Force limiting device
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Solution Overview
Problem
Existing energy absorbing devices face challenges in efficiently dissipating high frequency, high force, and low amplitude oscillations of short duration, and have a limited range of applicability.
Innovation Solution
A force limiting device comprising a set of parallel plates floating in a chamber filled with a working fluid, where the plates are axially movable and spaced by inter-plate gaps occupied by the fluid, allowing the fluid to be squeezed out under compressive load, effectively dissipating energy through molecular friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional energy absorbing devices are used, then they can absorb energy, but they cannot efficiently dissipate high frequency, high force and low amplitude oscillations of short duration
Solution Approach 1:
The device divides the energy dissipation function into multiple parallel plates that can independently move relative to each other. Each plate acts as an individual energy dissipation element, allowing the system to handle complex oscillation patterns through the collective action of multiple segmented components rather than a single monolithic structure.
Solution Approach 2:
The plates are designed to be axially movable rather than fixed, allowing them to dynamically adjust their positions in response to varying loads and frequencies. This dynamic capability enables the device to adapt to different operating conditions, resolving the contradiction between energy dissipation efficiency and adaptability.
2Loss of energy
If the plates are closely spaced to increase damping, then energy dissipation improves, but the device cannot respond to high frequency oscillations
Solution Approach 1:
By segmenting the damping function across multiple plates with inter-plate gaps, the device maintains effective damping while allowing fluid to rapidly flow between the gaps. This segmentation enables the system to respond to high frequency oscillations without sacrificing damping efficiency, as the fluid can quickly move between the spaced plates rather than being constrained by closely spaced configurations.
Solution Approach 2:
The device uses hydraulic principles by filling the inter-plate gaps with working fluid that must be squeezed out as plates move together. This hydraulic mechanism provides both damping through fluid resistance and rapid response through fluid compressibility and flow, resolving the contradiction between damping efficiency and response frequency.
3Ease of manufacture
If the device structure is simplified, then manufacturing cost decreases, but the device cannot protect against transient force peaks
Solution Approach 1:
The segmented plate structure provides complex protection capabilities against transient force peaks while maintaining manufacturing simplicity. Each plate is a simple component that can be easily manufactured, and the collective arrangement of these simple segments creates the sophisticated force distribution and energy dissipation needed for reliable protection.
Solution Approach 2:
The device relies on the natural hydraulic principles of fluid compression and flow between the plates, requiring no additional active control systems or complex mechanisms. The working fluid automatically provides the necessary damping and force distribution, allowing the simple structure to achieve reliable protection against transient loads through self-service hydraulic action.
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 device provides efficient energy dissipation and damping characteristics, with a self-compensating response to varying loads and frequencies, effectively attenuating high intensity short duration overloads and protecting down-line equipment from transient force peaks.
Implementation Method 1
efficiently dissipating high frequency, high force and low amplitude oscillations of short duration
Implementation Method 2
the viscous fluid to be at least partly squeezed out from between the plates
Data Source
AI summary
A force limiting device has a housing defining an axially extending chamber containing a working fluid. A force transmitting member may be mounted for linear reciprocable movement inside the chamber under the action of external loads. An axial array of plates is floatingly disposed in the chamber between the force transmitting member and an end wall of the chamber. At rest, each plate is spaced from an adjacent plate by a gap occupied by the working fluid. When the force transmitting member is displaced towards the array of plates, the fluid in the chamber causes the plates to be successively pushed against each other, thereby causing some of the fluid to be squeezed out from between the plates.