Patent Publication Number: US-2022216767-A1

Title: Vacuum Pump and Magnetic-Bearing-Integrated Motor

Description:
TECHNICAL FIELD 
     The present invention relates to a vacuum pump and a magnetic-bearing-integrated motor. 
     BACKGROUND ART 
     Conventionally, a vacuum pump a magnetic-bearing-integrated motor are known. Such a vacuum pump is disclosed in Japanese Patent No. 3854998, for example. 
     Japanese Patent No. 3854998 discloses a bearingless motor used in a vacuum pump such as a turbomolecular pump. 
     The bearingless motor disclosed in Japanese Patent No. 3854998 includes a rotor, a stator, and permanent magnets. In the bearingless motor disclosed in Japanese Patent No. 3854998, the permanent magnets are arranged such that the polarity orientations of the magnetic poles are opposite to each other in the radial direction of the rotor. Furthermore, in the bearingless motor disclosed in Japanese Patent No. 3854998, a support magnetic flux generated by a current flowing through a support winding wire provided in the stator penetrates the salient poles arranged between the permanent magnets. With this configuration, the stator generates a bearing force to magnetically support the rotor in a non-contact manner. 
     In the bearingless motor disclosed in Japanese Patent No. 3854998, a fixing member is provided on the outer peripheries of the permanent magnets in order to prevent scattering of the permanent magnets due to a centrifugal force generated by rotation of the rotor. Although not disclosed in Japanese Patent No. 3854998, the fixing member for preventing the scattering of the permanent magnets is conceivably made of stainless steel, for example, so as not to be damaged by a pressure applied during assembly of the rotor. 
     PRIOR ART 
     Patent Document 
     Patent Document 1: Japanese Patent No. 3854998 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, for example, when the annular fixing member for preventing scattering of the permanent magnets is made of stainless steel, a magnetic flux for generating a bearing force for magnetic support causes an eddy current in the fixing member. When an eddy current is generated in the fixing member, the power consumption becomes excessive, and power for driving the motor and power for generating the bearing force for magnetic support are disadvantageously lost. Therefore, the fixing member is made of a non-conductive material such as resin such that eddy current generation in the fixing member is conceivably significantly reduced or prevented. However, when the fixing member is made of resin, for example, the fixing member may be damaged by a pressure during assembly of the rotor. 
     The present invention is intended to solve at least one of the above problems. The present invention aims to provide a vacuum pump and a magnetic-bearing-integrated motor capable of significantly reducing or preventing damage to a fixing member during assembly and capable of reducing a loss caused by an eddy current generated in the fixing member. 
     Means for Solving the Problems 
     In order to attain the aforementioned object, a vacuum pump according to a first aspect of the present invention includes a rotor including a rotary shaft having an axial direction, a rotor blade provided on the rotary shaft, and a magnetic-bearing-integrated stator including a coil configured to apply a rotational force to rotationally drive the rotor and a bearing force to magnetically support the rotor. The rotor includes a pair of spacer members, a support member provided on an outer circumference of the rotary shaft to receive a pressure applied in the axial direction during assembly via the pair of spacer members, a permanent magnet provided so as to surround an outer circumference of the support member, and a non-conductive protective ring having an annular shape, the protective ring being provided on an outer circumference of the permanent magnet in non-contact with the pair of spacer members in the axial direction. In the axial direction of the rotary shaft, the support member has a mechanical strength higher than that of the protective ring. The non-conductive protective ring includes an insulator or a semiconductor. The mechanical strength in the axial direction refers to a strength (rigidity) with respect to a compressive load in the axial direction. 
     A magnetic-bearing-integrated motor according a second aspect of the present invention includes a rotor including a rotary shaft having an axial direction, and a magnetic-bearing-integrated stator including a coil configured to apply a rotational force to rotationally drive the rotor and a bearing force to magnetically support the rotor. The rotor includes a pair of spacer members, a support member provided on an outer circumference of the rotary shaft to receive a pressure applied in the axial direction during assembly via the pair of spacer members, a permanent magnet provided so as to surround an outer circumference of the support member, and a non-conductive protective ring having an annular shape, the protective ring being provided on an outer circumference of the permanent magnet in non-contact with the pair of spacer members in the axial direction. In the axial direction of the rotary shaft, the support member has a mechanical strength higher than that of the protective ring. 
     Effect of the Invention 
     According to the first aspect of the present invention, as described above, the rotor includes the pair of spacer members, the support member to receive a pressure applied in the axial direction during assembly via the pair of spacer members, the permanent magnet provided on the outer circumference of the support member, and the non-conductive protective ring having an annular shape, the protective ring being provided on the outer circumference of the permanent magnet, and in the axial direction of the rotary shaft, the support member has a mechanical strength higher than that of the protective ring. The support member is provided such that damage to the protective ring during assembly can be significantly reduced or prevented. Furthermore, the non-conductive protective ring is provided such that a loss caused by an eddy current generated in the protective ring can be reduced. Thue, damage to the protective ring during assembly can be significantly reduced or prevented, and a loss caused by an eddy current generated in the protective ring can be reduced. 
     According to the second aspect of the present invention, with the configuration described above, it is possible to provide the magnetic-bearing-integrated motor capable of significantly reducing or preventing damage to the protective ring during assembly and reducing a loss caused by an eddy current generated in the protective ring, similarly to the vacuum pump according to the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view schematically showing the overall configuration of a vacuum pump. 
         FIG. 2  is a schematic view showing an arrangement of a rotary body, a magnetic bearing unit, and a motor unit. 
         FIG. 3  is a block diagram illustrating the control configuration of the vacuum pump. 
         FIG. 4  is a schematic sectional view showing the magnetic bearing unit and the motor unit as viewed in the radial direction. 
         FIG. 5  is a schematic sectional view showing the motor unit as viewed in the axial direction. 
         FIG. 6  is a schematic sectional view showing a motor rotor as viewed in the axial direction. 
         FIG. 7  is a schematic sectional view showing the motor rotor as viewed in the radial direction. 
         FIG. 8  is a schematic sectional view showing a motor rotor according to a first modified example, as viewed in the radial direction. 
         FIG. 9  is a schematic sectional view showing a motor rotor according to a second modified example, as viewed in the radial direction. 
         FIG. 10  is a schematic sectional view showing a motor rotor according to a third modified example, as viewed in the radial direction. 
         FIG. 11  is a schematic sectional view showing a motor rotor according to a fourth modified example, as viewed in the radial direction. 
         FIG. 12  is a schematic sectional view showing a motor rotor according to a fifth modified example, as viewed in the axial direction. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     An embodiment embodying the present invention is hereinafter described on the basis of the drawings. 
     The configuration of a magnetic-bearing-integrated motor  22  and the configuration of a vacuum pump  100  including the magnetic-bearing-integrated motor  22  according to the embodiment of the present invention are now described with reference to  FIGS. 1 to 7 . 
     Configuration of Vacuum Pump 
     As shown in  FIG. 1 , the vacuum pump  100  is a pump to discharge gas from a container and evacuate (reducing the pressure) the container. The term “vacuum” refers to a state of pressure lower than the atmospheric pressure around the vacuum pump  100 . 
     The vacuum pump  100  includes at least one intake port  1 , at least one exhaust port  2 , and at least one pump  3 . The vacuum pump  100  suctions gas from the intake port  1  into the pump  3  by the operation of the pump  3 , and discharges the suctioned gas from the exhaust port  2 . The vacuum pump  100  includes a housing  4  to house the pump  3 . In an example of  FIG. 1 , one intake port  1  is formed in the housing  4 , and one pump  3  is housed in the housing  4 . An exhaust pipe  2   a  formed with the exhaust port  2  is connected to the housing  4 . The exhaust port  2  communicates with the intake port  1  via the exhaust pipe  2   a  and the pump  3 . 
     In the example of  FIG. 1 , the vacuum pump  100  includes a control unit  5  to control the operation of the pump  3 . The control unit  5  is attached to the bottom of the housing  4 . The control unit  5  may be provided separately from the vacuum pump  100  and may be communicably connected to the vacuum pump  100  by wire or wirelessly. 
     Pump 
     The pump  3  includes a rotary body  10  and a rotation mechanism  20 . The rotary body  10  and the rotation mechanism  20  are housed in the housing  4 . When the rotary body  10  is rotationally driven by the rotation mechanism  20 , a gas suction force is generated between the rotary body  10  and the housing  4 . 
     In the configuration example of  FIG. 1 , the pump  3  includes a first pump structure  3   a  and a second pump structure  3   b.  In the example of  FIG. 1 , the vacuum pump  100  is a composite vacuum pump with the first pump structure  3   a  and the second pump structure  3   b  connected in series. The gas taken into the pump  3  from the intake port  1  passes through the first pump structure  3   a  and the second pump structure  3   b  in this order, and is discharged from the exhaust port  2 . 
     The rotary body  10  includes a rotary shaft  11 , a blade support  12 , and rotor blades  13 . The rotary body  10  is provided such that the rotary shaft  11 , the blade support  12 , and the rotor blades  13  rotate integrally. The first pump structure  3   a  with the rotor blades  13  of the rotary body  10  and stator blades  71  of the housing  4  forms a turbomolecular pump. The rotary body  10  includes a cylindrical portion  14  extending from the blade support  12  toward a second end  11   b  of the rotary shaft  11  and forming the second pump structure  3   b  between the cylindrical portion  14  and the housing  4 . The rotary body  10  is provided such that the rotor blades  13  forming the first pump structure  3   a  and the cylindrical portion  14  forming the second pump structure  3   b  rotate integrally. 
     The second pump structure  3   b  with the cylindrical portion  14  of the rotary body  10  described below and a pump stator  73  of the housing  4  forms a molecular drag pump. 
     A direction in which the central axis of the rotary shaft  11  extends is hereinafter referred to as the axial direction or the thrust direction. The radial direction of the rotary shaft  11  is simply referred to as the radial direction. In each figure, the axial direction is defined as a Z direction. A Z 1  direction in the Z direction is referred to as the first end  11   a  side, and a Z 2  direction is referred to as the second end  11   b  side. 
     As shown in  FIG. 1 , the rotation mechanism  20  includes a magnetic-bearing-integrated motor  22  to rotationally drive the rotary body  10  and magnetically support the rotary body  10 . The rotation mechanism  20  is provided so as to surround the rotary shaft  11  centering on the rotary shaft  11 . 
     The magnetic-bearing-integrated motor  22  includes a motor stator  22   a  (see  FIG. 4 ) and a motor rotor  22   b  (see  FIG. 4 ). The motor rotor  22   b  includes the rotary shaft  11  having an axial direction. The motor stator  22   a  is configured to apply a rotational force to rotationally drive the motor rotor  22   b  and a bearing force to magnetically support the motor rotor  22   b.  The motor stator  22   a  and the motor rotor  22   b  are examples of a “magnetic-bearing-integrated stator” and a “rotor” in the claims, respectively. 
     The magnetic bearing is a 5-axis magnetic bearing including two sets of radial magnetic bearings and one set of thrust magnetic bearings. The term “5-axis” indicates that a position control and an attitude control are possible in five directions including three directions in the translation direction of the rotary body  10  and two directions in the tilt direction of the rotary body  10 . 
     That is, the rotation mechanism  20  includes a first radial magnetic bearing  40  and the magnetic-bearing-integrated motor  22  that functions as a second radial magnetic bearing, both of which are provided around the rotary shaft  11 . The rotation mechanism  20  includes a thrust magnetic bearing  60  provided around the rotary shaft  11 . The magnetic bearing magnetically levitates the rotary body  10  to support the rotary body  10  in non-contact with the rotary body  10  such that the rotary body  10  is rotatable. 
     One set of radial magnetic bearings enable a position control (two axes) in two radial directions (defined as an X direction and a Y direction) orthogonal to each other. Two sets of radial magnetic bearings arranged side by side in the axial direction enable an attitude control of tilt around the X direction and the Y direction. The thrust magnetic bearing enables a position control (one axis) in the thrust direction (Z direction). 
     In this embodiment, the rotation mechanism  20  includes at least a magnetic bearing unit  21  and the magnetic-bearing-integrated motor  22 . The magnetic bearing unit  21  includes at least the first radial magnetic bearing  40 . In this embodiment, in the configuration example of  FIG. 1 , the magnetic bearing unit  21  is a single unit integrally including the first radial magnetic bearing  40  and the thrust magnetic bearing  60 . The magnetic-bearing-integrated motor  22  is a unit that operates as both a motor that rotates the rotary shaft  11  and a second radial magnetic bearing that magnetically supports the rotary shaft  11 . Such a structure that operates as both a motor that rotates the rotary shaft  11  and a second radial magnetic bearing eliminates the need for a set of radial magnetic bearings usually provided separately from the motor, and thus it is called a bearingless motor or a self-bearing motor, for example. That is, the term “magnetic-bearing-integrated motor” refers to a motor that rotates the rotary shaft  11  at the same position in the axial direction and functions as a magnetic bearing of the rotary shaft  11 . The detailed configuration of the magnetic bearing unit  21  and the magnetic-bearing-integrated  22  is described below. 
     The housing  4  includes a base  4   a  and a case  4   b.  The rotation mechanism  20  is provided on the base  4   a,  and the rotary shaft  11  of the rotary body  10  is inserted thereinto. The exhaust pipe  2   a  is connected to the base  4   a.  The case  4   b  is attached to the upper surface of the base  4   a.  The case  4   b  has a cylindrical shape so as to surround the rotary body  10  installed on the base  4   a,  and the intake port  1  is formed on the upper surface thereof. 
     The vacuum pump  100  includes a plurality of mechanical bearings  6 , a plurality of displacement sensors  7   a,    7   b,    7   c,    7   d,  and  7   e,  and a rotation sensor  8 . The plurality of mechanical bearings  6  are provided on the base  4   a  in the vicinity of the first end  11   a  of the rotary shaft  11  and in the vicinity of the second end  11   b  of the rotary shaft  11 . The mechanical bearings  6  can come into contact with the rotary shaft  11  to support the rotary shaft  11  in the radial direction and the thrust direction. The mechanical bearings  6  are touch-down bearings that support the rotary body  10  instead of the magnetic bearing when the magnetic bearing is not operating (when the rotary body  10  is not magnetically levitated) or when a disturbance occurs. When the magnetic bearing operates, the mechanical bearings  6  and the rotary shaft  11  (rotary body  10 ) do not contact each other. 
     As shown in  FIG. 3 , the displacement sensors  7   a  to  7   d  detect displacements of the rotary shaft  11  in the radial direction (an X 1  direction, a Y 1  direction, an X 2  direction, and a Y 2  direction). The displacement sensor  7   e  detects a displacement of the rotary shaft  11  in the thrust direction (Z direction). The rotation sensor  8  detects the rotation angle of the rotary shaft  11 . 
     The control unit  5  includes a controller  81 , a power supply  82 , a unit drive  83 , and a sensor circuit  84 . 
     The power supply  82  acquires power from an external power supply and supplies power to the controller  81 , the unit drive  83 , and the sensor circuit  84 . The power supply  82  performs power conversion to convert AC power from the outside into DC power. 
     The unit drive  83  controls supply of a drive current to the rotation mechanism  20  based on a control signal from the controller  81 . The current is controlled in the unit drive  83  such that the magnetic-bearing-integrated motor  22  of the rotation mechanism  20  generates a driving force (torque) in the rotation direction, and the magnetic bearing generates a bearing force in each direction. The unit drive  83  includes inverters  85   a  and  85   b  to control current supply to the magnetic bearing unit  21 . The unit drive  83  includes inverters  85   c  and  85   d  to control current supply to the magnetic-bearing-integrated motor  22 . Each of the inverters  85   a  to  85   d  includes a plurality of switching elements. 
     The sensor circuit  84  includes the displacement sensors  7   a  to  7   e  and the rotation sensor  8 , and includes a circuit that performs a conversion process to input each sensor signal to the controller  81 , etc. Each sensor signal of the displacement sensors  7   a  to  7   e  and the rotation sensor  8  is input from the sensor circuit  84  to the controller  81 . 
     The controller  81  includes a computer including a processor such as a central processing unit (CPU) or a field programmable gate array (FPGA) and a volatile and/or non-volatile memory. 
     The controller  81  controls the operation of the rotation mechanism  20  via the unit drive  83 . The controller  81  acquires a sensor signal in each direction from the sensor circuit  84 , and outputs a control signal to perform an on/off control on the plurality of switching elements provided in the inverters  85   a,    85   b,  and  85   d  based on the acquired sensor signal. Thus, the controller  81  controls each magnetic bearing such that the rotary body  10  does not contact any fixed element of the vacuum pump  100  during the operation of the vacuum pump  100 . 
     The controller  81  outputs a control signal to perform an on/off control on the plurality of switching elements provided in the inverter  85   c  based on the sensor signal of the rotation sensor  8 . Thus, the controller  81  controls the magnetic-bearing-integrated motor  22  based on the rotation position of the rotary body  10 . 
     Structure of Rotary Body 
     As shown in  FIG. 2 , the rotary shaft  11  is a columnar member having the first end  11   a  and the second end  11   b  and extending in the axial direction. In the example of  FIG. 1 , the first end  11   a  is the upper end of the rotary shaft  11 , and the second end  11   b  is the lower end of the rotary shaft  11 . The rotary shaft  11  is supported by the rotation mechanism  20  rotatably around the central axis. Furthermore, the rotary shaft  11  is rotationally driven around the central axis by the rotation mechanism  20 . In the example of  FIG. 1 , an example of a vertical vacuum pump  100  including the rotary shaft  11  provided so as to extend along an upward-downward direction (vertical direction) is shown, but the direction of the rotary shaft  11  is not particularly limited. The rotary shaft  11  may be arranged in a horizontal direction or an oblique direction. 
     The blade support  12  is a portion of the rotary body  10  that mechanically connects the rotor blades  13  to the rotary shaft  11 . The blade support  12  is connected to the first end  11   a  side of the rotary shaft  11 . The blade support  12  extends so as to increase the inner diameter thereof toward the second end  11   b  side of the rotary shaft  11 . That is, the blade support  12  has a roughly conical shape toward the first end  11   a  of the rotary shaft  11 . The blade support  12  includes a tapered portion  12   a  that is inclined from the second end  11   b  side toward the first end  11   a  side of the rotary shaft  11 . The blade support  12  includes a flange  12   b  extending in the radial direction from the first end  11   a  of the rotary shaft  11 . The tapered portion  12   a  is mechanically connected to the outer peripheral end of the flange  12   b.    
     The rotary body  10  includes a plurality of rotor blades  13 . The rotor blades  13  are provided on the outer peripheral surface of the blade support  12 . The rotor blades  13  extend in the radial direction from the outer peripheral surface of the blade support  12  to the vicinity of the inner peripheral surface of the housing  4 . 
     As described above, the rotor blades  13  form the first pump structure  3   a  between the rotor blades  13  and the housing  4 . The plurality of rotor blades  13  are provided in a plurality of stages at intervals in the axial direction. The plurality of rotor blades  13  are aligned along the outer peripheral surface of the tapered portion  12   a  and the outer peripheral surface of the flange  12   b.    
     As shown in  FIG. 1 , a plurality of stator blades  71  are provided on the inner peripheral surface of the housing  4 . Each stator blade  71  extends inward in the radial direction (toward the rotary shaft  11  side) from the inner peripheral surface of the housing  4 . The plurality of stator blades  71  are arranged alternately with the plurality of rotor blades  13  one stage by one stage in the axial direction. Each stator blade  71  is placed on the base  4   a  via a spacer ring  72  stacked in the axial direction. The stacked spacer ring  72  is sandwiched between the base  4   a  and the case  4   b  such that each stator blade  71  is positioned. Thus, the pump  3  includes the first pump structure  3   a  including the rotor blades  13  (moving blades) of the rotary body  10  and the stator blades  71  (stationary blades) of the housing  4 . 
     The cylindrical portion  14  has a cylindrical shape coaxial with the rotary shaft  11 . The cylindrical portion  14  includes a first end  14   a  connected to the blade support  12  and a second end  14   b  on the side opposite to the blade support  12  in the axial direction of the rotary shaft  11 . The cylindrical portion  14  extends linearly along the axial direction from the first end  14   a  connected to the tapered portion  12   a  to the second end  14   b.    
     The cylindrical pump stator  73  is provided on the inner peripheral surface of the housing  4 . The inner peripheral surface of the pump stator  73  faces the outer peripheral surface of the cylindrical portion  14  in the radial direction with a small interval. A thread groove (not shown) is formed on the inner peripheral surface of the pump stator  73 . Thus, the pump  3  includes the second pump structure  3   b  including the cylindrical portion  14  of the rotary body  10  and the pump stator  73  of the housing  4 . The thread groove (not shown) may be formed on either the outer peripheral surface of the cylindrical portion  14  or the inner peripheral surface of the pump stator  73 . 
     Structure of Rotation Mechanism 
     In the example of  FIG. 1 , the rotation mechanism  20  includes two units of the magnetic bearing unit  21  and the magnetic-bearing-integrated motor  22 . 
     The magnetic bearing unit  21  is provided around the rotary shaft  11  between the rotary shaft  11  and the blade support  12 . The magnetic-bearing-integrated motor  22  is provided around the rotary shaft  11  at a position closer to the second end  11   b  of the rotary shaft  11  than the magnetic bearing unit  21 . 
     As shown in  FIG. 4 , the magnetic bearing unit  21  includes a magnetic bearing stator  21   a  and a magnetic bearing rotor  21   b.  The magnetic bearing stator  21   a  is provided with a first coil  41  forming the first radial magnetic bearing  40  and a thrust coil  61  forming the thrust magnetic bearing  60 . The magnetic bearing rotor  21   b  is configured by stacking a plurality of magnetic steel sheets in the axial direction. 
     Magnetic-Bearing-Integrated Motor 
     As shown in  FIG. 5 , the magnetic-bearing-integrated motor  22  (motor stator  22   a ) includes motor coils  24  forming the magnetic-bearing-integrated motor  22 , second coils  51  forming the second radial magnetic bearing, and a stator core  32  to which the motor coils  24  and the second coils  51  are attached in a plane orthogonal to the axial direction of the rotary shaft  11 . 
     In other words, in the magnetic-bearing-integrated motor  22  illustrated in  FIG. 5 , the second coils  51  of the second radial magnetic bearing are further assembled to the motor stator  22   a  including the motor coils  24  and the stator core  25 . 
     The stator core  25  includes a plurality of teeth  25   a  and a stator yoke  25   b.  The stator yoke  25   b  is formed in an annular shape so as to surround the rotary shaft  11 . The plurality of teeth  25   a  extend in the radial direction from the inner peripheral surface of the stator yoke  25   b  toward the center of the rotary shaft  11 . The plurality of teeth  25   a  are arranged at equal angular intervals in the circumferential direction, and a slot  25   c  is formed between the adjacent teeth  25   a  to house the coils. 
     The motor coils  24  and the second coils  51  are wound around the respective teeth  25   a.  In  FIG. 5 , the motor coils  24  and the second coils  51  are arranged side by side in the radial direction in the plane orthogonal to the axial direction of the rotary shaft  11 . That is, both the motor coils  24  and the second coils  51  are arranged in the same slot  25   c.  In an example of  FIG. 5 , the motor coils  24  are arranged inside in the radial direction, and the second coils  51  are arranged outside in the radial direction. 
     The motor coils  24  and the second coils  51  are separate coils and are electrically insulated from each other. The motor coils  24  are electrically connected to the inverter  85   c  (see  FIG. 3 ), and the second coils  51  are electrically connected to the inverter  85   d  (see  FIG. 3 ). The inverter  85   c  supplies three-phase currents (U-phase, V-phase, and W-phase) to the magnetic-bearing-integrated motor  22 , for example. The magnetic-bearing-integrated motor  22  includes three sets of motor coils  24  (Mu, Mv, and Mw) to which three-phase currents of U-phase, V-phase, and W-phase are supplied, respectively. The inverter  85   d  supplies three-phase currents (U-phase, V-phase, and W-phase) to the magnetic-bearing-integrated motor  22 , for example. The magnetic-bearing-integrated motor  22  includes three sets of second coils  51  (Su, Sv, and Sw) to which three-phase currents of U-phase, V-phase, and W-phase are supplied, respectively. 
     The motor rotor  22   b  is provided on the rotary shaft  11  so as to rotate integrally with the rotary shaft  11 . That is, the rotary shaft  11  is provided with permanent magnets  26  at a position (the same position in the axial direction) facing the stator core  25  in the radial direction with a gap. In the example of  FIG. 5 , the permanent magnet  26  magnetized to the N pole is provided over one circumferential half of the rotary shaft  11 , and the permanent magnet  26  magnetized to the S pole is provided over the other circumferential half of the rotary shaft  11 . 
     Although  FIG. 5  shows an example of a 2-pole and 6-slot structure, the number of poles and the number of slots are not particularly limited. Furthermore, in  FIG. 5 , each winding method for the motor coils  24  and the second coils  51  is not limited to a concentrated winding method, and may be another winding method such as a distributed winding method. 
     The controller  81  (see  FIG. 3 ) causes a current to be supplied to each motor coil  24  via the inverter  85   c  (see  FIG. 3 ), and causes magnetic fluxes of the motor coils  24  and magnetic fluxes of the permanent magnets  26  to interact with each other. That is, the magnetic-bearing-integrated motor  22  applies attractive and repulsive acting forces to the magnetic poles of the permanent magnets  26  by the magnetic fluxes of the motor coils  24 . The controller  81  generates the rotating magnetic fluxes by switching the motor coils  24  that supply a current according to the rotation angle position of the rotary body  10 , and rotates the rotary body  10  at a desired rotation speed. The rotation speed of the rotary body  10  by the magnetic-bearing-integrated motor  22  is 10,000 rpm or more and 100,000 rpm or less, for example. 
     The controller  81  (see  FIG. 3 ) causes a current to be supplied to the second coils  51  via the inverter  85   d  (see  FIG. 3 ), and forms the coarseness and fineness of the combined magnetic flux in the gap between the rotary shaft (motor rotor  22   b ) and the stator core  25  (motor stator  22   a ) by interaction between the magnetic fluxes of the second coils  51  and the magnetic fluxes of the permanent magnets  26 . Consequently, the magnetic-bearing-integrated motor  22  applies a bearing force to the rotary shaft  11  in a direction in which the magnetic fluxes of the second coils  51  and the magnetic fluxes of the permanent magnets  26  strengthen each other. 
     For example, in  FIG. 5 , magnetic fluxes of the two second coils  51  (Su) and the magnetic fluxes of the permanent magnets  26  strengthen each other in the gap on the north pole side of the motor rotor  22   b,  and weaken each other in the gap on the south pole side of the motor rotor  22   b.  Thus, the bearing force acts toward the north pole side (the right side in the figure) with a large amount of magnetic flux.  FIG. 5  illustrates the U-phase second coils  51  (Su), but the strength and direction of the current supplied to each second coil  51  are controlled such that a bearing force of any strength can be generated in any radial direction. The controller  81  controls current supply to the second coils  51  based on the sensor signals of the displacement sensors  7   c  and  7   d  and the rotation sensor  8  (see  FIG. 3 ) so as to control the bearing force of the magnetic-bearing-integrated motor  22  such that the rotary body  10  maintains a non-contact state in the radial direction. 
     Referring again to  FIG. 4 , an operation to attach the magnetic bearing unit  21  and the magnetic-bearing-integrated motor  22  to the rotary shaft  11  is now described. When the magnetic bearing unit  21  and the magnetic-bearing-integrated motor  22  are attached to the rotary shaft  11 , spacer members  29  are provided so as to sandwich each of the magnetic bearing unit  21  and the magnetic-bearing-integrated motor  22 . Specifically, when the magnetic bearing unit  21  and the magnetic-bearing-integrated motor  22  are attached to the rotary shaft  11 , a first spacer member  29   a,  the magnetic bearing unit  21 , a second spacer member  29   b,  the magnetic-bearing-integrated motor  22 , and a third spacer member  29   c  are fitted in this order into the rotary shaft  11 . After the magnetic bearing unit  21 , the magnetic-bearing-integrated motor  22 , and each spacer member  29  are fitted into the rotary shaft  11 , a pressure is applied to a ring  23  in the Z 2  direction such that the rotation mechanism  20  is attached to the rotary shaft  11 . That is, a support member  27  is sandwiched together with the spacer members  29  while a compressive load is applied in the axial direction to the first end  11   a  of the rotary shaft  11  and the ring  23 . Furthermore, the spacer members  29  are provided as positioning members for the rotation mechanism  20 . 
     As shown in  FIG. 6 , the motor rotor  22   b  includes the permanent magnets  26 , the support member  27 , and a protective ring  28 . The support member  27  is provided on the outer periphery of the rotary shaft  11 . The permanent magnets  26  are provided so as to surround the outer circumference of the support member  27 . The protective ring  28  is provided on the outer peripheries of the permanent magnets  26  in non-contact with a pair of spacer members  29  in the axial direction. In an example shown in  FIG. 6 , the permanent magnets  26  are provided on the support member  27  in direct contact with the support member  27 . 
     The support member  27  is provided to receive, via the pair of spacer members  29 , a pressure applied in the axial direction when the motor rotor  22   b  is attached to the rotary shaft  11  (during assembly). The support member  27  has an annular shape. Furthermore, the support member  27  includes a metal cylinder extending in the axial direction of the rotary shaft  11 . Specifically, the support member  27  is made of stainless steel. 
     The protective ring  28  is provided to significantly reduce or prevent scattering of the permanent magnets  26  due to a centrifugal force generated when the motor rotor  22   b  is rotating. The protective ring  28  has an annular shape. The magnetic-bearing-integrated motor  22  has a motor function and a magnetic bearing function. The magnetic bearing generates a magnetic field in a predetermined direction to apply a bearing force in a predetermined direction. Therefore, when the motor rotor  22   b  rotates, an eddy current may be generated. When an eddy current is generated, the power consumption becomes excessive, and power for driving the motor and power for generating a bearing force for magnetic support are lost. 
     Therefore, in this embodiment, the protective ring  28  is made of a non-conductive material. The non-conductive material of the protective ring  28  has a lower electrical conductivity than the metal of the support member  27 . Specifically, the protective ring  28  is made of a non-conductive resin. More specifically, the protective ring  28  is made of fiber-reinforced plastic. The protective ring  28  is made of carbon fiber reinforced plastic (CFRP), for example. CFRP has a high strength in a direction in which the inner carbon fibers extend and a low strength in a direction in which the carbon fibers are aligned. Therefore, the protective ring  28  is provided on the permanent magnets  26  such that the carbon fibers inside the CFRP extend along the rotation direction around the axial direction of the rotary shaft  11 . Thus, it is possible to significantly reduce or prevent scattering of the permanent magnets  26  due to a centrifugal force generated by rotation of the rotary shaft  11 . 
     In this embodiment, the permanent magnets  26  are fitted into the support member  27  and fixed with an adhesive, for example. Furthermore, the protective ring  28  is fitted into the permanent magnets  26  fitted into the support member  27  and fixed with an adhesive, for example. Then, the support member  27  to which the permanent magnets  26  and the protective ring  28  are fixed is fitted into the rotary shaft  11 . 
     Motor Rotor 
     The pair of spacer members  29  (the second spacer member  29   b  and the third spacer member  29   c ) shown in  FIG. 7  are arranged so as to sandwich the support member  27  in the axial direction. In this embodiment, the motor rotor  22   b  is attached to the rotary shaft  11  by application of a pressure in the Z 2  direction to the support member  27  via the spacer member  29  (third spacer member  29   c ). The magnetic-bearing-integrated motor  22  is a motor for high-speed rotation. Therefore, in order to prevent a variation in the position of the motor rotor  22   b  or the like in the axial direction during high-speed rotation, a large pressure is applied when the motor rotor  22   b  is attached to the rotary shaft  11 . Therefore, the mechanical strength of the rotary shaft  11  of the support member  27  in the axial direction needs to be high. Specifically, the mechanical strength of the rotary shaft  11  of the support member  27  in the axial direction needs to be higher than the mechanical strength of the protective ring  28  in the axial direction. 
     As shown in  FIG. 7 , the permanent magnets  26  each have a length  91  in the axial direction. The protective ring  28  has a length  92  in the axial direction. The support member  27  has a length  93  in the axial direction. In the axial direction, the length  93  of the support member  27  is larger than the length  92  of the protective ring  28 . The length  93  and the length  92  are examples of a “first length” and a “second length” in the claims, respectively. 
     The protective ring  28  is arranged at a position at which a first-side end  28   a  of the protective ring  28  in the axial direction is located between first-side ends  26   a  of the permanent magnets  26  and a first-side end  27   a  of the support member  27 . Furthermore, the protective ring  28  is arranged at a position at which a second-side end  28   b  of the protective ring  28  in the axial direction is located between second-side ends  26   b  of the permanent magnets  26  and a second-side end  27   b  of the support member  27 . That is, in this embodiment, in the axial direction, the length  92  of the protective ring  28  is larger than the lengths  91  of the permanent magnets  26  and smaller than the length  93  of the support member  27 . 
     In this embodiment, both end faces (end faces  27   c  and  27   d ) of the support member  27  in the axial direction contact the pair of spacer members  29 , respectively. Specifically, the end face  27   c  of the support member  27  contacts an end face  29   d  of the spacer member  29 . The end face  27   d  of the support member  27  contacts an end face  29   e  of the spacer member  29 . That is, the support member  27  is sandwiched by the pair of spacer members  29  from both sides in the axial direction, and is fixed while a compressive load is applied thereto in the axial direction. In an example shown in  FIG. 7 , contact surfaces between the end faces (the end face  29   d  and the end face  29   e ) of the spacer members  29  and both end faces (the end face  27   c  and the end face  27   d ) of the support member  27  in the axial direction are flat. 
     In this embodiment, at least one (an end face  28   c  or an end face  28   d ) of end faces of the protective ring  28  in the axial direction does not contact at least one of the pair of spacer members  29 . In the example of  FIG. 7 , both end faces (the end face  28   c  and the end face  28   d ) of the protective ring  28  do not contact the pair of spacer members  29 , respectively. Therefore, the protective ring  28  is supported by the support member  27  via the permanent magnets  26  without receiving a compressive load in the axial direction from any of the pair of spacer members  29 . 
     In this embodiment, in the radial direction of the rotary shaft  11 , the outer surface  28   e  of the protective ring  28  is located at substantially the same position as the outer surfaces  29   f  of the pair of spacer members  29  or is located inside the outer surfaces  29   f  of the pair of the spacer members  29 . In the example of  FIG. 7 , in the radial direction of the rotary shaft  11 , the outer surface  28   e  of the protective ring  28  is located at substantially the same position as the outer surfaces  29   f  of the pair of spacer members  29 . Specifically, a distance  94  from the rotation center  11   d  of the rotary shaft  11  to the outer surfaces  29   f  of the spacer members  29  and a distance  95  from the rotation center  11   d  of the rotary shaft  11  to the outer surface  28   e  of the protective ring  28  are substantially equal to each other. 
     Advantages of This Embodiment 
     In this embodiment, the following advantages are obtained. 
     In this embodiment, with the configuration described above, damage to the protective ring  28  during assembly can be significantly reduced or prevented. Furthermore, a loss caused by an eddy current generated in the protective ring  28  can be reduced. Thus, damage to the protective ring  28  during assembly can be significantly reduced or prevented, and a loss caused by an eddy current generated in the protective ring  28  can be reduced. 
     In this embodiment, as described above, in the axial direction, the length  93  of the support member  27  is larger than the length  92  of the protective ring  28 . Accordingly, a pressure applied during assembly can be applied only to the support member  27 . Consequently, damage to the protective ring  28  during assembly can be significantly reduced or prevented. 
     In this embodiment, as described above, the protective ring  28  is arranged at the position at which the first-side end  28   a  of the protective ring  28  in the axial direction is located between the first-side ends  26   a  of the permanent magnets  26  and the first-side end  27   a  of the support member  27 , and the second-side end  28   b  of the protective ring  28  in the axial direction is located between the second-side ends  26   b  of the permanent magnets  26  and the second-side end  27   b  of the support member  27 . Accordingly, in the axial direction around which the motor rotor  22   b  rotates, protrusion of both ends (ends  26   a  and  26   b ) of the permanent magnets  26  from both ends (ends  28   a  and  28   b ) of the protective ring  28  can be significantly reduced or prevented. Consequently, scattering of the permanent magnets  26  due to a centrifugal force can be significantly reduced or prevented when the motor rotor  22   b  is rotating. 
     In this embodiment, as described above, the pair of spacer members  29  are arranged so as to sandwich the support member  27 , both end faces (end faces  27   c  and  27   d ) of the support member  27  in the axial direction contact the pair of spacer members  29 , respectively, and at least one (the end face  28   c  or the end face  28   d ) of the end faces of the protective ring  28  in the axial direction does not contact at least one of the pair of spacer members  29 . Accordingly, when assembly is performed by applying a pressure to the support member  27  via the spacer members  29 , the pressure from the spacer members  29  can be applied only to the support member  27  instead of the protective ring  28 . Consequently, application of the pressure applied during assembly to the protective ring  28  can be further significantly reduced or prevented, and thus damage to the protective ring  28  can be further significantly reduced or prevented. 
     In this embodiment, as described above, in the radial direction of the rotary shaft  11 , the outer surface  28   e  of the protective ring  28  is located at substantially the same position as the outer surfaces  29   f  of the pair of spacer members  29  or is located inside the outer surfaces  29   f  of the pair of the spacer members  29 . Accordingly, protrusion of the motor rotor  22   b  from the spacer members  29  in the radial direction of the rotary shaft  11  can be significantly reduced or prevented. Therefore, even when the motor rotor  22   b  and the spacer members  29  are attached to the rotary shaft  11 , the amount of protrusion in the radial direction of the rotary shaft  11  can be made uniform with the amount of protrusion of the spacer members  29 . Consequently, the sizes of gaps between both the motor stator  22   a  and the magnetic bearing unit  21  and the rotary shaft  11  occurring when the motor stator  22   a  and the magnetic bearing unit  21 , for example, are attached become substantially constant, and thus the rotary shaft  11  can be rotated stably. 
     In this embodiment, as described above, the support member  27  has an annular shape. Accordingly, as compared with a configuration including a support member  27  formed by combining a plurality of members, for example, an increase in the number of components can be significantly reduced or prevented. 
     In this embodiment, as described above, the protective ring  28  is made of a non-conductive resin. Accordingly, as compared with a configuration including a protective ring made of ceramic, for example, an increase in the weight of the protective ring  28  can be significantly reduced or prevented. Consequently, the weight of the motor rotor  22   b  can be reduced while eddy current generation in the protective ring  28  is significantly reduced or prevented. 
     In this embodiment, as described above, the protective ring  28  is made of fiber-reinforced plastic. Accordingly, as compared with a case in which the protective ring  28  is made of a resin containing no fibers, for example, the mechanical strength of the protective ring  28  can be increased. Consequently, scattering of the permanent magnets  26  can be significantly reduced or prevented while the weight of the protective ring  28  is reduced. 
     In this embodiment, as described above, the magnetic-bearing-integrated motor  22  includes the motor rotor  22   b  including the rotary shaft  11  having an axial direction, and the motor stator  22   a  to apply a rotational force to rotationally drive the motor rotor  22   b  and a bearing force to magnetically support the motor rotor  22   b,  and the motor rotor  22   b  includes the pair of spacer members  29 , the support member  27  provided on the outer circumference of the rotary shaft  11  to receive a pressure applied in the axial direction during assembly via the pair of spacer members  29 , the permanent magnets  26  provided so as to surround the outer circumference of the support member  27 , and the protective ring  28  having an annular shape and provided on the outer circumference of the permanent magnets  26  in non-contact with the pair of spacer members  29  in the axial direction. In the axial direction of the rotary shaft  11 , the mechanical strength of the support member  27  is higher than the mechanical strength of the protective ring  28 . Accordingly, it is possible to provide the magnetic-bearing-integrated motor  22  capable of reducing a loss caused by an eddy current generated in the protective ring  28 , similarly to the vacuum pump  100  according to the aforementioned embodiment. 
     Modified Examples 
     The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is not shown by the above description of the embodiment but by the scope of claims for patent, and all modifications (modified examples) within the meaning and scope equivalent to the scope of claims for patent are further included. 
     First Modified Example 
     For example, while the example in which the ends  28   a  and  28   b  of the protective ring  28  do not contact the spacer members  29  has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, one of the ends (ends  28   a  and  28   b ) of the protective ring  28  may contact the spacer member  29  as long as the other (end  28   a  or  28   b ) of the ends of the protective ring  28  does not contact the spacer member  29 . Specifically, as shown in  FIG. 8 , the protective ring  28  and the spacer member  29  may contact each other due to contact of the end face  28   d  of the protective ring  28  with the end face  29   e  of the third spacer member  29   c.  Although not shown in the figure, the end face  28   c  of the protective ring  28  and the end face  29   d  of the second spacer member  29   b  may contact each other. 
     Second Modified Example 
     While the example in which the outer surface  28   e  of the protective ring  28  and the outer surfaces  29   f  of the spacer members  29  are located at substantially the same position has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, the outer surface  28   e  of the protective ring  28  may be located inside the outer surfaces  29   f  of the pair of spacer members  29 . Specifically, as shown in  FIG. 9 , the distance  95  from the rotation center  11   d  of the rotary shaft  11  to the outer surface  28   e  of the protective ring  28  may be smaller than the distance  94  from the rotation center  11   d  of the rotary shaft  11  to the outer surfaces  29   f  of the spacer members  29 . 
     Third Modified Example 
     While the example in which in the axial direction, the length  92  of the protective ring  28  is shorter than the length  93  of the support member  27  has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, as shown in  FIG. 10 , in the axial direction, the length  92  of the protective ring  28  may be larger than the length  93  of the support member  27 . Specifically, as shown in  FIG. 10 , when the distance  95  from the rotation center  11   d  of the rotary shaft  11  to the outer surface  28   e  of the protective ring  28  is larger than the distance  94  from the rotation center  11   d  of the rotary shaft  11  to the outer surfaces  29   f  of the spacer members  29 , in the axial direction, the length  92  of the protective ring  28  may be larger than the length  93  of the support member  27 . 
     Fourth Modified Example 
     While the example in which the motor rotor  22   b  includes a pair of spacer members  29  has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, as shown in  FIG. 11 , the rotary shaft  11  may include a rib  11   e  on the first end  11   a  side of the rotary shaft  11 , and the end face  27   c  of the support member  27  may contact an end face  11   f  of the rib  11   e.  Even when the spacer member  29  is not provided, both ends of the row of each member fitted into the rotary shaft  11  may be sandwiched so as to contact the end face  11   f  of the rib  11   e  and the ring  23  in the axial direction and may be fixed while a compressive load in the axial direction is applied to the whole. 
     Fifth Modified Example 
     While the example in which the support member  27  has an annular shape has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, as shown in  FIG. 12 , the support member  27  may include a first support member  27   e  and a second support member  27   f  each having an arcuate shape. Specifically, the support member  27  may be configured by arranging the first support member  27   e  and the second support member  27   f  on the outer circumference of the rotary shaft  11  and arranging the permanent magnets  26  and the protective ring  28  on the outer circumference. 
     Other Modified Examples 
     While the example in which the protective ring  28  is made of CFRP has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, the protective ring  28  may be made of fiber-reinforced plastic such as glass-fiber reinforced plastic (GFRP) or aramid fiber-reinforced plastic (AFRP). Alternatively, the protective ring  28  may be made of a material other than fiber-reinforced plastic such as ceramic as long as scattering of the permanent magnets  26  due to a centrifugal force generated by rotation of the motor rotor  22   b  can be significantly reduced or prevented. However, when the protective ring  28  is made of ceramic, for example, the weight of the protective ring  28  is heavier as compared with a case in which the protective ring  28  is made of fiber-reinforced plastic, and thus the protective ring  28  is preferably made of fiber-reinforced plastic. 
     While the example in which the magnetic bearing unit  21  is provided on the rotary shaft  11  has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, the magnetic bearing unit  21  may not be provided. When the magnetic bearing unit  21  is not provided, a mechanical bearing may be provided instead of the magnetic bearing unit  21 . 
     While the example in which the magnetic bearing unit  21  includes the first radial magnetic bearing  40  and the thrust magnetic bearing  60  has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, the first radial magnetic bearing  40  and the thrust magnetic bearing  60  may be provided separately. 
     While the example in which the permanent magnets  26  are provided on the support member  27  in direct contact with the support member  27  has been shown in the aforementioned embodiment, the present invention is not limited to this. For example, the permanent magnets  26  may be provided on the support member  27  in indirect contact with the support member  27  by an adhesive or the like. 
     Aspects 
     It will be appreciated by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects. 
     Item 1 
     A vacuum pump comprising: 
     a rotor including a rotary shaft having an axial direction; 
     a rotor blade provided on the rotary shaft; and 
     a magnetic-bearing-integrated stator including a coil configured to apply a rotational force to rotationally drive the rotor and a bearing force to magnetically support the rotor; wherein 
     the rotor includes:
         a pair of spacer members;   a support member provided on an outer circumference of the rotary shaft to receive a pressure applied in the axial direction during assembly via the pair of spacer members;   a permanent magnet provided so as to surround an outer circumference of the support member; and   a non-conductive protective ring having an annular shape, the protective ring being provided on an outer circumference of the permanent magnet in non-contact with the pair of spacer members in the axial direction; and       

     in the axial direction of the rotary shaft, the support member has a mechanical strength higher than that of the protective ring. 
     Item 2 
     The vacuum pump according to item 1, wherein in the axial direction, the support member has a first length larger than a second length of the protective ring. 
     Item 3 
     The vacuum pump according to item 2, wherein the protective ring is arranged at a position at which a first-side end of the protective ring in the axial direction is located between a first-side end of the permanent magnet and a first-side end of the support member, and a second-side end of the protective ring in the axial direction is located between a second-side end of the permanent magnet and a second-side end of the support member. 
     Item 4 
     The vacuum pump according to item 1, wherein
         the pair of spacer members are arranged so as to sandwich the support member;       

     in the axial direction, the support member has both end faces that contact the pair of spacer members, respectively; and
         in the axial direction, the protective ring has at least one end face in non-contact with at least one of the pair of spacer members.       

     Item 5 
     The vacuum pump according to item 4, wherein in a radial direction of the rotary shaft, the protective ring has an outer surface located at substantially the same position as outer surfaces of the pair of spacer members or located inside the outer surfaces of the pair of spacer members. 
     Item 6 
     The vacuum pump according to item 1, wherein the support member has an annular shape. 
     Item 7 
     The vacuum pump according to item 1, wherein the protective ring is made of a non-conductive resin. 
     Item 8 
     The vacuum pump according to item 7, wherein the protective ring is made of fiber-reinforced plastic. 
     Item 9 
     A magnetic-bearing-integrated motor comprising: 
     a rotor including a rotary shaft having an axial direction; and 
     a magnetic-bearing-integrated stator including a coil configured to apply a rotational force to rotationally drive the rotor and a bearing force to magnetically support the rotor; wherein 
     the rotor includes:
         a pair of spacer members;   a support member provided on an outer circumference of the rotary shaft to receive a pressure applied in the axial direction during assembly via the pair of spacer members;   a permanent magnet provided so as to surround an outer circumference of the support member; and   a non-conductive protective ring having an annular shape, the protective ring being provided on an outer circumference of the permanent magnet in non-contact with the pair of spacer members in the axial direction; and       

     in the axial direction of the rotary shaft, the support member has a mechanical strength higher than that of the protective ring. 
     Item 10 
     The magnetic-bearing-integrated motor according to item 9, wherein in the axial direction, the support member has a first length larger than a second length of the protective ring. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           11 : rotary shaft 
           13 : rotor blade 
           22 : magnetic-bearing-integrated motor 
           22   a:  motor stator (magnetic-bearing-integrated stator) 
           22   b:  motor rotor (rotor) 
           24 : motor coil (coil) 
           26 : permanent magnet 
           26   a:  end (first-side end of the permanent magnet) 
           26   b:  end (second-side end of the permanent magnet) 
           27 : support member 
           27   a:  end (first-side end of the support member) 
           27   b:  end (second-side end of the support member) 
           27   c:  end face (first-side end face of the support member) 
           27   d:  end face (second-side end face of the support member) 
           28 : protective ring 
           28   a:  end (first-side end of the protective ring) 
           28   b : end (second-side end of the protective ring) 
           28   c:  end face (first-side end face of the protective ring) 
           28   d:  end face (second-side end face of the protective ring) 
           29 : pair of spacer members 
           29   d:  end face (first-side end face of the spacer member) 
           29   e:  end face (second-side end face of the spacer member) 
           51 : second coil (coil) 
           92 : length (second length) 
           93 : length (first length) 
           100 : vacuum pump