Door Lock Assembly Inversion for Shear Resistance
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Solution Overview
Problem
Existing door locking systems that use threaded fasteners for attachment to wood surfaces rely on shear strength, which is inadequate when the wood is of poor quality or density, as the attachment force is primarily in a direction that pushes the screws out, reducing the lock's effectiveness.
Innovation Solution
A lock assembly with two plates, one attached to the door and one to the frame, where the plates' mounting surfaces are perpendicular to the direction of the opening force, utilizing screws that resist shear force more effectively, enhancing the lock's strength by aligning the screws' axis perpendicular to the opening force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If threaded fasteners are inserted through clearance holes and screwed directly into the inner face of the door panel and door frame, then the lock can be attached to the door and door frame, but the attachment strength is reduced because the screws are loaded in shear rather than in push out, particularly when the wood is of poor quality or density
Solution Approach 1:
The patent inverts the conventional attachment direction by having the mounting surfaces face each other across the thickness of the door, rather than facing away from the interior. This inversion changes the loading mechanism from shear (conventional) to direct compression (new), where the screws are loaded in push-out rather than being pulled parallel to the mounting surface, thereby significantly improving attachment strength and lock reliability even in poor quality wood.
2Ease of manufacture
If the mounting surfaces of the plates are parallel to the interior surface, then the plates can be easily attached to the door and door frame, but the screws are loaded in shear which reduces the holding strength
Solution Approach 1:
The patent applies inversion by rotating the mounting surfaces from being parallel to the interior surface to being perpendicular to it. This geometric inversion transforms the force vector from shear (parallel to mounting surface) to direct compression (perpendicular to mounting surface), making the attachment significantly stronger while remaining easy to manufacture with standard drilling and fastening procedures.
3Device complexity
If the plates are configured with mounting surfaces facing into the interior, then the lock structure is simple, but the attachment relies on the holding strength of screws in shear which is inadequate for poor quality wood
Solution Approach 1:
The patent maintains structural simplicity while achieving superior attachment strength by inverting the mounting surface orientation. The plates still have a straightforward construction with two mounting surfaces that face each other, but this inversion changes the mechanical loading from shear to direct compression, providing adequate attachment force even in poor quality wood without complicating the overall lock structure.
Data Source
AI summary
A lock assembly for securing a movable panel in a locked condition relative to an adjacent stationary frame, according to one embodiment of the present invention, includes a first plate defining a pair of first receiving apertures and being constructed and arranged with a first mounting portion having a substantially planar mounting surface for being attached to the movable panel, a second plate defining a pair of second receiving apertures and being constructed and arranged with a second mounting portion having a substantially planar mounting surface for being attached to the stationary frame, a pair of locking members constructed and arranged for insertion through a corresponding pair of the first and second receiving apertures when the movable panel is closed relative to the stationary frame and wherein the substantially planar mounting surface of the first mounting portion is substantially parallel with and facing the substantially planar mounting surface of the second mounting portion.