Free-Motion Sewing Thread Tension Control for Easier Fabric Handling
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Solution Overview
Problem
In free motion sewing, the resistance applied by the thread to the sewing workpiece makes it difficult for a user to manually move the workpiece, as the thread pulls the workpiece and impedes its movement.
Innovation Solution
A sewing machine with a thread tension control mechanism that adjusts thread tension pressure and disc spacing to reduce tension during periods when manual movement of the workpiece is required, enhancing maneuverability by controlling the spring length and thread tension pressure through an actuator and controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the thread tension is maintained at a normal level during free motion sewing, then the stitching quality is ensured, but the user experiences difficulty in manually moving the workpiece due to resistance from the thread
Solution Approach 1:
The thread tension is made dynamically adjustable through the actuator that changes the spring length in real-time. The controller adjusts the spring length to different values during different phases of the sewing cycle, allowing the tension to transition between low (for ease of movement) and high (for stitching quality) states as needed.
Solution Approach 2:
The thread tension is adjusted periodically in sync with the needle bar movement cycle. The controller changes the spring length during specific periods (needle up period and needle down period), creating a periodic variation in tension that matches the sewing operation rhythm - low tension during manual movement phases and high tension during stitching phases.
2Force
If the spring length is reduced to increase thread tension pressure, then the thread tension is improved for stitching, but the resistance to manual movement of the workpiece increases
Solution Approach 1:
The spring length is dynamically adjusted based on the operational phase. The actuator changes the spring length from a longer value (lower tension, easier movement) during manual movement phases to a shorter value (higher tension, better stitching) during stitching phases, resolving the contradiction between force and ease of operation.
Solution Approach 2:
The controller adjusts the spring length in advance during the needle up period before the needle descends to punch the thread. This preliminary action sets the tension to an appropriate level for the upcoming stitching operation, ensuring that when the needle punches the thread, the tension is already optimized for stitching quality rather than being high throughout the entire cycle.
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
The thread tension control mechanism improves the ease of manually moving the sewing workpiece by reducing thread tension during user-manipulated periods, thereby enhancing the maneuverability of the workpiece.
Implementation Method 1
The spring is configured to urge the thread tension disc to apply a thread tension pressure to the thread tension disc
Implementation Method 2
The actuator is configured to adjust a length of the spring... controlling the actuator to adjust the length of the spring
Data Source
AI summary
A controller performs a free motion sewing operation of driving a sewing machine motor to move a needle bar up and down in a state where an upper end of a feed dog is located below a needle plate. The controller performs a thread tension control operation of, while performing the free motion sewing operation, controlling an actuator to adjust a length of a spring during a first period to a first length and to adjust the length of the spring during a second period to a second length shorter than the first length. The first period is at least part of a needle up period in which a lower end of a sewing needle is located above the needle plate. The second period includes at least part of a needle down period in which the lower end of the sewing needle is located below the needle plate.