JPH10325810A - Automatic streak detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve streak detecting ability by detecting a reflected light amount of an illuminated surface of a sheet to be detected in a width direction, calculating a difference of reflected light amounts of a reference pixel and a comparison pixel disposed at an interval value of the reference pixel and predetermined number of pixels, and comparing it with a set threshold value to detect a streak fault. SOLUTION: When entrance of a sheet 11 to a position to be detected is recognized by a photoelectric sensor 14, a control computer 4 sends a signal for informing sheet entrance to an imaging unit 2, which starts imaging of the sheet 11. Image data sent from the unit 2 to the computer 4 is integrated in a flowing direction for all the pixels of a Width direction to be detected by set number of times of integrations. And, all the pixels except pixels at both ends in the width direction are used as reference pixels at each pixel. A difference of reflected light amount values from the comparison pixel disposed at the interval value of the predetermined number of pixels from the reference pixels is calculated. And, it is compared with a previously set threshold value to automatically detect a streak fault.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic streak detecting device capable of automatically detecting streak defects mainly occurring on the surface of coated paper.

[0002]

2. Description of the Related Art Streaks are defects mainly occurring on the surface of coated paper, and are streaked in the direction of paper flow. The color is very thin, and the width and width are from about 0.5 mm to about 3 mm. Various. The streak is different from other normal parts because the condition of the paper surface where it occurs is different
When printing is performed using streaked paper, the effect of printing differs between a portion where a streak occurs and a normal portion.

[0003] As with streaks, other defects that occur on the paper surface include black spots, brown spots, insects, and the like. However, unlike streaks, these defects are relatively dark.

[0004] In recent years, as the trend toward automation and labor saving at production sites has increased, there has been a strong desire for an automatic sorting apparatus that automatically detects defects occurring on the paper surface and removes the defective paper from the production line. It has become. The automatic sorting device consists of a transporter that transports sheets and an automatic detection device that automatically detects defects. When the automatic detection device detects a defect on a sheet, it immediately sends an electric signal to the transporter side. A signal is sent and the transporter separates the defective sheet from the normal sheet and deposits it at another location.

The automatic detecting device includes a light source unit for illuminating the inspected paper, an imaging unit for detecting the amount of reflected light in the width direction of the illuminated surface of the inspected paper, and converting the detected amount of reflected light into a numerical value. And a control computer that performs the arithmetic processing of

Generally, a CCD line sensor camera is used as an image pickup unit of the automatic detection device. The light emitted from the light source detects the amount of reflected light in each width direction by a CCD line sensor camera, and a defect occurring on the paper is detected as a difference in the amount of reflected light. This detection signal is calculated and determined by the control computer. Since the width that can be covered by one CCD line sensor camera is limited, a plurality of CCD line sensor cameras may be arranged side by side according to the inspection width.

As a light source of the automatic detection device, a high frequency lighting fluorescent lamp is often used. This means that the width of the paper may be more than 20 cm even if it is short, and more than 7 m if it is long,
This is because a length is required to illuminate this width direction.
On the other hand, incandescent lamps may be used side by side. In this case, a diffusion plate is often provided on the front surface of the incandescent lamps to reduce irradiation unevenness.

In general, when evaluating the ability of the automatic detection device to detect a defect, a signal component obtained by imaging is represented by a reflected light amount curve with the width direction pixel position on the horizontal axis and the reflected light amount value on the vertical axis. Is evaluated using the ratio (S / N ratio) of the height (S) of the noise component to the height (N) of the noise component. Here, the signal component is a peak that indicates the presence of a defect appearing on the reflected light amount curve, and the noise component is noise that appears on the reflected light amount curve.

Generally, as a condition for stably detecting a certain defect, it is preferable that the value of the S / N ratio of the obtained reflected light amount curve be large when the defect is measured.

The detection and selection of relatively dark-colored defects, such as black spots, brown spots, insects, etc., occurring on paper are currently performed at many production sites using automatic detection devices and automatic selection devices. However, when the target of detection / sorting is a streak, as described above, the streak has a very thin color different from a black point, a brown point, an insect, etc., so that the S / N ratio of the reflected light value curve is stable. The value does not become large enough to be necessary for detection, and it is difficult to perform automatic detection due to the limit of detection accuracy. Therefore, conventionally, the streak detection / sorting work has been mainly performed by a naked eye inspection of a site worker.

In order to achieve automatic streak detection,
Up to now, detection devices that have undergone some contrivances have been developed. For example, when the imaging unit detects the amount of reflected light at each pixel position in the width direction on a sheet and digitizes the reflected light amount and calculates the value with a control computer, the streak generated continuously in the flow direction on the paper surface is reduced. Using the features, the obtained numerical values are integrated in the flow direction, and the S
There is an apparatus using a method of increasing the / N ratio.

Further, the positional relationship between the image pickup unit and the light source is devised,
An imaging unit and a light source are installed so that each has a regular reflection angle relationship with the inspected position of the paper, and the regular reflection angle is set at a low angle of 60 ° to 85 °. Devices also exist.

Here, the relationship between the specular reflection angle and the regular reflection angle is based on the condition that the angle θ and the angle θ ′ of the image pickup unit 2 and the light source 5 with respect to the sheet 11 are the same as shown in FIG. Say. The regular reflection angle indicates the angle of θ and θ ′. This angle expression method is based on JIS P8142 (1
993).

[0014]

However, the conventional automatic streak detecting apparatus has a problem in that irregularities on a conveying surface of a conveying machine for conveying a paper, particularly irregularities generated in a flow direction, and unevenness in the amount of radiation from a light source are detected. In many cases, it is difficult to perform accurate streak detection. Therefore, the influence on the image due to the unevenness of the transfer surface of the transfer machine, the effect on the image due to the unevenness of the radiated light amount of the light source, etc. are minimized, and only the change in the reflected light amount value due to the streak is extracted. Accordingly, a streak automatic detection device capable of accurately detecting a streak has been desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a detection device having a high streak detection capability by minimizing the influence on the image such as unevenness of the transfer surface of the transfer device and unevenness in the amount of radiation of the light source. It is.

[0016]

The inventor of the present invention has conducted intensive studies to solve the above problems, and as a result, has come to invent the automatic streak detecting apparatus of the present invention.

That is, the automatic streak detecting device of the present invention comprises a light source unit for illuminating a paper to be inspected, an imaging unit for detecting the amount of reflected light in the width direction of the surface of the illuminated paper, and a detecting unit for detecting the amount of reflected light. A control computer for performing numerical processing of the numerical values and calculating the values; the control computer determines all pixels except pixels at both ends in the width direction as pixels (hereinafter referred to as reference pixels) based on each pixel; Calculate the difference between the amount of reflected light between the pixel and a comparative pixel positioned at a predetermined number of pixels from the reference pixel (hereinafter referred to as an interval value), and compare with a preset threshold to detect a streak defect. It has a streak automatic detection means.

Further, in the automatic streak detecting apparatus according to the present invention, preferably, the width of the number of pixels from the reference pixel to the comparison pixel is 1.5 to 3.0 mm.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The automatic streak detecting device of the present invention will be described in detail below.

FIG. 2 is a schematic diagram of the automatic streak detecting device of the present invention. The imaging unit 2 used in the present invention is C
It is a general device having a function of detecting the amount of reflected light from an object, such as a CD line sensor camera or a sensor.

The light source 5 used in the present invention is a fluorescent lamp lit at a high frequency. The purpose of this is to prevent the frequency of light from affecting the obtained reflected light amount value data as much as possible based on the high scan rate of the CCD line sensor camera. It is desirable that the light amount be as large as possible.

FIG. 3 is a schematic diagram of an automatic sorting apparatus showing an embodiment provided with the automatic streak detecting apparatus of the present invention.

Sheets 11 are fed one by one from a paper feeding unit 12.
It is sent out onto the conveyor belt 13. The fed sheet 11 is conveyed on a conveyor belt 13 and then reaches a position to be inspected.

Next, the arithmetic processing of the control computer according to the embodiment of the present invention will be described. FIG. 4 is a flowchart showing a data calculation algorithm in the automatic streak detection device of the present invention. Here, a description will be given together with the automatic sorting apparatus shown in FIG.

First, in STEP 1, the photoelectric sensor 14 recognizes that the sheet 11 has entered the inspection position of the sheet, and the STE
At P2, a signal indicating the entry of paper is sent to the control computer 4 side.

In STEP 3, the control computer 4 having received the signal relating to the entry of the paper transmits a signal notifying the entry of the paper to the imaging section 2, and accordingly, the imaging section 2 starts imaging the sheet 11.

The image data taken in by the image pickup unit 2 is sent to the control computer 4 and, in STEP 4, integration calculation processing in the flow direction is performed for all pixels in the width direction to be processed by the number of integrations set in advance. Is performed.

Next, based on the calculation result, the rightmost pixel (hereinafter referred to as a start pixel) excluding an arbitrary number of pixels not used as the rightmost reference pixel in the imaging direction set in advance in STEP5 Is used as the reference pixel, and the reflected light amount value detected by the reference pixel and the comparison pixel at the position spaced rightward from the reference pixel in the imaging direction by the predetermined interval value are detected. The difference between the calculated reflected light amount and the calculated reflected light amount is calculated, and the process proceeds to STEP6.

However, if the difference value at that time is 0, the reference pixel is shifted to the left by one pixel, and the evaluation in STEP 5 is started again.

If the difference value is a positive value in STEP 6, the magnitude relationship between the difference value and a preset threshold value is calculated in STEP 7, and the difference value is larger than the threshold value. If larger, go to STEP8.

On the other hand, if the difference value does not exceed the threshold value, the flow proceeds to STEP15.

In STEP 8, the difference between the reflected light amount value of the reference pixel and the reflected light amount value of the comparison pixel spaced leftward from the reference pixel in the imaging direction by the predetermined interval value is calculated. Is calculated, and the process proceeds to STEP9.

In STEP 9, whether the obtained difference value is positive or negative is determined. If the obtained difference value is positive, the process proceeds to STEP 10.

If the obtained difference value is negative, ST
Proceed to EP15.

In STEP 10, the magnitude of the difference value and the threshold value is evaluated. When the difference value exceeds the threshold value, the paper to be detected is determined as a defective paper, and a signal is output from the paper inspection device to the transporter.

If the difference between the difference value and the threshold value is evaluated and the difference value does not exceed the threshold value, the STE
Proceed to P15.

In STEP 15, the reference pixel is moved one pixel to the left in the imaging direction, and the processing from STEP 5 is started again.

The processing from STEP 5 to STEP 15 is continuously performed up to the leftmost pixel (hereinafter referred to as an end pixel) excluding an arbitrary number of pixels not used as reference pixels at the left end in the imaging direction.

If the difference value is a negative value in STEP 6, the magnitude relation between the difference value and a preset threshold value is calculated in STEP 11, and the difference value is larger than the threshold value. If smaller, go to STEP12. If the difference value does not exceed the threshold value, the process proceeds to STEP16.

In STEP 12, the difference between the reflected light amount value of the reference pixel and the reflected light amount value of the comparison pixel spaced leftward from the reference pixel in the imaging direction by the predetermined interval value is calculated. Is calculated, and the process proceeds to STEP13.

At STEP 13, the sign of the obtained difference value is determined. If the obtained difference value is negative, the process proceeds to STEP 14. If the obtained difference value is positive, STEP 16
Proceed to.

In STEP 14, the magnitude of the difference value and the threshold value is evaluated. If the difference value is smaller than (-threshold value), the paper to be detected is determined as a defective paper, and a signal is output from the paper inspection device to the transporter.

As a result of evaluating the magnitude of the difference value and the threshold value, if the difference value is smaller than (−threshold value),
Proceed to TEP16.

In STEP 16, the reference pixel is moved one pixel to the left in the imaging direction, and the processing from STEP 5 is started again.

The processing from STEP 5 to STEP 15 is continuously performed up to the leftmost pixel (hereinafter referred to as an end pixel) except for an arbitrary number of pixels not used as reference pixels at the left end in the imaging direction.

The above calculation process will be described in more detail with reference to the drawings. FIG. 5 is a diagram showing an example of a reflected light amount value curve after the integration processing by the automatic streak detection device of the present invention. The reflected light value curve obtained after the integration process is affected by unevenness of the radiated light amount of the light source, unevenness of the transporter, etc.
Low-frequency noise components often occur. (A) in the figure
Shows an example of low-frequency noise generated on the reflected light amount curve. Due to the influence of this low-frequency noise component, the next determination, that is, when the image curve indicates a value equal to or less than a certain fixed reflected light amount value, the imaged paper is recognized as a defective paper, that is, a so-called binarization process. Judgment cannot be made. Therefore, it is difficult to extract only the signal caused by the streak shown in (b) of the drawing by these processes and determine that paper as a defective paper.

Therefore, in the present invention, the following processing is performed in order to ignore the noise of the low frequency component and extract only the signal caused by the streak defect. An example will be described with reference to FIG. FIG. 6 is a diagram illustrating a data operation processing method in the automatic streak detection device of the present invention using an actual example. FIG. 6 shows an example of a reflected light amount curve obtained when the interval value 3 and the threshold value 7 are set prior to the detection and the detection is performed.

In FIG. 6, when the position of the reference pixel overlaps the streak defect occurrence position, the reflected light amount value of the comparison pixel spaced rightward by three pixels in the imaging direction is 1
27. Here, first, a difference from the reflected light amount value 117 of the reference pixel is calculated.

Since the reflected light amount value of the comparison pixel on the right side is larger than the reflected light amount value of the reference pixel, a difference value is obtained as follows. (Reflection light amount value of reference pixel) − (Reflection light amount value of right comparison pixel) = 117-127 = (− 10) The magnitude of the obtained difference value is determined by the value of (−threshold value). Is done. Here, since the value of (−threshold) is −7, (difference) <(− threshold). This condition is satisfied, and the process proceeds to the next step.

Next, the difference between the reflected light amount value 128 of the comparison pixel and the reflected light amount value 117 of the reference pixel spaced three pixels to the left in the imaging direction is calculated as follows. . (Reflection light amount value of reference pixel) − (Reflection light amount value of left comparison pixel) = 117−128 = (− 11) The magnitude of the obtained difference value is determined as (−threshold value). . Since (difference) <(− threshold),
This target paper is determined to be defective paper.

As a result, as shown in FIG. 3, a defective paper determination signal is output to the reject gate 15 on the transporter.
When it is determined that there is no streak, no signal is output to the outside.

The reject gate 15, which has detected the occurrence of the streak and received the output signal,
6 does not operate until the leading edge of the sheet 11 is detected, and the sheet 11 reaches the reject gate 15 position.
The reject gate 15 opens at the same time as the edge of the leading edge of the sheet 11 is detected by the photoelectric sensor 16. As a result, the sheet 11 having the streak falls into the reject box 17. The reject gate 15 closes when the sheet 11 has moved a certain distance after the photoelectric sensor 16 detects the edge of the rear end of the sheet 11.

The edge of the sheet 11 having no streak and the edge of the sheet 11 in which the streak has occurred but which cannot be detected by the automatic streak detecting device are detected by the photoelectric sensor 16. However, the reject gate 15 does not open and is sent to the normal paper delivery 18.

[0054]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an automatic streak detecting apparatus according to the present invention will be described with reference to embodiments. The present invention is not limited to these embodiments and can be variously modified.

Example 1 Streaks were measured by the automatic streak detecting device of the present invention. The imaging unit was a CCD line sensor camera with 5000 pixels and a 24 mm lens. The imaging unit is a CCD that covers the entire width of 1000 mm of the paper at a distance of about 1 m from the paper.
It was set to be included within the field of view of the line sensor camera. This corresponds to a width of about 0.3 mm per pixel. The light source was basically composed of a 40 W fluorescent lamp of about 2 m and a high frequency lighting device. The positional relationship between the imaging unit and the light source was set so as to have a regular reflection angle relationship with the detected position of the paper. The specular reflection angle was 75 °.

The sheet sample used was 100 coated papers having a basis weight of 75 g / m ² with streaks, and the streaks had low strength and a width of 1 mm. Also,
Thirty-three sheets without defects were randomly mixed into a sample of 100 sheets with streaks. In the measurement, 100 sheets with streaks and 33 sheets without defects were inspected using the automatic streak inspection device, and the good paper was determined as a good paper for the total number of conveyed sheets. Then, the ratio of the total number of sheet sheets in which the defective paper was correctly determined as a defective paper was evaluated as a defect detection rate. Before measurement, set the threshold and interval
The values were set to 7,5, respectively.

The sheet was conveyed at a speed of 180 m / min on a flat conveying machine which conveys the sheet. The number of signals of each pixel detected by the CCD line sensor camera per sheet is 5000 in the width direction and 10 in the flow direction.
There were no total of 500,000. On the flat transfer machine,
A photoelectric sensor for transmitting a signal indicating that the sheet has entered the control computer to the detection position of the paper was provided. And the start of imaging was performed using the signal of the photoelectric sensor. In addition, the end of the imaging is 500,000 in total.
This is the point in time when the signal of each pixel was detected. In the control computer, the signal of each pixel detected by the CCD line sensor camera by imaging was converted into a numerical value as a reflected light amount value, and integrated by 100 in the paper flow direction.

Next, in the control computer, of the integrated value obtained for each pixel in the width direction, the reflected light amount value detected by the reference pixel in the arbitrary width direction of the CCD line sensor camera and the comparison pixel The streak defect is detected by calculating the difference between the detected reflected light amount value and the threshold value set in advance, and the determination is performed for all pixels except for any number of pixels at both ends in the width direction. The pixels were regarded as reference pixels in order, and the defect detection rate at the time of finally determining whether the test paper was good or bad was evaluated. The width of the number of pixels assigned with the interval value 5 was 1.3 mm in the width direction.

COMPARATIVE EXAMPLE 1 In the control computer, of the integrated values obtained for each pixel in the width direction, an interval is set on both sides by the reference pixel and the interval value set in advance from the reference pixel. The streak was measured without performing the operation of calculating the difference between the integrated value and the comparison pixel. The positional relationship between the imaging unit and the light source was set so as to have a regular reflection angle relationship with the detected position of the paper. The specular reflection angle was 75 °.

In the control computer, of the integrated value obtained for each pixel in the width direction, a reference pixel and a comparison pixel spaced on both sides by an interval value set in advance from the reference pixel. The same conditions as in Example 1 were used, except that the operation of calculating the difference between the integrated value and was not performed.

Table 1 shows the stability of the automatic streak detection determined from the evaluation curves obtained in Example 1 and Comparative Example 1.

[0062]

[Table 1]

Evaluation result: It was confirmed that the use of the automatic streak detecting device of Example 1 detected streaks more stably than the case of using the streak detecting device of Comparative Example 1. From these results, it can be seen that the streak automatic detection device of the present invention of Example 1 is effective for automatic streak detection.

Examples 2 to 5 The sheet samples used were 100 coated papers having a basis weight of 75 g / m ² with streaks, and streaks having various widths were used at random. In addition, the sheet 10 on which the streak has occurred is replaced with 33 sheets on which no defect has occurred.
It was randomly mixed into zero samples. In the measurement, 100 sheets of the sheet with the streaks and 33 sheets of the sheets without the defect were inspected by using the automatic streak detecting apparatus, and the good sheet was regarded as a good sheet with respect to the total number of the conveyed sheets. Then, the ratio of the total number of sheet sheets in which the defective paper was correctly determined as a defective paper was evaluated as a defect detection rate.
Before measurement, the threshold value is set to 7, and the width in the width direction of the number of pixels assigned by the interval value in the arithmetic processing is set
1.5, 2.0, 2.5, and 3.0 mm. The evaluation of the detection power was the same as in Example 1. The conditions were the same as in Example 1 except that the width in the width direction of the number of pixels assigned by the streak width and interval value of the used sample was different.

[0065]

[Table 2]

Evaluation result: The interval value of Examples 2 to 5, ie, the width in the width direction of the number of pixels assigned by the interval value was 1.5 to
When it is 3.0 mm, it is understood that the detection of the streak defect is effective.

[0067]

According to the present invention, there is an effect that the automatic detection of streak defects mainly occurring on coated paper is made more accurate and stable, and the workability of automatic streak selection on site is improved.

[Brief description of the drawings]

FIG. 1 is a definition diagram of a regular reflection angle.

FIG. 2 is a schematic diagram of an automatic streak detection device of the present invention.

FIG. 3 is a schematic diagram of an automatic sorting device showing an example of an embodiment provided with the automatic streak detecting device of the present invention.

FIG. 4 is a flowchart showing a data calculation algorithm in the automatic streak detection device of the present invention.

FIG. 5 is a view showing an example of a reflected light amount curve after integration processing by the automatic streak detection device of the present invention.

FIG. 6 is a view for explaining a data arithmetic processing method in the automatic streak detection device of the present invention using an actual example.

[Explanation of symbols]

 2 imaging unit 3 lens 4 control computer 5 light source 6 mounting jig 11 sheet 12 paper feeding unit 13 transport belt 14 photoelectric sensor 15 reject gate 16 photoelectric sensor 17 reject box 18 normal paper delivery

Claims (2)

[Claims] 1. A light source unit for illuminating a paper to be inspected, an imaging unit for detecting the amount of reflected light in the width direction of the illuminated surface of the paper to be inspected, and a numerical processing of the detected amount of reflected light, and processing for calculating the value is performed. The control computer includes a reference computer and a predetermined number of pixels from the reference pixel as pixels (hereinafter referred to as “reference pixels”) each of which is based on every pixel except both ends in the width direction. A streak automatic detecting means for calculating a difference between a reflected light amount value with a comparative pixel located at a position separated by a minute (hereinafter referred to as an interval value) and comparing with a preset threshold value to detect a streak defect; Automatic streak detection device. 2. The automatic streak detecting device according to claim 1, wherein the width of the number of pixels from the reference pixel to the comparison pixel is 1.5 to 3.0 mm.