JP2000025986A - Double feed detection method for sheet material using ultrasonic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect any double feed of sheet materials continuously precisely, independently of changes in characteristics of an ultrasonic transmitter and an ultrasonic receiver as well as of errors in assembly among others. SOLUTION: Prior to double sheet feed detection where an ultrasonic transmitter 1 sends ultrasonic waves to an ultrasonic receiver 2 and the output waveform of the ultrasonic waves attenuated through the passage through paper sheets P-1 and P-2 is compared with a preset reference value, the ultrasonic transmitter 1 sends ultrasonic pulses to the ultrasonic receiver 2, which receives them and outputs corresponding signals whose maximum output times are detected as sampling times. During double sheet feed detection after this sampling time detection, the ultrasonic transmitter 1 sends ultrasonic signals having the same output form as the ultrasonic pulses to the ultrasonic receiver 2, which receives them and outputs corresponding signals that may be sampled at the sampling times as a double feed detection signal.

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.

[0003] As a mechanism for detecting the double feeding of paper, a mechanism utilizing ultrasonic waves has recently become widespread in various fields. One example of the use of ultrasonic waves is disclosed in, for example,
There is one described in Japanese Patent Application Laid-Open No. 9952, and its outline is shown in FIG.

[0004] The double feed detecting device described in this publication is intended for detecting bills, and as shown in FIG.
An ultrasonic transmitter 53 and an ultrasonic receiver 54 are arranged with the transfer lines 1 and 52 interposed therebetween, and a waveform analyzer 55 to which an output signal of the ultrasonic receiver 54 is input is provided.

The ultrasonic wave transmitted from the ultrasonic transmitter 53 passes through the bill 51 and is received by the ultrasonic receiver 54 as an ultrasonic signal. Then, the voltage is input to the waveform analyzer 55 as an output voltage, and is analyzed as an output signal as shown in FIG. Since the ultrasonic waves from the ultrasonic transmitter 53 are attenuated when passing through the banknote 51 and received by the ultrasonic receiver 54, the ultrasonic waves are received on the basis of the output voltage in the range A of one banknote 51. In FIG. 6B, the range of A is set as a reference output signal. When the area B where the banknotes 52 overlap passes, the amount of attenuation of the ultrasonic wave increases. Therefore, the output signal is analyzed as an output signal in the range B in FIG. Therefore, by detecting the difference between the reference output signal and the attenuated output signal, the bill 51,
52 can be detected.

[0006] Such detection of double feed of paper by ultrasonic waves is similarly employed 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. 1-115647. ing.

[0007] The detection of double feed of a sheet using ultrasonic waves is set anew based on the reception intensity when one sheet passes, and the reception intensity of the actually detected signal is set to this reference value. Basically, it is determined to be a double feed when it is lower than the above.

[0008]

When the ultrasonic signal from the ultrasonic transmitter 53 is received by the ultrasonic receiver 54, for example, as shown in FIG. A signal is obtained. In this case, when there is no detection target, a stable output waveform is obtained because the ultrasonic signal from the ultrasonic transmitter 53 is received as a direct wave without being attenuated and there is no generation of a reflected wave. Can be

On the other hand, when the ultrasonic receiver 54 receives a rectangular wave, that is, a pulsed ultrasonic wave from the ultrasonic transmitter 53, the output waveform strictly takes the form shown in FIG. That is, when a very short pulse (for example, 400 μsec) rectangular wave is transmitted from the ultrasonic transmitter 53 at time t0, it takes time for the output of the transmission to rise. The rising of the waveform output starts later than t0. That is, the output waveform synchronized with the transmission of the rectangular wave cannot be obtained from its response characteristics, resulting in a response delay, and as shown in FIG. It includes a steady waveform WS having a change rate of substantially zero and an attenuation waveform WD having a temporal change rate of the output value reduced.

FIG. 7 shows a response characteristic waveform obtained by integrating the output value from the ultrasonic receiver 54, which is obtained as the largest output value from the actual output waveform. It is included in the stationary waveform WS. This peak value appears at time t1 after a delay of time Δt from time t0. Therefore, in order to convert the rectangular wave from the ultrasonic transmitter 53 into the output value on the receiving side with the highest efficiency, the output in the time range at or near the time t1 is sampled and calculated by the calculation system. Accuracy can be increased.

However, the ultrasonic transmitter 53 and the ultrasonic receiver 54 are both ultra-precision devices, and rigorous inspection is performed during their manufacture. However, the characteristics of transmission and reception are slightly different depending on the product. It is inevitable that they are different. Also, since the ultrasonic transmitter 53 and the ultrasonic receiver 54 are assemblies that are fixed to predetermined positions of the apparatus by mechanical means such as screws, the distance between the two and the respective postures are delicate due to assembly errors. Changes to

As described above, when there are errors in the characteristics of the ultrasonic transmitters 53 and the ultrasonic transmitters 54 and the errors in the assembly, the time t1 at which the output value peaks as shown in FIG. 7 also varies. Therefore, if the sampling timing of the output wave from the ultrasonic receiver 54 is fixed at the time t1 with respect to the transmission start time t0 from the ultrasonic transmitter 53, the peak value cannot be captured depending on the condition. , The accuracy of double feed detection is reduced.

[0013] In addition to the influence of the transmission / reception characteristics and the assembly, even under the use condition in which the temperature atmosphere fluctuates considerably lower or higher than the normal temperature, the propagation speed of the transmitted ultrasonic wave changes. A similar situation occurs.

The problem to be solved in the present invention is that a multi-feed detection of a sheet material can always be obtained with high accuracy without being affected by changes in the characteristics of an ultrasonic transmitter and an ultrasonic receiver and errors in assembly. Is to be able to

[0015]

SUMMARY OF THE INVENTION According to the present invention, an ultrasonic wave is transmitted from a transmitting means for ultrasonic waves disposed on a line for conveying a sheet material to a receiving means, and the ultrasonic wave after passing through the sheet material is attenuated. A method for detecting a double feed of a sheet material by comparing an output waveform of a sound wave with a set reference value, and transmitting an ultrasonic pulse from the transmitting unit and receiving the ultrasonic pulse prior to the double feed detection. Test-derived the time at which the maximum value of the output signal is output from the receiving means as the sampling time,
In the double feed detection period after the test derivation of the sampling time, an ultrasonic signal is transmitted from the transmitting unit as the same output form as the ultrasonic pulse, and the output signal from the receiving unit at the sampling time is a double feed detection signal. And performs sampling.

In such a detection method, the time when the maximum value of the output signal on the receiving side is output at the stage before the double feed detection, for example, when the apparatus is started or when the conveyance of the sheet material is detected. Can be preliminarily obtained by a test as a sampling time, so that the output value at the sampling time can be input to the arithmetic system when the double feed is actually detected, and the double feed can be detected with high accuracy.

[0017]

According to the first aspect of the present invention, an ultrasonic wave is transmitted from an ultrasonic wave transmitting unit disposed across a line for conveying a sheet material to a receiving unit, and the ultrasonic wave passes through the sheet material and is attenuated. A method for detecting a double feed of a sheet material by comparing an output waveform of a subsequent ultrasonic wave with a set reference value, and transmitting an ultrasonic pulse from the transmitting unit prior to the double feed detection, wherein the ultrasonic pulse The time at which the maximum value of the output signal is output from the receiving means that has received the test is derived as a sampling time, and during the double feed detection period after the test of the sampling time is derived, the transmission is performed as the same output form as the ultrasonic pulse. Means for transmitting an ultrasonic signal from the means and performing sampling using an output signal from the receiving means at the sampling time as a double-feed detection signal, the method for detecting double feed of a sheet material using ultrasonic waves There, since specifying the time at which the maximum value of the output signal at the receiver side is outputted in advance as a sampling time, it is possible to actually accurate double feed detection by applying the sampling time in the double feed detection.

According to a second aspect of the present invention, the transmission of the ultrasonic pulse from the transmitting means is performed at a period of a range including a peak generation time of a direct wave which at least passes through the sheet material and reaches the receiving means directly. 2. A method for detecting double feed of a sheet material using ultrasonic waves according to claim 1, wherein only the direct wave necessary for determining the double feed of the sheet material can be captured and compared with a set reference value. By combining the maximum output value with sampling, there is an effect that double feed can be detected with higher accuracy.

According to a third aspect of the present invention, the period of the transmission of the ultrasonic pulse includes a lapse of time until the convergence of a series of reflected waves including a reflected wave or a standing wave following the direct wave. 3. A method for detecting a double feed of a sheet material using ultrasonic waves according to claim 1 or 2, wherein the method has an effect that an output waveform by a direct wave can be compared with a set reference value every period of an ultrasonic pulse. .

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 is provided with 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 amplifiers 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 section 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 generation circuit 3f, and the output at the time of reception is output. AD converter 3g with waveform attenuation
And is input to the control unit 3a. Then, the control unit 3a calculates based on the transmission timing and the attenuation of the output waveform and outputs a calculation result for double feed detection.

FIG. 3 shows a state in which another sheet P-2 is being fed under the sheet P-1 supplied a little later than the previously supplied sheet P-1. It is located between the receiver 2.

The double feed detection by the ultrasonic transmitter 1 and the ultrasonic receiver 2 is based on the ultrasonic transmitter 1 for one sheet P-1.
Based on the output waveform corresponding to the amount of the ultrasonic wave from the paper P-1 being attenuated by the sheet P-1, when the output waveform does not reach this standard, it is determined that the ultrasonic wave has a large attenuation and double feed has occurred. This is the same as in the prior art.

In the present invention, first, the ultrasonic transmitter 1
When the ultrasonic signal is received by the ultrasonic receiver 2, the time at which the output value reaches a peak is verified. That is, when a rectangular wave is output from the transmitting side and the reception output waveform and output value when the ultrasonic signal is directly input to the receiving side are as described in FIG. 7, the peak value of the output of the receiving side Is a sampling value to the arithmetic system, the accuracy of double feed detection is improved. Therefore, in the present invention, the ultrasonic transmitter 1 and the ultrasonic receiver 2 are operated, for example, each time the power is turned on to the apparatus before use or by using a signal from a sensor for detecting the conveyance of the sheet. The time when the output value on the receiving side reaches the peak value is derived in advance by a test operation. If only the time at which this peak value occurs is specified, multifeeding can be detected with high accuracy with respect to the feeding of the paper after the start, and the characteristics and characteristics of the ultrasonic transmitter 1 and the ultrasonic receiver 2 can be detected. Double feed detection in which errors in the respective assembly surfaces are corrected becomes possible.

FIG. 4 is a diagram for explaining such a test at the time of starting. When a rectangular wave is transmitted from the ultrasonic transmitter 1 at time T1, the output waveform received by the ultrasonic receiver 2 is changed. The peak of the output value is detected by the arithmetic system of the control unit 3a, and the time T2 when this peak value is detected is derived. As a result, the maximum value of the output value of the ultrasonic wave transmitted from the ultrasonic transmitter 1 at the time when the time T2 elapses from the transmission time can be input to the arithmetic system of the controller 3 as the sampling value.

After the derivation of the time T2, the same operation is repeated several times. That is, as shown in the figure, an ultrasonic wave is transmitted from the ultrasonic transmitter 1 at the time T3, and the occurrence time T4 of the peak value on the receiving side is obtained by the test. Then, based on the actual measurement values obtained by repeating such a test operation, a simple average value of the occurrence time of the peak value on the receiving side or a correction coefficient empirically obtained by several actual measurements is calculated based on the simple average value. The optimum time is determined by an operation such as multiplying by a value.

The determination of the optimum time is possible by incorporating the operation system into the controller 3, and the determined optimum time is applied to all the series of operations until the power is turned off or the paper detection is stopped. Then, the control unit 3a controls the ultrasonic wave generating circuit 3f. That is, if the ultrasonic generation circuit 3f is provided with functions such as time control of the transmission of the ultrasonic wave and setting of the wavelength, the input of the signal of the determined optimal time from the control unit 3a allows the signal at the optimal time. Output value sampling can be continued.

As described above, the optimum time at which the output value obtained on the receiving side becomes maximum before the sheet feeding operation is verified in advance, so that the ultrasonic transmitter 1 and the ultrasonic receiver 2 are verified.
Characteristics, inappropriate matching of each other, errors in the assembly surface, and fluctuations in ambient temperature are prevented from lowering the accuracy. In other words, the unsuitability of these characteristics and fluctuations in the ambient temperature are factors that affect the specific detection accuracy of the detection device.However, such factors are entangled with each other, regardless of this. It is possible to set a time at which the maximum value of the output value is sampled. Therefore, even if there are unpredictable factors such as temperature fluctuations,
Since the sampling operation of the maximum output value is continuously performed, double feed detection with high accuracy can be always performed.

In the present invention, the ultrasonic transmitter 1
The transmission of the ultrasonic wave from the P1 or the two sheets P-1 and P
An output waveform that is not affected by disturbance by capturing only the ultrasonic wave that has passed through -2 is obtained by computational analysis of the controller 3.

That is, in the method of continuously transmitting ultrasonic waves and detecting double feeds as in the prior art shown in FIG. Are likely to be combined and a signal larger than the actual direct wave is input. In this case, even when double feed occurs, a phenomenon occurs in which the output becomes higher than the set reference value, so that it is determined that there is no double feed, and the double feed is missed. Therefore, there is a problem that proper double feed detection cannot be performed particularly under a condition in which reflected waves including reflected waves or standing waves are likely to be mixed.

Therefore, in the present invention, the transmission from the ultrasonic transmitter 1 is performed with a pulse having a constant period so that a direct wave which is not affected by disturbance due to such a reflected wave or a reflected wave including a standing wave is obtained. And Then, with respect to the direct wave obtained on the receiving side, the optimum time at which the output value shown in FIG. 4 becomes the maximum value is tested in advance, and the output value at the determined optimum time is sampled and operated to perform double feed. Input to an arithmetic system for non-multifeed evaluation. By such an operation, the detection accuracy is improved by first targeting a direct wave that is not affected by disturbance, and at the same time, the maximum value of the output on the receiving side can be sampled, so that the detection accuracy can be further improved.

FIG. 5 is a diagram showing the transmission output of the ultrasonic wave from the ultrasonic transmitter 2 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 2 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 2 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.

Here, in the case of FIG. 1, the direct wave W1 passes through the sheet P-1, and the ultrasonic wave attenuated by an amount corresponding to the resistance is captured by the ultrasonic receiver 2 and output to the arithmetic system. Signal. The reflected wave W2 is an output waveform of a reflected component after passing through the sheet P-1 or a reflected component including a standing wave. As described above, by transmitting the ultrasonic wave from the ultrasonic transmitter 1 as a rectangular wave pulse in relation to the time domain, the direct wave W1 precedes and is divided into the reflected wave W2 component that follows. Can be output as

As described above, the waveform information required for the double feeding of the paper P is the direct wave W1, and this direct wave W1 is input as an output signal to the arithmetic system of the controller 3 and is analyzed. Therefore, when the ultrasonic wave is always transmitted from the ultrasonic wave transmitter 1, as described above, the direct wave W1
Reflected wave W partially including a pure reflected or standing wave with respect to
Although it is inevitable that the two are combined or interfere with each other, the direct wave W1 alone can be reliably extracted as information of the output signal by transmitting the rectangular wave as in the present invention.

It is to be noted that L shown in FIG.
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, since only the direct wave W1 is used as information and the reception intensity is compared with the set reference value to determine the double feed, the double feed can be detected with much higher accuracy than the conventional technique. Becomes Then, before the operation, the optimum time for sampling is preliminarily verified according to the procedure described with reference to FIG. 4, so that the characteristics of the ultrasonic transmitter 1 and the ultrasonic receiver 2, the unsuitability in terms of assembly, the temperature atmosphere, etc. Irrespective of the above, high-precision double feed detection is always maintained.

[0041]

According to the present invention, before the sheet material is conveyed, an ultrasonic pulse is transmitted from the transmitting means to the receiving means, and the time at which the maximum output value is obtained on the receiving side is verified and derived in advance. Since the sampling time is set, if the same conditions as those of the ultrasonic pulse at the time of the test are transmitted, it is possible to always input to the arithmetic system based on the output signal with high amplification. Therefore, even if the characteristics and matching of the transmitting and receiving means are inadequate, high-precision double-feed detection can be maintained, and the reliable weight is not affected by the assembly of the apparatus or the temperature and atmosphere. Transmission detection becomes possible.

Further, by capturing only a direct wave that passes through the sheet material and entering the ultrasonic receiver at a later time, and synthesizing a method of comparing the output waveform with a reference value, the accuracy of the polymerization detection is further improved. be able to.

[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 for explaining a test of a generation time of a maximum output value on a receiving side by transmitting a rectangular wave from an ultrasonic transmitter.

FIG. 5 is an output waveform on the receiving side with respect to a transmitted ultrasonic wave when passing through a sheet, and is a waveform diagram showing a pattern of a direct wave and a reflected wave and a decrease in output during double feeding.

FIG. 6 is a schematic diagram showing a conventional technique.

FIG. 7 is a diagram showing a reception output waveform and a response delay of an output value when a rectangular wave is transmitted from an ultrasonic transmitter to an ultrasonic receiver.

[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 P-1, P-2 Paper (sheet material)

Claims (3)

[Claims] 1. An ultrasonic wave is transmitted from a transmitting means of ultrasonic waves arranged across a line for conveying a sheet material to a receiving means,
A method of detecting the double feed of the sheet material by comparing the output waveform of the ultrasonic wave after attenuation through the sheet material with a set reference value, wherein, prior to the double feed detection, an ultrasonic pulse from the transmitting unit. And the time at which the maximum value of the output signal is output from the receiving unit that has received the ultrasonic pulse is derived as a test time as a sampling time. A sheet material using ultrasonic waves, wherein an ultrasonic signal is transmitted from the transmitting means as the same output form as a pulse, and sampling is performed using an output signal from the receiving means at the sampling time as a double feed detection signal. Double feed detection method. 2. The method according to claim 1, wherein the transmission of the ultrasonic pulse from the transmitting unit is performed at a period including at least a peak generation time of a direct wave that passes through the sheet material and reaches the receiving unit directly. A method for detecting double feed of a sheet material using ultrasonic waves according to claim 1. 3. A transmission cycle of said ultrasonic pulse is set to a length including a lapse of time until convergence of a series of reflected waves including a reflected wave or a standing wave following said direct wave. The method for detecting double feed of a sheet material using ultrasonic waves according to claim 1 or 2.