Real-time control of geometry and stiffness in adaptive structures

Abstract

Adaptive structures are those which can adjust their geometry, stiffness and damping on demand to] meet the changes in their loading environment. With the advents in the piezo-electric device and composite material technologies, such structures are already being considered seriously in aero-space industry. The success of these structures depends largely on the effective control of the structure through the actuators, and the sensors embedded in their load carrying members. This work outlines the basic theory for the geometry, stiffness and damping control. Necessary and sufficient conditions for stress free geometry control in statically determinate and indeterminate adaptive discrete structures are given. In particular, for the subset of discrete adaptive structures viz. adaptive truss structures the equations similar to the forward and inverse kinematic equations of open loop mechanical manipulators are derived. These equations describe the large geometry control under show motion (i.e., no inertia forces) assumption. Two criteria for choosing the optimum control from among the possible ones are established. A fast algorithm based on variable order variable step multistep method is given that can compute the controls for a large maneuver in real-time. Numerical results from the algorithm are presented. As an example of damping and stiffness alteration on demand, the vibration control in adaptive trusses by means of elongations and elongation-rates of the active elements is also given.