JP6579939B2 - Double feed detection device, double feed detection method and control program - Google Patents

Description

  The present invention relates to a double feed detection device, a double feed detection method, and a control program, and more particularly, to a double feed detection device, a double feed detection method, and a control program for detecting double feed using an ultrasonic oscillator and an ultrasonic receiver.

  An apparatus such as a scanner that conveys an original and reads an image of the conveyed original has a function of detecting whether or not a multi-feed in which a plurality of originals are conveyed is generated. In general, a multifeed detection device such as a scanner includes an ultrasonic oscillator that outputs an ultrasonic wave and an ultrasonic receiver that outputs a signal corresponding to the received ultrasonic wave, and the ultrasonic receiver when a document is conveyed Detects double feed based on the signal output by. However, since the way ultrasonic waves are transmitted changes depending on the environment such as temperature, humidity, or atmospheric pressure where the double feed detection device is used, the signal output from the ultrasonic receiver depends on the environment where the double feed detection device is used. May change, and double feed may not be detected correctly.

  A transmission sensor that transmits ultrasonic waves, a reception sensor that receives ultrasonic waves and outputs a signal indicating the received ultrasonic waves, an amplification circuit that performs amplification a plurality of times for the signals output by the reception sensors; An image forming apparatus is provided. This image forming apparatus determines whether or not the paper is being double fed between the transmission sensor and the reception sensor based on the signal amplified a plurality of times. Further, the image forming apparatus is a signal during amplification that is performed a plurality of times by the amplification circuit when the reception sensor receives an ultrasonic wave transmitted by the transmission sensor when there is no sheet between the transmission sensor and the reception sensor. Based on the above, the amplification factor of the amplifier circuit is adjusted (see Patent Document 1).

JP 2012-188177 A

  In a double feed detection device, it is desired that double feed can be detected correctly regardless of environmental changes.

  An object of the present invention is to provide a double feed detection device, a double feed detection method, and a control program capable of correctly detecting double feed regardless of environmental changes.

  The double feed detection device according to one aspect of the present invention includes an ultrasonic oscillator that outputs ultrasonic waves, an ultrasonic receiver that is disposed opposite to the ultrasonic oscillator and outputs a signal corresponding to the received ultrasonic waves, Based on the signal value and threshold value of the signal in a state where the maximum amplitude of the signal can be set to the first amplitude or less and the second amplitude less than the first amplitude, and the maximum amplitude of the signal is set to the first amplitude or less. And detecting the occurrence of double feeding of the paper, and setting the maximum amplitude of the signal to be equal to or lower than the second amplitude without passing the paper between the ultrasonic oscillator and the ultrasonic receiver. A first signal value based on the signal output from the storage device, and storing the first signal value in advance, and the maximum amplitude of the signal is equal to or less than the second amplitude without using paper between the ultrasonic oscillator and the ultrasonic receiver To obtain the second signal value based on the signal output from the ultrasonic receiver Has on the basis of the first signal value and a second signal value, and a correction unit for correcting the threshold value, the.

  The double feed detection method according to one aspect of the present invention includes an ultrasonic oscillator that outputs ultrasonic waves, an ultrasonic receiver that is disposed opposite to the ultrasonic oscillator and outputs a signal corresponding to the received ultrasonic waves, A multifeed detection method in a multifeed detection device having a storage unit, wherein the maximum amplitude of a signal is set when detecting that double feed of a sheet has occurred based on a signal value and a threshold value of the signal. It can be set below the first amplitude and below the second amplitude, and the maximum amplitude of the signal can be set below the second amplitude without using paper between the ultrasonic oscillator and the ultrasonic receiver. Then, the first signal value based on the signal output from the ultrasonic receiver is acquired in advance and stored in the storage unit, and the maximum amplitude of the signal is not interposed between the ultrasonic oscillator and the ultrasonic receiver. Is set to be equal to or smaller than the second amplitude, and the second amplitude is It acquires the signal value, based on the first signal value and a second signal value, for correcting the threshold value comprises.

  A control program according to one aspect of the present invention includes an ultrasonic oscillator that outputs ultrasonic waves, an ultrasonic receiver that is disposed opposite to the ultrasonic oscillator and outputs a signal corresponding to the received ultrasonic waves, and a storage unit And a first control program that is set when detecting that a double feed of a sheet has occurred based on a signal value of the signal and a threshold value. The amplitude can be set to be equal to or smaller than the second amplitude smaller than the first amplitude, and the maximum amplitude of the signal can be set to be equal to or smaller than the second amplitude without using a sheet between the ultrasonic oscillator and the ultrasonic receiver. The first signal value based on the signal output from the ultrasonic receiver is acquired in advance and stored in the storage unit, and the maximum amplitude of the signal is determined without using a sheet between the ultrasonic oscillator and the ultrasonic receiver. Set to 2 amplitude or less, and the signal output from the ultrasonic receiver Brute acquires the second signal value based on the first signal value and a second signal value, to correct the threshold value, to perform the double feed detection device that.

  According to the present invention, the double feed detection device can correct the threshold value for detecting the occurrence of double feed of sheets to an appropriate value according to the change in the environment. , Double feed can be detected correctly.

1 is a perspective view showing a document conveying device 100 according to an embodiment. 4 is a diagram for explaining a conveyance path inside document conveying apparatus 100. FIG. 2 is a block diagram illustrating a schematic configuration of a document conveying apparatus 100. FIG. 2 is a diagram illustrating a schematic configuration of a storage device 150 and a CPU 160. FIG. It is a flowchart which shows the example of operation | movement of the memory | storage process of a signal value. It is a graph for demonstrating the ultrasonic signal by which the maximum amplitude was changed. 6 is a flowchart illustrating an example of an operation of an activation process of the document conveying apparatus 100. It is a flowchart which shows the example of operation | movement of an ultrasonic sensor adjustment process. It is a figure for demonstrating the signal value of an ultrasonic signal. It is a figure for demonstrating the signal value of an ultrasonic signal. 5 is a flowchart illustrating an example of an operation of document reading processing. It is a flowchart which shows the example of operation | movement of a double feed determination process. It is a figure for demonstrating the characteristic of a 2nd ultrasonic signal. FIG. 10 is a block diagram illustrating a schematic configuration of another document feeder 200. 2 is a diagram showing a schematic configuration of a processing circuit 250. FIG.

  Hereinafter, an original conveying apparatus according to an aspect of the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a perspective view showing a document conveying device 100 configured as an image scanner.

  The document conveyance device 100 is an example of a double feed detection device. The document conveying apparatus 100 includes an upper casing 101, a lower casing 102, a document table 103, a discharge table 105, a plurality of operation buttons 106, a display device 107, and the like.

  The upper casing 101 is disposed at a position covering the upper surface of the document conveying apparatus 100, and engages with the lower casing 102 by a hinge so that it can be opened and closed when the document is blocked, for example, when the inside of the document conveying apparatus 100 is cleaned. Yes.

  The document table 103 is engaged with the lower housing 102 so that a document can be placed thereon. The document table 103 is provided with side guides 104a and 104b that are movable in a direction perpendicular to the document conveyance direction. Hereinafter, the side guides 104a and 104b may be collectively referred to as a side guide 104.

  The discharge table 105 is engaged with the lower casing 102 by a hinge so as to be rotatable in the direction indicated by the arrow A1, and holds the discharged document when it is opened as shown in FIG. Is possible.

  The plurality of operation buttons 106 are respectively arranged on the surface of the upper housing 101, and when pressed, generate and output an operation detection signal corresponding to each button.

  The display device 107 includes a display composed of a liquid crystal, an organic EL, and the like, and an interface circuit that outputs image data to the display, and displays the image data on the display.

  FIG. 2 is a diagram for explaining a transport path inside the document transport apparatus 100.

  The conveyance path inside the document conveying apparatus 100 includes a contact sensor 111, feed rollers 112a and 112b, brake rollers 113a and 113b, a first light emitter 114a, a first light receiver 114b, an ultrasonic oscillator 115a, an ultrasonic receiver 115b, 1st conveyance roller 116a, 116b, 1st driven roller 117a, 117b, 2nd light emitter 118a, 2nd light receiver 118b, 1st imaging device 119a, 2nd imaging device 119b, 1st illumination device 120a, 2nd illumination device 120b, second conveying rollers 121a and 121b, second driven rollers 122a and 122b, and the like.

  Hereinafter, the feeding rollers 112a and 112b may be collectively referred to as a feeding roller 112. Further, the brake rollers 113a and 113b may be collectively referred to as a brake roller 113. The first transport rollers 116a and 116b may be collectively referred to as the first transport roller 116. The first driven rollers 117a and 117b may be collectively referred to as a first driven roller 117. Further, the second transport rollers 121a and 121b may be collectively referred to as the second transport roller 121. The second driven rollers 122a and 122b may be collectively referred to as the second driven roller 122.

  The lower surface of the upper housing 101 forms an upper guide 108a in the document conveyance path, and the upper surface of the lower housing 102 forms a lower guide 108b in the document conveyance path. In FIG. 2, an arrow A2 indicates the conveyance direction of the document. Hereinafter, upstream means upstream in the document transport direction A2, and downstream means downstream in the document transport direction A2.

  The contact sensor 111 is disposed upstream of the feeding roller 112 and the brake roller 113 and detects whether or not a document is placed on the document table 103. The contact sensor 111 generates and outputs a first document detection signal whose signal value changes depending on whether a document is placed on the document table 103 or not.

  The first light emitter 114a and the first light receiver 114b are opposed to the downstream side of the feeding roller 112 and the brake roller 113 and the upstream side of the first conveyance roller 116 and the first driven roller 117 with the conveyance path of the document interposed therebetween. To be arranged. The first light emitter 114a emits light toward the first light receiver 114b. The first light receiver 114b detects the light emitted from the first light emitter 114a, and generates and outputs a second document detection signal that is an electrical signal corresponding to the detected light. That is, the second document detection signal is a signal whose signal value changes depending on whether or not a document exists between the first light emitter 114a and the first light receiver 114b. Hereinafter, the first light emitter 114a and the first light receiver 114b may be collectively referred to as the first optical sensor 114.

  The ultrasonic oscillator 115a and the ultrasonic receiver 115b are arranged in the vicinity of the document conveyance path so as to face each other across the conveyance path. The ultrasonic oscillator 115a outputs an ultrasonic wave. On the other hand, the ultrasonic receiver 115b receives the ultrasonic wave that has been oscillated by the ultrasonic oscillator 115a and passed through the document, and generates and outputs an ultrasonic signal that is an electrical signal corresponding to the received ultrasonic wave. Hereinafter, the ultrasonic oscillator 115a and the ultrasonic receiver 115b may be collectively referred to as an ultrasonic sensor 115. In addition, the ultrasonic signal output from the ultrasonic receiver 115b may be referred to as a first ultrasonic signal.

  The second light emitter 118a and the second light receiver 118b provide a document conveyance path on the downstream side of the first conveyance roller 116 and the first driven roller 117 and on the upstream side of the first imaging device 119a and the second imaging device 119b. It arrange | positions so that it may oppose on both sides. The second light emitter 118a emits light toward the second light receiver 118b. The second light receiver 118b detects the light emitted from the second light emitter 118a, generates and outputs a third document detection signal that is an electrical signal corresponding to the detected light. That is, the third document detection signal is a signal whose signal value changes depending on whether or not a document exists between the second light emitter 118a and the second light receiver 118b. Hereinafter, the second light emitter 118a and the second light receiver 118b may be collectively referred to as a second light sensor 118.

  The first image pickup device 119a has a reduction optical system type image pickup sensor including an image pickup element by a CCD (Charge Coupled Device) arranged linearly in the main scanning direction. This imaging sensor images the back side of the document and generates and outputs an analog image signal. Similarly, the second image pickup device 119b includes a reduction optical system type image pickup sensor including an image pickup element using a CCD arranged linearly in the main scanning direction. This imaging sensor images the surface of a document and generates and outputs an analog image signal. Note that only one of the first imaging device 119a and the second imaging device 119b may be arranged to read only one side of the document. Further, a CIS (Contact Image Sensor) of the same-magnification optical system type having an image pickup element of CMOS (Complementary Metal Oxide Semiconductor) can be used instead of the CCD. Hereinafter, the first imaging device 119a and the second imaging device 119b may be collectively referred to as an imaging device 119.

  The first illumination device 120a has a light source that illuminates the back surface of the document and a backing used for the surface of the document, and is between the first imaging device 119a and the document conveyance path and the second imaging device 119b. It is provided at an opposing position. Similarly, the second illumination device 120b has a light source that illuminates the surface of the document and a backing used for the back surface of the document, is between the second imaging device 119b and the document conveyance path, and the first imaging. It is provided at a position facing the device 119a. Hereinafter, the first lighting device 120a and the second lighting device 120b may be collectively referred to as the lighting device 120.

  The document placed on the document table 103 is conveyed in the document conveyance direction A2 between the upper guide 108a and the lower guide 108b as the feed roller 112 rotates in the direction of arrow A3 in FIG. . The brake roller 113 rotates in the direction of arrow A4 in FIG. When a plurality of documents are placed on the document table 103 by the functions of the feed roller 112 and the brake roller 113, only the documents that are in contact with the feed roller 112 among the documents placed on the document table 103 are displayed. Are separated. As a result, the operation of the document other than the separated document is restricted (preventing double feeding). The feed roller 112 and the brake roller 113 function as a document separation unit.

  The document is fed between the first conveying roller 116 and the first driven roller 117 while being guided by the upper guide 108a and the lower guide 108b. The document is fed between the first imaging device 119a and the second imaging device 119b by the first conveying roller 116 rotating in the direction of the arrow A5 in FIG. The document read by the imaging device 119 is discharged onto the discharge table 105 when the second conveying roller 121 rotates in the direction of arrow A6 in FIG.

  FIG. 3 is a block diagram illustrating a schematic configuration of the document conveying apparatus 100.

  In addition to the configuration described above, the document conveying apparatus 100 includes a first image A / D converter 140a, a second image A / D converter 140b, an ultrasonic detection circuit 141, a driving device 147, an interface device 148, and a storage device 150. And a CPU (Central Processing Unit) 160 and the like.

  The first image A / D converter 140a converts the analog image signal output from the first imaging device 119a from analog to digital, generates digital image data, and outputs the digital image data to the CPU 150. Similarly, the second image A / D converter 140b converts the analog image signal output from the second imaging device 119b from analog to digital, generates digital image data, and outputs the digital image data to the CPU 150. These digital image data are used as a read image. Hereinafter, the first image A / D converter 140a and the second image A / D converter 140b may be collectively referred to as an image A / D converter 140.

  In addition to the ultrasonic sensor 115, the ultrasonic detection circuit 141 includes a front-stage amplifier 142, a filter 143, a rear-stage amplifier 144, a peak hold circuit 145, an A / D converter 146, and the like.

  The intensity of the ultrasonic wave output from the ultrasonic oscillator 115 a can be changed by the CPU 160 and is set by the CPU 160. The CPU 160 changes the number of drive pulses of the ultrasonic oscillator 115a, thereby changing the number of ultrasonic oscillations output from the ultrasonic oscillator 115a and changing the intensity of the ultrasonic waves. Alternatively, the CPU 160 changes the amplitude of the ultrasonic wave output from the ultrasonic oscillator 115a by changing the ultrasonic oscillation voltage output from the ultrasonic oscillator 115a, that is, the oscillation voltage applied to the ultrasonic oscillator 115a. Change the intensity of the ultrasound.

  The preamplifier 142 amplifies the first ultrasonic signal output from the ultrasonic sensor 115 and outputs the amplified first ultrasonic signal to the filter 143. That is, the pre-stage amplifier 142 amplifies the first ultrasonic signal before the CPU 160 or the storage device 150 acquires it. The first amplification factor by the pre-stage amplifier 142 can be changed by the CPU 160 and is set by the CPU 160.

  The filter 143 applies a bandpass filter that passes a signal of a predetermined frequency band to the signal output from the front-stage amplifier 142 and outputs the signal to the rear-stage amplifier 144.

  The post-stage amplifier 144 amplifies the signal output from the filter 143 and outputs the amplified signal to the peak hold circuit 145. That is, the post-stage amplifier 144 amplifies the first ultrasonic signal before the CPU 160 or the storage device 150 acquires it. The second amplification factor by the post-stage amplifier 144 can be changed by the CPU 160 and is set by the CPU 160.

  The peak hold circuit 145 generates a signal obtained by taking a peak hold for the signal output from the post-stage amplifier 144 and outputs the signal to the A / D converter 146. The peak hold circuit 145 generates a signal having a peak hold by holding the maximum value of the signal output from the post-stage amplifier 144 for a certain hold period.

  The A / D converter 146 converts the analog signal output from the peak hold circuit 145 from analog to digital, generates a digital ultrasonic signal, and outputs the digital ultrasonic signal to the CPU 160. Hereinafter, the ultrasonic signal output from the A / D converter 146 and acquired by the storage device 150 and the CPU 160 may be referred to as a second ultrasonic signal.

  The driving device 147 includes one or a plurality of motors, and rotates the feeding roller 112, the brake roller 113, the first conveying roller 116, and the second conveying roller 121 according to a control signal from the CPU 160 to perform an original conveying operation. Do.

  The interface device 148 has an interface circuit conforming to a serial bus such as a USB, for example, and is electrically connected to an information processing device (not shown) (for example, a personal computer, a portable information terminal, etc.) to display a read image and various information. Send and receive. Instead of the interface device 148, a communication unit including an antenna that transmits and receives radio signals and a radio communication interface circuit that transmits and receives signals through a radio communication line according to a predetermined communication protocol may be used. The predetermined communication protocol is, for example, a wireless LAN (Local Area Network).

  The storage device 150 is an example of a storage unit. The storage device 150 includes a memory device such as a random access memory (RAM) and a read only memory (ROM), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk and an optical disk. In addition, the storage device 150 stores computer programs, databases, tables, and the like used for various processes of the document feeder 100. The computer program may be installed in the storage device 150 from a computer-readable portable recording medium using a known setup program or the like. Examples of the portable recording medium include a CD-ROM (compact disk read only memory) and a DVD-ROM (digital versatile disk read only memory). Further, the storage device 150 stores the read image, the signal value of the second ultrasonic signal acquired in advance before shipment from the factory, and the like.

  CPU 160 operates based on a program stored in storage device 150 in advance. Instead of the CPU 160, a digital signal processor (DSP), a large scale integration (LSI), or the like may be used. Instead of the CPU 160, an application specific integrated circuit (ASIC), a field-programming gate array (FPGA), or the like may be used.

  The CPU 160 includes an operation button 106, a contact sensor 111, a first optical sensor 114, an ultrasonic sensor 115, a second optical sensor 118, a first imaging device 119a, a second imaging device 119b, a first image A / D converter 140a, The second image A / D converter 140b, the driving device 147, the interface device 148, the storage device 150, and the like are connected to control these units. The CPU 160 performs drive control of the drive device 147, document reading control of the imaging device 119, and the like, and acquires a read image. The CPU 160 performs setting control of the ultrasonic detection circuit 141, double feed detection processing, and the like.

  FIG. 4 is a diagram illustrating a schematic configuration of the storage device 150 and the CPU 160.

  As illustrated in FIG. 4, the storage device 150 stores programs such as a setting program 151, an acquisition program 152, a control program 153, a correction program 154, an image generation program 155, and a detection program 156. Each of these programs is a functional module implemented by software operating on the processor. The CPU 160 reads each program stored in the storage device 150 and operates according to each read program, thereby setting the setting unit 161, the acquisition unit 162, the control unit 163, the correction unit 164, the image generation unit 165, and the detection unit 166. Function.

  FIG. 5 is a flowchart illustrating an example of operation of signal value storage processing in a test environment.

  Hereinafter, an example of the operation of storing the first signal value will be described with reference to the flowchart shown in FIG. The operation flow described below is mainly executed by the CPU 160 in cooperation with each element of the document feeder 100 based on a program stored in the storage device 150 in advance. The operation flow shown in FIG. 5 is executed in a test environment such as a factory in which environmental conditions such as temperature, humidity, and atmospheric pressure are kept constant before the document conveying apparatus 100 is shipped from the factory.

  First, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or lower than the first amplitude, and further sets the output of the ultrasonic wave by the ultrasonic oscillator 115a to OFF (step S101). The first amplitude is the maximum amplitude of the ultrasonic signal that is set when the detection unit 166 detects that the double feeding of the paper has occurred.

  The setting unit 161 sets the maximum amplitude of the ultrasonic signal so that the maximum amplitude of the ultrasonic signal input to the A / D converter 146 is equal to or less than the first amplitude. The setting unit 161 may set the maximum amplitude of the ultrasonic signal so that the maximum amplitude of the ultrasonic signal output from the ultrasonic receiver 115b is equal to or less than the first amplitude. Alternatively, the setting unit 161 may set the maximum amplitude of the ultrasonic signal so that the maximum amplitude of the ultrasonic signal input to the CPU 160 is equal to or less than the first amplitude.

  The setting unit 161 sets the maximum amplitude of the ultrasonic signal by setting the number of times of ultrasonic wave output from the ultrasonic oscillator 115a and changing the intensity of the ultrasonic wave output from the ultrasonic oscillator 115a. Alternatively, the setting unit 161 sets the ultrasonic oscillation voltage output from the ultrasonic oscillator 115a, that is, the oscillation voltage applied to the ultrasonic oscillator 115a, and changes the intensity of the ultrasonic wave output from the ultrasonic oscillator 115a. Thus, the maximum amplitude of the ultrasonic signal is set. Alternatively, the setting unit 161 may set the maximum amplitude of the ultrasonic signal by setting the first amplification factor by the front-stage amplifier 142 or the second amplification factor by the rear-stage amplifier 144.

  Next, the acquisition unit 162 displays a message for prohibiting the conveyance of the sheet to the operator on the display device 107 (step S102).

  Next, the acquisition unit 162 waits until it detects that there is no sheet on the conveyance path, that is, no sheet is present between the ultrasonic oscillator 115a and the ultrasonic receiver 115b (step S103). The setting unit 161 determines whether or not there is a sheet on the conveyance path based on the second document detection signal output from the first optical sensor 114 and the third document detection signal output from the second optical sensor 118. To do.

  Next, the acquisition unit 162 receives the second ultrasonic signal output from the ultrasonic detection circuit 141, and acquires the signal value of the received second ultrasonic signal as the first offset value (step S104). The second ultrasonic signal is transmitted from the ultrasonic receiver 115b in a state where the maximum amplitude of the ultrasonic signal is set to be equal to or lower than the first amplitude without passing a sheet between the ultrasonic oscillator 115a and the ultrasonic receiver 115b. It is generated based on the output first ultrasonic signal. In addition, the second ultrasonic signal is generated based on the first ultrasonic signal output in a test environment in a state where no ultrasonic wave is output from the ultrasonic oscillator 115a.

  Next, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or less than the first amplitude, and further sets the output of the ultrasonic wave by the ultrasonic oscillator 115a to ON (step S105). In step S101, since the maximum amplitude of the ultrasonic signal is already set to be equal to or less than the first amplitude, the setting of the maximum amplitude may be omitted.

  Next, the acquisition unit 162 displays a message on the display device 107 instructing the operator to convey the threshold calculation paper (step S106). The threshold calculation paper is, for example, paper (thick paper) having a thickness equal to or greater than the upper limit of the paper thickness supported by the document conveying apparatus 100.

  Next, the acquisition unit 162 waits until it is detected that the sheet has been transported to the transport path, that is, the presence of the sheet (step S107).

  Next, the acquisition unit 162 receives the second ultrasonic signal output from the ultrasonic detection circuit 141, and acquires the signal value of the received second ultrasonic signal as the first paper passage signal value (step S108). The second ultrasonic signal is output from the ultrasonic receiver 115b through a sheet between the ultrasonic oscillator 115a and the ultrasonic receiver 115b, with the maximum amplitude of the ultrasonic signal set to the first amplitude or less. Generated based on the first ultrasonic signal. The second ultrasonic signal is generated based on the first ultrasonic signal output in a test environment in a state where the ultrasonic wave is output from the ultrasonic oscillator 115a.

Next, the acquisition unit 162 calculates a first threshold value based on the first offset value and the first paper passage signal value (step S109). The first threshold value is used for comparison with the second ultrasonic signal in the paper double feed detection process by the detection unit 166 when the document conveying apparatus 100 is used in an environment similar to the test environment. The first threshold value is determined to be a value between the first offset value and the first paper passage signal value. The first threshold value is calculated by the following formula, for example.
(First threshold value) = (first paper passage signal value) × α + (first offset value) × β
Here, α and β are coefficients, and 0 <α <1 and 0 <β <1. For example, α is set to 0.9 and β is set to 0.1.

  Next, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or smaller than the second amplitude, and further sets the ultrasonic output by the ultrasonic oscillator 115a to ON (step S110). The second amplitude is smaller than the first amplitude. For example, the second amplitude is determined to be equal to or less than the input range of the A / D converter 146 when an ultrasonic signal is acquired without passing paper between the ultrasonic oscillator 115a and the ultrasonic receiver 115b. . As a result, the maximum amplitude of the first ultrasonic signal input to the A / D converter 146 is less than or equal to the input range of the A / D converter 146, and the ultrasonic signal is prevented from being saturated in the A / D converter 146. can do. Since the ultrasonic output from the ultrasonic oscillator 115a has already been set to ON in step S105, the setting of the ultrasonic output may be omitted.

  Next, the acquisition unit 162 displays a message prohibiting the conveyance of the paper to the operator on the display device 107 (step S111).

  Next, the acquisition unit 162 waits until it detects that there is no sheet on the conveyance path, that is, no sheet is present between the ultrasonic oscillator 115a and the ultrasonic receiver 115b (step S112).

  Next, the acquisition unit 162 receives the second ultrasonic signal output from the ultrasonic detection circuit 141, and acquires the signal value of the received second ultrasonic signal as the first paper non-passing signal value (step S113). . The second ultrasonic signal is transmitted from the ultrasonic receiver 115b in a state where the maximum amplitude of the ultrasonic signal is set to be equal to or smaller than the second amplitude without passing a sheet between the ultrasonic oscillator 115a and the ultrasonic receiver 115b. It is generated based on the output first ultrasonic signal. The second ultrasonic signal is generated based on the first ultrasonic signal output in a test environment in a state where the ultrasonic wave is output from the ultrasonic oscillator 115a. The first paper non-passing signal value is an example of a first signal value.

  Next, the acquisition unit 162 stores the first offset value, the first paper passage signal value, the first threshold value, and the first paper non-passing signal value in the storage device 150 (step S114), and ends a series of steps.

  FIG. 6 is a graph for explaining an ultrasonic signal in which the maximum amplitude is changed.

  In FIG. 6, the horizontal axis indicates time, and the vertical axis indicates the signal value of the ultrasonic signal. A graph 600 shown in FIG. 6 shows the first ultrasonic signal in a state where the maximum amplitude is set to be equal to or less than the first amplitude A, and a graph 601 is the first in a state where the maximum amplitude is set to be equal to or less than the second amplitude B. An ultrasonic signal is shown. As shown in FIG. 6, by setting the maximum amplitude so that the maximum amplitude of the ultrasonic signal becomes small, the signal value (level) itself of the ultrasonic signal also becomes low.

  FIG. 7 is a flowchart showing an example of the operation of starting processing of the document feeder 100.

  Hereinafter, an example of the operation of the starting process of the document conveying apparatus 100 will be described with reference to the flowchart shown in FIG. The operation flow described below is mainly executed by the CPU 160 in cooperation with each element of the document feeder 100 based on a program stored in the storage device 150 in advance. The operation flow shown in FIG. 7 is executed when the document conveying apparatus 100 is started up in an operating environment where the document conveying apparatus 100 is used by a user.

  First, the control unit 163 performs a test of the first optical sensor 114 and the second optical sensor 118 and determines whether or not the first optical sensor 114 and the second optical sensor 118 are normal (step S201). . The control unit 163 acquires the second document detection signal output from the first light receiver 114b in a state where the first light emitter 114a emits light, and whether or not the signal value of the acquired signal is within a predetermined range. Thus, it is determined whether or not the first optical sensor 114 is normal. Similarly, the control unit 163 acquires a third document detection signal output from the second light receiver 118b in a state where light is emitted to the second light emitter 118a, and the signal value of the acquired signal is within a predetermined range. Whether or not the second optical sensor 118 is normal is determined.

  If the first optical sensor 114 or the second optical sensor 118 is not normal, the control unit 163 determines that an abnormality has occurred and executes an abnormality process (step S202), and ends a series of steps. The control unit 163 notifies the user that an abnormality has occurred through an unillustrated speaker, LED (Light Emitting Diode), or the like as an abnormality process.

  On the other hand, when the first optical sensor 114 and the second optical sensor 118 are normal, the control unit 163 drives the driving device 147 so that no original is placed on the original table 103 (step S203). ). The control unit 163 drives the driving device 147 so that the conveyance of the document is completed even when the document of the maximum size (for example, A3 size) supported by the document conveyance device 100 is placed on the document table 103. .

  Next, the control unit 163 determines whether or not a document is placed on the document table 103 based on the first document detection signal output from the contact sensor 111 (step S204).

  When a document is placed on the document table 103, the control unit 163 determines that an abnormality has occurred and executes abnormality processing (step S202), and ends a series of steps.

  On the other hand, when a document is not placed on the document table 103, the control unit 163 outputs the second document detection signal output from the first optical sensor 114 and the third document detection signal output from the second optical sensor 118. Based on this, it is determined whether or not a document exists on the document transport path (step S205).

  If there is a document on the document transport path, the control unit 163 determines that an abnormality has occurred and executes an abnormality process (step S202), and ends a series of steps.

  Next, the CPU 160 executes an ultrasonic sensor adjustment process (step S206). Details of the ultrasonic sensor adjustment processing will be described later.

  In addition, the control unit 163 performs a test of the imaging device 119 and the illumination device 120, and determines whether the imaging device 119 and the illumination device 120 are normal (step S207). The control unit 163 acquires an image signal output from the imaging device 119 in a state where light is emitted to the illumination device 120, and the imaging device 119 and the image device 119 and the signal value of the acquired image signal are within a predetermined range. It is determined whether or not the lighting device 120 is normal. In addition, the control unit 163 sets a white reference plate (not shown) at a position facing the imaging device 119 across the document conveyance path, and acquires a white reference image obtained by imaging the white reference plate. This white reference image is used to correct a read image obtained by reading a document.

  Note that the tests of the imaging device 119 and the illumination device 120 are executed in parallel with the ultrasonic sensor adjustment processing. As a result, the document conveying apparatus 100 can shorten the activation time.

  Next, the control unit 163 determines whether or not an abnormality has been detected in the ultrasonic sensor adjustment processing or the test of the imaging device 119 and the illumination device 120 (step S208).

  When an abnormality is detected in the ultrasonic sensor adjustment process or the test of the imaging device 119 and the illumination device 120, the control unit 163 executes the abnormality process (step S202) and ends a series of steps.

  On the other hand, if no abnormality is detected in the ultrasonic sensor adjustment process or the test of the imaging device 119 and the illumination device 120, the control unit 163 determines that the activation process has been normally completed, and ends the series of steps. .

  FIG. 8 is a flowchart illustrating an example of the operation of the ultrasonic sensor adjustment processing.

  The operation flow shown in FIG. 8 is executed in step S206 of the flowchart shown in FIG.

  First, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or lower than the first amplitude, and further sets the output of the ultrasonic wave from the ultrasonic oscillator 115a to OFF (step S301).

  Next, the correction unit 164 receives the second ultrasonic signal output from the ultrasonic detection circuit 141, and acquires the signal value of the received second ultrasonic signal as a second offset value (step S302). The second ultrasonic signal is transmitted from the ultrasonic receiver 115b in a state where the maximum amplitude of the ultrasonic signal is set to be equal to or lower than the first amplitude without passing a sheet between the ultrasonic oscillator 115a and the ultrasonic receiver 115b. It is generated based on the output first ultrasonic signal. In addition, the second ultrasonic signal is generated based on the first ultrasonic signal output in a state where no ultrasonic wave is output from the ultrasonic oscillator 115a in the operating environment.

  Next, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or smaller than the second amplitude, and further sets the ultrasonic output from the ultrasonic oscillator 115a to ON (step S303). In step S301, since the ultrasonic output by the ultrasonic oscillator 115a has already been set to ON, the setting of the ultrasonic output may be omitted.

  Next, the correction unit 164 receives the second ultrasonic signal output from the ultrasonic detection circuit 141, and acquires the signal value of the received second ultrasonic signal as the second paper non-passing signal value (step S304). . The second ultrasonic signal is transmitted from the ultrasonic receiver 115b in a state where the maximum amplitude of the ultrasonic signal is set to be equal to or smaller than the second amplitude without passing a sheet between the ultrasonic oscillator 115a and the ultrasonic receiver 115b. It is generated based on the output first ultrasonic signal. In addition, the second ultrasonic signal is generated based on the first ultrasonic signal output in a state where the ultrasonic wave is output from the ultrasonic oscillator 115a in the operating environment. The second sheet non-passing signal value is an example of a second signal value.

  Next, the correcting unit 164 determines whether or not the acquired second sheet non-passing signal value is included in the reference range (step S305). The correction unit 164 determines that the second sheet non-passing signal value is included in the reference range when the second sheet non-passing signal value is not less than a predetermined lower limit value and not more than a predetermined upper limit value. On the other hand, the setting unit 161 determines that the second sheet non-passing signal value is not included in the reference range when it is less than a predetermined lower limit value or larger than a predetermined upper limit value.

  When the second paper non-passing signal value is included in the reference range, the correction unit 164 determines that the operation environment is similar to the test environment, and is stored in the storage device 150 and calculated in the test environment. It is determined that the threshold value is used as the threshold value for double feed determination (step S306).

On the other hand, when the second paper non-passing signal value is not included in the reference range, the correction unit 164 determines that the operation environment is significantly different from the test environment, and the second offset value and the first measured in the test environment are determined. A second threshold value is calculated based on the paper passage signal value (step S307). This second threshold value is used to compare with the second ultrasonic signal in the double feed detection process of the sheet by the detection unit 166 when the document conveying apparatus 100 is used in an environment different from the test environment. The second threshold value is determined to be a value between the second offset value and the second paper passage signal value. The second threshold value is calculated by the following formula, for example.
(Second threshold) = (first paper passage signal value) × α + (second offset value) × β
Here, α and β are the same coefficients as those used to calculate the first threshold value.

  As described above, the second threshold value is the second offset value measured in a state where the sheet is not conveyed in the operating environment, and the first sheet passage signal value measured in the state where the sheet is conveyed in the test environment. Is calculated based on Therefore, it is not necessary for the user to transport the threshold value calculation sheet in the operating environment in order to calculate the second threshold value, and the convenience for the user can be improved.

Next, the correcting unit 164 corrects the second threshold value to a value according to the operating environment based on the first paper non-passing signal value and the second paper non-passing signal value (step S308). For example, the second threshold value is corrected by the following equation.
(Second threshold value after correction) = (Second threshold value before correction) × {(Second paper non-passing signal value) ÷ (First paper non-passing signal value)} × γ
Here, γ is a coefficient. For example, γ is set to a value smaller than 1. Note that γ may be set to a value larger than 1. Alternatively, γ may be set to 1.

Note that the second threshold value may be corrected by the following equation, for example.
(Second threshold value after correction) = (Second threshold value before correction) + {(Second paper non-passing signal value) − (First paper non-passing signal value)} × γ

  Next, the correction unit 164 determines to use the first threshold value calculated in the test environment as the double feed determination threshold value (step S309).

  Next, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or less than the first amplitude, and further sets the output of the ultrasonic wave by the ultrasonic oscillator 115a to OFF (step S310), and a series of steps. Exit.

  Even when the second sheet non-passing signal value is included in the reference range in step S305, the setting unit 161 calculates the second threshold value in the same manner as in step S307, and sets the second threshold value calculated in step S307. You may decide to use as a threshold value for double feed determination. As a result, it is possible to determine the multifeed judgment threshold using an offset value according to the operating environment, so even if the operating environment is similar to the test environment, the multifeed judging threshold suitable for the operating environment is set. Can be used.

  Further, the setting unit 161 may execute the processes of steps S307 to S309 regardless of whether or not the second sheet non-passing signal value is included in the reference range in step S305. As a result, even when the operating environment is similar to the test environment, it is possible to use a multifeed determination threshold that is more suitable for the operating environment.

  Hereinafter, the significance of correcting the double feed determination threshold according to the flowchart shown in FIG. 8 will be described.

  9A and 9B are diagrams for explaining the signal value of the ultrasonic signal input to the A / D converter 146. FIG.

  9A and 9B, the horizontal axis indicates the altitude of the operating environment in which the document conveying apparatus 100 is installed, and the vertical axis indicates the signal value (voltage value) of the ultrasonic signal. Graphs 900, 901, 910, and 911 shown in FIGS. 9A and 9B show the A / D converter 146 in a state where the ultrasonic wave is output from the ultrasonic oscillator 115a in the document feeder 100 installed at each altitude. It is an example of the signal value of the ultrasonic signal input into.

  A graph 900 shown in FIG. 9A shows the signal value of the ultrasonic signal when the maximum amplitude of the ultrasonic signal is set to be equal to or lower than the first amplitude and the sheet is not being conveyed. On the other hand, the graph 901 shows the signal value of the ultrasonic signal in a state where the maximum amplitude of the ultrasonic signal is set to be equal to or less than the first amplitude and the paper is being conveyed. A dotted line 902 indicates the maximum value of the input range of the A / D converter 146.

  Since the way of transmission of ultrasonic waves changes depending on the environment such as temperature, humidity, or atmospheric pressure where the double feed detection device is used, as shown in FIGS. 9A and 9B, the signal value 910 of the ultrasonic signal is an original conveying device. It varies depending on the altitude at which 100 is installed. Therefore, it is desirable to change the double feed determination threshold according to the altitude at which the document conveying apparatus 100 is installed.

  As shown in FIG. 9A, the signal value 901 of the ultrasonic signal in the state where the paper is being conveyed is the maximum value 902 of the input range of the A / D converter 146 regardless of the altitude at which the document conveying apparatus 100 is installed. It becomes as follows. However, when the paper is not transported, the ultrasonic wave output from the ultrasonic oscillator 115a is not blocked by the paper, and thus is received by the ultrasonic receiver 115b with almost no attenuation. In particular, the lower the altitude at which the document feeder 100 is installed, the lower the attenuation rate of the ultrasonic wave output from the ultrasonic oscillator 115a. Therefore, as shown in FIG. 9A, when the document conveying apparatus 100 is installed in an environment with an altitude of 2 km or less, the signal value 900 of the ultrasonic signal in a state where the sheet is not conveyed is converted into an A / D converter 146. Is greater than the maximum value 902 of the input range. Therefore, when the document feeder 100 is installed in an environment with an altitude of 2 km or less, the signal value of the second ultrasonic signal is saturated and becomes the maximum value 902.

  Therefore, in the state where the maximum amplitude of the ultrasonic signal is set to the first amplitude or less, even if the signal value measured in the test environment and the signal value measured in the operation environment are simply compared, the difference between the respective signal values is correct. It cannot be calculated, and the double feed determination threshold value cannot be corrected appropriately. On the other hand, when the signal value of the second ultrasonic signal measured in the test environment is compared with the signal value of the second ultrasonic signal measured in the operation environment in a state where the paper is conveyed, the difference between the signal values can be calculated. It can be calculated correctly. However, if the user conveys the sheet for the correction process of the double feed determination threshold, the convenience for the user is lowered.

  A graph 910 shown in FIG. 9B shows the signal value of the ultrasonic signal when the maximum amplitude of the ultrasonic signal is set to be equal to or smaller than the second amplitude and the sheet is not being conveyed. On the other hand, the graph 911 shows the signal value of the ultrasonic signal in a state where the maximum amplitude of the ultrasonic signal is set to be equal to or smaller than the second amplitude and the paper is being conveyed.

  As shown in FIG. 9B, by setting the maximum amplitude of the ultrasonic signal to be equal to or smaller than the second amplitude, the signal value 910 of the ultrasonic signal in a state where the paper is not being conveyed is the altitude at which the document conveying apparatus 100 is installed. Regardless, the maximum value 902 of the input range of the A / D converter 146 is not more than 902. Therefore, if the signal value measured in the test environment is compared with the signal value measured in the operation environment with the maximum amplitude of the ultrasonic signal set to the second amplitude or less, the difference between the signal values is correctly calculated. And the double feed determination threshold value can be appropriately corrected.

  FIG. 10 is a flowchart illustrating an example of an operation of document reading processing of the document conveying device 100.

  Hereinafter, an example of the operation of the original reading process of the original conveying apparatus 100 will be described with reference to the flowchart shown in FIG. The operation flow described below is mainly executed by the CPU 160 in cooperation with each element of the document feeder 100 based on a program stored in the storage device 150 in advance. The operation flow shown in FIG. 10 is periodically executed.

  First, the control unit 163 waits until the operation button 106 for instructing reading of a document is pressed by the user and an operation detection signal for instructing reading of the document is received from the operation button 106 (step S401). ).

  Next, the control unit 163 determines whether or not a document is placed on the document table 103 based on the first document detection signal received from the contact sensor 111 (step S402).

  If no document is placed on the document table 103, the control unit 163 returns the process to step S401 and waits until a new operation detection signal is received from the operation button 106.

  On the other hand, when a document is placed on the document table 103, the control unit 163 drives the driving device 147 to rotate the feed roller 112, the brake roller 113, the first transport roller 116, and the second transport roller 121. Then, the document is conveyed (step S403).

  Next, the image generation unit 165 causes the imaging apparatus 119 to read the conveyed document, and obtains a read image via the image A / D converter 140 (step S404).

  Next, the image generation unit 165 transmits the read image to an information processing device (not shown) via the interface device 148 (step S405). Note that, when not connected to the information processing apparatus, the image generation unit 165 stores the read image in the storage device 150.

  Next, the control unit 163 determines whether or not a document remains on the document table 103 based on the first document detection signal received from the contact sensor 111 (step S406).

  If the document remains on the document table 103, the control unit 163 returns the process to step S403 and repeats the processes of steps S403 to S406. On the other hand, if no document remains on the document table 103, the control unit 163 ends the series of processes.

  FIG. 11 is a flowchart illustrating an example of the operation of the double feed determination process.

  Hereinafter, an example of the operation of the multi-feed determination process of the document conveying apparatus 100 will be described with reference to the flowchart shown in FIG. The operation flow described below is mainly executed by the CPU 160 in cooperation with each element of the document feeder 100 based on a program stored in the storage device 150 in advance. The operation flow shown in FIG. 11 is periodically executed during document conveyance. Before the operation flow shown in FIG. 11 is executed, the setting unit 161 sets the maximum amplitude of the ultrasonic signal to be equal to or lower than the first amplitude, and the output of the ultrasonic wave by the ultrasonic oscillator 115a is ON. Set to

  First, the detection unit 166 acquires a second ultrasonic signal from the ultrasonic detection circuit 141 (step S501).

  Next, the detection unit 166 determines whether or not the signal value of the acquired second ultrasonic signal is less than the double feed determination threshold (step S502).

  FIG. 12 is a diagram for explaining the characteristics of the second ultrasonic signal.

  In the graph 1200 of FIG. 12, a solid line 1201 indicates the characteristic of the second ultrasonic signal when a single original is being conveyed, and a dotted line 1202 indicates the second ultrasonic signal when the original is double fed. Show the characteristics. The horizontal axis of the graph 1200 represents time, and the vertical axis represents the signal value of the second ultrasonic signal. Due to the occurrence of double feeding, the signal value of the ultrasonic signal of the dotted line 1202 is lowered in the section 1203. Therefore, it is possible to determine whether or not a document double feed has occurred depending on whether or not the signal value of the second ultrasonic signal is less than the double feed determination threshold.

  If the signal value of the second ultrasonic signal is less than the double feed determination threshold value, the detection unit 166 determines that a double feed of the document has occurred (step S503). In that case, the detection unit 166 notifies the user that an abnormality has occurred through an unillustrated speaker, LED, or the like as an abnormality process, and ends a series of steps. On the other hand, when the signal value of the ultrasonic signal is equal to or greater than the double feed determination threshold, the detection unit 166 determines that no double feed of the document has occurred (step S504), and ends the series of steps. As described above, the detection unit 166 has detected that the double feed of the paper has occurred based on the signal value of the ultrasonic signal and the threshold for double feed determination with the maximum amplitude of the ultrasonic signal set to the first amplitude or less. Is detected.

  As described above in detail, the document conveying apparatus 100 can correct the multi-feed determination threshold to an appropriate value according to a change in the environment by operating according to the flowcharts shown in FIGS. This makes it possible to correctly detect double feeds regardless of environmental changes.

  FIG. 13 is a block diagram showing a schematic configuration of an original conveying apparatus 200 according to another embodiment.

  The document conveying device 200 includes a processing circuit 250 in addition to the units included in the document conveying device 100. The processing circuit 250 is a DSP, LSI, ASIC, FPGA, or the like, and executes setting processing and double feed detection processing of the ultrasonic detection circuit 141 instead of the CPU 160.

  FIG. 14 is a diagram showing a schematic configuration of the processing circuit 250. The processing circuit 250 includes a setting circuit 251, an acquisition circuit 252, a correction circuit 254, a detection circuit 256, and the like. Each of these units may be configured by an independent integrated circuit, a microprocessor, firmware, and the like.

  The setting circuit 251 is an example of a setting unit. The setting circuit 251 transmits an amplitude setting signal to the ultrasonic oscillator 115a, the preamplifier 142, or the postamplifier 144 so that the maximum amplitude of the ultrasonic signal is set to be equal to or lower than the first amplitude or the second amplitude. In addition, the setting circuit 251 transmits an ultrasonic control signal to the ultrasonic oscillator 115a so as to set the ultrasonic output from the ultrasonic oscillator 115a to OFF or ON.

  The acquisition circuit 252 is an example of an acquisition unit. The acquisition circuit 252 receives the second ultrasonic signal from the ultrasonic detection circuit 141, acquires the signal value of the received second ultrasonic signal, and stores it in the storage device 150. The acquisition circuit 252 calculates a first threshold value based on the first offset value and the first paper passage signal value, and stores the first threshold value in the storage device 150.

  The correction circuit 254 is an example of a correction unit. The correction circuit 254 receives the second ultrasonic signal from the ultrasonic detection circuit 141, acquires the signal value of the received second ultrasonic signal, and stores it in the storage device 150. Further, when the second sheet non-passing signal value is included in the reference range, the correction circuit 254 transmits a threshold setting signal to the detection circuit 256 so as to set the first threshold as the double feed determination threshold. In addition, when the second paper non-passing signal value is not included in the reference range, the correction circuit 254 calculates the second threshold based on the second offset value and the first paper passing signal value, and the first paper non-passing signal The second threshold value is corrected based on the value and the second sheet non-passing signal value. Then, the correction circuit 254 transmits a threshold setting signal to the detection circuit 256 so as to set the second threshold as the double feed determination threshold.

  The detection circuit 256 is an example of a detection unit. The detection circuit 256 receives the second ultrasonic signal from the ultrasonic detection circuit 141. When the signal value of the second ultrasonic signal is less than the double feed determination threshold, the detection circuit 256 transmits a detection signal indicating that double feed has been detected to the CPU 160.

  As described above in detail, in the document conveying device 200 as well as the document conveying device 100, it is possible to correctly detect double feeding regardless of environmental changes.

100, 200 Document conveying device 115a Ultrasonic oscillator 115b Ultrasonic receiver 142 Preamplifier 144 Subsequent amplifier 146 A / D converter 150 Storage device 161 Setting unit 164 Correction unit 166 Detection unit

Claims (6)

An ultrasonic oscillator that outputs ultrasonic waves;
An ultrasonic receiver that is disposed opposite to the ultrasonic oscillator and outputs a signal corresponding to the received ultrasonic wave;
A setting unit capable of setting the maximum amplitude of the signal to a first amplitude or less and a second amplitude or less smaller than the first amplitude;
A detection unit configured to detect that double feeding of paper has occurred based on a signal value of the signal and a threshold value in a state where the maximum amplitude of the signal is set to be equal to or less than the first amplitude;
A first signal based on a signal output from the ultrasonic receiver in a state where the maximum amplitude of the signal is set to be equal to or smaller than the second amplitude without using a sheet between the ultrasonic oscillator and the ultrasonic receiver. A storage unit for acquiring and storing signal values in advance;
In an operational environment in which a multifeed detection device is used by a user, the maximum amplitude of the signal is set to be equal to or less than the second amplitude without a sheet between the ultrasonic oscillator and the ultrasonic receiver. A correction unit that acquires a second signal value based on the signal output from the ultrasonic receiver and corrects the threshold based on the first signal value and the second signal value;
A double feed detection device comprising:   The multifeed detection device according to claim 1, wherein the setting unit sets the maximum amplitude by setting an oscillation frequency or an oscillation voltage of an ultrasonic wave output from the ultrasonic oscillator. An amplifier that amplifies the signal output from the ultrasonic receiver before the detection unit, the storage unit, and the correction unit obtain the signal;
The double feed detection device according to claim 1, wherein the setting unit sets a maximum amplitude of the signal acquired by the storage unit and the correction unit by setting an amplification factor by the amplifier. An A / D converter for analog-digital conversion of the signal;
The second amplitude is determined to be equal to or less than an input range of the A / D converter when the signal is acquired without a sheet between the ultrasonic oscillator and the ultrasonic receiver. Item 4. The multifeed detection device according to any one of Items 1 to 3. An ultrasonic oscillator that outputs an ultrasonic wave, an ultrasonic receiver that is disposed opposite to the ultrasonic oscillator and outputs a signal corresponding to the received ultrasonic wave, and a storage unit, and a storage unit. A transmission detection method,
The maximum amplitude of the signal is equal to or less than a first amplitude that is set when detecting the occurrence of double feeding of paper based on the signal value of the signal and a threshold value, and is equal to or less than a second amplitude that is smaller than the first amplitude. Can be set to
A first signal value based on a signal output from the ultrasonic receiver by setting a maximum amplitude of the signal to be equal to or lower than the second amplitude without passing a sheet between the ultrasonic oscillator and the ultrasonic receiver. Is acquired in advance and stored in the storage unit,
In an operating environment in which a multifeed detection device is used by a user, the maximum amplitude of the signal is set to be equal to or less than the second amplitude without using paper between the ultrasonic oscillator and the ultrasonic receiver, Obtaining a second signal value based on the signal output from the ultrasonic receiver, and correcting the threshold based on the first signal value and the second signal value;
A double feed detection method comprising: An ultrasonic oscillator that outputs ultrasonic waves, an ultrasonic receiver that is arranged opposite to the ultrasonic oscillator and outputs a signal corresponding to the received ultrasonic waves, and a storage unit, and is executed on a multifeed detection device A control program for causing
The maximum amplitude of the signal is equal to or less than a first amplitude that is set when detecting the occurrence of double feeding of paper based on the signal value of the signal and a threshold value, and is equal to or less than a second amplitude that is smaller than the first amplitude. Can be set to
A first signal value based on a signal output from the ultrasonic receiver by setting a maximum amplitude of the signal to be equal to or lower than the second amplitude without passing a sheet between the ultrasonic oscillator and the ultrasonic receiver. Is acquired in advance and stored in the storage unit,
In an operating environment in which a multifeed detection device is used by a user, the maximum amplitude of the signal is set to be equal to or less than the second amplitude without using paper between the ultrasonic oscillator and the ultrasonic receiver, Obtaining a second signal value based on the signal output from the ultrasonic receiver, and correcting the threshold based on the first signal value and the second signal value;
A control program for causing the double feed detection device to execute the above.

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