CMOS-based three-degree-of-freedom grating autocollimator with large range capability

One approach for resolving the significant limitations in the angular measurement range of current advanced grating readout heads, we propose a novel method for high-precision, large-range, three-degree-of-freedom (3-DOF) angular displacement measurement via CMOS imaging of laser speckle patterns. We establish a linear correlation between the centroid coordinates of the imaged speckle patterns and angular displacements, which is then calibrated for accurate measurement. This approach significantly expands the measurement range compared to traditional grating readout heads, offering the potential to achieve up to ±10,000′′. Additionally, the method can directly handle suboptimal speckle patterns, enhancing the robustness and reliability of the measurement process. Experimental results demonstrate error percentages below 0.33% across all 3-DOF within the measurement range of (𝜃𝑥,±720′′), (𝜃𝑦,±1080′′), and (𝜃𝑧,±2880′′), which is approximately five times the range of existing advanced grating encoder, confirming the high-precision and wide-range capabilities of this new technique.