Auto-Injector Single Spring Needle Retraction Mechanism
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Solution Overview
Problem
Current auto-injectors face challenges in ensuring complete dose delivery and safe needle retraction, particularly when the injection is interrupted, due to issues with spring mechanisms and user operation complexity.
Innovation Solution
An auto-injector design utilizing a single compression spring for both needle insertion and retraction, with a mechanism that locks the spring in a pressurized state and requires two user actions for activation, ensuring reliable retraction only when the device is removed from the injection site, thus preventing incomplete dose delivery and ensuring needle safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a spring mechanism is used to automatically inject the medicament, then the injection can be performed without continuous user pressure, but the spring may inadvertently release and inject the medicament if not properly controlled
Solution Approach 1:
The device performs preliminary actions by pre-loading the spring mechanism and pre-positioning the needle and syringe before actual use. The spring is compressed and locked in advance, and the needle is positioned but not yet activated. This ensures the system is ready for immediate injection when activated, while preventing inadvertent release since the spring remains locked until deliberate user activation occurs.
Solution Approach 2:
An intermediary mechanism (the locking mechanism and activation switch) is introduced between the spring and the needle/syringe assembly. This intermediary controls the release of the spring's stored energy, ensuring it only activates when the user deliberately presses the activation switch. The intermediary prevents direct coupling between the spring and injection components, thereby preventing inadvertent injection while maintaining automatic injection capability when properly activated.
2Object-affected harmful factors
If the needle and syringe are automatically retracted after injection, then user safety is improved, but the mechanism becomes more complex
Solution Approach 1:
The retraction function is merged with the existing spring mechanism and activation system. The same spring that drives needle insertion also drives retraction, eliminating the need for a separate retraction motor or mechanism. The activation switch serves dual purposes: initiating injection and triggering retraction. This merging reduces overall device complexity while maintaining automatic safety retraction functionality.
Solution Approach 2:
The spring mechanism is designed to perform multiple functions: it compresses to drive needle insertion, maintains pressure during injection, and then reverses to drive needle retraction. The activation switch is also multi-functional, controlling both injection initiation and retraction timing. This multi-functionality reduces the number of separate components needed, thereby reducing device complexity while achieving safe automatic retraction.
3Device complexity
If a single spring mechanism is used for both needle insertion and retraction, then the device complexity is reduced, but the control over injection timing becomes more difficult
Solution Approach 1:
The activation switch serves as an intermediary control element between the user and the spring mechanism. It provides precise timing control by determining when the spring's stored energy is released for injection and when it is released for retraction. This intermediary allows the simple single-spring mechanism to achieve complex timing control, as the switch can be activated at specific moments to control the spring's action without requiring complex mechanical timing mechanisms.
Solution Approach 2:
The system transitions from a static spring mechanism to a dynamic one where the spring's state changes based on user input. The activation switch creates dynamic control points where the spring can be released in different phases (insertion phase or retraction phase). This dynamic control allows precise timing adjustment while maintaining the simplicity of a single spring, as the timing control is achieved through the activation switch rather than through complex mechanical linkages.
4Reliability
If the button extension is made longer to ensure complete dose delivery, then the injection can be fully administered, but the user comfort is reduced due to extended reach requirements
Solution Approach 1:
The manual button-pressure mechanism is replaced with an automatic spring-driven injection system. Instead of requiring the user to continuously press a button for the entire injection duration, the spring automatically drives the syringe plunger to deliver the complete dose. This substitution eliminates the need for extended button travel, improving user comfort while ensuring complete dose delivery through the automatic spring mechanism.
Solution Approach 2:
The injection system performs self-service by using the spring mechanism to automatically advance the syringe and deliver the medicament without requiring continuous user intervention. The system self-regulates the injection process, controlling the timing and duration of dose delivery. This self-service capability eliminates the need for users to manually extend buttons or plunger for extended periods, improving comfort while ensuring complete dose administration through automatic control.
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 ensures reliable and complete medicament delivery and safe needle retraction, reducing the risk of incomplete doses and user error, while minimizing the part count and manufacturing costs.
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, operating the syringe to supply the dose of medicament, and retracting the syringe with the needle into the covered position after delivering the medicament
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
The invention relates to an auto-injector (1) for administering a dose of a liquid medicament (M), comprising: - an elongate housing (2), a syringe (3) with needle (4) and a stopper (6), - a drive spring (8) for pushing the needle (4) from a covered position into an advanced position, for operating the syringe and for retracting the syringe (3), - activating means (20) for locking or releasing the spring means (8). A retraction sleeve (10) is axially movable arranged in the housing (2). The drive spring (8) bears with its proximal end against a thrust face (17) of a decoupling member (14). At least one resilient decoupling arm (18) is arranged at the decoupling member (14) for bearing against a first shoulder (19) of the plunger (9). At least one aperture (34) is arranged in the retraction sleeve (10) allowing the decoupling arms (18) to be flexed outward thus allowing the first shoulder (19) to slip past the decoupling arm (18). The aperture (34) is arranged to be angularly misaligned with respect to the decoupling arm (18) and to rotate so as to align with the decoupling arms (18) upon translation of the retraction sleeve (10) out of the proximal position in distal direction (D).