The requirement of high performance in the industry have led to the introduction of industrial robots in the machining field. Machining robots have become a potential and promising alternative to standard machine tools because of their important workspace and their high flexibility in the machining of complex parts. However, their lack of precision and rigidity is still a limit for precision tasks.

Therefore, the modal identification of a machining robot is important for an accurate knowledge of its dynamic behavior. Usually, the characterization is carried out through an experimental modal analysis. However, the excitation, artificially, created by a hammer or a shaker is not representative of the real cutting force applied in machining. These tests are thus performed in rest. Unfortunately, the dynamic behavior of a machining robot in rest differ significantly from that identified in service.

In this paper, an experimental modal analysis of an ABB IRB 6660 robot is firstly investigated. Then, modal parameters are identified during a machining operation through an operational modal identification. A significant variability of modal parameters identified at rest from those identified in service is observed, which explicates the great need to identify modal parameters in operational machining conditions.

Keyword: Experimental modal analysis, Operational modal analysis, machining robots