Dose Setting Mechanism Over-Torque Protection
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Solution Overview
Problem
Existing injection devices with dose setting mechanisms using self-tightening ratchets can suffer damage when users exceed the maximum dose limit, as they lack effective protection against over-torque, leading to potential component damage.
Innovation Solution
An injection device with a ratchet ring, drive plate, and dose selector assembly that includes an over-torque feature to reduce the charging force transferred to the spring when the rotation exceeds a defined limit, using a ratchet arrangement between the drive plate and dose selector to prevent damage by disengaging the ratchet mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a self-tightening ratchet is used in the dose setting mechanism, then the dose can be increased or decreased reliably with audible and tactile feedback, but the device is vulnerable to component damage when the user exceeds the maximum dose limit
Solution Approach 1:
The patent implements a preliminary protective action by providing a hard endstop that prevents the dose from being dialed beyond the maximum limit. This endstop is positioned to engage before excessive torque can be applied to the spring or other components, thereby preventing component damage before it occurs. The endstop creates a mechanical barrier that limits the rotational travel of the dose selector, ensuring that the user cannot accidentally or intentionally overload the device.
2Reliability
If a hard endstop is provided to prevent further dialling up at maximum dose, then the maximum dose limit is enforced, but continued user torque application can still cause damage to components
Solution Approach 1:
The patent applies beforehand cushioning by designing a compliant interaction between the dose selector and the hard endstop. Rather than creating a rigid, damage-prone connection, the mechanism allows for controlled deformation or deflection as the endstop is engaged, cushioning the blow of excessive torque before it reaches critical components. This cushioning effect absorbs the excess energy from continued user rotation, protecting the spring and ratchet teeth from damage while still enforcing the maximum dose limit.
3Measurement precision
If the ratchet arrangement is made robust to prevent slippage during normal operation, then dose setting accuracy is improved, but the mechanism becomes more susceptible to damage under excessive torque
Solution Approach 1:
The patent applies local quality by differentiating the mechanical properties of different parts of the ratchet mechanism. The ratchet teeth and engagement surfaces are designed with high strength and precision to ensure accurate dose setting during normal operation. However, the interaction with the hard endstop and the overall mechanism are designed to be more compliant and damage-resistant when excessive torque is applied. This localized differentiation allows the mechanism to be both precise during normal use and resilient under abnormal conditions.
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 enhances the reliability and safety of dose setting by preventing component damage through the over-torque feature, ensuring smooth operation and reliable dose selection while providing protection against excessive torque.
Implementation Method 1
a spring capable of storing energy necessary for ejecting the dose from the injection device, wherein the spring is coupled to the dose setting mechanism such that a charging force can be transferred from the dose setting mechanism to the spring to increase the energy stored by the spring
Implementation Method 2
a ratchet ring rotationally and axially locked with respect to said housing, the ratchet ring including a ratchet component; a drive plate including a first set of splines forming a ratchet arrangement with said ratchet component
Data Source
AI summary
An injection device comprises a housing having a longitudinal axis, an axially-depressible dose button (430), a dose indicator (418), a dose setting mechanism operatively coupled to said dose indicator and capable of setting a dose to be ejected from the injection device and spring capable of storing energy necessary for ejecting the dose from the injection device. The spring (420) is coupled to the dose setting mechanism such that a charging force can be transferred from the dose setting mechanism to the spring to increase the energy stored by the spring. The dose setting mechanism comprises an assembly of three components, including: •a ratchet ring (410) rotationally and axially locked with respect to said housing, the ratchet ring including a ratchet component; •a drive plate (405) including a first set of splines forming a ratchet arrangement with said ratchet component; and•a dose selector (416) capable of being rotated about said longitudinal axis with respect to said housing to set the dose and including splines for disengaging said ratchet arrangement. The ratchet component is capable of interacting with both the splines on the dose selector and the splines on the drive plate.