Based on the linear-scan image recognition method, "image-type angular displacement measurement (I-ADM) technology" is a new photoelectric displacement measurement technology. I-ADM can achieve higher resolution than the traditional measurement methods when the line density of grating code disc is not high, and can achieve higher measurement frequency response.
However, due to the limitation of grating disk diameter, the line density of the miniaturized grating disk is generally sparse. When the linear-scan image sensor is used to identify the grating disk with low-density lines, there will be a certain measurement error, which restricts the measurement accuracy of the miniaturized I-ADM device.
In a study published in IEEE Transactions on Industrial Electronics, Prof. YU Hai from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) established the influence law of low-density code disk on linear-scan displacement measurement error. The model analysis showed that when the circumference of the circular grating contains 2^N lines, the influence on the error of I-ADM gradually increases with the decrease of the value of N. At the same time, researchers found that the measurement error caused by the circular grating can be expressed as the sum of 2^N+1, 2^N+2, 2^N+3,….
Therefore, an error compensation model based on harmonic error synthesis algorithm was proposed. In the experiment, when there are only 2^N=64 lines on the circular grating with diameter of 62mm, its measurement accuracy is 8.14". By the proposed compensation algorithm, the accuracy is improved to 4.78".
This study is the first in the industry to analyze the error of I-ADM with low-density grating disk. It reveals the mechanism that the error generated by low-density grating disk can be compensated by multiple harmonic components, and provides a theoretical basis for improving the accuracy of miniaturized I-ADM.
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