# Characteristics of Air Resistance in Aerostatic Bearings
## 1 Introduction  
With the rapid development of machining technology and precision measurements, the precision and speed of precision products and equipment continue to improve. Because conventional liquid lubrication methods can no longer meet the need for high precision, gas lubrication technology has emerged as an alternative [1]. Gas lubrication technology has been widely applied in the industry owing to its advantages, including high precision, fast movement, less pollution, and low cost [2, 3]. A key structure in gas lubrication technology is the throttle [4, 5]. The focus of research on throttles has been on the advantages of their design and characteristics, including low cost, large bearing capacity, high stability, and low thermal deformation with a large temperature rise [6]. The bearing capacity and stability of air films are contradictory. An increase in the bearing capacity will inevitably lead to a decrease in the stability of the throttle, whereas an increase in stability will decrease the bearing capacity of the throttle [7, 8]. Therefore, balancing the bearing capacity and stability of a restrictor is one of the purposes of studying the characteristics of aerostatic orifice throttling restrictors. Conventional research on the static and dynamic characteristics of aerostatic orifice throttling is mainly based on theoretical calculations, simulation analyses, and experimental observations. However, these methods have disadvantages, including difficulty in solving the Reynolds equation, excessively high simulation time, complicated experimental designs, and low accuracy [9]. Owing to the compressibility of air in turbulence, an accurate solution cannot be obtained through theoretical calculations [10]. Thus, to overcome this shortcoming, aerostatic resistance theory is considered. This theory relates to the air pressure drop with the change in temperature and energy of the aerostatic bearing, and it establishes the equivalent circuit model of the aerostatic restrictor or aerostatic bearing. Dynamic and static performance indicators, such as flow, bearing capacity, stiffness, and stability of aerostatic orifice throttling, have been analyzed [11], which significantly shorten the lengthy calculation. [PERSON] et al. experimentally proved that a low-viscosity gas will lead to a poor damping performance, and the damping performance of gas bearings can be enhanced through robust control methods [12; 13]. [PERSON] et al. comparatively analyzed the flow characteristics of an aerostatic bearing obtained using an experimental method, i.e., the lumped-parameter model, and the dynamic characteristics of gas flowing through a restrictor [14]. [PERSON] used the lumped-parameter model to establish a dynamic model of a thin-film aerostatic bearing and analyzed the factors affecting the stability of a throttle [15]. [PERSON] et al. compared the flow rate, hydraulic resistance, and pressure drop to the current, resistance, and voltage [16]. They established equivalent circuits to measure the flow through microfluidic components and systems (including micropumps and microvalves) and predicted the dynamic response characteristics of the microfluidics of fluid equipment quickly [16]. [PERSON] established pressure impedance models of double U-shaped, double-ring, and multi- microchannel aerostatic pressure restrictors and compared their bearing capacity and stiffness, which were calculated using a simulation and the pressure impedance model [17]. [PERSON] proposed an arrayed microhole restrictor (AMR) to suppress the vortex flow and reduce the vibration of aerostatic bearings. Through a computational fluid dynamics analysis, the transient flow features were studied for aerostatic bearings with an AMR and conventional restrictors, and the static performances of bearings were also compared. The vibration strength of the bearing was experimentally measured to validate the effectiveness of an AMR.