Abstract:
A detect control device is provided that monitors a position error signal signature associated with a transducer while being operably supported by an actuator at a substantially constant fly height adjacent a storage medium to characterize the extent to which the actuator contacts an unload ramp. A method is provided for: supporting a transducer at an end of an actuator at a substantially constant fly height adjacent a storage medium; moving the actuator toward an unload ramp while maintaining the substantially constant fly height; and detecting a contacting engagement between the actuator and the unload ramp by monitoring a position error signal signature associated with the transducer.

Description:
RELATED APPLICATIONS  
       [0001]     The present application makes a claim of domestic priority to U.S. Provisional Patent Application No. 60/722,827 filed Sep. 30, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The claimed invention relates generally to the field of data storage and more particularly, but not by way of limitation, to an apparatus and method for writing servo information to a data storage medium.  
       BACKGROUND  
       [0003]     Disc drives are data storage devices that store digital data in magnetic form on a rotating disc. Modem disc drives comprise one or more 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 tracks, typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads relative to the discs. During a write operation 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 millimeter). Increased track density requires more closely-spaced, narrow tracks, and therefore requiring 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”) during the manufacture of the disc drive. The STW records servo patterns on the discs following assembly of the disc drive. The STW receivingly engages a disc drive that has a disc pack with mounted discs that have not been completely pre-recorded with servo patterns. The STW essentially uses the drive&#39;s own read/write heads to record the requisite servo patterns directly to the mounted discs.  
         [0006]     These and other recent improvements in the art have significantly improved both, often competing, goals of enhanced quality and faster throughput. It is to the furthering of those efforts that the embodiments of the present invention are directed.  
       SUMMARY OF THE INVENTION  
       [0007]     Embodiments of the present invention are generally directed to the writing of servo information to a moving media data storage device.  
         [0008]     In some embodiments a detect control device is provided that monitors a position error signal signature associated with a transducer while being operably supported by an actuator at a substantially constant fly height adjacent a storage medium to characterize the extent to which the actuator contacts an unload ramp.  
         [0009]     In some embodiments a method is provided for: supporting a transducer at an end of an actuator at a substantially constant fly height adjacent a storage medium; moving the actuator toward an unload ramp while maintaining the substantially constant fly height; and detecting a contacting engagement between the actuator and the unload ramp by monitoring a position error signal signature associated with the transducer.  
         [0010]     In some embodiments an apparatus is provided with an actuator supporting a transducer in a data transfer relationship with a storage medium, and means for characterizing the extent to which the actuator contacts an unload ramp while flying the transducer at a substantially constant fly height adjacent the medium.  
         [0011]     In some embodiments a servo writer apparatus is provided having an external positioner that contactingly positions an actuator of a data storage device. The apparatus further has a detect control that monitors a position error signal signature associated with the external positioner to characterize the extent to which the actuator contacts an unload ramp.  
         [0012]     In some embodiments a method is provided including: contactingly engaging an external positioner against an actuator of a data storage device; moving the actuator toward an unload ramp by actuating the external positioner; and monitoring a position error signal signature associated with the external positioner to characterize the extent to which the actuator is contacting the unload ramp.  
         [0013]     These and various other features and advantages which characterize the claimed invention will become apparent upon reading the following detailed description and upon reviewing the associated drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an isometric view of a data storage device with which embodiments of the present invention can be practiced.  
         [0015]      FIG. 2  is a control block diagram of the data storage device of  FIG. 1 .  
         [0016]      FIG. 3  is a diagrammatic depiction of a servo track writer (STW) receivingly engaging a data storage device in accordance with embodiments of the present invention.  
         [0017]      FIG. 4  is a more detailed depiction of a portion of the STW of  FIG. 3 .  
         [0018]      FIG. 5  is a control block diagram of the STW of  FIG. 3 .  
         [0019]      FIG. 6  is a graphical depiction of obtaining a baseline PES signature when the head is flying at a nominal fly height and the actuator is not contacting the ramp.  
         [0020]      FIG. 7  is a graphical depiction of obtaining a PES signature when the head first contacts the ramp while still flying at the nominal fly height of  FIG. 6 .  
         [0021]      FIG. 8  is a graphical depiction of obtaining a PES signature when the head has stepped into the ramp more than in  FIG. 7 .  
         [0022]      FIG. 9  is a graphical depiction of obtaining a PES signature when the head has stepped into the ramp more than in  FIG. 8 .  
         [0023]      FIG. 10  is an indicative PES signature when the head is at the position of  FIG. 6 .  
         [0024]      FIG. 11  is an indicative PES signature when the head is at the position of  FIG. 7 .  
         [0025]      FIG. 12  is an indicative PES signature when the head is at the position of  FIG. 8 .  
         [0026]      FIG. 13  is an indicative PES signature when the head is at the position of  FIG. 9 .  
         [0027]      FIG. 14  is a flowchart of steps for practicing a method of RAMP DETECT in accordance with embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0028]     Referring to the drawings in general, and more particularly to  FIG. 1  that shows an isometric view of a data storage device  100  (or “drive”) constructed in accordance with embodiments of the present invention. The drive  100  preferably includes a base  102  and a cover  104  (partially cutaway), which together provide a housing for a number of components. The components include a motor  105  to which a clamp  106  is attached for fixing one or more storage mediums  108  (or “discs”) in rotation therewith. Adjacent the disc  108  is an actuator  112  that is pivotable around a bearing assembly  114  by selectively energizing a voice coil motor (“VCM”)  115 . The actuator  112  includes an arm  116  supporting a load arm  118  that, in turn, supports a head  120  (or “transducer”) at a distal end thereof in a data transfer relationship with the disc  108 . The heads  120  are moved beyond an outer diameter of the discs  108  and unloaded to a ramp  122  when the drive  100  is inactive. Each disc  108  can be divided into data tracks, and the head  120  is positioned to retrieve data from and store data to the tracks.  
         [0029]     To provide the requisite electrical conduction paths between the head  120  and drive  100  control circuitry, the head  120  advantageously has a flex circuit that is routed on the actuator  112  from the head  120 , along the load arm  118  and the arm  116 , and to a circuit portion  133  that is supported by a proximal end (sometimes referred to as “E block”) of the actuator  112 . The circuit portion  133  connects the head  120  flex circuit to another flex circuit  134  which passes through the base  102  to a printed circuit board (PCB)  138 . An electrical connector  140  attached to the PCB  138  has a plurality of contacts  142  for connecting the drive  100  to a mating connector (not shown), such as for placing the drive  100  in communication with external control circuitry.  
         [0030]      FIG. 2  is a functional block diagram illustrating types of control signals and data transfers that can be passed between the drive  100  and a remote device, such as with a host  144  via a bus  145 . The drive  100  generally has a read/write channel  143 , a servo control circuit  145 , and a motor control circuit  146 , all connected by a control bus  147  to a controller  148 . An interface circuit  150  is connected to the read/write channel  143  by bus  152  and to the controller  148  by bus  154 . The interface circuit  150  serves as a communications interface between the drive  100  and the host device (or other remote device as described below). Generally, in response to an access command from the host  144  and received by the controller  148  from the interface  150 , the controller  148  controls the flow of data to and from the disc  108 . The read/write channel  143 , in turn, provides store and retrieve signals to the head  120  in order to store data to the disc  108  and retrieve data from the disc  108 . The head  120  can, for example, provide an analog read signal to the read/write channel  143 , which in turn converts the analog read signal to digital form and performs the necessary decoding operations to provide data to the interface circuit  150  for output to the host  144 . A buffer  161  exists under the control of the controller  148  in order to temporarily store data associated with host  144  access commands with the disc  108 .  
         [0031]      FIG. 3  is a diagrammatic depiction of a servo track writer (“STW”)  170  that is used in accordance with some embodiments of the present invention to write servo information to the discs  108 . The STW  170  generally has a positioning system  172  for precisely rotating an external positioner  174  that can include a push-pin  176 . The push-pin  176  is insertable through an opening in the base  102  of the drive  100 , for making contacting engagement with the actuator arm  116 . In equivalent alternative embodiments the external positioner  174  can provide a noncontacting engagement with the actuator  112 , such as by providing a light source in combination with an optical diffraction grating on the actuator  1   12 . Although not particularly shown, the positioning system  172  also includes a position control element, such as an encoder or other interferometer element, and a fixed data transfer element for writing a clock track to the disc  108 .  
         [0032]     The STW  170  is a manufacturing article that receivingly engages a drive  100  for the purpose of writing some or all of the servo tracks to the discs  108 . Once the servo track writing procedure is completed, the drive  100  entirely embodies the article of manufacture; the STW  170  forms no part thereof. Hence, for purposes of this description and meaning of the appended claims, the term “external” such as in “external positioning device,” with respect to the drive  100 , means an item that is not part of the drive  100 .  
         [0033]     Preferably, the STW  170  is configured so as to be readily connectable to a drive  100  via a connector mating with the connector  140  ( FIG. 1 ). In this manner the STW  170  has entire access to the on-board control circuitry described in  FIG. 2 , in the same manner as the host  144  does.  
         [0034]      FIG. 4  is a more detailed depiction of a portion of the STW  170  of  FIG. 3 , illustrating a coil  177  of a VCM in the STW  170  that is selectively energized in order to radially position the external positioner  174 . Precise positional control is achieved by a positioner  178  in the STW  170  as the STW VCM is used to radially position the actuator  112 . During servo writing operations a bias current is applied to the actuator coil portion of the actuator VCM  115 , to maintain a continuous contacting engagement with the external positioner  174  throughout the external positioner  174  range of movement. This contacting engagement provides a transmission path for vibrations from the actuator  112  to the external positioner  174 . That is, excitations  179  acting on the actuator  112 , such as from airflow perturbations from the spinning discs  108  and/or vibration from the rotating spindle motor  105 , are transmitted through the contacting engagement to excitations  181  acting on the STW  170 . The excitations  181  can be measured with the positioner  178 .  
         [0035]      FIG. 5  is a diagrammatic depiction of the host  144 , now employed to write servo tracks, in communication with the STW  170  via a bus  180 . Key components of the STW  170  include a system microprocessor  182  providing top-level control of all the servo track writing activities, as they are directed by the host  144 . An interface  184 , motor driver  186 , and actuator VCM driver  188  communicate with the interface  150 , motor control circuit  146 , and servo control circuit  145 , respectively, of the data storage device  100  illustrated in  FIG. 2 . Also shown is the external positioner  174  that contactingly positions the actuator  112  in relation to the discs  108 .  
         [0036]     A detect control (“DC”)  190  is illustrated in the form of programming instructions stored in memory that are executable by the processor  182  for monitoring a position error signal (“PES”) signature associated with the excitations  181  acting on the external positioner  174 . It will be noted that this PES signature is unrelated to any data transfer relationship that may or may not be occurring between the head  120  and the disc  108 . As such, the present embodiments can be practiced with the interface  184  de-energized during a ramp detect routine. This advantageously precludes any opportunity for damaging the head  120  by possible pole tip protrusion issues stemming from lifting the head  120  away from the disc  108  at a time when the head  120  is active.  
         [0037]     The STW  170  supplies power to the spindle motor  105  for rotating the discs  108  in a data transfer relationship with the heads  120 . The external positioner  174  moves the heads  120 , via the contacting engagement of the push-pin  176  with the arm  116  in these illustrative embodiments, across the discs  108  to write servo information.  
         [0038]      FIGS. 6-9  illustrate four different radial positions of the head  120  as it is moved across the data storage space and ultimately contacts the ramp  122  during servo writing. In  FIG. 6  the head  120  is disposed adjacent the data storage area of the disc  108 , such as when the STW  170  is writing servo information to the discs  108 .  FIG. 7  illustrates the head  120  making a first contacting engagement with the angled surface of the ramp  122 . In  FIG. 8  the head  120  has been moved a short distance, such as would be measured in STW steps, into the ramp  122 .  FIG. 9  illustrates the head  120  having been moved a like number of STW steps into the ramp  122 .  
         [0039]      FIGS. 10-13  graphically depict how the DC  190  effectively characterizes the extent to which the head  120  has encroached into the ramp  122 .  FIG. 10  graphically depicts a baseline PES signature obtained by the DC  190  when the head  120  is at the position of  FIG. 6 . The amplitude and frequency of the time domain signal indicates a threshold amount of oscillations resulting primarily from the motor  105  rotation, and perhaps augmented by airflow perturbations acting on the actuator  112  and/or the external positioner  174 . The DC  190  preferably includes programming steps for converting the data to a frequency domain, such as by performing a Fast Fourier Transformation of the data. Experimentation during reduction to practice of the present embodiments revealed that the frequency domain spectrum is purely a 1F component, in this case at 120 Hz corresponding to the 7200 RPM motor  105  in the drive  100 .  
         [0040]      FIG. 11  graphically depicts how the PES signature changes instantaneously at the first contacting engagement of the head  120  against the ramp  122 . It will be noted that although the contacting engagement is against an inclined surface of the ramp  122 , nevertheless it has been observed that the unique characteristics of the PES signature incidental to this initial contacting engagement occur with the head  120  remaining at the nominal fly height as in  FIG. 6 . This advantageously permits detecting the absolute outer boundary of the data storage area of the disc  108 . In some embodiments this advantageously permits using the maximum available data storage space between the inner diameter and the ramp  122 . In other embodiments this advantageously permits using the present embodiments to precisely position the head  120 , such as for propagating servo tracks. The latter can be especially advantageous when defining the reference position for propagating spiral servo tracks therefrom.  
         [0041]     It will be noted by comparing the signature of  FIG. 11  to that of  FIG. 10  that the frequency of the time domain signal decreases and the amplitude increases at the position of initial contacting engagement. Threshold values for either or both can be determined, either predetermined or empirically defined during servo writing. Current values can then be compared to the threshold to indicate the position of initial contacting engagement. Note also that in the frequency domain spectrum of  FIG. 11  harmonic disturbances are evident, in this case at 240 Hz, 360 Hz, and 480 Hz.  
         [0042]      FIGS. 12 and 13  graphically depict the PES signatures associated with the head  120  positions of  FIGS. 8 and 9 , respectively. It has been observed that the amplitudes, both in the time domain and in one or more components of the frequency spectrum, continually increase as the head  120  is lifted away from the disc  108 . Experimentation with high-speed photography during reduction to practice of the present embodiments revealed at least one explanation for this phenomena. The lifting force of the inclined ramp  122  has an axial component (in relation to the load arm  118 ) represented by F up  in  FIG. 8 . The air bearing of the head  120  adjacent the disc  108  creates an opposing negative pressure represented by F down  in  FIG. 8 . These two opposing forces contribute axial forces tending to stretch the load arm  118  and increase the magnitude of the PES signature, as indicated by the changing PES signature characteristics.  
         [0043]      FIG. 14  is a flowchart illustrating steps for practicing a method  200  for RAMP DETECT in accordance with the embodiments of the present invention. The method  200  begins in block  202  with the STW  170  contactingly engaging the actuator  112 . As described above, preferably a bias current is applied to the drive VCM in order to ensure no separation of this contacting engagement throughout the range of the external positioner  174  movement. In block  204  the DC  190  obtains a threshold PES signature. In some embodiments this threshold can be recalled from memory; alternatively, the threshold can be obtained from readings obtained while the actuator  112  is disposed away from the ramp  122 . The latter provides a threshold that advantageously accounts for part-to-part variation amongst different drives  100 .  
         [0044]     In block  206  the STW  170  moves the actuator  112  near to but short of contacting the ramp  122 . The STW  170  then begins micropositioning the actuator  112  toward the ramp  122  in block  208 , such as in STW steps. For example, the micropositioning performed in the illustrative embodiments in obtaining data from the position of  FIG. 7  to  FIG. 8 , and from  FIG. 8  to  FIG. 9 , was selected as being 50 STW steps (about 120 microinches).  
         [0045]     In block  210  the STW  170  commands the actuator  112  to hold a constant position long enough to obtain the PES signature, and to convert it from time domain to frequency domain information as necessary. In block  212  the DC  190  determines whether the current signature exceeds the threshold. If the determination of block  212  is no, then control returns to block  208 . Otherwise, the edge detect position can be stored in block  214  and the method  200  ends. Additionally, the method  200  can include further comparisons of the current PES against expected changes in the signature, such as shown in  FIGS. 12-13 , to detect the extent to which the actuator  112  is contacting the ramp  122  beyond the initial contacting engagement.  
         [0046]     Generally, the embodiments described heretofore contemplate a servo writer apparatus with the external positioner  174  that contactingly positions the actuator  112  in the drive  100  in relation to the discs  108 , and means for characterizing the extent to which the actuator  112  contacts the unload ramp  112  independently of storing or retrieving data to or from the discs  108 , and while the head  120  remains at a constant fly height. For purposes of this description and meaning of the appended claims, the phrase “means for characterizing” contemplates embodiments employing the structure disclosed herein, including the DC  190 , capable of executing the steps of the method  200  for RAMP DETECT of  FIG. 14 . The claimed embodiments expressly do not contemplate previously attempted solutions such as those employing write and readback routines for ramp edge detection.  
         [0047]     In alternative equivalent embodiments the DC  190  ( FIG. 5 ) can be stored in the memory  161  ( FIG. 2 ) and executed by the controller  148  ( FIG. 2 ) of the data storage device  100  ( FIG. 1 ) itself. This arrangement would advantageously permit the practicing of the present embodiments in a self-servo write operation, where no STW  170  is used to contactingly position the actuator  112 . In such alternative embodiments the PES signature would be obtained from the transducer  120  as it is used to position the actuator  112  in relation to pre-existing servo information, such as in the form of preprinted servo or seed tracks of servo information used by the data storage device to propagate servo tracks therefrom.  
         [0048]     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 detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements 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 particular elements may vary in type or arrangement without departing from the spirit and scope of the present invention.  
         [0049]     In addition, although the embodiments described herein are directed to a servo track writer for writing spiral servo tracks to a data storage device, it will be appreciated by those skilled in the art that the claimed subject matter is not so limited and various other processing systems can be utilized without departing from the spirit and scope of the claimed invention.