Abstract:
Apparatus and method for controlling a fly height of a transducer adjacent a recording surface by adjusting a write voltage magnitude. In accordance with some embodiments, a write voltage with an initial magnitude is applied to a transducer. A write voltage change interval and a write voltage change amount are selected. The magnitude of the applied write voltage is thereafter successively reduced by the write voltage change amount over each of a plurality of successive write voltage change intervals.

Description:
RELATED APPLICATIONS 
       [0001]    The present application makes a claim of foreign priority under 35 U.S.C. §119(a) to Korean Patent Application No. 10-2011-0065077 filed Jun. 30, 2011. 
       BACKGROUND 
       [0002]    A hard disk drive is a memory device, including an electronic device and a mechanic device and records, which changes a digital electronic pulse into a permanent magnetic field to record and reproduce data. Since a hard disk drive can access a large amount of data at a high speed, it is widely used as an auxiliary memory device, or the like, of a computer system. 
         [0003]    As a capacity of a hard disk drive has increased, the size of a read/write sensor of a magnetic head is reduced and a flying height (FH) of a magnetic head tends to be gradually lowered. 
         [0004]    Namely, in order to manufacture a high capacity hard disk drive, when a high TPI Tracks/inch) or BPI (Bits/inch) is implemented, the width of tracks is reduced. When the width of tracks is reduced, the strength of a magnetic field weakens, so when the flying height rises, it s difficult to detect a magnetic field to result in a failure of a smooth operation of the hard disk drive. 
         [0005]    For these reasons, research into a method for effectively reducing a spacing loss between a disk and a magnetic head has been actively conducted. Namely, a method for reducing a flying height of a magnetic head with respect to a disk is studied as a condition precedent for maximizing read/write performance with respect to a magnetic head. 
         [0006]    In order to actively adjust a flying height of a magnetic head with respect to a disk, first, a flying height of a magnetic head should be estimated. In order to estimate a flying height of a magnetic head, a method for controlling a protrusion of a magnetic head by using a heater sensor within a slider has been adopted. This method has been an effective and useful solution for adjusting a required flying height. 
         [0007]    In the case of this method, a certain voltage (an FOD (Flying On Demand) voltage) is applied to a heater coil installed in a magnetic head to drive a hard disk drive, and while the hard disk drive is being operated, a pole tip, i.e., an end portion, of the magnetic head is thermally expanded to reduce a flying height of the magnetic head, and here, the flying height is estimated by using the reduction characteristics of the flying height of the magnetic head. This technique is called FOD. 
         [0008]    Employing FOD, in the general related art, the FOD voltage of a magnetic head is gradually increased to be applied, and an applied voltage when the pole top of the magnetic head is in contact with a flat surface of a disk is measured as a maximum FOD voltage. Substantially, an FOD voltage of an appropriate level lower than the maximum FOD voltage was estimated and uniformly applied to the magnetic head. 
         [0009]    However, in actuality, the flying height of a magnetic head is not uniform and each expansion degree of FOD varies, considerably making it difficult to apply FOD in the foregoing manner. 
         [0010]    In particular, when the FOD voltage is uniformly applied to the magnetic head, if the flying height of the magnetic head is excessively lowered, a so-called HDI (Head Disk Interface) may occur such that physical impact occurs between the magnetic head and the disk while the hard disk drive is being operated. Conversely, when the flying height of the magnetic head is too high or when a thermally expanded degree of the pole tip, an end portion of the magnetic head, is not protruded by a desired level, it may be difficult to secure an actually desired gap between the magnetic head and the disk. 
         [0011]    Also, there are various methods for detecting how much a gap between a magnetic head and a disk can be narrowed in applying a certain voltage and to what extent an FOD voltage can be applied, in order to determine an appropriate FOD voltage. The FOD voltage may greatly vary according to an RPM of spindle motor with a disk mounted thereon or an external environment, and repeatability thereof is not good, so in order to solve this problem, various methods have been proposed to date. 
       SUMMARY 
       [0012]    Various embodiments of the present disclosure are generally directed to controlling a fly height of a transducer adjacent a recording surface by adjusting a write voltage magnitude. 
         [0013]    In accordance with some embodiments, a write voltage with an initial magnitude is applied to a transducer. A write voltage change interval and a write voltage change amount are selected. The magnitude of the applied write voltage is thereafter successively reduced by the write voltage change amount over each of a plurality of successive write voltage change intervals. 
         [0014]    Other features and advantages of various embodiments will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an exploded perspective view of a data storage device in accordance with an embodiment of the present disclosure. 
           [0016]      FIG. 2  is a schematic block diagram of the device of  FIG. 1  in accordance with some embodiments. 
           [0017]      FIG. 3  is a block diagram showing a portion of a driving circuit of  FIG. 2 . 
           [0018]      FIG. 4  is a signal diagram showing signals for controlling a flying height of a magnetic head according to some embodiments. 
           [0019]      FIG. 5  is a flow chart illustrating a fly height control (FHC) method in accordance with some embodiments. 
           [0020]      FIG. 6  is a block diagram or a computer system including a hard disk drive (HDD) and a memory device according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Particular structural or functional descriptions of embodiments according to the present disclosure are merely illustrative, and the subject matter of the disclosure may be implemented in various forms and is not limited to the embodiments described herein. 
         [0022]      FIG. 1  is an exploded perspective view of a data storage device according to some embodiments of the present disclosure. The exemplary device is characterized as a hard disk drive  10  and may include a base  20 , a cover  30  shielding an upper opening of the base  20 , and a printed circuit board assembly (PCBA) coupled to a lower portion of the base  20 . 
         [0023]    The base includes a plurality of internal components related to reading and writing information mounted thereon. Namely, at least one disk  22  for recording and storing data, a spindle motor  23  provided in a central region of the disk  22  to rotate the disk  22 , a head stack assembly  24  relatively n zing toward the disk  22 . and the like. 
         [0024]    The disk  22  has a discus-like shape. The disk  22  is an element in which data is recorded and stored. A plurality of disks  22  may be provided. A circular hole may be formed at the center of the disk  22 , for a connection with a shaft of the spindle motor  23 . The disk  22  is divided into a plurality tracks which are concentric based on the center of the disk. One track is divided into a plurality of sectors. The tracks on the disk  22  may be divided by zone, each being an aggregation of a plurality of tracks. 
         [0025]    The disks  22  may include a plurality of layers. A smoothing layer, the uppermost layer, of the disk  22  may prevent a surface abrasion of the disk  22 . A protective layer is a layer for protecting a magnetic layer  14 . A touchdown sensing layer may sense a touchdown point of the magnetic head  25 . The magnetic layer may be a layer magnetized in a vertical direction such that data is stored, and a soft under layer providing a path of a magnetic field in a horizontal direction to allow the magnetic layer to be smoothly magnetized up and down. An interlayer is provided to easily form the magnetic layer on the soft under layer, and a substrate, as a basic layer of the disk  22 , may be made of hard glass or metal. 
         [0026]    The spindle motor  23  may rotatably drive the disk  22  upon receiving a driving current. Rotation angular velocities of the spindle motor  23  include 3,600 rpm, 5400 rpm, 7200 rpm, 10000 rpm, or other suitable velocities, 
         [0027]    In order to the spindle motor  23  to drive the disk  22 , an axial portion (not shown) of the spindle motor  23  should be fixedly connected with the disk  22 . Thus, a spindle motor hub may be provided. The spindle motor hub is coupled to an axial portion of the spindle motor  23 , and here, the spindle motor may be coupled to the axial portion of the spindle motor  23  in a state in which an outer surface of the spindle motor hub and a circular hole formed at the center of the disk  22  are in contact with each other. 
         [0028]    The head stack assembly  24  includes a magnetic head (transducer)  25  for recording data to a disk  22  or reproducing data from the disk  22 , and an actuator  26  flying the magnetic head  25  to allow the magnetic head  25  to access data on the disk. 
         [0029]    The magnetic head  25  may detect magnetic field formed on a surface of the disk  22  to reproduce data from the disk  22  or magnetize the surface of the disk  22  to record data to the disk  22 . A plurality of magnetic heads  25  may be provided to correspond to the number of record faces of the disk  22 . 
         [0030]    The magnetic head  25  may be installed at a front end of a head gimbal  29  extendedly connected to the actuator  26 , and when the plurality of disks  22  are rotated at a high speed, the magnetic head  25  is lifted according to an air current on the surface of the disk  22  and flies while maintaining an interval by a flying height (FH) with respect to the surface of the disk  22 . 
         [0031]    The flying height (FH) may be different for each magnetic head  25  according to physical properties of the respective magnetic heads  25 . Even in case of the same magnetic head  25 , the flying height may differ according to in which zone of the disk  22  the magnetic head  25  is positioned. This is because a linear velocity of each zone affecting levitation force of the magnetic head  25  is faster toward an outer zone. A coil may be installed in a pole tip of the magnetic head  25 . The coil generates heat upon receiving an FOD voltage. Namely, the flying height may be changed by thermally expanding the pole tip of the magnetic head  25  by changing the FOD voltage. 
         [0032]    The actuator  26  may be installed to be rotatable with respect to the disk  22  based on a pivot shaft  26   a.  Namely, when the actuator  26  is moved horizontally according to an operation of a voice coil motor (VCM)  28 , the magnetic head  25  installed at the other end moves in a radial direction on the disk  22  to write or read data to and from the track on the disk  22 . 
         [0033]    The voice coil motor  28  may rotatably drive the actuator  26  based on the pivot shaft  26   a.  The voice coil motor  28  may rotate the actuator  26  in a direction following Fleming&#39;s left-hand rule according to electromagnetic force generated according to an interaction between a magnetic force line generated by a magnet and a current flowing through a voice coil. 
         [0034]    Also, the voice coil motor  28  may be replaced by a stepper motor which rotatably drives the actuator  26  by certain angle each time according to an input signal. Here, the use of the voice coil motor  28  has advantages in that it is resistant to heat, is not necessarily formatted periodically, and has excellent reliability. 
         [0035]    The PCBA  40  includes a PCH  41  on which a plurality of circuit components are mounted and a plug  45  coupled to one side of the PCH  41 . A controller  42  handling various controlling operations of the hard disk drive  10  is provided as the plurality of circuit components on a surface of the PCB  41 . Although not shown, a memory storing various data and tables may be positioned in the vicinity of the controller  42 . 
         [0036]      FIG. 2  is a schematic block diagram of a hard disk drive driving circuit according to an embodiment of the present disclosure. 
         [0037]    The hard disk drive  10  may further include a pre-amplifier (pre-amp)  50 , a read/write (R/W) channel  4 , a host interface (I/F)  5 , a VCM driving unit (drvr)  2 , an SPM driving unit (drvr)  6 , and a controller  42  controlling these elements. 
         [0038]    The pre-amplifier  50  may amplify a data signal reproduced by the magnetic head  25  from the disk  22 . The pre-amplifier  50  may amplify a record current converted by the read/write channel  4  and record the same on the disk  22 . Also, the pre-amplifier  50  may control the controller  42  to supply an FOD voltage to the coil installed in the pole tip of the magnetic head  25 . The pre-amplifier  50  according to an embodiment of the present disclosure will be described in detail with reference to  FIG. 3 . 
         [0039]    The read/write channel  4  may convert the signal amplified by the pre-amplifier  50  into a digital signal and transmit the converted digital signal to the host device through the host interface  5 . The read/write channel  4  may receive data input by the user through the host interface  5 , convert the received data into a binary data stream that can be easily written, and input the same to the pre-amplifier  50 . 
         [0040]    Namely, the read/write channel  4  converts a signal amplified by the pre-amplifier  50  after being reproduced from the disk  22  by the magnetic head  25  into a digital signal in a data read mode and input the converted digital signal to the controller  42 . The read/write channel  4  may receive a user input data received by the host interface  5  in a data write mode through the controller  42 , convert the received data into a binary data stream that can be easily written, and output the same to the pre-amplifier  50 . 
         [0041]    The host device is used to have a meaning generally designating a device that generally controls and operates the entire computer including a hard disk drive  10  such as a CPU of a computer or an I/O controller. 
         [0042]    The host interface  5  may transmit the data which has been converted into a digital signal to the host device, or receive the user input data from the host device and output the same to the read/write channel  4  through the controller  42 . 
         [0043]    The VCM driving unit  2  may adjust an amount of a current applied to the voice coil motor  28  upon receiving a control signal from the controller  42 . 
         [0044]    The SPM driving unit  6  may adjust an amount of a current applied to the spindle motor  23  upon receiving a control signal of the controller  42 . 
         [0045]    In the data write mode, the controller  42  may receive user input data input from the host device through the host interface  5  and output the received data to the read/write channel  4 . In the data read mode, when the read/write channel  4  converts the data signal amplified by the pre-amplifier  50  into a digital signal, the controller  42  receives the converted digital signal and outputs the same to the host interface  5 . 
         [0046]    Also, the controller  42  inputs a voice coil motor control signal to the VCM driving unit  2  to control driving of the voice coil motor  28 , and inputs a spindle motor control signal to the SPM driving unit  60  to control driving of the spindle motor 
         [0047]    Also, the controller  42  may input an FOD voltage control signal to the pre-amplifier  50  to control the pre-amplifier  50  to supply an FOD voltage to the magnetic head  25 . The FOD voltage control signal generated from the controller  42  may be directly input to the pre-amplifier  50  or may be input to the pre-amplifier  50  through the read/write channel  4 . 
         [0048]    The controller  42  may be a micro-processor, a micro-controller, or the like. 
         [0049]      FIG. 3  is a block diagram showing a portion of the hard disk drive driving circuit according to an embodiment of the present disclosure. 
         [0050]      FIG. 4  is a signal diagram showing signals for controlling a flying height of a magnetic head according to an embodiment of the present disclosure. 
         [0051]    With reference to  FIG. 3 , a portion  10 - 1  of the hard disk drive  10  according to an embodiment of the present disclosure may include the pre-amplifier  50 , the controller  42  transmitting a plurality of signals to the pre-amplifier  50 , and the magnetic head  25  that writes data or reads written data upon receiving the FOD voltage output from the pre-amplifier  50 . 
         [0052]    Also, the pre-amplifier  50  according to an embodiment of the present disclosure may include a receiving unit  54  receiving a data read or data write command signal from the outside, a clock signal generating unit  56  generating an internal clock signal based on a pre-set clock rate, and an FOD block  52  setting a site of an initial write voltage among the FOD voltages according to the generated internal clock signal, and setting an amount with respect to a change in the initial write voltage. 
         [0053]    During a data write operation, the controller  42  may receive data output from the main processor, convert the received data into a plurality of signals that may be processed in the pre-amplifier  50 , and transmit various converted signals to the pre-amplifier  50 . 
         [0054]    With reference to  FIG. 3 , an SDATA signal refers to serial data transmitted to the pre-amplifier in response to a serial clock signal SCLK, and SEN refers to an enable signal. When the enable signal SEN is activated to have a high level, the pre-amplifier  50  may receive the serial data SDATA input in response to the serial clock signal SCLK, interpret, and perform an operation according to interpretation results. 
         [0055]    An RWn signal is an access signal indicating an access operation. For example, the pre-amplifier  50  may perform a write operation in response to the access signal having a low level, and perform a read operation in response to an address signal having a high level. 
         [0056]    The receiving unit  54  may receive a plurality of signals input from the controller  42 . the receiving unit  54  may transmit the received signals to the FOD block  52 . 
         [0057]    The clock signal generating unit  56  may be positioned within the pre-amplifier  50  and generate a clock signal. In this case, the clock signal generating unit  56  may generate a clock signal base don a change in absolute time. In detail, when a data write command signal is received by the receiving unit  54 , the clock signal generating unit  56  may generate at least one internal clock signal in any one write command signal among received data write command signals. 
         [0058]    Namely, in case in which an FOD voltage level is adjusted when a write command signal is received, if the hard disk drive  10  undergoes a 4K long sector change in a short sector of 512 MB, write gates to which a write command signal is input are increased 8 times, making it impossible to accurately control the FOD voltage. According to an embodiment of the present disclosure, when any one write command signal is input to have a low level, an internal clock signal is generated at short intervals while the low level is maintained, thus accurately controlling the FOD voltage. 
         [0059]    Also, the problem in which controlling of the FOD voltage is not uniform because the lengths of the write command signals having a low level are different in each zone of the disk can be solved. 
         [0060]    The size of the initial write voltage may be changed according to a clock signal generated from the clock signal generating unit  56 . 
         [0061]    The FOD block  52  may set a size of an initial write voltage and a length with respect to a change in an initial write voltage according to the internal clock signal generated from the clock signal generating unit  56  positioned within the pre-amplifier  50 . Also, the FOD block  52  may set an amount with respect to a change in the initial write voltage. The FOD block  52  may change the set size of the initial write voltage, the length with respect to a change, and the amount with respect to the change, and apply the same to the magnetic head  25 . 
         [0062]    For example, the FOD block  52  may set the size of the initial write voltage through a signal of FODALT. For example, as illustrated, the value of FODALT signal may be set to 140. A unit of this value may be Volt or W representing voltage or current, or may indicate a relative size. Namely, the number illustrated in the drawing to represent the size of a voltage or power may be variably modified and not limited thereto. When the FODALT signal is set to 140, when a write operation is performed in response to the access signal RWn having a low level, the FOD block  52  may set the size of the initial write voltage or power to 140. 
         [0063]    Also, the FOD block  52  may set the length with respect to a change in the initial write voltage through an FOD_WriteCount signal. According to a type of the hard disk drive  10 , the FOD block  52  may be set to change the size of a write voltage whenever one clock signal, among clock signals generated from the clock signal generating unit  56 , and set to change the size of the write voltage whenever two clock signals are generated. 
         [0064]    As illustrated, when FOD_WriteCount is 000, the size of the write voltage is regularly reduced whenever one internal clock signal is generated. 
         [0065]    Also, the FOD block  52  may set an amount with respect to a change in the initial write voltage through FOD_StepSize signal. Namely, when a length with respect to a change in the initial write voltage is set, the size of the FOD voltage changing accordingly is set. 
         [0066]    As illustrated, when FOD_StepSize is 111, the FOD voltage is reduced by 8 each time starting from the initial write voltage. 
         [0067]    The FOD block  52  may set the size of the initial write voltage or power such that it is greater than the size of voltage (FODR) or power supplied to the magnetic head  25  during reading. Namely, the FOD block  52  may set the initial write voltage among the FOD voltages such that it is greater than the record voltage before the initial write voltage is applied. Namely, FODR is smaller than the value of FODALT in size. 
         [0068]    The FOD block  52  may reduce the size of the initial write voltage according to the sequentially generated internal clock signal sequentially based on the set amount with respect to a change in the initial write voltage and apply the same to the magnetic head  25 . 
         [0069]    Also, when the changed size of the initial write voltage reaches the pre-set reference value (e.g., the FODW signal), the FOD block  52  may stop changing of the initial write voltage. The pre-set reference value may be set to a voltage or power required for a write operation. 
         [0070]      FIG. 5  is a flow chart illustrating a method of controlling a flying height of a magnetic head of the hard disk drive driving circuit according to an embodiment of the present disclosure. 
         [0071]    The FOD block  52  of the pre-amplifier  50  may set an initial write voltage (S 501 ). The controller  4  outside the pre-amplifier  50  may receive a data write command signal such that the set initial write voltage can be applied to the magnetic head  25  (S 503 ). 
         [0072]    When the data write command signal is received by the receiving unit  54  of the pre-amplifier  50 , the clock signal generating unit  56  may generate an internal clock signal based on a pre-set clock rate. The internal clock signal may be generated at least one or more times within one period in which a single write command signal, among received data write command signals, is maintained. 
         [0073]    The internal clock signal generated in the clock signal generating unit  56  is delivered to the FOD block  52 , and the FOD block  52  may set a length with respect to a change in the initial write voltage according, to the generated internal clock signal (S 505 ). 
         [0074]    Also, the FOD block  52  may set an amount with respect to a change in the initial write voltage (S 507 ). The FOD block  52  may apply the initial write voltage changed based on the set length and amount with respect to the change in the initial write voltage to the magnetic head  25  (S 509 ). In detail, the FOD block  52  may reduce the initial write voltage according to the internal clock signal sequentially continuously generated based on the set amount with respect to the change in the initial write voltage. 
         [0075]    The initial write voltage may be reduced by the set amount with respect to a change whenever the internal clock signal is generated. Also, when the internal clock signal is generated several times according to the set length with respect to the change, whether to reduce the initial write voltage is determined, and accordingly, the initial write voltage may be reduced by the set amount with respect to the change. 
         [0076]    The initial write voltage changed based on the set amount and length with respect to the change may be compared with a pre-set reference value (S 511 ). 
         [0077]    According to the comparison results, when the changed size of the initial write voltage is still greater than the reference value, the initial write voltage reduced according to the previous internal clock signal is reduced again according to the set length and amount with respect to the change (S 509 ). 
         [0078]    According to the comparison results, when the changed size of the initial write voltage reaches the reference value, changing of the write voltage may be stopped (S 513 ). 
         [0079]      FIG. 6  is a block diagram of a computer system including a hard disk drive and a memory device according to an embodiment of the present disclosure. 
         [0080]    The main processor  110  may control an operation of the hard disk drive  10  in order to write data to the disk of the hard disk drive  10  or read data from the disk. 
         [0081]    Also, the main processor  110  may control an operation of the hard disk drive  10  in order to write data to the memory device  120  or read data from the memory device  120 . Also, the main processor  110  may write data to the hard disk drive  10  or the memory device  120  as necessary. 
         [0082]    The memory device  120  may be connected to a host, namely, the main processor, and the hard disk drive  10  through an interlace (not shown), and may include a DRAM (Dynamic Random Access Memory) and a nonvolatile memory (NVM). The nonvolatile memory may include an EEPROM, a flash memory, an MRAM (Magnetic RAM), an MRAM (Spin-Transfer Torque MRAM), an FeRAM (Ferroelectiric RAM), a PRAM (Phase change RAM), an RRAM (Resistive RAM), a nano-tube RRAM, a polymer RAM, a nano-floating gate memory), a holographic memory, a molecular electronics memory device), or an insulator resistance change memory. 
         [0083]    The method for controlling a flying height of a head according to exemplary embodiments described above may be implemented in the form of programs which can be executed by various computer means, and recorded on a computer-readable medium. The computer-readable medium may include program commands, data files, data structures, alone, or a combination thereof. Program instructions recorded on the medium may be particularly designed and structured for the present disclosure or available to those skilled in computer software. Examples of the computer-readable recording medium include hardware devices, particularly configured to store and perform program commands, such as, magnetic media, such as a hard disk, a floppy disk, and a magnetic tape; optical media, such as a compact disk-read only memory (CD-ROM) and a digital versatile disc (DVD); magneto-optical media, such as floptical disks; a read-only memory (ROM); a random access memory (RAM); and a flash memory. Program commands may include, for example, a high-level language code that can be executed by a computer using an interpreter, as well as a machine language code made by a complier. The hardware devices may be configured to be operated by one or more software modules to implement the subject matter of the disclosure, and vice versa. 
         [0084]    Various embodiments have been described with reference to the accompanying drawings, and it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope of the disclosure. Thus, the technical concept of the present disclosure should be interpreted to embrace all such alterations, modifications, and variations in addition to the accompanying drawings.