Sewing Machine Thread Cutting Device with Conversion Link
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional thread cutting devices for sewing machines, particularly in eyelet buttonhole stitching, experience instability in thread cutting position, leading to uneven residual thread lengths due to high-speed movement of the lower knife, resulting in poor uniformity and quality of the sewn product.
Innovation Solution
A thread cutting device with an upper knife and lower knife configured to rotate, utilizing an open-close link and conversion link mechanism that converts back-and-forth movement into circular motion, decelerating the lower knife's speed and stabilizing the thread cutting position, ensuring uniform residual thread length through adjustable joint positions and movement conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the lower knife moves at high speed to improve productivity, then the thread cutting operation is faster, but the thread cutting position becomes unstable and residual thread length becomes ununiform
Solution Approach 1:
The patent applies dynamics by making the lower knife rotate at variable speed rather than moving at constant high speed. The rotation speed is dynamically adjusted to be lower when cutting threads in the rear region L1 and higher when cutting threads in the front region L2, optimizing both precision and productivity for different stitching positions
Solution Approach 2:
The patent changes the speed parameter of the lower knife based on the stitching position. By adjusting the rotation speed parameter according to whether the final stitch point is in region L1 or L2, the system achieves stable thread cutting position while maintaining appropriate cutting speed for each region
2Length of moving object
If the final stitch point is set in the rear region L1 to reduce residual thread length, then the thread cutting position moves backward, but the lower knife hits the thread earlier causing instability
Solution Approach 1:
The patent uses dynamic speed adjustment of the lower knife to handle the timing issue when cutting threads in region L1. By rotating the lower knife at a controlled, lower speed, it hits the thread at the appropriate moment rather than too early, ensuring stable cutting position and reliable residual thread length
Solution Approach 2:
The patent prepares the lower knife by setting its rotation speed in advance based on the expected stitching position. When the final stitch point is determined to be in region L1, the lower knife is pre-configured to rotate at a speed that ensures it will hit the thread at the correct timing, preventing instability
3Length of moving object
If the final stitch point is set in the front region L2 to increase residual thread length, then the thread cutting position moves forward, but the residual thread length becomes too long
Solution Approach 1:
The patent adjusts the lower knife rotation speed parameter when the final stitch point is in region L2. By increasing the rotation speed appropriately, the system achieves the desired forward cutting position while maintaining uniform residual thread length through precise speed control
Solution Approach 2:
The patent dynamically adjusts the lower knife speed to match the required cutting position in region L2. The variable speed rotation ensures that even when cutting position changes to achieve longer residual thread length, the uniformity is maintained through optimized cutting dynamics
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a thread cutting device (20) for a sewing machine (10). The thread cutting device (20) includes an upper knife (22), a lower knife (23), an open-close link (24) coupled to the upper knife (22) and the lower knife (23), a drive source (28) coupled to the open-close link (24) to move the open-close link (24) back and forth along a linear direction. A thread is cut by closing the upper knife (22) and the lower knife (23). The thread cutting device (20) further includes a conversion link (25) having one end rotatably coupled to the open-close link (24) and the other end rotatably coupled to the lower knife (23). The conversion link (25) converts the back-and-forth movement of the open-close link (24) into a circular movement and transmits the circular movement to the lower knife (23).