An encoder is a precision measuring device that tightly integrates mechanics and electronics. It converts a mechanical geometric displacement into an electronic signal (electronic pulse or data string) using photoelectric or electromagnetic principles. This electronic signal typically needs to be connected to a control system, which calculates the measured data to proceed with further operations.
Encoder Classification
Encoders can be classified into two categories based on their working principle: incremental and absolute. Incremental encoders convert displacement into periodic electrical signals, then convert these signals into counting pulses, using the number of pulses to represent the magnitude of the displacement. Absolute encoders, on the other hand, assign a unique digital code to each position; therefore, their reading depends only on the starting and ending positions of the measurement, and is independent of the intermediate steps.
Based on their working principle, they can be divided into photoelectric and electromagnetic types.
Features of magnetic encoders: robust, vibration-resistant, dust-resistant, dirt-resistant, and moisture-resistant; low cost;
Features of photoelectric encoders: high resolution, higher precision, and through-hole bushing.
Incremental
Incremental encoders typically have three output ports: A-phase, B-phase, and Z-phase outputs. The A-phase and B-phase outputs are pulses that are delayed by 1/4 cycle. The forward and reverse directions can be distinguished based on the delay relationship. Furthermore, the frequency can be multiplied by 2 or 4 by taking the rising and falling edges of the A-phase and B-phase outputs. The Z-phase outputs a single-turn pulse, meaning that one pulse is emitted per revolution.
The grating used in incremental measurement consists of periodic grating bars. Position information is obtained by calculating the number of increments (measurement steps) from a given point. Since the position value must be determined using an absolute reference point, the circular grating code disk also has a reference point track.
Absolute
An absolute encoder outputs a unique binary value corresponding to each reference angle for one revolution. Multiple positions can be recorded and measured using an external clocking device.
The encoder immediately obtains its position value upon power-up, which is readily available for subsequent signal processing circuitry. There is no need to move the axis to perform a reference point homing operation. Absolute position information comes from a circular grating code disk, consisting of a series of absolute codes. Individual incremental tracking signals generate position values through subdivision, and can also generate selectable incremental signals.
A single-turn encoder repeats its absolute position value information once per revolution. A multi-turn encoder can also distinguish the position value for each revolution.
