Patent Publication Number: US-6661142-B2

Title: Motor device wherein accurate sizing is possible

Description:
This application is a continuation application of U.S. application Ser. No. 09/625,833 filed on Jul. 26, 2000, entitled “MOTOR DEVICE WHEREIN ACCURATE SIZING IS POSSIBLE”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to motor devices used in magnetic disk drives, and in particular, relates to a motor device in which decentering during disk rotation can be suppressed. 
     2. Description of the Related Art 
     FIG. 11 is a perspective view of a bearing unit  50  which is a component of a motor device to be mounted on a magnetic disk drive for a floppy disk (FD). 
     The bearing unit  50  includes a cylindrical bearing  51  and a flange  53  provided integrally with the periphery of the cylindrical bearing  51 . The flange  53  is provided with U-shaped grooves  54  at the longitudinal ends of the flange  53  for positioning the bearing unit  50  on a mounting base. The flange  53  is also provided on an upper face  53   a  thereof with a pair of rectangular projections  55  at one of the longitudinal ends provided with the grooves  54  of the flange  53 . The cylindrical bearing  51 ,the flange  53 , and the projections  55  are integrally formed with each other by a method, such as by die-casting or sintering. 
     The bearing unit  50  receives a rotational shaft (not shown) in a coupling hole  52  of the cylindrical bearing  51 . Thus, the rotational shaft is rotatably supported. The rotational shaft is provided with a rotor, fixed thereto, having a magnet, the rotor being rotatable integrally with the rotational shaft. 
     The bearing unit  50  is provided with a core unit fixed to the upper face  53   a  of the flange  53 . The core unit is disposed inclined by being supported by a part of the upper face  53   a  and the projections  55  of the flange  53 . The core unit is thus supported slightly inclined with respect to a plane perpendicular to the rotational axis. 
     When the core unit is fixed to be inclined on the bearing unit  50 , decentering, or surface misalignment, that is, wow and flutter due to precession movements of the rotational shaft can be suppressed, whereby tracking errors due to off-tracking of a head from recording tracks on the disk can be avoided, the off-tracking being caused by the decentering. 
     However, a problem has been found in the above-described known motor device, which is described below. 
     During manufacturing, the above-described bearing unit  50  is proceeded in a sizing process in which the inner diameter of the coupling hole  52  is set by press-fitting a shaft or the like into the hole so as to obtain the accuracy in size. However, the sizing cannot be performed at a high accuracy when the projections  55  are formed on the upper face  53   a  of the flange  53 , as shown in FIG. 11, because the sizing is performed with the upper face  53   a  of the flange  53  being as a reference, thereby producing decentering of the rotational shaft; therefore, high on-tracking accuracy cannot be ensured. 
     Moreover, the bearing unit  50  having a complex shape including the projections  55  is made of a specified material to be formed integrally with the flange  53 , thereby increasing processing costs, whereby overall manufacturing cost is increased. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a motor device in which high sizing-accuracy is possible and which can be manufactured at a low cost. 
     To this end, according to a first aspect of the present invention, a motor device comprises a base, a bearing unit fixed to the base, a core unit including coils provided around cores to be fixed to the base side, a rotational shaft rotatably supported by the bearing unit, a rotor fixed to the rotational shaft, and a magnet fixed to the rotor and opposing the core unit. The bearing unit includes a flange extending along the base and a spacer disposed on the flange and having an inclined surface. The core unit is placed on the inclined surface of the spacer, whereby the core unit is disposed inclined with respect to an upper face of the base. 
     With this arrangement, sizing can be performed, before the spacer is placed on the flange and is fixed thereto, by using an upper surface of the flange as a reference, thereby enabling a highly accurate sizing. 
     According to the present invention, it is not necessary to integrally form a bearing unit of a specified metallic material, which has a complex shape by having projections as in a known bearing unit, thereby reducing costs, such as machining costs, of the motor device. 
     According to a second aspect of the present invention, a motor device comprises a base, a bearing unit fixed to the base, a core unit including coils provided around cores to be fixed to the base side, a rotational shaft rotatably supported by the bearing unit, a rotor fixed to the rotational shaft, and a magnet fixed to the rotor and opposing the core unit. The bearing unit includes an individual flange mating with a bearing at the periphery of the bearing, the flange having a bottom surface perpendicular to the rotational shaft and an upper surface inclined with respect to the bottom surface. The core unit is placed on the inclined upper surface of the flange, whereby the core unit is disposed inclined with respect to an upper face of the base. 
     With this arrangement, sizing can be performed by using the periphery of the bearing as a reference before the bearing is mated with the flange, thereby enabling highly accurate sizing. Moreover, the bearing can be made with a simple straight cylindrically formed material, thereby reducing the manufacturing cost. 
     According to a third aspect of the present invention, a motor device comprises a base, a bearing unit fixed to the base, a core unit including coils provided around cores to be fixed to the base side, a rotational shaft rotatably supported by the bearing unit, a rotor fixed to the rotational shaft, and a magnet fixed to the rotor and opposing the core unit. The motor device further comprises a positioning member for positioning the core unit on the base, and a supporting member formed integrally with the positioning member. The core unit is disposed inclined with respect to the base by being supported by the bearing unit and an upper surface of the supporting member. 
     With this arrangement, sizing can be performed by using a surface perpendicular to the rotational shaft as a reference before the supporting member is provided, thereby enabling highly accurate sizing. The supporting member is designed to have a surface for supporting the core unit at a level, for example, higher than that of the bearing unit, whereby the core unit is supported inclined in a given direction. 
     The supporting member is preferably supported by the bearing unit at a bottom surface of the supporting member. For example, the supporting member may include a tabular protrusion protruding from a positioning member toward the bearing unit, thereby providing the supporting member with resiliency so as to be vertically deflectable, whereby the supporting member is deflected when the core unit is loaded thereon, so that the supporting member is supported by the bearing unit. 
     According to the present invention, by the magnetic attraction between the magnet provided on the rotor and the core unit which is fixed inclined to the bearing unit, the rotor is inclined in the same direction as the core unit, thereby tilting the rotational shaft. The rotational shaft is urged to one side of the coupling hole with which the rotational shaft is rotatably coupled, whereby decentering of the rotational shaft is prevented, thereby suppressing tracking errors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a motor device according to a first embodiment of the present invention; 
     FIG. 2 is a perspective view of a bearing unit used in the motor device according to the first embodiment; 
     FIG. 3 is a plan view of the bearing unit shown in FIG. 2; 
     FIG. 4 is a sectional view along line IV—IV of the bearing unit shown in FIG. 3; 
     FIG. 5 is a plan view of a bearing unit used in a motor device according to a second embodiment of the present invention; 
     FIG. 6 is a sectional view along line VI—VI of the bearing unit shown in FIG. 5; 
     FIG. 7 is a perspective view of a bearing unit used in a motor device according to a third embodiment of the present invention; 
     FIG. 8 is a plan view of the bearing unit shown in FIG. 7; 
     FIG. 9 is an illustration of the bearing unit shown in FIG. 8, a critical portion thereof being shown in section along line IX—IX; 
     FIG. 10 is a sectional view of a critical portion of the motor device according to the third embodiment of the present invention provided with the bearing unit; and 
     FIG. 11 is a perspective view of a bearing unit used in a known motor device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  10  show embodiments of a motor device according to the present invention. A motor device (a spindle motor) is assembled in a disk drive for a floppy disk used as a recording medium for a computer. 
     FIGS. 1 to  4  show a first embodiment of a motor device according to the present invention. FIG. 1 is a sectional view of the motor device. FIG. 2 is a perspective view of a bearing unit used in the motor device according to the first embodiment. FIG. 3 is a plan view of the bearing unit used in the motor device according to the first embodiment. FIG. 4 is a sectional view along line IV—IV of the bearing unit shown in FIG.  3 . 
     A motor device  1  shown in FIG. 1 includes a base  7  made of, for example, a metallic plate, the base  7  being laminated with a printed-circuit board (PCB)  8  having predetermined electrode patterns formed on a glass epoxy substrate. The base  7  is provided thereon with a bearing unit  10  at the rotational center of the disk. A rotational shaft  14  is inserted into and is supported by the bearing unit  10 . A circular rotor  15  having a shape of a downwardly-disposed tray is fixed to the rotational shaft  14 , the rotor  15  being rotatable integrally with the rotational shaft  14 . 
     The bearing unit  10  is provided with a core unit  16  including a plurality of iron cores  16   b  extending in the radial directions, the cores  16   b  included in the core unit  16  being provided with coils  17 . A thrust block  19  is fixed to the base  7  at the bottom end of the rotational shaft  14 . The rotational shaft  14  rotates slidingly on the thrust block  19 . 
     The rotor  15  is fixed to the rotational shaft  14  so as to cover the core unit  16 . The rotor  15  is provided with an annular magnet  18  on the inner face of the periphery of the rotor  15  and around the core unit  16 . A predetermined gap is provided between the magnet  18  and ends of the cores of the core unit  16 . The magnet  18  opposes the electrode patterns formed on the PCB  8  across a predetermined gap therebetween. The core unit  16  is fixed to the base  7  by screws  5 , and the bearing unit  10  is fixed by being clamped by the core unit  16  and the base  7 . 
     The rotor  15  is provided thereon with a turntable (not shown). A chucking yoke is provided on the upper surface of the turntable. When a disk (a medium) is loaded into the disk drive, the chucking yoke and a hub disposed at a center of the disk are connected with each other by a magnetic effect, thereby transmitting the driving force of a motor to the disk. 
     The bearing unit  10  includes, as shown in FIGS. 2 to  4 , a cylindrical bearing  11  having a cylindrical inner wall and a cylindrical outer periphery and a flange  12  extending from the lower outer periphery of the cylindrical bearing  11  along the base  7  and the PCB  8 , the cylindrical bearing  11  and the flange  12  being formed integrally with each other. 
     The bearing unit  10  including the cylindrical bearing  11  and the flange  12  is formed integrally by die-casting an alloy such as a zinc-alloy or by sintering a powdered metal. The cylindrical bearing  11  functions as a bearing impregnated with lubricating oil. The lubricating oil oozes out due to changes in air pressure when the rotational shaft  14  rotates in the cylindrical bearing  11 , and returns into the cylindrical bearing  11  when the rotational shaft  14  stops rotating. 
     An upper face  12   a  of the flange  12  is formed in a plane perpendicular to the rotational shaft  14 . The flange  12  is provided with U-shaped grooves  3  at the longitudinal ends thereof. The grooves  3  serve for receiving the screws  5  for screwing the core unit  16  and the base  7 . 
     In a sizing process in manufacturing the bearing unit  10 , a rod-shaped material, such as a shaft, is pressed into a coupling hole  11   a  of the cylindrical bearing  11  to form the coupling hole  11   a  accurately with a designed inner diameter. The sizing is performed, before a spacer  13  is placed on the upper face  12   a , by using the upper face  12   a  of the flange  12  as a reference. 
     The spacer  13  is placed on the upper face  12   a  of the flange  12  after the sizing process. The outline of the spacer  13  made of a resin or a metal is the same as that of the flange  12 . The spacer  13  is provided with a through hole  13   b  which can receive the cylindrical bearing  11 . The spacer  13  is laminated on the upper face  12   a  of the flange  12  and fixed thereto by an adhesive or the like. As shown in FIG. 2, the spacer  13  is formed so that a thickness H2 at one of the longitudinal ends thereof is greater than a thickness H1 at the other longitudinal end. An upper face  13   a  of the spacer  13  is inclined with respect to a plane perpendicular to the rotational axis of the rotational shaft  14 . As shown in FIG. 4, the upper face  13   a  is inclined at an angle α with respect to a plane perpendicular to the rotational axis of the rotational shaft  14 . 
     The core unit (yoke)  16  of the bearing unit  10  shown in FIG. 1 is made of a magnetic metal. The core unit  16  is disposed on the upper face  13   a  of the spacer  13  fixed thereto in an inclined position due to the inclined upper face  13   a . In this case, the rotor  15  and the rotational shaft  14  are forced to be inclined along the core unit  16  which is disposed inclined on the upper face  13   a  fixed thereto, thereby urging the rotational shaft  14  to one side of the coupling hole  11   a  of the bearing unit  10 , whereby decentering of the rotational shaft  14  is prevented by the urging force. 
     The magnet  18  and the core unit  16  are continuously urged magnetically to each other because the core unit (yoke)  16  is made of a magnetic material, and the magnet  18  provided on the rotor  15  opposes the core unit  16  at the inner face of the magnet  18  across a minute gap therebetween. Although the inner wall of the cylindrical bearing  11  of the bearing unit  10  and the outer periphery of the rotational shaft  14  are accurately formed so that the inner diameter of the cylindrical bearing  11  and the outer diameter of the rotational shaft  14  are exactly as designed, a small gap is unavoidably formed between the rotational shaft  14  and the inner wall of the cylindrical bearing  11 . Due to this gap, decentering (wow and flutter), in which the direction of inclination of the rotational shaft  14  varies, is likely to occur when the core unit  16  is not inclined, because the direction of magnetic urging between the core unit  16  and the magnet  18  occasionally changes. 
     When the core unit  16  disposed on the upper face  13   a  of the spacer  13  is disposed inclined by a predetermined angle, the rotor  15  having the magnet  18  urged toward the core unit  16  is forced to be inclined in the same direction as that of inclination of the core unit  16 , whereby the rotational shaft  14  is urged to be tilted in the same direction, thereby preventing wow and flutter. 
     FIGS. 5 and 6 show a bearing unit used in a motor device according to a second embodiment of the present invention. FIG. 5 is a plan view of the bearing unit. FIG.  6  is a sectional view along line VI—VI of the bearing unit shown in FIG.  5 . 
     A bearing unit  20  shown in FIGS. 5 and 6 has the same external shape as that of the bearing unit  10 . The bearing unit  20  includes a cylindrical bearing  21  and a flange  22  formed independently and assembled with each other. The cylindrical bearing  21  is formed of a cylindrical substance made of any one of a resin, a metal, and a sintered alloy, and includes a coupling hole  21   a . The cylindrical bearing  21  is preferably an oil retaining bearing in the same fashion as in the cylindrical bearing  51  used in the motor device according to the first embodiment. The flange  22  is disposed extending from the lower periphery of the cylindrical bearing  21  along the same base  7  as shown in FIG. 1. A bottom face  22   b  of the flange  22  is formed perpendicular to the rotational axis of the rotational shaft  14 . An upper face  22   a  of the flange  22  is inclined by an angle β with respect to the bottom face  22   b  (see FIG.  6 ). The flange  22  is disposed around the cylindrical bearing  21  and is fixed thereto by a method such as press-fitting or bonding. 
     When manufacturing the bearing unit  20 , a sizing process of the coupling hole  21   a  of the bearing  21  is performed before the flange  22  is fixed to the cylindrical bearing  21 . In the sizing process, the outer periphery of the cylindrical bearing  21  is used as a reference by disposing the cylindrical bearing  21  on a given plane surface or by supporting the same at the periphery. 
     The bearing unit  20  is disposed at the rotational center of a disk in the same manner as in the bearing unit  10  shown in FIG. 1. A core unit  16  is placed on an upper face  22   a  of the flange  22  and is fixed to a base  7  by screws, whereby the bearing unit  20  is fixed to the base  7  by being clamped by the core unit  16  and the base  7 . 
     FIGS. 7 to  10  show a bearing unit used in a motor device  2  according to a third embodiment of the present invention. FIG. 7 is a perspective view of the bearing unit. FIG. 8 is a plan view of the same. FIG. 9 is an illustration of the bearing unit shown in FIG. 8, a critical portion thereof being shown in section along line IX—IX. FIG. 10 is a sectional view of a critical portion of the motor device  2 . 
     A bearing unit  30  shown in FIGS. 7 to  9  includes a cylindrical bearing  31  formed of a cylindrical substance and includes a coupling hole  31   a . A flange  32  is disposed around the lower periphery of the cylindrical bearing  31  extending along a base (not shown). The cylindrical bearing  31  and the flange  32  made of a sintered alloy or the like being formed integrally with each other in the same fashion as in the bearing unit  10 . U-shaped grooves  3  shown in the drawings have the same shape and function as those of the bearing units  10  and  20 . 
     The flange  32  is provided with steps  33  formed by cutting away the upper edges of the longitudinal sides of the flange  32 , each step  33  being disposed symmetrically at the longitudinal sides of the flange  32 . An upper face  32   a  of the flange  32  is perpendicular to a coupling hole  31   a  of the cylindrical bearing  31 . Sizing of the bearing unit  30  is performed while the bearing unit  30  is in a state shown in FIGS. 8 and 9. In this case, the sizing is performed with the upper face  32   a  of the flange  32  being a reference. 
     The core unit  16  and a POB  8  must be positioned in relation to a Hall element (not shown). Hall elements are typically formed in the shape of a thin plate by a material having a large Hall constant and a small temperature dependency, such as germanium, and are used for performing measurements or calculations by utilizing the Hall effect. Therefore, a positioning member  34  is used for positioning, as shown in FIG.  10 . The cylindrical positioning member  34  is made of a resin or metal, and is provided with a collar  35  formed integrally with the position member  34 . 
     As shown in FIG. 10, the positioning member  34  passes through a hole  16   a  formed in the core unit  16 , another hole  7   a  formed in the base  7 , and another hole  8   a  formed in the PCB  8 , thereby positioning the core unit  16  and the PCB  8 . In this case, the collar  35  comes into contact with an upper face of the PCB  8 , thereby restricting further downward movement of the positioning member  34 . 
     The positioning member  34  is also provided with a supporting member  36  at the periphery thereof and above the collar  35  protruding toward the cylindrical bearing  31 . As shown in FIG. 7, the supporting member  36  includes a tabular base end and a rectangular block  37  at the other end of the supporting member  36 , the rectangular block  37  extending upwardly so as to have a thickness greater than the tabular base end. The rectangular block  37  is formed integrally with the supporting member  36 . The supporting member  36  has the same width as the length of the step  33  or less so as to be received by the step  33 , and protrudes sufficiently for the bottom face of the supporting member  36  to make contact with the bottom face of the step  33 . The supporting member  36  is preferably positioned so that the bottom face of the supporting member  36  is disposed at the same level as that of the bottom face of the step  33  or slightly higher. The bottom face of the supporting member  36  may be positioned lower than the bottom face of the step  33  provided that the bottom face of the supporting member  36  can be brought into contact with the bottom face of the step  33 . The block  37  is formed so that an upper face  37   a  of the block  37  is positioned higher than the upper face  32   a  of the flange  32  when the supporting member  36  is placed on the step  33 . 
     The positioning member  34 , the collar  35 , and the supporting member  36  are integrally formed with a resin. However, these components may be independently made of individual materials. 
     The core unit  16  positioned in the bearing unit  30  as described above is fixed to the bearing unit  30  so as to be inclined by an angle γ with respect to a line perpendicular to the rotational axis (not shown), as shown in FIG.  10 . The core unit  16  is inclined to be supported by three points, namely, two points of the flange  32  and one point of the supporting member  36 . 
     According to the above-described three embodiments, the core unit  16  is supported inclined when the bearing unit  10 ,  20 , or  30 , respectively, is mounted on the motor device according to the present invention, whereby the rotational shaft  14  and the rotor  15  are inclined (as shown with respect to the first embodiment), thereby urging the rotational shaft  14  to one side of the coupling hole  11   a ,  21   a , or  31   a , respectively. With this arrangement, decentering of the rotational shaft  14  is prevented, whereby an accurate on-tracking control is possible, thereby preventing tracking errors. 
     The motor device according to the present invention is not limited to those described in the embodiments. In the bearing unit  10  included in the motor device described in the first embodiment, the spacer  13  may be provided with projections at one side thereof instead of being provided with the inclined upper face  13   a , or the base  7  or the PCB  8  may be provided with projections for supporting the core unit  16  in an inclined state instead of providing the spacer  13 . 
     According to the present invention described above, a motor device is obtainable in which an accurate sizing is possible, thereby ensuring on-tracking accuracy in disk accessing and preventing tracking errors. The motor device can be manufactured at low cost.