Auto-Injector Single Drive Spring and Interlock Sleeve Mechanism
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Solution Overview
Problem
Current auto-injectors face challenges such as the risk of inadvertent triggering, high injection forces, and discomfort due to manual operation, particularly for elderly or dexterity-impaired users, and issues with ensuring complete dose delivery and needle retraction.
Innovation Solution
An auto-injector design featuring a single drive spring for advancing and retracting the needle, with a sequenced operation requiring two user actions to initiate injection, including a skin interlock sleeve that locks the trigger button in the as-delivered state and only unlocks upon proper alignment with the injection site, ensuring the needle is safely retracted only after the device is removed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single drive spring is used for both advancing and retracting the needle, then the device complexity is reduced, but the reliability of needle retraction may be compromised
Solution Approach 1:
The single drive spring dynamically changes its functional role during the injection cycle. Initially, it advances the needle by expanding from a compressed state. After needle insertion and medicament delivery, the spring reverses its action to retract the needle by contracting. This dynamic reversal allows one spring to perform both advancement and retraction functions reliably
Solution Approach 2:
The drive spring undergoes parameter changes in its mechanical state throughout the injection process. It transitions from a compressed to expanded state for needle advancement, then reverses to a contracted state for retraction. The spring's force direction and magnitude are modulated through controlled mechanical interactions with the plunger and needle assembly, enabling reliable bidirectional movement
2Reliability
If a sequenced operation with two user actions is required, then the risk of inadvertent triggering is reduced, but the ease of operation increases in complexity
Solution Approach 1:
The first user action (pressing the device against the injection site) performs a preliminary function by unlocking the safety mechanism and positioning the needle. This preliminary action must occur before the second action (pressing the trigger button) can initiate injection. The sequenced design ensures that the device is properly positioned and ready before the actual injection begins, preventing inadvertent triggering
Solution Approach 2:
The safety unlock mechanism acts as an intermediary between the two user actions. The first action triggers this intermediary mechanism to transition from a locked to an unlocked state, enabling the second action. This intermediary step creates a deliberate pause and verification point in the operation sequence, ensuring intentional use while maintaining simplicity through automatic state transitions
3Object-affected harmful factors
If the needle is retracted only after device removal from injection site, then user safety is improved, but the duration of needle exposure increases
Solution Approach 1:
The device performs preliminary needle retraction automatically upon removal from the injection site. The spring mechanism is pre-configured to initiate retraction as soon as the device is withdrawn, before the user can accidentally contact the needle. This preliminary protective action minimizes exposure time while ensuring safety
Solution Approach 2:
The needle retraction process is rushed through immediately upon device removal. The spring mechanism rapidly drives the needle back into the device housing in a single swift motion, minimizing the time the needle remains exposed. This rapid retraction skips any intermediate states where the needle might be partially exposed, reducing injury risk
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 reduces the risk of inadvertent operation, minimizes injection force, ensures complete dose delivery, and provides a safer, more reliable needle retraction mechanism, enhancing user safety and ease of use.
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) arranged to contain a syringe (3), wherein the syringe is slidably arranged with respect to the housing, - spring means (8) capable of, upon activation: - pushing the needle (4) from a covered position inside the housing (2) into an advanced position - operating the syringe to supply the dose of medicament, and - retracting the syringe with the needle into the covered position after delivering the medicament, - activating means (20). The spring means is a single drive spring (8) for advancing the needle and for injecting the dose of medicament via a plunger (9). An interlock sleeve (45) is telescoped in the proximal (P) end of the housing. The activating means comprises a trigger button (20) arranged at the distal end (D) of the auto - injector, wherein the trigger button is locked, thereby preventing actuation when the interlock sleeve is in its proximal position in an as delivered state and wherein translation of the interlock sleeve unlocks the trigger button so as to allow actuation.