Abstract:
A rotary actuator motor is provided including a stationary coil section and a rotating magnet. The magnet is incorporated with the pivot bearing assembly, and the coil section is aligned with the magnet along an axis of rotation of the actuator. The magnet fully encircles the axis of rotation. The coil comprises one or more closed loops of electrically conductive material. The motor in this arrangement maintains a much smaller profile in comparison to a traditional voice coil motor that is mounted to a yoke extending away from the axis of rotation of the actuator.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part application of U.S. application Ser. No. 11/326,788, filed on Jan. 6, 2006, entitled “Rotary Actuator Motor for Disk Drive” and further identified as Attorney Docket No. 3123-713, which claims priority from U.S. Provisional Patent Application No. 60/642,184 filed on Jan. 7, 2005, entitled “Disk Drive Form Factor Enabling Rotary Magnet Pure Torque Actuator Motor” and further identified as Attorney Docket No. 3123-713-PROV, the disclosures of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to disk drives, and more particularly, to a rotary actuator motor used to control movement of an actuator assembly in a disk drive.  
       BACKGROUND OF THE INVENTION  
       [0003]     Disk drives generally utilize rotary actuators to position one or more magnetic read/write heads (also known as transducers), with respect to a similar number of magnetic disks rotatably mounted on a hub driven by a motor. The read/write heads are moved across selected tracks of the magnetic disks to gain access to the digital information recorded on the tracks and/or to write data to particular locations on the tracks. The read/write heads are mounted on an air bearing slider. The slider positions the read/write heads above the data surface of the corresponding disk by a cushion of air generated by the rotating disk. Alternatively, the slider may operate in contact with the surface of the disk. The slider is mounted to a suspension load beam. The suspension maintains the read/write heads and the slider adjacent to or in contact with the data surface of the disk.  
         [0004]     The suspension is connected to the distal end of an actuator arm that is pivotally installed within the housing of the disk drive. Typically, the actuator arm is mounted to a pivot bearing assembly that allows the actuator arm to rotate or pivot in response to torques generated by a voice coil motor mounted to the yoke portion of the actuator arm.  
         [0005]     The voice coil is integrated within a closed loop feedback system or servo system to dynamically position the heads directly over the desired data tracks. The principle of operation for the voice coil motor is controlled electromagnetic interaction between a coil and a permanent magnet. The voice coil typically includes a bundle of wires or coils that are mounted to the yoke arms that extend away from the central pivot axis of the actuator. The coil is immersed in an axially oriented bi-polar magnetic field generated by one or more permanent magnets positioned directly adjacent the coil. When a current is applied to the coil, a force is generated on the coil. By precisely controlling the current, positioning of the heads is achieved. The simplicity yet effectiveness of a voice coil comprising the coil of wires and the magnetic field makes such motors ideal for disk drives in terms of precise head positioning. However, the required orientation of the coils with respect to the magnets requires the actuator to have a somewhat elongated configuration to accommodate mounting of the coils to the yoke. Thus, the disk drive has a definable constraint in terms of size to account for the configuration of the actuator.  
         [0006]     As disk drive technology continues to develop, there is a continuing need to provide reliable yet preferably smaller and less mechanically/electrically complex assemblies which enables manufacturers to more economically produce such drives.  
         [0007]     While voice coil motors have proven to be effective for use in many disk drive applications, it would be advantageous to provide a motor to control actuator movement wherein part count and assembly complexity is reduced, yet standards of performance are maintained to handle the ever increasing track densities found on many data disks. Additionally, there is a need to provide such actuator control by use of a motor that is smaller in size, yet can handle the necessary torque requirements for precise actuator positioning.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with the present invention, a rotary actuator motor is provided that is integrated with the pivot bearing assembly. The motor of the present invention is considerably smaller than traditional voice coil motors, yet, the motor of the present invention reduces manufacturing part count, assembly complexity, and maintains acceptable performance standards.  
         [0009]     In a first preferred embodiment of the present invention, the primary components of the rotary actuator motor comprise a magnet that is mounted on and moves with the pivot bearing of the actuator assembly, and a fixed coil that is positioned adjacent the bearing and aligned with the magnet. In this preferred embodiment, the magnet may be ring-shaped and selectively polarized to have the desired number of poles, four poles being one preferable option. The magnet is mounted on its corresponding co-rotating magnetic back plate or back iron, and the coil is on its corresponding magnetic back plate or back iron. The magnet fully encircles the pivot bearing which defines the actuator center of rotation. The arrangement of the magnet and coil in this fashion makes the rotary actuator motor of the present invention similar to an axial flux motor. In general terms, the motor of the present invention may still be referred to as a voice coil motor since a magnet and a series of coils are used to generate torque.  
         [0010]     The coil of the present invention; however, distinguishes it from an axial flux motor. The coil is multi-stranded and may be arranged as a single loop or an array of loops connected in series. Further, the coil comprises a single phase and the angular pitch of the coil loops is similar to the angular pitch of the permanent magnet poles. As the coil is energized, a force acts on the current-carrying wires and an equal and opposite circumferential reaction force is generated on the magnet. Reversing the current results in a reversal of torque, thus providing bi-directional motion. The maximum stroke is determined by the angular pitch of the electro- and permanent magnet arrays. Torque linearity is assured, as in conventional voice coil motors, by limiting the motion to a fraction of the maximum stroke.  
         [0011]     In a second embodiment of the present invention, instead of a coil mounted to a fixed magnetic back iron, the coil is mounted to a separate fixed bracket that encircles the pivot bearing, and the magnetic back iron associated with the coil is mounted on and moves with the pivot bearing. Accordingly, in this embodiment, the magnet and its corresponding magnetic back iron, as well as the magnetic back iron for the coil rotate as a unit, and the coil remains stationary. The primary advantage of this second embodiment is to eliminate problems associated with hysteresis effects. Hysteresis refers to the tendency of the magnetic back iron to become magnetized and create a parasitic drag on the rotating magnet. By allowing the magnetic back iron associated with the coil to rotate with the magnet, parasitic drag is substantially eliminated.  
         [0012]     Most voice coil motors require two magnets in order to maintain the magnetic field perpendicular to the magnet plane. Failing to maintain this perpendicular or orthogonal arrangement results in generation of off-axis forces that can excite undesired resonance modes. Since the magnet of the present invention is symmetric about the center of rotation, off-axis forces are canceled, allowing pure in-plane torque to be delivered to the actuator.  
         [0013]     Since the coil is stationary in the present invention, no dynamic electrical connections are required to power the coil. Rather, fixed electrical leads may be provided to the coil, which simplifies manufacturing and also reduces flex loop bias.  
         [0014]     By incorporating the rotary actuator motor within the pivot bearing assembly, this design requires less space at the rear of the actuator. Accordingly, the disk drive can be made smaller for a given disk diameter when compared to drives which utilize traditional voice coil motors. Manufacturing costs can also be reduced since the overall part count for the motor is reduced.  
         [0015]     In one aspect of the invention, it can be considered a motor or a means for controlling rotary movement of a device such as an actuator used in a disk drive. According to another aspect of the invention, with the integration of the actuator motor within the pivot bearing assembly, the invention can be considered a combination of the pivot bearing and actuator motor elements. In yet another aspect of the invention, the invention can be considered a method of controlling actuator movement in a disk drive wherein the motor components are integrated with the pivot bearing assembly.  
         [0016]     Other features and advantages of the invention will become apparent from a review of the following detailed description taken in conjunction with the corresponding drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a simplified plan view of a prior art disk drive (top cover removed) illustrating basic components of the drive;  
         [0018]      FIG. 2  is a perspective view of one example of a prior art pivot bearing;  
         [0019]      FIG. 3  is an exploded perspective view of the motor of the present invention along with other components of a disk drive including a pivot bearing and actuator assembly;  
         [0020]      FIG. 4  is a perspective view illustrating the motor assembled with the pivot bearing and actuator assembly;  
         [0021]      FIG. 5  is a simplified schematic and cross-sectional view of the basic components of the motor of the present invention;  
         [0022]      FIG. 6  is a vertical section of the motor of the present invention according to the embodiment of  FIG. 3  illustrating further details of the motor components and the integration of these components with the pivot bearing;  
         [0023]      FIG. 7  is an exploded perspective view of the motor of the present invention in a second embodiment;  
         [0024]      FIG. 8  is a vertical section of the motor illustrated in  FIG. 7 ; and  
         [0025]      FIGS. 9-14  illustrate exemplary coil configurations that are suitable for use with the motor of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]      FIG. 1  shows a plan view of a disk drive assembly  10 , with the top cover removed.  FIG. 1  is representative of any number of common disk drives. The disk drive assembly as illustrated includes at least one disk  12 , typically having magnetic media both on the upper and lower surfaces thereof. The disk  12  along with other components of the disk drive, are contained within the housing  14 . The disk  12  is mounted over a hub  16  that is driven by a motor (not shown) enabling the disk to rotate at high rotational speeds during operation. An actuator assembly  18  is shown rotatably mounted to an actuator pivot bearing  20 . Basic components of the actuator assembly  18  are shown as including one or more read/write heads  22  mounted on a flexure arm or suspension arm assembly  24 . The suspension  24  is attached to actuator arm  26 . The actuator assembly  18  is rotated to a desired disk track by a voice coil motor including voice coil  30 . The voice coil  30  is typically mounted between the yokes  31  of the actuator assembly. The voice coil  30  is immersed in a magnetic field generated by a magnet assembly. The magnet assembly typically includes upper and lower magnets mounted to respective magnet plates. In  FIG. 1 , the upper magnet (not shown) and upper magnet plate  35  have been broken away thus exposing the lower magnet  32  and lower magnet plate  33 . An actuator control circuit causes current flow in the voice coil  30 , and ultimately controls the position of the actuator assembly  18  by varying current through the voice coil.  FIG. 1  illustrates other common elements of a disk drive including a dynamic communications bus  36  that transfers electronic signals to and from the read/write heads  22 .  
         [0027]     Now referring to  FIG. 2 , a prior art pivot bearing  40  is illustrated. Typically, a pivot bearing includes a stationary mounting shaft or core  42  that has its upper end fixed to the top cover, and its lower end fixed to the base of the housing  14 . The bearing further includes one or more inner races  44  which remain fixed to the mounting shaft  42 , and corresponding outer races  46  which surround the inner races  44 . A plurality of ball bearings (not shown) are positioned between the inner and outer races thereby allowing the outer race(s) to rotate about the inner race(s). Seals  45  are provided between the inner and outer races. Optionally, the bearing may include one or more outer flanges  48  which accommodate the particular configuration of the actuator bore which receives the bearing.  
         [0028]      FIG. 3  illustrates a preferred embodiment of the motor of the present invention. Components of the motor in this figure are shown in an exploded view to show the manner in which the motor is configured with respect to the pivot bearing and the actuator assembly. The pivot bearing  70  is shown as protruding from the base  86  of the housing  72 . As with the conventional prior art bearing shown in  FIG. 2 , the pivot bearing  70  may also include one or more inner and outer races with ball-bearings positioned in the gaps between the races, as illustrated and discussed further below with reference to  FIG. 6 . A lower fixed magnetic back plate or back iron  58  has a plurality of coil sections  60  mounted thereto. The coil sections  60  may be collectively referred to as the coil. The back iron  58  is positioned over the pivot bearing, but is secured to the base  86 , and therefore remains stationary. A sleeve  52  is mounted over and in contact with the outer race  74  of the bearing. The sleeve  52  includes an upper flange  53  that limits the uppermost position for elements secured to the sleeve. According to the preferred embodiment of  FIG. 3 , the actuator assembly  62  is the most upper element secured to the sleeve. A magnet  56  is secured to an upper magnetic back plate or back iron  54 . This upper back iron serves two functions: as a mounting for the magnet  56  and as a magnetic return path. Dotted lines  68  represent the separation in the respective poles of the magnet, four poles being illustrated in the figure. The upper back iron  54  and magnet  56  are disposed below the actuator assembly  62 . The magnet, upper back iron, actuator assembly and sleeve all rotate together as a unit when the motor is in operation. The opening  59  of the fixed magnetic back iron  58  is larger than the outer diameter of the bearing  70  and sleeve  52 ; therefore, there is no interference between rotation of the bearing and the fixed back iron.  
         [0029]     The upper back iron  54  includes an arcuate extension  57 . This extension is provided as a counterweight to help offset the weight of the actuator arm  63 , also thereby helping to balance rotation of the actuator about the pivot bearing in the x and y axes. The protrusion  57  may be sized and shaped to accommodate the particular weight and moment created by the actuator about the pivot bearing. In  FIG. 3 , the actuator assembly  62  represents any conventional actuator and includes a suspension  64  attached to the actuator arm  63 , with one or more read/write heads  66  secured to the distal end of the suspension.  
         [0030]     In lieu of the upper back iron  54  and magnet  56  disposed below the actuator arm, it is also contemplated that the upper back iron  54  with attached magnet  56  could be placed on top of the actuator  62 , it being understood that operation of the motor can still be conducted so long as the magnet maintains a predetermined distance from the coil sections  60 .  
         [0031]      FIG. 4  illustrates the motor being assembled to the pivot bearing. Because of the relatively compact configuration of the motor, the actuator may be positioned much closer to the corner of the housing as shown in  FIG. 4 , thereby enabling the housing to be smaller in size. With traditional voice coils secured to yoke arms of an actuator assembly, these voice coils require a much greater offset between the edges of the housing and the location of the pivot bearing. Additionally, since the magnet  56  of the present invention is centered about the axis of rotation, this feature of the present invention also helps to minimize the size of the disk drive since the drive does not have to accommodate magnets and magnet back irons that also must be offset from the pivot bearing and axially oriented with the voice coil.  
         [0032]      FIG. 5  is a simplified schematic diagram of the motor of the present invention. As shown, the sleeve  52 , upper back iron  54 , and magnet  56  are assembled and spaced from the coil sections  60  that are secured to the lower fixed back iron  58 . A center line  61  defines the central axis of rotation for a bearing secured to the inner surface of the sleeve.  
         [0033]      FIG. 6  is a cross sectional view illustrating additional details of the motor of the present invention incorporated with a pivot bearing in accordance with the preferred embodiment of  FIG. 3 .  FIG. 6  illustrates one example of a pivot bearing construction. The pivot bearing includes an inner race  76 , an outer race  74 , and a plurality of ball bearings  78  positioned between the races within respective bearing raceways  82 . Sleeve  52  is mounted over and in contact with the outer race  74 . The inner race  76  is mounted to a stationary shaft  80 . The shaft  80  is held in place by a pair of securing screws  84 , one extending through the top cover  90  of the housing, and the other extending through the base of the housing  86  that is secured to the PCB  88 . As also shown, the inner peripheral surface  59  of the fixed lower back iron  58  is spaced from the outer race of the bearing so as to prevent contact therewith. The coil sections  60  are disposed on the upper surface of the fixed lower back iron  58 . Accordingly, the magnet  56  and coil sections  60  are placed in facing positions. An electrical current applied to the coil sections  60  causes a torque reaction, and accordingly, the outer race, sleeve, magnet, upper magnetic back plate, and actuator rotate as a single unit.  
         [0034]      FIGS. 7 and 8  illustrate the motor of the present invention in a second embodiment. In this second embodiment, the lower fixed magnetic back plate or back iron  58  is mounted to the sleeve  52 , while the coil sections  60  are mounted separately to a bracket assembly  100  which is positioned in a gap between the magnet  56  and the lower back iron  58 . The bracket assembly  100  comprises an outer periphery  102 , an inner periphery  104 , and a body portion  106  that secures the various coil sections  60 . The body portion  106  can be a planar ring shaped member that interconnects the inner  104  and outer  102  peripheries, or the body portion  106  can be uniquely shaped to follow the particular coil pattern used.  
         [0035]     Referring specifically to  FIG. 8 , the bracket assembly is shown as extending in the gap between the magnet  56  and the lower back iron  58 , but not in contact with the lower back iron or the magnet. Preferably, the bracket assembly  100  is non-metallic, and should be made of a non-magnetic material. For example, the bracket assembly  100  could be made from a thermoplastic material formed in injection molding. The coil sections  60  could be placed within a mold, and then an injection molding process could take place to form the bracket assembly around the coil pattern. As also shown, the bracket assembly  100  comprises a plurality of mounting flanges  110  formed on the periphery of the bracket assembly. Each mounting flange includes a screw hole  112 . Screws  114  are used to secure the bracket assembly  100  in screw holes  116  formed in the base plate of the disk drive housing. Accordingly, the bracket assembly  100  suspends the coil sections  60  in the position as shown in  FIG. 8 .  
         [0036]     The inner periphery  104  of the bracket assembly  100  is spaced from the sleeve  52  surrounding the outer race of the bearing. Thus, the magnet  56 , upper back iron  54 , and lower back iron  58  are able to freely rotate with the bearing and without any contact with the bracket assembly  100  or the coil sections  60 .  FIG. 8  shows the coil sections  60  placed in a slot or channel formed between outer periphery  102  and inner periphery  104 . However, the coil sections  60  can be secured to the bracket assembly  100  in other ways, such as securing the coil sections to the upper surface of the body portion  106 , as shown in  FIG. 7 . As discussed above, this embodiment is particularly advantageous in eliminating hysteresis effects.  
         [0037]     Referring to  FIGS. 9-14 , various coil patterns are illustrated. A controlled current applied to the coil sections along with their particular arrangement and spatial relationship with the magnet determines the incremental torque forces created to control rotary positioning of the actuator. As mentioned above, a four-pole magnet is advantageous for use with any one of the coil arrangements shown in  FIGS. 9-14 . Those skilled in the art can envision other coil arrangements and magnetic pole arrangements that may be suitable for producing desired incremental forces in order to precisely control the actuator assembly.  
         [0038]     With respect to the second embodiment, the body portion  106  of the bracket assembly  100  may be shaped to accommodate any of the coil arrangements shown in  FIGS. 9-14 . Because the bracket assembly may be formed in an injection molding process, great flexibility is provided in implementing the second embodiment without substantial manufacturing cost.  
         [0039]     Unlike typical disk drive actuators that are driven by moving coils placed in a stationary magnetic field, the invention described herein is of a design that is especially adapted for low inertia actuators. The coil sections of the present invention are stationary while the magnet moves. The magnet may be ring-shaped and may be polarized with a desired number of poles. Since the magnet of the present invention is symmetric about the center of rotation, off-axis forces are canceled, and pure in-plane torque can be delivered to the actuator. Since the coil sections are stationary, no dynamic electrical connections are required to power the coil sections. Accordingly, power input design is greatly simplified. The construction of the motor simplifies assembly of the disk drive and reduces overall disk drive part count, thus manufacturability is enhanced. Clearly, less space is required in the housing of the disk drive; therefore, the disk drive can be made smaller.  
         [0040]     While the present invention has been set forth above with respect to preferred embodiments in both an apparatus and method, it shall be understood that other changes and modifications can be made within the spirit and scope of the invention commensurate with the scope of the claims appended hereto.