Post Hole Digger With Offset Pivot Linkage
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Solution Overview
Problem
Existing post hole diggers face challenges with a limited range of motion, weight, and ergonomic issues, particularly with traverse pivot points that require awkward hand positioning and increased effort due to the need for wider spans during operation.
Innovation Solution
A post hole digger design featuring a traverse pivot point located on the medial portions of handle members and an offset blade assembly pivot point, allowing for reduced range of motion and maintaining handles in a vertical, parallel orientation, along with a hand ledge for ergonomic support and reduced weight through shorter handle assemblies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If longer handles are used to increase lever arm and closing force, then the closing force on blade members is improved, but the tool becomes too heavy to lift repeatedly and too unwieldy to use comfortably
Solution Approach 1:
The tool is divided into separate components: handle members, blade members, and pivot points. This segmentation allows the handles to be optimized for leverage while the blade assembly is optimized for digging, reducing the need for excessively long handles to achieve sufficient closing force.
Solution Approach 2:
The invention introduces a second pivot point that creates a four-bar linkage mechanism, transforming the single-degree-of-freedom system into a two-degree-of-freedom system. This dimensional change in the mechanism's motion space allows for optimized force transmission without requiring proportionally longer handles.
2Force
If longer handles are used to increase lever arm, then the closing force on blade members is improved, but the range of motion and ergonomics deteriorate
Solution Approach 1:
The mechanism transitions from a static, rigid structure to a dynamic, articulated system with two pivot points. This allows the handle assembly to adapt its configuration during operation, maintaining ergonomic hand positions while delivering sufficient closing force through the mechanical advantage of the linkage.
Solution Approach 2:
By adding the second pivot point, the system gains an additional degree of freedom that allows independent optimization of handle length for ergonomics and blade closing force. The four-bar linkage enables the handles to move through optimized arcs that maintain comfortable wrist positions.
3Device complexity
If a single pivot point is used to couple handles and blades, then the device complexity is reduced, but the range of motion is insufficient and hand positioning becomes awkward
Solution Approach 1:
The single pivot point is segmented into two distinct pivot points: one coupling the handle members to each other, and another coupling the blade members to the handles. This segmentation allows independent optimization of each joint's function, improving hand positioning and range of motion.
Solution Approach 2:
The static single-pivot configuration is transformed into a dynamic two-pivot system that allows the handle and blade assemblies to move independently through optimized trajectories. This creates a more flexible, adaptive mechanism that maintains ergonomic hand positions throughout the digging cycle.
4Force
If the handle span is increased to allow greater blade closing force, then the force applied to handles is improved, but the tool requires wider holes and more effort from the worker
Solution Approach 1:
The direct mechanical advantage system (relying solely on handle length) is replaced with a four-bar linkage mechanism that provides mechanical advantage through geometric configuration rather than just leverage arm length. This substitution allows force multiplication without requiring proportionally wider handle spans.
Solution Approach 2:
The mechanism uses dynamic motion through the two pivot points to optimize force application throughout the digging cycle. The articulated linkage allows the handles to move through arcs that maintain optimal force vectors, reducing the total effort required compared to a rigid, single-pivot system.
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 enhances ease of use by minimizing the range of motion required, maintaining ergonomic hand positioning, and reducing the overall weight and size of the tool, making it more efficient for digging holes of varying depths without excessive strain on the user.
Implementation Method 1
The pivot points experience friction during rotation as the handles and blades move between positions
Implementation Method 2
The closing force acting on the blades is related to the force applied to the handles. The force applied to the handles was enhanced by the length of the lever arm created by the length of the handle.
Implementation Method 3
After the blades have been closed, the worker, while holding the blades in the second, closed position, lifts the post hole digger thereby removing the dirt from the hole.
Data Source
AI summary
This invention provides a post hole digger having a first, traverse pivot point, located on the lower section of two handle members, and a second, blade assembly pivot point located at the medial point of the blade assemblies. Because the first pivot point is a traverse pivot point, the handle members are only required to travel through a limited range of motion. Additionally, the second, blade assembly pivot point is preferably an offset pivot point. Thus, because the second, blade assembly pivot point is disposed at a medial point of the blade assemblies, the motion of the handle members, which are coupled to the upper ends of the blade assemblies, is reversed relative to the lower ends of the blade members.