Injection Device Dose Indicator Axial Engagement Mechanism
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Solution Overview
Problem
Existing injection devices face challenges in accurately displaying the set dose of medicament due to the central location of dose indicators, which can be obscured by the user's fingers, and existing solutions like odometers may not fully prevent unintentional rotation of the tens wheel.
Innovation Solution
The injection device incorporates a units wheel and tens wheel mechanism with a biasing means, where the tens wheel is normally engaged with the housing to prevent rotation, and the units wheel temporarily disengages it to allow incremental rotation, ensuring accurate dose indication and reducing the risk of unintentional movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a number sleeve is used as a dose indicator, then the dose can be clearly displayed, but the indicator takes up a large central area that is obscured by the user's fingers when gripping the device
Solution Approach 1:
The patent transitions from a planar number sleeve display to a three-dimensional odometer mechanism with multiple rotating wheels. The units wheel and tens wheel are arranged axially along the longitudinal axis of the device, utilizing the third dimension (axial direction) to accommodate the dose indicator. This allows the indicator to be positioned in a compact form factor that does not occupy excessive lateral space, reducing interference with user grip while maintaining clear dose visibility through a window in the housing.
2Ease of operation
If the tens wheel is freely rotatable to allow dose adjustment, then the dose can be easily changed, but the wheel may rotate unintentionally causing inaccurate dose indication
Solution Approach 1:
The patent implements a dynamic engagement system where the tens wheel alternates between locked and unlocked states. During normal operation, the tens wheel is engaged with the tens wheel engagement feature on the housing, preventing unintentional rotation and ensuring dose indication accuracy. When the units wheel completes a full rotation (indicating a dose increment of 10), it automatically disengages the tens wheel from the housing feature, allowing the tens wheel to rotate one increment. This dynamic mechanism ensures that the tens wheel is only rotatable when intentionally triggered by the units wheel rotation, eliminating accidental changes while maintaining ease of dose adjustment.
3Ease of operation
If the units wheel is always engaged with the tens wheel, then rotation of the units wheel always rotates the tens wheel, but this prevents the tens wheel from being selectively engaged only when needed
Solution Approach 1:
The patent introduces an intermediary axial movement mechanism between the units wheel and tens wheel. Instead of direct rotational coupling, the units wheel engages with the tens wheel through axial displacement. When the units wheel rotates, it first moves axially forward to disengage the tens wheel from the housing feature. Only after this axial disengagement occurs can the tens wheel rotate independently. This intermediary axial movement acts as a mediator that controls the engagement state, ensuring the tens wheel is selectively engaged only when the units wheel completes a full rotation and triggers the axial disengagement sequence.
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
This design improves the accuracy of the dose indicator by preventing unintentional rotation of the tens wheel and maintaining visibility when the device is handled, ensuring precise medicament delivery.
Implementation Method 1
a torsion spring for assisting injection of a dose of medicament from the injection device
Data Source
AI summary
An injection device comprises a housing (12) having a longitudinal axis. The injection device further comprises a dose selector (16) capable of setting a dose to be ejected from the injection device and a dose indicator comprising a units wheel (18) operatively connectable to the dose selector so that rotation of the dose selector about the longitudinal axis also rotates the units wheel, and a tens wheel (19) selectively engageable with the units wheel so that rotation of the units wheel also rotates the tens wheel. A biasing means biases the dose indicator axially-rearwardly in the housing. An internal surface of the housing is provided with a tens housing feature selectively engageable with the tens wheel to prevent rotation thereof. An internal surface of the housing is provided with a units housing feature capable of moving the units wheel axially-forward against said biasing means such that the units wheel engages and moves the tens wheel axially-forward and free of said tens housing feature so as to allow rotation thereof.