JPS605440A - Optical disk checking device - Google Patents

Abstract

PURPOSE:To check accurately the dropout of an optical disk having different reflection factors by setting the average quantity of reflected light given from the optical disk at a fixed level. CONSTITUTION:The output of a photodetector 13 is transmitted through an LPF16 and compared with the reference voltage of a reference voltage generating circuit 17 through a comparator 18. Then this differential voltage is supplied to a laser light source driving circuit 19 to vary the quantity of the laser sent from a laser light source 1. Thus the average quantity of reflected light given from an optical disk 7 having different reflection factors is set at a fixed level. Therefore it is possible to check the dropout of the disk 7 under the same conditions. Thus the dropout output can be checked accurately especially for a master disk having different reflection factors, a stamper disk, a replica disk and a completed disk after vapor deposition of a recording material respectively in their manufacturing processes.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disk inspection apparatus for inspecting dropouts due to dust, defects, etc. on optical disks such as video disks.

Conventional Structures and Problems In optical discs, dropouts due to adhesion of dust or defects during the manufacturing process affect the quality of the optical disc, so dropout inspection is important. The manufacturing process of an optical disk consists of four steps as shown in FIG. The first step is to create a master disc for an optical disc, in which a photoresist is coated on an ordinary glass disc, and a high-temperature (
A laser beam is irradiated to form information tracks or grooves for track addresses. The second step is a standby step, in which a standby disk is formed on the master by electroforming nickel or the like. The third process is the replica process.
Information tracks are copied from the stamper disk using ultraviolet curing resin or injection molding to create a large number of replica disks. The fourth step is a vapor deposition step, in which a recording material is vapor-deposited on the replica disk in the case of a recording optical disk, and aluminum is vapor-deposited in the case of a read-only optical disk. An optical disc is completed after going through the above four steps, but each of the steps results in the adhesion of dust and defects, resulting in dropouts of the optical disc.

A conventional optical disk inspection apparatus for inspecting dropouts will be described below.

FIG. 2 shows a schematic diagram of an example of a conventional optical disk inspection apparatus, in which numeral 1 denotes a laser light source which is composed of a semiconductor laser and emits a constant amount of laser light. A collimator lens 2 converts the laser beam from the laser light source 1 into parallel light. 3 is a polarizing beam splitter, and 4 is a λ/4 wavelength plate. 5 is an objective lens, 6 is an optical pickup that operates the objective lens 6 in the focusing and tracking directions, and splits reflected light from a known driving means such as a voice coil motor. 9 is a condensing lens, and 10 is a dividing mirror. Reference numeral 11 denotes a focus control photodetector, which is composed of two divided photodetectors, and obtains a focus error signal from the differential output of each photodetector. 12 is a photodetector for trunking control;
A tracking error signal is obtained with this configuration. A photodetector 13 receives reflected light from the disk 7. A dropout comparator circuit 14 compares the signal from the photodetector 13 with a dropout reference voltage to detect dropout. A dropout counter circuit 15 counters the signal from the dropout comparator circuit 14 and displays the number of dropouts. Note that the arrow drawn in the optical system section in the figure indicates the optical path of the laser beam.

The operation of the conventional optical disk inspection apparatus configured as described above will be described below.

The laser light emitted from the laser light source 1 passes through the collimator lens 2 and becomes a parallel beam, which is polarized by the polarizing beam sinter 3, λ/
The light is focused through a four-wavelength plate 4 onto an information track formed on a disk 7 by an objective lens 6. At this time, since the information track of the disk 7 is rotating with surface runout and eccentricity, in order to focus the laser beam on a predetermined information track, driving is performed based on a focus error signal and a tracking error signal, which will be described later. A voltage is applied to the optical pickup 6 to operate the objective lens 5 in the focusing and tracking directions, thereby causing the laser beam to follow a predetermined track. The reflected light from the disk 7 follows the incident optical path and the reverse optical path, passes through the λ/4 wavelength plate 4 twice, and becomes light that is 900 polarized with the incident light, and is transmitted to the polarizing beam splitter 3.
The 0-reflected light that travels straight ahead and enters the half mirror 8 is split into two directions by the Heifumi 5-8, one of which enters the condenser lens 9 and the other that enters the photodetector 13. The reflected light exiting the condensing lens 9 is divided by a splitting mirror 10, and one part is focused on a focus control photodetector 11, and the other part is focused on a tracking control photodetector 12. The focus control photodetector 11 and the tracking control photodetector 12 are composed of two divided photodetectors, and generate a focus error signal and a tracking error signal by obtaining a differential output from each photodetector. Put it out. Focus control and tracking direction are performed by feeding back these error signals to the drive circuit (not shown) of the optical pickup 6 described above.On the other hand, the photodetector 13 is composed of one photodetector, and An output proportional to the amount of light reflected from the information trunk 7 can be obtained.For example, if dust adheres to the information track of the disk 7, the amount of reflected light at that part will decrease, and the photodetector 13 will detect this as a change in the amount of light. Ru.

The output from the photodetector 13 is input to a dropout comparator circuit 14 and compared with a dropout reference voltage to detect dropouts, and then a dropout counter circuit 15 counts and displays the number of dropouts.

However, in the above configuration, since the amount of laser light emitted from the laser light source 1 is constant and the dropout reference voltage of the dropout comparator circuit 14 is constant, unless the optical discs have the same reflectance, the average Since the amount of reflected light is different, the output voltage of the photodetector 13 is also different due to dust, defects, etc., and the dropout count is also changed, making it impossible to perform a correct inspection. especially,
As mentioned above, the causes of dropouts on optical discs are due to the adhesion of dust and defects in the four processes of master, stamper, replica, and vapor deposition, and if we can accurately understand how dropouts occur in each process, Process improvements can be easily made, but in general, the reflectance of discs that fail in the four processes differs, making it impossible to perform correct dropout inspection with conventional optical disc inspection equipment, making it difficult to make accurate process improvements. The problem was that there was no.

Purpose of the Invention The present invention solves the above-mentioned problems of the conventional technology, and enables accurate inspection of disc dross and knob-out in each process of master discs with different reflectances, blanking, replicas, and vapor deposition using a single device. The purpose is to provide an optical disk inspection device.

Structure of the Invention The present invention is an optical disk inspection device having an information tranometer light amount control means formed on an optical disk, and by keeping the average amount of reflected light from the optical disk constant, dropout of optical disks with different reflectances can be accurately detected. It is something that can be inspected.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows a schematic diagram of an optical disk inspection apparatus according to a first embodiment of the present invention. Note that in FIG. 3, parts with the same numbers as in FIG. 2 indicate the same parts as in the conventional configuration, and a description thereof will be omitted. In FIG. 3, reference numeral 16 denotes a low-frequency filter circuit that extracts low frequency components of the output from the photodetector 13.

Reference numeral 17 denotes a reference voltage generation circuit, which sets the reference voltage to the average output voltage of the photodetector obtained by an optical disc having a reference reflectance. 18 is a comparison circuit, and low-pass filter circuit 1
6 and the voltage of the reference voltage generating circuit 17, and outputs the difference voltage.

Reference numeral 19 denotes a laser light source drive circuit that controls the drive current to the laser light source 1 based on the voltage from the comparison circuit 18 to vary the amount of laser light emitted from the laser light source 1.

The operation of the optical disk inspection apparatus of this embodiment configured as described above will be explained below.

Consider a case where the optical disc 7 is loaded with an optical disc having a reflectance different from the reference reflectance. Since the amount of laser light corresponding to the reflectance of the standard is normally emitted from the laser light source, the amount of reflected light from the disc 7 is different from that of the standard optical disc and is incident on the photodetector 13. The output of the photodetector 13 is distributed to a dropout converter circuit 14 and a low-nox filter circuit 16. However, at this point, the dropout comparator circuit 14 is not operated. The output of the photodetector 13 is sent to the low-pass filter circuit 1
6, so-called dropout components such as dust and defects, and high frequency components such as address signals in the information trunk are removed, and the voltage of the average reflected light amount of the information trunk of the optical disk 7 is output. This voltage is compared with the reference voltage from the reference voltage generation circuit 17 in the comparison circuit 18, and the difference voltage is outputted and inputted to the laser light source drive circuit 19. The laser light source drive circuit 19 superimposes a control drive current proportional to the output voltage from the comparator circuit 18 on the drive current supplied to the laser light source 1, thereby varying the amount of laser light emitted from the laser light source 1. The laser light amount control means described above is configured by a closed loop control system, and the above operation is repeated until the difference output of the comparator circuit 18 becomes 0, and the photodetector 13 detects the difference in the reflectance of the optical disk 7. A constant average amount of reflected light can be obtained regardless of the amount of light reflected. At this point in time, dropout can be detected by detecting, for example, the differential output of the comparison circuit 18 and operating the dropout comparator circuit 14.

As described above, according to this embodiment, the output of the photodetector 13 is passed through the low-pass filter circuit 16 to the reference voltage generation circuit 1.
The comparison circuit 18 compares the voltage with the reference voltage of 7 and inputs the difference voltage to the laser light source drive circuit 19 to drive the laser light source 1.
By varying the amount of laser light emitted from the optical disc 7, the average amount of reflected light from the optical discs 7 with different reflectances can be made constant. It is possible to accurately inspect the appearance of dropouts in master disks, stamper disks, replica disks, and finished disks with different reflectances during the disk manufacturing process, as well as finished disks after recording material deposition.

Although the photodetector 13 was provided separately in the above embodiment,
This may also be used as the focus control photodetector 11 or the tracking control photodetector 12. in this case,
The sum signal of the two divided photodetectors, the focus control photodetector 11 and the tracking control photodetector 12, is used instead.

Effects of the Invention The optical disk inspection apparatus of the present invention has a laser light amount control means for controlling the amount of laser light emitted from the laser light source so that the average amount of reflected light from the information tracks formed on the optical disk is constant. Since the dropouts of optical disks with different reflectances can be inspected under the same conditions, it is especially possible to check the dropouts of master disks, stamper disks, replica disks, and finished disks with different reflectances in the optical disk manufacturing process, as well as finished disks after recording material deposition. Since the inspection can be performed using a standard optical disk inspection device, accurate inspection can be performed without variations in the appearance of dropouts due to differences in optical systems, etc., and it is easy to understand the causes of dropouts in the optical disk manufacturing process. The practical effects are great.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the manufacturing process of optical discs, Figure 2
The figure is a schematic diagram of a conventional optical disk inspection device.
The figure is a schematic diagram of an optical disk inspection apparatus according to an embodiment of the present invention. 1... Laser light source, 2... Correlator lens, 3... Polarizing beam splitter, 4...
...λ/4 wavelength plate, 5...Objective lens, 6...
...optical pickup, finished...optical tisf,
8...Half mirror 19...Condenser lens, 10...Division mirror, 11...Photodetector for focus control, 12...Tracking control 13...Photodetector, 14...Dropout comparator circuit, 15...Dropout counter circuit, 16...Low pass filter circuit, 17... ...Reference voltage generation circuit, 18...
... Comparison circuit, 19 ... Laser light source drive circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3/7

Claims (3)

[Claims] (1) Laser light emitted from a laser light source is irradiated via an optical system onto an information track formed on an optical disk, and the reflected light from this information track is received by a photodetector to remove dust and debris from the information track. An optical disk inspection apparatus configured to inspect defects, etc., and provided with a laser light amount control means for controlling the amount of laser light so that the average amount of reflected light from the information track is constant. (2) The laser light amount control means includes a low-pass filter circuit that extracts low frequency components from the photodetector, a reference voltage generation circuit, and a comparison circuit that compares the voltage from the low-pass filter circuit with the voltage from the reference voltage generation circuit. and a laser light source drive circuit that varies the amount of laser light from the laser light source in accordance with the voltage from the comparison circuit. (3) Claim 1, wherein the photodetector doubles as at least one of a focus control photodetector and a tracking control photodetector for controlling laser light onto an information track on an optical disk. Or the optical disk inspection device according to item 2.