JPH0238242A - Paper double feed detecting circuit - Google Patents

Abstract

PURPOSE:To detect the double feed of paper with high precision by reducing the influence due to the ON resistance of a switching means by using the small input bias electric current as the second amplifier. CONSTITUTION:The voltage set by a voltage divider 9 connected with the output terminal of the first amplifier 1 is supplied into the input terminal of the second amplifier 8 through a switching means 10. The output of the second amplifier 8 is supplied into the input terminal of the first amplifier 1. Therefore, the electric current in the bright level in the case when paper does not exist and the dark level in the double feed can be distinctly distinguished. In this case, by using the small input bias electric current in the second amplifying means 8, the electric current value which flows in the switching means 10 can be reduced. Therefore, the influence due to the ON resistance in the switching means 10 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a paper sheet double feeding detection circuit, particularly a banknote conveying device,
The present invention relates to a paper sheet double feed detection circuit that can detect double feed with high accuracy in paper industry applications such as facsimile machines, optical character reading devices, and image input devices.

40 Supports 4 In paper sheet handling devices such as banknote conveying devices, facsimile machines, optical character reading devices, and image input devices that process information using paper sheets as media, paper sheets such as banknotes are generally fed one by one. The information recorded on the sheet of paper is read by a reflective photoelectric converter and converted into an electrical signal. Therefore, if two or more sheets are fed in an overlapping manner at one time, the information on the sheets that are not irradiated with light will not be read by the photoelectric converter, resulting in malfunction. In order to prevent such duplicate feeding, the paper sheet conveying device is provided with a duplicate feeding detection circuit that measures the thickness of the paper sheet based on the amount of light transmitted through the sheet and detects duplicate feeding of the paper sheet.

For example, in the conventional sheet double feeding detection circuit disclosed in Japanese Patent Application Laid-Open No. 61-193006, as shown in FIG.
and an operational amplifier 1 for amplifying the output voltage of the light receiving section 2, and an A/D converter 3 for A/D converting the output of the operational amplifier 1, determining overlapping feeding, and outputting a sheet thickness signal. Between the tip 2 and the inverting input terminal of the operational amplifier 1, a series circuit of a switch S□ and a resistor R and a series circuit of a switch S2 and a resistor R2 are connected in parallel. operational amplifier 1
The non-inverting input terminal of is grounded. Further, a feedback circuit including a resistor R1 is connected between the output terminal and the inverting input terminal of the operational amplifier 1. In this case, switch S1 is turned on S2
When OFF, the magnification (slope) S of the operational amplifier 1 is expressed as S=(R,/R,).

In this sheet double feed detector, the light receiving section 2 generates outputs of various voltage levels of a=d shown in FIG. 4(a).

That is, first, when there is no paper sheet, a "no paper sheet" signal is output from the voltage level a, which is the output value of the bright level. Therefore, when the analog switch S is closed, the output of the operational amplifier 1 becomes A. Resistors R1 and R3 are determined so as to be near the upper limit of the conversion input range of the /D converter 3.

Next, a "double feed judgment" signal is output from the voltage level b-d, which is the output value of the dark level due to the light transmitted through the paper sheet, but the level is low at the magnification of S = (R, /R). In addition, since the difference between levels b and d is extremely small, the A/D converter 3 cannot accurately determine the level. Therefore, when only switch S2 is closed, the amplifier magnification S is set by resistors R2 and R3 so that the output of operational amplifier 1 is near the upper limit of the A/D conversion input range.
3/R2). Further, since the levels b to d in the dark level are caused by the difference in the thickness of the paper sheet, it is determined from these values whether or not duplicate feeding is being performed.

Therefore, the sheet double feed detection circuit converts the dark level shown in FIG. 4(a) applied to the input terminal to the voltage levels b' to d' shown in FIG. 4(b) at a magnification of (R3/R2). After being amplified, the digital signal A/D-converted by the A/D converter 3 is output to a circuit for determining duplicate feeding. Incidentally, the voltage-current conversion type detection circuit described above is disclosed in Japanese Patent Application Laid-Open No. 56-42328,
It is disclosed in Japanese Patent Application Laid-Open No. 57-33848.

Furthermore, as shown in FIG. 5, a current-voltage conversion type detection circuit in which a series circuit of a switch S1 and a resistor R and a series circuit of a switch S2 and a resistor R2 are connected in parallel to a feedback circuit is disclosed in JP-A-58- Publication No. 152740 and JP-A-62-839
It is known from the publication No. 51. In this detection circuit, the output current of the light receiving section 2 that detects the amount of light transmitted through the paper sheet is converted into the output voltage of the operational amplifier 1. Therefore, op amp 1
The output voltage v0 of is V,=IR1 or V,=IR2.

The output voltage of the resistor R is V when there is no paper and only the switch S is turned on. is set so that it does not exceed the input range of the A/D converter 3. When paper sheets overlap, the output voltage V is generated at the resistor R1. Since the value of is too small and the measurement error becomes large, only switch S2 is turned on and the output voltage V when multiple sheets overlap. The resistor R2 is determined so that R2 is near the upper limit of the input range of the A/D converter 3 and does not exceed the upper limit. As a result, the voltage level V1=r when one sheet is missing is calculated, and the voltage level V,=I2R, when sheets overlap is calculated from R1, and the overlap of sheets is detected.

However, in the above-mentioned conventional voltage-to-current conversion type detection circuit that amplifies the small amount of transmitted light that has passed through the paper sheet by a large factor, variations in the values of the resistors RL and R, and the offset voltage of the operational amplifier 1 can be avoided. There is a drawback that a magnification error of the operational amplifier 1 occurs due to variations in the number of signals, and the accuracy of detecting duplicate feeds decreases.

In addition, in the current-voltage conversion type detection circuit, switches S□ and S
When switch 2 is turned on, the on-resistance of switches S1 and S2 remains. The on-resistance of the switch S2 has a large effect on the output voltage, and therefore the change in the output current r of the light receiving section 2 cannot be measured accurately. That is, the values of the resistors R1 and R2 are in the order of Ω to 10 in the order of Ω, and the values of the switches S□ and S2 are
The on-resistance (drain-source resistance) is several tens to several tens of
It is 0Ω.

Therefore, it is not possible to obtain a stable output from the operational amplifier 1 due to the voltage drop in the switches Si and S2, the temperature characteristics of each element, or variations in manufacturing quality. It was difficult to do so.

Furthermore, the switches S and S2 are CMO3 type O3 log switches with low resistance between drain and source.

However, when the light receiving section 2 is irradiated with light while the power is off, an electromotive force is generated in the light receiving section 2.
There is a risk that the element may be destroyed due to latch-up of S2.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a circuit for detecting duplicate feeding of paper sheets, which can detect duplicate feeding of paper sheets with high precision and eliminates the risk of element destruction.

The paper sheet double feeding detection circuit of the present invention includes a sensor means consisting of a light emitting part and a light receiving part which are arranged separately from each other with an interval that allows the paper sheet to pass therethrough, a first amplifier having an input terminal connected thereto and an output terminal connected to the determining means; a second amplifier having an output terminal connected to the input terminal of the first amplifier via a resistor; It has a voltage divider connected to the output terminal of the first amplifier and switching means connected in parallel between the input terminal of the second amplifier and the voltage divider.

The voltage set by the voltage divider connected to the output terminal of the first amplifier is supplied via switching means to the input terminal of the second amplifier. The second amplifier provides an output to the input terminal of the first amplifier. Therefore, it is possible to clearly distinguish between the bright level current when there is no paper sheet and the dark level current when the sheet is repeatedly fed. In this case, by using a second amplifier with a small manual bias current, the value of the current flowing through the switching means is reduced.

Therefore, the influence of on-resistance in the switching means can be reduced. In addition, since the light receiving section is connected to the output terminal side of the second amplifier, even if the light receiving section is irradiated with light when the power is off, the electromotive force generated in the light receiving section will not be transmitted to the switching means, which will prevent latch-up. It is possible to avoid the risk of element destruction due to

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will now be described with reference to FIGS. 1 and 2. In these drawings, parts that are the same as those shown in FIGS. 3 to 5 are designated by the same reference numerals, and explanations thereof will be omitted.

First, as shown in FIG. 1, there is a sensor means 6 consisting of a light emitting section 5 and a light receiving section 2 which are arranged separated from each other with an interval that allows paper sheets to pass through, and an input terminal connected to the sensor means 6. a first amplifier 1 having an output terminal connected to the determining means 7; a second amplifier 8 having an output terminal connected to the input terminal of the first amplifier 1 via a resistor R1; connected to the output terminal of the first amplifier 1 and resistor R
1 and R2, and a switching means 10 connected in parallel between the input terminal of the second amplifier 8 and the voltage divider 9.

The first amplifier 1 is an operational amplifier, and the second amplifier 8 can also use the same or a different operational amplifier.

The determining means 7 includes an A7'D converter 3, a memory circuit 11, a comparison control circuit 12 that compares the output of the A/D converter 3 with information in the memory circuit 11, and a non-converter driven by the output of the comparison control circuit 12. It has a control section 13. Switches S and S2 constituting the switching means 10 are controlled on and off by control signals output from the comparison control circuit 12, respectively. Resistors R1 and R2 forming voltage divider 9 are connected in series between the output terminal of first amplifier 1 and ground. A switch S□ is connected between the connection line between the resistors R1 and R2 and one input terminal of the second amplifier 8.

Further, the output terminal of the first amplifier 1 is connected to one input terminal of the second amplifier 8 via a switch S2. The other input terminal of the second amplifier 8 is connected to the output terminal by a feedback circuit. With this feedback circuit, the second amplifier 8 is configured to output a voltage at a level equal to the voltage applied to one input terminal to which the switch S or S2 is connected.

Therefore, if the output voltage of the first amplifier 1 is vo, the output voltage of the second amplifier 8 is also V. is equal to here,
If the current flowing through the light receiving section 2 is I, then when only the switch S2 is turned on, the output voltage is V. is V,=IR.

It is. When only switch S4 is turned on, the output voltage V. is R1. When there is no paper sheet, only switch S2 is turned on and R1 is set near the upper limit of the input range of the A/D converter 3. When one sheet is conveyed, only switch S4 is turned on and A Duplicate detection can be performed by setting the resistor R2 to be close to the upper limit of the input range of the /D converter 3.

In the sheet double feeding detection circuit according to the present invention, the switch S1
, S2 is only the input bias current of the second amplifier 8, and this input bias current is generally several pA (
It is on the order of from picoampere to several nA (nanoampere). Therefore, this input bias current is very small compared to the output current of the light receiving section 2, which is on the order of several mA (milliamperes) or several tens of mA. Therefore, measurement errors due to the on-resistance of the switches Si and S2 can be sufficiently removed.

Furthermore, by providing the second amplifier 3, the electromotive force of the light receiving section 2 that is generated when the light receiving section 2 is irradiated with light when the power is off is not directly applied to the switches S and S2. It is possible to avoid the risk of element destruction due to latch-up of S2.

Various modifications can be made to the above-described embodiments of the invention. For example, switch S as shown in FIG.

can be omitted and the connection between the resistors R1 and R2 can be directly connected to one input terminal of the second amplifier 8. In this case, when there is no paper sheet, only switch S2 is turned on and resistor R3 is set near the upper limit of the input range of A/D converter 3, and when one sheet is conveyed, switch S2 is turned off. Duplicate detection can be performed by setting the resistors R1 and R2 so that the input range of the A/D converter 3 is close to the upper limit.

Furthermore, another resistor may be connected between the resistor R2 and the first amplifier 1, or the output voltage of the second amplifier 8 may be set to a different level from the voltage applied to one of its input terminals. It is also possible to do so.

Furthermore, although the second amplifier 8 is shown as an IC type operational amplifier in the illustrated example, it can be configured using bipolar transistors or unipolar transistors.

As described above, in the sheet double feed detection circuit of the present invention, the current flowing through the second amplifier is made very small, and the reduced current flows through the switching means. It is possible to detect duplicate feeding of paper sheets with high accuracy by reducing the influence of resistance. In addition, even if the light receiving section is irradiated with light and an electromotive force is generated in the light receiving section when the power is off, the light receiving section is connected to the output terminal side of the second amplifier, so switching due to latch-up will occur. Destruction of elements such as means can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a sheet double feeding detection circuit according to the present invention;
FIG. 2 is a circuit diagram showing another embodiment of the present invention, FIG. 3 is a circuit diagram of a conventional sheet double feed detection circuit, and FIG. A graph showing the input voltage level of operational amplifier 1 when
3 is a graph showing the output voltage level of the operational amplifier 1 when the switch S2 is closed in the circuit of FIG. 3, and FIG. 5 is a circuit diagram of another conventional sheet double feeding detection circuit. 10. first amplifier, 21. Light receiving section, 5. . Light emitting part, 69. sensor means, 701 determination means, 80
．． second amplifier, 911 voltage divider, 10. . Switching means, R10, resistor.

Claims (1)

[Claims] It has a sensor means consisting of a light emitting part and a light receiving part arranged separately from each other with an interval through which a paper sheet can pass, and an output terminal which has an input terminal connected to the sensor means and is connected to a determination means. a first amplifier, a second amplifier having an output terminal connected to the input terminal of the first amplifier via a resistor, a voltage divider connected to the output terminal of the first amplifier, and a second amplifier. and switching means connected in parallel between an input terminal of the circuit and a voltage divider.