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.

The effectiveness of the designed control has been firstly evaluated by means of simulations and, successively, executing experimental tests on the test rig with and without the specimen under test.