| 摘要 |
PURPOSE:To cancel irregularity of rotation originating from a rotation detector in DC motor rotation and to obtain an excellent jitter-free picture by setting the frequency of the rotation detector to an integral multiple of the number of reflecting surfaces of a reflecting member. CONSTITUTION:A DC motor M3 is equipped with a rotary encoder 8 coaxially with a rotary polygon mirror 4' and a frequency signal output proportional to the number of rotations of the M3' is generated by the encoder. This signal is shaped by a circuit 9 into a rectangular wave, whose phase is compared by a phase comparing circuit 10 with that of an input from an oscillation circuit 11; and the circuit 10 inputs their difference signal to a driving circuit 14 after its high frequency component is removed by a low-pass filter 12, driving the M3'. The detected frequency of the encoder 8 is set to an integral multiple of the number of reflecting surfaces of the mirror 4' to cancel the irregularity of rotation, and control is carried out so that the signal from the encoder 8 is in phase with the output signal of the circuit 11, rotating the M3' at a constant speed precisely. |
