JPH0517619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tracking servo device, and particularly to a tracking servo device that records and/or plays back information signals using a light beam. The present invention also relates to a device for controlling the tracking of a light beam based on a guide track recorded in advance on an information signal recording disk (hereinafter referred to as a disk).

2. Description of the Related Art When recording an information signal on a disk using a light beam, it has been conventional to form a guide track with virtually no information on the disk in advance, and record the information signal while being guided by this guide track during recording. known (for example, JP-A-49-113601). Such guide tracks include a pair of grooves 2a and 2b of a predetermined depth formed on both sides of the track 1 to be recorded and reproduced, as shown in FIG. 8, or a single groove of a predetermined depth as shown in FIG. 9A. The grooves 3 are continuously formed. When recording or reproducing a disk having guide tracks 2a and 2b as shown in FIG. 8, the guide tracks 2a and 2b are located at positions shifted from each other in the track scanning direction and in the track width direction with respect to the main light beam MB for recording and reproducing information signals. Two sub-light beams TB ₁ and TB ₂ for tracking are provided, and the sub-light beam TB ₁ irradiates a part of the guide track 2a,
Further, tracking is controlled so that the sub light beam _TB2 irradiates a part of the guide track 2b. This allows the main light beam MB to accurately scan the track 1 to be recorded or reproduced.

A sectional view of the disk 4 having the guide tracks 3 as shown in FIG. 9A is shown in FIG.
As shown in 2, 3-3, 3-4, ..., depth λ/8
(where λ is the wavelength of the light beam B). When recording on the disk 4, the light beam B scans the guide track 3 to form an information signal recording pit in the guide track 3, and the light beam B scans the guide track 3 at a depth of λ/8.
Tracking control of the light beam B is performed using the first-order diffracted light emitted when the light beams (3-1 to 3-4) are irradiated. That is, when the light beam B irradiates the center position of the guide track 3, the light intensity of the left and right primary-order diffracted lights is equal, but when it deviates from the center position, there is a difference in the light intensity of the left and right primary-order diffracted lights. Tracking control is performed by detection.

Problems to be Solved by the Invention However, in the conventional method shown in FIG. 8, when recording an information signal with the main light beam MB, the conditions of the leading sub-light beam TB ₁ and the following sub-light beam TB ₂ are are different (only the trailing secondary beam TB ₂ is the main beam MB)
(influenced by the pits recorded by), so there was a problem that a correct tracking error signal could not be obtained. In addition, in the conventional method shown in FIGS. 9A and 9B, when the light beam B crosses the guide track 3 during reproduction, etc., a primary difference occurs between the groove portion where the guide track 3 is formed and the non-groove portion where the guide track 3 is not formed. The diffracted light sometimes comes out and sometimes it does not come out, sometimes the first
As shown in FIG. 0B, the reflected light projected onto the four-split detector 5 becomes asymmetrical as shown by diagonal lines, which sometimes causes the focus servo to malfunction. Here, the focus error detection method includes:
As shown in FIGS. 10A and 10B, the reflected light from the disk that has passed through the cylindrical lens is incident on the 4-split detector 5 consisting of four optical sensors, and when it is in focus, 6a is shown in A of the same figure. As shown in , the light-receiving surface on the 4-split detector 5 is a perfect circle, and if the disk is too close or too far away, it will become as shown by the two-dot chain line 6b and the three-dot chain line 6c. An astigmatism method is known in which the sum of each output is taken and an error signal is obtained from the sum.

In a device that detects a focus error using this astigmatism method, the above-mentioned light beam B is
10B, the light-receiving surface of the quadrant detector 5 becomes asymmetrical as shown in FIG. This was not a desirable situation. Therefore, in the device that uses the tracking control method shown in FIGS. 9A and 9B, it is not appropriate to use the astigmatism method for focus error detection, and a knife edge is set at the point where the reflected beam at the focused point is the narrowest. The reflected beam is received by a two-split optical detector,
From this, it is preferable to use the knife edge method to obtain a focus error signal. However, this knife edge method requires precision in the knife edge, the detector, the focal length of the lens, etc., and therefore has the problem that the optical system becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tracking servo device that solves the above-mentioned problems by performing tracking based on a signal reproduced from a guide track consisting of intermittent pits.

Means for Solving the Problems The tracking servo device according to the present invention generates switching pulses with a cycle corresponding to the recorded pit cycle of the guide track based on a reproduced signal obtained by scanning the guide track with a sub-light beam. and a polarity reversing means that generates and outputs a tracking error signal by alternately inverting the polarity of the reproduction signals of two adjacent guide tracks reproduced by the main light beam every half cycle using a switching pulse. It becomes more.

Effect: On the above guide track, a certain low frequency signal is recorded as intermittent pits, and
Recorded pits between adjacent guide tracks are recorded alternately in the radial direction. During recording and reproduction of a recording disk on which such guide tracks have been formed in advance, the main light beam that scans over the track to be recorded and reproduced between two adjacent guide tracks will be When scanning is performed in one direction, the output signal of the polarity reversing means is taken out as a positive or negative signal depending on the direction of the tracking deviation, and on the other hand, the main light beam scans the recording/reproducing track without tracking deviation. , the above-mentioned positive or negative intermediate level signal is extracted. Therefore, tracking servo can be performed by using the output signal of the polarity reversing means as a tracking error signal and providing it as a control signal for displacing the main light beam and the sub light beam in the track width direction.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 7.

FIG. 1 shows a block system diagram of an embodiment of a tracking servo device according to the present invention. In the figure, a playback signal of a guide track obtained by detecting the optical intensity of the reflected light of the main beam MB shown in FIG. 2A on the disk is input to the input terminal 10, and the input terminal
and 12 is the main light beam MB as shown in Figure 2A.
A tracking sub-light beam SB ₁ is irradiated to positions that are shifted forward and backward in the scanning direction and in opposite directions by a small fixed distance in the track width direction.
Reproduction signals of the guide track as shown by a and b in FIG. 2B, which are obtained by detecting the light intensity of each reflected light of SB ₂ and SB 2, are input. Here, the guide track is
It consists of pits P ₁₁ to _{P 35} etc. which are intermittent at a constant period, and pits P ₁₁ , P ₁₂ , ..., P ₁₅ represent, for example, pits in a part of the first guide track, P ₂₁ ,
P ₂₂ , P ₂₃ , P ₂₄ indicate the pits of a portion of the second guide track, P ₃₁ , P ₃₂ , ..., P ₃₅ indicate the pits of a portion of the third guide track, and these pre-recorded pits are (Hereinafter, this pit will be referred to as prepit). The guide track is an intermittent row of prepits, and between two adjacent guide tracks, an information signal recording track is formed by the main light beam MB during recording, and an information signal recording track is formed by the main light beam MB during reproduction. is played by. In FIG. 2A, -1 and -2 indicate the track center lines at the information signal recording track positions.

Here, to explain the guide track in more detail, on the recording disk 35 having a diameter of 30 cm, for example, shown in FIG. Prepits 37 are recorded or reproduced intermittently on both sides of the track center line. A center hole 38 is bored in the center of the disk 35, and a label portion 39 is formed around the center hole 38. The prepits 37 of two adjacent guide tracks sandwiching the information signal recording track are formed so as to be staggered. Specifically, by dividing one round of 360 degrees into an odd number of regions and forming prepits in every other region, adjacent prepits with information signal recording tracks in between are necessarily staggered.
As an example, by setting the number of areas per round to 525, the number of prepits 37 will be increased per round.
262 pieces and 263 pieces are formed alternately. Further, the length of each prepit 37 is selected to be equal to, for example, one horizontal scanning period (1H) of the video signal. Further, the distance between the track center lines of two adjacent guide tracks with the information signal recording track in between is selected to be, for example, 1.6 μm.

FIG. 5 shows another example track pattern of the disk. In the figure, the same components as those in FIG. 4 are denoted by the same reference numerals, and the explanation thereof will be omitted. The information signal recording tracks on the disk 40 are recorded or reproduced concentrically, as shown by two-dot chain lines 41 in FIG. Therefore, two adjacent guide tracks sandwiching this information signal recording track are also formed in concentric circles. The guide track is intermittently formed with prepits as shown at 42 in FIG. The prepits 42, like the prepits 37 in FIG. 4, are formed so as to be staggered in the radial direction on adjacent guide tracks. To this end, by dividing one 360° circumference of the disk 40 into an even number of areas and forming a prepit 42 in every other divided area, it is necessary to sandwich the recording track on the track center line 41. However, adjacent prepits 42 are staggered.

In FIG. 6, which shows a part of the track pattern of the disks 35 and 40 in an enlarged manner, the prepit 3
The respective starting ends and ending ends of the prepits 7 and 42 coincide with the individual ending ends and starting ends of the radially adjacent prepits 37 and 42, respectively. Boundary lines 43 connecting the starting and ending ends of the prepits 37 and 42 in the radial direction of the disk radiate at equal angular intervals in the radial direction from the center of the disk, as shown in FIG.
Further, the prepits 37, 42 are, for example, grooves with a length of 1H, and the cross-sectional shapes of the disks 35, 40 are as shown in _FIG . The wavelength is selected to be 1/4 times the wavelength of SB ₂ .

Returning to FIG. 1 again, input terminal 1
As can be seen from FIGS. 2A and 2B, the reproduced signals a and b obtained by separately and simultaneously reproducing the two adjacent guide tracks entering the guide tracks SB 1 and 12 are the sub-light beams SB 1 and SB ₁ . , SB ₂ scans over the prepit, a phase difference of λ/2 (where λ is the wavelength) occurs between the light reflected inside the groove of the prepit and the light reflected outside the groove. The light intensity is canceled out and greatly attenuated, so it is at a low level, for example.On the other hand, during the scanning period where there is no prepit, the sub light beams SB ₁ and SB ₂ are reflected with almost no attenuation, so their reflected light The light intensity is large, and thus becomes, for example, a high level. In addition, the second
Prepits P ₁₁ to P ₃₅ and beams MB, SB ₁ ,
The relationship between the SB ₂ and the spots is for illustration only; in reality, the deviations between the beam spots are extremely small.

The above reproduced signals a and b are square waves with a period corresponding to the prepit period as shown in Fig. 2B, but in reality, due to slight variations in the beam spot, etc. It will not be a waveform. However, even in this case, information on the ends of the prepits P ₁₁ to _{P 35} can be obtained from the edges of the reproduced signals a and b. Note that there is a relative phase shift in the reproduced signals a and b because the sub light beams SB ₁ and SB ₂ are slightly shifted back and forth in the track direction, but this has no direct bearing on the present invention.

The above reproduced signals a and b are supplied to differentiating circuits 15 and 16 through amplifiers 13 and 14, where they are differentiated and information on the edge of the prepit is extracted, resulting in differentiated pulses as shown in c and d in FIG. be done. These differential pulses c and d are supplied to the differential amplifier 17,
After being differentially amplified and converted into a pulse as shown in FIG. 2B, the signal is converted into a pulse as shown in FIG. Further, the above-described reproduced signals a and b are added by an adding circuit 20 and smoothed by a smoothing circuit 21 to have a level equal to the average value of the amount of reflected light. Comparison circuit 19
compares the level of the above pulse f with the average value of the amount of reflected light shown by the two-dot chain line in the pulse f of FIG. 2B from the smoothing circuit 21, and generates and outputs a pulse as shown by g in FIG. do.

Pulse g is a clock pulse with a period equal to the prepit period,
After that, it is made into a pulse shown as h in FIG. 2B by the phase lock loop (PLL) 23, and then made into a pulse shown by i in FIG. Figure B and Figure 3 B
are converted into pulses denoted by j, respectively. PLL23
is provided in order to generate and output a pulse i with a constant phase even if there is a drop in the clock pulse g, etc., to compensate for the above-mentioned drop. This pulse j is a square wave having a high level corresponding to the prepits on one side of the guide tracks on both sides of the information signal recording track and a low level corresponding to the prepits on the other side, and corresponds to the recording period of the prepits. The pulse has a cycle of 1, and is applied to the switch circuit 26 as a switching pulse.

On the other hand, the main light beam MB entering the input terminal 10
The reproduced signal is sent to the AGC control circuit 29, which will be described later.
On the other hand, it is supplied to the common terminal of the switch circuit 26 through the DC cut circuit 25. When the main light beam MB is correctly scanning the position between two adjacent guide tracks, part of the spot of the main light beam MB hits the prepits, and the amount of reflected light decreases slightly, but the amount of light attenuation is As explained in conjunction with FIG. 6, since the ends of the prepits are on the boundary line, the position remains constant even when transitioning from one preppit of one of the two guide tracks to the first preppit of the other track. It is. In other words, even though prepits are intermittently recorded, the amount of reflected light of the main light beam MB is not affected at all.

Now, for convenience of explanation, let us assume that the spot by the main light beam MB sequentially traces the positions indicated by C to N in FIG. 3A, and the output signal waveform of the DC cut circuit 25 is as shown by K in FIG. 3B. Become. Figure 3A
In the figure, P ₁₁ to _{P 15} indicate the prepits of the first guide track, P ₂₁ to _{P 25} indicate the prepits of the second guide track, and -1 indicates the track center line of the information signal recording track. When the main light beam spot is located at the positions indicated by A to E in FIG. As shown in Fig. 3B, when the main light beam spot falls on the prepits P ₁₁ , P ₁₂ , and P ₁₃ (A, C, E)
Since the amount of reflected light is small, the level is low, and the level is high at positions B and D because they have never been in the prepits P ₂₁ and P ₂₂ . Furthermore, between the top and the bottom, the main light beam spot is shifted toward the prepits of the lower second guide track, and the waveform of the output signal k changes depending on the presence or absence of the lower prepits P ₂₃ and P ₂₄ . changes as shown in FIG. 3B. Furthermore, numeral ``nu'' indicates the position when the main light beam spot is at the optimum position, and the main light beam spot is located at the pre-pit P _25.
, so that a reliability Hk at an intermediate level between the above-mentioned high level and low level can be obtained.

The switch circuit 26 receives the switching pulse j
During the high level period, the input signal k is selectively output to the non-inverting input terminal of the differential amplifier 27, and during the low level period, the input signal k is selectively output to the inverting input terminal of the differential amplifier 27. As a result, the signal k input to the non-inverting input terminal of the differential amplifier 27 is in the same phase, and the signal k input to the inverting input terminal is extracted in the opposite phase, as shown by l in FIG. 3B. AGC circuit 28
supplied to That is, when the output signal l of the differential amplifier 27 shown in FIG. 3B is lower than the center level shown by the two-dot chain line, the main light beam spot shifts upward, and when the level is high, it shifts downward. This is a tracking error signal corresponding to a tracking deviation, which indicates that there is no tracking deviation when it is at the center level.

This tracking error signal l is sent to the AGC circuit 28.
The level is controlled based on the control signal from the AGC control circuit 29. The AGC circuit 28 and the AGC control circuit 29 are circuits for compensating for fluctuations in the amount of reflected light. The effects of fluctuations in , etc. are removed. The output tracking error signal of the AGC circuit 28 is supplied to a tracking device 32 through an equalizer circuit 30 and an amplifier 31, respectively, where the main light beam MB and sub light beams SB ₁ ,
The optical paths of the three light beams are slightly displaced in the track width direction so that the main light beam MB scans the information recording track while keeping the SB ₂ in the same positional relationship. In this way, the main light beam MB is tracked and controlled so that it always scans the position shown by the dotted line in FIG. 3A.

Note that the tracking control according to this embodiment is performed not only when an information signal recording track is formed between two adjacent guide tracks, but also when reproducing the recorded information signal. This process is also performed when recording new information signal recording tracks between guide tracks. Furthermore, during the above reproduction, the information signal from the information signal recording track is simultaneously reproduced by the main light beam MB along with the information recorded on the guide track, but the band of the latter reproduction information signal (RF signal) is on the order of MHz. On the other hand, the reproduction information from the guide track is on the order of several kHz, and only the reproduction information from the guide track is frequency-selected by a band filter (not shown) and is supplied to the input terminal 10 shown in FIG.

Note that the switching pulse j can also be generated based on a reproduced signal obtained using only one of the two sub-light beams. Also, the differential amplifier 2
An inverter or the like may be used instead of 7.

Effects of the Invention As described above, according to the present invention, tracking control is performed based on the reproduction signal from the guide track, which is an intermittent row of pits, so that the guide track, which is made up of continuous grooves, is used for information signal recording. Compared to the conventional method in which two light beams are provided on both sides of the track, the two sub-light beams are used to create a signal corresponding to the prepit period, and the tracking error signal is obtained based on the prepit reproduction signal of the main light beam. , the difference in the conditions of the two sub-light beams is not a problem, more accurate tracking control is possible, and compared to other conventional methods in which an information signal recording track is formed on one guide track, the light beam is Even if playback is performed across the guide track, the depth of the groove in the guide track is λ/4, so the reflected light will not be diffracted and will not be affected by the diffracted light, making it difficult to detect focus errors. It can use the astigmatism method, and has many advantages such as being able to perform tracking control without complicating the optical system compared to conventional methods.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing an embodiment of the present invention, FIGS. 2A and 2B are an example of the positional relationship between each beam and a track, and signal waveform diagrams for explaining the operation of the main parts of the block system shown in FIG. Figures 3A and 3B show examples of the relative positional relationship between the main light beam and the prepits, and the first
FIGS. 4 and 5 are signal waveform diagrams for explaining the operation of other important parts of the illustrated block system, respectively, and FIG. FIG. 7 is a longitudinal sectional view of the disk shown in FIGS. 4 and 5, and FIGS. 8 and 9A are a partially enlarged view of the disc, and FIGS. Figure 9B is a diagram showing each example of the relationship between Figure 9B and Figure 9A.
FIGS. 10A and 10B are longitudinal cross-sectional views showing the generation of diffracted light in the recording disk shown in FIGS. 10A and 10B, respectively. 10...Reproduction signal input terminal by main light beam, 1
1, 12...Reproduction signal input terminal by sub-light beam;
15, 16...Differential circuit, 17, 27...Differential amplifier, 18...Double wave rectifier circuit, 19...Comparison circuit, 23
...Phase Locked Loop (PLL), 24...
1/2 multiplier circuit, 26... switch circuit, 32... tracking device, 35, 40... recording disk, 36, 41, -1, -2... recording track center line, 37, 42, P ₁₁ to _{P 35} ...Prepic.

Claims (1)

[Scope of Claims] 1. A guide track, which is a row of pits, is formed in advance on both sides of a spiral or concentric track position where an information signal is to be recorded, and
During recording and reproduction of a recording disk in which recorded pits of adjacent guide tracks are alternately recorded in the radial direction, the main light beam is used to scan the position of the track to be recorded and reproduced between the adjacent guide tracks. A tracking servo device for controlling the displacement of a beam in the track width direction based on a tracking error signal, the tracking servo device controlling the displacement of a beam in the track width direction based on a tracking error signal, which corresponds to the recorded pit period of the guide track based on a reproduction signal obtained by scanning the guide track with a sub-light beam. means for generating a periodic switching pulse, and a means for generating a reproduction signal of the two adjacent guide tracks reproduced by the main light beam, the polarity of which is alternately changed every half period of the switching pulse by the switching pulse. A tracking servo device comprising: polarity inverting means for inverting and generating and outputting the tracking error signal. 2. The tracking servo device according to claim 1, wherein the depth of the recorded pit of the guide track is 1/4 times the wavelength of the main light beam.