Patent Publication Number: US-2005141134-A1

Title: System and method for disk formatting

Description:
CLAIMS OR PRIORITY  
      This application claims priority to U.S. Provisional Application No. 60/532,473 entitled “Disk Formatting” filed Dec. 24, 2003 and U.S. Provisional Application No. 60/532,479 entitled “Method for Disk Formatting” filed Dec. 24, 2003. 
    
    
     FIELD OF THE INVENTION  
      The invention relates to rotating media storage devices such as hard disk drives.  
     BACKGROUND  
      Rotating media storage devices are an integral part of computers and other devices with needs for large amounts of reliable memory. Rotating Media Storage Devices are inexpensive, relatively easy to manufacture, forgiving where manufacturing flaws are present, and capable of storing large amounts of information in relatively small spaces.  
      A typical rotating media storage device includes a head disk assembly and electronics to control operation of the head disk assembly. The head disk assembly can include one or more disks. The disks include a recording surface to receive and store user information. For hard disk drives, the recording surface can be constructed of a substrate of metal, ceramic, glass or plastic with a thin magnetizable layer on either side of the substrate. Data is transferred to and from the recording surface via a head mounted on an actuator assembly. Heads can include one or more read and/or write elements, or read/write elements, for reading and/or writing data. Drives can include one or more heads for reading and/or writing. In magnetic disk drives, heads can include a thin film inductive write element and a magneto-resistive read element.  
      Hard disk drives can operate in one of more modes of operations. In a first mode or operation, often referred to as seek or seeking, a head moves from its current location, across a disk surface to a selected track. In a second mode, often referred to as track following, a head is positioned over a selected track for reading data from a track or writing data to a track.  
      In order to move a head to a selected track or to position a head over selected tracks for writing and reading, servo control electronics are used. In some disk drives, one disk can be dedicated to servo. The servo disk can have embedded servo patterns that are read by a head. Heads for data disks can be coupled to the servo disk head to be accurately positioned over selected tracks. In other disk drives, servo information can be embedded within tracks on the medium at regular intervals. Servo information is read as a head passes over a track to accurately position the head relative to a track.  
      While servo positioning circuitry is generally accurate, heads can drift from desired locations during track following operations. Reading or writing data with inaccurate head positioning can have adverse affects on drive performance.  
      In modern disk drives, tracks are placed increasingly closer together to increase data storage capacity. Narrower tracks are often used in order to increase the tracks per inch (TPI) on a disk. Measures should be used in drives to ensure that reliability and performance are maintained as data storage capacity increases.  
     BRIEF SUMMARY  
      Systems and devices in accordance with embodiments of the present invention use a write head with a gap that is at a non-perpendicular angle with respect to a line defined between the pivot of the actuator assembly and the center of the gap (arm chord). This can increase the skew angle and thus narrow the track size for a given write head width.  
      Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram showing components of an exemplary rotating media storage device that can be used in accordance with one embodiment of the present invention.  
       FIG. 2  is a top view of a rotatable storage medium that can be used in the drive of  FIG. 1 .  
       FIG. 3  is an illustration of a servo sector of a track on a disk of a rotating media storage device.  
       FIG. 4  is an example of a prior art actuator arm.  
       FIG. 5  illustrates the use of the prior art actuator arm on a disk of a rotating media storage device.  
       FIG. 6A and 6B  illustrate an actuator arm of one embodiment of the present invention.  
       FIG. 7  illustrates tracks produced using a actuator arm of the present invention.  
       FIG. 8  illustrates the use of the actuator arm on a disk.  
       FIG. 9  illustrates using alignment offsets with a method of the present invention. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows a rotating media storage device  100  that can be used in accordance with one embodiment of the present invention. In this example, the rotating media storage device  100  is a hard disk drive. The rotating media storage device  100  includes at least one rotatable storage medium  102  capable of storing information on at least one surface. Numbers of disks and surfaces may vary by disk drive. In a magnetic disk drive, storage medium  102  is a magnetic disk. A closed loop servo system, including an actuator arm  106 , can be used to position head  104  over selected tracks of disk  102  for reading or writing, or to move head  104  to a selected track during a seek operation. In one embodiment, head  104  is a magnetic transducer adapted to read data from and write data to the disk  102 . In another embodiment, head  104  includes separate read elements and write elements. The read element can be a magnetoresistive (MR) head. Multiple head configurations may be used.  
      The servo system can include an actuator unit  108 , which may include a voice coil motor driver to drive a voice coil motor (VCM) for rotating of the actuator arm  106 . The servo system can also include a spindle motor driver  112  to drive a spindle motor (not shown) for rotation of the disk  102 . Controller  121  can be used to control the rotating media storage device  100 . The controller  121  can include a number of arrangements. In one embodiment, the controller includes a disk controller  128 , read/write channel  114 , processor  120 , SRAM  110 , and control logic  113  on one chip. These elements can also be arranged on multiple chips. The controller can include fewer elements as well.  
      In one embodiment, the controller  121  is used to control the VCM driver  108  and spindle motor driver  112 , to accept information from a host  122  and to control many disk functions. A host can be any device, apparatus, or system capable of utilizing the data storage device, such as a personal computer or Web server. The controller  121  can include an interface controller in some embodiments for communicating with a host and in other embodiments, a separate interface controller can be used. The controller  121  can also include a servo controller, which can exist as circuitry within the drive or as an algorithm resident in the controller  121 , or as a combination thereof. In other embodiments, an independent servo controller can be used.  
      Disk controller  128  can provide user data to a read/write channel  114 , which can send signals to a current amplifier or pre-amp  116  to be written to the disk(s)  102 , and can send servo signals to the microprocessor  120 . Controller  121  can also include a memory controller to interface with memory such as the DRAM  118  and FLASH memory  115 . FLASH memory  115  can be used as non-volatile memory to store a code image. DRAM  118  can be used as a buffer memory and to store the code to be executed along with the SRAM  110 .  
      The information stored on a disk can be written in concentric tracks.  FIG. 2  is a top view of an exemplary rotatable storage disk  200 . A multiple of concentric tracks extend from near an inner diameter (ID)  202  of the disk  200  to near an outer diameter (OD)  204 . These tracks may be arranged within multiple data zones  206 - 216 , extending from the ID  202  to the OD  204 . Data zones can be used to optimize storage within the data storage tracks because the length of a track in inner data zone  206  may be shorter than the length of a track at outer zone  216 . While eight zones are shown in  FIG. 2 , any number of zones may be used. For example, sixteen zones are used in one embodiment. Disk  200  includes multiple servo sectors  218 , also referred to as servo wedges. In this example, servo sectors  218  are equally spaced about the circumference of storage disk  200 .  
      An exemplary servo sector  318  is illustrated in  FIG. 3 . The servo information shown includes a preamble  332 , a servo address mark (“SAM”)  334 , an index  336 , a track number  338 , and servo bursts  340 - 346 . These fields are exemplary, as other fields may be used in addition to, or in place of, the exemplary fields, and the order in which the fields occur may vary. The preamble  332  can be a series of magnetic transitions which can represent the start of the servo sector  318 . In the servo sector of  FIG. 3 , the SAM  334  specifies the beginning of available information from the servo sector  318 . The track number  238 , usually gray coded, is used for uniquely identifying each track. Servo bursts  340 - 346  are positioned regularly about each track, such that when a data head reads the servo information, a relative position of the head can be determined that can be used by a servo processor to adjust the position of the head relative to the track. This relative position can be determined by looking at the PES value of the appropriate bursts. The PES, or position error signal, is a signal representing the position of a head or element relative to a track centerline.  
       FIG. 3  shows prior art longitudinally encoded bursts. A centerline  330  for a given data track can be “defined” by a series of bursts, burst edges, or burst boundaries, such as a burst boundary defined by the lower edge of A-burst  340  and the upper edge of B-burst  342 . For example, if a read head evenly straddles an A-burst and a B-burst, or portions thereof, then servo demodulation circuitry in communication with the head can produce equal amplitude measurements for the two bursts, as the portion of the signal coming from the A-burst above the centerline is approximately equal in amplitude to the portion coming from the B-burst below the centerline. The resulting computed PES can be zero if the radial location defined by the A-burst/B-burst (A/B) combination, or A/B boundary, is the center of a data track, or a track centerline. In such an embodiment, the radial location at which the PES value is zero can be referred to as a null-point. Null-points can be used in each servo wedge to define a relative position of a track. If the head is too far toward the outer diameter of the disk, or above the centerline in  FIG. 3 , then there will be a greater contribution from the A-burst that results in a more “negative” PES. Using the negative PES, the servo controller could direct the voice coil motor to move the head toward the inner diameter of the disk and closer to its desired position relative to the centerline. This can be done for each set of burst edges defining the shape of that track about the disk.  
       FIG. 4  illustrates a prior art actuator arm. The actuator arm includes a pivot  402  about which the actuator arm rotates. The actuator arm also includes a write head having a gap  404 . The gap  404  is perpendicular to a line defined between the pivot  402  and the gap  404 .  
       FIG. 5  shows an advantage of the actuator arm of  FIG. 4 . When the actuator is at adjacent track positions, the fields written by the write head onto the disk  500  for a given disk position align. The alignment of the written fields is especially important for servo writing.  
       FIG. 6A and 6B  illustrate embodiments of the present invention.  FIG. 6A  shows, an actuator arm including a pivot  602 . The pivot can be a conventional pivot used in actuator assemblies. An arm portion  604  is operably connected to the pivot. The arm portion can include a suspension and/or other structures. A write head with a gap  606  is operably connected to the arm. The write head can be positioned on a slider (not shown). The gap  606  has an angle that is non-perpendicular to a line defined from the center of the gap to the center of the pivot. Such a non-perpendicular angle can increase the skew of fields written with the actuator arm.  
      In one embodiment, the angle is greater than 1 degree off of the perpendicular. In another embodiment the angle is greater than 5 degrees off the perpendicular. Yet in another embodiment the angle is greater than 10 degrees off of the perpendicular.  
      In some embodiments, the actuator assembly includes a separate read head. The read head can be orientated at the angle of the write head. In one embodiment, the read head is a MR read head with a MR strip orientated at the angle.  
       FIG. 6A  illustrates a straight arm  604 .  FIG. 6B  shows a bent arm  610 . The bent arm  610  includes a section  612  of the arm adjacent to the write head that is perpendicular to the gap in the write head  606 . The bent arm  610  can allow the use of a conventional slider design.  
       FIG. 7  is a diagram that illustrates an advantage of one embodiment of the present invention. When there is no skew in the written tracks the width of the tracks written is roughly the width of the write head. When the skew is provided by using a skewed write head gap, the width is reduced. In one example the width reduces to W=W head  cos θ.  
      The use of the additional skew angle allows a relatively wide write head to be used. Wider write heads are cheaper than narrow write heads.  
      Since the magnetizable material of the disk has granular magnetic domains, the sharpness of the transition between written fields may depend upon the length of the edge that interacts with the magnetic domains. By using a write head gap with an angle from the perpendicular, the edge length is increased thus potentially increasing the sharpness of the transition.  
      For conventional arms, the skew angle (yaw angle) with respect to the written circular track can be calculated for each track by knowing the arm pivot to write gap length (PG), the arm pivot to the spindle distance (PS) and the radius of the track. This angle is: α=sin −1 {(r i   2 +PG 2 −PS 2 )/(2*r i *PG)}. Because the write gap is not perpendicular to the tangent to the track, the written track will have a width of WW effective =WW*cos(α), where WW is the magnetic write width. As it can be seen from the equation, as the skew angle gets larger, the effective written track gets narrower.  
      As shown in the example of  FIG. 8 , using a write head gap that is not perpendicular to a line defined from the pivot to the gap can increase the skew. If the angle off of the perpendicular is β, the total skew α total =β+sin −1 {(r i   2 +PG 2 −PS 2 )/(2*r i *PG)}. The output voltage of Magnetoresistive (MR) and Giant Magnetoresistive (GMR) heads is a function of flux entering the reader and is independent of the magnetic transition velocity as passes under the reader. As the skew angle gets larger, the media velocity component, perpendicular to the reader gets smaller which will affect inductive heads but not MR. If the track is written with a skew angle, the effective track width is narrower and is a function of the skew angle. If we impose an additional angle β to force the total skew to be “Large” we can effectively make many “narrow” tracks. If a constant guard band approach is used, the number of tracks recorded on the media for a given recording band can be increased. Another advantage is that wider heads can be used to accomplish a high track density because the track width is defined by the projection of the gap length which is narrower than the actual gap length. Additionally, wider guard bands at locations of bad Track Misregistration (TMR) without affecting the track density.  
       FIG. 8  illustrates the use of an arm having a non-perpendicular gap with the disk  800 . The range of skew at the disk for a perpendicular write head gap can ranges from 20 to 20 degrees. By adding an additional skew factor, the skew at the disk is increased thus the track widths are narrowed.  FIG. 8  also illustrates that the added skew angle, β, causes a misalignment between written fields at different radii or tracks. Servo Fields of adjacent tracks do not align.  FIG. 9  illustrates adjacent tracks written with a write gap having skew angle β. One way to align the fields is to use an alignment offset value. A distance offset d, such as d=W track (Tan(α total )−Tan(α total −β)), is used to align adjacent fields in one example. The distance offset corresponds to timing offset of d/v, where v is the velocity of the head over the disk. The velocity, v depends on the rotation speed of the disk and the radius location of the head. By calculating offset values in the rotating media storage device, adjacent fields can be aligned. This is only important for servo fields. Alignment of data fields is typically not required.  
      The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to one of the ordinary skill in the relevant arts. The embodiments were chosen and described in order to best explain the principles of the invention and its partial application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scopes of the invention are defined by the claims and their equivalents.