Crane Rope Force Control for Slack Prevention
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Solution Overview
Problem
Existing crane control systems that regulate load position or speed can lead to slack rope issues, particularly in harsh environments like rough seas, causing significant loads on the rope and crane.
Innovation Solution
A crane control system that sets and maintains a constant rope force, using a cable force mode to prevent slack by controlling the winch speed and position based on cable force measurements, with feedback mechanisms and dynamic adjustments for elasticity and load weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If load position or speed control is used, then the crane can operate with simple control logic, but slack rope occurs when the load is placed causing significant loads on the rope and crane
Solution Approach 1:
The patent changes the control parameter from position/speed to rope force/tension. The hoist controller regulates the rope force to a desired setpoint value, which fundamentally changes how the system operates and prevents slack rope formation by maintaining constant tension control rather than position control.
Solution Approach 2:
The system uses feedback from rope force sensors (load cells) to continuously monitor actual rope tension and adjust hoist motor output accordingly. This closed-loop feedback mechanism ensures the rope force remains at the desired setpoint, preventing slack conditions while the load is being placed or moved.
2Reliability
If rope force mode is implemented, then slack rope is prevented and loads on the rope are reduced, but the control system becomes more complex
Solution Approach 1:
The system automatically determines the desired rope force setpoint based on load weight information without requiring manual intervention. The controller self-regulates by comparing actual rope force sensor readings with the calculated setpoint and adjusts motor output accordingly, making the complex control transparent to the operator.
Solution Approach 2:
The rope force control system serves multiple functions: it prevents slack rope, reduces dynamic loads on the crane structure, and provides stable positioning. By using rope force as the primary control parameter, the system achieves multiple benefits simultaneously without requiring separate control mechanisms for each function.
3Adaptability or versatility
If static force determination is used, then the system can account for cable weight in long lifts, but the control response may be slower
Solution Approach 1:
The system pre-calculates the desired rope force setpoint by determining the static force component (including cable weight for long lifts) before dynamic movements occur. This preliminary determination of the force setpoint allows the control system to account for cable weight in long lifts while maintaining rapid response capability during actual load movements.
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 system effectively maintains constant tension in the cable, preventing slack and reducing loads on the rope and crane, even in conditions with moving suspension points, thereby enhancing control and safety.
Implementation Method 1
the cable force determination unit determines the actual value of the cable force on the basis of a measurement signal from a cable force sensor
Implementation Method 2
The dynamic component of the forces acting in the rope can be removed, for example, by filtering
Implementation Method 3
the cable force determination unit determines the actual value of the cable force by filtering measured values or a model-based estimation. In particular, an observer can be provided, who determines the cable force on the basis of measured values and a physical model of the dynamics of the cable
Data Source
Figure 0
Figure 1
Figure 2~4
AI summary
The crane controller has a lifting mechanism (5) for lifting a load suspended on a rope (4), which is operated in cable power mode in which lifting is controlled, so that a target value of the rope force is adjusted. The speed and/or position of winch are controlled, so that the desired value of the cable force is established. The actual value of cable force is determined by comparing actual value and setpoint of cable force. Independent claims are included for the following: (1) a crane control system; (2) a method for controlling a crane; and (3) a software code for controlling a crane.