Dual Back-to-Back Force Spring Assembly for Symmetrical Plunger Loading
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Solution Overview
Problem
Medicament delivery devices using coiled strip springs face issues with non-symmetrical load on plunger rods, leading to potential breakage or jamming, and existing solutions do not efficiently manage different force levels during operations like penetration and injection.
Innovation Solution
A medicament delivery device featuring a dual back-to-back force spring assembly providing symmetrical load on the plunger rod, combined with a locking and release mechanism involving a rotator member and tubular actuation, ensures balanced force distribution and controlled actuation for safe and efficient dose delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a single coiled strip spring is used to drive the plunger rod, then the spring can provide sufficient force for dose delivery, but the load on the plunger rod becomes non-symmetrical causing bending forces that may lead to breakage or deflection
Solution Approach 1:
The single spring is divided into two separate coiled strip springs arranged back-to-back. Each spring is mounted in its own seat and acts on opposite sides of the plunger rod, providing symmetrical force distribution that eliminates bending moments while maintaining sufficient drive force.
Solution Approach 2:
The springs are arranged in a symmetrical configuration (back-to-back) rather than a single asymmetric position. This symmetrical arrangement ensures that the plunger rod experiences equal and opposite forces that cancel out bending components, leaving only axial compression forces.
2Force
If a compressed helical spring is used to provide large force, then the break loose force can be overcome, but the full extension force may cause breakage of the glass medicament container
Solution Approach 1:
The spring system is designed to provide dynamically adjusted force characteristics. The pre-tensioned coiled strip springs deliver high initial force to overcome break loose resistance, then progressively reduce force as the plunger rod moves, preventing excessive force at full extension that could break the container.
Solution Approach 2:
The force parameters are changed throughout the stroke by using pre-tensioned coiled strip springs that naturally provide high initial force that decreases as they unwind. This parameter change allows overcoming break loose force while avoiding container breakage at full extension.
3Force
If constant force springs are used to provide almost constant force throughout deflection, then dose delivery can be completed with controlled force, but the load on the plunger rod remains non-symmetrical causing bending forces
Solution Approach 1:
The single constant force spring is segmented into two identical constant force springs arranged back-to-back. Each spring provides constant force from its own seat, and together they create symmetrical loading on the plunger rod, eliminating bending forces while maintaining the constant force characteristic throughout the stroke.
4Reliability
If multiple components are used to achieve symmetrical load and controlled force levels, then plunger rod reliability improves, but device complexity increases
Solution Approach 1:
Multiple functions are merged into the spring assembly structure. The two coiled strip springs not only provide symmetrical force distribution but also inherently control force levels throughout the stroke. The seats and mounting structure are integrated to provide both mechanical support and force distribution, reducing the need for additional separate components.
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 device achieves symmetrical loading on the plunger rod, preventing breakage and jamming, while allowing for controlled force levels during medicament delivery, enhancing safety and operational reliability with fewer components.
Implementation Method 1
a dual back-to-back force spring assembly operatively connected to said plunger rod such as to provide a symmetrical load on said plunger rod; wherein said drive unit comprises an elongated plunger rod and a dual back-to-back force spring assembly
Implementation Method 2
a locking and release mechanism operatively connected to said drive unit and capable of releasing said drive unit upon activation
Data Source
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AI summary
The present invention relates to a medicament delivery device comprising a housing, which housing is arranged to accommodate a medicament container; a drive unit arranged in said housing and capable of acting on a movable stopper positioned inside said medicament container for expelling a dose of medicament, wherein said drive unit comprises an elongated plunger rod and a dual back-to-back force spring assembly operatively connected to said plunger rod such as to provide a symmetrical load on said plunger rod; a locking and release mechanism operatively connected to said drive unit and capable of releasing said drive unit upon activation, wherein the locking and release mechanism comprises a hold member operatively connected to the plunger rod, a rotator member operatively connected to the hold member, and a tubular actuation member linearly slidable in relation to the housing and operatively connected to the rotator member; where in the hold member is fixedly attached to the housing and comprises a generally tubular lock tube through which the plunger rod extends and two seats designed as half-cylinders open towards the proximal direction for housing the dual back-to-back force spring assembly, and wherein the lock tube comprises resilient locking and release means configured to interact with both the plunger rod and the rotator member.