An aspect of the invention relates to storage discs each of which stores therein pieces of servo information used for positioning a head, servo-information writing methods, disc devices, and methods for manufacturing the disc devices. The present technique relates to a storage disc which stores therein pieces of servo information in accordance with recording/reproducing characteristics the relationship between a head and the storage disc, a method for writing the pieces of servo information, a disc device, and a method for manufacturing the disc device.
In disc devices such as magnetic discs, pieces of data are read from and written to desired tracks of discs using heads which are positioned in the desired tracks of the discs. The discs each have pieces of servo information recorded in tracks with predetermined intervals in a circumferential direction, and the pieces of servo information are read and decrypted using the heads so that pieces of positional information of the heads are obtained.
A process of writing pieces of servo information on a medium before the medium is inserted into such a disc device is called servo track writing (STW). When the servo track writing is performed, pieces of servo information to be used by the disc device are written to the medium. After the disc medium is inserted into the disc device, all tracks to be used are checked. When a decryption error of one of the pieces of servo information is detected in one of the tracks, the track is determined to be a defect track which is not available.
Techniques of the related art are disclosed in Japanese Laid-open Patent Publication No. 07-249276, Japanese Laid-open Patent Publication No. 09-180355 and Japanese Laid-open Patent Publication No. 2003-338147.
According to an aspect of an embodiment, a disc apparatus includes a medium being capable of storing data and including a plurality of sets of servo information, each set of the servo information having identification information, a head for writing data into and reading data from the medium, an actuator for supporting the head and a controller for controlling the actuator in reference to selected one of the sets of the servo information on the basis of the associated identification information so as to move the head to a target position of the medium.
Each of the pieces of servo information 102-1 to 102-8 includes a preamble 110, a sync mark pattern 112 used for synchronization control, a servo sector number 114, a gray code 116 indicating a track position, and a burst signal 118 used for position control. A single or a plurality of sectors are arranged between the pieces of servo information 102-1 to 102-8. In the related art, the pieces of servo information 102-1 to 102-8 employ identical sync mark patterns.
In the related art, an identical writing parameter is used to write the pieces of servo information for each disc, and the writing parameter is determined in accordance with characteristics of each disc. Similarly, characteristics of pieces of servo information are identical for each disc in which the pieces of servo information are recorded by magnetic transfer.
An optimum value for the writing parameter used when the pieces of servo information are written depends on characteristics of a disc medium and a writing head. As a test process of a disc device before shipping, a head is positioned in accordance with the pieces of servo information and a read/write test is performed for individual tracks of a disc.
In this test, if the writing parameter does not coincide with the optimum value, a read error is likely to occur when the pieces of servo information are decrypted. When a read error is detected in one of the tracks, the track is determined to be a defect track which is not available, and accordingly, production yield is reduced.
In particular, when the magnetic disc device employs a perpendicular recording method in order to attain increased density, decryption quality of each of the pieces of servo information is considerably influenced by variation of characteristics of the disc medium since a range of the optimum value of the writing current in the perpendicular recording method is smaller than that in a horizontal recording method.
Therefore, the optimum value of the writing parameter should be adjusted when the characteristics of the disc medium are changed. However, the adjustment requires manual labor and time.
Furthermore, the optimum value of the writing parameter is varied due to variation of quality of the disc medium and variations of characteristics of the head for servo track writing. Therefore, when a fixed parameter is used to write the pieces of servo information, quality of the pieces of servo information varies.
A method for manufacturing a disc device, a servo-information writing method, a disc device, a servo-information measurement/selection process performed using the disc device, a process of measuring quality of servo-information, a servo-information evaluation/selection process, and a process of using servo-information according to an embodiment of the present technique, and other embodiments will be described hereinafter in this order with reference to the accompanying drawings. However, the present technique is not limited to these embodiments, and various modifications may be made.
Referring to
In step S10, pieces of servo information are recorded in a magnetic disc. As shown in
Formats of the three types of servo information 12-1 to 12-3 are identical. Each of the three types of servo information 12-1 to 12-3 includes a preamble 14 used to control a frequency, a phase, and an amplitude, a corresponding one of sync mark patterns 15-1 to 15-3 used for synchronization control, a servo sector number 16, a gray code 17 indicating a track position, and a burst signal 18 used for position control.
The three types of servo information 12-1 to 12-3 are written using writing currents different from one another and are written so as to have sync mark patterns 15-1 to 15-3 different from one another. For example, a first servo information 12-1 is written using a writing current of 16 mA and has a bit pattern of a sync mark of “00010100”, a second servo information 12-2 is written using a writing current of 20 mA and has a bit pattern of a sync mark of “00100100”, a third servo information 12-3 is written using a writing current of 24 mA and has a bit pattern of a sync mark of “101000100”.
In step S12, the disc medium 10 including M types of servo information each of which includes N pieces of servo information written thereto is incorporated into (mounted in) a disc device 30, which will be described with reference to
In step S14, the disc device 30 performs a reading/writing test using the selected pieces of servo information. In this reading/writing test, test patterns are written using heads to tracks other than regions in which the selected pieces of servo information are written, the written test patterns are read, and it is determined whether qualities of read/write operations satisfy a desired level. Accordingly, pieces of servo information which were not selected are removed by being replaced by the test patterns. As shown in
As described above, the optimum type of servo information is obtained for each head among the three types of servo information, and one of the sync mark patterns corresponding to the optimum type of servo information is stored in a nonvolatile ROM (Read-Only Memory) of the disc device 30 or a system area of the disc medium 10 for each head. Accordingly, in the disc device 30, the pieces of servo information of the optimum type are used as pieces of normal servo information used for positioning, and the regions in which pieces of servo information other than the pieces of normal servo information are written are used as user data regions. The pieces of servo information in the user data regions are overwritten with user data. Since the region on the inner circumference side and the region on the outer circumference side of the disc medium 10 are not used as the user data regions, even when writing of the user data to the entire disc medium 10 is attempted, the pieces of servo information other than the pieces of optimum servo information remain in the region on the inner circumference side and the region on outer circumference side of the disc medium 10.
In step S16, in a case where one of the sync mark patterns corresponding to the optimum type of servo information is stored in the system area of the disc medium 10, when the disc device 30 is first turned on after being shipped, information on the one of the sync mark patterns corresponding to the optimum type of servo information is not read. Therefore, the one of the sync mark patterns to be used to read the pieces of servo information of the optimum type is unknown. The nonvolatile ROM includes a table listing a plurality of types of sync mark patterns stored in advance. When each of the heads are loaded and a sync mark pattern is read, a sync-mark setting value of a read channel is successively replaced by a value read from the table listing the sync mark patterns whereby the pieces of servo information of the optimum type are read.
Since the pieces of servo information remain in the region on the inner circumference side and the region on the outer circumference side of the disc medium 10 as shown in
After the pieces of servo information are thus written to the disc medium 10 using different parameters and the disc medium 10 is mounted in the disc device 30, the heads included in the disc device 30 evaluate the qualities of the pieces of servo information, and the pieces of servo information of the optimum type are selected. Therefore, even when characteristics of the disc medium 10 and characteristics of the heads of the servo track writer are changed in quality, the heads of the disc device 30 maintain the pieces of servo information of the optimum type usable.
Furthermore, since the different sync mark patterns are assigned in order to allow the types of servo information to be distinguished between, the selected pieces of servo information can be distinguished between even after the disc device 30 is shipped, and furthermore, even if different types of servo information are selected between the surfaces of the disc medium 10 or among a plurality of disc media 10, the selected pieces of servo information can be readily used.
The servo track writer 20 further includes an optical sensor 28 which optically detects a position of the magnetic head 23-R which faces the reference disc 10-R, a control circuit 26 which controls the head moving motor 24 to be located in a position detected using the optical sensor 28 and which supplies the pieces of servo information and applies writing currents to the magnetic heads 23-1 to 23-P so as to perform writing control.
The control circuit 26 has a table 29 listing the relationships between the writing currents used to write the three types of servo information 12-1 to 12-3 described above and the sync mark patterns. The reference disc 10-R includes timing signals written thereto.
Note that, although each of the magnetic discs 10-1 to 10-P has a corresponding one of the magnetic heads 23-1 to 23-P for simplicity in
When the servo track writing is started, the spindle motor 21 rotates, and therefore, the magnetic discs 10-R and 10-1 to 10-P rotate. The timing signals read from the reference disc 10-R using the magnetic head 23-R are supplied to the control circuit 26. The optical sensor 28 detects a position of the magnetic head 23-R on the reference disc 10-R, and information on the detected position is supplied to the control circuit 26.
The control circuit 26 performs movement control (servo control) on the head moving motor 24 with reference to the position detected using the optical sensor 28, so that the magnetic heads 23-R and 23-1 to 23-P are located in desired positions, and supplies the writing currents and writing servo patterns (including the sync mark patterns) to the magnetic heads 23-1 to 23-P in accordance with the timing signals supplied from the magnetic head 23-R.
Then, the three types of servo information 12-1 to 12-3 described with reference to
After pieces of servo information of the three types are written to all the tracks, the servo track writing is terminated. Then, the discs 10-1 to 10-P are detached from the rotation shaft 22 of the spindle motor 21. In this way, magnetic discs similar to the magnetic disc show in
The magnetic head 31 is attached to a tip end of an arm 32 of a VCM (Voice Coil Motor) 33. A read channel circuit 34 performs signal shaping on a signal read from a preamplifier (not shown) using the magnetic head (read element) 31, generates a synchronization clock and a gate signal, and outputs the read signal. Furthermore, the read channel circuit 34 supplies a write signal to the magnetic head (write element) 31.
A SVC (Servo Combo Circuit) 37 receives a driving instruction value supplied from an MCU (Micro Controller Unit) 36, and outputs a driving current in accordance with the driving instruction value so as to drive the VCM 33.
The MCU 36 includes an MPU (Micro Processor) and a servo controller, decrypts positional information obtained in accordance with the read signal output from the read channel circuit 34, detects a current position, and calculates the VCM driving instruction value in accordance with a difference between the detected current position and a target position. That is, the MCU 36 performs servo control including a seeking operation and a following operation. Furthermore, the MCU 36 analyzes commands, monitors a status of the disc device, and controls units included in the disc device.
A memory (RAM (Random Access Memory)) 38 stores data used in processes performed using the MCU 36. A hard disc controller (HDC) 35 communicates with a host. The HDC 35 receives read data from the read channel circuit 34 in accordance with the gate signal and the clock output from the read channel circuit 34, stores the read data in a buffer, and transmits the read data to the host. Furthermore, the HDC 35 supplies write data output from the host to the read channel circuit 34 in accordance with the gate signal and the clock supplied from the read channel circuit 34.
The HDC 35 communicates with the host via an IF (interface) such as a USB (Universal Serial Bus), an IDE (Integrated Drive Electronics), an ATA (AT Attached), or an SCSI (Small Computer System Interface).
In the configuration shown in
In this embodiment, after the disc device 30 is assembled, the MCU 36 performs a servo-information selection process so that the disc medium 10 as shown in
In step S20, the MCU 36 drives the spindle motor so as to rotate the disc medium 10. Then, the MCU 36 assigns (selects) 0 to the head number “HD”.
In step S22, the MCU 36 assigns (selects) 0 to a servo information number S, and initializes a measurement result storage region included in the RAM 38 by assigning “0” thereto.
In step S24, the MCU 36 instructs the read channel circuit 34 to detect a sync mark corresponding to the servo information number S=0 (the first servo information 12-1, for example), and to perform a decryption operation. Accordingly, the read channel circuit 34 detects the sync mark corresponding to the servo information number S=0 (the first servo information 12-1, for example) from a signal read using the magnetic head (read element) 31 and decrypts pieces of servo information corresponding to the sync mark. The MCU 36 measures servo-information decryption characteristics in accordance with results of the decryptions, the results of the measurements are added to one another, and a result of the addition is stored in an addition-result storage region included in the RAM 38. The servo-information decryption characteristics includes, as will be described hereinafter with reference to
In step S26, the MCU 36 determines whether the servo-information number S is larger than a value Smax (Smax=2 in
In step S28, when the determination is affirmative, it is determined that the measurements of all the servo-information decryption characteristics using the specified head (for a disc surface) are terminated. Then, the MCU 36 selects pieces of servo information of an optimum type in accordance with results of the measurements. Such an evaluation/selection process will be described below with reference to
In step S30, the MCU 36 determines whether the head number HD is larger than a head number HDmax which is a maximum value of the head number (for example, the head number HDmax is “1” when a single magnetic disc is mounted in the device, and the head number HDmax is “3” when two magnetic discs are mounted in the device). When the determination is negative, the process returns to step S22, servo-information decryption characteristics of pieces of servo information corresponding to all servo information numbers are measured, and pieces of optimum servo information are selected in accordance with results of the measurements.
In step S32, when the determination is affirmative, it is determined that the measurements of all the servo-information decryption characteristics using the all heads (for all disc surfaces) are terminated. Accordingly, the MCU 36 stores the selected pieces of optimum servo information in the nonvolatile ROM (not shown) or the system area in the disc medium 10. The selection process is thus terminated.
Then, the selected pieces of optimum servo information are used for positioning the heads, and the read/write test is performed on the disc medium 10. Therefore, pieces of servo information which are not selected are overwritten, that is, removed. Accordingly, the regions other than the regions in which the selected pieces of optimum servo information are written are used as the user data regions.
A process of measuring quality of servo-information described in step S24 of
The measurement process of
In step S40, the MCU 36 assigns “0” to measurement zone information Z. As shown in
In step S42, the MCU 36 initializes various parameters used in the zone 0. First, the MCU 36 initializes a measurement start track t by assigning T[Z] thereto, a track step count ts by assigning TS[Z] thereto, and a measurement track count tn by assigning TN[Z] thereto.
In step S44, the MCU 36 initializes a parameter of an offset position. That is, the MCU 36 initializes a measuring offset count “to” by assigning TO[Z] thereto. As shown in
Here, the read element 31-1 is displaced from the track center before the measurement processes are performed since the pieces of servo information of the track Tr[1] to be measured are influenced by pieces of servo information written to an adjacent track (a track Tr[2] in this embodiment). Specifically, in magnetic recording, when a writing operation is performed on a specific track, adjacent tracks are influenced by magnetization intensity of the writing operation of the specific track. In particular, when track pitches are small, the adjacent tracks are considerably influenced by the magnetization intensity. Furthermore, it is difficult to precisely locate the magnetic head 31 in the track center at a time of a reading/writing operation due to environment conditions such as vibration. Accordingly, the process of measuring quality of servo information is preferably performed with the magnetic head 31 displaced from the track center.
In this embodiment, signals are measured in two offset positions so as to evaluate signal qualities (amplitude components, especially) in accordance with relative values obtained by the measurements of the signals. One of the offset positions which is obtained by displacing the read element 31-1 by a quarter track is effectively used when the influence of the writing operation performed on the adjacent track at a side bridge is to be evaluated. The other of the offset positions which is obtained by displacing the read element 31-1 by a half track is effectively used when quality characteristics of the signals at boundary of the track Tr[1] are to be evaluated.
In step S46, the MCU 36 calculates a specific track position (t+ts (tn−1)), and drives the VCM 33 through the SVC 37 so that the read element 31-1 moves to an offset position F[Z]·[tO−1] at the calculated specific track position.
In step S48, the MCU 36 determines whether the read element 31-1 has been moved to the offset position F[Z] [tO−1] by obtaining a positional difference. The movement is determined to fail when position control fails since none of the pieces of servo information in the track Tr[1] is read. When it is determined that the movement has failed, the process proceeds to step S50. On the other hand, when it is determined that the movement has been successfully performed, position decryption characteristics of the track Tr[1] in one full circuit of the disc are measured, and results of the measurements are stored in a measurement result storing area included in the RAM 38. This process will be described in detail with reference to
In step S50, the MCU 36 decrements the measuring offset count “t0” by one (t0=t0−1). Then, the MCU 36 determines whether the measuring offset count “t0” is equal to or smaller than 0. In
On the other hand, when the determination is affirmative in step S50, the measurement processes in the track Tr[1] are terminated, and the process proceeds to step S52 where the measurement track count tn in one of the zones currently processed (hereinafter referred to as a “zone of interest”) is decremented by one (tn=tn−1). Then, the MCU 36 determines whether the updated measurement track count tn is equal to or smaller than “0”. When the determination is negative, the process returns to step S44.
When the determination is affirmative in step S52, the measurement processes have been performed on all the specified tracks in the zone of interest. Accordingly, in step S54, the measurement zone information Z is incremented by one (Z=Z+1). Then, the MCU 36 determines whether the updated measurement zone information Z is larger than a value Zmax which is a maximum value of the measurement zone information Z. When the determination is negative, the process returns to step S42.
When the determination is affirmative in step S54, on the other hand, the measurement processes have performed on all the zones, and the process proceeds to step S56. In step S56, the results of the measurements stored in a measurement result storing area included in the RAM 38 are added to one another and a result of the addition processing is stored in an addition result storing area included in the RAM 38 (which will be described below with reference to
Next, the addition processing will be described with reference to
In step S60, the characteristics to be measured in step S48 include a sync-mark reading error count esm representing the number of errors which occur when the pieces of servo information are read in one full circuit of a disc, a gray-code reading error count egc, a difference p between a maximum value and a minimum value of a decryption position obtained in accordance with a burst signal, and an index value v of an amplitude of a decryption waveform. The read channel circuit 34 shown in
Similarly, the read channel circuit 34 issues a gray-code found signal to the MCU 36 only when the read channel circuit 34 reads one of the gray codes, and otherwise, the read channel circuit 34 does not issue the gray-code found signal. Accordingly, the MCU 36 measures the gray-code reading error count egc by counting gray-code found signals corresponding to the gray codes included in the pieces of servo information issued in one full circuit of the disc.
A difference between the decryption position obtained by decrypting the burst signal using the read channel circuit 34 and a target position is calculated using the MCU 36 every time the burst signal is decrypted using the read channel circuit 34, a maximum value and a minimum value of the decryption position in one full circuit of the disc are obtained, and a difference p between the maximum value and the minimum value is calculated.
Furthermore, the index value v of amplitude of a decryption waveform is associated with gains of an AGC (Automatic Gain Control) circuit included in the read channel circuit 34. The gains are automatically controlled so as to be used to read the pieces of servo information. Then, the MCU 36 reads the gains from the read channel circuit 34, and obtains an average of the gains for one full circuit of the disc as the index value v.
In step S62, the MCU 36 updates a table listing the relationships between the zones and the offset positions using the results of the calculations performed in step S60. Specifically, as shown in
As described above, the measurement processes are performed on the pieces of servo information in accordance with the flowcharts of
Referring to
In step S70, all determination flags included in a determination flag table 38-2 shown in
In step S72, the MCU 36 calculates minimum values Bsm of sync-mark reading error counts esm of all offset positions of all the zones shown in
In step S74, the MCU 36 calculates minimum values Bgc of gray-code reading error counts egc of all the offset positions in all the zones shown in
In step 76, the MCU 36 calculates minimum values Bps of integrated values Ps of decryption positions of all the offset positions in all the zones shown in
In step S78, the MCU 36 calculates absolute values ΔV of values obtained from differences between integrated values (average values) of the offset positions 0 and integrated values (average values) of the corresponding offset positions 1 in the individual zones shown in
In step S80 of
In step S82, the minimum value ΔVmin is subtracted from each of the maximum values ΔVmax[u] of the three types of servo information so that certain values Vdiff[u] are obtained. Then, each of the values Vdiff of three types of servo information is compared with a threshold value Sv, and when it is determined that one of the values Vdiff is larger than the threshold value Sv, determination flags corresponding to the one of the values Vdiff for a corresponding one of the three types of servo information are turned to “1”. That is, the degrees of influences of deviations between adjacent pieces of servo information are determined in accordance with the maximum values obtained using the differences of amplitudes in pairs of offset positions, and the maximum values are converted into certain values on the basis of a minimum value, and when the certain values are larger than a threshold value, the determination flags are changed to “1” representing a low grade.
In step S84, the determination flags for the three types of servo information in the determination flag table 38-2 are converted into hexadecimal numbers having high-order bits on the left sides thereof and low-order bits on the right sides thereof. The MCU 36 selects one of the three types of servo information which has a minimum hexadecimal number among the converted hexadecimal numbers. After one of the bit patterns of the sync marks corresponding to the one of the three types of servo information is stored in the system area included in the disc, the process is terminated.
As is apparent from the determination flag table 38-2 shown in
Note that if a plurality of types of servo information have identical minimum hexadecimal values, one of the plurality of types of servo information having the smallest pattern number is selected.
As described in step S16 of
Accordingly, the nonvolatile ROM includes a table listing a plurality of types of sync mark patterns stored in advance. When each of the heads is loaded and one of the sync mark patterns is read, a sync-mark setting value of a read channel is successively replaced by a value read from the table listing the sync mark patterns whereby the pieces of servo information of the optimum type are read.
In step S90, calibration for VCM current supply is started. The term “VCM current supply” means the following operation. When the magnetic head 31 does not perform a reading/writing operation, the magnetic head 31 is parked in a land outside of the magnetic disc. When the disc device is turned on to be used, the magnetic head 31 is moved from the land to be loaded onto the disc medium 10. Here, since the one of the sync mark patterns corresponding to the optimum type of servo information has not yet been read, the position control can not be performed on the magnetic head 31. Therefore, the magnetic head 31 is moved from the land to be loaded onto the disc medium 10 after a predetermined current is supplied to the VCM 33 (VCM current supply). Then, a read current is supplied to the read element 31-1 of the magnetic head 31. A signal output from the read element 31-1 is supplied to the read channel circuit 34.
In step 92, the MCU 36 stores a timeout value in a variable timer before activating the variable timer. Furthermore, the MCU 36 instructs the read channel circuit 34 to enter a sync mark search mode. Thereafter, the MCU 36 initializes a sync mark specifying variable K to “0”.
In step S94, the MCU 36 sets sync mark pattern SM[K] as a sync mark setting value, where K denotes the sync mark specifying variable, and supplies the sync mark setting value to the read channel circuit 34. The read channel circuit 34 searches the signal output from the read element 31-1 for one of the sync mark patterns in accordance with the instruction of the sync mark search mode and the sync mark setting value. When detecting the one of the sync mark patterns, the read channel circuit 34 notifies the MCU 36 of the detection of the one of the sync mark patterns. In a case where the MCU 36 does not receive any notification, the MCU 36 determines that the one of the sync mark patterns has not been detected, and the process proceeds to step S96. On the other hand, when receiving the notification of detection of the one of the sync mark patterns, the MCU 36 determines whether the read channel circuit 34 has detected a gray code corresponding to the one of the sync mark patterns within a predetermined period after the one of the sync mark patterns is detected. When the determination is negative, the process proceeds to step S96.
In step S96, the MCU 36 increments the sync mark specifying variable K by one (K=K+1), that is, the next sync mark pattern is specified. Thereafter, it is determined whether the sync mark specifying variable K is equal to or larger than a maximum value Kmax. When the determination is affirmative, “0” is assigned to the sync mark specifying variable K, which is an initial value.
In step S98, the MCU 36 determines whether time has run out using the timer. Since the time out value has been set to the timer for the sync mark search mode, when the determination is affirmative, the MCU 36 enters an error termination operation. That is, the error termination operation is performed since none of the sync mark patterns is detected within the predetermined period. On the other hand, when the determination is negative, the process proceeds to step S94, and the remaining next sync mark patterns are searched for.
When the MCU 36 determines that the read channel circuit 34 has detected a gray code corresponding to the one of the sync mark patterns within a predetermined period after the one of the sync mark patterns is detected in step S94, the process proceeds to step S100 where the MCU 36 instructs the read channel circuit 34 to enter a mode in which the pieces of servo information corresponding to the one of the sync mark patterns are decrypted with predetermined intervals.
In step S102, since the pieces of servo information are allowed to be decrypted, the MCU 36 drives the VCM 33 through the SVC 37 so that the magnetic head 31 is positioned in the system area (for example, the inner circumference side) of the disc medium 10. The MCU 36 controls the magnetic head 31 to read information in the system area, and the information is supplied to the RAM 38. As described above, since the sync mark patterns corresponding to the heads are stored in corresponding system areas, the sync mark patterns corresponding to the heads are stored in the RAM 38. Therefore, when selecting one of the heads, the MCU 36 controls the read channel circuit 34 to enter a mode in which the sync mark setting value is determined using one of the sync mark patterns selected from the RAM 38.
In this way, the sync mark patterns (selected pieces of servo information) for the heads are stored in the system areas of the discs. Even in a case where a sync mark pattern to be used to read one of the system areas is unknown, when each of the heads are loaded and one of the sync mark patterns is read, a sync-mark setting value of a read channel is successively replaced by a value read from the table listing the sync mark patterns whereby the pieces of servo information of the optimum type are read.
Even in a case where a plurality of heads are used, sync mark patterns for the plurality of heads are automatically set by this reading operation, that is, optimum sync mark patterns for all the heads can be obtained by performing the sync mark search operation on one of the heads.
In the forgoing embodiment, the qualities of the pieces of servo information is evaluated using four types of factor, that is, the sync mark patterns, the gray codes, the position decryption characteristics, and the amplitude characteristics. However, the qualities may be evaluated using some of them. For example, only two items, i.e., the sync mark patterns and gray codes may be used, or only three items, i.e., the sync mark patterns, gray codes, and position decryption characteristics may be used. Furthermore, although in the forgoing embodiment, the three types of servo information are written to the disc, two types of servo information or four or more types of servo information may be written to the disc. Similarly, although the writing parameters correspond to current values in the forgoing embodiment, the writing parameters may correspond to other parameters such as frequencies.
In the forgoing embodiment, the qualities are evaluated using firmware programs of the MCU 36 included in the disc device. However, an external evaluation device connected to the disc device may be used to measure and evaluate the qualities, and in accordance with results of the measurements and the evaluations, the MCU 36 may select one of the plurality of types of servo information. Furthermore, an oscilloscope may be used for monitoring the amplitude measurements.
Furthermore, although the magnetic disc is taken as an example of the disc medium in the forgoing embodiment, any storage medium which uses another type of servo information may be employed. A method for magnetically transferring pieces of servo information to a disc medium or a method for writing pieces of servo information after a disc medium is incorporated in a disc device (device servo track writing or self servo writing) may be employed as the operation of writing the pieces of servo information.
Note that the nonvolatile RAM may be used for storing a selected one of the plurality of servo information therein. In this case, the sync mark search process described with reference to
The embodiments of the present technique are described hereinabove. However, the present technique is not limited to these and various modifications may be made within a scope of the present technique.
Number | Date | Country | Kind |
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2007-208283 | Aug 2007 | JP | national |