Printed pattern and embossed pattern registration control system

Abstract

A system is disclosed for securing registration of a patterned embossing roll with a similarly patterned printed moving web. The purpose of the embossing roll is to indent the surface of the printed web in register with the printing in certain designated areas. In one embodiment, a series of randomly spaced register marks on the printed web selvage edge and identically spaced register marks on the embossing roll are viewed by appropriate scanners. Electrical signatures representing the two sets of register marks are generated by the sensors and fed to a signal correlator for comparison. The correlator determines the degree of statistical error between the two signatures and displays this error in the form of a time delay on a CRT (Cathode Ray Tube). If manual registration control is desired, an operator can manually adjust the speed or phase of the embossing roll by observing the peaked wave display on the CRT to bring the roll into a statistical best fit of the embossing pattern with the printed pattern. Automatic control of embossing roll speed and orientation to achieve registration is also possible if the correlator is interfaced with a digital computer and servo correction motors on the embosser drive system. The disclosed system is an improvement over conventional benchmark oriented registration sensing and control systems in that it is capable of continuous error determinations and asynchronous error corrections on demand rather than periodically at the end of pattern length intervals.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of applicant's copending application, Ser. No. 343,569, filed Mar. 21, 1973 and entitled "Printed Pattern and Embossed Pattern Registration Control System", now abandoned.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to, but not limited to, an embossing process for a pattern printed sheet and, more particularly, to a process and apparatus for securing registration between a patterned embossing roll and a similarly patterned printed web.

2. Description of the Prior Art

Current practice in automatic registration control is summarized in a recent article entitled "Web Controls: The State of the Art," by Geoffrey L. Phillips, in the "Gravure" magazine, Volume 17, No. 11, Nov. 1971. This article is then followed by another article which lists various registration control systems produced by different companies. Current practice involves the use of a registration mark at a specific location of each pattern repeat or one mark for several repeats and a cycle-by-cycle error detection with subsequent pattern phase and/or repeat length corrective action.

A registration system of the conventional type is marketed by Registron, a division of Bobst Champlain, Inc., and is sold as their Model R-500/R-425 system. The system is basically a specialized control system for maintaining printing registration on high-speed, multi-color web printing and converting machines. It has also been applied to embossing type operations. The Registron system consists of a web scanner, a phase micrometer, a correction computer, control station and servo correction motor. The task of each Registron system is to detect any misregister condition with each revolution of the printing cylinder and automatically control a servo correction motor(s) which restores the printing registration in a minimum time without overcorrecting. The need for automatic registration control is created by the web and press variables. Variations in web characteristics such as moisture content, caliber, curl, etc. will all effect the repeat length established by the first printing station. In addition, variations in dryer temperature, impression pressure, infeed tension, press room temperature, humidity, etc. will cause repeat length changes. An accumulation of such repeat length changes, coupled with any short-term register variables, would cause scrap if registration were not controlled.

In the above Registron system, the web scanner views the printed web as it passes under the scanner. As the register mark passes beneath the beam of light that is directed on the web by the web scanner, a pulse is produced. This pulse is compared to a cylinder reference pulse generated by the phase micrometer. The phase micrometer is driven by the printing cylinder. The phase micrometer has two functions. One is to produce a "live" electrical gate which is used to select the proper register target. The other function is to produce the reference pulse as described above. The correction computer is a device which receives the input signals from the web scanner and the phase micrometer and computes the magnitude and direction of the register error. Electrical output signals are generated by the computer to drive a servo correction motor at the proper speed in the proper direction to eliminate the misregister. The control station provides for either the manual or automatic control of both the running register and phase setting during the normal press operation. The way the corrections are actually made is that the output of the computer drives a servo correction motor at a speed proportional to the register error, the rate of register error and the press speed. As the register error is reduced towards zero, the servo correction motor runs slower and slower until at zero error, the servo correction motor is stopped.

The major deficiency of the prior art structures is that register error determinations are made only at specific points in the pattern and, therefore, provide an indication at some single point in time to indicate a change that has occurred over a time span period. This time span period may normally involve anywhere from 9 to 54 inches in web travel.

SUMMARY OF THE INVENTION

Unlike conventional registration systems that provide only periodic register error determinations, the invention described herein provides for continuous, high resolution error determinations. A web of material is passed through normal processing operations until it reaches a point where it has a printed design on the surface thereof, and it is just prior to the time that it is desirable to place an embossed pattern on the web in register with the printed design. Two phototransistor sensors are positioned to view two signature tracks. Both phototransistor sensors are spaced the same distance from the nip of the embossing roll structure. One is positioned to continuously view the moving web, while the other is positioned to continuously view either the circumference of the embossing roll or a signature disc coupled to the embossing roll. For optimum results, both these surfaces are provided with registration tracks. However, it is also possible to use the actual patterns on each surface in place of separate, but pattern-related tracks. As the pattern track changes, reflectivity of the surface changes, and this in turn is sensed by the phototransistor sensors. Since the printed pattern and the embossed pattern are similar, the output of both phototransistor sensors will be similar; moreover, if the object patterns are in register, the electrical signatures will be in time synchronization. The output from the two phototransistor sensors is fed to a statistical correlator which continuously compares the outputs. A very high resolution of error deviation from normal is provided by analysis in real-time of the cross-correlation function, and this then can be used manually or automatically to cause a change in the speed and/or phase of the embossing roll to bring the embossing into register with the printed design on the web.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 of the drawing is a schematic representation of the control system of the invention herein;

FIG. 2 is a showing of the selvage edge of a sheet with register marks;

FIG. 3 is a top view of a repeat pattern and the representation of the electronic signature of the pattern; and

FIG. 4 is a plotting of the correlation of the above-mentioned electronic signatures of the printed pattern and embossing roll.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The schematic representation of the apparatus for carrying out the invention herein is shown in the drawing as FIG. 1. The web being processed in the apparatus of the drawing in a conventional resilient vinyl covering material which has a design printed on the upper surface thereof. The invention is not specifically restricted to resilient vinyl floor covering, but could be used with any web which is moving and has a pattern printed thereon. For example, it could be utilized with a paper, plastic, rubber, etc. web with a part of a design printed thereon by one station of a press and it is now desired to print additional parts of the overall design in register with the first printing. The invention is applicable to the registration of any two moving patterned surfaces if one can be adjusted in relationship to the other. While the invention is shown on the drawing as an embossing roll structure, it is equally applicable to printing structures, etc. as described above.

Web 2 is passed through its appropriate processing steps so as to have on the upper surface thereof a printed design such as that of FIG. 3. The web moves towards an embossing roll assembly 4 which is composed of an embossing roll 6 and a back-up roll 8. The embossing roll 6 is provided with a pattern which is basically the same as that printed on the web 2. It is desired to place the embossed pattern on the roll 6 in register with the similar printed pattern on the web 2. The required registration is secured by the invention herein.

Two phototransistor sensors 12 and 14 are utilized to sense the patterns on the web 2 and the embossing roll 6. The patterns can be a plurality of prior art type register marks 7 which are placed along the edge of the embossing roll 6 and edge (selvage) of web 2 (or back of web 2) as shown in FIG. 2, or they can simply be the printed pattern and embossing roll pattern themselves as shown in FIG. 3 or a specially designed pattern track which is related to the printed pattern on the web 2. The same pattern of register marks or design pattern exists on both the embossing roll or an attendant device and the sheet to be embossed and the drawing shows these patterns on the sheet only. The pattern on the embossing roll will be the same as on the sheet. The phototransistor sensors are placed the same distance from the nip of the embossing roll 6 and the back-up roll 8. This distance may be a physical measurement distance or it can be a time distance in that the sensors are positioned so that the reference marks are in a timed synchronization whereby the reference signals generated are watched at the time registration exists. For example, if the phototransistor sensor 12 scanning the web was positioned 6 inches upstream from the nip of the embossing roll structure 4, then the second phototransistor sensor 14 would be placed 6 inches upstream from the nip of the embossing roll structure as measured along the periphery of the embossing roll 6. The second phototransistor sensor 14 is used to scan the pattern on the embossing roll while the first photo transistor sensor 12 scans the pattern on the moving web to be embossed and both patterns are the same.

The phototransistor sensor is a transistor which is sensitive to variations in light and converts these variations into electrical impulses. An illuminating means is designed to illuminate the areas to be scanned. As the pattern varies, there will be a variation in reflectivity, and this in turn will result in variations in the output signal of the phototransistor sensor. The output of the phototransistor sensor is directly related to the variations in reflectivity of the pattern. Each pattern has its own characteristic variations. The electrical signals of each pattern or the electrical signature of each pattern varies within each repeat length, but will repeat itself with each repeat length. The signal from the register marks 7 on the edge of the web 2 will provide an electrical signature 9 which is basically a straight line with a series of peaks spaced as per the spacing of the register marks (see FIG. 2). The electrical signature for the pattern as shown in FIG. 3 will be the electrical signature 11 as shown therein.

The signals from the two phototransistor sensors are then fed into a digital correlator 16. An example of one such instrument is a Hewlett-Packard Model 3721A Correlator. The phototransistors 12 and 14 transmit their varying output to the correlator. The correlator continuously calculates and updates the cross-correlation function of the two input signals. Briefly, this means that the correlator operates by repetitively solving the standard statistical equation ##EQU1## and continuously displays on its CRT the most recent values of the correlation coefficient as the function of the time between the two input signals x(t) and y(t). The calculated data are available for manipulation by a digital computer and, also, are displayed on the Cathode Ray Tube (CRT) of the correlator instrument. The point of maximum correlation is indicated on the CRT plot by a maximum (or, under certain conditions, a minimum). Thus, if the pattern signature of one phototransistor sensor is in phase with the pattern signature of another phototransistor sensor, the maximum correlation coefficient is at a time delay of zero. This also means that the embossing roll pattern is going to be in register with the printed pattern at the nip of the embossing roll structure 4 for the case of sensors placed at equal time distances from the nip.

The Hewlett-Packard Model 3721A Correlator, like other cross-correlators; is provided with two input channels A and B which receive the signals to be statistically compared. The phototransistor sensors of this invention are connected to these channels. The correlator is designed to compute the cross-correlation function of the input data. This is the process of establishing a similarity or, in other words, determining the statistical best fit between the data being fed into the machine. The cross-correlation function describes the relationship quantitatively and with respect to time shift between inputs A and B. The correlator continuously computes and displays 100 values of the correlation function. The correlator is constantly receiving new input data and the result is that the correlation function is continuously updated, and the statistical match between the electrical pattern signatures is known in real time period. The 100 value simultaneous comparison can be viewed on the CRT display which is part of the correlator and the operator may use this to manually make registration error corrections. Additionally, the Hewlett-Packard Correlator is designed to be used with a digital computer which provides a means for further data manipulation and automatic control. The Hewlett-Packard Correlator has a program control feature, an interface connection point, for permitting a computer to be interfaced with the correlator so that the error signal generated by the correlator, which is in effect an electronic binary signal representing the material which is displayed on the CRT, can be fed to a digital computer so that the digital computer in turn can operate the necessary correction apparatus to bring the patterns into synchronization.

With a visual readout of the cross-correlation function in the form of a 100 point plot on the CRT display of the correlator 16 as shown in FIG. 4, it is now possible for an operator to see errors in registration and take appropriate manual corrective action. With the correlation maximum displaced to the center of the CRT display by means of a time delay unit 28, it has been demonstrated that an operator can adjust the object pattern devices to be in registry to an accuracy of a few thousandths of an inch. Normally, a zero time delay error without the time delay unit 28, will put the display maximum on the left of the display screen and this would allow errors in one direction only to be viewed for control purposes. In FIG. 4 peak 15 is the time delay comparison maximum, displaced with respect to the zero reference at the center of the display through the use of time delay unit 28. By manually controlling a below described differential transmission in the drive train of the embossing roll, it is possible for an individual line operator to manually control registration by keeping the peak 15 of the display on the vertical cross 17 of the CRT screen.

It is also possible to automatically control registration using the invention herein. For the automatic mode of operation, rather than using the display on the CRT, the correlator will feed its output in the form of a digital data to a conventional digital computer; for example, a computer sold under the trade name of IBM, Hewlett-Packard, etc. The computer is simply hooked into the correlator at the proper computer connection point built into the correlator and this then provides the computer 18 with feed-out data from the correlator. The computer 18 acting upon an appropriate process algorithm and the data .DELTA.t it receives from the correlator and the data (v) from velocity transducer 30 can initiate corrective action f (.DELTA.s) to the embossing roll by means of a servo correction motor and/or motors 20 in the embossing drive train.

The drive train of the embossing structure 4 can be described as follows: A conventional drive motor 22 drives a conventional variable speed transmission 24. The variable speed transmission in turn drives the back-up roll 8 and a differential draw transmission 26 which is connected to and drives the embossing roll 6. The differential draw transmission 26 is typically a Graham transmission or a Fairchild Hiller "Specon" transmission, or the equivalent. This unit has associated with it a correction motor or motors 20 which are used to alter the output speed of the differential transmission 26 to effect registration of the embossing roll 6 with the printed web 2. The correction motor or motors 20 change the speed and/or phase of the embossing roll with respect to the moving web 2 and back-up roll 8 as a result of error determinations and manual operation or computer control calculations. The correction motors are remotely controlled by the operator through manual switches when the apparatus is in the manual mode of operation or by the computer when it is in the automatic mode of operation. Consequently, if the embossing roll 6 is out-of-register with the printed web 2, the embossing roll 6 will either be speed varied (up or down) and/or phase shifted to bring it into register with the printed pattern. A control unit 19 operates the correction motors 20 and this unit may be manually or computer controlled. If the repeat length of the printed pattern on the web is less than or more than the pattern on the embossing roll, then the speed control motor is used to speed up or slow down, respectively, the embossing roll speed to shrink or stretch out the pattern being embossed to match it with the printed pattern. If the pattern length being embossed equals the printed pattern length, but the patterns are out-of-register, i.e, out of phase, then the phase control motor is used. This causes a phase shift between the input drive and the output drive of the draw transmission and this in turn results in the patterns being placed in registry.

Therefore, this invention as described above, provides for a new and improved method of manually or automatically controlling registration of a pattern to be applied to a web with a pattern which has already been applied to the same web.

Claims

What is claimed is:

1. An apparatus for controlling the register between the pattern about to be placed upon a web of material and a pattern which has already been placed upon a web of material, said pattern being repeated on the web at a predetermined repeat length, and the pattern which is to be placed upon the web of material to be placed thereon in register with the pre-existing pattern, comprising:

a. two scanner means,

1. one scanner means scanning the pattern which exists upon the web of material,

2. said second scanner means scanning the pattern which is to be placed upon the web of material, said pattern which is about to be placed upon the web of material being on the surface of a rotary pattern-applying structure,

3. both said scanners being positioned the same time distance from the point where the pattern-applying structure engages the web of material to apply the pattern thereon,

b. a correlator means receiving continuous electrical signature signals from the two scanner means and comparing the electrical signature signals from the two scanner means for the best statistical match,

1. said correlator means continuously providing an indication of the phase relationship of the signals from the two scanner means, said phase relationship of the signals being related to the relationship of the two patterns being sensed,

2. said correlation means providing an indication of any error in the relationship between the two signals from the scanner means, and

c. control means connected with the drive for the pattern-applying means to adjust the operation of the pattern-applying means so that the pattern-applying means can be controlled to place its pattern in register with the pre-existing pattern on the web.

2. The apparatus of claim 1 wherein the correlation means provides a signal to a digital computer in combination with a signal from a web velocity transducer to develop a correction signal which is automatically fed to the control means for the pattern-applying structure to automatically correct the drive of the pattern-applying structure to bring the pattern thereon in registry with the pre-existing pattern of the web of material.

3. The apparatus of claim 1 wherein the pattern on the web and on the pattern-applying structure are composed of a main pattern and a control pattern on the edge of the web and this control pattern is what is viewed by the scanner means.

4. The method of controlling the register between a pattern about to be placed upon a web and a pattern which has already been placed upon the web, said pattern being repeated on the web at a predetermined length, and the pattern which is to be placed upon the web of material to be placed thereon in register with the pre-existing pattern, comprising the steps of:

a. scanning by a first scanner the pattern which is to be placed upon the web of material, said pattern is on the surface of a rotary pattern-applying means,

b. scanning by a second scanner the pattern which exists upon the web of material,

c. positioning both scanners the same time distance from the point where the pattern-applying means engages the web of material to apply the pattern thereon,

d. developing continuous pattern signature signals from the scanners as they scan the patterns, said signals being indicative of the patterns, and feeding these signals to a comparison means,

e. comparing the signals from the scanners by statistical means to secure the best statistical match therebetween and continuously providing an indication of the phase relationship of the signals from the scanners, said phase relationship of the signals being related to the relationship of the two patterns being scanned,

f. providing an indication of any error in the relationship between the two signals from the scanners, and

g. controlling the drive of the pattern-applying means to adjust the operation of the pattern-applying means so that the pattern-applying means can be controlled to place its pattern in register with the pre-existing pattern on the web.

5. The method of claim 4 wherein the signals are compared by statistical means which utilizes approximately 100 separate points of comparison between the pattern signatures to develop an error signal.

6. The method of claim 4 wherein there is the additional steps of:

a. developing a correction signal by relating the web velocity to the indicator of any error in the relationship between the two signals from the scanner, and

b. feeding the correction signal to the control drive means of the pattern-applying means to automatically correct the drive of the pattern-applying means to bring the pattern thereon in register with the pre-existing pattern of the web of material.

7. The method of claim 6 wherein the pattern on the web and on the pattern-applying structure are composed of a main pattern and a control pattern on the edge of the web and this control pattern is viewed by the scanners.