Capacitance-Based Dispense Volume Sensor for Needle Liquid Loss
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Solution Overview
Problem
Existing dispensing systems for medical diagnostic assays face inaccuracies due to liquid accumulation on the outer diameter of dispensing needles, leading to volume discrepancies and significant inaccuracies in assay results.
Innovation Solution
A dispense volume sensor using a concentric cylinder capacitor arrangement measures the capacitance change when the dispensing needle is inserted into a receiving cylinder, allowing for the accurate determination of the 'lost' volume by comparing measured capacitance values with calibration values, enabling precise calculation of the actual dispensed volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If needle-based dispensing systems are used to dispense liquid reagent droplets, then the target amount of liquid leaving the inner needle space is well controlled, but the actual amount of liquid reaching the receiving well shows irregularities due to liquid creeping along the outer diameter of the dispense needle
Solution Approach 1:
A receiving cylinder is introduced as an intermediary component between the dispense needle and the final destination. This cylinder captures the liquid creeping along the outer needle diameter, allowing separate measurement and compensation of the lost volume. The intermediary structure enables detection of the harmful liquid creep without disrupting the primary dispensing function.
Solution Approach 2:
The system implements feedback by measuring the capacitance change caused by liquid accumulation on the needle outer surface and using this information to calculate and compensate for the lost volume. The measured capacitance value provides feedback about the actual amount of liquid creep, enabling correction of the dispensing accuracy.
2Measurement precision
If capacitance measurement between dispense needle and surrounding chamber is used, then droplet volume can be calculated based on additional capacitance, but the measurement is affected by dielectric constant variations of materials on the needle tip surface
Solution Approach 1:
The measurement function is extracted from the original capacitance sensor design and relocated to a separate receiving cylinder. By moving the sensing element away from the dispense needle surface, the system eliminates interference from dielectric constant variations of materials on the needle tip, while maintaining the ability to measure liquid volume through capacitance changes.
3Productivity
If liquid accumulates on the outer needle diameter over successive dispensing acts, then a critical amount of liquid joins the dispensed droplet, but no mechanism exists to detect or compensate for this volume loss
Solution Approach 1:
The system performs preliminary measurement of the lost volume through capacitance detection before the accumulated liquid joins the dispensed droplet. By measuring and recording the capacitance change at each dispensing act, the system proactively tracks liquid accumulation and calculates compensation values in advance, preventing accuracy degradation.
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
This solution provides accurate measurement of the actual dispensed volume, reducing errors in medical diagnostic assays by accounting for the volume lost on the outer needle diameter, ensuring precise dispensing and improved assay reliability.
Implementation Method 1
a dispense volume sensor including a dispense needle for dispensing a liquid sample and a receiving cylinder for receiving the dispense needle wherein upon receipt of the dispense needle by the receiving cylinder a capacitor is formed
Data Source
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AI summary
In needle-based dispensing systems, the target amount of liquid to be dispensed is in many cases very well controlled. However, the amount of liquid that is actually reaching the receiving well may show a discrepancy, because part of the liquid leaving the inner needle space remains on the outer surface of the dispense needle, and so a small amount of liquid is "lost" in the dispensing act. A sensor arrangement according to the present invention is suitable for detecting the presence of any liquid from the aspiration reservoir that is left behind on the outside of the dispense needle, before the dispense step is actually started. The "lost" volume can also be measured very accurately by inserting the tip of a dispense needle into a hollow metallic cylinder, forming a capacitor, whereby the capacitance value depends on the volume of the "lost" dispense volume.