  The aim of this paper is to characterize the moveability of fully-parallel
manipulators in the presence of obstacles. Fully parallel manipulators are used
in applications where accuracy, stiffness or high speeds and accelerations are
required \cite{Merlet:97}. However, one of its main drawbacks is a relatively
small workspace compared to the one of serial manipulators. This is due mainly
to the existence of potential internal collisions, and the existence of
singularities. In this paper, the notion of free aspect is defined which
permits to exhibit domains of the workspace and the joint space free of
singularity and collision. The main application of this study is the
moveability analysis in the workspace of the manipulator as well as
path-planning, control and design.
