Sewing Machine Gripper Assembly with Alternating Drive Cams
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Solution Overview
Problem
Existing sewing machine looper arrangements experience high friction during knot formation, leading to thread jamming, irregular thread tension, and noise, which affects sewing speed and stitch quality.
Innovation Solution
A gripper arrangement with rotating hook and alternating drive cams, combined with a conical gripper track and elastic guidance, allows for frictionless upper thread passage and easy thread release, while a spring compensates for thread tension changes and lubrication reduces wear and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper thread loop is guided around the hook body with the bobbin, then knot formation is enabled, but friction increases causing thread jamming
Solution Approach 1:
The hook is designed to rotate during operation, transforming from a static to a dynamic component. This rotation creates varying clearance between the hook and gripper track, preventing the upper thread loop from becoming jammed while maintaining the knot formation path
Solution Approach 2:
The drive mechanism is segmented into multiple drive cams that engage with the hook at different positions. This segmentation allows continuous rotational driving while distributing the engagement forces, reducing friction and wear on the thread path
2Reliability
If the hook is mounted freely in the gripper track for rotation, then knot formation is enabled, but the upper thread becomes prone to jamming
Solution Approach 1:
The conical gripper track design combined with elastic axial guidance enables the hook to self-adjust its position. When thread jamming occurs, the elastic guidance allows the hook to move axially, creating clearance that automatically releases the jammed thread without operator intervention
Solution Approach 2:
The hook's rotational movement combined with axial elasticity creates a dynamic system that can adapt to thread jamming conditions. The rotating hook periodically changes the clearance geometry, providing opportunities for jammed threads to be released during rotation cycles
3Reliability
If the lower thread is drawn into the sewn material by the upper thread, then knot formation is completed, but thread tension changes occur causing sub-optimal stitch pattern
Solution Approach 1:
The brake element is positioned to act on the lower thread spool in advance of the thread draw-in process. By applying preliminary braking force, the system prevents excessive spool acceleration that would otherwise cause thread tension fluctuations and stitch pattern defects
Solution Approach 2:
The brake element applies a counteracting force to the lower thread spool rotation, opposing the accelerating effect of the upper thread draw-in. This preliminary anti-action stabilizes the thread tension by preventing spool overspeed, ensuring consistent stitch quality throughout the knot formation process
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 minimizes thread friction, prevents jamming, maintains consistent thread tension, and reduces noise and wear, thereby increasing sewing speed and improving stitch quality.
Implementation Method 1
A spring that is arranged between the bobbin and the bobbin case and can be pivoted along the circumference of the bobbin case compensates for changes in the thread take-off speed and tension peaks on the lower thread.
Implementation Method 2
The drive cams can be continuously lubricated with a lubricating element, thereby avoiding wear and the resulting increase in noise.
Data Source
Figure 1a~1b
Figure 2
Figure 3~4
AI summary
For the continuous drive of a sewing machine's hook, two drive cams (17) alternately engage the back of the hook. As the upper thread loop passes, the drive cam (17) on which the thread would otherwise catch is disengaged. The hook rests in a conical guide and is held in place by magnets.