Crane Load Mass Determination via Rope Force Compensation
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Solution Overview
Problem
Existing systems for determining the load mass of a load suspended from a crane's hoist rope face challenges in accuracy due to static and dynamic influences, particularly when the measuring arrangement is placed between the crane structure and the hoist cable, leading to inaccuracies in load mass calculation.
Innovation Solution
A system that includes a compensation unit based on a spring-mass model, which models and compensates for static and dynamic influences on the rope force, using data on crane position and movement, and accounts for factors like rope mass, deflection pulley friction, and acceleration, to improve the accuracy of load mass determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the measuring arrangement is arranged directly on the load handling device, then measurement precision is improved, but device complexity increases due to required power supply and signal lines
Solution Approach 1:
The patent introduces a compensation unit as an intermediary component that processes the raw cable force measurement and compensates for disturbing influences. This mediator allows the use of a simpler measuring arrangement location (on the crane structure rather than on the load handling device) while still achieving high measurement precision through software-based compensation of static and dynamic influences.
2Reliability
If the measuring arrangement is arranged on a deflection pulley or hoist, then device robustness is improved and wiring is simplified, but measurement precision deteriorates due to disturbing influences
Solution Approach 1:
The patent converts the harmful disturbing influences (static influences from rope mass and friction, dynamic influences from acceleration) into compensatable parameters by modeling them explicitly. The compensation unit uses these modeled influences to calculate correction values, thereby transforming what were previously sources of measurement error into known quantities that can be mathematically compensated for, achieving high precision despite the simplified robust measuring arrangement location.
3Measurement precision
If averaging filters are used to determine cable force, then some interfering influences are reduced, but signal delay increases and static influences cannot be eliminated
Solution Approach 1:
The patent applies preliminary action by pre-modeling the static and dynamic influences before they corrupt the measurement. The compensation unit uses the modeled influences to calculate compensation values in advance, allowing real-time or near-real-time correction of the cable force measurement without the time delays associated with averaging filters that react to past data.
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
This approach enables precise load mass calculation with reduced delays, allowing for more efficient load moment limitation and increased crane service life by accurately accounting for various influences on the rope force.
Implementation Method 1
a load mass observer, which is based on a spring-mass model of the cable and the load
Implementation Method 2
The rope force in the hoist rope essentially corresponds to the load mass, at least in a static state
Data Source
Figure 1
Figure 2
Figure 3a
AI summary
The system has a measurement arrangement for measuring a cable weight (22) in a hoist cable, and a calculation unit (26) for indirectly determining the exact load mass (24) based on the cable force. The calculation unit comprises a compensation unit describing influence of the indirect determination of the load mass via the cable force in a model and partly compensates the influence. The compensation unit works on the basis of data on a position and/or movement of a hoisting gear, boom and/or of a tower of the crane. An independent claim is also included for a method for determining a load mass of a load carried by a hoist cable.