| 摘要 |
A photoelectric transducer (14) produces first and second periodic signals (A), (B) which are 90 DEG out of phase with each other in response to rotation of a servo motor shaft (12a). The first and second signals (A), (B) are differentiated, directly full wave rectified and summed to produce a velocity signal (Vw+), (Vw-) having a magnitude proportional to the rotational velocity of the shaft (12a). The peaks of the first and second signals (A), (B) are detected to produce a reference signal (Vr) having a magnitude corresponding thereto. The magnitude of the reference signal (Vr) is reduced in accordance with the difference between the present position of the shaft (12a) and a command position to produce a velocity command signal (Vc+), (Vc-). The velocity signal (Vw+), (Vw-) is compared with the velocity command signal (Vc+), (Vc-) to produce a drive signal corresponding to the difference therebetween which is applied to the motor (12). Fluctations in the amplitude, D.C. component and phase of the first and second signals (A), (B) affect the reference signal (Vr) and the velocity signal (Vw+), (Vw-) equally and are thereby cancelled out.
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