Patent GB-895130-A (GB)
Title: Improvements in or relating to electric control systems
IPC: A01G17/06
Filed: 1960-06-20
Abstract: 895,130. Automatic control systems for rolling mills. CANADIAN WESTINGHOUSE CO. Ltd. June 20, 1960 [June 27, 1959], No. 21550/60. Class 38 (4). [Also in Group XXXVIII] In a rolling-mill electric control system comprising means for producing an electric signal which includes an unwanted periodic disturbance due to eccentricity of a roll of the mill, the signal is sampled during successive overlapping periods of time, each sample is averaged, and a control signal free of the periodic disturbance is derived from the averaged samples. Fig. 1 shows an arrangement in which strip material 6 is reduced in thickness by being passed under tension between the rolls 2, 3 of a rolling-mill 1. The rolls 2, 3 co-operate with back-up rolls 4, 5, roll 5 being rotated about a fixed axis by an electric motor (not shown) while roll 4 is journalled in plummer blocks 7 which are vertically movable in the mill-frame by a motor 11 acting through worm gears 10 meshing with pinions 9 on screw-down members 8. Variations of thickness &c. of the material entering the mill are compensated by deriving a signal proportional to the strain on the mill, i.e. to the separating force between the rolls, from strain gauges 12 responsive to the forces exerted by screw-down members 8, and passing the signal to a summing circuit 22 wherein it is combined with signals representing the spacing between the rolls, produced by transducers 15 operated by pinions 9, with a signal representing the desired thickness of the strip, produced in a manually-operated gauge-setting circuit 23, with a monitoring signal gauging the output thickness, from flying micrometers 25, and possibly with a signal from a potentiometer 24 representing mill speed, to produce an output signal which is used to control the tension of the material and the spacing of the rolls. Eccentricity of roll 4 or 5 produces a periodic spurious component in this output signal which is eliminated in a sampling and averaging circuit 26, shown in detail in Fig. 2. The signal from the summing circuit is amplified and, if necessary, converted, at 30 and fed simultaneously to five banks, A to E, of switch contacts, each bank comprising three contacts. The contacts of each bank are closed and opened successively, by a commutator 36 (Fig. 1) coupled through gearing to back-up roll 4, in the following manner: contact A1 is closed for a period equal to one revolution of the back-up roll during which capacitor 37 charges; A1 opens and A2 closes for one-third of a revolution while the capacitor 37 discharges through amplifier 47; A2 opens and A3 closes for one-third of a revolution while capacitor 37 completes its discharge through a resistor 42. This sequence is reproduced in the other banks in such a manner that one, and only one, capacitor is discharging through 47 at any time. The periodic disturbance is thus eliminated from the output of the circuit 26, which is passed via a circuit 27, Fig. 1, comprising manually set gate and limiting circuits 28, 29, to a tension control unit 20 and to screw-down motor 11. Gate 28 is set to prevent the motor 11 operating to correct errors during the early passes of material 6 through the mill, and the limiting circuit 29 is set to ensure that, in the final passes, motor 11 operates only when maximum tension control has been applied. The tension control unit 20, which is also responsive to a manually operated tension signal generator 21, controls the operation of motor-generators 18, 19 on reels 16, 17, respectively, between which the material 6 is exchanged during passes. The sampling and averaging device may comprise amplifiers employing negative capacitative feed-back, or electro-mechanical integrators such as motordriven potentiometers. The gauge monitor 25 may be a radiation or other thickness gauge and the gauge setting circuit 23 may be replaced by, e.g., a mechanical device for influencing the output of summing circuit 22. Specification 892,058 is referred to.