Abstract:
The present invention provides an adjustable crash stop. The stiffness or load of the crash stop may be varied by rotating the stop and thereby varying the point of contact between the actuator assembly and the crash stop. The point of contact is on an arcuate contact surface of a cantilever supported spring. The spring is supported by a stem that can be positioned in several different rotational positions such that the contact point is at different locations on the contact surface. The stiffness at each contact point changes as its distance from the hinge point of the spring changes.

Description:
FIELD OF THE INVENTION  
       [0001]     This application relates generally to movable actuators and more particularly to a crash stop assembly for a movable actuator.  
       BACKGROUND OF THE INVENTION  
       [0002]     In an apparatus such as a disc drive, information is written to and read from tracks on data storage device discs through the use of a pivoting actuator assembly. The actuator assembly includes heads, which each move in close proximity above the corresponding surface of the associated disc. A voice coil motor controls the track position of the heads by pivoting the actuator assembly. The voice coil motor typically includes a coil attached to the actuator assembly, as well as one or more permanent magnets, which establish a magnetic field in which the coil is immersed. A bottom pole proximal the data storage device base plate and a top pole distal from the base plate typically establishes the magnetic field. The controlled application of current to the coil causes magnetic interaction between the permanent magnets and the coil so that the actuator assembly pivots.  
         [0003]     Various approaches have been developed to securely position an actuator assembly in such an apparatus during a loss of power event or shutdown of the drive such that the heads do not land on a portion of the disc real estate that contains data. Typically these approaches involve either positioning the actuator assembly onto a shelf to hold the heads away from the discs or positioning the heads over portions of the disc surfaces that contain no data, such as the landing zones of the discs. The landing zones typically contain no magnetic recorded information or alternatively contain only historical servo information that is not pertinent to drive operation if damaged by the heads actually contacting the surfaces of the discs in this location. Approaches for holding the arm assembly in such as “park” position include mechanical latches, electromechanical latches and magnetic latches.  
         [0004]     To limit the range of motion of the actuator and heads under loss of power conditions and keep the heads in the landing zone, designers usually incorporate crash stops and a latch mechanism to position and hold the arm in the park position while the drive is without power. One concern in providing a latch and crash stop assembly is the level of energy absorbed by the crash stops. It is desirable that the crash stops absorb the impact of the actuator assembly as it stops without detrimentally affecting the head disc interface, even though the actuator assembly is designed to stop in a position away from the data region of the discs where the heads are parked. If excessive impact were to occur, the heads or the disc surface itself could be damaged by head slap. In addition, the actuator arm inertia and the impact energy varies depending on the individual deck design. This generally requires separate crash stop design to accommodate the change in impact energy, thereby increasing design and tooling costs.  
         [0005]     Accordingly, there is a need for a crash stop assembly with uniform design able to provide varying degrees of stiffness. The present invention provides a solution to this and other problems, and offers other advantages as well.  
       SUMMARY OF THE INVENTION  
       [0006]     One embodiment of the present invention may be viewed as an apparatus in which a pivotally supported actuator assembly mounted on the base plate, and one or more rotationally adjustable crash stops for limiting pivotal movement of the actuator assembly. Alternatively, the crash stops may be located in the base of the actuator assembly which is then attached to the data storage device base plate.  
         [0007]     These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a partially broken away plan view of a data storage device incorporating an embodiment of the present invention showing select primary internal components.  
         [0009]      FIG. 2  is a plan view of the embodiment of the crash stop in accordance with the present invention shown in  FIG. 1  separate from the data storage device.  
         [0010]      FIG. 3  is a perspective view of the crash stop shown in  FIG. 2 .  
         [0011]      FIG. 4  is a top view of an actuator arm assembly with a crash stop of the present invention inserted into the bottom pole plate of the voice coil motor fastened to the base plate of the data storage device along with top views of the crash stop showing various alternate points of contact between the actuator arm and the impact portion of the crash stop.  
         [0012]      FIG. 5  is a perspective exploded view of the actuator arm assembly and crash stop shown in  FIG. 4  showing a slotted aperture in the bottom pole plate (or in the base plate) receiving the crash stop in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to  FIG. 1 , data storage device  100  includes a base plate  102  to which various components of the data storage device  100  are mounted. A top cover  104 , shown partially cut away, cooperates with the base plate  102  to form an internal, sealed environment for the data storage device  100  in a conventional manner. The components include a spindle motor  106 , which rotates one or more discs  108  at a constant high speed. Information is written to and read from tracks on the discs  108  through the use of an actuator assembly  110 , which rotates during a seek operation about pivot or bearing shaft assembly  112  positioned adjacent the discs  108 . The actuator assembly  110  includes a head aspect  114  extending forwardly from the pivot  112  and a motor aspect  116  extending rearwardly from the pivot  112 . The head aspect  114  includes a plurality of actuator arms  118  which extend towards the discs  108 , with one or more flexures  120  extending from each of the actuator arms  118 . Mounted at the distal end of each of the flexures  120  is a head  122 , which includes an air bearing slider enabling the head  122  to fly in close proximity above the corresponding surface of the associated disc  108 .  
         [0014]     During a seek operation, the track position of the heads  122  is controlled through the use of a voice coil motor  124 , which typically includes a coil  126  attached to the motor aspect  116  of the actuator assembly  110 , as well as one or more permanent magnets  128 , which establish a magnetic field in a gap in which the coil  126  is immersed. The magnetic field is typically established through a bottom pole plate  130  mounted on the base plate  102 , which includes a permanent magnet  128  thereon, and a top pole  132 , shown partially cut away, spaced from the base plate  102 , which also includes a permanent magnet  128 . The controlled application of current to the coil  126  causes magnetic interaction between the permanent magnets  128  and the coil  126  so that the coil  126  moves back and forth in the gap between the magnets  128  in accordance with the well-known Lorentz relationship. As the coil  126  moves, the actuator assembly pivots about the bearing shaft assembly  112 , and the heads  122  are caused to move across the surfaces of the discs  108 .  
         [0015]     The spindle motor  106  is typically de-energized when the data storage device  100  is not in use for extended periods of time. The heads  122  are moved over park zones or landing zones  123  near the inner diameter of the discs  108  when the drive motor is de-energized. The heads  122  are secured over the park zones  123  through the use of an actuator latch arrangement (not shown), which prevents inadvertent rotation of the actuator assembly  110  when the heads are parked. A crash stop assembly  140  limits pivotal movement of the actuator assembly  110 . Alternatively, or in addition, the data storage device may comprise a crash stop located on the opposite side of the actuator assembly to limit the outward movement of the heads  122 . Such a design may be desirable, for example, where the parking zone consists of a ramp located adjacent the outer periphery of the discs  108 .  
         [0016]      FIGS. 2 and 3  show two views of one embodiment of a crash stop  140  in accordance with the invention. As shown in the top view ( FIG. 2 ), the crash stop  140  includes a spring portion  141  that wraps around, i.e. extends substantially circumferentially, around the stem portion  150 . The crash stop  140  has a spring support  143  radially supporting the spring portion  141  from the stem portion and a hinge area  142  joining the spring support  143  and the spring portion  141 . Preferably, the spring  141  extends circumferentially about the stem  150  such that the arc formed from the hinge area  142  to the terminal portion  144  is at least about 180°, and more preferably, at least about 270°. The spring  141  may extend fully around the stem  150  in an arc provided that the spring retains the ability to flex upon impact with the actuator assembly. Thus, the terminal portion  144  should not come in contact with the spring support  143 . The crash stop  140  is preferably made of a molded plastic material although other materials may be used such as metal. A combination of materials may also be used such as a metal spring attached to a plastic stem. The thickness, width and height of the spring portion of the crash stop  140  can be varied to obtain the overall range of desired spring characteristics. The outer curved surface of the spring portion  141  forms a contact surface  145 . The actual point of contact depends on the rotational position of the crash stop.  
         [0017]      FIG. 3  is a perspective view of crash stop  140 . The bottom end of the stem  150  is preferably shaped to form a key, and in the illustrated embodiment, a generally rectangular key that has parallel vertical surfaces  151 , 152  on the lower portion of the stem  150 .  FIG. 4  shows a top view of the actuator assembly  110  relative to the location of crash stop  140  mounted on the pole plate  130 . It is to be understood that the pole plate  130  may be shorter than that shown, such that the crash stop  140  is fastened directly to the base plate  102  rather than via the pole plate  130 . Also shown in  FIG. 4  are insets showing alternative rotational positions of the crash stop  140  that change the contact point of the contact arm  113  with the impact surface  145  of the spring portion  141 . The stiffness of the spring  140  will decrease as the contact point moves further from the hinge area. The amount of stiffness seen by the actuator  110  when contact arm  113  contacts the crash stop  140  depends on the length of the spring portion  141  between the contact point and the hinge area  142 . The closer the contact point is to the hinge area  142 , the greater the stiffness. The further the contact point is from the hinge area  142 , the less the stiffness, hence more cushion or resilient, the effect will be on the actuator contact arm  113  during contact. Since the contact surface  145  of the spring portion  141  extends in an arc around the stem  150 , the stiffness of the crash stop  140  that the actuator assembly  110  sees can be varied by simply changing the rotational position of the crash stop  140  about its axis relative to the actuator assembly.  
         [0018]      FIG. 5  is a perspective exploded view of the actuator assembly  110  and crash stop  140 . In this particular embodiment, aperture  115  in the pole plate  130  (or alternatively in the base plate  102 ) is defined by two intersecting perpendicular slots. This “cross shaped” aperture permits the key shaped bottom end of the stem  150  to fit in four orientations resulting in four positions of crash stop  140 , each position being offset from the next by 90 degrees. Additional slots may be added to increase the number of rotational positions of the crash stop  140  in the aperture  115 . Preferably, the aperture is machined into the base of the data storage device or base of the actuator assemble, as the case may be.  
         [0019]     Alternatively, the bottom portion of the stem  150  may be substantially cylindrical in shape. In this manner, the crash stop could be rotated to essentially any position within the 360 degree arc defined by the aperture. The aperture  115  in this case would be a smooth bore and the stem may be smooth to allow for limitless rotation. In this alternative embodiment, a securing means (not shown) would be needed to secure the crash stop in the desired position. Alternatively, the surfaces of the stem and aperture may comprise small flexible teeth that engage one another and allow position change by “clicking” from one rotational position to the next. Alternatively the teeth may also be inflexible, i.e. closely spaced splines that intermesh such that the crash stop must be rotated to the selected position, and then inserted into the complementary shaped aperture such that the teeth or splines are engaged and the crash stop cannot be further rotated while in this engaged position.  
         [0020]     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.