Thin soft layered actuator based on a novel fabrication technique

This paper presents a novel fabrication method for constructing thin soft layered actuators. The method is based on building up thin layers of elastomeric material with embedded strain-limiting and mask layers using a bespoke film applicator. This enables the fabrication of millimetre-scale soft actuators with complex integrated masks and/or strain-limiting layers, as demonstrated in a series of proof of concept prototypes. The prototype actuators can be cut into a desired shape via laser cutting the laminated sheet. This paper shows the feasibility of the fabrication method and the value of its use in creating thin soft layered actuators for application in soft robotics. The technique can be further developed to fabricate multi-material composite soft actuators which are thin, compact, flexible and stretchable

Development of a Fabrication Technique for Soft Planar Inflatable Composites

Soft robotics is a rapidly growing field in robotics that combines aspects of biologically inspired characteristics to unorthodox methods capable of conforming and/or adapting to unknown tasks or environments that would otherwise be improbable or complex with conventional robotic technologies. The field of soft robotics has grown rapidly over the past decade with increasing popularity and relevance to real-world applications. However, the means of fabricating these soft, compliant and intricate robots still poses a fundamental challenge, due to the liberal use of soft materials that are difficult to manipulate in their original state such as elastomers and fabric. These material properties rely on informal design approaches and bespoke fabrication methods to build soft systems. As such, there are a limited variety of fabrication techniques used to develop soft robots which hinders the scalability of robots and the time to manufacture, thus limiting their development. This research focuses towards developing a novel fabrication method for constructing soft planar inflatable composites. The fundamental method is based on a sub-set of additive manufacturing known as composite layering. The approach is designed from a planar manner and takes layers of elastomeric materials, embedded strain-limiting and mask layers. These components are then built up through a layer-by-layer fabrication method with the use of a bespoke film applicator set-up. This enables the fabrication of millimetre-scale soft inflatable composites with complex integrated masks and/or strain-limiting layers. These inflatable composites can then be cut into a desired shape via laser cutting or ablation. A design approach was also developed to expand the functionality of these inflatable composites through modelling and simulation via finite element analysis. Proof of concept prototypes were designed and fabricated to enable pneumatic driven actuation in the form of bending soft actuators, adjustable stiffness sensor, and planar shape change. This technique highlights the feasibility of the fabrication method and the value of its use in creating multi-material composite soft actuators which are thin, compact, flexible, and stretchable and can be applicable towards real-world application

Tindiprinditud pehmed täiturid

Väitekirja elektrooniline versioon ei sisalda publikatsiooneTuleviku biomeditsiini- ja robootikarakenduste täiturite jaoks on vaja usaldusväärseid, korratavaid ja skaleeritavaid valmistamismeetodeid. Johannes Gutenbergi näitel võib printimine ka tehislihaste tootmist revolutsioneerida: printimine võimaldab valmistada ühtlase paksuse ja keeruka mustriga täitureid. Selle doktoritöö raames arendati välja prinditud kolmekihilised kahest elektroodist ja neid eraldavast membraanist koosnevad juhtivpolümeeridel põhinevad täiturid. Tänu analoogsele käitumisele looduslike lihastega kutsutakse neid kuju muutvaid materjale ka tehislihasteks ning just selle funktsionaalse sarnasuse põhjal on tõenäolisteks rakendusvaldkondadeks robootika ja meditsiinitehnoloogia. Prinditud mikrotäiturite elektrilisi, mehaanilisi ja täituromadusi saab muuta kolme peamise strateegia abil. Esiteks modifitseeriti selles doktoritöös kommertsiaalse juhtivpolümeertindi koostist, lisades sinna süsinikaerogeeli. Saadud juhtivpolümeer-süsinik-komposiidil põhineval täituril näitas võrreldes ainult juhtivpolümeertäituriga suuremat jõudu. Teiseks varieeriti täituromaduste täppisreguleerimiseks elektroodi paksust, mis oli vähemalt 20 kihi ulatuses lineaarses sõltuvuses kihtide arvust. Paksuse kasvades suurenesid ka täituri jõud, liigutusulatus, pinnajuhtivus ja mahtuvus. Kolmandaks häälestati täituri sooritusvõimet sobivate alus- ehk membraanimaterjalide valikuga. Nitriilbutadieenkautšukile prinditud õhukesel täituril oli lineaarses liigutusrežiimis suurusjärgu võrra suurem liigutusulatus võrreldes tööstusliku polüvinülideendifluoriidmembraaniga täituriga. Selles töös näidati, et piisksadestusprintimise teel on võimalik valmistada pehmeid elektromehaanilisi süsteeme, hoolimata meetodi mõningatest piirangutest. Sobivalt valitud tindimaterjalid ja häälestatud printimisprotsess võimaldavad juba lähitulevikus valmistada pehmeid ja integreeritud elektromehaanilisi süsteeme täielikult printimise teel.Future soft micro actuator applications for biomedical and soft robotic applications need reliable, repeatable, cost-effective and scalable production methods. As an example of Johannes Gutenberg, printing could also revolutionize the production of artificial muscles – printing allows fabrication of homogeneous actuators with intricate patterns. In this thesis technology for fabricating actuators composed of two conducting polymer-based electrodes and a membrane separating them was developed. The actuators change their shape in response to electrical stimuli. Due to this functional similarity to natural muscles, applications in the fields of medicine and robotics are possible. The properties of printed micro actuators are tunable using various strategies. First, the composition of the conducting polymer ink was modified by adding carbon aerogel to the mix. The resulting composite showed superior force compared to pure conducting-polymer actuators. Second, the electrode thickness was controlled to fine-tune the properties. Increasing the thickness also increased the force, strain and capacitance of the actuator and conductivity of the electrodes. Third, the actuator performance was tailored by the selection of various membrane materials. Printing on spin-coated membranes from nitrile butadiene rubber resulted in extremely thin trilayer actuators that had an order of magnitude higher linear strain compared to commercial polyvinylidene based actuators. This work has showed that despite the known limitations of drop-on-demand printing, it is possible to prepare soft electromechanical systems using this technology. With the selection of compatible materials, and by using various strategies to tune the functional properties of the composite towards more preferred outcome it will be possible in the nearest future to realize applications with fully printed and integrated soft electromechanically active component

Modeling and Control of MEMS-based Multi-layered Prestressed Piezoelectric Cantilever Beam

Piezoelectric materials are the preferred smart materials for sensing and actuation in the form of micro and nano-engineering structures like beams and plates. Cantilever beams play a significant role as key components in atomic force microscopy and bio and chemical sensors. Adding an active layer such as lead zirconate titanate (PZT) thin-film to form smart cantilever beams with sensing and actuation capabilities is highly desirable to facilitate miniaturization, enhance performance and functionali- ties such as enabling on-chip high-speed parallel AFM. During the micro-fabrication process, residual stresses develop in the different layers of the cantilever beam, causes initial deflection. The residual stress in the different layers of the cantilever beam and the application of voltage to the PZT thin-film affects their dynamics. This the- sis investigates the dynamic behaviour and develops a control technique and a novel charge readout circuit to improve the performance of a micro-fabricated multi-layer prestressed piezoelectric cantilever beam as an actuator and a deflection sensor. Firstly, the fabrication process of a unimorph PZT cantilever beam is explained. A low thermal budget Ultra-high vacuum e-beam evaporated polysilicon thin-film (UHVEEpoly) process is used for the fabrication of multi-layered PZT cantilever beam in d31 mode. The sharp peaks at resonant frequencies in the frequency response of the PZT cantilever beam show very little damping and a large settling time of the cantilever beam. Secondly, the dynamic behaviour of the prestressed PZT cantilever beam is in- vestigated subjected to change in driving voltage. Experimental investigations show a shift in resonant frequencies of a PZT cantilever beam. However, there is no reported mathematical model that predicts the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam subjected to a change in driving voltage. This work developed a mathematical model with experimental val- idation to estimate the shift in resonance frequencies of such cantilever beams with the change in the driving voltage. A very good agreement between the model predic- tions and experimental measurements for the frequency response of the cantilever beam at different driving voltages has been obtained. A novel linear formulation has been developed to predict the shift in resonance frequencies of the PZT can- i tilever beam for a wide range of driving voltages. The formulation shows that the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam per unit of applied voltage is dependent on geometric parameters and material properties. Thirdly, a robust resonant controller has been designed and implemented to re- duce the settling time of a highly vibrating PZT cantilever beam. The controller design is based on a mixed negative-imaginary, passivity, and a small-gain approach. The motivation to design a resonant controller using the above-mentioned analyti- cal framework is its bandpass nature and the use of velocity feedback, as the charge collected from a vibrating PZT cantilever beam gives the velocity information of the beam. The proposed controller design results in finite gain stability for a pos- itive feedback interconnection between two stable linear systems with a large gain and phase margin. Experimental results demonstrate that the designed resonant controller is able to effectively damp the first resonant mode of a cantilever, signifi- cantly reducing settling time from 528 ms to 32 ms. The robustness of the designed resonant controller is tested against changes in the cantilever beam dynamics due to residual stress variation and or stress variation due to driving voltage. Finally, to facilitate the miniaturization of on-chip sensors and parallel high- speed AFM, a single layer of a PZT thin-film in a cantilever beam is used as a deflection sensor and an actuator instead of bulky optical deflection sensors. A novel charge readout circuit is designed for deflection sensing by capturing the electrical charge generated due to the vibration of the PZT beam. The signal-to-noise ratio and sensitivity analysis of the readout circuit shows similar results compared to the commercially available optical deflection sensors. Our work highlights very important aspects in the dynamic behaviour and perfor- mance of a multi-layered prestressed piezoelectric cantilever beam. The agreement between the proposed theoretical formulation and experimental investigations in modeling, control design, and a novel readout circuit will provide the platform for further the development and miniaturization of microcantilever-based technologies, including on-chip parallel HS-AFM

Ionic Polymer Actuators: Principle, Fabrication and Applications

Ionic-polymer based actuators have the advantages of low voltage and power requirements, being easily processable, flexibility, soft action and bio-mimetic activation, which are of considerable interests for applications in biomedical micro-devices and soft robotics. In this chapter, we firstly review the development of ionic polymer actuator and reveal the universal architecture and mechanism of ionic polymer actuators. We then introduce two kinds of typical polymer actuators: ionic polymer-metal composites (IPMC) and bucky gel actuator (BGA), including their basic principle, fabrication process and typical applications. The aim of this chapter is to give some perspectives on IPMC and BGA and provide a way and case in using this actuator for real applications

Additively Manufactured Dielectric Elastomer Actuators: Development and Performance Enhancement

The recently emerging and actively growing areas of soft robotics and morphing structures promise endless opportunities in a wide range of engineering fields, including biomedical, industrial, and aerospace. Soft actuators and sensors are essential components of any soft robot or morphing structure. Among the utilized materials, dielectric elastomers (DEs) are intrinsically compliant, high energy density polymers with fast and reversible electromechanical response. Additionally, the electrically driven work principle allows DEs to be distributed in a desired fashion and function locally with minimum interference. Thus, a great effort is being made towards utilizing additive manufacturing (AM) technologies to fully realize the potential of DE soft actuators and sensors. While soft sensors have received more attention and development due to their simpler implementation, DE actuators (DEAs) set stricter AM and electrode material requirements. DEAs’ layered structure, compliant nature, and susceptibility to various defects make their manufacturability challenging, especially for non-trivial biomimetic soft robotics geometries. This dissertation comprehensively analyzes DE materials’ transition into a soft actuator using AM to facilitate effective DEA soft actuator fabrication. Closely interrelated fabrication techniques, material properties, and DEA geometries are analyzed to establish a fundamental understanding of how to implement high-quality DEA soft actuators. Furthermore, great attention is paid to enhancing the performance of printed DEAs through developing printable elastomer and electrode materials with improved properties. Lastly, performance enhancement is approached from the design point of view by developing a novel 3D printable DEA configuration that actuates out-of-plane without stiffening elements

Monolayer MoS2 strained to 1.3% with a microelectromechanical system

We report on a modified transfer technique for atomically thin materials integrated onto microelectromechanical systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar structures and fragility of MEMS, while still providing precise positioning and crack free transfer of flakes. Further, our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time, increases the yield, and allowed us to exploit the strong mechanical coupling between 2D crystal and polymer to strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS2) with MEMS devices for the first time and achieved greater than 1.3% strain, marking a major milestone for incorporating 2D materials with MEMS We used the established strain response of MoS2 Raman and Photoluminescence spectra to deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment and literature.Published versio