GB901182A - Improvements in automatic gauge control systems - Google Patents

Abstract

901,182. Automatic thickness control systems. RANK PRECISION INDUSTRIES Ltd. Sept. 3, 1958 [Sept. 26, 1957], No. 30196/57. Class 38 (4). In an automatic control system for maintaining a dimension of a longitudinally-extending material within a tolerance band, a feed-back quantity inversely proportional to the speed of the material emerging from a forming device is caused to act in a manner tending to reduce the loop gain, defined as the rate at which a correction in response to a given error is applied, so that the rate of correction applied in response to a given error outside the tolerance band is made proportional to the speed and the effect of transportation lag is counteracted. As shown, Fig. 2, the thickness of a material 6, reduced by rolls 2, 2a, is detected by an electrical thickness gauge 7, the output signal of which through an amplifier 8 and relay controller 9 operates a screw-down motor 4 to correct deviation in strip thickness. Signals representative of the speed of the strip, sensed by a tacho-generator 11, and the speed of the screw-down motor, sensed by a tachogenerator 10, are fed to an analogue divider 12, the output of which is proportional to strip speed and inversely proportional to the screw-down speed. The output signal from the analogue divider is fed as a feedback signal to the amplifier 8 so as to turn off the controller 9 at an increasing rate as the speed of the strip decreases. In another embodiment, Fig. 4, the tachogenerators 10, 11 are interconnected by a transistorized arrangement and the feed-back signal is derived from the output of an armature 10a of the tachogenerator 10. The output from an armature 11a of the tachogenerator 11 is fed to the input of a groundedemitter transistor 17 in series opposition with a reference voltage across a tapped portion of a resistor 16. The, output of transistor 17 is direct-coupled through a Zener diode 19 to the input of a transistor 21, the collector circuit of which includes field windings 10b, 11b of the tachogenerators in series. The tapping on the resistor 16 is adjusted so that when armature 11a is stationary, the transistor 17 is biased near to the cut-off point. Movement of the material causes the output from the armature 11a to increase so reducing the bias on transistor 17 and increase the collector current through a resistor 18 and consequently reduce the bias current of the transistor 21 and so reduce the excitation of the tachogenerators so that the output from the armature 10a is rendered inversely proportional to strip-speed. In a further embodiment, Fig. 3, not shown, the voltage from the armature 11a is compared with a reference voltage in a comparator, the output of which, through a current amplifier, energizes the series-connected field windings 10b, 11b.