Servo signal recording apparatus, information recording apparatus, and tracking servo method

In the apparatus and method of the invention, a servo signal reproduction unit generates a PES from a servo signal reproduced from a magnetic tape, and a frequency conversion unit performs FFT processing of the PES to generate frequency component information. Then, a filter value generation unit generates filter values based on the frequency component information and writes these to a memory. When recording various data signals to the magnetic tape, the filter values are read from the memory and a control filter serving as a notch filter is incorporated into a feedback control for a tracking servo. This enables periodic and narrow-band noise to be removed from a PES, consequently reducing PESs. Accordingly, learning-type optimum notch filter control that allows a magnetic head to follow recording tracks at high speed and with high precision is possible even when the recording track width is reduced and the tape speed is increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a servo signal recording apparatus capable of recording a servo signal to a magnetic tape, and more specifically relates to an information recording apparatus capable of recording a variety of information to a magnetic tape while performing tracking servo control based on the servo signal recorded on the magnetic tape. In particular, the present invention relates to a learning-type optimum notch filter control system adaptable to a data storage system for a computer, and also relates to a recording and reproduction apparatus capable of implementing such a learning-type optimum notch filter control system.

2. Description of Related Art

Magnetic tape has a variety of applications such as audio tape, video tape, and computer tape. Particularly in the field of data backup tapes, magnetic tapes with a recording capacity of 800 GB (giga byte) or more per reel have been commercialized following increases in the capacity of hard disks for backup. High capacity backup tapes have been proposed with the development hereafter of techniques for backing up data exceeding 4 TB (tera byte).

One conceivable method of increasing the capacity of magnetic tape is, for example, to make the magnetic tape thinner to increase the tape length per reel, without increasing the reel diameter of the magnetic tape per reel. Another method involves shortening the recording wavelength of data recorded on the magnetic tape to increase the longitudinal recording density of the magnetic tape. A further method involves reducing the recording track width of the magnetic tape to increase the lateral recording density of the magnetic tape (high recording density technique).

When the recording track width is reduced by employing a high recording density technique for magnetic tape, the magnetic head is unable to accurately follow the recording track due to the lateral motion of the magnetic tape during data recording or reproduction, or the like. If the magnetic head is unable to accurately follow the recording track, errors are more likely to occur in writing information to the magnetic tape or in recording information from the magnetic tape. In view of this, currently, systems that are provided with a servo system using a servo signal recorded to a magnetic layer or a back-coat layer of the magnetic tape during manufacture have become mainstream.

As for servo systems, there is a magnetic servo system and an optical servo system. With the magnetic servo system, a servo signal is magnetically recorded to a magnetic layer of the magnetic tape, and the servo signal is magnetically read to perform servo control. With the optical servo system, a servo signal constituted by a recessed array is formed on a back-coat layer on the magnetic tape with laser irradiation or the like, and the recessed array is optically read to perform servo control.

These servo systems enable the magnetic head to follow the recording track when recording data to a magnetic tape or reproducing data from a magnetic tape, even when the magnetic tape moves laterally relative to the magnetic head. Specifically, the servo signal recorded on the magnetic tape is firstly read with a servo head. Then, according to the read servo signal, the position of a head unit (which includes at least a data recording head and a data reproducing head) along the width of the magnetic tape is controlled so as to allow the data recording head or the data reproducing head to follow the recording track. This enables information to be recorded to the correct position on a magnetic tape, and information recorded on a magnetic tape to be correctly reproduced.

Disclosed in Patent Document 1 (JP H8-30942A) and Patent Document 2 (U.S. Pat. No. 6,226,688) are timing based servo systems. With these timing based servo systems, the servo signal is a pattern that is at an angle relative to the width direction of the magnetic tape. An apparatus compatible with such timing based servo systems confirms the head position from the time intervals between the peaks of the reproduction waveform when the servo signal is reproduced.

Disclosed in Patent Document 3 (JP 2004-86959A) are a difference detector and a set value modification unit. The difference detector detects a difference between the resonance frequency of the head actuator and the center frequency set in the notch filter. The set value modification unit modifies the set value of the center frequency in the notch filter, based on the difference detected by the difference detector.

However, a problem with the techniques disclosed in Patent Documents 1 and 2 is that a PES (position error signal) must be of a lesser amplitude when the recording track width is narrowed following an increase in the information recording density of the magnetic tape. Patent Document 3 discloses a technique for reducing the resonance frequency of the actuator with the notch filter but does not disclose a technique for reducing other factors such as periodic noise, narrow-band noise, and the like.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the present invention to provide a servo signal recording apparatus that enables learning-type optimum notch filter control that allows a magnetic head to follow a recording track at high speed and with high precision even in the case where the recording track width is reduced and the tape speed is increased. Another object of the present invention is to provide an information recording apparatus that enables such learning-type optimum notch filter control, and still another object thereof is to provide a tracking servo method that enables such learning-type optimum notch filter control.

A servo signal recording apparatus of the present invention is capable of recording a servo signal on a servo track of a magnetic tape, and includes a servo signal reproduction unit that reproduces a servo signal recorded on the magnetic tape, a frequency conversion unit that generates frequency component information by applying a Fourier transform to a position error signal generated from the servo signal reproduced by the servo signal reproduction unit, a filter value generation unit that generates a filter value based on the frequency component information generated by the frequency conversion unit, and a recording control unit that writes the filter value generated by the filter value generation unit to a recording medium, wherein the filter value generation unit generates a filter value that enables removal of a periodic noise component included in the frequency component information.

Another servo signal recording apparatus of the present invention is provided with a servo signal recording unit capable of recording a servo signal on a servo track of a magnetic tape, and includes a servo signal reproduction unit that reproduces a servo signal recorded on the magnetic tape, a frequency conversion unit that generates frequency component information by applying a Fourier transform to a position error signal generated from the servo signal reproduced by the servo signal reproduction unit, and a filter value generation unit that generates a filter value based on the frequency component information generated by the frequency conversion unit, wherein the filter value generation unit generates a filter value that enables removal of a periodic noise component included in the frequency component information, and the servo signal recording unit modulates a servo signal based on the filter value generated by the filter value generation unit and records the modulated servo signal to the magnetic tape.

An information recording apparatus of the present invention includes a head unit that includes a data head capable of recording a data signal to a magnetic tape and a servo head capable of reproducing a servo signal recorded on the magnetic tape, the head unit being provided so as to be movable along a width of the magnetic tape, a control unit that calculates a position error signal based on the servo signal reproduced by the servo signal reproduction unit and calculates the amount of travel for the head unit based on the calculated position error signal, and a movement unit that moves the head unit along the width of the magnetic tape, based on the amount of travel calculated by the control unit. The control unit includes a frequency conversion unit that generates frequency component information by applying a Fourier transform to the position error signal generated from the servo signal reproduced by the servo signal reproduction unit, a filter value generation unit that generates a filter value based on the frequency component information generated by the frequency conversion unit, a recording control unit that writes the filter value generated by the filter value generation unit to a recording medium, and a filter that filters the position error signal based on the filter value read from the recording medium. The filter value generation unit generates a filter value that enables removal of a periodic noise component included in the frequency component information.

A tracking servo method of the present invention includes the steps of reproducing a servo signal recorded on a servo track of a magnetic tape, using a servo head, calculating a position error signal based on the servo signal, and performing control so that a head unit moves along the width of the magnetic tape, the head unit including the servo head and a data head capable of recording a digital signal to the magnetic tape based on the position error signal. The tracking servo method further includes the steps of generating frequency component information by applying a Fourier transform to the position error signal, generating a filter value that enables removal of a noise component included in the frequency component information, recording the filter value to a recording medium, and reading out the filter value from the recording medium to filter the position error signal.

The present invention enables periodic noise and narrow-band noise to be removed from the position error signal by incorporating a filter into feedback control, thereby consequently reducing position error signals.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described by way of illustrative embodiments with reference to the drawings.

FIG. 1is a block diagram of a servo signal recording apparatus according to Embodiment 1. The servo signal recording apparatus of Embodiment 1 is an apparatus for recording a servo signal to a pancake-like magnetic tape4wound on a reel1in the process of manufacturing magnetic tapes. In some cases, such an apparatus is called a servo writer.

As illustrated inFIG. 1, the servo signal recording apparatus includes a winding reel2, a motor3, guide rollers5, a controller6, a drive unit7, a pulse generation unit8, a servo signal reproduction unit9, a frequency conversion unit10, a filter value generation unit11, a memory control unit12, a first servo head14, and a second servo head15.

The winding reel2is rotatably driven by the motor3in a direction shown by the arrow A and is capable of winding up the magnetic tape4that is unwound from the reel1mounted on the apparatus of the present invention.

The motor3is drive-controlled by the drive unit7.

The guide rollers5are capable of guiding the magnetic tape4so that the magnetic tape4unwound from the reel1runs at a prescribed position.

The controller6controls the period and amplitude of pulses generated by the pulse generation unit8. The controller6outputs to the drive unit7an instruction to drive the motor3.

The pulse generation unit8generates pulses under the control of the controller6and outputs the generated pulses to the first servo head14. The first servo head14generates a servo pattern at a prescribed position on the magnetic tape4, based on the pulses output from the pulse generation unit8.

The servo signal reproduction unit9reproduces a servo signal based on an electric signal obtained by reading the servo pattern on the magnetic tape4with the second servo head15.

The frequency conversion unit10converts a PES obtained from the servo signal reproduced by the servo signal reproduction unit9into frequency components by fast-Fourier-transform processing (hereinafter referred to as FFT processing).

The filter value generation unit11analyzes the frequency component output from the frequency conversion unit10and generates the values of a notch filter, which will be described later.

The memory control unit12controls the writing of information to a memory13. Under the control of the memory control unit12, the filter values generated by the filter value generation unit11are written to the memory13.

Firstly, the controller6outputs an instruction to start driving the motor3, to the drive unit7. With the instruction from the controller6, the drive unit7starts actuating the motor3. When started up, the motor3rotatably drives the winding reel2in the direction shown by the arrow A and transports the magnetic tape4in the direction shown by the arrow B. This allows the magnetic tape4unwound from the reel1to slide into contact with the first servo head14and the second servo head15while being guided on the guide rollers5and thereby be wound on the winding reel2. The magnetic tape4wound in a pancake shape on the reel1has an overall length of, for example, approximately 10000 m. The transport speed of the magnetic tape4is, for example, about 10 m/sec.

During the transport of the magnetic tape4, on the other hand, the controller6outputs an instruction to generate pulses to the pulse generation unit8. The pulse generation unit8outputs pulses having a prescribed period and prescribed amplitude, based on the instruction from the controller6. The first servo head14is energized and un-energized repeatedly according to the pulses output from the pulse generation unit8, and magnetizes a servo track of the magnetic tape4to form a servo pattern. The servo pattern is formed at an angle relative to a direction along the length of the magnetic tape4. The servo pattern includes a first strip and a second strip. The first strip slants in a first direction. The second strip slants in a direction opposite to the slanting direction of the first strip. The first and second strips form approximately an inverted V-shaped configuration with an open apex.

Through the above operations, a servo signal is recorded on the magnetic tape4. However, when such a magnetic tape that has recorded a servo signal through the above operations is mounted and transported on an information recording apparatus (what is called a “drive”) that is capable of recording and reproducing a variety of data, periodic noise may be superimposed on a PES. One example of such periodic noise in Embodiment 1 is noise based on slitter components. The phrase “noise based on slitter components” as used herein refers to noise that occurs due to the curvature of the edge of a magnetic tape when running a magnetic tape that is produced from a pancake with a curved edge in an information recording apparatus; the curved edge of the pancake being formed in a slitting step of cutting up a bulk roll that is to be the basis of the magnetic tape4. Such edge distortion of a magnetic tape caused by a slitter has a periodicity along the length of the magnetic tape. From this, it can be said that the noise based on slitter components has a periodicity along the length of the magnetic tape.

The feature of Embodiment 1 is that, after recording a servo signal on a magnetic tape4with a servo signal recording apparatus, the servo signal on the magnetic tape4is reproduced, and filter values that enable removal of periodic noise included in a PES obtained from the servo signal is written to a memory or the like. Before recording a variety of data to the magnetic tape4, the information recording apparatus firstly reads out filter values from the memory, filters a PES so as to remove periodic noise therefrom, and performs tracking servo control based on the periodic-noise-free PES. Now, the operation of the servo signal recording apparatus that learns a PES obtained from a servo signal is described.

FIG. 2shows a procedure for the operation of the servo signal recording apparatus according to Embodiment 1.

Firstly, the reel1with the magnetic tape4wound in a pancake shape is mounted on the servo signal recording apparatus, and the end of the magnetic tape4is wound on the winding reel2on the servo signal recording apparatus side. The winding reel2is then rotatably driven by the motor3, starting transportation of the magnetic tape4. Then, pulses having a prescribed period are input into the first servo head14and a servo signal is recorded on a servo track of the magnetic tape4(in step S1).

Then, the second servo head15reads a servo pattern recorded on the magnetic tape4and outputs an electric signal. The servo signal reproduction unit9reproduces a servo signal based on the electric signal output from the second servo head15(in step S2).

Then, the servo signal reproduction unit9calculates a PES based on the reproduced servo signal. Specifically, a PES is calculated from Equation 1 as follows. In Equation 1, a first strip A1that slants in a first direction, a second strip B1that slants in a second direction, a third strip C1that slants in the first direction, and a fourth strip D1that slants in the second direction, are formed in the order mentioned along the length of the magnetic tape4:
PES=(AB−(A1B1/A1C1)×100)/2×tanY(Equation 1)
In Equation 1, “Y” is the tilt angle of the strips formed on a servo track of the magnetic tape4(in Embodiment 1, Y=6°). “AB” is the distance between the first strip A1and the second strip B1at the center across the width of the tape (in Embodiment 1, AB=50 μm). “A1B1” is the distance between the first strip A1and the second strip BP. “A1C1” is the distance between the first strip A1and the third strip C1. The PES is calculated using the above equation at prescribed periods. Such calculated PESs are sent in succession to the frequency conversion unit10(in step S3).

Note that the recording (S1) of a servo signal to the magnetic tape4with the first servo head14and the reproduction (S2) of a servo signal recorded on the magnetic tape4with the second servo head15may be performed simultaneously. Or another configuration is also possible in which, after a servo signal is recorded from the beginning to end of the magnetic tape4, the magnetic tape4is rewound to the beginning and then runs from the beginning for reproduction of the servo signal.

Then, the frequency conversion unit10performs FFT processing of the PES sent from the servo signal reproduction unit9to convert the PES into frequency components. At this time, such FFT processing is performed for every turn of the reel1.

FIG. 3shows analysis results obtained through such FFT processing. As indicated by the broken line inFIG. 3, it can be found that the values increase at certain frequency bands (in the example ofFIG. 3, in the vicinities of 20 Hz, 30 Hz, and 50 Hz). Usually there is no periodicity in the occurrence of a noise component due to the deterioration of a PES caused by LTM (Lateral Tape Motion). However, since the curvature of the edge of the magnetic tape4caused by the accuracy of slitting, as described above, has a periodicity, the values each obtained by converting a PES into frequency components concentrate at certain frequency bands as illustrated inFIG. 3. The frequency components of a PES calculated by the frequency conversion unit10are sent to the filter value generation unit11(in step S4).

Then, the filter value generation unit11generates the values of a notch filter based on the frequency components generated by the frequency conversion unit10. Specifically, the center frequency, the notch width, and the notch depth of a notch filter mounted on the information recording apparatus are calculated. The notch filter mounted on the information recording apparatus performs an arithmetic computation expressed by Equation 2.
GN(s)=(S2+2dζωns+ωn2)/(S2+2ζωns+ωn2)  (Equation 2)
The filter value generation unit11calculates the center frequency ωn, the notch width ζ, and the notch depth d that enables the removal of the periodic noise illustrated inFIG. 3. The center frequency ωn, the notch width ζ, and the notch depth d are at values that enable removal of the periodic noise illustrated inFIG. 3.

FIG. 4shows the filter characteristics generated by the filter value generation unit11. By providing the information recording apparatus with such a notch filter that is generated based on the filter characteristics as illustrated inFIG. 4, PESs caused by periodic noise can be reduced in amplitude as shown in the characteristics indicated by the solid line inFIG. 3(in step S5).

Next, the memory control unit12writes the filter values generated by the filter value generation unit11to the memory13. Note that the memory13is a semiconductor memory mounted on a cartridge that contains the magnetic tape4. The memory13is written with, in addition to the filter values, a variety of information on the magnetic tape4, a travel history of the information recording apparatus, and the like (in step S6).

The magnetic tape4that has recorded a servo signal through the above steps is cut to a prescribed length (e.g., 820 m), wound on the reel, and incorporated into a cartridge. The memory13is also mounted on the cartridge. With the above processing, a magnetic tape cartridge is completed.

In wiring a variety of data to a magnetic tape in such a magnetic tape cartridge that is produced according to Embodiment 1, firstly, the information recording apparatus reads out the filter values written in the memory13to generate a notch filter. This enables removal of periodic noise that occurs when recording a variety of data on the magnetic tape4.

Embodiment 1 enables the acquiring of periodic noise by reproducing a servo signal recorded on the magnetic tape4, calculating a PES from the reproduced servo signal, and converting the calculated PES into frequency components in the step of writing a servo signal using the servo signal recording apparatus. Further, by generating and writing to the memory13the filter values of a notch filter for reducing acquired periodic noise, the periodic noise in a PES can be removed at the time when the magnetic tape cartridge is mounted on the information recording apparatus and a variety of data is written to the magnetic tape4. This consequently reduces the amplitude of PESs.

Note that while Embodiment 1 describes the configuration in which the filter values generated in the servo signal recording apparatus are written to the memory13, a configuration in which the filter values are included in a servo signal recorded on the magnetic tape4is also possible.

FIG. 5is a block diagram of a servo signal recording apparatus that enables a servo signal to include filter values. The servo signal recording apparatus inFIG. 5is different from that inFIG. 1in that the filter values generated by the filter value generation unit11are input into the pulse generation unit8. The pulse generation unit8modulates the period of pulses that is output to the first servo head14, based on the filter values output from the filter value generation unit11. Usually, the stripes of a servo signal are formed at regular intervals on a magnetic tape; however, by forming the stripes at different intervals with prescribed regularity, the servo signal can have information about filter values.

For instance, with a magnetic tape based on the LTO (Linear Tape Open) standard, five or four stripes that slant in the same direction are considered as a single group, and within the group, the stripes are spaced at different intervals with prescribed regularity. Each group is configured to include two patterns having different intervals of stripes and to have binary information by assigning the value 0 to one of the patterns and the value 1 to the other. Thus, by converting the filter values generated by the filter value generation unit11into digital data with an analog-to-digital converter (not shown) and modulating the pulses generated by the pulse generation unit8based on the digital data, a servo signal that includes information about the filter values can be recorded on the magnetic tape4.

FIG. 6is a block diagram of a recording and reproduction apparatus according to Embodiment 2. As illustrated inFIG. 6, a recording and reproduction apparatus20includes an input terminal21, a recording signal processing unit22, an output terminal23, a reproduction signal processing unit24, a head unit25, a control unit27, an actuator28, and a memory control unit29. The recording and reproduction apparatus20is capable of attaching and detaching a magnetic tape cartridge33. The magnetic tape cartridge33is provided with a cartridge30, a magnetic tape31, and a memory32. The magnetic tape31is wound on a reel mounted within the cartridge30. The memory32is, for example, a semiconductor memory capable of writing and reading information. The memory32is incorporated in the cartridge30. Note that the recording and reproduction apparatus20is also provided with a mechanism for running the magnetic tape31, a control circuit, and the like, which are neither shown nor described herein.

The input terminal21inputs data to be recorded on the magnetic tape31. The data input into the input terminal21is digital data.

The recording signal processing unit22controls the current flowing in a data head25a, based on the digital data input into the input terminal21.

The output terminal23is capable of outputting digital data output from the reproduction signal processing unit24to another circuit or the like.

The reproduction signal processing unit24is capable of converting the data (analog signal) reproduced from the magnetic tape31into digital data with the data head25a.

The head unit25is provided with the data head25aand a servo head25b. The head unit25is provided to be movable along the width of the magnetic tape31. The data head25aincludes a data recording head and a data reproducing head. The servo head25bis capable of reproducing a servo signal by scanning the stripes formed in a servo band of the magnetic tape31.

The control unit27detects the current position of the head unit25along the width of the tape, based on the servo signal reproduced by the servo head25b. The control unit27calculates the amount of off-track based on the position information on the current head unit25and tape motion information output from a memory control unit29(described later), and generates a control signal that controls the operations of the actuator28based on the amount of off-track. The generated control signal enables the position of the head unit25to be controlled. The control signal includes at least information on the direction of travel of the head unit25and information on the amount of travel thereof. The control unit27is provided with a control filter49. The control filter49is capable of removing periodic noise and narrow-band noise included in a PES.

The actuator28is capable of moving the head unit25along the width of the magnetic tape31, based on the control signal output from the control unit27.

The memory control unit29communicates with the memory32mounted on the magnetic tape cartridge33and reads information recorded on the memory32. The memory control unit29outputs at least the tape motion information from among the information read from the memory32, to the control unit27. In Embodiment 2, the memory control unit29establishes noncontact communication with the memory32. Note that the present embodiment is not limited to the configuration in which the memory control unit29and the memory32establish noncontact communication therebetween, and it may adopt a configuration in which the memory control unit29and the memory32establish contact communication therebetween, such as magnetic communication, optical communication, or electrical communication.

In Embodiment 2, the magnetic tape cartridge33is based on the LTO standard. Such an LTO-based magnetic tape cartridge contains one reel with a magnetic tape wound thereon.

The magnetic tape31contains digital data recorded by the data head25a. In Embodiment 2, the magnetic tape31based on the LTO standard has a tape width of approximately 12.65 mm.

The memory32is written with a variety of information about the cartridge30, the magnetic tape31, and the magnetic tape cartridge33. The information written in the memory32includes the format of the magnetic tape31, recording current (%), the range of the magnetic tape31on which data is written, and the like. The memory32is also written with the filter values of the control filter49provided in the control unit27.

FIG. 7shows the internal configuration of the control unit27. As illustrated inFIG. 7, a servo signal reproduction unit42reproduces a servo signal based on an electric signal input via an input terminal41connected to the servo head25b(cf.FIG. 6).

A frequency conversion unit43performs FFT processing of a PES that is obtained from the servo signal output from the servo signal reproduction unit42to convert the PES into frequency components.FIG. 9shows the characteristics after the frequency component conversion.

A filter value generation unit44generates the values of a notch filter that operates in the control filter49, based on the frequency components output from the frequency conversion unit43. The generated filter values are output via an output terminal45to the memory controller29.

A filter value readout unit47reads the filter values recorded on the memory32from the memory controller29via an input terminal46.

A servo signal reproduction unit48reproduces a servo signal based on the electric signal input through the input terminal41connected to the servo head25b(cf.FIG. 6) and calculates a PES using the above Equation 1.

The control filter49generates a notch filter based on the filter values obtained from the above Equation 2 and sent from the filter value readout unit47and removes periodic noise and narrow-band noise included in the PES output from the servo signal reproduction unit48.

A control signal generation unit50calculates the amount of control (the amount of travel) of the head unit25based on the PES output through the control filter49and outputs a control signal to an output terminal51.

The output terminal51is connected to the actuator28.

In Embodiment 2, a learning operation is performed before data recording, for a magnetic tape cartridge33that is mounted for the first time on the information recording apparatus. The information recording apparatus is capable of grasping whether the mounted magnetic tape cartridge33is mounted for the first time or not, by analyzing drive history information (e.g., the serial number of the information recording apparatus) recorded on the memory32mounted on that magnetic tape cartridge33. When the drive history information has no historical record of the information recording apparatus concerned, the learning operation is started. On the other hand, when the drive history information has a historical record of the information recording apparatus concerned, the information recording apparatus, without performing the learning operation, becomes capable of recording a digital signal.

FIG. 8shows a procedure for the learning operation of the information recording apparatus according to Embodiment 2.

Firstly, the information recording apparatus draws a magnetic tape31included in the magnetic tape cartridge33out of the cartridge30using a loading mechanism (not shown) and winds the tape on a drive reel (not shown) within the information recording apparatus. Then, the drive reel is rotatably driven by a motor, starting the transportation of the magnetic tape31. The information recording apparatus transports (forwards) the magnetic tape31from beginning to end and then transports (reviews) the tape from end to beginning. Note that in Embodiment 2, the transport speed of the magnetic tape31is approximately 6.1 m/sec. Since the overall length of the magnetic tape31housed in one magnetic tape cartridge33is approximately 820 m, the time required for a single round-trip between the beginning and end of the magnetic tape31is about four minutes.

During a single round-trip between the beginning and end of the magnetic tape31, the servo head25breads the stripes formed on a servo track of the magnetic tape31and outputs an electric signal to the control unit27. InFIG. 7, an electric signal received at the input terminal41is input into the servo signal reproduction units42and48. The servo signal reproduction unit42reproduces a servo signal based on the input electric signal (in step S11). Note that the servo signal reproduction unit48, the control filter49, and the control signal generation unit50do not operate during the learning operation.

Next, the servo signal reproduction unit42calculates a PES based on the reproduced servo signal. Specifically, the PES is calculated from Equation 3 as follows. In Equation 3, a first strip A1slants in a first direction, a second strip B1slants in a second direction, a third strip C1slants in the first direction, a fourth strip D1that slants in the second direction, are formed along the length of the magnetic tape31in the order mentioned:
PES=(AB−(A1B1/A1C1)×100)/2×tanY(Equation 3)
In Equation 3, “Y” is the tilt angle of the strips formed on a servo track of the magnetic tape31(in Embodiment 2, Y=6°). “AB” is the distance between the first strip A1and the second strip B1at the center across the width of the tape (in Embodiment 2, AB=50 μm). “A1B1” is the distance between the first strip A1and the second strip B1. “A1C1” is the distance between the first strip A1and the third strip C1. The PES is calculated using the above equation at prescribed periods. Such calculated PESs are sent in succession to the frequency conversion unit43(in step S12).

Next, the frequency conversion unit43performs FFT processing of the PES sent from the servo signal reproduction unit42to convert the PES into frequency components.FIG. 9shows the analysis results obtained through such FFT processing. As illustrated inFIG. 9, the PESs sent from the servo signal reproduction unit42have larger values at certain frequency bands. Usually, there is no periodicity in the occurrence of PESs caused by LTM (Lateral Tape Motion); however, since the curvature of the edge of the magnetic tape31caused by the accuracy of slitting, as described above, has a periodicity, the values obtained by converting PESs into frequency components have peaks at certain frequency bands as illustrated inFIG. 9. Such frequency component information calculated by the frequency conversion unit43is sent to the filter value generation unit44(in step S13).

Next, the filter value generation unit44generates the values of a notch filter in the control filter49, based on the frequency component information output from the frequency conversion unit43. Specifically, the peaks (closed squares in the drawing) are detected from the frequency characteristics inFIG. 9, and then the center frequency, the notch width, and the notch depth of the notch filter for reducing noise at the frequency components, where the peaks are detected, are calculated. The notch filter mounted on the information recording apparatus performs an arithmetic operation expressed by Equation 4.
GN(s)=(S2+2dζωns+ωn2)/(S2+2ζωns+ωn2)  (Equation 4)
In the filter value generation unit44, the center frequency ωn, the notch width ζ, and the notch depth d, given by the above Equation 4, are calculated for every frequency where the peak is detected according to the results of FFT processing inFIG. 9. The generated filter values are output via the output terminal45to the memory control unit29(in step S14).

Next, the memory control unit29writes the filter values generated by the filter value generation unit44to the memory32(in step S15). Through the above steps, the learning operation is completed.

As described above, when writing a variety of data to the magnetic tape31in the magnetic tape cartridge33that is equipped with the memory32written with the filter values, firstly, the filter value readout unit47controls the memory control unit29and reads out the filter values written in the memory32. Then, the filter value readout unit47sends the filter values read from the memory32to the control filter49, and the control filter49generates the notch filter.

Next, the servo signal reproduction unit48reproduces a servo signal based on the electric signal input from the servo head25bvia the input terminal41. The servo signal reproduction unit48calculates a PES based on the reproduced servo signal. The calculated PES is sent to the control filter49. The control filter49passes the input PES to the notch filter to thereby remove periodic noise and narrow-band noise included in the PES. The PES output from the control filter49is input into the control signal generation unit50. The control signal generation unit50generates a control signal including information on the amount of control for driving the actuator28. That is, the control signal for moving the head unit25to a normal position across the width of the magnetic tape31is generated.

The actuator28moves the head unit25along the width of the tape based on the control signal generated by the control signal generation unit50.

Embodiment 2 enables periodic noise and narrow-band noise to be removed from a PES by incorporating the control filter49serving as a notch filter into a feedback control system. Consequently PESs can be reduced in amplitude. Note that such periodic noise and narrow-band noise in a PES include cartridge-reel components, drive-reel components, tape edge components, and the like. The cartridge-reel components are caused by deformation or decentering of a reel included in the magnetic tape cartridge33. The drive-reel components are caused by deformation or decentering of a drive reel mounted on the information recording apparatus. The tape edge components are caused by the curvature of the edge of a magnetic tape formed in the slitting step in the process of manufacturing the magnetic tape31.

In addition, Embodiment 2 enables periodic noise and narrow-band noise caused by deformation or decentering of a reel included in the magnetic tape cartridge33or of a drive reel to be removed by the information recording apparatus performing the learning operation. This allows PESs to have lower amplitudes than in a configuration in which the servo signal recording apparatus performs the learning operation.

Embodiment 2 further enables filter values to be written for each information recording apparatus to the memory32, by writing the calculated filter values to the memory32in correspondence with the serial numbers of the information recording apparatuses that have performed the learning operation. Therefore, even in the case where a single magnetic tape cartridge33is selectively used by a plurality of information recording apparatuses, periodic noise and narrow-band noise that differ among individual information recording apparatuses can be reduced by reading out the filter values corresponding to each individual information recording apparatus and passing PESs through the notch filter.

Note that the servo signal reproduction unit9, the second servo head15, and the servo head25bdescribed in Embodiment 1 or 2 are exemplary servo signal reproduction units of the present invention. In addition, the controller6, the pulse generation unit8, and the first servo head14in Embodiment 1 or 2 are exemplary servo signal recording units of the present invention. In addition, the frequency conversion units10and43in Embodiment 1 or 2 are exemplary frequency conversion units of the present invention. In addition, the filter value generation units11and44in Embodiment 1 or 2 are exemplary filter value generation units of the present invention. In addition, the memory control units12and29in Embodiment 1 or 2 are exemplary recording control units of the present invention. In addition, the control unit27in Embodiment 1 or 2 is an exemplary control unit of the present invention. In addition, the actuator28in Embodiment 1 or 2 is an exemplary actuator of the present invention. In addition, the control filter49in Embodiment 1 or 2 is an exemplary filter of the present invention.

The servo signal recording apparatus of the present invention is useful in apparatuses that are capable of recording a servo signal on a magnetic tape. Also, the information recording apparatus of the present invention is useful in apparatuses that use a magnetic tape as an information medium.