Showing papers by "Georg Schitter published in 2019"
TL;DR: The results demonstrate that the proposed flexure-guided nanopositioner with a nonlinear hybrid reluctance actuator can play a role of both long-stroke and high-speed scanners with the improved power consumption.
Abstract: While nanopositioners often use flexures for high quality motion avoiding nonlinearities, the achievable motion range and energy efficiency are limited, due to the force required for positioning against the flexures. To overcome the problem, this paper proposes a flexure-guided nanopositioner with a nonlinear hybrid reluctance actuator for a large range and energy efficiency. The actuator has nonlinear negative stiffness that partially cancels the flexures’ stiffness. Consequently, the nonlinearities reduce the required current by up to 67%. To compensate them for high-precision motion in the entire range of 2 mm, a feedback controller is designed, achieving a closed-loop bandwidth of 640 Hz and positioning resolution of 2.48 nm(rms). The mechatronic system is designed such that the stiffness nonlinearity has no influence on the closed-loop stability and bandwidth. Additionally for accurate periodic scanning motion, modeling-free inversion-based iterative control is combined to decrease the tracking error by a factor of 396 at most. The achieved error is 10 nm(rms) for a 1 Hz triangular motion of 1.6 mm range and for a 100 Hz triangular motion of 10 $\mu$ m range. The results demonstrate that the proposed nanopositioner can play a role of both long-stroke and high-speed scanners with the improved power consumption.
44 citations
TL;DR: In this article, a hybrid reluctance tip/tilt actuator was used for fast steering mirror (FSM) system. But the performance of the FSM was not evaluated.
29 citations
04 Mar 2019
TL;DR: In this paper, a generalized nonlinear SDOF model of an electrostatically actuated 1D resonant MOEMS mirror is proposed based on measured scanning trajectories and the current generated by the movement of the comb-drive electrodes.
Abstract: Accurate modeling of MOEMS mirrors is crucial for their design and fabrication, as well as for proper control within its target applications. This paper proposes a novel identification method using a generalized nonlinear SDOF model of an electrostatically actuated 1D resonant MOEMS mirror solely based on measured scanning trajectories and the current generated by the movement of the comb-drive electrodes. The nonlinear stiffness and damping are identified from a decay measurement while the comb-drive torque and the rotor inertia are derived from an actuated decay measurement, where a constant voltage is applied. The simulation with the identified parameters closely matches the measured frequency response including bifurcations and hysteresis. Furthermore a period-based modified index of agreement is proposed for nonlinear systems showing values of over 0.995 at each period along the decay.
14 citations
TL;DR: In this article, a fast steering mirror is used for high speed optical scanning, which is centered around an easy-to-manufacture membrane-like mechanical flexure and uses an optical sensor system for position measurement.
12 citations
TL;DR: By the proposed uncertainty analysis, the accuracy of the developed MEMS test bench shows up to 0.026° at the mirror angle of 15°.
11 citations
TL;DR: The interplay between process and control design, as well as the system integration with the example of a scanning laser triangulation system for high precision 3D metrology are discussed.
Abstract: Mechatronic imaging systems, ranging from nanoscale metrology to telescope systems and adaptive optics for astronomy, are complex machines that demand continual improvement of system speed, range, and precision. This demand requires advanced designs of the mechatronic components and a motion control scheme that carefully considers the interplay of a physical plant and the target application. A proper data acquisition system is required to synchronously acquire and process measurement and position data, and a sophisticated system integration is needed to obtain the maximum performance of the resulting system. This paper discusses the interplay between process and control design, as well as the system integration with the example of a scanning laser triangulation system for high precision 3D metrology. The integration process can be tailored to individual applications, and is discussed for raster and Lissajous scan trajectories, considering their individual requirements for the system and control design. Further it is demonstrated how these individually tailored system components can improve the performance in terms of precision and efficiency by several orders of magnitude.
11 citations
TL;DR: In this paper, an iterative trajectory learning algorithm is proposed to overcome the limitations due to local pointing model inaccuracies and dynamic effects during tracking, which reduces the tracking error by a factor of 11 and is ultimately limited by the uncertainty of the orbit prediction.
11 citations
TL;DR: In this paper, a high-precision, high-speed scanner using a hybrid reluctance actuator was proposed, which can be stronger than conventionally used comparable Lorentz force actuators.
Abstract: This paper proposes a high-precision, high-speed scanner using a hybrid reluctance actuator, which can be stronger than conventionally used comparable Lorentz force actuators. For compactness, its mover is guided by flexures and laterally moved by a hybrid reluctance actuator with a voltage amplifier. To reject disturbances such as thermal drift and hysteresis, the scanner is regulated by cascade control, for which parasitic resonances are damped partially mechanically. As a result, the closed-loop system realizes a high control bandwidth of 3.5 kHz and a high positioning resolution of 0.8 nm at a static point. For high-speed scanning motion, modeling-free inversion-based iterative control (IIC) is proposed to be combined with the cascade control as the scanner’s feedforward controller. Experiments demonstrate that the scanner with the cascade control realizes a 2 μm triangular motion at 400 Hz with a tracking error of 101 nm, and the modeling-free IIC successfully decreases this relatively large error by a factor of 26 to 3.8 nm. Consequently, this paper clearly demonstrates that the proposed scanner with the hybrid reluctance actuator can realize high-precision, high-speed scanning motion.
10 citations
TL;DR: Results clearly indicate a trade-off between thrust constant, linearity and dynamic behavior, which should be considered for employment in high-precision applications.
Abstract: This paper evaluates the performance of a hybrid reluctance actuator for application in high-precision motion systems. For this purpose, its properties are compared with those of a voice coil actuator, which is the choice actuator for many high-precision applications. To properly investigate the non-linearities of these systems, finite element analysis (FEA) is employed. Spacial-domain analysis shows that the hybrid reluctance actuator can deliver both higher forces per volume (by a factor up to app. 10.5) and thrust constant (by a factor up to app. 9.6) than the voice coil actuator. However, these values depend strongly on the position of the mover, causing a high non-linear stiffness. Frequencydomain analysis yields the power losses of the actuators, as well as the dynamic thrust constant. It is shown that at all frequencies the hybrid reluctance actuator suffers from higher iron loss (by a factor up to app. 5.1) than the voice coil actuator. Additionally, its thrust constant shows a large magnitude slope (app. −14.4 dB/dec) and phase lag (app. −71◦ at f =10 kHz) in the frequency domain, resulting in a narrowed control bandwidth. These results clearly indicate a trade-off between thrust constant, linearity and dynamic behavior, which should be considered for employment in high-precision applications.
8 citations
TL;DR: A novel scanning wavefront sensor approach is proposed which is faster than a coordinate measuring machine and more flexible than an interferometer to directly measure the performance of a freeform optical part.
7 citations
TL;DR: An iterative learning control for a micro stereo lithography setup to enhance both the speed and the quality of 3D printing is proposed and results demonstrate that ILC can improve uniformity of line thickness as well as accuracy of the trajectory.
TL;DR: It is shown that certain cross talk artifacts not only do manifest themselves in additional noise, reduced resolution, or an offset of the measured surface potential but can also lead to an inverted signal scale and, crucially, cannot be diagnosed with a known reference signal.
Abstract: Kelvin-probe force microscopy is a measurement mode of atomic force microscopy, which is used to quantitatively map the electrical surface potential of a sample. Inadequate hardware and electronic design can lead to signal cross talk and, in consequence, false results. Here, we show that certain cross talk artifacts not only do manifest themselves in additional noise, reduced resolution, or an offset of the measured surface potential but can also lead to an inverted signal scale and, crucially, cannot be diagnosed with a known reference signal. We show experimental data on an electrically homogeneous sample, describe a method to detect the artifact, and propose simple remedies, which should be well within the reach of most research and industrial laboratories.
TL;DR: A linear state-space model is derived with the estimated parameters, which serves as the basis for LQG controller design and provides sufficient accuracy for both the motion planning and leveling tasks.
TL;DR: The system design satisfies the Scheimpflug condition even though only the illumination path is scanned, such that an FSM with a small aperture size and high bandwidth can be used.
TL;DR: In this article, a fast steering mirror integrated into the optical path allows to compensate for the measured tip-tilt errors in order to reduce the influence of wind, ground vibrations and actuator imperfections.
TL;DR: Experiments demonstrate the effectiveness of the proposed vibration isolator and the capability of the hybrid reluctance actuators to handle floor vibrations and realizes nanometer positioning resolution in a vibrational environment.
TL;DR: In this paper, the phase of a nonlinear resonant MOEMS mirror is detected by an amplified current signal, generated by the movement of the comb-drive electrodes and a simple comparator circuit.
TL;DR: In this article, a magnetic flux estimation and control is proposed to compensate for the magnetic hysteresis in the ferromagnetic stator and mover in hybrid reluctance actuators for high precision motion control.
01 Dec 2019
TL;DR: A simple but so far unrecognized label-free method for surface-bound analyte detection, which could be applicable to a wide range of substances, and the use of an electrostatic principle for assay read-out is reported for the first time.
Abstract: Detection methods and analytical devices have drawn increasing attention in recent years due to their direct impact on early detection, monitoring and diagnosis of disease in medical research. In this work, we describe a simple but so far unrecognized label-free method for surface-bound analyte detection, which could be applicable to a wide range of substances. In this respect, the feasibility and practical aspects of a micrometer-scale, poly-l-lysine-based, solid-phase assay for label-free analyte detection with electrostatic read-out are investigated. Micropatterned poly-l-lysine layers were produced using soft-lithography on mica and their electrostatic surface potential was determined using Kelvin-probe Force Microscopy. Ribose, a natural sugar, was used as analyte. Upon exposure to ribose, the surface potential changed from positive to negative in a reversible manner. We report for the first time the use of an electrostatic principle for assay read-out. This purely physical effect could be used to develop label- and marker-free assays for sugars, various other substances or, possibly, biosensors.
TL;DR: In this article, an analytic model for self-weight surface deflection is used to determine the number of concentric continuous support rings and find their radii to sufficiently support the mirror.
04 Mar 2019
TL;DR: This publication investigates the total tip-tilt error of a terrestrial optical communication platform for reflective optical communication using a 14-inch telescope with tip-Tilt compensation and successfully demonstrates the system’s performance, effectively reducing the tip- tilt error up to a factor of 10.
Abstract: Atmospheric turbulences limit the achievable performance of free-space optical (FSO) satellite communication systems. Particularly in retro-reflective FSO satellite communication, tip-tilt disturbances are a dominant source of performance degradation and thus prevent the exploitation of the full potential of this communication system. This publication investigates the total tip-tilt error of a terrestrial optical communication platform for reflective optical communication using a 14-inch telescope with tip-tilt compensation. The compensation system consists of a fast steering mirror (FSM), a quad photo diode (QPD) and a controller. Dynamic error budgeting is used to systematically analyze the system components’ interplay and their contribution to the total error. Based on the results of the system analysis, a feedback controller for the compensation system is designed and tuned for disturbance rejection. The system’s performance is evaluated with a reflective FSO communication link over a distance of 600 m in urban environment. The atmospheric aberration statistic is put into relation with comparable measurements using satellite to earth communication links. Measurement results successfully demonstrate the system’s performance, effectively reducing the tip-tilt error up to a factor of 10.
01 Mar 2019
TL;DR: In this paper, the authors investigated temperature dependency of PSDs and its compensation that enables the usability of PSD in high temperature applications above 60°C and showed that the proposed temperature compensation scheme reduced the temperature-induced relative position sensing error from 44.7 % down to 0.2 % for temperatures up to 95°C.
Abstract: PSDs are used for fast and precise beam position measurements in various applications such as scanner characterization and scanning probe microscopy. However, PSDs suffer from systematic position sensing errors at high temperatures, limiting the possible application fields for usage of PSDs. This paper investigates temperature dependency of PSDs and its compensation that enables the usability of PSDs in high temperature applications above 60°C. The proposed compensation scheme is explained by the diode leakage current model, which is extended to the given semiconductor device structure of the PSD. For the validation of the proposed method, an experimental PSD characterization setup has been used, showing that the proposed temperature compensation scheme reduces the temperature-induced relative position sensing error from 44.7 % down to 0.2 % for temperatures up to 95°C.
01 Nov 2019
TL;DR: In this paper, a 3D printed 5-hole probe for high-dynamic wind measurements for UAV is presented, which is calibrated by means of a free jet wind tunnel and validated by dynamic angle of attack variations during an unmanned test flight.
Abstract: This paper focuses on the integration and characterization of a 3D printed 5-hole probe for high-dynamic wind measurements for UAV. The probe is calibrated by means of a free jet wind tunnel and validated by dynamic angle of attack variations during an unmanned test flight. The angle of attack and sideslip angle measurements show an RMS error of 24 mrad with a peak-to-peak noise of 3mrad in the range of −20° to 20°. The airspeed measurement shows an RMS error of 0.19ms−1 with a peak-to-peak noise of 0.09ms−1 and a range up to 28ms−1. Therefore, the probe fulfills the requirements for the planned purpose of active turbulence suppression for fixed-wing UAV. Furthermore, the probe appears also suitable for a variety of other applications.
TL;DR: In this paper, a hysteresis compensating control scheme that uses two piezoelectric transducers with similar hysteretic behavior is presented, where the transducers are supplied with the same voltage and the measured displacement of one of them is used to operate the other one in open-loop.
TL;DR: In this article, the authors investigated the benefit of active mechanical Q-control for electrical surface potential measurements in atomic force microscopy using an active analog Q-controller, while in lift-mode.