GB841503A - Improvements in or relating to electric motor control apparatus - Google Patents

Abstract

841,503. Control of several D.C. motors. WESTINGHOUSE ELECTRIC CORPORATION. March 28, 1958 [April 8, 1957], No.10031/58. Class 38 (3). [Also in Group XXXV] A rolling mill comprises a mill stand 10 having rolls 12, 14 for determining the gauge of strip 16 before it is passed to a delivery reel, screw-down mechanism 22 being operated by motor 24 for determining the spacing of the rolls. The speed of the stand is determined by motor 26 in response to a signal derived from strain gauges 31, 33, the control signal being passed to a first amplifier which, in turn passes the amplified signal to a second amplifier and to an integration device. The second amplifier is also provided with a control signal from the integrator and the resultant output signal from the amplifier is used to control the motor 26. If the resultant control signal exceeds a predetermined value, the screw-down mechanism comes into operation. The strain gauges 31, 33, sense the pressure between the rolls 12, 14, to vary the impedance relationship of a bridge circuit comprising variable impedances 40, 42, so energizing control windings 56, 58, of a push-pull magnetic amplifier 80. Control windings 60, 62 are energized in accordance with a predetermined gauge of the strip so that an error signal is developed across impedances 82, 84, for application to the control windings. 86, 88, of the amplifier 90. The error correction signal developed across impedances 108, 110, is applied to the control windings of an output amplifier 116 for varying the speed of the motor 26, and is also applied to control windings 118, 120 of amplifier 100 so that a pilot motor 136 adjusts potentiometer 132 by an amount corresponding to the integral of the error correction signal. A feedback signal is thus provided for control windings 102, 104, to bring to zero the error correction control signal resulting from the difference between the actual roll pressure and the predetermined pressure. The initial setting of the reference potentiometer 64 is made by clutching the arm of reference potentiometer to the motor 136, and de-clutching the arm of the potentiometer 132 from the motor. An error control signal is applied to windings 96, 98, of amplifier 100 whereby the pilot motor is energized to adjust the potentiometer 64 until the error signal is balanced by suitable energization of windings 60, 62, such that the voltage across impedances 82, 84 is reduced to zero. To prepare the system for normal operation, contact 95 is opened, and contacts 97, 99, 101, are closed to connect the windings 118, 120, across impedances 108, 110, and the feedback stabilization windings 122, 124 and 126, 128 across potentiometer 130, 132. The pilot motor is de-clutched from the potentiometer 64 and coupled to the potentiometer 132. The potentiometer 64 is also automatically re-set when the screwdown device is jogged by the motor 24, the potentiometer 132 being re-adjusted when the end of a particular coil of strip material is reached. The output windings of the amplifier 116 energize impedances 156, 158, connected in series with impedances 160, 162, which receive an IR compensating signal from amplifier 164. The series circuit also includes control windings 180, 182, of amplifier 178 for energizing field windings 176, 177 of the supply generator 174 for the motor 26. The system described corrects a major portion of the initial errors in strip thickness, a radiation gauge being provided to afford a subsequent and more accurate correction to either the mill motor 26 or the screw-down motor 24. Specification 841,504 and 841,505 are referred to.