Geared Hand Tool With Variable Leverage for One-Hand Cutting
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Solution Overview
Problem
One-hand operated cutting tools face challenges in delivering high cutting force due to the user's hand position, leading to smaller cutting strokes and increased fatigue, as the mechanical advantage is limited when handles are maximally spaced.
Innovation Solution
A hand tool with a variable mechanical advantage system, featuring a lever and jaws with non-circular bearing surfaces that provide maximum mechanical advantage at the full open position and minimum at the full close position, utilizing rolling contact and gear engagement to enhance cutting force and reduce user fatigue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the handles of a one-hand operated cutting tool are maximally spaced to allow user hand placement, then the user's hand can be positioned for operation, but the user cannot deliver high squeezing force to close the jaws, resulting in reduced cutting effectiveness
Solution Approach 1:
The patent applies a variable mechanical advantage system where the mechanical advantage changes dynamically throughout the cutting stroke. The bearing surfaces are non-circular (elliptical) so that mechanical advantage is maximum when handles are maximally spaced (full open position) and minimum when handles are closely spaced (full close position). This dynamic adjustment allows users to deliver maximum squeezing force when handles are spread for comfortable hand positioning, while still achieving effective cutting force when handles close together.
2Ease of operation
If the handles are maximally spaced for comfortable hand positioning, then ease of operation is improved, but the cutting stroke length is reduced requiring additional strokes
Solution Approach 1:
The variable mechanical advantage system with non-circular bearing surfaces enables the tool to maintain high mechanical advantage throughout a larger portion of the cutting stroke. By maximizing mechanical advantage at the full open position and maintaining effective force transmission through the stroke, the tool achieves longer effective cut lengths per stroke, reducing the number of strokes needed and improving productivity while preserving comfortable hand positioning.
3Device complexity
If conventional fixed mechanical advantage design is used, then the structure is simple, but user fatigue and muscle strain increase due to inability to deliver sufficient force
Solution Approach 1:
The patent implements a variable mechanical advantage system using non-circular (elliptical) bearing surfaces that adapt the mechanical advantage to the user's needs throughout the cutting stroke. This dynamic system maximizes mechanical advantage when handles are spread for comfortable hand positioning, enabling users to deliver sufficient squeezing force without fatigue or strain. While the structure is more complex than fixed mechanical advantage designs, the complexity is justified by the significant improvement in user comfort and reduction in fatigue.
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 tool increases cutting force at the full open position, allowing for longer cut lengths with less user effort, reducing fatigue and improving ease of use by matching hand strength characteristics throughout the cutting stroke.
Implementation Method 1
the first and second bearing surfaces are in rolling contact
Implementation Method 2
the first and second sets of projections are at least partially engaged
Data Source
AI summary
A hand tool includes a first jaw; a second jaw rotatably coupled to the first jaw, the second jaw including a first set of projections and a first bearing surface, the first bearing surface having a first curvature; and a lever coupled to the first jaw, the lever including a second set of projections and a second bearing surface, the second bearing surface having a second curvature. During a movement of the first and second jaws from a full open position to a full close position, the first and second sets of projections are at least partially engaged to prevent a slippage between the first and second bearing surfaces that are in a rolling contact during the movement of the first and second jaws from the full open position to the full close position.