Pen Injector Latch Mechanism for Reliable High-Force Spring Release
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Solution Overview
Problem
Existing pen injector devices face challenges with compact design, high force spring requirements, and potential issues with the spring catching on the syringe components, which can delay or prevent the injection mechanism from firing, especially when dealing with high viscosity drugs or small needle diameters.
Innovation Solution
The design incorporates a latch member that radially flexes and is biased by a compression spring, with a trigger mechanism that physically engages the plunger to overcome the retaining force of the latch member, ensuring accurate release and preventing the plunger from catching during injection, utilizing a cam surface and radially projecting members to facilitate smooth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high force springs are used to overcome high viscosity drugs or small needle diameters, then the injection force is sufficient, but the spring may catch on the syringe components which delays or prevents firing
Solution Approach 1:
A latch member is introduced as an intermediary component between the spring and the plunger. The latch member controls the transfer of force from the spring to the plunger, preventing the spring from catching on syringe components while ensuring reliable force transmission during injection.
Solution Approach 2:
The latch member is positioned and configured in advance to prevent spring catch-on issues before injection occurs. The latch member's geometry and positioning are designed preliminarily to clear the spring path and prevent interference with syringe components during the firing sequence.
2Volume of moving object
If the overall size of the injector is reduced for compact form, then portability and unobtrusiveness are improved, but the mechanism may become less resilient
Solution Approach 1:
The latch member is nested within the existing injector structure, utilizing available space efficiently. The latch member fits within the housing and syringe assembly without significantly increasing the overall volume, while adding the functional complexity needed for reliable operation with compact dimensions.
3Ease of operation
If the latch member is designed to radially flex for release, then the release mechanism is simplified, but precise control over the release timing may be compromised
Solution Approach 1:
The latch member's flexural properties are carefully controlled by adjusting geometric parameters such as thickness, length, and cross-sectional shape. These parameter changes allow the latch to provide precise control over release timing while maintaining the simplicity of the radial flexing mechanism.
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 solution enables more precise control over the injection process, ensures reliable operation with high stiffness springs, and prevents the plunger from getting caught, enhancing the usability and reliability of pen injectors for various medicament types.
Implementation Method 1
an actuation mechanism arranged in use to provide a forward biasing force on the plunger to express a dose from the syringe
Implementation Method 2
The radial displacement of the latch member may be provided by a portion of the latch member flexing or hinging
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
An injection device 1 comprises a plunger (60) for expressing medicament from a syringe (20). An actuation mechanism (40) is arranged in use to provide a biasing force to urge the plunger (60) from a first rearward position to a second forward position to express a dose from the syringe (20). The device further comprises a latch member (50) comprising an aperture (54) through which the rearward end of the plunger (60) extends in its rearward position so as to be retained against the force of the actuation mechanism (40). A trigger (70) is provided for releasing the plunger (60) from the latch member (50). The rearward end of the plunger is provided with an enlarged head (66) and the latch member (50) is arranged to at least partially radially displace such that the aperture (54) may expand to release the enlarged head. The trigger (70) is moveable between (1) a primed position in which it prevents displacement of the latch member (50) and a release position in which it allows displacement of the latch (50).