Sewing Machine Speed Control for Free Motion Stitching
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Solution Overview
Problem
Conventional sewing machines face difficulties in maintaining constant stitch pitch during dynamic manual movement of the workpiece, leading to stitch displacement and rhythm issues, especially for beginners or when sewing patterns require low-speed needle-bar movement.
Innovation Solution
A sewing machine with a sewing speed controller that adjusts the motor speed based on the stitch pitch and consumed needle-thread amount, allowing for smooth free motion sewing by controlling the sewing speed at either a predetermined reference speed or a target speed calculated from the stitch pitch and cloth movement amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the needle bar is moved at lower speed to allow dynamic manual movement of the workpiece, then the user can move the workpiece more freely, but the time period in which the workpiece is anchored in place by the sewing needle increases, reducing the time available for moving the workpiece and causing stitch displacement
Solution Approach 1:
The sewing machine implements dynamic speed control that automatically adjusts the needle bar speed based on real-time detection of workpiece movement amount. When the workpiece moves faster, the needle bar speed increases proportionally, maintaining optimal anchoring time. This dynamic adaptation resolves the contradiction by making the system flexible rather than fixed, allowing both free manual movement and consistent stitch pitch under varying conditions.
Solution Approach 2:
The system uses a sensor to detect the workpiece movement amount and feeds this information back to the control unit, which then adjusts the motor speed accordingly. This closed-loop feedback mechanism ensures that the needle bar speed always matches the workpiece movement rate, preventing stitch displacement while maintaining operational freedom. The feedback loop continuously monitors and corrects speed deviations.
2Force
If the user forces the movement of the workpiece with the sewing needle penetrating through it, then the workpiece can be moved against resistance, but the workpiece is pulled away from the sewing needle and becomes displaced by the sudden release of tension, resulting in displacement of stitches
Solution Approach 1:
The system dynamically adjusts the needle bar speed to match the workpiece movement speed in real-time. When the user applies force to move the workpiece, the sensor detects the increased movement rate and the control unit immediately increases the motor speed, ensuring the needle remains properly positioned in the workpiece throughout the movement. This prevents the workpiece from being pulled away and eliminates sudden tension releases that cause stitch displacement.
3Speed
If the user brings the workpiece movement to a sudden stop in response to the sudden workpiece movement and acceleration of the needle bar movement, then the workpiece can be stopped quickly, but the needle bar movement is suddenly decelerated, causing stitch displacement
Solution Approach 1:
The system implements dynamic speed matching where the needle bar speed automatically follows the workpiece movement speed. When the user suddenly stops the workpiece, the sensor detects the speed reduction and the control unit immediately decelerates the motor proportionally. This synchronized deceleration prevents sudden stops that would cause the needle bar to overshoot or create stitch displacement, maintaining consistent stitch pitch even during rapid speed changes.
Solution Approach 2:
The feedback mechanism continuously monitors workpiece movement speed and adjusts the motor speed in real-time. When sudden stopping occurs, the feedback loop quickly detects the speed change and commands the motor to decelerate smoothly, preventing the needle bar from maintaining high speed while the workpiece stops. This feedback control eliminates the time lag between workpiece stopping and needle bar response, preventing stitch displacement.
Data Source
AI summary
A sewing machine includes a sewing machine motor that vertically drives a sewing needle via a main shaft; a sewing speed commander that produces a command sewing speed determined by rotational speed of the sewing machine motor; a stitch-pitch specifier that specifies a stitch pitch to be applied to manually fed sewing operation; a consumed thread amount detector that detects a consumed needle-thread amount in each ongoing sewing cycle; a sewing speed controller that controls sewing speed at the command sewing speed when the command sewing speed is equal to or less than a predetermined reference sewing speed, and that controls sewing speed at a target sewing speed calculated based on the consumed needle-thread amount and the stitch pitch when the command sewing speed is greater than the reference sewing speed.