Small-angle latch system with concave cam profile

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Solution Overview

Problem

Conventional latch systems require a significant rotational angle of the lever or knob to fully retract the latch bolt, which can be stressful for users, especially for those with disabilities or the elderly, and do not efficiently minimize the mechanical advantage and torque required for operation within the constraints of maintaining the same lock footprint and torque limits.

Innovation Solution

A small-angle latch system that includes a cam with a concave perimeter and a drive member with convex portions, allowing the latch bolt to be retracted from an extended to a retracted position through a rotation of the lever or knob by up to 35 degrees, while maintaining the same mechanical configuration and torque limits, utilizing a cam with a concave surface that engages the latch member at a shallow angle to reduce the rotational stress and torque required.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a conventional latch system with coincident centers of rotation is used, then the mechanical advantage is high and torque required is low, but the lever rotation angle required to retract the latch bolt is large (at least 52 degrees)

Engineering Contradiction:

Improvelever rotation angleVSAvoidtorque required

Core Design Contradiction:

Ease of operationVSForce

Solution Approach 1:

The patent inverts the conventional cam profile geometry by using a concave cam surface instead of a convex one. This inversion changes the mechanical advantage characteristics, allowing for reduced lever rotation angle while maintaining acceptable torque levels. The concave surface creates a different force transmission path that prioritizes angular displacement over force multiplication.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the geometric parameters of the cam-latch interface by positioning the latch member closer to the cam center and modifying the cam profile curvature. These parameter changes alter the mechanical advantage curve throughout the rotation range, enabling the system to achieve full latch retraction with only 21 degrees of cam rotation (35 degrees of lever rotation) while keeping torque below the 28 inch-pounds limit.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the lever rotation angle is reduced to improve accessibility, then ease of operation improves, but the mechanical advantage decreases and torque required increases

Engineering Contradiction:

Improvelever rotation angleVSAvoidcam profile complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent employs a concave curved surface on the cam that is specifically profiled to achieve the desired motion transformation. The curved geometry is optimized to convert a larger lever rotation angle into a smaller cam rotation angle while maintaining smooth force transmission. The specific curvature radius and profile shape are designed to keep the torque requirement within acceptable limits throughout the motion range.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Force

If the cam center of rotation is positioned midway between contact points to achieve mechanical advantage, then torque required is minimized, but the lever rotation angle increases

Engineering Contradiction:

Improvetorque requiredVSAvoidlever rotation angle

Core Design Contradiction:

ForceVSEase of operation

Solution Approach 1:

The patent introduces asymmetry in the cam-latch system by positioning the latch member at an asymmetric location relative to the cam center, specifically closer to the cam center than in conventional designs. This asymmetric positioning creates an unequal moment arm relationship that reduces the required lever rotation angle. The system accepts a slight increase in torque as a trade-off for the significant reduction in rotation angle, achieving 21 degrees of cam rotation for full latch retraction.

Inventive Principle:

Principle #4Asymmetry

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 system significantly reduces the rotational angle needed to retract the latch bolt, achieving a 40% reduction in lever rotation from conventional systems, while keeping the torque below 28 inch-pounds, thus enhancing accessibility and reducing user effort.

Implementation Method 1

a cam adapted to be connected for rotation with the input member, the cam rotating about an axis of rotation, the cam having an outer perimeter including a concave portion

Methodology Applied

Scientific EffectCam mechanism: Cam

Implementation Method 2

a drive member disposed in the latch bolt housing, the drive member having a convex portion arranged to be engaged by a portion of the latch member to pivot the drive member relative to the latch bolt housing

Methodology Applied

Scientific EffectMechanical advantage: Mechanical Advantage

Data Source

PatentUS11585115B2Small-angle latch system for a lock

Publication Date: 2023.02.21 DORMAKABA USA INC

AI summary

A small angle latch is disclosed which moves a latch bolt from a fully extended position to a retracted position wherein the latch bolt is substantially flush with an outer surface of a faceplate through a rotation of an input device, such as a lever, in the range of from about 25 degrees to about 35 degrees, without exceeding a maximum torque upon the input member of 28 inch-pounds.