Research On Time Waveform Replication Control Strategy Of Redundant-driven Electro-hydraulic Shaking Tables

Our country is a more-earthquake country.As test platform of vibration environment simulation,shaking table experiment is the most direct and accurate test method to research the anti-seismic performance of large-span structure by replicating various vibration environment.Shaking tables can undertake multi-point collaborative vibration experiment and more truly simulate the seismic vibration of large-span structure specimen,and it becomes the main development trend of shaking table.Upon the background of project of Harbin institute of technology for Beijing University of technology: "Research of redundant-driven electro-hydraulic shaking tables system",the precise time domain waveform replication control scheme are researched.For redundant-driven shaking tables with large-span flex specimen,the system cannot work normally if the degree of freedom(DOF)control scheme is simply expanded to the more dimension,thus twelve DOFs control scheme is proposed.When shaking tables is static at initial position,the biases of servo-valve,machinery installation and electrical measurement not only makes each shaking table produce inner force,but makes the position error between two shaking tables,which leads to deformation of the specimen due to inner force.The formation and influence mechanism of inner force is analysisd and the corresponding inner force suppression method is proposed,which makes two shaking tables' initial positions are same.Simulation results show that the proposed inner force suppression method is right and feasible.During motion process of shaking tables,load eccentric and system parameters difference make dynamic characteristics of two shaking tables different,which leads to their output positions different.The difference has great destructiveness to the specimen.This paper eliminates inner force through synchronization control of two shaking tables.The performance and influence factors of shaking tables control system with cross-coupled synchronization control are analysisd.Combing the SMC with adaptive reaching law and the adaptive control for estimating the bounds of the uncertainty and external disturbance,a new novel adaptive reaching law SMC scheme is proposed and its stability is verified applying Lyapunov stability theory.Simulation verification is carried out and the results show analysis of cross-coupled synchronization control is right and the proposed control schemes have more better synchronization performance and can reduce synchronization error significantly compared with traditional scheme.Shaking tables exist system frequency width limitation,mechanical coupling,parameter uncertainty,hydraulic and specimen nonlinearity,it cannot realize precise acceleration waveform replication only using servo control and need add offline iterative control.System identification is very important in offline iterative control,it affects both the stability and iterative performance.The basic principle and detailed implementation of offline iterative control are introduced and the effect of identification precision on performance is analysisd.Aiming at drawbacks of traditional identification methods,combing the advantages of condition spectrum iterative algorithm,CZT spectrum refinement and wavelet threshold denoising algorithm,the compound system identification method is proposed.Simulation results show that the proposed identification method has high precision,frequency resolution and calculation efficiency and is very suitable for the application of shaking tables offline iterative control.During traditional offline iterative control,the impedance used is always the initial identified impendence and the iterative gain used is same and small gain is usually chosen to ensure system stable.Shaking tables system exists various nonlinearity,and the true model will change during iterative control,thus improve system identification precision will improve system performance to some extent.If the identified phase error is more than 180°,the iterative gain must be negative,and the same gain cannot ensure system stable convergent this moment.The iterative process is calculated in frequency domain,which contains amplitude and phase.By expanding the real domain optimization algorithm to complex domain and combing characteristics of shaking tables offline iterative control,optimal complex domain adaptive iterative control scheme based on complex domain optimization algorithm is proposed.Simulation results show that the proposed adaptive iterative control solves the problem of instability using traditional offline iterative control and it has faster convergence speed under the same system identification precision.Shaking tables experiment system is built applying rapid control prototyping technology.The experiments are carried out to verify the proposed time wavefrom replication control schemes.Experimental results show that the proposed control schemes are correct and feasible,realizing the acceleration time domain waveform replication of shaking tables quickly and stably.