Magnetic disk file recording with variable track width and variable track density

Abstract: A magnetic recording apparatus and method for the constant frequency recording of concentric data tracks on a magnetic recording disk in a manner to provide continuously reducing track width and continuously reducing track-to-track spacing from the disk's inner track to the disk's outer track. A magnetic recording head moves on a path from the disk's inner track to the disk's outer track. The head's gap-to-radius skew increases as the head moves from the inner track to the outer track. Thus, the gap's width-projection onto a disk radius at the location of each track continuously decreases in length, from the inner track to the outer track. As the track width progressively decreases, the track-to-track spacing also decreases, to thereby provide higher track density at the disk's outer tracks. A flying head having a parallelogram shaped slider is described, allowing use of the invention in non-contact recording.

Description: Technical Field of the Invention The present invention relates to the field of magnetic recording, and more specifically to the field of recording on magnetic disks. Background of the Invention In the constant frequency method of recording (CFR) on a magnetic disk, the disk's angular velocity (RPM) is held constant, and data is supplied to a recording head at a constant binary data rate (bits per second or bps). This method of recording produces a linear data density (bits per linear track unit length) that varies inversely with track radius. That is, linear recording density is greatest at the disk's inner track. The recording capability of a given recording head and magnetic media can therefore be maximized only at the inner track. Various methods have been used to more fully utilize the head/media recording capability. One prior art method is to decrease the disk's RPM as the head moves radially outward of the disk, so that a constant surface speed exists between the head and the disk with increased track diameter. When data is recorded at a constant data rate, constant density recording (CDR) results. As a result, utilization of the head/media recording capability can be maximized. This method is difficult to practice, however, due to the high inertia of a rotating disk, particularly where the disk is a hard disk, and the resulting difficulty in rapidly changing the disk's RPM in a random access environment. Another prior art method involves providing bands of recording tracks, and changing of the data rate for each recording band. In this method, each band's data rate or frequency is chosen such that at the inner track of each band the head/media capability is maximized. A disadvantage of this method is that different data channel characteristics must be provided for each of the different frequency bands. Additionally, the performance of a multi-frequency system using ferrite heads is degraded by the head's failure to perform optimally at the different frequencies. United States Patent 4,388,655 is directed to a arrangement for improving the density and fidelity of video recording. A recording head is moved across the surface of the recording disk along a non-radial path. The patent teaches that when the head is moved along the non-linear path the head gap is skewed relative to the disk radius. The patent also teaches that this skew should preferably remain constant. United States Patent 4,479,156 describes a video disk apparatus wherein adjacent tracks are recorded with heads of opposite gap skew, the skew remaining constant for each head across all corresponding tracks. United States 4,486,798 discloses an air bearing head of the conventional rectangular shape, where the slider's rails and the head gap are skewed to the data tracks on the disk. The gap skew remains constant from track to track. Rotary actuators are commonly employed in magnetic recording disk files. As the head is moved across the surface of the disk, the head gap becomes skewed at an angle to the data tracks. In such an actuator, it has always been a design objective to minimise the amount of skew in order to reduce the adverse effects of the skew on the flying characteristics of the flying head. Some effort has been directed at designing modifications to the conventional rectangular shaped slider of the recording head in order to improve the flying characteristics when the head gap is skewed to the data track. In an article entitled 'A UNIFORM FLYING HEIGHT ROTARY ACTUATOR BEARING SLIDER' by J W White (IEEE Transactions on Magnetics, Vol. Mag-22, No. 5 September 1986) the flying head is provided with small angle side tapers on the flying rails of the slider. These allow a partially lateral direction of flight of the slider relative to the data track. In JP-A-61 120 987, an increase in recording density at the outer periphery of the disk is effected by causing the recording gap of the magnetic head to be skewed at an increasing angle with respect to tangential velocity vector of the disk whereby the track width at the outer periphery is smaller than at the inner periphery. The track pitch is also decreased from inner to outer periphery. An article in the IBM Technical Disclosure Bulletin entitled `Magnetic read/write head having skew gap' (Vol. 28, No. 6, November 1985 p 2582) discloses a rectangular shaped read/write head incorporating a skewed head gap. The head is moved across the disk in such a manner as to cause a reduction in track width from inner to outer track. Disclosure of the Invention The present invention provides a method for recording data on a rotatable magnetic recording disk by means of a recording head having a recording gap, comprising recording the data in a plurality of data tracks including an inner and an outer track, the method comprising: moving the head between the inner and outer tracks in such a way to cause the recording gap of the head to be skewed at an angle to each of the data tracks, the skew varying monotonically as the head moves from the inner to the outer track thereby effecting a monotonic reduction in the width of the tracks from the inner to the outer track, and monotonically reducing the track to track spacing from the inner to the outer track, characterised in that: the head includes a non-rectangular parallelogram shaped slider having a plurality of parallel rails, the slider acting to maintain the head above the surface of the rotating disk during movement between the inner and outer tracks, the slider being oriented with respect to the direction of rotation of the rotating disk so that its outer leading corner is located in advance of its inner leading corner, and wherein the recording gap is parallel to the trailing edge of the slider. Thus in common with JP-A-61 120 987, the invention maximises the use of the head/media capacity by increasing the track density of the disk as a function of track radius. The lower linear density achieved with CFR near the outer radius of the disk is compensated for by providing a higher track density at outer disk radii as compared to inner disk radii. The invention thus provides a major portion of the increase in capacity produced by variable RPM CDR system without the need for means to vary the disk rpm. Similarly, the present invention produces a capacity increase comparable to a 3 band frequency system without requiring multiple frequency data channels. In contrast to the prior art, with the parallelogram shaped slider employed in the present invention, the head gap can be skewed relative the data track while the rails of the slider remain positioned in the conventional manner (ie generally perpendicular to the disk radius). The flying characteristics of the head are therefore not disturbed. Furthermore, this unique shape allows the head to be nearly conventionally fabricated where the heads are formed by angled cuts different from the typical 90 degree cuts. Preferably the head travels either a non-radial and/or a substantially arcuate path. It is a further preference that the disk is rotated at a constant angular velocity and the data is recorded on the disk at a constant frequency. The invention also provides a disk drive apparatus for recording data on a magnetic recording disk having a plurality of data tracks including an inner and an outer track, the disk drive apparatus comprising means for rotating such a disk, a recording head having a recording gap for recording the data on such a disk, and an actuator for moving the head across the surface of the disk, wherein the movement of the actuator causes the angle of skew between head recording gap and the data tracks to vary monotonically as the head moves between the inner and outer track, thereby resulting in a monotonic reduction in track width from the inner to the outer track, the disk drive apparatus further comprising means for controlling the movement of the actuator so that there is a monotonic reduction in track spacing from the inner to the outer track, characterised in that: the head includes a non-rectangular parallelogram shaped slider having a plurality of parallel rails, the slider acting to maintain the head above the surface of the rotating disk during movement between the inner and outer tracks, the slider being oriented with respect to the direction of rotation of the rotating disk so that its outer leading corner is located in advance of its inner leading corner, and wherein the recording gap is parallel to the trailing edge of the slider. The invention will be described with reference to the recording of concentric data tracks. However, the invention also finds utility, for example, in the recording of a spiral track, and the scope and content of the invention includes the recording of such other track formats. The invention will now be described by way of example only with reference to the accompanying drawings. Brief Description of the Drawings Fig. 1 shows a schematic of a contact recording rotary actuator embodiment according to the present invention; Fig. 2 shows a schematic of a non-contact recording, rotary actuator embodiment according to the present invention; Fig. 3 is an enlarged disk-side (under side) plan view of the head as employed in the actuator of Fig. 2. Fig. 4 is an enlarged trailing end view of the head shown in Fig. 3. The present invention finds utility in disk drives or files of many detailed configurations, including floppy disk drives and hard or rigid disk drives having various disk diameters. In addition, the reduction in track-to-track spacing that is provided by the present invention can be implemented in a number of ways known to those skilled in the art. For example, a stepping motor servo may be provided to move the head, open loop, through smaller and smaller steps, as the head moves from the inner track toward the outer track. This can be implemented, for example, by the use of cam driven mechanical leverage arrangements that are operable to move the head in either direction during a track seek or access operation. By way of another example, the disk itself may be formatted so as to contain a track identifier and a tracking servo pattern for each individual track. When this is done, a closed loop head moving servo moves the head to seek an identified target track, under servo input command. The head then reads track identifiers as it moves generally radially across the disk, providing a feedback signal that allows the proper head velocity and acceleration motion profile to be established, so that the servo stops moving the head, and the head centres on the target track. For optimum servo performance, the variable track density of the invention should be taken into account in determining the servo system parameters to be used during a track access operation. When this closed loop arrangement is used, formatting of the disk provides tracks of the required decreased spacing from the disk's inner track to its outer track. The details of construction of disk drives in which the invention finds utility are well known to those of skill in the art. As a result, the following description provides only such detail as is necessary to enable those skilled in the art to practice the present invention. Fig. 1 shows a top view of an embodiment of the invention which, without limitation thereto, is a contact recording disk drive having a button type head 31. For example, the disk drive is a floppy disk drive . This embodiment of the invention moves the disk drive's read/write head 31 in an arc by virtue of operation of a rotary actuator means or motor 10. While the invention finds utility with a variety of heads and head actuator means known to those skilled in the art, a requirement of the invention is the head be moved so as to transduce tracks of decreasing track width, from the disk's inner track to its outer track, and that track-to-track spacing decrease, from the disk's inner track to its outer track. Since a magnetic recording head's read/write efficiency increases as a function of head/media velocity, the transducing of narrower tracks at the disk's outer radii is compensated for, providing good signal to noise ratio throughout all disk tracks. A portion of a magnetic recording disk is shown at 12. As stated, this disk may be either a floppy disk or a hard disk, and it is of well known physical dimensions. Fig. 1 is a top view of disk 12. The disk is rotated CCW, see arrow 13, at a substantially constant angular velocity by means of a drive motor, not shown. Rotary actuator means 10 includes a swing arm 14 that is bidirectionally movable through a limited arc, for example 35 degrees, see arrow 15. Head 31 and a head suspension means (not shown) are mounted on arm 14. Fig. 1 shows the generally linear gap 16 of head 31. The physical dimensions of gap 16 are greatly exaggerated in the figure. Swing arm 14 is shown in three of its numerous operating positions. Position 14 is the position that arm 14 occupies when transducing the disk's inner track; position 14' is the position the arm occupies when transducing the disk's median track 22; and position 14'' is the arm's position when transducing outer track. Arm 14 rotates through a 21 degree arc when moving from the disk's inner track to the disk's median track 22, and rotates an additional 14 degrees when moving from the median track to the disk's outer track. Arrow 17 identifies the tangential velocity vector line of the disk's rotational velocity at the location of the disk's inner track. Dotted line 18 is a line that passes through the centre of gap 16 and is perpendicular to the gap. Numerals 17', 17'', 18' and 18'' identify corresponding parameters at the location of the disk's median track 22 and its outer track. As can be seen from Fig. 1, gap 16 is rotated or skewed CW relative to vectors 17,17',17'' by an angle identified as 19,19',19''. The disk radii at the inner track, at median track 22, and at the outer track is identified at 20,20,'20'', respectively. Actuator 10 bidirectionally moves head 31 and its gap 16 along an arc 21 that is non-radial of disk 12. As can be seen from Fig. 1, the projection of gap 16 onto disk radii 20,20',20'' results in an inner track, a median track 22, and an outer track whose width is always less than the length of gap 16, and whose width progressively decreases from the disk's inner track to its outer track. The construction and arrangement of this invention by which gap skew changes with head movement is such that the disk's track width progressively decreases, from the disk's inner track to its outer track. The exemplary CCW direction of disk rotation, and/or CW direction of gap skew change or rotation relative the disk radii, are not to be taken as a limitation on the present invention. In this example, at median track 22, gap skew angle 19' has increased from the 5 degrees at the inner track, to 44 degrees at the median track. At the outer track, skew angle 19'' has again increased to 60 degrees, and the skew angle is at its maximum value. It should be noted that the skew angle has increased in the same sense, in this case CW, and the skew angle has not passed through zero. When these skew angles are projected on disk radii 20, 20' and 20'', respectively, it can be seen that the track width progressively decreases from the inner track, to the median track, to the outer track. The gap skew angles shown in Fig. 1 yield about a 35 percent increase in capacity over a standard CFR design. A secondary advantage of providing a skewed gap 16 is that any scratches that may be on the disk's surface, for example scratches caused by the head moving across the disk during manufacture of the disk file, do not extend in the linear direction of gap 16. In such a situation, the gap skew minimizes problems associated with signal modulation. It is noted from Fig. 1 that median track 22 is physically closer to the outer track than it is to the inner track. In accordance with the invention, the disk's tracks are written, under the control of track servo 27, with progressively less track-to-track spacing, from the inner track to the outer track. Track servo 27 may be either an open loop or a closed loop servo. While not critical to the invention, the well known guard band between adjacent tracks preferably remains uniform throughout the disk. In a linear actuator embodiment of the invention (not shown), the head that includes gap 16 is bidirectionally moved by a linear actuator along non-radial path. Again, the skew of gap 16 at the inner track results in a continuous reduction in track width from the inner track to the outer track, and the track servo, which may be either a closed loop or an open loop servo, produces tracks having continuously reduced spacing from inner track to the outer track. It is also within the scope of the invention to provide for radial head movement, where the head gap rotates with such movement, to thereby transduce tracks of progressively decreasing width, from the disk's inner track to its outer track. While it is preferred that the track spacing continuously reduce from the inner track to the outer track, an application may exist where the reduction in track spacing is banded or zoned, or the inner to outer track format may be continuous, as in the form of a spiral. Figs. 2, 3 and 4 show an embodiment of the invention utilizing a flying head 50. The unique head/slider configuration shown in these figures provides a new and unusual means for producing the above mentioned head gap skew, while maintaining the head's conventional air bearing characteristics. In its broadest sense, the scope of the invention is not to be limited to this unique head/slider configuration. Fig. 2 does not show the inner track, median track 22, nor the outer track of disk 12. However, it is to be understood that the positions shown for arm 14 (i.e. positions 14, 14' and 14'') correspond to the transducing of these respective tracks by head 50. Rotary actuator means 10 is shown connected to move arm 14 on which head 50 is mounted. Three positions of arm 14 are shown. In position 14, head 50 is positioned to transduce the disk's inner track. In position 14', the head is transducing the disk's median track 22, and in position 14'' the head is transducing the disk's outer track. Arm 14 moves 14 degrees when moving from the disk's inner track to its median track, and moves an additional 11 degrees when moving from the disk's median track to its outer track. In Fig. 2, line 51' represents the disk's radius at the location of the disk's inner recording track, and line 51 represents the disk's radius at the outer track. Lines 53,53' of Fig. 2 represent the tangential velocity vector at the inner and outer disk tracks, respectively. Lines 54,54' extend normal to gap 16 at the location of these two tracks. Head gap 16 is skewed to disk radii 51,51' by the angle 52,52' at the location of these two disk tracks, respectively. In this exemplary showing, angle 52 is about 32 degrees, and angle 52' is about 55 degrees. The corresponding angle, when the head is positioned at the disk's median track (i.e. arm position 14'), is of a value intermediate 32 degrees and 55 degrees. Lines 40,40' of Fig. 2 extend parallel to flying rails 41 and 42 of head 50. These rails are best seen in Figs. 3 and 4. In this embodiment of the invention, rails 41, 42 are oriented -3 degrees (i.e. CCW from) the tangential velocity vector 53 at the location disk's inner track, and are oriented +20 degrees (i.e. CW from) the tangential velocity vector 53' at the location of the disk's outer track. Lines 43,43' of Fig. 2, one of which corresponds to the location of the inner track and the other of which corresponds to the location of the outer track, are parallel to and coincident with the slider's trailing edge, and are parallel to head gap 16. This trailing edge is best seen in Fig. 3. The angle between this trailing edge and radii 51,51' varies between 32 degrees at the location of the disk's inner track, and 55 degrees at the location of the disk's outer track. The geometry shown in Fig. 2 is generally of the type found in small diameter rigid disk drives or files. By way of example, disk 12 of Fig. 2 may be a 3 1/2 inch diameter rigid disk. With reference to Figs. 3 and 4, the slider of head 50 is of conventional detailed construction and arrangement, with the exception that the slider is of a generally parallelogram shape (i.e. the side of the slider that faces the disk, shown in Fig. 3, is of a parallelogram shape). This unique shape allows head 50 to be nearly conventionally fabricated, i.e. in groups of rows and columns of heads, where the heads are formed by angled cuts different than the typical 90 degree cuts, in a manner what will be readily understood by those skilled in the art. The slider's two linear flying rails 41,42 are generally parallel to each other. The leading ends of the rails terminate in generally linear leading edge 56. The trailing ends of the rails terminate in generally linear trailing edge 57. The leading ends of the rails are provided with leading edge tapers 70,71. The sides of the rails are provided with standard angled edges (not numbered). The leading/trailing edges 56,57 extend at an angle 72 of about 35 degrees (as measured opposite the direction of disk rotation) to the direction in which rails 41,42 extend. Gap 16 is generally parallel to the slider's leading edge 56 and its trailing edge 57. This new and unusual slider construction and arrangement for head 50 allows substantially conventional head fabrication techniques to be used, and yet provides a head having a skewed gap 16. With this construction and arrangement, the slider's flying characteristics remain substantially undisturbed due to the direction in which rails 41, 42 extend relative velocity vectors 53,53'. With the construction and arrangement of this invention, the flying characteristics of skewed gap head 50 are substantially the same as those of a conventional rectangular shaped head slider where the head gap is not skewed. The slider construction and arrangement, and the manner of moving the head, above described provide a normal head flying height at the inner tracks. At the outer tracks, where the head would normally fly higher due to the higher relative velocity between the head and disk, the head of the invention flies at about the same height as at the inner tracks, due primarily to the rotation, or change in angle of attack, of the flying rails that occurs as the head moves toward the disk's outer tracks. It is to be noted that in the embodiments of the invention above described, the variation that occurs in the skew of the head gap to disk radii is composed of two components. The first component is the direct angular rotation of the head gap by virtue of rotation of actuator means 10. The second component, which is indirectly produced by actuator means rotation, is due to a change in the angle of the disk radius that extends through the head gap 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 invention can be applied to the particular geometry by making use of these two component effects, to thereby provide the needed gap rotation or skew as the head moves across the disk.

Claims: A method for recording data on a rotatable magnetic recording disk (12) by means of a recording head (31) having a recording gap (16), comprising recording the data in a plurality of data tracks including an inner and an outer track, the method comprising: moving the head between the inner and outer tracks in such a way to cause the recording gap (16) of the head (31) to be skewed at an angle to each of the data tracks, the skew (19, 19', 19'') varying monotonically as the head moves from the inner to the outer track thereby effecting a monotonic reduction in the width of the tracks from the inner to the outer track, and monotonically reducing the track to track spacing from the inner to the outer track, characterised in that: the head (50) includes a non-rectangular parallelogram shaped slider having a plurality of parallel rails (41, 42), the slider acting to maintain the head above the surface of the rotating disk during movement between the inner and outer tracks, the slider being oriented with respect to the direction of rotation of the rotating disk so that its outer leading corner is located in advance of its inner leading corner, and wherein the recording gap is parallel to the trailing edge of the slider. A method as claimed in claim 1, whereby the head is moved along a non-radial path. A method as claimed in any preceding claim whereby the head is moved along an arcuate path by means of a rotary actuator (10) thereby causing the variation in skew angle. A method as claimed in any preceding claim whereby the disk is rotated at a constant angular velocity and the data is recorded on the disk at a constant frequency. Disk drive apparatus for recording data on a magnetic recording disk (12) having a plurality of data tracks including an inner and an outer track, the disk drive apparatus comprising means for rotating such a disk, a recording head (31) having a recording gap (16) for recording the data on such a disk, and an actuator (10) for moving the head across the surface of the disk, wherein the movement of the actuator causes the angle of skew (19, 19', 19'') between head recording gap and the data tracks to vary monotonically as the head moves between the inner and outer track, thereby resulting in a monotonic reduction in track width from the inner to the outer track, the disk drive apparatus further comprising means (27) for controlling the movement of the actuator so that there is a monotonic reduction in track spacing from the inner to the outer track, characterised in that: the head (50) includes a non-rectangular parallelogram shaped slider having a plurality of parallel rails (41, 42), the slider acting to maintain the head above the surface of the rotating disk during movement between the inner and outer tracks, the slider being oriented with respect to the direction of rotation of the rotating disk so that its outer leading corner is located in advance of its inner leading corner, and wherein the recording gap is parallel to the trailing edge of the slider. Apparatus as claimed in claim 5 wherein the angle between the recording gap (16) and the rails (41, 42) is 55 degrees. Apparatus as claimed in claim 5 or claim 6 wherein the actuator is a rotary actuator (10) which moves the head along an arcuate path thereby effecting the variation in skew angle.

Inventors: CUNNINGHAM EARL ALBERT, CUNNINGHAM, EARL ALBERT
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1989
Main classification: G11B5
IPC codes: G11B5, G11B21