Autoinjector Force Adjustment Mechanism for Syringe Safety
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Solution Overview
Problem
Existing autoinjectors face challenges such as painful needle insertion due to strong springs, risk of syringe breakage, and lack of clear user feedback on injection completion, while also being costly and complex to manufacture.
Innovation Solution
An autoinjector design featuring a force adjustment system with pivoting members and elastic elements that amplify the injection force, combined with a visual and/or audible indicator to signal injection completion, and a mechanism to reduce the force exerted during needle insertion to prevent syringe damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a strong spring is used to ensure the entire injection phase, then the injection reliability is improved, but the needle insertion becomes painful and the syringe collar may break
Solution Approach 1:
The injection process is segmented into two distinct phases with different force requirements: needle insertion phase and fluid injection phase. The first elastic element (spring) is designed to provide sufficient force only for needle insertion, while the second elastic element (pivoting members with elastic elements) provides additional amplification force specifically for disengaging the syringe plunger during the injection phase. This segmentation allows each phase to have optimized force characteristics without compromising the other.
Solution Approach 2:
The force exerted on the piston rod is made dynamic rather than static. The pivoting members with elastic elements create a variable force system that adapts to the injection process: initially providing amplification force when the piston rod moves from rest position, then gradually reducing as the injection progresses. This dynamic force adjustment ensures sufficient force for plunger disengagement while preventing excessive force that could cause pain or breakage.
2Force
If a strong spring is used to ensure the entire injection phase, then the injection force is sufficient, but the risk of breaking the syringe collar increases
Solution Approach 1:
The force application is segmented into two stages: the first elastic element provides base force for needle insertion, while the second elastic element (pivoting members) provides temporary amplification force only when needed for plunger disengagement. This segmentation ensures that the syringe collar experiences high force only briefly during plunger release, rather than continuous high force that would increase breakage risk.
Solution Approach 2:
The amplification force from the pivoting members acts periodically rather than continuously. The elastic elements are loaded and unloaded in cycles corresponding to the injection process, providing force amplification only during the critical moment of plunger disengagement, then relaxing to reduce force on the syringe collar for the remainder of the injection phase.
3Reliability
If the autoinjector is designed to be robust and reliable, then the injection safety is improved, but the manufacturing and assembly costs increase
Solution Approach 1:
The force adjustment system is segmented into two independent elastic elements (springs) that can be manufactured and assembled separately. The first elastic element is a standard compression spring, while the second consists of pivoting members with elastic elements. This segmentation allows each component to be optimized for its specific function and manufactured using appropriate processes, reducing overall manufacturing complexity and cost compared to a single complex spring system.
Solution Approach 2:
The pivoting members act as intermediaries between the first elastic element and the piston rod. Instead of directly connecting a single strong spring to the piston rod, the pivoting members mediate the force transmission, providing mechanical advantage and force amplification. This intermediary mechanism allows the use of milder springs that are easier and less expensive to manufacture while still achieving the required injection force through mechanical leverage.
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 autoinjector provides a safer, more comfortable user experience with reduced risk of syringe breakage, clear indication of injection completion, and simplified, cost-effective manufacturing.
Implementation Method 1
said pivoting members being connected to each other by two elastic elements... said elastic elements, loaded, at the beginning of the movement of the piston rod towards its injection position, causing said pivoting members to rotate in such a way as to relax said elastic elements, thus creating an amplification force F2 at the beginning of injection
Data Source
Figure 1
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AI summary
The invention relates to an autoinjector comprising a body (1, 2), a vessel (S) comprising a piston, said autoinjector comprising a piston rod (5) movable between an inoperative position and an injection position in which said piston rod (5) has moved the piston of the vessel (S) in order to inject the fluid product, a spring (6) being provided such as to bias said piston rod (5) toward the injection position thereof, the autoinjector including a force-adjustment system (7, 8) suitable for exerting at least one force (F2) on said piston rod (5), said force (F2) adding to the force exerted by said spring (6) at the start of the injection, said system including two pivoting members (7) engaging with said piston rod (5), said pivoting members (7) being connected to one another by two resilient elements (8), said body (1, 2) comprising a handle (3), said pivoting members (7) being mounted such as to pivot on said handle (3) about stationary shafts (79), said autoinjector including an end-of-injection indicator consisting of and/or secured to said handle (3) and comprising an indication portion which is movable and/or deformable relative to said body (1, 2) such as to engage, after the end of the injection, with at least one viewing window.