Research On Iterative Learning Control Of Underwater Hydraulic Motion Platform

As a test device in the research process of underwater launching technology,the underwater hydraulic motion platform shoulders the important mission of conducting model tests.Obviously,the performance of the test device will determine the accuracy and effectiveness of the test,which will have a direct impact on the economy,efficiency and reliability of the entire research process.As a widely used mechanical transmission method,because of its flexible layout,large transmission power,and infinitely variable speed,hydraulic transmission is particularly suitable for the power mechanism of the large-scale device such as the underwater hydraulic motion platform studied in this paper.The accuracy of the test puts forward higher requirements for the control of the hydraulic system.Using appropriate control strategies will effectively ensure the control accuracy and simplify the control system structure.Based on the basic requirements of the underwater launch test and the load conditions during the test,the actuator and hydraulic system of the underwater hydraulic motion platform have been designed.Furthermore,the transfer function model and state space model of hydraulic system,based on position servo control and speed servo control,have been analyzed and established.For the characteristics of complex load component and repeatable operation of the test device,iterative learning control is introduced as the control strategy of its servo system.Through theoretical analysis and proof of convergence of iterative learning control system,the convergence conditions of this system are obtained.Since the servo system of the underwater hydraulic motion platform has a high-order relative degree,in order to avoid the introduction of high-order differential operations and to facilitate the application in actual engineering project,the method of constructing a virtual system is adopted to obtain a special system which has a one-order relative degree.Therefore,the servo system can be controlled by the first-order differential iterative learning law,so that the servo system has the ability to converge to the desired output with a small enough error.In order to verify the control performance of the hydraulic system under the iterative learning law,the simulation software MATLAB is used to simulate and analyze the control system model.The simulation results show that: when the position servo mode is used and the error threshold is less than or equal to 0.08 rad,or when the speed servo mode is used and the error threshold is less than or equal to 0.035rad/s,the total number of system iterations does not exceed 25.The overall system performance is reliable and the system meets the model test requirements.In this paper,the research methods and achievements of the underwater hydraulic motion platform can be extended to the research of similar position servo systems and speed servo systems which with repeated operation characteristics.It has important theoretical and practical significance for expanding the research ideas of the servo system and improving the control accuracy of the servo system as well.