Drug Delivery Screw Thread Tilting Nut Last Dose Stop
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Solution Overview
Problem
Current drug delivery devices lack a reliable mechanism to prevent under-dosing by ensuring that the user cannot set a dose higher than the remaining amount of drug in the cartridge, which compromises safety and accuracy.
Innovation Solution
The assembly includes a screw member with a thread featuring two consecutive portions with different leads and a nut member that performs a tilting movement to accommodate these changes, preventing further rotation once the remaining drug amount is reached, thereby ensuring the last dose stop mechanism engages and limits the set dose to the available amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single lead thread is used in the dosing mechanism, then the structure is simple and easy to manufacture, but the device cannot reliably prevent under-dosing when the cartridge is empty
Solution Approach 1:
The thread is segmented into two consecutive portions with different leads (first lead and second lead). The first portion has a first lead and the second portion has a second lead that is different from the first lead. This segmentation allows the nut member to perform a tilting movement that enables reliable detection of the last dose position, thereby preventing under-dosing while maintaining a relatively simple overall structure.
Solution Approach 2:
Different portions of the thread have different local qualities (different leads). The first portion of the thread has a first lead optimized for normal dosing operation, while the second portion has a second lead optimized for detecting the last dose position. This local differentiation enables the mechanism to perform both normal dosing and last dose detection functions reliably.
2Adaptability or versatility
If the nut member maintains a fixed orientation relative to the screw member, then the mechanical cooperation is simple, but the nut member cannot accommodate the different leads of consecutive thread portions
Solution Approach 1:
The nut member is designed to perform a tilting movement relative to the screw member during rotation. This dynamic adjustment allows the nut member to accommodate the different leads of the consecutive thread portions. The tilting movement enables the interface feature of the nut member to properly engage with both the first and second portions of the thread having different leads.
3Reliability
If the thread has a constant lead throughout, then the dosing mechanism is simple to operate, but it cannot provide the tilting movement necessary for last dose detection
Solution Approach 1:
The thread is divided into two consecutive portions with different leads. The first portion extends over a first axial length and the second portion extends over a second axial length. This segmentation creates the necessary geometric variation to induce tilting movement in the nut member, enabling accurate last dose detection while maintaining ease of operation through automatic mechanical action.
4Adaptability or versatility
If the nut member rotates strictly about the rotational axis without tilting, then the mechanical interface is simple, but the interface feature cannot engage with thread portions having different leads
Solution Approach 1:
The rotation of the nut member is made dynamic by introducing a tilting movement component. During rotation about the rotational axis, the nut member simultaneously performs a tilting movement that allows its interface feature to engage with thread portions having different leads. This dynamic dual-motion mechanism enables universal compatibility with both first and second portions of the thread.
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 configuration enhances the safety and reliability of the drug delivery device by preventing under-dosing and ensuring that the user knows the exact amount of drug to be delivered, thereby maintaining device safety and accuracy.
Implementation Method 1
The screw member and the nut member are adapted and arranged to be rotated with respect to one another about a rotational axis during a dose setting operation of the assembly. During the relative rotation, the nut member is axially displaced along the screw member from a start position to an end position with respect to the screw member due to mechanical cooperation of the nut member with the thread.
Data Source
Figure 1~2
Figure 3~5
Figure 6a~7d
AI summary
An assembly for a drug delivery device (1) is provided comprising a screw member (23) comprising a thread (33), the thread (33) comprising at least two consecutive portions, the portions having different leads. The device (1) further comprises a nut member(22), wherein the nut member (22) and the screw member (23) are adapted and arranged to be rotated with respect to one another about a rotational axis (34) during a dose setting operation of the assembly, the nut member (22) thereby being axially displaced along the screw member (23) from a start position to an end position with respect to the screw member (23) due to mechanical cooperation of the nut member (22) with the thread (33).The assembly is configured such that, in a first portion (23a) of the thread (33), the nut member (22) comprises a first position with respect to an axis (43) transversal to the rotational axis (34) and in a second portion (23b) of the thread (33), the nut member (22) comprises a second position with respect to the axis (43) transversal to the rotational axis (34), wherein the nut member (22) is configured to perform a tilting movement from the first position into the second position when the nut member (22) passes from the first portion (23a) to the second portion (23b).Furthermore, a drug delivery device (1) comprising the assembly is described.