Static Force Model-Based Stiffness Model for Pneumatic Muscle Actuators

Abstract

Pneumatic muscle actuators (PMAs) differ from general pneumatic systems as they have no inner moved parts and there is no sliding on the surfaces. During action they reach high velocities, while the power/weight and power/volume rations reach high levels. The main drawbacks of PMAs are limited contraction (relative displacement), nonlinear and time variable behaviour, existence of hysteresis and step-jump pressure (to start radial diaphragm deformation) and also antagonistic connection of PMAs to generate two-direction motion. These make PMAs difficult to modelling and control. In this paper a new stiffness model and the variable-stiffness spring-like characteristics are described and tested using two Fluidic Muscles made by Festo Company. The muscles have the same diameter, but different length.