Smooth robust control of cooperating robot manipulators handling a constrained object

In this paper, by fully utilizing the properties of the system of multiple cooperating robots handling a constrained object, we propose a general approach, employing time-varying smooth robust compensators, to simultaneously control the position of the object, the interaction force between the object and the environment, as well as the “squeeze” force exerted on the object. The adverse effects caused by unknown robot link masses, unknown object mass and unknown stick-slip friction forces both at the internal robot joints and on the environmental contact surface can be compensated. Unlike other robust controllers, the proposed one is continuously differentiable, thus ensuring a smooth control input. Lyapunov´s direct method has been employed to prove the global asymptotic stability of the closed-loop system