Frost Protected Injection Device with Decoupling Mechanism
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Solution Overview
Problem
Injection devices face challenges in maintaining dose accuracy and preventing damage from temperature-induced drug expansion, particularly when exposed to freezing conditions, which can lead to excessive force on the piston rod drive mechanism, potentially causing malfunction or breakage.
Innovation Solution
The injection device features a reversible movement mechanism allowing the actuation member and movable wall to displace in response to forces acting on the movable wall due to temperature changes, with a bias means for automatic return and a coupling mechanism that decouples under high forces to prevent damage, ensuring synchronized movements and maintaining dose accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a unidirectional coupling mechanism is used to prevent slack between the piston rod and piston, then dose accuracy is improved, but the device becomes vulnerable to breakage when the drug freezes and expands
Solution Approach 1:
The coupling mechanism transitions from a rigid unidirectional coupling to a dynamic system with two-way coupling capability. The piston rod can couple with the piston during normal operation to ensure dose accuracy, and decouple when freezing forces exceed the retention force, allowing the system to adapt its coupling state based on operational conditions.
Solution Approach 2:
The system changes the coupling parameter dynamically - maintaining strong coupling under normal forces to ensure precision, and allowing decoupling when forces exceed a threshold (freezing conditions). The biasing element modifies the coupling parameter by applying a retention force that can be overcome by excessive expansion forces.
2Manufacturing precision
If the piston rod is firmly coupled to the piston to eliminate slack, then injection accuracy is improved, but excessive force from frozen drug expansion can cause component breakage
Solution Approach 1:
The biasing element (spring or elastomeric member) is pre-loaded to provide a retention force that maintains coupling during normal operation. This cushioning force ensures accurate coupling during injection while allowing the system to safely decouple when freezing forces exceed the pre-set retention threshold, preventing component breakage.
Solution Approach 2:
The biasing element acts as an intermediary between the piston rod and piston, mediating the force transmission. It provides controlled retention force during normal operation and allows decoupling when forces become excessive, serving as a protective intermediary that prevents direct transmission of damaging forces to the components.
3Reliability
If a ratchet and pawl mechanism is used to prevent backward movement of the piston rod, then dose delivery reliability is improved, but the mechanism may break when subjected to large forces from frozen drug
Solution Approach 1:
The invention extracts the one-way coupling function from a complex ratchet and pawl mechanism and implements it through a simpler biasing element that provides two-way coupling capability. The biasing element maintains coupling during normal operation and allows decoupling under excessive force, eliminating the need for complex ratchet and pawl components while maintaining reliability.
4Reliability
If the piston rod drive mechanism is made robust to withstand freezing forces, then device reliability under freezing conditions is improved, but normal operation may be affected and dose accuracy may deteriorate
Solution Approach 1:
The coupling mechanism dynamically adjusts its state based on the forces involved. During normal operation, the biasing element maintains strong coupling for precise dose delivery. Under freezing conditions, when forces exceed the retention threshold, the system automatically decouples, allowing the piston to expand freely without affecting the precision of the drive 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 configuration ensures reliable and accurate administration of drug doses without damaging the injection mechanism, even when the drug expands due to freezing, by allowing reversible movement and automatic return of components, thus maintaining dose accuracy and preventing device failure.
Implementation Method 1
If an injection device accommodating a liquid drug is for any reason exposed to temperatures below the liquid drug's freezing point, the liquid will expand in the reservoir
Implementation Method 2
the liquid will expand in the reservoir causing a relatively large pressure on the reservoir walls, including the piston
Data Source
AI summary
The invention relates to an injection device (100, 200, 300) which is capable of resisting proximal movements of a piston rod (107, 207, 307) relative to a housing (102, 202, 302), when the piston rod (107, 207, 307) is subjected to proximally directed forces below a threshold magnitude, and of allowing reversible proximal movements of the piston rod (107, 207, 307) relative to the housing (102, 202, 302), when the piston rod (107, 207, 307) is subjected to proximally directed forces of or above the threshold magnitude.