Cooperative and robust object handling by multiple manipulators based on the differential equation approximator.

The problem of transporting a rigid object by a team of robotic arms is studied in this article. The study aims to enable manipulators to move the object in the desired and predefined direction efficiently. It is also desired to keep the force applied to the object limited to avoid distortion of its shape. Since practical systems usually confront limitations such as lack of complete system model information and disturbances, the presented approach should confront the effects of such phenomena on the performance. To fulfill the purpose, based on the universal approximation property, a powerful approximator for estimating uncertainties and disturbances based on differential equations is presented. Then a robust approximator-controller structure is designed to solve the multi-objective issue of position, orientation, and force control in the cooperating robotic system. To confirm a stable object grasp, and transportation, Lyapunov analysis is utilized and based on a thorough mathematical analysis, it is shown that the presented approximator-controller structure assures system stability. Finally, the proposed scheme is applied to two three-degree-of-freedom (3-DOF) robot arms that cooperatively handle a common and rigid object. Various tests are performed assuming the unavailability of system model information and in the existence of perturbations, and the results are analyzed.