OPTICAL SYSTEM OF DETECTING PERIPHERAL SURFACE DEFECT OF GLASS DISK AND DEVICE OF DETECTING PERIPHERAL SURFACE DEFECT THEREOF

Abstract

In the present invention, since light beams are irradiated from a back face of a glass disk through the glass disk on to an outer peripheral chamfered portion at a front face side of the glass disk, a difference between extinction amounts in a received light due a foreign matter and a flaw increases, and the received light signal representing a defect detection signal in response to this difference can be obtained.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining one embodiment of a glass disk inspection device to which an optical system for the detection according to the present invention is applied,

FIG. 2( a) is a view for explaining a case in which no defect exists on a chamfered portion of a disk,

FIG. 2( b) is a view for explaining a case in which a foreign matter is deposited on a chamfered portion of a disk,

FIG. 2( c) is a view for explaining a case in which a flaw due to a chuck trace and the like exists at a chamfered portion of a disk,

FIG. 3 is a view for explaining a detection signal obtained during one round rotation along a track,

FIG. 4( a) is a view for explaining a signal waveform of a detection signal by a light receiver after being subjected to a filtering processing,

FIG. 4( b) is a view for explaining a defect detection signal that has passed through a reference level variation inhibiting circuit,

FIG. 5 is a view for explaining another embodiment of an optical system for the detection according to the present invention,

FIG. 6 is a block diagram of a defect detection circuit that uses another reference level variation inhibiting circuit for a received light signal,

FIG. 7( a) is a view for explaining a glass disk, and

FIG. 7( b) is a view for explaining an outer peripheral edge portion and a defect of the glass disk.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, numeral 10 is a defect inspection device and is constituted by a disk rotation mechanism 2, a defect detection optical system 3, a defect detection circuit 5, a data processing device 6 and a disk inverting mechanism 8.

The defect detection optical system 3 is constituted by a light illuminating system 3a and a light receiving system 4.

The disk rotation mechanism 2 is constituted by a spindle 21, a disk chuck provided at the head of the spindle 21, a supporting stand 23 provided at the bottom of the spindle 21 and an encoder 24. The disk chuck 22 is rotated after a glass disk (herein below will be called as a disk) 1 for the inspection object is mounted thereto. Further, the supporting stand 23 is fixed to a device base 7.

The light illuminating system 3a is constituted by a mirror 31 and a laser light source 32. The laser light source 32 is fixed to the device base 7 and irradiates a laser spot Sp to the mirror 31. The irradiation angle is an elevation angle θ1 seen from the side of the mirror 31. The mirror 31 which receives the irradiation light is fixed between the supporting stand 23 and the disk 1 in an inclined manner to a bracket 33 with an elevation angle θ2 with respect to the supporting stand 23 so as to align along the spindle 21 with a predetermined angle. The bracket 33 is fixed to the device base 7.

Herein, the above elevation angles θ1 and θ2 are selected in such a manner that the laser spot Sp is irradiated to the outer peripheral chamfered portion 1d at the front face side of the disk 1 from the inside of the disk 1 through the back face 1b of the disk 1. As a result, the laser spot Sp is irradiated to the back face side of the outer peripheral chamfered portion with an inclination of

Since the transmittance of glass is more than 90%, even when the laser spot Sp is irradiated from the back face side of the disk 1 to the back side of the outer chamfered portion 1d through a glass having thickness of about 0.5 mm˜1.3 mm in the above manner, the amount of reflection from the glass face to different directions is about a few %. Thus, almost all the irradiation light is refracted at the outer peripheral chamfered portion 1d and outgoes as outgoing light P.

Herein, when assuming the refraction factor N of glass as N=1.5 and the diameter of the disk 1 as 2.5 inch, and when adjusting the incident angle of the laser spot Sp making incident to the back face 1b of the disk 1 to assume about 65° with respect to the back face 1b in clockwise direction while selecting the elevation angles θ1 and θ2, the outgoing angle of the laser spot Sp from the outer peripheral chamfered portion 1d will assume about 85° with respect to the front face 1a of the disk 1 in anticlockwise direction. Thus, as shown in FIG. 2(a), the light receiver 43 in the light receiving system 4 is disposed at an obliquely upward position of the outer peripheral chamfered portion 1d so that a light receiving angle θ3 assumes an incident angle of about 85° with respect to the front face 1a of the disk 1 in anticlockwise direction.

FIG. 2( a) is a view for explaining a relation with the light receiver 43 when a laser spot Sp is irradiated to the outer peripheral chamfered portion 1d of a normal disk 1 with no defects, wherein the light receiver 43 receives the outgoing laser spot Sp refracted at the outer peripheral chamfered portion 1d through a stop hole 42a of a stop hole plate 42.

As shown in FIG. 1, the light receiving system 4 is constituted by an image-forming lens 41, the stop hole plate 42 and the light receiver 43. The stop hole plate 42 is provided between the light receiver 43 and the image-forming lens 41. As the case may be, the image-forming lens 41 could be omitted.

The light receiver 43 is an avalanche-photodiode (APD) and the light receiving face thereof receives outgoing light P from the outer peripheral chamfered portion 1d through the image-forming lens 41 and the stop hole plate 42.

Further, the size of the stop hole 42a has a size that only passes the outgoing light P from the outer peripheral chamfered portion 1d. The diameter of the hole is adjustable. The diameter of the laser spot Sp corresponds to the width of the outer peripheral chamfered portion 1d, and because of the existence of the stop hole 42a, only the outgoing light P from the outer peripheral chamfered portion 1d can be received.

In FIG. 1, numeral 5 is a defect detection circuit, which is constituted by a preamplifier (AMP) 51, an LPF (Low Pass Filter) 52, a HPF (High Pass Filter) 53, a comparing amplifier (COM) 54 and an A/D 55, and an output of the A/D 55 is sent out to a data processing device 6 and in the data processing device 6, number and size of defects at the outer peripheral chamfered portion 1d of the disk 1 are detected.

Herein, the LPF 52 is a circuit for extracting a reference signal in received light signals caused due to shifting in up and down direction of the disk outer peripheral surface, the HPF 53 is a circuit inserted between an output terminal of the LPF 52 and the ground GND and sinks high frequency noise components and detection signal components of such as flaws and foreign matters to the ground GND. Further, the comparing amplifier (COM) 54 functions as a circuit which cancels a variation of reference level in the received light signals caused due to shifting in up and down direction of the disk outer peripheral surface and generates detection signals of outer peripheral defects.

Detection signals of the light receiver 43 are input to (+) input of the comparing amplifier 54 via the preamplifier 51, the LPF (Low Pass Filter) 52 and the HPF (High Pass Filter) 53 in the defect detection circuit 5. (−) input of the comparing amplifier 54 receives an output of the preamplifier 51.

The data processing device 6 is constituted by such as an MPU 61, a memory 62, a display 63, a keyboard 64 and an interface circuit (I/F) 61 and these are mutually connected through a bus 66. Numeral 67 is an external memory device such as an HDD.

The memory 62 is provided with a defect detection program 62a, a defect size judgment program 62b, a disk good or no good judgment program 62c and a work area 62d.

Further, the MPU 61 receives from an encoder 2a provided at the side of the disk rotating mechanism 2 via the bus 66 an index signal IND obtained in response to one rotation of the disk 1 as an interruption signal.

Numeral 8 is the disk inverting mechanism and is disposed adjacent to the disk 1 to be mounted to the disk rotating mechanism 2. The disk inverting mechanism 8 chucks the outer peripheral side face of the disk 1 with a chuck mechanism and receives the disk 1 by lifting up the same from the disk rotating mechanism 2. Then, the disk inverting mechanism 8 retreats on a rail (not shown) and sidetracks the disk 1 from the position of the disk rotating mechanism 2, and inverts the disk 1 of which inspection on the outer peripheral chamfered portion at the front side has been completed to turn the back side face thereof to the front side face, advances on the rail and returns the disk 1 over the disk rotating mechanism 2 to remount the same to the disk rotating mechanism 2. Further, since varieties of disk inverting mechanisms are known, a detailed explanation thereof is omitted.

FIG. 2 is a view for explaining the outer peripheral defect detection in the defect detection optical system, wherein FIG. 2(a) is a view for explaining a case when there is no defect at the outer peripheral chamfered portion 1d as referred to above, FIG. 2(b) is a view for explaining a case when a foreign matter deposits on the chamfered portion 1d of the disk 1, and FIG. 2(c) is a view for explaining a case when a chip F due to chucking and the like exists on the chamfered portion 1d of the disk 1. Further, in these drawings, the stop 42 is omitted for the sake of convenient explanation.

As shown in FIG. 2(b), when foreign matters exist on the chamfered portion 1d, since the outgoing light P from the foreign matters gives scattering light and the incident light to the light receiver 43 among the outgoing light P decreases, which is reflected in the respective waveforms as shown by points P1, P2 and P3 in FIG. 3 appearing in a received light signal (detection signal S) of the light receiver 43, which receives the outgoing light P.

When a chip F due to chucking and the like exists on the outer peripheral chamfered portion 1d of the disk 1, as shown in FIG. 2(c), since the outgoing light P refracted in regular direction greatly decreases, the received light signal of the light receiver 43 reduces and a pulse shaped waveform as shown by point KF in FIG. 3 is obtained as a detection signal of the chip F. Contrary, the level reduction in the received light signal of the respective detection signals with the respective waveforms shown by point P1, point P2 and point P3 corresponding to foreign matters (herein below, will be called as detection signal at point P1, detection signal at point P2 and detection signal at point P3) is smaller than that of the detection signal with the waveform shown by point KF (herein below will be called as detection signal at point KF).

As shown by dotted lines, since the level reduction of a detection signal due to a chip F is comparatively large even when the detection signal at point KF positions at the crest of the detection signal S, the respective signals at points P1, P2 and P3 due to foreign matters can be separated from the detection signal due to a chip F with a simple filtering processing.

However, because of the penetration type defect detection of the present invention, in a case when the diameter of a foreign matter is large, since a amount of penetration light interrupted increases, when the level of the detection signal due to the chip F lowers and because of a variation of a reference level in the received light signal, when the level of the detection signal at point P3 having a pulse like waveform is larger than that illustrated, discrimination therebetween sometimes becomes difficult.

Therefore, the detection signal S is passed through the LPF (Low Pass Filter) 52 and the HPF (High Pass Filter) 53, wherein the signal components corresponding to the shifting of the disk 1 are caused to pass the LPF 52 and the remaining high frequency noises and the respective detection signal components at points P1, P2 and P3 and at point KF are sunk to the ground through the HPF 53 to remove the same, resultantly, a detection reference signal in a vibration waveform corresponding to the shifting of the disk 1 with substantially no noises are extracted from the detection signal S as shown in FIG. 4(a).

By applying this vibration waveform to (+) input of the comparing amplifier (COM) 54, the variation of the reference signal level in the received light signal at (−) input side is canceled.

Since the detection signal S is not a complete sinusoidal waveform, the signal is necessary to be passed through these filters, however, when the filters are constituted to pass the signal components corresponding to the shifting in up and down direction of outer peripheral surface of a 2.5 inch disk, and while assuming that the rotation number of the spindle is, for example, 10,000 rpm and a cutoff frequency of the LPF 52 is, for example, 200 Hz, the filters can be used in common in the case for a 1.5 inch disk.

Although indefinite depending on the rotation number of the spindle, the LPF 52 can use a BPF (Band Pass Filter), which extracts signal components in the detection signal S in correspondence with the frequencies thereof depending on the shifting in up and down direction of outer peripheral surface in the respective disks of one or plural diameters. Accordingly, the LPF 52 can be replaced by the BPF.

Therefore, as the result of comparing the signal in FIG. 4(a) and the detection signal S in FIG. 3 in the comparing amplifier 53, the comparing amplifier 53 can obtain a defect detection signal Sk as shown in FIG. 4(b) at positions of the respective detection signals at points P1, P2 and P3, which reduce in a pulse shaped signal and at point KF.

With this measure, not only the variation of the reference level in the received light signal is canceled, but also because the level reduction of the detection signals corresponding to foreign matters as shown by the respective detection signals at points P1 and P2 is small and comes close to those of noises, almost all such detection signals do not appear as an output from the comparing amplifier 54 as shown by dotted lines in FIG. 4(b).

Since the comparing amplifier 54 is a high gain non-inverting DC amplifier, although high frequency noises in an input signal at (−) input thereof are possibly amplified, these are removed some by an operation dead band of the non-inverting DC amplifier and further, these are removed when being sunk to the ground GND such as through a capacitor, although not illustrated. Thereby, the respective detection signals at points P1 and P2, which are close to high frequency noises, are removed.

As a result, the defect detection signal Sk as in FIG. 4(b) can be obtained as an output of the comparing amplifier 54. Herein, detection signals in connection with many foreign matters are eliminated. Of course, in this instance, the high frequency noises are also not output.

As a result, ones detected in this instance are the pulse like detection signal possibly at point P3 with a comparatively large level reduction corresponding to a foreign matter and the detection signal KF corresponding to the flaw F. Since the respective detection signals at point P3 and at point KF are different in connection with extinction levels of the received light, the difference appears in the output of the comparing amplifier 54 as pulse signals having the corresponding levels. Moreover, the generation of the pulse like detection signal at point P3 is infrequent.

The A/D 55 receives the pulse signals corresponding to the respective signals at point P3 and at point KF as defect detection signals Sk. The levels of the signals are converted into digital values every time when the defect detection signal is generated to successively store the same in the work area 62d.

The data processing device 6 receives the index signal IDX and when an inspection of a chamfered portion for one round rotation of the disk 1 is completed, calls the defect detection program 62a. The defect detection program 62a is executed by the MPU 61, and the MPU 61 detects defect detection signals Sk having levels more than a predetermined value as defects (including chuck traces) on the chamfered portion 1d, stores the level values at respective memory positions in the work area 62d and counts the number thereof. In this instance, the comparatively large pulse like detection signal at P3 is compared with the predetermined reference value and eliminated as a detection signal of a foreign matter.

Further, the above predetermined reference value is selected as a level that can eliminate the detection signal at point P3 in connection with a foreign matter and can detect a flaw due to a chuck trace or other flaws.

The MPU 61 subsequently calls the defect size judgment program 62b.

The defect size judgment program 62b is executed by the MPU 61, and the MPU 61 classifies the defects into three grades of large, medium and small from the levels of the respective defect detection signals Sk stored in a predetermined memory position in the work area 62d and stores the classification result in another predetermined memory position in the work area 62d. Then the MPU 61 calls the disk good or no good judgment program 62c.

The disk good or no good judgment program 62c is executed by the MPU 61, and the MPU 61 determines a disk having one large defect as no good with reference to the size classification data stored in the work area 62d. A disk having more than two medium defects is also determined as no good. Further, a disk having not less than five defects is also determined as no good. As the result of the good or no good judgment, when a disk of which front face side is determined as no good, the result is displayed on the display 63 and the no good disk is removed from the spindle 22 with a handling robot and is transferred to a no good cassette (NG cassette).

With regard to a disk that is determined as good in the inspection of the front face side chamfered portion ChU, the MPU 61 drives the disk inverting mechanism 8 to invert the good disk and to remount the same to the spindle 22 while setting the back face side chamfered portion ChD as the outer peripheral chamfered portion 1d.

Then, after waiting an index signal IND, the same inspection as above is performed for the back face side chamfered portion ChD.

At the time when the good or no good judgment has been completed for the back face side, the result of good or no good judgment of the inspected disk is displayed on the display 63 and a no good disk is transferred to the NG cassette.

As a result, a disk determined as no good either in connection with the front face or the back face is accommodated in the NG cassette and a disk as determined as G (good) is accommodated in a good (G) cassette, thereby, an inspection of a disk 1 is completed and the inspection moves subsequently to a new disk for inspection object.

FIG. 5 is a view for explaining another embodiment of an optical system for the detection according to the present invention.

The detection optical system in FIG. 5 uses two pieces of mirrors 31a and 31b in place of the one piece of mirror 31 in FIG. 1. Thereby, the laser beam source 52 can be fixed perpendicularly to the device base 7. Further, numerals 33a, 33b and 33c are brackets for fixing the mirrors 31a and 31b and the lens 41 employs a plural lens structure.

As shown in an enlarged view of a portion encircled by a dotted line at the right side in FIG. 5, an incident angle of the laser spot Sp is determined as 40° with respect to the back face 1b of the disk 1 in clockwise direction. In this instance, an incident angle with respect to a normal line of the back face 1b assumes 50° and the outgoing angle from the outer peripheral chamfered portion 1d assumes 21. 74° with respect to a normal line of the outer peripheral chamfered portion 1d. Accordingly, the light receiving angle θ3 of the light receiver 43 with respect to the side of the front face 1a of the disk 1 assumes θ3=113° with respect to the front face of the disk 1.

Now, as explained above, in FIG. 1 embodiment, although the pulse like inspection signal at point P3 is eliminated through comparison with the predetermined reference value, discrimination between the detection signal at point P3 and the detection signal at point KF can be performed through a provision between the comparing amplifier 54 and the A/D 55 of a comparator that compares a defect detection signal Sk with a predetermined reference value to thereby eliminate the detection signal at point P3 from the defect detection signal Sk. An example therefor will be explained in the followings.

FIG. 6 is a block diagram of a defect inspection circuit, which uses another reference level variation inhibiting circuit in a received light signal, wherein the defect detection device 10 uses a defect detection circuit 50 in place of the defect detection circuit 5 in FIG. 1.

In the defect detection circuit 50, the connecting relationship between the LPF 52 and the HPF 53 is inverted, in that at the back of the HPF 53 the LPF 52 is connected in cascade. The output of the LPF 52 is input to a comparator 54a and the output “1” or “0” of the comparator 54a is input to the A/D 55. Thereby, when the interval of “1” of the comparator 54a is long, the level “1” for the corresponding period is continuously A/D converted with a predetermined period.

Further, in place of the A/D 55, through provision of a defect bit memory, bit data corresponding to one round rotation of the disk can be stored so as to permit the MPU 61 to read the bit data.

Usually, the cascade connection of the LPF 53 to the HPF 52 constitutes a BPF (Band Pass Filter).

Herein, giving the cutoff frequency of the HPF 53 as 200 Hz, and keeping the variation frequency of the signal reference level in a received light signal corresponding to a frequency due to the shifting in up and down direction of the outer peripheral surface of a disk below the cutoff frequency, the frequency due to the shifting in up and down direction of the outer peripheral surface of the disk is eliminated and a smoothened signal of the signal reference level is extracted. Thereby, the variation of the reference level in the received light signal is suppressed.

The cutoff frequency of the LPF 52 is given as 3 MHz. The LPF 52 is a filter for cutting off high frequency noises from the received light signal and for eliminating defect detection signals including foreign matters.

Resultantly, through provision of a BPF having a band of 200 Hz˜3 MHz constituted by the HPF 53 and the LPF 52, the defect detection signals are extracted.

When the defect detection signals are inputted to (−) input of the comparator 54a to which (+) input side a reference value (threshold value) Vth serving as a comparison reference is applied, the high frequency noise components and the respective detection signals at points P1, P2 and P3 corresponding to foreign matters are cut off from the defect detection signals and the detection signal at point KF in which the detection signal at point P3 is removed from the defect detection signal Sk is obtained as shown in FIG. 4(b).

Further, the reference value Vth in the comparator 54a is adjusted as a value that removes the detection signal at point P3.

Although in FIG. 1 embodiment the use of the comparing amplifier has been explained, when the level of the received light signal amplified by an amplifier is large, a usual comparator or a differential amplifier can be used.

Further, although the light receiver in the embodiment uses the APD, the present invention can use varieties of light receiving elements such as a CCD and a photo multiplier and of light receivers.

Still further, although in the embodiment, only the front face side chamfered portion of a disk is assumed as the inspection object, in the present invention, through provision of a light receiver that corresponds to the back face side chamfered portion and through irradiation of light beams to the back face side chamfered portion, outer peripheral defects on the back face side chamfered portion can be detected with the light receiver provided at the back face side. Further, the present invention can be modified to detect outer peripheral defects at both front and back face chamfered portions at the same time.

Still further, although in the embodiment, as the irradiation light the laser beams are used, the irradiation light can, of course, be white light.

Still further, throughout the present specification, the term “defect” is used not only for such as breaks and chips but also used in a broad sense for flaws in general, and the same is true with regard to claims follows.

Claims

1. An optical system of detecting a peripheral surface defect of a disk for detecting a defect at an outer peripheral surface of the disk comprising: a light illuminating system which irradiates light beams from a back face of a rotating glass disk through an inside of the glass disk on to an outer peripheral chamfered portion at the front face side of the glass disk,a light receiver provided away from the outer peripheral chamfered portion by a predetermined distance anda stop provided in front of the light receiver,wherein the light receiver receives the light beams penetrated and refracted at the outer peripheral chamfered portion through the stop and a defect at the outer peripheral surface of the glass disk is detected based on a received light signal of the light receiver.

2. An optical system of detecting a peripheral surface defect of a glass disk according to claim 1, wherein a hole diameter of the stop is selected so as to permit the penetrated light corresponding to the width of the outer peripheral chamfered portion to pass therethrough.

3. An optical system of detecting a peripheral surface defect of a glass disk according to claim 2, wherein the light beams are laser beams, the light illuminating system includes a light source for the laser beams and a mirror to which the laser beams are irradiated and reflection light from the mirror is irradiated to a back face of the glass disk to produce the penetrated light.

4. An optical system of detecting a peripheral surface defect of a glass disk according to claim 3, wherein the glass disk is mounted to a spindle and the mirror is provided at the back face side of the glass disk in an inclined manner along the spindle.

5. An optical system of detecting a peripheral surface defect of a glass disk according to claim 4, further comprising a image-forming lens for receiving the light beams from the outer peripheral chamfered portion, wherein the stop is provided between the light receiver and the image-forming lens.

6. An optical system of detecting a peripheral surface defect of a glass disk according to claim 5, wherein the mirror is constituted by a first mirror and a second mirror, the laser light from the light source is irradiated to the first mirror and reflected there to the second mirror, reflected light from the second mirror is irradiated to the back face of the glass disk and the light source disposed at the back face side in an up-right manner.

7. A device of detecting a peripheral surface defect of a disk for detecting a defect at an outer peripheral surface of the disk comprising: a light illuminating system which irradiates light beams from a back face of a rotating glass disk through an inside of the glass disk on to an outer peripheral chamfered portion at the front face side of the glass disk,a light receiver provided away from the outer peripheral chamfered portion by a predetermined distance anda stop provided in front of the light receiver,wherein the light receiver includes an optical system of detecting the peripheral surface defect which receives the light beams penetrated and refracted at the outer peripheral chamfered portion through the stop.

8. A device of detecting a peripheral surface defect of a glass disk according to claim 7, further comprising: a reference level variation inhibiting circuit that suppresses or cancels out a variation of signal reference level in the received light signal of the light receiver due to shifting of the outer peripheral surface of the disk caused by rotation of the disk,wherein a detection signal for detecting a defect at the outer peripheral surface is obtained based on a signal obtained from the reference level variation inhibiting circuit.

9. A device of detecting a peripheral surface defect of a glass disk according to claim 8, wherein a hole diameter of the stop is selected so as to permit the penetrated light corresponding to the width of the outer peripheral chamfered portion to pass therethrough.

10. A device of detecting a peripheral surface defect of a glass disk according to claim 9, wherein the reference level variation inhibiting circuit includes a filter circuit of either a low pass filter or a band pass filter which passes a signal having a frequency corresponding to the variation of signal reference level, or a high pass filter which prevents the signal having the frequency corresponding to the variation of signal reference level and the detection signal of a defect at the outer peripheral surface is obtained based on a signal obtained after the received light signal has passed through the filter circuit.

11. A device of detecting a peripheral surface defect of a glass disk according to claim 10, wherein the light beams are laser beams, the light receiver is disposed in perpendicular direction with respect to the front face of the disk, the filter circuit includes either the low pass filter or the band pass filter and other high pass filter which removes high frequency noises and a defect detection signal, and the reference level variation inhibiting circuit removes the high frequency noises and the defect detection signal through the other high pass filter and obtains a signal having a frequency corresponding to the variation of the signal reference level as a detection reference signal through the other high pass filter and obtains the defect detection signal with regard to the defect at the outer peripheral surface through comparison of the detection reference signal with the received light signal.

12. A device of detecting a peripheral surface defect of a glass disk according to claim 11, wherein the detection reference signal and the received light signal are inputted to one of a comparing amplifier, a comparator and a differential amplifier and the defect detection signal of a defect at the outer peripheral surface is obtained from an output from the one thereof.

13. A device of detecting a peripheral surface defect of a glass disk according to claim 10, wherein the high pass filter is a band pass filter, the band pass filter eliminates a signal having a frequency due to the shifting of the outer peripheral surface and extracts the received light signal in which signal reference level is smoothened and the detection signal of a defect at the outer peripheral surface is obtained based on the extracted received light signal.

14. A device of detecting a peripheral surface defect of a glass disk according to claim 13, further comprising a comparator and wherein the light beams are laser beams, the light receiver is disposed in perpendicular direction with respect to the front face of the disk, the extracted received light signal is compared by the comparator with a predetermined reference value and the detection signal of a defect at the outer peripheral surface is obtained based on an output signal of the comparator.

15. A device of detecting a peripheral surface defect of a glass disk according to claim 14, further comprising an A/D converting circuit and wherein the defect detection signal is inputted to the data processing device after being converted into a digital value by the A/D converting device and the data processing device judges defects at the outer peripheral surface depending on the level of the defect detection signal and further judges good or no good of the disk based on the number of defects at the outer peripheral surface.

16. A device of detecting a peripheral surface defect of a glass disk according to claim 9, further comprising a image-forming lens for receiving the light beams from the outer peripheral chamfered portion, wherein the stop is provided between the light receiver and the image-forming lens.