Dynamic magnetic information storage or retrieval – General recording or reproducing – Signal switching
Reexamination Certificate
2001-08-31
2004-02-03
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Signal switching
C360S075000, C360S077080
Reexamination Certificate
active
06687073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a read/write head positioning system used in magnetic data storage devices, such as computer hard drives, and, more specifically, to a method of marking servo tracks in a way that expedites the servo writing process.
2. Description of the Related Art
Hard disk drives are commonly available memory storage devices. The typical hard disk drive includes a plurality of disks having surfaces of magnetic media that are rotating at high speeds about a spindle. A plurality of pivotable head assemblies are mounted with respect to the disk surfaces such that the combination of the rotation of the disks and the pivoting of the head assemblies allow a transducer or head to be positioned adjacent substantially all of the surface of the disk upon which data can be recorded.
Data is typically recorded by inducing the head to produce an electromagnetic field when in proximity to the disk surface so as to change the magnetic state of the disk. Typically, the head is positioned at a particular radial location and data is recorded in a generally circular data track. Similarly, when previously recorded data is being retrieved from the disk surface, the head is positioned adjacent the disk at the radial location containing the data, and the changing magnetic state of the disk surface is then detected by the head.
Increasingly, data tracks are being positioned closer and closer together so as to increase the amount of data that can be stored on a disk surface. In some implementations, the density of data tracks can be 35,000 tracks per inch or higher. As such, it is necessary for the control system of the hard drive to be able to identify the track and the region of the track that the head is positioned adjacent.
More specifically, as data tracks are positioned very close together, it is necessary for hard drive to be able to determine the location of the heads to ensure that the heads are properly positioned with respect to data tracks in order to write and read data to and from the appropriate track. To accomplish this, the magnetic media is also programmed to have servo tracks that provide servo signals to a servo control system that provides information as to the relative position between the heads and the tracks of the hard disks.
Servo tracks are typically arranged into concentric circles positioned around the middle of the disk at a multitude of radii. In an embedded servo system, these servo tracks are split into “wedges” spaced apart circumferentially at regular intervals. The hard disk manufacturer usually writes the servo tracks using a servo writer machine before any data tracks are written. Data tracks are subsequently written onto open areas on the disk surface adjacent the servo wedges such that the servo control system can determine the location of the head with respect to the data track from the positional information contained in the servo track.
Thus, in the typical embedded servo system, the head reads the servo track as it reads data, and the relation between an individual servo track and an individual data track allows the controller to calculate a position error signal (PES) and provide a correction current to the actuator. The correction current pivots the actuator in order to maintain the head's position over the desired track. Servo wedges are also detected during seek operations to monitor the location of the head when moving between tracks.
The servo wedges are written on the disk surfaces during the manufacturing process of the hard disk drive. Typically, the hard disk drive is positioned within a servo writing machine that then induces the disks to rotate and signals are sent to the head at appropriate intervals to record the servo wedges on the disk surfaces. In general, servo writing is a time consuming process that can take up to 10 hours to write all of the servo wedges on all of the servo tracks for a single drive. As such, servo writing comprises a significant portion of the time and cost to produce a hard drive.
Servo wedges can be written one wedge at a time, however, this is particularly time consuming and adds to the time and cost to fabricate the hard drive. Moreover, writing wedges,one at a time may result in the a set of wedges not being written before the servo disks: have rotated to the next circumferential wedge location. As such, writing wedges one at a time may require that the servo writer permit the wedges to rotate to the desired position without writing wedges during this period. This can further reduce the throughput of the servo writing process.
Various techniques have been used in order to expedite the servo writing process. For example, servo writers often implement a bank writing process whereby all the heads of the servo drive are simultaneously provided current to write servo wedges. Since the heads are typically coupled together, they are all positioned at a corresponding radial and circumferential position on the different disk surfaces. Consequently, an entire bank of servo wedges can thus be written on the plurality of disk surfaces. This process can be repeated circumferentially about a servo track for each of the servo wedges of the track until the track is completed. The actuator can move the heads to a different radial position and then repeat this process for each of the servo tracks of the disk surfaces.
While bank writing expedites the servo writing process, improvements in magnetic media have begun to limit the ability of the hard disk drive manufacturers to simultaneously write entire banks of servo wedges at one time. As is understood, to write a servo wedge, current must be sourced to each of the heads writing the wedge. The amount of current needed is, of course, dependent upon the magnitude of the magnetic field needed to be produced by the head to magnetically record the servo wedge of the disk surface.
Increasingly, the magnetic media being used to fabricate the disk surface is less sensitive to magnetic fields and, consequently, stronger magnetic fields have to be generated by the head in order to write the servo wedges. However, since the head assembly and head electronics that are being built into the disk drive are being used to write the servo wedges, the ability to source these greater currents are limited by the current carrying limitations within the head electronics.
To reduce both the cost of the disk drive and the size, the electronics, such as the pre-amp typically have design constraints directed towards normal operation of the hard disk drive, e.g., only single write and read steps being performed at a time. These types of head electronics are therefore less able to handle the simultaneous application of large servo wedge writing currents being sourced to multiple heads. Consequently, the servo writing process is becoming a greater manufacturing bottleneck thereby increasing the overall cost of the hard disk drive.
Hence, there is a need for an improved process of servo writing that allows for greater throughput in the servo writing process. To this end, there is a need for a servo writing process that allows for faster servo writing even with new magnetic media that require higher amplitude magnetic fields to write the servo wedges.
SUMMARY OF THE INVENTION
The aforementioned needs are satisfied by the method of writing servo tracks of the present invention, which involves simultaneously writing portions of servo tracks to thereby expedite the servo writing process.
In one aspect the method involves writing a plurality of servo tracks (x) each having a number of servo wedges on a plurality of disk surfaces. The corresponding servo wedges on each of the plurality of disk surfaces comprise a servo wedge set (z). A first step of the method comprises writing a subset (y) of a servo wedge set (z) for a servo track (x) on a subset of the disk surfaces such that the subset (y) is being written at one time. Then, a second step begins upon completion of the first step, wherein the next subset (y) of the servo wedge set (z)
Holder Regina N.
Kapadia Varsha A.
Knobbe Martens OIson & Bear
Shara, Esq. Milad G.
Western Digital Technologies Inc.
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