A Novel method based on operational modal analysis for monitoring the preload degradation of linear guideways in machine tools

Abstract

A novel method for automatically monitoring the preload degradation of linear guideway type (LGT) recirculating linear ball bearings of an X-Y table is proposed. Both simulations and experiments revealed that the reduction in the natural frequency corresponding to the yawing mode of the worktable was extremely sensitive to and varied linearly with the degradation of the LGT linear bearing preload. By attaching three accelerometers to the worktable of a machine tool and then exciting the worktable with a pulse from the servo motor of a feed drive, this study identified the natural frequencies of the worktable and their corresponding mode shapes by using operational modal analysis (OMA). Among all the natural frequencies obtained by OMA, the natural frequency corresponding to the specific yawing mode of the worktable was extracted using the modal assurance criteria, and the change in the extracted frequency was tracked; thus, the degradation of LGT linear bearing preload could be monitored automatically without exciting the worktable manually. In this study, the performance of this method was assessed experimentally, and this paper presents the method in detail.