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Abstract-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, and high structural stiffness for operational precision and high payload capability. This paper presents a new hyper-redundant 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.Index Terms -Variable neutral-line mechanism, snake-like manipulator, adjustable stiffness, medical robot.

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This paper presents a new method to identify the primary workspace of six-link industrial robots with Roll-Pitch-Yaw wrists in conjunction with four basic types of regional structures: the Cartesian, the cylindrical, the spherical and the articulated. The approach is to divide a robot into two subsystems, the regional structure and the wrist. Each subsystem is studied independently and then reassembled via a vector field analysis. Geometrical criteria are established to determine whether or not the kinematic connection between the wrist and the regional structure is valid. Conditions for a robot to access a point from a specified direction are derived first. The primary workpoints are then identified. Consequently, the boundaries of the primary workspaces (on the conservative side) of robots with Roll-Pitch-Yaw wrists, for the first time, can be analytically drawn. Some regional structures adopted in commercial robots which differ slightly from the standard ones are also included.

This paper presents an analytical study on the primary workspace of some simple six-link robots. The approach is to divide the structure of a six-link robot into two subsystems, the regional structure and the wrist. Taking advantage of the kinematic simplicity of three-link subsystems, we at the same time are able to solve the problem of reassemblage of the subsystems by using the concept of vector fields at the connection. Two types of wrist, the Euler Angle wrist and the Roll-Pitch-Yaw wrist are considered. (For Roll-Pitch-Yaw wrist, only Cartesian and articulated regional structures are included). Criteria for these robots to access points from specific directions are firstly developed. The theorems regarding accessing points from all directions are then derived. Finally clean statements on the boundaries of primary workspace are made.