The non-linear dynamic behavior of a hybrid air bearing-rotor system is very complicated and requires careful attention when designing to avoid spindle failure, especially under ultra-high speed condition. In this paper, the rotor trajectory of a hybrid air bearing-rotor system is obtained by solving the unsteady Reynolds equation and motion equations simultaneously. The typical non-linear behavior of hybrid air bearing-rotor systems is illustrated with the analysis of the rotor trajectory, the phase angle, time domain vibration and power spectral density. Furthermore, the influences of the rotor mass, external load, rotating speed and unbalanced mass on the non-linear behavior are investigated. Finally, the effect of structure parameters on the rotor trajectory is studied and the phenomenon under ultra-high speed condition is illustrated, which provides some new guidelines on the ultra-high speed air spindle design.

The spiral-grooved structure has been proposed for promoting the load capacity and stiffness of hybrid air journal bearings. In this paper, the dynamic characteristics of spiral-grooved hybrid bearings are first calculated. The stability criteria of the bearings are proposed and analyzed with different groove structure parameters using frequency domain analysis. It is found that the length of the spiral-groove has significant influence on the stability of the spindle system. Finally, the critical speed of the spiral-grooved hybrid bearing and rotor system is analyzed, and an experiment is carried out to validate the proposed model, finding that groove structure can promote the stability of the air bearing systems.