Patent GB-926476-A (GB)
Title: Improvements in and relating to electric control systems
Inventor: ABBINK-SPAINK PETER FRANCIS
IPC: B65H23/185
Filed: 1958-03-04
Abstract: 926,476. Control of motors. ENGLISH ELECTRIC CO. Ltd. June 4, 1959 [March 4, 1958], No. 6957/58. Class 38 (3). Strip material 10 is drawn off or wound on to a reel 11 under tension by a reversing rolling mill, the reel driving a tachometer generator 15 having its field winding 15a excited by a mill-driven tachometer generator 16 so that the output voltage of the generator 15 varies in proportion to the square of the strip speed. The reel also drives a selsyn generator 18 the output circuit of which comprises a resistor 20 across which is developed a biasing voltage. The combined output voltage is rectified and smoothed to provide a direct voltage whose magnitude varies cyclically between maximum and minimum positive values and which is applied to a pulse-forming device 23 supplying a positive potential to an electronic counter 24, each time the cyclic voltage exceeds a predetermined value (during coiling) or falls below a predetermined lower value (during uncoiling). The counter responds to all the pulses so generated and provides a constant output voltage until the reel has turned through a predetermined number of revolutions when being uncoiled, whereupon the output voltage is varied in accordance with the angular position of the reel. The output voltage of the counter is compared with a reference voltage derived from the generator 15 through potentiometer 26, the output voltage of the comparator being zero during coiling, but which, during an uncoiling pass, rises to a predetermined value when the output voltage of the counter falls below the reference voltage, whereupon automatic deceleration of the mill and coilers is initiated. The counter is also connected to a stopping device 28 which stop the mill when only a small number of turns of strip remain on the reel towards the end of the deceleration period. The pulse-forming device 23 comprises a pair of triode valves, the input signal from the smoothing device being applied to the grid of the first triode, whilst the second grid is supplied from a potential divider be tween the anode of the first triode and earth. The output pulse is taken alternatively during coiling and uncoiling from the anode circuits of the two triodes, a selector switch connecting the output circuit according to the direction of rolling, Fig. 2 (not shown). The counter comprises a number of stages in cascade, each stage including a multi-cathode counting tube which is triggered on receipt of an impulse from the preceding stage, the first stage being triggered by the device 23. The direction of counting is reversed on reversal of the direction of rotation of the reel. Each counting tube is associated with an impedance network across which is developed a voltage dependent on the total count, Figs. 3-6 (not shown). The stopping device comprises a triode valve controlling a relay, the grid being biased to cut-off and being responsive to the fall of count to a predetermined value to fire the valve and energize the relay. The grid is connected to one of cathodes of the first stage counting tube through a selector switch which may be automatically moved to the next higher cathode before each uncoiling pass, Fig. 7 (not shown). In operation, the number of turns wound on to the reel during a coiling pass is recorded, the comparison device being unresponsive to the output voltage of the counter. During the uncoiling pass, the counter is counted down at substantially the same angular positions of the reel as those at which the counter operated during the preceding pass. The output voltage of the counter remains constant until the count falls below ninety-nine whereupon the voltage falls with the count down. Automatic deceleration is initiated when the output voltage falls below the reference voltage, the mill being stopped at the end of the deceleration period. In a modification, the potentiometer slider 26a is adjusted to increase the reference voltage automatically in steps each time a change is made from a count-up to a count-down condition. Automatic deceleration is thus initiated at successively earlier angular positions of the reel. The selsyn generator may have a threephase winding associated with a stepper switch which advances the phase of the rectified output each time a change is made to the countdown condition. Specification 926,475 is referred to.