Vertical Motion Control of Crane Without Load Position Information Using Nonlinear Control Theory

When a load is lifted by a crane system, the load position may be unexpectedly vertically vibrated due to the elasticity of the rope. This problem reduces the system stability and load positioning accuracy. To resolve this actual problem, this paper describes a model for studying the dynamic behavior of the offshore crane system such that a control system design method is introduced to occupy desirable performance. The obtained model allows evaluating the fluctuations of the load arising from the elasticity of the rope. In addition, the rope is modeled as a mass-damper-spring system, and the winch as the main actuator coefficients are identified via experiments and simulation. Especially, in this paper, the authors design a control system in which winch a rotation angle and a rope tension are used to make control signals without load position information. In the real plants, the load position cannot be accurately measured because the load type is various and other environmental constraints. Considering these facts, the controller design based on input-output feedback linearization theory is presented which can handle the effect of the elasticity of the rope and track the load target trajectory. Besides that, for comparison study, a full order observer is designed to estimate unknown states. Finally, the experimental results show that the proposed method can successfully make something good control performance.