I. Introduction
THE commonly used method of dynamic optimization of machine tool bed and other complex system of mechanical structure is geometry optimization. That is the way of human-computer interaction by using modeling, performance analysis and the modifications according to the design requirements of structure. And then analyze repeatedly until the mechanical dynamic performance can meet the requirements. This is a re-design changing to the process of re-analysis [1]–[3]. To achieve optimization of dynamic performance of machine tool bed, domestic and foreign scholars have done a lot of research work. Xu Yanshen took the theory of elementary structure to discuss and analyze the machine tool bed, then the optimize structures were obtained [4]. Improving the type and layout of rib as an effective way to enhance the static and dynamic characteristics of the bed was presented by Ji Guowei [5]. Chenxin showed that taking the natural frequency and vibration displacement as evaluation criteria for grinding lathe bed's dynamic optimization [6].