Abstract:
A micro-actuator of the invention includes a support base having two actuator side arms and a rotatable bottom plate positioned between the actuator side arms; wherein at least one of the actuator side arms having a back-turned extension in a first end thereof; a pair of connection elements that connects the rotatable bottom plate to the actuator side arms in a second end thereof, respectively; at least one PZT elements bonded to the actuator side arms in its length and the back-turned extension. The rotatable plate rotates in a first direction when the at least one PZT elements expand, and a second direction when the at least one PZT elements contract. The invention also discloses a HGA and disk drive unit with such a micro-actuator.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to disk drives, such as hard disk drives (HDDs), and particularly to a rotatable micro-actuator and a head gimbal assembly (HGA) using the micro-actuator for the disk drives. 
   BACKGROUND OF THE INVENTION 
   Disk drives are information storage devices that use magnetic media to store data. A conventional disk drive comprises a magnetic disk having concentric magnetic tracks formed thereon, a HGA, and a drive arm that drives the HGA. The disk is mounted to a spindle motor, which causes the disk to spin. A voice-coil motor (VCM) controls the motion of the drive arm, which in turn controls the movement of the HGA, and then controls the slider to move from track to track across the surface of the disk for reading data from or writing data to the disk. 
   However, because of inherent tolerance resulting from the VCM and the suspension, the slider does not attain precise positional control during its displacement. This will affect data reading/writing of the slider. 
   To solve the above-mentioned problem, piezoelectric (PZT) micro-actuators are employed to modify the displacement of the slider. That is, the PZT micro-actuator corrects the displacement of the slider in a much smaller scale to compensate for the tolerance caused by the VCM and the suspension. The PZT micro-actuator enables a smaller recording track width, hence increasing the “tracks per inch (TPI)” value by 50%. It also reduces the head seeking and settling time, increases the disk surface recording density, and improves drive performance of the disk drive. 
   Referring to  FIGS. 1   a  and  1   b , a traditional HGA  277  comprises a slider  203 , a PZT micro-actuator  205 , and a suspension  213  to load the micro-actuator  205  and a suspension  213 . The PZT micro-actuator  205  comprises a U-shaped ceramic frame  297  having two spaced beams  207  on both sides of which two PZT elements (not labeled) are mounted. The PZT micro-actuator  205  is mounted to a suspension  213  of the HGA  277 . The suspension  213  comprises conductive traces  210  that are connected to the micro-actuator  205  by a plurality of electrical connection balls  209 , such as gold ball bonding (GBB) and solder ball bonding (SBB), on both sides of the frame  297  next to each beam  207 . In addition, a plurality of metal balls  208 , such as GBB and SBB, electrically connect the slider  203  to the conductive traces  210 . 
   Also referring to  FIG. 1   c , the slider  203  is positioned in the micro-actuator  205  between the beams  207 . The slider  203  is bonded to the beams  207  at two points  206  by epoxy dots  212  whereby the slider  203  is movable in unison with the beams  207 . When power is supplied through the traces  210 , the PZT elements of the micro-actuator  205  expand or contact, causing the beams  207  to deform and thus moving the slider  203  on the tracks of the disk. Thus, a fine head position adjustment of the slider  203  can be attained. 
   However, since the PZT micro-actuator  205  and the slider  203  are mounted to a suspension tongue (not labeled), the PZT micro-actuator  205 , when excited, undergoes pure translation, which sways the slider  203  due to the constraint imposed by the U-shaped frame  297  of the micro-actuator  205  and causes a suspension vibration resonance having a frequency the same as the suspension base plate exciting. This limits the servo bandwidth and capacity improvement of hard disk drive. 
   Thus, it is desired to provide a micro-actuator, a HGA and a disk drive to solve the above-mentioned problems. 
   SUMMARY OF THE INVENTION 
   An main feature of the present invention is to provide a micro-actuator and a head gimbal assembly, which can attain a bigger head position adjustment capacity and enhanced resonance performance when the micro-actuator is excited. 
   Another objective of the present invention is to provide a disk drive unit with large servo bandwidth and capacity. 
   To achieve the above-mentioned features, in accordance with an embodiment of the present invention, a micro-actuator comprises a support base having two actuator side arms and a rotatable bottom plate positioned between the actuator side arms; wherein at least one of the actuator side arms having a back-turned extension in a first end thereof; a pair of connection elements that connects the rotatable bottom plate to the actuator side arms in a second end thereof, respectively; at least one PZT elements bonded to the actuator side arms in its length and the back-turned extension; wherein the rotatable plate rotates in a first direction when the at least one PZT elements expand, and a second direction when the at least one PZT elements contract. 
   As an embodiment of the invention, the actuator side arm comprises a side arm body, the back-turned extension extends from one end thereof toward the other end thereof, and a notch is formed between the side arm body and the back-turned extension. The notch has additional material filled therein. The additional material is selected from epoxy, adhesive, polymer, metal material. As a further embodiment, the actuator side arm comprises a side arm body, and the back-turned extension bonded on an end of the side arm body. The back-turned extension has a solid structure. According to another embodiment of the invention, the back-turned extension further comprises an elongated portion for bonding with the side arm body firmly. Thus, in the invention, when a slider is mounted on the rotatable bottom plate, upon application of electrical power to the piezoelectric elements, the side arms are deflected in opposite directions due to the deformation of the piezoelectric elements, thereby rotating and thus displacing the slider in a larger scope as compared to prior art micro-actuators. In addition, because there is a back-turned extension on the side arm, the length of the side arms can thus be increased, which allows the PZT elements attached to the side arms to be elongated and thus improving the displacement performance of the micro-actuator. 
   A HGA of the present invention comprises a slider; a micro- actuator; and a suspension for supporting the micro-actuator; wherein a parallel gap exists between the suspension and a bottom of the micro-actuator; wherein the micro-actuator comprises a support base having two actuator side arms and a rotatable bottom plate positioned between the actuator side arms; wherein at least one of the actuator side arms having a back-turned extension in a first end thereof; a pair of connection elements that connects the rotatable bottom plate to the actuator side arms in a second end thereof, respectively; at least one PZT elements bonded to the actuator side arms in its length and the back-turned extension; wherein the rotatable plate rotates in a first direction when the at least one PZT elements expand, and a second direction when the at least one PZT elements contract; wherein the slider is bonded with the actuator side arms in two points which are diagonally opposite with each other, and at least one point is on the back-turned extension. 
   A disk drive unit of the present invention comprises a HGA, which comprising a slider, a micro-actuator and a suspension supporting the micro-actuator; a drive arm connected to the head gimbal assembly; a disk; and a spindle motor operable to spin the disk; wherein the micro-actuator comprises: a support base having two actuator side arms and a rotatable bottom plate positioned between the actuator side arms; wherein at least one of the actuator side arms having a back-turned extension in a first end thereof; a pair of connection elements that connects the rotatable bottom plate to the actuator side arms in a second end thereof, respectively; at least one PZT elements bonded to the actuator side arms in its length and the back-turned extension; wherein the rotatable plate rotates in a first direction when the at least one PZT elements expand, and a second direction when the at least one PZT elements contract; wherein the slider is bonded with the actuator side arms in two points which are diagonally opposite with each other, and at least one point is on the back-turned extension. 
   Compared with the conventional devices, the slider in accordance with the present invention is only partially bonded to the side arms of the support base of the micro-actuator in two diagonally points. This allows the slider to rotate when the micro-actuator is actuated for attaining fine position adjustment. In addition, suspension resonance is not caused when the micro-actuator is operated in lower frequency and only a pure micro-actuator resonance occurs in high frequency. This enlarges the servo bandwidth and thus improves the capacity of the disk drive. Further, the spring structure of the support base of the micro-actuator makes the position adjustment for the slider more freely as compared to the conventional devices. 
   The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, preferred embodiments in accordance with the present invention. In the drawings: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a perspective view of a conventional HGA; 
       FIG. 1   b  is a perspective view, in an enlarged scale as compared to  FIG. 1   a , showing a suspension tongue area of  FIG. 1   a ; 
       FIG. 1   c  schematically illustrates an assembling process for mounting a slider in a micro-actuator of the HGA in  FIG. 1   a ; 
       FIG. 2  is a perspective view showing a HGA constructed in accordance with a first embodiment of the present invention; 
       FIG. 3  is a perspective view in an enlarged scale showing a suspension tongue area of  FIG. 2 ; 
       FIG. 4  is a side view of  FIG. 3 ; 
       FIG. 5  is a partial, enlarged view of  FIG. 3  without a micro-actuator and a slider; 
       FIG. 6  is an end view of the micro-actuator with the slider mounted therein; 
       FIG. 7  is an exploded view of a micro-actuator constructed in accordance with  FIG. 2 ; 
       FIG. 8  is an assembled view of  FIG. 7 ; 
       FIG. 9  is a plan view illustrating the operation of the micro-actuator of  FIG. 8 ; 
       FIG. 10  is a perspective view of a micro-actuator and slider assembly constructed in accordance with a second embodiment of the present invention; 
       FIG. 11   a  is an exploded view of a support base of a micro-actuator in accordance with a third embodiment of the present invention; 
       FIG. 11   b  is an assembled view of the support base of  FIG. 11   a ; 
       FIG. 11   c  is an exploded view of the micro-actuator in accordance with the third embodiment of the present invention with the slider detached therefrom; 
       FIG. 11   d  is an assembled view of  FIG. 11   c ; 
       FIG. 12   a  is an exploded view of a micro-actuator constructed in accordance with a fourth embodiment of the present invention with the slider detached therefrom; 
       FIG. 12   b  is an assembled view of  FIG. 12   a ; 
       FIG. 13   a  is an exploded view of a support base of a micro-actuator in accordance with a fifth embodiment of the present invention; 
       FIG. 13   b  is an assembled view of the frame of  FIG. 13   a ; 
       FIG. 13   c  is an exploded view of the micro-actuator in accordance with the fifth embodiment of the present invention with the slider detached therefrom; 
       FIG. 13   d  is an assembled view of  FIG. 13   c ; 
       FIG. 14  is a perspective view showing a disk drive incorporating the HGA and the micro-actuator in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the drawings, and in particular to  FIG. 14 , a disk drive constructed in accordance with an embodiment of the present invention, generally designated with reference numeral  100 , comprises a housing  108  containing a set of circular disks  101  each having a surface on which a magnetic coating is provided for forming a plurality of concentric tracks (not shown). The disks  101  are mounted on a spindle motor  102  that selectively spins the disks  101 . A drive arm  3  is arranged in the housing  108  and is controlled by a voice-coil motor  107  to drive a HGA constructed in accordance with a first embodiment of the present invention, generally designated with reference numeral  200 , with respect to the disks  101 , whereby a slider  31  (see  FIG. 2 ) carried by the HGA  200  is movable across the surface of the disk  101  from track to track. 
   Also referring to  FIGS. 2-5 , the HGA  200  comprises a suspension  8  having a base plate  11 , made of for example metals, ceramics, and polymers, and a hinge  15  coupled to the drive arm  3  of the disk drive  100 , and a flexure  13  that connects with the base plate  11  to support a load beam  17 . The flexure  13  comprises a suspension tongue  328  that carries a rotatable micro-actuator  32  and the slider  31 . On the base plate  11 , a plurality of conductive pads  308  are mounted for coupling with a control system (not shown) of the disk drive  100 . Conductive traces  309 ,  311  are formed on the suspension  8  and extend from the pads  308  to conductive pads  310 ,  113  formed on the suspension tongue  328 , respectively, for electrically connecting the micro-actuator  32 , which is electrically connected to the pad  310  by metal balls  332 , such as GBB or SBB, and the slider  31  that are electrically connected to the pads  113  by metal balls  405 , such as GBB or SBB, respectively, to the control system. 
   Referring to  FIGS. 7 and 8 , which show a micro-actuator and slider subassembly constructed in accordance with a first embodiment of the invention. The micro-actuator  32  comprises a support base or frame  320   a  that receives and retains the slider  31  therein. The support base  320   a  comprises a bottom plate  357  and two side arms  358   a  mounted to opposite side edges of the bottom plate  357  and substantially perpendicular to the bottom plate  357 . The side arms  358   a  are connected to opposite ends of the bottom plate  357  by connecting elements  351  projecting from the ends of the bottom plate  357  in opposite directions whereby a notch  359  extending along each side edge of the bottom plate  357  is formed between the side edge of the bottom plate  357  and each side arm  358   a . Thus, each of the side arms  358   a  has an end fixed to the bottom plate  357  and an free end (not labeled). Both the free ends of the side arms  358   a  are in opposite positions. The notch  359  is of sufficient length to make the free end of the side arm  358   a  bendable and deflectable with respect to the bottom plate  357 . 
   Also referring to  FIGS. 7 and 8 , the slider  31  is received between and fixed to the back-turned sections  365  of the side arms  358   a  by epoxy dots  323 . Understandably, other adhesive dots can also be used here to replace the epoxy dots  323 . This allows for movement of the slider  31  with the deflection of the side arms  358 . The slider  31 , however, is separated from the bottom plate  357  of the support base  320  of the micro-actuator  32  by a predetermined gap  360 , see  FIG. 6 , which has a height of, for example 30 μm or higher. This facilitates smooth movement of the slider  31  when the micro-actuator  32  is operated. 
   Referring to  FIGS. 7 and 8 , two piezoelectric (PZT) elements  321  in the form of an elongate strip of thin film PZT elements, or ceramic PZT elements, are fixed to outside faces of the side arms  358   a . Obviously, the PZT elements  321  can be attached to the side arms  358   a  in any other suitable means, such as fixed to inside faces of the side arms  358   a . Preferably, the PZT elements  321  are of substantially the same shape and size as the outside faces of the side arms  358  with the back-turned section  365 , whereby the PZT elements  321  completely overlap the outside faces of the side arms  358  with the back-turned section  365 . Referring together with  FIGS. 2-3 , the PZT elements  321  have electrical contact pads  333  that are bonded with the metal balls  332  and are thus electrically connected to the control system of the disk drive  100  via the pads  310 , the conductive traces  311  and the associated conductive pads  308 . Such electrical connection allows the control system to apply electrical power to the PZT elements  321 , which, due to the attachment of the PZT elements  321  to the outside faces of the side arms  358 , causes deformation (deflection) of the side arms  358 . 
   Referring to  FIGS. 2-3 , the slider  31  has a trailing edge  355  which forms electrical pads  204  that are physically engageable with the metal balls  405  and are thus electrically connected to the control system of the disk drive  100  via the pads  113 , the conductive traces  309  and the conductive pads  308 . This establishes electrical communication between the slider  31  and the control system for transferring of data and signals. 
   Thus, referring to  FIGS. 2-4 , the slider  31  is carried by the micro-actuator  32 , which is in turn carried by the suspension tongue  328  that is supported on the load beam  17  of the suspension  8 . The load beam  17  forms a dimple  329  thereon to support the suspension tongue  328  whereby a loading force always acts upon a center of the slider  31 . The bottom plate  357  of the support base  320  of the micro-actuator  32  is positioned on and mounted to the suspension tongue  328 . A limiter  207  is formed on the load beam  17  and extends through the suspension tongue  328  to limit excessive movement of the suspension tongue  328  when the suspension tongue  328  is subject to undesired shocks and vibrations. 
   In the first embodiment of the micro-actuator  32  with reference to  FIGS. 7 and 8 , comprises a back-turned section  365  extending from the free end of each side arm  358   a  for fixing and supporting the slider  31  by the adhesive dots  323 , which allows the side arm  358   a  to be extended to a length substantially greater than the lateral side dimension of the slider  31 , as can be observed in  FIG. 8 . Thus, the length of the side arms  358   a  can be increased, which allows the PZT elements  321  attached to the side arms  358   a  to be elongated and thus improving the displacement performance of the micro-actuator  32 . In the invention, the two back-turned section  365  are formed diagonally opposite to each other so as to rotate the bottom plate  357  when actuating the PZT elements  321 . 
     FIG. 9  illustrates the operation of the micro-actuator  32   a . When no voltage is applied to the PZT elements  321  of the micro-actuator  32   a , the support base  320   a  of the micro-actuator  32   a  and the slider  31  stay in an initial position, where the side arms  358   a  are not deformed and the slider  31  is not moved by the deformation of the side arms  358   a . On the other hand, when a voltage of predetermined level, such as a positive voltage, is applied to the PZT elements  321 , the PZT elements  321  undergo deformation, which in turn causes deformation of the side arms  358   a  and the side arms  358   a  are deflected to the position shown in phantom lines and indicated by  358   a ′. With such a deformation, the slider  31  that is mounted to the side arms  358   a  is moved and the position of the slider  31 , which is indicated at  31 ′, is adjusted with respect to tracks on the surface of the disk  101 . When a reversed level of voltage, such as a negative voltage, is applied to the PZT elements  321 , deformation in opposite direction occurs and the slider  31  is moved in an opposite direction. Thus, by properly applying a voltage to the PZT elements  321 , the position of the slider  31  can be selectively adjusted in both directions. 
   Referring to  FIG. 10 , a micro-actuator constructed in accordance with a second embodiment of the present invention is shown, which, generally designated with reference numeral  32 b, comprises a modification of the micro-actuator  32   a  with reference to  FIGS. 7 and 8 , having the same construction with the difference in that an additional material  364  is filled in the free end of each side arm  358   a  for enhancing the performance of the micro-actuator  32   b  in for example displacement and resonance. That is the additional material  364  is interposed between the inside surface of each side arm  358   a  and the back-turned section  365 . Examples of the additional material  364  include epoxy, adhesives, polymers, ceramics, and metals. The remaining structure of the micro-actuator  32   b  is identical to that of the micro-actuator  32   a  with parts thereof identified with the same reference numerals, and thus no further description is needed herein. 
     FIGS. 11   a - 11   d  illustrate a micro-actuator in accordance with a third embodiment of the present invention, which is generally designated with reference numeral  32   c  for distinction. The micro-actuator  32   c  has a construction similar to the micro-actuator  32  with reference to  FIGS. 3   a  and  3   b  and thus similar parts are designated with the reference numerals and will not be further described. The difference between the micro-actuator  32   c  and the micro-actuator  32  is that a flat bar  366  is attached to the inside surface of each side arm  358 . The flat bar  366  forms a step  367 . The bars  366  are arranged to have the steps  367  diagonally opposite to each other as shown in  FIG. 11   b  and the steps  367  correspond to the free ends of the side arms  358 . The PZT elements  321  are mounted to the outside surfaces of the side arms  358 , opposite to the respective flat bars  366 . The slider  31  is received between the flat bars  366  and is fixed to the steps  367  by adhesive dots  323  interposed between each step  367  and corresponding lateral side of the slider  31 . With the slider  31  fixed to the steps  367 , the flat bars  366  allow the user of longer side arms  358  and thus longer PZT elements  321  attached to the side arms  358 . Longer PZT elements  321  have improved performance in deflecting the side arms  358 , which in turn enhances the overall performance of the micro-actuator  32   c.    
   Examples of material for making the flat bars  366  include metals, polymers, and ceramics. 
     FIGS. 12   a  and  12   b  show a micro-actuator in accordance with a fourth embodiment of the present invention, which is designated with reference numeral  32   d . The micro-actuator  32   d  has a construction that is mirror symmetric to the micro-actuator  32   a  with reference to  FIGS. 7 and 8 . The micro-actuator  32   d  has a support base  320   d  having two side arms  358   d  each having one end fixed to a bottom plate  357  and a free end having a back-turned section  365  connected to the side arm  358   d  by a connection  363 . The free ends of the side arms  358   d  are arranged to be mirror image of those of the side arms  358   b  of the micro-actuator  32   b.    
     FIGS. 13   a - 13   d  show a micro-actuator in accordance with a fifth embodiment of the present invention, which is designated with reference numeral  32   e . The micro-actuator  32   e  has a construction mirror symmetric to the micro-actuator  32   c  with reference to  FIGS. 11   a - 11   d . The micro-actuator  32   e  comprises a flat bar  366  attached to an inside surface of each side arm  358  and the flat bar  366  has a step  367 . The flat bars  366  of the micro-actuator  32   e  are arranged to have the steps  367  opposite to those of the micro-actuator  32   c , making the micro-actuator  32   e  a mirror image of the micro-actuator  32   c.    
   Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.