Encoder
It is the feedback device that converts shaft rotation into a pulse train. In the incremental type a certain number of pulses is produced per revolution (typically 100–1000); position is found by counting the pulses and speed from the number of pulses per unit time. Two channels 90 degrees out of phase with each other (A and B) also determine the direction of rotation.
Without an encoder a DC driver cannot know whether the motor is really turning or how far it has turned; it knows only the voltage it applies itself. If position counting, revolution counting or holding a constant speed under load is wanted, feedback is mandatory.
- Incremental encoder: It counts only change; when power is removed the counter resets and the system has to return to a reference (home) point.
- Absolute encoder: It gives a unique code for every angle, and the position information is not lost even if power is removed.
- Resolution and gearbox: A 100-pulse encoder means 5000 pulses per revolution at the output of a 50:1 gearbox; the mechanical multiplier increases the measurement resolution.
The current-sensing termination (AntiSwitch) approach of AXI DC drivers does not require an encoder to find the end point. The need for an encoder arises when you have to capture not the end point but an intermediate position repeatably.
Run the encoder cable separately from the motor supply pair and use shielded cable; noise coupled into the pulse line turns into counting errors.
The context in which this term is used: DC Motor Driver Selection Guide