The movement of rotation of each element of the manipulator arm about the shoulder, elbow and wrist pins is controlled by a motor and a cable consisting of two oppositely-acting lengths by means of a pulley-block which carries at least two lengths, two pairs of pulley-blocks being located within a barrel...http://www.google.fr/patents/US4078670?utm_source=gb-gplus-shareBrevet US4078670 - Cable-operated power manipulator
