Abstract:
A data storage device includes a disc stack, a rotary actuator having an arm coupled to a transducer head, and support structure for receiving the arm with a reduced incidence of sliding contact therewith. The arm is separated from the support means, and then moved so that the head is above a disc surface for storing data. After the disc stack reaches its nominal rotation speed, the head is loaded so that it can transfer data. During periods of non-activity, the head is raised (unloaded) again and the arm is placed on the support means. This reduces a risk of damage in the presence of shocks while minimizing particle generation induced by friction.

Description:
RELATED APPLICATIONS 
     This application claims priority of U.S. provisional application Serial Number 60/253,182 filed Nov. 27, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of mass storage devices. More particularly, this invention relates to loading and unloading sliders in a data storage device. 
     BACKGROUND OF THE INVENTION 
     One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc. 
     The transducer is typically housed within a small ceramic block. The small ceramic block is passed over the disc in a transducing relationship with the disc. The transducer can be used to read information representing data from the disc or write information representing data to the disc. When the disc is operating, the disc is usually spinning at relatively high revolutions per minute (“RPM”). These days common rotational speeds are 7200 RPM. Rotational speeds in high performance disc drives are as high as 15,000 RPM. Higher rotational speeds are contemplated for the future. These high rotational speeds place the small ceramic block in high air speeds. The small ceramic block, also referred to as a slider, is usually aerodynamically designed so that it flies over the disc. The slider has an air bearing surface (“ABS”) which includes rails and a cavity between the rails. The air bearing surface is that portion of the slider that is nearest the disc as the disc drive is operating. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the depression in the air bearing surface produces a negative pressure area at the depression. The negative pressure or suction counteracts the pressure produced at the rails. The different forces produced counteract and ultimately fly over the surface of the disc at a particular fly height. The fly height is the thickness of the air lubrication film or the distance between the disc surface and the head. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. 
     The best performance of the disc drive results when the ceramic block is flown as closely to the surface of the disc as possible. Today&#39;s small ceramic block or slider is designed to fly on a very thin layer of gas or air. In operation, the distance between the small ceramic block and the disc is very small. Currently “fly” heights are about 1-2 microinches or less. In some disc drives, the ceramic block does not fly on a cushion of air but rather passes through a layer of lubricant on the disc. A flexure is attached to the load spring and to the slider. The flexure allows the slider to pitch and roll so that the slider can accommodate various differences in tolerance and remain in close proximity to the disc. 
     Information representative of data is stored on the surface of the memory disc. Disc drive systems read and write information stored on tracks on memory discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the memory disc, read and write information on the memory discs when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disc. The transducer is also said to be moved to a target track. As the memory disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disc. Similarly, reading data on a memory disc is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information. 
     One of the most critical times during the operation of a disc drive occurs just before the disc drive shuts down or during the initial moment when the disc drive starts. When shutdown occurs, the small ceramic block or slider is typically flying over the disc at a very low height. In the past, the small block or slider was moved to a non-data area of the disc where it literally landed and skidded to a stop. Problems arise in such a system. Such a system is adequate for disc drives that had textured disc surfaces and which rotated at less than 7200 RPM. To improve magnetic performance, discs now are formed with a smooth surface. To improve access times, disc stacks are now rotated at speeds of 15,000 RPM in a high performance disc drive. Stiction, which is static friction, occurs between the air bearing surface of the slider and the smooth disc surface. Forces from stiction, in some instances, can be high enough to separate the slider from the suspension. When the disc is rotated at 15,000 RPM, the velocity between the slider and disc is high. At high velocity, the kinetic energy that must be dissipated when a contact between the disc and slider occurs is so high that particle generation is a distinct possibility. Still another problem is that landing a slider on the disc may limit the life of the disc drive. Each time the drive is turned off another contact start stop cycle occurs subjecting the slider to another high impact force which may cause the slider to chip or generate particles. The generated particles could eventually cause a head crash in the disc drive. 
     To overcome the stiction problem and to provide for a much more rugged design for disc drives used in mobile computers, such as portable computers and notebook computers, disc drive designers began unloading the sliders onto a ramp positioned on the edge of the disc. Disc drives with ramps are well known in the art. Such configurations are exemplified in U.S. Pat. 6,243,222 (“Load/Unload Method for Sliders in a High Speed Disk Drive”) issued Jun. 5, 2001 to Zine Eddine Boutaghou et al., also assigned to Seagate Technology LLC. 
     Conventionally, a portion of the ramp is positioned over the disc. Before power is actually shut off, the actuator assembly moves the suspension, slider and transducer to a park position on the ramp. Commonly, this procedure is referred to as unloading the heads. Unloading the heads helps to insure that data on the disc is preserved since, at times, unwanted contact between the slider and the disc results in data loss on the disc. When starting up the disc drive, the process is reversed. In other words, the suspension and slider are moved from the ramp onto the surface of the disc and into a transducing position. This is referred to as loading the heads or sliders onto the disc. 
     Use of a ramp to load and unload the disc overcomes many aspects of the stiction problem. However, during the loading process and the unloading process, it seems that it is fairly common for the slider to contact the disc. In such situations, high friction forces can develop between the head and the disc. The high friction forces can cause slider and media damage. The contact with the disc in the disc stack rotated at 15,000 RPM or higher still has the potential to cause damage. Some manufacturer&#39;s simply sacrifice the portion of the disc at the outer diameter and devoted that space for loading and unloading to and from the disc. In other words, data is not kept at the outer diameter of the disc so that if disc contact occurs there is no possibility of losing data from damage to the disc. This design strategy is suboptimal. First of all, the area of the disc where the most information representative of data can be stored is the outer diameter of the disc. Giving up the outer diameter is like giving up the best located and most valuable real estate when developing a parcel of land. In addition, slider and disc contact will still occur and this could eventually generate particles and cause a disc crash. The damage is greater at higher rotational speeds of the discs in the disc drives. Thus, this problem will only get worse as higher RPM design points are set. 
     What is needed is a better way to improve non-operating shock performance while generating particles at a lower rate. It is to this and other problems that the present invention is directed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for a reduced sliding contact upon an actuator of a data storage device. One embodiment includes a disc stack, a rotary actuator having an arm coupled to a transducer head, and support means for receiving the arm with a reduced incidence of sliding contact therewith. 
     Another embodiment includes several steps performed while rotating the disc stack. The arm is separated from the support means, and then moved so that the head is above a disc surface for storing data. The head is then loaded so that it can transfer data. During periods of non-activity, the head is raised (unloaded) again and the arm is placed on the support means. This reduces a risk of damage in the presence of shocks while minimizing a rate of friction-induced particle generation. 
     Additional features and benefits will become apparent upon a review of the following drawings and the corresponding detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exploded view of a Winchester-type disc drive in which the present invention is particularly useful. 
     FIG. 2 shows a side view of the disc drive of FIG. 1 highlighting the arrangement of the actuator assembly relative to the discs. 
     FIG. 3 shows a flowchart of a method of the present invention, usable with the data storage apparatus of FIGS. 1 &amp; 2. 
     FIG. 4 shows a highly magnified view of another disc-based data storage apparatus of the present invention. 
     FIG. 5 shows a method of transferring data consistent with FIG.  3  and usable with the device of FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     Definitions of certain terms are provided in conjunction with the descriptions below, all consistent with common usage in the art but some described with greater specificity. For example, a “usable disc surface” refers to an annular band bounded by the outer circumference of the disc and by an inner-diameter obstacle such as a disc clamp or spacer. It should be noted that devices of the present invention preferably do not waste usable disc surface on texturing and/or ramp overlap. 
     As used herein, sliding contact upon an actuator arm or head is “substantial” only if it is a non-intermittent and necessary part of the arm or head&#39;s operation lasting more than about 10 microseconds during a typical start or stop operation. Conventional ramp unloads and contact stops require substantial contact, typically generating huge numbers of particles large enough to interfere with head operation. 
     Turning now to the drawings and specifically to FIG. 1, shown is an exploded view of a disc drive  100  in which the present invention is particularly useful. The disc drive  100  includes a base member  102  to which all other components are directly or indirectly mounted and a top cover  123  which, together with the base member  102 , forms a disc drive housing which encloses delicate internal components and isolates these components from external contaminants. 
     The disc drive includes a plurality of discs  110  each having a radius  115  (e.g. 1.75″) which are mounted for rotation on a spindle motor (not shown). The discs are arranged in a conventional rotatable stack and are held in their respective positions by a clamp  114  (above) and spacers (between, not shown). The discs  110  include on their surfaces a plurality of circular, concentric data tracks  112  on which data is recorded via an array of vertically aligned head assemblies (one of which is shown at  134 ). The head assemblies  134  are supported by arm portions  161  of actuator  130 . Head assemblies  134  are constructed to fly on a thin air bearing above each respective disc data surface. (In this context, a frame of reference is defined by each disc data surface being “horizontal,” irrespective of the planet&#39;s position.) 
     Actuator  130  also includes coil  122 , which is part of a voice coil motor (VCM) that rotates actuator  130  relative to the base member  102 . The VCM also includes permanent magnets  120  that provide a magnetic field surrounding the VCM coil  122 . Actuator  130  is pivotable about an axis  117  as shown in FIG. 2 so that head  134  is positionable throughout a range of motion  138  across the tracks  112  of the disc  110 . When the disc drive  100  is to be powered down, the actuator  130  moves to its park position where head  134  is near the outer diameter of the disc  110 . 
     Base  102  includes a support member  170  with tapered tabs  173  that protrude between, above and below the discs  110  by a short horizontal distance (i.e. by less than the nominal disc thickness). These tabs  173  do not ordinarily contact the discs  110 , but a large disturbance on the discs will cause an outermost edge of the discs to collide with the tabs  173  before they build up much speed. The tabs are constructed and arranged to snub disturbances on the discs larger than a predetermined threshold distance roughly twice a typical disc flutter magnitude and less than the nominal disc thickness. 
     Unlike ramp or cam devices of the prior art, however, the horizontally protruding tabs  173  are not constructed so that any part of actuator  130  can contact them. Rather, the arms contact the support member  170  only after the heads  134  are lifted from the disc surface and moved outside the outer edge of the discs  110 . This is possible by virtue of lift actuators shown in more detail in FIG.  2 . 
     Electronic circuitry to control the operation of the disc drive  100  is provided on controller board  106 , which is coupled to each head  134  through preamplifier circuit  104 . Controller board  106  is coupled to preamp  104  and VCM coil  122  through flex circuit  180 , which is constructed to minimize mechanical bias forces acting on actuator  130 . 
     Turning now to FIG. 2, there is shown a side view of disc drive  100  highlighting the arrangement of actuator  130  relative to the discs  110 . Each of four heads  131 , 132 , 133 , 134  is supported above its respective data surface by a respective arm  190 . In addition to arm portion  141  of actuator  130 , as shown, arm  190  includes a load beam with a shape memory alloy strip  191  deposited on its upper side. When enough electricity passes through strip  191  so that it heats up by at least 3-10 degrees C., the strip shortens and head  131  approaches its respective data surface more closely. Each head  131 , 132 , 133 , 134  has a fly height that is thus controllable by a respective strip  191 , 192 , 193 , 194  that functions as a thermal lift actuator. 
     In an alternative embodiment, a conductive strip of a metal that expands upon heating is applied on a side of each arm opposite the side on which the head is mounted. Like the embodiment shown, this alternative bimetallic strip configuration decreases each head&#39;s fly height when powered. 
     In another alternative embodiment, the arm includes a distal load tang that extends horizontally beyond the head. A suitable tang is shown and described in U.S. Pat. No. 6,067,208 (“Adjustment Feature for Load/Unload Alignment Ramp Assembly”) issued to Peter Raymond Segar on May 23, 2000, also assigned to Seagate Technology LLC. 
     FIG. 3 shows a flowchart of a method  300  of the present invention, usable with the device of FIGS. 1 &amp; 2, comprising steps  305  through  365 . The disc stack is accelerated toward a nominal rotation speed (e.g. 7200 revolutions per minute) as the arm is lifted  310  from a support such as holding shelf. The actuator is then rotated so that each head is above its corresponding disc surface  315 . After the disc stack reaches nominal speed, the head are loaded onto the disc surfaces. The initial set down is preferably above a region that does not contain user data, to avoid media damage and data losses due to incidental contact. 
     After the the desired data is transferred, the heads are unloaded  325  (i.e. lifted from the disc surfaces). As with the loading step  320 , the initial lift is preferably performed above a region that does not contain user data. Once the heads are at least several microns away, the discs begin a deceleration  330  toward a speed that is preferably a fraction of the nominal rotation speed. The actuator arm simultaneously rotates  335  back towards the shelf, and is rested on the shelf  340 . Unlike a contact stop or ramp unload, this is performed without any substantial sliding contact or head contact. Once on the shelf, the drive may undergo a shock  350  much larger than can be withstood while operating. This is a desirable safeguard to perform for a drive that is in a standby mode, ready to transfer more data  355  or to power down  360 . 
     FIG. 4 shows a highly magnified view of another disc-based data storage apparatus  400  of the present invention (e.g., a multi-disc servo pattern writer or a disc drive). Features shown in FIG. 4 are to substantially to scale, except as necessary for clarity. Part of an outermost annular portion  459  of disc  410  is shown. The annular portion  459  is narrower than 1% of the radius of the disc  410 , and is bounded by the circumference  411 . The disc is rotating in the direction indicated at  444 . 
     Flying adjacent disc  410  is a first head  425  supported by a first arm  420 . A second arm  430  supports a second head  435  flying adjacent a second disc (not shown). Both arms shown include an arm portion  454  of a rotary actuator, the remainder of which is not shown. A pair of shape memory wires  421 , 422  each affixed by epoxy  477  at both ends control the fly height of first head  425  above disc  410 . A load beam of the arm is biased toward disc  410  so that the shape memory wires  421 , 422  are in tension. When the wires are energized, they shorten so that head  425  is lifted off disc  410 . The actuator can then rotate arm  420  out from between the discs, and in between two surfaces  428 , 438  of a shelf structure  488  supported from above (e.g. by affixation to the top cover of a Winchester-type disc drive). From this rotary position, the wires  421 , 422  are de-energized so that arm  420  comes to rest on shelf surface  428 . In this way, arm  420  is made to move substantially along path  401  so that it comes to rest at position  460 . Shape memory wires  431 , 432  of second arm  430  are similarly and simultaneously controlled to place arm  430  at position  470 . Note that each shelf surface  428  includes a protruding locking feature  429  that strongly resists actuator rotation and limits sliding when the arms  420 , 430  are at rest against the shell structure  488 . This locking feature is fast-acting and generates high torque. It can be used in lieu of a conventional inertial latch in some cases. 
     An electrical bus  468  provides power and communication from a controller  415  to heads  425 , 435  and also to the shape memory wires  421 , 422 . The wires  421 , 422  are not merely connected in series. A conductor in the bus (not shown) is coupled to both distal ends of the shape memory wires  421 , 422 . A voltage driven on that conductor can selectively cause one of the wires  421 , 422  to carry more current than the other  422 , 421 . In this way, a static roll position of each head can be controlled selectively. 
     FIG. 5 shows another method  500  of the present invention, comprising steps  505  through  535 , that takes advantage of this selective control feature. An error is found in a data block read from the outermost 1% of the usable disc surface  510 . The data block is re-read using a variety of fly heights and/or static roll angles, measuring a bit error rate for each combination  515 . Preferably, each bit error rate is derived as an average of several measurements. In this way, an optimum arm position (i.e. fly height H 1  and/or roll angle R 1 ) for the outermost (first) zone is detected  520 . This process is repeated for the innermost (Nth) zone  525 . For each of the annular zones  2  through N-1, an interpolated or similarly measured value for H i  and/or R i  is used. 
     Alternatively characterized, a first embodiment of the present invention is a method (such as  300 ) of operating a data storage apparatus (such as  100 ). The apparatus comprises a first rotary actuator (such as  130 ), a first stack of data storage discs (such as  110 ) and a first holding shelf (such as  170 ). The rotary actuator comprises a first arm (such as  190 ) coupled to a first transducer head (such as  131 ). The method comprises several steps generally performed while the disc stack rotates. 
     First, a lift actuator is used to separate the arm vertically from the holding shelf (e.g. by step  310 ). The actuator next moves the head over its data surface (e.g. by step  315 ) so that it can be lowered toward the surface (e.g. by step  320 ). After carrying out data transfer commands, the arm is raised again (e.g. by step  325 ) and rotated back toward the arm&#39;s parking location (e.g. by step  335 ) to be parked (e.g. by step  340 ). Meanwhile the disc stack is permitted to spin down (e.g. by step  330 ) for “standby mode” power conservation, preferably without braking. This method provides a high degree of protection against shock in a standby mode, with less particle generation than methods of the prior art. It is preferably performed, as illustrated in FIGS. 3 &amp; 4, without any substantial sliding contact upon the arm, head, or disc. 
     In a second embodiment, the method includes a step (e.g. by step  510 ) of reading a portion of the data from a radial position less than R/100 from a circumference of the disc, where R is a nominal radius of the disc(s). Note that disc snubber tabs (such as  173 ) are tapered to recede from each disc surface by a few degrees so that they overlap but do not contact the outermost data tracks (such as  412 ). From this outermost annular zone of the data surface, an error-containing data block is re-read at several selected gram load and static roll angle values (e.g. by step  515 ). An optimum gram load/roll angle combination is selected (e.g. by step  520 ) so as to minimize a bit error rate in that zone. 
     In a third embodiment, this process is repeated for a data block read from a radial position less than R/50 from a piece of the stack protruding higher than the first disc (e.g. by step  525 ). This optimum gram load/roll angle combination is preferably selected for bit error rate lower than the bit error rate initially found in the data block. For expedience, gram load and roll angle can each be determined for other zones within the data surface as an interpolation of these values at the innermost and outermost zones (e.g. by step  530 ). 
     A fourth embodiment of the present invention is a data storage apparatus (such as  100 , 400 ) includes a slider supporting a transducer head (such as  131 , 425 ), the slider supported by an arm of a rotary actuator (such as arm  190  of actuator  130 ). The apparatus also includes a rotatable stack comprising discs (such as  110 , 410 ) and a support element (such as  170 , 488 ) fixedly supported by a base. The support element is constructed and arranged to receive the arm without any sliding contact acting upon the arm. This allows the stack to maintain rotation at a nominal speed or a slower speed (e.g. by step  330 ). This is a significant energy savings, especially if the apparatus is a portable computer or if the stack contains multiple discs. 
     In a fifth embodiment, the apparatus is a Winchester-type magnetic disc drive containing a disc having a nominal radius R and a data surface accessible by the transducer head. The disc surface has data tracks within innermost and outermost annular portions of the disc each narrower than R/70 (such as item  412  and  459  of FIG.  4  and those in step  525  of FIG.  5 ). Note that one or both of these regions are normally not used in conventional Winchester-type magnetic disc drive. 
     In a sixth embodiment, the apparatus includes a first thermal actuator (such as  191 , 421 ) constructed and arranged to remove the arm from a recessed holding shelf surface (such as  428 ) when powered and to permit the arm to maintain compressive contact with the holding shelf when unpowered. The surface is recessed so that it latches the arm within the recess and so that the arm thereby resists a horizontal rotational shock upon the base. Note that FIG. 4 shows a configuration of opposing recessed surfaces that can withstand a simultaneous vertical shock and still have one arm (either  420  or  430 ) remain in full contact with its respective surface. Note also that an apparatus of the sixth embodiment preferably includes a second thermal actuator (such as  422 ) constructed and arranged to oppose a twisting motion induced by the first thermal actuator selectively so as to control a roll angle of the first head (i.e.  425 ). This configuration includes a controller (such as  415 ) configured to control the first and second thermal actuators independently so as to control the static roll angle between the transducer head and the data surface. 
     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. For example, while the various embodiments of the present invention have been described with respect to a disc drive, the present invention is also applicable to, and may be implemented in, other data storage devices such as optical disc drives and multi-disc servowriters. 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.