Medication Drive Mechanism Preventing Piston Rod Backlash
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Solution Overview
Problem
Existing medication delivery devices face challenges in achieving accurate dose delivery, as the piston rod can unintentionally move proximally during dose setting, leading to decreased accuracy.
Innovation Solution
A drive mechanism with a rotation member, drive member, and stop member that prevents rotational movement of the drive member during dose setting, ensuring the piston rod moves only distally during dose delivery, utilizing mechanical cooperation and uni-directional clutch mechanisms to maintain precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drive member is allowed to rotate freely during dose setting, then the device complexity is reduced, but the piston rod may unintentionally move proximally decreasing dose accuracy
Solution Approach 1:
The drive mechanism employs a dynamic engagement system where the drive member can rotate freely during dose setting (first direction) but becomes positively engaged during dose delivery (second direction). The lever mechanism transitions between engaged and disengaged states based on rotation direction, providing the necessary constraint only when required for dose accuracy while maintaining simplicity during setting.
Solution Approach 2:
The constraint function is extracted as a separate mechanism (lever with engagement features) rather than being integrated into the basic rotation-piston connection. This allows the drive member to rotate freely during dose setting while providing positive engagement only during dose delivery, resolving the contradiction between freedom of movement and positional accuracy.
2Measurement precision
If a stop member is added to prevent rotational movement of the drive member, then dose accuracy is improved, but the device complexity increases
Solution Approach 1:
The stop member function is merged with the lever mechanism that already provides drive engagement. The lever serves dual purposes: it acts as a stop member during dose setting by preventing rotation of the drive member, and simultaneously serves as a drive engagement member during dose delivery. This integration reduces the number of separate components while maintaining both functions.
Solution Approach 2:
The lever mechanism is designed with multi-functionality, serving as both a stop member during dose setting and a drive engagement member during dose delivery. The same component structure provides different functions based on the operational phase, reducing overall device complexity while achieving precise dose setting and delivery.
3Reliability
If the drive member is constrained to prevent rotation during dose setting, then unintended piston rod movement is prevented, but the ease of operation decreases
Solution Approach 1:
The constraint system is designed to be dynamic rather than static. During dose setting, the lever is disengaged from the drive member, allowing free rotation and easy operation. During dose delivery, the lever automatically engages to provide the necessary constraint. This dynamic behavior ensures ease of operation during setting while maintaining reliability during delivery.
Solution Approach 2:
The lever mechanism is positioned and configured to automatically engage and prevent rotation of the drive member during dose delivery, countering any potential unintended movement before it can occur. The stop member is preliminarily positioned to intercept rotational movement that would cause inaccurate dosing.
Data Source
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AI summary
A drive mechanism for a medication delivery device (1) is proposed, the drive mechanism comprising a housing (13, 17, 40) having a proximal end and a distal end, a rotation member (21) which is adapted to be rotated in a first direction with respect to the housing during setting of a dose of a medication and to be rotated in a second direction with respect to the housing during delivery of the dose, the second direction being opposite to the first direction, a piston rod (12) which is adapted to be displaced in a distal direction with respect to the housing for delivering the dose, a drive member (20) which follows rotational movement of the rotation member in the second direction during delivery of the dose, and a stop member (26) which prevents rotational movement of the drive member with respect to the housing in the first direction during setting of the dose, wherein the rotational movement of the drive member in the second direction is converted into movement of the piston rod in the distal direction with respect to the housing. Furthermore, a medication delivery device is provided for.