JP2006268142A - Method and device for testing paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide s method and a device for testing paper capable of performing stable measurement and soundness determination even in the case that transmitted light quantity of the paper and illumination of light change due to the effect of disturbance when performing a 100% inspection for the quality of watermark image of the paper on which the watermark image is formed as code information on a paper machine. <P>SOLUTION: In this method and device for testing, a threshold value is automatically changed according to the brightness of the transmitted light image in a region containing the watermark image and the transmitted light image data is input, a watermark part and a background part are divided apart, and measurement of the visibility of the watermark image from a concentration distribution and measurement of a pattern form of the watermark image from the binarized transmitted light image are performed to compare/inspect with watermark image quality as reference. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for inspecting the quality of a sheet, and more particularly, to a technique for inspecting a state in which code information is applied to a sheet by scraping.

  Conventionally, a visual inspection by a skilled worker has been performed for inspection of a creped paper in which a watermark has been processed. In this inspection, the creased paper is held over transmitted light, the watermark that emerges as a visual image is visually observed, the presence / absence of the crease, the shape, dust contamination, and the like are confirmed, and the defective paper is removed.

  In recent years, a technique for applying code information to paper by watermark has been adopted. Since this code information is used for machine processing, the shape of the inserted watermark is recognized as information. For this reason, the watermark as a normal image has been required to be visually recognizable as an image with a sharpness composed of a difference in brightness due to transmitted light, but the watermark as code information is In addition, it is required to manage shapes such as width, length, area, and number.

  The present applicant has applied for a penetration inspection apparatus as an apparatus capable of mechanically inspecting the penetration paper. The inspection apparatus separates a watermark image to be inspected by a pattern and inspects the defect based on the contrast with a reference image (see, for example, Patent Document 1).

Japanese Patent No. 3501967

  However, when such an inspection method is used, calculation processing is performed with a fixed threshold value that is defined in advance before the inspection. It was difficult to appropriately binarize the inserted image. In such a case, it is necessary to manually change the defined threshold value and input a new threshold value that is appropriate for the binarization processing of the scraped image. there were.

  Since such an inspection apparatus is an apparatus for recognizing a watermark image inserted into a sheet, it is not suitable for managing the width, length, number, etc. of code information.

  In the conventional visual inspection by a skilled worker, it takes a lot of time to perform the work to inspect all the sheets. In addition, it has been difficult to numerically manage the definition and shape of the watermark.

  The present invention performs quality control of the squeezed state such as the sharpness, width, length, area, and number of watermarks of the paper on which the watermark image pattern is formed as code information, which is difficult with such a conventional technique. It is an object of the present invention to provide an inspection method and an inspection apparatus for squeezed paper.

  The present invention inputs a transmitted light image using a threshold value automatically changed in accordance with a change in luminance of a transmitted light image in a region including a watermark image, and changes a transmitted light amount obtained from an object to be inspected. Accordingly, it is an object of the present invention to provide an inspection method and an inspection apparatus for a swept paper that can perform quality control without being affected by disturbance by automatically changing the threshold value at the time of image acquisition to an optimum value.

  In the method for inspecting a paper on which a watermark image pattern shape is formed as code information in the present invention, light is emitted from one surface side of the paper, and the light is emitted from the other surface side of the paper irradiated with the light. When the transmitted light image of the area including the watermark image is captured, and the transmitted light image of the area including the watermark image is acquired, automatically according to the luminance of the transmitted light image of the area including the watermark image The transmitted light image is input to the image processing unit using the changed threshold value, the transmitted light image of the region including the input watermark image is divided into a watermark portion and a background portion, and the watermark portion Measure the sharpness of the watermark image from the density distribution of the background and the background, binarize the transmitted light image of the area including the input watermark image, and convert the watermark image from the binarized transmitted light image. The watermark image is measured by measuring the pattern shape. Inspecting the quality of the watermark image of the creased paper by digitizing and comparing and inspecting the quality of the watermark image obtained from each measurement result with the quality of the watermark image as a reference Features.

  The code information may be a watermark image of a bar code or a two-dimensional code.

  The sheet inspection method is characterized in that the pattern shape measurement target of the watermark image is at least one of the width, length, area, and number of the barcode or two-dimensional code.

  According to the present invention, a watermark image quality inspection apparatus for a paper on which a watermark image is formed as code information, the inspection apparatus includes an illumination device, an imaging device, and an image processing device, and the illumination device includes the paper sheet. A light source unit that irradiates light on one surface of the sheet, and the imaging device captures a transmitted light image of a region including the watermark image from the other surface of the sheet irradiated with light on the one surface. And the image processing apparatus inputs the transmitted light image data by automatically changing the threshold value of the transmitted light image of the area including the captured watermark image in accordance with the luminance of the transmitted light image. An image input unit, an image analysis unit that separates the transmitted light image data of a region including the input watermark image into a watermark unit and a background unit, and a watermark image from a density distribution of the watermark unit and the background unit Measurement and binary of sharpness The pattern shape of the watermark image is measured from the transmitted light image, the quality of the watermark image is digitized, and the watermark image quality obtained from each measurement result is used as the reference watermark image quality value. A calculation unit that performs a comparison inspection and performs a calculation, a storage unit that stores the reference numerical value, a determination unit that determines a result of the calculation in the calculation unit, and an output display unit that displays the determination result It is characterized by that.

  The image pickup unit of the image pickup apparatus is a CCD line camera, and is a sheet inspection apparatus.

  Measures the sharpness, width, length, and area of the watermark on the entire surface of the creased paper, which was impossible with conventional visual sensory inspections, and makes it possible to judge pass / fail by numerical values. In addition, it has become possible to perform 100% inspection on a paper machine.

  Due to the influence of disturbance, stable measurement and pass / fail judgment can be performed even if the amount of light transmitted through the paper and the illumination illuminance change, and a uniform product inspection can be performed.

  Embodiments of the present invention will be described. In order to carry out the inspection method of the present invention, it is desirable to have a light source as illumination means, an image input means, and an image processing means (see FIG. 1).

  The object to be inspected is a scraped paper to which code information is given as a watermark, and is in a web state being conveyed on a paper machine. The watermark shape as the code information is a barcode-type rectangle, a two-dimensional code-type rectangle, or the like, and is recognized as the code information.

  The image pickup means used in the image input means is preferably operated by the CCD line camera 1, and the image processing means is operated by the image processing apparatus 6 using a real-time OS (see FIG. 2). It is also possible to install a plurality of CCD line cameras 1 and image processing devices 6 according to the width of the paper 3 to be inspected. In this case, as shown in FIG. 2, the network hub 10 may be used to connect to the real-time OS display / operation PC 7. The CCD line camera 1 is suitable for photographing an image in a web conveyance state such as during paper conveyance on a paper machine, and light is emitted from a transmissive illumination device to the interleaved paper 3 and is given as code information. The CCD line camera 1 sequentially acquires a one-dimensional image from the area including the watermark 4 and generates a two-dimensional image.

  At this time, the image picked up in the watermark area of the crease paper 3 is a transmission image, and is acquired from the other side different from the surface irradiated with light from one side of the paper surface. An image is displayed and acquired.

  From the acquired image data, four watermark portions given as code information are cut out, and the sharpness and shape of the watermark portions are measured to check the penetration quality. Specifically, the acquired image data is transferred to the memory of the image processing means, and known image processing such as pattern matching is performed on the reference data stored in the memory to obtain the inspection object. The inspection is carried out after separating the four watermarks given as code information from the blank paper 3.

  The quality of the image is digitized by measuring the sharpness of the watermark using the density distribution and measuring the shape from the binarized image for the image data of the four watermarks given as code information. It can be seen that it is very useful because the defect is immediately identified by comparing with the reference numerical value. Thereafter, various known techniques may be used as appropriate to eliminate defective products.

  Therefore, in order to carry out the present invention, an incandescent bulb is selected as a light source applied to the transmission illumination device 2 for a region including a watermark on a part or the entire surface of the inspection paper 3 to be inspected. . Other light sources that can be used may be appropriately selected from LED (light emitting diode), halogen lamp, sunlight, HID lamp (High Discharge Lamp), and the like. The light transmitted through the light source is acquired by the CCD line camera 1 of the imaging means. As a camera used for imaging, a CCD area camera or a CCD line camera 1 is preferably used. The CCD area camera is suitable for stationary imaging by so-called off-line inspection in which an object to be inspected is once taken out from the production line and inspected, such as an inspection table on a table. The CCD line camera 1 is suitable for photographing a traveling state in a so-called on-line inspection in which an object to be inspected is inspected on a production line such as during conveyance on a paper machine.

  Images captured by the respective CCD cameras such as the CCD area camera and the CCD line camera 1 are extracted as image data of a two-dimensional image.

  Pattern matching is applied to separate the four watermarks given as code information from the image data of the two-dimensional image. This compares image data of a captured two-dimensional image with image data serving as a reference prepared in advance, and separates four watermarks given as code information according to the degree of similarity such as the shape and brightness of the image. is there.

  The four watermarks provided as code information cut out from the image data of the two-dimensional image can be divided into a background portion and a white watermark portion depending on the amount of transmitted light. The white watermark here means a portion where the thickness of the paper layer is thinner than the surrounding background portion.

  The sharpness of the watermark 4 given as code information is measured by the difference in image brightness. This can be expressed as follows.

  Here, the maximum value is the luminance of the brightest pixel, and the luminance of the pixel in the white watermark is adopted. The minimum value is the luminance of the darkest pixel, and the luminance of the pixel in the background portion is adopted.

  The shape of the watermark 4 given as code information is measured by the width, length, area, and number of white watermarks. A binarization method is used to separate the background portion and the white watermark portion.

  When binarizing, the threshold value is automatically changed according to the brightness of the watermark image that changes due to the influence of disturbance such as the intensity of illumination and ambient light, and the degree of change at that time depends on the discriminant analysis method or An optimum value is automatically obtained from the luminance histogram of the image using a clustering method or the like. This can be expressed as follows.

Here, σ _B ² (T) is the interclass variance, and σ _W ² (T) is the intraclass variance. The threshold value T is obtained so that the degree of separation η (T) is maximized.

Here, μ _{1 and} μ ₂ are average values of luminance of pixels in each class. When the image is divided into two classes by the threshold value, a value that becomes T is set as the threshold value.

  Furthermore, performing known image processing such as a median filter on the image before binarization with the obtained threshold value is very effective for removing noise that becomes extra information from the image. is there.

  In order to measure the shape of the watermark from the binarized white watermark image, a general image processing method may be used. For example, the width and length can be obtained from the ferret diameter from the coordinate position of the image, and the area may be obtained by multiplying the number of pixels by the size of one pixel. Further, the number can be obtained from the number of labels by labeling an image.

  If the measured values of watermark sharpness and watermark shape measured in this way are within the allowable range, it is determined to be normal, and the product is treated as a normal product. It is determined and processed as an abnormal product.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an inspection apparatus for a slip sheet according to the present invention will be described in detail below with reference to the drawings. However, the contents of the present invention are not limited to these embodiments, and are easily estimated by technical categories. Are also included.

  As shown in FIG. 1, the inspection on the production line, such as the state of the watermark 4 given as online code information in the conveying state of the interleaving paper 3, is performed by the CCD line camera 1 and the transmission. In the apparatus configuration mainly composed of the illumination device 2, the image input device 5, and the image processing device 6, the inspection paper 3 to be inspected is conveyed on the line of the paper machine in a web state. As shown in FIG. 2, an image processing device 6 or the like may be added in accordance with the width of the sheet to be inspected.

  The flow of the inspection process by the inspection apparatus on the production line will be described using the flowchart of FIG. As shown in FIG. 1, the transmitted illumination device 2 irradiates light to the transported paper 3 being conveyed. The surface irradiated at this time is on the side of the paper surface opposite to the image receiving portion of the camera so that the transmitted light of the penetration paper 3 can be imaged by the camera. That is, the inspection paper 3 to be inspected is positioned between the transmission illumination device 2 and the camera.

  An image including a watermark area that is transmitted from the wiped paper 3 irradiated with light is imaged for each line by the CCD line camera 1 to obtain one-dimensional data of the image (S01). When the image is acquired, the timing signal from the print mark sensor 9 and the rotary encoder 8 can be used to efficiently acquire the image by narrowing down the watermark area. The one-dimensional image data of the watermark image area acquired by the CCD line camera 1 is sequentially input in time series by the image input means 12 to generate two-dimensional image data.

  When an image of the camera area is acquired, the brightness of the watermark image changes due to the influence of disturbance such as the intensity of illumination and ambient light. At that time, it is preferable to adjust the aperture of the camera in advance so that the highest luminance portion and the lowest luminance portion are not saturated and can be imaged as gradation.

  The acquired image data is input to a memory, and the image data is subjected to code matching from the acquired image data by pattern matching with a reference image of code information stored and stored in advance by a calculation unit provided in the image processing apparatus 6. A process of cutting out an area portion including the watermark 4 given as information is performed (S02).

  Next, in the image cut out in S02, the flow direction of paper conveyance is set as the X axis, and the width direction is set as the Y axis. In the range of the central portion 10 mm in the X-axis direction, the brightness of the image is scanned to obtain the degree of modulation (S03). The sharpness is measured by applying the maximum value and the minimum value to the calculation formula for obtaining the sharpness disclosed in Equation 1 (S04).

  Further, the threshold value is obtained by the discriminant analysis method from the luminance histogram of the image cut out in S02, and the image is binarized (S07). The shape of the code information watermark image (S08) separated by binarization is measured.

  In measuring the shape, the width and length of the watermark are determined from the ferret diameter. The area is determined by obtaining the area per pixel in consideration of the resolution of the image and multiplying it by the number of pixels of the binarized watermark image (S09). For the number of labels, a labeling process is performed on the image (S10), and the number of labels is defined as the number.

  The sharpness and shape of the watermark measured in this way are compared with a management range set in advance (S05, S11), and whether or not the damage is determined. If the result of the quality inspection is a loss based on this determination result, display or paper rejection is executed by a determination lamp. When the paper is rejected, IJP printing on the paper and output by a warning lamp are performed (S12). As this display and rejection means, known means may be used.

  Further, when the camera is not in the transport state as in the inspection on the table, if the camera is a CCD area camera, a watermark image can be obtained similarly by arranging the camera and illumination with the paper sandwiched therebetween. . Processing after image acquisition is realized by this embodiment. From the above, the processing after obtaining the two-dimensional image data can be determined in substantially the same manner both online and offline.

It is the schematic of the watermark inspection apparatus in this invention. 1 is a schematic configuration diagram of a watermark inspection apparatus according to the present invention. It is a flowchart of a watermark quality inspection of the present invention. It is an example of the penetration paper of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 CCD line camera 2 Transmission illumination device 3 Plowing paper 4 Water mark given as code information 5 Image input device 6 Image processing device 7 Display / operation PC
8 Rotary encoder 9 Print mark sensor 10 Network hub

Claims (5)

A method for inspecting a paper on which a pattern shape of a watermark image is formed as code information,
Irradiate light from one side of the paper,
From the other surface side of the paper irradiated with the light, to capture a transmitted light image of a region including a watermark image,
When acquiring the transmitted light image of the area including the captured watermark image, the transmitted light image is automatically used according to the threshold value automatically changed according to the luminance of the transmitted light image of the area including the watermark image. To the image processing unit,
The transmitted light image of the region including the input watermark image is divided into a watermark portion and a background portion,
Measure the sharpness of the watermark image from the density distribution of the watermark and the background,
Binarize the transmitted light image of the region including the input watermark image, measure the pattern shape of the watermark image from the binarized transmitted light image, and digitize the watermark image;
The quality of the watermark image of the inserted paper is inspected by comparing and inspecting the quality of the watermark image obtained from each measurement result by a calculation unit that compares the quality of the watermark image with the reference watermark image quality. Paper inspection method.   2. The sheet inspection method according to claim 1, wherein the code information is a watermark image of a barcode or a two-dimensional code.   3. The sheet inspection method according to claim 2, wherein the measurement target of the pattern shape of the watermark image is at least one of the width, length, area, and number of the barcode or two-dimensional code. . A watermark image quality inspection device for paper on which a watermark image is formed as code information,
The inspection device includes an illumination device, an imaging device, and an image processing device,
The illumination device includes a light source unit that irradiates light on one surface of the paper,
The imaging apparatus includes an imaging unit that captures a transmitted light image of a region including the watermark image from the other surface of the sheet irradiated with light on the one surface.
The image processing apparatus is an image input unit that automatically changes a threshold value of a transmitted light image of a region including the captured watermark image in accordance with a luminance of the transmitted light image and inputs transmitted light image data. An image analysis unit that separates into a watermark portion and a background portion from the transmitted light image data of a region including the input watermark image, and a sharpness of the watermark image from a density distribution of the watermark portion and the background portion. Whether to measure the pattern shape of the watermark image from the binarized transmitted light image, quantify the quality of the watermark image, and use the watermark image quality obtained from each measurement result as a reference A calculation unit that performs comparison and inspection with numerical values of image quality, a storage unit that stores the reference numerical value, a determination unit that determines a result of the calculation in the calculation unit, and a determination result is displayed. With an output display Inspection device of the paper characterized by.   The sheet inspection apparatus according to claim 4, wherein the imaging unit of the imaging apparatus is a CCD line camera.

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