Researth And Improvement On Air-Cushion Headbox Control System

With the development of the quality of life, the demand of paper increasesdramatically, it promotes the rapid development of paper industry. The head-boxis one of important equipments in whole papermaking process, it is the key partof connecting slurry preparation and paper shape, the head-box also decides thepaper quality and papermaking speed, it's the throat section of paper machine,and named the heart and accelerator of paper machine. Therefore, there are greatsignificance to strengthen the research and development of head-box automaticcontrol systemControl algorithms are the soul of control system, good algorithm haveprofound effects on control precision and hardware choice. Although advancedcontrol algorithms of controlling the air-cushion head box had been proposed inmany references, they are surely too complex to practice in engineering process.PID algorithm not depending on mathematical model of the object is proposed inthis paper, it's not only stable but also convenient, Generally speaking, there aretwo kinds of control schemes about head-box, the first scheme is to stabilize thepulp level and total pressure by controlling the pulp and air inflow respectively,but it's only suitable under the slow speed condition, or the system will haveworse stability. Because of the good compensation characteristics for totalpressure, the control scheme of stabilizing the total pressure and pulp levelthrough controlling the pulp and air inflow respectively is adopted in the paper.Based on the present situation of our paper industry, air-cushion head box isused as the research object in paper, through combining theory and practice, itscharacteristics and control parameters has been analyzed more further,meanwhile,the influence about the pulp and air flow to total pressure and pulp level aredescribed in detail, by using the form of data and charts, which provides theuseful information for research.Three layer head box control system is developed on the plat of SiemensS7-300PLC, Because the air-cushion head box needs manual operation during the start-up process, so that the automatic operation of whole machine is difficultto implement, and people have more work to do, the software method is used toassure the automatic running model of whole starting procedure, and the flowdiagram of software is also given, so that the swiftness and accuracy of systemare improved. The hardware configuration and wiring diagram are listed in detail,in this paper, the implementation of control program on S7-300plat is giventhrough the way of flow chart, and the two filter algorithms for analog quantityare also illustrated.The system debug is the last link of system design, it decides the operationreliability of system, the interference signal on the site brings great difficultiesfor system debug. The concrete operation flow chart of system debug has givenin this paper, the reliability, control accuracy and dynamicity of the system mustbe evaluated, so that the system effect reaches the expected purpose. The practiceshows that the system design scheme is reasonable, the reliable operation andgood algorithm have improved the performance of the air cushion head.