Light beam distance encoder

摘要

A light beam encoder for measuring absolute distance over a linear path with an accuracy of at least that provided by incremental optical encoders, but over longer ranges than can readily be achieved with optical linear encoders due to the difficulty of providing a sufficiently long optical scale with the requisite accuracy and resolution. The resolution provided by the light beam encoder can be approximately 1-10 microns. A high frequency amplitude modulated light beam is reflected by a reflector disposed at the distance to be measured, and the phase lag of the reflected light beam is determined to provide an absolute measure of the distance. The encoder mixes a local oscillator signal generated by a phase locked loop with both a reference oscillator signal and the distance signal. Thus, the heterodyne mixers provide two low frequency signals preserving the phase lag between the two optical signals. In a preferred embodiment, high-resolution computation of the phase lag is accomplished with a microprocessor receiving precise crossover time information indicating time delays and periods over several cycles of the low frequency signals using linear and nonlinear filtering and averaging algorithms.