1,274 research outputs found
Compliant polymeric actuators as robot drive units
A co-polymer made from Polyvinyl Alcohol and Polyacrylic Acid (PVA-PAA) has been synthesized to form new robotic actuation systems which use the contractile and variable compliance properties of this material. The stimulation of these fibres is studied (particularly chemical activation using acetone and water), as are the factors which influence the response, especially those relating to its performance as an artificial muscle.Mathematical models and simulations of the dynamics of the polymeric strips have been developed, permitting a thorough analysis of the performance determining parameters. Using these models a control strategy has been designed and implemented, with experimental results being obtained for a gripper powered by a flexor/extensor pair formed using these polymeric actuators.An investigation of a second property of the polymer, its variable compliance is also included. Use of this feature has lead to the design, construction and testing of a multi degree-of-freedom dextrous hand, which despite having only a single actuator, can exercise independent control over each joint
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
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Soft-Material Robotics
There has been a boost of research activities in robotics using soft materials in the past ten years. It is expected that the use and control of soft materials can help realize robotic systems that are safer, cheaper, and more adaptable than the level that the conventional rigid-material robots can achieve. Contrary to a number of existing review and position papers on soft-material robotics, which mostly present case studies and/or discuss trends and challenges, the review focuses on the fundamentals of the research field. First, it gives a definition of softmaterial robotics and introduces its history, which dates back to the late 1970s. Second, it provides characterization of soft-materials, actuators and sensing elements. Third, it presents two general approaches to mathematical modelling of kinematics of soft-material robots; that is, piecewise constant curvature approximation and variable curvature approach, as well as their related statics and dynamics. Fourth, it summarizes control methods that have been used for soft-material robots and other continuum robots in both model-based fashion and model-free fashion. Lastly, applications or potential usage of soft-material robots are described related to wearable robots, medical robots, grasping and manipulation
DEVELOPMENT OF FUNCTIONAL NANOCOMPOSITE MATERIALS TOWARDS BIODEGRADABLE SOFT ROBOTICS AND FLEXIBLE ELECTRONICS
World population is continuously growing, as well as the influence we have on the ecosystem\u2019s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity\u2019s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today\u2019s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices
A Thermodynamically Consistent Electro-Chemo-Hydro-Mechanical Model for Smart Polymers
Smart polymers are stimuli-responsive materials that undergo reversible and large changes of the material properties as a consequence of small environmental variations. Their light weight, biocompatibility, adaptability, mechanical strength and environment-friendly properties make them suitable for a wide range of applications, such as actuators, sensors and energy transducers.
Despite their very interesting properties, there are still many problems which need to be solved. In particular, there is a high demand by the scientific community to develop advanced theoretical models which aim at understanding the complex and unclear phenomena occurring in smart polymers.
In the present thesis, an innovative multiphysics electro-chemo-hydro-mechanical (ECHM) model is formulated within the framework of continuum mechanics. The proposed model assumes the solvent-ion-polymer mixture as a continuum homogenized body and takes into account four different physical fields, namely: (i) the electrical field, (ii) the chemical field related to the ion transport, (iii) the chemical field related to the water/solvent transport, and (iv) the mechanical field within the framework of large deformations. Couplings terms are derived at the constitutive level among the involved physical fields and allow to model a key aspect of smart polymers, i.e. the capability of transducing energy from one form to another.
Reduced versions of the ECHM model are used to investigate, numerically and analytically, three particular problems involving smart polymers, namely: (i) the chemical reactions occurring at the interface between the polymer membrane and the electrodes of electrochemical cells, (ii) the electro-chemo-mechanical state of a single polymeric membrane within a stack of membranes, and (iii) the swelling/shrinking process of constrained and stressed polymer gels.
The performed investigation confirm that the ECHM model and its reduced versions are capable of describing the complex multiphysics behavior of smart polymers. The current research improves the theoretical knowledge concerning the behavior of smart polymers and gives further contributions in literature. Starting from the outcomes of the proposed research, many interesting extensions can be potentially developed in order to address very important topics as, for example, fatigue in polymers.Smarte Polymere sind stimulierbare Materialien, die, verursacht durch die Ănderung ihrer Umgebung, eine reversible und groĂe Ănderung ihrer materiellen Eigenschaften erfahren. Ihr leichtes Gewicht, ihre BiokompatibilitĂ€t, ihr Anpassungsvermögen, ihre mechanische Beanspruchbarkeit und ihre umgebungsfreundlichen Eigenschaften machen sie attraktiv fĂŒr weite Anwendungsbereiche, z. B. als Aktoren, Sensoren oder Energiewandler.
Trotz ihrer exzellenten Eigenschaften gibt es noch viele Probleme, die gelöst werden mĂŒssen. Insbesondere die Nachfrage nach fortgeschrittenen theoretischen Modellen mit dem Ziel die komplexen physikalischen PhĂ€nomene zu beschreiben, die in smarten Polymeren ablaufen, ist sehr hoch.
In der eingereichten Doktorarbeit, wird ein elektro-chemo-hydro-mechanisches (ECHM) Modell basierend auf der Kontinuumsmechanik vorgestellt. In dem dargelegten Modell wird die Mischung aus Lösungsmittel, Ionen und Polymer als homogenisiertes Kontinuum betrachtet, wobei vier verschiedene physikalische Felder berĂŒcksichtigt werden: (i) das elektrische Feld, (ii) das auf den Ionentransport bezogene chemische Feld (iii) das auf den Wasser- bzw. den Lösungsmitteltransport
bezogene chemische Feld und (iv) das mechanische Feld unter der BerĂŒcksichtigung von groĂen Deformationen. Kopplungsterme werden auf konstitutiver Ebene aus den beteiligten physikalischen Feldern abgeleitet. Die elektro-chemo-mechanische Kopplung erlaubt die Modellierung einer der wesentlichen Eigenschaften smarter Polymere, nĂ€mlich die FĂ€higkeit zur Umwandlung der verschiedenen Energieformen.
Drei spezielle Problemstellungen von smarten Polymeren, wurden numerisch und analytisch auf Grundlage reduzierter Varianten des ECHM-Modells untersucht: (i) die auftretenden chemischen Reaktionen an der materiellen GrenzflÀche zwischen Polymermembran und den Elektroden der elektrochemischen Zelle, (ii) das elektro-chemo-mechanische Verhalten einer einzelnen Polymer-membran in einem Membranstapel und (iii) der Quellungs- bzw. Entquellprozess von vorgespannten Polymergelen.
Die durchgefĂŒhrten Untersuchungen bestĂ€tigen die Anwendbarkeit des ECHM-Modells und seinen reduzierten Varianten zur Beschreibung des komplexen physikalischen Verhaltens von smarten Polymeren. Die dargelegte Forschung verbessert das theoretische VerstĂ€ndnis hinsichtlich des Verhaltens von smarten Polymeren und leistet einen Beitrag zum aktuellen Stand der Wissenschaft. Auf den Resultaten der dargelegten Forschung basierend, können viele interessante Erweiterungen gemacht werden, welche sich auf wichtige Themengebiete, wie z. B. die ErmĂŒdung von Polymeren, beziehen
The 2nd International Electronic Conference on Applied Sciences
This book is focused on the works presented at the 2nd International Electronic Conference on Applied Sciences, organized by Applied Sciences from 15 to 31 October 2021 on the MDPI Sciforum platform. Two decades have passed since the start of the 21st century. The development of sciences and technologies is growing ever faster today than in the previous century. The field of science is expanding, and the structure of science is becoming ever richer. Because of this expansion and fine structure growth, researchers may lose themselves in the deep forest of the ever-increasing frontiers and sub-fields being created. This international conference on the Applied Sciences was started to help scientists conduct their own research into the growth of these frontiers by breaking down barriers and connecting the many sub-fields to cut through this vast forest. These functions will allow researchers to see these frontiers and their surrounding (or quite distant) fields and sub-fields, and give them the opportunity to incubate and develop their knowledge even further with the aid of this multi-dimensional network
New trends in 4D printing: A critical review
In a variety of industries, Additive Manufacturing has revolutionized the whole design-fabrication cycle. Traditional 3D printing is typically employed to produce static components, which are not able to fulfill the dynamic structures requirements and relevant applications such as soft grippers, self-assembly systems, and smart actuators. To address this limitation, an innovative technology has emerged and is called â4D printingâ. It processes smart materials by using 3D printing for fabricating smart structures that can be reconfigured by applying different inputs such as heat, humidity, magnetic, electricity, light etc. At present, 4D printing is still a growing technology and it presents numerous challenges regarding materials, design, simulation, fabrication processes, applied strategies and reversibility. In this work a critical review about 4D printing technologies, materials and applications is discussed
NOVEL ELECTROACTIVE SOFT ACTUATORS BASED ON IONIC GEL/GOLD NANOCOMPOSITES PRODUCED BY SUPERSONIC CLUSTER BEAM IMPLANTATION
Ionic electro-active polymers (IEAPs) constitute a promising solution for developing self-regulating, flexible and adaptive mechanical actuators in the area of soft robotics, micromanipulation and rehabilitation. These smart materials have the ability to undergo large bending deformations as a function of a low applied voltage (1 to 5 V), as a result of the ions migration through their inner structure when the network is liquid filled. Among this broad family of materials, ionic-polymer-metal composites (IPMC) based on DuPont\u2019s Nafion\uae have attracted an increasing interest for the production of light weight controllable soft machines due to their easiness to be metalized (e.g. by mean of electroless plating), fast response and capability of working exposed to air. However, the high cost of the material, its relatively low working density (i.e. the maximum mechanical work output per unit volume of active material that drives the actuation) and weak force output, as well as the considerable fatigue effects endured by the surface electrodes upon cycling, is limiting the performance of these IPMC actuators and hindering their implementation in traditional mechatronic and robotic systems. On the other hand, ionic hydrogels, such as poly(acrylic acid) (PAA) and poly-styrene sulfonate (PSS) based polymers, exhibit controllable mechanical properties and porosity and have shown to be excellent candidates to be used as electrically triggered artificial muscles and miniaturized robots operating in aqueous environments. Although the relatively low cost of these materials render them appealing for mass production scale up, the applicability of these polymeric actuators is limited to a liquid environment, which is intrinsically facilitating the solvent evaporation when the hydrogels are exposed to air. Furthermore, because of the difficulty encountered in fabricating stable and anchored metal structures on these polymer surfaces, these smart soft systems operate in a non-contact configuration with respect to the pilot electrodes, therefore increasing the actuators response time up to few tenths of seconds. In order to achieve an efficient electromechanical transduction along with a stable and durable performance for electro-active actuators operating in air, two main interplaying characteristics must be tailored when designing the system. On one hand side, the need of electrodes that are physically interpenetrating with the polymeric basis is of absolute priority, since the intercalation of ions into the electrode layers and the resulting material volumetric change are fundamental for strain generation. On the other hand, the formulation and engineering of new low cost materials able to merge highly elastic properties and efficient ionic transport features is of crucial importance.
The present thesis work deals with the formulation, synthesis and manufacturing of a novel ionic gel/metal nanocomposite (IGMN) that was designed and developed to merge the advantageous properties of both IPMCs and ionic hydrogel actuators and to contextually overcome many of the above mentioned drawbacks characteristic of these two families of polymers. These composites were obtained by mean of Supersonic Cluster Beam Implantation (SCBI). This technique, developed in-house, relies on the use of supersonically accelerated gas-phase metal cluster beams directed onto a polymeric substrate in order to generate thin conductive layers (few tenths to few hundreds of nanometers thick) anchored to the polymer. This scalable approach already proved to be suitable for the manufacturing of elastomer/metal functional nanocomposites, and, as described in this work, it enabled the production of cluster-assembled gold electrodes (100 nm thick) interpenetrating with an engineered ionic gel matrix. This novel approach led to the fabrication of highly conductive metal nanostructures, large surface area for ions storage and providing minimal interfacial stresses between the metal layer and the polymeric basis upon deformation. The key features of this novel system comprise the control on the polymer elasticity, bending actuation in air from 0.1V to 5V, fast response time ( 5 cm), high work density ( >10 J/cm3), minimal electrodes fatigue upon cycling and low manufacturing costs.
A bottom-up approach was firstly adopted to engineer and produce Uv photo-cross-linked ionic co-polymers (iongel) with tailored mechanical properties and provided with inorganic nano-structures embedded in the macromolecular matrix which show excellent long-term performance. The polymer is based on poly(acrylic acid)-co-poly(acrylonitrile) (PAA-co-PAN) co-polymers, which are chemically cross-linked in a hydrogel-like fashion and swollen with suitable imidazolium-based ionic liquid. The materials are produced as 100 um freestanding layers using a one-pot synthesis and a simple molding process. Due to the incommensurably low vapor pressure of the ionic liquid, issues concerning the shrinkage of traditional water swollen gels operating exposed to air could be avoided. An organic cation (tetraethyl ammonium, TEA+) is stably coordinated to the carboxyl groups of the PAA and free to move in the polymer sieve-like structure when a small voltage is applied at the electrodes. PAN was introduced to enhance the elastic properties of whole polymer. In the bulk polymer, halloysite nanoclays (HNC) are physically embedded into the gel in order to both improve the toughness of the gel and to improve the ionic conductivity of the system. In fact, the nanostructures interacts with the imidazolium cation of the ionic liquid through an oxygen reduction reaction, and therefore the latter is able to contribute to the charge transport phenomena induced by the electric field due to the solvent partial dissociation. Furthermore, the porosity of the polymer, tailored by the cross-linker, creates physical channels to favor the mobility of positive ions when an electric field is applied. The contribution of both the positive charged species (TEA+ and cations of ionic liquid) that accumulates at the nanostructured electrode in a double layer capacitance regime generates a differential swelling at the opposite sides of the actuator, which bends towards the anode.
As it will be shown in the next sections, the actuation mechanism of the IGMN could be modeled according to both the material structure and design, as well as to the experimental data on its electrochemical and electro-mechanical properties.Comparing with traditional soft polymers incompatibility with current metallization processes, like electroless plating or surface silver laminated electrodes fabrication, which are not suitable to guarantee long-term actuation of the components, SCBI demonstrated to be a suitable technique for the production of next generation electro-active soft actuators. The IGMN-based actuators showed superior performance, such as large bending displacement, fast response time, long durability in a low voltage regime during the actuation process. The combination of the SCBI fabrication technology with the ionic gel synthesis and fabrication renders the manufacturing of these systems time-saving and costs-effective, and the unique properties of these actuators render them good candidates for potential scale up and for applications in micro-electromechanical systems, microfluidics, soft robotics, and rehabilitation
Ioonsete elektromehaaniliselt aktiivsete polĂŒmeeride deformatsioonist sĂ”ltuv elektroodi impedants
VĂ€itekirja elektrooniline versioon ei sisalda publikatsioone.Elektromehaaniliselt aktiivsed materjalid on polĂŒmeeridel pĂ”hinevad mitmekihilised komposiitmaterjalid, mis muudavad oma vĂ€list kuju, kui neid elektriliselt stimuleerida; tihti nimetatakse neid ka tehislihasteks. Taolistest materjalidest valmistatud tĂ€iturid pakkuvad huvi nii mikrolaborseadmetes kui ka loodust matkivas robootikas, sest vĂ”imaldavad luua keerukaid ĂŒlipisikesi ajameid. VĂ”rreldes tavapĂ€raste elektrimootoritega vĂ”imaldavad EAP-d (elektromehaaniliselt aktiivsed polĂŒmeerid) helitut liigutust ning neid saab lĂ”igata konkreetse rakenduse jaoks sobivasse suurusesse. EAP-d jagunevad kahte pĂ”hiklassi: elektron- ja ioon-EAP. Doktoritöös kĂ€sitletakse kahte erinevat ioon-EAP materjali, kus mehaaniline koste on tingitud ioonide ĂŒmberpaigutumisest kolmekihilises komposiitmaterjalis. Kuna EAP-de elektromehaanilised omadused sĂ”ltuvad lisaks sisendpinge amplituudile ja sagedusele ka tugevasti ĂŒmbritseva keskkonna parameetritest (nt niiskus ja temperatuur), siis on nendest materjalidest loodud tĂ€iturite juhtimiseks tarvilik kasutada tagasisidet. TĂ€iendav tagasisideallikas vĂ”ib oma omaduste tĂ”ttu aga vĂ€hendada EAP-de rakendusvĂ”imalusi ning seetĂ”ttu on eesmĂ€rgiks luua n-ö isetundlik EAP ajam, mis funktsioneerib samaaegselt nii tĂ€ituri kui ka liigutusandurina. Doktoritööd esitatakse uuritud materjalide elektroodi impedantsi ja deformatsiooni vaheline seos ning kirjeldatakse vastav elektriline mudel. Eraldamaks andursignaali tĂ€ituri sisendpingest pakutakse vĂ€lja elektroodikihi piires tĂ€ituri ja anduri elektriline eraldamine. Loobudes ainult elektroodimaterjalist sĂ€ilitab polĂŒmeerkarkass tĂ€ituri ja anduri mehaanilise ĂŒhendatuse â seega taolises sĂŒsteemis jĂ€rgib sensor tĂ€ituri kuju, kuigi need on elektriliselt lahti sidestatud. Elektroodimaterjali valikuliseks eemaldamiseks kasutatakse mitmeid erinevaid meetodeid (freesimine, laserablatsioon jne) ning ĂŒhtlasi uuritakse nende kasutusmugavust ja protsessi mĂ”ju 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 actuatorsâcapable for simultaneous actuation and sensingâare desired. In this thesis, sensing based on deformation-dependent electrochemical impedance is demonstrated and modelled for two types of trilayer ionic EAPsâionic 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
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