Evaluating Mobility Behavior of Fluid Filled Fiber-Reinforced Elastomeric Enclosures

Abstract

Fluid filled Fiber Reinforced Elastomeric Enclosures (FREE) have been popular choices for actuators in prosthetics and soft robots owing to their large power density and cost effective manufacturing. While a narrow class of FREEs known as McKibben’s actuators have been extensively studied, there is a wide unexplored class that could be potentially used as actuators and load bearing members. This paper analyzes the mobility of a large class of FREEs based on simple geometric relationships that originate due to the inextensibility of fibers and incompressibility of fluids. The analysis conducted on various families of fibers reveal certain configurations that are locked under fluidic actuation. Furthermore the analysis reveals unrestricted motion in certain directions (freedom) and restrictions in certain other directions (constraint). Such an analysis is deemed to be useful as a preliminary design tool to pick the appropriate geometry for use in design of soft robots and actuators.