Non-uniform Helical Spring for Safety Syringe Latch Actuation
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Solution Overview
Problem
Existing safety syringe designs face issues with the spring's ability to adequately cover the needle due to diminished force during the last stages of expansion, leading to potential exposure of the needle point, and the need for stronger springs results in increased size and cost, as well as restricted needle exposure length.
Innovation Solution
A non-uniform helical spring with alternating angled and flat portions is used, providing a greater expansion force and terminal force to ensure the sheath locks into place effectively, while maintaining a compact size and allowing full needle exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the spring is made stronger by adding turns or increasing thickness, then the terminal expansion force is sufficient to actuate the latch mechanism, but the collapsed length of the spring becomes too great to allow full needle exposure
Solution Approach 1:
The patent modifies the spring's geometric parameters by introducing non-uniform coil spacing and varying wire diameter along the spring's length. This allows the spring to achieve sufficient terminal expansion force with fewer total turns, thereby reducing the collapsed length while maintaining the required force for latch actuation
Solution Approach 2:
The patent transitions from a uniform spring design to a non-uniform spring design where coil spacing and wire diameter vary along the longitudinal dimension. This dimensional variation allows optimization of force characteristics at specific positions without uniformly increasing the spring's collapsed length
2Reliability
If a stronger spring is used to ensure adequate expansion force, then the latch mechanism is reliably actuated, but the spring requires additional turns or greater thickness increasing device size and cost
Solution Approach 1:
The patent employs parameter changes by varying the coil spacing and wire diameter along the spring's length. This creates a non-uniform spring that achieves reliable latch actuation through optimized force distribution rather than uniformly increasing spring complexity throughout
Solution Approach 2:
The patent applies local quality by concentrating the spring's structural complexity only where needed - specifically in regions requiring higher force for latch actuation - while maintaining simpler geometry in other regions. This localized optimization achieves reliable latch engagement without uniformly increasing overall spring complexity
3Force
If the spring is made stronger by using different material or increased dimensions, then the expansion force is sufficient, but the spring size and manufacturing cost increase
Solution Approach 1:
The patent achieves increased expansion force through geometric parameter changes (non-uniform coil spacing and varying wire diameter) rather than material changes or uniform dimensional increases. This approach maintains manufacturing simplicity while achieving the required force characteristics through intelligent geometry design
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 non-uniform spring design enhances the locking mechanism's security and ensures the needle is fully covered and locked in its protective position, while reducing the syringe's weight and material usage, allowing for better needle placement and improved safety.
Implementation Method 1
the spring expanding to move the sheath forward, causing the sliding sheath to lock in a protective manner over the needle point
Implementation Method 2
A non-uniform helical spring with alternating angled and flat portions is used, providing a greater expansion force and terminal force
Data Source
AI summary
An improved safety hypodermic syringe includes a reciprocal tubular needle sheath disposed on the exterior of the syringe body, a latch mechanism engaging the syringe body and the sheath to latch the sheath in a needle-covering position after delivering contents from the syringe body, and a spring engaging the syringe body and the sheath and expandable to move the sheath to cover the needle point, where the spring is a non-uniform helical spring having multiple 360° turns each turn uniformly spaced from adjacent turns, each 360° turn comprising first and second alternating angled portions, the first of the alternating angled portions being at a first angle to a plane perpendicular to an axis through the center of the helical spring and the second angled portions being at a second lesser angle to the plane perpendicular to the axis.