Coherent LiDAR concepts for automotive or unmanned aerial vehicle (UAV) applications are of increasing interest due to their superior performance compared to standard pulse-based systems, especially at longer range. Proposed scanning methods include bulky and slow galvanometer- or polygon scanners that are often impractical for implementation in cars or UAVs. Here, micro-electro-mechanical-system (MEMS) mirrors can be used as an alternative compact scanning device. To merge the advantages of coherent LiDAR technology with the advantages of miniaturized scanning by MEMS mirrors, we present fiber-based frequency modulated continuous wave (FMCW) LiDAR point cloud generation using quasi-static MEMS mirrors. The unique feature of quasi-static MEMS mirrors is their ability to perform a point-to-point scanning and measurement process, while most conventional MEMS mirrors scan the scene continuously. Hence, they enable a compact monostatic system design. We demonstrate the operation of such a system for the first time, to the best of our knowledge. Here, we show the operating principle and design of those quasi-static MEMS mirrors. We also implement and test the generation of the mirror scan pattern using a digital IIR (infinite impulse response) filter method. Lastly, we show the LiDAR point cloud generation in an indoor environment and evaluate the point cloud output for different MEMS mirror sizes, angular resolutions, and ranges.
Despite the high linearity of Al(Sc)N as piezoelectric actuator material, quasi-static MEMS mirrors show exemplary differences due to intrinsic stress. To control the static and dynamic behavior of the mirror, an electronic control system may be used. Rapid control prototyping (RCP) can be a helpful tool for developing generic or application-specific control schemes. This paper provides a practical introduction to the RCP approach and demonstrates it in practice with a gimbal-less bi-axial micro mirror. The application example is a long-range LIDAR system with optical positioning tolerance <0.1 degree and <400 µs point-to-point transition rate. An open loop control is implemented with a digital filter (finite-duration impulse response, FIR), using standard functions from MATLAB®/Simulink® to generate a random signal, a model of the mirror and a Gaussian filter. The response to the filtered input signal is simulated before running the control scheme on the RCP system. The modeling process relies on automatic code generation to program the RCP target system or other supported platforms.
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