A Distance-Adaptive Method for Three-Axis Angle Measurement Based on an Optical Wedge

Existing non-contact three-axis angle-measurement methods are unsuitable for measuring the relative three-axis angles between the inner and outer ring frames of fifth-generation airborne optoelectronic gimbal platforms. Our previous study proposed a compact three-axis angle-measurement method based on an optical wedge for this application. However, the fixed-coefficient angle-solving model used in that method does not account for variations in the measurement distance L, which can produce distance-dependent nonlinear errors when axial displacement of the inner ring frame occurs. To address this limitation, the present study proposes a distance-adaptive method for three-axis angle measurements. An analytical measurement-distance model is established using ABCD ray-transfer-matrix theory, and L is incorporated into the fixed-coefficient angle-solving model. The fixed coefficients in the polynomial error-compensation model are thereby expressed as functions of L and updated according to the estimated measurement distance. Experimental results demonstrate that the proposed method significantly improves the measurement accuracy under varying-distance conditions. Taking the measurement-distance condition with the largest error, L = -2 mm, as an example, the RMS values of the measurement errors for the pitch, yaw, and roll angles are reduced from 13.0″, 8.4″, and 31.1″ to 5.6″, 3.8″, and 18.6″, respectively.