Rotational End Stop Dosing Mechanism for Accurate Dose Dispense
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Solution Overview
Problem
Existing pen-type drug delivery devices suffer from inaccuracies in dose delivery due to complex kinematic chains and manufacturing tolerances, which affect the precision and repeatability of dose dispensing.
Innovation Solution
A dosing mechanism with a rotational end stop mechanism that directly engages the piston rod, preventing further rotation at the end of dose dispense, thereby defining the end state of the dosing mechanism with greater accuracy and reliability, bypassing intermediate components to ensure precise dose delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a complex kinematic chain with intermediate components is used to transmit motion from the dose setting unit to the piston rod, then the dosing mechanism can achieve dose selection and dispensing functions, but manufacturing tolerances and component wear accumulate, reducing dose delivery accuracy and precision
Solution Approach 1:
The patent extracts and eliminates the intermediate components (drive sleeve, clutch sleeve, drive gear) from the kinematic chain. The rotational end stop mechanism directly engages the piston rod, bypassing these intermediate elements. This extraction removes the sources of tolerance accumulation and wear, directly improving dose delivery accuracy while preserving the dosing mechanism's core functionality.
Solution Approach 2:
Instead of using a complex multi-stage transmission system to achieve the dosing function, the patent inverts the approach by using a direct engagement mechanism. The rotational end stop on the piston rod directly interfaces with the dose setting unit through simplified elements (drive gear directly to piston rod), reversing the traditional complex transmission architecture to achieve higher precision.
2Ease of operation
If multiple intermediate components are used in the driving mechanism, then the dosing mechanism can provide controlled dose dispensing, but the complexity of the mechanism increases, affecting reliability and repeatability
Solution Approach 1:
The patent removes the clutch sleeve and drive sleeve from the mechanism, eliminating unnecessary intermediate components. The drive gear now directly engages the piston rod, and the rotational end stop provides direct control. This extraction simplifies the mechanism structure while maintaining controlled dose dispensing capability through the rotational end stop's direct engagement.
Solution Approach 2:
The patent segments the dosing mechanism into distinct functional zones: the dose setting unit with its own rotational end stop, the piston rod with its rotational end stop, and the simplified drive gear connection. This segmentation allows each component to perform its function independently with clear boundaries, reducing overall complexity while maintaining controlled operation.
3Measurement precision
If a rotational end stop mechanism directly engaging the piston rod is used, then the end state of the dosing mechanism is defined with greater accuracy, but the mechanism requires precise manufacturing of the engagement components
Solution Approach 1:
The rotational end stop mechanism uses a tooth-and-groove engagement system where the groove width is intentionally made slightly larger than the tooth width. This allows for partial engagement tolerance while ensuring that when the tooth engages the groove, the end state is precisely defined. The excessive groove width compensates for manufacturing variations, achieving high precision without requiring extremely tight tolerances on all components.
Solution Approach 2:
The drive gear acts as an intermediary element between the rotational end stop and the piston rod. While the rotational end stop provides the precise end state definition, the drive gear mediates the force transmission and accommodates minor misalignments, reducing the stringency of manufacturing requirements on the direct engagement components.
Data Source
AI summary
A dosing mechanism for a drug delivery device is provided for selecting and dispensing user-variable doses of a medicament. The mechanism includes a housing, a piston rod, and a drive configured to rotate the piston rod and/or a movement application component directly engaged with the piston rod in a dispense rotational direction relative to the housing. A rotational end-stop mechanism terminates dose dispense and includes a first engagement element rotationally fixed to the piston rod and/or the movement application component, and a second engagement element that is constrained against rotation relative to the housing at the end of dose dispense. To improve dose accuracy, the second engagement element remains out of direct engagement with the first engagement element during dispensing, and only at the end of dose dispense directly engages the first engagement element to provide a rotational stop. A drug delivery device incorporating the dosing mechanism is also disclosed.