Trimmer Head Line Removal Mechanism

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Solution Overview

Problem

Existing line mowing heads for brush cutters face difficulties in removing cutting lines due to their inaccessible design, especially when wearing work gloves, making disassembly cumbersome.

Innovation Solution

The line mowing head design incorporates a stop mechanism and a deflection element that allows the cutting line to be converted from a first position, where it is restricted, to a second position, enabling easy removal by bending the thread section around the opening, and a securing contour to hold the line in place during removal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the cutting line is inserted into the trimmer head with the stop limiting insertion length, then the cutting line is secured in place during operation, but the cutting line becomes difficult to access and remove

Engineering Contradiction:
Improvesecuring of cutting lineVSAvoidremoval of cutting line
Core Design Contradiction:
ReliabilityVSEase of operation

Solution Approach 1:

The cutting line is designed to be movable between two positions: first position where the stop limits insertion and secures the line during operation, and second position where the line can be completely pushed or pulled through the line opening for easy removal. This dynamic repositioning capability allows the same cutting line to serve both securing and removal functions

Inventive Principle:
Principle #15Dynamics

Solution Approach 2:

The deflector acts as an intermediary element that guides the cutting line from the first position to the second position. The deflector is arranged inside the trimmer head to facilitate the movement of the cutting line without requiring the operator to directly manipulate the line past the stop, making removal easier even when wearing work gloves

Inventive Principle:
Principle #24Intermediary (Mediator)

2Strength

If the cutting line is made stiff to maintain shape during operation, then the cutting line performs better during mowing, but the cutting line cannot be easily deformed to access the free ends for removal

Engineering Contradiction:
Improveinherent stiffness of cutting lineVSAvoiddeformation of cutting line
Core Design Contradiction:
StrengthVSEase of operation

Solution Approach 1:

The cutting line's deformation behavior is made dynamic based on the applied force. During normal operation, the line maintains its stiffness for proper mowing performance. During removal, when force is applied to move the line into the second position, the line can be deformed to bend around the opening and clear the stop, allowing easy removal without compromising operational stiffness

Inventive Principle:
Principle #15Dynamics

Data Source

PatentEP3400776B1String mower head for a string mower
Publication Date: 2020.11.18 ANDREAS STIHL AG & CO KG
  • EP3400776B1 patent drawingFigure 1
  • EP3400776B1 patent drawingFigure 2~3
  • EP3400776B1 patent drawingFigure 4~5

AI summary

The invention relates to a trimmer head for a brushcutter, wherein the trimmer head (5) can be driven to rotate about a pivot axis (7) during operation. The trimmer head (5) has a base body (10) to which at least one cutting line (8) is held. The cutting line (8) extends from an outer surface (14) of the base body (10) through a line opening (18) into an inner area (15) of the trimmer head (5) that is open to the environment. A stop (16) for the cutting line (8) is arranged on the trimmer head (5), wherein the stop (16) limits the length (f) of a line segment (19) of the cutting line (8) that can be inserted into the inner area (15) to an insertion length (b).Inside the inner area (15) of the trimmer head (5), at least one deflecting element (22) is arranged such that the cutting line (8) can be transferred from its first layer (28) to a second layer (29) without any longitudinal displacement of the cutting line (8). In its second layer (29), the cutting line (8) rests against the deflecting element (22), and the stop (16) does not limit the length (f) of the line segment (19) that can be inserted into the inner area (15).