Parallel robots enjoy enhanced mechanical characteristics that have to be contrasted with a more complicated design. In particular, they often have parallel singularities at some poses, and the robot may become uncontrollable, and could even be damaged, in such configurations. The computation of singularity free sets of reachable poses, called generalized aspects, is therefore a key issue in their design. A new methodology based on numerical constraint programming is proposed to compute a certified enclosure of such generalized aspects which fully automatically applies to arbitrary robot kinematic model.