Optical angular displacement sensor with high resolution integrated in silicon

Abstract

A novel optical angular displacement sensor has been developed. It consists of two parts: a rotating element with reflective patterns fabricated onto it, and a stationary part with optical detectors and readout circuitry, integrated in a standard BiFET process. A high-resolution absolute angular position measurement is realized by combining the information of a high-resolution incremental analog sensor part with that of a low-resolution absolute binary sensor part. The high-resolution sensor part is implemented by a reflective zigzag pattern on the rotor and a position-sensitive device (PSD) on the stator. The low-resolution part comprises a binary reflective code pattern on the rotor and a photodiode array on the stator. An angular displacement will cause the code on the photodiode array to alternate and the reflected light spot on the PSD to move over the full length of the PSD in between each code transition. The sensor enables a contactless angular measurement to be made over the full range of 360 degrees, without blocking at full scale. The sensor is insensitive to electric and magnetic fields and can be placed radially at any position on a rotating shaft.