JP2009035365A - Double feeding detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the occurrence of double feeding even in the case of conveying various kinds of paper sheets. <P>SOLUTION: In a paper supply device 10, an optical sensor 22 irradiates a conveyed paper sheet with the light and detects the quantity of the light transmitted through the paper sheet. An electric control section 28 computes the standard transmitted light quantity L<SB>THR</SB>provided with a standard margin in a direction for reducing a value relative to the average transmitted light quantity L<SB>AVE</SB>so that, as the average transmitted light quantity L<SB>AVE</SB>detected in a paper sheet conveyed in a preset mode is larger, a margin rate as a value obtained by dividing the standard margin with the reduced light quantity as a value, which is obtained by subtracting the average transmitted light quantity L<SB>AVE</SB>from the quantity of the light irradiated to the conveyed paper sheet, becomes smaller. The electric control section 28 determines the occurrence of double feeding when the average transmitted light quantity L<SB>AVE</SB>detected in the paper sheet conveyed in a continuous paper supply mode is smaller than the computed standard transmitted light quantity L<SB>THR</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a double feed detection device, and more particularly, to a double feed detection device that detects double feed of a sheet conveyed using an optical sensor.

A multifeed detection device using an optical sensor is known. In such a double feed detection device, the occurrence of double feed is detected by utilizing the fact that the amount of light transmitted through the paper decreases when the paper is double fed. At this time, for example, double feed detection that detects double feed by comparing the transmitted light amount of the second and subsequent sheets with the threshold value based on the value calculated based on the transmitted light amount of the first first sheet. A method has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 56-82989

  In recent years, there has been an increasing need to convey a wide variety of sheets in a sheet feeding device. However, for example, when a thin sheet or a sheet with a printed color is transported, the transmitted light amount of the sheet is large, so that the transmitted light amount is not greatly reduced even if double feeding occurs. In order to accurately detect the occurrence of double feed even for such a sheet, it is necessary to appropriately set a reference value of the amount of transmitted light that is a determination criterion for the occurrence of double feed.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to accurately detect the occurrence of double feeding even when conveying a wide variety of sheets.

  In order to solve the above problems, a multifeed detection device according to an aspect of the present invention is configured to detect an amount of transmitted light transmitted through a sheet by irradiating the conveyed sheet with light, and to determine the occurrence of multifeed. A reference value calculation unit that calculates a reference transmitted light amount in which a reference margin is provided in a direction in which the value is lower than the first transmitted light amount that is detected in the conveyed paper in order to obtain a used reference transmitted light amount; A double feed determining unit that compares the detected transmitted light amount of the paper with the calculated reference transmitted light amount to determine whether or not a double feed has occurred on the conveyed paper; The reference value calculation unit has a margin rate that is a value obtained by dividing the reference margin by a reduced light amount that is a value obtained by subtracting the first transmitted light amount from the irradiated light amount of the light irradiated on the conveyed paper as the first transmitted light amount increases. The reference transmitted light amount is calculated so that becomes smaller.

  As a result of earnest research and development by the inventor, when the reference transmitted light amount is calculated so that the margin ratio decreases as the first transmitted light amount increases, for example, when a thin paper or a paper with a thin printed color is conveyed It has also been found that there are cases where double feed can be detected accurately. Therefore, according to this aspect, it is possible to accurately detect the occurrence of double feeding even when conveying a wide variety of types of paper.

  The reference value calculation unit may calculate the reference transmitted light amount so that the margin rate decreases as the first transmitted light amount increases by performing exponential calculation or logarithmic calculation using the first transmitted light amount. According to this aspect, by performing exponential calculation or logarithmic calculation, the reference transmitted light amount can be easily calculated such that the larger the first transmitted light amount is, the smaller the margin rate is. In this case, the reference value calculation unit may calculate the reference transmitted light amount by subtracting a value obtained by raising the reduced light amount by a predetermined index from the irradiation light amount.

  The reference value calculation unit may calculate the reference transmitted light amount by a calculation method in which the margin rate decreases as the first transmitted light amount increases, when the detected transmitted light amount of the sheet is greater than a predetermined threshold.

  Thin paper with a large amount of transmitted light is generally more difficult to detect double feed than plain paper. According to this aspect, it is possible to set the reference transmitted light amount more accurately with respect to the type of paper for which it is difficult to detect the double feed.

  The reference value calculation unit may calculate the reference transmitted light amount by a calculation method in which the margin ratio is constant when the detected transmitted light amount of the sheet is smaller than a predetermined threshold value.

  According to this aspect, the reference transmitted light amount can be set by performing a simple calculation for a type of paper that is easily detected for double feeding. For this reason, it is possible to suppress the calculation of the reference transmitted light amount from becoming complicated.

  When the detected transmitted light amount of the sheet is smaller than a predetermined threshold, the reference value calculation unit uses a calculation method in which the reference transmitted light amount is larger than that calculated by a calculation method in which the margin rate decreases as the transmitted light amount increases. The reference transmitted light amount may be calculated.

  As a result of earnest research and development by the inventor, when the detected transmitted light amount of the paper is smaller than a predetermined threshold, the calculation of the reference transmitted light amount is performed by using such a calculation method, thereby accurately detecting double feed. It turns out that you can. Therefore, according to this aspect, it is possible to suppress a decrease in detection accuracy of double feeding of paper when the detected amount of transmitted light of the paper is smaller than a predetermined threshold.

  According to the present invention, it is possible to accurately detect the occurrence of double feeding even when conveying a wide variety of sheets.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is an overall configuration diagram schematically illustrating a sheet feeding device 10 according to the first embodiment. The sheet feeding device 10 includes a sheet feeding mechanism 12, an optical sensor 22, an electronic control unit 28, and a control panel 30.

  The paper feed mechanism 12 is provided in the upper right part of the apparatus in a paper storage unit for storing stacked paper. The paper storage unit is provided with a paper feed table (not shown), on which papers stacked on the paper feed table are placed. The paper feed table is configured to be movable up and down. A paper height sensor (not shown) is provided at the upper part of the paper storage unit, and the elevation of the paper feed table is controlled so that the uppermost paper of the stacked paper is positioned at a predetermined height. . The paper feeding mechanism 12 is disposed slightly above the uppermost paper of the stacked paper.

  The paper feed mechanism 12 includes an air paper feed mechanism 14 and a pair of transport rollers 16. The air sheet feeding mechanism 14 has a plurality of sheet feeding belts and two rollers. Each of the plurality of paper feeding belts has the same width and the same circumferential length, and is mounted on the outer circumference of the two rollers so as to be arranged at equal intervals in the axial direction. The paper feed mechanism 12 is disposed so that the axial direction of the rollers is directed in the front-rear direction of the apparatus and the two rollers are horizontally aligned in the left-right direction. One of the rollers is driven by the transport motor 20.

  The air feeding mechanism 14 is also provided with an air suction mechanism. The air suction mechanism has a fan, and when the fan operates, an air flow for sucking air from the lower surface of the paper feeding belt is formed. The air flow passage is provided with a lid, and this lid closes and opens the opening provided in the air flow passage in response to the operation and stoppage of the sheet feeding solenoid 18.

  When the paper feed solenoid 18 is actuated, the opening provided in the air flow passage is closed to form a strong air flow that sucks air from the lower surface of the paper feed belt, and the uppermost paper of the stacked paper is fed. Adsorbed to the lower surface of the paper belt. The sheet adsorbed on the lower surface of the sheet feeding belt is sent out in the right direction of the apparatus as the sheet feeding belt is driven. The pair of transport rollers 16 are arranged in the vertical direction on the downstream side of the air feeding mechanism 14 in the paper transport direction (hereinafter referred to as “downstream side”). One of the pair of transport rollers 16 is also driven by the transport motor 20. The sheet sent out by the air feeding mechanism 14 is sandwiched by a pair of transport rollers 16 and further transported in the right direction of the apparatus.

  When the operation of the paper feed solenoid 18 is stopped, the opening provided in the air flow passage is opened so that the air flow for sucking air from the lower surface of the paper feed belt cannot adsorb the paper to the lower surface of the paper feed belt. Weakened. For this reason, when the operation of the paper feed solenoid 18 is stopped, the feeding of the uppermost paper of the stacked paper is stopped. Instead of the air feeding mechanism 14, a so-called friction type feeding mechanism that feeds the uppermost sheet of the stacked sheets by the frictional force of the roller surface may be employed.

  An optical sensor 22 is provided between the air feeding mechanism 14 and the transport roller 16. The optical sensor 22 includes a light emitting element 24 and a light receiving element 26. The light emitting element 24 is disposed above the paper conveyance path between the air feeding mechanism 14 and the conveyance roller 16 and irradiates light by infrared rays toward the paper conveyance path. The light receiving element 26 is disposed below the paper conveyance path between the air feeding mechanism 14 and the conveyance roller 16, receives light emitted by the light emitting element 24, and outputs a signal corresponding to the intensity of the received light. To do.

  The paper feed solenoid 18, the transport motor 20, and the optical sensor 22 are connected to the electronic control unit 28. The electronic control unit 28 includes a CPU that executes various arithmetic processes, a ROM that stores various control programs, a RAM that is used as a work area for data storage and program execution, and the like. The electronic control unit 28 controls the feeding of the uppermost sheet of the stacked sheets by switching the supply and stop of power supply to the sheet feeding solenoid 18 to turn the sheet feeding solenoid 18 on and off. The electronic control unit 28 also controls the operation of the transport motor 20 by supplying a drive signal to the paper feed mechanism 12 and controls the drive of the paper feed belt of the air paper feed mechanism 14 and the pair of transport rollers 16. . At this time, the electronic control unit 28 receives a pulse signal indicating the rotation speed from the transport motor 20. Further, the electronic control unit 28 controls on / off of the light emitting element 24, further receives a signal from the light receiving element 26, and is conveyed with the amount of light irradiated by the light emitting element 24 using the received signal. The amount of light transmitted through the paper to be detected is detected. A control panel 30 is also connected to the electronic control unit 28.

  FIG. 2 is a functional block diagram of the sheet feeding device 10 according to the first embodiment. In FIG. 2, the electronic control unit 28 depicts functional blocks realized by cooperation of hardware such as CPU, ROM, and RAM, and software. Therefore, these functional blocks can be realized in various forms by a combination of hardware and software.

  The electronic control unit 28 includes a conveyance control unit 40, a reference value calculation unit 42, a double feed determination unit 44, a display control unit 46, and a storage unit 48. The transport control unit 40 controls the paper feed from the stacked paper by controlling the on / off of the paper feed solenoid 18 and the operation of the transport motor 20. The reference value calculation unit 42 calculates a reference transmitted light amount used for determining the occurrence of double feed. The multi-feed determining unit 44 determines whether or not a multi-feed in which a plurality of sheets are overlapped on the transported sheet is generated. In this way, the optical sensor 22 and the electronic control unit 28 function as a double feed detection device that determines whether or not a double feed has occurred in the conveyed paper. The display control unit 46 displays information on the display 32 provided in the control panel 30. The storage unit 48 is configured by a storage device such as a hard disk or a flash memory that retains stored contents even when power supply is stopped.

  FIG. 3 is a flowchart illustrating a procedure for setting the reference transmitted light amount in the sheet feeding device 10 according to the first embodiment. The display 32 of the control panel 30 is configured by an input touch panel. The user can select a preset mode by performing an input operation on the display 32. In the preset mode, double feed is not detected, but is used to detect double feed.

When the user presses the start button with the preset mode selected (S10), the paper feed mechanism 12 operates the air paper feed mechanism 14 and the transport roller 16 to remove the uppermost paper from the stacked paper. The paper feeding process for feeding is started (S12). The optical sensor 22 first detects the amount of light L _NOT emitted by the light emitting element 24 by detecting the amount of light before the paper is sent out. Next, the optical sensor 22 detects the transmitted light amount of the conveyed paper, and the reference value calculation unit 42 performs the transmitted light amount sampling process using the detection result by the optical sensor 22 (S14).

  In the transmitted light amount sampling process, the reference value calculation unit 42 first uses the detection result of the optical sensor 22 to determine whether, for example, the light amount received by the light receiving element 26 has decreased by a predetermined amount from the light amount irradiated by the light emitting element 24. By determining, it is determined whether or not the leading edge of the sheet has passed the detection location of the optical sensor 22. For this reason, the optical sensor 22 also functions as a paper transport sensor that detects the leading edge of the paper being transported.

  When it is determined that the leading edge of the paper has passed the detection location of the optical sensor 22, the reference value calculation unit 42 first receives a pulse signal from the transport motor 20 after the leading edge of the paper has passed the detection location of the optical sensor 22. Set the sampling time as the sampling reference time. Next, the reference value calculation unit 42 uses the pulse signal at the sampling reference as the first pulse signal, and receives the third pulse signal until receiving the fourth pulse signal. The transmitted light amount of the paper detected by the optical sensor 22 is acquired five times at intervals as a sample value. Further, the reference value calculation unit 42 transmits the amount of light transmitted through the paper detected by the optical sensor 22 five times at equal time intervals even after receiving the fourth pulse signal until receiving the fifth pulse signal. Is obtained as a sample value.

The reference value calculation unit 42 calculates, as the average transmitted light amount L _AVE , eight average values excluding the maximum value and the minimum value among the ten sample values thus obtained (S16). The reference value calculator 42 determines whether the calculated average transmitted light amount L _AVE is equal to or greater than the first threshold L ₁ (S18). The first threshold value L _1, the sheet in which the amount of transmitted light becomes higher value as a value that is necessary to calculate the high standards transmitted light amount accurate, those stored like in advance in the storage unit 48. When the average transmitted light amount L _AVE is equal to or larger than the first threshold L ₁ (Y in S18), the reference value light calculating unit 42 is required to set a highly accurate reference transmitted light amount because the conveyed paper is thin. First calculation processing for calculating a highly accurate reference transmitted light amount is performed (S20).

As a result of repeated verification by experiments by the inventor, the margin ratio is a value obtained by dividing the reference margin by the reduced light amount that is a value obtained by subtracting the average transmitted light amount L _AVE from the irradiation light amount of the light irradiated on the conveyed paper. It has been found that by calculating the reference transmitted light amount L _THR so that the margin rate decreases as the average transmitted light amount L _AVE increases, it is possible to accurately determine even a thin sheet having a large transmitted light amount. Specifically, in the first calculation process, the reference value calculation unit 42 calculates the reference transmitted light amount L _THR using the following equation, where the irradiation light amount is L _NOT .

上記の式は、以下のように変形することができる。

The above equation can be modified as follows.

このように、基準値演算部４２は、照射光量Ｌ_ＮＯＴから平均透過光量Ｌ_ＡＶＥを引いた値である減少光量を１．１という指数で累乗した値を照射光量Ｌ_ＮＯＴから引くことにより基準透過光量Ｌ_ＴＨＲを算出する。したがって、平均透過光量Ｌ_ＡＶＥが第１閾値Ｌ_１以上の場合は、平均透過光量Ｌ_ＡＶＥが大きいほどマージン率が小さくなるよう基準透過光量Ｌ_ＴＨＲが算出される。

As described above, the reference value calculation unit 42 subtracts, from the irradiation light amount L _NOT , a value obtained by subtracting the reduced light amount, which is a value obtained by subtracting the average transmitted light amount L _AVE from the irradiation light amount L _NOT, from the irradiation light amount L _NOT. The light quantity L _THR is calculated. Therefore, when the average transmitted light amount L _AVE is equal to or greater than the first threshold L _{1, the} reference transmitted light amount L _THR is calculated so that the margin rate decreases as the average transmitted light amount L _AVE increases.

When the average transmitted light amount L _AVE is smaller than the first threshold L ₁ (N in S18), it is possible to realize highly accurate double feed detection even if the reference transmitted light amount is simply set because the conveyed paper is not thin. Therefore, the reference value calculation unit 42 performs a second calculation process that can calculate the reference transmitted light amount with a simple calculation (S22). Specifically, the reference value calculation unit 42 calculates the reference transmitted light amount L _THR by the following equation in the second calculation process.

このように、基準値演算部４２は、減少光量に１．５という係数を掛けた値を照射光量Ｌ_ＮＯＴから引くことにより基準透過光量Ｌ_ＴＨＲを算出する。したがって、平均透過光量Ｌ_ＡＶＥが第１閾値Ｌ_１より小さい場合は、平均透過光量Ｌ_ＡＶＥの値にかかわらずマージン率は一定なるよう基準透過光量Ｌ_ＴＨＲが算出される。この１．５という係数は、上記の数式２の演算を実施することにより基準透過光量Ｌ_ＴＨＲを算出するよりも、算出される基準透過光量Ｌ_ＴＨＲが大きな値となるよう決定されたものである。第１演算処理または第２演算処理を終了し、基準透過光量Ｌ_ＴＨＲが算出されると、記憶部４８は、算出された基準透過光量を格納する（Ｓ２４）。

As described above, the reference value calculation unit 42 calculates the reference transmitted light amount L _THR by subtracting the value obtained by multiplying the reduced light amount by a coefficient of 1.5 from the irradiation light amount L _NOT . Therefore, when the average transmitted light amount L _AVE is smaller than the first threshold L _{1, the} reference transmitted light amount L _THR is calculated so that the margin rate is constant regardless of the value of the average transmitted light amount L _AVE . The coefficient of 1.5 is determined so that the calculated reference transmitted light amount L _THR is larger than that of calculating the reference transmitted light amount L _THR by performing the calculation of the above-described Expression 2. . When the first calculation process or the second calculation process is terminated and the reference transmitted light amount L _THR is calculated, the storage unit 48 stores the calculated reference transmitted light amount (S24).

FIG. 4 is a diagram illustrating a relationship between the average transmitted light amount L _AVE and the reference transmitted light amount _LTHR in the sheet feeding device 10 according to the first embodiment. As shown in FIG. 4, in the range where the average transmitted light amount L _AVE is smaller than the first threshold value L ₁ , the margin rate, that is, (reference margin / decreasing light amount) is a constant value of 0.5 from the above Equation 3. . However, the average amount of transmitted light L _AVE is the first threshold value L ₁ or more ranges, from Equation 2 described above, will become a gradually smaller value (reference margin / decrease amount). By calculating the reference transmitted light amount L _THR in this way, it is possible to accurately detect double feeding even in thin paper.

FIG. 5 is a flowchart illustrating a sheet feeding procedure in the continuous sheet feeding mode in the sheet feeding device 10 according to the first embodiment. The user can select the continuous paper feed mode by performing an input operation on the display 32. When the user presses the start button with the continuous paper feed mode selected (S30), the paper feed mechanism 12 starts the paper feed process by operating the air paper feed mechanism 14 and the transport roller 16 (S32). . The optical sensor 22 detects the amount of light L _NOT emitted by the light emitting element 24 before the paper is sent out, and then detects the amount of light transmitted through the conveyed paper. The reference value calculation unit 42 performs a transmitted light amount sampling process using the detection result of the optical sensor 22 (S34), and calculates an average transmitted light amount L _AVE . A procedure of calculating the average amount of transmitted light L _AVE is the same as the procedure of calculating the average amount of transmitted light L _AVE in the preset mode.

When the average transmitted light amount L _AVE is calculated, the double feed determination unit 44 determines whether or not the average transmitted light amount L _AVE is equal to or greater than the reference transmitted light amount L _THR calculated in advance in the preset mode (S36). When the average transmitted light amount L _AVE is equal to or greater than the reference transmitted light amount L _THR (Y in S36), the double feed determination unit 44 determines that double feed has not occurred, and the transport control unit 40 continues the transport of the sheet as it is. continue.

  At this time, the conveyance control unit 40 subtracts from the total conveyance number input by the user and determines whether or not the counter value indicating the number of remaining sheets to be conveyed is zero. It is determined whether the sheet determined not to be the last sheet to be transported (S38). If it is not the last sheet (N in S38), the conveyance control unit 40 decrements the counter value by 1, and returns to the process in S32 to send out the next sheet. In the case of the last sheet (Y in S38), the conveyance control unit 40 stops the operation of the sheet feeding mechanism 12 without sending out the next sheet, and ends the processing in this flowchart.

When the average transmitted light amount L _AVE is smaller than the reference transmitted light amount L _THR (N in S36), the double feed determination unit 44 determines that double feed has occurred, and the transport control unit 40 stops the operation of the transport motor 20. The feeding of the paper is stopped (S40). Further, the display control unit 46 displays a warning message on the display 32 to notify the user that double feed has occurred (S42). At this time, the display control unit 46 may display on the display 32 a guide screen illustrating the method of removing the double-fed paper. When the warning message is displayed on the display 32, the processing in this flowchart is temporarily terminated. When the double-fed paper is removed by the user and the start button is pressed again, the process is resumed from S30 for the remaining number of sheets to be transported.

(Second Embodiment)
FIG. 6 is a diagram illustrating a relationship between the average transmitted light amount L _AVE and the reference transmitted light amount L _THR in the sheet feeding device 10 according to the second embodiment. In the second embodiment, when the average transmitted light amount L _AVE is smaller than the first threshold L ₁ , the reference value calculation unit 42 calculates the reference transmitted light amount L _THR by the above-described Expression 3 in the second calculation process. On the other hand, when the average transmitted light amount L _AVE is equal to or _larger than the first threshold L ₁ , the reference value calculation unit 42 calculates the reference transmitted light amount L _THR by the following formula using the irradiation light amount as L _NOT in the first calculation process.

このように、第２の実施形態では、平均透過光量Ｌ_ＡＶＥが第１閾値Ｌ_１より小さい範囲では、マージン率は０．５になり、平均透過光量Ｌ_ＡＶＥが第１閾値Ｌ_１以上の範囲では、マージン率は０．３となる。このように平均透過光量Ｌ_ＡＶＥが大きい範囲では、平均透過光量Ｌ_ＡＶＥが小さい範囲よりも小さいマージン率を採用することにより、薄紙においても正確に重送を検知することが可能となる。

As described above, in the second embodiment, in the range where the average transmitted light amount L _AVE is smaller than the first threshold value L ₁ , the margin rate is 0.5, and the average transmitted light amount L _AVE is the range where the first transmitted light amount L _AVE is equal to or greater than the first threshold value L _1. Then, the margin rate is 0.3. As described above, in the range where the average transmitted light amount L _AVE is large, it is possible to accurately detect double feeding even in thin paper by adopting a margin rate smaller than the range where the average transmitted light amount L _AVE is small.

  The present invention is not limited to the above-described embodiments, and an appropriate combination of the elements of each embodiment is also effective as an embodiment of the present invention. Various modifications such as design changes can be added to each embodiment based on the knowledge of those skilled in the art, and embodiments to which such modifications are added can also be included in the scope of the present invention. Here are some examples.

In a modification, the reference transmitted light amount L _THR is acquired for each sheet of a sheet bundle composed of a plurality of sheets. Specifically, when the preset mode is selected and the number of sheets is input and then the user presses the start button, the paper feed mechanism 12 sequentially feeds the input number of sheets from the stacked sheets. . The reference value calculation unit 42 performs the processing of S14 to S24 for each of the plurality of fed sheets, and the storage unit 48 associates the sending order and the reference transmitted light amount L _THR for each of the plurality of sheets. Store.

Next, when the start button is pressed in the continuous paper feed mode, the multi-feed determination unit 44 determines whether or not the calculated average transmitted light amount L _AVE is equal to or greater than the reference transmitted light amount L _THR associated with the order in which the sheets are sent out. It is determined whether or not double feeding has occurred. When the conveyance for the number of sheets constituting the sheet bundle is completed, the multi-feed determining unit 44 resets the delivery order of the next paper to be sent out to 1, and the calculated average transmitted light amount L _AVE is in the order in which the paper is sent out. The process of determining whether or not the associated reference transmitted light amount _{LTHR is} greater than or equal to the occurrence of double feed is further repeated. In this way, the multi-feed determination unit 44 repeats the above-described processing until the conveyance of the set number of sheet bundles input by the user is completed. Thereby, for example, it is possible to accurately detect double feeding even for a sheet bundle formed by overlapping sheets on which different images are recorded.

In another modified example, when the start button is pressed by the user in the preset mode, the reference value calculation unit 42 performs each of a plurality of areas in the sheet conveyance direction for one sheet in the transmitted light amount sampling process in S14. The reference transmitted light amount L _THR is acquired for and stored in the storage unit 48. When the user presses the start button in the continuous paper feed mode, the double feed determination unit 44 calculates an average transmitted light amount L _AVE at a location corresponding to each of the plurality of reference transmitted light _amounts L _THR acquired in the preset mode.

At this time, for example, the reference value calculation unit 42 is detected by the optical sensor 22 five times at equal time intervals between the timing of receiving the seventh pulse signal and the timing of receiving the eighth pulse signal. The amount of light transmitted through the sheet is obtained as a sample value. Further, the reference value calculation unit 42 detects the sheet detected by the optical sensor 22 five times at equal time intervals between the timing of receiving the eighth pulse signal and the timing of receiving the ninth pulse signal. The amount of transmitted light is acquired as a sample value. The reference value calculation unit 42 calculates, as the average transmitted light amount _LAVE , eight average values excluding the maximum value and the minimum value among the ten sample values acquired in this way. The reference value calculation unit 42 calculates the reference transmitted light amount L _THR by performing the processing of S18 to S22 on the calculated average transmitted light amount L _AVE .

Hereinafter, the reference value calculation unit 42 obtains n as a natural number such that the transmitted light amount of the sheet is acquired as a sample value 5 times each between the 11th and 12th pulse signals and the 12th and 13th pulse signals ( A sample value is acquired 10 times between the 4n-1) th pulse signal and the (4n + 1) th pulse signal to calculate the reference transmitted light amount L _THR .

The double feed determination unit 44 determines that double feed has occurred when all of the calculated plurality of average transmitted light _amounts L _AVE are less than the corresponding reference transmitted light amount L _THR . Note, for example, a predetermined number of calculated multiple of the average transmission light amount L _AVE (e.g., such as the number obtained by subtracting 1 from the number of the calculated average quantity of transmitted light L _AVE) Average transmitted light quantity L _AVE of the corresponding reference transmitted light amount If it is less than L _THR , it may be determined that double feeding has occurred. As a result, even when an image having a dark portion or a thin portion is formed on the conveyed paper, it is possible to accurately detect the occurrence of double feeding.

In another variation, the reference value calculation unit 42 calculates the reference transmitted light amount L _THR using Lambert Beer's law. Specifically, the reference value calculation unit 42 calculates “−log (average transmitted light amount L _AVE / irradiation light amount L _NOT )” using the average transmitted light amount L _AVE acquired in the preset mode, for example. The threshold value of the virtual thickness of the paper is calculated using the value. The double feed determination unit 44 calculates “ _−log (average transmitted light amount L _AVE / irradiation light amount L _NOT )” using the average transmitted light amount L _AVE acquired in the continuous paper feed mode, and uses this value. Calculate the virtual thickness of the paper. The double feed determination unit 44 determines whether or not double feed has occurred by determining whether or not the calculated virtual thickness of the sheet exceeds the virtual thickness threshold calculated in the preset mode. Determine. Since Lambert Beer's law is a known law, a description thereof is omitted. Also according to such an aspect, the reference transmitted light amount L _THR can be accurately calculated, and the occurrence of double feed can be detected with high accuracy.

In another modification, the reference value calculation unit 42 sets the index in Equation 2 to a value according to the intensity of the irradiation light amount _LNOT . Specifically, the reference value calculation unit 42 sets the index in Equation 2 to a larger value when the irradiation light amount L _NOT is small than when the irradiation light amount L _NOT is large. Further, the reference value calculation unit 42 sets the coefficient in Equation 3 to a value according to the intensity of the irradiation light amount L _NOT . Specifically, the reference value calculation unit 42 sets the coefficient in Equation 3 to a larger value when the irradiation light amount L _NOT is small than when the irradiation light amount L _NOT is large. As a result, it is possible to ensure an appropriate margin between the average transmitted light amount L _AVE and the reference transmitted light amount L _THR . Further, it is possible to appropriately change the index in Expression 2 or the coefficient in Expression 3 according to the change with time of the irradiation light amount L _NOT due to the deterioration of the light emitting element 24.

1 is an overall configuration diagram schematically illustrating a sheet feeding device according to a first embodiment. FIG. 3 is a functional block diagram of a sheet feeding device according to the first embodiment. 4 is a flowchart illustrating a procedure for setting a reference transmitted light amount in the sheet feeding device according to the first embodiment. FIG. 5 is a diagram illustrating a relationship between an average transmitted light amount L _AVE and a reference transmitted light amount L _THR in the sheet feeding device according to the first embodiment. 6 is a flowchart illustrating a sheet feeding procedure in a continuous sheet feeding mode in the sheet feeding device according to the first embodiment. FIG. 9 is a diagram illustrating a relationship between an average transmitted light amount L _AVE and a reference transmitted light amount L _THR in a sheet feeding device according to a second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Paper feeder, 12 Paper feed mechanism, 14 Air paper feed mechanism, 16 Conveyance roller, 18 Feed solenoid, 20 Conveyance motor, 22 Optical sensor, 24 Light emitting element, 26 Light receiving element, 28 Electronic control part, 30 Control panel, 32 display, 40 transport control unit, 42 reference value calculation unit, 44 double feed determination unit, 46 display control unit, 48 storage unit.

Claims (6)

An optical sensor that detects the amount of light transmitted through the paper by irradiating the paper to be conveyed;
Calculates a reference transmitted light amount with a reference margin in a direction in which the value decreases with respect to the first transmitted light amount detected on the conveyed paper to obtain a reference transmitted light amount used to determine the occurrence of double feed. A reference value calculation unit to
A double feed determination unit that determines whether or not a double feed has occurred in the transported paper by comparing the detected transmitted light amount of the paper with the calculated reference transmitted light amount;
With
The reference value calculation unit is a margin obtained by dividing the reference margin by a reduced light amount that is a value obtained by subtracting the first transmitted light amount from the irradiated light amount of light irradiated on the conveyed paper as the first transmitted light amount increases. A double-feed detection device characterized in that a reference transmitted light amount is calculated so that the rate is reduced.   The reference value calculation unit calculates a reference transmitted light amount by performing an exponential operation or a logarithmic operation using the first transmitted light amount so that the margin rate decreases as the first transmitted light amount increases. Item 2. The multifeed detection device according to Item 1.   The multi-feed detection device according to claim 2, wherein the reference value calculation unit calculates a reference transmitted light amount by subtracting a value obtained by raising the reduced light amount by a predetermined index from the irradiation light amount.   The reference value calculating unit calculates the reference transmitted light amount by a calculation method in which the margin rate decreases as the first transmitted light amount increases when the detected transmitted light amount of the sheet is greater than a predetermined threshold. The double feed detection device according to any one of 1 to 3.   The multi-feed according to claim 3, wherein the reference value calculation unit calculates the reference transmitted light amount by a calculation method in which the margin ratio is constant when the detected transmitted light amount of the sheet is smaller than a predetermined threshold value. Detection device.   The reference value calculation unit is a calculation method in which, when the transmitted light amount of the detected paper is smaller than a predetermined threshold value, the reference transmitted light amount is larger than that calculated by a calculation method in which the margin rate decreases as the transmitted light amount increases. The multi-feed detection device according to claim 4, wherein the reference transmitted light amount is calculated by the following.

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