OPTICAL INFORMATION RECORDING/REPRODUCING APPARATUS

Abstract: In an optical information recording/reproducing apparatus for recording/reproducing information on or from an optical disc (1), a laser beam is focused on the surface of a substrate (12) of the optical disc so that the intensity or a high frequency component of a reflected laser beam is used to detect contaminants on the optical disc surface or a test signal containing a plurality of frequency components and recorded on a specified track on the optical disc is reproduced (4) and detected (8) so that the difference between amplitudes of the frequency components is used to detect contaminants on the optical disc surface. Scattering of the laser beam can be prevented and recording/reproducing can be effected with a proper level of laser power.

Description: BACKGROUND OF THE INVENTION This invention relates to optical information recording/reproducing apparatus for recording and reproducing information on and from an optical disc and more particularly to an optical information recording/reproducing apparatus which can afford to detect contaminants on an optical disc. Because of high convergency of laser beams and narrowness of the pitch between tracks, the optical information recording/reproducing apparatus adapted to record information on an optical disc can provide high recording density which is 10 or more times the recording density obtained with the magnetic disc apparatus. Especially, a write-once type optical disc and a magneto-optical disc are noticeable for the fact that information can be recorded and reproduced with these discs in contrast to a video disc and a compact disc which are dedicated to reproduction. Fig. 6 schematically shows a prior art optical information recording/reproducing apparatus. Referring to Fig. 6, information is recorded on an optical disc 1 which is rotated by a motor 2. An optical head 3 converges laser beams on the optical disc 1 for the purpose of recording a signal thereon and detecting a change in reflection of a laser beam to read the recorded information. A laser drive head amplifier circuit 4 is comprised of a laser drive unit for driving a laser included in the optical head 3 and a head amplifier for detecting a focus error signal 100, a tracking error signal 101 and a reproduction signal 102. A focus control circuit 5 generates a focus drive signal 106 which drives an actuator of the optical head so that a laser beam can be focused on a guide track on the optical disc 1. A tracking control circuit 6 drives the actuator of the optical head with a tracking drive signal 107 so that the laser beam can follow the guide track on the optical disc 1. A data modem circuit 7 digitally modulates an input data signal 103 and demodulates the reproduction signal 102 to deliver an output data signal 105. A control microcomputer 8 (CPU) performs system control for the apparatus. The microcomputer 8 issues a focus command signal 108 to the focus control circuit 5, a tracking command signal 109 to the tracking control circuit 6 and a command signal 110 to the data modem circuit 7. In the prior art optical information recording/reproducing apparatus constructed as above, laser beams emitted from the optical head 3 are converged on a guide track on the optical disc 1 rotating at a constant speed and a laser beam is caused to follow the track. The focus error signal 100 and the tracking error signal 101 which are detected by the optical head 3 are respectively applied to the focus control circuit 5 and the tracking control circuit 6, whereby the actuator of the optical head 3 is driven for focus/tracking controlling to permit the optical head 3 to irradiate laser beams which are focused on a guide track. For recording data, the input data signal 103 is modulated by the data modem circuit 7 and laser beams of the intensity suited for recording are modulated with a modulation data signal 104 so as to be irradiated on the optical disc 1. For reproducing data, laser beams of a low level insufficient for recording are irradiated on the optical disc 1 and a resulting reproduction signal 102 is demodulated by the data modem circuit 7 to produce an output data signal 105. Typically, reproduction power has a level of about 1 mW and recording power has a level of 5 to 10 mW. With the above construction, however, when the optical disc 1, which is typically rotated at a high speed of about 1800 rpm, is left to rotate for a long period of time during a continuous operation, dusts in the air are deposited onto the surface of the optical disc 1 because the optical disc 1 having a substrate made of an electrically insulating material such as resin or glass is electrified. The laser beams are partly absorbed and scattered by the deposited dusts and power of the laser beams is considerably attenuated by several of tens of percents. Consequently, when recording a signal on a recording layer of a photosensitive material which is vapor-deposited on a guide track, the requisite level of recording laser power, exemplarily 5 to 10 mW, becomes considerably deficient amounting to 3 to 6 mW, thus preventing excellent recording of the signal. In other words, since recording is not effected with an optimum level of recording power and so record of pits are not saturated, there result problems that the recording pits are degraded under the influence of a change in environment to decrease their life and that the amplitude of the reproduction signal is decreased, thus aggravating the bit error rate. SUMMARY OF THE INVENTION In view of the above, it is an object of this invention to provide an optical information recording/reproducing apparatus capable of detecting contaminants on the optical disc which make laser power deficient and prevent excellent recording and reproducing. According to an aspect of the invention, there is provided an optical information recording/reproducing apparatus comprising optical means for converging laser beams from a laser light source on an optical disc comprising a substrate and a recording layer of guide tracks included in the optical disc; first focus control means for focusing a laser beam on a guide track of said optical disc; second focus control means for focusing the laser beam on a surface of a substrate of said optical disc, said surface being an exterior surface subjected to contamination; and reflected beam intensity detection means for detecting intensity of reflection of the laser beam when focused on said surface of said optical disc substrate, said reflected beam detection means producing an output signal having a level which is representative of detection of contaminants on said surface of said optical disc. According to another aspect of the invention, there is provided an optical information recording/reproducing apparatus comprising optical means for converging laser beams from a laser light source on an optical disc comprising a substrate and a recording layer of guide tracks included in the optical disc; first focus control means for focusing a laser beam on a guide track of said optical disc; second focus control means for focusing the laser beam on a surface of a substrate of said optical disc, said surface being an exterior surface subjected to contamination; and high frequency component detection means for detecting a high frequency component in excess of a reference value from reflection of the laser beam when focused on the surface of said optical disc substrate, said high frequency component detection means producing an output signal having a level which is representative of detection of contaminants on the surface of said optical disc. Thus, in accordance with the teachings of the present invention, contaminants on the surface of the optical disc can be detected and recording of a signal on the optical disc can be inhibited when contaminants exceeding, in amount, a reference level are detected. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram illustrating an optical information recording/reproducing apparatus according to a first embodiment of the invention. Figure 2 illustrates intensity distributions of reflected beams from the surface of an optical disc substrate used in the first embodiment. Figure 3 is a schematic block diagram illustrating an optical information recording/reproducing apparatus according to a second embodiment of the invention. Figure 4 illustrates at sections (A) and (B) waveforms of reflected beams from the surface of an optical disc substrate used in the second embodiment. Figure 5 is a schematic block diagram illustrating a high frequency component detection circuit. Figure 6 is a schematic block diagram illustrating a prior art optical information recording/reproducing apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the invention will first be described. An optical information recording/reproducing apparatus according to the first embodiment of the invention is schematically illustrated in Fig. 1 in which components 1 to 4 and 6 to 8 and signals 100 to 107 and 109 to 110 are identical to the corresponding components and signals in Fig. 6. A first focus control circuit 9 focuses a laser beam converged by the optical head 3 on a recording layer of a guide track on the optical disc 1, a second focus control circuit 10 focuses the laser beam on a surface of the substrate of the optical disc 1, and a reflected beam intensity detection circuit 11 detects intensity of reflection of the laser beam which is focused on the surface of the substrate of the optical disc 1. The optical information recording/reproducing apparatus of this embodiment constructed as above operates as will be described below. When the optical disc 1 is mounted on the motor 2, the microcomputer 8 sends a command signal 111 to the second focus control circuit 10 and a focus drive signal 112 delivered out of the control circuit 10 causes the laser beam to be focused on the surface of the optical disc substrate. A laser beam irradiated on the substrate surface of the optical disc 1 is reflected at that surface and returned to the optical head 3. A signal representative of a reflected laser beam is amplified by the laser drive head amplifier circuit 4 and applied, as a reflection signal 113, to the reflected beam intensity detection circuit 11. Magnitude of the reflection signal 113 is compared with a reference voltage at the reflected beam intensity detection circuit 11. When the surface of the substrate of the optical disc 1 is contaminated, the laser beam irradiated on the substrate surface is partly absorbed and scattered by contaminants and the quantity of reflected beam is decreased to render a contaminant detection signal 114 enabled. The thus enabled contaminant detection signal 114 is read by the microcomputer 8. When detecting an enabled state, the microcomputer 8 inhibits recording of the modulation data signal 104 on the optical disc and informs the host of an error signal 115 to this effect. Contrarily, when a contaminant detection signal 114 is rendered disabled, the microcomputer 8 turns off the command signal 111 to the second focus control circuit 10 in order to execute recording of subsequent data and thereafter issues a command signal 116 which activates the first focus control circuit 9. This control circuit 9 focuses the laser beam on a recording layer of a guide track on the optical disc 1 to ensure that data can be recorded on or reproduced from the optical disc 1. The data recording/reproducing is carried out in the manner as detailed in connection with Fig. 11 and will not be described herein. Intensity distributions of reflected beams in accordance with the presence or absence of contaminants on the surface of the substrate of the optical disc 1 are illustrated in Fig. 2 in which the substrate and the recording layer included in the optical disc 1 are designated by 12 and 13, respectively. In Fig. 2, an intensity distribution A is for the absence of contaminants on the substrate of the optical disc 1 and an intensity distribution B is for the presence of contaminants on the substrate. The distribution B indicates that the reflected beam is decreased in peak value and the deflection direction is broadened. Since the laser beam is focused on the substrate surface which is liable to be contaminated, the intensity of the reflected beam greatly differs in accordance with the presence or absence of contaminants and the reflected beam intensity in the case of the presence of contaminants can accurately be discriminated from the reflected beam intensity in the case of the absence of contaminants. When the laser beam is focused on a guide track by operating the first focus control circuit 9, this laser beam is out of focus and has a somewhat large spot area on the substrate surface and a resulting reflection amount of beam reflected from the substrate surface less differs in quantity in accordance with the presence or absence of contaminants on the substrate surface, having less margin of discrimination and less reliability. As described above, the present embodiment comprises the second focus control circuit 10 for focusing the laser beam on the surface of the optical disc substrate and the reflected beam intensity detection circuit 11 for detecting intensity of the reflected beam from the substrate surface, whereby when the optical disc having a so-called dielectric substrate made of an electrically insulating material, for example, either resin such as polycarbonate and PMMA or glass rotates at a high speed so as to be electrified owing to friction between air and the substrate surface and the thus created electric charge attracts dusts floating in the air to form contaminants on the substrate surface, the contaminants can be detected to prevent the occurrence of trouble due to a deficient level of recording laser power. In consideration of the fact that the substrate is electrified by friction between air and the substrate and dusts are deposited in greater amounts on an outer circumferential portion of the disc, which rotates at a higher peripheral speed, than on the other portion, the detection of the quantity of reflected beam from the substrate surface may preferably be effected at the outer circumferential portion of the disc. A second embodiment of the invention will now be described. While in the first embodiment the magnitude of the reflection signal is monitored to detect contaminants on the substrate surface, a high frequency component of the reflection signal is monitored and an increase in the high frequency component representative of the presence of contaminants is detected in the present embodiment. An optical information recording/reproducing apparatus according to the second embodiment is schematically illustrated in Fig. 3. In Fig. 3, components 1 to 4 and 6 to 10 and signals 100 to 107 and 109 to 116 are identical to the corresponding components and signals in Fig. 1, and reference numeral 14 designates a high frequency component detection circuit which detects a high frequency component of reflection of the laser beam which is focused on the surface of the substrate of the optical disc 1. The optical information recording/reproducing apparatus of this embodiment constructed as above operates as will be described below. When the optical disc 1 is mounted on the motor 2, the microcomputer 8 sends a command signal 111 to the second focus control circuit 10 and a focus drive signal 112 from the control circuit 10 causes the laser beam by the optical head 3 to be focused on the surface of the substrate of the optical disc 1. A laser beam irradiated on the substrate surface of the optical disc 1 is reflected at that surface and returned to the optical head 3. A signal representative of a reflected laser beam is amplified by the laser drive head amplifier circuit 4 and applied, as a reflection signal 113, to the high frequency component detection circuit 14 in which a high frequency component of the reflection signal 113 is extracted and amplitude of the extracted high frequency component is compared with a reference voltage. When the surface of the optical disc substrate is contaminated with, for example, fine dusts, the reflected beam of the laser beam which is irradiated on the substrate surface contains a high frequency component. With the high frequency component being in excess of the reference value, a contaminant detection signal 114 is rendered enabled and read by the microcomputer 8. When detecting an enabled state, the microcomputer 8 inhibits recording of the modulation data signal 104 on the optical disc and informs the host of an error signal 115 to this effect. Contrarily, when a contaminant detection signal 114 is rendered disabled, the microcomputer 8 turns off the command signal 111 to the second focus control circuit 10 in order to execute recording of subsequent data and thereafter issues a command signal 116 which activates the first focus control circuit 9. This control circuit 9 focuses the laser beam on a recording layer of a guide track on the optical disc 1 to ensure that data can be recorded on or reproduced from the optical disc 1. The data recording/reproducing is carried out in the manner as detailed in connection with Fig. 6 and will not be described herein. When the laser beam is focused on the substrate surface of the optical disc 1 by means of the second focus control circuit, the reflection signal takes a waveform as shown at section (A) in Fig. 4 in the case of the absence of contaminants on the substrate surface of the optical disc 1 and a waveform as shown at section (B) in Fig. 4 in the case of the presence of contaminants on the substrate surface. In the waveform at (A), substantially no high frequency component exists but in the waveform at (B), an increased high frequency component exists which results from scattering of the reflected beam by contaminants such as fine dusts on the substrate surface. Since the laser beam is focused on the contaminated substrate surface, the amplitude of the waveform at (B) is as sufficiently large as several times the amplitude of the waveform at (A) and the former can accurately be discriminated from the latter. When the laser beam is focused on a guide track by operating the first focus control circuit 9, this laser beam is out of focus on the substrate surface and reflection of a resulting large laser beam spot at the substrate surface less differs in quantity in accordance with contaminants on the substrate surface, having less margin of discrimination and less reliability. Exemplarily, the high frequency component detection circuit 14 of Fig. 3 may be constructed as shown in Fig. 5. Only a high frequency component is extracted by a high-pass filter 15 from a reflection signal 113 representative of a reflected beam of the laser beam which is focused on the surface of the substrate of the optical disc 1 and its amplitude is compared at a comparator 16 with positive and negative reference voltages 116 and 117. An output signal of the comparator 16 is counted by a counter circuit 17. Thus, when the number of peaks of the high frequency component in excess of the positive and negative reference voltages exceeds a predetermined value, the contaminant detection signal 114 is rendered enabled. The counter circuit may be replaced with a timer circuit. In this case, the detection of contaminants is decided by totalling intervals of time during which the reference voltages are exceeded. As described above, the second embodiment comprises the focus control circuit 10 for focusing the laser beam on the surface of the optical disc substrate and the high frequency component detection circuit 14 for detecting a high frequency component of a reflected beam from the substrate surface, whereby contaminants deposited on the optical disc can be detected to prevent the occurrence of trouble due to a deficient level of recording laser power. Considering that the substrate is electrified by friction between air and the substrate and dusts are deposited in greater amounts on an outer circumferential portion of the disc, which rotates at a higher peripheral speed, than on the other portion, the detection of the quantity of reflected beam from the substrate surface may preferably be effected at the outer circumferential portion of the disc. As described above, according to the invention, since contaminants deposited on the surface of the substrate of the optical disc can be detected, a failure, caused by scattering of the laser beam, to record/reproduce information with a proper level of laser power can be prevented and significantly practical effects can be attained.

Claims: An optical information recording/reproducing apparatus comprising: optical means (3) for converging laser beams from a laser light source on an optical disc (1) comprising a substrate (12) and a recording layer (13) of guide tracks included in the optical disc (1); first focus control means (9) for focusing a laser beam on a guide track of said optical disc; second focus control means (10) for focusing the laser beam on a surface of said substrate (12) of said optical disc, said surface being an exterior surface subjected to contamination; reflected beam intensity detection means (11) for detecting intensity of reflection of the laser beam when focused on said surface of said optical disc substrate, said reflected beam detection means producing an output signal having a level which is representative of detection of contaminants on said surface of said optical disc. An optical information recording/reproducing apparatus according to Claim 1, wherein said second focus control means (10) is activated each time said optical disc is exchanged. An optical information recording/reproducing apparatus according to Claim 1 or 2, wherein said second focus control means (10) is activated in interlocked relationship with the outermost circumferential portion of said optical disc. An optical information recording/reproducing apparatus according to anyone of Claims 1 to 3, wherein said reflected beam intensity detection means inhibits recording on said optical disc by the output signal level lower than reference signal level. An optical information recording/reproducing apparatus comprising: optical means (3) for converging laser beams from a laser light source on an optical disc (1) comprising a substrate (12) and a recording layer (13) of guide tracks included in the optical disc (1); first focus control means (9) for focusing a laser beam on a guide track of said optical disc; second focus control means (10) for focusing the laser beam on a surface of a substrate (12) of said optical disc, said surface being an exterior surface subjected to contamination; high frequency component detection means (14) for detecting a high frequency component in excess of a reference value from reflection of the laser beam when focused on the surface of said optical disc substrate, said high frequency component detection means producing an output signal having a level which is representative of detection of contaminants on the surface of said optical disc. An optical information recording/reproducing apparatus according to Claim 5, wherein said second focus control means (10) is activated each time said optical disc is exchanged. An optical information recording/reproducing apparatus according to Claim 5 or 6, wherein said second focus control means (10) is activated in interlocked relationship with the outermost circumferential portion of said optical disc. An optical information recording/reproducing apparatus according to anyone of claims 5 to 7, wherein said high frequency component detection means (14) inhibits recording on said optical disc when it detects a high frequency component in excess of a predetermined reference value (116,117).

Inventors: ICHINOSE, MAKOTO, KUROKI, YUZURU, MURAI, KATSUMI, SATOH, ISAO
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1987
Main classification: G11B7
IPC codes: G11B19, G11B7