CA1272268A - Registration of press to existing pattern - Google Patents

Registration of press to existing pattern

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Publication number
CA1272268A
CA1272268A CA000497220A CA497220A CA1272268A CA 1272268 A CA1272268 A CA 1272268A CA 000497220 A CA000497220 A CA 000497220A CA 497220 A CA497220 A CA 497220A CA 1272268 A CA1272268 A CA 1272268A
Authority
CA
Canada
Prior art keywords
pattern
registration
press
patterning device
preexisting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000497220A
Other languages
French (fr)
Inventor
Robert L. Horst
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Armstrong World Industries Inc
Original Assignee
Armstrong World Industries Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Armstrong World Industries Inc filed Critical Armstrong World Industries Inc
Application granted granted Critical
Publication of CA1272268A publication Critical patent/CA1272268A/en
Expired legal-status Critical Current

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  • Inking, Control Or Cleaning Of Printing Machines (AREA)

Abstract

REGISTRATION OF PRESS TO EXISTING PATTERN

Abstract of the Disclosure A system for registering a punch or pattern press upon a pattern previously laid upon an intermit-tently moving web of material. Two active optical scanners sense the presence of two marks straddling the pattern, and the electrical outputs of the scanners are crosscorrelated by computer to statistically locate the signals representing the center of the marks. The press control then relocates either the press or the web to divide any error on the pattern between the leading and trailing edge of the pattern and thereby achieve visual best-fit registration.

Description

6~3 .

REGISTRATION OF PRESS TO EXISTING PATTERN

Summary of the Invention This invention deals with a process involving registration and more specifically with the registration of a pattern press in regard to a preexisting pattern on an intermittently moving material.
A frequent requirement in the flooring and other industries is the registration of a second process upon a visual pattern already existing upon a web or other piece of material which is moving through the production process. When the second process involves a punch or embossing press, an added requirement is that the second process activate when the web is not moving, but after it has advanced into position, so that the first pattern is properly located. A precise visual fit between the two patterns is required.
Such processes involve the considerable complication of properly aligning the web, with the first pattern upon it, with the apparatus for producing the second pattern. This alignment or registration must occur in two dimensionsl the direction of web motion, called the machine direction, and the web width dimension, the across-machine direction. Of these two, the machine direction is far the worst since it is the direction in which the material is constantly moving with production speeds.

~J;

CBP~7399 A very typical adjustment procedure for such a process is to place a registration mar]c on the web at the same time the first pattern is located, and to use this registration mark to register the second pattern.
The registration mark gives the advantage of being a standard recognizable mark regardless of changes in pattern, and, if the registration mark is beyond the useable area of the web, it may even be a hole in the webO
Such registration marks are usually sensed by mechanical or passive optical devices, the latter operating on either light passing through a punched hole or reflecting from the web and being changed by the passage of the registration mark.
In theory, an optical sensor in cooperation with an electronic control system stops the web in relation to the position of the reyistration mark and the first pattern is therefore aligned with the device producing the second pattern. However, in actual operation a great many factors can change this registration. I, for instance, the system requires the web to stop exactly a certain fraction of a second after the registration mark is recognized, the exact alignment will be affected by variations in such items as motor speeds, stretching or shrinking of the web, process temperature, error in the electronic timing circuit, electrical noise, and even the sharpness of the edge o the registration mark.
For many of these items, for instance, measurement of time and stretching of the web, the error will also be cumulative. With frequently repeating operations a small increase in the elongation of the web would, for example, quickly add up to cause the registration to be visibly in error on subsequent pattern repeats and misregistration or phase error occurs.
Until now, the correction of this type of error has usuallv been the task of an experienced operator who manually adjusted some parameter. In the above example, the operator would adjust the position of the sensor with respect to the patterning apparatus to compensate for the visible error. In reality/ most existing systems require constant operator adjustment to insure that phase error is eliminated and registration is achieved.
The present invention directly attacks the problem of cumulative error and phase error by locating two registration marks associated with the existing pattern and, once the product is in proximity to the patterning device, adjusting the spatial relationship between the registration marks and the patterning device by moving the patterning device or the product, to share any error between the leading and trailing edges of the patterns. In essence, centerline registration is achieved and no substantial accumulation of error can occur because each repeat of the pattern is individually adjusted before the second pattern is applied.
To further enhance the accuracy of this invention, it uses a crosscorrelation technique after optically sensing the position and timing of the two registration marks~ Crosscorrelation, in effect, locates the center of each registration mark and measures the time relationship between marks rather than, as previous systems did, attempting to sense the position of a leading edge of the single mark. The difficulty with sensing the leading edge of an electronic signal is that it actually involves sensing the point at which a particular amplitude or threshold value is reached, and, therefore, depending upon the rise of the slope of the signal, it can vary con-siderably in time. The slope of the leading edge of the signal in such situations as reflection from a printed mark will also vary with the sharpness of the edge of the printed mark. The center of the mark, that is, the location of the peak of the electronic signal is a more precise registration reference, and it is that point ~'7~68 which, in effect, is found when croscorrelation is used.
Actually, in this system the crosscorrelation technique mathematically matches one signal to another signal in a "statistical best~fit" type of comparison and then measures the timing error between them. Since the present invention actually uses two optical signals it ultimately compares the locations of two pattern reference points to precisely determine the pattern location, as opposed to evaluating the less reliable leading edge of a single reference point.
~ The present invention uses two digital line scan cameras as active scanners. The scanner beams move in a synchronized pattern, but are 180 degrees out of phase with each other, The synchronous scans move toward and then away from one another in an exact time and position relationship, so that when the two registration marks are located, one by each scanner, the timing between the marks can be determined.
To do this, the signals from the scanners are continuously crosscorrelated as described above to precisely establish their relative location or phase relationship. The error is then determined, and a press control system adjusts the relationship of the press to the material with the preexisting pattern to exactly center the press between the two registration marks, and the second pattern is then applied.
It can easily be appreciated that if, for instance, the web has stretched one-tenth of an inch between the registration marks, this system will, by centering the pattern, spread that error over the whole pattern, whereas a single registration mark system will cause a maximum error or misregistration o one-tenth inch at the edge of the pattern repeat. Such a visibly obvious error can make an otherwise sa~isfactory product into a reject.
The present invention, by using two registration marks, statistical crosscorrelation of signals, and adjustment of the press iteslf, can significantly increase product yield even under the same error produciny conditions which presently exist. It does so essentially by assuring that the errors will not accumulate and are minimized both within a single pattern repeat and from one repeat to another.
Brief Description of the Drawings The figure is a simplified schematic diagram of the preferred embodiment of the invention.
Detailed Description oE the Invention The figure is a simplified schematic represen-tation o the preferred embodiment of the invention in which embossing system 10 operates upon product 12 with preexisting pattern 1~ upon it. Product 12 is moved intermittently in direction A by conventional methods well known in the art, and is stopped so that press 16, moved vertically by power unit 18, can put a second pattern upon and in register with pattern 14.
Press 16 can also be used in other instances to punch holes in or die-cut product 16, also in register with a preexisting pattern.
To accomplish the desired registration, product 12 is initially supplied with registration marks 20. These may be printed marks or holes punched through product 12, but in either case they are produced simul-taneously with pattern 14 and are therefore already in register with pattern 14. Scanners 22 and 24 are digital line-scan cameras which are oriented such that their beams scan the region of the location of registry marks 20 and react to them.
Scanners 22 and 24 are attached to press 16 by holders 23 and 25. Their optical scans oscillate in synchronism, but exactly out of phase with each other along a line parallel to the direction of travel of product 12. Scanning speed is independent of the speed of the production process. The fixed position of the scanners is determined by the spacing of registry marks 20 and the pattern repeat length.
Scanners 22 and 24 are spaced apart an even ~7~
- 6 ~ CBP~7399 integral number of repeats of the pattern and they are substantially equally spaced on either side of press 16.
Their scanning action is parallel to the movement of registry marks 20, and the scan range must be sufficient S to include all possible errors of web positioning that may occur during normal operation of a production line.
Scanners 22 and 24 are spaced a known distance from the position of press 16 by being physically attached to press 16. Therefore, as they each sense registration marks 20 which have stopped beneath them when pro~uct 12 stops, the timing of the pulse each sensor develops indicates the relative position of the registration marks with respect to the centerline of press 16. If, for instance, the scanning beams are separating and scanner 22 develops an electrical signal from the reflection of light from its registration mark, before scanner 24 does, it is then apparent that the registration mark under scanner 22 is closer to the midpoint of the distance between the scanners than the registration mark under scanner 24. Crosscorrelation of the two pulses provides a measure of the timing difference, or phase error, between pattern 14 of web 12 and press 16 upon which scanners 22 and 24 are mounted.
Press controller 28 then produces a control signal which
2; is sent to press ad~uster 30 which moves press 16 slightly one way or the other, parallel to the direction of product motion, to center the new pattern between the existing registration marks and divide the existing registration error. Once this adjustment is made, press 16 is activated by power unit 18 and the second pattern is placed on product 12.
The present invention uses crosscorrelation to compare the signals from scanners 22 and 24 in order to accurately measure the difference in time between ~he signals.
Crosscorrelator 26, which is available as standard instrumentation, mathematically compares the signals from scanners 22 and 24, and measures the time ~L~7~8 ~ 7 - CBP-7399 difference between them. As described previously, such a system furnishes a more accurate measurement of the time difference between the two signals because it does not compare the times at which the signals reach a certain amplitude level. The present system, instead, compares the whole of each signal to evaluate statistically the time difference between them. A
visual "best-fit" results, which is, of course, the ultimate test of pattern registration of printed, embossed and die-cut media.
The measurement of the time difference between signals from scanners 22 and 24 which results from the operation of crosscorrelator 26 given information on the phase relationship between the "whole" signals. It is then sent to press controller 28 which converts it to a distance for which press 16 must be adjusted. Press controller 28 then activates press adjuster 30 to actually displace press 16 and thus change the spatial relationship between press 16 and product 12 to correct for measured registration error.
The present invention can also be beneficial in some processes although it is impractical to adjust press orientation. If, for instance, web rollers 32 can be reversed, web 12 rather than press 16 can be moved to correct for registration error. However, even in applications in which web 12 cannot be reversed to correct registration, additional forward motion can correct some errors. Moreover, press controller 28 can be replaced with web controller 34 which controls web drive 36, and web controller 34 can adjust web 12 so that the next pattern repeat will be corrected to at least prevent the registration error from repeating and to prevent accumulation o~ error.
The combination of the use of two registration marks to cont~-ol the adjustment of the press or the product permits the present invention to minimize registration error due to variable pattern length.
Additionally, use of crosscorrelation to process the !

~x~

signals from optical scanners eliminates errors that otherwise occur because of variations in signal shapes and the presence of signal noise.
It is to be understood that the form of this invention as shown is merely a preferred embodiment.
Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims.
For instance, the invention could also be used on individual tiles on a production line, in a fashion similar to the web described, and in such a case the sensors could be operated by the edges of the tiles rather than registration marks.
Moreover, the invention could also be used to adjust registration in the direction transverse to the movement of product.

Claims (4)

WHAT IS CLAIMED IS:
1. An apparatus for registering a second pattern with a preexisting pattern on material which is moved to and stopped in proximity to a patterning device which applies the second pattern, comprising:
a first optical scanner viewing a first registration mark related to a preexisting pattern on material and producing an electrical signal related to the location of the first registration mark;
a second optical scanner viewing a second registration mark related to the preexisting pattern and producing an electrical signal related to the location of the second registration mark;
electronic signal processing means, connected to the first and second optical scanners, which acts upon and interprets the signals from the first and second optical scanners, establishes the spatial relationship of the first and second registration marks to a patterning device, and produces a correction signal indicating the spatial adjustment necessary for registration of the patterning device with the preexisting pattern; and patterning device adjustment means connected to the electronic signal processing means and receiving the correction signal, which is connected to and moves the patterning device in relation to the correction signal in order to register it with the preexisting pattern.
2. The registration apparatus of claim 1 wherein the electronic signal processing means includes crosscorrelation means to more accurately determine the relationship between the electronic signals from the first and second optical scanners and their relationship to the patterning device.
3. An apparatus for registering a second pattern with a preexisting pattern on material which is moved to and stopped in proximity to a patterning device which applies the second pattern, comprising:
a first optical scanner viewing a first registration mark related to a preexisting pattern on material and producing an electrical signal related to the location of the first registration mark;
a second optical scanner viewing a second registration mark related to the preexisting pattern and producing an electrical signal related to the location of the second registration mark;
electronic signal processing means, connected to the first and second optical scanners, which acts upon and interprets the signals from the first and second optical scanners, establishes the spatial relationship of the first and second registration marks to the patterning device, and produces a correction signal indicating the spatial adjustment necessary for registration of the patterning device with the preexisting pattern; and material adjustment means connected to the electronic signal processing means and receiving the correction signal, which moves the material in relation to the correction signal in order to register the preexisting pattern with the patterning device.
4. The registration apparatus of claim 1 wherein the electronic signal processing means includes crosscorrelation means to more accurately determine the relationship between the electronic signals from the first and second optical scanners and their relationship to the patterning device.
CA000497220A 1985-04-26 1985-12-10 Registration of press to existing pattern Expired CA1272268A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US72773385A 1985-04-26 1985-04-26
US727,733 1985-04-26

Publications (1)

Publication Number Publication Date
CA1272268A true CA1272268A (en) 1990-07-31

Family

ID=24923824

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000497220A Expired CA1272268A (en) 1985-04-26 1985-12-10 Registration of press to existing pattern

Country Status (1)

Country Link
CA (1) CA1272268A (en)

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