Sewing Machine Thread Cutting Device Using Worm Gear Actuation

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Solution Overview

Problem

Conventional thread cutting devices for sewing machines are overly complex, large, prone to amplification errors, and energy-consuming due to their linear actuator mechanisms, which hinder miniaturization, accuracy, and efficiency.

Innovation Solution

An automatic thread cutting device featuring a worm gear rod actuated by a motor with a passive piece and interlocking coaxial design, allowing precise control and energy efficiency through a compact structure with a worm gear mechanism, minimizing size and enhancing thread cutting performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If a linear actuator with lever arm mechanism is used to actuate the thread hooking member, then the moving distance of the thread hooking member can be amplified, but the device size becomes too large and complicated

Engineering Contradiction:

Improvemoving distance of thread hooking memberVSAvoidstructure complexity

Core Design Contradiction:

Length of moving objectVSDevice complexity

Solution Approach 1:

The patent replaces the traditional linear actuator with lever arm mechanism with a rotating actuator that directly drives the thread hooking member through a rotating connection. This substitution eliminates the need for lever arms and connecting rods, significantly reducing structural complexity while maintaining the required moving distance through rotational motion conversion.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

Instead of using a linear actuator that pushes and pulls the thread hooking member back and forth, the patent inverts the approach by using a rotating actuator that rotates to drive the thread hooking member along a linear path. This inversion of the motion type (from linear to rotational actuation) simplifies the overall mechanism.

Inventive Principle:

Principle #13The other way round (Inversion)

2Length of moving object

If a lever arm mechanism is used to amplify the moving distance, then the thread hooking member can move the required distance, but any component mistake is amplified causing inaccurate positioning

Engineering Contradiction:

Improvemoving distance of thread hooking memberVSAvoidpositioning accuracy

Core Design Contradiction:

Length of moving objectVSManufacturing precision

Solution Approach 1:

The patent eliminates the lever arm amplification mechanism and replaces it with a rotating actuator that provides direct, controlled motion to the thread hooking member. This substitution removes the error amplification inherent in lever arm systems, as the rotational actuator can precisely control the position through its rotation angle without mechanical advantage amplification of component tolerances.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If a linear actuator with long lever arm is used, then the thread hooking member can move back and forth, but the structure consumes excessive energy and the actuator is prone to damage

Engineering Contradiction:

Improvethread cutting functionVSAvoidenergy consumption

Core Design Contradiction:

Ease of operationVSUse of energy by moving object

Solution Approach 1:

The patent replaces the energy-intensive linear actuator with lever arm mechanism with a rotating actuator that directly drives the thread hooking member. This substitution reduces energy consumption by eliminating the mechanical disadvantage of the lever arm system, where the actuator must generate sufficient force to overcome the long load arm. The rotating actuator operates more efficiently with shorter effective leverage distances.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 solution achieves precise thread cutting with reduced size, improved safety, and energy efficiency, enabling miniaturization and optimal performance while preventing damage to components.

Implementation Method 1

a worm gear rod of active piece actuated by a motor of driving piece

Methodology Applied

Scientific EffectWorm gear mechanism: Worm Drive

Data Source

PatentUS7357089B1Automatic thread cutting device for sewing machine

Publication Date: 2008.04.15 TSANG YU IND

AI summary

The present invention is an automatic thread cutting device for a sewing machine, which is equipped with an automatic thread cutting device on the position that a needle thread passes through. The automatic thread cutting device comprises a main body that is equipped with a worm gear rod of active piece actuated by a motor of driving piece, wherein the active piece is engaged with a worm gear denture of passive piece that motivates a thread hooking member, a knife base with a knife is fixed on the main body and cooperates with the thread hooking member to cut a needle thread. Thus the size of the whole device can be minimized effectively to fit in the small space of a sewing machine, and then the objective of effort-saving and fast thread cutting is attained.