Auto-Injector Torsion Spring Cam Mechanism for Safe Needle Retraction
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Solution Overview
Problem
Current auto-injectors face challenges such as user error leading to incomplete doses, high injection forces, and discomfort due to manual operation, and issues with needle retraction and syringe emptying, particularly with conventional spring mechanisms that can cause needlestick injuries or incomplete medication delivery.
Innovation Solution
An auto-injector design utilizing a torsion spring mechanism with a gear system and viscous damper to smoothly insert and retract a needle, ensuring complete dose delivery and safe retraction, featuring a variable lead screw pitch for controlled force application and a finger guard for enhanced safety and portability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional compression spring mechanism is used to deliver the injection, then the injection force can be generated, but the needle retraction becomes unreliable and may cause needlestick injuries
Solution Approach 1:
The patent replaces the conventional compression spring mechanism with a torsion spring-based cam mechanism. The torsion spring stores rotational energy that is converted to linear motion through a cam profile, providing more reliable and controlled force delivery for both injection and needle retraction. This mechanical substitution resolves the unreliability of needle retraction while maintaining adequate injection force.
Solution Approach 2:
The patent employs a cam mechanism with a specifically designed profile that dynamically adjusts the force application throughout the injection cycle. The cam profile ensures that the torsion spring's rotational motion is converted into the precise linear motion needed for needle insertion, medication delivery, and needle retraction. This dynamic control mechanism ensures reliable needle retraction while providing the necessary injection force.
2Reliability
If a torsion spring mechanism with cam profile is used, then reliable needle retraction and complete dose delivery are achieved, but the device complexity increases
Solution Approach 1:
The patent integrates multiple functions into a unified torsion spring-cam mechanism. The same mechanism that drives needle insertion also controls the plunger movement for medication delivery and finally retracts the needle. By merging these functions into a single coordinated mechanism, the patent achieves reliable operation while limiting the increase in complexity to what is necessary for the integrated system.
Solution Approach 2:
The torsion spring-based cam mechanism serves multiple functions: it drives the needle forward for insertion, operates the plunger to deliver the complete medication dose, and automatically retracts the needle to a safe position. This multi-functionality reduces the need for separate mechanisms for each operation, thereby achieving high reliability without excessive complexity.
3Device complexity
If manual button operation is used to control injection, then the device structure can be simpler, but user error leads to incomplete doses and high injection forces cause discomfort
Solution Approach 1:
The patent implements an automatic trigger mechanism that eliminates the need for manual button pressing during the injection process. Once activated, the torsion spring-based mechanism automatically controls needle insertion, medication delivery, and needle retraction without requiring continuous user input. This self-service approach prevents user errors that lead to incomplete doses while the automated force control reduces discomfort from excessive injection 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
The auto-injector provides a smooth and controlled injection process, ensuring complete medication delivery and safe needle retraction, reducing user error and discomfort, while being more portable and user-friendly.
Implementation Method 1
spring means capable of, upon activation: pushing the needle from a covered position inside the outer casing into an advanced position through the orifice and past the proximal end
Implementation Method 2
utilizing a torsion spring mechanism with a gear system and viscous damper to smoothly insert and retract a needle
Implementation Method 3
featuring a variable lead screw pitch for controlled force application
Data Source
Figure 1A~1B
Figure 2~3
Figure 4A~4E
AI summary
The invention relates to an auto-injector (1) for administering a dose of a liquid medicament (M), comprising: - an elongate outer casing (2) arranged to contain a syringe (3) with a hollow needle (4) and a stopper (25) for sealing the syringe (3) and displacing the medicament (M), the outer casing (2) having a distal end (D) and a proximal end (P) with an orifice (6) intended to be applied against an injection site, wherein the syringe (3) is slidably arranged with respect to the outer casing (2), - spring means (11) capable of, upon activation: - pushing the needle (4) past the proximal end (P), - operating the syringe (3) to supply the dose of medicament (M), and - retracting the syringe (3) with the needle (4) - activating means (10) arranged to lock the spring means (11) in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring means (11) for injection, wherein the spring means (11) is a torsion spring (11) grounded at one end (11.1) in the outer casing (2) and at the other end in a first gear member (13) rotatable about a longitudinal axis, wherein the first gear member (13), upon rotation, is arranged for translatively moving a second gear member (16) toward the proximal end (P), the second gear member (16) prevented from rotating and coupled to the stopper (25) in order to push it towards the proximal end (P), wherein the first gear member (13) is engaged with the activating means (10) prior to manual operation in a manner to prevent rotation and disengaged from the activating means (10) upon manual operation.