Line Trimmer Head Radial Guide Passage Prevents Line Retraction
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Solution Overview
Problem
Line trimmers often experience line breakage or wear close to the spool winding, causing the broken line to retract into the spool chamber, which prevents the feed mechanism from functioning properly, leading to frustration and operational issues.
Innovation Solution
A line trimmer head design featuring guide passages with primary and secondary wall members that protect the line, ensuring it unwinds and maintains sufficient tension, even after breakage or wear, by providing a radial guidance system that prevents line retraction and allows for continuous feeding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the cutting line is allowed to wear down to a shorter length to extend usage, then the duration of action increases, but the reliability decreases because the line can break too close to the spool winding and become unable to feed out
Solution Approach 1:
The patent applies preliminary action by providing a guide passage structure before the line can break and retract. The guide passage with primary and secondary wall members is pre-configured to maintain line tension and prevent retraction, ensuring that even when the line wears down to a shorter length, it remains functional and can still be fed out from the spool.
Solution Approach 2:
The guide passage acts as an intermediary structure between the spool and the external environment. It mediates the line's path, maintaining proper tension and positioning, and preventing direct contact between the line and the spool chamber that would cause retraction. This intermediary structure allows the line to wear down safely without compromising the feed mechanism.
2Reliability
If the line is protected from breakage by extending its effective length, then the reliability improves, but the device complexity increases due to additional guide structures
Solution Approach 1:
The guide passage is segmented into distinct functional zones: a primary wall member that provides initial guidance and protection, and a secondary wall member that extends the guidance function. This segmentation allows each portion to perform its specific function efficiently while keeping the overall structure manageable and not excessively complex.
Solution Approach 2:
Instead of trying to prevent line wear or breakage through complex external protective mechanisms, the patent inverts the approach by designing the internal guide passage structure to work with the natural wear process. The guide passage accepts that the line will wear down and is designed to maintain functionality throughout this process, turning a potential failure mode into a manageable condition.
3Ease of operation
If the spool is designed to rotate freely to pay out line, then the ease of operation improves, but the line may retract into the spool chamber when broken, worsening reliability
Solution Approach 1:
The guide passage serves as an intermediary between the freely rotating spool and the external environment. It allows the spool to rotate freely for easy line payout while simultaneously preventing the broken line from retracting into the spool chamber. The guide passage mediates these two requirements by maintaining line tension and directing the line's path away from the spool chamber.
Solution Approach 2:
The guide passage structure applies preliminary anti-action by preemptively preventing line retraction before it can occur. The primary and secondary wall members are positioned to intercept and redirect any line that might otherwise retract into the spool chamber, countering the retraction tendency before it can compromise the feed mechanism.
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 reduces the likelihood of line breakage near the spool and ensures reliable line feeding, maintaining sufficient tension to rotate the spool and feed out new line, even under abusive conditions, thus preventing the need for frequent replacements.
Implementation Method 1
Rapid rotation of the spool and line projecting therefrom, typically by electric or petrol motor applies a centrifugal load on the projecting line which becomes the cutting line to cut the grass or vegetation.
Implementation Method 2
guide passages with primary and secondary wall members that protect the line, ensuring it unwinds and maintains sufficient tension, even after breakage or wear, by providing a radial guidance system that prevents line retraction
Implementation Method 3
the remaining unworn/unbroken length of line is still able to generate enough tension in use to unwind the spool
Data Source
Figure 1~3
AI summary
This invention is concerned with a line trimmer or mower head (1). In particular it is concerned with a line trimmer or mower head (1) having an automatic and/or manual line feed system with reduced tendency for cut and worn line to retract fully back into the spool housing. We describe a line trimmer (1) including a rotatable spool assembly (2) of at least one feedable line, at least one primary wall member (4) adjacent a periphery of said spool assembly (2) and a guide passage (7) extending generally radially away from said primary wall member (4). The guide passage (7) is partly defined by a substantially radially extending first formation (11) arranged to bear upon line extending through said guide passage (7), such that in use line located within said guide passage (7) is restricted to a substantially radial orientation.