Abstract:
A disc drive has a disc rotatable about an axis, a slider carrying a transducing head for transducing data with a disc, and a dual stage actuation 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 and a suspension assembly supported by the actuator arm. The suspension assembly includes a gimbal. The dual stage actuation assembly further includes a microactuator. The microactuator includes a stator having a top surface and a bottom surface wherein the gimbal is connected to the top surface of the stator. A rotor is operatively connected to the stator and the rotor supports the slider. A magnetic keeper structure is supported by the stator such that the rotor moves with respect to the magnetic keeper structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]    This application claims priority from Provisional Application No. 60/262,895, filed Jan. 19, 2001, for “MOVING COIL MICRO ACTUATOR WITH REDUCED ROTOR MASS” by Peter Crane, Wayne Bonin, Roger L. Hipwell, Jr., and Zine Eddine Boutaghou. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a disc drive microactuator system and more particularly to an improved structure for reduced mass of the microactuator rotor.  
           [0003]    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 (VCM), to radially position a slider (which carries the head) on a gimbal 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.  
           [0004]    One particular design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby affecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. Microactuators typically include a stator portion and a rotor portion, the stator being attached to the gimbal and the rotor supporting the slider. The rotor is movable with respect to the stator such that the slider can be precisely positioned over a track of a disc.  
           [0005]    To accomplish fine positioning of the microactuator, a magnetic circuit allows the rotor to be moved in response to a current provided to the magnetic circuit. The magnetic circuit comprises a bottom keeper, magnets, a conductive coil, and a top keeper. The magnetic circuit generates a microactuator force to allow movement of the rotor in response to the current and the microactuator force is typically constant. Prior art microactuator configurations place a substantial amount of heavy magnetic circuit components on the rotor.  
           [0006]    The microactuator has suspension springs which can be arranged to provide linear motion of the slider by the microactuator. A disadvantage of linear microactuators is the inability to control large amplitude oscillation of the rotor caused by VCM actuator seeking. During seek acceleration of the VCM to coarsely position the actuator arm, the entire microactuator is in linear motion and large amplitude ringing occurs. The acceleration force of the VCM causes the suspension springs in the microactuator to oscillate the rotor carrying the slider within the stator at a resonant frequency causing the large amplitude ringing. Controlling the large amplitude oscillation of the rotor can be done by predisplacing the rotor to the position it would have during steady state VCM acceleration. For example, predisplacing the rotor may be accomplished by applying a current to the microactuator which generates a microactuator force sufficient to oppose the VCM acceleration force and reduce the net force exerted on the rotor. The microactuator force generated by the magnetic circuit to predisplace the rotor is a function of VCM acceleration and rotor mass.  
           [0007]    A high VCM acceleration is desirable to reduce the track seeking time and increase the data throughput of the drive. If the microactuator force remains constant during disc drive operation (as it typically does), the ability to increase the VCM acceleration requires reducing the mass of the rotor. There exists a need in the art for a microactuator having a reduced rotor mass.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    The present invention relates to a disc drive having a disc rotatable about an axis, a slider carrying a transducing head for transducing data with a disc, and a dual stage actuation 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 and a suspension assembly supported by the actuator arm wherein the suspension assembly includes a gimbal. The disc drive actuation assembly further includes a microactuator. The microactuator includes a stator having a top surface and a bottom surface wherein the gimbal is connected to the top surface of the stator. A rotor is operatively connected to the stator and the rotor supports the slider. A magnetic keeper structure is supported by the stator such that the rotor moves with respect to the magnetic keeper structure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of a conventional disc actuation system for positioning a slider over a track of a disc.  
         [0010]    [0010]FIG. 2 is an exploded perspective view of a portion of a disc drive including a microactuator.  
         [0011]    [0011]FIG. 3 is an exploded perspective view of a first embodiment of a microactuator.  
         [0012]    [0012]FIG. 4 is a bottom perspective view of the first embodiment of the microactuator.  
         [0013]    [0013]FIG. 5 is a bottom perspective view of the first embodiment of the microactuator with a bottom keeper attached.  
         [0014]    [0014]FIG. 6 is a perspective view of the first embodiment of the microactuator.  
         [0015]    [0015]FIG. 7 is a sectional view of the first embodiment of the microactuator taken along line A-A of FIG. 6.  
         [0016]    [0016]FIG. 8 is a perspective view of the first embodiment of the microactuator with a flex circuit attached.  
         [0017]    [0017]FIG. 9 is a perspective view of the first embodiment of the microactuator with the flex circuit substrate removed.  
         [0018]    [0018]FIG. 10 is a perspective view of a second embodiment of a microactuator.  
         [0019]    [0019]FIG. 11 is a sectional view of the second embodiment of the microactuator taken along line B-B of FIG. 10. 
     
    
     DETAILED DESCRIPTION  
       [0020]    [0020]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  (or main actuator) arranged to rotate an actuation arm  20  on a spindle around an axis  22 . A load beam  24  is connected to actuator arm  20  at a head mounting block  26 . A gimbal  28  is connected to an end of load beam  24 , and carries slider  12 . Gimbal  28  provides a spring connection between load beam  24  and slider  12 . Slider  12  carries a transducing head (not shown) for reading and/or writing data on concentric tracks  14  of disc  16 . Disc  16  rotates around axis  30 , so that windage is encountered by slider  12  to keep slider  12  aloft a small distance above the surface of disc  16 .  
         [0021]    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 high resolution actuation device is necessary.  
         [0022]    [0022]FIG. 2 is an exploded perspective view of a portion of the disc drive including a microactuator  32  for high resolution head positioning. A flex circuit  33  is attached to a bottom surface of gimbal  28  (shown in FIG. 1). Gimbal  28  is attached to load beam  24  and microactuator  32  is attached to flex circuit  33 . Microactuator  32  carries slider  12  above a surface of disc  16 . The transducing head (not shown) is carried by slider  12  to write and read the data to and from the disc. The transducing head is located on a disc opposing face  34  of slider  12 . Slider  12  has a trailing edge  36  with four slider bond pads  38  attached thereto which aid in providing the electrical connection between the disc drive and slider  12 , as discussed below.  
         [0023]    In operation load beam  24 , flex circuit  33 , and microactuator  32  carrying slider  12  are all moved together as coarse positioning is performed by VCM  18  (FIG. 1) moving actuator arm  20  (FIG. 1). To achieve fine positioning of the transducing head, microactuator  32  generates a force which causes bending of beam springs located on the microactuator. As a result, the portion of microactuator  32  carrying slider  12  moves slightly with respect to flex circuit  33  in the direction of arrows  40 , displacing the transducing head with high resolution for precise positioning of the transducing head over a selected track of the disc.  
         [0024]    [0024]FIG. 3 is an exploded perspective view of microactuator  32  with slider  12 . The microactuator comprises a top keeper  42 , a magnet  44 , a microactuator frame  46  and a bottom keeper  48 . Microactuator frame  46  includes a rotor  50 , a stator  52 , and a magnetic coil  54  (or moving coil). Rotor  50 , the moving part of microactuator  32 , is connected to stator  52  by beam springs  56 ,  58 ,  60  and  62 . Magnetic coil  54  and electrical interconnect lines  63  are embedded into rotor  50  on a top surface  64  of microactuator frame  46 . Magnetic coil  54  and interconnect lines  63  are preferably formed by a damascene process.  
         [0025]    Rotor  50  has a slider bonding tub  66  on a bottom surface  68  of microactuator frame  46 . Slider bonding tub  66  has a tub cap  69  and first and second sidewalls  70  and  72 . Slider  12  is positioned within slider bonding tub  66 . A bottom keeper tub  70  is formed on bottom surface  68  of microactuator frame  46  for receiving bottom keeper  48 . Bottom keeper  48  has standoffs  72  for attaching bottom keeper  48  to microactuator frame  46 . Standoffs  72  extend upward from a top surface  78  of bottom keeper  48 . Although bottom keeper  48  is shown with three standoffs  72 , other embodiments of bottom keeper  48  may include any number of standoffs  72 . Top keeper  42  has a bottom surface  80 . Standoffs  82  extend downward from bottom surface  80  of top keeper  42  to define a channel  84 . Standoffs  76  and  82  are preferably formed by etching.  
         [0026]    Rotor  50  is operatively connected to stator  52  by beam springs which are arranged to enable linear motion of slider  12 . Distal beam springs  56  and  58  are located on opposite sides of slider bonding tub  66  and connect rotor  50  and stator  52 . Proximal beam springs  60  and  62  are located on opposite sides of bottom keeper tub  74  and connect rotor  50  and stator  52 . Although FIG. 3 shows one configuration of a linear microactuator, those skilled in the art will recognize many other linear microactuators may be used in the present invention.  
         [0027]    [0027]FIG. 4 is a bottom perspective view of microactuator frame  46  showing bottom surface  68 , rotor  50  and stator  52 . Outer bars  86  and  88  form a portion of stator  52  and extend the entire length of microactuator frame  46  having a distal end  90  and a proximal end  92 . Beam springs  56 ,  58 ,  60 ,  62 , sidewalls  70 ,  72 , and a portion of microactuator frame  46  (where the magnetic coil  54 ) is located form rotor  50  of microactuator  32 . Sidewalls  70  and  72  of rotor  50 , along with tub cap  69 , support slider  12  within slider bonding tub  66 . A rear wall  94  is a third wall of slider bonding tub  66 . Rear wall  94  is located between slider bonding tub  66  and bottom keeper tub  74  such that it forms a part of rotor  50 . Each distal beam spring  56  and  58  attaches to a distal end of sidewalls  70  and  72 , respectively. Distal beam springs  56  and  58  extend longitudinally and attach to a mid-portion of outer bars  86  and  88 , respectively. Each proximal beam spring  60  and  62  attaches to rotor  50  near a mid-portion of the rotor. Proximal beam springs  60  and  62  extend longitudinally and attach to the proximal end  92  of outer bars  86  and  88 , respectively. Beam springs  56 ,  58 ,  60  and  62  thereby connect rotor  50  to stator  52  (via outer bars  86  and  88 ).  
         [0028]    Slider bonding tub  66  is located at the distal end of microactuator frame  46  adjacent rotor  50  and is recessed from bottom surface  68 . Bottom keeper tub  74  is positioned at the proximal end of microactuator frame  46  and adjacent to the location of magnetic coil  54 . Tubs  66  and  74  are preferably formed by an etching process. Tub  74  is recessed from bottom surface  68  of microactuator frame  46  proximate both rotor  50  and stator  52 . Tub  74  includes mounting points  96 ,  98  and  100  which are located on stator  52 . Mounting point  96  is located at the proximal end of microactuator frame  46  and mounting points  98  and  100  are located between distal beam springs  56  and  58  and proximal beam springs  60  and  62 , respectively, on opposite sides of microactuator frame  46 .  
         [0029]    [0029]FIG. 5 shows a bottom perspective view of microactuator frame  46  with bottom keeper  48  positioned within bottom keeper tub  74  and attached to stator  52 . When bottom keeper  48  is attached to microactuator frame  46 , standoffs  76  are attached to mounting points  96 ,  98  and  100  of stator  52  such that no part of bottom keeper  48  contacts rotor  50 .  
         [0030]    [0030]FIG. 6 is a top perspective view of an assembled microactuator  32  and FIG. 7 is a sectional view of microactuator  32  taken along line A-A of FIG. 6. Top keeper  42  is attached to top surface  64  of microactuator frame  46  on stator  52  adjacent magnetic coil  54 . Magnet  44  is attached to bottom surface  80  of top keeper  42  within channel  84 . Standoffs  82  are attached to stator  52  such that when assembled, magnet  44  is positioned adjacent magnetic coil  54 . Standoffs  82  space magnet  44  the proper distance above magnetic coil  54 . A top gap  102  or mechanical separation, is formed between magnet  44  and magnetic coil  54  on rotor  50 . Since top keeper  42  is attached to stator  52  and magnet  44  is attached to top keeper  42 , neither top keeper  42  nor magnet  44  are included in the mass of rotor  50 .  
         [0031]    Drive terminals  104  and  106 , ground terminals  108  and  110 , and dummy terminals  112  and  114  are located on stator  52  of microactuator frame  46 . Drive terminals  104  and  106  are used to provide drive current to microactuator  32 . Ground terminals  108  and  110  are used for a grounding trace. Dummy terminals  112  and  114  are used to provide a bonding surface for attaching gimbal  28  to microactuator  32  and increase the strength of that joint. Electrical interconnect lines  63 , preferably made of copper and formed by a damascene process, are embedded in distal beam springs  56  and  58  and rotor  50  to route the current between drive terminals  104  and  106  on stator  52  to magnetic coil  54  on rotor  50 .  
         [0032]    Bottom keeper  48  is attached to mounting points  96 ,  98  and  100  of bottom keeper tub  74 . Standoffs  76 , extending upward from top surface  78  of bottom keeper  48 , are attached to stator  52 . A bottom gap  116  is formed between bottom keeper  48  and rotor  50  of microactuator frame  46 , such that there is no contact between bottom keeper  48  and rotor  50 . Standoffs  76  define gap  116  between bottom keeper  48  and moving rotor  50 . Bottom keeper  48  is not included in the mass of rotor  50 .  
         [0033]    In operation, a magnetic circuit is comprised of a magnetic keeper structure including top keeper  42  and bottom keeper  48 , magnet  44 , and magnetic coil  54 . To actuate microactuator  32 , a current is driven through coil  54 . The magnetic circuit created between magnet  44  and coil  54  generates a force to actuate microactuator  32  and move rotor  50  in the direction of arrows  40  with respect to stator  52 . The movement of rotor  50 , and thereby slider bonding tub  66 , finely positions slider  12 , and thereby the transducing head, over a track of the disc. When microactuator  32  is assembled, top keeper  42  in conjunction with bottom keeper  48  closes the magnetic circuit used to actuate microactuator  32  and shields the rest of the disc drive from any stray magnetic field generated by the magnetic circuit.  
         [0034]    [0034]FIG. 8 is a top perspective view of microactuator  32  with flex circuit  33  attached (without gimbal  28 ) and FIG. 9 is a top perspective view of microactuator  32  showing a trace material  118  (with flex circuit  33  removed). Flex circuit  33  is attached to slider  12  (supported by rotor  50 ) and is also attached to stator  52  adjacent drive terminals  104  and  106 , ground terminals  108  and  110 , and dummy terminals  112  and  114 . The location of the terminals on stator  52  and the attachment of flex circuit  33  (and thereby gimbal  28 ) to stator  52  further reduces the mass of rotor  50 . Prior to attaching microactuator  32  to gimbal  28 , flex circuit material  33  is disposed on gimbal  28 . Flex circuits  33  consist of copper trace material  118  (shown in FIG. 9) and polyimide substrate material (shown in FIG. 9). Copper trace material  118  forms terminal pads  120  on top of terminals  104 - 114 , and terminal pads  122  adjacent slider bond pads  38  on trailing edge  36  of slider  12 . Terminal pads  122  are bond pads for electrical connection to slider  12 . Flex circuit  33  is able to move and deflect with rotor  50 . Trace material  118  completes a circuit connection between the electrical components of the disc drive, microactuator  32  and slider  12 .  
         [0035]    Flex circuit material  33 , as well as trace material  118 , travels along the underside of actuator arm  20 , load beam  24  and gimbal  28 . Trace material  118  terminates at terminals  104 - 114  and terminal pads  122 . Typically, a gold bond ball is disposed on each terminal pad  122  and bonded to its respective slider bond pad  38  to act as an electrical conduit and complete the electrical connection between slider  12  and the disc drive (through trace  118  and interconnect lines  63 ). Electrical interconnect lines  63  are embedded in distal beam springs  56  and  58  to route the drive current between the terminals on stator  52  and coil  54  on rotor  50 .  
         [0036]    With reference to FIG. 1, during seek acceleration of VCM  18 , actuator arm  20  is moved over the surface of disc  16  to coarsely position the transducing head carried by slider  12 . Stator  52  and slider  12  of microactuator  32  are connected to flex circuit  33  on gimbal  28 . Gimbal  28  is attached to load beam  24  and load beam  24  is connected to actuator arm  20 . Thus when VCM  18  moves actuator arm  20 , microactuator  32  is in linear motion as well. Slider  12  is carried by rotor  50  of microactuator  32  and rotor  50  is connected to stator  52  by beam springs  56 ,  58 ,  60  and  62 . The acceleration force of VCM  18  during seek acceleration is transferred through beam springs  56 ,  58 ,  60  and  62  to cause undesirable deflection of rotor  50  with respect to stator  52 . Seek acceleration transfers the acceleration force of VCM  18  to rotor  50 , thereby creating a large amplitude oscillation of rotor  50 . The large amplitude oscillation results in rotor disturbance or ringing. Microactuator  32  of the present invention maintains control of slider  12  position during track seeking and eliminates oscillations of rotor  50 .  
         [0037]    A high VCM acceleration is desirable to reduce the track seek time and increase the data throughput of the disc drive. The track seek acceleration by VCM  18  maybe as high as 200 gravities (g). The force generated by microactuator  32  is determined by the magnet and coil properties and how much current can be run through the magnetic circuit. Therefore the microactuator force remains substantially constant, and is preferably high enough to keep slider  12  from oscillating under the influence of VCM seek acceleration. Thus, since the VCM acceleration is determined by the seek time specification, the force required by the microactuator is mainly a function of rotor  50  mass. Also reducing the mass of rotor  50  increases the available VCM acceleration.  
         [0038]    The present invention microactuator  32  reduces the mass of rotor  50  by attaching bottom keeper  48  and top keeper  42 , along with magnet  44  to stator  52  rather than rotor  50 . The reduced rotor mass means a smaller current is required to generate the microactuator force needed to control rotor  50  during track seek acceleration by VCM (and maintain the desired high VCM acceleration). Furthermore, the reduced mass of rotor  50  enables the rotor, and thereby slider  12 , to move more rapidly during actuation of microactuator  32 .  
         [0039]    Prior art microactuators generally had either the bottom keeper or the top keeper (along with the magnet) attached to the rotor. For example, the magnetic coil (located on the rotor) was backed by the bottom keeper. Additionally, the magnet and top keeper were assembled into a magnet holder, however, the present invention eliminates the magnet holder thereby reducing the cost of mounting the magnet. These prior art configurations of the microactuator left the rotor with a large mass thereby requiring a large microactuator force (and current) to maintain the desired high VCM acceleration.  
         [0040]    [0040]FIG. 10 is a perspective view of a second embodiment of microactuator  32  and FIG. 11 is a sectional view of microactuator  32  taken along line B-B of FIG. 10. Microactuator  32  includes top keeper  42 , magnet  44 , microactuator frame  46 , bottom keeper  48  and slider  12 . Top keeper  42  has standoffs  82  to attach the top keeper  42  to stator  52  of microactuator frame  46 . Standoffs  82  space magnet  44  the proper distance above magnetic coil  54  such that a top gap  124  is formed between magnet  44  and magnetic coil  54 . In addition, distal standoffs  126  are formed on stator  52  adjacent slider bonding tub  66 . Standoffs  126  are preferably comprised of photo-imageable epoxy. Microactuator frame  46  includes bottom keeper tub  74  and mounting points  96 ,  98 , and  100  (not shown) for mounting and positioning bottom keeper  48 . The standoffs of bottom keeper  48  are attached to the mounting points of stator  52 . Bottom gap  116  is formed between bottom keeper  48  and rotor  50  adjacent magnetic coil  54 . Mounting bottom keeper  48  and top keeper  42 , along with magnet  44 , to stator  52  rather than rotor  50  reduces the mass of rotor  50 .  
         [0041]    In the second embodiment of microactuator  32 , drive terminals  128  and  130  for providing drive current to microactuator  32  are located on rotor  50 . Ground terminals  132  and  134  for providing a grounding trace are located on stator  52  and within a well  136  formed in distal standoffs  126 . Preferably, flex circuit  33  (not shown) is attached to microactuator  32  at drive terminals  128  and  130  and slider  12  adjacent trailing edge  36 .  
         [0042]    The microactuator configuration of the present invention reduces the mass of the microactuator rotor. A bottom keeper tub is formed on the bottom surface of the microactuator frame. The tub has mounting points on the stator portion of the microactuator frame for attaching the standoffs of the bottom keeper. Although the bottom keeper is attached to the stator, the bottom keeper is housed in the tub adjacent both the rotor and the stator. A top keeper of the present invention microactuator is attached to a top surface of the microactuator frame on the stator. Standoffs extending from the top keeper are used to attach the top keeper to the stator. The magnet is attached to the bottom surface of the top keeper and the standoffs define a gap, or mechanical separation, between the magnet and the magnetic coil.  
         [0043]    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.