Abstract:
In conjunction with a magnetic disk drive unit comprising a voice coil motor ( 14 ), an arm ( 12 ) extending from the motor, a magnetic head actuator ( 2 ) mounted at a distal end of the arm, a suspension ( 16 ) coupled to the actuator, and a magnetic head slider mounted on the suspension at its distal end, the magnetic head actuator ( 2 ) comprises a stator section ( 30 ) secured to the arm distal end, an attachment section ( 18 ) secured to the arm distal end together with the stator section, micro-beams ( 20, 22 ) extending from the attachment section, a rotor section ( 24 ) supported for swing motion by the micro-beams, a permanent magnet ( 32 ) disposed in the stator section, and a coil ( 28 ) disposed in the rotor section. Electric current is conducted through the coil in the magnetic field created by the permanent magnet for causing the micro-beams to be displaced for inducing swing motion of the suspension secured to the rotor section and the magnetic head slider mounted thereon.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2003-408829 filed in Japan on Dec. 8, 2003, the entire contents of which are hereby incorporated by reference. 
   TECHNICAL FIELD 
   This invention relates to a magnetic disk drive unit, and more particularly, to a magnetic head actuator for use therein. 
   BACKGROUND ART 
   The magnetic disk drive unit adapted for writing and reading of data on a rotating ferromagnetic medium, i.e., magnetic disk by scanning a magnetic head thereon is widely used in the modern information society as the major storage device. The magnetic head is carried on a slider, which is kept afloat on the magnetic disk with a gap of the nanometer order during the writing/reading operation. A drive force for moving the magnetic head to a selected position is typically produced by a voice coil motor (VCM). The voice coil motor includes a coil which is coupled to a pivoted arm, which is coupled to a magnetic head slider via a suspension including a load beam and a gimbal. The load beam is a spring for generating a load in balance with the float quantity of the slider. The gimbal is a spring for supporting the slider and allowing for elastic deformation in planes other than the plane parallel to the disk surface, for accommodating disk axial run-outs and inclinations associated with assembly without detracting from the tracking fidelity. This structure permits the magnetic head to be moved to the selected track on the rotating disk while maintaining a stable state. 
   Recent efforts are being made to increase the recording density of magnetic disk drive units to a higher level and hence, to reduce the track width. Since the magnetic head must be accurately positioned to such a narrow track, there is a need for improving the precision of head positioning. In the prior art, the head positioning is performed solely by large actuators such as voice coil motors as mentioned above, which lack sufficient precision to comply with the narrowing of track width. For high recording density disk drive units, high precision positioning mechanisms or micro-actuators are essentially needed. 
   In JP-A 2004-213818, 2004-213819 and 2004-213820, the inventors proposed a micro-actuator capable of high precision positioning utilizing electromagnetic force. In the micro-actuator, two plate springs, referred to as micro-beams, are used to couple rotor and stator sections. The micro-beams are formed integrally with the gimbal of the suspension, by bending. 
   Each micro-beam is of generally rectangular shape having a high aspect ratio and has a reduced gage in a tracking direction and an increased gage in a perpendicular direction, i.e., the direction in which the suspension load beam applies a load to the magnetic head slider. Then the micro-beams support the rotor for allowing swing motion of the rotor in the tracking direction and maintains high stiffness in the load direction. A permanent magnet and a coil are disposed in the rotor and stator sections, respectively, to construct a second stage of voice coil motor for achieving controlled high-precision positioning in the track transverse direction. The type of this micro-actuator is referred to as “slider drive type,” hereinafter, because the slider is driven via the gimbal. 
   As a result of performance improvement, the magnetic disk drive unit now finds wide-spreading applications in various fields including video image recording apparatus and car navigation systems. For small-size magnetic disk drives using magnetic disks having a diameter of less than 2.5 inches, studies have been made to incorporate them in portable equipment including digital still cameras, video cameras and audio players, and some are used in practice. In such applications, the impact resistance of the drive unit is important. Possible countermeasures for impact safe-guard, now under research and development, include a weight reduction of the overall drive unit, a casing having a damping structure, a size reduction and shape design of the slider, and a controlled structure for avoiding impact. 
   In the slider drive type micro-actuator the inventors previously proposed, the micro-beams are dimensioned about 0.03 mm by about 0.005 mm in cross section and are sometimes prone to deformation by strong impact. The micro-beams can be ruggedized and stiffened by increasing their cross-sectional area, but the spring constant of micro-beams in the tracking direction is also increased, posing a need to increase the volume of permanent magnet and coil. Simply increasing the weight of the suspension distal end, however, results in a lower resonance frequency and an increased inertia moment, which make the control by the coarse-adjustment actuator difficult, failing to increase the precision of head positioning by two stage actuators. For this reason, it is difficult to apply the slider drive type micro-actuator to portable recording equipment. 
   The references pertinent to the technology of the present invention include U.S. Pat. No. 6,295,185; U.S. Pat. No. 6,078,473; Fan et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 35, No. 2, March 1999, pp. 1000-1005; Koganezawa et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 35, No. 2, March 1999, pp. 988-992; and Koganezawa et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 32, No. 5, September 1996, pp. 3908-3910. 
   SUMMARY OF THE INVENTION 
   In conjunction with a magnetic disk drive unit comprising a voice coil motor, an arm extending from the motor, a magnetic head actuator mounted at a distal end of the arm, a suspension coupled to the actuator, and a magnetic head slider mounted on the suspension at its distal end, an object of the invention is to provide a magnetic head actuator mounted at a distal end of the arm of the voice coil motor for driving the overall suspension, which actuator can be increased in size, permits micro-beams to be increased in cross-sectional area, and is resistant to impact. 
   In a first aspect, the invention provides a magnetic head actuator in a magnetic disk drive unit, which is mounted at a distal end of an arm extending from a voice coil motor, and coupled to a suspension having a magnetic head slider mounted at its distal end for providing swing motion of the slider. The actuator comprises a stator section secured to the arm distal end, an attachment section secured to the arm distal end together with the stator section, metallic micro-beams extending from the attachment section and shaped by bending, a rotor section supported for swing motion by the micro-beams, a permanent magnet disposed in the stator or rotor section, and a coil disposed in the rotor or stator section. Electric current is conducted through the coil in the magnetic field created by the permanent magnet for causing the micro-beams to be displaced for inducing swing or arcuate motion of the suspension secured to the rotor section and the magnetic head slider mounted thereon. 
   In a preferred embodiment, a pair of the micro-beams are disposed at opposite sides of the rotor section for supporting the suspension and the magnetic head slider via the rotor section, and the micro-beams are flexible enough to be displaced by a drive force developed between the stator and rotor sections in a tracking direction on the magnetic disk, but highly stiff in other directions. 
   In a preferred embodiment, each micro-beam includes at least one fold. 
   In a preferred embodiment, the micro-beams are formed integrally with the arm attachment section and the rotor section. In an alternative preferred embodiment, the suspension includes a load beam section, and the micro-beams are formed integrally with the arm attachment section, the rotor section and the load beam section. 
   Preferably, the stator section is made of a ferromagnetic material. More preferably, the stator section is formed integrally with the arm which is made of a ferromagnetic material. Also preferably, the rotor section is made of a ferromagnetic material. 
   Typically, the actuator further includes an auxiliary yoke opposed to the stator section for forming a magnetic circuit, with the rotor section being interposed between the auxiliary yoke and the stator section. 
   In a preferred embodiment, the arm from the voice coil motor is provided at its distal end with two sets of the micro-beams, rotor sections and suspensions which are symmetrically arranged so as to interpose the arm between the sets, and the arm is provided at its distal end with one stator section. 
   In a second aspect, the invention provides a magnetic disk drive unit comprising a voice coil motor for rotating a pivot shaft, a voice coil motor arm having a proximal end pivoted to the pivot shaft and a distal end, a magnetic head actuator fixedly secure to the distal end of the arm, a suspension coupled to the actuator and including a load beam and gimbal, and a slider mounted on the suspension at its distal end and having a magnetic head carried thereon, the voice coil motor operating to pivotally move the arm for positioning the slider at a selected track on a magnetic disk. The magnetic head actuator comprises a member including an attachment section secured to the arm distal end, micro-beams and a rotor section where a coil or a permanent magnet is disposed, a stator section where a permanent magnet or a coil is disposed, and an auxiliary yoke, the permanent magnet, the stator section, and the auxiliary yoke forming a magnetic circuit, the permanent magnet and the coil being opposed to define a small gap therebetween and within the magnetic circuit. The micro-beams are integrally formed with the arm attachment section of the member at laterally opposed edges and stand along the edges at right angles toward the stator section. When electricity is conducted across the coil in the magnetic field created by the permanent magnet, the rotor section is arcuately moved by Lorentz forces in a lateral direction, so that the suspension and the magnetic head-carrying slider are also arcuately moved together with the rotor section. 
   Specifically, the member including the arm attachment section, micro-beams and rotor section is prepared by furnishing a blank in which the attachment section and the rotor section are bridged at laterally opposed sides by strips, folding inside the strips at a first intermediate point an angle of about 180° so that the rotor section overlies the attachment section, then folding back the strips at a second intermediate point an angle of about 180° so that the rear edge of the rotor section is situated close to the front edge of the attachment section, and finally folding the strips along their longitudinal inner side at right angles toward the stator section. 
   The magnetic head actuator of the invention is of simple structure, capable of accurate positioning, highly reliable, and impact resistant. The simple structure ensures increased productivity of magnetic head actuator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a magnetic head actuator in a first embodiment of the invention. 
       FIG. 2  is a perspective exploded view of the magnetic head actuator in the first embodiment of the invention. 
       FIG. 3  is a perspective exploded view showing one exemplary arrangement of a magnetic head actuator, a suspension and a magnetic head slider in the first embodiment of the invention. 
       FIG. 4  is a perspective exploded view showing another exemplary arrangement of a magnetic head actuator, a suspension and a magnetic head slider in the first embodiment of the invention. 
       FIG. 5  is a cross-sectional view of the stator and rotor sections in the first embodiment. 
       FIG. 6  illustrates the process of working a blank into a member including an arm attachment section, micro-beams and a rotor section. 
       FIG. 7  is a perspective exploded view of a magnetic head actuator in a second embodiment of the invention. 
       FIG. 8  is a perspective exploded view of a magnetic head actuator in a third embodiment of the invention. 
       FIG. 9  is a perspective exploded view of a magnetic head actuator in a fourth embodiment of the invention. 
       FIG. 10  is a cross-sectional view of the actuator in the fourth embodiment. 
       FIG. 11  is a perspective exploded view of a magnetic head actuator in a fifth embodiment of the invention. 
   

   Throughout the drawings, like parts are designated by the same numerals and their description is omitted in later embodiments. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates in plan view an exemplary magnetic disk drive unit  4  comprising a magnetic head actuator  2  according to the invention. In the illustrated embodiment, a coarse-adjustment actuator for positioning a magnetic head slider (not shown) at a selected track on a magnetic disk  8  is constructed by a voice coil motor (VCM)  14  having a VCM arm  12  which is mounted to a rotating pivot shaft  10  for rotation about the shaft  10 . A suspension  16  has a load beam which is attached to a distal end of the VCM arm  12  via the magnetic head actuator  2  of the invention. 
     FIG. 2  is a perspective exploded view of the magnetic head actuator  2  according to a first embodiment of the invention. For the sake of clarity, wires for supplying electric power to a coil are not shown. The magnetic head actuator  2  includes a stator member or section  30 , a member  26 , and an optional yoke  34 . The member  26  includes an attachment section  18  to be secured to the distal end of the VCM arm  12 , micro-beams  20  and  22 , and a rotor section  24 . To the rotor section  24  is attached a coil  28 . Disposed in the stator section  30  is a permanent magnet  32 . The stator section  30  is preferably made of a ferromagnetic material for helping form a magnetic circuit. The auxiliary yoke  34  made of a ferromagnetic material may be attached, if necessary, for enhancing the efficiency of the magnetic circuit. The member  26  (which includes the arm attachment section  18 , the micro-beams  20  and  22 , and the rotor section  24 ), the stator section  30 , and the auxiliary yoke  34  are assembled and secured to the VCM arm (not shown in  FIG. 2 ) by means of stakes, screws, rivets, welds or the like. 
   Specifically in the member  26  which includes the arm attachment section  18 , the micro-beams  20  and  22 , and the rotor section  24 , the micro-beams  20  and  22  are juxtaposed and integrally formed at laterally opposed edges of the arm attachment section  18  and stand along the edges at right angles toward the stator section  30 . More specifically, as described later in conjunction with  FIG. 6 , the micro-beams  20  and  22  are formed by furnishing elongated strips  20   a ,  22   a  extending forward from the front side of the arm attachment section  18  at opposed edges, folding the strips  20   a ,  22   a  inside an angle of 180° to form a first fold, then folding the strips inside an angle of 180° at a position backward of the attachment section front side to form a second fold (in the reverse direction to the first fold) and provide the last portions of the strips  20   a ,  22   a  which extend forward again. The rotor section  24  is integrally formed through transition portions  20   b ,  22   b  with the last forward extending portions of the strips  20   a ,  22   a.    
   Referring to  FIG. 3 , to the rotor section  24 , not only the coil  28  is attached, but an attachment section  38  of a load beam  36  of the suspension is also secured as by welding. The suspension  16  (see  FIG. 1 ) includes the load beam  36  and a gimbal  40 . The suspension  16  also has a slider  42  mounted at its distal end, the slider having a magnetic head (not shown) for reading and writing of data on the magnetic disk. Since the VCM  14  is operated such that the arm  12  is rotated about the pivot shaft  10 , the slider  42  at the distal end of the suspension  16  can be roughly moved to the selected track on the magnetic disk  8 . For simplicity&#39;s sake, signal lines to the magnetic head are not depicted. 
     FIG. 4  illustrates another arrangement of the suspension. As opposed to the load beam  36  shown in  FIG. 3  in which a load-applying section  44  is integrally formed with flexure sections  46 ,  48  and the rotor attachment section  38 , the embodiment of  FIG. 4  is designed such that flexure sections  50 ,  52  and a rotor attachment section  54  form an integral member  55  with a gimbal  56 . Instead, a load beam  57  is attached to an intermediate load beam attachment section  59  of the member  55  as by welding. Further the rotor attachment section  54  of the member  55  is attached to the rotor section  24  by adhesive bonding, welding or the like. 
   In the magnetic head actuator in one embodiment of the invention, in which a magnetic circuit is constructed by the permanent magnet  32  attached near the distal end of the VCM arm, the stator section  30  and the auxiliary yoke  34 , the permanent magnet  32  and the coil  28  secured to the rotor section  24  are opposed to maintain a small gap therebetween. As shown in  FIG. 5 , the permanent magnet is magnetized in a direction perpendicular to the plane of the opposed coil, to provide two magnetic poles which are laterally arranged as viewed from the front side of the slider. Instead, two singularly magnetized permanent magnets may be juxtaposed. The permanent magnet  32  is dimensioned to a magnetic pole area of 3 to 10 mm 2  and a thickness of 0.1 to 1 mm in the magnetizing direction. The permanent magnet  32  creates magnetic forces which largely affect the drive force of the magnetic head actuator of the invention. To produce sufficient magnetic forces with the above-described dimensions, the use of high strength rare earth magnets, typically Nd—Fe—B sintered magnets is preferred. 
   The stator section  30  and the auxiliary yoke  34  are made of a ferromagnetic material such as steel and have a gage of about 0.05 to 0.25 mm. The permanent magnet  32  is 
   The coil  28  is made using a copper wire or a printed wiring board. The coil  28  is wound so as to generate a magnetic field perpendicular to the magnetic pole plane of the opposed permanent magnet  32 . When the printed wiring board is used, a multilayer wiring board may be used depending on the necessary magnetic force or drive force. The coil  28  is secured to the rotor section  24  using an epoxy adhesive or the like. Power supply lines (not shown) to the coil  28  are secured to the VCM arm distal end while it is kept loose so as not to interfere with swing motion of the magnetic head actuator. 
   The member  26  including the VCM arm attachment section  18 , micro-beams  20 ,  22  and rotor section  24  is made of a steel-base flat spring and has a gage of about 0.025 to 0.15 mm. It is preferable to use non-ferromagnetic steel for the purpose of not disturbing the magnetic fields produced by the magnetic circuit ( 30 ,  32 ,  34 ) and the coil  28 . 
   As best shown in  FIG. 2 , a pair of micro-beams  20 ,  22  are extended from the VCM arm attachment section  18  toward the rotor section  24 , once folded back toward the VCM arm attachment section  18 , and folded again toward the rotor section  24  where they support the rotor section  24 . This double-folded structure exerts the same effect as the arrangement of three beams on each side, that is, provides increased resilience in the drive direction of the magnetic head actuator and maintains high stiffness against back and forth motion in a vertical direction, as compared with a single beam. To obtain predetermined resilience and translation stiffness, the number of folds may be only one or three or more. 
   As shown in  FIG. 5 , the drive of the magnetic head actuator of the invention is of the same basic structure as the VCM  14  which is a coarse-adjustment actuator. By conducting electricity across the coil  28  in the magnetic field created by the permanent magnet  32 , the rotor section  24  is arcuately moved by Lorentz forces in the direction of arrow X, and the suspension  16  and the magnetic head-carrying slider  42  integrated therewith are also arcuately moved. 
   Like the load beam or gimbal of the suspension in the prior art VCM, the micro-beams  20 ,  22  are prepared by punching out a thin blank by pressing or etching, followed by bending.  FIG. 6  illustrates the working and shaping process. The member  26  including the VCM arm attachment section  18 , micro-beams  20 ,  22  and rotor section  24  is prepared by first punching a configured blank  26 ′ out of a thin plate by pressing or etching, the blank  26 ′ being configured such that the attachment section  18  and the rotor section  24  are bridged or connected at laterally opposed sides by side strips  20   a ,  22   a  as shown in  FIG. 6   a . The side strips  20   a ,  22   a  at first intermediate points depicted by line A are folded an angle of about 180° as shown by arrow B, so that the rotor section  24  overlies the attachment section  18  as shown in  FIG. 6   b . Then the side strips  20   a ′,  22   a ′ at second intermediate points depicted by line C are folded back an angle of about 180° as shown by arrow D, so that the rear or inside edge of the rotor section  24  is situated close to the front or inside edge of the attachment section  18  as shown in  FIG. 6   c . Finally, the side strips  20   a ,  22   a  are folded along their longitudinal inner side at right angles as shown by arrows E, F, G and H in  FIG. 6   c , completing the member  26  as shown in  FIG. 6   d.    
   The order of folding is not limited to the above embodiment. The side strips may be previously provided with notches at fold lines to facilitate successive working steps. 
   Also the stator section  30  and the auxiliary yoke  34  are prepared by punching out a thin blank by pressing or etching, followed by bending. 
     FIG. 7  is a perspective exploded view of the magnetic head actuator according to a second embodiment of the invention. In the second embodiment, a rotor section  58  is provided at its distal end with a load beam section  66  of the suspension. That is, the VCM arm attachment section  60 , micro-beams  62 ,  64 , rotor section  58  and suspension load beam section  66  are combined as an integral member  72 , reducing the number of parts. 
     FIG. 8  is a perspective exploded view of the magnetic head actuator according to a third embodiment of the invention. In the third embodiment, the VCM arm  68  is integrally provided at its distal end with a stator section  70 . In the third embodiment, the VCM arm  68  may be made of a ferromagnetic material for forming a magnetic circuit efficiently. If desired, the member  26  including the VCM arm attachment section  18 , micro-beams  20 ,  22  and rotor section  24  may be replaced by the member  72  having a suspension load beam section integrated therewith as described in the second embodiment. The member  26  including the VCM arm attachment section  18 , micro-beams  20 ,  22  and rotor section  24 , the stator section  30 , and the auxiliary yoke  34  are secured to the VCM arm  68  by means of a caulking stake  74 . The securing means is not limited to caulking, and screws, rivets, welds or the like may be used. 
     FIGS. 9 and 10  are perspective exploded and cross-sectional views of the magnetic head actuator according to a fourth embodiment of the invention, respectively. In the fourth embodiment, the stator section in the third embodiment is replaced by an aperture  76  which penetrates throughout the distal end portion of the VCM arm  75 . A permanent magnet  78  is fitted in the aperture  76 . As best shown in  FIG. 10 , the fourth embodiment is advantageous in that when the VCM arm  75  is provided with a pair of magnetic head sliders  80 ,  82 , a pair of rotor sections  84 ,  86  can be driven by one stator section (permanent magnet  78 ). Herein, the VCM arm  74  is made of a non-ferromagnetic material for increasing the efficiency of the magnetic circuit. Illustrated in  FIG. 10  are suspension gimbals  106 ,  108 , suspension load beams  110 ,  112 , micro-beams  114 ,  116 , rotor sections  118 ,  120 , auxiliary yokes  122 ,  124 , caulking stakes  126 ,  128 , and VCM arm attachment sections  130 ,  132 . If desired, the member  72  having a suspension load beam section integrated therewith as described in the second embodiment may also be used in the fourth embodiment. 
     FIG. 11  is a perspective exploded view of the magnetic head actuator according to a fifth embodiment of the invention. In the fifth embodiment, a coil  90  is disposed in a stator section  88 , and a permanent magnet  94  is disposed in a rotor section  92 . Since the coil  90  from which a power supply wire extends is placed in the stator section  88  which is stationary, the wiring is simplified. In the fifth embodiment, a member  104  including a VCM arm attachment section  98 , micro-beams  100 ,  102  and a rotor section  92  is made of a ferromagnetic material for increasing the efficiency of the magnetic circuit. Alternatively, a yoke  96  made of a ferromagnetic material may be disposed between the permanent magnet  94  and the rotor section  92 . The arrangement of the permanent magnet in the rotor section is also applicable to the second to fourth embodiments. 
   Japanese Patent Application No. 2003-408829 is incorporated herein by reference. 
   Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.