The effect of scaling on the performance of elastomer composite actuators

Compact actuation that is integrated into a structure's material system has the potential to provide rapid structural reconfiguration while reducing weight. The effect of scale (diameter, overall length and segment length) on the performance of cylindrical fiber-reinforced McKibben-like Rubber Muscle Actuators (RMA) was investigated. An "activation" pressure was observed for all actuators at a value that depended upon the actuation construction. Upon pressurization past the activation threshold, the overall force, stroke, and work capacity increased with increasing actuation length and diameter. The actuation force per unit RMA cross-sectional area was predicted, and experimentally observed, to be roughly constant after activation. By segmenting a longer actuator, a larger contraction and lower actuation force could be achieved. Though actuation forces decreased as actuator diameter and length decreased, the force per unit actuator volume was shown to increase with decreasing diameter including a roughly 4-fold increase in force/volume between the 0.5" and 0.05" actuators. However, due to the small amount of total contraction for the smaller diameter actuators, the relative work per actuation volume was decreased by roughly 35% in comparing those same actuators. Thus, small diameter RMAs have great potential to provide needed linear actuation force within adaptive material systems.