About the resolution and accuracy of rotary encoder！

Incremental encoder resolution, frequency and subdivision

Incremental encoder code wheel is composed of many grating lines composed of two (or four, after discussing four light of the eye) photocell reading A, B signal, the density of the reticle determines the increment encoder resolution, that is read can distinguish the smallest change in the angle value. Parameter resolution incremental encoder is representative of PPR, which is the number of pulses per revolution.

Waveform incremental encoder A / B output generally there are two, one is a square wave signal steep steeply rising and falling, one is the slow rise and fall, similar to a sinusoidal waveform Sin / Cos output waveform signal curves, A and B differ 1 / 4T 90 degree phase cycle, if A is a sine curve Sin, Cos that B is a cosine curve.

For square wave signals, A, B two-phase phase difference of 90 degrees (1 / 4T), so that the phase angle of 0 degrees, 90 degrees, 180 degrees, 270 degrees phase angle, which has four positions rising and falling edges, Thus, in fact, 1 / 4T cycle square wave can have a change in angle of judgment, so 1/4 T cycle is the smallest measuring step, by a circuit judge for the rising and falling edges can be read four times PPR take angle changes, which is a square wave of fourth harmonic. This determination can also be used to do logic, 0 representing low, high 1 Representative, A / B two-phase change in one cycle is 0 0,0 0 1,1 1,1. This judgment not only 4x, you can also determine the direction of rotation.

Strictly speaking, a square wave can only do up to 4-fold, although someone with a finer time difference method can be divided, but that is not the basic recommended incremental encoder, use incremental higher division pulse signal SIN / cosine signal cOS class to do the follow-up circuit can be read by varying waveform phase, with the analog to digital conversion circuit segment, five times, 10 times, 20 times, or even more than 100 times, minutes after a good square wave waveform output (PPR). Frequency division multiple reality is limited, first, the analog to digital conversion time response of accuracy ADC speed and resolution is a contradiction, can not be infinitely subdivided, points too small, response and accuracy on there is a problem; secondly, the original class cosine signal encoder precision engraved line, the output itself consistency, the waveform is limited degree of perfection, points too small, only the original error code wheel is exposed more obvious, and bring error. Subdivision easier to do, but it is difficult to do, on the one hand it depends on the source disk reticle precision and perfection of the output waveform, on the other hand depending on the response speed of the division circuit and resolution accuracy. For example, Germany's industrial encoders, the best recommendation is subdivided 20 times higher segments of its recommended greater precision angle encoders, but the rotation speed is very low.

After the breakdown of an incremental encoder output A / B / Z square wave, it can also again 4x, but please note that the breakdown of the rotational speed encoder is required, are generally low. In addition, as the accuracy of the source code line engraved plate is not high, the waveform is not perfect, or limit the subdivision circuit itself, waveform segments may be severely distorted, the step size, lost step, etc., should pay attention to the selection and use.

Some incremental encoders, their original line can be engraved line 2048 (2 to the power 11, 11), by 16-fold (4) segments to give 15 PPR, again multiplied by 4. (2) to give 17-bit (bit) resolution, which is the high number of encoder 17 some Japanese coder's come, and it is generally expressed in the resolution on the use "bit, bit". This Japanese encoder at a faster speed, not broken down inside still use low signal to process the output, otherwise the response to keep up, so do not be its "17" confused.

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