Dynamic hybrid control of cooperating robots by nonlinear inversion

Abstract The manipulation of a rigid object by two cooperating robots is considered. If only the position of the object is of interest, the inverse dynamic problem is redundant, because the number of available actuators exceeds the number of degrees of freedom of the object. Introducing the internal force developed in the object as a controlled quantity removes this redundancy. In the present formulation the system is viewed as a closed mechanical chain, but with elastic restraint between the object and the hands of the robots. The inclusion of this compliance in the mathematical model makes it possible to have the internal force as an output of the system and to solve the inverse dynamic problem taking it into account. A solution is derived based on nonlinear inversion. It is shown that the system has relative or tracking order four, and a left-inverse system, which has as input the object position and the internal force and as output the actuator torques, is constructed.