GB1220739A - Improvements in or relating to colour printing - Google Patents

Abstract

1,220,739. Automatic control for colour printing. HURLETRON Inc. July 19, 1968 [April 3, 1968], No.34682/68. Heading G3R. An apparatus for controlling the colour density of ink applied to a moving web comprising means for applying ink to a fountain roller; means for transferring the ink to a printing cylinder; means for transferring ink from the cylinder to the web; means 40 for sensing the colour density on the surface of the web, means 41 for generating a control signal indicative of the colour density; means for comparing the control signal and a reference signal 46 to form an error signal; means 47 for storing the error signal; and means 48, 49, 50 connected between the storage circuit 47 and a motor 13a to control the supply of ink to the fountain roller the means 48, including a dead bond circuit 66 which only allows response to error signals of a magnitude outside the dead bond. The motor 13a drives the fountain roller at a speed which determines the colour density. The reference signal may be set at the press controls 51 by an operator and is added to the control signal. The error storage circuit comprises a high impedance resistor 61 in series with amplifier 60, an equal impedance feedback resistor 62 across the amplifier, and a capacitor 63 in parallel with resistor 62, the R.C. time constant of the feedback circuit being four seconds. The error storage signal is sampled every six seconds by an electronic relay 67 which closes relay contacts 64 in sampling circuit momentarily. The electronic relay comprises a relay coil in series with a silicon controlled rectifier which is triggered by a circuit including a unijunction transistor and rendered non-conducting by another circuit including a unijunction transistor Fig.6 (not shown). The storage signal is fed to a dead-band circuit 66 and if the signal lies outside its upper and lower values an error signal is fed to the time proportional correcting circuit 49. The storage signal causes relay 68 to close its contacts 69 for a time proportional to the magnitude of the error and one of the contact sets 73, 74 depending on the sense of the error. The motor controller 76 or 77 therefore applies a correction,to fountain roller motor 13a to correct the ink supply.