Micah Hodgins

Experimental comparison of bias elements for out-of-plane DEAP actuator system

This paper presents an experimental comparison of three different biasing elements utilized to produce out-of-plane actuation for a diaphragm dielectric electro-active polymer (DEAP). A?hanging mass, a linear coil spring, and a nonlinear (bistable) mechanism are individually paired with an unloaded DEAP actuator. High voltage (2.5?kV) is applied to the DEAP and the out-of-plane stroke of the DEAP is measured. The actuator stroke is notably different for each bias element. Results show that as the bias element stiffness increases, the actuator stroke decreases. However, the bistable element, when coupled with the DEAP, demonstrated improved actuation in a specific range of DEAP pre-deflection. Not only was the stroke larger for this case, the stroke also did not attenuate at higher voltage frequencies as much as the linear coil spring bias elements. This study demonstrates a promising method for obtaining high performance DEAP actuators in the future.

Modeling and experimental validation of a bi-stable out-of-plane DEAP actuator system

This paper presents modeling and experimental validation of a small profile, scalable DEAP actuator system. The actuator system consists of a bi-stable mechanism (a negative-rate bias spring, or NBS) coupled with an out-of-plane dielectric electro-active polymer (DEAP). The NBS biases the DEAP allowing actuation when the voltage is cycled and is shown to have a major impact on the overall system performance. Particularly in comparison with conventional linear springs, the NBS-biased actuator exhibits a considerably larger displacement stroke. A first order model of the NBS–DEAP coupled system is developed based on minimization of the systems potential energy. This approach allows for the determination of quasi-static force equilibria in the presence of multiple stable positions. The model is validated with experimental data and provides insight into system trends and related parameter optimization.

An electro-mechanically coupled model for the dynamic behavior of a dielectric electro-active polymer actuator

Dielectric electro-active polymer (DEAP) technology holds promise for enabling lightweight, energy efficient, and scalable actuators. The circular DEAP actuator configuration (also known as cone or diaphragm actuator) in particular shows potential in applications such as pumps, valves, micro-positioners and loudspeakers. For a quantitative prediction of the actuator behavior as well as for design optimization tasks, material models which can reproduce the coupled electromechanical behavior inherent to these actuators are necessary. This paper presents a non-linear viscoelastic model based on an electro-mechanical Ogden free energy expression for the DEAP. The DEAP model is coupled with a spring/mass system to study the dynamic performance of such a representative system from static behavior to 50 Hz. The system is identified and validated by several different experiments.

Modeling of the effects of the electrical dynamics on the electromechanical response of a DEAP circular actuator with a mass–spring load

This paper presents a modeling approach of an actuator system based on a dielectric electro-active polymer (DEAP) circular membrane mechanically loaded with a mass and a linear spring. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. A mass and a linear spring are used to pre-load the membrane, allowing stroke in the out-of-plane direction. The development of mathematical models which accurately describe the nonlinear coupling between electrical and mechanical dynamics is a fundamental step in order to design model-based, high-precision position control algorithms operating in high-frequency regimes (up to 150 Hz). The knowledge of the nonlinear electrical dynamics of the actuator driving circuit can be exploited during the control system design in order to achieve desirable features, such as higher modeling accuracy for high-frequency actuation, self-sensing or control energy minimization. This work proposes a physical model of the DEAP actuator system which couples both electrical and mechanical dynamics occurring during the actuation process. By means of numerous experiments, it is shown that the model can be used to predict both actuator current and displacement, and therefore to increase the overall displacement prediction accuracy with respect to actuator models which neglect electrical behavior.

A smart experimental technique for the optimization of dielectric elastomer actuator (DEA) systems

In order to aid in moving dielectric elastomer actuator (DEA) technology from the laboratory into a commercial product DEA prototypes should be tested against a variety of loading conditions and eventually in the end user conditions. An experimental test setup to seamlessly perform mechanical characterization and loading of the DEA would be a great asset toward this end. Therefore, this work presents the design, control and systematic validation of a benchtop testing station for miniature silicon based circular DEAs. A versatile benchtop tester is able to characterize and apply programmable loading forces to the DEA while measuring actuator performance. The tester successfully applied mechanical loads to the DEA (including positive, constant and negative stiffness loads) simulating biasing systems via an electromagnetic linear motor operating in closed loop with a force/mechanical impedance control scheme. The tester expedites mechanical testing of the DEA by eliminating the need to build intricate pre-load mechanisms or use multiple testing jigs for characterizing the DEA response. The results show that proper mechanical loading of the DEA increases the overall electromechanical sensitivity of the system and thereby the actuator output. This approach to characterize and apply variable loading forces to DEAs in a single test system will enable faster realization of higher performance actuators.

HIGH-FREQUENCY DYNAMIC MODEL OF A PRE-LOADED CIRCULAR DIELECTRIC ELECTRO-ACTIVE POLYMER ACTUATOR

In this work a high-frequency dynamic model of a pre-loaded circular DEAP actuator is developed and experimentally validated. The model is capable of predicting both the static and dynamic response of the actuator. The static response is modeled based on a free energy approach and consists of an Ogden term representing the elastic energy, and a electrical term representing the electrical-mechanical coupling [1]. The addition of viscoelastic elements (spring-dashpot configurations) enables the model to capture the dynamic response. The Ogden coefficients were first identified through a quasi-static force-displacement test of the actuator. A series of validation tests of the actuator at various pre-loads and voltage frequencies showed the model to be in good agreement with the experiments. The model is shown to accurately predict the actuators observed natural frequencies as the pre-deflection and the stiffness of the spring were changed. Future work will include additions to the model to account for relaxation and creep inherent in DEAP material.Copyright

DYNAMIC ELECTROMECHANICAL MODELING OF A SPRING-BIASED DIELECTRIC ELECTROACTIVE POLYMER ACTUATOR SYSTEM

This paper presents a dynamic electromechanical model for an actuator system based on a Dielectric Electro-Active Polymer (DEAP) membrane biased with a linear spring. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. A mass and a linear spring are used to pre-load the membrane, allowing stroke in the out-of-plane direction. The development of mathematical models which accurately describe the nonlinear system dynamics is a fundamental step in order to design model-based, high-precision position control algorithms. In particular, knowledge of the nonlinear electrical dynamics of the actuator driving circuit can be exploited during the control system design in order to achieve desirable features, such as self-sensing or control energy minimization. This work proposes an electromechanical physical model of the DEAP actuator system. By means of numerous experiments, it is shown that the model can be used to predict the current by measuring deformation and voltage (electrical dynamics), as well as predicting deformation and current by measuring the voltage (electromechanical dynamics).

Experimental analysis of biasing elements for dielectric electro-active polymers

This paper presents an experimental investigation of three different, small profile and scalable DEAP actuators. These actuators are designed for use in small scale pumping and valve applications. The actuators used in this paper consist of a biasing element (either a mass, linear spring, or a non-linear spring) coupled with a circular dielectric electro-active polymer (DEAP). These mechanisms bias the DEAP allowing out-of-plane actuation when the voltage is cycled. A constant force input, a linear spring, and a non-linear spring are separately tested as the biasing element of a circular/diaphragm DEAP. Tests are systematically performed at various DEAP pre-deflections, biasing stiffness and electrical loading rates. The displacement stroke performance of each test is examined and analyzed. It was found that the non-linear spring provided the largest displacement stroke over two other biasing elements. It also showed better performance at higher electrical loading rates. Thus, of the three types of biasing tested the non-linear spring shows most promise for use in fluid pump/valve applications. Future work will include optimizing this biasing element for the current DEAP design.

Systematic experimental characterization of dielectric elastomer membranes using a custom-built tensile test rig

This work presents the conceptualization, fabrication, and performance of a dielectric elastomer membrane testing rig. The custom-built rig is designed to electromechanically characterize dielectric elastomer membranes by measuring physical quantities such as force, displacement, film thickness, voltage/current, capacitance, and resistance simultaneously. Due to the thin and very compliant nature of dielectric elastomer membranes, this new design seeks to minimize setup imperfections and human error by considering the specimen preparation and placement from the start. The test rig includes optical thickness sensors which provide the first known dielectric elastomer membrane thickness profile measurements of stretched and/or activated membranes. The operation of the test rig is demonstrated by testing pure shear silicone membrane specimens. Finally, this versatile programmable test rig results in a highly useful tool for further repeatable electromechanical characterization studies of dielectric elastomer membranes.

Self-sensing at low sampling-to-signal frequency ratio: An improved algorithm for dielectric elastomer actuators

This paper presents a new self-sensing algorithm for Dielectric Elastomer actuators. The method allows to obtain accurate estimations of material capacitance and electrodes resistance from voltage and current measurements, by means of online identification algorithms, e.g., RLS. While the capacitance permits to reconstruct the actuator displacement (self-sensing), the resistance can be used to extract further information on the actuator state, e.g., fatigue (self-monitoring). The new self-sensing method is presented and compared with a different algorithm previously developed by the authors. Simulations and experiments show how capacitance and resistance predicted by the new algorithm are in agreement with the values measured with an LCR meter. Moreover, it is shown how the accuracy of the new method does not deteriorate when reducing the sampling-to-signal frequency ratio (the method is tested up to a ratio of 2.5). This result enables achieving reliable self-sensing without a significant amount of online computation effort.