Seismic isolator test rig control using high-fidelity non-linear dynamic system modelling

This paper concerns the modelling and the control design of a hydraulic actuator employed to carry out shear tests on seismic isolators. The testing machine requires a controller that can ensure the tracking of the target displacement in presence of the unknown restoring force of the isolation devices. To this aim, a model inversion based control, coupled with a feedback contribution, has been designed and implemented. A non-linear model has been derived and adopted for the feedforward synthesis through the inverse dynamics resolution. As a consequence, the feedback control has the function to compensate for the tracking error due to model uncertainties and the unknown isolator reaction force. The choice of a mixed approach allows to design a control action that results minimally invasive on the stability characteristics: it is possible to obtain good tracking results without the increasing of the feedback control gain.