| 摘要 |
Apparatus for controlling the rotational speed of a polygonal mirror adapted to scan a reflected light beam over a desired scanning area as each facet of the mirror is rotated into the path of an incident light beam. The apparatus comprises a poly-phase motor coupled to the mirror for driving same. The motor has a plurality of input terminals and a plurality of motor windings connected to the input terminals. First means responds to the reflected light beam for generating a first clock signal having a frequency proportional to the actual rotational speed of the mirror. Second means generates a second clock signal having a frequency proportional to a desired rotational speed of said mirror. Third means coupled to the first and second means responds to the first and second clock signals for generating a third clock signal having a frequency representative of the difference in phase or frequency between the first and second clock signals. A poly-phase generator is coupled to the third means and is responsive to the third clock signal for generating a plurality of mutually phase-displaced drive signals for respective application to the plurality of input terminals of the motor, whereby a plurality of mutually phase-displaced sinusoidal signals are respectively developed across the motor windings, each sinusoidal signal having a frequency proportional to the frequency of the third clock signal.
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