Hard disk drive device

Abstract: A hard disk drive motor (M) comprising a rotor (12) with an integral central cylindrical sleeve (14), a base (10) and a bearing assembly rotatably supporting the rotor (12) on the base (10). The bearing assembly includes a stepped shaft (1) having a larger diameter portion (1a) pressed into the base (10) and a smaller diameter portion (1b). A ball bearing (5) comprising an inner ring (6) having the same outer diameter as the larger shaft portion (1a), an outer ring (7) and a first set of balls is mounted on the smaller shaft portion (1b). A second set of balls runs between a raceway in the larger shaft portion (1a) and a further outer ring (3). The diameters of all the balls are the same and the outer rings (3,7) fit in enlarged recesses at opposite ends of the sleeve (14) and have the same inner diameter.

Description: The present invention relates to an improvement of a bearing portion of a motor of a hard disk drive device. The hard disk drive device employs in general a motor such as a spindle motor for rotating a magnetic disk means for storing data. The motor includes a shaft, a rotor, a base, and a stator. The rotor as rotating member is adapted to be journalled to extend vertically above the base by means of bearing means installed on the base. The bearing apparatus of the prior art as shown in Fig. 4 comprises a pair of ball bearing 21, 22 fitted on a shaft 23. The bearings 21, 22 are spaced apart for example by means of spacer 24 secured on the shaft 23. The major aim of hard disk drive designing is to reduce the size thereof. That is, it is desirable to make the rotor of the motor and the bearing means for supporting the rotor as small as possible. A way which can be used to reduce the size of the bearing means is to miniaturize both ball bearings of the pair. However, this leads to a reduction of the diameter of the shaft. A shaft of reduced diameter provides a problem of mechanical rigidity and impairs the reliability and vibration-proof property of the hard disk drive device. Further, a shaft of reduced diameter becomes resonant with members of the hard disk drive device surrounding it, e.g. the casing of the device. That is, the reduction of the resonance property will be accompanied by a reduction in the reliability of the hard disk drive device. EP-A-0758155 discloses a hard disk drive device comprising a double row bearing apparatus and includes a stepped shaft having larger and smaller diameter shaft portions. An inner raceway groove is provided on the outer peripheral surface of the larger diameter portion and balls are interposed between the inner raceway groove and an outer raceway groove formed on an inner surface of an outer race surrounding the larger diameter portion. A ball bearing including inner and outer races with balls interposed therebetween is fitted over the smaller diameter portion, with a spacer sleeve located between the outer race of the ball bearing and the outer race surrounding the larger diameter portion. The lower end of the larger diameter shaft portion of the double row bearing apparatus is installed and secured on a base of the hard disk drive device and a cylindrical sleeve provided on a rotor of a motor for rotating magnetic disk means is mounted on the outer races of the double row bearing apparatus. .The object of the present invention is to provide a hard disk drive device including a sufficiently compact double row bearing apparatus and having a shaft of sufficient mechanical rigidity. These and other objects are achieved by a hard disk drive device comprising a double row bearing apparatus, the apparatus including: a stepped shaft having larger and smaller diameter shaft portions, an inner raceway groove provided on the outer peripheral surface of the larger diameter portion, balls interposed between the inner raceway groove and an outer raceway groove formed on an inner surface of an outer race surrounding the larger diameter portion and a ball bearing including inner and outer races and balls interposed therebetween, wherein the ball bearing is fitted at its inner race over the smaller diameter portion, and a lower end of said larger diameter shaft portion is installed and secured on a base; said hard disk drive device further comprising a cylindrical sleeve of a rotor of a motor for rotating magnetic disk means for storing data, said sleeve being open at both its upper and lower ends, characterised in that said sleeve is provided on its inner surface with upper and lower larger inner diameter portions of the same diameter and a thick smaller inner diameter portion formed therebetween, said thick portion being clamped between the outer race provided around the larger diameter portion and fitted within the lower portion of the sleeve and the outer race of the ball bearing fitted within the upper portion of the sleeve. Thus the rotor of the motor is assembled securely to the double row bearing apparatus. In the hard disk drive device according to the present invention, the cylindrical sleeve is formed integrally with the rotor. The outer diameter of the inner race of the ball bearing is the same as that of the larger diameter portion of the stepped shaft, the inner diameter of the outer race of the ball bearing is the same diameter as that of the outer race of the ball of the ball bearing and the diameter of the balls interposed between the outer surface of the larger diameter portion and the outer race provided therearound are substantially equal. Further features of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following description of a preferred embodiment of the invention which is shown in the accompanying drawings in which: Fig. 1 is a perspective view of a hard disk drive device of the present invention; Fig. 2 is a longitudinal cross-sectional view of the motor employed in the hard disk drive device of the present invention; Fig. 3 is a longitudinal cross-sectional view of the double row bearing apparatus; Fig. 4 is a longitudinal cross-sectional view of the bearing apparatus in a motor employed in a hard disk drive device of a prior art apparatus. A preferred embodiment of a hard disk drive device in accordance with the present invention will now be described in detail with reference to the attached drawings. The hard disk drive device of the present invention includes a motor M for rotating a magnetic disk 17 for storing data. A bearing apparatus for the motor M is constructed as a double row bearing apparatus of unique structure. The structure of the double row bearing apparatus will be described with reference to Fig. 3. In Fig. 3, reference numeral 1 designates a stepped shaft including a larger diameter shaft portion 1a around the outer peripheral surface thereof in which an inner raceway groove 2a is provided, and a smaller diameter shaft portion 1b. Reference numeral 3 designates an outer race provided around the larger diameter portion 1a. The outer race is formed on its inner peripheral surface with an outer raceway groove 2b. A number of balls 4 are interposed between the inner and outer grooves 2a and 2b to provide one of the bearings of the double row bearing apparatus. A ball bearing 5 is removably fitted with its inner race 6 on the smaller diameter portion 1b of the stepped shaft 1. The ball bearing 5 includes an inner race 6 having an inner raceway groove 8a, an outer race 7 having an outer raceway groove 8b, and a plurality of balls 9 interposed therebetween. The outer diameter of inner race 6 of ball bearing 5 is made equal with the outer diameter of the larger diameter portion 1a of the stepped shaft 1. The inner and outer diameters of outer race 7 are the same as those of outer race 3. Consequentially, all of the balls 4 and 9 have the same diameter. The double row bearing apparatus is assembled on the base 10 as shown in Fig. 2. As can be seen in Fig. 2, the lower end of larger diameter portion 1a of shaft 1 is installed and secured in the base 10. A rotor 12 is adapted to be formed from a blank material by means for example of machining to have a cylindrical sleeve 14 therethrough. The sleeve 14 is enlarged at both ends to form upwardly and downwardly opening upper and lower larger inner diameter portions 16a and 16b. These portions are separated from each other by a thick smaller diameter portion 15. The outer race 7 of the ball bearing 5 is adapted to be fitted within upper portion 16a and the outer race 3 provided around the larger portion of the shaft is adapted to be fitted within the lower portion 16b. The thick portion 15 is adapted to be clamped between outer races 3 and 7 and secured therebetween. The reference numeral 11 found in this figure designates a stator around which a coil is provided, and the reference numeral 13 designates magnet means installed on an inner peripheral surface of the rotor so as to be opposite to the stator. Further, in Fig. 1, the reference numeral 18 designates a swing arm including at its distal end a magnetic head 19 for reading and writing data to the magnetic disk 17. In assembling the motor, the ball bearing 5 is removed from the double row bearing apparatus,then the lower end of larger diameter portion 1a of the shaft is secured to the base of the motor, and the lower portion 16b of sleeve 14 of rotor 12 is fitted over the outer race 3 provided around the larger diameter portion. Subsequently, the ball bearing 5 is fitted into the space formed between the top end of smaller diameter portion 1b and sleeve 14 via the upper opening of the sleeve to clamp thick portion 15 of sleeve 14 between outer races 7 and 3. The inner race 6 of the ball bearing is secured by means for example of adhesive to the smaller diameter portion 1b while applying appropriate pressure on the upper end surface of the inner race. Although the balls 4 and 9 have the same diameter in the above-mentioned embodiment, balls of different diameter can be used in some cases. The hard disk drive device apparatus in accordance with the present invention having a construction as mentioned will provide the following effects. The double row bearing apparatus of the motor of the hard disk drive device of the present invention includes an inner raceway groove formed on the outer peripheral surface of the larger diameter shaft portion. Accordingly, the inner race provided in the prior art apparatus around the shaft is no longer necessary. Further, the diameter of the shaft portion on which the inner race is provided can be increased to make it possible to provide the stepped shaft. Consequently, the diameter of the outer race of the bearing can be decreased without decreasing the mechanical rigidity of the shaft. In conclusion, the double row bearing apparatus and rotor can be miniaturized without sacrificing the mechanical rigidity of the shaft, so that miniaturizing of the hard disk drive device can be obtained without reducing the reliability and vibration-proof property thereof. The thick portion 15 of the cylindrical sleeve of the rotor can be clamped between the outer race provided around the larger diameter shaft portion and the outer race of the ball bearing while assembling the rotor on the double row bearing apparatus, since the ball bearing can be removed from the stepped shaft. In other words, the assembling operation can be effected easily. Finally, only one ball bearing of the prior art type is required so that only one inner race is required for the present invention. In addition, the thick portion of the sleeve functions as a spacer for spacing the upper and lower outer races. Accordingly, it is not necessary to provide an additional spacer between outer races. Integrally forming the rotor and the cylindrical sleeve will reduce the number of parts of the apparatus. While a particular embodiment of the present invention has been illustrated and described, it should be obvious to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention, which could be employed in other forms of disk drive motors such as a so-called floppy disk drive motor.

Claims: A hard disk drive device comprising a double row bearing apparatus, the apparatus including: a stepped shaft (1) having larger and smaller diameter shaft portions (1a,1b), an inner raceway groove (2a) provided on the outer peripheral surface of the larger diameter portion (1a), balls interposed between the inner raceway groove (2a) and an outer raceway groove (2b) formed on an inner surface of an outer race (3) surrounding the larger diameter portion (1a) and a ball bearing (5) including inner and outer races (6,7) and balls (9) interposed therebetween, wherein the ball bearing (5) is fitted at its inner race (6) over the smaller diameter portion (1b), and a lower end of said larger diameter shaft portion (1a) is installed and secured on a base (10); said hard disk drive device further comprising a cylindrical sleeve (14) of a rotor (12) of a motor (M) for rotating magnetic disk means (17) for storing data, said sleeve (14) being open at both its upper and lower ends, characterised in that said sleeve (14) is provided on its inner surface with upper and lower larger inner diameter portions (16a,16b) of the same diameter and a thick smaller inner diameter portion (15) formed therebetween, said thick portion (15) being clamped between the outer race (3) provided around the larger diameter portion (1a) and fitted within the lower portion (16b) of the sleeve (14) and the outer race (7) of the ball bearing (5) fitted within the upper portion (16a) of the sleeve (14). The hard disk drive device according to claim 1, wherein the cylindrical sleeve (14) is formed integrally with the rotor (12) The hard disk drive device according to claim 1 or 2, wherein the outer diameter of the inner race (6) of said ball bearing (5) is the same as that of the larger diameter portion (1a) of said stepped shaft (1), the inner diameter of the outer race (7) of said ball bearing (5) is the same as that of the outer race (3) provided around the larger diameter portion (1a) and the diameter of the balls (9) of said ball bearing (5) is the same as that of the balls (4) interposed between the outer surface of the larger diameter portion (1a) and the outer race (3) provided therearound. The hard disk drive device according to any preceding claim wherein the rotor (12) of the motor (M) is assembled stationary to the double row bearing apparatus. The hard disk drive according to any preceding claim, wherein the ball bearing (5) is removably fitted with its inner race (6) on the smaller diameter portion (1b) of the stepped shaft (1).

Inventors: OBARA RIKURO, OBARA, RIKURO
Applicants: MINEBEA KK, MINEBEA KABUSHIKI KAISHA
Application year: 1998
Main classification: G11B19
IPC codes: F16C19, H02K5, G11B19