GB989613A - Improvements in or relating to automatic control systems - Google Patents

Abstract

989, 613. Automatic control of thickness and tension. DAVY & UNITED INSTRUMENTS Ltd. June 29, 1961 [July 5,1960], No. 23450/60. Heading G3R. An automatic control system for a stand of a rolling mill enables strip thickness to be kept constant by variations of both tension and screwdown while maintaining tension otherwise constant or within set limits. As shown, a tension reference signal derived from a potentiomete 19 is continuously compared in a circuit 23 with a signal from a tension meter 25 indicating the actual tension in a strip 21 between rolls 12 and 13 of a tandem mill. If the actual tension departs from the reference tension a corrective output signal from circuit 23 is applied over an amplifier 27 to a control circuit 28 whereby the speed of the motor 29 for the rolls 13 is adjusted; the strip tension is thereby maintained constant. The thickness of the strip leaving rolls 13 is measured by a circuit 15 giving on output lines 16 and 17 signals representing the departure of the strip thickness from a desired value. The signal on line 17 modifies the reference tension signal derived from potentiometer 19, and the signal on line 16 is applied to a screwdown controller 18. If the thickness error is small, the adjustment of strip tension in response to the signal resulting from the modified reference is sufficient to remove the error before the screwdown controller becomes effective. If the error is large, the reference signal applied to circuit 23 is limited by a circuit 22 so the tension in strip 21 is brought to this limiting value with the error not completely eliminated. The screwdown controller 18 then has time to become effective and adjusts the setting of rolls 13 to reduce the thickness error to zero. The signals on lines 16, 17 then disappear and the tension in strip 21 is automatically returned to the reference value as set by potentiometer 19. The thickness is thus maintained constant by automatic control of tension and screwdown. In a modification (Fig. 2 not shown) the thickness error signal from the circuit 15 is applied to the screwdown controller only when the modified tension reference signal exceeds the limits determined by circuit 22.