Estimation of dynamic characteristics of machine structure by pseudo inverse matrix

Vibration problem on machine tools shows complex behavior during machining. Various measurement and analysis methods have been proposed such as impulse hammer, shaker and FEM. Both the impulse hammer and shaker methods are easy to apply and obtain reliable data using only the static simulations on machine tools. Because the vibration problems on machine tools occur during machining workpiece surface roughness and dimensional accuracy are affected directly, the dynamic characteristics of contact point between cutting tool and workpiece is not evaluated by conventional methods. Consequently, the modal parameters estimated from the measurement and analyses during machining are expected to predict the dynamic behavior of machine tools and/or to point out the structural modifications. These parameters should be estimated with data obtained during machining. We have developed a new evaluation method to obtain the dynamic characteristics directly by machining the polygon workpiece in the case of an NC lathe as the target machine tool. The reliability of the proposed calculation method is evaluated by using simple structural model excited by an impulse hammer. The usage of the pseudo inverse matrix shows enough accurate calculation results of transfer functions. In this report, the proposed method and its evaluation results by using simple structural model are reported. Further, the calculated results of transfer functions of an NC lathe are introduced.