JPH0979988A - Surface defect inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface defect inspecting device for preventing the contract of an image decreasing and for performing more precise and efficient inspection. SOLUTION: Light with a specific shading pattern is applied to a surface 3 to be inspected by a lighting device 1, the surface 3 is arranged so that the image can be picked up by a video camera 2, and the image is outputted to an image processing device 5 which is controlled by a host computer 6 and is displayed by a monitor 7. By controlling the lighting device 1 according to the curvature of the surface to be inspected, the contrast of the image, namely the brightness difference between a defect and its surrounding, increases, thus easily detecting the defect and achieving a more efficient inspection since a larger light can be used and further saving power since a surplus light source can be turned off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspecting apparatus for inspecting a surface defect of an object to be inspected, for example, a surface defect such as unevenness of a painted surface of an automobile body.

[0002]

2. Description of the Related Art As a conventional surface defect inspection apparatus, there is one disclosed in, for example, Japanese Unexamined Patent Publication No. 5-045142.

These project a predetermined light and dark stripe pattern on the surface to be inspected, and when there is a defect such as unevenness on the surface to be inspected, the difference in brightness (luminance) or the brightness (luminance) due to the defect.
This is a method of detecting a defect on the surface of the surface to be inspected by differentiating the received light image having a change.

[0004]

However, in the conventional surface defect inspection apparatus, for example, the coating surface of the automobile body is formed of a curved surface. Therefore, as shown in FIG. 1, in order to illuminate the same area, a curved surface requires more illumination than a flat surface (L1 <L2). That is,
Even if the angle of view of the image pickup means 102 is the same, the larger the curvature R of the surface 100 to be inspected, the larger the illumination required to illuminate the image pickup range. However, in the case of detecting a defect by utilizing irregular reflection of light due to an uneven defect, the larger the illumination, the smaller the difference in brightness between the defect and the surroundings (this is referred to as contrast in this specification). Therefore, it becomes difficult to find the defect. Therefore, in the prior art, since the flat surface and the curved surface were illuminated by the same and single illumination,
Since the contrast at the defect is reduced, the defect detection accuracy is reduced. On the contrary, if the illumination is downsized to increase the contrast, the imaging range is naturally narrowed and the inspection efficiency is lowered.

The present invention has been made in view of such conventional problems, and provides a surface defect inspection apparatus capable of preventing deterioration of image contrast and performing more precise and efficient inspection. The purpose is to

[0006]

In order to solve the above-mentioned problems, the present invention irradiates a surface to be inspected with light, creates a light-receiving image based on the light reflected from the surface to be inspected, and receives the light-receiving image. In a surface defect inspection apparatus for detecting a defect on a surface to be inspected, an illumination means for displaying a predetermined bright and dark pattern on the surface to be inspected and a lighting position of the illumination means according to the curvature of the surface to be inspected are controlled. Illumination control means, image pickup means for converting a light-receiving image obtained by picking up the surface to be inspected on which the bright and dark pattern is projected into image data of an electric signal, and image data obtained by the image pickup means for processing to detect defects. Defect detecting means for detecting

[0007]

According to the present invention, a predetermined light-dark pattern is projected on the surface to be inspected by the illumination means, and the light-dark pattern is imaged by the image pickup means to convert the light-dark pattern into image data of electric signals. At that time, the illuminating means turns on only the part necessary for illuminating the imaging range of the surface to be inspected, and the defect is detected by processing the image data thus obtained.

Further, the illumination means is controlled at a predetermined timing according to the curvature of the surface to be inspected, and the illumination means is controlled according to the curvature of the surface to be inspected obtained by the curvature measuring means.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 11 is a claim correspondence diagram showing the functional blocks of the present invention.

In FIG. 11, reference numeral 100 denotes a surface to be inspected, for example, a coated surface. Reference numeral 101 denotes an illuminating device that projects a predetermined bright and dark pattern on the surface to be inspected, and is, for example, an illuminating device shown in FIG. The illumination control means 104 performs predetermined control on the illumination means. Also, 1
Reference numeral 02 denotes an image pickup means for picking up an image of the surface to be inspected and converting the light-dark pattern into image data of an electric signal, for example, a CCD
A video camera such as a camera. Further, 103 is a defect detection unit that processes the image data obtained by the image pickup unit to detect a defect, and is composed of, for example, a computer.

The above-described structure corresponds to, for example, the embodiment described later with reference to FIGS.

The illumination control means is controlled at a predetermined timing according to the curvature of the surface to be inspected.

Alternatively, the illumination control means is controlled based on the measurement result of the curvature measuring means for measuring the curvature of the surface to be inspected.

FIG. 2A is a diagram showing an embodiment of the present invention.

In FIG. 2A, reference numeral 1 denotes an illuminating device, which is arranged so as to irradiate the surface 3 to be inspected with light of a predetermined bright and dark pattern. 1'is a lighting control device. Reference numeral 2 is a video camera (for example, a CCD camera), which is arranged so as to capture an image of the surface 3 to be inspected on which the light and dark patterns are displayed. Further, 4 is a camera control unit, in which an image signal of a light-receiving image captured by the video camera 2 is generated and output to the image processing device 5. Reference numeral 6 denotes a host computer, which has a function of externally displaying or outputting control of the image processing apparatus 5 and processing results. A monitor 7 displays a screen imaged by the video camera 2.

FIG. 3 is a block diagram showing the configuration of the image processing apparatus 5.

In FIG. 3, an image signal from the camera control unit 4 is sent to an A / D converter via a buffer amplifier 8.
It is converted into a digital value by the converter 9. Also, MPU
The (microprocessor) 10 performs predetermined calculation, processing, etc. on the image data. Reference numeral 11 denotes a memory that stores image data and processing results, and the processing results and the like can be output to the monitor 7 via the D / A converter 12 and displayed.

FIG. 4 is an exploded perspective view showing details of the illuminating device 1. In the present embodiment, description will be made assuming that a black and white stripe pattern illumination is used.

In FIG. 4, reference numeral 1a is a light source, and in the case of a fluorescent lamp, for example, it is turned on by a high frequency or direct current lighting power source (not shown). The light from the light source 1a is diffused by the diffuser plate 1b and applied to the surface to be inspected. The diffusion plate 1b is, for example, like frosted glass, and uniformly irradiates the surface 3 to be inspected with light. The stripe pattern may be formed by sticking a matte black tape or the like on the diffusion plate 1b at predetermined intervals, or by forming a slit in front of the diffusion plate. Therefore, by configuring the illuminating device in this way, a bright and dark (black and white) stripe pattern can be projected on the surface 3 to be inspected (see FIG. 2).

Next, the operation of the present embodiment will be described. In addition,
This embodiment corresponds to the block diagram of FIG.

If light and dark stripes are projected on the surface 3 to be inspected shown in FIG. 2, and there is a defect 13 in the bright portion of the stripe and a defect 13 'in the dark portion, the received light image is As shown in FIG. 5A, the irregularities of the defects cause irregular reflection of light, so that the defect 13 appears as a dark spot in the bright portion of the stripe and the defect 13 ′ appears as a bright spot in the dark portion of the stripe.

In the light-receiving image of FIG. 5A, when the coordinate axes x and y are taken with the upper left of the screen as the origin, the defects 13 and 13 'are obtained.
The luminance level in the x direction at is as shown in FIG. Note that in FIG. 5B, the large unevenness corresponds to the bright portion and the dark portion of the stripe, and the fine unevenness is noise. Then, the defects are shown as unevenness larger than noise in the unevenness of the stripe.

The image processing apparatus 5 takes in a light-receiving image as shown in FIG. 5A as a signal SO of the original image.
For example, when the image signal from the video camera 2 is A / D converted and the brightness level is converted to a digital value of 8 bits, as shown in FIG.
Is white at the maximum value, 0 is black, and one screen is 512 x 480.
When captured at pixel resolution, the horizontal axis is 0-512
Of pixels. It should be noted that the signal SO shown is a signal for a certain value in the y-axis direction (the value of the portion shown by the dotted line A), and such a signal exists for each value of the y-axis.

Next, the illumination control means will be described with reference to FIG.

FIG. 2A shows an embodiment of the present invention.
9A and 9B are schematic diagrams when this is applied to the coating surface inspection process of an automobile, respectively.

In FIG. 9, a vehicle 14 mounted on a carriage is conveyed in the direction of the arrow by a conveyor. When the painted surface of the vehicle surface is the surface to be inspected 3, the illumination 1 and CC
The D camera 2 is attached and fixed at a predetermined position so as to surround the vehicle 14 as illustrated. That is, the surface of the vehicle being conveyed by the conveyor is inspected as it passes through the arcuately fixed lighting and camera. Camera 2
Since the illumination 1 and the illumination 1 are attached in a direction perpendicular to the vehicle transport direction, the illumination lighting position control is performed in the vehicle transport direction.

As shown in FIG. 2 (a), when the surface 3 to be inspected is relatively flat in the vehicle conveying direction such as a door, if the light source 1a shown by ◯ is turned on, a stripe pattern appears in the visual field of the camera 2. Can be projected. Therefore, the light source 1a (● in the figure) that illuminates other than the field of view of the camera controls the illumination 1 so as to be turned off (light off).

As shown in FIGS. 2B and 2C, the surface 3 to be inspected
In the case where is a curved surface in the vehicle conveyance direction such as a fender, the imaging range of the camera 2 changes according to the curved surface as shown in the figure, and accordingly the lighting position of the light source 1a (◯ in the figure) is controlled.

By performing the control for turning on the light source necessary for illuminating the image pickup range of the camera, the irradiation area of the illumination is reduced and the contrast of the image is improved. Therefore, the image brightness cross-section without control is shown in FIG.
When there is control, the result is as shown in (b), and the brightness difference between stripes is increased by performing illumination control (C OFF <C
At the same time, the change in luminance due to the defect is increased and the SN ratio is improved, so that the defect detection process described later becomes easier.

Next, the defect detecting means will be described with reference to the flowchart showing the processing contents in the image processing apparatus 5 of FIG.

In the image processing apparatus 5, as shown in FIG. 6, from the original image P1, the smoothing process P11 and the enhancement process P are performed.
12, a binarization process P13, labeling, area and barycentric coordinate calculation P16, and area determination process P14 are performed to detect a defect. Further, as will be described later, the area processing P15 may be added as a measure against "discolored skin". Further, as post-processing after detecting a defect as described above, the results are displayed on a monitor or the like at P17 or output to a subsequent device.

The contents of each of the above processes will be described in detail below.

FIG. 7 is a diagram showing each image and its signal (at a certain y-coordinate value, in this example, the value at the portion shown by the dotted line A in FIG. 5). The contents of image processing will be described below with reference to FIG.

First, the original image S20 is subjected to a smoothing process (smoothing) of a predetermined mask size, and only a minute luminance change component due to noise or the like is removed to obtain S21. This smoothing processing is, for example, a simple averaging filter that obtains an average value of the brightness values of the pixel of interest and pixels in the vicinity thereof and sets it as a new brightness value of the pixel of interest. The mask size of the smoothing filter at this time may be determined according to the size of the noise (number of pixels) generated in the original image.

Next, the area in which the luminance changes is emphasized by emphasizing the processing in S21. This emphasis process is, for example, a differential process, and is the sum of absolute values of differential results in the x and y directions,
Alternatively, if the square root of the sum of squares is taken and all the brightness change regions are output to the positive (+) side, the result is as shown in S22.

When the result of S22 is binarized so that the brightness change region is white ("255") and the others are black ("0") with a predetermined threshold Th, the result is S23. S23
As shown in the binary image of No. 2, a region having a brightness change such as a defective portion and a stripe boundary portion is extracted.

Although the boundary line of the stripe is distorted and extracted depending on the condition of the surface to be inspected, it is extracted as one continuous region by smoothing the original image as described above. There is almost no side effect. However, in the vicinity of the boundary line of the stripe, there is a possibility that noise due to the "discolored skin" of the surface to be inspected may remain. Therefore, in order to remove it, area processing is performed. That is, S23
By performing a process of enlarging a white area (corresponding to a portion having a change in brightness) in the image, the stripe boundary area and the noise due to "yellow skin" are combined into one area. Thereafter, in order to restore the area to the original width, contraction processing opposite to the expansion may be performed.

Based on the binary image S23 thus obtained, labeling (labeling) of the brightness change region,
Perform area calculation and barycentric coordinate calculation. The area of each part is determined based on the result of the area calculation. As is clear from the image in S23, the area (size) of the defective portion is significantly smaller than the area of the stripe boundary portion, and therefore the defect processing is performed by performing a determination process such as determining a region having a predetermined area or less as a defect. Only can be extracted. The area determination result is as shown in S24, and it is possible to detect both the defect that appears black in the bright portion and the defect that appears white in the dark portion of the bright-dark stripe image. However, since the defect detection cannot be performed in the bright / dark boundary portion (the portion where the brightness changes), in order to inspect the entire surface to be inspected, the object to be inspected or the illumination means and the imaging means are sequentially moved, and the light / dark boundary is detected. Other parts are configured to scan the entire surface to be inspected. In this embodiment, the object to be inspected (vehicle) as shown in FIG.
Is moved, and the illumination means and the imaging means are fixed at such positions as to scan the entire surface to be inspected.

Next, as post-processing after the defect detection is completed as described above, the host computer 6 identifies, positions and ranks the defects based on the results, and uses them for display devices, printers and the like. Output to the output device. Alternatively, if there is a defect, control the line such as switching the inspection object from a normal line to a repair-only line (for example, in the case of a car body painting process, only the defective part is repair-painted), or the defect rank. (size),
It may be used for statistical processing of the occurrence location. next,
An example of the illumination control means will be described.

As shown in FIG. 9, the shape of the vehicle 14 is known in advance, the fender portion has a large curvature, and the door portion is almost flat. Therefore, in the present embodiment, information on the transport speed or conveyor speed of the vehicle is fetched, the current imaging range of the camera 2, that is, the vehicle position is calculated, and, for example, the imaging range moves from a fender to a portion such as a door where the curvature of the surface to be inspected changes. Switch the lighting position of the lighting at the timing. Taking the vehicle side surface (upper side in the figure) of FIG. 9A as an example, first, since the front fender as shown in FIG. 2C is reflected in the camera 2, the light source 1a indicated by a circle in the figure is turned on.
I do. Next, the illumination 1 is switched to the lighting position as shown in FIG. 2A at the timing when it is reflected on the door from the front fender. Next, at the timing of moving from the door to the rear fender, the illumination 1 switches to the lighting position as shown in FIG.
Finally, when the inspection is completed, that is, when the vehicle has passed the visual field of the camera 2, the illumination 1 is switched to the lighting position as shown in FIG. 2C in preparation for the next vehicle inspection.

Next, another embodiment of the illumination control means will be described.

In the present embodiment, as shown in FIG. 10, the curvature of the surface 3 to be inspected is measured by using the curvature measuring means, and the illuminating device 1 is controlled based on the measurement result. The curvature measuring means is, for example, a displacement sensor or a distance measuring sensor. As shown in the figure, the two sensors 15 measure the distance to the imaging range of the camera 2, that is, when the surface to be inspected is flat, the distance d1 = It is attached and fixed parallel to the position of d2. The illumination control device 1'reads the measured values of the two sensors, obtains the curvature from the difference d2 of d1, and determines the direction of the curved surface (difference between (b) and (c) of FIG. 2) from the magnitude of d1 and d2. Then, the lighting position of the lighting device 1 is controlled.

Therefore, even if the curved surface is attached differently depending on the type of vehicle, it is possible to perform appropriate lighting control.

[0045]

As described above, according to the present invention, since the illumination device is controlled according to the curvature of the surface to be inspected, the contrast of the image, that is, the difference in brightness between the defect and its surroundings is reduced. Since it becomes large, defect detection becomes easier. Moreover, since a large-sized illumination can be used, more efficient inspection is possible. Further, since the extra light source is turned off, there is an effect that power saving can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between an illumination area and a curvature.

FIG. 2 is an explanatory diagram showing an embodiment of a surface defect inspection apparatus according to the present invention.

FIG. 3 is a block diagram of an image processing apparatus in this embodiment.

FIG. 4 is an exploded perspective view of the lighting device according to the present embodiment.

FIG. 5 is a diagram showing a received light image and its image signal in the present embodiment.

FIG. 6 is a flowchart showing the processing contents in the present embodiment.

FIG. 7 is a correspondence diagram showing an image and its image signal in each processing of the present embodiment.

FIG. 8 is a correspondence diagram for explaining the effect of illumination control in the present embodiment.

FIG. 9 is a top view (a) and a side view (b) when the present embodiment is applied to an automobile body coating inspection line.

FIG. 10 is an explanatory view showing another embodiment of the surface defect inspection apparatus according to the present invention.

FIG. 11 is a functional block diagram showing a surface defect inspection apparatus according to the present invention.

[Explanation of symbols]

 1 Lighting Device 1a Light Source 1b Diffusion Plate 1'Lighting Control Device 2 CCD Camera 4 Camera Control Unit 5 Image Processing Device 6 Host Computer 7 Monitor 8 Buffer Amplifier 9 A / D Converter 10 MPU 11 Memory 12 D / A Converter 13, 13 'Defect 14 Vehicle 15 Sensor

Claims (3)

[Claims] 1. A surface defect inspection apparatus for irradiating a surface to be inspected with light, forming a light-receiving image based on light reflected from the surface to be inspected, and detecting defects on the surface to be inspected based on the light-receiving image. In, the illumination means for displaying a predetermined light and dark pattern on the surface to be inspected, the illumination control means for controlling the lighting position of the illumination means according to the curvature of the surface to be inspected, the surface to be inspected on which the light and dark pattern is projected. It is characterized by further comprising: image pickup means for converting a light-receiving image obtained by image pickup into image data of an electric signal; and defect detection means for processing the image data obtained by the image pickup means to detect a defect. Surface defect inspection device. 2. The surface defect inspection apparatus according to claim 1, wherein the illumination control means is controlled at a predetermined timing according to the curvature of the surface to be inspected. 3. The surface defect inspection apparatus according to claim 1, wherein the illumination control unit is controlled based on a measurement result of a curvature measuring unit that measures a curvature of a surface to be inspected. .