Fire Actuated Release Mechanism for Electronic Door Locks
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Solution Overview
Problem
Fire-rated electronic door locks face challenges in meeting high-temperature fire resistance standards due to the low ignition temperature of plastic materials, which limits the use of plastic in lock components and housings, necessitating the use of more expensive, non-flammable materials like metal.
Innovation Solution
The implementation of a fire actuated release mechanism using shape memory alloy (SMA) for electrical disconnection and meltable mounts for mechanical disconnection, allowing lock components to separate from the fire door before ignition, thereby preventing the spread of fire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plastic materials are used for lock housing and components, then cost is reduced and design flexibility is increased, but ignition temperature resistance deteriorates
Solution Approach 1:
The lock system is divided into two separate housings mounted on opposite sides of the fire door, connected by wiring. This segmentation allows the cold-side housing to be made of plastic while the hot-side housing provides fire resistance, resolving the contradiction between cost/design flexibility and temperature resistance.
Solution Approach 2:
A fire-rated barrier (the fire door assembly with specialized wiring routing) acts as an intermediary between the plastic lock components and the fire source. This intermediary protects the plastic components from direct heat exposure while allowing electrical connectivity, enabling use of low-cost plastic materials while maintaining fire resistance.
2Temperature
If metal housing is used for lock components, then ignition temperature resistance is improved, but cost increases
Solution Approach 1:
Fire-resistant metal housing is applied locally only where absolutely necessary (hot-side mounting and critical component areas), while plastic housing is used for the majority of the lock body on the cold side. This localized application of expensive materials minimizes cost while maintaining required fire resistance performance.
3Reliability
If wiring connects lock components across the fire door, then electrical connectivity is maintained, but fire resistance deteriorates due to heat conduction
Solution Approach 1:
The wiring is extracted from direct contact with the fire door surface and routed through specialized fire-rated pathways or protective sleeves. This extraction removes the heat conduction pathway from the main fire exposure zone while maintaining electrical connectivity between lock components.
Solution Approach 2:
Fire-rated wiring barriers and protective conduits act as intermediaries between the electrical wiring and the fire source. These intermediaries provide thermal insulation and physical protection, allowing wiring to maintain electrical connectivity while being protected from heat conduction during fire exposure.
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 solution enables the use of lower-cost plastic materials in electronic door locks by ensuring that lock components can drop away from the fire door during high-temperature exposure, preventing ignition and meeting fire resistance standards without the need for expensive, non-flammable materials.
Implementation Method 1
a fire actuated release mechanism using shape memory alloy (SMA) for electrical disconnection
Implementation Method 2
The SMA material is arranged so that the contraction exerts a pulling force on an electrical connector attached to the lock
Implementation Method 3
meltable mounts for mechanical disconnection, allowing lock components to separate from the fire door before ignition
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A release mechanism is actuated by the heat of a fire to electrically and mechanically disconnect electrical wiring from an electronic lock having a plastic housing. The electronic lock is mounted on a fire door and as it is heated by a fire on the opposite side of the fire door, mounts that hold the lock melt, releasing the electronic lock to drop away from the fire door and prevent ignition of the plastic housing. The release mechanism may use shape memory alloy wire to contract and disconnect a ribbon cable. Solder connectors may also be used to disconnect wires. Intumescent material that expands when heated is used to drive the lock mechanism away from the fire door and insulation is used to control the timing of melting.