Abstract:
A magnetic tape head assembly comprised of read and write elements and servo readers placed asymmetrically about the center of the head taken perpendicular to the direction of tape motion is provided. The tape head is capable of reading and writing in two directions of tape motion.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to magnetic tape heads. More specifically, the present invention relates to a method and apparatus for reducing the complexity of tape heads while accommodating an increased number of data tracks on record media. 
     2. Description of Related Art 
     Advanced record media (tapes) store data on multiple data tracks, which run parallel to each other over the length of the tape. However, there is an inherent problem associated with independent data tracks. As the tape moves past the tape head, lateral drift of the tape could result in the head reading or writing on the wrong data track. This would obviously degrade the quality of data storage and retrieval. To ensure that the tape heads are accurately positioned relative to the tape, dedicated servo tracks are usually recorded on the tape parallel to the data tracks. These servo tracks are read by servo readers on the tape head. The servo readers then signal mechanisms within the tape drive that are capable of adjusting the tape head in order to maintain proper alignment with the data tracks. The standard configuration in a three-module read/write/read head is to place servo readers symmetrically about the write module of the tape head. This placement allows the head to read or write in both directions of tape motion in a given position. 
     Increasing the amount of data on a fixed area of tape can be accomplished either by increasing the linear recording density or increasing the number of data tracks on tape. In the latter case, the data track width is reduced to accommodate the larger number of data tracks on a fixed width of tape. However, the larger number of data tracks requires an increase in the number of possible head positions relative to the tape, in order to accurately read and write the additional data tracks. For example, a 16-track head would require nine separate servo positions to write and read 144 tracks but 18 positions to write 288 tracks on the same tape. To accommodate the extra tracks, typical systems either increase the number of servo tracks on tape or increase the number of servo readers on the head. 
     However, both options have their drawbacks. If the number of servo tracks on the tape is increased, there will be less space available for data tracks. If the number of servo readers is increased, the tape heads will become more complex, which presents problems for manufacturing, especially as the size of the tape heads is reduced. 
     Therefore, a tape head design that can efficiently accommodate increased information storage, without increasing complexity is desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetic tape head assembly comprised of read and write elements and servo readers placed asymmetrically about the center of the head taken perpendicular to the direction of tape motion. The tape head is capable of reading and writing in two directions of tape motion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 depicts a two channel recording head with symmetric servo readers and a magnetic tape with four data tracks and one servo track in accordance with the prior art; 
     FIG. 2 depicts a two channel recording head with asymmetric servo readers and a magnetic tape with four data tracks and one servo track in accordance with the present invention; and 
     FIG. 3 depicts a two channel recording head with asymmetric servo readers in accordance with an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the figures, and in particular FIG. 1, a schematic diagram illustrating a prior art tape head data track positioning system using servo tracks and symmetric servo readers is depicted. A portion of the tape  101  is divided into data tracks  102 ,  103 ,  104 , and  105  and a servo track  106 , which run parallel to each other over the length of the tape  101 . In this example, all four data tracks  102 - 105  are written in the same direction of tape motion, as indicated by the arrows. The same tape head  107  as viewed looking down on the head/tape interface is represented twice, in different lateral positions relative to the tape  101 . 
     When the tape head  107  is in the first position, the read/write element  108 / 109  are aligned with data tracks  102  and  104 . Each read/write elements  108 / 109  has read elements  108 , which read any data recorded on the tape  101 , and write elements  109  that can record new data on the tape  101  if needed. 
     As the tape  101  passes over the tape head  107 , the tape  101  can drift laterally relative to the head  107 , resulting in track misregistration in which the read/write elements  108 / 109  mistakenly read or write on tracks  103  and  105 , instead of tracks  102  and  104 . Such track misregistration interferes with proper data storage and retrieval. 
     To prevent track misregistration, a servo track  106  recorded parallel to the data tracks  102 - 105  is read by dedicated servo readers  110 - 113 . The servo readers signal mechanisms within the tape drive, which are capable of adjusting the tape head  107  in order to maintain proper alignment between the tape  101  and the tape head  107 . 
     In the first head position, servo reader  111  reads the servo track  106  when the tape  101  is moving in the direction indicated by the arrows. The servo reader ensures that the read/write elements  108 / 109  remain in line with data tracks  102  and  104 . If the direction of tape motion is reversed from that shown, the servo track  106  would be read by servo reader  113 . It must be pointed out that the choice of which servo reader will read the servo track  106  in each direction of tape motion is arbitrary and depends on the specific application. For example, it is possible for servo reader  113  (rather than servo reader  111 ) to read servo track  106  in the direction of tape motion indicated by the arrows. The main idea is that there is a separate active servo reader designated for each direction of tape motion. 
     If the tape head  107  is moved to the second position, the read/write elements  108 / 109  would be aligned with data tracks  103  and  105 . In the direction of tape motion indicated by the arrows, the servo track  106  would be read by servo reader  110 . If the direction of tape motion is reversed, the servo track  106  would then be read by servo reader  112 . Again, which servo reader is active for each direction of tape motion is arbitrary, the important point being that there is a separate active servo reader for each direction. 
     Thus, in each position the tape head  107  is able to read and write in both directions of tape motion. In order to accomplish this task, the servo readers  110 - 113  are placed symmetrically about the write bumps containing write elements  109  and aligned on the read bumps containing read elements  108 . However, problems with this symmetric servo placement arise as information storage increases. 
     Increasing the amount of data on a fixed area of tape can be accomplished either by increasing the linear recording density or increasing the number of data tracks on tape. In the latter case, the data track width is reduced to accommodate the larger number of data tracks on a fixed width of tape. However, the larger number of data tracks requires an increase in the number of possible head positions relative to the tape, in order to accurately read and write the additional data tracks. For example, a 16-track head would require nine separate servo positions to write and read 144 tracks but 18 positions to write 288 tracks on the same tape. To accommodate the extra tracks, typical systems either increase the number of servo tracks on tape or increase the number of servo readers on the head. This problem becomes very clear when one considers the fact that modern tape drives might have to accommodate half-inch tape with as many as 288 data tracks moving at speeds of up to 2 meters per second. Future tape drives will have to deal with even greater track densities. 
     To accommodate the increased number of tracks on tape, either the number of servo tracks on the tape or the number of servo readers on the head must be increased. Unfortunately, both options have their drawbacks. If the number of servo tracks is increased, there will be less room available on the tape for data tracks. If more servo readers are added, the tape head will become more complex. 
     With reference to FIG. 2, a schematic diagram illustrating a tape head is depicted in accordance with the present invention. Like the prior art tape  101  depicted in FIG. 1, the tape  201  is divided into four data tracks  202 ,  203 ,  204 , and  205  as well as one servo track  206 . However, unlike FIG. 1, the four data tracks  202 - 205  are written in opposite directions of tape motion, as indicated by the arrows. Again, the same tape head  207  as viewed looking down on the head/tape interface is represented twice, in different lateral positions relative to the tape  201 . 
     When the head  207  is in the first position, the read/write elements  208 / 209  are aligned with data tracks  202  and  204 . The.servo track  206  is read by servo reader  210 . When the head  207  is moved to the second position, the read/write elements  208 / 209  are aligned with data tracks  203  and  205 , and the servo track  206  is read by servo reader  211 . As stated above in relation to FIG. 1, for each direction of tape motion, the placement of the active servo reader in relation to the write element  209  is arbitrary and depends on the specific application. Therefore, the asymmetric servo readers in FIG. 2 can also be placed so that they lead the write elements  209 . For example, servo readers  210  and  211  could be placed in the positions equivalent to those of servo readers  113  and  110  from FIG. 1, respectively, with no change in direction of tape motion. 
     In the present invention, each tape head position is reserved for one direction of tape motion, requiring only one servo reader for each position. Therefore, the servo readers  210  and  211  are placed asymmetrically about the write bumps containing write elements  209 , and aligned with the read bumps containing read elements  208 . By reducing the number of servo readers, the present invention produces a tape head  207  which is less complex than the standard tape head  107  found in the prior art. This reduction in complexity is especially important for manufacturing smaller tape heads in order to accommodate narrower data tracks. 
     To provide additional protection against track misregistration with the asymmetric servo placement, a small dead zone can be placed between data tracks written in opposite directions of tape motion. Such a dead zone would provide a cushion for lateral drift without requiring the same amount of space as a dedicated servo track. 
     Referring now to FIG. 3, a schematic diagram depicts an alternative embodiment of the present invention. In this embodiment all four data tracks  302 - 305  are written in the same direction of tape motion, as indicated by the arrows. Similar to FIG. 2, the first head position corresponds with reading/writing data tracks  302  and  304 , and the second head position corresponds with reading/writing data tracks  303  and  305 . In the first head position, servo reader  310  trails the write element  309 , due to the tape direction indicated. In the second head position, because the tape is moving in the same direction as position one, servo reader  311  leads the write element  309 . If the direction of tape motion was reversed from that shown, servo reader  310  would lead the write element  309  and servo reader  311  would trail the write elements  309 . 
     Since the read-to-write module alignment is fixed, this process of switching between leading and trailing servo readers does not affect track misregistration during the write process. When reading pre-written data tracks with the asymmetric head configuration, the reading is performed by the read element located on the same bump as the servo reader. 
     The asymmetric servo reader placement is relevant to head configurations other than the three-bump read/write/read tape head. In particular, asymmetric servo readers are applicable to two-bump head designs where the servo readers may be in the same module as the read and write elements. 
     By relying on an asymmetric servo placement, the present invention allows tape head designers to overcome constraints imposed by traditional, symmetric configurations. Whereas conventional tape head designs require more complexity to deal with increased data storage, the present invention has the double advantage of increasing yield while reducing tape head complexity. The asymmetric servo design provides the enabling technology for a new generation of high-density tape drives. 
     Although described primarily with reference to tapes with four data tracks and one servo track in the middle, one of ordinary skill in the art will recognize that the principles of the present invention apply equally to tapes with other data track/servo track configurations. 
     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.