Pruning Shears with Adjustable Gear Ratio and Power Cut Locking
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Solution Overview
Problem
Existing hand shears, particularly pruning shears and garden shears, have unreliable gear ratio adjustment mechanisms, requiring manual adjustment after each cut and lacking secure locking for power cuts, which affects handling and reliability.
Innovation Solution
The scissors feature a four-bar linkage system with elastically releasable force cut latching and normal section locking devices, allowing for secure power cut locking and easy return to normal cut position, with a spring mechanism for reduced resistance and clear user feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the linkage axis of the coupler is pre-tensioned to the smallest gear ratio, then the mechanism can return to the smallest gear ratio after cutting, but the adjustment of the gear ratio is unreliable and requires maximum open position before each cut at largest gear ratio
Solution Approach 1:
The system automatically returns to the normal cutting position (smallest gear ratio) after use through the spring element, without requiring manual intervention. The movable joint self-locks in the power cutting position during operation and self-returns to normal position when hand levers are moved together, making the system self-servicing.
Solution Approach 2:
The gear ratio is made dynamically adjustable during operation. The movable joint can shift between two fixed positions (normal cutting and power cutting) based on operational needs, allowing the transmission ratio to adapt to different cutting requirements without manual reconfiguration.
2Reliability
If a locking mechanism is added to secure the movable joint in power cut position, then reliable power cut locking is achieved, but the device complexity increases
Solution Approach 1:
A spring element acts as an intermediary force to enable the locking mechanism. The spring provides the necessary force to move the movable joint between positions and maintain locking in the power cut position, simplifying the overall locking mechanism while ensuring reliable security.
Solution Approach 2:
The locking function is extracted as a separate, simple mechanism that only activates when needed. The movable joint can be locked in the power cut position independently of the normal cutting operation, allowing the locking feature to be added without significantly complicating the overall shear mechanism.
3Ease of operation
If the spring force is reduced for easy return to normal position, then the return operation becomes easier, but the locking force in power cut position may be insufficient
Solution Approach 1:
The spring force is dynamically optimized to provide sufficient locking force in the power cut position while allowing easy return to the normal position. The spring element's elastic properties enable it to maintain strong locking force when needed but allow smooth return movement when the hand levers are moved together.
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 ensures secure locking in power cut position, easy transition between normal and power cuts, and high operational reliability with reduced spring force resistance, improving handling and usability.
Implementation Method 1
a first spring element is provided for returning the movable joint to the position corresponding to the normal cut
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A hand shear comprises a cutting element (42) arranged at one end of a first hand lever (41), a second cutting element (52) connected to the first via a first joint (2) with a drive lever (51) projecting beyond the first joint, and a second hand lever (61) connected to the first hand lever via a second joint (3), as well as a coupling (70) whose ends are connected via a third joint (8) arranged at the free end of the drive lever at an axial distance from the first joint and a fourth joint (9) arranged at a distance from the second joint on the second hand lever. The distance between the joints of at least one pair of joints (2, 8; 3, 9) can be changed between a normal cutting position and a power cutting position by sliding one of the joints in a slot guide in the second hand lever.A force-cut locking device (12) holds the movable joint in the force-cut position after the hand levers have been fully moved apart and can be released by fully moving the hand levers together.