Abstract:
A head flexure assembly having a flexure with a built in microactuator is disclosed. The flexure is divided into four portions: a base plate portion for attaching the flexure to an actuator arm; a load beam portion for suspending a transducing head; a parallelogram portion connecting the load beam portion and the base plate portion and allowing for the translational movement of the load beam portion with respect to the base plate portion; and a driving frame portion. The parallelogram portion has two substantially parallel members that attach the base plate portion to the load beam portion. The parallel members limit the movement of the load beam portion relative to the base plate portion to translational movement. The driving frame portion has piezoelectric element that in response to a control signal produces a force, orthogonal to the flexure&#39;s longitudinal axis, between the base plate portion and the load beam portion.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority of U.S. provisional application Serial No. 60/399,537, filed Jul. 30, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This application relates generally to data storage devices and more particularly to an actuator assembly for a data storage device.  
         BACKGROUND OF THE INVENTION  
         [0003]    One function of a data storage device such as a disc drive is reliable storage and retrieval of information. Using one common implementation of a disc drive as an example, data is stored on one or more discs coated with a magnetizable medium. Data is written to the discs by one or more transducers, typically referred to as read/write transducers, mounted to an actuator assembly for movement of the transducers relative to the discs. The information may be stored on a plurality of concentric circular tracks on the discs until such time that the data is read from the discs by the read/write transducers. Each of the concentric tracks is typically divided into a plurality of separately addressable data sectors. The transducers are used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the transducer senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the transducer over the center of the desired track.  
           [0004]    Conventionally, the transducers are positioned with respect to the disc surfaces by an actuator arm controlled through a voice coil motor. The voice coil motor is responsible for pivoting the actuator arm about a pivot shaft, thus moving the transducers across the disc surfaces. The actuator arm thus allows the transducers to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs. The actuator arm is driven by a control signal fed to the voice coil motor at the rear end of the actuator arm. A servo control system is used to sense the position of the actuator arm and control the movement of the transducer above the disc using servo signals read from the servo segments on the disc surface in the disc drive. The servo control system relies on servo information stored on the disc. The signals from this information generally indicate the present position of the transducer with respect to the disc, i.e., the current track position. The servo control system uses the sensed information to maintain transducer position or determine how to optimally move the transducer to a new position centered above a desired track. The servo system then delivers a control signal to the voice coil motor to rotate the actuator arm to position the transducer over a desired new track or maintain the position over the desired current track.  
           [0005]    As the demand for smaller disc drives increases, so does the demand for higher storage capacities. To meet this demand, manufacturers of disc drives are continually developing smaller yet higher storage capacity drives. Typically, to increase the storage capacity of a disc drive, the density of the concentric tracks on the disc is increased. In order to increase the track density, manufacturers either narrow the width of the concentric tracks or reduce the spacing between tracks. However, these means of increasing track density are limited by the precision of the actuator and voice coil motor assembly.  
           [0006]    Manufacturers have developed dual-stage actuators to increase the positioning accuracy of the read/write head. A dual-stage actuator includes the primary stage actuator controlled with a voice coil motor (as discussed above) and a microactuator controlled with a driving circuit. The microactuator may include one or more piezoelectric elements attached, coupled, bonded or integrated with the primary actuator. A piezoelectric element usually contains multiple layers of crystals. Applying a voltage potential across a portion of the crystal changes the dimensions of each crystal, and therefore, the piezoelectric element. Modern piezoelectric elements, or devices, are usually constructed of ceramic composites that exhibit piezoelectric characteristics. The ceramic composites are easily formed as thin layers on silicon substrates and integrated into electrical devices, such as microactuators.  
           [0007]    Typical piezoelectric microactuators use “bimorph” piezoelectric elements made of two or more opposed piezoelectric strips that operate in opposition, i.e. one is extended while the other is contracted. This allows the elements to bend in response to an applied voltage. Indeed, in typical designs most piezoelectric elements are structural elements of the microactuator and the bending action produced is desired or even necessary for the function of the microactuator. However, bimorph piezoelectric elements are inherently more expensive than single piezoelectric elements to produce.  
           [0008]    Accordingly there is a need for a microactuator design that utilizes a single piezoelectric element. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.  
         SUMMARY OF THE INVENTION  
         [0009]    Against this backdrop the present invention has been developed. One embodiment of the present invention includes a head flexure assembly having a flexure with a built in microactuator. The flexure is divided into four portions: a base plate portion for attaching the flexure to an actuator arm; a load beam portion for suspending a transducing head; a parallelogram portion connecting the load beam portion and the base plate portion and allowing for the translational movement of the load beam portion with respect to the base plate portion; and a driving frame portion.  
           [0010]    The parallelogram portion has at least two substantially parallel members that attach the base plate portion to the load beam portion. The members may be provided with hinges to assist their movement. The parallel members limit the movement of the load beam portion relative to the base plate portion to translational movement.  
           [0011]    The driving frame portion has piezoelectric element that in response to a control signal produces a force, orthogonal to the flexure&#39;s longitudinal axis, between the base plate portion and the load beam portion. Embodiments of the driving frame portion may include tabs or lever members to provide attachment points for the piezoelectric element and directing the force. The tabs and members may be attached to either the base plate portion, the load beam portion or both.  
           [0012]    These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a plan view of a disc drive incorporating a preferred embodiment of the present invention showing the primary internal components.  
         [0014]    [0014]FIG. 2 a  is a plan view of a flexure assembly in accordance with an embodiment of the present invention.  
         [0015]    [0015]FIG. 2 b  is a plan view showing the perturbed state of the flexure assembly of FIG. 2 a.    
         [0016]    [0016]FIG. 3 is a plan view of a flexure assembly in accordance with another embodiment of the present invention.  
         [0017]    [0017]FIG. 4 is a plan view of a flexure assembly in accordance with yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    A disc drive  100  constructed in accordance with one embodiment of the present invention is shown in FIG. 1. The disc drive  100  may include a base  102  to which various components of the disc drive  100  are mounted. A top cover  104 , shown partially cut away, may cooperate with the base  102  to form an internal, sealed environment for the disc drive in a conventional manner. The components typically include a spindle motor  106  which rotates one or more discs  108  at a constant high speed. Information is written to and read from tracks on the discs  108  through the use of an actuator assembly  110 , which in the illustrated embodiment rotates during a seek operation about a bearing shaft assembly  112  positioned adjacent the discs  108 . The actuator assembly  110  includes one or more actuator arms  114  which extend towards the discs  108 , with one or more flexures  116  extending from each of the actuator arms  114 . The actuator arms  114  may be individual, stacked pieces or may be formed out of a single piece, often referred to as an “E-block.” The flexures  116  attach to the actuator arms  114  at a connection point  115 . Mounted at the distal end of each of the flexures  116  is a head  118  which includes an air bearing slider enabling the head  118  to fly in close proximity above the corresponding surface of the associated disc  108 . Generally, the flexure  116 , head  118  and any additional components located on the flexure  116  such as a microactuator (not shown), may be referred to here as the head flexure assembly.  
         [0019]    During a seek operation, the track position of the heads  118  is controlled through the use of a voice coil motor (VCM)  124 , which typically includes a coil  126  attached to the actuator assembly  110 , as well as one or more permanent magnets  128  which establish a magnetic field in which the coil  126  is immersed. The controlled application of current to the coil  126  causes magnetic interaction between the permanent magnets  128  and the coil  126  so that the coil  126  moves in accordance with the well-known Lorentz relationship. As the coil  126  moves, the actuator assembly  110  pivots about the bearing shaft assembly  112 , and the heads  118  are caused to move across the surfaces of the discs  108 .  
         [0020]    The spindle motor  106  is typically de-energized when the disc drive  100  is not in use for extended periods of time. The heads  118  are moved over park zones  120  near the inner diameter of the discs  108  when the drive motor is de-energized. The heads  118  may be secured over the park zones  120  through the use of an actuator latch arrangement, which prevents inadvertent rotation of the actuator assembly  110  when the heads are parked.  
         [0021]    A flex assembly  130  provides the requisite electrical connection paths for the actuator assembly  110  while allowing pivotal movement of the actuator assembly  110  during operation. The flex assembly includes a printed circuit board  132  to which head wires (not shown) are connected; the head wires being routed along the actuator arms  114  and the flexures  116  to the heads  118 . The printed circuit board  132  typically includes circuitry for controlling the write currents applied to the heads  118  during a write operation and a preamplifier for amplifying read signals generated by the heads  118  during a read operation. The flex assembly terminates at a flex bracket  134  for communication through the base deck  102  to a disc drive printed circuit board (not shown) mounted to the bottom side of the disc drive  100 .  
         [0022]    [0022]FIG. 2 a  shows a plan view of a head flexure assembly  200  having a flexure  202  and one or more transducing heads  204  in accordance with an embodiment of the present invention. The flexure  202  has four main portions: a base plate portion  206 ; a parallelogram portion  208 ; a driving frame portion  210 , and a load beam portion  212 . The base plate portion  206  provides an attachment point allowing the attachment of the flexure  202  to the actuator arm  114  at the connection point  115 . The attachment may be effected by a fastener, an adhesive, or any appropriate fastening means and the attachment point will be appropriate for that means.  
         [0023]    The load beam portion  212  comprises a load beam body  214  and a head receiving body  216  at its distal end for locating one or more heads  204 . The edges and other locations of the load beam portion  212  may be crimped or bent to provide greater stability or stiffness as necessary.  
         [0024]    The flexure  202  is shown in FIG. 2 a  in an unperturbed state. When in an unperturbed state, a line  218  drawn through the center of the base plate portion  206  and the center of the load beam portion  212  defines a longitudinal flexure axis  218 . Note also that the load beam portion  206  has its own longitudinal axis  220 . In the unperturbed state, as shown in FIG. 2 a  the load beam axis  220  is parallel and collinear with the longitudinal flexure axis  218 .  
         [0025]    The base plate portion  206  is attached to the load beam portion  212  by means of the parallelogram portion  208 . The parallelogram portion  208  in FIG. 2 a  has two substantially parallel members  222   a  and  222   b  which serve to connect the base plate portion  206  to the load beam portion  212 . The parallel members  222   a  and  222   b  are also substantially parallel to the longitudinal axis  218 , when in the unperturbed state. In the embodiment shown, each member  222   a  and  222   b  also includes a hinge point  224  where the member  222   a,    222   b  connects to the base plate portion  206  and to the load beam portion  212 .  
         [0026]    The motive frame portion  210  is located between the substantially parallel members  222   a,    222   b  of the parallelogram portion  208 . The motive frame portion  210  has a tab  226  and a lever member  228 . The lever member  228 , similar to the substantially parallel members  222   a  and  222   b,  connects the base plate portion  206  to the load beam portion  212 . The lever member  228  is also shown in FIG. 2 a  as having two hinge points  224  similar to those on the parallel members  222   a  and  222   b.  The lever member  228  is also substantially parallel to the parallel members  222   a,    222   b  and the longitudinal axis  218 .  
         [0027]    Attached to the tab  226  and the lever member  228  and spanning the space between them is a piezoelectric element  230 . The piezoelectric element  230  is mounted such that when a voltage is applied it expands or contracts in a direction substantially orthogonal to the flexure axis  218 . When expanding, the piezoelectric element  230  produces a force that drives the tab  226  and the lever member  228  apart. When contracting, the piezoelectric element  230  produces a force that drives the tab  226  and the lever member  228  toward each other. More discussion of movement resulting from the application of force between the tab  226  and the lever member  228  can be found below with respect to FIG. 2 b.    
         [0028]    In FIG. 2 a  the head flexure assembly  200  is shown in its unperturbed state, i.e. the piezoelectric element  230  is not deforming to move the load beam portion  212  off the flexure axis  218 . In one embodiment, the unperturbed state occurs when there is no voltage applied to the piezoelectric element  230 . In an alternative embodiment, the piezoelectric element  212  must have a voltage applied to it to be in the unperturbed state as shown in FIG. 2 a.    
         [0029]    [0029]FIG. 2 b  shows a magnified view of the parallelogram portion  208  and the motive frame portion  210  of the head flexure assembly  200  illustrating the perturbed state wherein the load beam portion  212  has been translationally moved with respect to the longitudinal flexure axis  218 . The unperturbed state of FIG. 2 a  is also shown as a dashed outline  232  of the position of the parallel members  222   a  and  222   b,  the lever member  228  and the load beam portion  212 . In the embodiment shown a voltage is applied to the piezoelectric element  230  causing it to expand in length by some distance, d,  234 . The expansion applies a force that drives the tab  226  and the lever member  228  apart. In response, the parallel members  222   a,    222   b  deflect at the hinge points  224 . As a result, the load beam portion  212  moves translationally with respect to the base plate portion  206 . The resultant perturbed position of the load beam portion  212  is such that the load beam long axis  220  is displaced the distance, d, away from the flexure axis  218 , but the load beam long axis  220  remains substantially parallel to the flexure axis  218 .  
         [0030]    In the embodiment shown, a piezoelectric element  230  capable of both contraction and expansion is contemplated with respect to the unperturbed state. When contracting, the piezoelectric element  230  creates a force driving the tab  226  and the lever member  228  together. In response, the parallel members  222   a,    222   b  deflect at the hinge points  224  and the load beam portion  212  moves translationally in the direction opposite to that caused by the expansion of the piezoelectric element. The resultant perturbed position of the load beam portion  212  is such that the load beam long axis  220  is translationally displaced some distance away from the flexure axis  218 , but the load beam long axis  220  remains substantially parallel to the flexure axis  218 .  
         [0031]    The embodiment shown in FIGS. 2 a  and  2   b  offer several advantages over traditional designs of microactuator-equipped flexures. One is that the flexure  202  may be a unitary construction formed out of a single piece of material such as steel, aluminum or composite. The unitary construction will result in reduced cost for the flexure as a whole. The unitary construction also reduces complexity.  
         [0032]    Another advantage is that the single piezoelectric element  230  is not a primary structural element of the flexure assembly  200 . Other than loads caused by its own expansion or contraction, the piezoelectric element  230  is under little or no load. Thus it can be made of less material that would be necessary for a piezoelectric element  230  that is a structural element of the flexure assembly  200 .  
         [0033]    To one skilled in the art, many variations of the above design will be immediately suggested that will retain the advantages of the embodiment shown in FIGS. 2 a  and  2   b.  For example, in an embodiment the tab  226  may be connected to the load beam portion  212  rather than the base plate portion  206 . The embodiment above may also be provided with a piezoelectric element  230  that only drives the tab  226  and lever member  228  in one direction (i.e. either together or apart, but not both such as a piezoelectric element  230  that is attached so that it can only drive the tab  226  and lever member  228  apart). As another example, a separate spring (not shown) may be provided on the flexure  202  to create more resistance to the force applied by the piezoelectric element  230  when it deforms.  
         [0034]    An initial prototype of the embodiment described in FIG. 2 a  and  2   b  was fabricated and tested by the authors. The prototype was fabricated on a conventional flexure, with slider attached, of a hard disc drive using a wire cutting machining process. The piezoelectric element was adhered onto the flexure using epoxy resin. During testing, with an applied voltage of ±10 volts, the stroke of approximately ±0.5 micrometers (μm) was obtained.  
         [0035]    [0035]FIG. 3 presents another embodiment of a head flexure assembly  300  having a flexure  302  and one or more transducing heads  304  in accordance with the present invention. The flexure  302  has a base plate portion  306 , a load beam portion  312 , a parallelogram portion  308  and a motive frame portion  310 . When in an unperturbed state as shown in FIG. 3, a line drawn through the center of the base plate portion  306  and the center of the load beam portion  312  defines a longitudinal flexure axis  318 . The parallelogram portion  308  has two parallel members  322   a  and  322   b  connecting the base plate portion  306  to the load beam portion  312 . The parallel members  322   a,    322   b  are substantially parallel to each other and the longitudinal axis  318  of the flexure  302 . The members  322   a,    322   b  are shown as having hinges  324  at each location where they connect to the base plate portion  306  or the load beam portion  312 , although in alternative embodiments the hinges  324  are not provided.  
         [0036]    The motive frame portion  310  is again located between the parallel members  222   a,    222   b  and the base plate and load beam portions  306 ,  312 . However, in the embodiment shown the lever member  228  of the previous embodiment has been replaced by a second tab  328 . The first tab  326 , as in the previous embodiment shown in FIG. 2 a  and  2   b,  is attached to the base plate portion  306 . The second tab  328  is attached to the load beam portion  312 . Attached to the first tab  326  and the second tab  328  and spanning the space between them is a piezoelectric element  330 . The piezoelectric element  330  is mounted such that when a voltage is applied it expands or contracts in a direction substantially orthogonal to the longitudinal axis  318 . When expanding, the piezoelectric element  330  produces a force that drives the first and second tabs apart. When contracting, the piezoelectric element  330  produces a force that drives the first and second tabs  326 ,  328  toward each other. In either case, as in the previous embodiment the driving force will cause the load beam portion  312  to translationally move with respect to the base plate portion  306 .  
         [0037]    [0037]FIG. 4 presents yet another embodiment of a head flexure assembly  400  having a flexure  402  and one or more transducing heads  404  in accordance with the present invention. The flexure  402  has a base plate portion  406 , a load beam portion  412 , a parallelogram portion  408  and a motive frame portion  410 . When in an unperturbed state as shown in FIG. 4, a line  418  drawn through the center of the base plate portion  406  and the center of the load beam portion  412  defines a longitudinal flexure axis  418 . The parallelogram portion  408  has two parallel members  422   a,    422   b  attaching the base plate portion  406  to the load beam portion  412 . The parallel members  422   a,    422   b  are substantially parallel to each other and the longitudinal axis  418  of the flexure  402 . The members  422   a,    422   b  are shown as having hinges  424  at each location where they connect to the base plate portion  406  or the load beam portion  412 , although in alternative embodiments the hinges  424  are not provided.  
         [0038]    The motive frame portion  410  is again located between the parallel members  422   a,    422   b  and the base plate and load beam portions  406 ,  412 . However, in the embodiment shown the motive frame portion  410  includes first and second tabs  426 ,  428  and a third member  440 , located between the first and second tabs  426 ,  428 . The third member  440  is substantially parallel to the parallel members  422   a,    422   b  and connects the base plate portion  406  to the load beam portion  412 . Attached to the first tab  426  and the second tab  428  and spanning (not attached to) the third member  440  and space between the first and second tabs  426 ,  428 , is a piezoelectric element  430 . The piezoelectric element  430  is mounted such that when a voltage is applied it expands or contracts in a direction substantially orthogonal to the longitudinal axis  418 . When expanding, the piezoelectric element  430  produces a force that drives the first and second tabs  426 ,  428  apart. When contracting, the piezoelectric element  430  produces a force that drives the first and second tabs  426 ,  428  toward each other. In either case, as in the previous embodiments the driving force will cause the load beam portion  412  to translationally move with respect to the base plate portion  406 .  
         [0039]    The third member  440  in the embodiment shown in FIG. 4 is not a lever member in that no force is applied directly to the member. Rather, it provides additional support to the load beam portion  412  by essentially acting as an additional parallel member.  
         [0040]    The embodiments described above utilize a single piezoelectric element as means to produce a force between the tab and the lever member and thereby causing the load beam portion to move essentially translationally with respect to the base plate portion. Other means for producing the force are also possible including a second magnetic actuator or an electrically-driven piston or motor that creates a force between the lever member and the tab.  
         [0041]    The embodiments described above also position the force-producing means so that the force generated by the force-producing means is substantially in the direction parallel to the rotating disc but perpendicular to the longitudinal axis of the flexure. However, this positioning is not essential to produce the translational movement of the load beam portion with respect to the base plate portion. Because the parallelogram portion limits the movement of the load beam portion with respect to the base plate portion to only translational movement, any force-producing means positioned such that it has some vector force component in the direction perpendicular to the longitudinal axis of the flexure will also cause translational movement of the load beam portion with respect to the base plate portion. The reader will note that for alternative embodiments that do not have the force-producing means substantially orthogonal to the longitudinal axis of the flexure, the tab may no longer be necessary, i.e. the force-producing means is connected to (and applies a force between) either the base plate portion or the load beam portion proper at one end and the lever member at the other end.  
         [0042]    It should also be noted that the positioning of the piezoelectric electric element can be adjusted to obtain different amounts of mechanical advantage. This takes advantage of the inherent lever nature of the embodiments. For example, in the embodiment shown in FIG. 2 a  the closer to the load beam portion that the piezoelectric element is attached on the lever member, the greater the mechanical advantage will be. Thus, resulting in less force being required to achieve the same translation displacement.  
         [0043]    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 presently preferred embodiments have 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, the embodiments disclosed above include hinge points on the members. While these hinge points permit facilitate movement and thus permit the use of a smaller piezoelectric element, some or all of the hinges on the members may be omitted without substantially affecting the operation of the flexure. The parallel members may be reinforced, such as at the hinges, to reduce movement away from and toward the disc and improve structural stability. 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.