Torsion Spring Injector Mechanism for Fixed-Dose Release Control

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Solution Overview

Problem

Existing multi-use fixed dose injection devices require users to manually strain a torsion spring before each injection, leading to a complex construction with numerous parts and a cumbersome dosing process.

Innovation Solution

A torsion spring driven injection device with a simplified construction, utilizing a rotatable drive structure, nut element, and ratchet interface to automatically store and release torque, allowing for predetermined and equally sized dose volumes without manual straining.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a cartridge-based system with replaceable cartridges is used, then dosing flexibility and patient compliance are improved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improvedosing flexibilityVSAvoiddevice complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The device is divided into a reusable injector body and a disposable cartridge containing the medicament reservoir and plunger. This segmentation allows the flexible dosing functionality to be contained in the disposable cartridge, while the expensive reusable body maintains a simple, robust design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The cartridge is designed as a disposable component that is discarded after a single use or after a limited number of doses. This eliminates the need for complex cleaning, sterilization, and maintenance systems in the reusable body, reducing overall device complexity while maintaining dosing flexibility through cartridge replacement.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Force

If a torsion spring mechanism is used, then activation force and patient comfort are improved, but device complexity increases

Engineering Contradiction:

Improveactivation forceVSAvoiddevice complexity

Core Design Contradiction:

ForceVSDevice complexity

Solution Approach 1:

The torsion spring is integrated directly into the cartridge assembly, combining the actuation mechanism with the medicament delivery system. This eliminates the need for separate complex actuation mechanisms in the reusable body, reducing overall device complexity while providing smooth, controlled activation force.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The torsion spring is pre-loaded during cartridge manufacturing and requires no external power source or complex control systems. The spring automatically provides the necessary activation force when the cartridge is inserted and activated, simplifying the overall device design while ensuring consistent, comfortable administration.

Inventive Principle:

Principle #25Self-service

3Reliability

If robust sealing mechanisms are used, then sterility maintenance and infection prevention are improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvesterility maintenanceVSAvoidmanufacturing precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The cartridge with its sealing mechanisms is designed as a disposable component manufactured under controlled sterile conditions. Each cartridge is pre-sterilized and sealed, eliminating the need for complex sterilization systems in the reusable body. The single-use nature ensures sterility maintenance without requiring extremely tight manufacturing tolerances for the disposable components.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

Multiple sealing elements are pre-installed in the cartridge during manufacturing, including seals at the needle hub interface, reservoir closure, and plunger rod interface. These pre-installed seals ensure sterility is maintained throughout storage and use without requiring complex real-time sealing mechanisms, balancing reliability with manufacturability.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 simplifies the dosing process by automating the torsion spring straining, reducing the number of parts, and ensuring consistent dose volumes with a more user-friendly operation.

Implementation Method 1

The cartridge (220) may be actuated by a torsion spring (204). The torsion spring (204) may be disposed within the cartridge (220) and/or within the injector (200).

Methodology Applied

Scientific EffectTorsion spring: Torsion Spring

Data Source

PatentEP4277678B1A torsion spring driven fixed dose injection device

Publication Date: 2026.05.20 NOVO NORDISK AS

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Figure 2A~2B
Figure 3A~4

AI summary

The invention relates to a medical injection device for dispensing substantially equally sized dose volumes of a liquid drug. The injection is driven by a torsion spring which is strained prior to each dose release by rotation of a connector element connecting the torsion spring to the rotational drive structure. The dose release is controlled by an axial movement of the rotational drive structure which can only be moved axially when the connector element has been rotated to a specific rotational position.