JPS59171035A - Track access system in optical disk device - Google Patents

Abstract

PURPOSE:To increase a track shift signal level by detecting a tracking signal in a state that a read beam of an optical head is shifted from a focus against an optical disk, in a moving period by an access mechanism, in an optical disk device. CONSTITUTION:An optical head is moved, and a counting value of a track counting part 22 in said moving time, and a tracking information stored in a registor 24, namely, the number of tracks extending form a present position to a target track are compared by a comparator 23. At the time point when both of them coincide, a tracking stop signal is outputted by a VCM stop signal generating part 25, and a movement of the optical head is stopped. At this time point, an offset setting part 16 is reset so as to set a lens of the optical head to a focused state. At this position, an address signal of a sector address part is read out, and basing on it, the number of track errors to the target track is calculated. By a dense access mechanism, the lens of the optical head can be corrected and displaced to a prescribed track position.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to an optical disk device, and particularly to a track access method thereof.

(b) Technical background Recently, the development of optical disk devices for digital information has been attracting attention as a conventional high-density, high-quality recording/reproducing system.

In general, information recording and reproduction on an optical disk is performed by forming holes on a disc made of resin or the like by partially removing a hole with a diameter of about 1 μm or a reflective layer made of a thin metal film, etc., and forming written as different parts,
At the time of reproduction, a magnetic recording layer is provided on the same disk as a device for detecting changes in the intensity of reflected light in the portion, and a light beam is irradiated onto the recording layer to form a magnetization reversal portion,
A so-called magneto-optical disk has been proposed, which reads information by using the Faraday effect or the Kerr effect due to the magnetization reversal portion during reproduction.

Normally, these information billets are written on the disk in concentric or spiral rows with a pitch of about 2 μm (this one round is called a track), but the disk has a data area. The guide groove part and the bit string as address information such as trunk number and sector number are pre-grouped in advance, and when recording and reproducing information, the guide groove part and address information are detected and the bit string is pre-grouped. and sectors to write or read the desired information.

Therefore, in order to write and read information, it is necessary to accurately track the tracks on the rotating disk (hereinafter referred to as an optical disk).

Normally, in an optical disk device, as shown in FIG. 1, the optical head 1 is moved by a predetermined amount along the axis 3 of the coarse access mechanism 2 in a direction parallel to the surface of the optical disk 40, so as to be almost in the vicinity of a target track. reach.

In this case, as a drive source, for example, a voice coil motor (
VCM (not shown) is used.

In the movement by the rough access mechanism 2, the inertia of the optical head is large, and the drive accuracy by the VCH is generally not sufficient (1) This alone cannot guarantee accurate movement to the target track position. For this purpose, the optical head is moved a predetermined amount of movement by the coarse access mechanism 2, that is, after reaching almost the vicinity of the target track, the optical head is further moved by a fine access mechanism (not shown) provided inside the optical head. omitted) by
It is moved so that the positional error with respect to the track is compensated for.

In addition, in FIG. 1, 5 is a rotation mechanism for the optical disc 4.

(C1 Prior Art and Problems) When the optical head is moved by the coarse access mechanism as described above, the method of obtaining the position signal required is to count the number of movements of the moiré fringes as the optical head moves; Some use a trunking signal (commonly known as a track deviation signal) generated when a light beam crosses a trunk.

The former has the disadvantage that it is difficult to align the moiré fringes and the sensors used to detect them, and the cost is high to obtain high positional accuracy.On the other hand, the latter has the drawback that the light beam happens to hit the trunk When the trunk shift signal passes through the constituent track sector address portions, the waveform of the trunk shift signal is disturbed, resulting in a drawback of causing a counting error.

Below, some supplementary explanations will be given regarding the optical head and the track/track deviation signal. , FIG. 2 is a diagram showing an outline of the configuration of the optical head 1 in FIG. 1, in which the emitted light beam from a light source 6, such as a laser, enters a beam splinter, for example, and the polarized light component in the direction perpendicular to the plane of the paper is is reflected toward the lens 8 and projected onto the optical disk 4.

Since the λ/4 wavelength plate 9 is provided on the optical path of the light beam, the light beam that is reflected by the optical disk 4 and enters the beam block 7 again travels straight through this, and the optical sensor 1
0. The optical sensor 10 consists of two parts, and the output from each part is input to a differential amplifier 11.
The difference signal is taken out as the 1-rank shift signal.

The trunk shift signal is originally a position detection signal for controlling the optical axis of the optical head to face the center of the track width, but when the optical head moves on the optical disk, the light beam is It is used to detect the number of tracks crossed by counting the number of times the signal changes from positive to negative each time the rank is crossed.

FIG. 3 is an enlarged schematic diagram of a part of the track on the optical disk, and one revolution of each track is, for example, 35
The trunk (
(called a sector) is a tracking guide groove (approximately 1 μm wide,
depth λ/8) and sector address part (pit row corresponding to track number and sector number, depth λ/8) and sector address part (pit row corresponding to track number and sector number).
4). Several tens of thousands of such tracks are arranged in the radial direction of the optical disk at a pitch of about 2 μm.
It is arranged in about a book size.

By the way, when the optical head moves (tracks) to a predetermined track, it passes over the guide groove section (2) or the l-rank sector address section (2), as shown in FIG. The moving speed of the optical head during the tracking is, for example, several thousand times per rotation of the optical disk.
1- Since the speed is high enough to cross the rack, the guide groove portion (■) or the track sector address portion (■)
Which one you pass through is purely a matter of chance.

As mentioned above, the depth of the groove in the guide groove part ① is λ/8
The bit depth in the trunk sector address portion (2) is set to λ/4. This is because the largest track deviation signal output is obtained when the width of the guide groove part (2) is 0.8 μm and the depth is λ/8.
This is because the trunk sector address signal is at its maximum when the depth of the trunk is λ/4.

FIG. 4 is a diagram showing the magnitude of the trunk deviation signal output from the differential amplifier (see FIG. 2) with respect to the depth of the guide groove while the light beam crosses the trunk, The track deviation signal reaches a maximum when the depth is λ/8 and reaches a minimum when the depth is λ/4. Further, the output signal waveforms in these are S-shaped and distorted bimodal, respectively, as will be described later.

FIG. 5 is a diagram showing the magnitude of the trunk deviation signal with respect to the deviation of the optical beam from the center of the track width (off-trunk) when the depth of the guide groove is λ/8 and when the depth is λ/4. This corresponds to the track deviation signal waveform that occurs while the optical gutter crosses one 1-rank. Curves (a) and (b) in the same figure
correspond to the signal waveforms obtained at the depths indicated by arrows (a) and (b) in FIG. 4, respectively. As shown in FIG. 5, when the track depth is λ/8, it becomes an S-shape, while when it is λ/4, the S-shape is distorted and becomes a bimodal shape.

As is clear from the following, when the light beam crosses the I-rank sector address part in a certain track during l-racking, the trunk shift signal output may be small and not detected, or even if it is detected, multiple signals may be detected. This may cause an inconvenience in that the user may be detected as if he or she had crossed the line.

As a result, it becomes difficult to accurately count the number of passing tracks.

Note that during tracking, the track deviation signal detection system is normally set to a low frequency band, so even if the track sector address signal bit crosses the trunk sector address part as described above, the individual track sector address signal bits will not be detected separately. , can be handled in the same way as the guide groove section.

(d1 Purpose of the Invention The present invention provides a counting method that does not cause the above-mentioned tracking error, which has been a problem in conventional optical disk devices.
That is, it is an object of the present invention to provide a method that allows the amount of movement of the optical head by the phase access mechanism to be detected with high accuracy.

te1 Structure of the Invention The present invention includes an access mechanism for moving an optical head a predetermined amount in the radial direction of an optical disk, and uses a trunking signal obtained from the optical head to detect the amount of movement.
In an optical disk device, the tracking signal is detected while the read beam of the optical head is shifted from its focus with respect to the optical disk during a period of movement by the access mechanism.

(Example of f1 invention Embodiments of the present invention will be described below with reference to the drawings.

The gist of the present invention is that when the light beam is appropriately shifted from the focused state, the output of the trunk shift signal becomes large when it crosses the track sector address portion, and its waveform is It has been discovered that the output waveform of the groove portion has an S-shape, which is almost the same as that of the groove, and this is used to control the light beam to deviate from the focused state during tracking, thereby detecting the trunk shift signal.

FIG. 6 shows the magnitude of the track deviation signal when the light beam projected onto the optical disk is deviated from the focused state (that is, the deviation in the optical axis direction of the relative position of the lens of the optical head with respect to the optical disk). 2, the +Z side is the direction in which the lens moves away from the optical disk, and the -2 side is the direction in which the lens approaches (see FIG. 2).

As shown in the figure, the change in the track deviation signal with respect to the deviation from the in-focus state position differs depending on the guide groove or focus depth of λ/8 and λ/4, but depending on the appropriate deviation In both cases, it is possible to obtain a sufficiently large track deviation signal. That is, when the focus of the lens is shifted in the direction away from the optical disk, the track deviation signal level increases in both cases where the depth is λ/8 and λ/4, and the level of the track deviation signal increases from the depth λ/4. Signal waveform distortion is reduced. Therefore, in order to accurately count the number of trunks that have passed during tracking, it is effective to not shift the focus of the lens by an appropriate amount in the direction away from the optical disk, within the range where the light beam does not cross between I and rank. become.

FIG. 7 is a diagram showing the track deviation signal waveform, in which (A) is a waveform obtained in an in-focus state according to the conventional method, and (B) is a waveform obtained in an out-of-focus state according to the method of the present invention. This is the output waveform.

In the conventional waveform obtained in a focused state, the signal waveform output every time it crosses a guide groove portion whose depth is λ/8 is a regular sine wave, but when the depth is λ/4 The signal waveform (c) output every time it crosses a track sector address portion is distorted and has two peaks in one period of the waveform relative to the guide groove portion, and the height of the peaks is also low. Therefore, when determining the number of tracks passed by counting the zero-crossing points of these signals, counting errors are likely to occur.

On the other hand, in the case of the method of the present invention, a high-quality trunk deviation signal is obtained for both the guide groove portion and the track sector address portion, so that counting errors as in the conventional method are eliminated and accurate This makes it possible to determine the amount of tracking.

FIG. 8 is a functional block diagram for implementing the tracking method according to the present invention.

During data reading/writing (R/W), the focus shift signal 12 and the track shift signal 13 obtained from the optical head (not shown) are phase-adjusted by the respective phase compensators 14 and 15, and the output signal of the former is adjusted. Based on this, the offset setting unit 16 outputs a control signal to bring the focus state into focus, and the latter output signal is sent to the gate circuit 1.
7 and pass through current amplifiers 18 and 19, respectively, to one lens coil (driving coil for displacing the lens in the optical axis direction) and a track coil (for displacing the lens in the radial direction of the optical disk) of the optical head. The focus point control and tracking control are carried out by feed-hacking to the drive coil of the

Now, when an access command for the VCM of the coarse access mechanism (reference numeral 2 in FIG. 1) is input from the central processing unit (CPU) 20 to the input section 21 of the VCM control system, the gate circuit 17 is turned off and Truck counting section 2
2 starts counting the number of trunks based on the trunk deviation signal inputted from the track deviation signal 13. On the other hand, the off output to the gate circuit 17 is also input to the offset setting section 16, so that the offset setting section 16
sets the lens of the optical head to an off-center (out-of-focus) state by a predetermined value. .

The optical head is moved in the above state, and a comparator calculates the counted value by the tracking/7 counting unit 22 during this period and the tracking information stored in the register 24, that is, the number of tracks from the current position to the target track. Comparisons are made in 23.

Note that the tracking information is stored in the register 24 from the CPU 20 in advance.

Here, when the two match, the VCM stop signal generating section 25 outputs a tracking stop signal, and at the same time the movement of the optical head stops, the offset setting section 16 sets the lens of the optical head to a focused state. The gate circuit I7 is turned on again.

In this state, as described above, due to its own inertia, it cannot be guaranteed that the optical head is accurately positioned at the target L-rack. At this position, the address signal of the I-rack sector address part is read out, the number of trunk errors with respect to the target track is calculated based on the uplink, and the fine access mechanism moves the lens of the optical head to a predetermined position. The corrective displacement is made to the track position.

However, in the conventional method, the error in the track count value is large, and the error in the amount of movement due to the N/A mechanism becomes large. As a result, since the amount of correction becomes larger than the maximum displacement amount of the lens of the optical head, there are even cases where it is necessary to drive the rough access mechanism again to adjust the position.

After the position correction using the lens of the optical head for the above-mentioned tracking error is completed, write or read data while controlling the optical head to track a predetermined traverse tip in a focused state in one piece. be.

As described above, in the system of the present invention, since the coarse access mechanism can perform trunking with high precision, the amount of correction by the fine access mechanism is small, and the above-mentioned re-tracking by the coarse access mechanism 1. It eliminates the need for a king. High-speed random access becomes possible.

In addition, the influence of the information recorded in the guide groove on the track deviation signal, that is, the deterioration of the signal rail and the introduction of distortion due to the modulation of the reflected light by the information. However, it can be improved by applying the present invention. In the above embodiment, the case where the depth of the address sector portion is λ/4 has been explained, but if the depth of the address sector portion is λ/8. Even in this case, the trunk shift signal level can be increased by shifting the focus of the light beam as in the present invention, and the S/N ratio can be improved.

(g+Effects of the Invention According to the present invention, highly accurate 1-ranking is possible,
As a result, stable and high-speed random access is possible.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams for explaining the outline of the optical head moving mechanism in the optical disc device and diagrams showing the outline of the configuration of the optical head, respectively, and Figure 3 is a diagram for explaining the outline of the optical head movement mechanism in the optical disc device, and Figure 3 shows the tracks provided on the optical disc. FIG. 4 is a diagram showing the relationship between the depth of the track and the magnitude of the trunk deviation signal, and FIG. 5 is a diagram showing the relationship between the relative position of the track and the light beam and the magnitude of the track deviation signal. 6 is a diagram showing the relationship between the deviation of the light beam from the focused state on the optical disk and the magnitude of the track deviation signal, FIG. 7 is a diagram showing the track deviation signal waveform, and FIG. It is a functional block diagram showing an example. In the figure, 1 is an optical head, 2 is a coarse access mechanism, and 3 is an optical head.
is a shaft, 4- is an optical disk, 5 is an optical disk rotation mechanism,
6 is a light source, 7 is a beam splinter, 8 is a lens, 9 is λ
/4 wavelength plate, 1o is an optical sensor, 11 is a differential amplifier, 12
is an out-of-focus signal, 13 is an out-of-track signal, and 14 is an out-of-focus signal.
and 15 is a phase compensation section, 16 is an offset setting section, 1
7 is a gate circuit, 18 and 19 are current amplifiers, 20 is a central processing unit, 21 is an input section, 22 is a trunk counter,
23 is a comparator, 24 is a register, 25 is V(Jl
In the stop signal generation part, ``■'' is a guide groove portion, and ``■'' is a trunk sector address portion. Figure 1 Tora/2, 6th m, 7th floor, 1st person, 7th mouth◎

Claims (1)

[Claims] In an optical disk device that includes an access mechanism for moving an optical head a predetermined amount in the radial direction of an optical disk and uses a trunking signal obtained from the optical head to detect the amount of movement, during the period of movement by the access mechanism, A track access method in an optical disk device, characterized in that the tracking signal is detected with a read beam of an optical head shifted from its focus with respect to the optical disk.