JPH0831156B2 - Paper edge detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a paper edge detection device, and in particular, for measuring the size of bills and detecting breakage of bills in an ATM (automatic transaction machine), etc. ) Is accurately detected.

[Conventional technology]

The banknote discrimination unit built into the ATM has been developed using a contact image sensor that uses transmitted light. When the edge portion of the bill is detected by this sensor, the envelope of the sensor output becomes wavy due to uneven illumination and uneven sensitivity in the image sensor. When the wave input is binarized by the binarization circuit in the next stage, chattering occurs in the scanning direction. When such chattering occurs, it adversely affects the measurement of the size of bills (paper) and the detection of breakage.

FIG. 2 is a diagram showing a binarized waveform of the image sensor output. (A) is a relationship diagram between a paper edge portion and a field of view of a sensor, (b) is an output waveform diagram of an image sensor passing through an amplifier circuit, and (c) is a binary output diagram of the sensor output. When an edge portion of a sheet (for example, a bill) is detected by using an image sensor, as shown in FIG. 2 (b), unevenness appears in the sensor output due to a difference in sensitivity of the image sensor, uneven illumination, and the like. When this is binarized by using one threshold V _T , chattering occurs at a portion where the output is uneven, as shown in FIG. 2 (c). This chattering is caused by the image sensor field of view 6 as shown in FIG.
The closer the paper edge 7 is to the parallel, the easier it is to occur.

[Problems to be solved by the invention]

Due to this chattering, although there is no tear at the edge of the paper, the binarized output is the same as if there was a tear. For this reason, when it is attempted to measure the size of paper (banknotes) or detect breakage, folding, etc. using the image sensor, there is a problem that accurate measurement of the edge portion cannot be performed. As a circuit related to this kind of problem,
"Digital floating threshold value forming circuit" (JP-A-60-69)
785). In this circuit, the threshold value is calculated using the average value of the multi-value digitized signal and the minimum value in a predetermined number (N) of digital signals. As a result, the time difference between the input signal and the threshold value can be eliminated, and the unnecessary level signal can be reliably removed. However, when the target is binarized as shown in FIG. It is difficult to apply it in the pulse form.

An object of the present invention is to improve such conventional problems and prevent chattering from occurring at the edge portion at the time of detecting a sheet, thereby accurately measuring the dimension of the sheet and detecting the state (edge) such as folding or tearing. An object is to provide a paper edge detection device having a simple structure.

[Means for solving problems]

In order to achieve the above object, the paper edge detection device of the present invention has a first input terminal for inputting a reference potential signal, a second input terminal for inputting a signal from a paper edge sensor, and a first input terminal. One comparator 9 having an output terminal for comparing the signals input to the input terminal and the second input terminal and outputting the comparison result, a T input terminal for inputting a timing signal, and for setting regardless of the T input terminal S input terminal for inputting a signal of, a D input terminal for inputting a signal for resetting in synchronization with the input to the T input terminal, an affirmative output terminal (Q) for outputting an affirmative signal, a negative for outputting a negative signal And a D-type flip-flop 5 having an output terminal ().
Input to the D input terminal and the S input terminal of the flip flop, and the logical product of the signal and the strobe signal from the positive output terminal (Q) of the flip flop is input to the T input terminal as a timing signal. It is characterized in that the value of the reference potential signal to the first input terminal to the comparator is made variable by the signal from the negative output terminal () of the D-type flip-flop.

[Action]

According to the present invention, when binarizing the output in the state where the envelope curve is wavy when the paper edge is detected, the threshold level of binarization has hysteresis so that chattering occurs at the edge when the paper is detected. I didn't let it happen. For the target binarization, if the signal to be handled is a continuous output that is not in the form of a pulse, a general comparator circuit having hysteresis can be applied as it is. But the second
When the signal to be handled as shown in the figure is a pulsed image sensor output, it is necessary to devise a method of giving hysteresis to the comparator. In the present invention, in addition to the comparator, a flip-flop that is set or reset by the detection signal is provided to give the comparator hysteresis.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining the basic principle of the present invention. In FIG. 1, 1 is an image sensor which is the object of this embodiment, 2 is an amplifier circuit for amplifying the output signal of the image sensor 1, 3 and 4 are comparators for binarizing,
5 is a flip-flop that is set by the output of the comparator 3 and is reset by the output of the comparator 4, and 8 is AND of the strobe and the output of the flip-flop 5 to inhibit threshold detection and provide a hysteresis characteristic. It is an AND circuit for.

The output of the image sensor 1 is amplified by the amplifier circuit 2, and the output of the amplifier circuit 2 is divided into two and input to the comparators 3 and 4, respectively. Threshold voltages (threshold voltage) V _T1 and V _T2 are input to the comparators 3 and 4, respectively. For example, the threshold voltage is set to have a relationship of V _T1 <V _T2 , and the input of the comparator 3 is the threshold V _T2.
The output becomes larger as it becomes larger. On the other hand, in the comparator 4, the output increases as the input becomes smaller than the threshold value V _T1 . Further, by prohibiting the strobe input to the comparator 4 by the AND circuit 8,
When the flip-flop 5 is reset once by prohibiting the input detection and having the hysteresis characteristic, the reset state is continued even if the output of the comparator 4 is lost, and the flip-flop 5 is first set by the output from the comparator 3. To do so.

FIG. 3 is a timing chart of the binarized output detected in FIG. 1, in which (a) is the image sensor 1
(B) is a binarized output. As is clear from FIGS. 3A and 3B, when there is no paper, the comparator 3 outputs a large amount, but the output decreases as the paper is detected. As a result, when there is an input smaller than the threshold value V _{T1 of the} comparator 4, the flip-flop 5 is reset. Then, the flip-flop 5 is not inverted even if there is an input exceeding the threshold V _T1 again, and the flip-flop 5 is inverted only when the comparator 3 has an input larger than the threshold V _T2. . This operation is realized by operating the comparator 4 in synchronization with the strobe and prohibiting the strobe by the AND circuit 8.

Thus, in FIG. ₁ , due to the difference in threshold values of V _T1 and T _T2 , chattering does not occur even when an image sensor output with a wavy envelope is input, and binarization is possible. Yes, this allows the accurate state of the edge of the paper to be detected. Note that chattering is less likely to occur as the difference between the threshold V _T1 and the threshold V _T2 is larger, but there is a limit depending on the input signal value. The principle of giving the hysteresis characteristic to the comparator in this configuration example will be described in more detail.

In FIG. 1, the comparator 4 first sets the threshold value.
Detect that there was an input below V _T1 . That is, the comparator 4, a specific timing of the image sensor output by the strobe signal, the input has to determine whether the threshold is reached V _T1, which is the detection of low side level of pulsed output is It is necessary. Since the image sensor output is pulsed, the flip-flop 5 inputs the output to the AND circuit 8 in order to store that the input was below the threshold value at a specific timing, and strobes the set input. Is input to the comparator 4, and the determination operation is performed as a synchronization signal. After that, the strobe is prohibited by the AND circuit 8 so that the flip-flop 5 remains reset until the output of the image sensor exceeds the threshold V _{T2 of the} comparator 3. This gives the comparator 4 a hysteresis characteristic.

FIG. 4 is a block diagram of a paper state detection circuit showing the specific example of FIG. The lower left waveforms are the output at point P and the strobe output. In Figure 4, RS (Reset Set)
D-type flip-flops are used instead of type-type flip-flops, and the outputs of the comparators 3 and 4 are applied to the S and D input terminals and the strobe signal is applied to the T input terminal.
Although different from FIG. 1, the operation is the same. That is, the output of the image sensor 1 is passed through the amplifier circuit 2 and
Input to two comparators 3 and 4. Here, the strobe is strobed so as to cut out a specific timing of the output of the image sensor 1. In the D-type flip-flop 5, the S input is input and set regardless of the strobe signal, but the D input is input and reset in synchronization with the strobe signal. In the comparator 3, when the P point output exceeds the threshold value V _T2 , the output becomes “0”, so the flip-flop 5 is set. As a result, the Q output of the D-type flip-flop 5 becomes "1", and the AND circuit 8 opens to allow the input of the strobe signal. In the comparator 4, when the output at the point P falls below the threshold V _T1 , the output becomes “0”, so the flip-flop 5 is reset. Once D
Type flip-flop 5 is reset, Q output is "1"
From 0 to "0", the AND circuit 8 is closed and the strobe is prohibited, and thereafter, the output at the P point remains reset until the threshold V _{T2 of the} comparator 3 is exceeded.

Although the basic principle of the present invention has been described above, the above-described example requires two comparators, which complicates the device configuration. An embodiment of the present invention will be described below with reference to FIG. In FIG. 5, instead of using the two comparators 3 and 4, the output of the flip-flop 5 is used to change the threshold V _{T of the} comparator 9. Thereby, equivalently, the same operation as in the case of using two comparators is performed. Again, the strobe signal is
Cut out the specific timing of the image sensor output, and
It serves to trigger the type flip-flop 5. That is, in FIG. 5, the D-type flip-flop 5 is controlled to have a large threshold value V _T2 when the output is “1” and a small threshold value V _T1 when the output is “0”. Initially, when the D-type flip-flop 5 is in the reset state, the Q output is "0" and the output is "1", so the threshold value V _T2 is set in the comparator 9. When the output of the image sensor 1 passing through the amplifier 2 exceeds the threshold value V _T2 , the output of the comparator 9 is set to “0” and the D-type flip-flop 5 is set. As a result, the Q output becomes "1", so that the AND circuit 8 opens and the strobe signal is input to the T terminal. Also,
Since the output becomes “0”, the threshold value V _T1 is set in the comparator 9. When the output of the image sensor 1 passing through the amplifier 2 falls below the threshold value V _T1 , the D-type flip-flop 5 is reset in synchronization with the strobe signal and the Q output is changed from “1” to “0”. Input of strobe signal is prohibited. On the other hand, since the threshold value V _T2 is set in the comparator 9, D is input until an input exceeding the threshold value V _T2 arrives.
The type flip-flop 5 continues to be in the reset state. Thereby, the hysteresis characteristic of the comparator can be given.

〔The invention's effect〕

As described above, according to the present invention, a threshold value for binarization has a hysteresis characteristic for an image sensor having a pulsed output by using one comparator and one D-type flip-flop. Since it is possible to prevent chattering from occurring at the edge when detecting the paper, it is possible to accurately measure the size of the paper and detect the state (edge) of the paper such as folds and tears with a very simple configuration. Is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining the basic principle of the present invention, and FIG. 2 is a signal time chart for explaining the problems of the prior art. FIG. 3 is a signal time chart in FIG. 1 and the present invention, FIG. 4 is a modified configuration example of FIG. 1, and FIG. 5 is a configuration diagram showing an embodiment of the present invention. 1: image sensor, 2: amplifier circuit, 3, 4, 9: comparator, 5: flip-flop, 8: AND circuit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-55-64455 (JP, A) JP-A-60-14104 (JP, A) JP-A-59-171875 (JP, A)

Claims (1)

[Claims] 1. A first input terminal for inputting a reference potential signal, a second input terminal for inputting a signal from a paper edge sensor, and a first input terminal and a second input terminal. 1 having an output terminal for comparing signals and outputting a comparison result
Two comparators, a T input terminal for inputting a timing signal, an S input terminal for inputting a signal for setting regardless of the T input terminal, and a signal for resetting in synchronization with the input to the T input terminal And a D-type flip-flop having a positive output terminal for outputting a positive signal and a negative output terminal for outputting a negative signal. An inverted signal of the output of the comparator is supplied to the D input terminal of the D-type flip-flop and The signal is input to the S input terminal, the signal from the positive output terminal of the D flip-flop is ANDed with the strobe signal, and the result is input to the T input terminal as a timing signal. Signal to the comparator first
A sheet edge detecting device, wherein the value of the reference potential signal to the input terminal of the sheet is made variable.