Abstract:
A head support mechanism includes a rigid support arm, a suspension for supporting, at its leading end section, a head slider with at least one head element, the suspension having a balance structure that can be pivoted in a direction crossing a surface of a recording medium using as a fulcrum a load support point established between the suspension and the support arm, a load generation unit for generating a load applied to the load support point for pressing the head slider toward the surface of the recording medium, a horizontal rotation bearing unit for pivotally bearing the support arm and the suspension so that the support arm and the suspension are capable of rotatively moving in a direction parallel to the surface of the recording medium, and an weight unit coupled to a trailing end section of the suspension to match the center of gravity of the suspension including the head slider with the load support point. The weight unit is formed around at least a part of the periphery of the horizontal rotation-bearing unit.

Description:
PRIORITY CLAIM  
       [0001]     This application claims priority from Japanese patent application No. 2003-346583, filed on Oct. 6, 2003, which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a head support mechanism provided by assembling a support arm and a suspension, a head arm assembly (HAA) provided by mounting a flying type head slider for supporting a recording and/or reproducing head element such as a thin-film magnetic head or an optical head on the head support mechanism, and a disk drive apparatus provided with the HAA.  
         [0004]     2. Description of the Related Art  
         [0005]     In a magnetic disk drive apparatus, at least one magnetic head slider attached to a leading end section of an HAA is flying on a surface of a rotating magnetic disk. In this state, a thin-film magnetic head element formed on the magnetic head slider records and/or reproduces data on/or from the magnetic disk.  
         [0006]     The HAA mainly has a magnetic head slider, a suspension with an elastic flexure that supports the magnetic head slider, an elastic load beam that supports the flexure at its leading end section and a base plate that supports a trailing end section of the load beam, and a rigid support arm that supports the suspension. A load to be applied on the magnetic head slider toward the surface of the magnetic disk is generated in a plate spring section provided in the middle of the load beam of the suspension.  
         [0007]     Such a conventional HAA has a cantilever structure for supporting the suspension at its trailing end section. The cantilever structure is excellent in stabilizing the load applied on the magnetic head slider and saving a required space. However, the cantilever structure has a serious problem of a low shock resistance. Specifically, because the magnetic head slider is mounted at a leading end section of the HAA which is a free end of the cantilever structure, when a shock force is applied, the rotation moment of the magnetic head slider is added to a rotation moment based upon the mass of the whole system of the beam structure. As a result, a slap mode occurs in which the head slider jumps up from the magnetic disk surface or is slapped against the surface. According to the conventional HAA, this tendency is significantly observed, because the load beam, which is a beam structure supporting the magnetic head slider, is formed by a spring member of a low rigidity, namely a stainless steel plate slightly thicker than the flexure.  
         [0008]     In a magnetic disk drive for 3.5-inch disks, which is mounted in a computer called a high-end type or desktop type, an excessive shock force is rarely applied. However, in a magnetic disk drive for 2.5-inch disks, which is mounted in a notebook computer, an excessive shock force is likely to be applied. Accordingly, the low shock resistance is a serious problem.  
         [0009]     U.S. Pat. No. 6,751,064 B2 proposes a head support apparatus in which to improve the shock resistance of an HAA, a rigid arm is provided with a magnetic head slider at one end and voice coil motor (VCM) for horizontal rotation at the other end. Further, in this apparatus, the arm is configured to rotatively move in a radial direction of the magnetic disk around a bearing section and is also configured to have a balance structure in which the arm can be rotatively moved in a direction perpendicular to the magnetic disk surface around a bearing section. Moreover, a pivot is used to urge a plate spring plate provided in the bearing section to apply a load to the magnetic head slider.  
         [0010]     In such HAA with the balance structure, because the distance between the VCM and the magnetic head slider is short in case of a small-diameter magnetic disk apparatus such as a micro drive and a single disk, the weight of a part of the arm in the VCM side from the bearing section can be balanced with a part of the arm in the magnetic head slider side from the bearing section. However, in a larger-diameter magnetic disk drive for, for example, 1.8-inch or 2.5-inch disks, the arm is longer, so that it is difficult to ensure a sufficient shock resistance. Moreover, since the VCM is used to balance the balance structure, the magnetic disk apparatus cannot be configured so as to allow a plurality of HAAs with the balance structure to stack each other.  
         [0011]     To eliminate such an inconvenience, inventors of the present application proposed the employment of a balance structure at a leading end section of a support arm.  
         [0012]      FIG. 1  is a side view illustrating a schematic configuration of an HAA proposed by the inventors.  
         [0013]     In the figure, reference numeral  10  designates a support arm. Reference numeral  11  designates a load beam of a balance structure that uses as a fulcrum a load support point  12 , that is, a projection provided at a leading end section of the support arm  10 . Reference numeral  13  designates a support spring for coupling the load beam  11  and the support arm  10  together to urge the load beam  11  via the projection  12 . Reference numeral  14  designates a magnetic head slider supported at a leading end section of the load beam  11  via the flexure  15 . Reference numeral  16  designates a magnetic disk.  
         [0014]     In this HAA, since the load beam  11  of the balance structure is provided at the leading end section of the support arm  10 , the increased length of the support arm does not substantially reduce the shock resistance. Also, because this structure does not use a coil section of a VCM to balance the balance structure, the magnetic disk apparatus can be configured so as to allow a plurality of HAAs to stack each other.  
         [0015]     However, according to the HAA of the structure shown in  FIG. 1 , since a trailing end section (lying opposite the end at which the magnetic head slider  14  is mounted)  11   a  of the load beam  11  is extended to balance rotation moments, when the HAA receives a shock, the extended part is displaced. That is, in order to make the rotation moment of the part between the projection or load support point  12  and the leading end section (magnetic head slider side) equal to the rotation moment of the part between the projection or load support point  12  and the trailing end section (actuator (VCM) side), it is necessary to extend the trailing end section  11   a  of the load beam  11  or to attach a weight close to the trailing end section  11   a . In this case, when a shock is applied, the trailing end section is displaced to interfere with the support arm  10  or the magnetic disk  16 . Even when no shock is applied, if the magnetic disk apparatus employs a load unload system, the trailing end section  11   a  of the load beam  11  may contact with the surface of the magnetic disk  16 . Thus, any increase in the magnitude of displacement in this trailing end section is undesirable.  
         [0016]     Also, since the support arm is long, it is necessary to greatly increase its thickness to prevent the arm itself from being deformed by a shock. Furthermore, because the extended trailing end section  11   a  of the load beam  11  or the weight attached to the trailing end section is at a substantial distance from the horizontal axis of rotation (the center of seek rotation), disadvantageously, an inertia moment during a seek operation may directly increase. In addition, since the weight is provided in a gap between the support arm and the magnetic disk, it is difficult to optimize the shape of the weight. Namely, it is quite difficult to make a weight shape suitable for bending characteristics or torsion and sway characteristics.  
       BRIEF SUMMARY OF THE INVENTION  
       [0017]     It is therefore an object of the present invention to provide a head support mechanism, an HAA and a disk drive apparatus, whereby an excellent shock resistance can be obtained to prevent an increase in inertia moment during a seek operation.  
         [0018]     Another object of the present invention is to provide a head support mechanism, an HAA and a disk drive apparatus, whereby an excellent shock resistance can be obtained to allow a weight shape to be easily optimized.  
         [0019]     Further object of the present invention is to provide a head support mechanism, an HAA and a disk drive apparatus, whereby both an excellent shock resistance and a high flexural rigidity can be obtained to provide a configuration with a plurality of HAAs stacked each other.  
         [0020]     According to the present invention, a head support mechanism includes a rigid support arm, a suspension for supporting, at its leading end section, a head slider with at least one head element, the suspension having a balance structure that can be pivoted in a direction crossing a surface of a recording medium using as a fulcrum a load support point established between the suspension and the support arm, a load generation unit for generating a load applied to the load support point for pressing the head slider toward the surface of the recording medium, a horizontal rotation bearing unit for pivotally bearing the support arm and the suspension so that the support arm and the suspension are capable of rotatively moving in a direction parallel to the surface of the recording medium, and an weight unit coupled to a trailing end section of the suspension to match the center of gravity of the suspension including the head slider with the load support point. The weight unit is formed around at least a part of the periphery of the horizontal rotation-bearing unit.  
         [0021]     Also, according to the present invention, an HAA has the above-mentioned head support mechanism and at least one head element mounted on the suspension of the head support mechanism.  
         [0022]     Furthermore, according to the present invention, a disk drive apparatus includes at least one recording medium and at least one above-mentioned HAA.  
         [0023]     The weight unit is coupled to the trailing end section of the suspension to match the center of gravity of the suspension including the head slider with the load support point, and is formed at least in a part of the periphery of the horizontal rotation-bearing unit. This prevents an increase in inertia moment during a seek operation. Also, it is unnecessary to extend the trailing end section of the suspension of the balance structure in order to balance rotation moments. This prevents the trailing end section of the suspension from interfering with the horizontal rotation-bearing unit. Moreover, the length of the trailing end side can be freely set, thus enabling the moments to be easily balanced. Of course, a high shock resistance can be obtained. In addition, since the weight of the trailing end section can be reduced, so that the weight unit can be extended and located closer to the trailing end section and outside the recording medium. This avoids interfering with the surface of the recording medium.  
         [0024]     In the specification, the terms “leading end section” and “leading end side” refer to the section and direction of a side acting as a free end during operation, that is, the side on which the head slider is mounted. The terms “trailing end section” and “trailing end side” refer to the section and direction of the opposite side, on which the VCM is mounted.  
         [0025]     It is preferred that the weight unit is formed to surround the horizontal rotation-bearing unit all around the periphery of the horizontal rotation-bearing unit. Since load concentrates at the load support point, this part of the suspension may be deformed and distorted to absorb energy to prevent the desired load from being obtained. When the weight unit is formed to surround the load support point, the deformation of that part can be minimized.  
         [0026]     It is also preferred that the weight unit is formed around the periphery of the horizontal rotation bearing unit except for a trailing end section of the periphery of the horizontal rotation bearing unit.  
         [0027]     It is preferred that the weight unit is also formed in a leading end side of the suspension from the load support point. In this case, preferably, the weight unit is thicker at a section near the load support point than that at other section. More preferably, the weight unit is increasingly thinner away from a vicinity of the load support point toward its trailing end. The weight unit is formed to be thick around the load support point taking possible deformation into account but to be increasingly thinner away from the load support point. This is because the trailing end is unlikely to be affected by deformation even though its rigidity is somewhat low and because in contrast, reducing the weight of the trailing end enables a reduction in the magnitude of deformation and thus in inertia moment.  
         [0028]     It is preferred that the weight unit is formed only in a trailing end side of the suspension from the load support point. If the deformation at the load support point does not create any problems, the weight unit need not be formed to surround the load support point as described above.  
         [0029]     It is also preferred that the weight unit is made of a molded resin. In case that the weight unit is formed of a molded resin, the degree of freedom in shape is so high that the desired shape can be created. Further, because the thickness can be increased without an increase in weight, it is possible to improve the shock resistance. That is, the employment of the resin material enables the mass to be reduced than that employing the metal material at the sacrifice of a decrease in Young&#39;s modulus. Thus, the thickness can correspondingly be increased to allow the use of a material excellent in Young&#39;s modulus versus specific gravity or a material having a large Young&#39;s modulus in spite of a low specific gravity. This makes it possible to increase the bending rigidity higher than that of the metal material.  
         [0030]     It is further preferred that the load support point is a projecting section provided on the support arm or on the suspension.  
         [0031]     It is preferred that the support arm is fixed to the horizontal rotation-bearing unit.  
         [0032]     It is also preferred that the load generation unit includes a plate spring coupled with the suspension and the support arm.  
         [0033]     It is further preferred that the suspension includes a rigid load beam, and a flexure fixed to the load beam, the flexure having an elasticity to control a flying attitude of the head slider mounted at the leading end section of the suspension. In this case, preferably, the load generation unit includes a plate spring formed integrally with the load beam and coupled with the support arm.  
         [0034]     It is preferred that the head support mechanism further includes an actuator unit, that is a VCM, fixed to the horizontal rotation bearing unit to rotatively move the support arm and the suspension in a direction parallel to the surface of the recording medium.  
         [0035]     Furthermore, the disk drive apparatus preferably includes a plurality of recording media, a plurality of the HAAs sharing the horizontal rotation bearing unit, and the single actuator, that is, a VCM, fixed to the horizontal rotation bearing unit to rotatively move the plurality of the HAAs in a direction parallel to the surface of the recording media.  
         [0036]     Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0037]      FIG. 1 , already described, is a side view illustrating a schematic configuration of an HAA already proposed by the inventors;  
         [0038]      FIG. 2  is a plan view schematically illustrating a configuration of a main part of a magnetic disk drive apparatus as a preferred embodiment according to the present invention;  
         [0039]      FIGS. 3   a  to  3   d  are an elevation view, a plan view, a side view and a bottom view illustrating two HAAs mounted in the magnetic disk drive apparatus shown in  FIG. 2 ;  
         [0040]      FIG. 4  is an exploded perspective view illustrating the two HAAs shown in  FIGS. 3   a  to  3   d;    
         [0041]      FIG. 5  is a perspective view illustrating the two HAAs shown in  FIGS. 3   a  to  3   d;    
         [0042]      FIG. 6  is a perspective view illustrating the two HAAs of  FIGS. 3   a  to  3   d  as seen from the opposite direction;  
         [0043]      FIG. 7  is an exploded perspective view illustrating two HAAs and a VCM coil section mounted in the magnetic disk drive apparatus shown in  FIG. 2 ;  
         [0044]      FIG. 8  is a perspective view illustrating the HAAs and VCM coil section shown in  FIG. 7 ;  
         [0045]      FIG. 9  is a perspective view illustrating a configuration of a weight member in the embodiment of  FIG. 2 ;  
         [0046]      FIG. 10  is a side view illustrating a thickness distribution of the weight member in the embodiment of  FIG. 2 ;  
         [0047]      FIG. 11  is a side view illustrating a schematic configuration of the HAA in the embodiment of  FIG. 2 ;  
         [0048]      FIG. 12  is a view schematically illustrating operations of a balance structure in the HAA shown in  FIG. 11 ;  
         [0049]      FIG. 13  is a perspective view schematically illustrating a configuration of a weight member in another embodiment according to the present invention; and  
         [0050]      FIG. 14  is a perspective view schematically illustrating a configuration of a weight member in further embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]      FIG. 2  schematically illustrates a configuration of a main part of a magnetic disk drive apparatus as a preferred embodiment according to the present invention,  FIGS. 3   a  to  3   d  illustrate two HAAs mounted in the magnetic disk drive apparatus shown in  FIG. 2 ,  FIGS. 4 and 5  illustrate the two HAAS,  FIG. 6  illustrates the two HAAs as seen from the opposite direction, and  FIGS. 7 and 8  illustrate two HAAs and a VCM coil section mounted in the magnetic disk drive apparatus shown in  FIG. 2 . In all these figures, the illustration of a wiring pattern is omitted.  
         [0052]     In  FIG. 2 , reference numeral  20  designates a single magnetic disk with a diameter of about 1 inch, which rotates around a shaft  21 . Reference numeral  22  designates two HAAs having two magnetic head sliders that are mounted at leading end sections of the respective HAAs and opposed to the respective surfaces of the single magnetic disk  20 , and a single VCM coil section  23  mounted at the trailing end sections of the HAAs. Reference numeral  24  designates a bearing housing for rotatively moving a support arm  25  of the two HAAs in a horizontal direction.  
         [0053]     The VCM is configured by a coil section  23  and a yoke section (not shown). The VCM rotatively moves the two HAAs  22 , stacked along an axial direction of the bearing housing  24 , in parallel to a surface of the magnetic disk  20  around the axis of the bearing housing  24  to cause the magnetic head sliders, attached to the respective HAAs, to perform a seek operation.  
         [0054]     As shown in  FIGS. 3   a  to  8 , each HAA mainly has a very rigid support arm  30 , a suspension  31 , a magnetic head slider  32  mounted at a leading end section of the suspension  31 , a plate spring  33  used to generate a load force, and a weight member  34  secured to a trailing end section of the suspension  31  to balance rotation moments.  
         [0055]     The suspension  31 , the magnetic head slider  32  and the weight member  34  constitute a balance structure that pivots around a load support point  42  that is formed by of a pair of projections ( FIG. 11 ) in a direction substantially perpendicular to the surface of the magnetic disk. The suspension  31  is coupled by a plate spring  33  with the support arm  30 . This suspension  31  is in what is called a floating state in which it is not coupled with the support arm  30  or any other members except for the plate spring  33  and the pair of projections.  
         [0056]     The two support arms  30  are fixed to a bearing housing  35  ( 24 ) that can be rotatively moved in parallel to the surface of the magnetic disk or in a horizontal direction. More concretely, the bearing housing  35  is inserted into mounting holes in the two support arms  30  and is fixedly clamped so as to be sandwiched between a flange section  35   a  of the bearing housing  35  and a fixing sleeve  36  that is coaxial with the bearing housing  35 . A predetermined spacing is maintained between the two support arms  30  by inserting a spacer  37  that is coaxial with the bearing housing  35 , between the support arms  30 .  
         [0057]     Actually, as shown in  FIGS. 7 and 8 , a coil section  38  ( 23 ) of a VCM that is an actuator rotatively driving the support arm  30 , namely the bearing housing  35 , is attached to the rear of the spacer  37 .  
         [0058]     The support arm  30  is made of a very rigid material, for example, a thick stainless steel plate. Although not shown, a pair of projections constituting a load support point is provided on the back of leading end side sections  30   a  and  30   b . The plate spring  33  of the suspension  31  is fixed to the back of a leading end section  30   c  of the support arm  30 .  
         [0059]     The suspension  31  is constituted by a relatively rigid load beam  39 , an elastic flexure  40  supported by the load beam  39 , and a wiring member (not shown).  
         [0060]     The load beam  39  is formed of a single metal plate such as a stainless steel plate (for example, SUS304TA) with a thickness of about 40 to 60 μm, which is more rigid than the flexure  40 , or a multilayered plate member with a metal plate layer such as a stainless steel plate (for example, SUS304TA), a resin layer of polyimide or the like and a metal plate layer such as a stainless steel plate (for example, SUS304TA) stacked each other. Side edges of the load beam  39  are made more rigid by box-bending  39   a.    
         [0061]     In this embodiment, the load beam  39  is extended to the rear of the bearing housing  35 . In the middle of the load beam  39 , the plate spring  33  is integrally formed with the load beam  39  so as to couple the load beam  39  namely the suspension  31  to the support arm  30 . More concretely, the plate spring  33  is formed together with the load beam  39  by cutting out the same plate material, or the plate spring  33  is formed by welding a discrete plate spring to the load beam  39 .  
         [0062]     The plate spring  33  is pressed and bent by the projections  42  at the trailing end section of the load beam  39 . This plate spring  33  is deformed by the projection  42  into a three-dimensional bent shape in which the top of the spring plate extends toward the front of the load beam with leaving from a surface of the load beam.  
         [0063]     The flexure  40  is formed of a metal plate such as a single elastic stainless steel plate (for example, SUS304TA) with a thickness of about 20 to 30 μm. An elastic tongue section is formed at a leading end section of the flexure  40  to flexibly support the magnetic head slider  32  to stabilize its flying attitude. In this embodiment, the flexure  40  is entirely fixed to the load beam  39  except for a rear tail section  40   a  on or to which an external connection pad for the wiring member is formed or adhered.  
         [0064]     Although not shown, on the flexure  40  formed are trace conductors, connection pads and the like for a thin film magnetic head element as a wiring member. The wiring member may be configured by directly forming the trace conductors, the connection pads and the like on the surface of the flexure  40  or by adhering a flexible print circuit (FPC) formed by stacking the trace conductors on the resin layer to the surface of the flexure  40 .  
         [0065]     In this embodiment, on the magnetic head slider  32 , a composite thin-film magnetic head element with a write head element and an MR read head element.  
         [0066]     Position, shape and weight of the weight member  34  are determined so that the center of gravity of the suspension  31  including the magnetic head slider  32  coincides with the load support point. The weight member  34  is integrally formed at the trailing end section of the load beam  39  of the suspension  31 .  
         [0067]     The most important point of this embodiment is that the weight member  34  is formed so as to surround the bearing housing  35  all around its periphery. This allows the weight member  34  to be arranged around the bearing housing  35  so as to place this bearing housing center. It is thus possible to prevent an increase in inertia moment during a seek operation. Also, because it is unnecessary to extend the trailing end of the load beam of the suspension of the balance structure in order to maintain balance, inconvenient interference of the trailing end of the load beam with the bearing housing can be avoided. Further, since the length of the trailing end side of the load beam can be freely set, the balancing of moments can be easily performed. Of course, a high shock resistance can be obtained. In addition, the weight of the trailing end section of the load beam  39  can be reduced to allow the weight member  34  to be extended and located outside the magnetic disk. This avoids the interferences of the HAA with the magnetic disk surface.  
         [0068]     The second important point of this embodiment is that the weight member  34  is integrated with the load beam  39  by molding, for example, a liquid crystal polymer that is a molding resin or a resin such as polyphenylene sulfide. In case that the weight member  34  is formed of a molded resin, the degree of freedom in shape is so high that the desired shape can be created. Further, because the thickness can be increased without an increase in weight, it is possible to improve the shock resistance. That is, the employment of the resin material enables the mass to be reduced than that employing the metal material at the sacrifice of a decrease in Young&#39;s modulus. Thus, the thickness can correspondingly be increased to allow the use of a material excellent in Young&#39;s modulus versus specific gravity or a material having a large Young&#39;s modulus in spite of a low specific gravity. This makes it possible to increase the bending rigidity higher than that of the metal material.  
         [0069]     Moreover, according to this embodiment, the balance structure is employed. Namely, the load support point is operating as a fulcrum, and the suspension  31  and the magnetic head slider  32  located at the leading end side with respect to the fulcrum are balanced with the suspension  31  and the weight member  34  located at the trailing end side with respect to the fulcrum. This eliminates the need for each HAA to balance with respect to the VCM. Consequently, it is easy to provide a configuration in which a single VCM drives a plurality of HAAs stacked each other.  
         [0070]     As shown in  FIG. 9 , in this embodiment, furthermore, the weight member  34  is formed to surround not only the bearing housing  35  but also the plate spring  33  and load receiving sections  41   a  and  41   b  of the load beam  39 , against which load receiving sections the pair of projections of the support arm  30 , constituting the load support point, are abutted. Namely, the weight member  34  is also formed in the leading end side from the plate spring  33  and the load receiving sections  41   a  and  41   b.    
         [0071]     In general, since the load concentrates at the load support point, the load receiving sections of the load beam may be deformed and distorted to absorb energy to prevent the desired load from being obtained. However, because the weight member  34  is formed to surround the load support point as in this embodiment, the deformation of that part can be minimized.  
         [0072]     In this case, the thickness of the weight member  34  is desirably not uniform. As shown in  FIG. 10 , it is desired that the weight member  34  is configured to be thicker near the load support point than in the other parts. That is, the weight member  34  is desirably configured to be increasingly thinner from the vicinity of the load support point toward the trailing end. The weight member is thick around the load support point taking possible deformation into account but increasingly thinner away from the load support point. This is because the trailing end is unlikely to be affected by deformation even though its rigidity is somewhat low, and also because, in contrast, reducing the weight of the trailing end enables a reduction in the magnitude of deformation and thus in inertia moment. Such a shape of the weight member  34  can be easily accomplished by forming the weight member  34  using a resin mold. The weight member can also be realized using a metal plate but this is not practical in terms of the time and cost required for manufacture.  
         [0073]      FIG. 11  illustrates a schematic configuration of the HAA in this embodiment.  
         [0074]     As shown in the figure, the HAA of this embodiment has a fixed steady position in a direction substantially perpendicular to the surface of the magnetic disk  43  by fixing the support arm  30  to the bearing housing  35 . On the other hand, the load beam  39  is coupled only by the plate spring  33  with the support arm  30 . Also, using as a fulcrum the load support point  42  consisting of the pair of projections formed on the support arm  30 , the load beam  39 , the weight member  34 , the flexure  40  and the magnetic head slider  32  located between the load support point and the leading end is balanced with the load beam  39  and the weight member  34  located between the load support point and the trailing end. Therefore, in this balance structure, the HAA pivots in the direction substantially perpendicular to the surface of the magnetic disk  43 .  
         [0075]     The distance between the load support point  42  and the portion at which the support arm  30  is fixed to the bearing housing  35  is determined on the basis of the thickness of the support arm  30  and of the weight of the suspension  31  and the magnetic head slider  32 . Because it is necessary to suppress the deformation of the support arm  30  caused by an applied shock, if the weight of the suspension  31  and the magnetic head slider  32  varies, the thickness of the support arm  30  is set so as to prevent an increase in the magnitude of deformation. Normally, the magnitude of deformation is inversely proportional to the third power of the thickness. The previously described distance is determined on the basis of the thickness of the support arm  30  and of the weight of the suspension  31  and the magnetic head slider  32  so as not to increase the magnitude of deformation.  
         [0076]     It is empirically known that if the magnitude of deformation of the support arm  30  caused by the application of a shock is at most one-tenth of the distance between the load support point  42  and the surface of the magnetic disk  43 , the motion of the suspension of the balance structure is not substantially affected even when a shock is applied.  
         [0077]      FIG. 12  schematically illustrates operations of the HAA of the balance structure. In the figure, reference character m 1  designates the center of mass of a trailing end side region between the load support point and the trailing end (VCM side), and reference character m 2  designates the center of mass of a leading end side region between the load support point and the leading end (magnetic head slider side).  
         [0078]     The balance structure can be established to improve the shock resistance by matching the center of gravity of the system except for the fixed portion with the load support point  42 , that is, making right and left rotation moments m 1   1   1 , and m 2   1   2  with respect to the load support point  42  equal. In this case, when an external shock is applied, displacement also occurs at m 1  corresponding to the trailing end of the load beam. However, in this embodiment, because the weight member  34  is placed around the bearing housing  35  as previously described, it is not necessary to extend the trailing end of the load beam in order to maintain balance. As a result, the load beam does not interfere with the bearing housing  35 . Furthermore, since the length of the trailing end side of the load beam can be freely determined, the balancing of moments can be easily performed. Also, because the weight of the trailing end section of the load beam  39  can be reduced to allow the weight member  34  to be extended and located closer to the trailing end and outside the magnetic disk, it is possible to avoid the interferences of the trailing end of the load beam with the magnetic disk surface.  
         [0079]      FIG. 13  schematically illustrates a configuration of a weight member in another embodiment according to the present invention.  
         [0080]     As shown in the figure, in this embodiment, a weight member  34 ′ is configured to surround only the bearing housing. Namely, the weight member  34 ′ is formed only in the trailing end side from the plate spring  33  and the load receiving sections  41   a  and  41   b  of the load beam  39  against which the pair of projections of the support arm  30 , constituting the load support point  42  ( FIG. 11 ), is abutted. If the deformation of the load beam  39  at the load receiving sections  41   a  and  41   b  does not create any problems, the weight member need not be formed to surround the load support point as described above.  
         [0081]     Basically, other configurations, operations, advantages and variations of this embodiment are almost the same as those of the embodiment shown in  FIG. 2 .  
         [0082]      FIG. 14  schematically illustrates a configuration of a weight member in further embodiment according to the present invention.  
         [0083]     As shown in the figure, in this embodiment, a weight member  34 ″ and a load beam  39 ′ are U-shaped and formed to be present only around the periphery of the bearing housing except for its trailing end section. Namely, the weight member  34 ″ is formed only the leading end side from the plate spring  33  and the load receiving sections  41   a ′ and  41   b ′ of the load beam  39 ′ against which the pair of projections of the support arm  30 , constituting the load support point, is abutted.  
         [0084]     In other words, the weight member  34 ″ and the load beam  39 ′ in this embodiment is obtained by cutting the weight member  34  and the load beam  39  shown in the embodiment of  FIG. 2 , so as to eliminate the latter half of the bearing housing position. Such a shape enables the total length of the suspension to be reduced while providing a certain length of the trailing side. This provides a very high shock resistance performance.  
         [0085]     Basically, other configurations, operations, advantages and variations of this embodiment are almost the same as those of the embodiment shown in  FIG. 2 .  
         [0086]     In the above embodiments, the load support point is constituted by the pair of projections formed on the support arm. However, a pair of projections may be formed on the load beam of the suspension or a single linear projection may be used in place of the pair of independent dot-like projections.  
         [0087]     In the abovementioned embodiments, a single magnetic disk and two HAAs are provided in the magnetic disk drive apparatus. However, in modifications, a plurality of magnetic disks and three or more HAAs may be provided in the magnetic disk drive apparatus. In the latter case, the three or more HAAs may be attached to the bearing housing and be rotatively movably driven in the horizontal direction using a single VCM.  
         [0088]     The present invention has been described in conjunction with the HAA including the thin-film magnetic head element and magnetic disk drive apparatus with the HAA. However, the present invention is not limited to such HAA and magnetic disk drive apparatus. Obviously, the present invention is applicable to an HAA provided with a head element other than the thin-film magnetic head element, for example, an optical head element and a disk drive apparatus with the HAA.  
         [0089]     Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.