JPH1096423A - Static pressure air bearing spindle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a swing a main spindle when excited in a natural frequency of a main spindle-bearing system by arranging air supply rows of a single row or plural rows, where plural orifice holes opening in a bearing surface are arranged in the circumferential direction, in an air supply row intermediate part of two rows. SOLUTION: A main spindle 1 is supported in a noncontact condition to a housing 3 by thrust bearings 9 and 10 opposed to both surfaces of a thrust plate 2 integrally arranged on two journal bearings 7 and 8 and the main spindle 1. When an air supply row 13b is arranged on the circumference of a shaft directional central part besides air supply rows 13a of two rows in the vicinity of the shaft directional both ends in the journal bearings 7 and 8, pressure of the shaft directional central part becomes the pressure distribution higher than both end parts, and average pressure between bearing clearances becomes higher than an ordinary journal bearing. Therefore, damping performance in a high frequency area of the journal bearings 7 and 8 is improved, and a swing of a static pressure air bearing spindle to exciting force in the vicinity of a natural frequency of a main spindle-bearing system can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic air bearing spindle used as a work spindle or a tool spindle of a precision machine or a precision inspection device.

[0002]

2. Description of the Related Art A hydrostatic air bearing supports a main shaft in a non-contact manner with respect to a bearing surface, and therefore has a high rotational accuracy and is used for a work spindle or a tool spindle of a precision machine or a precision inspection device. Such a spindle is often driven by directly attaching a rotor of a motor to a main shaft without using a belt or the like in order to prevent intrusion of disturbance and enhance controllability.

FIG. 9 shows a conventional example of such a direct drive type hydrostatic air bearing spindle. In this direct-drive type hydrostatic air bearing spindle, a bearing sleeve 4,5,6 is fixed to a housing 3, and a journal 1 and a journal bearing 7,8 provided on a bearing sleeve 4,5 and a thrust integrally provided on the spindle 1. The plate 2 is supported by the pair of thrust bearings 9 and 10 provided on the bearing sleeves 5 and 6 in such a manner that the plate 2 is sandwiched from both sides in a non-contact manner with the housing 3 via a minute bearing gap.

[0004] A motor rotor 11 is integrally attached to the main shaft 1, and generates a rotational force by excitation with a motor stator 12 attached to the housing 3. Although various types of motors can be used, a motor that does not use a brush, such as a synchronous type or induction type AC motor, is often used in order to take advantage of the characteristics of the static pressure air bearing of non-contact support. When using the AC servomotor, the main spindle 1
A sensor for detecting the rotation angle of the main shaft 1 is required.
Is extended to the right side of the figure and a rotary encoder is attached.

The journal bearings 7 and 8 are provided with two air supply rows 13 in the vicinity of both ends in the axial direction of the bearing sleeves 5 and 6 in which a plurality of fine throttle holes opened in the bearing surface are arranged in the circumferential direction.
A circumferential groove 18 is provided on the outer diameter surface of the main shaft 1 at a position facing the two supply lines 13. With such a configuration, the static rigidity of the journal bearings 7, 8 can be increased with a relatively simple structure. Further, the thrust bearings 9 and 10 are provided with an air supply line 14 in which a plurality of fine throttle holes opening on the bearing surface are arranged in one line on the circumference. A circumferential groove may be provided on the bearing surfaces of the thrust bearings 9 and 10 so as to face the air supply row 14 in order to increase static rigidity.

[0006] When compressed air is supplied from the bearing supply port 15, the compressed air is supplied from the supply rows 13 and 14 to the journal bearings 7 and 8 through the supply passage 16 provided in the housing 3.
And, it flows into the bearing gaps of the thrust bearings 9 and 10 and generates a bearing reaction force balanced by the own weight of the main shaft 1 and the external load by the pressure of the air in the bearing gaps. The air flowing out of the journal bearings 7, 8 and the thrust bearings 9, 10 is discharged directly from the bearing ends or through the exhaust passage 17 to the outside of the spindle.

In the above-mentioned hydrostatic air bearing spindle, the exciting force causing whirling of the main shaft 1 is caused by an unbalance between the main shaft 1 and a rotating body including a work or a tool, and therefore, its frequency Is equal to the number of revolutions. Normally, the natural frequency of the main shaft-bearing system can be designed to be considerably higher than the rotational speed. Therefore, the static stiffness of the bearing is increased in the form of the journal bearings 7 and 8 with the double-row air circumferential groove shown in FIG. As a result, the runout accuracy of the spindle 1 could be improved.

[0008]

As described above, in a hydrostatic air bearing spindle, a run-out of a frequency equal to the number of revolutions caused by an imbalance between the main shaft 1 and a rotating body including a work or a tool, etc., is avoided. , Journal bearing 7,
Measures have been taken by improving the static rigidity and improving the accuracy of the unbalance correction. As a result, the vibration at the frequency equal to the rotation speed became considerably small.However, in order to further improve the vibration accuracy, the torque fluctuation of the motor, the uneven magnetization of the magnet, the disturbance of the driving current waveform, etc. Vibration generated at a frequency of an integral multiple of the number of revolutions related to the number of poles of the motor or the like has become a problem. When the excitation force caused by this motor has a frequency higher than the rotation speed of the main shaft 1 and includes a component close to the natural frequency of the main shaft-bearing system, the vibration of the main shaft 1 at the natural frequency becomes a problem. There are many.

To reduce the amplitude at the natural frequency of the main shaft-bearing system, it is necessary to increase the damping coefficient, not the rigidity of the bearing. Further, since the rigidity and damping coefficient of the static pressure air bearing change depending on the frequency, the effect of reducing vibration cannot be improved by focusing only on the static rigidity as in the related art.

Accordingly, an object of the present invention is to improve the dynamic characteristics of a direct drive type hydrostatic air bearing spindle and to reduce the run-out of the main shaft 1 when vibrated at the natural frequency of the main shaft-bearing system. I do.

[0011]

In order to achieve the above-mentioned object, the present invention provides a motor rotor mounted on a main shaft which is supported by a static air journal bearing and a static air thrust bearing in a non-contact manner with respect to a fixed portion. In a direct drive hydrostatic air bearing spindle that is mounted and driven directly,
In the vicinity of both ends in the axial direction of the journal bearing, there are provided two supply lines in which a plurality of throttle holes opened in the bearing surface are arranged in the circumferential direction, and circumferential grooves corresponding to the two supply lines are provided. An opening is provided in the bearing surface at the middle of the two supply lines so that the pressure is provided on the main shaft or the bearing surface of the bearing, and the pressure at the central portion in the axial direction of the bearing has a higher pressure distribution than the both ends. One or more supply lines in which a plurality of throttle holes are arranged in the circumferential direction are provided.

[0012] In addition to the two supply lines provided on the circumference in the vicinity of both ends in the axial direction of the journal bearing, one or more rows are provided on the circumference of the middle part of the two supply lines. By providing the air supply line, the pressure in the central part in the axial direction of the journal bearing becomes a pressure distribution higher than that at both ends, the average pressure in the bearing gap increases, and the damping performance of the journal bearing in the high frequency region is improved. In addition, it is possible to reduce the runout of the hydrostatic bearing spindle with respect to the exciting force near the natural frequency of the main shaft-bearing system. As a result, the dynamic characteristics of the direct drive type hydrostatic air bearing spindle can be improved, and a spindle with higher accuracy can be realized.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. It is to be noted that substantially the same members or portions as those of the conventional configuration shown in FIG. 7 are denoted by the same reference numerals throughout all the drawings, and redundant description will be omitted.

FIG. 1 shows a direct drive type hydrostatic air bearing spindle according to this embodiment. The direct drive type hydrostatic air bearing spindle of this embodiment is
As in the conventional configuration, the main shaft 1 is connected to two journal bearings 7, 8
In addition, the housing 3 is supported in a non-contact manner by thrust bearings 9 and 10 facing both surfaces of a thrust plate 2 provided integrally with the main shaft 1. The main shaft 1 has a motor rotor 11
Are attached integrally, and when the stator 12 is energized, the main shaft 1 rotates.

FIG. 2 is an enlarged view of the journal bearings 7 and 8 belonging to the hydrostatic air bearing spindle according to this embodiment. The journal bearings 7, 8 are
In the vicinity of both ends in the axial direction of No. 6, two rows of air supply rows 13a in which a plurality of fine throttle holes opening in the bearing surface are arranged in the circumferential direction are provided. Supply line 1
A circumferential groove 18a is provided at a position opposing the outer surface 3a, and a plurality of fine grooves opening in the bearing surface are provided at an intermediate portion (axial center portion of the bearing sleeves 5, 6) of the two supply lines 13a. One supply line 13b in which throttle holes are arranged in the circumferential direction is provided, and a circumferential groove 18b is provided on the outer diameter surface of the main spindle 1 at a position facing the supply line 13b at the center. . Further, the sum of the throttle outlet areas of the supply line 13b at the intermediate portion is smaller than the sum of the throttle outlet areas of the adjacent supply line 13a at the end. Here, the throttle outlet area of the air supply train is the area of the portion where the compressed air flow path cross-sectional area becomes the smallest when the compressed air passes through the throttle hole and actually acts as a throttle. As shown in FIG. 3, the area of the cross section 43 of the throttle hole 41 (so-called orifice throttle) and the area of the cylindrical surface 44 divided by the outer periphery of the throttle hole 41 and the bearing surface or the bottom surface 42 of the circumferential groove opposed thereto (so-called self-diaphragm). (Smaller stop). Therefore, in order to make the sum of the throttle outlet areas of the air supply rows 13b at the axially central portions of the journal bearings 7 and 8 smaller than the sum of the throttle outlet areas of the adjacent air supply rows 13a, To reduce the diameter of the throttle holes in the row 13b, reduce the number of throttle holes in the air supply row 13b, and in the case of self-generated throttle, make the circumferential groove 18b facing it shallow or eliminate the circumferential groove 18b. There are three ways.

In the journal bearings 7 and 8 of this embodiment, in addition to the conventional two supply lines 13a near both ends in the axial direction, an supply line 13b is provided on the circumference at the center in the axial direction. As a result, the state of the air flow in the bearing gap is shown in FIG.
4 (a) (FIG. 4 (b) shows a comparison of the state of air flow in the bearing gap of the conventional journal bearing), and as shown in FIG. Has a higher pressure distribution than both ends, so that the average pressure in the bearing gap is higher than that of the conventional journal bearing. For the following reasons, the damping performance of the journal bearings 7 and 8 in the high frequency region is improved, It is possible to reduce the run-out of the hydrostatic air bearing spindle due to the exciting force near the natural frequency of the bearing system.

That is, when the main shaft 1 vibrates, the supply train 13
The pressure in the bearing gap changes due to the action of the throttle holes a and 13b,
A bearing reaction force corresponding to the change of the main shaft 1 is generated. In a static pressure air bearing, since the bearing gap is small, the air in the bearing gap has almost the same temperature as the bearing surface and changes isothermally.
Pressure and density are in a proportional relationship. The local movement of air in the bearing gap due to the vibration of the main shaft 1 is divided into a part corresponding to a change in the volume of the bearing gap and a part corresponding to a change in the density of air in conjunction with a change in pressure. Since the rate of change of the local pressure (air density) is proportional to the local mass flow rate of the air, if the volume flow rate is constant, the higher the pressure (air density) in the bearing gap, the higher the mass High flow rate and fast pressure change. Therefore, the higher the pressure in the bearing gap,
A certain pressure change can be completed in a short time. This means that the delay of the bearing reaction force with respect to the axial displacement is small, in other words, the negative effect on the damping is small.

When the pressure in the bearing gap changes, air flows in the bearing gap, and the viscous resistance of the air at this time becomes a damping force against vibration of the shaft. When the frequency of the vibration increases, the change in the bearing gap becomes faster, and air near the center of the bearing cannot follow, and is compressed and expanded in place without flowing. Therefore, the viscous force associated with the flow of the air decreases, and the damping coefficient decreases. This tendency is particularly strong in the axial center portion of the journal bearing.

In this embodiment, the journal bearings 7,
8, the air supply line 13b and the circumferential groove 18b are provided at the axial center, so that air near the center of the bearing flows into and out of the throttle hole and the circumferential groove 18b of the air supply line 13b, so that vibration having a relatively high frequency is generated. Therefore, the flow tends to occur, and the damping coefficient of the journal bearings 7 and 8 in the high frequency region increases.
Further, the number of the supply lines 13a, 13b and the circumferential grooves 18a, 18
Since the ease of air flow changes depending on the depth of b, the air supply trains 13a and 13b are set according to the natural frequency of the main shaft-bearing system.
And the depth of the circumferential grooves 18a and 18b can be set.

On the other hand, regarding the static rigidity, there is an optimal pressure ratio between the outlet pressure of the throttle hole of the air supply line 13a, 13b and the air supply pressure of the bearing at which the static rigidity is maximum. If the outlet pressure of the throttle holes 13a and 13b is too high, the pressure in the entire bearing gap increases, and the above-described pressure ratio cannot be realized, and the static rigidity decreases. For this reason, it is necessary to suppress the pressure rise at the axial center of the bearing, where the pressure tends to rise, to the minimum necessary. In this respect, in the embodiment of the present invention, the supply line 13 at the axial center portion of the bearing in which the pressure tends to rise
b, the sum of the throttle outlet areas is calculated by dividing
Since it is smaller than 3a, it is possible to compensate for the pressure drop between the air supply lines in the case of two-line air supply and realize a minimum increase in the average bearing clearance pressure in order to increase the damping coefficient in the high frequency region. . Therefore, the dynamic characteristics can be improved while maintaining the static rigidity of the hydrostatic air bearing spindle.

As described above, in the direct drive type hydrostatic air bearing spindle according to the embodiment of the present invention,
The damping performance of the journal bearings 7 and 8 is improved, and sufficient vibration accuracy of the main shaft can be realized even when vibration occurs in a relatively high frequency range near the natural frequency of the main shaft-bearing system due to the motor.

FIG. 6 shows the compliance between the conventional direct-drive type hydrostatic air bearing spindle using the same spindle 1 and the direct-drive type hydrostatic air bearing spindle according to the embodiment of the present invention. The ratio of the magnitude of the deflection of the main shaft 1 to the magnitude of the force.) Is compared with the frequency of the exciting force on the horizontal axis. The smaller the compliance, the more the spindle 1 for the same excitation force
This is a high-precision spindle with small runout. In the spindle according to the embodiment of the present invention, three supply lines 13a and 13b are provided on the journal bearings 7 and 8, and the supply line 1 in the center is provided.
3b is also provided with a circumferential groove 18b (three-row air supply three-row circumferential groove), and is provided with a circumferential groove 18b in the central air supply row 13b (three-row air supply two-row circumferential groove). Groove) compliance. The natural frequency is 900Hz with the conventional spindle
Around 1500 Hz, 1100 for the spindle of the present invention.
Hz to around 1600 Hz. The spindle of the present invention has a compliance (reciprocal of static stiffness) near 0 Hz that is only 10% smaller than that of the conventional one, but is about half that of the conventional one when the maximum value at the natural frequency is compared. Thus, the effect of the present invention in a high-frequency region is exhibited.
Also, comparing the two types of the present invention, it is found that the central air supply line 13
By providing the circumferential groove 18b in b, the compliance becomes smaller in a high frequency region above about 1600 Hz and becomes larger in a low frequency region. In other words, the circumferential groove 18b depends on the frequency of the main excitation force and the natural frequency.
Can be changed to reduce the compliance at that frequency.

Further, in the present invention, by providing the air supply line 13b at the axial center of the journal bearings 7, 8, the bearing air flow rate is increased. For this reason, the cooling effect of the bearing part by the air supplied from the outside is increased, and the temperature rise of the bearing part is reduced even when the shaft is rotated at a high speed.

Incidentally, in the hydrostatic air bearing spindle according to the above-described embodiment, three supply lines 13 are provided in the journal bearings 7 and 8.
a and 13b are provided, but the supply line of the journal bearings 7 and 8 belonging to the hydrostatic air bearing spindle of the present invention is not limited to three lines, but three or more lines, for example, as shown in FIG. , Five supply lines 13c, 13d, 13e are provided,
In addition, five supply lines 13c, 13d,
13e, five rows of circumferential grooves 18c, 18d, 18e
It is also possible to provide. In this case, the central supply line 1
3e is the sum of the throttle outlet areas and the adjacent end-side supply line 1
While making it smaller than the sum of the 3d throttle exit areas,
The total sum of the throttle outlet areas of the air supply line 13d is made smaller than the total sum of the throttle outlet areas of the adjacent end side air supply line 13c.
However, if the number of supply lines is odd, compressed air flows from the center supply line toward both sides in the axial direction, so that the sum of the throttle outlet areas of the center supply line is adjacent to the end side. To be smaller than the total sum of the throttle outlet areas of the supply air trains.

FIG. 8 shows another embodiment of the direct drive type hydrostatic air bearing spindle of the present invention. In the direct drive type hydrostatic air bearing spindle of this embodiment, thrust bearings 9 and 10 are provided at both ends of a housing 3, and two thrust plates 2 facing the respective thrust bearings 9 and 10 are fixed to the main shaft 1. I have. Further, the circumferential grooves 18f of the journal bearings 7, 8 are provided only in the two supply lines 13f at both ends in the axial direction, and no grooves are provided in the two supply lines 13g at the center. This embodiment is suitable when the natural frequency of the main shaft-bearing system is relatively small.

In the above embodiment, the journal bearings 7,
8, air supply rows 13 a to 13 g are provided on the bearing surface on the inner diameter side, and circumferential grooves 18 a to 18 f are provided on the outer peripheral surface of the main spindle 1. Alternatively, a circumferential groove may be provided on the bearing surface on the inner diameter side of the journal bearings 7 and 8.

[0027]

As described above, according to the present invention,
2 provided on the circumference near the both ends in the axial direction of the journal bearing
In addition to the two supply lines, one or more supply lines are also provided on the circumference of the middle part of the two supply lines, so that the pressure at the axial center of the journal bearing is increased at both ends. The pressure distribution is higher than that of the bearing part, the average pressure in the bearing gap increases, the damping performance in the high frequency region of the journal bearing is improved, and the hydrostatic bearing spindle responds to the excitation force near the natural frequency of the main shaft-bearing system. Runout can be reduced, thereby improving the dynamic characteristics of the direct drive type hydrostatic bearing spindle and realizing a spindle with high accuracy. Also, the total sum of the throttle outlet area of each air supply line in the middle part is made smaller than that of the air supply line near the center of the bearing, so the minimum increase in the bearing gap average pressure must be minimized in order to increase the damping coefficient in the high frequency range. The dynamic characteristics can be improved without reducing the static rigidity of the direct drive type hydrostatic bearing spindle,
A spindle with higher accuracy can be realized. Further, the compressed air flow rate of the journal bearing increases, and the cooling effect of the bearing increases. Furthermore, the temperature rise of the bearing can be reduced,
The required processing technology is exactly the same as the conventional one, and the above effects can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a direct-drive type hydrostatic air bearing spindle according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a journal bearing belonging to the hydrostatic air bearing spindle according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a throttle exit area.

FIG. 4 is a developed view of a bearing surface (half) showing an air flow state of the present invention (three-row air supply) and a conventional (two-row air supply).

FIG. 5 is a diagram showing a pressure distribution in a bearing gap (half) of the present invention (three-row air supply) and a conventional (two-row air supply).

FIG. 6 is a diagram comparing the compliance between the present invention (three-row air supply) and the conventional (two-row air supply) compliance.

FIG. 7 is an enlarged view of another example of the journal bearing belonging to the hydrostatic air bearing spindle according to the embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of another embodiment of the present invention.

FIG. 9 is a longitudinal sectional view of a conventional direct-drive type hydrostatic air bearing spindle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft 2 Thrust plate 3 Housing 4-6 Bearing sleeve 7,8 Journal bearing 9,10 Thrust bearing 11 Motor rotor 12 Motor stator 13,13a-13g Supply line of journal bearing 14 Supply line of thrust bearing 15 Bearing supply port 16 air supply passage 17 exhaust passage 18, 18a-18f circumferential groove

Claims (6)

[Claims] 1. A direct-drive type hydrostatic air bearing spindle, wherein a motor rotor is mounted directly on a main shaft supported by a static pressure air journal bearing and a static pressure air thrust bearing in a non-contact manner with respect to a fixed portion, and Two supply lines are provided in which a plurality of throttle holes are circumferentially arranged in the bearing surface near both ends in the axial direction of the journal bearing, and circumferential grooves corresponding to the two supply lines are provided on the main shaft. Or provided on the bearing surface of the bearing, and such that the pressure in the axial center portion of the bearing has a higher pressure distribution than both ends,
A hydrostatic air bearing having one or a plurality of air supply rows in which a plurality of throttle holes opening in a bearing surface are arranged in a circumferential direction at an intermediate portion between the two air supply rows. spindle. 2. The hydrostatic air bearing spindle according to claim 1, wherein a circumferential groove facing the air supply line at an intermediate portion of said journal bearing is provided on a main shaft or a bearing surface of said bearing. 3. The static pressure of claim 1 or 2, wherein the sum of the throttle outlet areas of each supply line in the middle portion of the journal bearing is smaller in the supply line closer to the center of the bearing. Air bearing spindle. 4. The hydrostatic air bearing according to claim 3, wherein the diameter of the throttle hole of the air supply line near the center of the journal bearing is smaller than the diameter of the throttle hole of the air supply line on the adjacent end side. spindle. 5. The hydrostatic air bearing according to claim 3, wherein the number of throttle holes in the supply line near the center of the journal bearing is smaller than the number of throttle holes in the supply line at the adjacent end. spindle. 6. A method according to claim 1, wherein the depth of the circumferential groove of the air supply line closer to the center of the journal bearing is smaller than the depth of the circumferential groove of the air supply line on the adjacent end portion. 4. The hydrostatic air bearing spindle according to claim 3, wherein no circumferential groove is provided.