Method and controller for detecting a stall condition in a stepping motor during micro-stepping

A method for detecting a stall condition in a stepping motor, the stepping motor having two coils and a rotor, the stepping motor being micro-stepped by substantially continuously driving both of the two coils with out-of-phase time varying voltages, the method comprising:

• stepping the stepping motor to a next micro-step;
• determining that a predetermined motor parameter of a first coil of the two coils is to be sampled;
• opening the first coil for a predetermined period, wherein the predetermined period is less than or equal to a micro-step;
• sampling the predetermined motor parameter of the first coil during the predetermined period;
• closing the first coil;
• integrating the predetermined motor parameter;
• and
• comparing the integrated predetermined parameter to a threshold to produce a comparison result;
• and
• using the comparison result to determine if a stall condition exists.

A motor controller, comprising:

• a coil driving circuit for driving a first coil and a second coil of a stepper motor;
• a control circuit, coupled to the coil driving circuit, for causing the coil driving circuit to micro-step the stepper motor by supplying each of the first and second coils with substantially continuous out-of-phase time varying voltages, and the control circuit for causing either the first coil or the second coil to periodically open during a micro-step;
• and
• a stall detection circuit, coupled to the coil driving circuit, for sampling a predetermined motor parameter of one of either the first coil or the second coil during the micro-step when the one of either the first coil or the second coil is open, to determine if the stepper motor has stalled.