A smooth robust control approach to cooperation of multiple robot manipulators

By fully utilizing the properties of the nonlinear dynamics of the system of the multiple cooperating robots with a commonly held object, we propose in this paper a smooth robust controller for trajectory tracking control of the object as well as control of the squeeze force exerted on the object. The controller is robust with respect to unknown robot link masses, unknown object mass and unknown joint stick-slip friction. Moreover, the need to measure the joint acceleration or calculate the derivative of the contact force is eliminated in the proposed control design. Unlike other robust controllers, the proposed controller is continuously differentiable, thus ensures smooth control input. Lyapunov's direct method has been employed to prove the global asymptotic stability of the closed-loop system. A numerical example of the proposed controller applied to a two-robot system is presented as an illustration