AIAA 2004-1527 An Asymmetrically-Bistable Monolithic Energy-Storing Structure

The concept of binary robotic systems, in which continuous adaptive behaviour is approximated by the motion of a large number of discrete bistable elements, has created the need for fully-actuated structural bistable elements to be designed and manufactured. This paper discusses potential actuator technologies that could be suitable for such a design, and covers in detail the development, analysis and testing of a jumping bistable device. It is demonstrated that the symmetry of the structure's bistable behaviour has important implications for the selection of driving actuators. Additionally, it is shown that good predictions of the attained jump height, and hence the energy storage characteristics of the element may be made. The monolithic nature of the structure proposed is a distinct advantage over previous structures for integration into a binary robotic system. A novel approach to the design of variable-configuration, or adaptive structures is derived from the concept of binary robotic systems [1], i.e. robots that contain a number of two-state " binary " actuators. The idea is to approximate the continuous shape variation of a conventional adaptive structure by means of a large number of discrete configurations. This approach presents several advantages, in particular the reduction in the need for extensive feedback control: a bistable structural element can only be in one of its two stable states, as any intermediate configuration is unstable, and so a structure made of bistable elements can have only a finite number of configurations. Additionally, there is no requirement for power to be maintained to the actuators in order to hold the structure in any of its configurations. Finally, binary robotic systems can potentially be made from very low-cost components, as is already demonstrated by the existence of a vast number of bistable gadgets that one comes across every day. In November 2002, a meeting was held between the Deployable Structures Laboratory (DSL) of Cam-bridge University and the Field Space and Robotics Laboratory (FSRL) of the Massachusetts Institute of Technology (MIT), to discuss advances in the actu-ation of bistable mechanisms. The outcome of this meeting was the following design challenge, set to both groups: to design and construct a fully actu-ated bistable structure (of approximately 100 mm × 100 mm), capable of doing useful work over the transition between its stable states. As a demonstration of this ability to do useful work, it was required that the structure be able to jump at least 100 …