Dynamic design methodology of high speed micro-spindles for micro/meso-scale machine tools

With the increasing demands for high manufacturing accuracy and processing efficiency, micro/meso-scale machine tool systems are proposed. The availability of micro-spindles with ultra-high rotating angular speeds and ultra-small run-out are a key technology for micro/meso-scale cutting processes. Well-established design methods exist for traditional spindle systems, but there is a strong demand for a methodology to predict the dynamic characteristics, particularly at the micro-scale, which will dictate manufacturing accuracy. In this respect, the minimization of run-out is of paramount importance. In response to this, two problem areas are considered in this paper: (a) hybrid air bearing systems-a methodology related to the calculation of the load capacity and stiffness of hybrid air journal and thrust bearings, and (b) spindle rotor system-a methodology for the rotor dynamic analysis including critical speed, mode shape, and unbalanced response predictions. Mathematical models and simulation procedures are given, followed by explanations of their use. Finally, the proposed dynamic design method is demonstrated on a realized micro-spindle system model. Two designs namely the original design and a modified design are analyzed and comparisons are carried out. The numerical simulations and the experimental evidence available for the original design have substantiated the validity of the proposed dynamic design method. The proposed methodology lays the foundation for controlling run-out of the high speed micro-spindles in micro/meso-scale machine tools.