Abstract:
In a hard disk drive, for the purpose of solving a problem that a mass of the tip of a VCM actuator increases, a primary resonance frequency lowers and a control band lowers in a case where a balance driving mechanism which damps a vibration during the driving of a microactuator is mounted, a damping unit using a displacement enlargement mechanism by resonance is disposed to obtain a sufficient damping effect with a small mass, thereby setting a resonance frequency of the damping unit to be higher than a frequency of a resonance peak of a damping object.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a hard disk drive including a head positioning mechanism of a two-stage actuator system having a VCM actuator and an actuator for micromotion mounted on the side of the tip of the VCM actuator, and more particularly, it relates to a hard disk drive including a damping mechanism which contributes to the enhancement of a positioning precision of a magnetic head. 
       DESCRIPTION OF RELATED ART 
       [0002]    A hard disk drive includes a magnetic disk which is an information recording medium, a magnetic head which reads and writes magnetic information from and in the magnetic disk, and a voice coil motor (VCM) actuator which supports the magnetic head and moves the magnetic head to a predetermined radial position on the magnetic disk. In the hard disk drive, for the purpose of correctly reading and writing the magnetic information from and in the magnetic disk, it is necessary to precisely control the positioning of the magnetic head with respect to the magnetic disk. As to the positioning control of the magnetic head, with the increase of a recording capacity/recording density of the hard disk drive, a mechanism and a control method for realizing a higher positioning precision are required. 
         [0003]    To meet this requirement, there has been suggested a head positioning mechanism of a two-stage actuator system including, in addition to the VCM actuator, a microactuator (an actuator for micromotion) which finely moves the magnetic head in such a direction as to intersect with a track direction of the magnetic disk, thereby precisely positioning the magnetic head. When the recording capacity/recording density of the hard disk drive progressively increases so that a recording capacity of 500 GB or more can be realized with a disk, as the head positioning mechanism corresponding to the capacity, there has increased a need for a precise head positioning mechanism of the two-stage actuator system. 
         [0004]    As an example of the actuator for micromotion in such a head positioning mechanism of the two-stage actuator system, JP-A-2001-307442 discloses that a VCM actuator includes a piezoelectric element mount portion disposed between a load beam of the actuator and a carriage which supports this load beam, and two piezoelectric elements are arranged on this piezoelectric element mount portion substantially symmetrically with respect to a central axis of a suspension in a longitudinal direction. In this head positioning mechanism, during driving, a voltage signal is applied to the two piezoelectric elements to expand and contract the piezoelectric elements in opposite phases, and in response to the expansion and contraction, the suspension including the magnetic head mounted on a tip thereof is finely moved, whereby the actuator for micromotion precisely positions the magnetic head. 
         [0005]    Moreover, one or two magnetic heads are usually mounted on an arm of the VCM actuator of the hard disk drive. On the arm of the VCM actuator disposed between two magnetic disks, two magnetic heads are mounted so that the magnetic information is read and written from and in magnetic recording surfaces which are present above and under the arm, respectively. On the other hand, one magnetic head is mounted on the arm of the VCM actuator disposed with respect to the magnetic recording surface of the magnetic disk at the uppermost or lowermost end of the hard disk drive, because the actuator only has one corresponding magnetic recording surface. 
         [0006]    JP-B-3771076 discloses a head positioning mechanism of a two-stage actuator system in which for the purpose of improving frequency response characteristics at a position of a magnetic head during the driving of an actuator for micromotion, enhancing a positioning control band and realizing a more precise positioning performance, an arm of a VCM actuator is disposed between two magnetic disks and includes two mounted magnetic heads, while an actuator for micromotion drives a suspension including one mounted magnetic head, so that respective suspensions are driven in opposite phases. Furthermore, in this publication, with respect to an arm of a VCM actuator disposed to face the magnetic recording surface of a magnetic disk at the uppermost or lowermost end thereof, and including one mounted magnetic head, there is disclosed a constitution in which on the surface of the arm opposite to a magnetic disk side surface to which a suspension including one mounted magnetic head is attached, a balance driving mechanism is mounted. The balance driving mechanism includes a microactuator having a constitution similar to the actuator for micromotion which finely moves the suspension, and a mass member (a dummy mass) which has a mass equivalent to that of the suspension including the mounted magnetic head and finely moves by the driving of this microactuator. In the arm of the VCM actuator including this balance driving mechanism and the one mounted magnetic head, the microactuators of the suspension and the balance driving mechanism are driven in the opposite phases to each other, respectively, whereby it is possible to obtain an effect similar to that of the arm of the VCM actuator on which two magnetic heads are mounted. 
         [0007]    In the head positioning mechanism of the two-stage actuator system, in frequency characteristics of a head response during the driving of the microactuator, there appears a peak as a minimum order frequency peak corresponding to a vibration mode referred to as a sway mode in which the arm and the suspension are deformed in the operation surface of the microactuator. In the head positioning mechanism of the two-stage actuator system disclosed in the publication, when two magnetic heads mounted on the arm of the VCM actuator or one magnetic head and the dummy mass mounted on the arm are driven in the opposite phases to each other, it is possible to compensate the above minimum order frequency peak so as to cancel it. In consequence, the sway mode enhances up to a peak frequency at which a minimum order resonance peak next appears, and enhancement of frequency characteristics of a head response in a control band can be realized. 
         [0008]    Meanwhile, when the magnetic head can precisely be positioned by the above head positioning mechanism of the two-stage actuator system, a large capacity of 500 GB or 1 TB can be realized only with one disk. In consequence, in a personal computer or the like which occupies a large ratio of a use application of the hard disk drive, a sufficiently necessary recording capacity can be acquired by the hard disk drive on which only one disk is mounted. Therefore, it is considered that a demand for the hard disk drive including one disk is growing. 
         [0009]    In this head positioning mechanism of the hard disk drive including the one disk, the arm of the VCM actuator including one mounted magnetic head is disposed on the upper surface and/or the lower surface of the disk. 
         [0010]    Therefore, when the head positioning mechanism of the two-stage actuator system is applied to the head positioning mechanism of the hard disk drive including one disk, the balance driving mechanism and the head positioning mechanism of the two-stage actuator system are mounted on each arm of the VCM actuator on which one magnetic head is mounted. In this case, a mass of the balance driving mechanism disposed in each arm of the VCM actuator is substantially the same as a mass of the suspension including the mounted magnetic head and the microactuator which drives the suspension. In consequence, the mass of the tip of each arm of the VCM actuator on which one magnetic head is mounted increases twice as compared with a case where any balance driving mechanism is not mounted. 
         [0011]    However, owing to the increase of the mass of the arm tip of this VCM actuator, a primary resonance frequency of the VCM actuator which is an actuator for coarse motion is lowered, and the control band is decreased. To further improve the positioning precision of the positioning mechanism of the two-stage actuator system, it is necessary to enhance the control band of both the microactuator and the VCM actuator. Therefore, the enhancement of the resonance frequency characteristics of the VCM actuator has been an important theme in the same manner as in the enhancement of frequency characteristics of a vibration of the microactuator. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The present invention has been developed in view of the above theme, and an object thereof is to provide a hard disk drive which enhances a control band of both a microactuator and a VCM actuator, thereby further improving a positioning precision of a positioning mechanism of a two-stage actuator system. 
         [0013]    To achieve the above object, a hard disk drive according to the present invention realizes the enhancement of frequency characteristics of an actuator which displaces and drives a magnetic head, by use of a damping unit having a small mass. For this purpose, the hard disk drive of the present invention comprises a damping unit including a resonator in which a mass member is elastically supported to be displaced in a predetermined direction, a base portion in which a mount portion including the mounted resonator is elastically supported to be displaced in the predetermined direction and a micromotion actuator for damping which displaces and drives the mount portion of the base portion in the predetermined direction. The damping unit is disposed in an arm on which a magnetic head is mounted so that the predetermined direction of the damping unit becomes the same as a micromotion displacement direction of a magnetic head by a head positioning mechanism of a two-stage actuator system, and a micromotion actuator for the micromotion displacement of the magnetic head and the micromotion actuator for the damping of the damping unit are operated, respectively, so that the micromotion direction of the magnetic head and the displacement direction of the mount portion on which the resonator is mounted have opposite phases. 
         [0014]    Furthermore, the present invention may be characterized in that a resonance frequency of a vibration system of the resonator including the mass member and an elastic support member of the mass member is set to be higher than a frequency (also referred to as the control frequency) of a resonance peak which is an object of compensation by the damping unit. 
         [0015]    According to the present invention, for the purpose of compensating for vibration generated by the driving of the micromotion actuator for the micromotion displacement of the magnetic head, the micromotion actuator for the damping of the damping unit displaces and drives the mass member of the resonator in the damping unit in the opposite phase. At this time, in the mass member of the resonator, the deformation of the elastic support member by resonance is added to the displacement of the mount portion which is displaced and driven by the micromotion actuator for the damping in the opposite phase, whereby the mass member is more noticeably displaced, so that the damping unit can obtain a sufficient effect with a small mass. In consequence, the mass of the damping unit can be decreased, and hence as compared with a case where a dummy mass having a mass equivalent to that of a suspension is used, the mass of an arm tip can be decreased, and a primary resonance frequency of the VCM actuator can be enhanced. Therefore, a control band of both the microactuator and the VCM actuator enhances. 
         [0016]    Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING 
         [0017]      FIG. 1  is a perspective view of a hard disk drive according to an embodiment of the present invention; 
           [0018]      FIG. 2  is an enlarged view of a head-gimbal assembly shown in  FIG. 1 ; 
           [0019]      FIG. 3  is a perspective view showing a damping unit of  FIG. 2  as seen from a side opposite to a disk surface; 
           [0020]      FIG. 4  is a perspective view showing the damping unit of  FIG. 2  as seen from a disk surface side; 
           [0021]      FIG. 5  is an operation explanatory view of the damping unit shown in  FIG. 3 ; 
           [0022]      FIG. 6  is an operation explanatory view of the damping unit shown in  FIG. 4 ; 
           [0023]      FIG. 7  is an operation explanatory view of the head-gimbal assembly of the hard disk drive according to the present embodiment; 
           [0024]      FIG. 8  is a perspective view of a carriage of the hard disk drive according to the present embodiment; 
           [0025]      FIG. 9  is a perspective view of a carriage of a conventional hard disk drive according to a comparative example; 
           [0026]      FIG. 10  shows calculated frequency characteristics of the carriage of the hard disk drive according to the present embodiment shown in  FIG. 8 ; 
           [0027]      FIG. 11  shows calculated frequency characteristics of the carriage of the conventional hard disk drive according to the comparative example shown in  FIG. 9 ; 
           [0028]      FIG. 12  shows a calculated frequency response at a position of a magnetic head in a case where an only microactuator is operated in the carriage of the hard disk drive of the present embodiment shown in  FIG. 8 ; 
           [0029]      FIG. 13  shows a calculated frequency response at the position of the magnetic head in a case where the microactuator and the damping unit are operated in the carriage of the hard disk drive of the present embodiment shown in  FIG. 8 ; 
           [0030]      FIG. 14  is a perspective view of a head-gimbal assembly of another embodiment of the present invention; and 
           [0031]      FIG. 15  is an exploded perspective view showing the head-gimbal assembly of  FIG. 14  as seen from the backside. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Hereinafter, a hard disk drive according to an embodiment of the present invention will be described with reference to the drawing. 
         [0033]      FIG. 1  is a perspective view of the hard disk drive according to the embodiment of the present invention. It is to be noted that in  FIG. 1 , the hard disk drive has a state where a lid member is removed to see the inside of a housing. 
         [0034]    A hard disk drive  1  has a structure that a disk  2  provided on both surfaces with magnetic recording surfaces which can record information, a spindle motor  3  which rotates and drives the disk  2 , a voice coil motor (VCM)  4  as an actuator for coarse motion which rotates and drives a magnetic head mounted on the tip of an arm in a predetermined region of the disk  2  so as to intersect with a track direction of the disk  2 , and a carriage  5  which receives a driving force of the voice coil motor  4  are contained in a housing. The carriage  5  is rotatably attached to a pivot bearing  7  in a predetermined angle region around the pivot bearing  7 . The carriage  5  includes a carriage arm  6  extended from a base portion of the carriage engaged with the pivot bearing  7 , and to the tip of the carriage arm  6 , a head-gimbal assembly  10  (a suspension) is fixed. Further, to the tip of the head-gimbal assembly  10 , a slider  11  containing the magnetic head is fixed. 
         [0035]    In the shown example, a pair of carriage arms  6  are superimposed on each other with such a space being left therebetween that the disk  2  can be interposed between the arms in a vertical direction (an axial direction of the spindle motor  3  or the pivot bearing  7 ) with respect to the base portion of the carriage engaged with the pivot bearing  7 , and the magnetic head contained in the slider  11  of the head-gimbal assembly  10  fixed to each of the carriage arms  6  faces the magnetic recording surface (the disk surface) which is the upper surface (the front surface) or the lower surface (the back surface) of the disk  2 . The carriage  5  is operated by the voice coil motor  4  to rotate in the predetermined angle region around the pivot bearing  7 , whereby an arm of a VCM actuator including the carriage arm  6  and the head-gimbal assembly swings in a diametric direction on the disk surface, to position the magnetic head at an arbitrary radial position on the disk  2 . 
         [0036]      FIG. 2  is an enlarged view of the head-gimbal assembly shown in  FIG. 1 . 
         [0037]    The head-gimbal assembly  10  has a constitution in which a load beam  12  including the slider  11  containing the magnetic head on the side of the tip thereof is fixed to an attachment base  8  formed integrally with the tip of the carriage arm  6  via an actuator  13  for micromotion. The actuator  13  for micromotion has a constitution in which a pair of piezoelectric elements  15  and  16  having mutually different polarizing directions are assembled onto a mount plate  14 . The mount plate  14  is provided with a ring-like projection  17  fitted and fixed into an attachment hole  9  formed in the attachment base  8  at the tip of the carriage arm  6 , on one side of the plate in a longitudinal direction thereof. On the other side of the plate in the longitudinal direction thereof, ends of a pair of flexible arm portions  18  and  19  each having an intermediate portion projecting outwardly in a lateral direction and having a bent shape which can extend in the longitudinal direction are connected to each other, thereby forming a hollow portion  20 . The pair of piezoelectric elements  15  and  16  have both ends fixed to connecting portions  21  and  22  having rigidity, respectively, so as to bridge the hollow portion  20  on both end sides of the flexible arm portions  18  and  19 , and the elements are arranged in the hollow portion  20  line-symmetrically with respect to a center line x-x in a longitudinal direction X of the mount plate  14 . The load beam  12  has a base end side portion fixed to the connecting portion  22  on the other end side of the mount plate  14 . 
         [0038]    Consequently, in the actuator  13  for micromotion, the pair of piezoelectric elements  15  and  16  having mutually different polarizing directions mutually elongate and contract by a control signal, whereby the flexible arm portions  18  and  19  are, accordingly, deformed, and the connecting portion  22  and the load beam  12  swing with respect to the connecting portion  21  of the mount plate  14  around the center line x-x in the longitudinal direction X of the mount plate  14 . In consequence, the magnetic head contained in the slider  11  on the side of the tip of the load beam  12  is driven in such a shown direction A in the drawing as to intersect with the track direction of the disk  2 . 
         [0039]    Furthermore, in the hard disk drive  1  of the present embodiment, a damping unit  30  is disposed in a connecting portion  21  part on one end side of the mount plate  14  which is a part of the mount plate  14  between the attachment hole  9  and the hollow portion  20 . 
         [0040]      FIG. 3  is a perspective view showing the damping unit of  FIG. 2  as seen from a side opposite to a disk surface. 
         [0041]      FIG. 4  is a perspective view showing the damping unit of  FIG. 2  as seen from a disk surface side. 
         [0042]    The damping unit  30  includes a base portion  31  supported by the mount plate  14 , a resonator  35  mounted on the base portion  31 , and a pair of piezoelectric elements  41  and  42  having mutually different polarizing directions. 
         [0043]    In the shown example, the base portion  31  is formed by processing the mount plate  14 , and includes four beam portions  32  and a plate-like mount portion  33  connected to the mount plate  14  via the four beam portions  32 . Each of the four beam portions  32  has a constitution as a spring portion having a flexibility in a lateral direction Y of the mount plate  14  which is vertical to a center line x-x in a longitudinal direction X of the mount plate  14 . Furthermore, in the shown example, the four beam portions  32  are two pairs of beam portions  32   a  and  32   a  and beam portions  32   b  and  32   b , and the pairs of beam portions  32   a  and  32   a  and beam portions  32   b  and  32   b  are arranged symmetrically on both sides of the lateral direction Y of the mount plate  14 , across the center line x-x along the longitudinal direction X of the mount plate  14 . The beam portions  32   a  and  32   a  or the beam portions  32   b  and  32   b  of each pair are symmetrically arranged on both sides of the center line x-x along the longitudinal direction X of the mount plate  14 , across a center line y-y of the mount portion  33  in the lateral direction Y of the mount plate  14 . Moreover, the mount portion  33  is formed as a rigid plate-like portion having a shape which is line-symmetric with respect to the center line x-x along the longitudinal direction X of the mount plate  14 , and between both the ends of the mount portion  33  along the lateral direction Y of the mount plate  14  and the mount plate  14 , space portions  34  and  34  are formed to allow the movement of the mount portion  33  along the lateral direction Y of the mount plate  14 . 
         [0044]    On the other hand, the resonator  35  includes a rectangular frame  36  and a mass member  37  received in the frame  36 . The frame  36  includes a pair of rigid leg portions  38  and  38  fixed to the base portion  31  and extending in parallel to the lateral direction Y of the mount plate  14 , and a pair of flexible connecting portions  39  and  39  formed as leaf springs in the lateral direction Y of the mount plate  14  which are not fixed to the base portion  31 , connect both end sides of the leg portions  38  and  38  to each other and extend in parallel to the longitudinal direction X of the mount plate  14 . The mass member  37  received in the frame  36  is made of a rigid material having a shape which is line-symmetric with respect to the center line y-y of the mount portion  33 . In addition, the ends of the mass member  37  in the lateral direction Y of the mount plate  14  are secured to the facing connecting portions  39  and  39 , respectively, whereas the ends of the mass member in the longitudinal direction X of the mount plate  14  are not secured to the leg portions  38  and  38 , whereby the connecting portions  39  and  39  are bent and deformed to allow the movement of the mass member  37  along the lateral direction Y of the mount plate  14  in the frame  36 . It is to be noted that a groove formed in the mount portion  33  of the base portion  31  and extending along the lateral direction Y of the mount plate  14  is a guide groove  40  which guides the movement of the mass member  37  in the lateral direction Y of the mount plate  14 . 
         [0045]    With respect to the base portion  31  on which the resonator  35  is mounted, both ends of the pair of piezoelectric elements  41  and  42  are fixed to the ends of the mount portion  33  along the lateral direction Y of the mount plate  14  and to the mount plate  14 , respectively, so as to bridge the space portions  34  and  34 . In consequence, when the piezoelectric elements  41  and  42  elongate and contract by a driving voltage, respectively, the mount portion  33  of the base portion  31  deforms the flexible beam portions  32  to move in the lateral direction Y of the mount plate  14 , i.e., a driving direction A of the magnetic head, whereby the mass member  37  of the resonator  35  relatively moves with respect to the mount portion  33  in the direction A and in a direction opposite to the moving direction of the mount portion  33 . 
         [0046]      FIG. 5  and  FIG. 6  are operation explanatory views of the damping unit shown in  FIG. 3  and  FIG. 4 . 
         [0047]    As shown in  FIG. 5 , the piezoelectric elements  41  and  42  have mutually reverse polarizing directions. Therefore, when a repeating driving voltage having the same voltage polarity or size is applied, the one piezoelectric element  41  or the other piezoelectric element  42  elongates, and the other piezoelectric element  42  or the one piezoelectric element  41  contracts, to perform a push-pull operation. Consequently, the beam portions  32  of the base portion  31  are elastically deformed, and the mount portion  33  is displaced in the arrow direction A. In consequence, when the repeating driving voltage having a predetermined frequency (the alternate voltage) is applied to the piezoelectric elements  41  and  42 , the mount portion  33  of the base portion  31  is driven and vibrated in the shown direction A so as to intersect with the track direction of the disk  2 . 
         [0048]    In this way, when the mount portion  33  of the base portion  31  is displaced by applying the repeating driving voltage to the piezoelectric elements  41  and  42  of the base portion  31 , the resonator  35  is vibrated. In this case, the connecting portions  39  and  39  as the leaf springs are noticeably bent, and the mass member  37  is relatively displaced along the shown direction A so as to intersect with the track direction of the disk  2 . Here, a characteristic frequency of the resonator  35  determined by a spring constant of the connecting portions  39  and  39  and a mass of the mass member  37  is set to be higher than a frequency of a resonance peak which is a compensation object of the damping unit, i.e., a control frequency, and set to a frequency which is within twice the frequency of the control object. Moreover, a spring constant of the beam portions  32  ( 32   a  and  32   a , and  32   b  and  32   b ) which are springs of the base portion  31  is set to be higher than the spring constant of the connecting portions  39  and  39  which are the leaf springs of the resonator  35 . Therefore, owing to the displacement of the mount portion  33  of the base portion  31 , the mass member  37  can noticeably be displaced. Moreover, a displacement direction of the base portion  31  matches a displacement direction of the mass member  37 . That is, by the operation of the resonator  35 , the displacement of the mass member  37  in the shown direction A is enlarged as compared with the displacement of the mount portion  33  of the base portion  31 . As seen from an aspect of a function of the damping unit  30  which damps a vibration of a mounted material by a reactive force obtained by the operation of the mass member  37 , a larger reactive force can be obtained by the enlarged displacement. In other words, it is seen that an equivalent vibration damping effect can be obtained by use of the mass member  37  having a smaller mass. 
         [0049]      FIG. 7  is an operation explanatory view of the head-gimbal assembly of the hard disk drive according to the present embodiment. It is to be noted that in  FIG. 7 , unlike  FIG. 1  seen from the side opposite to the disk surface, the head-gimbal assembly  10  has a state seen from the disk surface side. 
         [0050]    In the shown example, gains G 1  and G 2  are independently applied to a control signal  51  by amplifiers  43  and  44 , respectively, to generate a driving voltage  52  of the piezoelectric elements  15  and  16  of the actuator  13  for micromotion and a driving voltage  53  of the piezoelectric elements  41  and  42  of the damping unit  30 . When the slider  11  is displaced in a direction a 1  by the operation of the actuator  13  for micromotion, the damping unit  30  is displaced in an opposite direction a 2 . 
         [0051]    Hereinafter, the results of comparison evaluation of the hard disk drive  1  of the present embodiment having the above constitution with respect to a conventional hard disk drive will be described. In this comparison evaluation, the carriage  5  shown in  FIG. 8  is applied to the hard disk drive  1  of the present embodiment, while the hard disk drive according to a conventional technology includes a carriage  105  shown in  FIG. 9 . 
         [0052]      FIG. 8  is a perspective view of the carriage of the hard disk drive according to the present embodiment. 
         [0053]    In  FIG. 8 , the arm of the VCM actuator including the carriage arm  6  and the head-gimbal assembly  10  of the carriage  5  is provided with the actuator  13  for micromotion, the damping unit  30  and a VCM coil  45 . It is to be noted that since the constitution of the head-gimbal assembly  10  including the actuator  13  for micromotion and the damping unit  30  has been described above in detail with reference to  FIG. 1  to  FIG. 7 , the same constitution is denoted with the same reference numerals, thereby omitting description thereof. 
         [0054]      FIG. 9  is a perspective view of the carriage of the conventional hard disk drive according to a comparative example. 
         [0055]    In  FIG. 9 , the arm of the VCM actuator including the carriage arm  6  and the head-gimbal assembly  10  of the carriage  105  is provided with the actuator  13  for micromotion, a balance driving mechanism  130  and the VCM coil  45 . The balance driving mechanism  130  includes a microactuator  131  having a constitution similar to the actuator  13  for micromotion which finely moves the head-gimbal assembly (the suspension)  10 , and a mass member (a dummy mass)  132  which has a mass equivalent to that of the head-gimbal assembly (the suspension)  10  including the mounted magnetic head and finely moves by the driving of the microactuator  131 . Owing to the driving of the actuator  13  for micromotion and the microactuator of the balance driving mechanism  130  in opposite phases, respectively, it is possible to obtain an effect similar to that of the arm of the VCM actuator on which two magnetic heads are mounted. 
         [0056]      FIG. 10  shows calculated frequency characteristics of the carriage of the hard disk drive according to the present embodiment shown in  FIG. 8 . A solid line shows gain characteristics. For the calculation, both ends of the pivot bearing  7  were fixed, an exciting force was input into the VCM coil  45  in such a direction as to rotate the carriage  5  around the pivot bearing  7 , and a frequency response of the displacement at a magnetic head position was calculated by a finite element method. 
         [0057]    Moreover, a weight of the suspension part (the head-gimbal assembly)  10  driven by the microactuator (the actuator for micromotion)  13  was 8 mg, a weight of the mass member  37  of the damping unit  30  (see  FIG. 3 ) was 1 mg, and a weight of the whole damping unit  30  was 2 mg. 
         [0058]      FIG. 11  shows calculated frequency characteristics of the carriage of the conventional hard disk drive according to the comparative example shown in  FIG. 9 . A solid line shows gain characteristics. For the calculation, both ends of the pivot bearing  7  were fixed, an exciting force was input into the VCM coil  45  in such a direction as to rotate the carriage  105  around the pivot bearing  7 , and a frequency response of the displacement at a magnetic head position was calculated. Moreover, a weight of the suspension part  10  driven by the microactuator  13  was 8 mg. Here, a weight of the balance driving mechanism  130  including the mass member (the dummy mass)  132 , the microactuator (the piezoelectric element)  131  and a mount plate  114  on which the mass member and the microactuator were mounted was 43 mg. 
         [0059]    When  FIG. 10  is compared with  FIG. 11 , as to frequencies of peaks  61  and  62  in a primary resonance mode having the lowest frequency, the peak  61  in the present embodiment shown in  FIG. 10  is 9 kHz, whereas the peak  62  in the comparative example shown in  FIG. 11  is 7.8 kHz. It is seen that as compared with the conventional technology, in the present embodiment, the primary resonance frequency of the carriage  5  of the VCM actuator as an actuator for coarse motion increases by about 15%. 
         [0060]      FIG. 12  shows a calculated frequency response at a position of a magnetic head in a case where the only microactuator (the actuator for micromotion)  13  is operated in the carriage of the hard disk drive of the present embodiment shown in  FIG. 8 . A peak  63  is a peak of a sway mode disclosed in JP-B-3771076, and a function of the damping unit  30  according to the conventional technology and the present technology is to suppress the sway mode which appears as the peak  63 , thereby improving vibration characteristics. 
         [0061]      FIG. 13  shows a calculated frequency response at the position of the magnetic head in a case where the microactuator (the actuator for micromotion)  13  and the damping unit  30  are operated in the carriage of the hard disk drive of the present embodiment shown in  FIG. 8 . A peak  64  of the sway mode is substantially suppressed, and a peak of the lowest frequency in a frequency response shifts to a peak  65 . In consequence, the frequency of the peak of the lowest frequency improves by about 20% from the peak  63  or  64  of 13 kHz to the peak  65  of 16 kHz. 
         [0062]    It is seen from the results of  FIG. 10  to  FIG. 13  that both the primary resonance frequency of the microactuator which is the actuator  13  for micromotion according to the present invention and the primary resonance frequency of the carriage  5  which is the actuator for coarse motion are enhanced. In consequence, the control band of both the coarse motion and the micromotion can be enhanced, and a higher positioning precision can be realized. 
         [0063]      FIG. 14  is a perspective view of a head-gimbal assembly of another embodiment of the present invention. 
         [0064]      FIG. 15  is an exploded perspective view showing the head-gimbal assembly of  FIG. 14  as seen from the backside (a disk surface side). 
         [0065]    In the present embodiment, a damping unit including a base portion  31 , a resonator  35  and a pair of piezoelectric elements  41  and  42  in the same manner as in the damping unit  30  shown in  FIG. 3  and  FIG. 4  has a constitution of a damping unit  70  as an assembly which can preliminarily be assembled, and the damping unit  70  can be joined to a mount plate  14  provided with an actuator  13  for micromotion. For example, to join the damping unit  70  to the mount plate  14 , the mount plate  14  is provided with an attachment hole  23  having a size corresponding to a size of the base portion  31  and the resonator  35  of the damping unit  70 , and a non-movable/non-deformable constituent part of the damping unit  70  may be joined to a plate portion around the attachment hole  23  by an adhesive or welding. 
         [0066]    In the present embodiment, when the damping unit  30  has the constitution of the assembly including the damping unit  70  as described above, the microactuator  13  required to be finely processed or assembled in the same manner as in the damping unit  30  can separately be processed, whereby a precision or a yield can be improved. 
         [0067]    Moreover, in the above embodiments, the hard disk drive including the suspension driving type microactuator as the actuator  13  for micromotion has been illustrated, but the present invention can be applied to a hard disk drive including a slider driving type microactuator which drives the slider  11 . 
         [0068]    It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.