JP2008038844A - Turbo molecular pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a turbo molecular pump easy of balance correcting work for a rotor and free from destruction of the rotor due to stress concentration resulting from balance correction with the cutting of a cylindrical thin portion on the lower part of the rotor. <P>SOLUTION: Through a column insertion hole 1a and an inspection hole 61b provided in the outer periphery of a lower-side axial electromagnet 6b of an axial magnetic bearing 6, a balance correcting screw 20 is threaded into a screw hole 61d in the outer periphery of a disc 6d of the axial magnetic bearing 6, when carrying out the balance correction of the rotor. After finishing balance correcting work, a bottom cover 8 is mounted on the lower face of a base 1 for shutting off the inside from outside air. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a turbo molecular pump that can easily correct a rotor balance.

  A turbo molecular pump rotates a rotor at a high speed of tens of thousands of rpm and exhausts gas by striking gas molecules between rotor blades and stator blades alternately stacked with a small gap between them. . Since the rotational speed of the rotor during operation is large, it is not possible to guarantee the quiet operation of the rotor unless the pump is assembled, the unbalance is measured while rotating at high speed, and the balance is corrected.

  Some rotors of turbo molecular pumps are provided with a multi-layered thin rotor blade on the outer periphery and a thin cylindrical part of a thread groove pump part on the lower side. In general, the upper part of the rotor is integrally fixed to the rotor shaft. The rotor shaft is supported by a bearing and is rotationally driven by a motor. Due to such a structure of the rotor of the turbo molecular pump and the rotor shaft, the rotor tends to be unbalanced particularly at the lower side thereof.

  Patent Document 1 discloses a technique for performing balance correction on the lower side of the rotor with an armature disk (the disk in the present invention) attached to the lower part of the rotor shaft, avoiding the thin cylindrical portion that tends to cause stress concentration of the rotor. Is disclosed.

  In Patent Document 1, screw holes are formed radially on the outer peripheral edge of an armature disk or the like, and a balance adjustment male screw is embedded in the screw holes to perform balance correction. The adjustment and removal of the balance adjustment male screw is performed through an exhaust port of the pump or a special adjustment hole.

  However, as in Patent Document 1, in order to correct the balance with a screw hole such as an armature disk and a male screw, a new adjustment structure is added to the pump exhaust port, or a newly provided adjustment hole is required. .

  That is, when the exhaust port is used, through holes 1b and 2b from the exhaust port 15 toward the outer peripheral edge of the armature disk 6d must be newly provided in the base 1 and the stator column 2, as shown in FIG. If the through holes 1b and 2b are left as they are after balance adjustment, the purge gas will be ejected from the through holes 1b and 2b. Therefore, the internal space of the axial magnetic bearing 6, the protective bearing 18, the radial magnetic bearing 5, There is a possibility that the gas cannot sufficiently flow through each gap of the motor 7 and cannot be protected by the purge gas.

  Therefore, the corrosive gas may corrode the magnetic bearings 5 and 6, the motor 7, and the protective bearing 18 during exhaust of the corrosive gas. In order to prevent such corrosion, it is necessary to prepare sealing means for the through holes 1b and 2b, and performing the balance correction work from the exhaust port 15 side to the armature disk 6d or the like is a cost due to an increase in the number of parts and an increase in man-hours. It is rising and not very economical.

  Further, when the adjustment hole is newly provided, an adjustment hole and a sealing means for sealing the adjustment hole are necessary. This is also not economical because the cost increases due to an increase in the number of parts and man-hours.

  In FIG. 10, 3 is a rotor, 6a and 6b are axial electromagnets, 6c is an annular spacer between the axial electromagnets 6a and 6b, and 6cn is a notch in the annular spacer 6c.

Japanese Utility Model Publication No. 6-14490 (Summary, Claim 3)

  In the present invention, the balance adjustment on the lower side of the rotor is not performed on the thin cylindrical portion of the rotor, it is difficult to be exposed to the corrosive atmosphere of the exhaust gas, and the influence of centrifugal force due to high-speed rotation is relatively small. Remove the screws from the existing opening of the pump other than the exhaust path to the balance adjustment section of the disk, adjust the insertion / removal, or remove the balance adjustment section of the disk partially to solve the above-mentioned problems. It is an object of the present invention to provide a turbo molecular pump that is efficient in the subsequent work of correcting the rotating body balance.

  In order to solve the above-described problems, the present invention provides a rotating part holder, a rotor shaft arranged with a gap in the rotating part holder, a rotor held integrally with the rotor shaft, and the rotor A radial bearing that is provided between the shaft and the rotating part holding body and that rotatably holds the rotor shaft in the radial direction, and is provided between the rotor shaft and the rotating part holding body, so that the rotor shaft can rotate freely. An axial bearing that holds in the direction, a motor that is provided between the rotor shaft and the rotating part holding body, and that rotates and drives the rotor shaft, and is disposed below the rotating part holding body, and houses the axial bearing. A storage space and a bottom cover that is attached to the lower surface of the rotating part holding body and closes the storage space from the outside, and the axial bearing includes an upper axial holding part and a lower axial part attached to the rotating part holding body. Protection And a turbo molecular pump that is arranged between these axial holding parts and is a disk attached to the rotor shaft, the disk is provided with a balance correction part, and the lower axial holding part has an outer peripheral part. A peephole is provided through which the balance correcting portion can be seen through from the bottom lid side.

  In the above invention, the balance correcting portion may have a plurality of screw holes provided in the axial direction of the rotor axis on the pitch circle of the disk, and a balance correcting screw screwed into the screw hole.

  In order to solve the above-mentioned problems, the present invention also includes a rotating part holding body, a rotor shaft arranged with a gap in the rotating part holding body, a rotor held integrally with the rotor shaft, A radial bearing provided between the rotor shaft and the rotating part holding body and rotatably holding the rotor shaft in the radial direction, and provided between the rotor shaft and the rotating part holding body, the rotor shaft is rotatable. Axial bearings that are held in the axial direction, a motor that is provided between the rotor shaft and the rotating part holder, and that rotates the rotor shaft, and a purge gas introduction purge that is provided on the side of the rotating part holder A port hole and a radial through hole for introducing purge gas provided in the rotating part holding body, and the axial bearing includes an upper axial holding part and a lower axial holding part attached to the rotating part holding body; this In the turbo molecular pump, which is interposed between the axial holding portions, and is composed of an annular spacer with a radial through portion having a radial through portion, and a disk attached to the rotor shaft and disposed inside the annular spacer, The disk is provided with a balance correcting portion, and the purge port hole, the radial through hole of the rotating portion holder and the radial through portion of the annular spacer are arranged in a straight line so that the balance correcting portion can be seen through from the purge port side. To do.

  In the above invention, the balance correction portion may include a plurality of screw holes provided in a radial direction of the rotor axis, and a balance correction screw screwed into the screw hole.

  In the above invention, the balance correction unit may be partially removed to correct the balance.

  In the present invention, the balance correction screw is screwed into the screw hole provided in the balance correction portion of the axial bearing disk from the lower side of the pump through the peephole provided in the outer peripheral portion of the lower axial holding portion of the axial bearing, or the balance Remove the correction part partially and perform the balance correction work, or screw the balance correction screw into the screw hole on the outer periphery provided in the balance correction part of the axial bearing disk from the side of the pump through the purge port hole, or Remove the balance correction part and perform the balance correction work, such as removing the screw from the existing opening of the pump other than the exhaust path to the balance correction part of the disk, adjusting the insertion / extraction or adjusting the balance correction part. Since it was partially removed, the balance adjustment work on the lower side of the rotor can be performed quickly and efficiently. Can Nau.

  Compared with the conventional balance correction in which a screw is attached to and removed from the exhaust port and adjusted to put in and out of the disc, a special sealing means for preventing leakage of purge gas is required in the present invention. There is no risk of efficiency reduction due to purge gas leakage.

  Axial bearing discs are not easily exposed to the corrosive atmosphere of exhaust gas, and the influence of centrifugal force due to high-speed rotation is relatively small. The balance of the parts is maintained.

[First Embodiment]
A first embodiment of the present invention will be described below with reference to FIGS. 1 is a longitudinal sectional view showing a first embodiment of the present invention, FIG. 2 is an enlarged sectional view of a main part of FIG. 1, FIG. 3 is a disk in FIG. 1, (a) is a sectional view, b) is a plan view, FIG. 4 shows a lower axial electromagnet in FIG. 1, (a) is a sectional view, (b) is a plan view, FIG. 5 shows an annular spacer in FIG. FIG. 6B is a side view, FIG. 6A is a cross-sectional view showing the balance correction work situation in FIG. 2, and FIG. 6B is a balance correction in the conventional example corresponding to FIG. It is sectional drawing which shows a work condition.

  In FIG. 1, 1 is a base, 2 is a stator column, 3 is a rotor shaft, 4 is a rotor, 5 is a radial magnetic bearing, 6 is an axial magnetic bearing, and 7 is a motor.

  A column insertion hole 1 a is provided at the center of the base 1. The cylindrical stator column 2 is inserted and fitted from the upper side to the column insertion hole 1a, and is bolted so as to protrude above the center of the base 1. Instead of bolting base 1 and stator column 2, base 1 and stator column 2 can be integrally formed.

  The column insertion hole 1 a is closed by a bottom lid 8 attached to the lower surface of the base 1.

  The rotor shaft 3 is coupled at an upper portion thereof to hold the rotor 4 integrally, and is inserted rotatably in the inner cylinder of the stator column 2 while maintaining a gap.

  That is, the radial magnetic bearing 5 and the axial magnetic bearing 6 are disposed between the rotor shaft 3 and the stator column 2, and the radial magnetic bearing 5 is provided so that the stator column 2 rotatably holds the rotor shaft 3. Holds the rotor shaft 3 in the radial direction, and the axial magnetic bearing 6 holds the rotor shaft 3 in the axial direction.

  The motor 7 is disposed between the rotor shaft 3 and the stator column 2, and the motor 7 rotates the rotor shaft 3 and the rotor 4 with respect to the stator column 2.

  There are slight gaps between the members on the stator column 2 side of the magnetic bearings 5 and 6 and the motor 7 and the members on the rotor shaft 3 side, and the gaps of the magnetic bearings 5 and 6 are controlled. Thus, the rotor shaft 3 and the rotor 4 are stably held in the space and are rotated at a high speed by the motor 7.

  As described above, the base 1 and the stator column 2 are integrated to form a rotating portion holder that holds high-speed rotating portions such as the rotor shaft 3 and the rotor 4.

  The configuration of the axial magnetic bearing 6 will be described in a little more detail. As a stationary portion attached to the stator column 2 of the axial magnetic bearing 6, an upper axial electromagnet (upper axial holding portion) 6a and a lower axial electromagnet (lower axial holding portion). ) 6b is disposed above and below the notched annular spacer 6c (see FIG. 5), and the disk 6d is disposed between the axial electromagnets 6a and 6b as a rotating portion attached to the rotor shaft 3 of the axial magnetic bearing 6. Is disposed inside the ring. The disk 6d is held in the axial direction by being sandwiched between the upper and lower axial electromagnets 6a and 6b, and the position of the disk 6d is controlled in the axial direction according to the control current flowing through the upper and lower axial electromagnets 6a and 6b. The vertical position of the body is controlled stably.

  11 is a cylindrical casing that is mounted above the base 1 and accommodates the stator column 2, the rotor shaft 3, and the rotor 4, and 12, 12,... Overlap with the upper inner wall surface of the casing 11 in the axial direction. A plurality of stator blades attached thereto. The stator blades 12, 12,... Are alternately overlapped with a plurality of rotor blades 4 a, 4 a,. And the stator blades 12, 12,... Form a turbo molecular pump section.

  A screw stator 13 is provided on the inner wall of the casing 11 between the base 1 and the stator blades 12, 12,..., And has a thread groove 13a formed on the inner peripheral surface. The screw groove 13a of the screw stator 13 is in close proximity to the outer peripheral surface of the thin cylindrical skirt portion 4b below the rotor 4, and the screw groove 13a and the skirt portion 4b form a screw groove pump portion.

  Reference numeral 14 denotes an intake port of the pump, 15 denotes an exhaust port, 16 denotes a purge port hole for introducing a purge gas provided on the side surface of the base 1, and 17 denotes a purge port attached to the inlet of the purge port hole 16. The intake port 14 is provided in the upper part of the pump, and the exhaust port 15 and the purge port hole 16 are provided in the base 1.

  The stator column 2 is provided with a radial through hole 2 a at a portion facing the purge port hole 16. And the notch 6cn of the said annular spacer 6c with a notch inserted between the upper axial electromagnet 6a and the lower axial electromagnet 6b is arrange | positioned facing this radial direction through-hole 2a, and radial direction penetration is carried out. Purge gas is introduced into the internal gaps of the magnetic bearings 5 and 6 and the motor 7 through the hole 2a and the notch 6cn.

  In this embodiment, the notch 6cn is provided in the annular spacer 6c to form the radial through portion. However, instead of the notch, a through hole may be provided in the annular spacer 6c to form the radial through portion.

  Reference numeral 18 denotes a protective bearing provided between the stator column 2 and the rotor shaft 3. The protective bearing 18 is used to prevent contact between the magnetic bearings 5 and 6 and each stator column side of the motor 7 and the rotor shaft side when the magnetic bearing cannot be controlled, such as during a power failure or circuit abnormality. .

  In the turbo molecular pump of FIG. 1, gas is sucked in from the inlet 14 connected to the vacuum chamber or the like by the action of the turbo molecular pump part and the thread groove pump part by the high-speed rotation of the rotor. It passes through the pump part and the thread groove pump part in this order, and is exhausted from the exhaust port 15 to the auxiliary pump or the like connected to the exhaust port 15 side.

  The above configuration is a well-known part.

  Next, features of the present invention will be described.

  The rotating body consisting of the rotor shaft 3, the rotor 4, the rotor shaft 3 side of the magnetic bearings 5 and 6, and the rotor shaft 3 side of the motor 7 is normally corrected to balance two surfaces in order to prevent vibration during high speed rotation However, in the present invention, the skirt portion 4b, which is often exposed to a corrosive atmosphere during the pump operation, is avoided as a balance correction portion of the lower balance correction surface of the two surfaces. The addition of parts is avoided and the disk 6d of the axial magnetic bearing 6 which is an existing part is used.

  Further, since the balance correction is performed after the pump is assembled, special work is not required before and after the balance correction work, and special parts are not prepared.

  In FIG. 2, an annular groove 60a is provided on the lower surface of the upper axial electromagnet 6a, and an annular groove 60b is provided on the upper surface of the lower axial electromagnet 6b. These grooves 60a and 60b serve as escape grooves that avoid interference with the revolving locus of the balance correcting screw 20 described later when the disk 6d rotates.

  The outer periphery of the disk 6d has a step 60d by forming a recess 60e by recessing the lower surface and reducing the thickness of the outer periphery. In this embodiment, the level difference 60d is the balance correction portion 60c.

  As shown in FIG. 3, a plurality of screw holes 61d are penetrated in the axial direction of the rotor axis along the balance correction portion pitch circle p in the step 60d (balance correction portion 60c) having a thin disk 6d. It is installed.

  A peep hole 61b is provided on the outer peripheral portion of the lower axial electromagnet 6b so as to face the balance correction portion pitch circle p of the disk 6d (see FIG. 4). The peep hole 61b can be seen through from the bottom lid 8 side. Thereby, the balance correction part 60c can be seen through from the bottom lid 8 side through the peephole 61b.

  A balance correcting screw 20 with a head is screwed into the screw hole 61d. The thread portion of the balance correction screw 20 is screwed into the screw hole 61d, and the head portion 20a of the balance correction screw 20 is positioned in the recess 60e of the step 60d. As a result, the center of gravity of the balance correcting screw 20 substantially coincides with the center of gravity of the disk 6d.

  The reason why the balance correction screw 20 with the head 20a is used in this way is to increase the balance correction mass of the screw so that the balance correction is effective. However, when the disk 6d rotates at a high speed, the centrifugal force generated in the head 20a having a large mass deforms the thin disk-shaped disk 6d so as to warp, and the distance between the electromagnets 6a and 6b of the axial magnetic bearing 6 and the disk 6d is increased. There is a risk that the control in the axial direction of the rotating body may become unstable due to slight fluctuations. Therefore, in this embodiment, the head 20a is positioned in the recess 60e, the vertical displacement of the balance correction screw 20 center of gravity from the center of the disk 6d is reduced, and the influence of the centrifugal force of the head 20a is reduced. 6d warpage and deformation are prevented.

  During the balance correction operation, the balance correction screw 20 having a predetermined mass is screwed into the screw hole 61d at a predetermined angular position in accordance with the unbalance measurement value of the rotating body to eliminate the unbalance. The balance correcting screw 20 is screwed by inserting a tool from the direction of arrow A through the column insertion hole 1a and the peeping hole 61b.

  The operation of screwing or removing the balance correction screw 20 with a tool from the arrow A (see FIG. 1) side is the tip of the column insertion hole 1a and the narrow peep hole 61b. Easy to drop. Therefore, in this embodiment, the portion f farthest from the rotor axial center of the opening on the disk 6d side of the peep hole 61b is equal to the wall surface (inner peripheral surface of the spacer 6c) w surrounding the disk 6d or from the wall surface w. Is far from the rotor axis.

  In this case, as shown in FIG. 6 (a), when the balance correction screw 20 is removed from the tool tip (20 (1)), it is caught on the upper surface of the lower axial electromagnet 6b and does not return to the hand. The balance correcting screw 20 can be recovered by dropping with its own weight (20 (2)). As shown in FIG. 6 (b), the portion f farthest from the rotor axial center of the opening on the disk 6d side of the viewing hole 61b is the rotor than the wall surface (inner circumferential surface of the spacer 6c) w surrounding the disk 6d. If it is on the axial center side, when the balance correction screw 20 is recovered, it is likely to be caught by the stepped portion k on the upper surface of the lower axial electromagnet 6b.

  Since the angular position of the screw hole 61d is determined in advance, and the mass of the balance correction screw 20 is limited, the single correction screw 20 is generally not necessary, and a plurality of correction screws 20 are screwed. Or, the correction screw 20 is screwed into all the screw holes 61d, and the balance is corrected while adjusting the mass of the correction screw 20.

  After the balance correction work, it is only necessary to close the bottom lid 8 and there is no need to seal the peep hole 61b. Therefore, the balance correction work and the structure for balance correction are simple.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. FIG. 7 is an enlarged cross-sectional view showing a main part of a second embodiment of the present invention, and FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG.

  In the second embodiment, as in the first embodiment described above, the balance correction screw is screwed into the balance correction portion of the disk to correct the balance of the lower balance correction surface. The difference from the embodiment is that the balance correction screw is screwed into the balance correction portion of the disk from the radial direction of the rotor axis through the purge port hole.

  In FIG. 7, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. A plurality of screw holes 261d are provided at equal intervals in the radial direction of the rotor axis in the balance correcting portion 60c on the outer periphery of the disk 26d.

  A balance correcting screw 21 without a head is screwed into the screw hole 261d.

  The balance correcting portion 60c of the disk 26d can be seen through from the purge port 17 side through the purge port hole 16 arranged in a straight line, the radial through hole 2a of the rotating portion holder, and the annular spacer radial through portion 6cn. Yes.

  At the time of balance correction work, the balance correction screw 21 having a predetermined mass is screwed into the screw hole 261d at a predetermined angular position in accordance with the unbalance measurement value of the rotating body to eliminate the unbalance. The balance correction screw 21 is screwed in by inserting a tool from the purge port hole 16 in the direction of arrow A.

  Since the screw hole 261d is provided in the radial direction of the rotor axis, an extremely fine balance correction can be performed by inserting and removing the screw 21 little by little.

  Since the angular position of the screw hole 261d is determined in advance, in general, one correction screw 21 is not sufficient, and a plurality of correction screws 21 are screwed in, or the correction screws 21 are inserted into all the screw holes 261d. Is screwed in, and the balance is corrected by replacing the correction screw 21 with a correction screw having a different mass.

  After the balance correction work, there is no problem of purge gas leakage, so no special sealing work is required.

[Third Embodiment]
A third embodiment of the present invention will be described with reference to FIG. FIG. 9 is an enlarged cross-sectional view of a main part showing a third embodiment of the present invention.

  The third embodiment is different from the first embodiment described above in that the balance is corrected by deleting the disk. 9, the same parts as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 9, reference numeral 60r denotes a removing unit that corrects the balance by cutting the balance correcting unit 60c of the disk 6d, and T denotes a router that deletes the balance correcting unit 60c.

  At the time of the balance correction work, the predetermined angular position and the predetermined mass 60r are scraped off by the router T according to the unbalance measurement value of the rotating body to eliminate the unbalance. The router T inserts the router T from the direction of arrow A through the column insertion hole 1a and the peeping hole 61b. Unlike the first embodiment in which screw holes are previously provided at predetermined intervals, the angular position to be scraped off can be set to an arbitrary angular position.

  In order to correct the balance by partially removing the balance correcting portion 60c, the radial direction of the purge port hole 16 and the rotating portion holder as in the second embodiment of FIG. 7 in addition to the third embodiment. The through hole 2a and the radial through portion 6cn of the annular spacer are arranged in a straight line so that the balance correcting portion 60c can be seen through from the purge port 17, and the router T is inserted in the direction of arrow A from here, and the balance correcting portion 60c The outer diameter portion may be partially removed to correct the balance.

  Further, in order to partially remove the balance correcting portion 60c and correct the balance, the balance correcting portion 60c can be removed by chemical or thermal melting or the like in addition to a cutting tool such as a router.

  In the above-described embodiment, magnetic bearings that are easy to perform accurate and stable control are used for all the bearings. However, the present invention is also applicable to turbo molecular pumps using other bearings such as oil-free bearings and fluid bearings. Can do.

1 is a longitudinal sectional view showing a first embodiment of the present invention. The principal part expanded sectional view of FIG. The disk in FIG. 1 is shown, (a) is sectional drawing, (b) is a top view. The lower axial electromagnet in FIG. 1 is shown, (a) is sectional drawing, (b) is a top view. The spacer in FIG. 1 is shown, (a) is a top view, (b) is a side view. (A) is sectional drawing which shows the balance correction work condition in FIG. 2, (b) is sectional drawing which shows the balance correction work condition in a prior art example. The principal part expanded sectional view which shows 2nd Embodiment of this invention. VIII-VIII sectional drawing of FIG. The principal part expanded sectional view which shows the 3rd Embodiment of this invention. The longitudinal cross-sectional view explaining patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base 1a Column insertion hole 2 Stator column 2a Radial through-hole 3 Rotor shaft 4 Rotor 4a Rotor blade 4b Skirt part 5 Radial magnetic bearing 6 Axial magnetic bearing 6a Upper axial electromagnet (upper axial holding part)
6b Lower axial electromagnet (lower axial holding part)
6c annular spacer 6cn radial through-hole (notch)
6d disk 7 motor 8 bottom lid 11 casing 12 stator blade 13 screw stator 13a screw groove 14 intake port 15 exhaust port 16 purge port hole 17 purge port 18 protection bearing 20 balance correction screw 21 balance correction screw 26d disk 60a groove 60b groove 60c Balance correction portion 60d Step 60e Recess 61b Peep hole 61d Screw hole 261d Screw hole f The farthest part from the rotor shaft center of the peep hole 61b p The balance correction portion of the disk 6d Pitch circle w The wall surface surrounding the disk 6d T router

Claims (7)

A rotating part holder,
A rotor shaft arranged with a gap in the rotating part holder;
A rotor held integrally with the rotor shaft;
A radial bearing provided between the rotor shaft and the rotating part holding body and rotatably holding the rotor shaft in a radial direction;
An axial bearing provided between the rotor shaft and the rotating part holder, and rotatably holding the rotor shaft in the axial direction;
A motor that is provided between the rotor shaft and the rotating part holder and that rotates the rotor shaft;
A storage space disposed in a lower portion of the rotating part holding body and storing the axial bearing;
A bottom cover that is attached to the lower surface of the rotating part holder and closes the storage space from the outside;
In the turbo molecular pump, the axial bearing includes an upper axial holding portion and a lower axial holding portion attached to the rotating portion holding body, and a disk attached between the axial holding portions and attached to the rotor shaft. ,
A turbo molecular pump characterized in that a balance correcting portion is provided on the disk, and a viewing hole through which the balance correcting portion can be seen from the bottom lid side is provided on the outer peripheral portion of the lower axial holding portion.   2. The turbo molecular pump according to claim 1, wherein the balance correcting portion includes a plurality of screw holes provided in a direction of an axis of a rotor axis on a pitch circle of the disk, and a balance correcting screw screwed into the screw holes.   The turbo molecular pump according to claim 2, wherein a step is formed by reducing the thickness of the disk along the pitch circle, and the head of the balance correcting screw is positioned in a recess of the step.   The turbo-molecular pump according to claim 2, wherein a portion of the peep hole in the disk side opening that is farthest from the rotor axis is equal to a wall surface surrounding the disk or farther from the rotor axis than the wall surface. A rotating part holder,
A rotor shaft arranged with a gap in the rotating part holder;
A rotor held integrally with the rotor shaft;
A radial bearing provided between the rotor shaft and the rotating part holding body and rotatably holding the rotor shaft in a radial direction;
An axial bearing provided between the rotor shaft and the rotating part holder, and rotatably holding the rotor shaft in the axial direction;
A motor that is provided between the rotor shaft and the rotating part holder and that rotates the rotor shaft;
A purge port hole for introducing a purge gas provided on a side surface of the rotating part holder;
A radial through hole for introducing a purge gas provided in the rotating part holder,
The axial bearing includes an upper axial holding portion and a lower axial holding portion attached to the rotating portion holding body, an annular spacer with a radial through portion interposed between these axial holding portions and having a radial through portion, In the turbo molecular pump that is arranged inside this annular spacer and consists of a disk attached to the rotor shaft,
The disk is provided with a balance correcting portion, and the purge port hole, the radial through hole of the rotating portion holder and the radial through portion of the annular spacer are arranged in a straight line so that the balance correcting portion can be seen through from the purge port side. A turbo-molecular pump characterized by   The turbo molecular pump according to claim 5, wherein the balance correcting portion includes a plurality of screw holes provided in a radial direction of the rotor axis, and a balance correcting screw screwed into the screw hole.   The turbo molecular pump according to claim 1, wherein the balance correcting unit is partially removed to correct the balance.

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