Abstract:
Disclosed is an actuator latch for keeping an actuator in a park position when the drive is subject to non-operating shock. Magnetic forces hold the latch in both its latched and unlatched positions. VCM-controlled actuator movement causes the latch to move both into and out of these positions. Airflow generated by spinning discs effect movement of the latch out of the latching position when the drive is powered up.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/333,026, filed Nov. 5, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to disc drive actuators.  
         BACKGROUND OF THE INVENTION  
         [0003]    Disc drives of the type known as “Winchester” disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 15,000 RPM.  
           [0004]    Data are recorded to and retrieved from the discs by ate least one read/write head assembly, also known as a head or slider, which are controllably moved from track to track by an actuator assembly. Where more than one head is used, an array of heads are typically vertically aligned. The read/write head assemblies typically comprise an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative pneumatic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by flexures attached to the actuator.  
           [0005]    The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. The actuator is mounted to the pivot shaft by precision ball bearing assemblies within a bearing housing. The actuator supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member.  
           [0006]    On the side of the actuator bearing housing opposite to the coil, the actuator assembly typically includes one or more vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. These actuator arms extend between the discs, where they support the head assemblies at their desired positions adjacent the disc surfaces. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved generally radially across the data tracks of the discs along an arcuate path.  
           [0007]    When the power to the disc drive is turned off, the disc stops rotating. This means that the slider stops flying and returns to the surface of the disc. Some disc drives have a specified landing zone on the disc surface for the slider to land on. This landing zone is typically near the outer edge or near the center of the disc surface, and it is designed so that the head can contact the landing zone without causing damage to the surface of the disc. This may be accomplished in a number of ways, but one conventional method is to texture the discs to prevent static friction, or “stiction” to develop between the surfaces of the disc and head. Other disc drive have a ramp which allows the actuator to move the head radially away from the disc and then lifted away from the surface of the disc.  
           [0008]    Whether the head is “parked” in a landing zone, on a ramp, or some other location, it is desirable that the actuator be held in the parked position when the power to the disc drive is turned off. This is because the voice coil motor no longer controls the actuator, so if the disc drive is subject to a shock, the actuator arm can drift onto the disc. This can cause permanent damage to a disc. Disc drives are typically provided with some sort of “latch” for this purpose. The latch must prevent movement of the actuator out of the parked position when the actuator is not driven by the VCM, but must also allow the actuator to pivot once power is restored to the drive.  
           [0009]    Historically, latches have taken a number of different forms. For example, some latches have a stationary magnet fixed to the deck and a ferromagnetic element attached to the actuator, such that the magnet holds the ferromagnetic element and thereby the actuator in place when the actuator is parked. The latching power of such a latch is often difficult to predict, and when too powerful can slow data access and increase power consumption. Others include springs which bias the latch toward a position in which it engages the actuator when it is in the parked position, and is moved out of engagement with the actuator by the use of an electromechanical device such as a solenoid when power is restored to the drive. However, such latches can be complex to manufacture and expensive to install. Still others rely on the mere inertia of a latch body to move it into engagement with the actuator when the drive is subject to shock. This type of latch is prone to rebounding away from the actuator after latching, however, such that it is incapable of responding to a second shock before the actuator has left the park position.  
           [0010]    One type of latch which is of particular relevance here is known as an air latch, which is biased toward a latch position but moves out of engagement with a parked actuator in response to airflow generated when power is restored to the drive and the discs begin to spin. A disadvantage of the air latch is that when power is removed from the drive and the discs slow down (called “spindown”), air currents are still capable of keeping the latch out of its latching position. Even when the actuator has been parked, a shock during spindown may unpark the actuator and return a head into contact with a disc surface.  
           [0011]    Yet another type of latch of particular relevance is what is known as a “bistable” latch. This type of latch is configured so as to use magnetic forces to hold it in place in both the latched and unlatched positions. VCM-controlled movement of the actuator is responsible for moving the latch into and out of both the latched and unlatched positions. When subject to shock, magnetic force in combination with the inertia of the latch body prevents movement out of the latched position despite the rotational force exerted upon it by the actuator. A difficulty with this type of latch is that while increasing the magnetic force in the latched position prevents unwanted actuator movement, it also increases the amount of VCM current required to move the actuator so as to force the latch out of the latched position when power is restored to the drive. This has the effect of increasing the time for the head to return to the disc and increases power consumption as well. Taken to an extreme, unlatching may be prevented altogether. In any case, it should be clear that the bi-stable latch will always present a trade-off between the forces required to latch the actuator in the face of shock and to unlatch the actuator when power is restored to the drive.  
           [0012]    What the prior art has been lacking is a low-cost actuator latch which effectively prevents movement of an actuator out of its parked position while minimizing the amount of power required to release the actuator when power is restored to the drive.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention is directed to an actuator latch for keeping an actuator in a park position when the drive is subject to non-operating shock. Magnetic forces hold the latch in both its latched and unlatched positions. VCM-controlled actuator movement causes the latch to move both into and out of these positions. Airflow generated by spinning discs effect movement of the latch out of the latching position when the drive is powered up.  
           [0014]    These and other features and benefits will become apparent upon review of the following figures and the accompanying detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 shows a plan view of a disc drive in which a first embodiment of the latch of the present invention is in a latching position, holding an actuator in a parked position.  
         [0016]    [0016]FIG. 2 shows a plan view of a disc drive in which the latch is moved out of its latching position.  
         [0017]    [0017]FIG. 3 shows a plan view of a disc drive in which the latch remains out of the latched position as the actuator moves over a surface of a disc.  
         [0018]    [0018]FIG. 4 shows a plan view of a disc drive in which the actuator is returning to its parked position.  
         [0019]    [0019]FIG. 5 shows a plan view of a disc drive in which the actuator has returned to its parked position, returning the latch to the latching position.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Turning now to the drawings and specifically to FIG. 1, shown is an exploded view of an example of a disc drive  100  in which the present invention is particularly useful. The disc drive  100  includes a deck  110  to which all other components are directly or indirectly mounted and a top cover (not shown) which, together with the deck  110 , forms a disc drive housing which encloses delicate internal components and isolates these components from external contaminants.  
         [0021]    The disc drive  100  includes at least one disc  200  which is mounted for rotation on a spindle motor (not shown). The disc or discs  200  include on their surfaces a plurality of circular, concentric data tracks on which data are recorded one or more vertically aligned head assemblies  330 . The head assemblies  330  are supported by flexures  320 , which are attached to arms  310  of actuator  300 . The actuator  300  is mounted to a bearing assembly  400  about which the actuator  300  rotates.  
         [0022]    Power to drive the actuator  300  about the pivot assembly  400  is provided by a voice coil motor (VCM). The VCM includes a coil  350  which is supported by the actuator  300  within the magnetic field of a permanent magnet assembly having spaced upper and lower magnets, the lower of which is illustrated at  360 . Electronic circuitry is provided on a printed circuit board (PCB, not shown) mounted to the underside of the deck  110 . Control signals to drive the VCM are carried between the PCB and the moving actuator  300  via a flexible printed circuit cable (PCC)  370 , which also transmits data signals to and from the heads  330 .  
         [0023]    When the drive  100  is to be shut down or power is cut to the drive  100  for some other reason, the actuator  300  is returned to its parked position. In the drive  100  illustrated in FIG. 1, the parked position is one in which the head  330  located on a ramp  120 , beyond the outer diameter of disc  200 . Ramp  120  is a sloped surface protruding over the edge of disc  200 , such that the head  330  is lifted away from the disc  200  and beyond its outer diameter along the surface of ramp  120  as the actuator pivots clockwise. The actuator  300  may be returned to the parked position by any of a number of known methods. For example, it could be driven to this position by the VCM as part of a power down procedure or returned using back EMF generated by discs  200  during spindown where power is cut to the drive.  
         [0024]    Also shown in FIG. 1 is one embodiment of a latch  500 . Latch  500  is pivotally attached to the deck  110  by pivot portion  510 . The latch  500  further includes two portions  520 , 530  extending away from the pivot  510 . Each portion  520 , 530  includes a corresponding ferromagnetic element  522 , 532  mounted to it. The elements  522 , 532  may be fixed to the latch  500  by any of a number of methods; for example, they may be injection molded into the latch  500  or fixed to it by adhesives or some other mechanical fasteners. Latch  500  is able to pivot through a range of motion. At one end of this range of motion, when the latch  500  has rotated fully counterclockwise and is latching the actuator  300  in its parked position, element  522  is located within the magnetic field generated by at least one of the magnets of the VCM. The attraction between the magnetic field and element  522  biases the latch  500  into the latching position. Portion  520  also includes a first engagement element, shown in FIG. 2 to take the form of a surface  524  engaging a projection  360  on the actuator  300 . While the latch  500  is in the latching position, surface  524  prevents movement of projection  380  when the drive is subject to shock, and thereby latches the actuator  300  in its parked position.  
         [0025]    When power is restored to the drive  100 , the VCM attempts to drive the actuator  300  in a counterclockwise direction, and projection  380  exerts a force against the surface  524  on portion  520  in an effort to pivot the latch  500  clockwise about pivot  510 . This movement is resisted by the attraction between magnetic element  522  and the magnetic field generated by the VCM as explained above, however, and it is for this reason that latch  500  is also provided with a mechanism for facilitating unlatching of the actuator  300 . The operation of this mechanism will now be described.  
         [0026]    Latch  500  also includes an element which is responsive to airflow generated by disc  200  when it is spinning. Operation is illustrated in FIG. 2, where the airflow-responsive element takes the form of an air vane  540 . When power is restored to the drive  100 , disc  200  begins spinning in a counterclockwise direction as depicted by arrow  210 . Air located above the surface of disc  200  begins moving along with it, and this moving air applies a force to air vane  540 . As projection  380  pushes against surface  524 , air pushes against air vane  540 , and the combined forces are sufficient to rotate the latch  500  in a clockwise direction as illustrated by arrow  550 , until surface  524  moves to an extent that projection  380  can move past it. Actuator  300  is now free to move in a counterclockwise direction, such that head  330  may descend ramp  120  and then pass over the surface of the disc to conduct read/write operations.  
         [0027]    [0027]FIG. 2 depicts the unlatching process just as projection  380  has cleared surface  524  and latch  500  has pivoted clockwise to its full extent. It can also be seen that in this position, while magnetic element  522  has left the magnetic field generated by the VCM, magnetic element  532  has entered the magnetic field. It should be clear that latch  500  is now locked into an unlatched position, where the actuator  300  is free to move without contacting latch  500 .  
         [0028]    [0028]FIG. 3 depicts a disc drive  100  in which the actuator  300  is in a position to allow head  330  to read or write data on disc  200 . Note that ferromagnetic element  532  remains in a position in which it is attracted to the magnetic field generated by the voice coil magnets  360 . Latch portion  520  may also be provided with a curved surface as illustrated in FIG. 3, allowing full travel of actuator projection  380 . Note also that ferromagnetic projection  532  is located in a projection of portion  530  which contacts magnet  360 , preventing further clockwise movement of latch  500 . A stop pin such as pin  130  illustrated in FIG. 3 may also be used.  
         [0029]    [0029]FIG. 4 depicts disc drive  100  in which actuator  300  has moved toward the parked position, just prior to latching of the actuator  300 . Note that head  330  has begun to ascend ramp  120 , at which point the rotation of disc  200  begins to slow down, as it is no longer necessary to fly the head  330  above disc  200 . Projection  380  has just come into contact with surface  534  of latch portion  530 .  
         [0030]    [0030]FIG. 5 depicts disc drive  100  in which actuator  300  has reached the parked position, head  330  having fully ascended the ramp. As the actuator  300  is driven clockwise, projection  380  exerts a force on surface  534  of portion  530 . This causes the latch  500  to rotate in a counterclockwise direction about pivot  510  as illustrated by arrow  560 . This causes ferromagnetic element  522  to enter the magnetic field generated by voice coil magnets  360  once again. Surface  524  is rotated into a position to obstruct movement of actuator projection  380  in a counterclockwise direction. While disc  200  continues to spin down, airflow alone is not sufficient to overcome the bias force provided by ferromagnetic element  522 . Only when power is restored to the drive  100 , as depicted in FIG. 2, will the combined forces of rotating actuator projection  380  and airflow be sufficient to unlatch the actuator  300 . Counter clockwise travel is limited by contact between a projection on portion  520  in which ferromagnetic element  522  is located, though a stop pin such illustrated pin  140  could also be provided.  
         [0031]    It should be apparent that the bi-stable inertial air latch  500  described above is particularly effective for preventing an actuator  300  from leaving the parked position during nonoperative shock, while also easily releasing the actuator  300  when power is restored to the drive  100 . However, it should also be understood that the latch and/or drive may take other forms without departing from the spirit of the claimed invention. For example, an air vane may be provided to assist a variety of other types of bi-stable inertia latches. One such latch carries a small magnetic element which pivots between two stationary ferromagnetic stop pins, and an air vane would be similarly useful in assisting to unlatch this type of latch. An air vane could also be added to a bi-stable latch which uses an over-center spring arrangement to assist in unlatching of an actuator. Moreover, the air vane  540  depicted in the accompanying drawings is merely illustrative, and could take a variety of other forms so long as it assists in rotation of a bi-stable latch out of a latching position. While the illustrated drive is shown to include a ramp  120 , the disclosed latch would be equally useful in a drive in which the parking zone is located on the surface of an outer diameter of disc  200 . It is also contemplated that a similar latch could be used in a drive in which a head  330  is parked at an inner diameter of a disc  200 , though of course this would require that the latch be position at the other end of magnet  360  and reversed so air vane  540  extends down the left side of a magnet  360  such as that in the accompanying figures. Furthermore, while the term “air” is used throughout this document, it should be understood that this term includes any type of gas and should not be limited to breathable air.  
         [0032]    In short, it is apparent that the present invention is particularly suited to provide the benefits described above. While particular embodiments of the invention have been described herein, modifications to the embodiments which fall within the envisioned scope of the invention may suggest themselves to one of skill in the art who reads this disclosure.  
         [0033]    Alternatively stated, a first contemplated embodiment of the invention takes the form of a latch for holding a rotatable element (such as  300 ) in a stationary position. The latch includes a latch body (such as  500 ), a first element (such as  522 ) configured to bias the latch body (such as  500 ) into a first position, a second element (such as  532 ) configured to bias the latch body (such as  500 ) into a second position, and a third element (such as  540 ) configured to urge the latch body (such as  500 ) out of the first position in response to air movement. The latch body (such as  500 ) may be rotatable between the first and second positions. Optionally, the first element (such as  522 ) may be ferromagnetic. The second element (such as  532 ) may be ferromagnetic. The third element (such as  540 ) may take the form of a protrusion. The latch may also include a pivot (such as  510 ) about which the latch body (such as  500 ) is rotatable where the latch body (such as  500 ) includes a first portion (such as  520 ) extending away from the pivot (such as  510 ) in a first direction and a second portion (such as  530 ) extending away from the pivot (such as  510 ) in a second direction, the first element (such as  522 ) being mounted to the first portion (such as  520 ) and the second element (such as  532 ) being mounted to the second portion (such as  530 ). The third element (such as  540 ) may be mounted to the second portion (such as  530 ). The latch may be configured to allow the rotatable element (such as  300 ) to move out of the stationary position when the latch body (such as  500 ) is in the second position.  
         [0034]    Alternatively stated, a second contemplated embodiment of the invention takes the form of a disc drive (such as  100 ), including a base (such as  110 ), at least one disc (such as  200 ) rotatably mounted to the base (such as  110 ), an actuator (such as  300 ) mounted to the base (such as  110 ) and being rotatable into a parked position, and a latch for holding the actuator (such as  300 ) in the parked position. The latch includes a latch body (such as  500 ) which is biased toward a first position when near the first position and is biased toward a second position when near the second position. The latch body (such as  500 ) is also configured to be urged away from the first position in response to air movement generated by rotation of the disc (such as  200 ). Rotation of the actuator (such as  300 ) out of the parked position may urge the latch body (such as  500 ) out of the first position. A protrusion (such as  380 ) may be mounted to the actuator (such as  300 ) and may be configured to contact the latch body (such as  500 ) when the actuator (such as  300 ) is in the parked position. The latch body (such as  500 ) may have a first surface (such as  524 ), such that the protrusion (such as  380 ) is configured to exert a force against the first surface (such as  524 ) so as to urge the latch body (such as  500 ) away from the first position when the actuator (such as  300 ) leaves the parked position. The latch body may include a second surface (such as  534 ), such that the protrusion (such as  380 ) is configured to exert a force against the second surface (such as  534 ) so as to urge the latch body (such as  500 ) toward the first position when the actuator (such as  300 ) approaches the parked position. The disc drive (such as  100 ) may further include a magnet (such as  360 ) for effecting movement of the actuator (such as  300 ), in which case the latch body (such as  500 ) includes a first ferromagnetic element (such as  522 ) for biasing the latch body (such as  500 ) toward the first position. The latch body may also include a second ferromagnetic element (such as  532 ) for biasing the latch body (such as  500 ) toward the second position. The latch body (such as  500 ) may include an air vane (such as  540 ) overlying a surface of the disc (such as  200 ) for urging the latch body (such as  500 ) away from the first position in response to air movement generated by rotation of the disc (such as  200 ). Movement of the actuator (such as  300 ) away from the parked position may urge the latch body (such as  500 ) away from the first position.