Autoinjector Dual-Locker Mechanism Drop Protection
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Solution Overview
Problem
Autoinjectors are prone to inadvertent activation during drop tests, particularly in the 'cap upward' orientation, due to high activation forces required to prevent accidental needle exposure, which can be challenging for users, especially in healthcare settings.
Innovation Solution
The autoinjector design incorporates a second locker that axially secures the first locker, preventing inadvertent axial movement and activation, while reducing the activation force by eliminating the need for protrusions that hinder movement, and features a robust axial abutment system to prevent accidental activation during drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hard dots (protrusions) are used to prevent inadvertent movement of the safety shield, then the autoinjector prevents inadvertent activation during drops, but the activation force becomes too high for end users
Solution Approach 1:
The locking mechanism is divided into two independent lockers (first locker and second locker) that operate sequentially. The first locker controls the safety shield movement while the second locker controls the plunger rod release. This segmentation allows the activation force to be distributed and reduced while maintaining reliable prevention of inadvertent activation through the second locker's drop protection function.
Solution Approach 2:
The second locker acts as an intermediary between the first locker and the plunger rod locking mechanism. It provides an additional layer of protection against drop-induced activation by preventing the first locker from releasing the plunger rod, even if the safety shield moves inadvertently. This intermediary mechanism resolves the contradiction by adding reliability without requiring high activation force on the safety shield itself.
2Reliability
If a second locker is added to axially secure the first locker, then inadvertent activation during drops is prevented, but the device complexity increases
Solution Approach 1:
The second locker combines multiple functions into a single component: it axially secures the first locker, prevents drop-induced activation, and controls the release sequence of the plunger rod. By merging these functions into one integrated component rather than using separate mechanisms, the design achieves high reliability while minimizing the increase in device complexity.
Solution Approach 2:
The second locker serves multiple purposes: it acts as a drop protection mechanism, a release control mechanism, and a sequential operation controller. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving robust protection against accidental activation.
3Ease of operation
If protrusions are eliminated to reduce activation force, then ease of operation improves, but the ability to prevent inadvertent movement of the safety shield deteriorates
Solution Approach 1:
The protrusions that created high activation force are extracted from the safety shield mechanism. Instead of relying on protrusions to prevent inadvertent movement, the design uses the second locker as a separate drop protection mechanism. This extraction allows the safety shield to move with low force while the second locker provides the necessary protection against inadvertent activation.
Solution Approach 2:
The drop protection function originally provided by protrusions is copied and implemented through the second locker mechanism. Rather than modifying the safety shield to maintain high activation force, the protective function is replicated in the second locker, which controls plunger rod release. This copying approach maintains reliability without compromising ease of operation.
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 effectively prevents inadvertent activation during drops and reduces the activation force, ensuring safe and reliable operation while maintaining robustness against accidental falls.
Implementation Method 1
an initially compressed spring for moving the plunger rod in the distal direction
Implementation Method 2
The axial abutment between the second locker and the housing is indeed strong enough to prevent such inadvertent axial movement of the first locker
Data Source
AI summary
The autoinjector includes a housing extending along a longitudinal axis A and configured to receive a medical container having a barrel defining a reservoir for containing a medical product. The barrel having a distal end provided with an injection needle and an opened proximal end configured to receive a plunger rod for pushing a stopper arranged inside the barrel. A needle cover is coupled to and axially movable with respect to said housing between a first extended position, a retracted position, and a second extended position. A plunger rod is axially movable inside the housing between a storage position and an injection end position, the plunger rod being configured to push the stopper in order to expel the medical product. The autoinjector also includes biasing means for biasing the plunger rod in a distal direction towards the injection end position, a retainer for maintaining the plunger rod in the initial position against the action of the biasing means, the retainer including a blocking member radially movable between a blocking position for blocking the plunger rod in the initial position, and a release position allowing for movement of the plunger rod in the distal direction. A first locker is axially movable with respect to the retainer between a locking position for maintaining the blocking member in the blocking position, and a release position, axial movement of the first locker from the locking position to the release position being caused by the needle cover moving from the first extended position to the retracted position. A second locker, is rotationally movable around the longitudinal axis A with respect to said housing, between a locking position for preventing axial movement of the first locker from the locking position to the release position, and a release position for allowing axial movement of the first locker from the locking position to the release position. The autoinjector further includes axial securing means for axially securing the second locker with respect to the housing.