| The lifting platforms play an important role in scientific experiments and industrial production.As an important transmission method,hydraulic transmission is widely used in the driving device of the lifting platform due to its inherent advantages of fast response,easy control,large driving force,high power density and stepless speed regulation.Limited by factors such as load or space position,the lifting platforms usually need to be driven by multiple actuators,which brings about the synchronization control problem of multiple hydraulic actuators(hydraulic cylinders or motors),which is one of the hot issues in the research of hydraulic control technology.The lifting platform studied in this article comes from an equipment test platform.According to the requirements of the test norm,the hydraulic system and its control system was designed,and the mathematical model of the control system based on the transfer function and the state space was established respectively.In order to improve the dynamic performance of the single-channel hydraulic system,the state feedback theory is used to configure the closed-loop poles of the system.The Luenberger state observer design method was adopted to reconstruct the state variables,and the state feedback based on the state observer was realized,for the sake of reducing the complexity and implementation cost of the state feedback system,and improving its engineering feasibility.The robustness of the state observer and the stability of the system was studied by means of simulation.The results show that as the distance between the closed-loop poles of the system and the origin in the complex plane increases,the robustness and stability decrease,but the dynamic stiffness of the system is improved.In order to improve the anti-load interference ability and control accuracy of the system,the idea of feedforward compensation was introduced.With the help of the design idea of the dimensionality reduction observer,the speed reduction caused by the load force is used as the augmented state variable,and the augmented dimensionality reduction state observer is designed,which avoids the direct measurement of the load force,and compensates the system for the perturbation by feedforward compensation.And the availability of this method was verified by means of simulation.Aiming at the problem of large synchronization error of each hydraulic cylinder caused by the eccentric load of the system,combining the advantages of the existing master-slave control and cross-coupling control,a master-slave coupling synchronization control structure is proposed.Select the control loop whose current output is closest to the control command as the master loop.The deviation between the output of the other three loops and the master loop is negatively fed back to each control input after the compensation link,so as to achieve the effect of synchronous control.The simulation results show that the control strategy can significantly improve the synchronization accuracy and synchronization error convergence speed of the system during operation.The idea of improving the dynamic performance of the system through the state feedback based on the state observer and predicting the load disturbance based on the dimensionality reduction observer based on the augmented system for the electrohydraulic proportional position system can be applied to other electro-hydraulic automatic control systems.The engineering practicability of the proposed master-slave coupling synchronization control strategy also shows high practical value,which provides some benefitial references for the selection of synchronization control strategies for multiple actuators. |
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