  This work investigates new kinematic features of parallel manipulators. It is
well known that parallel manipulators admit generally several direct kinematic
solutions for a given set of input joint values. The aim of this paper is to
characterize the uniqueness domains in the workspace of parallel manipulators,
as well as their image in the joint space. The study focuses on the most usual
case of parallel manipulators with only one inverse kinematic solution. The
notion of aspect introduced for serial manipulators in [Borrel 86] is redefined
for such parallel manipulators. Then, it is shown that it is possible to link
several solutions to the forward kinematic problem without meeting a
singularity, thus meaning that the aspects are not uniqueness domains. An
additional set of surfaces, namely the characteristic surfaces, are
characterized which divide the workspace into basic regions and yield new
uniqueness domains. This study is illustrated all along the paper with a 3-RPR
planar parallel manipulator. An octree model of spaces is used to compute the
joint space, the workspace and all other newly defined sets.
