Sewing Machine Thread Cutting Mechanism
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Solution Overview
Problem
Conventional sewing machines with thread cutting devices often fail to reliably cut lower threads due to strong thread tension, causing the thread to deviate from the cutting path and preventing effective cutting.
Innovation Solution
A sewing machine design featuring a bulged portion on the cloth feed base that separates the lower thread from the cloth, creating a gap for the upper knife to guide through and cut the thread, eliminating the need for a guide member integral with the knives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guide member is provided integrally with the moving knives to guide the lower thread, then the thread cutting function is improved, but the device complexity increases and the guide member may cause the thread to deviate when tension is strong
Solution Approach 1:
The invention removes the guide member from the knife assembly and extracts the thread guiding function to the bed structure. The bulged portion on the bed surface serves as the guide, separating the thread from the cloth and guiding it to the knife path without requiring an integral guide member, thus simplifying the device while maintaining cutting reliability
Solution Approach 2:
The bulged portion on the bed surface acts as an intermediary element between the cloth and the knives. It creates a gap that separates the lower thread from the cloth and guides the thread to the correct position for cutting, mediating the interaction between the thread path and the cutting action without requiring direct contact between the knives and guide structures
2Manufacturing precision
If the lower thread path is arranged parallel to the cloth feed base, then the sewing quality is improved by shortening remaining thread length, but the thread cannot be captured by the knives for cutting
Solution Approach 1:
The invention introduces a vertical dimension to the otherwise parallel thread path by creating a bulged portion that rises from the bed surface. This vertical protrusion creates a gap that allows the horizontally moving knives to access and cut the thread, adding a third dimension to the cutting geometry without changing the horizontal thread path alignment
Solution Approach 2:
The bulged portion is positioned in advance along the thread path to preliminarily separate the thread from the cloth before the knives arrive. This preliminary action creates the necessary gap and positions the thread for cutting, ensuring that when the knives reach the cutting position, the thread is already accessible and properly positioned for reliable cutting
Data Source
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AI summary
The present invention relates to a sewing machine (10). The sewing machine (10) includes a cloth feed base (16, 16a) on which a cloth is placed, a stitch forming means for forming stitches by an upper thread and a lower thread on the cloth placed on the cloth feed base (16, 16a), and a thread cutting device (50, 50A) disposed below the cloth feed base (16, 16a) and having a lower knife (51, 51a) and an upper knife (52, 52a) that cuts the lower thread (T1) in cooperation with the lower knife (51, 51a). The cloth feed base (16, 16a) has a bulged portion (161, 161a) protruding upward to separate the lower thread and the cloth from each other. The bulged portion (161, 161a) has a portion defining at least a part of a gap portion (163, 163a) serving as a movement path of the upper knife (52, 52a), the movement path being above a lower surface of the cloth feed base (16, 16a).