Energetic and Dynamic Effects of Operating Fluid on Fluidic Artificial Muscle Actuators

Pneumatic artificial muscles (PAMs) are a relatively common type of lightweight, fluid power actuation. Some disadvantages of PAMs include the compressibility of the working fluid and low damping. These characteristics result in low efficiencies, poor dynamic response, as well as undesired oscillations of the actuators. This paper presents utilizing hydraulic liquid as the working fluid instead of compressed air. Hydraulic operation resulted in almost triple the efficiency of pneumatic operation. The artificial muscles are experimentally characterized both quasi-statically and dynamically. The quasi-static experiments include the tension-strain relationship as a function of pressure, and an actuator net work efficiency analysis. The dynamic tests consist of a free vibration experiment to determine the change in effective spring constant and damping terms. These experiments are conducted for both PAMs and HAMs (hydraulic artificial muscles), and the results are presented herein.