Pruning Shears Ratchet Mechanism Direct Cut Transition
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Solution Overview
Problem
Ratchet mechanism in pruning shears requires multiple closing processes and increased manual force, making the cutting process unnecessarily complex and force-intensive, especially when dealing with thicker materials.
Innovation Solution
The design allows users to continue a cutting process as either a multi-stage ratchet cut or a direct cut without reversing the hand lever movement, using a power transmission geometry similar to conventional pruning shears, by engaging the ratchet lever in the first locking position and utilizing a rolling contact between convex and concave surfaces to reduce force resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a ratchet mechanism is used to reduce manual force for cutting thicker materials, then the force required to cut is reduced, but the cutting process becomes unnecessarily complex and requires multiple closing processes
Solution Approach 1:
The patent makes the power transmission mechanism dynamic by allowing automatic switching between ratchet-based power transmission and direct power transmission based on the closing position. The ratchet lever transitions from engaging ratchet stages at larger opening angles to disengaging and allowing direct transmission at smaller opening angles, eliminating the need for manual switching and reducing process complexity while maintaining force reduction benefits.
Solution Approach 2:
The hand lever is designed to perform multiple functions: it can transmit force through the ratchet mechanism for high-force cutting of thicker materials, and simultaneously serve as a direct power transmission path for lower-force cutting. This multi-functionality allows a single mechanism to adapt to different cutting scenarios without requiring separate mechanisms or complex switching procedures.
2Force
If a ratchet mechanism with multiple ratchet stages is used, then moderate hand strength can overcome higher resistance forces, but the user must partially open the hand lever between closing processes to engage the next ratchet stage
Solution Approach 1:
The ratchet lever is designed to automatically disengage from the ratchet stages and allow direct power transmission when the hand lever reaches a predetermined closing position. This self-service mechanism eliminates the need for the user to manually intervene to switch between ratchet and direct transmission modes, thereby simplifying operation while maintaining the force-reduction benefit of the ratchet mechanism during the initial closing stroke.
Solution Approach 2:
The ratchet lever is pre-configured to automatically transition from ratchet engagement to direct power transmission at a predetermined closing position. This preliminary arrangement ensures that the forceful initial closing stroke utilizes the ratchet mechanism for force multiplication, while subsequent closing movements automatically switch to direct transmission, eliminating the need for partial opening and re-engagement operations.
3Ease of operation
If the hand lever is designed for direct cut power transmission, then the cutting process is simple, but the user cannot overcome higher resistance forces of thicker materials with moderate hand strength
Solution Approach 1:
The power transmission system dynamically adapts based on the hand lever closing position. During the initial closing stroke from a relatively open position, the ratchet lever engages the ratchet stages to provide force multiplication for overcoming high resistance. As the hand lever approaches full closure, the ratchet lever automatically disengages and allows direct power transmission, providing operational simplicity. This dynamic switching enables the system to deliver both high force capability and operational simplicity without requiring complex manual switching.
4Force
If multiple closing processes are required to cut thicker materials, then the force required per stroke is reduced, but the cumulative hand lever travel increases and the cutting process takes more time
Solution Approach 1:
The ratchet lever is pre-configured to automatically transition from ratchet engagement to direct power transmission when the hand lever reaches a predetermined closing position. This preliminary arrangement enables the user to complete the entire cutting process in a single continuous closing motion, eliminating the need for multiple closing processes and partial openings. The force reduction benefit of the ratchet mechanism is utilized during the initial phase of the closing stroke, while the direct transmission path becomes available later in the same stroke, thereby maintaining productivity.
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
Enables users to cut thicker materials with a force comparable to conventional pruning shears, offering the option to switch between ratchet and direct cutting modes based on material resistance without additional actuation, simplifying the cutting process and reducing the complexity of ratchet mechanism usage.
Implementation Method 1
utilizing a rolling contact between convex and concave surfaces to reduce force resistance
Data Source
Figure 1~3
AI summary
For hand-operated garden shears, in particular tree-pruning shears, with a ratchet mechanism, it is proposed that, between a hand lever (H2) and a scissor lever (H1) between which a ratchet lever (RH) can engage in different latching positions according to the ratchet mechanism, there is also provided, in addition, a preferably rotatable abutment surface (AF) on the hand lever (H2) and a mating bearing surface (GF) on the lever extension, or vice versa, which, at the end of an initial closing operation with the ratchet lever (RH) in a first ratchet position, allow a continuation of the cutting operation as a direct cut without further use of the ratchet mechanism.