In order to provide operators with a force feedback during execution of some task, we use two haptic force feedback devices from Force Dimension (Switzerland), called Omega.3 and Omega.6. The Omega.3 consists of three motors and three position sensors. Depending on the Cartesian position of the end effector, a programmable Cartesian force can be applied to the users? hand, thereby allowing the force-feedback possibility. The Omega.6 differs from the former devise in the additional 3 measured (but not actuated) rotational degrees of freedom of the end-effector.