Shape change algorithm for a tensegrity device

Abstract

Tensegrity devices are special truss-like structures composed of struts in compression and cables in tension. In order to keep a tensegrity device rigid, its members must be prestressed. By using actuators to vary the lengths of the struts and cables a tensegrity devices can reconfigure its geometry i.e., change its shape. This ability makes tensegrity devices suited for applications such as self deploying structures, smart structures and even robots. Two key steps in the reconfiguration of tensegrity devices are form-finding, the process of identifying the geometries in which all the device's members are stressed known as its singular configurations, and shape change, the process of moving the device from one singular configuration to another without loosing its stiffness. Current known shape change methods rely heavily on time and processing power costly methods, like simulations and large scale optimizations, for these steps. This work presents a new shape change control strategy which is based on the special properties of Assur Trusses. The concept of Assur Trusses (also known as Assur Graphs), long known in the field of kinematics, has recently been reformulated by mathematicians from rigidity theory community, and new theorems and algorithms have been developed. The control strategy developed during the research is fast and does not require a lot of processing power. This strategy is applicable to any device whose topology is an Assur Graph, of which there is an infinite number. The proposed shape change algorithm allows the device to move from one singular position to another while maintaining its stiffness at all times. The shape change is accomplished by changing the length of the device's actuated members.