Research On The Friction And Leakage Properties Of Hollow Axis Hydraulic Servo Motor Applied On Flight Motion Simulator

Hollow-axis high precision electro-hydraulic servo motor is a drive component which applied in inner frame of flight motion simulator and its performance directly determines fidelity of simulation results. With the development of aerospace science and modern military technologies in China, the demands on technical performance, application range and application requirements of simulator and electro-hydraulic drive components become higher and higher. For example, In the semi-physical simulation of the massive or large axial length missile seeker, the hollow-axis electro-hydraulic servo motor will be needed. Since the control strategy has been able to maximize the capacity of the existing equipment, some basic research of hydraulic servo motor will be significant such as the design optimization for seal structure and seal material, leakage control and measurement and so on. Because that will overcome the problem of restricting the further development and application of hydraulic servo motor. After synthesizing numerously relevant literatures and materials, the performance and structure of electro-hydraulic servo motor applied in flight motion simulator are summarized. Some key technologies of hollow-axis hydraulic servo motor are introduced and the research contents basic on these technologies are put forward.The dynamic model of the hollow-axis electro hydraulic servo motor is constructed using relevant theories, and the nonlinear mathematical model of valve-controlled motor servomechanism is derived, which include the nonlinear friction, internal and external leakage. The completely mathematical model of hollow-axis hydraulic servo motor is established. Considering the high friction torque and severe slip-stick characteristic, two aspects were studied carefully to compensate the friction torque of hollow-axis hydraulic servo motor, which include optimization of seal material and design control strategy. The friction and wear properties of seal material is studied via experimental theory and the optimum proportion of compound materials for the improvement of low speed tracking performance can be chosen, which is a compensation based on the mechanism of tribology. Furthermore, slip-stick mechanism and different friction model are discussed and adaptive friction compensation based on LuGre model is applied here.Experience shows that the combined seals which are consist of PTFE and O-ring play an important role in the determination of friction and leakage characteristics of hydraulic servo motor. However, the designer still rely almost completely on empirical method for the combined seals in hydraulic servo component, which can not reflect the relation between parameters of seals and leakage. In this paper, the leakage characteristic of hollow-axis electro hydraulic motor is studied in two aspects. Firstly, the mechanism of leakage and working principle of dynamic self-compensation combined seals are analyzed. The line contact model of dynamic self-compensation combined seals is setup and nonlinear finite element analysis software ADINA is applied here to solve contact stress under different working conditions. Based on the results the leakage across the seals and the hydrodynamic viscous force are calculated via"Inverse Hydrodynamic theory". Secondly, the model of internal leakage and external leakage are setup and the effect on friction and low speed tracking performance are proposed. The principle of Extended Kalman filter(EKF) is introduced and EKF is employed to estimate both internal and external leakage. The optimized pressure in two chambers can be estimated by reconstruction of the system state and the measurement of internal and external leakage can be achieved by establish the mapping relation between pressure estimation error and leakage.The friction of hollow axis hydraulic motor is measured in test rig to verify the result of theory calculation and make it perfect. The parameters of friction model are identified by experiment and adaptive control is employed to compensate the friction torque of hollow axis hydraulic motor based on LuGre model. A practical measurement scheme is proposed to measure both internal and external leakage automatically and the leakage property can be study via this way. The theoretical analysis is verified and improved by comparing the results of FEM calculation and EKF estimation with experimental measurement.