Abstract:
A head gimbal assembly (HGA) allows gimbaling along pitch and roll axes, and utilizes an inexpensive spherical gimbal ball pressed into an etched hole in the load beam to provide a highly accurate and measurable pivot location of a slider. The head gimbal assembly includes a suspension of the type supporting a slider, and comprising the suspension. A gimbal opening is formed in the load beam, and extends therethrough so that it receives the spherical gimbal ball for attachment to the load beam. A resilient flexure is secured to the load beam and supports the slider. The backside of the gimbal ball remains visible for the option of optical bonding of the slider to the suspension and for measurement of the slider position relative to the gimbal ball subsequent to the assembly of the HGA. The backside of the gimbal ball can optionally be used as the mechanical datum to accurately bond the suspension to the slider.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to data storage devices such as disk drives. The invention particularly relates to a load beam that allows gimbaling along pitch and roll axes, and that utilizes an inexpensive spherical gimbal ball pressed into an etched hole in the load beam to provide a highly accurate and measurable pivot location of a slider. 
     2. Description of Related Art 
     In a conventional disk drive, a read/write head is secured to a rotary actuator magnet and a voice coil assembly by means of a suspension and an actuator arm, and is positioned over a surface of a data storage disk. In operation, a lift force is generated by the aerodynamic interaction between the head and the disk. The lift force is opposed by a counteracting spring force applied by the suspension, such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the disk. 
     The suspension includes a load beam and a flexure secured to a cantilevered end of the load beam. A slider is mounted to the flexure. The flexure provides a proper pivotal connection for the slider so that during operation, the slider can compensate for irregularities in the disk drive manufacture and operation, by pitching and/or rolling slightly in order to maintain the air bearing, while maintaining appropriate stiffness against yaw movement. Roll is defined as the rotation about an axis extending directly out from the actuator arm through the pivot contact point and parallel to the X-Y plane of the disk. Pitch is defined as rotation about an axis perpendicular to the roll axis through the pivot contact point and parallel to the X-Y plane of the disk. Yaw is gyration around an axis perpendicular to the air-bearing surface. The flexure has to achieve low enough pitch and roll stiffness for the air bearing flying height tolerances while at the same time achieving high enough yaw stiffness for track seeking. 
     Exemplary suspension designs are illustrated by the following references: 
     U.S. Pat. No. 5,786,961 to Goss; 
     U.S. Pat. No. 5,675,454 to Hatanai et al.; 
     U.S. Pat. No. 5,572,385 to Kuwamoto; 
     U.S. Pat. No. 5,504,640 to Hagen; 
     U.S. Pat. No. 5,381,288 to Karam, II; 
     U.S. Pat. No. 4,811,143 to Ohashi et al.; 
     U.S. Pat. No. 4,017,898 to Toombs et al.; 
     U.S. Pat. No. 3,422,412 to Linsley; 
     U.S. Pat. No. 3,403,388 to Linsley; 
     U.S. Pat. No. 3,202,772 to Thomas, Jr.; 
     U.S. Pat. No. 3,183,810 to Sampson; and 
     U.S. Pat. No. 3,158,847 to Pulkrabek. 
     In some conventional suspensions, the flexure includes a dimple that abuts against the load beam. In other suspensions, the dimple is formed in the load beam and pushes against the flexure. In these conventional suspensions, the dimple can be formed by stamping either the flexure or the load beam. 
     A stamped dimple presents several shortcomings, a few of which are mentioned herein. The dimple stamping process is necessarily separate from the process of etching the reference datum holes in the load beam or flexure. Stamping tooling accuracy causes variation between the datum holes and the stamped dimple. Additional variation is added in the case of flexures with stamped dimples when aligning/welding the flexure to the load beam. Further variance occurs when locating/aligning the mount plate to the load beam. Print tolerance shows a boss outer diameter to the load beam hole to be approximately in the range of ±0.0015 inch. Yet more variations exist between the concave side of the dimple that can be seen after assembly, and the actual contact point on the convex side that cannot be seen or measured after assembly. This latter variation can be approximately 0.0005 inch. In addition, measurement repeatability of stamped dimples is poor. 
     Another method of forming the dimple is to etch the load beam. While the dimple location is accurate relative to the datum holes in the load beam, the etched dimple approach presents several drawbacks, some of which are listed herein. The dimple formed by partially etching the load beam does not form a dome. Rather, its top surface is generally flat and circular. The contact point of the dimple and the flexure cannot be very accurately located, as it can be positioned along the circular top portion of the dimple. Once the suspension is assembled, the dimple location will no longer be measurable since the gimbal will no longer be visible for inspection. Forming of a partial etch area is still required to get the dimple to protrude forward in order to get the separation between the flexure/slider and the load beam, in order to achieve gimbaling. 
     In another design proposed in U.S. Pat. No. 5,786,961, supra, the suspension includes a load beam having proximal and distal ends and a bearing cover portion. A gimbal on the distal end of the load beam has a flexure pad with a slider-engaging first surface and a second surface opposite the first surface. A ball-receiving hole extends through the flexure pad, and a ball is mounted in the ball-receiving hole. The ball has a load point portion that extends from the second surface of the flexure pad and that engages the bearing cover portion of the load beam. The ball is obscured at assembly, which prevents direct location measurement after assembly, and also prevents viewing from the backside to aid in the assembly. 
     In yet another design proposed in U.S. Pat. No. 5,381,288, supra, the suspension includes a load beam and a spring assembly that are integrally formed. The spring assembly has a bonding tab suspended within the plane of the load beam by two flexible longitudinal arms connected to two flexible transverse arms. The flexible arms permit the bonding tab to roll about the longitudinal axis and pitch about the transverse axis, while preventing the bonding tab from sticking in an off-axis position. The bonding tab defines an aperture that receives a protuberance of the magnetic head to precisely index the magnetic head with the bonding tab, and thus center the magnetic head about a load support point. This design requires a V-shaped cross-slot to be machined in the slider into which the ball nests for registration. 
     The foregoing two proposed designs add cost, complexity to the design and assembly of the suspension, and lack optical measurement accessibility after assembly. Therefore, these designs do not appear to be suitable for next generation disk drives where simplicity and low cost will likely become primary considerations for successful head designs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a head gimbal assembly (HGA) that allows gimbaling along pitch and roll axes, and that utilizes an inexpensive spherical gimbal ball pressed into an etched hole in the load beam to provide a highly accurate, accessible and measurable pivot location of a slider. 
     The foregoing and other features and advantages of the present invention can be achieved by a new head gimbal assembly design. The head gimbal assembly includes a suspension of the type supporting a slider, and comprising the suspension. A gimbal opening is formed in the load beam, and extends therethrough so that it receives the spherical gimbal ball for attachment to the load beam. A resilient flexure is secured to the load beam and supports the slider. The backside of the gimbal ball remains visible for the option of optical bonding of the slider to the suspension and for measurement of the slider position relative to the gimbal ball subsequent to the assembly of the HGA. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein: 
     FIG. 1 is a fragmentary isometric view of a data storage system that uses a load beam design incorporating a gimbal ball according to the invention; 
     FIG. 2 is a top plan view of an assembled head gimbal assembly comprised of the load beam, a flexure, and a slider, and forming part of the data storage system of FIG. 1, for use in a head stack assembly; 
     FIG. 3 is an enlarged isometric view of the HGA of FIG. 2, illustrating the disposition of gimbal ball relative to the load beam; 
     FIG. 4 is a top plan view of the load beam of FIGS. 2 and 3; 
     FIG. 5 is an enlarged, isometric view of the flexure of FIG. 2; 
     FIG. 6 is a front elevational view of the HGA of FIG. 2; 
     FIG. 7 is a fragmentary, enlarged side elevational view of the HGA of FIGS. 2 and 6, further illustrating the position of the gimbal ball; and 
     FIGS. 8,  9 ,  10 , and  11  are enlarged, fragmentary, partly sectional, side elevational views of a trailing section of other suspension embodiments, illustrating an opening formed through the load beam to receive the gimbal ball; 
     FIG. 12 is a schematic, side, cross-sectional view of an assembly or test fixture of the present invention for assembling and testing the HGA of FIG. 2; and 
     FIG. 13 is an enlarged, partial, cross-sectional view of the head gimbal assembly and fixture of FIG. 12, illustrating the positioning and self-centering of the gimbal ball relative to the slider. 
    
    
     Similar numerals in the drawings refer to similar or identical elements. It should be understood that the sizes of the different components in the figures might not be in exact proportion, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a disk drive  10  comprised of a head stack assembly  12  and a stack of spaced apart magnetic data storage disks or media  14  that are rotatable about a common shaft  15 . The head stack assembly  12  is rotatable about an actuator axis  16  in the direction of the arrow C. The head stack assembly  12  includes a number of actuator arms, only three of which  18 A,  18 B,  18 C are illustrated, which extend into spacings above and below the disks  14 . 
     The head stack assembly  12  further includes an E-shaped block  19  and a magnetic voice coil (or rotor)  20  attached to the block  19  in a position diametrically opposite to the actuator arms  18 A,  18 B,  18 C. A voice coil  20  cooperates with a stator (not shown) for rotating in an arc about the actuator axis  16 . Energizing the voice coil  20  with a direct current in one polarity or the reverse polarity causes the head stack assembly  12 , including the actuator arms  18 A,  18 B,  18 C, to rotate about the actuator axis  16 , in a direction substantially radial to the disks  14 . 
     A head gimbal assembly (HGA)  28  is secured to each of the outer actuator arms, for instance  18 A and  18 C. A pair of HGA&#39;s  28  is secured to each inner actuator arm, for instance  18 B. With further reference to FIGS. 2 and 3, the HGA  28  is comprised of a suspension (or suspension assembly)  33  and a read/write head  35 . The suspension  33  includes a load beam  36 , a flexure  40  to which the head  35  is secured, and a gimbal mechanism or ball  44  as it will be described later in greater detail. The head  35  includes a slider  60  and a read/write element  61  secured to a trailing edge  55  of the slider  60 . 
     With reference to FIGS. 3 and 5, the flexure  40  includes a tongue  56  that extends inwardly, within a clearance  58 . The clearance  58  is contoured by a flexure body  80 , and two oppositely disposed peripheral ribs or outriggers  54 . The outriggers  54  provide the slider  60  with sufficient flexibility in the pitch rotation (illustrated by the arrow  51 ) about the X-axis  51 , and roll rotation (illustrated by the arrow  53 ) about the Y-axis  53 A, for accurate load distribution from the ball  44  pivot point  100  (FIG. 6) to the slider  60  air bearing surface  62 , in order to accommodate the uneven topology of the disk surface and other components and drive assembly tolerances, while the slider  60  is flying over the disk  14 . The flexure  40  is sufficiently stiff in a yaw direction (illustrated by the arrow  57 ) to resist deflection parallel to the plane of the disk  14 , caused by the rapid movement of the actuator arms  18 A,  18 B,  18 C. The slider  60  is secured to the tongue  56  by means of available techniques, for example UV curable epoxy. 
     FIG. 4 illustrates an exemplary load beam  36 . It should be clear that other load beam designs, such as the embodiment illustrated in FIGS. 8,  9 ,  10 , and  11  can alternatively be used. The exemplary load beam  36  includes a main body  64  that extends integrally into a tip  65 . The main body  64  includes two peripheral stiffening rails  67 . 
     The tip  65  is generally flat, and includes a gimbal opening  77  through which the spherical gimbal ball  44  is urged, for frictional attachment to the load beam  36 , as illustrated in FIGS. 2,  3 ,  6 , and  7 . The inner diameter of the gimbal opening  77  is slightly larger than the outer diameter of the gimbal ball  44 . The gimbal opening  77  is preferably formed along a central axis of the load beam  36 . The gimbal ball  44  has an outer diameter that preferably ranges between approximately 1 mil and 20 mils; however, other values can be selected. 
     When the gimbal ball  44  is pressed in position through the opening  77 , its backside  44 B protrudes, at least in part, above the tip (or trailing section)  65 , and provides a clear visual indication of the ball  44 , for referencing, measurement, and alignment purpose. Such visual accessibility to the gimbal ball  44  represents one of the important aspects of the present invention, in that such feature allows accurate measurement of the ball  44  location, and thus the pivot point  100  location with respect to the slider  60  after assembly. The pivot point  100  location is a critical factor in flying height control of the slider  60 . 
     For mechanical locating, the edges such as the edges  55  and  63  of the slider  60  are positioned mechanically relative to the load beam datum holes  92  and  95 , for taking advantage of the improved position of the pivot point  100  relative to the datum holes in the load beam  36 , over conventional stamped pivots or dimples. When the head gimbal assembly  28  is assembled, the gimbal ball  44  is urged against the tongue  56  at the contact point  100  (FIG.  6 ). 
     The present invention provides several advantages, some of which are mentioned herein. The gimbal mechanism or ball  44  remains accessible, and permits a highly accurate and measurable pivot location in that the backside  44 B of the gimbal ball  44  is visible for inspection measurement after assembly of the flexure  40  to the load beam  36  and assembly of the slider  60  to the flexure  40 . This represents a significant improvement of prior gimbal assemblies that become inaccessible and hidden from view after assembly. The visibility of the present gimbal ball  44  after assembly is important in that it allows the use of optical and mechanical equipment to accurately measure the ball  44 , hence the pivot point  100  with respect to the slider  60  edges  55 ,  63  from the backside  88  of the load beam  36  (FIGS. 6,  7 ). 
     Etching the gimbal ball opening  77  in the load beam  36  at the same time as datum holes  92 ,  94 ,  95  (FIGS. 2,  3 ,  4 ) yields outstandingly accurate location of the gimbal ball opening  77  relative to the datum holes  92 ,  94 ,  95 , compared to a stamped dimple, virtually eliminating approximately 0.0007 inch (0.7 mil) etch process to stamping process alignment variation. Furthermore, the gimbal ball  44  self centers when pressed in the opening  77 , giving vastly improved control of a pivot point  100  (FIGS. 6,  7 ) of the gimbal ball  44  relative to the datum holes  92 ,  94 ,  95 . 
     The accurate self-centering of the gimbal ball  44  within the hole  77 , within a tolerance of, for example, a few microinches, eliminates approximately 0.0005 inch (0.5 mil) variation between the concave side (visible for measurement) and the convex side (actual contact) of a stamped dimple. Additionally, non-spherical shape errors in stamping from wear or foreign material is eliminated. 
     For optical bonding, the options of viewing the backside  44 B of the gimbal ball  44  opposite the slider air bearing surface (ABS) directly, or viewing the datum holes  92 ,  94 ,  95  on the same side as the ABS are excellent choices. 
     Mechanical bonding is enhanced, as well, as a result of the close tolerances between datum holes  92 ,  94 ,  95  to the gimbal ball opening  44 B, ball sphericity accuracy, and self-centering capability of the gimbal ball  44  in the gimbal ball opening  44 B. 
     FIGS. 8 and 9 illustrate a tip or trailing section  120  of other suspension  133 A,  133 B, respectively. The gimbal openings  77 A (FIG. 8) and  77 B (FIG. 9) are formed through the load beam  36  to receive the gimbal ball  44 . The difference between the suspension  33  of FIG.  4  and the suspensions  133 A,  133 B of FIGS. 8 and 9, is that in suspensions  133 A,  133 B the rails  167  extend along substantially the entire length of the trailing section  120 . It should be clear that in another embodiment the rails  167  extend partially along the length of the trailing section  120 . 
     The suspensions  133 A and  133 B differ from each other in that the walls  177 A, and  177 B of the gimbal openings  77 A and  77 B, respectively, are different. In FIG. 8, the walls  177 A taper from both sides as produced from a doubled sided etch process for example. In FIG. 9, the walls  177 B taper in one direction to enhance ball retention. 
     FIG. 10 shows the ball  44  secured in place within the suspension  133 B, and illustrates the option of applying adhesive  45  at an inner location, and/or adhesive  46  at an outer location, for added retention of the ball  44  in the load beam  36 . 
     FIG. 11 illustrates the option of securing the ball  44  to the load beam  36 , such that the ball  44  does not protrude beyond an upper surface  190  of the load beam  36 . 
     FIGS. 12 and 13 illustrate a unique method for bonding the suspension assembly  33  to the slider  60 , using mechanical locating means, referencing directly on the ball  44 . An assembly fixture  200  includes a top plate  204  for holding the suspension assembly  33  and a bottom plate  208  for holding the slider  60 . The top plate  204  includes a vacuum port  206  that terminates in a chamfered side  210  which mates with the outer contour of the gimbal ball  44 . The suspension assembly  33  is placed in the assembly fixture  200  such that vacuum in the vacuum chamber  206  holds the ball  44  seated and self-centered against the chamfered side  210 . While placing the suspension assembly  33  in the assembly fixture  200  the load beam datum hole  95  (refer also to FIG. 2) is placed over the locating pin  212 . A second vacuum port  214  assists in holding the suspension assembly  33  to the top plate  204 . 
     The slider  60  is placed in a nest  216 , which is attached to the bottom plate  208  of the assembly fixture  200 . It is located against a Y wall  218  and X wall  220  and held by vacuum in a vacuum port  222  or mechanical clamp (not shown). 
     After adhesive  230  is applied to the slider  60  or to the tongue  56 , the tongue  56  and slider  60  are bonded. FIG. 12 shows the fixture  200  open while FIG. 13 shows a partial view of the fixture  200  closed with the tongue  56  mated and bonded to the slider  60 . This mating takes place by lowering the top plate  204  towards the bottom plate  208  until the tongue  56  rests on the slider  60 . The top plate  204  contains ball bushings  224  for example, which slide on shafts  226 . Shafts  226  are pressed in the bottom plate  208  to ensure repeatable attainment of the Y dim  228  (FIG. 13) and X dim (not shown), and also to ensure that the slider nest  216  is accurately located with respect to the chamfered side  210  of the vacuum port  206  which holds the ball  44  during tooling setup prior to production. 
     It can be seen that the ball  44  accurately controls the X-Y movement of the Suspension assembly  33  without interplay inside a clearance as is the case with conventional suspensions, which locate a pin in a hole in the suspension. The locating pin  212  in the slot  95  controls the rotation of the suspension about the gimbal ball  44 . 
     The method described herein for direct mechanical locating of the gimbal ball  44  relative to the slider  60 , presents several advantages over conventional mechanical locating methods using conventional suspensions, among which are the following advantages: Locating is on the primary X-Y locator (i.e., the gimbal ball) as opposed to a secondary X-Y locator (i.e., a hole in the suspension). The locational tolerance between the stamped dimple and the X-Y locating hole is eliminated. The clearance between the X-Y locator hole and the locating pin is also eliminated. 
     It should be understood that the above method is only one method of mechanically locating the suspension relative to the slider. If conventional mechanical locating is used, wherein a pin is located in a X-Y locator hole, there is still the advantage of the gimbal ball  44  being accurately located with respect to the X-Y locating hole. This is because the ball hole or gimbal opening  77  is etched at the same time as the X-Y locating hole is etched. Whereas with conventional suspensions, stamping is a separate operation with greater pivot point variation. Direct optical locating of the gimbal ball  44  to the slider is another viable alternative, and would be understood by those familiar with the art. 
     It should be understood that the geometry, compositions, and dimensions of the elements described herein may be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications may be made when implementing the invention for a particular environment.