Variable Force Springs in Cordless Window Coverings
Achieving "Effortless Push-Pull, Instant Stop" through unique non-linear stiffness characteristics and critical damping control
Core Working Principle
Variable force springs achieve the "effortless push-pull, instant stop" effect through non-linear stiffness characteristics. The key lies in how the spring's resistance changes with deformation - providing low initial resistance (easy to operate) while increasing resistance non-linearly as deformation increases (achieving instant stop). This characteristic stems from special geometric design that creates a "J-shaped" force curve rather than the linear characteristics of traditional springs.
Core Mechanism for "Effortless Push-Pull"
Low Resistance Startup Mechanism
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Variable pitch design
Larger initial pitch (8-10mm) with fewer active coils, stiffness coefficient only 3-5N/mm
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Progressive contact
Curved transition on spring-track contact surface reduces friction coefficient to 0.08
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Preload optimization
5-8% pre-compression during installation eliminates dead zone
Variable Stiffness Control Mechanism
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Variable wire diameter structure
Wire diameter gradually increases from 0.8mm to 1.2mm, stiffness gradient increases 40%
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Active coil count variation
Active working coils decrease from 12 to 8 during deformation, increasing stiffness by 50%
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Material strengthening treatment
Special heat treatment creates gradient elastic modulus (180-220GPa)
Mechanical Principle for "Instant Stop"
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J-shaped force curve
Spring force F and displacement X follow F=k₁X+k₂X³ relationship (k₁=3.5, k₂=0.15), resistance surges 200% at 70% displacement
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Critical damping design
Spring system damping ratio ζ=0.7-0.9 ensures complete stop within 0.3 seconds
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Self-locking structure
15° inclined locking design at spring end creates mechanical self-lock effect at >85% displacement
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Energy dissipation mechanism
Internal friction plates convert kinetic energy to heat, dissipating ≥0.8J per braking
Technical Value Summary
- Reduced initial force: Startup resistance ≤2N (traditional springs ≥5N)
- Faster braking response: Stop time ≤0.3s (traditional springs ≥1.2s)
- Improved positioning accuracy: Displacement error ≤±1mm (traditional springs ≥±5mm)
- Optimized operation experience: Achieves "floating feel" with 0.8-1.2N single-finger operation force
Through the "variable stiffness design + critical damping control" technical solution, variable force springs perfectly resolve the contradiction between easy operation and precise positioning, providing window coverings with an ultimate experience of "light as a feather initially, stable as a rock when stopping".
