Research On The Theory And Method Of Side Roll Displacement Control Of Four-roller Plate Bending Machine

The bending process of medium and thick metal plate has been widely used in the fields of petrochemical,aerospace,shipbuilding and high-pressure vessel manufacturing.Roller bending machine for metal plates is the key equipment to realize the bending process.With the rapid development of manufacturing industry in China,higher requirements have been put forward for the function,reliability,safety and automation of the roller bending machine.Compared with the traditional three-roller plate bending machine,the four-roller plate bending machine can realize the process of centering,clamping,pre-bending,and bending by using the coordination of each work roll.And it has the advantages of two-way pre-bending,convenient plate alignment,high rolling accuracy,small remaining straight edges and high rolling efficiency.However,in the process of four-roller bending,the rolling curvature of the metal plate can only be adjusted through the side rollers position by using a hydraulic servo system,which is often affected by multi-source nonlinearities and uncertainties,such as modeling errors,time-varying loads,asymmetry of hydraulic cylinder structure,and flow,pressure,controller output saturation,and sensor high-frequency measurement noise,etc.All these disadvantages have proposed a great challenge to the configuration of the side roller high-precision process positions.In order to improve the tracking performance of the side roller displacement of the four-roll plate bending machine,the control system and strategy of the side roller displacement of the four-roll plate bending machine were studied with the method of theoretical modeling,simulation and experimental research.The tracking control model of the side roller displacement was established,and the comprehensive influence of the dynamic characteristics of the side roller and various uncertain disturbance factors in the high-precision processing was deeply studied.The disturbance observation has been established,and theory and methods of real-time estimation and dynamic compensation mechanism of uncertain disturbance of the side roller displacement have been established and developed,which provided an effective solution for expanding the scope of process adaptation and improving the process quality,and rolling accuracy of the four-roller metal plate bending machine.The main contents of the dissertation are as follows:1.The market background and development status of the four-roller matal bending machine was discussed.The related control technology of the side-roller displacement of the four-roller bending machine and the research status at home and abroad were analyzed and reviewed.2.According to the uncertainties of load change,parameter perturbation and unmodeled dynamics of the side roller displacement tracking control of four roller bending machine,the side roller dynamic model of the four-roll bending machine was constructed.An adaptive sliding mode control strategy based on nonlinear disturbance observer was proposed.The backstepping method was used to design the adaptive sliding mode controller,and the observation disturbance error was dynamically compensated with the adaptive law to reduce the switch gain of the sliding mode controller.The prior requirement of the sliding mode switch gain to the upper bound of the system uncertainties was relaxed with the design method,and the influence of external disturbances and system uncertainties on the displacement tracking control performance of the side rollers was reduced.The stability of the closed-loop side roller displacement tracking system was verified using the Lyapunov method.According to actual engineering parameters,the simulation model was built and the numerical simulation was carried out,the results showed that the adaptive sliding mode control strategy based on the nonlinear disturbance observer has strong robustness to the system uncertaintie,especially to the variable loads in the side roller displacement control system of the four-roller bending machine.3.In view of the fragility of the mathematical model dependency and the difficulty for obtaining the system state,a linear active disturbance rejection control(LADRC)strategy was proposed.The linear extended state observers were designed for two situations,in which the information of the controlled plant model is partially known and completely unknown.And the stability of the closed-control systems were proved.4.Based on a simplified mathematical model of a valve-controlled asymmetric cylinder,a third-order linear active disturbance rejection controller was designed,and a simulation study was performed according to the actual engineering application conditions.The influences of parameters on the control performance were primarily revealed,such as the estimated value 0b of the forward control channel gain b,the observer bandwidth o~?,the controller bandwidth c~?,and the sensor measurement noise.Compared with the traditional proportional-integral-derivative(PID)control strategy,the multi-source uncertain disturbances existing in the electro-hydraulic servo systems of the valve-controlled asymmetric cylinder can be effectively suppress with the proposed method,and the control performance was better.5.Based on the analysis of the structure of the electro-hydraulic servo system,the mathematical model was further simplified.A second-order linear active disturbance rejection control method was proposed,and the controller parameters were given engineering physical meanings.General methods and steps of the controller structure and parameter design were given,and the control performance of the method was compared with that of the third order LADRC and PID by the simulation.Results showed that the actuator control performance of the four-roll bending machine can be improved by the the second-order LADRC,which can be well utilized to engineering practice.6.Aiming at the torque coupling problem of EHSS at the each ends of the side roll of the four-roller bending machine,under the framework of auto disturbance rejection control,the coupling force moment was regarded as a part of the respective uncertain comprehensive disturbance,thus the displacement tracking control problem of the side rollers was transformed into the displacement tracking control problem of the piston of the valve control cylinder under the uncertain disturbance.The real-time control experiment platform based on digital signal processing and control engineering(d SPACE)was built up,and the valve control cylinder experiments were carried out.The results showed that the active disturbance rejection control(ADRC)has a wider set point tracking range than PID in the same bandwidth.In the simulation and experiment,the parameters of the controller were easy to be adjusted,and it has strong robustness to the uncertainty disturbance in the system,especially the load change.It can meet the requirements of rapid and accurate tracking of the side roller displacement,so as to improve the process quality of the rolling plate,the precision of the components and the rolling efficiency,and reduce the energy consumption.