JPH0322228A - Method and device for detecting eccentricity - Google Patents

Abstract

PURPOSE:To detect exact eccentric quantity without being affected by the defect of a disk by demodulating a relative address, and counting the number of the addresses crossing a track in the sample servo system optical disk. CONSTITUTION:A gray code pattern, which is converted to parallel data (a) by a shift register 2, is demodulated to a relative address (b) by a demodulating circuit 3. The relative address (b) is inputted to a latch circuit 4 and a newest relative address (c) and a preceding relative address (d) are stored. A subtracter 5 outputs difference between the relative addresses (c) and (d) as relative velocity (e) to the track of the optical head. On the other hand, when the address crosses the boundary of a track block, a cross deciding circuit 6 outputs a count-up pulse (f) and a count-down pulse (g) according to a crossing direction. An up-down counter 7 counts the pulses (f) and (g) and outputs a count number (h) to an arithmetic circuit 8. Based on the track block cross count number (h) and relative velocity (e), the arithmetic circuit 8 calculates the total number of the tracks to be crossed. A calculated result is stored as the eccentric quantity in a memory 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an eccentricity detection method and apparatus for detecting track eccentricity of an optical disc in an optical information recording/reproducing apparatus.

[Prior Art] Conventionally, several eccentricity detection methods have been known for optical information recording and reproducing devices. Figure 4 is an example.

In FIG. 4, 1 is a sensor amplifier, 101 is a binarization circuit 1%, 102 is a binarization circuit 2, 103 is an F-V converter, 104 is a phase comparator, 105 is an AD converter,
106 is an arithmetic circuit, and 9 is a memory.

The sensor amplifier 1 is a part of an optical head (not shown), and a track error signal p and an on-track signal r are obtained from the sensor amplifier 1. The track error signal p and the on-track signal r are provided by binarization circuits 101 and 10, respectively.
It is binarized with 2.

Since the binarized track error signal S and on-track signal t are out of phase by 90 degrees, by comparing their phases, the direction of the relative speed between the optical head and the track can be determined.

Further, the magnitude of the relative speed between the optical head and the track is proportional to the frequency at which the optical head crosses the track. Therefore, the binarized track error signal S is subjected to F-V conversion (frequency/
After voltage conversion) and analog-to-digital conversion, the value signed by the output U of the phase comparator 104 becomes the relative speed between the optical head and the track.

Since the deviation distance can be obtained by integrating this relative velocity over time t, this value can be stored in the memory 9 at any time and used as the amount of eccentricity.

Figure 5(a) shows the track error signal p when the optical head is fixed and the disk is rotated, and shows how the frequency changes according to the relative speed between the track and the optical head. It is. FIG. 5(b) shows (a
) is a partially enlarged view. FIG. 5(c) is a binarized version of FIG. 5(b).

When FIG. 5(c) is subjected to F-V conversion, the relative speed between the optical head and the track can be obtained. Therefore, by integrating this relative velocity signal and storing it in memory, the amount of eccentricity can be detected.
You can use it.

[Problems to be Solved by the Invention] First, an example of a known format pattern of a sample servo type optical disk used in the eccentricity detection method of the present invention will be described with reference to FIG.

FIG. 6 is a diagram showing the servo area of a track of an optical disk. In the figure, 31a and 3lb are track servo wobbling bits, 32 is a clock pit, and 3
3 is a pattern called a Gray code, in which patterns 1 to 18 shown in FIG. 7 are written periodically and represent a relative address.

In this optical disc, one track includes 1376 servo areas, and each servo error signal for autofocus and autotracking is obtained by sampling and holding signals within the servo area.

First, the tracking error signal is generated by sampling and holding the amount of change in the amount of light from the optical head (not shown) at the timing of the two wobbling bits 31a and 3lb in FIG. 6, and calculating the difference between the two. You can get the error signal.

In addition, the focus error signal is a signal obtained from an optical system similar to the known astigmatism method or knife edge method.
Wobbling bit 31b and gray code 3 in Figure 6
The sample is held and detected on the mirror surface between 3 and 3.

In other words, when the optical head is fixed and the disk is rotated, the track error signal has a stepped waveform as shown in g in FIG. 5(b). Also, the signal obtained by converting this into a binary value is (d)
It is.

However, as is clear from FIG. 5(b), when the relative speed between the optical head and the track is large, the sampling frequency becomes close to the frequency of the track error signal, so the dotted line position in FIG. 5(d) If there is a defect in the disk, pulses may be missed.

In other words, this causes an error in eccentricity detection, and even if you try to detect the amount of eccentricity using the conventional method using this signal,
There was a problem in that it was not possible to accurately detect the amount of eccentricity.

[Means and operations for solving the problems] In order to solve the above-mentioned problems, the present invention records and reproduces information by irradiating a light beam, so that relative addresses provided intermittently on a data track are In an eccentricity detection method for detecting track eccentricity of an optical information recording disk consisting of a Gray code periodically recorded in the radial direction for each track block, the Gray code is demodulated to detect a relative address;
From the difference between the latest relative address and the previous relative address,
Calculating and determining the relative speed between the light beam and the track and the number of track blocks crossed, further calculating and determining the total number of tracks crossed at a predetermined time interval from the relative speed and the number of track blocks crossed, The present invention provides an eccentricity detection method characterized in that the amount of eccentricity corresponds to the rotational position of the disk.

In addition, by irradiating a light beam to record and reproduce information, relative addresses provided intermittently on the data track are
In an eccentricity detection device for detecting track eccentricity of an optical information recording disk consisting of a Gray code periodically recorded in the radial direction for each track block, a demodulation circuit demodulates the Gray code to detect a relative address. and a subtracter that calculates the relative speed of the light beam and the track from the difference between the latest relative address obtained by the demodulation circuit and the previous relative address, and , a cross determination circuit that outputs a crossing determination signal of the track block based on the difference from the previous relative address; an up/down counter that counts output pulses of the cross determination circuit; and the relative speed and the output of the up/down counter. Therefore, the above problem can be solved by an eccentricity detection device characterized by having an arithmetic circuit for calculating the total number of track crossings at a predetermined time interval as the amount of eccentricity, and a memory device for storing the total number of track crossings. This is what we are trying to solve.

According to the present invention, a relative address is detected from a Gray code pattern recorded at a predetermined period in the radial direction on a data track, and a change in the relative address at a predetermined time interval is calculated. , the relative speed of the light beam and the track, and the number of tracks crossing the block can be obtained.

Furthermore, by calculating the total number of track crossings within a predetermined time from this relative speed and the number of track crossings and storing it in memory, the amount of track eccentricity can be obtained.

Therefore, in order to detect the relative velocity, as in the conventional case,
By sampling the frequency of the tracking error signal,
There is no need for binarization, and the error in the relative velocity signal due to the occurrence of pulse dropouts described above can be eliminated.

[Example] Hereinafter, an example of the present invention will be described in detail using the drawings.

First of all, the Gray code shown in FIG. 7 will be explained.

In the gray code shown in Fig. 7, 2 bits out of 10 address bits are "1" (0 display area), 8 bits are "O", and there is a "l" between adjacent tracks. ” position has changed by only l bits. Therefore, even if the optical head passes across two tracks when the tracking servo is off or during seek, information can be reproduced almost correctly. That is, even when the optical head is off-track, it is possible to detect the address of either track on either side. Furthermore, since the pattern changes every l track, the position of the optical head can be detected with l track accuracy.

Since the relative address is intended to be read even when the tracking servo is off, it cannot take too many channel bits, and because it is a gray code, it is a pattern that changes periodically for each certain number of tracks (1B in Figure 7). (Hereinafter, a group of 18 tracks will be referred to as one track block). Therefore, accurately detecting that the track block boundary has been crossed is an essential condition for detecting the position of the optical head.

FIG. 1 is a diagram of an eccentricity detection circuit representing a first embodiment of the present invention. In the figure, l is a sensor amplifier, 2 is a shift register, 3 is a demodulation circuit, 4 is a latch circuit, and 5 is a subtraction circuit. 6 is a cross determination circuit, 7 is an up/down counter, 8 is an arithmetic circuit, and 9 is a memory.

A signal obtained from an optical head (not shown) is amplified by a sensor amplifier 1, and a gray code 1 is generated each time it passes through each servo area.
Serial data for 0 bits is converted into parallel data a by the shift register 2. The Gray code pattern converted into parallel data a by the shift register 2 is demodulated into relative address b by the demodulation circuit 3. The relative address b is input to the latch circuit 4, and the latest relative address C and the previous relative address d are stored. The subtracter 5 subtracts the previous relative address d from the latest relative address C and outputs the value as the relative speed e of the optical head with respect to the track.

When a track block boundary is crossed, the cross determination circuit 6 generates a count up pulse f depending on the crossing direction.
This circuit outputs one countdown pulse g, and will be explained in detail later.

When the count up pulse f and the count down pulse g are generated, the up/down counter 7 counts the number of pulses and outputs the counted number h to the arithmetic circuit 8. The calculation circuit 8 calculates the total number of tracks crossed based on the track block cross count number h and the relative speed e.

The result is stored in the memory 9 as an amount of eccentricity. There are two factors that cause the relative speed e between the optical head and the track: eccentricity of the disk and movement of the optical head during seek.
There is a point. Therefore, regarding these two points, the relationship with the relative velocity e will be explained.

The eccentricity of the disk is generally ±100 μm or less.

Therefore, the displacement of a certain track as seen from the optical head can be approximately approximated by the following equation.

y = 10-' ・sin2z ft lml
- (1) However, f is the number of rotations of the disk. (1)
Since the maximum relative speed represents the difference between the relative address and the previous relative address, let the number of segments in one track be X, and consider the maximum amount of movement of the track between one segment. The time required for the disk to rotate for one segment is ' [s1 ... (4) f-x, and if the track pitch is d, the maximum amount of track movement between one segment is (3 ). From equation (4), it can be expressed as. Here, d=1.5 (μml, x==
1300 (this differs depending on the format, so calculate with a small value to be sure), then the maximum amount of track movement between l segments will be: FIG. 2 is a diagram showing the trajectory of the light beam at the maximum relative velocity due to eccentricity. In FIG. 2, 21 is the center of the track, 22 is the part where the relative address (gray code pattern) is recorded, and 23 is the trajectory of the light beam when it crosses the track from the inner circumference side to the outer circumference side at the maximum speed.
24 is the trajectory of the light beam when it crosses the track from the outer circumferential side of the disk to the inner circumferential side at the maximum speed. In other words, the number of track crossings between l segments caused only by eccentricity is at most ±1.

Therefore, the cross determination circuit 6 performs a track block cross determination according to the rules shown in FIG. 3 from the latest relative address and the previous relative address.

In Figure 3, for example, the previous address was 1, and this time it was l.
If it is 8, it is impossible for the tracks to be in the same track block. In other words, it is always the previous track block, so a countdown pulse is sent. The same applies to other areas marked with "D". Also, for the same reason, since the area "U" is considered to be the next track block, a count-up pulse is sent out.

Furthermore, the portion indicated by "X" in FIG. 3 is an area that cannot exist due to eccentricity alone. In other words, this pattern occurs during seek or when the optical head moves due to disturbances such as external vibrations. Therefore, since accurate eccentricity detection cannot be performed, an error signal is sent and the eccentricity detection count is reset.

Here, for the error signal, a new signal line may be provided between the cross determination circuit 6 and the up/down counter 7, or
The count up pulse and the count down pulse may be sent out at the same time.

The arithmetic circuit 8 calculates the output e (=Dif (n)
=Ad(n)-Adr(n-1)) and the count value h of the up/down counter 7, the total number of tracks traversed T is calculated using the following formula.

T = ti, Dif(k) + h-N...
(7) l However, N represents the number of tracks in the l track block.

In other words, if the value of the total number of track crossings T is stored in the memory 9 at a predetermined time interval starting from a certain timing, then
The data represents the amount of eccentricity corresponding to the rotational position of the disk.

Furthermore, if an error signal occurs during counting, a quick recovery can be achieved by immediately resetting the count and counting again.

Further, in the present invention, the pattern shown in FIG. 7 has been described as the Gray code pattern recorded on the optical disc, but the scope of the present invention is within the scope of the present invention as long as relative addresses in which a predetermined cycle is repeated are recorded. is not limited to the pattern shown in FIG.

[Effects of the Invention] As explained above, according to the present invention, in a sample servo type optical disc, relative addresses are demodulated and
By counting the number of track crossings, it is possible to accurately detect eccentricity without being affected by disk defects.

Further, at the same time, disturbances such as external vibrations can be detected and the count can be reset, which has the effect of quickly returning to eccentricity detection.

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram showing the trajectory of a light beam spot when it crosses a track due to eccentricity.

FIG. 3 is an explanatory diagram of the operation of the cross determination circuit.

FIG. 4 is a block diagram of a conventional eccentricity detection device.

FIG. 5 is a diagram showing a track crossing signal.

FIG. 6 is a diagram showing a servo byte of a sample servo type optical disc.

FIG. 7 is a diagram showing a Gray code pattern.

sensor ambu shift register Demodulation circuit latch circuit subtractor Cross judgment circuit up down counter Arithmetic circuit memory

[Brief explanation of the drawing]

Claims (2)

[Claims] (1) A light beam is irradiated to record and reproduce information, and relative addresses provided intermittently on the data track are
In an eccentricity detection method for detecting track eccentricity of an optical information recording disk consisting of a Gray code periodically recorded in the radial direction for each track block, the Gray code is demodulated, a relative address is detected, and the latest The relative speed between the light beam and the track and the number of track blocks to be traversed are calculated from the difference between the relative address and the previous relative address, and further, from the relative speed and the number of track blocks to be traversed, A method for detecting eccentricity, characterized in that the total number of tracks crossed at an interval is calculated and determined, and the amount of eccentricity is determined according to the rotational position of the disk. (2) Recording and reproducing information is performed by irradiating a light beam, and the relative addresses provided intermittently on the data track are
In an eccentricity detection device that detects track eccentricity of an optical information recording disk consisting of a Gray code periodically recorded in the radial direction for each track block, a demodulation circuit that demodulates the Gray code and detects a relative address. and a subtracter that calculates the relative speed of the light beam and the track from the difference between the latest relative address obtained by the demodulation circuit and the previous relative address, and the latest relative address obtained by the demodulation circuit. , a cross determination circuit that outputs a crossing determination signal of the track block based on the difference from the previous relative address; an up/down counter that counts output pulses of the cross determination circuit; and the relative speed and the output of the up/down counter. An eccentricity detecting device comprising: an arithmetic circuit for calculating the total number of track crossings at a predetermined time interval as an amount of eccentricity; and a memory device for storing the total number of track crossings.