Cylindrical Spring Bobbin for Double Backstitch Sewing Machine
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Solution Overview
Problem
Existing hook designs for double-lockstitch sewing machines face challenges in achieving uniform braking torque and long extension distances for the spool, as the truncated cone spring configuration is difficult to optimize for these requirements.
Innovation Solution
A cylindrical helical spring is used as the braking and extension spring, which engages in a recess of the bobbin hub, allowing for precise control of braking moments and enabling larger extension distances, while also utilizing the space between the bobbin flange and case more efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a truncated cone spring is used as the braking and extension spring, then the spring can be compressed to the thickness of the windings when the hook thread bobbin is inserted, but it is very difficult to achieve both optimization of the long extension path for the spool and uniform braking torque exerted on the spool
Solution Approach 1:
The patent changes the geometric parameters of the spring from a truncated cone shape to a cylindrical shape with constant diameter. This parameter change allows the spring to provide consistent braking torque throughout its compression stroke while accommodating the required extension distance, resolving the contradiction between extension path optimization and uniform braking torque
Solution Approach 2:
The patent segments the spring into multiple active coils of equal length, where each coil contributes uniformly to the braking torque. This segmentation ensures that the force distribution remains consistent during compression, achieving uniform braking torque while maintaining the required extension distance
2Length of moving object
If a truncated cone spring is used, then the spring structure is compact, but the extension distance for the spool is limited
Solution Approach 1:
Instead of using a truncated cone shape that tapers to a smaller diameter, the patent inverts the approach by using a cylindrical shape with constant diameter throughout. This inversion allows the spring to extend fully along the axis without the geometric constraints of a tapered shape, achieving the required long extension distance
3Length of moving object
If a cylindrical helical spring is used, then large extension distances are possible and braking moments can be set very precisely, but the spring requires sufficient space in the recess of the hook thread spool
Solution Approach 1:
The patent uses a cylindrical spring that may extend slightly beyond the recess boundaries when fully compressed, accepting partial excess action to achieve the required extension distance. The constant diameter design allows the spring to maximize its axial length while minimizing the radial space required in the bobbin hub recess
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 ensures uniform gripper thread tension and allows for extended spool movement, with consistent braking torque and precise thread pulling, enhancing the operational efficiency of the sewing machine.
Implementation Method 1
an essentially cylindrical helical spring is used as the braking and extension spring
Implementation Method 2
the braking and extension spring does not have to be mathematically exactly cylindrical; the decisive factor is that it has sufficient space in the recess of the hook thread spool
Implementation Method 3
engages in a corresponding recess in the hub of the looper thread bobbin
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The gripper e.g. double-backstitch gripper (8), has a bobbin case (21) arranged in a cap-shaped gripping body (24) about an axis (9) and including a base (34) and a bearing pin (25). A gripper thread bobbin (26) is movably arranged on the pin in a direction of the axis, and includes flanges (28, 29) that are spaced apart from each other, where the flanges are connected to a hollow boss (27). A brake spring and an exhaust spring i.e. cylindrical helical spring, enclose the pin, and the case is reinforced at a region of the base, and the bobbin is reinforced in an opening (31) of the boss.