ABSOLUTE ROTARY ENCODER

ConstructionAbsolute digital type produces a unique digital code for each distinct angle of the shaft. They come in two basic types: optical and mechanical.[edit] Mechanical absolute encodersA metal disc containing a set of concentric rings of openings is fixed to an insulating disc, which is rigidly fixed to the shaft. A row of sliding contacts is fixed to a stationary object so that each contact wipes against the metal disc at a different distance from the shaft. As the disc rotates with the shaft, some of the contacts touch metal, while others fall in the gaps where the metal has been cut out. The metal sheet is connected to a source of electric current, and each contact is connected to a separate electrical sensor. The metal pattern is designed so that each possible position of the axle creates a unique binary code in which some of the contacts are connected to the current source (i.e. switched on) and others are not (i.e. switched off).[edit] Optical absolute encodersThe optical encoder's disc is made of glass or plastic with transparent and opaque areas. A light source and photo detector array reads the optical pattern that results from the disc's position at any one time.This code can be read by a controlling device, such as a microprocessor, to determine the angle of the shaft.The absolute analog type produces a unique dual analog code that can be translated into an absolute angle of the shaft (by using a special algorithm).