Design And Research On Pressure Control Of A Direct-drive Electro-hydraulic Servo System

Direct-drive electro-hydraulic servo system(DDVC),as a new type of electromechanical-hydraulic composite system,is the successful application of AC motor and its control technology in hydraulic field.The new control system has the advantages of simple structure,high efficiency,high load capacity and large displacement.It overcomes the shortcomings of traditional valve control system,such as low efficiency,high cost and high maintenance cost.In the dynamic response is not demanding occasions,this system can replace the valve control system,give full play to its energy efficient advantages.Direct-drive electro-hydraulic servo control system in the United States,Japan and other countries of the research has been more mature,and access to a wide range of applications,and achieved a certain economic benefits.However,our research work in this area is still late,there is a big gap of theoretical depth and product accuracy compared with the developed countries.Therefore,the direct-drive electro-hydraulic servo control system in-depth theoretical research,has important academic significance and application va lue.Compared with the advantages of DDVC system and valve control system,the principle and characteristics of direct-drive electro-hydraulic servo pressure control system used in injection molding machine are discussed in detail.The hardware and software of the system and the control scheme are designed.According to the principle and characteristics of platform hardware,the mathematical model of the control system is established.The model of the motor and the hydraulic part are simulated.Because of hydraulic system often work in the environment of hig h temperature and high pressure.The energy transmission medium of the system is hydraulic oil,temperature and pressure changes,will make the system show nonlinear character.In order to overcome the non-linearity,this dissertation proposes a method to extract variable parameters based on pressure and rotational speed,and identify the main parameters of the transient performance of the system.Using the identification results,the equivalent sliding mo de variable structure control Compensation,by changing the equivalent control part of the exponential reaching law coefficient,to speed up the system response speed.System of hydraulic pump often work in low speed,So it requires high-speed control performance,Aiming at this problem,this dissertation introduces fuzzy control Strategy,Lyapunov theorem is used to design fuzzy rules,and the chattering of sliding mode variable structure control is restrained,the steady pressure accuracy of the system is improved.Finally,the experimental results show that the theory is correct.The pressure control design of the direct-drive electro-hydraulic servo system for injection molding machine is realized in this dissertation,which achieves good dynamic response and steady-state effect.It provides a new theoretical support and a reference for the control,design and application of electro-hydraulic servo system,and has a good prospect of market application.