Abstract:
The embodiments disclose an orientation control bias point coupled to a magnetic index mark and having a bias point offset set at predetermined coordinates configured to substantially prevent concentricity run-out.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/844,423 filed Jul. 10, 2013, entitled “A METHOD OF FABRICATING AN ORIENTATION CONTROL BIAS POINT IN A BPM PATTERN”, by McLaurin, et al. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of an overview of a method for fabricating an orientation control bias point of one embodiment. 
       FIG. 2  shows a block diagram of an overview flow chart of a method for fabricating an orientation control bias point of one embodiment. 
       FIG. 3A  shows for illustrative purposes only an example of a concentric BPM pattern imprint of one embodiment. 
       FIG. 3B  shows for illustrative purposes only an example of a concentric r/w head path in same track without run-out of one embodiment. 
       FIG. 4  shows for illustrative purposes only an example of eccentric BPM pattern imprint run-out of one embodiment. 
       FIG. 5A  shows for illustrative purposes only an example of eccentric first wobble position of one embodiment. 
       FIG. 5B  shows for illustrative purposes only an example of eccentric second wobble position of one embodiment. 
       FIG. 5C  shows for illustrative purposes only an example of eccentric third wobble position of one embodiment. 
       FIG. 6A  shows for illustrative purposes only an example of a magnetic index mark (MIM) of one embodiment. 
       FIG. 6B  shows for illustrative purposes only an example of a MIM bias point offset of one embodiment. 
       FIG. 7  shows for illustrative purposes only an example of typical arc movement of the r/w head of one embodiment. 
       FIG. 8  shows for illustrative purposes only an example of using MIM bias point offset coordinates as virtual center of rotation of one embodiment. 
       FIG. 9A  shows for illustrative purposes only an example of positioning spindle clamps of one embodiment. 
       FIG. 9B  shows for illustrative purposes only an example of a pushed in position of spindle clamps of one embodiment. 
       FIG. 9C  shows for illustrative purposes only an example of pushing spindle clamps using MIM bias point offset of one embodiment. 
    
    
     DETAILED DESCRIPTION 
     In a following description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration a specific example in which the embodiments 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. 
     General Overview 
     It should be noted that the descriptions that follow, for example, in terms of a method for fabricating an orientation control bias point is described for illustrative purposes and the underlying system can apply to any number and multiple types bit patterned media (BPM) stacks. In one embodiment, the method for fabricating an orientation control bias point can be configured using a bias point in a servo sector. The method for fabricating an orientation control bias point can be configured to include a magnetic index mark and can be configured to include an optical mark. 
     In BPM the center of rotation is determined by the pattern not the physical center of the spindle on which a stack disc is mounted. The physical disc when placed on the spindle establishes the physical center of rotation. However the concentric pattern imprinted on the disc may not be concentric with the physical center of rotation of the disc itself. This eccentricity can lead to run-out wherein the read-write head of the drive crosses over two or more tracks due to a wobbling effect of the eccentric mismatch of centers of rotation. 
     The method for fabricating an orientation control bias point places an index mark on the BPM template pattern used to indicate a center of rotation of the BPM pattern. This index mark is transferred to the stack disc when imprinted. The index mark creates a bias point offset from the physical center of rotation to a virtual center of rotation which the drive uses to shift the head to read and write within each track to prevent run-out. The BPM pattern imprint index mark establishes the shifting of head track position to accommodate the eccentric rotation thereby maintaining the head within a single track and eliminating run-out. 
       FIG. 1  shows a block diagram of an overview of a method for fabricating an orientation control bias point of one embodiment.  FIG. 1  shows creating an orientation control bias point in a BPM pattern to establish the center of rotation of the pattern and the servo signal  100  of the BPM pattern. The fabrication process is using a magnetic index mark (MIM) to create the bias point  110 . The process includes aligning both sides of a BPM template concentrically and matching both aligned magnetic index marks  120 . Fabrication continues with imprinting the aligned templates in both sides of the magnetic layers of a stack at the same time  130  of one embodiment. 
     The imprinting the aligned templates in both sides of the magnetic layers of a stack at the same time  130  is used for establishing a bias point offset of the center of rotation of the stack with the concentricity of the BPM pattern servo signal  140 . The bias point offset is used to create a virtual center of rotation of the BPM pattern. The disc drive apparatus uses the bias point offset to position the read-write head according to the virtual center of rotation of the BPM pattern. The read-write head positioning using the virtual center of rotation eliminates the wobbling effect otherwise encountered by the read-write head due to the eccentric mismatch of centers of rotation. The method for fabricating an orientation control bias point using the two sided magnetic index mark bias point offset to control the positioning of the read/write head prevents run-out  150  of one embodiment. 
     DETAILED DESCRIPTION 
       FIG. 2  shows a block diagram of an overview flow chart of a method for fabricating an orientation control bias point of one embodiment.  FIG. 2  shows creating an orientation control bias point in a BPM pattern to establish the center of rotation of the pattern and the servo signal  100 . The bias point is the point where you want to push or minimize the clearance of the with respect to the spindle clamp  200 . The process creating an orientation control bias point in a BPM pattern to establish the center of rotation of the pattern and the servo signal  100  is using a magnetic index mark (MIM) to create the bias point  110 . The MIM is integrated into the BPM pattern on the master imprint templates for both sides of a stack. An apparatus is used for aligning both sides of a BPM template concentrically and matching both aligned magnetic index marks  120  including a center of BPM pattern  210 , side A MIM  220  and side B MIM  230 . An apparatus is used for imprinting the aligned templates in both sides of the magnetic layers of a stack at the same time  130  of one embodiment. 
     The imprinting is made into the magnetic layers on both sides of the stack being fabricated. The magnetic index mark can be made close to the 0° zero point of the first sector. The MIM is larger than a degree of rotation and will be larger than any one sector. Establishing a bias point offset of the center of rotation of the stack with the concentricity of the BPM pattern servo signal  140  will enable control of the read-write head positioning to coincide with the concentricity of the BPM pattern and servo signal of one embodiment. 
     The bias point offset is for recording and establishing the bias of the relative positions of the centers of the drive spindle and BPM pattern  240 . Establishing the bias of the relative positions of the centers of the drive spindle and BPM pattern  240  can be using eccentric bias adjustment factors based on x,y offsets of the centers of rotation  250 . The bias adjustment factors can be used by an apparatus to control the positioning of the read-write head to maintain a position within the track being written to or read from. Imprints of the BPM pattern in a stack using the two sided magnetic index mark bias point offset to control the positioning of the read/write head prevents run-out of one embodiment. 
       FIG. 3A  shows for illustrative purposes only an example of concentric BPM pattern imprint of one embodiment.  FIG. 3A  shows a BPM substrate with magnetic layers deposited thereon  300 . The magnetic layers are imprinted using one or more BPM pattern templates to transfer BPM pattern features into the magnetic materials. A BPM pattern template imprint  310  includes servo fields  312 , data fields  314  and tracks  316 .  FIG. 3A  shows a BPM substrate with concentric BPM pattern template imprint  320  features including tracks  316 . The BPM substrate with concentric BPM pattern template imprint  320  features including tracks  316  is mounted on a disc drive spindle  330 . The disc drive spindle  330  is used to rotate or spin the BPM substrate with concentric BPM pattern template imprint  320  about a spindle center of rotation  335  of one embodiment. 
       FIG. 3B  shows for illustrative purposes only an example of a concentric r/w head path in same track without run-out of one embodiment.  FIG. 3B  shows the BPM substrate with magnetic layers deposited thereon  300 . The BPM pattern template imprint  310  includes the servo fields  312 , data fields  314  and tracks  316 . In this example the imprinting process creates the BPM substrate with concentric BPM pattern template imprint  320  which is concentric with the spindle center of rotation  335  of the disc drive spindle  330 . The disc drive spindle  330  imparts a direction of rotation  350 . Rotating about the spindle center of rotation  335  a r/w head  340  to be position so as to follow a concentric r/w head path in same track without run-out  360  of one embodiment. 
       FIG. 4  shows for illustrative purposes only an example of an eccentric BPM pattern imprint run-out of one embodiment.  FIG. 4  shows a stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400 . The stack imprinting process has caused an eccentric BPM pattern imprint  450  which is common due to the nano scaled BPM pattern features. A BPM pattern center of rotation  470  is inherent in BPM patterns where the tracks  316  of  FIG. 3A  are concentric radial features. Where the BPM pattern center of rotation  470  is inherent in BPM patterns the spindle center of rotation  335  is inherent in the disc drive spindle  330 . 
     The r/w head  340  is positioned in accordance with concentricity of the spindle center of rotation  335 . The eccentric BPM pattern imprint  450  creates a misalignment of centers of rotation of the spindle and BPM pattern tracks  316  of  FIG. 3A . When the disc drive spindle  330  imparts the direction of rotation  350  a r/w head path concentric with spindle center of rotation  410  is created. The r/w head  340  path is misaligned with the tracks  316  of  FIG. 3A . This misalignment causes the r/w head path concentric with spindle center of rotation  410  to cross over back and forth with multiple tracks  316  of  FIG. 3A . The crisscrossing of the tracks  316  of  FIG. 3A  is referred to as track run-out  440 . Track run-out  440  can cause read and write errors of one embodiment. 
       FIG. 5A  shows for illustrative purposes only an example of eccentric first wobble position of one embodiment.  FIG. 5A  shows the stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400 . The stack is shown without the servo fields  312  of  FIG. 3A , data fields  314  of  FIG. 3A  and all but one of the tracks  316  of  FIG. 3A  to illustrate clearly the track run-out  440 .  FIG. 5A  shows a BPM pattern zero degree rotational point A  510  used in this description as a clear reference point to trace the impact of the eccentric BPM pattern imprint  450 . At this point in the disc drive spindle  330  direction of rotation  350  the r/w head  340  is in a head position within track  505  of an eccentric BPM pattern imprint track  500 . A first BPM pattern eccentric wobble relative to spindle concentric center of rotation  520  is seen and the points of track run-out  440  rotating toward the r/w head  340  of one embodiment. 
       FIG. 5B  shows for illustrative purposes only an example of eccentric second wobble position of one embodiment.  FIG. 5B  shows the stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400 . The direction of rotation  350  of the disc drive spindle  330  has rotated 60 degrees towards the r/w head  340 . A BPM pattern 60 degree rotational point A  530  show the relative position of the eccentric BPM pattern imprint  450 . The partial rotation has positioned the eccentric BPM pattern imprint track  500  under r/w head  340  in a track run-out  440  condition. The track run-out  440  condition shows a head position outside track  535 . A second BPM pattern eccentric wobble relative to spindle concentric center of rotation  540  is an indicator of the misalignment of the rotation centers of one embodiment. 
       FIG. 5C  shows for illustrative purposes only an example of eccentric third wobble position of one embodiment.  FIG. 5C  shows a BPM pattern 120 degree rotational point A  550  indicating the subsequent rotation from  FIG. 5B . The stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400  rotated by the disc drive spindle  330  in the direction of rotation  350  positioned the eccentric BPM pattern imprint  450  under the r/w head  340 . The head position outside track  535  of the eccentric BPM pattern imprint track  500  shows track run-out  440 . A third BPM pattern eccentric wobble relative to spindle concentric center of rotation  560  indicates the wobbling of the BPM pattern center of rotation  470  of  FIG. 4  relative to the spindle center of rotation  335  of one embodiment. 
       FIG. 6A  shows for illustrative purposes only an example of a magnetic index mark (MIM) of one embodiment.  FIG. 6A  shows the stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400 . The tracks  316  determine the eccentric BPM pattern center of rotation  470 . The disc drive spindle  330  determines the concentric spindle center of rotation  335 . The positioning of the r/w head  340  over the tracks  316  determines whether track run-out  440  of  FIG. 4  will occur. A magnetic index mark (MIM)  600  is added to the BPM pattern for imprinting to create a bias point offset as shown in detail “A”  610  of one embodiment. 
       FIG. 6B  shows for illustrative purposes only an example of a MIM bias point offset of one embodiment.  FIG. 6B  shows detail “A”  610  including the tracks  316 , disc drive spindle  330  and r/w head  340 . The magnetic index mark (MIM)  600  is an integrated part of the BPM pattern imprint. The magnetic index mark (MIM)  600  is integrated close to the 0° zero point of the first sector where servo writing is done. Adding the magnetic index mark (MIM)  600  to the BPM pattern master automatically transfer the MIM to any stacks fabricated using the BPM pattern master templates so it is inherently part of the process with no additional processing steps. This establishes the MIM and bias of the stack disc creating an index mark or bias point uniformly on the fabricated stacks. The magnetic index mark (MIM)  600  can be used as a reference point where you want to push or minimize the clearance of the with respect to the spindle clamp when mounting the stack disc. There are 360 degrees of rotation and typically there are 400-500 servo sectors within the BPM pattern. The MIM is larger than any one sector and therefore larger than a degree of rotation of one embodiment. 
     A bias point offset based on x,y coordinate offsets from spindle center of rotation to BPM pattern center of rotation  630  is created using the relative locations of the spindle center of rotation  335  and BPM pattern center of rotation  470 . The bias point offset coordinate data and other MIM identification information is written on the MIM section of the stack. The MIM information is recorded on the imprinted stack by writing bias point data on the magnetic index mark (MIM) during a servo writing process  620 . Integrating the MIM into the BPM pattern, imprint process and servo writing process saves any additional processing steps to create an indexing mark of one embodiment. 
       FIG. 7  shows for illustrative purposes only an example of typical arc movement of the r/w head of one embodiment.  FIG. 7  shows a disc drive stack platform  700  and a disc drive stack platform spindle  710 . The disc drive stack platform spindle  710  has the spindle center of rotation  335 . A pivoting r/w head and arm assembly  720  is used to position the r/w head  340  of  FIG. 3B  over the tracks of a BPM stack.  FIG. 7  shows a pivoted r/w head and arm assembly position  730  and a typical arc movement of the r/w head  740  to access the magnetic recording area of the stack of one embodiment. 
       FIG. 8  shows for illustrative purposes only an example of using MIM bias point offset coordinates as virtual center of rotation of one embodiment.  FIG. 8  shows the disc drive stack platform  700  with the stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400  mounted thereon. The stack includes the eccentric BPM pattern imprint  450  and shows the BPM pattern center of rotation  470 . The magnetic index mark (MIM)  600  is located in the servo area of the eccentric BPM pattern imprint  450  of one embodiment. 
     The disc drive stack platform spindle  710  shows the spindle center of rotation  335 . The pivoting r/w head and arm assembly  720  is positioned over the BPM pattern track. The pivoting r/w head and arm assembly  720  is in a r/w head path concentric with BPM pattern center  800 . The disc drive uses the magnetic index mark (MIM)  600  data for r/w head MIM bias point offset eccentric adjustment positioning  810 . The r/w head MIM bias point offset eccentric adjustment positioning  810  makes the nano scaled adjustments of the pivoting r/w head and arm assembly  720  position of one embodiment. 
     A r/w head moves to stay in track  820  using MIM bias point offset coordinates as virtual center of rotation  830  that were recorded in the magnetic index mark (MIM)  600 . The magnetic index mark (MIM)  600  enables the disc drive to compensate for any eccentric positioning of the BPM pattern imprint. The r/w head MIM bias point offset eccentric adjustment positioning  810  prevents track run-out  440  of  FIG. 4  and eliminates read and write errors otherwise caused by the eccentric misalignment of centers of rotation of one embodiment. 
       FIG. 9A  shows for illustrative purposes only an example of positioning spindle clamps of one embodiment.  FIG. 9A  shows the disc drive stack platform spindle  710 . The disc drive stack platform spindle  710  in this example includes spindle clamps  900 . The spindle clamps  900  are used for securely mounting a stack in the disc drive of one embodiment. 
       FIG. 9B  shows for illustrative purposes only an example of pushed in position of spindle clamps of one embodiment.  FIG. 9B  shows the disc drive stack platform spindle  710  with spindle clamps  900  of  FIG. 9A . In this example the spindle clamps  900  of  FIG. 9A  are shown after pushing against the spindle clamps  910  when a stack is being mounted. The pushed-in position of spindle clamps  920  where the pushing occurred in tandem causes a pushed-out position of spindle clamps  930  on other spindle clamps  900  of  FIG. 9A . The pushing adjustment of the spindle clamps  900  of  FIG. 9A  position enables the stack to be mounted in a concentric location of one embodiment. 
       FIG. 9C  shows for illustrative purposes only an example of pushing spindle clamps using MIM bias point offset of one embodiment.  FIG. 9C  shows the disc drive stack platform  700  and disc drive stack platform spindle  710 . The disc drive stack platform spindle  710  in this example includes spindle clamps  900 . The spindle clamps  900  are used for securely mounting the stack with eccentric (non-concentric) BPM template imprint (exaggerated for illustrative purposes)  400 . The spindle clamps  900  can move laterally when positioning a stack onto the disc drive stack platform spindle  710 . The lateral movement of the spindle clamps  900  can be used to push the stack when being mounted to minimize the positioning clearances of the stack with respect to the disc drive stack platform spindle  710  of one embodiment. 
     The magnetic index mark (MIM)  600  integrated into the BPM pattern includes the bias point offset coordinates recorded during the servo writing process. The magnetic index mark (MIM)  600  bias point offset coordinates can include the direction and distance from the BPM pattern center of rotation  470  of  FIG. 4  to the spindle center of rotation  335  from the magnetic index mark (MIM)  600  using the MIM as a point of reference of one embodiment. 
     The disc drive can include a device to reposition a stack to be mounted wherein the stack can be pushed against the spindle clamps  900  to a position which is concentric with the spindle center of rotation  335 . When mounting a stack with an eccentric BPM template imprint  940  a repositioning device is used for pushing against spindle clamps per bias point offset coordinates  950 . Once the spindle clamps  900  have been repositioned the clamps lock into position and securely hold the stack with an eccentric BPM pattern imprint  450  of  FIG. 4 . Concentricity between the BPM pattern center of rotation  470  and the spindle center of rotation  335  is created by repositioning the BPM pattern center of rotation  470  using the positioning eccentric stack using spindle clamps  960  process. The magnetic index mark (MIM)  600  enables the mounting repositioning to create concentricity. The stack mounting is repositioned using the two sided magnetic index mark bias point offset to control the positioning of the read/write head prevents run-out  150  of  FIG. 1  of one embodiment. 
     The foregoing has described the principles, embodiments and modes of operation. However, the invention should not be construed as being limited to the particular embodiments discussed. The above described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope as defined by the following claims.