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Identification of laterally positioned servo bands employing differentiating characteristics of servo patternsIdentification of laterally positioned servo bands employing differentiating characteristics of servo patterns description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20050286158, Identification of laterally positioned servo bands employing differentiating characteristics of servo patterns. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates to separate longitudinal servo bands which are laterally positioned on a linear data storage tape, and, more particularly, to identification of the servo bands for independent addressability. BACKGROUND OF THE INVENTION [0002] Linear data storage tape comprises a medium for storing large amounts of data, and typically comprises a plurality of data tracks that extend longitudinally along the tape. A common example comprises magnetic tape media, and a less common example comprises optical tape media. A tape head is employed for reading and/or writing data on the data tracks, and is typically shared between various data tracks or groups of data tracks, and is moved between tracks or groups of tracks in the lateral direction of the tape. In magnetic tape media, the tape head typically comprises a number of separate elements which read and/or write data with respect to a number of parallel tracks, and is provided with one or more separate servo read transducers, which are laterally offset from the read and/or write elements, so as to track follow a servo band and cause the read and/or write elements of the tape head to be guided along the data track or tracks. In optical tape media, the optical servo may be associated with an individual data track or a with a separate servo track. [0003] One type of servo system for linear data storage tape is one in which separate servo bands are laterally positioned on the linear data storage tape. Each of the servo bands provides the servo guidance for a group of data tracks, and the servo transducer of the tape head is repositioned laterally within a servo band so the read and/or write elements access different data tracks, and is repositioned laterally to another servo band to access still further data tracks. In one example, the servo bands are spaced apart and the data tracks are located between the servo bands. To insure that the servoing is precise, two servo heads may be provided at either end of the tape head, straddling the data read and/or write elements. The lateral positioning may be obtained from either or both servo bands. The servo bands are encoded with essentially identical patterns for determining lateral position, such that the bands are substantially indistinguishable. [0004] The lateral positioning of the tape head is typically accomplished by actuators, which may have mechanical or electromechanical components. Once the proper lateral positioning of the tape head has been accomplished, as the servo information being sensed by the servo transducer indicates, minor adjustments of the head to follow lateral movement of the tape or of the tracks on the tape may be made. During track following, sticking or other failure of the mechanical or electromechanical components can be ascertained from failure of the sensed servo information to show any correction. Similarly, lateral repositioning of the tape head to different tracks within the same servo band is accomplished by a continuous adjustment of position within the servo band. Hence, any sticking or other failure of the mechanical or electromechanical components can be ascertained by failure of the sensed servo information to show the desired movement. [0005] However, the lateral repositioning of the head between the servo bands is typically conducted by a coarse actuator, which may have mechanical or electromechanical components, such as a stepper motor, and which typically operates in open loop without feedback. Thus, as the tape head is repositioned between the servo bands, there is no feedback from the servo information to indicate that the switch from one servo band to any other servo band was successful, and, if the servo bands are substantially indistinguishable, at the supposed completion of the lateral movement, the tape head may be positioned at the wrong servo band, and the servo information will not indicate an error. [0006] One way of determining whether the lateral movement has caused the tape head to be positioned at the correct servo band, is to provide a separate "independent" sensor, for example, that determines the approximate lateral position of the head with respect to the tape. Such an independent sensor may comprise a coarse optical sensor that measures the physical position of the head. Such a coarse sensor cannot be used for track following, but provides a backup to the actual servo system. Such extra sensors add cost to a tape drive, which is always undesirable, if the extra cost can be avoided. Another example is shown by U.S. Pat. No. 6,169,640, in which timing based servo bands are longitudinally displaced or offset from each other, such that by simultaneously sensing two adjacent servo bands allows the servo system to determine longitudinal offset between servo bands, from which the data band location of the tape head can be determined. The system, however, requires that both servo bands be sensed simultaneously in order to establish a differentiation and make a determination. SUMMARY OF THE INVENTION [0007] The present invention comprises, in one embodiment, a linear data storage tape having servo information comprising a plurality of separate servo bands of patterns of detectable transitions positioned longitudinally along the linear data storage tape, at least one of which detectable transitions is non-parallel to another detectable transition in the pattern, and the separate servo bands positioned laterally across the linear data storage tape; and the patterns of the separate servo bands are laterally aligned, and at least one of the patterns of a separate servo band having at least one differentiating characteristic with respect to at least one of the laterally aligned patterns of another of the separate servo bands. The differentiating characteristic allows identification of the separate servo bands. [0008] The differentiating characteristic may comprise differing azimuthal orientations of the continuously longitudinally variable detectable transition of the laterally aligned patterns of the separate servo bands. In one example, the continuously longitudinally variable detectable transitions are inverted in the lateral direction. [0009] Where the laterally aligned patterns comprise a plurality of gaps between the detectable transitions; the differentiating characteristic may comprise variations in the gaps of the laterally aligned patterns of the separate servo bands, the variations in the gaps comprising at least one expanded gap offset by at least one narrowed gap in a pattern, such that the separate patterns of the separate servo bands maintain the lateral alignment. [0010] The differentiating characteristic may comprise variations in the number of the detectable transitions of the laterally aligned patterns of the separate servo bands. For example, where the laterally aligned patterns comprise at least one gap between the detectable transitions, the variations in the number of the detectable transitions of the laterally aligned patterns of the separate servo bands, may be offset by corresponding variations in the number of the gaps, such that the separate patterns of the separate servo bands maintain the lateral alignment. [0011] The differentiating characteristic may comprise variations in stripe width, comprising the longitudinal distance between sets of sequential alternating opposite polarity detectable transitions; or may comprise reversed polarities of stripes, comprising the sets of sequentially alternating opposite polarity detectable transitions. Lateral alignment, if any, is independent of the variations in width or reversal of polarities. [0012] Magnetic tape cartridges with the differentiating characteristic(s), servo writers, methods for providing the differentiating characteristic(s), and servo readers and tape drives for reading the servo information having the differentiating characteristic(s) are also provided. [0013] If lateral alignment of the separate patterns is not necessary, in one embodiment, where the patterns of detectable transitions are positioned longitudinally along the linear data storage tape, the detectable transitions comprising at least one continuously longitudinally variable detectable transition that extends in the lateral direction of the separate servo band, and is non-parallel to another detectable transition in the pattern; and the separate servo bands are positioned laterally across the linear data storage tape; at least one of the patterns of a separate servo band has differing azimuthal orientations of at least one continuously longitudinally variable detectable transition with respect to at least one of the patterns of another of the separate servo bands. For example, the differing azimuthal orientations may comprise inverting the continuously longitudinally variable detectable transition in the lateral direction with respect to at least one of the patterns of another of the separate servo bands. Where at least one continuously longitudinally variable detectable transition comprises a straight line that is slanted in the lateral direction, the differing azimuthal orientations may comprise differing azimuthal orientations of the slant of the continuously longitudinally variable detectable transition with respect to at least one of the patterns of another of the separate servo bands. [0014] In a further embodiment, if lateral alignment of the separate patterns is not necessary, and the patterns comprise at least one gap between the non-parallel detectable transitions; and the separate servo bands are positioned laterally across the linear data storage tape; at least one of the patterns of a separate servo band has variations in the gap of the pattern with respect to at least one of the patterns of another of the separate servo bands. For example, where the detectable transitions of a pattern are arranged with at least one of the detectable transitions in one orientation, and at least one detectable transition in a non-parallel orientation with respect to the one orientation, having a first gap therebetween, and the patterns comprise at least a second gap between the pattern and a sequentially adjacent pattern; and wherein the variations in the gap of the patterns of the separate servo bands comprises an expanded one of the first gap and/or the second gap, and a narrowed one of the first gap and/or the second gap. In another example, where the detectable transitions of a pattern are arranged in a first burst of at least one of the detectable transitions in a first azimuthal orientation, a second burst of at least one of the detectable transitions in a second azimuthal orientation, a third burst of at least one of the detectable transitions in the first azimuthal orientation, and a fourth burst of at least one of the detectable transitions in the second azimuthal orientation, and first gaps separating the first and the second bursts and separating the third and the fourth bursts, and second gaps separating the second and the third bursts and separating a sequentially adjacent pattern; and the variations in the gap of the patterns of the separate servo bands comprises an expanded one of a set of the first gaps and a set of the second gaps and narrowed one of a set of the second gaps and a set of the first gaps. This has the same effect as though one of the servo bands was offset laterally a small amount, and added to at one side and truncated at the opposite side, such that the servo system can easily adjust to either band. [0015] In another embodiment, if lateral alignment of the separate patterns is not necessary, and the patterns comprise detectable transitions positioned longitudinally along the linear data storage tape, at least one of which detectable transitions is non-parallel to another detectable transition in the pattern; and the separate servo bands positioned laterally across the linear data storage tape; at least one of the patterns of a separate servo band has variations in the number of the detectable transitions of the pattern with respect to at least one of the patterns of another of the separate servo bands. Additionally, for example, where at least one of the patterns of the separate servo bands comprises at least one gap between the detectable transitions, at least one of the patterns of a separate servo band additionally comprises variations in the number of the gaps with respect to at least one of the patterns of another of the separate servo bands. As another example, the variations in the number of the detectable transitions of the patterns of the separate servo bands, corresponds to the variations in the number of the gaps. Alternatively, the patterns may additionally comprise variations in the spacing between the detectable transitions. [0016] Magnetic tape cartridges, servo writers, methods, and servo readers and tape drives for reading the servo information are also provided for these embodiments. [0017] For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0018] FIG. 1 is a schematic representation of a tape head and a segment of a linear data storage tape with a plurality of separate servo bands in accordance with the present invention; [0019] FIG. 2 is a representation of a servo transducer as it tracks one of the servo bands of FIG. 1, along with a representation of the servo output signal it generates and the corresponding signal intervals; [0020] FIG. 3 is a representation of patterns of two separate servo bands of FIG. 1, having an embodiment of differentiating characteristics with respect to each other, in accordance with the present invention, comprising differing azimuthal orientations of continuously longitudinally variable detectable transitions of the patterns of the separate servo bands, in which the transitions are inverted; Continue reading about Identification of laterally positioned servo bands employing differentiating characteristics of servo patterns... 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