GB2312051A

GB2312051A - Internal drum plate setters

Info

Publication number: GB2312051A
Application number: GB9707288A
Authority: GB
Inventors: Rex William Davy; John Peter Ricketts
Original assignee: SYNECTIX Ltd
Current assignee: SYNECTIX Ltd
Priority date: 1996-04-10
Filing date: 1997-04-10
Publication date: 1997-10-15
Anticipated expiration: 2017-04-10
Also published as: GB9707288D0; GB2312051B; GB9607450D0

Abstract

An internal drum plate setter comprises a stiff lightweight expose drum 30 of fibre reinforced plastics material into which a plate may be loaded by wrapping it onto the outer cylindrical surface of an expandable transfer drum 28 over which the expose drum is then moved telescopically. The transfer drum is expanded to offer the plate up to the internal cylindrical surface of the expose drum and the plate is then released from the transfer drum and secured to the expose drum. The plate is exposed by directing a modulated beam along a fine helical scan line, whereafter the transfer drum may, be used to retrieve the exposed plate. An active registration system using sensors 88 for precisely registering the plate relative to the expose drum surface during the transfer phase is also described.

Description

Internal Drum Plate Setters This invention relates to internal drum plate setters.

In conventional examples of this type of plate setter, the film or plate to be exposed is located on the inner cylindrical surface of a massive drum normally made of cast iron or epoxy granite and weighing up to 300Kg. The drum needs special support infrastructure on account of its weight and the need to be free from vibration. Because of its mass, the drum has to be static, and often complex mechanisms have to be built around it to allow films or plates to be fed into and retrieved from the drum.

A film or plate is exposed by means of a modulated beam which is deflected by a spinner head comprising a spinning mirror on the axis of the drum to follow a fine pitched helical path over the film or plate and the remainder of the drum. These systems thus require the optics to both spin the mirror about the drum axis at high speed (typically around 20,000 to 40,000 rpm) and to traverse the length of the drum slowly, to provide the helical scan. These movements also need to be tracked or predicted extremely accurately to synchronise with the modulator and controlling electronics, so that the intended image is not distorted.

In existing machines, the cast iron or granite drum is essentially immovable once installed and so the optics may hamper access to the drum when a film or plate is inserted.

The system is awkward for handling, because users must move around the immovable drum. Also, the nature of the conventional drums means that they can only take films or plates up to about 2700 wrap angle (i.e. the angle subtended by the film or plate).

New thermal films or plates are being introduced which rely on the thermal effect of a laser to cure a photosensitive polymer material instead of the conventional silver-based photographic systems and are so insensitive that they can be handled in daylight. However, although of benefit for handling, they have such low sensitivity that it is important to have high duty cycles in the plate setter (i.e. to have a high useful proportion of the angular sweep of the laser beam) to make efficient use of the laser power.

Thus drums which have a wrap angle of only 1800 or at best 2700 are severely disadvantaged and it is desirable to get as near as 3600 as practical.

A need exists therefore for an internal drum plate setter which allows a high duty cycle, provides improved handling, and which mitigates some of the other disadvantages of existing systems.

Accordingly, in one aspect this invention provides an internal drum plate setter, comprising: a rotary spinner head located on a rotary axis, and an expose drum means defining a substantially unitary internal cylindrical surface concentric with said rotary axis for receiving a film or plate means for exposure, and having an axial end region through which a film or plate means for exposure may be introduced and withdrawn axially.

By this arrangement, the whole 3600 of the internal cylindrical surface of the expose drum means can be continuous and so, allowing for film or plate retaining means, wrap angles of 3000 or more may be achieved, thus considerably increasing the duty cycle relative to the conventional cast metal or graphite expose drums.

The expose drum means preferably comprises a generally continuous unbroken cylindrical wall means defining said internal cylindrical surface, although if required the drum may be made in sections which are then secured together.

The expose drum means is preferably formed wholly or principally of a fibre composite material, whereby the drum means is stiff and lightweight. A preferred material is carbon fibre reinforced plastics (CFRP).

A composite expose drum means will be extremely stiff but light and so the design of the plate setter and the infrastructure needed to support the machine can be totally revised.

The internal drum plate setter means preferably includes means mounting said expose drum means for linear movement relative to said spinner head parallel to said rotary axis, and expose drum drive means for moving said expose drum means relative to said spinner head, although in some arrangements the spinner head could be moved relative to the stationary expose drum means.

To facilitate loading and unloading of a film or plate means from said expose drum means the internal drum plate setter preferably includes a transfer drum means having an external generally cylindrical surface for receiving a film or plate means for exposure, said transfer drum means and said expose drum means being relatively moveable axially, whereby said expose drum means may be moved telescopically over said transfer drum means to allow the transfer of a film or plate means between the external surface of said transfer drum means and the internal surface of said expose drum means.

Advantageously, said expose drum drive means is operable to move said expose drum means over said transfer drum means.

To make efficient use of the expose drum drive means, the rotary axis of the spinner, the transfer drum means and the expose drum means are preferably generally concentric, with the spinner head disposed adjacent to one end of said transfer drum means. In this way, following loading of a film or plate, exposure of the film or plate can begin by moving the expose drum a short distance in the direction of the spinner head. In one arrangement, to increase the throughput of the plate setter and to avoid unnecessary retraces, two matching transfer drums may be provided aligned concentrically, one to either side of the spinner head.

Preferably, said transfer drum means is expandable from a retracted condition in which said transfer drum means and a film or plate means received or wrapped thereon may be received with clearance within said expose drum means, and an expanded condition in which said film or plate means is adjacent or urged against the internal surface of said expose drum means.

For this purpose the transfer drum means may have a resiliently contractible and/or expandable generally cylindrical wall means, and actuator means for expanding and/or contracting said generally cylindrical wall means.

In this instance, said actuator means, the generally cylindrical wall means, and the mountings therefor are preferably selected to maintain substantial concentricity in the expanded and retracted conditions.

The transfer drum means advantageously includes registration means for providing a datum reference on said transfer drum means for a film or plate means to be exposed.

The cylindrical wall means may be longitudinally split and said transfer drum means further include means for maintaining the longitudinal edge regions of said cylindrical wall means generally tangential to a cylindrical envelope when said cylindrical wall means is in its retracted state.

To assist transfer of the film or plate between the transfer and expose drum means, the outer surface of said transfer drum means may be resiliently compressible.

The film or plate may be held in place on the transfer drum means in a variety of ways, for example by various clamp arrangements, but is preferred to employ suction and to provide means for applying suction to the cylindrical surface of said transfer drum means, thereby in use to hold a film or plate against the external cylindrical surface thereof.

Likewise it is preferred to provide means for applying suction to the cylindrical surface of said expose drum means, thereby in use to hold a film or plate against the internal cylindrical surface thereof. In this way, the film or plate means may be transferred between the transfer and expose drum means without requiring release of mechanical clamps.

The image setter preferably includes rotary drive means for rotating said transfer drum means, thereby in use to facilitate wrapping and unwrapping of a film or plate means from the external cylindrical surface thereof, and feed means may be provided for feeding or locating a film or plate to be wrapped onto said transfer drum means, and also for feeding or receiving a film or plate unwrapped from said transfer drum means.

In other arrangements, the expose drum means may be removable from the plate setter in routine use, so that the users can carry and move the drum. The cost of a composite expose drum means and supporting infrastructure will be considerably less than that of the conventional cast iron or granite drums. These two features combined would allow a plate setter to be operated with multiple drums, treating them as cassettes.

In use, the expose drum means may receive a single film or plate for exposure, or it may include two or more in order to improve the duty cycle of the setter.

In another aspect, this invention provides an internal drum plate setter comprising: a rotary spinner head located on a rotary axis; an expose drum means defining an internal cylindrical surface means concentric with said rotary axis for receiving a film or plate means for exposure, and having an open axial end region; a transfer drum means defining an external cylindrical surface means generally concentric with said rotary axis, for receiving and locating a film or plate means for exposure, said transfer drum means and said expose drum means being relatively moveable axially and dimensioned whereby said expose drum means may be moved telescopically over said transfer drum means to allow the transfer of a film or plate means between the external surface of said transfer drum means and the internal surface of said expose drum means.

In a further aspect, the invention provides a method of setting an image on a film or plate using an internal drum image setter having an expose drum means with an internal cylindrical or part-cylindrical surface, which comprises providing a transfer drum means of substantially cylindrical form capable of fitting telescopically generally within said expose drum means, wrapping a film or plate means to be exposed around the external generally cylindrical surface of said transfer drum means and temporarily retaining it there, introducing said transfer drum means and the wrapped film or plate means into said expose drum means, so that the film or plate means lies adjacent said expose drum means, transferring said film or plate means to the internal cylindrical surface of said expose drum means, and retaining it there.

Preferably, the transfer drum means is fixed longitudinally and the expose drum means moves linearly with respect thereto.

The invention also extends to a method of operating an internal drum plate setter wherein a drum is loaded with a film or plate while off the machine, mounted on the plate setter, exposed, then removed from the machine and the exposed film or plate retrieved. This allows automation of the process, because mechanical handling of a robust drum is easier than precise handling of a flimsy film or plate.

Whilst the invention has been described above, it extends to any inventive combination or subcombination of features set out above or in the following description.

The invention may be performed in various ways, and an embodiment thereof will now be described in detail, by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of part of a first embodiment of an image setter in accordance with this invention; Figure 2 is a cross section view through the part of the image setter of Figure 1; Figures 3 (a) to (c) are views illustrating operation of the machine, at the beginning of the first line of the page, half way along the first line, and when half the page has been written; Figure 4 is a side view of a second embodiment of image setter in accordance with this invention; Figure 5 is an end view on the embodiment of image setter of Figure 4 but omitting the expose drum 30, for clarity, and Figure 6(a) and 6(b) are detailed end views on the transfer drum of the embodiment of Figures 4 and 5, in the expanded and retracted positions, respectively.

Referring initially to Figures 1 and 2, this embodiment of image setter comprises a cylindrical expose drum 10 of stiff, lightweight composite material - in this example of carbon fibre reinforced plastics (CFRP) material - which is extremely light, stiff and dimensionally stable. On the central axis 12 of the expose drum is located a spinner arrangement 14 which comprises a spinner head 16 and a spinner motor 18 which spins the spinner head at a speed typically of between 20,000 and 40,000 rpm. The spinner head includes a mirror 15 at about 450 to the central axis 12, and there is a fixed lens 20 in front of the spinner head. In use a modulated beam is directed along the central axis 12 and reflected to describe a helical scan path as the spinner head rotates and moves axially along the expose drum 10. In use a film or plate 22 is secured around the inside of the expose drum by an expanding clip or a suction arrangement (not shown), and the spinner arrangement 14 driven to scan the beam over the film or plate 22 as seen in Figures 3(a), (b), and (c). In this example the wrap angle is 3200.

In another arrangement two smaller films or plates may be applied to the interior of the expose drum 10.

The expose drum 10 is removably located relative to the spinner arrangement 14 and so can be removed and replaced or exchanged as required. This allows the film(s) or plate(s) 22 to be inserted in or removed from the expose drum 10 when the latter is off the image setter, thus allowing greater access to the expose drum 10.

Referring now to the second embodiment of image setter 24 illustrated in Figures 4 to 6(b), a base indicated generally at 26 supports a transfer drum 28, an expose drum 30 and the expose optics indicated generally at 32. In this embodiment, the transfer drum 28 and the expose optics 32 are longitudinally fixed with respect to the base 26, and the expose drum 30 may shuttle longitudinally between the position shown in Figure 4 and a position in which it completely surrounds the transfer drum 28, for the transfer of a film or plate to be exposed between the transfer drum 28 and the expose drum 30.

The transfer drum 28 comprises a longitudinally split cylindrical wall 34 which is supported at either end and at its mid portion by three support/actuator arrangements 36, each mounted on a common concentric shaft 38. Each support/actuator arrangement 36 comprises a plate 40 secured to the shaft 38. At its upper end, the plate 40 defines a datum or stop 42 for a film or plate to be exposed. At its lower end, the plate 40 supports an inverted channel-shaped flexural support 44, the outward turned edges of which are bonded to the inner surface of the cylindrical wall 34. The free ends 46 of the cylindrical wall 34 are each connected to a respective lever 48 which is pivotally coupled to a link 50 pivoted at its lower end to the plate 40. An actuator 52 (which may be electric, vacuum, pneumatic or hydraulic) is pivotally coupled between the links 48. The placement of the pivot points and the design of the flexural support 42 is selected to maintain concentricity of the cylindrical wall 34 as it moves between the expanded and retracted conditions. In addition, the levers 44 co-operate with the side of the plate 40 to constrain the edge regions of the cylindrical wall 34 to be tangential when the transfer drum is in the retracted condition.

The cylindrical wall 34 is perforated and carries on its outer surface a layer 54 of soft resiliently compressible and air permeable material such as an open cell foam of plastic or rubber. An inner flexible cylindrical wall 56 is provided whereby suction may be applied substantially uniformly over the outer cylindrical surface of the transfer drum. The outer surface of the cylindrical wall need not be resiliently compressible. It may be made of a hard porous material, e.g. porous aluminium expoxy.

The shaft 38 is mounted in bearings 58 and carries a pulley 60 to allow rotation of the transfer drum for loading and unloading of a film or plate.

As can be seen in Figure 5, the embodiment also includes delivery and feed trays 62 and 64 respectively disposed to either side of the transfer drum 28 to deliver or receive films or plates tangentially to or from the drum.

The expose drum 30 is rotationally fixed and mounted on a shuttle 66 constrained for movement along two longitudinal guides 68. A drive 70 is provided for moving the expose drum 30 from the right hand position shown in Figure 4 to a left hand position (not shown) in which it completely surrounds the transfer drum 28. The expose drum is made of a stiff, lightweight composite material, in this example carbon fibre reinforced plastics. The transfer drum 28 may conveniently be made of a similar material although this is not essential. The expose drum 30 comprises an unbroken, continuous cylindrical wall 72 which is perforated and an outer jacket 74 is provided to allow suction to be applied to the internal surface of the expose drum 30.

The optics system 32 comprises a laser 76, deflecting mirrors 78 to cause the laser to follow the path 80 indicated via a lens 82 to a spinner arrangement 84 located on the central rotary axis of the machine. The spinner comprises a mirror located at about 450 and a motor which spins the mirror at an accurately controlled speed of between 20,000 and 40,000 r.p.m. In Figures 4 and 5, the deflecting mirrors 78 and the spinner arrangement 84 are mounted on a common optically rigid support 85 extending down the central region of the expose drum. This does lead to a small loss in the sweep angle where the structure obscures the swept beam, but this is usually not problematic. The spinner arrangement could be mounted on the end of the transfer drum shaft 38 if required.

In use, a film or plate 86 to be exposed is located in the delivery tray 62 and, with the transfer drum 28 in its retracted condition, the drum 28 is rotated to bring the stop 42 into engagement with the upper edge of the plate 70.

Suction is then applied and the transfer drum 28 rotated to wrap the film or plate around the transfer drum. The transfer drum 28 is then stopped and located at a known angular registration position, and the shuttle drive 70 actuated to move the expose drum 30 over the transfer drum 28 to a position in which the expose drum and the transfer drum are in exact longitudinal and angular registration.

With the suction still applied, the actuators 54 are actuated to allow the cylindrical wall 34 to expand to offer the film or plate 86 against the cylindrical wall of the expose drum 30. Suction is then applied to the expose drum 30 whilst that to the transfer drum 28 is switched off, so that the film or plate 86 is now held firmly against the inner cylindrical surface of the expose drum 30 with the photographic emulsion facing inwardly. The actuators 52 are then retracted, thus lifting the cylindrical wall 34(and the resilient surface 54) off the film or plate 86. The shuttle drive 70 is then actuated to move the expose drum 30 and the film or plate 86 rightwardly until the spinner arrangement 84 is level with the first line to be scanned on the film or plate 86. The spinner arrangement 84 and laser 76 are then actuated in synchronism with the shuttle drive 70 to execute the usual fine helical modulated scan over the surface of the film or plate as the expose drum 30 is traversed towards the position seen in Figure 4.

Once the film or plate has been exposed, the shuttle drive 70 is actuated to move the expose drum 30 back over the transfer drum 28 and the above sequence of operations is reversed to transfer the exposed film or plate 70 from the expose drum 30 to the transfer drum 28.

The exposed film or plate may then be released from the transfer drum by removing the suction and a series of rollers (not shown) is provided to feed the exposed film or plate to a processor (not shown) or into the receiving tray 64.

In a modification, to allow actively controlled registration of the film or plate with the expose drum, the system may be provided with sensors 88 on the expose drum which during transfer monitor the position of the film or plate 86 at three positions, two on one side of the film or plate and one on an adjacent side. These signals are supplied to a control loop processor 90 which controls the longitudinal and rotary positions of the transfer drum 28 and its shape, so that the relative position of the film or plate 86 relative to the expose drum 30 may be adjusted in the vertical, horizontal and skew senses. The rotary and longitudinal control movements are provided by a precise motor 92 connected by a suitable drive arrangement to the transfer drum pulley, 60, and by the shuttle motor 70 respectively. For movement in the skew sense, respective shear actuators 94 are provided which can shift or shear the free ends 46 of the cylindrical wall 34 of the transfer drum relative to each other. The shear actuators 94 operate by applying differential longitudinal movement to the links 50 of the support/actuator arrangements 36, by means of shear rods 96.

In use, the transfer drum 28 is loaded with a plate 86 and is positioned in the usual way within the expose drum 30. The signals from the sensors 88 are used by the processor 90 to control the precision motor 92 and the shear actuators 94 to ensure that the film or plate 86 is correctly registered on the expose drum 30. The rotary drive is adjusted so that the rotational position of the film or plate 86 is controlled with respect to one sensor 88. The shear actuators 94 and the shuttle motor 70 are then used to register the two sides of the film or plate in the longitudinal and skew senses. In all, this arrangement provides three degrees of freedom and three positions to establish.

Claims

1. An internal drum plate setter, comprising: a rotary spinner head located on a rotary axis, and an expose drum means defining a substantially unitary internal cylindrical surface concentric with said rotary axis for receiving a film or plate means for exposure, and having an axial end region through which a film or plate means for exposure may be introduced and withdrawn axially.

2. An internal drum plate setter according to Claim 1, wherein said expose drum means is formed wholly or principally of a fibre composite material.

3. An internal drum plate setter according to Claim 2, wherein said expose drum means is formed wholly or principally of carbon fibre reinforced plastics material.

4. An internal drum plate setter according to any of the preceding Claims wherein said expose drum means has a generally continuous unbroken cylindrical wall means defining said substantially unitary internal cylindrical surface.

5. An internal drum plate setter according to any of the preceding Claims, including means mounting said expose drum means for linear movement relative to said spinner head along an axis parallel to said rotary axis, and expose drum drive means for moving said expose drum means relative to said spinner head.

6. An internal drum plate setter according to any of the preceding Claims including a transfer drum means having an external generally cylindrical surface for receiving a film or plate means for exposure, said transfer drum means and said expose drum means being relatively moveable axially, whereby said expose drum means may be moved telescopically over said transfer drum means to allow the transfer of a film or plate means between the external surface of said transfer drum means and the internal surface of said expose drum means.

7. An internal drum plate setter according to Claim 7, when dependent on Claim 6, wherein said expose drum drive means is operable to move said expose drum means over said transfer drum means.

8. An internal drum plate setter according to Claim 7, wherein the rotary axis of the spinner, the transfer drum means and the expose drum means are generally concentric, with the spinner head disposed adjacent one end of said transfer drum means.

9. An internal drum plate setter according to any of Claims 6 to 8, wherein said transfer drum means is expandable from a retracted condition in which said transfer drum means and a film or plate means received or wrapped thereon may be received with clearance within said expose drum means, and an expanded condition in which said film or plate is adjacent or urged against the internal surface of said expose drum means.

10. An internal drum plate setter according to Claim 9, wherein said transfer drum means has a resiliently contractible generally cylindrical wall means and actuator means for contracting said generally cylindrical wall means, and operable to allow expansion thereof.

11. An internal drum plate setter according to Claim 10, wherein said actuator means, the generally cylindrical wall means, and the mountings therefor are selected to maintain substantial concentricity in the expanded and retracted conditions.

12. An internal drum plate setter according to Claim 10 or Claim 11, wherein said transfer drum means includes registration means for providing a datum reference on said transfer drum for a film or plate to be exposed.

13. An internal drum plate setter according to any of Claims 10 to 12, wherein said cylindrical wall means is longitudinally split and said transfer drum means further includes means for maintaining the longitudinal edge regions of said cylindrical wall means generally tangential to a cylindrical envelope when said cylindrical wall means is in its retracted state.

14. An internal drum plate setter according to any of Claims 6 to 13 wherein the outer surface of said transfer drum means is resiliently compressible.

15. An internal drum plate setter according to any of Claims 6 to 14, including means for applying suction to the cylindrical surface of said transfer drum means, thereby in use to hold a film or plate against the external cylindrical surface thereof.

16. An internal drum plate setter according to any of the preceding Claims, including means for applying suction to the cylindrical surface of said expose drum means, thereby in use to hold a film or plate against the internal cylindrical surface thereof.

17. An internal drum plate setter according to Claim 6 or Claim 15 when dependent thereon, including drive means for rotating said transfer drum means, thereby in use to facilitate wrapping and unwrapping of a film or plate means from the external cylindrical surface thereof.

18. An internal drum plate setter according to Claim 17, including feed means for feeding or locating a film or plate means to be wrapped onto said transfer drum means.

19. An internal drum plate setter according to Claim 17 or Claim 18, including feed means for feeding or receiving a film or plate means unwrapped from said transfer drum means.

20. An internal drum plate setter according to Claim 6 or any Claim dependent thereon, including registration means operable during a transfer phase for detecting the position relative to said expose drum means of a film or plate means carried by said transfer drum means, and for controlling relative movement thereof to allow registration of said film or plate means with said expose drum means.

21. An internal drum plate setter according to Claim 20, wherein said registration means includes means for controlling at least one of the relative longitudinal and/or angular positions of said transfer drum means with respect to said expose drum and/or the shape of said transfer drum means during transfer phase.

22. An internal drum plate setter comprising: a rotary spinner head located on a rotary axis; an expose drum means defining an internal cylindrical surface means concentric with said rotary axis for receiving a film or plate for exposure and having an open axial end region; a transfer drum means defining an external cylindrical surface means generally concentric with said rotary axis, for receiving and locating a film or plate means for exposure, said transfer drum means and said expose drum means being relatively moveable axially and dimensioned whereby said expose drum means may be moved telescopically over said transfer drum means to allow the transfer of a film or plate means between the external surface of said transfer drum means and the internal surface of said expose drum means.

23. A method of setting an image on a film or plate means using an internal drum image setter having an expose drum means with an internal cylindrical or part-cylindrical surface, which comprises providing a transfer drum means of substantially cylindrical form capable of fitting telescopically generally within said expose drum means, wrapping a film or plate means to be exposed around the external generally cylindrical surface of said transfer drum means and temporarily retaining it there, introducing said transfer drum means and the wrapped film or plate into said expose drum means, so that the film or plate means lies adjacent said expose drum means, and transferring said film or plate means to the internal cylindrical surface of said expose drum means, and temporarily retaining it there.

24. A method according to Claim 21, wherein the transfer drum means is fixed longitudinally and the expose drum means moves linearly with respect thereto.

25. An internal drum plate setter substantially as hereinbefore described with reference to, and as illustrated in, any of the accompanying drawings.

26. A method substantially as hereinbefore described with reference to any of the accompanying drawings.