1. Field of the Invention
The present invention relates to a bearing device used in a head stack assembly for angularly moving a swing arm of a hard disc drive.
2. Description of the Related Art
An example of a hard disc drive (HDD) shown in FIGS. 15 and 16 has been known. In FIGS. 15 and 16, the HDD 1 is essentially composed of a substantially rectangular box-shaped base (base plate) 2, a spindle motor 3 disposed on the base 2, and a head stack assembly (hereinafter referred to and initialized as HSA) 6 having a magnetic head 5 for writing information at a predetermined position of a magnetic disc 4 to be rotated by the spindle motor 3 and reading out the information from any desired position of the magnetic disc 4.
The HSA 6 is essentially composed of a swing arm 7 having the magnetic head 5 at its distal end, a bearing device 10 fitted in a cylindrical portion 8 provided in the swing arm 7 and having an inner race (to be described later) fitted around a shaft 9 mounted on the base 2 for supporting the swing arm 7 rotatably to the shaft 9, and a drive portion (voice coil) 11 for rotatably actuating the swing arm 7. As shown in FIG. 17, the shaft 9 is composed of a sleeve-like shaft body 9a and a flanged portion 9b formed at one end of the shaft body 9a. The shaft 9 is mounted on the base 2 with its flanged portion 9b being located on the side of the base 2.
As shown in FIG. 17, the bearing device 10 is essentially composed of two (hereinafter referred to as first and second for the sake of explanation) single-row deep groove ball bearings (hereinafter referred to as ball bearings for the sake of explanation) 12 and 13 fitted around the shaft 9 with a space S having a predetermined length and a sleeve 14. One end of an inner race 12a of the first ball bearing 12 (hereinafter referred to as a first inner race whereas an inner race of the second ball bearing 13 will hereinafter be referred to as a second inner race 13a) is in contact with the flanged portion 9b.
The sleeve 14 is essentially composed of a cylindrical sleeve body 14a, an annular projection 14b provided on the inner circumferential side of the sleeve body 14a and a flanged portion 14c formed at one end of the sleeve body 14a. The annular projection 14b of the sleeve 14 is inserted into the space S formed between outer races (hereinafter referred to as first and second outer races) 12b and 13b of the first and second ball bearings 12 and 13, whereby the sleeve 14 covers the first and second ball bearings 12 and 13 circumferentially and the flanged portion 14c is positioned at one end of the first ball bearing 12.
In order to obviate an axial displacement of the bearing device 10, for example, a pre-pressure is applied as shown in FIG. 17. Namely, under the condition that, as described above, the annular projection 14b is inserted into the space S between the first and second outer races 12b and 13b, the first and second outer races 12b and 13b are fixed to the inner surface of the sleeve body 14a with adhesives, and the first inner race 12a is fixed to the shaft 9 with adhesives. On the other hand, the second inner race 13a is fitted around the shaft 9 to be slidable. Thereafter, a pre-pressure from the direction indicated by the arrows B in FIG. 17 is applied to the outer end of the second inner race 13a. Under the condition that this pre-pressure is applied, the second inner race 13a is fixed to the shaft 9 with adhesives so as to obviate the generation of the axial displacement.
For reference, the annular projection 14b of the sleeve 14 is provided for the purpose of meeting such requirement that an interval should be needed in order to prevent the first and second ball bearings 12 and 13 from coming into contact with each other when the pre-pressure is applied thereto.
Also, as the other type of the bearing device 10, as shown in FIG. 18, instead of the above-described annular projection 14b, a spacer 15 which is discrete from the sleeve 14 may be provided.
Under the condition that the spacer 15 is inserted into the space S between the first and second outer races 12b and 13b, the first and second outer races 12b and 13b are fixed to the inner surface of the sleeve body 14a with adhesives, and the first inner race 12a is fixed to the shaft 9 with adhesives. On the other hand, the second inner race 13a is fitted around the shaft 9 to be slidable. Thereafter, a pre-pressure from the direction indicated by the arrows B in FIG. 18 is applied to the outer end of the second inner race 13a. Under the condition that this pre-pressure is applied, the second inner race 13a is fixed to the shaft 9 with adhesives, whereby the bearing device 10 shown in FIG. 18 may obviate the generation of the axial displacement. In this case, instead of the annular projection 14b, the spacer 15 may be used to prevent the contact between the first and second ball bearings 12 and 13 when the pre-pressure is applied thereto.
Also, as shown in FIG. 19, a bearing device 10 in which the sleeve 14 shown in FIG. 18 is dispensed with may be used as another type bearing device.
In the bearing device 10 shown in FIG. 19, under the condition that the spacer 15 is inserted into the space S between the first and second outer races 12b and 13b, the first and second outer races 12b and 13b are held in place, and the first inner race 12a is fixed to the shaft 9 with adhesives. On the other hand, the second inner race 13a is fitted around the shaft 9 to be slidable. Thereafter, a pre-pressure from the direction indicated by the arrows B in FIG. 19 is applied to the outer end of the second inner race 13a. Under the condition that this pre-pressure is applied, the second inner race 13a is fixed to the shaft 9 with adhesives, whereby the bearing device 10 shown in FIG. 19 may obviate the generation of the axial displacement.
For reference, as another example in the conventional art, in which the above-described spacer 15 and annular projection 14b are dispensed with, a duplex bearing has been used. This duplex bearing has such a structure that two inner races and two outer races are brought into contact with each other, respectively, when the pre-pressure is applied thereto. From this structure, an amount of the pre-pressure to be applied is determined in accordance with the manufacturing precision of the bearing, therefore, it is difficult to perform the control of the pre-pressure amount. This is inconvenient. Also, in the case where this duplex bearing is used as the bearing for the pivot of the above-described HSA 6, whenever the pre-pressure amount must be changed, the duplex bearing should be redesigned. It is difficult to actually use this type bearing as the bearing for the pivot of the HSA 6.
However, recently, a portable type personal computer or the like has been miniaturized and made thin, and also an HDD that is a recording device having a large capacity used in the portable type personal computer or the like is demanded to be miniaturized or made thin.
The miniaturization of the HDD may be coped with by making the diameter of the magnetic disc small from 3.5 inches to 2.5 inches or 1.8 inches. Also, the miniaturization of the bearing (bearing device) for the pivot of the HSA used in the interior of such HDD may be coped with by decreasing the diameter of locus races (outer races and inner races).
Incidentally, in order to meet the requirement for the making-thin, it is necessary to shorten a width of the bearing (for example, in the vertical direction in FIG. 16) for the pivot of the HSA.
However, as a matter of fact, the mere selection of the bearing having a shorter width could not suitably meet the recent strong requirement for the super thinned type size for the super thinned card type HDD.