Spiral pitch correction based on micro-jog variation

During a self-servo write process, servo sectors that have uniform radial spacing are written on a disk surface. As part of the in-drive writing of the servo sectors, a radial offset between a reader element and a writer element of a magnetic head is measured. The measured radial offset, or micro-jog, is compared to a known nominal micro-jog value for the current radial position of the magnetic head. When the measured micro-jog value does not match the nominal micro-jog value, an appropriate correction to the self-servo write step size is applied to the radial spacing between the servo sectors being written. Variations from ideal servo spiral slope that are inherent in some servo spirals can be compensated for, thereby improving the uniformity of radial spacing of data tracks associated with the servo sectors.

BACKGROUND

In a typical hard disk drive (HDD), servo sectors on the disk are used to provide position information about the location of a magnetic head over a disk surface. A one approach for writing such servo information on a disk surface of an HDD is referred to as spiral-based self-servo writing, or spiral-based SSW. According to this approach, multiple spiral-shaped servo information patterns (or “servo spirals”) are written on at least one disk surface prior to the SSW process. During the SSW process, each magnetic head of the HDD is positioned relative to a disk surface based on the servo spirals, so that the final servo information (the servo sectors) can be written on the disk surface by the magnetic head.

Ideally, the servo sectors written on a disk surface during an SSW process are equally spaced on the disk surface in the radial direction, so that data track pitch, i.e., the radial spacing between each data track, is substantially the same across the entire disk surface. This is because variable data track pitch on different regions of a disk surface can cause data integrity problems and/or reduce HDD performance. Unfortunately, data track pitch is strongly affected by the slope of the servo spirals used to position the magnetic head while writing the data track servo sectors, and the servo spirals typically employed in the SSW process commonly include portions that vary significantly from the ideal servo spiral shape. Consequently, data track servo sectors can be written on a disk surface with unwanted variation in data track pitch. Accordingly, there is a need in the art for systems and methods of generating servo sectors on a disk surface of an HDD with more uniform data track pitch.

SUMMARY

One or more embodiments provide systems and methods for in-drive writing of servo sectors that have uniform radial spacing on a disk surface. During a self-servo write process, as servo sectors are written across the disk surface, micro jog is measured, which is the radial offset between a reader element and a writer element of a magnetic head. The measured micro jog value is compared to a known nominal micro jog value for the current radial position of the magnetic head, and when the measured micro-jog value does not match the nominal micro-jog value, an appropriate correction to the self-servo write step size is applied to the radial spacing between the servo sectors being written. Thus, the variations from ideal servo spiral slope that are inherent in some servo spirals can be compensated for, thereby improving the uniformity of radial spacing of the data tracks associated with the servo sectors.

A method of writing servo information, according to an embodiment, is carried out on a surface of a magnetic disk with a magnetic head having a read head and a write head that is offset from the read head by a fixed distance. The method includes writing servo sectors defining a first set of data tracks on the surface of the magnetic disk using the write head, wherein the write head is positioned during the writing of the first set of data tracks according to positioning signals generated by the read head, measuring a radial offset between the write head and the read head when the read head and the write head are positioned over the first set of data tracks, determining a track pitch adjustment based on a difference between the measured radial offset and an expected radial offset when the read head and the write head are positioned over the first set of data tracks, and writing servo sectors defining a second set of data tracks on the surface of the magnetic disk using the write head, wherein the write head is positioned during the writing of the second set of data tracks according to positioning signals generated by the read head and the track pitch adjustment.

A data storage device, according to embodiments, includes a magnetic disk with a writable surface, a magnetic head having a read head and a write head that is offset from the read head by a fixed distance, and a controller. In one embodiment, the controller is configured to cause servo sectors defining a first set of data tracks to be written on the surface of the magnetic disk using a write head, wherein the write head is positioned during the writing of the first set of data tracks according to positioning signals generated by the read head, cause a radial offset to be measured between the write head and the read head when the read head and the write head are positioned over the first set of data tracks, determine a track pitch adjustment based on a difference between the measured radial offset and an expected radial offset when the read head and the write head are positioned over the first set of data tracks, and cause servo sectors defining a second set of data tracks to be written on the surface of the magnetic disk using the write head, wherein the write head is positioned during the writing of the second set of data tracks according to positioning signals generated by the read head and the track pitch adjustment.

A method of manufacturing a hard disk drive with a magnetic head having a read head and a write head that is offset from the read head by a fixed distance, according to an embodiment, includes incorporating a magnetic disk in a housing of the hard disk drive and writing servo sectors defining a first set of data tracks on the surface of the magnetic disk using the write head, wherein the write head is positioned during the writing of the first set of data tracks according to positioning signals generated by the read head. The method further includes measuring a radial offset between the write head and the read head when the read head and the write head are positioned over the first set of data tracks, determining a track pitch adjustment based on a difference between the measured radial offset and an expected radial offset when the read head and the write head are positioned over the first set of data tracks, and writing servo sectors defining a second set of data tracks on the surface of the magnetic disk using the write head, wherein the write head is positioned during the writing of the second set of data tracks according to positioning signals generated by the read head and the track pitch adjustment.

DETAILED DESCRIPTION

FIG. 1is a schematic view of an exemplary hard disk drive, according to one embodiment. For clarity, hard disk drive (HDD)100is illustrated without a top cover. HDD100includes at least one storage disk110that is rotated by a spindle motor114and includes a plurality of concentric data storage tracks are disposed on a surface112of storage disk110. Spindle motor114is mounted on a base plate116. An actuator arm assembly120is also mounted on base plate116, and has a slider121mounted on a flexure arm122with a magnetic read/write head127that reads data from and writes data to the data storage tracks. Flexure arm122is attached to an actuator arm124that rotates about a bearing assembly126. Voice coil motor128moves slider121relative to storage disk110, thereby positioning read/write head127over a desired concentric data storage track. Spindle motor114, read/write head127, and voice coil motor128are coupled to electronic circuits130, which are mounted on a printed circuit board132.

Electronic circuits130include a read channel137, a microprocessor-based controller133, random-access memory (RAM)134(which may be a dynamic RAM and is used as a data buffer) and/or a flash memory device135and a flash manager device136. In some embodiments, read channel137and microprocessor-based controller133are included in a single chip, such as a system-on-chip131. In some embodiments, HDD100may further include a motor-driver chip that accepts commands from microprocessor-based controller133and drives both spindle motor114and voice coil motor128. Read/write channel137communicates with the read/write head127via a preamplifier (not shown) that may be mounted on a flex-cable that is itself mounted on base plate116or actuator arm120, or both.

HDD100also includes an inner diameter (ID) crash stop129and a load/unload ramp123. ID crash stop129is configured to restrict motion of actuator arm assembly120to preclude damage to read/write head127and/or storage disk110. Load/unload ramp123is typically disposed proximate the outer diameter (OD) of storage disk110and is configured to unload read/write head127from storage disk110. Typically, at the beginning of a self servo writing (SSW) process, actuator arm assembly120is pushed against ID crash stop129, so that ID crash stop129may serve as a position reference at the start of the SSW process.

For clarity, HDD100is illustrated with a single storage disk110and a single actuator arm assembly120. HDD100typically includes multiple storage disks and multiple actuator arm assemblies. In addition, each side of storage disk110typically has a corresponding read/write head associated therewith and coupled to a flexure arm.

When data are transferred to or from storage disk110, actuator arm assembly120sweeps an arc between the ID and the OD of storage disk110. Actuator arm assembly120accelerates in one angular direction when current is passed in one direction through the voice coil of voice coil motor128and accelerates in an opposite direction when the current is reversed, thereby allowing control of the position of actuator arm assembly120and attached read/write head127with respect to storage disk110. Voice coil motor128is coupled with a servo system known in the art that uses the positioning data read from servo wedges on storage disk110by read/write head127to determine the position of read/write head127over a specific data storage track. The servo system determines an appropriate current to drive through the voice coil of voice coil motor128, and drives said current using a current driver and associated circuitry.

In order for HDD100to perform SSW and write the above-described servo wedges on storage disk110with the necessary precision for proper operation of HDD100, position and timing information are provided to the disk drive servo system of HDD100. The position and timing information that enable the internal servo system of HDD100to perform SSW is typically in the form of reference spiral tracks or “servo spirals” written on storage disk110. One embodiment of such servo spirals is illustrated inFIG. 2.

FIG. 2illustrates storage disk110prior to undergoing a SSW process, according to one embodiment. As shown, storage disk110has a plurality of reference spirals210written thereon that are circumferentially spaced from adjacent reference spirals210. Reference spirals210may be written onto a substantially blank surface112of storage disk110using read/write head127and the servo system of HDD100with a bootstrap spiral-writing process, with an external media writer before assembly of HDD100, or with a servo writing machine that uses an external precision actuator to position the disk drive actuator. Reference spirals210enable the generation of servo wedges on storage disk110using closed-loop control in the servo system of HDD100. That is, servo wedges can be written while the servo system of HDD100uses closed-loop tracking of the reference spirals210. It is noted that the number of reference spirals210written on storage disk110is generally larger than that shown inFIG. 2, for example as few as ten or twenty, or as many as several hundred.

During the SSW process, the servo system of HDD100uses the timing and position information provided by the above-described reference spirals210to servo precisely over a radial position on storage disk110that corresponds to a particular concentric data storage track. Thus, while the read head of read/write head127is used to read position and timing information from reference spirals210, the write head of read/write head127is used to write servo wedges for a particular radial position on storage disk110, i.e., for a particular data storage track of storage disk110. It is noted that data track pitch, which is the radial spacing between each data track of storage disk110, is strongly affected by the slope of reference spirals210. One embodiment of reference spiral slope is illustrated inFIG. 3.

FIG. 3is a schematic illustration of a portion300of storage disk110indicated inFIG. 2prior to undergoing a SSW process. As shown, a plurality of reference spirals210are formed on storage disk110. Displacement along the x-axis inFIG. 3is illustrated in terms of angular displacement, such as radians or degrees. Assuming that read/write head127has written each of reference spirals210on storage disk110using the same radial velocity profile, reference spirals210may be assumed to be circumferentially separated from each other by a substantially uniform angular separation R at any particular radial location on storage disk110. Thus, reference spirals210can be depicted as parallel lines inFIG. 3. Assuming a constant rotational velocity for storage disk110, when read/write head127is positioned at any particular radial location, a time required for read/write head127to travel from one to another of reference spirals210is substantially a constant time interval.

Reference spiral slope, hereinafter referred to as a “spiral pitch”320, may be associated with a specific location on or a portion of a reference spiral210. In some embodiments, spiral pitch320may be defined as the ratio of a circumferential angular displacement301to a radial linear displacement302of the reference spiral210at the specific portion or location. In other embodiments, spiral pitch320at the specific location or portion may be defined as the ratio of radial linear displacement302to circumferential angular displacement301. Furthermore, any other applicable definition of “slope, “pitch,” or “gradient” may be used to quantify spiral pitch320at a specific location on or portion of a reference spiral210. It is noted that the geometrical meaning of spiral “pitch” is very different from the geometrical meaning of data track pitch. Specifically, data track pitch is a separation in the radial direction (between the centerline of adjacent data track pitches), whereas spiral pitch is a slope (of a reference spiral at a particular point on the reference spiral).

As noted, for a particular data track written on storage disk110via a SSW process, data track pitch is strongly affected by the value of spiral pitch320at the radial location corresponding to the particular data track. Consequently, when reference spirals210include portions with a non-ideal spiral pitch320, data track servo sectors may be written on storage disk110with unwanted variation in data track pitch, which is highly undesirable. A comparison of actual spiral pitch vs. ideal spiral pitch is illustrated inFIG. 4.

FIG. 4is a graph illustrating how actual spiral pitch of one or more reference spirals210formed on a particular surface112of storage disk110may vary as a function of radial position, according to an embodiment. As shown, actual spiral pitch profile401may be relatively constant in a region410corresponding to the middle diameter (MD) of storage disk110, but generally increases near the OD and ID of storage disk110. Reference spirals210that are written on storage disk110using a bootstrap spiral-writing process are generally more likely to have an actual spiral pitch profile401, since the velocity feedback for such a spiral-writing process is back electromotive force (EMF). Using back EMF for velocity feedback can cause actual spiral pitch profile401to vary from ideal spiral pitch profile402since back EMF generally varies with each drive, and is also more susceptible to inaccuracies near the ID and OD of storage disk110. Thus, the actual spiral pitch of reference spirals210may be different in a first radial region (near the ID), a second radial region (near the MD), and a third radial region (near the OD) of storage disk110.

By contrast, an ideal spiral pitch profile402maintains, in the embodiment illustrated inFIG. 4, a substantially constant value across all radial locations. In other embodiments, ideal spiral pitch profile402may include portions that are not a constant spiral pitch value, and may instead be a known function of radial position. In either case, for some or most radial locations on storage disk110, ideal spiral pitch profile402has a different value than actual spiral pitch profile401. At some radial locations, this difference may not be significant. In other radial locations, however, the difference403in spiral pitch value between actual spiral pitch profile401and ideal spiral pitch profile402can result in non-uniform data track pitch when an SSW process is performed using reference spirals210with actual spiral pitch profile401.

According to some embodiments, difference403from ideal spiral pitch profile402can be compensated for as servo sectors are written across the disk surface during a self-servo write process. Specifically, micro-jog, which is the radial location offset between a reader element and a writer element of a magnetic head, is measured for recently written data tracks. The measured micro jog value is compared to a known nominal micro-jog value for the current radial position of the magnetic head. When the measured micro-jog value does not match the nominal micro-jog value, an appropriate correction to the self-servo write step size is applied to the data track pitch of the next radial position at which servo sectors are written, so that data track pitch remains substantially uniform. Thus, during an SSW process, the nominal micro jog at the current radial position is used to confirm that data track pitch for the most recently written data tracks has not varied from the targeted data track pitch for storage disk110. In this way, the effect of non-ideal spiral pitch on data track pitch is reduced or eliminated.

FIGS. 5A and 5Bschematically illustrate read/write head127moving across surface112of storage disk110during an SSW process, according to an embodiment. Read/write head127includes a read element501and a write element502that is disposed on read/write head127with a radial offset, or radial gap, grand a longitudinal offset, or longitudinal gap, glfrom read element501. Also shown are reference spirals210, the centerlines510of previously defined data tracks, and the centerline520of a data track that is being defined on surface112as servo sectors (not shown) are written on surface112as part of the SSW process. Centerlines510and520are defined by servo sectors written on surface112by write element502earlier in the SSW process, but for clarity these servo sectors are omitted fromFIG. 5.

Arrow503indicates the direction of circumferential motion of read/write head127relative to surface112. Due to the curved stroke of actuator arm assembly120(shown inFIG. 1), read/write head127varies in angular orientation with respect to centerlines510and520based on the current radial location read/write head127, and generally is not oriented orthogonally to centerlines510and520. Consequently, a micro jog505(shown inFIG. 5B), which is the offset in the radial direction between a read element501and a write element502, varies as a function of the radial location of read/write head127. Thus, at most radial locations of read/write head127, micro jog505is different than radial gap gr.

According to some embodiments, a nominal value for micro-jog505may be characterized for each radial location across surface112, for example as a function of radial location. In some embodiments, such a function indicating variation of the nominal value for micro-jog505with respect to radial location across the surface of storage disk110may be determined by drive and head geometry for a particular model of HDD100, as described below in conjunction withFIG. 8. In such embodiments, a calibration process for a particular instance of this model of HDD100may be employed to modify the above-described function, and an example of such a calibration process is described below in conjunction withFIG. 9. Alternatively, the function indicating variation of the nominal value for micro-jog505with respect to radial location across the surface of storage disk110may be determined empirically for a particular model of HDD100, then modified with a calibration process for a particular instance of that model.FIG. 6illustrates one example of such a function that indicates variation of the nominal value for micro jog505with respect to radial location.

FIG. 6is a graph illustrating a nominal micro jog variation function600across the stroke of a particular instance of HDD100. Nominal micro jog variation function600indicates a nominal, or ideal, value for micro jog505for each radial location across surface112of storage disk110. For reference, also shown inFIG. 6is an actual micro-jog function650illustrating the actual values of micro-jog505for a particular instance of HDD100, if actual micro jog were measured at each radial location after completion of a conventional SSW process.

In the embodiment illustrated inFIG. 6, nominal micro-jog varies from approximately −30 tracks near the OD of storage disk110to approximately +30 tracks near the ID of storage disk110, where the micro-jog value is expressed in terms of tracks having ideal, uniform track pitch. In other embodiments, the micro-jog varies between the OD of storage disk110to the ID of storage disk110, but remains positive or negative across the entire stroke of actuator arm assembly120. If the actual (i.e., measured) value of micro-jog505is determined to be significantly different than the nominal value of micro jog505for recently written servo sectors, then the data track pitch for the recently written servo sectors can be assumed to be incorrect, i.e., too wide or too narrow. Thus, the radial step distance for subsequently written data tracks can be modified so that substantially ideal data track pitch (shown inFIG. 5B) is maintained during the SSW process.

For example, after the servo sectors for track 200,000 are written on storage disk110, an actual micro jog value601may be measured at the radial location corresponding to track 200,000. As shown, actual micro jog value601is significantly different than a nominal micro jog value602indicated for track 200,000, for example by a difference603. Therefore, the SSW write step distance between track 200,000 and track 200,001 is modified accordingly, so that the difference between actual micro-jog value601and nominal micro-jog value602for track 200,001 (and subsequently written tracks) is reduced or eliminated. Any suitable algorithm may be employed to determine by what value the SSW write step distance should be modified, and anyone of ordinary skill in the art, upon reading the disclosure herein, could determine such an algorithm.

InFIG. 6, the value of difference603is depicted to be multiple tracks. In practice, the SSW write step distance between a track that has just been written and the next track to be written may be modified in response to a much smaller value of difference603. For example, difference603may be as small as a fraction of a track, such as 1%, 10%, etc. Thus, the above-described corrections can be made with sufficient frequency that deviation between the actual data track pitch and the ideal data track pitch can be relatively small before being corrected, making data track pitch substantially equal to the ideal data track pitch for storage disk110across surface112. In this way, track pitch at all radial locations of storage disk110may be uniform despite inaccuracies introduced by servo spirals with non-ideal spiral pitch.

FIG. 7sets forth a flowchart of method steps for in-drive writing of servo sectors that have uniform radial spacing on a disk surface, according to an embodiment. Although the method steps are described in conjunction with HDD100inFIGS. 1-6, persons skilled in the art will understand that the method steps may be performed with other hard disk drives. The control algorithms for the method steps according to the embodiment may reside in microprocessor-based controller133, or alternatively, in some other embodiments, an external host device. For clarity, controller133is described performing said control algorithms for the method steps, although other external control devices can potentially be used in such a role.

As shown, a method700begins at step701, where microprocessor-based controller133or other suitable control circuit or system causes to be written, as part of an SSW process, servo sectors defining a set of data tracks on a surface112of storage disk110. For example, 100, 1,000, 10,000, or more tracks may be included in the set of data tracks. It is noted that the servo sectors defining the set of data tracks may be positioned based on a previously determined track pitch adjustment, described below in step706. In step702, microprocessor-based controller133determines whether all data tracks for surface112have been defined. If yes, method700proceeds to step703and ends; if no, method700proceeds700proceeds to step704.

In step704, microprocessor-based controller133causes the value of micro-jog505to be measured for a radial location associated with the set of data tracks written in step701. For example, in some embodiments, microprocessor-based controller133causes the value of micro jog505to be measured for one of the data tracks included in the set of data tracks written in step701. In some embodiments, the actual value for micro-jog505is measured by positioning the read head over the most recently defined data track in the set of data tracks written in step701. Generally, measurement of micro jog505is performed via read/write head127using procedures typically included in the capabilities of HDD100.

In step705, microprocessor-based controller133compares the actual value for micro-jog505measured in step704with an expected value for micro jog505, i.e., a nominal value for micro-jog505associated with the radial location corresponding to the micro jog measurement in step704. For example, the nominal value may be determined from nominal micro jog variation function600or from a table of nominal values for micro-jog505vs. radial location. In step706, microprocessor-based controller133determines a track pitch adjustment based on the difference between the actual value for micro jog505measured in step704and the nominal value for micro-jog505determined in step705. Method700then proceeds back to step701.

Generally, the track pitch adjustment is selected to reduce data track pitch of subsequently written data tracks when the absolute value of the actual micro jog is less than the absolute value of the nominal micro-jog value. The absolute value of the actual micro-jog is less than the absolute value of the nominal micro jog value when the actual data track pitch of the most recently written data tracks is greater than the ideal data track pitch for HDD100. Thus, when data track pitch is determined to be greater than the ideal data track pitch, data track pitch of subsequently written data tracks is reduced. Conversely, the track pitch adjustment is selected to increase data track pitch of subsequently written data tracks when the absolute value of the actual micro-jog is greater than the absolute value of the nominal micro jog value. The absolute value of the actual micro jog is greater than the absolute value of the nominal micro jog value when the actual data track pitch of the most recently written data tracks is less than the ideal data track pitch for HDD100. Thus, when data track pitch is determined to be less than the ideal data track pitch, data track pitch of subsequently written data tracks is increased.

In some embodiments, nominal micro jog variation function600employed in method700may be determined based on drive and head geometry for a particular model of HDD100. Generation of one such embodiment of nominal micro-jog variation function600is described below in conjunction withFIG. 8.

FIG. 8schematically illustrates a geometrical layout800of actuator arm assembly120and storage disk110for the determination of nominal micro-jog variation function600, according to an embodiment. The variation of micro-jog u across the stroke of actuator arm assembly120typically follows a well-defined curve with respect to the radial position of read/write head127, and may be determined by drive and head geometry. Therefore, micro-jog u can be computed from, and is a function of, dimensions ds, dw, gr, gl, and rw. Thus, u=ƒ(ds, dw, gr, gl, rw), where ƒ is a nonlinear function that can be derived from by well-known trigonometric techniques. As shown inFIG. 8, ds=the distance between the pivot point of arm actuator arm assembly120and the disk center110A of storage disk110; dw=the distance between the pivot point of arm actuator arm assembly120and the write element502; gr=the radial offset between read element501and write element502; gl=the longitudinal offset between read element501and write element502; rw=the distance between disk center110A and a center point of write element502, i.e., the radial location of write element502; and rr=the distance between disk center110A and a center point of read element501, i.e., the radial location of write element501.

In a typical disk drive, dsand dware accurately controlled by the manufacturing process, and dimension rwis accurately controlled by the servo system of HDD100. By contrast, grand glmay vary significantly for each manufactured instance of read/write head127due to manufacturing process inaccuracies, so these dimensions are not exactly known and require calibration. It is noted that grand glare two independent variables in the function u=ƒ(ds, dw, gr, gl, rw). Thus, the values for grand glfor a particular manufactured instance of read/write head127can be determined by solving a system of two equations in which the values of micro-jog u and the variables ds, dw,l, and rware all known. Specifically, by writing short bands of servo sectors that define data tracks at two different radial locations (rw1and rw2), micro jog u at those locations, i.e., micro-jog u1and u2, can be measured by HDD100. Substituting the known values micro-jog u1and rw1into the function u=ƒ(ds, dw, gr, gl, rw) yields Equation 1 and substituting the known values micro-jog u2and rw2into the function u=ƒ(ds, dw, gr, gl, rw) yields Equation 2:
u1=ƒ(ds,dw,gr,gl,rw1)  (1)
u2=ƒ(ds,dw,gr,gl,rw2)  (2)

Equations 1 and 2 can be solved simultaneously to determine the values for grand glfor the particular manufactured instance of read/write head127being calibrated. Once the values for grand glfor the particular manufactured instance of read/write head127have been determined, nominal micro jog variation function600inFIG. 6can be calculated, and a nominal value of micro jog u can be determined for any radial location of storage disk110for that particular read/write head127of HDD110.

In some embodiments, the accuracy of the values for grand gldetermined in this way may be increased by selecting values of rw1and rw2that correspond to a portion of the stroke of actuator arm assembly120in which there is relatively little data track pitch variation, such as in region410(shown inFIG. 4) corresponding to the MD of storage disk110. Because the majority of variation in micro jog u in this region can be assumed to be due to grand gl, inaccuracies in the values of grand glare reduced or minimized when the radial locations rw1and rw2are selected to be in such a region. Thus, in such embodiments, the values of radial locations rw1and rw2are not proximate the ID or OD of storage disk110. For example, radial location rw1may be disposed approximately equidistant from the ID and the MD (near the ⅓ stroke position), and location rw2may be disposed approximately equidistant from the MD and the OD (near the ⅔ stroke position).

FIG. 9sets forth a flowchart of method steps for determining a nominal micro jog function in a data storage device, according to an embodiment. Although the method steps are described in conjunction with HDD100ofFIGS. 1-8, persons skilled in the art will understand that the method steps900may be performed with other hard disk drives. The control algorithms for the method steps may reside in and/or be performed by microprocessor-based controller133and/or any other suitable control circuit or system, including an external host.

As shown, a method900begins at step901, where microprocessor-based controller133or other suitable control circuit or system causes servo sectors for multiple adjacent data tracks to be written in a first region of storage disk100. Typically, the multiple adjacent data tracks are written with read/write head127, which is positioned based on timing and location information provided by reference spirals210. In some embodiments, servo sectors for a sufficient number of data tracks are written in the first region to at least span in the radial direction the typical radial offset, or micro-jog, of read/write head127when located at a radial location that corresponds to the first region. Thus, when the micro-jog for read/write head127is on the order of 10 or 12 data tracks, servo sectors are written for 12 or more data tracks in step901.

In some embodiments, the first region is disposed in a portion of the stroke of actuator arm assembly120in which there is relatively little data track pitch variation from track to track, such as a region that corresponds to the MD of storage disk110. In some embodiments, the first region is disposed at approximately the ⅓ stroke position for actuator arm assembly120.

In step902, microprocessor-based controller133causes a first micro-jog value to be measured in the first region, where the unit of measure for the micro-jog value is written data tracks. Measurement of micro jog in terms of previously written data tracks is well-known in the art, and any technically feasible procedure for such measurement may be employed in step902. For example, in some embodiments, read/write head127continues to be positioned over a fixed radial location using reference spirals210, but the servo sectors written in step901are also read. The position information collected when reading the servo sectors at the fixed radial location indicates the current data track location of the read element of read/write head127. In addition, the position information collected when reading the timing and position information provided by reference spirals210can be used to calculate the track position of the write element of read/write head127, since reference spirals210were used to position the write element when the servo sectors written in the first region. Thus, micro jog associated with the first region can be computed, since the track position of the read element and the track position of the write element are known, and micro-jog is the radial distance (or number of written tracks) between the radial location of the read element and the radial location of the write element.

In step903, microprocessor-based controller133causes servo sectors for multiple adjacent data tracks to be written in a second region of storage disk100. Typically, the multiple adjacent data tracks are written with read/write head127, which is positioned based on timing and location information provided by reference spirals210. Similar to step901, in some embodiments, servo sectors for a sufficient number of data tracks are written in the second region to at least span the micro-jog of read/write head127when located at a radial location that corresponds to the second region. In some embodiments, the second region is disposed in a portion of the stroke of actuator arm assembly120in which there is relatively little data track pitch variation from track to track, such as a region that corresponds to the MD of storage disk110. In some embodiments, the second region is disposed at approximately the ⅔ stroke position for actuator arm assembly120.

In step904, microprocessor-based controller133causes a second micro jog value to be measured in the second region, for example using the same technique employed for measuring the first micro-jog value in step902.

In step905, microprocessor-based controller133determines a nominal micro jog function. The nominal micro jog function indicates a nominal, or expected, micro-jog value for each radial position of a specific read/write head127of HDD100, and is determined based on the first micro jog value measured in step902and the second micro-jog value measured in step904. As described above in conjunction withFIG. 8, the nominal micro-jog may be a non-linear function based on the geometric configuration of read/write head127, actuator arm assembly120, storage disk110, and/or other elements of HDD100. The nominal micro jog function may be stored in firmware and/or in nonvolatile memory associated with HDD100, and employed in method700ofFIG. 7.

FIG. 10sets forth a flowchart of method steps for manufacturing HDD100, according to an embodiment. Although the method steps are described in conjunction with HDD100inFIGS. 1-9, persons skilled in the art will understand that the method steps may also be performed for manufacturing other types of hard disk drives.

As shown, a method1000begins at step1001, where HDD100is assembled, including the incorporation of multiple storage disks110in the housing of HDD100. In step1002, a nominal micro jog function is determined for HDD100using method900, as set forth above. In step1003, servo sectors that have uniform radial spacing are written on surfaces of the multiple storage disk110that were incorporated in the housing of HDD100in step1001. The servo sectors are written using the embodiment of method700, as set forth above. In step1004, HDD100is tested for proper writing and reading operations.

In sum, embodiments herein provide systems and methods for in-drive writing of servo sectors that have uniform radial spacing on a disk surface. During a self-servo write process a radial offset between a reader element and a writer element of a magnetic head is measured. The measured radial offset, or micro-jog, is compared to a known nominal micro jog value for the current radial position of the magnetic head. When the measured micro jog value does not match the nominal micro jog value, an appropriate correction to the self-servo write step size is applied to the radial spacing between the servo sectors being written. Thus, the variations from ideal servo spiral slope that are inherent in some servo spirals can be compensated for, thereby improving the uniformity of radial spacing of data tracks associated with the servo sectors.