Device for detecting movement, and its direction, of a rotating body has an array of equally spaced slots around the circumference of a disk with three phase displaced optical sensors to ensure a sensor fault is detected

摘要

Device comprises a rotating body and 14 elements arranged concentrically around its circumference with 3 optical sensors for generation of signals from the elements. The elements consist of equal width slots and arms arranged along radii from the center of the rotation axis of the rotating body with light emitting and receiving transistors arranged in 3 sensor pairs above and below the disk. The sensors are displaced relative to each other so that the phase difference between first and second signals (A and B) is 90 degrees, while that between second and third (B and C) is 135 degrees. This ensures that 3 sensors will only all have a HIGH state or a LOW state simultaneously if one of the sensors is operating incorrectly.