Dynamic magnetic information storage or retrieval – Head mounting – For adjusting head position
Reexamination Certificate
2001-12-12
2004-07-06
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For adjusting head position
C360S294400, C360S245000
Reexamination Certificate
active
06760196
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to data storage systems such as disk drives, and it particularly relates to a read/write head, such as a thin film head, a MR head, or a GMR head for use in such data storage systems. More specifically, the present invention provides a novel design of a microactuator, such as a piezoelectric microactuator, for use in conjunction with a flexure tongue with offsetting hinges, to perform a fine positioning of the magnetic read/write head. The substantial gain in the frequency response bandwidth greatly improves the performance and accuracy of the track-follow control for fine positioning. Furthermore, the simplicity of the enhanced microactuator design results in a manufacturing efficiency that enables a high-volume, low-cost production.
BACKGROUND OF THE INVENTION
In a conventional magnetic storage system, a magnetic head includes an inductive read/write transducer mounted on a slider. The magnetic head is coupled to a rotary voice coil actuator assembly by a suspension over a surface of a spinning magnetic disk.
In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height (or fly height) is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk. The flying height is defined as the spacing between the surface of the spinning magnetic disk and the lowest point of the slider assembly.
One objective of the design of magnetic read/write heads is to obtain a very small flying height between the read/write element and the disk surface. By maintaining a flying height close to the disk, it is possible to record short wavelength or high frequency signals, thereby achieving high density and high storage data recording capacity.
The slider design incorporates an air bearing surface to control the aerodynamic interaction between the magnetic head and the spinning magnetic disk thereunder. Air bearing surface (ABS) sliders used in disk drives typically have a leading edge and a trailing edge at which read/write heads are deposited. Generally, the ABS surface of a slider incorporates a patterned topology by design to achieve a desired pressure distribution during flying. In effect, the pressure distribution on the ABS contributes to the flying characteristics of the slider that include flying height, pitch, and roll of the read/write head relative to the rotating magnetic disk.
In a conventional magnetic media application, a magnetic recording disk is comprised of several concentric tracks onto which magnetization bits are deposited for data recording. Each of these tracks is further divided into sectors where the digital data are registered.
As the demand for large capacity magnetic storage continues to grow, the current trend in the magnetic storage technology has been proceeding toward a high track density design of magnetic storage media. In order to maintain the industry standard interface, magnetic storage devices increasingly rely on reducing track width as a means to increase the track density without significantly altering the geometry of the storage media.
A smaller track width poses several mechanical and electrical problems to the operation of magnetic disk drives. One such problem lies in its actuation and control feature, which is critical to the operation of a magnetic disk drive. In order to appreciate the magnitude of this problem, it might be important to further describe the control aspect of a conventional magnetic read/write head.
In a conventional magnetic disk drive, a read/write head includes a transducer mounted on a slider. The slider is in turn attached to a stainless steel flexure. The flexure and the load beam to which the flexure is attached, form a suspension arm. The suspension arm is connected to one distal end of an actuator arm, which is driven by a voice coil motor (VCM) at the other distal end, to cause it to rotate at its mid-length about a pivot bearing.
The suspension arm exerts an elastic force to counteract the aerodynamic lift force generated by the pressure distribution on the ABS of the slider. The elastic force together with the stiffness of the suspension arm controls the stability of the actuator arm with respect to the pitch, roll, and yaw orientations. With respect to the control feature of the magnetic disk drive, during each read or write operation, there are usually two types of positioning controls: a track-seek control and a track-follow control.
A track-seek and follow control is typically commanded when data are to be retrieved from, or new data are to be written to a particular sector of a data track. Electronic circuitry incorporating an embedded feedback control software, supplies a necessary voltage to the VCM to actuate the VCM to drive the actuator arm, to which the read/write head is attached, to a target track. Thus, a track-seek control performs a low-resolution or coarse positioning of the read/write head from one data track to another data track and also following track of corresponding track pitch density
Upon the completion of a track-seek control, subsequent data operation is typically confined to within the target track. In the earlier stage of the magnetic storage technology, a typical data track is sufficiently wide so that small variations in the position of the read/write head resulting from external disturbances to the track-seek control plant do not cause the position of the read/write head to exceed the prescribed control error allowance.
As the track width reduces as a means to increase the track density and hence the storage capacity of magnetic disk drives, the foregoing single-stage actuation design encounters a significant degree of difficulty, mainly due to the excessive control error of the track-seek control using the VCM. In particular, a single-stage actuation using the VCM is found to be inadequate because the resulting control error due to external disturbances, such as inertial shock loading or noise sometimes, could cause the read/write head to be positioned over tracks that are adjacent to the target track, thus possibly causing a magnetic field disturbance of the existing data thereon.
In a worst case scenario, the data disturbances can result in a total erasure of data in the adjacent tracks after several repetitive write operations, or data corruption upon reading. Moreover, the VCM employed in a single-stage actuation is typically subjected to a mechanical resonance at the lowest natural frequency in the range of 2000 Hz-6000 Hz due to the flexibility of the actuator arm and followed by frequencies on the suspension arm in the range of 2 kHz-15 kHz.
The response of the servo-system further limits the frequency bandwidth to less than 1500 Hz. As a result, this low frequency bandwidth imposes a severe penalty on the single-stage actuation system in such a manner that the track-seek and track-follow control is unable to rapidly and precisely respond to a change in the position of the read/write head, thus causing a significant degradation in the performance of the magnetic disk drive.
To address this technical concern, it is recognized that in order to maintain the position of the read/write head in a manner that it follows a concentric path within a narrow track width of the target data track, necessary corrections to the motion of the actuator arm are required. This provision is made possible by a enhanced track-follow control, which uses a feedback on the position error signal (PES) to make an appropriate correction to the motion of the actuator arm, so as to have the position of the read/write head follow a concentric path of the target data track within a prescribed control error allowance.
Thus, in the presence of external disturbances, variations in the position of the read/write head would not cause the position of the read/write head to significantly deviate from the target
Fanslau, Jr. Edmund Bruno
Niu Yimin
Miller Brian E.
Western Digital, Inc.
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