Plunger Seal With Expandable Core For Reduced Leakage
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Solution Overview
Problem
Existing plunger seals for medicine cartridges lack an adjustable sealing force mechanism that effectively balances sealing integrity during storage and ease of drug discharge, often resulting in suboptimal sealing performance and increased friction resistance.
Innovation Solution
A plunger seal system with a parked and mobile state, where the seal can be adjusted to increase normal force between the seal and the inner wall of the reservoir by using a core to expand the cavity, enhancing sealing during storage while allowing easy movement for drug discharge, with a maximum distortion of less than 0.5 mm and a force increase of over 30% in the parked state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the plunger seal is designed with fixed sealing force, then the structure is simple, but the sealing performance during storage and ease of drug discharge cannot be optimized simultaneously
Solution Approach 1:
The plunger seal is designed to dynamically change its sealing force based on operational state. During storage, the seal maintains high normal force against the reservoir wall to ensure leak-proof sealing. During drug discharge, the seal transitions to a mobile state with reduced friction, enabling smooth movement. This dynamic adaptation resolves the contradiction between maintaining reliable sealing and avoiding excessive structural complexity.
Solution Approach 2:
The patent changes the physical parameters of the plunger seal by introducing a core that can be inserted into or removed from the seal cavity. When the core is inserted, it expands the seal radially outward, increasing the normal force and sealing pressure. When removed, the seal contracts, reducing friction for movement. This parameter change allows the same structure to provide different sealing characteristics without complex mechanisms.
2Reliability
If the normal force between plunger seal and reservoir wall is increased to improve sealing, then sealing integrity is enhanced, but friction resistance increases making drug discharge difficult
Solution Approach 1:
The system transitions between two distinct states: parked state with high normal force for sealing, and mobile state with reduced friction for discharge. The core insertion/removal mechanism enables this dynamic transition, allowing the plunger seal to provide strong sealing during storage then move easily during drug administration, resolving the contradiction between sealing integrity and ease of operation.
Solution Approach 2:
The core is pre-inserted into the seal cavity during assembly to establish the parked state with optimal sealing force before storage. When drug discharge is needed, the core is removed in advance to transition to the mobile state, reducing friction beforehand to facilitate smooth plunger movement. This preliminary action ensures both sealing integrity during storage and ease of operation during discharge.
3Reliability
If the plunger seal is made highly compliant to increase sealing force, then sealing performance improves, but the distortion during movement increases affecting precision
Solution Approach 1:
The patent controls the degree of seal compliance by using a removable core. The core provides structured support that limits excessive radial expansion of the compliant seal material. When inserted, it allows controlled expansion for sealing while preventing uncontrolled distortion. This parameter control enables the seal to be sufficiently compliant for sealing force while maintaining dimensional stability and precision during operation.
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 system provides enhanced sealing for long-term storage while facilitating easy drug discharge by adjusting the normal force between the plunger seal and the reservoir, reducing friction resistance and ensuring reliable sealing and sterility.
Implementation Method 1
expanding an inner diameter of the cavity with the core to cause the increased normal force
Implementation Method 2
the increased normal force resulting an increase in friction resistance to longitudinal movement of the plunger seal against the inner wall of the reservoir
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A plunger seal for a drug delivery device may have a mobile and an enhanced sealing parked state. Optionally, the cartridge is stored with the plunger seal in the parked state. Optionally, drug discharge occurs with the plunger seal in the mobile state. For example in the parked state there may be increased normal force between the plunger seal and an inner wall of the cartridge. Optionally there is limited deformation of the plunger seal between the parked and mobile states. Optionally the plunger seal is biased to the parked state. Optionally, a distal force switches the plunger seal to the mobile state. For example, the plunger seal may have an inner cavity that is expanded radially by core. A biasing element optionally biases the core wedging it proximally to the parked state. A distal force on the core may push it distally to the mobile state.