Research On Vibration Characteristics Of Uniaxial High-Frequency Electrohydraulic Shaking Table

Electrohydraulic shaking table is widely applied to the defense industries of aviation, aerospace, weapons, shipbuilding, nuclear industry, or the civilian industries of automotive, construction as a standard test equipment of simulating the environmental vibration. Its technology level reflects a country’s level of industrial development to some extent, thus all countries in the world attaches great importance to the research of electrohydraulic shaking table.Due to the restriction of frequency response characteristics of the electrohydraulic servo valve, the working frequency of conventional electrohydraulic shaking table is to a large extent limited to fairly narrow range. As a result, for some important military equipment, the low-frequency vibration test usually is operated by the electrohydraulic shaking table, vibration, whereas the high-frequency vibration test is done by the electric shaking table. In order to change this situation, upon the background of National Foundation of Natural Sciences,"Research on a New Electrohydraulic Exciting methods and Separate Control Strategy" and a major project of Zhejiang Provincal Natural Science Foundation of China,"Basic Research of Electrohydraulic Excitation Technique of Heavy load and High frequency", the new electrohydraulic shaking table based on2D valve and digital servo valve was proposed to enhance the working frequency by a large margin, the electrohydraulic shaking table can realize the vibration test from low-frequency band to high-frequency band. Therefore, this reasearch has not only the important engineering application value, but also the great theoretical value for the high-frequency electrohydraulic shaking table technology. The main research works and achievements of this paper are as follows:(1) The working frequency of the traditional electrohydraulic shaking table is difficult to improve by the restriction of frequency response characteristics of hydraulic servo valve, therefore the new electrohydraulic shaking table based on single-rod hydraulic cylinder controlled by2D valve and digital servo valve was put forward to enhance the working frequency. The working frequency of the electrohydraulic shaking table can achieve1000Hz.(2) The scheme of high-frequency electrohydraulic shaking table was analyzed, at the same time, the working principle of2D valve and digital servo valve were introduced and their mathematical models were set up. On this basis, the characteristics equations of high-frequency electrohydraulic shaking table were established, so the theoretical foundation for the high-frequency electrohydraulic shaking table was built.(3) The flow equation of throttle orifice of2D valve can not be treated as linear processing since it is a special rotating valve, so the nonlinear system analysis method was adopted for the high-frequency electrohydraulic shaking table, and its system control block diagram was set up. The simulation model was also constructed by the Simulink Toolbox of Matlab, the vibration waveform of uniaxial high-frequency electrohydraulic shaking table were simulated under the different working frequency and axial opening of2D valve. Under the axial opening of2D valve for0.5mm,1mm,1.5mm and the agitating frequency for100Hz,150Hz,200Hz,300Hz,400Hz,600Hz,800Hz,1000Hz, the vibration waveforms of uniaxial high-frequency electrohydraulic shaking table were got. As can be seen from the simulation waveforms, with the improvement of working frequency, the output load of uniaxial high-frequency electrohydraulic shaking table before the resonance point changes from small to big, after the resonance point, from large to small again. This is because the uniaxial high-frequency electrohydraulic shaking table will appear resonance phenomenon when it works in the resonance point, vibration amplitude increases suddenly. By adjusting the size of the axial opening of2D valve, the load amplitude of electro-hydraulic shaking table can be controlled.(4) The energy conservation principle was utilized to research the resonance phenomenon occurred in the uniaxial high-frequency electrohydraulic shaking table. Research results show that the oil in the sensitive cavity of the hydraulic cylinder is equivalent to a dynamic spring, in the working process of electrohydraulic shaking table, the kinetic energy, potential energy and total energy of electrohydraulic shaking table system changes over time. When the electrohydraulic shaking table has worked in the state of resonance, the phase angle of the exciting force is the same with speed, the exciting force of electro-hydraulic shaking table system do positive work, the energy gained from the electro-hydraulic shaking table system reaches maximum value. In order to get the load waveforms of the uniaxial high-frequency electrohydraulic shaking table in resonant state, Under the axial opening of2D valve for0.5mm,1mm,1.5mm and the inertial load of45kg and67.5kg, the resonant waveforms of the uniaxial high-frequency electrohydraulic shaking table were simulated. As can be seen from the simulation results, the load amplitude of electrohydraulic shaking table in resonant state suddenly increases. Finally, the variable resonance theory of the uniaxial high-frequency electrohydraulic shaking table was carried on for the theoretical analysis and simulation study. Single-rod hydraulic cylinder controlled by digital servo valve can realize the change of hydraulic intrinsic frequency by controlling the volume of non-rod chamber. Therefore, the uniaxial high-frequency electrohydraulic shaking table can work under different resonance frequency, the resonance waveforms of electrohydraulic shaking table for different length of non-rod cavity of hydraulic cylinder were simulated. Simulation results show that with the decrease of non-rod cavity volume of the hydraulic cylinder, the resonance frequency of electrohydraulic shaking table increases, the variable resonance theory was proved to be correct.(5) To verify the theoretical analysis and the real vibration waveform of uniaxial high-frequency electrohydraulic shaking table, the experimental system was constructed. Firstly, by changing the rotating speed and the axial opening of2D valve, the vibration waveforms of shaking table were measured under100Hz,150Hz,200Hz,300Hz,400Hz,600Hz,800Hz,1000Hz. The validity of the simulation results was verified. Secondly, The resonance waveforms of shaking table were measured under the different axial opening of2D valve and inertia load to validate the simulation results, the experimental results and simulation results were basically identical with each other; Finally, the volume of non-rod chamber of hydraulic cylinder was changed by the digital servo valve, the resonance waveforms under different non-rod cavity length were measured, the variable resonance theory of uniaxial high-frequency electrohydraulic shaking table was verified.