Door Latch Assembly Hardness Gradient Resolves Security Trade-off
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Solution Overview
Problem
Existing cockpit door locking mechanisms face challenges in balancing easy authorized access with sufficient security to prevent unauthorized entry, as the taper at the engagement end of the pin can compromise the retention capability during forced entry attempts.
Innovation Solution
A door latch assembly with a latch pin made of material with a hardness of 60 Rockwell C or more, and rollers with different hardness levels (33 Rockwell C or less for the first roller and 60 Rockwell C or more for the second roller) to impede rotational movement and enhance security, while allowing easy manual opening by deforming under sufficient force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a taper is provided at the engagement end of the pin to allow easy door opening, then the ease of operation is improved, but the retention capability against forced entry deteriorates
Solution Approach 1:
The latch pin employs different hardness values at different locations: the engagement end has a hardness of 33 Rockwell C or less (softer) to allow easy deformation and door opening, while the shaft portion has a hardness of 60 Rockwell C or more (harder) to resist forced entry and maintain retention capability. This local differentiation of material properties resolves the contradiction between ease of operation and security.
2Strength
If the pin material is made hard to prevent forced entry, then the strength is improved, but the ease of operation deteriorates
Solution Approach 1:
The latch pin employs different hardness values at different locations: the engagement end has a hardness of 33 Rockwell C or less (softer) to allow easy deformation and door opening, while the shaft portion has a hardness of 60 Rockwell C or more (harder) to resist forced entry and maintain retention capability. This local differentiation of material properties resolves the contradiction between ease of operation and security.
3Reliability
If the roller hardness is increased to match the latch pin, then the reliability of engagement is improved, but the ease of operation deteriorates
Solution Approach 1:
The first roller (on the catch arm) is made with a hardness of 33 Rockwell C or less to be softer than the latch pin engagement end, allowing it to easily deform the pin for door opening. The second roller (on the strike body) is made with a hardness of 60 Rockwell C or more to match the pin shaft hardness, ensuring reliable engagement and preventing forced entry. This differential hardness configuration resolves the contradiction between reliability and ease of operation.
Data Source
AI summary
A door latch assembly, includes: a catch support assembly, the catch support assembly including a strike body having a pin receiving aperture therein; a catch arm assembly rotatably mounted to the catch support assembly; a latch pin positioned in the pin receiving aperture and movable between a retracted position and an extended position, the latch pin protruding above the strike body in the extended position to impede rotational movement of the catch arm assembly; and a first roller mounted to the catch arm assembly and configured to engage a first side of the latch pin in the extended position; and a second roller mounted to the catch support assembly and configured to engage a second side of the latch pin in the extended position. The latch pin includes a material having a hardness of 60 Rockwell C or more, the first roller includes a material having a hardness of 33 Rockwell C or less, and the second roller includes a material having a hardness of 60 Rockwell C or more.