| Passive force loading system is used in the laboratory environment can provide a variety of loading forces for the experimental subjects. In the control of steering a ship, passive loading system is used to simulate the load force generated underwater streams. Owing to the low time constant, high precision, fast response, easy to control and so on, the way of electro-hydraulic load is used for passive force loading system more and more. In this paper, the basis for the study is electro-hydraulic servo positioning system, looking out for a kind of passive force loading system can simulate elastic force which is closely related to position system. The performance of electro-hydraulic passive force loading device is mainly affected by two aspects, one is the inherent characteristic of system itself, and the other is the extraneous force caused by active movement.In this paper, by consulting a large number of documents, the research for the electro-hydraulic passive loading system at home and abroad were summarized; the advantages and disadvantages, with the comparison and synthesis of ideas, were analyzed and then the research direction of this paper were determined.Firstly, to eliminate the extraneous force and to improve the loading precision of the electro-hydraulic loading simulator, a new designed spring force loading simulator, which is added an electro-hydraulic servo valve as the compensator valve, is proposed. Using the theory of hydraulic bridge and hydraulic resistance, a valve for compensation, an electro-hydraulic servo valve, is employed to discharge the forced flow. The influence of the extraneous force is overcome effectively and the performances of system are improved. Thus a complete physical model and system configuration are established.Secondly, giving full consideration to position system and force loading system of the characteristics of the coupling and influence between each other, the appropriate hydraulic component element parameters are selected, and its mathematical model is established. With the mathematical model, the force of passive loading system is analyzed thoroughly, the causes of extraneous force are determined and the effectiveness of the inhibited extraneous force method is proved. The simulation is carried out with the physical parameters under the environment of Simulink. The results show that the simulator can provide the spring force accurately to the position system and the lag time in the system response is about 0.03 s and error of output force is in the range of 1.3%。Finally optimize the system by improving the control strategy. The fuzzy PID is used to control electro-hydraulic position servo system to improve the system response speed and position accuracy. BP neural network PID is employed to control force loading system to accelerate response speed and effectively suppress extraneous force. By optimizing the control strategy, the amplitude error of the system is reduced to 1%, the phase lag is reduced to 0.02 s or less. The accuracy and stability of the passive force loading system in this paper is improved immensely. |
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