The self-calibration method for angle measurement is introduced, and the optimal arrangement of several equal distance
distribution groups of reading heads was proposed to realize highly effective restraint of the specified Fourier
components of angular measuring deviation in loosely restricted environment. Base on this method, a self-calibration
angle encoder system was developed using micro reading heads, glass scale disc, air bearing, and multi-channel counter.
According the method of examination of the angular measuring standard, the metrological performance of the system
was evaluated using national angle standard of China. The evaluation result revealed that the measuring deviation is
within ±1.5″, the measuring repeatability is less than 1.1″. Referring to the verification scheme of measuring
instrument for plane angle, the system can be used to calibrate the angular measuring instrument with max permissible
error worse than ±4.5″in situ.
The angle measurement technology is very important in precision manufacture, optical industry, aerospace, aviation and navigation, etc. Further, the angle encoder, which uses concept ‘subdivision of full circle (2π rad=360°)’ and transforms the angle into number of electronic pulse, is the most common instrument for angle measurement. To improve the accuracy of the angle encoder, a novel self-calibration method was proposed that enables the angle encoder to calibrate itself without angle reference. An angle deviation curve among 0° to 360° was simulated with equal weights Fourier components for the study of the self-calibration method. In addition, a self-calibration algorithm was used in the process of this deviation curve. The simulation result shows the relationship between the arrangement of multi-reading heads and the Fourier components distribution of angle encoder deviation curve. Besides, an actual self-calibration angle encoder was calibrated by polygon angle standard in national institute of metrology, China. The experiment result indicates the actual self-calibration effect on the Fourier components distribution of angle encoder deviation curve. In the end, the comparison, which is between the simulation self-calibration result and the experiment self-calibration result, reflects good consistency and proves the reliability of the self-calibration angle encoder.
At National Institute of Metrology, China (NIM), a portable and real-time self-calibration angle encoder was developed to meet the requirement of angular measurement with high accuracy, high speed, and high adaptability in limited size. In the development, the special arrangement of reading heads, the structure of bearing was designed base on the novel selfcalibration method, and the corresponding signal acquisition and processing system was set up with capability of high speed and multi-channel synchronous data acquisition and processing. The max rotary speed of this angle encoder gets 18 r/min (110°/s) in real-time mode. This angle encoder was compared with NIM’s primary angle standard. The calibration result shows that this angle encoder has angle measuring accuracy better than ±4″.
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