Magnetic disk vibration-suppressing mechanism having shroud-narrowing gap

Embodiments in accordance with the present invention relate to greatly decreasing vibrations of a rotary disk at a portion where vibration on the disks is to be suppressed in a vibration-suppressing mechanism for rotary disks while enabling the rotary disks to be incorporated in the shroud surface. In one embodiment, the vibration-suppressing mechanism for rotary disks comprises at least one rotary disk and a shroud surface extending along and facing the outer circumferential edges of the disk. The shroud surface is so formed as to possess a portion where a gap between the outer circumferential edge of the disk and the shroud surface becomes small near a portion where the vibration of the disk is to be suppressed.

CROSS-REFERENCES TO RELATED APPLICATIONS

The instant nonprovisional patent application claims priority to Japanese Patent Application 2006-068723, filed Mar. 14, 2006 and incorporated by reference in its entirety herein for all purposes.

BACKGROUND OF THE INVENTION

In an information recording device such as a magnetic disk drive or an optical disk device that records and reproduces information to and from a disk that rotates, vibration in the disk causes a deviation in position between the head for recording and reproducing information and the track which is a place where information is recorded on the disk, and has, therefore, been desired to be decreased. In recent years, in particular, the positioning maintaining a high precision has been requested along with an increase in the recording density, and it is becoming more important to decrease vibration in the disk caused by the disturbance in the flow of air in the device, which is called disk fluttering, accompanying an increase in the rotational speed of the disk.

A conventional magnetic disk drive has been disclosed in, for example, JP-A-11-232866 (patent document 1). The magnetic disk drive of the patent document 1 includes a rotary magnetic disk, a head for recording or reproducing information into or from the magnetic disk, and a head support mechanism for supporting the head, wherein a shroud is provided surrounding the outer circumference of the magnetic disk except a portion where a carriage arm linked to the head support mechanism is inserted, and a gap between the outer circumferential edge of the magnetic disk and the shroud surface is selected to be not smaller than 0.1 mm but not larger than 0.6 mm. There has been described that the above constitution eliminates a difference in the air pressure occurring on both surfaces (front and back surfaces) of the disk and, as a result, decreases the fluttering.

A conventional disk flutter-suppressing device has been disclosed in, for example, JP-A-2000-331460 (patent document 2). The disk flutter-suppressing device of the patent document 2 includes a disk spindle mechanism having one or a plurality of disks, wherein squeeze air bearing plates having a partial annular flat surface expanding in the circumferential direction and in the radial direction, are fixed onto the uppermost surface, onto the lowermost surface, or onto both disk surfaces, or onto the surfaces on one side of all disks facing the disk surfaces maintaining a gap of not larger than 0.3 mm. There has been described that the above constitution is effective in suppressing the disk fluttering owing to the damping effect of the squeeze air films.

In the magnetic disk drive of the above patent document 1, however, the outer circumferential edge of the magnetic disk is brought close to the whole shroud surface. At the time of incorporating the magnetic disk, therefore, the outer circumferential edge of the magnetic disk is likely to come into collision with the shroud surface leaving a problem from the standpoint of incorporating the magnetic disk.

In the disk flutter-suppressing device of the above patent document 2, the squeeze air bearing plates are brought close to the recording surface of the magnetic disk and are, therefore, likely to come in contact with the recording surface of the magnetic disk. In case they come in contact, the recording surface is damaged arousing a problem concerning reliability in the recording. In the slit shroud of the above patent documents 3 and 4, a gap between the disk and the slit shroud is uniform and the slit shroud is opened at a side which does not face the disk.

When a portion is specified for suppressing the vibration of the rotary disk, the portion where vibration is to be suppressed may be effectively handled. In information recording units such as a magnetic disk drive and an optical disk drive, it is becoming necessary to accomplish the positioning highly precisely on a track of a high recording density, and it is particularly important to lower the amplitude of vibration at the head position.

BRIEF SUMMARY OF THE INVENTION

Embodiments in accordance with the present invention relate to greatly decreasing vibrations of a rotary disk at a portion where vibration on the disks is to be suppressed in a vibration-suppressing mechanism for rotary disks while enabling the rotary disks to be incorporated in the shroud surface. In the particular embodiment shown inFIGS. 1-2, the vibration-suppressing mechanism for rotary disks comprises at least one rotary disk1and a shroud surface2aextending along and facing the outer circumferential edges of the disk1. The shroud surface is so formed as to possess a portion where a gap between the outer circumferential edge of the disk1and the shroud surface2abecomes small near a portion4where the vibration of the disk1is to be suppressed.

For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments in accordance with the present invention relate to a vibration-suppressing mechanism for rotary disk, information recording device and magnetic disk drive.

Embodiments of the present invention provide a vibration-suppressing mechanism for rotary disks, which is capable of greatly decreasing vibration at a portion where vibration on the disk is to be suppressed while enabling the rotary disk to be incorporated in the shroud surface.

Embodiments of the present invention also provide an information recording device and a magnetic disk drive which are capable of greatly decreasing vibration in the disk at the head position while enabling the disk to be incorporated in the shroud surface maintaining reliability in the recording of disk.

A first embodiment of the present invention comprises one or a plurality of rotary disks and a shroud surface extending along and facing the outer circumferential edges of the disks, wherein the shroud surface is so formed as to possess a portion where a gap between the outer circumferential edges of the disks and the shroud surface becomes small near a portion where the vibration of the disk is to be suppressed.

Described below are more configurations of the first embodiment of the invention.

(1) The shroud surface is positioned at a portion where the gap is the smallest between the shroud surface and the outer circumferential edges of the disks on a line that connects the axis of rotation of the disks to a portion where the vibration is to be suppressed, the shroud surface being so formed that the gap gradually increases as it goes away from the above portion.

(2) The shroud surface is so formed that portions thereof where the gap is increasing are symmetrical along the rotational direction of the disk starting from a portion where the gap is the smallest between the outer circumferential edge of the disk and the shroud surface.

(3) The shroud surface of a portion where the gap becomes the smallest between the outer circumferential edges of the disks and the shroud surface is formed in an arc of a radius of curvature greater than the arc of the shroud surface of any other portion.

(4) When a minimum gap between the disk and the shroud is denoted by d and the radius of the disk by r, the shroud surface is so formed that the ratio d/r is in a range of not larger than 0.002 but is not smaller than 0.0005.

(5) The portion where the shroud surface becomes narrow has an angle of not smaller than 90 degrees as measured with the axis of rotation as a center, and is so located as to include a line that connects the axis of rotation of the disks to the portion where the vibration is to be suppressed.

A second embodiment of the present invention is concerned to an information recording device having a spindle motor, a disk rotated by the spindle motor, a head for recording or reproducing information into or from the disk, and a shroud surface extending along and facing the outer circumferential edge of the disk, wherein the shroud surface is so formed as to possess a portion where a gap between the outer circumferential edge of the disk and the shroud surface becomes small near the head which is a portion where the vibration of the disk is to be suppressed.

Described below are more configurations of the second embodiment of the present invention.

(1) The shroud surface of a portion where the gap becomes small between the outer circumferential edge of the disk and the shroud surface is formed in an arc of a radius of curvature greater than the arc of the shroud surface of any other portion.

(2) When a minimum gap between the outer circumferential edge of the disk and the shroud is denoted by d and the radius of the disk by r, the shroud surface is so formed that the ratio d/r is in a range of not larger than 0.002 but is not smaller than 0.0005.

(3) The should is installed so as to move at a portion where a small gap is formed by the shroud surface near the head, the shroud forming the shroud surface facing the outer circumferential edge of the disk, and provision is made of a moving mechanism which holds the movable shroud close to the disk when the disk is rotating, and holds the movable shroud away from the disk when the disk is halting.

(4) In (3) above, the movable should is supported at an end on one side thereof so as to rotate, a magnetic member is installed on the movable shroud at an end on the other side thereof, and a solenoid coil is installed so as to adsorb and release the magnetic member.

A third embodiment of the present invention is concerned with a magnetic disk drive comprising a spindle motor, a magnetic disk rotated by the spindle motor, a magnetic head that moves on the magnetic disk in a radial direction to record or reproduce information into or from the magnetic disk, a shroud surface extending along and facing the outer circumferential edge of the magnetic disk, and an enclosure for containing the magnetic disk, the magnetic head and the shroud surface, wherein the shroud surface is so formed as to possess a portion where a gap between the outer circumferential edge of the disk and the shroud surface becomes small near the magnetic head which is a portion where the vibration of the magnetic disk is to be suppressed.

Further, a fourth embodiment of the invention is concerned to a magnetic disk drive comprising a spindle motor, a magnetic disk rotated by the spindle motor, a magnetic head that moves on the magnetic disk in a radial direction to record or reproduce information into or from the magnetic disk, a shroud surface extending along and facing the outer circumferential edge of the magnetic disk, and an enclosure for containing the magnetic disk, the magnetic head and the shroud surface, wherein the shroud surface is formed being partly brought close to the outer circumferential edge of the magnetic disk, so that the amplitude of the magnetic disk near the magnetic head is smaller than an average amplitude of the magnetic disk and that the amplitude at a position symmetrical to near the magnetic head with respect to the axis of rotation of the spindle motor is greater than the average amplitude of the magnetic disk.

According to the vibration-suppressing mechanism for rotary disks of the present invention, it is made possible to greatly decrease vibration at a portion where vibration on the disk is to be suppressed while enabling the rotary disk to be incorporated in the shroud surface.

According to the information recording device and the magnetic disk drive of the present invention, further, it is made possible to greatly decrease vibration in the disk at the head position while enabling the disk to be incorporated in the shroud surface and maintaining reliability in the recording of disk.

Hereinafter, a plurality of embodiments of the present invention will now be described with reference to the drawings.

The vibration-suppressing mechanism for rotary disks according to the first embodiment of the invention will now be described with reference toFIGS. 1 to 7.

The vibration-suppressing mechanism for rotary disks according to the embodiment will now be described with reference toFIGS. 1 and 2.FIG. 1is a perspective view of the vibration-suppressing mechanism for rotary disks of this embodiment, andFIG. 2is a plan view of the vibration-suppressing mechanism for rotary disks ofFIG. 1.

The vibration-suppressing mechanism for the rotary disks is constituted by a plurality of disks1that rotate, and a shroud surface2aextending along and facing the outer circumferential edges1aof the disks1. The plurality of disks1rotate about a common axis3of rotation as a center axis. The invention can be applied even when there is only one piece of rotary disk1. The shroud surface2ais constituted by the inner circumferential surface of the shroud2. The shroud2is partly arranged along the circumferential direction of the outer circumferential edges1aof the disks1.

The shroud surface2ais so formed as to possess a portion where a gap between the outer circumferential edges1aof the disks1and the shroud surface2abecomes narrow near a portion4where the vibration of the disks1is to be suppressed. In this embodiment, the whole shroud surface2aformed by the shroud2constitutes a portion that becomes narrow.

The gap between the outer circumferential edges1aof the disks1and the shroud surface2ais not uniform along the outer circumferential edges1aof the disks1, the gap a being the smallest at the central portion of the shroud2, and the gap b being the greatest at the ends. That is, the shroud surface2ais so formed as to possess a portion where the gap between the outer circumferential edges1aof the disks1and the shroud surface2abecomes the smallest near the portion4where the vibration of the disks1is to be suppressed. In other words, the shroud surface2ais formed being partly brought close to the outer circumferential edges1aof the disks1, so that the amplitude near the portion4where the vibration is to be suppressed is smaller than an average amplitude of the disk and that the amplitude at a position symmetrical to the portion4where the vibration is to be suppressed with respect to the axis of rotation of the disks1is larger than the average amplitude of the disks1.

The portion4where the vibration of the disks1is to be suppressed is the mesh portion4inFIG. 2where it is desired to suppress the vibration. In this embodiment, the central portion of the shroud2is positioned on an extension5of a line that connects the axis3of rotation to the portion4where the vibration is to be decreased.

Next, described below with reference toFIGS. 3 to 7is the effect of the gap that is non-uniformly distributed as described above upon the specific vibration mode of the disks1.

First, described below is the vibration mode of the disks1that rotates.FIG. 3schematically illustrates a mode (0, 0) and a mode (0, 1) among the specific vibration modes of an ordinary disk. These modes are principal ones among the disk flattering vibrations of, for example, a magnetic disk device. The upper stage of the drawing illustrates a mode of change when the disk1is viewed sideways, and the lower stage of the drawing illustrates a mode of when the disk1is viewed from the upper surface. Here, (+) and (−) represent displacements upward and downward, respectively. The points a, b, c and d along the outer circumference of the disk1are the same between the upper stage and the lower stage. Each mode includes four drawings (A), (B), (C) and (D) in the transverse direction, representing changes in different phases. In the mode (0, 0), changes take place in order of (A)→(B)→(C)→(D) with the passage of time while the mode (0, 1) includes a front-turn mode and a back-turn mode. If now the disk1rotates in the counterclockwise direction, i.e., in order of a→b→c→d, changes take place in order of (A)→(B)→(C)→(D) in the front-turn mode and in order of (A)→(D)→(C)→(B) in the back-turn mode.

The specific vibration mode of the disk1varies for the reasons as described below. The occurrence of aerodynamic damping force in the gap between the disks1and the shroud surface2ahas been disclosed in the Theoretical Consideration, 2006-1 (technical document 1) which is concerned with the aerodynamic damping of fluttering in the gap between the disk and the shroud, Proceedings of the Japanese Mechanical Association (Edition C), Vol. 72, No. 713. Though the damping force varies depending upon the gap, the technical document 1 presumes that the gap is constant. If expressed by a mode coordinate system, the equation of motion of the disk flattering inclusive of the aerodynamic damping effect is given by the following formula (1). Here, Ca that represents the aerodynamic damping force becomes a diagonal matrix when the gap between the disk1and the shroud surface2ais constant. When the gap between the disk1and the shroud surface2ais not constant as in this embodiment, however, the asymmetrical term of Ca does not become 0, and the modes often become continuous.

FIG. 4illustrates specific vibration modes obtained by analyzing the formula (1) for its specific values. In the upper graph ofFIG. 4, the abscissa represents the position (angle) in the circumferential direction and the ordinate represents the amplitude. In the lower graph ofFIG. 4, the abscissa, similarly, represents the position (angle) in the circumferential direction while the ordinate represents the phase. According to this analytical calculation, the shroud2faces the disks1from a position of 90 degrees up to a position of 270 degrees, and the gap between the disks1and the shroud surface2abecomes the smallest at the central position of 180 degrees. Further, the rotational direction of the disks1is a positive direction of the abscissa, i.e., is a direction from the left toward the right.

The upper graph of amplitudes ofFIG. 4tells that the amplitude is not constant along the circumferential direction. In the mode A and mode B shown in the graph, the amplitudes become the smallest near 180 degrees. In the mode C, on the other hand, the amplitude becomes the greatest near 180 degrees. The amplitudes shown here are so normalized that the maximum value is1and are not, therefore, the real amplitudes. In practice, it has been known that the mode damping ratio in the mode C is as very great as several tens of percent, and the amplitude is not almost of a problem. That is, vibration of the disks becomes the smallest at the 180-degree position, i.e., at central portion of the shroud where the amplitude becomes the smallest in the mode A and in the mode B.

Referring to the lower graph of phase inFIG. 4, the phase advances in the mode A with an increase in the rotational angle. In the mode B, on the other hand, the phase is delayed. This shows that the mode A is the back-turn mode and the mode B is the front-turn mode.

FIG. 5is a schematic diagram of mode shapes of the mode A and the mode B, wherein the signs are the same as those ofFIG. 3. In the mode A, however, the deformation proceeds in order of (A)→(D)→(C)→(B), and in the mode B, the deformation proceeds in order of (A)→(B)→(C)→(D).

FIG. 6shows the frequency spectra of vibration of the disks1measured by experiment. In this experiment, too, the shroud2is facing from a position of 90 degrees through up to a position of 270 degrees, and the gap between the disks1and the shroud surface2ais the smallest at the center of the shroud2, i.e., at a position of 180 degrees. In the graph ofFIG. 6, the abscissa represents the frequency and the ordinate represents the velocity of vibration of the disks2.

From the peaks in the mode A and the mode B in the graph, it will be learned that the vibration is decreased down to a level from which the peaks are not almost recognized at the 180-degree position. The aerodynamic damping force due to the gap between the disks1and the shroud surface2a, that varies the vibration mode, increases as the gap decreases and, according to the technical document 1, varies in proportion to the minus third power of the ratio of the gap d and the radius r of the disks, i.e., of the ratio d/r. Through experiment, it was learned that the effect for varying the vibration mode becomes conspicuous when d/r is not larger than 0.002. Due to variation in fabricating the device, however, it is difficult to suppress d/r to be 0, and it is considered that a value of about 0.0005 is a practical lower limit.

The effect for varying the vibration mode is further dependent upon the angle at which the shroud surface2ais facing the disks1. When the angle at which the shroud surface2afaces the disks1becomes too small, the effect decreases, the amplitude of vibration becomes the same at any position on the circumference, and the effect contemplated by the invention is not obtained.

FIG. 7illustrates the results of experiment obtained by varying the angle (shroud angle) at which the shroud2faces the disks1from 180 degrees to 60 degrees. Frequency spectra of vibration of the disks are compared being measured at a central point (central portion) of the shroud and at a point (opposite side portion) on the side opposite thereto with respect to the axis of rotation in each of the cases. When the shroud angle is not smaller than 90 degrees, the amplitude at the central point of the shroud becomes obviously smaller than the amplitude at the point on the opposite side at two peaks near 1350 Hz and 1550 Hz. When the shroud angle is 60 degrees, on the other hand, there is almost no difference between them. It, therefore, becomes obvious that the angle at which the shroud2faces the disks1must not be smaller than 90 degrees.

This embodiment includes the rotary disks1and the shroud surface2awhich extends along and facing the outer circumferential edges1aof the disks1, the shroud surface2abeing so formed as to possess a portion where the gap between the outer circumferential edges1aof the disks1and the shroud surface2abecomes small near the portion4where the vibration of the disks1is to be suppressed. According to this constitution, the disks1can be favorably incorporated relative to the shroud surface2aas compared to when the gap between the outer circumferential edges1aof the disks1and the shroud surface2ais narrow over the whole outer circumferential edges1aof the disks1. According to this constitution, further, the vibration can be greatly decreased at the portion4where the vibration of the disks is to be suppressed due to an increase in the vibration on the side opposite to the portion where the vibration of the disks is to be suppressed.

Next, a second embodiment of the invention will be described with reference toFIG. 8.FIG. 8is a plan view of the vibration-suppressing mechanism for rotary disks according to the second embodiment of the invention. The second embodiment is different from the first embodiment with respect to points described below. Concerning the other points, the second embodiment is basically the same as the first embodiment, and the overlapping description is not repeated.

The second embodiment includes rotary disks16and a shroud surface17awhich surrounds them, wherein part of the shroud surface17aof the shroud17facing the disks16constitutes a narrow shroud portion18in a curved shape having a radius of curvature larger than that of other portions. The gap between the disks16and the narrow shroud portion18is the smallest at the central portion of the narrow shroud portion18, and a portion19where the vibration of the disks is to be suppressed is located near the above portion. The second embodiment, too, exhibits the same effect as that of the first embodiment.

Next, third to fifth embodiments of the invention will be described with reference toFIGS. 9 to 12.FIGS. 9 to 12are plan views of the magnetic disk drive according to the third to10fifth embodiments of the invention. The third to fifth embodiments are different from the first embodiment with respect to that the invention is applied to the magnetic disk drive which is an information recording device, and the embodiments are different from each other concerning the points described below. In the third to fifth embodiments, the disks1used in the first embodiment are replaced by disks or magnetic disks.

The magnetic disk drive of the third embodiment shown inFIG. 9includes an enclosure comprising a base21and a cover, a spindle motor22mounted on the base21, magnetic disks23that rotate being fixed to the spindle motor22, an actuator25mounted on the base21, a magnetic head24attached to an end of the actuator25and moves on the magnetic disk23in the radial direction thereof to record or reproduce information to and from the magnetic disk23, and a narrow shroud26having a shroud surface26aextending along and facing the outer circumferential edges23aof the magnetic disks23.

The enclosure contains the magnetic disks23, magnetic head24and narrow shroud26. The narrow shroud26is installed near the magnetic head24which is a portion where vibration is to be suppressed. The gap between the magnetic disks23and the narrow shroud26is the smallest at the center of the narrow shroud26and is broadened toward both ends thereof. In other words, the shroud surface26ais formed being partly brought close to the outer circumferential edges23aof the magnetic disks23, so that the amplitude of the magnetic disks23near the magnetic head is smaller than an average vibration of the magnetic disks23and that the amplitude at a position symmetrical to near the magnetic head with respect to the axis of rotation of the spindle motor22is greater than the average amplitude of the magnetic disks23.

The constitution of the third embodiment makes it possible to so control the vibration mode of the magnetic disks23that the amplitude becomes the smallest near the magnetic head24, and the positioning error due to disk fluttering can be greatly decreased.

In the fourth embodiment shown inFIG. 10, magnetic disks33are fixed to a spindle motor32mounted on a base31, and an actuator35having a magnetic head34at an end thereof is mounted on the base31. A narrow shroud37having a curve of a curvature smaller than the shroud36is provided near the magnetic head34, and the gap between the circumferential edge33aof the magnetic disks33and the shroud surface37aof the narrow shroud37is the smallest at the center of the narrow shroud37and is broadened toward both ends thereof. Therefore, the vibration mode of the magnetic disks33is so controlled that the amplitude becomes the smallest near the magnetic head34, and the positioning error due to disk fluttering is greatly decreased, enabling the narrow shroud37to be easily formed.

In the fifth embodiment shown inFIGS. 11 and 12, magnetic disks43are fixed to a spindle motor42mounted on a base41, and an actuator45having a magnetic head44at an end thereof is mounted on the base41. A movable shroud46is provided near the magnetic head44. The movable shroud46is supported to rotate at a support portion47provided at an end thereof. A magnetic material48is buried in the other end thereof, and is adsorbed/released by a solenoid coil49provided on the base41.

In the fifth embodiment, the gap between the circumferential edge43aof the rotary magnetic disks43and the shroud surface46aof the movable shroud46can be set to be very narrow as shown inFIG. 11. When the magnetic disk drive is not in operation such as during the transit, it is a requirement that the magnetic disk drive withstands a large shock from the external side. In such a case, the magnetic disks43may collide with the movable shroud46due to the deformation of the spindle motor42which, in the worst case, may result in a fault. To avoid this, when not in operation, no current is supplied to the solenoid coil49and the magnetic material48is released permitting the movable shroud46to separate away from the magnetic disk43as shown inFIG. 12. Therefore, despite a shock is imparted from the external side, a strong shock that may cause a fault is prevented.

Next, described below is how to measure the disk fluttering in the magnetic disk drive with reference toFIGS. 13 and 14.

FIG. 13is a diagram illustrating a method of measuring the disk fluttering in the magnetic disk drive. According to this measuring method, a magnetic disk drive51is fixed on a stool52, an enclosure58is perforated at a point just over a point55on a disk53close to the magnetic head54and at a point just over a point57symmetrical to the point55with respect to the spindle motor56, and vibration of the disk53is measured through the above holes by using a laser Doppler vibrometer59.

FIG. 14is a diagram schematically illustrating frequency spectra measured inFIG. 13. When the invention is applied to the magnetic disk drive, the vibration mode of the disks51is controlled. Therefore, a frequency spectrum60of disk fluttering measured at the point55near the head is quite different from a frequency spectrum61measured at the symmetrical point57, from which it is confirmed that amplitudes of peaks are greatly decreasing in the frequency spectrum60measured at the point55near the head.

InFIGS. 15 to 17, embodiments of the present invention are applied to the magnetic disk drive employing an outer circumferential loading/unloading mechanism in which the magnetic head is evacuated to outside of the disk when the magnetic disk drive is not operated.

In the magnetic disk drive of the embodiment shown inFIG. 15, a magnetic disk63is fixed to a spindle motor62mounted to a base70, and an actuator65having a magnetic head64at a tip end thereof is mounted to the base70. A ramp67for evacuating the magnetic head64is provided so as to be partially overlapped with an outer circumferential edge of the disk.

A narrow shroud portion66has a gap which is narrow at a vicinity of the ramp67and becomes wider as going away from the vicinity of the ramp67with respect to the disk63. In this embodiment, a slit shroud68is provided at a side opposite to the narrow shroud portion66with respect to the ramp67. A gap between the slit shroud68and the disk63is most narrow at a vicinity of the magnetic head64or the ramp67and becomes wider as going away therefrom. The slit shroud68has a vertical wall69at an end thereof which does not face the disk.

FIG. 16shows a state that the magnetic head64is evacuated to the ramp67in this embodiment of the magnetic disk drive. The actuator65is removed from on the disk63and laid on the slit shroud68.

FIG. 17shows a cross-section taken along line A-A at that time. The slit shroud68faces the outer circumferential edge of the disk63and has the vertical wall69at a side thereof which does not face the disk63. The actuator65is evacuated to a position where it is covered by the slit shroud68. In a constitution of this embodiment, it is important that the gap between the slit shroud and the disk varies properly and the slit shroud is closed at a side thereof which does not face the disk by the vertical wall.

An effect of presence or absence of the vertical wall is explained with reference toFIG. 18. In a conventional slit shroud, vertical stream flowing through the gap between the disk and the shroud accompanied by vibration of the disk generates an aerodynamic damping force. In the present embodiment with the vertical wall69shown inFIG. 18(a), since the slit shroud68is closed at a side thereof which does not face the disk, the vertical stream71is generated in response to vibration of the disk63, and, in contrast, in a case shown inFIG. 18(b) where the slit shroud73is opened at a side thereof which does not face the disk72as in the conventional slit shroud, in-plane stream74is generated in response to vibration of the disk72. In case of the conventional slit shroud, an aerodynamic damping force is not generated and vibration reduction effect contemplated by the invention is not exhibited.

In the present embodiment, the slit shroud and the ramp are constituted by separate parts, but they may be constituted by one part. Similarly, the slit shroud, the ramp and the narrow shroud may be constituted by one part.

While the present invention has been described with reference to specific embodiments, those skilled in the art will appreciate that different embodiments may also be used. Thus, although the present invention has been described with respect to specific embodiments, it will be appreciated that the present invention is intended to cover all modifications and equivalents within the scope of the following claims.