JPS6069539A - Inspecting device for surface defect - Google Patents

Abstract

PURPOSE:To improve inspection ability and inspection efficiency by deciding on the photodetection level of reflected light from a body to be inspected and the extent and direction of a displacement in photodetection position, and discriminating whether a surface defect of the body to be inspected is present or not and its kind on the basis of said decision results. CONSTITUTION:A video disk 1 is set on an inspection table 3 and rotated at a constant speed, and its surface is irradiated with laser light 4a from a laser device 2. Its reflected light 4b is photodetected by a position detector 6 continuously, and amplified by an amplifying circuit 7 and processed by the addition and subtraction of an adding circuit 8 and a subtracting circuit 9 respectively to detect the photodetection level and displacement in photodetection position. Then, a pohotodetection level decision circuit 10 decides on the photodetection level obtained by the adding circuit 8. A displacement extent decision circuit 20, on the other hand, decides on the signal which is obtained by the subtracting circuit 9 and shows the displacement in photodetection position. Further, a displacement direction decision circuit 30 decides on the displacement in photodetection position. A decoder 40 discriminate on whether a defect is present or not and its kind on the basis of the respective decision results.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface defect inspection apparatus for inspecting defects such as scratches occurring on the surface of a video disc, for example.

[Technical background of the invention and its problems]

Conventionally, the surface of a video disc has generally been inspected by an inspector visually or using an optical instrument such as a microscope. However, such inspections have the drawback that the inspection accuracy varies greatly, and it requires skill and a lot of time to perform accurate inspections, resulting in very low inspection efficiency.

Therefore, automatic inspection devices have recently been developed, and one of them is one that determines the presence or absence of defects by detecting changes in the amount of light reflection on the surface of an object to be inspected. This device scans the surface of the object to be inspected with coherent light such as a laser beam, receives the reflected light with a photodetector with a limited light receiving area, and determines the presence or absence of defects based on the level of the received light. It was designed to do so. With such a device, if there is a scratch or foreign object on the surface of the object to be inspected, for example, the reflected light will cause diffuse reflection and the received light level will drop, so by detecting this drop in the received light level, The presence of the above-mentioned flaws and foreign matter can be recognized, and inspection thereof can be carried out automatically and efficiently.

However, although such conventional devices can detect defects that cause diffused reflection, they cannot determine the type of defects, and they cannot detect defects such as irregularities that are difficult to cause diffused reflection at all. I can't. For this reason, the inspection ability is low, and in order to compensate for this, it is necessary to use the above-mentioned visual inspection and microscopic inspection in combination, and a significant improvement in efficiency has not been achieved.

[Purpose of the invention]

An object of the present invention is to provide a surface defect inspection device that can automatically detect not only the presence or absence of any defect, but also the type thereof, and which has high inspection ability and enables a significant improvement in inspection efficiency. shall be.

[Summary of the invention]

In order to achieve the above purpose, the misfiring EA receives the reflected light from the surface of the object to be inspected, detects the received light level as well as the amount and direction of change in the light receiving position, and compares the received light level with the normal level. The amount of change in the light receiving position is compared with a preset reference value to detect the magnitude of the change, and the direction of change in the light receiving position is determined. The presence or absence of a defect and its type are determined based on the two determination results.

[Embodiment of the Invention] FIG. 1 is a schematic configuration diagram of a surface defect inspection apparatus according to an embodiment of the present invention, in which 1 is a video disk as an object to be inspected, and 2 is a laser device as an inspection light source. It shows. The video disc 1 is placed on an inspection table 3 and is rotated by this inspection table 3. On the other hand, the laser device 2 is configured to move in the diametrical direction of the video disc 1 by a moving mechanism (not shown), and irradiates the surface of the video disc 1 with a laser beam 4a via a half mirror 5.

Now, the reflected light 4b of the laser light 4a from the surface of the video disc 1 is received by a position detector 6 consisting of a cow-specific position detection element (PSD).

This position detector 6 has electrodes provided on opposite sides of a light receiving surface, and outputs a light receiving signal from these electrodes at a level corresponding to the receiving position of the reflected light on the light receiving surface. Each light reception signal outputted from the position detector 6 is separately amplified by an amplifier circuit 7 and then supplied to a power-log calculation circuit 8 and a subtraction circuit 9, respectively. The adder circuit 8 mutually adds the above-mentioned light reception signals, and the addition output,
In other words, a signal corresponding to the listening/receiving level of the reflected light 4b at the position detector 6 is supplied to the light receiving level determining circuit 10. This received light level determination circuit 10 has two circuits (D: FF 7 H L/- 11, 12) that compare the level of the addition output with a preset reference level B1. When the reference level is BJ, the comparator 1) generates an output of the ``H'' level, and when the addition output level<the reference level B, the comparator 12 generates an output of the 1H'' level. Here, the reference level B1 is set to the addition output level when there is no defect on the surface of the video disc 10. Therefore, the comparator 11,1
Each output of 2 indicates an increase or decrease in the received light level.

In addition, the received light level determination circuit 10 guides the outputs of the comparators 11 and 12 to an exclusive OR circuit 13, and when the outputs of the comparators 11 and 12 are both at the @H" level, L L L level signal is output.

After this signal is inverted by an inverter 14, it is supplied to a decoder 4Q, which will be described later, as a signal indicating that the received light level has not increased or decreased (no change signal). In addition,
In the figure, 15', 1611f, . . . are AND gates for preventing the outputs (1H level) of the comparators 11 and 12 from being output to the decoder 40 during the period in which the no-change signal is generated.

On the other hand, the subtraction circuit 9 calculates the difference between the respective light reception signal outputs of the position detector 6.
A signal indicating a change in the light receiving position of the reflected light 4b on the light receiving surface is supplied to the change amount determining circuit 2°. This change amount determination circuit 20 has two comparators 21 and 22 that compare the difference output with a preset reference level B2. Then, when the difference output is at the reference level B2, a 1H" level output is generated from the comparator 2, and when the difference output is at the reference level B2, an "L" level output is generated from the comparator 22, and these outputs are applied to the light receiving position. large amount of change,
/JX is supplied to the decoder 40 as a signal indicating /JX.

The change amount determination circuit 20 compares the difference output of the subtraction circuit 9 with "0" using comparators 23 and 24, and leads the valley output to the exclusive OR circuit 25, so that the difference output becomes "0". 0'', that is, when there is no change in the light receiving position, this exclusive OR circuit 25 generates a 1L level signal.After this signal is inverted by the inverter 26, it is determined that there is no change in the light receiving position. It is supplied to the decoder 40 as a signal.

Note that 27 and 28 in the figure are AND gates for preventing the outputs of the comparators 21 and 22 from being supplied to the decoder 40 when the above-mentioned no-change signal is generated.

Further, the difference output of the subtraction circuit 9 is also supplied to a light receiving position change direction determining circuit 30.

This change direction determination circuit 30 includes a sample hold circuit 3
1 and two comparators 32 and 33, the sample and hold circuit 31 samples and holds the difference output at a predetermined period, and the hold output is sent to each comparator 32.
, 33. Then, compare these comparators 32 and 33 with 10'', and if the sample hold output is positive, the comparator 32 outputs a ul level signal, and if it is negative, the comparator 33 outputs an ``H'' level signal. It outputs signals and supplies these signals to the decoder 40.

The decoder 40 is constructed of, for example, a logic gate circuit, and detects surface defects on the video disc 10 based on the outputs of the received light level determining circuit 10, the amount of change in light receiving position determining circuit 20, and the change direction determining circuit 30. The presence or absence of defects and, if any, the type thereof are determined, and the results of this determination are output as a signal from the corresponding output terminal.

The following table shows the relationship between the types of defects determined by this decoder 40 and the inputs.

Next, the operation of the apparatus configured as described above will be explained according to the inspection procedure. First, a video disc 1 as an object to be inspected is set on the inspection table 3 and rotated at a constant speed. and,
A laser beam 4a is generated from a laser device 2 and irradiated onto the surface of the video disc 1, and the irradiation position t is moved stepwise in the diametrical direction every time the video disc 1 rotates once. That is, the entire surface of the video disc 1 is scanned by the laser beam 4a.

Then, the reflected light 4a reflected by the surface of the video disc 1 due to this scanning is continuously received by the position detector 6, and the received light signal is amplified by the amplifier circuit 7 and then sent to the adder circuit 8 and the subtracter circuit 9. The reflected light 4 at the position detector 6 will be added and subtracted, respectively.
Changes in the light reception level of light 4b and the light reception position of reflected light 4b are detected. Of these detection outputs, the received light level obtained by the addition circuit 8 is determined by the received light level determination circuit 10 to detect whether the received light level has increased or decreased compared to the received light level when there is no defect. It is determined whether there is any.

On the other hand, the change direction determination circuit 20 determines whether the level of the signal representing the change in the light receiving position obtained by the subtraction circuit 9 is larger or smaller than a predetermined reference value B2, or whether there is no change.

At the same time, the signal representing the change 7 in the light receiving position obtained by the subtraction circuit 9 is used to determine whether the change in the light receiving position is in the positive direction or in the negative direction by the change direction determining circuit 30.

Once the determination is made, the decoder 40 determines whether or not there is a defect and, if there is a defect, the type thereof, based on the above-mentioned determination results.

For example, in the case of a scratch, as is clear from the above table, the received light level decreases and it is determined that there is no change in the light receiving position, so it can be determined based on the occurrence of these determination outputs. By the way, if the judgment is made only by the conventional light-receiving label, the light-receiving level will decrease even if foreign matter with low reflectance is attached to the disc surface.
It is not possible to distinguish between foreign objects with low reflectance and scratches.

Furthermore, if a bulge (convex portion) exists on the surface of the video disc 1, it is not determined as a change in the light reception level, but as shown in FIG. 2, the direction of reflection of the reflected light 4b changes due to the bulge. This appears as a change in the light receiving position on the light receiving surface of the position detector 6 as shown in FIGS. 3(a) and 3(b).

In the case of this bulge, the direction of change of the light receiving position is the fourth one.
As shown in the figure, it first changes in the positive direction.

Therefore, a bulge can be determined from the amount and direction of change in these light receiving positions. On the other hand, in the case of a dent (concavity), since the direction of change in the light receiving position first changes in the negative direction as shown in FIG. 7, it can be determined from this determination result and the amount of change 7 in the light receiving position. Note that FIG. 5 is a diagram showing the reflection state in the case of the above-mentioned depression, and FIG. 6 is a diagram showing the change in the light receiving position.

In this way, in this embodiment, not only the light reception level but also the amount of change in the light reception position and the direction of change are determined, and the presence or absence of a defect and the type of defect are determined from a combination of these determination results. Therefore, it is possible to accurately determine the type of defect without overlooking even the slightest defect. Furthermore, in this case, the entire process can be automatically inspected without requiring any visual inspection or microscopic inspection by skilled inspectors, thereby greatly increasing inspection efficiency. Being able to perform highly accurate inspection efficiently in this way is extremely effective in investigating the causes of defects and establishing preventive measures.

Note that the present invention is not limited to the above embodiments.

For example, each of the determination circuits 10, 20, 30 and the decoder 40 may be replaced with a microcomputer, and the valley/foot 1 discrimination may be performed by software processing.

Further, in the above embodiment, the determination of the received light level is performed by increasing, decreasing,
Although the determination was made for three types of no change, the amount of increase and amount of decrease in the received light level may also be determined together.

The same holds true when determining the amount of change in the light receiving position. In this way, it becomes possible to perform even more types of defect determination. In addition, the inspection light may be light from a white light source other than laser light, and a four-split sensor may be used as the position detector. In addition, the configuration of the Aiko circuit system, the configuration of the valley determination circuit, the configuration of the discrimination circuit, the type of object to be inspected, etc. may be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

As described in detail above, according to the present invention, the level of light reflected by the object to be inspected, the amount of change in the light receiving position, and the direction of change are determined, and defects on the surface of the object to be inspected are determined based on these determination results. By determining the presence or absence of a defect and the type of defect, it is possible to automatically detect not only the presence or absence of any defect but also the type, resulting in high inspection ability and a significant improvement in inspection efficiency. A surface defect inspection device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a surface defect inspection device according to an embodiment of the present invention, FIGS. 2 to 7 are diagrams used to explain the operation of the device, and FIGS. Schematic diagram showing the state of reflection of laser light on the surface, Figure 3 (
a), (b) and Fig. 6 (a), (b) Schematic diagrams showing the reception state of reflected light on the light receiving surface of the U position detector, Fig. 4 and Fig. 7 show the output signal of the subtraction circuit. FIG. 1...Videotisf, 2...Laser device, 3...
・Inspection table, 4a...Laser light, 4b...Reflected light, 5
.... Half mirror 16...position detector, 7...amplification circuit, 8...addition circuit, 9...subtraction circuit, 10...light reception level judgment circuit, 20...change amount judgment circuit, 3o・
...Changing direction determination circuit, 40...Decoder. Applicant's representative Patent attorney Takehiko Suzue Figure 2 Figure 3 (a) (b) 4th leap No. 57 (a) (b) Figure 7

Claims (1)

[Claims] An irradiation optical system that irradiates the surface of the object to be inspected with a spot light while moving it relative to the surface of the object to be inspected; and 2. Receives the reflected light of the spot light from the surface of the object to be inspected and detects the amount and direction of change in the received light level and light receiving position, respectively. a light reception detection circuit,
A received light level determination circuit that compares the received light level detected by the received light detection circuit with a normal level and determines whether there is an increase or decrease, and a standard that presets the amount of change in the received light position detected by the received light detection circuit. a change amount determination circuit that determines the magnitude of the change amount by comparing it with a value; a change direction determination circuit that determines the direction of change in the light reception position detected by the light reception detection circuit; these received light level determination circuits, and the amount of change. q! of the judgment circuit and change direction judgment circuit! rA discrimination circuit that discriminates surface defects of the inspected object based on the judgment results? A surface defect inspection device characterized by: