JP3890766B2 - Double feed detection device for sheet material using ultrasonic waves - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a detection method for preventing double feeding of two or more sheets such as sheets in a paper feeding mechanism of an image reading scanner or an automatic document feeder, for example, and in particular an ultrasonic sensor. The present invention relates to a double feed detection method that can detect double feed with high accuracy.
[0002]
[Prior art]
A copying machine and a scanner for reading an image are provided with a paper feeding device 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 feeding so that two or more sheets overlap and are not fed out simultaneously.
[0003]
A typical form of paper double feeding is shown in FIG. (A) in the figure shows a state in which another sheet B covers the rear end of the sheet A when the sheet A is fed in the direction of the arrow, and (b) in FIG. (C) in the figure shows a state where the paper B is almost entirely covered except for the front end side of the paper A, and (d) in the figure shows that the papers A and B are completely coincident with each other. It is in a state of covering.
[0004]
For such double feeding of the papers A and B, a sensor 61 for optically detecting the paper is provided in a portion along the paper conveyance path, and double feeding judgment is made by detecting the passage length of the paper. This is the conventional general detection method. That is, the entire length of the sheets A and B that have passed is detected by the time difference from when the sensor 61 detects the leading edge of the conveyed sheet A to when the trailing edge of the sheet B is detected, and the detected length is set. When the value is larger than the set value, it can be determined as double feeding. For example, in the form of (a), (b), and (c) in the figure, the length from the leading edge of the paper A to the trailing edge of the paper B is longer than the length of one of the papers A and B. Therefore, it is determined as double feeding.
[0005]
This double feed detection using the optical sensor 61 has been widely used in the past, but in the form of (d) in the same figure, the length of the double feed of the papers A and B is 1 of the papers A and B. Since it is the same as the length of the sheet, it is not possible to judge double feeding.
[0006]
From such a background, instead of an optical sensor that detects the length of the paper being conveyed, an ultrasonic sensor is used so that a portion where the paper is actually being fed can be determined as a detection target. It became so. This is to irradiate a square wave ultrasonic wave in a direction orthogonal to the conveyed paper, and to determine the double feed of the paper based on the transmittance of the ultrasonic wave passing through the paper. In other words, since the irradiated ultrasonic wave is attenuated when passing through the paper, it is converted into an output voltage after receiving the ultrasonic signal after passing through the receiving side so that the transmittance is obtained. If it is greater than a certain value, it is determined that there is no double feed, and if it is less than that, it is determined that double feed. Such double feed detection based on the transmittance of ultrasonic waves is used in the field of preventing double feed of paper in printers, copiers and printing machines, as described in, for example, Japanese Utility Model Laid-Open No. 1-156647. It has been adopted.
[0007]
[Problems to be solved by the invention]
However, depending on the timing of irradiating the sheet with ultrasonic waves or the irradiation position on the sheet determined by this timing, it may not be possible to correctly detect the double feeding of the sheet. For example, when a part of the sheets A and B overlap each other as shown in (a), (b), and (c) shown in FIG. The transmittance is detected only by the amount corresponding to the passage of one sheet. Therefore, even though a part of the sheets A and B overlap each other and are in a double feed state, this cannot be detected.
[0008]
Further, as shown in FIG. 5D, even when the two sheets A and B are completely coincident and double fed, it may not be determined as double feeding. That is, if an ultrasonic wave is applied to a portion where the two sheets A and B overlap, it should be possible to determine the double feed according to what the transmittance is with respect to the reference value. However, the amount of ultrasonic transmission varies depending on the thickness of the paper, and the transmittance changes at the irradiation position even for a single paper due to variations in the density of the fibers of the paper. Further, when air is confined between the sheets A and B, the attenuation of the ultrasonic waves increases and the transmittance tends to decrease. Under such various conditions, for example, when the thickness of the paper is locally thin and the density of fibers in that part is very low compared to other parts, or in addition to this condition, the paper When A and B are in close contact with each other and no air layer is interposed between them, the attenuation when ultrasonic waves are applied remains small. That is, if the portion irradiated with the ultrasonic wave corresponds to a condition that does not happen to provide an attenuation suitable for double feed detection, double feed determination cannot be performed.
[0009]
In this way, in the multifeed determination based on the transmittance after the ultrasonic irradiation as the determination criterion, when only a part of the paper is overlapped, the ultrasonic wave is irradiated to the unsuperposed portion, and the double feed is performed. Is overlooked. Even when the sheets are completely coincident with each other and overlapped, it is not possible to discriminate double feeding depending on conditions such as the thickness of the sheet and the fiber density depending on the position where the ultrasonic wave is applied.
[0010]
The problem to be solved by the present invention is to make it possible to make a double feed detection determination reliably without overlooking any form of double feed of a sheet material such as paper.
[0011]
[Means for Solving the Problems]
The sheet material double feed detection device using ultrasonic waves according to the present invention includes an ultrasonic transmission unit that transmits ultrasonic waves, an ultrasonic reception unit that receives ultrasonic waves transmitted by the ultrasonic transmission unit, and a preset setting. Based on the determined determination reference value, ultrasonic waves are transmitted from the ultrasonic transmission unit to a plurality of locations of the conveyed sheet material, and the attenuation amount of the ultrasonic wave received by the ultrasonic reception unit is greater than the determination reference value. And a controller that determines that the sheet material is double-fed when a low number exceeds a predetermined number .
[0012]
In such a detection method, when a predetermined number of scanning points whose output value on the receiving side is lower than a preset critical value during a scanning period of the sheet material is determined to be a double feed, for example, (a Even if a part of the sheets A and B slightly overlap each other as in (), if the number of scanning points lower than the previous critical value exceeds a predetermined number during scanning in the overlapping portion, it is determined to be double feeding. Even if the sheets A and B are completely coincident and overlapped as shown in FIG. 5D, even if the sheets A and B are thin and the fiber density is low, the double feed cannot be detected by scanning. It is possible to make a multi-feed determination when the number of scanning points lower than the critical value exceeds a predetermined number at several scanning points.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The invention according to claim 1 is based on an ultrasonic wave transmission unit that transmits ultrasonic waves, an ultrasonic wave reception unit that receives ultrasonic waves transmitted by the ultrasonic wave transmission unit, and a predetermined criterion value. When ultrasonic waves are transmitted from the ultrasonic wave transmission unit to a plurality of locations of the conveyed sheet material, and the number of ultrasonic attenuations received by the ultrasonic wave reception unit is lower than the determination reference value exceeds a predetermined number And a controller for determining that the sheet material is being multi-fed, and a multi-feed detection device using ultrasonic waves. For example, the sheet material is thin and the ultrasonic wave is attenuated. Even when the degree cannot be clearly obtained, the multifeed judgment can be executed with high accuracy .
[0014]
The invention according to claim 2 is the sheet material double feed detection method using ultrasonic waves according to claim 1, wherein the critical value is in a range of 40% or less of the reference output value. By appropriately setting the difference between the reference output value and the reference output value, it is possible to maintain a high accuracy of double feed determination.
[0015]
According to a third aspect of the present invention, the transmission of ultrasonic waves from the transmission means is executed in a cycle including a peak generation time of a direct wave that passes through the sheet material and reaches the reception means immediately. This is a sheet material double feed detection method using ultrasonic waves described in 1 or 2, and only the direct wave necessary for sheet material double feed judgment is captured to determine double feed, so highly accurate sheet material double feed detection. Is obtained.
[0016]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view of a detection apparatus used in the double feed detection method of the present invention.
[0017]
In FIG. 1, an ultrasonic transmitter 1 and an ultrasonic receiver 2 are arranged across a line to which a sheet P-1 as a sheet material is supplied. The ultrasonic transmitter 1 and the ultrasonic receiver 2 are arranged as a positional relationship for transmitting and receiving ultrasonic waves in a direction orthogonal to the line as in the conventional technique, and execute all the control related to double feed detection. It is connected to the controller 3.
[0018]
The controller 3 is provided with a device for analyzing the output waveform upon receiving the signal from the ultrasonic receiver 2 and the setting of the ultrasonic transmission period and transmission time of the ultrasonic transmitter 1. 1 shows a block diagram of the apparatus configuration including the ultrasonic transmitter 1 and the ultrasonic receiver 2.
[0019]
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. . In addition, DA converters 3d and 3e for controlling the amplification degree of these amplifier units 3b and 3c to an optimum value are provided, and an ultrasonic wave generation circuit 3f for inputting a 40 KHz signal waveform to the amplifier unit 3b is provided. An AD converter unit 3g is connected to the output side of the amplifier unit 3c on the ultrasonic receiver 2 side.
[0020]
By using such a controller 3, an ultrasonic wave is transmitted from the ultrasonic transmitter 1 to the ultrasonic receiver 2 side based on the input of the signal waveform from the ultrasonic wave generation circuit 3f, and the output waveform is attenuated at the time of reception. Is converted by the AD converter unit 3g and input to the control unit 3a. The control unit 3a calculates based on transmission timing and output waveform attenuation and outputs a calculation result for double feed detection.
[0021]
FIG. 3 shows a state in which another sheet P-2 is fed with a slight delay behind the sheet P-1 supplied in advance, and the superposition portion is an ultrasonic transmitter 1 and an ultrasonic receiver 2. Is located between.
[0022]
In the double feed detection by the ultrasonic transmitter 1 and the ultrasonic receiver 2, a threshold value is set in advance at the time of design or factory shipment for the magnitude of ultrasonic attenuation when two sheets are in a double feed state. In addition, the multifeed judgment is made by comparison with this threshold value. In the present invention, the transmission of the ultrasonic wave from the ultrasonic transmitter 1 is intermittent transmission with a constant period, so that the ultrasonic wave that has passed through the paper P-1 or the two papers P-1 and P-2. An output waveform that is captured only by the sound wave and is not affected by disturbance is obtained by calculation analysis of the controller 3.
[0023]
FIG. 4 is a diagram showing the transmission output of ultrasonic waves from the ultrasonic transmitter 1 and the reception output of ultrasonic waves received by the ultrasonic receiver 2 on the same time axis.
[0024]
The ultrasonic wave sent from the ultrasonic transmitter 1 is a rectangular wave output pattern having a frequency of, for example, 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 having such a time setting, the controller 3 can perform calculation analysis by including the direct wave W1 and the reflected wave W2 in one cycle. The reflected wave W2 is generated in various patterns depending on the positional relationship of the members in the measuring apparatus, and includes a so-called standing wave in addition to a pure reflection component.
[0025]
Here, in the case of FIG. 4, the direct wave W1 is an output waveform that the ultrasonic wave that passes through the paper P-1 and is attenuated by an amount corresponding to the resistance is captured by the ultrasonic receiver 2 and output to the calculation system. is there. The reflected wave W2 is an output waveform of a reflected component including a standing wave or a reflected component after passing through the paper P-1. In this way, by transmitting the ultrasonic wave from the ultrasonic transmitter 1 as a rectangular wave in relation to the previous time range, the direct wave W1 precedes and is divided into the components of the reflected wave W2 that follows it. It can be output as a waveform.
[0026]
As described above, the waveform information necessary for the double feeding of the paper P-1 is the direct wave W1, and this direct wave W1 is first received by the ultrasonic receiver 2 and analyzed. Therefore, when the ultrasonic wave is always transmitted from the ultrasonic wave transmitter 1, the reflected wave W2 including a pure reflection or standing wave as a part thereof is synthesized with respect to the direct wave W1 as described above. Although interference is unavoidable, only the direct wave W1 can be reliably extracted as information by using the rectangular wave transmission as in the present invention.
[0027]
In FIG. 4, L attached to the axis of the received wave is a determination reference value set in advance corresponding to the attenuation when the ultrasonic wave passes through one sheet P-1. The waveform drawn on the left side in the figure shows the output waveform of the ultrasonic wave that has passed through one sheet of paper P-1 in the state of FIG. 1, for example. That is, since the output value of the peak of the direct wave W1 of the output waveform exceeds the determination reference value L, it is assumed that only attenuation corresponding to the passage of one sheet of paper P-1 has occurred, and double feeding of sheets has occurred. Judge that there is no. Further, the waveform on the right side is, for example, the state shown in FIG. 3, and the attenuation amount of the ultrasonic wave from the ultrasonic 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 below the reference value L. Therefore, the calculation system of the output waveform of the controller 3 determines that paper double feeding has occurred.
[0028]
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.
[0029]
However, as described above, when the paper P-1 and P-2 shown in FIGS. 5A, 5B and 5C are partially overlapped and sent, If the ultrasonic wave passes through a portion where the paper P-2 is not overlapped, the double feed determination cannot be made. If the two sheets P-1 and P-2 are completely coincident and overlap each other as shown in FIG. 5D and enter the ultrasonic path for double feed detection, the setting is made for one sheet. However, in reality, such a phenomenon cannot be said to be steady.
[0030]
That is, in the case where the sheets P-1 and P-2 are thin and there is almost no air layer between them, the thickness of the sheets P-1 and P-2 is thin. 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 fibers and have a low density portion and a high density portion, the attenuation of ultrasonic waves that pass through the region where the low density portions overlap each other is also obtained. Get smaller. Therefore, when the overlapping portion of the sheets P-1 and P-2 is scanned with ultrasonic waves, the transmitted ultrasonic waves may be input to the receiving side without being attenuated even in the double feed state.
[0031]
As described above, when the sheets P-1 and P-2 are thin, the phenomenon that the ultrasonic waves are received without being attenuated easily occurs even in the double feed state, and the output on the receiving side is uniform throughout the entire scanning process. Is not detected as falling to 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 double feed is occurring, and this is overlooked.
[0032]
Therefore, in the present invention, when scanning of double feed detection by the ultrasonic transmitter 1 and the ultrasonic receiver 2 is performed simultaneously with the feeding of paper, the transmission state of ultrasonic waves is examined at a plurality of locations. Even when the output value output from the receiving side to the controller 3 includes a scanning point that exceeds the determination reference value L, the number of scanning points that are lower than a certain critical output value is greater than or equal to a predetermined number. It is determined as double feed.
[0033]
For example, in the example of FIGS. 1 and 3, if the paper P-1 and P-2 are A4 size and the long side direction is the feeding direction, the period of ultrasonic transmission from the ultrasonic transmitter 1 is 4500 μsec. When the sending time is 400 μsec, scanning points can be set at intervals of about 1 mm. In consideration of the margin sizes of the leading and trailing edges of the sheets P-1 and P-2, the number of scanning points is about 200 to 250.
[0034]
On the other hand, since the received 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, the output of the received waves is amplified by the amplifier unit 3c. At the same time, when converted by the AD converter unit and input to the control unit 3a, the output value at each scanning point is obtained as described above. 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 the double feed state. Note that the present inventors only need to have the number of scanning points lower than the critical value is about 2% of the total scanning points so that the multi-feed determination can be performed with high accuracy for various sizes of paper. Confirmed by experiment. For example, in the case of A4 size paper and the number of scanning points is 200, if it is observed that the number of scanning points is lower than the critical value at four scanning points, it is determined to be double feeding.
[0035]
Here, the critical value of the output on the receiving side, which is a criterion for determining the multifeed, is a value in a range of 40% or less of the output value on the receiving side when the sheets P-1 and P-2 are not multifed. That is, 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 since there is no synthesis of thin portions when the thickness is double fed, the ultrasonic wave The attenuation rate of the ultrasonic wave transmitted from the transmitter 1 is substantially uniform. Therefore, even if the output value on the receiving side at the time of non-multifeed is used as a reference, the value itself does not vary so much, and the critical value included in the range of 40% or less is less affected by relative variation.
[0036]
In this way, the critical value is determined based on the output on the receiving side when one sheet P-1 is sent, and a large number of scanning points are taken for the sheets P-1 and P-2, and the critical value is obtained. When a lower output value is detected at a predetermined number of scanning points, it can be determined that double feeding. Therefore, even if the sheets are thin and overlap each other so that the two sheets are almost completely coincident with each other, it is possible to reliably detect double feeding.
[0037]
Further, in the present invention, since the output value on the receiving side is obtained using only the direct wave W1 as information, and the double feed is determined with reference to the critical value, the double feed detection with higher accuracy can be performed.
[0038]
【The invention's effect】
In the present invention, when the sheet material is scanned with ultrasonic waves in the conveying direction and an output value below the critical value exceeds the predetermined number and is obtained on the receiving side, it is determined as double feeding, so a part of the two sheet materials. Even when the sheets are conveyed in an overlapping state, or even when the sheet material has a variation in the transmittance of ultrasonic waves depending on the location, it is possible to reliably detect double feeding.
[0039]
Further, instead of using 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. High precision double feed detection 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 the configuration of a controller including an ultrasonic transmitter and an ultrasonic receiver. Schematic diagram of an example in which two sheets of paper are detected by the detection device of FIG. 4 is a diagram showing waveforms of transmitted ultrasonic waves and received waves. FIG. 5 is a schematic diagram showing a form of double feeding of paper.
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)

An ultrasonic transmitter that transmits ultrasonic waves;
An ultrasonic receiver that receives the ultrasonic waves transmitted by the ultrasonic transmitter; and
Based on a preset criterion value, ultrasonic waves are transmitted from the ultrasonic wave transmitter to a plurality of locations of the conveyed sheet material, and the ultrasonic attenuation received by the ultrasonic wave receiver is the criterion value. if less than locations exceeds a predetermined number, double feed detection device of the sheet material which utilizes ultrasonic waves, characterized in that a and determining controller the sheet material is double feeding. The multi-feed detection apparatus for sheet material using ultrasonic waves according to claim 1 , wherein the determination reference value is in a range of 40% or less of the attenuation amount . The transmission of ultrasonic waves from the ultrasonic transmission unit is executed at a cycle including a peak generation time of a direct wave that reaches at least the ultrasonic reception unit immediately after passing through the sheet material. Item 3. A sheet material double feed detection device using the ultrasonic wave according to Item 1 or 2.

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