High Precision Distributed Control System For Sample Pretreatment Instrument

With the rapid increase in the number of samples tests in various testing center.There are some problems in sample pretreatment equipment,such as large error,long time period,few sample processing positions and low automation,etc.Fully automated sample preparation equipment has become a development trend in food safety,biomedical and other research fields.Therefore,this paper focuses on the technical requirements of sample preparation,and designs a fully automatic,high-precision sample preparation instrument with sample supplemented by an ultrasonic generator to improve processing efficiency,has certain economic benefits.The main contents of this paper are as follows:(1)In order to solve the problems of low automation and large errors in manual adding liquid.This paper studies a processing method of multiple sample position,multiple syringe pump and ultrasonic extraction device to increase the reaction rate of sample preparation,and designed the whole machine work flow and the timing of adding liquid,to ensure that the instrument adds liquid efficiency.(2)This paper studies a control method and system of distributed master-slave structure.According to the functional characteristics of the syringe pump,a distributed control system is designed with PLC as the main control unit and PC as the upper.Which adopts centralized management and decentralized control to improve the reliability of the system.The communication between the upper and lower computers of the instrument is introduced.The RS-485 serial communication mode is used to give instructions communication,so as to realize the automatic control of the instrument.(3)This paper studies a control method of high precision adding liquid.In order to ensure the accuracy of the system adding,including four steps of automatic cleaning,rinsing,liquid adding,and ultrasonic processing,combined the motor characteristics of the S-type acceleration and deceleration algorithm and non-contact liquid addition method,a motor control method suitable for adding is proposed.By controlling the acceleration during the deceleration phase during adding.The droplets suspended from the tip of the needle are better dropped off,At the same time,the adding error is analyzed,the actual adding curve is linear and polynomial fitting,and the segment function is used as its compensation.The test results show that the adding error is reduced from 1.17% to 0.141%,which is an increase adding accuracy.Finally,the function and performance of the instrument were tested.The results prove that the instrument has perfect functions,and the absolute error of adding liquid is within ± 0.05 ml,which meets the user’s design requirements.The fully automatic processing of the instrument improves the detection efficiency and effectively solves the problem of high labor intensity in sample pretreatment.The instrument is now used in the Hubei Provincial Institute for Food Supervision and Text with good feedback.