Folding Knife Tension Spring and Tendon Actuation
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Solution Overview
Problem
The size, weight, and length of folding knife blades are limited by the physical space and power of torsion springs used in existing designs, restricting the assembly's envelope and energy transfer efficiency.
Innovation Solution
A tension spring is positioned within the handle and connected to a flexible tendon, which is attached to the blade, allowing for increased blade size, weight, and length while keeping the spring internal and protected, with the tendon providing a longer moment arm for energy application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a torsion spring is used to power the blade, then the blade can be deployed automatically, but the blade size, weight, and length are limited by the physical space available near the blade axis point
Solution Approach 1:
The spring is extracted from its traditional location near the blade axis point and repositioned to a different location in the handle, specifically utilizing the end of the handle. This extraction allows the spring to operate outside the constrained volume near the pivot, enabling larger blade dimensions without increasing handle size.
Solution Approach 2:
A tendon is introduced as an intermediary element that connects the spring to the blade. The tendon transmits the spring's force over a longer distance and allows the spring to act upon the blade from a remote location, effectively decoupling the spring's position from the blade's rotation point and enabling larger blade dimensions.
2Length of moving object
If the spring is positioned near the blade axis point, then the mechanism is compact, but the blade size, weight, and length are restricted by the defined envelope
Solution Approach 1:
The tendon serves as a mechanical intermediary that extends the reach of the spring's force. By routing the tendon from the spring location through the handle to the blade, the system achieves a longer effective moment arm without proportionally increasing handle length, thereby enabling longer blades within compact handle dimensions.
Solution Approach 2:
The spring is repositioned to utilize the end of the handle, effectively using the longitudinal dimension of the handle rather than the radial space near the pivot. This dimensional reorganization allows the blade to extend further while the handle maintains its compact cross-sectional envelope.
3Reliability
If the spring is exposed externally, then it is accessible for operation, but it is vulnerable to damage, abuse, and environmental factors
Solution Approach 1:
The spring is extracted from external exposure and relocated to an internal position within the handle. This extraction protects the spring from environmental damage and physical abuse while maintaining its functional connection to the blade through the tendon mechanism.
Solution Approach 2:
The spring is nested within the handle structure, placing it inside the protective enclosure of the handle. This nesting arrangement shields the spring from external hazards while the tendon provides the necessary external interface for force transmission to the blade.
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 design enables larger, heavier, and longer blades without altering the handle size, with the tension spring and tendon combination providing enhanced energy transfer and protection from external damage.
Implementation Method 1
A tension spring contained within the handle of a folding knife is pinned on one end to the handle, and attached to a tendon on the opposite end of the spring
Implementation Method 2
The use of a tendon also allows a longer distance for the spring to act upon the blade, thus allowing more energy to be applied to the blade overall
Implementation Method 3
The tendon is attached to the outside edge of the blade, and the blade is pinned at an axle pin. The distance between the axle pin of the blade and the location of the pinned tendon provides a moment arm which is acted upon by the tension spring
Data Source
AI summary
A folding knife with a handle and blade connected at a axle pin, with a tension spring within the handle pinned to the handle on one end and pinned to a flexible tendon in the form of a chain on the opposite end. The flexible tendon in the form of a chain is pinned at opposite ends to the spring and the blade at a distance from the blade axle pin. When the blade is folded about the axle pin energy is stored in the tension spring by force transferring from the blade through the flexible tendon in the form of a chain to the spring. When the blade is folded a catch blocks the blade from unfolding, and when the user actuates this blocking catch the stored energy in the tension spring is released thus causing the blade to rotate about the axis point and deploy to the opened position.