Merits concerning energy-consumption and trajectory-tracking accuracy derived from elbow-bracing robot

Considering that humans perform handwriting task with reduced powers by contacting elbow or wrist on a table, it is reasonable to deem that manipulators can save energy and simultaneously accomplish writing tasks precisely like humans by bracing intermediate links such as elbow or wrist. First this paper discusses equation of motion of robot under bracing constraint condition, based on the robot's dynamics with constraint condition including motor dynamics. Then a control method to utilize the constraint dynamics is proposed to control simultaneously bracing force and hand's trajectory in work space. Even though the model used for the simulation analyses is simple four-links manipulator, the simple structure can help understand even more clearly the effects got by bracing part of the manipulator. This paper demonstrates the merits of the strategy to utilize bracing by comparing the contacting motions with non-contacting motions, including; (1) the energy consumption can be reduced; (2) the hand trajectory tracking becomes accurate; (3) there is an optimum contacting point that minimize the energy consumption on condition that trajectory-tracking task be given to the hand.