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An encoder is an electro-mechanical device monitors motion or position. A typical encoder uses optical sensors to provide a series of pulses that can be translated into motion, position, or direction. ill. 1 shows rotary encoders. ill. 1a reveals that the disk is very thin, and a stationary light-emitting diode (LED) is mounted so that its light will continually be focused through the glass disk. A light-activated transistor is mounted on the other side of the disk so that it can detect the light from the LED. The disk is mounted to the shaft of a motor or other device whose position is being sensed; when the shaft turns, the disk also turns. When the disk lines up so the light from the LED is focused on the phototransistor, the phototransistor will go into saturation and an electrical square wave pulse is produced. The diagram in ill. 1a shows an example of the square wave pulses that are produced by the rotary encoder. This type of disk was used in early applications but the size of the holes in the metal disk limited its accuracy. As more holes were cut in the disk, it became too delcate for industrial applications.
Above: ill. 1: (a) Diagram showing the internal operations of an incremental
optical encoder. (b) An of an optical rotary encoder.
