Patent Publication Number: US-6337781-B1

Title: Magnetic head device and magnetic disk drive for reading information from or writing information to a medium

Description:
This is a continuation of application Ser. No. 08/359,699, filed Dec. 20, 1994, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic head device and a magnetic disk drive which is capable of reading information from writing information to a magnetic recording medium, as the magnetic head device is kept in contact with the magnetic recording medium. 
     2. Description of the Related Art 
     Efforts continue to increase the recording density of a magnetic disk drive using a hard disk. Due to the increase of recording density, the spacing between a magnetic head device (called “head” hereinafter) and a magnetic recording disk (called “disk” hereinafter) serving as a magnetic recording medium, is decreasing. Ultimately, it will be necessary to read/write information on the disk as the head is kept in contact with the disk. 
     The most important problem for carrying out the contact reading/writing is to reduce wear of the head and the disk. In order to reduce the wear, it is necessary to keep the contact force applied between the head and the disk at a low level and stable. 
     A brief structure of a prior art head having a taper-flat type slider will be described with reference to FIG.  13 . 
     A taper-flat type slider  100  has a slider surface  102  which is opposed to a disk  101 . The slider surface  102  includes a tapered surface  102   a  being slanted in a direction close to the disk along the rotating direction of the disk(shown by the arrow in FIG.  13 ), and a flat surface  102   b  being substantially parallel to the disk, when the disk stops rotating. Dynamic pressure (gage pressure) Ph generated by fluid-flow caused by rotation of the disk is applied to the slider surface  102 . According to the flying slider method used in a prior art hard disk drive, the slider  100  flies above the disk  101  at a predetermined distance by means of the dynamic pressure Ph. In this case, however, the trailing edge serving as a contact portion  103  of the slider  102  is kept in contact with the surface of the disk  101 . A magnetic pole(not shown) is mounted on the contact portion  103  to read/write information on the disk  101 , as the magnetic pole is kept in contact with the disk. 
     There are three forces being applied to the slider  100  when the disk  101  rotates. They are a load F, a fluid force fh, and a contact force fc. The load F is applied at a pivot position  104  by a suspension (not shown). The fluid force is a sum of the dynamic pressure Ph. It is applied at the position  105  at the center of the distribution of the dynamic pressure Ph. The contact force is applied at the contact portion  103  from the disk  101 . 
     The relation of these forces (F, fh, fc) is shown in the following equation (1).              fc   =           1      h     -     1      p         1      h          F             (   1   )                         
     “lp” is the lateral distance between the pivot position  104  and the contact portion  103 , and “lh” is the lateral distance between the position  105  where the fluid force is applied and the contact portion  103 . 
     According to equation (1), it is necessary that the distance lh becomes long and a distance between the position  105  and the pivot position  104  is short, in order to keep the contact force fc at a low level. However, in the prior art taper-flat type slider, it is difficult to set the distance lh to be long, because the position  105  is located along the rotating direction of the disk  101  from the center of the total length of the slider  100 . 
     The variation of the contact force fc according to the positioning error between the slider surface  102  and the contact portion  103  will be described. 
     As shown in FIG. 14, the slider  100  has three degrees of freedom. They are pitching( 108 ), rolling( 107 ), and translational( 106 ) degrees of freedom. Stiffness of the fluid film between the slider surface  102  and the surface of the disk  101  keeps the condition of the slider  100  stable with regard to the three degrees of freedom. For example, the pitching stiffness will be described with reference to FIGS.  15 ( a )- 15 ( c ). FIG.  15 ( b ) shows the standard condition of the slider. If the angle α′ formed between the slider surface  102  and the surface of the disk  101  (pitch angle) becomes smaller than the pitch angle α in the standard condition, as shown in FIG.  15 ( a ), moment  109  occurs to restore the pitch angle. If the pitch angle α″ becomes larger than the pitch angle α in the standard condition, as shown in FIG.  15 ( c ), moment  110  also occurs to restore the pitch angle. According to the prior art taper-flat type slider, the slider surface  102  is formed long enough to secure the pitching stiffness in the rotating direction of the disk. 
     When a positioning error between the slider surface  102  and the contact portion  103  is made, the contact force fc varies. This variation of the contact force fc will be described with reference to FIGS.  16 ( a )- 16 ( c ). 
     FIG.  16 ( b ) shows the standard condition. FIG.  16 ( a ) shows the condition that the contact portion  103  extends further than the contact portion of the standard condition. In this case, as the pitch angle α′ in FIG.  16 ( a ) becomes smaller than the pitch angle α in the standard condition, the moment  109  occurs to restore the pitch angle. Therefore, the contact force increases by dfc to balance the moment  109 . 
     FIG.  16 ( c ) shows the condition that the contact portion  103  is recessed relative to the contact portion of the standard condition. In this case, as the pitch angle α″ becomes larger than the pitch angle α in the standard condition, the moment  110  occurs to restore the pitch angle. Therefore, the contact force decreases. Finally, the contact force fc becomes zero, and the slider  100  floats above the disk  101 . 
     The influence of inertia which occurs due to the undulation of the disk, the vibration of the disk, or shock applied to the device from outside will be described with reference to FIG.  17 . The inertia fg is applied at the center of gravity of the head (G) depending on the mass of the slider  100  and equivalent mass of the suspension (not shown). The position of G is located on the line connecting the center of gravity of the slider  100  (Gh) with the pivot position (Gp) where the equivalent mass of the suspension is applied. The inertia fg is divided between the variation of the fluid force dfh and the variation of the contact force dfc. The variation of the contact force dfc is shown in the following equation (2).              dfc   =           1      h     -     1      g         1      h          fg             (   2   )                         
     “lg” is the lateral distance between the position of G and the contact portion  103 . 
     According to equation (2), it is necessary for the distance lh between the position  105  where the fluid force is applied and the contact portion  103  to be long and for the position  105  to be located near the position of G in order to reduce the variation of the contact force dfc. But, in the prior art taper-flat type slider, it is difficult to set the distance lh to be long, because the position  105  and the pivot position (Gp) are located along the rotating direction of the disk  101  from the center of the total length of the slider  100 . 
     A phenomenon of stiction between the head and the disk will be described. In a prior art magnetic disk drive having a flying type slider, the slider lands on the disk and the slider surface is kept in contact with the surface of the disk, when the disk stops rotating. It is called a constant·start·stop method (CSS method) as usual. According to the CSS method, stiction occurs by the influence of water or lubricant existing between the slider and the disk. Stiction prevents the disk from starting to rotate. In the prior art, the surface of the disk is made uneven to prevent stiction. However, it is necessary for the surface of the disk to be flat in the case of contact reading/writing, so that the the contact condition is stable. Therefore, stiction is a significant problem in the practice of contact reading/writing. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a magnetic head device which can maintain a contact condition between the magnetic head device and a magnetic recording medium stably, which can maintain a contact force being applied to the magnetic head device from the magnetic recording medium at a low level, and which can reduce wear of the magnetic head device and the magnetic recording medium. 
     Another object of the present invention is to provide a magnetic disk drive for which life can be extended, as the wear of the magnetic head device and the magnetic recording medium is reduced. 
     In accordance with the present invention, there is provided a magnetic head device for reading information from or writing information to a rotating magnetic recording medium, comprising: a magnetic pole for reading the information from or writing the information to the medium; and a slider supporting the magnetic pole, and to move the magnetic pole on the medium; the slider including: a contact portion supporting the magnetic pole, and to contact the medium, a flying member to fly above the medium, having a first surface for confronting the medium to receive dynamic pressure generated by fluid-flow caused by rotation of the medium, and a connecting member having a mass less than that of the flying member, coupled between the contact portion and the flying member. 
     Also in accordance with the present invention, there is provided a magnetic head device for reading information from or writing information to a rotating magnetic recording medium, comprising: a magnetic pole for reading the information from or writing the information to the medium; a slider supporting the magnetic pole, and to move the magnetic pole on the medium; the slider including: a contact portion supporting the magnetic pole, and to contact the medium, a flying member to fly above the medium, having a first surface for confronting the medium to receive dynamic pressure generated by fluid-flow caused by rotation of the medium; and means for applying a load to the slider to balance with the dynamic pressure and a contact force applied to the contact portion from the medium, wherein the first surface is a curved surface, a center of curvature of the first surface being proximate a position where the load is applied. 
     Further in accordance with the present invention there is provided a magnetic disk drive, comprising: a magnetic recording disk; means for rotating the disk; and a magnetic head device for reading information from or writing information to the disk; the head device including; a magnetic pole for reading the information from or writing the information to the disk, and a slider supporting the magnetic pole, and to move the magnetic pole on the disk; the slider including: a contact portion supporting the magnetic pole, and to contact the disk, a flying member to fly above the disk, having a first surface for confronting the disk to receive dynamic pressure generated by fluid-flow caused by rotation of the disk, and a connecting member having a mass less than that of the flying member, coupled between the contact portion and the flying member. 
     Additionally in accordance with the present invention, there is provided a magnetic disk drive, comprising: a magnetic recording disk; means for rotating the disk; a magnetic head device for reading information from or writing information to the disk; the head device including: a magnetic pole for reading the information from or writing the information to the disk, and a slider supporting the magnetic pole, and, to move the magnetic pole on the disk; the slider including: a contact portion supporting the magnetic pole, and to contact the disk, and a flying member to fly above the disk, having a first surface for confronting the desk to receive dynamic pressure generated by fluid-flow caused by rotation of the disk; and means for applying a load to the slider to balance with the dynamic pressure and a contact force applied to the contact portion from the disk, wherein the first surface is a curved surface, a center of curvature of the first surface being proximate a position where the load is applied to the slider. 
     Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention, or may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BREIF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the present invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the present invention in which: 
     FIGS.  1 ( a )- 1 ( c ) show top, side and end schematic views of a magnetic head device according to a first embodiment of the present invention; 
     FIG. 2 is a explanatory view showing a variation of the position where the fluid force is applied in FIG. 1; 
     FIGS.  3 ( a ) and  3 ( b ) show top and end schematic views of a magnetic head device according to a second embodiment of the present invention; 
     FIGS.  4 ( a ) and  4 ( b ) show top and end schematic views of a magnetic head device according to a third embodiment of the present invention; 
     FIGS.  5 ( a )- 5 ( d ) are schematic views of a magnetic head device according to a fourth embodiment of the present invention; 
     FIGS.  6 ( a )- 6 ( c ) are top, side and end schematic views of a magnetic head device according to a fifth embodiment of the present invention; 
     FIGS.  7 ( a )- 7 ( c ) are top, side and end schematic views of a magnetic head device according to a sixth embodiment of the present invention; 
     FIGS.  8 ( a )- 8 ( c ) are top, side and end schematic views of a magnetic head device according to a seventh embodiment of the present invention; 
     FIGS.  9 ( a )- 9 ( c ) are top, side and end schematic views of a magnetic head device according to an eighth embodiment of the present invention; 
     FIG. 10 is a schematic view showing a magnetic head device according to a ninth embodiment of the present invention; 
     FIGS.  11 ( a )- 11 ( c ) are explanatory views showing the variation of the contact force according to the positioning error between the slider surface and the contact portion in FIG. 10; 
     FIG. 12 is a schematic view showing a magnetic disk drive in which the magnetic head device of the present invention is used; 
     FIG. 13 is a schematic view showing a prior art taper-flat type slider including a contact portion; 
     FIG. 14 is an explanatory view showing degrees of freedom in the prior art flying type slider; 
     FIGS.  15 ( a )- 15 ( c ) are explanatory views showing the pitching stiffness of the prior art flying type slider; 
     FIGS.  16 ( a )- 16 ( c ) are explanatory views showing the variation of the contact force according to the positioning error between the slider surface and the contact portion; 
     FIG. 17 is an explanatory view showing the variation of the contact force according to the influence of inertia. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to accompanying drawings. 
     A structure of a magnetic head device according to the first embodiment of the present invention will be described with reference to FIGS.  1 ( a )- 1 ( c ) which are top, side and end views, respectively. 
     A magnetic head device (called “head” hereinafter) comprises a magnetic pole (not shown) and a slider  2 . The slider  2  includes a flying member  3 , a contact portion  4 , and a connecting member  5 . The connecting member  5  is located between the flying member  3  and the contact portion  4 . The slider  2  is formed to have a generally T-letter shape. The magnetic pole is mounted on the contact portion  4 , so that it reads/writes information to a magnetic recording disk (call “disk” hereinafter, not shown). A load F is applied to the slider  2  at a pivot position  6  with a suspension (not shown). The load F is divided between a fluid force fh, which is a sum of dynamic pressure generated by fluid-flow caused by rotation of the disk, and a contact force fc applied to a contact surface  4   a  of the contact portion  4  from the disk. The relation of these forces (F, fh, fc) is shown in previously described equation (1). 
     The connecting member  5  has a surface  5   a  which confronts the disk. The area of the surface  5   a  is smaller than that of a surface  7  of the flying member  3  which confronts the disk (slider surface). The surface  5   a  is recessed from the slider surface  7 . The contact surface  4   a  has a very small area, so that the dynamic pressure applied to the contact surface  4   a  is small. According to this structure, the fluid force fh is mainly applied to the slider surface  7 . A position  8  where the fluid force fh is applied is located far from the contact portion  4 . As a result, it is possible to keep the contact force fc at a low level, because the distance lh between the position  8  and the contact portion  4  becomes long in equation (1). 
     The mass of the connecting member  5  is less than that of the flying member  3 . The center of gravity of the head (G) depends on the mass of the flying member  3  and equivalent mass of the suspension. In the previously described equation (2), a distance lg between the position of G and the contact portion  4  becomes long. As a result, it is possible to reduce the variation of the contact force fc caused by inertia which occurs due to the undulation of the disk, the vibration of the disk, or an external shock applied to the device. Particularly, when the distance lg is equal to the distance lh, the inertia is balanced with the fluid force fh only, so the contact force fc does not vary. 
     The maximum length L of the slider surface  7  along the rotating direction of the disk (shown by the arrow in FIG.  1 ( b )) is shorter than the maximum width W of the slider surface  7  along the direction substantially perpendicular to the rotating direction of the disk. This structure is opposite to the prior art taper-flat type slider. As the length L becomes shorter, the pitching stiffness of the fluid film between the slider surface  7  and the surface of the disk becomes lower. Therefore it is possible to reduce the variation of the contact force fc according to the positioning error between the slider surface  7  and the contact portion  4 . As the width W becomes larger, the translational stiffness and rolling stiffness of the fluid film between the slider surface  7  and the surface of the disk are higher. 
     According to the prior art flying type slider, it is necessary to provide a very small space between the slider and the disk, and the dimensional accuracy of the slider must be kept at a high level. If the dimensional accuracy is reduced, it is difficult to achieve sufficient read/write performance, and a collision occurs between the slider and the disk. However, by utilizing the head of the first embodiment, the flying member  3  is far from the contact portion  4 . Therefore, it is possible to have a larger spacing than that of the flying type slider, and it is not necessary to keep the dimensional accuracy so high. 
     FIG. 2 shows a variation of the position where the fluid force is applied, when the disk rotates constantly or starts to rotate. 
     The slider surface  7  includes a tapered surface  7   a  slanted in a direction close to the disk along the rotating direction of the disk, and a flat surface  7   b  substantially parallel to the disk, when the disk stops rotating. When the disk rotates at constant rate, the position  8  where the fluid force fh is applied is located at the flat surface  7   b , and the pivot position  6  is located along the rotating direction of the disk from the position  8 . However, when the disk starts to rotate, the position  8 ′ where the fluid force fh′ is applied is located at the tapered surface  7   a . Thus according to equation (1), the contact force fc is larger when the disk starts to rotate. Wear of the contact portion  4  or the disk may occur, when the disk starts to rotate. The best way to avoid such wear is to coincide the position  8  with the position  8 ′. For example, when an area of the tapered surface  7   a  is larger than that of the flat surface  7   b , the position  8  moves toward the side of the tapered surface  7   b . Therefore it is desirable to make the area of the tapered surface  7   a  larger than that of the flat surface  7   b . If the area of the tapered surface  7   a  becomes larger than that of the flat surface  7   b , a contact area between the slider surface  7  and the disk becomes small, and stiction may be reduced. This structure is useful to make the system of contact reading or writing information to a disk which is very flat. 
     A structure of a magnetic head device according to a second embodiment of the present invention will be described with reference to FIGS.  3 ( a ) and  3 ( b ) which are top and end views, respectively. 
     The slider surface  7  of this embodiment is formed to have a concave surface confronting the disk, the concave curvature occurring along the direction perpendicular to the rotating direction of the disk. When the disk stops rotating, the slider  2  is in contact with the disk at the edges  3   a ,  3   b  of the flying member  3 . The areas of these edges  3   a , 3   b  are very small, so it is possible to reduce stiction. 
     A structure of a magnetic head device according to a third embodiment of the present invention will be described with reference to FIGS.  4 ( a ) and  4 ( b ) which are top and end views, respectively. 
     The slider surface  7  of this embodiment is formed to have a convex surface confronting the disk, the convex curvature occurring along the direction perpendicular to the rotating direction of the disk. When the disk stops rotating, the slider  2  is in contact with the disk at the center portion  3   c  of the flying member  3 . The area of the center portion  3   c  is very small, so it is possible to reduce stiction. 
     A structure of a magnetic head device according to a fourth embodiment of the present invention will be described with reference to FIGS.  5 ( a )- 5 ( d ). 
     As seen in FIG.  5 ( d ) which is a top view of the head device, the connecting member  5  of this embodiment has a connecting surface  9  which connects between the slider surface  7  and the contact portion  4 . The surface  9  is raised relative to the remainder of the surface of the connecting member  5 . The slider surface  7 , the connecting surface  9 , and the contact portion  4  which confront the disk are formed to be convex along the rotating direction of the disk. When the disk stops rotating, the top of the convex surface, for example the part of the slider surface  7  and the connecting surface  9 , as shown in FIG.  5 ( a ) and designated by “(a)” in FIG.  5 ( d ), is kept in contact with the disk. The area of the top of the convex surface is very small, so it is possible to reduce stiction. 
     When the rotational speed of the disk is small, the part of the connecting surface  9 , as shown in FIG.  5 ( b ) and designated by “(b)” in FIG.  5 ( d ), is kept in contact with the disk because the pitch angle of the slider  2  is also small. When the disk rotates constantly, the pitch angle becomes large enough to keep the contact portion  4  in contact with the disk, as shown in FIG.  5 ( c ) and designated by “(c)” in FIG.  5 ( d ). In general, when the the rotational speed of the disk is small, the flying condition of the slider  2  is unstable, so that a large contact force may be applied to the contact surface of the slider  2 . According to this embodiment, when the rotational speed of the disk is small, the magnetic pole (not shown) is not worn down because the contact portion  4  is not kept in contact with the disk. 
     A structure of a magnetic head device according to a fifth embodiment of the present invention will be described with reference to FIGS.  6 ( a )- 6 ( c ) which are top, side and end views, respectively. 
     The slider surface  7  which is described in FIG. 1 is divided into two parts  7   c ,  7   d  by a groove  10 . The groove  10  is contiguous with the connecting surface  5   a  of the connecting member  5 . In this structure, the maximum length L of the slider surface  7  along the rotating direction of the disk is defined to be the same as in the first embodiment. The maximum width of the slider surface  7  along the direction perpendicular to the rotating direction of the disk is defined top be the sum of the maximum width W 1 , W 2  of parts  7   c ,  7   d  of the slider surface  7  in such direction: 
     
       
           W=W   1 + W   2   (3) 
       
     
     According to this definition, the maximum length L is shorter than the maximum width W. Since the pitching stiffness of the fluid film between the slider surface  7  and the surface of the disk becomes lower, it is possible to reduce the variation of the contact force caused by the positioning error between the slider surface  7  and the contact portion  4 . Also, the translational stiffness and rolling stiffness of the fluid film between the slider surface  7  and the surface of the disk become higher. 
     Sliders having a variety of structures can readily be constructed by means of etching methods. According to the same definitions of the maximum length L and the maximum width W, they produce the same effects as described above. 
     A structure of a magnetic head device according to a sixth embodiment of the present invention will be described with reference to FIGS.  7 ( a )- 7 ( c ) which are top, side and end views, respectively. 
     The slider surface  7  is a single flat surface. According to this structure, it is possible to reduce the variation of the position  8  (not shown) where the fluid force is applied, because the slider can readily be constructed to accurately have such a shape. For the same reason, the pivot position  6  (not shown) can be accurately controlled on the basis of the slider shape. Therefore, it is possible to determine the contact force accurately according to the equation (1). 
     A plurality of projections  11  are formed on the slider surface  7 . When the disk stops rotating, the slider surface  7  is in contact with the disk at the projections  11  only. If the area of the projections  11  is small, it is possible to reduce stiction. The structures of the projection  11  is not limited the structure shown in FIG.  7 . It is also possible to apply the structures as shown in FIG.  3  and FIG. 4 to this embodiment. 
     A structure of a magnetic head device according to a seventh embodiment of the present invention will be described with reference to FIGS.  8 ( a )- 8 ( c ) which are top, side and end views, respectively. 
     A slider surface  7  includes at least two steps along the rotating direction of the disk. The distance between the step and the disk becomes shorter along the rotating direction of the disk. The fluid force is applied at the edge  12  between the adjacent steps. This type of the slider surface can be readily constructed accurately by means of etching methods. According to this structure, it is possible to reduce the variation of the position  8  (not shown) where the fluid force is applied, because it is easy to make the outward form of the slider accurately. The pivot position  6  (not shown) can also be controlled accurately on the basis of the shape of the slider. Therefore it is possible to determine the contact force accurately according to equation (1). When the disk stops rotating, the slider surface  7  is kept in contact with the disk at the nearest step from the disk. If the area of the step is small, it is possible to reduce stiction. 
     A structure of a magnetic head device according to an eighth embodiment of the present invention will be described with reference to FIGS.  9 ( a )- 9 ( c ) which are top, side and end views, respectively. 
     Inertia is caused by the undulation of the disk, the vibration of the disk, or an external shock applied to the device. According to this embodiment, the inertia is balanced with the fluid force only, so the contact force does not vary. 
     The connecting member  5  has the same width as the flying member  3  along the direction perpendicular to the rotating direction of the disk. Since the slider  2  is formed to have a substantially rectangular shape, the outward form can be readily constructed. 
     The maximum length L of the slider surface  7  along the rotating direction of the disk is shorter than the maximum width W of the slider surface  7  along the direction perpendicular to the rotating direction of the disk. The connecting member  5  has a surface  5   a  which confronts the disk. The surface  5   a  of the connecting member  5  is recessed from the slider surface  7 . The contact surface  4   a  also has a very small area, so that only a small dynamic pressure is applied to the contact surface  4   a , therefore, the fluid force fh is mainly applied to the slider surface  7 . 
     In general, the center of gravity of the head (G) depends on the mass of the slider  2  and equivalent mass of the suspension (not shown). Relative to the above embodiments, the position of G in the structure, thus far described, would be located further along the rotating direction of the disk, according to equation (2), the greater part of the inertia is allocated to the contact force, because the distance lg (not shown) between the position of G and the contact portion  4  becomes short. This is a cause of the variation of the contact force. In order to move the position of G in the direction opposite to the rotating direction of the disk, a projection  13  for counter-weight is located at the opposite side of the slider surface  7 . If the position of G is located near the position where the fluid force is applied, the variation of the contact force may be reduced. In this case, the projection  13  requires only mass, so the structure or material are not limited. The structure of this embodiment can be applied to each of the embodiments described above. 
     A structure of a magnetic head device according to a ninth embodiment of the present invention will be described with reference to FIG.  10 . 
     The purpose of this embodiment is to reduce the variation of the contact force caused by the positioning error between the slider surface and the contact portion. 
     The slider surface  7  is a convex surface, which confronts the disk and is curved along the rotating direction of the disk. The center of its curvature is near the pivot position  6  where a load F is applied. The distribution of the dynamic pressure (gage pressure) Ph is shown in FIG.  10 . The position  8 , where the fluid force fh is applied, is located near the portion which is closest to the disk. 
     When the positioning error between the slider surface  7  and the contact portion  4  is made, the contact force fc varies. This variation of the contact force fc will be described with reference to FIGS.  11 ( a )- 11 ( c ). FIG.  11 ( b ) shows the standard condition. FIG.  11 ( a ) shows the condition that the contact portion  4  is recessed by Δ from the contact portion of the standard condition. FIG.  11 ( c ) shows the condition that the contact portion  4  is projected by Δ from the contact portion of the standard condition. 
     When the contact portion  4  is recessed by Δ, the posture of the slider  2  changes, so that the pitching angle increases (+θ″). The position  8  where the fluid force fh is applied is still located near the portion which is closest to the disk. The distribution of the dynamic pressure Ph does not change. If some conditions that will be described are satisfied, it is possible to keep the distribution of the dynamic pressure ph to be constant. These conditions relate the length of the slider surface  7  along to the rotating direction of the disk, and the radius of the curvature of the slider surface  7 . According to the combination of the length and the radius of the curvature, the dynamic pressure becomes equal to the atmospheric pressure in the range of the slider surface  7 . 
     According to the change of the the posture of the slider  2 , the distance lh between the position  8  and the contact portion  4 , and the distance lp between the pivot position  6  and the contact portion  4 , changes very little. The distance lh−lp between the pivot position  6  and the position  8  is shown in the following equation (4). 
     
       
         ( lh−lp )−( lh″−lp″ )= Rp·θ″   (4) 
       
     
     “Rp” is the distance between the center of the curvature (O) of the slider surface and the pivot position  6 . 
     This distance between positions  6  and  8  is shorter than that in the standard condition. The distance between the position  8  and the contact portion  4  changes very little. 
     
       
           lh″=lh   (5) 
       
     
     As a result, the variation of the contact force (dfc) is shown in the following equation (6).              dfc   =       Rp   ·     θ   ″         1      h               (   6   )                         
     If the center of the curvature (O) of the slider surface is located near the pivot position  6 , it is possible to reduce the variation of the contact force (dfc). If the center of the curvature of the slider surface (O) coincides with the pivot position  6 , the contact force does not vary. 
     With reference to FIG.  11 ( c ), when the contact portion  4  is projected by Δ, the posture of the slider  2  changes, so that the pitching angle decreases (−θ′). According to the change of the the posture of the slider  2 , the distance lh between the position  8  and the contact portion  4 , and the distance lp between the pivot position  6  and the contact portion  4 , changes very little. The distance between the pivot position  6  and the position  8  is shown in the following equation (7). 
     
       
         ( lh′−lp′ )−( lh−lp )= Rp·θ′   (7) 
       
     
     The distance between positions  6  and  8  is longer than that in the standard condition. The distance between the position  8  and the contact portion  4  changes very little. 
     
       
           lh′=lh   (8) 
       
     
     So the variation of the contact force (dfc) is shown in the following equation (9). 
     
       
         
           
             
               
                 
                   dfc 
                   = 
                   
                     
                       Rp 
                       · 
                       
                         θ 
                         ′ 
                       
                     
                     
                       1 
                        
                       h 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
         
         
             
         
       
     
     Thus, if the center of the curvature (O) of the slider surface is located near the pivot position  6 , it is possible to reduce the variation of the contact force (dfc). If the center of the curvature (O) of the slider surface is coincides with the pivot position  6 , the contact force does not vary. 
     According to this embodiment, if the dimensional accuracy of the pivot position is assured, it is possible to keep the contact force at a low level without the influence of the accuracy of manufacturing. The structure of this embodiment can be applied to each of the embodiments described above. 
     A structure of a magnetic disk drive in which use the head of the present invention is used, will be described with reference to FIG.  12 . 
     A disk  201  is set on a spindle  202 , and rotated at a constant rotational speed by the spindle  202 . A slider  203  carrying a magnetic pole is mounted on a tip end of a suspension  204 , and accesses to the disk  201  in order to read and write data. The suspension  204  is connected to an end of an arm  205  which has a bobbin portion holding a driving coil (not shown). The other end of the arm  205  has a voice coil motor  206 , which is a type of linear motor. The arm  205  is held by ball bearings (not shown) provided in two locations, i.e. above and below a fixing axis  207 , and the arm  205  can be freely rotated and/or oscillated by the voice coil motor  206 . The voice coil motor  206  has a driving coil wound around the bobbin portion of the arm  205 , and a magnetic circuit formed of a permanent magnet (not shown) arranged to sandwich the coil and to oppose each other, and an opposing yoke (not shown). 
     The head of the present invention is not limited to being applied to a magnetic disk drive in which a rotary actuator is used. It is possible to apply it to other types of magnetic disk drives, for example, a magnetic disk drive in which a linear actuator is used. 
     Thus in accordance with the magnetic head device according to embodiments of the present invention, a position where a sum of the dynamic pressure (fluid force) is applied, is located far from the contact portion, so a distance between the position where the fluid force is applied and the contact portion becomes long. Consequently, it is possible to keep the contact force low. 
     Further, a distance between the position of a center of gravity of the magnetic head device and the contact portion becomes long. So it is possible to reduce the variation of the contact force according to inertia which occurs by the undulation of the medium, the vibration of the medium, or the shock applied to the device from outside. 
     Further in accordance with the magnetic head device according to embodiments of the present invention, the inertia caused by the undulation of the medium, the vibration of the medium, or an external shock applied to the device is balanced with the fluid force only, so the contact force does not vary. 
     Also in accordance with the magnetic head device according to embodiments of the present invention, if the posture of the slider changes, it is possible to keep the distribution of the dynamic pressure constant. Consequently, it is possible to reduce the variation of the contact force caused by the positioning error between the slider surface and the contact portion. 
     Additionally in accordance with the magnetic disk drive according to embodiments of the present invention, it is possible to keep the contact force which is applied to the magnetic head device at a low level, and to reduce the variation of the contact force according to inertia caused by the undulation of the disk, the vibration of the disk, or an external shock applied to the device. Consequently, the life of the magnetic disk drive can be extended, because wear of the magnetic head device and the magnetic recording disk can be reduced. 
     Additionally in accordance with the magnetic disk drive according embodiments of the present invention, the inertia caused by the undulation of the medium, the vibration of the medium, or an external shock applied to the device is balance with the fluid force which is applied to the magnetic head device only, so the contact force does not vary. Consequently, the life of the magnetic disk drive can be extended, because wear of the magnetic head device and the magnetic recording disk can be reduced. 
     Further in accordance with the magnetic disk drive according to embodiments of the present invention, if the posture of the magnetic head device changes, it is possible to keep the distribution of the dynamic pressure constant. As a result, it is possible to reduce the variation of the contact force caused by the positioning error between the slider surface and the contact portion. Consequently, the life of the magnetic disk drive can be extended, because wear of the magnetic head device and the magnetic recording disk can be reduced. 
     Additional advantage and modifications will readily occur to those skilled in the art. Therefore, the present invention in its broader aspects is not limited to the specific details, representative devices, and illustrated examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.