Abstract:
A head supporting device with a loading/unloading mechanism and a disk drive unit using the head supporting device. The head supporting device and a voice coil motor (VCM) make up a head actuator of the drive system. The head actuator has i) a support arm rotatable on a bearing, moving in directions along the radius of a recording medium and vertical to the surface of the medium; ii) a magnetically levitating head on a slider facing the medium; and iii) resilient member for applying force to the arm in a direction close to the medium. The VCM has a pair of yokes, a magnet, and a coil. When the head is lead to a head retracting position, the other end of the arm is pulled by the interaction of a magnetic member and the magnet at the resting position and adjacencies. This eases the load on the VCM, contributing to a compact and slim disk drive unit with toughness and rapid data-access.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a head supporting device employing a magnetically levitated head, such as a magnetic head, optical head, and magneto-optic head, and a disk drive unit using the head supporting device. More particularly, it relates to the head supporting device equipped with loading/unloading mechanism (hereinafter referred to as L/UL mechanism) and a disk drive unit using the head supporting device. 
   BACKGROUND OF THE INVENTION 
   In recent years, portable electronic equipment, such as Personal Digital Assistance (PDA) and mobile phones, has been rapidly expanding its market, and getting smaller in size. At the same time, a magnetic disk drive unit, which has become commonly used as a handy storage device, has been required to have smaller and thinner body with increased toughness against shocks. Responding to the need for the unit with high-impact-resistance, various attempts have been made to offer improvements in a head supporting mechanism of a magnetic disk drive unit. 
   For example, employing a L/UL mechanism for a disk drive unit has been recognized as an effective way for providing an impact-resistant disk drive unit. Magnetic disk drive unit  129 , as shown in  FIG. 7 , has a head supporting device equipped with L/UL mechanism. Support arm  102  has guide  102   a  at its tip; and has magnetic head-mounted slider  101  in the proximity of the tip. Driven by spindle motor  105 , magnetic recording medium  112  starts rotating. During the rotating, slider  101  mounting a magnetic head (not shown) thereon levitates at a position over medium  112  for data writing or reading. This state is the loading mode in the U/L mechanism. 
   On the other hand, when medium  112  stops rotating, support arm  102  rotates on rotation axis  103   c  and moves toward the outside of medium  112 . The movement of arm support  102  is controlled by voice coil motor (hereinafter referred to as VCM)  124 , which operates on interaction between voice coil  116  disposed at support arm  102  and, magnet  120  and yokes (not shown) that sandwich voice coil  116  via a clearance. Ramp  118  having tapered portion  118   a  is formed at the outside of medium  112 . Driven by VCM  124 , support arm  102  withdraws from the surface to take guide  102   a  onto ramp  118 . This “withdrawal” allows slider  101  to keep off medium  112 —the magnetic head is in the unloading mode. The head supporting device shown in  FIG. 7  employs locking mechanism  130  using a piece of iron and a magnet for supporting the arm. 
   In magnetic disk drive unit  129  having the head supporting device as described above, the magnetic head is kept away from medium  112  during the unloading mode. The structure prevents the head and a medium against shocks from outside. Compared to other systems, the L/UL system has decreased the chance of mechanically or magnetically damaging medium  112  by collision with the head. 
   However, it is also true that the L/UL mechanism-employed disk drive unit has a problem to be tackled: a rather large sliding load. When guide  102   a  runs onto tapered portion  118   a  of ramp  118 , the load on the arm due to the “landing” surpasses the half of torque required for the VCM. In a multi-disk structure having a number of heads, the built-up load has been a serious problem. Besides, downsized magnetic disk imposes limitations on the VCM components including the coil, the yoke, and the magnet: the number of turns of the coil reduces due to the thinned coil; the magnetic circuit formed of thinned VCM components cannot capture sufficient fluxes. Such inconvenience inevitably reduces the torque of the VCM. 
   It has therefore been a significant challenge for manufacturers to reduce the load on the VCM. Addressing to the inconvenience, there have been many suggestions to decrease the load developed in the unloading motion of the arm. The followings are the examples: i) in Japanese Patent Publication No. JP7334955, a ball bearing is disposed on the surface of the guide where the tapered portion comes in contact so as to decrease the coefficient of friction of the tapered portion and the guide of the arm; ii) in Japanese Patent Publication No. JP1196699, a piece of iron and a locking magnet are added to a coil-holding member of the VCM. Magnetic interaction between the iron piece and the locking magnet provides the arm with a smooth turn, thereby reducing the load on the VCM. At the same time, the suggestion includes a guiding-and-locking system for a rotary actuator to protect components of the unit from an impact generated in the process of the unloading motion. 
   Still, the two suggestions shown above have problems to be solved: as for the former suggestion described in i), it needs an extremely high technique to dispose the ball bearing in the tiny space of the guide at the tip of the support arm in such downsized disk drive unit, thereby automatically decreasing productivity. Besides, mounting an additional part on the tip of the arm lowers the resonance frequency of the arm. When the arm is moved at a high speed, the lowered resonance frequency generates undesired various vibration modes, which requires the disk drive unit a time to get settled. The fact has been an obstacle to rapid data access. As for the latter one described in ii), disposing an extra locking system not only introduces a complication on downsizing the magnetic disk drive unit but also increases the cost. 
   Prior-art head supporting devices including the two examples above have similar structures: the support arm rotating on a spindle moves the slider substantially parallel to the surface of the recording medium; a resilient member including a spring is disposed between the spindle and the arm, or between the arm and a head-supporting member to apply force to the slider; the force works on the slider to levitate it with a fixed interval from the surface of the medium. In the prior-art, it has never been discussed the possibility that a vertical movement of the arm with respect to the medium surface can reduce the load on the VCM. Manufacturers have not reached subtle solutions to the reduction of the load on the VCM. 
   SUMMARY OF THE INVENTION 
   It is therefore the object of the present invention to provide a head supporting device equipped with L/UL mechanism capable of providing i) a simple structure; ii) higher impact resistance; iii) rapid data access, with the load on the VCM minimized. At the same time, it is the object of the invention to provide a disk drive unit using the head supporting device. 
   To address the problem above, the head supporting device of the present invention has i) a support arm and ii) a head mounted on a slider at one end of the support arm. The head is disposed on the surface facing to a recording medium. The arm rotates on a bearing not only to move in a direction along the radius of the medium but also move in the direction vertical to the medium. In addition, resilient means is employed for applying force to the head-mounted end of the arm in a direction closer to the medium. 
   The present invention has various aspects as follows:
         a) employing a magnetically attracting member for pulling the other end of the arm in order to reduce the force applied to the arm;   b) disposing a gimbal mechanism on the arm to hold the slider movable in the roll-and-pitch direction;   c) employing materials possessing high stiffness for the arm;   d) disposing a plate spring as resilient means between the bearing and the arm in the direction along the rotation axis;   e) disposing a pivot bearing having a pair of tops so that the arm can rotate, with the help of the tops as supporting points, in the direction vertical to the recording medium;   f) locating the tops of the pivot bearing so as to be vertical to the axial direction of the bearing and to the lengthwise direction of the arm, and so as to have contact with the arm on a line through the center of rotation in a direction along the radius of the medium;   g) disposing each top of the pivot bearing so as to be symmetrical with respect to the center line of the arm in the lengthwise direction;   h) disposing the pivot bearing so that each top of the bearing makes a point-contact with the arm, or makes a line-contact in which the line is parallel to the surface of the arm and is vertical to the arm in its lengthwise direction;   i) locating the center of gravity of the portion held by the resilient means at a point of intersection of the two rotation axes of the arm, one of which extends in the direction along the radius of the medium, and the other extends in the direction vertical to the recording surface of the medium.       

   As described above, the arm holder made of material having high stiffness not only can be resistant against shocks from the outside, but also offers the resilient force to be applied to the slider with a degree of flexibility. This allows the structure to have higher impact-resistant and higher resonance frequency, realizing a head supporting device with a quick-response and a rapid data access. 
   The disk drive unit of the present invention contains:
         a) a rotatably fixed recording medium;   b) a head supporting device further includes i) a support arm; and ii) a head mounted on a slider at one end of the support arm, iii) resilient means for applying a force to the arm in the direction close to a recording medium, and the arm rotates on a bearing not only to move in a direction along the radius of the medium but also move in the direction vertical to the medium;   c) a pair of yokes having a clearance therebetween disposed in the direction parallel to the rotating axis of the recording medium, which locates on the side opposite to the slider with respect to the rotation axis of the arm;   d) a magnet disposed in the clearance between the yokes;   e) a coil held by the arm, which is located in the clearance formed between the magnet and the yokes;   f) a rotator for rotating the recording medium;   g) a control circuit electrically connected with the head, the rotator, and the coil, controlling the rotation of the medium and the movement of the arm; and   h) a head retracting mechanism for supporting the head at a predetermined resting position to keep off the head from the medium.       

   When the head is lead to the resting position, an attracting member disposed at the resting position and in proximity to the position magnetically pulls the other end of the arm, thereby reducing the resilient force applied to the arm in a direction closer to the medium. 
   With the structure described above, the arm can be formed as a combination of rigidity and resiliency—the rigidity not only protects the arm from physical shocks from outside, on the other hand, the resiliency allows the force applied by the resilient means to be determined with a degree of flexibility, providing the disk drive unit with quick response and rapid data access. 
   Furthermore, to tackle with forgoing problems, the disk drive unit of the present invention has several aspects as follows:
         a) interaction between the magnet and a magnetic member integrally held by the coil drives the magnetically attracting mechanism. The magnetic member is disposed at a position on a circle having a radius greater than the radius of outer circumference of the magnet. The magnetic attracting mechanism magnetically pulls the other end of the arm to reduce the resilient force generated in the sliding motion of the guide of the arm and the ramp in the unloading mode. This movement eases the load on the VCM without interrupting the seek operation. With the structure, the disk drive unit of the present invention has a simple structure and high impact-resistance in its compact and slim body, providing rapid data access.   b) The disk drive unit has a magnet whose outer perimeter is overhung at a position corresponding to the head retracting position or in the proximity of the position. With such shaped magnet, the coil can capture greater amount of fluxes therein, thereby providing the VCM with higher torque.   c) The disk drive unit has a head retracting mechanism formed of a ramp disposed in a position at the outer or inner perimeter of the recording medium. The ramp can keep the head away from the medium during the unloading mode, protecting the head against damage by shocks from outside. The fact contributes to provide a higher impact-resistant disk drive unit.   d) The disk drive unit has a ramp made of materials with smooth texture, i.e., with lower coefficient of friction, such as Liquid Crystal Polymer (LCP) resin, Poly Phenylene Sulfide (PPS) resin, and Poly Oxy Methylene (POM) resin. Employing such material reduces resistance between the guide and the taper of the ramp in the unloading mode, thereby easing the load on the VCM.   e) The disk drive unit has a gimbal mechanism on the support arm. The mechanism holds the slider movable in the roll-and-pitch direction. The mechanism accommodates undesired slant of the slider in the roll-and-pitch direction with respect to the medium in the loading mode.   f) The disk drive unit has a support arm made of materials having high stiffness. The stiffness not only protects the arm against shocks, but also provides the arm with higher resonance frequency, allowing the disk drive unit to have higher access speed.   g) The disk drive unit has resilient means formed of plate spring disposed between the bearing and the arm in the axial direction of rotation. Disposing the plate spring provides the with rigidity and resiliency, whereby the resilient force to the slider can be determined with a degree of flexibility. As an additional plus, the structure realizes the disk drive unit having a low-profile head supporting device in the direction vertical to the recording medium.   h) The disk drive unit has a pivot bearing with a pair of tops that makes contact with the arm. The arm rotates, with the help of the tops of the pivot bearing as supporting points, in the direction vertical to the recording medium. The structure properly determines the center of rotation, whereby the head can be positioned with higher accuracy.   i) In the disk drive unit having a pivot bearing with a pair of tops, the tops of the bearing are located so as to be vertical to the axial direction of the bearing and to the lengthwise direction of the arm, and so as to have contact with the arm on the line through the center of rotation in a direction along the radius of the medium;   j) In the disk drive unit having a pivot bearing with a pair of tops, each top of the bearing is disposed in a symmetrical arrangement with respect to the centerline of the arm in its lengthwise direction. Such designed structure keeps the weight of the arm in balance in its widthwise direction, providing a disk drive unit equipped with high-impact-resistant head supporting device.   k) In the disk drive unit having a pivot bearing with a pair of tops, each top of the bearing makes a point-contact with the arm, or makes a line-contact in which the line is parallel to the surface of the arm and is vertical to the arm in its lengthwise direction. Such designed structure reduces the torque of the VCM to move the arm in the direction vertical to the medium, easing the load on the VCM.   l) The disk drive unit contains at least a bearing unit; a pivot bearing; resilient means; a support arm; and a coil holder having a coil. Together with a ring-shaped collar disposed under the coil holder, the components make up the head actuator arranged around the center of rotation of the arm. With such simple structure, the head actuator can offer movements in a direction along the radius of the recording medium and in the direction vertical to the surface of the medium. Also, the structure protects the head and the medium from undesired collision by shocks from outside, providing the disk drive unit with quick response and rapid data-access.   m) In the disk drive unit, the center of gravity of the portion held by the resilient means is located at a point of intersection of the two rotation axes of the arm, one of which extends in a direction along the radius of the medium, and the other extends in the direction vertical to the recording surface of the medium. Such designed structure minimizes undesired vibrations of the arm that can be caused by accidental shocks from outside.   n) The disk drive unit has a magnetic member in the shape of small cylinder, small ellipsoid, or small ball. Such designed structure reduces the load on the guide of the arm and the ramp in the unloading mode, thereby reducing the load on the VCM. This contributes to provide a compact and slim disk drive unit with a simple structure.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view illustrating the structure of a head supporting device and a disk drive unit using the same in accordance with a first preferred embodiment of the present invention. 
       FIG. 2  is a sectional view illustrating the structure of the head supporting device and the disk drive unit using the same in accordance with the first preferred embodiment. 
       FIG. 3  is an exploded perspective view illustrating the head actuator section having the head supporting device in accordance with the first preferred embodiment. 
       FIG. 4  is a plan view illustrating the head actuator section having the head supporting device in accordance with the first preferred embodiment. 
       FIG. 5  is a plan view illustrating the structure of a disk drive unit in accordance with a second preferred embodiment. 
       FIG. 6  is a plan view illustrating the shape of a magnet in accordance with the second preferred embodiment. 
       FIG. 7  is a plan view illustrating the structure of a prior-art disk drive unit. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings. 
   First Preferred Embodiment 
     FIG. 1  is a plan view illustrating the structure of a head supporting device and a disk drive unit using the same in accordance with a first preferred embodiment of the present invention.  FIG. 1  shows the state in which support arm  2  rests on ramp  18 , that is, shows the magnetic head in the unloading mode.  FIG. 1  bears some components in common with those in the structure of the prior-art in FIG.  7 . 
   A head element (not shown) responsible for reading and writing data is mounted on slider  1 . Slider  1  having the head element is fixed on the surface of support arm  2  so that the head element faces the recording medium  12 . First bearing unit  3  and second bearing unit  4 , which will be described in detail later, control the movement of support arm  2 . First bearing unit  3  allows arm  2  to swivel back and forth across the surface of medium  12 , while second bearing unit  4  allows support arm  2  to “swing” up and down with respect to the surface of medium  12 . 
   Spindle motor  5  journals recording medium  12 . In the magnetic head is ready for operation—in the loading mode, the head levitates over medium  12  for writing or reading data. The levitation of the head is offered by the interaction of airflow developed by the rotation of medium  12  and the force given by head supporting device  9  so as to urge slider  1  toward medium  12 . 
   Head actuator  26  includes support arm  2 ; first bearing unit  3 ; second bearing unit  4 ; coil  16 ; coil holder  17 ; upper yoke  19  (not shown in FIG.  1 ); magnet  20 ; and lower yoke  21 . 
   When medium  12  stops its rotation, guide  2   a  formed at the tip of support arm  2  withdraws from the surface of medium  12  to ramp  18 . Having tapered portion  18   a  and holder  18   b , ramp  18  accepts guide  2   a  to rest it thereon. The “withdrawal” protects slider  1  and medium  12  from collision by shocks. Housing  15  has control circuit  23  therein (as also shown in  FIG. 7  ). Circuit  23  is connected to actuator  26  via flexible wiring board  27  to provide head actuator  26  with signal-processing control. Circuit  23  may be disposed outside of housing  15 . Housing  15  maintains the proper relation between these components. Besides, housing  15  serves as a protector, fitted with a similarly shaped lid (not shown), blocking out an adversely effect caused by dust debris or changes in airflow. 
     FIG. 2  is a sectional view taken along the line A—A in FIG.  1 . Like  FIG. 1 ,  FIG. 2  shows the unloading mode in which support arm  2  rests on ramp  18 . The bearing unit and its proximity are not shown as a sectional view but as a side view in the figure. 
   First bearing unit  3  has a ball bearing (not shown) therein. Outer portion  3   a  is rotatable, whereas inner portion  3   b  is screwed down to housing  15 . Lower yoke  21  on which magnet  20  mounted is fixed to housing  15 , while upper yoke  19  is disposed so as to keep a clearance with magnet  20 . In the clearance between the two yokes, coil holder  17  accommodating coil  16  is disposed. In this way, a magnetic circuit is formed of the components above. Coil holder  17  is fixed to support arm  2 . Coil  16  (not shown in  FIG. 2  ), magnet  20 , upper yoke  19 , and lower yoke  21  make up VCM  24 . VCM  24  rotates support arm  2  on first bearing unit  3 , so that support arm  2  has radially-outward and inward movement. 
   Coil holder  17  has magnetic member  22 . In  FIG. 1 , two magnetic members are disposed each on tabs of coil holder  17  in FIG.  1 . Magnetic member  22  sits on a position radially beyond the outer arc of magnet  20  so as not to interrupt VCM  24  in a seek operation. 
   In head supporting device  9  of  FIG. 2 , gimbal  13  employing a gimbal spring is disposed on slider  1 . Gimbal  13  allows slider  1  to move, through dimple  14 , in the roll-and-pitch direction. Gimbal  13  can thus control slider  1  to have the proper position with respect to recording medium  12  by accommodating undesired tilt in the roll-and-pitch direction. 
     FIG. 3  is an exploded perspective view illustrating the structure of first bearing unit  3  and second bearing unit  4 . The explanation will be given with reference to the figure and FIG.  2 . Force applying means exerts force on slider  1  in the direction toward medium  12 . The first preferred embodiment employs as the force-applying resilient means a ring-shaped plate-spring  6 , which is made of stainless or phosphor bronze. Half-ring shaped fixing member  10  holds the “half ring” of resilient member  6 . The other half of member  6  lies under support arm  2  on the side of the coil. Fixing member  10  and the “half ring” of resilient member  6  fixed thereto are located within opening  2   b  of support arm  2  so as not to interrupt up-and-down movements of support arm  2 . 
   Support arm  2  and coil holder  17  with coil  16  make up head-supporting assembly  28 . Head-supporting assembly  28  with second bearing unit  4  and collar  7  as shown in  FIG. 3  completes head actuator  26 . Head actuator  26  is tightened by nut  8  at the bottom and, inner portion  3   b  of first bearing unit  3  is fixed to housing  15 . 
   In collar  7 , half-ring portion  7   a —the half on the side of slider  1 —is formed thicker than the opposite half-ring portion  7   b . Portion  7   a  is set in opening  2   b  of support arm  2  to hold resilient member  6  and fixing member  10  against second bearing unit  4 . On the other hand, projection  7   c  of collar  7  is fitted into pit  2   c  formed at opening  2   b  of support arm  2  to reach second bearing unit  4 . In this way, fixing member  10  and a part of resilient member  6  attached thereto are securely held by first bearing unit  3 ; second bearing unit  4 ; half-ring portion  7   a  and projection  7   c  of collar  7 ; and nut  8 . 
   In first bearing unit  3 , a bearing (not shown) disposed between outer portion  3   a  and inner portion  3   b  allows outer portion  3   a  to be rotatable. Second bearing unit  4  has a pair of pivots  4   a  and  4   b  that serve as supporting points for movements of support arm  2  in a direction vertical to the surface of medium  12 . 
   Pivots  4   a  and  4   b  of second bearing unit  4  should be positioned as shown in FIG.  4 : they should be symmetric about the center line of support arm  2  in its lengthwise direction (indicated by the line B—B in  FIG. 4  ); and also should be on the line perpendicular to line B—B (indicated by the line C—C). Although the embodiment employs a pair of pivots, it is not limited thereto: a wedge-shaped portion, with which a line-contact is obtained under the positional relation stated above, can offer the same effect. 
   Such designed structure allows support arm  2  and other components forming the head supporting device to be made of materials with high stiffness. Employing such rigid material not only protects support arm  2  from damage by shocks, but also provides support arm  2  with higher resonance frequency. Therefore, support arm  2  can be free from undesired vibration modes for which the prior-art has suffered, and therefore can be free from settling operation. This advantageous fact provides the arm with high-speed rotation and positioning, increasing the access speed of magnetic disk drive unit  29 . 
   In addition, resilient member  6  is separately formed from support arm  2 . Therefore, the strength and a spring coefficient of the plate spring are desirably determined by changing the material or thickness of the plate spring. 
   The center of gravity of the portion held by resilient member  6 , that is, in the case of employing VCM  24  to drive support arm 2 , the center of gravity of support arm  2  having coil holder  17  with coil  16  should be positioned on the point of intersection of rotation axis in a direction along the radius of medium  12  and rotation axis in the direction vertical to medium  12 . In other words, the center of gravity of support arm  2  has the position substantially the same as the middle point of the line connected between the pivots  4   a  and  4   b  (indicated by point P in FIG.  4 ). The positioning improves the stability of the head supporting device, eliminating undesired vibrations. In the structure, a slightly off-centered centroid position will be negligible on practical use. 
   The disk drive unit structured above goes into the loading mode through the steps below: i) rotation of medium  12  driven by spindle motor  5  generates airflow on the surface of medium  12 ; ii) movement of support arm  2  driven by VCM  24  takes slider  1  from ramp  18  to levitate over a position of a track of medium  12 ; iii) with slider  1  been levitated, data writing or reading is performed by a head element (not shown) mounted on slider  1 . 
   Now will be described how the magnetic head goes into the unloading mode in the disk drive unit of the present invention. 
   Ramp  18  is disposed outside of medium  12  as shown in  FIGS. 1 and 2 . During the unloading mode, the magnetic head retracts on ramp  18 . Ramp  18  is made of materials having smooth texture, such as Liquid Crystal Polymer (LCP) resin, Poly Phenylene Sulfide (PPS) resin, and Ply Oxy Methylene (POM) resin. 
   When medium  12  stops its rotating, i.e., on the process to the unloading mode, support arm  2  having slider  1  moves toward outside of medium  12  and guide  2   a  disposed at the tip of support arm  2  slides on tapered portion  18   a  of ramp  18 , then finally settles on pit  18   b . When guide  12   a  runs on tapered portion  18   a  of ramp  18 , head-supporting assembly  28  tilts, with the help of pivots  4   a  and  4   b  serving as supporting points, with respect to the surface of medium  12 . At this moment, the other end of support arm  2  (on the coil-disposed side) moves down, that is, magnetic member  22  comes close to magnet  20 . Magnetic member  22  is attracted by magnet  20  in the direction indicated by the arrow “X” in  FIG. 2 , whereby the tip having guide  2   a  further lift up from medium  12 . 
   This lift-up is effective in minimizing friction between guide  2   a  and tapered portion  18   a  of ramp  18 . That is, guide  2   a  can slide on tapered portion  18   a  without undue stress. The load caused by contacting guide  2   a  with ramp  18  can be thus reduced. By virtue of the reduced load, VCM 24  can start itself with smaller torque. This fact contributes to compact and slim disk drive unit  29  equipped with downsized but still powerful VCM 24 . 
   Although the embodiment introduces the structure employing two magnetic members  22  each disposed in different position, it is not limited to: the structure having a single magnetic member with an effectual positioning may offer the same effect. 
   Although the embodiment introduces the structure in which magnetic member  22  is disposed on a position radially beyond the outer arc of magnet  20 , it is not limited thereto: other positions are possible as long as the position faces to magnet  20  and has no ill effect on levitation of slider  1 . 
   Although the embodiment introduces the structure employing magnetic member  22  given the shape of small cylinder, it is not limited thereto: the magnetic member may also have the shape of small ellipsoid or small ball. 
   It will be understood that the present invention poses no limitations to the placement, the number, the shape of magnetic member  22 . 
   According to the head supporting device and the disk drive unit using the same of the embodiment, as described above, separately structured two sections—the first and second bearing units—control the movement of the arm. This contributes to flexible design principles, providing a compact and slim structure with stiffness and rapid data-access. 
   Second Preferred Embodiment 
     FIG. 5  is a plan view illustrating the structure of a disk drive unit in accordance with the second preferred embodiment. The figure shows the state in which arm  2  approaches tapered portion  18   a  of ramp  18 —just before the unloading mode.  FIG. 6  is a plan view showing magnet  20  as a component of VCM 24  of head actuator  26 . The disk drive unit of the embodiment differs in the shape of magnet  22  from that of the first preferred embodiment: magnet  20  has overhang portions  20   a  on the outer arc at a position corresponding to the unloading position. 
   Employing such shaped magnet increases the forces of attraction, ensuring the lift-up movement of guide  2   a  of arm  2  away from the surface of medium  12 . The friction between guide  2   a  and tapered portion  18   a , i.e., the load on both components is further reduced. With the structure, guide  2   a  can run on tapered portion  18   a  without undue stress. 
   Generally, an edge of a magnet has low density of magnetic flux. Considering the fact, VCM 24  cannot have a sufficient torque at a position corresponding to the edges of the magnet. According to the embodiment, however, disposing overhang portions  20   a  maintains the magnetic flux sufficient for coil  16 , allowing VCM 24  to operate with stabilized torque in the unloading position. This improvement can realize a smaller and thinner VCM 24 , allowing the whole structure of a disk drive unit to have a compact and slim body. 
   Although the embodiment employs the magnet having overhang portions on the outer arc, it is not limited thereto: other shaped magnets may be acceptable as long as the VCM can obtain the magnetic flux enough for smooth operation. 
   Although the two embodiments introduce the structure in which ramp  18  is disposed at the outside of medium  12 , it is not limited thereto: the structure having ramp  18  disposed on the side of the inner perimeter of the medium can offer the similar effect. 
   It will be understood that the present invention is applicable with the same advantages to disk systems in which the head has no contact with the medium during the disk halting, such as an optical disk drive unit and a magneto-optic disk drive unit. 
   According to the present invention, as described above, it becomes possible to provide a highly improved disk drive unit equipped with a head supporting device having high-impact-resistance and rapid data-access. The structure of the invention allows the support arm to swing up and down, thereby reducing the load on the VCM when the arm comes in contact with the ramp. The structure having the ramp offers another advantage: the magnetic head can rest on the ramp, being kept off the recording medium, during the unloading mode. The structure therefore decreases the chance of collision that can damage the medium and the head. 
   Furthermore, the structure of the present invention reduces the load developed by contacting the guide of the arm with the ramp, thereby minimizing the load on the VCM. It is thus possible to provide a compact and slim disk drive unit with high-impact-resistance and rapid data-access capability.