Circumferential control of the web has been the subject of extensive past development work. In U.S. Pat. No. 3,870,936, assigned to the assignee of the present invention, some of the past work is set forth. Related to the circumferential control is the problem of lateral control of the web, the subject of the present disclosure. In U.S. Pat. No. 3,949,282, also assigned to the assignee of the present invention, a system for circumferential or longitudinal control was disclosed. That system required a set of marks to be printed on the web by print-stand A while a downstream print-stand, call it B, printed a second set of marks on the web. Two scanners sensed the two sets of marks and the control system compared them in time. The difference in position detected in the two sets of marks was an error signal providing inputs to an error correcting device of some type. The adjustment was made on print-stand B. Thus, it can be seen that the position of print roller B was indirectly compared to the reference marks printed by print-stand A and an adjustment then made at print-stand B. The indirect measurement of the position of print-stand B off of a printed mark resulted in less accuracy than was desirable. Furthermore, the method of measurement inherently resulted in some misregistration since before an error signal could be generated, the web had been processed by print-stand B.
USPTO Backgrounds
USPTO Backgrounds