“…On the other hand, the representation using unit quaternions, which is employed in this work, constitutes a singularity-free orientation representation, without complicating the control design. Unit quaternions are employed in (Campa et al, 2006;Caccavale et al, 2000Caccavale et al, , 2008Aghili, 2011) for manipulation tasks and in (Erhart and Hirche, 2016) for the analysis of the interaction dynamics in cooperative manipulation.…”