Investigation of the Time-invariance and Causality of a Machine Tool for Performing Operational Modal Analysis

The dynamic behaviour of machine tools affects the work-piece quality and productivity. Generally, the difference between the dynamic properties at standstill and during machining is neglected by the commonly applied assessment methods for production systems. Operational modal analysis takes into account these cutting- and operation-dependent influences. However, operation conditions might cause violation of the common measurement assumptions regarding time-invariance and causality. The investigations consider the time-invariance by the measurement of frequency response functions over the working space including the evaluation of mode shapes. The causality is evaluated by dynamic measurements at TCP excited by feed motions.