| The precise positioning control of hydraulic cylinder is usually achieved by servo-valve,proportional-valve,or high-speed valve,and cost problem and reliability problem existed in these types of system.Using on/off directional control valve(OFDCV)as control elements for precise positioning control of hydraulic cylinders can reduce system cost and increase the reliability of long-term operation of the system,which is a better alternative.However,current research on the control method of the hydraulic cylinder with OFDCV as the main control element is scarce,and there is also a lack of systematic analysis for the control problems existed in this system.Due to the above situations,this thesis will conduct a comprehensive study on the hydraulic cylinder positioning control system based on OFDCV.Through the system design and component characteristics analysis,the basic control problems of precise positioning control are summarized,and then the specific controller design and implementation of control algorithm are carried out.This thesis consists of six chapters,the outline of each chapter is as follow:In Chapter 1,the existing hydraulic cylinder positioning control methods and their characteristics are sorted and analyzed.The research significance of hydraulic cylinder positioning control method based on OFDCV is pointed out.Then main control problems of the system are listed.Then though the summary of the essential ideas of the existing positioning control methods,it is pointed out that when the above problems exist simultaneously,the existing methods cannot be used,and the positioning feedback control method is needed.Consequently,the existing predictive methods and their applicability are further analyzed.They are still not directly applicable to the current system.The solving process and prediction methods should be redesigned.Chapter 2 models and analyzes the components of the research system.Firstly,the OFDCV is mathematically modeled and physically tested.The control problems caused by OFDCV are indicated.Secondly,the mathematical modeling of friction force is carried out.The nonlinear characteristics and model uncertainty of the hydraulic cylinder friction are verified by simulation and experiments.Thirdly,the pressure dynamics of hydraulic cylinder chambers is modeled and analyzed.The equivalent elastic modulus of oil changes as a function of pressure,also the pressure dynamic of hydraulic cylinder chambers have strong nonlinearity and,model uncertainty.In Chapter 3?the basic controller structure is designed,and an algorithm implementation scheme with lower complexity is given based on the structure.Firstly,a 'rewinding' derivation method is proposed to control law derivation.This method effectively solves the control law derivation problem that is difficult to solve by traditional receding horizon optimization.Secondly,a structure of the controller based on state-machine is designed according to the derived control law,so that the calculation required for the control can be reasonably allocated,and the real-time performance of control algorithm is improved.Thirdly,a simplified implementation scheme is proposed,based on the above basic controller structure,combined with the proposed simplified prediction algorithm.It is proved by experiments that the simplified scheme can achieve stable and accurate positioning control and has strong adaptive ability.Finally,the characteristics of the simplified scheme are summarized,and it is pointed out that in order to further improve the control performance,accurate state prediction under arbitrary initial state should be realized.In order to realize the above state predictor,research on accurate identification and simulation methods of the system is carried out in Chapter 4.Firstly,the accurate identification of the dynamic model of hydraulic cylinder is studied.There are three types of interference problems in actual identification,which will cause huge identification errors.The Random Sample Consensus(RANSAC)algorithm is effectively applied to the hydraulic system identification in this thesis.The inliers and outliers are correctly classified,and the identification accuracy is greatly improved compared with the traditional method.Then based on the valid data filtered by RANSAC,the total least squares method is used to identify the system parameters again.The estimation bias caused by random noise is eliminated,and the identification accuracy of the model parameters is further improved.The cavity pressure dynamic model identification considering the variation of the equivalent elastic modulus,and the dynamic model identification of the oil source pressure are also studied in this chapter.Finally,the above three-part identification results are integrated to establish a simulation prediction model of the overall system.The model parameters are optimized according to the prediction errors.The optimized simulation model is used in the next chapter to realize the state prediction required for controlIn Chapter 5,a general implementation of the control algorithm is designed.Firstly,the state predictor required for control is realized based on the simulation model of the previous chapter The predictor parameters are further optimized according to the prediction error of target state.Then,the general implementation scheme of the controller is given,and the switching constraint time is shortened to 250ms.The experiment proves that the scheme can achieve accurate and stable positioning,and the minimum time required to complete the control is smaller,and the process is more optimized.Chapter 6 summarizes the research work and innovation of this paper,and prospects the follow-up research direction of hydraulic cylinder positioning control based on OFDCV. |
PDF Full Text Request