Patent ID: 8174223

Claim:
A method of detecting a state of synchronization loss in a stepping motor, in which a means for applying one of control current and control voltage to a coil of each phase to thereby drive an N-phase stepping motor and a means for individually measuring a back EMF voltage induced at the coil of each phase are employed, wherein the method comprises the steps of: halting application of the one of the control current and the control voltage at the coil of each phase by turns phase by phase for such a short period of time as not to affect rotation of a rotor of the stepping motor at a predetermined timing within one step period of the rotor; measuring the back EMF voltage at the coil during the short period of time, the measuring being performed multiple, consecutive times; and judging that the stepping motor loses synchronization when a measurement result of the back EMF voltage at the coil of at least one phase satisfies a predetermined detection criterion, the measurement result of the back EMF voltage at the coil of at least one phase being individually analyzed.