Sewing Machine Thread Cutter with Moving Knife and Air Blow
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Solution Overview
Problem
In sewing machines, the sewing start end portion of the upper thread can get caught in the seam, leading to a 'bird's nest' situation, which deteriorates sewing quality.
Innovation Solution
A sewing machine with a needle vertical movement mechanism and a thread cutter, where the thread cutter includes a fixed knife and a moving knife with a through-hole for the sewing needle, and a controller to manage the position of the moving knife to pin and cut the upper thread effectively, along with an air blow mechanism to guide and capture the thread end portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the shuttle mechanism draws the sewing start end portion of the upper thread to the lower side of the cloth, then the thread is positioned for sewing, but the thread may be caught by the seam causing a bird's nest
Solution Approach 1:
The moving knife performs a preliminary pinching action on the thread before the sewing needle completes the second stitch. By pinching the thread at the timing of the second stitch rather than waiting for the first stitch to complete, the system prevents the thread end from being drawn into the seam and forming a bird's nest, while still allowing proper thread positioning to occur
Solution Approach 2:
The moving knife acts as an intermediary device between the shuttle mechanism and the thread. It pinches and controls the thread end portion, preventing the shuttle from drawing the thread too far into the lower side of the cloth where it would be caught by the seam, thus mediating the interaction between these components
2Reliability
If the moving knife pinches the thread before the first stitch completes, then thread control is improved, but the needle may collide with the moving knife
Solution Approach 1:
The moving knife is designed to move dynamically rather than remain stationary. It moves to the pinching position only at the appropriate timing (when the needle has moved down to a safe position before the second stitch), avoiding collision with the needle while still achieving effective thread control. The knife then returns to its original position, creating a dynamic system that adapts to the needle's motion cycle
Solution Approach 2:
The moving knife operates in a periodic cycle synchronized with the needle's vertical movement. It pinches the thread during specific phases of the sewing cycle (after the needle has descended sufficiently) and releases it during other phases, creating a rhythmic, periodic action that prevents needle collision while maintaining effective thread control throughout the sewing 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 setup effectively reduces the occurrence of bird's nest by maintaining the upper thread end portion in a controlled position and cutting it at the right time, improving sewing quality and eliminating the need for a dedicated device for thread management.
Implementation Method 1
an air blow mechanism to guide and capture the thread end portion
Data Source
AI summary
A sewing machine includes a controller and a thread cutter which cuts an upper thread passed through a sewing needle and which has a fixed knife, a moving knife, and a driving source to drive the moving knife. The moving knife cuts the upper thread by guiding the upper thread. The moving knife has a through-hole into which the sewing needle is loosely insertable and includes a thread cutting portion in an inner edge portion of the through-hole. By controlling the driving source, the controller makes a stitch point of a first stitch of the sewing needle with respect to the through-hole of the moving knife, and moves the moving knife to a position where the fixed knife and the moving knife cut a sewing start end portion of the upper thread after a stitch point of a second stitch of the sewing needle.