KR100288286B1 - Sero control method upon the error of a certain track and the error of servo timing - Google Patents

Abstract

PURPOSE: A servo control method in case of servo timing error generation and predetermined track error generation is provided to make servo recovery possible without carrying out parking control immediately, when a servo timing error or a predetermined track error is generated in case of head switching. CONSTITUTION: A servo control method in case of servo timing error generation and predetermined track error generation includes a first servo control step of carrying out search for offset control if an error is generated in a servo discontinuous section of a predetermined track when switching heads, thereby passing the switched head by a servo discontinuous section boundary, and a second servo control step of carrying out scanning of corresponding track via the switched head when an error is generated by the miss-servo timing when switching the heads, thereby confirming valid servo information.

Description

SERVO TIMING UPON THE ERROR OF A CERTAIN TRACK AND THE ERROR OF SERVO TIMING}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hard disk drive (hereinafter referred to as an HDD), and more particularly to a method for improving servo control in the event of a servo timing error and an error in a specific track.

The demand for high capacity disc drives has led to an increase in the number of tracks in the disc, which are recording media. This increase in the number of tracks in the disc means the appearance of high Track Per Inch (TPI). The sophistication of the heads and the demand for accuracy of the servolites by the servowriter and the corresponding technological advances have made possible the emergence of high TPI (Track Per Inch).

In the HDD, the head is used to read, write, and erase data on the disk, and is moved in the radial direction by the control of the servo mechanism to be located on a desired track in the track group in the disk. There are usually many disks in the HDD, and the number of heads corresponds to the disk surface. Therefore, in order for a specific head to be enabled to record and read data on a corresponding disk surface, and to access data on another disk surface, there must be instantaneous head switching to a head corresponding to the other disk surface.

There is a servo discontinuity section between before and after instantaneous head switching due to head deviation and recording quality of servo information. If the head deviation and servo record quality are not good, the head switching control on the disk with high TPI is very sensitive to the discontinuity section (which causes the servo control instability). An example thereof will be described with reference to FIG. 1.

In Fig. 1, the hatched area 2 means the servo discontinuity. The servo discontinuity may have a guard band between tracks. In the example of FIG. 1, there is a servo discontinuity 2 between track n-1 and track n. As shown in FIG. 1, when switching heads from track n-1 to track n, head 4 proceeds in the direction of the arrow indicated by reference numeral 6 to go from track n-1 to track n. In this case, unlike the track search, the head 4 becomes longer in the distance between the servo discontinuity sections 2, and thus the servo information is continuously failed. That is, a SAM (Servo Address Mark) error and a Position Error Signal (PES) error occur, and as a result, servo control in the system becomes impossible. The reason that servo information failure occurs easily during head switching is because the track search on the same disk surface is a search mode for controlling head movement (a predetermined value (current) is applied to the head mounted actuator), but at the time of head switching. This is because it is a tracking mode to control the head movement. In FIG. 1, S denotes a servo field portion in which servo information is present.

On the other hand, when servo writing is performed in the staggered method of the servo writing method, servo information is recorded in the same cylinder (track) of a plurality of discs as shown in FIGS. 2A and 2B. In FIG. 2A and FIG. 2B, the case where two disks, ie, the disk surface is four surfaces, is taken as an example. FIG. 2A illustrates the normal servo write and FIG. 2B illustrates the abnormal servo write. In the abnormal case as shown in FIG. 2B, when the head switching (head HD2-> HD1) occurs, the servo error continuously occurs because the position 20 of the actually recorded servo information is far from the position 22 assuming that the servo information exists.

This will be described in more detail with reference to FIG. 3. In FIG. 3, it should be understood that 30 indicates the SAM detection position by the previous head, 32-1 and 32-2 indicate the SAM detection position under normal assumption, and 34 indicates the actual SAM detection position. When head switching from head HD2 to head HD3, the system checks for SAM detection at the normal servo position 32-1, which is assumed to be the servo timing of the previous head, HD2. If SAM detection is not checked at that position, F_SAM is generated.Then, SAM detection is checked at normal servo position 32-2, which is assumed to be servo timing of HD2, and if SAM detection is not checked at that position, F_SAM is generated again. do. If F_SAM occurs twice in a row, all servo timings will not occur.

In the case of an error occurrence in a specific track described with reference to FIG. 1 and an error occurrence due to the servo timing described with reference to FIGS. 2A, 3, and 3, a conventional servo control operation as shown in FIG. 5 is performed.

Before describing with reference to FIG. 5, the configuration and operation of a conventional hard disk drive will be described with reference to FIG.

4 is a block diagram of a conventional hard disk drive, and shows two disks as an example. In FIG. 4 the disk 110 is rotated by the spindle motor 134. The head 112 is located on the surface of the disk 110 and is installed on a vertically extending arm of the arm assembly of the voice coil motor (hereinafter referred to as VCM) 130. The preamplifier 116 preamplifies the signal picked up by the head 112 at the time of reading data. The data amplifier is configured to drive the head 114 to read encoded write data applied from the read / write channel circuit 118 to the disc 110. Record it. The read / write channel circuit 118 detects and decodes a data pulse from a read signal applied from the preamplifier 116 and applies it to the DDC 120, and codes the write data applied from the DDC 120 to the preamplifier 116. do. The DDC 120 interfaces the communication between the host computer and the microcontroller 124 and between the host computer and the read / write channel circuit 118. The memory unit 126 includes a buffer RAM for temporarily storing data transferred between the host computer, the microcontroller 124 and the read / write channel circuit 118, and a ROM for storing the execution program of the microcontroller 124 and various setting values. The microcontroller 124 controls track search and track following in response to a read or write command received from the host computer. The VCM driver 128 generates a driving current for driving the actuator 130 by a signal for position control of the heads 114 generated from the microcontroller 124 and applies it to the VCM of the actuator 130. The actuator 130 moves the heads 112 on the disk 110 in response to the direction and level of the driving current applied from the VCM driver 128. The spindle motor driver 134 rotates the disk 110 by driving the spindle motor 134 according to a control value for the rotation control of the disk 110 from the microcontroller 124. The disk signal controller 136 generates various timing signals necessary for read / write, decodes the servo information, and applies it to the microcontroller 124.

4 and 5, the servo control operation based on the prior art in the case of an error occurrence in a specific track and in the case of an error caused by the servo timing is explained as follows.

When the microcontroller 124 of FIG. 5 becomes the servo control routine, the microcontroller 124 proceeds to step 200 of FIG. 6 to determine whether head switching is performed. If the head is switched, in step 202, a flag for servo control during head switching is set, and in step 204 and 206, F_SAM and gray code gray indicating a track address are detected when a SAM which is a reference for servo timing is not detected. It is determined whether F_GRAY that occurs when it is not detected. If F_SAM or F_GRAY is detected, the controller proceeds to step 210 and increases the error count EC by 1 and goes to step 212. In step 208, it is determined whether the difference between the current gray code value CUR_GRY and the previous gray code value PRE_GRY is greater than the validity verification range value (for example, '32') to determine whether the gray code is valid. If large, go to step 212 to increase the error count EC by one.

In step 212 of FIG. 5, the microcontroller 124 determines whether the value of the error count EC exceeds the servo control returnable limit value (eg, '7'). Then, the microcontroller 124 proceeds to step 214 to disable the servo and the parking control in step 216. And exit. If the value of the error count EC does not exceed the threshold (eg, '7'), the process returns to the next servo control routine and performs the process of FIG. 5 again.

In this conventional technique, if a servo timing error or an error in a specific track occurs during head switching, parking control is immediately performed. Therefore, even in such a case, a method for recovering the servo without performing the parking control has been desired.

Accordingly, an object of the present invention is to provide a method for recovering a servo without performing parking control immediately when a servo timing error and an error in a specific track occur during head switching.

Another object of the present invention is to provide a servo control method capable of restoring an instantaneous uncontrollable state due to a poor servo information during head switching to a controllable state.

According to the above object, the present invention performs a search for offset adjustment when an error occurs due to a servo discontinuity section of a specific track, servo control the head to pass the section, and if an error occurs due to a shift in the servo timing Scanning through the head is performed to control the servo.

1 is a diagram for explaining that head switching control in a disk having a high track per inch (TPI) is very sensitive to a discontinuity section (which causes servo control instability).

2A and 2B show servo information servowritten to the same cylinder (track) of disks in a staggered manner;

3 is a view for explaining the occurrence of a servo timing error due to head switching when servo information is abnormally servo written as in FIG. 2B.

4 is a block diagram of a conventional hard disk drive.

Fig. 5 is a flowchart of a conventional servo control operation in the case of a servo timing error and an error in a specific track.

6 is a flowchart of a servo control operation according to an embodiment of the present invention in the case of a servo timing error and an error in a specific track.

7a to 7b are views for comparing the servo control according to the prior art and the embodiment of the present invention when the servo timing does not match when switching the head.

8A and 8B are views for comparing the servo control according to the prior art and the embodiment of the present invention when an error occurs in a specific track when the head is switched (that is, when an error occurs because the track has a head in the servo discontinuity section 2). drawing.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same parts or the same components in the drawings represent the same reference numerals or the same reference signs wherever possible.

6A and 6B are flowcharts illustrating a servo control operation according to an embodiment of the present invention in the case of a servo timing error and an error in a specific track during head switching. Operation of steps 200 to 212 indicated by reference numeral 300 in FIG. 6A is the same as that of steps 200 to 212 in FIG. 5, which is a flowchart of performing a servo control operation according to the prior art. The operations of steps 200 to 212 are summarized by confirming the servo timing error and the occurrence of an error in a specific track during head switching.

Thereafter, in the present invention, the microcontroller 124 performs scan enable in step 302. That is, the operation enables the inspection of the servo information after the head switching. After scanning enable, in step 304, it is determined whether F_SAM or F_GRAY is detected. If not, proceed to step 306 to check whether the difference between the current gray code value CUR_GRY and the previous gray code value PRE_GRY is valid for gray code. It is determined whether it is larger than a range value (eg, '32'). If not large, it means that the servo information is detected. However, if vert CUR_GRY-PRE_GRY vert is less than the validity check value, the process proceeds to step 302 to determine whether the position error signal PES is PES_OVER indicating that an error condition is present. If PES_OVER is not normal, the process ends. If it is PES_OVER, however, the process proceeds to step 312 and rescans the servo information again. In step 312 after the rescan enable, it is determined whether F_SAM or F_GRAY is detected.

On the other hand, if the F_SAM or F_GRAY is detected in step 304 after the scan enable, the microcontroller 124 immediately proceeds to step 312. In step 312, it is determined whether F_SAM or F_GRAY is detected. If no F_SAM or F_GRAY is detected in step 312, the controller proceeds to step 314 to determine whether the difference between the current gray code value CUR_GRY and the previous gray code value PRE_GRY is valid for the gray code. 32 '). If it is not large, the gray code is valid. In that case, the process proceeds to step 316 to determine whether the PES_OVER is again. In this case, since the servo information is properly detected, if not PES_OVER, the flow proceeds to step 318 where the error count max_EC is cleared to determine whether the parking control is performed, and the process ends.

However, if F_SAM or F_GRAY is not detected in step 312 or if vert CUR_GRY-PRE_GRY vert is greater than the validity confirmation value, the microcontroller 124 determines whether the max_EC exceeds the set value MAX for determining whether the parking control is performed in step 320. If no, the flow proceeds to step 322 where search control for offset adjustment is performed. That is, SEEK DAC_OUT is outputted to the servo driver 128 of FIG. 4 to eventually move the head 112. This makes it possible for the head located in the servo discontinuity section of a particular track to pass the boundary of the servo discontinuity section to some extent, thereby increasing the possibility of the subsequent servo control. After performing step 322, the microcontroller 124 increases max_EC by 1 and returns in step 324.

However, if max_EC exceeds the set value MAX for determining whether the parking control is performed in step 320 of FIG. 6, the controller proceeds to step 326 to perform the servo disable, and performs the parking control in step 328.

7A and 7B are diagrams for comparing the servo control according to the prior art and the embodiment of the present invention when the servo timing does not match during head switching. 7A shows a timing during servo control according to the prior art, and FIG. 7B shows a timing during servo control according to an embodiment of the present invention. Referring to FIG. 7A, when the servo timing is not correct after the head switching, F_SAM occurs and F_SAM occurs twice. If such E_SAM still occurs, parking control is eventually performed. In contrast, referring to FIG. 7B, when an F_SAM occurs twice, an embodiment of the present invention is scanned, and if the servo timing is not correct, rescanning is performed. So set the servo timing.

8A and 8B are diagrams for comparing servo control according to the prior art and an embodiment of the present invention when an error occurs in a specific track (ie, an error occurs due to a servo discontinuity section 2 in the track) during head switching. . 8A illustrates a timing during servo control according to the prior art, and FIG. 8B illustrates a timing during servo control according to an embodiment of the present invention. Referring to FIG. 8A, the conventional technique generates a continuous error as the head 4 passes through the servo discontinuity section 2 after the head is switched. However, referring to FIG. 8B, in the present invention, after the head is switched, when the head 4 passes through the servo discontinuity section 2, when the position error signal PES is continuously in error state twice, search control by offset adjustment is performed. That is, SEEK DAC_OUT is outputted to the servo driver 128 of FIG. 4 to eventually move the head 4 slightly. After that, check the servo information (SAM, GRAY, etc.).

As described above, according to the present invention, when an error occurs due to a servo discontinuous section of a specific track, a search for offset adjustment is performed to servo control the head to pass through the section, and when the error occurs due to a shift in the servo timing, the corresponding head Since the servo control is performed by scanning, if the servo timing error and the error in a specific track occur during head switching, the servo can be recovered without performing the parking control.

Claims (4)

In the hard disk drive having a plurality of heads corresponding to the head of each of the disk surface of the at least one disk, in the servo timing error during head switching and servo control method when an error occurs in a specific track, A first servo control for performing servo search for offset adjustment by performing a search for offset adjustment when an error occurs due to a servo discontinuity section of the specific track during head switching between the plurality of heads; Process, If an error occurs due to the shift of the servo timing during head switching between the plurality of heads, a second servo control process is performed to perform servo scan to check valid servo information by performing a corresponding track scan through the switched head. Servo control method characterized in that. 2. The servo control method according to claim 1, wherein the parking control is performed when the first servo control process and the second servo control process fail. The servo control method according to claim 1 or 2, wherein rescanning is performed when the servo control fails due to the scan. 4. The servo control method according to claim 3, wherein a search for offset adjustment is performed when a position error signal is generated during scanning and rescanning.