Quadrangular Sewing Needle Asymmetry for Straight Stitch Lines
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Solution Overview
Problem
Conventional stitch line forming methods result in stitches that are inclined due to tension forces, failing to produce a straight stitch line that meets the demand for improved appearance in upholstered articles.
Innovation Solution
A stitch line forming method using a sewing needle with a quadrangular cross-sectional shape, where the diagonal lines are inclined opposite to the rotation direction of thread ends, forming needle receiving holes with flat inner surfaces to restrict rotation and maintain stitches aligned with the feeding direction, ensuring a straight stitch line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If tension is applied to the lower thread to ensure sewing quality, then the appearance is improved, but the thread ends rotate about the crossing part causing the stitch line to become inclined
Solution Approach 1:
The sewing needle is designed with an asymmetric quadrangular cross-section where the diagonal lines are inclined relative to the needle axis. This asymmetric geometry creates unequal clearance between the needle corners and the needle receiving hole walls, generating a counteracting force that offsets the rotation caused by thread tension, thereby maintaining stitch line straightness
Solution Approach 2:
The inclined diagonal lines of the quadrangular needle cross-section create a mechanical counterbalance to the rotation force generated by lower thread tension. The asymmetric clearance distribution produces a counteracting moment that balances the rotational tendency of thread ends about the crossing part, preventing stitch line inclination
2Ease of manufacture
If a circular cross-sectional sewing needle is used, then the manufacturing is simple, but the thread ends rotate along the curved inner circumferential surface causing inclined stitches
Solution Approach 1:
The sewing needle transitions from a symmetric circular cross-section to an asymmetric quadrangular cross-section with inclined diagonal lines. This asymmetric geometry creates non-uniform clearance in the needle receiving hole, generating a counteracting force that prevents thread end rotation and ensures straight stitch lines
Solution Approach 2:
The needle cross-sectional shape parameter is changed from circular to quadrangular with specific diagonal line inclination angles. This parameter modification alters the clearance distribution between the needle and needle receiving hole, creating a mechanical effect that counteracts thread tension-induced rotation
Data Source
AI summary
While feeding an upholstery member, a sewing needle is reciprocated to form needle receiving holes, and an upper thread is passed through each needle receiving hole, caused to cross a lower thread, and pulled out of the needle receiving hole. The sewing cycle is repeatedly performed to form a stitch, so that stitches form a stitch line in a surface sheet. A direction of a force, which is generated by applying tension to the lower thread and which acts to rotate thread ends of a pair of adjacent stitches in each needle receiving hole about a crossing part of the upper thread and the lower thread, is defined as a rotation direction. The sewing needle is rotated in a direction opposite to the rotation direction to incline a diagonal line of the quadrangular shape forming the cross section relative to the feeding direction of the upholstery member.