JPH10318260A - Hydrostatic bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrostatic bearing to improve load capacity by a dynamic pressure effect and reduce an influence exercised by penetration of water and oil and be excellent in at least reliability. SOLUTION: This hydrostatic bearing comprises a rotary body 2; a surrounding member 1 rotatably supporting the rotary body 2; and a feed air hole 3 formed in the surrounding member 1. Pressure gas for generating a static pressure is introduced between a rotary body 2 and the surrounding member 1 through the feed air hole 3, and the rotary body 2 is radially supported by a dynamic pressure generated between the two members 1 and 2. Feed air hole trains G1 and G2 consisting of a plurality of feed air holes 3 are separately formed in the two spots of the surrounding member 1. A groove W2 having width higher than or equal to a separate distance W1 between the feed air holes G1 and G2 is peripherally formed at least in either the outer peripheral surface of the rotary body 2 or the inner peripheral surface of the surrounding member 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic bearing.

[0002]

2. Description of the Related Art Conventionally, there has been generally known a hydrostatic bearing including a rotating body, a surrounding member rotatably supporting the rotating body, and an air supply hole formed in the surrounding member. This type of bearing is configured such that the rotating body is radially supported in a non-contact state by dynamic pressure generated between the rotating body and the surrounding member.

Usually, a bearing radial gap of about 20 to 50 μm is provided between the rotating body of the hydrostatic bearing and the surrounding member. Pressurized gas for generating a static pressure is introduced into such a bearing gap through the air supply hole. The air supply holes are provided in a row along the peripheral surface of the surrounding member.

[0004]

However, the conventional apparatus has the following problems. As shown in FIG. 4, the optimum bearing radial gap at which the load capacity of the hydrostatic bearing is maximized is relatively larger than that of the dynamic pressure bearing. With a bearing radius gap of 20 μm or less, the characteristics as a bearing tend to decrease, and in general, the optimal bearing radius gap of a hydrostatic bearing is around 25 μm. However, even with the optimum bearing radius gap, the load capacity varies depending on the shaft diameter, the shaft length, and the like.
A small-diameter hydrostatic bearing has a small load capacity, and thus may come into solid contact during high-speed rotation or the like.

[0005] It is known that when conditions such as shaft diameter, shaft length, and air pressure are regulated, an orifice throttle or the like may be provided at the outlet of the air supply hole. However, with such a static pressure bearing, while the load capacity is improved, the production becomes considerably difficult.

Therefore, there is a method in which both the load capacity and the rigidity are improved by setting the bearing radial gap to 15 μm or less and effectively utilizing the dynamic pressure effect obtained by the rotation of the rotating body. However, as shown in FIG. 5, when the rotational speed is low, only a small load capacity can be obtained, and there is a problem that the characteristics of the bearing deteriorate. Also,
When the bearing radial gap is set to be small in this way, when water, oil, or the like enters the bearing radial gap, the bearing characteristics are significantly reduced due to an increase in load due to viscous resistance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve the load capacity by the dynamic pressure effect, and to reduce the influence on the intrusion of water and oil and to improve the reliability. An object of the present invention is to provide an excellent hydrostatic bearing.

[0008]

According to the first aspect of the present invention, there is provided a rotary member, a surrounding member for rotatably supporting the rotary member, and a static pressure generated between the two. An air supply hole formed in the surrounding member to introduce a pressurized gas for use with a hydrostatic bearing in which the rotating body is radially supported by dynamic pressure generated between the rotating body and the surrounding member. An air supply hole array including a plurality of air supply holes is formed at two positions of the surrounding member at a distance, and at least one of an outer peripheral surface of the rotating body and an inner peripheral surface of the surrounding member, The gist of the present invention is a hydrostatic bearing characterized in that grooves having a width equal to or greater than the separation distance of the air supply hole array are arranged along the circumferential direction.

According to a second aspect of the present invention, in the first aspect, the bearing radial gap of the hydrostatic bearing is 3 μm to 15 μm.
μm. According to a third aspect of the present invention, in the first or second aspect, the depth of the groove is 1 to 10 times the bearing radial gap.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the groove is a circumferential groove extending over the entire peripheral surface. According to a fifth aspect of the present invention, in any one of the first to fourth aspects, at least one of the rotating body and the surrounding member is made of ceramics.

Hereinafter, the "action" of the present invention will be described. According to the first to fifth aspects of the present invention, even when the bearing radial gap is set to be small (for example, 15 μm or less) in order to effectively use the dynamic pressure effect, a static pressure is generated by introducing the bearing radial gap. The pressurized gas is quickly guided by grooves provided on the peripheral surface of the rotating body or the peripheral surface of the surrounding member.
Therefore, the pressurized gas spreads over the entire circumferential direction of the rotating body and the surrounding member. As a result, the static pressure distribution around the rotating body is made uniform, and the eccentricity of the rotating body is prevented.

In addition, with this configuration, a sufficient load capacity can be obtained even when the rotational speed is low, so that the characteristics of the bearing are not impaired. Further, in this configuration, since the bearing radial gap is partially widened, a problem such as an increase in load due to viscous resistance when water or oil or the like enters does not occur. Therefore, even in this case, the bearing characteristics do not deteriorate and the reliability is excellent. In addition, since the structure does not require the formation of the orifice diaphragm, the production does not become difficult.

Here, it is preferable that the groove is provided only on the outer peripheral surface side of the rotating body disposed in the surrounding member. The reason is that it is easier to groove the outer peripheral surface of the member than to groove the inner peripheral surface of the member, and high processing accuracy can be obtained.

The width of the groove may be equal to or greater than the separation distance of the air supply hole array. On the other hand, if the width is excessively increased, the area of the opposing surface for generating dynamic pressure is relatively reduced, and the load is reduced. May be reduced. Therefore, it is desirable that the value of the width of the groove is slightly larger than the separation distance of the air supply hole array.

According to the second aspect of the present invention, by setting the bearing radial gap of the hydrostatic bearing to 3 μm to 15 μm, a large load capacity and high rigidity can be obtained.

According to the third aspect of the present invention, since the depth of the groove is set in a preferable range of 1 to 10 times the radial gap of the bearing, it has a function as a static pressure bearing and supplies a pressurized gas. A groove having a sufficient size as a road can be obtained. That is, if the groove is too shallow, the groove may not function effectively as a pressurized gas supply path. Conversely, if the groove is too deep, the groove will not have a function as a hydrostatic bearing.

According to the fourth aspect of the present invention, no matter what position the rotating body is eccentric with respect to the enclosing member, the eccentricity results in the peripheral surface having a narrowest bearing radial gap. Pressurized gas is always supplied through a groove extending throughout. Therefore, even if the rotating body is eccentric, the rotating body can always reliably return from the eccentric position to the center position. Further, the pressurized gas for generating the static pressure is more quickly guided by the circumferential groove provided on the peripheral surface of the rotating body or the peripheral surface of the surrounding member. For this reason,
The pressurized gas reliably spreads over the entire circumferential direction of the rotating body and the surrounding member.

According to the fifth aspect of the invention, since it is a ceramic, it is resistant to sliding.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a radial hydrostatic bearing of a dental rotary drive device will be described below with reference to the drawings.

First, the overall configuration of the dental rotary drive will be described. FIG. 3 shows a dental rotary drive device of the present embodiment. The plate 16 is fixed to an opening at one end (right end in the figure) of the substantially cylindrical casing 21. An insertion hole 2a is formed through the center of the plate 16. The outer periphery of the plate 16 and the casing 2
An O-ring 26 is interposed between the inner ring 1 and the inner peripheral surface. The right end of the casing 21 is closed by these members 21, 16 and 26. On the other hand, a mounting ring 29 is formed on the other end (the left end in the drawing) of the casing 21 so as to extend over the entire inner peripheral surface of the casing 21. An annular packing 6 is provided on the left outside.
The attachment 5 is fixed via the. At the center of the attachment 5, an insertion hole 5a is formed. Then, the casing 2 is formed by these members 5 and 6.
1 is closed at the left end. The motor chamber 7 is defined in a region of the casing 21 closed by the plate 16 and the attachment 5.

As shown in FIG. 3, the attachment 5
A handpiece H is fitted on the outer peripheral surface of the. The handpiece H is a cylindrical member having a thin tip portion. At the joint between the attachment 5 and the handpiece H, a locking member P is provided. The handpiece H is detachably locked to the casing 21 by the locking member P. A dental cutting drill (not shown) is provided at the tip of the handpiece H. A handpiece-side shaft HS is rotatably inserted into the insertion hole 5a of the attachment 5. The shaft HS is supported by bearings B. The drill is
The shaft HS is rotated to be driven to rotate. An air outlet, a water outlet, and a light irradiation port (not shown) are provided near the drill.

Inside the attachment 5 and the handpiece H, a water pipe having a water jet at the tip and an air pipe having an air jet at the tip are provided.
These pipes communicate with each other. Water for dental treatment is supplied from a water jet through a water pipe, and air is supplied from an air jet through an air pipe. As shown in FIG. 2, an optical fiber 9b for illumination is provided in the insides of the both 5 and H. This optical fiber 9b
Thus, light is transmitted to the irradiation port. On the other hand, a passage 5b communicating with the insertion hole 5a is formed in the handpiece H. The air discharged from the motor chamber 7 is supplied to the air outlet through the passage 5b.

As shown in FIG.
, A plurality of motor wiring connector pins 28 and the air inflow holes 8 are provided concentrically therethrough. Casing 21
Pressurized air is sent into the motor chamber 7 from an external blower (not shown) connected to the dental rotary drive device.
The plate 16 and the mounting ring 29 are formed with a plurality of through holes 9 at positions facing each other. The water pipe 9a and the optical fiber 9b are inserted into the space 10 of the motor chamber 7 through the plate-side through-hole 9 and then into the ring-side through-hole 9. These 9a and 9b are connected to the attachment 5 side.

As shown in FIG. 3, a power transmission shaft 11 is rotatably accommodated in the motor chamber 7.
This shaft 11 extends in the longitudinal direction of the device. One end of the shaft 11 is loosely inserted into the insertion hole 2 a of the plate 16, and the other end is loosely inserted into the insertion hole 5 a of the attachment 5. The outer peripheral surface of the shaft 11 and each of the insertion holes 5a,
There is a space S of a certain size between the inner peripheral surface of 5a.

A rotor R is mounted in a region of the power transmission shaft 11 inside the motor chamber 7. Hereinafter, the rotor R will be described. Both ends of the power transmission shaft 11 are provided with annular bushes 12 respectively.
Has been fixed. A field magnet 13 is held between these bushes 12. Field magnet 1
3 is constituted by four permanent magnets 14 here. The four permanent magnets 14 are arranged alternately so that magnetic poles adjacent to each other around the shaft 11 have different polarities, and are arranged so as to be cylindrical as a whole.

As shown in FIG. 3, fitting step portions 15 are formed in the outer periphery of the opposing end surfaces of the bushes 12 in a ring shape. A cylindrical cover 2 forming a part of the rotor R is fitted between the bushes 12. The outer peripheral surface of the field magnet 13 is surrounded and protected by the cylindrical cover 2. The cylindrical cover 2 is a member formed in a cylindrical shape, and is made of a ceramic sintered material (in this embodiment, a silicon carbide sintered material).

Annular magnets 17a and 17b as magnetic members are fixed to the end faces of the bushes 12 that are not opposed to each other. An annular magnet 19a, also serving as a magnetic member, is fitted on the inner peripheral surface of the fitting step 18 of the plate 16 so as to face the annular magnet 17a. Similarly, a mounting ring 20 protruding from the attachment 5.
An annular magnet 19b, which is also a magnetic member, is fitted on the inner peripheral surface of the, facing the annular magnet 17b. These two sets of opposed annular magnets 17a, 1
9a and 17b, 19b are arranged such that the same magnetic poles face each other. Therefore, the paired annular magnets 17a and 19a are separated from each other by the magnetic repulsion with the space S1 therebetween. The same applies to another pair of annular magnets 17b and 19b. Thereby, the movement of the power transmission shaft 11 in the thrust direction is restricted.

The rotor R of this device is connected to the bush 12, the field magnet 13, the cylindrical cover 2, and the annular magnet 1 with respect to the power transmission shaft 11 as described above.
7a and 17b are integrally fixed. Further, the annular magnets 19a and 19b and the annular magnets 17a and 17b opposed thereto constitute a thrust magnetic bearing.

Next, the specific structure of the hydrostatic bearing provided in this device will be described in detail. As shown in FIGS. 1 to 3, the static pressure bearing includes a cylindrical cover 2 as a rotating body and an enclosing member 1 as constituent elements. Surrounding member 1
Is a fixed-side member formed in a cylindrical shape (in this embodiment, the outer diameter φ
13 mm) and is made of a ceramic sintered material (in the present embodiment, made of a silicon carbide sintered material). One end of the surrounding member 1 is supported by the fitting step 22 of the plate 16. The other end of the surrounding member 1 is supported by a fitting step 23 formed on a mounting ring 29 of the casing 21. The rotor R is entirely and rotatably accommodated on the inner peripheral surface side of the surrounding member 1. Therefore, the outer peripheral surface of the cylindrical cover 2 which is a part of the rotor R and the inner peripheral surface of the surrounding member 1 are opposed to each other at a predetermined interval (that is, a bearing radial gap) C. In addition, the inner peripheral surface of the surrounding member 1 is polished so as to have a peripheral surface excellent in contact slidability.

The bearing radial gap C shown in FIG.
Is preferably set to 3 μm to 15 μm, more preferably 5 μm to 14 μm, and particularly preferably 8 μm to 14 μm.
It is preferable that the distance be set to μm to 12 μm. This is because with such a setting, a static pressure bearing having a large load capacity and high rigidity can be obtained. Therefore, in the present embodiment, the gap C is set to 8 μm to 12 μm.

As shown in FIG. 1, the surrounding member 1 is formed with a plurality of (in this embodiment, a total of six) air supply holes 3. The air supply hole 3 allows the inner peripheral surface and the outer peripheral surface of the surrounding member 1 to communicate with each other. Each air supply hole 3 is connected to an air compressor (not shown). When the air compressor is operated, the pressurized air for generating dynamic pressure flows through each air supply hole 3 into the gap C.
Will be introduced. This pressurized air generates a dynamic pressure between the surrounding member 1 and the cylindrical cover 2.

In this embodiment, three of the air supply holes 3 constitute one first air supply hole array G1, and the other three air supply holes 3 separately form a second air supply hole array G2. . Each of these rows G1 and G2 extends along the circumferential direction of the surrounding member 1. The first air supply hole row G1 is located on the distal end side of the surrounding member 1, and the second air supply hole row G2 is located on the base end side of the surrounding member 1. That is, two air supply hole arrays G1, G2
Are formed at two places on the surrounding member 1 so as to be separated by a separation distance W1. The three air supply holes 3 constituting the air supply rows G1 and G2 are formed by a circle obtained by cutting the surrounding member 1 perpendicularly to the axial direction at 0 °, 120 °.
° and 240 °.

As shown in FIG. 1, the cylindrical cover 2 has a groove 4 on its outer peripheral surface. The groove 4 is a circumferential groove 4 and is formed so as to extend annularly over the entire outer peripheral surface of the cylindrical cover 2.

The circumferential groove 4 is formed so as to have a width W2 equal to or greater than the distance W1 between the air supply hole arrays G1 and G2. It is desirable that the value of the width W2 of the circumferential groove 4 is slightly larger (about several mm larger) than the separation distance W1. Circumferential groove 4
If the width W1 is excessively widened, the area of the facing surface used for generating the dynamic pressure is relatively reduced, and the allowable load of the load may be reduced. Therefore, the air supply hole array G1,
In the present embodiment in which the separation distance W1 of G2 is 14 mm, the width W2 of the circumferential groove 4 is set to 16 mm. Further, both of the supply hole arrays G1 and G2 are located at positions facing the circumferential groove 4.

The depth of the circumferential groove 4 is set to 0.5 to 15 times, more preferably 1 to 10 times, particularly 1.5 to 3 times the bearing radial gap C. Good to be. If the circumferential groove 4 is too shallow, there is a possibility that the circumferential groove 4 may not function effectively as a pressurized gas supply passage. Conversely, if it is too deep, the circumferential groove 4 will not have a function as a hydrostatic bearing. Incidentally, the preferable range of the depth W2 of the circumferential groove 4 depends on the dimensions of the cylindrical cover 2 and the surrounding member 1 and the like, but is generally about 1 μm to 20 μm.
It is preferably about 15 to 15 μm, and particularly preferably about 5 to 10 μm.

In this embodiment, in consideration of the above, the value of the bearing radius C of the circumferential groove 4 is set to about 1.7 times by setting the depth of the circumferential groove 4 to 7 μm. in this case,
In the region where the air supply hole arrays G1 and G2 are located, a bearing radius C1 larger than the original bearing radius gap C is apparently secured. In this embodiment, the bearing radius gap C1 in the partially widened region is 15 μm to 19 μm.

Next, the operation of the thus configured apparatus will be described. When the air compressor is driven in the above hydrostatic ^{bearings, 3kg / cm 2 ~5kg / cm} 2 of about pressurized air is supplied to each air supply hole 3. The pressurized air passes through the air supply holes 3 and is supplied to the inner peripheral surface side of the surrounding member 1. Then, the pressurized air passes through the circumferential groove 4 and forms the cylindrical cover 2.
Swiftly spread over the entire outer peripheral surface of the bearing and is reliably supplied to the bearing radial gaps C and C1. As a result, the cylindrical cover 2 floats with respect to the surrounding member 1 with the bearing radial gaps C and C1 therebetween, and is supported in the radial direction in a non-contact state.

By the way, oil is supplied to the bearing B supporting the shaft HS periodically as maintenance. If the lubricated handpiece HS is connected to a rotary drive, oil may enter the bearing radial gaps C and C1. In addition, since oil has a higher viscosity than pressurized air, problems such as generation of vibration during rotation are likely to occur. The graph of FIG. 6 shows the relationship between the elapsed time and the vibration value when oil is injected into the hydrostatic bearing. The horizontal axis of the graph is the elapsed time (seconds)
, And the vertical axis represents the vibration value (μp-p).
One curve in the graph is data of the hydrostatic bearing of the present embodiment having the circumferential groove 4. The other curve is data of a static pressure bearing (bearing radial gap C = 10 μm) of a comparative example (conventional example) having no such groove.
Then, after the lubrication was performed, the static pressure bearing was started after being left for several hours after the lubrication, and a test was performed to measure the vibration value at that time.

According to this, in the comparative example, abnormal vibration occurred, and did not return to the normal state even after a lapse of time. Further, the vibration value showed a high value of 2.5 μp-p or more. On the other hand, in the present embodiment, the vibration value becomes 1.
It was confirmed that the stability was 0 μp-p or less.

The graph of FIG. 5 shows the rotational speed (rpm) of the bearing.
m) and the load capacity (kg). Comparing the hydrostatic bearing used in the present embodiment with a hydrostatic bearing having no groove 4 and having a bearing radial gap C of 20 μm, when a radial load is applied to the rotating body (cylindrical cover) 2,
It was confirmed that the load capacity at 00 rpm was approximately doubled. This is due to both the dynamic pressure effect obtained by reducing the bearing radial gap C and the static pressure effect by pressurized gas.

Now, the characteristic effects of this embodiment will be listed below. (A) The hydrostatic bearing of this device is characterized in that the above-described circumferential groove 4 is arranged. Therefore, even if the bearing radial gap C is set to 15 μm or less in order to effectively use the dynamic pressure effect, the pressurized gas is quickly guided by the circumferential groove 4. Therefore, the pressurized gas spreads over the entire circumferential direction of the cylindrical cover 2 and the surrounding member 1. As a result, the static pressure distribution around the cylindrical cover 2 is made uniform, and the eccentricity of the rotor R is prevented.

(B) With this configuration, a sufficient load capacity can be obtained even when the rotational speed is low, so that the characteristics of the bearing are not impaired. Further, since a portion where the bearing radius C1 is partially widened is formed, a problem such as an increase in load due to viscous resistance when water or oil or the like enters does not occur. Therefore, even in this case, the bearing characteristics do not deteriorate and the reliability is excellent. Note that water, oil, and the like contained in the pressurized gas are released to the outside of the bearing by the pressurized gas.

(C) This static pressure bearing has a structure that does not require the formation of an orifice throttle. Therefore, unlike the conventional case, the production does not become difficult. (D) In the present embodiment, the circumferential groove 4 is provided only on the outer peripheral surface side of the cylindrical cover 2 disposed in the surrounding member 1. Therefore, the circumferential groove 4 having high accuracy can be formed by simply performing the groove processing.
Can be formed and the production can be facilitated.

(E) In this static pressure bearing, the cylindrical cover 2
Is eccentric with respect to the surrounding member 1 in any position. In other words, the pressurized gas is always and quickly guided and supplied to the portion where the bearing radial gap C becomes the narrowest as a result of the eccentricity, through the circumferential groove 4 extending over the entire peripheral surface. Therefore, even if the tubular cover 2 is eccentric, the tubular cover 2 can always reliably return from the eccentric position to the center position.

(F) In this hydrostatic bearing, the surrounding member 1 and the cylindrical cover 2 are both made of a silicon carbide sintered material. Therefore, compared to the case where only one is made of ceramics, it is more resistant to sliding and has higher mechanical strength. Therefore, the bearing characteristics can be further improved.

It should be noted that the present invention is not limited to the above embodiment, but can be changed to, for example, the following forms. The circumferential groove 4 may be provided only on the inner circumferential surface side of the surrounding member 1 instead of the configuration of the embodiment in which the circumferential groove 4 is provided only on the outer circumferential surface side of the cylindrical cover 2 which is a rotating body. Further, the circumferential groove 4 may be provided in both the surrounding member 1 and the cylindrical cover 2.

In place of the configuration of the embodiment in which the circumferential groove 4 is formed annularly (continuously) on the outer peripheral surface of the cylindrical cover 2 which is a rotating body, for example, an arc-shaped groove divided by a predetermined length One or a plurality of 4 may be formed so as to extend along the circumferential direction.

The ceramic sintered material used as the material of the surrounding member 1 and the cylindrical cover 2 is not necessarily a silicon carbide sintered material. For example, various sintered materials such as boron nitride, alumina, aluminum nitride, silicon nitride, and boron nitride may be used. It is also possible to select a metal material instead of ceramics.

The number of the air supply holes 4 is not limited to 3 × 2 rows. For example, the number of the air supply holes 4 belonging to one air supply hole array G1, G2 is set to two, or conversely, four, five, six,.
It may be. In addition, the number of air supply holes G1, G2 is not limited to two, but may be three or more, and they may be spaced from each other. For example, when three rows are provided, at least one of the outer peripheral surface of the cylindrical cover 2 which is a rotating body and the inner peripheral surface of the surrounding member 1 has a separation distance between the air supply hole rows located at both ends. The groove 4 having the above width may be arranged along the circumferential direction.

Here, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments are listed below together with their effects. (1) a rotating body, a surrounding member rotatably supporting the rotating body, and an air supply hole formed in the surrounding member to introduce a pressurized gas for generating a static pressure between the rotating body and the rotating body; A hydrostatic bearing in which the rotating body is radially supported by a dynamic pressure generated between the body and the surrounding member, wherein a row of air supply holes including a plurality of air supply holes is separated from each other at a plurality of locations of the surrounding member. A groove formed and formed on at least one of the outer peripheral surface of the rotating body and the inner peripheral surface of the surrounding member, and having a width equal to or greater than a separation distance between those located at both ends of the plurality of air supply hole arrays. A hydrostatic bearing, wherein are arranged along the circumferential direction. With this configuration, it is possible to provide a static pressure bearing that can improve the load capacity due to the dynamic pressure effect, has little influence on intrusion of water and oil, and is excellent in reliability.

(2) The hydrostatic bearing according to any one of claims 1 to 4, wherein the rotating body and the surrounding member are both ceramics. With this configuration, the bearing is more resistant to sliding than when only one is made of ceramics, so that the bearing characteristics can be further improved.

(3) The hydrostatic bearing according to any one of claims 1 to 4, wherein the rotating body and the surrounding member are both made of a silicon carbide sintered material. With this configuration, compared to the case where only one is made of ceramics, the sliding resistance is higher and the mechanical strength is higher, so that the bearing characteristics can be further improved.

(4) The hydrostatic bearing according to any one of claims 1 to 5, wherein the groove is arranged only on the outer peripheral surface side of the rotating body. With this configuration, it is possible to form a groove with high precision by simply performing the groove processing, and it is possible to facilitate the production.

(5) The casing, a shaft rotatably housed in the casing, a rotor housed in the casing so as to rotate integrally with the shaft, and a radial support for the rotor. A dental rotary drive device comprising the hydrostatic bearing according to any one of the technical ideas 1 to 3.

The technical terms used in this specification are defined as follows. "Sintered ceramic materials:
Silicon carbide, boron nitride, alumina, aluminum nitride,
It refers to a sintered material such as silicon nitride or boron nitride. "

[0056]

As described in detail above, according to the first to fifth aspects of the present invention, the load capacity can be improved by the dynamic pressure effect, and the influence on the intrusion of water, oil and the like is small, and the reliability is improved. Thus, an excellent static pressure bearing can be provided.

According to the second aspect of the invention, the load capacity is large and the rigidity is high. According to the third aspect of the present invention, a groove having a function as a static pressure bearing and having a sufficient size as a pressurized gas supply passage can be obtained, so that the bearing characteristics can be further improved.

According to the fourth aspect of the present invention, the rotator can always return to the center position at the time of eccentricity, and the pressurized gas can reliably spread over the entire circumferential direction of the rotator and the surrounding member. Thus, the bearing characteristics can be further improved.

According to the fifth aspect of the present invention, since the bearing is resistant to sliding, the bearing characteristics can be further improved.

[Brief description of the drawings]

FIG. 1A is a side sectional view of a hydrostatic bearing according to an embodiment of the present invention, and FIG. 1B is a front sectional view thereof.

FIG. 2 is a side view showing the dental rotary drive device of the embodiment.

FIG. 3 is a front sectional view showing the dental rotary drive device of the embodiment.

FIG. 4 is a graph showing a relationship between a bearing radial gap of a hydrostatic bearing and a load capacity.

FIG. 5 is a graph showing a relationship between the number of rotations of a hydrostatic bearing and a load capacity.

FIG. 6 is a graph showing a relationship between elapsed time and vibration value when oil is injected into a hydrostatic bearing.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Surrounding member, 2 ... Cylindrical cover as a rotating body, 3 ... Air supply hole, 4 ... Circumferential groove as groove, 5 ... Attachment, 5
a: insertion hole, 5b: passage, 6: packing, 7: motor chamber, 8: air inlet hole, 9: through hole, 9a: water pipe, 9b
... lighting optical fiber, 10 ... space, 11 ... power transmission shaft, 12 ... bush, 13 ... field magnet,
14: permanent magnet, 15, 18, 22, 23: fitting step
Reference numeral 16: plate, 17a, 17b, 19a, 19b: annular magnet as a magnetic member, 20, 29: mounting ring, 21: casing, 26: O-ring, 28: connector pin, C: bearing radial gap, C1: wide H: Handpiece, HS: Handpiece-side shaft, P: Locking member, R: Rotor, G1, G2
... air supply hole array, W1 ... separation distance of air supply hole array, W2 ... groove width.

Claims (5)

[Claims] A rotating member, a surrounding member rotatably supporting the rotating member, and an air supply hole formed in the surrounding member to introduce a pressurized gas for generating a static pressure between the rotating member and a surrounding member; A static pressure bearing in which the rotating body is radially supported by dynamic pressure generated between the rotating body and the surrounding member, wherein an air supply hole array including a plurality of air supply holes is separated at two locations of the surrounding member. And at least one of the outer peripheral surface of the rotating body and the inner peripheral surface of the surrounding member, a groove having a width equal to or greater than the separation distance of the air supply hole array is arranged along the circumferential direction. Hydrostatic bearing characterized by the following. 2. A bearing radial gap of the hydrostatic bearing is 3 μm.
The hydrostatic bearing according to claim 1, wherein the diameter of the hydrostatic bearing is in the range of 15 to 15 m. 3. The depth of the groove is 1 to 1 times the bearing radial gap.
The hydrostatic bearing according to claim 1, wherein the hydrostatic bearing is 0 times. 4. The hydrostatic bearing according to claim 1, wherein said groove is a circumferential groove extending over the entire peripheral surface. 5. The hydrostatic bearing according to claim 1, wherein at least one of the rotating body and the surrounding member is made of ceramic.