Injection Device Plunger Assembly Axial Length Control
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Solution Overview
Problem
In injection devices, a gap between the plunger and the bung can cause the plunger to accelerate excessively before engaging the bung, potentially damaging the syringe and causing discomfort during medicament delivery due to varying syringe fill volumes.
Innovation Solution
An assembly for the firing mechanism with a rear cap and plunger that allows for adjustable axial length, controlling the plunger's acceleration by varying the connection points between the plunger and the elongate member, ensuring controlled engagement with the bung.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the plunger is allowed to move in free space before engaging the bung, then the device can accommodate different fill volumes, but the plunger accelerates to excessively high velocities causing damage and discomfort
Solution Approach 1:
The patent applies preliminary action by pre-setting the axial length of the assembly during construction to control the plunger's travel distance. The plunger is releasably connected to the elongate member at specific positions that determine the axial length, ensuring the plunger starts from a controlled position and limits acceleration before engaging the bung, thereby preventing excessive velocity while accommodating different fill volumes.
Solution Approach 2:
The patent changes the parameter of axial length by providing multiple connection positions between the plunger and elongate member. During assembly, the plunger can be connected at different axial positions to adjust the axial length of the assembly, which directly controls the plunger's acceleration characteristics and ensures safe engagement with the bung regardless of fill volume variations.
2Object-affected harmful factors
If the axial length of the assembly is fixed, then the plunger acceleration is controlled, but the device cannot accommodate syringes with different fill volumes
Solution Approach 1:
The patent applies dynamics by making the axial length of the assembly adjustable rather than fixed. The plunger is releasably connectable to the elongate member at one of several positions, allowing the axial length to be dynamically adjusted during assembly to match different syringe fill volumes. This ensures controlled plunger acceleration for each configuration while maintaining adaptability to various syringe types.
Solution Approach 2:
The patent segments the connection interface between the plunger and elongate member into multiple discrete positions. These segmented connection points allow the assembly to be configured with different axial lengths suitable for different fill volumes, while each segment maintains controlled plunger acceleration characteristics through its specific axial position.
3Adaptability or versatility
If the plunger is releasably connected at multiple positions, then adaptability to different fill volumes is achieved, but the device complexity increases
Solution Approach 1:
The patent achieves universality by designing the elongate member and plunger with multiple connection features that serve dual purposes: they enable adjustment for different fill volumes while also providing controlled acceleration through the axial length configuration. The same structural features that increase adaptability also inherently control the plunger's motion characteristics, reducing the need for additional separate control mechanisms.
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 prevents excessive plunger acceleration, reducing the risk of syringe damage and user discomfort by ensuring controlled engagement with the bung, regardless of syringe fill volume.
Implementation Method 1
a plunger driver to drive the plunger axially forwards upon release of the connection to the elongate member
Data Source
Figure 1
Figure 2
Figure 3(a)~4(b)
AI summary
An apparatus for a firing mechanism 102 for use in an injection device 100 and comprising: a rear cap 104 having an elongate member 110 extending axially forwards when installed within the injection device; a plunger 106 releasably connected, directly or indirectly, to the elongate member and, upon release of the connection to the elongate member, axially displaceable in a forward direction; and a plunger driver 112 to drive the plunger axially forwards upon release of the connection to the elongate member, wherein the plunger and the rear cap define an axial length of the assembly, which in turn determines a start position of a forward end of the plunger before release of the connection to the elongate member, and wherein, during construction of the assembly, the plunger is releasably connectable, directly or indirectly, to the elongate member at one of a plurality of positions for controlling the axial length of the assembly.