KR19980015952A - Servo timing error and servo control method when an error occurs in a specific track - Google Patents

Abstract

end. TECHNICAL FIELD The present invention relates to a servo control method for a servo timing error when a head is switched in a hard disk drive and an error in a specific track.

I. SUMMARY OF THE INVENTION An object of the present invention is to provide servo recovery without performing a parking control immediately when a servo timing error and an error in a specific track occur at the time of head switching.

All. In the present invention, when an error occurs due to a servo discontinuity section of a specific track, a search for offset adjustment is performed to perform servo control so that the head passes over the section, and when the servo timing is out of order, And if so, performs a scan through the head to perform servo control.

la. An important application of the invention: Servo control in hard disk drives

Description

Servo timing error and servo control method when an error occurs in a specific track

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 servo timing error and a method for improving servo control when an error occurs in a specific track.

The demand for high capacity disk drives has led to an increase in the number of tracks in the disk that is the recording medium. The increase in the number of tracks in the disk means a high TPI (Track Per Inch) appearance. The sophistication of the head, the accuracy requirement of the servo light by the servo writer, and the corresponding technological development have made possible the appearance of high TPI (Track Per Inch).

In a HDD, a head is used to read, write, erase data on a disk, and is moved in a radial direction by control of a servo mechanism and positioned on a desired track in a group of tracks in the disk. There are usually a number of discs in the HDD, and the number of heads is corresponding to the number of discs. Therefore, in order to enable the specific head to be enabled, to record and read data on the corresponding disk surface, and to access data on the other disk surface, instantaneous head switching to the head corresponding to the other disk surface must be performed.

There is a servo discontinuity section before and after instantaneous head switching due to head deviation and recording quality of servo information. If the recording quality of the head deviation and the servo information is poor, the head switching control on the disk with a high TPI will be very sensitive to the discontinuous section (which becomes a servo control instability factor). An example will be described with reference to FIG.

In FIG. 1, the hatched area 2 means a servo discontinuity section. The servo discontinuity section may occur in a guard band between a track and a track. In one example of FIG. 1, there is a servo discontinuity section 10 between a track n-1 and a track n. As shown in Fig. 1, during head switching from track n-1 to track n, the head 4 moves along the arrow direction indicated by reference numeral 6 and goes from track n-1 to track n. At this time, unlike the case of track search, the head 4 has a longer distance to travel in the servo discontinuity section 10, so that the servo information continuously fails. That is, a SAM (Servo Address Mark) error and a PES (Position Error Siganl) error are generated. As a result, the servo control in the system becomes impossible. The cause of the servo information fail at the time of head switching is that the track search on the same disk surface controls the head movement (a predetermined value (current) is applied to the actuator equipped with the head) Is a follow-up mode in which no head movement is controlled. 1, S denotes a servo field portion having servo information.

On the other hand, when servo writing is performed in a staggered manner in the servo write method, servo information is recorded on the same cylinder (track) of a plurality of disks as shown in Figs. 2A and 2B. In FIGS. 2A and 2B, two discs, that is, four discs, are used as an example. FIG. 2A shows a case where servo writing is normally performed, and FIG. 2B shows a case where servo writing is abnormally performed. As shown in FIG. 2B, when the head switching (head HD2? HD1) occurs in the abnormal state, the servo error is continuously generated since the position 20 of the actually recorded servo information is far from the position 22 where the servo information is supposed to exist.

This will be described in more detail with reference to FIG. 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 normal SAM detection position, and 34 indicates the actual SAM detection position. When the head is switched from the head HD2 to the head HD3, the system checks the SAM detection at the normal servo position 32-1 assumed to be the servo timing of the previous head, HD2. If the SAM detection is not checked at that position, an F_SAM indicating that SAM is not detected is generated. Then, the SAM detection is checked at the normal servo position 32-2 assumed to be the servo timing of HD2, and if the SAM detection is not checked at that position, do. If F_SAM occurs twice in succession, all servo timings will not occur.

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

Prior to description with reference to FIG. 5, the structure and operation of a conventional hard disk drive will be described with reference to FIG. 4 to facilitate understanding of this technique.

FIG. 4 is a block diagram of a typical hard disk drive, showing two discs as an example. In Fig. 4, the disc 110 is rotated by a spindle motor 134. Fig. The head 112 is positioned on the surface of the disk 110 and is mounted on a vertically elongated arm of an arm assembly of a voice coil motor (VCM) 130. The preamplifier 116 pre-amplifies the signal picked up by the data-reading-out head 112 and drives the head 114 to write encoded data (Encoded Write Data) applied from the read / write channel circuit 118 to the disc 110 Let's record. A read / write channel circuit 118 detects and decodes a data pulse from a read signal applied from the preamplifier 116, applies the data pulse to the DDC 120, codes the write data applied from the DDC 120, do. The DDC 120 interfaces 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 transmitted between the host computer, the microcontroller 124, and the read / write channel circuit 118, and a ROM for storing programs and various setting values of the microcontroller 124. The microcontroller 124 controls track search and track following in response to a read or write command received from the host computer. The VCM driving unit 128 generates a driving current for driving the actuator 130 by a signal for controlling the position of the heads 114 generated from the microcontroller 124, and applies the driving current to the VCM of the actuator 130. The actuator 130 moves the heads 112 on the disk 110 in accordance with the direction and the level of the driving current applied from the VCM driving unit 128. The spindle motor driving unit 134 drives the spindle motor 134 according to a control value for controlling the rotation of the disk 110 from the microcontroller 124 to rotate the disks 110. The disk signal controller 136 generates various timing signals required for read / write, decodes the servo information, and applies the decoded servo information to the microcontroller 124.

Referring to FIGS. 4 and 5, the servo control operation based on the prior art will be described below in the case of an error in a specific track and the case of an error in servo timing.

When the microcontroller 124 of FIG. 5 becomes the servo control routine, the microcontroller 124 of FIG. 5 proceeds to step 200 of FIG. 6 to determine whether the head switching has been performed. If the head is switched, a flag for servo control at the time of head switching is set in step 202, and a F_SAM generated when a SAM as a reference of the servo timing is not detected in step 204 and a gray code GRAY indicating a track address are detected F_GRAY, which is generated when it is not detected, is detected. If F_SAM and F_GRAY are detected, the flow advances to step 210 to increase the error count EC by 1, and the flow advances 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 larger than the validation range value (for example, 32) to see whether the gray code is valid or not. If it is larger, the process proceeds to step 212, and the value of the error count EC is incremented by one.

The microcontroller 124 determines whether the value of the error count EC exceeds the servo control return limit value (for example, '7') in step 212 of FIG. 5. Then, the microcontroller 124 proceeds to step 214 to disable the servo, And ends. If the value of the error count EC does not exceed the limit value (for example, '7'), the process returns to the next servo control routine to perform the process of FIG.

Such a conventional technique causes the parking control to be performed immediately when a servo timing error occurs during head switching and an error occurs in a specific track. Therefore, a method of recovering the servo without performing the parking control has been desired.

Accordingly, an object of the present invention is to provide a servo recovery method that can perform servo recovery without performing a parking control immediately when servo timing error and an error in a specific track occur at the time of head switching.

It is another object of the present invention to provide a servo control method capable of restoring an instantaneously uncontrollable state due to servo information failure to a controllable state at the time of head switching.

According to the above-mentioned object, according to the present invention, when an error occurs due to a servo discontinuity section of a specific track, a search for offset adjustment is performed and servo control is performed so that the head passes over the section. When an error is caused by a deviation in servo timing And performs scanning through the head to go to servo control.

1 is a diagram for explaining that head switching control on a disk having a high TPI (Track Per Inch) is very sensitive to a discontinuous section (which becomes a servo control instability factor).

2A and 2B are diagrams showing servo information servo-written to the same cylinder (track) of disks in a staggered manner.

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

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

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

FIGS. 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 timings do not match at the time of head switching. FIG.

8A and 8B are diagrams for comparing servo control according to the prior art and the embodiment of the present invention when an error occurs in a specific track at the time of head switching (that is, when an error occurs due to a servo discontinuity interval 2 in the track).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same or similar elements among the drawings represent the same reference numerals or the same reference numerals whenever possible.

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

Then, in the present invention, the microcontroller 124 performs a scan enable operation in step 302. That is, the servo information is checked for operation after head switching. It is determined whether F_SAM or F_GRAY is detected in step 304. If it is not detected, it is determined in step 306 whether the difference between the current gray code value CUR_GRY and the previous gray code value PRE_GRY is valid or not Is greater than a verification range value (for example, '32'). If it is not large, it means that the servo information is detected, so the process is terminated as it is. But if CUR_GRY-PRE_GRY It is determined whether the position error signal PES is PES_OVER indicating that the position error signal PES is in an error state. If it is not PES_OVER, the process is terminated because it is normal. However, if PES_OVER is set, the process proceeds to step 312 to perform re-scan enable to check the servo information again. After re-scan enable, it is determined in step 312 that F_SAM or F_GRAY is not detected.

On the other hand, if the F_SAM or F_GRAY is detected in step 304 after the scan enable, the microcontroller 124 directly goes to step 312 to determine whether it is detected once more. In step 312, it is determined whether F_SAM or F_GRAY is detected. If F_SAM or F_GRAY is not detected in step 312, the process proceeds to step 314 where it is determined whether the difference between the current gray code value CUR_GRY and the previous gray code value PRE_GRY is valid, 32 '). If it is not big, it means that the gray code is valid. In this case, the process proceeds to step 316 to determine again whether the PES_OVER is granted. If it is not PES_OVER, the servo information is detected correctly. Therefore, the controller proceeds to step 318 to clear max_EC for error counting in order to determine whether the parking is controlled or not, and ends the process.

However, if F_SAM or F_GRAY is not detected in step 312 or CUR_GRY-PRE_GRY The microcontroller 124 determines in step 320 whether the max_EC exceeds the set value MAX for determining whether or not to perform the parking control. If not, the control proceeds to step 322 to perform search control by offset adjustment. That is, the SEEK DAC_OUT is outputted to the servo driver 128 shown in FIG. 4 to eventually move the head 112. In this case, since the head located in the servo discontinuity section of the specific track can pass through the section to some extent, the servo control becomes feasible in the future. After performing step 322, the microcontroller 124 increases max_EC by 1 in step 324 and returns.

However, if the max_EC exceeds the set value MAX for determining whether or not the parking control is performed in step 320 of FIG. 6, the process proceeds to step 326 to perform the servo disabling, and in step 328, the parking control is performed.

Figs. 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 at the time of head switching is not matched. Fig. FIG. 7A shows timing at the time of servo control according to the prior art, and FIG. 7B shows timing at the time of servo control according to the embodiment of the present invention. Referring to FIG. 7A, in the conventional technique, F_SAM occurs when the servo timing is not matched after head switching, and E_SAM occurs when F_SAM occurs twice. If such E_SAM continues to occur, parking control is performed. On the other hand, referring to FIG. 7B, when the F_SAM occurs twice, the present invention is scanned. However, if the servo timing does not match, the re-scan is performed. So we adjust the servo timing.

FIGS. 8A and 8B are diagrams for comparing servo control according to the prior art and the embodiment of the present invention when an error occurs in a specific track at the time of head switching (that is, when an error occurs due to a servo discontinuity interval 2 in the track) . Fig. 8A shows the timing at the time of servo control according to the prior art, and Fig. 8B shows the timing at the time of servo control according to the embodiment of the present invention. Referring to FIG. 8A, in the conventional technique, after the head is switched, the head 4 passes the servo discontinuity section 2, and when the position error signal PES successively enters the error state twice, offset control is performed by the offset adjustment. That is, the SEEK DAC_OUT is outputted to the servo driver 128 of FIG. 4 to eventually move the head 112 slightly. Then check the servo information (SAM, GRAY, etc.).

As described above, according to the present invention, when an error occurs due to a servo discontinuity section of a specific track, a search for offset adjustment is performed to perform servo control so that the head passes over the section. When an error occurs due to a deviation in servo timing, So that servo recovery can be performed without performing a parking control immediately when servo timing errors and errors in a specific track occur at the time of head switching.

Claims (4)

A servo control method for a servo timing error at the time of head switching and an error at a specific track in a hard disk drive having a head corresponding to the disk surface on a plurality of disks, A first servo control step of performing a search for offset adjustment if an error occurs due to a servo discontinuity section of the specific track and performing servo control so that the head passes over the section; And a second servo control step of performing servo control by performing a scan through the head when an error occurs due to a deviation of the servo timing. The servo control method according to claim 1, wherein the first servo control process and the second servo control process fail, and the parking control is performed. 3. The servo control method according to claim 1 or 2, wherein a re-scan is performed during the servo control by the scan. 4. The servo control method of claim 3, wherein a search for offset adjustment is performed when a position error signal is generated during a scan and a re-scan, respectively.