Magnetic disk apparatus with shield for magnetic head

In a magnetic disk apparatus, a function of shielding a magnetic head is improved while maintaining the form factor with an inexpensive structure. In one embodiment, a magnetic disk apparatus has a magnetic disk, a magnetic head that records or plays back information, a magnetic head support mechanism supporting the magnetic head, a positioning mechanism that moves the magnetic head in a radial direction of the magnetic disk to place the head in position, an enclosure made of a nonmagnetic material, and a shield member made of a magnetic material. The magnetic disk, magnetic head, magnetic head support mechanism, positioning mechanism, and shield member are housed in the enclosure. The shield member has an upper shield located above the magnetic head and extending over the range of movement of the magnetic head, a lower shield located on the opposite side of the surface where the magnetic head exists and extending over the range of movement of the magnetic head, and a connecting portion connecting an outer side end portion of the upper shield and an outer side end portion of the lower shield near the outer fringes of the magnetic disk.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. JP 2004-263305, filed Sep. 10, 2004, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic disk apparatus and is especially adapted for a magnetic disk apparatus that records information on a magnetic disk by a vertical magnetic recording method.

In a magnetic disk apparatus adopting a vertical magnetic recording method, in a case where a magnetic field is applied from the outside, there is the possibility that the following problem takes place. An external magnetic field is concentrated in the main magnetic pole by the magnetic head and data recorded on the disk is destroyed because of the structure of the magnetic head. Since it is impossible to weaken the strength itself of the external stray magnetic field applied to the magnetic disk apparatus, it is necessary to impart a function of producing a shielding effect (weakening the strength of the external magnetic field) against the external magnetic field to the magnetic disk apparatus.

Accordingly, one shown in JP-A-2003-77266 (Patent Reference 1) has been devised as a conventional magnetic disk apparatus. The magnetic disk apparatus of this Patent Reference 1 is constructed to consist of a magnetic disk of a rotary disk type for recording information by a vertical magnetic recording method, a magnetic head for recording information on the magnetic disk or playing back information from the magnetic disk, a disk drive mechanism that supports movably the magnetic head in a radial direction of the magnetic disk, an enclosure, and a shield member made of a magnetic material for magnetically shielding the magnetic head, the enclosure being made up of a base and a cover.

In an embodiment associated withFIGS. 1-16of Patent Reference 1, the magnetic disk, magnetic head, and disk drive mechanism are accommodated within the enclosure. The shield member is mounted over the top, lower, and side surfaces of the outside of the enclosure including spaces located above and under the range of movement of the magnetic head (Prior Art 1).

In an embodiment associated withFIG. 17of Patent Reference 1, magnetic disk, magnetic head, disk drive mechanism, and shield member are accommodated within an enclosure. A shield member is mounted only on the base portion and cover portion which are opposite to the magnetic head (Prior Art 2).

Furthermore, in an embodiment associated withFIG. 18of Patent Reference 1, magnetic disk, magnetic head, and disk drive mechanism are accommodated within an enclosure. A cutout portion is formed in a part of the enclosure. A shield member is installed in the portion. The front-end side of the shield member extends to both sides of the magnetic disk. Its end surface is positioned oppositely to an end surface of the magnetic head (Prior Art 3).

In addition, in an embodiment associated withFIG. 19of Patent Reference 1, magnetic disk, magnetic head, and disk drive mechanism are accommodated within an enclosure. A recessed portion is formed in the outer surface of the enclosure. A shield member is installed in the recessed portion. The front-end side of the shield member extends to both sides of the magnetic disk. Its end portion is located oppositely to an end portion of the magnetic head (Prior Art 4).

BRIEF SUMMARY OF THE INVENTION

In Prior Art 1, since the shield member is mounted outside the enclosure that is remote from the magnetic head, there is the problem that it is impossible to bring out the shielding function sufficiently. Furthermore, there is the problem that the outside contour dimension is increased by an amount corresponding to the shield member. The sizes of magnetic disk apparatuses of this type are restricted to 2.5 type (mobile type), 3.5 type, and so on. Also, in a case where a magnetic shielding function is imparted, it is important that the size be within a given size (form factor).

Furthermore, in Prior Art 2, the shield member is mounted only on the base portion and cover portion that are opposite to the magnetic head. Therefore, there is the problem that it is impossible to bring out the shielding function sufficiently.

Furthermore, in Prior Art 3 or 4, a cutout or recessed portion is formed in a part of the enclosure. The shield member is installed in the portion. Therefore, it is necessary that an enclosure of a special shape be prepared and that the function of the enclosure be given to the shield member. There is the problem that the cost is increased.

In Prior Arts 1-4, it has been impossible to sufficiently bring out the shielding function against external magnetic field from a lateral direction (side direction) relative to the magnetic head.

It is a feature of the present invention to provide a magnetic disk apparatus which maintains its form factor with an inexpensive structure and which can improve a function of shielding a magnetic head.

In accordance with an embodiment of the present invention, a structure comprises a disk-shaped rotary magnetic disk; a magnetic head that records information on the magnetic disk or plays back information from the magnetic disk; a magnetic head support mechanism that supports the magnetic head; a positioning mechanism that moves the magnetic head in a radial direction of the magnetic disk to place the head in position; an enclosure consisting of a base and a cover made of a nonmagnetic material; and a shield member made of a magnetic material to magnetically shield the magnetic head. The enclosure incorporates therein the magnetic disk, the magnetic head, the magnetic head support mechanism, the positioning mechanism, and the shield member. The shield member has an upper shield located above the magnetic head and extending over a range in which the magnetic head moves, a lower shield located on a side opposite to a plane in which the magnetic head exists and extending over the range in which the magnetic head moves, and a connecting portion connecting an outer side end portion of the upper shield and an outer side end portion of the lower shield near outer fringes of the magnetic disk.

A first aspect of the present invention comprises: a disk-shaped rotary magnetic disk that records information by a vertical magnetic recording method; a magnetic head that records information on the magnetic disk or plays back information from the magnetic disk; a magnetic head support mechanism that supports the magnetic head; a positioning mechanism that moves the magnetic head in a radial direction of the magnetic disk to place the head in position; an enclosure consisting of a base and a cover made of a nonmagnetic material; and a shield member made of a magnetic material to magnetically shield the magnetic head. The enclosure incorporates therein the magnetic disk, the magnetic head, the magnetic head support mechanism, the positioning mechanism, and the shield member. The shield member has an upper shield located above the magnetic head and extending over a range in which the magnetic head moves, a lower shield located on a side opposite to a plane in which the magnetic head exists and extending over the range in which the magnetic head moves, and a connecting portion connecting an outer side end portion of the upper shield and an outer side end portion of the lower shield near outer fringes of the magnetic disk. The upper shield has a roof portion located above the magnetic head and extending over the range in which the magnetic head moves and a step portion located closer to a surface of the magnetic disk than the roof portion and extending over the range in which the magnetic head moves, the roof portion and the step portion being integral.

In the first aspect of the present invention described above, a more preferable specific example of configuration is as follows.

(1) The step portion is placed close to the surface of the magnetic disk so as to be located at a side of an end surface of the magnetic head.

(2) In addition to (1) above, the step portion is made to have a wall thickness greater than that of the roof portion. The connecting portion is connected to the step portion and made to have a wall thickness greater than that of the roof portion.

(3) In addition to (1) above, the step portion is formed to have the same thickness as the roof portion.

A second aspect of the present invention comprises: a disk-shaped rotary magnetic disk that records information by a vertical magnetic recording method; a magnetic head that records information on the magnetic disk or plays back information from the magnetic disk; a magnetic head support mechanism that supports the magnetic head; a positioning mechanism that moves the magnetic head in a radial direction of the magnetic disk to place the head in position; a ramp mounted close to outer fringes of the magnetic disk such that the magnetic head is retracted to the outside of the magnetic disk when rotation of the magnetic disk has stopped; an enclosure consisting of a base and a cover made of a nonmagnetic material; and a shield member made of a magnetic material to magnetically shield the magnetic head. The enclosure incorporates therein the magnetic disk, the magnetic head, the magnetic head support mechanism, the positioning mechanism, and the shield member. The shield member has an upper shield located above the magnetic head and extending over a range in which the magnetic head moves, a lower shield located on a side opposite to a plane in which the magnetic head exists and extending over the range in which the magnetic head moves, and a connecting portion connecting an outer side end portion of the upper shield and an outer side end portion of the lower shield near outer fringes of the magnetic disk. The connecting portion is disposed in a dead space surrounded by side walls of the ramp and the base and by outer fringes of the magnetic disk.

In the second aspect of the present invention described above, a more preferable specific example of configuration is as follows. The upper shield, the lower shield, and the connecting portion are provided with cutout portions in side surfaces corresponding to the ramp. The magnetic head goes into and out of the ramp through the cutout portions.

A third aspect of the present invention comprises: a disk-shaped rotary magnetic disk that records information by a vertical magnetic recording method; a magnetic head that records information on the magnetic disk or plays back information from the magnetic disk; a magnetic head support mechanism that supports the magnetic head; a positioning mechanism that moves the magnetic head in a radial direction of the magnetic disk to place the head in position; an enclosure consisting of a base and a cover made of a nonmagnetic material; and a shield member made of a magnetic material to magnetically shield the magnetic head. The enclosure incorporates therein the magnetic disk, the magnetic head, the magnetic head support mechanism, and the shield member. The shield member has an upper shield located above the magnetic head and extending over a range in which the magnetic head moves, a lower shield located on a side opposite to a plane in which the magnetic head exists and extending over the range in which the magnetic head moves, and a connecting portion connecting an outer side end portion of the upper shield and an outer side end portion of the lower shield near outer fringes of the magnetic disk. The connecting portion acts also as a shroud member extending peripherally near outer fringes of the magnetic disk.

In the third aspect of the present invention described above, a more preferable specific example of configuration is as follows. A spindle mechanism for rotating the magnetic disk is fitted in a central portion, and the shroud member extends half round the magnetic head.

A fourth aspect of the present invention comprises: a disk-shaped rotary magnetic disk that records information by a vertical magnetic recording method; a spindle mechanism that supports and rotates the magnetic disk; a magnetic head that records information on the magnetic disk or plays back information from the magnetic disk; a magnetic head support mechanism that supports the magnetic head; a positioning mechanism that moves the magnetic head in a radial direction of the magnetic disk to place the head in position; an enclosure consisting of a base and a cover made of a nonmagnetic material; and a shield member made of a magnetic material to magnetically shield the magnetic head. The enclosure incorporates therein the magnetic disk, the magnetic head, the magnetic head support mechanism, the positioning mechanism, and the shield member. The shield member consists of a shield disk located above the magnetic head, a thin film of magnetic material coated on a lower surface side of the magnetic disk, and a part of the spindle mechanism that connects the shield disk and the thin film of magnetic material.

According to the present invention, it is-possible to obtain a magnetic disk apparatus which protects its form factor with an inexpensive structure and which can improve the function of shielding a magnetic head.

DETAILED DESCRIPTION OF THE INVENTION

Plural embodiments of the present invention are hereinafter described using the figures. Identical symbols in the figures of the embodiments indicate the same or corresponding objects. Note that more effective ones can be made by appropriately combining the embodiments according to the need.

First Embodiment

A magnetic disk apparatus of a first embodiment of the present invention is described usingFIGS. 1 to 8. The whole of a magnetic disk apparatus50of the present embodiment is described with reference toFIGS. 1 to 3.FIG. 1is a perspective view of the magnetic disk apparatus50of the present embodiment.FIG. 2is a cross-sectional view on A-A ofFIG. 1.FIG. 3is a cross-sectional view as viewed from B direction ofFIG. 1. Note that the magnetic disk apparatus50ofFIG. 1is shown in a state where the cover1bof the enclosure1has been removed.

The magnetic disk apparatus50has a spindle mechanism2, a magnetic disk3, a magnetic head support mechanism4, a positioning mechanism6, a shield member10, and a ramp30which are enclosed and housed within the enclosure1.

The enclosure1is made up of a lunch-box type base1aand a cover1bthat plugs up the upper surface opening in the base1a. The base1aand cover1bhave the same structure as the enclosure of a general magnetic disk apparatus and are made of a nonmagnetic material (e.g., aluminum). The base1aforms a shroud surface21accommodating the magnetic disk3. This shroud surface21is a cylindrical surface whose total periphery is partially cut out. A magnetic head slider9and the magnetic head support mechanism4go into and out of the disk surface side through the cutout portion.

The spindle mechanism2is intended to rotate the magnetic disk3, is mounted to a central portion of the bottom surface of the base1a, and is made up of a drive portion and a rotating portion.

The magnetic disk3consists of a disk-shaped rotary magnetic disk that records information on annular tracks by a vertical magnetic recording method. The disk is fixed to the rotating shaft portion of the spindle mechanism2and rotated at a high speed. The annular tracks are multiple in number and extend from the inner surface to the outer surface of the magnetic disk3. A magnetic head9athat is a device portion is moved to each track and placed in position such that a recording or playback operation is performed. The magnetic disk3is single in number. One magnetic head9ais installed on each of the front surface side (cover side) of the magnetic disk3and the rear surface side (base side). In the present embodiment, the magnetic disk3has an outside diameter of 65 mm and an inside diameter of 24 mm, and is a magnetic disk apparatus having such a size that it is generally known as a 2.5 type magnetic disk apparatus.

The magnetic head support mechanism4is intended to support the magnetic head9athat records information on the magnetic disk3or plays back information from the magnetic disk3. As shown inFIG. 2, the mechanism is made up of the magnetic head slider9and a suspension41. The magnetic head9ais carried on the slider, which floats over the magnetic disk3. The magnetic head slider9is supported to the front-end side of the suspension.

The magnetic head slider9is so constructed that the magnetic head9ais installed to the front-end side and that the slider is floated from the disk surface by an air stream created as a result of rotation of the magnetic disk3. The magnetic head slider9(magnetic head9a) is supported movably in a radial direction of the magnetic disk3. Also, the suspension41provides a pivot support of the magnetic head slider9such that motion of the slider is not restricted. The suspension gives a pressing load that presses the magnetic head slider9against the disk surface to the magnetic head slider9. The base side (i.e., the base side of the magnetic head support mechanism4) of the suspension41is connected to an arm5.

In the present embodiment, the magnetic head support mechanism4is mounted on both sides of the magnetic disk3. It may also be mounted only on one side of the magnetic disk3.

The positioning mechanism6is constructed such that it is made up of the arm5, a voice coil motor7, and a pivot bearing8. The arm5is rotated (swung) about the pivot bearing8by the voice coil motor7to place the magnetic head9ain position over a desired track on the magnetic disk3.

A ramp30is intended to retract the magnetic head9aout of the magnetic disk3during stop of rotation of the magnetic disk3(during unloading). The ramp is mounted in the position of the cutout portion in the shroud21near the outer fringes of the magnetic disk3. During the retraction, a tab42(seeFIG. 4) mounted at the front end of the magnetic head support mechanism4makes contact with the ramp30and slides upward. As a result, the magnetic head9ais also peeled off from the surface of the magnetic disk3. Also, when rotation of the magnetic disk3is started (during loading), the tab42of the magnetic head support mechanism4retracted to the outside of the magnetic disk3slides down the ramp30in a reverse manner. Thus, the magnetic head9ais lowered to the disk surface. This mechanism is used widely in 2.5 type magnetic disk apparatus and so on, and is known as a loading/unloading mechanism. To mount the ramp30near the outer fringes of the magnetic disk3, the upper shield11, lower shield12, and connecting portion13are partially cut out, and a cutout portion15is formed in the shield member10.

Then, the shield member10is described with reference toFIGS. 1-5.FIG. 4is an enlarged view of main portions ofFIG. 2.FIG. 5is an enlarged perspective view of a part of the shield member10ofFIG. 2when the member is in an isolated state. InFIGS. 4 and 5, the dimensions of various portions are also shown.

The shield member10is made of a magnetic material to magnetically shield the magnetic head9a. This shield member10is constructed such that it comprises an upper shield11located above the magnetic head9aand extending over a range of movement of the magnetic head9a, a lower shield12located on a side opposite to the surface where the magnetic head9aexists and extending over the range of movement of the magnetic head9a, a connecting portion13connecting an outer side end portion of the upper shield11and an outer side end portion of the lower shield12near the outer fringes of the magnetic disk3, and a mounting portion14mounted to the inner surface of the base1a, it being noted that these components are integral. In this integral structure, the various components may be made of one member. Alternatively, the various components may be made of separate members and firmly mounted together. The shield member10is shaped like the letter U when viewed from a side. The upper and lower shields11and12are mounted such that the magnetic disk3is sandwiched between them.

The upper shield11is constructed such that it comprises a roof portion11alocated above the magnetic head9aon the upper side of the disk and extending over the range of movement of the magnetic head9aand a step portion11blocated closer to the disk surface than the roof portion11aand extending over the range of movement of the magnetic head9a, it being noted that the roof portion and step portion are integral. The lower shield12is constructed such that it comprises a roof portion12alocated under the magnetic head9aon the lower side of the disk and extending over the range of movement of the magnetic head9a, and a step portion12blocated closer to the disk surface than the roof portion12aand extending over the range of movement of the magnetic head9a. The roof portion12aand step portion12bare integral.

In particular, the step portion11bis made to have a wall thickness greater than that of the roof portion11a. The cross-sectional shape of the upper shield11is shaped like the letter L. Making the shape like the letter L makes it possible to mount the shield member10close to the magnetic head9amounted on the end surface of the magnetic head slider9. The purpose is to increase the effect of shielding against external magnetic field. In other words, the roof portion11ais mounted on the mounting side of the suspension41of the magnetic head slider9. A step portion11bclose to the disk surface is mounted so as to cover the magnetic head9aon the rear-end side of the magnetic head slider9. The step portion11bmakes it possible to increase the effect of shielding against external magnetic field, especially from a lateral direction. Furthermore, by making the step portion11bhave a large wall thickness, the magnetic path resistance of the step portion11bcan be reduced. Consequently, magnetic flux applied to the roof portion11acan be guided to the connecting portion13through the step portion11bhaving a small magnetic path resistance. From this respect, too, the shielding effect can be increased.

The structure of the lower shield12is also identical in shape with the upper shield11, and is made up of roof portion11aand step portion11b. The step portion11bextends toward the surface of the disk3so as to cover the magnetic head9a. In this way, the lower shield12performs the same functions as the upper shield11and so repeated description is omitted.

The upper shield11and lower shield12extend from the inner surface to the outer surface of the magnetic disk3, and are connected near the end surface on the side of the disk outer surface by the connecting portion13. As shown inFIG. 3, the upper shield11is positioned such that the magnetic head9aof the magnetic head slider9is seen from the gap between the step shield11aand magnetic disk3.

The connecting portion13is connected to the thick-walled step portion11band made to have a wall thickness greater than that of the roof portion11a. Consequently, the magnetic path resistance of the connecting portion13can be reduced. Therefore, magnetic flux applied to the upper shield11or lower shield12can be guided to the upper shield11or lower shield12through the connecting portion13of low magnetic path resistance. From this respect, too, the shielding effect can be enhanced. Also, the connecting portion13is positioned in a dead space surrounded by the ramp30, side wall of the base1a, and outer fringes of the magnetic disk3. In consequence, the shield member10can be accommodated within the enclosure1while maintaining the form factor of the magnetic disk apparatus50.

A mounting portion14for the base1ais protrusively mounted to the base side of the connecting portion13. In the present embodiment, the mounting portion14is mounted to the connecting portion13. This mounting portion14may be eliminated, and the lower shield12may be directly mounted to the base1a. By adopting this structure, the height (thickness) of the magnetic disk apparatus50can be reduced, achieving a miniaturization. Also, a higher shielding effect can be obtained by increasing the thickness of the lower shield12.

The front end of the roof portion11aof the upper shield11extends to over the magnetic head slider9as shown inFIG. 4, and is connected to the step portion11bbehind the magnetic head slider9. The surface of the step portion11bopposite to the magnetic disk extends to the disk surface.

The length (3.6 mm) of the upper roof portion11ais greater than the sum of the length of the loading/unloading tab42mounted at the front end of the suspension41and the length of the magnetic head slider9. The length is so set that if the upper portion of the magnetic head slider9is fully covered by the upper roof portion11a, the tab42does not strike the step portion11b.

Furthermore, the distance (0.7 mm) between the roof portion11a(surface opposite to the suspension) and the back surface of the magnetic head slider9(suspension mounting surface) is set to a dimension that is required to prevent the suspension4from striking the roof portion11a. Also, the thickness (0.8 mm) of the roof portion11aand the thickness (1.5 mm) of the step portion11bare such thicknesses that the roof portion is accommodated within the 2.5 type magnetic disk apparatus without touching the cover1b. In addition, the thicknesses are set as large as possible to enhance the shielding effect. The distance (0.3 mm) between the step portion11band the disk surface is greater than the distance that the magnetic head slider9floats from the disk surface to prevent the magnetic disk3from coming into contact with the step portion11bif the disk3is deformed by external shock. In the present embodiment, it is assumed that the size of the magnetic head slider9is a so-called pico-sized (1.25 mm×1 mm×0.3 mm) slider. However, the present invention can also be applied to a slider of arbitrary size.

The length (7.2 mm) of the step portion11bis set to such a dimension that a space for mounting the connecting portion13on the end surface of the step portion11bis secured and that rigidity of the upper shield11can be secured as shown inFIG. 5. Also, a side surface13cof the connecting portion13, a side surface11cof the upper shield11, and a side surface12cof the lower shield are configured to form a cutout portion15(seeFIG. 1) when viewed from a flat plane. This cutout portion15is intended to secure the functions of the portions11,12, and13of the shield member10and to permit the loading/unloading ramp30to extend to over the disk surface. This cutout portion15can circumvent contact between the ramp30and shield member10. The positional relations among the shield member10, magnetic head support mechanism4, magnetic disk3, and loading/unloading ramp30are as shown inFIG. 1. That is, the shield member10has an open structure in which the sides of the connecting portion13on the magnetic head slider side, upper shield11, and magnetic head side on the outer side of the lower shield12are cut out. The member is located close to the ramp30.

The shielding effect in the shield member10of the present embodiment is next described with reference toFIGS. 6A and 6B.FIG. 6Ais an explanatory view of a model with a step.FIG. 6Bis a characteristic diagram showing a shielding effect owing to the stepped model.

The stepped model is of the same structure as the shield member10of the present embodiment, and consists of an upper shield11having a roof portion11aand a step portion11b, a lower shield12having a roof portion12aand a step portion12b, and a connecting portion13connecting them. A calculation using the stepped model was performed over the whole shield member10. Since the upper shield11and lower shield12have a symmetrical structure, only calculation meshes on each surface of the upper shield11, upper portion of the connecting portion13, and magnetic disk3are shown inFIG. 6A.

In this stepped model, the magnetic field strength at a magnetic head position in a case where an external magnetic field was applied perpendicularly to the surface of the magnetic disk3was calculated. The strength of the external magnetic field was set to300gauss. The sense of the magnetic flux was set to be perpendicular to the disk surface. The sense was set perpendicular to the disk surface because this was a direction in which the effect on the recording surface was greatest. The results of the calculation are shown inFIG. 6B.FIG. 6Bshows a relation between a disk radial position of the magnetic head9aand the magnetic field strength. The upper shield11extends from 13 mm to 29 mm in terms of the radial position of the disk. In a region with radial positions of 30 mm or more, the shield member10is not present. As heights from the surface of the magnetic disk3, calculations were performed at positions of 0.15 mm and 0.3 mm from the disk surface. Generally, the height of the magnetic head9aof the magnetic head slider9is 0.3 mm. The positions were selected to evaluate the effects at the same height as that height and at a height half that height.

As is obvious fromFIG. 6B, the strength was reduced down to about 100 gauss on the inner side of the magnetic disk3by the shield member10of the stepped model although the external magnetic field was 300 gauss. Also, the strength was reduced to about 70 gauss on the external side. Little variations of the height from the disk surface were observed. In this way, according to the present embodiment, the strength of the external magnetic field can be reduced to about one third or less at the position of the magnetic head.

When the radial position is 30 mm or more, the magnetic field strength increases suddenly, because the field is outside the upper shield11, i.e., the shielding effect is reduced by the cutout portion15. Here, radial positions of 30 mm or more are not used as the magnetic recording area and so no problems take place. If it is desired to use a wider range (outer periphery), the cutout portion should be reduced or otherwise be coped with.

Fundamentally, the shield member10may be made of any material as long as it is a magnetic material. In the present example of calculation, iron (SPCC) used in the voice coil motor7is assumed. Calculations were performed using its physical property values. At that time, the saturation magnetic flux density was set to 2.2 Tesla (T). Other usable materials include corrosion-resistant stainless (such as SUS430). Where iron is used, it is desired to form coating to prevent corrosion and dust generation. In particular, this is mounted inside the magnetic disk apparatus50. Because of rust and generation of dust, it is bitten in between the magnetic head slider9and the magnetic disk3, thus preventing deterioration of the floating characteristics of the magnetic head slider9.

The mechanism of the shielding effect of the embodiment is next described with reference toFIG. 5. Where the external magnetic field perpendicular to the disk surface is a magnetic field flowing from above the disk surface downwardly, for example, magnetic flux100is concentrated in the upper shield11as shown in a conceptual view of the flow inFIG. 5. The flux flows into the lower shield12via the connecting portion13, and is returned to the outside from the lower shield12. As is obvious from this, the magnetic flux of the external magnetic field flows so as to avoid the magnetic head3inserted in the shield member10. Therefore, the magnetic field is concentrated in the magnetic head9afor vertical recording. Malfunction such as erasure of information on the disk surface or writing of erroneous data into the disk surface can be prevented. Where the external magnetic field perpendicular to the disk surface flows from below the disk surface upwardly, the magnetic flux flows into the shield member10in a reverse manner. A similar shielding effect is exhibited.

The shielding effect in a case of a shield member having no step but having the same outside dimension as the stepped shield member ofFIG. 6is next described with reference toFIGS. 7A and 7B.FIG. 7Ais an explanatory view of a model having no step.FIG. 7Bis a characteristic diagram showing the shielding effect owing to the model having no step. The shield member10ofFIG. 7has no step portion unlike the shield member10ofFIG. 6. An upper shield11having the same thickness as the roof portion11ais fabricated in the same size as the upper shield11of the shield member10ofFIG. 6. A lower shield12is also fabricated similarly. Calculational conditions are the same as those ofFIG. 6.

As is obvious fromFIG. 7B, in the stepless shield member10, the magnetic field strength is about 160 gauss at the inner surface of the disk and about 130 gauss at the outer surface. It can be seen from this that even the stepless shield member10can reduce the external magnetic field by about 50% to 60%. It can be seen from this point of view that the present invention is effective if there is no step portion. However, provision of a step portion makes the shielding effect more effective.

A shield member10which has shortened the distance between the step portion11bof the upper shield11and the disk surface is next described with reference toFIGS. 8 and 9.FIG. 8is an explanatory view of a modified example of the shield member10of the present embodiment.FIG. 9is a characteristic diagram showing the shielding effect owing to the shield member10ofFIG. 8.FIG. 9Ais a characteristic diagram in a case where the distance Lg is 0 mm.FIG. 9Bis a characteristic diagram in a case where the distance Lg is 0.6 mm.

The shield member10shown inFIG. 8is placed close to the disk surface such that the distance Lg between the step portion11band the disk surface is smaller than the thickness Ls of the magnetic head slider9and that the step portion11bis located at a side of the magnetic head end surface. That is, the relation of the following formula (1) is established.
Ls−Lg=Ld>0  (1)

In the upper shield11ofFIGS. 4 and 6, the distance Lg between the step portion11band the disk surface is 0.3 mm, which is the same as the thickness Ls of 0.3 mm of the magnetic head slider9. It cannot be said that the step portion11bis close to the disk surface up to a side of the magnetic head end surface.

As shown inFIG. 8, a magnetic head device9ais mounted at an end surface (surface perpendicular to the disk surface) of the magnetic head slider9and so the magnetic head device portion9ais surrounded more as the distance Lg between the step portion11band the disk surface is reduced, increasing the shielding effect. Also, for an external magnetic field incident obliquely to the disk surface or an external magnetic field incident at an angle almost parallel to the disk surface, the magnetic flux less strikes the magnetic head device portion directly. Therefore, an improvement of the shielding effect can be expected. For this reason, malfunction in recording and playback with a more intense oblique magnetic field or parallel magnetic field occurs less frequently. The reliability of the apparatus can be improved. On the other hand, if the distance Lg is too small, there is the possibility that an external shock deforms the magnetic disk3, which in turn makes contact with the step portion11b. Therefore, it is necessary to secure appropriate distance Lg in a corresponding manner to the magnitude of the external shock.

Calculated magnetic field strengths in cases where the distance Lg is 0 mm and 0.6 mm are shown inFIG. 9. Where the distance Lg is 0 mm, i.e., the step portion11bis made to extend to the disk surface, the external magnetic field can be improved by about 30% compared with the case where the distance Lg is 0.3 mm (in the case ofFIGS. 4 and 6). On the other hand, where the distance Lg is set to 0.6 mm, the field deteriorates by about 20% compared with the case where the distance Lg is 0.3 mm. Therefore, the step portion11bis preferably placed closer to the disk surface with a view to improving the shielding effect.

As described so far, in the present embodiment, an external magnetic field incident perpendicularly to the disk surface can be reduced greatly. Therefore, even in a magnetic disk apparatus50of the vertical recording system, malfunction in recording and playback due to external magnetic field does not take place. The highly reliable, high recording density (large capacity) magnetic disk apparatus50can be accomplished. Furthermore, in the present embodiment, the shield member10is mounted in the magnetic disk apparatus50without modifying main constituent members such as cover1band base1a. Therefore, the shield member10is mounted while maintaining the form factor. A decrease in the productivity (cost increase) due to increased size of the apparatus or exchange of parts is prevented. With respect to the shape of the shielding member10, if the step is formed so as to surround the magnetic head10a(such that it protrudes to the magnetic disk surface), the shielding effect can be improved remarkably. Also, improvement of the shielding effect against a magnetic field incident obliquely or parallel to the disk surface can be anticipated.

Second Embodiment

A second embodiment of the present invention is next described usingFIG. 10.FIG. 10is a cross-sectional view of main portions of a magnetic disk apparatus of the second embodiment of the present invention. This second embodiment differs from the first embodiment in the respects described in the following. In the other respects, the second embodiment is fundamentally the same as the first embodiment.

The differences between this second embodiment and the first embodiment are (i) only one magnetic head9is on the top surface of the magnetic disk3, (ii) the shield member10is stamped out of a single metal sheet or plate, and (iii) the lower shield12is mounted parallel to the disk surface. In the same way as in the first embodiment, the lower shield12may be directly mounted to the base1a. This facilitates machining the shield member10. The productivity can be improved. Also, where there is only one magnetic head9on the upper surface of the disk as in the second embodiment, the shield member10can be reduced if the lower shield12is made flat. This makes it possible to reduce the thickness of the magnetic disk apparatus50further. In the second embodiment, too, a shielding effect against an external magnetic field can be obtained. There is the advantage that malfunction during recording and playback due to external magnetic field can be prevented. Furthermore, the shield member10can be installed while maintaining the form factor. In addition, the productivity can be improved. Since the shield member10can be thinned, the apparatus can be thinned further.

Third Embodiment

A third embodiment of the present invention is next described usingFIG. 11.FIG. 11Ais a plan view of a magnetic disk apparatus of the third embodiment of the present invention.FIG. 11Bis a cross-sectional view on C-C ofFIG. 11A. This third embodiment differs from the first embodiment in the respects described in the following. In the other respects, the third embodiment is fundamentally the same as the first embodiment.

The differences between the third embodiment and the first embodiment are (i) only one magnetic head9is on the top surface of the magnetic disk3, (ii) upper shield11and lower shield12are flat parallel plates, and (iii) the connecting portion13of the first embodiment acts also as a shroud member22around the disk. In the third embodiment, respective one end of the upper and lower shields11and12is connected to the shroud member22near the outer fringes of the magnetic disk3. The shroud member22is made of a magnetic material. That is, the shield member10is made up of upper shield11, lower shield12, and shroud member22.

As shown inFIG. 11A, the shroud member22is positioned at the outer fringes of the magnetic disk3, and is mounted to extend about half (about 180 degrees) round the magnetic disk3on the side where the magnetic head9aexists. The distance between the shroud member22and the outer fringes of the disk is preferably reduced from a viewpoint of reduction of flow-induced oscillations in the magnetic disk3. However, it is necessary to form an appropriate gap to avoid their contact because of variations in machining accuracy. In the third embodiment, this gap is set to about 0.6 mm. Reduction in the flow-induced oscillations in the magnetic disk3has become more important issues in 3.5 type magnetic disk apparatus and so on of higher rotational speed. The shroud member22can be placed close to the disk end surface more accurately by permitting the shroud member22to be mounted to the disk apparatus50from the outside. In this way, there is another advantage that the effect of reducing flow-induced oscillations in the magnetic disk3can be accomplished readily. Obviously, the third embodiment can be applied to a 3.5 type magnetic disk apparatus as well as to a 2.5 type magnetic disk apparatus.

As can be seen fromFIG. 11B, the height Lsh from the upper surface of the disk to the upper end (free end) of the shroud member22is greater than the thickness Ls of the magnetic head slider9(Lsh>Ls). However, in the portions into which the magnetic head support mechanism4and arm5move outside the outer fringes of the magnetic disk3, the height from the upper surface of the disk to the upper end of the shroud member22is smaller than the thickness of the magnetic head slider9.

In the third embodiment, the shroud member22acts also as the connecting portion between the upper shield11and lower shield12. The shroud member22is mounted to extend about half round the magnetic disk3about the magnetic head9a. Furthermore, by setting the height Lsh of the end surface of the shroud member22from the disk upper surface greater than the thickness Ls of the magnetic head slider9, when an external magnetic field almost parallel to the disk surface is applied, magnetic flux100enters from one end of the shroud member22because the height of the shroud member22is greater than the magnetic head slider9. The flux passes through the shroud member22and is guided to the other end of the shroud member22. A pictorial view of the flow of the magnetic flux100is shown inFIG. 11B. In this way, the magnetic flux flows off the magnetic head. Therefore, a shielding effect can be expected even against a magnetic field parallel to the disk surface.

It is to be noted that in the third embodiment, Lsh>Ls is set. Even when both are substantially identical, a shielding effect is exhibited although the effect of the shielding decreases.

As described so far, in the third embodiment, in a case where it is placed in an external magnetic field parallel to the disk surface, a shielding effect can be expected. Also, by making the shroud member22a connecting portion, the number of components can be reduced. In addition, fluid-induced oscillations due to the shroud member22can be reduced. In the third embodiment, too, there is a shielding effect against an external magnetic field incident perpendicularly to the disk surface in the same way as in the first embodiment.

In the third embodiment, a so-called contact start-stop (CSS) system is adopted, in which when the magnetic disk3is at rest, the magnetic head slider9makes contact with the disk surface, and during rotation, the slider floats over the disk surface. The CSS system is widely used in 3.5 type apparatus and so on. Therefore, a cutout portion for inserting a ramp for loading and unloading is not formed in the shield member10. Obviously, the present system can be applied to the loading/unloading system.

Also, in the present embodiment, the shroud member22is made to extend about a half circle, for the following reason. For magnetic flux incident parallel to the disk surface from the opposite side of the shroud member22, the magnetic head3is shadowed by the spindle mechanism2and so a shielding effect owing to the spindle mechanism2made of a magnetic material can be expected. However, it is obvious that if the shroud member22is made to extend the whole circle except for the portion in which the arm5is inserted, a higher shielding effect (shielding effect against magnetic flux from all the angles) can be expected. In addition, if the shroud member22extends over a range narrower than a half circle, a shielding effect against a magnetic field perpendicular to the disk surface is produced.

Fourth Embodiment

A fourth embodiment of the present invention is next described usingFIG. 12.FIG. 12is a cross-sectional view of main portions of a magnetic disk apparatus of the fourth embodiment of the present invention. This fourth embodiment is different from the first embodiment in the respects described in the following. In the other respects, the fourth embodiment is fundamentally the same as the first embodiment.

The differences between the fourth embodiment and the first embodiment are that (i) the upper shield11of the first embodiment is replaced by a shield disk23placed above the magnetic head slider9, (ii) the lower shield12of the first embodiment is replaced by a thin film of magnetic material24coated on the lower surface side of the magnetic disk3, and (iii) the connecting portion13of the first embodiment is replaced by the spindle mechanism2. The spindle mechanism2has a rotating shaft25, a spacer26, and a clamp27which are made of a magnetic material.

The shield disk23may be made of a magnetic material such as iron or stainless. Also, a shielding effect can be accomplished without fundamentally varying the configuration of the magnetic disk apparatus50by bringing the shape of the shield disk23into agreement with the shape of the magnetic disk for vertical. The upper shield is held by the clamp27. The clamp27is fixed to the spindle mechanism2by screws (not shown). A soft magnetic material (in particular, iron or the like) used as an underlying film of the disk for vertical is used as the thin film of magnetic material24. The rotating shaft25and spacer26are magnetically coupled to the shield disk23and thin film of magnetic material24, thus forming a connecting portion between the shield disk23and the thin film of magnetic material24.

In the fourth embodiment, the upper and lower disks23and24are used as shields and so the space between the upper and lower shields can be narrowed. In addition, it is not necessary to mount additional parts by making the connecting portion a spacer having magnetic characteristics. Additionally, the upper and lower shields can be increased compared with the first embodiment. Therefore, a shielding effect against magnetic flux oblique or parallel to the disk surface can be obtained. Further, in the fourth embodiment, too, a shielding effect against an external magnetic field perpendicular to the disk surface is obtained in the same way as in the first embodiment.