comment-itra98

\Copyright 1999 IEEE. Personal use of this material is permitted. However, permission to reprint/republish thismaterial for advertising or promotional purposes or for creating new collective works for resale or redistribution toservers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."Accepted for publication in IEEE Transactions on Robotics and Automation, 1999Comments on \Closed Form Forward KinematicsSolution to a Class of Hexapod Robots" yHerman Bruyninckx, Joris De SchutterKatholieke Universiteit Leuven, Dept. Mechanical EngineeringCelestijnenlaan 300B, B-3001 Heverlee, BelgiumAbstractThe paper [8] by Yang and Geng presents a class of parallel manipulators that has an e cient closedform solution to its forward kinematics. This Correspondence points to some missing insights in that paper(and in many others), especially with respect to singular con gurations.KeywordsParallel manipulators, closed form solutions, singularities.1 IntroductionMost literature on parallel manipulators considers so-called Stewart-Gough platforms, i.e., a xed base and amoving end e ector are connected by six prismatic, actuated \legs" attached to base and end e ector by meansof universal and/or spherical joints. It is well known that the forward kinematics of arbitrary Stewart-Goughplatforms are di cult to solve. However, these kinematics become much easier for some special geometries. Thecited paper, [8], proposes ...