JP4315062B2 - Paper feeder - Google Patents

Description

  The present invention relates to a paper feeding device having a double feed detecting means for detecting double feed of paper using an ultrasonic sensor.

  2. Description of the Related Art Conventionally, in a paper feeding device such as a copying machine or a multifunction machine, an optical type is generally used as a paper double feed detection method. In recent years, an ultrasonic method has been adopted as a new method in facsimiles and scanners.

  For example, in order to improve the detection accuracy of an ultrasonic double feed detection means, a double feed detection means that can perform stable double feed detection with a small change in the intensity of an ultrasonic reception signal has been proposed. (For example, refer to Patent Document 1).

  In this case, the moving surface of the detection target is inclined with respect to a plane perpendicular to the ultrasonic wave propagation axis formed by the ultrasonic transmitter and the ultrasonic receiver. As a result, although a part of the ultrasonic wave emitted from the ultrasonic transmitter passes through the detection target, the ultrasonic wave reflected by the surface of the detection target does not return to the transmitter, Go in the direction. Therefore, the ultrasonic wave does not form a standing wave between the transmitter and the detection object and between the detection object and the receiver, and the amount of the ultrasonic wave received by the receiver is the position of the detection object, Regardless of changes in tilt, surface condition, etc., it is almost constant. For this reason, the receiving intensity by the receiver is extremely stable, and it is possible to reliably detect the double feed of the detection object without averaging the received signal.

  In addition, for example, a double feed detection mechanism that improves double feed detection accuracy using ultrasonic waves has been proposed (see, for example, Patent Document 2).

  In this case, two or more double-feed sheets are bent and deformed to have a gap between them, and the attenuation of the ultrasonic signal is increased by the air layer in the gap to improve the double-feed detection accuracy.

  A high-frequency band signal generation device that generates a high-frequency band signal having a wide bandwidth has been proposed (see, for example, Patent Document 3).

  In this case, a plurality of baseband signal generating means for generating a baseband signal having a predetermined bandwidth based on the frequency setting data signal, and a plurality of baseband signal generating means are provided corresponding to each baseband generating means. A high frequency band signal is generated based on the frequency conversion signal and the frequency conversion signal. From the second stage onward, the high frequency band signal shifted to the high frequency region is generated based on the base band signal and the high frequency band signal generated in the previous stage. Generating frequency conversion means.

Japanese Utility Model Publication No. 5-56851 (page 5, Fig. 1) Japanese Patent Laid-Open No. 2001-199595 (pages 3, 4 and 2, 6) Japanese Patent Laid-Open No. 9-116577 (pages 3, 4 and 1)

  However, in the case of Patent Document 1 and Patent Document 2 described above, since the center frequency at which the sensitivity is large differs for each ultrasonic sensor, it is necessary to set the transmission frequency for each sensor.

  In addition, when the ultrasonic multi-feed detection means described in Patent Document 1 and Patent Document 2 described above is used in a copying machine or a multi-function machine, the temperature inside the machine becomes high due to heat of fixing, etc. In some places, the temperature inside the apparatus is lowered, so that the temperature change is severe and the transmission / reception sensitivity of the sensor changes due to the temperature characteristics of the ultrasonic sensor itself. When the sensitivity is lowered, there is a possibility that erroneous detection for determining one sheet as double feeding may occur.

  Therefore, at present, a method is used in which the double feed detecting means is arranged in the paper discharge unit of the copying machine or the multifunction machine. In this case, since detection is performed after image formation, there is a problem that a large amount of wasted paper is generated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a paper feeding device that absorbs variations in ultrasonic sensors and that can reduce the influence of temperature characteristics and perform multifeed detection with stable detection accuracy. .

In order to solve the above-described problems, a paper feeding device according to the present invention transmits ultrasonic waves from an ultrasonic transmitter disposed across a conveyance path for conveying paper to a receiver, passes through the paper, and is attenuated. In a paper feeding device that receives ultrasonic waves by a receiver and has double feed detection means for detecting double feed of paper based on the received signal, signal generation means for generating an oscillation signal to be supplied to the ultrasonic transmitter ; when the detection of the paper double feed, the control means and, receiving signal received by the receiver of ultrasonic waves whose frequency varies to control the signal generating means so as to continuously change at a predetermined range the frequency of the oscillation signal And a preset threshold value, and a double feed judging means for judging the double feed of the paper .

  According to the present invention, when detecting paper double feed, the frequency of the oscillation signal supplied to the ultrasonic transmitter by the control means is continuously changed within a predetermined range. For example, the frequency change range is a range of 4 kHz above and below the center frequency of the ultrasonic transmitter. Within the double feed detection period, the frequency of the oscillation signal is continuously changed at least once within a predetermined range. The double feed judging means judges the double feed based on the presence or absence of a peak of the received signal. Further, for example, it further includes integration processing means for integrating the received signal, and the double feed determining means compares the signal obtained by the integration processing means with a preset threshold value, and based on the comparison result, double feed. Is made to judge.

  As a result, since the oscillation frequency continuously changes within a predetermined range, the ultrasonic sensor always has the maximum sensitivity at a certain frequency. Therefore, it is not necessary to set the transmission frequency for each sensor, and the variation of the ultrasonic sensor is absorbed. In addition, it is possible to reduce the influence of changes in the transmission / reception sensitivity of the ultrasonic transmitter and the receiver due to the temperature change, and it is possible to perform stable detection. In addition, the temperature change range is wide, and it is possible to install in a place where it is difficult to install by the conventional method.

  Further, for example, a sheet position detecting unit for detecting the position of the sheet being conveyed is further provided, and the control unit controls the ultrasonic transmission timing of the double feed detecting unit based on the detection result of the sheet position detecting unit. Stable detection can be performed.

  According to the paper feeding device of the present invention, an ultrasonic wave is transmitted from an ultrasonic transmitter disposed across a conveyance path for conveying a sheet to a receiver, and the ultrasonic wave after passing through the sheet and attenuated is received by the receiver. In a paper feeding apparatus having a double feed detecting means for receiving and detecting double feed of paper based on the received signal, the control means continuously changes the frequency of the oscillation signal supplied to the ultrasonic transmitter within a predetermined range. In this way, the signal generating means is controlled so as to determine whether or not the paper is double fed based on the received signal received by the ultrasonic receiver.

  With this configuration, it is possible to absorb variations in the ultrasonic sensor and reduce the influence of changes in the transmission / reception sensitivity of the ultrasonic transmitter and receiver due to temperature changes. Therefore, it is possible to perform double feed detection with stable detection accuracy even in an installation location that is susceptible to the temperature characteristics of the ultrasonic sensor.

Hereinafter, a sheet feeding device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a configuration of a sheet feeding device 100 according to the first embodiment of this invention. A paper feeding device 100 shown in FIG. 1 is applied to a copying machine having a copying function using an electrophotographic system. For example, double feed detection is performed before an image is formed on paper, and based on this double feed detection. Thus, image formation control is executed.

  The sheet feeding device 100 includes a control unit 10, an operation unit 11, a display unit 12, a sheet feeding unit 13, a sheet detection sensor 14, a transport unit 15, a double feed detection unit 16, and a sheet position detection unit.

  The control unit 10 includes a CPU 10a, a ROM 10b, and a RAM 10c. The CPU 10a controls the overall operation of the sheet feeding device 100 while using the RAM 10c as a work area according to a control program stored in the ROM 10b.

  As a control means, the control unit 10 performs control so that the transmission frequency of the ultrasonic transmitter is swept within a predetermined range when paper double feed is detected. The control unit 10 also functions as a double feed determination unit together with a comparison circuit of the double feed detection unit 16 described later.

  Further, the control unit 10 controls the transport unit 15 based on the double feed detection information obtained by the double feed detection unit 16. For example, when the double feed of the paper is detected, the transport unit 15 is controlled by the control unit 10 so that a predetermined image indicating the occurrence of the double feed is formed on the paper related to the double feed and is discharged. At the same time, the control unit 10 holds the image data that was scheduled to form an image on the double-fed paper, and forms an image on the next paper conveyed by the conveying unit 15 based on the data. (See FIG. 2 described later). In addition, when a double feed occurs, the multi-feed paper is discharged to a predetermined paper discharge tray, and then the image forming operation is stopped and the display unit 12 is controlled to display that the double feed is generated. .

  The operation unit 11 is configured by a touch panel with a liquid crystal display function, for example, and functions as an interface for interacting with the user in settings such as a single-sided mode, a double-sided mode, and a post-processing mode. The paper size is also set. The operation unit 11 outputs operation information relating to image formation to the control unit 10. The operation unit 11 includes an operation unit that restarts the image forming operation of the image forming unit. When the double feed detection unit 16 detects a double feed of paper, the ultrasonic sensor 16s of the double feed detection unit 16 (FIG. 2). The user can issue an instruction to resume image formation (that is, a conveyance operation) of image data on the sheet from the operation unit 11 after temporarily stopping the sheet being conveyed to the upstream portion of (see).

  The operation unit 11 also functions as a selection unit that selects cancellation of double feed detection by the multifeed detection unit 16. The user can cancel the double feed detection with the operation unit 11 as necessary.

  The display unit 12 is a means for displaying the setting contents and the operation state when performing image formation, and includes, for example, an LCD (Liquid Crystal Display). The display unit 12 includes display means for displaying that double feed has occurred. When a double feed of the paper is detected by the double feed detecting means 16, a warning mark or the like is displayed to indicate the occurrence of double feed. The user can confirm the occurrence of double feed on the display unit 12.

  The paper feed unit 13 has a manual paper feed tray (not shown) and a paper feed cassette 13a (see FIG. 2). As shown in FIG. 2, a plurality of sheets P are accommodated in the sheet feed cassette 13a, and a sheet feed roller 21 is in contact with the uppermost one of these sheets P. When the paper feed roller 21 is driven to rotate counterclockwise in the drawing by a drive system (not shown), the paper P located at the uppermost position is moved between the rollers of the registration roller pair 22 from the paper feed unit 13. It is going to be discharged towards. Further, the paper feed unit 13 is provided with a paper detection sensor 14 that detects the presence or absence of the paper P.

  The transport unit 15 includes a paper feed roller 20, a transport roller 21, a registration roller 22, a pre-transfer roller 23, and a transport path 24 for the paper P (see FIG. 2). The registration roller 28 is provided at a demarcation point that separates the first paper feed and the second paper feed regarding the conveyance process of the paper P. The registration roller 22 is provided to synchronize the conveyance start timing in the second paper feed and the transfer start timing in the image forming unit. The image forming unit includes a developing unit 25, a transfer electrode 26, and a separation electrode 27 (see FIG. 2). The image forming unit performs processing such as rotation or enlargement / reduction of an image read by an image reading unit (not shown) of the copying machine, and then forms an image on the paper P conveyed by the conveying unit 15. To be made.

  The double feed detecting means 16 detects double feed using ultrasonic waves. The double feed detection means 16 includes an ultrasonic sensor 16s including an ultrasonic transmitter, a receiver, and the like. As shown in FIG. 2, the ultrasonic sensor 16 s is disposed in the conveyance path 24 for conveying the paper in front of the image forming unit. The configuration of the double feed detecting means 16 and the double feed detection state are shown in FIG.

  The paper position detection means 17 includes a paper position detection sensor. This paper position detection sensor is provided in the transport path in front of the ultrasonic sensor 16 s and transmits a detection signal to the control unit 10 when it is detected that the transported paper has arrived at a predetermined position. The control unit 10 controls the transmission timing of the transmitter 32 of the ultrasonic sensor 16s based on this detection signal.

  As shown in FIG. 3, the double feed detection unit 16 includes a transmission circuit 31, a transmitter 32, a receiver 33, a reception circuit 34, and a storage unit 35. The receiving circuit 31 includes an oscillation circuit 31a having a sweep function in a predetermined frequency range as a signal generating means, and a power amplification circuit 31b for amplifying an oscillation signal in the predetermined frequency range. The reception circuit 34 includes a resonance circuit 34a that converts vibration energy into an electrical signal, an amplification circuit 34b that amplifies the reception signal, a rectification circuit 34c that detects the amplified signal, a reception signal, and a threshold value (reference value). Is constituted by a comparison circuit 34d and an output circuit 34e.

  An electric signal in a predetermined frequency range output from the transmission circuit 31 is input to the transmitter 32, converted into acoustic energy (ultrasonic waves) by a transducer (piezoelectric element) in the transmitter 32, and the receiver via the paper P Radiated toward 33. A part of the ultrasonic wave emitted from the transmitter is reflected by the paper P in the transfer path. The ultrasonic wave that has passed through the paper P is received by the receiver 33, converted into an electrical signal by a transducer (piezoelectric element) in the receiver 33, and input to the receiving circuit 34. The reception circuit 34 converts the ultrasonic signal received by the resonance circuit 34a into an electric signal, and amplifies it by the amplification circuit 34b. The received signal is rectified by the rectifier circuit 34c. The comparison circuit 34d compares the attenuation amount after passing through one sheet and the sheet at the time of double feeding with the reference value stored in the storage means 35. Based on the result, that is, based on whether or not there is a peak output, the CPU 10a detects the presence or absence of double feeding of sheets. If double feed is determined, a double feed signal is output from the output circuit 34e. The RAM 10c is used as the storage unit 35.

  FIG. 4 is a diagram illustrating a configuration of the oscillation circuit. As the oscillation circuit 31a, a known oscillation circuit capable of frequency sweep is used. As shown in FIG. 4, the oscillation circuit 31 a includes a first baseband signal generation unit 1, a second baseband signal generation unit 2, a first frequency conversion unit 3, a second frequency conversion unit 4, and a local oscillation unit 5. ing.

  The first baseband signal generator 1 and the second baseband signal generator 2 include, for example, a direct digital frequency synthesizer, a D / A converter, a low-pass filter, and a phase shifter. The first frequency conversion unit 3 and the second frequency conversion unit 4 include, for example, a phase shifter, a balanced modulator, and an adder.

  The first baseband signal generator 1 generates a first baseband signal having a certain bandwidth according to the first frequency setting data signal from the outside, and outputs this signal to the first frequency converter 3. . The first frequency conversion unit 3 frequency-converts the first baseband signal based on the local oscillation frequency signal having a continuously single frequency output from the local oscillation unit 5, and the first baseband A first high-frequency band signal having the same bandwidth as the signal bandwidth is generated. The first high frequency band signal is output to the second frequency converter 4.

  The second baseband signal generation unit 2 generates a second baseband signal having a certain bandwidth according to the second frequency setting data signal from the outside, and outputs this signal to the second frequency conversion unit 4 . The second frequency conversion unit 4 frequency-converts the second baseband signal based on the first high frequency band signal, and a second high frequency signal having a bandwidth wider than the bandwidth of the second baseband signal. Generate and output a band signal.

  Note that the ultrasonic oscillation circuit is not limited to the oscillation circuit 31a described above. An ultrasonic oscillation circuit having another sweep function may be used.

  FIG. 5 is a diagram illustrating a reception signal when a single sheet is conveyed. As shown in FIG. 5, when an ultrasonic wave transmitted at the sweep frequency is received, a peak output appears at the center frequency of the ultrasonic sensor on the receiving side. Further, when different ultrasonic sensors are used, peak outputs appear at different positions. Therefore, when transmitting at the sweep frequency, the peak output can be obtained at a certain frequency without setting the center frequency of the ultrasonic sensor.

  FIG. 6 is a diagram showing a received signal at the time of double feeding. As shown in FIG. 6, there is almost no transmission amount regardless of the frequency during double feeding. As a result, the control unit 10 can determine the multifeed with or without the peak output. For example, when there is a peak output that is equal to or higher than a set reference value level as shown in FIG. If there is no peak output as shown in FIG.

Next, an example of operation when double feeding is detected in the paper feeding device 100 according to the first embodiment of the present invention will be described.
In this embodiment, when detecting double feeding of sheets fed out one by one from a predetermined sheet storage position, the sheet is first conveyed from the sheet feeding unit by the conveying unit 15. Next, it is detected whether or not the paper conveyed by the paper position detecting means 17 has reached a predetermined position. When it is detected that the paper has reached a predetermined position, the control unit 10 controls the oscillation circuit 31a, performs frequency sweep oscillation, supplies an oscillation signal to the transmitter 32, and emits ultrasonic waves from the transmitter 32. Here, the frequency change range of the frequency sweep oscillation is a range of 4 kHz above and below the center frequency of the ultrasonic transmitter 32. The receiver 33 receives the ultrasonic wave transmitted through the paper, processes the received signal, and supplies it to the comparison circuit 34d. The comparison circuit 34d compares with a preset threshold value. Based on the comparison result , the control unit 10 determines whether there is a peak output. Here, when it is determined that there is no peak output, it is detected as double feeding, displayed on the display unit, and notified to the user.

  As described above, in the present embodiment, the paper feeding apparatus 100 includes the oscillation circuit 31 a that has a frequency sweep function and supplies an oscillation signal to the ultrasonic transmitter 32, and controls when detecting paper double feeding. The unit 10 sweeps the oscillation frequency of the oscillation circuit 31a within a predetermined range. The receiver 33 receives the ultrasonic wave transmitted through the paper and determines whether or not the received signal has a peak output. If it is determined that there is no peak output, it is detected as double feed.

  As a result, since the oscillation frequency continuously changes within a predetermined range, the ultrasonic sensor 16s always has the maximum sensitivity at a certain frequency. Therefore, it is not necessary to set the transmission frequency for each sensor, and the variation of the ultrasonic sensor is absorbed. In addition, it is possible to reduce the influence of changes in the transmission / reception sensitivity of ultrasonic transmitters and receivers due to changes in temperature. It is possible to detect double feed with stable detection accuracy even at an installation location where it is easily received.

Further, since the double feed detecting means 16 can be arranged inside the apparatus, it is possible to prevent the generation of waste paper as in the conventional case.
In addition, since the ultrasonic transmission timing of the double feed detection unit 16 is controlled based on the detection result of the paper position detection unit 17, stable detection can be performed.

Hereinafter, a sheet feeding device according to a second embodiment of the present invention will be described. FIG. 7 is a diagram illustrating an example of the configuration of the sheet feeding device 200 according to the second embodiment of this invention.
7 includes a control unit 10A, an operation unit 11, a display unit 12, a paper feeding unit 13, a paper detection sensor 14, a transport unit 15, a double feed detection unit 16A, and a paper position detection unit 17. Yes.

  The control unit 10 includes a CPU 10a, a ROM 10b, and a RAM 10c. The CPU 10a controls the overall operation of the sheet feeding device 200 while using the RAM 10c as a work area according to a control program stored in the ROM 10b.

  As a control means, the control unit 10 performs control so that the transmission frequency of the ultrasonic transmitter is swept within a predetermined range when paper double feed is detected. The control unit 10 also functions as a double feed determination unit together with a comparison circuit of the double feed detection unit 16 described later.

  Further, the control unit 10 controls the transport unit 15 based on the double feed detection information obtained by the double feed detection unit 16A. For example, when the double feed of the paper is detected, the transport unit 15 is controlled by the control unit 10 so that a predetermined image indicating the occurrence of the double feed is formed on the paper related to the double feed and is discharged. At the same time, the control unit 10 holds the image data that was scheduled to form an image on the double-fed paper, and forms an image on the next paper conveyed by the conveying unit 15 based on the data. (See FIG. 2). In addition, when a double feed occurs, the multi-feed paper is discharged to a predetermined paper discharge tray, and then the image forming operation is stopped and the display unit 12 is controlled to display that the double feed is generated. .

  The operation unit 11 is configured by a touch panel with a liquid crystal display function, for example, and functions as an interface for interacting with the user in settings such as a single-sided mode, a double-sided mode, and a post-processing mode. The paper size is also set. The operation unit 11 outputs operation information relating to image formation to the control unit 10. The operation unit 11 includes an operation unit that resumes the image forming operation of the image forming unit. When the double feed detection unit 16A detects a double feed of paper, the operation unit 11 is upstream of the ultrasonic sensor 16s of the double feed detection unit 16A. After the paper being transported is temporarily stopped, the user can instruct the operation unit 11 to resume image formation (that is, the transport operation) of the image data on the paper.

  The operation unit 11 also functions as a selection unit that selects cancellation of double feed detection by the multifeed detection unit 16A. The user can cancel the double feed detection with the operation unit 11 as necessary.

  The display unit 12 is a means for displaying the setting contents and the operation state when performing image formation, and includes, for example, an LCD (Liquid Crystal Display). The display unit 12 includes display means for displaying that double feed has occurred. When double feed of the paper is detected by the double feed detection means 16A, a warning mark or the like is displayed to indicate that double feed has occurred. The user can confirm the occurrence of double feed on the display unit 12.

  The paper feed unit 13 has a manual paper feed tray (not shown) and a paper feed cassette 13a (see FIG. 2). As shown in FIG. 2, a plurality of sheets P are accommodated in the sheet feed cassette 13a, and a sheet feed roller 21 is in contact with the uppermost one of these sheets P. When the paper feed roller 21 is driven to rotate counterclockwise in the drawing by a drive system (not shown), the paper P located at the uppermost position is moved between the rollers of the registration roller pair 22 from the paper feed unit 13. It is going to be discharged towards. Further, the paper feed unit 13 is provided with a paper detection sensor 14 that detects the presence or absence of the paper P.

  The transport unit 15 includes a paper feed roller 20, a transport roller 21, a registration roller 22, a pre-transfer roller 23, and a transport path 24 for the paper P (see FIG. 2). The registration roller 28 is provided at a demarcation point that separates the first paper feed and the second paper feed regarding the conveyance process of the paper P. The registration roller 22 is provided to synchronize the conveyance start timing in the second paper feed and the transfer start timing in the image forming unit. The image forming unit includes a developing unit 25, a transfer electrode 26, and a separation electrode 27 (see FIG. 2). The image forming unit performs processing such as rotation or enlargement / reduction of an image read by an image reading unit (not shown) of the copying machine, and then forms an image on the paper P conveyed by the conveying unit 15. To be made.

  The double feed detecting means 16A detects double feed using ultrasonic waves. The double feed detection means 16A includes an ultrasonic sensor 16s including an ultrasonic transmitter, a receiver, and the like. As shown in FIG. 2 described above, the ultrasonic sensor 16s is disposed in the transport path 24 for transporting the paper in front of the image forming unit. FIG. 8 shows the configuration of the double feed detecting means 16A and the double feed detection state.

  As shown in FIG. 8, the double feed detection means 16A includes a transmission circuit 31, a transmitter 32, a receiver 33, a reception circuit 34A, and a storage means 35. The reception circuit 31 includes an oscillation circuit 31a (see FIG. 4) having a sweep function in a predetermined frequency range, and a power amplification circuit 31b that amplifies an oscillation signal in the predetermined frequency range as signal generation means. The reception circuit 34A includes a resonance circuit 34a that converts vibration energy into an electric signal, an amplification circuit 34b that amplifies the reception signal, an integration processing unit 34c ′ that integrates the amplified signal, a reception signal, and a reference value. Is constituted by a comparison circuit 34d and an output circuit 34e.

  An electric signal in a predetermined frequency range output from the transmission circuit 31 is input to the transmitter 32, converted into acoustic energy (ultrasonic waves) by a transducer (piezoelectric element) in the transmitter 32, and the receiver via the paper P Radiated toward 33. A part of the ultrasonic wave emitted from the transmitter 32 is reflected by the paper P in the transfer path. The ultrasonic wave that has passed through the paper P is received by the receiver 33, converted into an electrical signal by a transducer (piezoelectric element) in the receiver 33, and input to the receiving circuit 34. The reception circuit 34A converts the ultrasonic signal received by the resonance circuit 34a into an electrical signal, and amplifies it by the amplification circuit 34b. The received signal is integrated by the integration processing means 34c. The comparison circuit 34d detects the presence or absence of double feeding of paper based on the attenuation after passing one paper and the paper at the time of double feeding and the threshold value stored in the storage means 35. If double feed is determined, a double feed signal is output from the output circuit 34e. The RAM 10c is used as the storage unit 35.

  FIG. 9 is a diagram illustrating a double feed determination method in the paper feeding device 200. As shown in FIG. 9, the transmission amount obtained when the single sheet is obtained by the integration process is equal to or greater than the threshold value. Further, the transmission amount obtained by the double feed integration processing is equal to or less than the threshold value. As a result, double feed discrimination is performed. Therefore, when the transmission amount obtained by the integration process is equal to or less than the threshold value, it is determined that the feed is double feed.

Next, an operation example at the time of double feed detection in the sheet feeding device 200 according to the second embodiment of the present invention will be described.
In this embodiment, when detecting double feeding of sheets fed out one by one from a predetermined sheet storage position, the sheet is first conveyed from the sheet feeding unit by the conveying unit 15. Next, it is detected whether or not the paper conveyed by the paper position detection means 17 has reached a predetermined position. When it is detected that the paper has reached a predetermined position, the control unit 10 controls the oscillation circuit 31a, performs frequency sweep oscillation, supplies an oscillation signal to the transmitter 32, and emits ultrasonic waves from the transmitter 32. . Here, the frequency change range of the frequency sweep oscillation is a range of 4 kHz above and below the center frequency of the ultrasonic transmitter 32. The receiver 33 receives the ultrasonic wave transmitted through the paper, integrates the received signal, and supplies it to the comparison circuit 34d. The comparison circuit 34d compares with the threshold value and determines whether it is smaller than the threshold value. If it is determined that the value is smaller than the threshold value, it is detected as double feeding, displayed on the display unit, and notified to the user.

  As described above, in the present embodiment, the paper feeding device 200 includes the oscillation circuit 31a that has a frequency sweep function and supplies an oscillation signal to the ultrasonic transmitter 32, and controls the double feeding of the paper. The unit 10 sweeps the oscillation frequency of the oscillation circuit 31a within a predetermined range. The receiver 33 receives the ultrasonic wave transmitted through the paper, integrates the received signal, compares it with a threshold value, and determines whether it is smaller than the threshold value. If it is determined that it is smaller than the threshold value, it is detected as a double feed.

  As a result, since the oscillation frequency continuously changes within a predetermined range, the ultrasonic sensor 16s always has the maximum sensitivity at a certain frequency. Therefore, it is not necessary to set the transmission frequency for each sensor, and the variation of the ultrasonic sensor is absorbed. At the same time, it is possible to reduce the influence of the change in the transmission / reception sensitivity of the ultrasonic transmitter and receiver due to the temperature change, the environmental temperature changes drastically as in the copier, and it is easily affected by the temperature characteristics of the ultrasonic sensor. Double feed detection can be performed with stable detection accuracy even at installation locations.

  Further, since the double feed detecting means 16A can be arranged inside the apparatus, it is possible to prevent the generation of waste paper as in the conventional case.

  In addition, since the ultrasonic transmission timing of the double feed detection unit 16 is controlled based on the detection result of the paper position detection unit 17, stable detection can be performed.

  In the above-described embodiment, the paper feeding apparatuses 100 and 200 are applied to a copying machine, but are not limited to this. The present invention can also be applied to other sheet feeding apparatuses.

1 is a diagram illustrating a configuration example of a sheet feeding device 100 according to a first embodiment. It is a figure which shows the example of the arrangement position of an ultrasonic sensor. FIG. 3 is a diagram illustrating a configuration example of a double feed detection unit 16. It is a figure which shows the structural example of an oscillation circuit. It is a figure which shows the example of a received signal at the time of 1 sheet paper conveyance. It is a figure which shows the example of the received signal at the time of double feeding. It is a figure which shows the structural example of the paper feeder 200 of 2nd Embodiment. It is a figure which shows the structural example of 16 A of double feed detection means. It is a figure which shows the double feed judgment method.

Explanation of symbols

10 Control unit (control means)
DESCRIPTION OF SYMBOLS 11 Operation part 12 Display part 13 Paper feed part 14 Paper feed detection sensor 15 Conveyance means 16, 16A Double feed detection means 16s Ultrasonic sensor 17 Paper position detection means 24 Conveyance path 31 Transmission circuit 31a Oscillation circuit (signal generation means)
31b Power amplifier circuit 32 Transmitter 33 Receiver 34, 34A Receiver circuit 34a Resonant circuit 34b Amplifier circuit 34c Rectifier circuit 34c 'Integration processing means 34d Comparison circuit 34e Output circuit 35 Storage means 100, 200 Paper feeding device

Claims (6)

An ultrasonic wave is transmitted from an ultrasonic transmitter arranged across a conveyance path for conveying the paper to the receiver, and the attenuated ultrasonic wave is received by the receiver through the paper, and the paper is based on the received signal. In a paper feeder having double feed detection means for detecting double feed of
Signal generating means for generating an oscillation signal to be supplied to the ultrasonic transmitter ;
In detecting double feed before Symbol sheet, and control means for controlling said signal generating means so as to continuously change at a predetermined range of frequency of the oscillation signal,
A sheet feeding apparatus comprising: a double feed determination unit that determines a double feed of a sheet by comparing a reception signal received by the receiver with an ultrasonic wave whose frequency changes with a preset threshold value .
The multifeed judging means is
The sheet feeding device according to claim 1, wherein double feeding is determined based on presence or absence of a peak of the reception signal. Further comprising integration processing means for integrating the received signal;
The multifeed judging means is
The sheet feeding device according to claim 1, wherein the signal obtained by the integration processing unit is compared with a preset threshold value, and based on the comparison result, double feeding is determined. Paper position detecting means for detecting the position of the paper being conveyed;
The control means includes
The sheet feeding device according to claim 1, wherein the ultrasonic transmission timing of the double feed detection unit is controlled based on a detection result of the sheet position detection unit. 2. The sheet feeding device according to claim 1, wherein a frequency change range of the signal generation unit is a range of 4 kHz above and below the center frequency of the ultrasonic transmitter. The control means includes
2. The sheet feeding device according to claim 1, wherein the frequency of the oscillation signal is controlled to continuously change at least once within a predetermined range within a double feed detection period.

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