Abstract:
A track following control apparatus and method for a hard disk drive (HDD) is disclosed and includes an estimator receiving a position error signal from a HDA and generating estimated state information for a magnetic head in response to the position error signal, and a controller receiving the estimated state information and generating a control signal controlling operation of the HAD, wherein the estimator and controller are variably configured according to a write mode or a read mode.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a track following control method and apparatus for a hard disk drive (HDD). More particularly, the invention relates to a track following control method in which estimators and controllers according to operation modes of an HDD separately exist and an apparatus suitable for performing the track following control method. 
         [0003]    This application claims the benefit of Korean Patent Application No. 10-2006-0059244, filed on Jun. 29, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
         [0004]    2. Description of the Related Art 
         [0005]    Information is stored on a hard disk drive (HDD) within a concentric arrangement of data storage tracks. The magnetic read/write head (hereafter “head”) of the HDD must be aligned over a specified target track in order to perform read/write operations. Thus, read/write operations require a certain degree of accuracy in the positioning of the head throughout read/write operations. A track following control apparatus is commonly used within the HDD to maintain proper head positioning. 
         [0006]    Figure (FIG.)  1  is a general block diagram of a conventional track following control apparatus. The illustrated track following control apparatus includes an estimator  102  which estimates a position, velocity, and/or acceleration for the head based on a position error signal derived from a servo signal recorded at defined intervals on the disk. (The position velocity and/or acceleration are singularly or collectively referred to hereafter as “state information”. The track following control apparatus also includes a controller  104  generating a control signal that drives the head in accordance with the estimated state information obtained from estimator  102 . The control signal provided by controller  104  is applied to a head disk assembly (HDA)  106  which mechanically positions the head. 
         [0007]      FIG. 2  is a conceptual block diagram illustrating a mathematical model that describes the operation of the conventional track following control apparatus illustrated in  FIG. 1 . 
         [0008]    Referring collectively to  FIGS. 1 and 2 , estimator  102  is assumed to output estimation values x1h, x2h, and x3h respectively indicating the estimated state information (e.g., position, velocity, and acceleration) for the head. The estimation values x1h, x2h, and x3h may be obtained using the following well known equations: 
         [0000]        x 1 h=x 1 b+L 1*estimate, 
         [0000]        x 2 h=x 2 b+L 2*estimate, 
         [0000]        x 3 h=x 3 b+L 3*estimate. 
         [0009]    Controller  104  may be implemented using amplifiers that respectively multiply the estimation values x1h and x2h by gain factors K 1  and K 2 . Following gain factor multiplication, estimation values x1h and x2h are applied to a first adder. Estimation value x3h is applied to second adder with a unity gain factor along with the output of the first adder. The output of the second adder is applied to HAD  106  as the control signal. 
         [0010]    However, this straight forward approach to implementing a track following control apparatus may be complicated by certain emerging HDD designs. For example, the greatly increased recording density of contemporary disks with HDDs often motivates the use of separate read and write heads. Within this configuration, write heads are commonly wider than read heads in order to provide improved write operation performance. This physical size difference between read and write heads necessitates the use of a different (e.g., more strict) positioning tolerance for the write head. In addition, read operation failures are typically considered less critical than write operation failures, because it is relatively easy to “retry” a failed read operation. In contrast, a significant positioning error for a write head during a write operation may result in an overwrite of data stored in adjacent track. Thus, a relatively strict positioning tolerance for a write head during a write operation is mandated. 
         [0011]    As a result of the foregoing considerations, the tracking control implemented by an HDD controller is typically designed in relation to the write operation. The resulting tracking tolerance is also applied by the HDD controller to read operations, 
         [0012]    Unfortunately, as track densities have continued to increase, the characteristics (e.g., the detected amplitude) of the position error signal has become a limiting factor in the design and implementation of track following control apparatuses within emerging HDDs. That is, increased track densities result in narrower track widths. Narrower track widths yield a narrower recording width for the servo signal from which the position error signal is derived. That is, a narrower recording width for the servo signal results in a position error signal having reduced (and therefore less easily detected) amplitude. As a result, the operating margin for the constituent track following control apparatus decreases with the decrease in the amplitude of the position error signal. This reduced operating margin affords less protection from disturbances within operation of the HDD. 
         [0013]    However, since the tolerance for positioning errors during read operations is greater than that for write operations, read operations are generally less susceptible to the system design limitations cause by the reduced amplitude of the position error signal. However, conventional track following control apparatuses are designed with the same operating characteristics for both read and write operations. So, read operation tend to suffer under the same positioning error tolerances imposed by write operations. 
       SUMMARY OF THE INVENTION 
       [0014]    Embodiments of the invention provide a track following control method and apparatus having different operating characteristics for read and write operations with a hard disk drive (HOD). 
         [0015]    In one embodiment, the invention provides a method implementing track following control in a hard disk drive (HDD) operating in a write mode or a read mode, the HDD comprising; an estimator providing estimated state information for a head, and a controller controlling operation of a head disk assembly (HDA) moving the head in response to the estimated state information and generating a corresponding position error signal, the method comprising; selectively configuring the estimator and controller in accordance with the write mode or the read mode, and performing track following control using the selectively configured estimator and controller. 
         [0016]    In the related aspect, the method may further comprise; receiving a write command in the HDD indicating the write mode and in response to the write command selecting a write mode estimator and a write mode controller for operation. By operation of the write mode estimator at least one gain constant is applied to a signal derived from the position error signal received from the HDA to generate the estimated state information. By operation of the write mode controller, at least one gain constant is applied to the estimated state information to generate a control signal controlling movement of the head by the HDA during the write mode. 
         [0017]    In another related aspect, the method may further comprise; receiving a read command in the HDD indicating the read mode, and in response to the read command selecting a read mode estimator and a read mode controller for operation. By operation of the read mode estimator, at least one gain constant is applied to a signal derived from the position error signal received from the HDA to generate the estimated state information. By operation of the read mode controller, at least one gain constant is applied to the estimated state information to generate a control signal controlling movement of the head by the HAD during the read mode. 
         [0018]    In another aspect, the invention provides a track following control apparatus for a hard disk drive (HDD) comprising a head disk assembly (HDA) moving a magnetic head over a disk, the track following control apparatus comprising; an estimator receiving a position error signal from the HDA and generating estimated state information for the magnetic head in response to the position error signal, and a controller receiving the estimated state information and generating a control signal controlling operation of the HAD, wherein the estimator and controller are variably configured in a write mode and a read mode. 
         [0019]    In one related aspect, the estimator may comprise; a write mode estimator applying a first estimator gain constant to the position error signal to generate first estimated state information, and a read mode estimator applying a second estimator gain constant to the position error signal to generate second estimated state information, wherein the first and second estimator gain constants are different. 
         [0020]    In another related aspect, the controller comprises; a write mode controller applying a first controller gain constant to the first estimated state information to generate a control signal controlling operation of the HAD, and a read mode controller applying a second controller gain constant to the second estimated state information to generate a control signal controlling operation of the HAD, wherein the first and second controller gain constants are different. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Embodiments of the present invention will be described with reference to the attached drawings in which: 
           [0022]      FIG. 1  is a block diagram of a conventional track following control apparatus; 
           [0023]      FIG. 2  is a block diagram illustrating a mathematical model of the conventional track following control apparatus illustrated in  FIG. 1 ; 
           [0024]      FIG. 3  is a block diagram of a track following control apparatus for a hard disk drive (HDD) according to an embodiment of the present invention; 
           [0025]      FIG. 4  is a graph illustrating gain/frequency characteristics of the track following control apparatus illustrated in  FIG. 3 ; 
           [0026]      FIG. 5  is a schematic plan view of a head disk assembly (HDA) of an HDD to which the present invention is applied; and 
           [0027]      FIG. 6  is a block diagram of a control system for an HDD to which the present invention is applied. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    A track following control method and apparatus according to an embodiment of the present invention independently operate constituent estimator(s) and/or controller(s) in accordance with read and write operations. Thus, different track following operations may be selectively applied within a hard disk drive (HDD) using variably controlled (e.g., configured) estimator(s) and/or controller(s), where such variable control (configuration) is performed in relation to a read mode of operation and a write mode of operation. 
         [0029]    In one embodiment of the invention, the estimator(s) and/or controller(s) within the HDD may be conventionally configured and operated during write operations. That is, a write head may be conventionally controlled in its track positioning during write operations in view of a defined positioning tolerance. This defined positioning tolerance will take into account, as needed, the expected amplitude of a position error signal (PES) provided by the disk of the HDD. 
         [0030]    However, estimator(s) and/or controller(s) within the HDD may be differently configured in embodiments of the invention during read operations. That is, despite the strict positioning tolerance applied to the write head during write operations, the read head may be positioned with a reduced tolerance, thereby allowing faster read operations and reducing constraints on the read operation of the HDD. As a result, read operations will enjoy reduced susceptibility to operating disturbances even though the amplitude of the constituent PES is reduced. 
         [0031]    In the description that follows, it is assumed that the amplitude margin provided by a PES is relatively small during write operations and relatively large during read operations. Nonetheless, a track following control method and apparatus according to an embodiment of the invention may independently optimize track following operations during both read and write operations by selectively configuring an estimator and controller suitable for the operation being performed. 
         [0032]      FIG. 3  is a block diagram of a track following control apparatus for an HDD according to an embodiment of the present invention. Within this illustrated embodiment, a write estimator is provided with three (3) gain constants L 1 , L 2 , and L 3  suitable for write operations, and a read estimator is provided with three (3) gain constants L 1 , L 2 , and L 3  suitable for read operations. Further, a write controller is provided with two (2) gain constants K 1  and K 2  suitable for write operations, and a read controller is provided with two (2) gain constants K 1  and K 2  suitable for read operations. 
         [0033]    Referring to  FIG. 3 , the track following control apparatus comprises a write mode track following controller  302 , a read mode track following controller  304 , and a selector  306 . Write mode track following controller  302  and read mode track following controller  304  are designed to be selectively configured for operation during a write mode operation and a read mode of operation within the HDD, respectively. 
         [0034]    Write mode track following controller  302  includes a write mode estimator  302 A and a write mode controller  302 B, read mode track following controller  304  includes a read mode estimator  304 A and a read mode controller  304 B, and selector  306  includes a first selector  306 A and a second selector  306 B. 
         [0035]    First selector  306 A selects either write mode estimator  302 A or read mode estimator  304 A according to the operating mode (read/write) of the HDD. Second selector  306 B selects either write mode controller  302 B or read mode controller  304 B according to the operating mode of the HDD. 
         [0036]    Referring now to  FIGS. 2 and 3 , write mode estimator  302 A provides gain constants L 1 , L 2 , and L 3  suitable for write operations within the HDD, and read mode estimator  304 A provides gain constants L 1 , L 2 , and L 3  suitable for read operations with the HDD. (In this illustrative context, the terms L 1 , L 2 , and L 3  are used to denote different gain constants within each mode of operation. Thus, L 1  in write mode may not be the same value as I1 in the read mode). 
         [0037]    Similarly, write mode controller  302 B provides gain constants K 1  and K 2  suitable for write operations in the HDD, and read mode controller  304 B provides gain constants K 1  and K 2  suitable for read operations in the HDD. 
         [0038]      FIG. 4  is a graph illustrating gain/frequency characteristics for an exemplary track following control apparatus, such as the one illustrated in  FIG. 3 . In  FIG. 4 , reference numeral  402  denotes a gain/frequency characteristic for write mode track following controller  302 , and reference numeral  404  denotes a gain/frequency characteristic for read mode track following controller  304 . 
         [0039]    Referring to  FIG. 4 , in a frequency region greater than or equal to a defined crossover frequency, the gain of write mode track following controller  302  is smaller than the gain of read mode track following controller  304  However, in a frequency region less than the crossover frequency, the gain of write mode track following controller  302  is larger than the gain of read mode track following controller  304 . 
         [0040]    Considering the fact that most disturbances occur at a frequency less than 1 KHz and assuming that the crossover frequency is defined as 1 KHz, when a disturbance occurs, write mode track following controller  302  is less susceptible to the typical disturbance than read mode track following controller  304 . 
         [0041]    However, as described above, since the amplitude margin of the PES is relatively large in the read mode, even if the effect of the disturbance in read mode is larger than that in the write mode, the track following control apparatus illustrated in  FIG. 3  can sufficiently deal with the effect of the disturbance. 
         [0042]    In  FIG. 4 , the gain/frequency characteristic curves  402  and  404  have a comb pattern in the frequency region less than the crossover frequency in order to deal with repetitive disturbance. Since a repetitive disturbance typically appears as a series of harmonics, the gain/frequency characteristic of the track following control apparatus for dealing with the repetitive disturbance is designed to deal with a series of harmonics. That is, in the comb pattern gain/frequency characteristics of curves  402  and  404 , each comb tooth portion is designed to correspond with a harmonic component of the repetitive disturbance. 
         [0043]    Although write mode track following controller  302  and read mode track following controller  304  are illustrated in the embodiment of  FIG. 3  as having separate physical implementations, a single physical controller, or even a software routine running on a general (or system) controller may be used to implement these elements. Thus, write mode track following controller  302  and read mode track following controller  304  according to an embodiment of the invention may be implemented using various programs having different operational parameters, (i.e., gain constants). These parameters may be stored in memory associated with the HDD and selectively used according to the operational mode of the HDD. 
         [0044]      FIG. 5  is a schematic plan view showing a head disk assembly (HDA)  10  of an HDD to which the present invention may be applied. 
         [0045]    Referring to  FIG. 5 , HDA  10  includes at least one disk  12  rotated by a spindle motor  14 . HDA  10  also includes a magnetic head  16  floating above the surface of disk  12 . 
         [0046]    Head  16  is adapted to read data from or write data to rotating disk  12  by sensing a magnetic field from the surface of disk  12  or magnetizing the surface of disk  12 , respectively. Typically, head  16  is mounted to face the surface of the disk  12 . Though a single head  16  is illustrated, it may include a write head for magnetizing disk  12  and a separate read head sensing the magnetic field from disk  12 . The read head may be implemented using a magneto-resistive (MR) component. 
         [0047]    Head  16  is mounted on a slider  20 . Slider  20  generates an air bearing between head  16  and the surface of disk  12 . Slider  20  is connected to a head stack assembly (HSA)  22 . HSA  22  is attached to an actuator arm  24  associated with a voice coil  26 . Voice coil  26  is located adjacent to a magnetic assembly  28  to implement a voice coil motor (VCM)  30 . Electrical current supplied to voice coil  26  generates torque which rotates actuator arm  24  around a bearing assembly  32 . The rotation of actuator arm  24  moves head  16  across the surface of disk  12  containing concentric tracks  34 . Defined sectors along each track  34  store servo information and data. 
         [0048]      FIG. 6  is a block diagram of a control system for an HDD to which the present invention may be applied. Referring to  FIG. 6 , the HDD includes disk  12 , head  16 , a pre-amplifier  210 , a read/write (R/W) channel  220 , a buffer  230 , a controller  240 , a memory  250 , and a host interface  260 . 
         [0049]    Pre-amplifier  210  and R/W channel  220  may be implemented in a single circuit referred to as RAN circuit. 
         [0050]    Memory  250  stores software programs for controlling the HDD. Memory  250  may be implemented using flash memory or some other nonvolatile memory. Memory  250  may be used to store programs implementing the track following control apparatus illustrated in  FIG. 3 . 
         [0051]    During a read mode, the HDD amplifies an electrical signal sensed from disk  12  by head  16  in pre-amplifier  210  so as to be easily used for signal processing. R/W channel  220  encodes the amplified analog signal in the form of a digital signal, which can be read by a host device (not shown), converts the digital signal into stream data, temporarily stores the stream data in buffer  230 , and transmits the stored stream data to the host device via host interface  260 . 
         [0052]    During a write mode, the HDD receives data from the host device via host interface  260 , temporarily stores the received data in buffer  230 , sequentially outputs the data stored in buffer  230 , converts the output data into a binary data stream suitable for a write channel using RAN channel  220 , and records the binary data stream on disk  12  through head  16  using a write current amplified by pre-amplifier  210 . 
         [0053]    Controller  240  analyzes a command received from the host device through host interface  260  and performs control corresponding to the analysis result. If a write command is input from the host device, controller  240  writes data in data sectors existing between servo sectors while following a track by referring to servo information recorded in the servo sectors. 
         [0054]    The present invention can be implemented as a method, an apparatus, and a system. When the present invention is implemented in software, its various component elements are code segments that execute necessary operations. Programs or code segments can be stored in processor readable media and can be transmitted via a computer data signal that is combined with a carrier wave in a transmission medium or in a communication network. The processor readable medium can be any medium that can store or transmit data. Examples of the processor readable medium include electronic circuits, semiconductor memory devices, ROMs, flash memories, erasable ROMs (EROMs), floppy disks, optical disks, hard disks, optical fibers, radio frequency (RF) networks, etc. The computer data signal can be any signal that can be transmitted via transmission media, such as electronic network channels, optical fibers, air, an electronic fields RF networks, etc. 
         [0055]    As described above, according to the present invention, a track following control method can optimize a track following operation in each mode by respectively using estimators and controllers suitable for a write mode and a read mode. 
         [0056]    A track following control apparatus can improve track following performance against disturbances by selectively using proper operational parameters according to an operation mode of an HDD. 
         [0057]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the scope of the present invention as defined by the following claims.