Compact and lightweight variable stiffness mechanism using elastic band for medical robots

Current surgical robots for Minimally Invasive Surgery are generally rigid to achieve tasks with high precision. Therefore, there is a risk of injury to surrounding organs due to unexpected contact (e.g., while the surgical tool is invisible from the endoscopic view). In order to solve this problem, we introduce a Variable Stiffness Mechanism (VSM) that can actively change the joint stiffness of manipulator according to the situation. Although a number of studies have been conducted to provide VSM, it is difficult to implement them for surgical application where compactness and lightweight with a sufficient range of variable stiffness are required for not impeding the surrounding medical staffs and environment. In this study, we propose a new VSM that utilizes large deformation of elastic bands. The proposed mechanism let the stiffness be variable by changing the effective length of the elastic band shaped as a part of ring, minimizing the size and weight of the structure. The preliminary experiments showed the stiffness was successfully changed linearly, although the demonstrated range of stiffness was smaller than the previously presented VSMs. The reason of the limited range of stiffness was identified as the prototype implementation, and found to be further improved in the next research step.