Abstract:
Approaches to a rotary actuator assembly configured for use in a hard disk drive (HDD) include a voice coil interleaved between the pivot bearing and the actuator arm, providing a longer pivot-to-head dimension which reduces the radius of curvature of the arc in which the head slider travels over the disk for accessing portions of the disk. Reducing the arc radius of curvature reduces the maximum skew angles of the read-write head in association with the disk tracks. The width of the actuator arm can be widened to provide improved operating characteristics even in view of the longer pivot-to-head dimension.

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention relate generally to hard disk drives and more particularly to an actuator assembly for a hard disk drive read/write head. 
     BACKGROUND 
     A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator. 
     A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium. 
     Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present holy grails of hard disk drive design evolution, and has led to the necessary development and implementation of various means for reducing the disk area needed to record a bit of information. However, reducing the disk area needed to record a bit leads to corresponding challenges regarding the precision with which the read/write head can be positioned and maintained over the disk and the corresponding disk tracks to read and write smaller and smaller bits. 
     SUMMARY OF EMBODIMENTS OF THE INVENTION 
     Embodiments of the invention are directed towards a rotary actuator assembly configured for use in a hard disk drive (HDD), where the actuator assembly comprises an interleaved actuating portion that includes a distal end with which an actuator arm is coupled, a proximal end housing a pivot bearing, and a voice coil interleaved at the distal end between the pivot bearing and the actuator arm. Such a configuration is in contrast to typical actuator assemblies in which the pivot bearing is positioned between the voice coil and the actuator arm. 
     In comparison with typical actuator assemblies, an interleaved actuating portion according to embodiments provides for longer pivot-to-head and pivot-to-spindle dimensions which reduce the radius of curvature of the arc in which the head slider travels over the disk for accessing portions of the disk. Reducing the arc radius of curvature reduces the maximum skew angles of the read-write head in association with the disk tracks. Additionally, the width of the actuator arm can be widened to provide better operating characteristics of the actuator system in comparison with typical actuator systems having the pivot bearing between the voice coil and actuator arm, even in view of the longer pivot-to-head dimension of the described interleaved actuating portion. 
     Embodiments discussed in the Summary of Embodiments of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a plan view of a conventional hard disk drive (HDD); 
         FIG. 2  is a plan view of a conventional rotary actuator assembly; 
         FIG. 3  is a plan view of an interleaved rotary actuator assembly, according to an embodiment of the invention; and 
         FIG. 4  is a plan view of an HDD having an interleaved rotary actuator assembly, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Approaches to a hard disk drive (HDD) actuator assembly having an interleaved voice coil motor are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
     PHYSICAL DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION 
     Embodiments of the invention may be used in the context of a magnetic writer for a hard-disk drive (HDD). A plan view illustrating a conventional HDD  100  is shown in  FIG. 1 .  FIG. 1  illustrates the functional arrangement of components of the HDD including a slider  110   b  that includes a magnetic-reading/recording head  110   a . Collectively, slider  110   b  and head  110   a  may be referred to as a head slider. The HDD  100  includes at least one head gimbal assembly (HGA)  110  including the head slider, a lead suspension  110   c  attached to the head slider, and a load beam  110   d  attached to the lead suspension  110   c . The HDD  100  also includes at least one magnetic-recording media  120  rotatably mounted on a spindle  124  and a drive motor attached to the spindle  124  for rotating the media  120 . The head  110   a  includes a write element and a read element for respectively writing and reading information stored on the media  120  of the HDD  100 . The media  120  or a plurality (not shown) of disks may be affixed to the spindle  124  with a disk clamp  128 . 
     The HDD  100  further includes an arm  132  attached to the HGA  110 , a carriage  134 , a voice-coil motor (VCM) that includes an armature  136  including a voice coil  140  attached to the carriage  134 ; and a stator  144  including a voice-coil magnet. The armature  136  of the VCM is attached to the carriage  134  and is configured to move the arm  132  and the HGA  110  to access portions of the media  120  being mounted on a pivot-shaft  148  with an interposed pivot-bearing assembly  152 . In the case of an HDD having multiple disks, or platters as disks are sometimes referred to in the art, the carriage  134  is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. 
     With further reference to  FIG. 1 , electrical signals, for example, current to the voice coil  140  of the VCM, write signal to and read signal from the head  110   a , are provided by a flexible interconnect cable  156  (“flex cable”). Interconnection between the flex cable  156  and the head  110   a  may be provided by an arm-electronics (AE) module  160 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The AE  160  may be attached to the carriage  134  as shown. The flex cable  156  is coupled to an electrical-connector block  164 , which provides electrical communication through electrical feedthroughs provided by an HDD housing  168 . The HDD housing  168 , also referred to as a casting, depending upon whether the HDD housing is cast, in conjunction with an HDD cover provides a sealed, protective enclosure for the information storage components of the HDD  100 . 
     With further reference to  FIG. 1 , other electronic components, including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  140  of the VCM and the head  110   a  of the HGA  110 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  124  which is in turn transmitted to the media  120  that is affixed to the spindle  124  by the disk clamp  128 ; as a result, the media  120  spins in a direction  172 . The spinning media  120  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  110   b  rides so that the slider  110   b  flies above the surface of the media  120  without making contact with a thin magnetic-recording medium in which information is recorded. 
     The electrical signal provided to the voice coil  140  of the VCM enables the head  110   a  of the HGA  110  to access a track  176  on which information is recorded. Thus, the armature  136  of the VCM swings through an arc  180  which enables the HGA  110  attached to the armature  136  by the arm  132  to access various tracks on the media  120 . Information is stored on the media  120  in a plurality of stacked tracks arranged in sectors on the media  120 , for example, sector  184 . Correspondingly, each track is composed of a plurality of sectored track portions, for example, sectored track portion  188 . Each sectored track portion  188  is composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, information that identifies the track  176 , and error correction code information. In accessing the track  176 , the read element of the head  110   a  of the HGA  110  reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  140  of the VCM, enabling the head  110   a  to follow the track  176 . Upon finding the track  176  and identifying a particular sectored track portion  188 , the head  110   a  either reads data from the track  176  or writes data to the track  176  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
       FIG. 2  is a plan view of a conventional rotary actuator assembly  200 , including the HGA  110 .  FIG. 2  illustrates the functional arrangement of a head arm assembly (HAA) with respect to the HGA  110 . The HAA includes the arm  132  and HGA  110  including the slider  110   b  including the head  110   a . The HAA is attached at the arm  132  to the carriage  134 . As shown in  FIG. 2 , the armature  136  of the VCM is attached to the carriage  134  and the voice coil  140  is attached to the armature  136 . The AE  160  may be attached to the carriage  134  as shown. The carriage  134  is mounted on the pivot-shaft  148  with the interposed pivot-bearing assembly  152 . Note that conventionally the pivot is positioned between the voice coil  140  and the arm  132 , and that arm  132  has a maximum width, W2, and a pivot length (distance between pivot and head), PL2. 
     INTRODUCTION 
     In order to increase the storage density of HDDs, a reduction of the skew angle, which is the angle of the head slider relative to the disk track direction at a particular location on the disk, is desirable. Further, improvement in the position following performance, which is the ability of the head slider to maintain precise positioning along the track direction, is also desirable for realization of high storage densities. In order to reduce a skew angle, lengthening the distance between the head and the pivot is desirable. However, the control performance of an actuator generally falls as a result of lengthening the arm. 
     Actuator Assembly with Interleaved Voice Coil 
       FIG. 3  is a plan view of an interleaved rotary actuator assembly, according to an embodiment of the invention. Actuator assembly  300  comprises a head slider  302 , which includes a magnetic read/write head for reading data from and writing data to one or more magnetic recording disk. The head slider  302  is coupled to a flexure  304 , which is coupled to an actuator arm  306 . The actuator arm  306  is coupled to an actuating portion configured to move the head slider to access portions of the disk. The actuating portion has a distal end  312 , with which the actuator arm  306  is coupled, and a proximal end  314  which houses a pivot bearing  316 . The actuating portion further comprises a voice coil  318  positioned at the distal end  312 , between the pivot bearing  316  and the actuator arm  306 . The arm  306  of actuator assembly  300  is depicted as having a maximum width, W3, and a pivot length (distance between pivot and head), PL3. 
       FIG. 4  is a plan view of an HDD  400  having an interleaved rotary actuator assembly  300  ( FIG. 3 ), according to an embodiment of the invention. As discussed, it is noteworthy that the voice coil  318  is positioned between the pivot bearing  316  and the arm  306 , in contrast with conventional actuator assemblies such as rotary actuator assembly  200  ( FIG. 2 ), in which the pivot bearing  152  is positioned between the voice coil  140  and the arm  132 . Consequently, according to an embodiment, the pivot length PL3 of actuator assembly  300  is longer than the pivot length PL2 of conventional actuator assembly  200 . For example and according to an embodiment, an actuator assembly such as actuator assembly  300  is designed to have a pivot length PL3 of over 50 mm, compared with a pivot length PL2 of approximately 49 mm for a conventional actuator assembly  200  designed for the same HDD form factor. Further, and according to an embodiment, an actuator assembly such as actuator assembly  300  is designed to have a pivot length PL3 in a range of approximately 75-85 mm, significantly greater than what is achievable with a conventional actuator assembly  200  designed for the same HDD form factor. Thus, a longer pivot length PL3 allows for an installation of actuator assembly  300  in which the pivot is closer to the corner of the HDD and, therefore, farther from the disk (compare, e.g., HDD  400  of  FIG. 4  with conventional HDD  100  of  FIG. 1 ). 
       FIG. 4  depicts with a dashed circle generally where pivot bearing  152  would be located if actuator assembly  200  was installed in HDD  400  (see, e.g.,  FIG. 1  for the corresponding location of pivot bearing  152 ). The virtual location of pivot bearing  152  in conjunction with the pivot length PL2 of actuator assembly  200  would result in a disk access path radius of curvature R1 associated with actuator assembly  200 . By contrast, the location of pivot bearing  316  in conjunction with the pivot length PL3 of actuator assembly  300  provides for a disk access path radius of curvature R2 associated with actuator assembly  300 , where radius of curvature R2 is less than radius of curvature R1. As discussed and with further reference to  FIG. 4 , a longer pivot length PL3 allows for an installation of actuator assembly  300  in which the pivot is closer to the corner of the HDD and, therefore, farther from the disk, such as depicted by comparing spindle distance SD3 of actuator assembly  300  with spindle distance SD2 of actuator assembly  200 . For example and according to an embodiment, an actuator assembly such as actuator assembly  300  is designed to have a spindle distance SD3 of over 60 mm, compared with a spindle distance SD2 of approximately 56 mm for a conventional actuator assembly  200  designed for the same HDD form factor. Further, and according to an embodiment, an actuator assembly such as actuator assembly  300  is designed to have a spindle distance SD3 in a range of approximately 75-85 mm, significantly greater than what is achievable with a conventional actuator assembly  200  designed for the same HDD form factor. Therefore, an installation of actuator assembly  300  as depicted in  FIG. 4  can facilitate a flatter radius of curvature of the path of the head slider  302  over the disk, which provides for a reduced skew angle in comparison with a skew angle corresponding to the pivot length PL2 of actuator assembly  200 . For example, flying over the disk at the same track  176 , the skew angle corresponding with interleaved actuator assembly  300  would be less than the skew angle corresponding to conventional actuator assembly  200 . 
     Another design freedom that is enabled by the configuration corresponding to actuator assembly  300  is that the maximum arm width W3 corresponding to actuator assembly  300  ( FIG. 3 ) can be greater than the maximum arm width W2 corresponding to actuator assembly  200  ( FIG. 2 ). Implementing the pivot toward the corner of the HDD, as is enabled with actuator assembly  300 , provides for more clearance space between the actuator assembly  300  and the disk, thereby allowing for the greater maximum arm width W3. A wider arm provides for a more stable arm operationally and, therefore, the operational characteristics (e.g., the transfer function) of the actuator assembly  300  are better than the operational characteristics corresponding to a conventional actuator assembly  200 . For a non-limiting example, experimentation has shown that in the context of a conventional maximum arm width W2 equal to 13 mm, implementation of an interleaved rotary actuator assembly  300  enables a maximum arm width W3 equal to 21 mm, a non-trivial approximately 60% increase in maximum arm width. 
     In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.