Experimental investigation on the piezo-composite actuator with piezoelectric single-crystal layer

Studies on muscle mimicking actuators have increased in the last two decades due to the possibility of various applications for compact lightweight actuators including small unmanned aircrafts, missile, and biomimetic robots. Piezoelectric materials have been used in a variety of applications ranging from shape control of structure and active vibration control of structure to noise suppression due to compact size and good frequency response. Conventional polycrystal piezoelectric ceramic materials, however, have limited actuating strains and displacement, hindering their use in actuators for small aerospace vehicles. In this study, the design and fabrication method of an actuator with a piezoelectric single-crystal layer were investigated to increase the actuation strain and displacement. From a comparison of the performance of the LIPCA-C2 and LIPCA-S prototypes, it was found that the new LIPCA-S2, which has much higher coefficient of the unimorph actuator, can generate an actuating displacement more than twice that of LIPCA-C2.     

2D Arrays of Soft Actuators Performing Out-of-Plane Local Inflation for Shape Displays

Elementary actuators performing branching or surface swelling are the primary units in the actuator integration system that is leveraged in works requiring a high versatility and complex motion. However, those primary actuator units often lack scalability or compatibility at assembly into a compact form due to the complexity of the structure and the actuation interference between adjacent units. Herein, it is shown that the phase-change actuator in a simple bilayer structure of a top active layer and a bottom constraint layer achieves 1D surface swelling, such that the closely packed 2D array system of this actuator is easily constructed. Upon resistive heating, the active layer inflates based on the phase change of microliquid droplets embedded in an elastomer body. The inflation along the lateral direction of the actuator is suppressed by controlling the thickness ratio between the active and the constraint layers. The actuation of individual units in the array system is performed independently using a switching device with a microcontroller for the parallel application of resistive heating. The application of 2D shape morphing of the actuator arrays in beam steering and shape displays is investigated.     

Thin-Film Piezoelectric Actuators of Nonuniform Thickness and Nonhomogeneous Material Properties for Modulating Actuation Stress

The effects of the thickness variation and the material property variation of thin-film piezoelectric actuators on the actuation shear stress when the actuators are attached to an elastic plate are studied. A system of 2D equations for the flexure and shear of an elastic plate with symmetric piezoelectric actuators on the plate surfaces is derived. The equations are reduced to the case of elementary flexure without shear as a special case. The effects of the actuator thickness variation and material property variation on the actuation stress are examined using the equations obtained. It is shown that the distribution of the actuation stress depends on the thickness and material property variations of the actuators, and that actuators with varying thickness or varying material properties can be used to make modal actuators for producing a particular deformation or exciting a particular vibration mode.     

Preliminary study of an adaptive wing with shape memory alloy torsion actuators

This paper presents a preliminary design study aimed to verify the feasibility of an adaptive wing for a small unmanned aircraft (UAV), which is entirely actuated by shape memory alloy devices (SMA). The capability of the wing to bear the aerodynamic loads, the power required by the actuators and their force and torque during flight are assessed by finite element simulations. The wing consists of a sandwich box sub-structure with laminated faces, flexible ribs and a flexible skin. The adaptation capability to the changing flight conditions is obtained via airfoil shape change and local shape adjustments. Counter rotating, concentric torsion SMA tubes are employed for wing camber control, while levers powered by SMA wires are employed for local shape control. The external and the internal tubes control, respectively, the downward and the upward motions. They are connected to the flexible ribs through an electro-mechanical clutch and a positioning piezoelectric motor. Actuation occurs heating a tube at a time and making free the other by the clutch. With deformation limited to 4%, to allow a complete shape recovery by SMA, the wing appears capable to smoothly deform, with small stresses. A mean rotation of 21.7° of the flexible ribs and a rotation of 40° at the tip can be obtained, which are equivalent to a rotation of 30° of an aileron or flap of a conventional wing. A variable camber variation can be obtained at cruise speed, with a variation at least of 10° from the tip to the root. Also a local shape variation can be obtained, corresponding to a 4.5% increase of the thickness of the airfoil at 55% of the chord, while at 40% of the chord the thickness is reduced by 3.9%. The torque applied by the actuator tubes, which is up to 200 N m, and the peak power of 1223 W required for actuation appear compatible for an UAV.     

Shape memory alloy based motor

Design and characterization of a new shape memory alloy wire based Poly Phase Motor has been reported in this paper. The motor can be used either in stepping mode or in servo mode of operation. Each phase of the motor consists of an SMA wire with a spring in series. The principle of operation of the poly phase motor is presented. The motor resembles a stepper motor in its functioning though the actuation principles are different and hence has been characterized similar to a stepper motor. The motor can be actuated in either direction with different phase sequencing methods, which are presented in this work. The motor is modelled and simulated and the results of simulations and experiments are presented. The experimental model of the motor is of dimension 150 mm square, 20 mm thick and uses SMA wire of 0·4 mm diameter and 125 mm of length in each phase.     

A novel magnetic suspension cum linear actuator system forsatellite cryo coolers

Stirling cycle cryogenic coolers have been widely used for device cooling in satellites. Various types of magnetic bearings and linear actuators find application in such systems. The most widely used configurations have two-axis-radially-active suspension stations placed at either end of a reciprocating shaft in the compression and expansion sections. Separate or integral linear motors are provided in each section for axial shaft movement. It may be noted that such configurations are rather complicated and less reliable because of the presence of numerous electro-mechanical components, sensors and electronic servo channels. In this paper, a simple and reliable scheme is suggested which axially stabilizes and linearly perturbs the piston so that the need of a separate motor for axial actuation can be totally dispensed with. The piston is radially supported by passive repulsive bearings. In the axial direction, a servo actuator `balances' the piston and also actuates it bi-directionally. Implementation of this `bearing cum motor theme', reduces the number of electromechanical and electronic components required to operate the system and hence minimizes the chances of system failure. Apart from this, the system's power consumption is reduced and efficiency is improved as electrical heating losses caused by quiescent-operating currents are removed and electromagnetic losses on the moving parts are minimized. The necessary system parameters have been derived using finite element analysis techniques. Finally, the proposed design is validated by computer-aided system simulation     

直升机结构响应主动控制作动器优化设计研究

采用子结构综合法建立考虑作动器动特性与其相互影响的直升机机身／多作动器耦合系统频域数学模型，研究了直升机结构响应主动控制中采用作动器位置序号进行编码的遗传算法对多作动器位置进行优选，以及与电磁式惯性型作动器参数优化的综合优化问题，进行了结构响应主动控制试验研究，验证了多作动器减振的有效性和所提出的作动器位置优选方法的正确性。     

Development of Advanced Actuators Using Shape Memory Alloys and Electrorheological Fluids

Actuators are used to perform a variety of functions in almost every type of electromechanical system, ``smart' device, and instrument. Increasingly, in many applications, actuators need to achieve reduced size, mass, power consumption, and cost. Examples of industries that demand novel, miniature, and powerful actuators are medicine, biotechnology, information technology, space, manufacturing, entertainment, military, and micro- and nanotechnology. Conventional actuators such as DC motors, pneumatic motors, and hydraulic motors are energy-wasting, large-volume, and heavy-mass actuation systems. Novel design methodologies, materials, and paradigms are currently needed in order to develop such lightweight and powerful actuation systems. In this paper we present the development of two novel, compact, and powerful smart material-based advanced actuators. The first motor is a shape memory alloy (SMA) bundle actuator, and the second is a hybrid concept based on electrorheological fluids (ERFs) and electromagnetic components. A detailed review of the state of the art in SMA- and ERF-based actuators is also presented.     

双重驱动机器人柔性手臂的研究

本文研究了机器人柔性手臂的实验系统,针对柔性臂的振动问题和定位精度问题,提出了在单个关节柔性臂上实现宏／微结合双重驱动的基本思想。用伺服电机实现柔性臂的宏动,用压电陶瓷驱动器实现柔性臂的微动,通过有效地控制伺服电机和压电陶瓷驱动器抑制柔性臂的振动,并完成柔性臂的精密定位。     

智能写字机器人机构与递阶控制系统设计

设计了6自由度转动关节机器人机构.基于坐标变换,建立运动学模型.三级递阶控制的组织级采用PC机.利用视觉获取字符图像,通过网格化得到字符点阵.通过计算脊信息,得到笔画.利用笔画中心点的聚类分析确定书写顺序.协调级采用MSP430单片机实现通讯和多舵机协调运动.执行级基于舵机实现关节的位置闭环控制.在自主开发的样机上,开展了写字实验,验证了设计的有效性.     

新型纳米分辨率位移定位平移台的研制

为克服已有压电驱动器存在的结构及控制系统复杂、定位行程小等缺陷,利用压电陶瓷的逆压电效应设计并制作了一种新型的压电纳米步进驱动器,建立光栅测试系统对这种压电驱动器的动态性能进行了测试.将压电纳米步进驱动器与电磁伺服马达耦合,设计新颖驱动结构,利用微机通过步进运动控制卡统一控制,实现大范围一维纳米分辨率位移定位.系统样机解决了所研制压电纳米步进驱动器双向运动、实用定位等问题.位移定位分辨率为50 nm,定位行程为100mm,纳米分辨率定位最大速度为0.6 mm/s.     

Finite element modelling and vibration control study of active plate with debonded piezoelectric actuators

A finite element model for a piezoelectric plate with edge debonded actuators is presented. This model is employed to investigate the effect of edge debonding on actuation authority, natural frequencies and vibration control performance. The regions of the plate with the piezoelectric patches are modelled such that each layer undergoes rotation due to shear deformation independently. The necessary constraints for continuity of displacements at the interfaces of the layers are imposed. The plate with edge debonded actuators is idealized by dividing it into debonded regions and healthy regions. A finite element procedure for imposing the constraints regarding continuity of displacements at the interfaces of the adjacent regions is developed and is implemented using MATLAB. Experiments are conducted for finding the actuation authority and natural frequencies of the plate with debonded actuators. It has been found that the developed model has predicted the mechanics of actuator debonding properly. The investigations have revealed the fact that the edge debonding of actuators will result in considerable degradation in actuation authority and vibration control performance.     

电磁辅助压电致动器设计开发与性能测试研究

传统的压电致动器,受限于压电致动的小行程,通常只能测量较小的范围。研发了一种电磁辅助压电致动器,同时具备电磁式致动器长行程与压电式致动器高分辨率的特点,该致动器包含可动件、导引槽、挠性件、电磁铁、压电元件以及控制电路。首先调整挠性可调预压装置并设定电磁铁电流,使得电磁致动力处于最大静摩擦力与动摩擦力之间;再利用压电组件所产生的微震动,控制可动件与导引槽之间的接触情况在静摩擦与动摩擦之间切换,从而完成长行程(10mm)且高分辨率(1.5μm)的往复运动。实验结果表明该致动器具备出色的定位能力。     

Carbon Nanotube and Graphene‐based Bioinspired Electrochemical Actuators

Bio‐inspired actuation materials, also called artificial muscles, have attracted great attention in recent decades for their potential application in intelligent robots, biomedical devices, and micro‐electro‐mechanical systems. Among them, ionic polymer metal composite (IPMC) actuator has been intensively studied for their impressive high‐strain under low voltage stimulation and air‐working capability. A typical IPMC actuator is composed of one ion‐conductive electrolyte membrane laminated by two electron‐conductive metal electrode membranes, which can bend back and forth due to the electrode expansion and contraction induced by ion motion under alternating applied voltage. As its actuation performance is mainly dominated by electrochemical and electromechanical process of the electrode layer, the electrode material and structure become to be more crucial to higher performance. The recent discovery of one dimensional carbon nanotube and two dimensional graphene has created a revolution in functional nanomaterials. Their unique structures render them intriguing electrical and mechanical properties, which makes them ideal flexible electrode materials for IPMC actuators in stead of conventional metal electrodes. Currently although the detailed effect caused by those carbon nanomaterial electrodes is not very clear, the presented outstanding actuation performance gives us tremendous motivation to meet the challenge in understanding the mechanism and thus developing more advanced actuator materials. Therefore, in this review IPMC actuators prepared with different kinds of carbon nanomaterials based electrodes or electrolytes are addressed. Key parameters which may generate important influence on actuation process are discussed in order to shed light on possible future research and application of the novel carbon nanomateials based bio‐inspired electrochemical actuators.     

Design and performance analysis of a novel parallel servo press with redundant actuation

The large capacity servo press is traditionally realized by means of simultaneous actuation of multiple motors. But there exist the over-constraint problem and interference among actuators, which increases the control difficulty and product cost. This paper proposed a novel parallel servo press with redundant actuation, which can avoid the over-constraint and actuation interference. The kinematic and dynamic model of the present servo press are established and thus the kinematic and dynamic performances are obtained under three working modes, i.e. the same and opposite direction modes and non-synchronous mode. The prototype of the active mechanism with the redundant actuators has been manufactured. The kinematic experiments are carried out by using API laser tracking system and the theoretical calculation results agree with the measured data very well, which validates the theoretical model and the present press mechanism.     

Raptor wing morphing with flight speed

In gliding flight, birds morph their wings and tails to control their flight trajectory and speed. Using high-resolution videogrammetry, we reconstructed accurate and detailed three-dimensional geometries of gliding flights for three raptors (barn owl, Tyto alba; tawny owl, Strix aluco, and goshawk, Accipiter gentilis). Wing shapes were highly repeatable and shoulder actuation was a key component of reconfiguring the overall planform and controlling angle of attack. The three birds shared common spanwise patterns of wing twist, an inverse relationship between twist and peak camber, and held their wings depressed below their shoulder in an anhedral configuration. With increased speed, all three birds tended to reduce camber throughout the wing, and their wings bent in a saddle-shape pattern. A number of morphing features suggest that the coordinated movements of the wing and tail support efficient flight, and that the tail may act to modulate wing camber through indirect aeroelastic control.     

High Performance and Multifunction Moisture-Driven Yin–Yang-Interface Actuators Derived from Polyacrylamide Hydrogel

High actuation performance of a moisture actuator highly depends on the presence of a large property difference between the two layers, which may cause interfacial delamination. Improving interfacial adhesion strength while increasing the difference between the layers is a challenge. In this study, a moisture-driven tri-layer actuator with a Yin–Yang-interface (YYI) design is investigated in which a moisture-responsive polyacrylamide (PAM) hydrogel layer (Yang) is combined with a moisture-inert polyethylene terephthalate (PET) layer (Yin) using an interfacial poly(2-ethylhexyl acrylate) (PEA) adhesion layer. Fast and large reversible bending, oscillation, and programmable morphing motions in response to moisture are realized. The response time, bending curvature, and response speed normalized by thickness are among the best compared with those of previously reported moisture-driven actuators. The excellent actuation performance of the actuator has potential multifunctional applications in moisture-controlled switches, mechanical grippers, and crawling and jumping motions. The Yin–Yang-interface design proposed in this work provides a new design strategy for high-performance intelligent materials and devices.     

Design,analysis and testing of a smart fin

The paper presents a design concept for a control fin usually used in airborne vehicles such as UAV’s, Micro UAV’s and missiles. The research presents the design of a smart fin with integral piezoelectric actuators embedded in the airfoil skin. Electric field applied to the actuators would twist the airfoil leading to a change of the angle of attack. The study presents, analyze and demonstrates various lamination and actuation methods including a parametric performance investigation by finite elements models and closed form analytical model. The design and the theoretical results are verified by a manufactured smart wing demonstrator subjected to series of static and dynamic lab tests.     

Piezoelectrically driven morphing structures based on bistable unsymmetric laminates

Due to their anisotropy multilayered fibre-reinforced polymers tend to generate residual stresses, which are primarily influenced by thermal and hygroscopic processes. In the case of an unsymmetric reinforcement architecture, those residual stresses may induce large out-of-plane deformations in thin-walled laminates. Here, specific stacking sequences support the development of so called bistable laminates which are characterised by two distinct deformation states which can be converted by applying forces or bending moments. In combination with appropriate actuator systems, like piezoceramic transducers, such bistable composites can purposefully be used to design compliant mechanisms and novel morphing structures that stand out for a permanent change of shape only by a small energy supply. For the structural analysis and the computation of the necessary actuation voltage to initiate the snap-through of bistable composite structures with piezoceramic actuators, non-linear semi-analytical and numerical simulation methods have been elaborated. First active bistable prototypes have been manufactured and successfully tested.     

导电聚合物的电化学机械性能及其致动器

论述了导电聚合物优异的电化学机械性能,系统综述了新近研制的各种导电聚合物致动器的组装及特性.指出有些导电聚合物致动器具有传感和执行双重功能等性能特点,在机器人机械手、机器昆虫、人工假肢、分子发动机,细胞诊断等方面具有广阔而深远的应用前景.