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.     

Light‐Mediated Manufacture and Manipulation of Actuators

Recent years have seen a considerable growth of research interests in developing novel technologies that permit designable manufacture and controllable manipulation of actuators. Among various fabrication and driving strategies, light has emerged as an enabler to reach this end, contributing to the development of actuators. Several accessible light‐mediated manufacturing technologies, such as ultraviolet (UV) lithography and direct laser writing (DLW), are summarized. A series of light‐driven strategies including optical trapping, photochemical actuation, and photothermal actuation for controllable manipulation of actuators is introduced. Current challenges and future perspectives of this field are discussed. To generalize, light holds great promise for the development of actuators.     

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.     

Actuation of polypyrrole nanowires

Nanoscale actuators are essential components of the NEMS (nanoelectromechanical systems) and nanorobots of the future, and are expected to become a major area of development within nanotechnology. This paper demonstrates for the first time that individual polypyrrole (PPy) nanowires with diameters under 100 nm exhibit actuation behavior, and therefore can potentially be used for constructing nanoscale actuators. PPy is an electroactive polymer which can change volume on the basis of its oxidation state. PPy-based macroscale and microscale actuators have been demonstrated, but their nanoscale counterparts have not been realized until now. The research reported here answers positively the fundamental question of whether PPy wires still exhibit useful volume changes at the nanoscale. Nanowires with a 50?nm diameter and a length of approximately 6?μm, are fabricated by chemical polymerization using track-etched polycarbonate membranes as templates. Their actuation response as a function of oxidation state is investigated by electrochemical AFM (atomic force microscopy). An estimate of the minimum actuation force is made, based on the displacement of the AFM cantilever.     

Modeling of smart composites on account of actuation,thermal conductivity and hygroscopic absorption

The asymptotic homogenization models for smart composite materials are derived and effective elastic, actuation, thermal expansion and hygroscopic expansion coefficients for smart structures are obtained. The actuation coefficients characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a coordinated fashion. Examples of such actuators employed with smart composite material systems are derived from piezoelectric, magnetostrictive, and some other materials. The pertinent mathematical framework is that of asymptotic homogenization. The objective is to transform a general anisotropic composite material with a regular array of reinforcements and/or actuators into a simpler one that is characterized by some effective coefficients; it is implicit, of course, that the physical problem based on these homogenized coefficients should give predictions differing as little as possible from those of the original problem. The effectiveness of the derived models is illustrated by means of two- and three-dimensional examples.     

Net shape formed spiral and helical piezoelectric actuators

Piezoelectric actuators tend to be made from relatively simple shapes such as blocks, plates and beams. These shapes allow for a range of displacements from key actuation modes but, in order to expand this range, complex structures are required that cannot be made via conventional means. This study presents a novel manufacturing method for such structures using a green ceramic tape lamination process followed by plastic deformation. Furthermore, a helix and a spiral are introduced as examples of initially curved structures. Their actuated behaviour is described by simple but effective models in terms of the standard linear piezoelectric coefficients and is compared to experiments. It is shown that displacements are produced by actuation mechanisms not previously reported in the literature.     

A scalable model for trilayer conjugated polymer actuators and its experimental validation

Conjugated polymers are promising actuation materials for bio/micromanipulation systems, biomimetic robots, and biomedical devices. For these applications, it is highly desirable to have predictive models available for feasibility study and design optimization. In this paper a scalable model is presented for trilayer conjugated polymer actuators based on J. Madden's diffusive-elastic-metal model. The proposed model characterizes actuation behaviors in terms of intrinsic material parameters and actuator dimensions. Experiments are conducted on polypyrrole actuators of different dimensions to validate the developed scaling laws for quasi-static force and displacement output, electrical admittance, and dynamic displacement response.     

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.     

Experimental study on control fins of a small flying vehicle using piezo-composite actuators

A camber morphing control fin design and an all-moving control fin design using piezo-composite unimorph actuators are presented in this paper. The control fin of a small flying object is usually actuated using a servo motor system with an electromagnetic motor. Much research has been conducted to solve the structural complexity of servo actuation systems to convert the rotation of a servo motor to a linear actuation motion. To simplify this structural complexity, several types of smart actuators have been developed, such as bimorph or unimorph actuators with piezoelectric material layers and shape memory alloy actuators. In this study, a camber morphing type control fin and an all-moving type control fin actuated using piezo-composite actuators are designed to evaluate their ability to simplify the structural complexity of the gear transmission and electromagnetic servo motor system or hydraulic actuator system. Within the skin of the control fin, a piezo-composite actuator is mounted and the other end inserted in a slot of the control fin. As the piezo-composite actuator is excited by an electric field, the pitch angle of the control fin is changed. Experimental testing for the pitch rotation angle of a control fin in a 450 V electric field showed the deflection angle of the camber morphing control fin was 1.4° and the rotational angle of the all-moving control fin was 5.4°, which is obtained from the rotation angle magnification linkage structural system.     

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.     

Shape Memory Alloy (SMA)‐Based Microscale Actuators with 60% Deformation Rate and 1.6 kHz Actuation Speed

Shape memory alloys (SMAs) are widely utilized as an actuation source in microscale devices, since they have a simple actuation mechanism and high‐power density. However, they have limitations in terms of strain range and actuation speed. High‐speed microscale SMA actuators are developed having diamond‐shaped frame structures with a diameter of 25 µm. These structures allow for a large elongation range compared with bulk SMA materials, with the aid of spring‐like behavior under tensile deformation. These actuators are validated in terms of their applicability as an artificial muscle in microscale by investigating their behavior under mechanical deformation and changes in thermal conditions. The shape memory effect is triggered by delivering thermal energy with a laser. The fast heating and cooling phenomenon caused by the scale effect allows high‐speed actuation up to 1600 Hz. It is expected that the proposed actuators will contribute to the development of soft robots and biomedical devices.     

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.     

基于光控压电混合驱动悬臂梁独立模态控制

本文提出利用镧改性锆钛酸铅（PLZT）的光电效应,将PLZT作为电动势源来驱动压电作动器,从而实现光控板壳结构的振动控制。基于光控压电等效电学模型建立了光控压电混合驱动的数学模型,并进行了实验验证。为了实现光控悬臂梁的独立模态控制,针对悬臂梁结构,设计了正交模态传感器/作动器表面电极形状函数。提出PLZT与压电作动器正/反接控制的激励策略,并结合速度反馈定光强控制的控制算法,利用Newmark-β法对不同光照强度下悬臂梁的动态响应进行了数值仿真分析。分析结果证明了本文所设计的模态传感器/作动器及针对光控压电混合驱动提出的控制策略的正确性。     

Mechanical design of walking machines

The performance of existing actuators, such as electric motors, is very limited, be it power-weight ratio or energy efficiency. In this paper, we discuss the method to design a practical walking machine under this severe constraint with focus on two concepts, the gravitationally decoupled actuation (GDA) and the coupled drive. The GDA decouples the driving system against the gravitational field to suppress generation of negative power and improve energy efficiency. On the other hand, the coupled drive couples the driving system to distribute the output power equally among actuators and maximize the utilization of installed actuator power. First, we depict the GDA and coupled drive in detail. Then, we present actual machines, TITAN-III and VIII, quadruped walking machines designed on the basis of the GDA, and NINJA-I and II, quadruped wall walking machines designed on the basis of the coupled drive. Finally, we discuss walking machines that travel on three-dimensional terrain (3D terrain), which includes the ground, walls and ceiling. Then, we demonstrate with computer simulation that we can selectively leverage GDA and coupled drive by walking posture control.     

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     

Concept and model of a piezoelectric structural fiber for multifunctional composites

The use of piezoceramic materials for structural sensing and actuation is a fairly well developed practice that has found use in a wide variety of applications. However, just as advanced composites offer numerous benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered when using monolithic piezoceramic devices. Several new piezoelectric fiber composites have been developed, however almost all studies have implemented these devices such that they are surface-bonded patches used for sensing or actuation. This paper will introduce a novel active piezoelectric structural fiber that can be laid up in a composite material to perform sensing and actuation, in addition to providing load bearing functionality. The sensing and actuation aspects of this multifunctional material will allow composites to be designed with numerous embedded functions including, structural health monitoring, power generation, vibration sensing and control, damping, and shape control through anisotropic actuation. A one-dimensional micromechanics model of the piezoelectric fiber will be developed to characterize the feasibility of constructing structural composite lamina with high piezoelectric coupling. The theoretical model will be validated through finite element (FE) modeling in ABAQUS. The results will show that the electromechanical coupling of a fiber-reinforced polymer composite incorporating the active structural fiber (ASF) could be more than 70% of the active constituent.     

25th Anniversary Article: A Soft Future: From Robots and Sensor Skin to Energy Harvesters

Scientists are exploring elastic and soft forms of robots, electronic skin and energy harvesters, dreaming to mimic nature and to enable novel applications in wide fields, from consumer and mobile appliances to biomedical systems, sports and healthcare. All conceivable classes of materials with a wide range of mechanical, physical and chemical properties are employed, from liquids and gels to organic and inorganic solids. Functionalities never seen before are achieved. In this review we discuss soft robots which allow actuation with several degrees of freedom. We show that different actuation mechanisms lead to similar actuators, capable of complex and smooth movements in 3d space. We introduce latest research examples in sensor skin development and discuss ultraflexible electronic circuits, light emitting diodes and solar cells as examples. Additional functionalities of sensor skin, such as visual sensors inspired by animal eyes, camouflage, self‐cleaning and healing and on‐skin energy storage and generation are briefly reviewed. Finally, we discuss a paradigm change in energy harvesting, away from hard energy generators to soft ones based on dielectric elastomers. Such systems are shown to work with high energy of conversion, making them potentially interesting for harvesting mechanical energy from human gait, winds and ocean waves.     

Shape morphing of aircraft wing: Status and challenges

In this paper, the recent activity in conceptual design, prototype fabrication, and evaluation of shape morphing wing is concisely classified. Of special interest are concepts which include smart materials such as shape memory alloys (SMA), piezoelectric actuators (PZT), and shape memory polymers (SMP). We will also provide several concepts that have been developed and evaluated by the authors. Our work indicates that antagonistic SMA-actuated flexural structures form a possible enabling technology for wing morphing of small aircraft. The use of SMA-actuated structures in shape morphing wing designs reduces the weight penalty due to the actuation systems, because such SMA-actuated structures carry aerodynamic loads.     

Smart piezoelectric Fibre composites

Abstract

Piezoelectric materials are capable of actuation and sensing and have found uses in applications including ultrasonic transducers, hydrophones, micropositioning devices, accelerometers, and structural actuators. A composite configuration for structural actuation having significant advantages over conventional piezoelectric actuators has been conceived, and the recent development of piezoelectric ceramic fibres < 100 μ m in diameter has enabled this concept to be realised. It is envisaged that these composites will find uses in contour control, non-destructive testing, vibration suppression, and noise control. The possibility of computer control using closed loop systems has led to these composites emerging as potential 'smart' materials and structures. Since their conception, less than a decade ago, significant advances have been made in many areas concerned with composite performance, such as fibre and matrix technology and configuration optimisation. These advances are charted, the fibre, matrix, and electrode technologies are reviewed, and the manufacture, modelling, and applications of these new piezoelectric composites, known as active fibre composites, are discussed.