A Hydraulic Shake Table for Vibration Testing: Model Parameters Estimation and Validation

This paper presents the study of a test rig, with electro-hydraulic actuation, adopted to characterize vibration isolators (vibration absorbers for machineries, seismic isolators, etc.). The machine was designed primarily to characterize elastomeric seismic isolators in order to find their hysteretic response under periodic deformations and to give its mathematical expression by means of the Bouc-Wen model. The test rig can also be used as a vibrating table in order to simulate horizontal ground motions and to characterize the dynamic behavior of small isolated systems, sensitive to accelerations. An application could be the study of electric cabinets or statues subject to seismic accelerations. In the first application the motion of the shake table of the rig is contrasted by the insulators restoring force; in the second case the actions derive from the relative motion between the shake table itself and the suspended body; in both cases the control system must guarantee the desired motion of the shake table or the desired force acting on it. The goal of the paper is to present a mathematical model of the electro-hydraulic actuation necessary to develop an accurate control system. The model parameters have been obtained using an iterative optimization technique starting from experimental data. The proposed method can be also used in many systems hydraulically actuated, whereby the identification of several parameters, is required to study the system dynamics.