Abstract:
A rotating electric machine includes: a rotation shaft; a bearing retaining the rotation shaft; an electromagnetic brake that is provided on an outer peripheral side of the rotation shaft and is located between the bearing and a rotor, the electromagnetic brake locking the rotation shaft during non-excitation and releasing the locking during excitation; a magnetic-flux shielding unit provided on an outer peripheral side of the electromagnetic brake; and a slidable contact unit that is provided so as to be in contact with the magnetic-flux shielding unit and the rotation shaft and comes into contact with the magnetic-flux shielding unit and the rotation shaft at least at two locations on the bearing side and the rotor side, wherein a magnetic field generated from the electromagnetic brake forms a closed circuit through the rotation shaft, the magnetic-flux shielding unit, and the slidable contact unit.

Description:
FIELD 
       [0001]    The present invention relates to a rotating electric machine that includes a magnetic shield provided on the outer peripheral side of an electromagnetic brake. 
       BACKGROUND 
       [0002]    In the conventional rotating electric machines that have electromagnetic brakes, brake yokes are magnetized when a current is caused to flow through the electromagnetic coils forming the electromagnetic brakes. During such an excitation, in the electromagnetic brake, the armature is attracted to the brake yoke by the electromagnetic attraction force of the brake yoke. This magnetic attraction force creates an air gap between the rotating disk provided on the rotating shaft and the armature and thus the brake is released. Therefore, the rotor can freely rotate. 
         [0003]    In contrast, when the current flowing through the electromagnetic coil is interrupted, the electromagnetic attraction force of the brake yoke disappears. During such a non-excitation, in the electromagnetic brake, the armature is pushed back by the elastic force of the spring and the armature presses the rotating disk against the braking disk. As a result, the brake acts and thus the rotor is locked and thus stops (for example, see Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Patent Application Laid-open No. 2011-50129 (p. 6, FIG. 1) 
       SUMMARY 
     Technical Problem 
       [0005]    In the conventional rotating electric machines, leakage magnetic flux is generated from the excited electromagnetic brake, which is the source of magnetism, and this leakage magnetic flux is transferred to the rotation shaft through the bearing. This results in a problem in that the bearing, which is a magnetic body, is attracted toward the rotation shaft because of the leakage magnetic flux, and thus the bearing life is shortened and the bearing is damaged. Moreover, there is a problem in that the rotation shaft does not rotate smoothly because of the effect of the bearing that is magnetically attracted toward the rotation shaft, which causes vibration and noise. 
         [0006]    The present invention has been achieved to solve the problems as above and an object of the present invention is to obtain a rotating electric machine that can reduce the leakage magnetic flux leaking to the rotation shaft from the electromagnetic brake, which is the source of magnetism. 
       Solution to Problem 
       [0007]    The rotating electric machine according to an aspect of the present invention includes: a rotation shaft; a bearing that retains the rotation shaft; an electromagnetic brake that is provided on an outer peripheral side of the rotation shaft and is located between the bearing and a rotor, the electromagnetic brake locking the rotation shaft during non-excitation and releasing the locking during excitation; a magnetic-flux shielding unit provided on an outer peripheral side of the electromagnetic brake; and a slidable contact unit that is provided such that the slidable contact unit is in contact with the magnetic-flux shielding unit and the rotation shaft and comes into contact with the magnetic-flux shielding unit and the rotation shaft at least at two locations on the bearing side and the rotor side, wherein a magnetic field generated from the electromagnetic brake forms a closed circuit through the rotation shaft, the magnetic-flux shielding unit, and the slidable contact unit. 
       Advantageous Effects of Invention 
       [0008]    According to the present invention, it is possible to reduce the adverse effect on the bearing due to the leakage magnetic flux from the electromagnetic brake; therefore, the bearing life improves. Moreover, the rotation shaft rotates smoothly; therefore, vibration and noise are significantly reduced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a diagram of a planar cross-sectional view of a rotating electric machine illustrating a first embodiment of the present invention. 
           [0010]      FIG. 2  is a diagram of a magnetic shield of the rotating electric machine illustrating the first embodiment of the present invention. 
           [0011]      FIG. 3  is a diagram of a magnetic shield of the rotating electric machine illustrating the first embodiment of the present invention. 
           [0012]      FIG. 4  is a diagram illustrating closed circuits for the leakage magnetic flux in the rotating electric machine illustrating the first embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0013]      FIG. 1  is a diagram of a planar cross-sectional view of a rotating electric machine illustrating a first embodiment of the present invention. As illustrated in  FIG. 1 , a rotating electric machine  5  includes a stator  53  around which a wire is wound; a frame  54  having a larger inside diameter than the external shape of the stator  53 ; a rotor  51  rotating in the stator  53 ; and an electromagnetic brake  3  that is used for gripping a rotation shaft  52  in the case of a power failure or the like and is provided on the outer peripheral side of the rotation shaft  52 . An electromagnetic coil  35  is wound on the electromagnetic brake  3 . When the electromagnetic coil  35  is excited by causing a current to flow therethrough, an electromagnetic attraction force is generated in a brake stator  34  itself, which is a component of the electromagnetic brake  3 , and an armature  32  is attracted toward the brake stator  34  by overcoming the elastic force of the spring in the electromagnetic brake  3 . As a result, the rotor  51  is released and thus rotates. 
         [0014]    In contrast, when the current flowing through the electromagnetic coil  35  is interrupted so that the electromagnetic coil  35  is in a non-excited state, the electromagnetic attraction force of the brake stator  34  itself disappears in the electromagnetic brake  3 , and the armature  32  is pushed back by the elastic force of the spring in the electromagnetic brake  3 . As a result, the rotor  51  is braked and thus stops. 
         [0015]    A sensor magnet  1 , which is a magnetic encoder by which the rotation position of the rotating electric machine  5  is read, is attached to a boss  11 , and the boss  11  is fitted into the rotation shaft  52 , which is a component of the rotor  51 . A magnetic-field detecting element  2  detects the magnetic field generated from the sensor magnet  1 . The rotating electric machine  5  includes a bracket  55  and a bearing  56  on the counter-load side, which retains the rotation shaft  52 . Magnetic shields  4   a  and  4   b  are magnetic-flux shielding units provided on the outer peripheral side of the electromagnetic brake  3 . The magnetic shields  4   a  and  4   b  are located on the inner side of the bearing  56  in the rotating electric machine body. The bearing  56  is provided on the counter-load side of the rotation shaft  52 . Specifically, the magnetic shields  4   a  and  4   b  are located between the bearing  56 , which is provided on the counter-load side of the rotation shaft  52 , and the bearing (not illustrated), which is provided on the load side of the rotation shaft  52 . Brushes  41   a  to  41   d  are slidable contact units that are provided on the magnetic shields  4   a  and  4   b  and are slidably in contact with the rotation shaft  52 . A non-magnetic body  33  is interposed between the electromagnetic brake  3  and the magnetic shield  4   b.    
         [0016]      FIG. 2  and  FIG. 3  are diagrams of the magnetic shields of the rotating electric machine illustrating the first embodiment of the present invention. As illustrated in  FIG. 2  and  FIG. 3 , the brushes  41   a  to  41   d  are fixed to the magnetic shields  4   a  and  4   b  with screws or the like. The brushes  41   a  to  41   d  are such that the brush  41   a  and the brush  41   b  are provided on the counter-load side of the rotation shaft  52  and  41   c  and the brush  41   d  are provided on the load side of the rotation shaft  52 . The brushes  41   a  to  41   d  are in contact with the magnetic shields  4   a  and  4   b  and the rotation shaft  52 . 
         [0017]    The magnetic shield is composed of two types of magnetic shields, i.e., the cylindrical magnetic shield  4   a  with one end surface closed and the planar disk-shaped magnetic shield  4   b,  as illustrated in  FIG. 2  and  FIG. 3 , respectively. With the conventional technologies, the electromagnetic brake  3  is fixed, with screws or the like, at fixing points provided in the bracket  55 . In the first embodiment of the present invention, the electromagnetic brake  3  is fixed to the planar disk-shaped magnetic shield  4   b.  When the electromagnetic brake  3  is fixed to the magnetic shields  4   a  and  4   b,  first, the electromagnetic brake  3  is attached to the planar disk-shaped magnetic shield  4   b  with the non-magnetic body  33  therebetween. Next, the cylindrical magnetic shield  4   a  with one end surface closed is attached, with screws or the like, to the planar disk-shaped magnetic shield  4   b  to which the electromagnetic brake  3  is fixed. Finally, the magnetic shield  4   b  is fixed to the bracket  55  and the bracket  55  is attached to the frame  54  with screws or the like. 
         [0018]    While the rotating electric machine is rotating, a current flows through the electromagnetic coil  35  forming the electromagnetic brake  3 . In the excited state where the current flows through the electromagnetic coil  35 , the magnetic field is generated in the brake stator  34 , and the armature  32  is always attracted to the brake stator  34  side; therefore, the rotor  51  can rotate. However, the magnetic field generated in the brake stator  34  leaks to the rotation shaft  52  and a magnetic flux is generated. In the first embodiment of the present invention, the leakage magnetic flux that is generated because of the electromagnetic brake  3  and leaks to the rotation shaft  52  can be reduced by forming closed circuits through the rotation shaft  52 , the magnetic shields  4   a  and  4   b,  and the brushes  41   a  to  41   d  fixed to the magnetic shields  4   a  and  4   b . As a result, it is possible to reduce the adverse effect on the bearing  56  due to the leakage magnetic flux. 
         [0019]    Moreover, although the magnetic flux also leaks to the rotation shaft  52  because of the stator  53 , the leakage magnetic flux that leaks from the stator  53  can also be reduced by forming closed circuits through the rotation shaft  52 , the magnetic shields  4   a  and  4   b,  and the brushes  41   a  to  41   d  fixed to the magnetic shields  4   a  and  4   b . As a result, it is possible to reduce the adverse effect on the bearing  56  due to the leakage magnetic flux that leaks from the stator  53 . 
         [0020]      FIG. 4  is a diagram illustrating closed circuits for the leakage magnetic flux in the rotating electric machine illustrating the first embodiment of the present invention. As illustrated in  FIG. 4 , with regard to the leakage magnetic flux generated because of the electromagnetic brake  3 , the amount of magnetic flux leaking to the bearing  56  can be reduced by forming two closed circuits: a closed circuit  100   a,  which is formed through the rotation shaft  52 , the brush  41   a,  the magnetic shield  4   a,  the magnetic shield  4   b,  and the brush  41   c;  and a closed circuit  100   b,  which is formed through the rotation shaft  52 , the brush  41   b,  the magnetic shield  4   a,  the magnetic shield  4   b,  and the brush  41   d.  As a result, it is possible to reduce the adverse effect on the bearing  56  from the electromagnetic brake  3  due to the leakage magnetic flux; therefore, the life of the bearing  56  improves. Moreover, the rotation shaft  52  rotates smoothly; therefore, vibration and noise are significantly reduced. 
         [0021]    Moreover, as illustrated in  FIG. 4 , with regard also to leakage magnetic fluxes  110   a  and  110   b,  which are generated because of the stator  53  and leak to the rotation shaft  52 , the amount of magnetic flux leaking to the bearing  56  from the stator  53  can be reduced by forming two closed circuits: the closed circuit  100   a,  which is formed through the rotation shaft  52 , the brush  41   a,  the magnetic shield  4   a,  the magnetic shield  4   b,  and the brush  41   c;  and the closed circuit  100   b,  which is formed through the rotation shaft  52 , the brush  41   b,  the magnetic shield  4   a , the magnetic shield  4   b,  and the brush  41   d.  As a result, it is possible to reduce the adverse effect on the bearing  56  due to the leakage magnetic fluxes  110   a  and  110   b,  which are generated because of the stator  53  and leak to the rotation shaft  52 ; therefore, the life of the bearing  56  further improves. Moreover, the rotation shaft  52  rotates smoothly; therefore, vibration and noise are significantly reduced. 
         [0022]    Furthermore, in the first embodiment of the present invention, with regard also to the leakage magnetic flux that is generated because of the electromagnetic brake  3  and the stator  53  and leaks to the rotation shaft  52 , the amount of magnetic flux leaking to the sensor magnet  1  can be reduced by forming two closed circuits: the closed circuits  100   a  and  100   b.  As a result, it is possible to reduce the adverse effect on the sensor magnet  1  due to the leakage magnetic flux leaking to the rotation shaft  52 , thereby improving the accuracy of reading the rotation position of the rotating electric machine  5  with the magnetic-field detecting element  2 . 
       REFERENCE SIGNS LIST 
       [0023]      1  sensor magnet,  2  magnetic-field detecting element,  3  electromagnetic brake,  4   a  to  4   b  magnetic shield,  5  rotating electric machine,  11  boss,  32  armature,  33  non-magnetic body,  34  brake stator,  41   a  to  41   d  brush,  51  rotor,  52  rotation shaft,  53  stator,  54  frame,  55  bracket,  56  bearing,  100   a  to  100   b  closed circuit,  110   a  to  110   b  leakage magnetic flux.