Dynamic Overload Threshold for Snag Load Detection
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Solution Overview
Problem
Conventional overload protection systems in load lifting devices, such as container cranes, struggle to distinguish between normal lifting and 'snag load' conditions, leading to delayed reaction times and potential damage when the load is caught unexpectedly, as they rely on static overload thresholds that do not account for varying situations like lifting with or without a load.
Innovation Solution
Implementing a dynamic overload threshold system that defines a period for lifting with or without a load, determines an average weight force, sets a dynamic jump threshold, and monitors the signal for exceeding this threshold to initiate an emergency shutdown before reaching the nominal overload threshold, allowing for earlier detection of snag load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a static overload threshold is used for safety monitoring, then the system structure remains simple, but the response time to detect snag load conditions is delayed and damage risk increases
Solution Approach 1:
The patent applies dynamics by transitioning from a static overload threshold to a dynamic threshold system that adapts to current lifting conditions. The threshold is continuously adjusted based on the measured load weight, allowing the system to respond appropriately to snag load conditions while maintaining simplicity. This resolves the contradiction by making the threshold responsive without adding complex predictive algorithms.
Solution Approach 2:
The patent changes the parameter of the overload threshold from a fixed value to a variable that depends on the current load situation. By calculating the threshold as a function of the measured load (e.g., threshold = load + margin), the system achieves faster response to abnormal load increases while keeping the calculation simple. This parameter change enables both rapid detection and structural simplicity.
2Reliability
If a dynamic overload threshold system is implemented to detect snag loads earlier, then the response time and damage prevention improve, but the device complexity increases
Solution Approach 1:
The patent implements parameter changes by making the overload threshold a function of the measured load rather than a fixed value. The control unit calculates the dynamic threshold using simple arithmetic operations (adding a safety margin to the current load measurement), which maintains computational simplicity while significantly improving snag load detection accuracy. This avoids the need for complex predictive models or multiple sensors.
Solution Approach 2:
The system applies self-service by using its own load measurement data to automatically adjust the threshold without requiring external input or complex decision logic. The control unit continuously monitors the load and autonomously updates the threshold based on the current state, eliminating the need for manual threshold setting or complex control algorithms while improving detection accuracy.
3Productivity
If the overload threshold is set at the nominal rated load, then the maximum lifting capacity is utilized, but snag load conditions are not detected until after significant damage risk has accumulated
Solution Approach 1:
The patent changes the threshold parameter from a fixed nominal rated load to a dynamic value that adapts to the current load situation. When the actual load is significantly below the rated capacity, the dynamic threshold remains close to the rated load, allowing full productivity utilization. When a snag load occurs causing rapid load increase, the dynamic threshold detects this abnormal change immediately, enabling early shutdown before damage occurs. This resolves the contradiction by making the threshold context-dependent.
Solution Approach 2:
The system applies dynamics by making the threshold responsive to real-time load conditions rather than static. The threshold continuously adapts to the measured load, allowing the system to operate at maximum capacity during normal conditions while providing enhanced protection during abnormal situations. This dynamic behavior enables both high productivity utilization and early snag load detection.
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 reduces the risk of damage by enabling faster and more accurate detection of snag load situations, allowing for emergency shutdowns before maximum force is applied, with response times less than 5 ms and reduced risk of crane or ship damage.
Implementation Method 1
A measuring axis consists of a cylindrical force transducer, which is equipped with an electrical measuring system, such as strain gauges (DMS). As soon as these pins are brought into engagement with the container and the container is lifted using a hoist, the measuring ranges of the measuring axis are deformed, which in turn results in a corresponding measuring signal.
Data Source
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AI summary
The invention relates to a method for the dynamic detection of a faulty operation of a load lifting device, wherein the load lifting device has a force sensor, comprising the following steps: monitoring a signal of the force sensor for an increase; defining a time period required for lifting the load receiving means; monitoring the signal for an exceeding of the overload threshold; if the overload threshold is not exceeded during the defined time period, determining a weight force within the defined time period from the signal, and establishing the weight force determined as a base load; establishing a dynamic jump threshold as the nominal overload threshold, which is greater than the base load and smaller than the current overload threshold; and monitoring whether the signal is greater than or equal to the jump threshold, and generating a switch-off signal, if the signal is greater than or equal to the jump threshold.