Auto-Injector Spring Mechanism for Complete Dose and Needle Retraction
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Solution Overview
Problem
Existing auto-injectors face challenges such as user discomfort due to high injection forces, hand trembling, and the risk of incomplete doses, particularly in manual devices, while auto-injectors often require complex mechanisms and additional springs for needle retraction.
Innovation Solution
An auto-injector design utilizing a single compression spring for needle insertion, dose delivery, and retraction, with a simplified mechanism that includes a retraction sleeve and decoupling arms to manage the spring force, ensuring complete dose delivery and safe needle retraction without additional springs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single compression spring is used for needle insertion, dose delivery, and retraction, then device complexity is reduced and manufacturing costs are lowered, but the spring must handle multiple functional requirements with different force characteristics
Solution Approach 1:
The single compression spring is segmented into distinct functional zones along its length: an insertion zone for needle advancement, a delivery zone for medicament expulsion, and a retraction zone for needle withdrawal. Each zone is optimized for its specific function through differential winding density and coil spacing, allowing one spring to perform multiple operations reliably
Solution Approach 2:
The spring mechanism incorporates dynamic elements including a movable decoupling member that releases the spring from the syringe barrel after injection, and a retraction sleeve that controls the retraction phase. These dynamic components ensure the spring transitions smoothly between functions without interference, maintaining dose delivery completeness while reducing overall device complexity
2Reliability
If additional springs are added for needle retraction, then needle retraction reliability is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent merges the needle retraction function into the same compression spring that performs insertion and dose delivery. The single spring is configured with a longer coil section that provides the retraction force after the decoupling member releases it, eliminating the need for a separate retraction spring while maintaining safety
Solution Approach 2:
The compression spring is designed as a universal component that performs three functions: needle insertion, medicament delivery, and needle retraction. This multi-functional design reduces the total number of spring components from two or more to exactly one, lowering device complexity and manufacturing costs while maintaining reliable needle retraction through the spring's extended coil section
3Reliability
If the button/plunger extension is increased, then complete dose delivery is ensured, but user comfort is reduced due to hand trembling and discomfort
Solution Approach 1:
The auto-injector system performs the injection action automatically without requiring continuous user pressure on a button or plunger. The compression spring provides the necessary force to deliver the complete dose automatically, eliminating the need for user effort during the injection process and thereby preventing hand trembling and discomfort while ensuring complete dose delivery
Solution Approach 2:
The patent replaces the manual button/plunger mechanical system with an automatic spring-driven system. The compression spring substitutes for the user's manual pressure, providing consistent and sufficient force to deliver the complete dose without requiring continuous user intervention, thus improving user comfort while maintaining dose delivery completeness
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 design achieves reliable, complete dose delivery with reduced mechanical complexity, lower manufacturing costs, and enhanced safety by using a single spring for both insertion and retraction, minimizing user discomfort and ensuring the needle is safely retracted.
Implementation Method 1
spring means capable of, upon activation: pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end
Implementation Method 2
spring means capable of, upon activation: operating the syringe to supply the dose of medicament
Implementation Method 3
spring means capable of, upon activation: retracting the syringe with the needle into the covered position after delivering the medicament
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament includes an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end with an orifice intended to be applied against an injection site. The syringe is slidably arranged with respect to the housing. A spring capable of, upon activation: pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end (P), operating the syringe to supply the dose of medicament (M), and retracting the syringe with the needle into the covered position. After delivering the medicament, an activator arranged to lock the spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring for injection.