Medicament Injection Device Plunger Rod Two-Stage Motion
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Solution Overview
Problem
Existing medicament injection devices may fail to automatically protect the needle after use, especially for users with limited strength, making it difficult to prevent accidental reuse and ensuring safe disposal.
Innovation Solution
A medicament injection device with a plunger driver and needle cover mechanism that allows for automatic extension of the needle cover after use, utilizing a two-stage motion path for the plunger rod to release the needle cover with minimal additional force, and a final position-maintaining arrangement to lock the cover in place, preventing retraction without excessive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the needle guard assembly relies on a catch-mounting that must be broken by applying pressure on the grip plate, then the needle can be covered after injection, but users with limited strength cannot break the catch-mounting and the needle guard will not cover the needle
Solution Approach 1:
The plunger rod is designed to automatically perform the function of covering the needle after injection through its own movement, eliminating the need for the user to manually break a catch-mounting or apply additional force. The system uses the existing injection motion to trigger the protective action.
Solution Approach 2:
The plunger rod is pre-configured with a guide arrangement that enables it to automatically move into position to cover the needle after the injection is complete. The mechanism is prepared in advance to execute the protective action without requiring additional user intervention.
2Ease of operation
If the plunger rod moves only in axial direction, then the injection process is simple, but the plunger rod cannot be released from the plunger driver to enable needle cover extension
Solution Approach 1:
The plunger rod's motion path is made dynamic, transitioning from a fixed axial movement during injection to a rotated position after injection. This dynamic change in motion trajectory enables the plunger rod to disengage from the plunger driver and subsequently push the needle cover into position.
Solution Approach 2:
The plunger rod movement is extended from one dimension (axial direction only) to two dimensions (axial direction plus rotational movement). This additional rotational dimension allows the plunger rod to release from the plunger driver while maintaining the simplicity of the initial injection stroke.
Data Source
Figure 1~2a
Figure 2b~2c
Figure 3~4
AI summary
The present disclosure relates to a medicament injection device (1) comprising a housing (3) arranged to receive a medicament container (11a), a needle cover (9) movable relative to the housing (3), from a retracted position, in which it engages the housing (3) and enables medicament delivery, to an extended position, a plunger rod (7), and a plunger driver (5) movable relative to the housing (3) from an initial position to a final position, and arranged to actuate the plunger rod (7), wherein the plunger rod (7) has a first guide arrangement and the housing (3) has a second guide arrangement, the first guide arrangement (7d) and the second guide arrangement being arranged to cooperate to guide movement of the plunger rod (7) relative to the housing (3), wherein the first guide arrangement and the second guide arrangement in a first stage provide a linear motion path for the plunger rod (7), enabling the plunger rod (7) to initially move in the axial direction and in a second stage provide a rotation motion path for the plunger rod (7),enabling the plunger rod (7) to rotate relative to the housing (3) to release the plunger rod (7) from the plunger driver (5), whereby the plunger driver (5) attains a released state enabling movement of the plunger driver (5) to its final position, wherein in the released state the plunger driver (5) is arranged to release the needle cover (9) from the housing (3) and to actuate the needle cover (9) to its extended position.