Abstract:
One aspect of the invention relates to an apparatus and method for retaining a disc drive head disk assembly (HDA) during a servo track writing procedure. The HDA includes a base, a disc stack coupled to a spindle rotatably attached to the base by a spindle shaft, and an actuator assembly pivotally attached to the base at a pivot shaft. Attached to one end of the actuator assembly proximal the disc stack is one or more transducers for reading/writing information from/to the discs. In one embodiment, the method includes restraining the ends of the spindle shaft and pivot shaft during servo track writing so that relative deflection therebetween is minimized. That is, all but rotational motion of the components is substantially eliminated. An apparatus for restraining the ends of the spindle shaft and pivot shaft is also provided. By so restraining the shaft and spindle, the servo information written by the transducers is concentric to the rotation of the disk, reducing track misregistration and improving maximum track density.

Description:
RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Serial No. 60/114,272, filed Dec. 30, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of mass storage devices. More particularly, this invention relates to an improved apparatus and method for securing a portion of a high density disc drive during a servo track writing operation. 
     BACKGROUND OF THE INVENTION 
     One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc drive housing, a disc that is rotated, an actuator assembly that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc. 
     To read and write data to the disc drive, the actuator assembly includes one or more arms that support the transducer over the disc surface. The actuator assembly is selectively positioned by a voice coil motor which pivots the actuator assembly about a pivot shaft secured to the drive housing. The disc is coupled to a motorized spindle which is also secured to the housing. During operation, the spindle provides rotational power to the disc. By controlling the voice coil motor, the actuator arms (and thus the transducers) can be positioned over any radial location along the rotating disc surface. 
     The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (“ABS”) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equalize so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc. 
     Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on portions of the storage disc referred to as tracks. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto the track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write to or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is often divided between several different tracks. While most storage discs utilize a multiplicity of concentric circular tracks, other discs have a continuous spiral forming a single track on one or both sides of the disc. 
     During manufacture, servo feedback information is encoded on the disk and subsequently used to accurately locate the transducer. The servo information is used to locate the actuator assembly/transducer head at the required position on the disc surface and hold it very accurately in position during a read or write operation. The servo information is written or encoded onto the disc with a machine commonly referred to as a servo track writer (hereinafter STW). At the time the servo information is written, the disc drive is typically at the “head disk assembly” (hereinafter HDA) stage. The HDA includes most of the mechanical drive components but does not typically include all the drive electronics. During the track writing process, the STW precisely locates the transducer heads relative to the disc surface and writes the servo information thereon. Accurate location of the transducer heads is necessary to ensure that the track definition remains concentric. If the servo track information is written eccentrically, the position of the transducer head during subsequent operation will require relatively large, constant radial adjustments in order to maintain placement over the track center. When the tracks are sufficiently eccentric, a significant portion of the disk surface must be allotted for track misregistration. Accordingly, overall track density is degraded and disc drive capacity is reduced. 
     In order to ensure proper writing of servo information, STWs utilize an external, closed loop positioning system that precisely positions the transducer head during servo track writing. The positioning system comprises a contact member that engages the actuator assembly, a position indicator which indicates the position of the contact member, and a displacing mechanism which repositions the contact member based on feedback from the position indicator. To ensure accurate positioning, various position indicators are used (e.g., mechanical, capacitive, and optical transducers to name a few). The STW further includes the required circuitry for writing the servo information to the disc surface via the transducer heads. 
     As demand for higher capacity drives grows, manufacturers are constantly seeking to increase drive capacity by increasing track density. That is, by increasing the density or “tracks per inch” (TPI), a greater number of discreet tracks can be encoded on a given disc surface. However, higher track density requires more efficient use of the disc surface. Accordingly, track misregistration due to eccentricities in track formation must be minimized in order to maximize TPI (and thus disc capacity). 
     While it is advantageous to maintain substantial concentricity during the servo track writing process, many factors adversely impact the STW&#39;s ability to write servo information concentrically. For instance, induced resonance in the STW itself can adversely affect the track writing operation. Further, vibrations in the spindle or actuator components (e.g., imperfect bearings) may also produce non-repeatable track writing errors. Still yet another problem with current STWs is oscillations in the HDA itself (i.e., independent deflection of the actuator and spindle relative to the STW). The present invention is directed to reducing these problems, especially the effects of component deflection, and the remainder of this discussion will focus on the same. 
     Most current STWs support the HDA by engaging a plurality of points on the external drive housing. When the HDA is so engaged, the spindle and actuator are restrained only by the internal structure of the HDA (i.e., the drive housing). Still other HDAs fasten the drive cover to the pivot shaft and a spindle shaft to provide additional support thereto. However, these STW/HDA configurations still produce drives with limited track densities not because of the STW&#39;s positioning accuracy but rather because of the non-repeatable deflection and vibration of the HDA components. 
     Accordingly, what is needed is an apparatus and method for use with an STW that minimizes relative deflection between the components of the HDA during the track writing process. In particular, what is needed is a way to reduce HDA component deflection sufficiently to allow greater track densities to be formed on a given disk surface. The present invention addresses these needs. 
     SUMMARY OF THE INVENTION 
     In devising the method and apparatus of the present invention, the inventors realized that current STW systems were limited in the maximum track densities they could achieve. To address this problem, the inventors focused on a method and apparatus for securing the drive during the track writing process. 
     In one embodiment, a method of restraining a head disk assembly (HDA) within a servo track writing apparatus (STW) is provided. The HDA includes a housing and a spindle shaft coupled to the housing where the spindle shaft rotatably supports a spindle having at least one storage disc. The HDA further includes a pivot shaft coupled to the housing. The pivot shaft pivotally supports an actuator assembly for moving a transducer head relative to the disc. The method comprises the steps of placing the HDA into the STW where the STW has opposing clamp members with opposing contact points. The HDA is then clamped between the clamp members such that the contact points operatively engage each end of both the pivot shaft and spindle shaft. A compressive load is then applied to the HDA, wherein the opposing contact points load against the ends of the pivot shaft and the spindle shaft to restrain non-rotational movement of the actuator assembly and spindle. 
     In yet another embodiment, a servo track writing apparatus for securing a head disc assembly (HDA) during a servo track writing process is provided. The apparatus includes a base, a fixed block assembly attached to the base, and a basket assembly opposing the fixed block assembly. The basket assembly includes a movable carriage adapted to receive the HDA. The basket assembly further includes a displacing device adapted for moving the carriage toward the fixed block assembly and a loading device adapted for loading the carriage against the fixed block assembly. 
     In still yet another embodiment, an apparatus for restraining a head disk assembly (HDA) during a servo track writing operation is provided. Here, the HDA includes a spindle shaft supporting a rotating spindle which in turn supports one or more storage discs. The HDA also has a pivot shaft supporting an actuator assembly for reading and writing from and to the storage discs. The apparatus comprises a device for holding the HDA and a device for restraining each end of the spindle shaft and pivot shaft such that the spindle and actuator assembly are restrained from generally all but rotational motion. 
     Advantageously, the method and apparatus of the present invention produces disc drives with higher storage capacity than those drives produced by other methods/apparatuses. In particular, the instant invention permits precise, concentric writing of embedded servo information to the disc. By providing external constraint to all but rotational/pivotal motion of the spindle and actuator, the non-repeatable oscillations which frequently occur during servo track writing are minimized. A drive produced according to the present invention thus requires less misregistration budget that is normally required with drives having more eccentric track formation. Thus, the STW of the present invention is capable of producing disc drives with greater track densities—and thus higher capacities—while utilizing otherwise conventional track writing processes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a generic disc drive with a multiple disc stack. 
     FIG. 2 is a perspective view of a servo track writing apparatus according to one exemplary embodiment of the present invention, the apparatus shown in the “closed” or operating position. 
     FIG. 3 is a partial perspective view of the apparatus of FIG. 2 shown in the “open” position. 
     FIG. 4 is an exploded view of the apparatus of FIG.  2 . 
     FIG. 5 is an enlarged, partial perspective view of a basket assembly according to one embodiment of the invention. 
     FIG. 6 is an exploded view of the basket assembly of FIG.  5 . 
     FIG. 7 is a diagrammatic section view of a vacuum block assembly according to one embodiment of the invention. 
     FIG. 8 is an exploded view illustrating a fixed block assembly in accordance with one embodiment of the invention. 
     FIG. 9 is a diagrammatic view illustrating insertion of the HDA into the STW in accordance with one embodiment of the invention. 
     FIG. 10 is a diagrammatic view illustrating clamping of the HDA into the STW in accordance with one embodiment of the invention. 
     FIG. 11 is a diagrammatic view illustrating restraining the HDA within the STW in accordance with one embodiment of the invention. 
     FIG. 12 is a diagrammatic view illustrating writing of servo information to the HDA in accordance with one embodiment of the invention. 
     FIG. 13 is a diagrammatic section view showing the engagement of the HDA within the STW. 
     FIG. 14 is a perspective view of a servo track writing system according to one embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The invention described in this application is useful with most all mechanical configurations of disc drives utilizing either rotary or linear actuation. FIG. 1 is an exploded view of one type of a disc drive  100  having a rotary actuator. The disc drive  100  includes a housing or base  112 , and a cover  114 . The housing  112  and cover  114  form a disc enclosure. Rotatably attached to the housing  112  on an actuator pivot shaft  118  is an actuator assembly  120 . The actuator assembly  120  includes a comb-like structure  122  having a plurality of arms  123 . Attached to the separate arms  123  on the comb  122  are load beams or load springs  124 . Load beams or load springs are also referred to as suspensions. Attached at the end of each load spring  124  is a slider  126  which carries a magnetic transducer head  150 . The slider  126  with the transducer  150  form what is frequently called the head. It should be noted that many sliders have one transducer  150  and that is what is shown in the figures. However, this invention is equally applicable to sliders having more than one transducer, such as what is referred to as an MR or magneto resistive head in which one transducer  150  is generally used for reading and another is generally used for writing. 
     On the end of the actuator assembly  120  opposite the load springs  124  and the sliders  126  is a voice coil  128 . Located above and below the voice coil  128  is a first magnet  130  and a second magnet  131 . As shown in FIG. 1, the first magnet  130  is associated with the cover  114  while the second magnet is adjacent the housing  112 . The first and second magnets  130 ,  131 , and the voice coil  128  are the key components of a voice coil motor which applies a force to the actuator assembly  120  to rotate it about the actuator pivot shaft  118 . Also mounted to the housing  112  is a spindle motor (not shown). The spindle motor includes a rotating portion called the spindle hub  133 . In this particular disc drive, the spindle motor is within the hub. In FIG. 1, a number of discs  134  are attached to the spindle hub  133 . In other disc drives, a single disc or a different number of discs may be attached to the hub. The invention described herein is equally applicable to disc drives which have a plurality of discs as well as disc drives that have a single disc. The invention described herein is also equally applicable to disc drives with spindle motors which are within the hub  133  or, alternatively, under the hub. 
     The spindle hub  133 , in one embodiment, rotates about a stationary spindle shaft  138  which has a first end retained in the housing  112  and a second end adjacent to the cover  114 . When the discs are spinning, the spindle shaft  138  remains stationary. The spindle shaft  138  includes a female thread on the second end which permits coupling of the second end to the cover  114 . The pivot shaft  118  is of a similar construction in that it is also stationary and has a first end (in the housing  112 ) and a second end (adjacent the cover  114 ) with a female thread located on the latter (see FIG.  13 ). The purpose of these stationary shafts will become apparent in the following discussion. 
     The disk drive  100  includes the mechanical components discussed above as well as various electronic components such as a printed circuit board (not shown) typically attached to the lower (as viewed in FIG. 1) side of the housing  112 . Without the circuit board and other electronics, the disc drive is often referred to as a head disc assembly or HDA  152 . Stated alternatively, the mechanical components—including the drive housing  112 , cover  114 , actuator assembly  120 , pivot shaft  118 , arms  123 , transducer heads  150 , spindle hub  133 , spindle shaft  138 , and discs  134  among others—generally define the HDA  152 . The HDA is a convenient subassembly for completing various manufacturing processes including servo track writing. For instance, the HDA provides physical access to the voice coil  128  during manufacture via apertures  136  but can thereafter be sealed (hermetically if necessary) to ensure that the internal components remain substantially contaminant-free. Near the end of production, the drive electronics are assembled to the HDA  152  to produce the disc drive  100 . 
     Generally speaking, the present invention relates to an improved method and apparatus for loading and holding an HDA during the servo track writing process. In particular, the invention is directed to a method and apparatus of restraining the pivot shaft  118  and spindle shaft  138  between two sets of opposing clamp points located on relatively stiff, opposing clamp members. By restraining the shafts from all but rotational motion, eccentric track formation resulting from mechanical oscillations, bearing imperfections, and overall deflection of the HDA components is substantially reduced. Accordingly, the percentage of the disc surface required for track misregistration is minimized, yielding greater track densities and ultimately, a higher storage capacity for a given disc size. 
     Referring now to FIG. 2, a servo track writing machine or apparatus (hereinafter STW)  200  according to one embodiment of the invention is shown. The STW is used to write servo information to the individual discs  134  (see FIG. 1) of the HDA  152 . The STW is shown in a closed or writing position with the HDA  152  installed horizontally therein (i.e., the spindle shaft  138  and pivot shaft  118  are horizontal). FIG. 3 shows the HDA in an open or loading position with the HDA removed. 
     The STW  200  illustrated in the figures includes numerous aspects that are not central to the invention. For example, a clocking mechanism  510  (see FIG. 3) is provided to indicate the rotational position of the discs within the HDA during track writing. Since this and other track-writing aspects of the illustrated STW are not central to an understanding of the invention, they are not described in detail herein. 
     Referring now to FIG. 4, the STW  200 , in one embodiment, includes a base  300 , a moving block or basket assembly  400 , a fixed block assembly  500 , and a servo information writing system  900  which, in one embodiment, includes a laser assembly  600  and other components located within the fixed block assembly  500 . A cover  401  for covering a portion of the basket assembly  400  is also shown. Each of these items is described in detail below. 
     Base 
     The base  300  is, in one embodiment, formed from granite, diabase, or a similar dimensionally stable material which is machined to precise tolerances. As shown in FIG. 4, the base  300  has a plurality of threaded holes corresponding to mounting patterns provided on the various assemblies. Fasteners (not shown) couple the various assemblies  400 ,  500 , and  600  to the base. The base surface  301  provides a guide surface or datum for locating the assemblies relative to one another. 
     Basket Assembly 
     Coupled to one edge of the base  300  is the basket assembly  400  which is more clearly shown in FIGS. 5 and 6. The basket assembly  400  comprises a first, moving clamp member which is hereinafter referred to as the carriage  402 , and a fixed portion or backing block  404 . The carriage  402  includes a vacuum block  406  and a damper assembly  408 . The vacuum block  406  further comprises a linear air bearing and vacuum stiffener as further discussed below. The damper assembly  408  defines a receptacle or basket  410  for receiving the HDA  152  as shown in FIG.  2 . The sides of the basket  410  include a primary or first guide module  412  and a secondary guide module  414 . The face of the basket  410  is defined by the damper assembly  408 . The damper assembly further includes HDA lead-in guides  416  to assist in loading the HDA, and biased preload buttons  418  which bias the HDA against the guide modules  412 ,  414 . The damper assembly still further includes first and second contact points  419 ,  420  which engage the HDA  152  when the latter is installed. The first contact point  419  contacts the cover  114  where it couples to the spindle shaft  138  while a second contact point  420  contacts the cover  114  where the latter couples to the pivot shaft  118 . One or more additional contact points (not shown) may be provided to engage another stationary portion of the HDA housing  112  to better indicate or constrain the drive within the basket. 
     In one embodiment, the damper assembly  408  is made of aluminum. However, other materials having different damping characteristics are also possible within the scope of the invention. For instance, in another embodiment, the damper assembly comprises stainless steel impregnated with plastic. Other materials that provide particular damping capabilities are also possible. 
     The vacuum block  406  comprises a slide or air bearing surface  422  which slides along the surface  301  of the base  300  (see FIG.  2 ). The block  406  is selectively displaced along the base  300  under power of one or more linear actuators. In one embodiment, the actuators are pneumatic cylinders which receive pressurized air from a pressurized air source  431  (shown diagrammatically in FIG. 7) to extend and retract an actuator rod. While shown and described as pneumatic cylinders other linear actuation devices are also possible. For example, linear ball screws may also be used without departing from the scope of the invention. 
     In the exemplary embodiment shown in the figures, the basket assembly  400  includes a first pneumatic cylinder  424  (see FIG. 6) having a first extension rod  425  which displaces the carriage  402 , and a second pneumatic cylinder  426  having a second extension rod  427  which applies a preload force to the carriage. While the particular design of the pneumatic cylinders is not central to the invention, in one embodiment the pneumatic cylinder  424  is a BIMBA Manufacturing model 013-DPB-CT while the pneumatic cylinder  426  is a BIMBA Manufacturing model 173DP-CT. However, STWs using other cylinders or other displacing and loading devices are equally within the scope of the invention. Furthermore, only one or, alternatively, more than two actuators may be used to accomplish both displacement and loading. 
     The actuators  424 ,  426  are pivotally attached to the carriage  402  at rod end pivots  428  (see FIG.  6 ). The opposite or base end of the actuators  424 ,  426  attaches to the backing block  404  which is, in turn, fastened or otherwise coupled to the base  300 . Like the rod ends, the base ends of the actuators  424 ,  426  are pivotally coupled to the backing block  404 . By allowing the actuators to pivot at both ends, the direction of the carriage  404  is generally unconstrained by the actuators during extension and retraction. Further, by having pivoting ends, the actuators experience little or no side loading during operation. 
     Linear Air Bearing and Vacuum System 
     Pressurized air is provided to the basket assembly  400  to provide the actuation force to the pneumatic cylinders  424 ,  426 , thus permitting the cylinders to extend and retract and move the carriage  402 . Pressurized air is also provided to the slide surface  422  from the pressurized air source  431  as shown in FIG. 7 to form an air bearing  430 . The air bearing  430  comprises a plurality of ports or orifices  432  located along a perimeter of the slide surface  422  of the vacuum block  406 . When pressurized air is delivered, an air film develops between the surface  422  and the base surface  301 . This air film permits relatively friction-free travel of the vacuum block  406 , and thus the carriage  402 , along the base  300 . When the block  406  has been repositioned, flow to the orifices  432  is terminated and the block  406  falls into contact once again with the base surface  301 . 
     In addition to pressurized air, a vacuum stiffener having a vacuum source  435  is also provided. The vacuum source  435  is coupled to the vacuum block  406  at a vacuum port or orifice  436 . The vacuum orifice  436  is fluidly coupled to a recessed portion  438  of the block  406 . The vacuum stiffener serves multiple purposes. First, the vacuum stiffener is capable of selectively vacuum coupling the vacuum block  406  to the base  300 . Vacuum coupling occurs when flow of pressurized air is discontinued to the orifices  432  and the vacuum source is activated. Here, the surface  422  sits flush to the base surface  301  and the vacuum pressure couples the vacuum block  406  to the base  300 . In one embodiment, the vacuum source has an adjustable vacuum pressure, providing at least two different vacuum pressure settings for reasons that will become apparent below. 
     The vacuum stiffener is also used in conjunction with the air bearing to stiffen the latter. While air bearings are extremely effective at eliminating friction, they typically require an opposing air bearing or similar device to apply an opposing load or preload. Without the preload, the air bearing is unstable and has an inconsistent flying height due to the compressibility of the air film. Such inconsistent flying heights result in mis-alignment as well as random and unintended contact between the bearing surfaces (surfaces  422  and  301 ). To stiffen the air bearing and maintain a consistent flying height between the vacuum block  406  and the base surface  301 , the vacuum stiffener is, in one embodiment, used simultaneously with the air bearing  430 . The counteracting force of the vacuum provides the preloading force necessary to stabilize the air bearing  430 . By utilizing the vacuum stiffener, the STW does not require an additional air bearing or other preload device. Thus, space and cost savings are realized. 
     Fixed Block Assembly 
     Referring now to FIG. 8, mounted opposite the basket assembly  400  is a second, fixed clamp member hereinafter referred to as the fixed block assembly  500 . The fixed block assembly is adapted to engage the HDA  152  with third and fourth contact points  502 ,  503  (see FIG. 3) opposite to the first and second contact points  419 ,  420 . Accordingly, when the STW is closed, the HDA  152  is “sandwiched” between the contact points  419 ,  420  (see FIG. 5) and  502 ,  503  (see FIG. 3) so that the ends of the spindle shaft  138  and the pivot shaft  118  are restrained. That is, together the contact points  419 ,  420 ,  502 , and  503  define a means for engaging the HDA  152  by operatively contacting the ends of the spindle shaft  138  and the pivot shaft  118 . While the contact points shown herein engage the HDA as illustrated, any other engaging means that contacts the HDA in the vicinity of the spindle shaft and pivot shaft is also within the scope of the invention. It is noted that the contact points operatively engage the spindle shaft and pivot shaft ends without restriction rotation or pivoting of the spindle  133  or the actuator assembly  120 . 
     The fixed block assembly  500  further includes a guide rail  504  which extends from one side of the assembly  500  towards the basket assembly  400 . The guide rail  504  is fastened to the base  300  and includes a series of guiding devices which, in one embodiment, are rollers  506  (visible in FIGS. 3 and 8) that are selectively extended and retracted to guide to the carriage  402  and constrain lateral motion during movement of the carriage  402 . Mounted opposite the guide rail  504  is a side loading assembly  508  which is used to selectively load the carriage  402  against the guide rollers  506 . 
     Still referring to FIG. 8, the fixed block assembly  500  is, in one embodiment, coupled to a laser assembly  600 . The fixed block assembly  500  and the laser assembly  600  incorporate various portions of the servo track writing system  900 . The system includes, among other items, those components needed to physically and electronically interact with the HDA to write the servo information thereto. For example, the system typically includes: a contact member (not shown) which physically interfaces with the actuator assembly  120  via the apertures  136  (see FIG.  1 ); a position indicator (also not shown) which indicates the precise position of the contact member; and a displacing mechanism (also not shown) which moves the contact member in response to the position indicator. In order to precisely control the displacing mechanism, the position indicator is, in one embodiment, a model 10705A laser interferometer (also not shown) made by Hewlett-Packard. The interferometer uses the laser assembly  600  as its energy source. 
     Other conventional servo track writing system components are also possible. However, since the particular construction of these portions of the servo track writing system, including the hardware and electronics that are used to actually write the servo information to the discs, is not central to the present invention, it is not further discussed herein. 
     STW Operation 
     Having described an exemplary embodiment of the STW, attention is now focused on a method of securing the HDA in the STW in accordance with one embodiment of the present invention. The purpose of this description is to permit someone of skill in the art to practice the method. Accordingly, steps that are not critical or those that are well known in the art have been omitted for the sake of simplicity. The reader is also reminded that, while described in a particular order, steps may be rearranged to some degree to better accommodate particular manufacturing processes. In addition, steps may be modified to accommodate disc drives of different sizes and different configurations. And finally, although the method is described in terms of a single STW, other embodiments are also considered in which multi-unit arrays of STWs are created to accommodate high volume production. 
     Referring now to related FIGS. 9-12, the method, broadly speaking, comprises inserting the HDA  152  into the STW (FIG. 9) and clamping the HDA  152  between opposing clamp members (FIG.  10 ). The clamp members include opposing contact points which engage the ends of both the spindle shaft  138  and the pivot shaft  118  (see FIG.  13 ). Using a loading device such as the pneumatic cylinder  426 , a compressive load is applied to the contact points, restraining the ends of the spindle and pivot shaft (FIG.  11 ). With the ends so constrained, the servo track writing process according to conventional methods is executed by a servo writing system  900  as diagrammatically represented in FIG.  12 . By constraining the respective ends, relative motion between the spindle  133  and pivot shaft  118  is minimized during the track writing process, resulting in more concentric track formation and ultimately higher track densities. When clamped between the respective contact points, the compressive load is applied to stationary portions of the spindle shaft  138  and pivot shaft  118  such that rotation of the spindle and actuator assembly  120  are unrestrained. 
     The STW  200  described above and illustrated in FIGS. 2-8 is adapted to retain the HDA  152  according to the method described. In particular, with the STW in the “open” position (see FIG.  3 ), the HDA  152  is loaded into the basket  410  of the basket assembly  400 . Automated or manual methods may be used to insert/remove the HDA into the basket. In one embodiment, an identifying device  800  (shown in FIG. 14) such as a bar code scanner identifies the HDA and adjusts relevant STW parameters (clamp load, disc capacity, etc.) prior to securing the HDA therein. 
     Once inserted, the contact points  419 ,  420  of the damper assembly  408  are adjacent to the second ends of the spindle shaft  138  and the pivot shaft  118  respectively. The carriage  402  with the HDA  152  therein is then moved to the closed position as shown in FIG.  2 . To move the carriage, the pneumatic cylinder  424  pushes the carriage  402  toward the fixed block assembly  500 . In order to reduce friction between the carriage  402  and the base  300 , the air bearing  430  as described above is activated. The air bearing produces a thin air film between the carriage  402  and the surface  301 . In one embodiment, the air film thickness is approximately 0.002 inches. The vacuum stiffener as described herein is used to preload the air bearing and maintain a consistent flying height. The retractable guide rollers  506  (see FIGS. 3 and 8) are extended from the side rail  504  and the side loading assembly  508  (see FIG. 8) is extended to confine the moving carriage, aligning the HDA  152  with the opposing contact points  502 ,  503  located on the fixed block assembly  500 . The cylinder  424  then moves the carriage  402  towards the fixed block assembly  500 . Additional guide members  512  (see FIG. 3) are provided to guide the HDA into correct position as the STW is closed. When the cylinder  424  has completely extended the carriage  402 , the HDA  152  is located between the basket assembly  400  and the fixed block assembly  500  such that the spindle shaft  138  and pivot shaft  118  are sandwiched between the respective contact points  419 ,  420 ,  502 , and  503  as shown in FIG.  13 . In one embodiment, the cylinder  424  is adapted for displacement and is capable of exerting only about 5 pounds (about 22.2 Newtons) of force with a 85 pound-force per square inch (psi) input (approximately 586 kilopascals (kPa)) from the pressurized air source  431 . 
     At this point, the air supply to the air bearing orifices  432  is terminated, dropping the carriage  402  back to the base  300 . The vacuum source, which was activated in conjunction with the air bearing  430  as previously described, continues to apply a partial vacuum to the recessed portion  438  (see FIG.  7 ). In one embodiment, the partial vacuum pressure is less than one inch of Mercury (in Hg) or approximately 25.4 millimeters of Mercury (mm Hg). With this partial vacuum maintained, the guide rollers  506  and the side loading assembly  508  are disengaged or drawn away from the carriage  402  and the second pneumatic cylinder  426  is pressurized, applying a predetermined load to the carriage  402  and thus, the spindle shaft  138  and pivot shaft  118 . The partial vacuum maintains general alignment of the carriage yet still permits it to move and swivel to ensure even loading is maintained. In one embodiment, the load applied by the cylinder  426  is 150 lbs (667 Newtons). However, this may be adjusted to better accommodate the particular HDA  152 . Once the load is applied, full vacuum pressure (approximately 28 in Hg or 711 mm Hg) is applied to the recessed portion to secure the carriage  402  to the base  300 . In one embodiment, the cylinder  426  remains pressurized after full vacuum pressure is applied to ensure loading is maintained. In another embodiment, the actuator  426  is unloaded (i.e., pressure is no longer provided), leaving the vacuum coupling of the block  406  alone to function as the restraining means. Once again, other devices that can preload the HDA (electric ball screw for example) are also possible within the scope of the invention. 
     As the HDA is secured, electrical interconnection to the spindle motor, actuator assembly, and read/write circuitry is automatically or manually made. The STW can then initiate an otherwise conventional servo writing process based on the particular HDA model loaded therein. Because the pivot shaft  118  and spindle shaft  138  are restrained between two stiff structures, the respective axes of the two shafts remain substantially parallel throughout the writing process. Accordingly, non-repeatable movement of the actuator assembly  120  and the spindle  133  that is common with other STWs is minimized and higher track density is achieved. 
     The STW  200  can be incorporated into a complete servo track writing station  1000  as shown in FIG.  14 . In this particular embodiment, the station  1000  comprises the STW components discussed herein as well as a computer  1002  to monitor and control the process. Further, pneumatic and vacuum sources (not shown) may be included. Other equipment such as the scanner  800  (to identify HDAs for correct STW settings) may also be integrated into the station  1000 . While the station  1000  is shown as a stand-alone unit, other embodiments wherein the STW is arrayed with other units sharing common equipment (e.g., one workstation, one pneumatic air supply, etc. controlling multiple STWs) are also possible without departing from the scope of the invention. 
     To address particular dynamic characteristics of the HDA and STW, variations in STW parameters and components may be made without departing from the scope of the invention. For example, the damper assembly  408  and fixed block assembly  500  may be made of a material that provides improved damping to the spindle shaft and pivot shaft. Alternatively, the force applied to the HDA by the pneumatic cylinder  426  may be elevated or reduced depending on the particular HDA. In another embodiment, a force measuring transducer may be used with the cylinder  426  to more precisely apply the compressive load. In still yet another embodiment, a pneumatic servo valve is used to maintain the applied load via a feedback signal from the load cell. 
     Advantageously, the method and apparatus of the present invention produces disc drives with higher storage capacity than those drives produced by known methods/apparatuses. In particular, the instant invention permits precise, concentric writing of embedded servo information to the disc. By providing external constraint to all but rotational/pivotal motion of the spindle and actuator, the non-repeatable oscillations which frequently occur during servo track writing are minimized. A drive produced according to the present invention thus requires less misregistration budget that is normally required with drives having more eccentric track formation. Thus, the STW of the present invention is capable of producing disc drives with greater track densities—and thus higher capacities—while utilizing otherwise conventional track writing processes. 
     CONCLUSION 
     In conclusion, a method of restraining a head disk assembly (HDA)  152  within a servo track writing apparatus (STW)  200  is provided. The HDA  152  includes a housing  1   12  and a spindle shaft  138  coupled to the housing  112  where the spindle shaft rotatably supports a spindle  133  having at least one storage disc  134 . The HDA further includes a pivot shaft  118  coupled to the housing  112 . The pivot shaft  118  pivotally supports an actuator assembly  120  for moving a transducer head  150  relative to the disc  134 . The method comprises the steps of placing the HDA  152  into the STW  200 , where the STW has opposing clamp members  402 ,  500  with opposing contact points  419 ,  420 ,  502 , and  503 . The HDA  152  is then clamped between the clamp members  402 ,  500  such that the contact points  419 ,  420 ,  502 , and  503  operatively engage each end of both the pivot shaft  118  and spindle shaft  138 . A compressive load is then applied to the HDA  152 , wherein the opposing contact points  419 ,  420 ,  502 , and  503  load against the ends of the pivot shaft  118  and the spindle shaft  138  to restrain non-rotational movement of the actuator assembly  120  and spindle  133 . 
     In yet another embodiment, a servo track writing apparatus  200  for securing a head disc assembly (HDA)  152  during a servo track writing process is provided. The apparatus includes a base  300 , a fixed block assembly  500  attached to the base  300 , and a basket assembly  400  opposing the fixed block assembly  500 . The basket assembly  400  includes a movable carriage  402  adapted to receive the HDA  152 . The basket assembly  400  further includes a displacing device  424  adapted for moving the carriage  402  toward the fixed block assembly  500  and a loading device  426  adapted for loading the carriage  402  against the fixed block assembly  500 . 
     In still yet another embodiment, an apparatus for restraining a head disk assembly (HDA)  152  during a servo track writing operation is provided. Here, the HDA  152  includes a spindle shaft  138  supporting a rotating spindle  133  which in turn supports at least one storage disc  134 . The HDA also has a pivot shaft  118  supporting an actuator assembly  120  for reading and writing from and to the storage disc  134 . The apparatus comprises a device for holding the HDA and a device for restraining each end of the spindle shaft  138  and pivot shaft  118  such that the spindle  133  and actuator assembly  120  are restrained from generally all but rotational motion. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.