Research On Electro-hydraulic Control System For Plastic Forming Hydraulic Press With Slider Guidance

One of the most important characteristics of a thermoplastic forming hydraulic press(TFHP)is its high-speed motion process(max.speed up/down to 1200mm/s)under no-load conditions.Electro-hydraulic systems are widely used in hydraulic presses because they have a high response,a high precise,a high power-to-weight ratio,and a relatively high load-bearing capacity.An electro-hydraulic system of a hydraulic press has a large extent of parametric uncertainties,uncertain nonlinearities,and external load disturbances.To handle these types of problems,several advanced control methods ate provided in the present study.Another characteristic of a TFHP is that the size of the mould used to form plastic parts varies widely.In the forming process of a hydraulic press,the parallelism of the slider has to be controlled.In summary,research in depth on electro-hydraulic control for a TFHP is of academic value and engineering application value.This dissertation takes the electro-hydraulic system of a TFHP as its specific research object.The related research was carried through mathematical modeling,theoretical derivation,development of a control strategy,simulation analysis,and experimental verification.The nonlinear control theory of electro-hydraulic system for a thermoplastic forming hydraulic press is proposed.Some of the research findings have been applied in practice.The following discussion outlines this thesis:Chapter 1 details the research background of an electro-hydraulic control system for a TFHP,and summarizes the research difficulties existing in the slider leveling of an electro-hydraulic control system for high-speed hydraulic presses.The research status and methods of the most important technological advances involved in the system are introduced.Finally,the significance and contributions of the dissertation research are summarized.Chapter 2 describes the leveling-oriented electro-hydraulic system and establishes a nonlinear dynamic model of the system.A nonlinear cascade controller based on an extended disturbance observer(EDO)was designed.The EDO estimates speed variable and external disturbances.The outer position tracking loop of the nonlinear cascade controller was taken the desired driving force as control output.The inner pressure control loop of the nonlinear cascade controller applied the backstepping technique was derivated from a desired driving force to an actual control law.The controller performance of the leveling-oriented electro-hydraulic system was verified through simulations.The simulation results show that the proposed EDO-based nonlinear cascade controller achieves accurate position control for the desired trajectory and shows a stronger robustness control performanc.In addition,the proposed cross-coupling controller(CCC),together with the EDO controller,provides the better synchronous control performance of four axes.Chapter 3 describes the pressure-regulation-oriented electro-hydraulic system and establishes a nonlinear pressure dynamic model of the system.A command-filtered-based compound adaptive controller(CF-CAC)was developed.This Command-filtered-based control technology uses a second-order filter as the actual input signal for the virtual control signal,which solves the "differential explosion" problem of the differential calculation in the traditional backstepping method.The compound adaptive control method simultaneously uses the tracking and prediction errors to estimate unknown parameters and to achieve rapid adaptation control.The simulation results show that by using the proposed nonlinear pressure controller,the system achieves accurate pressure tracking control and the desired control effect.Chapter 4 describes the loading control for master hydraulic cylinder of the electro-hydraulic system and establishes a nonlinear dynamic model of the system.A motion controller based on a discontinuous projection adaptive robust controller(ARC)was constructed.The ARC controller guarantees that the parameter estimation value is limited to a range of estimates,reduces the parametric uncertainties,and satisfies the known lower and upper bounds of robust control.A parameter adaptive law eliminates model compensation error caused by parametric uncertainties,and a robust control law suppresses uncompensated uncertain nonlinearities.The ARC controller achieves the desired output tracking accuracy and the final steady state response performance.Finally,high-precision trajectory tracking control of the electro-hydraulic system was verified through simulations and experiments.Chapter 5 describes the micro-displacement-leveling electro-hydraulic system and establishes the nonlinear dynamic model of the system.A fast dynamic compensation adaptive robust controller(FDC-ARC)of an axis was introduced.Under the premise of ensuring the steady state tracking accuracy,the transient response performance of the system was improved.The nonlinear FDC-ARC controller together with a CCC controller was integrated to solve the slider leveling synchronization control system using four axes.The final tracking accuracy of an axis and an excellent synchronization motion performance of four axes were verified through experiments.Chapter 6 describes the slider-passive-leveling electro-hydraulic system and establishes the mathematical model of the system.First,the mechanical part of a hydraulic press was modeled in ADAMS simulation software.Second,the control part of a hydraulic press was modeled in ADAMS and MATLAB/Simulink simulation software that use the average type of synchronous control strategy and a PID control algorithm.Finally,the co-simulation of the system was performed.The simulation results show that each axis has a good tracking performance for the desired trajectory,and each high-response servo proportional valve has the opening extent of the spool.Chapter 7 summarizes the main research work,and concludes with major innovations of the research and prospects for future work.