Abstract:
An exemplary embodiment provides for a servo-controlled, head actuator design that has low profile characteristics in both the height and width dimensions. The low height allows the actuator to fit into a half-high tape drive form factor. The construction of the actuator, in one embodiment, reduces the width of the tape drive system, and allows the industry standard mounting with the necessary screw length. Additionally, in some implementations, the actuator comprises a smaller, concentrated moving mass coupled with a flexure construction having a narrowed width with added ribs for torsional stiffness. These aspects of the actuator provide a higher second mode of vibration compared to the flexure designs of the prior art. The actuator design includes a coarse actuator assembly for larger movements of the head, and a fine grain actuator, including a voice coil motor, responsive to analysis of servo signals. In some embodiments, the voice coil motor of the fine actuator and the coarse actuator shafts are in line. Since the centerlines of the shafts are in-line with the voice coil motor, the resonance response of the shaft spring-mass system is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/804,223 (attorney docket no. 6568/54002) filed on Jun. 8, 2006, which is incorporated herein by reference. 
     
     BACKGROUND 
       [0002]    Linear Tape-Open (“LTO”) is a computer storage magnetic tape format developed as an alternative to the proprietary Digital Linear Tape (“DLT”) format. The LTO roadmap calls for successive increases in capacity and speed. Due to these targets and the need to maintain, and perhaps shrink, a small drive housing form-factor, printed circuit board real estate is becoming very valuable as the need to include additional components increases. Due to this, it is becoming challenging to fit various drive mechanisms, included in previous generation LTO drives, into newer designs. 
         [0003]    Designing high bandwidth tracking servo systems, for use in LTO drives, presents the following technological challenges: high bandwidth amplifiers, faster sample rates for digital control algorithms, control of loop shaping to achieve robust and higher performance suppression capabilities, improved feedback sensors and high bandwidth actuators. Although each one of these is an important design or engineering task, the performance of the actuator basically limits the final tracking servo bandwidth. As a result, the actuator is often considered to be the most important requirement. 
         [0004]    As discussed in more detail below, the claimed embodiments are directed to high bandwidth actuators. Some of the issues with high performance actuators are: minimizing moving mass, optimization of the working lateral range of motion and controlling the high order unwanted resonance frequencies above a minimum frequency that is determined based on the tracking servo bandwidth requirements. 
         [0005]    In addition, drive form factors (for example LTO form factor requirements) and installation/mounting requirements are also a concern. Some computer industry requirements include the drive mounting configurations. For example, some computer manufactures specify a drive-mounting configuration requirement that the drive can be mounted on its lateral side or on its bottom side. The side-mounting configuration requires two sets of hole-patterns with a minimum screw length that will support the drive in a computer chassis. A typical screw length requirement is about 4 to 5 millimeters. In a LTO half-high drive (½ of the standard height of 3¼ inches) the pin threading mechanisms must be spaced away from the mounting screw. Thus, the actuator must fit between the pin threading mechanisms and the drive reel located in the back. The actuator must also fit in the limited space in the width dimension. Prior art actuator assemblies are typically not suitable for tape drives with smaller form factors where drive components are more tightly packed. In addition, some of the actuator configurations of the prior art force a lower 1st mode resonance frequency response at around 100 Hz. Generally, a lower 1st mode of the spring-mass system also results in a lower 2nd mode of resonance. 
         [0006]    In view of the foregoing, a need exists in the art for a high bandwidth actuator that meets the above-described technological requirements. 
         [0007]    The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
       SUMMARY 
       [0008]    The following embodiments and aspects thereof are described and illustrated in conjunction with systems, apparatuses and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated. 
         [0009]    One embodiment by way of non-limiting example provides for a servo-controlled, head actuator design that has low profile characteristics in both the height and width dimensions. The low height allows the actuator to fit into a half-high tape drive form factor. The construction of the actuator, in one embodiment, reduces the width of the tape drive system, and allows the industry standard mounting with the necessary screw length. Additionally, in some implementations, the actuator comprises a smaller, concentrated moving mass coupled with a flexure construction having a narrowed width with added ribs for torsional stiffness. These aspects of the actuator provide a higher second mode of vibration compared to the flexure designs of the prior art. The actuator design includes a coarse actuator assembly for larger movements of the head, and a fine grain actuator, including a voice coil motor, responsive to analysis of servo signals. In some embodiments, the voice coil motor of the fine actuator and the coarse actuator shafts are in line. Since the centerlines of the shafts are in-line with the voice coil motor, the resonance response of the shaft spring-mass system is reduced. 
         [0010]    In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting. 
           [0012]      FIG. 1  illustrates a typical LTO tape cartridge; 
           [0013]      FIG. 2  illustrates a typical LTO tape drive housing with the cartridge of  FIG. 1  inserted; 
           [0014]      FIG. 3  is a top-down view of the cartridge inserted into the tape drive which includes a head actuator assembly of the claimed embodiments; 
           [0015]      FIG. 4  is a perspective view of an actuator assembly, in accordance with an exemplary embodiment; 
           [0016]      FIG. 5  is an alternative perspective view of the actuator assembly, in accordance with an exemplary embodiment; 
           [0017]      FIG. 6  is a perspective view detailing a magnetic head and fine-grain actuator assembly, in accordance with an exemplary embodiment; 
           [0018]      FIG. 7  is an exploded view illustrating various components of the actuator assembly, in accordance with an exemplary embodiment; 
           [0019]      FIGS. 8A and 8B  are exploded views illustrating some of the components of the fine actuator, in accordance with an exemplary embodiment; and 
           [0020]      FIG. 9  is a top-down block diagram view illustrating flexible circuit orientation in relation to a tape travel path, in accordance with an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The following embodiments and aspects thereof are described and illustrated in conjunction with systems, apparatuses and methods which are meant to be exemplary and illustrative, not limiting in scope. 
         [0022]      FIG. 1  illustrates a typical LTO tape cartridge  10  and  FIG. 2  illustrates a typical LTO tape drive housing  200  with the cartridge  10  of  FIG. 1  inserted. Cartridge  10  is inserted into drive  200  in a direction specified by arrow  12 . Cartridge  10  also includes grip lines  14  for easy handling. Additionally, cartridge  10  includes various lock depressions  18  (also repeated on the opposite side) that mate with a male counterpart, in drive  200 , to ensure a snug fit after cartridge  10  is inserted into drive  200 . Drive  200  includes an eject button  202  and various indicators  204 . The drive  200  may be designed to fit into a 5.25 inch form factor for installation into a bay of a desktop or server box. Of course, other implementations are possible. For example, the drive  200  may be a stand-alone unit, such as a desktop drive that is external from a host computing system. 
         [0023]      FIG. 3  is a top-down view of the cartridge  10  inserted into the tape drive  200  which includes a head actuator assembly of the claimed embodiments. A full description of the various components of drive  200  is intentionally not included in order to not unnecessarily obscure the claimed embodiments. However, some of the major components include a take-up hub  300 , various tape-threading roller guides ( 302 ,  306 ), magnetic head  102  and flex cables ( 134 ,  136 ). Drive  200  will also typically contain one or more processors, a memory and a controller. Area  500  will be referred to later. 
         [0024]      FIGS. 4 and 5  show a head actuator assembly  100  comprising a magnetic head  102 , and a head carriage  104 . The magnetic head  102  is preferably retained in a forked shaped portion  103  (see  FIGS. 8A and 9 ) of the head carriage  104  preferably by an adhesive. Of course other types of fasteners may be used to fasten the magnetic head  102  to the head carriage  104  such as an interference fit or mechanical fasteners such as screws, for example. The actuator assembly  100 , illustrated in  FIGS. 4 and 5 , further includes a coarse actuator and a fine actuator. In one implementation, the head carriage  104  is operably attached to the fine actuator, while the fine actuator is attached to the coarse actuator. In one implementation, the coarse actuator comprises an actuator base  106  (to which the head carriage  104  and fine actuator are attached). The coarse actuator, in one implementation, includes a drive assembly  109  that displaces the coarse actuator base  106  along shafts  107  that protrude from base plate assembly  108 . The second shaft  107  is located on an opposite side of magnetic head  102 . In one implementation, the coarse actuator translates the entire fine actuator assembly across the tape for a travel distance of about 9 mm to, for example, move magnetic head  102  between tracks. Magnetic head  102  may include one to several bumps and each bump will usually include a plurality of read and write elements. 
         [0025]    It should be noted that the phrases “fine actuator” and “moving mass” can be used interchangeably and generally refer to the following collection of parts: coarse actuator base  106 , head carriage  104 , magnetic head  102 , voice coil motor  160  and top and bottom flexure springs ( 140 , 142 /refer to  FIGS. 7-8B ). Additionally, the phrase “coarse actuator” generally refers to the following collection of parts: base plate assembly  108 , shafts  107 , drive assembly  109  and the coarse actuator base  106 . 
         [0026]    The fine actuator controls the head carriage assembly  102 / 104 , relative to coarse actuator base  106 , using a voice coil motor (VCM) assembly (see  FIGS. 8A &amp; 8B ). The voice coil motor assembly includes a voice coil portion  160  and magnetic housing assembly  162 . The voice coil portion  160  is attached to the head carriage  104  to translate with the head carriage  104 , while the outer portion  162  is attached to the coarse actuator base  106 . In one implementation, the VCM of the fine actuator is a flat voice coil motor. The voice coil portion  160  is suspended in a magnetic field produced by one or more magnets in the magnetic housing assembly  162  of the voice coil motor. In one implementation, the fine actuator moves magnetic head  102  based on analysis of the servo signals, contained on a tape, to keep the magnetic head  102  in substantial alignment with a selected track. The voice coil motor assembly and associated magnets located in the magnetic housing assembly  162  are oriented relative to the direction of travel of the coarse actuator base  106 . This configuration also contributes to a reduced actuator assembly  100  size. In one implementation, the fine actuator functions under closed loop servo control, while the coarse actuator utilizes open loop control. 
         [0027]    The trigger point of the reference hall sensor magnet assembly  122  provides a known location for the head with respect to tape. The linear hall sensor magnet  124  (see  FIG. 5 ) along with the reference hall sensor magnet assembly  122  provides the translation information of the fine actuator. In one implementation, this information is used to provide the damping of the first mode resonance of the spring-mass system of the fine actuator. 
         [0028]    Regarding the reference hall sensor  800  (refer to  FIGS. 8A and 8B ) and the reference hall sensor magnet assembly  122  (refer to  FIGS. 4-5 ), during a read-write process of the tape drive  200 , the magnetic head  102  traverses across a tape width to seek a relevant track. There are a number of incidents when the magnetic head  102  is parked at a given known/reference location. Such events may include booting up the tape drive  200 , tape-loading sequence, etc. In order to send the magnetic head  102  to this reference location, the reference hall-sensor magnet assembly  122  and reference hall sensor  800  are utilized. The reference hall magnet assembly  122  is secured to the actuator base plate  108  and the reference hall sensor  800  is secured to the coarse base actuator  106 . The actuator base plate  108  is stationary to the drive  200 . Thus, when the reference hall sensor  800  arrives in the vicinity of the reference hall magnet assembly  122 , the reference hall sensor  800  is triggered. This information is utilized to locate the magnetic head  102  with respect to the tape. 
         [0029]    In reference to the linear hall sensor  124  and an associated dual pole magnet  125 , the fine actuator of the head actuator assembly  100  is utilized to keep the head on a track under a servo control. It should be noted that the dual pole magnet  125  is only partly visible in  FIG. 5 . Any movements in the tape or head carriage  104  can create a misalignment between a read/write element of the magnetic head  102  and a corresponding track on the tape. The linear hall sensor  124  is attached to the flex cable  134  which is attached to the head carriage  104 . The corresponding dual pole magnet  125  is attached to the coarse actuator base  106 . When the head carriage  104  moves, the linear hall sensor  124  will also move with respect to the dual pole magnet  125 . The dual pole magnet  125  has two poles—north and south. When the linear hall sensor  124  is aligned to a null line of the dual pole magnet, there is no signal. When the magnetic head  102  moves up, the linear hall sensor  124  produces the signal which is proportional to the head-translation. The same is true when the magnetic head  102  moves in the negative direction. As a result, the linear hall sensor  122  provides the signal which is proportional to the head translation. This information can be used in number of ways. Some examples include 1) damping of the servo loop and 2) when tape is at the end and it reverses the direction to move from forward to reverse, there is no servo information from the tape. The linear hall sensor  124  provides the head location information during this phase. 
         [0030]    With reference to  FIGS. 6-8B , flex cables ( 134 ,  136 ) are each attached to one of a pair of laterally extending arms ( 104   a ,  104   b ) of head carriage  104 . In one implementation, the flex cables ( 134 ,  136 ) are attached to the laterally extending arms ( 104   a ,  104   b ) via an adhesive. Flex cables  134  and  136  provide the electrical connection between the magnetic head  102  and a printed circuit board (not shown). The head flex circuit portion  132  also connects to the voice coil  160  via pad  178 . The screws  176  going through clamp  174  provide the force between the pads of the voice coil flex cable portion  132  and the VCM  160  for electrical continuity. This eliminates any need to provide additional wires between the voice coil and the main PCB (not shown). Thus, in this implementation, the voice coil  160  terminates at the main PCB via the traces in the flex cable  134 . 
         [0031]    Top flexure spring  140  further includes holes  180  that are utilized to secure top flexure spring  140  to the coarse actuator base  106  via additional screws (not shown). In one implementation, clamps may also be included with the screws. It should be noted that  FIG. 7  is an exploded view of various parts. As such, top flexure spring  140  is shown on one side of flex cables  134  and  136  for clarity.  FIGS. 8A and 8B  correctly characterize the placement of top flexure spring  140  in relation to flex cables  134  and  136 . 
         [0032]    As the head carriage  104  is secured to top flexure spring  140  via screws  176  and the top flexure is further secured to the coarse actuator base  106  via screws (not shown), it can be seen that head carriage  104  is mounted between opposing arms ( 106   a ,  106   b ) in area  103  of the coarse actuator base  106 . Head carriage  104  is also coupled to the actuator base  106  via a bottom flexure spring  142 . Similar to top flexure spring  140 , bottom flexure spring  142  is coupled with the head carriage  104  at an inner set of holes  184  via a clamp  186  and screws  188  (note only one screw  188  is intentionally included in  FIG. 8A  for clarity of the view). Bottom flexure spring  142  is further coupled to the coarse actuator base at holes  190  via clamps  192  and screws (not shown). 
         [0033]    Actuator assembly  100  has two separate resonance frequency vibration modes referred to as the first mode and the second mode. The first mode refers to up and down frequency vibrations of the actuator assembly and is generally low frequency. The second mode refers to torsional frequency vibration of the moving mass and is generally preferred to be kept as high as possible and preferably five to eight times higher than the closed-loop bandwidth frequency. 
         [0034]    Top and bottom flexures springs  140  and  142  each further include various ribs  194  that are oriented perpendicular to each flexure. In one implementation, the top and bottom flexure springs  140  and  142  are metal springs that apply opposing forces to bias the head carriage  104  towards a center position relative to the fine actuator thus providing a resonance frequency dampening effect. In one implementation, flexure springs are  140  and  142  are made from 300 series stainless steel. The ribs  194  allow for reductions in the width of top and bottom flexure springs  140  and  142  while maintaining desired spring forces. This is accomplished because ribs  194  add torsional stiffness to the top and bottom flexure springs  140  and  142 . Since the width of the flexures is reduced, the overall size of the actuator assembly  100  can be reduced accordingly to fit into a smaller drive enclosure. As previously indicated, it is also desirable to maintain a high second resonance mode. The placement of the top and bottom flexure springs  140  and  142  help to contribute the high second mode of vibration. The top and bottom flexure springs  140  and  142 , in one implementation, are mounted to be substantially aligned with the center of gravity of the moving mass corresponding to the fine actuator. This can be seen, for example, via  FIGS. 8A-8B  wherein the top and bottom flexure springs  140  and  142  are arranged at the top and bottom of head carriage  104  such they coincide at a lateral midpoint of head carriage  104  wherein the lateral midpoint divides head carriage  104  into front and back parts. It should also be noted that since the top and bottom flexure springs  140  and  142  are inline with the moving mass, the ribs  194  are also in-line with the moving mass. As a result, the ribs therefore also help to contribute to a higher second resonance mode. 
         [0035]    Furthermore, under servo control, the voice coil motor  160  is electrically coupled with a corresponding magnetic circuit that generates a force required to move the magnetic head  102  such that it stays aligned with a particular track on a tape. A magnetic moment caused by the force can also excite the shafts  107  and their associated spring-mass system. Since the voice coil  160  is in-line with the shafts  107 , the residual force of the moment arm is substantially zero and the resonance of the shaft&#39;s spring-mass system is also reduced substantially. 
         [0036]    Another advantage of the claimed embodiments is that the flex cables  134  and  136  are mounted parallel to the tape travel path and this allows for further separation of the two flex cables. Laterally extending arms ( 104   a ,  104   b /refer to  FIG. 7 ) are configured in a manner that defines the orientation of the flex cables ( 134 ,  136 ) such that the flex cables ( 134 ,  136 ) are parallel to the tape travel path. It is desirable to keep the flex cable as far apart as possible in order to minimize electrical interference between the two flex cables  134  and  136 . This aspect of the claimed embodiments is further explained via  FIG. 9  which is a top-down block diagram view  900  illustrating flexible circuit orientation in relation to a tape travel path. Included in top-down view  900  are the flex cables  134  and  136 , a portion of the head carriage  104 , magnet head  102 , tape/tape travel path  902  and prior art flex cable orientations  904 . As can be seen, the flex cable portions ( 134   a ,  136   a /also refer to  FIG. 6 ) of the flex cables ( 134 ,  136 ) are parallel to the tape/tape travel path  902 . The laterally extending arms ( 104   a ,  104   b ) extending of the head carriage  104  are oriented substantially parallel to the tape path in the opposing regions proximal to magnetic head  102 . This configuration allows the physical distance between the flex cables  134  and  136 , as they extend from the flex cable portions  134   a  &amp;  136   a , to be increased. This increased separation reduces the effects of interference or noise associated with a read signal traversing flex cable  136  caused by, for example, write signals traversing flex cable  134 . If the flex cables ( 134 ,  136 ) were not oriented parallel to the tape/tape travel path  902 , the distance between the flex cables ( 134 ,  136 ) would decrease as can be seen via prior-art flex cable orientations  904 . Furthermore, prior art flex cable orientations  904  are additionally limited in that there is very little room to further separate the two orientations  904  from each other. This is due to the fact that if either orientation  904  is moved away from the other, the flex cable will move into the area of the tape/tape travel path  902 . Orienting the flex cables ( 134 ,  136 ) parallel to the tape/tape travel path  902  resolves this deficiency of prior art tape drive systems. 
         [0037]    In one implementation, laterally extending arms ( 104   a ,  104   b ) form approximately 10 degree angles at either side of fork-shaped portion  103  as indicated by areas  906  and  908 . Since the flex cables ( 134 ,  136 ) are attached to the laterally extending arms ( 104   a ,  104   b ), flex cable portions  134   a  and  136   a  (refer to  FIG. 6 ) therefore also are oriented about 10 degrees inward in relation to the magnetic head  102 . 
         [0038]    Advantageously, the claimed embodiments provide for a reduced fingerprint actuator assembly capable of fitting into next generation LTO tape drives. Additionally, a higher second mode vibration is achieved by placing flexures with ribs inline with the moving mass/fine actuator. Furthermore, the reduced footprint actuator assembly provides the required extra room in a tape drive housing for tape grabber mechanics as well as providing the option to install the housing in various orientations due to multiple sets of mounting holes for screws. More specifically, area  500  of drive  200  (refer to  FIG. 3 ) is freed up to allow for additional mounting screw holes. 
         [0039]    Another advantage of the claimed embodiments is that a flat voice coil motor design is employed by the claimed embodiments. Prior art voice coils are typically circular. Using a circular voice coil results in an increased fine actuator moving mass. That increase in mass necessitates the use of wider flexures. In turn, wider flexures results in an enhanced width for the actuator as a whole. By using a flat voice coil, those prior art issues are avoided. Additionally, the flat voice coil contributes to the moving mass being concentrated in a small area which in turn helps to achieve the in-line/center of gravity aspects of the claimed embodiments. 
         [0040]    While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.