A State-Space Model Inversion Control Method for Shake Table Systems

摘要

Shake tables used to perform laboratory dynamic testing of structures are commonly powered by hydraulic servoactuators. Due to the inherent non-linearity of servohydraulic systems, advanced control algorithms are required to achieve accurate reference tracking. Traditionally, these algorithms have been based on estimating, at a first stage, the Frequency Response Function of the system and inverting it to yield the Impedance Function. The Impedance is then operated with the desired system output and the result transformed into time domain to obtain an initial estimate of the drive to be fed to the system. This estimate is improved during the test in an iterative fashion. One of the main drawbacks of this approach is the fact that references which are not known beforehand and change in real time, cannot be directly addressed. In this work, a control method based on the inversion of a state-space model of the servo-actuator is presented. First off, a non-linear model of the testing system is developed. Next, a Feedback Linearization procedure to minimize servovalve non linearities is explained and the state-space identification procedure is described. Then, the model inversion method is addressed, together with the state variables estimator required to perform real time control. Finally, the simulation results obtained are discussed. The suggested method shows an excellent performance in numerical experiments; nevertheless, further studies must be undertaken to ensure its successful implementation in actual shake table systems.