Metered-Dose Inhaler Dose Counter Gear Mechanism
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Solution Overview
Problem
Existing dose counters in metered-dose inhalers often fail due to variations in component tolerances, leading to undercounting or non-counting of doses, especially when users do not actuate the canister with a full reciprocating stroke, resulting in unreliable dosing and potential medication shortages.
Innovation Solution
A dose counter with a rotatably mounted gear wheel and an actuator mechanism that amplifies the linear stroke of the actuator shaft, using an engagement arm to drive the gear wheel along a circular path exceeding the linear travel, ensuring reliable incrementation of dose counts even with tolerance variations and reduced actuation force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional dose counter with direct linear actuation is used, then the device structure is simple, but the counting reliability deteriorates due to tolerance variations and insufficient actuator stroke
Solution Approach 1:
The patent applies curvature by replacing linear actuation with circular/rotational motion. The actuator arm rotates about a pivot point, causing the driver to follow a circular path that engages with the ratchet teeth on the gear wheel. This curved motion path amplifies the effective stroke length, ensuring reliable dose counting even when linear actuator displacement is insufficient or subject to tolerance variations.
Solution Approach 2:
The patent transitions from one-dimensional linear motion to two-dimensional circular motion. By pivoting the actuator arm and having the driver traverse a circular arc rather than move linearly, the system converts limited linear actuator stroke into amplified rotational displacement of the gear wheel, thereby improving counting reliability without requiring longer linear actuators.
2Reliability
If the actuator stroke is increased to ensure reliable counting, then the counting reliability improves, but the actuation force required increases
Solution Approach 1:
The patent applies local quality by concentrating the mechanical advantage at the critical engagement point between the driver and ratchet teeth. The pivoted actuator arm geometry is designed so that the driver's circular path provides sufficient engagement distance with the ratchet teeth only when needed for reliable counting, while the overall actuation force requirement remains manageable due to the localized nature of the force amplification at the pivot point.
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 significantly reduces the failure rate of dose counters by ensuring accurate counting of doses, even with imperfect actuation strokes and tolerance stacks, while maintaining a low increase in required actuation force compared to existing systems.
Implementation Method 1
the actuator shaft and the engagement arm are configured such that, in use of the dose counter, the travel of the driver along the root circle of the gear wheel exceeds the corresponding linear travel of the actuator shaft
Data Source
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AI summary
Disclosed herein is a dose counter for counting doses of medicament dispensed by or remaining in a metered-dose inhaler. The dose counter comprises a rotatably mounted gear wheel (130) having a circular arrangement of ratchet teeth (132) defining a root circle (134) and a display coupled to the gear wheel, the display having a visible array of dose counting indicia indexable in response to rotary motion of the gear wheel. The dose counter further comprises an actuator mechanism (118) having a driver (124) for rotatably driving the gear wheel in response to the dispensation of a medicament dose, the driver being arranged to engage the ratchet teeth of the gear wheel. The actuator mechanism includes an actuator shaft (120) mounted for linear movement in response to the dispensing of a dose of medicament and an engagement arm (122) pivotally mounted to the actuator shaft and carrying the driver. The actuator shaft and the engagement arm are configured such that, in use of the dose counter for counting a dispensed dose, the travel of the driver along the root circle of the gear wheel exceeds the corresponding linear movement of the actuator shaft.