GB1141241A - Tension member position regulating system - Google Patents

Abstract

1,141,241. Automatic control of moving strip. WESTINGHOUSE ELECTRIC CORP. March 14, 1967 [March 29, 1966], No. 11919/67. Heading G3R. In a system for automatically controlling the tension of a motor-driven travelling strip, variations of tension are corrected by error signals, derived from angular movement of a member pressing against the strip, which modify the datum of a closed loop automatic speed control system for the motor and are limited to a small value until the member nears its desired position. As shown, tension is applied to a travelling paper web 10 by a roller 22 carried by a lever 24 to which a constant force is applied by a pneumatic ram 40. With switches 138, 140 closed, variations in tension from a desired value corresponding to a vertical position of lever 24 produce movements of the lever which are detected by a selsyn transmitter 114 the rectified output V 3 of which corresponds in magnitude and polarity to the magnitude and sense of tension error. This output is applied through PI regulators 104, 80 to correct the tension by varying the datum of an automatic speed control system for a motor 18 driving rollers 16 transporting tape 10. The speed control system compares the output of a tachometer generator 100 with the output of a manually operated reference potentiometer 92 so that any difference is applied through regulator 80, a limiter 91, and another PI regulator 54 to stabilize the speed by varying the datum of an automatic current control system for a D.C. generator 58 supplying motor 18. The current control system feeds back the voltage across a series resistor 74 through a magnetic amplifier 90 to the input of regulator 54 which controls the generator field excitation through semi-conductor controlled rectifiers 64. If the tension error lies between predetermined limits in either sense, relays 156, 172 apply such bias to a limiter 144 that limiting of the control signal is small but, if the tension error is greater, it is effective through an amplifier 190 or 194 to cause the relays to operate so that there is considerable limiting of the control signal. This permits starting up under speed control only with switches 138, 140 open and then closing them without undue shock, regardless of the position of lever 24, since tension correction will proceed slowly until tension lies between the predetermined limits.