Study On Synchronous Control Of The Hot Platen Lifting System In Continuous Flat Press Based On Predicative Control

The hot platen lifting system is the core part of continuous flat press,which determines the stability and reliability of the continuous flat press.Highly precise and synchronous control of multiple hydraulic piston cylinders connected with hot platen are essential in the lifting process of the flat press.The hot platen lifting system has the nonlinear and strong coupling characteristics with multiple actuators.Moreover,the hot platen system tends to be influenced by the processing and manufacturing precision of the equipment,the hydraulic components performance and the system leakage.Therefore,the accuracy of synchronous motion control of multiple hydraulic cylinders is not good enough when the traditional PID control method is used.The position errors may exceed the allowable limit,which causes the slant and local uneven force of hot platen.As a result,products so made may not meet the requirements,the hot platen and control valves might be damaged,and the production might be halted,which may increase the production cost.In order to overcome the influence of the system intrinsic characteristics,manufacturing accuracy and components performance,in this paper,the cluster synchronous control technology is studied for the hot platen lifting system.Based on the predictive control method,a ring coupled synchronous control strategy is proposed,by which the accuracy of synchronous control is improved.A ring coupled synchronous controller is constructed by using predictive control method,tested by MATLAB simulation,implemented on a hot platen lifting system in continuous flat press,which has been successfully used in a production line in China.The main research contents and results of this paper are as follows:Firstly,On the basis of analyzing the existing problems of hydraulic systems of the hydraulic system of continuous flat press,a closed-loop control system for the hydraulic cylinders of continuous flat press is constructed and the mathematical model is deduced.The synchronous control requirements are analyzed in terms of the hot platen lifting system hydraulic control objectives,which are the high accuracy of the position tracking of a single cylinder and the cluster synchronization of multiple cylinders.Secondly,considering the control requirements of the hot platen lifting system in continuous flat press,the high accuracy position tracking control of a single cylinder is studied.On the basis of analyzing the characteristics of several main hydraulic synchronous control algorithms,the generalized predictive control algorithm is adopted to improve the position tracking control performance.The design method and process of the generalized predictive controller are introduced in detail.With the predictive control strategy,the tracking control performance of cylinder displacements in the hot platen lifting system are verified by MATLAB simulation experiments.Experimental results show that the generalized predictive control has satisfactory fixed value tracking and servo tracking performances and the strong of disturbance attenuation,which has a minor overshoot,fast response speed and high control precision.As a result,the position tracking control of cylinders in the lifting system could be well achieved.Thirdly,considering the high precision synchronous control requirements of the hot platen lifting system in continuous flat press,the high accuracy synchronous control method of multiple cylinders is studied.A clustering synchronous control strategy is proposed.Based on the analysis of the characteristics of several synchronous control modes,a ring coupling synchronous control method is selected according to the structure and characteristics of the hot platen lifting system.The controller design is verified by the experimental comparison between master-slave control strategy and the ring coupling control strategy.Aiming to improve the dynamic performance of the lifting system in flat press and enhance the system robustness,based on predictive control,a ring coupling synchronization control method is further proposed and a ring-coupling predictive controller is designed.The optimal performance index function including the synchronization errors and tracking errors is constructed and the synchronization control law is deduced.In this paper,the theoretical verification of the established system model is carried out.Both simulation and real tests are done on the hot platen lifting system in continuous flat press.Both the simulation and test results show that the proposed synchronization control method has better position tracking and synchronization performances and a stronger capacity of disturbance attenuation.The ring coupling synchronization control method is suitable for the hot platen lifting system in continuous flat press which has multiple controlled objects.Fourthly,the hardware configuration of the measurement and control platform in the hot platen lifting system and the software of the ring coupling control method based on predictive control are presented and the implementation results are collected.The system operation results show that the synchronous control precision in the left-right direction is up to 3mm and the precision in the fore-after direction is up to 10 mm.Compared with the precision of 4mm and 15 mm with the existing control strategy at home and abroad,the precision is improved 25% and 33%,respectively,which satisfies the process requirements of the hot platen lifting system.