Patent Publication Number: US-6667855-B2

Title: Disk drive capable of avoiding the contact of disk and head slider in loading

Description:
This is a division of application Ser. No. 09/708,835 filed Nov. 8, 2000 now U.S. Pat. No. 6,545,843. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a magnetic disk drive, and more particularly to a negative pressure type magnetic head slider for a load/unload type magnetic disk drive. 
     2. Description of the Related Art 
     In recent magnetic disk drives with decreasing size and increasing storage capacity, it has been desired to reduce the flying height of a head slider and realize contact recording/reproduction such that the head slider flies a microscopic height from a recording medium such as a magnetic disk or comes into contact with the recording medium. To reduce the flying height of the head slider, the surface roughness of the surface of the magnetic disk must be reduced. In a contact start and stop (CSS) type magnetic disk drive heretofore widely used, a flying surface of a magnetic head slider comes into contact with a magnetic disk upon stoppage of rotation of the magnetic disk, and flies above the surface of the magnetic disk during rotation of the magnetic disk by the action of an air flow produced in concert with the rotation of the magnetic disk. 
     However, if the surface roughness of the magnetic disk in the CSS type magnetic disk drive is reduces, the contact area between the flying surface (air bearing surface) of the magnetic head slider and the surface of the magnetic disk upon stoppage of rotation of the magnetic disk becomes large. Accordingly, there is a possibility of stiction between the magnetic head slider and the magnetic disk at the starting rotation of the magnetic disk. As a measure against this stiction problem, it has been proposed to apply texture forming by laser to a CSS zone of the magnetic disk or provide a plurality of pads (projections) on the flying surface (air bearing surface) of the head slider in the CSS type magnetic disk drive. 
     A portable personal computer such as a notebook personal computer is often carried, and it is therefore required to have high shock resistance. Accordingly, such a personal computer generally employs a load/unload type magnetic disk drive designed so that a head slider is unloaded from the surface of a magnetic disk when the computer is powered off or put into a sleep mode and that the head slider is loaded to the surface of the magnetic disk when the computer is operated. That is, when the computer is powered off or put into a sleep mode, a horn portion formed at the front end of a suspension is seated on a ramp (inclined portion) of a ramp member provided near the outer circumference of the magnetic disk to retract the head slider flying a microscopic height above the disk surface from the magnetic disk. Accordingly, even when the computer receives shock, it is possible to avoid the possibility that the head slider may collide with the magnetic disk to damage the magnetic disk. 
     Such a magnetic disk drive having a load/unload mechanism is required to have a highly reliable magnetic head slider that is prevented from coming into contact or collision with a magnetic disk not only while the head slider is flying above the disk, but also when the head slider is loaded to the disk. 
     A negative pressure type magnetic head slider is widely used in recent magnetic disk drives, so as to reduce the flying height of the magnetic head slider from the magnetic disk. A conventional negative pressure type magnetic head slider is mounted on a suspension so that the flying surface of the head slider becomes parallel to the magnetic disk at the instant when the head slider is loaded from the ramp member to the magnetic disk. Accordingly, there is a possibility that the head slider may come into contact with the disk because of a negative pressure generated on the head slider at the instant of loading. 
     Particularly in the case that a groove for generating a negative pressure is formed on the flying surface of the head slider so as to extend from a position upstream of the longitudinal center of the head slider to an air outlet end of the head slider, the head slider is inclined so that an air inlet end of the head slider is drawn to the magnetic disk by the negative pressure at the instant of loading, causing the contact of the air inlet end with the magnetic disk. Further, in the case that the head slider is mounted on a suspension having a pivot for supporting the head slider by applying a push load, the head slider is supported at its longitudinal center by the pivot. 
     Accordingly, in the case that the above-mentioned groove for generating a negative pressure is formed on the head slider, the attitude of the head slider cannot be controlled by the push load. As a result, the head slider is inclined so that the air inlet end is drawn to the magnetic disk by the negative pressure at the instant of loading, causing the contact of the air inlet end with the magnetic disk. Further, in the case that the head slider has a taper near the air inlet end or a pad having a raised surface and a step surface lower in level than the raised surface for generating a positive pressure near the air inlet end, and that the above-mentioned groove for generating a negative pressure is formed on the head slider, there is a possibility that the negative pressure may become greater than the positive pressure, depending upon the mounted attitude of the head slider. Accordingly, the head slider is inclined so that the air inlet end is drawn to the magnetic disk by the negative pressure at the instant of loading, causing the contact of the air inlet end with the magnetic disk. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a negative pressure type magnetic head slider for use in a magnetic disk drive having a load/unload mechanism which can reliably prevent the contact of the head slider with a magnetic disk at the time of loading. 
     It is another object of the present invention to provide a magnetic disk drive having a load/unload mechanism which can reliably prevent the contact of a magnetic head slider with a magnetic disk at the time of loading. 
     In accordance with an aspect of the present invention, there is provided a disk drive comprising a housing having a base; a disk rotatably mounted in the housing and having a plurality of tracks; a negative pressure type head slider having a transducer for reading/writing data from/to the disk, an air inlet end, and an air outlet end; an actuator for moving the head slider across the tracks of the disk; means for controlling the actuator to load/unload the head slider with respect to the disk; and a ramp member fixed to the base for supporting the head slider unloaded; the actuator comprising an actuator arm rotatably mounted to the base; and a head assembly mounted on a front end portion of the actuator arm; the head assembly comprising a suspension; a gimbal formed integrally with the suspension and having a slider mounting portion; the head slider mounted on the slider mounting portion of the gimbal; and a supporting plate fixed to the suspension and having a pivot kept in contact with the slider mounting portion of the gimbal to support the head slider; the pivot supporting the head slider at a position shifted from the longitudinal center of the head slider toward the air outlet end by a distance less than 20% of the length of the head slider. 
     Preferably, the pivot supports the head slider at a position shifted from the longitudinal center of the head slider toward the air outlet end by a distance falling in the range of about 4% to about 15% of the length of the head slider. 
     In accordance with another aspect of the present invention, there is provided a disk drive comprising a housing having a base; a disk rotatably mounted in the housing and having a plurality of tracks; a negative pressure type head slider having a transducer for reading/writing data from/to the disk, an air inlet end, an air outlet end, and a disk opposing surface; an actuator for moving the head slider across the tracks of the disk; means for controlling the actuator to load/unload the head slider with respect to the disk; and a ramp member fixed to the base for supporting the head slider unloaded; the actuator comprising an actuator arm rotatably mounted to the base; and a head assembly mounted on a front end portion of the actuator arm; the head assembly comprising a suspension; a gimbal formed integrally with the suspension and having a slider mounting portion and a neck portion for connecting the slider mounting portion and the suspension; and the head slider mounted on the slider mounting portion of the gimbal; the neck portion being bent in such a direction that the disk opposing surface of the head slider is inclined with respect to the disk so as to raise the air inlet end in order that a given pitch angle is given to the head slider when the head slider is separated from the ramp member and loaded above the disk. 
     In accordance with a further aspect of the present invention, there is provided a disk drive comprising a housing having a base; a disk rotatably mounted in the housing and having a plurality of tracks; a negative pressure type head slider having a transducer for reading/writing data from/to the disk, an air inlet end, an air outlet end, and a disk opposing surface; an actuator for moving the head slider across the tracks of the disk; means for controlling the actuator to load/unload the head slider with respect to the disk; and a ramp member fixed to the base for supporting the head slider unloaded; the actuator comprising an actuator arm rotatably mounted to the base; a suspension having a base end portion fixed to a front end portion of the actuator arm; and the head slider mounted on a front end portion of the suspension; the head slider comprising a pair of rails formed on the disk opposing surface, each of the rails having a flat air bearing surface for generating a flying force during rotation of the disk; a groove defined between the rails for generating a negative pressure by expanding air once compressed near the air inlet end; a first taper formed at an end portion of each rail near the air inlet end so as to continue to the air bearing surface, the first taper having a first taper angle; and a second taper formed at the end portion of each rail so as to continue to the first taper, the second taper having a second taper angle larger than the first taper angle. 
     Preferably, the first taper angle is in the range of 0.1° to 3°, and the second taper angle is not greater than 6°. 
     In accordance with a still further aspect of the present invention, there is provided a disk drive comprising a housing having a base; a disk rotatably mounted in the housing and having a plurality of tracks; a negative pressure type head slider having a transducer for reading/writing data from/to the disk, an air inlet end, an air outlet end, and a disk opposing surface; an actuator for moving the head slider across the tracks of the disk; means for controlling the actuator to load/unload the head slider with respect to the disk; and a ramp member fixed to the base for supporting the head slider unloaded; the actuator comprising an actuator arm rotatably-mounted to the base; a suspension having a base end portion fixed to a front end portion of the actuator arm; and the head slider mounted on a front end portion of the suspension; the head slider comprising a front pad formed on the disk opposing surface near the air inlet end, the front pad having a raised surface and a step surface lower in level than the raised surface; a groove for generating a negative pressure by expanding air once compressed by the front pad; and a taper formed adjacent to the air inlet end so as to continue to the step surface, the taper having a given taper angle. 
     Preferably, the given taper angle is in the range of 0.1° to 6°. 
     In accordance with a still further aspect of the present invention, there is provided a disk drive comprising a housing having a base; a disk rotatably mounted in the housing and having a plurality of tracks; a negative pressure type head slider having a transducer for reading/writing data from/to the disk, an air inlet end, an air outlet end, and a disk opposing surface; an actuator for moving the head slider across the tracks of the disk; means for controlling the actuator to load/unload the head slider with respect to the disk; and a ramp member fixed to the base for supporting the head slider unloaded; the actuator comprising an actuator arm rotatably mounted to the base; a suspension having a base end portion fixed to a front end portion of the actuator arm; and the head slider mounted on a front end portion of the suspension; the head slider comprising a front pad formed on the disk opposing surface near the air inlet end, the front pad having a raised surface, a first step surface lower in level than the raised surface, and a second step surface lower in level than the first step surface; and a groove for generating a negative pressure by expanding air once compressed by the front pad. 
     Preferably, the length of the second step surface in the longitudinal direction of the head slider is in the range of 10 μm to 100 μm. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a magnetic disk drive with a cover removed; 
     FIG. 2A is a side view of a ramp member; 
     FIG. 2B is a plan view of the ramp member shown in FIG. 2A; 
     FIG. 3A is a perspective view of a head assembly according to a first preferred embodiment of the present invention; 
     FIG. 3B is a longitudinal sectional view of the head assembly shown in FIG. 3A; 
     FIG. 4 is an exploded perspective view of the head assembly shown in FIG. 3A; 
     FIG. 5 is a schematic side view showing a pitch angle of a head slider in the first preferred embodiment; 
     FIG. 6 is a graph showing the relation between a pivot position and a pitch angle of a head slider; 
     FIG. 7A is a side view of a negative type magnetic head slider applicable to the head assembly according to the first preferred embodiment; 
     FIG. 7B is a bottom plan view of the head slider shown in FIG. 7A; 
     FIG. 8A is a plan view of a head assembly according to a second preferred embodiment of the present invention; 
     FIG. 8B is a side view of the head assembly shown in FIG. 8A; 
     FIG. 9A is a side view of a negative pressure type magnetic head slider according to a third preferred embodiment of the present invention; 
     FIG. 9B is a bottom plan view of the head slider shown in FIG. 9A; 
     FIG. 10 is a graph showing the relation between a first taper angle and a pressure generated in the third preferred embodiment; 
     FIG. 11A is a side view of a negative pressure type magnetic head slider according to a fourth preferred embodiment of the present invention; 
     FIG. 11B is a bottom plan view of the head slider shown in FIG. 11A; 
     FIG. 12 is a graph showing the proportion of a negative pressure to a positive pressure according to a taper angle in the fourth preferred embodiment; 
     FIG. 13A is a side view of a negative pressure type magnetic head slider according to a fifth preferred embodiment of the present invention; 
     FIG. 13B is a bottom plan view of the head slider shown in FIG. 13A; and 
     FIG. 14 is a graph showing the proportion of a negative pressure to a positive pressure according to the length of a second step surface in the fifth preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a plan view of a magnetic disk drive according to a first preferred embodiment of the present invention in the condition where a cover is removed. Reference numeral  2  denotes a housing consisting of a base  4  and the cover (not shown) fixed to the base  4 . A shaft  6  is fixed to the base  4 , and a spindle hub (not shown) is rotatably mounted on the shaft  6 . The spindle hub is driven by a DC motor (not shown) to rotate about the shaft  6 . A plurality of magnetic disks  8  and spacers (not shown) are mounted on the spindle hub so as to be alternately stacked. That is, the plural magnetic disks  8  are fixedly mounted on the spindle hub by securing a disk clamp  10  to the spindle hub by means of a plurality of screws  12 , and are equally spaced a given distance by the spacers. 
     Reference numeral  14  denotes a rotary actuator consisting of an actuator arm assembly  16  and a magnetic circuit  18 . The actuator arm assembly  16  is rotatable about a shaft  20  fixed to the base  4 . The actuator arm assembly  16  includes an actuator block  22  rotatably mounted on the shaft  20  through a pair of bearings (not shown), a plurality of actuator arms  24  extending horizontally from the actuator block  22  in one direction, and a head assembly  26  fixed to a front end portion of each actuator arm  24 . 
     Each head assembly  26  includes a negative pressure type head slider  28  having a magnetic head element (transducer) for reading/writing data from/to the corresponding magnetic disk  8 , and a suspension (load beam)  30  having a front end portion supporting the head slider  28  and a base end portion fixed to the corresponding actuator arm  24 . A coil  31  is supported on the opposite side of the actuator arms  24  with respect to the shaft  20 . The coil  31  is inserted in a gap of the magnetic circuit  18 . The magnetic circuit  18  and the coil  31  constitute a voice coil motor (VCM)  32 . Reference numeral  34  denotes a flexible printed circuit board (FPC) for supplying a write signal to the magnetic head element and for taking a read signal from the magnetic head element. One end of the flexible printed circuit board  34  is fixed to a side surface of the actuator block  22 . 
     A ramp member  36  is fixed to the base  4  at a position adjacent to the outer circumferences of the magnetic disks  8 . As shown in FIGS. 2A and 2B, the ramp member  36  has a plurality of ramps (inclined portions)  40  whose number corresponds to the number of the head sliders  28 , and a plurality of parking portions  42  each for allowing a horn portion  52  formed at the front end of each head assembly  26  to be stably parked thereon. Further, a plurality of side projections  44  for preventing the unloaded head sliders  28  from interfering with each other are formed on a side surface of the ramp member  36 . Reference numeral  38  in FIG. 1 denotes a latch mechanism for latching a projecting portion  39  of the actuator  14  in its unloaded condition. 
     The condition shown in FIG. 1 is an unloaded condition where the head sliders  28  have been unloaded from the magnetic disks  8 . In this condition, the horn portions  52  of the head assemblies  26  are parked on the parking portions  42  of the ramp member  36 , and the projecting portion  39  of the actuator  14  is latched by the latch mechanism  38 . When a computer connected to this magnetic disk drive is powered on or a sleep mode is canceled in this unloaded condition, the magnetic disks  8  first start to be rotated. Thereafter, the latch mechanism  38  is released to rotate the actuator  14  counterclockwise as viewed in FIG. 1, so that the horn portions  52  slide down on the ramps  40  and the head sliders  28  are loaded to the magnetic disks  8 . 
     When the computer is powered off or put into the sleep mode, control means such as an MPU mounted on a main printed circuit board (not shown) in the magnetic disk drive controls the actuator  14  so that the actuator  14  is rotated clockwise as viewed in FIG. 1 to move the head sliders  28  from the loaded condition through the outer circumferences of the magnetic disks  8  to the ramp member  36 . Accordingly, the horn portions  52  of the head assemblies  26  slide up on the ramps  40  of the ramp member  36  and are then parked on the parking portions  42  of the ramp member  36 . In this unloaded condition, the projecting portion  39  of the actuator  14  is latched by the latch mechanism  38 . 
     The head assembly  26  according to the first preferred embodiment of the present invention will now be described in detail with reference to FIGS. 3A to  7 B. FIG. 3A is a perspective view of the head assembly  26 , FIG. 3B is a longitudinal sectional view of the head assembly  26 , and FIG. 4 is an exploded perspective view of the head assembly  26 . As best shown in FIG. 4, the suspension  30  is integrally formed with a gimbal  47  having a slider mounting portion  48 . The slider mounting portion  48  is defined by forming a U-shaped slit  46  at a front end portion of the suspension  30 . The suspension  30  is formed of stainless steel, and it has a thickness of about 22 μm. 
     The suspension  30  includes a spring portion  30   a  for pressing the head slider  28  on the corresponding disk  8  and a rigid portion  30   b . A reinforcing plate (supporting plate)  50  is fixed to the back surface of the rigid portion  30   b  by spot welding or the like. The reinforcing plate  50  is formed of stainless steel, for example, and it has a thickness about 1.0 times to about 2.0 times, preferably, about 1.3 times to about 1.5 times the thickness of the suspension  30 . By setting the thickness of the reinforcing plate  50  in the above-mentioned range, the resonance frequency of the head assembly  26  can be increased and its mass increase can be minimized. If the thickness of the reinforcing plate  50  is set less than a value 1 times the thickness of the suspension  30 , the rigidity of the rigid portion  30   b  decreases to cause a reduction in the resonance point. 
     Conversely, if the thickness of the reinforcing plate  50  is set greater than a value 2 times the thickness of the suspension  30 , the mass of the head assembly  26  is increased to cause a reduction in impact acceleration upon separation of the head slider  28  from the disk  8 , causing a deterioration in shock resistance. The horn portion  52  adapted to be seated onto the ramp member  36  is formed integrally with the reinforcing plate  50  at a front end portion thereof. The reinforcing plate  50  is further integrally formed with a pivot  54  having a tip kept in contact with the back surface of the slider mounting portion  48  of the gimbal  47  to support the head slider  28 . Further, a spacer  56  formed of aluminum is fixed by spot welding to a base end portion of the suspension  30 . 
     Referring to FIG. 5, there is shown an attitude of the head slider  28  with respect to the disk  8  at the instant the head slider  28  parked on the ramp member  36  is loaded to the disk  8 . In this preferred embodiment, the position of the pivot  54  is shifted from the longitudinal center of the head slider  28  toward the air outlet end of the head slider  28 , thereby increasing a moment in a direction of lifting the air inlet end of the head slider  28 . 
     That is, by increasing the moment in the direction of lifting the air inlet end, a pitch angle of θ is given to the head slider  28  at the instant the head slider  28  is loaded to the disk  8 . In this manner, by increasing the moment in the direction of lifting the air inlet end to give the pitch angle θ to the head slider  28 , it is possible to suppress the possibility that the air inlet end of the head slider  28  may be tilted down by a negative pressure. Accordingly, the tilt-down of the head slider  28  at its air inlet end at the instant of loading can be suppressed to thereby prevent the contact of the air inlet end with the disk  8 . 
     Referring to FIG. 6, there is shown a relation between the position of the pivot  54  and the pitch angle θ of the head slider  28 . In FIG. 6, the horizontal axis rperesents the proportion (%) of the amount of shift of the pivot position from the longitudinal center of the head slider  28  to the length of the head slider  28 , in which the positive values for the proportion indicate that the pivot position is shifted toward the air outlet end. The vertical axis represents the pitch angle θ of the head slider  28 . As apparent from FIG. 6, in the case that the pivot position is shifted toward the air inlet end, the pitch angle θ of the head slider  28  becomes negative, so that the air inlet end of the head slider  28  comes into contact with the disk  8  at the instant of loading. Further, in the case that the pivot position is shifted 20% or more toward the air outlet end, the pitch angle θ becomes excessive, so that the air outlet end of the head slider  28  comes into contact with the disk  8  at the instant of loading. 
     In view of these circumstances, the position of the pivot  54  supporting the head slider  28  is shifted from the longitudinal center of the head slider  28  toward the air outlet end by a distance less than 20% of the length of the head slider  28  in this preferred embodiment. Preferably, the position of the pivot  54  is shifted from the longitudinal center of the head slider  28  toward the air outlet end by a distance falling in the range of 4 to 15% of the length of the head slider  28 . In this case, the pitch angle θ becomes about 0.5°. 
     Referring to FIGS. 7A and 7B, there is shown an example of the negative pressure type magnetic head slider  28  employable in the first preferred embodiment. FIG. 7A is a side view of the head slider  28 , and FIG. 7B is a bottom plan view of the head slider  28 . The head slider  28  is in the form of rectangular parallelepiped, and has an air inlet end  28   a  and an air outlet end  28   b . The bottom surface of the head slider  28  is a disk opposing surface adapted to face the corresponding disk  8 . A front pad  58  is formed on the disk opposing surface of the head slider  28  at a position adjacent to the air inlet end  28   a , and a pair of rear pads  60  and  62  are formed on the disk opposing surface of the head slider  28  at positions adjacent to the air outlet end  28   b  and transversely spaced from each other. 
     The front pad  58  is formed with a raised surface (air bearing surface)  64  extending in the transverse direction of the head slider  28  and a step surface  66  lower in level than the raised surface  64 . Similarly, the rear pads  60  and  62  are formed with raised surfaces (air bearing surfaces)  68  and  72  and step surfaces  70  and  74  lower in level than the raised surfaces  68  and  72 , respectively. The raised surface  68  is smaller in area than the raised surface  72 . Accordingly, a flying force applied to the raised surface  72  is larger than that applied to the raised surface  68  in the head slider  28 . 
     An electromagnetic transducer  76  is formed near the air outlet end of the rear pad  60 , and the distance between the head slider  28  and the disk surface during rotation of the disk  8  is minimum near the electromagnetic transducer  76 . When the disk  8  is rotated to generate an air flow along the disk surface, the air flow acts on the raised surfaces  64 ,  68 , and  72 . As a result, flying forces for flying the head slider  28  above the disk surface are generated on the raised surfaces  64 ,  68 , and  72 . In the head slider  28 , the area of the raised surface  64  is relatively large, so that a relatively large flying force is generated on the raised surface  64  during rotation of the disk  8 . As a result, the head slider  28  is maintained in an inclined attitude at a pitch angle α such that the air inlet end  28   a  is tilted up. This pitch angle α is different from the pitch angle θ shown in FIG.  5 . 
     A pair of side pads  78  and  80  extend from the transverse ends of the front pad  58  toward the rear pads  60  and  62 , respectively. A groove  82  for generating a negative pressure is defined between the side pads  78  and  80  on the downstream side of the front pad  58 . The groove  82  extends from a position upstream of the longitudinal center of the head slider  28  to the air outlet end  28   b . Accordingly, when passing the raised surface  64  of the front pad  58 , the air flow is expanded in the groove  82  in a direction perpendicular to the disk surface, thereby generating a negative pressure in the groove  82 . This negative pressure comes into balance with the above-mentioned flying forces applied to the raised surfaces  64 ,  68 , and  72 , thereby defining a flying height of the head slider  28 . 
     Referring to FIG. 8A, there is shown a plan view of a head assembly  83  according to a second preferred embodiment of the present invention. FIG. 8B is a side view of the head assembly  83 . In this preferred embodiment, the head assembly  83  has a suspension  84  integrally formed at its front end portion with a gimbal  86  having a slider mounting portion  90 . The slider mounting portion  90  is defined by forming a U-shaped slit  88  at the front end portion of the suspension  84 . The slider mounting portion  90  is integrally connected with the suspension  84  through a neck portion  92 . As shown in FIG. 8B, the neck portion  92  is bent in such a direction that the flying surface of the head slider  28  is inclined with respect to the disk surface so as to raise the air inlet end of the head slider  28 , thereby providing a given pitch angle θ. The pitch angle θ is set to less than 1°, preferably, about 0.5°. 
     The head slider  28  employable in this preferred embodiment may be selected from any negative pressure type magnetic head sliders including the head slider  28  shown in FIGS. 7A and 7B. Unlike the first preferred embodiment, the suspension  84  in the second preferred embodiment is integrally formed at its front end with a horn portion  94  adapted to be seated onto the ramp member  36  shown in FIG. 1 at the time of unloading. According to the second preferred embodiment, the given pitch angle is given to the head slider  28  in its unloaded condition where the head slider  28  does not fly above the disk surface. Accordingly, even when the air inlet end of the head slider  28  is drawn toward the disk surface by the negative pressure at the time of loading, the contact of the air inlet end with the disk surface can be prevented to allow stable loading of the head slider  28 . 
     Referring to FIG. 9A, there is shown a side view of a negative pressure type magnetic head slider  28 A according to a third preferred embodiment of the present invention. FIG. 9B is a bottom plan view of the head slider  28 A shown in FIG.  9 A. As shown in FIG. 9B, the head slider  28 A has an air inlet end  28   a  and an air outlet end  28   b . The bottom surface of the head slider  28 A is formed as a disk opposing surface adapted to face the disk surface. A pair of rails  96  and  98  for generating a positive pressure are formed on the disk opposing surface of the head slider  28 A. The rails  96  and  98  have flat air bearing surfaces  96   a  and  98   a  for generating flying forces during rotation of the disk  8 , respectively. 
     An end portion of the rail  96  near the air inlet end  28   a  is formed with first and second tapers  96   b  and  96   c  contiguous to each other, and an end portion of the rail  98  near the air inlet end  28   a  is formed with first and second tapers  98   b  and  98   c  contiguous to each other. A center rail  100  is formed between the rails  96  and  98  near the air inlet end  28   a . The center rail  100  is also formed with first and second tapers  100   b  and  100   c  contiguous to each other. A slit  102  is defined between the rail  96  and the center rail  100 , and a slit  104  is defined between the rail  98  and the center rail  100 . A groove  106  for generating a negative pressure by expanding the air once compressed near the air inlet end  28   a  is defined between the rails  96  and  98  on the downstream side of the center rail  100 . 
     An electromagnetic transducer  76  is formed on the rail  96  near the air outlet end  28   b  of the head slider  28 A. In each of the rails  96  and  98 , an intermediate portion extending between the opposite end portions near the air inlet end  28   a  and the air outlet end  28   b  is narrower than each opposite end portion, thereby suppressing fluctuations in flying height due to changes in yaw angle. Each of the first tapers  96   b ,  98   b , and  100   b  has a first taper angle θ1, and each of the second tapers  96   c ,  98   c , and  100   c  has a second taper angle θ2 larger than the first taper angle θ1. 
     FIG. 10 shows a pressure generated on the first tapers  96   b ,  98   b , and  100   b . In FIG. 10, the horizontal axis represents the first taper angle θ1, and the vertical axis represents the proportion of the pressure generated on the first tapers  96   b ,  98   b , and  100   b , in which P is the pressure generated on the first tapers  96   b ,  98   b , and  10   b , and pa is the atmospheric pressure. As apparent from FIG. 10, the pressure rapidly decreases for the first taper angle θ1 greater than 3°, so that a pressure required for flying the head slider  28 A cannot be ensured. Further, also when the first taper angle θ1 is less than 0.1°, the required pressure cannot be ensured. In view of these circumstances, the first taper angle θ1 is preferably set in the range of 0.1° to 3°. 
     In the head slider  28 A, the second tapers  96   c ,  98   c , and  100   c  are formed near the air inlet end  28   a  in addition to the first tapers  96   b ,  98   b , and  100   b . Thus, the head slider  28 A has a two-stage tapering portion near the air inlet end  28   a , thereby increasing a positive pressure generated near the air inlet end  28   a  of the head slider  28 A. 
     By increasing the positive pressure generated near the air inlet end  28   a , it is possible to suppress the possibility that the air inlet end  28   a  of the head slider  28 A may be tilted down by the negative pressure generated in the groove  106 . Accordingly, the tilt-down of the air inlet end  28   a  of the head slider  28 A at the time of loading can be prevented to thereby eliminate the contact of the air inlet end  28   a  with the disk surface. The second taper angle θ2 is preferably set greater than the first taper angle θ1 and not greater than 6°. If the second taper angle θ2 is greater than 6°, the positive pressure generated near the air inlet end  0 . 28   a  is reduced, so that there is a possibility that the air inlet end  28   a  of the head slider  28 A may come into contact with the disk surface at the time of loading. 
     Referring to FIG. 11A, there is shown a side view of a negative pressure type magnetic head slider  28 B according to a fourth preferred embodiment of the present invention. FIG. 11B is a bottom plan view of the head slider  28 B shown in FIG.  11 A. The head slider  28 B is similar to the head slider  28  shown in FIGS. 7A and 7B. Accordingly, the same parts are denoted by the same reference numerals and only different parts will now be described. The head slider  28 B has a taper  108  formed on the step surface  66  of the front pad  58  at a portion near the air inlet end  28   a . The taper  108  has a taper angle θ3. The taper  108  is not contiguous to the raised surface  64  of the front pad  58 . 
     By forming the taper  108  near the air inlet end  28   a  of the head slider  28 B, a positive pressure generated near the air inlet end  28   a  can be increased. Accordingly, it is possible to suppress the possibility that the air inlet end  28   a  of the head slider  28 B may be tilted down by the negative pressure generated in the groove  82 . As a result, the tilt-down of the air inlet end  28   a  of the head slider  28 B at the time of loading can be prevented to eliminate the contact of the air inlet end  28   a  with the disk surface. 
     FIG. 12 shows the proportion of a negative pressure to a positive pressure on the head slider  28 B according to the taper angle θ3. In FIG. 12, the horizontal axis represents the taper angle θ3 of the taper  108 , and the vertical axis represents the proportion of the negative pressure to the positive pressure, in which Pa is the positive pressure and Na is the negative pressure. As apparent from FIG. 12, the negative pressure becomes greater than the positive pressure for the taper angle θ3 greater than 6°, and the proportion of the negative pressure to the positive pressure changes to negative values. 
     If the negative pressure is greater than the positive pressure, the head slider  28 B is drawn to the disk surface, so that the contact of the head slider  28 B with the disk surface cannot be prevented. Accordingly, the taper angle θ3 must be not greater than 6°. The proportion of the negative pressure to the positive pressure for the taper angle θ3 equal to 6° is 0.02. Further, if the taper angle θ3 is less than 0.1°, the proportion of the negative pressure to the positive pressure becomes less than 0.02. Accordingly, the taper angle θ3 must be not less than 0.1°. In view of these circumstances, the taper angle θ3 is preferably set in the range of 0.1° to 6°. 
     Referring to FIG. 13A, there is shown a side view of a negative pressure type magnetic head slider  28 C according to a fifth preferred embodiment of the present invention. FIG. 13B is a bottom plan view of the head slider  28 C shown in FIG.  13 A. The head slider  28 C is similar to the head slider  28  shown in FIGS. 7A and 7B. Accordingly, the same parts are denoted by the same reference numerals and only different parts will now be described. The head slider  28 C has a second step surface  110  lower in level than the first step surface  66  near the air inlet end  28   a . That is, the front pad  58  in this preferred embodiment has the raised surface  64  and the first and second step surfaces  66  and  110 . The difference in level between the first and second step surfaces  66  and  110  is preferably set not greater than the depth of the groove  82  for generating a negative pressure. 
     Thus, the front pad  58  has the step surfaces  66  and  110  of different levels near the air inlet end  28   a  of the head slider  28 C, thereby increasing a positive pressure generated near the air inlet end  28   a  of the head slider  28 C. By thus increasing the positive pressure generated near the air inlet end  28   a , it is possible to suppress the possibility that the air inlet end  28   a  of the head slider  28 C may be tilted down by the negative pressure generated in the groove  82 . Accordingly, the tilt-down of the air inlet end  28   a  of the head slider  28 C at the time of loading can be prevented to thereby eliminate the contact of the air inlet end  28   a  with the disk surface. 
     FIG. 14 shows the proportion of a negative pressure to a positive pressure on the head slider  28 C according to the length of the second step surface  110  in the longitudinal direction of the head slider  28 C. In FIG. 14, the horizontal axis represents the length of the second step surface  110  in the longitudinal direction of the head slider  28 C, and the vertical axis represents the proportion of the negative pressure to the positive pressure, in which Pa is the positive pressure and Na is the negative pressure. As apparent from FIG. 14, the negative pressure becomes greater than the positive pressure for the length of the second step surface  110  greater than 100 μm, and the proportion of the negative pressure to the positive pressure changes to negative values. 
     If the negative pressure is greater than the positive pressure, the head slider  28 C is drawn to the disk surface, so that the contact of the head slider  28 C with the disk surface cannot be prevented. Accordingly, the length of the second step surface  110  must be not greater than 100 μm. The proportion of the negative pressure to the positive pressure for the length of the second step surface  110  equal to 100 μm is 0.02. Further, if the length of the second step surface  110  is less than 10 μm, the proportion of the negative pressure to the positive pressure becomes less than 0.02. Accordingly, the length of the second step surface  110  must be not less than 10 μm. In view of these circumstances, the length of the second step surface  110  is preferably set in the range of 10 μm to 100 μm. 
     According to the present invention, the contact or collision between the magnetic disk and the magnetic head slider at the time of loading can be reliably avoided to thereby improve the reliability of a magnetic disk drive having a load/unload mechanism.