10.1 Optical Encoding

Optical encoding relies on an encoding disc and an encoding sensor. The encoding disc is usually an opaque disc with slots that let light pass though. An encoding sensor has two sides. One side has an Infrared Emitting Diode (IrED), and the other side has a phototransistor. The encoding disc is placed between the IrED and the phototransistor. This way, as the disc rotates, the phototransistor sees transitions of light and darkness because the slots of the disc has motion relative to the sensor.

Optical encoders are commonly found in devices that operate in clean environments. Some printers use DC motors with optical encoding instead of stepper motors because it is less expensive. Small robots that operate in controled (indoor) environments also use optical encoders.

However, optical encoding cannot be used in dirty environments. Dust, sand, oil droplets, gunk can all easily render optical encoders useless. Most larger robots that operate in outdoor environments cannot use optical encoding unless the encoder is concealed (air-tight). This is still possible because motion can be clutched by magnets so that there is no mechanical linkage from the axle to be encoded to the encoder axle.