Fixed Dose Injector Pen Ratchet With Last-Dose Lockout
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Solution Overview
Problem
Existing injector pens allow users to freely select and deliver variable doses, which is undesirable for prescribed fixed doses, and may require a last dose lock-out mechanism when the cartridge is nearly empty.
Innovation Solution
A fixed dose injector pen design with a non-rotating piston rod and ratchet mechanisms that ensure a predetermined dose is delivered, and a last dose lock-out feature to prevent further use when the cartridge is nearly empty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the injector pen allows free dose selection by the user, then the ease of operation is improved, but the reliability deteriorates because partial doses may be delivered
Solution Approach 1:
A ratchet mechanism acts as an intermediary between the dose selector and the piston rod. The ratchet allows the dose selector to be adjusted freely to set the dose, but during delivery it ensures unidirectional movement of the piston rod, preventing reversal and ensuring the full prescribed dose is delivered even if the user releases the button early.
2Productivity
If the injector pen allows repeated uses from a single cartridge, then the productivity is improved, but the reliability deteriorates when the cartridge is nearly empty
Solution Approach 1:
The system performs preliminary action by tracking the piston rod position across multiple uses and automatically detecting when the cartridge is nearly empty. The last dose lock-out mechanism is activated in advance before the cartridge is completely depleted, preventing attempts to deliver incomplete doses and ensuring reliability while maintaining productivity during the valid usage period.
3Reliability
If a last dose lock-out mechanism is added to prevent further use when the cartridge is nearly empty, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The last dose lock-out mechanism is merged with the existing ratchet mechanism and piston rod assembly. The lock-out function is integrated into the same mechanical components that control dose delivery, using the existing ratchet structure to prevent both partial doses and further operation when the cartridge is depleted, thereby improving reliability without proportionally increasing device complexity.
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
Ensures fixed dose delivery and prevents partial doses, while automatically locking the pen when the cartridge is nearly empty, adhering to regulatory requirements.
Implementation Method 1
A first circular ratchet constrains the driver to rotate only in a direction that drives the piston rod to advance
Implementation Method 2
a driver is in threaded engagement with a piston rod, such that rotation of the driver causes the piston rod to move axially
Implementation Method 3
the locking element is biased in a second axial direction by a spring mounted between the collar and the locking element
Data Source
Figure 1a~1b
Figure 2
Figure 3~4
AI summary
A fixed dose injector pen comprises a transmission element (30) that is rotated to set and deliver a dose of a drug from a multi-dose cartridge (8). A circular ratchet (34) defines a small number of engagement positions around its circumference and selectively transmits the rotation of the transmission element (30) to a piston rod driver (24). Specifically, the circular ratchet (34) transmits the rotation of the transmission element (30) to the piston rod driver (24) only when the transmission element (30) is rotated in a dose delivery direction, and only if the transmission element (30) has previously been rotated in an opposite, dose setting direction through an angle sufficient to reach one of the engagement positions. Preferably, an axially moving injector element (4) is used to drive rotation of the transmission element (30) via a helical coupling (31, 32). When the piston rod (16) has advanced to a predetermined axial position, a last dose lock-out mechanism (42, 44) maintains the circular ratchet (34) in engagement to prevent a further dose being set.