Velocity analysis of parallel manipulators by truss transformations

A method of velocity analysis of general parallel manipulators is presented. The method consists of transforming the parallel manipulator to an equivalent variable-geometry truss (VGT), and then generating the set of linear velocity equations that govern the transformed manipulator. VGTs are a special class bf parallel manipulators. Their actuation is provided by extensible links terminating in spheric joints. A method for velocity analysis of VGT manipulators will be briefly reviewed. This method employs a connectivity chart to generate a system of linear algebraic equations for the manipulator velocity. In addition to the spheric joints and two-force member links that make up truss actuators, general parallel manipulators commonly contain revolute, prismatic, and cylindric joints and multi-force links, links that are more than two;force members. Further, a number of actuation schemes are possible. This work shows how such general parallel manipulators can be conceptually transformed into equivalent VGTs and thereby allow a straightforward velocity analysis approach. While this approach is applicable to general parallel manipulators, the method is most effective when applied to parallel manipulators with truss-like structures. (C) 1998 Elsevier Science Ltd. All rights reserved.