Floating head slider having uniform spacing from recording medium surface

A floating head slider has a pair of side rails and a central rail on a air bearing surface thereof. Each of the side rails has a first, leading region extending parallel to the longitudinal axis of the slider, a second, intermediate region extending from the first region and deviating from the direction of the longitudinal axis toward the other of the side rails, and a third, trailing region extending from the second region and further deviating from the direction of the first region. The directions of the first, second and third regions correspond to the direction of the air flow at the innermost track, intermediate track and the outermost track, to provide constant floating height and reduced roll. The central rail has a neck between a leading, small width region and a trailing, increasing width region.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
The present invention relates to a floating head slider for disk drives in 
which a read/write head floats over the surface of a rotating disk with a 
small spacing therefrom by an air bearing effect. 
(b) Description of Related Art 
In a magnetic disk drive used as an external storage device for a computer, 
a floating magnetic head slider, which floats over a surface of a 
recording medium with a constant spacing, is used to read and write 
information. The magnetic head slider has an air bearing surface 
(hereinafter referred to as an "ABS") opposing the recording medium. ABS 
receives a viscous flow of air which is produced by the rotation of the 
recording medium, and the magnetic head slider floats over the surface of 
the recording medium with a small spacing therefrom due to an air bearing 
effect. At a trailing edge of the ABS from which air exits, a magnetic 
head is attached such that the gap of the magnetic head opposes the 
surface of the recording medium. With this structure, non-contact 
recording and reproduction of information are performed to and from the 
recording disk. 
FIGS. 1A and 1B, FIGS. 2A and 2B and FIGS. 3A and 3B show examples of 
conventional floating head sliders as described above. FIGS. 1A and 1B 
show a plan view and an end view, respectively, of a two-rail slider in 
which two side rails parallel to each other are disposed on both 
transverse edges of the ABS. FIGS. 2A and 2B show, similarly to FIGS. 1A 
and 1B, a TPC (Transverse Pressure Contour) slider in which small steps 
are formed on both sides of each of the side rails to produce a negative 
pressure. FIGS. 3A and 3B show, similarly to FIGS. 1A and 1B, a three-rail 
slider in which a central rail is interposed between two side rails 
disposed at both transverse edges of the ABS. 
Here, the structure and performance of a floating head slider will be 
described in more detail using an example of the two-rail structure of 
FIG. 4. 
In FIG. 4, magnetic head slider 1 has a central recess 7 in the ABS 2 
opposing a recording medium. The recess 7 longitudinally penetrates the 
magnetic head slider 1 and has a constant width over the entire length 
thereof. Two side rails 3 are disposed on both sides of the recess 7 such 
that they extend in the direction of arrow "e" of an air flow produced due 
to the rotation of the recording medium. Slopes 6 are formed at leading 
edges of the side rails 3, and a magnetic head 5 is formed on the trailing 
end surface of the slider 1 with a magnetic gap thereof disposed at the 
trailing edge of one of the side rails 3. 
In operation, air enters along the slopes 6 and flows between the medium 
surface and the side rails 3, so, that air is compressed so as to form an 
air film between the surface of the recording medium and each of the side 
rails 3, thereby generating a positive pressure for bearing the magnetic 
head slider 1 over the medium surface. 
FIG. 5 shows movement of the magnetic head slider 1 effected by a 
positioner 9 for data accessing. The structure shown in the drawing is 
called a rotary actuator type. The positioner 9 swings, as indicated by 
arrow "f", along the medium surface 10 in a seeking operation. For data 
accessing, the magnetic head slider 1 is moved between the innermost track 
A and the outermost track B. During the seeking operation, the velocity of 
the magnetic head slider 1 relative to the medium surface varies depending 
upon of the radial position of the magnetic head slider 1 over the 
recording medium. This causes variations in the pressure generated along 
the ABS 2 of the magnetic head slider 1. The variation in pressure in turn 
generates the variation in the floating height of the slider dependent 
upon the radial position. 
In the rotary actuator type, the skew angle depends on the radial position 
of the slider over the medium surface 10. The skew angle is defined as an 
angle between the direction of the longitudinal axis of the slider and the 
direction of the air flow running along the line tangent to the track. In 
general, the skew angle .THETA.in at the innermost track is designed to be 
approximately zero or a minus value while the skew angle .THETA.out is 
designed to be between about 20 and 30 degrees, as shown in the drawings. 
Accordingly, the floating height, which also depends on the compression 
length of the air flow, varies between the innermost track and the 
outermost track. The skew angle also affects the attitude of the slider. 
The variation in the floating height of the magnetic head slider 1 causes 
variation in the efficiency of the magnetic head in electro-magnetic 
conversion, thereby deteriorating the SNR of reproduced signals. To 
achieve high density recording which is ever-requested in the field of 
magnetic disk drives, it is necessary to maintain a constant floating 
height of the magnetic head slider over all the tracks. 
Japanese Patent Publication No. JP-A-4(1992)-355289 discloses a floating 
head slider having a small width center or neck between a leading edge and 
a trailing edge of each of the side rails, so as to decrease variations in 
the floating height of the head slider. However, this structure has been 
used only in two-rail sliders and it is difficult to employ the structure 
in a three-rail structure because of its high pitch angle caused by the 
large width leading edges of the rails. Further, since the slider has a 
skew angle with respect to the flow of air, roll of the slider increases. 
The amount of roll also greatly affects the floating characteristics in 
such a two-rail slider, so that the floating height and roll should be 
severely selected to maintain constant read/write characteristics of the 
magnetic head over all the tracks. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the present invention to 
provide a floating magnetic head slider which can reduce variations in the 
floating height of the slider at different radial positions over a 
recording medium surface so as to provide a constant floating height over 
all the recording tracks, thereby improving the read/write characteristics 
and achieving constant density recording (CDR). 
According to a first aspect of the present invention, there is provided a 
floating magnetic head slider comprising an air bearing surface having a 
longitudinal axis thereof, the air bearing surface having a leading edge 
and a trailing edge extending perpendicular to the longitudinal axis, a 
pair of side rails disposed on the air bearing surface and in symmetry to 
each other with respect to the longitudinal axis, each of the side rails 
having a first region disposed adjacent to the leading edge and extending 
parallel to the longitudinal axis, a second region extending from the 
first region in a first direction deviated from the direction of the 
longitudinal axis toward the longitudinal axis by a first angle, and a 
third region extending from the second region in a second direction 
deviated from the direction of the longitudinal axis toward the 
longitudinal axis by a second angle, the second angle being larger than 
the first angle. 
According to a second aspect of the present invention, there is provided a 
floating head slider comprising an air bearing surface having a 
longitudinal axis thereof, the air bearing surface having a leading edge 
and a trailing edge extending perpendicular to the longitudinal axis, a 
pair of side rails disposed on the air bearing surface and in symmetry to 
each other with respect to the longitudinal axis, each of the side rails 
having a first region disposed adjacent to tile leading edge and extending 
substantially parallel to the longitudinal axis, and a second region 
extending from the first region and forming an arcuate shape, the arcuate 
shape being concave as viewed from the longitudinal axis. 
According to a third aspect of the present invention, there is provided a 
floating head slider comprising an air bearing surface having a 
longitudinal axis thereof, the air bearing surface having a leading edge 
and a trailing edge extending perpendicular to the longitudinal axis, a 
pair of side rails disposed on the air bearing surface and in symmetry to 
each other with respect to the longitudinal axis, and a central rail 
disposed on the air bearing surface between the pair of side rails, the 
central rail having a first region adjacent to the leading edge, a second 
region adjacent to the trailing edge, and a neck disposed between the 
first region and second region, the first region extending substantially 
parallel to the longitudinal axis, at least a portion of the first region 
has an increasing width as viewed toward the trailing region, the neck 
having a width smaller than the width of portions of the first region and 
second region adjacent to the neck.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will now be described with reference 
to the accompanying drawings. 
Referring to FIGS. 6A an 6B, FIGS. 7A and 7B, and FIGS. 8A and 8B, in which 
similar elements are designated by the 
same reference numerals, each of magnetic head sliders 31, 32 and 33 
according to first, second and third embodiments of the present invention 
has, on an air bearing surface (ABS) 12 thereof, a pair of side rails 301, 
302 or 303 having a slope 16 at the leading edge thereof, a central rail 
14 having a slope 19 at the leading edge thereof, and a recess 17. A 
magnetic head 15 is attached to the trailing end surface of each of the 
sliders, with a magnetic gap thereof being disposed at the trailing edge 
of the central rail 14. In addition, the magnetic head slider 31 has a 
pair of mechanically formed grooves 18 running parallel to each other in 
the ABS 12 and interposed between the side rails 301 and the central rail 
14. The grooves 18 should be formed if the recess 17 cannot be formed to a 
sufficient depth by etching. These sliders 31, 32 and 33 are supported by 
an unillustrated magnetic head support mechanism of a rotary actuator type 
at the surface opposite to the ABS 12. 
In the magnetic head slider 31 according to the first embodiment shown in 
FIG. 6A, side rails 301 extending parallel to the longitudinal axis of the 
slider are provided on both sides of the slider 31, with the central rail 
14 disposed therebetween. Each of the side rails 301 has a first, leading 
region L1 extending substantially in the direction of the longitudinal 
axis of the slider 31, a second, intermediate region L2 extending in the 
direction deviated from the direction of the longitudinal axis of the 
slider toward the longitudinal axis by angle .THETA.11, and a third, 
trailing region L3 extending in the direction deviated from the direction 
of the longitudinal axis of the slider toward the longitudinal axis by 
angle .THETA.12 (.THETA.12&gt;.THETA.11). The width of the second and third 
regions L2 and L3 is smaller than the width of the majority of the first 
region L1. 
The trailing edge of the trailing region L3 of the side rails 301 is 
located at the position significantly ahead of the trailing edge of the 
slider 31. If a track geometry is employed in which the skew angle of the 
magnetic head slider 31 is zero at the innermost track and increases as 
the slider 31 moves toward the outermost track, it is preferable that the 
angle .THETA.11 be equal to skew angle at the track located at the center 
of the track area. In this case, the angle .THETA.12 is preferably equal 
to skew angle at the outermost track. 
The central rail 14 has a leading region of a small width generating a 
small pressure, an intermediate region of a tapered width increasing as 
viewed toward the trailing edge of the slider 31, and a trailing region of 
a large width generating a large pressure. By this configuration, the 
effect of variations in pressure due to variations in the air velocity can 
be reduced compared to the case of a central rail having a tapered width 
increasing at a constant rate as viewed from the leading edge to the 
trailing edge. This configuration decreases the dependency of the pressure 
acting on the central rail on the circumferential velocity, thereby 
obtaining a uniform floating height. 
In the three-rail slider of the present embodiment, the length of the side 
rails 301 is smaller than that of the central rail 14, which prevent the 
magnetic head slider from contacting the medium surface even when the 
slider 31 rolls. However, the side rails 301 should have a sufficient 
length so as to obtain a pitch stiffness thereof. 
With the configuration as described above, the pair of side rails 301 have 
a structure in which each of the side rails 301 is bent toward the other 
of the side rails 301 at a plurality of positions. The amount of bending 
angle is smaller at a position near the leading edge and larger at a 
position near the trailing edge. The structure in which the bending angle 
is small at the first position near the leading edge provides the 
advantage that the total compression length of the ABS 12 is low compared 
to the case of a large bending angle at the first position, when the 
magnetic head slider resides over the outermost track so as to have a 
larger circumferential velocity. Namely, the small bending angle at the 
first position cancels the increase in the floating height caused by the 
increase in the circumferential velocity, thereby providing constant 
floating height over all the tracks. On the other hand, the structure in 
which the bending angle at the second position near the trailing edge of 
the side rail 31 is large provides the advantage that the side rails 31 
are located near the central rail 104. 
Referring to FIGS. 11A, 11B and 11C, the function of the side rails 301 in 
the first embodiment will be described. FIGS. 11B and 11C show pressure 
distribution along the lines B--B and C--C, respectively, in FIG. 11A, 
which again shows the magnetic head slider of FIG. 6A. In FIG. 11A, the 
direction of the air at the outermost track is shown by arrow "g", while 
the direction of the air flow shown by arrow "h" at the innermost track is 
parallel to the longitudinal axis of the slider 31. In FIG. 11A, 
X-coordinate is positive as viewed toward the disk center, with the origin 
thereof being at the center of the slider 31. 
In FIGS. 11B and 11C, dotted lines represent the pressure distributions at 
the innermost track while the solid lines represent the pressure 
distributions at the outermost track. As understood from these drawings, 
for each of the rails, the pressure distribution at the innermost track is 
in symmetry with respect to the central axis of each of the rails, while 
the pressure distribution for each of the rails at the outermost track 
deviates from the symmetry to roll the slider such that the outer side of 
the each of the rails is raised compared to the inner side of the each of 
the rails. 
However, as shown in FIG. 11C, the pressure acting on the inner side rail 
is raised at the outermost track as compared to the case at the innermost 
track, while the pressure acting on the outer side rail is reduced at the 
outermost track as compared to the case at the innermost track. This is 
because the air flow "g" at the outermost track is directed along the 
trailing region (L3 in FIG. 6B) of the inner side rail to generate an 
increased compression length, while the air flow "g" at the outermost 
track generates a reduced pressure acting on the outer side rail due to 
the reduced compression length of the trailing region of the outer side 
rail. 
Accordingly, the structure of the side rails according to the present 
embodiment cancels the roll generally caused by each of the rails at the 
outermost track. In other words, the dependency of the local stiffness on 
the track radius can be decreased so that the amount of roll or variations 
in roll of the slider can be minimized over all the track area, which 
makes it possible to maintain the stable attitude of the floating magnetic 
head slider. 
Turning back to FIGS. 7A and 7B, the magnetic head slider 32 according to 
the second embodiment has two side rails 302 and a central rail 14 which 
is similar to that of the first embodiment. Each of the side rails 302 has 
a first, leading region M1 having a first, large width in most of the 
region M1 and extending parallel to the longitudinal direction of the 
slider 32. The first region M1 has a second width smaller than the first 
width at the trailing edge thereof. Each of the side rails 302 further has 
a second region M2 having the second width and extending in the direction 
deviated from the direction of the longitudinal axis of the slider toward 
the longitudinal axis by angle .THETA.21, a third region M3 having the 
second width and extending in the direction rotated from the direction of 
the longitudinal axis of the slider toward the longitudinal axis by angle 
.THETA.22 (.THETA.21&lt;.THETA.22), and a fourth, trailing region M4 having 
the second width and extending in the direction deviated from the 
direction of the longitudinal axis of the slider toward the longitudinal 
axis by angle .THETA.23 (.THETA.22&lt;.THETA.23). 
Angle .THETA.21 is approximately equal to the skew angle at a track located 
outward from the innermost track by an amount corresponding to one third 
of the radial distance between the innermost track and outermost track. 
Angle .THETA.22 is approximately equal to the skew angle at a track 
located outward from the innermost track by an amount corresponding to two 
thirds of the radial distance between the innermost track and outermost 
track. Angle .THETA.23 is approximately equal to the skew angle at the 
outermost track. 
In the second embodiment, air flow at the respective tracks is directed in 
the directions of the respective regions of the inner side rail. 
Accordingly, the attitude of the slider is further improved over the first 
embodiment. 
Referring back to FIGS. 8A and 8B, the magnetic head slider 33 according to 
the third embodiment has two side rails 303 and a central rail 14 which is 
similar to that of the first embodiment. Each of the side rails 303 has a 
leading half region N1 and a trailing half region N2. The leading half 
region N1 extends substantially parallel to the longitudinal axis of the 
slider 33 while the second half region N2 has a arcuate shape curved 
toward the longitudinal axis of the slider 33. The arcuate shape of each 
side rail 303 has a radius and a center of curvature such that the angle 
(referred to as tangential angle hereinafter) between the longitudinal 
axis of the slider and the tangential line of the arc varies in accordance 
with a variation in the skew angle between the innermost track and the 
outermost track. In detail, the center of the curvature 01 is offset from 
the longitudinal center of the side rail (having a length N) toward the 
leading edge by an amount .DELTA.h (.DELTA.h&gt;0) so that the tangential 
angle .THETA.31 of the arc at the leading edge of the trailing region N2 
is roughly equal to skew angle at the intermediate track, and the 
tangential angle .THETA.32 of the arc at the trailing edge of the side 
rail is roughly equal to skew angle at the outermost track. The radius 
.rho.1 of the curvature is determined such that the tangential angle 
follows the variation in the skew angle in the whole track area of the 
medium. 
The magnetic head slider of the present embodiment provides advantages 
similar to those provided by the first and second embodiments in which the 
side rails are bent at a plurality of positions. Namely, a constant 
floating height of the magnetic head slider and a stable floating attitude 
can be provided similar to the first and second embodiments. Since the 
constant floating height can be obtained by changing the curvature of the 
side rails in accordance with track geometry, flexibility of design for 
the slider can be increased. In addition, since the smooth boundary of the 
rails prevents the generation of burrs in the slider during etching 
process, the throughput of the slider can be increased. 
Referring to FIGS. 9A, 9B and 9C and FIGS. 10A and 10B, there are shown 
magnetic head sliders 40 and 50 according to a fourth and a fifth 
embodiments of the present invention. Each of the magnetic head sliders 40 
and 50 according to the fourth and fifth embodiments of the present 
invention has, on an ABS 12 thereof, a pair of side rails 301 similar to 
those in the first embodiment, a central rail 401 or 402, a recess 17, and 
mechanically formed grooves 18. As previously described, the grooves 18 
should be formed if the recess 17 cannot be formed to a sufficient depth 
by etching. These sliders 40 and 50 are supported by an unillustrated 
magnetic head support mechanism of a rotary actuator type at the surface 
opposite to the ABS 12. 
In the fourth embodiment shown in FIGS. 9A, 9B and 9C, the central rail 401 
has a first, leading region D11 including a slope 16 and having a uniform 
small width W11, a second, tapered region D12 including a tapered width 
part having a linearly increasing width from the width W11 to a width W12 
as viewed toward the trailing edge of the slider 40 and a constant width 
part following thereto, a neck 401A having a small width W13, a third, 
tapered region D13 having a linearly increasing width from a width W13 to 
a width W14 as viewed toward the trailing edge thereof. The trailing edge 
of the third region D13 of the central rail 401 is flush with the trailing 
edge of the ABS 12, at which a magnetic head 15 has a magnetic gap 
thereof. 
The amount of decrease (W12-W13) in the width at the neck 401A, and the 
width W14 at the trailing edge of the central rail 401 are determined 
based on a theoretical or designed floating height of the magnetic head 
slider 40, a desired constant floating height, the size of the magnetic 
head 15 formed at the trailing edge of the slider 40, and the like. If the 
width W13 of the central rail 401 at the neck 401A is too small, a 
sufficient floating height cannot be obtained. On the other hand, when the 
width W13 of the neck 401A is too large, the effect provided by changing 
the width of the central rail 401 is decreased so that a constant floating 
height cannot be obtained. 
The longitudinal position of the neck 401A in the central rail 401 is also 
determined by taking a designed floating height into consideration. If the 
neck 401A is located more closely to the leading edge, the floating height 
will be too small. On the other hand, if the neck 401A is located more 
closely to the trailing edge, the effect provided by changing the width of 
the central rail 402 is decreased so that it will be difficult to obtain a 
constant floating height. In order to solely obtain a constant floating 
height, it would be preferred that the width of the central rail 401 be 
kept constant between the neck 401A and the trailing edge, or else, be 
decreased toward the trailing edge. However, to maintain the pitch 
stiffness of the slider 40 and to provide a sufficient width for bearing 
the magnetic head 15, it is preferred that the width of the central rail 
401 be increased toward the trailing edge thereof, as disclosed in this 
embodiment. 
In the fifth embodiment shown in FIGS. 10A and 10B, the floating head 
slider 50 has the same configuration as that of the fourth embodiment 
except for the structure of the central rail 402. The central rail 402 in 
this embodiment has a first, leading region D21 including a slope 16 and 
having a uniform small width W21, a second, tapered region D22 having a 
linearly increasing width as viewed toward the trailing edge of the slider 
50, a neck 402A having a width W22, a third, oblique region D23 having the 
width W22 and extending in a direction deviated from the direction of the 
longitudinal axis of the slider 50 toward the innermost track by angle 
.alpha., and a trailing, tapered region D24 extending in a direction 
deviated from the direction of the longitudinal axis of the slider 50 
toward the outermost track by angle .beta. and having an increasing width 
as viewed toward the trailing edge thereof. 
By the configuration as described above, the central rail 402 is bent at 
the neck 402A to be directed in the direction along the direction of the 
air flow at the innermost track, indicated by arrow "i". In the vicinity 
of the trailing edge, the central rail 402 is reversely bent at the 
position 402B to be directed in the direction along the air flow at the 
outermost track, indicated by arrow "j". Namely, the angle .alpha. of the 
first bending is determined based on the skew angle at the innermost track 
while the angle .beta. of the second bending is determined based on the 
skew angle at the outermost track. The position 402B of the second bending 
is determined based on the angle .beta. of the first bending and the angle 
.alpha. of the second bending. 
If the position 402B of the second bending is located more close to the 
trailing edge, the floating height at outer tracks decreases, while if the 
position of the second bending is located more closely to the neck 402A, 
the floating height at inner tracks decreases. These structure would 
deteriorate the floating characteristics of the slider at constant 
floating height. The position 402B of the second bending is determined in 
accordance with a desired track geometry, taking account of the position 
of the neck 401A and the amount of variations in the width of the central 
rail. 
In the fourth and fifth embodiments of the present invention, the central 
rail 401 or 402 has the neck or small width portion adjacent to the 
tapered region where the positive pressure produced in the ABS 12 is at a 
maximum, and the small width is kept constant or gradually increased 
toward the trailing edge. This configuration provides small variations in 
the pressure due to variations in the velocity of the air flow compared to 
the first through third embodiments. 
The configuration of the fifth embodiment is especially effective in 
magnetic disk drives which employ a track geometry such that the skew 
angle has a significant minus value at the innermost track. The third 
region D23 extends along the air flow at the innermost track to thereby 
prevent the bearing pressure at the innermost track from decreasing while 
the trailing region D24 extends along the air flow at the outermost track 
to thereby prevent the bearing pressure at the outermost track from 
decreasing, thereby maintaining pitch stiffness in the whole track area. 
FIGS. 12 and FIG. 13 show changes in normalized flying height in the 
magnetic head slider according to the fifth embodiment of the present 
invention as functions of skew angle and circumferential velocity, 
respectively. Changes in floating height in conventional sliders are also 
shown therein for comparison. FIG. 14 also shows minimum floating height 
dependence on track radius for a magnetic head slider according to the 
fifth embodiment and for conventional ones. In the drawings, the solid 
lines represent the characteristics of the fifth embodiment while the 
dotted lines and chain lines represent the characteristics of a 
conventional three-rail slider and a conventional two-rail slider, 
respectively. 
As will be understood from FIGS. 12 and 13, the floating height of the 
magnetic head slider according to the present invention exhibits a reduced 
dependency on skew angle and circumferential velocity as compared to those 
of the conventional sliders. As a result, as shown in FIG. 14, variations 
in minimum floating height of the slider depending on radial position can 
be decreased, thereby permitting a constant floating height to be obtained 
which is essential for obtaining a high density recording.