Abstract:
An actuator latch system of a hard disk drive keeps an actuator of the hard disk drive in place in a state in which a read/write head mounted to a swing arm of the actuator is parked. The latch system has first and second protrusions at upper and lower parts of a rear end portion of the swing arm, and a latch lever having first and second hooks at upper and lower parts of a leading end of the lever. The latch lever, like the actuator, is mounted to a base of the hard disk drive so as to be rotatable about a respective axis. The first hook engages the first protrusion of the swing arm when the arm is inadvertently rotated in a first direction to arrest such inadvertent rotation, and the second hook engages the second protrusion of the swing arm when the arm rotates for a second time in the first direction due to rebounding that occurs in the latch system after the first protrusion and the first hook collide.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a hard disk drive. More particularly, the present invention relates to an actuator of a hard disk drive and to a latch system which locks the actuator in position, when the disk of the hard disk drive is stopped, to prevent the actuator from being rotated by an external force. 
         [0003]    2. Description of the Related Art 
         [0004]    A hard disk drive (HDD) is an information storage device which includes a disk having at least one recording surface, and a read/write head which writes data onto and reads data from the recording surface of the disk while the disk is being rotated. In this respect, the HDD also includes an actuator which moves the read/write head over the recording surface of the rotating disk so that the read/write head can access a desired portion (track) of the recording surface, e.g. a portion onto which data is to be recorded or from which data is to be retrieved. 
         [0005]    When the HDD is not in use, that is, when the disk is not rotating, the read/write head is parked at a position away from the recording surface of the disk to prevent the read/write head from colliding against the recording surface of the disk. The parking systems for parking the read/write head include a contact start stop (CSS) type of parking system and a ramp loading type of parking system. In the CSS type of parking system, an inner circumferential part of the disk has a parking zone where no data is recorded, and the read/write head is parked in contact with the parking zone. In the ramp loading type of parking system, a ramp is disposed radially outwardly of the disk, and the actuator is moved onto the ramp to park the read/write head. 
         [0006]    However, in either case, an external force applied to the HDD, e.g., an impact or vibrations, could move the actuator arbitrarily while the read/write head is parked. Thus, such an external force could move the read/write head onto the recording surface of the disk. As a result, the read/write head or the recording surface of the disk could be damaged. In view of such a potential problem, the actuator is “locked” when the read/write head is parked so that the read/write head will remain in the parking zone or adjacent the ramp even when an external force is applied to the HDD. A variety of known actuator latch systems are employed by HDDs for this purpose. 
         [0007]      FIGS. 1A ,  1 B, and  1 C illustrate an example of a conventional actuator latch system  20 , known as a single lever type of inertial latch system, of an HDD. In this example, the HDD employs a ramp loading type of parking system having a ramp  15 . 
         [0008]    Referring to  FIG. 1A , an actuator  10  for moving a read/write head (not shown) to a desired position over a disk (also not shown) includes a swing arm  12  supported by a pivot  11  so as to be rotatable about an axis, and a suspension  13  disposed at an end portion of the swing arm  12 . The suspension  13  supports a slider  14  to which the read/write head is mounted, and elastically biases the read/write head toward the recording surface of the disk. The inertial latch system  20  includes a latch lever  21  supported so as to be freely rotatable about an axis parallel to that about which the swing arm  12  is rotated, a crash stop  24  limiting the clockwise rotation of the swing arm  12 , and a latch stop  25  limiting the clockwise rotation of the latch lever  21 . The latch lever  21  has a latch hook  22  at a leading end portion thereof. The swing arm  12 , on the other hand, defines a notch  23  in an end thereof that faces the latch lever  21 . 
         [0009]      FIG. 1B  shows the case in which a shock applied to the HDD causes the swing arm  12  of the actuator  10  and the latch lever  21  to rotate counterclockwise due to their moments of inertia. Accordingly, the latch hook  22  is received in the notch  23  such that the swing arm  12  of the actuator  10  cannot rotate any further in the counterclockwise direction. In contrast,  FIG. 1C  shows the case in which a shock applied to the HDD causes the swing arm  12  of the actuator  10  and the latch lever  21  to rotate clockwise due to their moments of inertia. In this case, the swing arm  12  collides against the crash stop  24 , rebounds, and thereby begins to rotate counterclockwise. The latch lever  21  collides against the latch stop  25 , rebounds and thereby also rotates counterclockwise. Accordingly, the latch hook  22  is received in the notch  23  so that the actuator  10  is basically locked in place. 
         [0010]    The conventional single lever type of inertia latch system  20  operates relatively reliably when the shock applied to the HDD causes the swing arm  12  of the actuator  10  to initially rotate counterclockwise. However, in the case in which shock applied to the HDD causes the actuator  10  and the latch lever to rotate clockwise and then rebound from the crash stop  24  and latch stop  25 , respectively, the resulting counterclockwise rotation of the swing arm  12  may not be timed with that of the latch lever  21 . That is, sometimes the latch hook  22  does not engage the swing arm  12 . 
         [0011]    Also, as described above, counterclockwise rotation of the swing arm  12  is normally limited by the engagement between the latch lever  21  and the swing arm  12  when the latch hook  22  is received in the notch. However, when the external shock which causes the swing arm  12  to rotate counterclockwise is relatively great, the latch hook  22  and the swing arm  12  collide with each other with such force that the swing arm  12  and the latch lever  21  rebound from each other. Accordingly, the swing arm  12  rotates clockwise, collides against the crash stop  24 , rebounds and then starts rotating counterclockwise. In this case, the counterclockwise rotation of the swing arm  12  is often not limited by the latch hook  22 , due to a mismatch in the timing of the latch system as described above. 
         [0012]    Therefore, the swing arm  12  continues to rotate counterclockwise, and the read/write head moves off of the ramp  15  and onto the recording surface of the disk. Accordingly, the read/write head or the recording surface of the disk may be damaged. 
         [0013]      FIGS. 2A ,  2 B, and  2 C illustrate a dual lever type of inertia latch system  40  that was developed to overcome the above-described problems of the conventional single lever type of inertia latch system  20 . Reference numeral  30  designates the actuator of the HDD, and reference numeral  32  designates the swing arm  32  of the actuator  30 . 
         [0014]    Referring to  FIG. 2A , the inertia latch system  40  includes two latch levers  41  and  42  each supported so as to be freely rotatable about a respective axis, and a crash stop  46  limiting the clockwise rotation of the swing arm  32 . Also, the first latch lever  41  has a latch pin  43 , whereas the second latch lever  42  has a latch hook  44 . The swing arm  32  of the actuator  30  defines a notch  45  at an end thereof which faces the second latch lever  42 . 
         [0015]      FIG. 2B  shows the case in which shock applied to the HDD causes the swing arm  32  of the actuator  30  and the first and second latch levers  41  and  42  to rotate counterclockwise due to their moments of inertia. Accordingly, the swing arm  32  of the actuator  30  is caught by the second latch lever  42 , i.e., the latch hook  44  is received in the notch  45 , whereupon the swing arm  32  cannot rotate any further in the counterclockwise direction. In contrast,  FIG. 2C  shows the case in which shock applied to the HDD causes the swing arm  32  of the actuator  30  and the first latch lever  41  to rotate clockwise due to their moments of inertia. The swing arm  32  then collides with the crash stop  46 , rebounds and thereby starts rotating counterclockwise. At the same time, the clockwise rotation of the first latch lever  41  causes the latch pin  43  to engage the second latch lever  42  and thereby cause the second latch lever  42  to rotate counterclockwise. As a result, the latch hook  44  is received in the notch  45  such that the second latch lever  42  engages the swing arm  32 . Accordingly, the swing arm  32  is prevented from rotating further in the counterclockwise direction. 
         [0016]    The conventional dual lever type of inertia latch system  40  operates reliably with respect to shock applied to the HDD which creates a moment acting on the swing arm  32  in either a clockwise or counterclockwise direction. However, the dual lever type of inertia latch system  40  is complex and requires a relatively large amount of space. Accordingly, the dual lever type of inertia latch system  40  is costly to fabricate and assemble, and is difficult to provide in a compact mobile disk drive. 
       SUMMARY OF THE INVENTION 
       [0017]    An object of the present invention is to solve the above-described problems, draw-backs and limitations of the prior art. 
         [0018]    A more specific object of the present invention is to provide a reliable actuator latch system in a hard disk drive. 
         [0019]    Another object of the present invention is to provide a reliable actuator latch system in a hard disk drive, and which system is simple and therefore easy to fabricate and install. 
         [0020]    According to one aspect of the present invention, there is provided in a hard disk drive an actuator latch system made up of two protrusions projecting from a rear end of the swing arm of the actuator, and a latch lever having two hooks at a leading end thereof. The latch lever, like the swing arm, is supported so as to be rotatable about a respective axis. The protrusions projecting from the swing arm are associated with hooks of the latch lever, respectively. In particular, The first hook engages the first protrusion of the swing arm when the arm is inadvertently rotated in a first direction to arrest such inadvertent rotation, and the second hook engages the second protrusion of the swing arm when the arm rotates for a second time in the first direction due to rebounding that occurs in the latch system after the first protrusion and the first hook collide. 
         [0021]    The distance between the second protrusion and the second hook is greater than the distance between the first protrusion and the first hook. Also, the distance between the second hook and the axis of rotation of the swing arm is shorter than the distance between the first hook and the axis of rotation of the swing arm. In this respect, the term “the distance” refers to the shortest straight line distance, i.e., approximately the distance that the respective protrusion will travel before colliding with the associated hook of the latch lever. 
         [0022]    Preferably, the first protrusion protrudes horizontally from a side surface of the rear end portion of the swing arm, and the first hook protrudes from a bottom surface of the latch lever. The first protrusion may be substantially triangular. On the other hand, the second protrusion preferably protrudes from an upper surface of the rear end portion of the swing arm, and the second hook extends horizontally at the most distal part of the leading end of the latch lever. The second protrusion may project beyond the side surface of the rear end portion of the swing arm. 
         [0023]    Also, the first hook is disposed at the same level as the first protrusion, and the second hook is disposed at the same level as the second protrusion. More specifically, the first hook and the first protrusion are both disposed in a first plane perpendicular to the first and second axes of rotation. Thus, the first hook and the first protrusion both move in the first plane as the swing arm and the latch lever rotate about their respective axes of rotation. The second hook and the second protrusion are both disposed in a second plane parallel to the first plane. Thus, the second hook and the second protrusion both move in the second plane as the swing arm and the latch lever rotate about their respective axes of rotation. 
         [0024]    The latch system may also include a first iron core carried by the rear end portion of the swing arm. The first iron core is attracted to a magnet of a voice coil motor of the hard disk drive to apply torque to the swing arm in a second direction that is opposite to the first direction. 
         [0025]    The latch lever also has a counterbalance at a rear end portion of the latch lever. Preferably, the counterbalance is engaged with the swing arm in the state in which the read/write head is parked. A second iron core is carried by the counterbalance of the latch lever. The second iron core is attracted to a magnet of a voice coil motor of the hard disk drive to apply torque to the latch lever in a second direction that is opposite to the first direction. The latch lever may also have a stopper protruding from the counterbalance toward a side wall of the base of the hard disk drive, and a buffer hole extending through the counterbalance. The stopper limits the rotation of the latch lever by colliding with the side wall of the base. The buffer hole absorbs shock caused by the collision between the stopper and the side wall of the base and deadens noise which would otherwise be produced by such a collision. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof made with reference to the attached drawings in which: 
           [0027]      FIGS. 1A ,  1 B, and  1 C are each a plan view of a conventional single lever type of inertia latch system of an HDD and together illustrate the operation of the latch system; 
           [0028]      FIGS. 2A ,  2 B, and  2 C are each a plan view of a conventional dual lever type of inertia latch system of an HDD and together illustrate the operation of the latch system; 
           [0029]      FIG. 3  is a plan view of a hard disk drive (HDD) having an actuator latch system according to the present invention; 
           [0030]      FIG. 4  is a perspective view of the actuator latch system of the HDD of  FIG. 3 ; 
           [0031]      FIG. 5A  is a perspective view of a portion of the swing arm of the HDD showing a first protrusion and a second protrusion at an end of the swing arm; 
           [0032]      FIG. 5B  is a perspective view of the latch lever of the actuator latch system according to the present invention; 
           [0033]      FIG. 6  is an enlarged plan view of the actuator latch system according to the present invention; 
           [0034]      FIG. 7  is a plan view of the actuator latch system according to the present invention and shows the actuator locked by the first protrusion and the first hook; 
           [0035]      FIG. 8  is another plan view of the actuator latch system but shows the actuator locked by the second protrusion and the second hook; and 
           [0036]      FIG. 9  is still another plan view of the actuator latch system and shows an operation of unlocking the actuator latch system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    Referring to  FIGS. 3 through 5B , a hard disk drive HDD  100  according to the present invention includes a base  110 , a spindle motor  112  mounted to the base  110 , a disk  120  mounted to the spindle motor  112  so as to be rotated by the motor, and an actuator  130  for positioning the read/write head over the disk  120  so that the read/write head can record and/or reproduce data on/from desired portions of the disk. The actuator  130  includes a swing arm  132  supported on the base  110  of the HDD  100  by an actuator pivot  131  so as to be rotatable about an axis of the pivot  131 , a suspension assembly  133  mounted to a lead end portion of the swing arm  132 , and a voice coil motor (VCM) coil  137  disposed on a rear end portion of the swing arm  132 . The suspension assembly  133  of the swing arm  132  supports a slider  134  having the read/write head mounted thereon, and elastically biases the read/write head toward the surface of the disk  120   
         [0038]    The VCM coil  137  is part of a voice coil motor (VCM)  136  for rotating the swing arm  132  about the axis of the pivot  131 . To this end, the VCM  136  also includes a VCM magnet  138  facing the VCM coil  137 . In this respect, segments of the VCM magnet  138  can be disposed under and above the VCM coil  137 , respectively, or the VCM magnet  138  can be provided only under or above the VCM coil  137 . In any case, the VCM magnet  138  is fixed to a yoke. 
         [0039]    Also, the VCM  136  is controlled by a servo control system and rotates the swing arm  132  in a direction according to Fleming&#39;s left hand rule, due to the interaction between current flowing through the VCM coil  137  and the magnetic field formed by the magnet  138 . In particular, when the HDD  100  is turned on and the disk  120  starts to rotate, the VCM  136  rotates the swing arm  132  counterclockwise to move the read/write head over a recording surface of the disk  120 . Conversely, when the power of the HDD  100  is turned off and the disk  120  is stopped, the VCM  136  rotates the swing arm  132  clockwise so that the read/write head is moved off of the disk  120 , i.e., is parked. 
         [0040]    The HDD also includes a ramp  140  disposed on the base  110  radially outwardly of the disk  120 . The read/write head is parked using the ramp  140 . More specifically, an end-tab  135  provided at the end of the suspension assembly  133  is moved onto the ramp  140  when the swing arm  132  is rotated clockwise by the VCM  136  to park the read/write head. 
         [0041]    The HDD  100  also includes an actuator latch system for “locking” the actuator  130  when the read/write head is parked. In other words, the actuator latch system prevents the read/write head from moving away from the ramp  140  and onto the disk  120  when forces created by an external shock or vibrations are applied to the actuator  130  while the disk  120  is stopped. Therefore, the actuator latch system prevents the read/write head from contacting the surface of the disk  120  which contact could otherwise damage the surface of the disk  120  or the read/write head. 
         [0042]    The actuator latch system includes two protrusions  151  and  152  extending from upper and lower parts of a rear end of the swing arm  132 , respectively, and a latch lever  160  installed on the base  110  via a latch pivot  163  so as to be freely rotatable. The latch lever  160  has two hooks  161  and  162  at upper and lower parts of a leading (front) end thereof, respectively, and a counterbalance  164  at a trailing (rear) end thereof. 
         [0043]    The rear end of a swing arm of an HDD is typically formed in a plastic injection mold and supports the VCM coil. Thus, the two protrusions  151  and  152  can be integrally formed at the rear end of the swing arm  132  by a plastic injection molding process. As mentioned above, the two protrusions  151  and  152  project at upper and lower parts of the rear end of the swing arm  132 , respectively. More specifically, the first protrusion  151  protrudes horizontally from the side surface of the rear end portion of the swing arm  132  and is roughly triangular. The second protrusion  152  protrudes from the upper surface of the rear end portion of the swing arm  132 . Part of the second protrusion  152  may also protrude beyond the outer peripheral edge of the rear end portion of the swing arm  152 . 
         [0044]    The first and second hooks  161  and  162  of the latch lever are positioned to interfere with the first and second protrusions  151  and  152 , respectively, to facilitate the locking of the actuator  130 . That is, the first hook  161  is disposed at the same level as the first protrusion  151  and the second hook  162  is disposed at the same level as the second protrusion  152 . In this respect, the first hook  161  protrudes from a bottom surface of the latch lever  160  and the second hook  162  protrudes at the leading end of the latch lever  160 . 
         [0045]    However, the present invention is not so limited. For example, the first protrusion  151  can be disposed on the bottom surface of the rear end portion of the swing arm  132  and the second protrusion  152  can be disposed on the side or upper surface of the rear end portion of the swing arm  132 . The first hook  161  can extend horizontally at the leading end portion of the latch lever  160  and the second hook  162  can protrude from the upper surface of the leading end portion of the latch lever  160 . 
         [0046]    Undesired counterclockwise rotation of the swing arm  132 , i.e., a counterclockwise rotation of the swing arm  132  while the read/write head is parked, is prevented by the engagement between the first and second protrusions  151  and  152  with the first and second hooks  161  and  162  of the latch lever  160 , respectively. This operation will be described in more detail later on. On the other hand, clockwise rotation of the swing arm  132  is restricted by the counterbalance  164  of the latch lever  160 . More specifically, the counterbalance  164  contacts the rear end portion of the swing arm  132  when the read/write head is parked to prevent the swing arm  132  from rotating clockwise. 
         [0047]    Also, the counterbalance  164  of the latch lever  160  includes a stopper  165  which protrudes horizontally toward a side wall  111  of the base  110 . When the latch lever  160  rotates in the counterclockwise direction, the stopper  165  contacts the side wall  111  of the base member  110 . Therefore, the stopper  165  serves to restrict the counterclockwise rotation of the latch lever  160 . The counterbalance  164  also has a buffer hole  166  extending therethrough adjacent the stopper  165 . The buffer hole  166  absorbs shock due to the collision between the stopper  165  of the counterbalance  164  and the side wall  111  of the base  110 . Thus, the buffer hole  166  prevents the latch lever  160  from being damaged and prevents noise from being created when the stopper  165  collides with the side wall  111  of the base  110 . 
         [0048]    Furthermore, a first iron core  171  and a second iron core  172  are respectively disposed on the swing arm  132  and the latch lever  160 . The first iron core  171  is formed of a magnetic body, preferably of an iron body that is ferromagnetic, so that a magnetic force acts between the magnet  138  and the first iron core  171 . The magnetic force creates torque which urges the swing arm  132  to rotate in the clockwise direction. The torque is sufficient to lock the actuator  130  in place when relatively weak external shocks or vibrations are transmitted to the actuator  130  while the read/write head is parked. 
         [0049]    The second iron core  172  is disposed on the counterbalance  164  of the latch lever  160 . The second iron core  172  is formed of a magnetic body, preferably an iron body that is a ferromagnetic, so that a magnetic force acts between the magnet  138  and the second iron core  172 . The magnetic force creates a torque which urges the latch lever  160  to rotate in the clockwise direction. The magnitude of the magnetic force applied to the first iron core  171  is greater than that of the magnetic force applied to the second iron core  172 . Therefore, the magnitude of the torque applied to the swing arm  132  is greater than that of the torque applied to the latch lever  160 . Thus, the magnet  138  and the first and second iron cores  171  and  172  maintain the actuator  130  in its locked state. 
         [0050]    Referring now to  FIG. 6 , the first protrusion  151  and the first hook  161  of the latch lever  160  prevent the swing arm  132  from rotating in the counterclockwise direction when an external force is applied to the HDD while the read/write head is parked. In this respect, the first hook  161  of the latch lever  160  is disposed close to the first protrusion  151 . That is, a first distance D 1  between the first hook  161  and the first protrusion  151  is relatively small when the latch lever  160  is in a position at which the counterbalance  164  contacts the swing arm  132 . 
         [0051]    Therefore, when the swing arm  132  of the actuator  130  is rotated counterclockwise by an external force while the read/write head is parked, the first hook  161  and the first protrusion  151  contact each other in a short amount of time. Therefore, the arresting function of the latch lever system is reliably performed. Also, the amount of shock transferred to the latch lever  160  via the first protrusion  151  is correspondingly small. Accordingly, even though the swing arm  132  and the latch lever  160  rebound, their momentum is relatively small. 
         [0052]    Nonetheless, even when a considerably heavy shock is applied to the HDD  100 , the swing arm  132  rebounds from the counterbalance of the latch lever  160  such that the swing arm  132  rotates counterclockwise for a second time. In this case, the second protrusion  152  and the second hook of the latch lever  160  guarantee that the counterclockwise rotation of the swing arm  132  will be arrested. In this respect, the second hook  162  is positioned relatively far from the second protrusion  152  when the read/write head is parked. That is, a second distance D 2  between the second hook  162  and the second protrusion  152  is greater than the first distance D 1 . The second hook  162  is located closer to the rotational axis of the swing arm  132 , that is, the actuator pivot  131 , than the first hook  161 . In other words, when the read/write head of the actuator  130  is parked, the distance between the second hook  162  and the axis of rotation the swing arm  132  is shorter than the distance between the first hook  161  and the axis of rotation of the swing arm  132 . Accordingly, as indicated by the chain lines of  FIG. 6 , even when the first hook  161  does not arrive in the path of the first protrusion  151 , the second hook  162  is located in the path of the second protrusion  152 . Thus, even if the first protrusion  151  is not caught by the first hook  161  as the swing arm  132  is rotating counterclockwise while the read/write head is parked, the second protrusion  152  will be caught by the second hook  162 . 
         [0053]    The operation of the actuator latch system according to the present invention will be described in even more detail below. 
         [0054]      FIG. 7  shows the case in which the actuator is locked by the first protrusion  151  and the first hook  161  of the actuator latch system. 
         [0055]    Referring to  FIG. 7 , the swing arm  132  is rotated clockwise about the central axis of the actuator pivot  131  by the VCM  136  when the HDD  100  is turned off and the read/write head mounted to the slider  134  is parked. At this time, the rear end portion of the swing arm  132  contacts the counterbalance  164  of the latch lever  160 . The latch lever  160  is thus pushed by the swing arm  132  so as to rotate counterclockwise around the central axis of the latch pivot  163 . As a result, the stopper  165  protruding from the counterbalance  164  of the latch lever  160  contacts the side wall  111  of the base  110 , and thereby stops the latch lever  160  from rotating further in the counterclockwise direction. 
         [0056]    At this time, the actuator  130  is locked in place, i.e., the latch lever system prevents the read/write head from moving toward the disk  120 . In particular, the actuator  130  is fixed in place by the clockwise torque exerted on the swing arm  132  by the magnetic force of attraction between first iron core  171  and the magnet  138 . As described above, the torque applied to the swing arm  132  is greater than that applied to the latch lever  160 . Thus, the actuator  130  is reliably held in place, i.e., the locked state of actuator is reliably maintained. 
         [0057]    However, the swing arm  132  is rotated counterclockwise due to its moment of inertia when an external force exerted on the HDD  100  produces a moment on the swing arm  132  that acts in the counterclockwise direction and is greater than the torque applied to the swing arm  132  due to the magnetic force of attraction between the first iron core  171  and the magnet  138 . In this case, the first protrusion  151  of the swing arm  132  is caught by the first hook  161  of the latch lever  160 . Thus, the swing arm  132  is prevented from rotating excessively in the counterclockwise direction while the read/write head is parked. 
         [0058]    Contrast this to the case in which shock applied to the HDD  100  and transmitted to the swing arm  132  and the latch lever  160  creates moments in the clockwise direction. In this case, the swing arm  132  and the latch lever  160  will not rotate in the clockwise directions because the rear end portion of the swing arm  132  and the counterbalance  164  of the latch lever  160  are disposed in contact each other. Instead, the swing arm  132  rebounds from the latch lever  160  and thereby begins to rotate counterclockwise. However, the first protrusion  151  is caught by the first hook  161  of the latch lever  160 . Thus, the counterclockwise rotation of the swing arm  132  is arrested. 
         [0059]    As described above, the first protrusion  151  normally collides with the first hook  161  of the latch lever  160  when an external shock applied to the HDD while the read/write head is parked causes the swing arm  132  and the latch lever  160  to initially rotate counterclockwise. When the shock is considerably severe, the swing arm  132  and the latch lever  160  rebound and thereby begin to rotate clockwise. The swing arm  132  then collides with the counterbalance  164  of the latch lever  160 . As a result of this collision, the swing arm  132  and the latch lever  160  each rotate for a second time in a counterclockwise direction. 
         [0060]    As shown in  FIG. 8 , in this case, the first hook  161  of the latch lever  160  might not rotate into the path of the first protrusion  151 . However, the second hook  162  of the latch lever  160  will be rotated into the path of the second protrusion  152 . That is, the second protrusion  152  is caught by the second hook  162  so that the secondary counterclockwise rotation of the swing arm  132  is arrested. 
         [0061]      FIG. 9  shows the “unlocking” of the actuator by the actuator latch system of the present invention. Referring to  FIG. 9 , when the HDD  100  is turned on, power is applied to the VCM coil  137  provided at the rear end portion of the swing arm  132 . As a result, the swing arm  132  is rotated counterclockwise by a torque greater than that the torque applied to the swing arm  132  in the clockwise direction due to the force of attraction between the first iron core  171  and the magnet  138 . Simultaneously, the latch lever  160  is rotated clockwise by the torque applied to the latch lever  160  due to the force of attraction between the second iron core  172  and the magnet  138 . As a result, the first hook  161  and the second hook  162  of the latch lever  160  do not interfere with the movement of the first protrusion  151  and the second protrusion  152 . 
         [0062]    Finally, although the present invention has been particularly shown and described with reference to the preferred embodiments thereof, the present invention is not so limited. For example, although the present invention has been shown and described in connection with a hard disk drive employing a ramp loading type of parking system, the present invention could also be applied to hard disk drive employing a CSS type of parking system. Thus, various changes in form and details may be made to the preferred embodiments without departing from the true spirit and scope of the invention as defined by the appended claims.