The quasistatic MEMS actuation is based on the LinScan concept for vertical comb drives, reported by Institute for Photonic Microsystems (IPMS) before. In this paper, we report on a novel two-dimensional (2-D) MEMS rater scanner with quasistatic resonant actuation, specially developed for an adaptive 3-D ToF camera. 3 Now, we extend the MEMS-based LIDAR to the novel concept of an adaptive 3-D ToF laser camera with foveation properties, 4 which could be used in future autonomous or service robots to better interact with their surroundings. 1 A first prototype-developed for a phase shifting distance measuring system 2-was limited to resonant one-dimensional scanning at 250 Hz and 60 deg FOV of a monolithic MEMS array with 80% optical filling factor and a total aperture of 334.2 mm 2, consisting of 2 × 7 driven MEMS mirrors synchronized to a separate sending mirror. To overcome the mentioned problems, Fraunhofer developed the concept for an MEMS-based LIDAR based on an array of identical synchronized driven MEMS elements. In contrast, the aperture of a single MEMS scanning mirror is limited to small values of typically 1- to 3-mm diameter due to the dynamic mirror deformation. A large mirror aperture of the receiver optics must be guaranteed in addition to sufficiently large optical scan angles ( > 40 deg) and high scan frequency of > 100 Hz. Its replacement by micromechanical scanning mirrors, which have the benefits of high scanning speed, low weight, and high mechanical reliability (e.g., no friction, high shock resistance) is not straightforward. Traditionally, a polygon scanner is used, but for high scanning speeds (e.g., > 30,000 turns / min) large design efforts for bearings are required to reduce abrasive wear (e.g., wearing free air bearings), resulting in heavy ( > 10 kg), and cost-intensive scanning units. Hence, a scanning mirror with large aperture is required for LIDAR systems, in order to collect small amounts of light reflected or scattered by the measured target. Typically, the precision of ToF distance measurement is limited by the amount of signal light available at the detector. On the other hand, traditional laser scanners for 3-D distance measurement require expensive, heavy, and large rotating or vibrating mirrors for light deflection of the scanning ToF distance measurement. Also a nearly unlimited number of 3-D data (voxels) can be measured with high measuring rates of up to 1 MVoxel / s with a low measurement uncertainty of typically 3 to 10 mm. Hence, the LIDAR detector collects light from signal and background (noise) in a relatively short time from a small measured area of the target, which significantly reduces the influence of background (noise). In comparison to focal plane array based ToF 3-D cameras, laser scanners have an advantage of higher measurement accuracy due to scanning principle because only single measuring points are illuminated sequentially within the scanned field of view (FOV). Laser scanners are widely used for time-of-flight (ToF) three-dimensional (3-D) distance measurement systems. 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 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. 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. For position feedback, piezo-resistive position sensors are integrated on chip for both axes. This mirror is 2.6× 3.6 mm and operates at 1600 Hz with an 80-deg optical scan range. Large quasistatic deflections of ± 10 deg are provided by vertical comb drives in the vertical direction in contrast to resonant horizontal scanning. 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.
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