Optical encoder having controllable lead-lag phase trim sensitivity

Abstract

An optical encoder having controllable lead lag phase trim sensitivity includes a light source, and a pair of coplanar photodetectors adjacent each another for generating phased electrical signals in response to light energy generated by the light source. A scale between the light source and photodetectors has alternating opaque and translucent regions extending substantially perpendicular to a locus of relative movement. A reticle has alternating opaque and translucent regions parallel to the regions of the scale so that relative movement of the scale and reticle alternately blocks and transmits light to the pair of photodetectors which put out phased electrical signals indicative of relative position and direction of movement of the scale and reticle. A substantially lineal light blocking zone formed on the reticle is arranged at a predetermined acute rotational angle relative to the locus of relative movement between the scale and reticle. A mechanism is provided for relatively rotating the scale and reticle about the centroid of said light blocking zone in order to adjust lead and lag trim of the phased electrical signals relative to a nominal phase difference, such as quadrature. The sensitivity of lead and lag trim is controlled by the particular acute rotational angle selected for the light blocking zone.