Patent Document

FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to data storage devices, and more particularly to methods and apparatus for ramp unload in such devices.  
       BACKGROUND OF THE INVENTION  
       [0002]     Disc drives are among the most widely used means for storing massive amount of data, and must therefore be very reliable. Recently, disc drives are increasingly found in hand-held or portable electronic devices such as audio-visual media players and recorders. Since the majority of these devices are battery-operated, there is now also a need for disc drives to operate with minimal power consumption.  
         [0003]     A disc drive typically includes one or more discs mounted on a spindle motor, as well one or more sets of read/write heads configured for writing data to or reading data from the discs. The read/write heads may be coupled to an actuator arm assembly and moved thereby to read data from or write data to various areas or tracks of the discs.  
         [0004]     While the read/write heads are configured to “fly” over the surface of a rotating disc when the disc drive is in operation, it is desirable to keep the read/write heads away from the disc surface when the drive is not in operation. This is to avoid inadvertent contact between these components, as they may result in damage to the disc and the corruption of data. For this and other reasons, a disc drive may at certain times “unload” the read/write heads to a ramp positioned next to the disc. In an unloaded state, at least part of the actuator arm bearing the read/write heads will be engaged by the ramp, with the read/write heads suspended away from the disc.  
         [0005]     In an exemplary unloading operation, the read/write heads are moved in a direction opposite to a retract direction until the actuator arm is brought to rest by collision with an inner stopper. The actuator arm is then driven by a constant voltage to move in the retract direction, all the way from the inner stopper, up the ramp, and to the rest position on the ramp.  
         [0006]     While this may be feasible for some types of disc drives, there remains a need for solutions that will be more efficient and less demanding on the limited power resources of disc drives intended for use with portable consumer electronic devices.  
         [0007]     The present invention provides a solution to this and other problems besides offering other benefits, as described below.  
       SUMMARY OF THE INVENTION  
       [0008]     Embodiments of the present invention provide methods of performing ramp unload in disc drives and disc drives configured to perform such methods.  
         [0009]     According to embodiments of the present invention, there are provided methods including holding read/write heads at an initial position before moving them towards a ramp disposed adjacent to the disc to reach a target velocity at the ramp. Optionally, the methods may include bringing the read/write heads to an initial position that is located at a recordable region of the disc. The movement of the read/write heads may be characterized by a substantially linear velocity profile or a substantially constant voltage across the motor controlling the movement of the read/write heads. Also provided are apparatus configured to perform methods according to embodiments of the present invention.  
         [0010]     Various advantages which characterize embodiments of the present invention will be apparent upon reading of the following detailed description and reviewing of the associated drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic top view of a disc drive for illustrating embodiments of the present invention;  
         [0012]      FIG. 2  is an enlarged partial sectional view of  FIG. 1 ;  
         [0013]      FIG. 3  is a schematic top view of a disc drive showing an unload operation according to embodiments of the present invention;  
         [0014]      FIG. 4  is an enlarged partial sectional view of  FIG. 3 ;  
         [0015]      FIG. 5  is a schematic top view of a disc drive for illustrating another aspect of unload operations according to embodiments of the present invention;  
         [0016]      FIG. 6  is an enlarged partial sectional view of  FIG. 5 ;  
         [0017]      FIG. 7  is a velocity-position chart for illustrating velocity profiles;  
         [0018]      FIG. 8  is a flowchart showing a method according to embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     For clarity, embodiments of the present invention will be described with reference to a disc drive having one disc and one set of read/write heads that are supported by an actuator arm. Nevertheless, it will be understood that embodiments of the present invention may be applied in various types of disc drives, such as disc drives with varying numbers and arrangements of discs and read/write heads, etc., and that the following description is provided solely for the purpose of illustration and is not intended to be limiting.  
         [0020]     Shown in  FIG. 1  is a disc drive  100  configured to perform ramp unload operations according embodiments of the present invention. The disc drive  100  includes a disc  110 , an actuator arm assembly  120  having an actuator arm  121 , read/write heads  130  supported by the actuator arm  121 , and a ramp  140  disposed adjacent to an outer perimeter  116  of disc  110 . For convenience, the recordable area of a disc may be described as consisting of three regions: an inner region nearest to the inner perimeter  114  (“ID”) of an annular disc, an outer region nearest to the outer perimeter  116  (“OD”) of the same, and a middle region (“MD”) therebetween. As these are terms of convenience, they may not correlate to or be defined by any particular track or radial dimensions of a disc, but are useful for referring generally to parts of the disc.  
         [0021]     Actuator arm assembly  120  is operable by a motor, in this example, a voice coil motor (VCM)  150  including a coil  122  coupled to the actuator arm  121  and a magnet  152 . When a voltage is applied to the VCM  150 , the resultant electromagnetic interactions between the moving current in the coil  122  and the magnet  152  produces torque forces that cause the actuator arm  121  to turn about a pivot  124 , and thereby move the read/write heads  130  to different areas or tracks of disc  110 . Actuator arm  121  may include some form of an extension or tang  126  that is suitably configured to engage ramp  140  as the actuator arm  121  moves towards the outer edge  116 .  
         [0022]     Ramp  140  may be shaped so that it includes a sloping surface near a surface of the disc  110  (to facilitate engagement with tang  126 ), a detent  144  shaped to keep the tang  126  from moving off the ramp  140  when the disc drive is not in operation, and an intermediate surface therebetween. The end of the sloping surface nearest to the disc surface will be referred to in this document as a first end  142 .  
         [0023]     A flexible printed circuit cable  160  operably connects VCM  150  and read/write heads  130  to a printed circuit board assembly (PCBA)  180 . PCBA  180  is mounted to a housing of disc drive  100 , and may communicate with printed circuit cable  160  via a connector  170 . The various disc drive components may be controlled by one or more controller devices that form part of PCBA  180 . For the purpose of convenience, reference to a controller  190  will be understood to collectively mean any number of devices, for example, as shown in  FIGS. 1, 3  and  5 , configured to perform such functions as will be described. In other words, controller  190  may be in the form of one or more devices or integrated circuit chips.  
         [0024]     In an unload operation according to one embodiment of the present invention, VCM  150  causes actuator arm  121  to move from wherever it was at that time to a track  112 , which will be referred to for convenience as an initial track  112 . Read/write heads  130  are then allowed to “follow” the initial track  112 . A track-following operation may involve reading and processing servo information and using the servo information to determine to what extent the read/write heads are mis-aligned relative to the initial track  112 . VCM  150  may then move actuator arm  121  appropriately to keep the read/write heads  130  aligned with the desired track. Next, current associated with a first voltage profile is fed to drive the VCM  150 , causing the actuator arm  121  to move from the initial track  112  towards the ramp  140  in a retract direction, until the tang  126  engages the first end  142 . Current associated with the first voltage profile or another voltage profile may continue to drive the tang  126  along the sloping surface, along the intermediate surface, and to the detent  144 . Thus, the read/write heads  130  can be brought into a state of rest parked away from disc  110 .  
         [0025]     According to another embodiment of the present invention, the disc drive in operation determines the position of the actuator arm  121  at the time where it is desired to initiate an unload operation. The required current is fed to the VCM  150  so that the actuator arm  121  stops moving. From the servo information read from the disc, the disc drive determines the distance of this initial position of the read/write heads  130  with respect to the first end  142 . Thus, the controller is able to determine the required velocity profile under which the actuator arm  121  may travel so that upon reaching the first end  142 , the actuator arm  121  will be at a target velocity that is within a desired range of velocity values. The desired range of target velocity values may be determined by the momentum required to overcome frictional forces posed by the ramp to the tang.  
         [0026]     In other embodiments, actuator arm  121  is allowed a period of time to settle upon reaching the initial position and thereby dissipate operational vibrations before beginning its movement towards the ramp  140 .  
         [0027]     According to some embodiments, upon engagement of the tang  126  by the ramp  140 , the actuator arm  121  is driven by a second voltage profile that is independent of the first velocity profile.  
         [0028]     In alternative embodiments of the present invention, a disc drive is configured to perform an unload operation by first positioning the read/write heads at MD  115  of disc  110 . Positioning read/write head  130  at a track  112  in the MD  115  provides advantages over positioning the read/write heads  130  at other locations because the seek time to an MD position is on the average shorter. Hence, the unload operation can be completed in a shorter period of time, saving power consumption as well as enabling the disc drive to respond more quickly to an emergency event that may favor a quick shut-down of the disc drive.  
         [0029]     One aspect of these advantages is further explained in the following. Preferably, the disc is kept spinning all the while when the read/write heads are not parked so as to ensure that the read/write heads  130  remain separated from the disc. In the traditionally larger disc drives, should the disc drive suddenly lose power, the inertia of the disc and motor assembly (disc stack assembly) may be relied upon to keep the disc spinning for a sufficient period of time until the read/write heads have been moved safely out of the recordable region of the disc. In disc drives that are intended for consumer applications, the inertia of the disc stack assembly is often able to keep the disc spinning only for a significantly shorter period of time. As described, embodiments of the present invention provide a much needed benefit of enabling unload operations to be completed more quickly. Advantageously, the embodiments are applicable whether or not the disc drive has experienced sudden power loss.  
         [0030]     When read/write heads  130  are positioned over an initial track  112  of disc  110 , and the initial velocity of actuator arm assembly  120  relative to ramp  140  may be zero or negligibly small. Accordingly to embodiments of the present invention, this initial velocity is used as a reference parameter for determining and controlling unload operations.  
         [0031]     Yet another embodiment of the present invention will be described with reference to an actuator arm  121  that is operable by varying the voltage applied to a motor such that read/write heads  130  supported by the actuator arm  121  may be positioned at various locations with respect to a disc  110  or a ramp  140 . At the beginning of an unload operation, read/write heads  130  are positioned over disc  110  at zero, or substantially zero, velocity at a distance from the ramp  140 . The distance between this initial position of the read/write heads and the ramp can be known because the location of the read/write heads  130  can be determined from the servo information. From previous measurements or from calculations, the momentum required of the actuator arm to successfully mount up the ramp and complete the unload operation can be determined. In other words, a target velocity value to be reached by the actuator arm at the first end  142  of the ramp  140  can be known. For convenience, the first end  142  of the ramp  140  is referred to as a first position  142 . Using a suitably configured controller  190 , a first voltage profile Vcvr is applied to the motor  150  controlling the movement of the actuator arm  121  so that the motor  150  provides a first torque τ 1  and thereby causes the actuator arm  121  to move from an initial velocity at the initial position to a target velocity at the first position  142 . This process is further illustrated by the following equations.  
         [0032]     The applied voltage Vcvr may be defined as: 
 
 Vcvr=Ivcm×Rvcm   equation (1) 
 
         [0033]     where Rvcm denotes the resistance of VCM  150  and Ivcm denotes the electrical current fed to VCM  150 .  
         [0034]     When fed with an electrical current Ivcm, VCM  150  generates the first torque τ 1  which may be represented by the following equation: 
 
τ1= Ivcm×Kt =Accel cvr   ×J   equation (2) 
 
         [0035]     where Kt denotes the torque constant of VCM  150 , Accel cvr  denotes the angular acceleration of actuator arm assembly  120 , and J denotes the moment of inertia of actuator arm assembly  120 .  
         [0036]     The angular acceleration Accel cvr  of actuator arm  121  may also be expressed according to the following equation:  
               Accel   cvr     =           ω   target   2     -     ω   0   2         2   ⁢           ⁢     θ   travel         =       ω   target   2       2   ⁢           ⁢     θ   travel                   equation   ⁢           ⁢     (   3   )               
 
         [0037]     where ω target  is the angular velocity of actuator arm  121  when tang  126  reaches first end  142  of ramp  140 . Tribological conditions between ramp  140  and tang  126  may determine an appropriate target velocity range within which the velocity of the tang preferably attains upon reading the first end  142 . ω 0  is the initial angular velocity of actuator arm  121  relative to ramp  140  when read/write heads  130  are positioned over the initial track  112  of disc  110 . θ travel  is the angular displacement (in radians) of actuator arm  121  between an initial position (shown in  FIGS. 1 and 2 ) and a first position when tang  126  reaches first end  142  of ramp  140  (shown in  FIGS. 3 and 4 ).  
         [0038]     When read/write heads  130  are positioned over an initial track  112 , actuator arm  121  may be considered stationary relative to ramp  140 . Alternatively, the initial angular velocity ω 0  of the actuator arm  121  is brought to at least one order of magnitude less than the target angular velocity ω target . The angular velocity of actuator arm  121  at the point when tang  126  reaches the first end  142  of the ramp  140  is referred to as the target angular velocity. In this example, it is desirable for the initial angular velocity to be negligible when compared to the target angular velocity (ω 0 &lt;&lt;ω target .). For calculation purposes, ω 0  can therefore be considered negligible, that is, set as zero. Further, since both ω target  and θ travel  are known, Accel cvr  can be obtained according to equations (2) and (3). Accordingly, the applied voltage Vcvr can be determined by the following equation:  
               V   cvr     =             Accel   cvr     ×   J       K   t       ×     R   vcm       =             ω   target   2       2   ⁢           ⁢     θ   travel         ×   J       K   t       ×     R   vcm                 equation   ⁢           ⁢     (   4   )               
 
         [0039]     By applying a first voltage profile represented by Vcvr to the VCM  150 , the read/write heads  130  are moved from the initial track  112  towards a first track represented by the first end  142  of ramp  140 .  
         [0040]     The corresponding time period t cvr  to apply the voltage to VCM  150  can be determined from equation (5):  
               t   cvr     =       ω   target       Accel   cvr               equation   .           ⁢     (   5   )               
 
         [0041]     According to equation (2), the angular acceleration of actuator arm  121 , Accel cvr , can be expressed as:  
               Accel   cvr     =       Kt   J     ×   Ivcm             equation   ⁢           ⁢     (   6   )               
 
         [0042]     Deriving from equations (1), (5) and (6), t cvr  can now be determined by the following equation:  
               t   cvr     =           ω   target     ×     R   vcm           Kt   J     ×     V   cvr         =     B     V   cvr                 equation   ⁢           ⁢     (   7   )               
 
         [0043]     where  
       B   =         ω   target     ×     R   vcm         Kt   J           
 
 denotes a retract time constant. 
 
         [0044]     Since the angular velocity ω target , resistance Rvcm of VCM, torque constant Kt of VCM  150  and moment of inertia J of actuator arm assembly  120  are known parameters, the retract time constant B and time period t cvr  can be determined accordingly. Further, as the mechanical variation of J and Kt can be very small, a relatively consistent target velocity may be achieved by implementing embodiments of the present invention.  
         [0045]     Optionally, after the time period t cvr  lapses, Vcvr may be removed. Actuator arm  121  rotates with respect to pivot  124  at the target angular velocity ω target  when tang  126  reaches first end  142  of ramp  140 , as shown in  FIGS. 3 and 4 . A second voltage profile, V climb(t) , may be applied to VCM  150  to further drive actuator arm  121 , and cause tang  126  to climb up ramp  140 , that is, to move beyond first end  142  and towards the detent. Determination of the second voltage profile V climb(t)  and a second torque τ 2  may take into consideration friction between tang  126  and ramp  140 .  
         [0046]     Derived according to equations (1) and (2), the relationship between the second torque τ 2  and frictional forces can be expressed as follows: 
 
τ2= Kt×V   climb(t)   /Rvcm =FrictionalForce( t )× d   equation (8) 
 
 V   climb(t) =( Rvcm ×FrictionalForce( t )× d )/ Kt   equation (9) 
 
         [0047]     where Kt denotes the torque constant VCM  150 , Rvcm denotes the resistance of VCM  150  and d denotes the distance from the first end to the pivot  124 .  
         [0048]     Since Rvcm, Kt and d are known, and FrictionalForce(t) can be determined by the design parameters and material properties of tang  126  and ramp  140 , the second voltage profile V climb(t)  can be determined.  
         [0049]     Preferably, the second voltage V climb(t)  is designed to generate a torque which is just enough to overcome the frictional forces such that actuator arm  121  may travel at a constant angular velocity from the first end  142  to the second end  144 . The time period t climb  for the travel is:  
               t   climb     =       θ   ramp       ω   target               equation   ⁢           ⁢     (   10   )               
 
         [0050]     where θ ramp  denotes the angular displacement between first end  142  to second end  144  with respect to pivot  124 , and ω target  is the angular velocity of actuator arm assembly  120 , when tang  126  travels from first end  142  to second end  144  of ramp  140 . It may be appreciated that t climb  defines the time period during which the second voltage profile V climb(t)  is applied to VCM  150 .  
         [0051]     It should be appreciated from the above that complicated circuits and control schemes may be eliminated. Disc drives configured for performing ramp unload operations according to embodiments of the present invention can thus be more reliable in operation, and cheaper to manufacture because of the simpler system architecture and control schemes.  
         [0052]      FIG. 7  is a velocity-position chart  700  showing the behaviour of an actuator system operating according to embodiments of the present invention. Upon start of an unload operation, read/write heads  130  are positioned at an initial track  112  of disc  110  at an initial velocity Vel- 0 . The initial velocity need not be absolutely zero, although preferably so. Alternatively, the initial velocity is negligibly small. The read/write heads are then moved according to a first velocity profile  702  until they approach the ramp at a target velocity Vel- 1  which is preferably within a desired range  704  of target velocity values. Subsequently, the read/write heads may continue their travel according to a second velocity profile  706 . Various other embodiments may exhibit different velocity profiles  710 , for example.  
         [0053]      FIG. 8  is a flow chart illustrating a method  500  for unloading read/write heads in a disc drive according to one embodiment of the present invention. The method involves holding the read/write heads at an initial position over a disc, as shown in step  510 . The read/write heads are then moved towards a ramp according to a velocity profile, to reach a target velocity at the ramp, as represented by step  520 .  
         [0054]     Although it can be appreciated that various embodiments of the present invention provide advantageous particularly useful to devices requiring low power consumption and high reliability in performance, it will be understood that the foregoing description of the embodiments is illustrative only, and that changes can be made by one skilled in the art without departing from the scope of the present invention.

Technology Category: g