An active-constraint robot, particularly for surgical use, is controlled by means of a series of motorized joints to provide a surgeon with real-time tactile feedback of an operation in progress. In continuous manufacturing of liquid-crystal display elements, the present invention can dramatically enhance product accuracy and manufacturing speed and drastically improve product yield. By using a current limit reference voltage that has two levels, the power switch 90 has two current limit thresholds. The call could be any call that a mobile handset user wants to send location information to the party that has been called. The processing electronics can then accurately determine the distance between the missile and the beam from the phase shift and correct the missile’s trajectory to maintain its position with respect to the beam.