Design principle of micro-mechanical probe for lateral-deflection-controlled friction force microscopy

Design principles of lateral-deflection-controlled friction force microscopy (FFM) are presented. Lateral-deflection-controlled FFM can overcome a fundamental problem of dual-axis FFM and can provide higher lateral resolution by compensating for friction force and providing effectively high rigidity to the probe. In this paper, key micro components are investigated: micro structures for detection of lateral probe deflection and for lateral drive of the probe. The micro structure for deflection detection is fabricated at the end of the probe and is used in combination with an optical lever method. The micro structure that reflects light (positive type) can provide higher sensitivity than a conventional structure that does not reflect light (negative type). For the probe lateral drive, a micro conduction structure that connects the probe with a support beam is used. A micro electrical conduction structure using stiction is introduced, and its feasibility is experimentally confirmed. These micro structures can improve the measurement accuracy.     

面向微粒操纵的介电泳芯片系统研究

针对目前在纳米器件及传感器的制造中尚无对大量粒子进行有效操纵的方法,我们利用介电泳方法对大量微粒进行定位和传输操纵,介绍了利用MEMS工艺进行介电泳芯片加工的过程以及整个观测与实验系统的建立,通过有限元软件对传统介电泳和行波介电泳中电极阵列的电场分布进行求解,并在该实验系统下实现了对微通道中的悬浮高度和微粒的运动速度的测量.该实验系统的研究为液体环境下微纳颗粒的装配和分离提供了一条有效的技术路径.     

纳米级动态粘着接触的有限元模型与仿真

对纳米级动态粘着接触过程进行仿真,是为了研究微纳米尺度的机电系统(如MEMS)中所存在的纳米级表面接触和摩擦,对系统进行减粘附设计.利用商用有限元分析软件ANSYS建立的纳米尺度的动态粘着接触模型,采用原子间Len-nard-Jones作用势函数来描述表面力,用数值求解的方法来描述基本球-盘模型的接触-分离行为,最终得到接触过程的力-位移曲线和枯着接触的分离点和粘着力的大小.将有限元粘着接触模型仿真所得结果与常用的接触模型(DMT模型、JKR模型)解析解对比,证明了有限元粘着接触模型的适用性.由于有限元模型不受接触副几何形状和材料性质的限制,可以进一步对表面形貌修饰后的粘性接触过程和多峰粘着接触过程进行仿真.     

Device level studies of adaptive optics sliding components in microprojectors

Integrated microprojectors are being developed to project a large image on any surface chosen by users. For a laser-based microprojector, a piezo-electric based adaptive optics unit is adopted in the green laser architecture. Nanolubrication of adaptive optics sliding components is needed to reduce friction and for stick–slip motion. Previous studies of the role of lubricant film thickness in nanolubrication of sliding components in adaptive optics have been carried out in an academic, coupon level fashion and need to be carried out on a device level in order to characterize the role of lubricant film thickness in an actual working device. In this paper, the effect that operating temperatures have on lubricant film thickness, adhesive force and coefficient of friction of used devices is investigated. The results and associated mechanisms are presented and compared with previous coupon level tests to show that the proposed AFM measurement techniques can be employed in other micro devices in which adhesion, film thickness, and coefficient of friction measurements are of interest.     

Sliding simulation for adhesion problems in micro gear trains based on an atomistic simplified model

The objective of this research work is to provide a systematic method to perform molecular dynamics simulation or evaluation for adhesion of micro/nano gear train during sliding friction in MEMS. In this paper, molecular dynamics simulations of adhesion problems in micro gear train are proposed. The perfect MEMS gear train model is very complicated by considering the computing time. A simplified model to simulate surface sliding between metals by molecular dynamics (MD) is proposed because the surface property is a dominant factor for the performance of gear systems. Based on analysis of sliding friction and the transmitting characteristics of micro gear train, a model is established by utilizing the Morse potential function. The Verlet algorithm is employed to solve atom trajectories. The simulation results show that adhesion tends to occur between two micro gears after certain cycles and such adhesion accounts for the friction force and the temperature increase. The simulation results are in consistence with the experimental results in the literature. The model is meaningful to prolong the lifetime of micro gear train by selecting proper parameters.     

Micro molding for double-sided micro structuring of SU-8 resist

Advances in micro and nano fabrication technologies for MEMS require high-level measurement techniques with regard to sampling and sensitivity. For this purpose at the Institute of Microtechnology (IMT) highly sensitive piezoresistive 3D force sensors based on SU-8 polymer have been developed. In this paper we present an improved micro fabrication process for a double-sided micro structured design. The sensors are produced by multilayer processing techniques such as UV lithography and coating methods. The double-sided micro structured design demands a photoresist application method which simultaneously features a top side structuring and a casting from a mold. We use a new micro molding process to meet the demands. The micro fabrication technology is described, focusing on the development of the molding structure for shaping of the bottom side and a capable release process for the detachment of the molded structures. The fabrication process of the SU-8 mold layer is optimized to fabricate molding structures with heights from a few μm up to 350 μm. Therefore different SU-8 formulations, namely with classification numbers 5, 25, 50, and 100, have been used. The fundamental limitations for the mold design result from the lithography process, which defines the smallest lateral resolution, and from the characteristics of a molding process, e.g. the impossibility to realize an undercut. To allow for reliable release, the molding structures have to be coated with a sacrificial layer. Silicon nitride is deposited onto the substrate with accompanying monitoring of the deposition temperature during the PECVD process.     

Micro robot arm utilizing rapid deformations of piezoelectric elements

A unique precise positioning mechanism is introduced. It utilizes inertial force and friction, and can make step-like motion of several nanometres up to several micrometres. Repeating step-like movements, precise positioning with a resolution of several nonometres and for an unlimited movable range is possible. Prototypes of joint mechanisms for a micro robot and a 4-degrees of freedom micro robot arm were constructed using this mechanism. These arms and joints proved to have a high positioning resolution and a practical maximum velocity. Applications of this micro robot arm are also discussed.     

半电极含金属芯压电纤维的动态微力传感器

半电极含金属芯压电纤维(HMPF)是一种新型压电传感器.建立了HMPF的动态微力传感理论模型.根据第一类压电方程,基于振动理论,用平均电荷方法,推导出悬臂梁结构HMPF自由端受到垂直动态微力作用后,产生电荷的解析表达式;分析了长度和半径比对产生电荷的影响.实验结果表明,HMPF可以测量动态微力的频率和幅值,具有较高的动...     

Design and experimental validation of a linear piezoelectric micromotor for dual-slider positioning

In this paper, a linear piezoelectric micromotor for dual-slider positioning by a single piezoelectric element (PZT) is proposed. A slider 1 and a permanent magnet are connected by the PZT, and a slider 2 is placed on the permanent magnet by the magnetic force. The slider 1 is a small steel cuboid and can be clamped and released by an electromagnet base. When it is released, it can be driven by impact friction force generated by the PZT. When it is clamped, it keeps stationary, and the slider 2 can be positioned based on the smooth impact friction drive of the micromotor. Both the sliders can be positioned independently with a long motion range as well as a high positioning resolution. Due to a single PZT used in the micromotor and miniaturized design of the mechanism, the proposed micromotor has been constructed with a compact size as well as a relatively high loading capacity.

     

Precision friction measurement between ultrathin wire and microprobe

In this study, using an experimental technique based on small-span bending, the friction behaviors of ultrathin Pt wires with the tungsten microprobes have been reported. In the technique, friction force for sliding of a simply supported wire under bending load applied by closely positioned two opposite probes is measured by a microforce sensor. The force sensor is a capacitive detection type double-beam passive cantilever. Specificity of the microforce sensor provides the technological advantage for precise measurement of friction and normal contact forces sequentially under the observation by a high-resolution digital microscope. Static and kinetic frictions due to externally applied force, internal adhesive force and relative motion are successfully determined. Furthermore, the measured friction in wire-probe contact is used in the determination of the mechanical properties of the wire material.     

Concerning a Technique for Increasing Stability of Climbing Robots

Legged-climbing robot is considered. Each foot of the robot has an electromagnet system for robot"s holding on a metal surface. This surface can be both vertical and inclined, including negative slope. Analytical calculation of robot stability under turn over or sliding conditions has been made. Critical slopes have been determined. One of these slopes corresponds to minimal reserve of robot stability towards sliding and another to minimal reserve of robot stability towards turning-over. As total reserve of stability of a robot is always equal to the minimal one of these reserves. Additional support elements of elastic material with high coefficient of friction, along with electromagnet, allows to increase minimal reserve of robot stability towards sliding. The use of such support elements leads to redistributing force of normal support reaction between electromagnet (which surface has low coefficient of friction) and additional support element (which surface has high coefficient of friction). It is just what leads to increasing the total friction force and as a consequence to increasing of minimal reserve of robot stability towards sliding.     

Exploring the applicability of gradient elasticity to certain micro/nano reliability problems

It has long been assessed that continuum mechanics can be used successfully to address a variety of mechanical problems at both macroscopic and microscopic scales. The term “micromechanics”, in particular, has been used in considering elasticity, plasticity, damage, and fracture mechanics problems at the micron scale involving metallic, ceramic and polymeric materials, as well as their composites. Applications to automobile, aerospace, and concrete industries, as well as to chemical and microelectronic technologies have already been documented. The recent developments in the field of nanotechnology have prompted a substantial literature in nanomechanics. While this term was first introduced by the author in the early 90’s to advance a generalized continuum mechanics framework for applications at the nanoscale, it is mainly used today in considering “hybrid” ab-initio/molecular dynamics/finite element simulations, usually based on elasticity theory, to interpret the mechanical response of nano-objects (nanotubes, nanowires, nanoaggregates) and extract information on nano-configurations (dislocation cores, crack tips, interfaces). The modest goal of this article is to show that continuum elasticity can indeed be extended to describe a variety of problems at the micro/nano regime. The resultant micro/nanoelasticity theory includes long-range or nonlocal material point interactions and surface effects in the form of (phenomenological) higher-order stress/strain gradients. Coupled thermo-diffuso-chemo-mechanical processes can also be considered within such a higher-order theory. Size effects on micro/nano holes and micro/nano cracks can conveniently be modeled, and some standard strength of materials formulas routinely used for micro/nano beams can be improved, with potential applications to MEMS/NEMS devices and micro/nano reliability components.     

A fast non-singular terminal sliding mode control based on perturbation estimation for piezoelectric actuators systems

Piezoelectric actuators (PEAs) are the key devices in micro/nano positioning system. However, the PEA performance is significantly degraded by the inherent non-linear behaviour. This behaviour is a consequence of the hysteresis properties contained within PEAs. Therefore, in micro/nano positioning applications, a robust control system has to be adopted for such actuators. This paper proposes a systematic control method that utilises a fast non-singular terminal sliding mode (FNTSM) based on online perturbation estimation technique for PEAs. Unlike other sliding mode methods, the FNTSM control method is characterised by chatter free. Besides, a zero error convergence can be guaranteed in finite time in the presence of disturbance and system uncertainties (i.e., hysteresis and gain changes). The design of the FNTSM control based on perturbation estimation (FNTSMPE) is presented. A model-free robust exact differentiator is used to estimate the states of the feedback system from merely measurable position signal. Theoretical analysis and the experimental results of FNTSMPE control reveal that high-precision and robust performance is achieved in comparison with ordinary FNTSM control.     

选择性化学机械抛光制作微拱形结构

为克服平面微机械结构无法释放残余应力、刚度小、跨度小,平面牺牲层工艺成拱出现非光滑台阶状边缘而造成器件失效或能量泄漏的缺点,改进现有成拱工艺在器件尺寸、结构稳定性及可靠性等方面的不足,提出一种用选择性化学机械抛光技术制作微拱形结构的方法。该方法是在化学机械抛光过程中,加入对牺牲层材料和硅材料抛光速度具有差异性的选择性抛光液,在牺牲层和硅材料的边界处利用滑动摩擦过程中的物理和化学作用,在牺牲层处形成连续平滑的拱形凸起,最后在其上制作微拱形结构。实验结果证实:微拱形结构有一定的曲率,拱起高度约为3.5μm,跨度大于100μm,微拱形表面光滑且为连续的曲面。该方法可为MEMS传感器、微型压电驱动器、薄膜体声波谐振器及滤波器的微拱形结构的制作提供参考。     

基于显微机器视觉的微纳米级构件的精密检测

随着微纳米技术的发展,大量精密微小型机电产品得到了广泛的应用。针对微机电产品中微纳米构件精密检测的技术需求,提出了一种万向体式显微镜与高分辨率CCD相机相结合的显微机器视觉测量系统。采用MATLAB软件对采集到的图像进行了图像预处理、阈值分割及数学形态学处理、边缘检测及提取等的分析与研究。并且测量了微小齿轮的齿根圆直径,对测量结果进行了分析。结果表明该测量系统的测量误差较小,测量精度高,满足对微纳米级构件的精密测量的要求。     

Multiwalled carbon nanotube AFM probes for surface characterization of micro/nanostructures

A multiwalled carbon nanotube (MWNT) probe was used as a scanning probe in an atomic force microscope (AFM) to obtain surface height maps of micro/nano structures. The surface height maps acquired by the MWNT probe are compared with those by a conventional silicon probe on the four samples: silicon ruler, polymer microchannels, silicon nanomembrane and nanocomposite metal particle (MP) tapes. The results of the silicon ruler, microchannels and membrane samples show that the surface height maps by the MWNT probe have a better resolution than those by a conventional silicon tip due to the sharper tip with the larger aspect ratio of the MWNT. A MWNT probe is especially useful to observe surface height maps of the structures that have larger aspect ratio.Financial support for this work was provided by the National Science Foundation (contract no. ECS-0301056). The authors are grateful to Prof. Derek Hansford and Nick Ferrell of the Micro MD laboratory for providing the samples and fruitful discussions, and Imation Corporation for the samples provided. Work by C.V.N. was supported by a NASA contract to ELORET Corporation.     

Mechanical and tribological characterization of a thermally actuated MEMS cantilever

The temperature effect on the mechanical and tribological behaviors of a microelectromechanical systems cantilever is experimentally investigated using an atomic force microscope. A nonlinear variation of the bending stiffness of microcantilevers as a function of temperature is determined. The variation of the adhesion force between the tip of atomic force microscope (AFM) probe (Si₃N₄) and the microcantilever fabricated in gold is monitored at different temperatures. Using the lateral mode operation of atomic force microscope, the influence of temperature on friction coefficient between the tip of AFM probe and microcantilever is presented. Finite element analysis is used to estimate the thermal field distribution in microcantilever and the axial expansion.     

Advanced LIGA technology for the integration of anelectrostatically controlled bearing in a wobble micromotor

This work concerns the alleviation of friction in a novel design of multistator electrostatic wobble motor. The output torque and the kinematic accuracy of this device are limited by the sliding friction between the rotor and the top surface of the bearing. A solution for an axial bearing has been developed using an advanced LIGA technique to integrate polymethylmethacrylate (PMMA) cylinders into nickel micro structures. A new version of the micromotor has been fabricated, utilizing an axial electrostatic field to hold the rotor against an engineered sliding surface. The integrated bearing stabilizes the rotor and potentially permits operation in liquid environments by sealing the stator electrodes     

Friction model of fingertip sliding over wavy surface for friction-variable tactile feedback panel

A friction-variable touch panel is capable of presenting virtual bumps and holes on its flat surface through the control of the surface friction when a fingertip slides over it. To improve the presentation, we developed a friction model of a fingertip sliding over a sinusoidal surface with an amplitude of 0.5–2.5 mm and a spatial wavelength of 20–50 mm. When a metal ball rolls over a wavy surface with a low friction and contact area, the ratio of the horizontal force to the normal force is equal to the gradient of the surface (this is referred to as the ball bearing model) and is hardly affected by the normal load and rolling speed. In contrast, the profile of the force ratio of a sliding finger is substantially skewed and affected by the sliding direction and normal force exerted by the finger. To model this skewed force ratio, we formulated the asymmetric pressure distribution in the finger-surface contact area and used the effects of the adhesion friction to model the dependency of the force ratio on the normal force and sliding direction. The developed model of a bare finger with these features was found to sufficiently simulate the experimentally observed force ratios. The model can be easily applied to friction-variable touch panels and enables the achievement of a wide variety of haptic contents with macroscopically concave or convex surfaces.     

Trajectory Tracking Control of XY Table Using Sliding Mode Adaptive Control Based on Fast Double Power Reaching Law

Currently, high velocity and precision are the main developing directions of the XY table. However, the nonlinear effects of friction at low speed deteriorate the precision of the XY table servo system. As a result, it is very important to design a control method to carry out friction compensation and trajectory tracking. In this paper, dual sliding mode state observers are used to estimate these immeasurable parameters in the dynamic LuGre model, and the Lyapunov function is used to design the adaptive update law. In addition, fast double power reaching law has the advantage of improving the global asymptotic convergence rate and overcoming these disadvantages where traditional sliding mode control reaching law causes severe chattering. Simulation results that compare the proposed method with exponent sliding mode control and PID control, demonstrate that the fast double power sliding mode control guarantees position and speed signals, tracking the desired references asymptotically.