Magnetic disk apparatus having a motor driven disk clamp

A magnetic disk apparatus has a sealed up space between a base plate and its cover. A magnetic disk with its spindle motor for driving the magnetic disk, and magnetic heads with respective carriages for displacing respective heads are enclosed in the sealed up space. Rotor unit of the spindle motor is supported by a bearing fixed to the base plate, and stator unit of tile motor is fixed to the cover.

BACKGROUND OF THE INVENTION 
This invention relates to a magnetic disc apparatus, and more specifically 
relates to an apparatus where a magnetic disk (or magnetic discs) and 
magnetic heads are contained in a sealed up space made between a base 
plate and its cover. 
FIG. 5 shows an example of a cross sectional view of such magnetic disc 
apparatus of prior art. The apparatus shown by FIG. 5 comprises a magnetic 
disk 1 rotated by a spindle motor 2, a magnetic head 3 which magnetically 
couples to the magnetic disc 1, a carriage 4 which displaces the magnetic 
head 3 in a radial direction of the magnetic disk 1, a base plate 5 on 
which the carriage 4 is mounted, and a cover 6 for making a sealed up 
space between the base plate 5 for containing the magnetic disk 1 with the 
spindle motor 2 and the magnetic head 3 with the carriage 4. 
A housing 11 of the spindle motor 2 is fixed to the base plate 5, and in a 
central portion of the housing 11, a ball bearing having an upper ball 
bearing 12 and a lower ball bearing 13, is fixed. A spindle 14 of the 
spindle motor 2 is supported rotation-free by the ball bearing. On top of 
the spindle 14, a cylindrical hub 15 having a hollow inner space is fixed 
at the axial center. 
The magnetic disc 1 is mounted on the perimeter of the hub 15, clamped by a 
clamper 16, and is rotated by the spindle 14. The spindle motor 2 
comprises a stator unit 18 and a rotor unit. The rotor unit is fixed to 
the hub 14 with its pole pieces 17 of permanent magnet and a yoke 19 which 
makes magnetic circuits between the pole pieces. The stator unit 18 
comprising stator windings and stator magnetic circuits, is fixed to the 
housing 11, surrounding the outer ring of the ball bearing. Thus, central 
axis of the rotor unit is aligned to that of the stator unit 18, and an 
adequate clearance is maintained between the faces of the pole pieces 17 
and the circumference of the stator unit 18. 
When the stator windings are excited, the rotor unit of the spindle motor 2 
rotates the hub 15 and the magnetic disk 1 clamped to the hub 15. 
In a heretofore known magnetic disc apparatus as shown in FIG. 5, all the 
component parts of the spindle motor 2 together with the housing 11 and 
the bearing of the spindle are fixed on the base plate 5, and spaces near 
the cover 6 are not effectively utilized. 
SUMMARY OF THE INVENTION 
Therefore, an important object of this invention is to design a magnetic 
disc apparatus wherein spaces near the cover is effectively utilized. 
In order to achieve the object, the stator unit of the spindle motor is 
attached to the cover in a space near the cover. 
Another object of this invention is to reduce the diameter of the housing. 
This is made feasible as the stator unit is removed from the housing. 
Still another object of this invention is to reduce number of pieces 
required for assembling the rotor unit. This is made feasible as the rotor 
unit is placed on a same side of the hub with the clamper, and the yoke of 
the rotor unit is combined to the clamper as one body. 
Thus, in an embodiment of this invention, a magnetic disc apparatus having 
a base plate and its cover making a sealed up space, comprises: 
a housing fixed to the base plate for housing a bearing, 
a spindle supported rotation-free by the bearing, 
a hub radially extended from the spindle, 
a clamper for fastening a magnetic disc to the hub, 
a rotor unit of the spindle motor fixed to the clamper, the rotor unit 
comprising pole pieces of permanent magnet and a yoke for making magnetic 
circuits between the pole pieces, 
a stator unit of the spindle motor fixed to the cover with its axis aligned 
to that of the rotor unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown an embodiment of this invention. The 
upper ball bearing 12, the lower ball bearing 13, and the spindle 14 in 
FIG. 1 are respectively similar to corresponding parts in FIG. 5, and will 
need no further explanation. The shape of the hub 15 of FIG. 1 is simpler 
than that of FIG. 5, since there are no stator unit and no rotor unit 
under the lower surface of the hub 15 of this invention. 
And the diameter of the housing 11 of FIG. 1 can be made much smaller than 
that of FIG. 5, since the stator unit 18 and the rotor unit of this 
invention are removed from the housing 11 of FIG. 1. 
In FIG. 1, at least one magnetic disc 1 is mounted on the hub 15 and is 
fastened by the clamper 16, in a similar manner as in FIG. 5. 
And on the clamper 16 is placed the rotar unit with pole pieces 17 of 
permanent magnet and the yoke 19. The stator unit 18 of this invention is 
fixed to the cover 6. The center axis of the stator unit 18 must be 
aligned to that of the rotor unit, and a predetermined clearance must be 
maintained between the faces of the pole pieces 17 and the periphery of 
the stator unit 18. Fine adjustment for the alignment is performed in a 
conventional way and is not described here. 
When stator windings of the stator unit 18 is excited, the rotor unit 
drives the hub 15 and rotates the magnetic disc 1 with the spindle 14. 
In an embodiment shown by FIG. 2, a driving circuit unit 20 for driving the 
spindle motor 2 is fixed to the cover 6. 
In an embodiment shown by FIG. 3, the clamper 16 and the yoke 19 are united 
to one body, wherein the clamper 16 is made of a magnetic material, and 
the rim of the clamper 16 is bent upward to form a short cylinder. The 
pole pieces 17 of permanent magnet are installed on the inner surface of 
the short cylinder. 
And, in an embodiment shown by FIG. 4, an inner ring of the ball bearing 
comprising the upper ball bearing 12 and the lower ball bearing 13 is 
united to the peripheral surface of the spindle 14. This unification 
further reduces the diameter of the housing 11.