Injection Device Asymmetric Plunger Latch Mechanism
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Solution Overview
Problem
Existing injection devices face challenges in preventing unintended release of the plunger, particularly due to the risk of the plunger overcoming the latch mechanism, which can lead to accidental medicament delivery.
Innovation Solution
The design incorporates a plunger with an asymmetric profile and a latch arrangement featuring resilient segments, along with complementary camming surfaces and non-rotational features, to ensure precise and controlled release, reducing the risk of accidental activation while maintaining ease of use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a latch mechanism is used to hold the plunger, then the plunger can be retained in the rearward position, but the plunger may accidentally overcome the latch leading to unintended release
Solution Approach 1:
The plunger head is given an asymmetric profile with a forwardly facing transition surface that has a specific asymmetric shape. This asymmetric geometry interacts with the latch mechanism to prevent accidental release while allowing controlled release through the trigger, thereby resolving the contradiction between reliable retention and preventing harmful accidental delivery.
Solution Approach 2:
The latch mechanism is designed with resilient segments that actively resist plunger movement in the forward direction before trigger actuation. The asymmetric plunger head profile creates a mechanical interference that preliminarily prevents accidental release by requiring a specific trigger action to overcome the latch, thus counteracting the harmful effect of unintended plunger release.
2Reliability
If the latch mechanism is made more secure to prevent accidental release, then safety is improved, but the device complexity increases
Solution Approach 1:
The latch mechanism is divided into multiple resilient segments that can deflect independently. This segmentation allows the latch to provide secure retention through the combined action of multiple segments while maintaining simplicity, as each segment is a relatively simple elastic element rather than a complex mechanical assembly.
Solution Approach 2:
The resilient segments are designed with specific elastic properties and geometric parameters that allow them to provide sufficient retention force while remaining simple in structure. The asymmetric plunger head profile parameters are optimized to work with the latch segments, achieving high reliability without increasing overall device complexity.
3Reliability
If the plunger head profile is made asymmetric to prevent accidental release, then safety is improved, but manufacturing precision requirements increase
Solution Approach 1:
The asymmetric plunger head profile is designed with practical manufacturing tolerances in mind. The asymmetric geometry provides sufficient safety functionality while being manufacturable with standard precision capabilities, resolving the contradiction between safety improvement and manufacturing precision requirements.
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 configuration provides a reliable and secure mechanism for delivering medicaments, preventing unintended release and ensuring accurate activation, even with high force springs or small needle diameters, thus enhancing safety and usability.
Implementation Method 1
at least two resilient segments which define opposing sections of an aperture within which a rearward end of the plunger is retained in the rearward position; and a trigger for releasing the plunger in use, the trigger being arranged to outwardly deflect at least one of the resilient segments such that the aperture is expanded to release the rearward end of the plunger
Data Source
AI summary
An injection device is disclosed comprising a plunger for expressing medicament from a syringe and a delivery mechanism arranged in use to provide a forward biasing force to urge the plunger from a first rearward position to a second forward position to express a dose from the syringe. A latch arrangement is provided that releasably holds the plunger against the force of the delivery mechanism. The latch arrangement comprising at least two resilient segments which define opposing sections of an aperture within which a rearward end of the plunger is retained in the rearward position. A trigger is provided for releasing the plunger in use, the trigger being arranged to outwardly deflect at least one of the resilient segments such that the aperture is expanded to release the rearward end of the plunger. A method of manufacturing the injection device is also enclosed.