Patent Application
20100073808
The present disclosure relates generally to position sensing in discrete track recording, and more particularly to position sensing in discrete track recording using groove modulation.
Discrete track media (DTM) includes patterned data tracks that can be used by a servo system to align a read/write head to particular data tracks. Unlike perpendicular and longitudinal magnetic recording in which data track trajectories could be defined independently of servo-pattern trajectories, in DTM recording, it is desirable that both the servo pattern trajectories and the data pattern trajectories match. Unfortunately, the servo position information may not be well-aligned to the data tracks.
Embodiments described below provide solutions to these and other problems, and offer other advantages over the prior art.
In a particular embodiment, a storage system is disclosed that includes a discrete track media having a plurality of concentric data tracks to store data and including a respective plurality of non-magnetic regions to separate adjacent data tracks. The non-magnetic regions include encoded position information. The storage system further includes a controller adapted to adjust a position of a read/write head relative to a center of a particular track based on the encoded position information.
In another particular embodiment, a method is disclosed that includes detecting first and second position information encoded at first and second grooves adjacent to a particular data track of a discrete track media and determining a position error of a read/write head relative to a center of the particular data track based on the first and second position information. The method further includes adjusting the position of a read/write head toward the center of the particular data track based on the determined position error.
In still another particular embodiment, a recording medium includes a plurality of patterned data tracks to store data and a respective plurality of non-magnetic regions to store servo position information, which can be used to determine a servo position error. Each data track of the plurality of patterned data tracks is separated from adjacent data tracks by at least one non-magnetic region.
Other features and benefits that characterize embodiments will be apparent upon reading the following detailed description and review of the associated drawings.
Servo patterns that include the first and second wedges 104 and 108 include only direct-current (DC) information. During fabrication, it may not be possible to selectively flip bits. Nevertheless, a DC-erased disc should be capable of providing a signal that can be used by a servo controller for positioning an associated read/write head. However, a DC-erased pattern can reduce readback signal amplitude from the first and second “servo burst” information 124 and 128 by a factor of two and can create transients as the AC-coupled read/write head moves from the first portion 106 across the servo wedge 108 to the second portion 116, for example. Such transients can be mitigated by re-polarizing the servo pattern during certification, but such re-polarization can increase the factory time, by at least 4n revolutions, where n represents a number of tracks to be written.
In a particular instance, a trajectory of the servo patterns may not be aligned with the data pattern trajectory. The servo pattern is written in separate passes from the data tracks, and the trajectory written to the data tracks can vary from the trajectory (position information) written to the servo tracks. The zap-type servo fields (i.e., the first and second continuous media regions 114 and 118) can be used to correct for such misalignment. To perform such correction, the read/write head must measure offsets (Z1 and Z2), which may not be trivial. Trajectory corrections using such offsets can only occur at the servo update rate, which means that high frequency trajectory deviations may be ignored at the expense of signal-to-noise ratio (SNR). Alternatively, a servo update rate can be increased by providing more servo wedges, which reduces a format efficiency of the discrete track media 100.
In a particular embodiment, the first, second, third, and fourth servo position information may be encoded using frequency modulation, phase modulation, or any combination thereof. In another particular embodiment, the first adjacent groove 214 can include servo position information that is encoded with a first frequency and the second adjacent groove 216 can include servo position information that is encoded with a second frequency. In a particular example, the frequency encoding may follow a pattern that alternates between two frequencies or that uses a repeating pattern of three or more frequencies. In another particular example, each groove may be encoded with servo position information using a unique frequency. In still another particular embodiment, instead of or in addition to using frequency modulation, the servo position information can be encoded using phase modulation, by applying alternating phases, patterns of phases, or unique phases to the multiple grooves.
In a particular example, a storage device can include a controller that is adapted to determine a position error of an associated read/write head relative to a center of a recording track, such as the first data track 204, based on a difference in relative amplitudes of the readback signals associated with the first and second servo position information.
A particular advantage provided by encoding the servo position information into the grooves between adjacent data tracks, such as the grooves 214 and 216, is that trajectory corrections for the read/write head can be made at a much higher frequency than traditional servo wedge (zap-type field) adjustments, allowing the controller to correct for higher-order pattern distortions. Further, the groove-modulation technique eliminates the need for traditional servo patterns and allows for generation of positioning information in the same passes that define the data tracks resulting in improved servo track position information alignment. Further, format efficiency can be improved by removing servo fields altogether.
In a particular embodiment, the first and second servo position information 304 and 306 are encoded at different frequencies or different phases. The third servo position information 310 can be encoded at the same frequency or phase as the first servo position information 304 if the system knows which track the head is on, which would be the case if traditional servo preambles were included. In an alternative embodiment, the third servo position information 310 can be encoded at a different frequency or phase from the first servo position information 304. In a particular example, each groove may include servo position information that is encoded at a unique frequency or phase. In another particular example, a pattern of frequencies or phases may be used in repeating blocks to encode the servo position information. In still another particular example, multiple frequencies can be used such that any combination of two frequencies from adjacent grooves can uniquely identify a particular track.
In a particular example, the first servo position information 304 is encoded at a first groove frequency (f1) and the second servo position information 306 is encoded at a second groove frequency (f2). In this particular example, a controller associated with a read/write head can determine its position to within a half of a width of the data track 302. The read/write head position can be fully determined by examining a relative amplitude of the two modulation frequencies according to the following equation:
where PES represents the position error signal and where the frequencies (F1 and F2) represent the readback response amplitudes at the first and second groove frequencies (f1 and f2). In a particular example, in Equation 1, the sign of the position error signal can alternate from track to track. In a particular embodiment, the servo position information can be patterned into the grooves using frequency or phase modulation to define the information. If advantageous, multiple frequencies can be used to differentiate the read/write head position information by modulating grooves at multiple frequencies (f1, f2, . . . , fn).
In the example shown in
The servo electronics 430 include control circuitry, sometimes referred to as a controller, to determine relative amplitudes of groove modulated servo position information read by the read/write head at the disc head slider 410 to determine a position of the disc head slider 410 relative to a center of a particular data track. In a particular embodiment, each groove includes respective servo position information encoded using frequency modulation, phase modulation, or any combination thereof.
In a particular example, by encoding the servo position information in the same pass that defines the data tracks, the fabrication process is simplified. Further, the servo position information can be more accurate because the servo position information is written when the track is defined. Additionally, by using groove modulation, the servo wedges can be eliminated, improving format efficiency.
In a particular embodiment, by encoding the servo position information in the groove between adjacent data tracks, traditional servo patterns can be eliminated, enhancing format efficiency of the discrete track media. Further, the controller can utilize the position information to adjust for higher-order pattern distortions, which might otherwise be ignored if only zap-type servo bursts were used. In this particular example, overall performance of the servo controller is improved using the encoded servo position information.
In this particular example, it is implicitly assumed that it is known in what direction to proceed. In particular, it is known whether a first track with a first frequency (F1) was on the top or the bottom (from a top view perspective). In a particular example, such information can be known if the information can be determined from a servo preamble or if the frequencies are structured such that lo the combination of a first frequency (F1) and a second frequency (F2) uniquely identifies a track. In a particular embodiment, the pattern of groove frequencies may be controlled such that a particular combination of frequencies uniquely identifies a particular track.
In conjunction with the systems, methods and discrete track recording media described above with respect to
It is to be understood that even though numerous characteristics and advantages of various embodiments of the invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for the discrete track media recording system while maintaining substantially the same functionality without departing from the scope and spirit of the present invention. In addition, although an embodiment described herein is directed to a disc drive system having a discrete track media patterned with data tracks and adjacent grooves including servo positioning information, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other discrete track positioning systems, without departing from the scope and spirit of the present invention.
