Electro-hydraulic Shaking Table Research Articles

Model reference sliding mode control for two-degree-of-freedom electro-hydraulic shaking table

The multi-axis electro-hydraulic shaking table (EHST) is capable of simulating complex vibration environments to assess product reliability under vibrational excitation. The random vibration control method plays a crucial role in simulating these environments. However, the unmolded disturbances and the nonlinearity of the system have a significant impact on the control accuracy of the EHST. Sliding mode control (SMC) can be used in single-input single-output electro-hydraulic servo systems (EHSS) to attenuate the influence of disturbance forces. The conventional SMC is not suitable for acceleration random vibration control of the multi-axis EHST because the coupling between the axes and the actuators and the null bias of the servo valve are not taken into account. A model reference sliding mode control (MRSMC) is presented in this paper based on the nonlinear dynamic model of the EHST. The MRSMC designed based on the backstepping method and Lyapunov theory is used to compensate for the disturbance forces and the null bias of the servo valve. Experimental acceleration random vibration responses show that the MRSMC enhances the accuracy of tracking the acceleration random signal.

Online learning compensation control of an electro-hydraulic shaking table using Echo State Networks

Electro-hydraulic shaking table (EHST) is widely used to simulate earthquake excitation in structural seismic tests. However, the nonlinear characteristics of the EHST, such as oil flow, friction, and dead zone, often lead to the distortion of seismic wave acceleration tracking and even cause the failure of the test. This paper describes the first application of Echo-State Networks (ESNs) to achieve high-precision seismic acceleration tracking of the EHST. The nonlinear control ability of the conventional three-variable control (TVC) algorithm in the EHST is discussed. An online learning compensation control framework using ESNs for “Transfer System” (The “Transfer System” denotes the nonlinear EHST controlled by TVC) is proposed. The least mean square (LMS) algorithm based on filtered-X is used to train the “ESN-Controller” online, and the initial transients of the “ESN-Controller” are reduced by using an estimation model of the actual “Transfer System” and a conditional switch. The offline iterative control (OIC) and nonlinear signal-based control (NSBC) are taken as the baseline algorithms of the proposed online learning compensation control. Simulation results show that the proposed online learning compensation control achieved excellent control with Pearson correlation coefficients of reference and responses above 99.6%, whereas the OIC and NSBC provided insufficient control. Moreover, the proposed online learning compensation control can also reduce the control error caused by the non-optimal TVC gains in the linear part of the EHST. This work throws new light on the study of the online learning control algorithm of the EHST.

Random Vibration Model Reference Sliding Mode Control of Electro-hydraulic Shaking Table with Valve Null Bias Compensation

Random Vibration Model Reference Sliding Mode Control of Electro-hydraulic Shaking Table with Valve Null Bias Compensation

Error Analysis of Matrix Control of Six Degree-of-freedom Electro-hydraulic Shaking Table

Error Analysis of Matrix Control of Six Degree-of-freedom Electro-hydraulic Shaking Table

Adaptive vibration control on electrohydraulic shaking table system with an expanded frequency range: Theory analysis and experimental study

Abstract Active vibration control using electrohydraulic shaking table (EHST) system is widely applied in civil engineering, automotive industry, environmental vibration testing and other situations where large actuating forces are needed. However, the electrohydraulic actuators (actuating systems) often suffer from drawbacks of limited frequency bandwidth, varying system parameters and so forth. In view of the limits mentioned above, this study hopes to seek out proper solutions to minimize the influence from those drawbacks. We first design a full state feedback-feedforward servo controller, which is able to extend the frequency bandwidth of EHST system, by constructing the analytical models of the servo valve and hydraulic cylinder. Numerical simulations show that the proposed servo controller is able to compensate for the attenuation-band of hydraulic cylinder and thus improve the upper frequency limit of the whole system to a degree that is higher than the natural frequency of servo valve. Afterwards, we propose a frequency domain adaptive power level control (APLC) algorithm for solving the problem of parametric variations of EHST system in application of power level control (i.e., simulate vibration based on certain power spectrum). Numerical simulations show that although APLC algorithm is not able to get exactly same spectrum and waveform at every independent trial, the power level of every trail will finally converge to the target power spectrum. Finally, an experimental validation was conducted based on an EHST system with 3 ton maximum force and 1.2 m × 1.2 m horizontal table. The results show that the proposed algorithms have greatly improved the effective bandwidth and the power level of the controlled system response can finally match the target power spectrum within an accuracy of ±3 dB.

Acceleration tracking control combining adaptive control and off-line compensators for six-degree-of-freedom electro-hydraulic shaking tables

An electro-hydraulic shaking table (EHST) is an essential experimental facility to simulate in real-time actual vibration situations. An adaptive controller combined with off-line compensators is proposed to improve the acceleration frequency bandwidth and tracking accuracy of a six-degree-of-freedom (6-DOF) EHST. A servo controller has been employed to implement acceleration closed-loop and coordinate control of the 6-DOF EHST. A recursive extended least-squares algorithm is employed to identify acceleration closed-loop transfer functions and a zero-phase-error tracking controller is used to design off-line inverse model compensators using the identified transfer functions. However, the off-line compensators cannot compensate in real-time varying dynamics of the 6-DOF EHST; so an online adaptive controller with a least-mean-squares (LMS) algorithm based on a delay compensator is employed. The proposed controller combines advantages of the off-line compensators and the online adaptive controller, which guarantees both a fast rate of convergence of the LMS algorithm and high-fidelity acceleration tracking accuracy of the 6-DOF EHST. Some experimental studies have been conducted on a 6-DOF EHST and experimental results show that acceleration tracking control performances, including the rate of convergence of the LMS algorithm and acceleration tracking accuracy, have been improved compared to a conventional three-variable controller and adaptive controllers.

Adaptive feed-forward compensation for hybrid control with acceleration time waveform replication on electro-hydraulic shaking table

This article presents a high fidelity acceleration time waveform replication (TWR) on an electro-hydraulic shaking table (EHST) using the hybrid control combined with an offline feed-forward compensator and an online adaptive inverse control (AIC). This study applies the acceleration and velocity feedback to improve the steady performance of the EHST, and employs the system inverse transfer function (ITF) of the acceleration closed-loop system to extend the frequency bandwidth and a modeling error compensator to improve the dynamic characteristics. Moreover, the investigation utilizes a Zero Phase Error Tracking Controller to improve the accuracy of the designed ITF. The proposed hybrid controller also utilizes an online AIC for a high fidelity TWR after that the dynamic characteristics has been improved by the feedback and feed-forward controllers. Thus, the proposed hybrid control strategy combines the merits of the offline feed-forward compensation and online AIC. Performance analysis and comparison of the experimental results demonstrate that better replication accuracy with the proposed hybrid control can be achieved in experiments on an actual EHST.

Feed-forward inverse control for transient waveform replication on electro-hydraulic shaking table

In this paper, an improved feed-forward inverse control scheme is proposed for transient waveform replication (TWR) on an electro-hydraulic shaking table (EHST). TWR is to determine whether a test article can remain operational and retain its structural integrity when subjected to a specific shock and vibration environment. Feed-forward inverse transfer function compensation is a useful technique to improve the tracking accuracy of the TWR on the EHST system due to their inherent hydraulic dynamics. Whenever a feed-forward inverse transfer function is employed, it is critical to design the identification accuracy of the inverse transfer function. A combined control strategy, which combines a feed-forward inverse transfer function compensation approach with a simple internal model control (IMC) and a real-time feedback controller, is proposed to minimize the effect of the system uncertainty and modeling error, and further to improve the tracking accuracy of the TWR. Thus, the proposed control strategy combines the merits of feed-forward inverse transfer function compensation and IMC. The procedure of the proposed control strategy is programmed in MATLAB/Simulink, and then is compiled to a real-time PC with Microsoft Visual Studio.NET for implementation. Simulation and experimental results demonstrated the viability of the proposed combined control strategy.

Implementation of electrohydraulic shaking table controllers with a combined adaptive inverse control and minimal control synthesis algorithm

This study presents a combined control strategy for electrohydraulic shaking table (EST) systems. The position frequency bandwidth of the EST system is so low that it results in a worse tracking accuracy during seismic tests, particularly when the frequency bandwidth of the desired position signal exceeds the frequency bandwidth of the EST position closed-loop system. In order to improve the position tracking accuracy, a combined control strategy is proposed, which utilises a recursive extended least square (RELS) algorithm to offline or online estimate the position closed-loop transfer function of the EST system, then uses the estimated transfer function to offline or online yield a feedforward inverse controller for extending the position frequency bandwidth, finally, employs a minimal control synthesis (MCS) algorithm to further improve the tracking performance of the EST position system. The proposed control strategy combines the merits of offline or online feedforward inverse compensation and adaptive control. The procedure of the proposed control strategy is programmed in MATLAB/Simulink, and is then compiled to a real-time PC with Microsoft Visual Studio.NET for implementation. A better tracking performance for the proposed control strategy is achieved in experiments by using actual EST.

Tracking control of an electro-hydraulic shaking table system using a combined feedforward inverse model and adaptive inverse control for real-time testing

An electro-hydraulic shaking table (EHST) is used for real-time replication of situations that occur in civil and architectural engineering, the automotive industry, and earthquake resistance testing. EHSTs are able to generate a large force at high speeds over a wide frequency range and this feature makes them invaluable in performing vibration tests. Unfortunately, due to the inherent dynamics of the EHST system’s hydraulics, the output response of an EHST system displays magnitude attenuation and phase delays in response to displacement and acceleration commands. A feedforward inverse model (FFIM) combined with adaptive inverse control (AIC) is proposed to improve the tracking performance of the EHST following specified displacement and acceleration commands. The proposed control strategy utilizes a FFIM to extend the EHST system’s frequency bandwidth and uses AIC based on a recursive least squares (RLS) algorithm to adaptively adjust the time domain drive signal of the EHST servo controller and improve the tracking accuracy. Experimental and simulation results demonstrate the effectiveness of the proposed combined control strategy.

A three-link arm type vibration control device using magnetostrictive actuators

In this paper, a three-link arm type vibration control device consisting of three links, two mounting plates and four universal joints incorporating giant magnetostrictive actuators is proposed. The device is able to produce controllable friction forces and torques in three translational and rotational directions, respectively. A trial vibration control device was made and the resisting force characteristics in three translational directions were measured. The seismic responses of a two-degree-of-freedom system and a three-degree-of-freedom system consisting of a mass and four coil springs and supported by the device were also measured using a two-dimensional electrohydraulic shaking table. The effects of the vibration suppression of the device are substantiated experimentally and analytically.

Application of H2 Control to an Electrohydraulic Shaking Table.

We have applied H2 control to an electrohydraulic shaking table. In the application of H2 control to this device, we propose a method in which the H2 controller is designed based on a model of a whole analog feedback control system to make as much use as possible of a loop shaping function of robust control. This method is very practical because no changes in the analog feedback system are needed. As a result of the application to a 1-axis electrohydraulic shaking table of National Research Institute for Earth Science and Disaster Prevention, the Characteristics of a position control have been improved by 30% from 10.6 Hz to 13.6 Hz.