Dynamic Manipulation and Stiffness Modulation of Cooperative Continuum Robots: Theory and Experiment

Cooperative continuum robots (CCRs) are composed of multiple coupled continuum arms to cooperatively conduct manipulation tasks. They can highly enhance the performance of individual continuum arms by providing extra stiffness, leading to increased accuracy, payload capacity, and dynamic stability of the robot. This study aimed to investigate the stiffness analysis of tendon-driven supportive-type CCRs (S-CCRs). For this purpose, first, a generalized framework for the dynamic mathematical formulation and numerical solution of S-CCRs was proposed and their dynamic response to complex scenarios was obtained and the accuracy of the model was experimentally evaluated. Then, the capability of stiffness modulation of S-CCRs was studied. Tendon-driven S-CCRs are potentially capable of changing the stiffness with structural configuration, providing active stiffness control at the design level. Hence, in this study, the effects of the connection point location/angle of the supportive arms to the operative arm, as well as the imposed tendon limitations of the supportive arm on the stiffness of the robot, and consequently on the dynamic payload manipulation were studied and practical solutions were proposed to develop a simple but effective stiffness control mechanism. It showed that a typical S-CCR can increase its stiffness, just by a modular connector design up to 84% during manipulation, bringing a novel opportunity for stiffness modulation of CCRs.