Patent Publication Number: US-2021194315-A1

Title: Motor and manufacturing method of motor

Description:
TECHNICAL FIELD 
     The present invention relates to a motor and a method for manufacturing a motor, and particularly relates to a motor including a shaft welded to or fused with a metallic member and a method for manufacturing such a motor. 
     BACKGROUND ART 
     It is known that in a structure of some conventional motors, a shaft is welded to or fused with a metallic member. 
     Patent Literature 1 shown below discloses performing laser welding to join a shaft of a rotator of a motor or a similar machine to a flat plate by irradiating a joint between the shaft and the flat plate with laser beams while rotating the flat plate. 
     DOCUMENT LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Publication No. 2004-090030 
     SUMMARY OF INVENTION 
     Technical Problem 
     It is an object of the present invention to provide a motor including a shaft welded to or fused with a metallic member and a method for manufacturing such a motor. 
     Solution to Problem 
     A motor according to an aspect of the present invention, accomplished to attain the object described above, includes: a shaft made of metal; and a base including a metallic member covered with a coating layer, wherein the coating layer has an opening, the metallic member includes an exposed part exposed through the opening, and an outer peripheral part of the shaft and the exposed part are fused or welded together. 
     Preferably, the outer peripheral part of the shaft has a recessed face extending in a peripheral direction, and the recessed face and the exposed part are fused or welded together. 
     Preferably, the outer peripheral part of the shaft has a cylindrical face, the recessed face and the cylindrical face are lined in a longitudinal direction of the shaft, and the recessed face is entirely inside the cylindrical face in a radial direction. 
     Preferably, the base is formed with a resin member, and wiring is formed at the resin member. 
     Preferably, the coating layer contains zinc. 
     Preferably, the shaft is made of martensitic stainless steel containing no lead. 
     Preferably, the motor includes: a rotor able to rotate relative to the shaft; and a polygon mirror attached to the rotor. 
     Preferably, the motor includes a bearing, wherein the polygon mirror is disposed at the bearing. 
     A method for manufacturing a motor, according to another aspect of the present invention, includes: a first step of removing a part of a coating layer coating a metallic member covered with the coating layer; and a second step of fusing or welding an outer peripheral part of a shaft made of metal to an exposed part of the metallic member, the exposed part being exposed in the first step. 
     Preferably, in the first step, a hole is formed in the metallic member by a cutting tool and the coating layer around the hole is cut to partially remove the coating layer, and in the second step, the outer peripheral part of the shaft inserted into the hole and the exposed part are fused or welded together. 
     According to these aspects of the present invention, a motor including a shaft welded to or fused with a metallic member and a method for manufacturing such a motor may be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A perspective view illustrating an example of a motor according to an embodiment of the present invention. 
         FIG. 2  A cross-sectional view of the motor. 
         FIG. 3  A cross-sectional view illustrating a part of a joint between a metal board and a shaft. 
         FIG. 4  A first drawing illustrating a manufacturing process for a motor. 
         FIG. 5  A second drawing illustrating the manufacturing process for the motor. 
         FIG. 6  A third drawing illustrating the manufacturing process for the motor. 
         FIG. 7  A fourth drawing illustrating the manufacturing process for the motor. 
         FIG. 8  A cross-sectional view of a motor according to a modification example of the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
     For the present embodiment, a description is given of a motor (a polygon mirror scanner motor) designed to rotate a polygon mirror used for laser scanning by a laser beam printer or other devices. 
     Embodiment 
       FIG. 1  is a perspective view illustrating an example of a motor  1  according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view of the motor  1 . 
     In the following description, a direction away from a polygon mirror  70  and toward a base plate  80  along a shaft  5  (a downward direction in  FIG. 2 ) may be referred to as a downward direction and a direction away from the base plate  80  and toward the polygon mirror  70  along the shaft  5  (an upward direction in  FIG. 1 ) may be referred to as an upward direction. 
     With reference to  FIGS. 1 and 2 , the motor  1  according to the present embodiment is used to drive the polygon mirror  70  attached to a rotor  10 . The motor  1  mainly includes the shaft  5 , the rotor  10 , a stator  20 , the polygon mirror  70 , and the base plate  80 . 
     The shaft  5  is fixed to the base plate  80 . The stator  20  is disposed above the base plate  80 . The rotor  10  is attached to the shaft  5  so as to be rotatable relative to the shaft  5 . 
     The rotor  10  includes a frame  11 , a magnet  12 , and a sleeve  40  (an example of a bearing). 
     The frame  11  is for preventing leakage of a magnetic field from inside the frame  11  and is, for example, made from a magnetic body. The frame  11  has a part extending in a direction perpendicular to the shaft  5  (an outer peripheral direction, a lateral direction in  FIG. 2 ) and a part extending in a direction parallel to the shaft  5  (an up-down direction in  FIG. 2 ) to constitute a side wall. The frame  11  has a cylindrical shape having a closed upper portion and an opening at the bottom. 
     The magnet  12  is annular and, more specifically, has a cylindrical shape. The magnet  12  is attached to an inner wall surface of an outer peripheral part of the frame  11 . 
     The sleeve  40  extends in the up-down direction so as to pass through a central part of the frame  11 . The sleeve  40  is fixed to a hole formed in a middle of an upper surface of the frame  11 . The polygon mirror  70  is fixed to an upper portion of the sleeve  40 . A middle of the sleeve  40  forms a cylindrical part  41  as a tubular portion, and the shaft  5  is inserted inside the cylindrical part  41 . A gap between the sleeve  40  and the shaft  5  is, for example, filled with a lubricant to form a dynamic fluid pressure bearing in a radial direction. This enables the rotor  10  to rotate relative to the shaft  5 . An inside of the cylindrical part  41  of the sleeve  40  has herringbone grooves (not illustrated). The herringbone grooves are formed at two locations separately in an axial direction. However, the scope of the present invention is not limited to this example. 
     A thrust plate  45  and a thrust cover  46  are attached to an upper portion of the cylindrical part  41  of the sleeve  40 . The thrust cover  46  covers an upper end portion of the cylindrical part  41 . The thrust plate  45  is disposed between the thrust cover  46  and an upper end face of the shaft  5 . 
     The stator  20  includes a stator core  21  having a plurality of teeth formed so as to extend from a middle outward radially and a stator coil  22  wound around the teeth. The stator  20  is disposed on an inner periphery side of the magnet  12  so as to face the magnet  12  through a space. The stator coil  22  generates a magnetic field when an electric current flows in the stator coil. An interaction between the magnetic field of the stator coil  22  and a magnetic field of the magnet  12  generates driving force (force enabling the rotor  10  to rotate). 
     The polygon mirror  70  is fixed to the upper portion of the sleeve  40  and is positioned above the frame  11 . The polygon mirror  70  is arranged between a spring  51  disposed above and a part of the sleeve  40 , and is fixed there. A grip ring  52  is disposed in the upper portion of the spring  51 , and the position of the up-down direction of the spring  51  is put in proper position by the grip ring  52 . 
     The base plate  80  (an example of a base) has a metal board  81  (an example of a metallic member) and a circuit board  89  (an example of a resin member). The circuit board  89  is layered on an upper surface of the metal board  81  to constitute a single base plate  80 . 
     The circuit board  89  is, for example, a printed wiring board. The printed wiring board is a resin member, and wiring is formed on the resin member. The resin member is, for example, made of an epoxy resin. An electronic component  95  is populated at an upper surface (a surface on an upper side in  FIG. 1 ) of the circuit board  89  via solder. The electronic component  95 , for example, includes a drive and control integrated circuit to drive and control the motor. The electronic component  95  is joined to the upper surface of the circuit board  89  with solder. A variety of circuit elements, other than the integrated circuit, may be disposed on the circuit board  89 . Such circuit elements are, for example, a Hall element used to detect a rotation angle or a rotation number of the magnet  12  based on a change in magnetic field received from the magnet  12 , chip-type circuit elements (a resistor, a capacitor), and a drive integrated circuit (IC) used to turn on or off the application of an electric current to each stator coil  22 . 
     The metal board  81  is, for example, composed of a board made of iron. A hole  85  is formed in the metal board  81 . The shaft  5  is inserted into the hole  85 . The shaft  5  and the metal board  81  are firmly fixed to each other by laser welding a joint of the shaft  5  and the hole  85  on a lower surface side of the metal board  81 , as described later. The motor  1  is manufactured, after the shaft  5  is fixed to the metal board  81 , by attaching the circuit board  89  to the metal board  81 , and attaching the stator  20  and the rotor  10 . 
     The shaft  5  has a protrusion  5   c  protruding downward from the base plate  80 . When the motor  1  is mounted to a device or another apparatus using the motor  1 , the protrusion  5   c  provided for the motor  1  allows the motor  1  to be put in proper position by fitting the protrusion  5   c  into a hole formed in the device side. Since an axis of the protrusion  5   c  coincides with a rotation axis of the polygon mirror  70  of the motor  1 , the polygon mirror can be put in proper position readily and precisely with respect to the device using the motor  1 . 
       FIG. 3  is a cross-sectional view illustrating a part of the joint between the metal board  81  and the shaft  5 . 
     In  FIG. 3 , the metal board  81  and the shaft  5  are shown, and other components are not shown. A cross section of the metal board  81  taken along a central axis of the shaft  5  is shown. 
     In the present embodiment, the metal board  81  is a sheet of galvanized steel pertinent to Japanese Industrial Standards (JIS) symbols such as “SECC”, “SECD”, “SECE”, “SECF”, and “SECG” specified by JIS standard numbers. In other words, a surface of the metal board  81  is covered with a coating layer  83 . The metal board  81  has the coating layer  83 , the coating layer  83  being a zinc coating layer. The coating layer  83  covers each of the upper surface and a lower surface. The coating layer  83  is provided for anticorrosion purposes. In  FIG. 3  and subsequent drawings, the coating layer  83  is schematically shown. The metal board  81  is made from a sheet of galvanized steel. The sheet of galvanized steel is in general circulation and widely available. This contributes to a reduction in manufacturing costs for the motor  1 . 
     The shaft  5  is composed of a metallic member. In the present embodiment, the shaft  5  is made of martensitic stainless steel containing no lead. The shaft  5  is, for example, made of stainless steel pertinent to JIS symbols such as “SUS420F”, “SUS420J2”, “SUS420J1”, “SUS403”, “SUS410”, “SUS416”, “SUS431”, and “SUS440C” specified by JIS standard numbers. The shaft  5  has a composition excellent in wear resistance, offers improved machinability, and has no lead added as a constituent (contains virtually no lead). Thus, the martensitic stainless steel containing no lead refers to stainless steel. Stainless steel has no lead added as a constituent (contains virtually no lead). The shaft  5  is made of stainless steel containing manganese as a constituent. This example, however, does not limit the material for the shaft  5 . 
     In  FIG. 3 , the metal board  81  has a recessed part  84  (an example of an exposed part) in a surface on a lower side of the metal board  81 . The recessed part  84  is, for example, a zone having a diameter D 2  in size and being recessed upward from the surface of the metal board  81  by a dimension t 1 . The recessed part  84  is formed to be substantially concentric with the hole  85 . A depth of the recessed part  84  (the dimension t 1 ) is slightly greater than a thickness of the coating layer  83 . The recessed part  84  is formed by cutting the surface of the metal board  81 , as described later. In other words, because of the recessed part  84  thus formed, the coating layer  83  on the lower side has an opening  83   b . To put it another way, the metal board  81  has an exposed part (the recessed part  84 ) to allow an iron portion not covered with the coating layer  83  to be exposed downwardly through the opening  83   b  formed in the coating layer  83 . 
     The shaft  5  is inserted into the hole  85  so as to pass through the metal board  81 . A diameter D 1  of the shaft  5  is slightly smaller than an inner diameter of the hole  85 . 
     For instance, in the present embodiment, the dimension t 1  is a dimension ranging from 0.01 mm to 0.1 mm inclusive, the diameter D 1  is 2.368 mm±0.0005 mm, and the diameter D 2  is a dimension ranging from 3.3 mm to 4.8 mm inclusive. The inner diameter of the hole  85  is a dimension ranging from 2.0 mm to 5.0 mm inclusive. 
     An outer peripheral part of the shaft  5  protruding downward from the hole  85  and the recessed part  84  are welded by laser welding. The welding is applied to an entire periphery of the shaft  5 . Owing to the welding, a recessed face  87  recessed in a radial direction is formed at an upper end portion of a part of the shaft  5  protruding downward from the recessed part  84 . The recessed face  87  extends in a peripheral direction along the shaft  5 . The recessed face  87  extends in a peripheral direction throughout the periphery of the shaft  5 . A welding mark is formed at a surface of the recessed face  87 . An alloy formed when welding appears as a welding mark at a surface of the recessed part  84  in a neighborhood of the shaft  5 . In other words, the recessed face  87  and the recessed part  84  are welded and joined to each other. 
     The outer peripheral part of the shaft  5  has a cylindrical face. The protrusion  5   c  and the recessed face  87  are lined in a longitudinal direction of the shaft  5 . The recessed face  87  is entirely inside a cylindrical face of the protrusion  5   c  in a radial direction. In other words, of the part where the recessed face  87  is formed, no part of the recessed face  87  is outside an outer peripheral surface of the shaft  5  having the diameter D 1 . 
     In this way, the recessed face  87  is formed at the shaft  5 . Thus, in a dimension Z 2  of the shaft  5  protruding downward from the lower surface of the metal board  81 , the cylindrical face of the shaft  5  formed with high precision is ensured throughout a dimension Z 1  other than a part of a dimension along the up-down direction of the recessed face  87 . This allows the motor  1  to be put in proper position with high precision using the protrusion  5   c  because the dimension Z 1  of the cylindrical face of the shaft  5  in the up-down direction can be ensured to a relatively large extent. The device having the motor  1  can be downsized because the dimension Z 2  of the shaft  5  protruding downward can be made relatively small. 
     In a manufacturing process for the motor  1 , the shaft  5  is fixed to the metal board  81  in steps described below. The motor  1  is manufactured, after the shaft  5  is fixed to the metal board  81  as described below, by attaching the circuit board  89  implemented with the electronic component  95  and other elements to the metal board  81 , and attaching the stator  20  and the rotor  10  to the base plate  80 . 
       FIG. 4  is a first drawing illustrating a manufacturing process for the motor  1 . 
     First, as illustrated in  FIG. 4 , the hole  85  is formed in the metal board  81  by a cutting tool  901  such as a drill, an end mill, and a reamer. Together with the formation of the hole  85 , the coating layer  83  around the hole  85  is cut to partially remove the coating layer  83 . This forms the recessed part  84  together with the hole  85 . The coating layer  83  can be partially removed in the same step for the formation of the hole  85 , for example, by processing the metal board  81  from underneath using a second cutting tool  903  coaxially arranged with the cutting tool  901 , the second cutting tool  903  being, for example, an end mill or a file. This helps shorten the manufacturing process. The formation of the hole  85  and the removal of the coating layer  83  (the formation of the recessed part  84 ) may be performed in separate steps. The tools and the technique used for the formation of the hole  85  and the removal of the coating layer  83  are not limited to the examples described above. For instance, the hole  85  may be formed by press working. 
       FIG. 5  is a second drawing illustrating the manufacturing process for the motor  1 . 
     Thereafter, as illustrated in  FIG. 5 , the shaft  5  is inserted into the hole  85 . The shaft  5  is preferably inserted from above the metal board  81 . 
       FIG. 6  is a third drawing illustrating the manufacturing process for the motor  1 . 
     Subsequently, as illustrated in  FIG. 6 , with part of the shaft  5  being inserted into the hole  85 , laser welding of the outer peripheral part of the shaft  5  and the recessed part  84 , as an exposed part, is performed. During welding, the metal board  81  and the shaft  5  are rotated relative to two lasers L 1  and L 2  such that two places in the neighborhood of a joint between the recessed part  84  close to the hole  85  and the shaft  5  are points irradiated with beams from the respective lasers L 1  and L 2 . For instance, the metal board  81  and the shaft  5  are rotated around the shaft  5  by 180 degrees without any change in positions of the lasers L 1  and L 2  such that the points irradiated with beams from the two respective lasers L 1  and L 2  are 180 degrees apart from each other around the shaft  5 . This means that the outer peripheral part of the shaft  5  and the recessed part  84  are welded together around the entire periphery and the shaft  5  may be fixed to the metal board  81 . Laser welding is preferably performed with the shaft  5  and the metal board  81  being upside down (the protrusion  5   c  of the shaft  5  positioned so as to face upward). 
       FIG. 7  is a fourth drawing illustrating the manufacturing process for the motor  1 . 
     In  FIG. 7 , a condition after the laser welding is performed is schematically illustrated. Because of the laser welding being performed, a portion of the outer peripheral part of the shaft  5  and a portion of the recessed part  84  melt to constitute a welded part  86  forming a welding mark. Since a part of the shaft  5  melts and is carried to constitute the welded part  86 , the recessed face  87  is formed on the outer peripheral surface of the shaft  5 . In the recessed part  84 , the welded part  86  extends in a radial direction from the neighborhood of the hole  85 . The welded part  86  stays inside the recessed part  84 . In other words, a size of the recessed part  84  is set such that the welded part  86  does not extend in a radial direction beyond the recessed part  84 . This prevents the welded part  86  from protruding from the surface of the metal board  81 , and allows the motor  1  to be put in proper position with increased precision with the surface of the metal board  81  as a reference surface. 
     In the present embodiment, as described above, the motor  1  is formed by a manufacturing method including a step of removing part of the coating layer  83  of the metal board  81  covered with the coating layer  83  and a step of welding the outer peripheral part of the shaft  5  made of metal to the recessed part  84  of the metal board  81 , the recessed part  84  having been exposed in the removing step. In other words, in the structure of the motor  1 , the recessed part  84  of the metal board  81  and the outer peripheral part of the shaft  5  are welded together. The shaft  5  is directly fixed to the metal board  81  by welding. This allows the shaft  5  to be firmly fixed while getting rid of a component substantially protruding to the lower surface of the metal board  81 . This allows the reliability of the motor  1  to be improved. This also allows the motor  1  to be thinned. This contributes to a reduction in manufacturing costs for the motor  1 . 
     If when welding a shaft  5  to a metal board  81  covered with a coating layer  83 , the coating layer  83  melts or evaporates, the melted or evaporated coating layer can adhere to the outer peripheral part of the shaft  5 , resulting in an undulation at the outer peripheral part of the protrusion  5   c . For instance, if the coating layer  83  is a zinc coating layer, melting of the coating layer  83  generates tin. The tin may adhere to the outer peripheral part of the shaft  5 . This can cause difficulty in putting the motor  1  in proper position using the protrusion  5   c . If stainless steel with a relatively high manganese content is used as the material for the shaft  5 , the manganese has a relatively low melting point, and tends to evaporate. In this case, the melting or evaporation of the shaft  5  may cause foreign matter to adhere to the outer peripheral part of the shaft  5 , and the problem described above may occur more noticeably. 
     By contrast, in the present embodiment, the coating layer  83  is removed from a portion of the metal board  81  to form the recessed part  84 , and the recessed part  84  is directly welded to the shaft  5 . This precludes the coating layer  83  and other elements from melting or evaporating, and thus can prevent the occurrence of the problem described above. 
     By appropriately adjusting points irradiated with beams from the lasers L 1  and L 2  for laser welding, and an angle, intensity, and other properties of the lasers L 1  and L 2  for laser welding, a melted area may be made smaller on the shaft  5  and the metal board  81 . For instance, the points irradiated with beams from the lasers L 1  and L 2  may be made closer to a part of the shaft  5  in the neighborhood of the hole  85 . This allows the shaft  5  to be reliably fixed to the metal board  81  with relatively low output of the lasers L 1  and L 2 . 
       FIG. 8  is a cross-sectional view of a motor  101  according to a modification example of the present embodiment. 
     As illustrated in  FIG. 8 , the motor  101  and the motor  1  according to the embodiment described above differ in a method for fixing the polygon mirror  70 . In other words, in the motor  101 , the spring  51  is put in proper position in the up-down direction by a protruding part  140   b . The protruding part  140   b  is formed on an upper portion of a sleeve  140  so as to protrude in a radial direction. In such a structure, the need for providing a grip ring or a similar part to put the spring  51  in proper position is eliminated, and a number of components of the motor  101  may be reduced. 
     [Others] 
     The shaft and the recessed part of the metal board may be joined to each other by fusing. Alternatively, these parts may be welded together by a method other than laser welding. 
     A configuration of the components of the motor is not limited to the configuration shown in the above-described embodiment. Different configurations designed to suit the object of the present invention may be applied. 
     The base plate is not limited to one including the metal board and the circuit board put together. The base plate may be a base plate including wires laid on an insulating layer put on a metal board, and is not limited to the composition of the layers such as in the embodiment described above, and may be a base plate having more layers. 
     The motor is not limited to a motor to rotate the polygon mirror as described above. The structure for attaching the shaft to the base plate shown in the above-described embodiment can be applied to motors including base plates and being used for various purposes. 
     It should be construed that the embodiment described above is illustrative in all aspects, and is not restrictive. The scope of the present invention is represented by the scope of the claims and not by the above description, and it is intended that all modifications within the sense and scope equivalent to the claims are included in the scope of the present invention. 
     LIST OF REFERENCE SIGNS 
     
         
           1 ,  101  motor, 
           5  shaft, 
           10  rotor, 
           40 ,  140  sleeve (an example of bearing), 
           70  polygon mirror, 
           80  base plate (an example of base), 
           81  metal board (an example of metallic member), 
           83  coating layer, 
           83   b  opening, 
           84  recessed part (an example of exposed part), 
           85  hole, 
           86  welded part, 
           87  recessed face, 
           89  circuit board (an example of resin member)