As a pair of "wise eyes" for autonomous vehicles to perceive the external environment, Lidar (Light detecting and Ranging) plays a crucial role in detecting target characteristics in driving scenarios. To ensure the accuracy and reliability of Lidar, precise measurement of target reflectance under θ/θ reflection conditions is an indispensable step. Determining the reflectance value of targets under θ/θ reflection conditions is a critical part of completing Lidar calibration and traceability. When designing the θ/θ optical path, a significant challenge lies in achieving almost perfect overlap between the lighting and detecting paths while ensuring system compactness and measurement accuracy. Fiber optic spectrometers, known for their fast and accurate measurement capabilities, can be directly applied to measure target reflectance. Therefore, combining a compact θ/θ reflection optical path with a fiber optic spectrometer is key to achieving small-angle reflectance measurements for Lidar, marking an important step towards improving the calibration and traceability chain. For Lidar under θ/θ reflection conditions, various "N+1" lighting/detecting combined optical paths based on fiber bundles have been designed. Simulation analysis of these designs has been conducted using ray-tracing methods, comparing the uniformity and optical flux efficiency of the tested samples. The results indicate that when N=6, the uniformity and incident flux efficiency are optimal. Based on the simulation results, a "6+1" lighting/detecting fiber optic spectrometer has been developed, and actual measurements have been performed on a standard diffuser. The measurement data shows that the angular accuracy under 0/0 and 45/45 conditions is better than 0.1°, and the optimal relative error of the reflection measurement results in the 905nm laser wavelength was less than 0.5%. This meets the requirements for on-site measurements and is significant for further improving the Lidar measurement traceability chain.
The 2-D galvo scanners refer to motorized mirror mounts and systems specifically designed for applications involving laser-beam steering or scanning. They excel in swiftly manipulating small laser beams, offering exceptional levels of accuracy and precision. Functioning as dynamic electro-optical components, galvo scanners employ a rotatable mirror with low inertia to accurately position a laser beam with a high degree of precision and repeatability. In a series of applications, achieving a repeatability of less than 2 μrad is critical for galvo scanner. However, the galvo scanner system could suffer from optical and control errors because of lacking researchers’ intervention. These errors may give rise to deviations between the actual motion of the galvo scanner and the desired motion, then impede the precise positioning and control of the beam. Hence, an exceedingly precise and accurate calibration of the galvo scanner is imperative to attain high-precision control. To realize the standard accuracy of 0.3 mm in applications, current methods still keep imperfections. To evaluate the accuracy of the galvanometer's scanning beam location across a specified voltage range and the variations in its scanning capabilities with signal frequency, this research introduces a high-precision calibration measurement method for the 2-D galvo scanner. This method serves as a valuable resource for future studies on galvanometer scanner calibration and trajectory matching algorithms, establishing a research foundation for the eventual implementation of uniform light field illumination by galvanometers.
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