This paper reports on a gimbaled MEMS scanning mirror with quasistatic resonant actuation, specially developed for adaptive raster scanning in an innovative three-dimensional (3-D) time-of-flight (ToF) laser camera with real-time foveation. Large quasistatic deflections of 10 deg are provided by vertical comb drives in the vertical direction in contrast to resonant horizontal scanning. This mirror is 2.6 x 3.6 mm and operates at 1600 Hz with an 80-deg optical scan range. For position feedback, piezo-resistive position sensors are integrated on chip for both axes. To guarantee the full reception aperture of effectively 5 mm, a synchronized driven MEMS scanner array consisting of five hybrid assembled MEMS devices is used in an innovative 3-D ToF laser scanner. This enables a distance measuring rate of 1 MVoxel/s with an uncertainty in distance measurement of 3 to 5 mm for a 7.5-m measuring range for a gray target. Flatness-based open loop control is used for driving control of quasistatic axis in order to compensate for the dynamics of the low damped MEMS system
This paper proposes a phase modulation method for Lissajous scanning systems, which provides adaptive scan pattern design without changing the frame rate or the field of view. Based on a rigorous analysis of Lissajous scanning, phase modulation constrains and a method for pixel calculation are derived. An accurate and simple metric for resolution calculation is proposed based on the area spanned by neighboring pixels and used for scan pattern optimization also considering the scanner dynamics. The methods are implemented using MEMS mirrors for verification of the adaptive pattern shaping, where a 5-fold resolution improvement in a defined region of interest is demonstrated.
This paper describes a nonlinear command tracking scheme for an electrostatic laser scanning micromirror assembly. The results are based on an innovative gimballed comb transducer concept developed at the Fraunhofer Institute for Photonic Microsystems. The outer mirror axis is designed as a Staggered Vertical Comb (SVC) in out-of-plane configuration and it shall provide a quasistatic operation with large deflection angles for triangular trajectories. The challenges for trajectory design and open loop command tracking are determined by the inherently nonlinear transducer characteristics and the lightly damped mass-spring dynamics. In this paper a flatness-based trajectory design is presented that considers the nonlinear transducer dynamics as well as the nonlinear elastic mechanical suspension with model parameters derived from ANSYS analysis. The paper discusses design constraints and detailed design considerations and it shows proof of concept performance results based on experimental verification with a real microscanner assembly.
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