Research On The Four-axis Leveling System With Sliding Mode Control For Composite Press

Composite press is the key equipment for the compression molding of advanced composite materials.It is used to manufacture the fiber reinforced plastics with complex structure and high dimension accuracy,and determines the forming quality of composite products directly.In recent years,the rapid development of new-energy vehicle industry and the increasingly demand of lightweight composite materials for vehicles have put forward new requirements for the advanced composite presses.In the process of composites molding,it will inevitably produce heat deformation resistance and then form an overturning moment causing a position offset of the beam press activities.It restricts the products forming quality,and even produces irreversible damage to the mold due to the unequal factors.Therefore,the research and development of advanced leveling system to balance the overturning moment,in order to ensure the horizontal precision of moving beam is not only the key to improve the quality of composite material molding,but also an important guarantee of composite materials products quality forming.In this paper,the four-axis leveling system based on the concept of sliding mode control with strong anti-interference ability of composite press is designed for the demand of high performance leveling of composite press.The details are as follows:Firstly,the hydraulic system of the passive quadrangle and the hydraulic circuit of four-axis leveling system are designed.They are based on the analysis of the molding process of the composite material,the movement rule and the control target of leveling hydraulic cylinder.On this basis,the main technical parameters of the compound material press are determined,and the calculation selection and performance check of key hydraulic components of the four-axis leveling control system are completed.Secondly,the mathematical model based on the servo control of leveling hydraulic cylinder is established.The state space equation of the valve control asymmetric cylinder system is established by combining the valve flow equation,the continuity equation of the hydraulic cylinder flow and the force balance equation.Through the transfer function of the valve control asymmetric cylinder,the reciprocating motion characteristics are analyzed.The mathematical model of proportional servo valve is established,and the PID control parameters are determined by particle swarm algorithm to obtain and analyze the influence of leakage coefficient and external load on the control effect.Then,the controller and control strategy of the leveling system are designed with the sliding mode control principle.The sliding mode controller is designed and compared with PID control.According to researching the problem of multi-cylinder synchronization,the sliding mode control effect is analyzed and synchronized with the control strategy,and the sliding mode controller with cross coupling is designed for large leakage and strong interference working conditions.In addition,the control effect of sliding mode control and PID control is analyzed under the special working condition of micro-opening mode.Finally,an example is given to verify the effectiveness of the sliding mode control method.A dual-cylinder synchronous control test platform and its measurement and control system are established to verify the reliability of the simulation model through the measured data.Based on the simulation model is validated,analyzed the PID control and sliding mode control under no-load and load,especially with the cross coupling control strategy of sliding mode control method,can significantly improve the synchronous control precision,verifies the analysis of above conclusion.The innovation of this article is the establishment of the four-axis leveling system with sliding mode control algorithm.The control strategy with cross-coupling compensation displacement among the cylinders are also given to further enhance the level accuracy of the hydraulic cylinder with time-varying load on this basis.The synchronization accuracy and precision for the composite mulding are improved with the new method proposed in this paper.