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

A six degree of freedom, magnetically levitated metrology platform is proposed and implemented to enable nano-scale measurements directly in a production environment by providing vibration isolation. The metrology platform maintains a constant distance between sample and nano-metrology tool, forming a nano-scale laboratory environment directly in the production line. This paper presents the design of the proposed metrology platform. Tracking of the sample is achieved by using six position sensors, a six degree of freedom actuator and feedback control. Experimental results demonstrate positioning of the platform in six degrees of freedom at a bandwidth of 35 Hz in the translational directions and at a bandwidth of more than 15 Hz in the rotational directions, respectively. This results in a tracking error that is smaller than 50 nm rms. This paper denotes the first successful attempt for six degree of freedom vibration isolation to enable in-line nano-metrology.@en

This paper presents the mechatronic analysis and performance estimation of a pulse-width modulated permanent magnet synchronous motor (PMSM), which is part of a direct-drive rotational servo system. Physical modeling together with dynamic error budgeting are applied to identify the minimal required switching frequency that maximizes the energy efficiency of the system while maintaining the required precision. The analysis is carried out for a wide velocity range and considers various friction phenomena. The disturbances induced by the switched amplifier are also considered and compared to a linear amplifier. The accuracy of the derived model and analysis is experimentally verified over the entire velocity range as well as for the considered range of switching frequencies.@en

Mechanical vibrations and precision of conventional positioning systems are limiting factors for using nano-metrology tools directly in production environments. Vibrations cause relative motion between workpiece and inspection tool, which distorts measurements at the nanometer level. To enable robot based in-line nano-metrology, this paper proposes a metrology platform that is mounted on a robot arm and maintains a constant and precise relative distance to the workpiece by means of a control loop. This paper presents the mechatronic system design of a 1 degree of freedom (DoF) metrology platform for tracking a vibrating sample in the sub-nanometer range. By incorporating control relevant requirements in the mechanical and electrical design, which is supported by a dynamic error budgeting analysis, the implementation of a high bandwidth feedback loop is enabled. The metrology platform consists of a 1 DoF Lorentz actuator with gravity compensator, a low stiffness flexure-based guiding mechanism and a moving mass of 4 kg with high structural resonance frequencies. A high-bandwidth PD based controller that utilizes the signal of an interferometer is implemented for feedback control. Experiments show a tracking error of 4 nm RMS when exposing the sample under test to on-site measured vibrations, which complies with the dynamic error budgeting analysis. This demonstrates viability of the implemented mechatronic design for in-line metrology applications requiring sub-nanometer precision.@en

Robust feedback control with large parameter uncertainties in a high precision stage with large sample mass variation is presented. Instead of expressing the nominal plant and its uncertainty by parametric models, they are expressed using the identified frequency response data. The open loop transfer function is mapped onto a Nyquist plot, to assess robust stability. Next, the complementary sensitivity function is derived from this data to describe tracking performance, which is verified by experiments. The advantage is that the parameter estimation step is omitted, without compromising robust stability and performance.@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.@en

Correct tuning of feedback gains is important for AFMs to cope with uncertainties of the system dynamics coming from a large range of different samples, cantilevers and scan parameters. For state of the art AFMs gains have to be adjusted manually by the operator. The typical operator such as biologist, physicist or material scientist may not have detailed knowledge about control engineering. In order to increase usability and acceptance an easy and intuitive approach is needed. The method presented in this paper is based on the commonly applied manual tuning strategy for AFM-imaging and copies the behavior of an experienced user. By spectral analysis ringing of the feedback loop is detected when feedback gains are increased beyond the stability margins. Increasing gains is stopped when an 1/f stop criteria is reached. The algorithm is successfully tested in simulation and practical AFM topography measurements with different cantilever - sample combinations, demonstrating that auto-tuning can be applied to achieve imaging performance close to ideal settings.@en

Due to the low photon-count of dark areas of the universe, signal strength of tip-tilt sensor is low, limiting sky-coverage of reliable tip-tilt measurements. This paper presents the low photon-count tip-tilt (LPC-TT) sensor, which potentially achieves improved signal strength. Its optical design spatially samples and integrates the scene. This increases the probability that several individual sources coincide on a detector segment. Laboratory experiments show feasibility of spatial sampling and integration and the ability to measure tilt angles. By simulation an improvement of the SNR of 10 dB compared to conventional tip-tilt sensors is shown.@en