  This paper aims to study a specific kind of parallel robot: Spherical
Parallel Manipulators (SPM) that are capable of unlimited rolling. A focus is
made on the kinematics of such mechanisms, especially taking into account
uncertainties (e.g. on conception & fabrication parameters, measures) and their
propagations. Such considerations are crucial if we want to control our robot
correctly without any undesirable behavior in its workspace (e.g. effects of
singularities). In this paper, we will consider two different approaches to
study the kinematics and the singularities of the robot of interest: symbolic
and semi-numerical. By doing so, we can compute a singularity-free zone in the
work- and joint spaces, considering given uncertainties on the parameters. In
this zone, we can use any control law to inertially stabilize the upper
platform of the robot.
