Auto-Injector Spring Layout for High-Viscosity Dose Delivery
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Solution Overview
Problem
Existing auto-injectors face challenges such as high injection forces, discomfort due to hand shaking, and incomplete doses, especially when administering high viscosity medicaments, and lack of safety features for needle retraction.
Innovation Solution
An auto-injector design with separate drive and control springs, where the drive spring is released only upon reaching the injection depth, ensuring smooth medicament delivery without user impact, and featuring a plunger release mechanism for reliable injection and a detent mechanism for safe needle retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a single strong drive spring is used to deliver high viscosity medicaments, then the injection force is sufficient, but the user experiences high impact and discomfort during needle insertion and triggering
Solution Approach 1:
The patent divides the single drive spring function into two separate springs: a control spring that manages needle insertion and retraction, and a drive spring that solely delivers the medicament. This segmentation allows each spring to be optimized for its specific function, with the drive spring providing sufficient force for high viscosity medicaments without transmitting insertion impact to the user.
Solution Approach 2:
The patent extracts the needle insertion and retraction functions from the drive spring system, assigning them to a separate control spring mechanism. This extraction allows the drive spring to focus exclusively on medicament delivery with optimized force characteristics, while the control spring handles the user-interaction aspects with appropriate force modulation.
2Length of moving object
If the button/plunger is extended greatly to reach full extension, then the injection can be completed, but it becomes inconvenient for users to reach and causes hand shaking
Solution Approach 1:
The patent implements automatic needle insertion and retraction through the control spring mechanism, eliminating the need for manual button extension. The system performs these functions autonomously based on trigger activation, removing the ergonomic problems associated with long button extensions while ensuring complete injection delivery.
3Device complexity
If manual pressing is used to deliver medicament, then the device is simple, but the user may deliver an underdose if not pressed fully
Solution Approach 1:
The patent employs automatic drive mechanisms using springs to deliver the medicament without requiring manual pressing. The drive spring automatically propels the plunger to its full travel distance, ensuring complete dose delivery regardless of user technique, while maintaining relative device simplicity through mechanical automation.
4Device complexity
If the needle is not automatically retracted, then the device is simpler, but the user is exposed to needle injury risks
Solution Approach 1:
The patent implements automatic needle retraction through the control spring mechanism, which automatically pulls the needle back into the device body after injection completion. This self-service feature eliminates needle exposure risks without requiring user intervention, while the overall device complexity remains manageable through the integrated spring-based control 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
The design allows for efficient delivery of high viscosity medicaments with reduced user discomfort, ensures complete doses, and provides safe needle retraction, improving reliability and safety.
Implementation Method 1
the energy to deliver the fluid is provided by a spring
Implementation Method 2
a control spring arranged in the case around the carrier and acting between the case and the carrier
Implementation Method 3
a detent mechanism arranged for coupling the chassis to the carrier for joint axial translation relative to the case, wherein the detent mechanism is arranged to decouple the chassis from the carrier upon actuation of the trigger button
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament includes an elongate tubular case and a carrier subassembly including a tubular carrier slidably arranged inside the case. The carrier is adapted to contain a syringe with a hollow injection needle, 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, wherein the drive spring acts between the carrier and the plunger, wherein the plunger, in an initial state, is locked to the carrier by a ramped engagement to the carrier and by being prevented from rotating out of this ramped engagement, depending on a relative longitudinal position of the carrier in the case, and wherein the plunger is arranged to be released for rotating out of the ramped engagement.