JP3862326B2 - Hydrostatic air bearing spindle - Google Patents

Description

[0001]
BACKGROUND 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 processing machine, a precision inspection apparatus, or the like.
[0002]
[Prior art]
Since the hydrostatic air bearing supports the main shaft in a non-contact manner with respect to the bearing surface, it has high rotational accuracy and is used for a work spindle or a tool spindle of a precision processing machine or a precision inspection device. In such a spindle, in order to prevent intrusion of disturbance and improve controllability, the motor rotor is often directly attached to the main shaft without using a belt or the like.
[0003]
A conventional example of such a direct drive type hydrostatic air bearing spindle is illustrated in FIG. In this direct drive type hydrostatic air bearing spindle, bearing sleeves 4, 5, 6 are fixed to a housing 3, journal bearings 7, 8 provided on the bearing sleeves 4, 5 and a thrust shaft provided integrally with the spindle 1. The plate 2 is supported in a non-contact manner with respect to the housing 3 through a minute bearing gap by a pair of thrust bearings 9 and 10 provided on the bearing sleeves 5 and 6 so as to be sandwiched from both sides.
[0004]
A motor rotor 11 is integrally attached to the main shaft 1, and a rotational force is generated by excitation with the motor stator 12 attached to the housing 3. Although various types of motors can be used, motors that do not use brushes such as synchronous or induction type AC motors are often used in order to take advantage of the non-contact support static pressure air bearing. In the case of using an AC servo motor, a sensor for detecting the rotation angle of the main shaft 1 is necessary. For example, a method of extending the main shaft 1 to the right side in the figure and attaching a rotary encoder is used.
[0005]
The journal bearings 7 and 8 are provided in the vicinity of both axial ends of the bearing sleeves 5 and 6 with two air supply rows 13 in which a plurality of fine throttle holes opened in the bearing surface are arranged in the circumferential direction. In addition, a circumferential groove 18 is provided at a position facing the two air supply rows 13 on the outer diameter surface of the main shaft 1. With such a configuration, the static rigidity of the journal bearings 7 and 8 can be increased with a relatively simple structure. Further, the thrust bearings 9 and 10 are provided with an air supply row 14 in which a plurality of fine throttle holes opened in the bearing surface are arranged in one row on the circumference. A circumferential groove may be provided on the bearing surfaces of the thrust bearings 9 and 10 to face the air supply row 14 for the purpose of increasing the static rigidity.
[0006]
When compressed air is supplied from the bearing air inlet 15, the compressed air passes from the air supply rows 13 and 14 to the bearing gaps of the journal bearings 7 and 8 and the thrust bearings 9 and 10 via the air supply passage 16 provided in the housing 3. The bearing reaction force that flows in and balances with the weight of the main shaft 1 and the external load is generated by the pressure of the air in the bearing gap. The air flowing out from the journal bearings 7 and 8 and the thrust bearings 9 and 10 is discharged to the outside of the spindle directly from the bearing end portion or through the exhaust passage 17.
[0007]
In the hydrostatic air bearing spindle, the excitation force causing the swing of the main shaft 1 is due to the unbalance between the main shaft 1 and a rotating body including a work or a tool, and therefore the frequency is the number of rotations. Is equal to Usually, the natural frequency of the main shaft-bearing system can be designed to be considerably higher than the rotational speed, so that the static rigidity of the bearing is increased in the form of journal bearings 7 and 8 with two-row air supply circumferential grooves shown in FIG. As a result, the deflection accuracy of the spindle 1 could be improved.
[0008]
[Problems to be solved by the invention]
As described above, in the hydrostatic air bearing spindle, the static stiffness of the journal bearings 7 and 8 against the vibration of the frequency equal to the rotational speed generated by the unbalance between the main shaft 1 and the rotating body including the workpiece or the tool. Measures have been taken by improving the accuracy of unbalance and correcting unbalance. As a result, the fluctuation of the frequency equal to the rotation speed has become considerably small, but in order to further improve the fluctuation accuracy, the torque fluctuation of the motor, magnet magnetization unevenness, disturbance of the drive current waveform, etc. There is a problem of vibration that occurs at a frequency that is a multiple of the number of rotations related to the number of poles of the motor. The excitation force resulting from this motor has a frequency higher than the rotational speed of the main shaft 1 and contains a component close to the natural frequency of the main shaft-bearing system, and vibration of the main shaft 1 at the natural frequency becomes a problem. There are many.
[0009]
In order 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. Furthermore, since the rigidity and damping coefficient of the hydrostatic air bearing change depending on the frequency, if attention is paid only to the static rigidity as in the prior art, the effect of reducing the vibration does not increase.
[0010]
Therefore, an object of the present invention is to improve the dynamic characteristics of a direct drive hydrostatic air bearing spindle and to reduce the vibration of the main shaft 1 when it is vibrated at the natural frequency of the main shaft-bearing system.
[0011]
[Means for Solving the Problems]
In order to achieve the above-described object, the present invention provides a motor rotor on a main shaft supported in a non-contact manner with respect to a fixed portion by a hydrostatic air journal bearing, a hydrostatic air thrust hydrostatic air journal bearing, and a hydrostatic air thrust bearing. In a direct drive type hydrostatic air bearing spindle that is directly driven by mounting a plurality of throttle holes that are open in the bearing surface in the vicinity of both axial ends of the journal bearing are arranged in a circumferential direction. In addition, a circumferential groove corresponding to the two air supply rows is provided on the main shaft or the bearing surface of the bearing, and the pressure in the axial central portion of the bearing has a pressure distribution higher than both ends. One or a plurality of air supply rows in which a plurality of throttle holes opened in the bearing surface are arranged in the circumferential direction are provided in the middle portion of the two air supply rows, and the air supply in the intermediate portion of the journal bearing is provided . For each column The number of throttle holes in the air supply row near the center of the journal bearing is set to be equal to the number of throttle holes in the adjacent air supply row so that the sum of the throttle outlet areas becomes smaller as the air supply row closer to the center of the bearing. Or the depth of the circumferential groove of the air supply row near the center of the journal bearing is shallower than the depth of the circumferential groove of the air supply row on the adjacent end side, or The air train was not provided with a circumferential groove.
[0012]
In addition to the two air supply rows provided on the circumference in the vicinity of both axial ends of the journal bearing, one or more air supply rows are also provided on the circumference of the intermediate portion of the two air supply rows. The journal bearing has a higher pressure distribution at the center in the axial direction than the both ends, resulting in a higher average pressure in the bearing gap, improving the damping performance in the high frequency region of the journal bearing, The vibration of the hydrostatic bearing spindle with respect to the excitation force near the natural frequency of the bearing system can be reduced. 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]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. Note that members and portions that are substantially the same as those in the conventional configuration shown in FIG. 7 are denoted by the same reference numerals throughout the drawings, and redundant description is omitted.
[0014]
FIG. 1 shows a direct drive type hydrostatic air bearing spindle according to this embodiment. In the direct drive type hydrostatic air bearing spindle of this embodiment, the main shaft 1 has two journal bearings 7 and 8 and a thrust bearing 9 opposed to both surfaces of a thrust plate 2 provided integrally with the main shaft 1, as in the conventional configuration. 10 supports the housing 3 in a non-contact manner. A motor rotor 11 is integrally attached to the main shaft 1, and the main shaft 1 rotates when the stator 12 is energized.
[0015]
FIG. 2 shows 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 and 8 are provided with two air supply rows 13a in the vicinity of both axial ends 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 18a is provided at a position facing the two air supply rows 13a on the outer diameter surface of the main shaft 1, and an intermediate portion of the two air supply rows 13a (the axial center of the bearing sleeves 5 and 6). Part) is provided with a row of air supply rows 13b in which a plurality of fine throttle holes opening in the bearing surface are arranged in the circumferential direction, and the air supply row 13b in the central portion of the outer diameter surface of the main shaft 1 is provided. Circumferential grooves 18b are provided at opposing positions. Further, the total sum of the throttle outlet areas of the intermediate air supply row 13b is made smaller than the sum of the throttle outlet areas of the adjacent air supply rows 13a on the end portion side. Here, the throttle outlet area of the air supply row is the area of the portion where the compressed air passage sectional area is the smallest when compressed air passes through the throttle hole and actually acts as a throttle. 3, the area of the cross-sectional 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 circumferential groove bottom face 42 (so-called self-restricted). The area of the smaller one of the apertures). Therefore, in order to make the sum of the throttle outlet areas of the air supply row 13b in the axial center of the journal bearings 7 and 8 smaller than the sum of the throttle outlet areas of the adjacent air supply rows 13a on the end portion side, The diameter of the throttle holes in the row 13b is reduced, the number of throttle holes in the air supply row 13b is reduced, and in the case of a self-contained throttle, the circumferential groove 18b facing it is shallowed or the circumferential groove 18b is eliminated. There are three ways.
[0016]
In the journal bearings 7 and 8 of this embodiment, in addition to the conventional two rows of air supply rows 13a in the vicinity of both axial end portions, the air supply row 13b is provided on the circumference in the central portion in the axial direction. FIG. 4A shows the state of air flow in the bearing gap (FIG. 4B shows the state of air flow in the bearing gap of the conventional journal bearing as a comparison). As shown in FIG. 5, the pressure in the central portion in the axial direction is higher than that at both ends, and the average pressure in the bearing gap is higher than that in the conventional journal bearing. The damping performance in the high frequency region is improved, and the vibration of the hydrostatic air bearing spindle with respect to the exciting force near the natural frequency of the main shaft-bearing system can be reduced.
[0017]
That is, when the main shaft 1 vibrates, the pressure in the bearing gap changes by the action of the throttle holes of the air supply rows 13a and 13b, and a bearing reaction force corresponding to the change in the main shaft 1 is generated. In the hydrostatic air bearing, since the bearing gap is small, the air in the bearing gap has almost the same temperature as the bearing surface and undergoes an isothermal change, so the 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 air density in conjunction with the pressure change. The rate of change in local pressure (air density) is proportional to the local air mass flow rate, so if the volumetric flow rate is constant, the higher the bearing clearance pressure (air density), the higher the mass. The flow rate is large and the pressure changes quickly. Therefore, a certain pressure change can be completed in a short time as the pressure in the bearing gap increases. 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.
[0018]
Further, when the pressure in the bearing gap changes, air flows in the bearing gap, and a damping force against the shaft vibration is generated by the viscous resistance of the air at this time. When the frequency of vibration increases, the change in the bearing clearance becomes faster, and the air near the center of the bearing cannot follow and compresses and expands on the spot without flowing. Therefore, the viscous force accompanying the air flow is reduced, and the damping coefficient is reduced. This tendency is particularly strong in the axial center portion of the journal bearing.
[0019]
In the present embodiment, since the air supply row 13b and the circumferential groove 18b are provided in the axial center of the journal bearings 7 and 8, the air near the center of the bearing enters the throttle hole and the circumferential groove 18b of the air supply row 13b. By entering and exiting, it becomes easy for flow to occur even with vibrations having a relatively high frequency, and the damping coefficient of the journal bearings 7 and 8 in the high frequency region increases. In addition, since the ease of air flow varies depending on the number of air supply rows 13a and 13b and the depth of the circumferential grooves 18a and 18b, the air supply rows 13a and 13b have different characteristics depending on the natural frequency of the main shaft-bearing system. The number and the depth of the circumferential grooves 18a and 18b can be set.
[0020]
On the other hand, as for the static stiffness, there is an optimum pressure ratio between the outlet pressure of the throttle hole of the supply air train 13a, 13b and the bearing supply air pressure at which the static rigidity is maximized, and the air supply train 13a, 13b with respect to the supply air pressure. If the outlet pressure of the throttle hole is too high, the pressure of the entire bearing gap increases, the above pressure ratio cannot be realized, and the static rigidity decreases. For this reason, it is necessary to suppress the pressure increase at the axial center portion of the bearing, where the pressure is likely to increase, to the minimum necessary. In this regard, in the embodiment of the present invention, since the sum of the throttle outlet areas of the air supply row 13b in the axial central portion of the bearing that is likely to increase in pressure is smaller than the air supply row 13a on the adjacent end side, 2 In order to compensate for the drop in pressure between the air supply trains in the case of the row air supply, and to increase the damping coefficient in the high frequency region, it is possible to realize a minimum increase in the bearing gap average pressure. Accordingly, the dynamic characteristics can be improved while maintaining the static rigidity of the hydrostatic air bearing spindle.
[0021]
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 the comparison is close to the natural frequency of the main shaft-bearing system caused by the motor. Even if vibration occurs in a high frequency region, sufficient swing accuracy of the spindle can be realized.
[0022]
FIG. 6 shows the compliance of the conventional direct drive hydrostatic air bearing spindle using the same main shaft 1 and the direct drive hydrostatic air bearing spindle according to the embodiment of the present invention (reciprocal of rigidity, large excitation force). Is a comparison of the frequency of the excitation force with respect to the horizontal axis. The smaller the compliance, the smaller the deflection of the spindle 1 with respect to the same excitation force, and the higher the precision of the spindle. In the spindle according to the embodiment of the present invention, the journal bearings 7 and 8 are provided with three air supply rows 13a and 13b, and the central air supply row 13b is also provided with a circumferential groove 18b (three rows of air supply 3 (Line circumferential groove) and the air supply line 13b in the center portion are not provided with the circumferential groove 18b (three-line air supply and two-line circumferential groove). The natural frequency is about 900 Hz to 1500 Hz for the conventional spindle and about 1100 Hz to 1600 Hz for the spindle of the present invention. The spindle of the present invention has a compliance (reciprocal of static stiffness) in the vicinity of 0 Hz that is only about 10% smaller than that of the conventional one, but the maximum value at the natural frequency is about ½ that of the conventional one. Thus, the effect of the present invention in the high frequency region is exhibited. Further, when the two types of the present invention are compared, by providing the circumferential groove 18b in the central air supply row 13b, the compliance becomes small in a high frequency region above about 1600 Hz and becomes large in a low frequency region. That is, the specification of the circumferential groove 18b can be changed in accordance with the frequency of the main excitation force or natural frequency to reduce the compliance at that frequency.
[0023]
Further, in the present invention, the air flow rate of the bearing is increased by providing the air supply row 13b in the central portion of the journal bearings 7 and 8 in the axial direction. For this reason, the cooling effect of the bearing part by the air supplied from the outside becomes large, and the temperature rise of the bearing part becomes small even when the shaft is rotated at a high speed.
[0024]
In the hydrostatic air bearing spindle according to the above embodiment, the journal bearings 7 and 8 are provided with three air supply rows 13a and 13b, but the journal bearings 7 and 8 belonging to the hydrostatic air bearing spindle of the present invention. The air supply row is not limited to three rows, but three or more rows, for example, as shown in FIG. 7, five air supply rows 13c, 13d, 13e are provided, and the outer diameter surface of the main shaft 1 is provided. It is also possible to provide five rows of circumferential grooves 18c, 18d, 18e facing the five rows of air supply rows 13c, 13d, 13e. In this case, the sum of the throttle outlet areas of the central air supply row 13e is made smaller than the sum of the throttle outlet areas of the adjacent end side air supply rows 13d, and the sum of the throttle outlet areas of the air supply rows 13d is adjacent. It is made smaller than the sum total of the throttle outlet area of the air supply row 13c on the end side. However, if the number of air supply rows is an odd number, the compressed air flows from the central air supply row toward both sides in the axial direction, so the total throttle outlet area of the central air supply row is adjacent to the end side. To be smaller than the sum of the throttle outlet areas of the air supply train.
[0025]
FIG. 8 shows another embodiment of the direct drive hydrostatic air bearing spindle of the present invention. The direct drive type hydrostatic air bearing spindle of this embodiment is provided with thrust bearings 9 and 10 at both ends of the housing 3, and two thrust plates 2 facing the thrust bearings 9 and 10 are fixed to the main shaft 1. Yes. Further, the circumferential grooves 18f of the journal bearings 7 and 8 are provided only in the two air supply rows 13f at both ends in the axial direction, and no grooves are provided in the two air supply rows 13g in the central portion. This embodiment is suitable when the natural frequency of the main shaft-bearing system is relatively small.
[0026]
In the above embodiment, the air supply rows 13a to 13g are provided on the bearing surfaces on the inner diameter side of the journal bearings 7 and 8, and the circumferential grooves 18a to 18f are provided on the outer peripheral surface of the main shaft 1. May be provided on the outer peripheral surface of the main shaft 1 or a circumferential groove may be provided on the bearing surface on the inner diameter side of the journal bearings 7 and 8.
[0027]
【The invention's effect】
As described above, according to the present invention, in addition to the two air supply rows provided on the circumference in the vicinity of both axial ends of the journal bearing, the circumference of the intermediate portion of the two air supply rows is provided. Since one or more air supply rows are also provided on the upper side, the pressure in the central portion of the journal bearing in the axial direction is higher than that at both ends, and the average pressure in the bearing gap is increased. The damping performance in the region is improved, and the vibration of the hydrostatic bearing spindle against the excitation force near the natural frequency of the main shaft-bearing system can be reduced, thereby improving the dynamic characteristics of the direct drive hydrostatic bearing spindle. In addition, a highly accurate spindle can be realized. In addition , the sum of the throttle outlet areas of each air supply row in the middle is smaller for the air supply row closer to the center of the bearing, so the minimum bearing clearance average pressure is increased to increase the damping coefficient in the high frequency range. Thus, the dynamic characteristics can be improved without lowering the static rigidity of the direct drive hydrostatic bearing spindle, and a spindle with higher accuracy can be realized. Further, the compressed air flow rate of the journal bearing is increased, and the bearing cooling effect is enhanced. Furthermore, while the temperature rise of a bearing part can be reduced, the required processing technique is exactly the same as the conventional one, the above effects can be realized at a low cost.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a direct-drive hydrostatic air bearing spindle according to an embodiment of the present invention.
FIG. 2 is an enlarged view of a journal bearing belonging to a hydrostatic air bearing spindle according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of a throttle outlet area.
FIG. 4 is a development view of a bearing surface (half) showing a state of air flow 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) between the present invention (three-row air supply) and the conventional (two-row air supply).
FIG. 6 is a diagram comparing the compliance of the present invention (3-row air supply) and the conventional (2-row air supply).
FIG. 7 is an enlarged view of another example of a journal bearing belonging to a hydrostatic air bearing spindle according to an 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 board 3 Housing 4-6 Bearing sleeve 7, 8 Journal bearing 9, 10 Thrust bearing 11 Motor rotor 12 Motor stator 13, 13a-13g Journal bearing air supply row 14 Thrust bearing air supply row 15 Bearing air supply port 16 Air supply passage 17 Exhaust passage 18, 18a-18f Circumferential groove

Claims (3)

In a direct drive type hydrostatic air bearing spindle that is directly driven by attaching a motor rotor to a main shaft supported in a non-contact manner with respect to a fixed portion by a hydrostatic air journal bearing and a hydrostatic air thrust bearing.
The journal bearing is provided with two rows of air supply rows in which a plurality of throttle holes opened in the bearing surface in the vicinity of both axial ends of the journal bearing are arranged in the circumferential direction, and circumferential grooves corresponding to the two rows of air supply rows are provided. Provided on the main shaft or the bearing surface of the bearing, and open to the bearing surface in the middle of the two air supply rows so that the pressure in the axial central portion of the bearing has a higher pressure distribution than both ends. Providing one or a plurality of air supply rows in which a plurality of throttle holes are arranged in the circumferential direction ;
The sum of the throttle outlet areas for each of the air supply rows in the middle portion of the journal bearing becomes smaller as the air supply row closer to the center of the bearing reduces the throttle hole of the air supply row closer to the center of the journal bearing. A hydrostatic air bearing spindle characterized in that the number thereof is smaller than the number of throttle holes in the air supply row on the adjacent end side .   2. The hydrostatic air bearing spindle according to claim 1, wherein a circumferential groove facing an air supply row at an intermediate portion of the journal bearing is provided on a main shaft or a bearing surface of the bearing. In a direct drive type hydrostatic air bearing spindle that is directly driven by attaching a motor rotor to a main shaft supported in a non-contact manner with respect to a fixed portion by a hydrostatic air journal bearing and a hydrostatic air thrust bearing.
The journal bearing is provided with two rows of air supply rows in which a plurality of throttle holes opened in the bearing surface in the vicinity of both axial ends of the journal bearing are arranged in the circumferential direction, and circumferential grooves corresponding to the two rows of air supply rows are provided. Provided on the main shaft or the bearing surface of the bearing, and open to the bearing surface in the middle of the two air supply rows so that the pressure in the axial central portion of the bearing has a higher pressure distribution than both ends. Providing one or a plurality of air supply rows in which a plurality of throttle holes are arranged in the circumferential direction;
The sum of the aperture exit area of each column of the charge air column in the middle portion of the journal bearing, the inboard air supply column as small Kunar so the bearing, circumferential air supply column close to the center of the journal bearing A hydrostatic air bearing spindle characterized in that the groove depth is shallower than the circumferential groove depth of the air supply row on the adjacent end side, or no circumferential groove is provided in the central air supply row .

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