GB1087484A - Improvements relating to register control in printing presses - Google Patents

Abstract

1,087,484. Photo-electric register control of a web. CROSFIELD ELECTRONICS Ltd. Feb. 18, 1966 [Feb.25, 1965], No. 8188/65. Heading G1A. Register marks on a moving web of printed paper are in the form of a transverse line 2 positioned in a clear space between two areas of printing 3 and are recognized by a linear array of photodiodes 7 to 11 sensing in succession a clear space by all diodes, a mark by some of the diodes but clear space for the remainder and finally clear space for them all again. The diodes are arranged in The Figure so that 8, 9 and 10 view areas 8a, 9a and 10a along a line of light 6 over which the register mark passes while diodes 7 and 11 view areas outside the path of the mark. Signals from the diodes pass via circuits 12 and 13 to shape the signals representing black and white areas to the correct height before passing to a circuit which recognises the correct sequence of signals. When all diodes see clear space, as prior to a mark, Schmitt trigger circuit S 1 has zero output and allows Miller integrator M 1 to charge at a rate proportional to the web speed and of “" of clear space is sensed M 1 will have reached a voltage sufficient to turn on trigger circuit T 1 . If the registration mark is subsequently sensed gate A 1 gives an output which is passed via the now open gate G 1 to set a monostable trigger circuit. If a mark, but not the registration one, is sensed A 1 gives no output but with the output from S 1 opens gate A 2 to reset the trigger circuit T 1 . Trigger circuit T 2 will revert to the original state after #" of web travel and differentiation circuit D provides a pulse to start Miller integrator M 2 charging as it does so. If at this point the diodes are still sensing the mark (i. e. it is thicker than the correct one) S 1 has an output and together with the differentiating pulse opens AND gate A 3 to reset the trigger. If however clear space continues to be sensed for a further #" the integrator M 2 reaches a potential to operate pulse generator PG to supply the registration pulse. If during this last #" of web a mark is sensed gate A 2 opens to reset trigger circuit T 1 and so reset integrator M 2 . The register pulse is used to activate a further scanning head which senses register marks to give a more accurate register pulse. The register mark may extend from one edge of the web, when only one of the outside diodes 7 and 11 will be needed. Instead of having continuous outputs from each diode they may be sampled in the order in which they are arranged. Individual diodes may again be used for this or a block of silicon having the diodes etched in may be used.