Prefilled Injection Device End-of-Content Mechanism
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Solution Overview
Problem
Existing medical injection devices with mechanical End-of-Content mechanisms struggle to operate effectively with axially movable parts, which are necessary for releasing doses without obstructing the End-of-Content mechanism.
Innovation Solution
A pre-filled injection pen design featuring a rotatable piston rod with an outer thread and longitudinal non-threaded area, a piston rod guide that only rotates during dose expelling, and an End-of-Content tube with a helical thread that prevents rotation when the piston rod is not rotated, ensuring the End-of-Content mechanism functions without obstructing axially movable parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If axially movable parts are added to release doses, then ease of operation is improved, but the end-of-content mechanism becomes obstructed and reliability deteriorates
Solution Approach 1:
The piston rod is segmented into a threaded portion and a non-threaded portion. The non-threaded portion allows axial movement for dose release while the threaded portion engages with the end-of-content mechanism to prevent rotation when content is depleted. This segmentation enables both axial movability for operation and rotational constraint for reliability.
Solution Approach 2:
Instead of preventing axial movement to protect the end-of-content mechanism, the invention allows axial movement but prevents rotation through the non-threaded portion engagement. This inverted approach achieves the same protective function while maintaining operational ease.
2Manufacturing precision
If the piston rod has a continuous thread for rotation, then dosing accuracy is improved, but axial movement for dose release is obstructed
Solution Approach 1:
The piston rod thread is segmented to include both threaded and non-threaded portions. The threaded portion enables precise rotational dosing, while the non-threaded portion enables axial movement for dose release. This segmentation resolves the contradiction between dosing accuracy and operational ease.
Solution Approach 2:
Different portions of the piston rod have different local qualities: the threaded portion provides precision for dosing accuracy, while the non-threaded portion provides freedom of movement for dose release. This local differentiation resolves the contradiction between precision and mobility.
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
Enables secure and accurate dosing by preventing further dose setting once the injectable content is depleted, ensuring the user cannot exceed the remaining drug amount, while allowing axially movable parts for dose release without obstructing the End-of-Content mechanism.
Implementation Method 1
a torsion spring encompassed between the housing or at least a part fixed to the housing and the drive element, which holds a torque for rotating the drive element during dose expelling
Implementation Method 2
On the outer surface, the EoC tube is provided with a helical thread
Data Source
AI summary
The invention relates to an injection device comprising an End-of-Content mechanism. The End-of-Content mechanism comprises a piston rod (10) being driven forward by a rotatable piston rod guide (20), a driver (50) attached to a dose setting tube (30) and an End-of-Content tube (40). The End-of-Content tube is moved axially forward during dose setting a distance which correlates to the size of the dose being set. When the accumulated set and ejected dose equals the injectable amount initially available in the cartridge (3), the End-of-Content tube engages a lock mechanism provided in the piston rod guide and the driver engages a stop surface on the End-of-Content tube. Once the End-of-Content mechanism is locked, no further dose can be set and the piston rod guide cannot be rotated. In order to provide a proper engagement between the piston rod guide and the driver, the End-of-Content mechanism is released during dose expelling.