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Image forming apparatus including motor-driven rotary scanner and system for judging if motor rotation comes to steady state and for maintaining rotation at steady state
Image forming apparatus including motor-driven rotary scanner and system for judging if motor rotation comes to steady state and for maintaining rotation at steady state
A polygonal mirror is rotated by a brush motor, and a laser beam deflected by the polygonal mirror is detected by a sensor for generating a signal which determines a printing start position of each scanning line. The rotating speed of the motor is proportional to the frequency of the signal, and when the frequency of the signal becomes equal to a reference value, the motor can be judged to come to a steady rotation state. In a control circuit, the rotating speed of the motor is detected from the frequency of the signal, and the difference between the detected speed and a reference value is calculated and is sent to a comparator. Based on the speed difference and the back electromotive force which occurs in the motor, the comparator controls the driving voltage of the motor.
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