Image measurement apparatus and image measurement method for liquid level

The present invention is a liquid level level image measuring device and measurement for automatically measuring the liquid level height in a container such as the water level in a water tank provided with a large number of partition plates for grasping the injection / spraying characteristics of a nozzle. Regarding the method.

Conventionally, as shown in FIG. 5, partition plates 12 are provided at a constant pitch to form a large number of slit-shaped water injection portions 13 in order to grasp the injection / spray characteristics of nozzles widely used for cooling steel materials and the like. A water tank 11 for measuring the distribution of nozzle sprinkling, which is usually made of a transparent resin, is used. Then, the nozzle 14 whose injection / spraying characteristics should be grasped is arranged directly above the water tank 11, water is supplied and discharged from the tip thereof, and the water level accumulated in each slit-shaped water injection portion 13 in the water tank 11, that is, By measuring the liquid level, the injection / spray characteristics of the nozzle such as the water amount distribution can be grasped.

Conventionally, the liquid level level is measured by applying a scale M to each slit-shaped water injection unit 13 after the injection is completed, or by using, for example, an ultrasonic water level gauge U as an automatic measuring means. Was there. On the other hand, there is disclosed a method of measuring the liquid level in a container such as a tank and the water level of a river, the sea, etc. by image processing an input image of a gauge or a water plate captured by an ITV camera (for example). See Patent Documents 1 and 2). The measurement method disclosed in Patent Document 1 is a method in which a container is installed on the wall surface of the tank and the position of the liquid surface is determined by using a reflection image of the container on the liquid surface or a refraction image under the liquid surface. In the measurement method disclosed in Patent Document 2, a water plate perpendicular to the water surface and an auxiliary inclined plate are provided, and the intersection of the side lines is obtained from the real image and the mapping of the upper part of the water surface of the auxiliary inclined plate by image processing. It is a method such as measuring the water level by reading the water surface boundary as a boundary with the scale of the water plate.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 8-14992 ([0006] to [0008])</text></patcit><patcit num="2"><text>Patent No. 2933158 ([0009] ~ [0028])</text></patcit>

<p> The method of reading by applying the measure M takes time and effort, and in the measurement method using the ultrasonic water level gauge U, the ultrasonic probe P is applied to the bottom surface of the container for measurement after the spraying is completed. Therefore, human power is required, and the automation of the moving mechanism of the probe has a drawback of poor reliability. Further, if the width of the slit-shaped water injection portion 13 is narrowed in order to measure the water amount distribution accurately at a short pitch, there is a problem that the ultrasonic probe is too large to measure. In the measuring methods disclosed in Patent Documents 1 and 2, since a measuring rod and a water plate are used, it is difficult to use these measuring tools in the slit-shaped water injection portion having a narrow width.</p><p> Therefore, an object of the present invention is to provide an apparatus and a measurement method capable of automatically measuring the liquid level in a container such as a water tank easily, efficiently and with high accuracy regardless of the internal structure such as the width of a slit-shaped water injection portion. It is to be.</p>

<p> In order to solve the above-mentioned problems, the following configuration was adopted in the present invention.</p><p> That is, the liquid level image measuring device according to claim 1 receives a light source arranged on one side of the water tank and a light emitted from the light source arranged on the other side and transmitted through the water tank. A liquid level image measuring device including a light receiver and an image processing means for the output video signal, and measuring the height of the liquid level in the water tank by image processing of the output video signal. The light source. Is a light source that radiates near infrared rays, and the receiver is a receiver that has sensitivity to near infrared rays. The brightness distribution of transmitted light is obtained by the image processing, and the height of the liquid surface is measured. It is characterized by.</p><p> As described above, when a light source that radiates near infrared rays is used, the absorption coefficient of water is relatively small in this wavelength range, and the difference in absorption coefficient between water and the material forming the water tank is large. The emitted near-infrared rays pass through the water tank in which water is accumulated and reach the receiver. Then, from the output video signal, the brightness distribution of the transmitted light can be obtained with good sensitivity by image processing. When the wavelength is longer than that of near infrared rays, the absorption coefficient of water becomes large, it is difficult for light to pass through the water tank, and the sensitivity of the receiver is lowered, so that the brightness of transmitted light cannot be measured accurately. In addition, since the absorption coefficient of water is extremely small in the visible light region, the difference between the brightness of the light transmitted through the portion where water is accumulated and the brightness of the light transmitted through the portion without water above it becomes small, and the liquid level is reduced. Becomes difficult to detect. As the water tank forming material, the absorption coefficient in the near infrared wavelength range is smaller than the water absorption coefficient, and for example, a synthetic resin such as acrylic or polypropylene can be used.</p><p> The liquid level image measuring device according to claim 2 is characterized in that the light source is formed by mounting a near-infrared LED in a plane shape and having a size at least equivalent to that of the water tank.</p><p> In this way, near-infrared rays having a uniform wavelength can be radiated to the entire surface on one side of the water tank, so that the brightness distribution of the transmitted light becomes uniform over the entire measurement surface. In particular, there is an advantage in that a partition is provided in the water tank to suppress a measurement error of the brightness distribution of transmitted light when the liquid level has a distribution.</p><p> In the liquid level level image measuring device according to claim 3, the receiver is a near-infrared CCD camera, and a reference index for measuring the liquid level is set around the near-infrared CCD camera. It is characterized by providing a means for projecting onto the measurement surface of the water tank.</p><p> In the CCD camera, pixels are regularly arranged in the light receiving portion, and an edge, that is, a liquid level is detected from the brightness distribution of transmitted light by image processing, and the position of the pixel corresponding to the liquid level and the measurement thereof. The liquid level can be measured easily, efficiently and accurately from the reference index projected on the surface. In particular, when a near-infrared CCD camera having high sensitivity in the near-infrared wavelength range is used, the detection accuracy of the liquid level is improved.</p><p> The liquid level image measuring device according to claim 4 is a computer in which the image processing means includes an image input board and a monitor, and takes in output video signals of the water tank empty state and the water tank water injection state and obtains them by image processing. The feature is that the brightness ratio is calculated from the brightness distribution of the transmitted light in the above two states to measure the height of the liquid surface.</p><p> In this way, if the liquid level height is measured using the brightness ratio of the transmitted light in the empty state of the water tank and the water injection state of the water tank, disturbances such as dirt in the water tank and the structure inside the water tank are canceled out and the influence is affected. The brightness distribution of only the water in the water tank can be extracted without receiving it, and the measurement accuracy of the liquid level level does not deteriorate.</p><p> In the liquid level image measurement method according to claim 5, a light source is arranged on one side of the water tank, and a receiver that receives light radiated from the light source that has passed through the water tank is placed on the other side. This is a liquid level image measurement method for measuring the height of the liquid level in the water tank by image processing the output video signal from the light receiver, and the light source that radiates near infrared rays as the light source is the light source. A light source having sensitivity to near infrared rays is used as a device, and the height of the liquid surface is measured by obtaining the luminance distribution of transmitted light by the image processing.</p><p> In the liquid level image measurement method according to claim 6, the light source is formed by mounting a near-infrared LED in a planar shape to have a size at least equal to that of the water tank, and the near-infrared CCD camera serves as the receiver. Is characterized by using.</p><p> The liquid level image measurement method according to claim 7 measures the brightness of the measurement surfaces in the two states by image processing from the output video signals of the water tank empty state and the water tank water injection state, and calculates the brightness ratio thereof. The liquid level is detected, the length per pixel is obtained in advance from the distance of the reference index displayed on the liquid level in advance at the required interval on the measurement surface, and the number of pixels from the reference index to the detected liquid level is lengthened. It is characterized in that the liquid level height is measured in terms of dimensions.</p><p> By doing so, by associating the distance between the reference indexes with the number of pixels of the CCD camera, the detected edge, that is, the number of pixels between the liquid level and one of the above reference indexes can be obtained. By counting, the distance between the reference index and the liquid level can be calculated, and therefore the liquid level height can be measured.</p>

<p> In the liquid level image measuring device of the present invention, a light source and a light receiver are arranged with a water tank in between, and a light source that radiates near infrared rays is used. Therefore, transmitted light is transmitted by image processing of the output video signal from the light receiver. The brightness distribution of the light source can be measured with good sensitivity and in a non-contact manner.</p><p> In addition, the edge is detected from the brightness ratio of the transmitted light in the empty state of the water tank and the water injection state of the water tank, and the liquid level height is measured. Detection can be performed.</p><p> Further, a near-infrared CCD camera is used as a receiver, and a reference index is projected on the measurement surface at predetermined intervals with the liquid surface sandwiched between them, and the distance between the reference indexes is associated with the number of pixels of the CCD camera. Since the distance of the liquid level from the reference index is calculated by counting the number of pixels between the liquid level and either one of the reference indexes, the liquid level height can be measured easily and accurately. ..</p><p> These, as a water tank, a case of using a container provided with a plurality of slit-like water injection unit, or the width of the water injection unit unchanged, to measure the liquid surface height of each water injection unit accurately efficiently It is possible to easily grasp the injection / spray characteristics of the nozzle.</p>

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4 attached.

In the liquid level level image measuring device of the embodiment shown in FIGS. 1 (a) and 1 (b), a plurality of slit-shaped water injection portions 13 are provided at equal intervals by a partition plate 12, for example, water made of transparent acrylic resin. A light source 1 that emits near-infrared rays arranged on one side, a near-infrared CCD camera 2 of a receiver arranged on the other side, and an output image thereof, sandwiching a water tank 11 into which a liquid such as a liquid is injected. It is equipped with an image analysis means consisting of a monitor 3a and an image analysis personal computer 3b incorporating an image input board that processes signals. The light source 1 is formed by mounting a near-infrared LED 1a on a surface having the same size as the measurement surface 11a of the water tank 11, and near-infrared rays having a wavelength of 800 nm to 2 μm are radiated from the back side of the measurement surface 11a. , The near-infrared rays transmitted through the water tank 11 are received by the near-infrared CCD camera 2. Then, the output video signal from the near-infrared CCD camera 2 is taken into the image analysis personal computer 3b via the image input board and image-processed. A reference index, that is, a reference line, parallel to the liquid level L at a predetermined interval Z with the liquid level L of each water injection portion 13 sandwiched around the near-infrared CCD camera 2, that is, near the mounting portion of the zoom lens 2a. Laser line projectors 4 and 4 for projecting 4a and 4a onto the total side surface 11a are attached. As shown in FIG. 1 (b), the near-infrared CCD camera 2 has its optical axis perpendicular to the measurement surface 11a, and its height is the approximate average height of the liquid level L of the water injection unit 13. It is set to. The image analysis personal computer 3b incorporates image analysis basic software for image measurement analysis and measurement result display.

Luminance of transmitted light when the water tank 11 is empty, measured by the image processing I₁(λ) [i, j], and the brightness of the transmitted light when water is injected I₂(λ) [i, j] are as follows.

<maths num="1"><img file="JP2005291830A_D0001.tif" /></maths>

Here, λ is the wavelength of near infrared rays, μ₁(λ) indicates the absorption coefficient of the constituent material of the water tank 11, for example, the acrylic plate, μ.₂(λ) is the water absorption coefficient, d₁Is the transmission length of the constituent material of near infrared rays, d₂Indicates the transmission length of near-infrared water. Further, [i, j] indicates an arbitrary position number of the pixel mounted on the light receiving surface of the near-infrared CCD camera 2. From equations (1) and (2), the brightness ratio I between the water injection state and the empty state_RIs as follows.

<maths num="2"><img file="JP2005291830A_D0002.tif" /></maths>

Taking the logarithm of both sides of equation (3) and swapping the left and right sides,

<maths num="3"><img file="JP2005291830A_D0003.tif" /></maths>

From Eq. (4), the difference between the brightness of the pixel [i, j] in the water injection state and the brightness of the pixel [i, j] in the empty state when logarithmic is taken is -μ on the left side.₂(λ) [i, j] * d₂be equivalent to. That is, by taking the brightness ratio, the transmitted light is only affected by the absorption by water, and the dirt on the water tank 11 and the disturbance such as the structure inside the water tank such as the partition plate 12 are offset, and the measurement surface 11a It does not appear on the captured image of.

FIG. 2 shows an image measurement analysis processing flow when the water amount distribution of the nozzle injection / spray characteristics is image-measured and analyzed using the water tank 11. First, as shown in FIGS. 1A and 1B, the light source 1 is positioned according to the water tank 11 (S1). Normally, the distance D between the water tank 11 and the light source 1₁(See Fig. 1 (b)) is about 200 mm. After starting up the image processing personal computer 3b (S2), determine the field of view of the near-infrared CCD camera 2 of the receiver, and perform focusing and calibration (S3). Distance D between water tank 11 and near-infrared CCD camera 2₂(See Fig. 1 (b)) is usually about 2000 mm. As shown in FIG. 1A, the calibration is performed on the distance between the two parallel reference lines 4a and 4a projected on the measurement surface 11a by the laser line projectors 4 and 4 on the image. From the number of pixels between the reference lines 4a and 4a, the length per pixel on the measurement surface 11a is calculated in advance. Next, measurement conditions such as nozzle injection and the range of the slit-shaped water injection unit 13 to be measured are set (S4). After these adjustments and settings, near-infrared rays are irradiated from the light source 1, and first, the measurement surface 11a is photographed with a near-infrared CCD camera while the water tank 11 is empty (S5). This shooting is performed the required number of times, and the average image is saved in the image processing personal computer 3b.

Next, water is sprinkled from the nozzle 14 arranged directly above the water tank 11 (S6), and after the water injection to each slit-shaped water injection unit 13 is completed, this water injection completion state is photographed by the near-infrared CCD camera 2 (S7). ). FIG. 3 schematically shows this captured image displayed on the monitor 3a. The state where water is accumulated in the slit-shaped water injection section 13 between the partition plates 12 between the reference lines 4a and 4a at the interval Z, that is, the liquid level L can be visually confirmed on the monitor 3a. Then, the difference image processing is further performed from the brightness of the equations (1) and (2) measured by the image processing, and the luminance ratio I shown in the equation (3) is further performed._R(S8). After performing image preprocessing (S9) such as smoothing and contrast adjustment, edge detection processing is performed (S10). In this edge detection process (S10), the gradient of the change in the luminance ratio is calculated for the pixel whose luminance ratio changes abruptly shown in the equation (3), and the pixel having the maximum magnitude is selected from the gradient. , The position E of the pixel is the liquid level L. In this way, by using the luminance ratio for detecting the liquid level, it is possible to prevent the measurement accuracy from being lowered because it is not affected by disturbances such as dirt on the water tank and transparency of the water tank. In FIG. 2, the flow shown by R1 and R2, that is, the output video signal obtained by the water tank filling state shooting (S7) without performing the water tank empty state shooting (S5) and the difference image processing (S8) is image-analyzed. The liquid level can also be measured by processing.

As described above, since the length per pixel on the measurement surface 11a is calculated in advance by calibration, the number of pixels from the reference line 4a to the pixel position E by the image measurement process (S11). It is possible to measure N and convert the number of pixels N into a length to easily and accurately calculate the height of the pixel position E, that is, the height of the liquid level L for each slit-shaped water injection unit 13. it can. Then, the calculated height of the liquid level L can be obtained by converting the measured number of pixels N to the pixel (pix) -length (mm) for each slit-shaped water injection unit 13 by the image measurement result display processing (S12). In addition, by the image measurement data output processing (S13), as shown in FIG. 4, the height of the liquid level L of each slit-shaped water injection unit 13 is graphed, and the water amount distribution of the nozzle is displayed so that it can be seen at a glance. be able to. Further, the image measurement data can be output as a form or a graph in any format. Image measurement data such as an original image, a preprocessed image, and an edge extracted image are stored in the image processing personal computer 3b (S14).

The above-mentioned image measuring device is not necessarily limited to the water tank 11, and can be used for measuring the liquid level in various containers. Further, as long as the container material can transmit near infrared rays to some extent, the image measurement is possible even if the container material is not necessarily transparent. Further, the type of the liquid to be measured is not necessarily limited to water, and any liquid that appropriately absorbs near infrared rays can measure the liquid level.

The image measuring device of the present invention can be used for automatically measuring the liquid level at each water injection part of a water tank provided with a large number of slit-shaped water injection parts used for grasping the spray characteristics of the nozzle. It can also be used to measure the liquid level height of liquid beverages filled in other containers that transmit near infrared rays, such as PET bottles.

<figref num="1">(a) It is explanatory drawing which shows the structure of the image measuring apparatus of embodiment. (b) The same explanatory view (side view).</figref><figref num="2">It is explanatory drawing which shows the flow of the image measurement analysis processing of embodiment.</figref><figref num="3">It is explanatory drawing which shows an example of the image measurement display of embodiment.</figref><figref num="4">It is explanatory drawing which shows an example of the display of the image measurement analysis result of embodiment.</figref><figref num="5">It is explanatory drawing which shows the measuring method of the liquid level of a prior art.</figref>

Code description

1: Light source 1a: Near infrared LED 2: Near infrared CCD camera 2a: Zoom lens 3a: Monitor 3b: Personal computer for image analysis 4: Laser line projector 4a: Reference line 5: Rack 5a: Caster 11: Water tank 11a: Measuring surface 12: Partition plate 13: Slit-shaped water injection part 14: Nozzle L: Liquid level M: Measure P: Ultrasonic probe U: Ultrasonic water level gauge