Abstract:
A system for loading a transducing head ( 22 ) to a flying elevation proximate a rotating surface of a disc ( 16 ) is disclosed. The system includes a piezoelectric device ( 40 ) that is selectively expanded and contracted to control a height of the head ( 22 ) on a flexure spring ( 14 ) from the surface of the disc ( 16 ). The system preferably includes control circuitry ( 50 ) for generating electrical control signals to manage the expansion and contraction of the piezoelectric device ( 40 ) according to operating characteristics of the disc ( 16 ).

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to positioning of heads in a disc drive, and more particularly relates to a device for loading and unloading a magnetic head for a disc drive utilizing a piezoelectric element for flexure control. 
     Rotating disc drives operate by positioning a transducing head on a slider a small distance from a rotating disc surface. The slider is mounted on a flexure to “fly” the head over the disc. Wind from the disc&#39;s rotation elevates the slider a small distance from the surface of the disc. The slider is designed with aerodynamic properties that allow the wind to keep it aloft. The flexure connects the head to an actuator arm and has a spring bias to land the head on the disc when the disc is not rotating, yet is sufficiently flexible to permit the slider to elevate over the disc surface due to dynamic wind forces. 
     Beginning and ending of the “flying” period can be problematic when the rotation (and thus wind) of the disc starts and stops. When the disc is not rotating, there is no wind resistance to keep the head aloft, which will cause the head to fall to the surface of the disc due to the bias of the flexure spring. This situation is typically handled by dedicating a portion of the disc as a “landing zone” for the head to land on. Landing zones are usually textured to reduce stiction and do not contain data. In this configuration, heads “take off” from a landing zone on the disc when the disc begins rotating, due to the wind created by the disc&#39;s rotation. The force required for takeoff is not always constant. Stiction between the slider and the landing zone of the disc changes with environmental conditions. Changes in takeoff force can result in inaccurate timing and lost data. The need for a dedicated landing zone reduces the available space for encoding data on the disc, and variable takeoff force from a contacting position on the disc negatively affects the operation of the disc drive system. Therefore, it is apparent that taking off and landing a head on the disc is an imperfect method of loading a head to read and write data. 
     One method developed to avoid the problems of taking off and landing a ramp or other mechanical engagement device to engage the flexure spring to hold the slider and head above the elevation of the disc surface. The disc begins rotating while the head is out of the disc region, so that the slider does not contact the disc and stiction is therefore not present. This solution involves extra design efforts, manufacturing, and complexity in the starting and stopping operations of the disc drive, and also requires extra space so that the actuator arm can swing into a parked position, off of the data cylinders associated with the disc. 
     Therefore, there is a need in the disc drive art for an improved head loading and unloading system to control the height of heads and position of flexure springs with respect to the surface of a disc. 
     SUMMARY OF THE INVENTION 
     The present invention is a system for positioning a transducing head at a flying elevation proximate a rotating surface of a disc. Control circuitry generates electrical control signals to manage the operation of the positioning system according to operating characteristics of the disc. The system includes an actuator arm and a flexure spring connected to the actuator arm and carrying the head. A piezoelectric device is operatively attached to the flexure spring to control an elevation of the head on the flexure spring from the surface of the disc in response to the electrical control signals from the control circuitry. 
     One aspect of the invention is an improvement to a disc drive system. The disc drive system includes a rotatable disc having a surface, a transducing head, an actuator arm, a flexure spring connected to the actuator arm and carrying the head, and control circuitry for generating electrical control signals to position the head proximate a predetermined area on the surface of the disc. The improvement is a piezoelectric device operatively attached to the flexure spring to control a height of the head on the flexure spring from the surface of the disc in response to the electrical control signals from the control circuitry. 
     Another aspect of the invention is a device for loading and unloading a transducing head in a disc drive system. The device includes an actuator arm and a flexure spring connected to the actuator arm and carrying the head. A system operates to move the head on the flexure spring to a first position distant from a disc during an unloading condition, and to move the head on the flexure spring to a second position closer to the disc surface than the first position during a loading condition. 
     A further aspect of the invention is a loading device for loading a transducing head in a disc drive system. The system includes a rotatable magnetic disc media device having a surface containing a plurality of tracks on which data may be recorded. The head is mounted to a flexure spring which is mounted to an actuator arm for positioning adjacent a selected track to communicate data to and from the selected track. The head has aerodynamic characteristics so that the head flies over the disc surface when the disc is rotated. The loading device includes a piezoelectric device mounted to an actuator arm and an operator mounted to the flexure spring engaging the piezoelectric device. The loading device further includes means for selectively expanding and contracting the piezoelectric device to move the operator engaging the piezoelectric device to selectively load the head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic illustration showing a top view of an actuator arm and flexure spring positioned proximate a rotating disc. 
     FIG. 2 is a diagrammatic illustration showing a side view of an E-block having a plurality of flexure springs and associated heads proximate several rotating discs. 
     FIG. 3 is a perspective view of a typical piezoelectric cube comprised of a plurality of piezoelectric layers. 
     FIG. 4 is a detailed diagrammatic illustration showing a side view of a single actuator arm, flexure spring and head on a slider positioned proximate a rotating disc, utilizing the piezoelectric positioning system of the present invention. 
     FIG. 5 is a detailed diagrammatic illustration showing a top view of the single actuator arm, flexure spring and head on a slider positioned proximate a rotating disc shown in FIG.  4 . 
     FIG. 6 is a detailed diagrammatic illustration showing a top view of an alternative embodiment of a single actuator arm of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a top view of a typical head positioning system  10 . The head positioning system includes an actuator arm  12 , which supports a flexure spring  14 . The flexure spring  14  carries a slider and head (not shown) at the distal end  15  for reading and/or writing information on disc  16 . Disc  16  rotates around its axis  18  so that data encoded on concentric tracks of the disc  16  pass by the head when it is positioned over a track of disc  16 . 
     The actuator arm  12  is movable between a position where the head engages data tracks of disc  16  (as shown in FIG. 1) and a disengaged position where the head does not engage a data track of disc  16 . The disengaged position may be off the cylinder of the disc, as shown in phantom in FIG. 1, or may be adjacent a dedicated landing zone on the disc. In either case, actuator arm  12  moves between the engaged and disengaged positions by pivoting around an axis  19  of an actuator spindle (not shown in FIG.  1 ). 
     FIG. 2 shows a side view of the typical head positioning system  10  in a multiple disc arrangement. The actuator arm  12  is implemented as an E-block, which is able to support a plurality of flexure springs  14  for a like plurality of surfaces of discs  16 . Discs  16  are coaxially stacked, with a common disc spindle axis  18  around which they rotate. Flexure springs  14  are biased toward discs  16 , but are compliant in nature to allow sliders  22  on which transducing heads are mounted to “fly” above the surface of the discs  16  due to the aerodynamic design of sliders  22 . In this way, the head on slider  22  can be positioned a small distance from the surfaces of discs  16  to allow reading and writing of data on the discs  16  when they are rotating. 
     FIG. 3 shows a stacked piezoelectric element  30 . Element  30  is shown with three axes, labeled d 31 , d 32  and d 33 . The d 33  axis is parallel to the direction of polarization in the piezoelectric element  30 . A positive voltage between spatially separated points along the d 33  axis causes expansion or contraction of element  30  in the d 33  direction, and a corresponding contraction or expansion of element  30  in the d 31  direction. The polarization of the applied voltage will determine whether the element expands or contracts in a given direction. Each layer of the stacked element  30  expands or contracts in the d 33  direction, and contracts or expands in the d 31  direction. Thus, a piezoelectric element  30  can be used to expand or contract in the d 33  direction based on an applied voltage, with a corresponding contraction or expansion in the d 31  direction. 
     FIG. 4 shows a detailed side view, and FIGS. 5 and 6 show detailed top views, of a portion of an actuator arm  12  designed to load the head slider  22  in position on flexure spring  14  at various heights from a disc  16 , in accordance with the present invention. Actuator arm  12  includes a piezoelectric element  40  comprising a stack of layers between contact plates  52  and  54 . The stack is mounted to the end of actuator arm  12  so that the principal expansion and contraction of piezoelectric element  40  is in the direction along arrows  41 . Flexure spring  14  is connected to actuator arm  12  by engaging a hole  46  in the actuator arm  12 , to ensure sturdy connection. Tab  42  is formed from spring  14  and bent to engage a distal end  41  of piezoelectric element  40 , such as at plate  54 . Tab  42  is biased against plate  54  by the spring action of flexure spring  14 . Tab  42  cooperates with element  40  to alter the angular orientation of the flexure spring  14  (and thus the height of slider  22  relative to disc  16 ) in response to horizontal expansion or compression of the piezoelectric element  40  in the direction of arrows  41 . Tab  42  may be any mechanism for varying the angular orientation of flexure  14  in response to movement of piezoelectric element  40 . The natural spring bias of flexure  14  is such that when element  40  is compressed, and the disc is not rotating, flexure  14  positions slider  22  well away from the surface of disc  16 . When element  40  is expanded, the flexure will position slider  22  on the disc or at a distance from the disc surface no greater than the flying height. The spring bias of flexure  14 , rotational speed (and thus windage) of disc  16 , and aerodynamic characteristics of slider  22  are all designed so that slider  22  is positioned precisely at the flying height from the disc surface when the disc is rotating and element  40  is expanded. 
     In operation, control circuitry  50  generates a voltage between terminal plates  52  and  54  at the ends of piezoelectric element  40  to control the expansion  6  and contraction of element  40  in the direction of arrows  41 , depending on the desired state of operation of the disc drive system. When disc  16  is not rotating, piezoelectric element  40  is maximally compressed, so that slider  22  on flexure spring  14  is a maximum distance away from disc  16 . This configuration of flexure spring  14  is shown in phantom in FIG. 4, and ensures that slider  22  will not inadvertently contact disc  16  while there is no wind to keep slider  22  aloft. Once disc  16  begins rotating, the piezoelectric element  40  is expanded a designated amount, so that head  22  on flexure spring  14  is positioned a designated distance from disc  16 , for reading and/or writing data on disc  16 . This configuration of flexure spring  14  is shown in solid lines in FIG.  4 . 
     In the embodiment shown in FIG. 6, piezoelectric element  40  is configured so that expansion and contraction in the direction of arrows  41  occurs in the d 31  mode, rather than the d 33  mode as depicted in FIGS. 4 and 5. Either configuration may be preferred, depending on the desired ratio of movement of piezoelectric element  40  to the applied voltage. 
     Disc  16  is rotated at a constant rotational velocity. As a result, the linear velocity of slider  22 , and hence the windage on the aerodynamic properties of the slider, is higher at the outer radial tracks than at the inner radial tracks. In one embodiment, control circuitry  50  controls the expansion and contraction of piezoelectric element  40  based on the radial position of slider  22 . Control circuitry  50  operates in response to servo information to expand piezoelectric element  40  a greater amount when slider  22  is positioned over an outer radial track of disc  16  than when slider  22  is positioned over an inner radial track of disc  16 , thereby compensating for different wind forces at different radial portions of disc  16  that tend to force slider  22  away from the disc surface. 
     The present invention simplifies head loading and unloading procedures, providing an “unloaded” configuration for holding slider  22  apart from disc  16  when disc  16  is not rotating, without moving the slider out of the region of the disc. In the example shown in FIG. 4, the “unloaded” position would be realized by full contraction of piezoelectric element  40 . In this way, slider  22  is maintained a safe distance from disc  16  when disc  16  is not rotating, to ensure that slider  22  does not contact and damage disc  16 . 
     The head on slider  22  can be loaded in position close enough to the disc  16  to effect reading and writing of data without ever actually contacting the disc  16 . In the example shown in FIG. 4, this is accomplished by full expansion of piezoelectric element  40 . Since slider  22  does not have to land or take off from disc  16 , areas on the disc that were formerly dedicated landing zones can instead be used to encode more data, increasing the storage capacity of disc  16 . 
     Utilizing a piezoelectric element on the actuator arm  12  enables the use of a stiffer flexure spring  14 . This provides greater shock loading capability, since a greater shock force is required to move flexure spring  14  and slider  22  to cause inadvertent contact with disc  16 . In addition, the stiffer flexure spring  14  lessens the need for superior aerodynamic design of slider  22 , since less wind resistance is required to keep slider  22  aloft. The stiffer flexure spring  14  will tend to help keep slider  22  “flying” over disc  16 . Head design can therefore be simplified. 
     By loading and unloading the head on slider  22  within the data cylinders of disc  16 , the present invention eliminates the need for extra space in the disc drive system to accommodate a separate disengaged position of actuator arm  12 , thereby saving space in the design of the disc drive system. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.