Sensing, Actuating and Controlling
Encoders & Position Feedback
13 min · 2 worked examplesFree
Knowing where the machine actually is, rather than where you told it to go.
After this lesson you can
- Read direction as well as movement from quadrature
- Choose between incremental and absolute
- Count encoder edges without missing any
Incremental encoders
An incremental encoder outputs pulses as a shaft turns. Count them and you know how far it moved.
One channel gives distance but not direction. Two channels offset by a quarter cycle, quadrature, give both: which channel leads tells you which way it is turning.
Resolution is pulses per revolution, and counting every edge of both channels multiplies it by four.
The catch is that it is incremental. It knows change, not absolute position, so power-up leaves it with no idea where it is. That is why machines home themselves against a limit switch at start-up: the encoder is precise but has no memory.
In the full lesson
- Incremental encoders
- Absolute and analogue
- Counting reliably
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.