Web tracking system

Abstract

A web tracking system for a continuous web of material which is transported from a supply to a takeup means along a predetermined path via one or more processing stations and comprises aligned tracking indicia along at least one edge of the web. Means are provided to observe the tracking indica as the web is transported along the system path and produce information either indicative of dimensional changes in the length and width of the web due to web shrinkage or expansion or indicative of a particular point along the length of the web useful at one or more of the processing stations in the system.

Description

RELATED APPLICATION

U.S. Application Ser. No. 444,144, filed Nov. 24, 1982 and entitled COLOR ELECTROGRAPHIC RECORDING APPARATUS and assigned to the assignee herein.

BACKGROUND OF THE INVENTION

The present invention relates to the transport of a continuous web of material and more particularly to a system and method for tracking of the web in its path of movement from a supply to a takeup means.

Many different kinds of systems have been devised to track the movement of a web of material in order to positively determine, for example, various locations along its length so that one or more operations may be performed in connection with the treatment of the web. In carrying out the treatment, the path of the web may have to be monitored to ensure that it mantainsabe free from signal noise. As an actual example, assume the value for M happens to be 448 pulses. Thus, where there is no dimensional change in the web, there should be 448 encoder pulses between negative mark sense intervals. Experience has shown that out of 448 pulses, a difference of ±8 encoder pulses may represent signal noise and the expected error may be only ±0.02 of that value. This is a typical signal to noise value. The noise may be caused by several factors including the treatment processes applied to the web and the resolution or print clarity of the tracking indicia itself. Also, the X and X' sensors operate with some noise. The remaining portion of the circuit diagram in FIG. 14 is devoted to eliminating this error from the mark sense interval error values or samples on line 374 and 376.

As previously mentioned, the mark sense intervals are known to comprise M encoder pulses in the time frame intervals between the mark sense transitions derived from the optical sensor pairs 1X and 2X; 1X' and 2X'. If the web has stretched, there will be one or more encoder pulses above the value M between mark sense intervals. Conversely, if the web has shrunk, there will be one or more encoder pulses below the value M between mark sense intervals. These pulses above and below the value M may be termed samples. As indicated above, experience having shown that a major portion of the sample values is signal noise. The effect of this noise may be significantly removed by effectively averaging several samples together and making error corrections according to N samples comprising a sample group. This is mathematically accomplished by taking a running average over N samples wherein a current sample is added to the sample group and the oldest sample in the sample group is dropped out. One manner of mathamatically accomplishing this through logic circuitry is by taking each current sample group and effectively dividing by N, i.e., the number of samples in the group and then carry out a summation of these values in a summation circuit. The value in the summation circuit will be the total value of error for the mark sense intervals over a series of N samples.

Another manner of mathamatically accomplishing this through logic circuitry is illustrated in FIG. 14. As shown in FIG. 14, the samples on lines 374 and 376 are serially fed to delay 378 via gate 377 and line 379. Line 379 is also directly connected to summation circuit 384. Gate 377 is controlled by mode control 380 via line 383 which can permit the gate 377 to enable X ONLY samples, or X' ONLY samples or a combination of both X and X' samples (CENTRAL) to delay 378. Mode control 380 also provides the advantage of being able to select samples developed from one side of web 18 when a failure exists in the detection circuits at the other side of the web, e.g., light source failure depended upon by the X sensors. The utility or utilizing both X and X' sources for samples is taking into account more information relative to X dimensional changes although, the use of one such sample source has been found sufficiently adequate.

Delay 378 comprises a shift register which can contain N samples at a time. In this manner, the samples are delayed in time compared to the same samples on line 379. Before each cycle of operation, a current sample is loaded into delay 378 from line 379 and the last one is loaded out on line 379. The values on line 379 are then converted to their complement value at complement 381 and provided on line 382 as the second output to summation circuit 384. The value in circuit 384 represents the combined average running mean for the samples.

The bigger the sample group N, the more noise present in the samples may be effectively averaged out. However, sample groups too large will take longer to process the sample group and corrective action will be unreasonably delayed. The varying error over long web distance for which correction is needed may be not applied in proximity to the affected web section. If both the amount and the "polarity" of the error is changing, tracking web dimensional error with large sample groups of errors is not possible because the detected error and applied correction will come too late at station 16.

Somewhere between a small and large sample group is a range of optimized sample averaging. In the system disclosed in FIG. 14, N=16 was chosen. However, N=8 or 32 could also easily have been employed.

The combined average running mean in circuit 384 is then supplied on line 388 to a summation circuit 386. In circuit 386, the running mean produced in each cycle of operation of the delay 378 is added to a running total value. This total value is called the sum of the running mean.

The run output of circuit 386 is supplied on line 387 to comparator 388 wherein the sum of the running mean is compared with an allowable reference error. The allowable reference error represents an allowable error band, e.g., from -1→0→+1. If the summed value from summing circuit 386 becomes equal to or greater than ±1, a correction command via line 389 is given at circuit 390. The action taken is that a correction pulse is issued on line 60 to processing station 16. At the same time, the total sum value in the summation circuit 386 is decremented by the same correction amount, i.e., the sum of the running mean is decremented each cycle by the value from correction circuit 390.

Line 383 from mode control 380 is also connected to comparator 388. If mode control 380 is set for X ONLY mode or X' ONLY mode, then the comparison value representative of the allowable reference error will be to set to N. If mode control 380 is set for CENTRAL mode, then the comparison value representative of the allowable reference error will be set to 2N since there are twice the samples involved in error correction.

In FIG. 15 discloses another circuit implementation control 42 or 44 in FIG. 1 for supplying control signals on line 400 to the position control logic circuit 340 in FIG. 13. This circuit implementation supplies correction signals for web skew in its path through system 10.

In FIG. 15, the X MARK SIGNAL LOAD on line 315 is supplied as a start signal for counter 393. Counter 393 is loaded with a count value equal to M encoder pulses from memory switch 393A. As each X MARK SIGNAL LOAD is inputted to counter 393, preloaded with the M value, the encoder pulses on line 40 decrement the counter. As soon as a signal, X' MARK SIGNAL LOAD, is received on line 316, the value in counter 393 is latched into register 394. This value then represents the phase difference between an incoming X mark sense interval and an incoming X' mark sense interval and represents an output line 395 the difference in distantial amounts on one side of the web as compared to the other and is indicative that the web is slightly skewed in its path through system 10.

These error values are fed into delay 396 which is the same as delay 378 in FIG. 14. A running average over N samples is examined per cycle wherein a current error sample is added to the sample group via line 395 into delay 396 and the oldest sample in the sample group is provided to the complement circuit 397. The delay complement signal and the original error signal are added by adder 398. The value here represents the combined average running mean. These values are added to a total value by summation circuit 399 which provides the sum of the running mean. This total summed value is compared to an allowable reference error, e.g., from +1 to +1, in comparator 403 to produce a logic signal on line 400 representative of a count value as measured in encoder pulses and determinative of whether X mark sense intervals are exceeding or diminishing relative to X' sense mark intervals.

FIG. 18 details an implementation for the tension servo control 98 of FIG. 1. The purpose of dancer roll 90 is to remove any loop that is produce produced in the web during its movement through system 10. Better control is maintained on web movement, particularly at higher velocities, keeping constant tension on the web and, also, provide for lower inertia. If movement of the web movement is primarily always at a slow velocity, the need for the dancer roll may be nonexistent.

Dancer roll 90 is pivotally supported for vertical movement on an arm 401 between two support rolls 402 and 404. Arm 401 is biased onto the surface of the web 18 by a preselected amount of force by compression spring 406. This force is indicated by arrow 161. Arm 401 has its pivot point connected to a movable commutator 408 of a reostat 410. Reostat 410 has linear resistance connected across a power source 412. As the tension and, thereof, the vertical elevation of dancer roll 90 varies vertically between rolls 402 and 404, commutator 408 will also move providing an analog output proportional to the movement of arm 401. This output on line 96 is supplied to a comparator 414 which may comprise the inverting input of a differential amplifier. The signal on line 412 is compared with a positive reference value, V_R which is supplied to the noninverting input of comparator 414 via switch 416. The value V_R, represents the value of the preselected tension desired on the surface of web 18 by dancer roll 90. The compared output provided on line 418 is, therefore, representative of differences, either negative or positive, from the predetermined value. This output is supplied as an input to the motor driver circuit 420 for supply roll motor 19. Circuit 420 provides conventional motor drive circuitry for drive motor 19 but also includes a power amplifier which takes the signal on line 418 and increases or decreases the constant torque via line 100 on motor 19 represented by arrow 20' according to whether the compared deviation from the desired dancer roll tension is respectively too little or too much.

While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and scope of the appended claims.

Claims

1. web tracking system for a continuous web of material which is transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat said web comprising

aligned tracking indicia comprising a line of registration marks of substantially uniform spacing and width along each edge of said web,

means mounted relative to the passage of said web to optically observe said tracking indicia along each of said web edges as said web is transported along said path and produce informational tracking signals based upon the passage of said tracking indicia relative to said observation means,

circuit means responsive to said informational signals to produce control signals indicative of changes in the lateral and longitudinal dimensions of said web,

means to provide relative translation between said processing stations and said web along said path,

said translation means responsive to said control signals to translate said processing stations according to changes in the lateral and longitudinal dimensions of said web.

2. The system of claim 1 wherein said translation means comprises web guide servo control to laterally translate a web supply roll at said supply means relative to said processing station.

3. The system of claim 1 wherein said translation means includes a processing station lateral position control to laterally postion said processing station relative to said web in said path.

4. The system of claim 1 wherein said translation means includes a processing station rotational position control to rotate said processing station relative to said web in said path.

5. The system of claim 1 wherein said tracking marks comprise registration marks of equal spacing and width.

6. The system of claim 5 wherein said registration marks are preceeded preceded by a plurality of aligned initializing marks at the beginning of said web, said initializing marks having a different geometric shape compared to said registration marks.

7. The system of claim 6 wherein said different geometric shape comprises a different mark width.

8. The system of claim 6 wherein the change from said initializing marks to said registration marks is indicative of a starting point for determining a particular location further along said web.

9. The system of claim 1 wherein determination of dimensional changes by said circuit means via said observation means is accomplished by monitoring the spacing between registration marks along at least one edge of said web indicative of changes in web length and monitoring lateral shift of said lines of registration marks relative to its respective observation means at both edges of said web indicative of either a change in web width or a lateral shift of said web relative to said observation means.

10. The system of claim 1 wherein said aligned tracking indicia comprises

a line of registration marks of substantially uniform spacing and width along each edge of said web for purposes of monitoring dimensional changes in the length of said web and

a solid line along each edge of said web ajacent to said line of registration marks for purposes of monitoring dimensional changes in the width of said web.

11. The system of claim 10 wherein determination of dimensional changes by said circuit means via said observation means is accomplished by monitoring the spacing between registration marks along at least one edge of said web indicative of changes in web length and monitoring lateral shift of said solid lines relative to its respective observation means at both edges of said web indicative of either a change in web width or a lateral shift of said web relative to said observation means.

12. web tracking system for a continuous web of material which is transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat said web comprising

aligned tracking indicia along at least one edge of said web,

said tracking indicia comprising a plurality of aligned of registration marks of substantially uniform spacing and width and a plurality of aligned initializing marks preceding said registration marks and having a different geometric shape compared to said registration marks,

means mounted relative to the passage of said web to optically observe said tracking indicia as said web is transported along said path and produce an informational signal signals indicative of distant predetermined lengths along said medium web useful at one or more of said processing stations,

circuit means responsive to said informational signal signals indicative of the recognition of said initalizing marks and determinative of the point of transition from the last of said initializing marks to the first of said registration marks, said circuit means further determinative of the distance between said transition point and a predetermined point further along said registration marks wherein the treatment of said web is desired to be initiated relative to any one of said stations.

13. In the web tracking system of claim 12 wherein said initializing marks are identical to said registration marks but are of a different dimensional width.

14. In the web tracking system of claim 13 wherein said initializing marks are smaller dimensional width than said registration marks. 15. The system of claim 1 wherein said circuit means comprises means for comparing said informational signals with a known value to produce said control signals representing a dimensional change in the lateral and longitudinal direction of the web,

means for averaging a plurality of said control signals together to produce a composite error signal representative of a running average in the lateral and longitudinal shrinkage or expansion of said web, and

means for utilizing said composite error signal to adjust the relative positional relationship of said web relative to one or more of said processing stations to compensate for any changes that have occurred in web lateral and longitudinal dimension. 16. The system of claim 1 wherein said circuit means comprises means to correct for misalignment between the lateral positional relationship of said web

relative to at least one of said processing stations. 17. The system of claim 12 wherein said circuit means comprises means for comparing said informational signals with a known value to produce control signals representing a dimensional change in the lateral and longitudinal direction of the web,

means for averaging a plurality of said control signals together to produce a composite error signal representative of a running average in the longitudinal shrinkage or expansion of said web, and

means for utilizing said composite error signal to adjust the relative positional relationship of said web relative to one or more of said processing stations to compensate for any changes that have occurred in web longitudinal dimension. 18. The system of claim 17 wherein said utilizing means comprises means to correct for lateral misalignment between the lateral positional relationship of said web

relative to at least one of said processing stations. 19. The system of claim 12 wherein there are aligned along at least two edges of said web, means to correct for lateral misalignment between (a) the lateral positional relationship of said web relative to one or more of said processing stations and (b) the lateral dimensional relationship of said web due to changes in the lateral shrinkage or expansion of said web

relative to at least one of said processing stations. 20. The system of claim 12 wherein there is means to translation between at least one of said processing stations and said web along said path. 21. The system of claim 20 wherein said translation means comprises web guide servo control to laterally translate said supply roll means relative to one or more of said processing stations. 22. The system of claim 20 wherein said translation means comprises a processing station lateral position control means to laterally position said processing station relative to said web in said path. 23. The system of claim 20 wherein said translation means comprises a processing station rotational position control to rotate said processing station relative to said web in said path. 24. The system of claim 12 wherein said tracking indicia comprise registration marks of substantially equal spacing and width. 25. The system of claim 12 wherein said different geometric shape comprises a different dimensional width. 26. A system for controlling the track or position of a continuous web of material traveling from a supply roll to a takeup roll along a predetermined path via one or more sequentially positioned processing stations for selectively treating a portion of the web comprising

aligned tracking indicia along at least one region of said web portion,

means mounted relative to the passage of said web to observe said tracking indicia as said web is transported along said path and produce informational tracking signals based upon the passage of said tracking indicia relative to said observations means,

circuit means for comparing said signals with a known value to produce error signals representing a dimensional change in the longitudinal direction of the web,

means for averaging a plurality of said error signals together to produce a composite error signal representative of a running average in longitudinal shrinkage or expansion of said web portion, and

means for utilizing said composite error signal to adjust the relative positional relationship of said web portion relative to one or more of said processing stations to compensate for any changes that have occurred in web longitudinal dimension. 27. The system of claim 26 wherein said utilizing means includes means to correct for lateral misalignment between the lateral positional relationship of said web portion relative to one or more of said processing stations. 28. The system of claim 26 wherein there are aligned tracking indicia along at least two regions of said web portion, said utilizing means including means to correct for lateral misalignment between (a) the lateral positional relationship of said web portion relative to one or more of said processing stations or (b) the lateral dimensional relationship of said web portion due to changes in the lateral shrinkage or expansion of said web portion relative to one or more of said processing stations. 29. The system of claim 26 wherein said utilizing means includes means to provide relative translation between at least one of said processing stations and said web portion along said path. 30. The system of claim 29 wherein said translation means comprises web guide servo control to laterally translate said supply roll relative to said processing station. 31. The system of claim 29 wherein said translation means comprises a processing station lateral position control means to laterally position said processing station relative to said web portion in said path.

32. The system of claim 29 wherein said translation means comprises a processing station rotational position control to rotate said processing station relative to said web portion in said path. 33. The system of claim 26 wherein said tracking indicia comprise registration marks of substantially equal spacing and width. 34. The system of claim 26 wherein said tracking indicia are preceded by initializing means indicative of a start point for processing of said web relative to any one of said processing stations and in conjunction with said utilizing means determinative of the distance between said start point and a predetermined point further along said tracking indicia wherein the treatment of said web is desired to be initiated relative to any one of said processing stations. 35. The system of claim 34 wherein said initializing means comprises

at least one tracking indicia. 36. The system of claim 26 which includes

increment means to translate longitudinally, laterally or rotationally one or more of said processing stations or a component part of one or more of said processing stations,

said observation means including paired sensing means positioned relative to said tracking indicia, the outputs of corresponding pairs of said paired sensing means coupled to produce separate summed outputs comprising said information signals,

differences in magitude between said information signals indicative of the

changes in said positional relationship. 37. web tracking system for a continuous web of material which is transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat regional portions of said web and wherein a desired positional relationship is to be maintained between said web and one or more of said processing stations and comprising

aligned tracking indicia continuous or closely spaced, intermittently continuous longitudinally along at least two regions of said web adjacent to said treated regional portions,

means mounted relative to the passage of said web to continuously observe said tracking indicia as said web is trasnported along said path and simultaneously produce on-the-fly informational signals based upon the passage of said tracking indicia relative to said observations means as said treated regional portions move into and through one or more of said processing stations,

means for utilizing said signals to correct on-the-fly for misalignment in the positional relationship of said web relative to at least one of said processing stations due to shrinkage or expansion changes in said web in either the lateral or longitudinal dimensions of said web or in both

dimensions thereof. 38. The system of claim 37 wherein said circuit means comprises means for comparing said informational signals with a known value to produce said control signals representing a dimensional change in the longitudinal direction of the web,

means for averaging a plurality of said control signals together to produce a composite error signal representative of a running average in the longitudinal shrinkage or expansion of said web, and

means for utilizing said composite error signal to adjust the positional relationship of said web relative to one or more of said processing stations to compensate for said changes that have occurred in web

longitudinal dimension. 39. The system of claim 37 wherein said utilizing means includes means to provide relative translation between at least one of said processing stations and said web along said path. 40. The system of claim 39 wherein said translation means comprises web guide servo control to laterally translate said supply roll means relative to one or more of said processing stations. 41. The system of claim 39 wherein said translation means comprises a processing station lateral position control means to laterally position said processing station relative to said web in said path. 42. The system of claim 39 wherein said translation means comprises a processing station rotational position control to rotate said processing station relative to said web in said path. 43. The system of claim 37 wherein said tracking indicia are preceded by initializing means indicative of a start point for processing of said web relative to any one of said processing stations and in conjunction with said utilizing means determinative of the distance between said start point and a predetermined point further along said tracking indicia wherein the treatment of said web is desired to be initiated relative to any one of said processing stations. 44. The system of claim 43 wherein said initializing means comprises

at least one tracking indicia. 45. The system of claim 37 which includes

increment means to translate longitudinally, laterally or rotationally one or more of said processing stations or a component part of one or more of said processing stations,

said observation means including paired sensing means positioned relative to each of said tracking indicia, the outputs of corresponding pairs of said paired sensing means coupled to produce separate summed outputs comprising said information signals,

differences in magnitude between said information signals indicative of the

changes in said positional relationship. 46. web tracking system for a continuous web of material transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat said web wherein a desired positional relationship is to be maintained between said web and one or more of said stations and comprising

aligned tracking indicia along at least two regions of said web,

means mounted relative to the passage of said web to observe said tracking indicia as said web is transported along said path and produce informational signals based upon the passage of said tracking indicia and a web edge relative to said observations means,

means for utilizing said signals to correct for misalignment in the positional relationship of said web relative to at least one of said processing stations due to changes in the lateral positional relationship of said web relative to said processing station or due to shrinkage or expansion changes in said web in either the lateral and longitudinal dimensions of said web or in both dimensions thereof. 47. The system of claim 46 wherein said circuit means comprises means for comparing said informational signals with a known value to produce said control signals representing a dimensional change in the longitudinal direction of the web, p1 means for averaging a plurality of said control signals produce a composite error signal representative of a running average in the longitudinal shrinkage or expansion of said web, and

means for utilizing said composite error signal to adjust the positional relationship of said web relative to one or more of said processing stations to compensate for said changes that have occurred in web longitudinal dimension. 48. The system of claim 46 wherein said utilizing means includes means to provide relative translation between at least one of said processing stations and said web along said path. 49. The system of claim 48 wherein said translation means comprises web guide servo control to laterally translate said supply roll means relative to one or more of said processing stations. 50. The system of claim 48 wherein said translation means comprises a processing station lateral position control means to laterally position said processing station relative to said web in said path. 51. The system of claim 48 wherein said translation means comprises a processing station rotational position control to rotate said processing station relative to said web in said path. 52. The system of claim 46 wherein said tracking indicia are preceded by initializing means indicative of a start point for processing of said web relative to any one of said processing stations and in conjunction with said utilizing means determinative of the distance between said start point and a predetermined point further along said tracking indicia wherein the treatment of said web is desired to be initiated relative to any one of said processing stations. 53. The system of claim 52 wherein said initializing means comprises at least one tracking indicia.

54. The system of claim 46 which includes

increment means to translate longitudinally, laterally or rotationally one or more of said processing stations or a component part of one or more of said processing stations,

said observation means including paired sensing means positioned relative to each of said tracking indicia, the outputs of corresponding pairs of said paired sensing means coupled to produce separate summed outputs comprising said information signals,

differences in magnitude between said information signals indicative of the changes in said positional relationship. 55. The system of claim 46 wherein said aligned tracking indicia are continuous or closely spaced, intermittently continuous indicia longitudinally along said at least two regions adjacent to regional portions of said web to be treated at said processing stations,

said mounted means to continuously observe said longitudinally continuous tracking indicia and simultaneously produce on-the-fly said information signals as said treated regional portions move into and thorugh one or

more of said processing stations. 56. web tracking system for a continuous web of material which is transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat regional portions of said web and wherein a desired positional relationship is to be maintained between said web and one or more of said processing stations and comprising

aligned tracking indicia continuous or closely spaced, intermittently continuous longitudinally along at least one region of said web adjacent to said treated regional portions,

means mounted relative to the passage of said web to continuously observe said tracking indicia as said web is transported along said path and simultaneously produce on-the-fly informational signals based upon the passage of said tracking indicia and a web edge relative to said observations means as said treated regional portions move into and through one or more of said processing stations,

means for utilizing said signals to correct on-the-fly for misalignment in the positional relationship of said web relative to at least one of said processing stations due to changes in the lateral positional relationship of said web relative to said processing station and due to shrinkage or expansion changes in said web in the longitudinal dimension of said web.

57. The system of claim 56 wherein said circuit means comprises means for comparing said informational signals with a known value to produce said control signals representing a dimensional change in the longitudinal direction of the web,

means for averaging a plurality of said control signals together to produce a composite error signal representative of a running average in the longitudinal shrinkage or expansion of said web, and

means for utilizing said composite error signal to adjust the positional relationship of said web relative to one or more of said processing stations to compensate for said changes that have occurred in web longitudinal dimension. 58. The system of claim 56 wherein said utilizing means includes means to provide relative translation between at least one of said processing stations and said web along said path. 59. The system of claim 58 wherein said translation means comprises web guide servo control to laterally translate said supply roll means relative to one or more of said processing stations.

0. The system of claim 58 wherein said translation means comprises a processing station lateral position control means to laterally position said processing station relative to said web in said path. 61. The system of claim 58 wherein said translation means comprises a processing station rotational position control to rotate said processing station relative to said web in said path. 62. The system of claim 56 wherein said tracking indicia are preceded by initializing means indicative of a start point for processing of said web relative to any one of said processing stations and in conjunction with said utilizing means determinative of the distance between said start point and a predetermined point further along said tracking indicia wherein the treatment of said web is desired to be initiated relative to any one of said processing stations. 63. The system of claim 62 wherein said initializing means comprises at least one tracking indicia. 64. The system of claim 56 which includes

increment means to translate longitudinally, laterally or rotationally one or more of said processing stations or a component part of one or more of said processing stations,

said observation means including paired sensing means positioned relative to said tracking indicia, the outputs of corresponding pairs of said paired sensing means coupled to produce separate summed outputs comprising said information signals,

differences in magnitude between said information signals indicative of the changes in said positional relationship. 65. web tracking system for a continuous web of material which is transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat said web wherein a desired positional relationship is to be maintained between said web and one or more of said stations and comprising aligned tracking indicia along at least two regions of said web,

means mounted relative to the passage of said web to observe said tracking indicia as said web is transported along said path and produce informational signals based upon the passage of said tracking indicia and a web edge relative to said observations means,

means for utilizing said signals to correct for misalignment in the positional relationship of said web relative to at least one of said processing stations due to changes in the lateral positional relationship of said web relative to said processing station or due to shrinkage or expansion changes in said web in the lateral dimension of said web or due to both of said changes. 66. The system of claim 65 wherein said circuit means comprises means for comparing said informational signals with a known value to produce said control signals representing a dimensional change in the longitudinal direction of the web,

means for averaging a plurality of said control signals together to produce a composite error signal representative of a running average in the longitudinal shrinkage or expansion of said web, and

means for utilizing said composite error signal to adjust the positional relationship of said web relative to one or more of said processing stations to compensate for said changes that have occurred in web longitudinal dimension. 67. The system of claim 65 wherein said utilizing means includes means to provide relative translation between at least one of said processing stations and said web along said path. 68. The system of claim 67 wherein said translation means comprises web guide servo control to laterally translate said supply roll means relative to one or more of said processing stations. 69. The system of claim 67 wherein said translation means comprises a processing station lateral position control means to laterally position said processing station relative to said web in said path. 70. The system of claim 67 wherein said translation means comprises a processing station rotational position control to rotate said processing station relative to said web in said path. 71. The system of claim 65 wherein said tracking indicia are preceded by initializing means indicative of a start point for processing of said web relative to any one of said processing stations and in conjunction with said utilizing means determinative of the distance between said start point and a predetermined point further along said tracking indicia wherein the treatment of said web is desired to be initiated relative to any one of

said processing stations. 72. The system of claim 71 wherein said initializing at least one tracking indicia.

. The system of claim 65 which includes

increment means to translate longitudinally, laterally or rotationally one or more of said processing stations or a component part of of one or more of said processing stations,

said observation means including paired sensing means positioned relative to each of said tracking indicia, the outputs of corresponding pairs of said paired sensing means coupled to produce separate summed outputs comprising said information signals, differences in magnitude between said information signals indicative of the changes in said positional relationship. 74. The system of claim 65 wherein said aligned tracking indicia are continuous or closely spaced, intermittently continuous indicia longitudinally along said at least two regions adjacent to regional portions of said web to be treated at said processing stations,

said mounted means to continuously observe said longitudinally continuous tracking indicia and simultaneously produce on-the-fly said informational signals as said treated regional portions move into and through one or

more of said processing stations. 75. web tracking system for a continuous web of material transported from a supply roll means to a takeup roll means along a predetermined path via one or more sequentially positioned processing stations to treat said web comprising

aligned tracking indicia along at least one region of said web,

initializing means preceding said aligned tracking indicia,

means mounted relative to the passage of said web to optically observe said tracking indicia as said web is transported along said path and produce informational signals indicative of the longitudinal dimension along said web useful at one or more of said processing stations,

circuit means responsive to said informational signals indicative of the recognition of said initializing means and determinative of the point of transition from said initializing means to said tracking indicia, said circuit means further determinative of the distance between said transition point and a predetermined point further along said tracking indicia wherein the treatment of said web is desired to be initiated

relative to any one of said stations. 76. The system of claim 75 wherein said initializing at least one registration mark on said

web. 77. The system of claim 75 which includes

paired sensing means positioned relative to said tracking indicia, the outputs of corresponding pairs of said paired sensing means coupled to produce separate summed outputs comprising said information signals,

differences in magnitude between said information signals indicative of said point of transition.