Dual-Crane Ship Motion Compensation Control
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Solution Overview
Problem
Conventional single-jib cranes face challenges in handling larger loads due to limitations in size, shape, and weight, and existing technologies lack efficient methods for coordinated control of multiple cranes in marine environments with base motion disturbances, leading to difficulties in accurate cargo transfer and payload stabilization.
Innovation Solution
A dual-crane control scheme that actively adjusts geometric parameters such as luff angle and hoist line length to maintain static equilibrium of the load, detuning the system's natural frequency from base motion excitation, allowing for coordinated lifting operations in marine environments with minimal payload swing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single-jib crane is used for cargo transfer, then the crane system is simple to operate, but it cannot handle larger loads that require multiple cranes
Solution Approach 1:
The patent combines multiple crane systems into a coordinated team-lift operation, where two or more cranes work together under a unified control algorithm to handle oversized and overweight cargo that exceeds the capacity of individual cranes
2Device complexity
If conventional crane control methods are used in marine environments, then the control system is simple, but payload pendulation increases due to ship motion disturbances
Solution Approach 1:
The control algorithm continuously receives feedback from sensors monitoring payload position, crane geometry, and ship motion, then dynamically adjusts crane commands to counteract pendulation and maintain payload stability during cargo transfer operations in marine environments
Solution Approach 2:
The system dynamically changes control parameters including hoist line length, boom angle, and slew rate based on real-time conditions such as ship motion state and payload position, optimizing performance while reducing pendulation effects
3Adaptability or versatility
If multiple cranes are coordinated for lifting, then the cargo handling capacity increases, but the control difficulty and system complexity increase
Solution Approach 1:
The control algorithm serves multiple functions simultaneously: it coordinates multiple crane movements, compensates for ship motion disturbances, prevents payload pendulation, and ensures synchronized operation, all through a single integrated control system that handles diverse operational requirements
4Measurement precision
If the hoist line length is increased to position the payload closer to the pedestal, then the payload placement accuracy improves, but the pendulum oscillation period increases causing resonance with ship motions
Solution Approach 1:
The control algorithm applies preliminary counteracting forces through coordinated crane movements before ship motion disturbances can cause significant pendulation, proactively preventing resonance conditions rather than merely reacting to oscillations after they occur
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The dual-crane control system effectively stabilizes payloads during lifting operations in marine environments with base motion disturbances, enabling accurate and efficient transfer of heavy or unwieldy loads, such as vehicle discharge ramps, while reducing payload swing and maintaining stability.
Implementation Method 1
A hoist line, together with its attached and suspended payload, constitutes a pendulum characterized by an oscillation period that may be responsive, to the point of resonance, with seaway-induced motion of the ship
Implementation Method 2
A dual-crane control scheme that actively adjusts geometric parameters such as luff angle and hoist line length to maintain static equilibrium of the load
Implementation Method 3
Coordinated control of two shipboard cranes for cargo transfer with ship motion compensation
Data Source
AI summary
The present invention is typically embodied to exert active control of two same-shipboard cranes performing joint lifting of a payload. Sensory signals indicative of ship motion, and of luff angle and hoist line length of both cranes, are transmitted to a computer. The sensory signals are processed by the computer using a ship motion cancellation algorithm, which solves for values of the respective luff angles and hoist line lengths of both cranes, such values achieving static equilibrium (e.g., zero motion horizontally, vertically, and rotationally in the same vertical geometric plane) of the suspended payload. Inverse kinematic control signals in accordance with the mathematical (e.g., minimum norm) solutions are transmitted by the computer to respective luff angle actuators and hoist line length actuators of both cranes so that the suspended payload tends toward steadiness. Inventive control thus acts on a continual basis to significantly reduce pendulation during the two-crane lifting operation.