Vibration monitoring of motorized spindles using spectral analysis techniques

High speed machining (HSM) technology is used in a broad range of applications to machine ferrous metals and nonmetallic material. The motorized spindle is one of the major elements to keep the machine running at high productivity. Though the motorized spindle will generate high power and torque at high speed, high removable rate, but the thermal characteristics are more dynamical, speed-dependent and non-linear. The air gap between rotor and stator changes with speed and time, the expansion of rotor, the highly complicated mechanical coupling as well as interface of the mechanical structure. All these factors create centrifugal force to the rotating bearings which not only heat these bearings up, causing bad tolerance, but also create the vibration problem. The worse situation may cause the bearings choked.In this paper, a piezo transducer is used to check the spindle vibration. Once the spindle is out of balance, the transducer gives a dialog response to computerized numerical controller (CNC) which is set with a control level. Based on ISO standard, 2 mm/s is the max acceptable vibration and designed in accordance with 2 V output voltage. Any higher voltage will enable the CNC shut down the spindle before the bearings are damaged. This new concept will prevent spindle from turning dead. As a result, the spectral analysis techniques can record the condition of spindle rotation even under the condition of misoperation.