Plunger Rod Shock Absorber for Syringe Stopper Impact

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Solution Overview

Problem

The initial contact between a plunger and a stopper in an injection device during an injection event causes shock, leading to syringe breakage, component deformation, and user discomfort, particularly in under-filled syringes.

Innovation Solution

Incorporating a retractable tip shock absorber on the plunger rod that deflects and absorbs the impact force upon contact with the stopper, utilizing a collapsible design with teeth engaging deflectable arms to reduce the impact force.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a plunger is designed to accelerate to high velocity before contacting the stopper, then injection speed and productivity are improved, but shock and impact force increase causing syringe breakage and user discomfort

Engineering Contradiction:

Improveinjection speedVSAvoidshock and impact force

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies beforehand cushioning by incorporating a shock absorber mechanism that is pre-positioned between the plunger and stopper. This mechanism includes a plunger tip with a shock absorber that can deflect or compress upon impact, creating a cushioning effect before the full force of the plunger reaches the stopper. The shock absorber is designed to engage only when needed, allowing high-speed injection while protecting against impact damage.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Object-affected harmful factors

If an initial gap is maintained between the plunger and stopper, then shock absorption is improved, but injection precision and dosing accuracy deteriorate

Engineering Contradiction:

Improveshock reductionVSAvoiddosing accuracy

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The patent introduces an intermediary shock absorber mechanism that fills the functional gap between the plunger and stopper. This intermediary component allows the plunger to maintain close proximity to the stopper for precise dosing while the shock absorber mechanism absorbs impact forces. The shock absorber acts as a mediator that decouples the positioning function (requiring minimal gap) from the shock absorption function (requiring sufficient clearance).

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If a shock absorber mechanism is added to reduce impact force, then user comfort and device reliability are improved, but device complexity increases

Engineering Contradiction:

Improvedevice reliabilityVSAvoidshock absorber mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies the nested doll principle by integrating the shock absorber mechanism within the existing plunger structure. The shock absorber is positioned inside or along the plunger rod, utilizing the existing cylindrical space and structural elements. This nested arrangement allows the shock absorption function to be added without significantly increasing external dimensions or overall device complexity, as the new component fits within the existing form factor.

Inventive Principle:

Principle #7Nested doll (Nesting)

4Device complexity

If the plunger is designed to contact the stopper directly, then device simplicity is maintained, but component deformation and syringe breakage occur

Engineering Contradiction:

Improvedevice simplicityVSAvoidcomponent integrity

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The patent employs flexible elements in the shock absorber mechanism, such as flexible walls or compressible materials, that can deform elastically to absorb impact energy. These flexible components are designed to flex or compress during the shock event, protecting the rigid plunger and stopper from direct impact forces while maintaining overall structural integrity. The flexible elements return to their original shape after the impact, providing reusable protection.

Inventive Principle:

Principle #30Flexible shells and thin films

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 shock absorber effectively reduces the impact force, minimizing syringe breakage and user discomfort while ensuring consistent dose delivery.

Implementation Method 1

The one or more teeth deflect the deflectable arm during retraction of the plunger rod tip, thereby absorbing a shock

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

The retractable tip may comprise compressible protrusions that are arranged to be compressed as the retractable tip collapses into the plunger rod body

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentEP3781238B1Shock absorber for injection devices

Publication Date: 2025.11.26 SANOFI SA(FR)

Figure 1~2a
Figure 2b~2c
Figure 3a~3b

AI summary

The present application relates to shock absorbers for injection devices. According to a first aspect, this specification discloses an injection device comprising: a medicament container; a stopper translatably disposed within the medicament container; and a plunger rod comprising: a plunger rod body; and a shock absorber, wherein the plunger rod is operable to displace the stopper; and wherein the shock absorber contacts the stopper during displacement of the stopper by the plunger rod, thereby reducing an impact force between the plunger rod and the stopper.