Incremental position encoder with direction sensing

摘要

An encoder with incremental scale has a sequence of at least three repeated markings (4,5,6), e.g. light reflecting markings on a rotating disc, where the first marking affects the sensor strongly, the second less strongly and the third least strongly. The amplitude of sensor response and the temporal sequence thus determines the direction of motion of the sensor. A light guide (9,9a) is connected between the light source (19) and a photosensitive sensor (12) with one end directed at a track (2) on the scale. The direction of motion is determined from the timing of the two comparator signals. The encoder has a second track (16) with three markings such that the third marking (17) reflects half as much light as the first (15). If the comparator signal lasts too long an error message is generated.