Repetitive nonlinear control for linear scanning micro mirrors

Various scanning applications like LIDAR sensors, OCT systems and laser projectors require a repeated periodic linear scanning trajectory performed by a quasi-static micro mirror. Since most MOEMS systems have inherent nonlinearities like a progressive spring stiffness and the quadratic voltage-deflection-relation of electrostatic drives, a nonlinear control scheme as presented in our previous paper significantly reduces parasitic oscillations of the resonance frequency and enables a high resolution raster scan combining a quasi-static axis with a cardanic mounted resonant axis. In this paper we address a novel control scheme using a flatness-based feedback control enhanced by a plug-in repetitive controller for the linear scanning axis. We demonstrate the applicability of this feedback control for a quasi-static moving micro mirror with electrostatic staggered vertical comb drives using a microcontroller-based driver. On-chip piezoresistive sensors serve as position feedback. We compare different scan trajectories and repetition rates with respect to the linearity and repeatability showing the robustness of the proposed control regime. Furthermore we discuss the advantage of this method to reduce the individual chip characterization for ramping up mass production.