JP2000095390A - Method of detecting double feed of sheet material using ultrasonic waves - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable a double feed detection judgment without fail to overlook even when a sheet material such as paper is almost completely matched and overlapped and fed. SOLUTION: An ultrasonic wave is transmitted from an ultrasonic transmitter 1 disposed on a line for conveying sheets P-1 and P-2 to an ultrasonic receiver 2 to detect a double feed, and one sheet of paper is detected. The output obtained by receiving and converting the passed ultrasonic wave by the ultrasonic receiver 2 is used as a reference output value, and a threshold value for judging double feed is set in advance as a value lower than the reference output value, and the ultrasonic transmission is performed. The paper is scanned in the transport direction while repeating the transmission of the ultrasonic waves from the unit 1, and when the number of scanning points having an output value lower than the critical value exceeds a predetermined value during the period of scanning the paper by the transmission of the ultrasonic waves, the overlap is detected. It is determined to be sent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection method for preventing a double feed of two or more sheet materials such as sheets in a paper feed mechanism of a copying machine or a scanner for reading an image or an automatic document feeder. In particular, the present invention relates to a double feed detection method capable of detecting a double feed with high accuracy using an ultrasonic sensor.

[0002]

2. Description of the Related Art Copiers and scanners for reading images are provided with a paper feeder and an automatic document feeder for supplying paper to a platen. In these paper feeders and automatic document feeders, it is necessary to prevent double feed so that two or more sheets are not overlapped and are not sent out at the same time.

FIG. 5 shows a typical example of the form of double feeding of sheets. FIG. 7A shows a state in which another sheet B is covering the rear end of the sheet A when the sheet A is being fed in the direction of the arrow, and FIG. FIG. 4C shows a state in which the sheet B covers almost the entire area of the sheet A except for the leading end side,
FIG. 6D shows a state in which the sheets A and B are completely aligned and covered.

A sensor 61 for optically detecting a sheet is provided at a portion along a sheet conveying path for such a double feed of the sheets A and B, and the length of the sheet is detected by detecting the passing length of the sheet. It is a conventional general detection method to determine the transmission. That is, the entire length of the sheets A and B that have passed is detected by the time difference between the time when the sensor 61 detects the leading edge of the sheet A being conveyed and the time when the trailing edge of the sheet B is detected, and the detected length is set. If the value is larger than the set value, it can be determined that the double feed is performed. For example, (a), (b),
In the case of (c), since the length from the leading end of the sheet A to the trailing end of the sheet B is longer than the length of one of the sheets A and B, it is determined that the sheet is a double feed.

The double feed detection using the optical sensor 61 has been widely used in the past. However, in the case of the form (d) in FIG. Since it is the same as the length of one sheet of B, it is not possible to determine the double feed.

From such a background, instead of an optical sensor for detecting the length of a sheet being conveyed, an ultrasonic sensor is provided so that a portion where the sheet is actually multiply fed can be determined as a detection target. Has come to be used. this is,
The ultrasonic wave of the square wave is irradiated in a direction orthogonal to the conveyed sheet, and the double feed of the sheet is determined based on the transmittance of the ultrasonic wave passing through the sheet. That is, since the irradiated ultrasonic wave is attenuated when passing through the paper, the ultrasonic wave signal after passing is received by the receiving side and then converted into an output voltage so that the transmittance can be obtained. If it is equal to or more than a certain fixed value, it is determined that there is no double feed. Such multi-feed detection of sheets based on the transmittance of ultrasonic waves is used in the field of preventing multi-feed of sheets in printers, copiers, and printing machines, as described in, for example, Japanese Utility Model Laid-Open No. 1-115647. Has been adopted.

[0007]

However, depending on the timing of irradiating the sheet with ultrasonic waves or the position of irradiation on the sheet determined by this timing, double feed of sheets may not be detected correctly. For example, as shown in FIGS. 5A, 5B, and 5C, when a part of the sheets A and B overlap each other, and an ultrasonic wave is applied to a non-overlapping part, The transmittance is detected only for an amount corresponding to the passage of one sheet. Therefore, even though the sheets A and B are partially overlapped and are in a double feeding state, this cannot be detected.

Further, as shown in FIG. 5D, even when two sheets A and B are completely fed in a state of being completely coincident with each other, it may not be determined that the sheet is a double feed. That is, if an ultrasonic wave is applied to a portion where the two sheets A and B overlap each other, it should be possible to make a multifeed determination depending on how the transmittance is relative to the reference value. However, the transmission amount of the ultrasonic wave varies in accordance with the thickness of the sheet, and the transmittance of even one sheet changes at the irradiation position due to the variation in the fiber density of the sheet. Further, when air is confined between the sheets A and B, the attenuation of the ultrasonic wave tends to increase and the transmittance tends to decrease. Under these various conditions, for example, when the thickness of the paper is locally reduced and the fiber density in that part is very low compared to other parts, When A and B are in close contact with each other and the air layer is not interposed, the attenuation when the ultrasonic wave is irradiated remains small. That is, if the portion irradiated with the ultrasonic wave happens to correspond to the condition that the degree of attenuation corresponding to the double feed detection cannot be obtained, the double feed determination cannot be performed.

As described above, in the multifeed determination using the transmittance after the irradiation of the ultrasonic wave as a criterion, when only a part of the sheets overlaps, the ultrasonic wave is irradiated to the non-overlapped portion. And the double feed is overlooked. Also, even if the papers are perfectly matched and overlapping,
Depending on the position where the ultrasonic wave is irradiated, the double feed cannot be determined depending on the conditions such as the thickness of the paper and the fiber density.

The problem to be solved in the present invention is to make it possible to reliably detect and determine the double feed without overlooking the form of the double feed of a sheet material such as paper.

[0011]

SUMMARY OF THE INVENTION The present invention is a method for detecting double feed of a sheet material by transmitting ultrasonic waves from a transmitting means of ultrasonic waves disposed across a line for conveying the sheet material to a receiving means. The output of the ultrasonic wave that has passed through one sheet material received and converted by the receiving means is used as a reference output value, and a critical value for multifeed determination is determined in advance as a value lower than the reference output value. Setting, scanning the sheet material in the conveying direction while repeating the transmission of the ultrasonic wave from the transmitting means, and scanning of the output value lower than the critical value during the scanning of the sheet material by the transmission of the ultrasonic wave. When the number of points exceeds a predetermined value, a double feed is determined.

According to such a detection method, when the number of scanning points whose output value on the receiving side is lower than a predetermined critical value during a scanning period of the sheet material becomes a predetermined number, it is determined that the multi-feed is performed. Even if the sheets A and B partially overlap each other as in (a), if the number of scanning points lower than the critical value exceeds a predetermined number during scanning at the overlapping portion, it is determined that the sheet is multi-feed. You. In addition, even if the sheets A and B completely overlap each other in FIG. 5D, even if the double feed cannot be detected by scanning the portion where the sheets A and B are thin and the fiber density is low, other operations are possible. A double feed can be determined when the number of scanning points lower than the critical value exceeds a predetermined number in several scanning points.

[0013]

According to the first aspect of the present invention, an ultrasonic wave is transmitted from an ultrasonic wave transmitting means disposed across a line for conveying a sheet material to a receiving means to detect double feeding of the sheet material. A method in which the output of the ultrasonic wave that has passed through one sheet material is received and converted by the receiving means is used as a reference output value, and a value lower than the reference output value is used to determine the criticality for multifeed determination. A value is set in advance, and the sheet material is scanned in the conveying direction while repeating the transmission of the ultrasonic wave from the transmitting means, and an output lower than the critical value during the scanning of the sheet material by the transmission of the ultrasonic wave. This is a method for detecting the double feed of a sheet material using ultrasonic waves, which is determined to be a double feed when the number of scanning points of the value exceeds a predetermined value, for example, when the sheet material is thin and the attenuation of the ultrasonic waves cannot be clearly obtained. Even if double feed Such an action can be performed with high accuracy.

According to a second aspect of the present invention, the critical value is:
2. A value range of 40% or less of the reference output value.
This is a method for detecting a double feed of a sheet material using the described ultrasonic wave, and has an effect that the accuracy of the double feed determination can be kept high by appropriately setting the difference between the critical value and the reference output value.

According to a third aspect of the present invention, the transmission of the ultrasonic wave from the transmitting means is executed at a period of at least a range including a peak occurrence time of a direct wave which passes through the sheet material and reaches the receiving means directly. A method for detecting double feed of a sheet material using ultrasonic waves according to claim 1 or 2, wherein the double feed is determined by capturing only a direct wave necessary for determining the double feed of the sheet material.
This has the effect that highly accurate double feed detection of sheet materials can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a detection device used in the double feed detection method of the present invention.

In FIG. 1, a sheet P-
An ultrasonic transmitter 1 and an ultrasonic receiver 2 are arranged with a line to which 1 is supplied interposed therebetween. The ultrasonic transmitter 1 and the ultrasonic receiver 2 are arranged in a positional relationship of transmitting and receiving ultrasonic waves in a direction orthogonal to the line, similarly to the conventional technology, and execute all controls related to double feed detection. Controller 3
It is connected to the.

The controller 3 includes a device for setting the transmission period and transmission time of the ultrasonic wave from the ultrasonic transmitter 1 and for analyzing the output waveform by receiving a signal from the ultrasonic receiver 2. FIG. 2 shows an ultrasonic transmitter 1 and an ultrasonic receiver 2.
FIG. 2 is a block diagram of the device configuration including

In FIG. 2, a control unit (CPU) 3a for controlling the whole is provided, and amplifier units 3b and 3c for signal amplification are connected to the ultrasonic transmitter 1 and the ultrasonic receiver 2, respectively. Have been. DA converters 3d and 3e are provided for controlling the amplification by the amplifiers 3b and 3c to an optimum value.
Is provided with an ultrasonic wave generating circuit 3f for inputting the ultrasonic wave to the input. An AD converter 3g is connected to the output side of the amplifier 3c on the ultrasonic receiver 2 side.

By using such a controller 3, an ultrasonic wave is transmitted from the ultrasonic wave transmitter 1 to the ultrasonic wave receiver 2 based on the input of the signal waveform from the ultrasonic wave generating circuit 3f, and the output at the time of reception is output. AD converter part 3
It is converted by g and input to the control unit 3a. And in this control unit 3a,
The calculation is performed based on the transmission timing and the attenuation of the output waveform, and the calculation result for double feed detection is output.

FIG. 3 shows a state in which another sheet P-2 is being fed under the sheet P-1 with a little delay from the sheet P-1 supplied earlier. It is located between the receiver 2.

In the double feed detection by the ultrasonic transmitter 1 and the ultrasonic receiver 2, the amount of attenuation of the ultrasonic wave when two sheets are in a double feed state is determined in advance at the time of design or factory shipment. A threshold value is set, and a double feed is determined by comparing the threshold value. In the present invention, the transmission of the ultrasonic wave from the ultrasonic transmitter 1 is performed intermittently at a constant cycle, so that the ultrasonic wave transmitted through the sheet P-1 or the two sheets P-1 and P-2 is transmitted. An output waveform that is captured only by sound waves and is not affected by disturbance is obtained by calculation and analysis of the controller 3.

FIG. 4 is a diagram showing the transmission output of the ultrasonic wave from the ultrasonic transmitter 1 and the reception output of the ultrasonic wave received by the ultrasonic receiver 2 on the same time axis.

The ultrasonic wave transmitted from the ultrasonic transmitter 1 is, for example, a rectangular wave output pattern having a frequency of 40 KHz, a period of 4500 microseconds, and a transmission time of 400 microseconds. With the output pattern of the ultrasonic wave from the ultrasonic transmitter 1 at such a time setting, the direct wave W
1 and the reflected wave W2 can be included in the calculation and analysis by the controller 3. Note that the reflected wave W2 is generated in various patterns depending on the positional relationship of members in the measuring device and the like, and includes a so-called standing wave as a part in addition to a pure reflection component.

In this case, in the case of FIG. 4, the ultrasonic wave in which the direct wave W1 passes through the sheet P-1 and is attenuated by an amount corresponding to the resistance is captured by the ultrasonic receiver 2 and output to the arithmetic system. It is an output waveform. Further, the reflected wave W2 is the one in which the reflected component after passing through the sheet P-1 is captured, or the output waveform of the reflected component including the standing wave. In this way, by transmitting the ultrasonic waves from the ultrasonic transmitter 1 as a rectangular wave in relation to the previous time range, the direct wave W1 is divided into the component of the reflected wave W2 that precedes the direct wave W1. It can be output as a waveform.

As described above, the waveform information necessary for the double feeding of the sheet P-1 is the direct wave W1, and the direct wave W1 is first received by the ultrasonic receiver 2 and is calculated and analyzed. Therefore, when the ultrasonic wave is always transmitted from the ultrasonic wave transmitter 1, as described above, the reflected wave W2 including a pure reflection or a standing wave partially with respect to the direct wave W1.
Are inevitably synthesized or interfered with,
The direct wave W
Only one can be reliably taken out as information.

Note that, in FIG. 4, L
Is a criterion value set in advance corresponding to attenuation when an ultrasonic wave passes through one sheet of paper P-1. And, the waveform drawn on the left side in the figure shows, for example, the output waveform of the ultrasonic wave that has passed through one sheet of paper P-1 in the state of FIG. That is, since the output value of the peak of the direct wave W1 of this output waveform exceeds the determination reference value L, it is determined that only attenuation corresponding to the passage of one sheet of paper P-1 has occurred, and that multi-feeding of sheets has occurred. Judge that there is no. The waveform on the right side is, for example, the state shown in FIG. 3, and the amount of attenuation of the ultrasonic wave from the ultrasonic wave transmitter 1 is large due to the overlap of the two sheets P-1 and P-2, and the peak output value is It is less than or equal to the judgment reference value L. Therefore, the calculation system of the output waveform of the controller 3 determines that double feeding of paper has occurred.

As described above, the double feeding of the sheets P-1 and P-2 is determined by comparing the determination reference value L with the output waveform on the receiving side.

However, as described above, when the sheets P-1 and P-2 shown in FIGS. 5A, 5B, and 5C are fed in an overlapping state, the sheet P If the ultrasonic wave passes through the portion where -1 and the sheet P-2 do not overlap, the double feed cannot be determined. If two sheets P-1 and P-2 are completely coincident and overlap as shown in FIG. 5D and enter the path of the ultrasonic wave for double feed detection, the setting is made for one sheet. It is expected that the value will fall below the determined reference value L, but such a phenomenon is not always steady in practice.

That is, in the case where the sheets P-1 and P-2 are thin and a layer of air is hardly contained between the sheets P-1 and P-2, since the thickness of the sheets P-1 and P-2 is small, an ultrasonic wave is generated. The attenuation is small, and since there is no air layer, there is no absorption of ultrasonic waves by air, so that attenuation is not promoted. Since the sheets P-1 and P-2 are a collection of fibrous materials and include a low density portion and a high density portion, the attenuation of the ultrasonic waves passing through the region where the low density portions overlap each other is also low. Become smaller. Therefore, when scanning the overlapping portion of the sheets P-1 and P-2 with ultrasonic waves, the transmitted ultrasonic waves may be input to the receiving side without attenuating even in the double feeding state.

As described above, when the sheets P-1 and P-2 are thin, a phenomenon in which the ultrasonic waves are received without being attenuated easily even in the multi-feed state easily occurs, and the output of the receiving side is output during the entire scanning process. Is not detected as falling uniformly.
If the output from the signal received by the ultrasonic receiver 2 is input to the controller 3 with a high value, it cannot be determined that a double feed has occurred, and this is missed.

Therefore, in the present invention, when scanning for double feed detection by the ultrasonic transmitter 1 and the ultrasonic receiver 2 at the same time as the paper is fed, the transmission state of the ultrasonic waves is checked at a plurality of places. Then, even if the output value output from the receiving side to the controller 3 includes a scanning point exceeding the determination reference value L,
If the number of scanning points having an output lower than a certain critical output value is equal to or greater than a predetermined number, it is determined that the scanning is multifeed.

For example, in the examples shown in FIGS. 1 and 3, if the papers P-1 and P-2 are A4 size paper and the long side direction is the feeding direction, the ultrasonic transmission from the ultrasonic transmitter 1 is performed. Period is 4500 μsec and sending time is 400 μsec
In this case, scanning points can be set at approximately 1 mm intervals. The number of scanning points is about 200 to 250 in consideration of the margins at the leading and trailing edges of the sheets P-1 and P-2.

On the other hand, the reception waves that have passed through the sheets P-1 and P-2 corresponding to the transmission of the ultrasonic waves from the ultrasonic transmitter 1 correspond to the respective scanning points. 3
When the signal is amplified by c and converted by the AD converter unit and input to the control unit 3a for calculation, an output value at each scanning point is obtained as described above. Then, if a predetermined number of scanning points whose output values are lower than a preset critical value are included, it is determined that the sheets P-1 and P-2 are in a multi-feed state. Note that the present inventors require that the number of scanning points lower than the critical value should be about 2% of the entire scanning points so that multi-feed determination can be performed with high accuracy for paper of various sizes. Confirmed by experiment. For example, A4
In the case of a plate-size sheet with 200 scanning points, if it is observed that the number of scanning points is lower than the critical value at four scanning points, it is determined that the sheet is a double feed.

Here, the critical value of the output on the receiving side as a criterion for the double feed determination is a value within a range of 40% or less of the output value on the receiving side at the time of non-multi feed of the sheets P-1 and P-2. I do. That is, since there is no double feeding of the sheets P-1 and P-2, and only one sheet P-1 does not include an air layer, and there is no combination of thin portions in the thickness and double feeding, the ultrasonic wave The attenuation rate of the ultrasonic wave transmitted from the transmitter 1 is substantially uniform. Therefore,
Even when the output value on the receiving side at the time of non-multiple feeding is used as a reference, the value itself does not change much, and the influence of the relative change on the critical value included in the range of 40% or less is small.

In this way, the critical value is determined based on the output of the receiving side when one sheet of paper P-1 is sent,
When a large number of scanning points are taken with respect to -1 and P-2, and an output value lower than the critical value is detected at a predetermined number of scanning points, it can be determined that double feeding has occurred. Therefore, even in the case of thin paper, even if the two sheets are overlapped so as to almost completely coincide, the double feed can be reliably detected.

Further, in the present invention, since the output value of the receiving side is obtained using only the direct wave W1 as information and the critical value is referred to to determine the double feed, the double feed detection with higher accuracy can be performed. You.

[0038]

According to the present invention, the sheet material is scanned by ultrasonic waves in the conveying direction, and when the output value below the critical value exceeds a predetermined number and is obtained on the receiving side, it is determined that the sheet is a double feed. Even if the sheet material is conveyed in a state where a part of the sheet material is overlapped, and even if the sheet material has a variation in the transmittance of the ultrasonic wave depending on the place, the double feed can be reliably detected.

Further, instead of a waveform output including a reflected wave or a reflected wave partially mixed with a standing wave as a disturbance, only a direct wave that passes through the sheet material and directly enters the ultrasonic receiver is captured. In addition, double feed detection with even higher accuracy is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a detection device used in the double feed detection method of the present invention.

FIG. 2 is a schematic block diagram showing an apparatus configuration of a controller including an ultrasonic transmitter and an ultrasonic receiver.

FIG. 3 is a schematic diagram of an example in which two sheets are detected by the detection device of FIG. 1;

FIG. 4 is a diagram showing waveforms of transmitted ultrasonic waves and received waves.

FIG. 5 is a schematic view showing a form of double feeding of sheets.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic transmitter 2 Ultrasonic receiver 3 Controller 3a Control unit 3b, 3c Amplifier part 3d, 3e DA converter 3f Ultrasonic wave generation circuit 3g AD converter part P-1, P-2 Paper (sheet material)

Claims (3)

[Claims] An ultrasonic wave is transmitted from an ultrasonic wave transmitting means disposed on a line for conveying a sheet material to a receiving means to detect double feeding of the sheet material. The output of the received ultrasonic wave received and converted by the receiving means as a reference output value, and presets a critical value for double feed determination as a value lower than the reference output value,
The sheet material is scanned in the transport direction while repeating the transmission of the ultrasonic wave from the transmitting unit, and the number of scanning points having an output value lower than the critical value during the scanning of the sheet material by the transmission of the ultrasonic wave. A multi-feed detection method using ultrasonic waves, wherein the multi-feed is determined when the value exceeds a predetermined value. 2. The method according to claim 1, wherein the critical value is within a range of 40% or less of the reference output value. 3. The transmission of ultrasonic waves from said transmitting means at a period including at least a peak generation time of a direct wave which passes through said sheet material and directly reaches a receiving means. Item 2. A method for detecting double feed of a sheet material using ultrasonic waves according to Item 1 or 2.