GB1204942A - Improvements in or relating to detecting and measuring registration errors of patterns of work on a moving web - Google Patents

Abstract

1,204,942. Automatic registration control. HURLETRON Inc. April 16, 1968, No. 17947/68. Heading G3R. [Also in Division G4] The magnitude of the error in registration of a web 1, Fig.1, with a printing or cutting station, for example cutting station E, is determined by counting clock-pulses produced by an incremental encoder 21 coupled to the main drive shaft 23, these pulses being counted in both an initial counter which is zeroized every time a datum mark on the cutting cylinder 17 is photo-electrically detected 22E, and in an error counter which counts for a period determined by the photo-electric detector 20E of a mark put on the web at the first station A, and the attainment by the initial counter of a count, determined during the initial adjustment of the machine, which corresponds to the instant at which the mark on the paper should be detected for perfect registration to occur, the count attained by the error counter then being proportional to the magnitude of the error in registration and the relative timing of the detection of the mark on the web with respect to the attainment by the initial counter of the registration count, being indicative of the sign error. Error determination is performed for each station, except for the first, of all the multi-station machine shown and each error count can be employed, in a retroactive loop, to control compensators 11a, 11b, 11c, 11d to vary the phasing of the web at each station in order to reduce the errors in registration. The error for each station once every four cycles for example, or a running average, can be indicated. In the preferred embodiment Fig. 4 (not shown) the initial counter comprises two counters, an adjustable counter, i.e. a counter of fixed capacity (4999 as described) but able to produce an output at any switch-set count, and a reference generator, i.e. a counter of fixed capacity (99 as described) able to produce an overflow output, and they are so arranged that the count which represents perfect registration is bracketed by two pulses respectively one hundred clock pulses before and afterwards, these two pulses demarcating an inspection zone and unless the sensing of the mark on the web falls within the inspection zone no corrective action is taken and a visual indication is given. This detail prevents excessive corrective action being taken. During the initial adjustment of the machine the switches of the adjustable counter are set so that it produces an output 100 clock pulses before perfect registration, this being determined by coupling the adjustable counter to the indicator for the period of initial adjustment. There after the in indicator is coupled to the error counter. Block diagrams, employing conventional techniques, are described for the individual component of the system.