Dose Limit Nut Mechanism for Pen Injector Overdose Prevention
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Solution Overview
Problem
Existing injection devices lack effective mechanisms to prevent users from setting doses larger than the remaining medicament volume, which is crucial for ensuring accurate and complete dosing, especially in reusable pen-injector devices.
Innovation Solution
The introduction of a dose limit nut with endstop features that engage with the plunger element's thread to limit axial travel, preventing the setting of doses greater than the available medicament volume, thereby providing both last dose protection and maximum/minimum dose limiting with a single component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a dose selector is provided to allow users to set any desired dose, then ease of operation is improved, but the risk of setting doses larger than remaining medicament volume increases
Solution Approach 1:
The dose limit nut is pre-configured with endstop features that engage with the plunger element's thread at predetermined positions corresponding to maximum and minimum doses, and with the worm gear to prevent last dose setting. This preliminary configuration prevents users from setting doses beyond available medicament volume while still allowing free selection within the safe range.
Solution Approach 2:
The dose limit nut acts as an intermediary component between the dose selector and the plunger element. It translates rotational movement of the dose selector into axial movement along the plunger element's thread, while simultaneously providing mechanical endstops that mediate and limit the range of motion to prevent overdosing.
2Reliability
If multiple separate components are used for last dose protection and maximum/minimum dose limiting, then reliability is improved, but device complexity increases
Solution Approach 1:
The dose limit nut combines multiple functions into a single component: it provides last dose protection by engaging with the worm gear, and simultaneously provides maximum and minimum dose limiting by engaging with the plunger element's thread at predetermined positions. This merging reduces the number of separate components while maintaining comprehensive dose control functionality.
Solution Approach 2:
The dose limit nut is designed as a multi-functional component that performs three distinct dose control functions: preventing last dose setting through engagement with the worm gear, limiting maximum dose through engagement with the plunger element's thread, and limiting minimum dose through engagement with the plunger element's thread at a different position.
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 solution effectively prevents over-dosing by limiting the user's ability to set doses beyond the available medicament, ensuring accurate dosing and simplifying the device's design by reducing the number of components required.
Implementation Method 1
said plunger element is threaded so that the dose limit nut is engaged with said plunger element via said thread, in order to guide relative axial movement between the dose limit nut and the plunger element
Data Source
Figure 1
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Figure 4
AI summary
An injection device comprises a dose selector, rotatable by a user to set a dose to be ejected from the injection device and a drive assembly including a drive shaft (140) and a plunger element (145), the drive assembly being capable of providing an axial force for ejecting a dose of medicament from a medicament container. A dose limit nut (141) is provided which is rotationally coupled to but not axially coupled to said drive shaft. The plunger element is threaded so that the dose limit nut is engaged with said plunger element via said thread, in order to guide relative axial movement between the dose limit nut and the plunger element. The dose limit nut is provided with dose limiting endstops which are capable of limiting axial travel of said dose limit nut with respect to said plunger element, so as to limit maximum and minimum doses of medicament which can be set by the user. In addition, the dose limit nut comprises a last dose rotary endstop feature which prevents further rotation of said dose limit nut with respect to said drive shaft so as to prevent the user setting a dose that is greater than an injectable volume of medicament remaining in said medicament container.