Plunger Rod Auto-Injector with Separate Springs for Viscous Doses
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Solution Overview
Problem
Existing auto-injectors face challenges such as high injection forces, discomfort due to hand shaking, and the risk of incomplete doses, especially when administering high viscosity medicaments, and often require complex manual operation.
Innovation Solution
An auto-injector design with separate control and drive springs, where the control spring manages needle insertion and retraction, allowing for a weaker spring to be used, reducing user impact and ensuring consistent injection depth, and featuring a sequence of operations to prevent accidental needle retraction or exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a strong drive spring is used to expel high viscosity medicaments, then the injection force is sufficient, but the impact felt by the user during needle insertion and triggering becomes too high
Solution Approach 1:
The patent divides the spring system into two separate springs: a control spring that manages needle insertion and retraction, and a drive spring that provides force for expelling the medicament. This segmentation allows each spring to be optimized for its specific function, with the drive spring being strong enough for high viscosity medicaments without causing excessive impact during needle insertion, since the control spring handles that phase separately.
2Ease of operation
If manual devices require continuous button pressing, then the user can control the injection, but the user must provide continuous mechanical energy and may deliver an underdose if not used properly
Solution Approach 1:
The auto-injector is designed to perform the injection function automatically once activated. The drive spring self-actuates to expel the medicament without requiring continuous user input, and the control spring automatically manages needle insertion and retraction. This eliminates the need for continuous button pressing while ensuring the complete dose is delivered reliably.
3Length of moving object
If the button/plunger extension is made great to reach full extension, then the plunger can be fully pressed, but it becomes inconvenient for the user to reach and causes hand shaking
Solution Approach 1:
The patent extracts the long button extension function from the user interface and replaces it with an automatic spring-driven mechanism. The control spring manages the needle insertion and retraction automatically, eliminating the need for a long button extension that would be inconvenient to reach and cause hand shaking.
4Device complexity
If a single spring is used for both needle insertion and medicament expulsion, then the device is simpler, but it cannot provide sufficient force for high viscosity medicaments without causing high impact
Solution Approach 1:
The patent segments the spring system into two specialized springs: a control spring for needle manipulation and a drive spring for medicament expulsion. This segmentation enables the drive spring to be optimized for high force output needed for viscous medicaments, while the control spring handles needle insertion and retraction, achieving both sufficient injection force and reduced impact during activation.
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 provides a safe, reliable, and user-friendly auto-injector that can administer high viscosity medicaments with consistent injection depth and reduced user discomfort, minimizing the risk of incomplete doses and needle exposure.
Implementation Method 1
a control spring arranged around the carrier for translating the carrier in a proximal direction for insertion of the needle through the chassis into an injection site
Implementation Method 2
The control spring is arranged to bias the case against the chassis in a distal direction so as to extend the chassis out of a proximal end of the case
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament (M) is present having a tubular chassis telescopable in a tubular case, a carrier subassembly comprising a tubular carrier slidably arranged relative to the chassis inside the case, where the carrier is 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 insertion of the needle through the chassis into an injection site.