Auto-Injector Mechanism Using One Spring for Dose Completion
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Solution Overview
Problem
Existing auto-injectors face challenges such as user discomfort due to injection force and hand-shaking, risk of incomplete doses, and complexity in operation, particularly for elderly or dexterity-impaired individuals, and often require multiple springs for needle insertion, retraction, and dose delivery.
Innovation Solution
An auto-injector design utilizing a single compression spring for both needle insertion and dose delivery, with a simplified mechanism that includes a retraction sleeve and decoupling arms to ensure complete dose delivery and safe needle retraction, featuring a safety button and a delay box to prevent premature retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple springs are used for needle insertion, retraction, and dose delivery, then the functions are reliable, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the functions of needle insertion, dose delivery, and retraction into a single spring mechanism. The single spring is configured to perform multiple functions sequentially: first driving needle insertion, then maintaining pressure during dose delivery, and finally enabling retraction when the dose is complete. This eliminates the need for separate springs for each function, reducing device complexity while maintaining reliability.
Solution Approach 2:
The single spring is designed as a universal driving mechanism that performs multiple functions throughout the injection cycle. It serves as the insertion driver, the pressure maintenance element during infusion, and the retraction actuator. This multi-functionality approach reduces the total component count and simplifies the overall device architecture.
2Device complexity
If a single spring is used for all functions, then device complexity is reduced, but the mechanism becomes more difficult to design and control
Solution Approach 1:
The single spring mechanism is segmented into distinct functional zones along its length and through its interaction with different components. The spring is configured with different sections that engage with the needle assembly, the syringe, and the retraction mechanism at different stages of the injection cycle. This segmentation allows the single spring to perform multiple functions while keeping the design manageable through modular functional zones.
Solution Approach 2:
The mechanism employs dynamic elements including a movable piston, a decoupling arm, and a retraction sleeve that interact with the spring in sequence. These dynamic components allow the spring's energy to be transferred differently at different stages: first to the needle for insertion, then to the syringe for dose delivery, and finally for retraction. The dynamic interaction manages the complexity through controlled energy transfer rather than requiring complex mechanical linkages.
3Object-affected harmful factors
If the needle is retracted automatically, then user safety is improved, but premature retraction may occur causing incomplete dose delivery
Solution Approach 1:
The mechanism performs preliminary actions to ensure complete dose delivery before enabling retraction. The piston is positioned and the syringe is primed before the injection cycle begins. During the cycle, the decoupling arm is designed to prevent premature retraction by mechanically interlocking components until the dose delivery is complete. Only after the full dose is administered does the mechanism allow the retraction sleeve to move and retract the needle, ensuring safety is improved without compromising dose completeness.
Solution Approach 2:
The mechanism incorporates feedback through the interaction between the piston, syringe, and retraction sleeve. The position of the piston and the pressure in the syringe provide feedback to the decoupling arm, which prevents retraction until the dose is complete. This feedback mechanism ensures that the retraction function is enabled only when appropriate, preventing premature retraction while maintaining automatic retraction for user safety.
4Measurement precision
If injection force is high to ensure complete dose delivery, then dosing accuracy is improved, but user discomfort and hand-shaking increase
Solution Approach 1:
The mechanism uses dynamic pressure control through the movable piston and spring configuration. The spring provides initial high force for needle insertion and early dose delivery, then gradually reduces pressure as the injection progresses. The decoupling arm and retraction sleeve work together to modulate the force delivery, ensuring complete dose accuracy while reducing peak forces that cause user discomfort and hand-shaking. The dynamic adjustment of force over time maintains dosing accuracy without compromising user comfort.
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 reduces user discomfort, ensures complete dose delivery, and minimizes manufacturing costs by using fewer parts, while enhancing safety and reliability.
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
Implementation Method 2
The tension spring moves an ampoule and the injection needle from a storage position to a deployed position when it is released. The content of the ampoule is thereafter expelled by the tension spring forcing a piston forward inside the ampoule.
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament includes an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end with an orifice intended to be applied against an injection site. The syringe is slidably arranged with respect to the housing. A spring 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 (P), operating the syringe to supply the dose of medicament (M), and retracting the syringe with the needle into the covered position. After delivering the medicament, an activator arranged to lock the spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring for injection.