised in that said transfer means is adapted to translate from a first position where it receives said sheet material from said first stage to a second position where said second stage can receive said sheet material.

12. System as claimed in claim 10 or claim 11 characterised in that said transfer means is adapted so that said sheet material is received by said second stage without relative movement between said transfer means and said sheet material

13. System as claimed in claim 12 characterised in that said transfer means is adapted to move along guide rails between said first and second positions.

14. System as claimed in any preceding claim characterised in that said transfer means is adapted to operate asynchronously to said first stage.

15. System as claimed in claim 14 characterised in that said control means is a torque controlled motor providing motive force to said transfer means.

16. System as claimed in any preceding claim characterised in that said transfer means is adapted to eject said material after being received by said second stage so that said transfer means can receive further sheet material from said first stage before said second stage has completed processing of previous sheet material.

17. System as claimed in claim 16 characterised in that said transfer means includes at least one pair of opposed rollers adapted to receive said material as it emerges from said first stage; said rollers contacting each other along a plane parallel with their axes and said rollers mutually rotating in response to at least one of said rollers being rotated by a motive force; said material thereby translated through said rollers so as to eject it from said transfer means.

18. System as claimed in claim 17 characterised in that said rollers are adapted to periodically separate when said material is being translated for ejection with at least one of said rollers remaining in contact with said material and continuing to be driven so as to maintain said sheet material in alignment with said second stage.

19. Method of transferring sheet material of a finite length between first and second processing stages by a buffer stage located intermediate said processing stages; said buffer stage operating so that said stages process said material independently; said first stage having a minimum retention force before slipping of said material; said method characterised in that; a sheet transfer means receives said sheet material as it emerges from said first stage and positions said material so that it can be received by said second stage; and a control means limits the force exerted by said transfer means to be less than said minimum retention force.

20. Method as claimed in claim 19 characterised in that said transfer means translates from a first position where it receives said sheet material from said first stage to a second position where said second stage receives said sheet material.

21. Method as claimed in claim 19 or 20 characterised in that said sheet material is received by said second stage without relative movement between said transfer means and said sheet material.

22. Method as claimed in any one of claims 19 to 21 characterised in that said transfer means operates asynchronously to the processing rate of said first stage.

23. Method as claimed in claim 22 characterised in that the motor providing motive force to said transfer means has its output torque controlled so as to limit the force exerted on said sheet material.

24. Method as claimed in any one of claims 19 to 23 characterised in that said transfer means ejects said material after being received by said second stage so that said transfer means can receive further sheet material from said first stage before said second stage has completed processing of previous sheet material.

25. Method as claimed in claim 24 characterised in that said transfer means receives said sheet material between at least one pair of opposed rollers as it emerges from said first stage; said rollers contacting each other along a plane parallel with their axes so that said rollers mutually rotate in response to at least one of said rollers being rotated by a motive force whereby said material is translated through said rollers so as to eject it from said transfer means.

26. Method as claimed in claim 25 characterised in that said rollers periodically separate when said material is being translated for ejection whereby at least one of said rollers remains in contact with said material and continues to be driven so that said sheet material in maintained in alignment with said second stage.