Base member, spindle motor, and hard disk drive device

Abstract

A base member capable of reducing the occurrence of blowholes in protruding portions is provided. [Solution] In a base member for a spindle motor having an upper surface and a lower surface, the base member is a casting, the upper surface is provided with a pin portion (430) extending upward, and the lower surface includes a first lower surface (440) and a second lower surface (450) located above the first lower surface (440), the first lower surface (440) and the second lower surface (450) being adjacent to each other via a step portion (460) that increases in height from the first lower surface (440) to the second lower surface (450). When the pin portion (430) is located at the center in a plan view and a circular region (R) having a diameter three times the diameter of the pin portion (430) is defined as a pin portion vicinity region (R), at least a portion of the step portion (460) overlaps with the pin portion vicinity region (R) in the vertical direction.

Description

Technical Field

[0001] The present invention relates to a base member of an electronic device such as a hard disk drive, and particularly to a technique for reducing a casting defect in a protrusion erected on the base member for mounting components.

Background Art

[0002] The base member of the spindle motor of a hard disk drive is formed by casting. In a hard disk drive filled with helium, from the viewpoint of preventing helium leakage, the protrusion for assembling the pivot bearing device is also integrally formed on the base member (see Patent Document 1).

[0003] The base member as described above is generally formed by die-casting. A recess (a blind hole) corresponding to the shape of the protrusion is formed in the upper mold of the die-cast mold. If the molten metal does not sufficiently spread inside the blind hole, a defect (casting defect) may occur in the molded product, leading to a decrease in the rigidity of the protrusion. On the other hand, in Patent Document 2, by forming a blind hole corresponding to the shape of the protrusion in the upper mold and providing a protrusion at a position corresponding to the blind hole in the lower mold, the molten metal riding on the protrusion heads toward the blind hole, so that it is said that the formation of casting defects can be reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above-described technology, it is conceivable that the molten metal flows around the projections of the lower mold, and there is a concern that the molten metal may not flow toward the stop hole. According to the experiments of the present inventors, when the above-described projections are provided on the lower mold, it has been confirmed that the generation rate of shrinkage cavities at the projection portions is higher than when they are not provided.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a base member capable of reducing the generation of shrinkage cavities in the projection portion. Another object of the present invention is to provide a spindle motor and a hard disk drive device having such a base member.

Means for Solving the Problems

[0007] In a base member of a spindle motor having an upper surface and a lower surface, the base member is a casting, the upper surface includes a projection extending upward, and the lower surface includes a first lower surface and a Flat second lower surface located above the first lower surface. The first lower surface and the second lower surface are adjacent to each other via a stepped portion whose height increases from the first lower surface to the second lower surface. When a circular region having a diameter three times the diameter of the projection is defined as a region near the projection in a plan view, at least a part of the stepped portion overlaps with the region near the projection in the vertical direction and the second lower surface extends to a position beyond the stepped portion to the vicinity region of the protrusion in a plan view base member.

[0008] In the casting of the base member having the above configuration, when a circular region having a diameter three times the diameter of the projection is defined as a region near the projection in a plan view, at least a part of the stepped portion overlaps with the region near the projection in the vertical direction and the second lower surface extends to a position beyond the stepped portion to the vicinity region of the protrusion in a plan view From this, when the molten metal reaches the portion of the mold that forms the stepped portion, the molten metal flows in the direction of the projection. Therefore, a sufficient amount of molten metal flows in the direction of the projection, and the generation of shrinkage cavities in the projection is suppressed.

Effects of the Invention

[0009] According to the present invention, generation of shrinkage cavities within the protrusions of the base member can be suppressed, so that the rigidity of the protrusions can be maintained.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0011] [1] First Embodiment 1. Hard Disk Drive FIG. 1 is a perspective view schematically showing the overall configuration of a hard disk drive 10 according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the hard disk drive 10 cut along a plane including a rotation axis. The hard disk drive 10 includes a spindle motor 100 and a plurality of hard disks 13 attached to and rotated by the spindle motor 100 on a base member 400. The hard disk drive 10 also includes a swing arm 11 that supports a plurality of magnetic heads 12 facing the hard disks 13 respectively, an actuator 14 that drives the swing arm 11, and a control unit 15 that controls these devices. The swing arm 11 is supported via a pivot assembly bearing 20 on a pin portion 430 standing upright integrally with the base member 400.

[0012] 2. Spindle Motor FIG. 3 is a cross-sectional view of the spindle motor 100 of the embodiment cut along a plane including a rotation axis. The spindle motor 100 includes a base member 400 and a shaft 102 fixed to the base member 400. Conical bearing members 201 and 301 are fixed to the shaft 102 so as to be spaced apart from each other in the axial direction, constituting bearings 200 and 300. A cylindrical portion 401a extending upward in the axial direction of the shaft 102 is formed on the base member 400, and a stator core 103 is fixed to the outer periphery of the cylindrical portion 401a. The stator core 103 is formed by laminating a plurality of thin plate-shaped soft magnetic materials (for example, electromagnetic steel sheets) having an annular shape in the axial direction, and includes a plurality of pole teeth protruding radially outward. The plurality of pole teeth are provided at equal intervals along the circumferential direction, and coils 104 are wound around each of them.

[0013] The spindle motor 100 includes a rotor 110. The rotor 110 includes a cylindrical portion 111, and an annular rotor magnet 113 is fixed to the inner peripheral surface side of the cylindrical portion 111. The rotor magnet 113 is magnetized such that adjacent portions along the circumferential direction alternate between S and N polarities. The inner circumference of the rotor magnet 113 faces the outer circumference of the pole teeth of the stator core 103 with a gap therebetween. Then, by supplying a driving current to the coil 104, a driving force is generated to rotate the rotor magnet 113, and the rotor 110 rotates about the shaft 102 with respect to the shaft 102 and the base member 400. This principle is the same as that of a normal spindle motor.

[0014] A flange portion 114 extending radially outward is formed at the peripheral edge of the lower end portion of the cylindrical portion 111. The flange portion 114 functions as a disk mounting portion for stacking a plurality of hard disks 13. As shown in FIG. 2, a hard disk 13 is mounted on the flange portion 114, and the hard disks 13 are successively stacked on the hard disk 13 via spacers 16, and a total of nine hard disks 13 are stacked. Note that ten or more hard disks 13 may be provided. The uppermost hard disk 13 is fixed to the rotor 110 by a clamp 18 attached to the upper surface of the rotor 110 with a screw 17. In FIG. 2, reference numeral 19 denotes a cover.

[0015] 3. Configuration of Base Member The base member of the first embodiment of the present invention will be described with reference to the drawings. Prior to the description of the embodiment, a conventional base member 401 that is the basis for the development of the present invention will be described. FIG. 4(A) is a plan view of the base member 401, and (B) is a rear view. The base member 401 is manufactured by die casting of aluminum. During casting, the molten metal is injected from a gate provided in the die casting mold downward from the upper side in the figure. In the figure, reference numeral 410 denotes the bottom portion, and the bottom portion 410 has a rectangular plate shape having a short side and a long side. Side wall portions 411 extending in a direction orthogonal to the bottom portion 410 are formed on the entire circumference of the bottom portion 410.

[0016] A through hole 420 is formed at a position slightly above the center in the left - right direction of the bottom 410. The shaft 102 of the spindle motor 100 is inserted into and fixed to the through hole 420. Further, a pin portion (protrusion) 430 is formed at a position near the lower left of the bottom 410. A seating surface 431 that is slightly higher from the surroundings is formed around the pin portion 430. The aforementioned pivot assembly bearing 20 is placed on this seating surface 431. Further, as shown in FIG. 5(B), a screw hole 432 for attaching the pivot assembly bearing 20 is formed at the upper end portion of the pin portion 430.

[0017] The base member 400 configured as described above is cast using a die - casting mold. FIG. 5(A) shows the base member 400 after casting, and (B) shows a state in which the outer diameter of the pin portion 430, the upper surface of the seating surface 431, and the screw hole 432 have been finish - machined after casting. As shown in these figures, a plurality of casting nests C are formed in the pin portion 430. The present embodiment is to reduce such casting nests C.

[0018] Next, the base member 400 of the first embodiment of the present invention will be described with reference to FIG. 6. In the following description, components equivalent to those shown in FIGS. 4 and 5 are denoted by the same reference numerals and their description is omitted. The base member 400 has the same configuration as the upper surface of the conventional base member 401 shown in FIG. 4(A). The lower surface 412 of the base member 400 includes a first lower surface 440 at the same height level as the lower surface 412 and a second lower surface 450 located above the first lower surface 440. That is, in FIG. 6(A), the second lower surface 450 is recessed with respect to the first lower surface 440. The first lower surface 440 and the second lower surface 450 are adjacent to each other via a stepped portion 460 whose height gradually increases from the first lower surface 440 to the second lower surface 450.

[0019] The step portion 460 is linear in plan view and obliquely (about 45° in this example) crosses between the first lower surface 440 and the second lower surface 450, and also overlaps with a portion extending from the outer periphery to the inner periphery side of the pin portion 430 in plan view. Further, the step portion 460 has a uniform height difference from the first lower surface 440 to the second lower surface 450. FIGS. 6(B) and (C) are cross-sections in a direction orthogonal to the step portion 460 in plan view passing through the central axis of the pin portion 430. The tangent line L in contact with the step portion 460 forms a predetermined angle θ (θ is 45° with respect to the second lower surface 450 in this example) from the first lower surface 440 toward the second lower surface 450, and the step portion 460 is a flat inclined surface. In this cross-section, the tangent line L of the step portion 460 passes between the lower end point P on the second lower surface 450 side and the lower end point Q on the first lower surface 440 side of the outer peripheral surface of the pin portion 430. In addition, in this embodiment, when a circular region having a diameter three times the diameter of the pin portion 430 is defined as the vicinity region of the pin portion (vicinity region of the protrusion) with the pin portion 430 located at the center in a plan view, at least a part of the stepped portion 460 is configured to overlap with the vicinity region of the pin portion in the vertical direction (axial direction). Further, the pin portion 430 overlaps with the second lower surface 450 in the vertical direction.

[0020] Here, in order to more effectively suppress the generation of shrinkage cavities in the pin portion 430, the angle formed by the tangent line L and the second lower surface 450 is preferably 15 to 90°, and more preferably 30 to 60°.

[0021] FIGS. 6(B) and (C) are examples where the step portion 460 is a flat surface. However, as shown in FIG. 6(D), when there are arc-shaped portions 461 at both ends of the step portion 460, the step portion 460 is configured such that the tangent line L drawn on the step portion 460 passes between the lower end point P on the second lower surface 450 side and the lower end point Q on the first lower surface 440 side of the pin portion 430. In the example of FIG. 6(D), arc-shaped portions 461 are formed at both ends in the width direction of the step portion 460. In this case, the tangent line L drawn on the step portion 460 forms an angle of 45° with respect to the second lower surface 450, and the tangent line L passes between the lower end point P on the second lower surface 450 side and the lower end point Q on the first lower surface 440 side of the outer peripheral surface of the pin portion 430.

[0022] 4. Operations and Effects of the First Embodiment In the casting of the base member 400 having the above-described configuration, in the die-casting mold, the molten metal flows from the upper side to the lower side as shown in FIG. 6(A), and from the right side to the left side in FIGS. 6(B) and 6(C). The molten metal flows from the upper side in FIG. 6(A), and when the molten metal reaches the portion that forms the stepped portion 460 of the die-casting mold, the molten metal flows along the inclined surface of the die-casting mold in the direction of the tangent line L (the direction of the blind hole). In the present embodiment, When a circular region having a diameter three times the diameter of the pin portion 430 is defined as the vicinity region of the pin portion (vicinity region of the protrusion) with the pin portion 430 located at the center in a plan view, at least a part of the stepped portion 460 is configured to overlap with the vicinity region of the pin portion in the vertical direction (axial direction) since it is configured as such, compared with the case of Patent Document 2, the amount of the molten metal that deviates from the direction of the blind hole that forms the pin portion 430 is small. Therefore, a sufficient amount of the molten metal flows in the direction of the blind hole, and the generation of shrinkage cavities in the pin portion 430 is suppressed. Thereby, the rigidity of the pin portion 430 can be maintained.

[0023] In particular, in the above-described embodiment, since the stepped portion 460 is linear and does not protrude in the direction in which the molten metal flows, the molten metal smoothly climbs the inclined surface of the die-casting mold without being stirred and flows in the direction of the blind hole. Therefore, a more sufficient amount of the molten metal is supplied to the blind hole, and the generation of shrinkage cavities can be effectively suppressed.

[0024] 5. Modification Example of the Stepped Portion FIG. 7 shows a modification example of the stepped portion 460 in the above-described embodiment. FIG. 7(A) shows an example in which the angle θ of the tangent line L of the stepped portion 460 with respect to the second lower surface 450 is made larger than in the case of the above-described embodiment, and FIG. 7(B) shows an example in which the angle θ of the tangent line L of the stepped portion 460 with respect to the second lower surface 450 is made smaller than in the case of the above-described embodiment. In any of these examples, the tangent line L of the stepped portion 460 passes through the outer peripheral surface of the pin portion 430. Therefore, in these examples as well, the same operations and effects as those of the above-described embodiment can be obtained.

[0025] FIG. 7(C) shows an example in which the angle θ of the tangent line L of the stepped portion 460 with respect to the second lower surface 450 is set to 90°. In this example, the tangent line L of the stepped portion 460 passes through the upper end surface of the pin portion 430. In this example as well, the same operations and effects as those of the above-described embodiment can be obtained.

[0026] Here, in the example shown in FIG. 7(B), the stepped portion 460 is located outside the pin portion 430 in a plan view. In the present invention, when a circular region having a diameter three times the diameter of the pin portion 430 is defined as the region near the pin portion (region near the protrusion portion) R with the pin portion 430 located at the center in a plan view, at least a part of the stepped portion 460 overlaps with the region near the pin portion R in the vertical direction (axial direction). Essential is adopted. In the example shown in FIG. 7(B), a part of the stepped portion 460 overlaps with the region near the pin portion R in the vertical direction in a plan view.

[0027] Also in the example shown in FIG. 7(B), along the inclined surface of the die-casting mold in the direction of the tangent line L, that is, since the molten metal flows in the direction of the pin portion 430, the same operations and effects as those of the above-described embodiment can be obtained.

[0028] [2] Second Embodiment 1. Configuration of the base member FIG. 8 is a diagram showing a second embodiment of the present invention. In the figure, reference numeral 500 is the base member of the second embodiment. The lower surface 512 of the base member 500 includes a first lower surface 540 at the same height level as the lower surface 512 and a second lower surface 550 located above the first lower surface 540. That is, in FIG. 8, the second lower surface 550 is recessed with respect to the first lower surface 540.

[0029] Adjacent to the first lower surface 540, a second lower surface 550 located above the first lower surface 540 is formed. That is, in FIG. 8(A), the second lower surface 550 is recessed with respect to the first lower surface 540. The first lower surface 540 and the second lower surface 550 are adjacent to each other via a stepped portion 560 whose height gradually increases from the first lower surface 540 to the second lower surface 550.

[0030] The stepped portion 560 intersects the first lower surface 540 and the second lower surface 550 in a straight line in the lateral direction (a direction parallel to the short side of the base member 500), and also overlaps with a portion slightly inward from the outer periphery to the inner periphery of the pin portion 430 in a plan view. Further, the stepped portion 560 has a uniform height difference from the first lower surface 540 to the second lower surface 550.

[0031] 2. Operation and Effects of the Second Embodiment In the base member 500 configured as described above, since the step portion 560 crosses the first lower surface 540 and the second lower surface 550 in a direction parallel to the short side of the base member 500, the molten metal injected from above the base member 500 flows into the slope forming the step portion 560 of the die-casting mold at a right angle. Therefore, the molten metal flowing toward the stop hole through the slope forming the step portion 560 of the die-casting mold is directly supplied to the stop hole without deviating in the left-right direction. Accordingly, the formation of shrinkage cavities in the pin portion 430 is effectively suppressed.

[0032] 3. Modification Example of the Step Portion FIG. 8(B) is a diagram showing a modification example of the second embodiment. In this modification example, the first lower surface 541 and the second lower surface 551 are adjacent to each other via a step portion 561 bent in a plan view. In other words, the first lower surface 541 and the second lower surface 551 are adjacent to each other via a step portion 561 that is convex in a plan view toward the pin portion 430 (in the direction from the first lower surface 541 to the second lower surface 551). The step portion 561 is parallel to the short side of the base member 500 and includes a first step portion 561a that extends from the left edge of the first lower surface 541 to the vicinity of the outer periphery of the pin portion 430 in a plan view, and a second step portion 561b that bends upward at the end of the first step portion 561a and reaches the right edge of the first lower surface 541. The first step portion 561a overlaps with a portion extending from the outer periphery to the inner peripheral side of the pin portion 430, and the second step portion 561b extends obliquely upward from the outer periphery of the pin portion 430.

[0033] In the base member 500 configured as described above, not only does it exhibit the same operations and effects as the second embodiment, but also a part of the molten metal that has flowed into the portion forming the second step portion 561b of the die-casting mold flows in the direction of the stop hole according to the inclination of the second step portion 561b. For this reason, since the amount of molten metal supplied to the stop hole increases, the formation of shrinkage cavities in the pin portion 430 is more effectively suppressed.

[0034] FIG. 8(C) is a diagram showing another modification example of the second embodiment. Also in this modification example, the first lower surface 542 and the second lower surface 552 are adjacent to each other via a stepped portion 562 that is convexly bent toward the pin portion 430 (in the direction from the first lower surface 542 to the second lower surface 552) in a plan view. The stepped portion 562 extends parallel to the short side of the base member 500 from near the outer periphery of the pin portion 430 in a plan view, and includes a first stepped portion 562a that reaches near the outer periphery of the pin portion 430. Further, the stepped portion 562 includes a second stepped portion 562b that bends upward at one end of the first stepped portion 562a and reaches the left side edge of the first lower surface 542, and a third stepped portion 562c that bends upward at the other end of the first stepped portion 562a and reaches the right side edge of the first lower surface 542. The first stepped portion 562a overlaps with a portion that reaches from the outer periphery to the inner peripheral side of the pin portion 430, and the second and third stepped portions 562b and 562c extend obliquely upward from the outer periphery of the pin portion 430.

[0035] In the base member 500 having the above configuration, not only does it exhibit the same operations and effects as the second embodiment, but also the molten metal that has flowed into the portions forming the second and third stepped portions 562b and 562c of the die-casting mold flows in the direction of the blind hole according to the inclination of the second and third stepped portions 562b and 562c. For this reason, since the amount of molten metal supplied to the blind hole further increases, the formation of shrinkage cavities in the pin portion 430 is more effectively suppressed.

[0036] [3] Third Embodiment 1. Configuration of Base Member FIG. 9 is a diagram showing a third embodiment of the present invention. In the figure, reference numeral 600 is the base member of the third embodiment, and the base member 600 includes a lower surface 612. A rectangular recess 514 is formed in the lower left portion of the lower surface 612. An arcuate stepped portion 660 extending upward from the upper right corner portion of the recess 514 is formed, and the left side of the stepped portion 660 is the first lower surface 640. Also in this embodiment, the first lower surface 542 and the second lower surface 552 are adjacent to each other via a stepped portion 562 that is convexly bent toward the pin portion 430 (in the direction from the first lower surface 542 to the second lower surface 552) in a plan view.

[0037] Adjacent to the first lower surface 640, a second lower surface 650 is formed above the first lower surface 640. That is, in FIG. 9(A), the second lower surface 650 is recessed with respect to the first lower surface 640. The first lower surface 640 and the second lower surface 650 are adjacent to each other via a stepped portion 660 whose height gradually increases from the first lower surface 640 to the second lower surface 650.

[0038] The stepped portion 660 crosses between the first lower surface 640 and the second lower surface 650 in an arc shape rising to the right, and the central portion thereof overlaps with a portion slightly inward from the outer periphery to the inner periphery of the pin portion 430 in plan view. Also, the stepped portion 660 has a uniform height difference from the first lower surface 640 to the second lower surface 650.

[0039] 2. Operations and Effects of the Third Embodiment In the base member 600 having the above configuration, when molten metal is poured into the die-casting mold, a part of the molten metal flows along the stepped portion 660 from the right end portion of the stepped portion 660 in the portion forming the stepped portion 660 of the die-casting mold. Then, when the molten metal flows to near the center of the portion forming the stepped portion 660, the molten metal is supplied beyond the portion forming the stepped portion 660 toward the stop hole. Therefore, the formation of shrinkage cavities in the pin portion 430 is effectively suppressed.

[0040] In particular, in the above embodiment, since the stepped portion 660 crosses between the first lower surface 640 and the second lower surface 650 in an arc shape rising to the right, the rigidity of the protrusion portion 430 and the base member 600 can be ensured when the pivot assembly bearing 20 is attached to the protrusion portion 430. That is, the swing arm 11 supported by the pivot assembly bearing 20 swings about the protrusion portion 430 in the diagonally upper left region of the protrusion portion 430, and the protrusion portion 430 receives the inertial force in the swinging direction. In the above embodiment, since the first lower surface 640 having a thickness exists along the direction of the inertial force, deformation of the first lower surface 640 and the protrusion portion 430 can be suppressed. The same effect can also be obtained in the first embodiment shown in FIG. 6(A) and the modification example shown in FIG. 9(B) described later.

[0041] 3. Modification Example of the Stepped Portion FIG. 9(B) is a diagram showing a modified example of the third embodiment. In this modified example, the stepped portion 661 has a semi-circular arc shape that protrudes from the position of the right end portion of the stepped portion 660 shown in FIG. 9(A) toward the pin portion 430. The first lower surface 641 and the second lower surface 651 are adjacent to each other via a stepped portion 661 that is convex (in the direction from the first lower surface 641 to the second lower surface 651) when viewed in plan. The radius of curvature of this stepped portion 661 is set to be equal to or greater than the outer diameter of the pin portion 430.

[0042] The central portion of the stepped portion 661 overlaps with a portion that slightly enters from the outer periphery to the inner periphery side of the pin portion 430 when viewed in plan. Also, the stepped portion 661 has a uniform height difference from the first lower surface 641 to the second lower surface 651.

[0043] In the base member 600 having the above configuration, when the molten metal is injected into the die-casting mold, the molten metal flows so as to gather from the portion forming the stepped portion 661 of the die-casting mold to its central portion, and is supplied to the stop hole beyond the portion forming the stepped portion 661. Therefore, the formation of shrinkage cavities in the pin portion 430 is effectively suppressed.

[0044] In the base member 600, the stepped portion 661 has an arc shape that protrudes downward to the right when viewed in plan, but it can be configured to have an arc shape that protrudes directly downward, and the central portion of the stepped portion 661 overlaps with the outer periphery of the pin portion 430. In that case, the right end position of the first lower surface 641 is shifted to the right from the position shown in FIG. 9(B), and the first lower surface 641 and the second lower surface 651 are arranged so as to be continuous directly downward.

[0045] 4. Modified Example of the First Lower Surface The modified example shown in FIG. 10 is obtained by forming a pair of grooves 662 in the pin portion vicinity region R shown in FIG. 7(B) within the first lower surface 641 of the base member 600 shown in FIG. 9(B). The pair of grooves 662 are inclined so as to taper in the direction in which the stepped portion 661 protrudes.

[0046] In the base member 600 configured as described above, since the portion for forming the first lower surface 641 of the die-casting mold has ridges for forming grooves 662, the molten metal flows along the ridges during casting and accumulates at the center of the stepped portion 662. As a result, the molten metal exceeding the portion for forming the stepped portion 662 is supplied to the blind hole. Therefore, the formation of casting cavities in the pin portion 430 is effectively suppressed.

[0047] [4] Other modification examples The present invention is not limited to the above-described embodiments, and various modifications are possible as follows. i) The protruding portion is not limited to the pin portion 430. For example, when pins for attaching the actuator 14 or other components in FIG. 1 are integrally cast with the base portion 400, the present invention can also be applied.

[0048] ii) The groove 662 described in FIG. 10 can be applied to all the base members 400 to 600 described in FIGS. 6 to 9. Further, the shape of the groove 662 when viewed from the back surface is not limited to a straight line and may be curved. Furthermore, the groove 662 is not limited to a long and narrow rectangle and may be willow leaf-shaped or the like.

[0049] iii) The cross-sectional shapes of the stepped portions 460, 560, 660, 661, the first stepped portions 561a, 562a, the second stepped portions 561b, 562b, and the third stepped portion 562c can be any shape such as a convex curved surface, a concave curved surface, or a combination thereof.

Example

[0050] Next, the effects of the present invention will be described with specific examples. The base member shown in FIG. 6 was fabricated as an inventive example. Further, as Comparative Example 1, the base members shown in FIGS. 4 and 5 were fabricated, and as Comparative Example 2, a base member in which a frustum-shaped recess was formed on the back surface of the pin portion of the base member of Comparative Example 1 was used. Test pieces were fabricated by cutting axially along the outer periphery of the seating surface of the fabricated base members. The test pieces were non-destructively observed by X-ray CT, and the ratio of the bubble volume to the volume of the test piece was calculated. This was defined as the porosity. When the porosity of Comparative Example 1 was set to 1, the porosity of the inventive example was 0.08, and the porosity of Comparative Example 2 was 1.25. From the above results, it was confirmed that the base member of the present invention has reduced casting defects and improved rigidity.

Industrial Applicability

[0051] The present invention can be applied to electronic devices such as spindle motors and hard disk drive devices, and base members used therein.

Explanation of Signs

[0052] 10…Hard disk drive device, 11…Swing arm, 12…Magnetic head, 13…Hard disk, 14…Actuator, 15…Control unit, 16…Spacer, 17…Screw, 18…Clamp, 19…Cover, 20…Pivot assembly bearing, 100…Spindle motor, 102…Shaft, 103…Stator core, 104…Coil, 110…Rotor, 111…Cylindrical portion, 113…Rotor magnet, 114…Flange portion, 200, 300…Bearings, 201, 301…Conical bearing members, 400, 500, 600…Base members, 401a…Cylindrical portion, 410…Bottom portion, 411…Side wall portion, 412, 512, 612…Lower surface, 420…Through hole, 430…Pin portion (protrusion), 431…Seating surface, 432…Screw hole, 440, 540, 640, 641…First lower surface, 450, 550, 650, 651…Second lower surface, 460, 560, 660, 661…Step portion, 461…Arc-shaped portion, 514…Recess, 561a, 562a…First step portion, 561b, 562b…Second step portion, 562c…Third step portion, 662…Groove, C…Casting defect, L…Tangent line, P…Lower end point on the second lower surface side, Q…Lower end point on the first lower surface side, R…Region near the pin portion (region near the protrusion).

Claims

1. In a base member of a spindle motor having an upper surface and a lower surface, the base member is a casting, the upper surface is provided with a protrusion extending upward, the lower surface includes a first lower surface and a flat second lower surface located above the first lower surface, the first lower surface and the second lower surface are adjacent to each other via a step portion where the height increases from the first lower surface to the second lower surface, When a circular region having a diameter three times the diameter of the protrusion is defined as a region near the protrusion with the protrusion located at the center in a plan view, at least a part of the step portion overlaps with the region near the protrusion in the vertical direction, The second lower surface is a base member that extends in a plan view to a position beyond the region near the protrusion from the step portion.

2. In a cross-section in a direction perpendicular to the step portion passing through the central axis of the protrusion in a plan view, when a tangent line is drawn to the step portion, the tangent line passes between the lower end point on the second lower surface side and the lower end point on the first lower surface side of the outer periphery of the protrusion. The base member according to claim 1.

3. The base member according to claim 1 or 2, wherein the protrusion overlaps with the second lower surface in the vertical direction.

4. The base member according to any one of claims 1 to 3, wherein the step portion has a linear shape or a convex shape that is convex toward the protrusion in a plan view.

5. A seating surface located above the surroundings is provided around the protrusion within the region near the protrusion in a plan view, and at least a part of the step portion overlaps with the seating surface in the vertical direction. The base member according to any one of claims 1 to 4.

6. The base member according to claim 2, wherein the angle formed by the tangent line and the second lower surface is 15 to 90°.

7. The base member according to claim 2, wherein the angle formed by the tangent line and the second lower surface is 30 to 60°.

8. The stepped portion includes a linear portion that is substantially linear in plan view, and at least a part of the linear portion overlaps with the vicinity region of the protrusion in the vertical direction. The base member according to any one of claims 1 to 7.

9. The stepped portion includes a curved portion formed of a curve that is convex toward the protrusion side in plan view, and at least a part of the curved portion overlaps with the vicinity region of the protrusion in the vertical direction. The base member according to any one of claims 1 to 7.

10. A groove extending toward the protrusion side is formed in the vicinity region of the protrusion on the first lower surface. The base member according to any one of claims 1 to 9.

11. A spindle motor including the base member according to any one of claims 1 to 10.

12. A hard disk drive including the spindle motor according to claim 11.

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