Variable Pitch Dose Setting Mechanism for Drug Delivery
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Solution Overview
Problem
Pen type drug delivery devices face challenges in preventing users from setting doses greater than the remaining medication in the cartridge, particularly under high torque loads, which can lead to thread damage and inaccurate dosing.
Innovation Solution
A dose setting mechanism featuring a rotatable shaft with a helical groove having different pitches along its length, where a nut member with radial stop faces prevents further rotation when attempting to set a dose exceeding the remaining medication, enhancing the system's strength and preventing over-dosing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a uniform pitch thread is used in the dose setting mechanism, then the structure is simple and manufacturing is easy, but the end surface area is limited and thread damage risk increases under high torque loads
Solution Approach 1:
The patent applies local quality by varying the pitch of the thread along its length. The thread has a first pitch for the majority of its length and a second, different pitch at the end portion. This allows the end portion to have optimized characteristics (larger end surface area) without changing the entire thread structure, thus improving strength under high torque loads while maintaining overall structural simplicity.
2Strength
If a larger pitch is used at the end of the thread to increase end surface area, then the thread can withstand higher torque loads, but the risk of thread damage increases under high stop torque loads
Solution Approach 1:
The patent changes the pitch parameter of the thread at different locations. By having a first pitch for most of the thread length and a second pitch at the end portion, the design optimizes both strength and reliability. The different pitch at the end provides larger end surface area for withstanding torque while the overall thread structure maintains reliability through the carefully designed pitch transition.
3Strength
If the thread end surface area is increased to prevent thread damage, then the device can withstand high torque loads, but the dose setting mechanism becomes more complex
Solution Approach 1:
The patent applies local quality by varying the pitch of the thread along its length. The thread has a first pitch for the majority of its length and a second, different pitch at the end portion. This allows the end portion to have optimized characteristics (larger end surface area) without changing the entire thread structure, thus improving strength under high torque loads while maintaining overall structural simplicity.
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 mechanism effectively limits the maximum dose that can be set, ensuring accurate dosing and reducing the risk of thread damage from high torque loads, thereby enhancing the reliability and safety of drug delivery devices.
Implementation Method 1
a rotatable shaft (30) with a helical groove (32) having a first pitch (P1) along a first portion (34) of the rotatable shaft (30) and a second pitch (P2) along a second portion (36) of the rotatable shaft (30)
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a dose setting mechanism (4), which is operable to be coupled to a medication cartridge (25) and which comprises means that prevent the user from setting a dose greater than the remaining medication in the cartridge (25). The dose setting mechanism comprises a shaft (30). A helical groove (32) having a first pitch is provided along a first portion (32) of the shaft (30). The dose setting mechanism (4) further comprises a nut member (40) disposed on the helical groove (32) of said shaft (30). During dose setting, the shaft (30) is rotated relative to the nut member (40) while the nut member (40) traverses along the groove (32) from a distal end (38) of the shaft (30) towards a proximal end (39) of the shaft (30). The mechanism further comprises means preventing a user of said dose setting mechanism (4) from setting a dose of said medication that is greater than said remaining medication in said cartridge (25), said means comprising a second pitch provided along a second portion (36) of said shaft (30), wherein said first pitch is different from said second pitch, wherein said second pitch is preferably greater than said first pitch.