Patent ID: 8371507

Claim:
In a laser scanning system including a laser source producing a laser beam that is scanned across a scanning field by a polygon mirror having mirror facets rotated by a DC multi-pole motor having a rotor with multiple magnet poles, and an internal Hall Effect sensor for sensing each magnet pole passing said internal Hall Effect sensor during each rotation of said rotor and generating a binary signal pulse for each sensed magnet pole, a method of determining an occurrence of a predetermined home transition point in said DC multi-pole motor, comprising the steps of: (a) rotating, said multi-pole rotor within said motor; (b) while said rotor is rotating, using said internal Hall effect sensor to generate a signal pulse train comprising sequential sets of two or more binary signal pulses for each revolution of said rotor; wherein each binary signal pulse has a time duration corresponding to a relative position of one said magnet pole; wherein, within a given revolution, each of said binary signal pulses has a pulse width that is different from pulse widths of other binary signal pulses generated by the other magnet poles, and these pulse width difference allow the binary signal pulses to be distinguished from each other during the revolution of said rotor; and wherein only one edge of one of said binary signal pulses is associated with said home transition point of said DC multi-pole motor; and (c) during each revolution of said multi-pole rotor, measuring the pulse widths of said binary signal pulses with appropriate accuracy to distinguish each said binary signal pulse by its said measured pulse width, tracking a ranking order of measured pulse widths of said binary pulse signals generated during each revolution of said rotor, and determining the occurrence of said predetermined home transition point associated with said DC multi-pole motor.