JP2006194203A - Air turbine spindle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air turbine spindle capable of accomplishing rotation accuracy on the order of several tens of nanometers even under ultra-high speed rotation of 100,000 rpm or higher. <P>SOLUTION: In the spindle in which an air turbine is used for a drive system and an air bearing is used for a bearing, it is constituted such that an exhaust flow passage of the turbine and an exhaust flow passage of the air bearing are independently provided respectively and further, the air turbine becoming a driving source of the spindle is provided on a circumference of a thrust plate. Air-feeding is performed from a direction perpendicular to a rotation shaft and a thrust plate outer periphery tangent direction to the air turbine and a ventilation part for releasing to an atmosphere is further arranged on an outer periphery of hydrostatic air-cushion bearings formed on both surfaces of the thrust plate. A non-contact labyrinth seal by a narrow gap is further provided on the outer periphery and an exhaust flow passage of the turbine and a porous hydrostatic exhaust flow passage are independently constituted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to high accuracy of a spindle apparatus using an air turbine as a drive system and an air bearing as a bearing.

  In recent years, demands for higher speed and higher accuracy of spindles used in machine tools have been accelerated. In particular, in the case of a machine tool for a mold, the minimum R of the mold becomes smaller as the target mold becomes more complicated, and it is desired to reduce the diameter of the tool. When the diameter of the tool is reduced, the peripheral speed of the tool inevitably decreases. Therefore, in order to compensate for the decrease in the peripheral speed, it is essential to rotate the spindle at a high speed. Further, when considering lens molds, rotation accuracy on the order of several tens of nanometers is also required.

  In order to satisfy these requirements, it can be said that it is best to adopt an air turbine for the drive train and an air bearing for the bearing. When a motor is used instead of an air turbine in the drive system, heat generation or run-out instability occurs during high-speed rotation (a phenomenon caused by a decrease in the critical speed due to an increase in shaft weight by the motor weight). When a contact bearing is used instead of a non-contact type air bearing as a bearing, not only the problem of the life at high speed rotation but also the problem of rotational accuracy is caused. For these reasons, it can be said that a configuration using an air turbine for the drive system and an air bearing for the bearing is the most effective in achieving ultra-high speed rotation of 100,000 rpm or more and rotation accuracy on the order of several tens of nanometers.

  Specifically, consider using a tool with a diameter of 2 mm at 200,000 rpm. An air bearing is appropriate for the bearing because of rotational accuracy. As for the drive system, it is necessary to make the bearing clearance of the air bearing 10 μm or more to avoid heat generation. However, if the clearance is increased, the stability limit mass becomes about 100 g, and if a motor is added, the stability limit mass is increased. It will exceed. That is, it is difficult to use a motor, and it can be said that an air turbine that does not increase in weight is effective.

  As a conventional example of a spindle using an air turbine as a drive system and an air bearing as a bearing, Patent Document 1 exists.

JP-A-9-166143

  In a spindle using an air turbine as a drive system and an air bearing as a bearing as proposed in Patent Document 1, an air turbine is arranged on the circumference of a plate on which a thrust bearing is formed in order to shorten the axial length. In most cases, the configuration is arranged.

  However, since the exhaust hole of the air turbine and the exhaust hole from the air bearing are common and the space to the exhaust hole is almost shared, the exhaust air of the air turbine and the exhaust air of the air bearing interfere with each other. It was. As a result, the pressure at the end of the air bearing, which is desirable to be stable in order to have stable characteristics, fluctuated, and fluctuations in bearing rigidity occurred.

  In addition, there is a problem that the exhaust air from the air bearing flows into the air turbine air supply passage and acts as a disturbance. For these reasons, it has been difficult to achieve an accuracy of the order of several tens of nanometers under a high-speed rotation of 100,000 rpm or more.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an air turbine spindle capable of achieving rotational accuracy on the order of several tens of nanometers even under ultra high speed rotation of 100,000 rpm or more. It is to be.

  A first means for achieving the above object is a spindle using an air turbine as a drive system and an air bearing as a bearing, wherein the turbine exhaust passage and the air bearing exhaust passage are provided independently of each other. That is.

  In the air turbine spindle, the second means constitutes an air turbine serving as a drive source of the spindle on the circumference of a thrust plate having thrust air static pressure bearings arranged on both sides, and is perpendicular to the rotation axis, and The air turbine is supplied with air from the direction of the tangent to the outer periphery of the thrust plate. With this configuration, it is possible to reduce the influence of air supplied to the air turbine on the thrust direction.

  The third means is that in the air turbine spindle, a vent for releasing the atmosphere is arranged on the outer periphery of the hydrostatic air bearing formed on both surfaces of the thrust plate, and a non-contact labyrinth seal with a narrow clearance is provided on the outer periphery. The turbine exhaust flow path and the porous static pressure exhaust flow path are independent of each other. With this configuration, pressure fluctuations can be suppressed by preventing interference between the turbine exhaust air and porous static pressure exhaust air, stable bearing rigidity and stable turbine supply pressure can be obtained, and high rotational accuracy can be obtained. Is possible.

  A fourth means is characterized in that, in the air turbine spindle, the clearance of the non-contact labyrinth seal provided on the outer periphery of the hydrostatic air bearing formed on both surfaces of the thrust plate is smaller than the bearing clearance in the thrust hydrostatic air bearing. The configuration is as follows. By adopting this configuration, it becomes possible to further enhance the effect of making the air supply passage and the exhaust passage to the turbine independent of the porous static pressure exhaust passage by the third means.

  According to the present invention, in a spindle using an air turbine as a drive system and an air bearing as a bearing, supply air to the air turbine is given from a direction perpendicular to the rotation axis, and supply air and exhaust air to the turbine are provided. And a structure that separates the exhaust air of the thrust air hydrostatic bearing can provide a spindle that can achieve rotational accuracy on the order of several tens of nanometers even under ultra high speed rotation of 100,000 rpm or more.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of a spindle using an air turbine as a drive system and an air bearing as a bearing. According to a second aspect of the present invention, an air turbine serving as a driving source of the spindle is formed on the circumference of a thrust plate having thrust air hydrostatic bearings disposed on both sides, and the supply air to the air turbine is rotated by a rotating shaft. In this case, the supply and exhaust to the turbine are not disturbed in the thrust direction of the spindle. By arranging the turbine on the circumference of the thrust plate formed with the thrust hydrostatic air bearings on both sides, the area required in the axial direction for turbine arrangement is saved.

  In order to separate the exhaust passage of the turbine and the exhaust passage of porous static pressure, there is a means of forming a plate for forming the turbine separately from the thrust plate. However, if such a measure is taken, there is a high possibility that the mass of the rotating shaft exceeds the stability limit mass due to an increase in the weight of the turbine forming plate. In addition, since the turbine portion and the thrust bearing forming portion are separated from each other in the axial direction, the supply air to the turbine adds moment to the shaft (because the thrust bearing portion is near the rotation center of the shaft), Problems also arise in terms of rotational accuracy.

  In addition, although the thing which employ | adopted the porous hydrostatic air bearing as both radial bearing and thrust bearing is shown in FIG. 1, the hydrostatic air bearing of other types, such as a self-made throttle, an orifice throttle, and a slot throttle, was adopted. Of course, this is also the subject of the present invention.

  FIG. 2 is an enlarged view of a region indicated by a broken-line circle in FIG.

  In order to prevent pressure fluctuation due to interference between the exhaust air of the turbine and the exhaust air of the thrust air hydrostatic bearing, and the interference air from flowing into the turbine supply air, the measures described in claim 3 are taken. A vent for air release is placed on the outer periphery of the static pressure air bearing component on the thrust plate surface, and a non-contact labyrinth seal with a narrow clearance is provided on the outer periphery. The exhaust air is separated. The ventilation portion has a structure in which a large number of holes are connected to an annular groove formed at a position facing the thrust plate surface.

  FIG. 3 shows a sectional view of the turbine portion of the spindle shown in FIG. 1 as viewed from the axial direction.

  The air supply path to the turbine is provided in the direction perpendicular to the rotation axis and in the direction of the tangent to the outer periphery of the thrust plate, reducing the influence of the supply air pressure to the turbine acting as a disturbance in the thrust direction. . Further, several sets of air supply holes arranged in the circumferential direction of the turbine are arranged so as to be opposed to the rotating shaft of the turbine. By facing in this way, only the moment is taken out as the force applied to the turbine from a pair of opposed air supply holes, the translational components cancel each other, and the force pushing the rotating shaft in the translational direction does not work, so high rotation Effective to achieve accuracy.

  Further, the jitter characteristic is stabilized by setting the number x of blades and the number y of air supply holes of the air turbine to “x> y and x ≠ ny (n is an integer)”. If the relationship between the number x of air turbine blades and the number y of air supply holes is “x = ny (n is an integer)”, the rotational force generated by supplying air to the turbine blades from each air supply hole periodically varies. As a result, jitter characteristics become unstable.

  FIG. 4 shows an embodiment of claim 4, wherein the clearance of the non-contact labyrinth seal provided on the outer periphery of the static pressure air bearing component on the thrust plate surface is more than the bearing clearance of the thrust static pressure air bearing. By reducing the size, the effect of separating the exhaust passage of the turbine and the exhaust passage of the thrust air hydrostatic bearing is enhanced. By adopting such a configuration, it is possible to achieve even higher rotational accuracy.

  FIG. 5 is a schematic view showing a conventional type of spindle using an air turbine as a drive system and an air bearing as a bearing. FIG. 6 is an enlarged view of a region indicated by a broken-line circle in FIG.

  5 and 6, the turbine exhaust air and the thrust air hydrostatic bearing exhaust air interfere with each other in the region indicated by the ellipse in FIG. Since the direction and the front and back of the thrust plate constantly change, this is a major obstacle to aiming for high rotational accuracy. Further, there is a risk that the exhaust air of the thrust air static pressure bearing will enter the turbine blades of the air turbine, destabilize the supply air pressure to the turbine, and cause disturbance in the radial direction and deterioration of jitter characteristics.

It is a figure which shows the spindle which performed the air pressure separation and used the air turbine for the bearing in the drive system and the air bearing. FIG. 2 is an enlarged view of a turbine outermost peripheral portion indicated by a broken-line circle in FIG. 1. It is sectional drawing which looked at the turbine blade center part of the spindle shown in FIG. 1 from the axial direction. FIG. 3 is an enlarged view of the outermost peripheral portion of the turbine that has been subjected to air pressure separation and further has a non-contact labyrinth seal clearance that is smaller than a bearing clearance. It is a figure which shows the conventional form of the spindle which used the air turbine for the drive system, and the air bearing for the bearing. FIG. 6 is an enlarged view of the outermost peripheral portion of the turbine indicated by a broken-line circle in FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating shaft 2 Bearing sleeve 3 Porous pad which forms a thrust hydrostatic bearing 4 Porous pad which forms a radial hydrostatic bearing 5a Air bearing air supply part 5b Turbine air supply part 6 Exhaust part 7 It arrange | positions on a thrust board circumference Air turbine blades 8 Areas causing air pressure interference 9 Exhaust section newly provided for air pressure separation

Claims (4)

  A spindle using an air turbine as a drive system and an air bearing as a bearing, wherein the turbine exhaust passage and the air bearing exhaust passage are provided independently of each other.   An air turbine serving as a drive source for the spindle is formed on the periphery of the thrust plate, and air is supplied to the air turbine in a direction perpendicular to the rotation axis and in a direction tangential to the outer periphery of the thrust plate. The air turbine spindle according to claim 1.   A vent for air release is placed on the outer periphery of the hydrostatic air bearing formed on both sides of the thrust plate, and a non-contact labyrinth seal with a narrow clearance is provided on the outer periphery. The air turbine spindle according to claim 2, wherein the pressure exhaust passage is made independent.   4. The air turbine spindle according to claim 3, wherein the clearance of the non-contact labyrinth seal provided on the outer periphery of the hydrostatic air bearing formed on both surfaces of the thrust plate is smaller than the bearing clearance of the thrust hydrostatic air bearing.

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