JPS6010104A - Defect detecting device - Google Patents

Abstract

PURPOSE:To enable accuracy and rapid detection of a surface defects, by memorizing an image signal of a work and operating a difference of the image signal obtained by slight change of an optical distance and the memorized one. CONSTITUTION:A ray of light is projected from a downward illuminating source 4 onto a video-disc on a support and its reflected light is formed on a real image forming plane 22 of a ITV camera 23 and its image is displayed on a monitor 26. When a flow is found by driving a work support 2 and scanning is performed all over the disc 1, then the scanning is stopped. A light source 17 is turned out, a ray of light from a laser 10 is projected onto an inspection plane 19 of the work and a mirror 15a through collimator lens 11 and beam splitter, and its interference image is formed on the splane 22. Its image signal is stored in a memory of an image processing unit 25 and a difference of the image signal issued when the surface mirror 15 is given with inching displacement by a micro- feed mechanism and the memorized signal is operated in an image analyzing unit 6 for tabe representation 26 and thus, a surface defect can be detected with high accuracy and rapidity.

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a defect inspection device used for detecting, for example, surface defects in shape. [Technical background of the invention and its problems] In recent years, video disks and multi-density recording disks for audio have been developed as image and audio recording media, but these disks are different from conventional music disks. The rotation speed is significantly faster than that of a record disc (for example, 900
rpm), or for example S2C (Single Car
Since the discs are recorded using a special method called the Rier Composite method, defects such as scratches and distortions on the disc, especially defects in shape, are extremely important problems in playing back video Shingetsu etc. with -111 accuracy. Become. Here, the above-mentioned defect in shape was detected when the disk material (PVC+L@'1.', t,
For example, the diameter D = 30 to 400 μm and the height H = 0.5.
It forms a mountain shape consisting of ~27zm. Therefore, in the past, the inspection worker inspected the meat
Defects are detected by thoroughly examining the surface shape of the disk using nine mirrors. However, such conventional methods are not suitable for testing. The quality of inspection was low, and inspection work required both skill and a great deal of time. Also,
In such a punch inspection with the naked eye, it was difficult to grasp the three-dimensional shape of the IP"≦-shaped defect. Moreover, it is an object of the present invention to provide a defect inspection device that can perform inspection with high accuracy and grasp the three-dimensional shape of defects. At the same time, the optical distance for obtaining the interference optical image is slightly changed, and the image signal of the interference optical image obtained at this time is stored in the image memory. By calculating the difference between the image and the captured image, it is possible to obtain a high-quality interference image without image noise and improve surface defect detection accuracy. [Example of the invention] □ Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.As shown in FIG. a mounting mechanism (2) capable of setting an angle of 11° at an arbitrary position; and an interference optical section disposed above the mounting mechanism (2) for obtaining an interference optical image of the video disc (1). (3) and regular gold 4
An epi-illumination unit (4) for obtaining an observation image of the video disk (1) similar to a microscope, and these interference optics j5Il (3
) and an epi-illumination unit (4), an image processing unit (5) that displays the image obtained from K, and an image analysis unit (6) that analyzes the image displayed in the outside LJ unit (5). ). The above-mentioned object mechanism (2) includes a mounting table (7) on which a video disc (11) is placed, and a video disc (1) placed on the mounting stage (7). Positioning device for positioning in the circumferential direction and radial direction (+
:Kl not shown). Further, the interference light beam 4 (3) is generated by a laser light source (10) installed such that the optical axis (8) is parallel to the defect inspection surface (9) of the video disc (1). (

[Collimator lens (II) that adjusts the laser beam from the Ol to the required diameter and parallelism; The laser beam transmitted through the surface 021 enters the beam splitter (!4), which splits the beam in the direction in which it is reflected on the surface (12) and enters the defect inspection surface (9) from above, and the laser beam is transmitted through the fine movement mechanism (14). A surface mirror that moves back and forth along the axis 191K (
The objective lens (161) is arranged above the beam splitter (I) and receives the laser beam reflected from the defect inspection surface (9) and the laser beam from the two-sided mirror a4. The defect inspection surface (9) and the mirror surface (15a) of the front mirror (151) are arranged symmetrically with respect to the plane 0 which is included in the beam splitter (13J).
Therefore, the laser beam reflected on the defect inspection surface (9) and the laser beam reflected on the mirror surface (15a) are mixed and interfere with each other. That is, the defect inspection surface (9
) and the optical distance from the surface (1z to the mirror surface (15a)). This is to realize a symmetrical arrangement on the order of wavelength.On the other hand, the epi-illumination section (4) includes a light source (17) such as a tungsten lamp or a halogen lamp, and this light source 117.
) collector lens (1→
Field lens #1 converts the light flux converged by this collector lens 08 into a parallel light flux, and the direction of the light flux exiting this field lens 4 is perpendicular to the inspection surface (9) K. The image display section (5) is arranged on the optical axis 0υ on the light output side of the objective lens across the half mirror pane to form a real image. an industrial television (ITV) camera (c) that converts the real image formed on the surface C! into a video signal SA; and an ITV camera (2)
A camera controller C14) that drives and controls the camera and inputs video signals; an image processing device (c) that is electrically connected to this camera controller (24) and performs various processing on the video signal SA; and this image processing device - an ITV monitor (2) that displays the processed video signal. As shown in FIG. 2, the image processing device (25) is electrically connected to the camera controller e4 and operates in modes M1, M2. An input selector switch (27) that can switch in three directions for M3, an image memory (c) whose input side is connected to mode M2 in mode M2, and Can be switched in 3 directions, mode M2 is image memory (to)
The output of (Jilt) and the mode M1 is the input selector switch (271), the output selector switch Chi is connected to the mode M1, and the input terminal is the bias setting circuit (to) 1
Image memory (c) output side and input selector switch (goods)
an operational amplifier 01) connected to mode M3 of the output selector switch and having an output terminal connected to mode M3 of the output selector switch;
It consists of a feedback switch 04 whose input side is connected to the output side of the operational amplifier 0) and whose output side is connected to the input side of the image memory (2). Therefore, the image memory (to) stores the video signal 8A output from the camera controller as an analog signal,
It may be of a type that outputs this analog signal to the operational amplifier C3), or it may be of a type that performs analog-to-digital (A/D) conversion on the video signal SA and stores and outputs this digital value. . Correspondingly, the operational amplifier c31) may also be an analog arithmetic unit or a digital arithmetic unit. This operational amplifier C1l+
is set to add the bias signal SB output from the bias setting circuit (to) and the stored video signal SC output from the image memory (c), and to subtract the actual video signal 8A from these sums. has been done. Further, the image analysis section (6) is electrically connected to the image memory (E). This image analysis section (6) is, for example, a microcomputer having calculation and storage functions, and is designed to automatically determine defects. Next, the operation of the defect inspection apparatus of this embodiment will be described. First, the input changeover switch 0η is set to mode M1, and the output changeover switch (c) is set to mode M1. Then, the light source (171) is turned on and the luminous flux is transferred to the collector lens t18.
1. The image is projected onto the video disk (1) on the stage (7) via the field lens, half mirror (A), objective lens (16) and beam splitter Q31. At this time, the reflected light from the video disc (1) is transmitted through the beam splitter (13), the objective lens ue, and the half mirror.
The real image formed on the real image forming surface (2) of the ITV camera (c) is converted into a video signal SA and sent to the monitor (a). The image is displayed on the video disc (1) by driving the loading mechanism (2) while looking at this monitor.
) Scan the entire surface. At this time, if a bulging defect is found on the monitor (c), the scanning is stopped and the bulging defect area is brought into the field of view of the monitor (c). Set. Next, the light source (”η
At the same time, the laser beam from the laser light source Ql is projected onto the beam splitter 0 via the collimator lens Uυ. Then, as shown in FIG. 3, on the one hand, the laser beam B is reflected vertically downward and projected onto the defect inspection surface (9) of the video disc (1). The projected laser beam BI is reflected vertically upward on the defect inspection surface (9), and the reflected beam B is transmitted through the collimator lens <11) and the half mirror (toward), and is transmitted through the ITV
The image is formed on the real image forming surface (22) of the camera (c).
On the other hand, the laser beam B is transmitted through the surface (9),
K is incident on the front surface of the mirror (15a). This mirror surface (1
The laser beam Bi is reflected at 5a), and the reflected light Bm is reflected vertically upward at the surface (L2) and forms an image on the real image forming surface (2-axis) via the half mirror. Therefore, as mentioned above, the defect inspection surface (9) and the mirror surface (15a)
are disposed at symmetrical positions with respect to the plane 02 of symmetry, so the light beams Br and Bm interfere with each other, and an interference optical image is formed on the real image forming surface (2). And S
/N (Signal To Nolse) ratio is not good, but until the pitch and direction of the stripes are the desired shape,
The fine movement mechanism I moves the surface *ttS forward and backward along the optical axis (8). By the way, FIG. 4(a) shows the illuminance distribution on an arbitrary line segment within this interference optical image, and this actual illuminance F(X, Y) can be expressed as follows. F (x, y) = N (x, y) + I (x, y) ----
-■ However, N(X, y) is the illuminance of the noise image, as shown in FIG. 4(b). In addition, I(x, y) is the illuminance of the interference fringe, which can be expressed by 2〇 (
(See Figure 4(C)). I(x,y)=Co+Ct"d(x+y)""'
■However, Co, C, are constants, and d(x, y) is the optical distance from the surface (121) to the defect inspection surface (9), and the optical distance from the surface 0 to the mirror surface (15a). This is the round-trip difference between
At the same time, the output selector switch (2) is switched to mode M2, and the video signal SA stored in the image memory (to) is stored as the video signal SC in the steady state. Output and display on the monitor (c) as Next, after switching the input changeover switch C2n to mode M3 and the output changeover switch (2nd floor) to mode M3, slightly move the front mirror (a) using the micromovement switch (1 (1)), and turn on the operational amplifier (31). Then, input the video signal SA of the fine movement image from the camera controller (24) and the stored video signal 8C from the image memory (2 types. Then, from this operational amplifier 131), the stored video signal SC and ii
The bias signal 8B output from the bias setting circuit C effect J is added, and the output image 16 (81) obtained by subtracting the stored image coefficient SC from the sum is sent to the monitor (2).
G) and output it to ii! Display the iI image. By the way, the fourth
Figure (d) shows the illuminance distribution on an arbitrary line segment in the interference optical image obtained after tracing, and the illuminance F(x,
y) can be expressed by the formula (■). F”(x,y)=N(x,y)+I+(x,y)++
++■ However, N(x, y) is the illuminance of the noise image υ, which is shown in FIG. 4(b). In addition, I"(x, y) is the illuminance of the interference fringe after the slight movement, and can be expressed by equation (2) (see FIG. 4(C) and (e)). I"(x, y) =C(, +and”(x, y)
−, ■ However, co and c are constants. Also, d”
(x, y) can be represented by two circles. d”(x,y)=d(x,y)+Δd(x,y)...
・・■However, d(x, y) is the plane l12, similar to the formula ■
The optical distance from to the defect inspection surface (9) and the surface (121
This is the round-trip difference between the optical distance from the mirror surface (15a) to the mirror surface (15a). Further, Δd(x, y) is a change in optical distance due to micromovement. Here, if Δd(x, y) is selected to be an odd multiple of a half wavelength, an image of only interference fringes without a noise image can be obtained. That is, the illuminance distribution ΔF on an arbitrary line segment of the difference image obtained from the output video signal SD can be obtained by equation (2). ΔF=F(x, y)−F'(x, y)...
・■This formula■ is calculated by formula■and formula■ΔF=(N(x, y)+I(x, y))−(N
(x, y) + I" (x, yl = engineering (x, y) - engineering 4
I(x, y)...■. Here, Δd(x,
When y) is an odd multiple of a half wavelength, equation (2) can be transformed as shown in the following equation. "(x+y) =Co"-C1ctad(x, y)
, -, , ■ However, co and CI are constants. Therefore, the expression can be rewritten as the expression ■ by combining the expression ■ and the expression ■. ΔF=2C, cosd(x, y)+(Co-Co”)
------ ■ In this formula ■ s Co Co >
2'-1, that is, the bias signal SB is set so that the result of the difference is always positive. Then, the difference image on the monitor (a) is shown in Fig. 4 (f).
As shown in the figure, the resulting interference image has unnecessary interference fringes and image noise removed. When the difference image with the best contrast is obtained, the feedback H is closed, the difference image at this time is stored in the image memory (to), and this tmin! The difference image stored in the memory (c) is displayed on the monitor Qυ. Thus, the cyst-like defect on the defect inspection surface (9) can be identified easily and reliably with the naked eye by the differential image on the monitor (a). Incidentally, Figure 5 is a raw interference optical image with a cyst-shaped defect in the center without the above-mentioned difference processing, but the interference fringe pattern is unclear, and the left side and bottom edge in particular are affected by noise. It is impossible to separate the interference fringes. Therefore, it becomes extremely difficult to identify the bulging defect image located within the circle (P) in FIG. On the other hand, in FIG. 6, difference processing has been performed on the image in FIG. 5, but image noise has been completely removed and only interference fringes have been extracted. Thus, the sac-like defect within the circle (Q) in FIG. 6 can be clearly identified from the distortion of the interference fringes. It should be noted that 1.
The image coefficient of the difference image is output from the image memory (to) to the image analysis unit (6), and this image analysis unit (6) performs, for example, binarization of the illuminance of the interference fringes, and converts this binarized data. Determination of the presence or absence of a cystic defect, quantitative shape estimation, etc. may also be performed. In the above embodiment, a laser light source is used as the light source of the interference optical section (3), but the invention is not limited to this, and for example, a halogen lamp and an interference filter for obtaining monochromatic light may be used in combination. It's okay. Furthermore, a half mirror may be used in place of the beam splitter a. Furthermore, the projection direction of the laser beam onto the video disc (1) is not limited to the vertical direction shown in FIG. The reflected light beam Br and the video disc (1
) may be caused to interfere with the laser beam Bj that does not hit the laser beam Bj. Furthermore, since the epi-illumination section is only for improving the efficiency of defect inspection work, it is not necessarily necessary to provide it if workability is not important. Furthermore, instead of slightly moving the surface mirror 09 side in the interference optical section (3), the stage (7) side may be slightly moved in the vertical direction (optical axis eυ direction). Further, the defect inspection apparatus of the present invention is not limited to video disks as the object to be inspected, and may be any object as long as it has a flat surface, and the object to be inspected is not limited to bulging defects. It can be used in a wide range of applications, such as detecting surface distortions and concave defects. [Effects of the Invention] Since the defect inspection device of the present invention removes image noise and extracts only necessary interference fringes, the detection accuracy and calibration efficiency of surface defects and bulging defects are greatly improved. .

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram of a defect inspection device according to an embodiment of the present invention, Fig. 2 is an electric circuit diagram of the image processing device shown in Fig. 1, and Fig. 3 shows the direction of projection of a laser beam onto an object to be inspected. Figure 4 (a), (b), (C)l (d), (e>,
<r> is a diagram showing the relationship between the inspection position and illuminance to explain the image processing performed in the image processing unit, FIG. 5 and @6
The figure is an image diagram for explaining image processing, and FIG. 7 is a diagram showing the projection direction of the laser beam onto the object to be inspected in another embodiment of the present invention. (1): Video disc (object to be inspected) (3): Interference optics section (5): Image processing section (1 unit: Fine movement mechanism (light path adjustment section) Agent: Patent attorney Noriyoshi Chika (and 1 other person) T 3 Figure! Y2 Figure Army 4 Figure

Claims (1)

[Claims] An interference optical section that projects light onto Table 1 (11) of the object to be inspected to obtain reflected light and obtains an interference optical image from this reflected light and the light projected onto the test rod; an optical path adjustment unit that changes the optical distance of the optical path to be generated; and an optical path adjustment unit that converts the interference optical image into a video signal and
1tlAI A defect inspection apparatus characterized by comprising: an image processing MIA section that calculates the difference in the video signal of the interference optical image before and after the change in the optical distance p11 due to the active part and generates a differential video signal. σ.