The prediction of modal parameters of a machine-tool structure is important for an accurate knowledge of the dynamic behavior during machining. Usually, the characterization is carried out through
an experimental modal analysis with impact and/or shaker tests. However, the excitation, artificially,
created by a hammer or a shaker is difficult even impossible to conduct on machine-tool structure or
robot structure during machining. These tests are thus performed on machines in rest. Unfortunately,
the conditions of a machine in rest are significantly different from its real conditions during machining
and accordingly its dynamic properties in service are different from static results of impact or shaker
tests.
This paper proposes an identification methodology based on operational modal analysis for a machinetool structure during machining operation. The modal identification is done by the transmissibility
function based method whose major advantage is the independence of the exciting force's nature and its
ability to eliminate harmonic components and reduce their effect on the identified modal model.