Tamper-Resistant Sash Lock with Over-Center Cam Mechanism
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Solution Overview
Problem
Conventional sash window locks are not tamper-resistant, allowing unauthorized access by enabling external manipulation of the cam mechanism.
Innovation Solution
A tamper-resistant sash window lock design featuring a housing, shaft, cam, and lever member, where the cam is biased into engagement with the housing upon rotation, providing over-center securement and resisting external forces to prevent unauthorized unlocking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional sash lock with a rotatable cam is used, then the lock can be operated easily from the exterior, but the lock is vulnerable to tampering and unauthorized manipulation
Solution Approach 1:
The lock mechanism is divided into separate functional components: a cam assembly for locking, a lever member for actuation, and a housing for protection. This segmentation allows the cam to be designed specifically for tamper resistance while the lever handles operation, resolving the contradiction between security and ease of use.
Solution Approach 2:
The lever member acts as an intermediary between the user's manual input and the cam mechanism. It translates external manipulation into controlled cam rotation, allowing easy operation from the interior while preventing direct external manipulation of the cam for unauthorized unlocking.
2Ease of operation
If the cam is made accessible from the exterior for easy operation, then the lock can be unlocked conveniently, but the lock becomes susceptible to surreptitious operation by unauthorized parties
Solution Approach 1:
The lock mechanism exhibits asymmetric accessibility: the lever member is accessible from the interior for convenient operation, while the cam is positioned and protected within the housing so it cannot be directly manipulated from the exterior. This asymmetric design provides both ease of operation and protection against unauthorized access.
Solution Approach 2:
The housing and cam positioning are designed in advance to prevent external manipulation before any unauthorized attempt occurs. The cam is mechanically configured to engage the keeper in a way that requires interior access via the lever, preliminarily blocking any surreptitious external operation.
3Device complexity
If a simple cam and keeper mechanism is used, then the lock structure remains simple, but the lock lacks protection against external forces and tampering
Solution Approach 1:
The patent merges the simple cam-and-keeper locking mechanism with a protective housing and lever actuation system. This combination maintains the fundamental simplicity of the cam engagement while adding layers of protection against external forces and tampering, achieving both structural simplicity and enhanced reliability.
Solution Approach 2:
The housing serves multiple functions: it protects the cam mechanism, provides structural support, and controls access to the operating components. This multi-functionality allows the addition of protective features without proportionally increasing overall device complexity.
Data Source
AI summary
A tamper-resistant sash window lock includes a housing, a shaft, a cam, and a lever member. An interior surface of the housing wall that defines a cavity. A portion of the interior surface of the housing wall is curved about a hole in the housing, with a distal end of the wall portion formed into a lock surface. The shaft is rotatably mounted in the hole, and a hub of the cam is rotatably mounted on the shaft. The cam has a cantilevered arm with a lock surface and an engagement surface. The lever member is fixedly secured to the shaft, for a first side thereof to engage and drive the cam hub in a first rotational direction into a lock position when the shaft is actuated in the first rotational direction, so the lock surface of the cantilevered arm engages the lock surface of the housing preventing forced entry.