Positive Displacement Pipette Ejection Rod Mechanism
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Solution Overview
Problem
Positive displacement pipettes with capillary-piston assemblies face issues of accidental ejection and liquid projection due to high spring stiffness, leading to ergonomic and productivity challenges during sampling and ejection operations.
Innovation Solution
A dedicated ejection rod is introduced to manage the ejection of the capillary-piston assembly, separate from the control rod, reducing the risk of accidental ejection and allowing for lower force requirements, thereby enhancing ergonomics and reproducibility of sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single control rod is used for both sampling control and piston ejection, then device complexity is reduced, but the risk of accidental ejection increases and ergonomic handling deteriorates
Solution Approach 1:
The control mechanism is segmented into two independent rods: a control rod for sampling operations and an ejection rod for piston ejection. This segmentation allows each rod to have dedicated functionality, eliminating the risk of accidental ejection while maintaining manageable device complexity through functional separation.
Solution Approach 2:
The ejection rod acts as an intermediary component between the operator and the piston ejection mechanism. By introducing this intermediate element, the system allows precise control over ejection timing and force, preventing accidental activation while improving ergonomic handling through dedicated control.
2Force
If a high stiffness spring is used for the second stroke (ejection), then the ejection force is sufficient, but the operational force requirement increases and ergonomics worsen
Solution Approach 1:
The force application is segmented into two phases: the control rod handles sampling with appropriate force levels, while the ejection rod delivers the high force needed for piston ejection. This segmentation allows the high stiffness spring to be engaged only when needed, maintaining sufficient ejection force while improving ease of operation during sampling.
Solution Approach 2:
The system dynamically engages different spring stiffnesses at different operational phases. The first spring (lower stiffness) operates during sampling, while the second spring (higher stiffness) is engaged only during intentional ejection. This dynamic switching allows sufficient ejection force while maintaining ergonomic operation during normal sampling.
3Device complexity
If the control rod directly actuates the piston ejection, then the mechanism is simpler, but liquid projection risk increases due to uncontrolled ejection
Solution Approach 1:
The ejection rod serves as an intermediary between the control mechanism and the piston, providing controlled and deliberate ejection activation. This intermediary ensures that ejection only occurs when intentionally triggered, preventing uncontrolled piston movement and reducing liquid projection risk while maintaining manageable mechanism complexity.
Solution Approach 2:
The system implements preliminary anti-action by requiring intentional activation of the ejection rod before piston ejection can occur. This preliminary control step prevents accidental or uncontrolled ejection that could cause liquid projection, while the overall mechanism remains relatively simple through this deliberate control approach.
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 effectively reduces the risk of capillary-piston assembly loss and improves ergonomic handling and productivity by decoupling the control and ejection functions, allowing for easier operation and precise sample handling.
Implementation Method 1
The first stroke of the control rod corresponds to the stroke for dispensing the sampled sample. It is performed by opposing to the return force of a first spring, preferably a compression spring.
Implementation Method 2
The second stroke of the control rod corresponds to the presentation and opening of the piston gripping clip. It is performed by opposing to the return force of a second spring, preferably a compression spring, arranged along the same direction as the first spring and having a much higher stiffness.
Implementation Method 3
During this raising, the liquid in contact with the low end of the piston enters the capillary.
Data Source
AI summary
A positive displacement sampling pipette which includes a control rod, the bottom end of which controls the displacement of a device for gripping the top end of a piston of a capillary-piston assembly intended to cooperate with said pipette. The pipette includes an ejection rod of the capillary-piston assembly, movably mounted with respect to the control rod such that its bottom end exerts an ejection strain on the top end of the piston accommodated in the gripping device during a relative displacement between the ejection rod and the control rod.