Study On Positioning Control For High Precision Basis Weight Valve

In the papermaking,chemical and other industries production process,fluid flow is one of the important process control variables.The control effect is directly related to the product quality,has been highly valued by the relevant industry.However,with the improvement of the flow control requirements,the control precision of common regulating valve has been unable to meet the requirements.High precision basis weight valve is favored in the flow control with the higher control precision and good dynamic characteristics.As the domestic has not yet produced high precision basis weight valve,therefore,the current domestic dependence mainly on imports.The high monopoly prices lead to increase the investment cost of enterprises.In order to break the monopoly of foreign technology,it is urgent to study the domestic high precision basis weight valve with certain competitiveness.This thesis is supported by the project of high precision basis weight control actuator(project number: 201311)and project of Shaanxi key science and technology innovation team(project number:2014KCT-15),the following study works were carried out around three aspects that design of mechanical structure and control unit,acceleration and deceleration positioning control,position closed loop intelligent control for high precision basis weight valve.I.Design of mechanical structure and control unit for high precision basis weight valveAiming at the selection problem that drive component of high precision basis weight valve,through simulation experiment,the open loop positioning precision of synchronous motor,asynchronous motor and stepper motor is tested.The stepper motor with the higher positioning precision is selected as the driving part by the test results.Combining with reducer,valve body and other components,the mechanical structure of high precision basis weight valve was designed.According to the functional demands of motor driving,fault alarming,position feedback and communication,a high precision basis weight valve control unit based on S7-200 PLC and step motor driver is proposed.II.Study on acceleration and deceleration positioning control for high precision basis weight valveAiming at the phenomenon that lost step and overshoot of drive component in the movement process,the positioning control algorithms based on triangle,trapezoid and S-shape was presented.Through analyzing the advantage and disadvantage of each algorithm,combining cost of controller,the fitting S-shape acceleration and deceleration algorithm was chosen to positioning control for high precision basis weight valve.Finally,the simulation experiment was used to verify the effect of fitting the S-shape acceleration and deceleration curve algorithm,and the algorithm of fitting S-shape acceleration and deceleration curve was further verified on the physical experimental platform.III.Study on the position closed loop intelligent control for high precision basis weight valveAiming at the final position deviation of the valve and the strong coupling and high nonlinear characteristics of stepper motor,a valve closed loop control strategy based on fuzzy PID was proposed.Through simulation experiment,comparing with the traditional PID controller,it found that the fuzzy PID controller can effectively and quickly correct the valve position deviation,and further improve the control precision of high precision basis weight valve,and achieved satisfactory dynamic characteristics.In this paper,the control precision and dynamic characteristics of high precision basis weight valve had been improved by positioning control,it had applied to the paper longitudinal basis weight control of a tissue machine in Sichuan.According to field flow history curve and basis weight sampling data,it found that the high precision basis weight valve can effectively improve the flow control precision and stability of the basis weight.