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Abstract

An analog optical position transducer for detecting angular position of a rotatable member of a motor. The transducer includes a plurality of sensing surfaces placed in one frame of reference and a modulator located in another frame of reference, one of the frames of reference being stationary and the other moving with the rotatable member. The relative angular position of the two frames of reference is determined from the amount of light varied by the modulator and detected by the sensing surfaces. The modulator employs a radiation source which is located on a diffusive surface or which irradiates the diffusive surface of the modulator. Radiation emitted from the diffusive surface is modulated by the modulator depending on the relative position of the modulator and the sensing surfaces. A lens focuses the emitted radiation onto the sensing surfaces. The sensing surfaces are symmetrically arranged about an axis passing through the center of rotation of the rotor, and their relative distribution with respect to the surfaces of the modulator enables differential detection. An analog circuit connected to the sensing surfaces continuously determines the angular position of the rotatable member from the amount of light detected at each of the sensing surfaces. The system is effective to accurately position a mirror in a high speed laser scanner.

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First Claim