Study on array of photo-detector based absolute rotary encoder

Abstract Absolute rotary encoder is an electromechanical device which indicates the absolute position of an object. In this paper, a low cost absolute rotary encoder is presented. Proposed encoder measures the rotational position of a moveable object with accuracy of ±1° and resolution of 0.1°. Here, Encoder disc does not carry any binary or gray coded positional information, instead of that it acts as a positional pointer over the array of photo-detector based circular track. The one forth segment of fiber glass disc is kept transparent and rest portion is covered up by a semi-transparent layer. The disc is placed between the circular track and a light source. A marker at the centre of transparent portion indicates the angular position of the object. Now during the rotation of disc along with the object, high intensity of light is passed through the disc’s transparent portion compared to the semi-transparent portion and impinged over a fixed circular track. Thus according to the variation of light intensity over the track surface area, absolute angular position of object is determined by analyzing the variation of photo-detector’s output. In order to proof of this concept, an experimental prototype has been designed, developed and tested.