Abstract:
A magnetic disk apparatus capable of generating a reference clock signal without using an external reference by writing a clock track only once using a head of the magnetic disk apparatus even if the head is of a read/write element separation type. Using the head of the magnetic disk apparatus, a clock track is recorded only once and the recorded clock track is played back to measure the total number of clock bits in one revolution. A time interval between servo sectors is determined by dividing the total number of clock bits thus measured by the number of servo sectors. By using as a timing reference the clock bits produced by playing back the clock track, the servo sectors are recorded in such a manner that they are located at the determined interval.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a magnetic disk apparatus and a servo signal recording method and more specifically to a servo write operation that records a reference clock signal used as a timing reference for writing a servo signal without using a dedicated clock head in a magnetic disk apparatus such as a hard disk drive. 
   In magnetic disk apparatus, several tens to more than several hundreds of servo signals (servo sectors) are placed on a recording surface of the disk in each cyclic movement (revolution) for position detection of the head. 
   In a normal servo write process, as described in JP-A-2000-123509, a dedicated head called a clock head is used to record a clock track on the recording surface to define a circumferential position of each servo sector. Reading this clock track produces a clock signal representing a position of the servo sector in a disk rotating direction (refer to reference  1 ). 
   Another proposed method, as described in U.S. Pat. No. 5,519,546, involves producing a clock signal by using a normal head of a magnetic disk apparatus without using a dedicated head. 
   The method described in the U.S. Pat. No. 5,519,546 requires a head of the magnetic disk apparatus to read a part of the clock track already recorded on the disk surface and at the same time write a new track to connect them in a circumferential direction. With magnetoresistive heads currently in use on general magnetic disk apparatus, since a writing element and a reading element are separated from each other, a problem arises that a newly recorded track does not connect to the already recorded track. 
   Further, conventional clock tracks, such as those described in JP-A-2000-123509, are generally managed strictly in such a manner that the number of clock bits in each revolution can be divided by the number of sectors. This makes it necessary to perform the writing operation again if a bit length of a write connecting portion in one revolution fails to fall within a certain range. 
   However, in cases where a head of a magnetic disk apparatus available in recent years, whose writing or reading element is only several hundred nm wide, is used to record tracks, there is a fear that the writing element may not be able to be positioned correctly on the clock track, failing to perform the rewriting operation described above. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention has been accomplished to solve the above-mentioned problems experienced with the conventional techniques and provides a magnetic disk apparatus and a servo signal recording method which allow even a head of a read/write element separation type to generate a reference clock signal by performing a clock track recording once. 
   These and other objects and novel features of the present invention will become apparent from the following description of this specification and the accompanying drawings. 
   Representative aspects of this invention may be summarized as follows. 
   That is, to solve the problems described above, the magnetic disk apparatus of this invention employs a method of writing a clock track only once for one or more revolutions. 
   Then, the written clock track is read to measure a total number of clock bits in one revolution, which is then divided by the number of servo sectors to determine a servo sector interval. 
   Next, the servo sectors are written at the determined interval while counting the clock bits that are obtained by reading back the clock track. 
   Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a perspective view showing a magnetic disk apparatus of one embodiment of this invention, with a housing cover open. 
       FIG. 2  is a diagram showing a sequence of steps from a clock track generation to an initial track recording in an initial stage of a servo write operation of the magnetic disc apparatus as one embodiment of the invention. 
       FIGS. 3A ,  3 B and  3 C are schematic diagrams showing a clock track pattern to be recorded by the magnetic disk apparatus. 
       FIG. 4  is a schematic diagram showing a signal path associated with a read/write operation of the magnetic disk apparatus. 
       FIG. 5  is a diagram showing an operation to measure the number of clock bits in a clock track to be recorded by the magnetic disk apparatus. 
       FIGS. 6A and 6B  are schematic diagrams showing an operation to record a first servo track based on a readback signal of the clock track in the magnetic disk apparatus. 
       FIGS. 7A ,  7 B and  7 C are diagrams showing a configuration to adjust a delay that occurs when writing each sector in the magnetic disk apparatus. 
       FIG. 8  is a diagram showing a timing adjust operation from a marker detection to a write start in the magnetic disk apparatus. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Now, one embodiment of the present invention will be described in detail by referring to the accompanying drawings. 
   Throughout the drawings of this embodiment, like reference numbers are assigned to those parts with identical functions and their repetitive explanations are omitted. 
   The present invention relates to a method of generating a reference clock used as a reference for timing when writing a servo pattern. 
     FIG. 1  is a perspective view showing an outline construction of a magnetic disk apparatus of one embodiment of this invention. 
   While the top of a housing  101  is normally attached with a housing cover to enclose inner constitutional elements,  FIG. 1  illustrates a state in which the housing cover is removed for the constitutional elements to be seen from outside. 
   The magnetic disk apparatus of this embodiment includes a disk-shaped medium  102  for recording information on a disk surface thereof, and a head  103  having a writing element (not shown) for writing information on the medium  102  and a reading element (not shown) for reading information from the medium  102 . 
   The head  103  is pivotally supported on a pivot  105  through a head arm  104  and is moved to a desired radial position on the medium  102  by an actuator having a moving coil and a stationary magnet  106   a.    
   The head  103  is driven by a read/write driver IC  109  to perform a writing or reading operation. When not performing the read/write operation, the head  103  is retracted onto a ramp mechanism  108  situated outside the medium  102  so that it is held completely off the recording surface of the medium  102 . 
   This control sequence is performed by a control circuit not shown which is connected to the magnetic disk apparatus. 
   The control circuit has a controller for system control, a signal processing circuit, an actuator driver, and a power supply circuit. 
   A feature of the magnetic disk apparatus of this embodiment lies in the fact that a clock track  111  is recorded by using the head  103  of the apparatus at an initial stage of the servo write operation and that, based on a readback signal (reference clock) of the clock track  111 , a write timing of a servo pattern is adjusted. 
     FIG. 2  shows a sequence of steps from the generation of clocks to the initial track recording in the initial stage of the servo write operation in the magnetic disk apparatus of this embodiment. 
   In the magnetic disk apparatus of this embodiment, at the first stage of servo write, the head  103  is loaded onto the disk surface of the medium  102  and then the actuator movable portion  106   b  is pressed against a movable range limit stopper  107  to hold the head  103  at a position on the disk innermost circumference side of the movable range. 
   The recording of the clock track  111  is performed by using the writing element when the head  103  is at the disk innermost position (step S 201 ). 
   A recording frequency of the clock track needs to be able to ensure a signal quality in terms of magnetic recording. In practice, it is also preferred from the standpoint of a circuit characteristic that the recording frequency be set almost equal to a servo signal frequency. In the case of a 2.5-inch magnetic disk apparatus currently in production, for example, the clock track recording frequency is set in a range of between 20 MHz and 40 MHz. 
   It is also possible to use a base clock signal in the control circuit as a reference if the frequency is within an appropriate range. In this embodiment, the clock track recording frequency is set equal to a frequency of a servo track to be recorded. 
   With the recording of the clock track  111  completed, a driving force of the actuator  106  is changed to move the reading element near a center of the clock track  111  (step S 202 ). 
   A geometrical relation between the writing element and the reading element of the head  103  is so set that the writing element is situated slightly on the outer circumferential side with respect to the reading element. 
   Therefore, at step S 202 , the writing element is situated slightly outside the clock track  111 . 
   The number of clock bits recorded by step S 201  is influenced by disk revolution speed variations characteristic of individual magnetic disk apparatus and varies from one write operation to another. 
   At the position to which the head was moved by step S 202 , the clock track  111  is read (step S 203 ) and, based on a readback signal, the number of clock bits in one disk revolution is measured (step S 204 ). 
   The number of clock bits in one disk revolution is determined, for example, by adding up measured time intervals at which the head  103  passes markers  111   a.    
   Then, the number of clock bits in one revolution is divided by the number of sectors to determine intervals in clock bits between adjacent sectors (servo sectors) (step S 205 ). 
   The number of clock bits in one revolution cannot necessarily be divided by the number of sectors to be recorded. 
   Errors caused by rounding a quotient of the division result in sector interval variations. Thus, the quotient of the division is calculated not only to an integral part but also to a fractional part. 
   With the sector interval determined, an electric current is applied to the writing element  103   b  at the interval calculated by step S 205  to record sectors in the first track while reading the clock track  111  and counting the clock bits in the clock track  111  (step S 206 ). 
   After the first track has been recorded and the sectors&#39; circumferential positions are determined, successive tracks are written according to this pattern progressively outwardly toward the outer circumference until the entire disk surface is written with the servo signal. 
   The process of generating a clock signal used as a timing reference for writing a servo signal in the magnetic disk apparatus of this embodiment has been shown. Each of the steps in this process will be described in more detail. 
   The writing of the clock track  111  in step S 201  will be explained with reference to  FIGS. 3A to 3C . 
     FIGS. 3A to 3C  illustrate a pattern of the clock track  111  recorded in the magnetic disk apparatus of this embodiment. 
     FIG. 3A  schematically shows the head  103 , the medium  102  and the track immediately after the clock track  111  has been recorded. 
   The writing of the clock track  111  begins with a position  301  on the disk surface of the medium  102  and ends with a position  302  after one revolution. A range in which this write operation is performed is shown by a dashed line arrow at an inner circumferential part of the medium. 
   Hence, what remains in a region  303  between the position  301  and the position  302  is a pattern written over in the second revolution. 
     FIG. 3B  shows a magnified view of the clock track  111  in the region  304  of  FIG. 3A . In  FIG. 3B , reference number  103   a  represents a reading element and  103   b  a writing element. 
   The clock track  111  is embedded with markers  111   a  at predetermined intervals. The remaining portion is recorded with a pattern A 11 - 1  of a single frequency. 
   The markers  111   a  are recorded at predetermined intervals for more than one revolution and at the end of the recording operation an index marker  111   b  distinguishable from other markers is recorded to finish the recording of the clock track  111 . 
   Since the time of one disk revolution cannot, strictly speaking, be divided without a remainder by the time interval of the markers  111   a , a segment  306  between the last recorded index marker  111   b  and the next marker  111   a  differs from the interval between the markers  111   a  themselves. 
   The number of clock bits in this segment  306  reflects the revolution speed of the disk in the magnetic disk apparatus in which the pattern is to be written. 
   For example, if the disk revolution speed in a magnetic disk apparatus is slightly faster than a design value due to variations in a reference oscillator frequency of each revolution speed control circuit, the number of clock bits in the segment  306  increases; and if the disk revolution speed is slightly slower than the design value, the number of clock bits in the segment  306  decreases. The number of clock bits in this segment  306  is measured after the writing operation. The measuring operation will be described later. 
     FIG. 3C  shows a magnified view of the clock track  111  for a segment  305  containing markers  111   a  in  FIG. 3B . A readback signal waveform  401  produced by reading the pattern is shown below the pattern such that the waveform corresponds to the pattern in an elapsed time. 
   The pattern of the marker  111   a  produces such a readback signal waveform as can be distinguished from other parts, and monitoring the readback signal can detect when the reading element passes the marker. 
   The operation of measuring the number of clock bits by reading the clock track  111  shown in  FIGS. 3A–3C  will be explained by referring to  FIG. 4  and  FIG. 5 . 
     FIG. 4  shows signal paths associated with the read/write operation of the magnetic disk apparatus of this embodiment, schematically showing how signals are processed during the writing and reading operations. 
     FIG. 5  illustrates the operation of measuring the number of clock bits in the clock track  111  recorded in the magnetic disk apparatus of this embodiment, showing how associated signals change in response to a readback signal. 
   A readback signal  401  read from the medium  102  by the reading element  103   a  of the head  103  is amplified by a preamplifier  109   a  in the read/write driver IC  109 . The amplified readback signal  402  is sent to a signal processing unit  410 . 
   From the readback signal  401 , the signal processing unit  410  detects the passage of the marker  111   a  and the index marker  111   b.    
   The marker detection is done by a marker detector  410   b  in the signal processing unit acquiring the presence or absence of di-bits of the readback signal every clock and at the same time checking a bit pattern. 
   As the clock used by the marker detector  410   b  to pick up bits, a PLL output clock  403  is used which is produced by a PLL unit  410   a  in phase with the amplified readback signal  402 . 
   Near the marker  111   a , a hold signal  406  from a system controller  411  to the PLL unit  410   a  is made active to temporarily hold a PLL clock  403 . 
   During this process, strictly speaking, when the disk revolution speed varies, a phase shift occurs between the waveform of the readback signal  402  and the PLL clock  403 . However, since the time during which to hold the PLL unit  410   a  is very short, about a few hundred ns, the effect of the speed change of a mechanism system, such as disk revolution, is negligible. 
   As a result, even near the marker  111   a , the operation of the marker detector  410   b  can be synchronized with the waveform of the readback signal  402  regardless of the presence or absence of di-bits. 
   The marker detector  410   b , upon detecting a bit pattern of the marker  111   a , produces a pulse  501   a  as a marker detection signal  404   a.    
   When the index marker  111   b  is detected, the marker detector  410   b  outputs a pulse  501   b  as an index marker detection signal  404   b.    
   Since the operation of the marker detector  410   b  is in synchronism with the readback signal at all times, as described above, these pulses ( 501   a ,  501   b ) are output a predetermined number of clocks, 2 or 3 clocks, after the reading element  103   a  of the head has passed the marker  111   a  or index marker  111   b.    
   After the marker  111   a  is detected, the hold signal to the PLL unit  410   a  is deactivated, allowing the PLL unit  410   a  to be in phase again with the signal A 11 - 1  to generate a PLL clock  403  following the variations of the disk rotation speed. 
   Since, during the recording of the clock track  111 , the interval of the markers  111   a  is constant, the amount of change in clock bits caused by the disk revolution speed variations appears as the number of clock bits contained in the segment  306  between the index marker  111   b  and the next marker  111   a.    
   The number of clock bits in the segment  306  is determined by measuring the number of clock cycles from the index marker detection pulse  501   b  to the next marker detection pulse  501   a  by a counter in a timing detection logic  411   a  of the system controller  411  ( 502  in  FIG. 5 ). 
   The total number of clock bits in one revolution is calculated from the number of clock cycles in the segment  306 , the number of clock bits between the markers during recording and the number of markers present in one clock track revolution. 
   For example, if the number of clock cycles in the segment  306  is m cycles, the number of clock bits between the markers during recording is n cycles, and there are k markers including indices in one track revolution, the total number of clock bits Nclk is as follows.
 
 Nclk =( k −1)* n+m   (1)
 
   Now, the operation of steps S 205  and S 206 , which, based on the total number of clock bits measured, calculates a sector start position and records a first servo track, will be explained by referring to  FIGS. 6A and 6B . 
     FIGS. 6A and 6B  illustrate the operation of recording the first servo track based on the readback signal of the clock track in the magnetic disk apparatus of this embodiment. 
     FIG. 6A  schematically shows the head  103 , the medium  102  and the track immediately after the first servo track  601  has been recorded while reading the clock track  111 .  FIG. 6B  shows a magnified view of a region  602  in  FIG. 6A . 
   The servo track  601  actually is not a contiguous pattern but made up of a series of intermittently recorded sectors  601   a - 1 ,  601   a - 2 ,  601   a - 3 ,  601   a - 4 . 
   The sector start position in the first servo track is preferably situated at one of positions that divide one circumference into equidistant segments. Thus, as shown at  604 - 1 ,  604 - 2 ,  604 - 3 ,  604 - 4  in  FIG. 6B , a delay time is individually set for each sector. 
   For instance, if the number of markers k is equal to the number of sectors, a Write delay Dw in writing an i-th sector is given by
 
 Dw ( i )={( Nclk/k )− n}*i+d   (2)
 
Where d is a fixed offset for all sectors and is selected so that the delays for all sectors are positive and that the writing start position of each sector is as close to the marker as possible.
 
   Next, referring to  FIGS. 7A ,  7 B and  7 C, the Write delay Dw during the sector recording will be explained. This embodiment uses intermittent clocks generated by taking the markers  111   a  as reference and adjusts the Write delay Dw for each sector  601   a  so as to write the sectors  601   a  at equal intervals. As shown in  FIG. 7A , from a time  501   a  at which the marker  111   a  is detected during the readback of the recorded track  111 , an intermittent Write clock  412  is initiated. Further, the Write delay Dw for each sector  601   a  is adjusted to an optimum value in recording the pattern so that the intervals W between the sectors  601  are equal. 
   If an actual disk revolution speed during the writing of the clock track is slower than a target speed indicated by a dashed line, as shown in  FIG. 7B , the marker writing position falls short of the sector&#39;s circumferential target position by an increasing distance as the marker distance from the write start position increases. To set the sectors at equal intervals, therefore, the Write delay Dw is adjusted to increase as the sector distance from the write start position increases, as shown in  FIG. 7C . 
   As the timing reference used in step S 206  when recording sectors by using the Write delay obtained by the method described above, a clock signal that can follow disk revolution speed variations is used. This clock signal is generated in the signal processing unit  410  by playing back the clock track  111  with the reading element  103   a , as in the clock bit number measuring operation in step S 203 . 
   In this case also, as in step S 203 , the PLL hold signal  406  is made active near the marker to hold the PLL clock  403 . 
   In addition, in regions where a readback signal cannot be acquired, sectors  601   a  are recorded by holding the PLL clock to ensure that the marker detection operation can be performed by the marker detector  410   b  without a trouble. 
   The timing management in the system controller  411  can follow disk revolution speed variations at all times if the PLL clock  403  generated by the signal processing unit  410  is used. However, if the clock signal can be put in phase with the marker detection pulses ( 501   a ,  501   b ) that are in synchronism with the disk revolution, no problem occurs with the recording of sectors  601   a  and therefore a base clock signal in the circuit may be used. 
   The operation of adjusting the writing start timing will be explained by referring to  FIG. 4  and  FIG. 8 . 
     FIG. 8  shows a timing adjust operation from the marker detection to the start of recording in the magnetic disk apparatus of this embodiment. Signals shown in the figure are those transferred to and from the system controller  411  before a write current is applied, in the process of writing a sector  601   a - 3  in a region marked by a dashed line  603  of  FIG. 6B  after the reading element has passed the marker  111   a - 3 . 
   When a marker detection pulse  501   a  is sent from the marker detector  410   b  to the system controller  411  when the reading element passes the marker  111   a - 3 , a clock phase adjuster  411   d  generates a phase adjust clock signal  412  optimum for the writing adjustment based on the time at which the marker detection pulse  501   a  was detected, and is used as a clock for sending Write data  408 . 
   As to an integral part of a value representing the sector interval in clock bits, a timing adjustment in phase with the readback waveform is done by a write data sending unit  411   c  waiting until its write start delay counter  701  reaches a predetermined count value and then outputting Write data  408 . 
   A Write driver  109   b , based on the Write data  408 , supplies a write signal  409  to the writing element  103   b  of the head  103  to write a servo signal in the medium  102 . 
   As to a fractional part of the value representing the sector interval in clock bits, a timing adjustment is done by deliberately shifting a phase relation between the marker detection pulse  501   a  and the phase adjust clock  412  by the clock phase adjuster  411   d.    
   This function enables an adjustment of the write start timing for the fractional part of the sector interval value even if the total number of clock bits in one revolution cannot be divided by the number of sectors in step S 205 . 
   The method of recording sectors  601   a  in a servo track at equal intervals in a circumferential direction by using the writing element  103   b  of the head  103  of the magnetic disk apparatus without using a dedicated clock head has been described. Subsequent servo tracks will then be written according to the recorded track until the entire disk surface is recorded with servo signals. 
   It will be understood that the foregoing description has been made on one embodiment of the invention and that the invention is not limited to the configuration of this embodiment and various changes and modifications may be made without departing from the spirit of the invention. 
   An effect produced by a representative aspect of this invention may be briefly summarized as follows. 
   The embodiment of this invention makes it possible to generate a reference clock signal and record servo sectors at equal intervals by using only the head of the magnetic disk apparatus. 
   It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.