| Launch vehicle fuels are generally highly toxic,flammable and explosive,so the automatic propellant filling technology has attracted wide attention in various countries.In essence,the automation of rocket fuel filling is to realize the automatic docking and shedding of umbilical connectors between the ground mechanism and the rocket.However,due to the wind load,the umbilical connector interface on the rocket will swing with the rocket body to a certain extent,so the automatic umbilical connector system needs the dynamic docking and follow-up capabilities,which makes the design and control of the automatic umbilical connector system very difficult.According to the research background of the automatic umbilical connector system,and combined with the specific application conditions,this paper proposes a scheme of the automatic docking umbilical connector system which contains an electro-hydraulic servo3-DOF(degrees-of-freedom)translational parallel platform and a 6-DOF compliant mechanism with spring branch chain.However,the servo control of the automatic umbilical connector system is very complex.Firstly,the electro-hydraulic servo parallel platform itself has strong nonlinearities and uncertainties.At the same time,due to its multi-input multi-output system nature,it also has dynamic coupling and kinematic coupling in the joint space,so its high-precision servo control is still a difficult task.Meanwhile,during the docking operation,there will be a certain interaction force between the ground mechanism and the rocket body.In practical application,if the controller lacks good anti-disturbance ability,it will probably cause the divergence and instability of the system,which makes the docking trajectory tracking control more difficult than the traditional non-interactive trajectory tracking control.Therefore,this paper studies the high-performance servo control of the electro-hydraulic parallel platform systematically and deeply.Specifically,the research work of this paper mainly includes the following aspects:(1)When the rocket is subjected to the wind load,the movement of the umbilical connector interface on the rocket is mainly reflected in the three translational degrees of freedom,and the movement in the three degrees of rotational freedom is small(? ±0.25°).In view of this characteristic,a new type of umbilical connector system based on an electro-hydraulic servo 3-DOF translational parallel platform and a 6-DOF compliant mechanism with spring branch chain is proposed.Subsequently,the docking trajectory planning is completed based on this docking mechanism,and the docking simulation under various working conditions is carried out based on the ADAMS software.Simulation results show that the system has good docking characteristics.Even when the compliant mechanism is in the maximum compensation range,the docking performance of the system is still far better than the index requirements.In addition,according to the simulation results,the load characteristics of the hydraulic actuators are analyzed,and the design of the hydraulic servo system of the parallel platform is then completed.(2)A complete nonlinear mathematical model of parallel platform is established,which includes the kinematic model and dynamic model.For the kinematic modeling,the forward and inverse position models of parallel platform,and the inverse models of velocity,acceleration and jerk are established.Meanwhile,the inverse dynamic model of parallel platform in workspace is established based on Kane method.Then the dynamic model in joint space is also derived.Subsequently,the state space equation of the hydraulic actuator is established based on the force balance equation of the hydraulic cylinder,the flow continuity equation and the flow equation of the servo valve.Furthermore,the nonlinear,uncertain and coupling characteristics of the electro-hydraulic servo parallel platform are analyzed.Based on these models and analysis work,the foundation can be laid for the following highperformance controller design.(3)Aiming at solving the dynamic coupling among joints of the parallel platform,the decentralized control method is studied.Firstly,a decentralized robust control strategy for parallel platform based on disturbance estimation is proposed.Before controller design,a disturbance estimation method based on extended state observer(ESO)is proposed for a class of SISO systems with unknown disturbances,and its stability is then analyzed.Subsequently,by treating the external disturbances and the model uncertainties as the joint matched and unmatched uncertainties,two extended state disturbance observers are designed to estimate and compensate them synchronously and accurately.Then,the indirect dynamic decoupling of the system in joint space is realized.Meanwhile,the robust control law is used to suppress the estimation error during the controller design.The simulation results show that ESOs has good estimation and compensation abilities for both matched and unmatched uncertainties.Compared with PID control and traditional single ESO based decentralized control,it has better trajectory tracking performance.In order to further improve the dynamic decoupling performance of the system in joint space,a decentralized indirect adaptive robust control(DIARC)strategy based on joint force measueing is proposed.In this method,the force sensor is used to measure and compensate the joint external disturbance directly,and then the direct dynamic decoupling of the system in joint space can be realized.At the same time,the controller adopts the parameter adaptive law and the nonlinear robust control law to realize the on-line identification of the joint's uncertain parameters and the effective suppression of the uncertain nonlinearities in system respectively.The controller is globally stable in theory,and the system has asymptotic tracking performance when the joint only has its own parameter uncertainties.The simulation results show that the force measuring has better decoupling performance than the disturbance observer.When the joint has no its own uncertain nonlinearities,the system has better tracking performance,and the uncertain parameters have good convergence characteristics.However,when the joint contains uncertain nonlinearities,the tracking accuracy deteriorates to a certain extent.(4)A decentralized continuous integral robust control(DCIRC)strategy combining force measuring and disturbance estimation is proposed to guarantee the asymptotic convergence performance of the system when both the external disturbance and the joint's own model uncertain nonlinearities exist.This method realizes the dynamic decoupling of the parallel platform in joint space through the force measuring,and introduces the disturbance observer and the continuous integral robust control law to realize the accurate estimation of the jonint's own model uncertainties and the effective suppression of the observation error.In theory,this strategy can guarantees the system to achieve global asymptotic tracking performance under the premise of continuous control input and low feedback control gain.The simulation results show that the control strategy can further improve the tracking performance and antidisturbance ability of the system in joint space by improving the disturbance compensation and suppression ability of the joint.(5)A robust synchronous control strategy for parallel platform based on cross-coupling control method is proposed to solve the kinematic coupling among joints of the parallel platform.Firstly,the decoupling dynamic model of the parallel platform in joint space is established by using the disturbance observer.Secondly,by using cross-coupling control method,a synchronization error is defined to describe the synchronization degree among joints,and then a robust controller is designed to ensure the convergence of joint trajectory tracking error and the trajectory synchronization error at the same time.The simulation results show that the robust synchronous controller can effectively improves the trajectory tracking accuracy of parallel platform in the workspace by improving the synchronization degree among joints without affecting the joint tracking performance.(6)The principle prototype of the automatic umbilical connector system is built and the various experiments are carried out.The experimental results show that the prototype scheme is reasonable and feasible,and the proposed control algorithms can meet the requirements of the docking performance of the system.The principle prototype has reached the design goal in the pre-research stage,which establishes the foundation for the next engineering application of the automatic umbilical connector system. |
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