The principle of rotary encoder

All incremental encoders have two channel signal outputs, A and B. This is because the code disk of the incremental encoder has two turns of wire grooves, and the two turns of wire grooves are offset by a certain Angle. This Angle will cause the two signals output by the photoelectric detection device to differ by 1/4 period (90°). The specific working mode of the code disk is shown in the following figure. In the picture, black represents light transmission and white represents light blocking. When the code disk rotates, the inner and outer wire grooves will successively allow light to pass through. The photoelectric detection device detects the change in the light's on and off state and will accordingly output A pulse signal. Due to the time difference between the inner and outer rings when they block light and when they allow light to pass through, there is a phase difference between the signals of the A and B channels.

The direction of movement can be determined by the sequence of changes in the two signals. By recording the number of output pulses, the magnitude of the displacement can be known. Meanwhile, the speed can be obtained through the frequency of the output signal.

Some incremental encoders have four turns of grooves, corresponding to the four confidence signals A, B, -A, and -B respectively. The difference between two adjacent confidence signals is also 1/4 period. However, this type of encoder inverts the -A and -B confidence signals and then superimposes them onto channel A and channel B to enhance the signal. In addition to Channel A and Channel B, many incremental encoders also set an additional channel Z output signal. The Z channel signal also has a corresponding cable slot on the code disk, but there is only one. The code disk will pass through it only once when it rotates once. The channel Z signal is generally used as the reference zero position to indicate the position of the device or clear the accumulated amount.

The counting starting point of the incremental encoder can be set arbitrarily, enabling multi-turn infinite accumulation and measurement. When it is necessary to increase the resolution, the rising and falling edges of the signals from channels A and B can be triggered to double the original pulse count. However, when the receiving device is shut down and restarted, the incremental encoder needs to re-search for the reference zero point.

The code disk of an incremental encoder is composed of alternating transparent (bright) and opaque (dark) lines, and the total number of physical lines is usually twice the nominal "number of lines".

For example, an encoder labeled as "1000 lines" actually has 2000 physical lines on the code disk (1000 bright + 1000 dark).

Industry standard definition of encoder line count:

The nominal "number of lines" (such as 1000 lines) refers to the number of complete period signals output per revolution (i.e., the complete square wave period of Phase A or Phase B), rather than the total number of physical lines.

Each complete cycle corresponds to 1 visible + 1 concealed line on the code disk. Therefore: The nominal line count (PPR) = physical scale bus /2

Principle of signal generation

When the photoelectric sensor of the encoder (such as an infrared pair tube) rotates the code disk, it will output A complete electrical signal cycle (the rising edge + falling edge of phase A or Phase B) every time it passes through 1 bright + 1 dark line.

Therefore: 1000 pairs of bright and dark lines (a total of 2000 lines) → output 1000 complete pulse cycles (PPR=1000).