JP2002112498A - Spindle motor and floppy disk (r) drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a spindle motor which can retain enough amount of grease in the bearing and provide a reliable thin floppy disk drive. SOLUTION: A spindle motor used in a floppy disk drive has a radial bearing 28 to radially support the spindle shaft 2 and a thrust ball bearing disposed outside the radial bearing 28 to support the thrust load. Part of the a ball pocket in the retainer 27 of the thrust ball bearing is filled with grease in place of the balls to prolong the greased life of the motor to improve its reliability. Thus, a reliable spindle motor and a thin floppy disk drive using this spindle motor are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor used for an external storage device such as a personal computer and a floppy disk drive using the same.

[0002]

2. Description of the Related Art Conventionally, in a spindle motor of this type, a thrust force of the spindle motor is supported by a thrust ball bearing as described in Japanese Utility Model Application Laid-Open No. 4-134155 or the like to constitute the spindle motor.

FIG. 9 is a plan view of a conventional spindle motor, and FIG. 10 is a sectional view of the conventional spindle motor. In a conventional spindle motor, an oilless metal bearing as a radial bearing member and a thrust bearing disposed on a substrate outside the oilless metal bearing are used. The shape of the fixed plate disposed on the lower side has been devised so as to improve the flatness by the thrust bearing against the warpage of the substrate. Also, it can be seen that balls are inserted into all pockets of the thrust bearing.

[0004]

As described above, in the conventional spindle motor and the floppy disk drive using the same, in the conventional thrust ball bearing, the grease interposed in the thrust ball bearing is provided on the retainer at substantially equal intervals by the ball. The gap between the holding pocket and the ball was filled. For this reason, there is a problem that the life of the bearing is shortened due to grease deterioration due to oxidation and contamination of the grease due to the small amount of grease. Moreover,
In response to the demand for thinner personal computers and the like, spindle motors and floppy disk drives using the same have become smaller and thinner, which has led to more severe thermal use conditions than before. In addition, it is difficult to secure a sufficient amount of grease, which may cause a problem of shortening the life of the grease.

The present invention solves the above-mentioned conventional problems, and is suitable for miniaturization and thinning. A sufficient amount of grease can be secured, the grease life can be prolonged, and longevity and improved reliability can be attained. It is another object of the present invention to provide a spindle motor which is reduced in weight and a floppy disk drive which is reduced in size and thickness by using the spindle motor.

[0006]

In order to achieve the above object, the present invention has a radial bearing for supporting a spindle shaft in a radial direction, and a thrust ball bearing disposed outside the radial bearing. And a grease instead of a ball is filled in a part of a pocket for holding a ball provided at substantially equal intervals in a retainer of a thrust ball bearing.

With this configuration, the amount of grease that can be sealed can be increased, the deterioration of grease characteristics can be reduced, the life of the thrust bearing can be extended, and the weight of the spindle motor can be reduced.

Further, according to the present invention, a thrust ball bearing comprises:
This is an open type spindle motor without a shield member.

According to this configuration, the rotational load generated by the shield can be reduced, the accompanying heat generation can be reduced, and the thermal deterioration of the grease can be reduced. Further, the structure can be simplified, and the cost can be reduced. Although it is an open type, the grease amount can be increased, so that sufficiently high reliability can be ensured also with respect to evaporation and deterioration of the grease due to invasion of foreign matter.

The present invention is a spindle motor in which a thrust ball bearing is mounted on a receiving seat provided on a part of a radial bearing member.

With this configuration, it is possible to easily secure the flatness and to make it difficult for an uneven load to be applied to the thrust ball bearing, as compared with the case where the magnetic metal base is used on a printed wiring board as conventionally used. This is advantageous for shaft runout and life. Further, the positioning of the assembly can be easily performed, and the workability can be improved.

According to the present invention, there is provided a spindle motor in which pockets filled with grease are arranged at discontinuous positions of pockets provided at substantially equal intervals.

According to this configuration, the range of the portion where the ball is not disposed is small, and a decrease in the rated load can be suppressed. Further, since the arrangement of the balls receiving the load is less likely to be deviated, the balance of the thrust bearing is not lost, so that a decrease in reliability can be prevented.

According to the present invention, there is provided a spindle shaft having a chucking portion on an upper portion of a rotor and directly pressed into the rotor,
A radial bearing that supports the spindle shaft in a radial direction, a thrust ball bearing disposed on a receiving seat of a radial bearing member outside the radial bearing, and a thrust load is supported. This is a floppy disk drive having a spindle motor in which a part of a pocket for holding balls provided at equal intervals is filled with grease instead of balls.

According to this configuration, it is possible to prevent a reduction in the life of the bearing due to oxidation or contamination of the grease, which is likely to occur due to a small amount of grease in the thrust ball bearing, and a highly reliable floppy disk device can be realized. Further, reliability can be ensured even when the use conditions for the miniaturization and thinning of the floppy disk device become severe.

The present invention is a floppy disk drive in which the thrust ball bearing is arranged so as not to overlap the movable range of the chucking portion in a plane.

With this configuration, it is not necessary to escape the movable range of the chucking portion, and the thickness of the floppy disk device can be easily reduced.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spindle motor according to the present invention and a floppy disk drive using the same will be described below with reference to the drawings.

FIG. 1 is a perspective view of a spindle motor according to an embodiment of the present invention, a part of which is shown in section for easy understanding. In FIG. 1, the spindle motor 20
Has a rotor yoke 1. The rotor yoke 1
A 0.6 mm thick galvanized steel sheet (SECC) is finished to the required shape by pressing. At the center of the rotor yoke 1, there is provided a burring hole 1 'into which the spindle shaft 2 is directly press-fitted. One side of the main magnet 5 disposed inside is magnetically short-circuited. The spindle shaft 2 is an output shaft of the spindle motor 20.

In the spindle motor according to the embodiment of the present invention, a SUS-420J2 bar material having a diameter of 4 mm is quenched, tempered and polished to a required shape. The spindle shaft 2 is directly press-fitted and fixed in a burring hole 1 ′ provided at the center of the rotor yoke 1.
The drive pin 3 operates to transmit a rotational force to a magnetic recording medium described later. The drive pin 3 is made of Nippon Kagaku Yakin's N
T-982 is used. After compression molding, firing, quenching and tempering are performed to impregnate the lubricating oil. Regarding the hardness, Hv200-4 to enable abrasion and caulking
00 is set. The hole 4 provided in the rotor yoke 1 allows the drive pin 3 to fly out and transmit the rotational force to the magnetic recording medium. Main magnet 5
Is a magnet for generating a torque for rotating the magnetic recording medium, and a sintered magnet of neodymium iron boron is
Polarized.

The hub magnet 6 is a magnet for attracting a metal center core provided on a magnetic recording medium described later, and is formed integrally with the rotor yoke 1. The portion that positions the magnetic recording medium and transmits the rotational force is called a chucking portion. The chucking part is
As shown in FIG. 1 and FIG. 2, it is constituted by a spindle shaft 2, a drive pin 3, a hub magnet 6, a hub spring 11, a drive shaft 13, and a P-spring 12. Two types of coils 7a and 7b having different outer shapes are used. In order to increase the space factor, a rectangular ribbon line is used. The difference in outer shape is to escape the Hall element 8 for detecting the position of the main magnet 5. FG
(Frequency generator) The magnet 9 is formed integrally with the outer periphery of the rotor yoke 1. Hub magnet 6 and FG
Both magnets 9 are ferrite plastic magnets using nylon 12 as a binder. The FG magnet 9 detects the rotation speed of the rotor, and
Magnetized to 20 poles. The silicon PCB 10 has a thickness of 0.
An electrical circuit is formed by providing a copper foil 10c on a 5-mm non-directional silicon steel plate 10a provided with an insulating layer 10b (see FIG. 3). This is the so-called silicon PCB (Pr
This is called an inted circuit board (printed circuit board). The reason for using a silicon steel plate instead of iron is to reduce the hysteresis loss of the motor and the current consumption. In the embodiment of the present invention, when the silicon steel sheet 10a was used and the iron sheet was compared, the current consumption in the no-load state could be reduced by about 50 mA when the silicon steel sheet 10a was used. Furthermore, since the density can be lower than that of iron, the weight can be reduced.

FIG. 2 shows a rotor assembly (rotor ASM).
FIG. 2 is an exploded perspective view in which the inside of FIG. In FIG. 2, the hub spring 11 has a drive pin 3 attached to the tip end by caulking, and the other end rotatably supported by a drive shaft 13 attached to the rotor yoke 1. The hub spring 11 is made of phosphor bronze having a thickness of 0.15 mm. The tip of the P-spring 12 urges the hub spring 11 upward and to the outer peripheral side, and the other end of the P-spring 12 is engaged with the engaging portion 14 by causing a part of the hub magnet 6 to protrude into a bar-like back surface. It is a wire spring. The material is
The required heat treatment is performed using a stainless spring material (such as SUS304CSP). The drive shaft 13 rotatably attaches the hub spring 11 to the rotor yoke 1 and is made of stainless steel (SUS303) and has a required stepped shape.

FIG. 3 is a sectional view of the spindle motor according to the embodiment of the present invention. In FIG. 3, the silicon PCB 10
Has an insulating layer 10b provided on a non-directional silicon steel plate 10a as a base material, and a copper foil 10c provided on an upper surface to form an electric circuit. Each layer is bonded by an adhesive or the like. Further, the spindle motor is of a flat facing type, and the silicon PCB 10 as a magnetic metal substrate works as an electric circuit and also as a stator (back yoke as a magnetic circuit). The hole 21 is for fitting and fixing a radial bearing member 22 provided on the stator, and is made by press working. Press working in this kind of silicon PCB10 etc. is usually
It is punched from the metal substrate side toward the insulating layer. The radial bearing member 22 includes a caulking portion 23 and a receiving seat 24 for mounting the thrust bearing 25, which are fixed to the radial bearing portion 28 and the hole 21 of the stator by caulking.
It is located outside the radial bearing 28. Seat 24
Is provided on the radial bearing member 22 and is made of silicon PC.
The wall higher than the receiving seat 24 is tapered in the inner diameter direction on the outer peripheral side so that the thrust bearing 25 can be mounted accurately with respect to the deterioration of flatness due to press working of B and the workability of mounting is improved. It is additionally provided.

The radial bearing member 22 according to the embodiment of the present invention uses a copper-based sintered oil-impregnated metal. More specifically, Nikamet NT-208 manufactured by Nippon Kagaku Yakin is used. An extreme pressure agent is added to the impregnated lubricating oil in consideration of the service life. The reason why copper is used is that, because the spindle shaft 2 is made of stainless steel (SUS-420J2), consideration is given to hardness differences, good initial adaptation, and caulking.

The thrust bearing 25 according to the embodiment of the present invention includes a fixed plate 25a, a rotating plate 25b, a ball 26, and a ball retainer 27, and supports the rotor ASM in the thrust direction. A thrust force is generated by the attraction force of the main magnet 5, and its magnitude is about 1
9.6 N (2.0 kgf). The ball 26 is made of chrome steel SUJ-2, and the fixed plate 25a and the rotating plate 2 are used.
5b is obtained by hardening and polishing the SK material. Fixing plate 25a
The rotary plate 25b is a flat plate and has no raceway groove (race groove) of the ball 26. This prevents the thrust bearing from being restricted in the radial direction. The main body 41 of the magnetic recording medium is attached to a metal center core 43. The positioning hole 45 and the spindle shaft 2 are fitted and positioned. The driving pin 3 enters a driving hole 44 provided in the metal center core 43 and is driven to rotate.

Next, the fixing of the radial bearing member 22 to the hole 21 for fitting and fixing to the stator will be described.
In the radial bearing member 22, the radial bearing portion 28, the receiving seat 24 and the like are finished with high accuracy in a single state. First, the radial bearing member 22 is set in the hole 21. Next, the caulking portion 23 is pushed outward by a spin caulking machine to bite into the hole 21 while the portion fitted to the hole 21 is slightly thickened. The fitting portion is further filled into a space formed between the metal substrate and the hole 21. Finally, the work is fixed by caulking, and caulking is performed so that the lower surface becomes the same surface (so-called sword). In the embodiment of the present invention, the caulking machine was US-1 manufactured by Yoshikawa Iron Works, and caulking was performed at an air pressure of about 3000 Pa (3 kg / square cm). At the time of caulking, the caulked portion 23 is deformed and this stress is propagated, and the influence thereof usually appears as a decrease in the inner diameter or a decrease in roundness in the radial bearing portion 28. For this reason, the radial bearing portion 28 is sizing and finished with high precision after caulking.

Conventionally, in order to cope with these, in order to avoid the influence of caulking on the inner diameter of the radial bearing portion 28, a relief is provided in the inner diameter of the radial bearing portion 28 corresponding to the thickness of the magnetic metal substrate. Was. For this reason, there has been a problem that the axial span as a radial bearing cannot be reduced and the radial runout of the spindle shaft cannot be reduced. The present invention is designed to prevent reduction of the axial span by sizing after caulking. As a result, problems such as difficulty in making the floppy disk device thinner and difficulty in achieving compatibility due to an error due to shaft runout can be solved.

FIG. 4A is a perspective view showing a state of balls, a retainer, and grease of a thrust bearing using the spindle motor according to the embodiment of the present invention, and FIG. 4B.
Is a sectional view showing a state of a pocket without a ball, and FIG. 4C is a sectional view showing a state of a pocket with a ball.

Referring to FIGS. 4A, 4B and 4C,
The description of the retainer 27 of the thrust bearing 25 will be described in more detail. A pocket 27 for holding a ball 26 as a rolling element provided on a retainer 27 (see FIG. 3) disposed between the fixed plate 25a and the rotating plate 25b.
a is arranged so that the entire circumference is equally divided into twelve. The retainer 27 according to the embodiment of the present invention is made of a polyacetal resin (POM) by injection molding. The pocket 27a has a spherical shape so that the ball 26 can be easily rotated when the ball 26 is inserted, and has a shape such that the ball 26 does not easily come out after the ball 26 is inserted.
In terms of shape, it is similar to a fir-shaped retainer. The ball 26 has a diameter of about 1.6 mm (1/16 "). The pocket 27a is formed so as to be larger than the diameter of the ball 26 by about 0.05 mm. Multemp SRL grease made of Kyodo Yushi, using lithium soap as the material.The reason for using lithium soap as the thickening material is that because of its excellent shear stability, vibration at low temperature startup is small. This is because the friction torque at room temperature can be reduced.
(B) shows a state in which the ball 27 is not filled in the pocket 27a and the grease 29 is filled. FIG. 4C shows a state where the ball 26 is inserted. FIG.
In the retainer 27 of (a), eight balls are inserted into twelve pockets. The grease 29 is filled at the positions corresponding to the four pockets without the balls. The pockets filled with grease 29 are not continuous.

The thrust bearing 25 is an open type without a shield member. Accordingly, the structure is simple, the weight can be reduced, and an increase in the rotational torque due to the addition of the shield member can be prevented. Further, it can be considered that the thrust bearing 25 is shielded as the whole spindle motor. Thrust bearing 25 according to an embodiment of the present invention
The rated load of 169.5N (1
7.3Kgf), 149.9N (15.3Kgf)
f), the number of which is 129.4 N (13.2 kgf) in eight pieces. The rotational life was determined from the number of rotations used (300 rotations per minute) and the thrust load, and the life as a spindle motor used in a floppy disk drive (L10
That is, it was found that four balls 26 are sufficient for the reliability of 90%. In the embodiment of the present invention, eight balls are inserted into twelve pockets, and grease 29 is filled into four pockets. The pockets filled with the grease 29 are arranged so as not to be continuous. Thereby, the filling amount of the grease 29 in the thrust bearing 25 can be increased,
Oxidation of the grease 29 and reduction of the grease life due to entry of foreign matter such as dust can be prevented. Furthermore, grease 29
However, since the pockets in which the balls 26 were not inserted were filled, the rotation torque could hardly be increased.

Next, a case where the present invention is applied to a floppy disk device will be described with reference to FIG.

FIG. 5 is a plan view of a main part of a floppy disk drive 30 using a spindle motor according to an embodiment of the present invention. In FIG. 5, the floppy disk drive 30
Are the necessary mechanical parts such as the holder 35 and the eject lever 34 on the base plate 31 and the magnetic head 3
The head carriage assembly 32 to which the 2a and 32b are attached is moved to a required track by a step motor 33 so that data can be recorded or reproduced. Please refer to FIG. 6 for understanding the positional relationship of the spindle motor 20. The magnetic recording medium is mounted in the direction of the arrow.

FIG. 6 is an exploded perspective view showing a spindle motor according to the present invention and a floppy disk drive using the same. FIG. 6 shows a state where the spindle motor 20 is attached from below the base plate 31 with the screws 36.

FIG. 7 is a perspective view showing a magnetic recording medium assembly 40 used in the floppy disk drive of the present invention. The magnetic recording medium assembly 40 according to the embodiment of the present invention is a so-called 3.5 "FD defined by JIS X-6223 or the like.
The main body 41 of the magnetic recording medium is also called a cookie, and a magnetic material is applied to both surfaces of a film such as PET. As a whole, it is housed in a plastic case called a shell. The case has a slidable shutter, a part of which is provided with a window 42 called a head window which is opened for the head to enter. The magnetic head records or reproduces data by sandwiching the cookie 41 from both sides of the window 42.

FIG. 8 is a perspective view showing the main body 41 of the magnetic recording medium. In FIG. 8, in the center of the cookie 41,
A metal center core 43 made of magnetic stainless steel such as SUS430 is attached. Metal center core 4
At the center of 3 is provided a square positioning hole 45 and a rectangular drive hole 44 for rotating the cookie 41. The compatibility in the floppy disk drive is based on the metal center core 43 provided at the center of the magnetic recording medium.
Due to the positioning accuracy between the positioning hole 45 and the spindle shaft 2 of the spindle motor, the positional deviation from the track written on the main body of the magnetic recording medium becomes a serious problem.
In particular, shaft runout of the spindle shaft results in eccentricity of the track, which is an important issue of compatibility in a floppy disk drive. The demand for thinner floppy disk drives also requires thinner spindle motors. As a result, securing the bearing span has become more important.

Since the spindle shaft 2 according to the embodiment of the present invention is directly press-fitted and fixed in a burring hole 1 'provided in the center of the rotor yoke 1, the shaft is attached to the rotor by using another component such as a hub. A sufficient space can be ensured above the radial bearing portion 28 because it is not attached. In addition, the radial bearing member 22 is sized after caulking to the magnetic metal substrate, thereby preventing a reduction in the shaft span. As a result, a sufficient shaft span can be secured in the radial bearing portion 28, and shaft runout can be reduced.

In order to secure the bearing span, a thrust ball bearing for supporting the thrust load of the rotor is disposed outside the radial bearing portion 28, and the thrust bearing 2 is provided.
5 and the radial bearing portion 28 are positioned so as not to overlap in a direction parallel to the central axis of the spindle shaft 2.
A sufficient bearing span of the radial bearing portion 28 can be obtained. The motor according to the embodiment of the present invention has a large thrust force because it is of the planar facing type. For this reason, a very small shaft loss (torque loss in terms of shaft) due to rolling friction was achieved by using a thrust ball bearing.

Further, since the center of rotation of the conical shaft runout is considered to occur at the center line of the rolling element of the thrust ball bearing, it is disposed at a position where the radial bearing portion 28 overlaps in the height direction. By doing so, the upper and lower ends of the radial bearing portion 28, which have the greatest effect on the shaft that limits the axial runout of the radial bearing portion 28, the bearing clearance (shaft clearance) and the shaft span, can be effectively used. Since the load can be shared by the parts, the life is also advantageous. These are very effective for reducing the thickness of the floppy disk device. Furthermore, by arranging them at positions overlapping in the height direction, they can be used as guides for assembling the radial bearing portion 28, so that workability can be improved. Further, the portions for positioning the magnetic recording medium and transmitting the rotational force, that is, the spindle shaft 2, the drive pin 3, the hub magnet 6, the hub spring 11, the drive shaft 13, and the p-spring 12 are provided as described above. Called the chucking unit. More specifically,
The hub spring 11 and the drive pin 3 move while bending downward when chucking the magnetic recording medium.
For this purpose, the thrust ball bearing is arranged so as not to overlap the movable range of the chucking portion in plan. That is, the fixed plate 25a, the rotating plate 25b, the ball 26, and the retainer 27 are arranged inside the movable range of the chucking unit. Thus, there is no need to escape the movable range of the chucking section, and the thickness of the floppy disk device can be easily reduced.

[0039]

As described above, the present invention has a radial bearing for supporting a spindle shaft in a radial direction, and supports a thrust load by a thrust ball bearing disposed outside the radial bearing. By filling grease in place of the ball in a part of the pocket that holds the ball provided at the ball bearing retainer at approximately equal intervals instead of the ball, the amount of grease that can be enclosed can be increased, the grease characteristics can be reduced, and the thrust can be reduced. An object of the present invention is to provide a spindle motor having an excellent effect that the life of the bearing can be extended and the reliability and the weight of the spindle motor can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a spindle motor according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a rotor assembly of the spindle motor according to the first embodiment of the present invention.

FIG. 3 is a detailed sectional view of a spindle motor according to the first embodiment of the present invention.

4A is a perspective view showing a state of a retainer and grease in the present invention, FIG. 4B is a sectional view showing a state of a pocket without a ball in the present invention, and FIG. 4C is a sectional view of a pocket with a ball in the present invention. Sectional view showing the state of

FIG. 5 is a plan view of a main part of a floppy disk device according to the present invention.

FIG. 6 is an exploded perspective view showing attachment of a spindle motor to a floppy disk device.

FIG. 7 is a perspective view showing an assembly of a magnetic recording medium according to the present invention.

FIG. 8 is a perspective view showing a main body of the magnetic recording medium.

FIG. 9 is a plan view of a conventional spindle motor.

FIG. 10 is a sectional view of a conventional spindle motor.

[Explanation of symbols]

 Reference Signs List 1 rotor yoke 1 'burring hole 1' 2 spindle shaft 3 drive pin 4 hole provided in rotor yoke 5 main magnet 6 hub magnet 7a coil 7b coil 8 hall element 9 FG magnet 10 silicon PCB 10a silicon steel plate 10b insulating layer 10c copper foil Reference Signs List 11 hub spring 12 P-spring 13 drive shaft 14 locking portion 20 spindle motor 21 hole 22 radial bearing member 23 caulking portion 24 receiving seat 25 thrust bearing 25a fixing plate 25b rotating plate 26 ball 27 retainer 27a pocket 28 radial bearing portion 29 grease Reference Signs List 30 floppy disk device 31 base plate 32 head carriage assembly 32a head 32b head 33 step motor 34 eject lever 35 holder 3 Screw 40 holes of the magnetic body of the recording medium assembly 41 magnetic recording medium (cookies) 42 window 43 metal center core 44 driving hole 45 for positioning

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G11B 19/20 G11B 19/20 E 5H621 H02K 5/167 H02K 5/167 A 21/24 21/24 M 29/08 29 / 08 29/14 29/14 F term (reference) 3J101 AA02 AA32 AA42 AA53 AA62 BA35 BA50 CA14 EA37 EA63 FA32 GA24 GA53 5D038 BA04 CA04 DA01 5D109 BB02 BB12 BB16 BB17 BB21 BB22 5H019 AA08 BB01 BB01 BB01 BB01 BB01 BB01 FF03 5H605 AA08 BB05 BB20 CC04 CC05 EB02 EB06 EB10 EB23 FF01 FF06 GG03 GG04 GG07 GG12 5H621 GB03 HH02 JK19

Claims (6)

[Claims] 1. A radial bearing for supporting a spindle shaft in a radial direction, a thrust ball bearing disposed outside the radial bearing supports a thrust load, and a retainer of the thrust ball bearing has substantially equal intervals. A spindle motor characterized in that a part of a pocket for holding a ball provided in the motor is filled with grease instead of the ball. 2. The spindle motor according to claim 1, wherein the thrust ball bearing is an open type without a shield member. 3. The spindle motor according to claim 1, wherein the thrust ball bearing is mounted on a receiving seat provided on a part of the radial bearing member. 4. The spindle motor according to claim 1, wherein the pockets for filling the grease are arranged at positions that are not continuous with pockets provided at substantially equal intervals. . 5. A radial bearing member having a chucking portion on an upper portion of a rotor and having a spindle shaft directly press-fitted into the rotor, and a radial bearing for supporting the spindle shaft in a radial direction, wherein a radial bearing member is provided outside the radial bearing. A thrust ball bearing arranged in a receiving seat supports a thrust load, and a spindle motor in which grease is filled in place of a ball in a part of a pocket holding a ball provided at substantially equal intervals in a retainer of the thrust ball bearing is provided. A floppy disk drive comprising: 6. The floppy disk drive according to claim 5, wherein the thrust ball bearing is arranged so as not to overlap a movable range of the chucking portion in a plan view.