Abstract:
A method is used for forming a magnet keeper assembly for use in a microactuator. The method comprises forming a keeper from a ferromagnetic material where the keeper has a plurality of notches for accepting a plurality of magnetic materials, securing the magnetic materials in the notches in the keeper, notching the magnetic material and the keeper transversely at a depth approximately equal to the depth of the magnetic material, removing any debris generated during notching, subjecting the keeper to a magnetic field such that the magnetic materials become magnetized, and cutting the keeper into magnet keeper assemblies.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a divisional U.S. patent application Ser. No. 09/315,005, filed May 19, 1999, now U.S. Pat. No. 6,268,984, issued on Jul. 31, 2001, for “Magnet Configuration for Head-Level Microactuator” by Zine-Eddine Boutaghou. 
     This application claims priority from provisional application Ser. No. 60/116,834, filed Jan. 22, 1999, for “Magnet Configuration, for Head Level Micro-Actuation” by Zine-Eddine Boutaghou. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a head-level microactuator having improved efficiency and improved ease of manufacture. More particularly, it relates to a magnetic microactuator located between a suspension and a slider in a disc drive system to selectively move a transducing head radially with respect to a rotatable disc. 
     The density of concentric data tracks on magnetic discs continues to increase (that is, the size of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the 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 head at the end of the actuator arm. The large-scale motor lacks a 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 promising approach 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 microactuation designs have been considered to accomplish high resolution head positioning. One design involves inserting a silicon-based thin film structure between the suspension and the slider in a disc drive assembly. A major technical challenge in implementing such a microactuator is to provide sufficiently large actuation force to overcome friction forces and spring bias forces to drive the head at a speed high enough to accommodate the required bandwidth. Such a design must be realized in a relatively small wafer area to keep costs reasonable and to allow easy integration into the disc drive design. 
     There is a need in the art for a microactuator design providing large actuation force with reasonable power consumption and within a reasonable wafer area to microposition a transducing head at a speed that accommodates the high bandwidth required by high performance disc drives and can be manufactured cost effectively. 
     BRIEF SUMMARY OF THE INVENTION. 
     The present invention is a dual-stage actuation assembly for positioning a slider carrying a transducing head in a disc drive system with respect to a selected radial track of a rotatable disc. The dual-stage actuation assembly includes a movable actuator arm controlled by an actuator motor and a suspension assembly, including a flexure, supported by the actuator arm. The assembly includes a microactuator having a stator attached to the flexure and a rotor attached to the slider. The rotor is transversely movable with respect to the stator and a horizontal plane generally parallel to the surface of the disc. The assembly contains a magnetic circuit arranged vertically in a plurality of horizontal planes configured to effect motion of the rotor with respect to the stator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a disc drive actuation system for positioning a slider over tracks of a disc. 
     FIG. 2 is an exploded perspective view of the distal portion of the disc drive actuation system of FIG,  1 . 
     FIG. 3 is a schematic diagram of a microactuation system for use in a dual-stage disc drive actuation system for high resolution positioning of a slider according to a first embodiment of the present invention. 
     FIG. 4 is a schematic view of a microactuation system for use in a dual-stage disc drive actuation system for high resolution positioning of a slider according to a second embodiment of the present invention. 
     FIG. 5 is a schematic view of a microactuator system for use in a dual-stage disc drive actuation system for high resolution positioning of a slider according to a third embodiment of the present invention. 
     FIGS  6 A and  6 B are a side view and a top view, respectively, of a keeper assembly according to the present invention. 
     FIG. 7 is a top view of the keeper assembly shown in FIGS. 6A and 6B after further processing. 
     FIG. 8 is a schematic diagram showing the keeper assembly of FIG. 7 subjected to an electromagnetic field. 
     FIG. 9 is a top view of the keeper assembly of FIGS. 6A and 6B after final processing. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a top view of a disc drive actuation system  10  for positioning a transducing head (not shown) over a track of a magnetic disc as known in the prior art. The actuation system  10  includes, as shown from left to right in FIG. 1, a voice coil motor (VCM)  12 , an actuator arm  14 , a suspension  16 , a flexure  18 , and a slider  20 . The slider  20  is connected to the distal end of the suspension  16  by the flexure  18 . The suspension  16  is connected to the actuator arm  14  which, in turn, is coupled to the VCM  12 . As shown on the right side of FIG. 1, the disc drive assembly includes a disc  22  having a multiplicity of tracks  24  which rotates about an axis  26 . During operation of the disc drive assembly, rotation of the disc  22  generates air movement which is encountered by the slider  20 . This air movement acts to keep the slider  20  aloft a small distance above a surface of the disc  22  allowing the slider to “fly” above the surface of the disc  22 . 
     The VCM  12  is selectively operated to move the actuator arm  14  around an axis  28 , thereby moving the suspension  16  and positioning the transducing head (not shown) carried by the slider  20  between tracks  24  of the disc  22 . Proper positioning of the transducing head (not shown) is necessary for reading and writing of data on the concentric tracks  24  of the disc  22 . For a disc  22  having a high track density, however, the VCM  12  lacks sufficient resolution and frequency response to position the transducing head (not shown) on the slider  20  overt a selected track  24  of the disc  22 . Therefore, a higher resolution actuation device is used. 
     FIG. 2 is an exploded perspective view of the distal portion of the disc drive actuation system,  10  (shown on the right hand side in FIG. 1) as known in the prior art. Shown in FIG. 2, from top to bottom, are the suspension  16 , the flexure  18 , and the slider  20  carrying the transducing head  29 . The flexure  18  is attached to the suspension  16  and the slider  20  attaches to a bottom surface of the flexure  18 . The transducing head  29  is carried by the slider  20 . 
     The flexure  18  provides a spring connection between the slider  20  and the suspension  16 . The flexure  18  is configured such that it allows the slider  20  to move in pitch and roll directions to compensate for fluctuations in the spinning surface of the disc  22 . Many different types of flexures  18 , also known as gimbals, are known to provide the spring connection allowing for pitch and roll movement of the slider  20  and can be used with the present invention. 
     During operation of the. disc drive actuation system  10 , the suspension  16 , the flexure  18 , and the slider  20  are all moved together as coarse positioning is performed by VCM  12  (shown in FIG. 1) moving actuator arm  14  (shown in FIG.  1 ). To achieve fine positioning of the transducing head  29 , the present invention uses a microactuator for effecting transverse motion of the slider  20  with respect to the flexure  18 . 
     FIG. 3 is a schematic diagram of a microactation system  30  for use in a dual-stage disc drive actuation system for high resolution positioning of a transducing head  29  according to first embodiment of the present invention. As shown from top to bottom in FIG. 3 the microactuation system  30  includes a top ferromagnetic keeper  32 , a magnet  34 , a coil  36 , a bottom magnet  38  and a bottom ferromagnetic keeper  40 . As shown in FIG. 3, the top ferromagnetic keeper  32  is attached to a top surface of the flexure  18  and the coil  36  is attached to a bottom surface of the flexure  18 . Also as shown in FIG. 3, the slider  20  is mounted to a bottom surface of the bottom ferromagnetic keeper  40 . The cross hatching of the flexure  18  and the slider  20 , in FIG. 3, is done solely for the purpose of distinguishing these components and is not intended to signify a sectional view. The top magnet  34  and the bottom magnet  38  are configured such that they generate magnetic flux flowing in a path illustrated by the arrows in FIG. 3, referred to as B g  (for flux in the air gap) and B k  (for flux in the, keepers), which forms a closed magnetic circuit. 
     During operation of the microactuation system  30 , an electric current is applied to the coil  36 . The current flowing through the coil  36  interacts with the magnetic flux field. This interaction causes a force to be exerted on the top magnet  34  and the bottom magnet  38  in a lateral direction (across the tracks  24  of the disc  22 ), the force being controllable to achieve high resolution movement for fine positioning of the transducing head  29  with respect to the tracks  24  of the disc  22 . 
     The actuation force achieved by the magnetic circuit shown in FIG. 3 is governed by the Lorentz equation, with the current through the coil  36  flowing at a 90 degree angle to the air gap flux (B g ), given as: 
     F y =N I B g  L m  where F y  is the actuation force, N is the number of coil traverses across the face of the top magnet  34  and the bottom magnet  38 , I is the current in the coil,B g  is the flux density in the air gap, and L m  is the length of the faces of top magnet  34  and bottom magnet  38  (the length into the paper as the magnets are shown in FIG.  3 ). In addition to the actuation force, there is a force of attraction between the top magnet  34  and the bottom ferromagnetic keeper  40  and between the top ferromagnetic keeper  32  and the bottom magnet  38 , given as:          F   z     =       AB   g   2         2                   μ   0                                             
     where F z  is the attraction force, A is the area of the faces of top magnet  34  and bottom magnet  38 , B g  is the air gap flux density, and μ O  is the permeability of the free space. 
     An actuation stroke (i.e., the amount of lateral displacement of the bottom keeper  40  with respect to a baseline position) can be determined from the designed resonant frequency of the microactuator and the actuation force achieved. The microactuator resonant frequency is generally controlled by the servo system of the disc drive, and is also affected by the mass of the microactuator springs and the offtrack stiffness of the springs. Large actuation stokes are achieved only with rather significant vertical attraction forces between the magnets  34 ,  38  and the keepers  32 ,  40 . The microactuator springs must be designed to support both this vertical attraction force and the vertical pre-load force applied to the slider with minimal vertical deflection. To accomplish this, the net loading point of the microactuation system  30  is located at a point where the bending moments from the air-bearing pre-load force and the magnetic attraction force sum to zero. 
     In the force equations given above, the air gap flux density (B g ) is given as:          B   g     =       B   r       (     1   +       T   g       T   m         )                              
     where B r  is the remanant magnetization of the magnetic material of top magnet  34  and bottom magnet  38 , T g  is the thickness of the air gap between top keeper  32  and bottom keeper  40 , including open-space and coil  36 , and T m  is the thickness of magnets  34 ,  38 . 
     The minimum thicknesses of top keeper  32  and bottom keeper  40  must be sufficient to carry the magnetic flux generated by top magnet  34  and bottom magnet  38  linking the closed magnetic circuit without saturating. This minimum thickness may be calculated using the following equation:          T   k     =       W   m            B   g       B   s                                
     where T k  is the minimum thickness of top keeper  32  and bottom keeper  40 , W m  is the width of magnets  34 ,  38  (the distance across the page as the magnets are shown in FIG. 3) and B s  is the saturation moment of the material used to form top keeper  32  and bottom keeper  40 . Thus, it can be appreciated that a design with a set of four magnets requires only half the keeper thickness of a design with two magnets, since each magnet face is half as wide. 
     FIG. 4 shows a schematic view of a microactuation system  50  for use in a dual-stage disc drive actuation system for high resolution positioning of a transducing head  29  according to a second embodiment of the present invention. As shown from top to bottom in FIG. 4, the microactuation system  50  includes a top ferromagnetic keeper  52 , top magnets  54   a ,  54   b , a coil  56 , bottom magnets  58   a ,  58   b , and a bottom ferromagnetic keeper  60 . As shown in FIG. 4, the top ferromagnetic keeper  52  is attached to a top surface of the flexure  18  and the coil  56  is attached to a bottom surface of the flexure  18 . The slider  20  is mounted to a bottom surface of the bottom ferromagnetic keeper  60 . The cross hatching of the flexure  18  and the slider  20 , in FIG. 4, is done solely for the purpose of distinguishing these components and is not intended to signify a sectional view. 
     The top magnets  54   a ,  54   b  and the bottom, magnets  58   a ,  58   b  are configured such that you generate a magnetic flux flowing in two closed magnetic circuits. The path of the first closed magnetic circuit is illustrated by the arrows on the left half of FIG. 4 referred to as the B 1   g  (for flux in the air gap) and B 1   k  (for flux in the keepers). The second closed magnetic circuit is illustrated by the arrows on the right half of FIG. 4 referred to as B 2   g  (for flux in the air gap) and B 2   k  (for flux in the keepers). The bottom keeper  60  is flexibly coupled to the top keeper  52  by microactuation springs  62   a ,  62   b  which allow movement of the bottom keeper  60  laterally with respect to the top keeper  52  as described by the above equations. 
     FIG. 5 shows a schematic view of a microactuation system  70  for use in a dual-stage disc drive actuation system for high resolution positioning of a transducing head  29  (not shown) according to a third embodiment of the present invention. As shown from top to bottom in FIG. 5, microactuation system  70  includes a top ferromagnetic keeper  72 , a coil  74 , a bottom magnet  76 , and a bottom ferromagnetic keeper  78 . This configuration generates magnetic flux flowing in a path illustrated by the arrows in FIG. 5, referred to as Bg (for flux in the air gap) and Bk (for flux in the keepers), which forms a closed magnetic circuit. Energizing the coil  74  causes lateral motion of the bottom ferromagnetic keeper  78  with respect to the top ferromagnetic keeper  72  consistent with the above equations. 
     As illustrated by the schematic diagram of FIGS. 3,  4 , and  5 , the portion of the microactuation systems  30 ,  50 ,  70  supporting the slider  20  is flexibly coupled to the portion of the microactuation systems  30 ,  50 ,  70  connected to the flexure  18 . This flexible connection may be achieved by any number of techniques generally known in the prior art. One particular technique is disclosed in U.S. patent application Ser. No. 09/315,006 filed May 19, 1999 by Crane, et al. entitled “Magnetic Microactuator” which is assigned to Seagate Technology, Inc., the assignee of the present application. 
     A significant advantage to the microactuation systems shown in FIGS. 3,  4 , and  5  is that they may be constructed using an efficient manufacturing process. The separation of the magnets  34 ,  38 (as shown in FIG. 3) into a top layer and a bottom layer allows for a simpler, more cost-effective manufacturing technique. 
     FIGS. 6A and 6B show a side view and a top view, respectively, of a keeper assembly  100  for manufacturing the keeper/magnet assemblies used in the present invention (shown in FIG. 3 as reference numerals  32  and  34  and as reference numerals  38  and  40 ). Any cross hatching appearing in FIGS. 6-9 is done solely for the purpose of ease of viewing and is not intended to indicate a sectional view. The keeper assembly  100  includes magnetic material  102  and a keeper  104 . The magnetic material  102  may consist of any magnetic material generally known to one of skill in the art. Some exemplary magnetic materials include ceramic magnets, neodymium iron boron, and samarium cobalt. Ceramic magnets and samarium cobalt magnets are able to withstand process temperatures of 220 degrees Celsius, typically experienced in solder reflow ovens. Neodymium iron boron is limited to process temperatures below 150 degrees Celsius. The keeper  104  is constricted from a ferromagnetic material such as cobalt-iron for example. 
     To assemble the keeper assembly  100 , parallel notches  103  are cut into and run the width of keeper  104 . The magnetic material  102  fits into the notches  103  and is attached to the keeper  104  as shown in FIGS. 6A and 6B. 
     The next step in the manufacturing process is to cut the magnetic material  102  into sizes that maybe used with the microactuation systems  30 ,  50 ,  70  of the present invention. FIG. 7 shows a top view of the keeper assembly  100  having grooves  106  cut into a top surface. As illustrated in FIG. 7, a series of parallel grooves  106  are cut longitudinally into a top surface of the keeper assembly  100  at a depth sufficient to completely sever the magnetic material  102 . The debris generated by this cutting process is then removed prior to continuing the manufacturing process. The removal of debris at this stage is facilitated by the fact that a magnetic material has not yet been magnetized and thus the debris does not tend to cling to the keeper assembly  100 . After removal of all debris, a protective layer may be deposited on the top surface of the keeper assembly  100 . 
     The next step in the manufacturing process is to magnetize the magnetic material  102 . FIG. 8 shows the keeper assembly  100  as subjected to a magnetic field generated by electromagnet  108 . The magnetic field may be generated by any technique known to those with skill in the art. The amount of magnetization achieved can be controlled by the strength of the magnetic field and the time of exposure. 
     After magnetization is complete, the keeper assembly  100  is cut into individual magnet/keeper units for use in the microactuation systems of the present invention. FIG. 9 shows a top view of the keeper assembly  100  after completion of the cutting step. During this cutting step, the keeper assembly  100  is cut completely through by making longitudinal cuts  116  and lateral cuts  118 . The final product is a magnet/keeper assembly  110  consisting of one magnet  112  and one keeper  114 . Where desired, the lateral cuts  118  may be placed before every other set of magnets  112  such that the resulting magnet/keeper assembly  110  includes two magnets  112  in the keeper assembly  114 . After cutting, the magnet/keeper assemblies  110  are removed from the non-magnetic carrier and are ready for use in constructing a microactuation system. 
     Magnet/keeper assemblies  110  may then be used to construct, for example, the microactuation system  30  of the present invention. To construct the microactuation system  30 , two magnet/keeper assemblies  110  are required. One of the microactuation assemblies  110  is rotated 180 degrees about a lateral axis and placed above the other magnet/keeper assembly  110  as shown in FIG.  3 . Two magnet/keeper assemblies are then attached to each other and to the other components of the microactuation system  30  as shown in FIG.  3 . 
     An advantage of the manufacturing process of the present invention is that all of the magnetic material  102  may be magnetized as one piece. This overcomes the problem faced in the prior art associated with magnetizing adjacent magnets with opposite polarities. 
     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.