Laser system for measurement of angular position - uses separator to generate beams in two incident planes for reflection by target mirror having half-mirrored perpendicular blade

摘要

A plane mirror acting, as a target, is fixed to a solid whose angular position varies. A semi reflecting blade is mounted perpendicularly on the mirror. A beam from a laser mounted firmly on a reference is directed onto separators to direct two beams onto the target in two parallel incident planes. Each beam divides into two further beams by reflectionat the blade and mirror to produce parallel reflected beams. The four reflected beams are subjected to variations which are a function of the angular variation of the solid. Four detectors each comprising four quadrant photocells are servo controlled to remain centred on the beams to provide a differential measurement w.r.t. a zero position, and thus indicate angular position change.