Jul 14, 2023
Introduction to Encoder Resolution and Accuracy
The accuracy of a rotary encoder is measured in angular minutes and angular seconds, which is somewhat related to resolution, but not entirely. For example, taking the ROD400 series from Heidenham, Germany as an example, for those below 5000 lines, Heidenham provides an accuracy of 1/20 of the line width (related to resolution), while for those between 6000 and 10000 lines, the accuracy is 12 angular seconds (unrelated to resolution). The RON series angle encoders of Heidelberg are also 9000 to 36000 lines, with an accuracy of 2.5 to 5 arcseconds for the RON200 series, 2 arcseconds for the RON700 series, 1 arcsecond for the RON800 series, and 0.4 arcseconds for the RON900 series, all of which are not determined by resolution. In fact, there are four parts that affect the accuracy of the encoder:
A: Optical part
B: Mechanical part
C: Electrical part
D: The installation and transmission receiving parts in use have decreased accuracy after use, resulting in deviations in the mechanical parts themselves.
A. The impact of the optical part of encoder A on accuracy:
Optical code disk - mainly refers to the accuracy of the motherboard, the number of lines per revolution, the accuracy of the lines, the consistency of the line width, and the accuracy of the edges.
Light emission source - parallelism and consistency of light, light attenuation.
Light receiving unit - reads the angle and response.
The impact of using optical systems - pollution, attenuation.
For example, the optical encoder disk, first and foremost, is the accuracy of the motherboard's engraving. Heidenhain's motherboard is said to be processed in a double floating studio several tens of meters underground, minimizing the impact of various external factors, and even considering the infrasound waves of the ocean and the vibration of distant car engines. Therefore, many encoder manufacturers even purchase motherboards from it. Secondly, the processing process, optical imaging time, temperature, physical and chemical changes, pollution, etc. can all affect the width and edge of the code disk marking. So, even if the number of lines on the same encoder is the same, the accuracy that each company can achieve is also different.
B. The impact of the mechanical part of encoder B on accuracy:
The machining accuracy and installation accuracy of the shaft.
The accuracy and structural accuracy of bearings.
The concentricity of code disk installation and the accuracy of optical component installation.
The concentricity between the installation positioning point and the shaft.
For example, in terms of the structure of bearings, the bearing deviation of a single bearing support structure cannot be eliminated, and after use, the deviation will be greater. However, a double bearing structure or multiple support structures can effectively reduce the deviation of a single bearing.
C. The impact of the electrical part of the C encoder on accuracy:
The stability accuracy of the power supply - the impact on the optical emission source and receiving unit.
Error caused by reading response and electrical processing circuit;
The impact of electrical noise depends on the anti-interference ability of the encoder electrical system;
For example, if electronic subdivision is used, it will also bring errors. According to the introduction provided by Heidelberg in Germany, the subdivision electrical error of the Heidelberg encoder and the error of the sine cosine curve is about 1% of the original reticle width.
D. The accuracy impact brought by the use of the D encoder:
The concentricity of the connection with the measuring shaft during installation;
Delay of output cable signal (at longer distances or faster frequencies);
Possible errors between the response of the receiving device and the internal processing of the receiving device.
The dynamic response deviation of the encoder during high-speed rotation.
The most common deviation is between our own installation method and the installation results.

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