Patent Publication Number: US-2010123968-A1

Title: Method of positioning electromagnetic conversion element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-293010, filed Nov. 17, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One embodiment of the invention relates to a recording medium drive apparatus such as a hard disk drive (HDD), particularly to a positioning method used to position an electromagnetic conversion element in the recording medium drive apparatus. 
     2. Description of the Related Art 
     A so-called spiral servo is well known in the field of the hard disk drive. In the spiral servo, a spiral servo pattern is formed on a surface of a magnetic disk. The spiral servo pattern extends along a spiral line from an innermost to an outermost of a recording region. The spiral line maintains a defined inclined angle with respect to a circumferential line in the whole area of the recording region. In the hard disk drive, the electromagnetic conversion element reads magnetic information from the spiral servo pattern with rotation of the magnetic disk. The electromagnetic conversion element is positioned in a radial direction of the magnetic disk based on the read magnetic information. The electromagnetic conversion element thus positioned writes the servo pattern in a servo sector on the magnetic disk. 
     The spiral servo pattern has a high-frequency region. In the high-frequency region, magnetic poles are alternately arrayed in a circumferential direction. A high-frequency reproduction signal is output when the electromagnetic conversion element traverses the high-frequency region. At the same time, synchronous marks are formed at defined intervals in the circumferential direction of the spiral servo pattern. The synchronous mark forms a gap between the high-frequency reproduction signals. The interval between the gaps corresponds to a track width. By the operation of the synchronous mark, the electromagnetic conversion element can be positioned at every recording track (for example, see U.S. Pat. Nos. 6,965,489, 6,943,978, 6,507,450, 7,113,362, 7,002,761, 7,307,806, 7,307,807, 7,139,144, 7,088,533, and 7,167,333). 
     In the spiral servo, the electromagnetic conversion element is positioned only based on a demodulated microscopic displacement of the electromagnetic conversion element when the electromagnetic conversion element traverses the spiral servo pattern. Accordingly, when the servo pattern writing is started in the servo sector, it is necessary to form a servo pattern (a normal servo pattern different from the spiral servo pattern, that is, an auxiliary servo pattern) in a restricted region on the magnetic disk. First the electromagnetic conversion element is positioned in the write start position based on the auxiliary servo pattern. Then the detection source of the servo information is switched from the auxiliary servo pattern to the spiral servo pattern. The electromagnetic conversion element runs on the track based on the spiral servo pattern in this manner. 
     In such cases, an extra process of writing the auxiliary servo pattern is necessary in operating a servo track writer (STW). In addition, because actually eccentricity is insufficiently removed between the auxiliary servo pattern and the spiral servo pattern, it is difficult to switch from the auxiliary servo pattern to the spiral servo pattern. 
     In the spiral servo, the interval between the synchronous marks of the spiral servo pattern has an influence on positioning accuracy of the electromagnetic conversion element read from the demodulation signal. As described above, when the interval between the synchronous marks is restricted to the track width, the interval between the synchronous marks cannot be optimized from the viewpoint of the demodulation of the signal. A demodulation noise increases. The positioning accuracy of the electromagnetic conversion element, based on the demodulation signal, is degraded. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A general architecture that implements the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
         FIG. 1  is an exemplary plan view schematically illustrating a hard disk drive according to an embodiment of the invention; 
         FIG. 2  is an exemplary partially enlarged plan view schematically illustrating a surface structure of a magnetic disk in the embodiment; 
         FIG. 3  is an exemplary partially enlarged plan view schematically illustrating a structure of a servo sector region of in the embodiment; 
         FIG. 4  is an exemplary block diagram of a tracking servo control system in the embodiment; 
         FIG. 5  is an exemplary plan view conceptually illustrating a spiral servo pattern of a magnetic disk in the embodiment; 
         FIG. 6  is an exemplary partially enlarged plan view illustrating the spiral servo pattern in details and also schematically illustrating a reproduction signal based on the spiral servo pattern in the embodiment; 
         FIG. 7  is an exemplary block diagram of a positioning device configured in a CPU in the embodiment; 
         FIG. 8  is an exemplary partially enlarged plan view schematically illustrating a relationship between the spiral servo pattern and counting of a servo clock in the embodiment; 
         FIG. 9  is an exemplary partially enlarged plan view conceptually illustrating switching of the spiral servo pattern in the embodiment; 
         FIG. 10  is an exemplary flowchart of spiral servo control in the embodiment; 
         FIG. 11  is an exemplary flowchart of an initial operation of the spiral servo control in the embodiment; and 
         FIG. 12  is an exemplary partially enlarged plan view of a surface of a magnetic disk, schematically illustrating a moving pathway of an electromagnetic conversion element during the initial operation of the spiral servo control in the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, an electromagnetic conversion element positioning method includes: counting a servo clock for every servo sector radially extending on a recording medium, the servo clock being changed in synchronization with a change in rotation angle of the recording medium; reading magnetic information from spiral servo patterns with an electromagnetic conversion element, the spiral servo patterns being arranged at equal intervals in a circumferential direction of the recording medium, the spiral servo patterns having magnetic materials arrayed along a spiral line maintaining a defined inclined angle with respect to a circumferential line over a predetermined radial region; specifying a position of the spiral servo patterns on the circumferential line based on the read magnetic information; correlating the count value of the servo clock with the specified position; and specifying a radial position of the electromagnetic conversion element based on the correlated count value. 
     An embodiment of the invention will be described below with reference to the accompanying drawings. 
       FIG. 1  schematically illustrates an internal structure of a specific example of a magnetic recording medium drive apparatus, that is a hard disk drive (HDD)  11 . The HDD  11  includes a chassis, that is, a housing  12 . The housing  12  includes a boxy base  13  and a cover (not illustrated). For example, the base  13  defines a flat, rectangular-solid inner space, that is, an accommodation space. The base  13  may be formed by casting a metallic material such as Aluminum. The cover is joined to an opening of the base  13 . The accommodation space is sealed between the cover and the base  13 . The cover may be formed from one plate material by press working. 
     A specific example of the magnetic recording medium, that is, at least one magnetic disk  14  is accommodated in the accommodation space. The magnetic disk  14  is mounted on a spindle shaft of a spindle motor  15 . The spindle motor  15  can rotate the magnetic disk  14  at high speed such as 5400 rpm, 7200 rpm, 10000 rpm, and 15000 rpm. As described later, each magnetic disk  14  includes a so-called vertical magnetic recording medium. 
     A carriage  16  is also accommodated in the accommodation space. The carriage  16  includes a carriage block  17 . The carriage block  17  is rotatably coupled to a support shaft  18  that is perpendicularly extended from a bottom plate of the base  13 . A plurality of carriage arms  19  are provided in the carriage block  17 . The carriage arms  19  are horizontally extended from the support shaft  18 . For example, the carriage block  17  may be formed from Aluminum by extrusion. 
     A head suspension  21  is attached to a leading end of each carriage arm  19 . The head suspension  21  is extended forward from the leading end of the carriage arm  19 . A flexure is bonded to the head suspension  21 . A floating head slider  22  is supported on the flexure. An attitude of the floating head slider  22  can be changed relative to the head suspension  21  based on the flexure. A head element, that is, an electromagnetic conversion element (not illustrated) is mounted on the floating head slider  22 . 
     The electromagnetic conversion element includes a write head element and a read head element. A so-called magnetic monopole head is used as the write head element. The magnetic monopole head produces a magnetic field by action of a thin-film coil pattern. The main magnetic pole causes the magnetic field acts on the magnetic disk  14  in a direction perpendicular to a surface of the magnetic disk  14 . Information is written in the magnetic disk  14  by the effect of the magnetic field. On the other hand, a giant magnetoresistive (GMR) element or a Tunnel junction magnetoresistive (TMR) element is used as the read head element. In the GMR element or TMR element, a resistance change of a spin valve film or a tunnel junction film is generated according to an orientation of the magnetic field acting from the magnetic disk  14 . The information is read from the magnetic disk  14  based on the resistance change. 
     When an air current is produced on the surface of the magnetic disk  14  based on the rotation of the magnetic disk  14 , a positive pressure, that is, a buoyant force and a negative pressure acts on the floating head slider  22  by the action of the air current. The buoyant force equilibrates with the negative pressure and pressing force of the head suspension  21 . In rotating the magnetic disk  14 , the floating head slider  22  can continuously be floated with relatively high rigidity based on the equilibrium. 
     A voice coil motor (VCM)  23  is coupled to the carriage block  17 . The carriage block  17  can be rotated about the support shaft  18  by the operation of the VCM  23 . The carriage arm  19  and the head suspension  21  are oscillated based on the rotation of the carriage block  17 . When the carriage arm  19  is oscillated about the support shaft  18  while the floating head slider  22  is floated, the floating head slider  22  can be moved along a radial line of the magnetic disk  14 . As a result, the electromagnetic conversion element on the floating head slider  22  can traverse a coaxial recording track between an innermost recording track and an outermost recording track. The electromagnetic conversion element is positioned relative to the target recording track based on the movement of the floating head slider  22 . 
     A load tub  24  extending forward from the leading end of the head suspension  21  is provided at the leading end of the head suspension  21 . The load tub  24  can be moved in the radial direction of the magnetic disk  14  based on the oscillation of the carriage arm  19 . On the moving pathway of the load tub  24 , a ramp member  25  is disposed outside the magnetic disk  14 . The ramp member  25  is fixed to the base  13 . The load tub  24  is received by the ramp member  25 . For example, the ramp member  25  may be formed by molding a hard plastic material. 
     A ramp  25   a  extending along the moving pathway of the load tub  24  is formed in the ramp member  25 . The ramp  25   a  is moved away from a virtual plane including the surface of the magnetic disk  14  as the distance from the rotating axis of the magnetic disk  14  is increased. Accordingly, when the carriage arm  19  is moved away from the rotating axis of the magnetic disk  14  about the support shaft  18 , the load tub  24  climbs the ramp  25   a , whereby the floating head slider  22  is separated from the surface of the magnetic disk  14 . The floating head slider  22  is retracted to the outside from the magnetic disk  14 . On the contrary, when the carriage arm  19  is oscillated toward the rotating axis of the magnetic disk  14  about the support shaft  18 , the load tub  24  goes down the ramp  25   a . The buoyant force acts on the floating head slider  22  from the rotating magnetic disk  14 . The ramp member  25  and the load tub  24  constitute a so-called load/unload mechanism. 
     As illustrated in  FIG. 2 , a plurality of (for example, 200) servo sector regions  28  extending in a curved state along the radial direction of the magnetic disk  14  are defined on the surface and backside of the magnetic disk  14 . The servo sector regions  28  are arranged in a circumferential direction at equal intervals. A servo pattern is formed in the servo sector region  28 . The electromagnetic conversion element on the floating head slider  22  reads the magnetic information written in the servo pattern. The floating head slider  22  is positioned in the radial direction of the magnetic disk  14  based on the information read from the servo pattern. One circular recording track is formed according to the positioning. The recording track is concentrically formed based on the radial displacement of the floating head slider  22 . The curvature of the servo sector region  28  is set based on the moving pathway of the electromagnetic conversion element. 
     A data region  29  is ensured between the adjacent servo sector regions  28 . The electromagnetic conversion element traces a recording track in the data region  29  according to the positioning based on the servo pattern. The write head element of the electromagnetic conversion element writes magnetic information along the recording track. The read head element of the electromagnetic conversion element reads the magnetic information along the recording track. 
       FIG. 3  illustrates the servo sector region  28  of a specific example. In each servo sector region  28 , a preamble region  31 , a servo mark address region  32 , and a phase burst region  33  are defined in this order from the upstream side. For example, a plurality of magnetization patterns  34  extending on a radius line of the magnetic disk  14  are formed in the preamble region  31 . The magnetization patterns  34  are arranged at equal intervals in the circumferential direction of the magnetic disk  14 . Therefore, the synchronization of the signal read from a read element  35  is ensured by the operation of the preamble region  31 . At the same time, a gain is adjusted based on the signal read from the read element  35 . The “upstream” and “downstream” are defined based on the traveling direction of the floating head slider  22  during the rotation of the magnetic disk  14 . 
     Magnetic poles, that is, an N pole and an S pole are arranged in a specific pattern in the servo mark address region  32 . The arrangement of the magnetic poles reflects a sector number and a track number. At the same time, a plurality of magnetization patterns extending on the radius line of the magnetic disk  14  are formed in the servo mark address region  32 . The magnetization pattern specifies a servo clock signal. A phase, which is described later, is specified based on the servo clock signal. The sector number and the track number are specified by the operation of the servo mark address region  32 . At the same time, reference timing of the phase is specified by the operations of the preamble region  31  and the servo mark address region  32 . 
     A plurality of magnetization patterns, that is, phase burst lines  36  extending with a predetermined inclined angle relative to the radius line of the magnetic disk  14  are formed in the phase burst region  33 . In forming the phase burst lines  36 , even regions  33   a  and odd regions  33   b  are alternately arranged in a phase burst region  38 . The even region  33   a  and the odd region  33   b  are used in pairs. In the even region  33   a , the phase is delayed as the read element  35  passing through the phase burst lines  36  is deviated toward the inner circumferential side of the magnetic disk  14 . On the other hand, in the odd region  33   b , the phase is gained as the read element  35  passing through the phase burst lines  36  is deviated toward the outer circumferential side of the magnetic disk  14 . 
     As illustrated in  FIG. 4 , a motor driver circuit  41  is connected to the VCM  23 . The motor driver circuit  41  supplies a drive current to the VCM  23 . The VCM  23  is displaced by a specified displacement amount based on the supplied drive current. The displacement amount is set according to a rotation amount (rotation angle) of the carriage block  17 . 
     A read/write channel circuit  43  is connected to a head IC  42 . The read/write channel circuit  43  modulates and demodulates the signal according to a determined modulation/demodulation system. The modulated signal, that is, a write signal is supplied to the head IC  42 . The head IC  42  amplifies the write signal. The amplified write signal is supplied to a write element  44 . The read signal supplied from the read element  35  is amplified by the head IC  42 , and then supplied to the read/write channel circuit  43 . The read/write channel circuit  43  demodulates the read signal. 
     A hard disk controller (HDC)  45  is connected to the motor driver circuit  41  and the read/write channel circuit  43 . The HDC  45  supplies a control signal to the motor driver circuit  41 . An output of the motor driver circuit  41 , that is, the drive current is controlled based on the control signal. The HDC  45  feeds the write signal to the read/write channel circuit  43  before the modulation, and the HDC  45  receives the read signal from the read/write channel circuit  43  after the demodulation. Before the modulation, the HDC  45  may produce the write signal based on data delivered from, for example, a host computer. The data may be transferred from a connector  46  to the HDC  45 . A control signal cable (not illustrated) or a power cable (not illustrated), which extend from a main board of the host computer, may be connected to the connector  46 . Similarly the HDC  45  reproduces the data based on the read signal after the demodulation. The reproduced data may be supplied from the connector  46  to the host computer. In transmitting and receiving the data, for example, the HDC  45  can utilize a buffer memory  47 . The data is temporarily stored in the buffer memory  47 . For example, a synchronous dynamic random access memory (SDRAM) may be used as the buffer memory  47 . 
     A micro processor unit (MPU)  48  is connected to the HDC  45 . The MPU  48  includes a central processing unit (CPU)  52  that is operated based on a program stored in, for example, a read only memory (ROM)  51 . The program includes an electromagnetic conversion element positioning program. The electromagnetic conversion element positioning program may be provided in the form of firmware. The CPU  52  can obtain the data from, for example, a flash ROM  53  when implementing its operation. The program and the data can temporarily be stored in a random access memory (RAM)  54 . The ROM  51 , the flash ROM  53 , and the RAM  54  may directly be connected to the CPU  52 . 
     In the tracking servo control, the read element  35  outputs a signal when the read element  35  passes through the preamble region  31 , the servo mark address region  32 , and the phase burst region  33  in this order. The HDC  45  produces a servo clock signal based on the passage of the read element  35  through the servo mark address region  32 . Then, the HDC  45  captures a signal waveform for every even region and every odd region based on the passage of the read element  35  through the phase burst region  33 . The HDC  45  averages the signal waveforms by fast Fourier transform. The HDC  45  computes a phase difference for every even region and every odd region based on the servo clock signal and the signal waveform. The HDC  45  outputs a position error signal based on the computed phase difference. The position error signal is supplied as the control signal to the VCM  23 . As a result, the electromagnetic conversion element can trace the target recording track. 
     It is assumed that the servo sector region  28  is now formed in the magnetic disk  14 . First, the spiral servo pattern is written in the new magnetic disk  14 . A servo track writer (STW) is used to write the spiral servo pattern. The magnetic disk  14  is mounted on the STW. The STW rotates the magnetic disk  14  at a constant rotating speed. At the same time, the STW radially moves the write element at a constant moving speed. For example, the write element may be mounted on the predetermined floating head slider. For example, the floating head slider may be moved on the radius line of the magnetic disk  14 . The magnetic field acts on the magnetic disk  14  from the write element. 
     As illustrated in  FIG. 5 , a spiral servo patterns  55  are arranged at equal intervals in the circumferential direction. The number of the spiral servo patterns  55  is set double the number of the servo sector regions  28 . That is, two spiral servo patterns  55  are allocated to one servo sector region  28 . Alternatively, three or more spiral servo patterns may be allocated to one servo sector region  28 . Also in such cases, the spiral servo patterns may be arranged at equal intervals in the circumferential direction. In  FIG. 5 , for convenience, the servo sector region  28  and the spiral servo pattern  55  are illustrated in a simplified manner. 
     Each spiral servo pattern  55  extends along a spiral line from an outermost track  56   a  to an innermost track  56   b  of the recording region. The recording region corresponds to a maximum range where the magnetic information can be written with the write element  44 . As illustrated in  FIG. 6 , the spiral line maintains a defined inclined angle φ with respect to the circumferential line in the whole area of the recording region. 
     In each spiral servo pattern  55 , magnetization regions are arrayed along the spiral line. The N poles and the S poles are alternately arranged in the circumferential direction. A high-frequency region  57  is formed based on the arrangement. A radial length of the magnetization region is set to a recording track width TW. The radial length is measured on the radius line of the magnetic disk  14 . In forming the high-frequency region  57 , the high-frequency write signal is supplied to the write element  44  according to the predetermined write clock. 
     Synchronous marks  58  are formed at defined intervals in the circumferential direction of the spiral servo pattern  55 . For example, the synchronous mark  58  includes a magnetic monopole. In forming the synchronous mark  58 , a write signal having a constant value is supplied to the write element  44 . The write signal having the constant value is maintained over a defined number of clock pulses of the write clock. Therefore, the high frequency is interrupted. 
     When the read element  35  traverses the high-frequency region  57 , the read element  35  outputs a high-frequency reproduction signal  61 . Amplitude of the reproduction signal  61  is gradually increased. When the read element  35  lies down on the spiral servo pattern  55  with a track width TW, the reproduction signal  61  exerts the maximum amplitude. Then, the amplitude of the reproduction signal  61  is gradually decreased. The synchronous mark  58  causes a gap  62  between the high-frequency reproduction signals  61 . The high-frequency reproduction signals  61  are separated from each other by the gap  62 . An interval between the synchronous marks  58  is arbitrarily set. However, when the position of the gap  62  is optimized on the reproduction signals of the read element  35 , the disturbance, that is, the noise can be suppressed to the minimum in the reproduction signal, that is, the high-frequency reproduction signal  61 . For the intervals between the synchronous marks  58 , it is not always necessary to specify a track pitch. The synchronous marks  58  are arranged at equal intervals in the circumferential direction. The read element  35  passes through at least two synchronous marks  58  when the read element  35  traverses one spiral servo pattern  55 . 
     When the writing of the spiral servo pattern  55  is completed, the magnetic disk  14  is dropped from the STW. Then, the magnetic disk  14  is incorporated in the hard disk drive  11 . Subsequently, the magnetization is written in the servo sector region  28  for every hard disk drive  11  based on the written spiral servo pattern  55 . In writing the spiral servo pattern  55 , the CPU  52  executes the electromagnetic conversion element positioning program. At this point, the CPU  52  acts as an electromagnetic conversion element positioning device based on the execution of the positioning program. 
       FIG. 7  is a block diagram of a positioning device  64  constructed in the CPU  52 . The positioning device  64  includes a servo clock producing module  65 . The servo clock producing module  65  produces the servo clock. The servo clock generates pulses in synchronization with the rotation of the magnetic disk  14 , that is, the change in rotation angle. In generating the pulses, for example, a phase lock loop (PLL) circuit  66  may be connected to the servo clock producing module  65 . The read/write channel circuit  43  is connected to the PLL circuit  66 . The read/write channel circuit  43  supplies phase information to the PLL circuit  66  based on a demodulation signal of the spiral servo pattern  55 . 
     A servo clock counter  68  counts the servo clock. The servo clock counter  68  specifies a count value of the servo clock. As illustrated in  FIG. 8 , the count value is reset when the count value reaches a predetermined value CW. After resetting the count value, the servo clock counter  68  starts the counting again. The predetermined value CW specifies the interval between the adjacent servo sector regions  28 . That is, one servo sector region  28  is allocated for one resetting, that is, for the turn-back of the counting. 
     For example, a write window setting module  71  sets a write window  72  based on the count value of the servo clock. As illustrated in  FIG. 8 , the write window  72  specifies a time frame having a predetermined length of time. The write element  44  can perform the write operation within the time frame. The write element  44  is prohibited to perform the write operation out of the time frame of the write window  72 . The write window  72  emerges in a predetermined period. A count value equal to or lower than the predetermined value CW is used to set the period. 
     A write track specifying module  73  specifies one recording track based on the count value of the servo clock. A physical track is formed when the magnetization of the preamble region  31 , the magnetization of the servo mark address region  32 , and the magnetization of the phase burst region  33  are written in the servo sector region  28  based on the specified count value. For example, when the recording tracks are sequentially formed toward the outside in the radial direction of the magnetic disk  14 , the write track specifying module  73  adds the number of clocks Tp (hereinafter referred to as “the number of clocks corresponding to track pitch”) corresponding to one track pitch to the current count value to specify a new recording track. On the other hand, when the recording tracks are sequentially formed toward the inside in the radial direction of the magnetic disk  14 , the write track specifying module  73  subtracts the number of clocks corresponding to track pitch Tp from the current count value to specify a new recording track. In both the cases, any count value, that is, an initial value Cs may be allocated to the innermost (or outermost) recording track. The maximum count value is derived by adding a product of a numeric value obtained by subtracting “1” from the number of recording tracks and the number of clocks corresponding to track pitch Tp to the initial value Cs. As described later, the write track specifying module  73  also acts as a target track setting module. 
     A track number setting module  74  sets the track number. In setting the track number, the write track specifying module  73  supplies a count value R to the track number setting module  74 . After the initial value Cs is subtracted from the count value R, the subtraction result is divided by the number of clocks corresponding to track pitch Tp, thereby specifying a track number Pt. 
     
       
         
           
             
               
                 
                   Pt 
                   = 
                   
                     
                       ( 
                       
                         R 
                         - 
                         Cs 
                       
                       ) 
                     
                     Tp 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     A demodulation window setting module  75  sets a demodulation window based on the demodulation signal of the spiral servo pattern  55 . As illustrated in  FIG. 8 , for example, a demodulation window  76  specifies the time frame corresponding to the demodulation signal of the spiral servo pattern  55 . For example, the time length of the demodulation window  76  is set equal to the time length of the demodulation signal. The demodulation window  76  is fixed to the demodulation signal of the spiral servo pattern  55 . Accordingly, the demodulation window  76  emerges every time the demodulation signal of the spiral servo pattern  55  is detected. The demodulation signal is taken out based on the demodulation window  76 . The demodulation signal is supplied from the read/write channel circuit  43 . The read element  35  supplies the read signal to the read/write channel circuit  43 . 
     A sector number setting module  77  is connected to the demodulation window setting module  75 . The sector number setting module  77  specifies the sector number based on the number of passages of the spiral servo pattern  55 . The number of passages is recognized based on the number of emergences of the demodulation window  76 . The number of emergences is counted. The initial value of the sector number may be set to “0 (zero)”. The initial value of the sector number is allocated to any demodulation window  76  in one rotation of the magnetic disk  14 . The maximum value of the sector number is set based on the number of servo sector regions  28 . When the initial value is set to “0”, the maximum value of the sector number is set to a numeric value obtained by subtracting “1” from the number of the servo sector regions  28 . As described later, the sector number setting module  77  also acts as a spiral passage counter. However, as described later, the sector number is corrected in switching the spiral servo pattern  55 . 
     A servo information producing module  78  is connected to the track number setting module  74  and the sector number setting module  77 . The track number setting module  74  notifies the servo information producing module  78  of the track number. Similarly, the sector number setting module  77  notifies the servo information producing module  78  of the sector number. The servo information producing module  78  produces servo information based on the track number and the sector number. 
     A servo sector write module  79  is connected to the servo information producing module  78 . The servo information producing module  78  notifies the servo sector write module  79  of the servo information. The servo sector write module  79  sets the magnetization of the preamble region  31 , the magnetization of the servo mark address region  32 , and the magnetization of the phase burst region  33  based on the servo information. At the same time, the write window setting module  71  and the servo clock counter  68  are connected to the servo sector write module  79 . The set magnetization is supplied to the read/write channel circuit  43  in predetermined timing. In setting the timing, the write window setting module  71  notifies the servo sector write module  79  of the count value of the write window  72 . The count value of the write window  72  is correlated with the counting of the servo clock. Thus, the read/write channel circuit  43  outputs the write signal. A write current of the write element  44  is produced based on the write signal. The write element  44  constructs the servo sector region  28 . 
     A local-area positional information obtaining module  81  is connected to the demodulation window setting module  75 . At the same time, the servo clock counter  68  is connected to the local-area positional information obtaining module  81 . The local-area positional information obtaining module  81  specifies the position of the electromagnetic conversion element in the radial direction of the magnetic disk  14  based on a count value C 1  of the servo clock. The count value C 1  specifies the position of the electromagnetic conversion element in the radial direction of the magnetic disk  14 . In specifying the position of the electromagnetic conversion element, the position of the spiral servo pattern  55  is specified in the circumferential direction of the magnetic disk  14 . In specifying the circumferential position, the servo clock counter  68  supplies the count value of the servo clock to the local-area positional information obtaining module  81 . The local-area positional information obtaining module  81  specifies the count value C 1  of the servo clock based on the demodulation signal of the spiral servo pattern  55 . 
     As illustrated in  FIG. 8 , when the read element  35  traverses the spiral servo pattern  55 , the amplitude of the reproduction signal RS forms a “rhomboid” along a temporal axis. In the rhomboid, one diagonal orthogonal to the temporal axis corresponds to the maximum amplitude. The diagonal corresponds to an intermediate position of a moving pathway MP of the read element  35  formed on the spiral servo pattern  55 . A change in amplitude over time forms a symmetric shape based on the diagonal. Accordingly, a relative position Cf of the diagonal with respect to the gap  62  can be specified by comparing an area A 1  of a reproduction signal RS specified between the pair of gaps  62  in the former half region of the temporal axis and an area A 2  of the reproduction signal RS specified between the pair of gaps  62  in the latter half region of the temporal axis. The areas A 1  and A 2  of the reproduction signal RS may be computed with, for example, an integrator. Alternatively, the relative position Cf can be specified based on a whole area A 0  of the “rhomboid” of the reproduction signal RS and an area A 3  in an intermediate region of the temporal axis. The intermediate region corresponds to a region that includes the diagonal and is sandwiched between the pair of gaps  62 , that is, a region sandwiched between the areas A 1  and A 2 . The position of the gap  62  is correlated with the counting of the servo clock. That is, the position of the gap  62  can be specified by the count value C 0  of the servo clock. 
         C 1= C 0+ Cf   (2) 
     Therefore, in each turn-back of the counting, the maximum amplitude position of the reproduction signal RS can be specified based on the count value C 1  of the servo clock. The position of the spiral servo pattern  55  is specified on the moving pathway of the read element  35 . 
     As illustrated in  FIG. 7 , a spiral switching setting module  82  is connected to the demodulation window setting module  75 . At the same time, the write window setting module  71  is connected to the spiral switching setting module  82 . The spiral switching setting module  82  compares the demodulation window  76  and the write window  72 . For example, when the interval between the demodulation window  76  and the write window  72  is lower than the predetermined number of clocks, the spiral switching setting module  82  determines the switching of the spiral servo pattern  55  as described later. The spiral switching setting module  82  instructs the demodulation window setting module  75  to switch the spiral servo patterns  55 . As illustrated in  FIG. 9 , the demodulation window setting module  75  moves the demodulation window  76  along the circumferential direction from the spiral servo pattern  55  of the current demodulation target to the preceding or subsequent spiral servo pattern  55 . The spiral switching setting module  82  produces a correction value C 2  of the counting according to the switching of the spiral servo pattern  55 . The correction value C 2  is determined based on the number of spiral servo patterns  55  allocated to one servo sector region  28  and a predetermined value CW. For example, as illustrated in  FIG. 9 , the correction value C 2  is set based on the following equation, when the spiral servo pattern  55  is set after switching in the rotating direction of the magnetic disk  14 . 
     
       
         
           
             
               
                 
                   
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                         2 
                       
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     On the other hand, the correction value C 2  is set based on the following equation, when the spiral servo pattern  55  is set after switching in the opposite direction to the rotating direction of the magnetic disk  14 . 
     
       
         
           
             
               
                 
                   
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     The initial value of the correction value C 2  is set to “0”. 
     As illustrated in  FIG. 7 , a wide-area positional information obtaining module  83  is connected to the demodulation window setting module  75 . At the same time, the servo clock counter  68  is connected to the wide-area positional information obtaining module  83 . The wide-area positional information obtaining module  83  specifies the position of the electromagnetic conversion element in the radial direction of the magnetic disk  14  based on a count value C 3  of the servo clock. The count value C 3  specifies the local area position in the radial direction of the magnetic disk  14  between the outermost track  56   a  and the innermost track  56   b  of the recording region. In specifying the local area position, the number of turned-back times Ns is counted during the counting of the servo clock. For example, when a decrease equal to or more than a defined value is detected in the count value of the servo clock during moving the electromagnetic conversion element, the number of turned-back times Ns is specified from the following equation. 
         Ns=Ns+ 1  (5) 
     On the other hand, when an increase equal to or more than the defined value is detected in the count value of the servo clock during moving the electromagnetic conversion element, the number of turned-back times Ns is specified from the following equation. 
         Ns=Ns− 1  (6) 
     The count value C 3  is specified from the following equation based on the number of turned-back times Ns and the predetermined value CW of the servo clock, that is, the maximum count value. 
         C 3= Ns×CW   (7) 
     The initial value of the number of turned-back times Ns is set to “0 (zero)”. 
     A whole-area positional information computing module  84  is connected to the local-area positional information obtaining module  81 , the spiral switching setting module  82 , and the wide-area positional information obtaining module  83 . The whole-area positional information computing module  84  specifies the position of the electromagnetic conversion element in the radial direction of the magnetic disk  14  based on the count value C 1 , the correction value C 2 , and the count value C 3 . The total number of clocks Ct of the count value C 1 , correction value C 2 , and count value C 3  are computed. 
         Ct=C 1+ C 2+ C 3  (8) 
     The count value C 1 , the correction value C 2 , and the count value C 3  are simply added in the computation. The total number of clocks Ct specifies the position of the electromagnetic conversion element in the radial direction of the magnetic disk  14  between the outermost track  56   a  and the innermost track  56   b  of the recording region. 
     A position error signal producing module  85  is connected to the whole-area positional information computing module  84 . At the same time, the write track specifying module  73  is connected to the position error signal producing module  85 . The position error signal producing module  85  checks the total number of clocks Ct from the whole-area positional information computing module  84  with the count value R specified by the write track specifying module  73 . A difference between the count value and the total number of clocks Ct is computed. The difference corresponds to a position error signal PES. The position error signal PES is supplied to the VCM  23 . The drive current of the VCM  23  is set according to the position error signal PES. As a result, the electromagnetic conversion element can be positioned on any recording track based on the spiral servo pattern  55 . 
     A processing operation of the spiral servo control implemented by the CPU  52  based on the execution of the positioning program will be described below. As illustrated in  FIG. 10 , initialization is performed in S 1 . The rotation of the magnetic disk  14  is started. The magnetic disk  14  is maintained at a constant rotating speed. The servo clock is counted. The servo clock is changed in synchronization with the change in rotation angle of the magnetic disk  14 . The clock pulse is generated. The servo clock is counted. The function of the servo clock counter  68  is implemented in counting the servo clock. At the same time, a predetermined variable is initialized. 
     Subsequently in S 2 , the write window  72  is set. The function of the write window setting module  71  is realized in setting the write window  72 . In S 3 , the write track is specified. The method of specifying the first write track is described later. For example, the initial value “Cs” of the count value is set to the innermost recording track. In S 4 , the track number Pt is specified. The function of the track number setting module  74  is realized in setting the track number Pt. At this point, the count value R is set to the initial value “Cs”. In S 5 , the CPU  52  confirms whether the demodulation signal of the spiral servo pattern  55  exists. 
     When the demodulation is confirmed in S 5 , the demodulation window  76  is set in S 6 . The function of the demodulation window setting module  75  is realized in setting the demodulation window  76 . The CPU  52  captures the demodulation signal of the spiral servo pattern  55 . In S 7 , the CPU  52  obtains the local-area positional information based on the demodulation signal. The function of the local-area positional information obtaining module  81  is realized in obtaining the local-area positional information. As a result, the count value C 1  is specified as illustrated in  FIG. 8 , for example. The position of the spiral servo pattern  55  is specified on one circumferential line. 
     In S 8 , necessity for the switching of the spiral servo pattern  55  is determined. The function of the spiral switching setting module  82  is realized in the determination. The correction value C 2  is maintained at the previous value when an interval Tc between the demodulation window  76  and the write window  72  is ensured to be not lower than the predetermined number of clocks. The processing operation of the CPU  52  goes to S 9 . In S 9 , the wide-area positional information is obtained based on the demodulation signal. The function of the wide-area positional information obtaining module  83  is realized in obtaining the wide-area positional information. 
     In S 10 , the CPU  52  computes the whole-area positional information. The function of the whole-area positional information computing module  84  is implemented in the computation. The total number of clocks Ct is computed. Thus, the count value of the servo clock is correlated with the demodulation signal of the spiral servo pattern  55 . The total number of clocks Ct specifies the position of the electromagnetic conversion element in the radial direction of the magnetic disk  14 . 
     Subsequently in S 11 , the CPU  52  produces the position error signal PES. The function of the position error signal producing module  85  is implemented in producing the position error signal PES. The position error signal PES is supplied to the voice coil motor  23 . The electromagnetic conversion element is positioned on a predetermined circular recording track based on the position error signal PES. When the electromagnetic conversion element is positioned, the servo information is written in the magnetic disk  14  in S 12 . The function of the servo sector write module  79  is implemented in writing the servo information. The servo sector region  28  is constructed. The function of the servo information producing module  78  is implemented in producing the servo information. The track number and the sector number are specified in the servo information. The function of the track number setting module  74  is implemented in specifying the track number (equation 1). The function of the sector number setting module  77  is implemented in specifying the sector number. At this point, the sector number is determined based on the number of passages H of the spiral servo pattern  55 . However, the sector number is corrected in switching the spiral servo pattern  55  when the post-switching spiral servo pattern  55  is set in the opposite direction to the rotating direction of the magnetic disk  14 . That is, when the electromagnetic conversion element passes through the spiral servo pattern  55  immediately after the post-switching spiral servo pattern  55  is set in the opposite direction to the rotating direction of the magnetic disk  14 , the sector number is determined by the following equation. 
         Ps=Ps+ 2  (9) 
     When the electromagnetic conversion element passes through the spiral servo pattern  55  in other situations, the sector number is determined by the following equation. 
         Ps=Ps+ 1  (10) 
     However, the sector number is determined by the following equation until the first write track is specified in S 3 . 
       Ps=H  (11) 
     When the servo pattern is written in one servo sector region  28 , the sector number is updated in subsequent S 13 . 
     In S 14 , the sector number is compared to a threshold. The threshold specifies one rotation of the magnetic disk  14 . The processing operation of the CPU  52  returns to S 5  when the sector number is lower than the threshold. When the demodulation is confirmed in S 5 , the processing in S 6  to S 13  is performed again. One circular recording track is formed on the magnetic disk  14  when writing of the servo patterns in all the servo sector regions  28  according to the rotation of the magnetic disk  14  is completed. The processing operation of the CPU  52  goes to S 15 . A determination whether the formed circular recording track is the final track is made in S 15 . The processing operation of the CPU  52  returns to S 3  when the circular recording track is not the final track. In S 3 , the number of clocks corresponding to track pitch Tp is added to the initial value “Cs” of the count value. The circular recording track is specified one by one toward the outside from the first circular recording track every time the number of clocks corresponding to track pitch Tp is added. In S 4 , the track number Pt is updated. Then, the position error signal PES is produced in S 11  as described above. The electromagnetic conversion element is positioned on the specified circular recording track. As a result of the repetition of the processing in S 5  to S 14 , another circular recording track is formed on the magnetic disk  14 . 
     As illustrated in  FIG. 9 , when the interval Tc between the demodulation window  76  and the write window  72  is lower than the predetermined number of clocks, the CPU  52  resets the demodulation window  76  in S 16 . The timing of the demodulation window  76  is put ahead. The demodulation window  76  is moved forward (toward upstream side in the moving direction of the electromagnetic conversion element) from the spiral servo pattern  55  of the current demodulation target. Thus, the spiral servo patterns  55  are switched. For example, the correction value C 2  is computed from Equation 3 described above according to the switching of the spiral servo pattern  55 . The correction value C 2  is updated every time the spiral servo patterns  55  are switched. 
     In S 9 , the number of turned-back times Ns is updated every time the decrease not less than the defined value of the count value of the servo clock is detected. The predetermined value CW of the servo clock is multiplied by the updated number of turned-back times Ns. Thus, the count value C 3  is computed. According to the count value C 3 , the position of the electromagnetic conversion element can be expressed by the count value of the servo clock throughout the regions in the radial direction of the magnetic disk  14  although the counting of the servo clock is turned back at the predetermined value CW. 
     When the circular recording track formed in S 15  is the final track, the processing operation of the CPU  52  is ended. Thus, the servo patterns of the circular recording track are written throughout the regions of the magnetic disk  14 . According to the positioning processing operation as described above, each circular recording track can correctly be specified using the total number of clocks Ct of the servo clock. 
     An initial operation of the spiral servo control will be described below. The first write track is specified in S 3  based on the initial operation. As illustrated in  FIG. 11 , the electromagnetic conversion element is positioned on the innermost track  56   b  of the recording region in T 1 . At this point, for example, the carriage arm  19  is maximally driven toward the spindle shaft of the spindle motor  15 . The drive current is supplied to the VCM  23 . The carriage  16  is rotated about the support shaft  18 . The carriage  16  abuts on a stopper (not illustrated). 
     In T 2 , the target count value R is set to a provisional value. The provisional value may be any numeric value. Alternatively, the count value R may be set after the first spiral servo pattern  55  is demodulated. At the same time, the number of turned-back times Ns and the correction value C 2  are set to zero as initial values. In T 3 , the CPU  52  confirms whether the demodulation signal of the spiral servo pattern  55  exists. 
     When the demodulation is confirmed in T 3 , the demodulation window  76  is set in T 4 . As with the processing in S 6 , the function of the demodulation window setting module  75  is implemented in setting the demodulation window  76 . The CPU  52  captures the demodulation signal of the spiral servo pattern  55 . In T 5 , the CPU  52  obtains the local-area positional information based on the demodulation signal. As with the processing in S 7 , the function of the local-area positional information obtaining module  81  is implemented in obtaining the local-area positional information. As a result, a count value Cb is specified as illustrated in  FIG. 12 , for example. The count value Cb is applied to the count value R. Subsequently in T 6 , the wide-area positional information is obtained. As with the processing in S 9 , the function of the wide-area positional information obtaining module  83  is implemented in obtaining the wide-area positional information. The count value C 3  is computed. Subsequently in T 7 , the whole-area positional information is computed. As with the processing in S 10 , the function of the whole-area positional information computing module  84  is implemented in the computation. Subsequently in T 8 , the position error signal PES is produced. As with the processing in S 11 , the function of the position error signal producing module  85  is implemented in producing the position error signal PES. Subsequently in T 9 , the position error signal PES is recorded. The processing in S 5  to S 11  can directly be used in performing the processing in T 3  to T 9 . 
     In T 10 , the number of passages H of the spiral servo pattern is counted. The initial value of the number of passages H is set to “0 (zero)” in advance. In T 11 , the number of passages H is compared to a threshold. The threshold may be set to any numeric value (natural number). For example, the number of passages of a plurality of rotations of the magnetic disk  14  may be set to the threshold. The processing operation of the CPU  52  returns to T 3  when the number of passages H does not reach the threshold. Then the processing in T 3  to T 9  is performed. When the number of passages H reaches the threshold in T 11 , the processing operation of the CPU  52  goes to T 12 . In T 12 , the innermost track is specified. The position error signals of several rotations, recorded in T 9 , are referred to in specifying the innermost track. As illustrated in  FIG. 12 , errors Cd 1 , Cd 2 , . . . are specified between the target count value R (=Cb) and the total number of clocks Ct every time the electromagnetic conversion element passes through the spiral servo pattern  55 . The position of the electromagnetic conversion element can correctly be correlated with the count value of the servo clock within the radial moving range of the electromagnetic conversion element based on the errors Cd 1 , Cd 2 , . . . . As a result, as illustrated in  FIG. 12 , a count value Ci of an innermost circular recording track TR can be specified by the following equation. 
         Ci=Cb−Cd 2  (12) 
     In the initial operation, irrespective of the periodic displacement of the electromagnetic conversion element due to the eccentricity, the position of the electromagnetic conversion element can correctly be specified in the radial direction. When the innermost circular recording track is specified, the write start track is specified in T 13 . The innermost circular recording track may be applied to the write start track. That is, the count value Ci is applied to the count value of the write start track. 
     In the spiral servo control as described above, not only the microscopic displacement of the electromagnetic conversion element can accurately be specified based on the “rhombic” reproduction signal RS, but also the position of the electromagnetic conversion element can accurately be specified throughout the movable range of the carriage arm  19 . Accordingly, like the initial operation, the electromagnetic conversion element can directly be positioned on the spiral servo pattern  55  from the state in which the carriage  16  abuts on the stopper. As a result, the write of the so-called auxiliary servo pattern can be neglected. The processing operation of the STW can be simplified in constructing the servo sector region  28 . The simplification contributes to the shortened work time and the reduction of the production cost. 
     As described above, according to the embodiment, the position of the spiral servo pattern can be specified on a moving pathway of the electromagnetic conversion element based on the counting of the servo clock. In the positioning method, the synchronous marks formed at intervals corresponding to the track widths in the spiral servo pattern are not used during the positioning, so that a disturbance of the reproduction signal, that is, the noise can be suppressed to enhance the positioning accuracy of the electromagnetic conversion element. 
     Moreover, according to the embodiment, the electromagnetic conversion element positioning method that can contribute to the improvement of the positioning accuracy can be provided. 
     The whole or part of the processing operation implemented by the positioning program may be implemented based on dedicated hardware. 
     The various modules of the systems described herein can be implemented as software applications, hardware and/or software modules, or components on one or more computers, such as servers. While the various modules are illustrated separately, they may share some or all of the same underlying logic or code. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.