GB1154788A - Signal Generator - Google Patents

Abstract

1,154,788. Control of A.C. motors. GOLAY BUCHEL & CIE S.A. 16 Oct., 1967 [14 Oct., 1966], No. 46963/67. Heading H2J. The commutation of an induction motor is controlled by signals representing the speed of the motor and the slip, the speed-responsive signal being derived from an apertured disc which is driven by the motor and co-operates with a photo-electric device, for example, and delivers a set number of pulses per revolution of the motor. In one arrangement, the signals representing the speed and slip respectively are added to form a signal which is applied to a frequency divider for controlling the rate of commutation. In a modification, the commutation-signal is subtracted from the speed-signal to form the slip-signal which, in turn, modifies the commutation signal. A circuit for subtracting the commutationsignal, applied to input 2, from the speedsignal, applied to input 1, comprises a bi-stable flip-flop formed by transistors 10, 11. If two successive pulses are applied to input 2 without an intervening pulse on input 1, transistor 11 is conductive at the same time as the transistor 16 and a subtraction pulse is delivered over line 18. A transistor 19 becomes conductive when it receives the pulses over line 18, and if the frequency of these pulses is sufficient, diode 20 conducts to reduce the potential on line 32. This potential sets the frequency of oscillation of a multi-vibrator comprising transistors 21, 22, for determining the commutation frequency. When the motor is started, the potential on line 32 is increased at a rate determined by resistor 24 and capacitor 25 to increase the commutation frequency until the limit set by potentiometer 35 and transistor 23 is reached. If an overload causes excessive slip, the transistor 19 responds automatically to reduce the commutation frequency in a manner to maintain maximum torque.