Rotary drive systems

Claim 1

A rotary drive system including a stepping motor having a permanent magnet rotor and a stator provided with a pair of pole pieces arranged in quadrature, each of said pole pieces being associated with a respective field coil, said system also including a source of timing pulses, switchable means for permitting or preventing the application of said pulses to a synthesizing means for generating two voltage waveforms, said synthesizing means comprising firstly, in combination, a multistage binary counter and a first summing ciruit connected to receive outputs from a selected set of said stages and secondly, in combination, said counter and a second summing circuit connected to receive outputs from a different set of said stages, and said waveforms being substantially sinusoidal and in phase quadrature and each of said waveforms comprising a plurality of contiguous voltage steps of varying amplitudes, and means for applying said waveforms to respective ones of said field coils, the system being such that, when said timing pulses are applied to said synthesizing means, said rotor is synchronously rotated whereas when the application of said pulses is discontinued, said rotor stops substantially instantaneously.