GB1588965A

GB1588965A - Detecting register marks on moving webs

Info

Publication number: GB1588965A
Application number: GB3714576A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-11-04
Filing date: 1977-11-04
Publication date: 1981-05-07

Description

(54) DETECTING REGISTER MARKS ON MOVING WEBS (71) I, KENNETH ARTHUR ROBINSON, a British Subject of 124 Upper Way, Upper Longdon, Rugeley, Staffordshire, England, do hereby declare the invention for which I pray that a Patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement : This invention relates to detecting register marks on moving webs.

In the manufacture of, for example paper, a commonly used method involves the production of a continuous web which at subsequent stages in processing, it is necessary or desirable to cut into sheets or lengths of predetermined size.

To many types of paper made in web form, identification marks are applied to the web at predetermined intervals along the length of the web, which intervals may be varied according to the particular requirements. One such form of identification mark, which on the eventual sheet can be recognised and identified visually or by instruments, is an impression made in the web whereby the section of the web is changed, i.e. the thickness of the paper is changed with consequent changes in the light transmission and/or reflection characteristics of the web at the impression. The general term for such impressions is "watermarking patterns" or "watermarks" and the are commonly found in banknote paper, fine writing paper etc. Alternatively, the identification mark may be in the form of a printed pattern or wording.

When the web is cut into the predetermined lengths or sheets it is usually necessary or desirable that the identification marks are positioned in a specific location on each length or sheet of paper. For this purpose, it is conventional to use a register mark applied to the web at regular intervals as a means for triggering, for example, a severing operation.

It is also advantageous to be able to use register mark positions both laterally and along the length of the web immediately after the paper has been made. This enables dimensional corrections to be made to earlier parts of the process to maintain accurate paper dimensions.

Using presently available techniques, it is difficult to trigger e.g. a severing operation on the web by using the identification marks as register marks. This is generally because the identification marks are large in area, and/or complicated in their design, and difficulty is encountered in the selection of a specific portion of the identification mark which will, and will alone trigger the severing operation as that specific portion of each identification mark in turn passes a predetermined point. Additionally, where the identification marks are in the form of "watermarks", an imperfect impression may be made which may result in a failure to trigger a required severing operation, or possibly even cause an undesired severing operation to be triggered.

For these reasons, it has been the practice for the manufacture to apply specific register marks at the edge margin of the paper web in addition to, and in a fixed relationship with, the identification marks.

These register marks are then used as a reference position for cutting the web into sheets as the web travels through the cutting machine. Usually, the register marks are themselves in the form of watermarks.

A commonly used method of identifying register marks is to use a tungsten filament lamp as a radiant energy source and a photoelectric cell or photo-diode as an energy sensing device. The sensing device responds to changes in the level or intensity of radiation being received by it, and may be placed relative to the web of material either on the same side as the radiant energy source, or on the opposite side, depending on whether the sensing device is to be responsive to change in reflected or transmitted radiation. Thus, when a register mark occurs in the web, a corresponding change in energy intensity is observed by the sensing device. Normallv the sensing device converts the energy it receives into an electrical signal which is amplified, for example, by means of an electronic circuit which is arranged to give an electrical response at its output only when the energy level on the sensing device falls to or rises by a predetermined level such as would be caused by a register mark. The output of the electronic circuit is then normally used to control the action of the cutting machine by means known in the art, and relatively accurate cutting is maintained.

Such single sensor systems are often combined with optical devices such as lenses to assist in sensing the energy changes.

Being smaller and simpler than the identification marks, the register marks may be used to trigger a severing operation, or dimensional correction to an earlier part of the process, relatively reliably. However, where the register marks are themselves in the form of watermarks, even these at times may be imperfectly applied.

For example, where parts of the impression are missing, the level or intensity of radiation transmitted through or reflected from the web may show little or no change compared with the surrounding sheet.

Additionally, the web of paper may contain flaws or even holes at the edge margin which would cause the energy change received by a sensor to be similar to that caused by a register mark. This in turn causes the electronic circuit to give output responses to such flaws. Thus, even where separately-applied register marks are used, even these may at times result in a failure to trigger a required operation or may cause an undesired operation to be triggered, although the occurrence of this is generally less frequent than would be the case where the identification marks are used as register marks.

According to this invention there is provided apparatus for sensing the presence of register marks in a moving web of material, radiant energy being applied to the web from one side thereof, said apparatus comprising: (a) a plurality of sensor units, each located at or comprising a part located at a fixed position adjacent to the path of the web, across which fixed positions the register marks will in turn pass, said sensor units being operative, in response to the radiation transmitted from areas of the web as they pass across said fixed position to provide an output dependent upon the level of such radiation, and (b) a trigger device adapted to provide a trigger signal when the outputs of a minimum of two of the sensor units increase or decrease by more than a predetermined amount, in response to the passage thereacross of a single register mark.

Thus, the sensor units may be disposed in a pattern corresponding to that of the register marks. By producing a trigger signal only when at least two sensor units are activated, the possibility of activating for example a severing operation by a flaw in a web, and also the possibility of failing to activate such an operation by an incomplete register mark, may be reduced.

In its simplest form, where the register mark is provided by a straight watermark extending a short distance inwardly from a side edge of the web (e.g. at right angles to the side edge) the sensor units will similarly be disposed, and a correctly applied register mark will pass over all the sensor units simultaneously, causing a response in all of them, and hence will cause the trigger device to generate a trigger signal. It is however feasible for the sensor units to be in a staggered disposition in relation to the register mark, activation of the trigger device being caused when at least two sensor units are activated in correct sequence.

It is also possible for the register mark to be other than a straight line, and indeed can be of any shape, provided that it is possible to use a sufficiently large part of the register mark to cause the sensor units to respond as aforesaid. Thus, it is possible, rather than to use specifically applied register marks, to use the identification marks as register marks. In such circumstances, a plurality of sensor units will be disposed in a pattern corresponding to that of or that of part of the identification mark, production of a trigger signal by the trigger device being caused by activation of the sensor units (or at least two of the sensor units) when each identification mark or part thereof passes across the sensor units. Care must however be taken to ensure that the pattern in which the sensor units is disposed, together with the specified minimum number needed to cause activation of the trigger device, is not such as will or will be likely to cause the generation of a trigger signal other than at the desired times.

The sensor units may be arranged to be responsive to radiation reflected from the web, or to radiation passing through the web, in which latter circumstances the sensor units will be located on the side of the web opposite to that to which the radiant energy is applied. Conveniently the sensor units are each adapted to provide an output signal proportional to the level of radiation transmitted from the web, the device being adapted to provide a trigger signal when the output signals provided by said specified minimum number of the sensor units decrease from a normal level by more than a predetermined amount. Conversely however, the trigger device may be adapted to provide a trigger signal when the output signals provided by said specified minimum number of the sensor units increase from a normal level by more than a predetermined amount.

The apparatus preferably comprises means to apply radiant energy to the web, conveniently being in the form of a light source. Thus, each sensor unit may comprise a photocell responsive to radiation transmitted from the web as it passes across one of said positions. Conveniently, the photocells are remote from the web, radiation transmitted from the web as it passes across each of said positions being conducted to one of the photocells by the fibre-optic means.

Advantageously, the output provided by each sensor unit is fed to an amplification unit comprising means to produce output signals having predetermined, substantially uniform average levels, irrespective of the sensitivity of the individual sensor units.

In this manner, the average level of the output signals from all the sensor units may be standardised, and conveniently this is effected by the use of an automatic gain control amplifier.

Desirably, the trigger device comprises selection means, which is operable to increase the specified minimum number of sensor units required to cause the trigger device to provide a trigger signal from two to any such greater number as may be desired.

This invention also provides apparatus for triggering a severing operation on a moving web of paper in accordance with watermarks applied to the web, said apparatus comprising: (a) means for directing light on to one side of the web; (b) sensor means for measuring the in tensity of light passing through areas of the web as they pass across a number of positions selected in ac cordance with the shape and size of the watermarks; and (c) a trigger means adapted to provide a trigger signal in response to the sensor means sensing that the inten sity of light passing through at least two such areas of the web has in creased from a normal level by more than a predetermined amount by the passage thereacross of a single water mark.

This invention also provides a method of triggering an operation on a continuous web of material to which register marks have been applied at positions placed along the length thereof, in which: (a) radiant energy is applied to the web; and (b) the energy transmitted from the web is detected at a plurality of positions, across which positions each register mark in turn will pass, the operation being triggered when the energy transmitted at at least two of said positions is detected to have varied by more than a predetermined amount in response to the passage hereacross of a single register mark.

The method set out in the last preceding paragraph is particularly suitable for carrying out an operation such as a cutting operation or a printing operation upon a continuous work of paper. The register marks may be in the form of register print marks, in which case the sensor units may be responsive to a decrease in energy transmitted from the web, as the print mark (or a portion thereof) passes through said position; alternatively the register mark may be in the form of an indentation or indentations, in which case the sensor units may be responsive to an increase or decrease of radiation reflected from the web as the indentation passes through one of said positions; or the register mark may be in the form of a watermark, in which case the sensor units may be responsive to generate a trigger signal as a result of an increase in the passage of radiation through the web as the watermark passes through said fixed position.

The positions may be selected such that a correctly applied watermark will pass over all the positions in sequence. Thus, desirably the trigger means will be responsive to the sensor means to generate a trigger signal as a result of said sensor means sensing that the intensity of light passing through the web at each of at least a specified number of said positions has increased by more than a predetermined amount, and in a correct sequence.

Conveniently the energy transmitted at all said positions is continuously measured by a plurality of sensor units, one corresponding to each position, and the operation to be performed is triggered by a trigger signal which is generated when the energy measured by said specified minimum number of sensor units varies by more than a predetermined amount.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a method which is part of a production process for the manufacture of sheet material from a continuous web thereof, and apparatus for use in carrying out said method. It is to be appreciated that both the method and the apparatus have been selected to illustrate this invention by way of example.

In the accompanying drawings: FIGURE 1 is a schematic perspective view illustrating the use of this invention in its application to the manufacture of a continuous web of paper; FIGURE 2 is a schematic view of electric circuitry of the apparatus; and FlGURE 3 is a view illustrating the voltage levels at various points during use of the apparatus.

The apparatus which is the preferred embodiment of this invention is specifically for sensing the presence of register marks in a moving web 4 of paper, to generate a trigger signal to cause a severing operation to be carried out on the web, in a manner whereby it is ensured that the severing operation is carried out at positions spaced correctly along the length of the web. It will however be appreciated that the apparatus itself, and in particular the principles thereof, may be used to generate trigger signals for causing other operations to be carried out, where similar or analoguous problems arise.

The apparatus comprises an energy source 6, for example in the form of one or more tungsten filament lamps, positioned relative to the moving web so as to direct radiant energy on to one side of the web as it passes the energy source, (see Figure 1).

The apparatus also comprises a plurality of sensor units each comprising receptor means 8 adapted to receive light, and responser means, responsive to the inten sity of light received by the receptor means.

Conveniently, the responser means is in the form of a photodiode 9. or other photoelectric transducer, and if desired the receptor means and the responser means may be integral (e.g. the receptor means being provided by the input aperture of the photodiode). Advantageously however the receptor means is provided by fibreoptic means, serving not only to receive light, but also to transmit such light to responser means situated remote from the receptor means.

The sensor units or at least the receptor means 8 thereof, are positioned relative to the web on the side thereof opposite that against which the energy source 6 directs light, and may be positionally adjusted. However. in use, they will each be located at a fixed position across which a portion of each register mark which is to be recognised will pass, the sensor units being arranged with respect to the web in the same configuration as the register mark. Thus, if the register mark is in a straight line, the sensor units (or receptor means thereof) are placed in a straight line, whilst if the register mark is curved, the sensor units will be placed in fixed positions along a similarly curved line.

Each sensor unit is operative. in response to the radiation transmitted from areas of the web as these areas pass across said fixed positions, to provide an output signal dependent upon the level of such radiation. Thus, where the register marks are in the form of watermarks, the output provided by each sensor unit will increase when a portion of the register mark or other watermark passes across the fixed position corresponding to that sensor unit.

The apparatus also comprises an electronic control unit, the circuit of which is shown schematically in Figure 2, affording a trigger device adapted to provide a trigger signal when the outputs of at least a specified number of at least two of the sensor units increases by more than a predetermined amount. The control unit comprises, for each sensor unit 8, an amplifier comprising an automatic gain control 16 whereby the average level of the outputs of each sensor unit may be amplified to a predetermined level, irrespective of the thickness of the web of material being operated upon, or the sensitivity of the individual sensor units. Thus, when a watermark or flaw passes across one of the fixed positions, causing an increase in the intensity of light falling on the receptor means of one of the sensor units, the output of that sensor unit will increase, the increase being seen in the form of a voltage pulse (points B1, B2, etc., Figure 3).

From the amplifiers, the output signals may be fed to units at which the background voltage is subtracted, producing a positive pulse against a zero voltage background (points C1, C2, etc., Figure 3).

The control unit comprises a logic device 18 into which the outputs of the sensor units (after amplification and any additional smoothing) are fed. The logic device is operative, when simultaneous pulses are present on at least a specified number of the input lines, to generate an output signal which (in the preferred embodiment) is used to trigger a severing operation on the web. Preferably, the logic device has control means, whereby the specified number, to which it is responsive to generate a trigger signal, may be varied.

In the use of the apparatus, each sensor unit will give individual responses to predetermined levels of light, or changes in the level of light, passing through one "strip" of the moving web which that sensor unit is viewing. If a register mark (in the form of a watermark) is a clear and perfect impression, as is indicated by the numeral 10, Figure 1, then at the moment that it is adjacent to the pattern of sensor units, all the sensor units will receive an increase in light energy, to cause output pulses to be applied to the logic device. However, if the water mark is incomplete or imperfect, as is indicated by the numeral 11, not all of the sensor units will so respond and a smaller number of input pulses will be applied to the logic device.

I have found that for the recognition of a watermark it is not necessary that every sensor unit produces a response. It is necessary only that some significant proportion qf the sensor units produce a response. The choice of the proportion of sensor units which must simultaneously respond to cause the logic device to generate a trigger signal varies widely with the material being processed. For paper of a typical thickness, it may be desired to set the proportion to 50% :- with 50% of the sensor units responding, there would be a statistically high probability that a watermark exists adjacent to the sensor units. The probability that defects or flaws (indicated at 12, Figure 1) would cause this 50% of the sensor units to respond is statistically extremely low. In such circumStances, it is, therefore, possible to distinguish relatively incomplete watermarks and to reject relatively large defects and flaws in the web thereby overcoming the defects of single sensor systems.

The correlation required in the sensor units can be adjusted to suit the type of paper passing through apparatus. For paper thicker than the above typical thickness, the size of flaws occuring will usually be smaller, and it is unlikely that any flaw will cause responses from more than 10% of the sensor units simultaneously. Such thicker papers may have very poor register water marks with only 40% of the area of the watermark present, and the correlation level pre-set for the logic device would therefore, advantageously be set on sucb a paper to react to simultaneous responses from say, one fifth of the sensor units, a 20% correlation.

Conversely, paper thinner than the above typical thickness, may have a high flaw content with flaws extending to cover an area equivalent of 50% of the size of a register watermark. Furthermore, on such thin papers the watermark is likely to have not less than 70% of its extent present.

The correlation level would, therefore, be advantageously set to, say 60%.

Many types of paper will be satisfactorily sensed with a fixed correlation of 50% to 50%, but it is advantageous to be able to adjust this setting to suit the varying types of grades of paper being made or processed.

By means of my invention, which involves the use of a plurality of sensor units arranged in the same configuration as the predetermined patterns of register marks (such as watermarks) in a web, connected to a similar plurality of electronic circuits and used in conjunction with a logic device which may be adjusted to react to a pre-settable proportion of simultaneous outputs from the sensor unites, the recognition of incomplete or imperfect predetermined patterns is improved and rejection of the electrical responses caused by flaws and defects is enhanced.

WHAT I CLAIM IS:- 1. Apparatus for sensing the presence of register marks in a moving web of material, radiant energy being applied to the web from one side thereof, said apparatus comprising: (a) a plurality of sensor units, each lo cated at or comprising a part located at a fixed position adjacent to the path of the web, across which fixed positions the register marks will in turn pass, said sensor units being op erative, in response to the radiation transmitted from areas of the web as they pass across said fixed position to provide an output dependent upon the level of such radiation; and (b) a trigger device adapted to provide a trigger signal when the outputs of a minimum of two of the sensor units increase or decrease by more than a predetermined amount, in response to the passage thereacross of a single register mark.

2. Apparatus according to claim 1 wherein the sensor units are responsive to radiation reflected from the web.

3. Apparatus according to claim 1 wherein the sensor units are responsive to radiation passing through the web and are located on the side of the web opposite to that side to which said radiant energy is supplied.

4. Apparatus according to any one of tlle preceding claims wherein the sensor units are each adapted to provide an output signal prpportional to the level of radiation transmitted from the web, the trigger device being adapted to provide a trigger signal when the output signals provided by said specified minimum number of the sensor units decrease from a normal level by more than a predetermined amount.

5. Apparatus according to any one of claims 1, 2 and 3 wherein the sensor units are each adapted to provide an output signal proportioned to the level of radiation transmitted from the web, the trigger device being adapted to provide a trigger signal when the output signals provided by said specified minimum number of the sensor units increase from a normal level by more than a predetermined amount.

6. Apparatus according to any one of the preceding claims comprising means to apply radiant energy to the web, said means being in the form of a light source.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. units will so respond and a smaller number of input pulses will be applied to the logic device. I have found that for the recognition of a watermark it is not necessary that every sensor unit produces a response. It is necessary only that some significant proportion qf the sensor units produce a response. The choice of the proportion of sensor units which must simultaneously respond to cause the logic device to generate a trigger signal varies widely with the material being processed. For paper of a typical thickness, it may be desired to set the proportion to 50% :- with 50% of the sensor units responding, there would be a statistically high probability that a watermark exists adjacent to the sensor units. The probability that defects or flaws (indicated at 12, Figure 1) would cause this 50% of the sensor units to respond is statistically extremely low. In such circumStances, it is, therefore, possible to distinguish relatively incomplete watermarks and to reject relatively large defects and flaws in the web thereby overcoming the defects of single sensor systems. The correlation required in the sensor units can be adjusted to suit the type of paper passing through apparatus. For paper thicker than the above typical thickness, the size of flaws occuring will usually be smaller, and it is unlikely that any flaw will cause responses from more than 10% of the sensor units simultaneously. Such thicker papers may have very poor register water marks with only 40% of the area of the watermark present, and the correlation level pre-set for the logic device would therefore, advantageously be set on sucb a paper to react to simultaneous responses from say, one fifth of the sensor units, a 20% correlation. Conversely, paper thinner than the above typical thickness, may have a high flaw content with flaws extending to cover an area equivalent of 50% of the size of a register watermark. Furthermore, on such thin papers the watermark is likely to have not less than 70% of its extent present. The correlation level would, therefore, be advantageously set to, say 60%. Many types of paper will be satisfactorily sensed with a fixed correlation of 50% to 50%, but it is advantageous to be able to adjust this setting to suit the varying types of grades of paper being made or processed. By means of my invention, which involves the use of a plurality of sensor units arranged in the same configuration as the predetermined patterns of register marks (such as watermarks) in a web, connected to a similar plurality of electronic circuits and used in conjunction with a logic device which may be adjusted to react to a pre-settable proportion of simultaneous outputs from the sensor unites, the recognition of incomplete or imperfect predetermined patterns is improved and rejection of the electrical responses caused by flaws and defects is enhanced. WHAT I CLAIM IS:-

1. Apparatus for sensing the presence of register marks in a moving web of material, radiant energy being applied to the web from one side thereof, said apparatus comprising: (a) a plurality of sensor units, each lo cated at or comprising a part located at a fixed position adjacent to the path of the web, across which fixed positions the register marks will in turn pass, said sensor units being op erative, in response to the radiation transmitted from areas of the web as they pass across said fixed position to provide an output dependent upon the level of such radiation; and (b) a trigger device adapted to provide a trigger signal when the outputs of a minimum of two of the sensor units increase or decrease by more than a predetermined amount, in response to the passage thereacross of a single register mark.

7. Apparatus according to any one of

the preceding claims wherein each sensor unit comprises a photo-transducer responsive to radiation transmitted from the web as it passes across one of said positions.

8. Apparatus according to claim 7 wherein said photo transducers are remote from the web, radiation transmitted from the web at said positions being conducted to the photo cells by fibre-optic means.

9. Apparatus according to any one of the preceding claims wherein the output provided by each sensor unit is a voltage signal proportional to the level of radiation sensed thereby.

10. Appartus according to claim 9 wherein each sensor unit has associated therewith an amplifier into which the output signal from the sensor unit is fed, the amplifiers each being operative to produce an output signal having a predetermined, substantially uniform, average level.

11. Appartus according to any one of the preceding claims wherein the trigger device is selectively operable whereby said specified minimum number of sensor units required to cause the trigger device to provide a trigger signal may be increased.

12. Apparatus for triggering a severing operation on a moving web of paper in accordance with watermarks applied to the web, said apparatus comprising: (a) means for directing light on to one side of the web; (b) sensor means for measuring the in tensity of light passing through areas of the web as they pass across a num ber of positions selected in accordance with the shape and size of the water marks; and (c) trigger means adapted to provide a trigger signal in response to the sen sor means sensing that the intensity of light passing through at least two of such areas of the web has increased from a normal level by more than a predetermined amount by the pas sage thereacross of a single watermark.

13. Apparatus according to claim 12 wherein the sensor means comprises a plurality of sensor units, each of which is responsive to light passing through the web at one of said positions.

14. Apparatus according to one of claims 12 and 13 wherein the positions are selected such that a correctly applied watermark will pass over all the positions simultaneously.

15. Apparatus according to any one of claims 12, 13 and 14 comprising means to increase the specified minimum number.

16. Apparatus according to any one of claims 12, 13, 14 and 15 comprising means to vary said predetermined amount.

17. A method of triggering an operation on a continuous web of material to which register marks have been applied at positions placed along the length thereof, in which: (a) radiant energy is applied to the web; and (b) the energy transmitted from the web is detected at a plurality of positions, across which positions each register mark in turn will pass, the operation being triggered when the energy trans mitted at at least two of said positions is detected to have varied by more than a predetermined amount in re sponse to the passage thereacross of a single register mark.

18. Apparatus for sensing the presence of register marks in a moving web of material, constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of triggering an operation on a continuous web of material to which register marks have been applied at positions spaced along the length thereof, when carried out substantially as hereinbefore described with reference to the accompanying drawings.