Restraining the instability of a stepper motor

Claim 1

In an apparatus for preventing instability of a stepper motor operated by a plurality of alternating currents of different respective phases and controlled by a sequence of control pulses, said control pulses defining an angular parameter of the stepper motor, the improvement comprising a timing generator for producing a pulse signal, a combined controllable delay element and pulse generator connected to the output of said timing generator, and operable to pulse time modulate said pulse signal, a sequence generator connected to the output of said combined controllable delay element and pulse generator, said sequence generator generating said control pulses, said control pulses controlling said stepper motor, a resistor connected to an output of said sequence generator for providing the sum of said phase currents, and for transforming said sum into a voltage fluctuating about an average value, a low-pass filter connected to said resistor for receiving said voltage, and for determining said average value with a substantially 90° phase shift, and a high-pass filter connected to an inut of said combined delay element and pulse generator for providing fluctuations about said average value to said combined delay element and pulse generator for pulse time modulating said pulse signal, said combined delay element and pulse generator including a counter, a high frequency pulse generator connected to an input of said counter, an analog-to-digital converter having an output thereof connected to another input of said counter, and a decoder having an input thereof connected to an output of said counter.