Patent Publication Number: US-2017366062-A1

Title: Motor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention claims priority under 35 U.S.C. §119 to U.S. Application No. 62/351,688 filed Jun. 17, 2016, the entire content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a motor. 
     DESCRIPTION OF THE RELATED ART 
     Conventionally, a housing for accommodating a motor is known. For example, the housing includes a cover member for covering a stator of a motor, and a cap member for covering the upper side of a motor. 
     When the top surface of the cap member is a planar surface extending in a direction perpendicular to a center axis, the cap member has low rigidity. Therefore, when a motor rotates, the natural frequency of the cap member and the natural frequency of the motor may resonate, whereby a noise is generated. 
     By increasing the rigidity of the cap member, it is possible to shift the natural frequencies of the cap member and the motor. For example, by installing a rib in a cap member or increasing the thickness of the cap member, the rigidity of the cap member increases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical sectional view of a motor. 
         FIG. 2  is a perspective view of a cap member. 
         FIG. 3  is a perspective view of the cap member. 
         FIG. 4  is a plan view of the motor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the subject specification, in the direction parallel to the center axis, the upper side in  FIG. 1  will be referred to as “upper side”, and the lower side in  FIG. 1  will be simply referred to as “lower side”. The expressions “upper side” and “lower side” do not necessarily have to coincide with the direction of gravity. In addition, the radial direction about the center axis will be simply referred to as “radial direction”, the circumferential direction about the central axis will be simply referred to as “circumferential direction”, and the direction parallel to the central axis will be simply referred to as “axial direction”. 
       FIG. 1  is a vertical sectional view of a motor  1  according to one exemplary embodiment of the present invention. The motor  1  is, for example, an inner rotor type motor used as a driving source for office equipment such as a copying machine, a printer, a multifunction machine or the like. 
     As shown in  FIG. 1 , the motor  1  includes a rotary unit  11 , a stationary unit  12 , two bearings  13 , an encoder  14 , and a cap member  15 . The rotary unit  11  rotates about a center axis J 1  extending in a vertical direction. The output shaft of the rotary unit  11  faces downward. Hereinafter, the portion of the motor  1  other than the cap member  15  will be referred to as a “motor body part  10 ”. 
     The bearings  13  are fixed to the stationary unit  12  and are arranged to rotatably support the rotary unit  11 . The bearings  13  include a first bearing  131  disposed on the lower side of a shaft  111  and a second bearing (not shown) disposed on the upper side of the shaft  111 . The bearings  13  are, for example, ball bearings. The bearings  13  may be oil-impregnated sleeves. The cap member  15  has a lid shape and covers the upper side of a stator  122 . The encoder  14  is arranged inside the cap member  15 . 
     The rotary unit  11  includes the shaft  111 , a rotor holder  112 , and a rotor magnet  113 . The shaft  111  is formed in a substantially circular columnar shape using the the center axis J 1  as a center thereof and is rotatably supported by the bearings  13 . The rotor holder  112  is connected to the side opposite to the output side of the shaft  111 . The rotor holder  112  includes a shaft fixing portion  211 , a connecting portion  212 , and a cylindrical portion  213 . The shaft fixing portion  211  is fixed to the shaft  111  on the upper side of the second bearing. The connecting portion  212  extends radially outward from the axial upper edge portion of the shaft fixing portion  211 . The cylindrical portion  213  extends downward from the radial outer edge portion of the connecting portion  212 . The rotor magnet  113  is attached to the outer surface of the cylindrical portion  213 . The rotor magnet  113  may have a cylindrical shape. Alternatively, a plurality of magnets may be arranged in the circumferential direction. The rotor holder  112  is formed by pressing a thin plate. The thin plate is made of, for example, a magnetic material which is a metal. 
     As shown in  FIG. 1 , the stationary unit  12  includes a cover member  121 , a stator  122 , and a circuit board  123 . 
     The cover member  121  includes an inner cylindrical portion  221 , an outer cylindrical portion  222 , and a bottom portion  223 . The inner cylindrical portion  221  and the outer cylindrical portion  222  are formed in a cylindrical shape using the center axis J 1  as a center thereof and are disposed coaxially. The bottom portion  223  connects the lower end of the outer cylindrical portion  222  and the lower end of the inner cylindrical portion  221 . The bottom portion  223  is preferably provided with a plurality of attachment holes  224  for attaching the motor  1  to a desired position. The inner cylindrical portion  221  supports the first bearing  131  on the inner surface thereof. The outer cylindrical portion  222  covers the outer periphery of the stator  122  and supports the stator  122  on the inner surface thereof. The cover member  121  is formed by pressing a single plate member made of a metal. Preferably, the cover member  121  is an electrically conductive member. More preferably, the cover member  121  is a magnetic body. 
     The stator  122  preferably further includes a spacer (not shown). The spacer is formed in an axially-extending cylindrical shape around the central axis J 1 . The spacer is arranged coaxially with the inner cylindrical portion  221  and the outer cylindrical portion  222  of the cover member  121 . The spacer includes a fixing portion fixed to the inner cylindrical portion  221  at the lower side and a bearing holding portion holding the second bearing at the upper side. The spacer is formed by pressing a single plate member made of a metal. Preferably, the spacer is an electrically conductive member. More preferably, the spacer is a magnetic body. 
     The stator  122  includes a stator core  231 , an insulator  232 , and a coil  233 . The stator  122  is formed in an annular shape with the center axis J 1  used as a center thereof. The stator core  231  is formed by stacking a plurality of thin magnetic steel plates in the vertical direction. Although not shown, the stator core  231  is preferably composed of an annular core back and a plurality of teeth. The core back is press-fitted into the outer cylindrical portion  222 . The teeth extend radially inward from the core back. The rotor magnet  113  is arranged inside the stator  122 . The tips of the teeth face the rotor magnet  113  in the radial direction. 
     The insulator  232  is made of a resin. The insulator  232  covers the stator core  231 . The insulator  232  is preferably composed of nine upper insulators  251  and nine lower insulators  252 . Each of the upper insulators  251  covers the upper surface and the upper half of the side surface of one tooth  242 . Each of the lower insulators  252  covers the lower surface and the lower half of the side surface of one tooth  242 . 
     Although not shown, each of the upper insulators  251  includes an outer protruding portion and an inner protruding portion. The outer protruding portion protrudes upward from the upper end of the outer cylindrical portion  222  on the radial outer side of the coil  233 . The outer protruding portion is also an upper portion of the outer cylindrical portion  222  of the insulator  232 . The inner protruding portion protrudes upward on the upper side of the tip of the tooth  242 . The outer protruding portion includes a projection protruding upward. That is, at least one of the upper insulators includes a projection protruding radially outward and upward. The projection protrudes relatively radially outward because the surrounding thereof is a recess. 
     Each of the lower insulators  252  includes an outer protruding portion protruding downward on the radial outer side of the coil  233  and an inner protruding portion protruding downward on the lower side of the tip of the tooth  242 . The stator core  231  is covered by the upper insulators  251  and the lower insulators  252 , except for the outer surface of the core back and the tip surfaces of the teeth. 
     The circuit board  123  is positioned above the stator  122  and extends in a direction perpendicular to the center axis J 1 . The circuit board  123  is held above the insulator  232 . 
     The coil  233  is formed by winding a conductive wire in multiple layers from the top of the insulator  232  to the respective teeth. When a current flows from the circuit board  123  to the coil  233 , a torque is generated between the coil  233  and the rotor magnet  113 . As a result, the rotary unit  11  rotates about the center axis J 1 . 
     While not shown, the encoder  14  includes a sensor portion and a plate portion. The sensor portion is attached to the upper surface of the circuit board  123 . The plate portion is perpendicular to the center axis J 1  and is attached to the shaft  111 . The rotation speed of the shaft  111  is detected as the sensor portion optically detects the passage of a slit formed in the plate portion. Instead of the encoder  14 , an FG (Frequency Generator) pattern may be formed on the circuit board  123 , and an FG magnet may be arranged on the connecting surface  212  of the rotor holder  112 . 
     A magnetic sensor (not shown) is attached to the lower surface of the circuit board  123 . The magnetic sensor is supported by the circuit board  123  above the rotor magnet  113 . The rotational position of the rotor magnet  113 , namely the rotation of the rotary unit  11 , is detected by the magnetic sensor. In the motor  1 , a Hall element is used as the magnetic sensor. As the magnetic sensor, an FG pattern formed on the circuit board  123  and supported by the circuit board  123  above the rotor magnet  113  may be used. 
       FIG. 2  is a perspective view of the cap member  15  as viewed obliquely from above. In the present embodiment, the cap member  15  is formed by injection molding of a resin. By the injection molding, the cap member  15  can be obtained with ease. Alternatively, the cap member may be formed by pressing a single metal plate member. The cap member  15  has a lid shape opened downward, and the encoder  14  is disposed inside the cap member  15 . The cap member  15  includes a top surface portion  151 , a bottom surface portion  152 , a connecting portion  153 , a snap fit portion  154 , an elastic portion  155 , and a cylindrical portion  156 . 
     The top surface portion  151  is the upper surface of the cap member  15  and extends perpendicularly to the center axis J 1 . The top surface portion  151  covers the upper side of the encoder  14 . The connecting portion  153  connects the top surface portion  151  and the bottom surface portion  152 . 
     The expression that the outer diameter of the bottom surface portion  152  is larger than the outer diameter of the top surface portion  151  includes a case where the maximum outer diameter of the bottom surface portion  152  is larger than the maximum outer diameter of the top surface portion  151 . That is, the expression that the outer diameter of the bottom surface portion  152  is larger than the outer diameter of the top surface portion  151  also includes a case where the outer diameter of a part of the bottom surface portion  152  is smaller than the maximum outer diameter of the top surface portion  151  as long as the maximum outer diameter of the bottom surface portion  152  is larger than the maximum outer diameter of the top surface portion  151 . 
     The connecting portion  153  includes a first connecting portion  1531  and a second connecting portion  1532 . The first connecting portion  1531  is a surface that connects the outer edge of the top surface portion  151  and the outer edge of the bottom surface portion  152 . That is, the first connecting portion  1531  is an inclined surface whose outer diameter increases from the axial upper side toward the axial lower side. The second connecting portion  1532  is a surface that connects the outer edge of the top surface portion  151  and an imaginary circle  157 . The imaginary circle  157  is smaller in diameter than the outer edge of the bottom portion  152  and larger in diameter than the outer edge of the top surface portion  151 . In the present embodiment, the second connecting portion  1532  is a surface perpendicular to the top surface portion  151 . That is, the second connecting portion  1532  is a surface parallel to the center axis J 1 . The second connecting portion  1532  may be an inclined surface whose outer diameter increases from the axial upper side toward the axial lower side. In this case, the angle between the line passing through the outer edge of the top surface portion  151  and parallel to the center axis and the second connecting portion  1532  is smaller than the angle between the line passing through the outer edge of the top surface portion  151  and parallel to the center axis and the first connecting portion  1531 . 
     The first connecting portion  1531  and the second connecting portion  1532  are adjacent to each other in the circumferential direction. That is, the first connecting portion  1531  has an axially-extending wall surface  158  disposed on the side to which the second connecting portion  1532  is adjacent. Accordingly, the first connecting portion  1531  serves as a beam for supporting the top surface portion  151  and the bottom surface portion  152 . This makes it possible to increase the rigidity of the cap member  15 . Therefore, a frequency difference occurs between the natural frequency of the cap member  15  and the natural frequency of the motor body part  10 . This makes it possible to suppress a noise due to resonance. 
     In the present embodiment, the cap member  15  includes a plurality of connecting portions  153 . More preferably, there are disposed three first connecting portions  1531 . The three first connecting portions  1531  are arranged at equal intervals in the circumferential direction, and the second connecting portions  1532  are disposed between the first connecting portions  1531 . The number of the connecting portions  153  is not limited to three and may be two or four or more. The number of the connecting portions  153  may be appropriately selected for the purpose of changing the rigidity of the cap member  15  to obtain a natural frequency different from the natural frequency of the motor body part  10 . 
     In the present embodiment, the first connecting portion  1531  is a single surface that connects the outer edge of the top surface portion  151  and the outer edge of the bottom surface portion  152 . The single surface may be divided into a plurality of surfaces. For example, when connecting the outer edge of the top surface portion  151  and the outer edge of the bottom surface portion  152 , a bent portion may be provided so that the outer edge of the top surface portion  151  and the outer edge of the bottom surface portion  152  can be connected by two surfaces. In this case, more preferably, the diameter of the imaginary circle  157  is different from the diameter of the bent portion. By virtue of these different diameters, it is possible to obtain a truss structure and to make the cap member  15  become a component with higher rigidity. 
     The cylindrical portion  156  extends downward from the outer edge portion of the bottom surface portion  152  toward the motor body part  10 . 
     The snap fit portion  154  protrudes downward from the cylindrical portion  156 . The snap fit portion  154  is annular when viewed from the radial outer side. The elastic portion  155  is circumferentially adjacent to the snap fit portion  154 . The cylindrical portion  156  includes a recess  159  extending downward from the upper end thereof, namely from the bottom surface portion, and recessed radially inward. The recess  159  is defined by a plurality of side surfaces parallel to the center axis J 1 . A plurality of snap-fit portions  154  having the same shape are arranged in the circumferential direction. A plurality of elastic portions  155  having the same shape are also arranged in the circumferential direction. In the present embodiment, the snap fit portions  154  are arranged at equal intervals in the circumferential direction. The elastic portions  155  are arranged at equal intervals in the circumferential direction. 
     At the lower end of the recess  159 , the elastic portion  155  extends radially outward from the surface defining the recess  159 . By providing the elastic portion  155  in this way, it is possible to easily manufacture a mold for injection molding. The elastic portion  155  is located inside the recess  159 . By providing the recess  159 , it is possible to secure a large space inside the cap member  15 . In addition, by providing the recess  159  so as to extend in the vertical direction, it is possible to easily perform the molding of the cap member  15 , especially the injection molding of the cap member  15  with a resin. 
     The snap fit portion  154  engages with a protrusion. Thus, the cap member  15  is fixed to the insulator  232 . The cap member  15  is attached to the outer surface of the outer protruding portion above the outer cylindrical portion  222 . 
     The first connecting portion  1531  is disposed at a position overlapping with the snap fit portion in the circumferential direction. That is, the first connecting portion  1531  is disposed at a fixed position. As a result, it is possible to further increase the rigidity of the cap member  15 . 
       FIG. 3  is a perspective view of the cap member  15  as viewed obliquely from below. A space  160  is provided inside the first connecting portion  1531 . The encoder  14  is disposed inside the space  160 . The space  160  may not be provided in the first connecting portion  1531 . That is, the thickness of the first connecting portion  1531  may be larger than the thickness of the top surface portion  151 . 
     In the present embodiment, the first connecting portion  1531 , the second connecting portion  1532  and the bottom surface portion  152  are planar surfaces such as inclined surfaces or the like. However, the present invention is not limited thereto. At least one of the first connecting portion  1531 , the second connecting portion  1532  and the bottom surface portion  152  may be a curved surface. In other words, the outer edge of the top surface portion  151  and the outer edge of the bottom surface portion  152  may be connected by the curved surface in which the first connecting portion  1531  and the bottom surface portion  152  are continuous. Similarly, in the first connecting portion  1531 , the outer edge of the top surface portion  151  and the outer edge of the bottom surface portion  152  may be connected by a curved surface. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention.