Locating an initial servo track in order to servo write a disk drive from spiral tracks

An embodiment of the present invention comprises a method of writing product servo sectors to a disk of a disk drive. The disk comprises a plurality of spiral tracks each having a high frequency signal interrupted at a predetermined interval by a sync mark. The head internal to the disk drive is used to read the spiral tracks to generate a read signal which is processed to detect the sync marks. An aberration is detected in the detected sync marks in order to locate an initial radial location of the head with respect to the disk. The read signal representing the high frequency signal in the spiral tracks is processed to generate a position error signal (PES) used to maintain the head along a substantially circular target path while using the head internal to the disk drive to write the product servo sectors along the circular target path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to disk drives for computer systems. More particularly, the present invention relates to locating an initial servo track in order to servo write a disk drive from spiral tracks.

2. Description of the Prior Art

When manufacturing a disk drive, product servo sectors20-27are written to a disk4which define a plurality of radially-spaced, concentric data tracks6as shown in the prior art disk format ofFIG. 1. Each product servo sector (e.g., servo sector24) comprises a preamble8for synchronizing gain control and timing recovery, a sync mark10for synchronizing to a data field12comprising coarse head positioning information such as a track number, and servo bursts14which provide fine head positioning information. During normal operation the servo bursts14are processed by the disk drive in order to maintain a head over a centerline of a target track while writing or reading data. In the past, external servo writers have been used to write the product servo sectors20-27to the disk surface during manufacturing. External servo writers employ extremely accurate head positioning mechanics, such as a laser interferometer, to ensure the product servo sectors20-27are written at the proper radial location from the outer diameter of the disk to the inner diameter of the disk. However, external servo writers are expensive and require a clean room environment so that a head positioning pin can be inserted into the head disk assembly (HDA) without contaminating the disk. Thus, external servo writers have become an expensive bottleneck in the disk drive manufacturing process.

The prior art has suggested various “self-servo” writing methods wherein the internal electronics of the disk drive are used to write the product servo sectors independent of an external servo writer. For example, U.S. Pat. No. 5,668,679 teaches a disk drive which performs a self-servo writing operation by writing a plurality of spiral tracks to the disk which are then processed to write the product servo sectors along a circular path. Each spiral track is written to the disk as a high frequency signal (with missing bits), wherein the position error signal (PES) for tracking is generated relative to time shifts in the detected location of the spiral tracks. In addition, the '679 patent generates a servo write clock by synchronizing a phase-locked loop (PLL) to the missing bits in the spiral tracks.

The '679 patent rotates an actuator arm until it contacts an outer diameter (OD) crash stop in order to position the head over an initial servo track at the beginning of the servo writing operation. However, utilizing an OD crash stop to locate the initial servo track may be undesirable for a number of reasons, including the loss of available recording area, or impracticality, such as in disk drives that employ ramp loading/unloading.

SUMMARY OF THE INVENTION

An embodiment of the present invention comprises a method of writing product servo sectors to a disk of a disk drive, the disk drive comprising control circuitry and a head disk assembly (HDA) comprising the disk, an actuator arm, a head connected to a distal end of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk. The disk comprises a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted at a predetermined interval by a sync mark. The head internal to the disk drive is used to read the spiral tracks to generate a read signal, and the read signal is processed to detect the sync marks in the spiral tracks. An aberration is detected in the detected sync marks in order to locate an initial radial location of the head with respect to the disk. The read signal representing the high frequency signal in the spiral tracks is processed to generate a position error signal (PES) used to maintain the head along a substantially circular target path while using the head internal to the disk drive to write the product servo sectors along the circular target path.

In one embodiment, at least one of the spiral tracks is missing at least one sync mark at the initial radial location, and in one embodiment, every other spiral track is missing at least one sync mark at the initial radial location.

In another embodiment, the sync marks comprise a first pattern at the initial radial location, and the sync marks comprise a second pattern at radial locations different than the initial radial location, wherein the first pattern is different than the second pattern. In one embodiment, detecting the sync marks comprises detecting the first pattern at the initial radial location and detecting the second pattern at radial locations different than the initial radial location.

Another embodiment of the present invention comprises a disk drive comprising a disk including a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted at a predetermined interval by a sync mark. The disk drive further comprises an actuator arm, a head connected to a distal end of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk. Control circuitry within the disk drive writes a plurality of product servo sectors to the disk to define a plurality of radially spaced, concentric data tracks. The head internal to the disk drive is used to read the spiral tracks to generate a read signal which is processed to detect the sync marks in the spiral tracks. An aberration is detected in the detected sync marks in order to locate an initial radial location of the head with respect to the disk. The read signal representing the high frequency signal in the spiral tracks is processed to generate a position error signal (PES) used to maintain the head along a substantially circular target path while using the head internal to the disk drive to write the product servo sectors along the circular target path.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention comprises a method of writing product servo sectors to a disk of a disk drive. The disk comprises a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted at a predetermined interval by a sync mark. The head internal to the disk drive is used to read the spiral tracks to generate a read signal, and the read signal is processed to detect the sync marks in the spiral tracks. An aberration is detected in the detected sync marks in order to locate an initial radial location of the head with respect to the disk. The read signal representing the high frequency signal in the spiral tracks is processed to generate a position error signal (PES) used to maintain the head along a substantially circular target path while using the head internal to the disk drive to write the product servo sectors along the circular target path.

The spiral tracks may comprise any suitable pattern and may be written to the disk using any suitable technique, such as using an external writer for writing the spiral tracks to the disk, or stamping the spiral tracks on the disk using magnetic printing techniques.FIGS. 2A and 2Bshow an embodiment wherein a plurality of spiral tracks200-20Nare written to a disk18of a disk drive16using an external spiral servo writer36. The disk drive16comprises control circuitry34and a head disk assembly (HDA)32comprising the disk18, an actuator arm26, a head28coupled to a distal end of the actuator arm26, and a voice coil motor30for rotating the actuator arm26about a pivot to position the head28radially over the disk18. A write clock is synchronized to the rotation of the disk18, and the plurality of spiral tracks200-20Nare written on the disk18at a predetermined circular location determined from the write clock. Each spiral track20icomprises a high frequency signal22(FIG. 4B) interrupted at a predetermined interval by a sync mark24.

The external spiral servo writer36comprises a head positioner38for actuating a head positioning pin40using sensitive positioning circuitry, such as a laser interferometer. Pattern circuitry42generates the data sequence written to the disk18for the spiral tracks200-20N. The external spiral servo writer36inserts a clock head46into the HDA32for writing a clock track44(FIG. 2B) at an outer diameter of the disk18. The clock head46then reads the clock track44to generate a clock signal48processed by timing recovery circuitry50to synchronize the write clock51for writing the spiral tracks200-20Nto the disk18. The timing recovery circuitry50enables the pattern circuitry42at the appropriate time relative to the write clock51so that the spiral tracks200-20Nare written at the appropriate circular location. The timing recovery circuitry50also enables the pattern circuitry42relative to the write clock51to write the sync marks24(FIG. 4B) within the spiral tracks200-20Nat the same circular location from the outer diameter to the inner diameter of the disk18. As described below with reference toFIG. 5, the constant interval between sync marks24(independent of the radial location of the head28) enables the servo write clock to maintain synchronization while writing the product servo sectors to the disk.

Referring again toFIG. 2B, while writing the spiral tracks200-20Nat an initial radial location45an aberration is written in the sync marks24which allows the initial servo track to be located when writing the product servo sectors. Any suitable aberration in the sync marks24may be employed in the embodiments of the present invention, such as by disabling the pattern circuitry42so that one or more of the spiral tracks200-20Nare not written at the initial radial location, or by writing a different sync mark in one or more of the spiral tracks200-20Nat the initial radial location.

In the embodiment ofFIG. 2B, each spiral track20iis written over a partial revolution of the disk18. In an alternative embodiment, each spiral track20iis written over one or more revolutions of the disk18.FIG. 3shows an embodiment wherein each spiral track20iis written over multiple revolutions of the disk18. In the embodiment ofFIG. 2A, the entire disk drive16is shown as being inserted into the external spiral servo writer36. In an alternative embodiment, only the HDA32is inserted into the external spiral servo writer36. In yet another embodiment, an external media writer is used to write the spiral tracks200-20Nto a number of disks18, and one or more of the disks18are then inserted into an HDA32.

Referring again to the embodiment ofFIG. 2A, after the external spiral servo writer36writes the spiral tracks200-20Nto the disk18, the head positioning pin40and clock head46are removed from the HDA32and the product servo sectors are written to the disk18. In one embodiment, the control circuitry34within the disk drive16is used to process the spiral tracks200-20Nin order to write the product servo sectors to the disk18. In an alternative embodiment described below with reference toFIGS. 8 and 9, an external product servo writer is used to process the spiral tracks200-20Nin order to write the product servo sectors to the disk18during a “fill operation”.

FIG. 4Billustrates an “eye” pattern in the read signal that is generated when the head28crosses over a spiral track20. The read signal representing the spiral track comprises high frequency transitions22interrupted by sync marks24. When the head28moves in the radial direction, the eye pattern will shift (left or right) while the sync marks24remain fixed. The shift in the eye pattern (detected from the high frequency signal22) relative to the sync marks24provides the off-track information (position error signal or PES) for servoing the head28.

FIG. 4Ashows an embodiment of the present invention wherein a saw-tooth waveform52is generated by clocking a modulo-N counter with the servo write clock, wherein the frequency of the servo write clock is adjusted until the sync marks24in the spiral tracks200-20Nare detected at a target modulo-N count value. The servo write clock may be generated using any suitable circuitry, such as a phase locked loop (PLL). As each sync mark24in the spiral tracks200-20Nis detected, the value of the modulo-N counter represents the phase error for adjusting the PLL. In one embodiment, the PLL is updated when any one of the plurality of sync marks24within the eye pattern is detected. In this manner the multiple sync marks24in each eye pattern (each spiral track crossing) provides redundancy so that the PLL is still updated if one or more of the sync marks24are missed due to noise in the read signal. Once the sync marks24are detected at the target modulo-N count values, the servo write clock is coarsely locked to the desired frequency for writing the product servo sectors to the disk18.

The sync marks24in the spiral tracks200-20Nmay comprise any suitable pattern, and in one embodiment, a pattern that is substantially shorter than the sync mark10in the conventional product servo sectors2ofFIG. 1. A shorter sync mark24allows the spiral tracks200-20Nto be written to the disk18using a steeper slope (by moving the head faster from the outer diameter to the inner diameter of the disk18) which reduces the time required to write each spiral track200-20N.

In one embodiment, the servo write clock is further synchronized by generating a timing recovery measurement from the high frequency signal22between the sync marks24in the spiral tracks200-20N. Synchronizing the servo write clock to the high frequency signal22helps maintain proper radial alignment (phase coherency) of the Gray coded track addresses in the product servo sectors. The timing recovery measurement may be generated in any suitable manner. In one embodiment, the servo write clock is used to sample the high frequency signal22and the signal sample values are processed to generate the timing recovery measurement. The timing recovery measurement adjusts the phase of the servo write clock (PLL) so that the high frequency signal22is sampled synchronously. In this manner, the sync marks24provide a coarse timing recovery measurement and the high frequency signal22provides a fine timing recovery measurement for maintaining synchronization of the servo write clock.

FIG. 5illustrates how the product servo sectors560-56Nare written to the disk18after synchronizing the servo write clock in response to the high frequency signal22and the sync marks24in the spiral tracks200-20N. In the embodiment ofFIG. 5, the dashed lines represent the centerlines of the data tracks. The sync marks in the spiral tracks200-20Nare written so that there is a shift of two sync marks24in the eye pattern (FIG. 4B) between data tracks. In an alternative embodiment, the sync marks24in the spiral tracks200-20Nare written so that there is a shift of N sync marks in the eye pattern between data tracks. In the embodiment ofFIG. 5, each spiral track200-20Nis wider than a data track, however, in an alternative embodiment the width of each spiral track200-20Nis less than or proximate the width of a data track.

The PES for maintaining the head28along a servo track (tracking) may be generated from the spiral tracks200-20Nin any suitable manner. In one embodiment, the PES is generated by detecting the eye pattern inFIG. 4Busing an envelope detector and detecting a shift in the envelope relative to the sync marks24. In one embodiment, the envelope is detected by integrating the high frequency signal22and detecting a shift in the resulting ramp signal. In an alternative embodiment, the high frequency signal22between the sync marks24in the spiral tracks are demodulated as servo bursts and the PES generated by comparing the servo bursts in a similar manner as the servo bursts14in the product servo sectors (FIG. 1).

FIG. 6shows details of control circuitry for synchronizing the servo write clock58according to an embodiment of the present invention. The read signal60emanating from the head28is sampled62, and the read signal sample values64are processed by a sync mark detector66for detecting the sync marks24in the spiral tracks200-20N. The sync mark detector66generates a sync mark detect signal68applied to a timing recovery circuit70. The timing recovery circuit70processes the sync mark detect signal68to generate a coarse timing recovery measurement, and the read signal sample values64representing the high frequency signal22in the spiral tracks200-20Nto generate a fine timing recovery measurement. The coarse and fine timing recovery measurements are combined to generate a control signal applied to a write oscillator72which outputs the servo write clock58. The servo write clock58clocks operation of write circuitry74for writing the product servo sectors560-56Nto the disk18. The servo write clock58is also fed back into the timing recovery circuit70and used to generate the coarse timing recovery measurement. The timing recovery circuit70generates a sync mark detection window over line78for enabling the sync mark detector66during a window where a sync mark24is expected to occur. The timing recovery circuit70also generates a control signal over line80to enable the write circuitry74to begin writing a product servo sector at the appropriate time.

Referring again toFIG. 5, when writing the product servo sectors560-56Nan initial servo track is located relative to an aberration in the sync marks24of the spiral tracks at an initial radial location45(FIG. 2B). In the embodiment ofFIG. 5, every other spiral track is missing (not written) so that the sync marks24are missing in every other spiral track. In other embodiments, there may be as few as one missing spiral track and corresponding missing sync mark. Referring again toFIG. 6, when the timing recovery circuit70enables the sync mark detector66over line78it also enables a missing sync mark detector82which detects the missing sync marks when the head is over the initial radial location45. For example, the missing sync mark detector82may detect no sync mark detect signal68over the entire sync mark detection window. Once missing sync marks24are detected at every other spiral track, the initial radial location45is detected at step84, and the write circuitry74is enabled over line86to begin writing the product servo sectors560-56Nalong the initial servo track as shown inFIG. 5.

Any suitable aberration may be detected at the initial radial location45for locating the initial servo track. In one embodiment, the sync marks24comprise a first pattern at the initial radial location45, and the sync marks24comprise a second pattern at radial locations different than the initial radial location45, wherein the first pattern is different than the second pattern.FIG. 7shows corresponding control circuitry for synchronizing the servo write clock58as well as two sync mark detectors66A and66B for detecting the initial radial location45. The first sync mark detector66A generates a sync mark detect signal68A when the first pattern is detected at the initial radial location45. Once the first sync mark pattern is detected reliably and repeatedly, the initial radial location45is detected at step84and the write circuitry74is enabled over line86to begin writing the product servo sectors560-56Nalong the initial servo track. In one embodiment, only the sync marks24comprising the first pattern are written at the initial radial location45, and in another embodiment a combination of sync marks24comprising the first and second patterns are written at the initial radial location45with as few as a single sync mark24comprising the first pattern written at the initial radial location45. In the embodiment ofFIG. 7, both sync mark detect signals66A and66B are used by the timing recovery circuitry70to synchronize the servo write clock58.

FIG. 8shows an embodiment of the present invention wherein after writing the spiral tracks200-20Nto the disk18(FIG. 2A-2B), the HDA32is inserted into an external product servo writer104comprising suitable circuitry for reading and processing the spiral tracks200-20Nin order to write the product servo sectors560-56Nto the disk18. The external product servo writer104comprises a read/write channel106for interfacing with a preamp108in the HDA32. The preamp108amplifies a read signal emanating from the head28over line110to generate an amplified read signal applied to the read/write channel106over line112. The read/write channel106comprises circuitry for generating servo burst signals113applied to a servo controller114. The servo controller114processes the servo burst signals113to generate the PES. The PES is processed to generate a VCM control signal applied to the VCM30over line116in order to maintain the head28along a circular path while writing the product servo sectors560-56N. The servo controller114also generates a spindle motor control signal applied to a spindle motor118over line120to maintain the disk18at a desired angular velocity. Control circuitry122processes information received from the read/write channel106over line124associated with the spiral tracks200-20N(e.g., timing information) and provides the product servo sector data to the read/write channel106at the appropriate time. The product servo sector data is provided to the preamp108which modulates a current in the head28in order to write the product servo sectors560-56Nto the disk18. The control circuitry122also transmits control information over line126to the servo controller114such as the target servo track to be written. After writing the product servo sectors560-56Nto the disk18, the HDA32is removed from the external product servo writer104and a printed circuit board assembly (PCBA) comprising the control circuitry34(FIG. 2A) is mounted to the HDA32.

In one embodiment, the external product servo writer104ofFIG. 8interfaces with the HDA32over the same connections as the control circuitry34to minimize the modifications needed to facilitate the external product servo writer104. The external product servo writer104is less expensive than a conventional servo writer because it does not require a clean room or sophisticated head positioning mechanics. In an embodiment shown inFIG. 9, a plurality of external product servo writers1040-104Nprocess the HDAs32i-i+Noutput by an external spiral servo writer36in order to write the product servo sectors less expensively and more efficiently than a conventional servo writer. In an alternative embodiment shown inFIG. 10, an external spiral servo writer36or an external media writer is used to write the spiral tracks, and the control circuitry34within each product disk drive16i-16i-i+Nis used to write the product servo sectors.