The inputs to many ‘real’ mechanical systems are not readily measurable. For example, the input to the tire patch of the tires of automotive road vehicles is neither measurable nor easy to estimate. As conventional system identification procedures require input measurements or at least estimates of the inputs, a new approach for nonlinear system identification of mechanical systems, in the absence of an input measurement, is presented here. This approach uses a combination of time domain (Restoring Force) and frequency domain (Nonlinear Identification through Feedback of the Outputs (NIFO)) techniques. The time domain is used to characterize the nonlinearities in the system and the observed nonlinear characteristics are used in the frequency domain to build a model of the system. The method is applied to experimental tire-vehicle suspension system data.
Frequency Domain Versus Time Domain Methods in System Identification – Revisited