JP3270259B2 - Document double feed detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile machine, and an image reading apparatus used for a scanner and the like, irrespective of the paper type, size, behavior and other transport conditions of a document. The present invention relates to a document double feed detection device capable of reliably detecting double feed of a document.

[0002]

2. Description of the Related Art In an image reading apparatus used for an image forming apparatus such as a copying machine, a printer, a facsimile apparatus and a scanner, an automatic document feeder for automatically feeding a document to a reading position such as a contact glass or a slit glass. A device is used. The automatic document feeder takes out documents one by one from a bundle of documents set in a stacked state on a platen and feeds them to the above-mentioned reading position. A separation mechanism is provided for separating the multi-feed state and conveying only one sheet to the reading position. However, no matter how the performance of the separation mechanism is improved, it is practically impossible to eliminate the double feed by 100%. In the image reading apparatus, when double feeding occurs, a page in a plurality of originals is lost, and a situation occurs in which the page is not read. In order to read the missing page, it is necessary to search for the missing page from among the read documents stacked on the document output tray, but to search for the missing page, the obtained copy paper It is necessary to perform while comparing. The larger the number of documents, the greater the amount of work and the longer the work time.

[0003] Japanese Patent Application Laid-Open No. Hei 5-43091 discloses that a transport path between a document feeding table and a document reading section is provided on a transport path.
A technique of arranging a paper thickness detecting means composed of a minute angle sensor or a transmission type photo sensor and a paper size detecting device, and judging the presence or absence of a double feed based on information on paper thickness and size obtained from two types of sensors. Is disclosed. However, the above-mentioned minute angle sensor has a limit in its accuracy when detecting a minute change in paper thickness in μm units, and if high accuracy is to be obtained, the cost may increase or failures may increase. There is. In addition, the transmission type photo sensor detects the presence or absence of double feeding based on the transmitted light amount of the detection light passing through the original.However, even if the paper thickness is the same, the density of the paper may vary depending on the manufacturer. Since there is variation, the method of determining the presence or absence of double feed based on only the amount of transmitted light is low in reliability. Further, since the amount of transmitted light varies depending on the presence or absence of an image on a document and the density, it is impossible to determine the presence / absence of double feeding only from the amount of transmitted light. Further, in this prior art, when the size of the document is different, the condition is satisfied on the assumption that the paper thickness is often different. There are many cases where the thickness is different or the paper thickness is the same even if the size is different, so that the reliability of this detection means has to be said to be extremely low.

In actual use of an image reading apparatus, a large number of originals of the same paper type and the same size, such as slips, are used as compared with a case where originals of different sizes and different paper types are used. Since the automatic feeding is often performed for reading, the above-described conventional example has an error in the precondition thereof, and its practicality is extremely doubtful. Also, Japanese Patent Application Laid-Open No. Sho 60-1
The double feed detecting method disclosed in Japanese Patent No. 44256 detects the amount of displacement by utilizing the fact that the paper feed roller is displaced in accordance with the thickness of the document passing through the nip portion of the paper feed roller pair. Thus, the double feed is not detected, but this detection method also has a problem in accuracy. That is, in this detection method, the movement of the end of the lever that moves up and down in conjunction with the vertical displacement of the rotation axis of the paper feed roller is detected as a change in resistance value using a variable resistor, or is detected using a photo interrupter. However, it is difficult to accurately detect a change in the sheet thickness in the unit of μm, and the mechanism around the sheet feeding roller is complicated, and the required assembling accuracy is high, which is a problem. In addition, since multiple parts are used, the amount of displacement of the paper thickness often fluctuates due to tolerance between parts, play, eccentricity of rollers, behavior of a document, and the like, and erroneous detection often occurs. In addition, in the above-described conventional method, unless the conveyance path of the document is substantially straight, the behavior of the document cannot be controlled, and there is a possibility that erroneous detection may be performed. Here, the behavior of the document includes
Ups and downs of the document, which are likely to occur when the transport conditions fluctuate,
Changes in the vertical and horizontal directions, such as bouncing, bending, bending (curling), and wrinkling.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has a high accuracy in the thickness of a document without increasing the number of parts, complicating the structure, increasing the cost, and increasing the mounting accuracy. An object of the present invention is to provide a document double feed detection device capable of detecting a difference and detecting occurrence of double feed. Further, the present invention provides a document double feed detecting device capable of detecting double feed relatively accurately even if there is a difference in light transmittance due to fiber density as long as the paper thickness is substantially the same.

[0006]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a document table, a paper feed mechanism for taking out a document from the document table, a reading section for reading an image of the document conveyed by the paper feed mechanism, And a document feeder comprising: a document leading edge detecting means and a document sheet thickness detecting means sequentially arranged on a transport path from the document table to the reading section; The presence / absence of double feeding of the document is determined based on the information on the passage timing of the leading edge of the document and the information on the document sheet thickness from the document sheet thickness detecting means. It is characterized in that it is set between a plurality of idler rollers arranged above along the width direction. Also, the axis of each idler roller is at an angle θ (0 ° <θ) with respect to a line parallel to the conveyance direction.
<90 °).

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the accompanying drawings. In the present invention, by focusing on the presence of a transport roller that is always disposed in the transport path of the document, the document sheet thickness detecting means is disposed between a plurality of idler rollers disposed in a direction intersecting the transport direction, so that the document is transferred. The characteristic feature is that the paper thickness can be accurately measured without being affected by the behavior of the document being conveyed by measuring the paper thickness in a state where the paper is securely pressed onto the conveyance path.

FIG. 1 is an explanatory view of a main part of an image reading apparatus to which a multi-document detection device of the present invention is applied. A document table 1 on which a plurality of documents D are set in a stacked state, and a document D from the document table. Paper feed mechanism 2 for taking out an image, a reading unit 3 for reading an image of a document conveyed by the paper feed mechanism 2, and a conveyance roller 4
(4a, 4b), a paper discharge roller 5, a document leading edge detecting means 10, a document paper thickness detecting means 11, which are sequentially arranged along the transport path, and a control unit (not shown). Paper feed mechanism 2
Is composed of a pickup roller 15 for taking out the original in contact with the original on the original table, and a separation roller pair 16 for separating the extracted original. The characteristic configuration of the present invention is that, as described later, the document paper thickness detecting means 11 is provided between one of the transport rollers 4 arranged in the transport path, for example, two rollers constituting an idler roller 4a. It exists at the point where it is placed.

The document leading edge detecting means 10 is a reflection type photo sensor, and detects the passage of the edge of the document due to the change in the amount of light when the detection light emitted from the light emitting element toward the transport path is received by the light receiving element. And outputs information of the leading edge of the document to the control unit. The control unit includes a document leading edge detection unit 10
The presence or absence of occurrence of double feed is determined based on the data on the leading edge of the document detected by the above and the data on the sheet thickness of the document described later.

Also, as shown in FIG.
1 includes a light-emitting element (LED) 21 and a position detection element (light-receiving element, for example, a position detection element manufactured by OMRON Corporation) 22 inside a hollow box 20 having a light-shielding property.
The detection light is emitted from an emission hole 20a formed through the surface of the box body facing the document guide plate 23, and the detection light reflected on the guide plate 23 or the upper surface of the document D passing therethrough is provided in an appropriate position. The light enters the box through the entrance hole 20b. Entrance hole 20
The detection light incident from b is received by the position detection element 22,
The difference in the light receiving position is detected as a difference in the reflection position of the light (detection light) emitted from the light emitting element 21 (on the guide plate 23, on the document D1, or on the document D2).

[0011] The control section includes the document leading edge detecting means 10.
The presence / absence of double feed is determined based on the information on the position of the leading edge of the original (passing timing) from the printer and the information on the original paper thickness from the original paper thickness detecting means 11. That is, the timing at which the leading edge of the document has passed through the detecting means 10 based on the detection signal from the document leading edge detecting means 10 and the transport speed of a pulse motor or the like for driving the original transport driving rollers (for example, rollers 16 and 4b). The timing at which the leading edge of the document D1 reaches the document sheet thickness detecting means 11 is recognized in advance, and the thickness of the document D1 detected at that timing is measured and stored in a memory. Subsequently, the data obtained by measuring the thickness of the original at several positions behind the leading edge is compared with the thickness of the original D1, and the value of the latter data is larger than the thickness of the original D1. When it is larger, the occurrence of double feed is determined.

The paper thickness detecting method by the original paper thickness detecting means 11 will be described. When there is no original on the guide plate 23, the light emitted from the light emitting element 21 is reflected on the guide plate 23 when the light is reflected on the guide plate 23. Is received from the entrance hole 20b to the detection surface of the position detection element 22. Information on the light receiving position is sent to the control unit. When the light emitted from the light emitting element is reflected on the upper surface of the first sheet D1 of the multi-feed document, the reflected light is transmitted through the path of S2 to the position detecting element 22.
Is received by the detection surface of the control unit, and this data is sent to the control unit. The outgoing light reflected on the upper surface of the second sheet D2 of the multi-fed original is S
The light is received by the position detecting element 22 via the path 3.

Here, the upper surface (reference surface) of the guide plate 23
Position of reflected light obtained by irradiating light from the light emitting element to the surface (position of incidence on the light receiving surface of the position detecting element 22)
Then, the data about the incident position of the reflected light obtained by irradiating the detection light on the upper surface of the first document D1 based on the movement timing of the leading edge of the first document D1 is input to the control unit. Thereby, the paper thickness t1 (distance from the reference plane to the upper surface of the document D1) of the document D1 is detected and stored in the memory. At this time, since the behavior on both sides in the width direction of the upper surface portion of the document D1 irradiated with the detection light is suppressed by the transport roller 4a, accurate detection is performed. Next, in the subsequent detection performed after the first detection, the detection light is applied to a further rear position of the document, and data on the position where the reflected light from the detection light is incident on the position detection element 22 is obtained. The distance (total paper thickness) t2 from the reference surface to the upper surface of the document D2 is measured. Based on the data relating to the paper thicknesses t1 and t2 and the paper thickness t3 of the thinnest document (previously stored in the memory), the control unit determines that these are at least (t1 +
When the relationship of (t3) ≦ (t2) is satisfied, it is determined that the document being conveyed causes double feeding.

FIGS. 3 (a) and 3 (b) are a plan view and a front view showing an example of the arrangement of the original sheet thickness detecting means 11, which are coaxial in a direction (width direction) intersecting with the original conveying direction. The document thickness detecting means 11 is arranged between the two transport rollers (idler rollers) 4a, 4a arranged in the direction of the arrow. Since the measurement is performed in a state where is flattened, it is possible to accurately detect the paper thickness in a state where the behavior of the document is suppressed. Reference numeral 23a is an upper guide plate.

Next, FIG. 4 shows that the axes of the transport rollers 4a, 4a are each at a predetermined angle θ with respect to a line L parallel to the transport direction.
(0.degree. <. Theta. <90.degree.), And the original paper thickness detecting means 11 is arranged between the rollers 4a, 4a. According to this embodiment, since the ability of the roller to suppress the deflection of the document is significantly improved as compared with the case of FIG. 3, the document of various paper types and sizes can be used without unreasonable resistance to the document being transported. Can be reliably suppressed, and the occurrence rate of erroneous detection can be reduced.

FIG. 5 is a diagram showing an example of a configuration for detecting the thickness of a document by using a paper thickness detecting means of the type shown in FIG. 2. In this example, a transport roller 30 is supported. Although the vertical displacement of the bracket 31 is detected as a change in the paper thickness, this method is indirect, and the detection error is likely to occur due to variations in precision of other parts, play, etc. Low. On the other hand, in each embodiment of the present invention, there is no such a problem, and high-precision detection can be performed.

[0017]

As described above, according to the present invention, the difference in the thickness of the original can be detected with high accuracy without increasing the number of parts, complicating the structure, increasing the cost, and increasing the mounting accuracy. Thus, the occurrence of double feed can be detected. Further, since the paper thickness is directly measured by the reflection type sensor, it is possible to prevent a decrease in measurement accuracy due to the presence of other components. Further, since the transmission type detection means is not used, double feed can be detected relatively accurately even if there is a difference in light transmittance due to the fiber density, as long as the paper thickness is substantially the same. In addition, since the number of components is small, erroneous detection can be prevented without being affected by tolerance of components, play, or the like.

[Brief description of the drawings]

FIG. 1 is a schematic configuration explanatory view of one embodiment of the present invention.

FIG. 2 is a configuration explanatory view of an example of a document sheet thickness detecting means of the present invention.

3 (a) and 3 (b) are a plan view and a front view showing an example of the arrangement of a document sheet thickness detecting means of the present invention.

FIG. 4 is a plan view showing another arrangement example.

FIG. 5 is a diagram showing a defect of a conventional example.

[Explanation of symbols]

1 platen, 2 paper feed mechanism, 3 reading section, 4, 4a,
4b Conveyance roller, 5 paper discharge roller, 10 document leading edge detecting means, 11 document paper thickness detecting means, 15 pickup roller, 16 separation roller pair, 20 box body, 21 light emitting element (LED), 22 position detecting element.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B65H 7/12 B65H 7/14 G03G 15/00 H04N 1/00

Claims (1)

(57) [Claims] A document feeder that includes a document table, a paper feed mechanism for taking out the document from the document table, a reading unit that reads an image of the document conveyed by the paper feed mechanism, and a control unit; A document leading edge detecting means and a document paper thickness detecting means are sequentially arranged on a transport path from the document table to the reading section, and the control section includes information relating to a timing of passage of the document leading edge from the document leading edge detecting means and the document. The presence / absence of double feeding of the original is determined based on the information on the original paper thickness from the paper thickness detecting means, and the plurality of locations where the original paper thickness detecting means are arranged along the width direction on the transport path are determined. Wherein the axis of each of the idler rollers is inclined at an angle θ (0 ° <θ <90 °) with respect to a line parallel to the conveyance direction.