JP6863196B2 - Airtightness inspection method and equipment - Google Patents

Description

The present invention relates to a method and an apparatus for inspecting the airtightness of an inspected object by filling the inside of the inspected object immersed in a liquid tank with a pressurized gas and detecting air bubbles leaking from the inspected object. .. In particular, the present invention relates to an airtightness inspection method and apparatus that can accurately detect even if the bubbles leaked from the object to be inspected are small.

For containers that require airtightness, such as gasoline tanks and radiators, it is necessary to inspect whether the airtightness is maintained before shipping the product.
As an airtightness inspection method, a container to be inspected is immersed in a liquid tank and filled with a pressurized gas (for example, compressed air), and leaks from the inspected object when the airtightness is insufficient. A method of inspecting the airtightness of an object to be inspected by detecting air bubbles is known.

Conventionally, in the above airtightness inspection method, air bubbles leaking from an object to be inspected have been detected by an operator visually observing air bubbles floating on the liquid surface of the liquid tank from above the liquid tank. However, such detection of air bubbles by visual observation by the operator has problems that human error is likely to occur and that the burden on the operator is heavy.

Therefore, various methods and devices for optically detecting leaked bubbles using a light source and an imaging device have been proposed (see, for example, Patent Documents 1 to 5).
However, since the methods and devices described in Patent Documents 1 to 5 directly detect by imaging the bubbles themselves, such as receiving scattered light from the bubbles, they are like pinholes generated in an object to be inspected. Very small bubbles leaking from minute holes cannot be detected and may be overlooked.

Japanese Unexamined Patent Publication No. 58-2630 Japanese Unexamined Patent Publication No. 61-148338 Japanese Unexamined Patent Publication No. 4-20831 Japanese Unexamined Patent Publication No. 4-188036 Japanese Unexamined Patent Publication No. 11-264781

The present invention has been made in view of the above-mentioned problems of the prior art, and by filling the inside of the object to be inspected immersed in the liquid tank with a pressurized gas and detecting air bubbles leaking from the object to be inspected. It is an object of the present invention to provide an airtightness inspection method and an apparatus for inspecting the airtightness of an object to be inspected, which can accurately detect even if the air bubbles leaking from the inspected object are small. To do.

As a result of diligent studies to solve the above problems, the present inventors have obtained the following findings.
(1) When air bubbles leaking from the object to be inspected float on the liquid surface of the liquid tank, ripples that spread radially around the surface (position) of the floating liquid surface are generated. Even if the leaked air bubbles are small, relatively large ripples will occur. Therefore, it may be possible to indirectly detect small bubbles by detecting ripples caused by floating bubbles.
(2) When the liquid surface of the liquid tank is irradiated with dot light in advance, when the ripples in (1) above occur, the dot light irradiated on the liquid surface is in the traveling direction of the ripples (the liquid in which bubbles have floated). It changes to a shape extending in a radial direction centered on the area of the surface) and is observed. When the ripple height is high, one dot light is observed in a state of being divided into a plurality of parts along the traveling direction of the ripple because a part of the irradiated dot light is not reflected in the observation direction. Sometimes. Also in this case, considering an aggregate of the divided portions, the aggregate has a shape extending in the traveling direction of the ripples as compared with the shape of one dot light when no ripples are generated. If the shape of the dot light to be irradiated is a circle or a regular polygon, it is easy to recognize the direction in which the dot light extends.
(3) When the dot light of the above (2) is arranged two-dimensionally in a matrix, for example, and irradiated, the dot light extends radially around a common liquid surface region based on the extending direction of the plurality of dot lights. Whether or not it can be determined. When a predetermined number or more of dot lights extend radially around a common liquid surface region, it can be determined that bubbles leaking from the object to be inspected have floated in the common liquid surface region.

The present invention has been completed based on the above-mentioned findings of the present inventors.
That is, in order to solve the above-mentioned problems, the present invention fills the inside of the object to be inspected immersed in the liquid tank with a pressurized gas and detects bubbles leaking from the object to be inspected. An airtightness inspection method for inspecting the airtightness of an object, wherein a light source is arranged above the liquid level of the liquid tank and above the liquid surface to be inspected, and the light source is circular with respect to the liquid level of the liquid tank. Alternatively, the light irradiation step of irradiating the dot light pattern, which is a pattern in which regular polygonal dot lights are arranged in two dimensions, and the extending direction of each dot light constituting the dot light pattern irradiated by the light irradiation step are determined. Of the direction determination step and the extension direction of each dot light determined in the direction determination step, the extension direction of a predetermined number or more of the dot light is centered on a predetermined region of the liquid surface irradiated with the dot light pattern. Provided is an airtightness inspection method comprising a bubble detection step of determining that bubbles leaking from the object to be inspected have floated in the region of the liquid surface at the center in the case of radial light. To do.

According to the airtightness inspection method according to the present invention, in the light irradiation step, the liquid surface of the liquid tank is covered by irradiating a dot light pattern, which is a pattern in which circular or regular polygonal dot lights are two-dimensionally arranged. When ripples are generated due to bubbles leaking from the inspection object, each dot light is changed to a shape extending in the traveling direction of the radial ripples and observed.
Therefore, in the direction determination step, it is possible to visually determine the direction in which each dot light extends, for example.
Next, in the bubble detection step, for example, when it can be visually confirmed that the extending direction of the dot light of a predetermined number or more is radial centering on the predetermined region of the liquid surface irradiated with the dot light pattern, the direction thereof is determined. It can be determined that the reason why the dot light is extended by a predetermined number or more is due to ripples. That is, it can be determined that the air bubbles leaking from the inspected object have floated in the region of the liquid surface which is the center of the radial pattern.
According to the airtightness inspection method according to the present invention, the ripples generated by the bubbles are detected based on the deformation of each dot light constituting the dot light pattern, instead of directly detecting the bubbles themselves, so that the airtightness is leaked from the object to be inspected. Even if the generated bubbles are small, the bubbles can be detected with high accuracy.
In the present invention, the "direction in which each dot light extends" refers to the divided portion when one dot light is observed in a state of being divided into a plurality of portions along the traveling direction of ripples. It means the extending direction of the aggregate (the entire divided part).

Preferably, the imaging step of capturing the dot light pattern irradiated by the light irradiation step is further included, and in the direction determination step, the captured image of the dot light pattern captured in the imaging step is image-processed. The extension direction of the dot light pixel region, which is a pixel region corresponding to each dot light constituting the dot light pattern, is determined, and in the bubble detection step, the extension direction of each dot light pixel region determined in the direction determination step. Of these, when the extending direction of the predetermined number or more of the dot optical pixel regions is radial centered on the predetermined pixel region in the captured image, the liquid surface region corresponding to the center pixel region is covered by the above. It is determined that the air bubbles leaking from the object to be inspected have surfaced.

According to the above preferred method, an imaging step of capturing a dot light pattern is further included, and by performing image processing on the captured image in the direction determination step, a direction in which the dot light pixel region, which is a pixel region corresponding to each dot light, extends. Can be automatically determined for each. Next, in the bubble detection step, when the extending direction of the predetermined number or more of the dot optical pixel regions is radial centering on the predetermined pixel region in the captured image, the predetermined number or more of the dot optical pixel regions are extended. It is possible to automatically determine that the cause is due to ripples. That is, it can be automatically determined that the air bubbles leaking from the inspected object have floated in the liquid surface region corresponding to the radial center pixel region.

Preferably, in the imaging step, the dot light pattern is continuously imaged a plurality of times, and in the direction determination step, the captured images of the dot light pattern captured a plurality of times are binarized and combined. A digitized composite image is generated, and the extending direction of each dot optical pixel region in the generated binarized composite image is determined.

According to the above preferred method, the dot light pattern is continuously imaged a plurality of times in the imaging step, and the captured images of the dot light patterns captured a plurality of times are binarized in the direction determination step. Since the area of the liquid surface irradiated with the dot light is brighter than the area of the liquid surface not irradiated with the dot light, the dot light pixel area corresponding to the dot light in the captured image is also brighter (increased in density), and is predetermined. The dot optical pixel region can be extracted by binarizing with the threshold value (concentration) of.
However, each of the extracted dot optical pixel regions may extend differently depending on the progress of ripples at the time of imaging. That is, although it depends on the exposure time of the imaging means used in the imaging process, the length of the dot light pixel region (in the extending direction) corresponding to the dot light irradiated to the region of the liquid surface where the ripples have just passed during imaging. Compared to the length), the length of the dot light pixel area (length in the extending direction) corresponding to the dot light applied to the area of the liquid surface where the ripples have not yet reached at the time of imaging, and the ripples already appear at the time of imaging. The length (length in the extending direction) of the dot light pixel region corresponding to the dot light applied to the region of the liquid surface that has passed may be small.
Therefore, in the above preferred method, a binarized composite image is generated by synthesizing a plurality of binarized captured images (binarized images) in the direction determination step. In other words, the logical sum (OR) of each corresponding pixel is calculated for the plurality of binarized images, and the calculation result is the density of each corresponding pixel in the binarized composite image. The dot light pixel region in this binarized composite image is less affected by the progress of ripples during imaging than the dot light pixel region in a single binarized image, and any dot light pixel region can be used. , There is a high possibility that it is in an extended state due to ripples. Therefore, in the above preferred method, it is possible to accurately determine the extending direction of each dot optical pixel region in the binarized composite image in the direction determination step.

Preferably, in the direction determination step, the contour length of each of the dot optical pixel regions in the binarized composite image is equal to or greater than a predetermined value, and the contour is an approximate ellipse or the long side of the circumscribing rectangle. A dot optical pixel region whose short side is equal to or greater than a predetermined value is extracted, and the direction of the long side of the approximate ellipse or circumscribing rectangle of the contour of each extracted dot optical pixel region is the extending direction of each extracted dot optical pixel region. In the bubble detection step, among the extending directions of the extracted dot optical pixel regions, the extending direction of a predetermined number or more of the dot optical pixel regions is the predetermined pixel region in the binarized composite image. When it is radial at the center, it is determined that bubbles leaking from the object to be inspected have floated in the area of the liquid surface corresponding to the pixel area at the center.

According to the above preferred method, in the direction determination step, the dot optical pixel region in which the contour length is equal to or greater than a predetermined value and the long side / short side of the contour approximate ellipse or circumscribing rectangle is equal to or greater than a predetermined value. Is extracted. In other words, it is highly possible that each dot optical pixel region in the binarized composite image is in an extended state due to ripples (because it is in an extended state, the contour length is predetermined. Only the dot optical pixel region, which is equal to or greater than the value and whose contour approximate ellipse or circumscribing rectangle has a long side / short side equal to or greater than a predetermined value, is used to calculate the extending direction.
Therefore, in the above preferred method, in the direction determination step, it is accurately determined that the direction of the approximate ellipse of the contour of each extracted dot optical pixel region or the long side of the circumscribing rectangle is the extending direction of each extracted dot optical pixel region. It is possible to do.

In the above preferred method, various methods can be considered as a method for determining whether or not the extending direction of the dot optical pixel region is radial around a predetermined pixel region in the binarized composite image. For example, , The following methods can be exemplified.
That is, preferably, in the bubble detection step, each dot optical pixel region extracted in the binarized composite image is included, and the contour direction of each dot optical pixel region is longer than the long side of the approximate ellipse or the circumscribing rectangle. A determination pixel region that is long and longer in the short side direction than the short side of the approximate ellipse or circumscribing rectangle of the contour of each dot light pixel region is specified for each of the extracted dot light pixel regions, and the dot light When a predetermined number or more of the determination pixel regions specified for each pixel region have overlapping pixel regions, the liquid surface region corresponding to the overlapping pixel regions leaks from the object to be inspected. It is determined that the bubbles that have emerged have surfaced.

According to the above preferred method, in the bubble detection step, each extracted dot light pixel area is wider than the dot light pixel area (longer in the long side direction than the long side of the approximate ellipse of the contour or the circumscribing rectangle, and moreover. (Longer in the short side direction than the short side of the approximate ellipse of the contour or the circumscribing rectangle) Specify the determination pixel area. The determination pixel regions specified for each dot optical pixel region intersect at the radial center when each dot optical pixel region is in a state of extending radially due to ripples, that is, overlapping pixel regions. Is likely to have.
Therefore, according to the above preferred method, in the bubble detection step, when a predetermined number or more of the determination pixel regions have overlapping pixel regions, the liquid level corresponding to the overlapping pixel regions It is possible to accurately determine that air bubbles leaking from the object to be inspected have floated in the region.

Further, in order to solve the above problems, the present invention comprises a liquid tank, a pressurized gas filling means for filling the inside of an object to be inspected immersed in the liquid tank with a pressurized gas, and a liquid level of the liquid tank. A light source that is arranged above the object to be inspected and that irradiates a dot light pattern, which is a pattern in which circular or regular polygonal dot light is two-dimensionally arranged with respect to the liquid surface of the liquid tank, and the above. The analysis device includes an image pickup device that captures an irradiated dot light pattern and an analysis device that detects bubbles leaking from the object to be inspected using the image pickup image of the dot light pattern captured by the image pickup device. Determines the extending direction of the dot light pixel region, which is a pixel region corresponding to each dot light constituting the dot light pattern, by performing image processing on the captured image of the dot light pattern captured by the imaging device. When the extending direction of each of the determined dot optical pixel regions is radial with the predetermined pixel region in the captured image as the center, the extension direction of the predetermined number or more of the dot optical pixel regions is the center. It is also provided as an airtightness inspection apparatus characterized in that it is determined that air bubbles leaking from the object to be inspected have floated in the region of the liquid surface corresponding to the pixel region to be inspected.

According to the airtightness inspection device according to the present invention, the dot light pattern is imaged by the image pickup device, and the captured image of the dot light pattern is image-processed by the analysis device, so that the dot light is a pixel region corresponding to each dot light. It is possible to automatically determine the extending direction of the pixel area. Further, when the direction in which the predetermined number or more of the dot optical pixel regions are extended by the analysis device is radial centering on the predetermined pixel region in the captured image, the factor that the predetermined number or more of the dot optical pixel regions are extended is a factor. Can be automatically determined to be due to ripples. That is, it can be automatically determined that the air bubbles leaking from the inspected object have floated in the liquid surface region corresponding to the radial center pixel region.

Preferably, the light source is two-dimensionally arranged on the same plane and includes a plurality of LEDs having an optical axis in a direction perpendicular to the plane, and the imaging device has a visual axis in a direction perpendicular to the plane. ..

In the airtightness inspection device according to the present invention, when an image is taken with the visual axis of the image pickup device tilted with respect to the optical axis of the light source, when ripples due to air bubbles are not generated on the liquid surface of the liquid tank ( Even if the liquid surface is a completely flat surface), the circular or regular polygonal dot light emitted from the light source is deformed according to the inclination of the visual axis of the image pickup device and is imaged. A predetermined correction may be required when determining the extending direction of the pixel region.
On the other hand, according to the above preferable configuration, since the optical axis of the light source and the visual axis of the imaging device are parallel (both are perpendicular to the plane in which the LEDs are two-dimensionally arranged), the liquid surface of the liquid tank When no ripples are generated, the circular or regular polygonal dot light emitted from the light source is imaged by the image pickup apparatus in almost the same shape. Therefore, the above correction is unnecessary, and the extending direction of the dot optical pixel region can be easily determined.
Further, according to the above preferable configuration, since the light source includes a plurality of LEDs, the brightness of each dot light irradiated to the liquid surface can be easily adjusted by adjusting the applied current of each LED. .. At this time, it is also possible to individually adjust the brightness of each dot light by individually adjusting the applied current of each LED, if necessary.

According to the airtightness inspection method and apparatus according to the present invention, even if the air bubbles leaking from the object to be inspected are small, they can be detected with high accuracy, so that the airtightness inspection can be performed with high accuracy.

It is a figure which shows the schematic structure of the airtightness inspection apparatus which concerns on one Embodiment of this invention. It is a flow chart which shows the schematic process of the airtightness inspection method which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the direction determination process shown in FIG. It is explanatory drawing for demonstrating the bubble | bubble detection process shown in FIG. It is a figure which shows an example of the result of the inspection using the airtightness inspection method which concerns on one Embodiment of this invention.

Hereinafter, the airtightness inspection method and the apparatus according to the embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.
FIG. 1 is a diagram showing a schematic configuration of an airtightness inspection device according to the present embodiment. FIG. 1A shows an overall configuration diagram. FIG. 1B shows the lower surface of the light source and the internal configuration of the control panel.
As shown in FIG. 1, the airtightness inspection device 100 according to the present embodiment includes a liquid tank 1, a pressurized gas filling means 2, a light source 3, an image pickup device 4, and an analysis device 5. The liquid tank 1 of the present embodiment is connected to the liquid feeding and absorbing means 6. The analysis device 5 of the present embodiment is housed in the control panel 7.

The liquid tank 1 is for immersing the object T to be inspected in the liquid (for example, water) W, and if necessary, the liquid W is sent from the liquid feeding means 6 and the liquid feeding means. Liquid W is sucked into 6.
The liquid feeding and absorbing means 6 includes a reserve liquid tank 61, a liquid feeding pump 62, and a liquid absorbing pump 63. If the volume of the liquid W in the liquid tank 1 is constant, the position of the liquid level of the liquid tank 1 (the upper surface of the liquid W in the liquid tank 1) changes according to the volume of the object T to be immersed. It is possible to drive the liquid feed pump 62 to feed the liquid W in the reserve liquid tank 61 toward the liquid tank 1 as necessary, such as adjusting the position of the liquid level. Similarly, if necessary, the liquid absorption pump 63 can be driven to absorb the liquid W in the liquid tank 1 into the reserve liquid tank 61.

The pressurized gas filling means 2 fills the inside of the object T to be inspected immersed in the liquid tank 1 with a pressurized gas (for example, compressed air). The pressurized gas filling means 2 of the present embodiment includes a compressor 21, a tank 22, a pressure adjusting valve 23, and a pressure meter 24. The pressurized gas generated by the compressor 21 is stored in the tank 22, and after the pressure is adjusted by the pressure adjusting valve 23 so that the indicated value of the pressure meter 24 becomes a desired value, the inside of the object T to be inspected. Is filled with.

The light source 3 is arranged above the liquid surface of the liquid tank 1 and above the liquid surface T to be inspected, and is a pattern in which circular or regular polygonal dot lights are two-dimensionally arranged with respect to the liquid surface of the liquid tank 1. It irradiates a dot light pattern. A plurality of light sources 3 (six in the example shown in FIG. 1A) are provided so that even if air bubbles leak from any part of the object T to be inspected, the light sources 3 of the present embodiment can be detected. The light source 3 of the above irradiates the entire liquid surface of the liquid tank 1 with a dot light pattern.

The light source 3 of the present embodiment includes a plurality of LEDs 32 that are two-dimensionally arranged on the same plane and have an optical axis in a direction perpendicular to the plane. Specifically, the light source 3 comprises a plate-shaped base 31 and a plurality of LEDs 32 arranged two-dimensionally in a matrix on the base 31 so that the optical axis is along the normal direction of the base 31. Equipped. Each LED 32 is connected to a power source 33 housed in the control panel 7, and emits light by an applied current applied from the power source 33. The dimensions of the two-dimensional array of the LEDs 32 may be set to appropriate values according to the size of the irradiation area of the required dot light pattern. It is considered that the smaller the array pitch of the LED 32 is, the higher the accuracy of detecting bubbles, as long as the illuminated dot lights do not overlap each other even if they are deformed. However, if the irradiation area of the dot light pattern is increased while the arrangement pitch of the LEDs 32 is excessively small, the number of LEDs 32 increases, which causes a problem that the cost and the labor for maintenance increase. Therefore, it is preferable to set the arrangement pitch so large that the detection accuracy of bubbles is not affected. The arrangement pitch of the LEDs 32 is, for example, about 10 mm to 100 mm, and is set to 75 mm in this embodiment.

Each LED 32 has circular or regular polygonal dots by making the outer shape of the exit surface circular or regular polygonal, or by attaching a filter having a circular or regular polygonal opening to the emission surface of each LED 32. It can emit light. In this embodiment, an LED 32 having a circular outer surface is used.

The image pickup device 4 captures a dot light pattern irradiated by the light source 3. The image pickup apparatus 4 has a visual axis in a direction perpendicular to the plane in which the LEDs 32 are two-dimensionally arranged. Specifically, the image pickup apparatus 4 is arranged on the base 31 and substantially at the center of the two-dimensional arrangement of the LEDs 32 so that the visual axis is along the normal direction of the base 31. The field of view of the image pickup apparatus 4 is set so that the entire dot light pattern emitted from one light source 3 can be captured.
As the image pickup device 4, for example, a two-dimensional CCD camera can be used. The image pickup apparatus 4 of the present embodiment is a two-dimensional CCD camera having a frame rate of 30 fps and an exposure time of 5 msec.

The analysis device 5 detects bubbles leaking from the object T to be inspected by using the captured image of the dot light pattern captured by the image pickup device 4. Specifically, the analysis device 5 of the present embodiment is composed of a personal computer in which a program for executing image processing and the like, which will be described later, is installed. Further, the analysis device 5 of the present embodiment also functions as a control device for driving the power supply 33 of the light source 3 and driving the image pickup device 4.

Hereinafter, an airtightness inspection method using the airtightness inspection apparatus 100 having the above configuration will be described.
The airtightness inspection method according to the embodiment of the present invention fills the inside of the object T to be inspected immersed in the liquid tank 1 with a pressurized gas, and detects bubbles leaking from the object T to be inspected. This is a method for inspecting the airtightness of the object T to be inspected.
FIG. 2 is a flow chart showing a schematic process of an airtightness inspection method according to an embodiment of the present invention.
As shown in FIG. 2, the airtightness inspection method according to the present embodiment includes a dipping step S1, a filling step S2, a light irradiation step S3, an imaging step S4, a direction determination step S5, and a bubble detection step S6. including. Hereinafter, each steps S1 to S6 will be described in order.

<Immersion step S1>
In the dipping step S1, the object T to be inspected is immersed in the liquid tank 1 filled with the liquid W. At this time, as described above, the liquid feeding pump 62 of the liquid feeding and absorbing means 6 is driven to feed the liquid W in the reserve liquid tank 61 toward the liquid tank 1. Further, if necessary, the liquid absorbing pump 63 of the liquid feeding means 6 is driven to absorb the liquid W in the liquid tank 1 into the reserve liquid tank 61.

<Filling step S2>
In the filling step S2, the pressurized gas is filled into the inside of the object T to be inspected immersed in the liquid tank 1 by the pressurized gas filling means 2. At this time, as described above, the pressurized gas generated by the compressor 21 of the pressurized gas filling means 2 and stored in the tank 22 is a pressure adjusting valve so that the indicated value of the pressure meter 24 becomes a desired value. After the pressure is adjusted at 23 (for example, 20 to 30 MPa), the inside of the object T to be inspected is filled.

<Light irradiation step S3>
In the light irradiation step S3, a circular or regular polygonal dot light (in the present embodiment) from the light source 3 arranged above the liquid surface of the liquid tank 1 and above the liquid surface T of the liquid tank 1 with respect to the liquid surface of the liquid tank 1. It irradiates a dot light pattern, which is a pattern in which circular dot light) is two-dimensionally arranged. The dot light pattern is irradiated in advance before the immersion step S1 is started, before the filling step S2 is started, or during the filling step S2, in addition to starting the irradiation after the immersion step S1 and the filling step S2 are completed. It is also possible to keep (continue irradiation even after the immersion step S1 and the filling step S2 are completed).

<Imaging step S4>
In the imaging step S4, the imaging device 4 captures the dot light pattern irradiated by the light irradiation step S3. At this time, in the present embodiment, the image is continuously imaged a plurality of times at a frame rate of 30 fps and an exposure time of 5 msec.

<Direction determination step S5>
In the direction determination step S5, the analysis device 5 processes the captured image of the dot light pattern captured in the imaging step S4 to form a dot light pixel region, which is a pixel region corresponding to each dot light constituting the dot light pattern. Determine each extension direction. Hereinafter, the direction determination step S5 will be described more specifically with reference to FIG.

FIG. 3 is an explanatory diagram for explaining the direction determination step S5.
In the direction determination step S5, first, the analysis device 5 binarizes the captured images of the dot light patterns captured a plurality of times at a predetermined threshold value to generate a binarized image. FIG. 3A is a diagram schematically showing a binarized image 41 generated by binarizing an captured image captured a plurality of times in succession. As shown in FIG. 3A, in each binarized image 41, a dot light pixel region 34 corresponding to each dot light constituting the dot light pattern is extracted (the dot light pixel region 34 has a density of 255). , The other region has a concentration of 0).

Next, in the direction determination step S5, the analysis device 5 synthesizes a plurality of binarized images 41 to generate a binarized composite image. In the present embodiment, two consecutive binarized images 41 are combined to generate a binarized composite image. FIG. 3B is a diagram schematically showing a binarized composite image 42 generated by synthesizing two consecutive binarized images 41 shown in FIG. 3A. That is, for each of the binarized images 41 shown in FIG. 3 (a), the logical sum (OR) of each corresponding pixel is calculated, and the calculation result corresponds to the binarized composite image 42 shown in FIG. 3 (b). It is the density of each pixel.

Next, in the direction determination step S5, the analysis device 5 extracts the contour of the dot optical pixel region 34 in the binarized composite image 42. For contour extraction, for example, contour tracking processing, which is a known image processing algorithm, is used.

Next, in the direction determination step S5, the contour length of each dot optical pixel region 34 in the binarized composite image 42 is equal to or greater than a predetermined value (20 in the present embodiment) by the analysis device 5, and The dot optical pixel region 34 in which the long side / short side of the approximate ellipse of the contour or the circumscribing rectangle is a predetermined value R (1.8 in this embodiment) or more is extracted. FIG. 3C is a diagram schematically showing a binarized composite image 42 including only the extracted dot optical pixel region 34. Of the dot optical pixel regions 34 shown in FIG. 3B, the dot optical pixel regions 34a to 34e are the above conditions (the contour length is equal to or greater than a predetermined value, and the contour is an approximate ellipse or an circumscribing rectangle. Since the long side / short side does not satisfy the predetermined value R or more), the binarized composite image 42 shown in FIG. 3C is deleted without being extracted.
The approximate ellipse of the contour of the dot optical pixel region 34 can be calculated, for example, by fitting the ellipse to the ellipse by the least squares method using the coordinates of the points constituting the contour. In the case of an approximate ellipse, the long side and the short side mean the long axis and the short axis, respectively.
In this embodiment, since the approximate ellipse of the contour is used, only the approximate ellipse will be described below, but the same applies when the circumscribed rectangle of the contour is used.

Finally, in the direction determination step S5, the analysis device 5 determines that the direction of the long side of the approximate ellipse of the contour of each extracted dot optical pixel region 34 is the extending direction of each extracted dot optical pixel region.

<Bubble detection step S6>
In the bubble detection step S6, among the extending directions of each dot optical pixel region 34 determined by the analysis device 5 in the direction determination step S5, the extending direction of a predetermined number or more of the dot optical pixel regions is the captured image (binarized composition). In the case of the radial shape centered on the predetermined pixel region in the image 42), it is determined that the air bubbles leaking from the object T to be inspected have floated in the liquid surface region corresponding to the center pixel region. Hereinafter, the bubble detection step S6 will be described more specifically with reference to FIG.

FIG. 4 is an explanatory diagram for explaining the bubble detection step S6. In FIG. 4, for convenience, the approximate ellipse 34P of the contour of the dot light pixel area 34 is shown instead of the dot light pixel area 34.
In the bubble detection step S6, first, each dot optical pixel region 34 extracted in the binarized composite image 42 by the analyzer 5 is included, and the contour direction of each dot optical pixel region 34 is longer than the long side of the approximate ellipse 34P. A determination pixel region 44, which is long and longer in the short side direction than the short side of the approximate ellipse 34P of the contour of each dot light pixel region 34, is specified for each extracted dot light pixel region 34.
Specifically, the first analysis device 5, as shown in FIG. 4 (a), dividing the binary combined image 42 G _W pieces laterally, longitudinally G _H number of a plurality of pixel areas A .. That is, when W the number of pixels in the horizontal direction of the binarized combined image 42, the number of pixels in the horizontal direction of the pixel region A and A _W, W = A _W × G _W is established. Similarly, if the number of pixels in the vertical direction of the binarized composite image 42 is H and the number of pixels in the vertical direction of the pixel area A is A _H , then H = A _H × _GH is established. Incidentally, W, _H, as the _G W, G _H, can be exemplified the following values.
W = 400 pixels, H = 360 _pixels, G _{W =} G H ₌ 40 pixels

Next, as shown in FIG. 4B, the analysis device 5 passes through the center of the approximate ellipse 34P of the contour of each dot optical pixel region 34 and extends the line segment 43 in the long side direction of the approximate ellipse 34P (FIG. 4 (FIG. 4). Create a line segment) indicated by a thick dashed line in b). This line segment 43 extends from the center of the approximate ellipse 34P to both sides by the same length, and the length on one side is (1 + r−R) × L. Here, in the above equation, r means the long side / short side of the approximate ellipse 34P of the contour of each dot optical pixel region 34, and R means the dot optical pixel region 34 in the above-mentioned direction determination step S5. Means the threshold value of, and L means a predetermined fixed value (for example, 100 pixels). However, the length of the line segment 43 is not limited to this, and it can be simply set to a fixed value L.
In FIG. 4B, the approximate ellipse 34Pa shown in FIG. 4A is shown as an example, but a line segment 43 is similarly created for the other approximate ellipse 34P shown in FIG. 4A. .. In other words, a line segment 43 is created for each of the extracted dot optical pixel regions 34.

Finally, the analysis device 5 determines an aggregate of the pixel areas A in which the distance from the center of the pixel area A to the line segment 43 _{is less than (A W} + A _H ) / 2 in the determination pixel area 44 (FIG. 4B). It is specified as a pixel area surrounded by a thick solid line). As described above, since the line segment 43 is created for each extracted dot light pixel area 34, the determination pixel area 44 is also specified for each extracted dot light pixel area 34. As can be seen from FIG. 4B, the determination pixel area 44 specified as described above includes each of the extracted dot light pixel areas 34, and the length of the approximate ellipse 34P of the contour of each dot light pixel area 34. The pixel area is longer in the long side direction than the side and is longer in the short side direction than the short side of the approximate ellipse 34P of the contour of each dot optical pixel area 34.

Next, in the bubble detection step S6, among the determination pixel regions 44 specified for each dot optical pixel region 34 by the analysis device 5, pixels in which a predetermined number or more (4 or more in the present embodiment) of the determination pixel regions 44 overlap. When the area is included, it is determined that the air bubbles leaking from the object T to be inspected have floated in the area of the liquid surface corresponding to the overlapping pixel areas.
Specifically, for example, all the pixel areas A constituting each determination pixel area 44 specified for each dot light pixel area 34 by the analysis device 5 (for example, the pixel area A hatched in FIG. 4B). ) Is given a score of 1 point. When a certain pixel area A constitutes one determination pixel area 44 and at the same time constitutes another one determination pixel area 44, the pixel area A is given a total score of 2 points. .. When such scoring is performed, the pixel area A with a total score of 4 points or more means that the determination pixel areas 44 of 4 or more are overlapping pixel areas A. As described above, the analysis device 5 can determine whether or not a predetermined number or more of the determination pixel regions 44 have overlapping pixel regions. FIG. 4C shows a predetermined number or more (4 or more) of the determination pixel areas 44 among the determination pixel areas 44 specified for each dot optical pixel area 34 in the binarized composite image 42 shown in FIG. 4A. Is a diagram schematically showing that has an overlapping pixel region (a hatched pixel region in FIG. 4C; hereinafter, this overlapping pixel region is referred to as an overlapping pixel region) 45. When the overlapping pixel region 44 is provided, as described above, the analysis device 5 determines that the air bubbles leaking from the inspected object T have floated in the region of the liquid surface corresponding to the overlapping pixel region 44.

According to the airtightness inspection method according to the present embodiment described above, in the light irradiation step S3, a liquid is irradiated by irradiating a dot light pattern which is a pattern in which circular or regular polygonal dot lights are two-dimensionally arranged. When ripples are generated on the liquid surface of the tank 1 due to bubbles leaking from the object T to be inspected, each dot light is imaged in a state of being changed to a shape extending in the traveling direction of the radial ripples.
Therefore, in the direction determination step S5, it is possible to determine the extending direction of each dot light (dot light pixel region).
Next, in the bubble detection step S5, if the extending direction of the predetermined number or more of the dot light (dot light pixel region) is radial centering on the predetermined region of the liquid surface irradiated with the dot light pattern, the predetermined direction is specified. It can be determined that the cause of the extension of more than a few dot lights (dot light pixel area) is due to ripples. That is, it can be determined that the air bubbles leaking from the inspected object T have floated in the region of the liquid surface which is the radial center.
According to the airtightness inspection method according to the present embodiment, the airtightness inspection method does not directly detect the air bubbles themselves, but detects ripples generated by the air bubbles based on the deformation of each dot light constituting the dot light pattern. Even if the air bubbles leaking from the are small, the air bubbles can be detected with high accuracy.

In the present embodiment, the analysis device 5 automatically determines the extending direction of each dot optical pixel region, and the extending direction of a predetermined number or more of the dot optical pixel regions is radial with the overlapping pixel region 45 as the center. In the above description, a case where it is automatically determined that air bubbles leaking from the object T to be inspected have floated in the area of the liquid surface corresponding to the overlapping pixel area 45 has been described as an example, but the present invention is not limited to this. Absent.
For example, the direction in which each dot light extends is determined by directly visually observing the irradiated dot light pattern without executing the imaging step S4 using the image pickup device 4, and the direction in which a predetermined number or more of the dot light extends is predetermined. When it can be confirmed that the light is radial around the region of, it is also possible to determine that the air bubbles leaking from the object T to be inspected have floated in the region of the liquid surface which is the center of the radial.
Further, for example, although the imaging step S4 using the imaging device 4 is executed, the analysis device 5 does not automatically determine the floating of bubbles, and any one of the captured image, the binarized image, and the binarized composite image. It is also possible to display an image on a monitor provided in the analysis device 5 and visually check the monitor to determine that air bubbles leaking from the object T to be inspected have floated.

FIG. 5 is a diagram showing an example of the result of the inspection using the airtightness inspection method according to the present embodiment. FIG. 5A shows the result when bubbles are generated in the liquid tank 1 using a Teflon (registered trademark) needle having an inner diameter of 0.3 mm in order to simulate a situation in which bubbles leak from the object T to be inspected. Is shown. The size (outer diameter) of the bubbles on the liquid surface of the liquid tank 1 was about 3.9 mm. FIG. 5B shows the result when the crane moves above the liquid tank 1. In FIG. 5C, in order to simulate a situation in which air bubbles leak from the object T to be inspected, a metal needle having an inner diameter of 0.21 mm is used to generate air bubbles in the liquid tank 1, and the wind blows from the liquid tank 1. The result when the liquid level is shaken is shown. The size (outer diameter) of the bubbles on the liquid surface of the liquid tank 1 was about 2.3 mm. The figures shown on the left side of FIGS. 5 (a) to 5 (c) are captured images (captured images before binarization) of the dot light pattern captured in the imaging step S4, and are images of FIGS. 5 (a) to 5 (c). The figure shown on the right side is a determination pixel area 44 and an overlapping pixel area 45 in the binarized composite image 42 corresponding to the captured image on the left side.

As shown in FIG. 5A, when bubbles having an outer diameter of about 3.9 mm are generated, overlapping pixel regions 45 are generated in the two-dimensional composite image 42, and the bubbles are generated by the airtightness inspection method according to the present embodiment. It was confirmed that it can be detected with high accuracy.
Further, as shown in FIG. 5B, the vibration caused by the movement of the crane caused almost no ripples on the liquid surface of the liquid tank 1, and the overlapping pixel region 45 did not occur in the two-dimensional composite image 42, so that an erroneous detection occurred. It did not occur.
Further, as shown in the upper part of the two-dimensional composite image 42 of FIG. 5 (c), although ripples are generated due to the fluctuation of the liquid surface caused by the wind, the direction of the ripples is one direction (almost lateral direction). Since the overlapping pixel region 45 did not occur, erroneous detection did not occur. On the other hand, as shown in the lower part of the two-dimensional composite image 42 of FIG. 5C, an overlapping pixel region 45 is generated at a portion where bubbles having an outer diameter of about 2.3 mm are generated, which is related to the present embodiment. It was confirmed that air bubbles can be detected accurately by the airtightness inspection method.

1 ... Liquid tank 2 ... Pressurized gas filling means 3 ... Light source 4 ... Imaging device 5 ... Analytical device 32 ... LED
100 ... Airtightness inspection device T ... Inspected object W ... Liquid

Claims (7)

It is an airtightness inspection method that inspects the airtightness of the object to be inspected by filling the inside of the object to be inspected immersed in the liquid tank with a pressurized gas and detecting air bubbles leaking from the object to be inspected. hand,
A light source is arranged above the liquid surface of the liquid tank and above the object to be inspected, and circular or regular polygonal dot light is two-dimensionally arranged from the light source with respect to the liquid surface of the liquid tank. A light irradiation process that irradiates a certain dot light pattern,
A direction determination step of determining the extending direction of each dot light constituting the dot light pattern irradiated by the light irradiation step, and a direction determination step.
When a predetermined number or more of the extending directions of the dot lights determined in the direction determination step are radial around a predetermined region of the liquid surface irradiated with the dot light pattern. In addition, a bubble detection step of determining that bubbles leaking from the object to be inspected have floated in the liquid surface region as the center.
An airtightness inspection method comprising. It further includes an imaging step of imaging the dot light pattern irradiated by the light irradiation step.
In the direction determination step, by performing image processing on the captured image of the dot light pattern captured in the imaging step, the direction in which the dot light pixel region, which is the pixel region corresponding to each dot light constituting the dot light pattern, extends. Judging each
In the bubble detection step, among the extending directions of the dot optical pixel regions determined in the direction determination step, the extending direction of a predetermined number or more of the dot optical pixel regions is centered on the predetermined pixel region in the captured image. When it is radial, it is determined that the air bubbles leaking from the object to be inspected have floated in the area of the liquid surface corresponding to the central pixel area.
The airtightness inspection method according to claim 1. In the imaging step, the dot light pattern is continuously imaged a plurality of times.
In the direction determination step, a binarized composite image is generated by binarizing and synthesizing each of the captured images of the dot light patterns captured a plurality of times, and each dot light in the generated binarized composite image. Determine the direction in which the pixel area extends,
The airtightness inspection method according to claim 2. In the direction determination step, in each of the dot optical pixel regions in the binarized composite image, the contour length is equal to or longer than a predetermined value, and the long side / short side of the contour approximate ellipse or circumscribing rectangle is A dot optical pixel region having a predetermined value or more is extracted, and it is determined that the direction of the long side of the approximate ellipse or circumscribing rectangle of the contour of each extracted dot optical pixel region is the extending direction of each extracted dot optical pixel region. And
In the bubble detection step, among the extending directions of each of the extracted dot optical pixel regions, the extending direction of a predetermined number or more of the dot optical pixel regions is radial around the predetermined pixel region in the binarized composite image. In a certain case, it is determined that the air bubbles leaking from the object to be inspected have floated in the area of the liquid surface corresponding to the pixel area at the center.
The airtightness inspection method according to claim 3. In the bubble detection step
Each dot optical pixel region including each dot optical pixel region extracted in the binarized composite image is longer in the long side direction than the long side of the approximate ellipse or circumscribing rectangle of the contour of each dot optical pixel region, and each dot optical pixel A determination pixel region that is longer in the short side direction than the short side of the approximate ellipse or circumscribing rectangle of the contour of the region is specified for each of the extracted dot light pixel regions.
Of the determination pixel regions specified for each dot optical pixel region, when a predetermined number or more of the determination pixel regions have overlapping pixel regions, the liquid surface region corresponding to the overlapping pixel regions is to be inspected. Judge that bubbles leaking from an object have surfaced,
The airtightness inspection method according to claim 4. Liquid tank and
A pressurized gas filling means for filling the inside of the object to be inspected immersed in the liquid tank with a pressurized gas,
A dot light pattern is a pattern in which circular or regular polygonal dot lights are two-dimensionally arranged with respect to the liquid surface of the liquid tank, which is arranged above the liquid level of the liquid tank and above the object to be inspected. The light source to irradiate and
An imaging device that captures the irradiated dot light pattern and
It is provided with an analysis device for detecting bubbles leaking from the object to be inspected by using the captured image of the dot light pattern captured by the image pickup device.
The analyzer is
By image processing the captured image of the dot light pattern captured by the imaging device, the extending direction of the dot light pixel region, which is the pixel region corresponding to each dot light constituting the dot light pattern, is determined.
When the extending direction of each of the determined dot optical pixel regions is radial with the predetermined pixel region in the captured image as the center, the extending direction of the predetermined number or more of the dot optical pixel regions is defined as the center. It is determined that the air bubbles leaking from the object to be inspected have floated in the area of the liquid surface corresponding to the pixel area.
An airtightness inspection device characterized by the fact that. The light source includes a plurality of LEDs arranged two-dimensionally on the same plane and having an optical axis in a direction perpendicular to the plane.
The imaging device has a visual axis in a direction perpendicular to the plane.
The airtightness inspection apparatus according to claim 6.

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