Mechanical decoupling poses a limit to the achievable positioning precision of a two-body system actuated by a single Lorentz actuator. To control such a system, the damping between the two bodies needs to be adjusted to a trade-off value, which allows both high control bandwidth of the directly actuated body and good isolation from environmental vibration. In this paper, hydraulic shock absorbers are employed to tune the damping. An experimental setup of a two-body system is built, with the shock absorbers mounted between the bodies. A higher level of damping of the decoupling mode is observed by using fluids with higher dynamic viscosity. The effectiveness of the proposed solution is confirmed by comparing the theoretical and experimental values of the damping coefficient for different values of the dynamic viscosity.@en

Fast steering mirrors (FMSs) are used in various applications like optical scanning of surfaces, feature detection or beam steering for optical communication systems. This paper introduces Lissajous scan trajectories to improve the tracking performance of a commercial FSM scanning system. The design of a dual tone (DT) feedback controller is presented that is tailored to this type of trajectory and the low-stiffness properties of electromagnetically actuated systems. It is shown that the controller can be used to eliminate periodic errors resulting from remaining cross-talk between the system axes. The DT controller significantly improves the tracking performance as compared to conventional wide bandwidth (WBW) control of the FSM. Applying the tailored controller with Lissajous trajectories reduces the RMS tracking error to 0.77%, as compared to more than 9.1% for the conventional raster scan with a WBW controller. The peak error is reduced from 16% for the raster scan to 1.1% for the Lissajous scan.

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Mechanical vibrations occuring in a production environment cause a relative motion between the sample and inspection tool that distorts measurements at the nanometer level. To overcome this problem, this paper proposes a metrology platform that maintains a constant relative distance to the sample by means of an H& inf;-feedback controller. Experiments in one degree of freedom show that the metrology platform can reduce vibrations as they occur in a production environment by one order of magnitude. Therefore, it enables in-line surface metrology at the nanometer level.@en