JPH0239021B2 - KOGAKUSHIKISAISEISOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical reproducing apparatus 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.

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 to scan the disk 1 in a spiral manner while reading the recorded information. 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
The signal reaches a reproducing photodetector 16 via a 2.1/4λ 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.

The 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, the focus control, is a laser beam 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, the 1/4λ plate 11,
The light is obliquely projected 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 a beam converging device 14 and a 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 this 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 27 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, is converted into a change in the beam position on the photodetector 25 to determine the distance (focus).
Detection can be performed.

In order to control the distance between the beam converging device 14 and the disk 1 by the output of the focusing photodetector 25, the output of the first photoelectric conversion element 26 is amplified by the amplifier 28 and then input to one side of the differential amplifier 30. The output of the second photoelectric conversion element 27 is amplified by the amplifier 29 and then becomes the other input of the differential amplifier 30. A comparison output between the two obtained from the differential amplifier 30 is sent to a gain adjuster 31 and a time constant circuit 3.
2. Beam focusing device 14 via drive amplifier 33
A voice coil type moving coil 34 is provided with a moving coil 34 that is capable of changing the direction perpendicular to the surface of the disk 1. The moving coil 34 is coupled to the beam focusing device 14, and moves the beam focusing device 14 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 41 by means of an optical recess or pit 40, as shown in FIGS. 2 and 3. Formed by recording. The width of the pit 10 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. The video disc 1 on which information signals are recorded with such pits 40 generally has pits 40 as shown in FIG.
The transparent resin layer 42 has an uneven surface corresponding to the above, a reflective film 43 that covers the uneven surface of the resin layer 42, and a protective film 44 that protects the reflective film 43.

The diameter of the reproducing beam 4, which is shown explanatory in FIG. When an area where the pit 40 is not provided is scanned, no cancellation occurs and the reflected output becomes large. Therefore, the pit 40 can be read depending on the strength of the reflected beam 15 at the photodetector 16. At this time, since the pit 40 is recorded in correspondence with the FM signal, a radio frequency (RF) output corresponding to the FM signal is 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. Such a problem can theoretically be solved by configuring the optical system so that even if a temperature change of several tens of degrees Celsius occurs, the beam deviation will be 1 μm or less. However, considering the coefficient of thermal expansion of materials in practical use, it is impossible to ignore distortions in the optical system due to temperature changes.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an optical reproducing device that can prevent an optimum focus state from being impossible to obtain due to temperature changes or the like.

To achieve the above object, the present invention includes a beam projection device that projects a beam onto an information recording medium, and a beam projection device that moves one or both of the recording medium and the beam projection device to beam a recording surface of the recording medium. a scanning drive device for scanning; a beam converging device for projecting the beam in a converged form onto the recording surface of the recording medium; and a reflected beam or reflected beam generated by projecting the beam onto the recording medium. an information reading device for reading information based on a transmitted beam; an oscillator; and an information reading device configured to minutely vibrate the beam focusing device in a direction perpendicular to the surface of the recording medium based on the output of the oscillator; A vibration and distance control device that controls the distance from the beam converging device; and a sudden change in the distance is optically detected based on the information reading beam or the focus control beam, and the vibration and distance control device is controlled. a frequency detection circuit that optically detects the information reading beam to detect a frequency signal corresponding to the minute vibration; and a frequency signal obtained from the frequency signal detection circuit and an output of the oscillator. a phase comparator that compares the phase of
a low-pass filter that forms a direct current or low-frequency correction signal based on the output of the phase comparator; and a low-pass filter that controls the vibration and spacing control device by the spacing detection device; An optical reproducing device comprising: a correction circuit that corrects, based on a signal, a focus shift based on direct current or low frequency fluctuations in the interval or the optical path length of the information reading beam. It is related to.

According to the above invention, the correction signal is formed based on the phase comparison between the output of the oscillator and the output of the frequency signal detection circuit, so that correction for correcting deviations due to temperature changes etc. can be performed with a relatively simple circuit configuration. I can get the signal. In Japanese Patent Application Laid-open No. 51-37248,
It is disclosed that a correction signal is formed based on an error signal in a focus servo loop and a high frequency reproduction signal, but this method requires a pulse shaping circuit, a sample hold circuit, etc.
The configuration becomes complicated.

Embodiments of the present invention will be described below with reference to the drawings. However, since the parts indicated by reference numerals 1 to 34 in FIG. 5 are substantially the same as those shown by the same reference numerals in FIG. 1, a description thereof will be omitted. In this embodiment, in addition to the main photodetector 16 and the split type photodetector 25 for focus, a photodetector 63 for detecting the focus state by a wobbling method is provided. A beam 15 a obtained by splitting the information reading beam 15 by a half mirror 60 enters the photodetector 63 via a pinhole 62 of the light restriction plate 61 . The output of the oscillator 64 is supplied to a vibration device 66 via a drive circuit 65. For this reason, the beam focusing device 14 uses the oscillator 64
In response to the output of the disk, it vibrates minutely in a direction perpendicular to the disk surface. In this method, the center of the convergence point of the reflected beam 15a becomes the position of the pinhole 62 when the reflected beam 15a is focused, and the convergence point vibrates back and forth around the pinhole 62. Also, depending on the change in the interval, the reflected beam 1
The vibration center of the convergence point 5a shifts forward or backward. As a result, if the output of the photodetector 63 is envelope-detected by the envelope detector 68 via the amplifier 67, a frequency component twice that of the oscillator 64 can be obtained at the focused point.
When the focus is out of focus on one side, a signal having the same frequency and the same phase as that of the oscillator 64 is obtained, and when the focus is out of focus on the other side, a signal is obtained that is in the opposite phase to that when the focus is out of focus on the other side. Therefore, by comparing the phase of the output of the oscillator 64 and the detection signal with the phase comparator 70 via the band pass filter 69 that passes the frequency component of the oscillator 64, it is possible to obtain an output corresponding to the focus shift. can.

In this device, the output of the phase comparator 70 is not directly used to drive the moving coil 34, and the time constant is considerably larger than that of the time constant circuit 32 (for example, 1 second or more).
A correction signal is formed by passing the signal through a low-pass filter 71 having an automatic gain control amplifier (AGC), and is applied to a correction circuit 58 having an automatic gain control amplifier (AGC) configuration. This results in
The low-pass filter 71 detects slow changes (direct current or low frequency fluctuations) in the spacing or optical path length due to temperature changes, etc., and operates to cancel out the slow changes.

As mentioned above, the time constant of the time constant circuit 32 of the servo lube including the photodetector 25 constituting the interval detection device is extremely small, and by making the beam 18 obliquely incident on the disk 1, changes in the longitudinal direction of the beam can be realized. Highly sensitive control is possible by detecting the interval by converting (change in interval) into a change in the horizontal direction (plane direction) of the reflected beam 23 at the photodetector 25. However, it also has the disadvantage that a change in optical path length due to a temperature change or the like extremely affects the focus detection accuracy, and that focus detection becomes impossible if the interval changes significantly.

If the normal state (or initial state) in which the temperature of the device shown in FIG. The output is equal to the output of the second photoelectric conversion element 27, and the output of the differential amplifier 30 is zero. Furthermore, the output of the low-pass filter 71 also becomes zero. Therefore, the correction circuit 58 does not adjust the input level of one of the differential amplifiers 30.

When the temperature is constant as described above, disk 1
If the distance between the beam focusing device 14 and the beam converging device 14 changes at high frequency, the reflected beam 23 changes in response, the output of the split photodetector 25 changes in response, and the output of the differential amplifier 30 changes in response. A focus control signal is generated to set the interval to a predetermined value, and the interval becomes the predetermined value.

On the other hand, when the temperature of the optical part begins to rise gradually,
The optical path length gradually changes due to the expansion of the optical system, and the reflected beam 23 no longer enters the dividing line of the photodetector 25 even when it is in focus. This means that since the focus servo system is a servo lube that makes the reflected beam 23 incident on the dividing line, if the correction circuit 58 is not operating, the optimum focus state cannot be obtained. Therefore, the interval also changes gradually following the temperature change. When a slow change (direct current or low frequency change) in the spacing and optical path length as described above occurs, a corresponding correction signal is obtained at the output stage of the low-pass filter 71 and applied to the correction circuit 58. Correction circuit 58 adjusts the input signal level of differential amplifier 30 in response to the correction signal. This input level adjustment is performed so that the output generated from the differential amplifier 30 is canceled out and no output is generated even at the focused point before correction. With this correction, even if the reflected beam 23 is not incident on the dividing line of the split type photodetector 25, the output of the differential amplifier 30 becomes zero at the in-focus point, allowing normal focus control. That is,
The focus control is the same as when there is no slow variation (direct current or low frequency variation) in the interval or optical path length.

As is clear from the above, according to the present device, even if a temperature change or the like occurs, information can be read in a state where no focus shift occurs.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be further modified. For example, the correction circuit 58 may be provided at the output stage of the differential amplifier 30 to correct the focus shift by changing the DC bias of the signal supplied to the moving coil 34. Alternatively, the photodetector 25 may be omitted, and both the spacing detection signal and its correction signal may be obtained based on the output of the photodetector 63 of the pinhole type spacing detection device shown in FIG. In addition, the low-pass filter 71 detects low-frequency (long-period) interval fluctuations caused by warping, bending, etc. of the disk 1, not only by defocusing caused by temperature changes.
It is also applicable to the case where the driving current of the moving coil 34 is changed so as to detect this variation and cancel this variation.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional disc player, Fig. 2 is an explanatory plan view of the disc, Fig. 3 is an enlarged sectional view of the disc, Fig. 4 is an optical path diagram showing an example of an interval detection method, and Fig. 5 1 is a block diagram showing a disc player according to an embodiment of the present invention. FIG. In the symbols used in the drawings, 1 is a disk, 14 is a beam focusing device, 16 is a photodetector, 25 is a split type photodetector, 30 is a differential amplifier,
34 is a moving coil, and 58 is a correction circuit.

Claims (1)

[Scope of Claims] 1. A beam projection device for projecting a beam onto an information recording medium; and a beam projection device for moving either or both of the recording medium and the beam projection device to scan the recording surface of the recording medium with the beam. a scanning driving device; a beam converging device for projecting the beam in a converged form onto the recording surface of the recording medium; an information reading device for reading information, an oscillator, and a device for causing the beam focusing device to minutely vibrate in a direction perpendicular to the surface of the recording medium based on the output of the oscillator; a vibration and interval control device that controls the interval between the vibration and interval control device; and an interval detection device that optically detects a sudden change in the interval based on the information reading beam or the focus control beam and controls the vibration and interval control device. a frequency signal detection circuit that optically detects the information reading beam to detect a frequency signal corresponding to the minute vibration; and a phase comparison between the frequency signal obtained from the frequency signal detection circuit and the output of the oscillator. a low-pass filter that forms a DC or low-frequency correction signal based on the output of the phase comparator; and a low-pass filter that controls the vibration and spacing control device by the spacing detection device; a correction circuit that corrects based on the correction signal obtained from the filter so as to cancel a focus shift caused by direct current or low frequency fluctuations in the interval or the optical path length of the information reading beam; Characteristic optical playback device.