Dynamic Thread Tension Control for Precise Knot Positioning
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Solution Overview
Problem
Existing sewing machines face challenges in precisely controlling the position of knots between the upper and lower threads, especially when sewing zigzag or caterpillar seams, due to variations in thread tension, fabric type, and needle bar movement, leading to unsatisfactory knot placement.
Innovation Solution
A device and method using a single actuator to control the thread tensioning force during knot formation, with a calculation unit adjusting the actuator's command variable based on parameters like thread tension, needle bar pivoting, and sewing speed to minimize knot position deviation from a target position, allowing for improved knot placement within the sewing material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed thread tension setting is used, then the device complexity is reduced, but the manufacturing precision of knot position deteriorates
Solution Approach 1:
The patent implements dynamic thread tension control by adjusting the tensioning force during the sewing process based on detected knot position deviations. The system transitions from a static fixed tension setting to a dynamic adjustable tension mechanism that responds to real-time feedback, resolving the contradiction between device simplicity and positioning precision.
Solution Approach 2:
The patent employs a feedback control mechanism where the actual knot position is detected and compared against the target position, and the thread tension is adjusted accordingly to minimize deviations. This closed-loop feedback system enables precise knot positioning while maintaining relatively simple device architecture.
2Manufacturing precision
If thread tension is increased to pull knots toward the fabric center, then the manufacturing precision of knot position is improved, but the force required increases causing thread damage
Solution Approach 1:
The system uses feedback control to detect knot position and apply only the necessary tension force to achieve centering. By measuring actual position and comparing it to the target, the system applies minimal corrective force rather than continuously high tension, preventing thread damage while achieving precise positioning.
Solution Approach 2:
The patent dynamically adjusts the thread tension parameter based on the detected knot position deviation. Instead of maintaining high constant tension, the system varies the tension level according to the specific positioning needs at each moment, achieving precise knot placement with minimized force application.
3Manufacturing precision
If manual adjustment of thread tensioner is used, then the ease of operation is reduced, but the manufacturing precision of knot position can be improved
Solution Approach 1:
The patent implements a self-adjusting system where the thread tensioner automatically modifies its own settings based on detected knot position. The system performs the adjustment function autonomously without requiring manual intervention, thereby maintaining ease of operation while achieving precise knot positioning through automated feedback control.
Solution Approach 2:
The automated feedback control system continuously monitors knot position and adjusts thread tension accordingly, eliminating the need for manual tensioner adjustment. This autonomous operation maintains ease of use while achieving consistent precise positioning that would be difficult to maintain through manual adjustment alone.
4Productivity
If sewing speed is increased to improve productivity, then the productivity increases, but the manufacturing precision of knot position deteriorates
Solution Approach 1:
The patent employs real-time feedback control that operates effectively at high sewing speeds. The system detects knot position deviations and adjusts thread tension dynamically during the sewing process, maintaining precise positioning even when productivity is increased through higher sewing speeds. The feedback loop operates fast enough to keep pace with increased production rates.
Solution Approach 2:
The dynamic thread tension adjustment system adapts to the increased sewing speed by making rapid tension modifications during knot formation. This dynamic response capability allows the system to maintain precise knot positioning despite the reduced time available for each adjustment, enabling both high productivity and high precision to coexist.
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
This solution enables precise control of knot placement, ensuring knots are consistently drawn into the middle of the fabric, even at higher sewing speeds, while allowing for creative patterns by varying knot positions between successive puncture points.
Implementation Method 1
an electromagnet acts as the actuator on a friction brake with two tensioning discs
Implementation Method 2
a friction brake with two tensioning discs
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
The device and method for influencing the position of knots (31) between the upper thread (23) and the lower thread (17) when sewing with a sewing machine (1) utilize a calculation unit (37) which calculates a control value for an actuator (39) for each stitch to be formed, with which the braking force of the thread tensioner (23) is controlled.