Research On Key Technologies Of Micro-pipetting System For Small Automatic Biochemical Analyzer

Biochemical analyzer as an essential analytical instrument for clinical in vitro diagnostic tests is widely used in clinical testing,epidemiology,immunology,endocrinology and other fields.It provides an important scientific evidence for physicians in the diagnosis,treatment and prevention of diseases.As an important function module of automatic biochemical analyzer,micro pipetting system is of great importance in accelerating reaction speed,reducing cost,increasing instrument life and reducing reagent consumption.It involves a number of key technologies,including multi-axis motion control technology,liquid level detection technology,pipetting process monitoring technology,pipetting results detection technology.For the requirement of high-precision and miniaturization of biochemical analyzer,the key technology of micro-pipetting system of biochemical analyzer was researched in this paper.The main work of the dissertation is as follows:(1)The multi-function micropipette manipulator was designed,and the automatic fluid transfer control method,the single axis motion control algorithm and the multi axis coordinated motion control strategy were studied.Using the STM32 core processor,a single-axis S-shaped acceleration and deceleration algorithm and multi-axis and multi-thread coordinated motion control are completed.The acceleration and deceleration curve is analyzed and optimized by the method of subsection,and the minimum pipetting amount of 0.40ul and the step resolution of 0.01ul are realized.The multi-axis control strategy of modular design and task encapsulation is established,which simplifies the execution of multi-tasking and improves the work efficiency of pipetting system.(2)The pressure monitoring system of pipetting process was designed.The pressure in the pipette cavity was monitored by the pressure sensor,which realized the liquid level detection of liquid reagents and the real-time monitoring of the pipetting fault.By coordinating the movement speed of injection arm and pipette piston rod,the influence of liquid foam on liquid level detection accuracy is avoided,and the accuracy and reliability of liquid level detection are improved.The pressure model of the normal pipetting process was established by the kinematic model of pipetting operation,and the pressure model parameters were corrected by the experimental method,which could better reflect the pressure change in the actual pipetting process.Through the real-time monitoring of the pressure and pressure derivative of the pipetting process,the double threshold method of segmented processing is established as the judging standard of the fluid shifting fault,which realizes the real-time monitoring of the pipetting fault phenomenon such as insufficient sample volume,blocking needle and bubble.(3)The quantitative detection system of pipetting amount was designed by image processing method.The camera was used to collect the pipette tip image in case of pipetting failure,and the liquid region boundary extraction algorithm based on the background comparison method and a quantitative identification algorithm of the liquid pipette incorporating the geometric characteristics of the pipette tips are established.The error of the recognition error is compensated by the least square method,which improves the detection accuracy.The pipetting system feeds back the deviation of pipetting quantity to the automatic pipetting controller,carries out the pipetting correction,and realizes the closed-loop regulation of pipetting quantity in the micro pipetting system and improves the pipetting accuracy and reliability.