A Genetic Algorithm Approach for Model Reference Adaptive Control of Ionic Polymer Metal Composites

Electroactive polymers undergo physical deformation to external voltage stimuli. These electrically activated polymers possess extraordinary features making them capable as lightweight sensors and actuators in manifold applications. The characteristics of applied voltage and environmental conditions, especially the moisture content surrounding the polymer, have a combined influence on the dynamical behavior of these polymers. In order to characterize these polymers under varying environmental conditions, this paper discusses the experimental procedure and modeling techniques used to derive a representative model. Ionic polymer metal composite polymers are used for this humidity relative electrodynamical study. Insight on the numerous applications of electroactive polymers as actuators and the built model enabled a controller is designed for a typical tracking problem. The control architecture includes a model reference adaptive scheme along with pole-placement control strategies to achieve the goal of tracking. A genetic algorithm approach is implemented to carryout an optimized control action. Tracking control of ionic polymer metal composites as actuator resembling that of a real-world scenario is simulated and reveals promising results

Control of an IPMC soft actuator using adaptive full-order recursive terminal sliding mode

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection

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

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

Development of a Novel Handheld Device for Active Compensation of Physiological Tremor

In microsurgery, the human hand imposes certain limitations in accurately positioning the tip of a device such as scalpel. Any errors in the motion of the hand make microsurgical procedures difficult and involuntary motions such as hand tremors can make some procedures significantly difficult to perform. This is particularly true in the case of vitreoretinal microsurgery. The most familiar source of involuntary motion is physiological tremor. Real-time compensation of tremor is, therefore, necessary to assist surgeons to precisely position and manipulate the tool-tip to accurately perform a microsurgery. In this thesis, a novel handheld device (AID) is described for compensation of physiological tremor in the hand. MEMS-based accelerometers and gyroscopes have been used for sensing the motion of the hand in six degrees of freedom (DOF). An augmented state complementary Kalman filter is used to calculate 2 DOF orientation. An adaptive filtering algorithm, band-limited Multiple Fourier linear combiner (BMFLC), is used to calculate the tremor component in the hand in real-time. Ionic Polymer Metallic Composites (IPMCs) have been used as actuators for deflecting the tool-tip to compensate for the tremor

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

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

Artificial Muscles

Course material for "Artificial Muscles" e-course