Encoders and Resolvers

Encoders and resolvers are sensors that measure the angular position of a rotating shaft, and sometimes linear position, providing the feedback needed for precise motion control. In a controlled motor system, the controller must know exactly where the shaft is and how fast it is turning in order to command movement accurately. Encoders and resolvers supply this information, closing the feedback loop that lets a machine position itself, follow a path or hold a fixed angle.

An optical encoder uses a disc marked with a pattern of transparent and opaque sections that rotates between a light source and a light detector. As the disc turns, the pattern interrupts the light, and the detector produces a stream of pulses. An incremental encoder generates pulses that are counted to track movement and, with a second offset track, to determine direction; counting the pulses over time also gives speed. An absolute encoder instead uses a coded pattern that gives a unique output for every position, so the exact angle is known immediately at power-up without needing to move to a reference point.

A resolver is an electromagnetic alternative built like a small rotary transformer. As its rotor turns, it varies the coupling between windings, and the resulting signals indicate the shaft angle. Resolvers contain no optical parts or delicate electronics in the sensing element, which makes them robust and able to work in hot, dirty or vibrating environments where an optical encoder might struggle. Both encoders and resolvers are widely used on the motors of industrial machinery, robots and servo systems, where accurate position feedback is essential.

Frequently asked questions

What is the difference between an incremental and an absolute encoder?

An incremental encoder outputs pulses that are counted to track movement, while an absolute encoder gives a unique code for each position, so the exact angle is known immediately at power-up.

How does an optical encoder work?

A patterned disc rotates between a light source and a detector; the alternating transparent and opaque sections interrupt the light, producing pulses that represent the shaft's motion.

Why choose a resolver over an optical encoder?

A resolver is an electromagnetic device with no optical parts, making it robust in hot, dirty or vibrating environments where an optical encoder might be less reliable.