Stroboscopic Imaging Interferometer for MEMS Performance Measurement

The insertion of microelectromechanical systems (MEMS) components into aerospace systems requires advanced testing to characterize performance in a space environment. Here, we report a novel stroboscopic interferometer test system that measures nanometer-scale displacements of moving MEMS devices. By combining video imagery and phase-shift interferometry with an environmental chamber, rapid visualization of the dynamic device motion under the actual operational conditions can be achieved. The utility of this system is further enhanced by integrating the interferometer onto the chamber window, allowing for robust interferometric testing in a noisy environment without requiring a floating optical table. To demonstrate these unique capabilities, we present the time-resolved images of an electrostatically actuated MEMS cantilevered beam showing the first-order to sixth-order plate modes under vacuum.     

MEMS结构离面微运动测试系统设计与实现

利用频闪成像和显微干涉技术设计开发了微机电系统（Micro Electro Mechanical Systems,MEMS）离面微运动测试系统。系统在计算机控制下通过相对延时和五步相移干涉技术自动采集MEMS结构运动周期内各不同时刻的干涉条纹图集,再通过五步相移算法和分割线去包裹算法分别对干涉条纹图和包裹相位图进行分析处理可得到被测MEMS结构的离面微运动情况。为实现浮点型相位图数据的有效存取,提出了一种新的相位图文件格式。通过实验对硅微悬臂梁在不同幅值正弦基础激励下的离面振动响应进行了有效测量,且测量重复性误差小于10 nm。     

基于协调同步控制的MEMS微运动测量

为协调有效地利用频闪成像、显微视觉和相移干涉技术实现微机电系统(MEMS,micro-electro-me-chanical systems)微运动的可靠测量,提出了一种改进的协调同步控制方法,该方法通过2块5 MHz频率的任意波形发生卡实现激光二极管(LD,laser diode)脉冲信号和MEMS激励信号的同频率相对延时,最小延时增量可达0.3 ns,最小脉冲宽度可达10 ns。基于该方法构建的测试系统可实现MEMS的离面(out-of-plane)和面内(in-plane)微运动的自动测量。通过对硅微悬臂梁离面振动以及硅微谐振器阵列面内振动的实验测量验证了新协调同步控制方法的有效性和实用性,其中离面微运动测量重复性误差小于10 nm,面内微运动测量重复性误差小于25 nm。     

Optimal shape error analysis of the matching image for a free-form surface

When using an optical non-contact scanning system to measure an object that has a large surface, large curvature, or a full 360° profile, one can acquire only one set of sectional measurement points each time. For reconstructing the entire object, every set of sectional measurement points acquired at different positions must match. Therefore, the optimal shape error analysis for the matching image of two or more sets of sectional measurement points is desired. This paper presents a measurement system that combines two CCD cameras, one line laser and a three-axis motion stage. It forms an optical non-contact scanning system in association with the mathematical method of direct shape error analysis for the use in reverse engineering. This analysis and measurement system can be used for the profile measurements of free-form objects. It analyzes the matching image of a free-form surface with high efficiency and accuracy. The validity and applicability of this system are demonstrated by two practical examples.     

Dynamics of droplet transport induced by electrowetting actuation

This study reports on the dynamics of droplets in the capillary regime induced by electrowetting-on-dielectric actuation. The configuration investigated allows for comparing the experimental results with respect to the predictions of Brochard’s theoretical model (Brochard in Langmuir 5:432–438, 1989). Firstly, side-view observations using stroboscopic recording techniques were used to measure and analyse droplet deformations as well as the front and rear apparent contact angles during motion. Secondly, the influence of viscosity on the droplet velocity as a function of the applied voltage was studied. This has revealed that low Reynolds number droplet motion can be described by the simple laminar viscous model of Brochard. Finally, the influence of the dielectric thickness on the droplet dynamics was studied. It is shown that droplet velocity is limited by a saturation effect of the driving electrostatic force and that this phenomenon is very similar to that occurring in static experiments.     

Measurement system for full three-dimensional motion characterization of MEMS

Advanced testing methods for the dynamics of mechanical microdevices are necessary to develop reliable, marketable microelectromechanical systems (MEMS). A key purpose for mechanically testing MEMS is to provide feedback of measurements that can help the designer progress in an iterative process from prototypes to fully developed products. The effectiveness of these procedures is markedly enhanced if the measurements include high-speed dynamic visualizations of mechanical structures in the microsystem. These data can be obtained using a measurement system that is capable of stroboscopic imaging, interferometry, and digital-image processing. We present such a system and demonstrate its capabilities in three disparate MEMS applications: a gimballed microactuator built for a miniaturized magnetic-disk information-storage system; a micromirror array for an adaptive-optics system; and a microgyroscope that can be applied in a number of microsystems.     

Dedicated image analysis techniques for three-dimensional reconstruction from serial sections in electron microscopy

This article describes the digital treatments needed to reconstruct spatial information at a 40-nm depth resolution of entire cells from transmission electron microscopic images of serial sections containing laser-induced topographical references. The use of a scanning transmission electron microscope (STEM) allows the acquisition of images with high contrast and good resolution at medium magnification. The scanning of our specimens at video frequencies is an attractive way to link a STEM with an image processing system. The magnetic hysteresis of the spools responsible for the electron scanning induces image deformations that have to be modelized and rectified before registering the images corrected for cutting-induced deformations.     

Nonlinear and hysteretic influence of piezoelectric actuators in AFMs on lateral dimension measurement

Piezoelectric actuators that are used in atomic force microscopes (AFM) have undesirable properties. The nonlinear and hysteretic characteristics of piezoelectric actuators introduce geometric deformations in the reconstructed AFM images. Due to these deformations, the quantitative interpretation of the absolute dimensions of surface features is difficult and often not accurate.A real-time measuring ‘Nano-metrological Atomic Force Microscope’ system equipped with an ultra-high resolution three-axis laser interferometer system is developed, in which the undesirable properties of piezoelectric actuators are compensated completely. Using this AFM and a one-dimensional (1D) grating reference standard with pitches of 240 nm, which is one of the widely used reference standards as nano-metrological lateral scales, the influences of nonlinear and hysteretic characteristics of piezoelectric actuators on image reconstruction and lateral dimension measurement are examined and compared quantitatively among three different measurement methods. The three measurement methods are: (1) the relative movement between probe tip and sample is controlled and measured directly by voltage signals applied on the XYZ scanner, the nonlinear and hysteretic characteristics of piezoelectric actuators are not compensated; (2) the relative movement between probe tip and sample is controlled by voltage signals applied on the XYZ scanner, but it is measured accurately by interferometers; (3) the relative movement between probe tip and sample in lateral directions are both controlled and measured accurately by interferometers. According to the comparison results, an accurate displacement control system is key to reduce the influences of undesirable properties of piezoelectric actuators and the developed AFM system with three-axis laser interferometer system is proved to eliminate the nonlinear and hysteretic characteristics of piezoelectric actuators completely.     

An all fibre white light interferometric strain measurement system

We report on an all fibre implementation of a white light interferometric fibre strain sensor. Utilising white light tandem interferometry, two all fibre Michelson interferometers are used, one to form the sensor element and the other the optical path scanning interferometer. Results are presented which demonstrate the performance of the system and the measurement of applied strain up to 10 000 με.     

嵌入式移动机器人目标搜集运动控制研究

本文基于移动机器人平台设计实现了核心嵌入式控制系统,采用上位机-下位机两级体系结构,开发了环境信息采集上位机软件及机器人运动控制下位机软件;通过激光测距仪实时测量与数据处理,实现机器人对环境目标的探测与感知,设计了电机控制器用于实现机器人运动控制;最后,针对目标搜集使命案例,验证了移动机器人对环境目标的自主探测与搜集的作业能力,实验结果表明：所设计的嵌入式控制系统及其运动控制器满足使命任务要求。     

双干涉式微位移测量系统的研究与性能改善􀀁

本文提出了光扫描光纤传输双Ｆａｂｒｙ－Ｐｅｒｏｔ干涉系统用于测量绝对为微位移,该系统把扫描波长作为内部转换参数,采用参考长度与敏感头间隙长度比较,从而得到绝对测量值。     

Learning object deformation models for robot motion planning

In this paper, we address the problem of robot navigation in environments with deformable objects. The aim is to include the costs of object deformations when planning the robot’s motions and trade them off against the travel costs. We present our recently developed robotic system that is able to acquire deformation models of real objects. The robot determines the elasticity parameters by physical interaction with the object and by establishing a relation between the applied forces and the resulting surface deformations. The learned deformation models can then be used to perform physically realistic finite element simulations. This allows the planner to evaluate robot trajectories and to predict the costs of object deformations. Since finite element simulations are time-consuming, we furthermore present an approach to approximate object-specific deformation cost functions by means of Gaussian process regression. We present two real-world applications of our motion planner for a wheeled robot and a manipulation robot. As we demonstrate in real-world experiments, our system is able to estimate appropriate deformation parameters of real objects that can be used to predict future deformations. We show that our deformation cost approximation improves the efficiency of the planner by several orders of magnitude.     

激光偏振干涉纳米定位系统的设计与实验研究

为适应工业发展和计量界对精密定位提出的越来越高的要求,本文提出了基于偏振激光干涉技术的纳米定位方法。在该干涉测长系统中,用偏振计取代传统单频激光干涉仪的光电传感器并配置偏振分光元件、起偏镜等,可将干涉仪出射光的干涉条纹相位细分为36000份,使用波长为633nm的激光源,可将理论测量分辨率提高到 10pm。将完成的偏振干涉测长系统与商用SIOS干涉仪的实验测量结果做了比对。本文还就完成的实验系统的各误差源做了实验研究,得到量化值。经不确定度评估计算,在标准实验室环境条件下,对于微米级行程的位移,其位置测量不确定度小于1.4nm。该方法可应用于纳米定位的各个领域。     

基于在线特征选择的实时多姿态人脸跟踪

针对复杂条件下的人脸跟踪问题, 将显著区域跟踪算法和基于 Adaboost 的人脸检测算法相结合, 研发了一个实时多姿态人脸跟踪系统. 系统采用数据关联结果, 自动选择和切换检测器与跟踪器, 并通过引入环境信息增强跟踪算法的稳定性. 实验表明, 系统可在目标姿态变化、摄像机运动等复杂条件下进行自动人脸检测与跟踪, 对 320x240 的图像序列处理速度达到 10-12帧/秒.     

Digital closed-loop nanopositioning using rectilinear flexure stage and laser interferometry

To enhance the accuracy of nanopositioning and the metrological capability of scanning probe microscopy, we construct a two-dimensional interferometric nanopositioning system consisting of rectilinear flexure stage, calibrated laser interferometer, and digital feedback control system. We implement a correlation matrix, determined by the piezoelectric constant and the crosstalk between two axes, into the closed-loop control algorithm to compensate the nonlinearity and the crosstalk of the PZT-driven stage. In the tests on nanopositioning, the 1-nm-step motion and the tracking along a 1-nm-radius circular target path are accomplished to verify the short-term repeatability and the subnanometer-level precision. Additionally, a scanning tunneling microscope equipped with the interferometric nanopositioning system is built up to demonstrate the metrological functions of scanning probe microscopy.     

基于在线特征选择的实时多姿态人脸跟踪

This paper presents a system that is able to reliably track multiple faces under varying poses(tilted and rotated)in real time.The system consists of two interactive modules.The first module performs the detection of the face that is subject to rotation. The second module carries out online learning-based face tracking.A mechanism that switches between the two modules is embedded into the system to automatically decide the best strategy for reliable tracking.The mechanism enables a smooth transit between the detection and tracking modules when one of them gives either nil or unreliable results.Extensive experiments demonstrate that the system can reliably carry out real time tracking of multiple faces in a complex background under different conditions such as out-of-plane rotation,tilting,fast nonlinear motion,partial occlusion,large scale changes,and camera motion.Moreover,it runs at a high speed of 10～12 frames per second(fps)for an image of 320×240.     

Adaptable Anatomical Models for Realistic Bone Motion Reconstruction

We present a system to reconstruct subject‐specific anatomy models while relying only on exterior measurements represented by point clouds. Our model combines geometry, kinematics, and skin deformations (skinning). This joint model can be adapted to different individuals without breaking its functionality, i.e., the bones and the skin remain well‐articulated after the adaptation. We propose an optimization algorithm which learns the subject‐specific (anthropometric) parameters from input point clouds captured using commodity depth cameras. The resulting personalized models can be used to reconstruct motion of human subjects. We validate our approach for upper and lower limbs, using both synthetic data and recordings of three different human subjects. Our reconstructed bone motion is comparable to results obtained by optical motion capture (Vicon) combined with anatomically‐based inverse kinematics (OpenSIM). We demonstrate that our adapted models better preserve the joint structure than previous methods such as OpenSIM or Anatomy Transfer.     

Airborne traffic monitoring in large areas using LiDAR data – theory and experiments

This article investigates the theoretical background for airborne LiDAR (light detection and ranging) and ALS (airborne laser scanning) systems that are used to monitor traffic from airborne platforms. An object moving with a velocity deviating from the assumptions incorporated in the scanning process will generally appear both stretched and sheared – motion artefacts. To study the impact of these deformations on the ALS data, the analytic relations between an arbitrarily moving object and its conjugate in the ALS data have been examined and adapted to concrete airborne specifications. Furthermore, a complete scheme is proposed to analyse urban traffic in real-life situations, which combines vehicle detection successively with the motion classification method, which is the main focus of this article. Finally, the velocity of the moving vehicle can be derived with knowledge about the vehicle shape. The experimental results obtained by using real ALS data were assessed with respect to the reference data concurrently acquired by a video camera to validate the theory.     

Visual Servo Control Achieving Nanometer Resolution in $X$ –$Y$–$Z$

This paper presents a three-axis vision motion sensor and its applications to visual servo control. The vision sensor is integrated with a three-axis piezo stage to form a visual servo control system that achieves nanometer resolution in all three $x$– $y$–$z$ motion axes. Motion measurement is achieved using a single interferometer-equipped optical microscope. A real-time image-processing algorithm that processes interference fringe patterns and that achieves nanometer out-of-plane resolution is presented. Furthermore, a feedback-control scheme is introduced to control the sensor plane using an Objective-Z-Positioner to enable automatic tracking of moving objects. It expands the out-of-plane measurement range of the vision sensor beyond its inherent depth of field of several micrometers to 100 $mu$m and beyond. An integrated visual servo system is implemented and experimental results are shown.