EFFECTS OF DIFFERENT EXCITATION MECHANISM IN MACHINE TOOLS WHEN PERFORMING OUTPUT-ONLY MODAL ANALYSIS

Output-only Modal Analysis makes possible to investigate the dynamic behaviour of machine tools especially under process conditions. The differences between standstill and process state, which are important to consider, result from process damping, gyroscopic moments of the rotating spindle and changes in preloads and clearance in bearing and joints. Output-only Modal Analysis assumes a complete excitation of the structure by white noise characteristics. There are several mechanism in a machine tool under process conditions that could cause a vibration response. Beside the cutting process itself, the movement of the NC-axes as well as rotating fans of control system and auxiliary units can be excitation sources. This paper investigates to what extent several excitation mechanism in machine tools fulfil the analysis assumption and in which way the identified modal parameters depend on the boundary conditions of the excitation characteristics.