Lifting Drum Overload Protection With Dual-Threshold Braking
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Solution Overview
Problem
Existing hoist systems lack reliability and accuracy in detecting overload thresholds, leading to potential failure in preventing operator falls and damage to helicopters due to complex friction clutch systems that require frequent maintenance and are sensitive to environmental and operational variations.
Innovation Solution
A method and device using two distinct operating thresholds: a first threshold for freewheel operation and a second threshold for braking, with a removable cartridge and braking means to manage overload, allowing for freewheeling and controlled rotation to give operators time to sever the cable if necessary, and adjustable thresholds for varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional friction clutch system is used for overload protection, then the system can release the drum in case of overload, but the system becomes sensitive, complex, and requires periodic controls
Solution Approach 1:
The overload protection system is segmented into two distinct thresholds: a first threshold that triggers freewheel operation and a second threshold that triggers braking. This segmentation allows the system to handle different overload scenarios appropriately, reducing complexity by addressing specific cases separately rather than using a single complex friction clutch mechanism.
Solution Approach 2:
The system dynamically adjusts its response based on the overload magnitude. When the first threshold is exceeded, the drum is allowed to freewheel. When the second threshold is exceeded, braking is applied to progressively stop rotation. This dynamic behavior replaces the static friction clutch system with a more adaptable mechanism.
2Reliability
If a friction clutch system with spring taring is used, then the system can trigger unwinding at a limit load, but the triggering threshold lacks accuracy due to environmental and operating principle trims
Solution Approach 1:
The system uses two distinct parameter thresholds instead of a single spring taring value. The first threshold triggers freewheel operation, and the second threshold triggers braking. This dual-threshold parameter approach eliminates the inaccuracies associated with spring taring and environmental trims, providing more precise and reliable triggering.
3Ease of operation
If the friction clutch system allows complete unwinding in case of overload, then the kinematic chain is freed, but the operator integrity is compromised due to sudden deceleration at the end position
Solution Approach 1:
The system applies braking before the cable is completely unwound, when the second threshold is exceeded. This beforehand cushioning prevents the sudden deceleration that would occur at the end position, protecting the operator while still allowing controlled unwinding during the braking phase.
Solution Approach 2:
The system converts the harmful sudden deceleration at the end of unwinding into a beneficial controlled deceleration through the braking mechanism. By applying brakes progressively, the harmful impact is transformed into a controlled stopping process that protects the operator.
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
Enhances safety by providing reliable overload protection with adjustable thresholds, reducing the risk of complete cable unwinding and ensuring controlled deceleration, thereby preventing severe impacts.
Implementation Method 1
a dome receiving two rings independent of one another... ensuring the freewheel operation of the lifting drum with respect to the motor, as soon as the torque exerted by the lifting cable on the drum is greater than a threshold value
Implementation Method 2
a friction clutch system, constituted of one or more friction discs and a spring... when the limit load is reached, the friction disc(s) no longer adhere(s), for example to the drum, releasing the rotation of it
Implementation Method 3
a friction clutch system, constituted of one or more friction discs and a spring, said spring being tared to a value corresponding to the limit mass or limit load
Data Source
AI summary
A method for protecting a lifting member against an overload is described. The lifting member includes a lifting drum over which a cable is wound at the end of which a load is fixed. The lifting drum is mechanically connected to an electric motor capable of ensuring its rotation. The mechanical connection includes a clutch or equivalent device, has at least two distinct operating thresholds: a first threshold, the exceeding of which generates the freewheel operation of the lifting drum with respect to the kinematic chain coming from the electric motor, and a second threshold, of value greater than that corresponding to the nominal load of the lifting member, but of value less than that of the first threshold, generating the braking of the rotation of the lifting drum, and an attempt to progressively stop said rotation of the drum.