Abstract
The force controlled robots can recognize the relations between their hands and the external objects, directly or indirectly, by measuring the elastic distortions of their wrists or arms, and can adapt themselves to unknown situations. For example, in the assembly process where the robot inserts a peg into a hole, a reaction force from the peg implies an indication of how much the peg is off the center while being pushed into the hole.
In such a case, if not only the prehension force but also the prehension stiffness are variable, the force controlled robots will be versatile. We propose a robot hand of which the prehension stiffness is adjustable, according to the shape of a work piece and the content of a job. Our robot hand has three elastic fingers, where each finger can be individually driven by a pulse motor through a coil spring. And the apparent stiffnesses of the coil springs are changeable arbitrarily, by the special control algorithm of finger forces.
After describing the algorithm, the analysis of the prehension system and the physical meaning of the system parameters are discussed. Subsequently we derive the method of the parameter adjustment in order to realize arbitrary prehension forces and stiffnesses. Finally the theoretical results and the usefulness of this control method are confirmed through the experiment by the developed robot hand.
