Oscillation reduction for overhead cranes with time-varying payload and rope length

Abstract

The overhead crane system is widely used in industry to move heavy payloads. To meet safety requirements, the movement of the payload should be performed with small oscillations. However, in many situations the hoisting mechanism must lift and lower payloads to avoid obstacles during movement, which may excite oscillations if not properly controlled. On the other hand, in some applications, it is required to perform loading/unloading operations during the movement of the crane which will also induce payload swing if not effectively treated. In this paper, we consider both cases to allow the crane to have varying rope length to meet geometric constraints and to allow the payload to have time-varying mass. These two effects are considered as uncertainties in our design, and the control of this crane system becomes extremely difficult. The Olfati transformation is used firstly to represent the system as a special cascade form so that an adaptive control strategy can be proposed. The function approximation technique is employed to estimate time-varying uncertainties in the system. The closed loop stability is justified by the Lyapunov-like technique. Simulation cases show that the system is able to track the desired trajectory quickly without overshoot and the swing angle is very small regardless of various uncertainties. Some simple modification of the design can further improve the performance.