JPH11351962A - Optical density detector for sheet and the like media - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical density detector for paper or sheet class media without being affected by an influence of an aging change of a sensor unit. SOLUTION: A switch 14 is switched to a low current circuit 13 except a paper money 2 by a regulation when shipped to drive a light emitting diode 3. A value directly received from the diode 3 by a photodiode 4 is converted into a digital value by an analog-digital converter 6 via a current-voltage converter 5, and stored in a memory 21 as an initial value. When measured, the diode 3 is previously driven by the circuit 13 in a no paper money state, a light reception amount at that time is converted into a digital value, and a correction coefficient is calculated from the digital value and the initial value by a correction coefficient calculator 22. Then, in an actual paper money measuring, the diode 3 is driven by a steady current circuit 12, and a digital value obtained at this time is multiplied by the coefficient by a correction processor 23, and corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting the optical density of a sheet medium, and more particularly to a sensor comprising a pair of a light source and a photodetector, which detects the print density of a sheet medium such as a banknote. The present invention relates to an optical density detection device suitable for use in determining the authenticity and type of a medium at the density level.

[0002]

2. Description of the Related Art For example, as an optical method for discriminating bills, a print density level of a bill is captured by a sensor for light emission / light reception, and a difference between the density level and a predetermined threshold value specific to a denomination is detected. It is common practice to discriminate denominations from size relations. A configuration example of an apparatus for detecting the printing density of such bills for denomination identification will be described with reference to FIGS.

FIG. 5 is a diagram showing a configuration example of a conventional denomination identification detection sensor. A light-emitting diode 102, which is a light-emitting element, is provided above the transport path for transporting the bill 100, and a photodiode 104, which is a light-receiving element, is provided at a position facing the light-emitting diode 102. A drive circuit 108 is connected to the light emitting diode 102 via a variable resistor 106. The photodiode 104 includes a current / voltage conversion circuit 110 and an analog / digital conversion circuit 11.
2 and the processing circuit 114 are connected.

When the bill 100 is conveyed on the optical path between the light emitting diode 102 and the photodiode 104, the light emitting diode 102 is pulse-driven by the drive circuit 108 to irradiate the moving bill 100 with light and transmit the light. The light is received by the photodiode 104, and the transmitted light intensity is converted into an electric signal. Since this signal is a current corresponding to the light intensity, it is converted into a voltage by the current / voltage conversion circuit 112 and further converted into a voltage by the analog / digital conversion circuit 11.
In step 2, it is converted to a digital signal.

[0005] Such a sensor includes a light emitting diode 1
There are several factors of output fluctuations in the initial stage, such as fluctuations in light emission of No. 02 and fluctuations in the sensitivity of the photodiode 104. In order to cope with these fluctuations in output, a medium having a uniform concentration is placed in advance on a transport path at the time of shipment. , The light emitting diode 102 with a variable resistor
Is adjusted by changing the drive current of

Next, an example in which a denomination is determined using such a sensor will be described below. Banknotes of Japan are printed in different colors for each denomination (1,000 yen, 5,000 yen, 10,000 yen). Therefore, when monochromatic light is applied to the printing surface of a different color, the intensity of the transmitted light changes depending on the denomination of the bill.

Here, the banknote is conveyed, for example, in the short direction, and, for example, five sensors are installed in the width direction of the conveyance path to simultaneously detect five transmitted light levels in the longitudinal direction of the banknote. I do. Here, for example, assuming that two sensors arranged on both sides are located near 70 mm from the transport center, different measurement results are obtained for 1,000 yen and 10,000 yen. That is, at such a detection position, 1,000 yen is a white portion where a pattern is hardly printed, and 10,000 yen is a portion where a pattern is printed. Therefore, the output detected by the photodiode 104 and subjected to analog / digital conversion is larger in the case of 1,000 yen than in the case of 10,000 yen. Utilizing this difference, the denomination is determined.
6 shows a frequency distribution of a digital conversion output.

FIGS. 6A and 6B are diagrams for explaining a method of distinguishing two denominations. FIG. 6A shows a frequency distribution of an analog / digital conversion output in an initial state, and FIG. 6B shows an analog / digital conversion after a change with time. The output frequency distribution is shown. Here, as shown in FIG. 6 (A), looking at the distribution of the analog / digital conversion output between the case of 1,000 yen and the case of 10,000 yen, the 1,000 yen is higher in the analog / digital conversion output. It is distributed, and 10,000 yen is distributed on the lower side. Thus, by setting a threshold value in the middle of the distribution and comparing the analog / digital conversion output with the threshold value, the denomination between 1,000 yen and 10,000 yen can be performed.

[0009]

However, such a sensor, during use, changes in temperature due to a change in the environment, deterioration of light output of a light emitting diode, deterioration of sensitivity of a photodiode, paper dust of bills, and the like. As a result, the analog / digital conversion output may fluctuate from the initially adjusted state due to a temporal change such as contamination of the light emitting / receiving surface caused by the light. For example, if the analog / digital conversion output decreases due to a change in the environmental temperature, the analog / digital conversion output decreases in both 1,000 yen and 10,000 yen. That is, as shown in FIG. 6B, the frequency distribution of 1,000 yen and 10,000 yen decreases in accordance with the rate of change from the initial value. On the other hand, since the threshold is fixed,
Some of the 1,000 yen have an analog / digital conversion output smaller than a threshold value. A thousand yen in an area smaller than this threshold is not correctly identified as a thousand yen, and thus has a serious problem such as erroneous determination.

The present invention has been made in view of such a point, and even if the analog / digital conversion output fluctuates due to a change over time, a process based on the analog / digital conversion output is performed. It is an object of the present invention to provide an optical density detecting apparatus for a sheet medium capable of performing correct processing.

[0011]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an apparatus for detecting the optical density of a pattern printed on a sheet medium. A light source for irradiating light to the light source, light source driving means for switching the light output of the light source to two levels of a low level and a high level, and light receiving the light output from the light source directly or transmitted through the paper sheet medium Means, an analog / digital conversion means for converting the amount of analog value received by the light receiving means into a digital value, and the light receiving means detecting when the light source is driven to a low level by the light source driving means at the time of initial adjustment. Initial value holding means for holding a first digital value of the received light amount, and a second digital value of the light amount detected by the light receiving means when the light source is driven at a low level. Correction coefficient calculating means for calculating, as a correction coefficient, a variation ratio from the first digital value held in the initial value holding means on the basis of the initial value holding means; and the sheet medium when the light source is driven at a high level. Correction means for correcting the third digital value of the amount of light detected by the light receiving means through the light receiving means with the correction coefficient. You.

According to such an apparatus for detecting the optical density of a sheet medium, there is no sheet medium between the light source and the light receiving means, and the optical density of a pattern printed on the sheet medium is measured. When not detecting, the light source driving means drives the light source at a low level. Thereby, the light receiving means directly receives the low-level light output radiated from the light source. The received light amount of the received analog value is converted into a digital value by the analog / digital conversion means, and how much the digital value varies from the digital value of the initial value holding means held in advance by the correction coefficient calculating means. Is calculated. Next, in a state where the sheet medium is placed between the light source and the light receiving means, the light source driving means drives the light source at a high level,
The light receiving means receives the transmitted light from the paper sheet medium and converts the output to a digital value by the analog / digital converting means. The digital value is input to the correction means, corrected at the variation ratio previously calculated by the correction coefficient calculation means, and output. As a result, the detection value of the light transmitted through the paper sheet medium is corrected at a change rate corresponding to the change with time, so that the output of the optical density detection device is not changed by the change with time, and therefore, There is no adverse effect on post-processing based on this correction value.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, taking an example in which the present invention is applied to a banknote denomination identifying device.

FIG. 1 is a diagram showing a configuration example of a sensor unit of a denomination identifying apparatus to which the present invention is applied. The sensor unit of the denomination discriminating apparatus includes a light emission control circuit 1, a light emitting diode 3 disposed on the upper side of the transport path for transporting the bill 2, a photodiode 4 disposed on the lower side, The current / voltage (I /
V) a conversion circuit 5 and an analog / digital (A / A / D) converting the output of the current / voltage conversion circuit into a digital signal.
D) It is composed of a conversion circuit 6 and a fluctuation correction circuit 7, and the output of the fluctuation correction circuit 7 is connected to a denomination identification processing circuit 8. The light emission control circuit 1 includes a light emitting diode (LE)
D) Drive unit 11 and steady-state current circuit 12 composed of a variable resistor
And a switch 14 for connecting either the output of the steady current circuit 12 or the output of the low current circuit 13 to the light emitting diode 3. Further, the fluctuation correction circuit 7 includes a memory 21 for storing values adjusted at the time of product shipment, and a correction coefficient calculation unit 22 for calculating a temporal change ratio of the sensor unit as a correction coefficient.
And a correction processing unit 23 that corrects the detected digital value using a correction coefficient.

At the time of shipment, adjustment of the sensor unit is performed. First, a predetermined medium having a transmittance similar to that of a bill is placed in the bill transport path, and the switch 14 is turned on in the steady current circuit 1.
2, the light emitting diode 3 is driven, and the photodiode 4 receives light so that the voltage output from the current / voltage conversion circuit 5 becomes a predetermined voltage, that is, an initial output voltage Vs. To adjust. Next, the medium is removed from the bill transport path, the switch 14 is switched to the low current circuit 13 side, the light emitting diode 3 is driven, and the value received by the photodiode 4 is converted into an analog value by the current / voltage conversion circuit 5. And the initial output voltage Vn
Is converted into a digital value by the analog / digital conversion circuit 6 and stored in the memory 21. As a result, in the initial state, the amount of light received directly when the light output when the light emitting diode 3 is driven at the low level is stored as the initial value. The low-level driving of the light-emitting diode 3 does not saturate the light-receiving output by the photodiode 4,
That is, the light receiving output is converted to the analog / digital conversion circuit 6
Of the light emitting diode 3
Are set so that the current-light output characteristics of the device are within a linear range as much as possible.

Next, at the time of a normal denomination identification operation of a bill,
Preferably, just before the bill 2 is conveyed and reaches the optical path between the light emitting diode 3 and the photodiode 4, a variation ratio due to a temporal variation from the initial state, that is, a correction coefficient is obtained. That is, in the light emission control circuit 1, the switch 14 is switched to the side of the low current circuit 13, and the light emitting diode 3 is driven. Thereby, the photodiode 4 receives the light output emitted by the light emitting diode 3,
The current / voltage conversion circuit 5 outputs a corresponding time-varying output voltage Vn ′, and the analog / digital conversion circuit 6 outputs a corresponding digital value (Vn ′). In the fluctuation correction circuit 7, the correction coefficient calculation unit 22 calculates the correction coefficient kn, based on the temporal fluctuation output voltage Vn ′ and the initial output voltage Vn stored in the memory 21 according to the following equation.

[0017]

Kn = Vn / Vn '(1)

After the correction coefficient kn is determined, the sensor unit detects the density of the bill 2 by the transmitted light. First,
In the light emission control circuit 1, the switch 14 is switched to the side of the steady current circuit 12, and the light emitting diode 3 is driven to irradiate the bill 2. The light transmitted through the banknote 2 is received by the photodiode 4, and its output is converted into a time-varying output voltage Vs ′ by a current / voltage conversion circuit 5, and a digital value corresponding thereto is converted by an analog / digital conversion circuit 6. (Vs'). In the fluctuation correction circuit 7, the correction processing unit 23 calculates the correction output S, based on the time-varying output voltage Vs' and the correction coefficient kn obtained earlier by the following equation.

[0019]

S = kn · Vs ′ (2) Then, in the denomination identification processing circuit, the denomination identification processing of the banknote 2 is performed based on the correction output S in which the variation with time is corrected.

As described above, the correction of the sensor output is performed in such a manner that the output fluctuation due to the aging change is caused by the initial output voltage Vs and the aging fluctuation output voltage Vs ′ when the light emitting diode is driven by the steady current circuit 12 and the light emitting diode driving by the low current circuit 13. The characteristic that the initial output voltage Vn at the time and the time-varying output voltage Vn ′ are in a proportional relationship (Vs / Vs ′ = Vn / Vn ′) is used.

Next, in this sensor unit, when a temporal change such as a decrease in sensor output occurs due to a temporal change such as a temperature change of the environment, a light output deterioration of the light emitting diode 3 and a sensitivity deterioration of the photodiode 4. The correction of the sensor output will be described in more detail with reference to FIG.

FIG. 2 is a diagram for explaining the operation of sensor output correction. In this figure, the horizontal axis represents the current value flowing according to the amount of light received by the photodiode 4, and the vertical axis represents the output voltage of the analog / digital conversion circuit 6. Here, a solid line 31 shows a change in the output voltage with respect to the received light current value when the steady-state current circuit 12 is adjusted in the initial state, and a broken line 32 shows a change in the current value when there is a temporal variation. A change in the output voltage is shown. A solid line 33 indicates a change in the output voltage with respect to the light receiving current value when the low current circuit 13 is changed for setting in the initial state. The change of the output voltage with respect to the current value when there is a change is shown. In this example, the steady current circuit 12 sets the current flowing when the photodiode 4 receives light to be Is, and the low current circuit 13 sets the current flowing when the photodiode 4 receives the light to In. It indicates that it has been done.

From this figure, at the time of initial setting, the output voltage of the analog / digital conversion circuit 6 when the steady current circuit 12 is used is the initial output voltage Vs, and the analog / digital conversion circuit when the low current circuit 13 is used. It is assumed that the output voltage of the analog-to-digital conversion circuit 6 has decreased from the initial output voltage Vn to the temporally varying output voltages Vs 'and Vn' due to temporal variation. Here, before the bill is measured, first, a correction coefficient is calculated. The correction coefficient kn at this time is obtained according to the above equation (1) using Vn stored at the time of shipment. After that, the switch 14 is switched to the steady-state current circuit 12 to measure the bill, and the time-varying output voltage Vs' obtained is multiplied by the correction coefficient kn to obtain a correction output S. As a result, the denomination discriminating circuit 8 can process the output of the analog / digital conversion circuit 6 with the time-varying output voltage Vs' as the initial output voltage Vs. In this example, the update of the correction coefficient kn is performed every time the banknote to be determined is input, but may be performed at fixed time intervals when there is no banknote.

FIG. 3 is a diagram showing the frequency distribution of the two denominations before and after the output fluctuation correction. FIG. 3A shows the frequency distribution of the analog / digital conversion output before the output fluctuation correction.
(B) shows the frequency distribution after the output fluctuation correction. Here, before the output fluctuation correction, as shown in FIG. 3A, the analog / digital converted output has a frequency distribution of 1,000 yen and 10,000 yen in which the lower the output in accordance with the fluctuation ratio from the initial value. However, the frequency distribution can be returned to the same frequency distribution as the initial state by performing the fluctuation correction in the fluctuation correction circuit 7.

Next, a second embodiment of the present invention applied to a bill denomination discriminating apparatus will be described in detail with reference to FIG. FIG. 4 is a diagram illustrating a configuration example of a sensor unit of the denomination identification device according to the second embodiment. In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals. The sensor unit of the denomination discriminating apparatus includes a light emission control circuit 1, a light emitting diode 3 disposed on an upper side of a transport path for transporting a bill 2, a photodiode 4 disposed on a lower side, and a photodiode 4 A current / voltage (I / V) conversion circuit 5 for converting the current output of the current / voltage conversion circuit into a voltage signal, an amplification circuit 40 for amplifying the output of the current / voltage conversion circuit, and an analog for converting the amplified analog signal to a digital signal. / Digital (A / D) conversion circuit 6
The output of the fluctuation correction circuit 7 is connected to a denomination identification processing circuit 8. The light emission control circuit 1 includes a light emitting diode (LED) driving unit 11
And a steady-state current circuit 12 including a variable resistor. The output range of the current / voltage conversion circuit 5 is adjusted by a resistor R so as to be 1 / n of the effective input range of the analog / digital conversion circuit 6. The subsequent amplification circuit 40 is set to have an amplification factor of n times by the feedback resistance Rf and the ground resistance Rg. A switch 41 is connected to the feedback resistor Rf in parallel with the feedback resistor Rf.
0 is configured to operate as a voltage follower with a gain of 1. Further, the configuration of the fluctuation correction circuit 7 is the same as the configuration shown in FIG.

Here, at the time of shipment, the stationary current circuit 1
After the adjustment of 2, the initial value is stored. First, a predetermined medium that transmits light similar to a bill is placed in the bill transport path, the switch 41 is closed, and the light emitting diode 3 is driven. A current signal generated by the photodiode 4 receiving light is converted into a voltage signal by a current / voltage conversion circuit 5, passed through an amplifier circuit 40 having a gain of 1, and converted into a digital signal by an analog / digital conversion circuit 6. . This digital value is stored as an initial value in a memory in the fluctuation correction circuit 7.

Next, at the time of a normal bill denomination identification operation,
Before the measurement of the banknote 2, the switch 41 is closed to lower the gain of the amplifier circuit 40, and then the light emitting diode 3 is driven. When the photodiode 4 receives the light output from the light emitting diode 3, the current / voltage conversion circuit 5 outputs a corresponding time-varying output voltage, which is converted into a digital value by the analog / digital conversion circuit 6 via the amplifier circuit 40. The data is converted and input to the fluctuation correction circuit 7. The fluctuation correction circuit 7 calculates a correction coefficient from the digital value and the initial value stored in the memory.

Next, the switch 41 is opened and the amplifier circuit 4 is opened.
After setting the amplification factor n to 0, the banknote 2 is measured by the sensor unit. That is, the light emitting diode 3 is driven and the bill 2 is
Is irradiated. The photodiode 4 receives the light transmitted through the bill 2, and its current output is converted into a voltage signal by a current / voltage conversion circuit 5, amplified by an amplification circuit 40 n times, and then converted into an analog / digital conversion circuit. At 6, it is converted into a digital value and input to the fluctuation correction circuit 7. The fluctuation correction circuit 7 multiplies the input digital value by the correction coefficient kn obtained earlier and outputs the result.

[0029]

As described above, according to the present invention, first, a value measured without a medium to be measured is stored in a memory as an initial value, and the medium is measured immediately before or immediately after measuring the medium. When it is not, periodically check the fluctuation of the sensor unit over time to obtain a correction coefficient which is a fluctuation ratio from the initial value, and correct the measured value based on the correction coefficient when actually measuring the medium. It was configured. As a result, even if the output of the sensor fluctuates due to a change over time such as a temperature change, deterioration, or contamination, the performance in the initial state can be maintained. Erroneous discrimination of bills can be prevented beforehand.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a sensor unit of a denomination identification device to which the present invention has been applied.

FIG. 2 is a diagram for explaining an operation of sensor output correction.

3A and 3B are diagrams showing frequency distributions of two denominations before and after output fluctuation correction, wherein FIG. 3A shows a frequency distribution of an analog / digital conversion output before output fluctuation correction, and FIG. The subsequent frequency distribution is shown.

FIG. 4 is a diagram illustrating a configuration example of a sensor unit of a denomination identification device according to a second embodiment.

FIG. 5 is a diagram illustrating a configuration example of a conventional denomination identification detection sensor.

FIG. 6 is a diagram illustrating a method of identifying two denominations,
(A) shows the frequency distribution of the analog / digital conversion output in the initial state, and (B) shows the analog / digital conversion output after the change with time.
The frequency distribution of the digital conversion output is shown.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light emission control circuit 2 bill 3 light emitting diode 4 photodiode 5 current / voltage conversion circuit 6 analog / digital conversion circuit 7 fluctuation correction circuit 8 denomination identification processing circuit 11 light emitting diode drive section 12 steady current circuit 13 low current circuit 14 switch 21 Memory 22 Correction coefficient calculation unit 23 Correction processing unit 40 Amplification circuit 41 Switch Vs, Vn Initial output voltage kn Correction coefficient S Correction output

Claims (7)

[Claims] An apparatus for detecting the optical density of a pattern printed on a sheet medium, comprising: a light source for irradiating the sheet medium with light; and a light output of the light source. Light source driving means for switching between two levels: a high level and a high level; a light receiving means for receiving the light output from the light source directly or through the paper sheet medium; and a light receiving amount of an analog value received by the light receiving means. Analog / digital converting means for converting to a digital value; and initial setting for holding a first digital value of the amount of light detected by the light receiving means when the light source is driven to a low level by the light source driving means during initial adjustment. Value holding means, and the second value held by the initial value holding means based on a second digital value of the amount of light detected by the light receiving means when the light source is driven at a low level. A correction coefficient calculating means for calculating a change ratio from the digital value of 1 as a correction coefficient; and a third light receiving amount detected by the light receiving means through the paper sheet medium when the light source is driven at a high level. And a correcting means for correcting the digital value of the above by the correction coefficient. 2. A light source driving unit comprising: a driving source for driving the light source; a stationary current circuit for supplying a predetermined current from the driving source; and a predetermined current source which is less than the stationary current circuit from the driving source. A low-current circuit for supplying a current, and when the sheet medium is present between the light source and the light-receiving means, the supply current of the steady-state current circuit is output to the light source and the light-receiving means is directly output from the light source. 2. The optical density detecting apparatus according to claim 1, further comprising: a switch configured to switch a supply current of the low current circuit to the light source when receiving the light. 3. The correction coefficient calculation means calculates the correction coefficient on a regular basis by calculating from the second digital value obtained by driving the light source at a low level when the sheet medium is not present. 2. The optical density detecting apparatus for a paper sheet medium according to claim 1, wherein the optical density is updated. 4. The correction coefficient calculating means, based on the second digital value obtained by driving the light source at a low level, immediately before driving the light source at a high level to irradiate the paper sheet medium. 2. The apparatus according to claim 1, wherein the correction coefficient is calculated. 5. An apparatus for detecting the optical density of a pattern printed on a sheet medium, comprising: a light source for irradiating the sheet medium with light; and a light source drive for driving the light source. Means, light receiving means for receiving the light output from the light source directly or through the paper sheet medium, and gaining the amount of analog value received by the light receiving means by 2
Variable gain amplifying means for switching and amplifying in steps, analog / digital converting means for converting an analog value amplified by the variable gain amplifying means into a digital value, and detecting the variable gain amplifying light by the light receiving means upon initial adjustment. Means for holding a first digital value of the amount of light received at a low gain by the means; and a first value of the amount of light received at the low gain detected by the light receiving means and amplified by the variable gain amplifying means. The first value held in the initial value holding means based on the digital value of
Correction coefficient calculating means for calculating the variation rate from the digital value of the as a correction coefficient, the light amount of light received through the paper medium and detected by the light receiving means and amplified by the variable gain amplifying means with a high gain And a correcting means for correcting the digital value of No. 3 by the correction coefficient. 6. The correction coefficient calculating means calculates the correction coefficient from the second digital value obtained by switching the variable gain amplifying means to a low gain when there is no paper medium. 6. The optical density detecting apparatus for a paper sheet medium according to claim 5, wherein is updated periodically. 7. The second digital signal obtained by switching the variable gain amplifying means to a high gain before the light receiving means detects the transmitted light from the paper sheet medium. 6. The apparatus according to claim 5, wherein the correction coefficient is calculated from a value.