Metal Hydride Fluidic Artificial Muscle Actuation System
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1129-V05-01
Metal Hydride Fluidic Artificial Muscle Actuation System Alexandra Vanderhoff and Kwang J. Kim Active Materials and Processing Laboratory, Mechanical Engineering Department, University of Nevada, Reno, Reno, NV 89557, U.S.A.
ABSTRACT The study determines the feasibility of a new actuation system that couples a fluidic artificial muscle designed by Festo [1] with a metal hydride hydrogen compressor to create a compact, lightweight, noiseless system capable of high forces and smooth actuation. An initial model for the complete system is developed. The analysis is restricted in some aspects concerning the complexity of the hydriding/dehydriding chemical process of the system and the three-dimensional geometry of the reactor, but it provides a useful comparison to other actuation devices and clearly reveals the parameters necessary for optimization of the actuation system in future work. The system shows comparable work output and has the benefits of biological muscle-like properties [2] for use in robotic systems. When compared to other previously developed metal hydride actuation systems the potential for increasing the reaction kinetics and improving the overall power output of the system is revealed. A comparison of the system to common actuation devices, including a biological muscle, shows similar stress and strain relations, but a lower power and frequency range due to the slow actuation time. Improving the reaction kinetics of the system will be the first approach to enhancing the system, along with optimization of the mass and type of metal hydride used in the reactor to produce a full actuation stoke of the fluidic muscle while minimizing system weight.
INTRODUCTION The actuation system of this study couples a fluidic artificial muscle that is driven by pressure input and a metal hydride compressor designed to reversibly absorb and desorb hydrogen gas. The actuator and metal hydride reactor create a closed system that operates by heating the reactor containing the activated metal hydride resulting in the desorption of hydrogen gas which pressurizes the artificial muscle causing it to contract; the reactor is then cooled and the hydrogen gas is reabsorbed by the metal hydride causing the artificial muscle to relax. The fluidic artificial muscle used in the system was developed by Festo [1] and is an improved design over the common Braided Artificial Pneumatic Muscle (BPAM). The reactor design is a copper containment unit for the metal hydride pellets that is heated and cooled by thermoelectric elements attached to the outer walls of the unit, along with cooling fans to improve the heat transfer rate. The system was designed with the goals of creating a lightweight (high force to weight ratio), compact, innovative system that is durable, has smooth actuation, and noiseless operation. The actuator was characterized following a general method used for pneumatic muscles, and a thermal circuit model was created as a baseline for the system feasibility and the future development of the project. The two
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