JP2002510112A - How to determine the position of the magnetic tape in the vertical direction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for determining a vertical position of a tape with respect to a tape head. The tape defines a high (31) and a low (30) data field that identifies data bits (33) in a servo stripe (13) containing at least two frames (14, 15). Applied in sequence, these bits (33) are grouped into 22 bit strings in the position count field (34, 36) and 26 bit strings in the synchronization field (35).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the technical field of dynamic magnetic information storage or retrieval. More specifically, the present invention relates to the technical field of automatic control of a recorder mechanism. More specifically, the present invention relates to vertical position determination using a servo pattern. More specifically, but not exclusively, the present invention is a method for determining the vertical position of a magnetic tape by reading a servo pattern.

[0002]

[Description of Related Technology]

Magnetic tape recording has long been used to record voice or data information. For information storage and retrieval, magnetic tape has proven to be particularly reliable, cost-effective, and easy to use. In an effort to further increase the usefulness and cost effectiveness of magnetic tape, attempts have been made to store more information within a given tape width and length. This has generally been achieved by providing more data tracks within a given tape width, so that more data is stored within a given tape length. In many systems, multiple volumes of data are written to a single reel or tape cartridge. This increase in data storage density requires more accurate vertical positioning of the tape / tape head. That is, the more data that is written to a single track, the more important is the accurate positioning of the tape in the vertical direction with respect to the tape head. Here, the term "vertical direction" means a direction along the length of the magnetic tape.

[0003] To increase the accuracy of the data tracks, servo stripes have been used to provide a reference point to maintain proper positioning of the tape across the tape read / write head. Here, the width direction means a direction crossing the width of the magnetic tape. One or more servo stripes can be used, depending on the number of data tracks located on the tape. The servo·
The signal detected from the stripe is sent to a control system, which moves the head to maintain the servo signal at a predetermined value. This predetermined signal is obtained when the servo read gap is at a specific position with respect to the servo stripe. Referring to FIG. 1, a half-inch wide magnetic tape 11 has multiple data bands 12.
Above, up to 288 or more data tracks can be provided. In order to use such a large number of data tracks, it is desirable to provide up to five or more servo stripes 13 to improve the performance of the data read / write function. The servo stripe 13 can take various patterns or frequency ranges to enable accurate positioning of the tape and the tape head.

Referring to FIG. 2, a portion of a conventional servo stripe 13 having two frames 14 and 15 is shown. The first frequency signal 16 has been written across the width of the servo stripe 13. The erasure frequency is written on the first frequency signal 16 in a predetermined pattern, for example, a pattern of five rectangles 17 provided in each of the frames 14 and 15. 5 rectangles 1 in each frame
By creating 7, there are nine horizontal boundaries 18 between the frequency signal 16 and the erase pattern 17. The tenth boundary 19 along the bottom line does not serve this purpose. Although FIG. 2 shows five rectangles, it should be understood that the number of erase patterns may be increased or decreased from this in consideration of technical design. The dashed line 21 passes along the boundary 18 and the read gap 22 of the tape read head 23.
Pass through. Now, assuming that the servo pattern 13 has passed over the gap 22 from right to left, the gap 22 reads the read frequency 16 over the entire width of the read gap 22 in the region 25, and reads the read frequency 16 in the region 26. One half reads the frequency 16 and the other half of the full width 24 reads the erasure frequency from the pattern 17 and alternates between them. The servo control system in the tape drive is
The ratio of the full signal amplitude in field 25 to half the signal amplitude in field 26 is used to stay on the track. While allowing for positioning of the tape head relative to the tape width, these prior art servo patterns are not intended for vertical positioning of the tape. In other words, it is important for the servo to know where along the length of the tape the data volume is stored. Such information is available in modern systems where multiple volumes of data are written on a single reel or tape cartridge.
It is becoming increasingly important.

Many prior art systems use a tachometer to measure the speed of rotation of the reel motor, and know the reel dimensions and tape thickness to determine how many meters the tape is positioned relative to the tape head. Can be estimated. However, along with data compression and other techniques, the data stream is compressed and becomes increasingly shorter in tape length, making position estimation within a few meters inadequate. It would be desirable to be able to more accurately determine the location along the length of the tape where the desired data volume is stored.

[0006]

SUMMARY OF THE INVENTION

The present invention is a novel method for determining the vertical position of a tape with respect to a tape head. One data field is contained within each frame of the tape servo pattern. Each data field contains a digital signal (high or low). Successive data fields are arranged in a predetermined sequence to define a position count field and a synchronization field. The data field in each frame of the servo stripe is detected by the tape read head as the frame passes over the tape head. The column of the detected data field is recognized as a position count field. This allows the tape controller to obtain vertical position information from each frame and determine the position of the row of frames on the tape relative to a reference point such as a tape head.

[0007]

[Description of preferred embodiments]

Reference will now be made to the drawings wherein like reference numerals indicate like elements throughout. FIG. 1 illustrates multiple servo stripes 13 written on a given tape portion 11 to enable accurate positioning of the data stripes 12 with respect to a tape head (not shown). FIG. 3 illustrates one servo pattern written as a servo stripe 13 on the tape 11. FIG.
No. 804,445, filed Feb. 21, 1997, and assigned to the assignee of the present invention, entitled "Servo Pattern of Tape with Enhanced Synchronization Characteristics," filed and claimed. Of the invention. Referring to FIG. 3, a first synchronization frequency signal has been written in a first area 27 across the width of the servo stripe 13. A second frequency signal different from the first frequency signal is written in a second area 28 across the width of the servo stripe 13. The first area 27 and the second area 28 together form the frame 14. The first synchronous frequency domain 27 and the second different frequency domain 28 are alternately written on subsequent servo stripes 13 and continue along the length of the tape 11 to the next frame 15 and so on. The third erase frequency signal is written on the second area 28 of each frame in a predetermined clear pattern. In a preferred embodiment, the third frequency is written as a parallelogram 17 erasure signal, which may be square or rectangular.
FIG. 3 shows five parallelograms, but as will be apparent to those skilled in the art,
It should be understood that the number may increase or decrease depending on the application. During tape drive operation,
The lateral position of the tape head relative to the tape is controlled by a servo reader, which monitors the output signal when the servo reader is at the edge of the erasure zone 17.

Referring to FIG. 3, fields 25 and 26 in frames 14 and 15
May be the same as that shown in FIG. However, the signal frequency in the area 27 is about twice the signal frequency in the second frequency area 28. Therefore, the read gap 22
The frequency in the area 29 of the signal detected by the frame 14 is about twice the detection frequency in the adjacent field 25, and when the increase in the frequency is detected, the frame 14
, 15 can be determined.

FIG. 4 illustrates the present invention. Data fields 31 and 32 have been added to field 29. Field 31 represents the high (1) signal and field 32 represents the low (0) signal. By arranging these data fields in a predetermined sequence, a series of data bits 33 can be identified. FIG.
, The servo stripe 13 is shown as a plurality of bits 33. The bits 33 are grouped into a 22-bit column in the position count fields 34 and 36 and a 26-bit column in the synchronization field 35. Each bit 33 represents a value of either "1" or "0" in field 31 or 32 in frame 14 or 15. As a result, each of the position count fields 34 and 36 and the synchronization field 35 have a sequence of "0" and "1" as shown in FIG. Placing these "0s" and "1s" in a unique pattern allows the tape controller to determine each position count field. That is, the vertical position of the tape head with respect to a series of frames on the tape can be determined.

Referring to FIG. 6, respective data counts (“0” and “1”) for the position count fields 34 and 36 and the synchronization field 35 are described. The synchronization field 35 is used to separate the position count fields 34, 36 and allow identification of the position count field. The synchronization field 35 alternates with each of the position count fields 34, 36, etc., along the length of the tape.

[0011] The position count fields 34 and 36 are provided for each position count field.
It consists of 22 bits having a unique combination of "0" and "1". Each position count field 34, 36 can be decoded by the tape controller to identify the vertical position of the tape relative to the tape head at the position of that particular position count field. In a preferred embodiment, the vertical position is
It is encoded in the position count field by binary encoding. The position count field 34 consists of 21 “0” followed by one “1”. This is obtained by encoding position 1 in the vertical direction. Position count
The field 36 is composed of 20 “0”, one “1”, and then one “0”.
It is made up of This is obtained by encoding position 2 in the vertical direction.
Similarly, the position count fields that follow along the tape have the encoded vertical position of each position count field. The vertical position of each position count field increases by one for each position count field along the length of the tape.

When the tape controller has just located the vertical position information, the servo read head could be adjacent to any position along the length of the tape. For example, the servo read head could start reading in the middle of the position count or synch field. Then, synchronization field 3
5 identifies the beginning and end of the position count fields 34,36. In this way, the controller determines that the next 22 bits are the position count field, no matter when it detects the 26 bit sequence representing the sync field. In the preferred embodiment, the sync field 35 as well as all other sync fields along the tape have one "0" bit followed by 24 "1" bits, followed by one "0" bit. Is made of things. The selection of the particular pattern of "1" s and "0s" that make up the sync field 35 depends on the controller's use of the sync field on the tape, regardless of the vertical position encoded in the adjacent position count field. Care must be taken to ensure correct detection.

Each bit (31 or 32) of the vertical position data is written into a servo stripe (FIG. 4) by a servo writer. Preferably, each position count field (eg, 34, 36) represents a number that increases from the beginning to the end along the length of the tape. That number can be used to find the vertical position of the tape at all standard reading speeds. Such an encoding scheme allows the controller to accurately identify the tape position, even if no user data has been stored on the tape.

The position count fields 34, 36, etc., consist of 22 bits. As a result, a total of 2 22, that is, 4,194,304 counts is possible. In a preferred embodiment, 48 servo frames (
22 frames in the position count field 34 or 36 and 26 frames in the sync field 35) are used. Assuming that the length of one servo frame is 200 μm, a tape length of 40.3 km can be accommodated in this way (a normal reel is only a few hundred meters of tape), and the accuracy of determining the vertical position is as follows. 8. 48 frames of frame size (200 μm in preferred embodiment) or 9.
6 mm. Prior art methods using tachometer and reel diameter estimation have levels of accuracy in excess of 1 m. Thus, the present invention provides a 100
It is possible to determine the vertical position with more than double precision.

[0015] Of course, it should be clearly understood that the number of bits used to construct the position count field or the synchronization field can be varied without departing from the scope of the present invention. That is, the number of frames used to compose the position count field or the synchronization field may be 20, 28, 30, or more (or less). If the number of bits used in the count field is reduced, the total count can be reduced, and a shorter tape length can be handled with higher accuracy. Also, by counting the number of frames after the position count field has been detected, the resolution will be increased. Similarly, the size of the servo frame is a matter of design choice known to those skilled in the art and does not constitute the present invention.

In an alternative of the invention, the vertical position can be encoded in the position count field by means other than just binary encoding. For example, the position in the vertical direction may be binary-coded together with an error correction code to form a position count field. With such a scheme, the vertical position can be obtained even if there is an error when detecting the data bits constituting the position count field. As a preferable error correction, a position count field is formed by adding a 6-bit Hamming code (error correction code) to the 22-bit binary coded data. This enables error correction for each bit in the position count field and 2-bit error detection. Increasing the position count field requires the use of a longer sync field. A 1-bit correction Hamming code capable of 2-bit detection is sufficient for this application, but a stronger code such as a BCH code or a Reed-Solomon code may be used to correct an error exceeding 1 bit. It will be understood by those skilled in the art.
A discussion of these codes, as well as the theory of their evolution, can be found in the text "Error Correcting Codes" Peterson & Weldon, MIT Press (1972). Increasing the position count field requires the use of a longer sync field.

For an encoding scheme given for the vertical position, even if an error exists when a data bit consisting of the position count field surrounding the synchronization field 35 and the synchronization field itself is detected, the synchronization field is appropriately adjusted. So that the expression can be optimized. The problem of identifying the optimal representation of the synchronization field 35 (hereinafter the synchronization character) can be calculated. Given a synchronization character, a position count field arbitrarily containing an error correction code, and a bit sequence representing another synchronization character, the synchronization character is used only when the synchronization character matches the synchronization character in the bit sequence. The solution is to match with any bit string in this string. It is also desirable to maximize the difference between the synchronization character and any other bit strings in the string. It should be understood that the position count field in the above bit sequence can be encoded with any valid position count. For simplicity of calculation, when comparing a sync character to a bit string, it is possible to assume the worst case where a portion of the sync character compared to the bit string in the position count field matches. To further simplify the calculations, the considerations can be limited to certain classes of synchronization characters. Although the synchronization characters described so far have been symmetric, another class with desirable characteristics is the class of anti-symmetric synchronization characters. Symmetric sync characters can be detected by the same decoder regardless of the direction of the bit string,
For an antisymmetric synchronization character, only a minimum change is detected by the decoder depending on the direction of the bit string. The antisymmetric sync character class is desirable, but it belongs to this class and extends to the position count field which overlaps the selected sync character at all positions which do not overlap the position count field. The reason is that the selection can be made by eliminating the possibility that such mismatched bit sets may occur. One preferred embodiment utilizes a class of 32-bit anti-symmetry synchronization characters, a synchronization including the position count field of 26 binary encoded data bits and 6 error correction code bits. Used for fields. The sync character selected under these constraints was 0032b3ff (hexadecimal). Failure to identify this synchronization character from the bit sequence is when at least four bits are incorrect.

Intelligence can be added to the tape transport controller to eliminate the need for the frame counter to start from a count of one. For example, the controller can identify a count for a particular tape position (leading, middle or trailing). The controller can then determine what the count will be at all locations on the tape (assuming the tape length is known). If necessary, the controller can also recognize and correct the rotation of the counter, even if the number of frames exceeds the maximum count obtained from the 22-bit position count field.

While the present invention has been described with respect to particular embodiments thereof, it is not intended to be limited thereto, but may be varied and varied within the scope of the invention as defined in the appended claims. For example, although specific numerical values of the servo stripe and the data track are disclosed, the present invention can use more or less of the servo stripe or the data track. Although the specific number of bits defining the synchronization field and the position count field are disclosed in the preferred embodiment, increased or decreased numbers of bits may be used without departing from the scope of the invention as defined by the appended claims. It is possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of multiple servo stripes and data bands on a magnetic tape.

FIG. 2 is an explanatory diagram of a servo stripe including multiple erase bands.

FIG. 3 is an explanatory diagram of a servo stripe including a synchronization frequency region.

FIG. 4 is an explanatory diagram of a servo stripe including a data field in a synchronization area.

FIG. 5 is an explanatory diagram of a servo stripe having multiple frames that are grouped.

FIG. 6 is an explanatory diagram of grouping of data bits in the grouped frames of FIG. 5;

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] October 28, 1999 (1999.10.28)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Travert, Steven, Gregory United States, Colorado 80303, Boulder, Hartford Drive, 815 (72) Inventor Manti, John, Paul United States, Colorado 80303-3504, Boulder, Caddo Park Way, 3980 (72) Inventor Boyer, Keith, Gary United States, Colorado 80241, Tomton, Jackson Place, 13450 F-term (reference) 5D042 FA02 GA01 HA01 HB01 HC02

Claims (20)

[Claims] 1. A method for determining a vertical position along a magnetic tape that includes at least one servo stripe with a plurality of servo frames to be read by a servo tape head: Detecting a data field in a predetermined portion of a number of the servo frames; recognizing the detected data field as a position count field; and, based on the position count field, Determining a vertical position of the magnetic tape relative to the tape head. 2. The method according to claim 1, wherein the step of recognizing the detected data field as the position count field includes a step of grouping a predetermined number of detected data fields into one synchronization field. The method for determining a vertical position of a magnetic tape according to claim 1, wherein: 3. The method according to claim 2, wherein the synchronization field includes a row of uniquely identifiable data fields. 4. The method according to claim 1, wherein said position count field is configured to include 22 adjacent servo frames. 5. The data field comprises a high (1) signal and a low (0) signal.
2. The method according to claim 1, wherein the method includes a digital signal representing any one of the signals. 6. The method of claim 1, wherein recognizing the detected data field as the position count field includes detecting the synchronization field before and after the position count field. 3. The method for determining a vertical position of a magnetic tape according to claim 2, wherein: 7. The method according to claim 6, wherein the synchronization field includes a sequence of uniquely identifiable data fields. 8. The method according to claim 2, wherein the synchronization field includes an anti-symmetry synchronization character. 9. The method according to claim 2, wherein the position count field includes an error correction code. 10. A method for generating a vertical position indicator for a plurality of adjacent servo frames written on one magnetic tape, comprising: a data field at a predetermined portion of a predetermined number of the adjacent servo frames; Grouping predetermined ones of the detected data field signals into one unique position count field; and grouping the grouped data included in the position count field. Recognizing a unique pattern of fields; and generating a count signal from the unique position count field indicating a vertical position of the unique position count field on the one magnetic tape. Generating a marker for the vertical position of the magnetic tape. 11. The step of grouping the detected data field into the position count field comprises identifying the position count field by identifying a synchronization field at the beginning and end of the position count field. 2. The method according to claim 1, wherein the method includes a step.
0. A method for generating a marker for a vertical position of a magnetic tape according to 0. 12. The method according to claim 11, wherein the synchronization field includes a sequence of uniquely identifiable data fields. 13. The magnetic tape of claim 10, wherein the position count field is configured to include data fields from 22 adjacent servo frames. Sign generation method. 14. The apparatus of claim 10, wherein the detected data field is configured to include a digital signal representing either a high (1) signal or a low (0) signal. A method for generating a marker for the vertical position of a magnetic tape 15. The step of grouping the detected data field into the position count field comprises:
11. The method according to claim 10, further comprising the step of grouping into one synchronization field before and after the position count field. 16. The method according to claim 15, wherein the synchronization field includes a sequence of uniquely identifiable data fields. 17. The method of claim 11, wherein the synchronization field includes an anti-symmetry synchronization character. 18. The method according to claim 11, wherein the position count field includes an error correction code. 19. The method according to claim 9, wherein the error correction code is configured to include a 6-bit Hamming code. 20. The method of claim 18, wherein the error correction code includes a 6-bit Hamming code.