Mr. Jason W. Fox Profile

Jason W. Fox

Graduate Student at Virginia Polytechnic Institute and State Univ

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Proceedings Article | 10 April 2008 Paper

Nonlinear dynamic characteristics of dielectric elastomer membranes

Jason Fox, Nakhiah Goulbourne

Proceedings Volume 6927, 69271P (2008) https://doi.org/10.1117/12.776692

KEYWORDS: Dielectrics, Protactinium, LabVIEW, Actuators, Nonlinear dynamics, Sensors, Relays, Switches, MATLAB, Nonlinear optics

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The dynamic response of dielectric elastomer membranes subject to time-varying voltage inputs for various initial inflation states is investigated. These results provide new insight into the differences observed between quasi-static and dynamic actuation and presents a new challenge to modeling efforts. Dielectric elastomer membranes are a potentially enabling technology for soft robotics and biomedical devices such as implants and surgical tools. In this work, two key system parameters are varied: the chamber volume and the voltage signal offset. The chamber volume experiments reveal that increasing the size of the chamber onto which the membrane is clamped will increase the deformations as well as cause the membrane's resonance peaks to shift and change in number. For prestretched dielectric elastomer membranes at the smallest chamber volume, the maximum actuation displacement is 81 microns; while at the largest chamber volume, the maximum actuation displacement is 1431 microns. This corresponds to a 1767% increase in maximum pole displacement. In addition, actuating the membrane at the resonance frequencies provides hundreds of percent increase in strain compared to the quasi-static strain. Adding a voltage offset to the time-varying input signal causes the membrane to oscillate at two distinct frequencies rather than one and also presents a unique opportunity to increase the output displacement without electrically overloading the membrane. Experiments to capture the entire motion of the membrane reveal that classical membrane mode shapes are electrically generated although all points of the membrane do not pass through equilibrium at the same moments in time.

Proceedings Article | 5 April 2007 Paper

An experimental study on the dynamic response of dielectric elastomer membranes

J. Fox, N. Goulbourne

Proceedings Volume 6524, 65241Z (2007) https://doi.org/10.1117/12.716824

KEYWORDS: Protactinium, Dielectrics, Electrodes, Actuators, Spherical lenses, Phase shifts, Dielectric elastomer actuators, Carbon, LabVIEW, Intelligence systems

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Dielectric Elastomer Actuators (DEAs) have received considerable attention recently due to their large strains, over 100% in some cases, when subject to an electric field. Previous research yielded a large deformation quasi-static model that describes the out of plane deflections of clamped diaphragms. The numerical modeling results compare well with experimental results for the same configuration. A theoretical dynamic model has also been developed for the dynamic inflation of a spherical DEA membrane. With relevance to dynamic applications, the time varying response of dielectric elastomer membranes configured for out-of-plane deflections has not been reported until now. In this paper, an experimental investigation and analysis of the dynamic response of a dielectric elastomer membrane is reported. The experiments were conducted with DEAs fabricated from VHB 4905 films and carbon grease electrodes. The experiments covered the electromechanical spectrum by investigating membrane behavior due to (i) a voltage time varying input and (ii) a mechanical time varying input, resulting in a combined electromechanical loading state during the experiments. The results reveal that the response of the membrane is a departure from the classical dynamic response of continuum membrane structures. As a result of this work, we have identified which typical modeling assumptions are valid and hence can authentically be used to develop new dynamic predictive modeling tools.

Proceedings Article | 4 April 2007 Paper

Self-sensing McKibben actuators using dielectric elastomer sensors

N. Goulbourne, S. Son, J. Fox

Proceedings Volume 6524, 652414 (2007) https://doi.org/10.1117/12.716274

KEYWORDS: Actuators, Sensors, Dielectrics, Capacitance, Data modeling, Electrodes, Statistical modeling, Protactinium, Bladder, Carbon

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In this paper, a self-sensing McKibben actuator using dielectric elastomer sensors is presented. Fiber-reinforced cylindrical actuators offer one potential solution to the low-force output problem that plagues many artificial muscle actuators. Placing a cylindrical dielectric elastomer sensor in direct contact with the inner surface of the McKibben actuator facilitates in situ monitoring of actuator strains and loads. The deformation of the McKibben actuator and hence the cylindrical dielectric elastomer sensor results in a change in the electrical signal read from the electroded surfaces of the dielectric elastomer. In this paper, we present a model for predicting the response of fiber reinforced cylindrical constructs (McKibben actuators) that are actuated by an inflation pressure, which is used to support an axial load. The model is based on Adkins and Rivlin's large deformation model for the inflation and contraction of tubes reinforced with inextensible fibers. In this model, the McKibben actuator is considered as a surface of revolution since the initially near cylindrical shape is nearly always compromised during mechanical loading. A series of experiments measuring the force versus contraction behavior of the actuators are used to validate the numerical model. The material constants for an Ogden model were determined by uni-axial extension of cylindrical samples. A comparison of the numerical and experimental results shows that the correlation is good. The model enables a number of key analyses such as the effect of the braid angle and the tension generated in the fibers.

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