JPH0725682Y2 - Disk inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a disc inspection apparatus, and in particular, an optical pickup is used to apply focus servo so that a light beam is focused on the disc surface, The present invention relates to a disk inspection device for inspecting defects and the like.

[Problems to be Solved by Conventional Techniques and Inventions] As is well known, an optical disc is one in which minute pits are accurately arranged on the disc surface, and the presence or absence of the pits and the length of the pits are detected by an optical pickup. However, it is read out as a signal. Such optical discs are inspected for defects such as material defects, scratches, and dust at the manufacturing stage.

FIG. 6 is a diagram showing a relationship between a disc and an optical pickup in a conventional disc inspection apparatus. In FIG. 6, the optical disk 1 to be inspected is composed of a disk substrate (substrate) made of plastic or glass. This optical disk 1 is rotated by a spindle motor 2. Then, the signal surface of the optical disc 1 on which a signal is recorded is irradiated with laser light from the optical pickup 4 through the objective lens 3 from the lower side of the optical disc 1 through the substrate, and focusing is performed. The reflected light beam is received by the optical pickup 4, the signal is read, and it is determined whether or not the signal surface of the optical disc 1 is defective.

The diameter of the light beam with which the back surface of the optical disc 1 is irradiated is, for example, about 1 mm, which is narrowed to a minute spot of 1 μmm on the signal surface. Therefore, even if dust or the like adheres to the back surface of the optical disc, the light beam spreads on the back surface side, so that the reflected light is not blocked by dust and the signal can be read accurately. is there.

Further, not only the above-mentioned optical disk 1, but also a magnetic disk in which glass is used as a substrate and magnetism is applied on the substrate is used recently. Such a glass substrate is transparent or semi-transparent, and as described above, it is possible to focus a light beam spot on the surface and detect a defect.

However, the conventional disc inspection apparatus only focuses the light beam on the signal surface of the optical disc 1 to detect the defect on the signal face, and cannot inspect the defect on the back surface of the optical disc 1.

Therefore, a main object of the present invention is to provide a disc inspection apparatus capable of inspecting defects on the front surface and the back surface of the disc.

[Means for Solving the Problems] The present invention is a disk inspection device for inspecting a defect on the front surface or the back surface of a disk by applying a focus servo using an optical pickup so that a light beam is focused on the disk surface. Drive means for driving the optical pickup by switching the focus of the light beam so that the light beam is focused on the front surface or the back surface of the disk, and a focus position determination means for detecting whether the light beam is focused on the front surface or the back surface of the disk. And a defect determination means for determining a defect on the front surface or the back surface of the disk based on the output of the optical pickup when the focus position determination means determines that the focus is achieved on the front surface or the back surface of the disk. Composed.

[Operation] A disc inspection apparatus according to the present invention switches an optical pickup by switching so that the light beam is focused on the front surface or the back surface of the disc, and inspects that the light beam is focused on the front surface or the back surface of the disc. At this time, it is possible to determine the defect on the front surface or the back surface of the disc based on the output of the optical pickup.

[Embodiment of the Invention] FIG. 1 is a diagram showing a configuration of an embodiment of the invention.

In FIG. 1, the optical disc 1 is rotationally driven by a spindle motor 2. An optical pickup 4 is provided on the back surface of the optical disc 1. The optical pickup 4 includes a permanent magnet 5 and a focus coil 6 which constitute an actuator for driving the objective lens 3 in the vertical direction. Further, below the focus coil 6, a quarter-wave plate 7, a beam splitter 8, a lens 9, and a photodiode 10 divided into four are arranged.

Further, a collimator lens 11 and a laser diode 12 are provided so as to face the beam splitter 8. The laser light emitted from the laser diode 12 is collimated by the collimator lens 11
Is collimated into parallel light and is incident on the beam splitter 8. The laser light incident on the beam splitter 8 is reflected upward and passes through the quarter-wave plate 7. At this time, the linearly polarized laser light is converted into circularly polarized light and is irradiated onto the optical disc 1 through the objective lens 3. Then, a part of the laser light is reflected to become circularly polarized light which is the reverse rotation of the incident light, and when this again passes through the 1/4 wavelength plate 7, it becomes linearly polarized light having a plane of polarization parallel to the paper surface. Then, the laser light reflected on the disk surface passes through the beam splitter 8 this time, and passes through the lens 9 to the photodiode 10.
Detected by.

The detection output of the photodiode 10 is given to the focus error detection circuit 13. A focus position determination circuit 14 is provided in association with the focus error detection circuit 13. The focus position discriminating circuit 14 discriminates whether the laser beam applied to the optical disc 1 is focused on the front surface or the rear surface. The output of the focus error detection circuit 13 is given to the adder circuit 15 and added to the output of the focus search circuit 16. The phase of the output of the adder circuit 15 is controlled by the phase circuit 17, and is given to the drive circuit 18. The drive circuit 18 controls the focus coil 6 to focus the objective lens 3 on the front surface or the back surface of the optical disc 1.

2 to 4 are diagrams showing the relationship between the optical disc and the optical pickup for explaining the operation of the embodiment of the present invention, and FIG. 5 is a diagram showing the focus error signal.

First, as shown in FIG. 2, the optical pickup 4 is lowered from the optical disk 1, and then the optical pickup 4 is gradually raised as shown in FIGS. 3 and 4. That is, assuming that the distance between the upper surface of the objective lens 3 and the upper surface of the optical disc 1 is x, the optical pickup 4 is moved from the large direction to the small direction. Here, as shown in FIG. 3, the position where the laser light is focused on the lower surface of the optical disc 1 is x _L, and the position where the laser light is focused on the upper surface of the optical disc 1 is x _U , as shown in FIG. Then, for the displacement x, the focus error signal is x = x _L , x _{U as} shown in FIG.
In, draw a so-called S curve. When the normal optical disk 1 is used, the focus servo is applied at the zero point at the center of the S curve when x = x _U.

On the other hand, in the embodiment of the present invention, the optical disc 1
In order to perform the focusing on the lower surface of, the focus is controlled so as to be in focus at the zero point of x = x _L. That is, when the optical pickup 4 is raised from below, the focus servo is applied with the S curve (when x = x _L ) that occurs first. This first S curve generated is discriminated by the focus position discriminating circuit 14 shown in FIG. 1, and the discriminating signal is given to the focus error detecting circuit 13. The focus error detection circuit 13 gives a focus error detection signal to the addition circuit 15 so that the focus is achieved at the zero point of the first S curve.

The adder circuit 15 outputs the error signal and the focus servo circuit 16
And the output of the above are added and given to the focus coil 6 via the phase circuit 17 and the drive circuit 18. As a result, the focus coil 6 drives the objective lens 3 to focus on the lower surface of the optical disc 1 as shown in FIG. Then, the flaw is detected based on the output of the photodiode 10. That is, the presence / absence of a scratch is determined by the magnitude of the reflected light amount signal from the optical disc 1 which is the output of the photodiode 10. Usually, when there is a scratch or the like, the reflected light is scattered and the reflected light amount signal is lowered, but there are some defects that increase this. This data signal is compared by a window comparator (not shown) to detect a defect.

Although the defect on the lower surface of the optical disk 1 is detected as described above, the defect on the upper surface of the optical disk 1 may be detected. In this case, the focus search circuit 16
Outputs a signal so that the laser beam is focused on the upper surface of the optical disc 1, as shown in FIG. As a result, the optical pickup 4 is further raised, and focus servo control is performed so that the upper surface of the optical disc 1 is in focus. The focus error detection circuit 13 outputs the signal of the second S curve. At this time, the focus position determination circuit 14
The focus error detection circuit 13 determines that it is the S curve of the second time, and performs focus servo control so that the focus is adjusted at the zero point of the S curve of the second time. Then, based on the output of the photodiode 10, a defect such as a scratch on the surface of the optical disc 1 is determined.

In the above-described embodiment, the case where the pickup 4 is arranged below the optical disc 1 has been described. However, the present invention is not limited to this, and the pickup 4 may be arranged above the optical disc 1 to prevent defects such as scratches on the front or back surface of the optical disc 1. You may make it detect.

[Advantage of the Invention] As described above, according to the present invention, when the focus servo is applied using the optical pickup so that the light beam is focused on the disk surface, the light beam is focused on the front surface or the back surface of the disk. Since the focus servo is switched as described above, it becomes possible to easily detect a defect on the front surface or the back surface of the optical disk.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. 2 to 4 are views showing the relationship between the optical disk and the optical pickup in order to explain the operation of the embodiment of the present invention. FIG. 5 is a diagram showing a focus error signal. FIG. 6 is a diagram showing a relationship between an optical disc and an optical pickup in a conventional disc inspection apparatus. In the figure, 1 is an optical disk, 2 is a spindle motor,
3 is an objective lens, 4 is an optical pickup, 5 is a permanent magnet,
6 is a focus coil, 7 is a quarter wavelength plate, 8 is a beam splitter, 9 is a lens, 10 is a photodiode, 11 is a collimating lens, 12 is a laser diode, 13 is a focus error detection circuit, and 14 is a focus position determination circuit. , 15 is an adder circuit, 16 is a focus search circuit, 17 is a phase circuit, and 18 is a drive circuit.

Claims (1)

[Scope of utility model registration request] 1. A disc inspection apparatus for inspecting a defect on a front surface or a back surface of a disc by applying focus servo using an optical pickup so that the light beam is focused on the disc surface. Driving means for driving the optical pickup by switching so as to match the front surface or the back surface of the disk, a focus position determination means for detecting whether or not the focus of the light beam is the front surface or the back surface of the disk, and the focus position determination In response to the determination by the means that the focus was on the front or back surface of the disc,
A disc inspecting apparatus, comprising a defect discriminating means for discriminating a defect on a front surface or a back surface of the disc based on an output of the optical pickup.