JPS588054B2 - optical reproduction device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a disk-shaped recording medium (hereinafter referred to as a disk) on which signals are recorded in a predetermined track form, such as a spiral shape.
The present invention relates to an optical reproducing device that optically reproduces an information signal by projecting a light beam onto the surface.

Devices for recording or reproducing video signals using lasers have already been developed.

FIG. 1 is a schematic plan view showing a conventional video disk 1 for optical reproduction.This disk 1 has a spiral track form as shown by a track 2, and a composite video signal (for example, NT
SC color television signal) is recorded.

As shown in FIG. 2, in addition to the video signal period T, the composite video signal has a vertical blanking period, ie, a vertical blanking period Ts, for each field of the television screen. Since one frame is recorded in one rotation of the disc 1, a vertical blanking period portion 34 appears on the video disc 1 in the area indicated by hatching.

The vertical blanking period portions 3 and 4 are equivalent pulse periods T1 of 3H (where H is one horizontal scanning time of 63.5 μs, for example), vertical synchronizing pulse periods T2 of 3H, and equivalent pulse periods T3 and 12H of 3H. This corresponds to a vertical blanking period Ts consisting of a horizontal synchronizing pulse period T4 and a horizontal synchronizing pulse period T4, in which the above-mentioned synchronizing pulse signal is recorded.

Normally, the composite video signal is FM modulated and then recorded on the disc 1 in focus (grooves) as shown in FIG.

That is, an information signal is recorded by projecting a modulated light beam onto a transparent resin layer 5, which is a recording medium made of vinyl chloride or the like, and forming pits 6 corresponding to FM modulated waves in a predetermined track form.

For example, the width of the pit is about 1μ, and the depth of the bit is about 1/4λ.
(Here, λ is the wavelength of the laser beam.) The pit length differs between the inside and outside of the disk, and also depends on the frequency of the FM modulated wave, and is, for example, 1.5 to 6 μ.

Reference numeral 7 denotes a light reflecting surface provided by depositing or plating metal after the pits are formed, and is essential for reading recorded signals using reflection of light.

8 is a protective film that protects the reflective surface 7.

FIG. 4 shows a disk rotation mechanism, an optical device, and a feeding mechanism for the optical device, which are the main parts of a device for optically reading signals from the disk 1 as described above.

The rotation mechanism engages the center engagement hole 10 of the disk 1 with the boss of the turntable 9, so that the center of the disk substantially coincides with the center of rotation of the turntable, and tightens and fixes the disk 1 with a clamper 11. The motor 2 is configured to rotate a disc 1 fixed on a turntable 9 at a constant speed, and the optical device 13 projects a reproducing light beam 14 onto the disc 1 and detects the reflected light 15, and a tracking light beam 14. The feeding mechanism is configured to project a light beam and a focusing light beam onto the disk and detect the reflected light, and the feeding mechanism moves an endless belt 34 locking an optical device 13 in the radial direction of the disk 1 using a motor 30. The optical device 13 is configured to be displaced in the radial direction of the disk 1.

Note that the feeding of the light beam projected onto the disk 1 from the optical device 13 in the disk radial direction does not depend only on the displacement of the optical device 13 due to the rotation of the motor 30, but also on the rotation of the rotating mirror 16 provided in the optical device 13. It is also configured to be performed by

When reading information signals from the disk 1, as is clear from FIGS. 3 and 4, a light beam 14 is projected onto the disk from the lower surface 1a side of the disk 1,
The pits 6 are read by optically scanning the reflecting surface 7 that substantially coincides with the .

When the track in which pits 6 are formed is scanned by the light beam 14, the intensity of the reflected light 15 changes depending on the presence or absence of pits, and the information pits can be optically read.

By the way, in the above-mentioned video disc player, it is necessary to faithfully scan a track on which an information signal is recorded with a light beam.

A contact-type disc player that uses a stylus as a scanner to scan a groove with the stylus does not require a special tracking mechanism, but a non-contact disc player such as the one described above that uses an optical device as a scanner Since there is no mechanical guide means, it is necessary to provide a special tracking mechanism.

Therefore, whether or not the reproduction light beam 14 is projected onto the pit 6 of the predetermined track 2 is determined by the tracking light beam 1γ having a predetermined geometric positional relationship with the reproduction light beam 14 as shown in FIG. , 18 onto the disk 1 from the optical device 13 and detecting the reflected light.

The tracking light beam 1718 is the reproduction light beam 14
is not located at the center of the trunk 2 when in its normal position, the leading tracking light beam 17 is biased below the pit or track, and the trailing tracking light beam 18 is biased above the pit or trunk. Therefore, it is located.

Note that the reproduction light beam 14 and the tracking light beam 17
．． 18 are respectively displaced in the disk radial direction following the displacement of the optical device 13 in the disk radial direction, and are rotating mirrors 1
6 also causes displacement in the disk radial direction.

a reproduction light beam 14 and a tracking light beam 17;
18 is projected to a desired position is detected by the device shown in FIG.
3 or the rotating mirror 16 is controlled.

In FIG. 6, 19 is a photoelectric converter that detects the reflected light of the beam 17, and 20 is a photoelectric converter that detects the reflected light of the beam 18.

The beam reflected outputs obtained from the photoelectric converters 19 and 20 are amplified by preamplifiers 21 and 22, and then sent to bandpass filters 23 and 24, where high frequency components in a band corresponding to the recording frequency of the information signal, that is, pits, are amplified. Only intermittent signals that change in accordance with the arrangement of are extracted.

The high frequency intermittent signal obtained from the filters 23 and 24 is AM
Although the demodulators 25 and 26 perform envelope detection, for example, and thereby project the light beams 17 and 18 onto the tracks 2 on which the FM recording techs 6 are disposed intermittently to obtain their reflected output. , the output is similar to the reflected output when a light beam 17, 18 is scanned over a trunk in which pits 6 are continuously arranged.

The outputs of the AM demodulators 25 and 26 become inputs to the error amplifier 27, from which the difference between the inputs is output.

If the tracking light beams 17 and 18 are projected at the correct position, they scan the pits 6 under the same conditions, so the reflected outputs are equal and the output of the error amplifier 27 is zero.

However, if the light beam 17 is displaced upward or downward in FIG.
．． The amount of light applied to the pit 6 of the 18 spots is different, resulting in a difference in reflected output.

Therefore, a positive or negative output is generated from the error amplifier 27.

Incidentally, since the trunk 2 has a spiral shape as shown in FIG. deviate from

Therefore, by applying the output of the error amplifier 27 to the motor 30 after passing through the low-pass filter 28 and the drive amplifier 29, the light beams 14, 17, and 18 are projected onto predetermined positions on the track 2. The optical device 13 is displaced in the disk radial direction.

If the response characteristics of the motor 30 are good, tracking is possible only by feeding the optical device 13 in the disk radial direction by the motor 30.

However, since the response characteristics of the motor 30 are poor, a rotary mirror 16 is provided to compensate for this, and the rotary mirror 16 is rotated by the output of the error amplifier 2γ, so that the light beam 14.17.18
is projected onto the desired track.

The position of the light beam by the rotating mirror 16 is determined by the error amplifier 2.
This is achieved by applying an output of 7 to a coil 32 disposed in a permanent magnet via a drive amplifier 31 to rotate the rotating mirror 16.

To explain this operation in detail, as shown in FIG. When a positive or negative current is applied to the coil 32, the rotating mirror 16 connected to the coil 32 rotates clockwise or counterclockwise together with the coil 32, displacing the light beam, and when the current in the coil 32 disappears, the rotating mirror 16 16 is returned to the neutral position by the spring 33, and the heel is also placed in a corresponding position.

As is clear from the above, the displacement of the light beams 14, 17, 18 in the disk radial direction for spiral scanning is mainly caused by the rotation of the motor 30, and is caused by the difference between the center of the disk 1 and the center of the disk drive shaft. The rotation of the rotating mirror 16 provides beam displacement for controlling to prevent the optical beam from leaving the track and for controlling switching of the scanning trunk to obtain a still image.

By the way, if there is a dropout of the information signal on the disc 1, that is, a portion where the information pit 6 is missing, not only will the information signal not be detected by the reproducing light beam 14, but the information signal will not be detected by the reproduction light beam 14.
The tracking light beams 17 and 18 make it impossible to obtain a tracking control signal.

Therefore, in the tracking circuit shown in FIG. 6, the output of the error amplifier 27 becomes zero, and the rotating mirror 16 rotates in the direction of returning to the neutral position.

If the light beam is projected to the normal position on the track with the rotating mirror 16 rotated by a certain angle, the rotating mirror 16 will rotate in the direction to return to the neutral position, causing the track to be different from the desired one. The light beam may be projected onto the area or onto another track nearby.

If the light beam is projected onto the adjacent track that has just been scanned, since there is no dropout in that track, a tracking control signal is generated and scanning of that track is started.

However, when the scanning of that track is completed, the dropout occurrence point is scanned again, the output of the error amplifier 27 becomes zero again, and the rotating mirror 16 rotates in the direction to return to the neutral position.

This causes the light beam to be projected onto another track again,
The tracking servo becomes unstable or static image playback occurs.

Furthermore, even if the rotary mirror 16 is in the neutral position immediately before dropout occurs, and the motor 30 continues to rotate due to the delayed output of the low-pass filter 28, the optical device 13 is sent in the disk radial direction. In general, since the center of the disk does not coincide with the center of the disk drive axis, it is impossible to keep the light beams 14, 17, 18 on a given track, and the light beams 14, 17, 18 are located on the adjacent track that has just finished scanning. The next track may be scanned again, and the same operations as those leading to the dropout may be repeated, resulting in a still image.

Furthermore, even when the rotary mirror 16 is at the neutral position and the motor 30 stops moving the optical device 31 in the radial direction, the image may become a still image.

Furthermore, the rotating mirror 16 is not provided and the optical device 1
Even in a device that performs tracking servo using only feed (3) or a device that performs tracking servo using only a rotating mirror, if the tracking control signal is no longer generated due to dropout from the error amplifier 27, etc., the light beam will move in the radial direction. The feed of the track may stop and the light beam may move to the adjacent track, resulting in a still image.

The above-mentioned phenomenon also occurs when the information pits 6 are not used for tracking, but a dedicated tracking signal is recorded on the disk, and tracking control is performed based on this detection.

Either case is extremely undesirable for sequentially reproducing information signals.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical reproducing device in which the above-described defects are corrected.

An optical reproducing apparatus according to the present invention capable of achieving the above object includes a rotation mechanism for rotating a disc-shaped recording medium on which information signals are recorded in a predetermined track form, and the disc-shaped recording medium is provided with at least one for reproduction. an optical device that projects a light beam; a light beam sending device that sends the reproducing light beam in a radial direction of the disc-shaped recording medium; and whether or not the reproducing light beam is correctly projected onto a predetermined recording track. a beam position detection device that detects the information signal based on the recorded information signal or the recorded tracking signal; and a beam position detection device that detects the reproduction light beam based on the recorded information signal or the recorded tracking signal; a tracking control device that controls the light beam sending device so that the light beam is projected onto a track of the light beam; and a dropout detection device that detects a dropout of the information signal or tracking signal on the disc-shaped recording medium for a predetermined period or longer. and a reproduction track switching control device that controls the optical beam sending device so that the reproduction optical beam moves onto one or more preceding tracks in response to the output of the dropout detection device, The present invention is characterized in that when a dropout occurs for a period longer than the predetermined period, the information signal is optically reproduced by skipping all or part of the dropout.

If configured as described above, even if dropout occurs,
This prevents static image scanning and optical beam scanning from being disturbed.

Next, embodiments of the present invention will be described with reference to the drawings.

However, the components indicated by numerals 19 to 32 in FIG. 8 are the same in structure and operation as those indicated by the same numerals in FIG. 6, and therefore the explanation thereof will be omitted.

Furthermore, since the portions related to FIG. 8 are constructed as shown in FIGS. 1 to 7, their explanation will be omitted.

No. 8 showing a tracking control unit according to an embodiment of the present invention.
In the figure, a holding circuit 41 is branched and connected to the output stage of the error amplifier 27, and only when a dropout occurs, the output of the holding circuit 41 is connected to the rotating mirror 16 and the rotating mirror 16 via a switching circuit 42. The signal is sent to the circuit of the motor 30.

The holding circuit 41 is, for example, a circuit that can hold the output of the error amplifier 27 immediately before dropout by about 30 μm, and is a circuit that generates a pseudo beam position detection output during the dropout occurrence period.

The input terminal of this holding circuit 41 is always connected to the error amplifier 27, but its output terminal is not always connected to the rotating mirror 16 circuit and the motor 30 circuit, and only during the dropout period is an electronic switch configuration. switching circuit 42
connected by.

The information signal and tracking signal dropout detection device includes a photoelectric converter 43 that detects the reflected light of the reproduction light beam 14, a preamplifier 44 that amplifies the signal corresponding to the pit 6 obtained from the photoelectric converter 43, and a recording signal. a high-pass filter 45 that passes signals higher than the frequency; and a dropout detection circuit 46 that detects dropouts based on the presence or absence or magnitude of the signal obtained from the filter 45.
For example, it is constituted by a comparison circuit 47 that compares a predetermined reference period of 30 μm with a dropout occurrence period detected by the dropout detection circuit 46.

This dropout detection device detects dropouts based on the reflected light output of the reproduction light beam 14 in order to simultaneously perform dropout detection necessary to compensate for dropouts in the reproduced information signal.

If a dropout detection circuit for the reproduced information signal is provided separately, the tracking light beam 17.1
Dropout may be detected based on the presence or absence or magnitude of the reflected light output.

The output of the dropout detection circuit 46 is applied to the switching circuit 42 and also to the switch circuit of the dropout compensation circuit for the reproduced information signal.

Reference numeral 48 denotes a pulse generator, which generates a pulse in response to the comparison circuit 47 detecting a relatively large dropout lasting longer than a predetermined period.

In this embodiment, pulses generated from the pulse generator 48 are applied to the coil 32 for rotating the rotating mirror 16.

Note that the voltage value of the pulse is set to a value that can give the rotating mirror 16 a rotation angle sufficient to shift the light beams 14, 17, and 18 to the immediately adjacent preceding trunk.

In this embodiment, a pulse is applied to the coil 32, but
It is also possible to configure it so that it is applied to the motor 30 as shown by the dotted line.

When the information signal is normally reproduced from the disc 1 in the apparatus configured as described above, the reproduction light beam 14 and the tracking light beams 17 and 18 scan the pit 6 of the trunk 2, so that the photoelectric converter Outputs corresponding to the focus are obtained from 19, 20, and 43.

Therefore, a high frequency output is also generated from the high pass filter 45 of the dropout detection device, a dropout detection output is not generated from the dropout detection circuit 46, the switching circuit 42 is in a non-operating state, and the circuit a is Connected to the switching circuit.

Further, no dropout detection output is generated from the comparator circuit 47 either.

In this state, the position of the light beam is detected by the beam position detection device consisting of the circuit from the photoelectric converters 19, 20 to the error amplifier 27, and a normal beam position detection output is generated from the error amplifier 2γ. It is applied to the motor 30 and the coil 32 which function as a tracking control device, and the tracking control of the light beam 14 is performed as described above.

During playback, a dropout portion of about 1 μsec to 30 μsec, that is, a portion where the pit 6 is missing, is caused by the light beams 14, 17,
18, the photoelectric converters 19, 20, and 43 no longer provide high frequency outputs corresponding to the pits, but direct current outputs are obtained.

Therefore, no detection output is generated at the output stage of the filters 23, 24, 45, and no normal beam position detection output is generated from the error amplifier 27.

Furthermore, as the output of the high pass filter 45 becomes zero, a dropout detection output is generated from the dropout detection circuit 46, which is applied to the switching circuit 42, turning off circuit a and turning on circuit b. become.

As a result, transmission of the zero output of the error amplifier 27 to the coil 32 and motor 30 circuits via the circuit a is cut off, and at the same time, the holding circuit 41 is transmitted to the coil 3 via the circuit b.
2 and the motor 30 circuit.

Even if the output of the error amplifier 27 becomes zero, the output of the holding circuit 41 does not immediately become zero in response, but is maintained at the output of the error amplifier 27 immediately before the dropout occurs.

This holding output continues to be generated from the holding circuit 41 as a pseudo position detection output during the dropout period.

Although the pseudo beam position detection output generated from the holding circuit 41 does not necessarily match the regular beam position detection output, since the signal immediately before dropout is stored, it can be used during the dropout period of approximately 1 μsec to 30 μsec. They almost match.

This pseudo beam position detection output is applied to the coil 32 via the amplifier 31 in the same way as the regular beam position detection output,
The rotating mirror 16 has a rotating angle corresponding to the pseudo beam position detection output.

As a result, the rotating mirror 16 becomes uncontrolled due to the occurrence of dropout, and is significantly rotated toward the neutral position, causing the light beams 14, 17, and 18 to move to the adjacent trunk, resulting in a still image reproduction state. Disturbances in light beam scanning will no longer occur.

At this time, of course, the pseudo beam position detection output is applied from the holding circuit 41 to the circuit of the motor 30, and the optical device 13 continues to be fed in the disk radial direction.

Furthermore, a video signal IH delay circuit is connected to the output stage based on the output of the dropout detection circuit 46, so that dropout of the reproduced information signal is compensated for by the IH delayed video signal.

In this embodiment, the reference period of the comparator circuit 47 is 30 μsec.
Since the dropout is set to c, even if a dropout smaller than this is detected by the circuit 46, no comparison output is generated and the scanning trunk is not switched.

If a dropout of 30 μm or more occurs, it will no longer be possible to perform tracking control using the pseudo beam position detection output sent from the holding circuit 41.

Therefore, if a dropout of 30 μsec or more is detected by the comparator circuit 47, the pulse generator 48 is triggered by this detection output to generate a track switching pulse.

When a track switching pulse is applied to the coil 32, the rotating mirror 16 is forcibly rotated, and the light beams 14, 17.1
8 jumps over all or part of the dropout portion and moves onto the adjacent leading trunk.

Since dropout does not normally occur in the adjacent preceding track, normal tracking control is started.

If the trunk spacing is small and there is a very high probability that dropout will occur in adjacent tracks, the light beams 14, 17, and 18 are displaced so as to skip several tracks.

In other words, the pulse generator 48 sends out a pulse signal that skips several tracks.

This allows you to escape from dropout.

In the embodiment described above, the holding circuit 41 holds the output level of the error amplifier 27 immediately before dropout, and sends out the pseudo beam position detection output at substantially the same level during the dropout occurrence period. There is no problem in creating a circuit in which the output level decreases somewhat as the dropout progresses.

Such a holding circuit 41 may be formed by a time constant circuit that delays the fall of the output of the error amplifier 27.

In this way, when dropout occurs, the error amplifier 27, the holding circuit 41 using a time constant circuit, and the switching circuit 4
2. A circuit consisting of an amplifier 31 and a coil 32 is formed,
The pseudo beam position detection output is generated only during the delay period due to the time constant of the entire control circuit including the holding circuit 41 consisting of a time constant circuit, and the rotating mirror 16 is thereby controlled.

Furthermore, when a dropout occurs, the switching circuit 42 allows the time constant of the filters 23, 24, the AM demodulators 25, 26, the drive amplifier 31, etc. to be dropped out without connecting the time constant circuit to the output stage of the error amplifier 27. Only the detection period may be increased.

This time constant switching is performed by the output of the dropout detection circuit 46.

Alternatively, the holding circuit 41 may be configured with a delay circuit for 1H or a time corresponding to dropout, and a signal for a predetermined period before the occurrence of dropout may be sent from the delay circuit as a pseudo beam position detection output during the dropout period.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and can be further modified.

For example, the rotating mirror 16 may be used to send the light beam in the radial direction.
Alternatively, only one of the optical device 13 and the optical device 13 may be used.

In addition, the tracking optical beam 1 is used to detect dropouts.
7, 18 may also be used.

Alternatively, the beam position detection for trunking control may not be performed by projecting a light beam onto the trunk of the information signal, but by recording a control signal dedicated to tracking and detecting this dedicated control signal.

In this case, of course, dropout detection may be performed based on the detection of the control signal, or the beam position may be detected using the reproduction light beam 14.

Further, the pseudo beam position detection output may be generated regardless of the regular beam position detection output.

It is also applicable to disc players other than video players.

Further, the predetermined reference period may be less than or more than 30 μSec.

Furthermore, compensation for dropouts within a predetermined reference period may be omitted depending on the case.

That is, the holding circuit 41 and the switching circuit 42 may be omitted, and the dropout may be escaped only by switching the trunk.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view of a video disc, Fig. 2 is a waveform diagram of a composite video signal recorded on the disc, Fig. 3 is a partially enlarged sectional view of the disc, and Fig. 4 is a schematic side view of a video disc player. , FIG. 5 is a plan view showing the relationship between pits and light beams, FIG. 6 is a circuit diagram of the tracking control section, and FIG.
8 is a perspective view of a rotating mirror, and FIG. 8 is a circuit diagram showing a tracking control section of a disc player according to an embodiment of the present invention. In addition, in the symbols used in the drawings, 1 is a disk,
2 is the trunk, 6 is the pit, 12 is the disc motor, 1
3 is an optical device, 14 is a light beam, 16 is a rotating mirror, 1
7 and 18 are optical beams for tracking, 19 and 20 are photoelectric converters, 27 is an error amplifier, 30 is a motor, 32 is a coil, 41 is a holding circuit M, 42 is a switching circuit, 46 is a dropout detection circuit, and 47 is a The comparison circuit 48 is a pulse generator.

Claims (1)

[Scope of Claims] 1. A rotation mechanism that rotates a disk-shaped recording medium on which information signals are recorded in a predetermined trunk form, an optical device that projects at least a reproduction light beam onto the disk-shaped recording medium, and the reproduction device. a light beam sending device that sends a playback light beam in the radial direction of the disc-shaped recording medium; a beam position detection device that detects based on a tracking signal obtained from the beam position detection device; and a beam position detection device that detects the beam position based on a tracking signal obtained from the beam position detection device; a tracking control device that controls the beam feeding device; a dropout detection device that detects dropout of the information signal or tracking signal in the disc-shaped recording medium for a predetermined period or more; and an output of the dropout detection device a playback track switching control device that controls the light beam sending device so that the playback light beam moves onto a preceding track of one trunk or more in response, and when dropout occurs for a period longer than the predetermined period; An optical reproducing device that optically reproduces an information signal by skipping all or part of the dropout. 2. The dropout detection device has a comparison circuit that compares the dropout occurrence period detected by the dropout detection circuit with a predetermined reference period, and the dropout occurrence period is longer than the reference period. Claim 1, which is a device that generates an output when the length of the
Optical reproducing device as described in Section 1. 3. The optical reproducing apparatus according to claim 1, wherein the information signal is a composite video signal, and the predetermined period is approximately 30 μsec. 4. The optical system according to claim 1 or 3, wherein the information signal is a composite video signal, and the movement of the reproduction light beam onto the preceding track is approximately one frame of the video signal. reproduction device. 5. The optical system according to claim 1, wherein the light beam sending device is a rotating mirror arranged in a path of the reproducing light beam for sending the reproducing light beam in the radial direction of the disc-shaped recording medium. reproduction device. 6. The optical reproducing apparatus according to claim 1, wherein the light beam feeding device is a mechanism for feeding the optical device in a radial direction of the disc-shaped recording medium. 7. The light beam sending device includes a mechanism for sending the optical device in the radial direction of the disk-shaped recording medium, and a mechanism for sending the reproduction light beam in the radial direction of the disk-shaped recording medium. 2. The optical reproducing device according to claim 1, wherein the optical reproducing device is both a rotating mirror provided in 8. The light beam position detection device projects a tracking light beam onto the disc-shaped recording medium in a certain geometrical relationship with the reproduction light beam, and the tracking light beam projection position and the information signal or The optical reproduction according to claim 1, which is a device for detecting the position of the reproduction light beam based on a change in reflected light or transmitted light of the tracking light beam based on the relationship with the recording position of the tracking signal. Device. 9. The optical reproducing device according to claim 5, wherein the tracking control device is a device for controlling rotation of the rotating mirror. 10. The optical reproducing device according to claim 6, wherein the tracking control device is a device for controlling a mechanism for sending the optical device in a radial direction. 11. The optical reproducing device according to claim 2, wherein the reproducing track switching control device is a pulse generator that applies a scan trunk switching pulse to the tracking control device in response to the output of the comparison circuit.