CONTACT TRANSITION CONTROL WITH SEMIACTIVE SOFT FINGERTIPS

We address the problem of controlling contact forces generated when th e fingers of a robot close on an object or make contact with surfaces in the robot's environment. The use of controllable fingertip material s is proposed to enhance system performance and avoid contact instabil ity problems that can arise with noncollocated sensors and actuators. We describe a novel fingertip employing an electrorheological fluid an d present the results of experiments to evaluate its capabilities when used with a robot contacting a stationary object at various speeds. H aving characterized the fingertip behavior as a function of applied vo ltage, we turn to the question of optimal control. Using a simplified dynamic model of a robot equipped with a controllable electrorheologic al fingertip, we obtain a piece-wise optimal solution for the fingerti p damping as a function of time, to minimize settling time while satis fying constraints on the contact forces.