JPH07306963A - Paper sheet quality determination device and paper sheet quality determination method - Google Patents

Abstract

PURPOSE:To discriminate the normal/defective condition of paper having plastic threads by extracting different wavelength components from transmitted light based on the absorption wavelength of plastic threads and photoelectrically converting respective wavelength components to perform the signal processing. CONSTITUTION:This discriminating device 1 consists of a carrying part 2, a transmitted light generation part (transmitted light generation means) 3, a pass sensor 4, and a signal processing part (signal processing means) 5. Transmitted light 21 transmitted through paper 7 is detected, and the obtained detection result is subjected to signal processing. The change of the detection result accompanied with absorption of infrared light 19 to plastic threads of the paper 7 is used to discriminate the presence or the absence of plastic threads. Consequently, the normal/defective condition of the paper 7 having plastic threads is discriminated. Since the paper 7 is scanned by infrared light 19 to generate time series data, information of not only the presence or the absence of plastic threads but also the position and the size is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet quality determining device for optically determining the quality of a sheet having a plastic thread.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open No. 61-72387 and Japanese Patent Application Laid-Open No. 63-301393 disclose techniques for determining the quality of paper sheets. And
In the past, magnetic, color, or
A watermark or the like formed on the paper sheet was detected. There was also a technology to detect security threads embedded in paper sheets. Some security threads are made of aluminum, and a magnetic or electrical determination method has been adopted to determine the quality of the paper sheet in which the aluminum threads are incorporated.

[0003]

By the way, some of the current paper sheets use a security thread as a key for determining whether the thread is good or bad. Even if a discriminating technique using magnetism, color, or watermark is adopted for such paper sheets, it is difficult to discriminate with high precision, and the discrimination reliability is low.

Although some security threads are made of plastic, the determination technology for aluminum threads cannot be directly applied to the quality determination of paper sheets having plastic threads.

An object of the inventions of claims 1 and 2 is to provide a sheet quality determining device capable of determining the quality of a sheet having a plastic thread.

It is another object of the present invention to provide a paper sheet quality determination method capable of determining the quality of a paper sheet having a plastic thread.

[0007]

In order to achieve the above-mentioned object, the invention of claim 1 relatively scans the discriminating light on a sheet having a plastic thread, and transmits the discriminating light to the sheet. In a paper sheet quality determination device that forms transmitted light and detects the transmitted light to determine the quality of a paper sheet, different wavelength components are extracted from at least one transmitted light based on the absorption wavelength of a plastic thread, and This is a paper sheet quality determination device that photoelectrically converts wavelength components to perform signal processing.

According to a second aspect of the present invention, the sheet having a plastic thread is scanned with the discriminating light, the discriminating light is transmitted through the sheet to form the transmitted light, and the transmitted light is the first.
And transmitted light forming means for splitting into the second split light, first band extracting means for extracting the absorption wavelength component of the plastic thread from the first split light, and a paper portion of the paper sheet from the second split light. Second band extraction means for extracting a transmission wavelength component common to the plastic thread, first and second light detection means for detecting the wavelength component extracted by the first and second band extraction means, and A paper sheet quality determining apparatus comprising: a signal processing unit that performs arithmetic processing on the detection results of the first and second light detection units to remove noise from the detection result of the first light detection unit.

Further, according to the invention of claim 5, a sheet having a plastic thread is scanned with the discriminating light, the discriminating light is transmitted to the sheet to form a transmitted light, and the transmitted light is detected to detect the sheet. In a paper quality determination method for determining quality, a first step of performing data sampling on good sheets and calculating an average value and standard deviation of the obtained time series data,
A second step of setting a threshold value based on the distribution of the calculation results, and a third step of calculating an average value and standard deviation of time-series data obtained by performing data sampling on an arbitrary sheet. And a fourth step of comparing the calculation result of an arbitrary paper sheet with a threshold value to judge the quality of the arbitrary paper sheet. And
These inventions make it possible to determine the quality of a paper sheet having a plastic thread.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5 show a first embodiment of the present invention, and reference numeral 1 in both figures is a sheet quality determination device (hereinafter
It is referred to as a discriminating device).

The discriminating device 1 is composed of a carrying section 2, a transmitted light forming section (transmitted light forming means) 3, a passage sensor 4, and a signal processing section (signal processing means) 5. Of these, the transport unit 2 has a conveyor 6. The conveyor 6 supports the rectangular paper sheet 7 and supports the paper sheet 7 with the longitudinal direction thereof oriented in the traveling direction. Then, the conveyor 6 horizontally conveys the paper sheet 7 at a constant speed, as indicated by an arrow A in FIG.
Here, it is possible to adopt various general ones as the transport unit 2.

The paper sheet 7 handled in this embodiment is shown in FIG.
As shown in FIG. 3, it has a plastic security thread (hereinafter referred to as a plastic thread) 8. The plastic thread 8 is put into the paper sheet 7 and oriented in the width direction of the paper sheet 7. The plastic thread 8 has a characteristic of absorbing light of a specific wavelength, and the wavelength to be absorbed (hereinafter referred to as absorption wavelength) is determined by the material of the plastic thread 8. For example,
When the material of the plastic thread 8 is polyethylene, the absorption wavelength is 5.8 μm. Further, in this case, the transmission wavelength common to the plastic thread 8 and the paper portion 10 is 5.2 μm.

The transmitted light forming section 3 includes an infrared light source 11 as a light source, an irradiation optical system 12, a condensing optical system 13, and a half mirror 14. The first and second optical sensors 15 and 16 are arranged at the rear stage of the half mirror-14,
A first interference filter (first band extracting means) 17 and a second optical sensor (second band extracting means) 16 are attached to each of the optical sensors 15 and 16.

The infrared light source 11 emits infrared light 19, which passes through the irradiation optical system 12 and forms a spot 20 on the paper surface of the paper sheet 7. Further, the infrared light 19 passes through the paper sheet 7 and becomes a transmitted light 21. This transmitted light 21 passes through the condensing optical system 13 and is then transmitted by the half mirror 14 to the first divided light 22 and the second divided light 22. It is divided into the divided light 23. And
The first split light beam 22 passes through the first interference filter 17 and enters the first optical sensor 15, and the second split light beam 23 is divided into the second
Through the interference filter 18 and enters the second optical sensor 16.

The first interference filter 17 extracts only the wavelength component absorbed by the plastic thread 8 from the first split light beam 22. In addition, the second interference filter 18
Extracts only the transmission wavelength component common to the plastic thread 8 and the paper portion 10 from the second split light 23.

The passage sensor 4 has a light source 24 and a third optical sensor 25. The light source 24 and the optical sensor 25 are arranged so as to sandwich the passage path of the paper sheet 7, and the light (not shown) emitted from the light source 24 is taken into the optical sensor 25. The wavelength component of the light from the light source 24 does not pass through the paper sheet 7. When the paper sheet 7 passes between the light source 24 and the optical sensor 25, the light from the light source 24 is blocked by the paper sheet 7.

The signal processing section 5 has a first
And second A / D converters 26 and 27, a division circuit 28, a comparator 29, and a result display section 30.
The detection result of the first optical sensor 15 is input to the first A / D converter 26. Further, the detection results of the second and third optical sensors 16 and 25 are input to the second A / D converter 27.

The outputs of both A / D converters 26 and 27 are input to a division circuit 28, and the output of the division circuit 28 is sent to a comparator 29. The comparator 29 compares the output of the division circuit 28 with a predetermined threshold value, and the result display unit 3
0 indicates the result of the quality judgment of the paper sheet 7 based on the comparison result of the comparator 29.

Next, the operation of the discriminating apparatus 1 will be described. First, as shown in FIG. 1, the paper sheet 7 is conveyed at a constant speed by the conveyor 6 with the paper surface facing up and down, and the passage sensor 4
Sent to. When the front end of the paper sheet 7 reaches between the light source 24 and the third optical sensor 25, the light of the light source 24 is blocked by the paper sheet 7 and the output voltage of the third optical sensor 25 changes. Both A / D converters 26 are triggered by this change in output voltage,
27 starts to operate, and the first and second optical sensors 15, 1
The output signals f (t) and g (t) from 6 are fetched.

When the sheet 7 reaches the spot 20 of the infrared light 19 of the transmitted light forming portion 3, the intensity signals f (t) and g (t) of both photosensors 15 and 16 are indicated by the red of the sheet 7. A change occurs depending on the external light transmission characteristic. In addition, 8 plastic threads
When reaches the spot 20 of the infrared light 19, the transmitted light 21 in which the absorption wavelength component of the plastic thread 8 is removed is generated.

FIGS. 5A and 5B show each optical sensor 1
5 shows an example of time-series data of intensity signals f (t) and g (t) of 5 and 16. Until the plastic thread 8 reaches the vicinity of the spot 20, f (t), g (t)
Has changed in a similar manner. However, when the plastic thread 8 reaches the vicinity of the spot 20, the first interference filter 17 transmits only the absorption wavelength of the plastic thread 8, so that f (t) as indicated by an arrow IV in FIG.
Drops sharply. On the other hand, the second interference filter 18 extracts only the transmission wavelength component that is common to the plastic thread 8 and the paper portion 10, so that a large change does not appear in g (t).

When the plain paper sheet has no stains or folds, ideally, only the information based on the transmitted light intensity distribution of the plastic thread 8 should appear in f (t), but in reality, the paper sheet 7 Noises due to dirt, folds, ink, or fluctuations in the output of the infrared light source 11 are superimposed. This noise also appears in g (t), but the first split light 22 and the second split light 22
Considering that the wavelengths of the divided lights 23 are close to each other, and that the spectral characteristics of the ink and the wavelength characteristics of the infrared light source 11 are not independent from each other, both noises can be regarded as the same. Therefore, in g (t), all transmitted light intensity distributions except the absorption wavelength of the plastic thread 9 are f
It appears as in (t).

The intensity signal f (t) is supplied to the first A / D converter 2
6, and g (t) is sent to the first A / D converter 26 via the second A / D converter 27. Two-channel data is output from the first A / D converter 26 to the division circuit 28, and the division circuit 28 performs the following calculation.

[0024]

[Equation 2]

As a result of this calculation, the noise component common to g (t) is cut from f (t), and the intensity change due to the absorption of the plastic thread 8 is emphasized as shown in FIG. 5 (c). Then, this h (t) is guided to the comparator 29, and the absorption peak value (minimum value of intensity) is compared with a predetermined threshold value (for example, Th ₁ in FIG. 5C). If the absorption peak value exceeds the threshold value, the presence of the plastic thread 8 is detected. Further, the paper sheet on which the plastic thread 8 exists is determined to be good, and the paper sheet on which the plastic thread 8 does not exist is determined to be bad. Then, the result of the quality determination is displayed on the result display unit 30.

The position where the absorption peak (arrow V) appears in the time-series data h (t) (absorption peak position) represents the existing position of the plastic thread 8 on the paper sheet 7.
Therefore, the timing at which the absorption peak appears can be predicted on the basis of the actual existing position of the plastic thread 8 which is known in advance. And the comparator 2
9 refers to the timing at which the paper sheet 7 reaches the passage sensor 5 and the transport speed of the paper sheet 7 to determine the timing at which the absorption peak will appear, and h (t) at this timing and the threshold value Th Compare with ₁ .

In the discrimination device 1 as described above, the transmitted light 21 transmitted through the paper sheet 7 is detected, and the obtained detection result is signal-processed. Since the presence or absence of the plastic thread 8 is determined by utilizing the change in the detection result associated with the absorption of the infrared light 19 by the plastic thread 8, it is possible to determine the quality of the paper sheet 7 having the plastic thread 8. is there. Further, since the infrared light 19 is scanned on the paper sheet 7 to create time-series data, the plastic thread 8
In addition to the presence or absence of information, it is possible to obtain information such as position and size.

Further, since the transmitted light intensity distribution is measured by utilizing the absorption wavelength peculiar to the plastic thread 8, the plastic is not affected by the reflectance of the paper surface unlike the case where the reflected light is utilized. The thread 8 can be detected.

Further, in this embodiment, the transmitted light 21
Is split into first and second split lights 22 and 23, and different wavelength components are extracted from the split lights 22 and 23.
Then, the intensity distributions of the two divided lights 22 and 23 are simultaneously detected at two wavelengths set based on the absorption wavelength of the plastic thread 8. Further, the first and second optical sensors 1
The detection results of 5 and 16 are arithmetically processed, and the first optical sensor 1
From the detection signal of No. 5, noise caused by the intrinsic difference of the paper sheet 7 or disturbance is removed. Therefore, it is possible to clarify the signal change associated with the absorption of the plastic thread 8 and obtain a high S / N ratio.

Now, a second embodiment of the present invention, which is an application of the first embodiment of the present invention, will be described. For example, in FIG.
When the output data of the division circuit as shown in (c) is obtained, the transmitted light intensity distribution is sampled for a statistically significant quantity for h (t) to determine i (t). This h
An example of the relationship between (t) and i (t) is shown in FIG. Here, the calculation (integration in the sampling period) according to the equation (2) is further performed to obtain the correlation function j (t) between h (t) and i (t). Note that α is the shift amount, and here α = 0.

[0031]

[Equation 3]

Then, the threshold value is determined by the value calculated by the equation (2). It is assumed that sheets that are closer to the maximum value of j (t) than this threshold value are good sheets, and sheets that are closer to the minimum value of j (t) are defective sheets.

The paper sheet quality determining apparatus of this embodiment is
It shall be equipped with a posture measuring device that measures the front and back sides and front and back of a paper sheet during conveyance. This embodiment has the following effects. First, by comparing h (t) and i (t), it becomes easy to specify the position of the plastic thread for any paper sheet, and thus it is easy to determine the quality of the paper sheet. Further, not only the position of the plastic thread but also the similar judgment such as printing on the surface of the paper sheet can be easily performed, so that it is easy to judge the quality of the paper sheet.

Next, the essential parts of the third embodiment of the present invention will be described with reference to FIGS.
It will be described based on 9. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. Figure 7
Shows a signal processing unit (signal processing means) 32 provided in a paper sheet quality determination device (hereinafter referred to as a determination device) 31 of the third embodiment of the present invention. The signal processing unit 32 is provided with a calculation unit 33 and a comparator 34, and the output data of the first A / D converter 26 is input to the calculation unit 33 on two channels. Further, the calculation unit 33 has a function of calculating an average value and standard deviation of time-series data for each channel. Further, the comparator 34 compares the calculation result of the calculation unit 33 with a predetermined threshold value. The threshold value of the comparator 34 is set based on the average value and the standard deviation obtained by the calculation unit 33.

Next, the operation of the discriminating device 31 will be described. First, in order to set the threshold value of the comparator 34, basic data (transmitted light intensity distribution) is taken for a statistically significant quantity of good paper sheets and bad paper sheets. That is, while the good paper and the bad paper are being conveyed, the good paper and the bad paper are scanned with the infrared light 19, and the divided lights 22 and 23 of the transmitted light 21 are converted into the corresponding interference filters 17 and 18.
It is taken into the optical sensors 15 and 16 through the. The first interference filter 17 extracts only the wavelength component absorbed by the plastic thread 8 from the first split light 22. The second interference filter 18 extracts only the transmission wavelength component common to the plastic thread 8 and the paper unit 10 from the second split light 23. And the two optical sensors 15,
The detection result of 16 is input to the arithmetic unit 33 after A / D conversion.

The calculation unit 33 calculates the average value and standard deviation of the data of the individual transmitted light intensity distributions for each of a number of good and bad paper sheets. For example, when the calculation result is displayed as a point on the space defined by the coordinate axis of the average value and the coordinate axis of the standard deviation, the data of the good paper sheets and the data of the bad paper sheets are collected in an area of a certain size. Therefore, the area surrounding the data of the good paper among these is set to the threshold Th in consideration of the erroneous determination rate.
₂ , set Th ₃ and use.

After the thresholds Th ₂ and Th ₃ are set, the infrared light 19 is scanned on an arbitrary paper sheet 7 of which the quality is unknown, and the first and second divided lights 22 and 23 interfere with each other. The light enters the optical sensors 15 and 16 through the filters 17 and 18. The computing unit 33 computes the average value and the standard deviation of the output data of the optical sensors 15 and 16, and the result display unit 30 displays the computation results for the good and bad paper sheets. Then, when the calculation results of the output data of both optical sensors 15 and 16 are both within the corresponding threshold values Th ₂ and Th ₃ , the paper sheet 7
Is judged to be good, and if either of them does not fit, it is judged to be no. The calculation result of the calculation unit 33 is displayed on the result display unit 30 when the defective sheet is determined.

According to the discriminating device 31 as described above, the transmitted light 21 transmitted through the paper sheet 7 is detected, and the obtained detection result is subjected to signal processing. Then, since the presence or absence of the plastic thread 8 is determined by utilizing the change in the detection result associated with the absorption of the infrared light 19 of the plastic thread 8, the paper sheet 7 having the plastic thread 8 is detected as in the first embodiment. It is possible to determine pass / fail.

Further, since the transmitted light intensity distribution is measured by utilizing the absorption wavelength peculiar to the plastic thread 8, the plastic is not affected by the reflectance of the paper surface unlike the case where the reflected light is utilized. The thread 8 can be detected.

[0040] Further, in this embodiment, the transmitted light intensity distribution is detected by the two wavelengths as in the first embodiment, data of good paper sheet - set the threshold Th _2, Th ₃ based on data . Further, time series data of paper 7 to be inspected - data is compared with a threshold Th _2, Th ₃ corresponding, two thresholds Th _2, Th
_It is judged whether or not both of them fit into ₃ . Therefore, as compared with the case where the average value and the standard deviation are simply calculated from the data of one transmitted light, the quality determination can be performed with higher accuracy.

Now, a fourth embodiment of the present invention to which the third embodiment of the present invention is applied will be described. Figure 10
In the example of (a), how to set the threshold Th _a becomes a problem, so in order to solve this, the threshold Th _b is set as shown in FIG. 10 (b). Therefore, as a method in multivariate analysis, Mahalanobis distance calculation is applied here. The Mahalanobis distance is defined by the equation (3) in the case of univariate x. Here, if the Mahalanobis distance is D, m is the average value of x and s is the variance of x.

[0042]

[Equation 4]

The Mahalanobis distance is defined as p variable x _p
When expanded (i.e., generalized) to (p: natural number), the conjugate covariance matrix is considered to obtain Expression (4).

[0044]

[Equation 5]

A specific method for determining the quality of a paper sheet using the Mahalanobis distance will be described in detail below. Since the configuration of the sheet quality determining device is the same as that of the third embodiment, the detailed configuration will not be described here, and the same components as those of the third embodiment will be denoted by the same reference numerals. I shall.

First, in order to set the threshold value of the comparator 34, basic data (transmitted light intensity distribution) is taken for a statistically significant quantity of good and bad paper sheets. . That is, while conveying the good paper sheet and the bad paper sheet, the good light sheet and the bad paper sheet are scanned with the infrared light 19 to transmit the transmitted light 2
The divided light beams 22 and 23 of 1 correspond to the corresponding interference filter 17,
It is taken into the optical sensors 15 and 16 through 18. And
The detection results of the two optical sensors 15 and 16 are input to the arithmetic unit 33 after A / D conversion.

The first interference filter 17 extracts only the wavelength component absorbed by the plastic thread 8 from the first split light beam 22 as in the first embodiment. Also,
The second interference filter 18 extracts only the transmission wavelength component common to the plastic thread 8 and the paper unit 10 from the second split light 23.

The calculation unit 33 calculates the average value and the standard deviation value of the individual transmitted light intensity distribution data for each of the good paper sheet and the bad paper sheet. Then, the transmitted light intensity distribution data of the first interference filter 17 of the individual good paper sheet First - the value m _a obtained by averaging the average value of the data, the first interference filter 17 of the individual good paper sheet Value m _b obtained by averaging the standard deviations of the transmitted light intensity distribution data of the above, and m _c obtained by averaging the average values of the transmitted light intensity distribution data of the second interference filters 18 of the individual good paper sheets. , The Mahalanobis distance from the average value m _d of the standard deviations of the transmitted light intensity distribution data for the second interference filter 18 of each good paper sheet, and the individual transmitted light intensity of the good paper sheet. The distribution data is obtained by the equation (5).

[0049] That is, in this operation, the x _a, the transmitted light intensity distribution data of the first interference filter 17 of the individual good paper sheet respectively - by substituting the average value of the data, the x _b, the individual good the first interference filter 17 transmitted light intensity distribution data of the of the paper each - substituting the standard deviation of the data, the x _c, the transmitted light intensity for the second interference filter 18 for each individual good paper sheet The average value of the distribution data is substituted, and the standard deviation of the transmitted light intensity distribution data for the second interference filter 18 of each individual good paper sheet is substituted for x _d .

[0050]

[Equation 6]

Where m _a is the average value of x _a and m _b is x _b
, M _c is the average value of x _c , and m _d is the average value of x _d . Then _{x a, x b, x c} , x d and m _a, m _b, m
_c , m _d , and variances a ₁ , s _b2 , s _c3 , s _d4 and covariance s
_a2 , s _a3 , s _a4 , s _b1 , s _b3 , s _b4 , s _c1 , s _c2 ,
The relationship between s _c4 , s _d1 , s _d2 , and s _d3 is expressed by the formula (6).
become that way.

[0052]

[Equation 7]

It should be noted that the transmitted light intensity distribution data of the above-mentioned first good interference filter 17 of the individual good papers for the good papers and the bad papers and the papers used for the actual measurement after sampling these papers. -The average value m of the
_The value m _{b obtained} by averaging a and the standard deviation of the transmitted light intensity distribution data for the first interference filter 17 of each good paper sheet.
And a value m _c obtained by averaging the average values of the transmitted light intensity distribution data of the second good interference filters 18 of the individual good paper sheets, and the transmitted light of the second good interference filters 18 of the individual good paper sheets. The Mahalanobis distance from the value m _d obtained by averaging the standard deviations of the intensity distribution data has a normal distribution as shown in equation (7). Note that x _m is the calculated Mahalanobis distance (random variable), and m _m is the average value of x _m . That is, it becomes N (m _m , (s _m ) ² ).

[0054]

[Equation 8]

Next, the transmitted light intensity distribution data of the first interference filter 17 of the individual good paper sheet - the value m _a the average value obtained by averaging the data, the first interference filter 17 of the individual good paper sheet Value m _b obtained by averaging the standard deviations of the transmitted light intensity distribution data of the above, and an average value m of the average values of the transmitted light intensity distribution data of the second interference filters 18 of the individual good paper sheets.
and _c, the transmitted light intensity distribution data of the second interference filter 18 of the individual good paper sheet - the Mahalanobis distance from the value m _d where the standard deviation was average data, the individual transmission in poor paper The light intensity distribution data is obtained by the equation (5).

[0056] That is, in this operation, the x _a, the transmitted light intensity distribution data of the first interference filter 17 of the individual defective paper each - substituting the average value of the data, the x _b, individual defective transmitted light intensity distribution data of the first interference filter 17 of the paper each - substituting the standard deviation of the data, the x _c, transmitted light intensity distribution for a second interference filter 18 for each defective paper each The average value of the data is substituted, and the standard deviation of the transmitted light intensity distribution data for the second interference filter 18 of each defective sheet is substituted for x _d .

FIG. 12 (a) shows the result of obtaining the above Mahalanobis distance for good and bad paper sheets. It should be noted that f _a (x _m ) and f _b (x _m ) are the results for defective paper sheets.

[0058] While Figure 12 an enlarged view of the dotted line in (a) is a diagram 12 (b), f _a, as shown in FIG. 12 (b)
(X _m ) and f _b (x _m ) are f _a (x _m ) and f _b (x
_m ) and the limit value (this is because expression (7) does not become 0)
Overlap near to.

Here, as shown in FIG. 12B, there are an area where a defective paper sheet is determined to be a good paper sheet and an area where a defective paper sheet is determined to be a good paper sheet. Therefore, here, the threshold value Th ₄ is set so that the probability of determining a defective sheet as a good sheet is small.

Further, regarding the value m _a obtained by averaging the average values of the transmitted light intensity distribution data for the first interference filters 17 of the individual good paper sheets, and the first interference filter 17 of the individual good paper sheets. Value m _b obtained by averaging the standard deviations of the transmitted light intensity distribution data of m and the average value m of the average value of the transmitted light intensity distribution data of the second interference filters 18 of the individual good paper sheets.
_c and transmitted light intensity distribution data of the second interference filter 18 of the individual good paper sheet - the Mahalanobis distance from the value m _d where the standard deviation was average data, said individual transmitted light intensity distribution de −Eq. (5) is obtained.

[0061] In this operation, the x _a, actual transmitted light intensity distribution data of the first interference filter 17 of each of the paper each used for measurement - by substituting the average value of the data, the x _b,
Substituting the standard deviation of the transmitted light intensity distribution data for the first interference filter 17 of each individual sheet used for the actual measurement, and x _c is the first deviation of each individual sheet used for the actual measurement. No. 2 interference filter 18 transmitted light intensity distribution data
The average value of the transmitted light intensity distribution data for the second interference filter 18 of each individual sheet used for the actual measurement is substituted for x _d .

[0062] Note that the measurement results of the individual sheet to be used for actual measurement, the 13 Uri, f _c
(X _m ), when the area of the shaded area in the figure up to the threshold value Th ₄ is obtained, the individual paper sheets used for the actual measurement are
It is possible to obtain the probability of taking X _m up to the threshold value Th ₄ .

By performing such a process, it is possible to handle multiple variables with a single value, which has the effect of facilitating the evaluation of the threshold value. Incidentally, regarding another embodiment of the present invention,
The following are also possible.

For example, in each of the above-mentioned embodiments, the Hafmira-14 is used to divide the transmitted light 21, but
The present invention is not limited to this, and it is possible to use an element such as a dichroic mirror that splits the transmitted light and the reflected light based on the cutoff wavelength.

Further, in each embodiment, the infrared light 19 causes the paper sheet 7
However, it is also possible to form a linear scanning light 41 as shown in FIG. 14 and superimpose the scanning light 41 on the plastic thread 8.

Further, the paper sheet 7 is conveyed to scan the paper sheet 7 with the infrared light 19, but the paper sheet 7 may be stopped and the infrared light source 11 may be moved, for example. Alternatively, both may be moved in opposite directions. A monochromatic light source represented by a laser oscillator may be used as the light source.

[0067]

As described above, according to the first, second and fifth aspects of the present invention, it is possible to determine the quality of a paper sheet having a plastic thread.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a paper sheet quality determination device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a signal processing unit of the paper sheet quality determination apparatus according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a scanning state of infrared light.

FIG. 4 is a flow chart showing a paper sheet quality determination method according to the first embodiment of the present invention.

FIG. 5 is a graph showing an example of an output signal of an optical sensor and a calculation result.

FIG. 6 is a graph showing an example of an output signal of an optical sensor for using a correlation coefficient according to the second embodiment of the present invention.

FIG. 7 is a block diagram showing a signal processing unit of a paper sheet quality determination apparatus according to a third embodiment of the present invention.

FIG. 8 is a graph showing an example of distribution of average values and standard deviations.

FIG. 9 is a flow chart showing a paper sheet quality determination method according to the fourth embodiment of the present invention.

FIG. 10 is a graph showing a method of setting a threshold value according to the fourth embodiment of the present invention.

FIG. 11 is a flow chart showing a method for determining quality of paper sheets according to the fourth embodiment of the present invention.

FIG. 12 is a graph showing a Mahalanobis distance between a good paper sheet and a defective paper sheet, which is measured by the paper sheet quality determining apparatus according to the fourth embodiment of the present invention.

FIG. 13 is a graph showing the Mahalanobis distance of an actually measured paper sheet measured by the paper sheet quality determining apparatus according to the fourth embodiment of the present invention.

FIG. 14 is a diagram showing a modification of the optical scanning method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Paper quality determination device, 2 ... conveyance means, 3 ... transmitted light forming means, 5 ... signal processing part (signal processing means), 7 ... paper sheet,
8 ... Plastic thread, 15 ... 1st photosensor (1st photodetection means), 16 ... 2nd photosensor (2nd photodetection means), 17 ... 1st interference filter (1st filter means) ), 18 ... Second interference filter (second filter means), 19 ... Infrared light (discrimination light), 21 ... Transmitted light, 22 ...
First split light, 23 ... Second split light, 28 ... Division circuit,
31 ... Paper quality determination device, 32 ... Signal processing unit, 33 ...
Arithmetic section.

Claims (7)

[Claims] 1. A paper sheet having a plastic thread is relatively scanned with discrimination light, the discrimination light is transmitted to the paper sheets to form transmitted light, and the transmitted light is detected to determine the quality of the paper sheet. In a paper sheet quality determining apparatus for determining whether a sheet is a paper sheet, different wavelength components are extracted from at least one transmitted light based on the absorption wavelength of the plastic thread, and each wavelength component is photoelectrically converted to perform signal processing. Leaf quality determination device. 2. A paper sheet having a plastic thread is scanned with a discriminating light, the discriminating light is transmitted through the paper sheet to form a transmitted light, and the transmitted light is divided into first and second split light. Transmitted light forming means for splitting, first band extracting means for extracting an absorption wavelength component of the plastic thread from the first split light, and paper portion of the paper sheet and the plastic thread from the second split light. Second band extracting means for extracting a transmission wavelength component common to the first and second light detecting means for detecting the wavelength components extracted by the first and second band extracting means, and the second A paper sheet quality determination device comprising: a signal processing unit that performs arithmetic processing on the detection results of the first and second light detection units to remove noise from the detection result of the first light detection unit. 3. The signal processing means performs the following calculation: The paper sheet quality determination device according to claim 2, wherein 4. The sheet quality determining apparatus according to claim 2, wherein the signal processing means calculates a correlation coefficient between the measured sheet and the good sheet. 5. Time-series data is input to the signal processing unit from the first and second light detecting means, and the signal processing unit calculates an average value and a standard deviation based on the time-series data. 3. The paper sheet quality determination device according to claim 2, wherein. 6. The time series data is inputted from the first and second light detecting means to the signal processing section, and the signal processing section is based on the time series data, an average value, a standard deviation and a Mahalanobis. 3. The paper sheet quality determination device according to claim 2, wherein the distance is calculated. 7. A sheet having a plastic thread is scanned with a discriminating light, the discriminating light is transmitted to the sheets to form a transmitted light, and the transmitted light is detected to discriminate the quality of the sheet. In the paper quality determination method, data regarding good paper is
Data sampling, a first step of calculating the average value and standard deviation of the obtained time series data, a second step of setting a threshold value based on the distribution of the calculation results, and an arbitrary step The third step of calculating the average value and the standard deviation of the time-series data obtained by performing data sampling on the paper sheet, and comparing the calculation result of any paper sheet with the above threshold value. And a fourth step of judging whether the paper sheet is good or bad, as described above.