JP2004156666A - Hydrostatic bearing, and air spindle motor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrostatic bearing capable of equalizing radial rigidity in a circumferential direction of the bearing, and thus improving rotation precision of an air spindle. <P>SOLUTION: This hydrostatic bearing is provided with a radial bearing surface 11 to rotatably support a rotary shaft 4, an axial bearing surface 12 to support front and rear end surfaces of a radially expanded thrust collar part 9 of the rotary shaft 4, radial supply air holes 13 formed in the radial bearing surface 11 at a constant interval in a circumferential direction, and axial supply air holes 14 formed in the axial bearing surface at a constant interval in the circumferential direction. Between two of the radial supply air holes 13 or axial supply air holes 14 adjacent to each other in the circumferential direction, a hole of the other is disposed at a center angular position between the two holes. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrostatic bearing and an air spindle motor using the same. More specifically, the present invention relates to an air spindle motor used for a precision machine tool, a precision inspection device, and the like, and a hydrostatic bearing suitable for the air spindle motor.
[0002]
[Prior art]
A conventional air spindle motor has a rotating shaft having a thrust collar bulged radially in a disk shape, a radial bearing surface rotatably supporting the outer peripheral surface of the rotating shaft, and both front and rear surfaces of the thrust collar portion. A bearing portion having an axial bearing surface and a motor portion disposed on the opposite side of the supported portion supported by the bearing portion on the rotating shaft (see Patent Documents 1 and 2).
[0003]
The radial bearing surface is formed with a radial air supply hole for supplying compressed air to a gap between the outer peripheral surface of the rotating shaft and the axial bearing surface for supplying compressed air with the thrust collar portion surface. An axial air supply hole is formed. A plurality of radial air supply holes are formed at equal intervals along the circumferential direction of the radial bearing surface, and a plurality of axial air supply holes are formed at equal intervals on a circumference concentric with the rotating shaft on the axial bearing surface. As described above, each of the radial air supply hole and the axial air supply hole is formed at equal intervals, but no attention is paid to the positional relationship between the radial air supply hole and the axial air supply hole.
[0004]
Manufacturers of air spindle motors have made various efforts to improve the rotation accuracy. On the other hand, the recent demands of the user for the rotation speed of the air spindle are increasing from several thousand revolutions per minute to several tens of thousands revolutions per minute. Nano-level accuracy has also been required for rotational accuracy (centering of the spindle).
[0005]
[Patent Document 1]
JP-A-10-96423 [Patent Document 2]
Japanese Utility Model Registration No. 2574581
[Problems to be solved by the invention]
The inventor of the present invention has found, after extensive research, that the relationship between the arrangement position of the radial air supply holes and the arrangement position of the axial air supply holes affects the radial rigidity of the bearing. It was made possible to use it. An object of the present invention is to provide an air spindle motor with improved rotation accuracy of an air spindle, and a hydrostatic bearing suitable for the air spindle.
[0007]
[Means for Solving the Problems]
The hydrostatic bearing of the present invention comprises: a radial bearing surface rotatably supporting an outer peripheral surface of a rotating shaft; an axial bearing surface supporting both front and rear end surfaces of a thrust collar portion bulging in a radial direction of the rotating shaft; A radial air supply hole formed in the bearing surface at equal circumferential intervals, and an axial air supply hole formed in the axial bearing surface at equal circumferential intervals, and one of the radial air supply hole and the axial air supply hole is provided. The other one hole arranged between two circumferentially adjacent holes is arranged at a central angular position between the one holes.
[0008]
With this configuration, when the arrangement of the air supply holes is viewed in the axial direction of the hydrostatic bearing (when viewed from the front), the arrangement of the radial air supply holes and the axial air supply holes does not overlap. Further, since one air supply hole is located at the center of the space between the other air supply holes, the radial rigidity of the bearing is made uniform in the circumferential direction. As a result, the rotation accuracy of the rotating shaft supported by the bearing is improved.
[0009]
And, on the radial bearing surface, a static pressure bearing further formed with a circumferential radial air supply groove passing through the position of a radial air supply hole formed in the circumferential direction, and / or on the axial bearing surface, A hydrostatic bearing in which a circumferential axial air supply groove passing through the position of the formed axial air supply hole is preferable. This is because the pressure loss in the direction along the circumferential direction of the gas supplied from the air supply holes to the bearing surface is suppressed, and this contributes to uniform radial rigidity.
[0010]
Further, the number of axial air supply holes formed on one circumference is set to an integral multiple of the number of radial air supply holes formed on one circumference, and each radial air supply hole formed on one circumference is circumferentially formed. It is also possible to arrange at the central angular position between two adjacent axial air supply holes. With such a configuration, radial rigidity can be made uniform.
[0011]
In addition, a plurality of radial air supply holes, each having the same number of radial air supply holes arranged at equal intervals in the circumferential direction, are arranged at intervals in the axial direction of the hydrostatic bearing, and each radial air supply hole is adjacent in the circumferential direction. The two axial air supply holes may be arranged at a central angular position between the two air supply holes. With such a configuration, radial rigidity can be made uniform.
[0012]
In such a static pressure bearing, four or more even-numbered rows of the radial air supply holes are arranged at intervals in the axial direction of the hydrostatic bearing, and the corresponding radial air supply holes of the odd-numbered radial air supply hole rows are provided. Are arranged in a straight line in the axial direction of the hydrostatic bearing, and the corresponding radial air supply holes of the even-numbered radial air supply hole rows are arranged in a straight line in the axial direction of the hydrostatic bearing. A hydrostatic bearing in which the radial air supply holes of the air hole row and the radial air supply holes of the even-numbered radial air supply hole row are arranged at different angular positions in the circumferential direction is preferable.
[0013]
The air spindle motor according to the present invention includes any one of the above-described hydrostatic bearings, a rotating shaft rotatably supported by the hydrostatic bearing, and a portion of the rotating shaft supported by the hydrostatic bearing. And a motor unit disposed on the side.
[0014]
With this configuration, the rotation accuracy of the air spindle is improved.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of a hydrostatic bearing and an air spindle motor of the present invention will be described with reference to the accompanying drawings.
[0016]
FIG. 1 shows an air spindle motor 1 used in an apparatus for inspecting a hard disk of a computer, which is one embodiment of the present invention. The air spindle motor 1 has a motor housing (hereinafter simply referred to as a housing) 2, a bearing member 3 fitted and fixed to an inner peripheral surface of the housing 2, and one end side rotatably supported by the bearing member 3. And a motor unit 5 disposed on the other end side of the rotating shaft 4.
[0017]
The rotating shaft 4 has a large-diameter supported portion 6 whose outer peripheral surface is rotatably supported by the bearing member 3, a small-diameter rotor mounting portion 8 to which the rotor 7 a of the motor portion 5 is mounted, and a supported portion 6. A thrust collar portion 9 bulging radially in the shape of a disk near the boundary between the rotor and the rotor mounting portion 8. An encoder 10 is attached to the tip of the small diameter portion, and a table 18 for attaching a work is attached to the end of the large diameter portion. Reference numeral 7b indicates a stator of the motor.
[0018]
The bearing member 3 has a radial bearing surface 11 that rotatably supports the outer peripheral surface of the supported portion 6 of the rotating shaft 4 and a pair of axial bearing surfaces 12 that support both front and rear surfaces of the thrust collar portion 9 in the axial L direction. I have. The bearing member 3 can be divided from the pair of axial bearing surfaces 12 to facilitate disassembly and assembly. Therefore, as shown, the bearing member 3 is composed of two long and short flanged cylindrical members 3a, 3b. As shown in FIG. 2, the housing 2 is also made divisible from the same portion as the bearing member 3, corresponding to the fact that the bearing member 3 is made divisible.
[0019]
As shown in FIGS. 1 and 2, a plurality (four in the present embodiment) of radial air supply holes 13 are formed at equal intervals (90 °) in the circumferential direction in the radial bearing surface 11 in a gap with the outer peripheral surface of the rotating shaft. A plurality of (eight in the present embodiment) axial air supply holes 14 are formed at each axial bearing surface 12 at equal circumferential intervals (45 °) in each axial bearing surface 12 so as to face the gap with the opposing surface of the thrust collar portion 9. It is formed. The axial air supply holes 14 on the front surface of the thrust collar portion 9 and the axial air supply holes 14 on the rear surface (rear surface or back surface) are arranged at the same angle position. An air supply passage 15 for supplying compressed air to all the air supply holes 13 and 14 is formed in the housing 2, and the radial air supply holes 13 are arranged on an inner peripheral surface of the housing 2 where the bearing member 3 is fitted. An air supply channel 15 a communicating with the air supply passage 15 is formed in the circumferential direction. With such a configuration, all of the air supply holes 13 and 14 communicate with the air supply passage 15, which is connected to an air supply source (not shown).
[0020]
Further, in order to make the rotation shaft supporting pressure by the air supply as uniform as possible in the circumferential direction of the radial bearing surface 11, all radial air supply holes 13 (radial air supply holes described later) formed in one circumferential direction are formed in the radial bearing surface 11. A radially shallow radial air supply groove 16 passing through the position of (row) is formed. For the same purpose, the axial bearing surface 12 is formed with a shallow axial air supply groove 17 having a circular outer shape and passing through the positions of all the axial air supply holes 14 formed in the circumferential direction. Each of the grooves 16, 17 has a cross-sectional shape shown in FIG. Compressed air is ejected from the air supply holes 13 and 14 into the gap between the rotating shaft 4 and the bearing surfaces 11 and 12, and this air goes around the grooves 16 and 17 and escapes to the outside through an exhaust passage 25 described later. Therefore, the air pressure in the gap is highest at the positions of the air supply holes 13 and 14 and decreases as the air pressure increases as the air pressure increases. However, each of the grooves 16 and 17 has a smaller flow path resistance and a smaller pressure loss than other gaps. In the present invention, the arrangement of the radial air supply holes 13 and the axial air supply holes 14 is further devised for the purpose of equalizing the rotation shaft support pressure (equalizing the radial rigidity) as described later.
[0021]
Although the radial air supply groove 16 and the axial air supply groove 17 are formed on the bearing surfaces 11 and 12, the present invention is not limited to such a structure. For example, FIG. 8 is a cross-sectional view showing the rotating shaft 4, and as shown here, these air supply grooves 16a are provided on the surface of the rotating shaft 4 (including the surface of the thrust collar portion 9) opposed to the grooves 16 and 17. , 17a may be formed on both the rotating shaft 4 and the bearing surfaces 11, 12. In FIG. 8, reference numeral 26 denotes an air passage for making the recess 18a (FIG. 1) formed in the table 18 a positive pressure or a negative pressure.
[0022]
FIG. 3 is a view taken along the line III-III in FIG. 1, and the arrangement of the radial air supply holes 13 and the axial air supply holes 14 is clarified with reference to FIG. 3. The radial air supply holes 13 are formed at four positions at two positions spaced apart in the direction of the axis L at equal angular intervals (90 °) in the circumferential direction (FIG. 3). The row of the radial air supply holes 13 arranged in one circumferential direction is called a radial air supply hole array. The radial air supply holes 13 of the two radial air supply hole rows that are separated from each other are arranged on a straight line parallel to the axis L direction (FIGS. 1 and 2). On the other hand, the axial air supply holes 14 are formed at eight locations at equal angular intervals (45 °) on a concentric circle with the bearing member 3 (FIG. 3).
[0023]
As shown in FIG. 3, when the formation positions of the air supply holes 13 and 14 are viewed in the direction of the axis L (when viewed from the front), the position of each radial air supply hole 13 is determined by the distance between the axial air supply holes 14 adjacent in the circumferential direction. It is located at the center between them, that is, at a position that bisects the angle formed by adjacent axial air supply holes 14 about the axis L. In the present embodiment, the number of the radial air supply holes 13 is four, and the number of the axial air supply holes 14 is eight, so that the arrangement is as shown in FIG. 3, but the dual supply as in the bearing member 19 shown in FIG. If the number of the air holes 13 and 14 is the same, the air supply holes 13 and 14 are formed at equal angular intervals. In short, irrespective of the number of both the air supply holes 13 and 14 in a front view, the other of the radial air supply holes 13 and the axial air supply holes 14 is disposed between two circumferentially adjacent ones. It suffices if one hole is arranged at a central angular position between the one holes.
[0024]
As described above, the radial rigidity of the bearing member in which the air supply holes are arranged is uniform in the circumferential direction as compared with a conventional bearing that does not have such an arrangement. That is, the rotation accuracy of the rotating shaft is improved. The reason for this will be described by comparing the bearing member 3 with an example (comparative example shown in FIG. 11) 51 of a bearing member having no configuration.
[0025]
In Comparative Example 51, three radial air supply holes 52 are formed at equal angular intervals in the circumferential direction, and four axial air supply holes 53 are formed at equal intervals in the circumferential direction. In addition, one radial air supply hole 52 is formed at the same angle as one axial air supply hole 53 in a front view. The other air supply holes 52 and 53 do not necessarily coincide with each other as shown in the figure, and the air supply holes 52 and 53 do not have an equal interval. That is, the radial air supply holes (axial air supply holes) arranged between two adjacent axial air supply holes (radial air supply holes) are not arranged at the central angular position.
[0026]
As a result, the radial rigidity (indicated by a dashed line in the graph of FIG. 5) in the circumferential direction of Comparative Example 51 is less uniform than that of Embodiment 3 (indicated by a solid line). The horizontal axis of the graph of FIG. 5 shows the range of 360 ° in the circumferential direction of the radial bearing surface developed in 16 equal parts (every 22.5 °), and the vertical axis shows the radial rigidity (N / μm). For the embodiment, the dividing points from No. 1 to 16 are numbered in FIG. 3, and for the comparative example, the dividing points from No. 1 to 16 are numbered from FIG. I have. The radial stiffness is a load value (unit: N) for causing a deflection of 1 μm when a load perpendicular to the axial direction is applied to the rotating shaft. Such a difference between the embodiment and the comparative example is caused by the air supply from the radial air supply hole and the air supply from the axial air supply hole when a load perpendicular to the axial direction is applied to the tip of the rotating shaft or the like. It can be considered that this is caused by the difference in the resistance moment.
[0027]
As shown in FIG. 6, when a load W perpendicular to the axial direction is applied to the tip of the rotary shaft or the like, the moment applied to the rotary shaft by the component R of the radial air supply that opposes the load direction and the same as the load W The moment applied to the rotating shaft by the axial air supply A at the angular position opposes the moment applied to the rotating shaft by the load W. Therefore, in the case of Comparative Example 51, since the radial air supply hole coincides with the axial air supply hole at the position of No. 8, the resistance moment at the position of No. 8 is increased, and conversely, the resistance at the positions of No. 6 and No. 10 is increased. Since the moment is small, the radial rigidity lacks uniformity as shown in FIG. However, in the case of the embodiment, the radial air supply holes and the axial air supply holes do not overlap at the same angular position, and uniformity of radial rigidity can be obtained as compared with the comparative example.
[0028]
As described above, it is desirable that the number of radial air supply holes and the number of axial air supply holes be the same from the viewpoint of uniformity of radial rigidity. Further, it is desirable that one of the radial air supply holes and the axial air supply holes is an integral multiple of the other number.
[0029]
FIG. 9 shows another embodiment. This bearing member 23 is different from the above-mentioned bearing member 3 in the arrangement of the air supply holes, and as a result, the arrangement of the air supply passage (not shown) is also different. Since other configurations are common, the same components are denoted by the same reference numerals and description thereof will be omitted.
[0030]
In this bearing member 23, radial air supply holes are formed at four positions separated in the direction of the axis L. In each radial air supply hole row, radial air supply holes 13 are formed at four locations at equal angular intervals (90 °) in the circumferential direction. Of the four radial air holes arranged apart, the radial air holes 13a of the odd-numbered radial air holes from one end of the bearing member 23 are arranged on a straight line parallel to the axis L direction. The radial air supply holes 13b of the even-numbered radial air supply hole rows are also arranged on a straight line parallel to the axis L direction. However, the angular positions of the radial air supply holes 13a of the odd-numbered radial air supply hole rows and the radial air supply holes 13b of the even-numbered radial air supply hole rows are not coincident with each other, and are shifted by 45 °. Therefore, when viewed from the front, the radial air supply holes 13 are located every 45 °. The reason why the radial air supply holes 13 are arranged in this way is to reduce the change in the air pressure in the circumferential direction and make the radial rigidity uniform.
[0031]
On the other hand, the axial air supply holes 14 are formed at eight locations at equal angular intervals (45 °) on a concentric circle with the bearing member 23. Therefore, when viewed from the front, the radial air supply holes 13 and the axial air supply holes 14 are arranged at equal angular intervals of 22.5 °. As a result, the radial rigidity of the bearing member 23 becomes uniform.
[0032]
In this embodiment, four radial air supply holes are arranged, but the present invention is not limited to this configuration. For example, an even number of radial air holes of six or more may be provided, and the number and arrangement of the axial air holes corresponding to the radial air holes may be selected so as to conform to the above-described concept.
[0033]
The exhaust passage 25 will be described with reference to FIGS. The compressed air ejected from the air supply holes 13 and 14 escapes from the air supply grooves 16 and 17 to the outside through the gap between the rotating shaft 4 and the bearing surfaces 11 and 12, but at this time, most of the air passes through the exhaust passage 25. Escape to the outside. A plurality (six in the present embodiment) of radial exhaust holes 27 are formed in the radial bearing surface 11 at equal angular intervals (60 °) in the circumferential direction toward the gap between the rotating shaft 4 and the bearing surfaces 11 and 12. ing. If this is called an exhaust hole array, two exhaust hole arrays are formed at intervals in the axis L direction. A radial exhaust groove 28 is formed in the outer peripheral surface of the rotating shaft 4 facing each exhaust hole row in the circumferential direction (see FIG. 8). Of course, instead of the radial exhaust groove 28, or in addition to the radial exhaust groove 28, a circumferential radial exhaust groove may be formed in a portion of the opposed radial bearing surface 11. An exhaust channel 25 a communicating with the exhaust passage 25 is formed on the inner peripheral surface of the housing 2 where the bearing member 3 is fitted, in the circumferential direction in which the radial exhaust hole 27 is arranged.
[0034]
Axial exhaust holes 29 are also formed on the axial bearing surface 12 at equal intervals in the circumferential direction. The axial exhaust hole 29 communicates with the exhaust passage 25.
[0035]
With this configuration, all the exhaust holes 27 and 29 are communicated with the exhaust passage 25, so that the supply air is exhausted to the outside through this route.
[0036]
In the embodiment described above, the number of radial air supply holes in front view is the same as or smaller than the number of axial air supply holes, but the present invention is not limited to this configuration. For example, the bearing may be such that the number of radial air supply holes is greater than the number of axial air supply holes in a front view. The smaller number of air supply holes may be arranged at the center angular position between the larger number of air supply holes.
[0037]
【The invention's effect】
According to the present invention, the radial rigidity is made uniform along the circumferential direction of the bearing, and as a result, the rotation accuracy of the air spindle is improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of an air spindle motor of the present invention.
FIG. 2 is a longitudinal sectional view showing a part of a bearing member and a housing in the air spindle motor of FIG.
FIG. 3 is a view taken along line III-III in FIG. 1;
FIG. 4 is a view (front view) of the air spindle motor according to another embodiment of the present invention viewed in the axial direction from the center, and is a view corresponding to FIG. 3;
5 is a graph conceptually showing the distribution of radial rigidity of the bearing member in FIG. 1 and a conventional bearing member (comparative example).
FIG. 6 is a cross-sectional view schematically showing a relationship between a disturbance load applied to a rotating shaft and an air supply force opposed thereto.
FIG. 7 is an enlarged view of a portion VII in FIG.
FIG. 8 is a longitudinal sectional view showing a rotation shaft in FIG. 1;
9 (a) is a front view showing a bearing member according to another embodiment of the present invention and is a view corresponding to FIG. 3, and FIG. 9 (b) is a plan view of FIG. 9 (a). FIG. 9C is a sectional view taken along the line AA of FIG. 9A and a sectional view taken along the line BB of FIG. 9B.
FIG. 10 is a longitudinal sectional view showing a part of a bearing member and a housing in the air spindle motor of FIG. 1, which is cut from an angular position different from that of FIG. 2;
11 is a view (front view) of the conventional bearing member (comparative example) viewed from the center in the axial direction (a front view), and is a view corresponding to FIG.
[Explanation of symbols]
1 Air spindle motor 2 Housing 3 Bearing members 3a and 3b Cylindrical member 4 Rotating shaft 5 Motor unit 6 Support portion 7a Rotor 7b Stator 8 Rotor mounting portion 9 Thrust collar portion 10 Encoder 11 Radial bearing surface 12 Axial bearing surface 13 ... radial air supply hole 14 ... axial air supply hole 15 ... air supply passage 15a ... air supply channel 16, 16a ... radial air supply groove 17, 17a ... axial Air supply groove 18 Table 18a Recess 19 (of table) Bearing member 23 Bearing member 25 Exhaust passage 26 Air passage 27 ..Radial exhaust holes 28 ... radial exhaust grooves 29 .. Axial exhaust hole 51 ... (Comparative Example) bearing member 52 .... (Comparative Example) radial supply hole 53 ... (Comparative Example) axial supply hole

Claims (7)

A radial bearing surface for rotatably supporting the outer peripheral surface of the rotating shaft;
An axial bearing surface for supporting the front and rear end faces of the thrust collar portion bulging in the radial direction of the rotating shaft;
Radial air supply holes formed at equal intervals in the circumferential direction on the radial bearing surface,
An axial bearing surface and axial air supply holes formed at equal intervals in the circumferential direction,
The other one of the radial air supply holes and the axial air supply hole, which is arranged between two circumferentially adjacent two holes, is arranged at a central angular position between the one holes. Hydrostatic bearing. 2. The hydrostatic bearing according to claim 1, wherein a circumferential radial air supply groove passing through a position of the radial air supply hole formed in the circumferential direction is formed on the radial bearing surface. 2. The hydrostatic bearing according to claim 1, wherein a circumferential axial air supply groove passing through a position of the axial air supply hole formed in the circumferential direction is formed on the axial bearing surface. The number of axial air supply holes formed on one circumference is an integral multiple of the number of radial air supply holes formed on one circumference, and each radial air supply hole formed on one circumference has a circumferential direction. 2. The hydrostatic bearing according to claim 1, wherein said hydrostatic bearing is disposed at a central angular position between two axial air supply holes adjacent to said air supply hole. A plurality of rows of radial air supply holes, each having the same number of radial air supply holes arranged at equal intervals in the circumferential direction, are arranged at intervals in the axial direction of the hydrostatic bearing, and each radial air supply hole is adjacent in the circumferential direction. 2. The hydrostatic bearing according to claim 1, wherein the hydrostatic bearing is disposed at a central angular position between the two axial air supply holes. Radial air supply hole rows in which the same number of radial air supply holes are arranged at equal intervals in the circumferential direction, four or more even-numbered rows are arranged at intervals in the axial direction of the hydrostatic bearing,
The corresponding radial air holes of the odd-numbered radial air holes are arranged in a straight line in the axial direction of the hydrostatic bearing, and the corresponding radial air holes of the even-numbered radial air holes are arranged in the axial direction of the hydrostatic bearing. Are arranged on a straight line,
6. The hydrostatic bearing according to claim 5, wherein the radial air supply holes of the odd-numbered radial air supply hole row and the radial air supply holes of the even-numbered radial air supply hole row are arranged at different angular positions in the circumferential direction. A hydrostatic bearing according to any one of claims 1 to 6, a rotating shaft rotatably supported by the hydrostatic bearing, and a side of the rotating shaft opposite to a portion supported by the hydrostatic bearing. An air spindle motor, comprising: a motor unit disposed in the air spindle motor;

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