Multimodal Deformation in Tensegrity Manipulators: Preprogrammable Bend-Twist Modules for Dexterous Grasping Inspired by Elephant Trunks

Tensegrity-based continuum manipulators (TCMs) are rigid-flexible coupling mechanisms that show great promise for applications in unstructured environments by actively or passively conforming to objects. However, the coupling effects of TCMs require significant effort in resolving the actuation redundancy for performing dexterous manipulation tasks. Inspired by the functions of the elephant trunk, this article proposes a modular TCM composed of preprogrammable bend-twist modules (PBTMs) that employ enhanced segmented actuation. This actuation strategy effectively decouples adjacent segments and separates curvature and directional control, simplifying both mechanical integration and control implementation. By designing a preprogramming template attached to the end module, various twisting motions can be achieved <i>in situ</i>, achieving the multimodal deformation of the PBTM. In this setup, the manipulator is capable of bending or twisting in various planes, enabling the manipulator to better conform with objects of varying shape and pose. Then, we derived a dynamic model in terms of natural coordinates with clustered cable (CTC) elements to predict the configuration of the manipulator. Based on the numerical results, we analyze the effect of the CTCs' rest length on the cable slack phenomenon during the bending motion, as well as the <i>in situ</i> preprogrammed twist motion of the manipulator. Finally, we fabricated a manipulator prototype consisting of two PBTMs and showcased its versatile multimodal deformation in experimental scenarios for object wrapping and obstacle avoidance. The experimental results demonstrate that our proposed modular TCM provides a feasible paradigm, which reduces the control complexity of the continuum manipulator system.