Method for storage of self-servowriting timing information

Details Method for storage of self-servowriting timing information Method for storage of self-servowriting timing information

2001-01-31

2004-05-11

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data clocking

C360S077080, C360S078140, C360S077050, C360S053000, C360S075000, C360S048000

Reexamination Certificate

active

06735031

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to the field of rotating media mass storage devices, and in particular relates to recording servodata timing information on hard disk drives for non-overlapping read and write heads.
2. Description of Related Art
High track densities in rotating media mass storage devices are becoming possible with newer drive technologies in voice-coil and other types of servo positioners as well as the ability to read and write narrower tracks by using, for example, magnetoresistive (MR) head technology. When track densities are very great mechanical error of a lead screw-stepper motor combination becomes significant compared to track-to-track spacing, and an embedded servo helps determine the position of the head from the signals it reads.
Conventional disk drive manufacturing techniques, for example, include writing servotracks on the media of a head disk assembly (HDA) with a specialized servowriter instrument. Laser positioning feedback is used in such instruments to read the actual physical position of a recording head used to write the servotracks. Unfortunately, it is becoming more and more difficult for such servowriters to invade the internal environment of a HDA for servowriting because the HDAs themselves are exceedingly small and depend on their covers and castings to be in place for proper operation. Some HDAs are the size and thickness of a plastic credit card. At such levels of microminiaturization, traditional servowriting methods are inadequate.
Conventional servo-patterns typically comprise short bursts of a constant frequency signal, very precisely located offset from a data track's center line, on either side. The bursts are written in a sector header area, and can be used to find the center line of a track. Staying on center is required during both reading and writing. Since there can be sixty or more sectors per track, that same number of servo data areas must be dispersed around a data track. Further, the servodata is generally dispersed around the data track by writing short bursts in each of the sixty or so sector header areas of the data track. Such data bursts can be used by the embedded servo mechanism to find the center line of the data track. This allows the head to follow the track center line around the disk even when the track is out of round (e.g., due to spindle wobble, disk slip, and/or thermal expansion). As the size of disk drives is reduced and track density is increased, the servodata must be more accurately located on the disk.
Servodata is conventionally written by dedicated, external servowriting equipment, and typically involves the use of large granite blocks to support the disk drive and quiet outside vibration effects. An auxiliary clock head is inserted onto the surface of the recording disk and is used to write a reference timing pattern. An external head/arm positioner with a very accurate lead screw and a laser displacement measurement device for positional feedback is used to precisely determine transducer location and is the basis for track placement and track-to-track spacing. The servo writer requires a clean room environment, as the disk and heads will be exposed to the environment to allow the access of the external head and actuator.
A conventional servodata pattern on a disk comprises circular data tracks that are broken into sectors. Each sector typically has a sector header area followed by a data area. Each sector header area includes sector header information followed by a servodata area that provides radial position information. The sector header information includes a servo-identification (SID) field and a gray code field that must be precisely aligned from track to track to prevent destructive interference in the magnetic pattern. Such interference can reduce the amplitude of the signal and cause data errors.
During conventional drive manufacturing, the disk drive is typically mounted in a mastering station that is known as a servowriter. The servowriter has sensors that are positioned outside of the disk drive to locate the radial and circumferential position of at least one of the drive's internal heads. Using information from the sensors, the servowriter causes the head to write a pattern, typically magnetic information, (i.e., servodata) onto the disk. As explained above, the servopattern becomes the master reference used by the disk drive during normal operation to locate the tracks and sectors for data storage. When such a station is used to perform the servo-writing, manufacturing expenses increase because each disk drive must be mounted in the servowriter. Additionally, the mechanical boundary conditions of the disk are altered because the external sensors must have access to the actuator and the disk spindle motor. Thus, mechanical clamping and disassembly of the drive may also be required.
According to another conventional servo-writing process, a master clock track is first written on the disk by a separate head to serve as a timing reference for the entire servo-track writing operation. After writing the master clock track, “even” servodata bursts are written over the entire surface of the disk by first moving the arm to the outer crash stop and then radially moving the arm a distance that is less than a data track width for each revolution of the disk.
After reaching the inner diameter of the disk, the arm is once again moved to the outer crash stop and then radially moved for each revolution of the disk to write “odd” servodata bursts. After servo-writing is completed, the number of steps of the arm from the outer crash stop to the inner crash stop is compared with the desired number of tracks. If the number of steps is different from the desired number of tracks, a bias is introduced and the process is repeated so that the number of steps will equal the desired number of tracks.
Such conventional servo-writing procedures require the use of an external timing sensor in order to write the timing patterns that are used to determine the circumferential head position. Because external sensors are needed, the servo-writing must be performed in a clean room environment. Additionally, an external clock source and auxiliary clock heads are required to write the timing information. Further, in such procedures, an entire disk of information must be written to determine the track pitch to use to write the servopattern. This takes times and leads to higher manufacturing costs.
To overcome such problems, self-servo-writing timing generation processes have recently been developed. These processes allow accurately aligned servodata tracks to be written sequentially at each servo data radius without using any mechanical, magnetic, or optical positioning systems to control the circumferential positioning of the servo data. Further, the need for auxiliary clock heads to write a reference timing pattern on the disk is eliminated.
According to one method, first timing marks are written at a first radial position of the storage medium. Timing marks are defined here to be data patterns from which an accurate time of passage can be determined. Timing marks can be the servo data itself or separate timing marks written only to assist in maintaining accurate circumferential positioning of the servodata during the servowrite process. Time intervals between selected pairs of the first timing marks are measured during revolutions of the disk. The head is moved to a second radial position. Next, additional timing marks are written by recording the time of passage of every other timing mark (say the odd numbered ones) during revolutions of the disk and then writing the intervening time marks (the even numbered ones) at calculated delays thereafter. Time intervals between selected pairs of the first timing marks are measured during revolutions of the disk. Then the head is moved to a second radial position.
Next, additional timing marks are written by recording the time of passage of every other timing marks at the circumferential positions just wr

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