Plunger Rod Segmentation for Compact Injection Device Dosing
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Solution Overview
Problem
There is a need for a compact injection device that can deliver specific, selected doses of medication efficiently while minimizing storage space, especially for prefilled devices that require precise dosing and storage at low temperatures, and preventing inadvertent movement of the plunger rod past a predetermined limit.
Innovation Solution
A plunger rod with a distal and proximal element slidingly coupled, featuring a radially flexible branch and locking means that allows for selective locking in multiple axial positions, enabling the plunger rod to change length between a restricted and extended position, allowing for precise dose delivery and reducing overall device length for storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the plunger rod is made extendable to deliver multiple doses, then the dosing versatility is improved, but the storage volume increases
Solution Approach 1:
The plunger rod is divided into a distal element and a proximal element that can move relative to each other. The proximal element can be displaced axially with respect to the distal element to extend the plunger rod length, enabling multiple dose deliveries. When not in use, the proximal element retracts to minimize storage volume.
Solution Approach 2:
The plunger rod transitions from a static structure to a dynamic one where the proximal element can be selectively displaced axially. This dynamic extension allows the device to adapt between compact storage mode and extended dosing mode, providing versatility without permanently increasing storage volume.
2Measurement precision
If the plunger rod is locked in multiple positions for precise dosing, then the dosing precision is improved, but the device complexity increases
Solution Approach 1:
The locking mechanism utilizes the radially flexible branch that automatically engages with locking surfaces at predetermined axial positions. The system self-locks at these positions without requiring additional actuators or complex control mechanisms, achieving precise dosing positions through the inherent flexibility and elasticity of the branch structure.
Solution Approach 2:
The radially flexible branch changes its radial dimension to enable locking and unlocking. By varying the radial flexibility parameter of the branch, the system achieves multiple locked axial positions for precise dosing while maintaining a relatively simple overall structure without additional locking components.
3Volume of stationary object
If the plunger rod is made compact for storage, then the storage efficiency is improved, but the ease of operation for dose delivery is worsened
Solution Approach 1:
The plunger rod is designed to be dynamic rather than static, allowing the proximal element to be displaced axially when needed for operation. During storage, it remains compact; during use, it extends to provide the necessary stroke length for dose delivery, thus maintaining both compact storage and ease of operation.
Solution Approach 2:
The proximal element is designed to nest within or alongside the distal element in the retracted position, minimizing the overall storage volume. When operation is required, the nested structure allows smooth axial displacement to extend the plunger rod to the required length for dose delivery.
Data Source
Figure 1~3
Figure 4A~5B
Figure 6~7
AI summary
The present invention relates to a plunger rod (1) for an injection device, comprising a distal element (20) slidingly coupled to a proximal element (30) having one radially flexible branch (33), locking means (23, 33, 35) for selectively locking the distal element and the proximal element in a plurality of relative axial positions defining a plurality of intermediate positions of the plunger rod, wherein the locking means is movable from a locked state, in which the distal element and the proximal element are fixed with respect to each other in the axial direction, and an unlocked state, in which the distal element and the proximal element are displaceable in the axial direction with respect to each other, when the radially flexible branch is displaced radially. The invention also relates to an injection device comprising such a plunger rod.