A Circumferential Closed Angle Displacement Measurement Method Based on the Light Intensity Orthogonal Modulation

In order to achieve high precision measurement with low manufacturing process, we propose a new angular displacement measurement method, which uses light filed as a measurement medium and can realize simultaneous measurement of whole circumference. Firstly, through the orthogonal modulation of time and space for the ring light field, four channels of standing wave light field uniformly distributed along the circumference are obtained. Then, electric traveling wave signal is synthesized by photoelectric conversion and phase-shifting processing. Finally, the angular displacement is measured by using the method of phase discrimination through calculating the phase difference between electric traveling wave signal and reference signal. Through the derivation of the sensor measurement principle, the error characteristics of the sensor caused by non-uniform distribution of light field are analyzed. Based on it, lots of confirmatory experiments were carried out, and the results prove the correctness of the theoretical analysis. According to the theoretical analysis and experimental results, the errors caused by the light field distribution is clarified, and the sensing structure and parameters are optimized. Finally, the measuring accuracy of the sensor reaches ±1.5″by using an equi-transmissive surface with a central angle of 4°.