Abstract:
A dual stage actuated (DSA) suspension uses two shear-mode PZT microactuators to finely position the head slider. The bottom surfaces of the PZTs are affixed to the flexure, and the PZT top surfaces move forward and backward, respectively, in push-pull fashion when the PZTs are activated. Flexible connector arms attach the tops surfaces of the PZTs to the gimbal tongue such that activating the PZTs causes the gimbal tongue to rotate, with the connector arms acting as levers to magnify the motion such that a relatively small shear movement of the PZTs results in a significantly larger lateral movement of the head slider across the data disk.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. provisional patent application No. 62/216,941 filed Sep. 10, 2015, the disclosure of which is incorporated by reference as if set forth fully herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of a dual stage actuated suspension having shear-mode PZT actuators that rotate the gimbal tongue. 
     2. Description of Related Art 
     In a typical disk drive assembly, the suspension is the part that holds the read/write head over the correct position on a spinning data disk such as a magnetic data medium or optical data medium containing a number of concentric data tracks. The suspension typically includes a beam portion or load beam, and a flexure that includes a gimbaled portion, with the load beam typically mounted to a baseplate at the proximal end of the suspension, and the flexure mounted at the distal end of the load beam. The read/write head, or head slider, is affixed to the gimbaled portion of the flexure so that it can pitch and roll freely. The suspension is typically mounted at the end of an actuator arm, with the actuator arm moved by a voice coil motor (VCM). 
     Dual stage actuated (DSA) suspensions are well known. In a DSA suspension, the suspension is not only activated by the voice coil motor which moves the entire suspension, but an additional actuator is placed on the suspension itself for effecting fine movements of the head slider in order to keep it properly aligned over the correct data track on the spinning disk. The secondary actuator(s) provide finer control and higher bandwidth of the servo control loop than does the voice coil motor alone, which is only capable of effecting relatively coarse, slow movements of the suspension and hence the head slider. The secondary actuator(s) are sometimes referred to as milliactuators if they are mounted near the proximal end of the suspension, and microactuators if they are mounted near the distal end of the suspension. As used herein, the term “microactuator” will be used as an umbrella term that refers to any small actuator motor that is located on the suspension itself. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible. 
     In order to achieve the best performance in a suspension, it is important to maximize the stroke length in the microactuation mechanism. The term “stroke length” is a shorthand expression for the distance that the read/write head moves radially across a data disk per unit of voltage input to the microactuator motor. 
     Linear-mode PZTs are commonly used as microactuators on DSA suspension. U.S. Pat. No. 8,879,210 issued to Hahn et al. is an example of a DSA suspension that uses linear-mode PZTs to position the read/write head. The two PZTs act in push-pull fashion to rotate the head slider and thus to precisely position its read/write transducers. 
     D 31  is the transverse piezoelectric coefficient of a linear-mode piezoelectric device; it represents the amount of linear expansion a PZT device undergoes in the transverse direction (i.e., normal to the electric field gradient) when an activation voltage is placed across the device&#39;s electrodes. D 33  is the longitudinal piezoelectric coefficient; it represents the amount of linear expansion of a PZT in the longitudinal direction (i.e., in the direction of the electric field gradient) when an activation voltage is placed across the device&#39;s electrodes. 
     SUMMARY OF THE INVENTION 
     In addition to linear-mode PZTs, shear-mode PZTs exist. In a shear-mode PZT, in response to an activation voltage the PZT deforms in shear. For example, the top surface moves horizontally relative to the bottom surface. D 15  is the shear piezoelectric coefficient of a shear-mode PZT. The present invention employs a shear-mode PZT operating in the d 15  mode, or shear mode, in order to maximize the stroke length. 
     According to an exemplary embodiment, first and second shear-mode PZTs operating in the d 15  mode are mounted on a flexure. The PZTs may be mounted on separate flexible outrigger arms than can flex in the vertical dimension at least somewhat independently. Respective first and second flexible connector arms extend from the PZTs to the gimbal tongue. When the PZTs are activated, the two PZTs act in opposite directions in push-pull fashion, thereby pushing on and pulling respectively opposite sides of the gimbal tongue through the respective connector arms, to rotate the gimbal tongue together with the head slider that is mounted on the gimbal tongue. Rotating the gimbal tongue positions the read/write data transducers that are embedded in the head slider, usually close to the distal end of the slider, over the desired data track on the data disk. The mechanical coupling from the PZTs to the head slider acts as a lever to magnify the shear movement of the PZTs into significantly greater spatial displacement at the read/write transducers. 
     The gimbal tongue may be supported by only the flexible connectors, with the freedom of movement provided by the flexible connectors combining with the freedom of movement provided by the independently flexing flexible outrigger arms to provide the desired gimbaling action at the head slider in the pitch and roll directions. 
     Exemplary embodiments of the invention will be further described below with reference to the drawings, in which like numbers refer to like parts. The drawing figures might not be to scale, and certain components may be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top oblique view of a suspension according to an exemplary embodiment of the invention. 
         FIG. 2  is a top plan view of the trace gimbal assembly of the suspension of  FIG. 1 . 
         FIG. 3  is a bottom plan view of the trace gimbal assembly of  FIG. 2 . 
         FIG. 4  is a top oblique view of the flexure gimbal of  FIG. 2 . 
         FIG. 5  is a closeup of the flexure gimbal of  FIG. 4 . 
         FIG. 6  is a bottom oblique view of the flexure gimbal of  FIG. 4   
         FIG. 7A  is a cross sectional view of the flexure of  FIG. 5 , taken along section line  7 A- 7 A, when the PZTs are activated. 
         FIG. 7B  is a cross sectional view of the flexure of  FIG. 5 , taken along section line  7 B- 7 B, when the PZTs are activated. 
         FIG. 8  is a side sectional view of the flexure of  FIG. 5  taken alone section line  8 - 8 . 
         FIG. 9  is a top plan view of the flexure of  FIG. 4  when the PZTs are activated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As used herein, the “bottom” side of a suspension is the side on which the read/write head is mounted, i.e., the side which faces the data disk, and the “top” side is the side opposite the bottom side. The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end nearest to the base plate which is swaged or otherwise mounted to an actuator arm. The “distal” end of a suspension or load beam is the end that is opposite the proximal end, i.e., the “distal” end is the cantilevered end. 
       FIG. 1  is a top oblique view of a suspension  2  according to an exemplary embodiment of the invention. Suspension  2  includes: a base plate  4 ; and a load beam  6 , or beam portion, or simply beam extending from baseplate  4  and attached to baseplate  4  via hinge springs at a proximal end of load beam  6 . A trace gimbal assembly (TGA)  10  which carries head slider  42  is attached to load beam  6  at the distal end of load beam  6 . 
       FIG. 2  is a top plan view of TGA  10  of the suspension  2  of  FIG. 1 , and  FIG. 3  is a bottom plan view thereof. TGA  10  includes flexure  11  and flexible circuit  9 . Flexible circuit  9  includes layers of a dielectric insulator which is typically polyimide, and electrical signal traces formed of a conductor which is typically copper or copper alloy. Both load beam  6  and the flexure  11  are typically made of stainless steel, and are typically welded together using laser spot welding. Flexure  11  includes two elongate flexible outrigger arms  12  on the left and right lateral sides of the flexure, and outer gimbal ring  18 . The proximal end of flexure  11  is connected to load beam  6  and is therefore relatively fixed. Because outrigger arms  12  are thin and flexible, their distal ends can move vertically relative to one another relatively freely as the outrigger arms  12  flex up and down and without any direct rigid coupling between those distal ends. Head slider  42  is bonded and rigidly affixed to gimbal tongue  40  such as by epoxy adhesive. Flexible circuit  9  carries read/write signals and data tracking servo control loop signals to and from head slider  42 . 
       FIG. 4  is a top oblique view of the distal portion of flexure  11  of  FIG. 2 . Flexible circuit  9  is not shown for clarity of illustration. Outrigger arms  12  include generally laterally extending portions  13 . Gimbal tongue  40  defines a gimbaled portion  14  of the TGA  10  to which head slider  42  is mounted, and hence gimbal tongue  40  also defines a gimbaled portion of suspension  2 . 
       FIG. 5  is a closeup of the flexure gimbal of  FIG. 4 , showing the PZTs and their mechanical coupling to gimbal tongue  40  in detail. Flexible outrigger arms  12  include generally laterally extending portions  13 , portions of which define bases  20 ,  30  on which one, and preferably two, piezoelectric devices  22 ,  32  are mounted. The piezoelectric devices  22 ,  32  define microactuators, which will be referred to simply as PZTs. PZTs  22 ,  32  operate in the d 15  mode; such PZTs are referred to as shear-mode PZTs. 
     PZTs  22 ,  32  are attached at the distal ends of respective flexible outrigger arms  12 . In the preferred embodiment there is no direct mechanical connection extending between the two PZTs or tying them closely together. The PZTs  22 ,  32  thus enjoy a certain amount of freedom of movement such that one PZT  22  can move vertically relative to the other PZT  32 . 
     PZTs  22 ,  32  can be bonded directly to flexible outrigger arms  12 . Because flexure  11  is typically made of stainless steel which is electrically conductive and is grounded through load beam  6 , if PZTs  22 ,  32  are bonded to flexible outrigger arms  12  using conductive adhesive such as epoxy containing silver particles, then assuming that the bottom surfaces of the PZTs are electrodes, the bottom electrodes are thus grounded; the actuating drive voltage for the PZTs would be supplied to the drive electrode which would normally be located on the top surface of the PZTs. If the PZTs are electrically isolated from flexible outrigger arms  12  such as via the insulating layer of the TGA  10 , then either the top or bottom surface can be the drive electrode, with the other surface being the ground electrode. Although normally the top and bottom surfaces of the PZTs constitute the two electrodes for the device, other possibilities exist including PZTs having wrap-around electrodes such that both electrodes are accessible from a single face of the PZT. 
     The actual electrical connections to the PZTs  22  and  32  are omitted for clarity of illustration. Examples of electrical connections to PZTs in suspensions can be seen in, e.g., U.S. Pat. No. 8,254,065 to Inoue et al.; U.S. Pat. No. 9,251,817 to Hahn et al.; U.S. Pat. No. 8,810,972 to Dunn; and U.S. Pat. No. 8,189,301 to Schreiber. The actual connections of the PZT actuating voltage and ground to the PZTs is a matter of design choice; a number of possibilities would be apparent to the designer of ordinary skill in the art of suspension design. 
     PZTs  22 ,  32  are coupled to gimbal tongue  40  via flexible connector  50 . Connector  50  includes left connector arm  24  which includes generally longitudinally extending portion  25  and generally laterally extending portion  26 , and right connector arm  34  which includes generally longitudinally extending portion  35  and generally laterally extending portion  36 . Connector arms  24 ,  34  may be bonded to PZTs  22 ,  32  such as by epoxy adhesive. Preferably connector  50  is unitarily formed of a single piece of spring material such as stainless steel. The generally longitudinally extending portions  25 ,  35  are angled slightly inwardly, preferably at an angle of 0-30°, so that as they extending distally from the PZTs they also extend slightly inwardly toward a central longitudinal axis of the flexure and of the suspension. In the embodiment shown, connector  50  attaches to gimbal tongue  40  at a single location that corresponds to spacer or standoff  44 , and gimbal tongue  40  is supported only by connector  50 , such that connector  50  including its flexible connector arms  24 ,  34  provide the sole mechanical support for gimbal tongue  40 . The freedom of movement provided by flexible outrigger arms  12  combined with the freedom of movement provided by flexible connector  50  provides a gimbaling action that allows head slider  42  to pitch and roll freely to accommodate vibrations, inertial events such as bumping, and irregularities in the disk platter surface as the disk platter moves underneath the head slider. Preferably the generally longitudinally extending portions  25 ,  35  of connector  50  are narrower in the lateral direction than PZTs  22 ,  32 . More preferably, portions  25 ,  35  of connector  50  are less than one third as wide as the lateral widths of each of the PZTs  22 ,  32 . 
     In the embodiment, generally laterally extending portions  26 ,  36  of connector  50  are connected to gimbal tongue  40  via standoff  44  which separates connector  50  from gimbal tongue  40  by approximately the same distance as thicknesses of PZTs  22 ,  32 , such as a distance that is 50%-150% of the thicknesses of the PZTs. Standoff  44  could be conductive epoxy to electrically connect to the tongue. Alternatively, connector  50  and gimbal tongue  40  could be welded together. If connector  50  comprises an electrically conductive material such as stainless steel and is bonded to the PZTs using conductive adhesive such as conductive epoxy, then a single common PZT driving voltage could be supplied to one of the PZTs&#39; top electrodes, and connector  50  will carry that driving voltage to the other PZT&#39;s top electrode. Thus, using connector  50 , only a single driving voltage connection is necessary in order to drive both PZTs. 
       FIG. 6  is a bottom oblique view of the flexure gimbal of  FIG. 4 . 
       FIG. 8  is a side sectional view of the flexure of  FIG. 5  taken alone section line  8 - 8 . 
       FIG. 7A  is a cross sectional view of the flexure of  FIG. 5 , taken along section line  7 A- 7 A, when the PZTs are activated, and  FIG. 7B  is a cross sectional view of the flexure of  FIG. 5  taken along section line  7 B- 7 B, when the PZTs are activated. When PZTs  22 ,  32  are activated by applying a voltage across their electrodes  27 / 29  and  37 / 39 , PZT  22  moves in shear, i.e. in its d 15  mode, with its top surface  29  moving in a more distal direction while PZT  32  moves in shear with its top surface  39  moving in a more proximal direction, as shown in  FIGS. 7A and 7B , or vice versa. Connector  50  defines a mechanical coupling that couples the push-pull movement of PZTs  22 ,  32  into rotational movement of gimbal tongue  40  and hence of head slider  42 . Connector  50 , and in particular the generally longitudinally extending portions  25 ,  35 , act as lever arms to multiply the relatively small longitudinal movements of top faces  29 ,  39  of PZTs  22 ,  32  to a much larger lateral movement at gimbal tongue  40  and hence at the center of head slider  42  and also at the particular loci where the read and write magnetic data transducers are located within head slider  42 . Additionally, because the d 15  (shear) coefficient of PZT devices is generally higher than the d 31  (linear) coefficient, using shear-mode PZTs, particularly coupled with a mechanical coupling such as the one disclosed herein to amplify the shear movement of the PZTs, produces a large stroke length, which is the highly desired result. 
     The PZTs are poled and mounted such that a single common activation voltage applied to the top electrodes at top surfaces  29  and  39  causes PZT  22  to shear in the forward direction indicated by the arrow in  FIG. 7A , and PZT  32  to simultaneously shear in the backward direction indicated by the arrow in  FIG. 7B . That is, the top surface  29  of PZT  22  moves towards gimbal tongue  40  thus pushing a first side of gimbal tongue  40 , and the top surface  39  of PZT  32  moves away from gimbal tongue  40  thus pulling a second side of the tongue that is laterally opposite the first side. When that happens, the mechanical coupling including connector  50  causes the head slider to rotate, which moves the data read and data write transducers embedded within the head slider across the data disk laterally, i.e., in a direction that is perpendicular to the data tracks on the disk. The rotational motion of the gimbal tongue therefore causes the head slider to be positioned properly over the data track, or moved to a different data track altogether. 
     In the embodiment, a proximal tail portion  41  of gimbal tongue  40  extends between the two PZTs  22 ,  32 , such as at least as far as the midpoint of PZTs  22 ,  32 . Tail portion  41  can provide moment-balancing for gimbal tongue  40 . Furthermore, tail portion  41  may be formed such as by bending to interact with other features of the flexure to act as a vertical travel limiter for head slider  42 . 
       FIG. 9  is a top plan view of the flexure of  FIG. 4  when the PZTs are activated such as shown in  FIGS. 7A and 7B . The top surface of PZT  22  has moved in shear toward the distal end of the suspension, and the bottom surface of PZT  32  has moved in shear toward the proximal end of the suspension. Acting through connector  50 , the shear movement of the PZTs acts in push/pull fashion to rotate gimbal tongue  40  and hence head slider  42 . The magnetic read/write transducers (not shown) that are embedded in head slider  42  therefore move with a radial component across the concentric data tracks on the data disk (not shown) within the disk drive assembly. 
     It will be understood that the terms “generally,” “approximately,” “about,” and “substantially,” as used within the specification and the claims herein allow for a certain amount of variation from any exact dimensions, measurements, and arrangements, and that those terms should be understood within the context of the description and operation of the invention as disclosed herein. 
     It will further be understood that terms such as “top,” “bottom,” “above,” and “below” as used within the specification and the claims herein are terms of convenience that denote the spatial relationships of parts relative to each other rather than to any specific spatial or gravitational orientation. Thus, the terms are intended to encompass an assembly of component parts regardless of whether the assembly is oriented in the particular orientation shown in the drawings and described in the specification, upside down from that orientation, or any other rotational variation. 
     It will also be appreciated that the term “present invention” as used herein should not be construed to mean that only a single invention having a single essential element or group of elements is presented. Similarly, it will also be appreciated that the term “present invention” encompasses a number of separate innovations which can each be considered separate inventions. Although the present invention has thus been described in detail with regard to the preferred embodiments and drawings thereof, it should be apparent to those skilled in the art that various adaptations and modifications of the present invention may be accomplished without departing from the spirit and the scope of the invention. For example, a suspension could employ only a single PZT, and/or could employ mechanical coupling mechanisms other than the exemplary coupling mechanism shown in the drawings. Accordingly, it is to be understood that the detailed description and the accompanying drawings as set forth hereinabove are not intended to limit the breadth of the present invention, which should be inferred only from the following claims and their appropriately construed legal equivalents.