Incremental optical encoder having partially opaqued quadrature detectors

Claim 1

An incremental optical encoder device for measuring an angle of rotation around an axis of a movable member as a function of time and for determining the direction of rotation of said member, comprising a light source emitting a light beam along an optical path, an encoder disc arranged coaxially with respect to said movable member and provided with a series of opaque zones and of light transmissive zones, said zones being arranged so as to cross said optical path and to modulate said light beam upon movement of said encoder disc, and detection means including at least one group of four light detectors, each detector having a light-sensitive surface arranged to receive the modulated light beam, each of said light-sensitive surfaces forming substantially a plane quadrilateral comprising two segments of concentric circles the centers of which are the point of intersection of the plane of said light-sensitive surface with the axis of rotation of said disc, said detection means being arranged for generating output signals in quadrature upon movement of said encoder plate, each of said light-sensitive surfaces comprising at least one zone covered by an opaque layer and an adjacent free zone in such a manner that said four light detectors generate the said output signals in quadrature, each light detector generating an output signal of a single phase.