Abstract:
An integral recording head, for use in a linear tape drive system, includes a circumferentially grooved roller guide assembly and a recording head actuator assembly. The circumferential groove feature is incorporated on the surfaces of the roller guide assembly, and provides a substantial frictional contact force that acts to reduce the lateral motion, and further attenuates high frequency lateral disturbances of the magnetic tape. The reduced high frequency content of the lateral disturbances significantly improves the ability of the actuator to achieve a desired track following control. The grooved roller guide assembly is formed integrally of two solid cylindrical contact surfaces separated by a circumferential slot that accommodates the recording head actuator assembly.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates in general to data storage systems and in particular to linear tape drive systems. More specifically, the present invention provides a new design for substantially improving track density in linear tape drive systems.  
       BACKGROUND OF THE INVENTION  
       [0002]     Magnetic media represent a common form of digital data storage for computer systems. Among the magnetic storage systems, linear tape drive systems are in use in many enterprise applications for data management. Magnetic media are also currently used in hard disk drive systems. Hard drive systems typically have a larger storage capability than linear tape drive systems owing to their higher areal density, linear density, and track density. Areal density is a physical measure of storage systems that relates the number of data bits per unit surface area of magnetic storage media. Similarly, linear density is a measure of the number of data bits per unit length of data tracks, and track density is the number of data tracks that can be packed into a given form of magnetic media. In general, a larger density value corresponds to a higher storage capacity for a magnetic storage system.  
         [0003]     In one conventional tape design, the roller guide assembly employs a smooth surface with which the magnetic tape is in contact during a read write operation. The smooth roller surface does not allow for a sufficient frictional contact force to be developed thereon. The insufficient frictional contact force causes the magnetic tape to develop a significant lateral motion during a read write operation.  
         [0004]     Yet another problem with the conventional design of linear tape drive systems is the large spacing between the rollers, which causes the magnetic tape to be unsupported over a large span. The unconstrained magnetic tape between the rollers tends to develop lateral motion that generates a high frequency lateral disturbance, as the magnetic tape leaves the rollers and the supply reels, that can propagate to the recording head.  
         [0005]     The performance of conventional linear tape drive systems is further inhibited by placing the actuator containing the recording head distally from the rollers. As a result, any lateral disturbance in the magnetic tape will propagate to the recording head. Typically, the actuator that houses the recording head is designed to perform track following by closed-loop servo control. The track following servo control commands the actuator to move in the lateral direction so as to follow a target data track on the magnetic tape.  
         [0006]     As the magnetic tape experiences high frequency lateral disturbances, the track following servo control may not be able to maintain the desired track following performance within its frequency bandwidth. The resulting error due to the inability of the actuator to follow a target data track, herein also referred to as a track following error, thus imposes a performance limitation on the track width of the magnetic tape (in a conventional design) in that it cannot be smaller than the track following error. This limitation thus dictates the track density of the conventional design of linear tape drive systems.  
         [0007]     In view of the unresolved problems with the conventional designs of the linear tape drive, there is a need for an improved design that can effectively address the forgoing problems. Preferably, the improved design should be able to reduce substantially high frequency lateral disturbances of the magnetic tape. Moreover, the improved design should also be able to significantly reduce the track following error. By successfully resolving the forgoing concerns, an improved design should enable linear tape drive systems to achieve a higher track density, and hence a larger storage capacity.  
       SUMMARY OF THE INVENTION  
       [0008]     It is a feature of the present invention to provide a new integral recording head for use in a linear tape drive system. The recording head includes a circumferentially grooved roller guide assembly and a recording head actuator assembly. The circumferential grooves are incorporated on the surfaces of the roller guide assembly, thereby providing substantial frictional contact force that acts to reduce the tape lateral motion and to attenuate any high frequency lateral disturbances of the magnetic tape. The reduced high frequency content of the lateral disturbances significantly improves the ability of the actuator to achieve a desired track following control.  
         [0009]     In a preferred embodiment, the grooved roller guide assembly is formed integrally of two solid cylindrical contact surfaces separated by a circumferential slot having a constant width. The recording head actuator assembly includes a U-shaped head.  
         [0010]     In another preferred embodiment, the grooved roller guide assembly is formed by two removable hollow cylindrical surfaces that are designed to accommodate, within a hollow interior space therebetween, a recording head actuator assembly that is not constrained to fit within a circumferential slot.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The features of the present invention and the manner of attaining them will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein:  
         [0012]      FIG. 1  is a perspective view of a conventional linear tape drive system;  
         [0013]      FIG. 2  is a perspective view of a linear tape drive system of the present invention, shown comprising a grooved roller guide assembly and a recording head actuator assembly;  
         [0014]      FIG. 3  is a perspective view of a preferred embodiment of the grooved roller guide assembly of  FIG. 2 , shown formed of two solid cylindrical surfaces with a circumferential slot therebetween;  
         [0015]      FIG. 4  is a perspective, enlarged view of a U-shaped recording head actuator assembly that fits within the circumferential slot in the grooved roller guide assembly of  FIG. 2 ;  
         [0016]      FIG. 5  is an exploded view of  FIG. 4  showing a recording head, an actuator, and a U-shaped magnet that form the recording head actuator assembly of  FIG. 4 ;  
         [0017]      FIG. 6  is a perspective view of the grooved roller guide assembly of  FIG. 3  shown with the recording head actuator assembly of  FIG. 4  and a coarse lead screw actuator mounted on top and bottom support bases;  
         [0018]      FIG. 7  is a perspective view illustrating a portion of the magnetic tape wrapped around the grooved roller guide assembly of  FIG. 3 , which contains the recording head actuator assembly of  FIG. 4  therein;  
         [0019]      FIG. 8  is a perspective view of an alternative embodiment of the grooved roller guide assembly of  FIG. 2  provided with two removable cylindrical hollow surfaces designed to accommodate a recording head actuator assembly therebetween; and  
         [0020]      FIG. 9  is a perspective view of an alternative embodiment of the recording head actuator assembly designed to fit within the hollow interior of the grooved roller guide assembly of  FIG. 8 . 
     
    
       [0021]     Similar numerals in the drawings refer to similar elements. It should be understood that the sizes of the different components in the figures might not be in exact proportion, and are shown for visual clarity and for the purpose of explanation.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]      FIG. 1  illustrates a conventional linear tape drive system  100  that comprises a plurality of roller guide assemblies, a recording head actuator assembly  110 , a magnetic tape  115 , a supply reel  120 , and a take-up reel  125 . The conventional roller guide assemblies  105 ,  106 ,  107 ,  108  are generally separated by a substantial distance from each other, which typically ranges from approximately 1 to 2 inches. Further, each of these roller guide assemblies  105 ,  106 ,  107 ,  108  generally has a relatively smooth surface that contacts the magnetic tape  115 . The recording head actuator assembly  110  is also separated from the roller guide assemblies  105 ,  106 ,  107 ,  108  by a significant distance.  
         [0023]     During a read write operation, the magnetic tape  115  is driven by the take-up reel  125  as its travel is guided by the roller guide assemblies  105 ,  106 ,  107 ,  108  and the recording head actuator assembly  110 . The movement of the magnetic tape  115  causes the roller guide assemblies  105 ,  106 ,  107 ,  108  to rotate. The fixed locations of the roller guide assemblies  105 ,  106 ,  107 ,  108  significantly constrain the movement of the magnetic tape  115  along a tape path direction, and the smooth contact surfaces of the roller guide assemblies  105 ,  106 ,  107 ,  108  do not provide sufficient motion constraint for the magnetic tape  115  along the lateral direction that is denoted by the arrow  130 .  
         [0024]     The unconstrained lateral motion of the magnetic tape  115  over the open span between two contiguous roller guide assemblies, such as  107 ,  108 , can generate lateral disturbances with high frequency components, which, in certain cases, can exceed the bandwidth limit of a track following servo control utilized by the recording head actuator assembly  110 . The resulting track following error can therefore be significant and, as a result, it can impose a lower limit on the track width, which directly affects the track density of the magnetic tape  115 .  
         [0025]      FIG. 2  illustrates a linear tape drive system  200  of the present invention. The present linear tape drive system  200  generally comprises a platform  202 , a grooved roller guide assembly  205 , a recording head actuator assembly  210 , a plurality of roller guide assemblies  215 ,  216 , a top support base  220 , a bottom support base  222 , a lead screw actuator  224 , a magnetic tape  225 , a supply reel  230 , and a take-up reel  235 .  
         [0026]     In a preferred embodiment, the recording head actuator assembly  210  is disposed, at least in part, within the grooved roller guide assembly  205 . The roller guide assemblies  215 ,  216  may be of a conventional design similar to the conventional roller guide assemblies  105 - 108  or of the same design as the grooved roller guide assembly  205 .  
         [0027]     The top support base  220  is mounted on the upper surface of the platform  202 , and supports the grooved roller guide assembly  205 . The bottom support base  222  is mounted on the bottom surface of the platform  202 , in alignment with the top support base  220 .  
         [0028]     The lead screw actuator  224  provides a coarse adjustment of the grooved roller guide assembly  205  along the lateral direction. The magnetic tape  225  can have a higher track density than that of the conventional magnetic tape  115  of  FIG. 1 . The supply reel  230  and the take-up reel  235  can be of a conventional design.  
         [0029]      FIG. 3  illustrates a preferred embodiment of the grooved roller guide assembly  205 . The grooved roller guide assembly  205  is generally formed of two solid cylinders  240 ,  245  having the same or similar outer diameter. Cylinders  240 ,  245  are spaced apart by a gap that forms a circumferential slot  255 , and are interconnected by a rigid connecting shaft  250 . The connecting shaft  250  extends axially through the cylinders  240 ,  245  and between the two outer surfaces  248 ,  249  of the cylinders  240 ,  245 , respectively.  
         [0030]     The connecting shaft  250  has a hollow end  252  that allows the grooved roller guide assembly  205  to be mounted to the support base  220 . The cylinders  240 ,  245  and the connecting shaft  250  can either be integrally formed, or alternatively, they can be individually formed and then assembled into a single integral unit.  
         [0031]     One feature of the present invention is the plurality of circumferential grooves  260  that are integrally formed on the surface of the cylinders  240  and  245 . The circumferential grooves  260  have a raised profile, and are designed to eliminate the air bearing effect on the magnetic tape  225 , by allowing the air to escape between the grooves  260 . In so doing, the circumferential grooves  260  come into a direct contact with the magnetic tape  225 , thereby generating a frictional contact force therebetween. This frictional contact force significantly reduces any relative motion developed between the magnetic tape  225  and the grooved roller guide assembly  205 , thereby effectively reducing the amplitude and frequency of the lateral motion of the magnetic tape  225 . The raised profile of the roller acts as a hydrodynamic air bearing surface for the tape  225 , thereby preventing the tape  225  from sagging into the slot  255 . The air bearing surface is configured to control a wrap angle on a recording head element  270  ( FIG. 4 ). The recording head element  270  is movable within the slot  255  by approximately 0.1 mm to 0.2 mm.  
         [0032]     With reference to  FIGS. 4 and 5 , the recording head actuator assembly  210  includes a U-shaped carrier  265 , the recording head element  270 , a short stroke voice coil actuator  275 , and two ribbon cables  280 ,  285  that are electrically connected to the recording head element  270 . The U-shaped carrier  265  is generally constructed from a permeable ferromagnetic material and has a constant thickness of substantially the same width as the circumferential slot  255 , in order to allow an inner U-shaped surface  291  of the carrier  265  to engage the rigid connecting shaft  250  within the slot  255 , as further illustrated in  FIG. 6 . In one embodiment, the recording head actuator assembly  210  includes a high frequency, short stroke tracking system.  
         [0033]     Further, the U-shaped carrier  265  has an arcuate outer contour  290  of substantially the same diameter as that of the cylinders  240  and  245 . A rectangularly (or square)-shaped cutout  295  ( FIG. 5 ) is formed in the U-shaped carrier  265  along the centerline of the cylindrical surface  290 . A generally cylindrical cavity  300  is formed at the center of the cutout  295  and connects to a rectangular key way  305  that leads to a rectangular notch  310  that is formed on the cylindrical surface  290 . A thin wall plate  312  is formed at the bottom of the circular cavity  300  to inhibit the magnetic flux from reading the head.  
         [0034]     The voice coil actuator  275  includes a cylindrical coil  315  with an integrally formed rectangular key  320 , a plurality of cylindrical magnets  325  and  330 , a return path magnet  335 , and two flexure elements  340 ,  345 . The cylindrical coil  315  fits within the cylindrical cavity  300  and is rotationally constrained in the circumferential direction by the engagement of the key  320  within the keyway  305 . The cylindrical magnets  325 ,  330  are generally made of a hard magnetic material and are placed within the cylindrical coil  315 . The return path  335  is generally made of a permeable ferromagnetic material and is disposed immediately on top of the cylindrical magnet  330  within the cylindrical  315 .  
         [0035]     The recording head element  270  has a generally rectangular outline, and includes a left module  272  and a right module  274  that are formed on either side of the centerline of the recording head element  270 . The flat ribbon cables  280 ,  285  carry the electrical current to the recording head element  270  via a connection to the left and right modules  310  and  315 , respectively.  
         [0036]     The flexure elements  340 ,  345  are generally similar in shape and construction. Each flexure element, e.g.,  340  includes a thin rectangular cutout with a substantially arcuate interior feature that allows the flexure element  340  to engage the coil of the voice coil actuator  275 . The flexure element  340  is disposed against the bottom surface of the rectangular recess  295  to connect the coil to the flexure element  340 .  
         [0037]     During a track following operation, the voice coil actuator  275  actuates the flexure elements  340 ,  345  to cause them to undergo a flexural deflection. This deflection enables the recording head element  270  to move along the lateral direction in order to follow a target data track on the magnetic tape  225 .  
         [0038]     With reference to  FIG. 6 , the grooved roller guide assembly  205  and the recording head actuator assembly  210  are assembled within the circumferential slot  255  ( FIG. 3 ), as an integral unit. The grooved roller guide assembly  205  is mounted directly on top of the top support base  220 , which, in turn, is attached to the bottom support base  222 .  
         [0039]     The top support base  220  is formed of an L-shaped bracket that includes a rectangular base  350  and a rectangular riser  355 . The rectangular base  350  provides a mounting surface for the grooved roller guide assembly  205 . The rectangular riser  355  rises above the rectangular base  350  to a height immediately below the U-shaped carrier  265 , which rests thereupon. The lead screw actuator  224  extends through an opening within the U-shaped carrier  265 , adjacent to the rectangular riser  355 .  
         [0040]     The bottom support base  222  has a generally substantially rectangular shape. A block  360  extends from the bottom support base  222  and connects the top support base  220  to the bottom support base  222 , via a pin  365 . The top support base  220  and the bottom support base  222  are separated by a gap  369 , where a gear  370  is disposed. The gear  370  is further connected to the lead screw actuator  224  to provide a driving mechanism for a coarse actuation.  
         [0041]     Generally, during a read/write operation, the coarse actuation is used for data band access and for following a large slow lateral motion of the magnetic tape  225 . Generally, the tape width is subdivided into several databands. To access a different data band or track on the magnetic tape  225 , a voltage command signal is sent to the gear  370  to cause it to rotate. The rotation of the gear  370  results in a rotation of the lead screw actuator  224  that is connected thereto. The resulting rotation of the lead screw actuator  224  thus causes the grooved roller guide assembly  205  to undergo a translational motion along the lateral direction, so as to position the recording head actuator assembly  210  at the desired data band or track on the magnetic tape  225 .  
         [0042]     In connection with  FIG. 7 , the magnetic tape  225 , shown in dashed lines, passes over the grooved roller guide assembly  205  where the recording head actuator assembly  210  is disposed. As the magnetic tape  225  translates along the tape path, prior to arriving at the grooved roller guide assembly  205 , a lateral disturbance may be generated as it passes through the roller guide assemblies  215 . As the magnetic tape  225  comes into a direct contact with the circumferential grooves  260 , a significant frictional contact force is developed therebetween. This frictional contact force causes the magnetic tape  225  to move with the grooved roller guide assembly  205 , thereby significantly reducing any relative motion developed between the magnetic tape  225  and the grooved roller guide assembly  205 . This effectively reduces the amplitude of the lateral motion of the magnetic tape  225 . Moreover, since the inertia of the grooved roller guide assembly  205  is substantially greater than the inertia of the magnetic tape  225 , high frequency lateral disturbances generally are significantly reflected and dampened at the grooved roller guide assembly  205 .  
         [0043]     Thus, the present invention as embodied by the grooved roller guide assembly substantially improves the performance of the linear tape drive system  200  by concurrently reducing the amplitude as well as high frequency components of the lateral motion of the magnetic tape  225 . The amplitude reduction of the lateral motion of the magnetic tape  225  thus enables the recording head actuator assembly  210  to perform a track following operation much more effectively. Also, the reduction in the high frequency components allows the track following servo control to capture the frequency of the lateral motion of the magnetic tape  225  within the control bandwidth. This directly results in a reduction in the track following error in the linear tape drive system  200 .  
         [0044]      FIG. 8  illustrates an alternative embodiment of a hollow two-piece grooved roller guide assembly  375  according to the present invention. The grooved roller guide assembly  375  is generally formed of two hollow cylinders  380 ,  385  having the same outer diameter. A plurality of external circumferential grooves  390 ,  391  are formed on the outer surfaces of the two hollow cylinders  380 ,  385 , respectively.  
         [0045]     The circumferential grooves  390 ,  391  have a raised profile. A connecting shaft  395  connects the two cylinders  380 ,  385  through a circular bushing  400 . The hollow cylinders  380 ,  385  are interconnected in such a way that their hollow interior volumes are oppositely disposed from each other. The connecting shaft  395  and the two hollow cylinders  380 ,  385  are fabricated as individual units and are then assembled in a manner that allows them to be completely dismantable. Hollow cylinder  380  includes a bottom cap  381 , and hollow cylinder  385  includes an upper cap  386 . When the two hollow cylinders  380 ,  385  are assembled, an internal chamber  388  is formed therebetween.  
         [0046]     With further reference to  FIG. 9 , the grooved roller guide assembly  375  is designed to accommodate a recording head actuator assembly  405  that is not constrained by the same or similar design as the recording head actuator  210 . The recording head actuator assembly  405  is disposed within the hollow interior volume formed by the two hollow cylinders  380 ,  385 . The recording head actuator assembly  405  is shown disposed atop the bottom cap  381  of the hollow cylinder  380 .  
         [0047]     The recording head actuator assembly  405  is generally comprised of a carrier  410 , a recording head element  415 , a short stroke voice coil actuator  420 , and a ribbon cable  425 . The voice coil actuator  420  is attached to the connecting shaft  395  and is further connected to the recording head element  415 . A flexure element  430  is disposed adjacent to the voice coil actuator  420  and the recording head element  415 . The flat ribbon cable  425  connects the recording head element  415  to an electrical voltage source that registers signals generated by the recording head element  415 .  
         [0048]     The carrier  410  is disposed atop the hollow cylinder  380 . A constant width cylindrical portion  435  is formed as a feature of the carrier  410  and has a generally rectangular cutout  440  to provide a physical space, so that the recording head element is accessible to the magnetic tape  225 . A faceted flat portion  445  is connected to, and oppositely disposed from the cylindrical portion  435 . A circular cavity  450  is formed within the carrier  410  to allow the recording element  415  and the voice coil actuator  420  to be disposed completely within the hollow cylinder  380 . To complete the hollow two-piece grooved roller guide assembly  375 , the hollow cylinder  385  is inserted onto the connecting shaft  395  through the circular bushing  400 .  
         [0049]     As the active span of the recording head actuator assembly  405  becomes smaller to accommodate a mechanical expansion of the magnetic tape  225  with a higher track density, the hollow two-piece grooved roller guide assembly  375  could present an advantage over the grooved roller guide assembly  205  in that it allows for a higher performance recording head actuator assembly with a design that can be physically accommodated by the hollow interior volume within the hollow two-piece roller guide assembly  375 . Moreover, it also offers added physical space for routing electrical wires.  
         [0050]     It is to be understood that the specific embodiments of the invention that have been described are merely illustrative of certain applications of the principle of the present invention. Numerous modifications may be made to the system for substantially improving track density in linear tape drive systems, as described herein, without departing from the spirit and scope of the present invention.