Medicament Injector Trigger with Axial Dosing and Rotational Reset
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Solution Overview
Problem
Existing injection devices for self-administration of medicaments often lead to errors in dose selection, potentially reducing medication efficacy and causing harmful side effects due to their complex operation and lack of clear differentiation between dosing and resetting motions.
Innovation Solution
A medicament dispensing mechanism featuring a trigger with distinct ready and fired positions, allowing axial translation for dosing and rotational resetting, coupled with an anti-retrograde mechanism to prevent reverse movement, ensuring accurate and safe administration of successive fixed doses without user error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a unidirectional transmission mechanism or cam barrel with ratchet is used to advance the piston rod in successive axial steps, then multiple doses can be administered, but the device complexity increases and the ease of operation decreases due to the complex trigger mechanism
Solution Approach 1:
The trigger mechanism is segmented into distinct functional zones: a dead zone that prevents accidental activation, a dosing zone that advances the plunger, and a resetting zone that returns the trigger without dosing. This segmentation simplifies the overall mechanism by clearly separating dosing and resetting functions into distinct spatial regions along the trigger's linear path.
Solution Approach 2:
Instead of using a complex cam barrel or ratchet mechanism to enforce unidirectional motion, the patent inverts the approach by using a linear trigger path with strategically placed dead zones. The resetting motion naturally follows the same linear path as dosing, but the dead zone prevents dosing during reset, eliminating the need for complex mechanical enforcement mechanisms.
2Device complexity
If the trigger return stroke follows the same path as the dosing stroke in opposite direction, then the mechanism is simplified, but errors in dose selection occur because the user cannot clearly distinguish between dosing and resetting motions
Solution Approach 1:
Different functional qualities are assigned to different segments of the trigger's path. The dead zone has the quality of being non-functional (neither dosing nor resetting), the dosing zone has the quality of advancing the plunger, and the resetting zone has the quality of returning the trigger without dosing. This local differentiation ensures users can clearly distinguish between dosing and resetting actions based on tactile feedback and trigger position.
Solution Approach 2:
The dead zone acts as an intermediary element between the dosing zone and resetting zone. It provides a transitional region that prevents accidental dosing during reset while maintaining the simplicity of a linear trigger path. The dead zone mediates between the conflicting requirements of mechanism simplicity and dose selection accuracy.
3Measurement precision
If the dose volume is preset and fixed, then dosing accuracy is improved, but the adaptability decreases as users cannot adjust between priming dose and injection dose
Solution Approach 1:
The device performs preliminary action by automatically delivering a priming dose when the trigger is first pulled from the initial position. This priming action prepares the system for subsequent adjustable dosing. The fixed dosing mechanism is activated only after this preliminary priming action, ensuring accurate dosing while maintaining adaptability through the optional priming function.
Data Source
AI summary
A medicament dispensing mechanism is disclosed that is configured to eject successive doses of the medicament from a medicament chamber. An embodiment of the dispensing mechanism includes a housing and a plunger rod configured for ejecting the doses of medicament from the chamber. The dispensing mechanism further includes an actuation mechanism that comprises a trigger associated with the housing and having a ready and a fired position with respect thereto. The trigger is configured for manipulation by a user for successive movement in a generally axial dosing motion from the ready position to the fired position in which the trigger is associated with the plunger rod to cause the plunger rod to eject one of the doses of a predetermined volume and a resetting motion from the fired position to the ready position that comprises axial rotation, wherein the trigger is uncoupled from the plunger rod during the resetting motion.