A systematic procedure for the design of piezoelectric inchworm precision positioners

Design equations are developed and integrated into a computerized design tool in order to facilitate the creation of inchworm piezoelectric based positioners. Fundamental to the development of the design tool is the piezoelectric actuator and motor frame stiffness interaction and its influence on positioner performance. A generalized motor frame configuration for each of the motor subsystems is presented and used to generate key initial positioner frame geometry. An inchworm precision positioner is implemented based on the generalized motor frame and the computerized design tool and it is shown experimentally and through finite-element analysis that the design approach is effective for precision positioner design. The prototype of the inchworm positioner developed is shown to have a stiffness in the direction of motion of 88 N//spl mu/m, a maximum thrust of 150 N and a traversing speed of up to 20 mm/s.     

Implementation of a novel large moving range submicrometer positioner

A novel, compact and two degree-of-freedoms (DOF) submicrometer positioner with a large moving range is presented in this paper. The design of the positioner utilizes a monolithic parallel flexure mechanism with built-in electromagnetic actuators and eddy current sensors to achieve the precision 2-DOF motion. The travel range of the positioner is 1000 μm/5 mrad and which depend on the eddy current sensor’s range of measurement (ROM) and electromagnetic actuator’s effective length. The analytical model and its dynamics were analyzed and derived. The whole control architecture takes the measured configuration parameters and endeavors to control the positioner motion by regulating the currents in the electromagnetic actuators. To increase the compactness and stability of the positioner, a self-tuning adaptive (STA) controller was analyzed and proposed. From the experimental results, satisfactory performances of the system, including stiffness and precision, have been successfully demonstrated.     

Fabrication of low-stress low-stiffness leveraged cantilever beam for bistable mechanism

This paper presents the fabrication and application of a leveraged cantilever beam with low-stress and low-stiffness. This cantilever beam is overhanged with two free ends and suspended in air by the supporting torsion flexures fixed at its middle. The teeterboard-typed cantilever features a low-stiffness with 1.63 N/m, and a low-stress with ±6.27 MPa. The cantilever beam was prepared by a laminated photoresist sacrificial layer process (LPSLP), that is, a multilayered photoresist film for supporting the suspended cantilever beams. In this work, two main problems related to microfabrication process were discussed. One is the control of residual stress in permalloy cantilever with varying the contents of additive saccharin to minimize the deformation of the free end of the beams. The other is an improved wet release method to avoid the adhesion or stiction of the all metal microstructures. The proposed leveraged cantilever beam has a potential application on the bistable switching mechanism in single-pole-double-through (SPDT) latching relay fields. Switching between two stable states of the microbeam mechanism was successfully validated with WYKO NT1100 optical profiling system.     

单轴半蝶形柔性铰链在快速反射镜中的设计与应用

针对提高激光武器系统光束指向控制稳定精度的战术需求,设计了一款适用于光束指向快速反射镜的单轴半蝶形柔性铰链。首先,根据快速反射镜系统运动形式及功能需求,推演单轴半蝶形柔性铰链的物理模型;然后,采用基于卡氏第二定理的卡氏法简化并求解数学模型,并优化模型参数;最后进行有限元仿真与实验测试,并对单轴半蝶形柔性铰链机械谐振频率的理论计算、仿真分析以及实验测试结果进行分析比较。实验结果表明:单轴半蝶形柔性铰链工作方向机械谐振频率为165.29 Hz,满足设计指标要求。理论计算与实验测试结果相差1.3%,有限元仿真与实验测试结果相差3.2%。从而证明了单轴半蝶形柔性铰链结构形式合理,数学建模准确,为提高激光武器系统光束指向控制稳定精度提供了有力的支撑。     

A new preload mechanism for a high-speed piezoelectric stack nanopositioner

Piezoelectric stack actuators are the actuator of choice for many ultra-high precision systems owning to its fast responses and high pushing force capabilities. These actuators are constructed by bonding multiple piezoelectric layers together. An inevitable drawback of these actuators is that there are highly intolerant to tensile and shear forces. During high-speed operations, inertial forces due to effective mass of the system cause the actuators to experience excessive tensile forces. To avoid damage to the actuators, preload must be applied to compensate for these forces. In many nanopositioning systems, flexures are used to provide preload to the piezoelectric stack actuators. However, for high-speed systems with stiff flexures, displacing the flexures and sliding the actuators in place to preload them is a difficult task. One may reduce the stiffness of the flexures to make the preload process more feasible; however, this reduces the mechanical bandwidth of the system. This paper presents a novel preload mechanism that tackles the limitations mentioned above. The preload stage, which is connected in parallel mechanically to a high-speed vertical nanopositioner, allows the piezoelectric stack actuator to be installed and preloaded easily without significantly trading of the stiffness and speed of the nanopositioning system. The proposed vertical nanopositioner has a travel range of 10.6 μ m. Its first resonant mode appears at about 24 kHz along the actuation direction.     

Verification and use of Herrmann's optical theory of thermal velocity effects in electron beams in the low perveance regime

A comparison between Herrmann's optical theory and a pinhole probe study of a highly converged, perveance 0.015 × 10^-6A/V^3/2, electron beam in a confining magnetic field is presented. This comparison shows the theory to be obeyed with a good degree of accuracy. The application of the theory to the problem of optimizing the transmission of such thermal beams through long drift tubes is shown to lead to criteria which differ radically from those prescribed by the laminar theory.     

CMOS compatible bulk micromachined silicon piezoresistive accelerometer with low off-axis sensitivity

The CMOS compatible bulk micromachined piezoresistive accelerometer presented in this paper consists of four flexures supporting a proof mass. Four pairs of boron-diffused piezoresistors are located at maximum stress points on the flexures near the proof mass and frame ends. Because of the opposite nature of stress at the two ends, these piezoresistors can be connected to form a Wheatstone bridge such that the off-axis responses are practically cancelled while the on-axis (along perpendicular to proof mass) response is maximized. The device is simulated using CoventorWare. In the fabrication process, dual-doped TMAH solution is used for wet anisotropic etching. The novelty of this etching process is that the bulk micromachining can be performed after aluminum metallization. The etched surface is also smooth. The fabrication is thus CMOS compatible. The accelerometer exhibits good linearity over 0-10 g.     

空间遥感相机大口径变方位反射镜设计

随着遥感技术的发展,新型相机对变方位反射镜提出了口径更大,精度更高的需要。针对1 000 mm×700 mm大口径变方位反射镜提出了一种新式背部高稳定支撑设计,相对于常规变方位反射镜设计,具有体积包络小、重量轻、适应性广的特点。反射镜采用ULE材料,蜂窝夹层的轻量化结构形式,通过背部三点关节球铰卸载了反射镜的装配应力和在轨热变形应力,达到反射镜的无应力静定支撑。通过重力卸载结构的设计和卸载力的优化,解决了光学反射镜地面测试结果天地一致性问题。仿真分析表明地面重力环境下,在90°反射镜面型测试方位时,面型为0.006λ(λ=632.8 nm);在75°整机成像方位Ⅰ测试时,面型为0.005λ;在45°整机成像方位Ⅱ测试时,反射镜面型为0.011λ。反射镜组件的一阶频率达到83.2 Hz,具有较高的刚度,能够满足发射时力学环境要求。这种大口径变方位反射镜组件设计能够满足新型遥感相机的需求,也可为同类反射镜的设计提供参考。     

静电驱动蝴蝶结状双端固支梁的节点分析法

为了在节点化设计方法中对静电驱动的蝴蝶结状双端固支梁进行分析,采用伽辽金残余法建立了静电驱动梯形梁单元的节点化模型,在HSpice中构建了相应的等效电路模型. 与有限元仿真结果及文献中给出的实验结果进行了比较,结果表明模型具有较高的精度,可在相关设计中作为参考.     

Online-Erkennung von Wicklungsfehlern in Asynchronmaschinen

The operation of induction machines with fast switching power electronic devices puts additional stress on the stator windings which leads to an increased probability of machine faults. These faults can cause considerable damage and repair costs and — if not detected in an early stage — may end up in a total destruction of the machine. To reduce maintenance and repair costs many methods have been developed and presented in literature for an early detection of machine faults. This paper gives an overview of today’s detection techniques and describes algorithms and results of some methods with special emphasis to inverter fed operation.     

Flip chip on board solder joint reliability analysis using 2-D and3-D FEA models

This study investigates the effects of employing different two-dimensional (2-D) and three-dimensional (3-D) finite element analysis (FEA) models for analyzing the solder joint reliability performance of a flip chip on board assembly. The FEA models investigated were the 2-D-plane strain, 2-D-plane stress, 3-D-1/8th symmetry and 3-D-strip models. The different stress and strain responses generated by the four different FEA models were applied to various solder joint low cycle fatigue life prediction relationships. The investigation shows that the 2-D-plane strain and 2-D-plane stress models gave the highest and lowest solder joint strains, respectively. The 3-D-strip and 3-D-1/8th symmetry model results fall in between the 2-D-plane strain and 2-D-plane stress model results. The 3-D-1/8th symmetry model agrees better with the 2-D-plane strain model, while the 3-D-strip model agrees better with the 2-D-plane stress model results. The results for the fatigue life prediction analyses also show similar trends     

1.5m口径垂直状态短筒长焦距平行光管次镜支撑系统设计

非球面次镜相对于主镜的位置和稳定性对光管的检测和校验性能起着非常重要的作用。从原理上分析了次镜支撑系统,同时建立改进的支撑桁架动力学模型;然后,使用降维处理的方法通过有限元分析对结构进行优化设计;最后,分析温度变化对1.5 m光管性能的影响。结果表明,采用的切向三翼支撑结构,减小了系统的遮拦比而且保证了结构的刚度,改进桁架的比刚度得到改善,从而使整个支撑系统的一阶谐振达到62 Hz;改变局部结构材料降低了温度变化对光学系统的影响,使波像差由/20减小为/30。提出的设计方案精度高,稳定性好,可以满足设计要求。     

Optimization of a hybrid magnetic bearing for a magnetically levitated blood pump via 3-D FEA

In order to improve the performance of a magnetically levitated (maglev) axial flow blood pump, three-dimensional (3-D) finite element analysis (FEA) was used to optimize the design of a hybrid magnetic bearing (HMB). Radial, axial, and current stiffness of multiple design variations of the HMB were calculated using a 3-D FEA package and verified by experimental results. As compared with the original design, the optimized HMB had twice the axial stiffness with the resulting increase of negative radial stiffness partially compensated for by increased current stiffness. Accordingly, the performance of the maglev axial flow blood pump with the optimized HMBs was improved: the maximum pump speed was increased from 6000 rpm to 9000 rpm (50%). The radial, axial and current stiffness of the HMB was found to be linear at nominal operational position from both 3-D FEA and empirical measurements. Stiffness values determined by FEA and empirical measurements agreed well with one another. The magnetic flux density distribution and flux loop of the HMB were also visualized via 3-D FEA which confirms the designers’ initial assumption about the function of this HMB.     

Characterization of AlGaAs microstructure fabricated by AlGaAs/GaAsmicromachining

An AlGaAs/GaAs micromachining technique that is compatible with laser diode fabrication process is described. AlGaAs structural layers and GaAs sacrificial layers are prepared by metal organic vapor phase epitaxy. Reactive dry etching with chlorine is used to fabricate high-aspect structures. Peroxide/ammonium hydroxide solution is used for selective etching of the sacrificial layer. Since the epitaxial layer has low stress, precise undeformed microstructures are obtained. Good compatibility with the LD process makes it possible to integrate microcantilever beams with LD's without degradation of LD characteristics. Microcantilever beams of AlGaAs are characterized by directly measuring stiffness and natural frequencies. A fracture test is also performed on the AlGaAs microcantilever beams. The average fracture stress of AlGaAs is found to be 1 GPa at 1% strain, which shows that the material is strong enough to support the micrometer scale structures     

三自由度柔性镜框结构力学性能分析

为实现小型光学元件的柔性安装和精密调整,设计了一种三自由度柔性安装结构,并对其力学特性进行了理论研究。首先,从柔性镜框的工作原理出发,建立了柔性结构的力学模型,推导了模型的刚度表达式,并利用有限元分析方法进行了验证分析。然后,根据推导的刚度表达式分析了主要结构参数对柔性镜框力学特性的影响,并讨论了减小寄生运动的措施。最后,以通光口径为135 mm的平面反射镜为例,进行了柔性结构的设计计算和参数优化,并对其力学性能进行了仿真分析。验证结果表明:给定的参数范围内,刚度的理论计算和有限元分析结果的相对误差5.5%,表明所推导的刚度计算公式具有足够的精度,验证了理论模型与计算的正确性。同时,柔性镜框力学特性分析结果对柔性镜框的结构设计、力学性能分析和参数优化具有理论指导意义。     

Design, fabrication, and real-time neural network control of athree-degrees-of-freedom nanopositioner

A nanometric precision three-degrees-of-freedom positioner is designed and fabricated. Actuation is based on piezoelectric stacks. Capacitive gap sensors with less than 1.0-nm resolution are used for position feedback. In order to design a proper closed-loop controller, the open-loop characteristics of the nanopositioner (static stiffness, hysteresis, drift, frequency response, and the coupling effects) are experimentally investigated. A cerebellar model articulation controller neural network control algorithm was applied in order to provide real-time learning and better tracking capability compared to a standard proportional-integral-derivative control algorithm     

An accurate intrinsic capacitance modeling for deep submicrometerMOSFET's

This paper presents a new approach to the modeling of MOSFET capacitive characteristics for accurate simulation of deep submicrometer integrated circuits. The C-V characteristics of our new quasistatic intrinsic capacitance model accurately describes the short channel effects of deep submicrometer MOSFET's by accounting for velocity saturation and series resistance effects. The use of charge equations consistent with the short channel I-V characteristics leads to C-V characteristics which preserve all major short channel effects. The C-V calculation, based on nonpinned surface potential approach and drift-diffusion model, shows highly accurate short-channel effects and inherently smooth transitions for all conditions of device operation. The accuracy of the C-V characteristics has been demonstrated by comparison with the Ward-Dutton model and PISCES simulation results     

Nano-Electro-Mechanical Nonvolatile Memory (NEMory) Cell Design and Scaling

The design and scalability of a nano-electro-mechanical memory (NEMory) cell are investigated via analytical modeling and finite element analysis (FEA) simulation. Proportionate scaling of all the cell dimensions provides for improved storage density together with low operating voltages and fast program/erase times. From FEA simulation, a 75-nm-long aluminum cantilever-beam NEMory cell is expected to have sub-1-ns erase and program times for sub-1-V operation. Because there are practical limits to beam and air-gap thickness scaling, it will be difficult to achieve low-voltage operation for very short beams $(L_{rm beam} ≪ hbox{50} hbox{nm})$, unless a beam material with a low Young's modulus is used. Fracture strain imposes a fundamental limit for beam-length scaling. Thus, a high fracture-strain beam material is desirable to extend NEMory scalability.      

基于权值的微机械数模转换器

提出了一种新颖的基于权值的微机械数模转换器 ,它的原理与电路中的权电阻数模转换器类似。通过改变纵向梁的长度获得不同的刚性值作为比例因子 ,从而实现由二进制电压输入到模拟位移输出的转换。为了减小误差 ,对结构作了优化设计 ,同时还考虑并解决了零稳定性问题 ,提高了输出位移的精度。文中给出了有限元方法对由热执行器阵列驱动的数模转换器的输出位移分析的结果 ,并对几种微机械数模转换器的设计进行了比较。     

Thermomechanical effects in metal lines on integrated circuits analysed with a differential polarimetric interferometer

We present a new laser probe, a differential polarimetric interferometer, which is dedicated to the study of common failure mechanisms in microelectronic interconnects. Our investigation is mainly concentrated on the study of thermomechanical stress build-up and electromigration in metal lines. In the differential interferometer, two laser beams, separated by a few microns, are reflected from the surface of the device under test. Reflectance, phase and polarization changes between the two beams can be observed, this allows surface temperature and surface bending measurements together with the observation of stress induced in the silicon dioxide layer by Joule thermal expansion. The laser probe provides unique and useful information about local thermal effects due to electromigration. It also shows, for the first time to our knowledge, induced local stress effects due to the mismatch of thermal expansion coefficients of the metal, Si and SiO₂ involved in running interconnect lines.