JP2555180B2 - Tracking servo information error detection method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to tracking control in a disc as a recording medium, and more specifically, a head running on a track formed on the disc surface has a predetermined shape. The present invention relates to a tracking servo information abnormality detection method used when performing positioning control of the head so as not to deviate from a correct track position.

[Conventional technology]

FIG. 5 is an explanatory diagram showing a conventional method for detecting tracking servo information.

In the figure, 1 is a servo pattern area on a track formed on the disk surface, 2 is a data area, 3 is a track ID field (area in which a track identification number is written), and 8 is a disk surface. Tracks, 9 is a reproducing head (a magnetic head if the disk is a magnetic disk), 4 is a servo signal waveform reproduced and output by the head 9 when the reproducing head 9 travels on the servo pattern area 1, and 5 is a flaw. , 6 and 7 are also servo signal waveforms reproduced and output by the head 9.

Referring to FIG. As can be seen in the track ID field 3, track 8 with track number n and track 8 with track number (n-1) are shown. As can be seen in the servo pattern area 1, the track 8 with the track number n has the A-phase servo pattern, and the track 8 with the track number (n−1) has the B-phase servo pattern.
The C-phase servo pattern is provided over the track 8 having the track number n and the track 8 having the track number (n-1), and the track 8 having the track number n and the track 8 having the track number (n + 1) not shown. The D-phase servo pattern spans the track number (n-
1) Track 8 and unillustrated track number (n-2)
The D-phase servo pattern is applied to each of the tracks 8.

Assuming that the reproducing head 9 correctly travels on the track 8 of track number n without causing tracking deviation, the servo signal waveform reproduced and output by the head 9 when the reproducing head 9 travels in the servo pattern area 1. Is as shown in 4. That is, the A phase servo pattern is
Since it exists over the entire width of the track 8 of the track number n, the waveform of the signal reproduced and output by the head 9 also becomes large, and the C-phase and D-phase servo patterns extend over the 1/2 width of the track 8 of the track number n. It will be appreciated that the waveform of the signal reproduced and output by the head 9 is approximately half because it is present.

In other words, the head 9 is the track 8 with the track number n.
When traveling above, the head 9 reproduces the C-phase servo pattern to obtain the peak level Cpeaklevel of the signal.
And the peak level Dpeaklevel of the signal obtained by reproducing the D-phase servo pattern | Cpeaklevel−Dpe
If the positioning control of the head 9 is performed so that the aklevel | is constantly 0, the head 9 can be correctly run without causing tracking deviation with respect to the track 8 of track number n.

The reproduction output signal of the servo pattern used in the tracking positioning control of the head is called tracking servo information.

[Problems to be Solved by the Invention]

Now, in FIG. 5, it is assumed that the scratch 5 is generated for some reason on the track of the track number n across the C-phase servo pattern and the D-phase servo pattern. Then, even if the reproducing head 9 travels correctly on the track, the waveform of the reproducing output signal by the head 9 at that time is such that the reproducing output by the scratch 5 is added to the reproducing output by the servo pattern. If the damage is 5 in nature, the signal waveform is as shown in 6, and the C-phase or D-phase servo pattern is reproduced rather than the peak level of the signal obtained by reproducing the A-phase servo pattern. There is a logical contradiction that the peak level of the obtained signal is higher.

Further, in the C-phase or D-phase servo pattern, if the scratches 5 are such that the playback output is reduced in the portion that overlaps with the scratches 5, the playback output signal waveform as shown in 7 appears and the playback head 9 Even though the vehicle is traveling correctly on the track, there arises a disadvantage that a reproduction output signal (servo signal for positioning control of the head 9) by the C-phase or D-phase servo pattern cannot be obtained. That is, if such an incomplete servo signal is used, an abnormal off-track of the head (displacement of the head from the center position of the track) and runaway of the head during track access may be caused.

An object of the present invention is to solve the problems in the prior art as described above, and to obtain tracking servo information when a flaw is caused for some reason across the C-phase servo pattern and the D-phase servo pattern. An object of the present invention is to provide a method for detecting abnormality in tracking servo information, which is capable of quickly detecting an abnormality in.

[Means for solving the problem]

In order to solve this problem, after digitizing the peak level of each phase of the servo signal, it was digitized,
Based on the values (A, B, C, D) of each phase (A phase, B phase, C phase, D phase),
Find the magnitude relationship of each phase. The relationship is a logical relationship that can be confirmed by the arrangement of servo patterns, for example, C when B> A.
> B and D <C or C <B and D> C, an error is generated if they do not match (logical pattern matching). Similarly, from the servo pattern layout, If the value of is supposed to be always constant, a window is provided with this value and an error is made outside the window (absolute pattern matching). In addition, obtained in the previous sample,
The difference between the value (A ', B', C ', D') and the current value (A, B, C, D) is set according to a certain standard to establish a window for judgment (absolute pattern matching ).

[Operation] It is possible to obtain highly reliable servo information by digitizing the value of each phase which is servo information, performing logical pattern matching and absolute pattern matching, and detecting an abnormality.

〔Example〕

FIG. 1 is a chart showing an outline of a processing flow for performing abnormality detection of servo information as an embodiment of the present invention. First, the servo pattern written for each sector of the disk is sampled and held, and then digitized. Next, the magnitude relationship is determined from the peak value of each phase, processing S11 is performed as logical pattern matching, and then processing S12 is performed as absolute pattern matching.
Perform S13.

2 and 3 show the processing flow shown in FIG. 1 and the data for pattern matching.

In FIG. 2, the digitized A phase values: A and M /
2 (M: maximum detection value of each phase), Then, A = Big is set (process S1). This is because the value of the phase closest to the head is> M / 2 due to the characteristics of the servo pattern. what if Assuming that is established, and if the process further proceeds to S2, S3, S4,
The magnitude relationship is D>C>B> A, and A = Big, B = Bi
g, C = Big, D = Big. In this way, the magnitude relationship in each phase is determined.

In FIG. 3, (D = Bi
If g, C = Big, B = Big, A = no Big), this is (0,0,0,1)
Is represented. When the result of the processing performed in FIG. 2 and each pattern in FIG. 3 are matched and the ERROR data, for example, (A, B, C, D) = (1,1,1,1), is matched, ERROR
To determine. In this way, the servo information can be checked from the logical contradiction.

Wakasen will supplement this point. For example,
When B> A and C> B and D> C are represented by the above logical pattern, (D = Big, C = Big, B = Big, A = Big) = (0,0,0, 0) or (0,0,0,1). This pattern causes an error as shown in the data example of FIG.

Considering the positional relationship between the head and the servo pattern, as shown in FIG. 6, when B> A and C> B, the area where the center of the head can exist is G1, then B> A and D
Similarly, when G> 2 when> C, there is no region where G1 and G2 intersect. Therefore, when B> A, C> B and D
The pattern of> C is an error.

FIG. 4 is an explanatory diagram showing absolute pattern matching. Depending on the characteristics of the servo pattern, be sure to Then (see (a)), this value (M) is compared with the obtained servo information, and if they do not match, it is determined to be ERROR (see (b) and (c)). As a result, the error 5 can be determined even when the scratch 5 is present as shown in FIG. 4 (see (d)) and the D phase does not appear in the servo signal.

Next, absolute pattern matching is performed. this is,
Head position error information (| A'-B '|, or | C'-D' calculated by the preceding sampled servo information
)) And the current position error information (| A-B |, or | C-D |) has a dimension of velocity, and if this value is above a certain threshold, It is judged as ERROR.
For this threshold value, the maximum speed that can occur in normal disturbance (disk eccentricity, etc.) may be selected. With this function, the absolute value of servo information can be evaluated.

As described above, highly reliable servo information can be obtained, and at the time of ERROR, the previously sampled servo information can be used for control, and a powerful ERROR correction function can be added to the position. It is possible to prevent erroneous operation during control or speed control and perform stable control.

[Advantages of the Invention] By performing logical pattern matching or absolute pattern matching on servo information, highly reliable servo information can be obtained. As a result, in position control, it is possible to prevent abnormal off-track of the head due to inaccurate servo information.

[Brief description of drawings]

FIG. 1 is a chart showing a processing flow as an embodiment of the present invention, FIG. 2 is a flowchart showing processing of logical pattern matching, FIG. 3 is an explanatory view of an example of data used for logical pattern matching, and FIG. FIG. 5 is an explanatory diagram showing an absolute pattern matching process, FIG. 5 is an explanatory diagram of a conventional tracking servo information detecting method, and FIG. 6 is an explanatory diagram of error processing by logical pattern matching. Explanation of symbols 1 ... Servo pattern area, 2 ... Data area, 3 ...
Track ID field, 4 ... Servo signal waveform, 5 ...
Scratches, 6,7 ... Servo signal waveform, 8 ... Track, 9 ...
… Playhead.

Claims (1)

(57) [Claims] 1. A method for detecting an abnormality of tracking servo information used when performing positioning control of a head running on a track formed on a disk surface so that the head does not deviate from a predetermined correct track position. Servo patterns are applied in advance, and tracking servo information as a reproduction output obtained by reproducing the patterns by the head traveling on the tracks is compared with time, and from the arrangement of the patterns applied on the tracks, When the comparison result is not logically correct, or the tracking servo information as the reproduction output obtained over time from the head is arithmetically processed, and the absolute value of the processing result deviates from the predetermined threshold range. Playback, or when the head travels over a certain section of the track. The tracking servo information as the above is compared with that obtained when the head runs in the next predetermined section, and when the difference deviates from a predetermined threshold range, the tracking servo information as the reproduction output A method for detecting abnormality in tracking servo information, which is characterized by determining that the is abnormal.