JPS6032263B2 - Optical information recording and reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information recording and reproducing device, which irradiates light as a minute spot onto a disc-shaped recording medium and records information signals such as video signals and audio signals concentrically or spirally. The present invention provides an excellent focus control system for an apparatus that sequentially records or reproduces data on a medium-narrow recording track.

For example, a photoresist is coated on a disc substrate, the laser beam is intensity-modulated with a signal corresponding to an information signal while rotating at a constant speed, and the signal is recorded by focusing the light onto the photoresist using a lens. A video disc player system in which an original recording disc is produced through processing such as development and plating, and then a large number of duplicate discs are made in the same manner as conventional audio records, and the signals are played back using an optical playback device. Using special photosensitive materials such as silver halide film and manganese bismuth, information signals are recorded on a disk-shaped recording medium as a light and dark pattern of narrow tracks by varying length and period.
Many playback devices have been proposed.

In these devices, during recording or reproduction, a small amount of light is applied to the recording area of the disc-shaped medium. It is necessary to condense and irradiate light into a small spot, and the distance between the objective lens that condenses the light and the recording part of the recording medium is kept constant with an accuracy of ±IA skin regardless of distortion, warpage, vibration, etc. of the recording medium. must be maintained. For this purpose, the distance between the objective lens and the recording medium is generally detected optically using a photodetector, and the distance between the objective lens and the recording section of the recording medium is determined by storing the objective lens or controlling a drive device based on the near motor principle. It was controlled to remain constant. However, conventionally known control methods do not take any measures against changes in optical properties such as a decrease in reflectance or transmittance due to dirt or discoloration of the recording medium, and differences in optical properties due to initial variations in reflectance. However, when a recording medium with a low reflectance is used, the loop gain of the control system decreases, the precision of the control system deteriorates, and the quality of information signals during recording and reproduction deteriorates. The present invention eliminates these drawbacks, prevents variations in optical properties of recording media, changes in optical properties over time, and prevents adverse effects caused by dirt, etc., and provides a stable and highly accurate focus control system. A detailed explanation will be given below according to the drawings.

FIG. 1 shows an embodiment of an optical information recording/reproducing apparatus according to the present invention, which uses a light source such as a helium neon laser or a semiconductor laser. A light beam 2 from a light source 1 (only the central ray is shown for simplicity) is transmitted through a light modulator 3 and an intermediate lens 4.
, passes through a fixed half mirror 5, is reflected by a tracking vibrating mirror 6 that moves the light beam in the radial direction of the recording medium so that the light is irradiated onto the signal track during playback, and the objective lens 7 is housed. The light beam is sent to an objective lens driving device 8 based on the near motor principle, and is incident on a position shifted from the central optical axis of the objective lens 7, and is irradiated onto the disc-shaped recording medium 10. The light beam 2 irradiated onto the recording medium 10 is partially reflected, passes through the objective lens 7 again, is reflected again by the vibration mirror 6 for tracking, and is reflected by the half mirror 5.
The light is partially reflected by the two photodetecting elements 16a and 16b.
The light is projected onto a photodetector 15 consisting of: The output of photodetector 15 is applied to control circuit 17. The output of the control circuit 17 is applied to the drive coil 9 of the objective lens drive device 8, and the distance between the objective lens 7 and the recording medium 10 is maintained at a predetermined value regardless of distortion, warpage, vibration, etc. of the recording medium. Koto 2
is controlled so that the light is focused on the recording medium 10 as a minute spot (approximately one mountain surface ◇). On the other hand, the recording medium 101 is placed on a transparent disc-shaped turntable 11 made of glass or the like, and is driven at a constant rotation speed by an electric motor 13 attached to a support device 12, and is driven by a feed mechanism 14 associated with the support device 12. It is transferred in the radial direction to the light east 2 as indicated by an arrow 21. In the above device, the switch SWI is connected to the R terminal during recording and to the P terminal during playback, and when recording, the switch SWI is connected to the V terminal related to the information signal to be transmitted to the protector 19.
in (for example, an FM modulation signal of an information signal to be recorded), an optical modulator drive circuit 18 for driving the optical modulator 3, and the optical modulator 3 modulates the intensity of the optical east 2 with the signal Vjn, An information signal is recorded on the recording medium 10 as a brightness (shade) pattern according to Vin, and at the time of reproduction, a constant bias voltage Vo is applied to the terminal 20, and the optical modulator drive circuit 18 and the optical modulator 3 The intensity of the light beam 2 is adjusted to a constant level as strong as possible without optically affecting the recording medium 10, and the vibration mirror 6 for tracking is used to irradiate the light beam 2 onto the recording track. The information signal based on the light and dark pattern recorded by the king servo is detected by the photodetector 22 as a change in the amount of transmitted light in the best condition to detect the mystery. A method for detecting the distance between the objective lens 7 and the recording medium 10 using the photodetector 15 using the apparatus according to the embodiment shown in FIG. 1 will be described with reference to FIG. 2. In FIG. 2, the same parts as in FIG. 1 are designated by the same numbers. The light beam 2 reflected by the tracking immersion mirror 6 is incident on the objective lens 7 at a position off the optical axis 23, and is refracted by the objective lens 7 and irradiated onto the green medium 10 described below. When the recording medium 10 is at a position a predetermined distance away from the objective lens 7 (a position where the focal length of the objective lens 7 is approximately away from the condensing position), the reflected light of the luminous flux irradiated onto the recording medium is represented by the solid line 2. The light is projected so that the same amount of light irradiates both detection elements 16a and 16b, which are provided adjacent to each other, of the photodetector 15 through the optical path shown in FIG. In case C, where the position of the recording medium 10 is far from the condensing position, the reflected light takes on the shape shown by the dashed line 2', and the amount of light projected onto the detection element 16a increases, causing detection. The amount of light projected onto element 16b is reduced. Conversely, if the position of the recording medium 10 is shifted in the direction approaching from the condensing position, the light detecting element 16 passes through the optical path shown by the dotted line 2''.
The amount of light projected onto b increases, and the amount of light projected onto detection element 16a decreases. Therefore, the relationship between the difference output e of the detection elements 16a and 16b and the distance between the objective lens 7 and the recording medium 10 is, for example, as shown by the solid line in FIG. 3, and when the recording medium 10 is at the mouth position, the difference output is zero. The value corresponds to the deviation of the distance between the objective lens 7 and the recording medium 10 from the condensing position opening. The objective lens driving device 8 is controlled by this differential output, and the position of the objective lens 7 is changed according to distance changes such as distortion of the recording medium 10, warping, vibration, etc., and the objective lens 7 is always at the focused position. Just control it. The details of the control system for this purpose are shown in FIG. In FIG. 4, the same parts as in FIGS. 1 to 3 are indicated by the same numbers, and the portion surrounded by a dotted line 17 corresponds to the control circuit. The outputs of the detection elements 16a and 16b are applied to a differential amplification circuit 24, and the difference output e between the two detection elements is amplified and taken out. The output of the differential booster 24 is applied to a characteristic compensation filter circuit 25 of the control system, passes through a variable gain booster 26 whose boost rate is controlled by voltage, and then is increased in power by a power booster 27. is applied to the drive coil 9 to control the objective lens drive device 8 and perform focus control.
In addition, the outputs of both detection elements 16a and 16b are connected to an in-phase amplifier circuit 28.
The sum output of both detection elements is incremented by this, and is used to control the amplification rate of the variable gain intensifier circuit 26 via a suitable filter circuit 29 (preferably a reduction filter). The in-phase enhancement circuit 28, the filter circuit 29, and the variable gain enhancement circuit 26 are used to compensate for adverse effects on the focus control system due to changes in reflectance due to dirt or discoloration of the recording medium 10, changes in reflectance due to material variations, etc. The in-phase enhancement circuit 28 and filter circuit 29 are for detecting the reflectance of the information medium. In the focus control system, the objective lens must be controlled to have an error of less than 1 mm, which is extremely important, even when positional fluctuations due to distortion, warpage, vibration, etc. of the recording medium, which can exceed 500 mm, occur. High precision characteristics are required. However, if the reflectance of the recording medium decreases due to dirt or discoloration, the amount of light reflected from the recording medium in Figure 1 decreases, and therefore the detection element's sensitivity to the deviation of the recording medium from the condensing position decreases. The relationship of the difference output e is, for example, as shown by the dotted line in FIG. 3, and the slant is gentler than the solid line. In other words, the error detection sensitivity has decreased. A decrease in error detection sensitivity causes a decrease in the loop gain of the focus control system, resulting in a decrease in control accuracy, resulting in uneven recording of signals or changes in the output of the reproduced signal, which has a serious adverse effect on recording and reproduction. Conversely, when the reflectance increases due to material unevenness, etc., the error detection sensitivity increases and the loop gain of the control system increases as shown by the chain line in FIG. As the loop gain increases, control accuracy increases, but if the loop gain becomes too high, the control system becomes unstable and may cause oscillation, making recording and reproduction impossible. In the present invention, such variations in reflectance and changes in reflectance of the recording medium due to dirt or discoloration are detected as the sum output of both detection elements 16a and 16b. Since the light projected onto the photodetector 15 has a certain relationship with the reflectance of the recording medium 10, both the detection elements 16a,
The reflectance can be detected by detecting the amount of light projected onto the light beam 16b, ie, the sum of both outputs. If the increase rate of the variable gain increase circuit 26 is controlled so that the loop gain changes in inverse proportion to the output of the in-phase increase circuit 28, which is the increase signal of the Kazuyo force, it will not be affected by changes in reflectance, etc. A stable focus control system can be constructed. Such a variable gain increasing circuit can be easily realized by a circuit as shown in FIG. In FIG. 5, 32 is an inverting multiplier, 33 is a multiplier, and 34 and 35 are resistors. If voltages e and e2 are applied to the terminals 30 and 31, respectively, in this circuit, a voltage proportional to e and /e2 is obtained at the output terminal 36. Therefore, the filter circuit 29 is connected to the terminal 31.
If the output voltage of the filter circuit 29 is added, the gain will change in inverse proportion to the output voltage of the filter circuit 29. In configuring the control system, the filter circuit 29 is designed to prevent the compensation loop formed by the in-phase multiplier circuit 28 and filter circuit 29 from interfering with the main loop formed by the differential multiplier circuit 24, characteristic compensation filter circuit 25, etc., resulting in instability. It is preferable to make the time constant sufficiently larger than the time constant of the characteristic compensation filter circuit 25. As mentioned above, by configuring the focus control system based on the present invention, it is possible to eliminate the adverse effects of variations in reflectance due to unevenness in the material of the recording medium, and changes in reflectance due to stains on the recording medium or discoloration due to aging. Furthermore, even if the intensity of the light source changes, contamination may occur on the lenses and other parts that make up the optical system, and stable, high-quality recording and playback can be performed even if the transmission efficiency and reflection efficiency change. . In the above description, the recording and reproducing apparatus was described, but there is no difference in application to a reproducing-only apparatus or a recording-only apparatus such as a video disc player. Furthermore, the method of detecting reflectance etc. is not limited to the embodiments, for example, it may be detected by the output of a photodetector element for detecting information signals, or by installing a photodetector at an appropriate location in the optical path. It may also be detected by

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the optical information reproducing device of the present invention, Fig. 2 is a diagram explaining the principle of means for detecting deviation from the focusing position, and Fig. 3 is a diagram showing the principle of the means for detecting deviation from the focusing position. FIG. 4 is a diagram showing the configuration of the focus control system, and FIG. 5 is a diagram showing the configuration of the variable gain increasing circuit. 0 1... light source, 2... light east, 7...
...Objective lens, 8...Objective lens drive device, 10...Recording medium, 15...Photodetector, 1
6a, 16b...Detection element, 17...Control circuit, 24...Differential intensifier, 25...Filter, 26...Variable gain Multiplier, 28...
...In-phase multiplier, 29...filter. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. A condenser lens for condensing light from a light source onto the information medium in order to optically record or reproduce information on the information medium, and a condenser lens for condensing light from a light source onto the information medium; a driving means for moving the information medium closer or farther away; a first detection means for generating an output according to the distance between the condensing lens and the information medium; and the driving means according to the output of the first detection means. and a second detection means for detecting the amount of reflected light from the information medium, and the gain of the control circuit is varied according to the output of the second detection means. Features of optical information recording and reproducing device. 2. The optical information recording and reproducing apparatus according to claim 1, wherein a time constant for making the gain of the control circuit variable by the second detection means is larger than a time constant of the control circuit.