Modeling and Experimental Validation of a Compliant Underactuated Parallel Kinematic Manipulator

© 1996-2012 IEEE. Parallel kinematic manipulators (PKMs) are increasingly used in a wide range of industrial applications due to the characteristics of high accuracy and compact structure. However, most of the existing PKMs are structured with heavy actuators and high stiffness. In this respect, this article proses a simple, yet effective, parallel manipulator that distinguishes itself through the following basis. First, underactuation: it employs only a single motor and a driving cable to actuate its three legs. Second, novel foot location: it uses a smart shape memory alloy clutch-based driving system (SCBDS), which catches/releases the driving cable, thus, making possible the robot underactuation. Finally, adjustable compliance: its double compliant joints on each limb with a stiffness-adjustable section, which renders a safe human-robotic interaction. To support and predict the performance of this underactuated compliant manipulator, a novel kinetostatic model was developed by considering the generalized internal loads (i.e., force and moment) in three compliant limbs and the external loads on the upper platform. Finally, based on the physical prototype, a set of experiments were conducted to validate the model proposed in this article. It was found that the proposed kinetostatic model can be validated with the average deviations of 1.8% in position and 2.8% in orientation, respectively. Furthermore, the workspace of the system (e.g., discrete and continuous workspace) was studied when different actuating strategies were employed, thus, emphasizing the advantages and the limitations of this novel system

Simultaneous use of shape memory alloys and permanent magnets in multistable smart structures for morphing aircraft applications

This Thesis considers the simultaneous use of shape memory alloys and permanent magnets for achieving multistable smart structures aiming towards morphing applications. Motivation for this approach lies in the poor energetic efficiency of shape memory alloys, which can void system-level benefits provided by morphing technologies. Multistability can therefore be adopted to prevent continuous operation of shape memory alloy actuators. Objectives of the study involve the combination of shape memory alloys and permanent magnets in new geometrical arrangements to achieve multistable behavior; the development of a numerical modeling procedure that is able to simulate the multi-physics nature of the studied systems; and the proposal of a geometric arrangement for morphing applications that is based on a repeating pattern of unit cells which incorporate the combined use of shape memory alloy wires and permanent magnets for multistability. The proposed modeling strategy considers a geometrically nonlinear beam finite element; a thermo-mechanical constitutive behavior for shapememoryalloys;theinteractionofcuboidalpermanentmagnetswitharbitraryorienta- tions; and node-to-element contact. Experiments are performed with three distinct systems, including a proof-of-concept beam, a three cell morphing beam metastructure, and a morphing airfoil prototype with six unit cells. Results show that the combination of shape memory alloys and permanent magnets indeed allows for multistable behavior. Furthermore, the dis- tributedactuationcapabilitiesofthe morphingmetastructureallowforsmoothandlocalized geometrical shape changes.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorCNPq - Conselho Nacional de Desenvolvimento Científico e TecnológicoTese (Doutorado)Esta Tese considera o uso simultâneo de ligas com memória de forma e ímãs permanentes para a obtenção de estruturas inteligentes multiestáveis, com vistas a sua aplicação em aeronaves de geometria variável. A motivação para tal abordagem reside na baixa eficiência energética associada às ligas com memória de forma, a qual pode eliminar benefícios oriundos de tecnologias relacionadas a geometria variável. Multiestabilidade pode, desta forma, ser adotada para prevenir operação contínua de atuadores baseados em ligas com memória de forma. Objetivos do estudo envolvem a combinação de ligas com memória de forma e ímãs permanentes em novos arranjos geométricos para a obtenção de comportamento multiestável; o desenvolvimento de um procedimento de modelagem numérica que pode simular a natureza multifísica dos sistemas estudados; e a proposição de um arranjo geométrico para aplicações que envolvem geometria variável, o qual é baseado num padrão repetitivo de células unitárias que incorporam o uso combinado de ligas com memória de forma e ímãs permanentes para mul- tiestabilidade. A estratégia de modelagem proposta considera um elemento finito de viga com não-linearidades geométricas; um modelo constitutivo termomecânico para ligas com memória de forma; a interação entre ímãs permanentes cúbicos com orientação arbitrária; e contato entre elemento-e-nó no contexto de elementos finitos. Experimentos são realizados com três sistemas distintos, incluindo uma viga para prova de conceito, uma metaestrutura do tipo viga com geometria variável composta por três células unitárias, e um protótipo de aerofólio com geometria variável composto por seis células unitárias. Resultados mostram que a combinação de ligas com memória de forma e ímãs permanentes permite a obtenção de comportamento multiestável. Além disso, a característica de atuação distribuída das metaestruturas com geometria variável permite alterações de forma suaves e localizadas

Bistable Actuation Based on Antagonistic Buckling SMA Beams

Novel miniature-scale bistable actuators are developed, which consist of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to have opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snap-through motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography, and systems integration. The stationary force–displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact to a low-temperature heat source in the range of 130–190 °C. The bistable actuation is characterized by a large stroke up to 3.65 mm corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature. The bistable actuation at low-temperature differences provides a route for waste heat recovery

Low power consumption mini rotary actuator with SMA wires

Shape memory alloys (SMAs) are smart materials widely used as actuators for their high power to weight ratio despite their well-known low energy efficiency and limited mechanical bandwidth. For robotic applications, SMAs exhibit limitations due to high power consumption and limited stroke, varying from 4% to 7% of the total length. Hysteresis, during the contraction and extension cycle, requires a complex control algorithm. On the positive side, the small size and low weight are eminently suited for the design of mini actuators for robotic platforms. This paper describes the design and construction of a light weight and low power consuming mini rotary actuator with on-board contact-less position and force sensors. The design is specifically intended to reduce (i) energy consumption, (ii) dimensions of the sensory system, and (iii) provide a simple control without any need for SMA characterisation. The torque produced is controlled by on-board force sensors. Experiments were performed to investigate the energy consumption and performance (step and sinusoidal angle profiles with a frequency varying from 0.5 to 10 Hz and maximal amplitude of 15?). We describe a transient capacitor effect related to the SMA wires during the sinusoidal profile when the active SMA wire is powered and the antagonist one switched-off, resulting in a transient current time varying from 300 to 400 ms

Ioonsete elektroaktiivsete täiturite elektromehaaniline modelleerimine ja juhtimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneIoonsed elektroaktiivsed polümeerid e. tehislihased on polümeermaterjalid, mille oluline iseärasus on võime muuta elektrienergiat mehhaaniliseks energiaks. Elektroaktiivsetest polümeeridest valmistatud pehmetel täituritel on mitmed huvipakkuvad omadused, näiteks suur deformatsioon madala rakendatud pinge korral, märkimisväärne tekitatud jõu ja massi suhe ning võime töötada nii vesikeskkonnas kui õhus. Niisuguste täiturite kasutamine on paljutõotav eriti just miniatuursetes elusloodusest inspireeritud robootikarakendustes. Näiteks võib tuua aktiivsed mikro-manipulatsioonisüsteemid või isepainduvad pehmed kateetrid, mis on iseäranis nõutud meditsiini-tehnoloogias. Käesoleva väitekirja uurimissfääriks on sellistest materjalidest valmistatud täiturmehhanismide modelleerimine, valmistamine ja juhtimine, päädides sisuliselt ühes tükis valmistatud mitme vabadusastmega paralleelmanipulaatorite väljatöötamisega. Kasutades kompleksset füüsikalistel, elektrokeemilistel ning mehaanilistel alusteadmistel põhinevat mudelit kirjeldatakse ja ennustatakse sellist tüüpi täiturmehhanismide elektrilise sisendi ja mehhaanilise väljundi vahelisi seoseid. Mudel kirjeldab ioonide transpordi dünaamikat elektriväljas, kombineerides Nernst-Plancki ja Poissoni võrrandeid. Mitmekihilise polümeermaterjali mehhaaniline käitumine on seotud laengu- ja massitasakaalu poolt põhjustatud eri kihtide erineva ruumilise paisumisega ja kahanemisega. Kõike seda kokku võttes ning rakendades numbrilist modelleerimist lõplike elementide meetodil saadakse kvantitatiivsed tulemused, mis suudavad prognoosida täiturmehhanismi käitumist ja võimaldavad projekteerida, simuleerida ja optimeerida ka neil täituritel põhinevaid keerulisemaid mehhanisme. Koostatud mudeli valideerimiseks modelleeriti ja valmistati kaks tööpõhimõtteliselt sarnast, kuid erinevatel elektroaktiivsetel polümeermaterjalidel põhinevat ning eri metoodikatel valmistatud mitmest täiturist koosnevat mitme vabadusastmega mikromanipulaatorit. Väitekirjas demonstreeritakse, et koostatud mudel on suure täpsusega võimeline ennustama nii iga individuaalse täituri kui ka mõlema manipulaatori käitumist. Demonstreerimaks piisksadestusprintimismeetodil valmistatud manipulaatori efektiivsust, kirjeldatakse kahte erinevat kontrollrakendust. Esmalt näidatakse tagasisidestamata kontrollitavat seadet, kus pööratakse nelja täituri abil peeglit, suunates laserikiirt X-Y tasapinnas ettemääratud punktidele. Teiseks näidisrakenduseks on tagasisidestatud kontrollmetoodikaga juhitav mikroskoobi preparaadiliigutaja, mille abil saab preparaati nii tõsta-langetada kui ka pöörata. Manipulaatorite valmistamise käigus leiti, et piisksadestusprintimise meetodi täpsus, jõudlus ja skaleeritavus võimaldavad suure tootlikkusega valmistada identseid keerulisi mitmeosalisi manipulaatoreid. See tulemus näitab ilmekalt uue tehnoloogia eeliseid traditsiooniliste valmistamisviiside ees.Ionic electroactive polymers (IEAPs) actuators are kind of smart composite materials that have the ability to convert electrical energy into mechanical energy. The actuators fabricated using IEAP materials will benefit from attractive features such as high compliance, lightweight, large strain, low voltage, biocompatibility, high force to weight ratio, and ability to operate in an aqueous environment as well as in open air. The future of soft robotic actuation system with IEAP actuators is very promising especially in the microdomain for cutting edge applications such as micromanipulation systems, medical devices with higher dexterity, soft catheters with built-in actuation, bio-inspired robotics with better-mimicking properties and active compliant micromechanisms. This dissertation has introduced an effective modelling framework representing the complex electro-chemo-mechanical dynamics that can predict the electromechanical transduction in this kind of actuators. The model describes the ion transport dynamics under electric field by combining the Nernst-Planck and Poisson’s equation and the mechanical response is associated with the volumetric swelling caused by resulting charge and mass balance. The framework of this modelling method to predict the behavior of the actuator enabled to design, simulate and optimize compliant mechanism using IEAP actuators. As a result, a novel parallel manipulator with three degrees of freedom was modelled and fabricated with two different types of electrode materials and is characterized and compared with the simulation model. It is shown that the developed model was able to predict the behavior of the manipulator with a good agreement ensuring the high fidelity of the modelling framework. In the process of the fabrication, it is found that the manipulator fabricated through additive manufacturing method allows to fabricate multipart and intricate patterns with high throughput production capability and also opens the opportunity to print a matrix array of identical actuators over a wide size scale along with improved performance. Finally, to showcase the competence of the printed manipulator two different control application was demonstrated. At first, an open loop four-way optical switch showing the capability of optically triggering four switches in the X-Y plane in an automated sequence is shown followed by closed-loop micromanipulation of an active microscope stage using model predictive control system architecture is shown. The application of the manipulator can be extended to other potential applications such as a zoom lens, a microscope stage, laser steering, autofocusing systems, and micromirror. Overall this dissertation results in modelling, fabrication, and control of ionic electroactive polymer actuators leading to the development of a low cost, monolithic, flat, multi DOF parallel manipulator for micromanipulation application.https://www.ester.ee/record=b524351

A 3D-Printed Omni-Purpose Soft Gripper

Numerous soft grippers have been developed based on smart materials, pneumatic soft actuators, and underactuated compliant structures. In this article, we present a three-dimensional (3-D) printed omni-purpose soft gripper (OPSOG) that can grasp a wide variety of objects with different weights, sizes, shapes, textures, and stiffnesses. The soft gripper has a unique design that incorporates soft fingers and a suction cup that operate either separately or simultaneously to grasp specific objects. A bundle of 3-D-printable linear soft vacuum actuators (LSOVA) that generate a linear stroke upon activation is employed to drive the tendon-driven soft fingers. The support, fingers, suction cup, and actuation unit of the gripper were printed using a low-cost and open-source fused deposition modeling 3-D printer. A single LSOVA has a blocked force of 30.35 N, a rise time of 94 ms, a bandwidth of 2.81 Hz, and a lifetime of 26 120 cycles. The blocked force and stroke of the actuators are accurately predicted using finite element and analytical models. The OPSOG can grasp at least 20 different objects. The gripper has a maximum payload-to-weight ratio of 7.06, a grip force of 31.31 N, and a tip blocked force of 3.72 N

Design of a composite morphing wing

Morphing aircraft components can increase the possibility of optimising the performance of an aircraft at various flight conditions. A morphing aircraft wing can change the wing shape to modify the lift and drag distribution on the wing surface, allowing the lift-to-drag ratio to be tailored to the desired performance. A camber morphing and a trailing edge morphing wing changes the aerodynamic lift by altering the camber and by deflecting the wing trailing edge, potentially reducing the aerodynamic drag by eliminating the gaps; which exist between the main wing and the control surfaces of a conventional wing. Among the technology used to achieve camber morphing and trailing edge morphing, were mechanical and smart actuations, such as piezoelectrics and shape memory alloys (SMAs). Compliant structures, cellular structures, shape memory polymers, and multi-stable structures were exploited to improve the flexibility of the aerofoil sections or wings. SMA wires were one of the smart actuators which had been extensively utilised to morph various aerofoils/wings, mainly due to the high actuation force and compatibility, which reduce the volume and weight of the actuators and the complexity of moving mechanical components. In this research, a user defined material model (UMAT) was developed within the explicit LS-DYNA FE code, for NiTi shape memory alloy (SMA) wires, and used for actuation of the composite morphing wing. The Tanaka SMA constitutive model was implemented in MATLAB and FORTRAN codes for the SMA-actuation of various structures. The UMAT was used to simulate actuations of various complex morphing structures, including several aluminium and composite aerofoils with corrugated sections, and a pre-curved corrugated plate. Actuations of the two aluminium aerofoils, with corrugated sections in the lower surface and the middle cantilever section, by a 0.5mm-diameter SMA wire with a maximum recoverable strain or a pre-strain of 1.6%, resulted in trailing edge (TE) deflections of 7.8 mm and 65.9 mm, respectively. Actuation of the carbon fibre (CF) composite aerofoil, with the corrugated section as a middle cantilever section, and with 8 layers of CF in ±45° directions, produced a TE deflection of 52.0 mm. To demonstrate the SMA-actuated morphing concept, a composite 3D-printing technology was explored to manufacture a carbon fibre (CF) composite structure, consisted of a flat vertical front plate, a corrugated section, and a rear trailing edge (TE) section. Due to the nature of 3D-printing, two layers of CF were 3D-printed along the circumference of the corrugation and the TE section, and the minimum thickness of the structure was 3 mm. Experimentally, actuation of the CF composite corrugated structure by a NiTi SMA wire with a diameter of 0.2 mm and a pre-strain of 4.77%, and with a diameter of 0.5 mm and a pre-strain of 1.68%, aligned in the chordwise direction, resulted in 1.1 mm and 6.0 mm TE deflections, respectively. Cyclic tests (10 and 30 cycles) of the actuation of the CF composite corrugated structure showed the TE deflection converged after few cycles. A 1.25m-span composite morphing wing was finally designed and manufactured, consisted of a CF composite D-nose spar which resisted the main aerodynamic loading, and rear sections which were made of rigid and flexible foams. CF composite spar flanges, spar web, front and rear ribs, were 3D-printed, and were assembled with a CF composite skin which was autoclave-manufactured, to form the CF composite D-nose spar. Sections of rigid and flexible foams were CNC-machined and were attached to the front CF composite D-nose spar, 3D-printed long rear ribs, trailing edge sections and the morphed corrugated structure, to form a complete composite morphing wing.Open Acces

Development of novel micropneumatic grippers for biomanipulation

Microbjects with dimensions from 1 μm to 1 mm have been developed recently for different aspects and purposes. Consequently, the development of handling and manipulation tools to fulfil this need is urgently required. Micromanipulation techniques could be generally categorized according to their actuation method such as electrostatic, thermal, shape memory alloy, piezoelectric, magnetic, and fluidic actuation. Each of which has its advantage and disadvantage. The fluidic actuation has been overlooked in MEMS despite its satisfactory output in the micro-scale. This thesis presents different families of pneumatically driven, low cost, compatible with biological environment, scalable, and controllable microgrippers. The first family demonstrated a polymeric microgripper that was laser cut and actuated pneumatically. It was tested to manipulate microparticles down to 200 microns. To overcome the assembly challenges that arise in this family, the second family was proposed. The second family was a micro-cantilever based microgripper, where the device was assembled layer by layer to form a 3D structure. The microcantilevers were fabricated using photo-etching technique, and demonstrated the applicability to manipulate micro-particles down to 200 microns using automated pick-and-place procedure. In addition, this family was used as a tactile-detector as well. Due to the angular gripping scheme followed by the above mentioned families, gripping smaller objects becomes a challenging task. A third family following a parallel gripping scheme was proposed allowing the gripping of smaller objects to be visible. It comprises a compliant structure microgripper actuated pneumatically and fabricated using picosecond laser technology, and demonstrated the capability of gripping microobject as small as 100 μm microbeads. An FEA modelling was employed to validate the experimental and analytical results, and excellent matching was achieved

A Review of SMA-Based Actuators for Bidirectional Rotational Motion: Application to Origami Robots

Shape memory alloys (SMAs) are a group of metallic alloys capable of sustaining large inelastic strains that can be recovered when subjected to a specific process between two distinct phases. Regarding their unique and outstanding properties, SMAs have drawn considerable attention in various domains and recently became appropriate candidates for origami robots, that require bi-directional rotational motion actuation with limited operational space. However, longitudinal motion-driven actuators are frequently investigated and commonly mentioned, whereas studies in SMA-based rotational motion actuation is still very limited in the literature. This work provides a review of different research efforts related to SMA-based actuators for bi-directional rotational motion (BRM), thus provides a survey and classification of current approaches and design tools that can be applied to origami robots in order to achieve shape-changing. For this purpose, analytical tools for description of actuator behaviour are presented, followed by characterisation and performance prediction. Afterward, the actuators’ design methods, sensing, and controlling strategies are discussed. Finally, open challenges are discussed