JPS6071903A - Device for inspecting optical disc - Google Patents

Abstract

PURPOSE:To obtain an exact value with simple constitution by providing a photodetector which measures the extent of the movement of the diffracted light of the same + or - order from the information track of an optical disc and measuring the plane run-out and warpage angle of the optical disc from the sum signal and difference signal of photodetectors. CONSTITUTION:The laser light emitted from a laser light source 16 is made incident via a mirror 17 on a disc 14 and is divided to the light reflected on the surface thereof and the light transmitted through the surface of the disc and reflected by an information track 14a. The light reflected from the surface of the disc 14 is reflected along the axis of the incident light. The light reflected from the track 14a is eventually diffracted in the radial direction of the disc 14. The diffracted light of the same + or - order are made incident on photodetectors 18, 19. The light reflected from the surface of the disc 14 is not made incident on the photodetectors 18, 19. The outputs from the photodetectors 18, 19 are inputted to a sum outputting circuit 20 by which the rate of the plane run-out is measured in the output stage. The warpage angle is measured in the output stage of a difference outputting circuit 21.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disk inspection device for measuring the amount of surface runout and warpage of optical disks used for video disks and the like.

Conventional Structure and Problems In an optical disk, if the amount of surface runout or warpage is large, the servo 2 page followability of the optical pickup of the optical disk device will be poor and recording and reproduction will not be possible. Therefore, it is necessary to inspect the amount of surface runout and warpage of the optical disk.

A conventional optical disk inspection apparatus will be explained below.

FIG. 1 shows a schematic configuration diagram of an example of a conventional optical disk inspection apparatus. Reference numeral 1 denotes an optical disk, and concentric or spiral information tracks 1a having the same pitch interval are formed in the radial direction. 2 is a disk motor that rotates the optical disk.

3 is a laser light source that generates a laser beam that generates a coherent light beam. A collimator lens 4 converts the laser beam from the laser light source 3 into parallel light. 6 is a polarizing beam splitter, and 6 is a λ/4 wavelength plate. Reference numeral 7 uses an aperture lens to focus the laser light into a minute spot and irradiate it onto the information track 1a of the optical disc 1. 8 is an optical pickup, and a lens holder 8a houses an aperture lens 7.
, a detection plate 8b fixed to the end of the lens holder 8a, and a driving means 8C including a voice coil or the like that drives the lens holder 8a in the focus direction (plane vibration direction). 9 is a convex lens that narrows down the reflected light from the disk 1, and 1o is a cylindrical lens that causes astigmatism. Reference numeral 11 denotes a four-divided photodetector arranged near the focal point of the cylindrical lens 10, which obtains a focus control signal. 12 is a non-contact displacement meter that detects the movement of the lens holder 8d. Reference numeral 13 denotes an optical transfer table on which the optical components 3 to 13 described above are mounted, and is configured to be movable in the radial direction of the disk by a linear motor (not shown).

Regarding the optical disk inspection device configured as above,
The operation will be explained below.

A laser beam emitted from a laser light source 3 passes through a collimator lens 4 to become parallel light, and then passes through a polarizing beam splitter 6 and a λ/4 wavelength plate 6, and is irradiated onto the information track 1a of the disk 1 by an aperture lens 7. The reflected light from the information track 1a of the disk 1 travels in the same direction as the incident light, but by passing through the λ/4 wavelength plate twice, it becomes a laser beam with a plane of polarization different from that of the incident light. Therefore, the reflected light goes straight through the polarizing beam splitter 6, and then passes through the convex lens 9.
, passes through the cylindrical lens 10, and is irradiated onto the photodetector with a beam having astigmatism.

At this time, the optical diameter of the light beam irradiated onto the photodetector 11 varies depending on the surface wobbling of the optical disc 1, and a focus error signal is generated on the photodetector 11. A drive current is applied to the drive means 8C of the optical pickup 8 according to the focus error signal, and the lens holder 88 housing the aperture lens 7 is operated to follow the surface wobbling of the optical disc 1 to perform focus control. A non-contact displacement meter 12 detects the movement of a detection plate 8b fixed to a lens holder 8a that follows the surface wobbling of the optical disk 1, and the surface wobbling of the optical disk 10 is measured. In addition, the optical transfer table 13 is moved by a linear motor.
The deflection angle in the radial direction of the optical disc 1 is measured by moving the optical disc 1 in the radial direction to measure the surface runout between two points, and by dividing the difference in the average amount of each surface runout by the distance between the two points. .

However, with the above configuration, the device is complicated6,-
It is expensive and has little practicality. Furthermore, since the warpage angle is calculated by dividing the difference between the average values of surface runout by the distance between two points, there is a drawback that it is difficult to determine an accurate warp angle.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks, and an object of the present invention is to provide an optical disk inspection device that can accurately measure the surface runout and warpage angle of an optical disk with a simple configuration.

Structure of the Invention The present invention is an optical disk inspection device equipped with a photodetector that measures the amount of movement of ten-homogeneous order diffraction light from an information track of an optical disk, and detects the surface runout of the optical disk using the sum signal and difference signal of the photodetector. It can measure the sled angle.

DESCRIPTION OF THE EMBODIMENT FIG. 2 shows a schematic diagram of an optical disk inspection apparatus in an embodiment of the present invention. In FIG. 2, reference numeral 14 denotes an optical disk, on which concentric or spiral information troughs 6 and 14a are formed with the same pitch in the radial direction. 16 is a disk motor that rotates the optical disk 14. Reference numeral 16 denotes a laser light source that generates a coherent light beam, and is composed of a laser with a narrow divergence angle, such as a He-Ne laser. Reference numeral 17 denotes a mirror configured so that the laser beam is perpendicularly incident on the optical disk without surface wobbling. 18.19 is optical disc 1
The first and second photodetectors receive the diffracted light from the information track 14a of No. 4, and are located at the same distance from the optical disk without surface wobbling and on the diffraction optical axis of the optical disc. It is made up of sensors that can detect the amount of movement, such as a linear image sensor. It is also assumed that the photodetectors 18 and 19 output positive outputs in the A and B directions as shown in FIG. 20 is an addition output circuit that adds the detection signals from the photodetectors 18 and 19, and 21 is a differential output circuit that obtains differential outputs of the detection signals from the photodetectors 18 and 19. FIG. 3 is an explanatory diagram of the operation of the optical disk inspection apparatus in the embodiment of the present invention. 14a is the information track surface (
(hereinafter referred to as the measurement surface). 14b is the information track surface of the disc without surface runout 7 (hereinafter referred to as the reference surface)
It is. 14c is a surface obtained by moving the measurement surface 14a in parallel to the reference surface 14b. It is assumed that the angle between the measurement surface 14a and the reference surface 14b (hereinafter referred to as the warp angle) is θ, and the distance between the measurement surface 14a and the reference surface 14b is t (hereinafter referred to as the amount of surface runout). 2
The incident optical axis of the 2-digit laser beam, 23.24 is the reference plane 14b
This is the diffracted light of the same order from . At this time, the output of the photodetector 18°19 is o(V). 25 and 26 are diffracted lights from the surface 14c, and 27 and 28 are diffracted lights from the measurement surface 14a.

The operation of the optical disk inspection apparatus of this embodiment constructed as described above will be explained below with reference to FIGS. 2 and 3.

The laser light emitted from the laser light source 16 passes through the mirror 17
The light enters the disk 14 through the . The laser beam is divided into light that is reflected on the surface of the optical disk 14 and light that is transmitted through the surface and reflected on the information track 14a. optical disc 14
The reflected light from the surface of is reflected along the incident optical axis. The reflected light from the information track 14a is diffracted in the radial direction of the optical disc 14, since the information track 14a has a concave structure with equal intervals in the radial direction, so it functions in the same way as a single diffraction grating. . The diffracted light of the fourteen beams is incident on photodetectors 18 and 19. Further, the reflected light from the surface of the optical disk 14 does not enter the photodetectors 18 and 19. The principle of measuring the surface runout and warpage angle of a disk will be explained using FIG. The diffracted lights 27 and 28 from the measurement surface 14a are equivalent to the diffracted lights 25 and 26 from the measurement surface 14c that are translated by the distance. Diffracted light from surface 14C 25°2
6 has a bending angle of θ with respect to the reference surface 14b, so it has an angle of 2θ with respect to the diffracted light 23.24 of the reference surface. Since the photodetectors 18 and 19 are equidistant, ,
The output of the photodetector 18 for the diffracted light 25 is +X (V),
The output of the photodetector 19 for the diffracted light 26 is -X(V). In addition, the amount of movement of the diffracted light corresponding to the surface deflection amount t of the measurement surface 14a is the parallel movement of the diffracted light 25.26 by t, so the output of +y(v) is added to the output of one diffracted light 25.26. 97,-ji. In other words, the photodetector output for the diffracted light of the measurement surface 14a with the warp angle θ9 and the surface runout amount t is the photodetector e
r 18 K +X+Y (V), light detection er 19
An output of K-X+Y (V) is obtained. By inputting these outputs to the addition output circuit 20, a 2Y function output proportional to the surface runout amount t is obtained at the output stage of the addition output circuit 20, and the surface runout amount can be measured. Further, an output of 2X (V) proportional to the warp angle θ is obtained at the output stage of the differential output circuit 21, and the warp angle can be measured.

As described above, according to this embodiment, two photodetectors for detecting the amount of movement of the diffracted light of the laser beam irradiated onto the information track formed on the optical disk are arranged along the incident optical axis of the laser beam. By installing an addition output circuit that adds the output of each photodetector and a differential output circuit that obtains a differential output, it is possible to accurately measure the amount of surface runout and warpage angle of the optical disk at once. can be measured.

Effects of the Invention The optical disk inspection apparatus of the present invention inspects optical disks with a shape of 10"-
-Two photodetectors are installed at symmetrical positions with respect to the incident optical axis of the laser beam, and each photodetector detects the movement amount of the diffracted light of the laser beam irradiated on the digitalized information track. By providing an addition output circuit that adds the output of the photodetector and a differential output circuit that obtains differential output, it is possible to accurately measure the amount of surface runout and warpage angle of an optical disk with a simpler configuration than before. The practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of a conventional optical disk inspection device, FIG. 2 is a principle diagram of an optical disk inspection device according to an embodiment of the present invention, and FIG. 3 is an operation diagram of an optical disk inspection device according to an embodiment of the present invention. It is a figure for explanation. 14... Optical disk, 16... Disc motor. 16...Laser light source, 17.Old...mirror,
18...First photodetector, 19...Second photodetector, 2゜...Addition output circuit, 21...
...Differential output circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 □□ Figure 3

Claims (1)

[Claims] A laser light source that generates a coherent light beam is provided, and two photodetectors are installed to detect the amount of movement of the diffracted light of the light beam irradiated onto the information track formed on the optical disk. An optical disk inspection device installed at a symmetrical position with respect to the incident optical axis of a laser beam, and equipped with an addition output circuit that adds the outputs of each photodetector and a differential output circuit that obtains a differential output.