GB2271744A

GB2271744A - Registration in printing and other operations.

Info

Publication number: GB2271744A
Application number: GB9321506A
Authority: GB
Inventors: Leonard Norton-Wayne
Original assignee: De Montfort University
Current assignee: De Montfort University
Priority date: 1992-10-24
Filing date: 1993-10-19
Publication date: 1994-04-27
Anticipated expiration: 2013-10-19
Also published as: GB9222380D0; GB9321506D0; GB2271744B

Abstract

There is disclosed a method and apparatus for registering successive operations on a moving substrate (11) in which a register mark is placed during an operation, the movement of which past a sensing arrangement generates a signal indicative of any registration error. A sensor 13 may detect registration marks on a loop of flexible backing web located beneath three printing screens 15 - 17, the substrate passing between the web and screens. The speeds and positions of the screens are controllable in response to the detected out-of-registry of the marks. <IMAGE>

Description

REGISTRATION IN PRINTING AND OTHER OPERATIONS This invention relates to registration in printing and other operations. In multi-colour screen printing inks or dyes or other substances such as adhesive are placed on a substrate such as paper or fabric by a succession of screens which must be in register so that the desired pattern is produced without colours overlapping or leaving gaps.

Conventionally, registration is effected by printing registration marks on the selvedge of fabrics or on the edges of paper webs so that corrections can be made to the orientation of screens during the procedure of setting up the printing machine for a print run. If the registration slips for any reason, visual inspection of the registration marks will reveal the fault and the machine can be stopped and the errant screen or screens adjusted.

Stopping the machine is generally inconvenient should the print for any reason go out of register, as can happen due to bowing of rollers, for example.

Moreover, the out-of-register condition may pass unobserved for some time and, during that time, substandard print will be produced. And the initial setting up procedure is a matter for manual adjustment and further test printing to check if the adjustment has been correct with a further round or rounds of correction if not.

The present invention provides a method which avoids these difficulties.

The invention comprises a method for registering successive operations on a moving substrate in which a register mark is placed during an operation, the movement of which past a sensing arrangement generates a signal indicative of any registration error.

The register mark may be placed in relation to a reference mark and the sensing arrangement may then generate a signal indicative of any error in the position of the register mark in relation to the reference mark. The register and reference marks may be such that a signal generated by movement of the marks by the sewing arrangement is indicative of error both in lateral and lengthwise registration.

The register mark may comprise a feature inclined to the direction of movement of the substrate, detection of a point on which by the sensing arrangement gives an indication of error in lateral and lengthwise registration.

The register mark may comprise a chevron.

The register mark may cooperate with a reference mark which has a feature inclined to the direction of movement of the substrate. The register mark may comprise a chevron and the reference mark comprise a solid triangle nested in the chevron.

The sensing arrangement may comprise an optical sensor.

The register mark may be placed on the substrate.

The substrate may be a web of material carried on a backing web and the register mark may then be placed on the backing web.

The substrate may comprise a web to be printed, the operation being a printing operation. The operation may be a multi-colour screen printing operation, the register marks being applied by the screens. The reference marks may be carried on a backing for the substrate and the register marks also printed on the backing, but the register marks could also be printed on the substrate when the reference marks are carried on the backing.

The register marks may be printed on the substrate by the first-encountered screen and the reference marks printed on the substrate, adjacent the corresponding reference marks, by subsequent screens.

The signal may be used to adjust the registration.

The invention also comprises apparatus for registering successive operations on a moving substrate comprising register mark placing means adapted to place register marks during an operation and a register mark sensing arrangement adapted to generate a signal on movement of a registration mark therepast, such signal being indicative of any registration error.

The sensing arrangement may comprise an optoelectronic arrangement.

Embodiments of apparatus and methods for registering successive operations on a moving substrate will now be described with reference to the accompanying drawings, in which : Figure 1 is a diagrammatic plan view of a multi-colour printing machine adapted to the invention; Figure 2 is a diagrammatic side-elevation of the machine of Figure 1; Figure 3 is a view of a group of register and reference marks; Figure 4 is a trace of a signal from an opto electronic device; Figure 5 is a view of a group of register and reference marks showing registration errors; Figure 6 is a trace like Figure 4 for the marks of Figure 5; and Figure 7 is a view of a group of register and reference marks showing how one set of marks can be on a substrate and one on a backing, and an opto electronic sensor arrangement.

The methods for registering successive operations on a moving substrate 11 illustrated in the drawings comprise placing a register mark 12 during an operation the movement of which mark 12 past a sensing arrangement 13 generates a signal indicative of any registration error.

Figures 3, 5 and 7 illustrate the register mark 12 placed in relation to a reference mark 14 so that the sensing arrangement 13 generates a signal indicative of any error in the position of the register mark 12 in relation to the reference mark 14.

Figures 4 and 6 illustrate the signals produced by an opto-electronic sensor as the marks of Figures 3, 5 and 7 pass the sensor, which is aimed at the dashed line L. These figures illustrate signals from a group of three marks which might be used, say, in a threecolour printing press as illustrated in Figures 1 and 2.

Figure 3 shows a group of three marks which indicate that the screens 15,16,17 of the press are in register. The corresponding signals shown in Figure 4 consist of three groups each of three pulses.

The register and reference marks 12,14 are such that the signal generated by movement of the marks 12,14 past the sensing arrangement 13 is indicative of error both in lateral and lengthwise registration. Each register mark 12 comprises a feature inclined to the direction of movement of the substrate 11 - detection of a point on the inclined feature, which extends both in the lateral and the lengthwise direction of the substrate 11, gives an indication of error in lateral and lengthwise registration. As illustrated, the register mark 12 comprises two oppositely inclined line features in the form of a chevron.

It would be possible to detect both lateral and lengthwise registration error from the chevron alone.

The chevron is sensed twice by the opto sensor, once as each line of it passes the sensor. Any error in lateral registration will be revealed as a difference in the interval between the two signals produced by passing the sensor. Any error in lengthwise registration will be manifest as an error in the time of the mid-point of the interval between the two signals.

However, even for a significant lengthwise registration error, the error in the time of passage of the mid-point will, in a conventional screen printing machine, be very small compared to the interval between successive register marks from one cylinder and it is preferred that the register mark 12 cooperates with a reference mark 14 which also has a feature inclined to the direction of movement of the substrate 11. The reference mark 14 as illustrated comprises a solid triangle nested in the chevron register mark.

The signal as illustrated in Figures 4 and 6 now comprises three sets each of pulses, the outer pulses being derived from the register mark 12, the inner, longer, pulse from the reference mark 14. When everything is in register, each set of three pulses is symmetrical. When, as illustrated in regard to the middle reference/register mark 12,14 of Figure 5, there is an error in lengthwise registration, the set of pulses (middle set, Figure 6) is asymmetric.

When, as illustrated in regard to the right hand register/reference mark 12,14 of Figure 5, there is a lateral error in registration, the chevron 2 is closer to the triangle 14 and the error is manifest in the outer pulses of the signal being closer in time to the inner pulse. Of course, both errors may be present at the same time.

It is possible by appropriate signal processing to derive a measurement of the errors in registration.

The printing machine illustrated in Figures 1 and 2 is a three-colour screen printing machine in which the substrate 11 is carried on a flexible backing web 18 which runs over rollers 19 beneath the three rotary screens 15,16,17. The screens 15,16,17 are driven independently of the rollers 19 (but essentially at a speed which matches the screen peripheral speed to the speed of travel of the web 11) by controllable motors 21 which are controlled from a control unit 22 into which are fed the signals from the sensing arrangement 13.

Any error in lengthwise registration is corrected by the control unit 22 sending an appropriate signal to the appropriate motor 21 to speed it up or slow it down fractionally and momentarily in order to bring the screen back into registration. Any error in lateral registration is corrected by the control unit 22 sending an appropriate signal to an axial position adjuster 23 for the appropriate screen.

The sensing arrangement 13 is depicted in Figures 1 and 2 as being deployed by the backing web 18, the register and reference marks 12,14 being printed on the backing web 18.

For a particular printing machine, the reference marks 14 can be permanently printed on the backing web 18, the register marks 12 alone being printed by the respective screens 15,16,17. However, the reference marks can be printed by the leading screen 15, the other screens 16,17 printing register marks cooperating with the reference marks printed by the first screen 15.

Ink or other marks on the backing web 18 can be wiped clean after sensing if the backing web is of a material such as rubber that permits such erasing.

The marks 12,14 could, however, be made on the substrate 11. In the case of a fabric, the marks would normally be made on a selvedge so as not to appear in the pattern being printed on the fabric.

The register marks 12 can be printed in a selvedge of the substrate 11 while the reference marks 14 are printed on the backing web 18. In such a case, the chevron does not nest so snugly with the triangle and indeed the triangle will not actually fit inside the chevron. However, by using two photo-sensors 13a,13b sensing chevron and triangle respectively along lines La, Lb, as shown in Figure 7, the same kind of signal is produced.

The roles of the marks may be reversed, namely the chevron can be the register mark, the triangle the reference.

While the methods have been described particularly with reference to a screen printing machine, they clearly have application to other kinds of printing machine and indeed to other machines in which substances, for example adhesives, are applied to substrates or in which substrates are treated by exposure to radiation such as ultraviolet radiation for photo-resist preparation.

Claims

1. A method for registering successive operations on a moving substrate in which a register mark is placed during an operation, the movement of which past a sensing arrangement generates a signal indicative of any registration error.

2. A method according to claim 1, in which the register mark is placed in relation to a reference mark and the sensing arrangement generates a signal indicative of any error in the position of the register mark in relation to the reference mark.

3. A method according to claim 2, in which the register and reference marks are such that a signal generated by movement of the marks past the sensing arrangement is indicative of error both in lateral and lengthwise registration.

4. A method according to any one of claims 1 to 3, in which the register mark comprises a feature inclined to the direction of movement of the substrate, detection of a point on which by the sensing arrangement gives an indication of error in lateral and lengthwise registration.

5. A method according to claim 4, in which the register mark comprises a chevron.

6. A method according to claim 4 or claim 5, in which the register mark cooperates with a reference mark which has a feature inclined to the direction ofmovement of the substrate.

7. A method according to claim 6, in which the register mark comprises a chevron and the reference mark comprises a solid triangle nested in the chevron.

8. A method according to any one of claims 1 to 7, in which the sensing arrangement comprises an optical sensor.

9. A method according to any one of claims 1 to 8, in which the register mark is placed on the substrate.

10. A method according to any one of claims 1 to 8, in which the substrate is a web of material carried on a backing web and the register mark is placed on the backing web.

11. A method according to any one of claims 1 to 10, in which the substrate comprises a web to be printed and the operation is a printing operation.

12. A method according to claim 11, in which the operation is a multi-colour screen printing operation and the register marks are applied by the screens.

13. A method according to claim 12, in which the reference marks are carried on a backing for the substrate and the register marks are also printed on the backing.

14. A method according to claim 12, in which the reference marks are carried on a backing and the register marks are printed on the substrate.

15. A method according to claim 12, in which the register marks are printed on the substrate by the firstencountered screen and the reference marks are printed on the substrate, adjacent the corresponding reference marks, by subsequent screens.

16. A method according to any one of claims 1 to 15, in which the signal is used to adjust the registration.

17. Apparatus for registering successive operations on a moving substrate comprising register mark placing means adapted to place register marks during an operation and a register mark sensing arrangement adapted to generate a signal on movement of a registration mark therepast, such signal being indicative of any registration error.

18. Apparatus according to claim 17, in which said sensing arrangement comprises an opto-electronic arrangement.