| Hydraulic press is a kind of high-pressure fluid transfer equipment to provide theworking pressure. With the rapid development of the aerospace, automotive,shipbuilding and other industries, the demand for hydraulic machines which islarge-scale, high-precision, intelligent and environment friendly is increasing. In orderto improve the output of hydraulic machines, multi-cylinder hydraulic machine isdesigned. But multi-cylinder hydraulic machine’s slider is generally connected witha plurality of hydraulic cylinders, which causes the system to produce a strongmechanical structure coupling, hydraulic cylinder overactuated and synchronizationissues. The hydraulic servo valve achieves the conversion between the transfermedium’s flow and pressure. The square root relationship between flow and pressureresulting in a non-linear characteristics of the hydraulic system. On the subject of thehydraulic system’s coupled, nonlinear, overactuated and synchronized and otherissues, Some research was carried out in this parper:(1) Simplifies the mechanical structure of the double-acting hydraulic press, and amodel is established by mechanism modeling method. Assuming the forgings is cube,forging force against the two sliders can be equivalent to the product of displacementand the elastic modulus. And then considering the dynamic movement of the twosliders in three degrees of freedom:linear motion, rotation around the X axis androtation around the Y axis, a dynamic model of the slider was created. After that, amathematical model of the hydraulic mechanism was builded. And the model of thehydraulic mechanism integrated with the model of slider is the overall mathematicalmodel of the hydraulic system.(2) After analyzing the overactuated problem of the multi-cylinder hydraulicsystem, giving several common static control allocation algorithm and analyzing thelatest dynamic control allocation algorithm. For an overactuated example, static anddynamic control allocation were used for simulation, and the simulation resultsdemonstrate the dynamic control allocation has better dynamic response.(3) On the subject of multi-cylinder forging hydraulic press system, consideringthe uncertainty of large loads and the coupling of multi-cylinder, a mathematicalmodel of this nonlinear system is established, and the hydraulic cylinder over actuated is solved by using control allocation method based on generalized inverse. And then atwo-level nonlinear controller is proposed in order to solve above problems. Theinner-loop controller by using Lyapunov Direct Method controls the four SISOhydraulic cylinder pressure system, to achieve accurate and fast tracking for thedesired pressure. Furthermore, the outer-loop controller, due to control the uncertainlarge load MIMO system, is designed by using adaptive control strategy, withreference to the control allocation theory, aim at obtaining the desired pressure ofeach cylinder. Finally, the simulation and experiments demonstrate that the strategyproposed is better than using sliding mode variable structure control strategy withsingle controller, and achieves high-accuracy of the leveling and tracking controlunder slow running.(4) Double-faced pressure hydraulic system is a eight-input six-output system, themodel of the hydraulic mechanism and the slider has a total of20state variable.Based on dynamic control allocation, double-loop control method was designed. Theinner loop is pressure control loop, and the nonlinear internal model controller isdesigned to achieve fast and accurate tracking for the desired pressure. The outer loopis a synchronization control loop, a robust controller was designed to achievehigh-precision position tracking and leveling. Simulation results show that under thesame or two different slider velocity, the system has good dynamic and steady-stateperformance, which verifing the effectiveness of the control method. |
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