Abstract:
A disc drive having a recording disc rotatable about an axis, a slider supporting a transducing head for transducing data with the disc, and a dual-stage actuation assembly supporting the slider to position the transducing head adjacent a select radial track of the disc. The dual-stage actuation assembly includes a movable actuator arm, a suspension assembly supported by the actuator arm including the flexure, a slider bonding pad supporting the slider and a microactuator. The microactuator includes a rotor attached to the slider bonding pad and a stator attached to the flexure. A beam structure operatively connects the rotor to the stator so as to permit movement of the rotor with respect to the stator. The beam structure includes a first beam pair element and a second beam pair element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from Provisional Application No. 60/218,279, filed Jul. 13, 2000 for “Micro-Actuator Structure With Rotary Access Mode” by Peter Crane and Zine-Eddine Boutaghou. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a disc drive microactuator system and more particularly to an improved structure for increased stability of the microactuator rotor. 
     The density of concentric data tracks on magnetic discs continues to increase (that is, the width of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the transducing head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a slider (which carries the head) on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks. 
     One particular design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby effecting head positioning through dual stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. In particular, magnetic microactuator designs featuring a magnet/keeper assembly and coil have been developed. Magnetic microactuators typically include a stator portion and a rotor portion, the stator being attached to the flexure and the rotor supporting the slider. The rotor is movable with respect to the stator such that the slider can be positioned more precisely over a track of a disc. 
     Some existing magnetic microactuators use flexible beam springs in a “wagon wheel” design located on top of the slider to support the rotor. The beam springs have a limited thickness, generally 20 to 30 microns, with their thickness being constrained by the total microactuator thickness. Thin beam springs are highly stressed by normal disc drive loads, such as head slap deceleration. During head slap deceleration, a load in a disc drive causes the suspension, microactuator and slider to lift off the disc momentarily and then crash back into the disc surface with a very high deceleration, sometimes approaching 600 gravities (g). Under 600 g, the flexible beam springs bear a weight of 0.1 Newton (N). The force applied during head slap deceleration induces high stress in the flexible beam springs. 
     Prior art designs utilizing a linear accessing motion suffer from uncontrolled rotor shifting caused during hard seek acceleration of the voice coil motor (VCM). The large shift in rotor position stresses the beam springs to approximately 8.8% of their breaking strength and because of the time-varying nature of the VCM acceleration induces fatigue failure. There is a need in the art for an improved microactuator beam structure to increase the rotor stability. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a disc drive having a recording disc rotatable about an axis, a slider supporting a transducing head for transducing data with the disc, and a dual-stage actuator assembly supporting the slider to position the transducing head adjacent a selected radial track of the disc. The dual-stage actuation assembly includes a movable actuator arm, a suspension assembly supported by the actuator arm and including a flexure, a slider bonding pad supporting the slider and a microactuator. The microactuator includes a rotor attached to the slider bonding pad and a stator attached to the flexure. A beam structure operatively connects the rotor to the stator so as to permit movement of the rotor with respect to the stator. The beam structure includes a first beam pair element aligned with the width of rotor and a second beam pair element aligned with the length and the width of the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a conventional disc actuation system for positioning a slider over a track of a disc. 
         FIG. 2  is an exploded perspective view of a portion of a disc drive including a microactuator according to the present invention. 
         FIG. 3  is a top perspective view of the microactuator with a slider and a rotor in a neutral position. 
         FIG. 4  is a top view of the microactuator with the slider and the rotor in a neutral position. 
         FIG. 5  is a top view of the microactuator with the slider and the rotor in movement. 
         FIG. 6  is a top view of the microactuator showing beam deflection under longitudinal loading. 
         FIG. 7  is a top view of the microactuator with deflection limiters. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a disc drive actuation system  10  for positioning a slider  12  over a track  14  of a disc  16 . Actuation system  10  includes a voice coil motor (VCM)  18  arranged to rotate an actuator arm  20  on a spindle around an axis  22 . A head suspension  24  is connected to actuator arm  20  at a head mounting block  26 . A flexure  28  is connected to an end of head suspension  24 , and carries slider  12 . Slider  12  carries a transducing head (not shown in  FIG. 1 ) for reading and/or writing data on concentric tracks  14  of disc  16 . Disc  16  rotates around an axis  30 , so that windage is encountered by slider  12  to keep it aloft a small distance above the surface of disc  16 . 
     VCM  18  is selectively operated to move actuator arm  20  about axis  22 , thereby moving slider  12  between tracks  14  of disc  16 . However, for disc drive systems with high track density, VCM  18  lacks significant resolution and frequency response to position a transducing head on slider  12  precisely over a selected track  14  of disc  16 . Therefore, a higher resolution actuation device is necessary. 
       FIG. 2  is an exploded perspective view of a portion of a disc drive including a microactuator  32  for high resolution head positioning. Flexure  28  is attached to head suspension  24  and microactuator  32  is attached to flexure  28 . Microactuator  32  carries slider  12  above a surface of disc  16 . A transducing head  34  is carried by slider  12  to write and read data to and from the disc. In operation, head suspension  24 , flexure  28 , and microactuator  32  carrying slider  12  are all moved together as coarse positioning is performed by VCM  18  ( FIG. 1 ) as it moves actuator arm  20  (FIG.  1 ). To achieve fine positioning of transducing head  34 , a magnetic circuit generates a force which causes bending of beam springs associated with microactuator  32 . The magnetic circuit is formed between a keeper and coil component  35  bonded to the top of microactuator  32  with a magnet (shown in  FIG. 3 ) carried by microactuator  32 . As a result, the portion of microactuator  32  carrying slider  12  moves slightly with respect to flexure  28  in the direction of arrows  36 , displacing transducing head  34  with high resolution for precise positioning of transducing head  34  over a selected track of the disc. The horizontal plane of microactuator  32  lies parallel to the surface of disc  16 . 
       FIG. 3  is a top perspective view of microactuator  32  for attachment to flexure  28 . Microactuator  32  comprises a stator  38 , slider bonding pad  40  attached to slider  12 , magnet bonding pad  42  and magnet  44 . Flexure  28  ( FIG. 2 ) is attached to microactuator  32  at stator  38 . Slider bonding pad  40 , magnet bonding pad  42  and magnet  44  comprise the rotor of microactuator  32 . A magnetic circuit (not shown) actuates microactuator  32  and moves the magnet  44  in the direction of arrows  45 , causing slider  12  to move in the direction of arrows  36  with respect to stator  38 , finely positioning the transducing head  34  carried by slider  12  over a track of a disc. The width dimension of the rotor is substantially parallel to the direction of arrows  36  (the direction of the rotor movement) and the length dimension of the rotor is substantially perpendicular to the direction of arrows  36 . 
     Flexible beam elements operatively connect the rotor to stator  38 , permitting movement of the rotor with respect to stator  38 . The flexible beam elements form a beam structure  46  comprised of a first beam pair element  48  and a second beam pair element  50 . First beam pair  48  has a left first beam  48   a  and a right first beam  48   b . A rotation center  52  located at the intersection of left first beam  48   a  and right first beam  48   b  defines the center of in-plane rotation for the rotor. The rotor is balanced about rotation center  52  and perfect balance is approached by use of beam structure  46 . 
       FIG. 4  shows a top view of microactuator  32  and beam structure  46 . First beam pair  48  extends from a first stator arm  56  to a second stator arm  58  and lies between slider bonding pad  40  and magnet bonding pad  42 . First beam pair  48  is substantially aligned with the width of the rotor. A distal connector  60  connects a proximal end of slider bonding pad  40  with a distal end of magnet bonding pad  42  and bisects first beam pair  48 . Rotation center  52  is located at distal connector  60 . 
     Second beam pair  50  includes a left lateral beam  50   a  and a right lateral beam  50   b . Both left lateral beam  50   a  and right lateral beam  50   b  have a dog-leg configuration such that one length of each lateral beam  50   a  and  50   b  is aligned with the length of the rotor alongside magnet bonding pad  42  between pad  42  and stator  38 . A transverse length  50   c  and  50   d  of lateral beams  50   a  and  50   b  are aligned with the width of the rotor and lie between the proximal end of magnet bonding pad  42  and stator  38 . Left lateral beam  50   a  is attached to first stator arm  56 , while right lateral beam  50   b  is attached to second stator arm  58 . A connector  62  connects the rotor (at the proximal end of magnet bonding pad  42 ) to second beam pair  50  at its approximate midpoint. Transverse length  50   c  of left lateral beam  50   a  and transverse length  50   d  of right lateral beam  50   b  are connected at connector  62 . 
     Left lateral beam  50   a  and right lateral beam  50   b  allow connector  62  to move transversely, in the direction of arrows  45  (as seen in FIG.  5 ). The transverse lengths  50   c ,  50   d  of second beam pair  50  also allow connector  62  to move laterally, in the direction of arrows  63  (as seen in FIG.  6 ). Therefore connector  62  can move transversely and laterally around rotation center  52  in a plane parallel to the disc surface, thus tracing an arc around rotation center  52  (as seen in FIG.  5 ). 
       FIG. 5  is a top view of microactuator  32  with the rotor in a displaced position. Upon actuation of microactuator  32 , a force is generated to move magnet  44 , thereby bending beam structure  46  and moving the rotor with respect to stator  38 . Beam structure  46 , and more particularly second beam pair  50 , allows sufficient flexibility for the proximal end of the rotor (magnet bonding pad  42 ) to move in the direction indicated by arrows  45  when microactuator  32  is actuated and in the direction indicated by arrows  63  when the rotor is pulled away from the stator (as seen in FIG.  6 ). Flexibility in beam structure  46  is required for side to side movement of the rotor during actuation of microactuator  32 . When the rotor finally positions slider  12  over a track of a disc it rotates side to side and slightly traces an arc  64  around rotation center  52 . Prior art beam structures allowed a vertical deflection of approximately 100 microns. Beam structure  46  of the present invention prevents the rotor from significantly shifting vertically out of the horizontal plane of microactuator  32  and minimizes the amount of vertical deflection. 
     Head slap deceleration is a condition that occurs when a load in the disc drive causes head suspension  24 , attached to flexure  28  (FIG.  2 ), microactuator  32  and slider  12  to momentarily lift off of disc  16  and then crash back into the disc surface with very high deceleration. The deceleration approaches 600 gravities (g), thus the weight of suspension borne by microactuator  32  is about 0.1 Newtons (N). Some existing magnetic microactuators use flexible beam springs in a “wagon wheel” design located on top of the slider to support the rotor. The beam springs have a limited thickness, generally 20 to 30 microns. The beam spring thickness is constrained by the total microactuator thickness. The limited thickness of the beam springs in the prior art increases the stress borne by those beam springs during a head slap event. Beam elements  48  and  50  of the present invention have a typical beam height of approximately 200 microns, which is enabled by packaging beam structure  46  around the sides of the rotor, thereby not increasing overall height of microactuator  32 . Generally as the beam spring thickness increases, the stress in the beam decreases. Increasing the height of beam elements  48  and  50  reduces the stress in that beam under head slap loading according to the following relation: 
       S   =         M   ⁢           ⁢   y     I     =       6   ⁢           ⁢   F   ⁢           ⁢   L       Wh   2             
 
For example, to calculate the stress in left lateral beam  50   a , S equals the stress in the beam element (N/m 2 ), M is the bending moment (N−m), y is the half height (m) of left lateral beam  50   a , and I is the area moment of inertia (m 4 =wh 3 /12). F is the vertical loading under head slap deceleration (N), L is the length (m) from the beam root point (where left lateral beam  50   a  attaches to first stator arm  56 ) to loading (where head suspension  24  bears down on slider  12  during a head slap event), w is the width (m) of left lateral beam  50   a , and h is the height (m) of left lateral beam  50   a . Comparing the present invention having beam heights (for beam elements  48  and  50 ) of approximately 200 microns with the prior art microactuator having beam heights of 25 microns, the stresses in the beam elements are reduced by approximately a factor of 32.
 
     In some prior art embodiments of the microactuator, uncontrolled shifting of the rotor occurs during hard seek accelerations of VCM  18 , that is movement of the slider across a large number of tracks. A large, in-plane shift in rotor position (approximately 24.8 microns) stresses some prior art beam elements to about 8.8% of their breaking strength. Because of the time-varying acceleration of VCM  18 , fatigue failure in the beam elements may be induced. In the present invention, first beam pair element  48  defines rotation center  52 . The rotor is balanced about the rotation center  52 . The design of beam structure  46  and near perfect balance of the rotor results in substantially less rotor shifting (approximately 0.56 microns) during acceleration of VCM  18 . The stress induced in beam structure  46  is significantly less, approximately 0.6% of the breaking strength, and a safe level for fatigue stress. 
       FIG. 6  is a top view of microactuator  32  under stiction loading. Stiction loading occurs when water and/or a lubricant forms on the disc and the water or lubricant film attaches to a transducing head  34 , forcing transducing head  34  to drag along with the disc as it rotates. During stiction loading slider  12  carrying transducing head  34  is longitudinally pulled away from the stator. The stiction load deflects beam structure  46  when the rotor is longitudinally pulled away from stator  38  in direction  63 . First beam pair  48  and transverse lengths  50   c ,  50   d  of lateral beams  50   a ,  50   b  are pulled out of position and bow out towards slider  12  and slider bonding pad  40 . The dragging of transducing head  34  along the disc continues until the film is broken or beam structure  46  collapses. 
     Beam structure  46  is preferably designed to be relatively compliant in the longitudinal direction. As illustrated by  FIG. 7 , the present invention includes deflection limiters  66  and  68  to constrain the deflection of beam structure  46 . As the stiction load increases, beam structure  46  can not accommodate the load without risking failure and deflection limiters  66  and  68  bear part of the stiction load. Each deflection limiter  66 ,  68  has a proximal hook  70 ,  72  formed in slider bonding pad  40  and a distal stop wall  74 ,  76  formed in stator  38  respectively. After slider  12  is pulled away from stator  38  in direction  63  approximately 50 microns, proximal hooks  70  and  72  are engaged by distal stop walls  74  and  76 , thus stopping further movement of slider  12  away from stator  38 . If the deflection were not constrained by deflection limiters  66 ,  68  the resultant stress could cause the beam structure  46  to collapse and break, resulting in microactuator failure since replacing beam structure  46  is not practical. 
     Beam structure  46  operatively connects the rotor of microactuator  32  to stator  38  and prevents excessive movement and twisting of the stator out of the horizontal plane of microactuator  32 . Beam structure  46  is comprised of first beam pair element  48  aligned with the width of the rotor and second beam pair element  50  in a dog-leg configuration and aligned with the length and the width of the rotor. During a head slap event, the increased thickness of beam elements  48  and  50  and the arrangement of beam structure  46  around the sides of the rotor, reduces the stress in the beam elements, prevents failure of the beam elements and keeps the rotor from significant movement out of the horizontal plane of microactuator  32 . The rotor of the present invention is balanced about rotation center  52  defined by first beam pair  48 . During hard seek acceleration by VCM  18 , near perfect balance of the rotor about rotation center  52  results in significantly less stress induced in beam structure  46  by uncontrolled rotor shifting, thus decreasing the likelihood of fatigue stress in beam structure  46 . During stiction loading of micro actuator  32 , deflection limiters  64  and  66  prevent slider  12  from being completely pulled out of stator  38 . The inability for the rotor of the present invention to maintain its position within the horizontal and vertical planes of micro actuator  32  is an advantage over prior art microactuators. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.