Method and apparatus for increasing data density in magnetic data storage disk drives

A method and apparatus for increasing recording density in zone bit recording on a magnetic recording disk without increasing track density by maximizing the data density the at disk's outer track. A magnetic recording head is attached to a parallelogram shaped slider such that the head's gap-to-radius skew and the slider rail skew changes continuously as the slider moves in an arcuate path from the disk's inner track to the disk's outer track. The parallelogram slider is designed to reduce the loss of data density at the outer track by minimizing the head's gap-to-radius skew while maximizing the rail skew angle at the outer track to maintain an essentially constant low fly height across the disk.

FIELD OF THE INVENTION 
The present invention relates to the field of magnetic disk drives. More 
particularly, the present invention relates to a method of transducing 
data onto a rotating disk surface using a transducer-slider structure 
which increases recording density and also relates to a read/write 
transducer and slider structure designed to increase recording density. 
BACKGROUND OF THE INVENTION 
Computer systems employ a number of storage devices to store data. One of 
these storage devices is a disk drive. A disk drive includes one or more 
magnetic storage disks mounted on a spindle and spaced apart so that the 
separate disks do not touch each other. 
The surface of each disk is divided into portions, known as tracks, where 
data is stored. The tracks are arranged in concentric circles. In zone bit 
recording, a data storage disk is subdivided into a set of concentric 
bands of data tracks. Each zone of recording tracks is provided with a 
data rate which is adapted to the radius of the particular recording zone. 
In this method, a substantially constant data rate is maintained within 
each radial disk zone. Each zone's data rate is chosen such that the 
storage capacity is maximized at the inner track of each zone. 
Currently, magnetic data storage disks are formed of precisely formed 
aluminum alloy, glass or ceramic substrates upon which magnetic media 
layers and protective overcoat layers are deposited as thin films by 
sputtering techniques. 
Information is stored onto the magnetic data storage disks in the form of 
transitions in magnetic flux on the magnetic surface of the disk. An 
electromagnetic transducer, also known as a read/write head is typically 
contained at a trailing edge of a ceramic slider structure, which flies 
upon an air cushion or bearing directly above (e.g. 1-5 micro inches) a 
magnetic recording disk. The read/write head is usually formed from two or 
more elongated pole pieces of a suitable ferromagnetic material such as a 
nickel iron (NiFe) alloy and a wire coil. At one s end, the pole pieces 
are touching and at the other end there is a slight gap between the pole 
pieces. The head is positioned so that the gap is directed towards the 
disk surface. When electric current is impressed on the coil, a magnetic 
flux is generated, which is impressed upon the pole pieces. At the gap, 
the magnetic flux is directed through the magnetic material in the 
adjacent disk surface, impressing an area of the track with magnetic flux 
to represent data. 
The transducer-slider structure is positioned over the data storage surface 
by a head positioner actuator, such as a rotary voice coil actuator 
positioner. The actuator positioner includes a head-gimbal assembly which 
enables the transducer-slider assembly structure to manifest pitch and 
roll characteristics, while being maintained precisely in position 
radially relative to the rotating disk surface. The actuator rapidly 
displaces the transducer-slider structure from a departure track to a 
destination track during track seeking operations; and it maintains the 
transducer-slider structure in registration with the destination track 
during subsequent data writing or reading operations. These positioning 
operations are controlled in large part by transducer position information 
read by the transducer as it passes over each embedded servo sector within 
each data track. 
The conventional design for a hard disk drive slider utilizes a two rail, 
taper flat air bearing which is created by machining a slider row bar. 
This slider design and row bar machining process has been available for a 
number of years. One example of a conventional two-rail slider in 
accordance with contemporary prior art techniques is described in U.S. 
Pat. No. 4,928,195 entitled "Improved Floating Magnetic Head for High 
Density Recording". 
When the disk rotates, air is dragged between the rails and the disk 
surface causing pressure, which forces the head away from the disk. The 
head is thus said to fly over the rotating disk at a "fly height". This 
method of recording, where the head flies in close proximity to the 
rotating disk surface on an air bearing is known as "non-contact 
recording". 
The disadvantage of most non-contact magnetic disk recording methods, is 
that the relative velocity between the head and disk is greater at the 
outer radius of the disk than at the inner radius. Thus the head has a 
tendency to fly higher at the outer radius where the relative velocity is 
greatest. Consequently, this method of recording produces a linear data 
density (bits per linear track unit length) that varies inversely with 
track radius. That is, within each zone, the data density at the inner 
radius track is greatest while the data density at the outer radius tracks 
has a tendency to be lower. 
In the context of zone bit recording, the outer track of each zone tends to 
lose data storage capability. More detrimentally, the outermost tracks of 
a disk, which offer the most data storage capacity, tends to be under 
utilized, drastically reducing total data storage capability of the disk. 
One method of maintaining a constant low fly height across the disk, is to 
severely skew the angle of the slider rails at the outer diameter. This 
known method reduces the inverse relationship between radius and data 
density. 
FIG. 1 shows a typical prior art conventional rectangular shaped two rail 
slider 10 wherein the flying rails 13 are essentially parallel to line 21, 
which is tangent to the innermost track 20 and severely skewed by an angle 
.theta., from tangent line 21', at the outermost track 30. However, using 
a conventional rectangular shaped slider, with this design the skew angle 
of the head gap is coupled with the skew angle of the rails, that is, by 
skewing the rail angle, the head gap is effectively skewed as a result. 
FIG. 1 illustrates this dependency wherein the gap 12 is essentially 
parallel to the disk radius at innermost track 20 and skewed by gap skew 
angle .beta., measured from the disk radius at the outermost track 30. 
The high skew angles of the head gap to the track width direction have two 
detrimental effects on read/write performance. Both of these effects 
depend upon the cosine of the skew angle. 
FIGS. 2a and 2b illustrate these detrimental effects. In FIG. 2a, G 
represents the projection of the gap, having a width W, onto a track T 
when the head gap is not skewed. Note that G also represents an areal bit 
of storage. In this non-skewed orientation, a transition spacing, S, is 
defined by a perpendicular distance between the edges of a bit. 
When the head gap is skewed by an angle .theta., as illustrated in FIG. 2b, 
a effective track width, W', is reduced by the cosine of .theta.. As the 
head gap skew angle, .theta., increases, the effective track width also 
decreases. Accordingly, since the amplitude for all frequencies decreases 
in direct proportion with track width, as is well known by those skilled 
in the art of magnetic recording, the first detrimental effect is that 
linear bit density of each track indirectly decreases because the loss in 
amplitude requires even larger transition spacing. 
The second detrimental effect is further illustrated in FIG. 2b, using 
basic principles of trigonometry. FIG. 2b shows that a effective 
transition spacing, S', is increased by the inverse of cosine theta. Since 
transition spacing is the inverse of bit spacing, the head gap skew angle 
has a direct impact on increasing transition spacing and consequently on 
the loss of linear data density. In other words, as head gap skew angle 
increases, transition spacing also increases, thereby decreasing data 
density. 
Since the linear data density of a disk is directly proportional to 
transition spacing and indirectly proportional to track width, it is 
critical to minimize the transition spacing at the outer track in order to 
maximize data density without increasing track density. 
Various prior art methods have attempted to improve data density at the 
outer diameter track. One method is described in U.S. Pat. No. 4,945,427 
('427). This patent maximizes the head/media capacity by increasing the 
track density and decreasing the track widths at the outer radius tracks. 
To record onto the narrower tracks at the outer radius tracks, the '427 
patent uses a parallelogram shaped slider/head arrangement whose gap is 
skewed in a progressively increasing manner, to the disk radius at the 
location of each track, from the inner to the outer track. Thus the track 
widths become progressively narrower as the head moves from the inner to 
the outermost track. 
The disadvantage of '427 is that it practices constant frequency recording, 
which is a lesser preferred method of recording by those skilled in the 
art. Further, the head gap of the two rail slider described in '427 is 
skewed from a large angle, at the inner diameter track, to an even larger 
angle at the outer diameter track. In addition, complex disk drive 
functions must be provided to format the disks and incrementally advance 
the actuator arm from one narrow track to the next. 
What is needed in the art of zone bit recording is a new and improved 
method of increasing recording density of magnetic disks by maximizing 
data density at the outer diameter tracks without increasing track density 
or using complex disk drive functions. The method should include an air 
bearing two rail slider having an essentially constant fly height across 
the disk. 
SUMMARY OF THE INVENTION 
Accordingly, a general object of the present invention is to provide a new 
and improved apparatus and method for zone bit magnetic recording in a 
manner which overcomes limitations and drawbacks of the prior art. 
Another object of the present invention is to provide a new and improved 
method and apparatus for increasing recording density in zone bit magnetic 
recording using a parallelogram shaped slider designed to maintain an 
essentially constant fly height and maximize data density without 
increasing track density. 
Another object of the present invention is to provide a new and improved 
apparatus and method for increasing magnetic recording density of the 
above mentioned kind without requiring a complex disk drive head 
positioner to incrementally advance the actuator arm through progressively 
narrower position increments, as the head moves from the inner to the 
outer track. 
In accordance with the present invention, a parallelogram shaped 
air-bearing slider is provided such that its head gap skew changes from a 
counter clockwise (CCW) angle from the disk radius at the innermost track 
to a clockwise (CW) angle from the disk radius at the outermost track when 
the arm rotates in a CW direction, moving the slider from the innermost 
track to the outermost track. At a median track between the innermost and 
outermost track, the head gap is parallel with the disk radius. The gap 
skew angle is designed to minimize the detrimental effects of the cosine 
of the gap skew on track width, averaged over the disk surface. Therefore, 
areal data density is maximized without increasing track density. 
In accordance with a feature of the present invention, the parallelogram 
shaped slider mounting is designed such that the flying rails are skewed 
progressively at an angle from the tangential velocity vector as the 
slider moves across the disk such that an essentially constant low fly 
height is maintained across the disk. 
In accordance with a feature of the present invention, the parallelogram 
shaped slider is oriented such that the inside leading corner is located 
in advance of the outside leading corner at the inner track. 
In accordance with a feature of the present invention, the parallelogram 
shaped slider is oriented such that the outside leading corner is located 
in advance of the inside leading corner at the outer track. 
The invention will be described with reference to the recording of 
concentric data tracks. However, the invention also finds utility in other 
track formats, for example in the recording of a single continuous spiral 
track. Thus, the scope and content of the invention includes the recording 
of such other track formats.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
The present invention finds utility in disk drives or files of many 
detailed configurations, including hard or rigid disk drives having 
various disk diameters. 
The details of construction of disk drives in which the invention finds 
utility, including the fabrication of the parallelogram shaped slider, are 
well known to those skilled in the art. As a result the following 
description provides only such detail as is necessary to teach the best 
mode of the present invention, and is necessary to enable those skilled in 
the art to practice the invention. 
FIG. 3 shows a top view of a preferred embodiment of the present invention 
using a new and improved parallelogram shaped slider 50 designed to 
maximize linear data density at the outer diameter tracks while 
maintaining a constant low fly height across the surface of the disk. The 
advantage of the present invention over the prior art is that track 
density is not increased, thus eliminating the need for a complex head 
positioner and control circuit to format the disk and control incremental 
advancement of the head. More importantly, this design is meant to allow 
for zone bit recording at the maximum possible linear bit density (BPI). 
FIG. 3 shows a rotary actuator structure 10 connected to rotate a movable 
actuator arm 15. The slider 50 is mounted on the arm 15, and a read/write 
head 16 having a gap 17 is carried by the slider 50. As the disk 60 
rotates, the head 16 flies in close proximity to the surface of the disk 
60. Two positions of arm 15 are shown. In position 14, head 16 is 
positioned to transduce at the innermost track 20. In position 14' the 
head is positioned to transduce at the outermost track 30. 
Line 51 represents the disk's radius at the location of the disk's 
innermost recording track 20 and line 51' represents the disk's radius at 
outermost track 30. 
Tangent lines 53 and 53' of FIG. 3 are tangent to innermost and outermost 
tracks 20 and 30, respectively. Lines 54 and 54' extend normal to head gap 
17 at the location of these two tracks. 
Head gap 17 is skewed to disk radii 51 and 51' by the angle .beta. and 
.beta.' at the location of these two disk tracks, respectively. In the 
exemplary showing, where the actuator structure 10 is located on the right 
hand side of disk hub 90, angle .beta. is about -7.5 degrees (i.e. CCW) 
from the disk radius and angle .beta.' is about +7.5 degrees (i.e. CW) 
from the disk radius. The corresponding angle, when the head is positioned 
at the disk's median track (not shown) is about 0 degrees. That is, the 
head gap is essentially parallel to the disk radius. It should be noted 
that in an alternative embodiment, angle .beta. may be about +7.5 degrees 
(i.e. CW) from the disk radius and angle .beta.' may be about -7.5 degrees 
(i.e. CCW) from the disk radius. The orientation of angles .beta. and 
.beta.' will depend on factors such as location of the actuator means 10 
and direction of disk rotation 13. 
Lines 40 and 40' of FIG. 3 extend parallel to flying rails 41 and 42 of 
slider 50, which are shown in FIG. 4. Rails 41 and 42 are oriented about 
+5 degrees (CW) from tangent line 53 at the location of the innermost 
track 20 and are oriented about +20 degrees (CW) from tangent line 53' at 
the outermost disk radius 30. Similar to gap skew angles .beta. and 
.beta.', in alternative embodiments, rails 41 and 42 may be oriented about 
-5 degrees (CCW) from tangent line 53 at the location of the innermost 
track 20 and about -20 degrees (CCW) from the tangent line 53' at the 
outermost disk radius 30, depending on the location of the actuator 
structure 10 and direction of disk rotation 13. 
Lines 43 and 43', extend from the slider's trailing edge 57 at innermost 
track 20 and outermost track 30, respectively. The trailing edge 57 is 
shown in FIG. 4. Lines 43 and 43' are also parallel to head gap 17. The 
angle between this trailing edge and the radii 51 and 51' varies between 
-7.5 degrees (CCW) from the disk radius at the innermost track 20, to +7.5 
degrees (CW) from the disk radius at the outermost track 30. Again, as 
with gap skew angles .beta. and .beta.' the angles between the trailing 
edge and the radii 51 and 51' may be +7.5 degrees (CW) and -7.5 degrees 
(CCW) from the disk radius at tracks 20 and 30, respectively, depending on 
the embodiment. 
FIG. 4 shows the bottom plan view of the slider 50 shows that the slider is 
of a generally parallelogram shape (i.e. the side of the slider that faces 
the disk, shown in FIG. 4 is of a parallelogram shape) having an internal 
obtuse angles .epsilon. and .epsilon.' and internal acute angles .gamma. 
and .gamma.'. This unique shape enables slider 50 to be nearly 
conventionally fabricated i.e. in groups of rows and columns of heads, 
where the heads are formed by angled cuts e.g. by gang saws at cut angles, 
different than the typical 90 degree cuts, in a manner that will be 
readily understood by those skilled in the art. 
The slider's two linear flying rails 41 and 42 are generally parallel to 
each other and may be of generally equal length, as shown in FIG. 4. 
However, in an alternative preferred embodiment of the present invention, 
flying rails 41 and 42 may be of unequal length, as shown in FIG. 5 as 141 
and 142. The leading ends 60 and 61 of rails 41 and 42 terminate in a 
generally linear leading edge 56. The trailing ends 90 and 91 of the rails 
terminate in a generally linear trailing edge 57. The leading/trailing 
edges 56 and 57 extend at an angle .phi. of about 12.5 degrees (as 
measured in the direction of disk rotation) to the direction in which 
rails 41 and 42 extend. Gap 17 is generally parallel to the slider's 
leading edge 56 and its trailing edge 57. 
In its operating arrangement, the internal obtuse angles .epsilon. and 
.epsilon.' and internal acute angles .gamma. and .gamma.' of the slider 50 
are fixed such that the average of the cosine of the gap skew angle across 
the disk is maximized, consequently minimizing the detrimental effects of 
the skew, while maximizing the rail skew angle at the outer diameter, to 
maintain a constant low fly height across the disk surface. The track 
widths are consequently maintained in essentially constant width across 
the disk 60, as shown in FIG. 3a and illustrated by 65. To fully maximize 
the data storage capability of the disk, the internal obtuse (.epsilon.) 
and acute (.gamma.) angles of the slider should preferably be set so as to 
maximize the average of the cosine of the gap skew angle across the disk 
while maintaining an essentially constant low fly height. In the 
embodiment illustrated in FIG. 3, the leading inside corner 80 is located 
in advance of the leading outside corner 81 at the inner diameter track 
and the inverse occurs at the outer diameter track. It should be noted 
that it is this particular parallelogram shaped slider and it's mounted 
orientation, relative to the disk, which enables the linear data density 
to be increased without increasing track density at the outer diameter 
tracks. 
It should also be noted that the variation that occurs in the skew of the 
head gap to disk radii and the skew of the slider rail to the tangential 
velocity vector is composed of two components. The first component is the 
direct angular rotation of the slider 50 by virtue of rotation of rotary 
actuator structure 10. The second component, which is indirectly produced 
by actuator rotation, is due to a change in the angle of the disk radius 
that extends through the slider 50 at the location of each disk track. 
Those skilled in the art, when faced with the design of a disk file of a 
particular geometry, will readily find that the present invention can be 
applied to the particular geometry by making use of the effects of these 
two component to thereby provide the needed gap and rail rotation or skew 
as the slider moves across the disk. 
Having thus described an embodiment of the invention, it will now be 
appreciated that the objects of the invention have been fully achieved, 
and it will be understood by those skilled in the art that many changes in 
construction and widely differing embodiments and applications of the 
invention will suggest themselves without departing from the spirit and 
scope of the invention. The disclosure and description herein are purely 
illustrative and are not intended to be in any sense limiting.