Dynamic magnetic information storage or retrieval – Head – Plural gaps
Reexamination Certificate
1999-10-15
2002-03-19
Huber, Paul W. (Department: 2651)
Dynamic magnetic information storage or retrieval
Head
Plural gaps
Reexamination Certificate
active
06359749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to direct access storage devices and, more particularly, to read/write head assemblies for use in such storage devices.
2. Description of the Related Art
In a conventional computer direct access storage device (DASD) having a rotating storage medium, such as a magnetic or magneto-optical disk, data is stored in a series of concentric or spiral tracks across the surface of the disk. A magnetic disk, for example, can comprise a disk substrate having a surface on which a magnetic material is deposited. The digital data stored on a disk comprises magnetic information that is represented as a series of variations in magnetic orientation of the disk magnetic material. The variations in magnetic orientation, generally comprising reversals of magnetic flux, represent binary digits of ones and zeroes. A read/write assembly produces and detects variations in magnetic orientation of the magnetic material as the disk rotates relative to the head, thereby reading data from, and writing data to, the disk surface.
The surface area of each disk in a DASD may be partitioned into sectors having a short servo track information area followed by a user data area. Each sector can be defined by an imaginary radial line extending from the disk center to the disk outer diameter, or circumference. The servo track information generates a readback signal that is used to position the transducing head across the disk surface. The user data area of a sector contains data tracks in which data is recorded by an end user, or disk drive customer. The servo track information area of a sector typically includes a sector marker, track identification data, and a servo burst pattern, which are recorded at the time of disk manufacture. The transducing head used for reading the servo track data is typically the same head that is used for reading the customer data, but typically a different magnetic head is used for writing the customer data. Such dual-element heads permit optimal exploitation of transducer characteristics for the read and write functions. Increased track densities permit storing more customer data in a DASD with no increase in physical disk size. Such higher track densities have been achieved with transducer advancements such as magneto-resistive heads.
A magneto-resistive (MR) head assembly is a dual-element head that typically includes an MR element for reading user data and servo pattern information, and a different element (typically an inductive element) for writing customer data to the disk. A dual-element assembly having an MR read element and a write element will be referred to as an MR head. The MR element of an MR head exhibits a change in resistance when in the presence of a changing magnetic field. The change in resistance of the MR element is transformed into a voltage signal by passing a constant bias current through the MR element. The MR head generates a fluctuating voltage readback signal as the MR head is passed over the magnetic information recorded on the disk magnetic material. In a DASD using digital demodulation, the fluctuating readback signal is digitized and the digital data values of the sampled readback signal are processed to recover the recorded data.
A disk drive DASD typically includes two signal paths for the head readback signal, comprising a data channel and a servo channel. When the MR head is over a customer data field, the readback signal is processed by the data channel so the system can read and write customer data to and from the disk. When the MR head is over a servo field of the disk, the readback signal is processed by the servo channel to read the servo pattern information that is pre-recorded on the disk at the time of manufacture.
A read/write head assembly is mounted on a disk arm that is moved across the disk by a servo. A disk drive servo control system controls movement of the disk arm across the surface of the disk to move the read/write head assembly from data track to data track and, once over a selected track, to maintain the assembly in a path centered over the selected track. Maintaining the head assembly centered over a track facilitates accurate reading and recording of customer data. With the very high track density of current disk drives, even the smallest head positioning error can potentially cause a loss of customer data.
In the servo information area of a disk sector, the sector marker indicates to the read/write transducing head that servo information immediately follows in the track. The track identification area contains a binary representation of the servo track (or data track) associated with the servo information. The servo burst pattern contains data that generates an analog voltage signal whose magnitude is such that the position of the transducer head relative to a single track can be determined. That is, as the position of the head changes from one edge of a track to the other edge of the track, the magnitude of the readback signal changes, and this is used to keep the head centered in the track for optimal reading and writing of customer data.
Track Misregistration (TMR) Error
A read/write head in a rotary disk drive actuator will exhibit positioning error called track misregistration (TMR) error, which produces errors in reading and writing data to a disk. The total disk TMR is generally made up of two types of error: (1) write-to-read error (WR TMR), comprising the error in reading data from a track into which the data was previously written, and (2) write-to-write error (WW TMR), comprising the error in writing new data into a data track that is adjacent to previously written data. There are various types of disk drive characteristics that can contribute to the total TMR.
For example, some types of error contribute to both WR TMR and WW TMR. These include disk spindle motor runout, which generates an off-center condition to the disk rotation, airflow induced vibration of the read/write head, head seek settling time, electrical and magnetics system noise, and external disturbances such as shock to the drive. These components of total TMR are generally greater toward the outside diameter of the disk (OD), and are lesser toward the inner diameter of the disk (ID). Disk controllers generally include signal processing that is designed to minimize or compensate for such error. Part of such processing may, for example, compensate for the offset between the disk head write element and the disk head read element. These signal processing systems may, themselves, contribute a read-write element compensation error component to the total TMR error, although generally such compensation systems are only involved in read operations subsequent to write operations, and so such errors will only contribute to WR TMR.
Some disk drive design involves minimizing such components of total TMR. For example,
FIG. 1
illustrates a conventional MR head assembly in which the read element and the write element are aligned. The servo control system of a disk with such a read/write head will compensate for WR TMR such as described above. Generally, the head configuration of
FIG. 1
will result in no tracking error at the inside diameter (ID) of the disk. As the disk head assembly moves toward the outer diameter (OD) of the disk, the servo control system compensates for the skew, or offset, between the tracking of the read element and the write element at the middle of the disk.
FIG. 1
is a view looking down on the read/write MR head assembly
100
, where the MR head is indicated as having a write element
102
spaced apart from a read element
104
, in position above a data track
106
of the disk
108
. It can be seen that the write element and read element are aligned along the longitudinal axis
110
of the head assembly, which is also the longitudinal axis of the data track
106
above which the head is positioned. The head assembly
100
has a separation “d” between the write element and the read element.
In a different head configuration, the read and write el
Hall David A.
Huber Paul W.
International Business Machines - Corporation
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