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Abstract

A stepper motor drive which sequentially energizes the windings of a stepper motor (1,2,3,4). The drive includes a binary counter (11) fed by a clock signal and two multipliers (D.A.C.1, D.A.C.2) which are fed by the binary counter (11) and a reference signal. An adjustable feedback network (30) is arranged to combine a fraction of the output of the multipliers (V.sub.1, V.sub.2) with the reference signal so that the output of the multiplier represents unequal steps of a staircase waveform. A switching network (13) under the control of the counter (11) applies to the windings drive signals in accordance with the output of the multipliers. Each winding has its own amplifier (15,17) to control its current, and pairs of antiphase signals from the switching network (13) are combined in the amplifiers to produce symmetrical changes of current in a respective pair of coils (1 and 2 or 3 and 4). The feedback network (30) distorts the otherwise linear outputs from the multipliers (D.A.C.1, D.A.C.2) and the degree of distortion can be adjusted to compensate for non-linearity in the stepper motor.

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