Contact transition control with semiactive soft fingertips

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