When it is required to determine the angular position of rotating shafts then a rotary encoder or optical encoder is used. They usually take the form of a miniature electric motor in appearance, and sometimes get mistaken for stepper motors.
The optical encoder drive shaft is directly coupled to a rotating spindle via a flexible coupling. An electric signal is derived from the unit in a system of digital pulses. This pulse train is produced by a combination of a calibrated disc and light emmitting diode.
The disc, which is attatched to the encoder shaft, rotates, cutting a beam of light produced by the diode. The number of pulses obtained is dependant on the number of graduations set out on the disc. There is a very wide range of encoders available and it is important to select for particular applications. Pulse lines can be as low as 1 pulse/rev to as high as 20000 pulses/rev and can be powered at 5v or 11-30v. Greenbank stock the Italsensor Encoder TK561 with 1024ppr and 11/30V supply.
Example Rotary Encoder
Encoders are an ideal solution where there is a requirement for computer control and automated production. It is used extensively in robotics, machine tool, batching systems, and in fact any application where precise angular monitoring is required. They are also used for speed sensing, and control of rotating machinery. There are basically two types used in industry to-day:
With incremental encoders, when the electric power is removed, the encoders positional data is lost; whereas with absolute encoders the data is retained, this is very useful in indexing applications such as machine tool operation.