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.

Design Strategy for a Surgical Manipulator based on a Compliant Mechanism : Rigidity and Range of Motion: Finding the Optimized Balance Compliant mechanisms have drawn the attention recently in developing surgical robotic manipulators for minimally invasive surgery (MIS) owing to their capabilities in making miniaturized, simple, dexterous mechanical structures. Robotically assisted MIS demands instruments with higher precision, higher output force and a higher range of motion (ROM) for better performances. On the other hand, because of the behaviour of the elastic elements, compromising these factors is challenging. In a compliant mechanism, the rigidity of the elastic element determines the precision and output force. In this paper, we study the behaviour of rigidity and the ROM of elastic elements using previously developed surgical robotic forceps based on a compliant mechanism. To tackle this problem, we studied the variation of ROM of the compliant mechanism at different rigidity values of the compliant structure by changing its thickness. The results showed the linear relationship between the ROM and the rigidity of a compliant mechanical manipulator, suggesting the optimized balance point in this tradeoff.