JP2973475B2 - Document leading edge detection method of document reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for detecting the leading edge of a document used in an image reading apparatus. The purpose is to automatically detect the leading edge of the document in the document reading apparatus. In the apparatus, an image signal detection circuit that detects an image signal in a read signal of the image reading unit, a signal width holding circuit that holds a value of a reference signal width, and the detected image signal is output from the signal width holding circuit. A signal width determination circuit that determines that the width is equal to or larger than the supplied reference signal width, wherein a presence signal of an image signal having a predetermined width or more detected by the signal width determination circuit is used as a leading edge detection signal of the document. I do.

[Industrial applications]

The present invention relates to a document leading edge detection method of a document reading device used for image input such as a facsimile, a character reading device, and an electronic file device.

[Prior Art] The configuration of a conventional document reading apparatus is shown in FIG.

Conventionally, in a method of detecting the leading edge of a document in a document transport type image reading apparatus, a document detection sensor 5 is provided before a document reading point 7.

The document detection sensor used here is based on a mechanical principle or is electrically or optically used to detect the presence of a document at a detection point.

Then, after the document arrives at the document detection sensor 5 and the presence of the document is detected, the document is transported by a distance 8 between the document detection sensor 5 and the document reading point 7, and the transport time is estimated from the distance. After a lapse of the transport time, the image at the original reading point is read by the image sensor 1 such as a CCD and an image signal is output.

At the original reading point 7, the lamp 4 illuminates, and the mirror 3 and the lens 2 collect the light at the original reading point 7 on the image sensor 1 to electrically convert the image signal.

In this method, in the case of an optical character reading device (OCR), it is necessary to determine the character device, so that the original detection sensor 5
And the positional accuracy of the original reading point 7 is required, and the higher the accuracy, the higher the cost. Actually, since it is impossible to maintain the positional accuracy constant, the document feed amount from the document detection sensor to the document reading point is obtained for each apparatus, and the value of the document feed amount is set by a switch or the like. Was.

For this reason, adjustment of the apparatus is complicated, and it has been difficult to manufacture and maintain the apparatus.

[Problems to be solved by the invention]

As described above, the conventional document leading edge detection method of the image reading apparatus requires an adjustment operation, and has a problem that the manufacture and maintenance of the apparatus are difficult.

In view of such a point, an object of the present invention is to provide a means for automatically detecting the leading edge of a document of an image reading apparatus.

[Means for solving the problem]

The above problem can be solved by a document leading edge detection method of an image reading apparatus configured as described below.

 FIG. 1 is a diagram illustrating the principle of the present invention.

In the document reading apparatus having the image reading unit 10, an image signal detection circuit 26 that detects an image signal in a read signal of the image reading unit 10, and a signal width holding circuit 27 that holds a value of a reference signal width
And a signal width determination circuit 28 for determining that the detected image signal is equal to or larger than the reference signal width supplied from the signal width holding circuit 27, and the fixed width detected by the signal width determination circuit 28. The presence signal of the above image signal is configured to be a leading edge detection signal of the document.

(Operation)

In FIG. 1, an image signal output from the image sensor 1 of the image reading unit 10 enters an image signal detection circuit 26.

The image signal detection circuit 26 compares the image signal with the threshold value supplied from the threshold value holding circuit and counts the width of the input equal to or larger than the threshold value.

The signal width holding circuit 27 holds a reference signal width that can be recognized as the leading edge of the sheet.

The signal width determination circuit 28 compares the input width equal to or larger than the threshold value counted by the image signal detection circuit 26 with the reference signal width held by the signal width holding circuit 27, and holds the determination result in the bistable circuit. , And use the result as a tip detection signal.

〔Example〕

FIG. 2 is a block diagram showing the configuration of the embodiment of the present invention.

An image sensor 1 for reading an image; an amplifier 11 for amplifying the output of the image sensor 1; an analog-to-digital converter (A / D converter) 12 for converting the output of the amplifier 11 into a digital signal; And a circuit 13, 14, 15 in which three one-line memories for holding one-line image signals are connected in series in three stages.

The document leading edge detection circuit 20 includes an image signal detection circuit 26, a signal width holding circuit 27, and a signal width determination circuit 28, as shown in detail in FIG.

FIG. 4 shows a time chart of the operation in the embodiment.

The output of the image sensor 1 that has read the image is output from the amplifier 11.
And enters the A / D converter 12.

As shown in part A of the time chart, the output of the amplifier 11 is low when there is no original (corresponding to black), and the output level increases when the original enters (corresponds to white).

The scan start signal is output at the beginning of one line to instruct the start of the line, and an image signal of one line is serially transmitted from the image sensor.

The signal input to the A / D converter 12 is converted into a digital value, and the output is stored as an image signal 21 in a one-line memory and supplied to a document leading edge detection circuit 20.

In the document leading edge detecting circuit 20, the image signal detecting circuit 26 compares the image signal 21 with the threshold value held by the threshold value holding circuit, and counts a signal higher than the threshold value as an image signal for each line. The clock used at this time is a video synchronization clock, and the clock is a transfer clock of an image signal used for transfer from the image sensor 1 and transfer in one-line memory.

The counted value is compared with the value held in the signal width holding circuit 27 by the signal width determination circuit 28, and the comparison result is set in the bistable circuit 25 by the scan start signal.

The output of the bistable circuit 25 set according to the comparison result is used as the tip detection signal. This signal is shown as part B in the time chart of FIG.

When the image reading apparatus is used as an OCR, a black signal line is required as a reference line at the leading end of the sheet, so that a one-line memory is connected in multiple stages in series to hold a plurality of lines of the black signal.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, there is a remarkable industrial effect that the leading edge of the document of the image reading apparatus can be automatically detected.

[Brief description of the drawings]

 FIG. 1 is a principle diagram of the present invention, FIG. 2 is a block diagram showing a configuration of an embodiment of the present invention, FIG. 3 is a detail of a document leading edge detection circuit, FIG. 4 is a time chart in the embodiment of the present invention, FIG. 5 shows the structure of a conventional document reading apparatus. In the figure, 1 is an image sensor, 2 is a lens, 3 is a mirror, 4 is a lamp, 5 is a document detection sensor, 6 is a document, 7 is a document reading point, 8 is a conveyance distance, 10 is an image reading unit, and 11 is an image reading unit. Amplifier, 12 is A / D converter, 13, 14, 15 is 1 line memory, 20 is original leading edge detection circuit, 21 is image signal, 22, 24 is comparator, 23 is counter, 25 is bistable circuit, 26 denotes an image signal detection circuit, 27 denotes a signal width holding circuit, and 28 denotes a signal width determination circuit.

Claims (1)

(57) [Claims] An image reading device having an image reading section, an image signal detecting circuit for detecting an image signal in a read signal of the image reading section, and holding a value of a reference signal width. And a signal width determination circuit (28) for determining that the detected image signal is equal to or larger than the reference signal width supplied from the signal width storage circuit (27). A document leading edge detection method for a document reading apparatus, wherein a presence signal of an image signal having a predetermined width or more detected by the signal width determination circuit (28) is used as a document leading edge detection signal.