BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a head suspension of a hard disk drive incorporated in an information processor such as a personal computer.  
         [0003]     2. Description of the Related Art  
         [0004]     A head suspension of a hard disk drive includes a load beam, a head supported with the load beam, and a slider attached to the head. The head suspension has a shock property that determines a lift-off of the slider from the surface of a hard disk when a shock is applied. The shock property of the head suspension is dependent on the weight of the load beam.  
         [0005]     For example, a first head suspension has a load beam having a thickness (t) of 51 μm, a length (lL) of 7 mm, and a gram load of 2.5 gf that is applied by the load beam to a head, and a second head suspension has a load beam having a thickness (t) of 30 μm, a length (lL) of 5.5 mm, and a gram load of 2.5 gf. If a shock of 1 msec duration (1 msec in half wavelength) is applied to these head suspensions, a slider of the first head suspension lifts at an acceleration of 628 G and a slider of the second head suspension lifts at an acceleration of 1103 G.  
         [0006]      FIG. 13  and  FIG. 14  show a relationship between lift-off G of a head suspension and lift-off G of a hard disk drive, in which  FIG. 13  is a graph showing the result of a 2.5-inch hard disk drive and in which  FIG. 14  is a graph showing the result of a 1-inch hard disk drive.  
         [0007]     The shock property of the head suspension is expressed with the magnitude of a shock at which a slider of the load beam of the head suspension is lifted from the surface. The shock property of the head suspension is referred to as “lift-off G” indicative of the magnitude of the shock that causes a lift-off of the slider. The “lift-off G” is also indicative of the shock property of the hard disk drive.  
         [0008]     In the 2.5-inch hard disk drive of  FIG. 13 , shock input including two kinds of waveforms, one having a half wavelength with 1 msec duration and the other having a half wavelength with 0.4 msec duration is applied. In the 1-inch hard disk drive of  FIG. 14 , shock input including three kinds of waveforms, one having a half wavelength with 2 msec duration, another having a half wavelength with 1 msec duration, and the remaining having a half wavelength with 0.4 msec duration is applied.  
         [0009]     In the 2.5-inch hard disk drive of  FIG. 13 , even if the lift-off G of the head suspension is increased, the lift-off G of the hard disk drive does not increase so much. In the 1 msec duration, a slope thereof is y≈0, and in the 0.4 msec duration, a slope thereof is y=0.27.  
         [0010]     On the other hand, in the 1-inch hard disk drive with a small size of  FIG. 14 , when the lift-off G of the head suspension is increased, the lift-off G of the hard disc drive increases evenly. In the 2 msec duration, a slope thereof is y=0.90, in the 1 msec duration, a slope thereof is y=0.85, and in the 0.4 msec duration, a slope thereof is y=0.81.  
         [0011]      FIG. 15  and  FIG. 16  is respectively a graph showing a change of generated acceleration to shock input at a front end of an arm to which a head suspension attached according to a time change. An abscissa indicates time and an ordinate indicates acceleration. The data shown in  FIG. 15  relates a 2.5-inch hard disk drive and the data shown in  FIG. 16  relates to a 1-inch hard disk drive. In  FIGS. 15 and 16 , magnitude of shock input is set to have 0.4 msec duration and 200 G.  
         [0012]     As is apparent from  FIG. 15  and  FIG. 16 , the 2.5-inch hard disk drive generated an arm action larger than that in the 1-inch hard disk drive. Therefore, in the 2.5-inch hard disk drive, the shock property of the hard disk drive is largely dependent on not only the weight of the head suspension but also the arm action. In contrast, in the 1-inch hard disk drive, the shock property of the hard disk drive is hardly dependent on the arm action and it is mainly dependent on the weight of the head suspension.  
         [0013]     Thereby, in a miniaturized hard disk drive such as a 1-inch hard disk drive, it has been found that the shock property of the hard disk drive can be improved by only increasing the lift-off G of the head suspension.  
         [0014]     Accordingly, to improve the shock property of a head suspension in the miniaturized hard disk drive, thinning a load beam of the head suspension to reduce weight is effective.  
         [0015]      FIG. 17  is a perspective view showing a head suspension  101  according to a related art. The head suspension  101  has a base plate  103 , a load beam  105  integrated with the base plate  103 , and a flexure  107  supported to the load beam  105 . The load beam  105  includes a rigid part or beam  109  and a resilient part or hinge  111 .  
         [0016]      FIG. 18  is a partly sectioned view showing an example of a hard disk drive in which the head suspensions  101  of  FIG. 17  are arranged. As shown in  FIG. 18 , for example, the base plate  103  of the head suspension  101  is attached to an arm  115  of a carriage  113  by swaging.  
         [0017]     The carriage  113  is turned around a spindle  119  by a positioning motor  117  such as a voice coil motor. A head  121  of the head suspension  101  is moved to a target track on a disk  123  according to pivoting of the carriage  113  around the spindle  119 .  
         [0018]     When the disk  123  rotates at high speed, the head  121  slightly floats from the disk  123  against gram load.  
         [0019]     In such a head suspension  101  including the load beam  105  integrated with the resilient part, the load beam  105  with a length l L  is made thin as countermeasure considering such a weight as described above.  
         [0020]     However, the load beam  105  made thin in order to improve the shock property, the resilient part  111  becomes thin together with the load beam. This causes higher stress acting on the resilient part  111 , so that it is impossible to increase a spring load for determing the gram load as the load applied onto the head  121  to a certain value or more.  
         [0021]     On the other hand, there is a head suspension including a rigid part and a resilient part separated from and fixed to the rigid part. According to the head suspension, the resilient part is made thinner than the rigid part in order to set the resilient part to a low spring constant and secure rigidity of the rigid part. When the load beam is made thin entirely in order to improve the shock property while keeping the relationship between the thicknesses of the rigid part and resilient part, the resilient part is also made thin. It is impossible to increase a spring load to a certain value or more like the above case.  
         [0022]     To solve the problem, expanding a width of a base end side of the load beam  105 , namely, a width of the resilient part  111  is effective.  
         [0023]      FIG. 19  is a plan view showing a hard disk drive  125  in which the head suspension  101  of  FIG. 17  is incorporated.  
         [0024]     As shown in  FIG. 19 , the head suspension  101  is installed in the hard disk drive  125  for example. The hard disk drive  125  has the arms  115 , a wire  127 , disks  123 , and the like. When a width B of the base end side of the load beam is expanded, the width of the arm  115  to which the head suspension  101  is attached is also expanded. This results in overlapping of the arm  115  with the disk  123  or interference thereof with the wire  127  in plan view of  FIG. 19 . Overlapping the arm  115  with the disk  123  involves a risk that the arm  115  and the disk  123  come in contact with each other due to shock input. Therefore, the overlapping of the arm  115  with the disk  123  and interference of the arm  115  with the wire  127  must be avoided.  
         [0025]     Even if the width B of the base end side of the load beam  105  is expanded such that the arm  115  of the head suspension  101  does not overlap with the disk  123  or it does not interfere with the wire  127 , it prevent the hard disk drive  125  from miniaturizing. The related art mentioned above is disclosed in Japanese Unexamined Patent Application Publication H09-282624.  
       SUMMARY OF THE INVENTION  
       [0026]     An object of the present invention is to solve the problem of a head suspension, having a thin load beam to satisfy required shock property, that requires an extension of a width of a base end side of the load beam to increase a spring load of the resilient part.  
         [0027]     In order to accomplish the object, an aspect of the present invention provides a head suspension having a rigid part and resilient part whose thickness being set to be relatively grater than that of the rigid part in order to make a load beam thin and increase a spring load of the resilient part, and allow miniaturization of a hard disk drive.  
         [0028]     Accordingly, the spring load of the resilient part can be increased while the shock property of the head suspension being maintained without extensions of a base end side of the load beam. The hard disk drive can be miniaturized while the shock property thereof being improved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a perspective view showing a head suspension according to a first embodiment of the present invention;  
         [0030]      FIG. 2  is a plan view showing the head suspension of  FIG. 1 ;  
         [0031]      FIG. 3  is a partly sectioned side view partly showing the head suspension of  FIG. 2 ;  
         [0032]      FIG. 4  is a list showing a relationship among a thickness of a beam (rigid part) of a load beam of the head suspension, a thickness of a hinge (resilient part) of the load beam, and shock property of the head suspension according to the first embodiment;  
         [0033]      FIG. 5  is a graph based on the list of  FIG. 4 ;  
         [0034]      FIG. 6  is a graph showing a relationship between a gram load and a width of the hinge (hinge width) measured on load beams having different thicknesses (beam thickness) according to the first embodiment;  
         [0035]      FIG. 7  is a graph showing a relationship between the gram load and the width of the hinge measured on load beams having different lengths according to the first embodiment;  
         [0036]      FIG. 8 a  graph showing a relationship between the thickness of a load beam and a lift-off level (G-lift-off) according to the first embodiment;  
         [0037]      FIG. 9  is a graph showing a relationship between a gram load and a width of the hinge according to the first embodiment;  
         [0038]      FIG. 10  is a graph showing a relationship between the gram load and the width of the hinge according to the first embodiment;  
         [0039]      FIG. 11  is a perspective view showing a head suspension according to a second embodiment of the present invention;  
         [0040]      FIG. 12  is a partly sectioned side view partly showing the head suspension of  FIG. 11 ;  
         [0041]      FIGS. 13 and 14  are respectively a graph showing a relationship between lift-off G of a head suspension and lift-off G of a hard disk drive according to a related art;  
         [0042]      FIGS. 15 and 16  are respectively a graph showing a change of a generation acceleration when shock is input into a front end of an arm of the hard disk drive to which the head suspension according to a related art is attached;  
         [0043]      FIG. 17  is a perspective view showing a head suspension according to a related art;  
         [0044]      FIG. 18  is a partly sectioned view showing an example of a hard drive disk drive in which the head suspension of  FIG. 17  is installed; and  
         [0045]      FIG. 19  is a plan view partly showing the hard disk drive of  FIG. 18 . 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0046]     Head suspensions according to embodiments of the present invention will be explained in detail.  
         [0047]     Each embodiment sets a resilient part of a head suspension to be relatively thicker than that of a rigid part of the head suspension, to miniaturize a hard disk drive while improving shock properties of the head suspension and the hard disk drive.  
       First Embodiment  
       [0048]      FIG. 1  and  FIG. 2  show a head suspension according to a first embodiment of the present invention, in which  FIG. 1  is a perspective view and  FIG. 2  is a plan view.  
         [0049]     The head suspension  1  shown in  FIGS. 1 and 2  is for 1-inch size, for example. The head suspension has a load beam  3 , an arm  5 , and a flexure  7 .  
         [0050]     The load beam  3  applies a load onto a head  9 . The head  9  is arranged at a front end of the load beam  3 , to write and read data to and from the disk. The load beam  3  includes a beam  11  serving as a rigid part and a hinge  13  serving as a resilient part.  
         [0051]     The hinge  13  is prepared separately from the beam  11 . A first end  15  of the hinge  13  is fixed and supported to a base end  17  of the beam  11 , while a second end  19  of the hinge  13  is fixed and supported to the arm  5 .  
         [0052]     The arm  5  includes an integral base plate  21  serving as a base for supporting the second end  19  of the hinge  13 . The arm  5  has a fitting hole  23  to be fitted to a carriage of the hard disk drive, so that the head suspension  1  may turn around a spindle of the carriage.  
         [0053]     The flexure  7  includes a conductive thin plate made of, for example, a resilient stainless-steel rolled plate (SST). On the thin plate, an insulating layer is formed. On the insulating layer, wiring patterns are formed. The flexure  7  is fixed to the beam  11  by, for example, laser welding. One end of the wiring patterns are electrically connected to write and read terminals supported on a slider  25  of the head  9 . The other end of the wiring patterns are extended toward the arm  5 .  
         [0054]     The beam  11  is made of, for example, a nonmagnetic SUS304 (Japanese Industrial Standard) stainless-steel plate. The beam  11  extended from a front end  27  to the base end  17  is generally narrow. The beam  11  includes a main body  29  with a joint  31  at an end of the main body  29 . The joint  31  is connected to the first end  15  of the hinge  13 . Each side edges of the joint  31  in an across-the-width direction are constituted as remaining cut portions which is cut along the same when a plurality of beams are formed from a plate material. The front end  27  of the beam  11  has a load/unload tab  29 . In vicinity of the front end  27 , the beam  11  has a dimple  35 .  
         [0055]     Each side edge of the main body  29  in an across-the-width direction of the beam  11  has a rail  37  that is formed by box-bending the side edge of the beam  11  in a thickness direction of the beam  11 . The rail  37  is extended along the side edge of the main body  29 .  
         [0056]     The hinge  13  is made of, for example, a resilient SUS301 (Japanese Industrial Standard) stainless-steel plate. The hinge  13  is divided into two branches to have in a bifurcated shape in the plan view of  FIG. 2 . The bifurcated shape of the hinge  13  is for reducing or eliminating a step formed between the arm  5  and the load beam  3  when the flexure  7  is extended from the main body  29  side of the load beam  3  to the base plate  21  side of the arm  5 .  
         [0057]     The first end  15  of the hinge  13  is fixed to the joint  31  of the beam  11  in the across-the-width direction at weld spots  39  by, for example, laser welding. The second end  19  of the hinge  13  is fixed to the base plate  21  at weld spots  41  and  43  by, for example, laser welding.  
         [0058]      FIG. 3  is a partly sectioned side view partly showing the head suspension of  FIG. 2 . As shown in  FIG. 3 , the head suspension  1  is set a thickness t 1  of the hinge  13  to be relatively larger than a thickness t 2  of the beam  11 . This configuration is effective to thin the load beam  3  and improve a spring load of the hinge  13 . The spring load determines the gram load as the load applied onto the head  9 . According to the first embodiment, the thicknesses t 1  and t 2  are set to 25 μm and 20 μm, respectively.  
         [0059]     The thicknesses t 1  and t 2  may be optionally set based on a hard dirk drive in which the head suspension  1  is installed, provided that the thickness t 1  of the hinge  13  is greater than the thickness t 2  of the beam  11  to thin the load beam  3  and improve the spring load of the hinge  13 .  
         [0060]      FIG. 4  is a list showing a relationship among a beam thickness, a hinge thickness, and shock property of a head suspension, and  FIG. 5  is a graph based on the list of  FIG. 4 . The shock property of the head suspension is expressed with the magnitude of a shock at which a slider of the load beam is lifted from the surface of a disk. The phenomenon that a slider of a load beam lifts off from the surface of a disk in response to the application of a shock is referred to as “G-lift-off.” The “G-lift-off” is also indicative of the magnitude of the shock that causes a lift-off of the slider. Further, the “G-lift-off” is also indicative of the shock property of the hard disk drive.  
         [0061]     In  FIGS. 4 and 5 , the thickness t 1  of the hinge  13  is fixed at 25 μm, and the thickness t 2  of the beam  11  is changed as 35, 30, 25, and 20 μm. In response to these reductions in the thickness, the head suspension  1  increases its G-lift-off as 357.2 G/gf, 386.0 G/gf, 419.1 G/gf, and 462.3 G/gf.  
         [0062]     When the thickness t 2  of the beam  11  is 20 μm that is smaller than the thickness t 1  of the hinge  13  of 25 μm, the head suspension  1  greatly improves its G-lift-off as shown in grayed cells in the table of  FIG. 4 .  
         [0063]     FIGS.  6  to  8  are graphs showing test results that verify that thinning a beam thinner than a hinge improves the shock property of a head suspension.  
         [0064]      FIG. 6  shows a relationship between the width of a hinge and a gram load measured on load beams having different thicknesses. An abscissa indicates the width of a hinge (hinge width), and an ordinate indicates gram load. The load beams shown in  FIG. 6  each include a beam and a hinge that are integral with each other. The load beams have thicknesses of 20 μm, 25 μm, and 30 μm, respectively, a length (lL) of 6.25 mm, and a stress limit of 70 kgf/cm 2  because each is made of SUS304.  
         [0065]     If a width allowed for a hinge is 2.0 mm, the hinge may be drilled to have a hole to realize an effective width of, for example, 1.2 mm. If a hinge has an effective width of 1.5 mm and a thickness of 20 μm which is equal to the thickness of a load beam, a limit gram load applied by the hinge is 1.5 gf as shown in  FIG. 6 . A hinge having an increased thickness of 30 μm and an effective width of 1.2 mm can achieve a gram load of 2.0 gf.  
         [0066]      FIG. 7  is a graph showing a relationship between the width of a hinge and a gram load measured on load beams having different lengths. An abscissa indicates the width of a hinge, and an ordinate indicates gram load. The load beams shown in  FIG. 7  have lengths of 5.50 mm, 6.25 mm, and 7.00 mm, respectively, a thickness (t) of 20 μm, and a stress limit of 70 kgf/cm 2  because each is made of SUS304.  
         [0067]     As is apparent in  FIG. 7 , changes in the length of a load beam only slightly influence the gram load of the load beam.  
         [0068]     It is understood from  FIGS. 6 and 7  that the thickness, not length, of a load beam greatly influences a gram load applied by the load beam. Namely, a narrow load beam for a miniaturized hard disk drive must have a thick of the hinge.  
         [0069]      FIG. 8  is a graph showing a relationship between the thickness of a load beam and a lift-off level (G-lift-off). An abscissa indicates the thickness of a load beam and an ordinate indicates G-lift-off.  
         [0070]     It is clear in  FIG. 8  that the thicker the load beam, the poorer the G-lift-off or shock property of the load beam.  
         [0071]     From FIGS.  6  to  8 , it is apparent that the hinge must be thick and the beam must be thin to secure a high G-lift-off level and a high gram load.  
         [0072]     For this, the first embodiment makes the thickness t 1  of the hinge  13  thicker than the thickness t 2  of the beam  11 , to thereby thin the load beam  3 A and increase the resilience of the hinge  13 . As a result, the head suspension  1 A of the second embodiment can secure a high G-lift-off level and a high gram load.  
         [0073]     In generally, a load beam is made of SUS304 as nonmagnetic stainless-steel material in order to avoid electrically affecting on the head  9 . According to the first embodiment, the hinge  13  is separated from and connected to the beam  11 . Therefore, SUS301 as resilient stainless-steel material whose magnetism is stronger than that of SUS304 can be used as material for the hinge  13 , as described above.  
         [0074]      FIG. 9  is a graph showing a relationship between a gram load and a width of a hinge made of SUS304, while  FIG. 10  is a graph showing a relationship between a gram load and a width of a hinge made of SUS301. In  FIGS. 9 and 10 , an abscissa indicates a hinge width and an ordinate indicates a gram load. In  FIGS. 9 and 10 , a load beam has a beam and a hinge integrated with the beam. The length of the load beam is set to 6.25 mm, and the thickness thereof is set to 20 μm, 25 μm, and 30 μm. According to the head suspension of  FIG. 9 , the stress limit is 70 kgf/cm 2 . According to the head suspension of  FIG. 10 , the stress limit was 90 kgf/cm 2 .  
         [0075]     When the hinge width is 1.2 mm and the hinge thickness is 25 μm, the limit of the gram load is 1.4 gf according to the head suspension of  FIG. 9 . In contrast, the limit of the gram load is 1.8 gf in the same condition as  FIG. 9  according to the head suspension of  FIG. 10 .  
         [0076]     Therefore, the first embodiment separates the hinge  13  from the beam  11  and applies SUS301 as material of the hinge  13  in addition to the thickness setting, so that it is possible to realize high spring load of the hinge  13 . When the spring load is constant, the hinge width can be made further narrow, and the spring constant can be reduced.  
         [0077]     When only the shock property of the head suspension is taken into consideration, it is advantageous to shorten the load beam. However, the length of the load beam influences frying height characteristic. Accordingly, when the frying height characteristic is taken into consideration, a head suspension must be maintained the load beam in a certain length. Although the length of the load beam, therefore, is selected optionally, the load beam can not be shortened extremely. In general, a head suspension having a load beam with a length of 7 mm is used in a 2.5-inch hard disk drive, and a head suspension having a load beam with a length of 6.25 mm is used in a 1-inch hard disk drive.  
         [0078]     According to the first embodiment, even if the load beam  3  with a length of 6.25 mm is used in the 1-inch hard disk drive, the required shock property of the head suspension  1  can be satisfied because the hinge thickness influences the gram load largely as compared with the load beam length as apparent from  FIGS. 6 and 7 .  
         [0079]     In this way, the head suspension  1  of the first embodiment has the rigid part or beam  11  and the resilient part or hinge  13  whose thickness is relatively greater than that of the beam  11  so as to thin the load beam  3  and increase the spring load of the hinge  13 . With this configuration having no extension of the base end side of the beam  11  in the across-the-width direction, the first embodiment can increase the spring load to maintain the G-lift-off of the head suspension  1 , while miniaturizing the hard disk drive and improving the G-lift-off of the hard disk drive.  
       Second Embodiment  
       [0080]      FIGS. 11 and 12  show a head suspension  1 A according to a second embodiment of the present invention, in which  FIG. 11  is a perspective view and  FIG. 12  is a partly sectioned side view of  FIG. 11 . Parts of the second embodiment that are the same as those of the first embodiment are represented with the same reference numerals or the same reference numerals plus “A”.  
         [0081]     As shown in  FIGS. 11 and 12 , the head suspension  1 A has a load beam  3 A which supports a head  9 A. The load beam  3  includes a beam  11 A and a hinge  13 A integrated with the beam  11 A. In this case, the load beam  3 A is made of SUS304 which does not electrically affect on the head  9 A.  
         [0082]     Each side edge in an across-the-width direction of the beam  11  has a rail  37 A. The rail  37 A is extended from a front end to a base end of the beam  11 A along the side edge to reach a first end  15 A of the hinge  13 A. Therefore, longitudinal stiffness of the load beam  3 A is increased and the property of the head suspension  1 A is improved.  
         [0083]     Even in the second embodiment, a thickness t 1  of the hinge  13 A is set to be relatively larger than a thickness t 2  of the beam  11 A so that the load beam  3 A is made thin and the spring load of the hinge  13 A is increased. In the second embodiment, t 1  is set to 25 μm and t 2  is set to 20 μm. An area, having the thickness t 2 , of the beam  11 A is spread from a base end part  51  of beam  11 A adjacent to the hinge  13 A to a position  53  short of a tab  33  of the beam  13 A in an extending direction of the beam  11 A and is spread between the side edges in the across-the-width direction of the load beam  11 A.  
         [0084]     Setting the thickness t 2  of the beam  11 A is performed by partial etching the beam  11 A, for example.  
         [0085]     Accordingly, even in the second embodiment, operation and effect similar to those in the first embodiment can be achieved.  
         [0086]     In the second embodiment, the number of parts can be reduced.
A head suspension for a disk drive is capable of improving shock property of the hard disk drive while miniaturizing the hard disk drive. A head suspension has a base plate to be attached to a carriage and turned around a spindle of the carriage, a load beam which includes a beam and a hinge, a base end of the beam being supported to the base plate through the hinge and which applies a load onto a head for writing and reading data to and from a disk at a front end side thereof, and a flexure which connects the head to writing and reading wires and supports the head and which is attached to the load beam, where the hinge is set to be relatively thicker than the beam so that the load beam is made thin and the load is increased.