Pruning Shear Cutting Head with Coaxial Gear Segmentation
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Solution Overview
Problem
Existing cutting heads for pruning shears are heavy, require significant actuating forces, and have a large thickness, making them cumbersome and prone to getting caught in branches, especially when used in densely overgrown trees or bushes.
Innovation Solution
A cutting head design with a closed housing containing all mechanism parts, featuring a gear wheel with coaxially connected partial wheels of different diameters, where the larger diameter part is arranged in the plane of the shearbar, allowing for a lightweight and compact construction, and a pivotable connection to the handle that prevents the cutting head from pivoting when closed, reducing the overall length and increasing force efficiency as the blade closes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the cutting head is designed with a robust base plate and double chain pulley system to transmit actuating forces, then the cutting capability and force transmission are improved, but the weight and thickness of the cutting head increase significantly
Solution Approach 1:
The gear wheel is segmented into two coaxially connected partial wheels with different diameters. The first partial wheel (smaller diameter) transmits force from the movable blade to the cable, while the second partial wheel (larger diameter) provides mechanical advantage for cable actuation. This segmentation allows optimized force transmission without requiring a robust base plate, reducing overall weight.
Solution Approach 2:
The patent transitions from a planar chain pulley system to a three-dimensional gear wheel configuration with coaxial partial wheels of different diameters. This dimensional change enables more efficient space utilization and force transmission, reducing the thickness perpendicular to the blade plane while maintaining actuating force capability.
2Ease of operation
If the second part of the double chain pulley is positioned at a considerable distance from the base plate to accommodate cable routing, then the cable actuation is improved, but the base plate must be made relatively robust preventing deformation
Solution Approach 1:
The patent merges the functions of the base plate and the gear wheel mounting into a integrated housing structure. The housing supports the gear wheel and provides cable routing pathways, eliminating the need for a separate robust base plate. This integration maintains structural strength while improving cable actuation geometry.
3Force
If the cutting head is designed with considerable thickness to accommodate the double chain pulley system, then the force transmission mechanism is improved, but the cutting head becomes unsuitable for working with densely overgrown trees or bushes
Solution Approach 1:
The patent reconfigures the force transmission mechanism from a thick, planar double chain pulley system to a compact, coaxial gear wheel arrangement. By utilizing the radial dimension with partial wheels of different diameters, the system achieves effective force transmission with minimal thickness perpendicular to the blade plane, enabling access to densely overgrown areas.
4Weight of moving object
If the cutting head is designed with a lightweight and compact construction, then the ease of operation and access to hard-to-reach areas are improved, but the actuating forces required may increase
Solution Approach 1:
The gear wheel configuration with partial wheels of different diameters provides preliminary mechanical advantage in the actuation mechanism. The larger diameter second partial wheel amplifies the cable pulling force before it reaches the blade, reducing the effort required by the operator while maintaining a lightweight compact design.
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 design results in a lightweight, efficient, and compact cutting head that reduces actuating forces and prevents the cutting head from getting caught in branches, maintaining a closed construction for cleanliness and ease of use in hard-to-reach areas.
Implementation Method 1
a gear wheel (11) formed from two coaxially connected partial wheels (111, 112) of different diameters... The first partial wheel (111), having a smaller diameter than the second partial wheel (112)... The second partial wheel (112), having a larger diameter
Implementation Method 2
The first partial wheel (111) is at least partially enclosed by a first chain (10), through which this first partial wheel (111) is connected to a lever arm (61) of the blade (6)
Implementation Method 3
arrange the cable pull on the lever arm of the movable knife in such a way that the cable pull acts essentially perpendicular to the axis of the lever arm and approaches a right angle more and more as the shears come into their closing position
Data Source
Figure 1
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AI summary
A cutting head, particularly of a pruning shear, comprises a blade pivotable about a shaft fixed in a housing and a counter blade. Blade drive devices arranged in the housing include a first connecting element engaging a lever arm of the blade, a second connecting element extending to actuating devices at a handle connection, and a gear wheel (11) rotatably mounted in the housing with two coaxially connected circular first and second parts of different diameters. The first part (111) with the smaller diameter is arranged essentially in the plane of the blade (6) and is enclosed by the first connecting element (10), the first end of which is connected to the first part and the second end of which is connected to the lever arm of the blade.The second part (112) is essentially arranged in the plane of the counter-blade (3) and is enclosed by the second connecting element (15), one end of which is attached to the second part and which extends via a deflection pulley (23) into the handle connection.