Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2001-07-16
2004-08-24
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S077010, C360S077120
Reexamination Certificate
active
06781778
ABSTRACT:
TECHNICAL FIELD
The invention relates to data storage media and, in particular, to recording and reading from magnetic and optical storage media.
BACKGROUND
Storage media are used for storage and retrieval of data, and come in many forms, such as magnetic tape, magnetic disks, optical tape and optical disks. For most media, a head assembly, which includes one or more read transducer heads, reads data from the storage medium. Many forms of media, such as magnetic tape and rewritable optical disks, allow data to be written to the medium as well as read from the medium. A write transducer head or a read/write transducer head writes data to the storage medium.
The data stored on the medium are usually organized into “data tracks,” and the transducer heads write data to and/or read data from the data tracks. A typical storage medium includes several data tracks.
As the number of data tracks on a medium increases, the data storage capacity of the medium increases. The data tracks also usually become narrower, as more data tracks are crowded onto the recording surface of the medium.
For proper data storage and recovery, the transducer head must locate each track where data are to be written or read, and follow the path of the data track accurately along the media surface. A servo controller typically is provided to control the positioning of the head relative to the data tracks.
Earlier servo controllers positioned the heads relative to the expected position of the medium as the medium passed the head. Other servo controllers measured the position of a data track relative to an edge of the recording medium. As more and narrower data tracks were added to media, however, these methods of locating data tracks became less satisfactory and were not able to support the precision needed for head placement.
A more modern approach was to place, during the medium manufacturing process, pre-recorded servo position information at pre-selected sites on the medium. This servo position information was then used by the servo controller to control head motion when seeking between tracks, and to regulate head position on a track during reading and/or writing.
With some forms of storage media such as magnetic tape, the servo information is stored in specialized tracks in the medium, called “servo tracks.” Servo tracks serve as references or landmarks for the servo controller. Servo tracks hold no data except for information that is useful to the servo controller.
The servo tracks are sensed by a servo read head. A servo read head may be a dedicated head that reads only servo tracks and does not read data tracks. Once a particular servo track is located by the servo read head, a data track can be located on the medium according to the data track's displacement from the servo track.
Other forms of storage media, such as magnetic disks, store servo information in one or more specialized sectors. In a magnetic disk, for example, servo information may be recorded in a single sector that extends from the outer circumference of the disk to the inner circumference, or may be recorded in multiple zones or wedges. The servo controller uses the information stored in the servo portion of each sector first to locate the desired track and then to appropriately position the transducer head with respect to the centerline of the desired track.
SUMMARY
The present invention combines the benefits of sectored servo data with the benefits of time-based servo data. A wide variety of forms of storage media can store servo data in a time-based sectored servo format. In particular, magnetic tape, magnetic disks, optical tape and optical disks can store servo data in a time-based sectored servo format.
Servo data stored in a time-based format are arranged in a different way than servo data stored in a conventional format. In magnetic media, for example, conventional servo tracks may store magnetic flux transitions of varying phases or frequencies. Time-based servo tracks apply a different approach, storing servo data in a series of patterns. A simple form of a pattern consists of a pair of marks. The marks are not coincident with each other, nor are the marks parallel. Rather, the marks are angularly offset from one another, in a pattern such as a diamond or zigzag.
As a servo read head reads a time-based servo track, the servo read head generates a signal when encountering each of the marks. The time between the signals is indicative of the lateral location of the servo read head relative to the servo marks, due to the angular offset between the marks. The timing of the signals varies continuously as the servo read head is moved laterally across the width of the pattern.
The timing of signals generated by the servo read head is decoded by appropriate circuitry. The decoder circuitry can determine from the timing of the signals whether the servo read head is reading near an edge of the servo pattern, for example, or whether the servo read head is reading in the center of the servo pattern.
The time-based servo patterns are arranged in sectors that intersect one or more data tracks. Dedicated servo tracks on the medium are not required. The sectored format potentially uses less space on the medium than conventional servo information formats. In many embodiments, the format may be read by a data transducer head, and consequently the head assembly does not require a dedicated servo read head.
In one embodiment, the invention presents a medium for recording data. The medium includes a data track extending in a longitudinal direction and a time-based servo pattern adjacent to the data track in the longitudinal direction. A transducer head tracking the data track in the longitudinal direction encounters and senses a time-based servo pattern. A servo controller uses signals from the transducer head to control a head actuator, which moves the transducer head proximate to a particular data track or adjusts for tracking errors.
In a typical implementation, the data track may be one of a group of data tracks, and the width of the time-based servo pattern in the lateral direction, which is perpendicular to the longitudinal direction, is substantially equal to the width of the group of data tracks in the lateral direction. The medium may include magnetic tape, a magnetic disk, optical tape and an optical disk.
In another embodiment, the invention presents a method comprising performing a coarse adjustment of the position of a transducer head relative to a recording medium, sensing a time-based servo pattern on the recording medium with the transducer head and performing a fine adjustment of the position of a transducer head relative to a recording medium as a function of the sensed time-based servo pattern. A system implementing this method may employ a head actuator and a servo controller that cooperate to bring the transducer head proximate to the desired data track.
The method may also include commencing a timing interval and writing to a data track on the recording medium during the timing interval. In addition, the method may include suspending writing to a data track when the timing interval expires. In this manner, a transducer head that is writing to a data track in the medium will be less likely to overwrite a time-based servo pattern.
In a further embodiment, the invention presents a system. The system comprises a transducer head that reads data from data tracks on a recording medium, a servo controller and a head actuator. The servo controller and head actuator perform a coarse adjustment of the position of the transducer head relative to the recording medium. The servo controller and the head actuator cooperate to perform a fine adjustment of the position of the transducer head as a function of a servo pattern sensed by the transducer head.
In an additional embodiment, the invention presents a recording medium having a servo pattern. The servo pattern comprises a first servo line, a second servo line and a third servo line. The first servo line is a substantially straight line, the second servo line is a substantially stra
Johnson Douglas W.
Molstad Richard W.
Richards Durkee B.
Davidson Dan I.
Hudspeth David
Imation Corp.
Levinson Eric D.
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