Variable Spring Coupling for Autoinjector Needle Safety
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Solution Overview
Problem
Existing injection devices face challenges in balancing spring forces during the injection and retraction processes, leading to inefficiencies and increased risk of device malfunction or breakage, particularly in automatic injectors where precise control of needle movement is required.
Innovation Solution
The use of a thrust spring and a return spring, where the return spring is decoupled from the thrust spring during the dispensing movement, allowing for effective dispensing of the product without opposing forces, and coupled during retraction to ensure safe needle withdrawal, reducing stress on the device and minimizing the risk of injury.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the return spring is coupled with the thrust spring during the emptying movement, then the spring forces can be balanced, but the product dispensing efficiency is reduced due to opposing forces
Solution Approach 1:
The patent applies the dynamics principle by making the coupling between the return spring and thrust spring variable rather than fixed. The coupling is dynamically adjusted based on the operational phase: uncoupled during emptying movement to maximize dispensing efficiency, and coupled during retraction to enable spring force balance. This is achieved through a coupling mechanism that engages or disengages the springs based on plunger position or actuator state.
2Reliability
If the return spring opposes the thrust spring during dispensing, then the spring forces are balanced, but the risk of device malfunction or breakage increases
Solution Approach 1:
The patent applies segmentation by dividing the operational sequence into distinct phases (emptying movement and retraction) with different spring coupling states. During the emptying movement, the return spring is decoupled from the thrust spring, eliminating opposing forces that could cause device malfunction or breakage. The coupling is re-established only during the retraction phase when balanced forces are beneficial.
3Device complexity
If the needle retraction is manual, then the device complexity is reduced, but the user safety is compromised compared to automatic retraction
Solution Approach 1:
The patent applies the self-service principle by enabling automatic needle retraction through the spring mechanism. After product dispensing is complete, the coupled return spring and thrust spring automatically retract the needle without requiring additional user action. This reduces user exposure to the needle while maintaining a relatively simple mechanical structure based on the existing spring system.
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 solution enhances the efficiency of product dispensing, reduces the risk of device malfunction, and ensures safe automatic retraction of the needle, improving user safety and device reliability.
Implementation Method 1
a thrust spring that advances an injection needle from an initial position to an insertion position
Implementation Method 2
a return spring that retracts the injection needle from the insertion position into the distal end of the injection device counter to the force of the thrust spring
Data Source
AI summary
An injection device, in some embodiments an autoinjector, which includes a thrust spring that advances an injection needle from an initial position to an insertion position from the distal end of the injection device and that causes a product to be emptied from the product reservoir by an emptying movement, and a return spring that retracts the injection needle from the insertion position into the distal end of the injection device counter to the force of the thrust spring, wherein the return spring is decoupled from the thrust spring during the emptying movement.