JPS6233648B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking servo pull-in device for an optical information recording and reproducing device that optically records and/or reproduces information on a disc-shaped information carrier such as an optical disk, and in particular a tracking servo pull-in device for an optical information recording and reproducing device that optically records and/or reproduces information on a disc-shaped information carrier such as an optical disk. The present invention relates to a tracking servo retraction device for an information carrier having a groove-like guide track formed in the carrier.

As an optical information recording/reproducing device, for example, a disc-shaped information carrier coated or vapor-deposited with a photosensitive material is rotated, and a light beam from a laser light source or the like is focused onto the disc-shaped information carrier to a diameter of 1 μm or less. By irradiating a minute spot light and modulating its optical output intensity with a recording signal, real-time changes in optical properties such as phase changes, refractive index changes, reflectance and transmittance changes due to unevenness are recorded on the information carrier. An apparatus has been proposed that is capable of recording information such as a video signal or digital signal, and is capable of reproducing the recorded information by detecting the change in the optical characteristics.

In such a device, a guide track is provided in advance in a concentric circle or a spiral shape to guide the track to be recorded in order to increase the density of the recording track, discrete partial writing or erasing, etc., and the track follows the guide track. An optical information recording and reproducing apparatus can be considered that records information on a predetermined track while applying tracking control and reproduces information from the track.

The guide track formed on the information carrier is suitably, for example, a groove-like structure with an uneven surface. Information is recorded on a recording medium, such as an amorphous metal deposited on the information carrier provided with this guide track. Information is stored in the form of holes or local blackening due to evaporation of the recording medium.

The guide track is identified by the far-field pattern of the laser beam reflected by the guide track, which is biased in the light intensity distribution on both sides of the guide track. This deviation is photoelectrically converted by a photodetector having two light receiving sections arranged so that the dividing boundary is parallel to the tangential direction of the guide track, and is applied to the tracking control means.

The tracking control in the optical recording/reproducing device is pulled in and released every time the user searches for a desired track. Therefore, it is necessary to perform tracking control reliably. However, when the light spot illuminated on the optical disk happens to be not directly above the guide groove track while crossing the guide groove track (in the flat area between the guide groove tracks, that is, between the guide groove tracks), the tracking control cannot be performed. If the guide groove is retracted, tracking may not be applied to the guide groove, and the tracking actuator may oscillate. This oscillation occurs within a tracking control system, that is, a loop of a photodetector in the tracking direction, a drive circuit, and a tracking actuator (tracking mirror, etc.). The cause of the oscillation is thought to be as follows. When the optical spot is between the grooves, the output of the tracking error signal is large. This is because the reflected light spot from the optical disk is largely concentrated on one side. When the tracking control is pulled in in this state, a large force acts on the tracking mirror to move the reflected light spot toward the other two-split photodetector. Since the tracking mirror drive mechanism relies on a magnetic circuit, a certain degree of hysteresis is unavoidable. Due to this hysteresis and inertial force, when the above-mentioned large force acts, the reflected light spot moves further away from the central dividing line of the two-split photodetector. A reflected light spot that deviates greatly and enters the photodetector on one side causes the tracking mirror to move largely back toward the original direction again, as described above.

An object of the present invention is to provide stable tracking pull-in by suppressing the oscillation phenomenon of the tracking mirror during such tracking control pull-in. For this purpose, as mentioned above, when the light spot crosses the guide groove track, it is necessary to pull in the tracking control at the moment when the light spot is irradiated directly above the guide groove.
The tracking control pull-in operation is not performed only when the optical recording/reproducing apparatus is powered on or when the optical disk is replaced, unlike the focus control pull-in operation, but the pull-in operation is performed every time a track is searched. Therefore, a particularly stable retracting operation is required. The present invention aims to achieve stable tracking control pull-in by limiting the timing of tracking control pull-in to only when a light spot passes over a guide groove track.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical recording and reproducing apparatus equipped with a tracking pull-in device of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an optical recording/reproducing apparatus. A light beam 2 emitted from a light source 1 such as a semiconductor laser passes through a tracking mirror 4 for changing the direction of the light beam and making it follow a track on the disk 3, and then is directed onto the disk 3 by an aperture lens 5. The light is focused on the track as a light spot 6. The reflected light 7 from above the disk 3 passes through the aperture lens 5, the tracking mirror 4, and then the semi-transparent mirror 8.
The optical path is separated and changed. This reflected light 7
is the focusing direction 10 by the optical wedge 9.
and a tracking direction 11. The separated light beams are projected onto two divided photodetectors 12 and 13, respectively. Since the light spot moves on the photodetector 12 in accordance with the surface wobbling of the disk 3, the light is input from the two-split photodetector 12 to the pre-differential amplifier 14, and a focus error signal 15 is obtained. This error signal is applied to a voice coil 17 that drives the aperture lens 5 up and down via a drive circuit 16, and a light spot 6 is placed on the disk 3.
control to focus the light.

On the other hand, the disk 3 is being rotated by the disk motor 18, but if the center of rotation of the disk motor 18 and the center of the track of the disk 3 are misaligned, the light spot 6 on the disk 3 will accurately move the track. Do not follow and cross the track. When the light spot 6 crosses the track, the photodetector 1
3, a change in the light component occurs as will be described later. Detecting this change and inputting it to the pre-differential amplifier 19,
A tracking difference signal 20 is obtained. This difference signal 20 is input to a tracking drive circuit 21 and drives the tracking mirror 4. The tracking mirror 4 changes its angle in accordance with the difference signal 20 so that the optical spot 6 accurately follows the track on the disk 3, thereby performing tracking control.

22 is a signal processing circuit shown in FIG.
A tracking control pull-in timing signal is input to the drive circuit 21. 25 is a linear motor for track search. 26 is a presum amplifier, which is a two-split photodetector 13 in the tracking direction.
Tracking sum signal 27 of signals detected by
is outputting. Further, the recording/reproduction signal from the optical disk 3 is detected by the photodetector 13 and input to the pre-high frequency amplifier 28, which outputs a reproduction RF signal 29.

Next, one embodiment of the structure of the optical disk 3 used in the present invention will be described based on FIG. 2. FIG. 2 is a diagram showing a part of the disk of the optical disk 3. On the surface R side of the optical disk 3, groove-shaped guide tracks 30a to 30e with a width w, a pitch P, and a depth δ are provided in a concentric or It is carved in a spiral shape. 31a-31e
indicates the groove. A photosensitive recording material is applied from the surface R side to form a recording surface 32. The light spot 6 is focused on the surface R. During recording and reproduction, tracking control is applied so that a light spot is projected onto the groove-shaped guide track 30.
During recording, the optical output of the light source 1 is increased, and the optical energy of the light spot projected onto the groove-shaped guide track 30 on the disk 3 is increased to expose the recording material coated on the guide track 3. As a result, the reflectance of the recorded portion on the groove-like guide track changes. If this change in reflectance is detected using a light spot with a smaller optical output than during recording, the recorded signal can be reproduced. 33 shows how the recording material in the groove-shaped guide track is exposed to light during recording. This case shows an example in which the recording material became black and the reflectance increased. Said guide track 30
Specific values of the width w, pitch P, and depth δ of a to 30e are, for example, width w = 0.6 μm pitch P = 1.6 μ
m, and the depth δ is approximately 1000 Å (an optical path length of 1/8 of the optical wavelength of the laser light source 3).

FIG. 3 shows the light in the tracking direction (the groove-like guide track is the normal direction) when the light spot 6 is projected onto the groove-like guide track 30 (end recording section) on the optical disk 3 shown in FIG. It shows a change in the light amount distribution of the detector 13. FIG. 3 is a view of the disk 3 viewed from the cross-sectional direction. 13a is a photodetector in the inner diameter direction of the optical disk 3; 13b is a photodetector in the inner diameter direction of the optical disk 3;
The photodetector is shown in the outer radial direction. 34 represents a light spot on which the reflected light 7 from the optical disk 3 is projected onto the photodetector 13. The shading within the circle of the reflected light spot 34 represents a change in the light quantity distribution within the light spot. Figure 3a shows the grooved guide track 3.
The light spot 6 is shown being projected onto the flat part of the groove 31 where there is no zero. In this case, since the incident light beam 2 is uniformly reflected, the reflected light spots 34 on the photodetector 13 are uniformly distributed, so that the difference signal output 20 of the photodetector 13 becomes zero.

FIG. 3b shows that the light spot 6 is located on the groove-shaped guide track 3.
It shows how it was once projected onto the edge 35b on the outer diameter side of 0. If the depth of the groove-shaped guide track 30 is an optical path length of 1/8 of the wavelength of the laser light, the incident light beam 2 will be diffracted and the reflected light 7b will be bent to the outside of the groove. Therefore, the light amount distribution is shifted toward the photodetector 13b in the outer diameter direction. Assuming that the input of the pre-differential amplifier 26 is the outer radial photodetector 13b as a positive input and the inner radial photodetector 13a as a negative input, the difference signal output 20 becomes positive in the case of FIG. 3b.

FIG. 3C includes bidirectional edges 35a, 35b of the grooved guide track 30;
It shows how a light spot 6 is projected over the entire area. In this case, the incident light beam 2
a and 35b, the reflected light 7C is diffracted to the outside of the groove in both directions. Since the aperture of the aperture lens 5 is finite, the diffracted reflected light is vignetted.
Therefore, the total amount of light from the spot projected onto the photodetector 13 is reduced. Therefore both directions 13a, 13b
The sum signal output 27 of the photodetector is shown in Fig. 3 a, b, d.
Its amplitude decreases compared to . In the case of FIG. 3C, if the centers of the reflected light spot 6 and the groove-shaped guide track 30 coincide, the photodetectors 13a in both directions
Since the light intensity distribution of the reflected light spot projected onto the light beam 13b is uniform, the amplitude of the difference signal output 20 is zero.

In Fig. 3d, the light spot 6 is at the edge 3 in the inner diameter direction.
5a shows how it was previously projected. In this case, contrary to FIG. 3b, the reflected light 7d is directed in the inner diameter direction.
is diffracted, and the light amount distribution is shifted towards the photodetector 13a in the inner diameter direction. The difference signal output 20 is therefore negative.

FIG. 4 shows the configuration of the tracking control pull-in timing generation circuit of the present invention, which is the signal processing circuit 22. In FIG. FIG. 5 shows the signal waveforms of each part a to k in FIG. 4, and 1 represents a radial cross-sectional view of the guide groove track on the optical disk corresponding to the waveform of each part. As described above, the signal detected from the photodetector 13 in the tracking direction is input to the preamplifiers 19, 26, and 28. a indicates a tracking difference signal 20, which is output every time the optical spot crosses the guide groove track 30. b is tracking sum signal 27, C is reproduction
An RF signal 29 is shown. As explained with reference to FIG. 3, when the entire groove is irradiated with a light spot, the tracking sum signal 27 has a lower reflectance and takes on a signal waveform as shown in b. When the light spot crosses the recorded track 30', a reproduced RF signal 29 is detected as shown in C. In this case, as described above, the reflectance of the groove bottom increases, so that the change in the reflectance of the tracking sum signal 27 becomes small as shown at 50 in FIG. 5b. Therefore, the groove portion of the recorded track 30' cannot be detected using only the tracking sum signal 27. For this purpose, the tracking sum signal 27 is used to detect the crossing of the groove portion of the final recording track, and the reproduction RF signal 29 is used to detect the crossing of the recording track 30'. The reproduced RF signal 29 is sent to the envelope detector 5
1, the waveform is shaped by the waveform shaper 52, and the logical sum of the waveform-shaped signal d and the signal e, which is also a tracking sum signal b whose waveform is shaped by the waveform shaper 53, is output to the OR circuit 56. Output f from
be done. Although the logical sum output f accurately represents the timing of the groove, since the pulse width is wide, the rising or falling edge of the pulse does not accurately represent the groove center. The center of this pulse width is exactly the center of the groove. By the way, the zero crossing point of the tracking difference signal 20 in FIG. 5a accurately represents the timing of the groove center. Because the two-split photodetector 13
This is because, as shown in FIG. 3c, this indicates the timing at which an equal amount of reflected light is received. Therefore, Figure 5 a
The tracking difference signal 20 shown in
After amplification g in step 4, the waveform is shaped by a waveform shaper 55 to obtain a pulse train signal h indicating a zero crossing point.
However, the tracking difference signal 20 has zero crossing points not only at the center of the groove, as shown in FIG. 5a, but also when the light spot crosses the flat part between the grooves. Therefore, if the AND circuit 57 performs the logical product of the above-mentioned logical sum output f indicating the groove section and this zero-crossing pulse, a pulse train signal i accurately indicating the groove center is output. If this pulse train signal i is used for the timing of tracking control pull-in, the timing will be accurate at the center of the groove.
Tracking control can be started. That is, by setting and inputting the groove center pulse train signal i to the RS flip-flop 58, the tracking ON command pulse signal k can be output in accordance with the tracking control pulse signal j from the deck control section 59, and this ON command pulse By inputting the signal k to the tracking drive circuit 21, the tracking mirror 4 can be pulled in and released at the tracking ON timing shown in FIG. 5k.

As explained above, the present invention processes the tracking difference signal, the sum signal, and the reproduced RF signal, and uses the tracking difference signal and the tracking sum signal to detect the crossing of the groove of the last recorded track, and uses the tracking sum signal to detect the crossing of the groove of the recording track. Using the reproduced RF signal, tracking control can be pulled in at the timing when the optical spot crosses the center of the groove, regardless of whether it is an unrecorded track or a recorded track, limiting the control pull-in range and achieving stable tracking servo pull-in. can do.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an optical recording/reproducing device, FIG. 2 is a diagram showing the structure of an optical disk, FIG. 3 is a diagram showing changes in the light intensity distribution of reflected light, and FIG. 4 is a tracking control pull-in timing of the present invention. FIG. 5 is a diagram showing the configuration of the generating circuit, and is a signal waveform diagram of each part in FIG. 4. DESCRIPTION OF SYMBOLS 1...Light source, 3...Optical disk, 4...Tracking mirror, 6...Light spot, 7...Reflected light, 12,
13... Two-split photodetector, 20... Tracking difference signal, 21... Tracking drive circuit, 22... Tracking control pull-in circuit, 27... Tracking sum signal, 29... Reproduction RF signal, 30, 30a to 30e
...Groove-shaped guide track, 30'...Recording track, 3
1... Groove gap, 33... Recording track, 51... Envelope detector, 52, 53, 55... Waveform shaper, 5
4...Absolute value amplifier, 56...OR circuit, 57...AND circuit, 58...RS flip-flop.

Claims (1)

[Claims] 1. In an optical information recording and reproducing device that records and reproduces information on an optical disk having a groove-shaped guide track and coated with a recording material that is exposed to a laser light source,
When a minute light spot created by focusing the laser light source crosses the groove-shaped guide track, the reflected light shifted in the tracking direction obtained from the optical disk is received by a two-split photodetector, and the two-split photodetector The difference and sum of outputs are calculated and outputted as a tracking difference signal, a tracking sum signal, and a reproduced RF signal recorded on the groove-shaped guide track, and the tracking sum signal and the reproduced RF signal are subjected to envelope detection and then waveform shaped. Take the logical OR with the signal,
The timing at which the level of the tracking difference signal crosses zero is detected and the logical sum output signal is ANDed, and the moment when the optical spot passes directly above the groove-shaped guide track is detected, and tracking is performed based on this timing. A tracking servo retracting device characterized by starting a king servo.