One design of the state-of-the-art laser scanner systems in automotive applications is based on oscillating mirror modules. The requirement of a large mirror surface for eye-safe transmission beams and long measurement distances is a major drawback for fast and reproducible scanning. Tolerances of angular positioning, position sensing, and vibrational perturbations limit the position accuracy of such a mirror and, thus, the accuracy of the transmission spot position in the field of view (FoV). Our approach for a scanner module with maximum transmission beam diameter combines a microlens array with an objective lens for generating one optical telescope assembly for each angular scan position exclusively. Aperture stops define the beam positions in the FoV and avoid positioning errors caused by angle deviations of the scanner mirror. This increases the reliability of the angular position accuracy of the scanner module significantly. To minimize the shadings between adjacent scan spots in the target distance, created by beam cutoffs at the aperture stop of the objective lens, an array of optimized microwedge prisms is provided in combination with the microlens array. Therefore, we can increase the throughput of transmission power into the FoV and improve the measurement distance, especially at large scan angles.
One design of state of the art laser scanner systems in automotive applications is based on oscillating mirror modules. The requirement of a large mirror surface for eye-safe transmission beams is a major drawback for fast and reproducible scanning. Tolerances of angular positioning, position sensing as well as vibrational perturbations limit the position accuracy of such a mirror and thus, the accuracy of the transmission spot position in the field of view (FoV). In contrast to scanner modules, Flash LiDAR systems provide high accuracy of spot positions. However, due to simultaneous illumination of the entire FoV, the maximum measurable range degrades. Our approach for a scanner module, presented in this paper, combines a micro lens array (MLA) with an objective lens for generating one optical telescope assembly for each angular scan position exclusively. The consequence is a maximum transmission beam diameter without angular FoV reduction along with minimum mirror dimensions. In order to avoid shadings between adjacent scan spots in the target distance, created by beam cut-offs at the aperture-stop of the objective lens, an array of optimized optical elements is provided additionally to the MLA. With adequate design of the MLA, the reliability of the scanner module regarding the angular positioning accuracy increases significantly. We demonstrate that the noise of the spot position is suppressed in dependence on the aperture-stop dimensions of the MLA. In conclusion, we present a new solution for a 3D LiDAR scanner module with a reliable spot-position accuracy comparable to 3D-camera/Flash LiDAR systems but with higher distance measurement range.
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