A machine tool is an assembly structure fitted by some moveable substructures, which the relative motion between the substructures creates normal and limit operating positions. Along with the substructures moving, the distributions of masses, stiffness and damping of the machine in space vary, leading to variety of structure distributions and dynamic properties. For exploring the dynamic properties distributions of machine tools, this paper presents a testing method under practical operational excitations, which is under operating excitations from remaining unbalanced value in the spindle, and collecting vibration signals of time and frequency at the spindle foreside at working positions. To identify resonance characteristics, a judging matrix is established by comparing vibration energy and vibration amplitude at 1st octave. By this method, MDH50 active pole horizontal machining center is tested, and the dynamic characteristics is determined. It reveals that dynamic characteristics of resonance come from the substructure independent resonance and their superposition in operating excitation. For verifying this result, FEA is conducted, in which 20 nodes brick element and spring element are applied to build the model entities and interfaces. The analysis result by FEM is consistent to the testing results. The research provides foundation for how setting up machining programs to avoid the resonance vibration of the machine in the operating.
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