A circular static pressure air bearing with a concave middle part of the working surface

Abstract

The present invention discloses a circular hydrostatic air bearing with a concave middle part of the working surface. The present invention is an effective method for improving the comprehensive performance of the hydrostatic air bearing. The present invention solves the technical problem that the existing hydrostatic air bearing cannot improve its comprehensive performance. A rotating free-form surface is used as the transition structure of the bearing working surface, and a circular hydrostatic air bearing with a concave middle part of the working surface is designed, which can effectively improve the bearing's bearing capacity, static stiffness, damping and other properties. At the same time, less turbulence is generated in the air film flow field, and the bearing has better stability. The present invention is conducive to improving the comprehensive performance of my country's hydrostatic air bearings and expanding my country's advantages in the fields of ultra-precision measurement and processing.

Description

Technical Field

[0001] The invention relates to the technical field of precision machinery and instruments, and in particular to a circular static pressure air bearing with a concave middle portion of a working surface. Background Art

[0002] Hydrostatic air bearing is a commonly used lubrication and support component with the advantages of low friction, high precision, high speed and zero pollution. Therefore, it is widely used in mechanical processing, measurement, semiconductor and food industries, such as coordinate measuring machines, ultra-precision machine tools and wafer moving platforms. As one of the key components in the equipment, the performance of hydrostatic air bearing will directly affect the accuracy of the equipment or the quality of the product. Therefore, industrial development has a higher demand for the comprehensive performance of hydrostatic air bearing.

[0003] At present, there are mainly the following problems with static pressure air bearings:

[0004] First, the main structure of the hydrostatic air bearing has not changed much compared with decades ago. Some hydrostatic air bearings with novel structures, such as hydrostatic air bearings with flexible surfaces, diaphragm valve hydrostatic air bearings and piezoelectric controlled hydrostatic air bearings, mostly have the disadvantages of complex structure and low economic benefits;

[0005] Second, due to the high compressibility and low viscosity of gas, the poor static and dynamic performance of hydrostatic air bearings has never been effectively solved. Usually, the improvement of a single performance often means the decline of another performance. Therefore, the improvement of bearings with a single performance can no longer meet industrial needs.

[0006] Third, the stability of hydrostatic air bearings has received more and more attention. The root cause of instability phenomena such as self-excited oscillation and vortex motion is still unclear, but a widely recognized cause is related to the structure of traditional hydrostatic air bearings.

[0007] In view of the above three main problems, how to design a static pressure air bearing with high economic benefits and good comprehensive performance is a technical problem that needs to be solved urgently. Summary of the invention

[0008] The purpose of the present invention is to make up for the defects of the prior art and provide a circular static pressure air bearing with a concave middle part of the working surface to solve the problem of poor comprehensive performance of the static pressure air bearing and have higher economic benefits.

[0009] The present invention is achieved through the following technical solutions:

[0010] A circular static pressure air-floating bearing with a concave middle portion of a working surface comprises a bearing body, a concave surface is provided in the middle portion of the bearing working surface of the bearing body, the concave surface is tangent to the bearing working surface at every location, an air inlet is provided on the bearing body, a throttle hole is provided on the bearing working surface of the bearing body, the throttle hole passes through the bearing working surface and the interior of the bearing body and is communicated with the air inlet, compressed gas enters the interior of the bearing body from the air inlet, flows through the throttle hole, forms an air film between the bearing working surface and the thrust surface and fills the concave surface.

[0011] The concave surface is a rotating free-form surface formed by a smooth curve whose tangent vectors at both end points are parallel to the bearing working surface and which rotates around the bearing center line.

[0012] The diameter of the concave surface is 0.4 times the diameter of the bearing body, and the maximum depth of the concave surface is 0.1 mm to 1 mm.

[0013] The diameter of the throttling hole is 0.1mm~0.2mm.

[0014] There may be four throttling holes, which are distributed 90 degrees in the circumferential direction and are located on a pitch circle that is 0.6 times the diameter of the bearing body.

[0015] There can be one throttling hole, which is located at the lowest point in the center of the concave surface.

[0016] The air inlet is located on the side of the bearing body.

[0017] The advantages of the present invention are: (1) compared with the conventional planar hydrostatic air bearing, the hydrostatic air bearing with the middle concave portion of the bearing working surface of the present invention has better comprehensive performance, including load-bearing capacity, static stiffness and damping;

[0018] (2) The present invention uses a rotating free-form surface as a transition structure of the bearing working surface, which can make the gas flow smoother, effectively reduce the generation of turbulence, and make the bearing run more stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of a circular four-throttle hole static pressure air bearing with a concave middle portion of the working surface provided by the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of a circular single throttle hole static pressure air bearing with a concave middle portion of the working surface provided by the present invention;

[0021] Figure 3 It is a cross-sectional view of a circular four-throttle hole static pressure air bearing with a concave middle portion of the working surface provided by the present invention;

[0022] Figure 4 It is a cross-sectional view of a circular single throttle hole static pressure air bearing with a concave middle portion of the working surface provided by the present invention;

[0023] Figure 5 It is a schematic diagram of the principle that the smooth curve provided by the present invention constitutes a rotating free-form surface;

[0024] Figure 6 This is a schematic diagram of the air film pressure distribution of the circular static pressure air bearing provided by the present invention ( Figure 6 (a) is the air film pressure distribution diagram of the traditional circular plane static pressure air bearing; Figure 6 (b) is a diagram showing the air film pressure distribution of a circular static air bearing with four throttle holes and a concave middle portion of the working surface of the present invention; Figure 6 (c) is a diagram showing the air film pressure distribution of a circular static air bearing with a single throttle hole and a concave middle portion of the working surface of the present invention);

[0025] Figure 7 This is a schematic diagram of the flow field of the circular four-throttle hole static pressure air bearing with a concave middle part of the working surface provided by the present invention ( Figure 7 (a) is the flow field of square concave surface; Figure 7 (b) is the circular concave flow field; Figure 7 (c) is the concave flow field of the present invention);

[0026] Figure 8 The present invention provides a cross-sectional streamline diagram of a circular single throttle hole static pressure air bearing with a concave middle portion of the working surface.

[0027] Numbers in the figure: 1. thrust plate; 2. thrust surface; 3. bearing body; 4. throttle hole; 5. bearing working surface; 6. concave surface; 7. smooth curve; 8. air inlet; 9. turbulence; 10. large-scale low-speed vortex; 11. tangent vector at the end point of the smooth curve; 12. bearing center line. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] The circular static pressure air bearing with a concave middle portion of the working surface described in this embodiment includes a four-throttle hole static pressure air bearing and a single-throttle hole static pressure air bearing.

[0030] Embodiment 1: Circular four-throttle hole static pressure air bearing with concave middle part of working surface

[0031] like Figure 1As shown, the main structure of the circular four-throttle hole static pressure air bearing with a concave middle part of the working surface includes: a bearing body 3, a throttle hole 4, a bearing working surface 5, a concave surface 6 and an air inlet 8. The circular four-throttle hole static pressure air bearing with a concave middle part of the working surface includes four throttle holes 4 distributed at 90 degrees in the circumferential direction, the diameter of the throttle holes 4 is 0.1mm~0.2mm, and is located on a pitch circle 0.6 times the diameter of the bearing body 3. The concave surface 6 is located in the middle of the bearing working surface 5, the diameter of the concave surface 6 is 0.4 times the diameter of the bearing body 3, and the maximum depth of the concave surface 6 is 0.1mm~1mm.

[0032] like Figure 3 As shown, the air inlet 8 of the circular four-throttle hole static pressure air bearing with a concave middle part of the working surface is connected to the throttle hole 4, and the compressed gas flows into the interior of the bearing body 3 from the air inlet 8, and flows into the space between the bearing working surface 5 and the thrust surface 2 of the thrust plate 1 through the four throttle holes 4, forming an air film and filling the concave surface 6. Among them, the inflow direction of part of the gas is the atmosphere, and the inflow direction of part of the gas is the center of the bearing.

[0033] like Figure 5 As shown, the concave surface 6 is a rotating free-form surface formed by a smooth curve 7 whose tangent vectors 11 at both end points are parallel to the bearing working surface 5 and which rotates around the bearing center line 12 for one circle. The concave surface 6 is tangent to the bearing working surface 5 at every location.

[0034] The technical effects of this implementation are:

[0035] (1) If Figure 6 As shown in the figure, compared with the traditional flat hydrostatic air bearing, the equivalent air film thickness of the circular four-throttle hole hydrostatic air bearing with a concave middle part of the working surface is increased, but the air pressure in the central area is greater, and the area of ​​the high air pressure area is also larger, which means that the air film has greater bearing capacity and static stiffness, and the air pressure distribution is more uniform, which can make the thrust of the hydrostatic air bearing more stable, and the pitch and yaw degrees are also smaller;

[0036] (2) If Figure 7 As shown, compared with the square concave surface and the circular concave surface, the rotating free-form surface formed by the smooth curve 7 rotating around the bearing center line 12 is used, that is, the concave surface 6, as the transition structure of the bearing working surface 5, which can make the gas flow smoother, so the turbulence 9 generated is also less, or even close to zero, which can effectively reduce the micro-vibration of the static pressure air bearing during operation and suppress the occurrence of self-excited oscillation;

[0037] (3) Compared with the traditional flat hydrostatic air bearing, the circular four-throttle hole hydrostatic air bearing with a concave middle part of the working surface has better damping characteristics. Experimental tests have found that the improvement effect is most significant in the high-frequency area, and the average increase in the damping coefficient can reach 30%.

[0038] Embodiment 2: Circular single throttle hole static pressure air bearing with concave middle part of working surface

[0039] like Figure 2 As shown, the main structure of the circular single throttle hole static pressure air bearing with a concave middle part of the working surface comprises: a bearing body 3, a throttle hole 4, a bearing working surface 5, a concave surface 6 and an air inlet 8. The circular single throttle hole static pressure air bearing with a concave middle part of the working surface has a throttle hole 4 located at the center of the bearing concave surface 6, the throttle hole 4 has a diameter of 0.1mm~0.2mm, and is also located at the lowest point of the bearing concave surface 6.

[0040] like Figure 4 As shown, the air inlet 8 of the circular single throttle hole static pressure air bearing with a concave middle part of the working surface is connected to the throttle hole 4, and the compressed gas flows into the interior of the bearing body 3 from the air inlet 8, and then flows out from the throttle hole 4. The gas first fills the concave surface 6, and then flows into the space between the bearing working surface 5 and the thrust surface 2 of the thrust plate 1 to form an air film. Different from the circular four throttle holes static pressure air bearing with a concave middle part of the working surface, since the throttle hole 4 is located at the center of the bearing body 3, the airflow direction is the atmosphere.

[0041] like Figure 5 As shown, the concave surface 6 of the circular single-throttle-hole static pressure air bearing with a concave middle portion of the working surface is completely consistent with the concave surface 6 of the circular four-throttle-hole static pressure air bearing with a concave middle portion of the working surface, and their smooth curves 7 are also completely consistent.

[0042] The technical effects of this implementation are:

[0043] (1) If Figure 6 As shown, compared with the traditional plane static pressure air bearing and the circular four-throttle hole static pressure air bearing with a concave working surface in the middle, the equivalent air film thickness of the circular single-throttle hole static pressure air bearing with a concave working surface in the middle is the same as that of the circular four-throttle hole static pressure air bearing with a concave working surface in the middle, but the air pressure in the central area is greater than that of the former two, and the area of ​​the high air pressure area is also larger, which means that the bearing capacity and static stiffness of the air film are greater than those of the former two, and the air pressure distribution of the air film is more uniform, which can make the thrust of the static pressure air bearing more stable, and the pitch and yaw degrees are also smaller;

[0044] (2) If Figure 7 , 8As shown, the distance between the throttle hole 4 and the thrust surface 2 of the circular single throttle hole static air bearing with a concave middle part of the working surface (greater than 1mm) is much greater than the conventional air film thickness (5μm~20μm), so when the airflow flows out of the throttle hole 4 located at the center of the bearing concave surface 6, the impact on the thrust surface 2 is smaller. Due to the instability of the airflow boundary layer, the gas separates from the boundary layer and forms a large-scale vortex 10 in the concave surface 6, but the flow rate is very low, so the vortex 10 does not belong to turbulence 9, but to laminar flow. In the area gradually approaching the bearing working surface 5, the streamlines of the airflow become neater and straighter, and flow into the space between the bearing working surface 5 and the thrust surface 2 in a laminar state without generating excess turbulence 9, and finally flow into the atmosphere. From the throttle hole 4 to the atmosphere, the gas flow rate of the circular single throttle hole hydrostatic air bearing with a concave middle part of the working surface shows a trend of continuous decrease, rather than the trend of first rising and then decreasing shown by the traditional planar hydrostatic air bearing. Therefore, the circular single throttle hole hydrostatic air bearing with a concave middle part of the working surface eliminates the "Laval nozzle" type airflow channel near the throttle hole 4, effectively reduces the flow rate of the gas in the air film, and solves the problem of pressure drop near the throttle hole 4.

Claims

1. A circular static pressure air bearing with a concave middle working surface. Features: The invention comprises a bearing body, a concave surface is provided in the middle of the bearing working surface of the bearing body, the concave surface is tangent to the bearing working surface at all places, an air inlet is provided on the bearing body, a throttle hole is provided on the bearing working surface of the bearing body, the throttle hole penetrates the bearing working surface and the interior of the bearing body and is communicated with the air inlet, and compressed gas enters the interior of the bearing body from the air inlet, flows through the throttle hole, forms an air film between the bearing working surface and the thrust surface, and fills the concave surface; The concave surface is a rotating free-form surface formed by a smooth curve whose tangent vectors at both end points are parallel to the bearing working surface and which is rotated around the bearing center line for one circle; The diameter of the concave surface is 0.4 times the diameter of the bearing body, and the maximum depth of the concave surface is 0.1 mm to 1 mm; There are four throttling holes, which are distributed at 90 degrees in the circumferential direction and are located on a pitch circle that is 0.6 times the diameter of the bearing body.

2. A circular static pressure air bearing with a concave middle portion of the working surface according to claim 1, Features: The diameter of the throttling hole is 0.1mm~0.2mm.

3. A circular static pressure air bearing with a concave middle portion of the working surface according to claim 1, Features: The air inlet is located on the side of the bearing body.

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