Injection Device Plunger Velocity Regulator Cam Mechanism
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Solution Overview
Problem
Existing injection devices face limitations in plunger velocity control during needle insertion and drug delivery, particularly with high viscosity drugs, due to the need for relative rotation between the plunger and cam member, which can lead to stalling and design constraints.
Innovation Solution
The injection device incorporates a plunger velocity regulator with a cam surface and cam member that limits forward velocity initially, using a releasable coupling that disengages after an initial movement, allowing full force application during drug delivery, and eliminates the need for relative rotation, providing increased design flexibility and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a velocity regulator with relative rotation between plunger and cam member is used, then plunger velocity control during needle insertion is improved, but stalling and design constraints occur
Solution Approach 1:
The patent extracts the relative rotation requirement from the velocity regulator mechanism. The cam member is designed to rotate independently without requiring the plunger to rotate relative to it, eliminating the stalling issue while maintaining velocity control functionality during needle insertion.
Solution Approach 2:
The velocity control function is segmented into a dedicated cam member that handles rotation independently from the plunger's linear motion. This separation allows the plunger to move linearly while the cam member provides the necessary rotational movement for velocity regulation, resolving the conflict between velocity control and stalling.
2Speed
If relative rotation between plunger and cam member is required, then velocity regulation is achieved, but design flexibility and plunger strength are reduced
Solution Approach 1:
The rotational function is extracted from the plunger and assigned to a separate cam member. This allows the plunger to be designed optimally for its function (strong, hollow, or telescopic) without being constrained by rotational requirements, while the cam member independently provides the necessary rotation for velocity regulation.
Solution Approach 2:
The cam member serves multiple functions: it provides the rotational movement necessary for velocity regulation while being independent of the plunger's design. This multi-functionality allows the plunger to be optimized for specific applications (e.g., hollow plunger for indication) without compromising velocity control capability.
3Power
If a releasable coupling is used to disengage cam member after initial movement, then full force application during drug delivery is improved, but coupling mechanism complexity increases
Solution Approach 1:
The releasable coupling is designed to automatically disengage based on the plunger's position or movement characteristics. The coupling mechanism self-regulates, transitioning from engaged to disengaged state without requiring external control, thereby providing full force application during drug delivery while minimizing control complexity.
Solution Approach 2:
The coupling is preliminarily engaged to provide velocity control during needle insertion, then automatically disengages when the needle insertion phase is complete. This preliminary engagement followed by automatic release allows the system to switch from controlled velocity mode to full force mode without complex external control mechanisms.
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
This solution improves the sequencing and reliability of the velocity regulator, reduces the size of connecting features, and allows for stronger plungers or hollow designs, effectively managing high viscosity drugs by limiting initial velocity and ensuring consistent delivery.
Implementation Method 1
The velocity regulator arrangement includes a cam surface (associated with one of the housing or the plunger) and a cam member (associated with the other of the plunger or the housing). Engagement of the cam surface with the cam member causes axial movement of the plunger, under the drive of the delivery mechanism, to cause relative rotational movement of the cam member and limits the forward velocity of the plunger movement.
Implementation Method 2
The actuation mechanism may comprise a drive spring (for example a compression spring) which is held in an energised (or primed position) prior to release by the trigger.
Data Source
AI summary
An injection device for delivering a dose of medicament from a syringe (5), the injection device comprising a housing (10), a plunger (210) moveably mounted within the housing (10), an actuation mechanism (200), a trigger mechanism (40), and a plunger velocity regulator. The actuation (mechanism (100) is arranged to provide a forward biasing force to urge the plunger (210) forward in use to express a dose of medicament, and the trigger mechanism (40) is arranged to releasably hold the plunger (210) against the force of the actuation mechanism (200). The plunger velocity regulator comprises a cam surface (262) associated with the housing, and a cam member (252) associated with the plunger (210) and arranged to engage the cam surface (262) during actuation movement of the plunger (210) such that axial movement of the plunger (210) relative to the housing (10) causes relative rotational movement of the cam member (252) which limits the forward velocity of the plunger movement. The plunger (210) is axially connected to the cam member (252) by a releasable coupling (300), and the plunger velocity regulator further comprises a coupling member (350) which blocks release of the releasable coupling (300) when the plunger (210) is in a rearward position and wherein forward movement of the plunger (210) moves the releasable coupling (300) out of engagement with the coupling member (350) such that the plunger (210) may disengage the cam member (252) after an initial movement of the plunger (210).