Trigger Assembly Camming Mechanism for Low-Force Injection
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Solution Overview
Problem
Automatic injection devices often require large forces to operate due to the spring force opposing the trigger mechanism, making them difficult for users to operate, especially with larger plungers or more viscous medications.
Innovation Solution
A trigger assembly with a button, lock member, and engagement surfaces that utilize a camming effect to release a biased element for movement, allowing for low-force operation and tunability during manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional trigger assembly directly opposes the spring force to drive the syringe plunger, then the device can achieve the required injection force, but the operation becomes difficult for users due to the large force required
Solution Approach 1:
The trigger assembly transitions the operation from direct axial force opposition to a rotational dimension. The lock member rotates about an axis perpendicular to the spring force direction, allowing the camming surfaces to convert rotational motion into axial plunger movement. This dimensional change enables users to apply smaller forces through rotational motion rather than directly opposing the large spring force axially.
Solution Approach 2:
The camming surfaces act as an intermediary mechanism between the user's trigger input and the spring force-driven plunger movement. The first and second camming surfaces on the lock member and biased element respectively, transfer and transform the triggering force into rotational motion that releases the spring's stored energy, rather than allowing direct force opposition.
2Power
If larger spring forces are used to accommodate increasing plunger diameters or more viscous medications, then the injection capability is improved, but the trigger assembly requires even larger forces to operate
Solution Approach 1:
By introducing rotational motion as an intermediate dimension, the system decouples the injection power requirement from the trigger operation force requirement. The lock member's rotation allows the spring force to be accumulated and released effectively, enabling high injection power through larger springs while keeping the trigger activation force manageable through rotational leverage.
Solution Approach 2:
The trigger assembly utilizes dynamic camming surfaces that change their mechanical advantage during rotation. As the lock member rotates, the camming surfaces progressively engage and disengage, allowing the system to build up and release energy dynamically. This dynamic mechanism enables the spring force to be effectively harnessed for high-power injection while requiring only moderate trigger forces.
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 convenient operation with reduced force required for injecting medications, improving usability and allowing for design adjustments during manufacturing.
Implementation Method 1
At least one of the first and second engagement surfaces is ramped for camming effect between the first and second engagement surfaces
Data Source
AI summary
A trigger assembly for an automatic injection device which by its operation releases a biased element of the device for movement. The trigger assembly includes a button pressable by a user, and a lock member. Prior to the button being plunged, a blocking element on the button is abutted by a button-engaging surface of the lock member to prevent lock member rotation, thereby allowing an engagement surface on the lock member to remain in engagement with an engagement surface of the biased element so as to restrain motion of the biased element. When the button is plunged, the blocking surface moves clear of the button-engaging surface to allow the lock member to rotate, during which rotation the engagement surfaces disengage to release the biased element for movement.