Digital coder for angular position of shaft - employs vernier principle and has photoelectric devices to provide accurate measurement

摘要

The shaft encoder contains a disc (1) fixed to a shaft (2) running in bearings (3). Light from the annular sources (51, 52) impinges on the ring of detectors(41) through two concentric rings of slots (11, 12) in the disc. The outer (Vernier) ring has equidistantly-spaced slots whereas the inner (Key bit) ring has not. Signals from the photodetectors (41) and clock (7) are processed in logic circuits (9) to give the angular position of the shaft. The high redundancy of linear coding provides both good resolution and some self-correction and fault diagnosis if a sensor fails.