Design and Analysis of High-Stiffness Hyperredundant Manipulator With Sigma-Shaped Wire Path and Rolling Joints

High stiffness is desirable for wire-driven underactuated hyperredundant manipulators used in minimally invasive surgery. However, limited structural stiffness can cause lateral and angular deflections by the lateral force and moment applied to the distal end of the manipulator. This letter proposes a Σ-shaped wire path, which is a combination of parallel and convergent wire paths, for a hyperredundant manipulator with rolling joints. The Σ-shaped wire path applied to the manipulator has the ability to maintain the position and orientation of its distal end for an applied lateral force on the surgical instrument tip. The simple mechanics of deflection of the manipulator with the Σ-shaped wire path are described, and straight-pose experiments were conducted to verify the deflection characteristics of the Σ-shaped wire path. An arbitrary bending-pose experiment was also conducted to verify the stiffness performance. It was observed that the proposed method could enhance the stiffness of the manipulator in both straight and arbitrarily bent poses.