Shaking Table Control Research Articles

The feedforward minimal control synthesis algorithm and its application to the control of shaking-tables

Since the early 1990s, research in Europe, the Far East, and America on the control of shaking-tables for seismic investigations has been made all the more urgent, following a series of catastrophic earthquakes across the globe. The fidelity of the results from shaking-table tests, on which many designs of earthquake-proof systems depend, is largely governed by the accuracy of the controlled motion of the table and the test structure. Coincident with these events has been the development of more advanced, adaptive, control systems that provide an opportunity for high-precision motion control in the face of dynamic interaction, non-linearity, and parameter variation within the test system. This paper discusses a new adaptive control algorithm, called the feedforward minimal control synthesis (FFMCS) algorithm, which offers improved shaking-table control, when used in conjunction with a more conventional fixed-gain controller. FFMCS has been developed as part of a joint Japan-UK initiative, motivated by prior testing of shaking-tables located in both Japan and Europe. This paper describes the dynamic modelling of a typical shaking-table, in order to emphasize the key features required of its controller. Also detailed are the three-variable control (TVC) strategy, a conventional algorithm that is widely used within shaking-table test facilities, together with the development and stability proof of the FFMCS algorithm. A motivating and comparative implementation study of FFMCS on the control of a simple single-axis servohydraulic rig is also included, as well as comparative simulation studies on the previously modelled shaking-table.

Improvement in Shaking-Table Control Performance by Real-Time Compensation of Reaction Force Caused by a Specimen (Verification with Large-Scale Shaking Table)

We have developed a new control method for a shaking table that compensates the reaction force caused by a specimen in real-time. In this work, we executed a series of verification tests to confirm the effectiveness of the developed method with a large-scale shaking table with a payload of fifty thousand kilo-grams. The reaction force was calculated from the drive force of actuators and accelerations of the table. A compensator was designed to cancel any reaction force with frequency components ranging from DC to ten hertz. The specimen used for the tests consisted of a twenty-thousand-kilo-gram mass and four columns to support the mass above the table. When the specimen was excited with a large acceleration, the columns were deformed to a plastic range. The characteristics of the specimen, therefore, became non-linear. The results of these tests show that the compensator successfully cancelled the reaction force. Therefore, the control method is effective for using a shaking table with a specimen whose characteristics change during excitation.

NONLINEAR SHAKE TABLE IDENTIFICATION AND CONTROL FOR NEAR-FIELD EARTHQUAKE TESTING

The primary focus of a structural shake table system is the accurate reproduction of acceleration records for testing. However, many systems deliver variable and less than optimal performance, particularly when reproducing large near-field seismic events that require extreme table performance. Improved identification and control methods are developed for large hydraulic servo-actuated shake table systems that can exhibit unacceptable tracking response for large, near-field seismic testing. The research is presented in the context of a 5-tonne shake table facility at the University of Canterbury that is of typical design. The system is identified using a frequency response approach that accounts for the actual magnitudes and frequencies of motion encountered in seismic testing. The models and methods developed are experimentally verified and the impact of different feedback variables such as acceleration, velocity and displacement are examined. The methods show that shake table control in testing large near-field seismic events is often a trade off between accurate tracking and nonlinear velocity saturation of the hydraulic valves that can result in severe acceleration spikes. Control methods are developed to improve performance and include both acceleration and displacement feedback to reduce the acceleration spikes, and record modification, where the reference signal is modified to conform to the shake table's operational parameters. Results show record modification gives exact tracking for near-field ground motions, and optimal system response for reference signals with velocity components greater then the system capabilities. Overall, the research presents a methodology for simple effective identification, modelling, diagnosis and control of structural shake table systems that can be readily generalised and applied to any similar facility.

Improvement of Shaking-Table Control by Real-Time Compensation of Reaction Caused by a Specimen (2nd Report, Verification with Large Scale Shaking Table)

We have developed a new control method for a shaking table that compensates the reaction force caused by a specimen in real-time. In this work, we executed a series of verification tests to confirm the effectiveness of the developed method with a large-scale shaking table with a payload of fifty tons. The reaction force was calculated from the drive force of actuators and accelerations of the table. A compensator was designed to cancel any reaction force with frequency components ranging from DC to ten hertz. The specimen used for the tests consisted of a 20-ton mass and four columms to support the mass above the table. When the specimen was excited with a large acceleration, the columns were deformed to a plastic range. The characteristics of the specimen, therefore, became non-linear. The results of these tests show that the compensator successfully cancelled the reaction force. Therefore, the control method is effective for using a shaking table with a specimen whose characteristics change during excitation.

Shaking-Table Control by Real-Time Compensation of the Reaction Force Caused by a Nonlinear Specimen

An improved shaking-table control method has been developed. This method compensates the reaction force caused by a nonlinear specimen in real time, and thus maintains a desired table acceleration. To do so, it identifies the difference between the desired and the actual transfer characteristics of the shaking table, then compensates for the difference. Because the required time for this combination of identification and compensation is less than one second, the method can compensate, in real time, for the disturbance caused by a nonlinear specimen. By means of a series of experiments, it is confirmed that the method can maintain a desired table acceleration even when a nonlinear specimen is under excitation.

Development of Control Method for Shaking Table Considering Dynamic Interaction with Non-Linear Structures (2nd Report, Medium-Scale Shaking Table Control Experiments and their Theoretical Understanding)

Development of Control Method for Shaking Table Considering Dynamic Interaction with Non-Linear Structures (2nd Report, Medium-Scale Shaking Table Control Experiments and their Theoretical Understanding)

303 振動台制御を目的とした加速度出力フィードバックによる 3 変数制御器設計手法について

303 振動台制御を目的とした加速度出力フィードバックによる 3 変数制御器設計手法について

Improvement of Shaking-Table Control with Adaptive Filter(2nd Report,Verification with Large Scale Shaking Table)

A new control method for a shaking table-which compensates the reaction force caused by a non-linear specimen in real-time was previously developed. This method estimates the error in the transfer function by using the recursive least-square method, then the error is compensated by an adaptive filter. Verification tests with a large-scale shaking table controlled by this method were carried out in the present work. Even when the characteristics of the specimen change during excitation, the desired pseudo-velocity response spectra of the table acceleration which is three dimensional artificial earthquake wave can be achieved with the adaptive filter. The results of these tests show the effectiveness of this method.

Improvement of Shaking-Table Control by Real-Time Compensation of Reaction Force Caused by a Specimen. 1st Report. Scheme for Controller Design and Verification by Simulation.

An improved shaking-table control method that can compensate the reaction force caused by a non-linear specimen in real-time has been developed. This method measures the reaction force and generates a drive force to cancel it. The compensation signal to generate the drive force is calculated by a reaction-force compensator, which consists of the inverse transfer function of the shaking-table actuating system, a filter to reduce the noise in the measured reaction-force signal, and a proportional element to stabilize the shaking-table characteristics. The motion of a shaking table loading a non-linear specimen was simulated. This simulation shows that the compensator effectively cancels the reaction force and that increasing the SN ratio of the measured reaction force increases this effect. Moreover, two means to measure the reaction force are presented. The first means are the loadcells between the table and the specimen. The second means are the loadcells between pistons and the table.