Coupling Analysis And Its Control Strategy Of Redundant Multi-axis Shaking Table

China is a country prone to earthquakes. Shaking table, the equipment simulating seismic signals in lab environment, is widely used in vibration test for high-rise buildings, bridges and large structures. Redundant multi-axis shaking table can solve the accuracy problems from small size scale model test. Meanwhile, it is capable of analyzing damage mechanisms of large-scale structures under earthquake condtions and evaluating the overall seismic capacity.Upon the background of National Natural Science Foundation of China: "Inner Force Coupling and Its Rejection of Seismic Simulator with Hyper-Redundant Parallel Actuation and Long Stroke" and " The Study on Mode Modeling and Force Balance Control Algorithm in Seismic Simulator with Hyper-Redundant Actuation and Long Stroke ", the corresponding decoupling control strategies of redundant shaking table aiming at flexible foundation coupling, internal forces coupling and dynamics coupling are researched.In order to reduce the acceleration distortion caused by nonlinear flow of servovalves in a redundant hydraulic shaking table, a nonlinear hydraulic model is designed and nonlinear flow compensation is achieved according to the inverse model of the nonlinear equation of flow and pressure. The effectiveness of the method is verified through simulation. At the same time, the three variable control(TVC) of the degrees of freedom(Do Fs) is designed based on the state feedback in state space. The stability condition of TVC, as well as the control parameters corresponding to the ideal third-order transfer function, is also analyzed.As the increase of flexible from the reaction wall of redundant shaking table, the overall features will be affected, which results in the reduction of bandwidth of the shaker. A model of hydraulic shaking table with flexible foundation coupling is built. The relationship between integrated natural frequency, hydraulic natural frequency and foundation natural frequency is discovered through the modal analysis of two degrees of freedom equivalent system, and the impact on dynamic characteristic of the system with different flexible parameters are analyzed. Then, a improved feedforward control is provided instead of traditional TVC. Simulation result shows that the bandwidth of the system with flexible foundation coupling can be effectively expanded by the modified feedforward control method. Meanwhile, in order to improve the tracking accuracy of high-frequency sinusoidal signal and avoid the complicated parameter settings of traditional amplitude and phase control, a novel amplitude and phase control strategy is proposed. The amplitude error, phase error and center position error of sinusoidal signal are identified in the time domain. Combined with the identification error, iterative sequences of the three parameters are established, and a piecewise iterative rate is given by taking both the rapidity in low frequency and stability in high frequency into account. The proposed identification and iteration are realized through the State Flow programs.Hydraulic actuators of redundant shaking table are much more than the Do Fs. As the dynamic characteristics of the actuators are inconsistent, it may lead to severe coupling of internal forces. In order to analyze the coupling characteristics of internal forces, an internal force coupling model under Do F control of a single redundant system is established at first. It provides the relationship among the steady internal forces, servo valve bias, mounting accuracy, measurement error and platform rigidity. And then, the internal forces are simulated under Do F control through coupled dynamics models by meshing the platform in horizontal and vertical directions. Finally, according to the relationship between static internal force and servovalve bias, the static internal force integral compensation control strategy is proposed to eliminate the static internal forces. While the dynamic internal forces, however, are reduced through dynamic pressure equalization control. Under the analysis of internal force space, internal forces calculated by force synthesis matrix are compensated in a closed loop and decomposed to the inputs of the servovalves through redundant deformation matrix. Simulation results show that this control method can effectively reduce the static and dynamic internal forces of a redundant hydraulic shaking table, and it has less control parameters comparing to traditional internal force control.Due to the eccentric load of redundant shaking table, dynamic coupling occurs between the various degrees of freedom. The dynamic model of redundant shaking table is built. Coupling force observaction based on coupling model is introduced to the Do Fs control structure. The coupling forces are controlled as disturbance forces on hydraulic system by distributing it to each actuator through Jacobi matrix transformation. Decoupling control is given based on the dynamic model as well as a feedforward disturbance force compensation control strategy. However, due to the fact that differentiating acceleration which contains large noise is needed in decoupling control based on dynamic model, modal decoupling control is given. Modal equation of redundant shaking table is given by considering hydraulic cylinder as a hydraulic spring. Through standard modal matrix and its inverse matrix, the redundant shaking table is controlled in non-coupling modal space instead of Do Fs space. By analyzing the relationship between the modal matrix and the coupling characteristics of different modal Do Fs, an experimental method is given for determining the modal matrix. Simulation analysis shows that compared with decoupling control based on dynamic model, the modal space decoupling control can more effectively reduce the dynamic coupling among Do Fs of the redundant shaking table.A control system of the redundant shaking table is developed using rapid control prototyping technology based on x PC Target. Detailed experimental analysis and research are carried out on the proposed coupling characteristic analysis and decoupling control strategies. Experimental results demonstrate that the proposed decoupling control strategies are effective and advanced.