SHAFT_ENCODER

Published:2009/7/13 22:44:00 Author:May | From:SeekIC

The electro-optical shaft encoder is a combination of encoding disk, photosensors, and counters. The encoding disk and photosensors generate a pulse train that can be counted to determine rate. The disk's direction of rotation can be sensed and used to determine count direction (for example, count up for clockwise and count down for counterclockwise). The disk need not be a precision part; it can be tytade from clear plastic with dark sections or lines painted on it. The number of lines on the disk determines how many pulses are generated per revolution. If two photosensors are used, two signals in quadrature are generated; from those, the direction can be sensed. A simple encoding disk is shown in A; note the alternating transparent and opaque sections. A pair of electro-optical photosensors are positioned (as shown) so that when one is centered over a section, the other is positioned over a transition. As the disk is rotated, each photosensor will be alternately illuminated and obscured and will produce outputs (as shown). A clockwise rotation is indicated when there is a positive transition (from dark section to light section) at sensor B while sensor A is low (obscured by a dark section), a positive transition at A while B is high (over a light section), a negative transition of B (going from light to dark) while A is high, and so forth. A counterclockwise rotation is indicated when there is a positive transition of B when A is high, a negative transition of A when B is high, etc.



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