Injection Device Metering Mechanism with Cartridge Dose Limiter
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Solution Overview
Problem
Existing drug delivery devices lack a safety feature to prevent setting a dose that exceeds the dischargeable amount of liquid left in the cartridge, leading to potential underdosage and health risks.
Innovation Solution
A metering mechanism with a limiter that includes a piston rod and a coupling element, featuring a stop and a counter-stop that abut to prevent further dose setting when the maximum dose is reached, ensuring the set dose does not exceed the available medicament, and allowing for resettable devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a metering mechanism allows free dose setting without limits, then ease of operation is improved, but reliability deteriorates due to risk of underdosage when cartridge is nearly empty
Solution Approach 1:
The limiter is designed to preemptively prevent the user from setting a dose that exceeds the remaining medicament in the cartridge. The stop and counter-stop mechanism activates before the user can inadvertently set an impossible dose, thereby preventing the harmful outcome (underdosage) before it can occur. This resolves the contradiction by maintaining ease of operation for valid doses while automatically blocking invalid dose settings.
2Reliability
If a limiter mechanism is added to prevent excessive dose setting, then reliability is improved, but device complexity increases
Solution Approach 1:
The limiter functionality is merged with the existing dose setting mechanism by integrating the stop and counter-stop elements into the actuating element and piston rod assembly. Rather than adding a completely separate limiting system, the patent combines the dosing and limiting functions into a unified mechanical structure, thereby improving reliability while minimizing the increase in device complexity.
Solution Approach 2:
The limiter operates automatically based on the physical state of the piston rod and coupling element, without requiring external control systems or additional power sources. The mechanical stop and counter-stop engage or disengage based purely on the relative positions of components, allowing the system to self-regulate dose setting limits based on remaining medicament volume.
3Reliability
If the stop and counter-stop are positioned to limit maximum dose, then reliability is improved by preventing underdosage, but ease of operation deteriorates due to restricted dose setting range
Solution Approach 1:
The limiter mechanism is designed to be dynamic rather than static, allowing the stop and counter-stop to engage only when the piston rod and coupling element reach positions corresponding to the maximum available dose. For all dose settings below this limit, the mechanism operates freely without restriction. This dynamic behavior ensures reliability by preventing excessive dose settings while maintaining ease of operation and full flexibility for all valid dose amounts.
Data Source
AI summary
The present disclosure provides a metering mechanism for an injection device. The mechanism comprises an actuating element for setting or discharging a dose from the injection device, a piston rod for producing an advance movement for dispensing a dose, a piston rod sleeve in which the piston rod is accommodated such that the piston rod can be non-rotatably connected to the piston rod sleeve, and a coupling element with which the actuating element and the piston rod sleeve can be coupled for discharge of the dose set with the actuating element. To prevent underdosage, the piston rod comprises a stop and the coupling element comprises a counter-stop which move relative to each other at least during setting of a dose and which abut each other in a maximum dose stop position, thereby preventing further setting of a dose.