Patent Publication Number: US-2010128379-A1

Title: Guide assembly for reducing lateral tape motion in a tape drive

Description:
BACKGROUND 
     Magnetic storage tapes are commonly used to store relatively large amounts of information in digital form. These storage tapes, also known as cartridges, have become increasingly efficient to use due to their low cost, portability, and substantial storage capacity. In contrast to hard disks that are relatively inaccessible within the hard disk drive assembly, the cartridge is easily removed from a tape drive, and can be economically transferred to remote locations for use in another tape drive. A typical cartridge includes a tape having a substrate, a coating of magnetic recording material on one side of the substrate, and a high durability “back coating” on the other side of the substrate. The tape drive includes a head assembly that transfers data to and from the tape. For multi-track tape drives, the head assembly includes a tape head that can move to the appropriate vertical location along the width of the tape for reading data from and/or writing data to a particular track on the tape. 
     In one type of tape drive, the tape runs between a supply reel within the cartridge and a take-up reel within the tape drive. A guide assembly, which typically includes a set of tape rollers, guides the tape along a tape path that passes across the head assembly. This type of guidance must be performed accurately and consistently to avoid lateral tape motion (“LTM”), which can lead to data reading and writing errors. “Lateral tape motion” is defined herein as any deviation from the perfect plane path of the tape near the head assembly as the tape travels between the supply reel to the take-up reel, in either direction. One measure of LTM is the peak-to-peak distance that the tape moves perpendicular to a prescribed longitudinal direction of motion of the tape past the head assembly. 
     Causes of LTM can include planar misalignment of the cartridge, the rollers, and or the take-up reel relative to one another. In addition, rotating components in the tape drive, such as the cartridge reel, the take-up reel, guide rollers, etc., can contribute to LTM. Further, any surface condition or anomaly that tends to inflict a deviation from the perfect path can cause LTM. For example, surface conditions resulting from roller design or contamination and vibration can result in excessive LTM. In addition, thinner tape tends to be less rigid than thicker tape, which can lead to decreased control over movement of the tape  26 . Because cartridges are currently manufactured using relatively thin tape, i.e. 0.5 mil or less, preventing LTM has become increasingly difficult. Decreasing perpendicular misalignment in all directions has been used to reduce LTM. Other attempts at reducing LTM include increasing the mechanical precision of rotating structures within the tape drive. 
     In certain tape drives, the positioning and type of rollers used in the guide assembly can cause a condition that is known as “directional continuity shift” (also sometimes referred to herein as “DC shift”). DC shift can occur when orientation of the rollers and/or a groove pattern on the rollers tends to cause the tape to move laterally in one direction, i.e. perpendicular to the direction of the moving tape. Reversal of the tape direction then causes an abrupt change in the lateral tape motion, so that the tape is moving laterally in the opposite direction. The result of DC shift is that a track of data in one direction is not at the precise vertical location when read in the opposite direction. 
     Today&#39;s cartridges utilize tape with more densely positioned data tracks. Tape drives attempt to precisely register data tracks using servo tracks and servo systems. By positioning the tracks closer together, more data can be stored in a given length of tape. The addition of more tracks leads to a decrease in the physical separation between the tracks, thereby lowering the “guard band” or margin of safety between the tracks. A lower guard band requires a decreased LTM and/or DC shift during operation in order to reduce reading and writing errors. 
     SUMMARY 
     The present invention is directed toward a guide assembly for guiding movement of a tape past a head assembly in a tape drive. The tape moves along a tape path, with the tape having a first side that contacts the head assembly, and an opposing second side. In one embodiment, the guide assembly includes a rotatable roller and a non-rotatable tape guide. The rotatable roller and the tape guide each guides the tape along the tape path. In certain embodiments, the tape guide is positioned to contact the first side of the tape. Further, the tape guide is positioned between the rotatable roller and the head assembly relative to the tape path. 
     In some embodiments, the tape guide includes a first flange that contacts the tape during movement of the tape along the tape path. The tape drive also includes a housing. The tape guide includes a proximal end that is secured to the housing. In one embodiment, the first flange is positioned near the proximal end. The tape guide also includes a distal end opposite the proximal end. In one embodiment, the tape guide can include a second flange that is positioned near the distal end. In accordance with one embodiment, the tape moves along the tape path guided by the first flange and the second flange. In certain embodiments, the tape guide is positioned more closely to the head assembly than the tape guide is to the rotatable roller. In some embodiments, the tape guide is positioned less than approximately 5 mm from the head assembly. Further, the tape path can be uninterrupted between the rotatable roller and the tape guide. In one embodiment, the tape guide is movable in a direction that is approximately perpendicular to the direction of the tape path. Additionally, in one embodiment, the tape forms a tape wrap angle relative to the tape guide that is less than approximately 20 degrees. 
     The present invention is also directed toward a method for guiding a tape along a tape path across a head assembly in a tape drive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a top plan view of a portion of a tape drive-including a guide assembly having features of the present invention: 
         FIG. 2A  is a simplified top view of a portion of a tape, a tape head and one embodiment of the guide assembly including a rotatable roller and a non-rotatable tape guide; 
         FIG. 2B  is a simplified top view of a portion of a tape, a tape head and another embodiment of the guide assembly including a rotatable roller and a tape guide, 
         FIG. 3A  is a side view of one embodiment of the tape guide; 
         FIG. 3B  is a side view of another embodiment of the tape guide; 
         FIG. 3C  is a side view of yet another embodiment of the tape guide; 
         FIG. 3D  is a side view of still another embodiment of the tape guide; 
         FIG. 3E  is a side view of another embodiment of the tape guide, 
         FIG. 3F  is a side view of yet another embodiment of the tape guide; 
         FIG. 4A  is a graph illustrating experimental results of position error signal over time using a prior art guide assembly; and 
         FIG. 4B  is a graph illustrating experimental results of position error signal over time using one embodiment of the guide assembly having features of the present invention. 
     
    
    
     DESCRIPTION 
       FIG. 1  is a top view of a portion of a tape drive  10  designed for use with a tape cartridge  12  (also referred to herein as “cartridge”). In one embodiment, the tape drive  10  includes a drive housing  14 , a head assembly  16 , a take-up reel  18 , a cartridge receiver  20  (illustrated with dashed lines), and a guide assembly  22 . 
     The design of the tape drive  10  can vary. A detailed description of various components of one embodiment of the tape drive  10  is provided in U.S. Pat. No. 5,371.638, issued to Saliba, and assigned to Quantum Corporation, the Assignee of the present invention. To the extent permitted, the contents of U.S. Pat. No. 5,371,638 are incorporated herein by reference. The drive housing  12  retains the various components of the tape drive  10 . 
     The cartridge  12  can vary in size and shape. The cartridge  12  includes a cartridge reel  24 , a storage tape  26  (sometimes referred to herein as “tape”) and a substantially rectangular cartridge housing  28  that encloses the cartridge reel  24  and the tape  26 . During use, the cartridge  12  inserted into the cartridge receiver  20  of the tape drive  10 . 
     In a typical cartridge  12 , the tape  26  is positioned on the cartridge reel  24 . The tape  26  stores data in a form so that the data can be subsequently retrieved. The tape  26  moves along a tape path  29  (as illustrated by arrow) between the cartridge reel  24  of the cartridge  12  and the take-up reel  18  of the tape drive  10 . The specific angle and positioning of the tape path  29  varies within the tape drive  10  depending upon the positioning and configuration of the guide assembly  22  that guides the tape  26  within the drive housing  14 . For example, arrow  29  is representative of the direction of the tape path  29  in one specific location within the tape drive  10 . It is recognized that the orientation of arrow  29  changes along the length of the tape path  29  in other locations within the tape drive  10 . 
     The tape  26  includes a first side  30  and an opposing second side  32 . In one embodiment, one of the sides  30 .  32  stores the data. In the embodiment illustrated in  FIG. 1 , the first side  30  directly faces and contacts the head assembly  16 . Thus, in this embodiment, the first side  30  is configured to store data. It is recognized that in other embodiments, the second side  32  can additionally or alternatively be adapted to store data. 
     The drive housing  14  generally houses and/or surrounds the components within the tape drive  10 . 
     The head assembly  16  is coupled or directly secured to the drive housing  14 . The head assembly  16  includes a tape head  34  that reads data from and writes data to the tape  26 . In one embodiment, the head assembly  16  can also include an actuator (not shown) that moves the tape head  34  in a direction that is approximately perpendicular to the direction of movement of the tape  26  along the tape path  29 , i.e. in and out of the page in  FIG. 1 . With this design, the tape head  34  can adjust for slight variations in the position of the tape  26  when the tape moves along the tape path  29  across the tape head  34 . 
     The guide assembly  22  guides the tape  26  along the tape path  29  past the head assembly  16  and onto the take-up reel  18 . The guide assembly  22  inhibits lateral tape motion during operation of the tape drive  10 , as described in greater detail below. In one embodiment, all or some of the guide assembly  22  is coupled or directly secured to the drive housing  14 . 
     In one embodiment, the guide assembly  22  includes one or more tape rollers including at least a first roller  36 A. In the embodiment illustrated in  FIG. 1 , the guide assembly  22  includes six rollers  36 A- 36 F. However, the number of rollers  36 A- 36 F can be varied to suit the design requirements of the tape drive  10 . The design of the rollers  36 A- 36 F can vary. In one embodiment, all of the rollers  36 A- 36 F are rotatable. In another embodiment, some of the rollers  36 A- 36 F can be rotatable, and some of the rollers  36 A- 36 F can be fixed. Further, the rollers  36 A- 36 F can be identical to one another, or one or more of the rollers  36 A- 36 F can be different from one another. In one embodiment, at least roller  36 A is rotatable. 
     As used herein, the “first roller  36 A” is the one roller of the plurality of tape rollers  36 A- 36 F that is most closely positioned to the head assembly  16  on a cartridge  12  side of the tape path  29  (as opposed to a take-up reel  18  side of the tape path  29 ). Stated another way, the first roller  36 A is positioned between the head assembly  16  and the cartridge  12  relative to the tape path  29 , with no other rollers  36 B- 36 F being positioned between the first roller  36 A and the head assembly  16  relative to the tape path  29 . 
     In the embodiment illustrated in  FIG. 1 , the guide assembly  22  also includes a tape guide  38  that contacts and guides movement of the tape  26  along the tape path  29 . The configuration of the tape guide  38  can be varied depending upon the design requirements of the guide assembly  22  and the tape drive  10 . In certain embodiments, the tape guide  38  is non-rotatably mounted or coupled to the drive housing  14 . With this design, any rotational vibration from the tape guide  38  is eliminated. In an alternative embodiment, the tape guide  38  can be rotatably mounted or coupled to the drive housing  14 . 
     The positioning and configuration of the tape guide  38  causes a reduction in LTM as provided herein. In the embodiment illustrated in  FIG. 1 , the tape guide  38  is positioned substantially between roller  36 A and the head assembly  16  relative to the tape path  29 . In one embodiment, the tape guide  38  is positioned on the same side of the tape  26  as the head assembly  16 . In other words, the tape guide  38  contacts the same side of the tape  26  as does the head assembly  16 . In the embodiment illustrated in  FIG. 1 , the tape guide  38  contacts the first side  30  of the tape  26 . With this design, the tape path  29  does not extend directly between the tape guide  38  and the head assembly  16 . 
     In one embodiment, the tape guide  38  is positioned adjacent to the head assembly  16  to provide a relatively stable and/or substantially immobile surface that aligns and/or guides the tape  26  immediately adjacent to the tape head  34 . For example, in accordance with one embodiment, the tape guide  38  can be positioned as close as possible to the head assembly  16  without being in contact with the head assembly  16 . In one embodiment, the tape guide  38  is positioned more proximate the head assembly  16  than the tape guide  38  is to the first roller  36 A. In non-exclusive alternative embodiments, the tape guide.  38  can be positioned less than approximately 5 mm, 4 mm, 3 mm, 2 mm, 1 mm, 0.5 mm or 0.1 mm from the head assembly  16 . Due to the proximity of the tape guide  38  to the tape head  34 , LTM disturbances that can be caused by the rollers  36 A- 36 F or other structures along the tape path  29  are attenuated immediately prior to the tape  26  passing across the tape head  34 . In alternative embodiments, the tape guide  38  can be positioned further than 5 mm from the head assembly  16 . 
     Further, in one embodiment, the tape guide  38  is continuously in contact with the tape  26  during normal movement of the tape  26  along the tape path  29 . With this design, any “bounce” associated with an initiation of contact between the tape guide  38  and the tape  26  is inhibited or eliminated completely. In another embodiment, the tape guide  38  can be movably positioned to selectively contact the tape  26  at certain times during operation of the tape drive  10 , i.e. during reading and/or writing operations, for example. In this embodiment, the guide assembly  22  can include a guide actuator (not shown) that movably positions the tape guide  38  relative to the tape path  29 , as necessary, based on the design requirements of the tape drive  10 . For example, the guide actuator can move the tape guide  38  between a first position in which the tape guide  38  contacts the tape  26 , and a second position in which the tape guide  38  is not in contact with the tape  26 . The guide actuator can use any actuation means known to those skilled in the art for movement of structures within the tape drive  10  or other similar device. 
       FIG. 2A  is a simplified top view of a portion of the tape  226 , and a portion of one embodiment of the tape drive  210 A. In this embodiment, the tape drive  210 A includes the head assembly  216  and one embodiment of the guide assembly  222 A including the rotatable first roller  236 A and the tape guide  238 . In the embodiment illustrated in  FIG. 2A , the first roller  236 A, the tape guide  238  and the head assembly  216  are each positioned to contact the first side  230  of the tape  226 . With this design, the tape  226  is more easily positioned during loading and unloading because each of these structures, i.e. the first roller  236 A, the tape guide  238  and the head assembly  216  is positioned on the same side of the tape  226 . 
     Additionally, in this embodiment, the tape  226  forms a relatively small tape wrap angle  240 A at the tape guide  238 . In one embodiment, the tape wrap angle  240 A is less than approximately 30 degrees. In non-exclusive alternative embodiments, the tape wrap angle  240 A is less than approximately 20 degrees, 15 degrees, 10 degrees, 5 degrees or 2 degrees. In still an alternative embodiment, the tape wrap angle  240 A can be greater than 30 degrees. 
     Moreover, in one embodiment, the tape guide  238  can be substantially circular, and can have a diameter that is less than approximately 5 mm. In non-exclusive alternative embodiments, the tape guide  238  can have a diameter that is less than approximately 4 mm, 3 mm or 2 mm. In still another embodiment, the tape guide  238  can have a diameter that is greater than approximately 5 mm. In yet another embodiment, the tape guide  238  can have a non-circular shape. For example, in certain embodiments, because only a portion of the tape guide  238  contacts the tape  226  due to the non-rotation of the tape guide  238 , the tape guide  238  can be elliptical, semi-circular or can have any other suitable configuration. 
       FIG. 2B  is a simplified top view of a portion of the tape  226 , and a portion of another embodiment of the tape drive  210 B. In this embodiment, the tape drive  210 B includes the head assembly  216  and another embodiment of the guide assembly  222 B including the rotatable first roller  236 A and the tape guide  238 . In the embodiment illustrated in  FIG. 2A , the first roller  236 A, the tape guide  238  and the head assembly  216  are each positioned to contact the first side  230  of the tape  226 . With this design, the tape  226  is more easily positioned during loading and unloading because each of these structures, i.e. the first roller  236 A, the tape guide  238  and the head assembly  216  is positioned on the same side of the tape  226 . 
     Additionally, in this embodiment, the tape  226  forms a relatively small tape wrap angle  2408  at the tape guide  238 . In one embodiment, the tape wrap angle  240 B is less than approximately 30 degrees. In non-exclusive alternative embodiments, the tape wrap angle  240 B is less than approximately 20 degrees, 15 degrees, 10 degrees, 5 degrees or 2 degrees. In still an alternative embodiment, the tape wrap angle  240 B can be greater than 30 degrees. 
       FIGS. 3A-3F  illustrate various side views of different embodiments of the tape guide  338 A- 338 F. Each tape guide  338 A- 338 F is coupled or directly secured to the drive housing  14  (illustrated in  FIG. 1 ). Further, each tape guide  338 A- 338 F includes a corresponding proximal end  342 A- 342 F that is secured to the drive housing  14 , and a distal end  344 A- 344 F that is not secured to the drive housing  14 . In an alternative embodiment, the distal end  344 A- 344 F can also be secured to the drive housing  14  at a different location from the proximal end  342 A- 342 F. 
       FIG. 3A  illustrates one embodiment of the tape guide  338 A having a substantially cylindrical configuration. In this embodiment, the tape  326  (illustrated in phantom) moves against the tape guide  338 A along the tape path  329  (indicated by bidirectional arrow). The dimensions of the tape guide  338 A can vary. In one embodiment, the tape guide has a height that is at least as great as the width of the tape  326 . 
       FIG. 3B  illustrates another embodiment of the tape guide  338 B having a substantially cylindrical core  346 B and a first flange  348 B. In this embodiment, the first flange  348 B is substantially disk-shaped, and can have a substantially rectangular cross-section, as illustrated in  FIG. 3B . In accordance with this embodiment, the tape  326  (illustrated in phantom) moves against the core  346 B of the tape guide  338 B, while simultaneously contacting the first flange  348 B. Thus, in this embodiment, the first flange  348 B can support the tape  326  as the tape  326  moves along the tape path  329 . With this design, the first flange  348 B can maintain the proper vertical position of the tape  326  as the tape  326  passes across the head assembly  16  (illustrated in  FIG. 1 ), thereby reducing the likelihood and extent of LTM. 
       FIG. 3C  illustrates another embodiment of the tape guide  338 C having a substantially cylindrical core  346 C and a first flange  348 C. In this embodiment, the first flange  348 C can include a chamfer  350 C and a contact surface  352 C, as illustrated in  FIG. 3C . In accordance with this embodiment, the tape  326  (illustrated in phantom) moves against the core  346 C of the tape guide  338 C, while simultaneously contacting the contact surface  352 C of the first flange  348 C. Thus, in this embodiment, the first flange  348 C can support the tape  326  as the tape  326  moves along the tape path  329 . With this design, the first flange  348 C can maintain the proper vertical position of the tape  326  as the tape  326  passes across the head assembly  16  (illustrated in  FIG. 1 ), thereby reducing the likelihood and extent of LTM. 
       FIG. 3D  illustrates another embodiment of the tape guide  338 D having a substantially cylindrical core  346 D and a first flange  348 D. In this embodiment, the first flange  348 D can include a chamfer  350 D that slopes substantially downward away from the core  346 D, as illustrated in  FIG. 3D . In accordance with this embodiment, the tape  326  (illustrated in phantom) moves against the core  346 D of the tape guide  338 D, while simultaneously contacting the chamfer  350 D of the first flange  348 D. Thus, in this embodiment, the first flange  348 D can support the tape  326  as the tape  326  moves along the tape path  329 . Further, because of the chamfer  350 D, buckling of the tape  326  can be inhibited or eliminated. With this design, the first flange  348 D can maintain the proper vertical position of the tape  326  as the tape  326  passes across the head assembly  16  (illustrated in  FIG. 1 ), thereby reducing the likelihood and extent of LTM. 
       FIG. 3E  illustrates another embodiment of the tape guide  338 E having a substantially cylindrical core  346 E and a first flange  348 E. In this embodiment, the first flange  348 E can include a curved support surface  354 E that gradually slopes substantially downward away from the core  346 E, as illustrated in  FIG. 3E . In accordance with this embodiment, the tape  326  (illustrated in phantom) moves against the core  346 E of the tape guide  338 E, while simultaneously contacting the curved support surface  354 E of the first flange  348 E. Thus, in this embodiment, the first flange  348 E can support the tape  326  as the tape  326  moves along the tape path  329 . Further, because of the curved support surface  354 E, buckling of the tape  326  can be inhibited or eliminated. With this design, the first flange  348 E can maintain the proper vertical position of the tape  326  as the tape  326  passes across the head assembly  16  (illustrated in  FIG. 1 ), thereby reducing the likelihood and extent of LTM. 
       FIG. 3F  illustrates another embodiment of the tape guide  338 F having a substantially cylindrical core  346 F, a first flange  348 F and a second flange  356 F. In this embodiment, the first flange  348 F can include a first contact surface  352 F, and the second flange  356 F can include a second contact surface  358 F. In one such embodiment, the distance between the first contact surface  352 F and the second contact surface  358 F is substantially similar to the width of the tape  326 . In accordance with this embodiment, the tape  326  (illustrated in phantom) moves against the core  346 F of the tape guide  338 F, while simultaneously contacting the first contact surface  352 F of the first flange  348 F and the second contact surface  358 F of the second flange  356 F. Thus, in this embodiment, the first flange  348 F and the second flange  356 F can maintain the proper vertical positioning of the tape  326  as the tape  326  moves along the tape path  329 , thereby reducing the likelihood and extent of LTM. 
       FIG. 4A  is a graph illustrating experimental results of a head position signal over time in the absence of a guide assembly having features of the present invention. In  FIG. 4A , the graph shows that the head position signal varies to a significant extent over time, as indicated by a sensor which monitors the extent of vertical movement of the tape head. In other words, the more variation in the vertical adjustment of the tape head that is detected by the sensor, the more LTM is occurring. In this embodiment, a variable inductance (VI) sensor was utilized. However, it is understood that other suitable types of sensors could be utilized during this type of experimentation process. 
       FIG. 4B  is a graph illustrating experimental results of the head position signal over time using one embodiment of the guide assembly having features of the present invention. As illustrated in  FIG. 4B , the variation of the head position signal is reduced, and is more constant than that illustrated in  FIG. 4A . Stated another way, vertical adjustment of the tape head has been reduced, which is indicative of a corresponding reduction in LTM. 
     While the particular tape drive  10  and guide assembly  22  as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.