Abstract:
A microactuator ( 30 ) is provided for positioning a read/write head relative to a mounting region of a head suspension assembly of a magnetic disk drive. The microactuator ( 30 ) comprises a substantially C-shaped member ( 32 ) having a first end  (34 ) and a second end ( 38 ) defining an air gap ( 42 ) therebetween. In one embodiment the member ( 32 ) is a piezoelectric bimorph expander; in another embodiment the member is a ferromagnetic core. Under an applied electric or magnetic field as appropriate, the size of the air gap ( 42 ) may be altered and, because the member ( 32 ) is resilient, the original air gap may be restored on removing the applied field. The microactuator may be mounted on the load beam of the head suspension assembly, or between the load beam and head slider supporting the read/write head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a head suspension assembly for a magnetic disk drive, and more particularly to a microactuator for moving a read/write head relative to a mounting region of the head suspension assembly 
     2. Description of the Related Art 
     Information storage devices typically include a read/write head for reading and/or writing data onto a storage medium such as a magnetic disk within a rigid disk drive. An actuator mechanism driven by a servo control is used to position the head at specific radial locations or tracks on the magnetic disk. Both linear and rotary type actuators are well known in the art. Between the actuator and the head, a head suspension is required to support the head in proper orientation relative to the disk surface. 
     The head suspension carries the read/write head so that the head can “fly” over the surface of the rigid disk while the disk is spinning. The head is typically located on a head slider having an aerodynamic design so that the head slider flies on an air bearing generated by the spinning disk. The combination of the head slider and the head suspension is referred to as a head suspension assembly. The head suspension includes a load beam which has a radius or spring section, a rigid region, and a flexure. The flexure is a spring or gimballing connection typically included between the head slider and the rigid section of the load beam so that the head slider can move in the pitch and roll directions of the head to accommodate fluctuations of the disk surface. The mounting region of the load beam is typically attached to an actuator arm which supports the suspension assembly over the rotating disk. A base of the actuator arm is coupled to an actuator. 
     When no external forces (with the exception of gravity) are acting on the head suspension assembly to deform it in any way, it is in a “neutral un-loaded” state. When the head is flying over the spinning surface of a disk and is acted upon only by the force of the air bearing generated by the spinning disk, the head suspension assembly is in a “neutral loaded” state. However, the head suspension assembly can experience deformations that cause motion of the head away from either the neutral loaded or neutral un-loaded positions. 
     One way these deformations can occur involves a head suspension&#39;s tendency to bend and twist in a number of different modes, known as resonant frequencies, when driven back and forth at certain rates. Any such bending or twisting of a suspension can cause the position of the head to deviate from its neutral loaded or neutral un-loaded position. Alternatively, beneficial deformations of the suspension can be induced using a secondary-actuation or microactuation device designed to move the head relative to the remainder of the head suspension assembly. 
     Employment of secondary actuators working in tandem with primary Voice Coil Motors (VCMs) is an option available for obtaining high servo bandwidths in disk drives. In the case of slider-based designs, their inherently high bandwidths (by virtue of their low mass and inertia) help to overcome virtually all the lower structural modes present in the head suspension assembly. However, this would be possible only if the secondary actuator provides sufficient gain (displacement) to reject the track run-out disturbances at the required frequencies. It must also be remembered that this gain must be effected with minimal use of voltage and current because of the complexities associated with power delivery and dissipation within microstructures. 
     Another challenge faced by microactuator designers is provision of high degrees of in-plane shock resistance to the microactuator, as it conflicts with the aim of achieving high displacement gains in the cross-track direction. The designers eager to enhance the actuator gain compromise the lateral stiffness (in-plane stiffness in the cross-track direction) which lowers the shock-resistance of the assembly drastically. Mass is also a factor that lowers the shock resistance 
     Also, there are issues like contamination control, reliability etc. which are major concerns with the slider-based electrostatic actuators. While improving such features, care must also be taken that they do not reflect on the overall cost of the system. In summary, it might be stated that it is desirable to have high displacement microactuators with high bandwidth and high shock resistance. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, there is provided a microactuator for positioning a read/write head relative to a head suspension assembly of a disk drive, comprising a substantially C-shaped member having first and second ends, each end having an end face with the end face of one end being opposed to and spaced from the end face of the other, wherein the member is resilient and responsive to an applied magnetic or electric field, with end face to end face separation being controllable by the magnetic or electric field applied. 
     The substantially C-shaped member may be planar and may have a substantially annular or toroidal body with an air gap or opening communicating between the radial inner and outer peripheries and providing the first and second ends. Being resilient, the member is able to deform elastically in response to the applied magnetic or electric field, and return to its original shape once the field is removed. 
     The substantially C-shaped member may comprise a piezoelectric material. The member may comprise an inner region and an outer region, with the outer region surrounding the inner region, the outer region being adapted to expand relative to the inner region, or the inner region being adapted to contract relative to the outer region, in response to an applied electric field. Such relative expansion/contraction of the inner and outer regions between the first and second ends may be used to control the end face to end face separation of the first and second ends. 
     The member may comprise a piezoelectric bimorph. With this arrangement, the inner and outer regions are selected to expand/contract differently under the same electric field. In this way, a given applied field tends to produce different internal movements in the inner and outer regions, giving rise to a net change in the end face to end face separation. The inner and outer regions may comprise different piezoelectric materials, or possibly the same material but polarized oppositely. 
     The member may comprise a piezoelectric monolith, uniformly polarized with pairs of electrodes adapted to apply a first electric field to the inner region and a second electric field to the outer region. The first and second regions may be differentially energised to control the deflection of one end with respect to the other. 
     The microactuator may further comprise a further substantially C-shaped member or the kind hereinbefore defined, the further member being stacked above the aforementioned member to form a multi-layer structure. 
     In another embodiment, the substantially C-shaped member may comprise a body of a soft magnetic material (i.e. ferromagnetic material). The body may have a cable wound around the body, with an electric current carried by the cable inducing a magnetic field in the body to control end face to end face separation. 
     In accordance with a second aspect of the present invention, there is provided a head suspension assembly for a magnetic disk drive, comprising a load beam, a head slider and a microactuator for positioning the head slider relative to a rigid mounting end of the load beam, the microactuator comprising a substantially C-shaped member having first and second ends, each end having an end face with the end face of one end being opposed to and spaced from the end face of the other, wherein the member is resilient and responsive to an applied magnetic or electric field, with end face to end face separation being controllable by the magnetic or electric field applied. Various embodiments of the microactuator for the head suspension assembly are as defined with respect to the first aspect of the invention. 
     The microactuator may be mounted on the load beam. The load beam may have a slit extending from a free edge of the load beam, the microactuator being mounted such that reducing the end face to end face separation exerts a force narrowing the slit in the load beam a corresponding amount. For example, the microactuator may be mounted with a surface adjacent a first end fixed to one side of the slit and a surface adjacent the second end fixed to the other side of the slit. In this way, the air gap between the first and second ends is registered with the slit. The slit adjacent the air gap may be parallel or perpendicular to a longitudinal axis of the load beam. 
     The microactuator may be mounted between the load beam and the head slider. The load beam may comprise a flexible coupling and the microactuator may be sandwiched between the flexible coupling and the head slider. An upper surface of the microactuator adjacent one of the ends may be attached to the flexible coupling. A lower surface of the microactuator adjacent the other of the ends may be attached to the head slider. Such a “piggy-back” mounting arrangement may improve the shock resistance of the assembly whilst providing the required amplification at the trailing edge of the slider, particularly if the geometric center of the head slider is attached to the microactuator. 
     Alternatively, an end face of the other of the ends may be attached to the head slider. Such a “side-by-side” arrangement—with the microactuator adjacent the leading edge of the head slider—may help reduce stack height of the assembly. 
     In accordance with a third aspect of the invention, there is also provided a magnetic disk drive comprising a head suspension assembly according to the second aspect of the invention. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 illustrates schematically a head suspension assembly in accordance with the present invention; 
     FIG. 2 illustrates schematically a first embodiment of a microactuator embodying the present invention; 
     FIG. 3 illustrates schematically a second embodiment of a microactuator embodying the present invention; 
     FIG. 4 illustrates schematically a third embodiment of a microactuator embodying the present invention; 
     FIG. 5 illustrates a first arrangement using a microactuator according to any of FIGS. 2 to  4 ; 
     FIG. 6 illustrates a second arrangement using a microactuator according to any of FIGS. 2 to  4 ; 
     FIG. 7 illustrates a third arrangement using a microactuator according to any of FIGS. 2 to  4 ; 
     FIG. 8 is a side view of the arrangement of FIG. 7; and 
     FIG. 9 is a modified version of the arrangement of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates schematically a head suspension assembly  10  which includes a load beam  12  having: a rigid mounting region  14  for attachment to an actuator arm (not shown); an elongate portion  16  and a flexible coupling  18 . A head slider  20  is carried by flexible coupling  18  which is typically a spring or gimballing connection. For the sake of illustration, FIG. 1 shows—highly schematically—a load beam-mounted microactuator  22  which is coupled to the rigid mounting region ( 14 ) and the elongate portion ( 16 ) and a slider-mounted microactuator  24  which is coupled to head slider  20  and flexible coupling  18 . 
     The load beam-mounted microactuator  22  controls the position of the elongate portion  16  relative to the rigid mounting region  14 . The slider-mounted microactuator  24  controls the position of the head slider  20  relative to the remainder of the assembly—the head suspension. In practice, only one of the microactuators  22  or  24  would be required to produce the fine lateral displacements of the slider head  20 —see arrows A indicating “fine tracking”. In response to tracking control signals, whichever of the two microactuators  22  or  24  employed would adjust the position of the read/write elements in the slider head  20  with respect to individual information tracks on the disk (not shown). 
     FIG. 2 illustrates schematically a microactuator  30  which may be employed in either of the load beam-mounted or slider-mounted positions. Microactuator  30  is a substantially C-shaped piezo bimorph expander which comprises a body  32  having a first end  34  with a first end face  36  and a second end  38  with a second end face  40 . The first and second end faces  36 ,  40  oppose each other and are separated by a gap  42 . The body  32  consists of a near-complete inner ring  44  which is surrounded by and coupled to a near-complete outer ring  46 , the rings being incomplete to provide gap  42 . 
     The inner and outer rings  44 ,  46  are of piezo electric (electrostrictive) material and are axially polarized in opposite directions such that one tries to contract whilst the other tries to expand under the influence of an applied electric field. The resulting strains manifest in the form of an expansion/contraction of the body  32  thereby changing gap  42 . If first end  34  is coupled to a (relatively) proximal part of the head suspension assembly (either mounting region  14  or flexible coupling  18  depending upon where the microactuator is mounted) and second end  38  is coupled to a (relatively) distal part of the head suspension assembly, controlling the size of the gap  42  will produce fine tracking movement of the head slider  20 . 
     FIG. 3 illustrates schematically a microactuator  50  which may be used in place of microactuator  30 . The microactuator  50  is also of piezoelectric material, but the body  52  is a monolith rather than a bimorph. (The microactuators  30  and  50  have the same overall geometry, and so end parts/features in common share the same reference numerals). 
     The top planar surface  54  and bottom planar surface (not shown) are each provided with a pair of substantially C-shaped electrodes—an inner electrode  56  and an outer electrode  58 . The inner and outer electrodes  56 ,  58  are electrically separated by a thin insulating annular region  60 . The pairs of inner and outer electrodes  56 ,  58  are used to provide two different electric fields (e.g. equal, but of opposite directions; for instance, the first causing the region of the body  52  between the inner electrodes  56  to contract, and the second causing the region of the body  52  between the outer electrodes  58  to expand. Such simultaneous contraction/expansion brings the opposed end faces  36 ,  40  closer together, thereby narrowing the gap  42 . 
     FIG. 4 illustrates schematically a microactuator  70  which may be used in place of either of microactuators  30  or  50 . The microactuator  70  comprises a body  72  with a ferromagnetic core wound with a few turns of copper wire  74 . (The microactuator  30 ,  50  and  70  have the same overall geometry, and so parts/features in common share the same reference numerals). In use, an electric current applied through the copper wire generates a magnetic field which induces magnetism in the body  72 . The first and second ends  34 ,  38  behave as opposite poles (N and S) of an electromagnetic, and mutually attract, reducing the size of the gap  42 . 
     With all three microactuators  30 ,  50 ,  70 , the respective bodies  32 ,  52 ,  72  of each is resilient in the sense that applying/altering the electric/magnetic field produces a displacement bringing the first and second ends closer together/farther apart, thereby reducing/increasing the size of the gap  42 . Within the operational limits of the device, the greater the field strength, the greater the displacement. Upon removal of the electric/magnetic field, the gap  42  is restored to its initial size, in other words the body  32 ,  52  or  72  returns to its original shape. 
     The microactuators  30 ,  50 ,  70  may be mounted in one of three ways in the head suspension assembly. The following three examples illustrate the mounting principles. In each case, the microactuator is labelled according to whether it is load beam-mounted (i e microactuator  22 ) or head slider-mounted (i.e. microactuator  24 ). 
     EXAMPLE 1 
     FIG. 5 illustrates a head suspension  80  with a load beam-mounted microactuator  22 . The load beam  12  has a slit  82  running transverse to the longitudinal axis (XX) of the head suspension  80 . The slit  82  enhances the lateral compliance of the load beam  12 , making it easier to fine track in the direction of arrows A+A−. The C-shaped microactuator  22  is positioned with the gap  42  in registration with the slit  82 . Two underside regions of the microactuator  22  are glued to the load beam  12 . The first region, adjacent first end  34 , is glued to the load beam  12  on the proximal (rigid mounting region  14 ) side of the slit  82 . The second region, adjacent second end  38 , is glued to the load beam  12  on the distal (elongate portion  16 ) side of the slit  82 . Anchoring the microactuator  22  to the load beam  22  in this way means that the distal side of the slit  82  moves in sympathy with changes in the gap  42  (the proximal side of the slit  82  is rigidly mounted). Thus, reducing/increasing the size of the gap  42  by actuating the microactuator  22  causes flexible coupling  18  to move in the direction of A−. 
     In a modified form, the slit  82  may have a transverse component and a component running parallel to the axis XX. (See Figure). With such an arrangement, the C-shaped microactuator  22  may be positioned with the gap  42  in registration with the component of the slit  82  which is parallel to the axis XX. The first region, adjacent the first end  34 , would be glued to the load beam on one side of the slit (the side underneath the first end); and the second region, adjacent the second end  38 , would be glued to the load beam on the other side of the slit (the side underneath the second end). 
     EXAMPLE 2 
     FIG. 6 illustrates a slider-mounted microactuator  24  attached to a head slider  20 , complete with read/write elements  90 . (The flexible coupling  18 , which would be attached to the top of microactuator  24 , has been omitted for the sake of clarity). The C-shaped microactuator  24  is positioned with the gap  42  aligned with read/write elements  90 . An underside region of the microactuator  24 , adjacent first end  34 , is glued  92  to the head slider  20 . An upper-surface region of the microactuator  24 , adjacent second end  38 , is glued  94  to a plate (not shown) which is part of the flexible coupling  18 . Using the microactuator  24  in this way to couple the head slider  20  to the flexible coupling  18  means that the head slider  20  moves in sympathy with changes in the gap  42  (the flexible coupling  18  being rigidly held relative to the head slider  20 ). Thus, reducing the size of the gap  42  by actuating the microactuator  24  causes the head slider  20  to move in the direction of A+. 
     EXAMPLE 3 
     FIG. 7 illustrates a slider-mounted microactuator  24  for attachment to a head slider  20  placed alongside it. (The flexible coupling  18  and the head slider  20  have been omitted for the sake of clarity). 
     FIG. 8 illustrates the mounting from the side. The C-shaped microactuator  24  is positioned with the gap  42  beside the head slider  20 . The first end face  36  of the first end  24  is glued to a projecting lug  100  which extends out of the gap  42  before engaging a leading edge  102  of the head slider  20 . An upper-surface region of the microactuator  24 , adjacent second end  38  is glued  94  to plate  104  which is part of the flexible coupling  18  (as before). Using the microactuator  24  in this way to couple the head slider  20  to the flexible coupling  18  means that the head slider moves in sympathy with changes in the dimensions of the gap  42 . Also, by mounting the microactuator  24  and head slider  20  side by side at the leading edge  102  of head slider  20  can help reduce stack height of the microactuator-slider assembly (compare with the piggy-back arrangement of Example 2).