Closed loop position and pre-stress control for a morphing aircraft wing with distributed multi-axis pneumatic actuation

This paper presents the design and control of a morphing wing structure using an active tensegrity structure. A tensegrity structure, which is a set of compressive members (struts) stabilized by a set of tensile members (cables) is a good basis for creating a lightweight active structure, due to its potentially high stiffness-to-weight ratio, and the ease with which actuators can be embedded by replacing selected members in the structure. In this work, a multi-axis control scheme is developed for closed loop control of the shape and internal force (pre-stress) of the structure. An experimental prototype has been built, with 6 unidirectional pneumatic cylinders controlled by pulse-width-modulated switching valves. Shape change in terms of twisting and span-wise bending are demonstrated, and an optical motion tracking system is used to help investigate the dynamic position control of the structure. The structure can achieve ±15° twist change for wing angle of attack or ±10° span-wise bending in a 300mm span length. By simultaneously controlling the structural pre-stress, the geometric stiffness of the structure can also be varied. Future research is discussed, which will involve embedding the active structure in a wing aerofoil and testing in a wind tunnel.