Integrated static and dynamic modeling of an ionic polymer–metal composite actuator

Ionic polymer–metal composites have been widely used as actuators for robotic systems. In this article, we investigate and verify the characteristics of ionic polymer–metal composite actuators experimentally and theoretically. Two analytical models are utilized to analyze the performance of ionic polymer–metal composites: a linear irreversible electrodynamical model and a dynamic model. We find that the first model accurately predicts the static characteristics of the ionic polymer–metal composite according to the Onsager equations, while the second model is able to reveal the back relaxation characteristics of the ionic polymer–metal composite. We combine the static and dynamic models of the ionic polymer–metal composite and derive the transfer function for the ionic polymer–metal composite’s mechanical response to an electrical signal. A driving signal with a smooth slope and a low frequency is beneficial for the power efficiency

Modeling and Optimal Control of Curvatures in IPMC's

There has been a growing number of research activities in the area of using smart materials in day to day lives because of their ability to serve both as sensors and actuators. Ionic Polymer Metal Composites (IPMCs) are one of such materials which have been extensively studied in the past few decades to not only understand its working principles but to also model and control their curvature. The problem of building an electromechanical model in order to explain the functioning of IPMCs under favorable and unfavorable conditions is still unsolved. This work proposes a control oriented electromechanical model for induced bending curvature in the IPMC material based on the empirical data received on Nafion based IPMC specimen. This model is further utilized to formulate a control oriented dynamic model from which an Optimal Control System was suggested for the IPMC actuator and supported by experimental results on the tip displacement

Control-Oriented Nonlinear Modeling of Polyvinyl Chloride (Pvc) Gel Actuators

Polyvinyl chloride (PVC) gel-based actuators are a new class of soft, electroactive polymer actuators with several attractive properties, including low cost, large compliance, large strain output, high-stress output, fast response, and stability against thermal influence. While PVC gel actuators are quickly gaining attention, they remain largely unexplored despite their great potential in a long list of applications compared with many other smart material actuators. In particular, little work has been reported on modeling nonlinear dynamics of PVC actuators. In this work a nonlinear, control-oriented Hammerstein model, with a polynomial nonlinearity preceding a transfer function, is proposed to capture the amplitude-dependent frequency responses of PVC gel actuators. A systematic procedure for identifying the model parameters is developed. The efficacy of the modeling approach is demonstrated with experimental voltage-displacement data collected from a PVC gel actuator prototype, where the model is able to predict the input amplitude-dependent dynamic response

Ioonsete elektromehaaniliselt aktiivsete polümeeride deformatsioonist sõltuv elektroodi impedants

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Elektromehaaniliselt aktiivsed materjalid on polümeeridel põhinevad mitmekihilised komposiitmaterjalid, mis muudavad oma välist kuju, kui neid elektriliselt stimuleerida; tihti nimetatakse neid ka tehislihasteks. Taolistest materjalidest valmistatud täiturid pakkuvad huvi nii mikrolaborseadmetes kui ka loodust matkivas robootikas, sest võimaldavad luua keerukaid ülipisikesi ajameid. Võrreldes tavapäraste elektrimootoritega võimaldavad EAP-d (elektromehaaniliselt aktiivsed polümeerid) helitut liigutust ning neid saab lõigata konkreetse rakenduse jaoks sobivasse suurusesse. EAP-d jagunevad kahte põhiklassi: elektron- ja ioon-EAP. Doktoritöös käsitletakse kahte erinevat ioon-EAP materjali, kus mehaaniline koste on tingitud ioonide ümberpaigutumisest kolmekihilises komposiitmaterjalis. Kuna EAP-de elektromehaanilised omadused sõltuvad lisaks sisendpinge amplituudile ja sagedusele ka tugevasti ümbritseva keskkonna parameetritest (nt niiskus ja temperatuur), siis on nendest materjalidest loodud täiturite juhtimiseks tarvilik kasutada tagasisidet. Täiendav tagasisideallikas võib oma omaduste tõttu aga vähendada EAP-de rakendusvõimalusi ning seetõttu on eesmärgiks luua n-ö isetundlik EAP ajam, mis funktsioneerib samaaegselt nii täituri kui ka liigutusandurina. Doktoritööd esitatakse uuritud materjalide elektroodi impedantsi ja deformatsiooni vaheline seos ning kirjeldatakse vastav elektriline mudel. Eraldamaks andursignaali täituri sisendpingest pakutakse välja elektroodikihi piires täituri ja anduri elektriline eraldamine. Loobudes ainult elektroodimaterjalist säilitab polümeerkarkass täituri ja anduri mehaanilise ühendatuse – seega taolises süsteemis järgib sensor täituri kuju, kuigi need on elektriliselt lahti sidestatud. Elektroodimaterjali valikuliseks eemaldamiseks kasutatakse mitmeid erinevaid meetodeid (freesimine, laserablatsioon jne) ning ühtlasi uuritakse nende kasutusmugavust ja protsessi mõju kogu komposiitmaterjalile.Electromechanically active materials are polymer-based composites exhibiting mechanical deformation under electrical stimulus, i.e. they can be implemented as soft actuators in variety of devices. In comparison to conventional electromechanical actuators, their key characteristics include easy customisation, noiseless operation, straightforward mechanical design, sophisticated motion patterns, etc. Ionic EAPs (electromechanically active polymers) are one of two primary classes of electroactive materials, where actuation is caused mostly by the displacement of ions inside polymer matrix. Mechanical response of ionic EAPs is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore a major challenge lies in achieving controlled actuation of these materials. Due to their size and added complexity, external feedback devices inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators—capable for simultaneous actuation and sensing—are desired. In this thesis, sensing based on deformation-dependent electrochemical impedance is demonstrated and modelled for two types of trilayer ionic EAPs—ionic polymer-metal composite and carbon-polymer composite. Separating sensing signal from the input signal of the actuator is achieved by patterning the electrode layers of an IEAP material in a way that different but mechanically coupled sections for actuation and sensing are created. A variety of concepts for pattering the electrode layers (machining, laser ablation, masking, etc.) are implemented and their applicability is discussed

IPMC materjali hp-FEM mudel

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Ioonjuhtivaid polümeer-metall komposiitmaterjale (edaspidi lühendatud IPMC ehk ionic polymer-metal composite) on uuritud juba vähemalt kaks aastakümmet nende huvipakkuvate omaduste tõttu. Võimalikeks kasutusaladeks on vaiksed aktuaatorid või sensorid. IPMC eelised teiste elektroaktiivsete polümeeride ees on töötamine madalal pingel (1...5V), suur paindeulatus, ja toimimine veekeskkonnas. Kuigi põhiliselt on uuritud materjalide omadusi aktuaatoritena, on hiljuti materjalide sensor-omadused rohkem tähelepanu saanud. Et materjali toimimisest aru saada ning seda kirjeldada erinevate rakenduste tarbeks, on vajalik füüsikal baseeruvat mudelit. Sellest lähtuvalt on välja töötatud Poisson-Nernst-Planck-Navier võrranditel baseeruva IPMC mudel. See baseerub füüsikalistel printsiipidest, ehk et saab kasutada võimalikult palju mõõdetavaid suurusi ääretingimustena (nagu materjali paindumine, rakendatud pinge jne). Lisaks on oluline, et meetod millel mudel baseerub, oleks efektiivne ning võimaldaks arvutusi väikese või vähemalt teadaoleva maksimaalse arvutusveaga. Käesoleva töö keskendub peamiselt just arvutusmeetodil ja annab ülevaate uudsest hp-FEM (finite element method) ehk hp lõplike elementide meetodist ja sellel baseeruvast IPMC mudelist. Kõigepealt on täielikult tuletatud võrrandid ja nende integraalne esitus Newtoni meetodi jaoks. Seejärel antakse lühike ülevaade hp-FEM meetodist adaptiivse väljapõhise võrguga ning kogu süsteemi Jakobiaani tuletus hp-FEM tarkvara Hermes jaoks. On näidatud kuidas automaatne adaptiivne hp-FEM võimaldab probleemi suuruse hoida väiksena (süsteemi vabadusastmeid ja kasutatud mälu silmas pidades). Kõige pealt on lahendatud Poisson-Nernst-Plancki võrrandisüsteem ja on käsitletud erinevaid adaptiivusalgoritme. Üks huvitav tulemus on, et adaptiivsed algoritmid võimaldavad lahendada probleemi tingimustel, kus Debye pikkus jääb nanomeetri suurusjärku – seda süsteemis mille mõõtmed on millimeetri skaalas. Nendest tulemustest lähtuvalt esitatakse lahendus terve Poisson-Nernst-Planck-Navier võrrandite süsteemile IPMC paindumise arvutustes. Taaskord on lõplikud võrrandid koos tuletuskäiguga esitatud. Lisaks on analüüsitud suur hulk simulatsiooni tulemusi arvutusprobleemi suurust ja kulutatud arvutusaega silmas pidades ja sellest lähtuvalt leitud parim adaptiivuse algoritm seda liiki probleemide jaoks. On ka näidatud kuidas meetod võimaldab arvutusdomeeni geomeetriat arvesse võtta – domeeni pikkuse ja laiuse suhtest tulenevad ääreefektid on automaatselt arvutustes käsitletud. Kokkuvõtteks, käesolevas töös on detailselt kirjeldatud kuidas kasutades uudne hp-FEM meetod koos adaptiivsete algoritmide ja väljapõhise võrguga võimaldab Nernst-Planck-Poisson-Navier probleemi lahendada efektiivselt, samal ajal hoides lahenduse arvutusvea etteseatud piirides.Ionic polymer-metal composites (IPMC) have been studied during the past two decades for their potential to serve as noiseless mechanoelectrical and electromechanical transducers. The advantages of IPMC over other electroactive polymer actuators are low voltage bending, high strains (>1%), and an ability to work in wet environments. The main focus has been on the electromechanical transduction property – the material’s ability to exhibit large bending deformation in response to a low (typically 1...5 V) applied voltage. However, lately research on the mechanoelectrical transduction properties of the material has gained more attention. In order to describe both deformation in response to applied voltage (electromechanical transduction) and induced voltage in response to applied deformation (mechanoelectrical transduction) properties of IPMC, an advanced physics based model of the material is necessary. Ongoing research has been focused on creating such model where real measurable quantities can be imposed as boundary conditions in order to reduce the number of unknown parameters required for calculations. In this dissertation, a physics based model that is based on novel hp-FEM (finite element method) is proposed. From the fundamental aspect, previously proposed and validated physics based model consisting of a system of Poisson-Nernst-Planck-Navier’s equations is described in detail and used in IPMC deformation calculations. From the mathematical aspect, a novel hp-FEM method was researched to model the equations efficiently. The main focus of this disseration is on the mathematical aspect. Full derivation of the equations with an in-depth study of the benefits of using higher order FEM with automatic adaptivity is presented. The explicit weak form of the Poisson-Nernst-Planck system for Newton’s method is presented. Thereafter, a brief overview of the adaptive multi-mesh hp-FEM is introduced and the residual vector and Jacobian matrix of the system is derived and implemented using hp-FEM library Hermes. It is shown how such problem benefits from using individual meshes with mutually independent adaptivity mechanisms. To begin with, a model consisting of only the Poisson-Nernst-Planck system is solved using different adaptivity algorithms. For instance, it is demonstrated that the problem with set of constants that results Debye’s length in the nanometer scale can be successfully solved. What makes it even more remarkable is the fact that the calculation domain size is in the millimeter scale. Based on those results, the complete Poisson-Nernst-Planck-Navier’s system of equations is studied for IPMC electromechanical transduction calculations. Again, the entire mathematical derivation including weak forms, the residual vector and Jacobian matrix are presented. Thereafter, a number of simulations are analyzed in terms of problem size and consumed CPU time. The best automatic adaptivity mode for such problem is determined. It is also shown how hp-FEM helps to keep the problem geometrically scalable. Additionally, it is demonstrated how employing a PID controller based time step adaptivity helps to reduce the total calculation time. Overall, by using hp-FEM with adaptive multi-mesh configuration the Nernst-Planck-Poisson-Navier’s problem size in IPMC deformation calculations is reduced significantly while a prescribed precision of the solution is maintained

Theoretical and Experimental Investigation on the Multiple Shape Memory Ionic Polymer-Metal Composite Actuator

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as biomimetic robotics, advanced medical devices and human affinity applications. Here, we report a Multiple Shape Memory Ionic Polymer-Metal Composite (MSM-IPMC) actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. Theoretical and experimental investigation on the MSM-IPMC actuator were performed. To date, the effect of the surface electrode properties change on the actuating of IPMC have not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC are presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. This study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators. In our study, we introduce a soft MSM-IPMC actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of our knowledge, this MSM-IPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability. The shape memory properties of MSM-IPMC were theoretically and experimentally studied. We presented the multiple shape memory properties of Nafion cylinder. A physics based model of the IPMC was proposed. The free energy density theory was utilized to analyze the shape properties of the IPMC. To verify the model, IPMC samples with the Nafion as the base membrane was prepared and experiments were conducted. Simulation of the model was performed and the results were compared with the experimental data. It was successfully demonstrated that the theoretical model can well explain the shape memory properties of the IPMC. The results showed that the reheat glass transition temperature of the IPMC is lower than the programming temperature. It was also found that the back-relaxation of the IPMC decreases as the programming temperature increases. This study may be useful for the better understanding of the shape memory effect of IPMC. Furthermore, we theoretically modeled and experimentally investigated the multiple shape memory effect of MSM-IPMC. We proposed a new physical principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSM-IPMC was developed. Based on our previous study on the electro-mechanical actuation effect of IPMC, we proposed a comprehensive physics-based model of MSM-IPMC which couples the actuation effect and the multiple shape memory effect. It is the first model that includes these two actuation effects and multiple shape memory effect. Simulation of the model was performed using finite element method. To verify the model, an MSM-IPMC sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the experimental results, both results have a good agreement. The multiple shape memory effect and reversibility of three different polymers, namely the Nafion, Aquivion and GEFC with three different ions, which are the hydrogen, lithium and sodium, were also quantitatively tested respectively. Based on the results, it is shown that all the polymers have good multiple shape memory effect and reversibility. The ions have an influence on the broad glass transition range of the polymers. The current study is beneficial for the better understanding of the underlying physics of MSM-IPMC. A biomimetic underwater robot, that was actuated by the MSM-IPMC, was developed. The design of the robot was inspired by the pectoral fish swimming modes, such as stingrays, knifefish and cuttefish. The robot was actuated by two soft fins which were consisted of multiple IPMC samples. Through actuating the IPMCs separately, traveling wave was generated on the soft fin. Experiments were performed for the test of the robot. The deformation and the blocking force of the IPMCs on the fin were measured. A force measurement system in a flow channel was implemented. The thrust force of the robot under different frequencies and traveling wave numbers were recorded. Multiple shape memory effect was performed on the robot. The robot was capable of changing its swimming modes from Gymnotiform to Mobuliform, which has high deformability, maneuverability and agility

Finite element modeling of dielectric elastomer actuators for space applications

A special actuator device with passive sensing capability based on dielectric elastomer was studied and specialized to be used in space applications. The work illustrates the research project modeling procedure adopted to simulate the mechanical behavior of this material based on a finite element theory approach. The Mooney-Rivlin’s hyperelastic and Maxwell’s electrostatic models provide the theoretical basis to describe its electro-mechanic behavior. The validation of the procedure is performed through a numerical-experimental correlation between the response of a prototype of actuator developed by the Risø Danish research center and the 3D finite element model simulations. An investigation concerning a possible application in the space environment of dielectric elastomer actuators (DEA) is also presented