Frequency Response Evaluation by a Scaling Method Considering the Structure Change

Abstract

Under operating conditions of machine tool, the structure’s dynamic is usually evaluated by operational modal (OM) analysis that is difficult to be used to estimate the frequency response function (FRF) because of the unknown state of complex input forces. In this paper, the scaling factor of OM shape was evaluated by the proposed scaling method which was based on the structure change. Firstly, OM parameters of the selected machine tool structure were estimated at four different positions. Results indicated that the mode shapes and the damping ratios were not influenced obviously by the structural change, but the natural frequency can be affected evidently. Secondly scaling factors were calculated by the frequency changes of the machine tool and the mode shapes of the movable components such as the worktable and the stocks, using the proposed method. Thirdly, machine tool’s FRF was calculated from the scaled operational modal parameters. Besides, it has been found an interesting phenomenon that different natural frequencies were sensitive to different movable components of the machine tool.