Evaluation of resonant MEMS scanner for optical ranging application

Abstract

Light detection and ranging (lidar) is considered as a key component for future automated vehicles because of its high resolution 3D information about the surroundings. Microelectromechanical systems (MEMS) mirrors are one of the most promising techniques for lidars due to their high performance and cheap production cost. This thesis deals with the characterization and evaluation of a 1D comb drive actuated MEMS mirror for the lidar application. The first part proposes a nonlinear single degree of freedom model of the MEMS mirror and a parameter estimation method based on experimental data. A measurement principle and analysis method is developed, which extracts the nonlinear parameters from the measured trajectories using a 2D position sensitive detector (PSD) and current through the comb drives. By performing a decay measurement, the nonlinear stiffness is estimated by solving a least-square problem at each angular displacement of the mirror and subsequently the nonlinear damping is approximated by analyzing the decay envelope. The comb drive torque as well as its angle dependent capacitance and the moment of inertia are derived by simultaneously measuring current and the mirror trajectory. The simulation based on the estimated parameters is able to reproduce the measured decay behavior with good agreement. The second part of the thesis describes two measurement principles to evaluate a MEMS scanning system for use in a high performance lidar system. First the long and short term variation of the trajectory is measured using a 2D PSD and analyzed in time and frequency domain. The mirror movement is compared to the synchronization signal provided by the mirror demo board, which shows almost a 5 times higher frequency jitter. The second principle evaluates the ability of making stationary images, i.e. the point stability, using a CCD camera. Single shot measurements show that the maximum point uncertainty has a standard deviation of 22.5mdeg, which corresponds to a pixel distortion rate of 53.96 pixels per second (2.63%) at the center of scan, assuming a requirement of 0.1◦ resolution.