Distributed Actuation and Control of a Morphing Tensegrity Structure

Abstract

Structures and actuation systems need to be closely integrated together in the future to create faster, more efficient, lightweight dynamic machines. Such actuated structures would be used for morphing aircraft wings, lightweight actuated space structures, or in robotics. This approach requires actuators to be distributed through the structure. A tensegrity structure is a very promising candidate for this future integration due to its potentially excellent stiffness and strength-to-weight ratio, and the inherent advantage of being a multi-element structure into which actuators can be embedded. This paper presents methods for analysis of the structure geometry, for closed-loop motion control, and includes experimental results for a structure actuated by lightweight pneumatic muscles. In a practical morphing tensegrity structure, it cannot be assumed that tension and compression members always meet at a point. Thus, a form-finding method has been developed to find stable geometries and determine stiffness properties for tensegrity structures with nodes of finite dimension. An antagonistic multi-axis control scheme has been developed for the shape position and motion control. In the experimental actuated tensegrity system presented the pneumatic muscles are controlled by on-off valves, for which a dead-band switching controller is designed based on a new stability criterion. The experimental system demonstrates accurate control of shape change while maintaining a desired level of internal preload in a stiff structure, showing considerable promise for future lightweight dynamic machines.