Determining nonlinearity in written servo patterns
One embodiment includes positioning a magnetic tape head having at least three servo readers such that a first of the readers is located within a first servo band of a magnetic tape, a second of the readers trailing the first reader is located within the first servo band, and a third of the readers is located within a second servo band of the tape. A lateral position of the head is measured, and a head skew angle is measured. The lateral position and the skew angle of the head are varied while recording y-position values of the first and second readers and the skew angles measured using the first and third readers Nonlinearity values are calculated at discrete y-positions over a range of the servo pattern in the first servo band using at least some of the measured y-positions and skew angle measurements. The nonlinearity values are stored and/or output.
1 . A method, comprising:
positioning a magnetic tape head having at least three servo readers such that a first of the readers is located within a first servo band of a magnetic tape, a second of the readers trailing the first reader is located within the first servo band, and a third of the readers is located within a second servo band of the magnetic tape;
measuring a lateral position of the head using a y-position measured from one or more of the readers;
measuring a head skew angle based on positions of the first and third readers relative to servo patterns in the first and second servo bands;
varying the lateral position and the skew angle of the head over at least a portion of the height of at least one of the servo patterns while recording y-position values of the first and second readers and the skew angles measured using the first and third readers;
calculating nonlinearity values at discrete y-positions over a range of the servo pattern in the first servo band using at least some of the measured y-positions and skew angle measurements; and
storing and/or outputting the calculated nonlinearity values.
2 . The method as recited in claim 1 , wherein the lateral position of the head is stepped or ramped across the servo pattern while the skew angle of the head is varied.
3 . The method as recited in claim 1 , comprising using at least some of the measured y-positions and skew angle measurements for determining a value d representing a ratio of a distance between the first and second readers and a distance between the first and third readers.
4 . The method as recited in claim 3 , comprising using at least some of the measured y-positions and skew angle measurements to determine an offset s representing a misalignment distance between the first and second readers in a direction parallel to a longitudinal axis of the tape head.
5 . The method as recited in claim 4 , comprising selecting a fraction of the measured y-position and skew angle values for calculating the nonlinearity values.
6 . The method as recited in claim 5 , comprising using the calculated values of d and s to calculate the nonlinearity values.
7 . The method as recited in claim 1 , comprising selecting a fraction of the measured y-position and skew angle values for calculating the nonlinearity values.
8 . The method as recited in claim 1 , comprising controlling a track following system using averages of at least some of the measured y-positions.
9 . The method as recited in claim 1 , comprising controlling a skew following system using the measured skew angle.
10 . The method as recited in claim 1 , where the servo patterns are timing-based servo (TBS) patterns that comprises bursts of servo stripes.
11 . A magnetic tape cartridge, comprising:
a magnetic tape having a plurality of timing-based servo patterns written thereon;
a housing for at least partially enclosing the magnetic tape; and
a cartridge memory coupled to the housing, the cartridge memory having stored therein unique nonlinearity values calculated by the method of claim 1 .
12 . An apparatus configured to perform the method of claim 1 , the apparatus comprising:
a controller configured to perform the method; and
the magnetic head coupled to the controller.
13 . A computer program product comprising:
one or more computer readable storage media; and
program instructions stored on the one or more computer readable storage media to perform operations comprising:
positioning a magnetic tape head having at least three servo readers such that a first of the readers is located within a first servo band of a magnetic tape, a second of the readers trailing the first reader is located within the first servo band, and a third of the readers is located within a second servo band of the magnetic tape;
measuring a lateral position of the head using a y-position measured from one or more of the readers;
measuring a head skew angle based on positions of the first and third readers relative to servo patterns in the first and second servo bands;
varying the lateral position and the skew angle of the head over the height of at least one of the servo patterns while recording y-position values of the first and second readers and the skew angles measured using the first and third readers;
calculating nonlinearity values at discrete y-positions over the range of the servo pattern in the first servo band using at least some of the measured y-positions and skew angle measurements; and
storing and/or outputting the calculated nonlinearity values.
14 . The computer program product as recited in claim 13 , wherein the lateral position of the head is stepped or ramped across the servo pattern while the skew angle of the head is varied.
15 . The computer program product as recited in claim 13 , comprising program instructions for using at least some of the measured y-positions and skew angle measurements for determining a value d representing a ratio of a distance between the first and second readers and a distance between the first and third readers.
16 . The computer program product as recited in claim 13 , comprising program instructions for using at least some of the measured y-positions and skew angle measurements to determine an offset s representing a misalignment distance between the first and second readers in a direction parallel to a longitudinal axis of the tape head.
17 . The computer program product as recited in claim 16 , comprising program instructions for selecting a fraction of the measured y-position and skew angle values for calculating the nonlinearity values.
18 . The computer program product as recited in claim 17 , comprising program instructions for using the calculated values of d and s to calculate the nonlinearity values.
19 . The computer program product as recited in claim 13 , comprising selecting a fraction of the measured y-position and skew angle values for calculating the nonlinearity values.