Method and apparatus for reading or writing on tape using a servo positioned multiple channel head

Abstract: Disclosed is a method for reading or writing data on a tape which has a plurality of data tracks and at least a first dedicated servo track. A multiple channel head with at least three channels, each having at least one element for reading or writing, is used to access the tracks on the tape. The head is moved proximate one of a plurality of predetermined positions. The channels are located so that, in any one predetermined position of the head, one channel accesses the center of a dedicated servo track on the tape and at least two other channels will access the center of distinct data tracks. Depending on the predetermined position of the head, different channels will access a dedicated servo track. The position information on a dedicated servo track is used to move the head to one of the predetermined positions once the head has been moved proximate that predetermined position.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reading or writing data on magnetic tape using a multiple channel head which is transversely movable with respect to the recording tape. The present invention also relates to magnetic head mechanisms, particularly with respect to a multiple channel head controlled by a servoing system. 2. Description of the Prior Art Data recording cartridges containing magnetic tape and recorders adapted for their use are disclosed and claimed in U.S. Patent No. 3,692,225 (von Behren). The recorders adapted to use such data cartridges originally employed fixed multitrack heads for accessing the tracks on the magnetic tape in the data cartridge. These fixed, multitrack heads were complex, expensive and difficult to maintain in proper alignment. To eliminate the multitrack heads, U.S. Patent No. 4,313,143 (Zarr) disclosed a head positioning mechanism by which a single track head could be transversely positioned with respect to the width of a magnetic tape having a plurality of parallel tracks. The system disclosed in Zarr works satisfactorily but a different system was needed when the data cartridges and recorders were miniaturized. The type of head positioning mechanism which works satisfactorily in a smaller recorder is disclosed in U.S. Patent No. 4,750,067 (Gerfast). Gerfast uses a stepper motor to accurately move the head in a direction transverse to the tape. Even with the head positioning mechanism of Gerfast, the number of tracks on the magnetic tape which can be accessed by a head is limited by the accuracy of head positioning possible with a stepper motor system and the variability of tape position within a cartridge as the tape crosses the head. In a further prior art document, JP-A-58,097,129 there is disclosed an information recorder and reproducer using a magnetic tape having a servo track recorded in parallel with magnetic data tracks on the tape and a magnetic head body having plural transversely spaced heads and a further spaced servo head. This document is used to form the preamble of the appended claims. Summary of the Invention In contrast with the fixed position multitrack heads disclosed in the ′225 patent and the transversely positionable single track heads disclosed in the ′143 and ′067 patents, the present invention uses a transversely positionable, multitrack head. With such a head, the number of tracks on a magnetic tape which can be accurately accessed is increased, and hence so is the amount of data which can be stored on a tape. This multiple channel head is servo positioned by having one of the head channels access a dedicated servo track containing position information on the magnetic tape, thus accurately positioning at least two other channels of the head on data tracks for reading or writing data. According to a first aspect of the present invention there is provided a method of recording and reproducing data on magnetic recording tape, comprising: recording servo tracking data on at least a first longitudinally extending servo track within a section of magnetic recording tape, and controllably transversely positioning a multiple channel head having at least three channels, with respect to said servo track, characterised by: performing said recording step such that said section of said tape is nominally located midway across the width of the tape, thereby dividing the tape into two portions, defining along each of said portions a plurality of additional longitudinally extending sections, adjacent to each other across the width of the tape and having the same Predetermined width and within each of which additional sections at least one track of data may be recorded and reproduced; providing a multiple channel head having the additional following features: the center-to-center distance between at least two of said channels being equal to the center-to center distance (D1) between said adjacent sections, and the center-to-center distance (D2) between a third channel and the closest of the other channels being equal to twice the center-to-center distance (D1) between said adjacent sections, positioning the head at predetermined transverse locations each of said predetermined locations, being such that one of the channels will always be located to reproduce said servo tracking data from the servo track while the other channels access said additional sections at which data tracks may be located, and thereby enabling the section containing said servo track to be reproduced and at least two of said additional sections to be recorded or reproduced. According to a second aspect of the present invention there is provided a system for recording and reproducing data comprising: a magnetic recording tape having servo tracking data recorded on at least a first longitudinally extending servo track within a section of said tape, a multiple channel head having at least three channels and means for controllably transversely positioning the head, characterised by: said section of said tape being nominally located midway across the width of the tape thereby dividing the tape into two portions along each of which may be located a plurality of additional longitudinally extending sections, all sections being adjacent to each other across the width of the tape and having the same predetermined width, within each of which additional sections, at least one track of data may be recorded and reproduced; the center-to-center distance (D1) between at least two of said channels of the head being equal to the center-to-center distance (D1) between said adjacent sections, and the center-to-center distance (D2) between a third channel and the closest of the other channels being equal to twice the center-to-center distance (D1) between said adjacent sections; and said positioning means being operable to position the head at any of a plurality of predetermined locations such that one of the channels is always located to reproduce said servo tracking data from the servo track while the other channels access said additional sections at which data tracks may be located. Thus there is disclosed a method which uses a multitrack head for reading or writing data on a tape which has servo data recorded on at least one longitudinally extending track within a section nominally located midway across the width of the tape, thereby dividing the tape into two portions along each of which may be located a plurality of additional longitudinally extending sections, all sections being adjacent to each other and having the same predetermined width. Within each of the additional sections, at least one track of data may be recorded and reproduced. The multiple channel head has at least three channels, each having at least one element for reading or writing, is used to access the tracks on the various sections on the tape. The channels are located so that, in any one predetermined position of the head, one channel accesses the center of a dedicated servo track on the tape and at least two other channels will access the center of distinct data tracks. Depending on the predetermined position of the head, different channels will access a dedicated servo track. The position information on a dedicated servo track is used to move the head to one of the predetermined positions once the head has been moved proximate that predetermined position. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more thoroughly described with reference to the accompanying drawings, wherein like numbers refer to like parts in the several views, and wherein: FIG. 1 is a diagrammatical view of a multiple channel head in varying positions with respect to magnetic tape having seven tracks; FIG. 2 is a diagrammatical view of the preferred embodiment of the side of the multiple channel head of FIG. 1 facing the magnetic tape; FIG. 3 is a diagrammatical view of a multiple channel head in varying positions with respect to magnetic tape having seventy tracks; and FIG. 4 is a side elevational block diagram of a servo positioned multiple channel head and magnetic tape system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 is a diagrammatical view of a multiple channel head, generally indicated as 10, accessing a multitrack tape, generally indicated as 12, in three different positions, 34, 36 and 38. Head 10 has three channels, generally indicated as 14, 16 and 18. Channels 14, 16 and 18 each have at least one element on the side that faces the tape that can be used to access tracks 20, 22, 24, 26, 28, 30 and 32 on tape 12 to read data from the tracks or write data on the tracks. Head 10 is movable in a direction transverse to the length of tape 12. Track 26 is a dedicated servo track containing prestored position information. Tracks 20, 22, 24, 28, 30 and 32 are data tracks on which data can be magnetically stored. All the tracks on tape 12 run in the direction of the length of tape 12 and are substantially parallel to each other and substantially equally spaced across the width W of tape 12. Tape which is generally known in the industry as quarter-inch tape is provided in the preferred embodiment. The actual width of quarter-inch tape is approximately one quarter inch, although it is not exactly one quarter inch. As seen in Figure 1, the spacing between channels 14 and 16 on head 10 is equal to the distance D₁ between adjacent tracks on tape 12. The distance D₂ between channels 16 and 18 on head 10 is equal to twice the distance between adjacent tracks on tape 12 so that D₂ = 2D₁. Figure 1 shows head 10 in three different positions 34, 36 and 38, with respect to tape 12. Positions 34, 36 and 38 are shown in a lateral direction for clarity even though head 10 only moves in a direction transverse to the length of tape 12. In position 34, channel 14 accesses the center of dedicated servo track 26 and channels 16 and 18 access the center of data tracks 28 and 32, respectively. When head 10 is in position 36, channel 16 accesses the center of dedicated servo track 26 and channels 14 and 18 access the center of data tracks 24 and 30, respectively. When head 10 is in position 38, channel 18 accesses the center of dedicated servo track 26 and channels 14 and 16 access the center of data tracks 20 and 22, respectively. The spacing of channels 14, 16 and 18 on head 10 is such that for each position 34, 36 and 38, two distinct data tracks are accessed. Thus, all of the data tracks on tape 12 can be accessed by using just one dedicated servo track and just three different head positions. The method of reading or writing data according to the present invention can now be more fully explained. Data can be read from or written on tape 12 by moving head 10 in a direction transverse to the length of tape 12 proximate one of positions 34, 36 or 38. If head 10 is moved proximate position 34, for example, channel 14 is proximate dedicated servo track 26. Channel 14 reads the position information that has been prestored on dedicated servo track 26 and uses this information to determine the error between the present position of head 10 and position 34 of head 10. This error information is then used to accurately position channel 14 on the center of dedicated servo track 26, thus accurately positioning channels 16 and 18 on the center of data tracks 28 and 32, respectively. Thus, data can be written on or read from any data track on tape 12 by moving head 10 proximate the position where a channel on head 10 accesses that track. A variety of configurations of channel elements for reading and writing could be used. For example, each channel could have one element that both reads and writes; each channel could have one read element and one write element; each channel could have, in order, a read element, a write element and another read element; or each channel could have, in order, a write element, a read element, and another write element. Figure 2 is a diagrammatical illustration of the preferred embodiment of the side of head 10 which faces tape 12 and shows channels 14, 16 and 18 in more detail. Channel 14 is shown at the bottom of head 10 and comprises read element 40, write element 42 and read element 44 spaced apart along the length of the tape. Channel 16 is shown above channel 14 and comprises read element 46, write element 48 and read element 50 spaced apart along the length of the tape. Channel 18 is shown at the top of head 10 and comprises read element 52, write element 54 and read element 56 spaced apart along the length of the tape. Read elements 40, 44, 46, 50, 52 and 56 are magnetic heads configured to read data that has been magnetically stored on tape. Write elements 42, 48 and 54 are magnetic heads that are configured to magnetically store data on magnetic tape. The preferred order of read element, write element and read element on each channel allows data to be confirmed once it has been written on a tape regardless of the direction the tape is moving. Read elements 40, 46 and 52 are in a line perpendicular to the tape path, write elements 42, 48 and 54 are in second line perpendicular to the tape path and read elements 44, 50 and 56 are in a third line perpendicular to the tape path. Figure 3 is a diagrammatical illustration of the preferred embodiment of the invention. In the preferred embodiment, tape 120 is provided with seventy tracks, as opposed to the seven tracks shown in Figure 1. For the purpose of explaining Figure 3, each of the track areas shown in Figure 1 can be thought of as a section in Figure 3. For example, referring to Figure 3, section 200 corresponds to the area around track 20 in Figure 1. In a similar manner, sections 220, 240, 260, 280, 300 and 320 shown in Figure 3 correspond to the areas around tracks 22, 24, 26, 28, 30, and 32, respectively. It can be seen from Figure 3 that each section has 10 tracks, a-j, in each section. The 10 tracks in section 200 are referred to as 200a-200j. The tracks in the rest of the sections are similarly numbered. All the tracks run in the direction of the length of tape 120 and are substantially parallel to each other and substantially equally spaced across the width W of tape 120. Just as track 26 in Figure 1 was a dedicated servo track, tracks 260a-260j in Figure 3 are all dedicated servo tracks containing prestored position information. The tracks in sections 200, 220, 240, 280, 300 and 320 are all data tracks on which data can be stored. The channel locations on head 10 in Figure 3 are the same as shown in Figure 1 but can be described differently with respect to Figure 3. Focusing on Figure 3, the spacing between channels 14 and 16 can be described as equal to the width of a section on tape 120. Furthermore, it can be seen from Figure 3 that the spacing between channels 16 and 18 can be defined as twice the width of a section on tape 120. This spacing allows for the efficient and accurate accessing of data tracks on tape 120. Head 10 is shown in thirty different positions, 58a-58j, 60a-60j, and 62a-62j, with respect to tape 120 in Figure 3. The positions are shown in a lateral direction for clarity even though head 10 only moves in a transverse direction with respect to tape 120. In each of the positions of head 10 shown in Figure 3, one of channels 14, 16 or 18 is centered on one of dedicated servo tracks 260a-260j and the other two channels are centered on distinct data tracks. In head 10 positions 58a-58j, channel 18 accesses dedicated servo tracks 260a-260j, respectively, and channels 14 and 16 access data tracks 200a-200j and 220a-220j, respectively. In head positions 60a-60j, channel 16 accesses dedicated servo tracks 260a-260j, respectively and channels 14 and 18 access data tracks 240a-240j and 300a-300j, respectively, In head 10 positions 62a-62j, channel 14 accesses dedicated servo tracks 260a-260j, respectively, and channels 16 and 18 access data tracks 280a-280j and 320a-320j, respectively. As explained above, it is the spacing of channels 14, 16 and 18 on head 10 which allows for the efficient accessing of 60 data tracks with just 10 servo tracks. As can be seen in Figure 3, since two unique data tracks are accessed for each combination of channel and dedicated servo track, only 30 different positions of head 10 are necessary to access all 60 data tracks on tape 120. The method for using the system diagrammatically shown in Figure 3 is similar to the method disclosed with respect to Figure 1. Namely, head 10 is moved proximate one of the positions 58a-58j, 60a-60j and 62a-62j shown in Figure 3. The channel that is proximate a dedicated servo track in that position reads the position information prestored on that dedicated servo track and uses the information to reposition the head such that the channel is centered on the dedicated servo track, thus accurately positioning the other two channels on data tracks. The two channels that have been accurately positioned on data tracks can then, with the element or elements thereon, read data from or write data on the data tracks being accessed. These steps can be repeated for all the unique combinations of channels and dedicated servo tracks, the 30 positions of head 10 shown in Figure 3, to read data from or write data on any data track on tape 120. A block diagram of the apparatus of the present invention is shown in Figure 4 along with tape 112. Head 100 is movable in the direction of the arrows shown on head 100 by head positioning mechanism 102. Channels 114, 116 and 118 are located on head 100 in the same relationship with respect to tape 112 as disclosed above for channels 14, 16 and 18 with respect to head 10 and tape 12. Head positioning mechanism 102 could be the type shown in U.S. Patent No. 4,750,067 (Gerfast) with the exception that head positioning mechanism 102 would be servo controlled in a manner well known in the art. Thus, data tracks on tape 112 would be accessed by head positioning mechanism 102 moving head 100 to a position where one of channels 114, 116 and 118 was proximate a dedicated servo track on tape 112. One of the read elements on that channel would read the position information prestored on that dedicated servo track. This information would be used to calculate the error between the present position and the position where the channel would be centered on the dedicated servo track. Head positioning mechanism 102 would then move head 100 such that the channel is centered on the dedicated servo track which would accurately position the other two channels on data tracks. The two channels accessing data tracks could then, with the elements thereon, read data from or write data on the data tracks. Although the preferred embodiment of the present invention includes a magnetic tape having 60 data tracks and 10 dedicated servo tracks and a multiple channel head having three channels, it is to be understood that a tape with different numbers of data tracks and dedicated servo tracks and/or a head with a different number of channels could be used. For instance, with very few changes, the preferred embodiment could be modified so that the tape had more or less than 70 total tracks as long as the ratio of data tracks to dedicated servo tracks was 6 to 1. For example, a tape could have 5 dedicated servo tracks and 30 data tracks. In this embodiment, the 3-channel head disclosed above could access the 30 data tracks by moving the head to 15 unique positions where each position is defined by a unique combination of channel and dedicated servo track. It is also to be understood that other modifications could be made and that all such modifications falling within the scope of the appended claims are intended to be included in the present invention.

Claims: A method of recording and reproducing data on magnetic recording tape, comprising: recording servo tracking data on at least a first longitudinally extending servo track (26) within a section (260) of magnetic recording tape (12,120), and controllably transversely positioning a multiple channel head (10,100) having at least three channels (14,16,18), with respect to said servo track, characterised by: performing said recording step such that said section (260) of said tape is nominally located midway across the width of the tape (12,120), thereby dividing the tape into two portions, defining along each of said portions a plurality of additional longitudinally extending sections (200-240, 280-320), adjacent to each other across the width of the tape and having the same predetermined width and within each of which additional sections at least one track (20-24, 28-32) of data may be recorded and reproduced; providing a multiple channel head having the additional following features: the center-to-center distance between at least two of said channels (14,16) being equal to the center-to center distance (D1) between said adjacent sections, and the center-to-center distance (D2) between a third channel (18) and the closest (16) of the other channels being equal to twice the center-to-center distance (D1) between said adjacent sections, positioning the head at predetermined transverse locations (34,36,38), each of said predetermined locations (34,36,38) being such that one of the channels (14,16,18) will always be located to reproduce said servo tracking data from the servo track (26) while the other channels (14,16,18) access said additional sections (200-240,280-300) at which data tracks (20-24, 28-32) may be located, and thereby enabling the section containing said servo track to be reproduced and at least two of said additional sections to be recorded or reproduced. A method according to claim 1, further comprising: controllably positioning (102) the head (10, 100) such that one of the channels (14, 16, 18) thereof is proximate said track (26) having servo tracking data recorded thereon; reproducing servo tracking data from said servo data containing track; and using the reproduced servo tracking data in a servo loop to continuously reposition the head such that one of the channels thereof is at the center of said servo data containing track (26). A method according to claim 2, wherein the using step comprises reading the servo tracking data from the first dedicated servo track (26) with the channels (14, 16, 18) that is accessing the first dedicated servo track to obtain position information, using the position information to determine the error between the position of the head (10) and the one predetermined position, and using the error information to move the head (10) to that predetermined position. A method according to claim 1, further characterized by providing the first dedicated servo track (26) as one of a plurality of dedicated servo tracks, with a ratio of data tracks (20-24, 28-32) to dedicated servo tracks equal to six. A method according to claim 4, wherein 60 data tracks and ten dedicated servo tracks are provided on the tape. A method according to claim 1, further characterized in that each of said sections (200-320) is sufficiently wide to contain a predetermined number of tracks, and by recording said predetermined number of servo tracks within the midway located section, such that said predetermined number of data tracks may be record and reproduced along each of the other sections. A method according to claim 1, further characterized in that each of said sections (200-320) is substantially one track wide, and by recording one servo track (26) within the midway located section (260), such that one data track may be recorded and reproduced within each of the other sections. A method according to claim 1, wherein said multiple channel head (10) includes three channels (14, 16, 18), each having at least one read (40, 44, 46, 50, 52, 56) and one write (42, 48, 54) element, and wherein each of said two portions of the tape on either side of the midway located section is adapted to have three sections on which data tracks may be recorded and reproduced, whereby by positioning said head at one of said predetermined locations, one of said channels (14, 16, 18) will always be positioned to access said servo track (26) and the other channels (14, 16, 18) will always be located to access six track locations, one within each of the data track containing sections. A method according to claim 10, wherein each of said sections (200-320) is sufficiently wide to contain ten tracks, ten servo tracks are recorded within the midway located section (260) and ten data tracks may be recorded and reproduced within each of the other sections, thereby enabling sixty tracks of data to be recorded and reproduced. A system for recording and reproducing data comprising: a magnetic recording tape (12, 120) having servo tracking data recorded on at least a first longitudinally extending servo track (26) within a section (260) of said tape, a multiple channel head (10) having at least three channels (14, 16, 18) and means (102) for controllably transversely positioning the head (10, 100), characterised by: said section (260) of said tape being nominally located midway across the width of the tape (12, 120) thereby dividing the tape into two portions along each of which may be located a plurality of additional longitudinally extending sections (200-240, 280-320) , all sections (200-300) being adjacent to each other across the width of the tape (12, 120) and having the same predetermined width, within each of which additional sections (200-240, 280-320) at least one track of data may be recorded and reproduced; the center-to-center distance (D1) between at least two (14, 16) of said channels of the head being equal to the center-to-center distance (D1) between said adjacent sections (20-32), and the center-to-center distance (D2) between a third channel (18) and the closest (16) of the other channels being equal to twice the center-to-center distance (D1) between said adjacent sections; and said positioning means being operable to position the head at any of a plurality of predetermined locations such that one of the channels is always located to reproduce said servo tracking data from the servo track while the other channels access said additional sections at which data tracks may be located. A system according to claim 10 , comprising means (102) for reading the servo tracking data from the first dedicated servo track with the channel that is accessing the first dedicated servo track to obtain position information, means (102) for using the position information to determine the error between the position of the head and the one predetermined position, and means (102) for using the error information to move the head to that predetermined position. A system according to claim 10 , wherein said tape (12, 120) includes the first dedicated servo track as one of a plurality of dedicated servo tracks, the tape further including a ratio of data tracks to dedicated servo tracks equal to six. A system according to claim 10, wherein said multiple channel head (10) includes three channels, the center-to-center distance (D1) between two (14, 16) of which is equal to the center-to-center distance (D1) between said adjacent sections (200-320) and the center-to-center distance (D2) between the third channel (18) and the closest (16) of the other two channels is equal to twice the distance (D1) between said adjacent sections. A system according to claim 10 , wherein each- of said sections (200-320) is sufficiently wide to contain a predetermined number of tracks, said predetermined number of servo tracks recorded within the midway located section (260) and a said predetermined number of data tracks may be recorded and reproduced along each of the other sections.

Inventors: YOUNGOUIST ROBERT J C O MINNES, YOUNGOUIST, ROBERT J. C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1990
Main classification: G11B5
IPC codes: G11B5