Sewing Machine Presser Foot Dynamics for Thread Drawing
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Solution Overview
Problem
Existing sewing machines face difficulties in reliably drawing the thread to the back side of a workpiece during the starting of a sewing operation, especially when the thickness of the workpiece varies, due to timing issues with the presser foot movement, which can be exacerbated by the need for complex control systems like potentiometers to maintain synchronized operations.
Innovation Solution
A sewing machine design that incorporates a holding bar constantly biased downward by a first biasing force, an actuator with an operating member that can change states, and a connecting portion with a gap, where a second biasing force reduces this gap, allowing the presser foot to be positioned accurately based on workpiece thickness without the need for a potentiometer, ensuring reliable thread drawing through controlled movement states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the presser foot is moved up at a fixed timing to draw the thread, then the thread can be drawn to the back side, but when workpiece thickness varies, the presser foot may not reach its initial position, causing timing variations and unreliable thread drawing
Solution Approach 1:
The patent applies the dynamics principle by making the presser foot position adaptive rather than fixed. The presser foot is allowed to move up and down dynamically in response to varying workpiece thickness, ensuring it maintains proper positioning regardless of the workpiece dimensions. This dynamic adjustment capability resolves the contradiction between maintaining reliable thread drawing timing and adapting to different workpiece thicknesses.
2Manufacturing precision
If a potentiometer is attached to detect the lift lever rotational angle for compensating gap, then the presser foot timing can be optimized, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies the self-service principle by designing a mechanism where the presser foot automatically adjusts its own position based on the workpiece thickness without requiring external sensing devices like potentiometers. The mechanical linkage and spring system enable the presser foot to self-compensate for thickness variations, eliminating the need for complex electronic control systems while maintaining positioning precision.
Solution Approach 2:
The patent applies the extraction principle by removing the potentiometer and electronic control components from the system. Instead of using complex sensing and control mechanisms, the invention extracts only the essential mechanical elements needed for presser foot movement, simplifying the overall device while achieving the desired positioning accuracy through pure mechanical means.
3Device complexity
If the presser foot is moved down by spring biasing force, then the structure is simplified, but when workpiece thickness varies, timing synchronization between the air cylinder and presser foot deteriorates
Solution Approach 1:
The patent applies dynamics by allowing the presser foot to move dynamically in response to both the spring biasing force and the workpiece thickness. The presser foot's position is not statically determined by the spring alone but adjusts dynamically based on the actual workpiece dimensions, maintaining timing synchronization without requiring complex control systems.
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 design simplifies the structure and control of the sewing machine, enabling reliable thread drawing to the back side of the workpiece at the start of the sewing operation across varying workpiece thicknesses without the use of a potentiometer, ensuring efficient and synchronized presser foot movement.
Implementation Method 1
A front end portion of a lift lever 109 comes in contact with a lower face of one end portion of a holding bar bracket 108. The lift lever 109 is substantially in an L shape, and moves up the holding bar 107 and the presser foot 106 by lifting the holding bar bracket 108.
Data Source
AI summary
A sewing machine includes a needle, a needle bar which supports the needle, an upper feeding foot operable to feed the workpiece interlockingly with an up and down movement of the needle bar, a presser foot operable to press the workpiece, a holding bar which supports the presser foot, an actuator including an operating member operable to be changed to a first state, a second state or a no-load state, and a connecting portion which couples the operating member and the holding bar. The holding bar is constantly biased downward by a biasing force. The actuator moves the presser foot up against the first biasing force when the operating member is in the first state, and moves the presser foot down when the operating member is in the second state.