The incremental encoder encoder disk is composed of many grating lines, with two (or four, later discussed as four optical eyes) optical eyes reading A and B signals. The density of the lines determines the resolution of this incremental encoder, which is the minimum change angle value that can be resolved by reading. The parameter representing the resolution of the incremental encoder is PPR, which is the number of pulses per revolution. For example, if there are 360 lines per revolution and A and B output 360 pulses per revolution, the resolution parameter is 360PPR. So what is the minimum angle change that this encoder can distinguish? Is it just 1 degree?

There are generally two types of waveforms output by incremental encoders A/B. One is a square wave signal with steep rising and falling edges, and the other is a slow rising and falling Sin/Cos curve waveform signal output with a waveform similar to a sine curve. A and B have a 90 degree phase difference of 1/4T period. If A is a sine like Sin curve, then B is a cosine like Cos curve.

For a square wave signal, A and B are 90 degrees apart (1/4T), so there are rising and falling edges at the 0 degree, 90 degree, 180 degree, and 270 degree phase angles. In fact, angle changes can be determined within the 1/4T square wave cycle, and 1/4 of the T cycle is the minimum measurement step. By using the circuit to determine these rising and falling edges, the angle change can be read four times faster than PPR, which is the fourth harmonic of the square wave. This judgment can also be made using logic, where 0 represents low, 1 represents high, and A/B phases change by 0 0, 0 1, 1 1, 1 0 within one cycle. This judgment can not only be multiplied by 4, but also determine the direction of rotation.

So, the minimum resolution angle of the square wave signal is 360 degrees/(4xPPR).

Previous question: An incremental encoder with a square wave A/B output of 360PPR, with a minimum resolution angle of 0.25 degrees.

Strictly speaking, square waves can only be divided into multiples of up to 4 times. Although some people can use the time difference method to divide them more finely, that is not recommended by incremental encoders. Higher frequency division requires the use of incremental pulse signals such as SIN/COS sine and cosine signals. Subsequent circuits can use analog-to-digital conversion circuits to segment the waveform phase changes by 5 times, 10 times, 20 times, or even 100 times or more, and then output the square wave waveform (PPR) after segmentation. The multiples of frequency division are actually limited. Firstly, there is a time response issue with analog-to-digital conversion. The speed of analog-to-digital conversion is contradictory to the accuracy of resolution, and it is impossible to infinitely divide it. If the division is too fine, there will be problems with response and accuracy; Secondly, the engraving accuracy of the original encoder, the consistency of the output sine and cosine like signals, and the completeness of the waveform are limited. If the division is too fine, it will only expose the errors of the original encoder more clearly, resulting in errors. Subdivision is easy to do, but it is difficult to do well. On the one hand, it depends on the accuracy of the original code wheel's engraving and the perfection of the output waveform. On the other hand, it depends on the response speed and resolution accuracy of the subdivision circuit. For example, Heidenhain's industrial encoder in Germany recommends a best subdivision of 20 times, and higher subdivisions recommend angle encoders with higher accuracy, but the rotation speed is very low.