Research On Theory And Experiment Of The Generalized Load Simulator Based On Electro-hydraulic Parallel 6DOF Manipulator

Along with the development of national defense and aerospace industry, it's imperative to develop load simulator that can output multi-dimension wrench. However, current researches on load simulator are mostly limited on the independent control of one or several single simulators, which could not meet the needs of wrench simulation. Considering the charater of both hydraulic system and parallel manipulator, this paper adopts electro-hydraulic parallel 6DOF manipulator as load simulator to realize wrench simulation, and adopt Stewart-type compliant mechanism to realize cushion, respectively. The study was carried out from the aspects of principles, features, optimization, control and experiment. The main contents are as follows:In chapter 1, on the basis of referring to domestic and international associated documents, the situation of study on load simulators was summarized, key issues and relative solutions were proposed and compared; current research on parallel 6-DOF manipulators was briefly introduced, its applications in the varies branches were summed up; Considering the charaters of both load simulator and parallel manipulators, the evaluating indicators of generalized load simulator are analyzed and designed. Finally the main study work was proposed.In chapter 2, the components of generalized load simulation system was introduced. The models of load mechanism and compliant mechanism were established repectively. The dynamic model of load mechanism is built, and its inverse dynamic model is deduced as theory evidence for the dynamic analysis of actuators. The static model of compliant mechanism is built, and the analytical expression of stiffness matrix is given by total differentiation method and tiny element method. A iterative method based Newton-Raphson is given, when wrench is known, the real-time and accuracy of iterative method is tested by simulation.In chapter 3, the load workspace of compliant mechanism is researched, which take predefined wrench as constraint, and relative testing process is designed. Take bounded stiffness, global stability and isotropy as purpose, based on Rayleigh quotient analysis, the stiffness performance evaluation functions were designed. Aiming at the non-zero elements in stiffness matrix, the coupling evaluation functions was analyzed and designed. Influence of structure parameters to the evaluation functions was discussed via simulation, and global optimum functions were designed. Finally, genetic algorithm was adopted to optimize the structure parameters of compliant mechanism and satisfying results were obtained.In chapter 4, the dynamic properties and its influencing factors of leg actuator of load mechanism is researched. The single-channel transfer functions of actuators were deduced considering the inverse dynamics of paralle manipulators and nonlinear functions of electro-hydraulic actuator, the influencing factors to its dynamic properties were pointed out. An approximately standardization method of transfer functions was proposed for the convenience of engineering application, together with frequency domain simulation, influence to the dynamic properties by large scale time-varying system parameters was analyzed. The influence of twist of loaded plant to output target variable is investigated; take force and position as target variable respectively, mechanisms of influence were pointed out and guide the control strategy design.Mechanism of multi-channel strong coupling was analyzed, together with simulation analysis, its charaters were pointed out to provid evidence for decoupling control.In chapter 5, the control strategy and algorithem of generalized load simulator were studied. A wrench outer loop/position inner loop compliant control strategy was proposed; this strategy has the convergency of wrench loop and robustness of position loop. To eliminate the influence of twist of loaded plant, its estimated twist was used as synchroballistic to eliminate its influence, simulation results show that this method could make the system work in a near active loading state. Based on structure invariance principle, a feedforward decoupling net was designed, and extended to force feedforward complement, simulation results show that this method effectively remove effection of force disturbance to position tracking. Aiming at the large scale, nonlinear, time-varying charaters of system parameters, a self-learning hierarchical fuzzy logic control system is designed, which take SFLC to adjust elastic factors of inputs of FPID. And training law was designed by using state of tracking error, according to expert experience. Simulation results show that the position error and wrench error gradually converged to zero. And even when system parameters varied in large scale, the control system was still rubst.In chapter 6, experimental platform was built, and Hardware In the Loop simulation system is designed based on computer hierarchical control system. Exploratory experiments were carried out by using control strategies and algorithems proposed in chapter 5, and the experimental results proved the rationality and validity of control system. Based on the present experimental conditions, the load scale index, load accuracy index and dynamic index were tested, which provided reference for further study.In chapter 7, the major work of the study was summarized, and the conclusions and innovations of the study were elaborated. And the future study of the generalized load simulator was also prospected.