Frequency versus Time D O M a I N Parameter Estimation: Application to a Slot Milling Operation

The time domain recursive least squares estimation of parameters in the presence of additive output noise of harmonic form leads to biased estimates. However, frequency domain least squares parameter estimation, where the frequency range contaminated by the noise is eliminated, can be used to obtain good parameter estimates. Both the time domain and frequency domain methods are described, and applied to the example of a slot milling operation. A model of the resultant force response to feedrate changes in slot milling, based on previously reported experimental studies, is presented. The force measurement is corrupted by harmonic noise arising from runout on the milling cutter. Simulation studies are performed, using a fiat band width multi-frequency test signal to persistently excite the system. The time domain approach leads to poor estimates as expected, while the frequency domain approach gives good parameter estimates. The advantages and disadvantages of both methods are discussed.