In robotic single-port surgery, it is desirable for a manipulator to exhibit the property of variable stiffness. Small-port incisions may require both high flexibility of the manipulator for safety purposes, as well as high structural stiffness for operational precision and high payload capability. This paper presents a new hyperredundant tubular manipulator with a variable neutral-line mechanisms and adjustable stiffness. A unique asymmetric arrangement of the tendons and the links realizes both articulation of the manipulator and continuous stiffness modulation. This asymmetric motion of the manipulator is compensated by a novel actuation mechanism without affecting its structural stiffness. The paper describes the basic mechanics of the variable neutral-line manipulator, and its stiffness characteristics. Simulation and experimental results verify the performance of the proposed mechanism.

This paper presents a novel “layer jamming” mechanism that can achieve variable stiffness. The layer jamming mechanism exploits the friction present between layers of thin material, which can be controlled by a confining pressure. Due to the mechanism's hollow geometry, compact size, and light weight, it is well suited for various minimally invasive surgery applications, where stiffness change is required. This paper describes the concept, the mathematical model, and a tubular snake-like manipulator prototype. Various characteristics of layer jamming, such as stiffness and yield strength, are studied both theoretically and experimentally.

This paper introduces a new mechanism for achieving tunable stiffness, named layer jamming, and presents a hollow snake-like manipulator having tunable stiffness capability. The layer jamming mechanism is composed of multiple layers of thin Mylar film, and makes use of amplified friction between the films by applying vacuum pressure. In contrast to other tunable stiffness technology, such as particle jamming or field-activated materials (MR or ER fluids), layer jamming occupies a small volume and thus can be applied to small, light weight manipulators. The snake-like manipulator presented here is composed only of Mylar film and wires, and has highly flexible and under-actuated properties without application of a vacuum; however, it becomes highly stiff when a vacuum is applied. In this paper the characteristics of layer jamming are explored: its stiffness and breaking strength are obtained both theoretically and experimentally, and a prototype manipulator is developed and experimentally characterized.