Abstract
A dynamic model of swing system of bridge-type ship unloader is established by considering the elastic factor of wire rope in this paper. Based on this model, an improved Negative Zero Vibration (NZV) shaper with optimal control parameters of variable rope length system is proposed to restrain the swing of grab. Then the control effects, influence of elasticity factor and parameter sensitivities are analyzed based on numerical simulation. The results show that the proposed control strategy can reduce the working cycle time of the grab ship unloader about 11% when considering the elastic factor of the wire rope, and the grab's maximum residual swing angle decreases by 67% when discharging at full load, and decreases by 79% when taking the cargos at empty load. This implies that the improved NZV control method provides better swing angle control performance and shorter operation time compared with the Zero Vibration (ZV) and Zero Vibration and Derivative (ZVD) methods. Moreover, elastic rope model can improve the swing angle control effect of grab based on the proposed control strategy compared with rigid rope model. The parameter sensitivity analysis displays that the grab's maximum residual swing angle by using the improved NZV method is sensitive to the change of the grab's center of gravity, and this angle is more sensitive to the wire rope diameter deviation compared with the elastic modulus deviation.
Highlights
The hoisting swing of crane will seriously affect its efficiency and even induce safety problems
Compared with the Zero Vibration (ZV) control method, the maximum residual swing angle of grab with the Negative Zero Vibration (NZV) control method decreases by 67% when discharging at full load, and it decreases by 79% when taking the cargos at empty load
This paper proposes an improved NZV input shaper with the optimal control parameters of the variable rope length to improve swing control precision and the efficiency of bridge type grab ship unloader
Summary
The hoisting swing of crane will seriously affect its efficiency and even induce safety problems. Zhou et al [24] proposed an improved ZV method to control the payload swing of grab ship unloader considering single pendulum model with variable rope length. This paper studies the dynamics of swing system of bridge-type ship unloader by considering the elastic factor of wire rope, and an improved Negative Zero Vibration (NZV) input shaper for. The dynamic model of the trolley-grab swing system with the elastic wire rope is obtained as shown, in which, Og(xg, yg) is the center of gravity for the grab; mt is the quality of the trolley; mg is the quality of the grab; u is the angle between the wire rope and the vertical direction; k1 is the stiffness coefficient of the lifting rope; b1 is the damping coefficient of the lifting rope; l is the length of the hoisting rope for a certain moment; h is the amplitude of the grab along the direction of lifting rope due to the rope elasticity; Mhd, Jhd, ’hd, and rhd are driving torque, moment of inertia, angular displacement and radius of fixed pulley (drum) respectively; f is friction. If the equation (12) does not consider the elasticity factor of the wire rope and the radius of the lifting drum, it is consistent with the motion differential equation of undamped system of existing single pendulum model
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