A New High Precision Linear Displacement Sensor Based on Single Light Field Orthogonal Modulation

Abstract

This paper present a single light field orthogonal modulation displacement measurement method which is based on time and space modulation technology. This method uses an alternating light intensity modulation in the time domain and modulation of four sinusoidal light-transmitting surfaces in the spatial domain to synthesize a traveling wave signal. The displacement was accurately reflected in the phase shift of the traveling wave signal, which could be measured by the time difference. A prototype with a measuring range of 500 mm and a pitch of 0.6 mm was fabricated to evaluate the proposed method. Combined with the measurement mechanism, the measurement errors caused by the spatial modulation were analyzed in detail. To reduce those primary periodic errors, we proposed an optimization structure of continuous cosinusoidal transmitting surfaces and demonstrated the effectiveness of this method by simulations and experiments. The experimental results indicate that the short period measurement accuracy reached ±0.29 $\mu \text{m}$ with 1 nm resolution within one period of 0.6 mm, which means that the accuracy in one period (0.6 mm) exceeded 0.1%. Furthermore, the original measurement accuracy of the full range of 500 mm was ±1.3 $\mu \text{m}$ , the error showed great regularity, and the better performance of the sensor could be obtained by digital calibration for the measurement data or improvement in the structure. Therefore, compared with the traditional measurement methods, the sensor described in this paper can achieve high-precision measurement with a low cost of manufacture.