Patent Abstract:
A head gimbal assembly includes a slider, a rotatable micro-actuator and a suspension to load the slider and the rotatable micro-actuator. The rotatable micro-actuator horizontally rotates the slider with a central portion of the slider as an axis, which includes a bottom plate to be connected with the suspension, two arm plates symmetrically disposed on the bottom plate with a central portion of the bottom plate as symmetry point and at least one piezoelectric pieces to be connected with the arm plates. Selectively, the amount of the arm plates can be four and four piezoelectric pieces to be connected with the four arm plates, respectively.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to disk drive units, and particularly relates to a micro-actuator, and a head gimbal assembly using the micro-actuator. 
   BACKGROUND OF THE INVENTION 
   Disk drives are information storage devices that use magnetic media to store data. Referring to  FIG. 1   a , a typical disk drive in related art has a magnetic disk and a drive arm to drive a head gimbal assembly  277  (HGA) (the HGA  277  has a suspension (not labeled) with a slider  203  mounted thereon). The disk is mounted on a spindle motor which causes the disk to spin and a voice-coil motor (VCM) is provided for controlling the motion of the drive arm and thus controlling the slider  203  to move from track to track across the surface of the disk to read data from or write data to the disk. 
   However, Because of the inherent tolerance resulting from VCM and the suspension that exists in the displacement (off track) of the slider  203 , the slider  203  can not attain a fine position control which will affect the slider  203  to read data from and write data to the magnetic disk. 
   To solve the above-mentioned problem, piezoelectric (PZT) micro-actuators are now utilized to modify the displacement of the slider  203 . That is, the PZT micro-actuator corrects the displacement of the slider  203  on a much smaller scale to compensate for the resonance tolerance of the VCM and the suspension. It enables a smaller recording track width, increases the ‘tracks per inch’ (TPI) value by 50% of the disk drive unit (it is equivalent to increase the surface recording density). 
   Referring to  FIG. 1   b , a traditional PZT micro-actuator  205  comprises a ceramic U-shaped frame  297  which comprises two ceramic beams  207  with two PZT pieces (not labeled) on each side thereof. With reference to  FIGS. 1   a  and  1   b , the PZT micro-actuator  205  is physically coupled to a suspension  213 , and there are three electrical connection balls  209  (gold ball bonding or solder ball bonding, GBB or SBB) to couple the micro-actuator  205  to the suspension traces  210  in each one side of the ceramic beam  207 . In addition, there are four metal balls  208  (GBB or SBB) to couple the slider  203  to the suspension  213  for electrical connection.  FIG. 1   c  shows a detailed process of inserting the slider  203  into the micro-actuator  205 . The slider  203  is bonded with the two ceramic beams  207  at two points  206  by epoxy dots  212  so as to make the motion of the slider  203  dependent of the ceramic beams  207  of the micro-actuator  205 . 
   When power supply is applied through the suspension traces  210 , the PZT pieces of the micro-actuator  205  will expand or contract to cause two ceramic beams  207  of the U-shaped frame  297  deform and then make the slider  203  move on the track of the disk. Thus a fine head position adjustment can be attained. 
   However, because the PZT micro-actuator  205  and the slider  203  are mounted on the suspension tongue (not labeled), when the PZT micro-actuator  205  is excited, it will do a pure translational motion to sway the slider  203  due to the constraint of U-shaped frame  297  of the micro-actuator  205 , and cause a suspension vibration resonance which has a same frequency as the suspension base plate. This will limit the servo bandwidth and the capacity improvement of HDD. As shown in  FIG. 2 , numeral  201  represents a resonance curve when shaking the suspension base plate and numeral  202  represents a resonance curve when exciting the micro-actuator  205 . The figure clearly shows the above-mentioned problem. 
   Hence, it is desired to provide a micro-actuator, head gimbal assembly, disk drive to solve the above-mentioned problems. 
   SUMMARY OF THE INVENTION 
   A main feature of the present invention is to provide a micro-actuator and a HGA which can attain a fine head position adjustment and a good resonance performance when exciting the micro-actuator. 
   Another feature of the present invention is to provide a disk drive unit with big servo bandwidth and head position adjustment capacity. 
   To achieve the above-mentioned features, a HGA of the present invention comprises a slider, a rotatable micro-actuator; and a suspension to load the slider and the rotatable micro-actuator. The rotatable micro-actuator horizontally rotates the slider with a central portion of the slider as an axis. 
   In an embodiment, the rotatable micro-actuator of the present invention comprises a bottom plate to be connected with the suspension; two arm plates symmetrically disposed on the bottom plate with a central portion of the bottom plate as symmetry point; and at least one piezoelectric pieces to be connected with the arm plates. In another embodiment, the rotatable micro-actuator of the present invention comprises a bottom plate to be connected with the suspension; four arm plates symmetrically disposed on the bottom plate with a central portion of the bottom plate as symmetry point; and four piezoelectric pieces to be connected with the arm plates, respectively. In the present invention, the arm plates are perpendicularly connected with the bottom plate. Each of arm plates has a free end and an end to connect with the bottom plate. In the present invention, the slider is partially bonded with the rotatable micro-actuator, for example, the slider is bonded with the free ends of the arm plates by its two opposing side surface, one is trailing edge side surface and the other is leading edge side surface. In addition, a parallel gap exists between the suspension and the bottom plate. 
   In the present invention, the bottom plate is connected with the suspension by epoxy, adhesive, ACF or laser welding. The at least one piezoelectric pieces are thin film piezoelectric pieces or ceramic piezoelectric pieces, which are electrically bonded with the suspension by gold ball bonding, solder ball bonding or conductive adhesive. As an embodiment, the at least one piezoelectric pieces have a single layer structure or a multi-layer structure comprising a substrate layer and a piezoelectric layer. The piezoelectric layer is a single-layer PZT structure or a multi-layer PZT structure, the substrate layer is made of metal, ceramic, or polymer. The at least one piezoelectric pieces may also have a single-segment structure or a multi-segment structure. 
   A disk drive unit of the present invention comprises a HGA, a drive arm to connect with the head gimbal assembly; a disk; and a spindle motor to spin the disk. The HGA comprises a slider, a rotatable micro-actuator; and a suspension to load the slider and the rotatable micro-actuator; wherein the rotatable micro-actuator horizontally rotates the slider with a central portion of the slider as an axis. 
   Compared with the prior art, the micro-actuator of the invention can rotate both trailing side and leading side of the slider in different directions so as to make the slider get a bigger swing. Accordingly, a big head position adjustment capacity can be attained. In addition, because the slider is partially bonded with the rotatable micro-actuator and suspended on the bottom plate of the rotatable micro-actuator, when the micro-actuator is excited, it will rotate and cause the slider to rotate so as to attain a fine head position adjustment. Furthermore, a suspension resonance has not happened in a low frequency, but only a pure micro-actuator resonance happened in a high frequency, this would enlarge the servo bandwidth and then improve the capacity of the HDD. Finally, the structure of the rotatable micro-actuator will make the head position adjustment of the slider more freely. 
   For the purpose of making the invention easier to understand, several particular embodiments thereof will now be described with reference to the appended drawings in which: 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a perspective view of a HGA of related art; 
       FIG. 1   b  is an enlarged, partial view of  FIG. 1   a;    
       FIG. 1   c  shows a detailed process of inserting a slider to a micro-actuator of the HGA in  FIG. 1   a;    
       FIG. 2  shows a resonance curve of the HGA of  FIG. 1   a;    
       FIG. 3  is a perspective view of a HGA according to a first embodiment of the present invention; 
       FIG. 4  is an enlarged, exploded partial perspective view of the HGA of  FIG. 3 ; 
       FIG. 5  is an enlarged, partial perspective view of the assembled HGA of  FIG. 3 ; 
       FIG. 6  is a partial, side view of the HGA of  FIG. 3  in the micro-actuator area; 
       FIG. 7  is an exploded, perspective view of the micro-actuator and a slider of the HGA in  FIG. 3  according to a first embodiment of the present invention; 
       FIG. 8  shows the assembled micro-actuator and the slider of  FIG. 7 ; 
       FIG. 9  is a side view of  FIG. 8 ; 
       FIG. 10   a  shows an electrical connection relationship of two PZT pieces of the micro-actuator of  FIG. 8 , which have a same polarization direction according to an embodiment of the present invention; 
       FIG. 10   b  shows an electrical connection relationship of two PZT pieces of the micro-actuator unit of  FIG. 8 , which have opposing polarization directions according to another embodiment of the present invention; 
       FIG. 10   c  shows two waveforms of voltages which are applied to the two PZT pieces of  FIG. 10   b , respectively; 
       FIG. 10   d  shows a waveform of voltage which is applied to the two PZT pieces of  FIG. 10   a , respectively; 
       FIG. 10   e  show an initial status of the micro-actuator and the slider when no voltage is applied to the micro-actuator; 
       FIGS. 10   f  and  10   g  show two different operation methods of the two PZT pieces in  FIG. 10   a  or  10   b  which causes the slider to rotate in a direction parallel to disk surface; 
       FIG. 11  shows a resonance curve of the HGA of  FIG. 3 ; 
       FIG. 12  is an exploded, perspective view of the micro-actuator and the slider of the HGA in  FIG. 3  according to a second embodiment of the present invention; 
       FIG. 13  shows the assembled micro-actuator and the slider of  FIG. 12 ; 
       FIG. 14  is an exploded, perspective view of a micro-actuator according to a third embodiment of the present invention; 
       FIG. 15  is an exploded, perspective view of a micro-actuator according to a fourth embodiment of the present invention; 
       FIG. 16  is an exploded, perspective view of a micro-actuator and the slider according to a five embodiment of the present invention; 
       FIG. 17  shows the assembled micro-actuator and the slider of  FIG. 16 ; 
       FIG. 18  is an exploded, perspective view of a micro-actuator and the slider according to a six embodiment of the present invention; 
       FIG. 19  shows the assembled micro-actuator and the slider of  FIG. 18 ; 
       FIG. 20  shows an exploded micro-actuator and the slider according to a seven embodiment of the present invention; 
       FIG. 21  is perspective view of a disk drive unit according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 3 , a head gimbal assembly (HGA)  3  of the present invention comprises a slider  31 , a micro-actuator  32  and a suspension  8  to load the slider  31  and the micro-actuator unit  32 . 
   Also referring to  FIG. 3 , the suspension  8  comprises a load beam  17 , a flexure  13 , a hinge  15  and a base plate  11 . The load beam  17  has a plurality of dimples  329  (see  FIG. 6 ) formed thereon. On the flexure  13  a plurality of connection pads  308  are provided to connect with a control system (not shown) at one end and a plurality of electrical multi-traces  309 ,  311  is provided in the other end. Referring to  FIGS. 4 and 5 , the flexure  13  also comprises a suspension tongue  328  which are used to support the micro-actuator  32  and the slider  31 , and keep the loading force always being applied to the center area of the slider  31  through the dimples  329  of the load beam  17 . 
   Referring to  FIGS. 4-6 , a limiter  207  is formed on the load beam  17  which extends through the suspension tongue  328  for preventing the suspension tongue  328  from being bent overly during normal operation of disk drive or any shock or vibration happening to the disk drive. The suspension tongue  328  has a plurality of electrical bonding pads  113  and  310  formed thereon. The slider  31  has a plurality of electrical bonding pads  204  on an end thereof corresponding to the electrical bonding pads  113  of the suspension tongue  328 . 
   Referring to the  FIG. 7 , according to a first embodiment of the invention, the micro-actuator  32  comprises a support frame  320  with a spring structure and two PZT pieces  321 . The support frame  320  can be made of metal (i.e. stainless steel), ceramic or polymer, which comprises a bottom plate  322  and two side plates  325 ,  326  which vertically extend from two sides of the bottom plate  322 . The bottom plate  322  have two ends  350  and  352 , and a notch  324  starting from the end  350  is formed on a connecting portion between the bottom plate  322  and the side plate  325 , while a notch  327  starting from the end  352  is formed on a connecting portion between the bottom plate  322  and the side plate  326 . The two PZT pieces  321  are preferably made of thin film PZT material which can be a single-layer PZT element or a multi-layer PZT element. Also, the two PZT pieces  321  can be made of ceramic PZT material which can be a single-layer PZT element or a multi-layer PZT element. The two PZT pieces  321  are bonded with the support frame  320  by traditional bonding method, such as epoxy bonding, anisotropic conductive film (ACF), and each of the PZT pieces  321  has a plurality of electrical bonding pads  333  corresponding to the electrical bonding pads  310  (see  FIG. 4 ). 
   Also referring to  FIGS. 7-9 , the slider  31  is partially coupled with the support frame  320  by two epoxy dots  323 , in an embodiment, one epoxy dot  323  is positioned on an end of the side plate  325  adjacent to the end  350  of the support frame  320 , and the other is positioned on an end of the side plate  326  adjacent to the end  352  of the support frame  320 . In addition, there is a parallel gap  401  formed between the slider  31  and the support frame  320 . Here, because the slider  31  has a partial bonding method with the support frame  320  and a parallel gap  401  forming therebetween, the slider  31  will move smoothly when being driven by the micro-actuator  302 . 
   Referring to  FIGS. 4-6 , in an embodiment of the present invention, the two PZT pieces  321  are bonded with the support frame  320  to form the micro-actuator  32 ; then, the slider  31  is coupled with the micro-actuator  32 ; after that, the slider  31  and the micro-actuator  32  are mounted on the suspension  8  to form the HGA  3  as follows: firstly, the support frame  320  is partially coupled with the suspension tongue  328  of the flexure  13  by laser welding, ACF, adhesive or epoxy; then, a plurality of metal balls  332  (GBB, SBB or conductive adhesive) are used to electrically connects the electrical bonding pads  333  of the two PZT pieces  321  of the micro-actuator  32  with the electrical bonding pads  310  of the suspension tongue  328  so as to electrically connect the micro-actuator  32  with the two electric multi-traces  311  of the suspension  8 . Simultaneously, a plurality of metal balls  405  are used to electrically connect the electrical bonding pads  204  of the slider  31  with the electrical bonding pads  113  so as to electrically connect the slider  31  with the electric multi-traces  309 . Through the electric multi-traces  309 ,  311 , the connection pads  308  electrically connect the slider  31  and the micro-actuator  32  with the control system (not shown). Obviously, the assembly of the HGA  3  can also be performed as follows: firstly, coupling the micro-actuator  32  with the suspension  8 , and then mounting the slider on the micro-actuator  32 . 
     FIGS. 10   a ,  10   d ,  10   e ,  10   f  and  10   g  show a first operation method of the micro-actuator  32  for performing a position adjustment function. In the embodiment, the two PZT pieces  321  have a same polarization direction, as shown in  FIG. 10   a , which are common grounded by one end  404  and the other ends  401   a  and  401   b  thereof are applied two voltages with a same sine waveform  407  (see  FIG. 10   d ).  FIG. 10   e  shows an initial status of the micro-actuator  32  when no voltage is applied to the PZT pieces  321  of the micro-actuator  32 . When the sine voltage  407  is applied to the two PZT pieces  321 , in a first half period, both PZT pieces  321  will contract gradually till to a shortest position (corresponding to a largest displacement position) with the drive voltage increasing, and then gradually spring back till to its original location with the drive voltage reducing. In the first half period, when the drive voltage increases, the left side plate  326  will be bent by the PZT piece  321  to left side and the right side plate  325  will be bent by the PZT piece  321  to right side; when the drive voltage reduces, both side plates  325 ,  326  will return back to its original positions. In the present invention, the side plates  325 ,  326  of the support frame  320  will generate a rotate torque when being bent. In the present invention, because the slider  31  is partially mounted on the support frame  320  by two epoxy dots  323  and a parallel gap  401  forming therebetween, the slider  31  may rotate from an original axis  501  to a largest displacement location  502  and then back to its original location  501  under the rotate torque of the support frame  320 , as shown in  FIG. 10   f . When the drive voltage goes down to a second half period (having an opposed phase with the first half period), both PZT pieces  321  will expand gradually till to a biggest displacement position with the negative drive voltage increasing, and then gradually back to its original location with the drive voltage reducing. Similarly, it will cause both side plates  325 ,  326  to bent and then back to its original position. In the present invention, the side plates  325 ,  326  of the support frame  320  will generate a rotate torque when being bent. Under the rotate torque of the support frame  320 , the slider  31  may rotate from an original axis  501  to a largest displacement location  503  and then back to its original location  501  because the slider  31  is partially bonded with the support frame  320  by two epoxy dots  323  and a parallel gap  401  forming therebetween, as shown in  FIG. 10   g . Thus a head position adjustment can be attained. 
     FIGS. 10   b ,  10   c ,  10   e ,  10   f  and  10   g  show another operation method of the two PZT pieces  321  for performing head position adjustment function. In the embodiment, the two PZT pieces  321  have two opposing polarization directions, as shown in  FIG. 10   b , which are also common grounded by one end  404  and the other ends  401   a  and  401   b  thereof are applied two voltages with different phase waveforms  406 ,  408  (see  FIG. 10   c ). Under the drive of the voltages, both PZT pieces  321  will contract gradually and then back to its initial position during a same half period, and when the voltages go to next half period, both PZT pieces  321  will expand and then back to its initial position. Similarly, the slider  31  is thus circularly rotate about the initial axis  501  to attain a fine head position adjustment. 
     FIG. 11  show a testing result of the resonance performance of the HGA of the invention, here,  701  represents a base plate exciting resonance curve, and  702  represents a micro-actuator exciting resonance curve. It shows that a suspension resonance has not happened in a low frequency, but only a pure micro-actuator resonance happened in a high frequency when exciting the PZT micro-actuator  32 , this would enlarge the servo bandwidth and improve the capacity of the HDD, reduce the slider seeking and settling time. 
   According to another embodiment of the invention, referring to  FIGS. 12 and 13 , a micro-actuator comprises two PZT pieces  321  and a support frame  320 ′ having a bottom plate  322 ′ and two side plates  325 ,  326 . The bottom plate  322 ′ have two ends  350 ′ and  352 ′, and a notch  324 ′ starting from the end  352 ′ is formed on a connecting portion between the bottom plate  322 ′ and the side plate  325 , while a notch  327 ′ starting from the end  350 ′ is formed on a connecting portion between the bottom plate  322 ′ and the side plate  326 . The slider  31  is partially coupled with the support frame  320 ′ by two epoxy dots  323 , in an embodiment, one epoxy dot  323  is positioned on an end of the side plate  325  adjacent to the end  352 ′ of the support frame  320 ′, and the other is positioned on an end of the side plate  326  adjacent to the end  350 ′ of the support frame  320 ′. Also, there is a parallel gap  401  formed between the slider  31  and the support frame  320 ′. 
   According to a third embodiment of the invention, referring to  FIG. 15 , a micro-actuator comprises two PZT pieces  321 ″ and a support frame  320  having a bottom plate  322  and two side plates  325 ,  326 . Each of the PZT pieces  321 ″ has a multi-layer structure, which comprises an inner substrate layer  802 , and an outer PZT layer  801 . The substrate layer  802  can be made of ceramic, polymer or metal. The out PZT layer  801  can be a single layer PZT element or a multi-layer PZT element. Referring to  FIG. 14 , in a fourth embodiment, the PZT pieces  321 ′ not only has a multi-layer structure (consisting of an out PZT layer  801  and an inner substrate layer  802 ), but the outer PZT layer  801  consists of a plurality of PZT segments (multi-segment structure). Such structures of the PZT pieces can attain not only good resonance performance and good stability, but also a fine head position adjustment. 
   According to a five embodiment of this invention, referring to  FIGS. 16 and 17 , the micro-actuator also comprises a support frame  38  and two PZT pieces  321 . The support frame  38  comprises a bottom plate  380  and two side plates  381  and  382  extending from the bottom plate  380  vertically. The side plate  381  has two ends  386  and  387 , the end  386  connects with the bottom plate  380  and the end  387  is a free end. Similarly, the side plate  382  has an end  385  connecting with the bottom plate  380  and an end  384  is a free end. The slider  31  is mounted on the support frame  38  by disposing two epoxy dots  323  between the free ends  384 ,  387  and the slider  31 . The free end  384  is adjacent to trailing edge  301  of the slider  31  and the free end  387  is adjacent to leading edge  302  of the slider  31 . The slider  31  is bonded with the free ends  384 ,  387  by its two opposing side surface, one is trailing edge side surface and the other is leading edge side surface. A parallel gap (not labeled) about 30˜50 microns exists between the slider  31  and the bottom plate  380  of the support frame  38 , this is going to keep the slider  31  rotate freely from its original position  601  to a largest displacement location  602  or  603  when exciting the micro-actuator. In the embodiment, each of the PZT pieces  321  may be a single-layer PZT element or a multi-layer PZT element. Selectively, the PZT piece  321  has a multi-layer structure and/or a multi-segment structure. 
   According to a six embodiment of this invention, referring to  FIGS. 18 and 19 , a micro-actuator comprises a support frame  38 ′ and two PZT pieces  321 . The support frame  38 ′ comprises a bottom plate  380  and two side plates  381 ′ and  382 ′ extending from the bottom plate  380  vertically. The side plate  381 ′ has two ends  386 ′ and  387 ′, the end  386 ′ connects with the bottom plate  380  and the end  387 ′ is a free end. Similarly, the side plate  382 ′ has an end  385 ′ connecting with the bottom plate  380  and the end  384 ′ is a free end. The slider  31  is mounted on the support frame  38 ′ by disposing two epoxy dots  323  between the free ends  384 ′,  387 ′ and the slider  31 . The free end  384 ′ is adjacent to the leading edge  302  of the slider  31  and the free end  387 ′ is adjacent to the trailing edge  301  of the slider  31 . A parallel gap (not labeled) about 30˜50 microns exists between the slider  31  and the bottom plate  380  of the support frame  38 ′, this is going to keep the slider  31  rotate freely with a central portion of the slider  31  as an axis when exciting the micro-actuator. In the embodiment, each of the PZT pieces  321  may be a single-layer PZT element or a multi-layer PZT element. Selectively, the PZT piece  321  has a multi-layer structure and/or a multi-segment structure. 
   According to a seven embodiment of this invention, referring to  FIG. 20 , a micro-actuator comprises a support frame  39  and four PZT pieces  321 . The support frame  39  has a bottom plate  390  and four side plates  391 ,  392 ,  393 ,  394  extending from the bottom plate  390  vertically. Each of the side plate  391 ,  392 ,  393 ,  394  has two ends, one of which connects with the bottom plate  390  and the other is a free end. The slider  31  is mounted on the support frame  39  by disposing four epoxy dots  323  between the free ends of the four side plates  391 ,  392 ,  393 ,  394  and the slider  31 . When exciting the PZT pieces  321 , the four side plates  391 ,  392 ,  393 ,  394  will be bent so that the side plates  391 ,  394  of the support frame  39  will generate a rotate torque while the side plates  392 ,  393  will generate another rotate torque. Under the two rotate torques of the support frame  39 , the slider  31  may rotate freely with a central portion of the slider as an axis. In the embodiment, each of the PZT pieces  321  may be a single-layer PZT element or a multi-layer PZT element. Selectively, the PZT piece  321  has a multi-layer structure and/or a multi-segment structure. A parallel gap of 30˜50 microns exists between the slider  31  and the bottom plate  390  of the support frame  39 . This is going to keep the slider  31  rotate freely when exciting the micro-actuator. 
   Compared with the prior art, the micro-actuator can rotate both trailing side and leading side of the slider in different directions, while the micro-actuator of the prior art can only move trailing side of the slider like a swing (because its leading side is fixed). So, the present invention can make the slider get a bigger swing than the prior art because both trailing and leading side of the slider can move. Accordingly, a big head position adjustment capacity can be attained. 
   In the present invention, referring to  FIG. 21 , a disk drive unit of the present invention can be attained by assembling a housing  108 , a disk  101 , a spindle motor  102 , a VCM  107  with the HGA  3  of the present invention. Because the structure and/or assembly process of disk drive unit of the present invention are well known to persons ordinarily skilled in the art, a detailed description of such structure and assembly is omitted herefrom.

Technology Classification (CPC): 6