Offshore Crane Adaptive Control Without Velocity Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing control systems for offshore cranes face challenges in managing complex external disturbances, such as irregular waves and winds, leading to difficulty in payload positioning and sway suppression due to 6-degree-of-freedom motion, nonlinear characteristics, and the need for precise velocity feedback which is often unmeasurable and noisy.
Innovation Solution
A three-dimensional dynamic model is constructed using Lagrange modeling equations, incorporating roll and pitch motions, with an adaptive controller that replaces velocity feedback using auxiliary variables and inverse trigonometric saturation functions to achieve sway suppression and positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If velocity feedback is used in existing controllers, then control precision is improved, but measurement difficulty and system complexity increase due to unmeasurable and noisy velocity signals
Solution Approach 1:
The patent introduces auxiliary variables as intermediaries to replace the difficult-to-measure velocity signals. These auxiliary variables are constructed from position signals and control inputs, serving as substitutes that are easier to obtain while maintaining the necessary control information for the adaptive controller to function effectively.
Solution Approach 2:
The patent substitutes the mechanical/physical velocity measurement system with a computational approach. Instead of relying on direct velocity sensors or numerical differentiation of position signals (which amplify noise), the system uses auxiliary variables derived from the dynamic model and control inputs to represent velocity information computationally.
2Device complexity
If two-dimensional control systems are used, then controller design is simplified, but control effectiveness deteriorates due to inability to handle three-dimensional spatial motion and ship motions
Solution Approach 1:
The patent extends the control system from two-dimensional to three-dimensional by incorporating roll, pitch, and yaw motions of the ship into the dynamic model. This dimensional expansion allows the controller to handle the full complexity of spatial motion while maintaining adaptability through the adaptive control mechanism.
Solution Approach 2:
The patent employs adaptive control with time-varying parameters that can adjust to changing operating conditions. The controller dynamically adapts to the complex nonlinear dynamics of the offshore crane system under various sea states, making it versatile enough to handle three-dimensional motion without requiring overly complex fixed-structure control laws.
3Loss of information
If numerical differentiation is used to obtain velocity signals, then velocity information is obtained, but noise amplification increases affecting system stability and safety
Solution Approach 1:
The patent uses auxiliary variables as intermediaries that avoid the noise amplification problem of numerical differentiation. These auxiliary variables are constructed from smooth position signals and control inputs, providing velocity information without the noise amplification that plagues direct numerical differentiation approaches.
Solution Approach 2:
The patent replaces the noisy numerical differentiation process with a computational model-based approach. Instead of differentiating position signals directly (which amplifies noise), the system uses auxiliary variables derived from the dynamic model and control inputs to obtain velocity information in a noise-free manner.
Data Source
AI summary
An adaptive control method for offshore cranes without requiring velocity feedback, in which parameters of an offshore crane system are obtained, and a three-dimensional dynamic model of an offshore crane system is constructed based on ship's roll and pitch motions; a total energy function is constructed based on the three-dimensional dynamic model, and an energy change is described according to a change rate of a total energy of the offshore crane system; based on the three-dimensional dynamic model, auxiliary variables are constructed to replace a velocity signal of a state variable in a controller; based on an inverse trigonometric saturation function and the auxiliary variables, an adaptive controller without requiring velocity feedback is constructed; and the offshore crane system is controlled based on the adaptive controller for control to realize positioning and sway suppression. An adaptive control system is also provided.