Auto-injector Dual-spring Mechanism for Viscous Medicament Delivery
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Solution Overview
Problem
Current auto-injectors face challenges in delivering high viscosity medicaments without causing discomfort to users, often requiring strong drive springs that result in high impact during needle insertion and uneven dose delivery, and may lead to wet injections due to improper mechanism design.
Innovation Solution
The auto-injector employs a dual-spring mechanism with a control spring and a drive spring, where the control spring opposes the user's action, allowing for a weaker spring force during triggering and needle insertion, and releases the drive spring at injection depth to prevent medicament leakage, featuring a wrap-over trigger sleeve for easy operation and a low part count for cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a strong drive spring is used to deliver high viscosity medicaments, then the injection force is sufficient, but the impact during needle insertion and triggering becomes uncomfortably high
Solution Approach 1:
The patent divides the spring system into two separate springs: a control spring that limits the force during needle insertion and triggering, and a drive spring that provides sufficient force for injecting high viscosity medicaments. This segmentation allows each spring to perform its specific function without the harmful effects of using a single strong spring throughout the entire process.
2Object-affected harmful factors
If the drive spring is released early to reduce triggering force, then user comfort improves, but medicament leakage (wet injection) occurs
Solution Approach 1:
The control spring is pre-loaded during the triggering phase to provide the necessary force for needle insertion without requiring the user to overcome a strong spring. The drive spring is held in check by the plunger stop mechanism, which releases at the precise moment when the needle reaches injection depth, ensuring medicament is delivered without leakage while maintaining user comfort during triggering.
3Device complexity
If manual pressure is applied to deliver medicament, then device simplicity is maintained, but injection force may be insufficient and button extension is too great
Solution Approach 1:
The drive spring automatically provides the force needed to deliver high viscosity medicaments without requiring the user to manually press a button or plunger. The spring self-activates when the needle reaches the appropriate depth, eliminating the need for continuous user pressure and ensuring sufficient injection force for difficult-to-administer medications.
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 design enables the delivery of highly viscous medicaments with reduced user discomfort, prevents wet injections, and allows for versatility in viscosity and volume adjustments by changing springs or plunger length, making it suitable for various medicaments and user dexterity levels.
Implementation Method 1
a control spring arranged around the carrier, first interlock means for coupling a proximal end of the control spring to either the carrier for advancing it for needle insertion or to the chassis for needle retraction depending on the relative axial position of the carrier and the trigger sleeve
Implementation Method 2
a drive spring and a plunger for forwarding load of the drive spring to a stopper of the syringe
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
The invention refers to an auto-injector (1) and to a method for operating it, the auto-injector comprising: a tubular chassis (2), a carrier subassembly comprising a tubular carrier (7) slidably arranged in the chassis (2), the carrier (7) containing a syringe (3) with a hollow injection needle (4), a drive spring (8) and a plunger (9) for forwarding load of the drive spring (8) to a stopper (6) of the syringe (3), a wrap-over trigger sleeve (12) arranged over the distal end (D) of the auto- injector (1), the trigger sleeve (12) extending at least almost over the whole length of the auto-injector (1), a control spring (19) arranged around the carrier (7), first interlock means (20, 22, 23, 24) for coupling a proximal end of the control spring (19) to either the carrier (7) for advancing it for needle insertion or to the chassis (2) for needle retraction, second interlock means (11, 13, 15) arranged for releasing the drive spring (8) for injection, third interlock means (16, 17, 18) arranged for coupling the chassis (2) to the carrier (7) for joint axial translation relative to the trigger sleeve (12), fourth interlock means (21, 25, 26, 28) arranged for coupling a distal end of the control spring (19) to either the carrier (7) for needle retraction or to the trigger sleeve (12) otherwise.