JP2015003795A - Sheet overlapped-feeding detection method and sheet overlapped-feeding detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly perform overlapped-feeding determination from a thin sheet to a thick sheet without generating misdetection by a reversal phenomenon between one thick sheet and two thin sheets generated in sheet overlapped-feeding detection using only a peak value or misdetection by influence of exogenous noise.SOLUTION: A sub CPU 180B obtains at least two sample hold values of timing of discharge completion and timing of a peak about an obtained peak detection signal S, the sub CPU 180B obtains a gradient of the peak detection signal Son the basis of the obtained sample hold values, and performs overlapped-feeding determination of a sheet 10 passing a first feeding path by the obtained gradient, and the sub CPU 180B determines that a signal level of the peak detection signal Sobtained by a detection circuit 50 when the sheet 10 passing the first feeding path is in an overlapped-feeding state is reduced, by the gradient of the peak detection signal S, and detects the overlapped-feeding state of the sheet 10.

Description

  The present invention relates to a paper double feed detection method and a paper double feed detection device for detecting double feed of paper using ultrasonic waves.

  Image forming apparatuses such as copiers, printers, facsimiles, and multi-functional machines are provided with a post-processing device such as a staple finisher for performing staple processing on discharged paper, thereby improving work efficiency. Getting to get done. There is also provided an offline type staple finisher for efficiently performing stapling on a sheet printed by a printer in an offline manner.

  In the staple finisher for performing the stapling process on the discharged paper, if there is a double feed, that is, when two or more sheets separated from each other are conveyed while being stacked, waste paper is generated. There is a problem such as requiring labor for removing the paper that has been generated with white paper, and a means for detecting the double feed state is mounted.

  Conventionally, as a double feed detecting means, light from a light emitting LED or the like is received by a light receiving element, and the amount of light is compared with a certain threshold value to determine whether or not there is one sheet of paper. There is known an ultrasonic detection system that uses one sheet or a plurality of sheets to detect whether the sheet is fed.

  In the light detection method, erroneous detection may occur in the case of preprinted paper or colored paper, and in recent years, detection methods using ultrasonic waves have been used.

  In the ultrasonic detection method, for example, the reception-side ultrasonic sensor receives the ultrasonic signal output from the transmission-side ultrasonic sensor, and whether the sheet is fed based on the level (wave height) of the received ultrasonic signal. Detect whether there are multiple sheets. In other words, when the document is not transported in the transport path, when only one document is transported, and when two or more documents are overlapped, that is, when transported in a double feed state The reception amount of the ultrasonic signal received by the side ultrasonic sensor is different, and the reception amount decreases as the number of originals increases. Therefore, if the level of the received ultrasonic signal is higher than the threshold, it is determined that one sheet is fed. If it is lower than the threshold, it is determined that double feeding has occurred (see, for example, Patent Document 1).

  Also, in the ultrasonic detection method, there is a risk of erroneous detection due to reflected waves from the surroundings. Therefore, in order to eliminate the influence of reflected waves, reception is performed at the timing when the intensity of the ultrasonic signal received by the receiving ultrasonic sensor is maximized. It has been proposed to determine the double feed by sampling the signal level of the signal (see, for example, Patent Document 2).

  Furthermore, in the ultrasonic detection method, the output level of the ultrasonic sensor varies depending on the paper thickness to be detected. For example, the sensor output level for transporting one sheet of thick paper and the transport of two sheets of thin paper overlapped. Since the sensor output level is reversed and there is a risk of false detection, set a threshold value that can reliably detect double feed even when there is fluctuations in the ultrasonic sensor output due to variations in the sensitivity and sound pressure of the ultrasonic sensor. Has been proposed (see, for example, Patent Document 3).

JP 05-193786 A JP 07-318335 A JP 2004-269241 A

  However, in the ultrasonic detection type double feed detection means described in Patent Documents 1 to 3, etc., even if environment or external factors (sensor variations, calibration using the basic paper (initial adjustment) is performed, There was a problem that the received ultrasonic wave changes depending on the sheet thickness, elastic force, density, environmental temperature, reflected wave, external noise), and the set absolute value (threshold) may not be the condition. Further, as in Patent Document 2 above, the shaped wave of the received signal is differentiated by a differentiating circuit to determine the timing of the shaped wave peak, and the peak value of the shaped wave is determined by the sample and hold circuit at this peak timing. If the hold is performed, there is a problem that the timing is easily affected by external noise.

  The present invention has been made in view of the above-described conventional situation, and a state where two sheets of thin paper overlapped with one sheet of thick paper that has been generated in the paper double feed detection using only the peak value. A paper double feed detection method capable of reliably determining the double feed from thin paper to thick paper without causing false detection due to the reverse phenomenon of the sensor output level in the case of transporting the paper and the influence of external noise, and An object of the present invention is to provide a paper double feed detection device.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  In the present invention, when detecting paper double feed using ultrasonic waves, the received ultrasonic signal is peak detected, and paper double feed determination is performed based on the slope of the peak detection signal.

  That is, the present invention is a paper double feed detection method, an ultrasonic wave transmission step of transmitting an ultrasonic signal by ultrasonic wave transmission means driven by a burst drive signal of a predetermined frequency, and the ultrasonic wave transmission means and the paper An ultrasonic wave transmitting step of receiving an ultrasonic signal transmitted from the ultrasonic wave transmitting unit by an ultrasonic wave receiving unit disposed at a position facing the conveyance path, and a received signal obtained by the ultrasonic wave receiving unit are Based on the transmission start timing of the burst drive signal, the detection means supplied via the bandpass filter means for extracting a signal component of a predetermined frequency is reset to a discharge state, and then the received signal is peak detected by the detection means. The detection step and the peak detection signal obtained by the detection means are discharged by the sample and hold means. A sample-hold step for obtaining at least two sample-hold values of the timing and peak timing, and a slope of the peak detection signal by the multifeed determining means based on the sample-hold value obtained by the sample-hold means And a double feed determination step for determining double feed of the paper passing through the conveyance path according to the obtained slope, and the signal level of the peak detection signal obtained by the detection means in the double feed state of the paper is reduced. This is characterized in that the double-feed determining means detects the double-feed state of the sheet by determining the slope of the peak detection signal.

  In the paper double feed detection method according to the present invention, in the sample and hold step, for example, a timing between the discharge completion timing and the peak timing is detected for the peak detection signal obtained by the detection means by the sample and hold means. At least three sample and hold values are obtained, and in the multifeed judgment step, the slope of the peak detection signal is obtained in the multifeed judgment means based on the sample and hold value obtained by the sample and hold means. Thus, it is possible to determine whether or not to double-feed a sheet passing through the conveyance path based on the obtained inclination.

  The present invention is also a paper multi-feed detection device, wherein the ultrasonic transmission means is driven by a burst drive signal having a predetermined frequency and transmits an ultrasonic signal, and the ultrasonic transmission means is opposed to the paper with a paper conveyance path interposed therebetween. Ultrasonic wave receiving means disposed at a position where the signal is received, bandpass filter means for extracting a signal component of the predetermined frequency contained in a reception signal obtained by the ultrasonic wave reception means, and a received signal that has passed through the bandpass filter means Based on the detection start means for detecting the peak, the sample and hold means supplied with the peak detection signal obtained by the detection means, and the transmission start timing of the burst drive signal, the detection means is reset to a discharge state, With respect to the peak detection signal obtained by the detection means by the sample and hold means, the discharge completion timing and peak Control means for performing control to obtain sample and hold values at at least two points of timing; and the slope of the peak detection signal is obtained based on the sample and hold value obtained by the sample and hold means; And a double feed judging means for judging the double feed of the paper passing through the paper, and the peak detection in the double feed judging means that the signal level of the peak detection signal obtained by the detection means in the double feed state of the paper is lowered. Judgment is made based on the inclination of the signal, and the double feed state of the paper is detected.

  In the paper double feed detection device according to the present invention, the control means includes, for example, a timing between a discharge completion timing and a peak timing for the peak detection signal obtained by the detection means by the sample and hold means. The control for obtaining at least three sample and hold values is performed, and the multifeed determining means obtains the slope of the peak detection signal based on the sample and hold value obtained by the sample and hold means, It is possible to make a multi-feed determination of a sheet passing through the conveyance path.

  Further, the paper double feed detection device according to the present invention includes, for example, an analog / digital conversion unit that quantizes the signal level of the peak detection signal obtained by the detection unit and converts the signal level into a digital value, and the analog / digital conversion unit. Computation processing means for inputting a digital value indicating the signal level of the peak detection signal is provided. The computation processing means functions as the sample-and-hold means, control means, and double feed determination means, and the analog-digital conversion means A digital value indicating the signal level of the peak detection signal input via the digital signal is fetched at a predetermined timing, the slope of the peak detection signal is obtained, and the double feed determination of the paper passing through the conveyance path is performed based on the obtained slope. It can be.

  In the present invention, when detecting paper double feed by ultrasonic waves, the received ultrasonic signal is peak detected, and paper double feed judgment is performed based on the slope of the peak detection signal. Misdetection due to the reverse phenomenon of the sensor output level when transporting one sheet of thick paper that was generated in the paper double feed detection used and when transporting two sheets of paper overlapped, or error due to the effect of external noise It is possible to reliably determine the double feed from thin paper to thick paper without causing detection.

  In the present invention, even if the absolute value of the maximum amplitude varies due to external factors such as sensor variations, sensor-to-sensor distance, and environmental temperature, the slope of the amount of charge that is not easily affected by external factors stored in the capacitor of the detection means. Since it is used, there is no need for calibration (initial adjustment) because a wider margin can be taken than before for external factors.

It is sectional drawing which shows typically the principal part structure of the staple finisher to which this invention is applied. It is a block diagram which shows the electrical principal part structure of the said staple finisher. FIG. 6 is a waveform diagram illustrating the operation of a double feed detection unit mounted on the staple finisher as a paper double feed detection device according to the present invention, and each signal when a double feed detection process is performed in a state where there is no paper passing through the conveyance path. The waveforms are shown in (A) to (F). It is a wave form diagram which shows operation of the above-mentioned double feed detection part, and shows each signal waveform at the time of performing double feed detection processing in the state where thin paper was passed as a paper which passes a conveyance way to (A)-(F). ing. It is a wave form diagram which shows operation of the above-mentioned double feed detection part, and shows each signal waveform at the time of performing double feed detection processing in the state where a thick paper was passed as a paper which passes a conveyance way to (A)-(F). ing. It is a wave form diagram which shows operation of the above-mentioned double feed detection part, and (A)-(F) each signal waveform at the time of performing double feed detection processing in the state where two sheets of thin paper were passed as a sheet passing through a conveyance path. It shows. It is a figure which shows typically the mode of secondary radiation at the time of irradiating a paper with the ultrasonic signal transmitted from the above-mentioned ultrasonic transmission element, and the case where (A) the case where an ultrasonic signal is irradiated to one sheet of paper FIG. 4B shows a case where an ultrasonic signal is applied to two sheets of paper. It is a wave form diagram which shows the double feed determination signal in the said double feed detection part.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.

  The present invention is applied to a staple finisher 100 configured as shown in FIG. 1, for example.

  The staple finisher 100 is an off-line type staple finisher that performs off-line stapling on the paper 10 printed by the printer. The staple finisher 100 is placed on the paper feed table 110 on which the paper 10 is placed and the paper feed table 110. The fed paper 10 is fed one by one by the paper feed roller 120A, and the fed paper 10 is transported through the first transport path 120 for transporting by the transport rollers 120B and 120C, and the first transport path 120. A staple processing unit 130 that performs stapling on the incoming paper 10, and the stapled paper 10A that has been stapled by the staple processing unit 130 is transported by the transport rollers 140A and 140B, and discharged from the discharge port 150 to the discharge tray 160. Second transport path 154 for discharging upward, the first transport path 1 Multifeed detection unit 170 provided in the 0, comprises a control unit 180 for controlling these operations.

  The staple finisher 100 is equipped with a paper double feed detection device according to the present invention as a double feed detection unit 170.

  Then, as shown in the block diagram of FIG. 2, the configuration of the electrical main parts of the staple finisher 100 is as follows. The control unit 180 controls the operations of the main CPU 180A and the multifeed detection unit 170 for controlling the overall operation of the staple finisher 100. A sub CPU 180B is provided for control.

  When the operation unit 181 and the display unit 182 are connected to the main CPU 180A, and the setting of the binding position and the number of bindings by the operation of the operation unit 181 is accepted, the set binding position and the number of bindings are displayed on the display unit 182. In this state, when a start command is received by operating the operation unit 181, the motor 190 is driven via the motor driver 183, and the sheets 10 placed on the sheet feeding table 110 are fed one by one to the first transport path. When the set number of sheets 10 are conveyed to the staple processing unit 130, the staple processing unit 130 is driven to perform the stapling process, and the stapled paper 10A is transferred. Control that repeats the operation of conveying through the second conveying path 154 and discharging from the discharge port 150 onto the discharge tray 160 is performed. Cormorant.

  The double feed detection unit 170 in the staple finisher 100 is a paper double feed detection device according to the present invention, and an ultrasonic transmission element 20A disposed at a position facing the first conveyance path 120 and an ultrasonic wave. A receiving element 20B is provided.

The ultrasonic wave emitting element 20A is operated by the transmission control signal S _D output from the sub CPU180B is connected to a transmission circuit 70 which is controlled, the output from the transmission circuit 70 in response to the transmission control signal S _D The piezoelectric ultrasonic transducer is driven by a burst drive signal S ₁ having a predetermined frequency (300 kHz in this example) and functions as an ultrasonic transmission means for transmitting the ultrasonic signal S ₂ .

Further, the ultrasonic wave receiving element 20B, the first conveyor line 120 interposed therebetween opposing receiving ultrasonic signals S ₂ transmitted from placed the ultrasonic transmitter element 20A to position the ultrasonic received signal Is composed of a piezoelectric ultrasonic transducer that functions as an ultrasonic receiving means for outputting.

  A band pass filter (BPF) circuit 40 is connected to the ultrasonic receiving element 20 </ b> B via an amplifier circuit 30.

  The ultrasonic reception signal obtained by the ultrasonic reception element 20B is amplified by the amplification circuit 30 and supplied to the BPF circuit 40.

  The BPF circuit 40 functions as a band-pass filter unit that extracts a signal component of the predetermined frequency (300 kHz in this example) included in the ultrasonic reception signal obtained by the ultrasonic reception element 20B.

  An analog / digital (A / D) conversion circuit 60 is connected to the BPF circuit 40 via a detection circuit 50.

In this double-feed detection unit 170, the detection circuit 50, which functions as a detecting means for peak detecting the ultrasonic wave reception signal S ₄ signal passed through the BPF circuit 40, a peak hold detection circuit comprising a diode and a capacitor It is used. The detection circuit 50 is adapted to be a reset and discharge state by a reset signal S _R to be output from the sub CPU180B.

Further, the A / D conversion circuit 60 functions the signal level of the peak detection signal S ₅ obtained by the detection circuit 50 as an analog-to-digital conversion means for converting into a digital value by quantization.

  The A / D conversion circuit 60 is connected to the sub CPU 180B, and inputs a digital value corresponding to the signal level of the peak detection signal to the sub CPU 180B.

  Here, FIG. 3 shows signal waveforms when the double feed detection process is performed in the double feed detection unit 170 in a state where there is no sheet 10 passing through the first transport path 120 (A) to (F). ).

  FIG. 4 shows signal waveforms when the double feed detection unit 170 performs a double feed detection process in a state where a thin paper is passed as the paper 10 passing through the first transport path 120. To (F).

  FIG. 5 shows signal waveforms when the double feed detection unit 170 performs a double feed detection process in a state where a thick paper is passed as the paper 10 passing through the first transport path 120. To (F).

Further, FIG. 6 shows signals when the double feed detection unit 170 performs double feed detection processing in a state where two sheets of thin paper are passed as the paper 10 passing through the first transport path 120. It shows the waveform of the S ₀ to S ₅ in (a) ~ (F).

In this double-feed detection unit 170, the sub CPU180B outputs a transmission control signal _{S 0} as shown in (A) of FIGS. 3 to 6, transmission as shown in (B) of FIGS. 3-6 circuit performs control to output the burst driving signals S ₁ to 70, and outputs the reset signal S _R based on the transmission start timing t ₀ of the burst driving signals S _1, as shown in (C) of FIGS. 3 to 6 Thus, control is performed to reset the detection circuit 50 to a discharge state.

Further, the sub CPU180B includes at least a timing t _A after discharge completion of the peak detection signal S ₅ digital values the peak detection signal S ₅ a corresponding to the signal level of the inputted through the A / D converter circuit 60 _A digital value indicating the signal level LA of the peak detection signal captured at the timing t _C at the two peak points, the timing t _A after completion of the discharge, and the signal of the peak detection signal S ₅ captured at the peak timing t _C obtains the inclination delta _AC said peak detection signal S ₅ represented by the difference between the digital value indicating the sample-and-hold value of the level L _C, multifeed detection of the sheet 10 passing through the first conveyance path 120 by the slope obtained It functions as a double feed judgment means for performing

A sample-and-hold (S / H) signal S ₃ indicating the timing at which the digital value corresponding to the signal level of the peak detection signal input to the sub CPU 180B via the A / D conversion circuit 60 is captured in the sub CPU 180B is obtained. As shown in FIG. 3 to FIG. 6D, in the present embodiment, the sub CPU 180 </ b> _B has the above-described three points including the timing t _A after the completion of the discharge, the peak timing t _C, and the timing t _B therebetween. signal level _L a peak detection signal _{S 5,} L _B, takes in the digital value indicating the sample and hold values of _{L C,} the signal level _L a of the peak detection signal _{S 5} at three points _above, L B, the _{L C} based on the digital value indicating the sample and hold values, the slope of the peak detection signal S ₅ by the least squares method as an example Δ Seeking _BC, by the slope delta _ABC obtained doing multifeed detection of the paper passing through the first conveyance path 120. When obtaining the slope, the method is not limited to the least square method, and can be realized by using other complement methods such as spline complement and Lagrange complement.

That is, the double feed detection unit 170 passes the ultrasonic reception signal amplified by the amplification circuit 30 through the BPF circuit 40, thereby forming a predetermined frequency component (300 kHz in this example). As shown in (F) of FIG. 3 to FIG. 6, which is obtained by obtaining the ultrasonic reception signal S ₄ as shown in (E) and performing peak detection on the ultrasonic reception signal S ₄ in the detection circuit 50. With respect to the peak detection signal S ₅ , the sub CPU 180B determines the signal level L _A , the signal level L _A , of the peak detection signal S ₅ at three points including the timing t _A after the discharge is completed, the timing t _C of the peak, and the timing t _B therebetween. L _B, L _C and functions as a sample-and-hold means for sampling and holding, further, the signal level of the peak detection signal S ₅ at three points above L _a L _B, obtains the slope delta _ABC said peak detection signal by the least squares method based on the digital value indicating the sample and hold values of L _C, the slope delta _ABC obtained the paper passing through the first conveyance path 120 It functions as a double feed judging means for performing double feed judgment.

In a state where there is no sheet 10 passing through the first transport path 120, when the multi-feed detection unit 170 performs the multi-feed detection process, the ultrasonic receiving element 20B sandwiches the first transport path 120. Since the ultrasonic wave transmitted from the ultrasonic wave transmitting element 20A arranged at the opposite position is directly received, the signal level of the obtained ultrasonic wave reception signal sharply rises to the peak value and becomes a high peak value. A peak detection signal S ₅ as shown in FIG. 3F is obtained by the detection circuit 50.

When the multifeed detection unit 170 performs a multifeed detection process in a state where one sheet 10 passes through the first transport path 120, the ultrasonic receiving element 20B transmits from the ultrasonic transmitting element 20A. The ultrasonic wave S ₂ ′ generated as secondary radiation by ultrasonic vibration of the paper 10 is received by irradiating the paper 10 passing through the first conveyance path 120 with the ultrasonic wave to be transmitted. will be the signal level of the peak detection signal S ₅ obtained in the detection circuit 50, the sheet 10 of the vibration easily thin paper, increased to promptly peak value as shown in (F) in FIG. 4, the vibration In the case of thick paper 10 which is difficult to perform, as shown in FIG.

On the other hand, when the double feed detection unit 170 performs the double feed detection process in a state where the two sheets of paper 10 pass through the first conveyance path 120, the air is interposed between the two sheets of paper 10. There is a layer space, and the ultrasonic signal S ₂ ′ generated as the secondary radiation by the vibration of the first sheet 10 makes the power for vibrating the second sheet 10 extremely small, and the ultrasonic receiving element 20B. ultrasound signals received will be reduced to noise level, as shown in (E) of FIG. 5, the peak to peak detection signal S ₅ obtained in the detection circuit 50 does not appear.

That is, when irradiated with ultrasonic signals S ₂ transmitted from the ultrasonic wave emitting element 20A on one sheet 10, as shown in (A) in FIG. 7, the two due to the printed sheet 10 is ultrasonic vibration As the secondary radiation, an ultrasonic signal S ₂ ′ is generated. When the ultrasonic wave transmitted from the ultrasonic transmission element 20A is applied to the two sheets of paper 10, as shown in FIG. The ultrasonic wave S ₁ ′ generated as the secondary radiation due to the vibration of the _first sheet 10 hits the surface of the second sheet 10 and causes reflection and interference at the same time, so that two sheets regardless of the thickness of the sheet 10. The power for vibrating the eye paper 10 becomes extremely small, and secondary radiation does not occur in the second paper 10.

Said the overlap feed detection unit 170, by using a set of tilt delta _ABC threshold peak detection signal S ₅ corresponding to the thickness of the sheet 10 to be determined, determining the slope delta _ABC said peak detection signal S ₅ Therefore, it is possible to detect from the thin paper to the thick paper without causing a false detection due to the reverse phenomenon of one thick paper and two thin papers or the influence of external noise, which has occurred in the conventional paper double feed detection using only the peak value. performed reliably double feed determination to, for example, as shown in FIG. 8, it is possible to obtain a multifeed detection signal S ₆ indicating the multifeed state at a low level.

That is, in the overlap feed detection unit 170, a predetermined frequency (in this example, 300kHz) by ultrasonic wave emitting element 20A that is driven by the burst driving signals S ₁ of (ultrasonic wave transmission unit) transmits ultrasonic waves, the ultrasonic receiving the transmitting element 20A and the ultrasonic signal S ₂ transmitted from the ultrasonic wave emitting element 20A by the first across the conveyance path 120 located in a position opposite to the ultrasonic receiver element 20B (ultrasonic receiving means) The detection circuit 50 (detection means) to which the reception signal obtained by the ultrasonic transmission element 20A is supplied via the BPF circuit 40 (bandpass filter means) for extracting the signal component of the predetermined frequency is supplied to the burst drive signal S. after the reset discharge state based on the _first transmission start timing, the received signal peak detection by the detection circuit 50, the detection For the peak detection signal S ₅ obtained via road 50, the sub CPU180B (sample-and-hold means), to obtain a sample and hold values of at least two points of the timing of the discharge completion of the timing and the peak, the sample-and-hold values obtained based on, the sub CPU180B (multifeed detection means) calculates the slope of the peak detection signal S _5, performs multifeed detection of the sheet 10 passing through the first conveyance path 120 by the slope obtained, the first determining that the signal level of the peak detection signal S ₅ obtained by the detection circuit 50 is lowered by the slope of said peak detection signal S ₅ in the sub CPU180B when the sheet 10 is double feed state which passes through the conveying path 120 Thus, the double feed state of the paper 10 is detected.

  When the sub CPU 180B outputs the result of the double feed determination to the main CPU 180A and determines that the paper 10 passing through the first transport path 120 is in a double feed state, After the main CPU 180A stops the conveyance of the paper 10 by the first conveyance path 120 and controls the display unit 172 to display that it is in the double feeding state, the first conveyance path 120 is reversed. Control is performed so that the sheet 10 on the first conveyance path 120 is returned to the sheet feeding table 110.

  Further, in the multifeed detection unit 170, the characteristics of the ultrasonic transmitting element 20A and the ultrasonic receiving element 20B vary. The ultrasonic reception signal obtained by the ultrasonic receiving element 20B is obtained by external factors such as the distance between sensors and the environmental temperature. Even if the absolute value of the maximum amplitude varies, the double feed judgment is performed using the slope of the amount of charge that is not easily affected by the external factor accumulated in the capacitor of the detection means, so that the external factor can be compared with the conventional method. A wide margin can be taken, and there is no need for individual calibration (initial adjustment).

  In the embodiment of the present invention described above, the present invention is applied to the off-line type staple finisher 100. However, the present invention is mounted on an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these. The present invention can also be applied to a staple finisher, and the stapling function is not an essential component of the invention, and it can be detected by detecting the double feed of paper by applying it to a paper transport device that transports paper one by one. .

  Here, the intensity of the ultrasonic wave propagating in the air is attenuated as the propagation distance becomes longer due to the diffusion loss that diffuses into a spherical shape due to the diffraction phenomenon and the absorption loss that absorbs energy in the medium, and the frequency of the ultrasonic wave increases. The attenuation rate increases and the reach distance decreases.

  At a low frequency of less than 300 kHz, it overlaps the audible region, and not only the resolution cannot be obtained, but also the ultrasonic transducer becomes large.

  In addition, at a high frequency of 300 kHz or higher, the ultrasonic reach is shortened, and an ultrasonic reception signal is supplied in order to perform multifeed determination using the ultrasonic reception signal obtained by the ultrasonic reception element 20B. Therefore, an operational amplifier having a large gain bandwidth product and a large slew rate is required on the circuit side.

  Therefore, although the double feed detection unit 170 uses 300 kHz ultrasonic waves, which are well-balanced frequencies, in the present invention, it is not always necessary to use 300 kHz ultrasonic waves.

  In addition, as shown in FIG. 1, the double feed detection unit 170 is arranged at a position immediately after passing the transport roller 120A, so that when a double feed occurs, the double feed is detected on the upstream side of the paper transport path. Therefore, the user can easily remove the paper. In addition, it is possible to expect an effect of preventing the occurrence of a paper jam due to the paper being transported into the main body of the image forming apparatus in the double fed state.

  10 sheets, 10A sheets, 20A ultrasonic transmission elements, 20B ultrasonic reception elements, 30 amplifier circuits, 40 bandpass filter (BPF) circuits, 50 detection circuits, 60 analog-digital (A / D) conversion circuits, 100 staple finishers, 110 paper feed table, 120A paper feed roller, 120B, 120C transport roller, 120 first transport path, 130 staple processing unit, 140A, 140B transport roller, 150 discharge port, 154 second transport path, 160 discharge tray, 170 Double feed detection unit, 180 control unit, 180A main CPU, 180B sub CPU, 181 operation unit, 182 display unit, 183 motor driver, 190 motor

Claims (5)

An ultrasonic transmission step of transmitting an ultrasonic signal by ultrasonic transmission means driven by a burst drive signal of a predetermined frequency;
An ultrasonic wave transmitting step of receiving an ultrasonic signal transmitted from the ultrasonic wave transmitting unit by an ultrasonic wave receiving unit disposed at a position facing the ultrasonic wave transmitting unit and the paper conveyance path;
The detection means to which the reception signal obtained by the ultrasonic wave reception means is supplied through the band-pass filter means for extracting the signal component of the predetermined frequency is reset based on the transmission start timing of the burst drive signal to be in a discharge state. From the detection step of detecting the peak of the received signal by the detection means,
A sample and hold step for obtaining at least two sample and hold values of discharge completion timing and peak timing by the sample and hold means for the peak detection signal obtained by the detection means,
Based on the sample and hold value obtained by the sample and hold means, the double feed judgment means obtains the slope of the peak detection signal, and uses the obtained slope to judge the double feed of the paper passing through the transport path. A determination step, and
Detecting that the signal level of the peak detection signal obtained by the detection means in the double feed state of the paper has decreased by the slope of the peak detection signal in the double feed determination means, and detecting the double feed state of the paper. Characteristic double feed detection method. In the sample hold step, the sample hold means obtains at least three sample hold values including the timing between the discharge completion timing and the peak timing for the peak detection signal obtained by the detection means,
In the double feed determination step, the double feed determination means obtains the slope of the peak detection signal based on the sample and hold value obtained by the sample and hold means, and the sheet of paper passing through the conveyance path by the obtained slope is obtained. 2. The paper double feed detection method according to claim 1, wherein double feed determination is performed. Ultrasonic transmission means for transmitting an ultrasonic signal driven by a burst drive signal of a predetermined frequency;
Ultrasonic receiving means disposed at a position facing the ultrasonic transmission means across the paper conveyance path;
Bandpass filter means for extracting the signal component of the predetermined frequency contained in the received signal obtained by the ultrasonic wave receiving means;
Detection means for detecting a peak of the received signal that has passed through the bandpass filter means;
Sample and hold means to which a peak detection signal obtained by the detection means is supplied;
Based on the transmission start timing of the burst drive signal, the detection means is reset to a discharge state, and the peak detection signal obtained by the detection means by the sample and hold means Control means for controlling to obtain at least two sample and hold values;
A double feed determining means for determining the slope of the peak detection signal based on the sample and hold value obtained by the sample and hold means, and determining the double feed of the paper passing through the transport path by the determined slope;
Detecting that the signal level of the peak detection signal obtained by the detection means in the double feed state of the paper has decreased by the slope of the peak detection signal in the double feed determination means, and detecting the double feed state of the paper. Characteristic paper double feed detector. The control means controls the sample / hold means to obtain at least three sample / hold values including a timing between a discharge completion timing and a peak timing for the peak detection signal obtained by the detection means. ,
The double feed determination means obtains the slope of the peak detection signal based on the sample hold value obtained by the sample hold means, and performs the double feed judgment of the paper passing through the conveyance path based on the obtained slope. The sheet double feed detection device according to claim 3, wherein: Analog-digital conversion means for quantizing the signal level of the peak detection signal obtained by the detection means and converting it to a digital value;
Computation processing means for inputting a digital value indicating the signal level of the peak detection signal through the analog-digital conversion means,
The arithmetic processing means functions as the sample-and-hold means, control means, and double feed determination means, and outputs a digital value indicating the signal level of the peak detection signal input via the analog-digital conversion means at a predetermined timing. 5. The sheet weight according to claim 3, wherein a slope of the peak detection signal is obtained, and a multi-feed determination of the sheet passing through the conveyance path is performed based on the obtained slope. Feed detection device.