Study Of Theoretical Analysis And Simulation On Electro-hydrostatic Servo Loading System

A multi-channel servo loading system is significant equipment on structure testing for static performance, fatigue performance, detailed fatigue, frontal strength, fracture toughness, fatigue crack propagation performance, corrosion fatigue, structural strength, fatigue/durability, tolerable limit designing, and so on. This kind of testing provides theoretical basis for the design of structures and possesses advantages on reducing developing funds, shortening developing cycle, realizing diverse possible testing situations.In this dissertation, the present achievements on multi-channel electro hydraulic servo loading systems and major control methods on the servo loading systems are introduced at first. Then the main subjects and schemes of the dissertation are mentioned.The loading performance of a symmetrical valve controlled asymmetrical cylinder, the actuator of a multi-channel servo loading system, is different from that of symmetrical valve controlled symmetrical cylinder, which however has few references. The author believes that the servo valve orifice differential pressure is an important determining factor on static and dynamic characteristics of the hydraulic system. It would help us to understand system static and dynamic characteristic, by analyzing the change principle of the double-chamber pressures of valve controlled asymmetrical cylinder in typical loading form. It is found that the double-chamber pressures of the asymmetrical cylinder in a position servo system have a jump when the motion direction is changed, which causes an influence on the steady of system tracking. Then, on how much influence the property of servo loading system caused by the pressure jump, the author has a different view than ever in this dissertation. Based on the work mentioned above, the mathematical model of servo loading system of symmetrical valve controlled asymmetrical cylinder, and the mathematical model of hydraulic inherent part of servo loading system with differential pressure feed-back compensation are set up. The experimental researches show that the mathematical models are perfectly accurate.There are many factors which affect multi-channel electro-hydraulic servo loading properties, some major factors are researched by theoretical analyses and experiment in this dissertation. At first, the influences on system static and dynamic characteristics caused by the different geometric size of cylinder, testing structures stiffness, and output force are analyzed. Secondly, the non-linearity of valve controlled asymmetrical cylinder are analyzed and its compensation measures are discussed briefly. Consequently, some methods for lightening the coupling influence are discussed by enhancing the ability of system resistance disturbance based on regarding the couple as a disturbance. Power cylinder has little leak flow, but has great frictional force, so the author derives the frictionalforce formulation of the cylinder with composite sealing. The frictional force calculated according to the formulation is close to the experimental result. The author found that the output force jumps to the direction contrary to its motion when direction is changed in square loading procedure. The output force ascends smoothly, while descends non-smoothly in sine loading procedure. The author analyzed such phenomenon and discussed its origin.It would provided guidance on designing a system control strategy that analyzing the relationship between the-10° and-90° phase shift index of close loop and the open loop frequency feature. For this reason, the relationship between the -10° and-90° phase shift index of close loop and the open loop frequency feature are analyzed, and the key to enhance the-10° and -90° phase shift index of system close loop are pointed out. A lap-lead control strategy with compensation of local differential pressure feedback and feed forward is designed. Simulations and experiments show that the control strategy has a significant effect on enhancing the system performances index of-10° and-90° phase shift index of close loop.Based on the work mentioned above, the single-channel dynamic loading experimental researches and the single-channel, double-channel and four-channel loading debug of " four-channel automatically cooperated static loading system " are all carried out. The experimental results are consistent with that of theoretical analyses and simulations.