Working modes and aspects in fully parallel manipulators

The aim of this paper is to characterize the notion of aspects in the workspace and in the joint space for parallel manipulators. In opposite to the serial manipulators, the parallel manipulators can admit not only multiple inverse kinematic solutions, but also multiple direct kinematic solutions. Two Jacobian matrices appear in the kinematic relations between the joint-rate and the Cartesian-velocity vectors, which are called the "inverse kinematics" and the "direct kinematics" matrices. The study of these matrices allow one to define the parallel and the serial singularities respectively. The notion of working modes is introduced to separate inverse kinematic solutions. Thus we can find out the domains of the workspace and the joint space which exempt of singularity. An application of this study is the movability analysis in the workspace of the manipulator as well as the path-planning and control. This study is illustrated with a RR-RRR planar parallel manipulator.