High accuracy optical position sensing system

Abstract

An optical position sensing system for sensing the position of a displaceable element. 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 surface of the displaceable element in order to provide a position sensing optical signal. A reference reflecting element is disposed in the optical path upstream of the displaceable element for partially reflecting the transmitted modulated optical signal in order to provide a reference optical signal. A transducing unit receives the rf signal at one input and has another input optically coupled for receiving the position sensing optical signal and the reference optical signal which have, respectively, first and second time delays with respect to the chirped rf signal. The transducing unit produces a multi-frequency electrical signal which includes first and second frequencies corresponding to the first and second time delays, respectively. A position detecting unit coupled to the output of the transducing unit processes the multi-frequency signal in order to determine a difference frequency corresponding to the difference between the first and second frequencies and representing the position of the displaceable element.