JPH0434067A - Cloth inspecting machine - Google Patents

Abstract

PURPOSE:To correctly and quantitatively judge defect by subjecting output signal of a camera element illuminating a running fiber structural matter and detecting reflected light or transmitted light from the structural matter to shading correction and signal expansion treatment and converting into binary value. CONSTITUTION:A fiber structural matter 1 such as woven cloth, knitted cloth or nonwoven cloth is continuously or intermittently run and illuminated by a standard light source 3 at a central part between two feed rollers 2, then reflected light or transmitted light from the structural matter is detected by a CCD camera sensor 4. Detected signal outputted from said sensor 4 is inputted to a shading-correcting circuit 5 and sent to a signal expansion circuit 6, then converted to binary value with subjecting to threshold, thus the binary value is indicated on an indication part 7 to judge defect existing in said fiber structural matter such as spot, crease, dirt, abrasion, hole, color unevenness, yarn hanging or weaving unevenness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a "fabric inspection device" that detects defects inherent in fiber structures such as woven fabrics, knits, and nonwoven fabrics. More specifically, in the fiber structure, there are defects caused by optical density modulation, or C which causes optical density modulation.
This invention relates to a "fabric inspection device" that detects defects. More specifically, examples of defects targeted by the present invention include, but are not limited to, "stains,""wrinkles," and "dirt."
“Faint” “Scratch” “Protrusion” “Blurry” “
hole,” “dent,” “cloudy,” “foreign object,” “uneven color,” “scratches,” “pockmark,” “crater,” “
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, inspections using human vision and tactile sense require skill on the part of those conducting the inspection, and are not necessarily efficient or 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 the process of detecting defects based on 1. Furthermore, it is a task to extract particularly large deviations after taking into account the influence of other disturbance noises, etc., and a certain standard should originally 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, 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 previously relied 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 build level.

For example, as seen in Japanese Unexamined Patent Publication No. 62-283453, shading correction is widely used in automatic inspection equipment for films, metal foils, metal plates, etc., and has a truly beneficial effect industrially. This is what is given.

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 QC, that is, thorough quality control.In recent years, it has become possible to stabilize the quality of industrial products at a high level through thorough quality control. I cannot hide my surprise at the quality control that has been carried out.

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 from fluctuations in the output of the image sensor, signal expansion is performed after shading correction of the signal output of the image sensor, and then a threshold is applied. This is a fabric inspection device characterized by having a signal processing system.

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, signal expansion is required.

As shown in FIG. 2, signal expansion is a signal processing method in which a part of an input signal is sliced and only the sliced part is amplified to obtain an output signal. In the present invention, the preferable slice level is 45% or more of the average level of the input signal, and more preferably 70%.
or more, and a more preferable range is 75% or more and 95%
% or less. In the present invention, the amplification factor of the sliced portion is preferably 1.5 times or more and 10 times or less, more preferably 1.8 times or more and 6 times or less, and even more preferably 2.0 times or more and 4.5 times or less. be.

In the present invention, the slice level, amplification factor, and threshold level in signal expansion 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. Further, there are no particular limitations on the signal expansion characteristics and 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, 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.
It is also possible to perform signal processing in the preferred form of the present invention for each of the IG and B outputs, and perform defect detection using the logical sum of the obtained binarized 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 effects of other disturbance noise, some kind of filtering and enhancement as well as optimization of observation conditions are necessary. .

In addition, especially when it comes to human success, the level at which defects, that is, changes in optical density, can be determined differs depending on the color tone of the object to be inspected. Therefore, simply fixing the threshold level mechanically can only be done based on human joy. This is truly unreasonable when it is desired to determine the presence or absence of a defect.

In particular, in the present invention, performing a signal expansion in a limited range on a signal after shading correction and further setting an appropriate threshold level to perform defect detection results in extremely effective defect detection. This has been shown to have a significant effect on

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.

After passing through a shading correction circuit and a signal expander circuit, the RGB outputs of the CCD image sensor are binarized using a predetermined threshold. In this embodiment, the slice level was set to 82% of the average signal level after shading correction, and the amplification factor of the slice portion was set to 2.5 times. The threshold level was set to 88% of the average signal level after signal number expansion.

Each binarized signal is logically operated by an OR circuit,
Defect detection is performed 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. Roller width is 190
The feeding speed of the cm5 fiber structure was varied between 0 and 75 m/min by controlling the drive motor of the conveying system using an inverter.

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 position of the defect whose line of sight was zero coincided with at least the previously obtained defect map.

Comparative Example Using the same equipment as in the example, the following tests were carried out in the same manner as in the example, with the signal expansion and threshold level set to 88% of the average signal level after shading correction. The defect detection rate was only 51%, a result that should be judged to be of no value for practical use.

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

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of shading correction. FIG. 2 is an explanatory diagram of signal expansion. FIG. 3 is a schematic explanatory diagram of a fabric inspection device according to the present invention. (a) Signal to be inspected ■ Textile structure (cloth) (ref) reference signal ■ Feed roller (
b) Shading corrected signal b=a/ref Vsb threshold value (C) Binarized signal ■ Standard light source ■ CCD image sensor ■ Shading correction circuit ■ Signal expansion circuit ■ Judgment and display section

Claims (1)

[Claims] (1) It has a mechanism that conveys the fiber structure continuously or intermittently, a mechanism that illuminates the fiber structure, and an image sensor that detects reflected light or transmitted light from the fiber structure, and A fabric inspection device having a mechanism for determining defects based on fluctuations in the output of an image sensor, characterized by having a signal processing system that performs signal expansion after shading correction of the signal output of the image sensor, and then applies a threshold. inspection equipment.