Abstract:
A base mounting portion connects the gimbal spring to a load beam and thereby to the actuator of the disc drive which positions the gimbal and slider over a desired track on the disc. The gimbal includes opposed spaced flexure arms which are formed of elongated members, each having a proximal end and a distal end which define an opening therebetween. The proximal ends of the flexure arms are operably coupled to the base, and the distal ends are cantilevered. A mounting tab is positioned between the ends of the flexure arms and supports the slider. Bridge sections are provided which connect the distal ends of the flexure arms to the mounting tab, the bridge sections extending at an angle relative to the flexure arms and being angled back toward the base section of the gimbal. The bridge sections support a limiter extending over said load beam to limit vertical movement of said load beam.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/059,451, filed Sep. 22, 1997, and entitled DEFLECTION LIMITER FOR AN OPTICALLY ASSISTED WINCHESTER DRIVE. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a disc drive assembly. In particular, the present invention relates to an improved suspension design for supporting a head relative to a disc surface. 
     Disc drive systems are known which read data from a disc surface during operation of a disc drive. Such disc drive systems include conventional magnetic disc drives and optical disc drive systems. Optical disc drive systems operate by focusing a laser beam onto a disc surface via an optical assembly which is used to read data from the disc surface. Conventional magnetic disc drive systems use inductive type heads for reading or writing or magneto-resistive (M) heads for reading data. Discs are rotated for operation of the disc drive via a spindle motor to position discs for reading data from or writing data to selected positions on the disc surface. 
     Known optical assemblies include an objective lens which is positioned between the objective lens and the disc surface . The SIL is positioned very close to the data surface of the disc and is described in U.S. Pat. No. 5,125,750 to C. Orle et al., which issued Jun. 30, 1992, and in U.S. Pat. No. 5,497,359 to Mamin et al., which issued Mar. 5, 1996. In these optical systems, a laser beam is focused onto the SIL using an objective lens. The SIL is preferably carried on a slider and the slider is positioned close to the disc surface. Use of an SIL increases storage density. 
     The slider includes an air bearing surface to fly the SIL above the disc surface. The slider includes a leading edge and a trailing edge. Rotation of discs creates a hydrodynamic lifting force under the leading edge of the slider to lift the leading edge of the slider to fly above the disc surface in a known manner. The slider preferably flies with a positive pitch angle in which the leading edge of the slider flies at a greater distance from the disc surface than the trailing edge via a suspension assembly which includes a load beam and gimbal spring. The slider is coupled to the load beam via the gimbal spring. The load beam applies a load force to the slider via a load button. The load button defines an axis about which the slider pitches and rolls via the gimbal spring. The slider is preferably resilient in the pitch and roll direction to enable the slider to follow the topography of the disc. 
     The flexure of the gimbal spring permits the air bearing slider to pitch and roll as the slider flies above the disc surface. It is important to maintain the proximity of the SIL and slider relative to the disc surface to maintain the proper focus of light onto the disc surface as is known for optical disc drive systems. It is important that the flexure system including the load beam and the gimbal spring be designed to stably and accurately support the slider during operation of the disc drive system. In a magneto-optic (M-O) system, a magnetic transducer element is carried on the slider to write data to the disc surface. It is also important to accurately support and position the magnetic transducer elements relative to the disc surface during operation of an M-O system. 
     An actuator mechanism is coupled to the suspension assembly to locate the SIL relative to selected disc positions for operation of the disc system. During movement of the suspension system, force is transmitted through the load beam and gimbal spring to move the slider. Operation of the actuator mechanism, air bearing surface, and spindle motor introduce external vibration to the slider and suspension assembly. Depending upon the mass and stiffness of the suspension assembly, including the gimbal spring and load beam, external vibration may excite the load beam and gimbal spring at a resonant frequency. Thus the input motion or external vibration may be amplified substantially, causing unstable fly characteristics and misalignment of the slider relative to the disc surface. 
     External vibration or excitation of the suspension assembly and slider may introduce varied motion to the slider and suspension assembly. Depending upon the nature and frequency of the excitation force, the slider and suspension assembly may cause torsional mode resonance, sway mode resonance, and bending mode resonance. Torsional mode motion relates to rotation or twisting of the suspension assembly about an in-plane axis. Bending mode resonance essentially relates to up-down motion of the suspension assembly relative to the disc surface. Sway mode vibration relates to in-plane lateral motion and twisting. It is important to limit resonance motion to assure stable fly characteristics for the SIL. In particular, it is important to control the torsion and sway mode resonance, since they produce a transverse motion of the slider, causing head misalignment with respect to the data tracks on the disc surface. 
     The resonance frequency of the suspension assembly is related to the stiffness or elasticity and mass of the suspension system. Thus, it is desirable to design a suspension system which limits the effect of sway mode and torsion mode resonance in the operating frequencies of the disc drive while providing a suspension design which permits the slider to pitch and roll relative to the load button, and which has relatively high lateral rigidity and stiffness for maintaining precise in-plane positioning of the slider along the yaw axis. 
     It is also highly desirable to incorporate a deflection limiter in the design of the suspension assembly. 
     Deflection limiters are beneficial for several reasons. During a shock event, such as dropping the disc drive or HGA shipping tray, the mass of the head and lens can pull the gimbal away from the load beam if there is no deflection limiter. This deflection will induce stress in the gimbal. The stress could be high enough to yield the gimbal and result in dimple separation and changes to the pitch and roll static angle of the gimbal. A deflection limiter will prevent this from happening by ensuring that the deflection is not large enough to cause the stress to reach the yield point. Deflection limiters are also beneficial for ramp load/unload applications, especially with negative pressure air bearings. 
     SUMMARY OF THE INVENTION 
     Thus it is an object of the present invention to provide an improved suspension system for a disc drive. More specifically, it is an objective to provide an improved suspension design which utilizes a simplified design approach to providing a deflection limiter in a suspension system. 
     A further object of this invention is to provide an improved suspension which limits the resonance motion and the vertical travel of the gimbal to assure stable flying characteristics for the gimbal. More specifically, the objective of the invention is to limit the rotational or twisting motion of the suspension as well as the up-down motion of the suspension or gimbal relative to the disc surface. 
     These and other objectives of the invention are achieved by providing a gimbal spring which flexibly supports the slider relative to the disc surface. The design incorporates a base mounting portion which connects the gimbal spring to a load beam and thereby to the actuator of the disc drive which positions the gimbal and slider over a desired track on the disc. The gimbal includes opposed spaced flexure arms which are formed of elongated members, each having a proximal end and a distal end which define an opening therebetween, the proximal ends of the flexure arms being operably coupled to the base portion, and the distal end being cantilevered. A mounting tab is positioned between the ends of the flexure arms and supports the slider. Bridge sections are provided which connect the distal ends of the flexure arms to the mounting tab, the bridge sections extending at an angle relative to the flexure arms and being angled back toward the base section of the gimbal. More specifically, the bridges are curved to conform to the curvature of an optical lens mounted on the slider to be used to read information from or store information on the surface of the disc. 
     In a further feature, a deflection limiter is provided by defining a limiter comprising a continuous member extending across the width of the load beam tongue. The limiter extends over one surface of the load beam tongue; the opposite surface of the load beam tongue supports the slider. Preferably, the limiter extends from one section to the other so that the load beam is captured, and its vertical movement restrained, between sections and the limiter. 
     Another unique feature of this design approach is that it places the limiter and bond tongue towards the leading edge of the slider. This is beneficial for a ramp load/unload device since it will tend to lift the slider by the leading edge and prevent the leading edge of the slider from crashing into the disc as other gimbal/limiter concepts do that constrain motion at the trailing edge of the gimbal. 
     Other features and advantages of the invention can be found by reference to the attached drawings and accompanying description of an exemplary embodiment 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of operation of an optical disc drive system. 
     FIG. 2 is a side view of a slider supporting an SWL. 
     FIG. 3 is a top view of a suspension assembly coupled to an actuator mechanism for supporting a slider relative to a disc surface (not shown). 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a simplified diagram illustrating an optical storage system using a solid immersion lens (SIL). Obviously, the invention can be used with many other slider designs and associated lenses. Optical system  10  includes an optical disc  12  having a data surface which carries optically encoded information. Disc  12  rotates about spindle  14  and is driven by a spindle motor  16  mounted on base  18 . A slider  20  is movably supported relative to disc surface  12  via an actuator mechanism  22 . 
     The slider  20  supports an SIL  24  for focusing a laser beam of an optical system on the disc surface for reading optically-encoded information. The actuator mechanism  22  preferably includes a voice coil motor  26 . The slider  20  is coupled to the voice coil motor via a suspension assembly  28 . The optical system includes an optical head  30  which preferably is coupled to the actuator mechanism  22  and operated thereby. The optical head  30  includes a laser beam which is focused onto the disc surface via the SIL  24  in a known manner for operation of the optical disc drive system. 
     FIG. 2 illustrates the slider  20  and SIL  24  construction. Preferably, the slider is formed of a transparent material, such as a cubic zirconia. The SIL  24  is bonded to the slider  20  or, alternatively, the slider  20  and SWI  24  may be formed of an integral material machined from a single piece of crystal. For example, the integrated SIL  24  and slider  20  can be formed by injection molding a single piece of transparent material such as a commercially available polycarbonate in a known manner. The slider  20  includes an upper surface  32  and a lower air bearing surface (ABS)  34  (surface not visible in FIG. 2) which is formed in a known manner to provide a hydrodynamic lifting force to the slider  20  and the lens  24  via rotation of optical disc  12  in a known manner. 
     The slider  20  is supported by a suspension assembly  28  operably coupled to the actuator mechanism. In particular, as illustrated in FIG. 3, the suspension assembly  28  includes a load beam  36  and a gimbal spring  40 . Preferably, the load beam  36  is formed of an elongated flexible material which includes side rails  44  and a load tab  46  having load button  48  (on a lower surface of load tab  46 ) at an extended end of the load beam  36  as will be explained. Side rails  44  provide lateral and bending stiffness and a means for connecting wires (not shown) to the slider  20 . 
     The gimbal spring  40  is coupled to the load beam  36  and flexibly supports slider  20  relative to the load beam  36 . The load button  48  applies a load force to the upper surface  32  of the slider and defines a gimbal pivot axis  50  about which the slider  20  can pitch, and pivot axis  68  about which the slider  20  can roll, relative to the disc surface for operation of the disc drive. 
     The lower air bearing surface  34  of the slider  20  (not shown) faces the disc surface so that rotation of disc  12  provides a hydrodynamic lifting force to the slider  20  which flies above the disc surface as data is read and written to the disc surface. The load force counteracts the hydrodynamic lifting force of the ABS. 
     The slider is lifted via the ABS surface to fly at a pitch angle relative to the disc surface. During operation of the disc drive, it is important to maintain a stable fly height for slider  20  close to the disc surface and that the slider  20  be able to pitch and roll to follow the topography of the disc surface. Thus, the gimbal spring  40  should be designed to support the slider relative to the load beam to allow sufficient pitch and roll of the slider  20  during operation. If the pitch and roll stiffness of the gimbal spring is too low, it will be difficult to control the fly characteristics of the slider and the gimbal will exhibit undesirable resonance behavior. If the gimbal spring  40  is too stiff in the pitch and roll axes, then the slider will not be able to follow the topography of the disc surface. 
     During operation, the actuator mechanism  22  moves the suspension assembly to position the slider  20  and SIL  24  relative to selected positions on the disc surface. Rotation of the disc supplies a lifting force to the slider  20  at the ABS surface. Operation of the slider thus introduces vibration to the suspension system which, depending on the construction of the suspension assembly and gimbal spring  40 , may coincide with the resonance frequencies of the suspension system, causing the external motion to be amplified. Vibration of the suspension system at the resonance frequencies may interfere with placement and operation of the slider  20 . Typical excitation forces are fairly low-frequency, less than 10,000 Hz. Thus, it is desirable to design the gimbal spring so that its resonance frequencies are high to avoid resonance vibration at typical operation frequencies of the disc drive. 
     Further, as discussed, during operation of an optical disc drive, a slider  20  supports an SIL  24  above the disc surface via operation of the ABS surface and the load force of the load beam  36 . Depending upon the position of the load button  48  and gimbal pivot  50 , the weight of the SIL  24  may be unbalanced relative to the load position and during operation may excite the gimbal spring  40 . Depending upon the design of the suspension system, this vibration is amplified at the resonance frequency, thus degrading the performance of the slider and SIL  24 . The gimbal spring  40  of the present invention is designed to provide desirable pitch and roll stiffness with desired resonance frequency as will be explained. 
     Further, during a shock event the mass of the head and lens can pull the gimbal away from the load beam in the absence of some deflection limiting mechanism. This deflection will induce stress in the gimbal. The stress could be high enough to yield the gimbal and result in dimple separation and changes to the pitch and roll static angle of the gimbal. A deflection limiter will prevent this from happening by ensuring that the deflection is not large enough to cause the stress to reach the yield point. 
     As shown in FIG. 3, the slider includes a leading edge  52  and a trailing edge  54 , and the distance between the leading edge and trailing edge defines the longitudinal extent of the slider. The SIL  24  is positioned toward the trailing edge  54  of the slider  20  on a rear portion of the slider  20 . Since the SIL  24  is positioned along the rear portion, the distribution of weight between forward portion and rear portion is unbalanced. The load tab  46  extends from the leading edge  52  over a forward portion  58  of the slider. The load tab  46  is sized to extend over the forward portion  58  to a center portion of the slider so that the pivot axis  50  is generally at the center portion of the slider  20  for flight stability of the slider  20  during operation. 
     The suspension assembly illustrated in FIG. 3 illustrates an embodiment of a gimbal spring  40  of the present invention for supporting slider  20  designed to optimize pitch and roll stiffness and gimbal resonance characteristics while incorporating deflection limiting capability. As shown, the gimbal spring  40  generally includes spaced flexure arms  62 ,  64  and a slider mounting tab  66 . The gimbal spring  40  is cantileveredly supported relative to the load beam  36  via a mounting portion (not shown but well known in the industry). Spaced flexure arms  62 ,  64  are supported by and extend from the mounting portion in spaced cantilevered relation. Slider mounting tab  66  is operably coupled to the flexure arms  62 ,  64  and is fixedly secured to the slider  20  to flexibly support the slider  20  relative to the load beam  36  to gimbal (pitch and roll) relative to pivot axis  50  and  68 . 
     The flexure arms  62 ,  64  are spaced relative to the width of the slider  20  a certain distance from the centerline  68 , and width  70  of each of the flexure arms  62 ,  64  is sized to provide desired roll characteristics. If the flexure arms  62 ,  64  are spaced too far apart, roll stiffness increases and if spaced too close, roll stiffness is too low. If the width  70  of the flexure arms  62 ,  64  is too thick, roll stiffness increases and if too thin, roll stiffness is too low. Flexure arms  62 ,  64  include a proximal end  72  and a distal end  74 . The proximal end  72  is coupled to the mounting portion and distal end  74  is coupled to mounting tab  66 . The proximal end  72  is fixed relative to the load beam  36  and the distal end  74  flexibly supports slider  20  relative to the pivot axis  50 . As shown, the distal end  74  is cantilevered beyond the pivot axis  50  of slider  20  to provide desired pitch stiffness relative to load button  48  at pivot axis  50 . The extent or length of the flexure arms  62 ,  64  tends to decrease the pitch stiffness based upon the width and thickness of the flexure arms  62 ,  64 . The extent between the proximal and distal ends  72 ,  74  is sufficient so that when mounting tab  66  is coupled to the upper surface of the slider  20  and load button  48  is aligned generally at the center portion  59  of the slider  20 , a portion of the flexure arms extends beyond pivot axis  50  to provide sufficient pitch stiffness for desired fly characteristics. 
     As shown, the length of the flexure arms  62 ,  64  is designed so that when the mounting tab  60  is secured to the load beam  36  and load beam  36  is positioned so that the load button supplies a load force to the center portion  59  of the slider, the distal end  74  extends beyond the pivot axis  50  but does not extend along the entire rear portion  56  to the trailing edge of the slider  20 . The shortened length provides increased gimbal resonance frequencies for bending or torsion of the gimbal as compared to flexure arms having a greater flexure length for movably supporting the slider relative to the pivot axis  50 . The design also provides a reduced width and offset flexure arms  62 ,  64  having lower roll stiffness. 
     As shown, mounting tab  66  couples the distal end  74  of flexure arms  62 ,  64  to slider  20 . For an optimal disc drive system, placement of mounting tab  66  is restricted by the SIL  24 . In the embodiment shown, the SIL  24  is supported in the rear portion  56 , thus interferes with placement of mounting tab  66  in alignment with the distal end  74  of flexure arms  62 ,  64 . 
     Thus as shown, the distal ends  74  of flexure arms  62 ,  64  are coupled to a proximally spaced mounting tab  66  via bridges  76 ,  78 . Bridges  76 ,  78  extend at a sloped angle to connect distal ends  74  of flexure arms  62 ,  64  to the proximally spaced mounting tab  66 . The sloped design of bridges  76 ,  78  provides a direct connection between distal end  74  of flexure arms  62 ,  64  and mounting tab  66  which does not require additional width between arms  62 ,  64 . The angled relation between distal end  74  and bridges  76 ,  78  defines a gap  82  between flexure arms  62 ,  64  and bridges  76 ,  78  for desired flexure of the gimbal spring. Sides  83 ,  84  of bridges  76 ,  78  are preferably curved to the contour of the SIL for placement close to the SIL and a side  86  of the mounting tab  66  is also curved to the contour of the SIL. The length of the flexure arms from axis  50  to distal end  74  is important in providing a pitch stiffness low enough to allow proper flying characteristics. The curved shape of the flexure mounting tabs or bridges  76 ,  78  allows this increased length. This design also keeps the dimple in the midsection of the arms. 
     Thus, as described, the gimbal spring  40  of the present invention is not limited to the shape of the particular mounting tab  66  shown; alternately designed mounting tabs  66  may be designed to secure the flexure arms  62 ,  64  relative to the slider  20 . If there is not sufficient area, SIL  24  will restrict placement of the load button  42  toward the center of slider  20 . Preferably, the load button  48  is formed by an etching process. The load button or dimple  48  formed by the etching process requires less surface area to form the dimple than traditionally formed dimples. Thus, the load button  48  formed by the etching process limits the contact to the slider  20  and provides sufficient surface area to mount the mounting tab  66  and wire termination pads relative to the upper surface  31  of the slider  20 . 
     Thus, as described, the bridge design of the present invention illustrates the shape of a preferred embodiment of the gimbal spring  40  of the present invention. 
     In summary, in addition to significantly lower roll stiffness, the new gimbal design also greatly increases the resonance frequencies of the gimbal resonance modes. The reduced roll stiffness is further aided by reducing the thickness of the gimbal from 0.0015″ to 0.001″ and reducing the width of the arms  62 , 64 . However, if these were the only changes, the gimbal would probably have unacceptably low gimbal resonance frequencies. To overcome this problem, the bond or slider mounting pad  66  was moved from the trailing edge of the lens  24  to the leading edge. This reduced the length of the gimbal arms  62 ,  64  and greatly increased the resonance frequencies of the gimbal modes. 
     If the gimbal arms  62 ,  64  are shortened too much, the entire length of the gimbal arms would be on the leading edge side of the load point. It is highly desirable for pitch stiffness to have some length of the gimbal arms on both sides of the load point. To accomplish that with this design, a unique feature was incorporated. The unique feature is the circular shape or edge to the bond pad. The circular shape follows the profile of the objective lens  24  and allows the gimbal arms  62 ,  64  to be extended past the load point towards the trailing edge of the slider. In FIG. 3, if the straight lead edge  69  of the bond pad  66  were extended-straight out until it intersected the gimbal arms  62 ,  64  the region  73  would be filled in and solid. As a result, the pitch stiffness would be approximately 50% higher. 
     This design is also especially adaptable to incorporate a deflection limiter. The deflection limiter in this application comprises a continuous member  90  supported from the slider mounting pad  66  and extending across the width of the low beam tongue  46 . The limiter extends across the opposite surface of the tongue which contacts the dimple  48 . This makes the limiter  90  which is supported from the bonding pad  66  very strong and able to resist great forces without bending or otherwise allowing the limiter to become disengaged and maintains the load tab  46  in contact with the load button  48 . Another benefit of the design is that the limiter is very strong and able to resist great forces without bending or otherwise allowing the limiter  90  to become disengaged and allowing the slider to deflect without restriction. 
     A further feature of this design approach is that it places the limiter  90  and the bond tongue  46  toward the leading edge of the slider. This is very beneficial for a ramp load/unload device since it will tend to lift the slider by the leading edge and prevent the leading edge of the slider from crashing into the disc as other gimbal/limiter concepts may do, which constrain motion of the trailage edge of the gimbal. The construction of the present invention is further shown in FIG. 4 at the left-hand side the load beam  36  is shown with upraised tabs  92 ,  94  which are used to hold the electrical connectors in the load beam as they extend out to the transducer (not shown) supported on the slider. The figure also shows the slider  20  supporting the lens  24 , with movement of the slider relative to the mounting tab  66  being freely available over contact  66  and the dimple  48 . The limiter is formed by providing a substantially vertical connecting portion  92  between the rear of the mounting tab  66  and the limiter  90  so that the limiter  90  is substantially parallel in a parallel plane but in a different elevation. The low beam  46  can be extended through an opening  95  (FIG. 3) between mounting tab  66  and limiter  90 , encaptured between these two sections to restrain vertical movement of the load beam  46  relative to the slider, so that the slider cannot easily separate itself from the load beam. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.