Auto-injector Single Spring Dynamic Grounding Mechanism
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Solution Overview
Problem
Current auto-injectors face challenges in ensuring complete dose delivery and safe needle retraction, particularly when the injection is interrupted, due to manufacturing tolerances and the need for precise triggering mechanisms, which can lead to incomplete medicament delivery or residual medicament in the syringe.
Innovation Solution
An auto-injector design utilizing a single drive spring for both needle insertion and retraction, with a mechanism that locks the spring in a pressurized state and requires two user actions for activation, ensuring reliable retraction only when the device is removed from the injection site, thus preventing inadvertent operation and ensuring full dose delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single compression spring is used for both needle advancement and syringe retraction, then device complexity is reduced and manufacturing costs decrease, but reliable retraction after incomplete injection becomes difficult to ensure
Solution Approach 1:
The spring mechanism transitions from a static single-function design to a dynamic multi-state design. The compression spring dynamically switches between two functional states: (1) advancing the needle and injecting medicament when distally grounded, and (2) retracting the syringe when distally ungrounded and proximally grounded. This dynamic reconfiguration allows one spring to reliably perform both functions including safe retraction even after incomplete injection.
Solution Approach 2:
The invention changes the grounding parameter of the spring in the housing to switch between functions. By switching the ground position from distal to proximal end, the spring's force direction and magnitude change, enabling it to first advance the needle and then retract the syringe. This parameter change ensures reliable retraction while maintaining a simple single-spring structure.
2Reliability
If the spring ground position is switched from distal to proximal end, then the syringe can be reliably retracted after injection, but the mechanism requires two user actions for activation which increases operational complexity
Solution Approach 1:
The user must first perform a preliminary action of pressing the device against the injection site before the actual injection activation. This preliminary action initiates the sequence that leads to reliable retraction, as it sets up the conditions for the spring to switch grounding positions and ensures the device is properly positioned for both injection and subsequent retraction.
Solution Approach 2:
The mechanism incorporates feedback through the grounding switch that responds to the injection process state. The spring automatically switches from distal to proximal grounding based on the completion of the injection, providing feedback-based control that ensures retraction only occurs at the appropriate time, enhancing reliability while maintaining operational simplicity.
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 ensures reliable and complete medicament delivery and safe needle retraction, reducing the risk of incomplete doses and residual medicament, while simplifying the mechanism and reducing the part count, weight, and manufacturing costs.
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, operating the syringe to supply the dose of medicament, and retracting the syringe with the needle into the covered position after delivering the medicament
Data Source
AI summary
The invention relates to an auto-injector for administering a dose of a liquid medicament, comprising:an elongate housing, a syringe with needle and a stopper,a drive spring for pushing the needle from a covered position into an advanced position, for operating the syringe and for retracting the syringe,activating means for locking or releasing the spring means. A retraction sleeve is axially movable arranged in the housing. The drive spring bears with its proximal end against a thrust face of a decoupling member. At least one resilient decoupling arm is arranged at the decoupling member for bearing against a first shoulder of the plunger. At least one aperture is arranged in the retraction sleeve allowing the decoupling arms to be flexed outward thus allowing the first shoulder to slip past the decoupling arm. The aperture is arranged to be angularly misaligned with respect to the decoupling arm and to rotate so as to align with the decoupling arms upon translation of the retraction sleeve out of the proximal position in distal direction.