Abstract:
A disk drive suspension comprising a load beam utilizing a piezoelectric microactuator has multiply reversely deflected arcuate spring portion elements that further curl or flatten in response to contraction or expansion of the piezoelectric microactuator to facilitate greater distance beam displacement at lower levels of voltage.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/159,907 filed Oct. 15, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to disk drive suspensions and, more particularly, to load beams for disk drive suspensions displaced by microactuators and having features allowing greater stroke sensitivity (or displacement response to microactuator elongation and contraction) for increased distance of stroke without loss of torsion performance with a given voltage input. The invention suspensions utilize microactuation by a piezoelectric crystal to shift the load beam distal end relative to the beam base portion over the disk to be read. The invention uses plural reverse deflections (or turns of direction) along the length of the suspension spring elements to provide a softer resistance to lateral movement and less constraint of the suspension movement that is responsive to longitudinal dimensional change in the piezoelectric crystals, while maintaining the structural integrity of the suspension. Manufacturing advantages accrue from the inventive use of the plural reverse deflections over the use of single deflections. Single deflections tend to spring back and plural, reverse deflections counteract this tendency. The invention enables effective microactuation of suspensions with the use of greatly reduced voltages, e.g. 5 volts, rather than 40 volts heretofore employed by virtue of heightened stroke sensitivity. Stroke sensitivity, measured in NM/VOLT, is increased, for example, to over 41 NM/VOLT from the just about 31 NM/VOLT obtained with single deflection in the suspension spring elements. 
     2. Related Art 
     Load beams are used to carry sliders containing read/write heads adjacent spinning disks. The load beam has a base portion anchored to an actuator arm that pivotally shifts the load beam and its associated slider angularly to move between tracks on the disk. The mass and inertia of conventional actuators means it requires considerable power to operate them. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved suspension. It is a further object to provide a load beam of novel design and a method of forming such load beams and suspensions. It is a further object to provide for the actuation of a suspension load beam with microactuators acting against a beam spring portion having an improved expansion and contraction capability. It is a further object to utilize piezoelectric crystals acting between the load beam base potion and the beam portion across the spring portion under voltages of less than about 40 volts to as little as 5 volts or less and to increase the stroke sensitivity of microactuated suspensions to greater than 40 NM/VOLT. It is a still further object to provide a load beam having specially conformed spring elements bent from the plane of the load beam to be disposed vertically to the load beam to support the beam portion from the base portion and also to readily allow changes in dimension of the spring portion through the decrease or increase in repeating reversed arcuate sections of the spring elements. 
     The invention accordingly provides a disk drive suspension comprising a load beam having a base portion, a spring portion and a beam portion adapted to carry a slider in operating proximity to a disk, a dimensionally variable electrodynamic microactuator coupled to the base portion and the beam portion and across the spring portion in beam portion angularly displacing relation to the base portion over a distance that is a function of an applied voltage to the microactuator and the resistance of the spring portion to changes in dimension, the spring portion comprising a plurality of longitudinally extended, multiply reversely deflected spring elements providing low resistance change in spring portion dimensions, whereby the beam portion is displaced an increased distance at a given applied voltage. 
     In this and like embodiments, typically, the suspension includes right and left hand microactuators acting on the beam portion in displacing relation, the microactuator comprises a piezoelectric crystal, and the suspension has a stroke sensitivity above about 35 NM/VOLT. 
     In a further embodiment, the invention provides a disk drive suspension comprising a load beam having a base portion, a spring portion and a beam portion adapted to carry a slider in operating proximity to a disk, a dimensionally variable piezoelectric crystal microactuator coupled to the base portion and the beam portion and across the spring portion in beam portion displacing relation to the base portion over a distance that is a function of an applied voltage to the microactuator and the resistance of the spring portion to changes in dimension, the spring portion comprising a plurality of longitudinally extended, multiply reversely deflected spring elements providing low resistance change in spring portion dimensions, whereby the beam portion is displaced an increased distance at a given applied voltage. 
     In this and like embodiments, typically, the spring portion comprises right and left spring elements, and the microactuator comprises right and left piezoelectric crystals coupled between the base and beam portions inboard of the right and left spring elements, the load beam spring portion extends in a plane, the spring portion having right and left side rails extending normal to the spring portion plane and defining respectively opposed right and left spring elements that extend laterally of the load beam, the spring elements being reversely deflected at spaced locations along their longitudinal extent to form spaced proximate and distal local arcuate sections, the sections extending parallel to the spring portion plane, the proximate arcuate sections open inwardly and are open toward each other across the spring portion, the distal arcuate sections open outwardly and are closed toward each other, and the spring elements converge on one another from their proximate ends to their distal ends. 
     Further, while the microactuators are typically bonded to the load beam, the invention contemplates a positive coupling of the load beam to the microactuators in lieu of or in addition to an adhesive bond. For this purpose, the microactuator and the load beam define cooperating interfitting structures, the microactuator acting through the interfitting structures to displace the load beam. 
     The right and left piezoelectric crystals thus have proximate portions attached to the base portion and distal portions attached to the beam portion (includes a continuation of the spring portion attached to the beam portion), and intermediate portions between the proximate and distal portions, the arcuate sections being disposed opposite the crystal intermediate portions. 
     Typically, the arcuate sections are each deflected a like amount from their respective spring elements, the piezoelectric crystals each have outer edges, and the distal arcuate sections are closer to the crystal outer edges than the proximate arcuate sections, the suspension having a stroke sensitivity above about 35 NM/VOLT. 
     In a further embodiment, the invention provides a center spring element as well as right and left spring elements. Thus, the invention in this embodiment provides a disk drive suspension comprising a load beam having a base portion, a spring portion and a beam portion adapted to carry a slider in operating proximity to a disk, a dimensionally variable piezoelectric crystal microactuator coupled to the base portion and the beam portion and across the spring portion in beam portion displacing relation to the base portion over a distance that is a function of an applied voltage to the microactuator and the resistance of the spring portion to changes in dimension, the spring portion comprising right, left, and central longitudinally extended, multiply reversely deflected spring elements providing low resistance change in spring portion dimensions, whereby the beam portion is displaced an increased distance at a given applied voltage. 
     In this and like embodiments, typically, the microactuator comprises right and left piezoelectric crystals coupled between the base and beam portions inboard of the right and left spring elements and on opposite sides of the central spring element, including by the aforementioned cooperating interfitting structures between the load beam and microactuator crystals. 
     The disk drive suspension load beam spring portion extends in a plane, the spring portion having right and left side rails extending normal to the spring portion plane and defining respectively the right and left spring elements that extend in opposed relation and laterally of the load beam, the spring portion further having a center part generally extending in the spring portion plane, the center part defining the central spring element extending normal to the spring portion plane and parallel to the right and left side rails, the right, left and central spring elements each being reversely deflected at spaced locations along their longitudinal extent to form spaced proximate and distal local arcuate sections, the distal arcuate sections being formed with the side rails in the spring portion plane and simultaneously, typically by a common forming tool, in a common direction from the spring portion, the side rails being subsequently turned normal to the plane. The proximate arcuate sections are similarly, and oppositely formed with the side rails in the spring portion plane and simultaneously in a common direction from the spring portion, the side rails again being subsequently turned normal to the plane. 
     The right and left proximate arcuate sections open inwardly and are open toward each other and the central spring element, while the distal arcuate sections open outwardly and are closed toward each other. 
     The disk drive suspension right and left piezoelectric crystals have proximate portions attached to the base portion and distal portions attached to the beam portion, and intermediate portions extending between the proximate and distal portions, the right piezoelectric crystal intermediate portion being located between and opposite the right arcuate sections and the central arcuate sections, the left piezoelectric crystal being located between and opposite the left arcuate sections and the central arcuate sections. The proximate and distal arcuate sections on the right, left and center spring elements are each deflected a like amount from their respective spring elements. As in previous embodiments, the suspension typically has a stroke sensitivity above about 35 NM/VOLT. 
     In yet a further embodiment, the invention provides a disk drive suspension comprising a load beam having a base portion, a spring portion and a beam portion adapted to carry a slider in operating proximity to a disk, right and left dimensionally variable piezoelectric crystal microactuator coupled to the base portion and the beam portion and across the spring portion in beam portion angular displacing relation to the base portion over a distance that is a function of an applied voltage to the microactuator and the resistance of the spring portion to changes in dimension, the spring portion comprising right, left and central longitudinally extended, multiply reversely deflected spring elements bracketing the microactuators and providing low resistance change in spring portion dimensions, whereby the beam portion is displaced an increased distance at a given applied voltage. 
     In this and like embodiments, typically, the right, left and central spring elements each comprise a unitary part of a common web with the beam base portion and the beam portion, each spring element having fore and aft tabs connected to the beam and base portions respectively and distal arcuate sections connected to the fore tabs and proximate arcuate sections connected to the aft tabs in beam supporting relation relative to the base, the arcuate sections being deflected a like amount from their respective spring elements and substantially parallel to each other when the right and left spring elements are folded outward to be parallel to the plane of the spring portion. The arcuate sections tend to flatten to a greater radius curve when the spring element is elongated by action of the piezoelectric crystal and to curl to a lesser radius curve when the spring portion element is contracted by action of the piezoelectric crystal and individually for each of the arcuate section. 
     In its method aspects, the invention provides a method of forming a disk drive suspension comprising a load beam having a base portion, a spring portion and a beam portion adapted to carry a slider in operating proximity to a disk and a dimensionally variable piezoelectric crystal microactuator coupled to the base portion and the beam portion and across the spring portion in beam portion displacing relation to the base portion over a distance that is a function of an applied voltage to the microactuator and the resistance of the spring portion to changes in dimension, including providing right and left spring elements comprising coplanar right and left continued extents of the right and left edges respectively of the spring portion, deflecting oppositely the proximate and the distal portions of the spring elements from their common plane with the spring portion, and folding the spring elements at the respective edges of the spring portion to have the right and left spring elements normal to the spring portion and the deflections therein parallel to the spring portion for less resistance to increased distance change in spring portion dimensions at a given applied voltage. 
     The method further includes providing a central spring element between the right and left spring elements comprising a central part of the spring portion, and deflecting oppositely the proximate and distal portions of the central spring element from the plane of the spring portion simultaneously with the deflection of the right and left spring elements to have the central spring element and the deflections therein normal to the spring portion, and attaching right and left piezoelectric crystals across the spring portion between the central spring element and the right and left spring elements respectively with adhesive and/or through cooperating interfitting structures on the piezoelectric crystals and the load beam, whereby the crystals are attached to the load beam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be further described as to certain illustrative embodiments in conjunction with the attached drawings in which: 
     FIG. 1 is an oblique view of the invention suspension; 
     FIG. 2 is top plan view thereof; and, 
     FIG. 3 is an oblique view of an alternate embodiment. 
    
    
     DETAILED DESCRIPTION 
     The invention uses piezoelectric crystal material as a microactuator in a data recording head suspension. Conventional servo actuation is not effective when the disks have a high density of tracks-per-inch (TPI) such as about 25 to 30 KTPI since they are no longer able to follow the tracks for magnetic reading and writing. Further, the mass and inertia of the conventional actuator system requires considerable power to operate. In the invention the piezoelectric crystal is used as a microactuator variable member (motor) after being fastened to the base portion and the beam portion of the load beam, across the spring portion. 
     To increase the response of the suspension to microactuation, particularly at low applied voltages, it is desirable to increase the stroke sensitivity, or distance of displacement per volt. Measured as nanometers/volt, the stroke sensitivity in the present invention can exceed 40 NM/VOLT. It has been found that the present invention using a reversely deflected spring element is far more effective than using a single deflection in the spring element. The deflections should be opposed and plural, forming a sinusoidal pattern, possibly separated by intervening lands of undeflected spring element between the deflections. The requirement is that there be at least two oppositely extending deflections that will preferentially yield to bending forces imposed on the load beam spring portion by the microactuators, so that the planar, undeflected parts of the spring portion do not have to yield to obtain movement in the spring portion and commensurate displacement of the beam portion and the slider over the disk tracks. Multiple deflections, even corrugations, of the spring elements can be used to achieve the ease of movement sought in the spring portion and enable sufficient movement with ever decreasing amounts of applied voltage. 
     With all the improvements in stroke sensitivity there cannot be a decrease in the torsion performance characteristic of the suspension. A suspension having a single deflection in its spring elements and a stroke sensitivity of about 30 NM/VOLT and a 1 st  torsion value of 6000 Hz, can be improved by adding a second reversely directed deflection to each spring element in accordance with the invention to obtain a stroke sensitivity of over 40 NM/VOLT while also obtaining a 1 st  torsion value of 6400 Hz. 
     The invention introduces dimensional flexibility to the load beam spring portion without reducing or altering its spring portion effectiveness by fabricating the spring portion elements to have reversely deflected arcuate sections. These sections while they support the load beam beam portion just as a conventional spring portion have the capability, separately and independently, to flatten or curl under elongating or contracting loads imposed by the crystal element mounted to the load beam. 
     The invention uses a plurality of spring portion elements, typically two or three, each with a “double C-shape”, that is two or more arcuate or “C-shaped” sections are defined along the length of each spring element, and oppositely. The radius of the spring element arcuate sections can vary depending on the specific structure; their location is on either side of piezoelectric element in the load beam spring area. The arcuate section offers less constraint than that of flat, noncurved designs. With the elongation and compression of the piezoelectric element, the arcuate sections provide a physical conformation for the spring elements to extend or compress. With a small excitation force from the piezoelectric element, there is reconformation in the off-plane arcuate figures with less stress that involved in reshaping a conventional spring portion. 
     The orientation of the arcuate sections can range from vertical to the load beam to lateral of the load beam, that is from 90° to 0° relative to the plane of the load beam, but are preferred for manufacturing reasons and performance reasons to be oriented normal to the plane of the load beam spring portion. 
     With reference now to the drawings in detail, in FIGS. 1 and 2 load beam  10  comprises a unitary web  12  of stainless steel or other suitable spring material supported by a mount plate  14  having a boss  16 . Load beam  10  has a base portion  18 , fixed on the mount plate boss  16 , a spring portion  20  and a beam portion  22  for carrying a slider (not shown). Electrodynamic microactuators in the form of piezoelectric crystals  32 ,  34  are bonded to the base portion  18  and the beam portion  22  with glue or by other means. The crystals  32 ,  34  are arranged to traverse the openings  19  in the spring portion  20  at a desired angle relative to the longitudinal axis of the load beam  10 . Crystals  32 ,  34  function independently to elongate or contract in response to a positive or negative voltage being applied, exerting a force on the immovable base portion  18  and the displaceable beam portion  22 . The beam portion  22  is displaced in the Y-axis a distance that is a function of the applied voltage and the mechanical resistance of the beam spring portion  20  to bending to accommodate the beam portion displacement. 
     Spring portion  20  comprises left and right hand spring elements  24 ,  26 . Spring elements  24 ,  26  are unitary with the web  12  and formed to have forward and rearward tabs  28 ,  30 , and distal arcuate sections  36 ,  38  and proximate arcuate sections  37 ,  39  intermediate the length of the spring elements and connected to the base portion  18  and beam portion  22  by their respective tabs  28 ,  30 . The arcuate sections  36 ,  37 ,  38  and  39  are generally C-shaped, extend reversely on each spring element  24 ,  26  and are disposed normal to the lateral plane of the spring portion  20 . Proximate arcuate sections  37 ,  39  are open to that plane, see FIG. 1, whereas arcuate sections  36 ,  38  are closed to that plane. 
     Thusly conformed, the spring elements  24 ,  26  will lengthen or contract in response to relative movement between the base portion  18  and the beam portion  22 . This accommodation of relative movement is the product of the radius of curvature of the arcuate spring sections  36 ,  37 ,  38  and  39  changing. A displacement of the beam portion  22  by the elongation of the piezoelectric crystals  32 ,  34  will extend or contract the spring elements  24 ,  26  by changing their arcuate sections  36 ,  37 ,  38  and  39  radius of curvature to larger (flatter) for an elongation of the crystals, or smaller (more curled) for a contraction of the crystals. 
     The change in curvature of the arcuate sections  36 ,  37 ,  38  and  39  of spring elements  24 ,  26  makes changes in the apparent length of these elements (measured as the distance between the base portion  18  and the beam portion  22  at the elements, as opposed to real length which is the length from end-to-end) a simple, nearly mechanical resistance-free step, in contrast to the forcing of real length changes in the spring portion. The FIGS. 1 and 2 embodiment simply changes the curvature of the arcuate sections  36 ,  37 ,  38  and  39  without acting against the tensile strength of the metal web  12 . 
     With further reference to FIGS. 1 and 2, the suspension load beam has a third spring element  25 . Thus, load beam spring portion  20  comprises three spring elements:  24 ,  25  and  26 , with the added spring element  25  being central to the load beam, disposed along the longitudinal axis thereof and between the left and right hand spring elements  24 ,  26 . Central spring element  25  is reversely deflected to form two oppositely arcuate sections, distal arcuate section  21  and proximate arcuate portion  23 . 
     The load beam spring portion  20  is formed with the load beam web  12  in a flat condition. The forming tool (not shown) that forms right and left hand spring elements  24 ,  26  into reversely paired arcuate sections  36 ,  37 ,  38  and  39  preferably also forms the spring element  25  into both its distal and proximate arcuate sections  21  and  23 . The spring elements  24 ,  26  are later folded to be at a right angle to the lateral plane of the remainder of the spring portion  20 . The central distal and proximate arcuate sections  21  and  23  are in parallel with the distal and proximate arcuate sections  36 ,  37 ,  38  and  39  in outboard spring elements  24 ,  26  while the web  12  is flat, and thereafter in planes normal to the planes of the outboard spring element arcuate sections. 
     The functioning of the spring elements  24 ,  25  and  26  is as just described. Arcuate sections  36 ,  37 ,  38 ,  39 ,  21  and  23  flex and change in curvature to accommodate displacement of the beam portion  22  by the dimensionally variable piezoelectric crystals  32 ,  34 . 
     The spring elements  24 ,  26  lie in a common plane that includes the load beam base  18  and beam or rigid portion  22 . Arcuate sections  36 ,  37 ,  38 ,  39 ,  21  and  23  are typically of like extent of deflection and have a like curvature. The illustrated embodiment in which the spring elements are normal to the plane of the web  12  is advantageous in enabling the suspension to be stiffer in the vertical direction and the same or less stiff in the sway direction. The piezoelectric crystal functions better when pushing against something that is not so stiffly resisting. Also, bending of the suspension in the areas of piezoelectric crystal attachment can cause breakage or detachment of the crystal due to the tremendous mechanical advantage between the beam distal end where the load is applied and the beam proximate end acting as a fulcrum near the mount plate. The crystal area is about one-fifth to one-eighth of the beam distance, so it sees a force of 5 to 8 times the load. This force is resisted by the crystal in bending and shear, and the crystal is stressed to either break or shear its adhesive bond to the beam. Stiffening the beam in the crystal area will reduce or eliminate this phenomenon. The laterally disposed spring elements  24 ,  26  are formed as rails opposite the crystal mounting, thereby stiffening the beam in this area. The beam then tends to bend in the spring area, as intended, rather than in the crystal area where bending is not wanted. 
     Further, a vertically disposed web, like spring elements  24 ,  26  in FIGS. 1-3, is softer in lateral stiffness than a horizontal web (no folding). The difference in stiffness is approximately the cube of the relative lateral dimension. Vertically disposed spring elements offer a decrease in lateral stiffness and an increase in vertical stiffness because the spring element is folded to lie on its side (face to the edge of the load beam) as opposed to having its face facing the face of the load beam. For example, for a 0.008 wide element made from 0.0025 thick spring steel the improvement from the orientation change is (0.008/0.0025) 3  or 32 times. 
     The invention with double arcuate section spring elements has the following performance in comparison with a single arcuate section spring element: 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 STROKE 
                 1 ST   
                 2 ND   
                 1 ST   
                 2 ND   
                   
               
               
                   
                 SENSITIVITY 
                 BENDING 
                 BENDING 
                 TORSION 
                 TORSION 
                 SWAY 
               
               
                   
                 (NM/VOLT) 
                 (HZ) 
                 (HZ) 
                 (HZ) 
                 (HZ) 
                 (HZ) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 SINGLE ARC 
                 31 
                 2523 
                 4289 
                 6000 
                 11180 
                 10548 
               
               
                 DESIGN 
               
               
                 DOUBLE ARC 
                 41.2 
                 2700 
                 5277 
                 6471 
                 11606 
                 10902 
               
               
                 IDEA 
               
               
                   
               
             
          
         
       
     
     In FIG. 3, in which like parts have like numerals plus  100 , an alternate embodiment is shown that uses positive interconnection of the load beam  110  and the crystals  132 ,  134 . Specifically, the crystals  132 ,  134  each define a series of notches  44  arranged substantially at the corners of the crystals, and an interfitting series of tab elements or rails  46  formed by bending the load beam portions  18  and  22  at locations substantially opposite the notches during formation of the load beam. Thus coupled, the load piezoelectric crystals will act through the interfitting notch and rail structures, rather than through a lap-shear bond, to selectively displace the beam portion  22  relative to the base portion  18  so that the stress on an adhesive bond between the crystals and the load beam areas will be relieved. 
     The invention thus provides an improved suspension of novel design and a method of forming such load beams and suspensions wherein microactuators act against a beam spring portion having an improved expansion and contraction capability. Piezoelectric crystals act between the load beam base potion and the beam portion across the spring portion under voltages of less than about 40 volts to as little as 5 volts or less with an increased stroke sensitivity to greater than 40 NM/VOLT through specially conformed spring elements bent from the plane of the load beam to be disposed vertically to the load beam to support the beam portion from the base portion and also to readily allow changes in dimension of the spring portion through the decrease or increase in repeating reversed arcuate sections of the spring elements. 
     The foregoing objects are thus met.