GB1354424A - Electrical stepper motors and methods of operating them - Google Patents

Abstract

1354424 Control of brushless motors ULTRA ELECTRONICS Ltd 8 March 1972 10892/72 Headings H2A and H2J The windings SW1-SW4 of a stepper motor are energized in dependence on rotor position under the control of a rotor position sensor comprising a ferromagnetic vane rotatable with the motor rotor and associated with at least one winding energized by an oscillator. The windings are energized through power transistors 150, 152, 166, 167 and a current limiter circuit 168. The rotor position sensor disclosed comprises two centre-tapped windings 27, 29, Fig. 4A (not shown) displaced by 90 degrees round the motor axis and connected in parallel with a voltage divider (47) across the oscillator output. The voltage differences between the winding centretaps and a centre tap of the voltage divider provide a measure of rotor position and are obtained as positive or negative voltages on capacitors (54, 59). These voltages are transformed into signals on lines 108, 109, 122, 123 controlling the power transistors through NOR circuit 128, NAND circuits 137, 138 and transistors 145, 151, 157 and 158. Forward and reverse command signals are supplied to the NAND circuits through terminals 143, 144. To stop the rotor in a predetermined position a circuit 175, Fig. 4C (not shown), produces eight pulses per rotor revolution in one direction on one output and eight pulses per rotor revolution in the opposite direction on another output, these pulses being fed to a computer which counts the pulses and controls the inputs to terminals 143, 144 accordingly.