Modeling and control alternatives for robots in dynamic cooperation

A general control-oriented formalism has been introduced by DeLuca and Manes (1991, 1994) to describe robot-environment interaction in the case of a single robot in contact with a possibly dynamic environment. Two possibilities were obtained in the design of hybrid motion-force control laws depending on whether motion or force is explicitly controlled along properly defined dynamic directions. An extension of this formalism for modeling and controlling cooperating robots in the manipulation of a payload is presented. Several contact arrangements and environmental constraints on the object can be considered, mixing the presence of kinematic constraints and dynamic interactions. The modeling approach leads to the characterization of complementary directions in the task space: those where only end-effector velocities are admissible, those where only reaction forces may exist, and those in which energy can be transferred between each robot and the payload. Two classes of model-based hybrid force-motion controllers are then designed similarly to the single robot case. The authors show that the classical approach of controlling payload motion and internal forces for cooperating robots is recovered as one special case. Moreover, within this framework a new control alternative naturally arises, namely the possibility of controlling both internal forces and active forces producing motion. Numerical simulation results are reported for power grasp and hard finger point contacts and with the two alternative control laws