Theory of Isotropic Transmission for Tendon-Driven Manipulators

This paper deals with the synthesis of the mechanical power transmission structure in tendon-driven manipulators. Based on the analysis of static force transmission from the actuator space to the end-effector space, a general theory is developed for the synthesis of tendon-driven manipulators with isotropic transmission characteristics. It is shown that an n-dof (degree of freedom) manipulator can possess these characteristics if it is made up of n+1 or 2n tendons and if its link lengths and pulley sizes are designed according to two equations of constraint. Two examples are used to demonstrate the theory. It is also shown that manipulators with an isotropic transmission structure do have more uniform force distribution among their tendons.

Geometry and Position Analysis of a Novel Class of Hybrid Manipulators

This paper presents a novel class of hybrid manipulators composed of two serially connected parallel mechanisms, each of which has three degrees of freedom. The lower and upper platforms respectively control the position and orientation of the end-effector. The advantages of this type of hybrid manipulator are larger workspace (as compared with parallel manipulators) and better rigidity and higher load-carrying capability (as compared with serial manipulators). The closed-form solutions of the forward and inverse position analyses are discussed. For forward position analysis, it is shown that the resultant equation for the positional mechanism is an 8-th order, a 6-th order, a 4-th order, or a 2-nd order polynomial, depending on the geometry and joint types of the passive subchain, while for the orientational mechanism, it is an 8-th order, or a 2-nd polynomial depending on the geometry. For inverse position analysis, it is demonstrated that the positional and orientational mechanisms both possess analytical closed-form solutions.

A Modular, Long-Reach, Truss-Type Manipulator for Waste Storage Tank Remediation

This paper will introduce a new type of modular manipulator system that is particularly well suited for performing long-reach, high-payload operations such as waste storage tank remediation. These new capabilities are achieved by employing an “all-truss” design in which discrete truss modules are used to construct a reconfigurable manipulator system. Each module of the manipulator is either a static truss “link” or one of several possible Variable Geometry Truss “joints.” This paper presents background information, system requirements, a description of the individual components used to construct the manipulator, and an overview of the kinematic analysis algorithms developed to address the redundant nature of the manipulator.

Identification for Manipulators With Joint Compliances and Link Deflections

An iterative forward transformation algorithm is developed to compute the pose at the end effector of a manipulator when subjected to joint compliances and link deflections. The algorithm is based on the homogeneous transformation matrices and a gravity term associated with each joint. In addition, an identification algorithm has been developed to determine the kinematic and structural parameters of a flexible manipulator used in the forward transformation algorithm. As most of the links of a manipulator are not simple beams, the identification algorithm is particular useful to obtain a set of correct parameters. Results of the simulation tests for a 6-DOF robot are shown to check these algorithms.

Emulating Micro-Gravity in Laboratory Studies of Space Robotics

Experimentally evaluating micro-gravity control and planning algorithms for space robotic systems on earth is difficult because gravity masks the more subtle dynamic forces which dominate in space. Previous experimental test beds for micro-gravity have been largely restricted to planar motion, or have other limitations. Recently developed is a fully spatial system called the VES which overcomes many of these problems. However, compensating for the effects of gravity with the VES is a challenge. Here, two methods of gravity compensation are presented which allow fully spatial emulation of the micro-gravity interaction between a space manipulator and its supporting structure or spacecraft. Experimental results show the effectiveness of the methods.