Delayed-reference anti-swing control of overhead crane systems

This paper presents a non-time based control strategy for the simultaneous path-tracking and swing control of overhead crane systems. The model of the system has four degrees of freedom (dofs): two dofs describe the crane motion, while a two-dof swing angle is associated to the suspended load motion. The basic idea behind the suggested control scheme, named delayed reference control (DRC), is to make the path reference of the crane a function of the difference between the time and a variable which plays the role of a time delay. This latter, which is affected by the measured oscillation, is properly calculated on- the-fly in order to reduce the swing phenomenon. The fundamental difference between the proposed scheme and the traditional ones is that it allows exerting the oscillation control while ensuring an accurate tracking of the desired path through space and the coordinated motion of the crane dofs. A significant advantage of the DRC scheme is its ease of implementation. As a matter of fact it can be employed by simply adding an outer loop to standard crane position controllers, as long as they ensure high dynamic response. The effectiveness of the proposed control scheme is demonstrated through numerical results.