Pivot Post Design for Trimmer Head Line Retention
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Solution Overview
Problem
Existing trimmer heads with pivoting line holders face issues such as line breakage, difficulty in removing used trimmer line, and wear on the plastic posts due to sawing motion, leading to frictional melting and fusion with the line, making replacement challenging and frustrating for consumers.
Innovation Solution
The design of improved pivot posts that pivot about a central vertical axis, featuring a combination of plastic and metal components, a single channel instead of parallel passageways, and metal pins to retain the folded line, minimizing wear and deformation, and facilitating easy removal of used lines without tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plastic pivot posts with parallel passageways are used to hold trimmer line, then the line can be retained and the post can pivot, but the plastic wears down due to sawing motion causing frictional melting and fusion with the line
Solution Approach 1:
The invention replaces the plastic pivot post with a metal pivot post. This material substitution eliminates the wear and fusion problems between the plastic post and trimmer line, as metal does not undergo frictional melting with nylon line. The metal post maintains the pivoting function while significantly extending the component lifespan.
Solution Approach 2:
The invention changes the surface properties of the pivot post by using metal instead of plastic. This parameter change in material composition and surface characteristics prevents the adhesive fusion that occurs between plastic and trimmer line under friction and heat, thereby eliminating the wear issue.
2Ease of operation
If parallel passageways are used in the pivot post, then the line can be inserted and retained, but the design causes line breakage and makes removal difficult
Solution Approach 1:
The invention inverts the traditional design by using a single passageway instead of parallel passageways. This reversal of the structural configuration changes how the line interacts with the post, allowing the line to be retained during operation but easily removed when needed by simply pulling it through the single channel.
Solution Approach 2:
The invention segments the line retention function from the line removal function. The single passageway design with specific geometric features allows the line to be held in place during trimming through friction and geometry, while permitting easy removal by applying pulling force in the opposite direction.
3Ease of manufacture
If the pivot post is made as a single piece of plastic, then manufacturing is simple, but the design causes line breakage upon impact with solid objects
Solution Approach 1:
The invention replaces the plastic material with metal material for the pivot post. This material substitution provides the necessary strength and durability to prevent line breakage during impact with solid objects, while the metal can still be manufactured as a single piece through casting or forging processes.
Solution Approach 2:
The invention incorporates curved surfaces and rounded edges in the pivot post design, particularly at the passageway entrances and along the post surface. These curved features prevent sharp edges that could cause line breakage, allowing the line to glide smoothly against the post during impact situations.
4Reliability
If the pivot post allows pivoting motion, then line breakage is minimized during operation, but the post experiences wear and fusion with the line
Solution Approach 1:
The invention uses metal material for the pivot post instead of plastic. This material change eliminates the frictional melting and fusion problem between the post and trimmer line, as metal does not undergo thermal softening and adhesion with nylon line under the same operating conditions.
Solution Approach 2:
The invention introduces a different material interface between the pivot post and trimmer line. The metal post acts as an intermediary that does not chemically or thermally bond with the line, preventing fusion while still allowing the necessary friction for line retention and pivoting motion.
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 new pivot post design significantly reduces line breakage, eases line removal, and extends the lifespan of the trimmer head by minimizing wear and fusion, making it more forgiving of deformed lines and suitable for various trimmer machines and line materials.
Implementation Method 1
pivot posts and trimmer heads utilizing the same... pivot posts for holding strips of folded line in trimmer heads... capable of pivoting to minimize line breakage upon impact with solid objects and dense vegetation
Implementation Method 2
the ends of each folded piece of trimmer line will extend out radially due to the centrifugal force created by the rotation of the trimmer head
Implementation Method 3
wear on the plastic posts due to sawing motion, leading to frictional melting and fusion with the line
Data Source
AI summary
A trimmer head having at least two pivoting line holders for holding multiple folded strips of trimming line is presented wherein said pivoting line holders are retained within said housing between said housing and said cover and extend upward through apertures in said cover, said line holders being capable of movement around a vertical axis of rotation, at least three embodiments are disclosed which provide a rounded landing for supporting the inner radius of a folded strip of trimming line, the rounded geometry of the landing prevents line stress and breakage, the various embodiments include a pivot post having two parallel straight through holes with a rounded vertical wall between the through holes, a single open passageway having a center metal post, and a single open passageway having a series of at least two metal pins through the center of the passageway.