JPS61156540A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To eliminate the instability of immediately after a loop gain of a servo-system has been switched, by holding an output of a driving controlling circuit in a prescribed time immediately after a loop gain of a focus control use servo-system and/or a tracking control user servo-system has been switched. CONSTITUTION:A sample holding circuit 21 is constituted of a switch 22, a resistance 23 and a capacitor 24. Monostable multivibrators 18, 19 are started by a rise and a fall, respectively, of a recording enable signal (a) from a sequence controlling circuit 17 and generate output signals, OR of these outputs is taken by an OR gate 20 and a signal is obtained. The sample holding circuit 21 sample-holds an output signal of an amplifier 14 by said signal (d) and outputs it to a power amplifier 15. In this way, a turbulence of a focus signal (c) caused by switching of the gain of the amplifier 14 is eliminated. A pulse width (t) of the signal (d) is selected so as to eliminate the turbulence of the focus signal (c), and it will suffice that the holding time is determined by selecting a time constant of the sample holding circuit 21 to match said (t).

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical information recording/reproducing device such as an optical disk device.

(Prior Art) FIG. 2 shows an example of the configuration of an optical pickup in a conventional optical information recording/reproducing device. A light beam from a light source 1 consisting of a semiconductor laser is converted into parallel light by a coupling lens 2, and a polarizing beam splitter 3.1 The light is focused by the objective lens 5 via the /4 wavelength plate 4 onto the information recording medium 6 (a disk on which guide grooves are formed in advance) as a minute spot of about 1 μm. The reflected light from the information recording medium 6 is reflected by the objective lens 5, 174.
The light is condensed by a condenser lens 7 via a wavelength plate 4 and a polarizing vinyl splitter 3, 172 light beams thereof are blocked by a light shielding plate 8, and the remaining 172 light beams are received by a two-split light receiving element 9. This two-split light-receiving element 9 is divided into two light-receiving elements A and B.
Focus detection is performed using reflected light (transmitted light may also be used) from the information recording medium 6.

This focus detection method is called a knife method because the light shielding plate 8 acts as a knife, and the principle of focus detection is shown in FIG. That is, when focusing, the amount of light received by light receiving elements A and H is equal, but when the information recording medium 6 is closer to the objective lens 5 than the in-focus position, the amount of light received by light receiving element A is equal to that of light receiving element B.
On the other hand, when the information recording medium 6 moves away, the amount of light received by the light receiving element A becomes smaller than the amount of light received by the light receiving element B. Generally, focus detection is performed so that the focus of the objective lens 5 is located within ±1 μm from the recording surface of the information recording medium 6, and the focus is controlled by moving the objective lens 5 in the optical axis direction using a servo system (not shown) based on the detection signal. Do the following.

Furthermore, information is recorded in the guide groove by modulating the light intensity of the semiconductor laser 1 with a signal corresponding to the information and irradiating the rotating information recording medium 6 with pulsed strong light. When 6 is irradiated with strong light, small holes called pits are formed by melting, etc., and the presence or absence of these small holes is determined by shining weak light from the semiconductor laser 1 onto the rotating information recording medium 6 and using the reflected light. Information is reproduced by detection.

Since the ratio of the light intensity during reproduction and the light intensity during recording of the light irradiated to the information recording medium 6 is generally 10 times or more, the servo loop gain is different during recording and reproduction in the focus control servo system described above. The focus changes greatly, making it impossible to perform correct focus control.

Therefore, conventionally, the loop gain of the servo system was changed to be constant during recording and playback. FIG. 4 shows the servo circuit of a 21-division light-receiving element A.

Each output current of B is converted into a voltage by a precurrent amplifier 10.11, and the difference between the voltages is calculated by a differential amplifier 12. The relationship between the output voltage of the differential amplifier 12 and the defocus amount is a so-called S-shaped curve as shown in FIG. 5, and servo control is performed so that the output voltage of the differential amplifier 12 becomes zero. The output voltage of the differential amplifier 12 is called a focus signal, and is sent to the servo coil 16 via the phase compensation circuit 13, the amplifier 14 that performs gain switching, and the power amplifier 15, and the servo coil 16 electromagnetically controls the objective lens 5. Driven in the direction of the optical axis. Gain switching of the amplifier 14 is performed by a signal indicating the recording mode (recording enable signal) from the sequence control circuit 17 6 Figure 6 shows the waveform of each signal 6 Although the light intensity changes like a rectangular wave, the frequency characteristics of the focus signal detection circuits 9 to 12 in the above-mentioned servo system are generally low frequency characteristics because the objective lens 5 only needs to follow the rotation of the information recording medium 6. .

Further, in order to prevent oscillation of the servo system, the pass band of the servo loop is usually limited by the phase compensation circuit 13. Therefore, even if the intensity of the reflected light from the information recording medium 6 changes rectangularly, the voltage of the focus signal corresponds to the average value of the reflected light. When the average value of reflected light changes between recording and reproduction, the voltage change of the focus signal takes on an integral waveform as shown in FIG. The gain of this focus signal is recorded by the amplifier 14 using the enable signal a.
When the gain is switched, the output of the amplifier 14 is disturbed immediately after the start of recording and immediately after the end of recording, as shown in FIG. , the servo system becomes unstable.

In addition, in the optical information recording/reproducing apparatus, the deviation between the guide groove on the information recording medium 6 and the above-mentioned spot is detected from the reflected light or transmitted light from the information recording medium 6, and the optical information including the objective lens 5 is detected according to this detection signal. A tracking control servo system is provided that controls part or all of the system to position the spot on the guide groove. Even in this servo system, if the servo loop gain is changed to be constant during recording and reproduction, it becomes unstable immediately after the start of recording and immediately after the end of recording, similar to the focus control servo system described above.

(Objective) An object of the present invention is to provide an optical information recording/reproducing apparatus that eliminates instability of a servo system due to switching of servo loop gain.

(Structure) The present invention is provided with means for suppressing the output of the drive control circuit for a certain period of time immediately after switching the loop gain of the focus control servo system and/or the tracking control servo system.

FIG. 1 shows a focus control servo circuit in one embodiment of the present invention. In this embodiment, monostable multivibrators 18, 19, an OR gate 20, and a sample and hold circuit 21 are provided in the optical information recording and reproducing apparatus described above, and the sample and hold circuit 21 includes a switch 22,
It is composed of a resistor 23 and a capacitor 24.

The monostable multivibrators 18 and 19 are activated at the rise and fall of the recording enable signal a from the sequence control circuit 17, respectively, and produce output signals as shown in FIG.
A signal as shown in FIG. 7d taken at 0 is obtained. The sample-and-hold circuit 21 samples and holds the output signal of the amplifier 14 using the signal d, and outputs the sample-and-hold signal to the power amplifier 15. That is, when the signal d is at a low level, the switch 22 is turned on, and the output signal C of the amplifier 14 is outputted to the power amplifier 15 and added to the capacitor 24. When the signal d becomes high level, the switch 22 is turned off, and the capacitor 24 holds the signal C at the time when the switch 22 was turned off, and outputs it to the power amplifier 15. Therefore, the output of the sample and hold circuit 21 becomes as shown in FIG. 7e, and the disturbance in the focus signal C caused by the gain switching of the amplifier 14 is removed. The pulse width t of the signal d may be selected so as to remove disturbances in the focus signal C, and the time constant of the sample and hold circuit 21 may be selected in accordance with this t to determine the hold time.

Further, the present invention can be similarly applied to a tracking control servo system in an optical information recording/reproducing apparatus to eliminate instability immediately after recording. To explain this tracking control servo system, in FIG. 2, the light shielding plate 8 uses two divided light receiving elements C and D, as shown in FIG. 9, and receives one reflected light P. The information recording medium 6 has a guide groove (recording track) PG called a pregroove formed in a spiral or concentric shape, and the detection of the recording track is based on the position of reflected light depending on the optical distance between the recording track and the area between the recording tracks. This is done by detecting the symmetry of the far-field image of reflected light with respect to the center of the recording track based on the phase difference.

In other words, when the above spot is shifted from the recording track and light is incident on the end of the recording track with a phase difference of about π/2 with respect to the part between the recording tracks, the far field image of the reflected light is as shown in Figure 8 (a). , (C), the areas with high light intensity shift in the direction in which the spot is shifted. Therefore, this change in light intensity is detected by the two-split light receiving elements C and D, and by detecting the difference between the currents flowing through the light receiving elements C and D, a tracking control signal is detected, and the objective lens 5 is adjusted accordingly. By driving part or all of the optical system, the spot can be controlled to be positioned on the recording track. Such tracking control is performed by a servo system, and the servo circuit is constructed in the same manner as in the above embodiment. However, light receiving element A.

Light receiving cables C and D are used instead of B, and servo coil 1
6, a servo motor is used to drive part or all of the optical system in a direction transverse to the recording track.

(Effects) As described above, according to the present invention, the output of the drive control circuit is held for a certain period of time immediately after switching the loop gain of the focus control servo system and/or the tracking control servo system in an optical information recording/reproducing device. Therefore, instability immediately after switching the loop gain of the servo system can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a servo circuit in an embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of an optical pickup in an optical information recording/reproducing device, and FIGS. 3(a) and (b)
Figure 4 shows each focus state of the same optical pickup.
The figure is a block diagram showing a conventional focus control servo circuit, Figure 5 is a characteristic curve diagram showing the relationship between the focus signal and defocus amount of the servo circuit, and Figure 6 is a waveform showing each signal of the servo circuit. 7 is a waveform diagram showing each signal of the above embodiment, FIG. 8 is a diagram showing the principle of an example of recording track detection, and FIG. 9 is a diagram showing the optical pickup and its two-split light receiving element. 18.19...monostable multivibrator, 20...
・OR gate, 21...sample hold circuit. 31 Figure 1! Voice 2 Figure 5 Figure (θ) Sacred 4 Gu Rikiu 6 Figure Vines 7 Figure 0 □

Claims (1)

[Claims] This is a device that optically records and reproduces information on an information recording medium on which guide grooves are formed in advance, and includes a light source for recording and reproducing information, and a light source that converts light from the light source into a minute spot onto the information recording medium. a first detection means for detecting the distance between the lens and the information recording medium from reflected light or transmitted light from the information recording medium; and a first detection means according to an output signal of the first detection means. a first drive control circuit that controls the distance by driving the lens; and a second detection means that detects a deviation between the guide groove and the spot from reflected light or transmitted light from the information recording medium. a second drive control circuit that controls a part or the entire optical system including the lens in response to the output signal of the second detection means so that the spot is positioned in the guide groove;
a switching means for switching the light intensity level from the light source during recording and reproduction; a switching means for switching the gain of the first drive control circuit and/or the second drive control circuit in accordance with switching of the switching means; An optical information recording/reproducing apparatus comprising means for holding the output of the gain switching drive control circuit for a certain period of time immediately after switching of the switching means.