This paper presents the design, assembly, and evaluation of a novel integrated two degree of freedom (2DoF) actuator design for tip/tilt motion and its integration into a fast steering mirror with ...comparably large range. The system is designed for scanning applications, such as in optical metrology systems, and comprises an integrated symmetric 2DoF hybrid-reluctance-force actuator and mover-flexure-design. The actuator design employs a permanent magnet for biasing the actuator with a constant flux and two actuator coils per axis to generate a steering flux for positioning the mover. The system prototype has an angular range of <inline-formula><tex-math notation="LaTeX">\pm 3^\circ</tex-math> </inline-formula> in tip and tilt and achieves a closed-loop control bandwidth of 1 kHz based on the signal of eddy current sensors. Compared to the only so far realized state-of-the-art reluctance force actuated fast steering mirror system with integrated sensors, the presented design enables to improve the product of range times' bandwidth, representing a measure for the system performance, by more than 85%.
In scan-based 3-D systems, the achievable measurement time is strongly restrained by the moving mass. This limitation can be relaxed, by scanning the optical path instead of moving the entire sensor, ...such that a higher measurement speed can be achieved. This article deals with the design, the control, and the measurement results of a scanning triangulation sensor, in which the illumination and reflection paths of the sensor are scanned by a fast steering mirror (FSM). The system architecture is determined using ray-tracing simulations, such that the performance of the scanning system can be determined in advance. To scan the area of interest with the FSM, conventional raster trajectories and Lissajous trajectories are employed, which provide an early overview of the scan area. For tracking these trajectories, PID and dual-tone controllers are used, respectively. The experimental results demonstrate that for both scan trajectories, the sample can be captured correctly, with a frame rate of 1 frame/s, a maximum spatial resolution of 130 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>, and a field of view of <inline-formula> <tex-math notation="LaTeX">11.5\,\,\times 18.5\,\,{\mathrm{ mm}}^{2} </tex-math></inline-formula>.
This paper focuses on the prediction of disturbance effects of the vertical acceleration of an aircraft flying in atmospheric turbulence. To this end, 5-hole probes with high-dynamic differential ...pressure sensors are installed in front of a fixed-wing unmanned aircraft system (UAS) and a manned experimental aircraft to measure the local airspeed and angle of attack of the airflow. Test flights are performed in light, moderate and severe turbulence to assess the anticipating character and the accuracy of the predicted acceleration. Thereby, depending on the flown airspeed, anticipation times up to 0.1 s are observed. For the UAS the prediction accuracy is assessed to be 71.19% for moderate turbulence and 71.05% for severe turbulence, where vertical acceleration disturbances higher than 30 m/s
2
are measured. The first manned test flight revealed a prediction accuracy of 61.97%.
This work presents the design, simulation, control and experimental result of an optical scanning laser sensor for 3D imaging. The system design satisfies the Scheimpflug condition even though only ...the illumination path is scanned by a compact fast steering mirror (FSM). To reconstruct the surface profile from measured quantities and model parameters, geometrical relations are used. The influence of a misalignment on the achievable resolution is determined, using ray-tracing simulations. To scan the area of interest an adapted scan trajectory is employed, such that a uniform spatial resolution is generated. The system captures the sample with 100 x 100 pixels and achieves a frametime of 10 s. The lateral scan area of 15 x 23 mm is obtained with a maximum lateral resolution of 60 µm. Through the optical scan the measurement time can be reduced by a factor of 400 compared to a mechanical scanning triangulation sensor system.
This article proposes a mechatronic system design for atomic force microscopes (AFMs) in order to realize a large range and high control bandwidth of the vertical probe motion by a flexure-guided ...voice coil actuator. The first mechanical resonant frequency of the actuator is decreased to 67 Hz for a large motion, whereas the second resonant frequency is maximized to 1.15 kHz. The frequency band between the resonances enables two-degree-of-freedom control with a position sensor to realize a control bandwidth of 881 Hz, which is 13 times higher than the first resonance that is the limitation of conventional AFMs. The closed-loop actuator achieves a positioning resolution of 1.7 nm and a nonlinearity of 0.02% for a motion range of 700 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m. Consequently, the actuator realizes a range-bandwidth product of 617 kHz<inline-formula><tex-math notation="LaTeX">\cdot \mu</tex-math></inline-formula>m, breaking through a theoretical limit of piezoelectric actuators (567 kHz<inline-formula><tex-math notation="LaTeX">\cdot \mu</tex-math></inline-formula>m). The high performance of the actuator is further confirmed by 400 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m topography measurement in the constant force mode with a bandwidth of 197 Hz. The achieved resolution of the topography measurement is 2.9 nm, and it is demonstrated by successfully imaging nanostructures on a CD-ROM disk.
Laser triangulation sensors are one of the most commonly used optical sensors in dimensional metrology and quality control. This article presents a method for simulating the laser speckle-induced ...measurement uncertainty, representing a major performance limitation of these sensors, as well as the effects of speckle reduction mechanisms based on spatio-temporal averaging. To investigate the relation between triangulation angle and the resulting speckle-induced uncertainty, simulations are performed for three sensor geometries, revealing that a larger angle results not only in a smaller measurement range but also in a reduced influence of laser speckle and a smaller uncertainty. A parameter study on a speckle-reducing moving diffuser mechanism, integrated into the optical sensor path, investigates the achievable improvement for various combinations of motion frequency and amplitude. The accuracy of the simulation results is validated by measurements conducted with an experimental setup, demonstrating good agreement between the measured and simulated uncertainty values with and without the speckle reduction mechanism. It is shown that the diffuser is capable of reducing the resulting speckle-induced measurement uncertainty by up to 63%.
Satisfying the Scheimpflug condition in a rotational scanning 3D triangulation sensor system can be challenging. By violating this condition an reproducible measurement error is generated, which is ...caused by the out of focus projected laser point on the detector. In this work a ray-tracing simulation of the scanning system is performed, in order to determine potential aberrations. With the reference measurement of a flat surface the error due to violation of the Scheimpflug condition is obtained. The error is systematic and reproducible and can be compensated by a correction polynomial, with coefficients determined by using the least squares method. Experimental results reveal, that the measurement error can be significantly reduced by the correction polynomial.
This paper investigates the influence of eddy currents on the dynamic behavior of a novel hybrid-reluctance-force actuator for tip/tilt systems. The effects of eddy currents on the mechatronic system ...dynamics are identified and modeled by a first order system approximation. Their influence on the achievable performance of a closed loop controlled system is studied by investigating two configurations of the ferromagnetic actuator yoke. An initial solid steel configuration of the yoke is compared to a layered yoke structure with isolated steel sheets, with the aim to improve the system bandwidth, which is limited by the eddy currents. Robust PID feedback controllers are designed for controlling the mover position of both system configurations, resulting in comparable phase margins. Experiments demonstrate that the closed loop bandwidth of the prototype setup can be increased from 370 Hz to 1 kHz by changing the yoke structure, which equals a bandwidth improvement by a factor of 2.8.
Due to the trend towards small lot sizes and fast changes of relevant product features in production processes, the demands for flexible measurement systems with high precision and throughput are ...constantly growing. By using optical scanning sensor systems, e.g. comprising a laser triangulation sensor and a fast steering mirror, the demands on speed and precision can be partially satisfied, leaving the flexibility of adapting to various measurement tasks to be solved. A common use-case is the need to measure a certain feature on a sample with a higher spatial resolution than the rest of the sample. By using machine vision such features can be detected automatically, enabling an automated adaptation of the scanning system to the measurement task. This work presents the combination of an optical scanning sensor system with an agglomerative clustering algorithm for detecting features and their dimensions. Based on the identified features, offset and scan amplitudes for high resolution rescans can be derived, resulting in a flexible metrology tool. Experimental results show that several individual features on a sample can be precisely detected and that an automatically parametrized rescan can significantly increase the lateral resolution of the acquired image.
PDF
