Patent Abstract:
A microactuation system selectively alters a position of a transducing head carried by a slider in a disc drive system with respect to a track of a rotatable disk having a plurality of concentric tracks. The microactuation system includes a head suspension having a first portion and a second portion coupled by one or more flexible hinges. An electroactive element is attached to the first portion of the head suspension at one end and the second portion of the load beam at the other end. The electroactive element bends in response to a control signal applied thereto. The hinge is sufficiently compliant to permit movement of the first portion with respect to the second portion of the head suspension.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from provisional application No. 60/161,692, filed Oct. 26, 1999 for “PIEZOELECTRIC IN-PLANE BIMORPH ON LOAD BEAM SUSPENSION-LEVEL MICROACTUATOR” by James Morgan Murphy, Richard August Budde, Markus E. Mangold, and Peter Crane. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a suspension-level microactuator having an improved stroke length. More particularly, it relates to a microactuator located in-plane along a suspension in a disc drive system and having an electroactive element to selectively move a transducing head radially with respect to a rotatable disc. 
     Disc drive systems include disc drive suspensions for supporting transducing heads over information tracks of a rotatable disc. Typically, suspensions include a load beam having a mounting region on a proximal end, a flexure on a distal end, a relatively rigid region adjacent to the flexure, and a spring region between the mounting region and the rigid region. An air bearing slider which supports the transducing head is mounted to the flexure. The mounting region is typically attached to a base plate for mounting the load beam to an actuator arm. A motor which is controlled by a servo control system rotates the actuator arm to position the transducing head over the desired information tracks on the disc. This type of suspension is used with both magnetic and non-magnetic discs. 
     In an effort to increase the storage capacity of hard disc drives, the density of concentric data tracks on magnetic discs continues to increase (i.e., the size of data tracks and radial spacing between the data tracks continues to decrease). Therefore, a corresponding improvement in the accuracy of the positioning system that locates the transducing head over a particular track is needed. Conventionally, the positioning system uses a single-stage, closed-loop feedback system in which a large-scale actuation motor, such as a voice coil motor, acts in response to a control signal based on position error information from the read head to radially position a head on a slider at the end of the actuator arm. This system is approaching the limit of its ability to follow the ever-narrower tracks and to reject the vibrations and disturbances present in the drive environment. This inability to follow the narrow tracks is due in large part to the significant length of structure between the voice coil motor and the head and the in-loop resonances which result from the structure. Thus, a high resolution head positioning mechanism is needed to accommodate the more densely spaced tracks. 
     One promising design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional low resolution actuator motor, thereby effecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. These designs, however, have shortcomings that limited the effectiveness of the microactuator. Many designs increased the complexity of designing and assembling the existing components of the disc drive, while other designs were unable to achieve the force and bandwidth necessary to accommodate rapid track access. Therefore, the prior designs did not present ideal microactuator solutions. 
     The positioning of a transducing head through dual-stage actuation using electroactive elements has been disclosed in prior patent applications. One such application is U.S. patent application Ser. No. 09/311,086, filed May 13, 1999 by Budde et al. entitled “PIEZOELECTRIC MICROACTUATOR SUSPENSION ASSEMBLY WITH IMPROVED STROKE LENGTH,” which is assigned to Seagate Technology, Inc., the assignee of the present invention, and is hereby incorporated by reference. Another such application is U.S. patent application Ser. No. 09/553,220, filed on even date herewith by Boutaghou, Crane, Mangold, and Walter entitled “BENDING MICROACTUATOR HAVING A TWO-PIECE SUSPENSION DESIGN,” which is assigned to Seagate Technology, Inc., the assignee of the present invention, and is hereby incorporated by reference. There remains a need in the art, however, for an electroactive element microactuator design that provides efficient high resolution head positioning in a dual-stage actuation system, allows for a greater range of motion than current designs, has reduced in-loop resonances, and is easy to manufacture and install. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a microactuator for selectively altering a position of a transducing head carried by a slider, in a disc drive system, with respect to a track of a rotatable disc having a plurality of concentric tracks. The disk drive system includes an actuator arm. The microactuator includes a load beam attached to a distal end of the actuator arm. The load beam has a first section and a second section. A flexure is connected to the second section of the load beams for supporting the slider carrying the transducing head. A hinge is attached between the first section and the second section, the hinge being flexible to permit movement of the second section with respect to the first section in the general plane of the load beam. A bending motor is connected between the first section and the second section of the load beam along a longitudinal centerline of the load beam. The bending motor is deformable in response to a control signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a disc drive system including a microactuation system for positioning a transducing head over selected tracks of a rotating disc. 
     FIG. 2A is a top view of a microactuation system, shown in a neutral position, for use in a dual-stage disc drive actuation system for high resolution positioning of a transducing head according to the present invention. 
     FIG. 2B is a top view of the microactuation system of FIG. 2A, shown in a first actuated position, for use in a dual-stage disc drive actuation system for high resolution positioning of a transducing head according to the present invention. 
     FIG. 2C is a top view of the microactuation system of FIG. 2A, shown in a second actuated position, for use in a dual-stage disc drive actuation system for high resolution positioning of a transducing head according to the present invention. 
     FIG. 3 is a top perspective view of the microactuation system of FIG.  2 A. 
     FIG. 4 is a bottom perspective view of the microactuation system of FIG.  2 A. 
     FIG. 5 is a top perspective view of the microactuation system of FIG. 2A shown with the bending motor removed. 
     FIG. 6 is a top view of a portion of the microactuation system of FIG.  2 A. 
     FIG. 7A is a cross-sectional view of a bending motor according to a first embodiment of the present invention. 
     FIG. 7B is a cross-sectional view of a bending motor according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a perspective view of disc drive system  10 , as known in the prior art, for positioning a transducing head (not shown) over a selected track of a magnetic disc. The system  10  includes, as shown generally from left to right in FIG. 1, a voice coil motor (VCM)  12 , an actuator arm  14 , a suspension  16 , a flexure  18 , and a slider  20 . The slider  20  is connected to the distal end of the suspension  16  by the flexure  18 . The suspension  16  is connected to the actuator arm  14  which is coupled to the VCM  12 . As shown on the right side of FIG. 1, the system  10  includes a disc  22  having a multiplicity of tracks  24  that rotate about an axis  26 . During operation of the disc drive system  10 , the rotation of the disc  22  generates air movement which is encountered by the slider  20 . This air movement or windage acts to keep the slider  20  aloft a small distance above the surface of the disc  22  allowing the slider to “fly” above the surface of the disc  22 . Any wear associated with physical contact between the slider  20  and the disc  22  is thus minimized. 
     The flexure  18  provides a spring connection between the slider  20  and the suspension  16 . The flexure  18  is configured such that it allows the slider  20  to move in pitch and roll directions to compensate for fluctuations in the spinning surface of the disc  22 . Many different types of flexures  18 , also known as gimbals, are known to provide the spring connection allowing for pitch and roll movement of the slider  20  and can be used with the present invention. The VCM  12  is selectively operated to move the actuator arm  14  around an axis  28 , thereby moving the suspension  16  and positioning the transducing head (not shown) carried by the slider  20  between tracks  24  of the disc  22 . Proper positioning of the transducing head (not shown) is necessary for reading and writing of data on the concentric tracks  24  of the disc  22 . For a disc  22  having a high track density, however, the VCM  12  lacks sufficient resolution and frequency response to accurately position the transducing head (not shown) on the slider  20  over a selected track  24  of the disc  22 . Therefore, a higher resolution actuation device is used in combination with the VCM  12 . 
     FIGS. 2A-2C show three top views of a microactuation system  30  for use in a dual stage disc drive actuation system for high resolution positioning of a transducing head (not shown) according to the present invention. As shown from right to left in FIGS. 2A-2C, the microactuation system  30  includes a bending motor  32  and a load beam  34 . A mounting region  38  of the load beam  34  connects to a base plate (not shown) which connects to the actuator arm  14 . The bending motor  32 , the load beam  34 , and the base plate are all components of the suspension  16  (as shown in FIG.  1 ). As shown on the far right side in FIGS. 2A-2C, the distal end of the load beam  34  is coupled to the flexure  18 , which holds the slider  20 . 
     FIGS. 2A-2C when viewed together illustrate the general operation of the microactuation system  30  of the present invention. FIG. 2A shows the microactuation system  30  in a neutral position. As is apparent from FIG. 2A, in the neutral position the bending motor  32  is generally straight along its longitudinal axis. FIG. 2B shows the microactuation system  30  in a first actuated position in which the bending motor  32  is curved or bent to the left of the neutral position. FIG. 2C shown the microactuation system  30  in a second actuated position in which the bending motor  32  is curved or bent to the right of the neutral position. The amount of displacement of the slider  20  shown in FIG.  2 B and FIG. 2C is exaggerated for purposes of illustration. The bending of the bending motor  32  operates to cause a displacement of the slider  20  and thus the transducing head (not shown), which in turn causes an adjustment of the position of the transducing head (not shown) with respect to a selected track  24  of the disc  22 . 
     FIG. 3 shows a top perspective view of the microactuation system  30  of the present invention (absent the mounting region  38 ). As shown in FIG. 3, moving from left to right, or from a proximal end to a distal end, the load beam  34  includes two pre-load bend legs  40   a ,  40   b  and a head suspension  42 . The head suspension  42  is flexibly coupled to the mounting region  38  (shown in FIGS. 2A-2C) by the two pre-load bend legs  40   a ,  40   b . The head suspension  42  includes a proximal section  44  and a distal section  46  separated by an air gap or a space  47 . The distal section  46  is connected to the proximal section  44  by two hinges  48   a  and  48   b . The distal section  46  of the head suspension  42  supports the flexure  18 , which supports the slider  20 , which supports the transducing head (not shown). 
     As further shown in FIG. 3, the bending motor  32  is mounted to a top surface of the head suspension  42  in a plane generally parallel to the plane of the head suspension  42 . The bending motor  32  is mounted to the proximal section  44  and the distal section  46  of the head suspension  42 . In a preferred embodiment, the bending motor  32  is mounted to the head suspension  42  using an adhesive. The bending motor  32  can also be mechanically fastened to the head suspension  42 . The fastening of the bending motor  32  to the head suspension  42  is described in greater detail below with reference to FIG.  5 . 
     The configuration of the bending motor  32  with respect to the head suspension  42  has significant advantages. The configuration allows for the use of longer bending motors  32 , which allows for a greater stroke or cross-track deflection of the transducing head. Also, the bending motor  32  is supported by the head suspension  42  and the head suspension  42  acts to absorb the majority of shock loads applied to the slider  20  so that less force is transmitted through the bending motor  32 . This results in improved robustness and shock resistance. Also, the configuration of the present invention results in a stiffer structure, which increases the resonance frequencies. Finally, the placement of the bending motor  32  near the slider  20  and the transducing head results in decreased in-loop resonances and vibrations as there are fewer components between the bending motor  32  and the transducing head (which supplies the position error information). The significance of in-loop resonances is further detailed in the above-referenced copending U.S. patent application Ser. No. 09/553,220, by Boutaghou, Crane, Mangold, and Walter et al. entitled “BENDING MICROACTUATOR HAVING A TWO-PIECE SUSPENSION DESIGN.” 
     A bottom perspective view of the microactuation system  30  of the present invention is shown in FIG. 4, which more clearly illustrates the flexure  18  and the slider  20  mounted to a distal end of the head suspension  42 . FIG. 4 also shows the location of the transducing head  49  carried by the slider  20 . 
     FIG. 5 shows a top perspective view of the microactuation system  30  of the present invention with the bending motor  32  removed to reveal additional features of the head suspension  42 . As further shown in FIG. 5, the distal section  46  of the head suspension  42  includes two slots  50   a ,  50   b  and an adhesive region  52 , and the proximal section  44  includes, near a proximal end, an adhesive region  54 . The bending motor  32  is generally mounted to the proximal section  44  of the head suspension  42  at the adhesive region  54  and to the distal section  46  of the head suspension  42  at the adhesive region  52 . The slots  50   a  and  50   b  act to prevent the adhesive used to mount the bending motor  32  to the distal section  46  of the head suspension  42  from moving or wicking along the bending motor  32 . This, in turn, helps to maximize the effective length, or the area between attachment points, of the bending motor  32 . The present invention, by employing elements having increased effective lengths, has increased stroke or cross-track deflection of the transducing head. 
     FIG. 6 shows a top view of the hinge region of the head suspension  42 . As shown in FIG. 3, the proximal section  44  is rotatably coupled to the distal section  46  of the load beam  42  by hinges  48   a  and  48   b . The hinges  48   a  and  48   b  are generally formed by bending the material of the head suspension  42  normal to the general plane of the head suspension  42 . This configuration provides increased compliance for rotation about a virtual pivot VP to facilitate rotation and displacement of the distal section  46  with respect to the proximal section  44  in a plane generally parallel to that of the disc  22 . At the same time, this configuration provides substantial stiffness to resist undesired movements and vibrations out of a plane generally parallel to the disc  22 . The location of the virtual pivot VP is generally identified by the intersection of two lines extending from and parallel to the two hinges  48   a ,  48   b  (as shown by the dashed lines in FIG.  3 ). In a preferred embodiment, the hinges  48   a ,  48   b  are configured such that the virtual pivot VP is located near a longitudinal and transverse center point of the bending motor  32 . One advantage of the configuration of the head suspension  42  is that the location of the two hinges  48   a ,  48   b  reduces deformation resulting from application of the preload force. Because the hinges  48   a ,  48   b  are located close to the point of application of the preload force, lower bending moments result. 
     The specific pivotal structures flexibly coupling the distal portion  46  of the head suspension  42  to the proximal portion  44  of the head suspension  42  shown in FIGS. 3-6 are intended to be exemplary only. Many other pivotal structures can also be used between the distal portion  46  and proximal portion  44  of the head suspension  42 . For example, the hinges  48   a ,  48   b  can be disposed at a variety of angles with respect to the longitudinal centerline of the head suspension  42 . Also, one or more appropriately sized beams can be used to connect the two portions  44 ,  46  of the head suspension  42 . Other structures generally known to those of ordinary skill in the art can also be employed. 
     The bending motor  32  is a structural element operable as a bendable cantilever to alter the position of the distal section  46  with respect to the proximal section  44  of the head suspension  42  (as illustrated by the sequence of FIGS.  2 A- 2 C). By causing rotation and displacement of the distal section  46  of the head suspension  42 , the bending motor  32  effects high resolution positioning of the transducing head carried by the slider  20 . In a preferred embodiment the bending motor  32  is constructed from an electroactive material such as piezoelectrics, electroactive ceramics, electroactive polymers, or electrostrictive ceramics. In another preferred embodiment the bending motor  32  is constructed from thermoactive elements. The remainder of this disclosure will describe the preferred embodiment of the present invention employing piezoelectric elements such as zinc oxide (ZnO), lead zirconate titanate (PbZrTiO 3 , also known as PZT), aluminum nitride (AlN), or polyvinylidene fluoride (PVDF). 
     FIG. 7A shows a sectional view of a oppositely poled bending motor  60 , which represents a first preferred embodiment of the bending motor  32  described with reference to FIG.  3 . The view shown in FIG. 7A is a transverse cross-section taken across the width of the oppositely poled bending motor  60 . The oppositely poled bending motor  60  operates using a “single-ended” approach as further explained below. The oppositely poled bending motor  60  includes a bottom electrode  62 , a oppositely poled piezoelectric element  64 , and a top electrode  66 . The oppositely poled piezoelectric element  64  is divided generally along a longitudinal centerline into a first portion  68  (shown on the left side of FIG. 7A) and a second portion  70  (shown on the right side of FIG.  7 A). The oppositely poled piezoelectric element  64  is formed such that the first portion  68  and the second portion  70  have opposite poling. For example, the first portion  68  is poled in the direction of the arrow  72 , and the second portion  70  is poled in the direction of the arrow  74 . 
     During operation, an electric potential is applied to the bottom electrode  62  and the top electrode  66 . Generally, the bottom electrode  62  is connected to electrical ground, and the driving voltage is applied to the top electrode  66 . Alternatively, voltages of opposite polarities can be applied to the top electrode  66  and the bottom electrode  62  to create an overall potential between the electrodes greater than the voltage applied to either single electrode. The potential difference between the bottom electrode  62  and the top electrode  66  causes expansion or contraction of the first portion  68  and the second portion  70  of the oppositely poled piezoelectric element  64 . For example, if a positive voltage is applied to the top electrode  66 , the first portion  68  (poled in a positive direction) will contract in the direction normal to the electrodes  62 ,  66 , which, in turn, will cause the first portion  68  to expand longitudinally (in the direction parallel to the electrodes  62 ,  66 ). Conversely, the same positive voltage applied to the top electrode  66  will cause the second portion  70  to contract longitudinally. 
     The expansion of the first portion  68  and the concurrent contraction of the second portion  70  generates a bending moment in the piezoelectric element  64  in-plane. This moment results in a bending motion of the oppositely poled bending motor  60 , toward the right as illustrated in FIG. 2C, which will effect rotation and displacement of the distal section  46  with respect to the proximal section  44  of the head suspension  42 . This rotation and displacement of the distal section  46  will, in turn, cause movement of the transducing head carried by the slider  20 . The amount of bending of the oppositely poled bending motor  60 , and thus the amount of displacement of the transducing head, is precisely controlled by the magnitude of the voltages applied to the electrodes  62 ,  66 . The direction of the bending motion is controlled by the polarity of the voltage applied to the electrodes  62 ,  66 , and the amount of displacement is controlled by the magnitude of the voltages applied. The bending motion will occur in a direction toward the side that is contracting longitudinally. 
     FIG. 7B shows a sectional view of a uniformly poled bending motor  80 , which represents a second preferred embodiment of the bending motor  32  described with reference to FIG.  3 . The view shown in FIG. 7B is a transverse cross-section taken across the width of the uniformly poled bending motor  80 . The uniformly poled bending motor  80  operates using a “differential” approach as further explained below. The uniformly poled bending motor  80  includes a bottom electrode  82 , a piezoelectric element  84 , a first top electrode  86 , and a second top electrode  88 . The first top electrode  86  is deposited over the top surface of one longitudinal half of the piezoelectric element  84 , and the second top electrode  88  is placed over the other longitudinal half of the piezoelectric element  84 . The entire piezoelectric element  84  is poled in the direction of the arrow  90 . 
     During operation, an electric potential is applied to the bottom electrode  82  and the top electrodes  86 ,  88 . Generally, the bottom electrode  82  is connected to electrical ground, and the driving voltage is applied to the top electrodes  86 ,  88 . Alternatively, two bottom electrodes can be used, placed generally opposite the two top electrodes  86 ,  88 , and a voltage can also be applied to the two bottom electrodes. The potential difference between the bottom electrode  82  and the top electrodes  86 ,  88  causes expansion or contraction of the portion of the piezoelectric element  84  located between the respective top electrode and the bottom electrode. For example, if a positive voltage is applied to the first top electrode  86 , the portion of the piezoelectric element  84  located between the first top electrode  86  and the bottom electrode  82  will contract in the direction normal to the electrodes  82 ,  86 , which, in turn, will cause the that portion to expand longitudinally (in the direction parallel to the electrodes  82 ,  86 ). At the same time, a negative voltage is applied to the second top electrode  88 , which causes the portion of the piezoelectric element located between the second top electrode  88  and the bottom electrode  82  to contract longitudinally. 
     The expansion of the first portion and the concurrent contraction of the second portion generates a bending moment in the piezoelectric element  84 . This moment results in a bending motion of the uniformly poled bending motor  80 , toward the right as illustrated in FIG. 2C, which will effect rotation and displacement of the distal section  46  with respect to the proximal section  44  of the head suspension  42 . This rotation and displacement of the distal section  46  will, in turn, cause movement of the transducing head carried by the slider  20 . The amount of bending of the uniformly poled bending motor  80 , and thus the amount of displacement of the transducing head, is precisely controlled by the magnitude of the voltages applied to the electrodes  82 ,  86 ,  88 . The direction of the bending motion is controlled by the polarity of the voltages applied to the first top electrode  86  and the second top electrode  88 , and the amount of displacement is controlled by the magnitude of the voltage applied. The bending motion will occur in a direction toward the side that is contracting longitudinally. 
     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.

Technology Classification (CPC): 6