Patent GB-841504-A (GB)
Title: Improvements in or relating to electric motor control apparatus
IPC: B21B37/16
Filed: 1958-03-28
Abstract: 841,504. Control of several D.C. motors. WESTINGHOUSE ELECTRIC CORPORATION. March 28, 1958 [April 8, 1957], No. 10032/58. Class 38 (3). [Also in Group XXXV] In a strip rolling mill, a control signal received from a radiation gauge 18 passes through amplifier 20 to provide a voltage across potentiometer 106 which varies as a function of thickness error of the strip. A control winding of magnetic amplifier 62 is energized in accordance with the voltage developed across potentiometer 106, the control signal from the gauge 18 being also applied to an integration device 26 which in turn energizes a second control winding of the magnetic amplifier. The output windings of amplifier 62 are connected across impedances 64, 66, which are in series with impedances 74, 76, exciter 130, and generator 128. A mill stand motor 24 is supplied from the generator, the series circuit being adapted to determine the excitation of control windings of a magnetic amplifier 70 which controls the field windings 158, 159, of the generator. The impedances 74, 76, receive an IR-compensating feedback control signal. A strain gauge 28 supplies an amplifier 34 which operates with reference source 35 to provide an output signal representing the difference between the actual rolling pressure of stand 10 and a predetermined desired rolling pressure. The output signal is supplied to amplifier 36, and is secondly supplied through integration device 38 to amplifier 36, for energizing a third control winding of the magnetic amplifier 62. A screwdown motor 44 is also controlled by the voltage developed across impedances 64, 66, an up or down relay being energized in accordance with the polarity of this voltage. The relays do not become effective until the magnitude of the voltage across the impedances reaches a predetermined value, and the screw-down motor is operated for a short period only, after which it is stopped for a longer period for the effect to be measured by the strain gauge 28 and the radiation gauge 18. This sequence continues until the output voltage of the amplifier 62 is reduced to a predetermined value, Fig. 3 (not shown). In another arrangement, the control signal received from the radiation gauge is supplied through a circuit, Fig. 8 (not shown), which does not provide an output signal until its input signal has exceeded a predetermined value. The output signal is used to control the field winding of a generator supplying the screwdown motor, which is also provided with manual control. A generator supplying a motor, which drives a reel from which strip is taken for passage through the mill stand 10, has its field winding controlled in accordance with a signal derived from the strain gauge 28 and also with regard to the position of the screwdown mechanism. The field winding of the reel motor is controlled in accordance with the speed of the mill stand, and as a function of the armature current and voltage of the reel motor. A current-limiting circuit, Fig. 9 (not shown), is associated with the field winding of the reel generator to limit the strip tension to a safe value. If the strip thickness is excessive, the strain gauge provides a control signal to cause the reel motor to increase the striptension and, at the same time, the radiation gauge causes the screw-down device to reduce the spacing between the rolls provided that the control signal therefrom exceeds a predetermined value, Fig. 4 (not shown). In a further embodiment, the radiation gauge operates to vary the speeds of several stands of a rolling mill, the strain gauge operating to vary the speed of one stand only, for varying the strip-tension between that stand and the preceding stand and correcting errors in the strip-thickness, Fig. 6 (not shown). Specifications 841,503 and 841,505 are referred to.