| Extra-large-scale sheet metal thermoforming hydraulic presses(ESMTHPs),with the capability of bengding,drawing sheet metal whose plane size is exceedingly large,used for producing the curved sheets of large metal structures,such as nuclear reactor containments and shipbuildings etc.,are improtant basic equipment playing an irreplaceable important role in many pillar manufacturing industries.Body structure design and electrohydraulic control are two main aspects of key technologies involved in ESMTHPs:1)the body structure of an ESMTHP is outsize,resulting in sensitivity to structural processing technology and manufacturing costs while development;2)the technical specifications for the electrohydraulic system are extreme,such as multi actuator(10 master hydraulic cylinders totally),exceedingly heavy load(about 1200ton),very wide speed range(about 0.5mm/s-80mm/s)etc.;3)the guide stiffness of ESMTHP body is poor(due to thermoforming process),however the slider must keep strict plane parallel movement(the inclination should be less than 1/2500);4)Energy consumption is huge(peak power is about 1500KW),so energy saving and efficiency problems are highlighted.In summary,research in depth on body structure design and electrohydraulic control for ESMTHPs is of academic value,practical significance and necessity.This dissertation focuses on an 80MN ESMTHP.Taking into account the process characteristics of sheet bending and the dynamic characteristics of slider drive system,systematic and in-depth research is carried out around body structure design and electrohydraulic control technology for ESMTHPs.A series of targeted key technologies are proposed,including split prestressed combination frame structure(SPCFS)and its design method,volume control and throttle control based three-stage hydraulic compound drive method and its motion-pressure compound electrohydraulic controller based on hydraulic control unit matching,task coordinate based plane-parallel-motion control method for sliders with super large table,and optimization technologies for the electrohydraulic system of ESMTHPs.The actual effect and performance of these technologies presented above are tested and validated through experiment.Related research findings also have been applied in practice.The outline of this thesis is as follows,Chapter 1 details the research background of body structure design and electrohydraulic control technology for ESMTHPs,and concludes the difficulties faced in related research.The progresses of researches on the key technologies involved are reviewed.The contributions and significance of the dissertation research are summarized.Chapter 2 details the body structure of conventional sheet metal forming hydraulic presses and its deformation under load.A SPCFS is raised for body structure design of ESMTHPs which have super large table and extremely long stroke.Structural characteristics and implementation of a SPCFS are discussed,while design way for structural parameters of a SPCFS is concluded.A standard design flow for a SPCFS is developed base on depth analysis of the coupling association among each structural parameter.The SPCFS of an 80MN ESMTHP is presented and verified by finite element simulation.Chapter 3 establishes the scheme that master hydraulic cylinders(MHCs)are regulated independently with the capability of leveling slider in view of the limits of body structure,the demand of slider leveling and the distribution uniformity of forces acting on the body etc.The moving velocity of a MHC is regulated in a wide range by a proposed hydraulic three-stage compound drive circuit based on volume control and throttle control.The dynamic model of a MHC electrohydraulic system is built,and an adaptive robust motion controller as well as a nonlinear disturbance observer based pressure controller are designed for this system.The hydraulic three-stage compound drive method and the controllers mentioned above are integrated by means of hydraulic control unit matching.A motion-pressure compound control strategy is developed based on the principle of switch according to displacement and minimum value of control law,making the transition between motion control and pressure control smooth for MHCs.All the electrohydraulic control theories proposed above are validated by targeted experiment on a 1000t hydraulic press.Chapter 4 gives a task coordinate transformation method,and constructs the dynamic state matrix space of the MHC-slider coupling assembly via the task coordinate transformation.The task coordinates represent the moving states and leveling states of the slider directly.A task coordinate decomposition for desired plane-parallel-moving states based decoupling motion control method and a task coordinate transformation based coupling motion control method are raised.Each one of these two motion control methods can be combined with the pressure controller designed in Chapter 3 by the proposed motion-pressure compound control strategy,resuling in the plane-parallel-motion controller for the slider.Experiment is carried out on a 4000ton hydraulic press used to manufacture car longitudinal beam.Experimental results reveal that the proposed plane-parallel-motion controllers both achieve well motion leveling ability for the slider,and the one based on coupling motion control performs stronger robustness and excellent coordinate ability of leveling control and tracking control.Chapter 5 presents some optimization technologies for ESMTHP electrohydraulic systems,such as graded pressurization,constant power control,slider passive gravity balance and synchronous relief,which are introduced or raised to address the practical problems of energy consumption,efficiency and safety etc.faced in the engineering applications of theoretical framework proposed in this dissertation.The body structure design and electrohydraulic control theory are applied for an 80MN ESMTHP,which performs satisfiedly.With the raised technologies actively promoting,desired target products are manufactured successfully by the 80MN ESMTHP.Chapter 6 summarizes main research work that has been done,also concludes major innovations of the research and further-prospect. |
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