JPS6244740B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document reading method for reading a document and converting it into an electrical signal in a copying machine, facsimile machine, printer, or the like.

In general, conventional copying machines, facsimile machines, etc. use a one-dimensional image sensor as a photoelectric conversion element to read a document and convert it into an electrical signal. By using the dimensional image sensor, the image is read while simultaneously being moved in the sub-scanning direction by moving the original or moving an optical system such as a mirror.

However, when using a one-dimensional image sensor,
Since the light amount accumulation time can only be taken for a time equal to the scanning time of one line, there is a risk that the light amount will be insufficient during high-speed reading. Therefore, it is possible to increase the amount of light by using a halogen lamp as the light source, but
It is not preferable to use a halogen lamp as a light source because the compatibility with the spectral sensitivity characteristics of the image sensor or the resolution characteristics deteriorate particularly with respect to infrared light.

Furthermore, since the sub-scanning is continuous movement, there is a possibility that the resolution may deteriorate. Therefore, it is conceivable to use a step motor, but considering its response characteristics, if a one-dimensional image sensor is used, it will be equivalent to continuous movement, and resolution deterioration cannot be prevented.

In order to solve this problem, the reading line in the main scanning direction (hereinafter simply referred to as "line")
It is conceivable to read the document using a two-dimensional image sensor having multiple rows of images on one chip. That is, the use of a two-dimensional image sensor has the following advantages over the case of using a one-dimensional image sensor.

(1) The light intensity accumulation time can be multiple times the scanning time of one line, thereby increasing the intensity of the light source,
Directly, it becomes possible to lower the image plane illuminance.

(2) In the case of a one-dimensional image sensor, in order to increase light utilization efficiency, it is necessary to illuminate only the area of the document to be read with one line of the image sensor, and if the light source is a fluorescent lamp, an aperture should be provided on a part of the fluorescent screen. This required measures such as adding a cylindrical lens. However, when a two-dimensional image sensor is used, a relatively wide area of the document is illuminated, so there is no burden on the light source.

(3) Since the image is stopped during light intensity conversion, there is less deterioration in resolution.

In this way, by reading a document using a two-dimensional image sensor, it is possible to eliminate the problems that occur when a one-dimensional image sensor is used, especially during high-speed reading.

However, due to manufacturing problems, two-dimensional image sensors currently have a maximum number of lines of about 500 lines, and there is no element that can read the entire surface of a document at once. Therefore, when reading the entire surface of a document using an existing two-dimensional image sensor, the surface of the document must be divided into several parts in the sub-scanning direction and the reading must be performed multiple times.

Here, if the number of lines required to read the entire document is L and the number of effective lines read by the two-dimensional image sensor at one time is n, then the number of readings N is N=L/n.

In this way, when using a two-dimensional image sensor, reading is required N times, and if the image moves continuously at this time, resolution becomes impossible. For this purpose, the image must be moved intermittently, but it is extremely difficult to control the amount of movement of each movement step to be exactly equal. Therefore, the intermittent movement may impair the continuity of reproduced images, resulting in, for example, overlapping or missing images.

This invention has been made in view of the above-mentioned points.
A two-dimensional image sensor having multiple rows of reading lines in the main scanning direction sequentially reads a predetermined range that partially overlaps in the sub-scanning direction of the document at each conveyance step of the document and converts it into an image signal as an electric signal. The actual step feed amount of the document is detected for each transport step, and the first effective reading line for the next document reading is determined based on this step feed amount. To provide a document reading method that removes image signals and corrects joints in the sub-scanning direction of images, enables high-speed reading with good resolution, and does not impair the continuity of reproduced images. .

Embodiments of the present invention will be described below with reference to the accompanying drawings.

1 and 2 are schematic perspective views showing the configurations of different parts of a document reading device embodying the present invention, respectively. In FIG. 1, numeral 1 denotes a document, and 2 denotes a conveyor belt that intermittently conveys the document 1 in the direction of arrow A for sub-scanning. The conveyor belt 2 rotates intermittently in the direction of arrow B under the control of the step rotation of feed rollers 3 and 3' driven by a step motor (not shown), and the set movement amount for each step is shown in FIG. Image sensor 9 shown in
The width W in the sub-scanning direction of the imaging range P for one time is made smaller than the width W in the sub-scanning direction.

A rotary encoder 4 is connected to the feed roller 3 by a shaft 5, and detects the amount of step movement of the conveyor belt 2 in each conveyance step and outputs a position signal c. Since the conveyance belt 2 and the document 1 can be regarded as one body, this position signal c indicates the actual step feed amount of the document 1 at each conveyance step.

In FIG. 2, 6 is a contact glass serving as a document table, and 7 is a slit illumination light source consisting of a fluorescent lamp 7a and a reflecting mirror 7b. illuminate. Reference numeral 8 denotes a lens that reduces and forms an original image formed by reflected light from the original 1 on the photoelectric conversion surface 9a of the image sensor 9.

The image sensor 9 is a two-dimensional type element having a photoelectric conversion surface 9a made up of a plurality of reading lines 9b, and simultaneously reads the screen of the original 1 within a single imaging range P, converts it into an electrical signal, and generates an image signal. a
is output sequentially for each line. Reference numeral 10 denotes a signal processing circuit that inputs the position signal c output from the rotary encoder 4 and the image signal a output from the image sensor 9, respectively, and outputs an effective image signal b. The configuration and operation of this circuit will be described in detail later. do.

Next, a method of reading a document using the document reading device configured as described above will be described. The document 1 is intermittently placed on the contact glass 6 by the conveyor belt 2.
Move upward in the direction of arrow A. Each time the original 1 stops, the image sensor 9 accumulates light on the original screen located within the imaging range P according to the amount of light reflected from each part, generates a charge according to the amount of light, and transfers it from the controller described later. The charges are transferred to a shift register by a pulse, and read out sequentially by a reading pulse to output an image signal a. This image signal a is outputted as an effective image signal b via the signal processing circuit 10. The entire screen of the document 1 can be read by the image sensor 9 performing the above-described reading N times.

By the way, the set movement amount for each step of the conveyor belt 2 is the width W in the sub-scanning direction of the imaging range P at one time.
Therefore, even if the actual movement amount changes somewhat for each transport step, a portion of the image of the document 1 that comes to the position of one imaging range P will overlap one after another. Therefore, among the signals of each line constituting the image signal a output from the image sensor 9, the signals of one part of the lines will be outputted redundantly, and if the image signal a is used as a reproduced image signal, Image duplication occurs in the reproduced image. Therefore, in this invention, together with the image signal a, the rotary encoder 4
The position signal c of the document 1 detected by the above is input to the signal processing circuit 10, and correction is thereby performed to cut out the signal of the overlapping line.

FIG. 3 is a block circuit diagram showing an example of this signal processing circuit 10. In the figure, 11 is a controller that controls the image sensor 9 and the signal processing circuit 10. As shown in FIG. 12 is a feed amount detection circuit that detects the step feed amount of the document 1 in each transport step based on the signal fl from the controller 11 and the position signal c from the rotary encoder 4;
13 is a numbering circuit that outputs a reference number signal Rn indicating the first effective reading line and the last effective reading line when reading each document; 14;
is a line counter that counts the line synchronization signal sl output by the controller 11 in synchronization with the reading of each line.

A comparator 15 compares the reference number signal Rn of the numbering circuit 13 and the line count value nl of the line counter 14 at the time of reading each document;
6 is a latch circuit controlled by the output signal s of the comparator 15; 17 is the output signal g of the latch circuit 16;
This is an analog switch that is controlled on and off by the .

The operation of cutting overlapping lines by the signal processing circuit 10 configured in this way will be explained.

First, to explain the method of outputting the image signal a from the image sensor 9, if the number of lines of the image sensor 9 is M, one imaging range P is M lines from the 1st line to the Mth line. be read. When the screen of the document 1 is photoelectrically converted from the first line to the Mth line, the controller 11 outputs a transfer pulse as an image sensor control signal d, and sends a signal to the shift register corresponding to each line in the image sensor 9. is transferred, and then a read pulse is output to sequentially read out the signal line by line from the first line to the Mth line. In this way, the image signal a obtained by reading the document screen within the imaging range P at one time is output.

In this embodiment, the first effective reading line at the first reading of the original is set to the K-th line, and the last effective reading line at each reading of the original is set to the L-th line.

Here, if the number of lines corresponding to the preset one step feed amount is n, and the number of lines from the 1st line to the K'th line is k', then the Lth line is L=k'+n- 1...(1) becomes.

Next, a method of cutting the signals of overlapping lines to match the seams of images will be explained.

First, when the document 1 is conveyed and the first document reading is performed, the image signal a from the image sensor 9 and the rotary encoder 4 output the step feed amount of the document 1 in proportion to the amount of rotation of the shaft 5, for example. The position signals c converted into the number of pulses are respectively input to the signal processing circuit 10. In this case, the controller 11 outputs the frame signal fl to the feed amount detection circuit 12 and the line counter 14 at the beginning of document reading in each transport step, and
A signal indicating that the first valid read line is the K'th line and a signal indicating that the line following the last valid read line is the L+1th line are output to the numbering circuit 13, respectively.

The feed amount detection circuit 12 receives the first frame signal.
When fl is input from the controller 11,
Feed amount x from position signal c of rotary encoder 4
The numbering circuit 1 generates a signal indicating that is zero.
Enter 3. Thereby, the numbering circuit 13 inputs to the comparator 15 a signal k' indicating that the reference number Rn is the K'th line. On the other hand, the line counter 14 is cleared by the frame signal fl of the controller 11, counts the number of input line synchronization signals sl that the controller 11 outputs first every time each line is read, and indicates the line count value nl. The signal is outputted and used as the other input of the comparator 15.

The comparator 15 uses the line count value nl of the line counter 14 as the reference number of the numbering circuit 13.
When there is a match with the K'th line Rn, that is, when the number of input line synchronizing signals sl reaches k', a match signal s is output and the latch circuit 16 is set.
Thereby, the latch circuit 16 outputs the gate signal g to turn on the analog switch 17. Therefore, the analog switch 17 switches to the first effective reading line when reading the document for the first time.
The image signal a is passed from the K' line.

On the other hand, in response to the match signal s from the comparator 15, the numbering circuit 13 inputs to the comparator 15 a signal in which the reference number Rn is switched to the L+1th line. Then, the comparator 15 outputs the coincidence signal s again when the line count value nl of the line counter 14 matches the number of lines l+1 from the first line to the L+1th line, that is, when the number of line synchronization signals sl reaches l+1. The latch circuit 16 is then reset.
Thereby, the latch circuit 16 outputs the gate signal g to turn off the analog switch 17. Therefore, the analog switch 17 cuts off the image signal a from the L+1th line, which is the next line after the valid last read line (Lth line).

In this manner, in the first reading of the document, the effective image signal b read in n lines from the K'th line to the Lth line is output.

When the document 1 is further conveyed one step and the second document reading is performed, and the second frame signal fl is output from the controller 11, the feed amount detection circuit 12 detects the position at the time of the first document reading. The feed amount x is calculated from the signal c ₁ and the position signal c ₂ during the second document reading. In this case, the feed amount x is x=
It is determined by the formula c ₂ − _{c 1} .

The numbering circuit 13 calculates the current first effective reading line based on the feed amount x output by the feed amount detection signal 12. In this case, if the number of lines corresponding to the feed amount x is nx, the part of the document 1 corresponding to the L+1 line during the first document reading is moved in the direction of the first line of the image sensor 9 by nx times. That means you did it. Therefore, this first
If the effective reading line is the K-th line, then K=L+1-nx...It is determined by the equation (2), and by substituting equation (1) into equation (2), K=k'+(n-nx)... …(3) becomes.

In other words, the current first effective reading line K is the number k' of lines up to the K'th line which is the first effective reading line set in advance, the number n of lines corresponding to the preset amount of one step feed, and the actual number of lines. It corresponds to the line obtained by adding the difference of the number of lines nx corresponding to the feed amount x.

When the K-th line, which is the first effective read line for the second time, is calculated in this way, the numbering circuit 13 inputs a signal indicating that the reference number Rn is the K-th line to the comparator 15. The comparator 15 outputs a match signal s when the line count value nl of the line counter 14 matches the number of lines k from the 1st line to the Kth line, and the latch circuit 16
The analog switch 17 is turned on by setting the gate signal g output by the switch to a high level "H". Further, the numbering circuit 13 switches the reference number Rn to the L+1th line according to the coincidence signal s of the comparator 15, so the comparator 15 switches the reference number Rn to the line counter 14.
When the count value nl of matches the number of lines l+1 from the first line to the L+1th line, a match signal s is generated.
is output, and the gate signal g output from the latch circuit 16 is set to low level "L", and the analog switch 1
7 is turned off.

Therefore, during the second reading of the document, the effective image signal b read in nx lines from the K-th line to the L-th line is output.

By repeating the above operations N times, the entire screen of the original 1 can be read.

This will be briefly explained with reference to FIG. 4, which shows the number of times the document has been read by frame numbers. At the beginning of each document reading (hereinafter referred to as "frame"), the frame signal fl shown in FIG. ”, and the next line (L+th line) after the last valid read line (Lth line)
1 line), the gate signal g becomes low level "L". In the second and subsequent frames, the gate signal g becomes high level on the Kth line (K=L+1-nx) and becomes low level "L" on the L+1th line. The position of this Kth line varies depending on the actual step feed amount x (K ₁ , K ₂ , K ₃ , . . . ).

Therefore, when the image signal a shown in FIG. 4E passes through the analog switch 17, it is controlled by the gate signal g shown in FIG. 4D, and the effective image signal b shown in FIG. That is, as shown in Figure C, the number of effective read lines in the first frame is n, which corresponds to the set movement amount of one step, and the number of effective read lines in the second and subsequent frames is the actual number of lines between each frame. The number of lines is nx (nx ₁ , nx ₂ , nx ₃ , . . . ) corresponding to the feed amount x. Therefore, the image formed by this effective image signal b has continuous seams, and no overlap or omission occurs.

In this embodiment, the effective final reading line is always fixed to the Lth line, but the number of effective reading lines at one time is fixed (n lines), and the effective final reading line is the first effective reading line (Kth line). ) may be set to the K+nth line.

As described above with respect to the embodiments, according to the present invention, a predetermined range that partially overlaps in the sub-scanning direction of the document is read at each conveyance step of the document by a two-dimensional image sensor, and the image signals are overlapped. The entire screen of the document is read by cutting out the image signal of the line that is being scanned and correcting the seams in the sub-scanning direction of the image, which enables high-speed reading with high resolution.Moreover, the intermittent feeding of the document allows for reproduction. Image continuity is not impaired.

[Brief explanation of the drawing]

1 and 2 are schematic perspective views showing the configurations of different parts of a document reading device embodying the present invention, and FIG. 3 is a block circuit diagram showing an example of a signal processing circuit in an embodiment of the invention, and FIG. Figure 4 I~
F is a time chart for explaining the operation. 1...Document, 2...Transport belt, 4...Rotary encoder, 6...Contact glass, 7...
Light source for slit illumination, 8... Lens, 9... Two-dimensional image sensor, 10... Signal processing circuit, 11
... Controller, 12 ... Step amount detection circuit, 13 ... Numbering circuit, 14 ... Line counter, 15 ... Comparator, 16 ... Latch circuit, 17 ... Analog switch.

Claims (1)

[Claims] 1 While conveying the document intermittently in the sub-scanning direction,
A two-dimensional image sensor having multiple rows of reading lines in the main scanning direction sequentially reads a predetermined range that partially overlaps in the sub-scanning direction of the document at each conveyance step of the document and converts it into an image signal as an electrical signal. , detects the actual step feed amount of the document for each of the above-mentioned conveyance steps, determines the first effective reading line when reading the next document based on the number of reading lines corresponding to this step feed amount, and determines the first effective reading line for the next document reading. A document reading method characterized by reading the entire screen of the document while correcting the joints in the sub-scanning direction of the image by removing image signals of overlapping reading lines from among the signals.