JP5080379B2 - Magnetic tape unit - Google Patents

Description

  The present invention relates to a magnetic tape device using a magnetic tape as an information medium such as a data storage system for a computer.

  Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc. Especially in the field of data backup tapes, recording capacity of several TB per volume is accompanied by the increase in capacity of hard disks to be backed up. Has been commercialized. Also, in order to cope with further increase in the capacity of hard disks in the future, it is essential to increase the capacity of backup tapes.

  In order to increase the capacity of the magnetic tape, for example, there is a method of reducing the thickness of the magnetic tape. In such a method, the tape length per reel is not increased without increasing the winding diameter of the magnetic tape with respect to the reel. The recording capacity can be increased by increasing the length.

  On the other hand, the magnetic tape device performs tracking servo so that the magnetic head can trace a target track on the magnetic tape. The tracking servo system includes a magnetic servo system and an optical servo system. The magnetic servo system is a system in which a servo signal is magnetically recorded on a magnetic layer of a magnetic tape, and servo tracking is performed by magnetically reading the servo signal. The optical servo system is a system in which a servo signal composed of a concave array is formed on a back coat layer of a magnetic tape by laser irradiation or the like, and the concave array is optically read to perform servo tracking.

  With these servo systems, when recording data on the magnetic tape or reproducing data from the magnetic tape, even if the position of the magnetic tape fluctuates in the width direction relative to the magnetic head, the magnetic head is recorded on the recording track. Can be followed. Specifically, first, a servo signal recorded on a magnetic tape is read by a servo head. Next, PES (Position Error Signal) is calculated based on the read servo signal. Next, the position of the magnetic head unit (including the servo head, the data recording head, and the data reproducing head) in the width direction of the magnetic tape is controlled based on the calculated PES, and the data recording head or the data reproducing head is controlled. To follow the target data track. As a result, information can be accurately recorded on the magnetic tape, and information recorded on the magnetic tape can be accurately reproduced.

As an example of the above servo system, Patent Document 1 discloses a timing-based servo system. In the timing-based servo system, servo signals are recorded on the magnetic tape in a pattern inclined with respect to the width direction of the magnetic tape. The head position is recognized from the time interval of the peak of the reproduced waveform when the servo signal is reproduced.
JP-A-8-309442

  However, in the conventional configuration, if the thickness of the magnetic tape is reduced in order to increase the recording capacity of the magnetic tape, the thickness of the magnetic layer is also reduced, and the servo signal output and the S / N ratio are reduced. Therefore, the accuracy of the tracking servo is lowered. For example, since a servo signal conforming to the LTO (Linear Tape Open) standard has a considerably long wavelength, the servo signal output and the S / N ratio are lowered when the magnetic layer is thinned.

  An object of the present invention is to provide a magnetic tape device capable of suppressing a decrease in servo signal output and S / N ratio even when a magnetic layer of the magnetic tape is thinned.

The magnetic tape device of the present invention is a magnetic tape device capable of reading a servo stripe recorded with an inclination in the longitudinal direction of the magnetic tape with a servo head and executing tracking servo, and the servo reproduced by the servo head. N delay means connected in series for delaying a signal for a predetermined time; servo signals reproduced by the servo head; and N servo signals output from each of the N delay means; Adding means, signal processing means for generating tracking information from the servo signal output from the adding means, and delay time control means for setting a delay time in the delay means, and the interval between the servo stripes. W, wherein when the transport speed of the magnetic tape is V, the servo Stora delay time D of the N delay means, as D = W / V And controls to match the period of the flop.

  According to the present invention, the servo signal output and the S / N ratio can be improved even when the magnetic layer of the magnetic tape is thinned.

(Embodiment)
[1. Configuration of magnetic tape unit]
FIG. 1 is a block diagram showing the configuration of the magnetic tape device according to the present embodiment.

  In FIG. 1, a head unit 1 is arranged so as to be movable in the width direction (arrow Y direction) of the magnetic tape by an actuator (not shown), and is included in the data head group 12 when performing tracking servo on the magnetic tape. Movement of the data head is controlled in the width direction (arrow Y direction) of the magnetic tape so that a predetermined data track can be traced. The head unit 1 includes a first servo head 11, a data head group 12, and a second servo head 13.

  The first servo head 11 reads a servo pattern recorded on the magnetic tape and outputs a servo signal based on the read servo pattern. A servo signal output from the first servo head 11 is sent to the preamplifier 2.

  The data head group 12 includes eight data heads, and can read a data pattern recorded on a magnetic tape or form a data pattern on a magnetic tape. In the present embodiment, the data head group 12 is composed of eight data heads, but this number is an example, and for example, it may be composed of sixteen.

  The second servo head 13 can read the servo pattern recorded on the magnetic tape. Since the second servo head 13 performs the same operation as the first servo head 11, detailed description thereof is omitted.

  The preamplifier 2 amplifies the servo signal output from the first servo head 11. The servo signal output from the preamplifier 2 is sent to the first delay circuit 3a and the adder circuit 5.

  The delay circuits 3a to 3c are connected in series with each other. The first delay circuit 3a delays the servo signal sent from the preamplifier 2 by time D and outputs it. The servo signal output from the first delay circuit 3 a is sent to the second delay circuit 3 b and the adder circuit 5. The second delay circuit 3b delays the servo signal output from the first delay circuit 3a by time D and outputs it. The servo signal output from the second delay circuit 3 b is sent to the third delay circuit 3 c and the adder circuit 5. The third delay circuit 3c delays the servo signal output from the second delay circuit 3b by a time D and outputs the servo signal. The servo signal output from the third delay circuit 3 c is sent to the adder circuit 5. The delay time D in the delay circuits 3 a to 3 c is set in the delay time control circuit 4.

  The delay time control circuit 4 calculates the delay time D based on the interval W between the servo stripes formed on the magnetic tape, the transfer speed V of the magnetic tape, and the following formula 1.

D = W / V (Formula 1)
The adder circuit 5 adds the servo signals output from the preamplifier 2 and the delay circuits 3a to 3c. The servo signal added by the adding circuit 5 is sent to the signal processing circuit 6.

  The signal processing circuit 6 generates a PES (Position Error Signal) that is tracking information based on the servo signal output from the adder circuit 5. A method for generating PES will be described later.

[2. (Servo signal playback operation)
FIG. 2A is a diagram schematically showing servo stripes formed on the magnetic tape. As shown in FIG. 2 (a), the servo stripe conforming to the LTO standard is composed of stripes C1 to C4 inclined in the first direction with respect to the longitudinal direction of the magnetic tape as shown in FIG. 2 (a). The first stripe group 21, the second stripe group 22 composed of stripes D1 to D4 inclined in the second direction which is the opposite direction of the first direction, and the stripe A1 inclined in the first direction. To A5 and a fourth stripe group 24 composed of stripes B1 to B5 (stripes B2 to B5 are not shown) inclined in the second direction. . The first stripe group 21 and the second stripe group 22 are each composed of four stripes, and the third stripe group 23 and the fourth stripe group 24 are each composed of five stripes. The first stripe group 21 and the third stripe group 23 are inclined at the same angle in the same direction, and the second stripe group 22 and the fourth stripe group 24 are inclined at the same angle in the same direction.

  FIG. 2B shows the waveform of the servo signal reproduced by the first servo head 11. FIG. 2C shows the waveform of the servo signal output from the first delay circuit 3a. FIG. 2D shows the waveform of the servo signal output from the second delay circuit 3b. FIG. 2E shows the waveform of the servo signal output from the third delay circuit 3c. 2B to 2E show servo signals obtained when the first servo head 11 is tracing on the broken line L2 in FIG. Also, between the servo signal shown in FIG. 2 (b) and the servo signal shown in FIG. 2 (c), between the servo signal shown in FIG. 2 (c) and the servo signal shown in FIG. 2 (d), FIG. There is a time D difference between the servo signal shown in (d) and the servo signal shown in FIG. FIG. 2F shows the waveform of the servo signal output from the adder circuit 5.

  The servo signal reproduced by the first servo head 11 (see FIG. 2B) is input to the first delay circuit 3a and the addition circuit 5 via the preamplifier 2. Based on the delay time D set by the delay time control circuit 4, the first delay circuit 3a delays and outputs the servo signals output from the preamplifiers 2a to 2c. The servo signal output from the first delay circuit 3a (see FIG. 2C) is input to the second delay circuit 3b and the adder circuit 5. The second delay circuit 3b delays and outputs the servo signal output from the first delay circuit 3a based on the delay time D set by the delay time control circuit 4. The servo signal (see FIG. 2D) output from the second delay circuit 3b is input to the third delay circuit 3c and the adder circuit 5. The third delay circuit 3 c delays the servo signal output from the second delay circuit 3 b based on the delay time D set by the delay time control circuit 4 and outputs the delayed signal to the adder circuit 5. Therefore, the four servo signals shown in FIGS. 2B to 2E are input to the adding circuit 5.

  The adder circuit 5 adds the servo signals shown in FIGS. 2B to 2E to generate the servo signal shown in FIG. As shown in FIG. 2 (f), the servo signal output from the adder circuit 5 indicates that the first servo head 11 is the m-th (m = 1 to 4) stripe (this embodiment) in each stripe group. Then, m = 4, that is, the level becomes the highest at the timings T1, T2, and T3 when the stripes C4, D4, and A4) are read. The servo signal level at this time is about four times the servo signal level shown in FIGS.

  The signal processing circuit 6 calculates PES based on the servo signal output from the adder circuit 5.

  Specifically, the signal processing unit 6 compares the servo signal output from the adder circuit 5 (see FIG. 2 (f)) with a reference value having a predetermined threshold level TH to perform peak detection, and detects the threshold level. Pulses synchronized with servo signals exceeding TH (pulses synchronized with timings T1, T2, and T3) are generated.

  Next, the signal processing circuit 6 calculates PES. In the PES, the inclination angle of the stripe is Y (Y = 6 ° in the present embodiment), the nth (n = 1 to 4) stripes in the first servo stripe group 21 and the n in the second servo stripe group 22. The distance at the center (one-dot chain line L1) in the servo stripe width direction with the nth (n = 1 to 4) stripe is cd (cd = 50 μm in the LTO of the present embodiment), and the first servo head position at that time The distance between the nth (n = 1 to 4) stripe in the stripe group 21 and the nth (n = 1 to 4) stripe in the second stripe group 22 is expressed as CD (servo stripe on the servo head). 2 varies depending on the position, for example, the distance between the stripes C4 and D4 on the broken line L2 in FIG. 2, the nth (n = 1 to 4) stripes and the third stripes in the first stripe group 21. When the distance from the n-th (n = 1 to 4) stripe in the stripe group 23 is CA, it can be calculated by the following mathematical formula 2. The distances cd, CD, and CA are measured from the pulses generated based on the servo signal in the signal processing unit 6.

PES = (cd− (CD / CA) × 100) / 2 tan Y (Formula 2)
The PES is calculated for each predetermined period based on Equation 2 above. The calculated PES is converted into a drive current for driving an actuator (not shown) and sent to the actuator. The actuator moves the head unit 1 in the width direction of the magnetic tape (arrow Y direction in FIG. 1) based on the drive current. Note that a tracking servo method using a servo signal is well known, and a detailed description thereof will be omitted in this specification.

  When LTM (Lateral Tape Motion) occurs in the magnetic tape, the position of the magnetic tape varies in the tape width direction with respect to the head unit 1 during traveling. FIG. 3A schematically shows servo stripes formed on the magnetic tape, and the thick line in the figure indicates the scanning path of the servo head when the LTM is generated on the magnetic tape. Actually, when the LTM is generated in the magnetic tape, the magnetic tape moves in the width direction. However, for convenience of explanation, the scanning path of the servo head is illustrated as changing in the width direction of the magnetic tape.

  As shown in FIG. 3A, when an LTM having a wavelength shorter than that of the servo frame (200 μm) is generated, the head unit 1 cannot follow the position variation in the width direction of the magnetic tape even if tracking servo is performed. The head scans obliquely with respect to the servo band. When the servo head scans in this way, the peak position of the servo signal shifts as shown in FIGS. 3B to 3E. Therefore, as shown in FIG. 3F, the waveform of the servo signal output from the adder circuit 5 is distorted, and the nth (n = 1 to 4) servo stripes in the first servo stripe group 21; There is a possibility that the distance from the nth (n = 1 to 4) servo stripes in the second servo stripe group 22 cannot be measured. However, since the deviation of the peak position is usually not so large, the PES calculated by the signal processing circuit 6 does not deviate greatly from the correct value.

[3. Effects of the embodiment, etc.]
According to the present embodiment, the waveform of the servo signal output from the first servo head 11 is delayed for a predetermined time by the delay circuits 3 a to 3 c and the delayed servo signal is added by the adder circuit 5. The output level of the servo signal can be quadrupled. In addition, the S / N ratio can be increased twice (√4 times). Thereby, the accuracy of PES can be improved and the amount of off-track can be reduced. That is, according to the present invention, when a servo signal is delayed and added using N delay circuits, the output level of the servo signal becomes (N + 1) times and the S / N ratio becomes √ (N + 1) times. Thereby, the accuracy of PES can be improved and the amount of off-track can be reduced.

In the present embodiment, the number N of delay circuits is “3”, but N ≧ 2 is sufficient. However, when the number of stripes included in one servo stripe group is M,
N = M−1 (Formula 3)
Is a condition. The number M of stripes is composed of servo stripe groups having different numbers of stripes such as LTO standard servo patterns (for example, a servo stripe group including four stripes and five stripes). When there is a servo stripe group), the minimum value is applied.

  In the present embodiment, the servo signal (analog signal) reproduced by the servo head 11 is delayed by the delay circuits 3 a to 3 c and added by the adder circuit 5. It is good also as a structure which performs a process. That is, an analog / digital conversion circuit for digitally converting a servo signal read by a servo head, a delay memory for adding the digital data string in a time series after delaying the digital data string for a predetermined time, and adding A digital / analog conversion circuit that converts a data string into a servo signal that is an analog signal may be included, and the signal processing circuit may generate tracking information (PES) based on the servo signal generated by the digital / analog conversion circuit. .

  Further, the delay circuits 3a to 3c in the present embodiment are an example of the delay means of the present invention. Further, the adding circuit 5 in the present embodiment is an example of the adding means of the present invention. The signal processing circuit 6 in the present embodiment is an example of the signal processing means of the present invention.

  The magnetic tape device of the present invention is useful for a device that performs tracking servo by a time-base servo system.

1 is a block diagram showing the configuration of a magnetic tape device in an embodiment (A) is a schematic diagram showing a configuration of a servo stripe, (b) to (e) are waveform diagrams of a servo signal output from a servo head, and (f) is a waveform diagram of a servo signal output from an adder circuit. (A) is a schematic diagram showing the configuration of the servo stripe, (b) to (e) are waveform diagrams of servo signals output from the servo head when the LTM is generated, and (f) is output from the adder circuit when the LTM is generated. Servo signal waveform diagram

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Head unit 11 1st servo head 2 Preamplifier 3a, 3b, 3c Delay circuit 4 Delay time control circuit 5 Adder circuit 6 Signal processing circuit

Claims (1)

A magnetic tape device that can read a servo stripe recorded with a tilt in the longitudinal direction of a magnetic tape with a servo head and execute tracking servo,
N delay means connected in series for delaying a servo signal reproduced by the servo head for a predetermined time;
Adding means for adding the servo signal reproduced by the servo head and N servo signals output from each of the N delay means;
Signal processing means for generating tracking information from the servo signal output from the adding means;
Delay time control means for setting a delay time in the delay means, when the interval between the servo stripes is W, and the transfer speed of the magnetic tape is V,
The delay time control means includes
A magnetic tape device that controls the delay time D of the N delay means to be equal to the period of the servo stripe , with D = W / V.

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