JPH0334578B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a surface defect inspection device for inspecting defects such as damage occurring on the surface of a video disc, for example. [Technical Background of the Invention and Problems thereof] Conventionally, the surface inspection of a video disk has generally been carried out 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 an 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. This is how it was done. 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 it has not been possible to significantly improve efficiency. [Object of the invention] The present invention enables automatic detection of not only the presence or absence of any defects but also the type thereof.
It is an object of the present invention to provide a surface defect inspection device that has high inspection ability and enables a significant improvement in inspection efficiency. [Summary of the Invention] In order to achieve the above object, the present invention receives reflected light from the surface of an object to be inspected, detects the received light level as well as the amount and direction of change in the light receiving position, and determines the above received light level. Compare it with the normal level to determine whether it has increased or decreased, compare the amount of change in the light receiving position with a preset reference value to detect the amount of change, and determine the direction of change in the light receiving position. Based on these three determination results, the presence or absence of a defect and its type are determined. [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. Video disc 1 is
It is placed on an inspection table 3 and 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 disk 1 is received by a position detector 6 made of a semiconductor position detection element (PSD). The position detector 6 is provided with electrodes at opposing positions on the 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 output from the position detector 6 is separately amplified by an amplifier circuit 7 and then supplied to an addition circuit 8 and a subtraction circuit 9, respectively. The adder circuit 8 mutually adds the respective light reception signals, and the addition output, that is, a signal corresponding to the total light reception level of the reflected light 4b at the position detector 6 is sent to the light reception level determination circuit 10.
is supplied to. This received light level determination circuit 10
are two comparators 11, 1 that compare the level of the addition output with a preset reference level B1.
It has 2. When the addition output level is at the reference level B1, the comparator 11 generates an output at the "H" level, and when the addition output level is at the reference level B1, the comparator 12 generates an output at the "H" level. Here, the above reference level B1
is set to the addition output level when there are no defects on the surface of the video disc 1. Therefore, each output of the comparators 11 and 12 indicates an increase or decrease in the received light level. Further, the received light level determination circuit 10 leads the outputs of the respective comparators 11 and 12 to an exclusive OR circuit 13, and from this circuit 13 the outputs of the comparators 11 and 12 are connected to
When the outputs of 1 and 12 are both at the "H" level, a "L" level signal is output. After this signal is inverted by an inverter 14, it is supplied to a decoder 40, which will be described later, as a signal indicating that the received light level has not increased or decreased (no change signal). Note that 15 and 16 in the figure indicate the respective comparators 11 and 16 during the period when the no-change signal is generated.
This is an AND gate for preventing the output of No. 12 (“H” level) from being output to the decoder 40. On the other hand, the subtraction circuit 9 calculates the difference between the respective light reception signal outputs of the position detector 6, and changes the difference output, that is, a signal indicating a change in the light reception position of the reflected light 4b on the light reception surface of the position detector 6. It is supplied to the quantity determination circuit 20. 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 reference level B2 is reached, an "H" level output is generated from the comparator 21, and when the difference output reference level B2 is, an "L" level output is generated from the comparator 22, and these outputs are used to reflect changes in the light receiving position. It is supplied to the decoder 40 as a signal indicating whether the amount is large or small. Further, the change amount determination circuit 20 compares the difference output of the subtraction circuit 9 with "0" in comparators 23 and 24, and leads each output to an exclusive OR circuit 25, so that the difference output is "0". '', that is, when there is no change in the light receiving position, the exclusive OR circuit 25 generates an "L" level signal. After this signal is inverted by the inverter 26, it is supplied to the decoder 40 as a signal with no change in the light receiving position. In addition, 27,2 in the figure
8 is an AND gate for preventing the outputs of the comparators 21 and 22 from being supplied to the decoder 40 when the 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 is composed of a sample and hold circuit 31 and two comparators 32 and 33. has been introduced.
Then, these comparators 32 and 33 compare it with "0", and if the sample hold output is positive, the comparator 32 outputs a "H" level signal, and if it is negative, the comparator 33 outputs a "H" level signal.
"H" level signals are outputted from the decoder 40, and these signals are supplied to the decoder 40. The decoder 40 is configured, for example, by a logic gate circuit, and detects surface defects on the video disc 1 based on the respective outputs of the received light level determining circuit 10, the light receiving position change amount 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 determination results 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.

〔Effect of the invention〕

As detailed 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 based on these determination results, the presence or absence of defects on the surface of the object to be inspected is determined. This system automatically detects the presence or absence of any defects, as well as the types of defects, such as foreign objects with low or high reflectance, scratches, bulges, and dents, and has high inspection capabilities. Moreover, it is possible to provide a surface defect inspection device that can significantly improve inspection efficiency.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration 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.
The figure is a schematic diagram showing the state of reflection of laser light on the surface of a video disc. Figures 3a and b and Figures 6 a and b are schematic diagrams showing the state of reception of reflected light on the light receiving surface of the position detector. Figure 4 and FIG. 7 is a waveform diagram showing the output signal of the subtraction circuit. 1... Video disk, 2... Laser device, 3
...Inspection table, 4a...Laser light, 4b...Reflected light, 5...Half mirror, 6...Position detector, 7
...Amplification circuit, 8...Addition circuit, 9...Subtraction circuit, 10...Received light level judgment circuit, 20...Change amount judgment circuit, 30...Change direction judgment circuit, 40...
…decoder.

Claims (1)

[Claims] 1. An irradiation optical system that irradiates the surface of the object to be inspected with spot light while moving it relative to the surface of the object to be inspected, and electrodes provided at opposing parts of the light-receiving surface, and these electrodes detect the reflected light of the spot light from the surface of the object to be inspected. a position detector that receives light and outputs each light reception signal from each of the electrodes according to the amount of light received, an adding circuit that adds and outputs each light reception signal output from this position detector, and an output from the position detector. a subtraction circuit that obtains the difference output of each received light signal; and a subtraction circuit that compares the addition output level of the addition circuit with a first reference level when no defect exists in the object to be inspected to determine whether there is an increase or decrease. A light reception level determination circuit compares the difference output level of the subtraction circuit with a second reference level when there is no change in the light reception position of the spot light received by the position detector, and determines the amount of change in the light reception position. a change direction determination circuit that determines the change direction of the light receiving position of the spot light received by the position detector; the received light level determination circuit; the change amount determination circuit; and the change direction A surface defect characterized by comprising a discrimination circuit that receives each judgment result of the judgment circuit and judges whether the surface defect of the object to be inspected is at least one of a foreign object with a low or high reflectance, a scratch, a bulge, or a dent. Inspection equipment.