JPS6118811B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical system that optically reproduces information such as video or audio by keeping the distance between a recording medium and a beam converging device at an optimum value even when temperature changes occur. The present invention relates to a playback device.

An example of a recently developed optical disc player for video or audio will be described with reference to FIGS. 1 is rotated by a main scanning motor 2 at a constant speed of, for example, 1800 rpm, and
A beam 4 is projected onto the disk 1 from a reading device 3, and this reading device 3 is further transferred to a feeding device 5 for sub-scanning.
The beam 4 is sent in the radial direction of the disk 1 by the beam 4, and the recorded information is read while scanning the disk 1 in a spiral manner. More specifically, the laser beam emitted from the laser light source 6 as a beam projection device is transmitted through a first half mirror 7, a concave lens 8,
Diffraction grating 9, beam splitter 10, 1/4λ plate 1
1, the light beam reaches a beam converging device 14 via a first mirror 12 and a rotary mirror 13 for minute movement of the light beam, where it is converged to become a beam 4 for reproduction. This reproducing beam 4 is projected so as to converge on the disk 1, and by scanning the recording track with this beam 4, a reflected beam 15 corresponding to the presence or absence of a recording signal is obtained, and this reflected beam 15 becomes a beam convergence. device 14, rotating mirror 13, first mirror 1
2. The signal reaches a reproducing photodetector 16 via a 1/4λ plate 11 and a beam splitter 10, where it is converted into an electrical signal, amplified by a radio frequency (RF) amplifier 17, and then sent to a demodulation circuit. .

A focus beam 18 for controlling the distance between the beam converging device 14 and the disk 1, which is schematically shown by one condensing lens, that is, controlling the focus, is a laser beam that is reflected by a half mirror 17. obtained by the second mirror 1
9, reaches the beam splitter 10 via the convex lens 20, the third mirror 21, and the fourth mirror 22,
After that, similarly to the reproduction beam 4, 1/4λ plate 1
1. The beam is projected obliquely onto the disk 1 via the first mirror 12, the rotating mirror 13, and the beam converging device 14. A focused reflected beam 23 obtained by reflecting the focused beam 18 on the disk 1 is transmitted through the beam focusing device 14 and the rotating mirror 1.
3. The light passes through the first mirror 12, the 1/4λ plate 11, the beam splitter 10, and the fifth mirror 24 in order to reach the two-split focusing photodetector 25. In this example, the focus photodetector 25 includes a first photoelectric conversion element 26 and a second photoelectric conversion element 27, and changes the optical path of the focused reflected beam 23 according to the focus state (interval state). Detect.

FIG. 4 is an explanatory diagram of distance (focus) detection. If the position of disk 1 shown by the solid line is the optimal position, the reflected beam 2 shown by the solid line
3a is obtained and projected onto the dividing line of the two-segment photodetector 25. Therefore, at this optimum focus, outputs of the same level can be obtained from the first photoelectric conversion element 26 and the second photoelectric conversion element 27. On the other hand, when the disk 1 is at the position shown by the dashed-dotted line, the reflected beam 23b is shown by the dashed-dotted line, and is projected onto the second photoelectric conversion element 7 with a biased angle. When the disk 1 is at the position indicated by the two-dot chain line, the reflected beam 23c becomes a reflected beam 23c indicated by the two-dot chain line, and is projected onto the first photoelectric conversion element 26 in a biased manner. Therefore, a change in the height of the disk 1, that is, a change in the distance between the beam converging device 14 and the disk 1, can be converted into a change in the beam position on the photodetector 25 to detect the distance (focus).

In order to control the distance between the beam focusing device 14 and the disk 1 based on the output of the focusing photodetector 5, a distance control device 28 is provided as shown surrounded by a dotted line in FIG. To explain this in more detail, the output of the first photoelectric conversion element 26 is amplified by the amplifier 29 and then becomes one input of the differential amplifier 30, and the output of the second photoelectric conversion element 27 is amplified by the amplifier 31. It later becomes the other input of the differential amplifier 30. The comparison output of both obtained from the differential amplifier 30 is applied to a voice coil type moving coil 32 capable of displacing the beam focusing device 14 in a direction perpendicular to the surface of the disk 1. The moving coil 32 is the beam focusing device 1
4, and the beam focusing device 14 is displaced depending on the magnitude of the current flowing therein. Such a focus control section is called a focus actuator in a video disc player, and is well known, so further detailed explanation will be omitted.

The disk 1 used in the apparatus of FIG. 1 generally transmits an information signal, such as a video signal or an audio signal, to a spiral track 34 by means of an optical recess or pit 33, as shown in FIGS. 2 and 3. Formed by recording. The width of the pit 33 in this disc 1 is, for example, approximately 1 μm, the depth of the pit is approximately 1/4λ (here, λ is the wavelength of the laser beam), and the length of the pit is the inner and outer sides in the case of a video disc. There is a difference depending on the size, for example, 1.5 to 6 μm. Generally, the video disc 1 on which information signals are recorded has a transparent resin layer 35 having an uneven surface corresponding to the pits 33, as shown in FIG.
and a reflective film 36 coated on the uneven surface of the resin layer 35.
and a protective film 37 that protects the reflective film 36.

The diameter of the reproducing beam 4, which is illustrated in FIG. 2, is larger than the width of the pit 33, and when scanning the pit 33, the reflected light inside the pit and the reflected light outside the pit cancel each other out. When scanning an area where no pit 33 is provided, the reflected output becomes large because no cancellation occurs. Therefore, the pit 33 can be read depending on the strength of the reflected beam 15 at the photodetector 16. At this time, since the pit 33 was recorded in correspondence with the FM signal, a radio frequency (RF) output corresponding to the FM signal was obtained from the photodetector 16.

The tracking control beam, although not shown in FIG. This leads to a tracking photodetector (not shown).

By the way, if the optical system of a disk player as described above goes out of order due to temperature changes or the like, an optimal convergence state may not be obtained even if the focus control system is operating normally. If the optimum convergence state is not obtained, the beam spot on the reproducing photodetector 16 will become blurred and protrude from the detector, resulting in a decrease in the output level and a decrease in the S/N ratio, and similar problems will occur with the reflected beam for tracking control. This may cause tracking control to become unstable. Although the disk player shown in FIG. 1 has been described as an example, similar problems naturally occur in various playback devices that use optical systems.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an optical reproducing device that can perform focus control with less deviation due to temperature changes and the like.

To achieve the above object, the present invention has a beam converging device disposed opposite to a recording medium on which information is recorded by an array of optically detectable unit recording areas, and the beam converging device focuses the beam. a beam projection device that converges and projects the beam onto the recording medium; a device (for example, a moving coil 32) that displaces the beam converging device so as to adjust the distance between the beam converging device and the recording medium; a scanning drive device for scanning the recording surface of the recording medium with a beam by moving either or both of the beam projection device; and a reflected beam generated by projecting the beam onto the recording medium. an information reading device for reading information, a split-type photodetector that optically detects a change in the distance between the beam converging device and the recording medium based on the reflected beam; A spacing control circuit (for example, a differential amplifier 30) that forms a signal for controlling the spacing based on the output and supplies it to the displacing device, and controls the spacing between the recording medium and the beam focusing device to A periodic signal that is periodically varied within a range that does not make it impossible to read the information seal is supplied to the displacing device, and the period of this periodic signal is the unit recording area of the output of the information reading device. a periodic signal generator set to be longer than a fluctuation period corresponding to the array; and an interval fluctuation frequency component for detecting a frequency component generated based on the interval fluctuation due to the periodic signal from the output of the information reading device. a detection circuit; a phase comparator that compares the phases of the periodic signal and the signal detected by the interval variation frequency component detection circuit and generates an output corresponding to the interval; The present invention relates to an optical reproducing device characterized in that it includes a correction circuit that corrects the output of the split-type photodetector or a signal for controlling the interval using the output of the phase comparator.

According to the above invention, since interval control (focus control) is performed using a split photodetector, the focus control range of the wobbling method (several microns)
It is also possible to control focus (interval) deviations that are larger, for example, on the order of several hundred microns. When a split photodetector is used, control errors occur due to deviations in the optical system due to temperature changes, etc. However, in the present invention, the above control errors are eliminated by outputting a phase comparison between a periodic signal and an interval variation frequency component detection signal. Correct. Therefore,
Despite having a relatively large focus control range, focus control with less influence from temperature changes is possible.

Embodiments of the present invention will be described below with reference to the drawings. However, in Figures 5 and 8, numbers 1 to 3
Components designated by 2 are substantially the same as those designated by the same reference numerals in FIG. 1, so their explanation will be omitted.

In FIG. 5 illustratively showing an optical focus player according to an embodiment of the present invention, a frequency of several Hz (for example, 7.5 Hz) is used to periodically vary the distance between the disk 1 and the beam focusing device 14. An oscillator 40 is provided which generates an output, the output of which is applied to an adder 41 provided at the output of the differential amplifier 30. Therefore, a composite signal of the output of the differential amplifier 30 and the output of the oscillator 40 is applied to the moving coil 32 for controlling and driving the interval.
The moving coil 32 and the beam focusing device 14 vibrate in a direction perpendicular to the recording surface of the disk 1 with an amplitude that does not interfere with pit reading. The period of this oscillation naturally corresponds to the frequency of the oscillator 40.

AM detector 42 coupled to the output of amplifier 17
The detector detects how the RF output of the photodetector 16 changes due to the vibration of the beam converging device 14 including a condensing lens, and can also be called an envelope detector. A bandpass filter 43 coupled to the output of AM detector 42 passes only frequency components related to the oscillator output. A waveform shaping circuit 44 coupled to the output of the filter 43 is used to form a waveform suitable for phase comparison in a phase comparator 45.
The phase comparator 45 compares the phase of the envelope signal of the RF output provided from the waveform shaping circuit 44 and the output of the oscillator 40, and when the phase difference between the envelope signal and the oscillator output is 90 degrees, or The output is zero when the alternating current component of This is a known phase comparator. A correction circuit 46 provided between the amplifier 29 and the differential amplifier 30 is a circuit that adjusts the level of the detection signal in response to the output of the phase comparator 45 to correct the focus control signal.

Next, the operation of the apparatus shown in FIG. 5 will be explained with reference to FIGS. 6 and 7.

When the output of the oscillator 40 and the output of the differential amplifier 30 shown in FIG.
4 vibrates in a direction perpendicular to the surface of the disk 1. As a result, the convergence state of the reproducing beam 4 on the disk 1 naturally changes. However, since the vibration is within a readable range, reading of the pit by the reflected reproduction beam 15 continues.

By the way, the level of the radio frequency (RF) output corresponding to the presence or absence of pits obtained from the photodetector 16 is as follows.
Changes depending on focus state. That is, as shown in FIG. 6, the relationship between the RF output level of the reproduced output and the distance between the beam focusing device 14 and the disk 1 is as shown by a curve 47, and if the distance is D ₂ corresponding to the focused point, the most Large RF output can be obtained. On the other hand, as the spacing becomes narrower or wider as shown by D ₁ and D ₃ , the RF
Output level decreases. Now, if for some reason the center of the interval becomes _D1 , the interval changes as shown by waveform a with _D1 as the center. and,
As is clear from the relationship with curve 47, the RF output level is high during the period when the interval is larger than D _{1 , and the RF output level is low during the period when the interval is smaller than D 1 .} Therefore, from the photodetector 16 to the seventh
An RF output RF ₁ as shown in Figure B is obtained. Then, an envelope signal having a phase corresponding to the envelope waveform 48 of this RF output RF ₁ is input to the phase comparator 45 . Since the other input of the phase comparator 45 has the waveform shown in FIG. 7A,
The two inputs are in phase with each other, and the phase comparator 4
A positive output is generated from 5 and applied to correction circuit 46. The correction circuit 46 performs correction to increase the output of the amplifier 29, and the differential amplifier 30 generates an output that further widens the gap, and the gap is corrected from _D1 to _D2 . This brings the camera into a focused state.

On the other hand, if the interval is oscillating with waveform b around the interval D ₁ corresponding to the focal point in Fig. 6, then
Since the RF output level decreases both when the interval becomes larger and smaller around _D1 , a frequency component corresponding to the vibration waveform b is not generated in the output of the photodetector 16, and the seventh As shown in Figure C, an RF output RF ₂ with almost no level fluctuation is obtained. In this case, since there is no level variation in the RF output RF ₂ , the envelope waveform 49 naturally becomes flat, no comparison output is generated from the phase comparator 45 , and no correction is performed by the correction circuit 46 .

As shown in waveform c in Figure 6, if the interval is changing around interval D ₃ , the RF output level will decrease when the interval is larger than D ₃ , and when the interval is smaller than D ₃ . Since the RF output level becomes high, the situation shown in Figure 7 D, contrary to the case of D ₁ , is
RF output RF ₃ is obtained from photodetector 16 . this
The envelope waveform 50 of the RF output RF ₃ is the oscillator 4
Since it is in a phase opposite to the output of 0, a negative output is generated from the phase comparator circuit 45, and a correction is made in the correction circuit 46 to reduce the output of the amplifier 29. As a result, the distance from the differential amplifier 30 is increased.
An output that changes D ₃ to D ₂ is generated and becomes a focused point.

As is clear from the above, according to this example,
Even if the optical system for focus control becomes distorted due to temperature changes, etc., it is corrected or compensated by the output of the phase comparator 45, so it is possible to always obtain the optimum spacing and focus state. become. Therefore, it is possible to prevent a state in which regeneration is impossible or regeneration is unstable due to a temperature change.

FIG. 8 shows another embodiment of the invention. In this embodiment, a holding circuit 51 is provided between the phase comparator 45 and the correction circuit 46 in the apparatus shown in FIG. This holding circuit 51 is connected to the phase comparator 45 during times other than normal playback (forward play).
The output is directly applied to the correction circuit 46, but during normal reproduction, the immediately previous value is held and applied to the correction circuit 46. Since deviations due to temperature changes, etc. do not always change, accurate focus control can be achieved simply by correcting them before the start of playback.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be further modified. For example, the present invention can be applied to cases in which information is recorded not by pits but by optical contrast. In addition, the photodetector 25 is
It is also applicable to a case where the present invention is not constituted by one photoelectric conversion element 26, 27 but is constituted by four photoelectric conversion elements. Furthermore, the output of the phase comparator 45 may not be applied to the front stage of the differential amplifier 30, but may be applied to its output side. Furthermore, when a semiconductor laser is used as a light source, information may be read by changes in the semiconductor laser due to the reflected beam. Furthermore, instead of using the correction circuit 46 as a level control circuit, it may be used as an addition or subtraction circuit for the output of the amplifier 29 and the output of the phase comparator 45.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a conventional optical disc player, Fig. 2 is a plan view illustratively showing the disc, Fig. 3 is a partially enlarged sectional view of the disc, and Fig. 4 is an explanatory diagram showing interval detection. , FIG. 5 is an explanatory diagram showing an optical disc player according to an embodiment of the present invention,
Figure 6 is a graph showing the relationship between interval and RF output level, Figure 7 is oscillator output A and RF output B, C,
FIG. 8 is an explanatory diagram showing an optical disc player according to another embodiment of the present invention. In addition, in the symbols used in the drawings, 1 is a disk, 2 is a motor, 3 is a reading device, 4 is a reproduction beam, 5 is a feeding device, 6 is a laser light source, 14
is a beam focusing device, 15 is a reflected beam for reproduction, 1
6 is a reproduction photodetector, 18 is a focus beam, 23 is a focus reflected beam, 25 is a focus photodetector, 26 is a first photoelectric conversion element,
27 is a second photoelectric conversion element, 28 is a spacing control device, 30 is a differential amplifier, 32 is a moving coil, 40 is an oscillator, 41 is an adder, 42 is an AM detector, 45 is a phase comparator, 46 is a correction It is a circuit.

Claims (1)

[Claims] 1. A beam converging device disposed opposite to a recording medium on which information is recorded by an array of optically detectable unit recording areas, and converging the beam with the beam converging device. a beam projection device that projects onto the recording medium; a device that displaces the beam focusing device so as to adjust a distance between the beam focusing device and the recording medium; and either one of the recording medium and the beam projection device. or a scanning drive device for scanning the recording surface of the recording medium with a beam by moving both; and an information reading device for reading information based on a reflected beam generated by projecting the beam onto the recording medium. a split-type photodetector that optically detects a change in the distance between the beam converging device and the recording medium based on the reflected beam; and a split-type photodetector that controls the distance based on the output of the split-type photodetector. an interval control circuit that forms a signal for the displacement and supplies it to the displacing device; and periodically varying the interval between the recording medium and the beam focusing device within a range that does not make it impossible to read information by the beam. A periodic signal that supplies a periodic signal to the displacement device, the periodic signal having a period longer than a fluctuation period corresponding to the arrangement of the unit recording areas of the output of the information reading device. a generator; an interval variation frequency component detection circuit for detecting a frequency component generated based on interval variation due to the periodic signal from the output of the information reading device; a phase comparator that compares the phase with the detected signal and generates an output corresponding to the interval; and a signal for controlling the output of the split photodetector or the interval so that the interval is optimal. an optical reproducing device, comprising: a correction circuit that corrects the output of the phase comparator using the output of the phase comparator.