“…Contour tracking is, on the contrary, an example of a complex task that requires the manipulator to continuously and autonomously modify its path, coping with the uncertainties typical of unstructured environments (Siciliano & Villani, 1999). In many applications a robot is required to follow a contour while applying a normal force; these tasks include grinding (Thomessen & Lien, 2000), deburring (Ferretti et al, 2000;Ziliani et al, 2005), shape recovery (Ahmad & Lee, 1990), polishing and kinematic calibration (Legnani et al, 2001). The problem of tracking (known and) unknown contours has been studied by many researchers in the last two decades.…”