JPH0648847B2 - Offset correction method in image reading apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding a fixed document type image reading apparatus, for the purpose of automatically compensating for variations in the offset from the home position of the carrier to the document reading start position, A white sheet is provided on the back side of the frame plate that abuts the leading edge of the original when setting, the carrier is moved from the home position in advance, the white sheet is scanned, the width before and after that is measured, and the resulting value is read as an image. It is stored in the apparatus, and when the document is read, the carrier is moved from the home position to detect the front edge of the white sheet first, and then from that position, the width of the stored white sheet is determined to be a predetermined value. Image reading is started when the carrier moves by the distance obtained by subtracting the fixed value.

[Industrial application field]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed original image reading apparatus, and more particularly to a method for automatically correcting variations in each apparatus with respect to an offset from a home position of a carrier to an original reading start position.

[Conventional technology]

FIG. 7 is a rear view of a conventional general fixed original image reading apparatus.

In the figure, 1 is a frame plate, 2 is a reading surface, 3 is a document, 4 is a carrier, 5 is a home position of the carrier 4, and 6 is a reading start position.

During the document reading operation, the document 3 is placed on the reading surface 2 in the frame plate 1,
It is set so that the tip end abuts against the frame plate 1. The carrier 4 moves from the home position 5 in the direction of the arrow to sub-scan the reading surface 2, but the reading start position 6 is set slightly ahead of the reading surface 2, and when the carrier 4 comes to this position, CCD output is performed. The video gate that enables is opened and the reading is actually started.

The distance from the reading start position 6 to the tip of the reading surface is called an offset (fixed value α in FIG. 1).

Conventionally, there are the following two methods for determining the offset.

FIG. 8 (a) shows the first method, in which the position where the carrier 4 is separated from the home position 5 by a constant distance is set as the reading start position 6, and it is called the home position method because the home position is used as a reference.

FIG. 8 (b) shows the second method, in which a start mark is printed on the back surface of the frame plate 1 and reading is started when the carrier 4 detects this start mark during scanning. It is called the mark method.

[Problems to be Solved by the Invention]

The conventional home position method for determining the offset in the image reading apparatus has a problem that the accuracy of the carrier mechanism varies and is easily affected by the temperature change and the inclination of the installation surface of the apparatus. However, it is difficult to eliminate the variation in the reading start position for each device by a simple means.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a means for easily correcting a variation in offset of each image reading apparatus in an image reading apparatus at low cost.

[Means for Solving the Problems]

According to the present invention, a white sheet is provided on the back surface of a document abutting frame plate of an image reading apparatus, and a position at a certain distance forward from the trailing edge of the white sheet, that is, the edge where the document front end is abutted, is set as a reading start position. Therefore, the front and rear widths of the white sheet are measured in advance for each device and stored in the device, and if the front edge of the white sheet is detected by moving the carrier from the home position during the document reading operation, the memory is stored. The width of the white sheet is subtracted from a predetermined small fixed value, and the carrier is further moved as the distance from the leading edge of the white sheet to the reading start position. I am trying to do it.

FIG. 1 is an explanatory view of the principle of the present invention.

In the figure, 1 is a frame plate whose back surface is not white (for example, black),
3 is a document, 4 is a carrier, 5 is a home position, 6 is a reading start position A, 7 is a white sheet, 8 is a glass plate, 9 is a control unit, 10 is a white sheet width measurement processing unit, and 11 is a document reading processing unit. , 12 is the width W of the white sheet, 13 is the front edge position B of the white sheet, 14 is the rear edge position C of the white sheet, 15 is a fixed value α common to each device, 16 is the reading start from the front edge position B of the white sheet. The moving distance R, 17 to the position A is a video gate.

The white sheet width measurement processing unit 10 is activated at the time of shipment adjustment of the apparatus and moves the carrier 4 from the home position 5 to the right (sub scanning direction) to move the front edge position B and the rear edge position of the white sheet 7. C is detected, and the white sheet width W is calculated by W = C−B and stored in the ROM or the like.

The document reading processing unit 11 is activated at the time of reading each document, moves the carrier 4 from the home position 5 to the right, first searches the white sheet 7, and if the leading edge position B is detected, first. From the stored white sheet width W and the fixed value α, the moving distance R from the leading edge position B of the white sheet to the reading start position A is calculated by R = W−α, and the position A is further determined. , When the carrier 4 moves from B to R and reaches the position of A,
The video gate 17 is opened, a video signal is output, and reading is started.

It should be noted that the white sheet can also be used as the white sheet that has been conventionally provided for the white reference.

[Action]

In FIG. 1, the mechanical accuracy of the carrier 4, the width W of the white sheet 7, the leading edge position B, the trailing edge position C, and the like may vary depending on the image reading apparatus. The reading start position A, which is moved from B by R = W-α, is located at the trailing edge position C of the white sheet 7, that is, the position ahead of the leading end position of the original 3 by the fixed value α. It can be set independently of this.

〔Example〕

FIG. 2 is a rear view of a document table of the image reading apparatus according to the embodiment of the present invention, in which 1 is a frame plate, 2 is a reading surface, 3 is a document, and 4 is a document.
Indicates a carrier, and 7 indicates a white sheet.

The white sheet 7 is provided entirely along the inner edge of the frame plate 1, and in the present invention, only the white sheet portion at the upper part of the rotation where the leading end of the original 3 is abutted is mainly involved.

FIG. 3 is a hardware configuration diagram of a control unit of the image reading apparatus according to the embodiment of the present invention, in which 4 is a carrier, 17 is a video gate, 18 is an MPU, 19 is a motor control unit, 2
0 is a timer, 21 is a flip-flop F. F. Reference numeral 22 is an address / data bus, and 23 is an image data bus.

When the operation of the apparatus is started, the MPU 18 sends control data to the motor control section 19 via the address / data bus 22 to drive the motor and move the carrier 4 from the home position in the sub scanning direction. Further, the MPU 18 sets a timer time in the timer 20 for each line of each main scan and activates the timer.

This timer time is for sampling the image data bus at the center of each line, and when the timer 20 counts the timer control signal corresponding to the pixel clock from the start of each line to the pixel position at the center of the line, the timer 20 The output OUT is turned on and the flip-flop F. F. The clock terminal CLK of is activated.

Flip-flop F. F. Are actually multiplexed by the number of bits of image data, and each of them is multiplexed when the clock terminal CLK rises.
The above image data is read and held until the timer output OUT turns on next.

The MPU 18 is a flip-flop F. F. Image data is read to determine whether the value is black or white, and the leading edge of the white sheet 7 in FIG. 2 is detected.

When the MPU 18 detects the front edge of the white sheet 7, the MPU 18 next calculates the moving distance to the reading start position by the method described above. When the carrier moves by the moving distance, the video gate 17 is opened and the image data bus is opened. The image data on 23 is output to the host.

FIG. 4 is an explanatory diagram showing a specific example of the control value for offset correction in the embodiment of the present invention.

In the example shown, the width (W) before and after the white sheet is 7 ± 0.
It is 5 mm, and the positions of its leading edge and trailing edge are 69.4 mm and 76.4 mm from the home position HP, respectively. The search operation for detecting the leading edge of the white sheet is performed within a range of 6 mm between the two positions S1 and S2 where the leading edge of the white sheet is definitely included. In this case, the position S1 is set 9 mm ahead of the video gate open position, that is, the original reading start position, and the video gate open position is set 1 mm ahead (corresponding to the fixed value α) of the trailing edge position of the white sheet. ing.

FIG. 5 and FIG. 6 are the control flow (1) and (2) of the offset correction according to the present invention, and both figures are combined to represent one flow.

In the illustrated control flow, the leading edge position of the white sheet is determined by examining the continuity of black pixels and white pixels in the sub-scanning direction at the center of each line. A black counter 24 and a white counter 25 for counting the continuous lengths are used. For each of the counts 24 and 25, a count that gives a full count of 20 is used.

When the document reading process is started, the black counter 24 and the white counter 25 are cleared, the timer time is set in the timer of FIG. 3, and the search of the leading edge of the white sheet shown in FIG. 4 is started. Position S1 and search end position S2
Is calculated and set. When the carrier moves and reaches the search start position S1, the control flow of FIGS. 5 and 6 is executed.

First, in FIG. 5, when a horizontal synchronizing signal for each line is generated, an interrupt is generated, and the flip-flop F. F. The multivalued image data is read by the MPU 18. In this example, if the multi-valued data is larger than X "12", it is determined to be black, and if it is smaller, it is determined to be white.

If the multi-valued image data is determined to be black, the black counter is incremented by 1 unless the black counter value is 20 or more (the full counter is operated within the range of 20), and the black counter value is 20. Is exceeded,
The white counted by the white counter until then is regarded as noise and the white counter is cleared. The value of the black counter is 10
The white counter is cleared when the above is reached.

On the other hand, when the multivalued image data is determined to be white, the white counter is incremented by +1 unless the value of the white counter is 20 or more. Where the white counter value is 1
If so, it is determined to be the first white, and the carrier position at that time is retracted (since it may be the leading edge of the white sheet). If the white counter value is a value other than 1, if the white counter value is 10 or more, it is considered that the black counted by the black counter at that time is noise, and the black counter is cleared. The black counter remains unchanged.

Further, when the white counter value is 1 and the carrier position is retracted, if the black counter value is 5 or more, it is changed to 5, and if it is less than 5, the black counter value is not changed, and then the white counter is changed to 10 It is checked whether or not there is the above. If it is 10 or more, the black counter is cleared, and if it is less than 10, it is not cleared.

The control of these complicated counters uses a black counter and a white counter with a small capacity to detect the leading edge of the white sheet while eliminating short continuous whites and blacks in the respective black and white areas. It is done.

After the values of the black counter and the white counter are determined in the flow of FIG. 5, the process of determining the leading edge and the offset position of the white sheet is performed in the flow of FIG. 6 based on these values.

That is, in FIG. 6, it is first checked whether the carrier position has reached the search end position S2 in FIG. 4 (*
1) If it has not arrived, the search is continued and the interrupt process is terminated. If it has arrived, the value of the white counter is checked.
If the value of the white counter is less than 10, it means that the white sheet itself could not be detected. Therefore, it is assumed that the white sheet front edge cannot be detected, and the interrupt correction interrupt process is stopped. The interrupt mask for prohibiting re-interruption for processing is set and the interrupt processing is completed. In this case, the conventional offset control method described in FIG. 8 is used instead.

On the other hand, when the value of the white counter is 10 or more, the previously retracted carrier position is determined as the white sheet front edge position, and when determined, is stored in the ROM next (stored in a predetermined fixed address). ) Read the white sheet width (W). In addition,
The same applies when the white counter value is 20 or more and is confirmed in FIG.

If the white sheet width value read here is 0, it is considered that the value has not been set (* 2). As in the case where the white counter value is less than 10, the offset control by the conventional method of FIG. 8 is performed. Perform, set the interrupt mask, and end the interrupt process.
Moreover, if the white sheet width value is other than 0, the value is already set, and the value is used to set the position for opening the video gate and the position for starting the white sheet follow-up control, and after setting the interrupt mask, the interrupt is set. The process ends.

〔The invention's effect〕

According to the present invention, as a white sheet used for offset correction, a conventional white sheet provided for white reference can be used as it is, there is almost no need to add new hardware, and offset variations among devices can be reduced. Can be easily corrected, and the image reading start position can be controlled with high accuracy at low cost.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention, FIG. 2 is a rear view of a document table of an image reading apparatus according to an embodiment of the present invention, FIG. Is an explanatory view showing a concrete example of the offset correction control value, FIGS. 5 and 6 are control flow charts of the embodiment of the present invention, FIG. 7 is a rear view of a document table of a conventional image reading apparatus, and FIG. 8 is an offset. It is explanatory drawing of the prior art example of a determination system. In FIG. 1, 1: frame plate, 3: document, 4: carrier, 6: reading start position, 7: white sheet, 9: control unit, 10: white sheet width measurement processing unit 11: document reading processing unit 12: White sheet width W, 13: White sheet front edge B, 14: White sheet rear edge C, 15: Fixed value α (offset).

Claims (1)

[Claims] 1. A method of correcting an offset from a home position of a carrier to a document reading start position in a fixed document type image reading apparatus, wherein a frame plate (1) against which the front end of the document abuts when the document is set.
The white sheet (7) is provided on the back side of the carrier, the carrier (4) is moved from the home position in advance, the white sheet (7) is scanned, and the width before and after that is measured,
The resulting value is stored in the image reading device, and the carrier (4) is moved from the home position to detect the leading edge of the white sheet (7) at the time of the document reading operation.
Next, image reading is started when the carrier (4) further moves from that position by a distance obtained by subtracting a predetermined fixed value from the width of the stored white sheet (7). Correction method in an image reading apparatus that performs