Patent Document

FIELD OF THE INVENTION 
     The present invention relates to disk drive units, and particularly relates to a micro-actuator unit and a head gimbal assembly with vibration canceller. 
     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 quick and 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, and also compensates 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 and also can reduce the head seeking and settling time (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 traces  210  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 the 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  are mounted on the suspension tongue (not labeled), when the PZT micro-actuator  205  is excited, it will only do a translational motion to sway the slider  203  above the disk, the sway movement will generate a reaction force exerted to the suspension tongue so as to cause a suspension vibration resonance which has a same resonance as shaking the suspension base plate. This will affect the dynamic performance of the HGA and limit the servo bandwidth and the storage capacity improvement of HDD (hard disk drive). 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 . Under a frequency of 20K, there are a lot of gain peaks of suspension frequency response in plus side and minus side, which indicate a bad characteristic of resonance. The figure clearly shows the above-mentioned problem. 
     Hence, it is desired to provide a micro-actuator unit, 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 HGA which can attain a good resonance performance when exciting its micro-actuator unit. 
     Another feature of the present invention is to provide a micro-actuator unit with vibration canceller. 
     A further feature of the present invention is to provide a disk drive unit with big servo bandwidth and storage capacity. 
     To achieve the above-mentioned features, a HGA of the present invention comprises a slider; a micro-actuator for adjusting the position of the slider; wherein the micro-actuator comprising a first base-part plate, a pair of actuator side arms extending from the first base-part plate in a first direction, and at least one of side arms has a PZT element thereon; a suspension to load the slider and the micro-actuator; and a vibration canceller interposed between the micro-actuator and the suspension. 
     In an embodiment, the vibration canceller comprises a second base-part plate to connect with the micro-actuator and the suspension; and at least one canceling arm extending from the second base-part plate in the first direction or in a second direction, wherein at least one of canceling arms has a PZT element thereon. The first direction and the second direction are perpendicular to the second base-part plate. In another embodiment, the vibration canceller has two canceling arms extending from the second base-part plate in the first direction or in the second direction; and both the canceling arms have their free ends connected with each other. In a further embodiment, the vibration canceller has a single canceling arm extending from-the second base-part plate in the first direction or in the second direction; and the single canceling arm extends from a middle portion or a side portion of the second base-part plate. 
     In the present invention, a first parallel gap is formed between the micro-actuator and the vibration canceller, and a second parallel gap exists between the suspension and the at least one canceling arm. The at least one PZT elements are thin film PZT elements or ceramic PZT elements. Each of the at least one PZT elements have a single-layer structure or a multi-layer structure. 
     A micro-actuator unit of the present invention comprises a micro-actuator for adjusting the position of the slider; wherein the micro-actuator comprising a first base-part plate, a pair of actuator side arms extending from the first base-part plate in a first direction, and at least one of side arms has a PZT element thereon; and a vibration canceller connected with the micro-actuator. In the present invention, the vibration canceller comprises a second base-part plate to connect with the micro-actuator; and at least one canceling arm extending from the second base-part plate in the first direction or in a second direction, wherein at least one of canceling arms has a piezoelectric element thereon. 
     A disk drive unit of the present invention comprises a HGA; a drive arm to connect with the HGA; a disk; and a spindle motor to spin the disk. The HGA comprises a slider; a micro-actuator to adjust the position of the slider; a suspension to load the slider and the micro-actuator; and a vibration canceller interposed between the micro-actuator and the suspension. The micro-actuator comprising a first base-part plate, a pair of actuator side arms extending from the first base-part plate in a first direction, and at least one of side arms has a PZT element thereon. The vibration canceller comprises a second base-part plate to connect with the micro-actuator and the suspension; and at least one canceling arm extending from the second base-part plate in the first direction or in a second direction, wherein at least one of canceling arms has a PZT element thereon. 
     Compared with the prior art, the present invention provides a vibration canceller between the micro-actuator and the suspension, so when the micro-actuator is excited and do a movement, a first reaction force resulting therefrom will be transferred to the vibration canceller, then the vibration canceller is also being excited and self-generating another opposition reaction force to counteract the first reaction force. Thus, no additional force will be exerted to the suspension and accordingly suspension vibration resonance due to operating the micro-actuator can be cancelled. In addition, because suspension resonance has been cancelled in a low frequency, but only a micro-actuator resonance happened in a high frequency, this would enlarge the servo bandwidth and then improve the capacity of the HDD. 
     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, partial perspective view of the HGA of  FIG. 3 ; 
         FIG. 4   a  is an enlarged, partial, cross-sectional view of a PZT piece of the HGA of  FIG. 4 ; 
         FIG. 5  is an exploded view of  FIG. 4 ; 
         FIG. 6  is a partial, side view of the HGA of  FIG. 3  in micro-actuator area; 
         FIG. 7   a  shows an electrical connection relationship of two PZT pieces of the HGA of  FIG. 3 , which have a same polarization direction according to an embodiment of the present invention; 
         FIG. 7   b  shows an electrical connection relationship of two PZT pieces of the HGA of  FIG. 3 , which have opposing polarization directions according to another embodiment of the present invention; 
         FIG. 7   c  shows two waveforms of voltages which are applied to the two PZT pieces of  FIG. 7   b,  respectively; 
         FIG. 7   d  shows a waveform of voltage which is applied to the two PZT pieces of  FIG. 7   a,  respectively; 
         FIG. 7   e  shows a view to show working principle of a vibration canceller of the HGA of  FIG. 3 ; 
         FIGS. 8   a  and  8   b  are comparison resonance curves of the HGA of  FIG. 3 ; 
         FIGS. 9   a - 9   g  are perspective views of the vibration canceller according to seven different embodiments of the invention; 
         FIG. 10  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  32 . The HGA  3  further comprises a vibration canceller  33  interposed between the micro-actuator  32  and the suspension  8 . 
     Also referring to  FIG. 3 , the suspension  8  comprises a load beam  17 , a flexure  13 , a hinge  15  and a base plate  11 . 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 vibration canceller  33 , micro-actuator  32  and the slider  31 . Referring to  FIG. 6 , the load beam  17  has a dimple  329  formed thereon to support the suspension tongue  328 . 
     Referring to  FIGS. 3-5 , 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 a moving part of the suspension tongue  328 . 
     In the present invention, referring to  FIGS. 3-5 , the micro-actuator  32  comprises a U-shaped frame which having two side beams  321 ,  323  and a bottom beam  320  to connect with the two side beams  321 ,  323 . Each of the side beams  321 ,  323  has at least one PZT piece, such as PZT piece  321   a  or  323   a  bonded thereon, and also has a plurality of electrical bonding pads  327  corresponding to the suspension electrical bonding pads  310  (see  FIG. 5 ). In an embodiment, the PZT pieces  321   a  is bonded to an outer side of the side beams  321 , and the PZT pieces  323   a  is bonded to an outer side of the side beams  323 . 
     In the present invention, the vibration canceller  33  comprises a frame and at least one piezoelectric piece to be bonded with the frame. The frame is bonded with the micro-actuator  32  and the suspension  8 . 
     Referring to the  FIG. 5 , according to a first embodiment of the invention, the frame is also a U-shaped frame which comprises two side plates  331 ,  333  and a bottom plate  330  to connect with the two side plates  331 ,  333 . When the frame is bonded with micro-actuator  32 , the side beams  321 ,  323  extending from the bottom beam  320  in a first direction while the side plate  331 ,  333  extending from the bottom plate  330  in an same direction as the first direction. Each of the side plates  331 ,  333  has a plurality of electrical bonding pads  337  corresponding to the electrical bonding pads  310 . The U-shaped frame can be made of metal (i.e. stainless steel), ceramic, silicon or polymer. Two PZT pieces  331   a,    333   a  are respectively bonded on the side plates  331 ,  333  by traditional bonding method, such as epoxy bonding, anisotropic conductive film (ACF). In an embodiment, the PZT pieces  331   a  is bonded to an inner side of the side plates  331 , and the PZT pieces  333   a  is bonded to an inner side of the side plates  333 . 
     The PZT pieces  321   a,    323   a,    331   a,    333   a  are preferably made of thin film PZT material which can be a single-layer PZT element or a multi-layer PZT element. Also, the PZT pieces  321   a,    323   a,    331   a,    333   a  can be made of ceramic PZT material which can be a single-layer PZT element or a multi-layer PZT element. Referring to  FIG. 4   a,  as an embodiment, the PZT piece  321  a has a multi-layer structure, which has two kinds of electrodes  352  and  358  laminated alternatively, and in one end the two kinds of electrodes  352 ,  358  are connected with two electrical pads  355 , respectively. In an embodiment, the PZT pieces  321   a,    323   a,    331   a,    333   a  have a single-segment structure or a multi-segment structure. 
     Also referring to  FIGS. 3-5 , in an embodiment of the present invention, the slider  31  is partially coupled with the two side beams  321 ,  323  at two points (not labeled) by two epoxy dots  324 . The micro-actuator  32  is bonded with the vibration canceller  33  by using epoxy  404  to bond the bottom beam  320  with the bottom plate  330 . The vibration canceller  33  is partially coupled with the suspension tongue  328  of the flexure  13  through the bottom plate  330  thereof by ACF, adhesive or epoxy. Then, a plurality of metal balls  305  (GBB, SBB or conductive adhesive) are used to electrically connect the electrical bonding pads  327  of the micro-actuator  32  with the electrical bonding pads  337  of the vibration canceller  33 ; simultaneously, a plurality of metal balls  380  (GBB, SBB or conductive adhesive) are used to electrically connect the electrical bonding pads  337  of the vibration canceller  33  with the electrical bonding pads  310  of the suspension tongue  328 . Thus the micro-actuator  32 , the vibration canceller  33  are electrically connected with the two electric multi-traces  311  of the suspension  8 . In addition, 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  of the moving part of the suspension tongue  328  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). 
     In the present invention, referring to  FIG. 6 , a parallel gap  505  is formed between the vibration canceller  33  and the suspension tongue  328  so as to assure a free movement of the vibration canceller  33 . In addition, there is also a parallel gap  503  formed between the micro-actuator  32  and the vibration canceller  33 . Here, because the slider  31  has a partial bonding method with the two side beams  321 ,  323  and the parallel gap  503  formed between the micro-actuator  32  and the vibration canceller  33 , the slider  31  will move freely when being driven by the micro-actuator  32 . 
     Taking injunction with  FIGS. 7   a - 7   e,  the following gives a detail description of how the vibration canceller works.  FIG. 7   a  shows that an electrical connection relationship between the two PZT pieces  323   a,    333   a,  which are positioned adjacent to a same side of the suspension tongue  328 . In an embodiment, referring to  FIG. 7   a,  the two PZT pieces  323   a,    333   a  have a same polarization direction, 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. 7   d ). When the sine voltage  407  is applied to the two PZT pieces  323   a,    333   a,  in a first half period, both PZT pieces  323   a,    333   a  will contract with the drive voltage increasing, and then gradually spring back till to its original location with the drive voltage reducing. Because the PZT piece  323   a  is bonded on the outer side of the side beam  323 , the side beam  323  will be bent to outer side and accordingly a reaction force F 1  will be generated on the bottom beam  320 . The reaction force F 1  will immediately be transferred to the canceller bottom plate  330  because the bottom beam  320  of the micro-actuator  32  is bonded with the bottom plate  330  of the vibration canceller  33 . At the same time, the side plate  333  will be bent to inner side because the PZT pieces  333   a  is bonded on the inner side of the side plate  333 . A reaction force F 2  will be generated on the bottom plate  330  of the vibration canceller  33 . Here, the reaction force F 1  and F 2  are controlled to have opposition directions and a same value, so the resultant force exerted to the bottom plate  330  is zero. Understandably, the suspension  8  will not be influenced by motion of the side beam  323 . When the sine voltage  407  goes down to a second half period (having an opposed phase with the first half period), both PZT pieces  323   a,    333   a  will expand with the drive voltage increasing and then back to its original position with the drive voltage reducing. Accordingly, both the reaction force F 1  and F 2  change their directions and the resultant force exerted to the bottom plate  330  is still zero. The PZT pieces  321   a,    331   a  have a same work principle with the PZT pieces  323   a,    333   a,  thus a detailed description is omitted herefrom. 
     According to another embodiment of the invention, the two PZT pieces  321   a,    331   a  have two opposing polarization directions, as shown in  FIG. 7   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. 7   c ). Under the drive of the voltages, both PZT pieces  321   a,    331   a  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   a,    331   a  will expand gradually and then back to its initial position. Similarly, the reaction force F 1  and F 2  will be generated and the resultant force exerted to the bottom plate  330  is still zero. 
       FIGS. 8   a  and  8   b  show a testing result of the resonance performance of the HGA of the invention. Here, numeral  802  shows a micro-actuator operation resonance curve, which has a phase curve  806 , and numeral  803  show a resonance curve of vibration canceller operation, which has an opposed phase curve  804 . With the help of the vibration canceller  33 , the vibration of the suspension  8  is cancelled. Numeral  805  shows a resonance gain curve of the HGA of the invention and numeral  808  shows a phase curve thereof. It also shows that a suspension resonance has not happened in a low frequency, this would enlarge the servo bandwidth and improve the capacity of the HDD, reduce the slider seeking and settling time. 
     According to a second embodiment of the invention, referring to  FIG. 9   a,  the micro-actuator  32  and the vibration canceller  33  can be bonded together as the following status: the side beams  321 ,  323  extending from the bottom beam  320  in a first direction while the side plate  331 ,  333  extending from the bottom plate  330  in an opposite direction to the first direction. 
     According to a third embodiment of the invention, referring to  FIG. 9   b,  the frames of the micro-actuator  32  and the vibration canceller  33  can be integrally formed as a frame which has an integral bottom plate  23 , and two side plates  27 ,  29 . Two gaps  25  are respectively formed in the two side plates  27 ,  29 , and thus divided the side plate  27  as a first side plate  321 ′ and a second side plate  331 ′, and divided the side plate  29  as a first side plate  323 ′ and a second side plate  333 ′. 
     According to a fourth embodiment of the invention, referring to  FIG. 9   c,  the frame of the vibration canceller  33  may further comprise a top plate  334  to connect with the two side plates  331 ,  333 . In a five embodiment, referring to  FIG. 9   d,  the two PZT pieces  333   a  may be bonded to outer side of the side plates  331 ,  333 . 
     According to a six embodiment of the invention, referring to FIG  9   e,  the vibration canceller  33  may have a frame comprising a bottom plate  330  and a single side plate  337  which extending from a middle portion of the bottom plate  330 . Two PZT pieces  337   a,    337   b  are bonded to both sides of the side plate  337 . According to a seven embodiment of the invention, referring to  FIG. 9   f,  the vibration canceller  33  may have a frame comprising a bottom plate  330  and a single side plate  338  which extending from an end portion of the bottom plate  330 . Two PZT pieces  338   a  are bonded to both sides of the side plate  338 . 
     According to an eight embodiment of the invention, referring to  FIG. 9   g,  the vibration canceller  33  has a frame comprising a bottom plate  330  and a single side plate  339  which extending from an end portion of the bottom plate  330 . Two PZT pieces  339   a  are bonded to both sides of the side plate  339 . The vibration canceller  33  is bonded with the micro-actuator  32  by bonding the bottom beam  320  with the bottom plate  330 , at the time, the side beams  321 ,  323  extends from the bottom beam  320  in a first direction while the side plate  339  extending from the bottom plate  330  in an opposite direction to the first direction. The above-mentioned embodiments have a similar work principle with the first embodiment, a detailed description thereof is thus omitted. 
     Compared with the prior art, the present invention provides a vibration canceller between the micro-actuator and the suspension, so when the micro-actuator is excited and do a movement, a first reaction force resulting therefrom will be transferred to the vibration canceller, which self-generating an opposition reaction force to counteract the first reaction force. Thus, no additional force will be exerted to the suspension and accordingly suspension vibration and suspension resonance can be cancelled. In addition, because suspension resonance has been cancelled in a low frequency when operating the micro-actuator, and only a micro-actuator resonance happened in a high frequency, this would enlarge the servo bandwidth and then improve the storage capacity of the HDD. 
     In the present invention, referring to  FIG. 10 , a disk drive unit with vibration canceller 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 Category: g