Research On The Control System Of Gas Mixture For Cell Culture

Objective:Research shows that gas environment is an important factor for cell culture in vitro.Oxygen provides the energy for cell culture,and it could influence cellular respiration.Meanwhile,carbon dioxide could regulate acidity-alkalinity in the culture fluid,and it is an indispensable element in the plant cell culture.The regulating gas environment in cell culture mainly includes the concentration of carbon dioxide and oxygen,and various gas blenders with different features are developed to achieve the regulation function,which exist defects in control performance and generality.The control system of gas mixture exists the characteristics of nonlinearity,time-varying,and it is difficult to establish a mathematical model precisely.However,the conventional PID controller is linear,and the coefficient adjustment process by operator experience is time consuming.Therefore,it is difficult to control gas mixture system by the conventional PID controller.A new control system of gas mixture based on PID optimized by improved genetic algorithm is designed to overcome defects of poor precision and long settling time of the traditional control system of gas mixture in this paper,which also could improve the generality to satisfy various cell culture devices.Methods and Contents:A control system of gas mixture based on PID optimized by improved genetic algorithm is designed by generality and control performance of the system in this paper.The main work undertaken is as follows:?1?The whole scheme for the control system of gas mixture is designed.It summarizes the problems of various control system of gas mixture by investigation and research on different control system.The paper presents a control system of gas mixture based on dynamic configuration with mass flow control method,which could separately achieve the mixing of carbon dioxide and air,and oxygen and air.And it designs the main function and target parameter of the system based on PID optimized by genetic algorithm.?2?The hardware of the control system is designed,which includes the module of controlling and detecting of gas flow rate,the module of detecting of gas concentration,the upper computer based on controller chip and human-computer interaction,the circuit of gas controlling,and the serial port communication and power supply.The mass flow controller of LF400 is used to accurately control and real-time detect the gas flow rate,which can communicate via RS-232 or RS-485 with the upper computer.The carbon dioxide concentration in gas mixture is detected by the module of SGA-MK-CO₂,and the oxygen concentration in gas mixture is detected by the module of SGA-MK-O₂.It selects the PLC of the Delta's DVP14SS211R as the controller chip,which is characterized by steady performance and capable of connecting multiple types of I/O modules to meet the system demands.It adopts the embedded touch screen of TPC7062TX as the human-computer interface,which has an independent development platform.Solenoid valves controlled by relays control the circuit of gas controlling,and relays are operated by the PLC instruction.?3?The software program of the control system is designed.The model identification experiment based on the control system of gas mixture in this paper is carried out,and the system mathematical model is established.An optimized PID algorithm based on genetic algorithm based on the characteristics of the control system is presented.Meanwhile,an improved genetic algorithm is designed based on the deficiency of standard genetic algorithm,which includes generation of initial population based on the Ziegler-Nichols method to minimize the blindness of the initial population,and an improved selection operator is proposed to preserve individuals with high fitness farthest,and the algorithm sets crossover and mutation probability by adaptive method.Then it uses gradient graph language to achieve PLC development,and the embedded touch screen is developed in the MCGS configuration software in this paper.PLC and the touch screen establish the communication correctly to achieve the function of the human-computer interface in the control system of gas mixture.?4?Performance analysis of the system.Research on simulation experiments and real experiments.These experiments are implemented with the control system platform in this paper to compare improved ZN-PID,SGA-PID with IGA-PID by control performance.And the prototype tests are implemented to verify whether the system performance can meet the targets.Finally,to analyzing of the system's practical applications and actual effects,cell culture experiments are carried out.Results:In simulation experiments on the control system of mixing carbon dioxide and air,the overshoot is about zero in the IGA-PID,and the setting time of the IGA-PID is 72s,the fitness of the IGA-PID is stable after 23 generations.Meanwhile,in simulation experiments on the control system of mixing oxygen and air,the overshoot is about zero in the IGA-PID,and the setting time of the IGA-PID is 22s,the fitness of the IGA-PID is stable after 29 generations.The prototype tests indicate that the system completely achieves the control parameter,and control accuracy is less than 1%.In real experimental on the system,the control performance of the IGA-PID is much better than the other two control algorithms.And the cell culture experiment results show that the gas mixture control system could provide the gas environment for cell growth.Conclusion:Compared with the existing gas blenders,the new control system of gas mixture based on IGA-PID in this paper has better generality and excellent control performance,such as reaching the stable state quickly and acquiring better precision.The results of experiments reveal that the new control system of gas mixture based on IGA-PID is effective and reliable,which has the advantages of remarkable control performance,and could overcome the shortcomings of the conventional PID and the standard genetic algorithm.Therefore,the new control system of gas mixture based on IGA-PID in this paper is excellently suitable for various cell culture devices,which can provide a better ideal gas environment for cell culture.