DOUBLE FEEDING DETECTION APPARATUS, AUTO SHEET FEEDER AND DOUBLE FEED DETECTION METHOD

Abstract

A double feed detection apparatus includes a first element and a second element at positions where they are opposite to each other across a sheet, and a direction in which an ultrasonic wave or a light passes through the sheet is vertical to a conveyance direction of the sheet. An auto sheet feeder includes the first element and the second element of the double feed detection apparatus in a range from a downstream side of a joining point of an outside conveyance path and an inside conveyance path in the sheet conveyance direction to a near side of a read part.

Description

FIELD

The present invention relates to a double feed detection apparatus, an auto sheet feeder and a double feed detection method.

BACKGROUND

When sheets such as papers or bank notes are processed by an equipment, it is necessary to detect double feed in order to avoid a jam and a read error.

With respect to this point, a technique is proposed in which an ultrasonic wave is irradiated in parallel to a conveyance direction of a sheet so as to pass through the conveyed sheet.

FIG. 10 and FIG. 11 are views showing levels of ultrasonic waves passing through sheets, which are detected by this related art. FIG. 12 is a view showing an ultrasonic wave irradiation direction when the levels shown in FIG. 10 are obtained, and FIG. 13 is a view showing an ultrasonic wave irradiation direction when the levels shown in FIG. 11 are obtained.

As shown in FIG. 10 and FIG. 11, according to the related art, when the width of a double feed portion is as narrow as 3 mm, the double feed can not be detected since the level is low as in FIG. 10, or the double feed can not be detected at high accuracy since the ultrasonic wave passes through a gap between the sheets and its level becomes abruptly high as in FIG. 11.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a structure of a double feed detection apparatus.

FIG. 2 is a view showing an arrangement relation of a first ultrasonic element and a second ultrasonic element with respect to a conveyance direction of a sheet.

FIG. 3 is a view seen in an arrow A in FIG. 2.

FIG. 4 is a view in which widths of detectable double feed portions are compared.

FIG. 5 is a view showing detection levels of transmitted ultrasonic waves by the double feed detection apparatus.

FIG. 6 is a block diagram showing a structure of the double feed detection apparatus.

FIG. 7 is a view showing a case where an angle θ1 shown in FIG. 3 becomes an angle θ2 which is 90°.

FIG. 8 is a view showing a structure of an auto sheet feeder including the double feed detection apparatus.

FIG. 9 is a views showing the structure of the auto sheet feeder.

FIG. 10 is a view showing levels of ultrasonic waves passing through sheets, which are detected by the related art.

FIG. 11 is a view showing levels of ultrasonic waves passing through sheets, which are detected by the related art.

FIG. 12 is a view showing an irradiation direction of an ultrasonic wave passing through sheets, which is detected by the related art.

FIG. 13 is a view showing the irradiation direction of the ultrasonic wave passing through sheets, which is detected by the related art.

DETAILED DESCRIPTION

Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods of the present embodiments.

Hereinafter, embodiments of a double feed detection apparatus, an auto sheet feeder and a double feed detection method will be described in detail with reference to the drawings.

A double feed detection apparatus includes a control section to generate a control signal, a transmission signal generation section to generate a transmission signal from the control signal of the control section, a transmission amplifying section to amplify the transmission signal, a first element to output an amplified signal to a sheet in a direction perpendicular to a conveyance direction of the sheet, a second element to receive the signal of the first element passing through the sheet, a reception amplifying section to amplify a received signal, and an A/D converter to convert the received signal as the amplified analog signal into a digital signal and to output it to the control section.

An auto sheet feeder includes a paper feed tray on which documents to be read are placed, a pickup roller to take out a sheet one by one from the paper feed tray and to deliver it to a conveyance mechanism, the conveyance mechanism which includes an outside conveyance path and an inside conveyance path, receives the sheet from the pickup roller and conveys it, a front surface read section to read a front surface of the sheet, a rear surface read section to read a rear surface of the sheet, a storage tray on which the read sheet is stacked, a control section to generate a control signal, a transmission signal generation section to generate a transmission signal from the control signal of the control section, a transmission amplifying section to amplify the transmission signal, a first element to output an amplified signal to the sheet in a direction perpendicular to a conveyance direction of the sheet, a second element to receive the signal of the first element passing through the sheet, a reception amplifying section to amplify a received signal, and an A/D converter to convert the received signal as the amplified analog signal into a digital signal and to output it to the control section.

A double feed detection method includes generating a control signal by a control section, generating a transmission signal from the control signal by a transmission signal generation section, amplifying the transmission signal by a transmission amplifying section, outputting an amplified signal to a sheet in a direction perpendicular to a conveyance direction of the sheet by a first element, receiving the signal of the first element passing through the sheet by a second element, amplifying a received signal by a reception amplifying section, and converting the received signal as the amplified analog signal into a digital signal by an A/D converter and outputting it to the control section.

Double Feed Detection Apparatus

First Embodiment

FIG. 1 is a block diagram showing a structure of a double feed detection apparatus of an embodiment. As shown in FIG. 1, the double feed detection apparatus includes a CPU 101 as a control section, a transmission signal generation section 102 to generate a transmission signal from the control signal of the control section, a transmission amplifying section 103 to amplify a transmission signal, a changeover switch 104 to Switch between an output destination and an input destination, a first ultrasonic element 10A as a first element to transmit and receive an ultrasonic wave, a second ultrasonic element 10B as a second element, a reception amplifying section 105 to amplify a received signal; an A/D converter 106 to convert an analog signal into a digital signal, and a storage device 107 as a memory such as a ROM or a RAM.

The CPU 101 generates a signal to control transmission and outputs it to the transmission signal generation section 102. The transmission signal generation section 102 converts the control signal from the CPU into a transmission signal to drive an element and outputs it to the transmission amplifying section 103. The transmission amplifying section 103 amplifies the input signal and outputs it to the first ultrasonic element 10A through the changeover switch 104. The first ultrasonic element 10A irradiates an ultrasonic wave to a sheet.

The second ultrasonic element 10B receives the ultrasonic wave passing through the sheet, converts it into an electric signal, and outputs it to the reception amplifying section 105 through the changeover switch 104. The reception amplifying section 105 amplifies the input signal and outputs it to the A/D converter 106. The A/D converter 106 converts the input analog signal into a digital signal and outputs it to the CPU 101.

The changeover switch 104 changes a connection relation of the first ultrasonic element 10A and the second ultrasonic element 10B with respect to the transmission Amplifying section 103 and the reception amplifying section 105.

That is, when the first ultrasonic element 10A is connected to the transmission amplifying section 103, the changeover switch 104 connects the second ultrasonic element 10B to the reception amplifying section 105. When the second ultrasonic element 10B is connected to the transmission amplifying section 103, the changeover switch connects the first ultrasonic element 10A to the reception amplifying section 105.

Accordingly, since the output side element to irradiate the ultrasonic wave and the reception side element are periodically interchanged with each other, heat generation of the first ultrasonic element 10A and the second ultrasonic element 108 are dispersed to the two elements. Thus, the output can be increased and the life of the element can be extended.

The storage device 107 stores a threshold for a level. The CPU 101 determines that when the level of the input signal is lower than the threshold read from the storage device 107, the sheet is doubly fed.

FIG. 2 is a view showing the arrangement relation of the first ultrasonic element 10A and the second ultrasonic element 108 with respect to the conveyance direction of the sheet. FIG. 3 is a view seen in an arrow A in FIG. 2. As shown in FIG. 2 and FIG. 3, the double feed detection apparatus includes the first ultrasonic element 10A at a front surface side of a sheet P1, P2, and includes the second ultrasonic element 108 at a rear surface side of the sheet P1, P2 and in front of the first ultrasonic element 10A in an ultrasonic wave irradiation direction.

The double feed detection apparatus includes the first ultrasonic element 10A and the second ultrasonic element 10B which are arranged such that the ultrasonic wave irradiation direction is perpendicular to conveyance direction X of the sheet P1, P2.

Further, the double feed detection apparatus includes the first ultrasonic element 10A and the second ultrasonic element 10B which are arranged such that the incident angle of the ultrasonic wave with respect to the surface of the sheet P1, P2 becomes an angle θ1. Since the ultrasonic wave is attenuated according to the length L of a distance between the ultrasonic elements 10A and 10B, it is desirable that L is short. The angle θ1 is an angle larger than 0°, and when the distance L between the first ultrasonic element 10A and the second ultrasonic element 10B is the same, it is desirable that the angle is small. However, when the angle θ1 is excessively small, the arrangement of the respective ultrasonic elements becomes difficult. Besides, when the angle θ1 becomes larger than 40°, the irradiated ultrasonic wave collides and interferes with the reflected wave reflected by the sheet and returned to the transmission side element, and is attenuated. Accordingly, as θ1 becomes large, the ultrasonic wave transmitted to the reception side becomes small, and the detection of the double feed becomes difficult.

A transmission wave B1 of an ultrasonic wave irradiated by the first ultrasonic element 10A is transmitted in air while spreading gently and concentrically, and is irradiated at the angle θ1 to a double feed portion C of the sheet P1 and the sheet P2 indicated by oblique lines. Accordingly, the transmission wave 81 reaches the sheet P1, P2 in a transmission range B3 indicated as a hatched portion, and a transmission wave B2 of the ultrasonic wave passing through the transmission range B3 reaches the second ultrasonic element 10B.

Here, the transmission range B3 has an elliptical shape extending in the direction perpendicular to the sheet conveyance direction X. Accordingly, since the width of the transmission range B3 in the sheet conveyance direction X becomes narrow, even if the width of the double feed portion C in the sheet conveyance direction is narrow, the double feed detection apparatus of this embodiment can detect the double feed at high accuracy.

FIG. 4 is a view in which widths of detect-able double feed portions are compared. FIG. 5 is a view showing detection levels of transmitted ultrasonic waves by the double feed detection apparatus of this embodiment. As shown in FIG. 4 and FIG. 5, in a forward direction of the related art, that is, in the case of FIG. 12 in which the subsequent sheet P2 overlaps on the preceding sheet P1, and in a reverse direction of the related art, that is, in the case of FIG. 13 in which the subsequent sheet P2 is overlapped by the preceding sheet P1, when the width of the double feed portion C becomes as narrow as about 3 mm, the double feed can not be detected.

On the other hand, the double feed detection apparatus of this embodiment can detect the double feed even when the sheets P1 and P2 overlap with each other in either direction and even when the width of the double feed portion C becomes narrow.

Second Embodiment

FIG. 6 is a block diagram showing a structure of a double feed detection apparatus of this embodiment. As shown in FIG. 6, the double feed detection apparatus includes a CPU 101 as a control section, a transmission signal generation section 102 to generate a transmission signal from the control signal of the control section, a transmission amplifying section 103 to amplify a transmission signal, a first light emitting element 20A as a first element to irradiate a light to a sheet, a second light reception element 20B as a second element which includes a lens 20C, receives the light passing through the sheet and generates an electric signal, a reception amplifying section 105 to amplify a received signal, an A/D converter 106 to convert an analog signal into a digital signal, and a storage device 107 as a memory such as a ROM or a RAM.

The CPU 101 generates a control signal and outputs it to the transmission signal generation section 102. The transmission signal generation section 102 converts the input signal from the CPU into an element drive signal and outputs it to the transmission amplifying section 103. The transmission amplifying section 103 amplifies the input signal and outputs it to the light emitting element 20A. The light emitting element 20A irradiates a light to a sheet.

The light receiving element 20B receives the light passing through the sheet, converts it into an electric signal, and outputs it to the reception amplifying section 105. The reception amplifying section 105 amplifies the input signal and outputs it to the A/D convert 106. The A/D converter 106 converts the input analog signal into a digital signal and outputs it to the CPU 101.

The storage device 107 stores a threshold for a level. The CPU 101 determines that when the level of the input signal is lower than the threshold read from the storage device 107, the sheet is doubly fed.

The positional relation between the light emitting element 20A and the light receiving element 20B may be the same as the positional relation between the first ultrasonic element 20A and the second ultrasonic element 10B of the first embodiment shown in FIG. 2 and FIG. 3.

FIG. 7 is a view showing a case where the angle θ1 shown in FIG. 3 becomes an angle θ2 which is 90°.

As shown in FIG. 3 and FIG. 7, the double feed detection apparatus includes the light emitting element 20A at the front surface side of the sheet P1, P2, and the light receiving element 20B at the rear surface side of the sheet P1, P2 and in front of the light emitting element 10A in the light irradiation direction. The positions of the light emitting element 20A and the light receiving element 208 may be reversed.

The double feed detection apparatus includes the light emitting element 20A and the light receiving element 208 which are arranged such that the light irradiation direction is perpendicular to the conveyance direction X of the sheet P1, P2.

Further, the double feed detection apparatus includes the light emitting element 20A and the light receiving element 20B so as to have the angle θ1 with respect to the surface of the sheet P1, P2. It is desirable that the angle θ1 is larger than 0° and smaller than 90°. When the angle is excessively small, the arrangement of the light emitting element 20A and the light receiving element 20B becomes difficult.

The incident beam B1 of the light irradiated by the light emitting element 20A is irradiated at the angle θ1 to the double feed portion C of the sheet P1 and the sheet P2 indicated by oblique lines. Accordingly, the incident beam B1 reaches the sheet P1, P2 in the transmission range B3 indicated as the hatched portion, and the transmission beam 52 of the light passing through the transmission range B3 reaches the light receiving element 20B.

Here, the transmission range B3 has the elliptical shape extending in the direction perpendicular to the sheet conveyance direction X. Accordingly, since the width of the transmission range B3 in the sheet conveyance direction X becomes narrow, even if the width of the double feed portion C in the sheet conveyance direction is narrow, the double feed detection apparatus of this embodiment can detect the double feed at high accuracy.

Incidentally, as shown in FIG. 7, differently from the ultrasonic wave, even if θ1 becomes θ2 which is 90°, although an incident beam 85 is attenuated by reflection at the sheet P1 or P2, the incident beam is transmitted and becomes a transmission beam B4. Accordingly, when the light is used, the degree of freedom with respect to the angle is higher than that of the ultrasonic wave.

Auto Sheet Feeder

Structure of Auto Sheet Feeder

FIG. 8 is a view showing a structure of an auto sheet feeder including the double feed detection apparatus of this embodiment. As shown in FIG. 8; an auto sheet feeder 700 includes a paper feed tray 701 on which a document P to be read is placed, a pickup roller 702 to take out the sheet P one by one from the paper feed tray 701 and to deliver it to a conveyance mechanism, the conveyance mechanism to receive the sheet P from the pickup roller 702 and to convey it, a front surface read section 723 to read a front surface of the sheet P, a rear surface read section 720 to read a rear surface of the sheet P, and a storage tray 724 on which the read sheet is stacked.

The conveyance mechanism includes an inlet roller 704 to receive the sheet P from the pickup roller 702, a first conveyance roller 707 to receive the sheet from the inlet roller 704 and to convey it, a flapper 709 to change a conveyance path of the sheet P, an outside conveyance path D1 as a first conveyance path, and an inside conveyance path D2 as a second conveyance path whose conveyance distance is shorter than the first conveyance path.

The flapper 709 moves up and down as indicated by an arrow F and alternately changes over the sheet conveyance path between the outside conveyance path D1 and the inside conveyance path D2. The outside conveyance path D1 includes an outside conveyance roller 711 and an OUT sheet passing sensor 715 to detect the passing of the sheet. The inside conveyance path θ2 includes an inside conveyance roller 713 and an IN sheet passing sensor 716 to detect the passing of the sheet.

The outside conveyance path D1 and the inside conveyance path D2 join each other at the downstream side of the OUT sheet passing sensor 715 and the IN sheet passing sensor 716 in the sheet conveyance direction.

The joined conveyance path includes a second conveyance roller 717 at the downstream side of the joining point in the sheet conveyance direction, the front surface read section 723 at a read part 722, a third conveyance roller 718 at the downstream side of the read part 722 in the sheet conveyance direction, the rear surface read section 720, and a paper discharge roller 721.

The pickup roller 702 is moved up and down by a solenoid 703. The flapper 709 is moved up and down by a solenoid 710.

The inlet roller 704 is driven by an inlet motor 705, the first conveyance roller 707 is driven by a first motor 708, the outside conveyance roller 711 is driven by an outside motor 712, the inside conveyance roller 713 is driven by an inside motor 714, the second conveyance roller 717 and the third conveyance roller 718 are driven by a second motor 719A, and the paper discharge roller 721 is driven by a discharge motor 719B.

The auto sheet feeder 700 includes the double feed detection apparatus, and includes a first element S1 and a second element S2 of the double feed detection apparatus in a range which is indicated by an arrow Z and extends from the downstream side of the joining point of the outside conveyance path D1 and the inside conveyance path D2 in the sheet conveyance direction to a near side of the read part.

When the first element S1 is an ultrasonic element, the second element S2 is an ultrasonic element. When the first element S1 is a light emitting element, the second element S2 is a light receiving element.

FIG. 9 is a view showing a structure of the auto sheet feeder 700. As shown in FIG. 9, the auto sheet feeder 700 includes the double feed detection apparatus. The double feed detection apparatus may be the double feed detection apparatus of the first embodiment or the double feed detection apparatus of the second embodiment. FIG. 9 shows the auto sheet feeder 700 including the double feed detection apparatus of the first embodiment.

The auto sheet feeder 700 includes, as the double feed detection apparatus, a CPU 101 as a control section, a transmission signal generation section 102 to generate a transmission signal from a control signal of the CPU 101, a transmission amplifying section 103 to amplify the transmission signal, a changeover switch 104 to switch between an output destination and an input destination, a first ultrasonic element 10A as a first element to transmit and receive an ultrasonic wave, a second ultrasonic element 10B as a second element, a reception amplifying section 105 to amplify a received signal, an A/D converter 106 to convert an analog signal into a digital signal; and a storage device 107 as a memory such as a ROM or a RAM.

The auto sheet feeder 700 further includes a pickup sensor 801 to detect pick-up of a sheet, an OUT sheet passing sensor 715, an IN sheet passing sensor 716, a paper discharge sensor 802 to detect discharge of the sheet, a pickup roller drive section 803 to drive the pickup roller 702, a flapper drive section 804 to drive the flapper 709, and a sheet conveyance mechanism drive section 805 to drive rollers to convey the sheet along a sheet conveyance path.

A rear surface read section 720 and a front surface read section 723 output a read signal of a document to an upper-level machine control section 810 as a control section of an upper-level machine such as a printer.

Operation of the Auto Sheet Feeder

The auto sheet feeder 700 takes up a first sheet P1 by the pickup roller 702 from the paper feed tray 701 and delivers it to the inlet roller 704. The flapper 709 is displaced to an upper side.

The auto sheet feeder 700 conveys the first sheet P1 to the read part 722 through the inside conveyance path D2 whose conveyance distance is shorter than the outside conveyance path D1. The flapper 709 is displaced to a lower side.

The auto sheet feeder 700 conveys a second sheet P2 to the read part 722 through the outside conveyance path D1. The flapper 709 is again displaced to the upper side.

When the IN sheet passing sensor 716 detects the passing of the sheet P1, the auto sheet feeder 700 drives the outside conveyance roller 711 to convey the sheet P2 to the joining point.

In the auto sheet feeder 700, at this time, the double feed detection apparatus detects whether the trailing edge of the sheet P1 and the leading edge of the sheet P2 are doubly fed. When the double feed is detected, the auto sheet feeder 700 operates to deal with the double feed. When the double feed is not detected, the sheet P2 is conveyed to the read part 722.

The auto sheet feeder 700 causes the front surface read section 723 and the rear surface read section 720 to read the preceding sheet P0, the next conveyed sheet P1 and the finally conveyed sheet P2 in that order, and discharges the sheets to the storage tray 724.

Operation in the Case of Sensor Abnormality

When the OUT sheet passing sensor 715 or the IN sheet passing sensor 716 is damaged to be ON, the auto sheet feeder 700 does not use the conveyance path having the damaged sensor, and conveys the sheet to only the conveyance path having the normal sensor.

That is, in this case, the flapper 709 is displaced so that the sheet is conveyed to the conveyance path at one side.

When the OUT sheet passing sensor 715 or the IN sheet passing sensor 716 is damaged to be OFF, the auto sheet feeder 700 continuously detects a jam in the conveyance path on the same side.

In this case, when the number of times in which the jam occurs continuously exceeds a threshold, the auto sheet feeder 700 does not use the conveyance path where the jam occurs continuously, and conveys the sheet to only the normal conveyance path.

That is, in this case, the flapper 709 is displaced so that the sheet is conveyed to the normal conveyance path.

Effects of the Embodiments

As described above, the double feed detection apparatus of the embodiment includes the first element S1 and the second element S2 at positions where they are opposite to each other across the sheet, and the direction in which the ultrasonic wave or the light passes through the sheet is vertical to the conveyance direction of the sheet.

Accordingly, there is an effect that even when the width of the double feed portion of the sheet is narrow, the double feed can be detected at high accuracy.

Besides, the auto sheet feeder 700 of the embodiment includes the first element S1 and the second element S2 of the double feed detection apparatus in the range from the downstream side of the joining point of the outside conveyance path D1 and the inside conveyance path D2 in the sheet conveyance direction to the near side of the read part.

Accordingly, there is an effect that the sheet can be fed while the double feed of the sheet is detected at high accuracy.

While certain embodiments have been described, these embodiments have been presented by way of example only, and, are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are indeed to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

1. A double feed detection apparatus comprising: a control section to generate a control signal;a transmission signal generation section to generate a transmission signal from the control signal of the control section;a transmission amplifying section to amplify the transmission signal;a first element to output the amplified signal to a sheet in a direction perpendicular to a conveyance direction of the sheet;a second element to receive the signal of the first element passing through the sheet;a reception amplifying section to amplify the received signal; andan A/D converter to convert the received signal as the amplified analog signal into a digital signal and to output it to the control section.

2. The apparatus of claim 1, wherein the first element is a first ultrasonic element and the second element is a second ultrasonic element.

3. The apparatus of claim 2, wherein the first ultrasonic element and the second ultrasonic element are provided to have an ultrasonic wave incident angle of 40° or less with respect to a surface of the sheet.

4. The apparatus of claim 3, further comprising a changeover switch, wherein when the first ultrasonic element is connected to the transmission amplifying section, the second ultrasonic element is connected to the reception amplifying section, and when the second ultrasonic element is connected to the transmission amplifying section, the first ultrasonic element is connected to the reception amplifying section.

5. The apparatus of claim 1, wherein the first element is a light emitting element, and the second element is a light receiving element.

6. The apparatus of claim 5, wherein the light emitting element and the light receiving element are provided to have a light incident angle of 90° or less with respect to a surface of the sheet.

7. An auto sheet feeder comprising: a paper feed tray on which documents to be read are placed;a pickup roller to take out a sheet one by one from the paper feed tray and to deliver it to a conveyance mechanism;the conveyance mechanism which includes an outside conveyance path and an inside conveyance pat, receives the sheet from the pickup roller and conveys it;a front surface read section to read a front surface of the sheet;a rear surface read section to read a rear surface of the sheet;a storage tray on which the read sheet is stacked;a control section to generate a control signal;a transmission signal generation section to generate a transmission signal from the control signal of the control section;a transmission amplifying section to amplify the transmission signal;a first element to output the amplified signal to the sheet in a direction perpendicular to a conveyance direction of the sheet;a second element to receive the signal of the first element passing through the sheet;a reception amplifying section to amplify the received signal; andan A/D converter to convert the received signal as the amplified analog signal into a digital signal and to output it to the control section.

8. The feeder of claim 7, wherein the first element is a first ultrasonic element and the second element is a second ultrasonic element.

9. The feeder of claim 8, wherein the first ultrasonic element and the second ultrasonic element are provided to have an ultrasonic wave incident angle of 40° or less with respect to a surface of the sheet.

10. The feeder of claim 9, further comprising a changeover switch, wherein when the first ultrasonic element is connected to the transmission amplifying section, the second ultrasonic element is connected to the reception amplifying section, and when the second ultrasonic element is connected to the transmission amplifying section, the first ultrasonic element is connected to the reception amplifying section.

11. The feeder of claim 7, wherein the first element is a light emitting element, and the second element is a light receiving element.

12. The feeder of claim 11, wherein the light emitting element and the light receiving element are provided to have alight incident angle of 90° or less with respect to a surface of the sheet.

13. The feeder of claim 7, wherein the first element and the second element are provided in a range from a downstream side of a joining point of the outside conveyance path and the inside conveyance path in the sheet conveyance direction to a near side of a read part.

14. The feeder of claim 7, wherein when one of an OUT sheet passing sensor to detect passing of the sheet along the outside conveyance path and an IN sheet passing sensor to detect passing of the sheet along the inside conveyance path is damaged to be ON, the conveyance path having the damaged sensor is not used, and the sheet is conveyed to only the conveyance path having the normal sensor.

15. The feeder of claim 7, wherein when one of an OUT sheet passing sensor to detect passing of the sheet along the outside conveyance path and an IN sheet passing sensor to detect passing of the sheet along the inside conveyance path is damaged to be OFF, the conveyance path where a jam occurs continuously is not used, and the sheet is conveyed to only the normal conveyance path.

16. A double feed detection method comprising: generating a control signal by a control section;generating a transmission signal from the control signal by a transmission signal generation section;amplifying the transmission signal by a transmission amplifying section;outputting the amplified signal to a sheet in a direction perpendicular to a conveyance direction of the sheet by a first element;receiving the signal of the first element passing through the sheet by a second element;amplifying the received signal by a reception amplifying section; andconverting the received signal as the amplified analog, signal into a digital signal by an A/D converter and outputting it to the control section.

17. The method of claim 16, wherein the first element is a first ultrasonic element and the second element is a second ultrasonic element.

18. The method of claim 17, wherein the first ultrasonic element and the second ultrasonic element are provided to have an ultrasonic wave incident angle of 40° or less with respect to a surface of the sheet.

19. The method of claim 18, wherein a changeover switch is used and when the first ultrasonic element is connected to the transmission amplifying section, the second ultrasonic element is connected to the reception amplifying section, and when the second ultrasonic element is connected to the transmission amplifying section, the first ultrasonic element is connected to the reception amplifying section.

20. The method of claim 16, wherein the first element is a light emitting element,the second element is a light receiving element, andthe light emitting element and the light receiving element are provided to have a light incident angle of 90° or less with respect to a surface of the sheet.