Auto-injector Plunger Driver Latch Mechanism
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Solution Overview
Problem
Reusable auto-injectors face challenges in safely deploying a safety shroud without premature deployment, risking accidental needle exposure due to the spring force of the drive spring, especially when the shroud is biased towards a closed position.
Innovation Solution
An auto-injector design featuring a plunger driver latch that moves between positions to control the deployment of the safety shroud, using a biasing member like a spring to ensure the shroud is only deployed after the injection is complete, and a mechanism that decouples the plunger driver from the syringe to apply a continuous forward force for safe shroud deployment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drive spring biases the safety shroud towards the closed position, then the safety shroud deployment is controlled, but the spring force may force the auto-injector off the injection site causing premature deployment
Solution Approach 1:
The plunger driver latch is configured in advance to latch the plunger driver at a pre-insertion position before needle insertion. This preliminary latching action prevents the drive spring from acting on the safety shroud during the critical insertion phase, eliminating the risk of premature deployment while maintaining deployment control through the biased configuration.
Solution Approach 2:
The plunger driver latch acts as an intermediary mechanism between the drive spring and the safety shroud. It intercepts and controls the spring force by latching the plunger driver at specific positions, preventing direct transmission of spring force to the safety shroud until the appropriate moment, thus resolving the contradiction between controlled deployment and premature activation risk.
2Ease of operation
If the plunger driver is allowed to move freely, then the safety shroud can be deployed, but the drive spring force may cause accidental needle exposure
Solution Approach 1:
The system performs preliminary latching of the plunger driver at the pre-insertion position before the injection process begins. This preliminary action restricts plunger driver movement during needle insertion, preventing accidental needle exposure while maintaining the capability for controlled safety shroud deployment at the appropriate time.
Solution Approach 2:
The plunger driver latch dynamically transitions between latched and unlatched states based on the injection phase. During insertion, the latch is engaged to prevent movement; during deployment, the latch releases to allow movement. This dynamic behavior resolves the contradiction by adapting the system's mechanical constraints to the current operational requirements.
3Reliability
If a separate shroud deployment spring is used, then the safety shroud can be deployed reliably, but the device complexity increases
Solution Approach 1:
The plunger driver latch is designed to perform multiple functions: it latches the plunger driver at the pre-insertion position, controls the injection process, and simultaneously serves as the deployment mechanism for the safety shroud by unlatching at the appropriate time. This multi-functionality eliminates the need for a separate deployment spring, reducing device complexity while maintaining reliable shroud deployment.
Solution Approach 2:
The invention merges the deployment control function with the existing plunger driver latch mechanism. By combining the latching control and shroud deployment control into a single integrated mechanism, the system achieves reliable safety shroud deployment without adding the complexity of a separate deployment spring system.
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 ensures safe and reliable deployment of the safety shroud, reducing the risk of accidental exposure and eliminating the need for a separate shroud deployment spring, while allowing for safe handling of the auto-injector and syringe post-injection.
Implementation Method 1
using a biasing member like a spring to ensure the shroud is only deployed after the injection is complete
Implementation Method 2
a drive spring that are arranged to couple to and apply a force to the plunger of the syringe
Data Source
AI summary
An auto-injector comprising: a housing for receiving a syringe having a barrel containing a medicament, a plunger and a needle; a plunger driver configured to act on the syringe plunger to move the syringe plunger through the housing during a needle insertion phase and an injection phase; a safety shroud; and a plunger driver latch coupled to said safety shroud and moveable between first and second positions and configured to: while in the first position before the needle insertion phase, latch the plunger driver at a pre-insertion position in the housing, move to the second position as a result of pressure applied to the safety shroud, to unlatch the plunger driver from the pre-insertion position and allow forward movement of the plunger driver to a post-insertion and injection position in the housing and latch the plunger driver at the post-insertion and injection position, and return to the first position upon removal or reduction of pressure on the safety shroud, to unlatch the plunger driver from the post-insertion and injection position and allow forward movement of the plunger driver to deploy the safety shroud.