Resettable Drug Delivery Drive Mechanism with Interlocking Piston Rod
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing drug delivery devices lack a reliable and efficient mechanism for setting and dispensing doses, particularly in terms of preventing proximal movement of the piston rod during dose setting and ensuring accurate dose delivery.
Innovation Solution
A drive assembly with a piston rod featuring axially spaced ratchet pockets and protrusions, allowing for precise rotational movement and axial displacement, coupled with a resettable mechanism using a spring for resilient bias, to securely lock and unlock interlocks for dose setting and dispensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional drive mechanism is used in drug delivery devices, then the structure is simple, but the reliability of dose setting and dispensing is insufficient
Solution Approach 1:
The piston rod is segmented into multiple functional zones with distinct features: distal ratchet pockets for drive member engagement, proximal ratchet pockets for stop member engagement, and intermediate features for interlock mechanisms. This segmentation allows each segment to perform a specific function reliably while the overall system remains manageable in complexity
Solution Approach 2:
The patent introduces intermediary elements such as pawl elements that mediate between the drive member and piston rod, and interlock mechanisms that mediate between the piston rod and stop member. These intermediaries enhance reliability by providing controlled engagement and disengagement points without requiring complete redesign of the entire drive system
2Stability of the object's composition
If the piston rod is designed with multiple ratchet pockets and interlock mechanisms, then the stability during dose setting is improved, but the number of resilient parts increases
Solution Approach 1:
The patent merges multiple functions into the piston rod structure itself: the ratchet pockets are formed directly on the piston rod body, the interlock features are integrated into the piston rod geometry, and the drive and stop mechanisms share common structural elements. This merging reduces the need for separate resilient parts while maintaining stability
Solution Approach 2:
The piston rod features self-locking ratchet pockets that automatically engage with pawl elements through their tapered geometry, and self-regulating interlock mechanisms that engage and disengage based on axial position. These self-service features reduce the need for additional resilient parts to maintain stability during dose setting
3Measurement precision
If a ratchet pocket system is used to prevent proximal movement, then the accuracy of dose delivery is improved, but the complexity of the locking mechanism increases
Solution Approach 1:
Different regions of the piston rod have locally optimized features: distal ratchet pockets with specific taper angles for precise drive member engagement, proximal ratchet pockets for stop member interaction, and localized interlock features at specific axial positions. This local quality approach ensures accurate dose delivery at each critical point without requiring the entire mechanism to be complex
Solution Approach 2:
The ratchet pockets are designed with asymmetric tapered geometries where the engagement face has a specific inclination that allows easy engagement in the distal direction but prevents proximal movement. This asymmetric design provides accurate dose delivery through controlled unidirectional locking without requiring complex bilateral locking mechanisms
4Reliability
If the piston rod features are made more complex to ensure secure locking, then the reliability is improved, but the ease of manufacture decreases
Solution Approach 1:
The ratchet pockets and interlock features are designed with specific geometric parameters (taper angles, axial spacing, radial dimensions) that can be directly controlled through standard CNC machining or injection molding processes. By optimizing these parameters within manufacturable ranges, the patent achieves reliable locking without requiring complex multi-step manufacturing procedures
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 reliable mechanism for setting and dispensing doses with enhanced accuracy and stability, ensuring the piston rod is securely locked during dose setting and accurately dispensed, while minimizing the number of resilient parts.
Implementation Method 1
a spring, in particular a compression spring, which is used for storing energy for driving a rotation of a piston rod in a second rotational direction with respect to the housing by interacting with the piston rod for biasing the piston rod in the second rotational direction during setting of the dose
Data Source
AI summary
According to one aspect, a resettable drive assembly for a drug delivery device is provided for. The resettable drive assembly may comprise a housing having a proximal end and a distal end, a piston rod being rotatable with respect to the housing and being axially displaceable with respect to the housing between a proximal start position and a distal end position, a drive member for distally displacing the piston rod towards the end position when dispensing a dose, and a stop member. The drive assembly may be configured such that the drive member is operable to interact with the piston rod for forming an unlockable first interlock, the first interlock being operable to block proximal movement of the piston rod with respect to the drive member. The drive assembly may be configured such that the stop member is operable to interact with the piston rod for forming an unlockable second interlock, the second interlock being operable to block proximal movement of the piston rod with respect to the housing. The drive assembly may be configured such that, when the drive assembly is in a drive mode, the first and second interlocks are locked such that proximal movement of the piston rod from the end position to the start position is prevented by the first interlock and the second interlock. The drive assembly may be configured such that, for switching the drive assembly from the drive mode to a reset mode, the piston rod is rotatable with respect to the drive member for unlocking the first interlock and the stop member and the piston rod are rotatable with respect to each other for unlocking the second interlock. The drive assembly may be configured such that, when the drive assembly is in the reset mode, the first interlock and the second interlock are unlocked such that proximal movement of the piston rod to the start position is allowed. Further, a drug delivery device and a use of a spring are provided for.