Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
1998-10-29
2001-02-13
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S510000, C250S23700G
Reexamination Certificate
active
06188484
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic storage devices and, more particularly, to a method and apparatus of writing servo information onto a magnetic disk surface without contacting an actuator arm associated with the magnetic disk surface. Accordingly, the magnetic disk surface can be enclosed in a head disk assembly (HDA) prior to servo writing so that servo writing may be performed outside of a clean room environment (provided that the clock reader is also of the non-contact variety, as will be understood by those skilled in the art).
BACKGROUND OF THE INVENTION
A disk drive system is a data storage device. Among other things, a disk drive system includes a plurality of disks which are mounted for rotation about a common axis. Generally, each of the disks has a pair of disk surfaces which are coated with a magnetic material that is capable of changing its magnetic orientation in response to an applied magnetic field. Data is stored digitally within concentric tracks on one or more of the disk surfaces.
Each disk surface has at least one magnetic transducer associated therewith. Generally, each of the magnetic transducers is attached on the end of an actuator arm. All of the actuator arms, and hence the transducers, are ganged together so that they move over their respective disk surfaces in unison. However, only one transducer is capable of reading data from or writing data to a disk surface at any given time.
During operation of a disk drive, each of the disks are rotated about an axis at a substantially constant rate. To read data from or write data to a disk surface, a magnetic transducer is positioned above a desired track of the disk while the disk is spinning.
Writing is performed by delivering a write signal having a variable current to the transducer while the transducer is held close to the desired track. The write signal creates a variable magnetic field at a gap portion of the transducer that induces magnetic polarity transitions into the desired track. The magnetic polarity transitions are representative of the data being stored.
Reading is performed by sensing the magnetic polarity transitions on a track with the transducer. As the disk spins below the transducer, the magnetic polarity transitions on the track present a varying magnetic field to the transducer. The transducer converts the varying magnetic field into an analog read signal that is then delivered to a read channel for appropriate processing. The read channel converts the analog read signal into a properly timed digital signal that can be further processed and then provided to a host computer system.
The transducer can include a single element, such as an inductive read/write element for use in both reading and writing, or it can include separate read and write elements. Transducers that include separate elements for reading and writing are known as “dual element heads” and usually include a magneto-resistive (MR) read element for performing the read function.
As is well known in the art, in order to properly position transducers over their respective disk surfaces, a disk drive system includes a servo system which uses servo information recorded on one or more of the disk surfaces. In general, there are two main types of servo systems. The first type of servo system is known as a dedicated servo system, where a single dedicated disk surface only includes servo information. The dedicated disk surface cooperates with a dedicated servo transducer, which is ganged together with data transducers, to provide positioning information to the data transducers so that the data transducers may be appropriately positioned over their respective disk surfaces. The second type of servo system is known as a sectored servo system and includes sectors of servo information which are interspersed between sectors of data on each of the disk surfaces. As a transducer flies over its respective disk surface it periodically obtains positioning information from the sectors of servo information recorded on the disk surface so that it can be properly positioned over the surface.
For the two types of servo systems described above, servo information is either written over an entire disk surface (as in the case of a dedicated servo system) or over periodic sections of a disk surface (as in the case of a sectored servo system). In either case, however, it is crucial that the servo information be written accurately.
Servo information is written during the manufacturing process. The process of writing servo information onto one or more of the disk surfaces is known as servo writing or servo track writing. In most conventional systems, an external device known as a servo track writer (STW), which includes its own transducer (STW transducer), is used to write a servo clock track onto a disk surface upon which servo information is to be written. The transducers of the disk drive system (as opposed to the STW transducer) are used to write servo information onto one or more of the disk surfaces.
More specifically, the transducers of the disk drive system are “placed” and “held” at an appropriate radial distance from the center of the disk using a variety of well-known techniques, such as by use of mechanical push-pin systems or optical push-pin systems (see description of mechanical push-pin systems and optical push-pin systems below). As the STW transducer reads timing information from the servo clock track, one of the transducers of the disk drive system is instructed to write servo information at a specified location (i.e., the position the transducer is being “held” at) on its respective disk surface based on the timing information read from the clock track. The transducer is then moved to a different radial location and the process is repeated. If servo information is to be written onto other disk surfaces, the above process is repeated with the transducers corresponding to the other disk surfaces. Accordingly, servo information is placed on one or more disk surfaces at specified radial distances and is based on the timing information read by the STW transducer from the servo clock track.
Of the well-known techniques used to “place” and “hold” transducers of a disk drive system at predetermined radial distances from the center of a disk, mechanical push-pin systems and optical push-pin systems have been most widely used. One type of mechanical push-pin system includes both a master arm (associated with an external device) having a master voice coil motor and an actuator arm (associated with the disk drive system) having a voice coil motor. The master arm and the actuator arm are mechanically linked by component known as a mechanical push-pin, wherein the actuator arm is biased towards the mechanical push-pin via its voice coil motor. By accurately positioning the master arm, the actuator arm may be accurately positioned at a predetermined location relative to the center of a disk. A transducer associated with the actuator arm is then used to write servo information onto a surface of the disk. The master arm is then repositioned to another predetermined location (the actuator arm moving with the master arm due to the mechanical link therebetween) and the actuator arm is then used to write additional servo information onto the disk surface.
Mechanical push-pin systems suffer from a number of significant drawbacks. For example, mechanical push-pin systems prevent disk drive systems from being sealed prior to servo writing due to their mechanical link. As is well-known to those skilled in the art, disk drive systems are commonly sealed prior to being shipped to an end user in order to prevent contaminants from interfering with the interface between a disk drive's transducers and the transducers' associated disk surfaces, among other reasons. Because mechanical push-pin systems require a physical link to be made between a master arm, which is external to the disk drive system, and an actuator arm of the disk drive system, the disk drive system cannot be sealed prior to servo writing. Accordingly, the
Garner, Jr. Harry Douglas
Guo Lin
Lee Kok-Meng
Maxtor Corporation
Sheridan & Ross P.C.
Turner Samuel A.
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