JPS6233650B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention records information such as video or audio in an optical form with an information track on an information medium, irradiates a light beam, and records the information track on an information medium. The present invention relates to an optical information reading device that reads information.

[Prior art] As this type of device, for example,
As described in Publication No. 26041, in this example, two gratings are provided in the optical path of the light beam irradiated to the information track, and photoelectric elements are arranged behind the first grating and the second grating, respectively. The tracking control of the information track is performed by the potential difference generated between both photoelectric elements, and the shift of the focus of the beam spot on the information medium due to vibrations caused by distortion of the information medium, etc. 1. A lens is placed between the second grating, and the position of the resulting image moves back and forth,
It takes advantage of the fact that the grid spacing changes.

[Problems to be Solved by the Invention] However, the width of the information tracks on this type of disk is about 2 μm, and although they are formed in a lattice shape including adjacent tracks, compared to the first and second lattices, It is difficult to form the track width accurately, and this difference in accuracy is a fatal drawback in accurately reading information.

In view of the above points, the present invention extracts optical information using a single light beam and a differential photodiode formed by joining a photoelectric element, and focuses the information by moving the beam spot with respect to the information track. It is an object of the present invention to enable accurate and reliable detection of recorded information and control signals without affecting the detection of focus control signals.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a single light beam 14 to the information track 2 of the optical information medium 1.
The pulse amplitude changes are extracted from the continuous changes in the reflected light of the light beam 14, and the information recorded on the information medium 1 is reproduced from the changes in the pulse width and pulse gap. In an optical information reading device that moves in a direction substantially perpendicular to the information track 2 direction of the information medium 1 and performs tracking control of the light beam 14 with respect to the information track 2, an image of the irradiated portion of the information medium 1 is formed. A joint 37 of the differential photodiode 23 formed by joining the photoelectric elements 23a and 23b is placed in a position where the beam spot 17' of the reflected light that irradiates the differential photodiode 23 is directed to the joint 37.
The diameter is made sufficiently larger than the gap, and the joint portion 37 is arranged substantially perpendicular to the information track 2 direction of the information medium 1,
The photoelectric elements 23a and 23b are characterized in that the focusing control signal of the beam spot 17 of the light beam 14 that irradiates the information medium 1 is detected by a change in the difference in the amount of light received from the beam spot 17'.

[Operation] By employing the above-mentioned means and arranging the junction of the differential photodiode approximately perpendicular to the direction of the information track of the information medium, the light beam can be used to track the information of the information medium in order to control the tracking of the light beam with respect to the information track. Even if it moves in a direction substantially perpendicular to the track direction, this movement does not affect the detection of the focus control signal of the light beam, and the beam spot of the reflected light is made sufficiently larger in diameter than the gap at the joint. By doing so, the beam spot does not enter the joint, and the state of non-detection of signals that occurs when the beam spot enters is eliminated, and recorded information and control signals can be detected accurately and reliably.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a disk-shaped information medium, and information is recorded on the upper and lower surfaces of the disk 1 by means of information tracks 2. As shown in FIG. FIG. 2 shows a very small portion of the information track 2 recorded on the disk as an example of the recording state. For convenience, here
The information track 2 is constructed by arranging small bits 5 of a low reflection area 4 in an optical high reflection area 3.
The width 5a of the small bits 5 in the radial direction on the disk is constant, and the lengths 5b, 5b'... in the track direction and the intervals 5c, 5c'... are different, so that signals such as images and sounds are recorded. There is.

The above recording condition records a disk with a diameter of 30 cm at a rate of 30 cm per second.
Rotate the pulse repetition by small bit 5 to approx.
2.5MHz to 4.2MHz, the recording and reading time for one side is 30 to 40 minutes, and the width of the small bit is set to 30 to 40 minutes to record and read NTSC or PAL (25 rotations per second) images and audio. 5a is about 1 μm, and the track direction lengths 5b, 5b'... can be arbitrarily changed depending on the information, but the shortest length is about 2 μm.
It is desirable that the intervals 5c, 5c', . . . between the small bits 5 of the information track be approximately 2 μm.

To explain the method of most effectively recording the image signal G and audio signal O on this disk, the video signal G
(0 to 3.5 MHz) and the audio signal O (0 to 20 KHz) are made into one signal, but simply combining them makes it impossible to separate the video signal G and the audio signal O after they are read. Therefore, as shown in Fig. 4, the audio signal O is modulated 6 by putting it on a carrier wave centered at 4.5 MHz with a width of 20 KHz, and then synthesized with the video signal 7.
do. However, considering human audiovisual perception, the distortion of the audio signal O is more perceivable than the distortion of the video signal, and it is desirable to increase the S/N of the audio signal O. If you apply FM modulation 8 with a relatively small frequency deviation to the synthesized wave as described above, it will have sidebands (frequency spectrum) symmetrically above and below the center frequency as shown in Figure 4b. become. Of these sidebands, part of the upper side wave O'' generated by the audio signal O' and the upper side wave G' generated by the video signal G is shown in Figure 4c.
This FM wave is converted into pulse FM using a limiter 9 or the like to form one information pulse 10.

The information pulse 10 thus obtained is recorded on the disk 1 as a small bit 5. The mechanical arrangement used to read information from this disk is shown in FIG. The disk 1 is placed on a turntable 12 driven by a motor 11 so as to rotate at a substantially constant speed. A light beam 14 from a light beam generating device 13 for reading (preferably a laser to obtain a good signal-to-noise ratio) passes through a reflecting mirror 15 and reaches a pickup device 16 . The outline of this pick-up device 16 is as shown in FIG.
It is comprised of an automatic focusing device 19 for keeping the irradiation diameter on the disk 1 within a certain range, a focusing lens 20 for focusing the light beam 14 to form a minute spot 17, and the like. This pick-up device 16
is retracted in the radial direction of the disc 1 along the orbit by an idler 22 driven by a feed motor 21. In addition, the pick-up device 16 includes
A photoelectric element 23 is provided which converts the light beam 14 after irradiating the disk 1 into an electrical signal.

Now, the reflected beam output after irradiating the information track 2 on which video and audio information has been recorded with modulation that does not change the carrier wave, such as pulse frequency modulation or pulse width modulation, is the reflected beam output from the spot 17 on the disk 1. Assuming that the size is constant, when the beam spot 17 and the information track 2 exactly match, they can be read by the photoelectric element 23 as shown in FIG. Further, when the beam spot 17 and the information track 2 are fluctuating, the result is as shown in FIG. That is, 24 in FIGS. 8 and 9 is the output of the light beam received by the photoelectric element 23 obtained by the reflective area of the disk 1, and 25 is the output obtained by the small bit 5 formed by the low reflection area of the disk 1. level. In other words, when the beam spot 17 is tilted into the reflective area, the beam 25 has a high output, and conversely, when the beam spot 17 is tilted too far into the low reflection area, the beam 25 has a low output. By using the difference in these output levels, the beam deflector 18 controls the beam spot 17 so as not to separate from the track 2. A block diagram of this control method is shown in FIG. That is, the photoelectric element 23
The output is amplified by an amplifier circuit 26, and passes through a clamp circuit 27, which is configured by taking out the difference output from the reference output, in order to separate the output level part 24 and the output level part 25. Only the output will be output. Next, after obtaining the envelope output by the integrating circuit 28 which obtains the envelope output, the beam spot 17
a level adjustment unit 29 for obtaining a difference between the output and the second reference output corresponding to the reference setting position for the information track 2;
is extracted as a tracking signal. Although high frequency noise may be removed from the extracted signal using a filter or the like, the beam deflector 18 is operated to control the beam spot 17.

However, due to the manufacturing and handling of the disc 1, the reflectance of the surface of the disc 1 is considerably different in each part of the disc 1. In extreme cases, the variation may be larger than the signal level, and as shown in FIG. 11, the reflectance is as shown in 25b in a low reflectance part, and 25a in a high reflectance part as shown in 25a. Further, even if the output of the light beam generator 13 fluctuates, the same result will be obtained.
In other words, the ratio of the signal spectral output to the total optical output is almost constant, but if this waveform is used as it is for the control described above, it will be strongly influenced by the variation in the total optical output, and it will be difficult to match it exactly with Track 2. Deflection control becomes impossible. Therefore, a control method as shown in FIG. 12 is used. That is, photoelectric element 2
When the output from 3 is passed through a high-pass filter 30, only the pulse portion is obtained. The integration circuit 31
After the envelope output is obtained, it can be extracted as a tracking signal by the level adjustment section 29 which obtains the difference from the reference output as in FIG. 10 described above. In addition, the output is branched at the stage of the pulse,
Amplified by the amplifier circuit 32 and level cut circuit 3
3 or is detected as a normal video signal by the shaping circuit 34.

In this way, the beam spot 17 is aligned with the deflection device 1
8 performs deflection control, and the pulsed output of the photoelectric element 23, that is, the information pulse, is subject to fluctuations, and the control signal is mixed into the information to be read. For this reason, when performing detection as shown in Figure 12 above, the frequency band H determined by the mechanical/electrical closed-loop characteristics of the deflection control system must overlap the frequency band of the recording pulse as shown in the frequency spectrum of Figure 13. Set to low frequency band.

A part of the output for deflection control obtained as described above is used as a control signal for the feed motor 21 of the pickup device 16. In other words, the feed motor 21 is controlled to feed the disk 1 in the radial direction approximately in synchronization with the rotation of the disk 1 using a constant motor control voltage, and the direct current of the tracking control voltage that enters the deflection device is controlled. By adding this amount to the control voltage of the motor 21, the rotation of the feed motor 21 is controlled.

Next, an explanation will be given of the automatic focusing device 19 and its control circuit for always focusing the light beam 14 on the surface of the disk 1 even when the disk 1 changes in the vertical direction.

The reflected light of the light beam 14 irradiated onto the disk 1 is irradiated onto the photoelectric element 23 via the reflecting mirror and lens as described above, but this element 23 has two light receiving surfaces 23.
a and 23b, and if the signal used for the tracking control described above indicates the sum of the amounts of light received by the two light receiving surfaces 23a and 23b, then the automatic focusing device 19, that is, the focus control The signals to be used are the two light receiving surfaces 23a and 23b.
What is necessary is to detect the difference in the amount of light received as a signal. Then, as shown in FIGS. 15 and 16, this signal moves the lens that focuses the light beam on the disk 1, so that a constant beam spot is always formed on the disk 1. In this way, tracking control and focus control can be controlled independently using one light beam 14 and one differential photodiode 23 without interfering with each other.

15 to 17 show the optical system device 19 for focus control and tracking control.
FIG. 5 shows a state in which a light beam is focused on the differential photodiode 23, and the incident light 14 (in this embodiment, parallel light is used) that is not focused on the half mirror 35 is approximately near the center of rotation of the half mirror 35. ) is incident. A part of the reflected light 14 of the incident light 14 by the half mirror 35 enters the lens 20 and is focused on the disk 1. The light 14' reflected by this disk 1 passes through the lens 20 and the half mirror 35, reaches the second lens 36, is focused in front of the differential photodiode 23, and is further expanded to a certain extent to the junction of the differential photodiode 23. Reach 37. A method for detecting defocus using this device will be explained. 16 and 17 only show the optical axis of the light beam, with arrows indicating the track direction, and FIG. 17 is a side view of FIG. 16, with the half mirror 35 etc. omitted. The angle of change of the incident optical axis P due to the rotation of the half mirror 35 is
5 It can be regarded as a ray of light that spreads out from above. The focal position of the optical axis caused by the rotation of the half mirror 35 is turned back on the disk 1, and after passing through the lens 20, the position changes around the virtual image point T. Therefore, after the reflected light P' passes through the half mirror 35, the second lens 36 is arranged as described above, and the differential photodiode 23 is positioned at a position slightly shifted from the convergence position of the virtual image point T by the second lens 36. The oblique beam spot 17' is fixed to a part of the junction 37 of the differential photodiode 23 without changing the position on the junction 37. Also, if the disk 1 changes by X, the optical axis folded back by the disk 1 changes as K, K ₁ , and after passing through the half mirror 35 and the second lens 36. A deviation of β occurs at the junction 37, and this deviation is taken out and transferred to the lens 20.
move. In the embodiment described, the junction 37 of the differential photodiode 23 must be at right angles to the aforementioned deflection direction. Because of this configuration, even if the half mirror 35 is rotated for tracking control of the information track, the beam spot 1
Since 7' is fixed on the element, it does not shift from the junction, and the differential photodiode is not affected by the rotation of the half mirror, allowing highly accurate focus control.

The differential photodiode 23 has two light-receiving surfaces 23a and 23b, and the gap between the junctions 37 is
It is about 50 to 100 μm. Therefore, in order to use this differential photodiode 23 to detect both the sum and the difference in the amount of received light as described above, the diameter of the beam spot 17' that irradiates the junction 37 of the differential photodiode 23 is equal to the diameter of the junction 37. It must be sufficiently larger than 37, and although it varies depending on the gap length of the joint, a range of about 500 μm to 2 mm is sufficient. As described above, since the diameter of the beam spot 17' is made larger than the gap length of the joint 37, there is no signal non-detection state caused by the beam spot 17' of the reflected light entering the joint 37.
Recorded information and control signals can be detected continuously, accurately and reliably. In this way, even if the beam is deflected by rotating the half mirror, it is possible to always obtain an effective spot diameter that remains stationary on the differential photodiode, and the relative positional deviation X between the disk and the lens can cause the differential photodiode to In order to obtain movement, each member, as shown in Figs. 16 and 17,
When a set value is given to the distance between each position, the distance α between the second lens 36 and the differential photodiode 23 is given by the following equation. f ₁ is the focal length of the lens 20,
f ₂ is the focal length of the second lens 36.

For lens 20, 1/a+1/c=1/f ₁ c=a・f ₁ /(a−f ₁ ) d=c−f ₁ , and e=f ₁ −d=2f ₁ −G Lens 20 For 1/e-1/e'=1/f _1For the second lens 36 1/(e'+a+b)+1/α=1/f ₂ α=f ₂・(e'+a+b)/( e + a + b - f ₂ ) Putting the above in order, α = (2a + b - 2f ₁ ) · f ₂ / (2a + b - 2f ₁ - f ₂ ) Also, for the displacement of the beam spot 17' at the junction 37 of the differential photodiode 23, Yotsute lens 2
The displacement β of the beam spot 17' is given by the following equation (see FIG. 17).

where _, Indicates the distance between the intersection of the optical axes of the parallel light and the changing light.

△X ₁ = 2t・X/f ₁ △X ₂ = △X ₁・(a+b−f ₁ )/f ₁ β=△X ₂ (1−a/l) Here, 1/l=(a+b−f ₁ −f ₂ ) /f ₂・(a+b−f ₁ ), and rearranging the above, β=2X・t・f ₂・(a−f ₁ )/f ₁ ²・(2a+b−2f ₁ −f ₂ ) becomes.

The extracted difference signal is detected through a circuit substantially similar to that in the tracking control described above. 1st
As shown in a block diagram as shown in FIG. 8, the outputs from the two light-receiving surfaces 23a and 23b of the differential photodiode 23 are each amplified by an amplifier circuit 38, and the difference output from the reference is extracted by a clamp circuit 39. The difference output is inputted to an integrating circuit 41 which obtains an envelope output via a differential circuit 40, and a level adjustment section 42 which obtains a difference with a reference output corresponding to a reference setting position.
is extracted as a focal signal. This signal activates the automatic focusing device to control the focus of the beam spot 17.

This embodiment combines the tracking control circuit and focus control circuit as described above by using one differential photodiode, and its outline is shown in FIG. 19. The result will be as shown in Fig. 20. Explaining according to this block diagram, the light reception signals on the two light receiving surfaces 23a and 23b are converted into electrical signals and the amplification circuits 43a and 4
3b and filter circuits 44a and 44b,
By this filter 44a, 44b circuit, the disk 1
2.5~ of the information recorded in the upper information track 2
It only passes the 4.2MHz frequency band.
This is because parts of the disk 1 have different reflectances due to dirt, etc. that are not related to information, and the total light intensity changes slightly depending on the position of the spot irradiated onto the differential photodiode 23, as shown in FIG. This is because noise is generated at frequencies ranging from several 10 to several 100 KHz.

The two signals thus detected are used to detect a tracking signal, a focus signal, and information signals such as video and audio, respectively.

That is, as a tracking signal, the above two signals are sent to the two light receiving surfaces 23a,
A sum signal indicating the sum of the amounts of light received by the beam deflector 23b is transmitted through the clamp circuit 46, the integration circuit 47, and the phase compensation circuit 48 as described above, and is then sent as a control signal for operating, for example, a reflector in the beam deflection device 18 or a pickup device. It is detected as a control signal for driving the 16 feed motors 21. The phase compensation circuit 48 mainly compensates for the delay of the mechanical control devices such as the pickup device 16 and the beam deflection device 18 with respect to the control signal, and processes the signal into a signal whose phase is advanced in advance to stabilize the control system. This is to improve performance, quick response, and accuracy. Also, the phase compensation circuit 4
8, or if amplifier circuits 49 and 50 are installed before the beam deflection device 18 and pickup device 16, the accuracy can be further improved. Furthermore, since information such as video and audio is recorded as a pulse width in the sum signal, it can be detected from the sum circuit 45 via the amplifier circuit 51 and level adjustment circuit 52.

On the other hand, the focus signal is detected as follows.
Two light receiving surfaces 23a, 2 of the differential photodiode
The two signals obtained from 3b are input to clamp circuits 53a, 53b after passing through filter circuits 44a, 44b as described above. The clamp circuits 53a and 53b control how the beam spot 17 irradiating the disc 1 hits the information track 2, and how the light receiving surface 23 of the differential photodiode 23
Since the reference potential changes depending on how the beam spot 17' hits the beam spot 17' with respect to a and 23b, a constant reference potential is determined to improve the accuracy of the signal. The two signals that have passed through the clamp circuits 53a and 53b are sent to a difference circuit 54 that extracts the difference between the two voltage signals.
The signal is inputted into a single difference signal, which operates the automatic focusing device 19 via an integrating circuit 55 and a phase compensation circuit 56, similarly to the tracking control circuit described above.
This phase compensation circuit 56 is similar to the compensation circuit 48 in the tracking control circuit described above, and an amplifier circuit 56 is provided before the phase compensation circuit 56 and the automatic focusing device 35.
Similarly to the above, the accuracy can be further improved by installing 7 and 58.

[Effects of the Invention] As described above, the present invention is capable of extracting optical information using a single light beam and a differential photodiode formed by joining a photoelectric element, and is also capable of extracting optical information from a beam spot for an information track. Detection of the focus control signal is not affected by the movement of the focus control signal. Furthermore, since the diameter of the beam spot that irradiates the junction of the differential photodiodes is made sufficiently larger than the diameter of the junction, recorded information and control signals can be detected accurately and reliably.

[Brief explanation of the drawing]

FIG. 1 is an explanatory plan view of the disk-shaped information medium, FIG. 2 is an enlarged view showing the recording state of the disk-shaped information medium, and FIG.
The figure is a schematic diagram showing audio and image signals.
A schematic diagram showing the progress of image signal synthesis, Figure 5 shows audio,
A block diagram showing the process of converting an image signal into an information pulse, FIG. 6 is an overall side view of the reading device, FIG. 7 is a schematic diagram of the pickup device, FIGS. 8 and 9 are output waveform diagrams obtained from the photoelectric element, FIG. 10 is a block diagram of an electrical method for obtaining positional deviation information between a beam spot and an information track from an output waveform, and FIG. 11 is an output waveform diagram showing the influence of reflected light from a disk-shaped information medium on the output of a photoelectric element. Fig. 12 is a block diagram of an electrical method for separating positional deviation information between the beam spot and the information track from the output waveform, Fig. 13 is a diagram showing the frequency spectra of audio, image signals, and control signals, and Fig. 14 is a diagram showing the difference in position between the beam spot and the information track. Dynamic photodiode 2
An explanatory diagram showing the position of the beam spot irradiated onto two light receiving surfaces, FIG. 15 is a schematic diagram of the automatic focusing device,
Fig. 16 is an explanatory diagram showing only the optical axis of Fig. 15;
Fig. 17 is a side explanatory view of Fig. 16, Fig. 18 is a block diagram of an electrical method for separating information on the defocus of the beam spot on the information track from the output waveform, and Fig. 19 shows an outline of the present invention. block diagram,
FIG. 20 shows a block diagram of an electrical method for simultaneously separating information on the positional deviation between the beam spot and the information track and information on the focal deviation of the beam spot on the information track from the output waveform of the differential photodiode. 1... optical information medium, 2... information truck,
14...Light beam, 17'...Beam spot,
23...Differential photodiode, 23a, 23b
...Photoelectric element, 37...Joint part.

Claims (1)

[Claims] 1. A single light beam 14 is irradiated onto the information track 2 of the optical information medium 1, changes in pulse amplitude are extracted from continuous changes in the reflected light of this light beam 14, and the said information is extracted from changes in pulse width and pulse gap. Optical information reading for reproducing information recorded on the medium 1 and controlling the tracking of the light beam 14 with respect to the information track 2 by moving the light beam 14 in a direction substantially perpendicular to the direction of the information track 2 of the information medium 1 In the apparatus, photoelectric elements 23a and 23b are provided at positions where the image of the irradiated portion of the information medium 1 is not formed.
The junction portion 37 of the differential photodiode 23 formed by bonding the differential photodiode 23 is arranged.
The beam spot 17' of the reflected light that irradiates the photoelectric elements 23a, 23b is made sufficiently larger in diameter than the gap between the joints 37, and the joints 37 are disposed substantially perpendicular to the two directions of the information tracks of the information medium 1. A control signal detection device in an optical information reading device that detects a focal point control signal of a beam spot 17 of a light beam 14 that irradiates an information medium 1 based on a change in the difference in the amount of light received from the beam spot 17'.