Abstract:
A dual stage actuated (DSA) suspension includes two PZT microactuators that are attached at their first ends to a non-gimbaled portion of the suspension such as the portion of the flexure that is rigidly attached to the load beam, and are attached at their second ends to the gimbaled portion of the suspension such as the gimbal tongue through flexible connectors that can be formed integrally with the suspension&#39;s flexure. The flexible connectors are flexible enough so as not to interfere with the suspension&#39;s gimballing action. The flexible connectors transmit force from the PZTs to the gimbal as the PZTs expand and contract in order to rotate the gimbal and thus effect fine movements of the head slider.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application No. 61/535,349 filed Nov. 30, 2011, which is hereby incorporation by reference as if set forth fully herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of dual stage actuator (DSA) type suspensions for disk drives including hard disk drives. More particularly, this invention relates to the field of a dual stage actuator suspension in which the microactuators are connected to the gimbaled region through flexible connectors. 
     2. Description of Related Art 
     Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known.  FIG. 1  is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit  100  includes a spinning magnetic disk  101  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 (not shown). Disk drive unit  100  further includes a disk drive suspension  105  to which a magnetic head slider (not shown) is mounted proximate a distal end of load beam  107 . The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end nearest to base plate  12  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. 
     Suspension  105  is coupled to an actuator arm  103 , which in turn is coupled to a voice coil motor  112  that moves the suspension  105  in an arc in order to position the head slider over the correct data track on data disk  101 . 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 voice coil motor  112  moves suspension  105 . 
     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 voice coil motor  112  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 and to keep it properly aligned over the desired data track on the spinning disk. The microactuator(s) provide much finer control and increased bandwidth of the servo control loop than does the voice coil motor alone, which only effects relatively coarse movements of the suspension and hence the magnetic head slider. Various locations have been proposed for the microactuator(s). The PZTs can be located within baseplate  105 , on the load beam  107 , or at or near the head gimbal assembly which is located at the distal end of load beam  107 . Mei FIGS. 1 and 10 show embodiments in which the microactuators extend from the mount plate, and in which the microactuators are mounted in the middle of the load beam, respectively. Patent publication no. US2001/0096438 by Takada et al. and US2009/0244786 by Hatch show DSA suspensions in which the microactuator are located on the gimbal. U.S. Pat. No. 6,760,196 to Niu et al. shows a collocated microactuator, i.e., a microactuator that lies directly underneath the head slider. U.S. Pat. No. 6,376,964 to Young at al. shows microactuators that bend from side to side and that extend from the distal end of the suspension to the gimbal to effect fine movements of the slider through a hinged linkage structure. 
       FIG. 2  is a top plan view of the prior art DSA suspension  105  of  FIG. 1 . Microactuators  14 , which are usually but not necessarily piezoelectric (PZT) devices, are mounted on microactuator mounting shelves  16  that are formed in mount plate  12 . Microactuators  14  span gap  18 . 
     DSA suspensions having the microactuators on the mount plate such as in  FIG. 2  generally have high stroke length per unit of input voltage. This will be referred to simply as having high stroke length for shorthand. Such suspensions, however, usually suffer from low servo bandwidth due to resonances in the part of the suspension that is distal to the PZTs. Slider based (collocated) DSA suspension designs variously have the disadvantages of: requiring additional piece parts; requiring complicated tracing routing, electrical connections, and slider bonding; having heavy slider/tongue assemblies which is undesirable because the extra mass can affect dynamic performance especially under shock conditions; and requiring one or more dedicated tongue features that are prone to manufacturing tolerance issues. Other gimbal-based designs require thin-film PZTs for high stroke lengths, and/or can be difficult to adjust for pitch and roll static attitude. 
     In the discussion which follows, the microactuator(s) will be referred to as two PZTs for shorthand, although it will be understood that the invention applies equally to suspensions having only a single microactuator and/or microactuator(s) that are not necessarily PZT devices. 
     SUMMARY OF THE INVENTION 
     The present invention is of a DSA suspension have one or more PZTs that extend from the load beam, or more generally from a non-gimbaled portion of the suspension, and more specifically from a non-gimbaled or rigid portion of the flexure, to a gimbaled part of the suspension such as the slider tongue. The PZTs are connected to the gimbaled portion through thin ribbons of stainless steel and/or other materials that act as flexible connectors to transmit tensile and compressive forces, and thereby transmit push/pull movement of the PZTs, to the gimbaled portion to which the head slider is attached, the connectors being flexible enough to allow the gimbal to pitch and roll relatively freely and thus not interfere with the normal gimbal action as the head slider pitches and rolls in response to surface irregularities in the surface of the data disk, which is necessary for proper gimbal and suspension operation. The invention provides a DSA suspension with good stroke length per unit of input voltage to the PZTs, high servo bandwidth, and good shock susceptibility. The PZTs can be relatively inexpensive single-layer bulk PZTs as compared to more costly PZT configurations such as thin-film or multilayer PZTs which are called for in some prior designs. 
     In one aspect therefore, the invention is of a dual stage actuator (DSA) type suspension for a disk drive, the suspension including a load beam and a flexure, the flexure having a rigid part that is secured to the load beam and a gimbaled part that is allowed to pitch and roll freely via gimballing action, a pair of linear actuators such as bulk piezoelectric (PZT) devices attached at one end thereof to the rigid part of the flexure or other rigid part of the load beam and being attached at opposite ends to the gimbaled part through ribbon-like flexible connectors. The flexible connectors can be ribbon-like pieces of stainless steel that are formed integral with the flexure, so as to be extensions that extend from the gimbaled portion to the PZTs. When one PZT contracts and the other expands, the PZT that contracts pulls on one flexible connector, while the PZT that expands pushes on the flexible connector. Those tensile and compressive forces, respectively, pull and push the slider tongue in push/pull fashion to cause the gimbal tongue and hence the slider which is mounted thereon to rotate, thus realizing the desired fine movements of the slider over the data disk. The flexible connectors are strong enough in compression so as to not significantly buckle, thus allowing the PZTs to push on the slider tongue through the flexible connectors. At the same time, the ribbon-like connectors are flexible enough so that they do not significantly interfere with the gimballing action, thus allowing the gimbal to pitch and roll freely per the usual gimballing action of a suspension, and allowing the slider tongue to rotate in response to the push/pull action that the flexible connectors exert on the slider tongue. 
     Additionally, the PZTs are mounted at a slight angle with respect to the central longitudinal axis of the suspension. The gimbal includes outer gimbal struts, and bridge struts extending from and connecting the outer gimbal struts to the flexible connectors. The bridge struts connect to the flexible connectors at a position that substantially eliminates transverse (side-to-side) force on the slider tongue and hence substantially eliminates linear transverse motion of the slider as the slider rotates. This greatly decreases fretting wear on the dimple, which is of concern because fretting of the dimple produces particle shed, which particles can contaminate the disk drive and can even cause catastrophic head crashes. 
     The invention presents several advantages over various prior art DSA suspensions. In comparison to gimbal mounted PZT designs, because the PZTs of the present invention are attached at one end to a rigid part of the suspension, the design allows for higher stroke length (movement of the slider per voltage of input applied to the PZTs). The present design can also accommodate longer PZTs, and hence greater stroke, than certain prior art designs. Additionally, the PZTs are located far away from the slider compared to certain gimbal-mounted prior art designs. This improves shock lift-off performance, i.e., the amount of shock as measured in g-forces that the suspension can sustain in operation before the head slider lifts off the disk platter or crashes into the disk platter. Additionally, because of their stroke efficiency, single layer bulk parts can be used in the design instead of multi-layer bulk PZTs or thin film PZTs which are more expensive. 
     Exemplary embodiments of the invention will be 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 an oblique view of a prior art hard disk drive assembly with a DSA suspension. 
         FIG. 2  is a top plan view of the prior art suspension  105  of  FIG. 1 . 
         FIG. 3  is an oblique, partially exploded view of a DSA suspension according to an illustrative embodiment of the invention. 
         FIG. 4  is a top plan view of the flexure  220  of the suspension of  FIG. 3 , viewed from what is sometimes referred to as the “gimbal top.” 
         FIG. 5  is a bottom plan view of the flexure  220  of the suspension of  FIG. 3 , viewed from what is sometimes referred to as the “gimbal bottom.” 
         FIG. 6  is a bottom plan view of the flexure of  FIG. 5  with the PZTs actuated in order to rotate the slider. 
         FIG. 7  is a close-up of the area around one of the flexible connectors  230  in  FIG. 5 . 
         FIG. 8  is a cross section view taken alone section line  8 - 8 ′ in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     For discussion purposes, the present disclosure will refer to the microactuator as being “PZTs,” although it will be understood that other types of microactuators could be used as well, and thus the invention is applicable to DSA suspensions using other types of micro actuators. 
       FIG. 3  is an oblique, partially exploded view of a DSA suspension according to an illustrative embodiment of the invention. Suspension  205  includes base plate  212 , load beam  207 , a flexure  220  welded or otherwise affixed to the load beam, and magnetic read/write head slider  240  affixed to the distal and gimbaled portion of flexure  220 . For purposes of the present discussion, load beam  207  and the portion of flexure  220  rigidly affixed to load beam  207  will be referred to as being rigid or non-gimbaled. 
       FIG. 4  is a top plan view of the flexure  220  of the suspension of  FIG. 3 , viewed from what is sometimes referred to as the “gimbal top,” and  FIG. 5  is a bottom plan view of the flexure  220  of the suspension of  FIG. 3 , viewed from what is sometimes referred to as the “gimbal bottom.” Flexure  220  typically includes rigid flexure base or non-gimbaled portion  250 , a gimbaled portion  260  including slider tongue  262  to which a magnetic read/write head slider  240  is attached, a flexible electrical circuit  238 , and a gimbal structure. The gimbal structure allows the gimbaled portion including slider tongue  262  to pitch and roll freely in response to surface irregularities in the data disk as the disk spins underneath slider  240 . Slider  240  is supported for rotational movement in 3 degrees (pitch, roll, and yaw) by a dimple in load beam  207 , at a location on load beam  207  that corresponds to dimple location  242  shown in  FIG. 5 . A number of various gimbal designs exist and are commercially used; in the illustrative embodiment shown, the gimbal takes the form of a ring gimbal including outer gimbal struts, or simply outer struts,  234 . Bridge struts  232  connect from outer gimbal struts  234  to flexible connectors  230 . 
     Flexible connectors  230  can be integrally formed with the rest of flexure  220 . Flexible connectors  230  take the form of ribbon-like sections of the same stainless steel or other material from which flexure  220  is formed. Electrical circuit  238  which is formed as part of flexure  220  on the stainless steel substrate layer includes layers of an insulating material such as polyimide, copper alloy signal conductors on top of the polyimide, and an insulating and protective covercoat such as another insulative layer of polyimide over the copper signal conductors. Flexure  220  can be formed using either a subtractive process or an additive process. In an additive process, the layers are built up sequentially over the stainless steel layer into the patterns desired. In a subtractive process, the manufacture begins with a composite laminate of stainless steel/polyimide/copper and the various layers are selectively masked and etched away to form the desired flexure  220 . Flexible connectors  230  may comprise only stainless steel over their whole lengths, or at least a majority of their lengths; they have no insulating material such as polyimide or copper for their entire lengths, or at least for a majority of their lengths. Alternatively, flexible connectors  230  may have insulating material such as polyimide on them so as to increase the stiffness of those connectors. The polyimide may be in controlled patterns on flexible connectors  230  so as to increase their stiffness to controlled extents at particular locations. 
     Flexible connectors  230  should be strong enough so that when pushed by a first PZT  214  in expansion, they do not buckle significantly. Rather, they transmit a compressive force to gimbaled portion  260 . Meanwhile, the second PZT  214  contracts, pulling on its respective flexible connector. The two PZTs therefore operate in push-pull fashion to rotate slider tongue  262 . At the same time, flexible connectors  230  should be sufficiently flexible so as to not interfere significantly with the gimballing action of the head slider  240 , and allow the non-gimbaled portion  260  to rotate freely when PZTs  214  are actuated. 
     PZTs  214  or possibly some other type of microactuator are attached at their proximal ends to non-gimbaled flexure base  250 , and at their distal ends are attached to flexible connectors  230  such as by either a solder or an epoxy, either non-conductive or conductive depending on whether electrical termination is to the stainless steel body of flexure  220  or to the flexible circuit  238 . 
     Bridge struts  232  connect from outer gimbal struts  234  to flexible connectors  230  at a location that is a distance F distal of dimple center point dimple location  242 . Distance F is preferably at least 0.05 mm, and preferably 0.05-0.25 mm. Other preferred dimensions are listed in provisional patent application No. 61/535,349 from which priority is claimed, and which is incorporated herein by reference. Additionally, PZTs  214  are mounted at a slight angle φ with respect to a central longitudinal axis  266  of the suspension, with the distal end of microactuators  214  being closer to central longitudinal axis  266  than the proximal ends of the microactuators. Preferably φ is at least 1 degree, and more preferably 2-12 degrees, and more preferably still about 2-4 degrees. The PZT line of action distance to dimple location can also influence both the stroke sensitivity and the dimple y-force. 
     The inventors discovered via analysis and extensive finite element analysis modeling that when the suspension is constructed according to the preferred dimensions, slider  240  experiences very little transverse (side-to-side) linear force and hence very little transverse movement when PZTs are actuated. Depending on the exact dimensions used for the flexure including the gimbal, the longitudinal distance F from the bridge strut connection point to the dimple location  242  can be adjusted to obtain negligible transverse linear force and movement of slider  240 . The inventors were able to achieve a transverse force of &lt;0.01% of the gram load of the suspension (i.e., &lt;0.0002 gram for gram load of 2.0 gmf), and a transverse force of &lt;0.01 gram per volt for each of the two microactuators. Since the design has low dimple y-force tendency, the contact friction force under the gram load (dimple contact force) is strong enough to hold the tongue and dimple together and act as a pivot (static friction condition, without sliding). Therefore, there is no significant transverse movement between dimple and tongue, and thus less fretting wear. By selecting the dimensions and angles properly, the designer can substantially eliminate transverse (side-to-side) force on the slider tongue and hence substantially eliminate linear transverse motion of the slider as the slider rotates. This greatly decreases fretting wear on the dimple. 
     Electrical connections from flexible circuit  238  to PZTs  214 , and grounding of the PZTs through either electrical circuit  238  and/or to the stainless steel body of flexure  220 , can be made by conventional methods that are well known, or by straightforward modifications to those methods. Examples of possible electrical connections are described in provisional patent application No. 61/535,349 from which priority is claimed, and which is incorporated herein by reference. Additional illustrative embodiments of the invention are also disclosed therein. 
       FIG. 6  is a bottom plan view of the flexure of  FIG. 5  with the PZTs actuated and the slider  240  rotated by the action of the PZTs. Flexible connectors  230  are slightly bent, thereby allowing for the rotation. Slider  240  is essentially rotated in place about the dimple point with only negligible side-to-side linear movement, and thus experiences almost or essentially pure rotation about the dimple. 
       FIG. 7  is a close-up of the area around one of the flexible connectors  230  in  FIG. 5 , and  FIG. 8  is a cross section view taken alone section line  8 - 8 ′ in  FIG. 7 , with slider  240  removed for clarity of illustration. Stainless steel flexible connector  230  has a dam  231  thereon. In the preferred embodiment, dam  231  is a dam of insulating material such as polyimide, defined by a raised mass of material. Polyimide dam  231  can be formed at the same time as the rest of the flexure is formed and does not require an additional manufacturing step. Raised dam  231  extends across the entire width, or substantially the entire width, of flexible connector  230 . Polyimide dam  231  controls or stops the flow of slider adhesive from the slider area during manufacturing. More specifically, dam  231  helps to prevent the adhesive that is used to bond slider  240  to slider tongue  262  from wicking past dam  231 , which could affect the mass, stiffness, and other characteristics of flexible connector  230  and/or bridge strut  232 , and hence adversely affect the performance of the suspension. 
     It will 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. 
     All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     It will 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, PZT microactuators have been proposed to be placed at locations on a suspension other than the gimbal region, and the invention should therefore not be considered to be limited to a DSA suspension having a co-located microactuator. 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.