  The aim of this paper is to characterize the notion of aspect 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. The
notion of aspect introduced for serial manipulators in [Borrel 86], and
redefined for parallel manipulators with only one inverse kinematic solution in
[Wenger 1997], is redefined for general fully parallel manipulators. 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 to
respectively define the parallel and the serial singularities. The notion of
working modes is introduced to separate inverse kinematic solutions. Thus, we
can find out domains of the workspace and the joint space exempt of
singularity. Application of this study is the moveability analysis in the
workspace of the manipulator as well as path-planing and control. This study is
illustrated in this paper with a RR-RRR planar parallel manipulator.
