Sheet feeding device, image forming apparatus, sheet feeding method

A sheet feeding device comprises sheet storage for storing a sheet, a merging conveying unit for feeding the sheet from the sheet storage to an image forming apparatus, a transmitting element for transmitting an ultrasonic signal to the sheet conveyed on the merging conveying unit, and a receiving element for receiving the ultrasonic signal having passed through the sheet and outputting an output signal according to strength of the received ultrasonic signal. When the sheet is a Japanese paper, the sheet feeding device detects double feeding of the sheet according to an average value of a plurality of the output signals and variation in a plurality of the output signals obtained for the one sheet. If the sheet is not double fed, the sheet is fed to the image forming apparatus. If the sheet is double fed, the sheet is discharged to the escape tray.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a sheet feeding device for feeding a sheet to an image forming apparatus such as a printer, a copying machine, and the like.

DESCRIPTION OF THE RELATED ART

The image forming apparatus performs image formation on a sheet which is fed one by one by a sheet feeding device. To feed the sheet one by one, some sheet feeding devices comprise a double feeding detection sensor which detects double feeding of the sheet. Japanese Patent Application Laid-open No. 2000-95390 discloses a double feeding detection method which detects the double feeding of the sheet by the double feeding detection sensor. The double feeding detection sensor includes an ultrasonic transmitting unit and an ultrasonic receiving unit which are arranged so as to sandwich a sheet conveyance path through which the sheet is conveyed. An output value which is output by the ultrasonic receiving unit according to an ultrasonic wave received from the ultrasonic transmitting unit when one sheet is conveyed is defined as a reference output value. A value which is lower than the reference output value is set as a threshold value for determining the double feeding. When the sheet is conveyed, the double feeding detection sensor scans the sheet in a conveying direction. During that time, in a case where a number of units with the output value of the ultrasonic receiving unit being lower than the threshold value exceeds a predetermined number, it is determined that the sheet is double fed. Japanese Patent Application Laid-open No. 2015-147659 discloses a double feeding detection method for determining the double feeding of the sheet according to variation (a difference between a maximum value and a minimum value, a variance value, a standard deviation) in an ultrasonic signal having passed through the sheet.

In the double feeding detection using the conventional sheet feeding device, even when determining the double feeding by at least one of the signal strength and its variation, as to the sheet with non-uniform fiber orientation (grain) and density such as a Japanese paper, a false detection may occur. This is because, in case of the sheet with the non-uniform fiber orientation and density such as the Japanese paper, depending on a detecting part of the sheet, even one sheet, the variation in the signal strength becomes large. The main subject of the present disclosure is to provide a sheet feeding device capable of accurately detecting the double feeding even when the sheet is a sheet with the non-uniform fiber orientation and density such as the Japanese paper.

SUMMARY OF THE INVENTION

A sheet feeding device according to the present disclosure includes: a sheet storage configured to store a sheet, a sheet feeder configured to feed the sheet stored in the sheet storage, a transmitter configured to transmit a signal to the sheet fed by the sheet feeder, a receiver configured to receive the signal which passes through the sheet and output an output signal according to strength of the received signal, and a controller configured to determine double feeding of the sheet fed by the sheet feeder according to an average value of values of a plurality of the output signals and variation in the values of the plurality of the output signals obtained for the one sheet if the sheet stored on the sheet storage is a first type sheet.

DESCRIPTION OF THE EMBODIMENTS

In the following, embodiments are described in detail with reference to the accompanying drawings.

FIG. 1is a configuration diagram of an image forming system to which double feeding detection technology of the present embodiment is applied. An image forming system S comprises a sheet feeding device301, an image forming apparatus300, an operation unit4, a reader scanner303, and a post-processing device304. A user performs setting of various processing (for example, sheet processing setting) to the image forming system S through the operation unit4or an external host computer (not shown). The operation unit4or the external host computer (not shown) functions as a reception part for receiving an operation input from the user. Further, image information to be processed is image data read by the reader scanner303, image data sent from the external host computer, or the like. The image forming system S feeds and conveys the sheet, performs the image formation, performs the post-processing, and the like based on the sheet processing setting, the image information, and the like and outputs the sheet on which the image is formed as deliverables. In the following, a description is provided with regard to each configuration included in the image forming system S and a series of process flows of the image formation.

Sheet Feeding Device

The sheet feeding device301comprises a double feeding detection sensor76, a sheet detection sensor23, an escape tray101, a full-stack detection sensor102, an upper sheet feeder311, a lower sheet feeder312, an upper conveying unit317, a lower conveying unit318, and a merging conveying unit319. The sheet feeding device301also comprises an escape conveying unit333and a conveyance sensor350. An upper sheet feeder311comprises sheet storage11and a suction conveying unit361. The lower part sheet feeder312comprises sheet storage372and a suction conveying unit362. A double feeding detection sensor76consists of a transmitting element6and a receiving element7.

The upper sheet feeder311feeds the sheet stored in the sheet storage11. The lower sheet feeder312feeds the sheet stored in the sheet storage372. The escape tray101is arranged on a top surface of the sheet feeding device301. The double fed sheets (a plurality of overlapped sheets) are discharged from the escape tray101. It means that the sheet which is discharged to the escape tray101is not conveyed to a secondary transfer position (described later). The full-stack detection sensor102detects whether the sheet discharged to the escape tray101is fully loaded or not.

Sheet feeding operation by the sheet storages11and372is started from the suction conveying units361and362. It is noted that, in the present embodiment, a description is provided in case of air sheet feeding control as an example. Thereby, a plurality of fans (not shown) are arranged in each of the suction conveying units361and362. Operation of the fans at the time of the sheet feeding operation is controlled so that air is sent between the sheets from upstream with respect to a conveying direction to the sheets stored in the sheet storages11and372. When the sheet is separated by the air, it is sucked on an endless belt by a fan for sucking a sheet arranged inside the endless belt and then the sheet is fed and conveyed. Details of the sheet feeding and conveying operation by the suction conveying units361and362are described later.

The sheet which is fed from the upper sheet feeder311is conveyed to the merging conveying unit319where it merges with the lower sheet feeder312by the upper conveying unit317. The sheet which is fed from the lower sheet feeder312is conveyed to the merging conveying unit319where it merges with the upper conveying unit317by the lower conveying unit318. Though not shown, a stepping motor for conveyance is provided in each conveying unit. A driving force of the stepping motor provided in each conveying unit is mechanically transmitted so that a conveying roller of each conveying unit is rotated. Thus, the sheet conveyance is being performed.

The transmitting element6and the receiving element7, consisting of the double feeding detection sensor76, are arranged in the merging conveying unit319. A conveyance path of the sheet is provided between the transmitting element6and the receiving element7. The transmitting element6functions as a transmitter for transmitting the ultrasonic signal to the sheet. The receiving element7functions as a receiver for receiving the ultrasonic signal having passed through the sheet. Details of the double feeding detection sensor76are described later.

When receiving sheet feeding request notification from the image forming apparatus300, which is a sheet feeding destination, the sheet feeding device301sequentially feeds and conveys the sheet stored in each of the sheet storages11and372. The sheet feeding device301conveys the sheet to a conveyance sensor350positioned at a delivery portion to the image forming apparatus300. When the conveyance sensor350detects the sheet, the sheet feeding device301notifies the image forming apparatus300of completion of preparation for delivery. The image forming apparatus300receives the notification of the completion of preparation for delivery from the sheet feeding device301and notifies a delivery request. The sheet feeding device301receives the notification of the delivery request and conveys the sheet one by one to the image forming apparatus300from the delivery portion. The sheet which is fed out from the sheet feeding device301is pulled out by the conveying roller of the image forming apparatus300at a time point when a front end of the sheet arrives at a nip of the conveying roller provided uppermost of the sheet conveyance path of the image forming apparatus300and is discharged from the sheet feeding device301. When the sheet feeding device301conveys the number of sheets requested from the image forming apparatus300, the sheet feeding device301ends the sheet feeding operation. When the sheet feeding device301ends the operation after the number of the requested sheets is pulled out by the image forming apparatus300, it is turned into a standby state.

Image Forming Apparatus

The image forming apparatus300comprises an image reference sensor305, a registration control unit306, an image forming unit307, a fixing unit308, a reverse conveying unit309, a flapper310, a toner bottle351, and a laser scanner unit354. The image forming unit307comprises a developing unit352, a photosensitive drum353, and an intermediate transfer belt355. As shown inFIG. 1, the operation unit4through which the user performs operation setting for the image forming system S and the reader scanner303for reading an original image are disposed on an upper part of the image forming apparatus300.

The image forming apparatus300notifies the sheet feeding device301of the sheet feeding request. In addition, the image forming apparatus pulls out the sheet one by one from the sheet feeding device301and sequentially performs the image formation on the sheet. After receiving the sheet from the sheet feeding device301, the image forming apparatus300controls each conveying unit to perform the sheet conveyance.

The flapper310is connected to a driving mechanism (not shown) and moves. The flapper310is positioned so that, when the double feeding detection sensor76detects the double feeding of the sheet, the sheet is conveyed to the escape tray101. The flapper310is positioned so that, when the double feeding detection sensor76does not detect the double feeding of the sheet, the sheet is conveyed to the image forming unit307. It means that, when the double feeding of the sheet is detected, the sheet is discharged to the escape tray101. When the double feeding of the sheet is not detected, the image forming operation based on the image data is performed in the image forming unit307with sheet detection by the image reference sensor305as a starting point. It is noted that, in the present embodiment, a case where the escape conveying unit333for discharging the sheet to the escape tray101is arranged in the image forming apparatus300is illustrated. Not limited to this, for example, the escape conveying unit333may be arranged in the sheet feeding device301.

The image forming apparatus300turns on and performs light control of semiconductor laser in the laser scanner unit354. In addition, the image forming apparatus300controls a scanner motor which controls the rotation of a polygon mirror (not shown). Laser light which is emitted from the laser scanner unit354and is modulated by the image data is reflected by the rotating polygon mirror and scans a surface of the photosensitive drum353. Thereby, a latent image is formed on the photosensitive drum353. The image forming apparatus300supplies toner to the developing unit352from the toner bottle351. The developing unit352develops the latent image on the photosensitive drum353with the toner. Thereby, a toner image is formed on the surface of the photosensitive drum353. The toner image is transferred to the intermediate transfer belt355from the photosensitive drum353. The toner image having transferred to the intermediate transfer belt355is transferred to the sheet. Thereby, the toner image is formed on the sheet.

The registration control unit306is arranged just before the secondary transfer position where the toner image is transferred to the sheet from the intermediate transfer belt355to a conveying direction of the sheet. The registration control unit306performs sheet conveyance control including screw correction to the sheet which is just before the secondary transfer position, fine adjustment of the front end position of the sheet to align with the toner image formed on the intermediate transfer belt355with the front end position of the sheet, and the like. By applying heat and pressure to the sheet after secondary transfer, the fixing unit308melts the toner and fixes the melted toner on the sheet. Thus, the image forming processing on the sheet is ended. The image-formed sheet is conveyed to the reverse conveying unit309when the image formation is continuously performed on its back surface or when reversing of front and back is necessary. When the image formation ends, the image-formed sheet is conveyed to the sheet feeding destination provided on downstream.

The post-processing device304is one example of the sheet feeding destination provided on downstream of the image forming apparatus300. The post-processing device304performs desired post-processing set by the user through the operation unit4(for example, fold, staple, punching, and the like). The post-processing device304discharges the sheet after the post-processing to any of the discharge trays360as the deliverables.

Sheet Feeding Unit

FIG. 2is a configuration diagram of the upper sheet feeder311of the sheet feeding device301. The upper sheet feeder311mainly comprises the sheet storage11, an air loosening unit33, and the suction conveying unit361. It is noted that the lower sheet feeder312has the same configuration with the upper sheet feeder311. The sheet storage11comprises a tray12on which a plurality of sheets are placed, a rear end regulating plate13for regulating an upstream side in the conveying direction of the sheet (sheet rear end), a side end regulating plates14and16for regulating a direction orthogonal to the conveying direction (width direction), and a slide rail15. It is noted that a sheet rear end pressing member17for pressing the sheet rear end is arranged on an upper part of the rear end regulating plate13.

The user pulls out the sheet storage11from the sheet feeding device301, sets the sheet in the sheet storage11and stores the sheet storage11at a predetermined position of the sheet feeding device301. When a sensor (not shown) detects that the sheet storage11is stored at the predetermined position, a driving unit (not shown) starts to raise the tray12in an arrow A direction. Thereafter, when a sensor (not shown) detects that a distance to a suction conveying belt21becomes B, the tray12stops at that position.

The suction conveying unit361comprises a belt driving roller41for driving the suction conveying belt21, a suction duct34for making a negative pressure space for sucking the sheet by the driving of the suction fan36, and a suction shutter37for adjusting applying degree of the negative pressure in the suction duct34. The sheet sucked on the suction conveying belt21is conveyed to a pulling-out roller pair42provided downstream in the conveying direction by the conveying force of the suction conveying belt21.

The air loosening unit33comprises a loosening fan32and a loosening and separating duct31. The loosening and separating duct31has a nozzle for spraying exhaust gas of the loosening fan32on a front end of the sheet as loosening air and separating air. The loosening and separating duct31sprays the loosening air in a direction C inFIG. 2and sprays the separating air in a direction D inFIG. 2.

FIGS. 3A to 3Care explanatory diagrams of a sheet feeding method in the upper sheet feeder311.FIG. 3Ais an explanatory diagram at the start of the air loosening.FIG. 3Bis an explanatory diagram when the sheet is sucked.FIG. 3Cis an explanatory diagram at the start of the conveyance. It is noted that the lower sheet feeder312feeds the sheet in a similar method.

The sheet feeding device301receives a sheet feeding signal in a state in which the tray12stops at a position where a distance between an uppermost sheet35ain the sheet storage11and the suction conveying belt21becomes B (refer toFIG. 2). In response to the reception of the sheet feeding signal, as shown inFIG. 3A, the sheet feeding device301drives the suction fan36of the suction conveying unit361to start air discharge in an arrow F direction. Thus, the negative pressure space is formed in the suction duct34. Moreover, the sheet feeding device301drives the loosening fan32to spray the loosening air in a direction C inFIG. 3A. Further, the sheet feeding device301sprays the separating air in a direction D inFIG. 3Ato start the air loosening.

The sheet feeding device301detects by a sensor (not shown), that, due to the air loosening, the distance between a paper surface position of the uppermost sheet35aand the suction conveying belt21of the suction conveying unit361becomes B′ (FIG. 3A). In response to the detection, as shown inFIG. 3B, the sheet feeding device301opens the suction shutter37disposed in the suction duct34in an arrow G direction by a driving unit (not shown). Thus, inner spaces of the suction duct34divided into two spaces through the suction shutter37become the negative pressure space. As a result, suction air for sucking the uppermost sheet35ais generated in an arrow H direction. The uppermost sheet35ais sucked on the suction conveying belt21in this way.

As shown inFIG. 3C, the sheet feeding device301rotates the belt driving roller41in an arrow J direction in a state in which the uppermost sheet35ais sucked on the suction conveying belt21. Thereby, the uppermost sheet35ais conveyed in an arrow K direction. When the pulling-out roller pair42eventually rotates in an arrow M direction and an arrow P direction, respectively, the uppermost sheet35ais conveyed to the next conveyance path.

Controller

FIG. 4is a block diagram showing a controller by each function unit of the sheet feeding device301. The controller is incorporated in the sheet feeding device301.

A CPU (Central Processing Unit)1functions as a control unit which controls operation of the sheet feeding device301. The CPU1controls operation of a driving circuit which drives various loads such as various motors, fans, and the like of the sheet feeding device301. The operation unit4(DISP) is a setting unit capable of inputting sheet information such as a sheet size, basis weight, a surface property and the like. A memory3is a storage unit for storing the sheet information input through the operation unit4, various data, a PWM (pulse width modulation) value and a target value used for adjusting the fan.

Various sensors such as a sheet storage open/close sensor48, a lower sheet surface detection sensor57, an upper sheet surface detection sensor18, a sheet detection sensor23, and the like are connected to the CPU1. The sheet storage open/close sensor48detects opening/closing state of the sheet storage11. The lower sheet surface detection sensor57and the upper sheet surface detection sensor18detect an upper surface position of the sheet loaded on the tray12. The sheet detection sensor23detects presence/absence of the sheet conveyed along the merging conveying unit319. The CPU1monitors output of the various sensors.

The CPU1receives a rotational frequency signal (FG) of the loosening fan32and the suction fan36and performs PWM control of each fan so that each fan rotates at a target rotational frequency. To this end, a loosening fan driving circuit22and a suction fan driving circuit40, both being drivers, are connected to the CPU1. The loosening fan driving circuit22transmits the PWM signal output from the CPU1to the loosening fan32. Also, the loosening fan driving circuit22supplies power to the loosening fan32. The suction fan driving circuit40transmits the PWM signal output from the CPU1to the suction fan36. Also, the suction fan driving circuit supplies power to the suction fan36.

A suction solenoid driving circuit39is connected to the CPU1. The suction solenoid driving circuit39is a driving circuit of a suction solenoid38which rotary drives to open and close the suction shutter37.

A sheet feeding motor driving circuit46, a pulling-out motor driving circuit47, a lifter motor driving circuit20, a lower part conveying motor driving circuit26, an upper part conveying motor driving circuit43, a merging conveying motor driving circuit50, and an escape conveying motor driving circuit66are connected to the CPU1. The sheet feeding motor driving circuit46is a driving circuit for driving the sheet feeding motor44which rotates the belt driving roller41of the suction conveying unit361. The pulling-out motor driving circuit47is a driving circuit for driving a pulling-out motor45which rotates the pulling-out roller pair42. The lifter motor driving circuit20is a driving circuit for driving a lifter motor19which is a lifter driving unit for elevating/lowering the tray12. The lower unit conveying motor driving circuit26is a driving circuit for driving a lower unit conveying motor10which rotates the conveying roller of the lower conveying unit318. The upper unit conveying motor driving circuit43is a driving circuit for driving an upper unit conveying motor49which rotates the conveying roller of the upper conveying unit317. The merging conveying motor driving circuit50is a driving circuit for driving a merging conveying motor51which rotates the conveying roller of the merging conveying unit319. The escape conveying motor driving circuit66is a driving circuit for driving an escape conveying motor67which rotates the conveying roller of the escape conveying unit333.

A transmitting circuit8and a receiving circuit9of the double feeding detection sensor76are connected to the CPU1. Through the control of the CPU1, the transmitting circuit8generates a transmission signal and transmits the generated transmission signal to the transmitting element6of the double feeding detection sensor76. The receiving circuit9receives an output signal, which is an analog signal, from the receiving element7of the double feeding detection sensor76. The receiving circuit9comprises an amplification circuit (AMP) which amplifies the output signal, a peak hold circuit which holds a peak voltage of the amplified output signal, and an A/D converter which performs A/D conversion of the analog signal which is peak-held. The output signal which is A/D converted in the receiving circuit9is sent to the CPU1. The CPU1determines whether the sheet is double fed or not according to the value corresponding to the output signal and the data such as the sheet information stored in the memory3.

In the sheet feeding device301of the present embodiment, the description has been provided with regard to the configuration example in which the operation unit4and the memory3are directly connected to the CPU1. Not limited to the configuration, the CPU1may, for example, be connected to the operation unit and the memory provided in the image forming apparatus300. Further, instead of the sheet information input through the operation unit4, the CPU1may use the sheet information automatically recognized by a sheet information detecting device provided in the sheet feeding device301.

Double Feeding Detection Sensor

FIG. 5is an explanatory diagram of an arrangement of the transmitting element6and the receiving element7of the double feeding detection sensor76. It is noted that, in the present embodiment, a description is provided assuming that the double feeding detection sensor76consisting of the transmitting element6and the receiving element7is an ultrasonic sensor. In the double feeding detection sensor76, the transmitting element6and the receiving element7are arranged opposite to each other spaced by a distance d so that the transmitting element6is arranged at a lower side and the receiving element7is arranged at an upper side with the conveyance path of the sheet therebetween. Moreover, the transmitting element6and the receiving element7are arranged so that a transmission axis shown by a dotted line is inclined by an angle θ to the conveyance path of the sheet. The transmitting element6transmits the ultrasonic signal to the sheet. The receiving element7receives the ultrasonic signal transmitted from the transmitting element6and passed through the sheet. The receiving element7outputs the output signal which is the analog signal of a voltage value according to strength of the received ultrasonic signal. The conveyance path between the transmitting element6and the receiving element7becomes a detection position of the double feeding detection sensor76.

FIG. 6is an explanatory diagram of the input/output signal of the transmitting circuit8and the receiving circuit9in the double feeding detection sensor76. It is noted that, inFIG. 6, the input/output signal is shown with a vertical axis as a voltage V and a lateral axis as a time (sec).

FIG. 6shows the input/output signal when the sheet which passes through between the transmitting element6and the receiving element7is a plain sheet. The plain sheet means a sheet on a surface of which no special processing such as coating and the like is applied. A waveform (a) represents the input signal from the CPU1to the transmitting circuit8. It shows an input of a burst wave of a predetermined voltage and a predetermined frequency by a predetermined number of pulses (here, 8 pulses) per one detection operation. A waveform (b) represents the output signal of the peak hold circuit of the receiving circuit9when the number of the sheets to be conveyed is one. A waveform (c) represents the output signal of the peak hold circuit of the receiving circuit9when two sheets are double fed.

An output signal voltage of the peak hold circuit of the receiving circuit9after a lapse of predetermined time t second from the pulse input to the transmitting circuit8becomes Vb V (waveform (b)) when the number of the sheets is one. Moreover, in case of the double feeding, the output signal voltage becomes Vc V (waveform (c)) which is approximately equal to 0 V. Comparing a case where the number of the sheet is one (non-double feeding) with a case where the sheet is double fed, a difference between the output signal voltages is very large. It means that, from a comparison result comparing these output signal voltages with a predetermined setting value (threshold value), it is possible to easily distinguish when the number of the sheets is one from when the sheet is double fed.

FIGS. 7A to 7Care explanatory diagrams of received data sent from the receiving element7of the double feeding detection sensor76to the CPU1. The received data is data obtained by A/D converting the output signal voltage of the peak hold circuit (Vb, Vc) in the receiving circuit9after a lapse of the predetermined time t second from the input of the burst wave described inFIG. 6to the transmitting circuit8. InFIGS. 7A to 7C, a description is provided with regard to the received data when the sheet which passes through between the transmitting element6and the receiving element7is a coated thin paper having a coated surface property and basis weight of which is less than a predetermined value.

FIGS. 7A and 7Bshow the received data of two types of sheets with different tendency when the sheets are double fed (a state in which a plurality of sheets are overlappingly conveyed with no deviation) and operation values obtained from the received data. At the time of feeding the sheet, the sheet feeding device301inputs the burst wave described inFIG. 6to the transmitting element6of the double feeding detection sensor76six times and receives six ultrasonic signals by the receiving element7. The receiving element7transmits the output signal corresponding to the received six ultrasonic signals to the receiving circuit9. The CPU1obtains six received data.

The burst wave is input to the transmitting element6six times so that the ultrasonic wave is transmitted at intervals of 20 milliseconds from a position 40 mm from the front end of the conveying direction of the sheet along an approximately center unit in a sheet width direction which is orthogonal to the conveying direction of the sheet. The six received data for the input of six burst waves are shown as “data1to data6” inFIG. 7A. InFIG. 7A, the received data of a first sheet to a fifth sheet of the sheets to be fed are shown. Moreover, a maximum value (Max), a minimum value (Min), an average value (Ave), and a difference between the maximum value and the minimum value (Max−Min) of the six received data (data1to data6) are shown for each sheet. The difference between the maximum value and the minimum value (Max−Min) is one of the parameters indicating variation in the received data. The received data of the first sheet which is double fed inFIG. 7Ais “1”, “7”, “5”, “3”, “9”, and “1” in order from the data1, in which the maximum value is “9”, the minimum value is “1”, the average value is “4.3”, and the difference between the maximum value and the minimum value is “8”. The received data of the first sheet which is double fed inFIG. 7Bis “1”, “7”, “14”, “10”, “9”, and “16” in order from the data1, in which the maximum value is “16”, the minimum value is “1”, the average value is “9.5”, and the difference between the maximum value and the minimum value is “15”. The received data is obtained by amplifying the output signal of the receiving element7by the receiving circuit9and A/D converting a peak-hold voltage value. The peak-hold voltage value of the received data becomes a value obtained by multiplying the received data described inFIGS. 7A to 7Cby 20 mV.

FIG. 7Cshows the received data when the sheet is not double fed and the operation value obtained from the received data. Similar toFIGS. 7A and 7B, inFIG. 7C, the six received data obtained by feeding one sheet is represented as “data1to data6”. Further, the maximum value (Max), the minimum value (Min), the average value (Ave), and the difference between the maximum value and the minimum value (Max−Min) of the six received data are shown for each sheet. For example, the received data of the first sheet is “21”, “20”, “20”, “20”, “20”, and “20” in order from the data1, in which the maximum value is “21”, the minimum value is “20”, the average value is “20.2”, and the difference between the maximum value and the minimum value is “1”.

InFIG. 7A, in the received data of the five conveyed sheets of the first to fifth sheets, the average value is equal to or less than 5. InFIG. 7B, in the received data of the five conveyed sheets which are double fed of the first to fifth sheets, the average value is equal to or more than 9, and the difference between the maximum value and the minimum value is within a range of “9 to 15”. InFIG. 7C, in the received data of the five conveyed sheets of the first to fifth sheets, the average value is equal to or more than 19, and the difference between the maximum value and the minimum value is within a range of “1 to 3”. Thus, the average value of the received data becomes smaller when the sheet is double fed than when the sheet is not double fed. The sheet used inFIG. 7Bhas the larger average value and the larger variation in the received data than the sheet used inFIG. 7A. According toFIG. 7C, the average value of the received data becomes larger and the variation becomes smaller when the sheet is not double fed than when the sheet is double fed.

The CPU1sets the threshold value for determining the double feeding to “8” for example to the average value of the received data (Ave). Further, the CPU1sets the threshold value for determining the double feeding to “5” for example to the difference between the maximum value and the minimum value (Max−Min). This enables the CPU1to detect the double feeding of the sheet when the average value of the received data is equal to or less than the threshold value “8” or when the difference between the maximum value and the minimum value is equal to or more than the threshold value “5”. In a case other than this condition, the CPU1determines that the sheet is not double fed. Thus, the double feeding detection of the coated thin paper can surely be performed.

FIGS. 8A to 8Dare explanatory diagrams of received data sent from the receiving element7of the double feeding detection sensor76to the CPU1by a particular type of sheet which is different from those inFIGS. 7A to 7C. The received data is data obtained by A/D converting the output signal voltage of the peak hold circuit (Vb, Vc) in the receiving circuit9after a lapse of the predetermined time t second from the input of the burst wave described inFIG. 6to the transmitting circuit8. InFIGS. 8A to 8D, a description is provided with regard to the received data when the sheet which passes through between the transmitting element6and the receiving element7is the Japanese paper with non-uniform fiber orientation and density depending on a unit on the sheet.

FIG. 8Arepresents the received data when the sheet is double fed and the operation values obtained from the received data. Similar toFIGS. 7A to 7C, at the time of feeding the sheet, the sheet feeding device301inputs the burst wave to the transmitting element6of the double feeding detection sensor76six times and receives six ultrasonic signals by the receiving element7. The receiving element7transmits the output signal corresponding to the received ultrasonic signals of six inputs to the receiving circuit9. The CPU1obtains received data of six inputs.

FIG. 8Arepresents the received data of the first to fifth sheets to be fed. Further, the maximum value (Max), the minimum value (Min), the average value (Ave), and the difference between the maximum value and the minimum value (Max−Min) of the received data of six inputs (data1to data6) are shown for each sheet. The received data of the first sheet which is double fed inFIG. 8Ais “1”, “5”, “0”, “3”, “1”, and “0” in order from the data1, in which the maximum value is “5”, the minimum value is “0”, the average value is “1.7”, and the difference between the maximum value and the minimum value is “5”. The received data is obtained by amplifying the output signal of the receiving element7by the receiving circuit9and A/D converting the peak-hold voltage value. The peak-hold voltage value of the received data becomes a value obtained by multiplying the received data described inFIGS. 8A to 8Dby 20 mV.

FIGS. 8B, 8C, and 8Drepresent the received data when the sheet is not double fed and the operation values obtained from the received data. InFIGS. 8B, 8C, and8D, the six received data obtained by feeding one sheet is represented as “data1to data6”. Further, the maximum value (Max), the minimum value (Min), the average value (Ave), and the difference between the maximum value and the minimum value (Max−Min) of the six received data (data1to data6) are shown for each sheet. Similar toFIG. 8A,FIGS. 8B, 8C, and 8Drepresent the received data of the five conveyed sheets and the operation values.

The received data of the first sheet inFIG. 8Bis “15”, “5”, “7”, “3”, “13”, and “10” in order from the data1, in which the maximum value is “15”, the minimum value is “3”, the average value is “8.8”, and the difference between the maximum value and the minimum value is “12”. The received data of the first sheet inFIG. 8Cis “32”, “32”, “33”, “32”, “33”, and “32” in order from the data1, in which the maximum value is “33”, the minimum value is “32”, the average value is “32.3”, and the difference between the maximum value and the minimum value is “1”. The received data of the first sheet inFIG. 8Dis “32”, “32”, “18”, “23”, “19”, and “32” in order from the data1, in which the maximum value is “32”, the minimum value is “18”, the average value is “26”, and the difference between the maximum value and the minimum value is “14”.

InFIG. 8A, in the received data of the five conveyed sheets of the first to fifth sheets, the average value is less than “3”, and the difference between the maximum value and the minimum value is within a range of “1 to 5”. InFIG. 8B, in the received data of the five conveyed sheets which are not double fed of the first to fifth sheets, the average value is equal to or more than 5 but less than 9 and the difference between the maximum value and the minimum value is within a range of “8 to 13”. InFIG. 8C, in the received data of the five conveyed sheets which are not double fed of the first to fifth sheets, the average value is equal to or more than 30 but less than 33 and the difference between the maximum value and the minimum value is within a range of “1 to 3”. InFIG. 8D, in the received data of the five conveyed sheets which are not double fed of the first to fifth sheets, the average value is equal to or more than 26 but less than 31 and the difference between the maximum value and the minimum value is within a range of “9 to 16”. Thus, the average value of the received data becomes smaller and the variation in the received data also becomes smaller when the sheet is double fed than when the sheet is not double fed. The sheet used inFIG. 8Bhas the smaller average value of the received data and the larger variation in the received data than the sheets used inFIGS. 8C and 8Dwhen the sheet is not double fed. The sheet used inFIG. 8Chas the larger average value of the received data and the smaller variation in the received data than the sheets used inFIGS. 8B and 8Dwhen the sheet is not double fed. The sheet used in FIG.8D has the larger average value of the received data and the larger variation in the received data than the sheets used inFIG. 8Bwhen the sheet is not double fed.

The CPU1sets the threshold value for determining the double feeding to “15” for example to the average value of the received data (Ave). Further, the CPU1sets the threshold value for determining the double feeding to “6” for example to the difference between the maximum value and the minimum value (Max−Min). This enables the CPU1to detect the double feeding of the sheet when the average value of the received data is equal to or less than the threshold value “15” or when the difference between the maximum value and the minimum value is equal to or less than the threshold value “6”. In a case other than this condition, the CPU1determines that the sheet is not double fed. This enables to surely perform the double feeding detection of the Japanese paper. Unlike the contents as described inFIGS. 7Ato7C, when the sheet is the Japanese paper, even when the average value of the received data is equal to or less than the reference value, when the variation in the received data exceeds a predetermined value, it is determined that it is not the double feeding.

Sheet Feeding Processing

FIGS. 9, 10, and 11are flowcharts representing the sheet feeding processing performed by the sheet feeding device301. In this flowchart, a description is provided with regard to an example where the sheet is fed from the upper sheet feeder311. Similar processing is performed when the sheet is fed from the lower sheet feeder312. In response to the reception of the sheet feeding signal from the image forming apparatus300, the sheet feeding device301executes the processing.

According to the sheet feeding signal, the CPU1obtains the sheet information of the sheet loaded in the sheet storage11which performs the sheet feeding (Step S901). The CPU1obtains the sheet information showing the type of the sheet which is previously input from the user through the operation unit4with reference to the memory3. The sheet information includes the information regarding the type, the surface property and the basis weight of the sheet to be fed. The sheet information enables the CPU1to determine whether the sheet to be fed is the Japanese paper or not.

If it is determined that the type of the sheet to be fed is the Japanese paper (Step S902: Y), the CPU1starts the sheet feeding from the sheet storage11(Step S903). After the start of the sheet feeding, the CPU1monitors arrival of the front end of the sheet fed to the sheet detection sensor23by the sheet detection sensor23(Step S904). When the sheet detection sensor23detects the front end of the sheet fed (Step S904: Y), the CPU1stands by for a predetermined time until the sheet conveyed on the conveyance path arrives at the detecting position of the double feeding detection sensor76(Step S905).

When the sheet arrives at the detection position of the double feeding detection sensor76, the CPU1causes the transmitting element6to transmit the ultrasonic signal (Step S906). By the transmission of the transmitting element6, the CPU1obtains the received data corresponding to the output signal which is output from the receiving element7(Step S907). The CPU1stands by for a predetermined time after obtaining the received data (Step S908). The CPU1repeatedly performs the transmission of the ultrasonic signal to the sheet and the obtaining of the received data until it reaches a predetermined number of times required to determine a sheet status (Step S909: No). In the examples ofFIGS. 7A to 7CandFIGS. 8A to 8D, the CPU1repeatedly performs the transmission of the ultrasonic signal and the reception of the received data six times. During this time, the sheet is being conveyed. Thus, the CPU1obtains the received data of a plurality of units in a conveying direction of the sheet to be conveyed.

After performing the transmission of the ultrasonic signal and the obtaining of the received data a predetermined number of times (Step S909: Y), the CPU1compares the average value of the obtained predetermined number of received data with a predetermined threshold value X (Step S910). In the examples ofFIGS. 8A to 8D, the threshold value X for performing the double feeding determination of the sheet is set to “15”.

If the average value is equal to or less than the threshold value X (Step S910: Y), the CPU1calculates the difference between the maximum value and the minimum value of the predetermined number of received data obtained (Max−Min) (Step S911). The difference between the maximum value and the minimum value of the received data (Max−Min) represents the variation in the received data or the variation in the output signal which is output from the receiving element7. The CPU1compares the calculated variation with a predetermined threshold value Y (Step S912). In the examples ofFIGS. 8A to 8D, the threshold value Y is set to “6” which is a value for performing the double feeding determination of the sheet. If the variation is equal to or less than the threshold value Y (Step S912: Y), the CPU1determines that the sheet which is being conveyed is double fed (Step S913). In this case, the CPU1selects the conveyance path so that the sheet is discharged to the escape tray101. Thus, the sheet which is determined as the double feeding is discharged to the escape tray101(Step S914).

If the variation is larger than the threshold value Y (Step S912: N), the CPU1determines that the sheet which is being conveyed is not double fed (Step S915). In this case, the CPU1selects the conveyance path so that the sheet which is being conveyed is conveyed to the image forming unit307of the image forming apparatus300. Thus, the sheet which is being conveyed is conveyed to the image forming unit307(Step S916).

If the average value is larger than the threshold value X (Step S910: N), the CPU1determines that the sheet which is being conveyed is not double fed (Step S917). In this case, the CPU1selects the conveyance path so that the sheet which is being conveyed is conveyed to the image forming unit307of the image forming apparatus300. Thus, the sheet which is being conveyed is conveyed to the image forming unit307(Step S918).

If it is determined that the type of the sheet to be fed is not the Japanese paper (Step S902: N), the CPU1determines whether the sheet to be fed is the coated thin paper which has the coated surface property and the basis weight of which is less than a predetermined value based on the sheet information obtained (Step S919).

If it is determined that the type of the sheet to be fed is the coated thin paper (Step S919: Y), the CPU1starts the sheet feeding from the sheet storage11(Step S920). After starting the sheet feeding, the CPU1monitors the arrival of the sheet fed to the sheet detection sensor23by the sheet detection sensor23(Step S921). When the sheet detection sensor23detects the front end of the sheet fed (Step S921: Y), the CPU1stands by for a predetermined time until the sheet conveyed on the conveyance path arrives at the detecting position of the double feeding detection sensor76(Step S922).

When the sheet arrives at the detection position of the double feeding detection sensor76, the CPU1causes the transmitting element6to transmit the ultrasonic signals (Step S923). By the transmission of the transmitting element6, the CPU1obtains the received data corresponding to the output signal output from the receiving element7(Step S924). The CPU1stands by for a predetermined time after obtaining the received data (Step S925). The CPU1repeatedly performs the transmission of the ultrasonic signal to the sheet and the obtaining of the received data until it reaches a predetermined number of times required to determine a sheet status (Step S926: N). In the examples ofFIGS. 7A to 7CandFIGS. 8A to 8D, the CPU1repeatedly performs the transmission of the ultrasonic signal and the reception of the received data six times. During this time, the sheet is being conveyed. Thus, the CPU1obtains the received data of a plurality of units in a conveying direction of the sheet to be conveyed.

After performing the transmission of the ultrasonic signal and the obtaining of the received data a predetermined number of times (Step S926: Y), the CPU1compares the average value of the obtained predetermined number of received data with a predetermined threshold value Q (Step S927). For example, in the examples ofFIGS. 7A to 7C, the threshold value Q is “8”, which becomes a reference value for determining whether the sheet is double fed or not.

If the average value is equal to or less than the threshold value Q (Step S927: Y), the CPU1determines that the sheet is double fed (Step S928). In this case, the CPU1selects the conveyance path so that the sheet is discharged to the escape tray101. Thus, the sheet which is being conveyed is discharged to the escape tray101(Step S929).

If the average value is larger than the threshold value Q (Step S927: N), the CPU1calculates the variation which is the difference between the maximum value and the minimum value of the predetermined number of received data obtained (Max−Min) (Step S930). The CPU1compares the calculated variation with a predetermined threshold value R (Step S931). In the examples ofFIGS. 7A to 7C, the threshold value R for performing the double feeding determination of the sheet is set to “5”. If the variation is equal to or more than the threshold value R (Step S931: Y), the CPU1determines that the sheet which is being conveyed is double fed (Step S932). In this case, the CPU1selects the conveyance path so that the sheet is discharged to the escape tray101. Thereby, the sheet which is being conveyed is discharged to the escape tray101(Step S933).

If the variation is smaller than the threshold value R (Step S931: N), the CPU1determines that the sheet which is being conveyed is not double fed (Step S934). In this case, the CPU1selects the conveyance path so that the sheet which is being conveyed is conveyed to the image forming unit307of the image forming apparatus300. Thus, the sheet which is being conveyed is conveyed to the image forming unit307(Step S935).

If it is determined that the type of the sheet to be fed is not the coated thin paper (Step S919: N), the CPU1starts the sheet feeding from the sheet storage11(Step S936). After starting the sheet feeding, the CPU1monitors the arrival of the front end of the sheet fed to the sheet detection sensor23by the sheet detection sensor23(Step S937). When the sheet detection sensor23detects the front end of the sheet fed (Step S937: Y), the CPU1stands by for a predetermined time until the sheet conveyed on the conveyance path arrives at the detecting position of the double feeding detection sensor76(Step S938).

When the sheet arrives at the detection position of the double feeding detection sensor76, the CPU1causes the transmitting element6to transmit the ultrasonic signal (Step S939). By the transmission of the transmitting element6, the CPU1obtains the received data corresponding to the output signal output from the receiving element7(Step S940). The CPU1stands by for a predetermined time after obtaining the received data (Step S941). The CPU1repeatedly performs the transmission of the ultrasonic signal to the sheet and the obtaining of the received data until it reaches a predetermined number of times required to determine a sheet status (Step S942: N). In the examples ofFIGS. 7A to 7CandFIGS. 8A to 8D, the CPU1repeatedly performs the transmission of the ultrasonic signal and the reception of the received data six times. During this time, the sheet is being conveyed. Thus, the CPU1obtains the received data of a plurality of units in a conveying direction of the sheet to be conveyed.

After performing the transmission of the ultrasonic signal and the obtaining of the received data predetermined number of times (Step S942: Y), the CPU1compares the average value of the obtained predetermined number of received data with a predetermined threshold value Z (Step S943). For example, the threshold value Z is set to a value corresponding to a voltage between Vb and Vc inFIG. 6.

If the average value is equal to or less than the threshold value Z (Step S943: Y), the CPU1determines that the sheet is double fed (Step S944). In this case, the CPU1selects the conveyance path so that the sheet is discharged to the escape tray101. Thus, the sheet which is being conveyed is discharged to the escape tray101(Step S945).

If the average value is larger than the threshold value Z (Step S943: N), the CPU1determines that the sheet which is being conveyed is not double fed (Step S946). In this case, the CPU1selects the conveyance path so that the sheet which is being conveyed is conveyed to the image forming unit307of the image forming apparatus300. Thus, the sheet which is being conveyed is conveyed to the image forming unit307(Step S947).

Through the above mentioned processing, it is determined whether the sheet is double fed or not. When the sheet is double fed, the sheet is not fed to the image forming apparatus300. Instead, the sheet is discharged. Even when the type of the sheet such as the Japanese paper with different density and fiber orientation depending on a unit on the sheet and with difficulty in determining the double feeding is fed, by performing the double feeding determination based on the average value of the received data and the variation in the received data, it is possible to suppress possibility of wrongly detecting the double feeding.

In the present embodiment, when the average value of the received data is equal to or less than the reference value (threshold value X), by comparing the variation in the received data (Max−Mix) with the set value (threshold value Y), the double feeding of the Japanese paper is determined. This determination method suppresses the possibility to wrongly detect the double feeding of the Japanese paper. It means that, when conveying one Japanese paper, the possibility of determining the conveyance as the double feeding is suppressed. Moreover, it is possible to surely determine the double feeding for a particular type of sheet (Japanese paper).

It is noted that, through the above processing, the received data is obtained at a plurality of units of the sheet being conveyed and the difference between the maximum value and the minimum value of the received data is used as the variation in the received data; however, a variance value, a standard deviation, and the like may be used instead for the variation. Further, the average value of the receive data is compared with the threshold values X, Q, Z at a plurality of units of the sheet being conveyed. However, by using a predetermined value such as the maximum value and the minimum value of the received data other than the average value, a similar effect can be obtained through the similar processing. The sheet feeding device301may be integrated in the image forming apparatus300.

As mentioned, in the present embodiment, the double feeding determination is performed according to a predetermined value and variation in a plurality of output signals. Thereby, even with the sheet with the non-uniform fiber orientation and density such as the Japanese paper, it becomes possible to accurately detect the double feeding.

Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that includes one or more circuits (e.g., application specific integrated circuit (ASIC) or SOC (system on a chip)) for performing the functions of one or more of the above-described embodiment(s).

This application claims the benefit of Japanese Patent Application No. 2016-242410, filed Dec. 14, 2016 which is hereby incorporated by reference herein in its entirety.