Compliant Actuation Based on Dielectric Elastomers for a Force-Feedback Device: Modeling and Experimental Evaluation

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact force-feedback devices such as, for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the present paper addresses the development of a force feedback controller for an agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliant mechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the visco-hyperelastic nature of the DE material. The model is then linearized and employed for the design of a force controller. The controller employs a position sensor, which determines the actuator configuration, and a force sensor, which measures the interaction force that the actuator exchanges with the environment. In addition, an optimum full-state observer is also implemented, which enables both accurate estimation of the time-dependent behavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminary experimental results are provided to validate the proposed actuator-controller architecture

Compliant actuation based on dielectric elastomers for a force-feedback device: modeling and experimental evaluation

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE)seem to be a promising technology for the implementation of light and compact force-feedback devices such as,for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivialowing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changingdeformations. In this context, the present paper addresses the development of a force feedback controller foran agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliantmechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelasticnature of the DE material. The model is then linearized and employed for the design of a forcecontroller. The controller employs a position sensor, which determines the actuator configuration, and a forcesensor, which measures the interaction force that the actuator exchanges with the environment. In addition, anoptimum full-state observer is also implemented, which enables both accurate estimation of the time-dependentbehavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminaryexperimental results are provided to validate the proposed actuator-controller architectur

Compliant actuation based on dielectric elastomers for a force-feedback device: modeling and experimental evaluation

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact force-feedback devices such as, for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the present paper addresses the development of a force feedback controller for an agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliant mechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelastic nature of the DE material. The model is then linearized and employed for the design of a force controller. The controller employs a position sensor, which determines the actuator configuration, and a force sensor, which measures the interaction force that the actuator exchanges with the environment. In addition, an optimum full-state observer is also implemented, which enables both accurate estimation of the time-dependent behavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminary experimental results are provided to validate the proposed actuator-controller architecture&nbsp

Model-Based Design Optimization of Soft Polymeric Domes Used as Nonlinear Biasing Systems for Dielectric Elastomer Actuators

Due to their unique combination of features such as large deformation, high compliance, lightweight, energy efficiency, and scalability, dielectric elastomer (DE) transducers appear as highly promising for many application fields, such as soft robotics, wearables, as well as micro electromechanical systems (MEMS). To generate a stroke, a membrane DE actuator (DEA) must be coupled with a mechanical biasing system. It is well known that nonlinear elements, such as negative-rate biasing springs (NBS), permit a remarkable increase in the DEA stroke in comparison to standard linear springs. Common types of NBS, however, are generally manufactured with rigid components (e.g., steel beams, permanent magnets), thus they appear as unsuitable for the development of compliant actuators for soft robots and wearables. At the same time, rigid NBSs are hard to miniaturize and integrate in DE-based MEMS devices. This work presents a novel type of soft DEA system, in which a large stroke is obtained by using a fully polymeric dome as the NBS element. More specifically, in this paper we propose a model-based design procedure for high-performance DEAs, in which the stroke is maximized by properly optimizing the geometry of the biasing dome. First, a finite element model of the biasing system is introduced, describing how the geometric parameters of the dome affect its mechanical response. After conducting experimental calibration and validation, the model is used to develop a numerical design algorithm which finds the optimal dome geometry for a given DE membrane characteristics. Based on the optimized dome design, a soft DEA prototype is finally assembled and experimentally tested

Fully Polymeric Domes as High-Stroke Biasing System for Soft Dielectric Elastomer Actuators

The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a threedimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed

A Review of Cooperative Actuator and Sensor Systems Based on Dielectric Elastomer Transducers

This paper presents an overview of cooperative actuator and sensor systems based on dielectric elastomer (DE) transducers. A DE consists of a flexible capacitor made of a thin layer of soft dielectric material (e.g., acrylic, silicone) surrounded with a compliant electrode, which is able to work as an actuator or as a sensor. Features such as large deformation, high compliance, flexibility, energy efficiency, lightweight, self-sensing, and low cost make DE technology particularly attractive for the realization of mechatronic systems that are capable of performance not achievable with alternative technologies. If several DEs are arranged in an array-like configuration, new concepts of cooperative actuator/sensor systems can be enabled, in which novel applications and features are made possible by the synergistic operations among nearby elements. The goal of this paper is to review recent advances in the area of cooperative DE systems technology. After summarizing the basic operating principle of DE transducers, several applications of cooperative DE actuators and sensors from the recent literature are discussed, ranging from haptic interfaces and bio-inspired robots to micro-scale devices and tactile sensors. Finally, challenges and perspectives for the future development of cooperative DE systems are discussed

Fully Polymeric Domes as High-Stroke Biasing System for Soft Dielectric Elastomer Actuators

The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a three-dimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed

Conception et évaluation expérimentale d'un manipulateur actionné par des muscles pneumatiques binaires moyennés élastiquement

Actuellement, les médecins utilisent l'échographie pour visualiser la prostate lors de la biopsie. La technique actuelle de biopsie offre un taux de détection du cancer contenant entre 20 et 36 % de résultats faux négatifs, ce qui retarde le traitement du cancer. Ces faux négatifs sont causés en partie par le manque de perceptibilité sous échographie des tumeurs ayant un diamètre inférieur à 5 mm. L'imagerie par résonnance magnétique (IRM) pourrait résoudre ce problème puisque cette technique d'imagerie offre une meilleure résolution et une perceptibilité des tumeurs meilleures que celles obtenues avec l'échographie. Toutefois, l'intervention sous IRM est peu sécuritaire et peu ergonomique pour le médecin en raison de l'intense champ magnétique nécessaire à l'imagerie et de l'accès restreint au patient. Le présent travail présente le développement d'un prototype de manipulateur robotisé permettant aux médecins d'effectuer des interventions précises et rapides à la prostate à l'intérieur même du scanner IRM. Le manipulateur est conçu de manière à ne pas influencer ou être influencé par le champ magnétique de l'IRM, soutenir les forces induites par l'insertion de l'aiguille dans le patient, atteindre une cible avec précision et être suffisamment petit pour être introduit avec le patient dans l'IRM. L'architecture du manipulateur utilise une approche binaire moyennée élastiquement dans une architecture parallèle. Chacun des actionneurs compte seulement deux états discrets. Les actionneurs retenus sont des muscles pneumatiques en raison de la forte densité de force qu'ils génèrent. De plus, ces actionneurs permettent d'éliminer les joints complexes nécessaires à la construction de manipulateur parallèle en utilisant l'élasticité intrinsèque des actionneurs. Un prototype a été construit dans le but d'étudier l'erreur de positionnement obtenue avec le manipulateur et valider l'atteinte des requis cliniques. La justesse a été mesurée à 3,3 mm et la précision a été mesurée à 0,5 mm. La raideur a aussi été mesurée et atteint ~1,14 N/mm au bout de l'aiguille pour s'assurer que le manipulateur est en mesure de soutenir l'insertion d'aiguille sans trop dévier de la trajectoire prévue. Une preuve de concept de valve pneumatique compatible à l'IRM a été prototypée. La valve utilise un actionneur de polymère diélectrique rotatif en raison de la grande compatibilité à l'IRM de cette technologie. Les travaux montrent que la solution proposée est viable et très prometteuse. Le robot est simple, peu couteux et est capable de rencontrer les requis cliniques. Néanmoins, plusieurs travaux sont encore à faire sur le manipulateur, car seulement l'orientation de l'aiguille a été traitée. De plus, l'assemblage des muscles pneumatiques a été réalisé à l'aide de tubes offerts commercialement. Plusieurs modifications pourraient améliorer les performances du manipulateur, dont notamment, mouler les muscles pneumatiques

High-Performance Dielectric Elastomer Actuators

Dielectric elastomer actuators (DEAs) feature high energy efficiency, lightweight, design flexibility and the use of low cost materials and processes. This holds particularly true for membrane actuators, which, in addition to the dielectric elastomer comprise a separate biasing system. The particular design of the biasing system may dramatically improve the DEA performance, but at the same time, it adds complexity to such a design process. Therefore, in this work, a systematic design approach to adapt DEA systems to specific applications is developed. It allows calculation of all relevant design parameters and incorporates experimentally validated scaling laws to account for actuator geometry effects. Finally, the capability of the design process is illustrated at two examples. In the first one, the force output of circular membrane DEAs, which is typically in the hundreds of millinewton range, is increased by more than two orders of magnitude. For the first time, record-high forces of 100 Newton are generated, while an innovative overall system design maintains compactness. The second system is designed for high reversible actuation strains in the range of >50%. The use of silicone as elastomer additionally results in high-speed actuation. DEA systems with such outstanding performance prove that they are capable of competing with existing technologies such as solenoids, while adding additional functionality and, in the future, smartness through “self-sensing” properties.Dielektrische Elastomeraktoren (DEA) weisen eine hohe Energieeffizienz, geringes Gewicht und Designflexibilität, bei gleichzeitig geringen Herstellungskosten, auf. Dies trifft speziell auf Membran DEA zu, die zusätzlich über einen Vorspannmechanismus verfügen. Diese Kombination zu einem DEA System ermöglicht eine deutliche Leistungssteigerung, birgt jedoch eine deutlich erhöhte Komplexität. Daher wird in dieser Arbeit ein systematischer Auslegungsprozess entwickelt, um solche Aktorsysteme anwendungsspezifisch anzupassen. Dieser erlaubt, unter anderem mit empirisch ermittelten Skalierungsgesetzen zur Aktorgeometrie, alle notwendigen Aktorparameter zu bestimmen. Abschließend wird die Leistungsfähigkeit des Auslegeprozesses an zwei Beispielen illustriert. Im ersten wird die Kraft eines Membran DEA, die typischerweise im Bereich von einigen hundert mN liegt, um zwei Größenordnungen erhöht. Erstmals erreicht ein solcher Aktor Kräfte von 100 N, während eine innovative Konstruktion dennoch für Kompaktheit sorgt. Mit dem zweiten Aktor können wiederholbare und schnelle (bis zu 0,3 m s -1 ) Aktuierungsdehnungen von >50% erzeugt werden. DEA Systeme, die eine solche Leistungsfähigkeit aufweisen, zeigen, dass sich die Technologie mit herkömmlichen Aktorprinzipien (z.B. elektromagnetische) messen kann. Darüber hinaus bieten DEA zusätzliche Funktionalität und können in Zukunft durch ihre Möglichkeit des „Self-sensing“ auch zur Entwicklung intelligenter Systeme für die Industrie 4.0 beitragen