Trigger Assembly Resilient Fingers for Injection Device
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Solution Overview
Problem
Automatic injection devices often have inconsistent triggering mechanisms due to manufacturing variability, requiring large spring forces that can lead to trigger deformation, making operation difficult, especially with viscous medications, and are constrained by cost and space limitations.
Innovation Solution
A trigger assembly with a button molded from durable material, featuring a set of resilient fingers and a tapered flange that cams a prong for consistent operation, combined with a dual-functioning biasing member and damping collar to manage spring force and ensure smooth triggering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple prongs are used in the triggering mechanism, then the device can be actuated reliably, but manufacturing variability causes the prongs to release in stages that are noticeable to users, reducing consistency
Solution Approach 1:
The trigger assembly is divided into multiple independent resilient fingers (first resilient finger, second resilient finger, third resilient finger) that are segmented along the longitudinal axis. Each finger can deflect and release independently, allowing the trigger to overcome manufacturing variability by distributing the triggering function across multiple discrete elements rather than relying on a single multi-prong component.
Solution Approach 2:
Each resilient finger is positioned at a different longitudinal location along the trigger assembly, creating local variations in the triggering sequence. The fingers are arranged such that they engage and release at different positions, providing a progressive release mechanism that maintains reliability while accommodating manufacturing tolerances through localized functional distribution.
2Force
If large spring force is used to drive the syringe plunger, then the device can handle larger plunger diameters and viscous medications, but the trigger assembly requires larger forces to overcome the spring, leading to trigger deformation
Solution Approach 1:
The resilient fingers are designed to be flexible and dynamic, capable of deflecting under load and returning to their original position. This dynamic flexibility allows the trigger assembly to accommodate high spring forces without permanent deformation, as the resilient material can elastically deform to absorb and release the stored energy from the biased member during the triggering sequence.
Solution Approach 2:
The trigger assembly incorporates resilient fingers made from elastomeric or polymer materials that combine flexibility with sufficient structural strength. These composite material properties allow the trigger components to withstand large spring forces while maintaining their structural integrity and resisting deformation, effectively decoupling the force requirement from the trigger strength requirement.
3Strength
If the trigger assembly is made larger or from more expensive materials to accommodate larger forces, then trigger deformation is reduced, but the device size and cost increase
Solution Approach 1:
The resilient fingers are designed with optimized geometric parameters including thickness, length, and cross-sectional area that are specifically tailored to provide the required strength-to-weight ratio. By carefully controlling these dimensional parameters, the trigger assembly achieves sufficient strength to handle large spring forces while maintaining a compact size and using cost-effective elastomeric or polymer materials rather than expensive metals.
Solution Approach 2:
The trigger assembly is designed as a disposable component that can be manufactured using inexpensive elastomeric or polymer materials through molding processes. This disposable approach allows the use of simpler, cheaper materials that would not be suitable for reusable applications, reducing both material costs and manufacturing complexity while maintaining adequate strength for the intended single-use application.
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
The solution provides a consistent and robust triggering experience across devices, reducing the risk of deformation and improving usability, even with larger plunger diameters or viscous medications, without increasing size or cost.
Implementation Method 1
a first resilient finger (160) positioned at a first longitudinal location... a second resilient finger (160) positioned at a second longitudinal location... a third resilient finger (160) positioned at a third longitudinal location
Implementation Method 2
a biasing member (155) positioned within the housing (24) and biased to urge the plunger element (136) in a second direction toward the piston
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
Automatic injection device with trigger assembly. The trigger assembly includes a button (25), and a single prong (160) extending from a biased element of the device toward the button. A button- engaging surface (167) of the prong and a support surface of the device define a radially extending opening in which an actuating element (52) of the button fits for a radially outward face of the actuating element to be backed up by the support surface. For release of the biased element, when the button is pressed to shift the actuating element to cause a latching surface of the prong to disengage from a latch surface of the device, motion of the actuating element in a direction away from the prong is limited by the radially outward face of the actuating element abutting the support surface.