JP2754408B2 - Servo information demodulation control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a servo information demodulation control method for demodulating servo information for positioning control of a head at a command position without error, and aims at eliminating a determination error when demodulating servo information. An A / D converter for reading servo information combining a track bit indicating a track number by a gray code and a position bit indicating a position displacement, and converting a peak value of a read signal of the servo information into a digital signal; The peak value of the read signal of the track bit converted by the / D conversion unit is compared with a plurality of slice levels to determine whether the track bit is "1" or "0" or uncertain. Unit, a position displacement determination unit that determines a position displacement using a peak value of the read signal of the position bit converted by the A / D conversion unit, and an uncertainty in the determination unit. A correction unit that corrects the fixed result, wherein the uncertainty determination bit in the determination unit determines the direction of deviation from the track boundary by the position displacement determination unit, and the adjacent track number by gray code. The correction is made on the basis of the 1-bit change.

[Industrial applications]

The present invention relates to a servo information demodulation control method for demodulating servo information for positioning control of a head at a command position without error.

Servo information is recorded to position a head for writing information on a recording medium or reading information from the recording medium at a command position. The servo information is read and demodulated to obtain the current position of the head. Thus, the movement is controlled so that the difference from the command position becomes zero, and the head is positioned at the center of the track. Therefore, in order to accurately position the head at the command position, it is necessary to correctly demodulate the servo information.

[Conventional technology]

Generally, servo information in a magnetic disk device uses one phase or a servo pattern. Further, there are a servo surface servo system in which servo information is entirely recorded on a predetermined surface of a magnetic disk, and a sector servo system in which servo information is recorded in a specific sector. There is known a digital servo control system in which such servo information is read by a magnetic head and demodulated by digital processing to control the positioning of the magnetic head.

Also, in the servo surface servo method, the track number is indicated because the number of tracks from the reference position to the command track position cannot be reliably detected with only one-phase or two-phase servo patterns due to high-density recording. A method of recording a track bit in combination with a servo pattern is also known. In the sector servo method, since the servo information cannot be read continuously, a track bit indicating a track number is also recorded.

In general, the track number is represented by a natural binary number. However, since the number of bits that change at the time of carry is large, a gray code (the track bit indicating the adjacent track number) changes by only one bit is used. Gray code)
A method using such a method is also known.

[Problems to be solved by the invention]

As the recording density increases, the track interval and the bit interval gradually become narrower, and reading errors tend to occur. The reading time is reduced by moving the head at a high speed. In this case, in the digital servo control method, the read servo information is sampled and converted into a digital signal, a track boundary is identified by a digital signal processor or the like, and the number of passages from the track boundary is used to determine the distance from the reference position. The current track position will be identified. Therefore, it is necessary to have a relationship between the moving speed and the processing speed so that the next track is not passed while the position information is obtained by digital processing. That is, the moving speed of the head is limited by the processing speed of the digital signal processor.

Therefore, the servo information obtained by combining the track bits indicating the track number is used, and the track position can be identified without detecting the track boundary. However, if there is an error in demodulation of the servo information, the track number will be erroneously identified. Therefore, positioning to the wrong track will occur, or control will fail and runaway will occur. Runaway is likely to result in a head crash.

Also, by using a track number based on a gray code, compared with the case using a natural binary number, only one bit change is required between adjacent tracks, but there is a disadvantage that a one-bit error cannot be avoided.

An object of the present invention is to eliminate a determination error when demodulating servo information.

[Means for solving the problem]

The servo information demodulation control method of the present invention corrects an erroneous determination of a track bit indicating a track number using the properties of a gray code and a direction of deviation from a track boundary. explain.

The servo information is read by combining a track bit indicating a track number by a code in which a binary code represented by a gray code changes by one bit and a position bit indicating a position change, and a peak value of a read signal of the servo information is digitally read. A / D conversion unit 1 for converting a signal
The peak value of the read signal of the track bit converted by the conversion unit 1 is compared at a plurality of slice levels, and it is determined whether the track bit is “1” or “0” or an uncertain one other than these. A determination unit 2 for determining, a position displacement determination unit 3 for determining a position displacement using the peak value of the read signal of the position bit converted by the A / D conversion unit 1, and an uncertain determination result in the determination unit 2 And a correction unit 4 for correcting

Then, the correction unit 4 corrects the uncertainty determination bit in the determination unit 3 based on the direction of deviation from the track boundary by the position displacement determination unit 3 and the 1-bit change of the adjacent track number by the gray code. Things.

[Action]

The peak value of the read signal of the servo information is converted into a digital signal by the A / D converter 1 and is applied to the determination unit 2 and the position displacement determination unit 3. The determination unit 2 determines “1” if the peak value of the track bit is equal to or higher than the slice level at which the track bit reliably becomes “1”. It is determined, and if it is not any of them, an uncertain determination bit is set. That is, when the head moves near the track boundary, the read signal level becomes low, and the track bit cannot be reliably determined to be "1" or "0". . The reason why “1” or “0” is determined by comparing with the slice level is that, for example, if “1” is set at the time of the value “a”, there is a high possibility that erroneous reading will occur due to fluctuations in the flying height of the head. is there.
This part can be replaced with a hardware comparator circuit and a register circuit, and the I / O access time of software can be reduced.

Further, the position displacement determination unit 3 determines position information based on the position bit to determine in which direction the current position of the head is shifted from the track boundary. The correction section 4 corrects the uncertainty determination bit in the determination section 2 based on the direction of deviation from the track boundary in the position displacement determination section 3 and outputs track information. In this case, the track number is a bit pattern that changes by one bit sequentially according to the gray code. For example, if the total bit of “1” in the odd track is an odd number, the total bit of “1” in the even track is an even number and the odd number is In the case where the track is shifted from the track boundary of the numbered track toward the even numbered track, if the total bit of “1” excluding the uncertainty determination bit is an odd number, the uncertainty determination bit is corrected to “1”. Even numbers can be used as track information indicating tracks. Further, the determination unit 2, the position displacement determination unit 3, and the correction unit 4 can be realized by an arithmetic processing function of a digital signal processor.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, showing a case where the present invention is applied to a magnetic disk drive.
Is a signal regeneration circuit, 13 is an A / D converter, 14 is a gate signal generation circuit, 15 is a digital signal processor (DS
P) and 16 are memories (MEM), 17 is a D / A converter, 18 is an amplifier, and 19 is a drive device for moving a magnetic head by a voice coil type motor or the like.

The servo information recorded on the magnetic disk (not shown) is a combination of a track bit indicating a track number by a gray code and a position bit indicating a position displacement, and is read by the magnetic head 11. The read signal of the magnetic head 11 is equalized and amplified by the signal reproducing circuit 12.
It is added to the A / D converter 13 and the gate signal creation circuit 14.

The A / D converter 13 converts the peak value of the read signal into a digital signal. The A / D converter 13 can be replaced with a peak hold + A / D converter. A gate signal that identifies the area and identifies each bit position is created, and the A / D converter 1
3 and the digital signal processor 15. When the sector servo method is used, a gate signal can be formed based on identification data of a sector in which servo information is recorded. Based on this gate signal
The A / D converter 13 converts the peak value corresponding to each bit into a digital signal.

The digital signal processor 15 realizes the functions of the determination unit 2, the position displacement determination unit 3, and the correction unit 4 in FIG. 1 by an arithmetic processing function. , The peak value of the track bit converted by the A / D converter 13 is compared with a slice level L1 that can be reliably determined to be “1” and a slice level L2 that can be reliably determined to be “0”. , Slice level
If the peak value is equal to or greater than L1, it is determined to be "1". If the peak value is equal to or less than the slice level L2, it is determined to be "0". Things.

For example, for the analog display signal shown in FIG.
The slice levels L1 and L2 are set, and the signal a indicated by a solid line having a peak value equal to or higher than the slice level L1 is determined to be “1”, and the signal c indicated by a dotted line having a peak value equal to or lower than the slice level L2 is determined to be “0”. A signal b indicated by a dashed line of the peak value between the slice levels L1 and L2 is used as an indetermination determination bit. The slice levels L1 and L2 are, for example, assumed normal “1”.
70% and 30% with respect to the peak value of
In the case of performing by hardware, two comparators having respective slice levels of L1 and L2 are provided, and both are “1” when both are “H”, “0” when both are “L”, and one is “H” When the other is "L", it is determined to be an indefinite bit.

A function corresponding to the position displacement determining unit 3 is used to determine a deviation from a track boundary. For example, in the case of a two-phase servo pattern, it is indicated as N and Q signals shown in FIG. For these servo signals N and Q, when N> Q is “1” and N <Q is “0”, (b)
The case where> -Q is "1" and N <-Q is "0" is shown in (c), which is 2-bit position information. In this case, for example, if the position information “00” and “11” having a 2-bit configuration correspond to even track numbers, “01” and “10” correspond to odd track numbers.

The in-track displacement is obtained by a known digital processing, and the positioning control to the track center position is performed.

The function corresponding to the correction unit 4 corrects the uncertainty determination bit to a correct bit using the position information obtained from the position bit and the property of the gray code.

Then, since the current position information of the magnetic head 11 is obtained, control information of a difference from the command position information is added to the D / A converter 17, converted into an analog signal, amplified by the amplifier 18, and transmitted to the drive device 19. Drive signal is applied to the magnetic head
11 is movement-controlled and positioned at the command position.

FIG. 5 is a flowchart of the embodiment of the present invention, in which reading of servo information is started, pulse peak data and bit identification data are fetched, and first pulse peak data and bit identification data are set. In this case, the pulse peak data uses the A / D
The data converted by the converter 13 is shown, and the bit identification data is data obtained by converting the read signal of the position bit by the A / D converter 13.

Next, it is determined whether or not it is a track bit. This can be determined based on the gate signal by the gate signal generation circuit 14. If it is not a track bit, it is a position bit, so position information is generated. In the case of a track bit, it is determined whether or not it is higher than the slice level L1 (see FIG. 3).
The bit of the track information is set to “1”. If the slice level is smaller than the slice level L1, it is determined whether the slice level is smaller than the slice level L2. If the slice level is smaller, the bit of the track information is set to "0". If the slice level is larger than L2,
The bit number of the track information is stored in the correction bit number. That is, it is set as an uncertainty determination bit and stored for correction.

Next, the presence / absence of bit data is determined. If there is any remaining bit data, the next pulse peak data and bit identification data are set, and the process proceeds to step. If there is no remaining bit data, it is determined whether or not there is a correction bit number. If there is a correction bit number, "1" and "0" of the correction bit are identified based on the position information obtained in the step. , Track information and position information are determined. That is, since the current position of the magnetic head 11 is obtained, the data servo control process is performed based on the current position.

FIG. 6 is an explanatory diagram of the gray code.
9 shows a natural binary and a gray code in comparison with each other. In the gray code, as described above, the bit sum of "1" is an even number corresponding to an even number of a decimal number, and is an odd number. Correspondingly, it has the property that the bit sum of "1" is odd.

As described with reference to FIG. 4, since the position information of the two-bit configuration [(b), (c)] can indicate whether the track number is an odd track number or an even track number, the correction bit is determined based on the position information. In the step of identifying “1” and “0” of the (indetermination determination bit), it is determined whether the track number is odd or even based on the 2-bit position information. It is determined whether the total bit of “1” is odd or even. For example, when the bit total of “1” excluding the uncertain determination bit is an odd number, if the total bit of “1” is an odd number, When the bit sum of “1” excluding the uncertainty determination bit is an even number, the uncertainty determination bit is forcibly set to “0”.
Is corrected.

Therefore, even when the level fluctuation of the read signal of the servo information is large due to the high-density recording, the track information can be demodulated correctly, so that the head positioning control can be performed without error. Further, the present invention can be applied not only to the magnetic disk drive but also to various systems for controlling the positioning of the head.

〔The invention's effect〕

As described above, according to the present invention, the peak value of the servo information is converted into a digital signal by the A / D converter 1 and compared with a plurality of slice levels L1 and L2. The determination unit 2 determines whether the data is uncertain, and the correction unit 4 corrects the uncertainty determination bit based on the direction of deviation from the track boundary from the position displacement determination unit 3 and the gray code to output track information. Since accurate track information can be obtained, there is an advantage that a malfunction due to servo information accompanying high-density recording and high-speed operation can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a diagram for explaining a judging operation, and FIG.
FIG. 5 is an explanatory diagram of a phase servo pattern, FIG. 5 is a flowchart of an embodiment of the present invention, and FIG. 6 is an explanatory diagram of a gray code. 1 is an A / D conversion unit, 2 is a judgment unit, 3 is a position displacement judgment unit, 4
Denotes a correction unit.

Claims (1)

(57) [Claims] An A / D converter for reading servo information obtained by combining a track bit indicating a track number with a gray code and a position bit indicating a position displacement, and converting a peak value of a read signal of the servo information into a digital signal. And comparing the peak value of the read signal of the track bit converted by the A / D converter with a plurality of slice levels to determine whether the track bit is “1” or “0”. A determination unit (2) that determines whether the position bit is uncertain or not; and a position displacement that determines a position displacement by using a peak value of the read signal of the position bit converted by the A / D conversion unit (1). A determination unit (3); and a correction unit (4) for correcting the uncertainty determination result in the determination unit (2). In the correction unit (4), the determination unit (2) The uncertainty determination bit in the position displacement determination unit ( ) And shift direction from the track boundary by servo information demodulation control scheme and correcting on the basis of a 1-bit change in the adjacent track number by a gray code.