Fixed Bobbin Case Sewing Machine Thread Supply
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Solution Overview
Problem
Conventional sewing machines form stitches where the upper thread ties the lower thread loosely, leading to easy unraveling and wrinkles, and fail to maintain the integrity of sewn portions.
Innovation Solution
A lower-thread supply device with a bobbin case and hook body configuration where the bobbin case is fixed not to rotate, and the outlet is positioned for the needle to pass to the left of the drawn-out lower thread, ensuring the upper thread is caught and dragged by the hook from the left, forming a stable knot-like stitch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper thread loosely ties the lower thread in conventional sewing machines, then the stitching process is simple, but the sewn portion easily unravels and forms wrinkles
Solution Approach 1:
The thread supply device is segmented into distinct functional zones: the bobbin case with outlet positioned at specific location, the hook body with hook portion, and the needle path. This segmentation allows precise control of thread interaction points, enabling the upper thread to form secure knots around the lower thread at multiple locations along the stitch path, thereby improving seam integrity without excessive complexity
Solution Approach 2:
The hook body acts as an intermediary mechanism between the upper thread and lower thread. It catches the upper thread and drags it to position it precisely for knot formation around the lower thread. This intermediary device enables controlled thread interaction that prevents unraveling while maintaining reasonable device complexity
2Stability of the object's composition
If the bobbin case is fixed not to rotate, then the lower thread position is stable, but the device structure becomes more complex
Solution Approach 1:
The bobbin case is preliminarily fixed in position before the stitching operation begins. This preliminary fixation ensures that the lower thread emerges from the outlet at a consistent, predetermined position throughout the sewing process. The outlet is specifically positioned so that when the needle moves downward, it passes to the left of the drawn-out lower thread, creating stable geometric relationships that maintain thread position stability without requiring complex active control mechanisms
3Reliability
If the outlet is positioned for the needle to pass to the left of the drawn-out lower thread, then the upper thread is caught and dragged from the left forming stable knots, but the geometric configuration becomes more specific and complex
Solution Approach 1:
The device employs asymmetric geometric configuration: the outlet is positioned specifically to the right of the needle path, causing the lower thread to emerge to the right of the needle. This asymmetric arrangement ensures that when the needle moves downward, the upper thread is caught by the hook from the left side and dragged to form knots around the lower thread in a consistent left-to-right direction. This asymmetric design creates reliable knot formation geometry without requiring overly complex mechanisms
Data Source
AI summary
Disclosed herein are a lower-thread supply device of sewing machine and a sewing method. The device includes a bobbin case (300) having an outlet (330) from which lower thread is drawn out, and a needle through-hole (340) through which a needle (600) moving downwards with upper thread (a) being fitted passes, and a hook body (200) in which the bobbin case (300) is mounted, the hook body being installed to be rotatable by a power device of a sewing machine, guiding upper thread (a2) on a sewn fabric side to a front area of the bobbin case (300) while catching and dragging the upper thread (a) via a hook (210), and guiding upper thread (a1) on a spool side to a rear area of the bobbin case (300). The bobbin case (300) is installed not to be rotated when the hook body (200) rotates.