Research On Control Methods And Experiments Of The Fabrication System For Plastic Microfluidic Chips

Microfluidic chip is one of the important aspects of μTAS (micro total analysis system), and it has good characteristics, such as high speed, high-efficiency, low consumption, etc. It has wide application prospects in the fields of gene analysis, medical diagnosis, medicine filtration, etc. The fabrication process of microfluidic chips using polymer materials, such as PMMA, is the key to extend the application range of micro-fluidic chips and realize their industrialization production. The hot-embossing and bonding machines are important parts of the fabrication of microfluidic chips. This article researches control theory and technologies of the machines, finishes designing and programming the control software, and analyses and test the control system performance.The development and present situation of plastic microfluidic chips and the machines were summarized. The development and characteristics of industry process control were summed up. Temperature and pressure control system of the machines were studied.The task and demand of the temperature control system were analyzed, and close-loop control scheme was adopted, and PID controller was chosen as base controller. On the base of model identification and simulation, Ziegler-Nichols toning and manual toning experiment were carried out. But common PID cannot reach the control demand proved by simulation and experiment. Improved numeric PID control methods were applied. Experiments show that the control precision is below ±0.2℃. The step response is fast and smooth, and system reaches static states with little overshot.The task and demand of the pressure control system were analyzed, and close-loop control scheme was adopted, and PID controller was chosen as base controller. On the base of analyzing pressure control characteristics, improved numeric PID control methods were applied. Pulsant integral accelerate PID control algorithm was presented, which can weaken friction and clearance nonlinearity effectively. Time-varying period sampling and control methods was proposed, which can increase average sampling frequency, and improve control performance to quick-response object. Experiments show that the control precision is below ±20N. The step response is fast and smooth, and system reaches static states with little overshot. The ramp response has small lag and error.The task and demand of the control software design was analyzed. General structure and user interface were designed. Visual C++ was chosen as the program language, and classes were designed. Linear integral compare method was proposed to realize PWM square wave, which can increase the wave frequency. The source code of the software has 26000 lines.The hot embossing and bonding machines have been used practically in microfluidic chip automatic fabrication, and the chips have satisfactory quality, precision, repetition and consistency.