JPH0424276A - Fabric inspection device - Google Patents

Abstract

PURPOSE:To carry out accurate and quantitative inspection of cloth by illuminating a traveling fiber structure, subjecting the output signal obtained by detecting the reflected light or transmitted light by a pickup element to shading correction and gamma correction and then applying threshold thereto. CONSTITUTION:A fiber structure 1 such as woven and knit fabric or nonwoven fabric is continuously or intermittently traveled and simultaneously illuminated using a halogen lamp, incandescent lamp or leaf lamp, etc., especially a light source 3 having wavelength distribution expending to long wavelength and the reflected light or transmitted light is detected with CCD pickup sensor 4. Output signal of the sensor 4 is sent to shading correction circuit 5 and gamma correction circuit 6 to carry out correction treatment and then converted into binary digit by applying threshold thereto to detect defect of stain, crease, dirt, flaw, hole, unevenness of color, hanging yarn, woven unevenness, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fabric inspection device for detecting defects inherent in fiber structures such as woven fabrics, knitted fabrics, and nonwoven fabrics.

More specifically, the present invention relates to a fabric inspection device that detects defects caused by optical density modulation or defects that cause optical density modulation in the fiber structure. More specifically, examples of defects targeted by the present invention include, but are not limited to, "stains,""wrinkles,""dirt,""fading,""scratches,""protrusions," and "blurring."
"Dents""Dents""Cloudy""Foreignobjects""Unevencoloring""Scratches""Pockmarks""Craters"
Examples include ``hanging thread'' and ``uneven weaving''.

(Prior Art) Conventionally, inspection of defects inherent in these fiber structures 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. Instead, defects are detected from the subtle movements of the image that continuously change from moment to moment due to vibrations caused by transportation, fluctuations in lighting, and 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 fiber structures produced in large quantities using multiple production machines. In particular, fiber structures have extremely complex structures even in normal parts, and detecting defects is based on this complex structure, in other words, from among "variations" and also due to other disturbance noise etc. This is a process of extracting particularly large deviations after taking into account the influence, and a certain standard should be set for this. 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, as CCD image sensors have become available at low cost as solid-state video devices to replace image pickup tubes, and with the development of signal processing technology and image processing technology, these sensory systems that have been dependent on human vision have become less expensive. Many attempts are being made to replace inspection 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 to be inspected with a machine, such as an optical image sensor, This is literally just the result of observing the object to be inspected from one side, and the amount of information obtained is extremely small.

With the current signal processing technology and computer image processing technology, it is not possible to automatically make advanced judgments such as defect detection in real time from such a small amount of information using a machine within a practical range and in real time. However, it is extremely difficult.

From the above discussion, it is impossible to increase a satisfactory defect detection rate with signal processing that simply binarizes the obtained image signal by observing the object to be inspected with an image sensor, etc. is obvious. Some kind of filtering and enhancement is essential when making advanced judgments from one-sided information provided by a machine.

Now, shading correction is known as such a filtering and enhancement method.

Shading correction is a method used to correct aberrations, brightness irregularities, illumination irregularities, etc. of the optical system that is often placed in front of the imaging element when obtaining images with an imaging element. be. More specifically, shading correction is to divide the image to be inspected by a reference image read in advance, as shown in FIG. It is technically not difficult to perform division electrically. The result of such an operation is
In the normal part of the video signal, the size is "1".
If the signal level fluctuates due to a defect, the defect can be easily detected by providing a threshold level.

For example, as seen in Japanese Patent Publication No. 62-263453, shading correction is performed using film, metal foil, etc.
It is widely and commonly used in automatic inspection equipment for metal plates, and has a truly beneficial effect in industry.

However, such powerful filtering and shading correction with enhancement effects also
Its power cannot be fully demonstrated when inspecting fiber structures. This is because, as mentioned above, fiber structures have extremely complex structures even in their normal parts, and their width is quite wide. Therefore, in the normal part signal divided by the reference part signal, these so-called noise components may be amplified in some cases.

Particularly when the object is limited to textile structures, it is not possible to obtain satisfactory results with such simple shading correction alone.

(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. Further, as for fabric inspection equipment that automatically performs defect detection mechanically in real time within a practical range, there is still no one that can be used at a practically satisfactory level.

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.
The reality is that this is being done.

In recent years, it has become possible to stabilize the quality of industrial products at a high level through QCl, or 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 device that can detect defects with good reproducibility and according to a certain standard.

(Means for Solving the Problem) That is, the present invention provides a mechanism for conveying a fiber structure continuously or intermittently, a mechanism for illuminating the fiber structure, and a mechanism for reflecting or transmitting light from the fiber structure. In a fabric inspection device that has an image sensor that detects light and has a mechanism that determines defects based on output fluctuations of the image sensor, γ (gamma) correction is performed after shading correction of the signal output of the image sensor,
This is a fabric inspection device characterized by having a signal processing system that then applies a threshold.

In the present invention, for example, in a part of the roller system that continuously conveys the fibrous structure that is the object to be inspected,
This method attempts to detect defects by illuminating the fiber structure and observing modulation of optical density due to defects inherent in the fiber structure using an imaging device.

The image sensor used in the present invention may be, for example, an image pickup tube, a COD image sensor, or the like.

Further, the shading correction used in the present invention has the same content as described above.

An essential requirement of the present invention is that the signal after shading correction is
Furthermore, gamma correction is performed.

Gamma correction is γ Vout =: Vln
(1) Where, Vln: Input signal level Vout: Output signal level γ: Gamma correction coefficient, that is, as expressed in equation (1), it is a factor that multiplies the input signal to the γ (gamma) power, and serves to enhance the signal level. have. In the present invention, the preferred range of γ is 1.4
It is in the range of 2 or more and 6.0 or less, more preferably 1.
It is in the range of 75 or more and 4.0 or less. The most preferable range is 2.0 or more and 3.2 or less.

In the present invention, the gamma correction coefficient and the threshold level can be varied based on the "color coordinate values" read from the reference portion of the fiber structure. There are no particular limitations on the algorithm used to determine which level these should be set to. 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.

There are also no particular limitations on the mata-comma correction characteristics and the threshold level setting means. 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.

Note that in the present invention, the gamma correction characteristic may have an offset.

The preferred offset range is 0 to 4 of the incoming signal level.
0%, preferably 0-20%.

In the present invention, there are no particular limitations on the means of illumination. However, as a preferred lighting method, it is preferable to use "light generated from a heating element", more specifically, use of halogen lamps, incandescent bulbs, reflex lamps, etc., and in particular use lighting equipment with a wavelength distribution extending toward the long wavelength side. be able to.

Furthermore, the color temperature of the light source is preferably 3100 or higher. However, in some cases it may be preferable to use a lighting fixture with a wavelength distribution that extends particularly towards shorter wavelengths, such as a "blue-white fluorescent lamp". Preferably, these illumination means should be set so that the most preferable method can be switched, taking into account the selection of the output of the color image sensor.

Further, in special cases, a light source having extremely narrow spectral radiation characteristics such as a laser beam may be used, and when such a light source is used, an illumination method such as scanning laser light may be used.

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, from the horizontal direction of the textile structure that is the object to be inspected
It may be preferable to center the device illuminating the fibrous structure at an angle of 15 degrees. 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, a plurality of image sensors are provided in the direction of fabric conveyance, and the "sum" of signal portions corresponding to the same location on the object to be inspected detected by the plurality of image sensors is calculated. It is also possible to perform signal processing such as canceling out the defects and emphasizing the signal caused by the defect.

Furthermore, in the present invention, defects may be detected by appropriately combining signals obtained from a plurality of image sensors having different spectral characteristics. More specifically, for example, but not limited to, R of a color image sensor.
, G, B, each output may be subjected to signal processing in a preferred form according to the present invention, and defect detection may be performed using the logical sum of the obtained binary signals.

Furthermore, in this case, the image sensors having different spectral characteristics do not necessarily need to be installed at the same location. In addition, each has different spectral radiation characteristics,
Any suitable lighting means may be used.

(Function) The defects that the present invention attempts to detect in the objects to be inspected, that is, fiber structures such as woven fabrics, knits, and nonwoven fabrics, are defects caused by optical density modulation or optical This is a defect that causes a modulation of the target concentration.

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 there is a defect in the standard.

In particular, the present invention is capable of performing defect detection by performing gamma correction in a limited range on the signal after shading correction and further setting an appropriate threshold level. It is a thing that has not been able to bring about a very large effect.

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. 3 is a schematic explanatory diagram showing the detection part of the "fabric inspection device" in the present invention. As shown in the figure, two feed rollers are installed as part of the roller system that continuously conveys the fiber structure to be inspected, and the fiber structure is illuminated at the center of the two rollers to capture CCD images. A sensor is used to observe the fiber structure and detect defects.

The output of the CCD image sensor is binarized using a predetermined threshold after passing through a shading correction circuit and a gamma correction circuit. In this example, γ=2.2, and the threshold level was set to 85% of the average signal level after gamma correction. Each binarized signal is logically operated by an OR circuit, and defects are detected from the finally obtained results. A D65 standard light source is used for illumination, and the light source is installed at a position perpendicular to the center of the object to be inspected.

The width of the roller is 190 cm.The feeding speed of the fiber structure is 0 to 100 cm by controlling the drive motor of the conveyance system with an inverter.
It was made variable over a period of 75 m and 7 minutes.

Defects were detected separately for a total of 4 types of fabrics with a total length of 5000 m 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, gamma correction was performed, and the threshold level was set to 85% of the average signal level after shape ink correction. 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 inspection by human visual inspection, it does not require skill and is superior in terms of efficiency and accuracy, and it is also possible to quantitatively determine judgment criteria. Ta.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of shading correction. FIG. 2 is an explanatory diagram of gamma correction. FIG. 3 is a schematic explanatory diagram of a fabric inspection device according to the present invention. (a) Signal to be inspected ■Fibre structure (cloth) (ref
) Reference signal ■Feed roller (b) Shading ■Standard light source

Claims (1)

[Claims] It has a mechanism for conveying the fiber structure continuously or intermittently, a mechanism for illuminating the fiber structure, and an image sensor for detecting reflected light or transmitted light from the fiber structure, A fabric inspection device having a mechanism for determining defects based on output fluctuations, characterized in that the fabric inspection device has a signal processing system that performs gamma correction after shading correction of the signal output of the image sensor, and then applies a threshold.