Abstract:
The present invention relates to a disc drive that includes a base and a disc rotatably attached to the base. The disc drive further includes an actuator assembly that is attached to the base such that the actuator assembly is in an actuating relationship with respect to the base and the rotating disc. A servo drive controls the movement of the actuator arm assembly during track follow-and-seek operations of the disc drive. The actuator assembly includes a shell and a support structure that is attached to the shell. Adding the support structure to the shell increases the stiffness-to-mass ratio of the actuator assembly in comparison to the shell alone. The increased stiffness-to-mass ratio elevates the resonance frequency of the actuator assembly such that the resonance frequency of the actuator assembly falls outside the range of operating frequencies of the servo drive without significantly increasing the mass of the actuator assembly.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/254,270, filed Dec. 8, 2000 under 35 U.S.C. 119(e). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to the field of mass storage devices. The invention particularly relates to an actuator assembly that is used to support a slider in a disc drive.  
         BACKGROUND OF THE INVENTION  
         [0003]    One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive.  
           [0004]    The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. A microprocessor controls most of the operations of the disc drive, such as exchanging data with the requesting computer, and encoding the data so that it can be efficiently exchanged with the disc.  
           [0005]    A typical disc drive includes at least one transducer that interfaces with the disc to exchange data with the disc. The transducer is part of a small ceramic block, or slider, that is aerodynamically designed to fly over the disc in close proximity to the disc. The slider is attached to the actuator assembly.  
           [0006]    Servo feedback information is used to accurately locate the transducer relative to the disc surface. Based on the servo feedback information, a controller moves an actuator assembly to a required position and holds the transducer very accurately in that position during a read or write operation.  
           [0007]    The actuator assembly is typically either linear or rotary. A rotary actuator includes a rotating pivot assembly, one or more actuator assemblies and a voice coil yoke assembly. The voice coil yoke assembly is controlled by a motor drive system with input from the servo system. The actuator assembly is attached to the pivot assembly such that the voice coil yoke assembly rotates the pivot assembly to maneuver the actuator assembly over the disc.  
           [0008]    A typical actuator assembly includes an arm that is attached at one end to the pivot assembly and further includes a slider mounted at the other end. The length of the arm is one of many factors that affect the resonance frequency of an actuator assembly.  
           [0009]    The arm restricts motion of the slider with respect to the radial and circumferential directions of the disc. The arm may also include a gimbal that allows the slider to pitch and roll and follow the topography of the imperfect disc surface.  
           [0010]    The actuator assembly is cantilevered and acts as a dampening system during operation of the disc drive such that the actuator assembly resonates at a particular frequency. When the operating range of frequencies of the servo motor system includes the resonance frequency of the actuator assembly, there will be a negative effect on the performance of the servo system. Since the actuator assembly is one key source of unwanted mechanical resonance, the actuator assembly is typically designed so that its resonance frequency is outside the operating range of the servo system.  
           [0011]    Advances in disc drive technology have resulted in ever increasing amounts of data being stored on disc surfaces. The increased data density of data storage discs requires the servo motor systems to move the transducer over the disc more quickly and accurately. The efficiency of a servo system improves when it operates at higher frequencies. However, these higher frequencies typically encompass the resonance frequency of known actuator assemblies. Therefore, as servo systems improve to monitor discs with increasing recording densities, actuator assemblies with higher resonance frequencies need to be developed.  
           [0012]    The arms in an actuator assembly are typically made of solid materials. Making the arm in an actuator assembly stiffer increases the resonance frequency of actuator assembly. One common method for increasing the stiffness of the actuator assembly is to make at least a section of the arm thicker. However, increasing the thickness of the arm adds mass to the arm that increases the moment of inertia of the actuator assembly. Increasing the moment of inertia of the actuator assembly is undesirable because it will take longer for the servo motor to move the transducer over the disc.  
           [0013]    In addition, increasing the mass of the actuator assembly requires more power to move the actuator assembly over the disc. The higher power level generates more heat within the disk drive enclosure and raises the operating temperature of the disc drive. Raising the operating temperature of the disc drive can have a negative effect on some of the components in the disc drive.  
           [0014]    What is needed is an improved actuator assembly for a disc drive. The actuator assembly should have a higher stiffness-to-mass ratio without significantly increasing the mass or moment of inertia of the actuator assembly. The improved actuator assembly would have a resonance frequency that is well above the operating frequencies of a corresponding servo motor system that is used to drive the actuator assembly.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention relates to a disc drive that includes a base and a disc rotatably attached to the base. The disc drive further includes an actuator assembly that is attached to the base such that the actuator assembly is in an actuating relationship with respect to the base and the rotating disc. A servo system controls the movement of the actuator arm assembly during track follow-and-seek operations of the disc drive. The actuator assembly is configured to have an improved stiffness-to-mass ratio.  
           [0016]    The improved actuator assembly includes a shell and a support structure that is attached to the shell. Adding the support structure to the shell increases the stiffness-to-mass ratio of the actuator assembly in comparison to the shell alone. The increased stiffness-to-mass ratio elevates the resonance frequency of the actuator assembly such that the resonance frequency of the actuator assembly falls outside the range of operating frequencies of the servo drive without significantly increasing the mass of the actuator assembly.  
           [0017]    The present invention also relates to a method of fabricating an actuator assembly that is used in a disc drive. The method includes providing a shell and attaching a support structure to the shell such that the actuator assembly has a higher stiffness-to-mass ratio than the shell without the support structure. Attaching the support structure to the shell elevates the resonance frequency of the actuator assembly. The shell may include a first piece and a second piece such that attaching a support structure to the shell includes connecting the first piece to the second piece.  
           [0018]    The disc drive and method of the present invention improve the stiffness-to-mass ratio of an actuator assembly. The shell and support structure arrangement also has decreased inertia with similar stiffness when compared to a solid actuator assembly having a similar exterior geometry. The improved stiffness-to-mass ratio increases the resonance frequency of the actuator assembly such that the resonance frequency of the actuator assembly falls outside the operating bandwidth of frequencies of a servo drive that controls the actuator assembly. Since the resonance frequency of the actuator assembly is outside the operating frequency bandwidth of the servo drive, there is reduced off-track motion of the transducer during track follow-and-seek operations.  
           [0019]    In addition, the resonance frequency of the actuator assembly is improved without significantly increasing the mass of the actuator assembly. Therefore, the disc drive has better data tracking capability which may lead to utilizing discs with higher recording densities in the disc drive. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is an exploded perspective view of a disc drive.  
         [0021]    [0021]FIG. 2 is an enlarged exploded perspective view illustrating a portion of a prior art actuator assembly.  
         [0022]    [0022]FIG. 3 is an enlarged perspective view illustrating the portion of the prior art actuator assembly shown in FIG. 2.  
         [0023]    [0023]FIG. 4 is a schematic section view of the prior art actuator assembly shown in FIG. 3 taken along line  4 - 4 .  
         [0024]    [0024]FIG. 5 is an enlarged perspective view illustrating a portion of an actuator assembly that encompasses the present invention.  
         [0025]    [0025]FIG. 6 is a schematic section view of the actuator assembly shown in FIG. 5 taken along line  6 - 6 .  
         [0026]    [0026]FIG. 7 is a schematic section view similar to FIG. 6 with the actuator assembly exploded.  
         [0027]    [0027]FIG. 8 is a schematic section view similar to FIG. 6 illustrating another embodiment of the actuator assembly.  
         [0028]    [0028]FIG. 9 is a schematic section view similar to FIG. 6 illustrating another embodiment of the actuator assembly.  
         [0029]    [0029]FIG. 10 is a schematic section view similar to FIG. 9 illustrating still another embodiment of the actuator assembly.  
         [0030]    [0030]FIG. 11 is a schematic section view similar to FIG. 10 illustrating yet another embodiment of the actuator assembly.  
         [0031]    [0031]FIG. 12 is a top view of the actuator assembly shown in FIG. 11.  
         [0032]    [0032]FIG. 13 is an enlarged exploded perspective view illustrating another embodiment of an actuator assembly that encompasses the present invention.  
         [0033]    [0033]FIG. 14 is an enlarged perspective view illustrating the portion of the actuator assembly shown in FIG. 13.  
         [0034]    [0034]FIG. 15 is a schematic view of a computer system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which illustrate specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes made without departing from the scope of the present invention.  
         [0036]    The invention described in this application is useful with all mechanical configurations of disc drives having either rotary or linear actuation. In addition, the invention is also useful in all types of disc drives including hard disc drives, zip drives, floppy disc drives and any other type of drive.  
         [0037]    [0037]FIG. 1 is an exploded view of one type of disc drive  100  that includes a rotary actuator. The disc drive  100  includes a base  112  and a cover  114  that form an enclosure. An actuator assembly  120  is rotatably attached to the base  112 . Although the actuator assembly can include any number of arms, in the illustrated embodiment, the actuator assembly  120  includes a comb-like structure  122  having a plurality of arms  123 . Attached to the separate arms  123  on the comb  122 , are load beams or load springs  124 . Load beams or load springs are also referred to as suspensions. Some embodiments of the arm  123  may not include a suspension.  
         [0038]    Attached at the end of each load spring  124  is a slider  126 , which carries a magnetic transducer  150 . It should be noted that while the illustrated sliders  126  each include one transducer  150 , this invention is equally applicable to sliders having more than one transducer. One example of a slider that includes more than one transducer is a magneto resistive head in which one transducer is generally used for reading and another is generally used for writing.  
         [0039]    The actuator assembly  120  also includes a voice coil motor  128 . The voice coil motor  128  includes a voice coil  129 , a first magnet  131  attached within the base  112  and a second magnet  130  attached with the cover  114 . The voice coil  129  works in conjunction with the first and second magnets  130 ,  131  to rotate the actuator assembly  120  about a shaft  118 .  
         [0040]    A spindle motor is also mounted to the base  112 . The spindle motor includes a rotating portion called the spindle hub  133 . In this particular disc drive, the spindle motor is within the hub  133 . In the embodiment illustrated in FIG. 1, a number of discs  134  are attached to the spindle hub  133 . In other disc drives a single disc or a different number of discs may be attached to the hub  133 . The invention described herein is equally applicable to disc drives which have a plurality of discs as well as disc drives that have a single disc.  
         [0041]    A portion of an arm  200  that is used in a prior art actuator assembly is shown in FIGS.  2 - 4 . The arm  200  includes a shell  202  that is formed from a first plate  204  and a second plate  208 . The first plate  204  includes an arched body  205  and flanges  206 A,  206 B that extend along the lateral edges of the arched body  205 . The second plate  208  also includes an arched body  209  and flanges  210 A,  210 B that extend along the lateral edges of the arched body  209 . The first plate  204  is assembled to the second plate  208  by joining the flanges  206 A,  206 B on the first plate  204  to the flanges  210 A,  210 B on the second plate  208 . The flanges  206 A,  206 B,  210 A,  210 B are typically joined together using spot welds  211 , although the first and second plates  204 ,  208  may be joined together by other types of welding, or by the use of adhesives.  
         [0042]    The arm  200  illustrated in FIGS.  2 - 4  is cantilevered and acts as a dampening system during operation of a disc drive such that the arm  200  resonates at a particular frequency. Adding the adhesive or welding material to the arm  200  adds unwanted mass to the arm  200 . The additional mass often lowers the resonance frequency of the arm  200  into the operating range of frequencies of a servo motor system that positions an actuator assembly which includes the arm  200 . When the arm  200  resonates, there is a negative effect on the performance of the servo system.  
         [0043]    FIGS.  5 - 7  illustrate one example embodiment of an arm  300  that is used in an actuator assembly of the present invention. The arm  300  includes a shell  302  that is made up of a first member  304  and a second member  308 . Although the first member  304  is connected to the second member  308  by a support structure  312 , it should be noted that the shell  302  may be a single member or multiple members without departing from the scope of the present invention.  
         [0044]    The support structure  312  is preferably a sheet  313  of stainless steel that is formed to include one or more orthogonal bends  314 . The formed sheet  313  also includes one or more flat sections  315  that are secured to the first member  304 , and one or more flat sections  316  that are secured to the second member  308 . Although the flat sections  315 ,  316  of the sheet  313  are secured to the first and second members  304 ,  308  using any known method, the sheet  313  is preferably secured to the first and second members  304 ,  308  using an adhesive.  
         [0045]    In the illustrated embodiment, the lateral edges  320  of the first member  304  and the lateral edges  321  of the second member  308  are each aligned with some the bends  314  in the sheet  313 . Aligning some of the bends  314  in the sheet  313  with the lateral edges  320 ,  321  of the first and second members  304 ,  308  causes the sheet  313  to form the sidewalls  324 A,  324 B of the arm  300 .  
         [0046]    Although the first and second members  304 ,  308  are shown as planar sheets in FIGS.  5 - 7 , the first and second members  304 ,  308  can have a variety of configurations. One example configuration for the first and second members  304 ,  308  is shown in FIG. 8. The first member  304  includes an arched body  330  separated by flanges  331 A,  331 B, and the second member  308  similarly includes an arched body  332  separated by flanges  333 A,  333 B. The number and location of the bends  314  may be arranged such that some of the bends  314  in the sheet  313  are aligned with the lateral edges  320 ,  321  and/or the flanges  331 A,  331 B,  333 A,  333 B of the first and second members  304 ,  308 . It should be noted that there may be a single support structure that extends along the entire length of the arm  300 , or a portion of the length of the arm  300 . In addition, there may be several support structures  312  positioned at discrete locations along the length of the arm  300 .  
         [0047]    [0047]FIG. 9 shows another example embodiment of an arm  400  that is used in an actuator assembly of the present invention. The arm  400  includes a similar shell  402  that is made up of a first member  404  and a second member  408  with the first and second members  404 ,  408  connected together by a support structure  412 .  
         [0048]    The support structure  412  includes a plastic first portion  416 A that extends between a lateral edge  420 A of the first member  404  and a lateral edge  421 A of the second member  408 . The support structure  412  further includes a plastic second portion  416 B that extends between an opposing lateral edge  420 B of the first member  404  and an opposing lateral edge  421 B of the second member  408 . The first portion  416 A is connected to the second portion  416 B by a connecting portion  424  that extends between the first and second members  404 ,  408 .  
         [0049]    The first and second plastic portions  416 A,  416 B each include a body  417  that is positioned between the first and second members  404 ,  408 , and a cap  418  that is positioned outside the lateral edges  420 A,  420 B,  421 A,  421 B of the first and second members  404 ,  408 . The cap  418 , body  417  and connecting portion  424  are preferably integral with one another and fabricated as part of the same injection molding process.  
         [0050]    In the example embodiment shown in FIG. 10, the first and second portions  416 A,  416 B of the support structure  412  each include fingers  428  that extend from the respective bodies  417  through openings in the first and second members  404 ,  408 . As shown most clearly in FIG. 11, there are several support structures  412  along the length of the arm  400 . Each support structure  412  may be formed on the arm  400  during the same injection molding process.  
         [0051]    [0051]FIG. 12 shows that the first and second members  404 ,  408  may be secured to the support structure  412  by melting that portion of the fingers  428  that extends through the first and second members  404 ,  408  to form plugs  440 . The plugs  440  seal the first and second members  404 ,  408  against the bodies  417  and caps  418  of the first and second portions  416 A,  416 B. Although the fingers  428  are shown as extending from the bodies  417  of the first and second portions  416 A,  416 B, the fingers  428  may also extend through the first and second members  404 ,  408  from one or more locations along the connecting portion  424  of the support structure  412 .  
         [0052]    [0052]FIGS. 13 and 14 show a portion of another example arm  500  that may be used in an actuator assembly of the present invention. The arm  500  includes a shell  502  and a support structure  512  attached to the shell  512 . The shell  502  includes a first member  504  and a second member  508 . The first and second members  504 ,  508  are connected together by a support structure  512 .  
         [0053]    The support structure  512  is an etched polymer core  520  and the first member  504  is preferably, although not necessarily, a 300 series stainless steel sheet that has a thickness in the range of 15-25 microns. The first member  504  is etched to include load springs  510 A,  510 B, an opening  514  for distal tooling, and a relief window  516  that allows pitch motion of a transducer (not shown) that would be mounted to the arm  500 . The invention encompasses other forms of the first member  504  beyond those shown in FIGS. 13 and 14.  
         [0054]    The polymer core is preferably, although not necessarily, a polyimide that is between 25-250 microns thick. The polyamide core is laminated to the first member  504 , and then etched with potassium hydroxide or oxygen plasma to form a similar distal tooling opening  534  and pitch relief window  536 . The etched core  520  includes outer dimensions that are similar to a portion of the first member  504 . The distal tooling openings  514 ,  534  and pitch relief windows  516 ,  536  are aligned on the first member  504  and the etched core  520 . It should be noted that the core  520  may be further etched to remove additional mass from the arm  500 . The etching may include any type of pattern that minimizes the mass of the arm  500  without significantly decreasing the stiffness of the arm  500 . The etched pattern is preferably in a form that increases the resonance frequency of the arm  500 .  
         [0055]    In other forms of the invention, the core  520  may be formed by photo-curing or thermo-curing instead of removing material by etching. In addition, the core  520  may be formed in a plurality layers.  
         [0056]    The second member  508  is also preferably a 300 series stainless steel sheet that has a thickness between 15-25 microns. The second member  504  is configured with similar outer dimensions to the etched core  520 . The second member  508  is laminated to the etched core  520  and then etched to form a similar distal tooling opening  554  that is aligned with the distal tooling openings  514 ,  534  on the first member  504  and the etched core  520 . In the illustrated example embodiment, the second member  508  covers the pitch relief windows  516 ,  536  in the first member  504  and the etched core  520  to increase the stiffness of the arm  500 .  
         [0057]    [0057]FIG. 15 is a schematic view of a computer system  6000  that includes the present invention. The computer system  6000  may be any type of electronic system or information handling system. The computer system  6000  includes a central processing unit  6004 , a random access memory  6032  and a read only memory  6034 . A system bus  6030  electrically couples the central processing unit  6004  to the random access memory  6032  and the read only memory  6034 . The computer system  6000  may also include an input/output bus  6010  that connects the central processing unit  6004  to several peripheral devices  6012 ,  6014 ,  6016 ,  6018 ,  6020 ,  6022 . The peripheral devices may include hard disc drives, magneto-optical drives, floppy disc drives, monitors, keyboards and other such peripherals. Any type of computer system  6000  may include an actuator assembly as described above.  
       CONCLUSION  
       [0058]    The present invention relates to an actuator assembly  120  for supporting a slider  126  in a disc drive  100 . The actuator assembly  120  includes a shell  302  and a support structure  312  connected to the shell  302 . The support structure  312  increases a stiffness-to-mass ratio of the shell  302  to elevate the resonance frequency of the shell  302 . The shell  302  in the actuator assembly  120  may include a first member  304  and a second member  308  such that the support structure  312  connects the first member  304  to the second member  308 .  
         [0059]    The first and second members  304 ,  308  of the shell  302  may be in the form of substantially parallel plates, and the support structure  312  may be a sheet  313  that includes a plurality of orthogonal bends  314 . The plurality of bends  314  in the sheet  313  may form at least one flat section  315 ,  316  in the sheet  313  that is connected to the shell  302 . In an example embodiment, the sheet  313  forms at least one side wall  324 A,  324 B of the arm  300 .  
         [0060]    In an alternative embodiment, the support structure  412  may include a plastic first portion  416 A that extends between a lateral edge  420 A on the first member  404  and a lateral edge  421 A on the second member  408 , and a plastic second portion  416 B that extends between an opposing lateral edge  420 B on the first member  404  and an opposing lateral edge  421 B on the second member  408 . The support structure  412  may further include a molded plastic connecting portion  424  that extends between the first and second portions  416 A,  416 B of the support structure  412 . The first and second portions  416 A,  416 B may include one or more fingers  428  that extend through openings in the first and second members  408  such that the fingers  428  could be melted to form plugs  440  that secure the first and second members  404 ,  408  to the first and second portions  416 A,  416 B.  
         [0061]    In another example embodiment, the support structure  512  may be an etched core  520  that connects the first and second members  504 ,  508 . One of the first and second members  504 ,  508  could be etched into a pattern that is similar to the etched core  520 .  
         [0062]    The present invention also relates to a disc drive  100  that includes a base  112  and a rotating disc  134  attached to the base  112 . The disc drive  100  further includes a transducer  150  and a servo system that produces transducer  150  position information. An actuator  120  is attached to the base  112  and responds to position information from the servo system to move the transducer  150  relative to the rotating disc  134 . The actuator  120  includes a shell  302  and a support structure  312  that is attached to the shell  302  to increase the resonance frequency of the shell  302 .  
         [0063]    The present invention also relates to a method of fabricating an actuator assembly  120  that is used in a disc drive  100 . The method includes providing a shell  302  and attaching a support structure  312  to the shell  302  such that the actuator assembly  120  has a higher stiffness-to-mass ratio than the shell  302  without the support structure  312 . Attaching the support structure  312  to the shell  302  elevates the resonance frequency of the shell  302 . The shell  302  and support structure  312  arrangement also has decreased inertia with similar stiffness when compared to a solid actuator assembly having a similar exterior geometry. The shell  302  may include a first piece  304  and a second piece  308  such that attaching a support structure  312  to the shell  302  includes connecting the first piece  304  to the second piece  308 .  
         [0064]    It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should be determined with reference to the appended claims, along with the fall scope of equivalents to which such claims are entitled.