Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-02-17
2003-06-03
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S077120, C369S044410, C369S120000
Reexamination Certificate
active
06574066
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to reading/writing data on a data storage medium. More particularly, the present invention pertains to an optical time-based servo system and method for positioning a transducing head relative to one or more tracks located on a storage medium.
BACKGROUND
Electronic data storage devices are known in the art. In general, these devices are classified by how they read and write data. Magnetic data storage devices use a transducing or “read/write” head that alters the magnetic state of a portion of a magnetic disk or tape. Optical devices, on the other hand, utilize a read/write head having a low-power laser beam to read and write digitized data encoded in the form of tiny changes in reflectivity on the surface of an optical disk.
At higher track densities, the recording and reading of data in tracks on data storage media requires precise positioning of the read/write heads. The read/write heads must be quickly moved to and centered over particular tracks as reading/writing of data is performed. The heads can read/write data from a particular track as the media moves relative to the transducing head in a transducing direction. To access other tracks, the read/write heads move laterally across the media in a translating direction that is generally perpendicular to the track.
In the case of storage devices that read/write data on magnetic and optical media, servo control systems are sometimes used to accurately position the data read/write heads in the translating direction (e.g., across the width of the tape or across the radius of the disk). The servo control system generally provides a position signal from one or more servo read heads that read position control information recorded in one or more servo tracks on the storage medium. The position control information is then used to accurately center the data read/write heads over the data tracks.
One type of servo system relies on signal amplitude to determine position. An example of such an amplitude-based servo system often found in tape drives is referred to as a boundary system. In boundary systems, at least one servo track or servo track pattern extends along the length of the media (e.g., along the tape or along a circumferential segment of the disk). The servo track is laterally divided into two or more regions separated by distinct boundaries. The distinct regions have different properties that can be detected by the servo read head. For example, the regions may be recorded at different frequencies or phases, or they may contain bursts occurring at distinct times. Generally, the servo head elements straddle the boundary between the regions, and the ratio of the optical or magnetic amplitude of the response of the servo head to each region provides the position signal upon which the track-following servo operates.
While effective, boundary type servos are particularly susceptible to errors in position signal. In addition, servo head instabilities, head wear, localized debris on the head or media, and media defects all contribute to temporary or long-term shifts in the spatial response of the servo head to the recorded servo pattern in the servo track. When this occurs, the servo system cannot effectively track.
Another amplitude-based optical servo system is found on removable magnetic disk drives where the disks are provided with an optically readable servo pattern. Here, an optical servo signal is generated by a laser which is attached to a servo head. The laser forms a pattern of offset spots on the disk which are then reflected to various photodetectors. The intensity of reflected light from the spots is altered when the spots are incident on servo indicator marks on the disk surface. As the disk rotates and the marks pass through the spots, the reflected signal oscillates with an amplitude determined by the relative track position (e.g., maximum when the spots are precisely aligned with the marks and minimum when the spots are exactly between the marks).
While more than adequate, amplitude-based servo systems like those described above are necessarily sensitive to fluctuations in the amplitude of the servo position signal. Accordingly, as the servo read head's sensitivity to amplitude is diminished over time, its ability to effectively track is hindered.
To address the problems associated with amplitude based servo systems, time-based systems for magnetic storage media have been described. U.S. Pat. No. 5,689,384 to Albrecht, et al., entitled “Timing Based Servo System For Magnetic Tape Systems,” issued Nov. 18, 1997, describes a track following servo control system for use with magnetic media tape systems which derives head position information from one or more specially patterned magnetic servo tracks. The servo patterns are comprised of magnetic transitions recorded at more than one azimuthal orientations in a servo track, such that the timing of the servo position signal pulses derived from reading the servo pattern are decoded to provide a position signal used by the servo system to position data heads over desired data tracks of the storage media.
While such time-based servo systems have numerous advantages over boundary and other amplitude-based servo systems, problems remain. For example, depending upon the type of time-based servo pattern recorded in the servo track and the method of recording such a time-based servo pattern, the system may be sensitive to media speed variations at the time the servo pattern is recorded in the servo track. Thus, specialized servo writing equipment having special speed control features is generally necessary to perform such time-based servo recording. Furthermore, the servo writing equipment must be able to write complex servo patterns to the media.
For these and other reasons, conventional time-based servo systems have proven less than optimal for many applications. What is needed is a time-based servo system and method that overcomes the problems discussed above when used with either optical or magnetic media in either disk or tape formats.
SUMMARY OF THE INVENTION
To overcome these problems, a time-based optical servo systems and methods according to the present invention are provided. In one embodiment of the invention, an optical detection apparatus for use with a data storage device is provided. The apparatus includes a servo read assembly having two or more elongate optical detection devices spaced apart along a transducing direction in a non-parallel relationship.
In yet another embodiment of the invention, a method for positioning a transducing head adjacent a data storage track on a data storage medium is provided. The method includes moving a storage medium in a transducing direction relative to the transducing head where the storage medium has at least one optical indicator mark thereon. The method further includes positioning the transducing head over the storage medium in a translating direction generally perpendicular to the transducing direction, wherein the transducing head is operatively coupled to an optical servo read head assembly having a first elongate detection device and a second elongate detection device arranged in a spaced-apart, non-parallel configuration. The method further includes determining the position of the transducing head in the translating direction by measuring a time period required for the at least one optical indicator mark to pass between the first detection device and the second detection device. The position of the transducing head in the translating direction is adjusted based on the time period.
In still yet another embodiment of the invention, an optical servo system for positioning a transducing head assembly adjacent a surface of a data storage medium is provided where the storage medium moves in a transducing direction relative to the transducing head assembly. The system includes an optical detection apparatus for determining the position of the transducing head assembly relative to the storage medium in a translating direction which is transverse to the transducing
Jackson Robert S.
Stubbs Daniel P.
Habermehl James L
Imation Corp.
Levinson Eric D.
Sniezek Andrew L.
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