WO1996004139A1

WO1996004139A1 - Alignment and affixing of printing plates

Info

Publication number: WO1996004139A1
Application number: PCT/AU1995/000472
Authority: WO
Inventors: Steven John Sneyd; Robert James Wallin; Bengt A. Jonsson
Original assignee: Tetra Pak Manufacturing Pty Ltd
Current assignee: Tetra Pak Manufacturing Pty Ltd
Priority date: 1994-08-05
Filing date: 1995-08-04
Publication date: 1996-02-15
Anticipated expiration: 1997-02-05
Also published as: AUPM731994A0

Abstract

This invention provides an automated process for applying a printing plate (3) onto a printing cylinder (2) including: visually detecting registration markers on the printing plate (3); determining the relative alignment between the printing plate (3) and the printing cylinder (2); adjusting the relative alignment between the plate (3) and the cylinder (2) so as to bring the plate (3) and cylinder (2) into registration; and subsequently applying the plate (3) to the cylinder (2) in registered alignment. The invention also provides a system for applying a printing plate (3) onto a printing cylinder (2) in registered alignement, including: a detection means for visually detecting registration markers on the plate (3); control means responsive to signals from the detection means to detect and adjust the relative alignment between the plate (3) and the cylinder (2); and an applicator means adapted to apply the plate to the cylinder (2) whilst maintaining registration. The invention further provides apparatus for mounting a printing plate (3) onto a printing cylinder (2), including: means for placing the printing plate (3) in registration with a printing cylinder (2); holding means adapted to secure the plate (3) and the cylinder (2) in registration; and an applicator means adapted to apply at least a portion of the plate to the cylinder (2).

Description

ALIGNMENT AND AFFIXING OF PRINTING PLATES FIELD OF THE INVENTION

This invention relates to the alignment and affixing of printing plates on printing cylinders. BACKGROUND TO THE INVENTION

Prior art systems use manual techniques to align and affix printing plates to printing cylinders. These systems are slow, require considerable operator expertise and are prone to produce inferior quality printed products.

In one prior art system the cylinder is suspended horizontally in a frame at operator working height. Positioned above the cylinder is a template of the plate to be applied to the cylinder. The template takes the form of a cylinder with a series of grid markings that are used in the alignment of the printing plate on the printing cylinder. To utilise the grid markings on the template cylinder, the operator views the printing cylinder through a mirror arrangement. The mirror arrangement projects the grid markings on the template cylinder onto the surface of the printing cylinder. The operator places the leading edge of the printing plate onto the printing cylinder and aligns the plate with the projected grid of the template. When the operator is satisfied with the alignment, the plate is pressed onto the surface of the cylinder by hand. Double sided tape, which has been pre-applied to the surface of the cylinder, is often used to affix the plate to the cylinder. The accuracy of alignment is dependent upon and limited by the accuracy and judgement of the operator. It is further limited by parallax errors that occur due to the mirror arrangement that projects the template onto the surface of the printing cylinder. Once the leading edge of the plate is affixed to the cylinder, pressure is applied to the surface of the plate whilst the cylinder is rotated so as to wrap the plate around the circumference of the cylinder and ensure that the plate is affixed. Typically the plate wraps around the circumference of the cylinder so that the trailing edge of the plate is adjacent the leading edge of the plate and thus the plate appears to form a continuum around the cylinder.

Misalignment of the printing plate often occurs after the plate has been initially aligned and the operator is subsequently applying pressure to the plate to affix the plate to the surface of the printing cylinder. Misalignment in this instance arises from slippage between the plate and the cylinder or the between the plate and the double sided tape.

The effects of misalignment are particularly significant in colour printing processes. With colour printing it is necessary to utilise an individual printing cylinder for each colour. Typically five colours may be used in a colour printing process and to utilise these five colours five separate cylinders must be used, with an individual printing plate affixed to each cylinder.

In colour printing where the printing plates on the respective printing cylinders are not accurately aligned with respect to each other and the print medium mis-registration will occur. This form of printing error arises as there is a limit to the accuracy with which an operator can mount a printing plate onto a cylinder.

Some colour printing presses allow for adjustment of one printing cylinder with respect to other printing cylinders in order to compensate for misalignment and thereby minimise mis-registration. However the compensating adjustments that the press can make are limited and are often insufficient to correct the mis¬ registration between all five of the cylinders. When mis-registration cannot be compensated for by adjustments to the printing press it is necessary for the plates to be removed and for the operator to re-apply the printing plates to the cylinders.

A further prior-art printing system has attempted to overcome this problem by using cameras to project alignment targets onto a video display unit. The operator places the leading edge of the printing plate onto the print cylinder and views a video display unit. When the registration markers on the plate are aligned within the targets on the video display unit the operator knows that alignment of the plate falls within acceptable limits. However this system does not adequately address the problems of the first system. It is still labour intensive and time consuming and is still limited by the accuracy of the operator. The plate is still affixed to the cylinder manually and mis-registration from errors in this part of the process still arise. It is therefore an object of the present invention to reduce mis-registration errors that arise in affixing printing plates to printing cylinders.

It is also an object of the present invention to reduce the time and labour required to align and affix printing plates to printing cylinders. It is a further object of the present invention to provide for the automation of the process of aligning and affixing a printing plate to a printing cylinder. SUMMARY OF THE INVENTION

Accordingly, one aspect the present invention provides a system for applying a printing plate to a printing cylinder so as to be in registered alignment, said system including: detection means for visually detecting the position of the said plate; control means responsive to signals from said detection means to: i) determine relative alignment between said plate and said cylinder, and ii) adjust the relative alignment between said plate and said cylinder so as to be in registered alignment; applicator means adapted to apply said plate to said cylinder while maintaining registered alignment between the printing plate and the printing cylinder. Advantageously this system minimises and preferably eliminates operator error which may arise in the process of aligning and affixing a printing plate to a printing cylinder.

Preferably the control means includes a microprocessor which operates a motorised system to effect relative movement between the printing plate and the printing cylinder so as to bring the printing plate and the printing cylinder into registered alignment. It is further preferable that the control means is calibrated with the position of the print cylinder. It is also preferred that the control means utilises feedback signals from the detection means to determine relative alignment between the plate and the cylinder and adjust the relative alignment between the plate and the cylinder so as to be in registered alignment.

Preferably the printing plate is provided with registration markers which are visually detected by the detection means. It is further preferable that the detection means includes one or more cameras focused so as to facilitate detection of the position of the printing plate or registration markers on the printing plate.

According to another aspect of the present invention there is provided an apparatus for applying a printing plate to a printing cylinder, said apparatus including: means for placing the printing plate in registration with a printing cylinder; holding means adapted to secure said plate and said cylinder in registration; and an applicator means adapted to apply at least a portion of said plate to said cylinder wherein said cylinder is positioned intermediate the leading edge and the trailing edge of the plate so that said plate can be applied to said cylinder in a two part process thereby maintaining registration during application of the plate to the cylinder. By utilising a two part application process, one portion of the plate can be applied to the cylinder whilst the other portion of the plate is held in registration with the cylinder. This eliminates or at least minimises operator error in the process of applying printing plates to printing cylinders once registered alignment between the printing plate and the printing cylinder is achieved. Further apparatus of the present invention utilises a table to position a printing plate in registration with a printing cylinder; said table including a separation spanning the width of the table and positioned intermediate opposing ends of the table. In use the printing plate is positioned across the separation so that a leading edge of the plate and a trailing edge of the plate are positioned on opposite sides of the separation. The print cylinder is positioned at the separation in the table so as to facilitate contact between the printing plate and the printing cylinder. A portion of the table is adapted to rotate about an axis substantially parallel to the axis of the print cylinder whereby the plate is wrapped about the surface of the cylinder. Preferably an applicator means applies pressure to the plate to affix the plate to the surface of the cylinder. According to a further aspect the present invention there is provided an automated process for applying a printing plate to a printing cylinder, said process including the steps of: visually detecting registration markers on the plate; determining the relative alignment between the plate and the cylinder; adjusting the relative alignment between the plate and the cylinder so as to bring the printing plate and printing cylinder into registration; and applying said plate onto said cylinder in registered alignment.

Advantageously the present invention enables the speed and efficiency of the process of applying a printing plate to a printing cylinder to be improved and which ensures consistently high quality print is achieved. A further advantage is the reduction in printing waste which arises from the subsequent reduction in printing errors.

BRIEF DESCRIPTION OF THE DRAWINGS Reference is made to the accompanying drawings which illustrate preferred features of the present invention and in which:

Fig. 1 is a schematic side view of one preferred embodiment of the printing plate alignment and affixing apparatus illustrating the vacuum aligning table and the relative movement of the rotational portion of the split table. Fig. 2 is a schematic front view of the table depicting the primary arms supporting a printing cylinder in contact with a printing plate.

Fig. 3 is a schematic top view of the table arrangement showing how the vacuum support portion of the table rotates to enable registration of the printing plate and printing cylinder to be achieved. Fig. 4a-4c are schematic representations showing the cylinder being loaded into the machine.

Fig. 4d-4f are schematic representations of the double sided tape being applied to the cylinder.

Fig. 4g-4h are schematic representations of the applicator roller being brought into contact with the plate.

Fig. 4i is a schematic representation of the applicator roller being rotated about the cylinder so as to affix the first portion fo the plate to the cylinder. Fig. 4j is a schematic representation of the of the cylinder being rotated to apply the portion of the plate clamped to the vacuum table.

Fig. 4k-4l show the cylinder being removed from the apparatus once the plate has been applied to the cylinder. Fig. 5 is a side view of a preferred embodiment of the apparatus showing the rotary vacuum table, the cylinder lift arms, the slew rings for rotating the table and the applicator roller and the cylinder loading mechanism.

Fig. 6 is a front view of a preferred embodiment showing the frame that supports the cameras of the vision system and the tape applicator. Fig. 7 is a top view of a preferred embodiment that shows the rotational centre of the rotational vacuum support table. DESCRIPTION OF THE PREFERRED EMBODIMENT

Features of the preferred embodiment of the present invention will now be discussed with reference to the accompanying drawings. Whilst the preferred embodiment is directed to the application of a flexible printing plate to a printing cylinder, the process and apparatus can be equally utilised in the application of non-flexible printing plates to suitable printing cylinders.

A preferred embodiment of the invention will now be discussed with particular reference to Fig. 1 , Fig. 2 and Fig. 3. The printing plate alignment and affixing apparatus is generally referred to by the reference numeral 1. The printing cylinder is denoted by the numeral 2 whilst the printing plate to be applied to the printing cylinder is referred to by the numeral 3. The printing plate 3 may be a flexible polymer plate, such as a photo polymer plate, or may be a non-flexible printing plate. The metal print cylinder 2 is placed on primary lift arms 16 of the plate applicating apparatus. The arms 16 are adapted to hold the cylinder so that the principal axis 9 of the cylinder lies in a substantially horizontal plane.

Double sided tape may be used to adhere the flexible printing plate 3 to the surface of the printing cylinder 2. To apply this tape to the surface of the printing cylinder it is preferable that the cylinder 2 be loaded onto the apparatus 1 before the printing plate 3 is laid onto the surface of table 4. The table 4 is preferably split so as to comprise two portions or segments

13 and 14 which are separated by a gap 10. One portion of the table 13 is preferably adapted to rotate about the principle axis 9 of the printing cylinder 2.

The portion 13 also preferably carries an applicator roller 11 adapted to apply pressure to the plate 3 so that the plate adheres to the print cylinder 2.

The table 4 also preferably contains a vacuum operated clamping system so as to ensure there is no movement of the plate on the table once the plate has been correctly positioned and aligned. The features of the table 4 will be discussed in greater detail when discussing Figs. 4 to 7 inclusive. Once tape has been applied to the surface of the cylinder 2 the printing plate 3 is placed and positioned on the table 4 by an operator. The leading edge 5 of the plate 3 is positioned on one side of the split 10 in the table and the trailing edge 6 is positioned on the opposite side of the split. In the embodiment depicted the leading edge 5 of the plate lies on portion 13 of the table whilst the trailing edge 6 lies on portion 14 of the table.

The printing plate 3 is then manoeuvred by the operator on the surface of the table to a predetermined position. Where the plate is provided with registration markers the operator positions the plate so that the registration markers are located within the field of view of cameras of a vision system. The vision system will be described in greater detail when discussing Figs. 4a-l and Figs. 5 to 7 inclusive.

The vacuum system within the table 4 is then activated by the operator. The vacuum system serves to temporarily secure the plate 3 in position on the table 4. Securing the plate 3 in position on the table ensures that during the process of bringing the plate and cylinder into registration the plate does not move relative to the table and whilst affixing the plate to the cylinder 2 the plate does not move from registration with the cylinder.

A control system then automatically brings the plate 3 into registered alignment with the printing cylinder 2. For registered alignment to be achieved the control system preferably utilises feedback signals from the vision system. This feedback causes the table 4 on which the plate 3 is positioned to be manoeuvred relative to the axis 9 of the printing cylinder 2 until registered alignment between the plate 3 and the cylinder 2 is achieved. In the preferred embodiment depicted the portion 14 of the table 4 is adapted to undergo rotational movement about a vertical axis 22 so as to achieve registered alignment between the plate 3 and the cylinder 2. Preferably the cylinder 2 is now brought into contact with the plate 3 through the gap or split 10 in the table 4. In one preferred embodiment an applicator roller 11 is brought into contact with the plate 3, so that the plate 3 is positioned between the cylinder 2 and the applicator roller 11. The applicator roller 11 is used to apply pressure to the plate 3 so that it adheres to the cylinder 2.

The applicator roller 11 is preferably mounted on the first segment 13 of the table 4. The segment 13 is adapted to rotate around the principle axis 9 of the cylinder 2. Rotating the first table segment 13 in this manner effects two functions. The first function is that a flexible plate 3 under the action of gravity naturally wraps around the outer surface of the cylinder 2. The second function is that the applicator roller 11 follows the first table segment 13 around the cylinder 2, applying pressure to the plate 3. This pressure ensures that the plate 3, if non-flexible, is wrapped around the cylinder. It also ensures that the plate adheres to the double sided tape 12 on the surface of the cylinder. The first table segment 13 and the applicator roller 11 then return to their home position. The process of applying pressure may then be repeated so that the roller 11 applies pressure to the plate 3 for a second time. In this step the roller 11 maintains pressure on the plate and the cylinder 2 is caused to rotate so as to draw the remainder of the plate located on the second segment of the table 14 onto the cylinder. The plate 3 will automatically wrap around the cylinder 2 as a consequence of the cylinder rotating. The applicator roller 11 applies pressure to the plate so as to affix the plate with the surface of the cylinder 2.

When this process is completed the leading edge 5 and the trailing edge 6 will preferably abut so that the printing plate 3 forms a continuum around the surface of the cylinder 2. When a non-flexible cylinder is used, the plate may be positioned onto the table in the manner described above. However the plate may be affixed to the cylinder by the provision of a lip on either or both the leading and trailing edges of the non-flexible plate. When this system is used, the plate may be positioned relative to the cylinder so that when the 3 is wrapped about the cylinder 2, the lip on the trailing edge will be received within a recess in the cylinder.

The process of applying the remainder of the plate to the cylinder by rotating the cylinder may still be utilised. In this embodiment the applicator roller may operate to assist with wrapping the non-flexible plate around the cylinder. A preferred embodiment will now be discussed with particular reference to Figs. 4a-l and Figs. 5 to 7 inclusive.

The apparatus includes a table 4 mounted on a frame 15. The table is preferably split so as to comprise two portions 13 and 14. The apparatus further includes primary arms 16 which are adapted to receive the printing cylinder 2. Preferably the primary arms 16 are adapted to guide the cylinder 2 into receiving arms 17 of a positioning apparatus 18 preferably in the form of a hydraulic or mechanical lifting means, such as a jack. The receiving arms 17 and the positioning apparatus 18 are positioned vertically below the table 4. Preferably the receiving arms 17 on the apparatus are positioned within the frame 15 such that the axis 9 of the cylinder 2 will be aligned with the gap 10 in the table 4. This process of loading the cylinder onto the apparatus is schematically represented in Figs. 4a to 4c.

The receiving arms 17 preferably contain adjacent rollers 19 on which the cylinder 2 rests. These rollers 19 are driven, preferably by an electric motor. The driven rollers 19 enable the cylinder 2 to rotate so that double sided tape 12 can be applied to the surface of the cylinder and so that the portion of the plate 3 located on the second segment of the table 14 can be transferred onto the surface of the cylinder 2.

The purpose of the positioning apparatus 18 is to move the cylinder 2 into contact with the plate 3. The step is usually performed when vacuum has been applied to the table so as to secure the plate 3 in position on the surface of the table and registered alignment between the cylinder 2 and plate 3 has been achieved.

Double sided tape 12 may be applied to the surface of the cylinder 2 by a tape applicator means 20 which may be suspended from the support frame 15. The applicator means 20 is preferably located adjacent the cylinder and to one end of the cylinder when the cylinder has been positioned adjacent the gap 10 in the table 4

To commence application of the tape, the applicator roller 1 1 is brought into contact with the cylinder 2. The first segment 13 of the table 4 rotates about the axis 9 of the cylinder through an arc, preferably approximately 145 degrees.

This allows the tape applicator apparatus 20 to be positioned in close proximity to the cylinder 2.

Control means may now guide the tape 12 into contact with the cylinder 2 by positioning the tape between the applicator roller 11 and the cylinder 2. The cylinder is caused to rotate by the driven rollers 19 and the applicator means 20 moves across the width of the cylinder 2 so that the tape 12 is applied across the entire width of the surface of the cylinder 2. Once the cylinder 2 has been covered the tape 12 is severed and the applicator means 20 returns to its home position. The tape 12 may be severed by an operator or by a guillotine controlled by the control system. This process is schematically illustrated by figures 4d-4f.

The vision system preferably consists of two cameras 8 mounted on the frame 15. A camera 8 is preferably positioned adjacent each longitudinal edge 31 , 32 of the plate 3. The cameras 8 are focused onto the plate 3 so as to facilitate detection of the registration markers 7 on the plate. in one embodiment of the invention, when an operator places the plate 3 on the table 4, the operator manoeuvres the plate 3 until it is within the field of vision of the cameras 8. This can be achieved in a number of ways, for instance video display units may show the field of view of the cameras 8. Alternatively the plate 3 may have additional positioning markers that are provided on the plate at the operators end of the apparatus. These additional markers may enable the operator to position the plate within a predetermined zone on the table 4, which corresponds to the field of view of the vision system.

Preferably once the markers 7 are within the field of vision of the cameras 8 and the vacuum on the table has been activated to secure the plate to the table, a control system is utilised to position and align the plate 3 relative to the print cylinder 2. The vision system may be interlinked with the control system via a feedback loop. In this way the vision system could be regarded as an integral element of the control system.

Preferably the vision system and the control apparatus are calibrated with respect to the axis 9 of the cylinder 2 as located in the receiving arms 17 of the positioning apparatus 18. This enables the control apparatus to manoeuvre the table 4 so that the plate 3 is aligned in registration with the cylinder 2.

To align the plate 3, the vision system acts to detect the orientation of an actual or imaginary line that extends through cooperating registration markers 7 located adjacent opposing edges of the plate 3. Manoeuvring the vacuum table 4 to which the plate 3 is fixed or clamped will alter the orientation of this line with respect to the axis 9 of the cylinder 2. Registered alignment occurs when this line is parallel with the principal axis 9 of the cylinder 2.

Preferably the registration markers 7 comprise one or more pairs of cooperating markers, preferably in the form of dots. In a preferred arrangement the markers 7 are integrally formed on the surface of the printing plate with one marker 7a adjacent one longitudinal edge of the plate 31 and a cooperating marker 7b located on an opposing longitudinal edge 32 of the plate. It is preferred that the markers are positioned on an upper face of the plate so that a real or imaginary horizontal line can be projected between the pair of markers which can be orientated so as to be parallel with the axis 9 of the cylinder. Preferably a further line extends through one or more of the markers which will be oriented to be perpendicular to the axis 9 of the cylinder.

The vision system is preferably capable of detecting the registration markers in grey scale and on a sub-pixel level. Detecting the markers on this scale enables the control system to determine the orientation of a line of best fit through each horizontal line of the markers. The sub pixel detection of the registration markers will preferably enable the control system to located the plate within ten micro-metres of registration. The control system acts to preferably rotate the table 4 until the orientation of these two lines is parallel with the axis of the cylinder. The table 4 is split so as to comprise two segments 13 and 14, one on either side of the gap 10. The first segment 13 of the table 4 preferably carries an applicator roller 11 and preferably rotates about the axis 9 of the cylinder 2. The second segment 14 of the table 4 preferably contains the vacuum clamping system and preferably rotates within the plane of the table 4 to align the plate 3 with the cylinder 2. Alternatively the second segment 14 of the table 4 may be adapted to perform translationai movement within the plane of the table so as to achieve alignment of the plate with the cylinder.

The first segment 13 of the table 4 preferably allows a portion of the plate, preferably corresponding to approximately seventy degrees of arc, to be located on the cylinder 2 during a first phase of applying the plate to the cylinder. It is preferable that a sufficient amount of plate 3 be affixed to the cylinder 2 so that the plate will not move out of registration under its own weight during a second phase of affixing the plate 3 to the cylinder 2. An amount of plate corresponding to approximately seventy degrees of arc is preferred. This ensures that the plate will not move out of registration under normal conditions.

Any portion of the plate 3 located on the first segment 13 that exceeds ninety degrees will not automatically lie on the cylinder surface when the first segment 13 of the table 4 rotates about the axis 9 of the cylinder 2. It is therefore preferable that the portion of the plate 4 that can be located on the first segment 13 of the table 4 is not greater than ninety degrees.

In a further preferred embodiment the table 4 incorporates an air cushion and air vacuum system. This system will preferably be facilitated by a plurality of air holes distributed across the surface the table 4. This system is preferably located in both the first and second segments 13 & 14 of the table although it may be simply located in the second segment 14.

When the plate 3 is placed onto the table 4 by the operator, preferably air will be blowing through the air holes 33 in the table. This will create an air cushion on which the plate 3 will glide. This assists the operator with positioning the registration markers 7 within the field of view of the cameras 8 .

Once the operator has determined that the registration markers 7 are within the field of vision of the cameras 8, the air cushion is preferably replaced by a vacuum. The vacuum is created between the plate 3 and the table 4 by drawing air from the surface of the table through the air holes 33.

The vacuum effectively operates as a releasable clamp that holds the plate 3 position relative to the table 4 during the first phase of applying the plate to the cylinder. The vacuum in the first segment will preferably be reduced during this first phase. This will allow the plate to slide off the first segment of the table in preference to the second segment. The vacuum preferably remains in place for the second phase of the plate affixing process to ensure that the plate 3 does not move out of registration with the cylinder 2.

The second segment 14 of the table 4 preferably rotates on a turntable 21. The axis of rotation 22 of the turntable 21 is preferably vertical and coincides with the centre of the second segment 14 of the table.

In one preferred embodiment the turntable is rotated by a lead screw 23 that engages a gear positioned in a plane parallel with the upper surface of the table 4. When the lead screw 23 rotates it imparts rotational movement to the table about vertical axis 22.

The control system engages a motor 25 which is coupled to the lead screw 23. The motor 25 drives the lead screw and causes it to turn in response to signals from the control system microprocessor. When the control system, preferably via feedback form the vision system determines that the plate 3 is aligned with axis 9 of the cylinder 2, the control system will halt table rotation. Preferably the gearing ratio between the lead screw 23 and the gear will be selected so that lags in the control system will have minimal effect on the accuracy of the positioning of the table.

The turntable 21 may be located on an x-y table 24. In this embodiment, the table 4, can not only rotate but it can also translate in lateral and longitudinal directions within the plane of the table 4. The x-y table may be of particular assistance when a non-flexible plate is to be applied to a cylinder. The x-y table will enable a lip on the plate to be aligned with a recess in the cylinder, so that when the plate is wrapped around the cylinder, the lip will be received within the recess.

The applicator roller 11 is preferably connected to the first segment 13 of the table 4 so that rotation of the first segment 13 of the table will be accompanied by corresponding rotation of the applicator roller 11. Slew rings 26 may be used to effect rotation of the first segment the table. The slew rings 26 are preferably mounted onto the support frame 15 and they are preferably crescent shaped so that the cylinder 2 can be received axially within the slew rings 26.

The first segment preferably 13 of the table preferably rotates about an axis 27 that is parallel and preferably displaced from the principle axis 9 of the cylinder 2 as shown in Fig. 1. The displacement between the axes 9 and 27 is preferably equal to the radius of the applicator roller 11. This ensures that the applicator roller maintains even pressure of the plate as it rotates about the cylinder.

It is preferable for the applicator roller 11 to extend the width of the cylinder 2. It is also preferably supported at either end by positioning arms 28 as depicted in Fig. 1. The positioning arms 28 are preferably pivotally connected to the first segment 13 of the table 4 adjacent the leading edge 5 of the plate 3. Preferably an extending arm 29 elevated off the surface of the table by a support member 30 engages the positioning arm mid way along its length. Preferably the extending arm 29 is hydraulic. By extending the hydraulic arm 29 the applicator roller 11 is brought into contact with the plate 3. Retracting the hydraulic arm 29 brings the applicator roller 11 out of contact with the plate 3. The control system may engage the extending arms 29 to locate the applicator roller 11 in contact with the plate 3 so that pressure is exerted on the plate 3.

Slew rings preferably operate to rotate the first segment 13 of the table around the cylinder 3. In the preferred embodiment the first segment 13 can rotate through up to one hundred and forty five degrees. As the first segment 13 of the table 4 drops away from its home position gravity will cause the plate 3 to slide off this first segment 13 and to wrap around the cylinder 3. The applicator roller 11 will follow the first segment 13 of the table 4 around the cylinder 2 applying pressure to the plate so that it adheres to the double sided tape 12 on the cylinder 2. This process is preferably repeated to ensure that no air is trapped between the plate and the cylinder. This process is schematically illustrated in Figs. 4g to 4i.

The cylinder 2 may now be rotated by the adjacent 19 rollers on the receiving arm 17 of the positioning apparatus 18. Preferably the applicator roller 11 remains in pressure contact with the plate 3. Rotation of the cylinder 2 draws the portion of the plate 3 that was located on the second segment of the table onto the cylinder 2. As the plate 3 is drawn onto the cylinder 2 , the applicator roller 11 pressures the plate into contact with the double sided tape 12. Application of the plate 3 to the cylinder 2 is now preferably completed and the cylinder may be ejected from the apparatus as shown in figures 4j, 4k and 41.

The present invention affords a significant reduction in the incidence of printing errors and subsequent waste which arises from incorrectly aligning and affixing printing plates to printing cylinders. There is also a notable reduction in the time and labour required to align and affix a printing plate to a printing cylinder. When compared to known methods, the present invention has been shown to provide reductions in the lead time for mounting a photo polymer plate to a printing cylinder of up to 75%.

Claims

THE CLAIMS DFFININΩ THF INVENTION ARE AS FPU OWR-

1. A system for applying a printing plate to a printing cylinder so as to be in registered alignment, said system including: detection means for visually detecting the position of the printing plate; control means responsive to signals from said detection means to: i) determine relative alignment between said plate and said cylinder, and ii) adjust the relative alignment between said plate and said cylinder so as to be in registered alignment; applicator means adapted to apply said plate to said cylinder whilst maintaining registered alignment between the printing plate and the printing cylinder.

2. The system for applying a printing plate to a printing cylinder as claimed in Claim 1 wherein said control means includes a microprocessor which operates a motorised system to effect relative movement between the printing plate and the printing cylinder so as to bring the printing plate and printing cylinder into registered alignment.

3. The system for applying a printing plate to a printing cylinder as claimed in Claim 2 wherein the control means is calibrated with the position of the print cylinder.

4. The system for applying a printing plate to a printing cylinder as claimed in Claim 1 wherein the control means utilises feedback signals from the detection means to determine relative alignment between said plate and said cylinder and adjust the relative alignment between said plate and said cylinder so as to be in registered alignment.

5. The system for applying a printing plate to a printing cylinder as claimed in Claim 1 wherein one or more registration markers are provided on the printing plate which are visually detected by the detection means.

6. The system for applying a printing plate to a printing cylinder as claimed in Claim 1 wherein said detection means includes one or more cameras focused so as to facilitate detection of the position of the printing plate.

7. The system for applying a printing plate to a printing cylinder as claimed in Claim 6 wherein said one or more cameras are focused so as to facilitate detection of registration markers on the printing plate.

8. The system for applying a printing plate to a printing cylinder as claimed in Claim 1 wherein said system includes a table upon which said printing plate is positioned prior to application to said printing cylinder, said table including a vacuum means adapted to hold said printing plate in position on said table during application of at least a portion of the printing plate to the printing cylinder.

9. An apparatus for applying a printing plate to a printing cylinder so as to be in registered alignment, said apparatus including: means for placing the printing plate in registration with the printing cylinder; holding means adapted to secure said printing plate and said printing cylinder in registration; and applicator means adapted to apply at least a portion of said plate to said cylinder wherein said cylinder is positioned intermediate a leading edge and a trailing edge of the plate so that said plate can be applied to said cylinder in a two part process whilst maintaining registered alignment between the plate and the cylinder.

10. An automated process for applying a printing plate to a printing cylinder so as to be in registered alignment, said process including the steps of: visually detecting registration markers on the printing plate; determining the relative alignment between the printing plate and the printing cylinder; adjusting the relative alignment between the plate and the cylinder so as to bring the printing plate and the printing cylinder into registered alignment; and applying said printing plate to said printing cylinder in registered alignment.

1 1. The process as claimed in Claim 10 wherein the printing plate is applied to the printing cylinder in a two part process wherein a first portion of the plate is applied to the cylinder whilst a second portion of the plate is secured in a position so as to be in registration with the cylinder.