JP3185599B2 - Surface defect inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an 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, for example, JP-A-2-73139 and JP-A-5-45142 are known.
For example, there is one disclosed in Japanese Patent No. 45144. These show a predetermined light and dark fringe (stripe) pattern on the surface to be inspected, and when there is a defect such as unevenness on the surface to be inspected, a received light image having a difference in brightness (brightness) and a change in brightness (brightness) due to the defect. Is differentiated to detect a defect on the surface of the surface to be inspected.

[0003]

However, the conventional surface defect inspection apparatus as described above detects a defect by processing a received light image as an independent still image for each screen. Therefore, if noise occurs in the received image, it may be erroneously detected as a defect.If the object to be inspected moves, it may be affected by the influence of the timing of capturing the received image. There is a problem that the defect is not reflected in the received light image, and the detection of the defect may be missed.

The present invention has been made to solve the problems of the prior art as described above, and there is no possibility of erroneous detection or omission of detection, and accurate defect detection is performed even when the surface to be inspected is a curved surface. It is an object of the present invention to provide a surface defect inspection apparatus that can perform the inspection.

[0005]

In order to achieve the above object, the present invention is configured as described in the appended claims. FIG. 1 is a diagram corresponding to the claims of the present invention. In FIG. 1, reference numeral 100 denotes a surface to be inspected, for example, a painted surface. Reference numeral 101 denotes an illuminating unit that projects a predetermined light-dark pattern (light-dark stripe pattern) on the surface to be inspected, and is, for example, an illuminating device shown in FIG. 9 described later (details will be described later). Reference numeral 102 denotes an imaging unit that images a surface to be inspected and converts the light-receiving image of the light and dark pattern into image data of an electric signal, for example, a video camera such as a CCD camera. Reference numeral 103 denotes a driving unit that drives the received light image obtained by the imaging unit 102 to sequentially move on the surface to be inspected in a predetermined direction at a predetermined speed. This driving means 1
Reference numeral 03 may be a device that moves only the object to be measured (the surface to be inspected 100) with the illumination unit 101 and the imaging unit 102 fixed, for example, an inspection line such as a belt conveyor that carries the object to be measured and moves. Alternatively, the object to be measured (inspection surface 100) may be fixed, and the illumination unit 101 and the imaging unit 102 may be moved. In general, it is structurally easier to move the object to be measured. However, if the object to be measured is difficult to move with a large-sized device, the lighting unit 101 and the imaging unit 102 may be moved as a set. You may comprise. The above-mentioned predetermined direction is, for example, x
Not only in one direction such as the x direction in y orthogonal coordinates,
It may be one that moves in both the x and y directions and sequentially scans the entire wide inspection surface. Further, the predetermined speed is
Normally, it is easier to perform subsequent signal processing at a certain speed, but any speed can be applied as long as the speed of change is known or measurable. Also,
Numeral 104 denotes an arithmetic unit for detecting a defect on the surface to be inspected from the received light image obtained by the imaging unit 102. This arithmetic means 10
4 is composed of, for example, a computer. The defect detected by the arithmetic unit 104 is displayed on a display unit (not shown) (for example, the monitor 7 in FIG. 2) or input to a subsequent control device (for example, a coating control device) for use.

[0006]

As described above, in the present invention, the illuminating means 1 is used.
In step 01, a predetermined light and dark stripe pattern is projected on the surface 100 to be inspected, and the light and dark stripe pattern is converted into electric signal image data by the imaging means 102. Then, the driving unit 103 drives the light receiving image obtained by the imaging unit 102 so as to sequentially move on the surface to be inspected in a predetermined direction at a predetermined speed. Then, the arithmetic unit 104 performs image processing on a plurality of temporally different images obtained by the imaging unit 102, that is, a moving image, and detects a defect. For example, as described in claim 5, at least the moving amount of the moving object in the image is detected from the moving image, and the theoretical moving amount corresponding to the moving speed in the driving unit 103 and the moving amount of the moving object in the image are determined. A moving object that matches within a predetermined error range is determined to be a defect.

The above-mentioned theoretical movement amount is the amount of movement between a light receiving image at a certain point in time and the next light receiving image when the surface to be inspected moves at the moving speed of the driving means. Is considered to move by the theoretical movement amount on the received light image. At that time, the image of the light and dark stripe pattern,
Always stay in the same place and do not move. Therefore, a defect can be detected by detecting a moving object having a movement amount substantially equal to the theoretical movement amount. As described above, since the defect is detected by processing the moving image and detecting the moving object, there is no possibility that the erroneous detection due to noise or the omission of the defect detection due to the position or movement of the defect occurs. . However, as will be described in detail in the section of Examples below, when the surface to be inspected 100 is not flat but has a curved portion, the received light image of the imaging unit 102 is distorted at the curved portion. As a result, the bright and dark stripe pattern at that portion may move, and the portion may be erroneously determined to be defective.

In order to solve the above-mentioned problem, in the first aspect of the present invention, the image pickup means 102 is formed by using unequally spaced stripe patterns corresponding to the surface to be inspected.
The light and dark stripe pattern in the received light image obtained in step (1) is made substantially uniform regardless of the curvature of the surface to be inspected. Specifically, for example, as described in claim 2, the illumination unit 101 emits light of a bright and dark stripe pattern toward the surface to be inspected, and the interval between the stripe patterns is The stripe pattern in the light-receiving image obtained by the imaging unit 102 is set so that the part farthest from the installation position of the imaging unit 102 is the largest, the middle part is the smallest, and the nearest part is the middle size between the two. Are set to be substantially uniform regardless of the curvature of the surface to be inspected. This configuration corresponds to, for example, the embodiment of FIG. 9 described later. In claim 3,
The curvature of the surface to be inspected is detected, and the interval between the stripe patterns is changed unequally according to the curvature, so that the interval between the stripe patterns in the received light image obtained by the imaging means 102 is substantially uniform regardless of the curvature of the surface to be inspected. It is set to become. This configuration corresponds to, for example, an embodiment of FIG. 12 or FIG. 13 described later. According to the fourth aspect of the present invention, the curvature of the surface to be inspected is detected, the angle of illumination with respect to the surface to be inspected is changed in accordance with the curvature, and the interval between the stripe patterns in the light-receiving image obtained by the imaging means 102 is obtained. Are set to be substantially uniform regardless of the curvature of the surface to be inspected. This configuration corresponds to, for example, an embodiment of FIG. 11 described later.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
FIG. 2 is a diagram showing one embodiment of the present invention. In FIG. 2, reference numeral 1 denotes an illumination device, which is arranged so as to irradiate the surface 3 to be inspected with light having a bright and dark stripe pattern. Reference numeral 2 denotes a video camera (for example, a CCD camera or the like), which is arranged to capture an image of the inspection surface 3 on which a bright and dark stripe pattern is projected. Reference numeral 4 denotes a camera control unit, which generates an image signal of a received image picked up by the video camera 2 and outputs the image signal to the image processing device 5. Reference numeral 6 denotes a host computer, which has a function of controlling the image processing apparatus 5 and displaying or outputting processing results to the outside. Reference numeral 7 denotes a monitor which displays a screen captured by the video camera 2 and the like. As will be described in detail later, the inspection surface 3 is moved at a predetermined speed in a predetermined direction by a moving device (for example, an inspection line 15 in FIG. 22 described later).

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 converted into a digital value by an A / D converter 9 via a buffer amplifier 8. Further, an MPU (microprocessor) 10 performs a predetermined operation, processing, and the like on the image data. Reference numeral 11 denotes a memory for storing image data and processing results.
It can be output to the monitor 7 via the / A converter 12 and displayed.

Next, FIG. 4 is an exploded perspective view showing the details of the lighting device 1. In the present embodiment, description will be made assuming that illumination of a light and dark stripe pattern is used. In addition,
The configuration shown in FIG. 4 shows a basic structure when the surface to be inspected is a plane. In FIG. 4, reference numeral 1a denotes a light source, the light of which is diffused by a diffusion plate 1b and radiated to a surface to be inspected through a stripe plate 1c.
The diffusion plate 1b is, for example, like frosted glass,
Light is uniformly applied to the surface 3 to be inspected. Stripe plate 1c
Is a transparent or diffuser plate with black stripes at predetermined intervals. When the surface 3 to be inspected includes a curved surface, as shown in FIG.

FIG. 5 is a perspective view showing an example of an illumination device when the diffusion plate 1b is not used. In FIG. 5, if the light source 1a is a light source that generates light diffused in advance, such as a general fluorescent lamp, the same stripe light as described above can be obtained by making the background 1d black. Therefore, by configuring the illumination device in this manner, a bright and dark (black and white) stripe pattern can be projected on the surface 3 to be inspected.

Next, the principle of displaying a defect on the surface of an object to be inspected in a received light image using the above-described stripe illumination will be described with reference to FIGS. 6 and 7. FIG. In FIG. 6, it is assumed that there is a convex defect 13 on the surface 3 to be inspected.
Point P1 is an arbitrary point on a normal surface without defects, and point P2 is an arbitrary point on defect 13. When the defect 13 is convex as shown in the figure, each of the arbitrary points on the defect 13 has an angle between a tangent line of the point and a normal surface to be inspected. I do. In this case, the vicinity of the defect 13 and the point P1 is within the bright stripe of the stripe illumination (the part irradiated with light).
It is assumed that When an angle between the video camera 2 and the surface 3 to be inspected is an incident angle θi, a point P which is a normal plane
At 1, the light is specularly reflected (θi), and there is a bright portion of the stripe illumination in that direction, so that the point P 1 is projected by the video camera 2 as a bright (white) portion. However, at the point P2 on the defect 13, the incident light from the video camera 2 is not specularly reflected but irregularly reflected due to the inclination angle θ, and there is a black stripe in that direction, so that the point P2 is projected black by the video camera 2. Assuming that the irregular reflection angle at this time is θh, the defect point P
2, the angle (incident angle) in a certain direction of the video camera 2 is θi, so that θh = θi + 2θ (Equation 1) (see FIG. 7). That is, in the direction of the angle θh, a bright (white) portion of the stripe is projected white, and a black portion of the stripe is projected black (dark). Also,
As described above, since the light is specularly reflected on the normal plane, it can be expressed as θh = θi (Equation 2). Therefore, from the formulas (1) and (2), the irregular reflection due to the defect can be expressed as 2θ based on the regular reflection direction θi.

In the above description, the video camera 2 is used as a starting point, but the same applies to the case where the lighting device 1 is used as a starting point. FIG. 7 shows a point P on the right slope of the defect.
This is an example of a case where P2 is present, but the description is omitted because the concept is the same when P2 is on the left slope.
Contrary to the above description, it is possible to project a defect white in a stripe projected black on the surface to be inspected using the above principle, but since the light of the illumination device 1 is diffused light, Is bright and not large (it looks dark gray instead of white, and the area of the bright part is small)
Not used in this embodiment.

In the above description, the reason why the defect appears in the received light image is limited to the defective portion. However, the whole received light image falling within the visual field of the video camera 2 will be described below. As shown in FIG. 8A, when the surface 3 to be inspected is a flat surface, if the illuminating device 1 irradiates the stripe light at an equal interval of the pitch p ₀ , the received image of the video camera 2 is always as shown in FIG. Images at equal intervals as shown in (c) are obtained. In this case, even if the inspection surface 3 moves, the position of the stripe in the received light image does not change. However, FIG.
As shown in (b), when the surface 3 to be inspected is a curved surface, when the illumination device 1 irradiates stripe light of equal pitch, the reflection angle changes depending on the curvature R of the surface 3 to be inspected. The image is as shown in FIG. 8D, and the interval between stripes changes. Therefore, if the portion of the inspected surface that enters the visual field of the video camera 2 with the movement of the inspected surface 3 moves from a flat portion to a curved portion or vice versa, the position of the stripe in the received light image changes. Will do. As will be described later in detail, in the present invention, a moving object in an image is detected from a moving image, and a predetermined condition (for example, a moving amount is substantially equal to a theoretical moving amount corresponding to the moving speed of the driving unit) is determined. Since the moving object to be satisfied is determined to be a defect, if the position of the stripe changes as described above, there is a possibility that the portion is erroneously determined to be a defect. As a method for solving the above problem, as shown in FIG. 8B, it is conceivable to set the pitch of the stripes in the lighting device 1 so as to gradually decrease in the installation direction of the video camera 2. In FIG. 8B, p ₃ > p ₂ > p ₁ , and the pitch p gradually decreases in the installation direction of the video camera 2. In this way, in the case of the leftward downward movement as shown in the drawing, the stripes in the received light image of the portion that falls within the field of view of the video camera 2 can be made substantially equally spaced.

FIG. 9 is a diagram showing an example of a case where all the curved surfaces including the downward slope are supported. As shown in FIG. 9, the plane portion of the inspected surface 3 enters the field of view of the video camera 2 when light B from the central portion of the illumination device 1 enters. In this case, light-receiving images at the same intervals as the stripe pattern irradiated as described above are obtained. Next, when the light A from the right end portion of the illumination device 1 is incident, a curved portion falling to the right in the figure comes into the visual field of the video camera 2 due to the relationship between the incident angle and the reflection angle. In this case, when the equally-spaced stripe pattern is irradiated, the stripe interval of the received image becomes slightly narrower. Next, the curved surface portion falling to the left enters the visual field of the video camera 2 when the light C from the left end portion of the illumination device 1 is incident. In this case, the angle of incidence and the angle of reflection with respect to the surface to be inspected are the largest, so that the interval between the stripe patterns in the received light image is further reduced.

As described above, when the stripe intervals of the illuminating device 1 are equal, the stripe interval in the received light image is the narrowest on the left-downward curved surface, then the right-downward curved surface, and then the plane. Therefore, as shown in FIG.
The stripe spacing in the lighting device 1 is made unequal so as to be the reverse of the above, that is, the portion farthest from the installation position of the video camera 2 is maximized, the portion corresponding to the intermediate plane is minimized, and If the near portion is set to have an intermediate size between the two, the interval between the stripe patterns in the received light image can be made substantially uniform regardless of the curvature of the surface to be inspected. Specifically, for example, the stripe interval of the stripe plate 1c in FIG. 4 may be set so as to be larger, smaller, and middle in the order from the position where the video camera 2 is installed. The plurality of stripes at the portion corresponding to the plane may all be at equal intervals, but at a far portion (the portion corresponding to the curved surface descending to the left in FIG. 9), the distance is gradually increased. In the portion corresponding to the downward-sloping curved surface), the interval is gradually increased as the distance becomes closer. Further, in order to set the actual stripe interval, the stripe interval is set on an experiment or drawing according to the mutual positions of the illumination device 1, the inspection surface 3, and the video camera 2, the expected curvature of the inspection surface, and the like. . With the above configuration, it is possible to accurately detect a defect even on a surface to be inspected, which is a flat surface and a curved surface.

Next, FIG. 10 and FIG.
FIG. 10 is an overall configuration diagram, FIG.
FIG. 3 is a diagram showing a configuration of a part for measuring a curvature of a surface to be inspected.

In this embodiment, the curvature of the surface 3 to be inspected is measured, and the angle of the illuminating device 1 with respect to the surface 3 to be inspected is changed accordingly to make the stripe intervals in the light-receiving image of the video camera 2 substantially equal. It is configured as follows. 10 and 11, 17 and 18
Is a distance sensor (for example, a non-contact distance sensor using an ultrasonic wave or a laser beam), which measures distances h ₁ and h ₂ from a predetermined position to a surface to be inspected. The distance sensor circuit 19 includes:
The curvature R of the surface 3 to be inspected is calculated from the distances h ₁ and h ₂ (the difference Δh = h ₁ −h ₂ ) and the distance L between the distance sensors 17 and 18. That is, when the surface to be inspected is a plane, Δh =
Although it is 0, Δh increases as the curvature R increases. Therefore, the curvature R can be estimated from this value and the interval L. The illumination control device 20 changes the angle between the surface 3 to be inspected and the illumination device 1 in accordance with the curvature R obtained above, and controls the stripe width in the light-receiving image of the video camera 2 to be the most uniform. .

Next, FIG. 12 is a diagram showing a third embodiment of the illuminating device 1 and shows a schematic top view of the illuminating device main body. FIG.
In the figure, 21 and 21 'are double shielding plates, which are installed before the diffusion plate 1b in FIG. At least one of the double shielding plates is arbitrarily movable in the direction of the arrow in the drawing (movable by an arbitrary width for each shielding portion of the shielding plate). In accordance with the curvature measured by the curvature measuring means as shown in FIG. 11, the driving means (not shown) moves the shielding plate 21 or 21 'to control, for example, to form unequally spaced stripes as shown in FIG. I do. In this case, since the stripe interval is changed according to the curvature of the surface to be inspected, it is possible to cope with the curved surface well.

Next, FIG. 13 is a diagram showing a fourth embodiment of the illuminating device 1 and shows a schematic top view of the illuminating device main body. FIG.
In the figure, 22 is a plurality of shielding members, each of which has a shaft 2
The light-shielding member 3 is configured to be rotatable, and these shield members generate stripe light. And FIG.
According to the curvature measured by the curvature measuring means, the angle of each shielding member is rotated by a driving means (not shown) so as to control, for example, to form unequally spaced stripes as shown in FIG. Also in this case, since the stripe interval is changed according to the curvature of the surface to be inspected, it is possible to cope with the curved surface well.

Next, the defect detection processing will be described. Assuming that a bright and dark stripe is projected on the surface 3 to be inspected and that a convex or concave defect 13 exists in the bright portion of the stripe, the received light image is as shown in FIG. 13 is projected black in the bright stripe. Further, as shown in FIG. 15A, when the object to be measured (the surface 3 to be inspected) moves in the direction of the arrow (the x-axis direction in the received light image) in a state where the illumination device 1 and the video camera 2 are fixed, The defect 13 moves to the position 13 '. Therefore, as shown in FIG. 15B, the received light image is an image in which only the defect 13 moves in the x-axis direction while the bright and dark stripes remain stationary. Therefore, a defect can be accurately detected by processing a plurality of continuous light-receiving images and detecting a moving object therein. Note that the same applies to the case where the object to be measured (the surface 3 to be inspected) is fixed and the illumination device 1 and the video camera 2 are moved. However, in general, it is structurally easier to move the object to be measured. However, when it is difficult to move the device under test using a large-sized device, the illumination device 1 and the video camera 2 may be configured to be moved as a set.

Next, a first embodiment of a process for detecting a defect from a moving object on an image will be described. This embodiment is an example of a case where the object to be measured moves at a constant speed in the x-axis direction. Figure 16 is a diagram showing two consecutive frames, i.e. the moving object from the difference image between the image in the image and the time point f _{t + 1} at time f _t, i.e. the method of detecting defects, (a) shows the time f _t , (B) shows the image at time _{ft + 1} , and (c) shows the difference image between them. In the above _ft image and _{ft + 1} image, the defect 13 is y
It hardly moves in the axial direction, and moves only in the x-axis direction. The moving amount and the moving direction thereof, is known from the moving direction and the moving amount of the object to be measured, and a constant sampling intervals of Δt between f _t image and f _{t + 1} images. Therefore, the theoretical movement amount ΔD of the defect 13 in the received image can be easily obtained. Therefore, the moving amount Δd of the moving object obtained from the difference image in FIG. 16C is compared with the theoretical moving amount ΔD, and if the difference between the two is within a predetermined range, the moving object is determined to be a defect. You can judge. Note that the above-described predetermined range (error range) is an error range due to a change in moving speed, a change during image processing, and the like, and may be appropriately set according to the inspection line movement accuracy and the like. Further, if the above comparison is performed in consideration of not only the moving amount but also the moving direction, the inspection accuracy can be further improved.

FIG. 17 is a flowchart showing the sequence of the above-described defect detection method. FIG. 18 is a diagram showing a change in the luminance signal at a certain y value (corresponding to a portion where a defect exists) in the received light image. Hereinafter, the flow of FIG. 17 will be described with reference to FIG. 17, in step S1, reads the image at time f _t. The luminance signal in this case is as shown in FIG.
The light portions of the stripe are at a high level, the dark portions are at a low level, and the defective portions are indicated by recesses in the high level. In step S2, the image at the time point _{ft + 1} is read. In this case, as shown in FIG. 18B, the light and dark positions of the stripe do not change, and only the defect position moves. Next, in step S3,
The difference image | f _{t + 1} −f _t | between the two images is calculated. As described above, since the bright and dark positions of the stripe do not change, only the defective portion remains in the difference image, as shown in FIG. If a slight shift occurs between the light and dark positions of the stripes of both images at the signal processing stage, a thin noise remains at that part as shown in the figure. It can be easily removed by the process of S9.

Next, in step S4, the difference image is binarized at a predetermined threshold value Th. The binarized waveform is as shown in FIG. 18D, and the x and y coordinates of the position expected to be a defect are obtained. Next, in step S5, a movement amount Δy (= y _t −y _{t + 1} ) of the center of gravity position in the y-axis direction is obtained. Next, in step S7, it is determined whether or not the difference between the movement amount Δy and the theoretical movement amount ΔDy in the _y- axis direction is equal to or smaller than a predetermined value. In this case, since the measured object moves only in the x-axis direction, the theoretical movement amount ΔD _y ≒ 0. If “NO” in the step S7, that is, the theoretical movement amount ΔD
_{Since the} signal having a large difference from _y is not a defect, the data is determined one after another, and the process goes to step S8 only for the signal of "YES". In step S8, the amount of movement Δx (= x _t −x _{t + 1} ) of the position of the center of gravity in the x-axis direction is obtained.

Next, in step S9, the movement amount Δx
It is determined whether or not the difference between the distance and the theoretical movement amount ΔD _{x in} the x-axis direction is equal to or smaller than a predetermined value. In this case, the amount of movement of the object to be measured becomes the stoichiometric amount of movement [Delta] D _x. Step S9 in the case of "NO", i.e., a large difference signal between the theoretical amount of movement [Delta] D _x is not a defect, to determine the data one after another, "YE
The process goes to step S10 only for S ".
Narrow noise contrast boundary portions of FIG 18 (d) are the amount of movement [Delta] x ≒ 0, large difference between the theoretical amount of movement [Delta] D _x, therefore, be removed in the process of this step. Next, in step S10, the portion where the difference between the movement amount and the theoretical movement amount is equal to or smaller than a predetermined value in both the y-axis direction and the x-axis direction is stored as defect portion data. As described above, in the present embodiment, a defect is detected by processing a moving image and detecting a moving object. There is no danger of missing detection.

Next, a description will be given of a second embodiment of the processing for detecting a defect. In this embodiment, a motion vector (optical flow) of each frame is obtained from a moving image, and thereby a defect is detected. The brightness at frame coordinates (x, y) at a certain time t in a moving image is represented by f
(x, y, t). Then, assuming that the brightness of the point (x, y) after the time δt for moving by δ _x and δ _{y in the} x direction and the y direction does not change, the following equation (3) holds. f (x, y, t) = f (x + δ x, y + δ y, t + δt) ... ( Equation 3) points to the equation (3) (x, y, t) when Taylor expansion for the following equation (4) below Is obtained.

[0028]

(Equation 4)

Here, if the terms of second order or higher are ignored, the following equation (5) is obtained from the above equations (3) and (4).

[0030]

(Equation 5)

Further, when the object to be measured is moved in the x-axis direction, it hardly moves in the y-axis direction. Therefore, ignoring the y term, the following equation (6) is obtained.

[0032]

(Equation 6)

The following equation (7) is obtained from the above equation (6).

[0034]

(Equation 7)

In the equation (7), ∂f / ∂x: change in brightness in the x direction at the point (x, y) = differentiation of the image f in the x direction ∂f / ∂t: at the point (x, y) Temporal change of brightness = difference between both frames dx / dt: x component of motion vector at point (x, y) Therefore, a motion vector at each point is obtained from the differential image and the difference image. The moving direction of the defect is known (determined by the moving direction of the object to be measured).
Since the moving speed of the (measurement object) is also almost constant and known,
A defect can be detected from the obtained movement vector of the received light image.

FIG. 19 is a flowchart showing the processing sequence when detecting a defect by the above method. FIG.
In 9, first, in step S20, it fetches the original image f _t at time t, in step S21, the time t + 1
The original image _{ft + 1 in} is acquired. Next, step S2
In 2, x-direction differential value of the original image f _t a (∂f / ∂x) determined, in step S23, obtains a difference (∂f / ∂t) of the original image f _{t + 1} and the original image f _t . Next, step S24
Then, from the results of S22 and S23, the motion vector (dx
/ Dt) is calculated by the above equation (7). Next, in step S25, of the motion vectors obtained in step S24, only points having a movement amount (corresponding to movement of the device under test) within a predetermined range in a predetermined movement direction are detected as defects. Next, in step S26, labeling (numbering), area calculation, centroid calculation, and the like of the detected defect are performed.

In the case where there is a processed hole or a design irregularity on the inspection surface of the object to be measured,
Since they also move together in the received light image, they may be erroneously detected as defects. However, while the size of a defect is generally about several mm or less in diameter, the area of a processed hole or an unevenness provided as a design is considerably large, and the shape is predetermined and constant, so that the nature of the defect is small. Can be distinguished from true defects. For example, in the flowchart of FIG. 19, a step of determining only a defect whose area of the defect obtained in step S26 is equal to or smaller than a predetermined value as a true defect may be provided. This process is the same in the flowchart of FIG.

Next, a description will be given of a third embodiment of the processing for detecting a defect. In this embodiment, a disturbance (irregular movement) of a stripe boundary generated when a defect crosses a boundary between light and dark stripes is detected, and a defect is detected based on the detected disturbance. This method is particularly effective in the case of a defect having a small angle that reflects illumination light due to a small angle. FIG.
FIG. 21 is a diagram for explaining a disorder of a stripe boundary line generated when a defect crosses a boundary between light and dark stripes. FIG. 20 is a diagram illustrating a light receiving image when the defect is near the boundary between the stripes. FIG. 21 is a diagram showing a luminance signal of a defective portion (a luminance signal of a broken line portion in FIG. 20A). 20 and 21 (a) to (e) correspond to the same reference numerals. In this case, it is also assumed that the defect 13 moves with the movement of the measured object.

In FIGS. 20 and 21, as shown in FIGS. 20A and 20B, a defect 13 in a white (bright) stripe is shown.
Becomes blacker as it approaches the black (dark) stripes,
It is projected larger. Also, as shown in (b) and (c), when the defect 13 is on the boundary of the stripe, white and black are reversed around the boundary. Further, when the defect 13 moves and enters the black stripe,
As shown in (d) and (e), the defect appears white in the black stripe. In the above operation, the defect 13 shows a constant movement from left to right in the figure, as shown by the broken line B in FIG. However, the stripe boundary traversing the defect behaves as shown by the broken line A in FIG.
Moves from the right to the left in the figure, and shows a movement opposite to the defect. Therefore, since a defect exists at a position moving in a direction different from other positions, a motion vector is extracted from a moving image, and by determining that a defect exists at a position where the stripe boundary has moved in the opposite direction, Defects can be detected. As described above, in the present embodiment, instead of detecting the defect itself, the defect is detected based on the change in the boundary between the light and dark stripes caused by the defect. Even a defect having a shallow angle that cannot be detected can be accurately detected.

Next, the processing for determining the start and end timings of the defect detection processing will be described. This process is to detect the presence or absence of an object to be inspected using the luminance information of the received light image. In the present embodiment, a case where a luminance histogram of the received light image is used will be described. FIG. 22 is a side view showing an outline of an inspection line for an object to be inspected. FIG.
As shown in FIG. 2, when the inspected object 14 moves on the inspection line 15 in the direction of the arrow, the visual field 16
If there is no object to be inspected, a dark background that is not illuminated by the video camera 2 appears, so that the luminance histogram is as shown in FIG. 23A, and the position of the peak value is biased in the dark direction. Further, when the inspection object 14 is present in the visual field, the result is as shown in FIG. 23B, and the position of the peak value is shifted in the bright direction. Therefore, the presence or absence of the object to be inspected can be determined by determining whether or not the luminance value at which the peak value of the luminance histogram occurs is equal to or greater than a predetermined value, and the start and end of the defect detection process are controlled using the result. Can be done automatically. For example, when the inspected object changes from “absence” to “presence”, the defect detection process starts and “presence”
It may be terminated when it changes from “to” to “absent”. With the configuration described above, there is no need to provide a special sensor for detecting the presence or absence of the object to be inspected, and the presence or absence of the object to be inspected can be reliably and easily determined from the received image of the video camera provided for defect detection. And the defect detection processing can be automatically performed only when the inspection object exists.

[0041]

As described above, in the present invention, a defect is detected by processing a moving image and detecting a moving object, so that erroneous detection due to noise, the position of the defect, In addition to eliminating the risk of defect detection being missed due to movement, the illumination device is configured so that even if the surface to be inspected is a curved surface, a constant light and dark pattern can be obtained on the received light image. Can accurately detect defects in
The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of the present invention.

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

FIG. 3 is a block diagram of an example of an image processing apparatus 5 in the embodiment of FIG.

FIG. 4 is an exploded perspective view of an example of the illumination device 1 in the embodiment of FIG.

FIG. 5 is a perspective view of another example of the illumination device 1 in the embodiment of FIG. 2;

FIG. 6 is a view showing the principle of displaying a defect on the surface of an inspection object in a received light image.

FIG. 7 is a view showing the principle of displaying a defect on the surface of the inspection object in a received light image.

FIG. 8 is a diagram for explaining a case where the surface to be inspected is a curved surface.

FIG. 9 shows a first example of the illumination device when the surface to be inspected is a curved surface.
FIG.

FIG. 10 is a diagram showing a second embodiment of the illumination device when the surface to be inspected is a curved surface.

FIG. 11 is a diagram showing a configuration for detecting a curvature of a surface to be inspected.

FIG. 12 is a diagram showing a third embodiment of the illumination device when the surface to be inspected is a curved surface.

FIG. 13 is a diagram showing a fourth embodiment of the illumination device when the surface to be inspected is a curved surface.

FIG. 14 is a diagram showing light and dark stripes and defects in a received light image.

FIG. 15 is a diagram showing the movement of a defect when the surface to be inspected moves.

[16] moving object from the difference image between the image in the image and the time point f _{t + 1} at time f _t, ie illustrates a method of detecting defects.

FIG. 17 is a flowchart illustrating a calculation process according to the first embodiment of the present invention.

FIG. 18 is a diagram showing a luminance signal waveform in the processing of FIG. 17;

FIG. 19 is a flowchart illustrating a calculation process according to the second embodiment of the present invention.

FIG. 20 is a diagram showing a change in a stripe boundary in the third embodiment of the present invention.

FIG. 21 is a diagram showing a change in a luminance signal waveform in FIG. 20;

FIG. 22 is a side view schematically showing an inspection line for an object to be inspected.

FIG. 23 is a characteristic diagram showing a change in a luminance histogram depending on the presence or absence of an object to be inspected.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Illumination device 10 ... MPU 1a ... Light source 11 ... Memory 1b ... Diffusion plate 12 ... D / A converter 1c ... Stripe plate 13 ... Defect 1d ... Background 14 ... Object to be inspected 2 ... Video camera 15 ... Inspection line 3 ... Object Inspection surface 16 ... Video camera field of view 4 ... Camera control unit 17, 18 ... Distance sensor 5 ... Image processing device 19 ... Distance sensor circuit 6 ... Host computer 20 ... Lighting control device 7 ... Monitor 21, 21 '...
Shielding plate 8 Buffer amplifier 22 Shielding member 9 A / D converter 23 Axis

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-171345 (JP, A) JP-A-62-173009 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01N 21/84-21/958

Claims (5)

(57) [Claims] An object to be inspected is irradiated with light on a surface to be inspected, a light-receiving image is created based on light reflected from the surface to be inspected, and a defect on the surface to be inspected is detected based on the light-receiving image. In the surface defect inspection apparatus, illumination for projecting unequally spaced stripe patterns set on the inspected surface so that the intervals between the stripe patterns in the received light image obtained by the imaging means are substantially uniform regardless of the curvature of the inspected surface. Means for imaging the surface to be inspected and converting the received light image into electric signal image data; and the received light image obtained by the imaging means sequentially moves at a predetermined speed in a predetermined direction on the surface to be inspected. A plurality of temporally different images obtained by the imaging means, that is, a moving image, at least a moving amount of a moving object in the image is detected, and a predetermined moving condition is shifted based on the detected moving amount. A surface defect inspection device, comprising: a calculation unit that determines that a moving object is defective. 2. The illumination means emits light of a bright and dark stripe pattern toward a surface to be inspected, and the interval between the stripe patterns is the farthest from the installation position of the imaging means. The portion is the largest, the middle portion is the smallest, and the closest portion is set to have an intermediate size between them, and the interval of the stripe pattern in the received light image obtained by the imaging means is independent of the curvature of the surface to be inspected. 2. The surface defect inspection apparatus according to claim 1, wherein the apparatus is set so as to be substantially uniform. 3. The illuminating means emits light of a bright and dark stripe pattern toward a surface to be inspected, detects a curvature of the surface to be inspected, and generates the stripe according to the curvature. Means for changing the pattern interval at irregular intervals and setting the interval of the stripe pattern in the light-receiving image obtained by the imaging means so as to be substantially uniform irrespective of the curvature of the surface to be inspected. The surface defect inspection apparatus according to claim 1, wherein: 4. A method for irradiating a surface to be inspected of an object to be inspected with light, forming a light-receiving image based on light reflected from the surface to be inspected, and detecting a defect on the surface to be inspected based on the light-receiving image. In a surface defect inspection device, light of a light and dark stripe pattern is emitted toward the surface to be inspected, and the curvature of the surface to be inspected is detected, and the angle of illumination with respect to the surface to be inspected is changed according to the curvature. Illumination means having means for setting the interval of the stripe pattern in the light-receiving image obtained by the imaging means to be substantially uniform irrespective of the curvature of the surface to be inspected; and capturing the light-receiving image by imaging the surface to be inspected. An imaging unit that converts the image data into electric signal image data; a driving unit that drives the received light image obtained by the imaging unit to sequentially move on the surface to be inspected in a predetermined direction at a predetermined speed; Time differences Calculating means for detecting at least the amount of movement of the moving object in the image from the number of images, that is, the moving image, and judging the moving object with the predetermined moving condition as a defect based on the detected amount. Surface defect inspection equipment. 5. The moving means determines that a moving object in which the theoretical moving amount corresponding to the moving speed of the driving means and the moving amount of the moving object in the image match within a predetermined error range is a defect. The surface defect inspection apparatus according to any one of claims 1 to 4, wherein: