Robust Control of Friction-Driven Reconfigurable Adaptive Structures

Traditional design methods for engineering applications aim to achieve optimal performance for specific conditions or moderate performance for a broader range of conditions. However, the optimal performance for a wide spectrum of situations can be facilitated if such systems possess reconfiguration capability. It can be illustrated in the example of structures with steerable joints, which is a popular approach in robotics. By rotating the joints to a different degree, a plethora of resulting configurations can be achieved – configurations that might be specifically suited for the required conditions. Systems based on these principles can be implemented on the macroscopic level in adaptive facades, on the mesoscopic level in mechanical metamechanisms, and at the microscopic level in microelectromechanical devices. In general, adaptive structures often require numerous actuators to facilitate a wide range of reachable configurations, leading to increasing energy demands as the system size increases. This can be seen in the case of robotics when each joint can be independently actively rotated to drive the motion corresponding to the specific degree of freedom. This paper analyzes an alternative situation, when the joins are semi-active and can exist only in either a locked or unlocked state, with only one (last joint) being actively steered. In the ideal case, the energy should be consumed only for switching between states, while maintaining the state should be free with locking achieved via switchable friction. While theoretically improving energy efficiency, such a system makes it much more challenging to control the resulting shape of the structure as compared with its counterpart with actively rotating joints. In this paper, we develop a motion planning algorithm to facilitate the achievement of the desired shape via control over the state of the joints and the position of the last link. In particular, the change of shape is performed by a sequence of single-degree-of-freedom motions determined by a motion planning algorithm based on Rapidly exploring Random Trees and sub-slider-crank systems (RRT-SC). One application of the proposed method is evaluated for reconfigurable building facades and paves the way for the next generation of structures in smart cities.