How to choose the accuracy of the rotary encoder What will the accuracy and resolution of the encoder affect

When we choose a rotary encoder, we usually need to know the accuracy of the encoder to be selected. Today we will understand how to calculate the accuracy of the rotary encoder? And what will the accuracy and resolution of the encoder affect?

How to calculate the accuracy of the rotary encoder?

The accuracy of the encoder refers to the error and accuracy between the signal data output by the encoder and the real data of the measured physical quantity. The calculation of encoder accuracy can be divided into: absolute and relative.

The characteristic of absolute output is that it does not need a counter and directly outputs numbers. Each light generates a separate number every time it crosses a code channel. The more code channels, the higher the resolution.

The output of the relative type is the pulse, and the rotation angle needs to be determined by the counting of the counter. Its code disc is simpler and higher in resolution than the absolute type. Generally, it is 3 code channels, A, B and ZCOM end ("-" end) ) Connect to each other. Connect the power terminal and the "+" terminal to A and B (pulse output) and connect to the high-speed counting terminal of the PLC. Pay attention to the response time of the PLC input when connecting. Some rotary encoders also have a shielded wire, and the shielded wire should be grounded when using it.

Encoder accuracy calculation formula:

Wheel circumference (mm) ÷ encoder resolution (P/R) × gear ratio =? mm/P How many millimeters send a pulse

P/R: Number of Pulse/Run pulses/turn, how many pulses are sent out per turn Circumference length=diameter Φ×circumference rate 3.14

What will the accuracy and resolution of the rotary encoder affect?

For the encoder, the "resolution" is not only related to the number of reticles, but also changes due to the influence of the electrical signal. It is adjustable and controllable, and it can be changed with the subdivision of the signal. The higher the subdivision factor, the smaller the resolution, but the higher the subdivision factor, the greater the error introduced.

The accuracy is more inclined to the mechanical aspect. After a product is produced, its accuracy is basically fixed (some high-precision products can compensate for the signal to improve the accuracy). This value is detected through detection. It is compared with The workmanship, material and other comprehensive functions of the product are closely related. It is difficult for us to calculate a detailed value as the basis for accuracy. Most of the accuracy can only be judged in the process of use.

For example, for 13bit, the absolute number of positions on the code wheel is: 8192, then: the calculated resolution is 158 arcsec, that is to say, when reading the value, the jump between the values ​​is required to be 158 arcsec If the first value to be read is 0, then the second value to be read must be greater than 158. If it is less than 158, we need to select a smaller resolution. When the value of 158 is to be read, because of the error, it is impossible to get the absolute 158 seconds. The error between the 158 seconds read by the encoder and the absolute true 158 seconds depends on the accuracy. Therefore, accuracy is discussed on the basis of resolution.

And it is not that the smaller the resolution, the better, because the subdivision will introduce errors and enlarge the error, excessive subdivision will not guarantee the accuracy! How many times of subdivision is needed, and how many times of subdivision can be achieved, the condition must be carried out on the basis of ensuring the accuracy, and the high subdivision is irresponsible due to the invisibility of accuracy before use. The higher the quality of the code disc, the better the marking, the better the signal quality and the smaller the error generated after subdivision. This is affected by the comprehensive performance of an encoder, which is why it will be under the same parameters. There are different brands and different price encoders for one reason.

For example, the values we want to read are 1, 2, 4, 7, and 8. I have to choose at least 1 unit of resolution. It is obviously not feasible to choose 2 units of resolution, because we read the value of 1. , Then 2 cannot be read. On the basis of choosing 1 unit resolution, the error between the 1 we read out and the true absolute 1 is the accuracy. The numerical control system on the machine tool has a resolution setting for the straight grating. The numerical value that needs to be read is less than the resolution, and the machine tool may jitter or make mistakes.

For absolute encoders with incremental signals, the absolute position value of the serial transmission can be accurately kept synchronized with the incremental value. The absolute value corresponds to an incremental signal, and the position value must be within the sine period of an incremental signal. Inside.

For example, 13-bit absolute type, with 512-line incremental signal, the absolute position distance is 158 seconds, if you want to read a position in the middle of the two code disc positions, it is different, but we can increase the 1Vpp it carries. The signal is subdivided. For example, subdivided by 100 times, it is commensurate with the introduction of several subdivided positions between the two absolute positions. We can calculate the subdivided increase based on the absolute position value. Read a position value between two absolute positions by measuring the number of pulses, such as: 512 lines are subdivided 100 times, the value of absolute position 1 is 0, and the value of absolute position 2 is 158, then read the position between these two positions You can add one more pulse on the basis of position 1: the value 0 is 25, and two pulses are 25x2=50...

However, the absolute encoder with incremental signal does not have subdivision, which requires users to subdivide the incremental signal by themselves.