Abstract:
Described herein is a read/write transducer for a hard disk drivewith dual actuation stage, comprising at least one hard disk and at least one suspension carrying the read/write transducer. The read/write transducer comprises a supporting body having a substantially parallelepipedal shape, a read/write head arranged on a front face of the supporting body, and a grating defined on one of the side faces of the supporting body during the process of manufacture of the read/write transducer. The grating enables measurement of the position of the read/write transducer with respect to the corresponding suspension in an optical way using a laser transmitter emitting and directing towards the grating a laser beam, and a laser receiver arranged to intercept the laser beam reflected by the grating and outputting a position signal on the basis of which it is possible to calculate, in a simple way, the position of the read/write transducer with respect to the corresponding suspension.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a read/write transducer for hard disk drives with dual actuation stage and to the manufacturing process thereof.  
           [0003]    2. Description of the Related Art  
           [0004]    As is known, hard disk drives are the media most widely used for storing data in personal computers; consequently they are produced in very large volumes and the maximum data storage density increases year by year.  
           [0005]    The structure of a known hard disk drive is shown in FIGS.  1 - 3 .  
           [0006]    The hard disk drive, designated as a whole by  1 , comprises a group of hard disks  2  rotating jointly with and parallel to each other around a rotation axis A and carried by a supporting structure  4  mounted on ball bearings (not shown) and actuated by a synchronous motor (not shown), generally known as “spindle motor.” 
           [0007]    The hard disk drive  1  further comprises a read/write device  6  for reading/writing the hard disks  2 , comprising a supporting structure generally known as “E-block”  8  because of its E-like shape in side view (see FIG. 2), which is angularly mobile around an oscillation axis B parallel to the rotation axis A of the hard disks  2  and is provided with a plurality of arms  10  orthogonal to the oscillation axis B and each carrying one or two suspensions  12 , each formed by a steel lamina cantilevered with respect to the corresponding arm  10 .  
           [0008]    At the end not fixed to the corresponding arm  10 , each suspension  12  carries a joint, generally known as “gimbal” or “flexure”  14 , also made of steel, holding in turn a read/write transducer generally known as “slider”  16  and arranged, in operating condition, facing onto a surface of a corresponding hard disk  2 , as shown in FIG. 2.  
           [0009]    As shown in greater detail in FIG. 3, each gimbal  14  is generally formed from the corresponding suspension  12  and is composed, for example, of a rectangular plate  14   a  cut around on three and a half sides starting from the suspension  12  itself and having a portion  14   b  connected to the suspension  12  and allowing flexure of the plate  14   a  under the weight of the slider  16 , which is therefore able to perform rolling and pitching movements in order to follow the surface of the corresponding hard disk  2 .  
           [0010]    Each slider  16  is formed by a supporting body  20  having a generally parallelepipedal shape with typical dimensions 1×1.2×0.3 mm, made of ceramic material, generally an alloy of aluminum, titanium and carbon (Al—Ti—C), and carrying, on its front face, a read/write head  22  (magneto/resistive and inductive) which constitutes the proper reading and writing device. Electrical bonding wires, not shown, extend from the read/write head  22  along the corresponding gimbal  14  and the corresponding suspension  12  to a signal processing device (also not shown) fixed to the mother board of the personal computer or other apparatus in which the hard disk drive is installed.  
           [0011]    In the hard disk drives  1  currently on the market, each of the sliders  16  is glued directly onto the corresponding gimbal  14  and the movement of the read/write device  6  across the hard disks  2  is achieved with a motor, generally known as “voice coil motor”  24  (FIG. 1), coupled to the E-block  8  to move it angularly around the oscillation axis B.  
           [0012]    After having been subjected to all the surface finishing operations and having been fitted on the E-block  8 , and before the final closing of the protective external casing in which the hard disk drive  1  is placed, control information is stored in each of the hard disks  2  in specific so-called pilot traces of specific so-called servo control sectors or servo sectors. During operation, this control information is then read by the sliders  16  and supplied to servo control devices (not shown) which process it to determine the position of the suspensions  12 , and therefore of the sliders  16  integral with them, with respect to the corresponding hard disks  2 , and to realize a closed loop control of the position of the sliders  16  so as to keep the reading heads  22  in an optimum reading position.  
           [0013]    The market demand for a constant increase of the data storage density of hard disk drives  1  leads to an increasingly closer packing of the traces of the hard disks  2  and so the intrinsically poor precision of the voice coil motor  24  does not provide sufficient guarantees for the execution of the initial operation of writing the control information in the pilot traces of the servo sectors of the hard disks  2 .  
           [0014]    To overcome this inconvenience, an external precision actuation device is currently used, generally known as “spin-stand”  26  (schematically illustrated in FIG. 1), which moves the E-block  8  with micrometric precision, and therefore also the sliders  16  on the corresponding hard disks  2 , by means of its own output control shaft  28  coupled to one of the suspensions  12  and provided with an optical encoder (not shown).  
           [0015]    Recently, however, to obtain more precise and finer control of the position of the slides  16  with respect to the corresponding hard disks  2 , it has been proposed to use a moving device with dual actuation stage, in which a first rougher actuation stage including the voice coil motor  24  which moves the assembly formed by the E-block  8 , the suspensions  12 , the gimbals  14  and the sliders  16  across the hard disks  2  during the track coarse search, while a second finer actuation stage includes a plurality of integrated microactuators  30  (one of which is shown in FIG. 3) each arranged between a corresponding slider  16  and a corresponding gimbal  14  and having the aim of carrying out a finer regulation of the position of the sliders  16  during the tracking.  
           [0016]    An example of an embodiment of a rotary electrostatic microactuator  30  is described in the European patent application number 98830269.1, filed May 5, 1998 in the name of the applicant.  
           [0017]    The introduction of a degree of freedom of movement between each slider  16  and the corresponding suspension  12  resulting from the introduction of a microactuator  30  means that, in order to be able to carry out the aforementioned initial operation of writing the control information in the pilot traces of the servo sectors of the hard disks  2  with the spin-stand  26 , it is necessary to know, not only the position of the suspensions  12  with respect to the corresponding hard disks  2 , but also the position of the sliders  16  with respect to the corresponding suspensions  12 .  
           [0018]    The determination of the position of a slider  16  with respect to the corresponding suspension  12  could, at least theoretically, be carried out indirectly by determining the position of the microactuator  30 , to which the slider  16  is restrained, with respect to the corresponding suspension  12 , on the basis of the driving signals supplied to the microactuator  30 , or by measuring the capacitive coupling existing between the rotor and the stator of the microactuator  30 , since this coupling is correlated to the position of the microactuator  30 .  
           [0019]    In practice, however, this solution is difficult to put into practice, as the precision of determination of the position of the slider  16  with respect to the suspension  12  which may be obtained with this solution has proven to be insufficient for the execution of the initial operation of writing the control information in the pilot traces of the servo sectors in high data storage density applications in which the distances between the traces of the hard disks  2  are extremely reduced.  
           [0020]    In fact, in the hard disk drives  1  with a dual actuation stage moving device of the type described above, the slider  16  is restrained to the corresponding microactuator  30  by gluing and generally the positioning of the slider  16  with respect to the microactuator  30  obtained with this type of connection presents a rather high degree of uncertainty, which has a significant influence on the precision of determination of the position of the slider  16  with respect to the suspension  12 , making it insufficient for applications with high data storage density.  
         BRIEF SUMMARY OF THE INVENTION  
         [0021]    An embodiment of the present invention provides a slider for a hard disk drive, a hard disk drive, a system for measuring the position of the slider, and a procedure for manufacturing said slider which allow the determination of the position of the slider with respect to the corresponding suspension with sufficient precision for any application with high data storage density.  
           [0022]    According to an embodiment of the present invention, a read/write transducer for a hard disk drive is provided.  
           [0023]    According to another embodiment of the present invention, a procedure for manufacturing a read/write transducer for a hard disk drive is further provided.  
           [0024]    According to a further embodiment of the present invention, a hard disk drive is moreover provided.  
           [0025]    Additionally, according to an embodiment of the present invention, a system for measuring the position of a read/write transducer for a hard disk drive is provided.  
           [0026]    A method of operation of a device according to an embodiment of the invention is also provided. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0027]    For a better understanding of the present invention, a preferred embodiment is now described, purely as an example without limitation, with reference to the enclosed drawings, in which:  
         [0028]    [0028]FIG. 1 is a top view of a known hard disk drive;  
         [0029]    [0029]FIG. 2 is an enlarged side view of some parts of the hard disk drive in FIG. 1;  
         [0030]    [0030]FIG. 3 is an exploded view of a micrometric actuation stage forming part of the hard disk drive in FIG. 1;  
         [0031]    [0031]FIG. 4 is a perspective view of a slider according to the present invention;  
         [0032]    FIGS.  5 - 7  show steps of a process for manufacturing the slider in FIG. 4;  
         [0033]    FIGS.  8 - 10  show steps of a different process for manufacturing the slider in FIG. 4;  
         [0034]    [0034]FIG. 11 shows a basic diagram for measuring the position of the slider in FIG. 4;  
         [0035]    [0035]FIG. 12 schematically shows an optical apparatus for measuring the position of the slider in FIG. 4; and  
         [0036]    [0036]FIG. 13 is a perspective view of a different embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]    [0037]FIG. 4 shows a slider, designated as a whole by  32 , according to the present invention. For clarity, parts indicated in FIGS.  4 - 13 , which are similar to those in FIGS.  1 - 3 , are indicated with the same reference numbers.  
         [0038]    According to an embodiment of the present invention, during the slider manufacturing process, on one of the four side faces, here indicated with  34 , of the supporting body, here indicated with  36 , of the slider  32 , a grating  38  is defined, which, as is known, is an optically detectable structure, periodic in reflection (transmission) and essentially formed by zones that reflect (transmit or refract) an incident electromagnetic radiation (light), alternating with zones that are non-reflective with respect to said incident electromagnetic radiation.  
         [0039]    In particular, in its most general form a grating is formed by a pattern of lines or slits preferably parallel to one another, having the same width and spaced at the same interval, and, when impinged by a light beam, it produces fringe effects, in particular it generates a spatially periodic light distribution which appears as a so-called fringe pattern.  
         [0040]    The structure and the optical properties of a grating are indeed widely known in the field of optical physics and are dealt with in many publications in the sectors, so they will not be analyzed any further hereinafter.  
         [0041]    The grating  38  is formed during the slider manufacturing process in the way schematically illustrated in FIGS.  5 - 7 , that is by initially depositing an oxide layer  40  on the side face  34  of the supporting body  36 , then defining the oxide layer  40  through a chemical etch using a resist mask  42 , later removed, reproducing the pattern of the grating  38 , in particular reproducing the arrangement of the reflecting zones and of the non-reflective zones that one wishes to obtain, and finally metallizing (layer  44 ) the oxide layer  40  thus defined.  
         [0042]    In particular, for the metallization of the oxide layer  40 , for example, an alloy of aluminum and chrome (Al—Cr) may be used or the same alloy (aluminum, titanium and carbon Al—Ti—C) with which the supporting body  36  of the slider  32  is made.  
         [0043]    The portions of the oxide layer  40  removed and not removed define a succession of crests and depressions alternating with one another. The metallized zones deposited at the removed portions of the oxide layer  40  define the non-reflective zones of the grating  38 , while the metallized zones deposited at the non removed portions of the oxide layer  40  define the reflecting zones of the grating  38 .  
         [0044]    Alternatively, as schematically illustrated in FIGS.  8 - 10 , the grating  38  could be realized without resorting to the deposition of the oxide layer  40 , but rather by defining directly, with a chemical etch, the side face  34  of the supporting body  36  of the slider  32  using a mask reproducing the pattern of the grating  38 , and then metallizing the supporting body  36  thus defined.  
         [0045]    The determination of the position of the slider  32  with respect to the corresponding suspension  12  may therefore be carried out using the basic scheme illustrated in FIG. 11, that is using a laser transmitter  46 , essentially composed of a laser light source, able to emit, and to direct towards the grating  38 , a laser beam, indicated with R 1 , and a laser receiver  48 , essentially composed of a suitably calibrated photodiode, arranged in such a way as to intercept the laser beam, indicated with R 2 , reflected by the grating  38  and outputting a position signal on the basis of which it is possible to calculate simply the position of the slider  32  with respect to the corresponding suspension  12  in an absolute Cartesian reference system external to the hard disk drive  1 .  
         [0046]    The choice of the metal material for metallizing used in the definition of the grating  38  depends on the wave length of the laser light beam used for measurement.  
         [0047]    [0047]FIG. 12 shows a more detailed diagram of a measuring apparatus applicable to the spin-stand  26  for determining the position of the slider  32  with respect to the corresponding suspension  12  during the aforementioned initial operation of writing the control information in the pilot traces of the servo sectors of the hard disks  2 .  
         [0048]    As shown in FIG. 12, the measuring apparatus, designated as a whole by  50 , comprises a laser light transmitting/receiving device  52  essentially formed by the aforementioned laser transmitter  46  and laser receiver  48 ; an optical fiber  54  optically coupled, at a first end  54   a , to the laser light transmitting/receiving device  52  and passed through, in use, by the emitted laser beam R 1  and by the reflected laser beam R 2 ; a supporting structure  56 , for example composed of an articulated arm, coupled to the output shaft  28  of the spin-stand  26  so as to be able to travel along a translation axis Z parallel to the oscillation axis B of the E-block  8  (orthogonal to the sheet) and onto which the second end  54   b  of the optical fiber  54  is fixed; an actuator  58 , composed essentially of a electric step motor, coupled to the output shaft  28  of the spin-stand  26  and to the supporting structure  56  to move it along the translation axis Z; and a collimator  60  carried by the supporting structure  56  and optically coupled to the second end  54   b  of the optical fiber  54  with its own symmetry axis orthogonal to the grating  38  of the slider  32 .  
         [0049]    The determination of the position of the slider  32  with respect to the corresponding suspension  12  is carried out in the way described above with reference to FIG. 10 and the position of the slider  32  with respect to the corresponding suspension  12  which may be calculated with the measuring apparatus  50  in FIG. 11 is referred in a corresponding Cartesian reference system integral with the suspension  12 .  
         [0050]    In particular, it is stressed that the possibility of movement of the supporting structure  56  of the optical fiber  54  along the translation axis Z makes it possible to measure the position of all the sliders  32  (generally 6-8) of the hard disk drive  1  using the same laser light transmitting/receiving device  50 .  
         [0051]    From an examination of the characteristics of the slider  32  made according to the present invention the advantages that may be obtained with it are clear.  
         [0052]    Firstly, the grating  38  may be formed on one of the side faces of the slider  32  in an extremely simple way during manufacturing of the slider  32  itself, as it requires only the definition of an oxide layer previously deposited on the side face of the slider  32  or the definition of the side face itself and its subsequent metallization.  
         [0053]    Moreover, the definition of a grating  38  directly on one of the side faces of the slider  32  allows measurement of the position of the slider  32  with respect to the corresponding suspension  12  using optical apparatuses which, as is known, present extremely high precision suitable for the execution of initial operation of writing the control information in the pilot traces of the servo sectors of the hard disks  2  in high data storage density applications in which the distances between the traces of the hard disks are extremely reduced.  
         [0054]    Moreover, being defined directly on one of the side faces of the slider  32  during the manufacturing process, the grating  38  does not constitute an added weight for the slider  32  and therefore it does not interfere in any way either with determining the characteristics of the slider  32 , of the corresponding suspension  12  and of the corresponding microactuator  30  (which consists essentially of determining the system oscillation modes and, depending on these, of the system mechanical properties, such as the torsional stiffness) nor with the closed loop control of the position of the read/write head  22 , contrary to what would occur on the other hand if macroscopic optical systems were used, such as lenses, prisms, etc., glued onto the slider  32 , and which, due to the extremely light weight of the slider  32  (1.6 mg) would represent additional masses comparable with the weight of the slider  32  itself and would therefore make it more difficult to establish both the closed loop control of the position of the read/write head  22 , and the characteristics of the slider  32 , of the corresponding suspension  12  and of the corresponding microactuator  30 .  
         [0055]    Lastly it is clear that modifications and variations may be made to the grating  28 , to the slider  32  and to the manufacturing process thereof herein described and illustrated without departing from the scope of the present invention, as defined in the enclosed claims.  
         [0056]    For example, the grating  38  could be produced on the supporting body  36  of the slider  32  in positions different from the one described and illustrated, in particular on different faces from the one indicated.  
         [0057]    Moreover, a grating  38  according to the present invention could also be used advantageously in hard disk drives with a single actuation stage in which the slider is glued onto the gimbal. In fact, the grating may be used on this type of hard disk drive both during the writing of the control information in the servo sectors to carry out a further measurement of the position of the slider  32  with respect to the suspension in addition to the one already carried out by the optical encoder of the spin-stand, and during the normal operation of the hard disk drive to determine with precision, at any time, the exact position of the slider  32  with respect to the corresponding suspension  12 .  
         [0058]    Moreover, when used in hard disk drives with a single actuation stage, the grating  38  could be provided on other parts of the hard disk drives apart from the slider  32 , in particular it could be provided on the suspensions  12 .  
         [0059]    [0059]FIG. 13 shows one of the possible positions of the grating  38  on a suspension  12 . In particular, the suspension  12  shown in FIG. 13 is of the type provided with so-called side rails, indicated with  62 , and the grating  38  is positioned on the side rails  62 .  
         [0060]    Another possibility, not illustrated, could be that of providing the grating  38  on the gimbal  14 ; this positioning, however, is rather difficult to realize due to the small thickness of the gimbal  14  itself (a few tens of micron).  
         [0061]    It should be noted that while this text makes reference to a read/write head, it is known in the industry that read only and write only heads may also be employed, and that, according to the principles of the invention, the exact nature of the transducer is not a limiting factor.  
         [0062]    From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.