JP2000329683A - Method for detecting particle size of bulk material conveyed by belt conveyor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bulk particle size detecting method which solves the above-mentioned drawbacks of the conventional bulk particle size detecting method for a bulk material conveyed on a belt conveyor. And That is, the present invention provides a detection method that can be applied to a more realistic bulk material having a large amount of overlapping masses after sizing, even if the mixture is a mixture of masses and powders. With the goal. SOLUTION: The present invention irradiates a loose object at an observation position on a belt conveyor with light from a light source installed diagonally above the observation position, and emits light scattered from the loose object.
Sampling is performed by a camera installed substantially directly above the intersection of the irradiation optical axis and the belt conveyor surface, and image processing is performed on the sampled image to obtain a luminance distribution of the sampled image.From the peak height of the maximum peak in the luminance distribution, The present invention relates to a method for detecting the particle size of bulk materials conveyed on a belt conveyor, which detects the particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the particle size of bulk materials conveyed by a belt conveyor, such as raw ores in a cement production process or the like. More specifically, the present invention relates to a method of capturing an image of a bulk material conveyed on a belt conveyor with a camera and accurately monitoring the granularity of the bulk material conveyed from the luminance distribution of the captured image.

[0002]

2. Description of the Related Art In various manufacturing industries including cement manufacturing, bulk raw materials or products of various shapes and sizes which are continuously carried into or out of a system without being packed, ie, bulk materials, are handled. There are many things. Measurement of the shape and size of these bulk materials is very important for quality control of products. These bulk materials are often transported on a belt conveyor, but the method of continuously monitoring the state of such bulk materials is to capture images with a camera →
An image processing method of sequentially performing image processing of captured images → output of information is often used.

In image processing, after digitizing an image taken by a camera, an appropriate threshold value is set in accordance with a measurement item, and binarization processing is generally performed. For example, in the particle size measurement of a bulk material, which is most often performed, a difference in intensity of light reflected from a lump and a gap between the lump, that is, a luminance difference is measured, and 2 is determined based on an appropriately set threshold.
By performing the binarization, the presence / absence of a lump at a certain pixel position is determined, and based on the determination, information on the actual shape and size of the lump, that is, information on the outline of the lump is obtained.
Although this method is very effective as a means for measuring the shape and size of a lump that exists at a distance from each other, it has a drawback that an overlapping lump is mistakenly recognized as one lump. ing. In particular, in the case of a lump having a small particle diameter that has been sized by sieving or the like, the particle diameter has a continuous distribution close to a normal distribution, so that it is difficult to set a threshold value and, in addition, contact between particles is difficult. Is inevitable, and the frequency of erroneous recognition due to the overlapping of blocks becomes extremely high.

[0004] This method based on binarization is as follows.
It does not provide any information on powder properties with a particle size of about 5 mm. This is because with the resolution of the current image processing apparatus, the size of one pixel is not much different from or smaller than the powder particle size in this range. In the method using a belt conveyor, powder and lump of a certain size or less are often conveyed simultaneously,
For such an object, accurate information on the granularity and shape cannot be obtained by the conventional binarization processing.
As a countermeasure against the shortcomings of the binarization method, various methods of performing a filtering process on an electric signal in an image processing process have been studied, but they have not been a definitive solution. It is the current situation.

[0005]

SUMMARY OF THE INVENTION The present invention relates to the above-mentioned,
It is an object of the present invention to provide a method for detecting a particle size of a bulk material in which the disadvantages of the conventional method for detecting a particle size of a bulk material conveyed on a belt conveyor are eliminated. That is, the present invention provides a detection method that can be applied to a more realistic bulk material having a large amount of overlapping masses after sizing, even if the mixture is a mixture of masses and powders. With the goal.

[0006]

If the present inventor devises the positions of the light source and the camera, the peak height of the maximum peak, that is, the peak value, in the luminance distribution diagram showing the scattered light from the sample is determined by the bulk of the sample. The present invention was found to provide accurate information on the particle size, and completed the present invention. That is, the present invention irradiates a loose object at an observation position on a belt conveyor with light from a light source installed diagonally above the observation position, and emits light scattered from the loose object with an irradiation optical axis and a belt conveyor. Sampling is performed by a camera installed substantially directly above the intersection of the surfaces, image processing is performed on the collected image to obtain a luminance distribution of the collected image,
The present invention relates to a method for detecting a particle size of bulk material conveyed on a belt conveyor, wherein the method detects a particle size from a peak value of a maximum peak in the luminance distribution. Hereinafter, the present invention will be described in detail.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that the luminance distribution of a sampled image is measured as information on the particle size of the bulk material. This method is the same as general image processing in that a sampled image is divided into pixels and the luminance of each pixel is measured, but the measured value is binarized based on a set threshold value. Instead, the number of pixels having a certain luminance (frequency) is counted, and information included in the image is shown as a luminance distribution in which the frequency is plotted against the luminance.

[0008] The bulk sample that has been pulverized and classified generally has a particle size distribution close to a normal distribution, and the luminance obtained by performing image processing on a photographed image of the bulk sample also has a distribution close to the normal distribution. Further, the state of the luminance distribution changes according to the particle size distribution of the bulk specimen. For example, it has been found that the spread of the luminance distribution changes in parallel with the spread of the particle size distribution, but the value of the peak value is reduced in a sample containing a sample having a large particle size. As will be described later in detail with examples, the particle size distribution of the bulk material can be measured using this knowledge.

FIG. 1 shows the arrangement of observation instruments according to the present invention. In order to observe the luminance, it is necessary to irradiate the light from the light source to the rose 2 on the belt conveyor 1 which is the subject, but in the present invention, the position is observed on the belt conveyor, that is, within the observation field of view of the camera 4. Light from a light source 3 installed obliquely above the coming bulk specimen is irradiated onto the screen to be observed from an oblique direction. The irradiation angle of the light with respect to the observation screen may be larger than 0 degree, but in combination with the camera 4 installed almost directly above the center of the observation screen, information with high accuracy and good reproducibility can be obtained. In order to obtain the angle, the angle between the optical axis and the observation screen, that is, the irradiation angle is preferably set to 45 degrees or more.

As a light source, either visible light or infrared light can be used. Not only can a camera having excellent characteristics as a means for detecting scattered light from a specimen be obtained at a low cost, but also it can be directly compared with a specimen color by visual observation. It is most convenient to utilize visible light, where possible, and it is therefore most preferred to use a visible light source as the light source.

The scattered light from the specimens on the belt conveyor is photographed by an imaging camera installed just above the center of the screen to be observed, and is taken into an image processing apparatus as image information. The camera will be selected according to the light type of the light source. As described above, in the present invention, it is most preferable to use visible light, and therefore, a video camera used for general photographing, A CCD camera can be suitably used. In addition, since the luminance is measured, the camera does not need to be used for color, but functions sufficiently for monochrome.

The installation positions of the light source and the camera are affected by their performance, for example, the intensity and the irradiation area of the light source, the sensitivity of the camera, the size of the visual field, and the like. Since it is affected by the influence, it cannot be determined in a straightforward manner, and the actual measurement is performed to determine the optimum position that matches the performance of the device and the use environment.

Although the width of a belt conveyor that is usually used is various, the belt width is adapted to the field of view and the installation position of a camera so that the entirety of the bulk material on the belt conveyor in the width direction of the conveyor can be expanded by one photographing. Can cover. If the shooting speed, the image processing speed, and the conveyor speed are adjusted, monitoring that covers the entire area in the conveyor traveling direction can be performed by repeated shooting. In other words, if necessary, it is possible to monitor the entire amount of bulk materials conveyed by the belt conveyor, but it is often sufficient to perform sampling inspections that perform partial or intermittent photography, and You will have to choose between them.

[0014] After image information of a certain bulk sample in the position to be observed on the belt conveyor taken from the camera is converted into an electric signal, it is sent to a computer and image processing is performed. In the present invention, image processing for dividing the imaging screen into tens of thousands of pixels, measuring the luminance of each pixel, performing integration of the number of pixels having the luminance for each luminance, and outputting the result as a luminance distribution of the imaging screen However, this processing is not special, and can be handled by a generally used image processing method. The output of the luminance distribution can be output as an analog diagram showing the distribution or as a peak value. Of course, by using an appropriate control device, the output can be used for controlling the entire manufacturing apparatus.

The output peak value can be converted into information on the particle size of the bulk material from the relationship between the peak value and the particle size determined in advance, and the temporal change of the peak value continuously photographed at regular intervals can be continuously changed. , It is possible to detect an abnormality that has occurred in the particle size of the conveyed bulk material. Hereinafter, the present invention will be described in more detail with reference to specific examples.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an example in which the method of the present invention is applied to the transport of crushed limestone of various particle sizes by a belt conveyor will be described. (1) Bulk material After grinding, 5 mm or less, 20 mm or less, 5 to 20 mm, 2
Limestone sized to four types of particle sizes of 0 to 40 mm was used as a bulk material to be inspected. (2) Transport conditions A conveyor belt with a width of 1200 mm is moved at a speed of 140 m /
Activated in minutes. (3) Light source A fluorescent lamp with an output of 80 watts and 30 KHz was placed at a position of 2000 mm above the conveyor surface, and the optical axis was approximately 45 degrees from the conveyor surface.
It was installed so as to be at an angle of degrees. (4) Camera 500m above the conveyor at almost equal distance from the left and right ends of the conveyor
At position m, a monochrome video camera was installed. The screen that can be shot in one shot is 50
It is a rectangle of 0 mm x 500 mm. FIG. 1 shows the relative arrangement of the conveyor, the light source, and the camera. (5) Imaging, Image Processing, and Output Imaging was performed once a minute. The sampled image is divided into 512 x 512 divided by 260,000 pixels using commercially available image processing software, and the luminance of each pixel is measured. Then, the number of pixels having the same luminance is integrated for each luminance, and the integrated result is represented by a luminance distribution diagram. And the peak value of the maximum peak was output as information indicating the particle diameter of the specimen.

FIG. 2 shows the output luminance distribution of the raw material specimen of each particle size. FIG. 3 shows the change with time in the peak value of the maximum peak for each particle size. In the figure,
Lines indicating (average value + 2σ) and (average value -2σ) calculated from the average peak value and the standard deviation σ during the measurement time are also drawn.

As can be seen from the results shown in FIG. 3, the luminance peak values of the bulk specimen shown here do not overlap in the range of the average value ± 2σ. That is, according to the method of the present invention, it is possible to supervise the bulk material conveyed by the belt conveyor at the risk factor of 4.5% only by the peak value in the luminance distribution.

FIG. 4 shows the observations made during the practice of the present invention.
The following is an example of an accident involving the inclusion of lumps having greatly different particle sizes. What is shown here is the luminance distribution shown on the monitor when limestone having a particle size of 20 mm or less is mixed with stone having a particle size of 40 mm. The abnormality is indicated on the luminance distribution monitor screen as an abnormality in the peak shape. Further, since the low-luminance portion increases with the increase in the shadow portion of the lump, it can be detected as an abnormal peak value where the peak value decreases.

[0020]

According to the present invention, even if the sample is sized and the powder and agglomerate coexist or the sample has a large number of overlapping lumps, the particle size is less erroneously recognized. Further, it is possible to cope with a method of adding general image processing to an image obtained by a general method without requiring special processing. Therefore,
The method is effective in continuous monitoring of realistic bulk specimens conveyed on a belt conveyor, which is a problem in the conventional method.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the arrangement of devices in the measurement method of the present invention.

FIG. 2 is a diagram illustrating an example of a sample particle size dependency of a luminance distribution. Sample particle size: (A) 5 mm or less (B) 20 mm or less (C) 5 to 20 mm (D) 20 to 40 mm

FIG. 3 is a diagram showing an example of a temporal change of a measured peak value: (A) to (D) have the same meaning as in FIG.

FIG. 4 is a diagram illustrating an example of a change in luminance distribution due to inclusion of a lump having a significantly different particle diameter.

[Explanation of symbols]

 1 Belt conveyor 2 Objects to be measured 3 Light source 4 Camera

Claims (4)

[Claims] 1. An object at an observation position on a belt conveyor is irradiated with light from a light source installed diagonally above the observation position, and light scattered from the object is irradiated with an irradiation optical axis and a surface of the belt conveyor. Sampled by a camera installed just above the intersection of
A method for detecting the particle size of a bulk material conveyed by a belt conveyor, comprising performing image processing on a collected image to obtain a luminance distribution of the collected image, and detecting a particle size from a peak value of a maximum peak in the luminance distribution. 2. The particle size of bulk material conveyed by a belt conveyor according to claim 1, wherein an angle formed between the belt conveyor surface and an optical axis irradiated from the light source is 45 degrees or more and smaller than 90 degrees. Detection method. 3. The method according to claim 1, wherein a visible light source is used as the light source. 4. The method according to claim 1, wherein the bulk material is a limestone pulverized material.