Search Results (5)

With the widespread use of high-speed motorized spindles in precision machining, conventional contact loading methods are no longer adequate for stiffness loading tests under high-speed operating conditions. Non-contact loading technology based on a partial-arc aerostatic radial bearing offers an effective alternative. In this study, a CFD-based hydrodynamic model was developed for the gas-film flow field in a partial-arc aerostatic radial bearing. The effects of bearing geometric parameters, such as chamber configuration, supply-orifice structure, and eccentricity, on loading characteristics were investigated. The influence of hydrodynamic effects under high-speed rotation on the loading force stability and stiffness-testing accuracy was analyzed, and an asymmetric shallow–deep composite chamber design was proposed to mitigate these effects. The results indicate that the partial-arc aerostatic radial bearing, designed based on both static characteristics and rotational performance analysis, can effectively suppress hydrodynamic effects and improve loading force stability and stiffness-testing accuracy. Full article

In the application of an aerostatic motorized spindle, given the different requirements for the optimal gas film thickness of gas bearing under various processing conditions, this paper puts forward the tapered aerostatic bearing as the radial support element of the spindle and realizes the adjustability of gas film gap in a particular range through the axial fine-tuning mechanism. A 5-DOF dynamic model of the bearing rotor system is established, and the transient Reynolds equation is solved using the finite difference method to obtain the pressure distribution characteristics of the gas film. Based on this, the spindle’s translation and angular displacement responses are determined by solving the spindle’s motion equation. The simulation results show that the tilting motion of the spindle significantly affects the pressure distribution of the gas film, and the nonlinear gas film force will lead to nonlinear severe vibration of the spindle. The study also reveals that reducing the gas film thickness under low-speed and heavy-load conditions effectively decreases the amplitude and offset of the spindle. However, increasing the gas film thickness enhances the system’s speed and stability under high-speed and light-load conditions. Full article

In the working process of the gas bearings, the unbalanced force of the rotor will increase nonlinearly with the increase in the rotating speed, resulting in an increase in the rotor’s vibration amplitude. On the other hand, with the increase in the rotating speed, the hydrodynamic effect will increase, and the nonlinear increase in the gas film force and stiffness will inhibit the increase in the vibration amplitude. In order to deeply study the influence of the unbalanced force and nonlinear gas film force on the vibration amplitude of the ultra-precision aerostatic motorized spindle, taking the double slit throttling gas bearing as an example, according to the equilibrium equation of the rotor under the combined action of gravity, the gas film force, and the unbalanced force, a calculation program based on the finite difference method for solving the rotor’s equilibrium position is completed. The calculation results show that: the hydrodynamic effect can significantly increase the bearing capacity and cause the change of the static equilibrium position of the rotor, but the offset amplitude of the static equilibrium position of the rotor gradually slows down with the increase in the rotating speed. The hydrodynamic effect improves the stiffness near the static equilibrium position of the rotor, making the rotor vibration track tend to be more “round”. Although the unbalanced force of the rotor increases nonlinearly as the rotating speed increases, the maximum offset between the dynamic equilibrium position and the static equilibrium position of the rotor under the action of the rotating unbalanced force is approximately linear with the rotating speed. Compared with the air supply pressure, the rotor unbalance and rotating speed are the main factors affecting the rotor dynamic equilibrium position offset. This study has a reference role in the in-depth study of the influence of rotating speed and rotor unbalance on the rotor static equilibrium position and dynamic equilibrium position offset, as well as in the design of gas bearings and the prediction of rotor vibration amplitude. Full article

In the working process of ultra-precision aerostatic motorized spindles, the journal and the rotor must have a certain eccentricity to have a certain bearing capacity and stiffness, which will induce the unbalanced magnetic pull (UMP). The intercoupling of the UMP and the gas film force will affect the motion state of the rotor and the accuracy of spindles. In order to deeply study the influence of the UMP caused by the rotor eccentricity on the equilibrium position of aerostatic spindles, a physical model of an aerostatic spindle based on slit throttling gas bearing is established and the coupling effect between the rotor and the motor rotor is studied and analyzed as a whole. The equilibrium position of the rotor under the combined action of gravity, the gas film force and the UMP is deduced, and a gas–magnetic field coupling calculation program based on the finite difference method is proposed. The calculation results show that with the increase in rotational speed, the equilibrium position of the rotor will move to the center of the journal in the micron scale, and the moving amplitude will gradually slow down. The UMP caused by rotor eccentricity can offset the rotor equilibrium position in nanometer scale, and the influence degree decreases sharply as the rotor moves to the journal center. With the increase in rotational speed, the direct stiffness and the cross stiffness will increase, and the amplitude of the cross stiffness is greater than the direct stiffness. This study is of great significance for further studying the influence of the rotor eccentricity on the equilibrium position and the accuracy of the rotor. Full article

The aerostatic spindle in the ultra-precision machine tool shows the complex multi-field coupling dynamics behavior under working condition. The numerical investigation helps to better understand the dynamic characteristics of the aerostatic spindle and improve its structure and performance with low cost. A multi-field coupling 5-DOF dynamics model for the aerostatic spindle is proposed in this paper, which considers the interaction between the air film, spindle shaft and the motor. The restoring force method is employed to deal with the times varying air film force, the transient Reynolds equation of the aerostatic journal bearing and the aerostatic thrust bearing is solved using ADI method and Thomas method. The transient air film pressure of aerostatic bearings is obtained which clearly presents the influence induced by the tilt motion of the spindle shaft. The motion trajectory of the spindle shaft is obtained which shows different stability of the shaft under different external forces. The dynamics model shows good performance on simulating the multi-field coupling behavior of the aerostatic spindle under external force. which is quite meaningful and useful for the further research on the dynamic characteristics of the aerostatic spindle. Full article