JPS5828657B2 - optical reproduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention optically reads signals by rotating a disk on which information signals are recorded in the form of concentric circles or spiral tracks and projecting a light beam for reading information signals onto the disk. The present invention relates to an optical reproduction device.

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, the composite video signal has a vertical blanking period, that is, a vertical blanking period, for each field of the television screen, and one field corresponds to half a rotation of the disk 1, and one frame corresponds to one rotation of the disk 1. Since the vertical blanking period portions 3 and 4 appear in the hatched area on the video disc 1, the vertical blanking period portions 3 and 4 appear in the hatched area.

The vertical blanking period portions 3 and 4 are an equivalent pulse period T1 of 3H (here, H is one horizontal base scanning time of 63.5 μs, for example), a vertical synchronization pulse period T2 of 3H, and an equivalent pulse period T3 of 3H. 12H horizontal sync pulse period T4
Corresponding to the vertical blanking period Ts consisting of , various synchronizing pulse signals are recorded here.

Normally, a composite video signal is FM modulated and then recorded in pits as shown in FIG.

That is, recording is performed by projecting a modulated light beam onto the transparent resin layer 5 constituting the disc 1 and forming pits corresponding to the FM modulated wave in a predetermined track form.

For example, the width of the pit is about 1μ, the depth of the pit is about ±λ (where λ is the wavelength of the laser beam), the length of the pit differs between the inside and outside of the disc, and the frequency of the FM modulated wave For example, it is 1.5 to 6μ.

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

When reading a signal from the video disc 1 as described above, after the central engagement hole 8 is engaged with the shaft of the turntable, the disc is fixed to the turntable with a clamper and the disc 1 is rotated at a constant speed.

Further, by gradually sending the reproducing light beam 9 in the radial direction of the disc, the track 2 is sequentially scanned by the light beam 9, and reflected light 10 from the disc 1 is detected.

Since the reflected light 10 changes depending on the presence or absence of pits, it is possible to read the recording signal based on the change in the reflected light.

By the way, information signals are recorded while the disk 1 is rotating at a constant speed, and one frame of information is recorded in one revolution, so there is a difference in the peripheral speed of light beam scanning, and even if the signals are of the same frequency, Also, as shown in FIG. 1, the circumferential length of the pit 6a of the inner track 2a is smaller than the circumferential length of the pit 6b of the outer track 2b.

As a result, the frequency characteristics of the response during reproduction differ between the inner part and the outer part.

Figure 4 shows the frequency characteristic curve a of the response of the inner track.
and the frequency characteristic curve of the outer track.

If it is possible to reproduce only in the flat frequency band of the characteristic curve shown in Figure 4, no problem will occur, but since a band of up to about 10 MHz is required, it is necessary to use a high frequency range that reduces the response. Must be.

If the frequency characteristics are not flat, the signal obtained through the path of the preamplifier, bandpass filter, limiter, etc. will not have the desired waveform, and there is a risk that beats will occur on the reproduced image.

Therefore, an equalizer amplifier is generally inserted to perform high-frequency compensation, but in order to obtain exactly the same frequency characteristics inside and outside the disk, the time constant of the equalizer amplifier must be changed between the inside and outside of the disk. .

However, even if the time constant of the equalizer amplifier was simply changed to correspond to the position of the optical beam in the disk radial direction, it was difficult to match the inner frequency characteristics with the outer frequency characteristics.

In order to solve the above problem, there may be a method in which the shape of the pit is changed between the inner and outer circumferences of the disk, or a method in which the shape of the spots is changed between the inner and outer circumferences of the disk.

However, no method has yet been proposed that uses a simple and inexpensive configuration to change the shape of the spot in response to changes in the position in the radial direction of the disk.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical reproducing device that can change the shape of a spot and obtain flat frequency characteristics with a simple and inexpensive configuration.

To achieve the above object, the present invention records an FM modulated wave corresponding to an information signal in a concentric circle or a spiral track shape by an arrangement of pits, and even if the length of the pit is the same frequency signal, A disk on which information is recorded so as to gradually form a dog toward the outer periphery, a disk drive device for driving the disk to rotate at a constant speed, and a device for projecting a reading light beam onto the disk to read the pits.
a fifth pickup; a feeding device for causing radial feeding of the disk between the light beam and the disk; and a slit for changing the shape of the spot of the light beam on the disk. a slit plate that is disposed along the optical path of the light beam so that the light beam occurs and is movably attached to the pickup in order to change the width of the slit; and a slit plate operating mechanism that displaces the plate and changes the width of the slit so that the length of the spot in the circumferential direction of the disk gradually increases from the inner circumference to the outer circumference of the disk. This relates to playback devices.

According to the above invention, a slit plate is used and the shape of the spot is changed by changing the width of the slit in conjunction with the feed, so a desired spot can be obtained with a simple and inexpensive configuration.

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

FIG. 5 is a schematic side view showing an optical reproducing device according to the present invention.

The same video disc 1 as shown in FIG. 1 is fixed on a turntable 11 with a clamper 12.

13 is a disk motor connected to the turntable 11, which rotates the disk 1 at a constant speed.

14 is an optical pickup, and a reading light beam 9
is projected onto the disk 1 and its reflected light 10 is detected.

The pickup 14 is slidably guided in the radial direction of the disk 1 by a guide rail 15, and is engaged with an endless belt 16 that is extended and wound around the disk 1 in the radial direction. It is arranged so that it can be displaced in the radial direction of the disk by driving.

Reference numeral 18 denotes a laser light source that emits a reading light beam 9.

19 is a mirror for changing the optical path of the light beam 9.

When reading information signals recorded on the disc 1 by the optical reproducing apparatus configured as described above, the disc 1 is rotated at a constant speed by the disc motor 13.

Further, the optical pickup 14 is gradually fed by the feed motor 17 from the inside to the outside of the disk 1 or from the outside to the inside.

Furthermore, a light beam 9 is emitted from the laser light source 18 and is projected onto the track of the disk 1.

If the disk 1 is rotated at a constant speed and the light beam 9 is gradually sent in the radial direction of the disk, the scanning trajectory by the light beam 9 will be the first one.
It has the same spiral shape as the spiral track 2 shown in the figure.

Since it is impossible to make the light beam 9 perfectly coincide with the spiral track 9, a tracking beam (not shown) is used to control the light beam 9 so that it is always projected onto the track. .

Note that this tracking control is performed by a rotating mirror disposed on the optical path within the pickup 14.

In conventional apparatuses, the same light beam scans the disk 1 from the inside to the outside.

For this reason, as described above, the frequency characteristics of the response differed between the inside and outside.

Therefore, in the present invention, the shape of the beam spot is changed as the light beam 9 is fed in the disk radial direction.

That is, the distribution of the beam spot in the disk circumferential direction is made uniform from the inner track to the outer track.

For example, if a beam with a spot shown in FIG. 7A is projected on the inner track 2a, a beam with a spot shown in FIG. 7B is projected on the outer track 2b.

Now, if the same frequency signal is recorded on the inner track 2a and the outer track 2b, the length of the inner pit 6a will be 11 and the length of the outer pit 6b will be 12, as shown in FIG. 6, for example.

In the present invention, the shape of the beam spot is changed in accordance with the change in pit length.

The beam spot 20a shown in FIG. 7A is located on the inner track 2.
The beam spot 20b shown in FIG. 7B is projected onto the outer track 2b.

Width W1 of the beam spot in the disk circumferential direction. The change in W2 is the change in pit length and the inner and outer track radius'
R, a, II (corresponds to changes in b).

For example, as described above, if the beam spot is changed to follow changes in the track radius, the light beam 9 can be
The frequency characteristics of the signal read by projecting the light onto the disk and detecting the reflected light 10 become the same over the entire area of the disk 1.

Therefore, it is possible to compensate for high frequencies in the entire area of the disk using one equalizer, and it is possible to obtain substantially flat frequency characteristics in the entire area of the disk.

FIGS. 8, 9, and 10 show an apparatus for changing the beam spot in accordance with the feeding of the light beam 9. FIG.

In this drawing, reference numeral 21 denotes a mounting plate disposed on the lower surface of the pickup 14, and various mounting holes are provided here.

22a and 22b are slit plates, which are pressed against the mounting plate 21 via bearings 23.

The pressure of these slit plates 22a and 22b is caused by the bearing 2
4 and the spring plates 25a and 25b.

That is, the mounting plate 21 and the spring plate 25a that can be attached to the mounting plate 21.
, 25b, a ball bearing 23, a slit plate 2
2a, 22b, and the ball bearing 24 are configured to be pressed in order.

The slit plates 22a and 22b are not fixedly held, but have long holes 26a drilled therein.

A portion of the bearing 23 is inserted into the long holes 26b and the long holes 27a and 27b bored in the mounting plate 21, respectively, and the bearing 24 is also inserted into the long hole 26a.

Since a part of it is inserted into 26b,
The slit plates 22a and 22b are slidable in a direction perpendicular to the feeding direction of the pickup 14, that is, in a circumferential direction of the disk.

28a and 28b are pins planted in the slit plates 22a and 22b, and guide grooves 30a and 3 of the operating gear 29
0b.

A guide groove 30a provided in the gear 29. As is clear from FIG. 9, the distance from the center of the gear to the guide groove 30b gradually changes from one end to the other.

Reference numeral 32 denotes a holding frame attached to the mounting plate 21, which rotatably holds the gear 29 by means of a bearing 32 mounted thereon.

33 is a speed reduction device consisting of first and second gears 34 and 35, in which the first gear 34 meshes with a rack 37 fixed to the chassis 36, and the second gear 35 meshes with the operating gear 29. It is attached to the pickup 14 in a stable and rotatable manner.

In the beam spot variable device described above, when the pickup 14 is slid along the guide rail 15, that is, when the optical beam 9 is sent in the radial direction of the disk, the first and second gears 33 and 35 follow this movement. The operation gear 29 rotates in a predetermined direction and meshes with the second gear 35 .

As a result, the pins 28a, 28b inserted into the guide grooves 30a, 30b of the operating gear 29 receive forces in the direction of approaching or separating from each other, and the plates 22a, 22b also move toward the sulin 1, which is integrated with the pins 28a, 28b. Slide toward or away from each other.

FIG. 9 shows a slit plate 22a. 10 shows a state where the slit plates 22b are separated from each other and the distance between them is widened, and FIG.
, 22b are close together to form a slit 38.

Now, assuming that 39 is a through hole for the light beam 9 to pass through which is bored in the mounting plate 21, in the state shown in FIG. 9, the light beam 9 passes through the slit plate 22a.

22b, but in the state shown in FIG. 10, the through hole 39 and the slit plate 22a.

It is possible to pass through only the substantially rectangular slit 38 formed by 22b.

As a result, when the light beam emitted from the laser light source passes through the slit 38, a beam spot is obtained on the disk 1 in which the length and width of the slit 38 are reversed due to a diffraction phenomenon (Fraunhofer diffraction phenomenon) caused by the slit.

In this device, the sliding direction of the slits 22a and 22b coincides with the circumferential direction of the disk 1, that is, the track direction, and furthermore,
Since the width of the slit 38 becomes narrower as the pickup 14 moves toward the outside of the disk 1, the distribution of the beam spot in the disk circumferential direction becomes dog-shaped in response to the outward displacement of the pickup 14.

In order to always keep the amount of beam light projected onto the disk 1 constant even if the shape of the beam spot changes, the laser light source 1
8 or the optical path, the intensity of the beam may be changed in accordance with the change in the shape of the spot.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment and can be further modified.

For example, the beam spot may not be changed continuously but may be changed stepwise.

For example, the inner track may be scanned with one beam, and the outer track may be scanned with a beam that is a combination of two beams.

In addition, in the example, the relationship is W, = l, = T (a), but if a uniform frequency characteristic cannot be obtained in the entire area of the disk, change the relationship to an appropriate one. Good too.

[Brief explanation of drawings]

Fig. 1 is an explanatory plan view of a conventional video disc, Fig. 2 is a waveform diagram of a composite video signal recorded on the disc, Fig. 3 is an enlarged sectional view of the disc, and Fig. 4 shows the inner track and outer track. A frequency characteristic diagram of the rack, FIG. 5 is a schematic side view of an optical reproducing device according to an embodiment of the present invention, FIG. 6 is a plan view showing the inner and outer pits, and FIG. 7 is the inner and outer pits. FIG. 8 is an exploded perspective view of the beam spot deforming device, and FIGS. 9 and 10 are bottom views of the operating gear and slit plate in the assembled state of the beam spot deforming device. be. In the symbols used in the drawings, 1 is a video disc, 2 is a track, 6 is a pit, 14 is an optical pickup, 17 is a feed morph, and 20a. 20b is a spot.

Claims (1)

[Claims] 1. An FM modulated wave corresponding to an information signal is recorded in a concentric circle or a spiral track shape by an arrangement of pits, and the length of the pits increases from the inner circumference to the outer circumference even if the frequency signal is the same. A disc on which recording is gradually performed, a disc drive device for rotating the disc at a constant speed, a pickup for projecting a reading light beam onto the disc to read the pits, and a pickup for reading the pits by projecting a reading light beam onto the disc, and a disc drive for driving the disc to rotate at a constant speed. and a feeding device for causing radial feeding of the disk between the disk and the disk, and a slit in the optical path of the light beam to create a slit for changing the shape of a spot of the light beam on the disk. a slit plate disposed along the slit and movably attached to the pickup in order to change the width of the slit; and a slit plate operating mechanism that changes the width of the slit so that the circumferential length of the disk gradually increases from the inner circumference to the outer circumference of the disk.