Kinematically Stabilized Microbubble Actuator Arrays

In this paper, the concept, fabrication, and characterization of a kinematically stabilized polymeric microbubble actuator (endoskeletal microbubble actuator) for a pneumatic tactile display application are presented. The kinematic stabilization is achieved by the combination of two polymeric layers with complementary functions: a microcorrugated parylene diaphragm layer as a ldquoskeletonrdquo to provide a directional deflection in a desired axial direction while suppressing undesired lateral deflections and an overcoated elastomer diaphragm layer as a ldquoskinrdquo to help the extended membrane recoil to its original shape, ensuring diaphragm stability. Arrays of microcorrugated diaphragms are implemented in a mass producible fashion using inclined rotational UV lithography, micromolding, and pattern transfer techniques. Both the number of corrugations and the corrugation profile of the endoskeletal actuator are determined through numerical analysis, taking into account the constraints of the microfabrication processes utilized. A prototype of a single endoskeletal bubble actuator with a diameter of 2.6 mm has been fabricated and characterized. For comparison purposes, elastomer microcorrugated diaphragm (skin only) actuators and parylene microcorrugated diaphragm (skeleton only) actuators of the same materials and dimensions have also been fabricated and tested. While the skin-only diaphragm actuators demonstrated undesired omnidirectional inflation and the skeleton-only diaphragm actuators have shown unstable and irreversible deformation during extension, the proposed endoskeletal microbubble actuators have shown stable reversible axial extensions with a deflection of approximately 0.9 mm. A 6 6 array of endoskeletal polymer microbubble actuators integrated with a microfluidic manifold has been successfully fabricated, demonstrating its mass manufacturability.     

Observer-based Adaptive Robust Control of Soft Pneumatic Network Actuators

International Journal of Control, Automation and Systems - Fabricated by elastomer materials, soft pneumatic network actuators (PNAs) not only enable versatile applications but also bring...     

Design and fabrication of twisted monolithic dielectric elastomer actuator

This paper presents a novel design of dielectric elastomer actuator (DEA), called single body dielectric elastomer actuator (SDEA), to improve the performance of existing DEAs. The DEA is typically configured with stacking multiple dielectric elastomer film and linearly contracted according to the applied voltage. SDEA is fabricated monolithically without external frame and has the advantages of flexibility and light weight. Thus, it is applicable to various configurations of actuators such as twisting or bending, etc. By exploiting the advantages of SDEA, we propose a new 2-ply design of SDEA. The design is configured with plying couples of monolithically fabricated SDEA. We explain how it can amplify the stroke with its basic principles of operations. In addition, its fabrication method is addressed. Finally, the results of performance evaluations are included with respect to stroke, force, speed, etc.     

A large-displacement 65Pb(Mg1/3Nb2/3)O3–35PbTiO3/Pt bimorph actuator prepared by screen printing

In this paper we present a novel approach to preparing large-displacement 65Pb(Mg_1/3Nb_2/3)O₃–35PbTiO₃/Pt (65/35 PMN–PT/Pt) bimorph actuators. These “substrate-free”, bending-type actuators were prepared by screen-printing the 65/35 PMN–PT and Pt thick-film pastes as the electrodes on alumina substrates. After this screen printing and the subsequent firing the 65/35 PMN–PT/Pt composites were peeled off from the substrates. Displacements of nearly 100 μm at 18 V were achieved for actuators with dimensions of 1.8 cm × 2.5 mm × 50 μm for the 65/35 PMN–PT layer. The normalized displacement (the displacement per unit length) was 40 μm/cm at 18 V. The experimental results together with a computation procedure were used to obtain the material parameters for a finite-element analysis of the 65/35 PMN–PT/Pt bimorph actuators.     

介电弹性体材料致动器的非线性动态行为研究

介电弹性体材料(Dielectric Elastomer,简称DE),是制造柔性智能致动器最有潜力的电活性聚合物(Electroactive polymer,缩写EAP)材料之一,可在电压驱动下产生大幅度的厚度与面积变形,最大面积应变高达1600%.由于DE材料的固有阻尼特性,从而使其变形具有时间依赖性,因此动态变形中,其能量转换、宏观变形等特性也必然受到阻尼的影响.借助热力学自由能理论,考虑DE材料致动器面内动态变形过程中的惯性力和阻尼力,构建平面DE材料致动器的非线性动力学模型.研究了交变电载荷下DE系统的非线性动态特性,包括其幅频曲线、位移响应和相平面图.研究表明,存在阻尼的时候,DE系统的振动会随着时间的增加出现锁频现象,最后变成一种具有恒定振幅的振动.相平面图和Poincaré映射图研究表明,考虑阻尼后DE系统的稳态相平面图是一条闭合的曲线,其Poincaré映射点集是有限的,代表其产生周期性运动.研究成果为DE材料致动器在各种动态驱动器或传感器中的应用提供理论依据.     

Domain decomposition for near-wall turbulent flows

Modeling near-wall high-Reynolds-number turbulent flows is a time-consuming problem. A domain decomposition approach is developed to overcome the problem. The original computational domain is split into a near-wall (inner) subdomain and an outer subdomain. The developed approach is applied to a model 2D equation simulating major peculiarities of near-wall high-Reynolds-number flows. On the base of the Calderon–Ryaben’kii potential theory it is possible to consider the near-wall (inner) problem independently on the outer problem. The influence of the inner problem can exactly be represented by a pseudo-differential equation formulated on the intermediate boundary. In a 1D case, it leads to the wall functions represented by Robin boundary conditions, which can be determined either analytically or numerically. It is important that the wall functions (or boundary conditions) are mesh independent and can be realized in a separate routine. Thus, the original problem can only be solved in the outer domain with some specific nonlocal boundary conditions called nonlocal wall functions. The technique can be extended to 3D problems straightforward.     

智能材料DE 驱动的两态串并联机器人系统的运动特性

本文利用电活性绝缘弹胶体DE 的机电驱动特点,结合两态驱动的概念,设计了一种包含3 个两态驱 动器件的并联机构,将其作为串—并联离散驱动机器人系统的基本单元,并据此构建多个单元串联组成的多级离散 驱动系统．文中首先利用智能DE 材料制作满足这一驱动特性的圆柱形两态驱动器件,先测试其直线驱动特性,即 变形值．其次,将该变形值作为并联机构数学模型的驱动值,分析单级及多级并联机构的运动状态、特性及工作空 间的特点．最后,利用数学工具Mathematica 描绘出上述两态驱动并联机构系统所能达到的工作空间分布点云图, 分析了结构参数与驱动量对系统工作空间的范围、精度的影响．     

Large-Stroke Dielectric Elastomer Actuators With Ion-Implanted Electrodes

In this paper, we present miniaturized polydimethylsiloxane (PDMS)-based diaphragm dielectric elastomer actuators capable of out-of-plane displacement up to 25% of their diameter. This very large percentage displacement is made possible by the use of compliant electrodes fabricated by low-energy gold ion implantation. This technique forms nanometer-scale metallic clusters up to 50 nm below the PDMS surface, creating an electrode that can sustain up to 175% strain while remaining conductive yet having only a minimal impact on the elastomer's mechanical properties. We present a vastly improved chip-scale process flow for fabricating suspended-membrane actuators with low-resistance contacts to implanted electrodes on both sides of the membrane. This process leads to a factor of two increase in breakdown voltage and to $RC$ time constant shorter than mechanical time constants. For circular diaphragm actuator of 1.5–3-mm diameter, voltage-controlled static out-of-plane deflections of up to 25% of their diameter is observed, which is a factor of four higher than our previous published results. Dynamic characterization shows a mechanically limited behavior, with a resonance frequency near 1 kHz and a quality factor of 7.5 in air. Lifetime tests have shown no degradation after more than 4 million cycles at 1.5 kV. Conductive stretchable electrodes photolithographically defined on PDMS were demonstrated as a key step to further miniaturization, enabling large arrays of independent diaphragm actuators on a chip, for instance for tunable microlens arrays or arrays of micropumps and microvalves.$ hfill$[2009-0107]      

A new method for actuating parallel manipulators

This paper presents a new technique of actuating a parallel platform manipulator using shape memory alloy (SMA). This is a type of smart materials that can attain a high strength-to-weight ratio, which makes them ideal for miniature application. The work is mainly to develop a new SMA actuator and then incorporating the actuator in building the parallel manipulator prototype. The SMA used in this study is a commercial NiTi wire. The SMA wire provides an actuating force that produces a large bending and end displacement. A 3-UPU (universal–prismatic–universal) parallel manipulator using linear SMA actuators was developed. The manipulator consists of a fixed platform, a moving platform and three SMA actuators. The manipulator workspace was specified based on the restrictions due to actuator strokes and joint angle limits. System identification techniques were used to model both heating and cooling processes. An ON/OFF control was performed and the results showed closeness in simulation and experimental results. This study showed that shape memory alloy actuated beam can successfully be used to provide linear displacement. The built prototype indicates the feasibility of using SMA actuators in parallel manipulators.     

Control design for suppressing transversal patterns in reaction–(convection)–diffusion systems

The stabilization of planar stationary fronts solutions in a two-dimensional rectangular or cylinder domain, in which a diffusion–convection–reaction process occurs, is studied by reducing the original two-variable PDEs model to an approximate one-dimensional model that describes the behavior of the front line. We consider the control strategy based on sensors placed at the designed front line position and actuators that are spatially-uniform or space dependent. We present a systematic control design that determines the number of required sensors and actuators, their position and their form. The control used linear analysis of a lumped truncated model and concepts of finite and infinite zeros of linear multidimensional systems.     

A water-tight packaging of MEMS electrostatic actuators for biomedical applications

This paper presents a flip-chip based packaging technique for encapsulating MEMS electrostatic actuators for biomedical applications. High-performance electrostatic inchworm actuators are used to demonstrate the packaging technique. A wall structure is put around the actuator surrounding it completely but leaving a small clearance where the actuator shuttle can extend off the edge of the chip. A cap chip is fabricated separately, and flip-chipped onto the actuator. Au–Au thermal bonding technique is used to fix the cap. Finally, rendering the surfaces of the clearance hydrophobic prevents the water ingress when the actuator operates in water.     

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.     

Effect of electrode size and silicon residue on piezoelectric thin-film membrane actuators

Piezoelectric micro-electromechanical systems (MEMS) often adopt a membrane structure to facilitate sensing or actuation. Design parameters, such as membrane size, thickness of the piezoelectric thin film, and electrode types, have been studied to maximize actuation, sensitivity, or coupling coefficient. This paper is to demonstrate numerically and experimentally that the size of silicon residue and its relative size to the top electrode are two critical yet unrecognized parameters in maximizing the actuation displacement of PZT thin-film membrane actuators. To study effects of the silicon residue, we have developed a finite element model using ANSYS. The model consists of five components: a square passive silicon membrane, a silicon substrate, a PZT thin film, a square top electrode, and a silicon residue region. In particular, the silicon residue has a circular inner diameter and a square outer perimeter with a trapezoidal cross section. Predictions of the finite element model lead to several major results. First, when the silicon residue is present, there exists an optimal size of the top electrode maximizing the actuator displacement. Second, the optimal electrode size is roughly 50–60% of the inner diameters of the silicon residue. The displacement of the membrane actuator declines significantly as the electrode overlaps with the silicon residue. Third, the maximal actuator displacement decreases as the inner diameter of the silicon residue decreases. Aside from the finite element analysis, a mechanics-of-material model is also developed to predict the electrode size that maximizes the actuator displacement. To verify the simulation results, eight PZT thin-film membrane actuators with progressive electrode sizes are fabricated. These actuators all have a square membrane of 800 μm × 800 μm with the inner diameter of the silicon residue controlled between 500 and 750 μm. A laser Doppler vibrometer is used to measure the actuator displacements. The experimental measurements confirm that there exists an optimal size of the top electrode maximizing the actuator displacement.     

基于DSP的振动主动控制系统的设计与实现

介绍了阻尼元件与压电陶瓷作动器相结合的主被动混合振动控制系统，讨论了以定点数字信号处理器TMS320F240为核心的数字控制硬件系统的构成以及A／D，D／A等外围电路的设计，并给出了软件设计流程。实验表明，以TMS320F240为核心的数字控制系统不仅能够满足实时控制的要求，而且易于实现各种先进的控制策略。     

A comparison of methods for the control of redundantly-actuated robotic systems

Mechanical hands, legged vehicles and cooperating manipulators are robotic systems containing closed kinematic chains which are typically driven by more actuators than required. As a result, the force distribution existing in these systems cannot be determined simply from the governing rigid-body statics or dynamics equations since these equations are underdetermined. Techniques have been proposed to overcome this obstacle — the most common being to formulate an optimization problem whose solution will be a force distribution which is optimal in a prescribed sense. A second approach which has been suggested is one in which the elasticity of the constituent bodies is considered in order to render the force-distribution problem determinate, in a manner analogous to the techniques typically used in structural mechanics to analyze hyperstatic structures. A third approach would be to deactivate certain actuators in order to reduce the number of unknowns so that the problem becomes determinate. In the present paper, these methods are compared and the first is shown to yield the best results.     

Short-Period Communication and the Role of Zero-Order Holding in Networked Control Systems

We discuss controller design for a networked control system (NCS) in which a stochastic linear time invariant (LTI) plant communicates with a controller over a shared medium. The medium supports a limited number of simultaneous connections between the controller and the plant's sensors and actuators, possibly subject to transmission delays. We restrict communication to periodic medium access sequences which preserve the structural properties of the plant, thus decoupling the selection of the communication from that of the controller. Using the plant's controllability/observability indices as a guide for allocating access, we show that the period of the sequences in question can be shorter than previously established. In addition, we explore the use of sequences designed for a simple NCS model, in which sensors and actuators are “ignored” by the controller when they are not actively communicating, in a more complex, but practical, setting that includes zero-order holding. We include a numerical experiment that illustrates our results in the context of LQG control.      

Identification of linear dynamic systems operating in a networked environment

This paper studies a networked system identification problem, which aims at identifying mathematical models required in networked control/estimation/filtering systems. Specifically, we consider the off-line identification of open-loop stable linear time-invariant processes working in a networked environment. In the networked environment, how the actuators (D/A conversion) operate plays a key role in the complexity of the related identification problems. In particular, it is reasonable to consider the configuration of event-driven actuators subject to random network-induced delays and packet dropouts; as a result, the networked identification problem is formulated as the one to identify continuous-time linear time-invariant models, based on the general non-uniformly non-synchronized sampled data. A modified version of the simplified refined instrumental variable method is proposed to solve this problem, and is validated in a networked identification experiment based on the Matlab/Simulink simulator TrueTime.     

A New Approach for the Dynamic Analysis of Parallel Manipulators

A new approach for the dynamic analysis of parallel manipulators is presented in this paper. This approach is based on the principle of virtual work. The approach is firstly illustrated using a simple example, namely, a planar four-bar linkage. Then, the dynamic analysis of a spatial six-degree-of-freedom parallel manipulator with prismatic actuators (Gough–Stewart platform) is performed. Finally, a numerical example is given in order to illustrate the results. The approach proposed here can be applied to any type of planar and spatial parallel mechanism and leads to faster computational algorithms than the classical Newton–Euler approach when applied to these mechanisms.     

Average power control and positioning of polysilicon thermal actuators

This paper reports on characterizing and modeling the behavior of micromachined polysilicon thermal actuators when driven by DC or pulsed drive signals. Thermal actuators can be controlled and positioned using a pulsed input with a period much less than the thermal time constant of the device as demonstrated by data collected in air and vacuum. Both pulse width and pulse amplitude modulation were successfully employed to position lateral actuators, lateral actuator arrays, and piston micro-mirrors. A SPICE model for polysilicon thermal actuators was developed using relationships between resistance, deflection, and average power. This model incorporates the polysilicon thermal actuator's electrical load, transient response, and deflection characteristics necessary for predicting actuator performance and developing microsystems. The SPICE model exhibits very close agreement with the measured performance of the polysilicon thermal actuators.     

Fault-tolerant actuators and drives—Structures, fault detection principles and applications

As fault detection and fault diagnosis methods are more and more finding their way into modern industrial mechatronic products, it is now time to take the next step. Based on the research efforts for fault detection and diagnosis, a status report has been prepared for research on fault management, i.e. automatic reactions of the system to continue operation after the detection of faults. These reactions may employ hardware redundancy (i.e. switching from a faulty actuator to another, intact one) or analytical redundancy (i.e. switching from a faulty sensor to a “model sensor” or “soft sensor”).A total fault-tolerance concept must encompass all components of a system, i.e. the actuators and drives, the process itself, the sensors as well as the controller and communication. In many cases, a degradation of functions has to be accepted after a fault has appeared. Concentrating on some widespread actuation principles, the paper will focus on electric drives and hydraulic actuators.First, a review is given on fault-tolerance principles and general structural considerations, e.g. hot-standby and cold-standby, focusing on the scheme of an overall fault-tolerant control system. Then, fault statistics for existing actuators and drives will be presented. These fault statistics give hints on the parts of the actuators which are most susceptible to faults. Different designs of fault-tolerant actuators and drives, which have been realized as laboratory prototypes or even on an industrial scale, shall be presented and evaluated with respect to their capabilities of withstanding faults. Finally, an outlook for fault-tolerant mechatronic systems will be given.