Top > Electrical & electronic components > Position encoder

Position encoder

Encoders serve as devices for detecting rotational and linear positions of machines such as servomotors, linear actuators, tachometers, and the like. They allow accurate positioning of such machines, and determination of such quantities as velocity and acceleration. Position encoders are used to generate an electronic signal that indicates an absolute mechanical position, or an incremental mechanical movement relative to a reference position. Rotary encoders and linear encoders are known. There are many known ways of generating a position signal, including magnetic sensors, capacitive sensors, and optical sensors. Linear and rotary type encoders are used extensively as detectors for control over feed rates and stop positions of various actuators. Classified in another way, these encoders fall into two broad types: incremental and absolute. The incremental type encoder detects and outputs increases and decreases in relative movement between coder and detector. A typical incremental encoder includes a wheel with tally marks arranged in a circular array about the wheel. A sensor detects the passage of tally marks as the orientation of the wheel is changed. Absolute position encoders provide a readout of absolute position, thereby avoiding the problem with initialization movements that plagues incremental encoders. The absolute type encoder reads the relative position between coder and detector using a fully periodic array pattern scale of the coder. The relative position, after suitable processing, is output as an absolute position. Encoders can employ different ways to detect angular or rotary motion such as mechanical means utilizing brush contacts or magnet/inductive methods. But the most common, reliable and widely used devices are non-contact optical receptors employed by optical encoders. An optical encoder comprises a light emitting unit which emits a light beam and photoelectric converting elements which are disposed behind two diffraction gratings. A photoelectric rotary encoder is a kind of a sensor that is used to detect rotation angle, rotation number, rotational speed and the like of a rotating unit as digital signals. Optical shaft encoders generally consist of an optical shutter, such as a disk or drum, which is rigidly attached to the shaft whose position is to be determined. Such encoders are used in various types of machinery and machine tools where information concerning the precise angular relationship or speed between a shaft and another component is needed.