Handheld Injection Device Last Dose Mechanism
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Solution Overview
Problem
Existing drug delivery devices lack accuracy and compactness in their last dose mechanisms, often requiring user force transmission through elastic components that can affect precision and requiring components to translate out of the housing during dose setting.
Innovation Solution
A handheld injection device with a housing, piston rod, driver, dose setting means, and power reservoir, featuring a last dose protection mechanism with a nut interposed between the dial grip and housing, and an epicyclic gearbox for precise dose display and compact design, reducing the need for components to translate during dose setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a last dose protection mechanism with a nut is used, then accuracy of the last dose mechanism is improved, but device complexity increases
Solution Approach 1:
The last dose nut is nested within the existing driver structure, utilizing the driver's rotational movement to advance the nut along a helical path. This nesting approach allows the additional last dose protection functionality to be integrated without adding separate external components, thereby improving accuracy while minimizing the increase in device complexity.
Solution Approach 2:
The driver serves multiple functions: it acts as both the dose setting mechanism and the drive for the last dose protection nut. By making the driver multi-functional, the patent avoids adding dedicated separate mechanisms, thus improving last dose accuracy while keeping the overall device complexity manageable through component reuse.
2Ease of operation
If components are made to translate out of the housing during dose setting, then ease of operation is improved, but device compactness deteriorates
Solution Approach 1:
The patent utilizes the rotational dimension of the driver to achieve axial translation of the piston rod through the helical thread engagement. This allows dose setting to occur within the existing housing volume by converting rotational motion to linear motion in a compact manner, maintaining device compactness while preserving ease of operation.
Solution Approach 2:
The driver is designed to be rotationally movable relative to the housing during dose setting, allowing dynamic adjustment of the piston rod position. This dynamic capability enables the dose setting mechanism to operate within the housing without requiring permanent external translations, thus maintaining compactness while providing operational flexibility.
3Ease of operation
If user force is transmitted through elastic components, then ease of operation is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent replaces elastic components with a direct mechanical thread engagement system between the driver and the piston rod. This substitution eliminates the elasticity-related precision losses while maintaining ease of operation through the rotational-to-linear conversion mechanism, achieving both operational ease and manufacturing precision.
Solution Approach 2:
The force transmission path is segmented into distinct mechanical stages: user input rotates the driver, which through helical threads converts this rotation to linear piston rod movement. This segmentation allows each stage to be optimized independently, ensuring precise force transmission without relying on elastic components that would introduce variability.
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 solution provides a highly accurate and compact drug delivery device with improved last dose mechanism accuracy, reducing user force requirements and eliminating the need for components to extend during dose setting, enhancing handling and usability.
Implementation Method 1
a power reservoir (100) which drives the driver (80, 90) during dose dispensing
Implementation Method 2
the dial grip (40) comprises a threaded section (42) having an end stop
Implementation Method 3
an epicyclic gearbox for precise dose display and compact design
Data Source
Figure 1~3
Figure 4a~6
Figure 7a~8c
AI summary
The invention refers to a handheld injection device comprising a housing (10, 20, 30), a piston rod (60), defining a first longitudinal axis (I) and located within the housing (10), a driver (70, 80, 90) coupled to the piston rod (60), a dose setting means (40), which is rotatable during dose setting, a power reservoir (100) for driving the driver (70, 80, 90), and a number wheel (130) for displaying a dose set by the dose setting means (40).