Abstract:
An ex-situ Servo Track Writer (STW) uses a support element that can extend between discs in a stack, and can also retract, permitting a high level of variation in the stack&#39;s positioning. The support element preferably has an engagement surface that is wide enough to permit the element to support the actuator throughout the element&#39;s range of (rotary) motion. Because the support structure is retractable, it can use low angles of approach like those of hyperbolic-shaped cams, without losing access to the outermost portions of the discs. The support structure may therefore be moved out of the servowriter actuator&#39;s path while position data is written to the outermost portions of the data surface.

Description:
Related Applications  
       [0001]    This application claims priority of U.S. provisional application Serial No. 60/295,275 filed Jun. 1, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This application relates generally to data storage devices and more particularly to recording position data onto discs thereof.  
         BACKGROUND OF THE INVENTION  
         [0003]    Disc drives are data storage devices that store digital data in magnetic form on a rotating disc. Modern disc drives comprise one or more rigid information storage discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers mounted to a radial actuator for movement of the heads relative to the discs. During a data write operation sequential data is written onto the disc track, and during a read operation the head senses the data previously written onto the disc track and transfers the information to an external environment. Important to both of these operations is the accurate and efficient positioning of the head relative to the center of the desired track on the disc. Head positioning within a desired track is dependent on head-positioning servo patterns, i.e., a pattern of data bits recorded on the disc surface and used to maintain optimum track spacing and sector timing. Servo patterns or information can be located between the data sectors on each track of a disc (“embedded servo”), or on only one surface of one of the discs within the disc drive (“dedicated servo”). Regardless of whether a manufacturer uses “embedded” or “dedicated” servos, the servo patterns are typically recorded on a target disc during the manufacturing process of the disc drive.  
           [0004]    Recent efforts within the disc drive industry have focused on developing cost-effective disc drives capable of storing more data onto existing or smaller-sized discs. One potential way of increasing data storage on a disc surface is to increase the recording density of the magnetizable medium by increasing the track density (i.e., the number of tracks per inch). Increased track density requires more closely-spaced, narrow tracks and therefore enhanced accuracy in the recording of servo-patterns onto the target disc surface. This increased accuracy requires that servo-track recording be accomplished within the increased tolerances, while remaining cost effective.  
           [0005]    Servo patterns are typically recorded on the magnetizable medium of a target disc by a servo-track writer (“STW”) assembly during the manufacture of the disc drive. One conventional STW assembly records servo pattern on the discs following assembly of the disc drive. In this embodiment, the STW assembly attaches directly to a disc drive having a disc pack where the mounted discs on the disc pack have not been pre-recorded with servo pattern. The STW does not use any heads of its own to write servo information onto the data surfaces, but uses the drive&#39;s own read/write heads to record the requisite servo pattern to mounted discs.  
           [0006]    In light of the explosive trend toward higher track densities in recent years, some exceeding 100,000 tracks per inch, this conventional method has become excessively time consuming. As the trend continues, it will apparently be necessary for every disc drive manufacturer to obtain and operate much larger numbers of STW&#39;s to maintain comparable numbers of disc drives. One strategy to mitigate this need is to utilize multi-disc “ex situ” STW&#39;s, which are are capable of recording servo patterns to multiple discs mounted in a stack. After writing some of the position information using (dedicated) servo recording heads, sequentially or simultaneously, the discs are then removed and loaded into disc drives for use. The disc drives write additional position information.  
           [0007]    Several problems have made the use of ex situ writers commercially unfeasible. For example, it is not feasible to unload their servowriter heads onto a textured landing zone after servowriting. Applicant has limited knowledge of an ex situ multi-disc STW with an unload ramp structure that can be positioned near the outer diameter of a stack of horizontal discs. This STW, developed by Phase Metrics of Fremont, Calif., uses a sliding plate to position the ramp structure and a rotary actuator simultaneously. Unfortunately, the exact composition and operation of this ramp structure might not be public and is not known to Applicant. From extensive experience in this field, however, Applicant does know that positioning a ramp structure affixed to a massive plate that also supports a rotary actuator for accessing a disc stack is unduly expensive and/or imprecise.  
           [0008]    To support cost effective ex situ STW operation in high volume, what is needed is a workable system for unloading an actuator that can extend between discs in a stack for load/unload, and retract for easy removal of the disc stack. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.  
         SUMMARY OF THE INVENTION  
         [0009]    Servo Track Writers implementing the present invention use a support element that can extend between discs in the stack, and can also retract, permitting a high level of variation in the stack&#39;s positioning. In a preferred embodiment, the support element has an engagement surface that is wide enough to permit the element to support the actuator throughout the element&#39;s range of motion. For precise and cost effective operation, the element may also use a rotary actuator for a rigidly limited range of motion, preferably with an axis of rotation substantially parallel to those of the disc stack and the actuator.  
           [0010]    Because the support structures are retractable, they can use low angles of approach (like those of hyperbolic-shaped cams) without losing access to the outermost portions of the discs. Disc drive ramps typically use an approach angle of 30 to 45 degrees relative to the disc surface, too steep to permit a low-flying STW head from loading without colliding with the disc surface. In a preferred method of the present invention, the support structure is moved out of the servowriter actuator&#39;s path while position data is written to the outermost portions of the data surface.  
           [0011]    Additional features and benefits will become apparent upon reviewing the following figures and their accompanying detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows a data storage device containing position data written by means of the present invention.  
         [0013]    [0013]FIG. 2 shows a flowchart of a method of the present invention  
         [0014]    FIGS.  3 - 5  shows the relative positions of basic components of a Servo Track Writer (STW) configured to implement the present invention, in unloaded, transitional, and loaded positions respectively.  
         [0015]    [0015]FIG. 6 shows a much more detailed (top) view of the STW of FIGS.  3 - 5 .  
         [0016]    [0016]FIG. 7 shows a detailed perspective view of the STW of FIGS.  3 - 5 .  
         [0017]    [0017]FIG. 8 shows a detailed magnified view of the stack of discs, the actuator and the support structure in a loaded position. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Although the examples below show more than enough detail to allow those skilled in the art to practice the present invention, subject matter regarded as the invention is broader than any single example below. The scope of the present invention is distinctly defined, however, in the claims at the end of this document.  
         [0019]    Numerous aspects of data storage device technology that are not a part of the present invention (or are well known in the art) are omitted for brevity, avoiding needless distractions from the essence of the present invention. For example, this document does not include much detail about how to use “embedded” servo reference marks to position a disc drive&#39;s transducers. Neither does it include specific methods for handling pre-written discs or installing them into a disc drive with minimal distortion. Specific materials for constructing components described herein are likewise omitted, typically being a simple matter of design choice.  
         [0020]    Definitions and clarifications of certain terms are provided in conjunction with the descriptions below, all consistent with common usage in the art but some described with greater specificity. For example, “position data” refers herein to any data that pertains to a physical location on a media surface such as a track number, a defect table entry, or a servo burst.  
         [0021]    Turning now to FIG. 1, there is shown a data storage device  100  constructed in accordance with a preferred embodiment of the present invention. Device  100  is a disc drive including base  102  to which various components are mounted. Top cover  123  cooperates with base  102  conventionally to form a sealed chamber. The components include a spindle motor which rotates data storage discs  110  at several thousand revolutions per minute. Information is written to and read from tracks  112  on discs  110  is through the use of an actuator assembly  161 , which rotates during a seek operation about a bearing shaft assembly  130  positioned adjacent discs  110 . Actuator assembly  161  includes a plurality of actuator arms which extend above and below each disc  110 , with one or more flexures extending from each of the actuator arms. Mounted at the distal end of each of the flexures is a transducer head  134  which includes an air-bearing slider enabling transducer head  134  to fly in close proximity above the corresponding surface of associated disc  110 .  
         [0022]    Servo and user data travels through transducer head  134  and flex cable  180  to control circuitry on controller board  106 . Flex cable  180  maintains an electrical connection by flexing as transducer heads  134  traverse tracks  112  along their respective radial paths  138 . By “radial,” it is meant that path  138  is substantially aligned with a radius of the disc(s)  110 , although their directions may be offset from a perfectly radial direction by up to about 20 degrees due to head skew, as is understood in the art.  
         [0023]    During a seek operation, the overall track position of transducer heads  134  is controlled through the use of a voice coil motor (VCM), which typically includes a coil  122  fixedly attached to actuator assembly  161 , as well as one or more permanent magnets  120  which establish a magnetic field in which coil  122  is immersed. The controlled application of current to coil  122  causes magnetic interaction between permanent magnets  120  and coil  122  so that coil  122  moves. As coil  122  moves, actuator assembly  161  pivots about bearing shaft assembly  130  and transducer heads  134  are caused to move across the surfaces of discs  161  between the inner diameter and outer diameter of the disc(s)  161 . Fine control of the position of head  134  is optionally made with a microactuator (not shown) that operates between the head  134  and the actuator arm.  
         [0024]    [0024]FIG. 2 shows a method  200  of the present invention comprising steps  205  through  265 . Discs are assembled coaxially (alternated with spacers) into a stack  210 . A support element is extended between the discs so that the servowriter head can load  215 . A servowriter head (also between discs) writes servo marks onto a data surface  220 . (Typically many millions of such servo marks are thus written.) Many suitable techniques for writing servo marks are known in the art. The actuator supporting the head then moves out from between the discs, sliding onto an engagement surface of a support element also extending between the discs  225 . After the actuator is moved out from between discs, the support element starts to move out also  235 . Each continues moving until it reaches an extreme position in its (limited) range of motion  240 . The discs are removed (axially) from the stack  250 , and at least one of them is installed into a disc drive  255  (such as  100 , which shows two pre-written discs  110 ). The marks are “pre-written,” as are the discs, because the writing precedes installation into the disc drive  100 . Finally the pre-written servo marks are used to position the disc drive&#39;s transducer(s) as additional position data is written onto the data surface. This may include self-written servo tracks, “Zero Acceleration Path” factors or similar position correction factors, defect tables, and the like.  
         [0025]    FIGS.  3  -  5  show basic components of a servo track writer for implementing the present invention. Prior to installation in a disc drive  100 , a stack of discs  110  having a nominal radius  119  is positioned for rotation about an axis  113 . The discs have a conventional textured landing zone  117  and a useable data surface having a width  118  that is very flat and smooth.  
         [0026]    Near the outer circumference of the discs  110  is a servowriter actuator  320  having a load tang  325  on each arm thereof, each load tang  325  resting on an a respective engagement surface  416  of a comb-like support structure  310 . Support structure  310  is rotatable about its axis  313 , and actuator  320  is rotatable about its axis  323 . As the discs begin to rotate (counterclockwise as shown in FIG. 4), support structure  310  likewise rotates counterclockwise until it extends between (and on both ends of) the stack of discs  110 . This can occur because the actuator  320  slides along each engagement surface  416 . The discs  110  continue to accelerate, meanwhile, to a load velocity so that the actuator can rotate counterclockwise to load the servowriter heads onto (i.e. flying adjacent) the disc  110 . Once the heads are loaded, the support structure moves to a partially retracted position about 5 or 10 degrees clockwise from that shown in FIG. 5) and the discs are decelerated by at least 5% for servo writing operations.  
         [0027]    The depicted embodiment of FIGS.  3  -  5  have several advantageous features. Note that the support element  310  is elongated enough to extend between the discs by a distance greater than R/10, where R is the nominal disc radius  119 . This elongation permits the engagement surface  416  to include a sloped portion  517  that is less than about 25 degrees, and more preferably about 7 degrees, relative to the disc surface. Ordinarily, approach angles in this range would not be feasible because of the significant portion of the disc rendered inaccessible. Gradual approach angles are desirable, however, because they prevent low flying heads from diving into the disc upon loading. (Servowriter heads that fly at 0.7 to 1.0 microinch or less are highly desirable, for example with magnetic discs, because they make it possible to use a medium having a higher coercivity, which in turn permits higher data density.) Because the present invention makes use of a retractable support element  310 , a gradual approach is possible without losing access to the outermost portions of the disc  110 .  
         [0028]    [0028]FIG. 6 shows a much more detailed view of a servo writer  600  implementing the present invention. The writer  600  has several components supported by a substantially immobile and horizontally positioned platform  612 . The platform  612  is substantially resistant to movements from impact type collisions, preferably implemented as a granite slab or comparably heavy material weighing tens or hundreds of pounds. A sliding assembly  602  is connected to the platform  612  via a slide mechanism  614  for lateral movement (as indicated by arrow  616 ) over the platform  612  between a servo recording position  618  and a component access position  619 , as is discussed in greater detail below. The spindle motor hub assembly  606  and vacuum chuck  608  are directly and non-moveably secured to the platform  612 .  
         [0029]    In the preferred embodiment as shown, the sliding assembly  602  and the spindle hub assembly  606  of the STW  600  are both upright. Thus, the plurality of discs  110  secured to the spindle hub assembly  606  are vertically positioned relative to the platform  612 . It is believed that the substantially vertical orientation of the discs  110  improves the accuracy of the servo pattern that is written to each of the discs by the STW  600 , as explained in greater detail below. Similarly, the sliding assembly  602  includes a rotary actuator  320  (see FIG. 3) having a plurality of actuator arms  824  (see FIG. 8) that are also arranged for movement in substantially vertical planes relative to the platform  612 . Each actuator arm  824  includes one or more flexures  826  connecting a distal end of the actuator arm to a corresponding one of the servo-writing heads  804 . The vertical orientation of the actuator arms  824  also increases the accuracy of the servo writing process as described below.  
         [0030]    [0030]FIG. 6 illustrates the STW  600  in the load/unload position  619  where the sliding assembly  602  has been moved away from the spindle hub assembly  606  via the slide mechanism  614 . In this position, a stack of discs  110  may be loaded onto spindle hub assembly  606  to start the servo writing process. The spindle hub assembly  606  optionally includes a detachable spindle hub  828  (of FIG. 8) so that the hub  828  and the stack of discs  110  may readily be detached from a spindle motor (not shown in FIG. 8) to ease the process of loading and unloading the discs  110  from the spindle hub  828 .  
         [0031]    Once the discs  110  have been loaded on the spindle hub assembly  606  with a predetermined gap between adjacent discs, the discs  110  are secured to the spindle hub assembly  606  by means of a clamp ring  730 . The sliding assembly  602  is then preferably moved laterally along the platform  612  (in the direction of arrow  616 ) toward the spindle hub assembly  606 . While the flexures  826  on each of the actuator arms  824  tend to bias their corresponding heads  804  as is well known in the art, a support element  310  is used to maintain proper separation between the heads  804  so that the sliding assembly  602  and the disc stack on the spindle hub assembly  606  may merge without unintentional contact between the heads  804  and the discs  110 . The support element  310  preferably moves together with the sliding assembly  602  as shown in FIG. 8 and acts to separate the heads  804  against the bias force of the flexures  826 . Once the sliding assembly  602  is locked into the servo writing position  618  so that the heads  804  are positioned within the gaps between the adjacent discs  110 , the support element  310  is rotated away from the actuator  320  to allow the heads  804  to engage their respective discs as a result of the bias force provided by the flexures  826 . Of course, the heads  804  do not make physical contact with the data regions of their respective disc surfaces. Rather, the spindle hub assembly  606  is activated to spin the discs  110  at a predetermined rate prior to disengaging the support element  310 . As described above, the rotational motion of the discs  110  generates wind so that the heads  804  ride an air bearing in lieu of actually contacting the disc surface. This air bearing counters the bias force applied by the flexures  826  and protects the fragile magnetic coatings on the disc surfaces.  
         [0032]    Once the support element  310  is removed so that the heads  804  are fully engaged with their respective discs  110 , servo writing signals are applied to the heads  804  to begin the process of recording the servo pattern. During the recording process, the actuator  320  is rotated about a horizontal axis by a motor and bearing assembly within the sliding assembly  602  so that the heads  804  move radially across the surface of their respective discs  110 . The position of the heads  804  is determined by the laser interferometer  610  which utilizes interferometric techniques to track movement of the heads along the disc radius, and the interferometer  610  sends position signals back to control the operation of the sliding assembly  602  and thus the radial position of the heads  804 .  
         [0033]    Upon completion of the servo writing process, the actuator  320  is rotated back to position the heads  804  adjacent an outer circumference of the discs  110 , while the support element  310  is rotated into contact with the flexures  826  to disengage the heads  804  from the discs  110 . The sliding assembly  602  is then moved laterally away from the spindle hub assembly  606  to the load/unload position  619  so that the discs  110  (complete with their newly written servo patterns) can be removed from the spindle hub assembly  606  and ultimately installed in the disc drive  100 .  
         [0034]    Advantageously, the vertical orientation of the sliding assembly  602  prevents the force of gravity from pulling the heads  804  downward. This is important both during the loading and unloading of the heads  804  onto the discs  110  as well as during the servo writing process itself. For instance, while the support element  310  acts to separate the heads  804  prior to the loading process, it is noted that the support element  310  typically contacts the flexures  826  rather than the fragile heads  804  located at a distal end of the flexures  826 . Thus, with horizontally-oriented STWs, the force of gravity may tend to pull the heads  804  downward below the level of the individual support element arm or tine, thereby creating a danger of inadvertent contact between the hanging head  804  and the disc  110  prior to the disengagement of the support element  310  from the flexures  826 . This danger is avoided in the current invention since the force of gravity does not tend to pull the heads  804  in the direction of the discs. Additionally, during the servo writing process utilizing the present invention, the force of gravity does not tend to pull the heads  804  either toward or away from their respective disc surfaces as in the prior art. That is, in a horizontally-oriented STW, half of the heads are typically positioned adjacent a top surface of a disc, while the other half of the heads are positioned adjacent a bottom surface of a disc. For those heads positioned above their respective discs, the force of gravity on the flexure  826  and the head  804  is support elementined with the preload force generated by the flexure  826 , while for those heads positioned below their respective discs the force of gravity acts against the preload force. This dichotomy can create fluctuations in the preload force for the different heads within the STW which ultimately leads to discrepancies in the “fly height” of the head over the disc surface. While the preload force provided by the flexure is typically much greater than the weight of the flexure and head support elementined, even minor discrepancies in the fly height of the head during the servo writing process can lead to errors in the servo pattern.  
         [0035]    In addition to the above-described benefits relating to the substantially vertical orientation of the sliding assembly  602  (i.e., the movement of the actuator arms  824 , the flexures  826  and the heads  804  in a vertical plane), the substantially vertical orientation of the discs  110  on the spindle hub assembly  606  also provides benefits over prior art horizontally-oriented STWs. Specifically, while the discs  110  are formed from a relatively stiff material (such as aluminum), the discs are nonetheless subject to gravity-induced warping, particularly along the outer circumference of the discs. As described above, even miniscule amounts of disc warpage can lead to unacceptable servo-writing errors, particularly in light of the higher track densities utilized with the discs. However, by maintaining the discs  110  in a vertical orientation during the servo writing process, the force of gravity does not act to pull the disc surface from its nominal vertical plane. Thus, the vertical orientation of the STW  600  of the present invention (i.e., the substantially vertical orientation of both the sliding assembly  602  and the discs  110 ) provides a number of benefits over prior art horizontally-oriented STWs.  
         [0036]    A perspective view of the sliding assembly  602  in relation to the STW of FIG. 6 is shown in FIG. 7. The sliding assembly  602  includes an sliding block  762  housing a rotational air bearing and a translational air bearing (not labeled), an actuator  320  that includes an E-block, several actuator arms  240  carrying recording heads  140  thereon, a DC torque, brushless motor  768  or like motor for actuating the rotational air bearing  152 , a sliding mechanism  754  for translational movement of the sliding block  762 , and a laser transducer assembly for coordinating the motor&#39;s movement with the servo recording head&#39;s position.  
         [0037]    The slide mechanism  754  is used, in coordination with the translational air bearing, to laterally move the sliding assembly  602  over the platform  612  toward and away from the spindle motor hub assembly  606 . The slide mechanism  754  attaches to a lower edge of a side face of the sliding assembly  602 , and preferably to a lower edge of the side face adjacent the vacuum chuck. The slide mechanism  754  includes a pneumatically sliding cylinder attached to the platform  612  by a flexure or bracket. A pair of stops  782  extend along the lower edge of the side face of the sliding block  762  on opposite sides of the actuator block attached sliding mechanism. Each stop  782  extends beyond the front face and back face  786  of the sliding block  762 . A pair of catch block  787  is positioned on the platform  612  on opposite sides of the sliding block  762  to contact each stop when the sliding mechanism  754  laterally moves the sliding assembly  602  to the servo recording position on the platform.  
         [0038]    [0038]FIG. 8 shows a magnified view of the stack of discs  110 , the actuator  320 , and the support structure  310  positioned to permit the servo-writing heads  804  to operate. Notice that the clamshell-shaped air dam  889  protrudes between the discs and that the support structure  310  does not, in this position.  
         [0039]    Alternatively characterized, a first embodiment of the present invention is an apparatus (such as  100 ,  600 ) for writing position data onto a first data storage disc (such as  110 ). A spindle assembly (such as  606 ) is configured to support first and second discs (such as  110 ) rotatably in a stack. An actuator (such as  320 ) is configured to support a servowriter head (such as  804 ) between the discs to write several servo marks onto a data surface of the first disc (such as in step  220 ). A support element (such as  310 ) is configured to allow sliding contact with the actuator to unload the servowriter head from the data surface (such as contain tracks  112 ). The embodiment further includes means for retracting the actuator and the support element from between the first and second discs. Such means may be an engagement surface of a cam structure configured to support the actuator while the cam structure rotates out from between the first and second discs.  
         [0040]    In a second embodiment, the stack has a substantially horizontal axis of rotation. The support element optionally had a substantially parallel axis of rotation, although it is conceivable that the support element may be linearly actuated. The support element may also be a rotary actuator having an axis of rotation skewed to that of the disc stack, such as that of U.S. Pat. No. 5,283,705 (“Head Retraction Mechanism for a Magnetic Disk Drive”) issued Feb. 1, 1994 to Masanori Iwabuchi.  
         [0041]    In a third embodiment, the actuator is rigidly but rotatably supported by a first rigid body (such as  602 ). The spindle assembly is likewise rigidly but rotatably supported (by a second rigid body such as  612 ). Automated means such as an air bearing/vacuum chuck mechanism are provided for coupling the first and second rigid bodies together temporarily during a servowriting operation.  
         [0042]    A fourth embodiment is a method for writing position data. Several discs, preferably at least 8, are assembled coaxially in a stack (such as in step  210 ). A servowriter head supported by an actuator writes several servo marks onto the data surface (such as in step  220 ). The actuator is moved out from between the discs by sliding (an arm of) the actuator onto an engagement surface of a support element (such as  310 ) that extends between the first and second discs. The support element is moved out from between the to discs as the actuator slides on the engagement surface (such as in steps  235  and  240 ). After these movements, the discs can easily be removed from the stack (such as in step  250 ).  
         [0043]    All of the structures and methods described above will be understood to one of ordinary skill in the art, and would enable the practice of the present invention without undue experimentation. It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only. Changes may be made in the details, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the position data written can take the form of a pattern of holes in the magnetic media, rather than being written as a pattern of magnetized portions of the disc, without departing from the scope and spirit of the present invention. In addition, although the preferred embodiments described herein are largely directed to magnetic disc drives, it will be appreciated by those skilled in the art that many teachings of the present invention can be applied to optical and magneto-optical disc drives without departing from the scope and spirit of the present invention.