JPH0516221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a double feed detection circuit for automatic paper conveyance for inputting images in an image input device.

Background of the technology In image input devices that automatically transport paper,
When two or more sheets of the input original are being conveyed at once, this is detected, the operation is temporarily interrupted, and the operator returns the double-fed original to its original position and reads it again.

Conventional technology and problems Conventionally, the double feed detection method uses a fixed pair of light sources and a photodetector to determine the amount of light transmitted through the paper, and when the output of the detector is lower than the reference value, the paper I believe there are more than one. However, since a photodetector is used, the detection position on the paper is fixed, making it impossible to detect double feed at any physically arbitrary position. Therefore, the double feed detection area, that is, the blank area where printing is not possible, is at a fixed position on the document, resulting in a problem in that the document format is restricted.

OBJECT OF THE INVENTION In view of the above-mentioned problems with the detection method in the conventional apparatus, an object of the present invention is to detect reflected light from an arbitrarily set white detection area within the entire document area using an image sensor that reads image input. Based on the idea of comparing the light intensity with the standard value,
The object of the present invention is to significantly relax restrictions on the document format when detecting double feed.

Structure of the Invention In the present invention, in a double feed detection circuit in an image input device that reads reflected light of an image written on paper through an image sensor,
A memory circuit that stores the format of a white detection area on paper, an analog-digital conversion circuit that converts the output of the image sensor from analog to digital, and an analog-digital conversion output value of each pixel of the image sensor for one sheet of white paper. a reference value generation circuit for storing, a gate circuit for gating the output of the analog-to-digital converter according to the format of the white detection area stored in the storage circuit, and storage of the output of the gate circuit and the reference value generation circuit. A comparison circuit for comparing the contents is provided, and when the output value of the gate circuit is higher than the memory contents of the reference value generating circuit by a predetermined value or more, it is detected that a plurality of sheets of paper have been fed. A double feed detection circuit for an image input device is provided.

Embodiment of the Invention A block circuit diagram of a double feed detection circuit in an image input device as an embodiment of the invention is shown in FIG.

A document 10 is conveyed in the direction of an arrow 11, and document information is read by an image sensor 2 through a lens 1. This information is the reflection level of the paper surface, and is output from the image sensor 2 as a voltage level. The output from the image sensor 2 is A/D converted by an analog-digital (A/D) converter 3 based on a fixed voltage V1 and a voltage level V2 (approximately 0 volts) when the image sensor 2 is shielded from light. . The fixed voltage V1 is the output level when the highest output bit of an image sensor consisting of 2048 pixels, that is, the highest bit of the photoelectric conversion rate, looks at a 100% white target (total reflection). FIG. 2 shows, by way of example, a curve 22 representing the output voltages for the pixels 1 to 2048 of the image sensor, and the highest point 21 of the curve 22 corresponds to the output of the bit with the maximum output.

The output from the A/D converter 3 is input to the gate 4, and the gate 4 receives an instruction from the central processing unit (CPU) 8 to detect the document in the white detection area with no characters or graphics on the paper stored in the memory circuit 9. According to the format, when scanning the white detection area, the gate is opened and a signal is sent to the comparator 6.

On the other hand, the reference value generation circuit 5 generates a gradation value corresponding to the output value of each pixel of the image sensor from the A/D converter 3 for the paper thickness of the input original according to instructions from the CPU 8. The A/D converter 3 performs conversion with a conversion level of 256 gradations. FIG. 3 is a diagram showing an example of the gradation values generated by the reference value generation circuit 5 using paper thickness (expressed as weight per fixed area) and pixels (bits) t1 to t2048 in the image sensor as parameters. . According to this figure, it can be seen that the standard pixel t1 portion of paper with a paper thickness of 50 kg is outputted from the A/D converter 3 as a gradation of 120 when the paper is not printed. The comparator 6 compares the signal from the gate 4 with the signal from the reference value generation circuit 5, and when the input from the gate 4 is higher than a predetermined value, a double feed detection signal is sent out.

The reflectance of the white paper portion of a document differs depending on the thickness of the paper when the backing of the document is black, and similarly shows different values when there is only one sheet of paper and when two sheets are stacked. Therefore, for each bit of the image sensor, the output level of one sheet of paper for each original paper thickness is memorized in advance, and when reading the original, that area of the image sensor is measured in the white detection area, and the output level is compared with the stored reference value. By comparison, double feed of paper is detected.

In the circuit of this embodiment, the image sensor 2
The A/D converter 3 can also be used as an image input device, and the output of the A/D converter 3 becomes an image input signal. Therefore, any part of the entire document can be set as a white detection area by specifying it in advance as document format information. In other words, without providing a special detection mechanism for double feed,
Double feed can be detected at any location on the document without contact using an image sensor that reads the document.

Effects of the Invention According to the present invention, it is possible to detect a double feed using an image sensor and an A/D converter of an image input device, and to greatly alleviate restrictions on document format for detection.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a double feed detection circuit in an image input device as an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing an example of each pixel of the image sensor and its output voltage in the circuit of FIG.
3 is a diagram showing an example of the reference tone value generated by the reference value generation circuit in the circuit of FIG. 1 using paper thickness and pixels as parameters. 1...Lens, 2...Image sensor, 3...
A/D converter, 4...gate, 5...reference value generation circuit, 6...comparator, 8...CPU, 9...memory circuit, 10...manuscript.

Claims (1)

[Claims] 1. In a double feed detection circuit in an image input device that reads the reflected light of an image written on paper through an image sensor, a memory circuit that stores the format of the white detection area on the paper and converts the output of the image sensor from analog to digital. an analog-to-digital conversion circuit; a reference value generation circuit for storing the analog-to-digital conversion output value of each pixel of the image sensor for one sheet of white paper; The digital converter includes a gate circuit that gates the output of the digital converter, and a comparison circuit that compares the output of the gate circuit with the memory contents of the reference value generation circuit, and the output value of the gate circuit is the memory content of the reference value generation circuit. 1. A double feed detection circuit for an image input device, characterized in that when the value is higher than a predetermined value, it is detected that a plurality of sheets of paper have been fed.