JPH0749414Y2 - Optical disc inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an optical disc inspection apparatus, and more specifically to an optical disc inspection apparatus capable of inspecting a disc in each process from a substrate to a finishing disc in an optical disc manufacturing process. Regarding

(Prior Art) FIG. 7 shows an example of a conventional optical disk inspecting apparatus (Japanese Patent Laid-Open No. 2000-242242)
59-148145). In the figure, 1 is a semiconductor laser, 2 is a collimator lens, 3 is a polarization beam splitter, 4 is a λ / 4 wavelength plate, 5 is an objective lens, 6 is an optical pickup for operating the objective lens 5 in the focus and tracking directions, and 7 is Optical disk for inspection, 8 is a condenser lens, 9 is a split mirror, 10 is a photodetector for focus control which is a photodetector of two splits, and 11 is a photodetector for tracking control which is a split photodetector. . In this optical disc inspection apparatus, the focus sum signal which is the sum output of the focus control photodetector and the tracking sum signal which is the sum output of the tracking control photodetector are added to obtain an RF signal. The output amplitude of the RF signal changes according to the amount of reflected light from the disc track.For example, if there is a foreign substance in the disc substrate, the amount of reflected light decreases. A waveform appears on the + side. this
The dropout was detected by comparing the RF signals with a dropout detection voltage that is constant above and below with a comparator.

Further, in Japanese Patent Laid-Open No. 61-273781, even if the defects of the optical disk are the same, the amplitude of the RF signal is different between the inner circumference and the outer circumference of the optical disk, so that the dropout cannot be detected correctly. In order to solve the above problem, there is described an optical disk inspection device capable of varying the dropout detection voltage in accordance with the RF signal amplitude.

(Problems to be solved by the device) However, in the configuration of the conventional device, the reflectance is different between the optical discs due to the characteristics of the recording film, so that even if the defects are the same, the defects are detected by the optical disc. It may or may not be detected, which may cause detection errors.Since the discs in each process from the substrate to the finishing disc in the optical disc manufacturing process differ greatly in reflectivity,
Since all of these defects cannot be detected, and the defect is detected by tracking the guide groove of the optical disk, the substrate without the groove cannot be inspected.

The present invention has been made in view of the above point, and provides an optical disc inspection apparatus capable of accurately measuring the size, position, and amount of a defect in an optical disc, investigating the cause of the defect, and reducing the occurrence of the defect. The purpose is to do.

(Means for Solving Problems) The present invention is an optical disc for irradiating an optical disc with laser light through an optical system, detecting the reflected light by an optical pickup, and inspecting the optical disc according to the level of a detection signal of the optical pickup. In the inspection device, the AGC circuit that automatically adjusts the level of the detection signal, the comparator that compares the output signal of the AGC circuit with a reference voltage, and whether or not there is a guide groove on the optical disk from the signal from the optical pickup. Guide groove presence / absence detecting means for detecting the presence of the guide groove, a rotation speed control circuit for controlling the feed mechanism of the optical pickup when the guide groove is not present, and a tracking control for controlling the optical pickup along the groove when the guide groove is present. An optical disc inspection apparatus comprising: a circuit.

(Operation) The guide groove presence / absence detecting means in the present invention determines whether or not the optical disc has a guide groove based on the tracking error signal, and outputs the guide groove presence / absence signal to the CPU. The CPU selects the means for tracing the disk accordingly. Thus, the disc can be inspected with or without the guide groove.

In addition, the AGC circuit for RF signals according to the present invention has the function of making the RF signals of defects of the same shape have the same amplitude regardless of the reflectance of the disc, so that the inspection of the optical disc is performed regardless of the reflectance. To be able to do.

(Embodiment of the Invention) Hereinafter, the present invention will be described with reference to the drawings showing an embodiment.

FIG. 1 is a circuit block diagram showing an embodiment of an optical disk inspection apparatus of the present invention. In FIG. 1, 12 is a sample disk, 13 is an optical pickup including an actuator that traces the guide groove of the disk 12 or the disk surface, and 14 is the optical pickup 13 moved in the inner and outer peripheral directions of the sample by a screw nut and a motor. Feeding mechanism, 15
Is a focus control circuit that outputs the focus control drive signal 15a to the actuator, 16 is a tracking control circuit that outputs the tracking control drive signal 16a to the actuator, 17 is the presence or absence of the guide groove based on the tracking error signal 16a from the tracking control circuit Then, a guide groove presence / absence detection circuit that outputs a guide groove presence / absence signal 17a, 18 is an RF signal 13a
Keeps the amplitude constant regardless of the reflectivity of the disc
An AGC circuit, 19 is a comparator for detecting a dropout from an RF signal, 20 is a switch for selecting a disc tracing means according to the presence or absence of a guide groove, 21 is an actuator of an optical pickup feed mechanism 14, the inner and outer circumferences of the disc. A rotation speed control circuit for applying a rotation speed control voltage 21a to a motor for sending in the direction, 22 is a photodetector for focus or tracking control, and 23 is a CPU.

The optical disc inspection apparatus of the present invention is an optical pickup 1
3, the conventional optical disc inspection device including the feed mechanism 14, the focus control circuit 15, the tracking control circuit 16, the comparator 19 and the like, and the guide groove presence / absence detection circuit 17 and
It has a configuration in which the AGC circuit 18 for RF signals is combined.

FIG. 2 is a diagram showing an example of the guide groove presence / absence detection circuit 17 according to the present invention. As shown in FIG. 2, a guide groove presence / absence detection circuit
Reference numeral 17 includes a peak hold circuit including a diode 24, a resistor 25, and a capacitor 26, a comparator 28 that sets a detection voltage with the resistors 27a and 27b, and a comparator circuit with a resistor 29.

FIG. 3 shows the waveform in the guide groove presence / absence detection circuit 17,
(A) shows the input waveform of the guide groove presence / absence detection circuit 17, and (b) shows the output waveform of the peak hold circuit. In the figure, 30a
Is a groove error, 31a is a tracking error waveform without a groove, 3
0b shows the output waveform of the peak hold circuit when there is a groove, and 31b shows the output waveform when there is no groove. The tracking control circuit 16 outputs a tracking error waveform 16a shown in FIG. 3 (a) depending on the presence or absence of the guide groove when the rotating disk is focused. The guide groove presence / absence detection circuit 17 detects the peak of the tracking error waveform 16a and compares it with the detection voltage 32 by the comparator 28. If the detection voltage is exceeded, the guide groove is present and "H".
Is output, and if it is not exceeded, “L” is output without a guide groove.

As the rotation speed control circuit 21, any one can be used as long as it can control the rotation speed of the motor that feeds the actuator in the inner and outer peripheral directions of the disk.

FIG. 4 is a drawing showing an example of the AGC circuit 18 for RF signals. As shown in FIG. 4, the AGC circuit 18 is a circuit for adding a focus control photodetector output (c) consisting of resistors 33a and 33b and a tracking control photodetector output (d), a low pass filter (LPF). Disk reflectivity detection circuit consisting of 34, current corresponding to the detected reflectivity is photocoupler 35
Constant current circuit consisting of resistors 36a and 36b, operational amplifier 37 and photocoupler 35, and capacitors 38a and 38b, resistors 39a, 39b, 39c and 39d, transistor 40, and resistance of photocoupler 35, which flow through the light emitting diode (LED) 35a of (Rx) 35b and AC amplifier.

FIG. 5 is an explanatory diagram of the AGC principle of the AGC circuit 18. As shown in FIG. 5, in the case of a disc with a low reflectance, the RF signal amplitude and the focus control photodetector output (c) and the tracking control photodetector output (d) are low, and
The current flowing through the LED 35a is reduced. And this LED35a
The resistance value Rx is increased and the gain of the AC amplifier is increased because the resistance value Rx is inversely proportional to the current flowing through the resistance value Rx. On the other hand, in the case of a disk having a high reflectance, the operation is reversed, and the gain of the AC amplifier is reduced. Therefore, if the defects have the same shape, the output of the AGC circuit has a constant amplitude even if the reflectances of the disks are different.

Next, the operation of the optical disk inspection apparatus of the present invention will be described.

Focus is applied while rotating the disk 12, and the presence or absence of the guide groove is determined by the CPU before starting tracking.
The presence or absence of the guide groove is determined based on an output signal (guide groove presence / absence signal 17a) obtained by inputting the tracking error signal 16a from the tracking control circuit 16 to the guide groove presence / absence detection circuit 17. The guide groove presence / absence signal 17a is input to the CPU 23, and the tracing means of the disk 12 is selected based on this signal, and then the inspection is started. The selection is made by the trace means selection switch 20. When the groove is present, the tracking is performed according to the usual method. When the groove is not present, the optical pickup 13 is controlled by the rotation speed control circuit 21 and the surface of the disc 12 is spirally traced.

When the guide groove is provided, the feed mechanism 14 is driven to perform tracking. That is, the tracking servo O
N command is issued, servo voltage is applied to the tracking coil of the actuator, and the tracking error signal 16a is sent to the motor that sends the actuator to the inner and outer circumferences of the disk.
Add the DC component of. At this time, the light beam traces all the guide grooves on the disk surface.

Further, when there is no guide groove, since tracking cannot be performed, the CPU 23 issues a tracking servo OFF command, and no voltage is applied to the tracking coil of the actuator. Then, a rotation speed control voltage is applied from the rotation speed control circuit 21 to the motor that sends the actuator in the inner and outer peripheral directions of the disk. At this time, the light beam spirally traces on the disk surface at a track pitch determined by the relationship between the disk rotation speed and the actuator feed speed.

FIG. 6 shows a waveform diagram of the RF signal (e) and the output (f) of the comparator 19. If the disk 12 has a defect, the amplitude of the RF signal (e) changes, for example, as shown in FIG.
The dropout can be detected by comparing the RF signal (e) with the dropout detection voltage (light amount increase or light amount decrease detection voltage) which is constant in the upper and lower directions by the comparator 19. However, if the reflectance of the disk 12 is different, the amplitude of the RF signal is also different. In the present invention, the RF signal (e) is sent to the AGC.
The RF signal (e) of the defect having the same shape is passed through the circuit 18 to have the same amplitude regardless of the reflectance of the disk 12. Then, by comparing the RF signal after the AGC process with the detection voltage by the comparator 19, it is possible to detect the dropout without omission regardless of the reflectance.

(Effect of the Invention) Since the optical disk inspection apparatus of the present invention is configured to remove the influence of reflectance regardless of the presence or absence of the guide groove of the sample as described above, the present invention provides: It is possible to inspect the disc in each process from the substrate to the finishing plate in the optical disc manufacturing process with a small error.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical disc inspection apparatus according to the present invention, FIG. 2 is a diagram showing an example of a guide groove presence / absence detection circuit according to the present invention, and FIG. In the input / output waveform, (a) is an input waveform and (b) is an output waveform. FIG. 4 is a drawing showing an example of an AGC circuit for RF signals according to the present invention, FIG. 5 is an explanatory view of the AGC principle of the AGC circuit, and FIG.
Waveform diagram of RF signal (e) and comparator output (f),
FIG. 7 shows a schematic view of an example of a conventional optical disk device. 17 ... Guide groove presence / absence detection circuit, 18 ... AGC circuit, (c) ... Focus control photodetector output, (d) ... Tracking control photodetector output.

Claims (1)

[Scope of utility model registration request] 1. An optical disc inspection apparatus for irradiating an optical disc with laser light through an optical system, detecting the reflected light by an optical pickup, and inspecting the optical disc according to the level of the detection signal of the optical pickup. AGC circuit for automatically adjusting the level, a comparator for comparing the output signal of the AGC circuit with a reference voltage, and a guide groove presence / absence detecting unit for detecting whether or not the optical disk has a guide groove based on a signal from the optical pickup. And a rotation speed control circuit for controlling the feed mechanism of the optical pickup when the guide groove is absent, and a tracking control circuit for controlling the optical pickup along the groove when the guide groove is present. Optical disc inspection device.