Describing function approximation of a two-relay system configuration with application to Coulomb friction identification

The paper shows the use of describing function approximation for identifying a relay nonlinearity of the plant. For this purpose, the system configuration contains an inherent relay (plant nonlinearity) and another relay introduced in the loop, to control the system. The frequency behaviour of this two-relay system configuration is reported-the inherent relay models Coulomb friction while the other relay controls the system's output and produces limit cycles. The harmonic balance method yields an algorithm for estimation of Coulomb friction tested on illustrative examples, both in simulation and on a physical plant. (C) 2002 Elsevier Science Ltd. All rights reserved.