Electroactive Polymer Technology Electroactive polymers (EAPs) are promising as actuators in intelligent material systems, where large deformations are required. Electromagnetic, piezoelectric or shape memory alloy actuators are either too heavy, too complex or too slow for such applications. EAPs however are relatively lightweight, rather simple and quick enough. In particular, dielectric electroactive polymers were shown to have good overall performances. Because their capabilities correspond to the performance of natural muscles, dielectric EAP actuators are often referred to as „artificial muscles“. Arm wrestling competition: EAP activated robot versus human, planned for SPIE Conference in March, Working Principle of Dielectric EAPs An EAP actuator is basically a compliant capacitor, where a thin elastomer film is sandwiched between two compliant electrodes. When a high DC voltage (kV) is applied to the electrodes, the arising electrostatic pressure squeezes the elastomer film in thickness and thus the film expands in planar directions. When the voltage is switched off, the elastic film returns to its original shape. C +Q -Q A d Activated U U CoCo Q=0 AoAo dodo Deactivated Electroactive Polymer (EAP) Actuators Characteristics of Dielectric EAPs Large actuation strains (up to 215%) High energy densities (3.4 J/g, 3.4 J/cm 3 ) Response time in the order of milliseconds Mechanically compliant and flexible Can be tailored to various applications Working Principle and Characteristics of Dielectric Electroactive Polymers Possible Actuator Configurations Various actuator designs are possible such as: Single-layer or multilayer planar actuators Cylindrical actuators (electroactive polymer coiled up around a spring) Balloon-like Inflatable actuators Dielectric EAP actuator in passive (left) and activated state (right). Cyclindrical actuator. Balloon actuator in deactivated (left) and activated state (right). 10 mm Research Group at Lab. 121 Gabor Kovacs, Silvain Michel, Michael Wissler, Patrick Lochmatter and Rui Zhang Project Partners ETH, Institute of Mechanical Systems (IMES): Center of Product-Development, Center of Mechanics and Center of Structure Technologies EMPA: Lab. 140 “Functional Polymers” and Lab. 114 “Polymers/Composites” National Centre of Competence in Research CO-ME (Computer Aided and Image Guided Medical Interventions)..

Design of the EAP Actuator System The chain-like actuator consisting of a sequence of several planar EAP actuators is mounted to a rubber glove. One end of the chain is attached to a nylon band around the wrist while the other end is fixed to a ring around the fingertip. Goal Development of a powerful, lightweight, non- obstructive force feedback glove for the simulation of open surgeries and other haptic display tasks in virtual environments. Operation of the Chain-Like Actuator During a voluntary motion of the surgeon, the actuator is controlled to follow the finger movements. As soon as the human operator touches a virtual object, the actuator is deactivated and tries to contract to its initial shape. Thus, it gives a resistance force via the ring onto the ventral side of the fingertip, blocking the finger's motion. Characterization of an Elementary EAP Actuator Isometric and isotonic measurements were carried out to characterize single and multilayer actuator elements. The isometric measurement gives the contractile force versus driving voltage while the actuator's length is kept constant. The isotonic measurement determines the relative actuator's length change versus driving voltage when a constant load is applied to the actuator. Results and Conclusions Concerning the lightweight, contractile force (0.7 N) and the elongation (10.2%), the dielectric elastomer actuator is promising to provide the required force feedback to the user (force: 0-5 N, elongation: 8%). The performance might be enhanced by diverse actuator configurations (multilayer, multi-element or its combination). Further, insulation issues have to be studied to provide sufficient electrical safety to the user. Left: Schematic of a chain-like actuator for the index finger. Right: Demonstrator for the chain-like actuator. Top: Isometric measurement. Bottom: Isotonic measurement. EAP-based Portable Force Feedback Device in Open Surgery Simulation (Rui Zhang) Supervision Prof. Dr. Markus Meier, Center of Product-Development at ETH Dr. Andreas Kunz, Center of Product-Development at ETH..

Electromechanical Characterization and Modeling of Electroactive Polymers (Michael Wissler) Goal The goal is to characterize the electromechanical behavior of dielectric electroactive polymers (EAP) and to develop appropriate theoretical models. The coupling of the electrical and the mechanical behavior will be investigated as well. The models will allow simulating the behavior of geometrically complex actuators, to optimize the design and to ensure their reliability. Left: Comparison between experiment and modeling. Passive Mechanical Behavior The nominal stress is plotted against the stretch ratio. Research Approach Mechanical behavior: Characterization and modeling of the passive properties in a one and a two dimensional state Electrical behavior: Characterization of the passive properties Electromechanical coupling: Investigation of planar actuators Implementation in a software tool: Analyzing geometrical complex actuators The nominal stress is plotted against the time. Hyperelasticity The hyperelastic behavior is described by a strain energy potential (reduced polynomial form) through three coefficients. Viscoelasticity The viscoelastic behavior is described by an eight parameter spring/damper system (Prony series). Combined Tensile-relaxation Test Combined tensile-relaxation tests were carried out in order to evaluate the hyper- and the viscoelastic model (left). The sample was loaded with a constant strain rate, interrupted by phases of relaxation under constant strain ε. The result of this comparison indicates that a quasi-linear viscoelastic model is able to describe the behavior for strains up to 50%. However, for nominal strains beyond 50% the model must be adapted. Whether the discrepancies between the experiment and the model are due to plasticity or not is an open question. Evaluation of the Model Supervision Prof. Dr. Edoardo Mazza, Center of Mechanics at ETH Prof. Dr. Mehdi Farshad, Lab. 114 at EMPA Dr. Gabor Kovacs, Lab. 121 at EMPA..

Evaluation of actuator designs. Investigation of suitable manufacturing processes. Development of an appropriate control system. Characterization of the overall performance of the resulting adaptive system. Development of a Shell-like Electroactive Polymer (EAP) Actuator (Patrick Lochmatter) The Goal of this PhD thesis is to build a shell-like, large-scale, dielectric EAP actuator, which has the capability to take a predetermined shape. Furthermore, the adapted surface shape should be maintained by a control system even when external forces are applied. Research Approach Inactivated planar shell-like actuator (left) takes a predetermined shape when activated (right). No detailed model for the mechanical film behaviour is existing so far. A simple phenomenological model of elementary actuators was introduced. It consists of a perpendicular spring system to generate an elastic behaviour in the three space directions. A superposed incompressible fluid constitutes the observed incompressibility of low-modulus elastomers. With this model the influence of various parameters on the overall actuator characteristic can be estimated. Preliminary Result: A Spring-Fluid Model Supervision Prof. Dr. Paolo Ermanni, Centre of Structures Technologies at ETH Dr. Gabor Kovacs, Lab. 121 at EMPA.. The research activities mainly focus on the: F(x,t) On Shell-like Actuator Control and Energy Supply 30 cm Off Goal Spring system k sx soso lolo bobo hoho k sy k sz Fluid Spring-fluid model of elementary actuator configurations. Possible Applications Drag-reduction of fluid-exposed structures Propulsion of vehicles in fluid Shell-like actuators shall be applied to the surfaces of structures in order to generate an interaction between the adaptive surface and the environment. Thus, possible fields of applications may be: Similarity of the propulsion movements of stingrays (left) and the vision of continually deformable shell-like actuators (right). Film behaviour under external pressure p in thickness direction. p h..