Optical Encoder

A high-precision encoder that measures rotation angle by shining light through a marked disc.

An optical encoder is built from a light source, a code disc, and a photodetector: the disc is etched with alternating transparent and opaque stripes, and as it turns with the motor shaft, the light is periodically interrupted; the detector converts that into pulses, or reads a coded track, which is translated into a rotation angle. By output type, it can be incremental (counting pulses, needing to be re-homed after a power loss) or absolute (a unique code for every position, so the angle is known the instant it's powered on). Its advantages are high resolution and accuracy, and no sensitivity to magnetic fields, which is why it's common in industrial servo motors and high-end robot-arm joints; its downsides are sensitivity to dust, oil, and shock, plus higher size and cost than a magnetic encoder, which is why low-cost robot joints tend to use magnetic encoders instead.

ExampleAn industrial servo motor commonly carries a 17-bit-or-higher absolute optical encoder at its rear, resolving 2^17 = 131,072 distinct positions per revolution.

Also called

Optical-Type Encoder

Related

Rotary Encoder · Incremental Encoder · Absolute Encoder · Magnetic Encoder · Dual Encoder · Servo Motor

Sources

Rotary encoder - Wikipedia