Experimental Characterization and Static Modeling of McKibben Actuators

McKibben actuators are pneumatic actuators with very high force to weight ratios. Their ability to match the behavior of biological muscles better than any other actuators has motivated much research into the characterization and modeling of these actuators. The purpose of this paper is to experimentally characterize the behavior of McKibben artificial muscles with basic geometric parameters, and present a model that is able to predict the static behavior accurately in terms of blocked force and free displacement. A series of experiments aimed at understanding the static behavior of the actuators was conducted. The results for three different lengths (4 in., 6 in., and 8 in.), three diameters (1/8 in., 1/4 in., and 3/8 in.), and one wall thickness (1/16 in.) at pressures ranging from 10 psi to 60 psi illustrate the key design trends seen in McKibben actuator geometry. While existing models predict this static behavior, there are varying degrees of accuarcy, which motivates the present study. Using knowledge gained from the experimental study, improvements for the two modeling approaches were explored, including effects from elastic energy storage, noncylindrical shape, and variable thickness. To increase model accuracy, another set of experiments was used to characterize the elasticity of the rubber tubes and fibers of the braid. Comparisons of the measured data to the improved model indicate that the ability to accurately predict the static behavior of McKibben actuators has increased.