Pen-Type Injection Device Dose Resetting Ratchet Mechanism
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Solution Overview
Problem
Existing drive mechanisms for injection devices require users to retract the dial member to reset or reduce a set dose, which is considered cumbersome, and often involve complex clutch systems that complicate dose setting and resetting processes.
Innovation Solution
A drive mechanism featuring a detent engagement as the second clutch with ratchet clicker teeth having differently ramped angles for clockwise and anti-clockwise directions, allowing for easy dose reduction with tactile and audible feedback, and utilizing a torsion spring to store energy while preventing back-winding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a self-tightening ratchet with vertical flanks is used for dose resetting, then the dose can be reduced by retracting the dial member, but the operation becomes cumbersome and complex
Solution Approach 1:
The ratchet teeth are designed with asymmetric ramped flanks having different angles for clockwise and anti-clockwise rotation. The first ramped flank (clockwise) has a smaller angle than the second ramped flank (anti-clockwise), creating different resistance characteristics in each direction. This asymmetry enables easy dose reduction without requiring dial member retraction, while maintaining a simple clutch structure.
Solution Approach 2:
Instead of requiring the dial member to be retractable to reduce dose (as in conventional designs), the invention inverts the approach by using a ratchet mechanism that allows the dial member to rotate freely in the anti-clockwise direction for dose reduction. The ratchet teeth are designed to engage during clockwise rotation (dose setting) but disengage during anti-clockwise rotation (dose reduction), eliminating the need for retraction.
2Force
If differently ramped tooth angles are used in the ratchet clicker, then user torque requirements are reduced for dose reduction, but the mechanism complexity increases
Solution Approach 1:
The ratchet clicker teeth incorporate asymmetric ramped flanks with different angles optimized for clockwise and anti-clockwise rotation. The first ramped flank (clockwise) has a smaller angle to provide low resistance during dose setting, while the second ramped flank (anti-clockwise) has a larger angle to provide higher resistance during normal operation but allows easy override during dose reduction. This asymmetric design reduces user torque requirements for dose reduction while maintaining a compact mechanism.
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
Enables easy reduction of an already set dose with reduced user torque requirements, providing a simpler and more intuitive user experience while maintaining accurate dose dispensing and resetting.
Implementation Method 1
a torsion spring fixed between the housing and the dial member such that energy is accumulated in the torsion spring upon rotation of the dial member relative to the housing
Implementation Method 2
the second clutch comprises a ratchet clicker with teeth having in the clockwise and the anti-clockwise direction differently ramped tooth angles such that the teeth are allowed to override each other in the de-coupled state of the second clutch with a different resistance in the clockwise and the anti-clockwise direction
Data Source
Figure 1~2
Figure 3~4
Figure 5a~6
AI summary
The present invention relates to a pen type drug injection device (1; 101) comprising a housing (4, 5; 104, 105), a dose dial member (6; 106), a torsion spring (12; 112) fixed between the housing and the dial member such that energy is accumulated in the torsion spring upon rotation of the dial member relative to the housing, a drive member (8; 108) engaging a lead screw (9; 109), a first clutch (18; 118) rotationally coupling the drive member (8; 108) and the housing in a coupled state and allowing relative rotation between the drive member and the housing in a de-coupled state, and a second clutch (19; 119) rotationally coupling the drive member and the dial member in a coupled state and allowing relative clockwise and anti-clockwise rotation between the drive member and the dial member in a de-coupled state. The second clutch comprises a ratchet clicker with teeth (19a, 19b; 119a, 119b) having in the clockwise and the anti-clockwise direction different ramped tooth angles such that the teeth are allowed to override each other in the de-coupled state of the second clutch with a different resistance in the clockwise and the anti-clockwise direction, such that a dose can be set and also corrected by the user thereby tensioning respectively relaxing the torsion spring.