| 摘要 |
PURPOSE:To detect the rotation velocity at a high accuracy by making the shape of a spot light approximate to the shape of a reflecting and absorbing parts of a rotary disc. CONSTITUTION:As the reflected light of a square spot light 8' enters a photoelectric conversion element 7 and the incident light is photoelectrically converted with the photoelectric conversion element 7, a triangular wave signal is outputted. When differentiated with a differentiation circuit 9, the triangular wave signal is turned to a square wave. As variation in the amplitude due to deviation in the surface of a rotary disc 2 and in the core of a rotating shaft is almost free from time in the square wave, the detection of slice levels at slice levels S and L with a slice circuit 10 is in no way affected by the amplitude variation. Slight change in the slice levels S and L of the slice circuit 10 causes no deviation in the phase as the slice level points are set at the rising and falling of the square wave. This eliminates deviation in the detection of phase with a phase detection circuit 11 by sampling at the slice level points set with the slice circuit 10 enabling the detection that the rotation velocity of the rotary disc 2 is constant with which correct phase can be detected at a semicycle T. |
