Research On Modeling And Control Of Piezoelectric Actuated Precise Gas Flow Valve

With the development of pneumatic technology,the application of gas precision control in intelligent robots,industrial automation,medical machinery and other fields is increasing,and the requirements for gas flow control technology are getting higher and higher.The piezoelectric driven precision gas flow valve using piezoelectric bimorphs as the driver has a series of advantages such as low power consumption,large displacement,and fast response speed.However,in practical applications,the inherent hysteresis and other nonlinear characteristics of the piezoelectric bimorph material will cause problems such as poor control accuracy and slow response speed of the piezoelectric driven gas flow valve.This paper mainly studies the modeling and control technology of piezoelectricdriven precision gas flow valves for the field of pneumatic control.On the basis of comprehensive analysis of domestic and foreign gas flow valve modeling and control research,a comprehensive mathematical model of piezoelectric drive precision gas flow valve is first established.Especially for the hysteresis nonlinearity caused by piezoelectric bimorphs,a hysteresis nonlinear model of the gas flow valve is established.Finally,a composite control scheme combining feedforward compensation control based on the improved PI inverse model and fuzzy adaptive PID control is designed to solve the problem of the deterioration of the control performance of the gas flow valve caused by the hysteresis and nonlinearity of the piezoelectric material.The main work of this paper is as follows:(1)Modeling and analysis of piezoelectric-driven precision gas flow valve.By analyzing the characteristics of piezoelectric materials,gas flow characteristics and the working principle of piezoelectric-driven precision gas flow valves,a comprehensive mathematical model of piezoelectric-driven precision gas flow valves has been established,including the electrical model of the piezoelectric drive link of the gas flow valve,the kinematic model of the piezoelectric bimorph and the displacement-flow conversion model,and deduced the open-loop transfer function of the system.Considering that the hysteresis nonlinearity of the piezoelectric bimorph has a great influence on the control performance of the flow valve,the analysis of the displacement-flow conversion link shows that the piezoelectric driven gas flow valve has the same hysteresis nonlinearity as the piezoelectric bimorph.The hysteresis nonlinear model of the piezoelectric actuator can be used to establish the hysteresis nonlinear model of the piezoelectric driven gas flow valve.(2)The establishment of the hysteresis nonlinear model of the piezoelectrically driven precision gas flow valve.First,the hysteresis mechanism of piezoelectric ceramics is studied.By analyzing the hysteresis mechanism of piezoelectric ceramics,it can be known that the physical modeling is more complicated.Therefore,the phenomenological modeling method is used to establish the hysteresis nonlinear model of the piezoelectric-driven precision gas flow valve.Secondly,on the basis of the traditional PI model,the dead zone operator and the traditional PI model are superimposed to establish an improved PI hysteresis nonlinear model for piezoelectricdriven precision gas flow valves,so that the improved model has non-convex,nonsingular symmetry and other coincidence pressures,which are in line with piezoelectric-driven precision gas flow valves.Finally,experimental research,improved PI model parameter identification and model verification are carried out.An experimental platform was set up to collect the input voltage and its corresponding output flow data,and the model parameters were identified through the initial load curve method and the particle swarm algorithm,and compared with the measured data,the effectiveness of the improved PI model was verified.(3)Research on piezoelectric drive precision gas flow valve control.First,a compound control scheme based on the feedforward inverse compensation control of the improved PI inverse model combined with fuzzy adaptive PID control is designed.Secondly,the inverse model of the improved PI model is solved and the feedforward inverse compensation controller is designed,and a Simulink simulation model is built to verify the inverse model and the effect of inverse compensation.Then the fuzzy adaptive PID feedback controller of the gas flow valve is designed,and the feedforward inverse compensation control and the fuzzy adaptive PID control are combined into a composite controller.Finally,a system Simulink simulation model was built to complete the gas flow valve control simulation experiment.The simulation results show that the combined control scheme of feedforward inverse compensation control based on the improved PI inverse model and fuzzy adaptive PID control is effective and can achieve rapid and stable control of the output flow.(4)Piezoelectric drive precision gas flow valve control experiment.First,an experiment platform was built,and the control flow of the system hardware circuit and software was introduced.Then the step response experiment of different expected flow signals was carried out.The experimental results show that the composite control scheme based on improved PI hysteresis model inverse compensation combined with fuzzy adaptive PID realize the fast and stable control of the output gas flow of the piezoelectric drive precision gas flow valve.