GB2154216A - Accurately positioning hole punching station over intermittently forwarded web - Google Patents

Abstract

A web (1) is intermittently fed through a hole-punching station and, whilst the web is stationary, the relative position between a registration mark on the web and the punching station is measured, eg by photodiodes. The punching station is then moved longitudinally, transversely and/or rotationally relative to the stationary web, eg by stepping motors (73, 80, 82) to accurately position it prior to punching apertures in the web. The position of the registration mark may be measured several times prior to punching a hole in the web, eg comprising dry transfer printing characters. An audible and/or visual warning may be given if the punching station is not accurately positioned. <IMAGE>

Description

SPECIFICATION Mechanical treatment of web materials This invention relates to mechanical treatment of web materials.

It is often desired to carry out a mechanical treatment to a sheet material in the form of a continuous web, the position of that mechanical treatment being related to the position of some other treatment previously effected on the web. A common such operation is that of perforating or guillotining a web which has been pre-printed with a sequence of images.

For a considerable while it has been common practice in such circumstances to print, in addition to the desired printing on the web, register or crop marks which can be detected as the web passes through appropriate apparatus, e.g. using optoelectronic devices such as photocell arrangements which are coupled to mechanical devices, e.g. for perforating or guillotining the web. The position or accuracy of such systems is adequate for many purposes but leaves much to be desired. Tolerances oft 1 mm may often be acceptable but where very close tolerances are required, the means heretofore employed become unworkable.

A particular problem arises in the manufacture of perforated dry transfer sheets which are to be used with alignment systems. British Patent Specifications Nos. 2007154 and 2013573, the whole of the disclosures of which are incorporated herein by this reference, describe alignment systems for use in sign-making which uses a sheet of dry transfer material in which successive lines of letters are spaced from one another by integral multiples of a unit distance and wherein the sheets may be mounted on a suitable apparatus. In order that sheets may be interchanged during use of such a device, it is necessary to provide some sort of registration system such as a pin registration system on the device over which the dry transfer sheets may engage. Such a system is shown specifically in Specification 2013573.It is therefore necessary to provide apertures in the dry transfer sheet accurately positioned with respect to the printed lines of letters and other symbols thereon.

It is possible to prepare such sheets by prepunching sheets of carrier film and laying them up accurately on register pins on a hand bench where they are screen printed. Such a method is very cumbersome and time consuming and the number of sheets which can be economically produced this way is very small. This accordingly substantially increases the cost of the sheets which is disadvantageous. It is far more advantageous to print sheets in continuous web form, and then cut them up into sheet form. The problem arises of cutting apertures in the sheets in precisely the right positions to fit overthe register pins or the like.

According to a first feature of the present inven- tion there is provided a method of carrying out a mechanical operation on a web at a precise position relative to a marking on the web which comprises feeding the web intermittently through a mechanical treatment station, and during each period when the web is stationary at the station, measuring the relative position and orientation of the mark on the web relative to the station, using the measured values to move the station to the desired orientation, and causing the mechanical operation to take place.

Preferably the measurement of the difference between the desired position of the mark relative to the station and the actual position of the mark relative to the station is measured more than once, the station being moved each time in accordance with the deviations, until the deviations are below a predetermined level.

The mark is preferably of substantial extent in order to give accuracy of measurement and positioning and the measurement means associated with the station are most preferably arranged to measure the difference between actual and desired relative positions in two mutually perpendicular directions of translation and as an angle representing the degree of rotation necessary to align the mark with the station appropriately.

In the case of a pre-printed web, spaced registration marks generally lying at the vertices of a right-angled triangle are conveniently used. In order to secure high accuracy, the marks are preferably sensed optically by high accuracy positional sensors. The preferred system is to use a linear photodiode array on to which an image of the register mark is directed. Using integrated circuit fabrication techniques, the distance between one photodiode and the next may be made very small and accordingly very small changes in position may be accurately monitored. Such monitoring may take place automatically and extremely rapidly by appropriate electronics. Photodiode arrays for positional measurement are known and are widely used into opto-electronic industrial control systems. They are commercially available, for example, from Integrated Photomatrix Limited of Dorchester, Dorest.

The web treatment method described above is of particularvalue in punching register apertures in preprinted webs which are subsequently sheeted to form sheets of dry transfer material for use in apparatus in which the relative position of the printing and the register apertures is critical.

Thus, according to a particular feature of the present invention there is provided apparatus for repetitively punching a pre-printed web of material, the web having a series of identical images preprinted thereon and register marks printed in association with each such pre-printed image, wherein the apparatus comprises a punching station, means for feeding the web intermittently through the punching station and for stopping the web while a punching operation is carried out, means fixed to the punching station and adapted to detect the actual positions of register marks and to compare these with stored positions corresponding to the desired relative positioning between the printed image and the punching station, means for converting the comparisons into two translational and one rotational adjustment of the position of the punching station relative to the web, means for effecting movement of the punching station relative to the web in accord ance with the converted values and means for actuating the punching station to punch two or more apertures in the web.

Preferably the measurement and evaluation is carried out both before and after the punching station is moved relative to the web, punching only being effected when the correction values generated after one such evaluation lie below predetermined tolerances.

Preferably the positions of the register marks are detected by photodiode arrays as indicated above.

Preferably the punch unit consists of a base and a punch mounted thereon and normally positioned to define a path through which the web may be passed.

The base is, itself, preferably mounted on a rotary bearing in turn set on a suitable su b-base which can be moved in two perpendicular directions. Movement of the rotary bearing and of the base relative to the sub-base is preferably effected by stepper motors using appropriate gearing to enable adjust mentofposition by very small amounts. Such gearing and any linkages associated therewith should, of course, be free of backlash.

It is naturally necessary to provide that the intermittent drive to the web is only actuated following a punching operation but this may be obtained by appropriate control interlock mechanisms known as such. While the web is stationary, means must be provided to hold it quite still to allow the punch to move to the desired position.

Means may be provided associated with the electronic control of such apparatus to give an audible and visible warning if the difference between desired and actual positions of the printing relative to the punch is greater than the maximum amount of movement which the punch station may undergo.

Such a set of circumstances may automatically stop the apparatus which otherwise may run continuously automatically.

The apparatus may consist of conventional web unreeling and take-up mechanisms, including means for separating the pre-printed web from a strip of interleaving release paper if the web has been reeled with release paper following the application of adhesive thereto.

In such dry transfer punching apparatus, care should be taken in handling the printed and possibly adhesed web of dry transfer material in order to prevent damage to the printed letters. Contamination by stamping wastes should be avoided, e.g. by arranging for pneumatic collection of the stamped out portions. In addition, it is preferable to ensure that the contact of parts of the apparatus with the printed (and possibly adhesed) side of the web is minimised, particularly sliding contact. In particular, means may be provided to lift the web from a table constituting the punch base during its movement. A convenient method of achieving this is to perforate the punch base and blow air up through that base while the web is being advanced through the punching station after one image has had punch marks associated therewith made and while the next image is being brought into position.

While the web may, if desired, be re-reeled, it is convenient, since the machine operates on an intermittent basis, to provide downstream of the punching station a guillotining station which cuts the web into sheets. Internally there will be an adequate margin between successive images on the web to enable the guillotining operation to operate between successive images without difficultly and without any special precautions to keep it in position. The automatic accurate positioning of the web just upstream from the guillotining station avoids any major departures in longitudinal position along the web of the material presented each time the guillotine is operated.

The invention is illustrated by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic plan of a section of a pre-printed web showing successive sheets of dry transfer material printed thereon and showing the position of register marks printed therewith and the desired approximate position of perforations.

Figure 2 is a diagram showing the relative positions of actual register marks and notional register marks.

Figure 3 is a diagrammatic side view of a punching and guillotining apparatus for use with a pre-printed web of dry transfer material, and Figure 4 is a diagrammatic side view of the punching station of the apparatus shown in Figure 3.

Referring to Figure 1, this shows a web 1 having on it successive printed areas corresponding to a dry transfer sheet, successive areas being designated 2, 3 and 4. Only parts of areas 2 and 4 are visible.

As shown, area 3 consists of two halves 5 and 6, one printed upside down with respect to the other.

Between them there is a blank space 7 into which two perforations 8 and 9 are to be made. At each end of blank space 7 there is a register mark 10, 11 and corner register marks 12,13, 14 and 15 are associated with each area 3.

In order for the sheet to be useful in connection with a mechanical alignment system, it is necessary that the positions of perforations 8 and 9 are made accurately both translationery and rotationally relative to the registration marks.

Referring now to Figure 2, this shows in plan diagrammatically a typical difference between the actual positions of register marks 10, 11 and 12 on a web which can be thought of as brought to rest at a punching station, and the positions which those marks ought to be in if the punches at the punching station were punching holes in the correct position.

These theoretical register mark positions are denoted 16,17 and 18. As can be seen, the centre line of the sheet runs between marks 16 and 17 and a line between marks 16 and 18 is precisely perpendicular to a line between marks 16 and 17.

For the sake of simplicity, the positions can be thought of as being on a standard pair of orthogonal X and Y axes, 19 and 20 respectively, with positions 16 and 17 lying on the Y axis.

The difference between actual and desired positions of the three register marks are denoted 21, 22 and 23 and, from simple simple geometrical considerations it can be seen that in order to bring the two sets of register marks into coincidence, the sheet and punch table need to be moved in the X axis direction by an amount 23, and in the Y axis direction by half the sum of the distances 21 and 22.

Furthermore, if a rotational correction is to be applied by moving the end of an arm centred on the origin where X and Y axes cross and of length half the distance between register marks 10 and 11, it can be seen that the linear distance through which the end of that arm is to be moved is approximately half the difference between distance 21 and distance 22.

Thus, by measuring the distances 21, 22 and 23, and very simple arithmetic, first order corrections can be evaluated which, when applied to the relative position of web and punch which bear the printed register marks and the theoretical positions respectively, the two may be brought into proper alignment. Using the simplified geometrical approach, and using mechanical equipment with inevitable tolerances, it is, of course, desirable to carry out the measurement and evaluation several times until a best position is found with no subsequent improvement being possible within the limits of the apparatus in question.

An apparatus for effecting this is shown in Figures 3 and 4. Referring first to Figure 3, this shows a general arrangement consisting of a machine having a frame 50 including means for suspending a stock reel 51 of pre-printed and adhesed dry transfer material interleaved with release paper. Working from left to right, the apparatus has a separating station for printed web and release paper 52, a punching station 53 through which the printed web, which is denoted 54, is fed, a re-combination station 55 at which the punched web and release paper strip are brought together again, a guillotine 56 and a sheet stacker 57. The web 54 is securely guided upstream and downstream of the punching station 53 by means of suitable rollers and driven by a suitable electric motor, not shown.

Associated with the punching station 53 is a photocell 55 arranged to detect the passage of the register marks near the edge of the sheet. By suitable control means, it is arranged that the web is driven at high speed until the corner registration mark at the trailing edge of the just punched area 3 is detected by photocell 55, whereafter the transport speed is slowed down until the adjacent register mark is detected by the photocell whereon the web is stopped. At that position, the web is positioned with a area of printing located in the punching station but due to printing tolerances not precisely in the right position relative to the punch.

At this stage, with the web held still in the machine frame 50, the punching station itself is moved.

As can be seen by referring to Figure 4, the punching station consists of a platen 60 having mounted therein dies 61. These cooperate with punch member 62, each of which is mounted on a press head 63, which is accurately mounted for sliding movement relative to base 60. The vertical position of press head 63 is controlled by a hydraulic cylinder 64, actuated in customary fashion. Press head 63 carries three light sources 65, which each project a parallel beam of light downwardly through apertures in base 60 towards the lens of cameras 66 located fixedly mounted on base 60. In the focal plane of each camera there is located a photo-diode array on to which an image or a register mark located below each light source 65 when an image bearing area 3 is roughly in the right position to be punched is projected.

Base 60 is mounted on a large diameter rotary bearing 70, the base being mounted on the outer of two concentric shells forming the bearings. The inner is mounted on a base plate 72. Fixed to base plate 72 is stepping motor 73 having an output gearing connected to a shaft 74 which is pivotally connected to the external shell of bearing 70.

Accordingly, by longitudinal movement of bar 74, base plate 60 may be caused to rotate relative to base plate 72.

Base plate 72 is itself mounted on a sub-base 76 in such a fashion that it is capable of moving in the direction of arrow 77 or 78, these directions corresponding to the longitudinal and transverse directions of the web 54. Sub-base 76 is fixed to frame 50.

Base 72 may be moved relative to sub-base 76 in the direction of arrow 77 by means of a stepper motor 80 and in the direction of arrow 78 by a stepper motor 82, in both cases using appropriate gearing and mechanical connection without backlash.

When a printed area 3 has been brought into position between press head 63 and base 60, and as soon as the web has come to rest, photo diode arrays in cameras 66 are interrogated by suitable electronics to determine the required positional corrections as indicated above. Once the appropriate corrections have been worked out, the electronics sends suitable command signals to stepper motors 73,80 and 82 and once those command signals have been executed the positional comparison is carried out again. If the evaluated corrections are smaller than a predetermined given amount, for example corresponding to less than 3 steps on any of the three stepper motors, then the electronics may emit an enabling signal to appropriate electrohydraulic devices to operate cylinder 64, following which the web may be advanced by one unit.At the same time as cylinder 64 is actuated, guillotine 56 may also be actuated to sheet the web.

The electronics may be programmed to carry out as many positional evaluations and corrections as are necessary to bring the sheet and punch sufficiently accurately into line. If that cannot be effected within a given maximum number of operations, or if the correction desired would be outside the range of possible movement of the punch, an appropriate indication may be given and the apparatus automatically halted.

Although the apparatus described above is particularly dedicated to the punching of holes in preprinted webs of dry transfer material, it will be clearly apparent that a similar apparatus may be constructed and operated to effect any analogous treatment on a web where a subsequent treatment has to be effected accurately positioned relative to a previous treatment.

Claims (12)

1. A method of carrying outa mechanical operation on a web at a precise position relative to a marking on the web which comprises feeding the web intermittently through a mechanical treatment station, and, during each period when the web is stationary at the station, measuring the relative position and orientation of the mark on the web relative to the station, using the measured values to move the station to the desired orientation, and causing the mechanical operation to take place.

2. A method according to claim 1 wherein the measurement of the difference between the desired position of the mark relative to the station and the actual position of the mark relative to the station is measured more than once, and the station is moved each time in accordance with the deviations, until the deviations are below a predetermined level.

3. A method according to claim 1 or 2 wherein the measurement means associated with the station are arranged to measure the difference between actual and desired relative positions in two mutually perpendicular directions of translation and as an angle representing the degree of rotation necessary to align the mark with the station appropriately.

4. A method of carrying out a mechanical operation on a web at a precise position substantially as hereinbefore described with reference to the accompanying drawings.

5. Apparatus for repetitively punching a preprinted web of material, the web having a series of identical images pre-printed thereon and register marks printed in association with each such preprinted image, wherein the apparatus comprises a punching station, means for feeding the web intermittently through the punching station and for stopping the web while a punching operation is carried out, means fixed to the punching station and adapted to detect the actual positions of register marks and to compare these with stored positions corresponding to the desired relative positioning between the printed image and the punching station, means for converting the comparisons into two translational and one rotational adjustment of the position of the punching station relative to the web, means for effecting movement of the punching station relative to the web in accordance with the converted values and means for actuating the punching station to punch two or more apertures in the web.

6. Apparatus according to claim 5 and including means for carrying out the measurement and evaluation both before and after the punching station is moved relative to the web, and for effecting punching only when the correction values generated after one such evaluation lie below predetermined tolerances.

7. Apparatus according to claim 5 or 6 and including photodiode arrays and associated optical components for detecting the positions of the register marks.

8. Apparatus according to claim 5,6 or7 wherein the punch unit consists of a base and a punch mounted thereon and normally positioned to define a path between them through which the web passes.

9. Apparatus according to claim 8 wherein the base is mounted on a rotary bearing, the bearing being set on a sub-base which can be moved in two perpendicular directions.

10. Apparatus according to claim 9 and including stepper motors and appropriate gearing to enable adjustment of the position of the bearing and base by very small amounts.

11. Apparatus according to any one of claims 5 to 10 and including means forming part of electronic control means for such apparatus and adapted to give an audible and visible warning if the difference between desired and actual positions of the printing relative to the punch is greater than the maximum amount of movement which the punch station may undergo.

12. Punching apparatus substantially as hereinbefore described with reference to the accompanying drawings.