ACTUATION STRATEGIES FOR NEUTRALLY STABLE COMPOSITE TAPE-SPRINGS

摘要

The unique properties of neutrally stable structures suggest a new class of efficient large motion monolithic actuators. Neutrally stable structures are engineered so that stresses due to elastic deformations are balanced during motion and neither aid nor resist actuation. This is in contrast to a bulk material piezoelectric actuator, which is limited to relatively small motions due to the actuator material elastic stiffness. This paper investigates actuation strategies for a recently devised neutrally stable structure, composite tape-springs for deployable space structures. The tape-springs can use a variety of combinations of material orthotropy and prestress to achieve their neutral stability. Additionally, there are several options for incorporation of an actuation material. The best choice among these options is not obvious. An analysis methodology based on classical laminate theory is presented that predicts the neutral stability and actuation characteristics of appropriately prestressed orthotropic laminates. The methodology is used to compare several tape-spring fabrication and Nickel-Titanium (NiTi) shape memory alloy actuation configurations. Experimental results for the best determined configuration are presented and compared to the analytical predictions.