Abstract:
The claimed embodiments provide methods, apparatuses and systems directed to a servo-actuated positioner for a read/write head that uses a piezoelectric super fine actuator that moves the read/write head to maintain alignment with data tracks on a magnetic tape. The servo-actuated positioner, in one implementation, uses flexures to mechanically support the read/write head. Piezoelectric elements are attached to the flexures in strategic locations to effect movement of the read/write head when the elements are actuated. This configuration achieves a large actuator motion using small piezoelectric elements. Additionally, manufacturability is improved since the piezoelectric elements, which are typically brittle, are attached to the mechanically robust flexures.

Description:
TECHNICAL FIELD 
     The present invention relates generally to micro-actuators used in linear tape drive systems 
     BACKGROUND 
     Linear tape drive systems provide for high-density recording on multiple tracks of a magnetic tape. In certain arrangements, parallel tracks extend along a longitudinal direction of the magnetic tape. During recording or playback, the read/write elements of the head should be aligned with the desired track as the tape moves in a longitudinal direction across the read/write bump. Closed loop positioners are often used in tape systems having higher track densities, In high-density tape systems, the tape may wander in the lateral direction as it moves in the longitudinal direction across a read/write head, which results in an offset between the read/write head and the track center line. To avoid these types of problems, tape cartridges for high-density tape drives are preformatted with information often called servo information, which is used to maintain the correct lateral position of the tape with respect to the read/write head. Servo information provides the system with feedback to determine the continuous position of the tape relative to the head. Analysis of the servo signals allows for a determination of an offset and the distance of the offset between the track and the head. Based on the information, the head is moved by a positioner to the center line of the track so that write/read operations can occur properly. Closed loop positioners generally use fine positioners to move the head during a write/read operation. These fine positioners are used to maintain the position of the head at the center line of the track under a closed loop servo control using the preformatted servo information on the tape. 
     Linear Tape Open (“LTO”) is a computer storage magnetic tape format that employs a servo-based, closed loop control mechanism. The LTO roadmap calls for successive increases in capacity and speed. As track densities increase with each new generation of LTO tape drives, the ability to precisely control the read/write head relative to the magnetic tape also needs to be improved. Due to this, a need exists in the ad for improved head positioner systems. 
     SUMMARY 
     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. 
     The claimed embodiments provide methods, apparatuses and systems directed to a servo-actuated positioner for a read/write head that uses a piezoelectric super fine actuator that moves the read/write head to maintain alignment with data tracks on a magnetic tape. The servo-actuated positioner, in one implementation, uses flexures to mechanically support the read/write head. Piezoelectric elements are attached to the flexures in strategic locations to effect movement of the read/write head when the elements are actuated. This configuration achieves a large actuator motion using small piezoelectric elements. Additionally, manufacturability is improved since the piezoelectric elements, which are typically brittle, are attached to the mechanically robust flexures. 
    
    
     
       In addition to the 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 
       Example 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. 
         FIG. 1  illustrates a typical LTO tape cartridge; 
         FIG. 2  illustrates a typical LTO tape drive housing with the cartridge of  FIG. 1  inserted; 
         FIG. 3  is a top-down view of the cartridge inserted into the tape drive which includes an actuator assembly of the claimed embodiments; 
         FIG. 4  is a perspective view of an example actuator assembly; 
         FIGS. 5A-5C  are various views of an actuator assembly with a bimorph piezoelectric micro-actuator, in accordance with an example embodiment; 
         FIG. 6  is a diagram illustrating characteristics of bimorph piezoelectric material, in accordance with an example embodiment; 
         FIGS. 7A-7C  are various views of an actuator assembly with a monomorph piezoelectric super fine actuator attached to flexures, in accordance with an example embodiment; 
         FIGS. 8A-8B  are various views of an actuator assembly with a different monomorph piezoelectric super fine actuator attached to a flexure, in accordance with an example embodiment; 
         FIG. 9  is a diagram illustrating characteristics of monomorph piezoelectric material on a flexure, in accordance with an example embodiment; 
         FIG. 10  is a view of another monomorph piezoelectric super fine actuator on a modified flexure, in accordance with an example embodiment; 
         FIG. 11  is a diagram illustrating mechanical amplification characteristics of the super fine actuator of  FIG. 10 ; and 
         FIG. 12  is a schematic cross-section of an example single stage VCM with a free moving mass that can be utilized by the claimed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, apparatuses and methods which are meant to be illustrative, not limiting in scope. 
       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. 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. 
       FIG. 3  is a top-down view of the cartridge  10  inserted into the tape drive  200  which includes an 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 nor components include a take-up hub  300 , various tape-threading roller guides ( 302 ,  306 ), read/write head  102  and flex cables ( 134 ,  136 ). Drive  200  will also typically contain one or more processors, a memory and a controller. Read/write head  102  is typically attached to the actuator assembly whose location is generally indicated by arrow  108 . The actuator assembly&#39;s general purpose is to correctly orient the read/write head  102  in relation to a magnetic tape. This is accomplished, in part, by moving the read/write head  102  up or down in a direction substantially perpendicular to a magnetic tape travel path. 
       FIG. 4  is a perspective view of an example actuator assembly  400  which can be utilized by the claimed embodiments. The actuator assembly  400  includes the read/write head  102 , and a head carriage  402 . The read/write head  102  can be retained by the head carriage  402  by a fastener such as an adhesive, an interference fit, mechanical fasteners such as screws, etc. The actuator assembly  400  further includes a coarse actuator and a fine actuator. In one implementation, the head carriage  402  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  404  (to which the head carriage  402  and fine actuator are attached). The coarse actuator, in one implementation, includes a coarse positioner  406  that displaces the actuator base  404  along shafts  408  that protrude from base plate assembly  410 . In one implementation, the coarse actuator translates the entire fine actuator across the tape for a travel distance of about 9 mm to, for example, move read/write head  102  between tracks. Read/write head  102  may include one to several bumps and each bump will usually include a plurality of read and write elements. 
     The fine actuator generally includes the actuator base  404 , head carriage  402 , read/write head  102 , voice coil motor  412  and first and second flexure springs ( 414 ,  416 —see  FIGS. 5B and 7B  for fuller views of the second flexure spring  416 ). Flexures  414  and  416  further include side wings  450  which help to stiffen the flexures in order to increase flexure resonance frequencies. The coarse actuator generally includes the base plate assembly  410 , the shafts  408 , the coarse positioner rack  406  and the actuator base  404 . 
     The fine actuator controls a head carriage assembly (typically comprising the read/write head  102  and the head carriage  402 ) relative to actuator base  404 , using a voice coil motor (“VCM”) assembly. The VCM assembly includes a voice coil (not shown) which is attached to the head carriage  402  to translate with the head carriage  402 , while a magnetic housing assembly  412  is attached to the actuator base  404 . The voice coil is suspended in a magnetic field produced by one or more magnets in the magnetic housing assembly  412  of the voice coil motor. In one implementation, the fine actuator moves the read/write head  102  based on analysis of the servo signals, read from servo read elements disposed over corresponding servo tracks of a moving tape, to keep the read/write head  102  in substantial alignment with a selected track. In one implementation, the fine actuator can move the read/write head  102  a distance of about ±60 to ±100 microns. 
     Aspects of the claimed embodiments provide for one or more of the following advantages. Embodiments of the invention allow for more precise control of the read/write head  102  than known fine actuators can typically provide. In addition, some embodiments provide positioner systems with increased high frequency response by allowing for additional decreases in the moving mass displaced by the positioner mechanisms under closed-loop servo controls These and other advantages are accomplished, in one implementation, through a “super fine” actuator which utilizes piezoelectric elements and flexures. Since the typically brittle piezoelectric material is attached to mechanically robust flexures, manufacturability is improved. In one implementation, the disclosed super fine actuators are operative to move the read/write head a distance of about 5 microns. 
     All of the following disclosed embodiments are used in conjunction with control logic operative to control a superfine and a fine actuator under closed loop servo control. A variety of algorithms can be used to move each of the super fine and the fine actuators in response to lateral movement detected by monitoring servo signals. 
     A first embodiment provides for a super fine actuator made up of two “bimorph” layers of piezoelectric material ( 500 ,  502 ) attached to the head carriage  402  at distal ends of the read/write head  102  and is illustrated via  FIGS. 5A-5C . Read/write head  102  is movable relative to head carriage  402  by activation of piezoelectric actuation layers. The term “bimorph” refers to a double layer of piezoelectric materials as shown in  FIG. 6 . The layers ( 600 ,  602 ) are arranged such that the top layer  600  extends and the bottom layer  602  contracts, or vice versa, when the layers ( 600 ,  602 ) are electrically excited. Due to this arrangement, the combined bimorph layers will bend upwards when the top layer  600  extends and the bottom layer  602  contracts as indicated by the dashed lines. The total displacement of the read/write head  102  through activation of the piezoelectric layers, in one implementation, can be about ±4 to ±5 microns. 
     Portion  502  of the super fine actuator is attached to the head carriage  402  at the bottom distal end of the read/write head  102  such that later  600  contacts the head carriage  402 . For portion  500  at the opposite, top distal end of the read/write head  102 , layer  602  is in contact with the head carriage  402  It should be noted that in  FIG. 5C  that it may appear that the portion  500  of the super fine actuator is attached to the flexure  414 . That is not the case, however, as the portion  500  is indeed attached to the head carriage  402 . 
     The super fine actuator may assume different configurations. In another implementation, as shown in  FIGS. 7A-7C , a super fine actuator is formed from flexures  700  and  702  that are placed on the head carriage  402  at distal ends of the read/write head  102  and each of the additional flexures have two pieces of monomorph (single layer) piezoelectric material ( 700   a,    700   b,    702   a,    702   b ). An electrically excited monomorph piece of piezoelectric material will change length when electrically stimulated. Since two pieces of the monomorph material ( 700   a  and  700   b,    702   a  and  702   b ) are placed on the flexures ( 700 ,  702 ), when they contract, they will tend to bend the flexure upward such as indicated by the dotted lines in  FIG. 9  which is a cross section of a flexure  760  and monomorph piezoelectric material  750  used in an implementation similar to the one of  FIGS. 7A-7C . Similar to  FIG. 5C , it should be noted that the view of  FIG. 7C  may appear to indicate that the flexure  700  is attached to the flexure  414 . Flexure  700  is actually attached to the head carriage  402 . 
     In another implementation, piezoelectric material can be disposed on other components of the positioner system to create a superfine actuator.  FIGS. 8A-8B  illustrate an implementation wherein a super fine actuator is made from tour pieces of monomorph piezoelectric material ( 800   a  and  800   b,    802   a  and  802   b ) that are placed on flexures  800  and  802 . Similar to the implementation of  FIGS. 7A-7C ,  FIG. 9  indicates how an electrically stimulated monomorph piezoelectric material  750  will bend a flexure  760  as indicated by the dotted lines. In this implementation, the read/write head is fixed relative to the head carriage  402 . 
     The implementation of  FIGS. 8A-8B  do not utilize side wings on the flexures  800  and  802  to facilitate displacement of the flexures and head carriage assembly by the piezoelectric actuators. Specifically, side wings such as side wings  450  as shown in  FIG. 4 . Additionally, the configurations of  FIGS. 8A-8B  can be used with or without a voice coil motor  412  and related voice coil. Without a voice coil motor, an overall moving mass is reduced and frequency response is increased. 
     Other implementations of the invention can involve modified flexure designs. For example, yet another implementation of a super fine actuator is conceptually disclosed via  FIG. 10  which illustrates top and bottom flexures ( 1000 ,  1002 ) separated by a head block  1004  to which a read/write head can be attached. On each flexure ( 1000 ,  1002 ) are two pieces of monomorph piezoelectric material ( 1000   a  and  1000   b,    1002   a  and  1002   b ). Each of the flexures ( 1000 ,  1002 ) are modified at each piece of monomorph piezoelectric material ( 1000   a,    1000   b,    1002   a,    1002   b ) to form angles ( 1000   c,    1000   d,    1002   c,    1002   d ) where flexure portions meet at these points at an angle. The mechanical amplification of the flexure is defined by the tilt angle of the monomorph piezoelectric material ( 1000   a,    1000   b,    1002   a,    1002   b ). This is further demonstrated via  FIG. 11  wherein the mechanical amplification for the flexure is proportional to the distance “x” divided by the distance “y.” In one implementation, a general shape of the region between the flexures ( 1000 ,  1002 ) and the monomorph piezoelectric materials ( 1000   a,    1000   b,    1002   a,    10002   b ) is generally triangle-shaped, 
     The conceptual representation of  FIG. 10  can be incorporated into an actual device such as the generic actuator of  FIG. 4 . For example, the flexures ( 1000 ,  1002 ) can be mounted to a coarse actuator to move a read/write head and head carriage combination relative to a coarse actuator base. 
     Another example of an actuator that may employ the claimed embodiments is shown in  FIG. 12  which is a schematic cross-section of a single stage VCM system  1200  with a free moving mass Included in system  1200  is an electric coil  1202 , a magnet  1204 , a piezoelectric super fine actuator  1206 , a read/write head  1208 , a read/write element  1210  which can read data from or write data to tape  1212 , a bearing surface  1214  and rollers  1216 . Typically, the VCM positioner portion of system  1200  can move the read/write head  1208  in the range of about 9000 microns while the piezoelectric super fine actuator  1206  can move the read/write head  1208  in the range of about 5 microns. Any of the previously described embodiments may be implemented via the piezoelectric super fine actuator  1206 . 
     Implementations of the invention can be configured to enjoy a number of advantages over the prior art such as a reduced moving mass, more precise placement control of the read write head via the super fine actuator and improvements in manufacturability by attaching typically brittle piezoelectric material to mechanically robust flexures. 
     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.