JPH0369076A - Foreign substance detector - Google Patents

Abstract

PURPOSE:To detect a foreign substance with high accuracy by forming light from a light source to be spot light, irradiating an information recording medium with the light, converting the photodetection amount of the spot light from the information recording medium to an electric signal and discriminating the presence and absence of the foreign substance. CONSTITUTION:The spot light irradiates from a laser diode 10 through a collimator lens 11 and a slit 12. The spot light incident to an optical disk 1 is diffracted on the surface and reflected in a recording layer 2. Afterwards, the reflected light is incident to a condenser lens 13. The condensed spot light is converged on the photodetecting surface of a two-dimensional semiconductor position detector 14 as a photodetector and the quantity of light is detected. Output voltages X1 and X2 at both ends of the detector 14 are added by an adder 20 and a signal as an added result is compared with a reference voltage by a comparator 21. Then, a discriminating circuit 22 discriminates the presence and absence of the foreign substance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a device for detecting foreign matter such as dirt and dust attached to a recording medium such as an optical disk or a magnetic disk.

[Conventional technology]

Optical disks are used as large-capacity storage media.
Information is stored on its surface at intervals of 1.5 to 1.6 μm. Compared to magnetic disks, optical disks can be separated from the medium, so they are less susceptible to the effects of foreign substances such as dust in the air.

In addition, in an optical disk, the size of the pit in which information is recorded is approximately 1 μm, and the beam of the spot light used to detect this is approximately 1 μm in diameter on the recording surface, but is approximately 1 μm in diameter on the optical disk surface. Since the area is one million times larger than the bit area, it is less susceptible to dust and local dirt of about 20 μm.

Furthermore, error detection and correction technology has been introduced in optical disk drives, making it possible to correct errors caused by defects such as scratches and dust on the recording surface of several tens of micrometers. ing.

(Problems to be Solved by the Invention) However, since the optical disk rotates at high speed, static electricity may be generated due to friction with the air, which may cause large-diameter foreign matter to adhere to the optical disk. If a detection error that exceeds the correction ability occurs due to the attachment of large-diameter foreign matter or scratches, the error will be reproduced as is, and erroneous data will be reproduced.

In conventional optical disk drive devices, when a detection error occurs, it is impossible to detect a foreign object, so it is not possible to determine whether the cause is a defect in the medium or a foreign object.

This invention was made in view of the above circumstances, and it is possible to detect foreign objects with high precision based on fluctuations in the amount of spot light received from a light source through a medium, and it also prevents detection errors in the medium drive device. An object of the present invention is to provide a foreign object detection device that can suppress the occurrence of.

(Means for Solving the Problems) A foreign object detection device according to the present invention includes a light source, an optical system that converts light emitted from the light source into a spot light and irradiates an information recording medium, and a spot light from the information recording medium. receives light,
A light receiving element that converts the amount of received light into an electrical signal is provided, and the presence or absence of foreign matter is detected based on discontinuous changes in the amount of received light.

[Effect]

In this invention, when there is a foreign object, the spot light irradiated on the information recording medium is scattered by the foreign object, and the amount of received light changes discontinuously. By detecting this, the foreign object can be detected with high accuracy. It can be detected by

[Example] Hereinafter, the present invention will be described based on drawings showing one example thereof.

FIG. 1 is a block diagram showing the configuration of a foreign object detection device according to the present invention. In the figure, l denotes an optical disk as a recording medium, and the optical disk 1 has a recording layer 2 for recording information.

A spot light is irradiated onto the surface of the optical disk 1 facing an optical head (not shown) from a laser diode (hereinafter referred to as LD) 10, which is a light source attached to the optical head, through a collimator lens 11 and a slit 12. Collimator lens 11
The slit 12 is for converting the laser beam from the LDIO into parallel light, and the slit 12 is for converting the parallel light into a spot light having a predetermined shape. The spot light is irradiated onto the optical disk 1 with its optical axis forming an angle θi with the vertical direction. The spot light incident on the optical disc l is refracted on its surface, and the recording layer 2
After being reflected, the light enters the condenser lens 13. The incident spot light is condensed by a condensing lens 13, and the light receiving element 2
Position Sen
The light is focused on the light receiving surface of the singDevice (hereinafter referred to as PSD) 14, and the amount of light is detected.

FIG. 2 is a plan view showing an example of the configuration of the PSD 14,
The PSD 14 detects a foreign object and uses the position detection function of the PSD 14 to detect a tilt angle, which is not shown in the figure.
The inclination of the surface of the optical disk 1 in the circumferential direction and the radial direction is detected.

PSD 14 for two-dimensional detection has a light receiving surface of 2L each in the vertical and horizontal directions.
The output voltages at both vertical and horizontal ends are Y + and Y, respectively.
If Z and x, ,X, the coordinates (x, y) of the position where light is received when the center of the light receiving surface is the center point are
It can be expressed as t.

The tilt of the optical disk 1 can be determined by detecting the deviation of the light receiving position from the center point.

However, when detecting foreign objects, there is no need to calculate the slope.
For example, a foreign object is detected by adding the output voltages X+ and Xz at both ends of the PSD 14. That is, the output voltage X7. which is output by the adder 20 at each predetermined detection timing. X2 is added, the signal of the addition result is input to one end of the comparator 21, and by comparison with a reference voltage manually applied to the other end, the determination circuit 22 determines the presence or absence of foreign matter.

Note that by similarly determining the output voltages Y + and Y z , foreign matter can be detected more reliably.

Further, the signal resulting from the addition is applied to a low-pass filter 23 and smoothed, and the maximum value at each detection timing is held by a maximum value hold circuit 24. The maximum value held is A/
The signal is applied to a D converter 25, where it is converted into a digital value. The digitally converted maximum value is given to the level ratio detection circuit 26, which calculates the level ratio of the maximum value at each detection timing, and the foreign object shape determination circuit 27 determines the relationship between the foreign object size and the level ratio determined in advance. Based on this, the shape (size) of the foreign object is determined. Furthermore, the output voltage Y +
, By making the same determination for Y 2, XI
, Xz, and the shape (size) of the foreign object in the direction perpendicular to Xz is determined, allowing for more accurate determination.

Next, the foreign object detection operation will be explained.

FIG. 3 is a diagram showing the scattering state of the spot light when dust, which is a foreign substance, adheres to the optical disc l. The spot light below the optical axis Ox is scattered by the dust, and the optical disc l
does not reach the recording layer 2. Therefore, the light is not received by the PSD 14, and only approximately half of the spot light is received due to dust as shown in FIG.

Therefore, the amount of light received decreases, and the output voltage X1. The sum of Xz (
or the sum of Y, , Y2) decreases.

Then, the presence of foreign matter is determined based on the fact that the sum of the output voltages XI and X (or Yl and Y) is smaller than the reference value.

Next, another embodiment will be described using FIG. 5.

FIG. 5 is a block diagram showing the configuration of another embodiment of the foreign object detection device of the present invention. In the embodiment described above, the output of the PSD 14 was used as is to detect a foreign object, but in this embodiment, the inclination angle is detected by the inclination angle detection circuit 30, and this is used to detect a foreign object. That is, the output voltages Xr, Xz (or Y
, , Y, ), the spot light receiving position X (or y)
is calculated from the above formula.

Here, the PSD 14 is positioned so that the spot light can be received at the center of its light-receiving surface when the optical disc does not rotate, and the tilt angle in the X direction (or Y direction) can be determined from the light receiving position of the spot light. In other words, if the distance from the reflection position of the spot light on the optical disk to the light receiving surface of the PSD 14 is h, then the inclination angle θ of the optical disk in the X direction is
X (or inclination angle θ, in the Y direction) is expressed by the following formula.

The tilt angle θX (or θV) detected by the tilt angle detection circuit 30
) is A/D converted by the A/D converter 31 and stored in the memory 32.
is stored in The stored tilt angle θ8 is Fourier-transformed by a fast Fourier transformer 33, and then inverse Fourier-transformed 'P'
134 and undergoes inverse Fourier transform, and the data at the tilt angle θ8 is averaged. This removes the high frequency range of the inclination angle θ8. And the tilt angle θ8 stored in the memory 32
A comparison circuit 35 compares the data and the averaged data, and a determination circuit 36 determines whether there is a foreign object based on the comparison result.

FIGS. 6 to 8 are graphs showing variations in inclination angles in the X and Y directions in circumferential and radial positions. Figure 6 is X
Figure 7 shows the variation in the circumferential position of the inclination angle θ8 of the Y
3A and 3B respectively show variations in the circumferential position of the inclination angle θ7. Further, FIG. 8 shows the variation of the inclination angle θ8 in the X direction with respect to the radial position. In addition, in Figures 6 and 7, the vertical axis shows the inclination angle θ.
8. θ7, and the circumferential position is taken on the horizontal axis, and the 8th
In the figure, the vertical axis represents the inclination angle θ8, and the horizontal axis represents the radial position.

At the circumferential position, the inclination angle θ8 is approximately 310° at the circumferential position shown by section A in FIGS. θ7 is changing rapidly, and this change is cut by Fourier transform-inverse transformation, and this and the inclination angle θ8 at the same circumferential position stored in the memory 32. A sudden change can be detected by comparison with θ, and thus a foreign object can be detected.

Further, as shown in FIG. 8, there is a sudden change in the inclination angle θ8 at approximately 50 am in the radial position, and the comparator circuit 35 can similarly detect a foreign object. That is, when there is no foreign object, the inclination angle θ8 changes slowly as shown by the broken line in FIG. 8, and when there is a foreign object, it changes suddenly. In this embodiment, since the position of the foreign object can be recognized, for example, if the optical disk drive device is provided with a means for adsorbing the foreign object and configured to remove the foreign object, the foreign object can be reliably removed and detection errors can be suppressed. .

In the above embodiments, a PSD was used as the light receiving element, but the present invention is not limited to this. Any type of light receiving element, such as a CCD or a linear IC, can be used as long as it can detect the scattering of spot light by foreign objects. It may be an element.

Further, although a two-dimensional PSD is used in this embodiment, a one-dimensional PSD shown in FIG. 2(b) may be used instead.

Furthermore, in the above embodiments, the case of detecting foreign matter on an optical disk was explained as an example, but the present invention is not limited to this.
It goes without saying that the present invention can also be applied to other storage media such as magnetic disks.

〔Effect of the invention〕

As explained above, in the present invention, the light emitted from the light source is turned into a spot, the reflected light is received by a light receiving element, and the scattering of the spot light by the foreign matter is detected, thereby detecting foreign matter attached to the information recording medium. In addition to being able to detect with high accuracy, when this is used in an optical disk drive device, it has excellent effects such as being able to reliably determine the cause of a detection error and suppressing the occurrence of a detection error.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a foreign object detection device according to the present invention, FIG. 2 is a diagram showing an example of the configuration of a PSD, and FIG.
FIG. 4 is a diagram showing the state when foreign matter is attached, FIG. 5 is a block diagram showing the configuration of another embodiment of the foreign matter detection device of the present invention, and FIGS. 6 to 8 are graphs showing variations in the tilt angle. DESCRIPTION OF SYMBOLS 1... Optical disk 10... LD 11... Collimator lens 12... Slit 13... Condensing lens 14... PSD22... Judgment circuit Note that in the figures, the same symbols are the same or equivalent Show parts.

Claims (1)

[Claims] (1) An apparatus for detecting foreign matter adhering to an information recording medium, comprising: a light source; an optical system that converts light emitted from the light source into a spot light and irradiates the information recording medium; and the information recording medium. A foreign object detection device comprising: a light receiving element that receives spot light from a medium and converts the amount of the received light into an electrical signal; and a foreign object determining means that determines the presence or absence of a foreign object based on the electrical signal from the light receiving element. Device.