Design of soft robotic actuators using fluid-filled fiber-reinforced elastomeric enclosures in parallel combinations

Complex controlled motions, soft human interaction, and minimal moving mass all drive the need for soft robots using fluid filled fiber reinforced elastomer enclosures (FREEs). While a narrow class of FREEs known as McKibben´s actuators have been extensively studied, there is a wide unexplored class with complex sets of motion patterns. Combining these actuators in parallel can yield versatile motion patterns resulting in a large overall workspace. Mobility of individual actuators is enforced by inextensibility of fibers and incompressibility of fluids, which in turn drives the net attainable motions. In this paper, we map the mobility of individual FREE actuators to all possible resultant motions that a combination of three sets of actuators arranged in a triangular configuration would undergo. This understanding has resulted in a preliminary design tool that determines individual FREE topologies for a required set of motion patterns. Five case studies that result from this methodology are prototyped and tested for comparison of the predicted and obtained motion directions.