Research On The Control Strategy Of Digital Hydraulic Cylinder Position System

Digital hydraulic cylinder is a typical nonlinear electro-hydraulic servo system,which contains many nonlinear links and external disturbances.It is difficult to improve its operation stability and control precision by traditional control strategy.Therefore,this paper has taken the digital hydraulic cylinder position control system as the research object,proposed a variety of composite control strategies for the control strategy problems under factors such as non-linearity and external interference of the digital hydraulic cylinder,and carried out in-depth theoretical analysis and experimental research.The main research contents were as follows.Firstly,the existing technical schemes were analyzed in detail.On this basis,the structure of internal indirect feedback digital hydraulic cylinder and indirect digital control hydraulic cylinder were finally referred,and the position closed-loop feedback control was added to become a new type of double closed-loop digital hydraulic cylinder.Then,the mathematical model of servo motor,the nonlinear dynamic model of feedback mechanism,the mathematical model of asymmetric hydraulic cylinder controlled by symmetrical four-sided slide valve,the mathematical model of nonlinear hydraulic spring and nonlinear Lu Gre friction were established,and the high-order state equation of digital hydraulic cylinder position system was derived.In order to design and implement the controller,based on the idea of ADRC strategy,the high-order state equation was equivalent to the second-order integral series state equation.In order to improve the performance of the digital hydraulic cylinder position control system,combined with the advantages of switching control and ADRC,a switching ADRC strategy was proposed by using the multiple Lyapunov function method and the minimum Lyapunov function switching rule.A simulation model of the digital hydraulic cylinder position control system based on MATLAB/Simulink was established.The performance influence of the digital hydraulic cylinder position control system under the switching ADRC strategy was studied and verified by experiments.Aiming at the problems of numerous adjustment parameters and low sensitivity of ADRC,in order to reduce the adjustment parameters,combined with sliding mode variable structure control and ADRC,a sliding mode ADRC strategy was proposed.In order to reduce the chattering caused by sliding mode control,the reaching law was introduced into the sliding mode ADRC strategy.Combined with the characteristics of global fast terminal sliding mode variable structure control and RBF neural network approximation nonlinear function,the control law and adaptive law based on Lyapunov function were derived.The digital hydraulic cylinder position control system was simulated by MATLAB/Simulink,and the stability of the digital hydraulic cylinder position control system under various control strategies were studied.The research showed that the sliding mode ADRC strategy had the least adjustment parameters.The controller can effectively improve the rapidity of the system,but it will reduce the steady-state accuracy of the system.The global fast terminal sliding mode ADRC strategy can improve the response speed of the system,but the system will produce self-sustaining oscillation,which will cause damage to the system and its equipment.The neural network sliding mode ADRC strategy can improve the response speed of the system,improve the control precision and increase the stability of the system.In order to reduce the chattering of the system,ensure the closed-loop stability of the system,and further improve the performance of the digital hydraulic cylinder position control system,a model reference ADRC was proposed by combining model reference adaptive control and ADRC.The control law and adaptive law based on Lyapunov function were derived.Considering the nonlinear feedback term in the model reference adaptive disturbance rejection control strategy,and the RBF neural network was used to approximate the nonlinear function.The neural network model reference adaptive disturbance rejection control strategy was proposed,and the control law and adaptive law based on Lyapunov function were derived.The digital hydraulic cylinder position control system was simulated by MATLAB/Simulink,and the stability of the digital hydraulic cylinder position control system under different control strategies were studied.The research results showed that the neural network model reference adaptive disturbance rejection control strategy can well reduce the static error of the system under different input command signals of the system,overcame the influence of external interference on the stability and control precision of the system,and had strong robustness.At the same time,the parameters to be adjusted by the control strategy were less than those in the switching ADRC.In order to verify the effectiveness of the various control strategies proposed in this paper to improve the performance of the digital hydraulic cylinder position control system,according to the principle of consistency between simulation modeling and experimental construction,the digital hydraulic cylinder position control strategies experiment were carried out.And the switching ADRC strategy,neural network sliding mode ADRC strategy and neural network model reference adaptive disturbance rejection control strategy were carried out under different command signals.The experimental results were basically consistent with the simulation curves,which verified the feasibility and effectiveness of the proposed control strategy.This paper has 142 figures,24 tables and 245 references.