High accuracy optical rotation sensing system

Abstract

An optical sensing system with a rotation sensor head for sensing the rotation of a rotatable object while simultaneously sensing the position of a displaceable object with a position sensor head. An electro-optical unit outputs a modulated optical signal and a chirped rf signal. The envelope of the modulated optical signal has a phase that has a known relation to the phase of the chirped rf signal. The electro-optical unit is coupled to a light guide element and receives and transmits the modulated optical signal along an optical path for reflection off a disk secured to the rotatable object in order to provide a rotation sensing optical signal. A transducing unit receives the rf signal at one input and has another input optically coupled to receive the rotation sensing optical signal while simultaneously receiving position sensing optical signals from the position sensor heads. The transducing unit produces a multi-frequency electrical signal which includes first and second frequencies, the first frequency corresponding to the rotation sensor location and the difference between the first and second frequencies corresponding to the rotation rate of the rotatable object. A rotation detecting unit coupled to the output of the transducing unit processes the multi-frequency signal in order to determine the difference frequency corresponding to the rotation rate of the rotatable object.