GB1279394A - Improvements in or relating to the control of electric motors - Google Patents

Abstract

1279394 Control of stepping motors HAWKER SIDDELEY DYNAMICS Ltd 8 Oct 1969 [8 Oct 1968] 47689/68 Heading H2J The rotor of a polyphase motor is made to follow a magnetic field vector that shifts round angularly as a result of the switching of the field currents in the several field windings, the switched current pulses applied to the various fluid windings of the stepping motor being pulse width-modulated so that the magnetic field vector rotates smoothly instead of stepwise. A reversible digital counter 12 provides sequentially switched outputs to the motor field windings and receives, at its forward and reverse inputs, a pair of pulse trains f1, f2, the frequency of one being variable with respect to the other. The counter may be a Johnson counter with internal connections to inhibit an output of all binary "ones" or all binary "zeros". A unit 15 ensures that corresponding pulses from the separate trains are not applied simultaneously to the counter but one is delayed before reaching the counter input. The unit comprises respective channels to transmit the two pulse trains, each channel comprising an input bi-stable stage followed by a gate which is cross-coupled with the corresponding gate of the other channel so that when one gate is passing a pulse the other is inhibited, each bi-stable stage being reset after a time delay, by an output pulse from its respective following gate. Both gates feed a common clock channel for the counter through a respective differentiator. The motor is of the three-phase type driven in a six-step mode by the outputs of a three-stage counter applied through respective power amplifiers 13 to the motor field windings. The motor may meter the flow of fluid to an hydraulic motor which is thereby slaved to the electric motor.