JPH0424543A - Inspecting method - Google Patents

Abstract

PURPOSE:To detect a defect with good reproducibility at a constant reference by setting threshold levels based on the color data of the reference part of a material to be detected. CONSTITUTION:The color data of a material to be detected are measured with a color/chromaticity meter 10 every time the material to be detected is set. The measured values are read with a CPU 11. The threshold levels for the output signals of corrected RGB are automatically set based on a converting sequence which is obtained beforehand. The outputs of RGB from color linear sensors 4 are binary-coded with the specified thresholds through shading correcting circuits 5 and gamma correcting circuits 6. The binary-coded signals undergo logic operation in an OR circuit 8. A defect is detected based on the finally obtained result.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inspection method for detecting defects inherent in fibrous structures such as woven fabrics, knits, nonwoven fabrics, or film-like objects. More specifically, the present invention relates to an inspection method for detecting defects caused by optical density modulation or defects that cause optical density modulation in the fiber structure or film-like material. More specifically, examples of defects targeted by the present invention include, but are not limited to, "stains,""wrinkles,""dirt,""scratches,""scratches,""protrusions," and "blurring." ” “hole” “dent”
Examples include ``cloudy'', ``foreign matter'', ``uneven coloring'', ``scratches'', ``pockmarks'', ``craters'', ``strings'', ``uneven weaving'', etc.

(Prior Art) Conventionally, inspection of defects inherent in these fibrous structures or film-like materials has relied entirely on the visual or tactile sense of an expert.

Detection of the presence of a defect by a skilled person is not simply based on the results obtained by observing the object to be inspected from a certain direction. Although it is extremely difficult to quantify or even explain qualitatively, it is known that humans recognize events based on extremely multidimensional information. This also applies to defect detection, and the recognition of a defect is the result of observing the object to be inspected from many different angles.

For example, when inspecting an object to be inspected while continuously transporting it, humans may be able to recognize defects simply by looking at the image of the object at a certain moment, according to their sense of vision. There is no vibration due to transportation.
In other words, defects can be read from the subtle movement of images that continuously change from moment to moment due to factors such as fluctuations in lighting or other factors.

As mentioned above, the mechanism by which human senses detect defects is astonishing and even mysterious.

However, while humans have excellent judgment, recognition, and discrimination abilities, human visual and tactile inspection requires skill on the part of those conducting the inspection, and is not always efficient and accurate. That cannot be said. These problems are fatal when inspecting fibrous structures or film-like products that are produced in large quantities using a large number of production machines. In particular, fiber structures have an extremely complex structure even in normal parts, and defect detection is based on this complex structure, or in other words, "variations", as well as other disturbance noise, etc. The task is to extract particularly large deviations, taking into account the influence of However, even with the eyes of an experienced expert, it is virtually impossible to constantly inspect many fiber structures with a constant standard.

In recent years, COD sensors have become available at low cost as solid-state imaging devices that replace image pickup tubes, and with the development of signal processing technology and image processing technology, these sensory tests that have previously relied on human vision have changed. Many attempts are being made to replace them with machines.

However, as mentioned above, compared to humans who make comprehensive judgments, recognition, and identification based on multifaceted information, the information obtained when observing an object with a machine, such as an optical sensor, is , it is literally just the result of observing the object to be inspected from one side, and the amount of information obtained is extremely small.

From such a small amount of information, it is essential to have it within a practical range and in real time! ! Even with current signal processing technology and computer image processing technology, it is extremely difficult to automatically make a high-level judgment such as 111M output by a machine.

(Problems to be Solved by the Invention) In other words, in the conventional defect detection that relies on the visual or tactile sense of an expert, the person performing the inspection requires skill, and it is not always efficient and accurate. This cannot be said to be sufficient, and problems remain in terms of reproducibility, etc. Furthermore, as far as fabric inspection devices are concerned, there is still no one that can be used at a practically satisfactory level, even though it is capable of automatically detecting defects mechanically in real time.

As a result, even though the efficiency and accuracy are not necessarily sufficient, and there are still problems with reproducibility, inspections still rely on the eyes of experts.
This is actually true.

In recent years, it has become possible to stabilize the quality of industrial products at a high level through QC, that is, thorough quality control. I can't hide my surprise at how things have been managed.

In view of this situation, the present inventors have conducted extensive research, and as a result,
We have achieved the next invention related to a method for detecting defects with good reproducibility and according to a certain standard.

(Means for Solving the Problem) That is, the present invention illuminates the inspected object while conveying the inspected object continuously or intermittently, and the reflected light from the inspected object due to the illumination or the transmitted light. In an inspection method that detects light with a color sensor and determines defects based on the output fluctuations of the color sensor, the presence or absence of defects is determined based on the color information read from the reference part of the object to be inspected based on the output fluctuations of the color sensor. This is an inspection method characterized by setting a threshold level for determining.

In the present invention, for example, in a part of a roller system that continuously conveys a fibrous structure or a film-like object to be inspected, the fibrous structure or film-like object is illuminated, and the fibrous structure or film-like object is illuminated. This method attempts to detect defects by observing the optical density modulation due to defects inherent in the object using a color sensor.

The color sensor used in the present invention refers to a so-called image sensor that obtains a signal output in the form of color separation into the three primary colors of RGB, such as a color image pickup tube or a color COD.

A color line sensor or the like can be used.

The present invention does not limit which output of the color sensor is used for defect detection. In the present invention, a single output among the RGB outputs may be used, or if necessary, defects may be detected from the sum, difference, product, quotient, logical sum, logical product, etc. of two or three outputs. It is also possible to do this.

In the present invention, a fiber structure or a film-like object is observed with a color sensor, and defects are detected from fluctuations in the signal output obtained from the color sensor. A feature is that the threshold milled level for determination is determined based on "color information" read from the reference portion of the fiber structure or film-like material.

"Color information" in the present invention means information included in the spectral reflection characteristics or spectral transmission characteristics from the object to be inspected, such as the peak value of the spectral characteristics, the color coordinate value, the centroid wavelength of the spectral characteristics, etc. means.

To read the color information, a known commercially available colorimeter, spectral reflection (transmission) meter, etc. may be used. In some cases, the color coordinates corresponding to the Ostwald color table or the Munsell color table may be determined by visual observation.

Regarding the correspondence between "color information" and threshold level Vsh, it is important to know which of the RGB outputs of the color sensor should be used, or in what combination.
It is difficult to determine this easily because it is greatly influenced by the spectral sensitivity of the output color sensor, the illumination method described later, i.e. the color rendering effect of the illumination light, etc., but as a guideline, it should be determined based on the brightness in human visual perception. In other words, it is preferable to set it in accordance with the correspondence between value and brightness in the Munsell color system, for example.

It is also preferable that these are set in a form that follows the color discrimination characteristic of human vision known as Maffadam's ellipse.

Focusing on the spectral reflection (transmission) characteristics of the object to be inspected, if the center wavelength or peak wavelength of the spectral reflection (transmission) characteristics, or the single spectral wavelength of the same hue is in the range of 350 to 475 nm, Vsh is the signal. 475 to a level of 0.7 to 0.9, more preferably 0.75 to 0.85.
In the range of ~510 nm, Vsh is set to 0 of the signal level.
．． 8 to 0.98, more preferably 0.85 to 0.95, 510
In the range of ~585 nm, Vsh is set to 0 of the signal level.
．． 75 to 0.95, more preferably 0.8 to 0.88, 565 to 0.95, more preferably 0.8 to 0.88.
In the range of B2Onm, Vsh is set to 0.
85-0.98, more preferably 0.90-0.95, 620
In the range of ~700 nm, Vsh is set to 0 of the signal level.
．． It is preferable to set it in the range of 70 to 0.95, more preferably 0.80 to 0.90.

In addition, in the area where 71j is 40 or more in the C I E L *axb* coordinate system, VSh is set to 0.7 of the signal level.
In the range of 0 to 0.95, more preferably 0.80 to 0°90, where Lr" is less than 40,
It is preferable to set the signal level in the range of 0.80 to 0.98, more preferably in the range of 0.85 to 0.95.

Also C I E 1. In the area where the square root of the sum of the square of az and the square of bX is 30 or more, the signal L/H/l/(DQ, 80
-0, 98, more preferably 0.85 to 0.95, and in a region where the square root of the sum of 31 squared and 5 squares is smaller than 30, Vsh is set to 0.70 of the signal level.
It is preferable to set it in the range of 0.90 to 0.90, more preferably 0.80 to 0.88.

There are no particular limitations on the algorithm used to determine "at what level the threshold level should be set."

The judgment may be made by an operator, or in some cases may be made automatically by a machine. Preferably, a method of automatically making the determination using a microprocessor or the like incorporating a program for making such a determination is preferable.

Further, there is no particular limitation on the means for setting the threshold level. Setting may be performed automatically or may be set manually by an operator. These essentially do not have a large influence on the effects of the present invention.

In the present invention, there are no particular limitations on the means of illumination. However, when performing defect detection using R output, the preferred illumination method is to use "light generated from a heating element," more specifically, a halogen lamp, incandescent bulb, reflex lamp, etc., especially with long wavelengths. It is preferable to use a lighting fixture with a wavelength distribution extending laterally, and the color temperature of the light source is preferably 3100 or higher. Further, when detecting defects using the G output or the B output, it is preferable to use a lighting fixture having a wavelength distribution particularly extending toward the shorter wavelength side, such as a "blue-white fluorescent lamp." Preferably, these illumination means should be set so that the most preferable method can be switched in consideration of the selection of the output of the color sensor.

Regarding the position where the illumination means is provided in the present invention,
Although not particularly limited, it is preferable to provide it in a direction perpendicular to the object to be inspected. However, this is not the case especially when the focus is on detecting a specific type of defect.
For example, it may be preferable that the center of the device for illuminating the fibrous structure or film is positioned at an angle of 0 to 15 degrees from the horizontal direction of the fibrous structure or film that is the object to be inspected. be. Preferably, the illumination means in the present invention should be arranged so that illumination means from a plurality of directions can be switched or used in combination as necessary.

In the present invention, in order to increase the ability to detect defects, it is also possible to use a method of detecting defects by applying a threshold after performing shading correction and γ (gamma) correction on the signal output of the sensor. Further, in this case, a method may be used in which the γ (gamma) correction level and threshold level are set for each object to be inspected depending on the color tone, surface condition, etc. of the object to be inspected. In addition, by installing multiple sensors in the direction of fabric conveyance and calculating the "sum" of the signal portions corresponding to the same location on the inspected object detected by the multiple sensors, noise can be canceled out and defects detected. It is also possible to perform signal processing such as emphasizing signals caused by.

(Function) The defects that the present invention attempts to detect in the object to be inspected, that is, fiber structures such as woven fabrics, knits, nonwoven fabrics, or film-like objects, are defects caused by optical density modulation. , or a defect that results in a modulation of optical density.

In these detections, as mentioned above, when using the visual sense of an expert, judgments are not made based on the results obtained by simply observing the object to be inspected from a single direction, but are multidimensional. , judgments are made based on the results of observing the inspected object from multiple angles. However, when automatically detecting defects based on one-dimensional information obtained by machines, and also taking into account the influence of other disturbance noise, some kind of filtering and enhancement as well as optimization of observation conditions are necessary. .

In addition, especially for human visual sense, the level at which defects, that is, changes in optical density, can be discerned differs depending on the color tone of the object to be inspected, so simply fixing the threshold level mechanically will only affect human visual sense. This is truly unreasonable when it is desired to determine whether or not there is a defect in the standard.

In the present invention, it has been shown that setting the threshold level by paying particular attention to the color tone of the object to be inspected, that is, the color information, results in a very large effect on defect detection. Furthermore, the present invention simultaneously achieves the filtering and enhancement effects described above.

EXAMPLES The present invention will be explained in more detail by way of Examples below, but the present invention is not limited thereto.

(Embodiment) Embodiment FIG. 1 is a schematic explanatory diagram showing a detection portion of a fabric inspection device according to the present invention. As shown in the figure, two feed rollers are installed as part of the roller system that continuously conveys the fibrous structure or film-like object to be inspected. This method illuminates the object, observes the fiber structure or film-like object using a color linear sensor, and detects defects.

After passing through a shading correction circuit and a γ (gamma) correction circuit, the RGB outputs of the color linear sensor are binarized by a predetermined threshold build.

Each binarized signal is logically operated by an OR circuit,
Defect detection is performed from the finally obtained results.

A DG5 standard light source is used for illumination, and the light source is provided at a position perpendicular to the center of the object to be inspected. Roller width is 190c
The feeding speed of the m1 fiber structure or film-like material can be adjusted from 0 to 0 by controlling the drive motor of the conveyance system with an inverter.
It was made variable between 75 m/min.

This inspection device operates based on the flowchart shown in FIG. The "color information" of the reference portion of the object to be inspected is measured using a colorimeter at an appropriate portion of the introduction section of the object to be inspected each time the object is set up. The measured values are read into the CPU online, and threshold levels are automatically set for each corrected RGB output signal based on a conversion sequence determined in advance.

For a total of 40 types of fabrics with a total length of 5000 m, defects were detected separately using this fabric inspection device and a skilled inspector at an average conveyance speed of 50 m/min.

The fabrics used in the tests are repeatedly and carefully inspected by multiple experienced inspectors, and defects are mapped out.

Now, the defect detection rate of the fabric inspection device was 97%, and the defect detection rate of the skilled inspector was 93%. The location of the detected defect is
At least it matched the defect map previously obtained.

Comparative Example Using the same equipment as in the example, the threshold level was fixed at a level exactly between the background and the average level of the test object, and the following tests were carried out in the same manner as in the example. The defect detection rate was only 57%, a result that should be judged to be completely unsuitable for practical use.

(Effects of the Invention) According to the present invention, compared to human visual inspection, it does not require skill and is superior in terms of efficiency and accuracy, and it is also possible to quantitatively define judgment criteria.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a fabric inspection device according to the present invention. FIG. 2 is an example of an operation flowchart of the fabric inspection apparatus according to the present invention. ■ Object to be inspected ■ Feed roller ■ Standard light source ■ Color linear sensor ■ Shading correction circuit ■ Gamma correction circuit ■ Judgment circuit ■ OR circuit ■ Result display section ■ Colorimeter ■ CPU

Claims (1)

[Claims] While conveying the test object continuously or intermittently, the test object is illuminated, and a color sensor detects the reflected light or transmitted light from the test object due to the illumination, and the output fluctuation of the color sensor is detected. In an inspection method for determining defects, a threshold level is set for determining the presence or absence of defects based on output fluctuations of the color sensor, based on color information read from a reference portion of the object to be inspected. Characteristic inspection method.