Design of a tracking controller for cooperating hydraulic manipulators handling a rigid object

This paper addresses the problem of tracking control of multiple hydraulic manipulators handling a rigid object while sharing the load and maintaining an acceptable internal force on the object. The parasitic effect of friction in the actuators, as well as parametric uncertainties in the manipulators´ dynamics, hydraulic functions and the payload, is considered through augmentation of the controller by a set of on-line updating laws. Additionally, an adaptive observer is used along with the controller to avoid acceleration feedback, which could be difficult to obtain in practice. Using Lyapunov analysis, the position tracking error is proven to asymptotically converge to zero while the internal force remains bounded. Simulations are carried out using two MAGNUM hydraulic manipulators and the results clearly illustrate the effectiveness of the developed controller