Force Reduction in Injection Devices via Damping Mechanisms
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Solution Overview
Problem
Auto-injector devices face challenges in varying the force applied to the plunger to prevent damage and ensure a comfortable user experience, as high impact forces can cause pain and rapid injection.
Innovation Solution
Incorporating a force reduction feature with a tapered bore and compressible walls within the medicament container, which dampens the plunger rod motion, and additional features like O-rings, chamfered heads, and flexible arms to reduce the net force on the plunger, allowing for adjustable resistance and smoother medicament expulsion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a drive mechanism applies high force to the plunger to expel medicament quickly, then the injection speed increases, but the impact force on the stopper causes device damage and user pain
Solution Approach 1:
The patent implements a force reduction feature with a tapered bore and compressible walls that dampens plunger rod motion before the plunger head impacts the stopper. This beforehand cushioning reduces the impact force on the stopper, preventing device damage and user pain while maintaining effective medicament expulsion speed.
Solution Approach 2:
The force reduction feature acts as an intermediary element between the drive mechanism and the plunger rod. The compressible bore walls and damping features mediate the force transmission, reducing peak impact forces while maintaining the overall drive function, thus protecting both the device and user.
2Ease of operation
If the drive mechanism applies variable force to accommodate different medicament properties, then the injection comfort improves, but the device complexity increases
Solution Approach 1:
The patent uses a tapered bore with compressible walls where the geometry parameters (taper angle, wall compliance) are optimized to provide automatic force modulation. As the plunger rod moves through the tapered bore, the varying wall compression provides progressive damping without requiring complex active control systems, thus maintaining injection comfort while limiting device complexity.
Solution Approach 2:
The force reduction feature is designed to automatically adapt to different medicament properties through its passive mechanical damping characteristics. The compressible bore walls self-regulate the force profile based on the resistance encountered, eliminating the need for sensors or active control mechanisms while maintaining injection comfort across varying conditions.
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
The force reduction feature allows for a consistent and comfortable injection experience across different medicament properties, reducing user discomfort and preventing device damage, while enabling the use of a single spring for various medicament indications.
Implementation Method 1
the bore has compressible walls, which are compressible by the plunger head as the plunger head passes through the bore to damp at least a part of a plunger rod motion
Implementation Method 2
the bore has compressible walls, which are compressible by the plunger head as the plunger head passes through the bore
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3c
AI summary
This application relates to force reduction in injection devices. According to a first aspect, the specification describes an injection device comprising: a medicament container; a stopper translatably disposed within the medicament container; a plunger rod, the plunger rod comprising a plunger head; a drive mechanism for displacing the plunger rod into the medicament container; and a force reduction feature, wherein the plunger rod is operable to displace the stopper; and wherein the force reduction feature is arranged to damp at least a part of a plunger rod motion when the plunger rod is driven by the drive mechanism.