Patent Publication Number: US-10789978-B2

Title: Disk drive suspension tri-stage actuator having pseudo feature integrally constructed on trace gimbal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/668,594 filed on Aug. 3, 2017, which claims priority from U.S. Provisional Patent Application No. 62/371,690 filed on Aug. 5, 2016, each of which is hereby incorporated by reference in their entirety. 
    
    
     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 disk drive suspension having tri-stage actuation, and having pseudo-symmetry features integrally constructed on the trace gimbal. 
     2. Description of Related Art 
     Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known. A typical hard disk drive includes a spinning magnetic disk containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor. The disk drive further includes a disk drive suspension to which a magnetic head slider is mounted proximate a distal end of a load beam. The head slider contains magnetic read transducers and magnetic write transducers to respectively read data from, and write data to, the magnetic disk. The “proximal” end of a suspension or a load beam is the end that is supported, i.e., the end nearest to an actuator arm to which the suspension is attached. 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. 
     The suspension is typically coupled to an actuator arm, which in turn is coupled to a voice coil motor that moves the suspension arcuately in order to position the head slider over the correct data track on the spinning data disk. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk&#39;s surface. 
     Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspension are known. In a single stage actuated suspension, only the voice coil motor moves the suspension. 
     In a DSA suspension, as for example in U.S. Pat. No. 7,459,835 issued to Mei et al. as well as many others, in addition to the voice coil motor which moves the entire suspension, at least one microactuator is located on the suspension in order to effect fine movements of the magnetic head slider to keep it properly aligned over the data track on the spinning disk. The microactuator(s) provide much finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider. 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 the discussion that follows, for simplicity the microactuator will be referred to simply as a “PZT,” although it will be understood that the microactuator need not be of the PZT type. 
     DSA designs in which the PZT microactuators are located on or at the gimbal have also been proposed. Such designs are generally referred to as “GDA” designs. U.S. Pat. No. 8,879,210 to Hahn et al. and owned by the assignee of the present application shows such a GDA suspension. DSA suspensions having a single microactuator on one lateral side of a suspension and a pseudo feature on the other lateral side in order to counterbalance the single microactuator have also been proposed, such as in U.S. Pat. No. 8,559,138 to Hahn et al. and owned by the assignee of the present application. 
     Suspensions having tri-stage actuation have also been proposed. U.S. Pat. No. 8,810,971 to Vitikkate et al. purports to disclose a third-stage actuator in a hard disk drive, with the third actuator stage being a co-located and differently-poled PZT device which bends in rotation in response to an actuation voltage being applied to the device. 
     GDA designs such as the ones shown in U.S. Pat. No. 8,879,210 have been shown to exhibit a servo bandwidth of approximately 4-5 kHz. The continuing trend of increased area data density and tracks per inch (TPI) will continue to require higher servo bandwidths. 
     SUMMARY OF THE INVENTION 
     The present invention is of a disk drive suspension having dual-stage or tri-stage actuation, and having a pseudo feature integrally formed on the trace gimbal assembly (TGA) to provide mass and inertial balance to balance out a single microactuator mounted off-center on the TGA. 
     In one aspect, the invention is of GDA suspension having a single PZT device or simply “PZT” for shorthand used as a microactuator on a first lateral side of the TGA, and a pseudo feature opposite the PZT in generally mirror relation thereto in order to balance out the PZT in mass and stiffness, with the pseudo feature being integrally formed with the TGA as part of the TGA. The pseudo feature is therefore formed of the same layers and materials as is the TGA, which typically includes a metal base layer such as stainless steel, an insulating layer such as polyimide, and a conductive trace layer such as copper or copper alloy, with optionally a coverlayer on top. The pseudo feature will sometimes be referred to herein as a counterbalance, keeping in mind that the counterbalance preferably balances out not only the mass and mass distribution of the PZT but also the stiffness of the PZT. The counterbalance thus preferably balances out both static and dynamic properties of the PZT. Because the counterbalance according to the present invention is integrally formed with the TGA, it is not necessary to separately manufacture such a counterbalance and then affix it to the TGA. This simplifies the manufacturing process. 
     A first PZT and a corresponding pseudo feature as disclosed herein mounted at or near the gimbal, may be combined with a second PZT actuator located proximal of the first PZT such as on the baseplate, making for a tri-stage actuated (TSA) design in which the second PZT provides finer movement of the head slider than does the voice coil motor, and the first PZT provides even finer movement still. The second PZT at the baseplate may be combined with either a third PZT opposite the second PZT with the second and third PZTs moving the load beam in push-pull fashion, or a second pseudo feature may be provided on the baseplate generally opposite the second PZT in order to balance out that PZT. A suspension may thus be a TSA suspension having two PZTs located at different longitudinal locations on the load beam, such as one PZT at the baseplate and one PZT on the TGA, with each PZT being balanced out by a respective pseudo feature laterally opposite to its associated PZT. 
     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 tri-stage actuated suspension having a single PZT at the baseplate and a pseudo feature associated therewith, according to a first illustrative embodiment of the invention. 
         FIG. 2  is bottom oblique view of the suspension of  FIG. 1 . 
         FIG. 3  a top plan view of the suspension of  FIG. 1 . 
         FIG. 4  is a bottom plan view of the suspension of  FIG. 1 . 
         FIG. 5  is a bottom oblique view of a GDA suspension having a single PZT on the TGA and a pseudo feature associated therewith, according to a second illustrative embodiment of the invention. 
         FIG. 6  is a closeup view of the TGA of the suspension of  FIG. 5 . 
         FIG. 7  is a bottom plan view of the TGA of  FIG. 6 . 
         FIG. 8  is an exploded bottom view of the suspension of  FIG. 5 . 
         FIG. 9  is a closeup of the suspension of  FIG. 5  presented in color for clarity of illustration of the constituent components and layers. 
         FIG. 10  is an oblique view of a metal base layer having an integrally formed spring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a top oblique view of tri-stage actuated suspension  10  having a single PZT  14  at the baseplate  12  and a pseudo feature  16  associated therewith, according to a first illustrative embodiment of the invention. Expansion and contraction of the PZT  14  moves load beam or beam  20  of suspension  10 , and more specifically, rotates the entire load beam  20 . Ideally, pseudo feature  16  balances out the mass, mass distribution, and stiffness of PZT  14 . Pseudo feature  16  could be manufactured separately and then affixed to baseplate  12  such as by laser welding or by adhesive. Pseudo feature  16  could also be partly or wholly manufactured integrally with baseplate  12 . Because baseplate  12  is typically made from stainless steel (SST), pseudo feature could be unitarily formed with baseplate  12  from a single piece of stainless steel. Etching or laser ablation could create areas of greater and lesser thickness and width within pseudo-structure  16 . Furthermore, laser treatment could locally alter the mechanical properties of the stainless steel within pseudo feature  16 , such as creating locally softer areas, to help fine tune the properties of pseudo feature  16 . 
       FIG. 2  is bottom oblique view of the suspension  10  of  FIG. 1 . Two PZTs  80 / 82  on opposite lateral sides of the suspension act in push-pull fashion on the gimbal to rotate head slider  90 . Head slider  90  contains a magnetic read transducer and a magnetic write transducer in order to respectively read data from, and write data to, the disk drive platter (not shown). Only part of the electrical circuit traces are shown; in reality, the electrical circuit traces would normally extend from head slider  90  to beyond baseplate  12 , i.e., to the upper left of baseplate  12  in the figure, defining a tail region of the circuit. 
       FIG. 3  a top plan view of the suspension  10  of  FIG. 1 . 
       FIG. 4  is a bottom plan view of the suspension  10  of  FIG. 1 . 
       FIG. 5  is a bottom oblique view of a GDA suspension  110  having a single PZT  80  on the TGA  195  and a pseudo feature  70  associated with PZT  80 , according to a second illustrative embodiment of the invention.  FIG. 9  is a closeup of the suspension of  FIG. 5  presented in color for clarity of illustration of the constituent components and layers. 
       FIG. 6  is a closeup view of the TGA  195  of the suspension  110  of  FIG. 5 . TGA  195  includes flexure gimbal made from the stainless steel (SST) layer  30 , polyimide layer  50 , and electrical circuit traces  62  which carry information including data to and from head slider  90 . Copper contact pad  64  carries the driving or activation voltage for PZT  80  which causes PZT  80  to expand or contract lengthwise, thus finely positioning head slider  90 . A conductive bridge  86  typically comprising conductive epoxy carries the PZT driving voltage from copper pad  64  to the top electrode of PZT  80 . An unused copper pad  66  laterally opposite copper pad  64  provides symmetry to copper pad  64 . A pseudo feature  70  acts as a counterbalance to PZT  80 , ideally balancing out the mass, mass distribution, and stiffness of PZT  80 . Pseudo feature  70  can include a copper portion  68  made from the conductive layer, and a polyimide portion  58  made from insulative layer  50 . Pseudo feature  70  could also include a portion made from stainless steel base layer  30  as shown in  FIG. 10 . Pseudo feature  70  could also include coverlayer coating (not shown) of the type normally used for insulation and corrosion protection for the otherwise exposed copper layer of a suspension. In generally, therefore, pseudo feature  70  is integrally formed with trace gimbal assembly  195 , and comprises portions(s) of one or more of base metal layer  30 , insulating layer  50 , conductive layer  60 , and coverlayer. 
       FIG. 7  is a bottom plan view of the TGA  195  of  FIG. 6 , explicitly showing PZT  80  on a first lateral side  111  of TGA  195  and hence of suspension  110 , and the pseudo feature  70  on the second and opposite lateral side  113  of TGA  195  and hence of suspension  110 . Central longitudinal axis L-L divides TGA  195  into first lateral side  111  and second lateral side  113 . Pseudo feature  70  can include a metal part, made from either the stainless steel layer or the copper layer  60 , that has selectively wider and narrower portions as desired in order to “dial in” the correct mass, mass distribution, and stiffness. In the embodiment shown, copper portion  68  is positioned directly opposite PZT  80  and has two narrower sections having width W 1  on either side of a wider section having width W 2 . The wider section provides mass, and the narrower sections reduce the overall stiffness of the structure. For example, the widest portion(s) can have a width W 2  that is at least three times the width W 1  of the narrower portion(s). If the copper layer is used to contribute in significant part to the mass of the pseudo feature  70 , then typically the widest part(s) of copper portion  68  would be at least three times the average width of the copper signal traces  62  that carry data to and from head slider  90 , and would have a mass that is at least 10% of the mass of PZT  80 . Copper portion  68  is preferably electrically isolated from any circuit traces carrying electrical signals in order to avoid degrading the dynamic performance of those circuit traces. 
       FIG. 8  is an exploded bottom view of the suspension of  FIG. 5  including TGA  195 . TGA  195  includes base metal layer  30  which is typically stainless steel, and which defines the flexure gimbal. Stainless steel layer  30  includes both first pad  34  to which PZT  80  is affixed and through which PZT  80  acts to move head slider  90 , and also includes a second pad  36  that generally mirrors first pad  34  for the purpose of providing symmetry thereto and therefore has no PZT attached directly to it. 
     Insulative layer  50  is typically polyimide. Polyimide layer  50  includes a portion  58  that defines part of pseudo feature  70 . Polyimide portion  58  supports copper portion  68 . In the embodiment as illustrated, pseudo feature  70  is mostly defined by insulative layer portion  58  and conductive layer portion  68 . If an additive manufacturing process is used to make TGA  195 , then polyimide portion  58  is laid down at the same time as the rest of polyimide layer  58 . If a subtractive manufacturing process is used, then polyimide portion  58  starts off as unitary with the rest of polyimide layer  50 , with a removal process such as etching removing the unwanted portions of that layer. 
     Conductive layer  60  is typically copper or copper alloy (hereafter, generally “copper”). Conductive layer  60  includes copper electrical circuit traces  62 , copper pads  64  and  66 , and copper portion  68  of pseudo feature  70 . If an additive manufacturing process is used to make TGA  195 , then copper portion  68  is laid down at the same time as the rest of copper layer  60 . If a subtractive manufacturing process is used, then copper portion  68  starts off as unitary with the rest of copper layer  60 , with a removal process such as etching removing the unwanted portions of that layer. Theoretically the copper portion  68  could be made to be thicker or thinner than other portions of copper layer  60  such as the circuit traces  62 ; in practice due to manufacturing consideration, however, it is expected that copper portion  68  would have nominally the same thickness as the rest of copper layer  60  including circuit traces  62 . 
     Typically, a cover layer or coverlay (not shown) is deposited over at least the exposed copper portions of TGA  195  in order to electrically insulate the electrical circuit traces and pads, and to prevent corrosion of the copper. Portions of the cover layer could form part of the pseudo feature. In general, therefore, the counterbalance  70  includes one or more of stainless steel layer  30 , polyimide layer  50 , copper layer  60 , and coverlayer. For purposes of this specification and the appended claims, any coverlayer that is part of the pseudo feature  70  and which is laid down at the same time as the standard coverlayer over electrical traces  62 , is considered to be integrally formed with the TGA. 
     Areas  88  and  89  of adhesive such as epoxy affix PZT  80  to the suspension, and conductive adhesive  86  electrically bridges from copper pad  64  to the top surface of PZT  80  which defines the driving voltage electrode of that PZT. 
     Suspension  110  thus has a piezoelectric device  80  on a first lateral side of the suspension and more specifically one on a first lateral side of the TGA  195 , and a pseudo feature or counterbalance  70  on a second and opposite lateral side of the TGA opposite the piezoelectric device, the counterbalance  70  counterbalancing to the extent practical the mass and stiffness of piezoelectric device  80 . Counterbalance  70  is integrally formed with TGA  195 ; the counterbalance is not separately formed and then later affixed to the suspension such as using adhesive. Adhesives create potential contamination issues within the disk drive suspension clean room assembly environment, so minimizing the use of adhesives helps to decrease manufacturing complexity and cost, and to increase the reliability of the disk drive assembly. 
     For purposes of this specification and the appended claims, unless the context otherwise makes clear, when it is stated that the counterbalance  70  partially or completely counterbalances the mass, mass distribution, and/or stiffness of PZT  80 , the weight and characteristics of the adhesives  86 ,  88 , and  89  are considered as being part of PZT  80 , such that the counterbalancing accounts for not only PZT  80  by itself but also the adhesives and any other components of features associated with the PZT  80 . 
     In a preferred embodiment the PZT  80  has no separately formed counterbalance at all, with all of the counterbalance to PZT  80  being provided by the integrally formed pseudo-symmetry feature  70 . Of course, it is not practical or not possible to counterbalance PZT  80  with complete and total precision. Thus, the integrally formed pseudo feature or counterbalance  70  preferably has a mass of at least 50% of the mass of PZT  80 . Additionally, counterbalance  70  preferably has a stiffness that is within at least 50% of the stiffness of PZT  80 . More preferably, counterbalance  70  is positioned in generally mirror relation to PZT  80  and has a mass that is within 30% of PZT  80 , and more preferably within 10% of PZT  80 . 
     There will always be at least some small amount of variability from one suspension to the next in the mass and position of PZT  80  and its associated adhesives. Accordingly, it would be desirable to be able to finely control the mass and mass distribution of pseudo-structure  70 . The mass and mass distribution of pseudo feature  70  can be precisely trimmed user laser ablation, such as by micromachining using a femtosecond laser. Using femtosecond lasers for micromachining is discussed for example in Liqiu Men et al., “Femtosecond Laser Trimmed Fiber Taper for Simultaneous Measurement of Axial Strain and Temperature,” IEEE P HOTONICS  T ECHNOLOGY  L ETTERS , Vol. 23, No. 5 (Mar. 1, 2011), which is hereby incorporated by reference for its teachings of micromachining using lasers. Additionally, lasers such as femtosecond lasers could be used to locally alter characteristics of the material such as making it softer and less stiff. 
     It is possible that some other device such as a temperature sensor, strain gauge, resistive heater, or other sensor or device is separately formed and then adhered to the suspension, with that other device providing at least some of the counterbalance to PZT  80 . Thus, in another preferred embodiment, the suspension has no separately formed and later affixed counterbalance to PZT  80  that has a mass that is one quarter or more of the mass of PZT  80 . 
       FIG. 10  is an oblique view of a stainless steel layer or flexure gimbal  30  according to a variant in which the pseudo feature  70  includes a spring  138  integrally formed of the stainless steel layer. In the embodiment shown spring  138  takes the form of a serpentine section of stainless steel. More generally, the pseudo feature could include a spring integrally formed of the stainless steel layer of the flexure such as spring  138  shown, and/or a spring integrally formed of the metal conductive layer. Such a spring could provide a wide stiffness range, so that the stiffness of the pseudo feature could be dialed in to closely match the stiffness of PZT  80 . Such a spring  138  could be incorporated into the stainless steel layer  30  shown in  FIG. 8 . 
     In another embodiment (not shown) the suspension includes both a first piezoelectric device and an associated pseudo feature such as PZT  80  and associated pseudo feature  70  located on the TGA as shown in  FIGS. 5-8 , and a second piezoelectric device and associated pseudo-symmetry such as PZT  14  and associated pseudo feature  16  mounted proximal of first PZT  80  such as on baseplate  12  as shown in  FIGS. 1-4 . Such a suspension would define a tri-stage actuated suspension, with the standard voice coil motor providing coarse position adjustments, second PZT  14  mounted on the baseplate providing medium position adjustments, and first PZT  80  mounted on or at the gimbal providing fine position adjustments. Alternatively, the suspension could have two baseplate-mounted PZTs and no baseplate-mounted pseudo-structure, and one gimbal-based PZT  80  and a corresponding pseudo-structure  70 , optionally including integrally formed spring  138 . 
     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 be appreciated that the term “invention” or “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. The pseudo feature integrally formed on the trace gimbal as disclosed herein could be used in a suspension regardless of whether the suspension is dual stage actuated or tri-stage actuated. Similarly, tri-stage actuation as disclosed herein does not require the use of one or more pseudo features. 
     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. 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.