Patent GB-750256-A (GB)
Title: Improvements relating to register control systems for moving webs
Inventor: CROSFIELD JOHN FOTHERGILL
IPC: B65H23/188
Filed: 1953-11-05
Abstract: 750,256. Automatic control systems. CROSFIELD, Ltd., J. F. Oct. 29, 1954 [Nov. 5, 1953], No. 30643/53. Class 38 (4). The invention relates to maintaining longitudinal and lateral registration in e.g. multicolour printing machines, by scanning marks made on the moving web at each operation, and is in part similar to the longitudinal registration system described in Specification 641,830. According to the invention a pair of inclined lines such as Y, Y1 ; R, R1, Fig. 2 (or alternatively wedgeshaped marks) are printed at each operation to be scanned by photo-cells y1 r1; the time between the occurrence of pulses corresponding to the position of lines Y, R (shown in register) determines the error in longitudinal registration; the width of pulses corresponding to the distances y, r between each pair of inclined lines gives a measure of the lateral deviation (r is shown out of register). Derivation of signal pulses.-Signals from the photo-cells pass through cathode follower amplifiers, Fig. 3 (not shown), to identical signal channels each comprising a gated limiting amplifier, Fig. 4 (not shown), to separate the " mark signals "17, Fig. 5A (not shown), from the printed design signals 16, which will also appear in the photo-cell output. The pair of output pulses from the amplifier are applied to a flip-flop circuit, Fig. 8 (not shown), to produce a rectangular output L, Fig. 9 (not shown), having a width w corresponding to the distance y or r for lateral control. This pulse is also applied to a differentiating circuit to produce a steep pulse M, Fig. 9, corresponding to the position of line Y or R, for longitudinal control. The output of the amplifier, Fig. 4, is also used to trigger a timing circuit, Fig. 12 (not shown), for switching on the control circuits periodically to reduce hunting. The gating signals for controlling the amplifier of Fig. 4, are derived from a magnetic pick-off on the printing cylinder in the form of two short pulses which 'are applied to a flip-flop circuit in the gating signal amplifier, Fig. 6 (not shown). to provide a rectangular wave to switch on the gated amplifier only during the time at which mark-signals will occur. Longitudinal control.-The output pulses M (from the circuit of Fig. 8) derived from each photo-cell are applied to an error detecting circuit, Fig. 10 (not shown), comprising identical " master " and " slave channels, to develop an integrated error signal in one channel or the other, depending on which pulse arrives first, and having a magnitude dependent on the time interval between the arrival of the pulses. A two-channel servo amplifier, Fig. 11 (not shown), is periodically connected to the error-signal output from Fig. 10 by a sampling relay A controlled by the timing circuit, Fig. 12. Lateral control.-The rectangular output pulses L from each photo-cell channel are applied to the two channels of an integrator/ amplifier circuit, Fig. 13 (not shown), and the outputs applied to a servo amplifier such as Fig. 11, controlling the lateral correction servomotor. Circuit details.-(i), Fig. 4 (not shown), gated limiting amplifier; comprises a variablemu pentode 15, feeding through a triode amplifier 19 to a triode-gate-valve 23 supplied at the anode with gating pulses and providing cathodefollower output to a triode amplifier 33 having a limiter diode 38 in the anode circuit and also supplying an A.V.C. amplifier 40 and diode 41 providing bias for the pentode 15. (ii), Fig. 10 (not shown), longitudinal error detecting circuit; comprises two identical cross-connected channels each with a flipflop circuit 102 connected to a cathode follower 114 to apply a blocking pulse to the flip-flop circuit in the other channel. Thus the arrival of the first pulse triggers the flip-flop in its channel and blocks that in the other channel so that the arrival of the second pulse on the other channel merely resets the first flip-flop, whereby there is generated in that channel a rectangular wave having a width representative of the time interval between the pulses. The wave is taken from the cathode-follower 114 through a diode 118 to discharge a capacitor 117 (which is charged through a resistor 120) to provide an integrated error signal. A cathode follower output 119 is provided. (iii), Fig. 11 (not shown), servo-amplifier; comprises three double triodes providing a twochannel amplifier cross-connected so that operation of one channel blocks the other channel. Relays B, C in the output stages control (through repeater relays D, E) a reversible D.C. servomotor. (iv), Fig. 12 (not shown), tuning circuit, comprises a flip-flop circuit 168, triggered by the pulses from the photo-cell amplifier, Fig. 4, to produce rectangular pulses to charge a capacitor 197 to operate a trigger circuit 169 which causes momentarily energization of a relay F to discharge capacitor 197 and reset the circuit ready for another cycle. Relay F also energizes relay A in the servo-amplfier circuit, Fig. 11, to periodically connect the amplifier to the error signal.