Abstract:
A magnetic bearing device has a rotational member mounted for undergoing rotation about a rotary axis, a permanent magnet disposed on the rotational member, and a motor for rotating the rotational member. The motor has a core, projecting portions extending from the core, and motor coils each wound around a respective one of the projecting portions. The motor is disposed opposite to and spaced-apart from the permanent magnet for rotating the rotational member and contactlessly controlling an axial position of the rotational member along the rotary axis only by a magnetic forces generated between the permanent magnet, the core and the motor coils. A magnetic radial bearing contactlessly controls a radial position of the rotational member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a magnetic bearing device and, more particularly, to a magnetic bearing device in which the need for detection of and control of the position of a rotational member in the axial direction is eliminated to reduce the number of component parts, and which, therefore, can be smaller in size and can have lower manufacturing cost and lower power consumption. 
     2. Description of the Related Art 
     FIG. 5 illustrates an example of a conventional magnetic bearing device  10  of a five axes control type. An upper radial electromagnet  1  in the arrangement shown in FIG. 5 is capable of adjusting the position in the radial direction (hereinafter referred to simply as “radial position”) of an upper portion of an inner rotor  3  with an adjustment meter or the like (not shown) based on a radial position detected by an upper radial position detection sensor  2 . On the other hand, a lower radial electromagnet  5  is capable of adjusting the radial position of a lower portion of the inner rotor  3  with an adjustment meter or the like (not shown) based on a radial position detected by a lower radial position detection sensor  6 . 
     A motor  7  is provided between the upper radial electromagnet  1  and the lower radial electromagnet  5  to cause the inner rotor  3  to rotate at a high speed in a state of floating by magnetic force. A disk  9  is fixed to a portion of the inner rotor  3  below the lower radial position detection sensor  6 . The disk  9  is attracted upward by an upper axial electromagnet  11   a  and is attracted downward by a lower axial electromagnet  11   b.    
     An axial sensor  13  is provided in a lower portion of a cylindrical casing  15  so as to face the lower end of the inner rotor  3 . The position in the axial direction (hereinafter referred to simply as “axial position”) of the inner rotor  3  can be adjusted by balancing the attractions of the upper and lower axial electromagnets  11   a  and  11   b  with an adjustment meter or the like on the basis of the axial position detected by the axial sensor  13 . 
     In the above-described conventional magnetic bearing device  10 , however, the axial sensor  13 , the upper axial electromagnet  11   a  and the lower axial electromagnet  11   b  are required for supporting the rotor at the predetermined axial position. 
     The number of component parts of the magnetic bearing device  10  is thereby increased, so that it is difficult to reduce the manufacturing cost and size of the magnetic bearing device. Moreover, since electric power is consumed by the upper and lower axial electromagnets  11   a  and  11   b , there is a limit to reduction of the power consumption. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described problems of the conventional art, an object of the present invention is to provide a magnetic bearing device in which the need for detection of and control of the position of a rotating member in the axial direction is eliminated to reduce the number of component parts, and which, therefore, can be smaller in size and can have lower manufacturing cost and lower power consumption. 
     To achieve the above-described object, according to the present invention, there is provided a magnetic bearing device comprising: a rotational member floated and supported by magnetic force; at least one permanent magnet arranged on the rotational member; magnetic means for rotating the rotational member by magnetic fields generated through a core on which motor coils are formed, and which is spaced apart from the permanent magnet in the radial direction so as to form a predetermined gap therebetween; at least one set of radial position detection means for detecting the radial position and/or the inclination of the rotational member; and at least one set of radial position adjustment means for adjusting the radial position and/or the inclination of the rotational member based on the radial position and/or the inclination of detected by the radial position detection means. According to the present invention, the rotational member is supported at the desired axial position by axial direction components of magnetic attractions generated between the permanent magnet and the core. 
     The rotational member rotates in a state of floating by magnetic force. The rotational member comprises an inner rotor and an outer rotor. The magnetic bearing device is assumed to comprise an electric motor and a generator capable of floating a rotational member by magnetic force. The rotational member is provided with at least one permanent magnet. The core on which the motor coils constituting the magnetic means are formed is spaced apart from the permanent magnet so as to form a predetermined gap therebetween. The rotational member is rotated by magnetic attraction forces generated between the permanent magnet and the magnetic means. 
     The radial position detection means detects the radial position and/or the inclination of the rotational member. The radial position adjustment means adjusts the radial position and/or the inclination of the rotational member based on the radial position and/or the inclination detected by the radial position detection means. 
     In the case of three axes control, a radial position control is formed by one set of radial position detection means and one set of radial position adjustment means. In the case of five axes control, a radial position control is formed by two sets of radial position detection means respectively provided in two places distanced apart from each other along the axial direction, and two sets of radial position adjustment means also provided in two places along the axial direction. 
     There is no particular limitation in the order in which the radial position detection means and the radial position adjustment means are arranged in the axial direction. 
     The rotational member is supported at the desired axial position by axial direction components of magnetic attractions generated between the permanent magnet and the core. 
     As described above, the need for detection of and control of the position of the rotational member in the axial direction can be eliminated. Accordingly, the number of component parts can be reduced, and the magnetic bearing device can be small in size and can have low manufacturing cost and low power consumption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a longitudinal sectional view of a magnetic bearing device which represents an embodiment of the present invention; 
     FIG. 2 is a cross-sectional view taken along the lines I—I and V—V of FIG. 1; 
     FIG. 3 is a cross-sectional view taken along the line III—III of FIG. 1; 
     FIG. 4 is a cross-sectional view taken along the lines II—II and IV—IV of FIG. 1; and 
     FIG. 5 is a diagram showing an example of a conventional magnetic bearing device of a five axes control type. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described below with reference to FIGS. 1 through 4, in which components identical or corresponding to those shown in FIG. 5 are indicated by the same reference symbols. The description for the corresponding components will not be repeated. 
     Referring to FIG. 1, an upper radial position detection sensor  2 , an upper radial electromagnet  1 , a motor  7 , a lower radial electromagnet  5  and a lower radial position detection sensor  6  are mounted in this order on the circumferential surface of a stator  21  from an uppermost position to a lowermost position thereon. A rotational member comprises a shaft  23  which is passed through a central portion of the stator  21 . A stopper  24  is fixed to the lower end of the shaft  23 , while an outer rotor  25  of the rotational member is fixed to the upper end of the shaft  23 . The stopper  24  prevents the rotating member from coming off the stator  21 . 
     The outer rotor  25  is a rotational member having a hollow cylindrical shape such as to cover the upper radial position detection sensor  2 , the upper radial electromagnet  1 , the motor  7 , the lower radial electromagnet  5 , and the lower radial position detection sensor  6 . 
     The upper radial position detection sensor  2  (having the same construction as the lower radial position detection sensor  6 ) is formed by winding radial position detection coils  2   c  around projecting portions  2   b  extending from an iron core  2   a , as shown in FIG.  2 . The projecting portions  2   b  and the radial position detection coils  2   c  are formed in four circularly-distributed places such as to form magnetic pole pairs in X- and Y-directions. 
     That is, the projecting portions  2   bx   1  and the radial position detection coils  2   cx   1  are provided in the X-axis plus direction; the projecting portions  2   bx   2  and the radial position detection coils  2   cx   2 , in the X-axis minus direction; the projecting portions  2   by   1  and the radial position detection coils  2   cy   1 , in the Y-axis plus direction; and the projecting portions  2   by   2  and the radial position detection coils  2   cy   2 , in the Y-axis minus direction. 
     Also, the upper radial electromagnet  1  (having the same construction as the lower radial electromagnet  5 ) is formed by winding radial position adjustment coils  1   c  around projecting portions  1   b  extending from an iron core  1   a , as shown in FIG.  4 . The projecting portions  1   b  and the radial position adjustment coils  1   c  are formed in four circularly-distributed places such as to form magnetic pole pairs in X- and Y-directions, respectively. 
     That is, the projecting portions  1   bx   1  and the radial position adjustment coils  1   cx   1  are provided in the X-axis plus direction; the projecting portions  1   bx   2  and the radial position adjustment coils  1   cx   2 , in the X-axis minus direction; the projecting portions  1   by   1  and the radial position adjustment coils  1   cy   1 , in the Y-axis plus direction; and the projecting portions  1   by   2  and the radial position adjustment coils  1   cy   2 , in the Y-axis minus direction. 
     The radial position detecting coils  2   c  of the upper radial position detection sensor  2 , and the radial position adjustment coils  1   c  of the upper radial electromagnet  1  are provided in the same directions. 
     The motor  7  is formed by winding motor coils  7   c  around projecting portions  7   b  extending from an iron core  7   a , as shown in FIG.  3 . The core of the motor  7  is formed by the iron core  7   a  and the projecting portions  7   b . The projecting portions  7   b  and the motor coils  7   c  are formed in twelve places circularly arranged at regular intervals. 
     On the inner surface of the outer rotor  25 , an upper radial position detection target  32  is fixed circularly while being positioned so as to face the projecting portions  2   b  of the upper radial position detection sensor  2 . Similarly, a lower radial position detection target  36 , an upper radial position adjustment target  31 , and a lower radial position adjustment target  35  are fixed on the inner surface of the rotor  25  while being positioned so as to face projecting portions  6   b  of the lower radial position detection sensor  6 , the projecting portions  1   b  of the upper radial electromagnet  1 , and projecting portions  5   b  of the lower radial electromagnet  5 , respectively. 
     Each of the upper radial position detection target  32 , the lower radial position detection target  36 , the upper radial position adjustment target  31 , and the lower radial position adjustment target  35  is formed a laminated piece of steel. 
     A motor permanent magnet  37  is fixed on the inner surface of the rotor  25  while being positioned so as to face the projecting portions  7   b  of the motor  7 . The motor permanent magnet  37  is magnetized so as to have a predetermined number of magnetic poles. 
     The operation of the embodiment of the present invention will now be described. 
     An X-direction displacement of an upper portion of the outer rotor  25  is detected with the radial position detection coils  2   cx   1  and  2   cx   2 , and an X-direction displacement of a lower portion of the outer rotor  25  is detected with the radial position detection coils  6   cx   1  and  6   cx   2 . This detection is performed based on a change in the inductance between each sensor and the outer rotor  25 . 
     Also, a Y-direction displacement of the upper portion of the outer rotor  25  is detected with the radial position detection coils  2   cy   1  and  2   cy   2 , and a Y-direction displacement of the lower portion of the outer rotor  25  is detected with the radial position detection coils  6   cy   1  and  6   cy   2 . 
     The radial position adjustment coils  1   cx   1  and  1   cx   2  are excited through an adjustment meter or the like (not shown) on the basis of the detected X-direction displacements, while the radial position adjustment coils  1   cy   1  and  1   cy   2  are excited through an adjustment meter or the like (not shown) on the basis of the detected Y-direction displacements. The excited coils attract the outer rotor  25  to adjust the radial position of the upper portion of the outer rotor  25 . The radial position adjustment of the lower portion of the outer rotor  25  is also performed in the same manner. 
     The motor permanent magnet  37  and the motor coils  7   c  drive and rotate the outer rotor  25  by the magnetic attractions generated between them, and also support the outer rotor  25  in the predetermined position in the axial direction by their magnetic attractions. This support is also effected when the outer rotor  25  is in a stationary state. 
     In the above-described arrangement, there is no need for additional means for supporting the axial position of the outer rotor  25  at the predetermined position, such as required for the conventional magnetic bearing device shown in FIG. 5, i.e., the axial sensor  13 , the upper axial electromagnet  11   a , the lower axial electromagnet  11   b , and the targets facing these components. 
     Therefore, the manufacturing cost and the size of the magnetic bearing device  20  can be reduced by reducing the number of component parts, as described above. Further, since the axial sensor  13 , the upper axial electromagnet  11   a  and the lower axial electromagnet  11   b  which are required for the conventional magnetic bearing device shown in FIG. 5 are not necessary in the magnetic bearing device of the present invention, electric power can be correspondingly saved. 
     In the bearingless motor, the magnetic forces generated by the motor coils  7   c  are unbalanced by the magnetic forces generated by the radial position adjustment coils  1   c  or the radial position adjustment coils  5   c  to magnetically adjust the radial position while producing a rotating force. 
     The present invention can also be applied to a magnetic bearing device using an integral bearingless motor constructed in such a manner that the motor coils  7   c  and radial position adjustment coils  1   c  or the radial position adjustment coils  5   c  are formed on one iron core. Also in such a case, the axial sensor  13  and other components can be eliminated. 
     According to the present invention, as described above, the rotational member is supported at the desired axial position by axial direction components of magnetic attractions generated between the permanent magnet and the magnetic thereby eliminating the need for detection of and control of the position of the rotational member in the axial direction. Consequently, the number of component parts can be reduced.