Auto-Injector Dual Spring Mechanism for Precise Needle Insertion
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Solution Overview
Problem
Current auto-injectors face challenges such as high injection forces, discomfort due to trembling hands, and the risk of incomplete doses, particularly when administering high viscosity medicaments, as they rely on strong drive springs that cause high impact and force during needle insertion and drug delivery.
Innovation Solution
An auto-injector design featuring separate control and drive springs, where the control spring inserts the needle and the drive spring delivers the medicament, with a plunger release mechanism and a peg system to prevent premature release of the drive spring, ensuring accurate dosing and reducing user effort and discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If strong drive springs are used to expel high viscosity medicaments, then the injection force is sufficient, but high impact and discomfort are felt by the user during needle insertion and triggering
Solution Approach 1:
The patent divides the single spring system into two separate springs: a control spring for needle insertion/retraction and a drive spring for medicament delivery. This segmentation allows each spring to be optimized for its specific function, with the drive spring providing sufficient force for high viscosity medicaments without the control spring transmitting excessive impact to the user during needle insertion.
Solution Approach 2:
The patent extracts the needle insertion function from the drive spring system by introducing a separate control spring. This removes the harmful impact and discomfort caused by the strong drive spring from the needle insertion process, while preserving the drive spring's ability to deliver high viscosity medicaments effectively.
2Device complexity
If a single spring is used for both needle insertion and drug delivery, then the device structure is simpler, but it is difficult to accommodate different viscosities and volumes without altering insertion or retraction mechanisms
Solution Approach 1:
By segmenting the spring system into control and drive springs, the patent enables independent optimization. The drive spring can be selected based on medicament viscosity and volume requirements, while the control spring maintains consistent needle insertion and retraction performance across different medicament types.
Solution Approach 2:
The control spring serves multiple functions: needle insertion, needle retraction, and maintaining syringe positioning. This multi-functionality allows the system to accommodate different medicament viscosities and volumes through drive spring selection alone, without requiring changes to the insertion or retraction mechanisms.
3Device complexity
If the trigger button is directly coupled to the carrier throughout the injection process, then the control is simpler, but the trigger button cannot remain in position while the carrier moves for needle advancement
Solution Approach 1:
The patent implements a dynamic coupling mechanism where the trigger button's connection to the carrier changes during operation. Initially coupled, the trigger button allows carrier movement for needle insertion. After insertion, the coupling is released, allowing the trigger button to return to its original position while the carrier remains in the advanced position for medicament delivery.
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 enhances user safety and comfort by allowing precise control over needle insertion and drug delivery, preventing 'wet injections' and accommodating different viscosities and volumes without altering the insertion or retraction mechanisms, while minimizing manufacturing costs and improving reliability.
Implementation Method 1
a control spring arranged around the carrier for translating the carrier in a proximal direction for advancing the needle beyond a proximal end of the auto-injector
Implementation Method 2
a drive spring arranged inside the carrier and biased to move the plunger in the proximal direction for delivering the dose of the medicament through the injection needle
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament (M) is presented having an elongate case, a carrier subassembly comprising a tubular carrier slidably arranged inside the case, where the carrier adapted to contain a syringe with a hollow injection needle. The injector also has, a drive spring and a plunger for forwarding load of the drive spring to a stopper of the syringe, wherein the syringe is lockable for joint axial translation with the carrier. A control spring is arranged around the carrier for translating the carrier in a proximal direction (P) for advancing the needle beyond a proximal end of the auto-injector, and a trigger button is used for releasing the control spring on actuation.