Opto-electronic scale-reading apparatus

摘要

Opto-electronic linear encoding apparatus includes a scale (110) and a readhead (112) movable relative to the scale in a direction of spacing of the scale lines. The readhead (112) is formed of a single semi-conductor substrate (120), typically made of gallium arsenide. The substrate (120) is divided into two regions (114,116); the region (114) includes a light emitting diode (118) having a plurality of elongate electrodes (124) provided on its upper surface and spaced in the direction of spacing of the scale lines. The light emitting diode region (118), the electrodes (124) and the common electrode (120) co-operate to produce a plurality of coplanar elongate light emitting regions in between the electrodes (124) which perform the combined functions of a diffuse light source and an index grating. Region (116) is an analyser having a plurality of elongate photosensitive elements spaced apart in the direction of spacing of the scale lines. The photosensitive elements are divided into a plurality of sets and are interleaved on the substrate (120) in a repeating pattern with the outputs of elements of a given set being connected in common. The analyser (116) thus performs the combined functions of an analyser grating and a plurality of photodetectors which generate a plurality of phase-shifted cyclically varying signals.