Research On Control Technologies Of Simulation Of Vibration Environment Using Hydraulic Vibration Table

Vibration environment simulation has been applied in the fields of the aspects of aeronautics, astronautics, national defense and so on. Now the vibration environment simulation is an important means for increasing the reliability of the products. By simulating the particular vibration environment that products will exposed to in use, transform and storage using the specific test equipments and the control technologies, weakness of design can be early found and the information for correcting design is obtained in time.Upon the background of the project"Digital control system rebuilding of single horizontal direction hydraulic vibration table"which is developed by IEST (Institute of Electro-hydraulic Servo Simulation & Test System) of Harbin Institute of Technology, the key control technologies of the random and sine vibration environment simulation has been theoretically and experimentally studied,in order to enhance the capability of the hydraulic vibration table in the field of the vibration environment simulation.The real time control unit of the hydraulic vibration table consists of the servo controller and the vibration controller. The servo controller is the basic to provide vibration environment simulation by a digital closed loop. Due to the low resonance frequency and small damp ratio of the power element, the Three Variable Controller (TVC) is proposed in order to extent the frequency band and improve system stability. Considering the effect of the servo valve dynamic characteristics on the performace of the electro-hydraulic shaker, the root locus method is used to design the TVC parameters. And the validity of this method is confirmed by experiment.Gaussian random process is common in engineering. The power spectrum density (PSD) is equivalent condition. But the signal to excite vibration table must be in time-domain, therefore how to transform the PSD into the time-domain signal is the first work to simulate this kind of vibration environment. This paper firstly presents an overview of numerical simulation techniques to this kind of vibration environment. Then a numerical simulation method based on the Auto-Regressive (AR) model and the Ziggurat algorithm is proposed. The Stationary, ergodic and independent Gaussian White Noise is filtered by the AR model constructed in real-time, so that the accurate simulation of drive PSD is implemented. Simulation results show that this simulation algorithm has higher precision and low computation complexity, and it can also meet requirement about the statistics, besides, it can support xPc Target Rapid Control Prototyping (RCP) technology, so that the process generating time-domain drive signal is greatly simplified. On the basis of the numerical simulation, considering the effect of the dynamics of actuator and load on control accuracy, it is necessary to update drive PSD constantly. The PSD of the response signal at control points is not only the feedback quantity but also the control quantity. The estimated value of the quantity is closely related to the degree of freedom (DOF). So, the statistical characteristics about the response PSD estimation are analyzed in detail. An optimal method for averaging response PSD is proposed. The optimal method has increased confidence and accuray of the estimated response PSD, and has shortened the loop time,so that the real-time characteristics of the iterative process is increased.Classical spectrum equalization technique, either log-domain integral or linear- domain integral, corrects the control error by the closed loop feedback. In order to guarantee the stability, the feedback gain is usually enough small theorefore may result in very slow control system convergence. To solve the limitation, the frequency-domain filtered-X variable step-size least mean square (LMS) algorithm is introduced into control process, and thus adaptive control strategy of random vibration for PSD replication is proposed. The system impedence function,which is the inverse of the frequency response function, is refined in frequency-domain in real-time. The improved system impedance function has allowed a higher feedback gain parameter, which can speed up equalization process and guarantee the stability. The simulation results have validated that the control strategy has better stability, higher convergence rate and control precision.Swept sine testing can be used to determine resonance frequency and damage frequency, and to conduct durability testing. To non-stationary characteristics of the swept sinewave exciting signal, the swept-sine wave generation has been accomplished by solving the governing differential equation of the phase function associated with the linear sweep and the logarithmic sweep mode. The digital tracking filter is designed based on the signal synthesis method. This synthesis method has increased the accuracy of the output signal and has the suitability of heterodyne generation. The purpose of the heterodyne is to translate the response signal spectrum about 0-Hz. The term at DC represents the real and imaginary components of its AC amplitude.The 0-Hz intermediate frequency detector implements tracking filter by a low-pass filter that extracts the DC component. The simulation results have proved that the proposed digital tracking filter can be applied to time-variable spectral analysis of the swept-sine wave. On the other hand, the conventional amplitude control method can not be suitable for various frequency segment and various the system characteristics due to a fixed compression ratio. The optimal control concepts is applied to design an integral controller with a variable compression ratio (VCR) for frequency-devison section so as to provide better control accuracy. Simulation results have proved the effectiveness of the designed controller.The multi-level computer control system for the random vibration PSD replication and swept sine vibration is established using RCP technology based on xPc Target. A series of experiments are respectively carried out using various control strategies. Experimental results further proved the conclusions from the simulation study, and validated that the proposed control techniques are advanced and effective.