JP6316012B2 - Double feed detection device and image forming apparatus - Google Patents

Description

  The present invention relates to a double feed detection device that detects double feed of a sheet during sheet feeding and an image forming apparatus including the same.

  Conventionally, as an apparatus for detecting double feed of a sheet, an ultrasonic transmission unit and an ultrasonic receiver for receiving ultrasonic waves transmitted from the ultrasonic transmission unit are provided, and double feeding of a sheet is performed based on an attenuation amount of ultrasonic waves transmitted through the sheet. What is detected has been proposed (see Patent Document 1). In this proposal, when the overlapping portion between sheets is small, it is possible to cope with the case where even one sheet changes the transmittance of ultrasonic waves for each irradiation position due to fiber variation of the sheet. Specifically, when ultrasonic waves are received at a plurality of locations on the sheet, it is determined to be double feed when the number of locations lower than the reference value exceeds a predetermined number.

JP 2000-95390 A

  For example, a thin paper coated paper with a small basis weight and a special processing such as coating on the surface of the sheet has a low thickness of the sheet itself and a high adhesion between the sheets due to the coating of the sheet surface. From the above, it is known that it is difficult to form an air layer between sheets. In the conventional sheet double feed detection technology, when such thin paper-coated paper is double fed, the attenuation amount of the ultrasonic wave transmitted through the sheet may not be lower than a reference value. As a result, there remains a problem that it may not be possible to detect double feeding of sheets.

  The present invention has been made in view of such a problem, and performs a multifeed determination of a sheet using variation in signal intensity of an ultrasonic signal transmitted through the sheet, thereby improving a multifeed detection capability. The main purpose is to provide a double feed detection device.

The present invention relates to a multifeed detection device, which obtains information on a type of a sheet, a transmission unit that transmits an ultrasonic signal toward the sheet, a reception unit that receives the ultrasonic signal transmitted through the sheet. The transmitting unit and the receiving unit so that the transmitting unit transmits the ultrasonic signal and the receiving unit receives the ultrasonic signal transmitted through the sheet at a plurality of locations on the acquisition unit and the sheet being conveyed. Control means for controlling the means, wherein the control means calculates an index representing variation from a set of signal intensity data of the ultrasonic signals received at the plurality of locations, and the index is a first setting. A first determination method for determining that the sheet is double-fed when the value is greater than a value, and a portion of a set of signal intensity data of the ultrasonic signals received at the plurality of locations. And a second determination method for determining that the sheet is being double fed when the number of data less than or equal to the second set value is greater than or equal to a second set value, wherein the sheet information acquired by the acquisition means is the first if it represents the type of sheet is determined double feed on the basis of the first-size measuring method, when the information of the sheet obtained by the acquisition unit indicates a second type of sheet based on the second-size measuring method And determining double feed.

  According to the present invention, it is possible to provide a double feed detection device that performs double feed determination of a sheet using variation in the signal intensity of an ultrasonic signal transmitted through the sheet, thereby improving the double feed detection capability. Thereby, even in the case of a sheet such as a thin paper coated paper in which the attenuation amount of the ultrasonic wave at the time of double feeding does not become small, double feeding detection can be performed more reliably. In addition, since it is possible to suppress the occurrence of erroneous detection that the sheet is single-feeded even though the sheet is a single sheet, it is possible to detect the double-feed of the sheet more stably.

1 is a schematic longitudinal sectional view of an image forming apparatus to which a double feed detection device according to a first embodiment is applied. FIG. 3 is a schematic longitudinal sectional view of an upper sheet feeding unit of a sheet feeding apparatus included in the image forming apparatus. Explanatory drawing of operation | movement of a sheet feeding apparatus. The block diagram which shows the control system by each function part of a sheet feeding apparatus. The figure for demonstrating arrangement | positioning of the transmitting element and receiving element of the double feed detection apparatus with which a sheet feeding apparatus is equipped. The figure for demonstrating the input-output signal of the transmission circuit and receiving circuit in a double feed detection apparatus. The figure for demonstrating the reception data sent to the CPU from the receiving element of a double feed detection apparatus. FIG. 4 is an explanatory diagram of a control procedure executed by a CPU in double feed detection by the image forming apparatus. The figure for demonstrating the reception data sent to CPU from a receiving element in the double feed detection apparatus which concerns on 2nd Embodiment. FIG. 4 is an explanatory diagram of a control procedure executed by a CPU in double feed detection by the image forming apparatus. The figure for demonstrating the reception data sent to CPU from a receiving element in the double feed detection apparatus which concerns on 3rd Embodiment. FIG. 4 is an explanatory diagram of a control procedure executed by a CPU in double feed detection by the image forming apparatus. The figure for demonstrating the reception data sent to CPU from a receiving element in the double feed detection apparatus which concerns on 4th Embodiment. FIG. 4 is an explanatory diagram of a control procedure executed by a CPU in double feed detection by the image forming apparatus. FIG. 15 is an explanatory diagram of a control procedure executed by the CPU following FIG. 14. FIG. 16 is an explanatory diagram of a control procedure executed by the CPU following FIG. 15.

  Hereinafter, a case where the multifeed detection device according to the present invention is applied to an image forming apparatus will be described in detail with reference to the drawings. Specifically, there is provided a sheet feeding device provided with the double feed detection device, and an image forming device configured to include an image forming unit that forms an image on a sheet fed from the sheet feeding device. An example will be described.

[First Embodiment]
In the present embodiment, the maximum value (Max) and minimum value (Min) of a plurality of received signals acquired by the receiving element and the result (Max-Min) obtained by subtracting the minimum value from the maximum value are calculated and based on this. An image forming apparatus that performs multifeed determination based on the variation width of the received signal strength will be described.

FIG. 1 is a schematic longitudinal sectional view of an image forming apparatus to which the double feed detection device according to the present embodiment is applied. The image forming apparatus S illustrated in FIG. 1 includes a sheet feeding device 301, an image forming unit 300, an operation unit 4, a reader scanner 303, and a post-processing device 304. The user performs various processing settings (for example, sheet processing settings) for the image forming apparatus S via the operation unit 4 or an external host PC (not shown). Thus, the operation unit 4 or the external host PC (not shown) functions as a reception unit that receives an operation input from the user. The image information to be processed is image data read by the reader scanner 303 or image data transmitted from the external host PC. The image forming apparatus S performs sheet feeding and conveyance, image formation, post-processing, and the like based on sheet processing settings, image information, and the like, and outputs a sheet on which an image is formed as a product.
Hereinafter, each configuration included in the image forming apparatus S and a flow of a series of image forming processes will be described.

[Sheet feeding device]
The sheet feeding device 301 includes a transmitting element 6, a receiving element 7, a storage 11, 372, a sheet detection sensor 23, an escape tray 101, a full load detection device 102, an upper sheet feeding unit 311, a lower sheet feeding unit 312, and an upper conveyance unit. 317, the lower conveyance part 318, and the confluence | merging conveyance part 319 are comprised. The sheet feeding apparatus 301 also includes an escape conveyance unit 333, a conveyance sensor 350, and suction conveyance units 361 and 362. The description will be given assuming that the upper paper feed unit 311 includes the storage case 11 and the suction conveyance unit 361, and the lower paper feed unit 312 includes the storage case 372 and the suction conveyance unit 362. In addition, the double feed detection device included in the sheet feeding device 301 includes a transmission element 6 and a reception element 7 that function as a double feed detection sensor.

In the upper sheet feeding unit 311, the sheets stored in the storage 11 that is a stacking unit that stacks a plurality of sheets are fed as needed. In the lower sheet feeding unit 312, the sheets stored in the storage 372, which is a stacking unit that stacks a plurality of sheets, are fed as needed.
The escape tray 101 is provided on the top surface of the sheet feeding apparatus 301 and is a tray to which the multi-feed paper discharged from the image forming apparatus S is discharged. The full load detection device 102 detects whether or not the multi-feed paper discharged to the escape tray 101 is full.

The sheet feeding operation from each storage is performed by each of the suction conveyance units 361 and 362 provided in each sheet feeding unit. In the present embodiment, the case of air feed control will be described as an example. Therefore, it is assumed that a plurality of fans (not shown) are arranged in each of the suction conveyance units 361 and 362.
The operation of the fan during the paper feeding operation is controlled so that air is sent between the sheets in the storage boxes 11 and 372 from the upstream in the transport direction. When a sheet is rolled, the sheet is sucked onto the endless belt by a sheet suction fan arranged inside the endless belt, and is fed and conveyed. The details of the sheet feeding / conveying operation of the suction conveying units 361 and 362 will be described later.

  The sheet fed from the upper sheet feeding unit 311 is continuously conveyed by the upper conveying unit 317, and the sheet conveyed from the lower sheet feeding unit 312 is continuously conveyed by the lower conveying unit 318. Each of them is configured so as to be continuously transportable to a confluence transport unit 319 that joins 317. Although not shown in the drawings, each conveyance unit has a conveyance stepping motor. The stepping motors are controlled by the conveyance control unit, and the driving of the stepping motors provided in the respective conveyance units is mechanically transmitted to rotate the conveyance rollers of the respective units. Thereby, sheet conveyance is performed. Further, in the merging / conveying unit 319, the transmitting element 6 and the receiving element 7 which are double feed detection sensors are arranged so as to sandwich the sheet conveying path.

  The double feed detection sensor includes a transmission element 6 that functions as a transmission unit that transmits an ultrasonic signal toward the sheet, and a reception element 7 that functions as a reception unit that receives the ultrasonic signal transmitted through the sheet. The Details of the double feed detection sensor will be described later. The sheet feeding device 301 sequentially feeds and conveys the sheets in each storage according to the sheet request information from the image forming unit 300. The sheet feeding apparatus 301 conveys the sheet to a conveyance sensor 350 in a delivery unit with the image forming unit 300, and notifies the image forming apparatus of completion of delivery preparation from the sheet feeding apparatus 301. In response to the completion of preparation from the sheet feeding apparatus 301, the image forming unit 300 notifies the delivery request. The sheet feeding device 301 sequentially conveys the sheets one by one to the image forming apparatus every time a delivery request is notified. When the leading edge of the sheet fed from the sheet feeding device 301 reaches the uppermost transport roller nip of the image forming unit 300, it is pulled out by the transport roller of the image forming unit 300 and discharged from the sheet feeding device 301. The sheet feeding device 301 ends the sheet feeding operation when the number of sheets requested by the image forming unit 300 is conveyed. Then, after the sheet is pulled out and discharged by the image forming unit 300, the operation is finished, and the sheet feeding device 301 enters a standby state.

[Image forming unit]
The image forming unit 300 includes an image reference sensor 305, a registration control unit 306, an image forming unit 307, a fixing unit 308, a reverse conveyance unit 309, a flapper 310, a toner bottle 351, a developing unit 352, and a photosensitive drum 353. The The image forming unit 300 also includes a laser scanner unit 354 and an intermediate transfer belt 355. Note that the operation unit 4 for performing operation settings and the like for the image forming apparatus S by the user and the reader scanner 303 for reading a document image are arranged on the upper part of the image forming unit 300 as shown in FIG.

The image forming unit 300 notifies the above-described sheet feeding device 301 of a delivery request, pulls out the conveyed sheets one by one from the sheet feeding device 301, and sequentially forms an image. After receiving the sheet from the sheet feeding apparatus 301, the image forming unit 300 controls each conveying unit to convey the sheet.
The flapper 310 is connected to a drive mechanism (not shown), and to the escape tray 101 when the double feed detection sensor detects the double feed of the sheet, and to the image forming unit 307 when the double feed of the sheet is not detected. The transport path is selected so that the sheet is transported. That is, when the double feeding of the sheet is detected, the sheet is discharged to the escape tray 101. When the double feeding of the sheet is not detected, the image forming operation based on the image data received by the image forming unit 307 is performed with the sheet detection by the image reference sensor 305 as a starting point. In this embodiment, the case where the escape conveyance unit 333 for discharging the sheet to the escape tray 101 is provided in the image forming unit 300 is illustrated. For example, the sheet feeding apparatus 301 may be arranged in the sheet feeding apparatus 301.

The image forming unit 300 turns on the semiconductor laser in the laser scanner unit 354 and controls the amount of light, and also controls a scanner motor that controls rotation of a polygon mirror (not shown), and the photosensitive drum 353 is driven by laser light based on image data. A latent image is formed on the surface.
The image forming unit 300 feeds toner from the toner bottle 351 to the developing unit 352. As a result, the toner is developed on the latent image on the photosensitive drum 353. The developed toner image is primarily transferred from the photosensitive drum 353 to the intermediate transfer belt 355.
The toner image transferred onto the intermediate transfer belt 355 is secondarily transferred to the sheet, whereby a toner image is formed on the sheet.

  The registration control unit 306 is provided immediately before the secondary transfer position, and corrects the skew of the sheet immediately before the transfer position, and finely adjusts the toner image formed on the intermediate transfer belt 355 and the sheet leading edge position. The sheet conveyance control is performed without stopping the sheet, for example, by combining them. The fixing unit 308 applies heat and pressure to the sheet after the secondary transfer, thereby melting the toner and fixing the toner to the sheet. The fixed sheet is continuously printed on the back side or conveyed to the reverse conveying unit 309 when the sheet needs to be reversed, and conveyed to the downstream paper discharge device when printing is completed.

[Post-processing equipment]
The post-processing device 304 is connected to the downstream side of the image forming unit 300 and performs desired post-processing (for example, folding, stapling, punching, etc.) set by the user via the operation unit 4 on the sheet after image formation. After that, the paper is sequentially discharged to any one of the paper discharge trays 360 as a product.

FIG. 2 is a schematic longitudinal sectional view of the upper sheet feeding unit 311 of the sheet feeding apparatus 301. The lower paper feed unit 312 has the same configuration as the upper paper feed unit 311. The upper paper feed unit 311 mainly includes the storage 11, the air blowing unit 33, and the suction conveyance unit 361.
The storage 11 shown in FIG. 2 includes a tray 12 on which a plurality of sheets are placed, a rear end regulating plate 13 that regulates the upstream side (sheet rear end) of the sheet in the conveyance direction, and a direction (horizontal) perpendicular to the conveyance direction. Side end regulating plates 14 and 16 and a slide rail 15 for regulating the direction). Note that a sheet rear end pressing member 17 for pressing the sheet rear end is disposed on the upper portion of the rear end regulating plate 13.

  The user pulls out the storage case 11, sets sheets, and stores the storage case 11 at a predetermined position. In response to this, the tray 12 starts to rise in the direction A in the figure by a driving means (not shown). Thereafter, the tray 12 stops at a position where the distance from the suction conveyance belt 21 becomes B.

  The suction conveyance unit 361 shown in FIG. 2 includes a belt driving roller 41 that drives the suction conveyance belt 21, a suction duct 34 that creates a negative pressure space for sucking sheets by driving the suction fan 36, and negative pressure in the suction duct 34. A suction shutter 37 for adjusting the condition is included. The sheet adsorbed by the suction conveyance belt 21 is sent to the drawing roller pair 42 downstream in the conveyance direction by the conveyance force of the adsorption conveyance belt 21.

  The air blowing unit 33 shown in FIG. 2 includes a blowing fan 32 and a blowing / separating duct 31 having a nozzle that blows exhaust of the blowing fan as blowing air and separation air to the front end of the sheet. The whirling / separating duct 31 blows air in the direction C in the figure and the separating air in the direction D in the figure. Hereinafter, the suction / conveying operation of the sheet feeding apparatus 301 will be described in detail.

3A and 3B are explanatory diagrams of the operation of the sheet feeding apparatus 301, where FIG. 3A is an explanatory diagram at the start of air blowing, FIG. 3B is an explanatory diagram at the time of sheet adsorption, and FIG. 3C is an explanatory diagram at the start of conveyance. It is.
The image forming apparatus S receives the feeding signal at a position where the distance between the uppermost sheet 35a of the storage 11 and the suction conveyance belt 21 is B (see FIG. 2). The distance between the uppermost sheet 35a and the suction conveyance belt 21 is detected by a sensor (not shown).
Upon receiving the feeding signal, the image forming apparatus S drives the suction fan 36 of the suction conveyance unit 361 and starts air discharge in the arrow direction indicated by F in the drawing, as shown in FIG. Thereby, the inside of the suction duct 34 becomes a negative pressure space. Further, the image forming apparatus S drives the blowing fan 32 and blows air in the direction C in the figure. The image forming apparatus S further blows separation air in the direction D in the figure and starts air blowing.

  The image forming apparatus S detects that the distance between the paper surface position of the uppermost sheet 35a and the suction conveyance belt 21 of the suction conveyance unit 361 has become B '(FIG. 3A) by air blowing. In response to this detection, as shown in FIG. 3B, the image forming apparatus S rotates the suction shutter 37 provided in the suction duct 34 in the direction of the arrow indicated by G in the drawing via a driving means (not shown). Let As a result, the internal space of the suction duct 34 that has been divided into two spaces via the suction shutter 37 becomes a negative pressure space. As a result, suction air for sucking the uppermost sheet 35a is generated in the arrow direction indicated by H in the drawing. In this way, the uppermost sheet 35 a is adsorbed to the adsorption conveyance belt 21.

  As shown in FIG. 3C, the image forming apparatus S rotates the belt drive roller 41 in the arrow direction indicated by J in the state where the uppermost sheet 35a is adsorbed to the adsorbing and conveying belt 21. Thereby, the uppermost sheet 35a is conveyed in the arrow direction indicated by K in the drawing. The uppermost sheet 35a is finally sent to the next conveyance path when the drawing roller pair 42 rotates in the directions indicated by arrows M and P in the drawing.

FIG. 4 is a block diagram illustrating a control system by each functional unit of the sheet feeding apparatus 301.
A CPU (Central Processing Unit) 1 functions as a control unit that controls the operation of the sheet feeding apparatus 301. An ASIC (application specific integrated circuit) 2 drives various loads of the sheet feeding apparatus 301 such as various motors and fans based on instructions from the CPU 1. The storage device 3 stores various data input via the operation unit 4 which is a setting unit capable of inputting sheet information such as sheet size, basis weight, and surface property, a target value used for fan adjustment, and PWM (pulse width modulation). ) Store the value etc.

  The ASIC 2 is connected to various sensors such as a paper surface detection sensor 18, a storage opening / closing sensor 48, a lower position detection sensor 55, a paper presence / absence detection sensor 56, an upper position detection sensor 57, a suction completion sensor 58, and a sheet detection sensor 23. . The ASIC 2 is also connected to various drive circuits (drivers) such as a lifter motor drive circuit 20, a blower fan drive circuit 22, a lower conveyance motor drive circuit 26, a suction solenoid drive circuit 39, and a suction fan drive circuit 40. Also connected to the ASIC 2 are an upper transport motor drive circuit 43, a paper feed motor drive circuit 46, a drawing motor drive circuit 47, a merging transport motor drive circuit 50, and an escape transport motor drive circuit 66.

The paper surface detection sensor 18 detects the upper surface of the sheets stacked on the tray 12. The storage opening / closing sensor 48 detects the open / closed state of the storage 11. The lower position detection sensor 55 and the upper position detection sensor 57 detect the position of the tray 12 in the storage 11. The paper presence / absence detection sensor 56 detects the presence / absence of a sheet on the tray 12. The suction completion sensor 58 monitors the negative pressure state in the suction duct 34 when a sheet is sucked by the suction fan 36 of the suction conveyance unit 361, and detects that the sheet suction is completed. The sheet detection sensor 23 detects the presence / absence of a sheet in the merging / conveying unit 319.
The ASIC 2 monitors sensor outputs from various connected sensors and outputs a drive start command to a drive circuit that drives each load of the sheet feeding device. Further, the ASIC 2 receives the rotation speed signal (FG) of the fan 32 and the suction fan 36 and performs PWM control so that the fan rotates at the target rotation speed.

  The firing fan drive circuit 22 sends the PWM signal output from the ASIC 2 to the firing fan 32 and supplies power. The suction fan drive circuit 40 sends the PWM signal output from the ASIC 2 to the suction fan 36 and supplies power. The suction solenoid drive circuit 39 is a drive circuit for a suction solenoid 38 that rotates and drives the suction shutter 37 to open and close. The paper feed motor drive circuit 46 is a drive circuit that drives a paper feed motor 44 that rotates the belt drive roller 41 of the suction conveyance unit 361. The drawing motor driving circuit 47 is a driving circuit that drives a drawing motor 45 that rotates the drawing roller pair 42. The lifter motor drive circuit 20 is a drive circuit that drives a lifter motor 19 that is lifter drive means for moving the tray 12 up and down. The lower transport motor drive circuit 26 is a drive circuit that drives the lower transport motor 10 that rotates the transport rollers of the lower transport unit 318. The upper transport motor drive circuit 43 is a drive circuit that drives an upper transport motor 49 that rotates the transport rollers of the upper transport unit 317. The merging / conveying motor driving circuit 50 is a driving circuit that drives the merging / conveying motor 51 that rotates the conveying rollers of the merging / conveying unit 319. The escape conveyance motor drive circuit 66 is a drive circuit that drives an escape conveyance motor 67 that rotates the conveyance rollers of the escape conveyance unit 333.

The transmission circuit 8 generates a transmission signal and transmits the generated transmission signal to the transmission element 6 of the double feed detection sensor. The reception circuit 9 receives a reception signal from the reception element 7 of the double feed detection sensor.
The reception circuit 9 includes an amplification circuit that amplifies the reception signal, a peak hold circuit that holds the peak voltage of the amplified reception signal, and an A / D conversion circuit that A / D converts the peak-held analog signal. Is done. The reception signal A / D converted in the reception circuit 9 is sent to the CPU 1 via the ASIC 2. Then, the CPU 1 compares the calculation with the data stored in the storage device 3, thereby determining whether or not the double feed is performed. In this manner, the function of the double feed detection device provided in the sheet feeding device 301 is realized.

  In the sheet feeding apparatus 301 according to the present embodiment, the configuration example in which various loads such as a motor, a fan, and a sensor are controlled from the CPU 1 via the dedicated ASIC 2 has been described. For example, the CPU 1 may be directly controlled. In the sheet feeding apparatus 301 according to the present embodiment, the configuration example in which the operation unit 4 and the storage device 3 are directly connected to the CPU 1 has been described. For example, an operation unit and a storage device included in the image forming unit 300 may be used. Further, sheet information automatically recognized by a sheet information detection device installed in the sheet feeding device 301 can be used instead of the sheet information input from the operation unit 4.

FIG. 5 is a diagram for explaining the arrangement of the transmitting element 6 and the receiving element 7 of the double feed detection device provided in the sheet feeding apparatus 301. The description will be made assuming that the double feed detection sensor including the transmitting element 6 and the receiving element 7 is an ultrasonic sensor.
As shown in FIG. 5, the double feed detection sensors are arranged so as to face each other with a distance d so that the transmitting element 6 is on the lower side and the receiving element 7 is on the upper side across the sheet conveyance path. Further, each of the transmitting element 6 and the receiving element 7 is arranged so that the transmission axis between the transmitting element 6 and the receiving element 7 indicated by a dotted line in FIG. 5 is inclined by an angle θ with respect to the sheet conveyance path. .

FIG. 6 is a diagram for explaining input / output signals of the transmission circuit and the reception circuit in the double feed detection device. 6A and 6B, the vertical axis represents voltage [V] and the horizontal axis represents time [sec].
FIG. 6A illustrates input / output signals when the sheet passing between the transmitting element 6 and the receiving element 7 is plain paper on which the sheet surface is not subjected to special processing such as coating. FIG. A waveform (A) shown in FIG. 6A is an input signal from the ASIC 2 to the transmission circuit 8, and a burst wave having a predetermined voltage and a predetermined frequency is a predetermined number of pulses per detection operation (8 in the waveform (A)). Pulse) is being input. A waveform (A) shown in FIG. 6A shows an output signal of the peak hold circuit of the receiving circuit 9 when there is one sheet. A waveform (c) shown in FIG. 6A shows an output signal of the peak hold circuit of the receiving circuit 9 when the sheets are double-fed and are two sheets.

  The output signal voltage of the peak hold circuit of the receiving circuit 9 after a predetermined time t [sec] from the pulse input to the transmitting circuit 8 becomes Vb [V] in the waveform (A) for one sheet. Further, in the waveform (c) at the time of sheet double feeding, the output signal voltage is Vc [V] which is almost 0 [V]. It can be seen from FIG. 6A that the difference in output signal voltage is very large when the output signal voltage in the waveform (A) for one sheet is compared with the waveform (C) in double sheet feeding. That is, by comparing these output signal voltages with a predetermined set value (threshold value), it is possible to easily distinguish between the time of one sheet and the time of double feeding.

  FIG. 6B shows the input / output when the sheet passing between the transmitting element 6 and the receiving element 7 is a thin paper coated paper having a small basis weight and a special processing such as coating on the surface of the sheet. It is a figure for demonstrating a signal. A waveform (D) shown in FIG. 6B is an input signal to the transmission circuit 8, and a burst wave having a predetermined voltage and a predetermined frequency similar to the waveform (A) is set to a predetermined number of pulses (8 pulses in the waveform (D)). ) Indicates that you are entering. A waveform (e) shown in FIG. 6B shows an output signal of the peak hold circuit of the receiving circuit 9 when there is one sheet. A waveform (f) shown in FIG. 6B shows an output signal of the peak hold circuit of the receiving circuit 9 when the sheets are double-fed and are two sheets.

  The output signal voltage of the peak hold circuit of the receiving circuit 9 after a predetermined time t [sec] from the pulse input to the transmitting circuit 8 becomes Vd [V] in the waveform (e) for one sheet. Further, in the waveform (f) during sheet double feeding, the output signal voltage is Ve [V] slightly smaller than Vd [V]. When the coated papers are in close contact with each other, there is almost no air layer between them, so that the waveform attenuation is reduced. When the output signal voltage Vd [V] in the waveform (v) for one sheet is compared with the output signal voltage Ve [V] in the waveform (f) during double sheet feeding, there is almost no difference in the output signal voltage. Can be seen from FIG. Here, when the output sensitivity variation of the ultrasonic sensor and the circuit output variation of the receiving circuit 9 are taken into consideration, based on a predetermined threshold as described with reference to FIG. And it becomes very difficult to distinguish.

  FIG. 7 is a diagram for explaining received data sent from the receiving element 7 of the double feed detecting device to the CPU 1. The received data is input as a burst wave to the transmission circuit 8 described with reference to FIG. 6, and output signal voltages (Vb, Vc, Vd, Ve) of the peak hold circuit in the reception circuit 9 after a predetermined time t [sec]. Is A / D converted data.

FIG. 7A is a table showing received data when sheets are double-fed (a plurality of sheets are overlapped without deviation in the conveyance direction) and calculated values calculated by the CPU 1 based on the received data. It is.
In the sheet feeding apparatus 301 in the following description, the burst wave described in FIG. 6 is input to the transmitting element 6 six times for one sheet, and the reception signal corresponding to six times is input to the receiving element 7. Shall be obtained. For example, the burst wave starts at a position 40 [mm] from the front end of the sheet in the sheet conveyance direction with respect to a substantially central portion in a direction orthogonal to the conveyance direction of the conveyed sheet, and exceeds 20 [msec] intervals. A sound wave is input to the transmitting element 6 so as to be transmitted.

In the row direction of the table shown in FIG. 7A, received data for six times transmitted to the CPU 1 via the receiving circuit 9 is shown as data 1 to data 6 for one sheet. Further, the first to fifth data shown in the column direction of the table indicate the data in the first to fifth sheets to be conveyed. Furthermore, the maximum value (Max) and minimum value (Min) of the received data (data 1 to data 6) for six times and the result (Max-Min) obtained by subtracting the minimum value from the maximum value are shown in the row direction of the table. .
For example, the received data described as “first time” in FIG. 7A is 1, 7, 14, 10, 9, 16 in order from the data 1, and the maximum value is 16, and the minimum value is 1. The result of subtracting the minimum value from the maximum value is 15. Note that a value obtained by multiplying the reception data shown in FIG. 7 by 20 [mV] is the voltage value of the actual peak-hold reception data.
In FIG. 7A, it can be seen that the values (differences) obtained by subtracting the minimum value from the maximum value in the received data for the first to fifth sheet transports 5 times are within the range of 9 to 15, respectively. .

FIG. 7B is a table showing received data when the sheets are not double-fed and calculated values calculated by the CPU 1 based on the received data. As in FIG. 7A, the reception data (data 1 to data 6) for six times in the column direction, the maximum value (Max), the minimum value (Min), and the minimum value from the maximum value for each reception data. The result of subtracting the value (Max-Min) is shown.
For example, the received data described as “first time” in FIG. 7B are 21, 20, 20, 20, 20, 20 in order from data 1, and the maximum value is 21 and the minimum value is 20. The result of subtracting the minimum value from the maximum value is 1.
In FIG. 7B, it can be seen that the values obtained by subtracting the minimum value from the maximum value in the received data for the first to fifth sheet conveyances 5 are within the ranges of 1 to 3, respectively.

  Here, with respect to a value (Max-Min) obtained by subtracting the minimum value from the maximum value of the received data, for example, a threshold value is set to 5, and if the threshold value is 5 or more, the sheets are double-fed (FIG. 7A). If the threshold value is less than 5, a criterion for determining that sheets are not double-fed (FIG. 7B) is set. In this way, an index (value (Max-Min)) representing variation is calculated from a set of signal intensities of ultrasonic signals received at a plurality of locations on the sheet, and when this index is greater than a predetermined set value, the sheet It is determined that multiple feeds have been made. Thereby, it is possible to more reliably detect the double feeding of the sheets.

  FIG. 8 is an explanatory diagram of a control procedure executed by the CPU 1 in the double feeding detection by the sheet feeding device 301. The description will be made assuming that processing is started when the sheet feeding apparatus 301 receives a feeding signal from the image forming apparatus.

  The CPU 1 starts feeding from the storage box upon receiving the feeding signal (S801). The CPU 1 determines whether or not the leading edge of the sheet fed via the sheet detection sensor 23 has been detected (S802). When the leading edge of the sheet is detected (S802: Yes), the CPU 1 waits (waits) for a predetermined time (S803). The predetermined time is a time from when the leading edge of the sheet is detected until the sheet reaches between the transmitting element 6 and the receiving element 7 arranged to face each other across the sheet conveying path. For example, a timer (not shown) The progress is detected by. Moreover, this predetermined time can also be set as the time required for the distance between the transmitting element 6 and the receiving element 7 to reach a position of, for example, 40 [mm] from the front end of the sheet.

  The CPU 1 transmits an ultrasonic signal via the transmitting element 6 after the sheet reaches between the transmitting element 6 and the receiving element 7 after a lapse of a predetermined time (S804). Thereafter, the CPU 1 receives the transmitted ultrasonic signal via the receiving element 7 (S805). The ultrasonic signal received by the receiving element 7 is amplified in the receiving circuit 9, and the amplified signal is A / D converted after peak hold. Received data converted into digital data by A / D conversion is sent to the CPU 1.

The CPU 1 waits for a predetermined time after receiving the ultrasonic signal via the receiving element 7 (S806). The predetermined time is a time (for example, 20 [msec]) set in accordance with the sheet conveyance speed in order to transmit an ultrasonic signal to different positions on the sheet.
The CPU 1 determines whether or not the number of transmissions and receptions of ultrasonic signals for one sheet has reached a predetermined number (for example, 6 times) (S807). If the predetermined number of times has not been reached (S807: No), the process returns to step S804. Otherwise (S807: Yes), the CPU 1 specifies the maximum value and the minimum value from the received data for a predetermined number of times, and subtracts the minimum value from the specified maximum value (S808).

  The CPU 1 determines whether or not the calculation result in the process of step S808 is equal to or greater than a predetermined set value (threshold value) X (for example, 5 or greater when the threshold is set to 5) (S809). When it is determined that the calculation result is equal to or greater than the predetermined value X (S809: Yes), the CPU 1 determines that the sheets are being double fed (S810). Then, the CPU 1 drives the flapper 310 and selects a conveyance path so as to discharge the double-fed sheets to the escape tray 101. In this way, the CPU 1 discharges the double fed sheets to the escape tray 101 (S811), and ends a series of processing.

  If not (S809: No), the CPU 1 determines that the sheets are not double fed (S812). Then, the CPU 1 drives the flapper 310 and selects a conveyance path so that the sheet is conveyed to the image forming unit 307 of the image forming unit 300. In this way, the CPU 1 conveys the sheet to the image forming unit 307 (S813), and ends a series of processes.

  According to the sheet feeding apparatus of the present embodiment, even in the case of a sheet in which the attenuation amount of ultrasonic waves at the time of double feeding such as thin paper coated paper does not become small, double feeding detection can be performed more reliably. In addition, since it is possible to suppress the occurrence of erroneous detection that the sheet is single-feeded even though the sheet is a single sheet, it is possible to detect the double-feed of the sheet more stably.

[Second Embodiment]
In the present embodiment, a sheet feeding apparatus that calculates a dispersion value of received signals at a plurality of locations acquired by a receiving element and performs multi-feed determination based on a variation width of the signal strength of the received signal based on the calculated value. In addition, the same thing as the already demonstrated structure attaches | subjects the same code | symbol, and abbreviate | omits the description.

  FIG. 9 is a diagram for explaining received data sent from the receiving element 7 to the CPU 1 in the double feed detection device according to the present embodiment. The received data is input as a burst wave to the transmission circuit 8 described with reference to FIG. 6, and output signal voltages (Vb, Vc, Vd, Ve) of the peak hold circuit in the reception circuit 9 after a predetermined time t [sec]. Is A / D converted data.

  FIG. 9A is a table showing received data when sheets are multi-fed and calculated values calculated by the CPU 1 based on the received data. In the sheet feeding apparatus 301 in the following description, the burst wave described in FIG. 6 is input to the transmitting element 6 six times for one sheet, and the reception signal corresponding to six times is input to the receiving element 7. Shall be obtained.

In the row direction of the table shown in FIG. 9A, received data for six times transmitted to the CPU 1 via the receiving circuit 9 is shown as data 1 to data 6 for one sheet. Further, the first to fifth data shown in the column direction of the table indicate the data in the first to fifth sheets to be conveyed. Further, the variance values of the received data (data 1 to data 6) for six times are shown in the row direction of the table.
For example, the received data described as “first time” in FIG. 9A is 1, 7, 14, 10, 9, 16 in order from the data 1, and the variance is 23.6. . This variance value 23.6 is the arithmetic mean of the square of the value obtained by subtracting the value of each data from 9.5 which is the arithmetic mean value of 1, 7, 14, 10, 9, 16 of data 1 to data 6. Value. This arithmetic expression is as shown in Expression 1 below.

  23.6 = ((9.5-1) 2+ (9.5-7) 2+ (9.5-14) 2+ (9.5-10) 2+ (9.5-9) 2+ (9.5- 16) 2) / 6 (Formula 1)

  Note that a value obtained by multiplying the reception data shown in FIG. 9 by 20 [mV] is the voltage value of the reception data actually peak-held. Further, in FIG. 9A, it can be seen that the variance values in the received data for the first to fifth sheet conveyances are within the range of 7.8 to 23.6, respectively.

FIG. 9B is a table showing received data when the sheets are not double-fed and calculated values calculated by the CPU 1 based on the received data. Similarly to FIG. 9A, in the column direction, received data for six times (data 1 to data 6) and the dispersion value of the received data for each time are shown.
For example, the received data described as “first time” in FIG. 9B is 21, 20, 20, 20, 20, 20 in order from data 1, and the variance value is 0.1. . Also, in FIG. 9B, it can be seen that the dispersion values in the received data for the first to fifth sheet conveyances are within the range of 0.1 to 0.9.

  Here, with respect to the dispersion value of the received data, for example, a threshold value is set to 3, and if the threshold value is 3 or more, the sheet is double fed (FIG. 9A), and if it is less than the threshold value 3, the sheet is double fed. A determination criterion is set that does not exist (FIG. 9B). In this way, an index (dispersion value) representing variation is calculated from a set of signal intensities of ultrasonic signals received at a plurality of locations on the sheet, and when this index is greater than a predetermined set value, the sheet is double fed. It is determined that Thereby, it is possible to more reliably detect the double feeding of the sheets. In addition, although the case where the variance in the description is calculated as a sample variance has been described as an example, it may be calculated as an unbiased variance.

  FIG. 10 is an explanatory diagram of a control procedure executed by the CPU 1 in the double feeding detection by the sheet feeding device 301 according to the present embodiment. The description will be made assuming that processing is started when the sheet feeding apparatus 301 receives a feeding signal. Moreover, since each process from step S1001 to step S1007 shown in FIG. 10 is equal to each process of step S801 to step S807 already described in FIG. 8, the description thereof is omitted.

  The CPU 1 calculates a variance value based on a predetermined number of received data (S1008). The CPU 1 determines whether or not the calculation result (dispersion value) in the process of step S1008 is equal to or greater than a predetermined value Y (for example, 3 or more when the threshold is 3) (S1009). When it is determined that the calculation result is equal to or greater than the predetermined value Y (S1009: Yes), the CPU 1 determines that the sheets are being double fed (S1010). Then, the CPU 1 drives the flapper 310, selects a conveyance path so as to discharge the double-fed sheets to the escape tray 101, and discharges the double-fed sheets to the escape tray 101 (S1011). A series of processing ends.

  Otherwise (S1009: No), the CPU 1 determines that the sheet is not double-fed (S1012). Then, the CPU 1 drives the flapper 310 to select a conveyance path so that the sheet is conveyed to the image forming unit 307 of the image forming unit 300, thereby conveying the sheet to the image forming unit 307 (S1013). A series of processing ends.

  According to the sheet feeding apparatus of the present embodiment, even in the case of a sheet in which the attenuation amount of ultrasonic waves at the time of double feeding such as thin paper coated paper does not become small, double feeding detection can be performed more reliably. In addition, since it is possible to suppress the occurrence of erroneous detection that the sheet is single-feeded even though the sheet is a single sheet, it is possible to detect the double-feed of the sheet more stably.

[Third Embodiment]
In the present embodiment, a sheet feeding apparatus that calculates standard deviations of received signals at a plurality of locations acquired by a receiving element and performs multi-feed determination based on the variation width of the signal intensity of the received signals based on the standard deviation will be described. In addition, the same thing as the already demonstrated structure attaches | subjects the same code | symbol, and abbreviate | omits the description.

  FIG. 11 is a diagram for explaining received data sent from the receiving element 7 to the CPU 1 in the double feed detection device according to the present embodiment. The received data is input as a burst wave to the transmission circuit 8 described with reference to FIG. 6, and output signal voltages (Vb, Vc, Vd, Ve) of the peak hold circuit in the reception circuit 9 after a predetermined time t [sec]. Is A / D converted data.

  FIG. 11A is a table showing received data when sheets are multi-fed and calculated values calculated by the CPU 1 based on the received data. In the sheet feeding apparatus 301 in the following description, the burst wave described in FIG. 6 is input to the transmitting element 6 six times for one sheet, and the reception signal corresponding to six times is input to the receiving element 7. Shall be obtained.

In the row direction of the table shown in FIG. 11A, received data for six times transmitted to the CPU 1 via the receiving circuit 9 is shown as data 1 to data 6 for one sheet. Further, the first to fifth data shown in the column direction of the table indicate the data in the first to fifth sheets to be conveyed. Further, standard deviations of received data (data 1 to data 6) for six times are shown in the row direction of the table.
For example, the received data described as “first time” in FIG. 11A is 1, 7, 14, 10, 9, 16 in order from data 1, and the standard deviation is 4.9. . This standard deviation 4.9 is the arithmetic mean of the square of the value obtained by subtracting the value of each data from 9.5 which is the arithmetic mean value of 1, 7, 14, 10, 9, 16 of data 1 to data 6. The square root of the value. This arithmetic expression is as shown in Expression 2 below.

4.9 = √ (((9.5-1) 2+ (9.5-7) 2+ (9.5-14) 2+ (9.5-10) 2+ (9.5-9) 2+ (9. 5-16) 2) / 6) (Formula 2)

  Note that the value obtained by multiplying the reception data shown in FIG. 11 by 20 [mV] is the voltage value of the reception data actually peak-held. Also, in FIG. 11A, it can be seen that the standard deviations in the received data for the first to fifth sheet transports 5 times are within the range of 2.8 to 4.9, respectively.

FIG. 11B is a table showing received data when the sheets are not double-fed and calculated values calculated by the CPU 1 based on the received data. Similarly to FIG. 11A, the received data (data 1 to data 6) for 6 times and the standard deviation of the received data for each time are shown in the column direction.
For example, the received data described as “first time” in FIG. 11B is 21, 20, 20, 20, 20, 20 in order from data 1, and the standard deviation is 0.4. . Further, in FIG. 11B, it can be seen that the standard deviations in the received data for the first to fifth sheet transports 5 times are within the range of 0.4 to 0.9, respectively.

  Here, with respect to the standard deviation of the received data, for example, a threshold value is set to 2, and if the threshold value is 2 or more, the sheet is double fed (FIG. 11A), and if it is less than the threshold value 2, the sheet is double fed. A determination criterion is set that does not exist (FIG. 11B). In this way, an index (standard deviation) representing variation is calculated from a set of signal intensities of ultrasonic signals received at a plurality of locations on the sheet, and when the index is larger than a predetermined set value, the sheet is double fed. It is determined that Thereby, it is possible to more reliably detect the double feeding of the sheets.

  FIG. 12 is an explanatory diagram of a control procedure executed by the CPU 1 in the double feeding detection by the sheet feeding device 301 according to the present embodiment. The description will be made assuming that processing is started when the sheet feeding apparatus 301 receives a feeding signal. In addition, since each process from step S1201 to step S1207 shown in FIG. 12 is the same as each process from step S801 to step S807 already described with reference to FIG.

  The CPU 1 calculates a standard deviation based on the received data for a predetermined number of times (S1208). The CPU 1 determines whether or not the calculation result (standard deviation) in the process of step S1008 is equal to or greater than a predetermined value Z (for example, 2 or greater when the threshold is 2) (S1209). When it is determined that the calculation result is equal to or greater than the predetermined value Z (S1209: Yes), the CPU 1 determines that the sheets are being double fed (S1210). Then, the CPU 1 drives the flapper 310, selects a conveyance path so as to discharge the double-fed sheets to the escape tray 101, and discharges the double-fed sheets to the escape tray 101 (S1211). A series of processing ends.

  If not (S1209: No), the CPU 1 determines that the sheets are not double-fed (S1212). Then, the CPU 1 drives the flapper 310 to select a conveyance path so that the sheet is conveyed to the image forming unit 307 of the image forming unit 300, thereby conveying the sheet to the image forming unit 307 (S1213). A series of processing ends.

  According to the sheet feeding apparatus of the present embodiment, even in the case of a sheet in which the attenuation amount of ultrasonic waves at the time of double feeding such as thin paper coated paper does not become small, double feeding detection can be performed more reliably. In addition, since it is possible to suppress the occurrence of erroneous detection that the sheet is single-feeded even though the sheet is a single sheet, it is possible to detect the double-feed of the sheet more stably.

[Fourth Embodiment]
In the present embodiment, a sheet feeding apparatus capable of determining a multifeed determination method based on sheet information including sheet size information, basis weight information, and surface property information will be described.
Specifically, based on the sheet information, when the number of points that are lower than a predetermined reference value in the set of determination criteria and signal strengths described in the first embodiment is greater than a predetermined set number, double feeding is performed. Of the determination criteria for determination, the presence / absence of double feeding is determined by at least one determination method. In the following description, the former criterion is referred to as a first condition, and the latter criterion is referred to as a second condition.
Depending on the sheet type, it may be difficult to determine the double feed of the sheet only by the double feed judgment based on the signal intensity variation width obtained by calculating from the received signals at a plurality of locations acquired by the receiving element 7 on the receiving side. Such a sheet is, for example, a sheet generally called plain paper whose surface is not coated. Hereinafter, a case where multi-feed detection is performed on plain paper will be described in detail as an example.

  FIG. 13 is a diagram for explaining received data sent from the receiving element 7 to the CPU 1 in the double feed detection device according to the present embodiment. The received data is input as a burst wave to the transmission circuit 8 described with reference to FIG. 6, and output signal voltages (Vb, Vc, Vd, Ve) of the peak hold circuit in the reception circuit 9 after a predetermined time t [sec]. Is A / D converted data.

  FIG. 13A is a table showing received data when sheets are double fed and calculated values calculated by the CPU 1 based on the received data. In the sheet feeding apparatus 301 in the following description, the burst wave described in FIG. 6 is input to the transmitting element 6 six times for one sheet, and the reception signal corresponding to six times is input to the receiving element 7. Shall be obtained.

In the row direction of the table shown in FIG. 13A, received data for six times transmitted to the CPU 1 via the receiving circuit 9 is shown as data 1 to data 6 for one sheet. Further, the first to fifth data shown in the column direction of the table indicate the data in the first to fifth sheets to be conveyed. Furthermore, the maximum value (Max) and minimum value (Min) of the received data (data 1 to data 6) for six times and the result (Max-Min) obtained by subtracting the minimum value from the maximum value are shown in the row direction of the table. . The threshold for the value (Max-Min) obtained by subtracting the minimum value from the maximum value of the received data described in the first embodiment is referred to as a first threshold.
Furthermore, the second threshold value is 15, and the number of data that is equal to or less than the second threshold value in the received data (data 1 to data 6) for six times is shown in the row direction of the table.

  For example, the received data described as “first time” in FIG. 13A is 2, 0, 0, 0, 0, 0 in order from the data 1, and the maximum value is 2, and the minimum value is The result of subtracting the minimum value from 0 and the maximum value is 2. In addition, the number of data below the second threshold 15 is 6. Note that the value obtained by multiplying the reception data shown in FIG. 13 by 20 [mV] is the voltage value of the actual peak-hold reception data.

  In FIG. 13 (a), it can be seen that the values obtained by subtracting the minimum value from the maximum value in the received data for the first to fifth conveyances are within the range of 1 to 11, respectively. Also, it can be seen that the number of data below the second threshold 15 is all six.

FIG. 13B is a table showing the received data when the sheets are not double-fed and the calculated values calculated by the CPU 1 based on the received data.
Similarly to FIG. 13 (a), the reception data for six times (data 1 to data 6), the maximum value (Max), the minimum value (Min), and the minimum value from the maximum value are received in the column direction. The result of subtracting the value (Max-Min) is shown. Further, the second threshold value is 15, and the number of data that is equal to or less than the second threshold value in the received data (data 1 to data 6) for six times is shown in the row direction of the table.
For example, the received data described as “first time” in FIG. 13B is 31, 30, 33, 32, 32, 32 in order from data 1, and the maximum value is 33 and the minimum value is 30. The result of subtracting the minimum value from the maximum value is 3. The number of data below the second threshold 15 is zero.
In FIG. 13 (b), it can be seen that the values obtained by subtracting the minimum value from the maximum value in the received data for the first to fifth transports are within the range of 3 to 6, respectively. It can also be seen that the number of data below the second threshold 15 is all zero.

Here, it is assumed that a first threshold value for determining sheet double feeding is set for a value (Max-Min) obtained by subtracting the minimum value from the maximum value of the received data. In this case, as shown in FIG. 13, when the sheet is double fed (FIG. 13A) and the sheet is not double fed (FIG. 13B), a value (Max− There is no gap in the difference of Min). For this reason, it is not possible to specify (set) a threshold value for determination of double feeding, and as a result, it becomes difficult to detect double feeding of sheets.
However, if attention is paid to the number of data that is equal to or less than the second threshold value 15 with respect to the received data (data 1 to data 6) for six times, the case where the sheets are double-fed (FIG. 13A) is “6”. “, When the sheets are not double-fed (FIG. 13B),“ 0 ”. In this way, it is possible to clearly distinguish whether or not the sheets are being double fed. For example, if there are two or more data specified based on the second threshold, the sheet is double-fed (FIG. 13A), and if it is less than two, the sheet is not double-fed (FIG. 13 ( b)) is set.
Thus, the number of locations lower than a predetermined reference value (for example, the second threshold) in the set of signal intensities of ultrasonic signals received at a plurality of locations on the sheet is a predetermined set number (for example, 2). When the number is larger, it is determined that the sheets are being double fed. That is, when at least one of the first condition and the second condition is satisfied, it is determined that the sheets are being multi-fed. Thereby, it is possible to more reliably detect the double feeding of the sheets.

  14, 15, and 16 are explanatory diagrams of control procedures executed by the CPU 1 in the double feeding detection by the sheet feeding device according to the present embodiment. The description will be made assuming that processing is started when the sheet feeding apparatus 301 receives a feeding signal.

The CPU 1 acquires sheet information indicating sheet characteristics preset by the user (S1401). The sheet information is information indicating the characteristics of the sheet such as the surface property information indicating the size, basis weight, presence / absence of a surface coat, and the like of the sheets stored in the storages 11 and 372. For example, the sheet information functions as a receiving unit. This is information set by the user via the operation unit 4. Hereinafter, a case where the sheet basis weight is set as sheet information will be described as an example.
The CPU 1 determines a sheet multi-feed determination method based on the acquired sheet information (S1402). Specifically, based on the sheet information, the double feed determination described in the first embodiment, and the double feed is determined when the signal strength of the received signal is equal to or less than a predetermined value is greater than or equal to a predetermined number. It is determined whether to use either one or both of the multifeed judgment methods.
In the following description, when a sheet to be determined is a coated paper whose surface is subjected to special processing such as coating, and is a sheet having a predetermined basis weight (e.g., 80 g / m ^ 2) or less. Assume that only the double feed determination (FIG. 14) using the first threshold is performed.
In addition, even if the sheet surface is not subjected to special processing such as coating, or coated paper is subjected to special processing, the sheet is larger than a predetermined basis weight (eg, 180 g / m ^ 2). Only the double feed determination using the second threshold (FIG. 15) is performed.
In addition, when the sheet surface is a coated paper in which special processing such as coating is applied and the sheet has a predetermined basis weight range (for example, 80 g / m ^ 2 to 180 g / m ^ 2), It is assumed that the double feed determination (FIG. 16) using the threshold value and the second threshold value is performed.

When the CPU 1 determines to perform the multi-feed determination based on the signal intensity variation width, that is, the multi-feed determination using only the first threshold (S1402: Yes), the CPU 1 starts feeding from the storage (S1403). . Otherwise (S1402: No), the process proceeds to step S1416 (FIG. 15).
Each process from step S1403 to step S1415 shown in FIG. 14 corresponds to each process from step S801 to step S813 already described in FIG.

The CPU 1 determines a sheet double feed determination method based on the acquired sheet information (S1416). Specifically, it is determined whether or not only signal level determination using the second threshold value is performed. When it is determined that the multi-feed determination using only the second threshold is performed (S1416: Yes), the CPU 1 starts feeding from the storage (S1417). Otherwise (S1416: No), the process proceeds to step S1429 (FIG. 16).
In addition, since each process from step S1417 to step S1422 shown in FIG. 15 corresponds to each process of step S801 to step S807 already described in FIG.

  The CPU 1 determines whether or not there is a predetermined number (for example, 2) or more of data specified based on the second threshold among the predetermined number of received data (S1424). When there is a predetermined number or more of data specified based on the second threshold value (S1424: Yes), the CPU 1 determines that the sheets are being double fed (S1425). Then, the CPU 1 drives the flapper 310 and selects a conveyance path so as to discharge the double-fed sheets to the escape tray 101. In this way, the CPU 1 discharges the double fed sheets to the escape tray 101 (S1426), and ends a series of processing.

  If not (S1424: No), the CPU 1 determines that the sheets are not double-fed (S1427). Then, the CPU 1 drives the flapper 310 and selects a conveyance path so that the sheet is conveyed to the image forming unit 307 of the image forming unit 300. In this manner, the CPU 1 conveys the sheet to the image forming unit 307 (S1428), and ends a series of processes.

Subsequently, a procedure after the process of step S1429 will be described. Here, the double feed determination is performed using the first threshold value and the second threshold value.
Note that each processing from step S1429 to step S1438 shown in FIG. 16 corresponds to each processing from step S1417 to step S1426 already described in FIG.

When the CPU 1 determines that the data specified based on the second threshold value is less than the predetermined number in the process of step S1436 (S1426: No), the CPU 1 specifies the maximum value and the minimum value from the received data for the predetermined number of times. Then, the minimum value is subtracted from the specified maximum value (S1439).
The CPU 1 determines whether or not the calculation result in the process of step S1439 is a predetermined value (threshold value) X or more (for example, 5 or more when the threshold value is 5) (S1440). When it is determined that the calculation result is equal to or greater than the predetermined value X (S1440: Yes), the CPU 1 determines that the sheets are being double-fed (S1441). Then, the CPU 1 drives the flapper 310 and selects a conveyance path so as to discharge the double-fed sheets to the escape tray 101. In this way, the CPU 1 discharges the double fed sheets to the escape tray 101 (S1442), and ends a series of processing.

  If not (S1440: No), the CPU 1 determines that the sheets are not double fed (S1443). Then, the CPU 1 drives the flapper 310 and selects a conveyance path so that the sheet is conveyed to the image forming unit 307 of the image forming unit 300. In this way, the CPU 1 conveys the sheet to the image forming unit 307 (S1444), and ends a series of processes.

  As described above, according to the sheet feeding apparatus of the present embodiment, the condition for determining the multi-feed is determined based on the sheet information. This makes it possible to detect double feed more reliably not only for sheets that do not reduce the attenuation of ultrasonic waves during double feed, such as thin paper-coated paper, but also for plain paper that has no surface coating. it can. In addition, since it is possible to suppress the occurrence of erroneous detection that the sheet is single-feeded even though the sheet is a single sheet, it is possible to detect the double-feed of the sheet more stably.

  Note that only when it is determined that both the multifeed determination using the first threshold and the multifeed determination using the second threshold are performed according to the sheet type, the sheets are double-fed. It can also be configured to determine. In addition, the multifeed determination can be performed using the variance value described in the second embodiment and the standard deviation described in the third embodiment.

  Further, in each embodiment of the present invention, as an example of an index representing the variation of the ultrasonic signal transmitted through the sheet, a mode in which the difference between the maximum value and the minimum value, the variance value, and the standard deviation are used as the index has been described. . However, the present invention is not limited to these, and it is possible to employ other indexes representing variation.

  The embodiment described above is for explaining the present invention more specifically, and the scope of the present invention is not limited to these examples.

  DESCRIPTION OF SYMBOLS 1 ... CPU, 3 ... Storage device, 4 ... Operation part, 6 ... Transmission element, 7 ... Reception element, 8 ... Transmission circuit, 9 ... Reception circuit, 300 ... Image formation part, 301 ... Sheet feeding apparatus, 303 ... Reader Scanner, 304... Post-processing device, S.

Claims (8)

A transmission means for transmitting an ultrasonic signal toward the sheet;
Receiving means for receiving the ultrasonic signal transmitted through the sheet;
Obtaining means for obtaining information on the type of the sheet;
The transmitting unit and the receiving unit are controlled so that the transmitting unit transmits the ultrasonic signal and the receiving unit receives the ultrasonic signal transmitted through the sheet at a plurality of locations of the sheet being conveyed. Control means,
The control unit calculates an index representing variation from a set of signal intensity data of the ultrasonic signals received at the plurality of locations, and the sheet is double-fed when the index is larger than a first set value. A first determination method for determining that the number of pieces of data having a predetermined intensity or less is equal to or greater than a second set value among a set of signal intensity data of the ultrasonic signals received at the plurality of locations; sheet and a second determination method determines that are multi-fed, if the information of the sheet obtained by the acquisition unit indicates a first type of sheet double feed on the basis of the first-size measuring method determined, information of the sheet obtained by the obtaining unit if it represents a second type of sheet and judging the double feed on the basis of the second-size measuring method,
Double feed detector. The indicator is a difference between a maximum value and a minimum value in the signal strength data set,
The multifeed detection device according to claim 1. The indicator is a variance of the set of signal strength data,
The multifeed detection device according to claim 1. The indicator is a standard deviation of the set of signal strength data,
The multifeed detection device according to claim 1. Wherein, when said information of the sheet obtained by the obtaining unit represents the third type of sheet, the first of greater than the first-size index is the first set value representing the variation in the constant process conditions, and, of the second condition that the number of following data the predetermined intensity is the second set value or more among the set of data of the signal intensity in the second-size measuring method, one of the at least one When the condition is satisfied, it is determined that the sheet is being double fed.
The multifeed detection device according to claim 1. The first type sheet is a sheet having a surface coated and having a basis weight of less than the first basis weight, and the second type sheet is a sheet having an uncoated surface or a surface coated. The basis weight is a sheet larger than the second basis weight, which is larger than the first basis weight,
The multifeed detection device according to any one of claims 1 to 5. The third type sheet is coated on the surface, and the basis weight is not less than the first basis weight and not more than the second basis weight.
The multifeed detection device according to claim 6 quoting claim 5. A sheet feeding device provided with the double feed detection device according to any one of claims 1 to 7,
An image forming unit that forms an image on a sheet fed from the sheet feeding device,
Image forming apparatus.

Images