Torsion-Spring Self-Injector for Complete Needle Retraction
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Solution Overview
Problem
Existing self-injectors are costly, complex, and pose risks of needle injury or infection due to incomplete needle retraction, with insufficient force for complete ejection of syringe contents.
Innovation Solution
A self-injector design featuring a swivel lever articulated to a pivotable spring leg of a torsion spring, where the piston is actuated by a piston slide guided along a rail, ensuring safe and complete needle retraction into the housing after use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a spiral spring is used to drive the piston, then the device can be simpler and cheaper, but the force applied is too weak to guarantee complete ejection of syringe contents
Solution Approach 1:
The patent changes the physical parameters of the spring system by using a torsion spring instead of a spiral spring, and employs a lever mechanism to amplify the force output. The torsion spring provides greater stored energy, and the lever multiplies this force to achieve both complete ejection and needle retraction, resolving the contradiction between simplicity and sufficient force.
2Ease of manufacture
If the device uses fewer parts and less metal, then manufacturing cost decreases, but functional safety and reliability may be compromised
Solution Approach 1:
The patent merges multiple functions into fewer components. The torsion spring both drives piston ejection and powers needle retraction. The lever serves as both a force amplifier and a mechanical linkage. This consolidation reduces part count and metal usage while maintaining reliability through carefully designed geometric relationships and material properties.
Solution Approach 2:
The device is designed to be self-actuating through the torsion spring's stored energy, eliminating the need for additional power sources or complex control systems. The mechanism automatically completes both ejection and retraction phases, ensuring functional safety without adding complexity that would increase manufacturing cost.
3Ease of manufacture
If the needle retraction mechanism is simplified, then the device becomes easier to manufacture, but complete retraction and prevention of needle injury cannot be guaranteed
Solution Approach 1:
The torsion spring is pre-loaded with sufficient energy before use to guarantee both complete piston ejection and full needle retraction. This preliminary energy storage ensures that the simplified retraction mechanism has more than enough force to reliably retract the needle completely, eliminating injury risk without requiring complex additional 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
The design provides a cost-effective, user-friendly, and safe self-injector with fewer metal parts, ensuring easy handling and preventing needle injuries by fully retracting the needle into the housing.
Implementation Method 1
a pivotable spring leg of a prestressed torsion spring with a plurality of coils
Implementation Method 2
a swivel lever articulated to the same, and the other end of the pivot lever is articulated to a pivotable spring leg of a prestressed torsion spring
Data Source
AI summary
The auto-injector contains a torsion spring with stored energy for administration of a liquid active substance. It has a housing with a holder for securing an insertable syringe with barrel, sealing plug and needle, the active substance of which it can discharge hydraulically when triggered to do so. The piston in the barrel can be actuated by a pivot lever articulated on a piston slide guided along a rail in the housing. The other end of the pivot lever is articulated on a pivotable leg of a biased torsion spring. By means of the triggered pivoting movement of the biased spring leg, the piston can slide into the syringe in a pivoting phase with a piston slide, and a barb on the piston slide can latch onto the syringe. In a subsequent pivoting movement, the syringe can be retracted into the housing, such that the needle disappears in the housing.