Improvement of a Stiffness Tunable Mechanism by Design of Horizontally Asymmetrical Beam Structure

Stiffness tunable mechanisms are crucial for enhancing the noninvasiveness and stability of organ manipulation during laparoscopic surgeries. They allow for flexible adaptation to organ shapes in a low stiffness state, providing a larger grasping area, while maintaining high bending rigidity in a high stiffness state for stable force transmission. Our group developed a rapid pneumatical stiffness switching mechanism using identical two-beam structure, but the stiffness gain was insufficient for miniaturization. In this study, we improved the identical two-beam structure by proposing a horizontally asymmetrical beam structure, which is composed of differently shaped upper and lower beams. In the low stiffness state, the horizontally asymmetrical beam structure can satisfy the requirement of liver shape followability. In the high stiffness state, the horizontally asymmetrical beam structure achieves greater bending stiffness because the contact surface between the beams is shifted from the center—where shear forces are maximal—to the upper and lower ends, which reduces the slippery at the contact surface. Moreover, the horizontally asymmetrical beam structure maintains bending stiffness at any angle of bend. The new design improved the stiffness tunable mechanism by providing a higher stiffness gain and greater potential for miniaturization, which is necessary for being used by minimal invasive surgery assistant robot.