JP4929968B2 - Hydrostatic gas bearing mechanism, shaft rotating device and spindle motor using the same - Google Patents

Description

  The present invention relates to a static pressure gas bearing mechanism using a floating bush and a shaft rotating device using such a static pressure gas bearing mechanism, and more particularly to a spindle motor capable of rotating a cutting tool such as a small-diameter drill at high speed.

Naruyoshi Yoshimoto and two others, "Study on floating bush hydrostatic gas journal bearings" (1st report, using slot restriction), Transactions of the Japan Society of Mechanical Engineers (C), Volume 56, No. 521 (1990-1), p116 -121 Naruyoshi Yoshimoto and one other, "Study on Variable-Throttle Hydrostatic Gas Journal Bearing Using Floating Bush" (Static Characteristics), Transactions of the Japan Society of Mechanical Engineers (C) Vol.61 No.591 (1995-11) p321 327

  In spindle motors that rotate cutting tools such as drilling drills at high speeds, there is a growing demand for higher precision and higher speeds in microfabrication due to downsizing and higher performance of information machines. The minimum drill diameter for drilling is 100 μm or less, and accordingly, a spindle for drilling is required to have high-speed rotation and high-precision rotation in order to ensure cutting speed and increase processing efficiency.

  In a static pressure gas bearing that uses a self-formed throttle or orifice throttle to rotatably support the spindle in a spindle motor, it is determined by bearing rigidity, bearing gap distance, damping characteristics in the bearing gap, shaft inertia moment, etc. About twice as much as the primary resonance speed, self-excited vibration (Whirl phenomenon) occurs and the rotation of the spindle becomes unstable. The maximum rotation speed of the spindle is the bearing rigidity, bearing gap distance, damping characteristics in the bearing gap, Although it depends on the moment of inertia of the shaft, etc., it is approximately 150,000 rpm, and if it exceeds that, the rotational operation of the spindle becomes unstable due to self-excited vibration.

  For example, in the static pressure gas bearing mechanism using the floating bush proposed in Non-Patent Documents 1 and 2, it is said that relatively high rigidity and excellent high-speed stability can be obtained. In the gas bearing mechanism, the supply of high-pressure air to the bearing clearance around the outer peripheral surface and inner peripheral surface of the floating bush is limited only from both end surfaces of the floating bush. It is difficult to effectively attenuate the vibration of the floating bush in the radial direction, and even in the proposed hydrostatic gas bearing mechanism using the floating bush, a higher primary resonance speed cannot be achieved. The stability limit speed is about 1300 rps, and 150,000 rpm or more cannot be obtained.

  In addition, in the static pressure gas bearing mechanism described in Non-Patent Documents 1 and 2, since the high pressure air is supplied from the both end surfaces of the floating bush to the outer peripheral surface and the inner peripheral surface of the floating bush, the structure is It becomes complicated and increases the manufacturing cost.

  The present invention has been made in view of the above points, and the object of the present invention is to utilize the features of the floating bush that can obtain relatively high rigidity and excellent high-speed stability, and more An object is to provide a static pressure gas bearing mechanism capable of achieving a high primary resonance speed, further improving the stability limit speed, and having a simple structure, and a shaft rotating device and a spindle motor using the same. .

  The static pressure gas bearing mechanism of the present invention includes a hollow body, a floating bush disposed inside the hollow body with a gap in a radial direction and an axial direction with respect to the hollow body, and the hollow body and the floating bush. A shaft that is arranged inside the hollow body with a gap in the radial direction and the axial direction and that is rotatable with respect to the hollow body, and supply of high-pressure air from the outside of the hollow body to the inside of the hollow body An air passage and an exhaust passage for exhausting high-pressure air from the inside of the hollow body to the outside of the hollow body, and the floating bush is arranged in the axial direction and has a cylindrical porous metal structure. At least two floating bush bodies made of a ligated body, and the shaft passes through the two floating bush bodies in a radial direction with respect to the two floating bush bodies and at least one of the floating bush bodies. Inside edge A shaft body that protrudes to the outside of the body, and a flange that is integrally formed with the shaft body and that is disposed between the two floating bush bodies with a gap in the axial direction with respect to the two floating bush bodies The shaft is supported so as to be relatively rotatable in a floating state with respect to the hollow body via a floating bush arranged in a floating state between the hollow body and the shaft. .

  According to the hydrostatic gas bearing mechanism of the present invention, the shaft is relatively floated in the radial direction and the axial direction with respect to the hollow body via the floating bush arranged in a floating state between the hollow body and the shaft. Each of the two floating bush bodies of the floating bush has a large number of pores inside and a porous surface with a large number of such pores open on the surface. Since it is made of a sintered metal, high-pressure air supplied from the air supply passage into the hollow body can be introduced into a large number of pores inside the floating bush body. Since the air can be supplied to both gaps again from the small pores, both gaps can be secured reliably, and even if the gap distance is increased, high rigidity can be maintained and the stability limit speed can be further improved. Can be made.

  The shaft rotating device of the present invention includes the above-described static pressure gas bearing mechanism and a rotating means that is provided inside the hollow body and rotates the shaft relative to the hollow body.

  A spindle motor of the present invention as a preferred example of a shaft rotating device includes a hollow body, a floating bush disposed in the hollow body with a gap in a radial direction and an axial direction with respect to the hollow body, the hollow body, and the floating bush A spindle that is arranged with a gap in the radial direction and in the axial direction and is rotatable with respect to the hollow body, an air supply passage for supplying high-pressure air from the outside of the hollow body to the inside of the hollow body, and A static pressure gas bearing mechanism having an exhaust passage for exhausting high-pressure air from the inside of the hollow body to the outside of the hollow body, and a spindle that is provided inside the hollow body and is relatively positioned relative to the hollow body A spindle motor having a rotating means for rotating, wherein the floating bush is arranged in the axial direction and has at least two floats made of a cylindrical porous metal sintered body. The spindle has a bush body, and the spindle penetrates the two floating bush bodies with a gap in the radial direction, and at least one end protrudes outside the hollow body. And a flange portion formed integrally with the spindle body and disposed between the two floating bush bodies with a gap in the axial direction with respect to the two floating bush bodies. The hydrostatic gas bearing mechanism is configured to support the spindle so as to be relatively rotatable in a floating state with respect to the hollow body via a floating bush arranged in a floating state between the hollow body and the spindle. ing.

  The floating bush preferably has at least one annular groove on its cylindrical outer peripheral surface.

  By having such an annular groove, high-pressure air can be reliably introduced into the pores inside the floating bush body, and the high-pressure air from the air supply passage can be introduced by the numerous pores inside the floating bush body. As a result, high pressure air can be supplied to both gaps again from a large number of pores, so that even if the gap distance is increased, higher rigidity can be maintained, and the stability limit speed can be further increased. Can be improved.

  The porous metal sintered body contains at least tin, phosphorus, and copper, and further includes a metal powder containing at least one of nickel, chromium, and manganese, and graphite, boron nitride, fluorinated graphite, and fluoride. A preferable example is a product obtained by mixing and sintering an inorganic powder containing at least one of calcium, aluminum oxide, silicon oxide, and silicon carbide. Therefore, the static pressure of the present invention is preferably used. The floating bush body made of a porous metal sintered body of a gas bearing mechanism includes a metal portion containing at least tin, phosphorus and copper, and an inorganic portion including graphite, boron nitride, graphite fluoride, calcium fluoride, and oxidation. It contains at least one of aluminum, silicon oxide and silicon carbide, and in another preferred example, the float of the hydrostatic gas bearing mechanism of the present invention. Bush bodies, metal parts, nickel, may further comprise at least one of chromium and manganese, the invention is not limited thereto. By firing such a mixture of metal powder and inorganic powder, a passage composed of a large number of pores is formed in the floating bush. Furthermore, the surface of the porous metal sintered body is opened by cutting or grinding the surface including the cylindrical outer peripheral surface and inner peripheral surface and both end faces of the porous metal sintered body after firing. The aperture can be formed in the pores in the porous metal sintered body by the opening, and the floating bush body made of the porous metal sintered body whose surface is cut or ground is used. As a result, the high pressure air introduced into the floating bush can be supplied again from a large number of pores in the floating bush through the surface restriction and supplied to both the gaps. Extremely high rigidity can be maintained, and the stability limit speed can be further improved. In the case of a floating bush body having an annular groove on a cylindrical outer peripheral surface, the pores of the porous metal sintered body defining the annular groove are not narrowed by the opening in the annular groove wall surface. It is recommended that no cutting or grinding be performed so that high-pressure air can be easily introduced into the pores in the floating bush through this non-squeezed opening. Each diameter of a large number of pores in the floating bush is, for example, an average of about 80 μm, and each opening diameter of the narrowed pores after cutting or grinding is an average of about 30 μm.

  The rotating means may include an air motor having a turbine blade fixed to the flange portion and an air supply means for supplying high-pressure air to the turbine blade. An electric motor having a fixed rotor and a stator for rotating the rotor may be provided.

  According to the present invention, the characteristics of the floating bush capable of obtaining relatively high rigidity and excellent high-speed stability can be utilized, and a higher primary resonance speed can be obtained, and the stability limit speed can be further increased. It is possible to provide a static pressure gas bearing mechanism which can be improved and can have a simple structure, and a shaft rotating device and a spindle motor using the same.

  Next, the present invention will be described in more detail based on an example of a preferred embodiment shown in the drawings. The present invention is not limited to these examples.

  1 to 4, a spindle motor 1 as a shaft rotating device of this example includes a static pressure gas bearing mechanism 2 and a rotating means 3.

  The hydrostatic gas bearing mechanism 2 includes a hollow body 11, a floating bush 15 disposed in the inside 14 of the hollow body 11 with a gap 13 in the radial direction A and the axial direction B with respect to the hollow body 11, and the hollow body 11. A shaft that is arranged in the inside 14 of the hollow body 11 with a gap 16 in the radial direction A and the axial direction B with respect to the floating bush 15 and that is rotatable in the direction R about the axis C with respect to the hollow body 11. As a spindle 17, an air supply passage 19 for supplying high-pressure air from the outside 18 of the hollow body 11 to the inside 14 of the hollow body 11, and from the inside 14 of the hollow body 11 to the outside 18 of the hollow body 11. And an exhaust passage 20 for exhausting high-pressure air.

  The hollow body 11 includes an outer hollow member 31 and an inner hollow member 32 disposed inside the outer hollow member 31, and the outer hollow member 31 is formed on the cylindrical member 33 and both end surfaces of the cylindrical member 33. The inner hollow member 32 includes a pair of cylindrical members 37 and 38 fixed to the cylindrical inner peripheral surface 36 of the cylindrical member 33, and a pair of cylindrical members 37. And 38, an annular member 39 disposed between the facing one end portions and fixed to the one end portion, and lid members 40 and 41 fixed to the other end portions of the cylindrical members 37 and 38. .

  The floating bush 15 includes two floating bush bodies 45 and 46 that are arranged in the axial direction B and are formed of a cylindrical porous metal sintered body, and includes at least tin, phosphorus, and copper. And an inorganic portion mixed with the metal portion and containing at least one of graphite, boron nitride, graphite fluoride, calcium fluoride, aluminum oxide, silicon oxide, and silicon carbide. Each of the floating bush bodies 45 and 46 has an annular groove 48 on its cylindrical outer peripheral surface 47.

  The floating bush body 45 having a large number of pores inside and having each of the numerous pores opened on the entire surface has a radial direction of about 10 μm between the outer peripheral surface 47 and the inner peripheral surface 50 of the cylindrical member 37. A cylindrical member is formed in the inside 14 of the inner hollow member 32 with a gap 51 of A and a gap 54 in the axial direction B of about 10 μm between one annular end surface 52 and the annular inner side surface 53 of the lid member 40. 37, the floating bush body 46 having a large number of pores therein and each of the numerous pores opening on the entire surface has an outer peripheral surface 47 and an inner peripheral surface 55 of the cylindrical member 38. Further, a gap 56 in the radial direction A of about 10 μm is provided, and an gap B in the axial direction B of about 10 μm is similarly provided between the one annular end surface 57 and the annular inner side surface 58 of the lid member 41. Inside the inner hollow member 32 It is arranged in the cylindrical member 38 concentric to.

  The spindle 17 has two floating bush bodies 45 with gaps 68 and 69 having an outer peripheral surface 67 of about 10 μm in the radial direction A with respect to the cylindrical inner peripheral surfaces 65 and 66 of the two floating bush bodies 45 and 46. And a spindle main body 71 as a shaft main body having one end 70 protruding to the outside 18 of the hollow body 11 and two floats integrally formed with the spindle main body 71. Side surfaces 74 and 75 are approximately 10 μm in the axial direction B with respect to the annular end surfaces 72 and 73 of the two floating bush bodies 45 and 46 between the other annular end surfaces 72 and 73 of the bush bodies 45 and 46 facing each other. And an annular flange portion 78 disposed with gaps 76 and 77.

  The spindle main body 71 penetrates the lid member 40 with an annular gap 82 at the other end 81, and the lid member 41 with an annular gap 84 at a portion 83 between the end 70 and the flange portion 78. It penetrates through the lid member 35 with an annular gap 85 on the end 70 side. Similarly to the end portion 70, the end portion 81 may penetrate the lid member 34 with an annular gap.

  The flange portion 78 is arranged concentrically with the annular member 39 with an annular gap 93 on the outer peripheral surface 92 with respect to the annular inner peripheral surface 91 of the annular member 39.

  Each of the gaps 82, 84, and 85 has a width in the radial direction A that is sufficiently larger than the width in the radial direction A of the gaps 68 and 69.

  In the floating bush 45, the outer peripheral surface 47, the end surfaces 52 and 72, and the inner peripheral surface 65 are cut or ground except for the annular groove wall surface 49 that defines the annular groove 48, so that a large number of pores inside. The outer peripheral surface 47, the end surfaces 52 and 72, and the inner peripheral surface 65 are narrowed. Similarly, the floating bush body 46 has the outer peripheral surface 47, except for the annular groove wall surface 49 defining the annular groove 48. Cutting or grinding is performed on the end surfaces 57 and 73 and the inner peripheral surface 66, and openings at the outer peripheral surface 47, the end surfaces 57 and 73, and the inner peripheral surface 66 of a large number of internal pores are narrowed.

  The air supply passage 19 includes a through hole 95 formed in the cylindrical member 33 and the cylindrical member 37, and a through hole 96 formed in the cylindrical member 33 and the cylindrical member 38. The through holes 95 and 96 are respectively provided. Is open to the respective annular grooves 48 of the floating bush bodies 45 and 46 at one end thereof and is opened in the gaps 51 and 56 in the interior 14 respectively. One end of each of the air supply plugs 97 and 98 is fitted, and each of the plugs 97 and 98 is connected to a high-pressure air source via a pipe 99.

  The air supply passage 19 is formed in such a manner that the high-pressure air from the plugs 97 and 98 connected to the high-pressure air source passes through holes 95 and 96 in the gaps 51 and 56 in the inside 14 in the substantially central portion in the axial direction B, that is, in an annular shape. Air is supplied to each portion where the groove 48 is located.

  The exhaust passage 20 has a hollow portion 110 between the lid member 34 and the lid member 40 inside the outer hollow member 31, and opens to the outside 18 at one end and opens to the hollow portion 110 at the other end and is drilled in the cylindrical member 33. A plurality of through-holes 111, one end opening into the hollow portion 110 and the other end opening into the interior 14 and drilling in the lid member 40, and the lid member 35 inside the outer hollow member 31. And the hollow portion 113 between the cover member 41, one end opening to the outside 18 and the other end opening to the hollow portion 113 and drilling through the cylindrical member 33, and one end opening to the hollow portion 113. At the other end, a plurality of through-holes 115 opened in the inner part 14 and perforated in the lid member 41 are opposed to the outer peripheral surface 92 of the flange portion 78 and at one end opened to the gap 93 and at the other end. And and a plurality of through-holes (not shown) drilled in the cylindrical member 33 and the annular member 39 and the outside 18.

  The exhaust passage 20 opens high-pressure air on the floating bush body 45 side of the interior 14 on the one hand through the through hole 112, the hollow portion 110 and the through hole 111, and on the other hand, opens into the gap 93 and perforates the cylindrical member 33. The air is exhausted to the outside 18 through a plurality of through holes (not shown), and the high-pressure air on the floating bush body 46 side of the inside 14 is on the one hand through the through hole 115, the hollow portion 113, and the through hole 114. Then, the air is exhausted to the outside 18 through a plurality of through holes (not shown) opened in the gap 93 and drilled in the cylindrical member 33.

  The above-described hydrostatic gas bearing mechanism 2 is configured such that the spindle 17 is floated relative to the inner hollow member 32 via the floating bush bodies 45 and 46 arranged in a floating state between the inner hollow member 32 and the spindle 17. Thus, it is rotatably supported in the direction R.

  The rotating means 3 that is provided in the inside 14 of the hollow body 11 and rotates the spindle 17 in the direction R relative to the hollow body 11 includes a plurality of turbine blades 121 fixed to the outer peripheral surface 92 of the flange portion 78. And an air motor 123 having air supply means 122 for supplying high-pressure air to the turbine blades 121, and the air supply means 122 is connected to a high-pressure air source via a pipe 124. In addition, the outer hollow member 31 and the annular member 39 have a pair of nozzles 125 fitted in opposition to each other, and the high-pressure air injected from the nozzle 125 toward the turbine blades 121 is flanged via the turbine blades 121. The portion 78 is rotated in the direction R, and the high-pressure air obtained by rotating the flange portion 78 in the direction R opens into the gap 93 and is cylindrical. And it is discharged to the outside 18 through a through hole (not shown) drilled in wood 33.

  In the above spindle motor 1 in which the floating bush body 45 side and the floating bush body 46 side are substantially the same, the spindle body 71 is also moved in the same direction by rotating the flange portion 78 in the direction R by the rotating means 3. It is rotated. In the rotation of the spindle 17 in the direction R, when high-pressure air is supplied to the interior 14 through the supply passage 19, the high-pressure air is converted into the gap 13 including the gaps 51, 54, 56 and 59, and the gap 68, As a result of being supplied to the gap 16 consisting of 69, 76 and 77 and causing the floating bush bodies 45 and 46 to float between the inner hollow member 32 and the spindle 17, the spindle 17 passes through the floating bush bodies 45 and 46. The inner hollow member 32 is supported so as to be rotatable relative to the direction R in a floating state.

  The high-pressure air supplied to the interior 14 by the air supply passage 19 is, as shown by the flow P in FIG. 5, the annular groove 48, the surface restriction between the outer peripheral surface 47 and the inner peripheral surface 50, and the outer peripheral surface 47. Is directly ejected into the gaps 51 and 56 through a surface restriction between the inner circumferential surface 55 and the inner peripheral surface 55, while floating from a large number of openings in the annular groove wall surface 49 of the floating bush bodies 45 and 46 in the annular groove 48. As a result of being partially introduced also into the pores inside the bush bodies 45 and 46, the high-pressure air introduced into the pores becomes the surface of the floating bush bodies 45 and 46 as shown by the flow Q in FIG. The high-pressure air that is jetted out again from the narrowed opening into the gap 13 and the gap 16 and is supplied to the interior 14 by the air supply passage 19 maintains the gap 13 and the gap 16, and the gap 51, 54, 56, 59, 68, 69, The fluctuations in the gap width of either 6 or 77 can be eliminated, and the gaps 13 and 16 can be reliably held stably. Therefore, even if both gap widths are increased, high rigidity can be maintained, and the spindle 17 The stability limit speed with respect to the rotation in the direction R can be further improved.

  In the above example, the rotating means 3 is configured with the air motor 123. Instead, as shown in FIG. 6, the rotating means 3 includes a rotor 131 fixed to the flange portion 78 and a rotor 131. An electric motor 134 having a stator 133 fixed to the cylindrical member 33 for rotation may be provided.

  Furthermore, in the above example, the floating bush bodies 45 and 46 are not constrained to the inner hollow member 32 so as to be able to rotate together with the rotation in the direction R of the spindle 17, but instead, as shown in FIG. One end portion of the locking pin 141 is implanted in the lid member 34 and the other end portion of the locking pin 141 is loosely fitted in the recess 142 formed in the end surface 52 of the floating bush body 45 so that the locking pin 141 is inserted. The floating bush body 45 may be constrained by the inner hollow member 32 to prevent the floating bush body 45 from rotating more than a certain amount together with the rotation in the direction R of the spindle 17. Similarly to the floating bush body 45, the floating bush body 46 may not be able to rotate more than a certain amount together with the rotation in the direction R of the spindle 17.

  In the above example, the floating bush 15 includes the two floating bush bodies 45 and 46. However, when the plurality of flange portions 78 are separated from each other in the axial direction B and are formed integrally with the spindle main body 71, the floating bush 15 is formed in a single body. Correspondingly, the floating bush 15 may include three or more floating bush bodies including the floating bush body disposed between the flange portions 78. In this case, the floating bush 15 is disposed between the flange portions 78. The floating bush body supports the spindle 17 so as to be rotatable in a floating state mainly in the radial direction A. Further, in the above, the annular groove wall surface 49 is not subjected to cutting or grinding, and the pores inside the floating bush bodies 45 and 46 opened by the annular groove wall surface 49 are narrowed by the annular groove wall surface. However, instead of this, the pores inside the floating bush bodies 45 and 46 opened by the annular groove wall surface 49 by cutting or grinding the annular groove wall surface 49 are also formed in the annular groove wall surface 49. The high-pressure air may be introduced into the pores inside the floating bush bodies 45 and 46 from the openings thus restricted, and the introduced high-pressure air is introduced into the inside of the floating bush bodies 45 and 46. You may make it eject to the clearance gap 13 and the clearance gap 16 from the surface with the opening restrict | squeezed through the pore.

It is sectional drawing of a preferable example of embodiment of this invention. It is II-II arrow directional cross-sectional explanatory drawing of the example shown in FIG. FIG. 3 is a cross-sectional explanatory view taken along the line III-III of the example shown in FIG. 1. It is a perspective view of the floating bush body of the example shown in FIG. It is operation | movement explanatory drawing of the example shown in FIG. It is sectional drawing of another preferable example of embodiment of this invention. FIG. 10 is a partial cross-sectional view of still another preferred example of an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spindle motor 2 Static pressure gas bearing mechanism 3 Rotating means 11 Hollow body 13, 16 Crevice 14 Inside 15 Floating bush 17 Spindle 18 Outside 19 Supply passage 20 Exhaust passage

Claims (7)

A hollow body, a floating bush disposed inside the hollow body with a gap in the radial direction and the axial direction with respect to the hollow body, and a hollow body with a gap in the radial direction and the axial direction with respect to the hollow body and the floating bush A shaft which is arranged inside and rotatable about the hollow body, an air supply passage for supplying high-pressure air from the outside of the hollow body to the inside of the hollow body, and a hollow from the inside of the hollow body and comprising an exhaust passage for the exhaust of the high pressure air to the body of the external floating bush, I Do a cylindrical porous metal sintered body with being arranged in the axial direction, the through-hole At least two floating bush bodies, and the shaft passes through the through holes of the two floating bush bodies in a radial direction with respect to the two floating bush bodies in each through hole. And at least A shaft main body having one end projecting outside the hollow body, and the shaft main body formed integrally with the shaft main body and between the two floating bush bodies in the axial direction. And a flange portion arranged with a gap, and supports the shaft so as to be relatively rotatable in a floating state with respect to the hollow body via a floating bush arranged in a floating state between the hollow body and the shaft. Each floating bush body having a large number of pores therein includes a cylindrical outer peripheral surface having at least one annular groove, an annular groove wall surface defining the annular groove, a shaft One annular end surface in the direction, the other annular end surface in the axial direction, and a cylindrical inner peripheral surface defining the through hole, and a large number of pores are constricted in the annular groove wall surface. Without opening and cylindrical outer peripheral surface One and the end face of the annular, the other annular end face and a cylindrical narrowed in the inner peripheral surface opening to which the externally pressurized gas bearing mechanism. The floating bush body includes a metal portion containing at least tin, phosphorus and copper, and is mixed with the metal portion and is made of graphite, boron nitride, graphite fluoride, calcium fluoride, aluminum oxide, silicon oxide and silicon carbide. The hydrostatic gas bearing mechanism according to claim 1, further comprising an inorganic portion including at least one of the following. 3. A shaft rotating device comprising: the static pressure gas bearing mechanism according to claim 1; and a rotating means that is provided inside the hollow body and rotates the shaft relative to the hollow body. The rotation means includes an air motor having a turbine blade fixed to the flange portion and an air supply means for supplying high-pressure air to the turbine blade, or a rotor fixed to the flange portion, and rotates the rotor. The shaft rotation device according to claim 3, comprising an electric motor having a stator. A hollow body, a floating bush disposed in the hollow body with a gap in the radial direction and the axial direction with respect to the hollow body, and a gap in the radial direction and the axial direction with respect to the hollow body and the floating bush. And a spindle that is rotatable with respect to the hollow body, an air supply passage for supplying high-pressure air from the outside of the hollow body to the inside of the hollow body, and exhaust of high-pressure air from the inside of the hollow body to the outside of the hollow body A spindle motor comprising a static pressure gas bearing mechanism having an exhaust passage for the motor and a rotating means provided inside the hollow body and rotating the spindle relative to the hollow body. The floating bush includes at least two floating bush bodies that are arranged in the axial direction and are formed of a cylindrical porous metal sintered body and that have through holes. A spindle in which each through hole penetrates each through hole of the two floating bush bodies with a gap in the radial direction with respect to the two floating bush bodies, and at least one end protrudes outside the hollow body. A main body and a flange portion formed integrally with the spindle main body and disposed between the two floating bush bodies with a gap in the axial direction with respect to the two floating bush bodies; Each floating bush body having a large number of pores therein includes a cylindrical outer peripheral surface having at least one annular groove, an annular groove wall surface defining the annular groove, and one annular end face in the axial direction. And the other annular end surface in the axial direction and a cylindrical inner peripheral surface defining the through hole, and a large number of pores are opened without being constricted on the annular groove wall surface. Both the cylindrical outer peripheral surface, the one annular end surface, the other annular end surface, and the cylindrical inner peripheral surface are squeezed and opened, and the hydrostatic gas bearing mechanism includes a hollow body and a spindle. A spindle motor adapted to rotatably support the spindle in a floating state relative to the hollow body via a floating bush arranged in a floating state between the two. The rotation means includes an air motor having a turbine blade fixed to the flange portion and an air supply means for supplying high-pressure air to the turbine blade, or a rotor fixed to the flange portion, and rotates the rotor. The spindle motor according to claim 5, comprising an electric motor having a stator. The floating bush body includes a metal portion containing at least tin, phosphorus and copper, and is mixed with the metal portion and is made of graphite, boron nitride, graphite fluoride, calcium fluoride, aluminum oxide, silicon oxide and silicon carbide. The spindle motor according to claim 5, further comprising an inorganic portion including at least one of the following.

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