JP2002269543A - Density-measuring method and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a density-measuring device, capable of precisely correcting a density unevenness, even if the carrying quantity error of a scanner or the carrying quantity error of paper is uneven. SOLUTION: This method includes steps in which print data are imparted to a recording head to print a test pattern, the scanner is relatively moved, in relation to the test pattern to read the image of the test pattern, and the density data of the read image is measured; a plurality of indexes every dot line are printed along the relatively moving direction of the test pattern and the scanner to the test pattern, relatively intermittently moving the test pattern and the scanner to successively read the image of the test pattern between adjacent indexes, normalizing the density data of the read image and the density data number thereof, on the basis of the dot line number between the indexes between the adjacent indexes; and the density data corresponding to each dot line of the test pattern; are calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a density measuring method and an image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus having a recording head in which a large number of recording elements (ink jet nozzles) are arranged in a line has conventionally been known. Such a recording head is
Due to the manufacturing error, the ink ejection amount differs for each nozzle. For this reason, even if the recording head is manufactured in the same process, there is a variation in density when actually printing.

Conventionally, therefore, print data of a certain gradation is given to a print head for printing, read by an image scanner, a correction value is calculated based on the read density data, and the print data is calculated. Uneven density correction, which is corrected by image processing, was performed.

[0004] This will be described more specifically below. here,
When the number of nozzles of the recording head is 128 (see FIG. 18A), the density gradation that can be expressed by the ink ejection amount is 2
There are 56 tones. Also, if the number of pixels of the image scanner is 1
The number of test patterns is 28, and the test patterns are read at the same magnification. In addition,
It is assumed that the reading resolution of the image scanner is equal to the printing resolution of the printer.

First, the printer gives data of a density gradation 120 which is an intermediate density to all 128 nozzles, and prints a belt-shaped test pattern having a width of one head (128 nozzles) at a predetermined position on the paper. Print. FIG. 18B shows a state of the test pattern on the paper.

Next, the paper on which the test pattern is printed is placed at a predetermined position on the image scanner, and the test pattern is read. This state is shown in FIG.

In FIG. 19A, reference numeral 112 denotes a print sheet, 113 denotes an original glass table, and 114 denotes an index. The line sensor (not shown) of the image scanner is shown in FIG.
9 (A) are arranged in the Y direction, and the line sensor is X
The image of the test pattern is read by moving in the direction in units of the nozzle pitch. That is, since the movement pitch of the line sensor matches the nozzle pitch, that is, the dot pitch, an ink dot line image is read by each nozzle for each intermittent movement of the line sensor.

Next, a distribution chart of the data read by the image scanner with respect to the nozzle addresses (1 to 128) is created. If the read gradation of the image scanner is 256 gradations (0 is white, 255 is black), the data distribution is 12 gradations.
Although the gradation is centered on the 0th gradation, the data of the address of the nozzle with the large ejection amount is larger than 120, and the data of the address of the nozzle with the small ejection amount is 12
It becomes smaller than 0. The state of the density data of each nozzle of the head is shown in FIG.

The gain for the nozzle address is set based on the obtained nozzle data distribution. That is, a minus gain (a gain smaller than 1) is given to a nozzle with a large ejection amount, and a plus gain (a gain greater than 1) is given to a nozzle with a small ejection amount. FIG. 19C shows a nozzle gain distribution with respect to the nozzle data distribution of FIG.
Shown in

A density unevenness correction table is created based on the obtained nozzle gain distribution diagram. This density unevenness correction table is simply realized by the RAM. As a result, RA
The print data and the nozzle address are input to M in synchronization with each other, and correction data obtained by multiplying the print data by a preset gain is output from the data path.

Next, the drive signal of the density gradation 120 is corrected by the density unevenness correction table and applied to the recording head to perform printing. Actually, when a test pattern printed with correction data is read by an image scanner to create a nozzle data distribution diagram, a nozzle data distribution diagram as shown in FIG. 19D is obtained, and the density unevenness of the head is corrected. You can see that.

[0012]

When trying to read a test pattern with a scanner, it is necessary to move the scanner with respect to the test pattern as described above, or to move the test pattern with respect to the scanner.

For example, in the conventional example, when the test pattern is read by moving the scanner, the amount of one transfer of the scanner is made to coincide with the nozzle pitch (dot pitch). Therefore, the conveyance is repeated 128 times, and each time,
The image (dot line) of the test pattern at that position is read.

However, if the transport mechanism for transporting the scanner has looseness or the like, even if the transport amount corresponding to the dot pitch is to be transported, the actual transport amount of the scanner does not match the dot pitch. I will. In other words, even if the scanner itself is not actually transported in the unit of one dot pitch, it always determines that the scanner is transported in the unit of the predetermined one dot pitch. Even if it is off, it cannot be recognized. Since the error of the transport amount of the scanner leads to the error of the measurement position of the scanner, even if the correction data is created based on the obtained density data, the correction data cannot be supplied to the position where the correction should be originally performed. This causes a problem that density unevenness cannot be correctly corrected.

In the above conventional example, the scanner is transported with respect to the test pattern. Therefore, only the transport amount error of the scanner has been described. Needless to say, a paper conveyance error becomes a problem.

The present invention has been made in view of the above-mentioned problems, and it is a first object of the present invention to provide a density measuring method capable of accurately correcting density unevenness even when there is a variation in a transport amount error of a scanner or a paper transport amount error. Aim.

It is a second object of the present invention to provide an image forming apparatus capable of accurately correcting density unevenness even if there is a variation in a transport amount error of a scanner or a paper transport amount error.

[0018]

According to a first aspect of the present invention, there is provided a method for measuring density, comprising printing data having a predetermined density level on a recording head having a plurality of recording elements. Giving a test pattern, printing a test pattern, moving a scanner relative to the test pattern, reading an image of the test pattern, and measuring density data of the read image. Printing a plurality of indices for each predetermined dot line along the direction of relative movement of the scanner with respect to the test pattern;
(2) step of relatively intermittently moving the test pattern and the scanner to sequentially read the image of the test pattern between adjacent indexes; and (3) density data of the read image and the density between the adjacent indexes. Normalizing the number of data based on the number of dot lines between indices, and calculating density data corresponding to each dot line of the test pattern.

According to a second aspect of the present invention, there is provided an image forming apparatus capable of printing a test pattern having a predetermined density level for performing density measurement, wherein the test is performed when the density of the test pattern is measured by a scanner. A plurality of index marks are printed for each predetermined dot line along the reading movement direction of the scanner relative to the pattern.

According to a third aspect, in the image forming apparatus according to the second aspect, in the relative reading movement direction of the scanner, the first index mark is printed inward of the test pattern from the front end of the test pattern. The last index mark is printed inside the test pattern rather than at the end of the test pattern.

[0021]

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

(First Embodiment) The first embodiment relates to printing an index for only one test chart and reading it using an ink jet printer having a configuration as shown in FIG. In FIG. 1, 10
Denotes a carriage on which a CCD scanner 11 and a recording head 12 are mounted. The paper 13 is a transport roller pair 1
The sheet is conveyed in a state where it is nipped by the pair of rollers 4 and 15 and the pair of discharge rollers 17 and 18. A platen 16 is provided on the opposite side of the carriage 10 from the paper 13. 19 is a fan.

In performing full-color printing, a plurality of colors,
For example, in an ink jet printer that handles six colors of black, cyan, magenta, light cyan, light magenta, and yellow, although six recording heads are provided for each color, head shading correction of each head is performed by the same method. Here, one of them,
For example, only black will be described, and description of the remaining five color heads will be omitted. Here, the number of nozzles in the black recording head is 496.
The description will be made on the assumption that the nozzle pitch is 360 dpi.

When the test pattern is read, the paper 13 is conveyed to the CCD scanner 11, and the conveyance of the paper 13 is carried out by a convey motor for conveying one dot pitch (nozzle pitch). Are 20 drive pulses.

From now on, the test pattern is printed by 360 dpi, one-pass, one-way printing in order to perform density unevenness correction in a print mode such as 360 dpi, one-pass, one-way printing.

The printing of a test pattern will be described below with reference to FIGS. 2A and 2B. First, all the nozzles (496 nozzles) of the black recording head are
By giving print data as a test pattern having a certain gradation, a test pattern 100 as shown in FIG. 2A is printed on paper in one pass. The test pattern 100 to be printed has 600 lines (from 1 line to 60 lines).
The test pattern 100 is printed by scanning the head twice or three times (three times in the present embodiment) in order to make the line zero.

Although the number of nozzles is 496, the number of dot lines of the test pattern 100 is shown in FIG.
The fact that 600 lines are used as shown in FIG. If the number of dot lines of the test pattern 100 is 496, which is the same as the number of nozzles, the first line (the test pattern 100
When the CCD scanner 11 reads the line 496 (the boundary at the lower end of the test pattern 100) as the reading end line and the 496th line (the boundary at the lower end of the test pattern 100), the density of the adjacent area (in this case, a white background) is affected. (In this case, the density data to be read is low), so that accurate density data cannot be read. Therefore, as a countermeasure, the density data of the read start line and the read end line can be calculated more accurately by adding a plurality of dot lines of the same density data image to the upper end of the read start line and the lower end of the read end line. Becomes Here, the test pattern 100 is configured as 600 lines by adding 52 dot lines each to the upper end and the lower end.

In FIG. 2A, 1 to 52 lines indicated by A are printed by the first main scanning, and 5 lines indicated by B.
Lines 3 to 548 are printed in the second main scan, and C
Are printed in the third main scan.

Further, in addition to the image data corresponding to the test pattern 100, 5
3rd line, 153rd line, 253rd line, 353
For the nozzles that form the images of the lines 453, 549, and 549, a line-shaped index 101-1 to 101-6 indicating a reading start line, a line every 100 lines, and a reading end line is formed. The index 101-1 to 101-6 is printed adjacent to the test pattern 100 as shown in FIG.

The six indexes 101-1 to 101-
No. 6 is printed as a straight line having a predetermined length outward at right angles from one long side of the test pattern 100 parallel to the paper transport direction.

Here, in order to simplify the explanation,
The 53rd line of the test pattern 100 is
The first nozzle is used for printing.
The 53rd line is the 101st nozzle, the 253rd line is the 201st nozzle, the 353rd line is the 301st nozzle,
The description will be made on the assumption that the 453rd line is printed by the 401st nozzle and the 548th line is printed by the 1st nozzle in the next head scan.

FIG. 2B shows a test pattern 100 when there is no margin.

As shown in FIG. 3, the brightness of the CCD of the CCD scanner 11 can be adjusted at the same time as the printing of the test pattern 100 or before or after the printing. Are printed, and a reference line 103 (vertical line: standby position in the head scanning direction, horizontal line: standby position in the paper transport direction) 103 indicating the standby position of the CCD is printed.

The black pattern 102 is obtained by printing a predetermined rectangular area in solid black. The reference line 103 is composed of the black pattern 102 and the test pattern 1
Horizontal line 1 along the head scanning direction
03-1 and a vertical line 103-2 along the paper transport direction. The gap between the horizontal line 103-1 and the first line (top line) 101-1 of the index in the paper transport direction is set to a predetermined dimension (for example, a distance of 200 dot lines). Also, the vertical line 103-2
Are located in the head scanning direction at the indices 101-1 to 101-1.
Printing is performed so as to match the center of each line 101-6 in the head scanning direction.

The images to be printed, including the test pattern 100 and the indexes 101-1 to 101-6, are printed in a state where the paper 13 is nipped by the pair of transport rollers 14, 15 and the pair of discharge rollers 17, 18. Printed.

Also, when an image of a test pattern 100 described later is read, the test pattern 100 is nipped by the pair of transport rollers 14, 15 and the pair of discharge rollers 17, 18.

As described above, the paper 13 sandwiches the recording area,
By performing printing and paper transport in a state where the paper 13 is nipped by the transport roller pairs 14 and 15 and the paper discharge roller pairs 17 and 18 in the transport direction, a more accurate test pattern 100 can be printed, and the paper transport is performed. A shift in the amount can be suppressed.

Next, reading of a test pattern formed by the above method will be described with reference to FIG. The paper 13 is once transported to the downstream side in the transport direction of the paper 13 (at least the test pattern 100
The paper 13 is conveyed so as to be located downstream of the position of the D scanner 11 in the direction of the paper 13). Further, the carriage 10 is driven so that the CCD scanner 11 is positioned above the black pattern 102.

Since the amount of movement of the carriage 10 at this time is predetermined, the amount of movement of the carriage 10 with respect to the
The position of the D scanner 11 is not always constant. For example, in this embodiment, the position of the CCD scanner 11 when the movement of the carriage 10 is completed is
Description will be made assuming that the position is as shown in FIG.

With respect to the vertical line 103-2 of the reference line 103,
The center of the CCD scanner 11 is located on the left side in the figure,
In addition, the CCD scanner 11 is positioned so as to face a white portion of the paper on which the black pattern 102 is not formed.

At this position, the focus of the CCD scanner 11 is adjusted. When the focus adjustment is completed, the CCD scanner 11 is used at that position by using the white portion of the paper.
Adjust the white level of. The adjustment method of the brightness adjustment is performed by a known method.

When the white level adjustment is completed, C
With the position of the CD scanner 11 fixed, the paper 13 is transported upstream in the transport direction of the paper 13. This transport is C
The process is continued until the CD scanner 11 detects the black pattern 102. When the paper 13 is transported, the CCD 13
Since the density of the image pickup area of the scanner 11 changes from the white background of the paper 13 to the black background of the black pattern 102, the printer control unit (not shown) determines that the black pattern 102 is facing the CCD scanner 11 by the CCD. It can be recognized from the detection output from the scanner 11, and the conveyance of the sheet 13 is stopped according to the detection output.

FIG. 5 is a diagram showing a state when the CCD scanner 11 is positioned at a position facing the black pattern 102. At the position shown in FIG.
Is adjusted. The adjustment method of the brightness adjustment is performed by a known method.

When the brightness adjustment of the CCD scanner 11 is completed, the paper 13 is further transported upstream in the transport direction of the paper 13. This conveyance is continued until the CCD scanner 11 detects the horizontal line 103-1 of the reference line 103. When the CCD scanner 11 faces the horizontal line 103-1 of the reference line 103 as shown in FIG. 6, the conveyance of the sheet 13 is stopped, and then the vertical line 103-2 of the reference line 103 and the center of the CCD scanner 11 are moved. To match the carriage 10
Drive.

In FIG. 6, the CCD scanner 11 has already captured the vertical line 103-2 of the reference line 103 in the image pickup area. A printer control unit (not shown), based on the detection output of the CCD scanner 11 (density data to be read),
The carriage 10 is moved rightward in the figure.

FIG. 7 shows a state where the center of the CCD scanner 11 coincides with the intersection of the vertical line 103-2 and the horizontal line 103-1 of the reference line 103.

The center of the CCD scanner 11 is the reference line 103
Is reached, the sheet 13 is transported at a time by 190 dot lines slightly smaller than 200 dot lines (the distance from the reference line 103 to the reading start line of the first index 101-1). The reason why the 200 dot line up to the position of the reading start line of the sheet 13 is not conveyed at once is a margin in consideration of the error of the conveying mechanism.

When the reading start line reaches just before the CCD scanner 11, a small amount of conveyance is performed from there, for example, the conveyance amount when the driving pulse of the conveyance motor is set to 20 pulses (ideally, one dot line). The paper 13 is conveyed at a distance corresponding to the length of the paper 13 until the CCD scanner 11 detects the reading start line.
3 is carried upstream in the carrying direction.

As shown in FIG. 8, the CCD scanner 1
Each imaging element arranged in one line is functionally divided into a test pattern reading element 11-1 and an index reading element 11-3 in the arrangement direction. That is, the central element (dimension shorter than the index length) of the CCD scanner 11 is set as the index reading element 11-3. The test pattern 10
With the element 11-2 of the CCD scanner 11 corresponding to the boundary between 0 and the indexes 101-1 to 100-6, the element on the left side from the center is set as a test pattern reading element for reading the test pattern 100. Keep it. Note that the detection output from the element of the CCD scanner 11 corresponding to the boundary portion is not adopted as data.

The paper 13 is intermittently conveyed by a small amount, and when the 53rd line of the test pattern 100 reaches the image pickup area of the CCD scanner 11, the CCD scanner 11
Will read the index reading start line. If detected, the first image is read at that position by the test pattern reading element 11-1 of the CCD scanner 11. The density data of the read image is stored in the memory together with the number of times of reading (first time).

When the first image reading is completed, another 20 times are read for the second image reading.
The sheet is transported by a transport amount corresponding to the pulse. After being conveyed, the second image reading is performed, and the density data of the image and the number of times of reading (second time) are stored in the memory. This operation is continued until the sixth index, that is, the read end line is detected. Alternatively, after the reading end line can be detected, the reading end line is conveyed by a predetermined distance (for example, a distance enough to detect the reading and the end line), and the image is read until the conveyance is completed. You may let it.

Now, the paper is transported by driving the transport motor for 20 pulses. However, as described above, in practice, backlash in the transport mechanism and slippage of the transport rollers occur. Paper cannot be transported for the transport distance of one dot line. Here, as in the case described above, a description will be given assuming that a conveyance shortage of 5% actually occurs (that is, 0.95 dot line is conveyed).

The test pattern 100 is conveyed by 0.95 dots at a time between 0.9 dots from the index reading start line to the second line, and each time the image is read and density data is acquired.
For the 00 density data, 105 density data are obtained.

When the CCD scanner 11 detects the second line, a density distribution is created based on the 105 pieces of density data. This is shown in FIG.

Next, the density distribution based on the 105 pieces of density data is normalized as a density distribution based on 100 pieces of density data corresponding to 100 dot lines between indices. Specifically, the target number of 100 is divided by the actually obtained number of 105, and the value at this time is multiplied by, for example, 99 to obtain the 99th line position.

Further, a specific method of normalization will be described with reference to FIG. FIG. 10 shows the density characteristics when the number of density data actually acquired is 5 (the white circle) and normalized to the target number of density data 4. The solid line indicated by A in FIG. 10 is the characteristic of the actually acquired density data. When normalizing the characteristic, the point on the characteristic A at the position where the distance from 1 to 5 is divided into three equal parts (the black circle part) ) Are obtained and connected to obtain a normalized characteristic B.

FIG. 11 shows a density distribution obtained by normalizing the density distribution of FIG. 9 by the above method. 100 density data can be obtained from this density distribution, and this becomes the density data of each dot line. That is, the density number of the density data of the read image is normalized (converted) to the number of dot lines 100 between the indexes, and
The density data is also normalized according to the 0 dot line. Then, density data corresponding to each of the 100 dot lines is calculated.

The density data after normalization obtained here is
The density profile from the read start line to the second line in the test pattern is stored in the memory.

Hereinafter, similarly, the density data for each 100 dot line from the second line to the third line, the third line to the fourth line, the fourth line to the fifth line, and the fifth line to the reading end line of the index are similarly shown. To get. Then, it is set to 10 according to the 100 dot line.
Normalized as 0 density data (normalized as 96 density data from the 5th line to the reading end line)
Then, when a density profile for each 100 dot line (a density profile for every 96 dot lines between the last indexes) is created, the density profile is stored in the memory as a density profile for the entirety (496 nozzles for one recording head).

As described above, all the nozzles 496 of the recording head
It is possible to measure density data of 496 lines corresponding to the individual pieces, and at the time of actual printing, image data to which correction data according to the density data of each line is added is given to each head.

Therefore, the paper transport amount differs from the predetermined value,
Even if the reading position of the density data by the CCD scanner 11 shifts, the position of each index recorded at predetermined intervals (100 dot lines, 96 dot lines) in the test pattern 100 is detected, and the number of the density data taken in is detected. By normalizing to the number of density data corresponding to the predetermined number of dot lines, density data corresponding to each dot line can be obtained, and appropriate density correction can be performed.

In the above embodiment, the case where one test pattern is printed has been described. However, actually, a plurality of test patterns are generally printed. In this case, the data printed by the first nozzle in the first test pattern is not necessarily printed by the same first nozzle when the next test pattern is printed. In such a situation, the first index position in the test pattern will give information indicating which nozzle has printed the data.

(Second Embodiment) The second embodiment of the present invention relates to a range for capturing an image of a test pattern for acquiring density data.

In the first embodiment, the index 101-
The image reading for density data acquisition was performed from the detection of the reading start line of No. 1 to the detection of the reading end line of the index 101-6.
The reading of an image for acquiring density data may be started from a position where the CCD scanner 11 does not reach the reading start line. For example, in the first embodiment, after the center of the CCD scanner 11 reaches the position of the reference line, the paper 1
3 is transported by 190 dot lines (200 dot lines from the position of the reference line to the reading start line), and when the transport of the paper 13 for the 190 dot lines is completed, the image reading for density data acquisition is performed. May be started. That is, the index 101
The image is read from about 10 dot lines before the reading start line of −1, and the density data is stored in the memory. The density data that is actually necessary (valid) for creating the density profile is index 101. -1
May be read after detecting the read start line of the image.

In the first embodiment, index 1
If the read end line 01-6 is detected, the image reading has been completed, and the image reading has been performed for the lines corresponding to all the nozzles of the recording head 12, that is, 496 nozzles. However, the image reading may be continued for several tens of dot lines after detecting the reading end line of the index 101.

(Third Embodiment) The third embodiment relates to the shape and number of test patterns, and the following (1) to (3)
Can be considered.

(1) Parallel arrangement of test patterns (in-line arrangement) As shown in FIG. 12A, test patterns 1 (100-1) and 2 (100-2) having different densities are arranged in the head scanning direction. Record alongside. An index 10 is set between the two test patterns 100-1 and 100-2.
Record 1.

In the CCD scanner 11, an index reading element 11-5 is set at the center thereof, and a reading element 11-4 for the test pattern 1 is read on the left side in the figure, and a test pattern 2 is read on the right side in the figure. Element 11-6 is set. For each scan (actually, paper transport) of the CCD scanner 11, two test patterns 100-
1, 100-2 are simultaneously read in parallel. This is effective in reducing the time for creating a density profile.

(2) Serial arrangement of test patterns (vertical arrangement) As shown in FIG. 12B, two different density test patterns 1 (100-1) and 2 (100-2) are conveyed on the paper. Record alongside the direction. An index 101 for each test pattern is recorded on the right side of the two test patterns 100-1 and 100-2.

(3) Parallel and Series Arrangement of Test Patterns As shown in FIG. 12C, this is a configuration in which the configuration of (1) and the configuration of (2) are combined.

In each of the test patterns (1), (2), and (3), the length of the test paper in the transport direction is larger than one band (for a width of 496 nozzles) in one-pass printing.

In the above-described embodiment, at least 496 nozzle dot lines are printed in one-way one-pass printing of the test pattern based on "one-way one-pass printing" as a printing condition.

On the other hand, when the printing condition is “bidirectional one-pass printing”, the density of an image obtained by printing at the time of forward printing differs from that of an image obtained by printing at the time of recovery, and uneven density occurs. It is different. For this reason, it is necessary to prepare both a test pattern for forward recording and a test pattern for return recording. For example, FIG.
The result is as shown in FIG.

That is, 496 dot lines as the test pattern portion for the forward recording, 496 dot lines as the test pattern portion for the reverse recording, and 32 dot lines above and below as the test pattern portion for the margin. Thus, a test pattern for a total of 1056 dot lines is formed.

When the recording condition is "bidirectional two-pass printing", the test pattern is the same as the test pattern of "bidirectional one-pass printing" described above. That is, the nozzles that form the image of each dot line include: 1. The head upper nozzle at the time of going and the head lower nozzle at the time of returning; Since there is a lower nozzle on the head in the forward direction and an upper nozzle on the head in the reverse direction, the minimum length required for reading is 992 nozzles.

As described above, although the test pattern differs depending on each recording condition, the length of the cycle of the density unevenness pattern and the length of the test pattern when the head is driven under each recording condition may be made to match. In the first embodiment, since one-way one-pass printing is performed, the density unevenness generation cycle is every 496 dot lines for the nozzles of the head, so that the test pattern must be at least 496 dot lines long. In the case of bidirectional two-pass printing, the density irregularity occurs every 992 dot lines corresponding to the nozzles of two heads.
It requires 92 dot lines (applicable to unidirectional one-pass printing).

To improve the accuracy of the density profile, a test pattern may be recorded at a multiple of the length of the density unevenness generation period, and the average of the read density data may be obtained.

(Fourth Embodiment) The above embodiment has been described on the assumption that the paper 13 is transported at a constant dot interval. However, when the paper 13 is transported at a constant dot interval in this manner, the paper 13 is transported. Due to the regularity of the deviation, the density at the same dot position becomes large and the density becomes uneven. Therefore, the fourth embodiment is characterized in that the transport amount of the paper 13 is made random in order to prevent such density unevenness.
More specifically, in the present embodiment, the condition of 5 ± 3 pulses, that is, a number of pulses between a minimum of 2 and a maximum of 8 is randomly given to a pulse motor for sheet conveyance to perform one sheet conveyance. I have. In this case, a random number table composed of numbers from 2 to 8 is used. At the same time, 10 papers 13
The total number of pulses used for transporting the data is 50 pulses.

(Fifth Embodiment) The fifth embodiment of the present invention relates to the type of index. In the first embodiment, the shape of the index is a linear shape protruding outward from the long side of the test pattern along the paper transport direction, but the shape is not limited to this. in short,
As long as the CCD scanner 11 can recognize a predetermined reading range in the test pattern 100, for example, the shape of the index may be the same linear shape as in the first embodiment, or as shown in FIG. May be recorded away from the long side of the test pattern 100, or the index 101 may be recorded inward from the long side of the test pattern 100 as shown in FIG.

In FIGS. 13A and 13B, the portion of the CCD scanner 11 indicated by hatching to the right is an element for reading a test pattern, and the portion indicated by hatching to the left is an element for reading an index. here,
In the case of the index 101 of the type shown in FIG.
Is preferably formed not white but white, that is, without printing.

The index 101 corresponds to FIG.
As shown in (A), (B) and (C), an area index may be used instead of a linear index. As shown in FIG. 14A, for example, an area-like index 101 having a length of 100 dot lines is set to 100
Recording is performed at dot line intervals. FIG. 14 (A)
14B is a type in which the test pattern is printed outward from the long side along the paper transport direction, FIG. 14B is a type in which the test pattern is spaced apart, and FIG. 14C is a type in which the test pattern is printed inward. .

When a sheet is skewed and conveyed, the CCD
The relative positions of the scanner 11, the test pattern 100, and the index 101 in the head scanning direction are shifted. As a result, the test pattern 1 from the imaging area of the test pattern reading element in the CCD scanner 11
00 deviates, or the index 101 deviates from the imaging area of the index reading element in the CCD scanner 11. However, since the boundary of the density of the long side of the test pattern 100 along the paper transport direction serves as a reference for the position in the head scanning direction, the CCD scanner 11 follows the boundary of the density. As you do, CC
By moving the D scanner 11 in the head scanning direction, it is possible to solve the problem that the test pattern 100 and the index 101 cannot be detected.

However, when such an index serving as a reference for the position in the head scanning direction is not formed in the test pattern 100, as shown in FIGS. 15A and 15B, Reference part 120 in
May be formed on the index 101 side.

(Sixth Embodiment) The sixth embodiment of the present invention relates to density gradient correction.

At least when the image from the read start line to the read end line is read and conveyed at, for example, a 1/4 dot pitch, the acquired density data, especially the density data when the read start line is detected, Since the density data when the reading end line is detected is an image recorded with the same nozzle,
Originally, they must have the same concentration. But CC
Due to the shading of the D-scanner, the average density data has a slope even though the density is the same, and as a result, a density difference may occur in the density data when the above-described two lines are detected. is there.

Therefore, the density when the reading start line is detected and the density when the reading end line is detected are connected so that no density difference occurs in the density data when the above two lines are detected. The rotation correction is performed so that the elliptical line becomes flat without gradient.

(Seventh Embodiment) The seventh embodiment of the present invention relates to converting the order of acquired density data. In the first embodiment, the image of the test pattern 100 (5
The image of the third line) is recorded by the first nozzle of the recording head 12, but is not limited to this, and the image on the reading start line may be recorded by nozzles other than the first nozzle. Good.

(Eighth Embodiment) The eighth embodiment of the present invention relates to a density correction process. In the first embodiment, density data values of an image to be read are normalized, and density correction processing is performed on the normalized 496 density data. The average value of the 496 density data is calculated, and the average density value is set as the target density value of the corrected print data.
A density correction process is performed by calculating a correction value to be applied to each line (nozzle) so that the density value of the corrected print data matches the target density value. Details of this embodiment are disclosed in FIGS. 20 and 21 of Japanese Patent Application Laid-Open No. 05-318767.

(Ninth Embodiment) The ninth embodiment relates to the relationship between a CCD scanner and a printer. In the first embodiment, it has been described that the CCD scanner is mounted on the carriage on which the head of the printer is mounted. However, the CCD scanner can be applied to the following embodiments.

(1) A configuration in which another carriage is provided in the printer in addition to the head mounting carriage, and a CCD scanner is mounted on the other carriage.

(2) A printer and a CCD scanner are completely separated from each other. A test pattern recorded by the printer is discharged from the printer, and the test pattern is automatically or manually conveyed and read to the position of the CCD scanner. . In this case, there are two types, a type that moves the CCD scanner with respect to the test pattern and a type that moves the test pattern with respect to the CCD scanner.

(Tenth Embodiment) The tenth embodiment of the present invention relates to shifting the order of storing the acquired density data in the memory. In the first embodiment, the first index (reading start line) is recorded by the first nozzle, and the density data acquired after the first index is stored in the memory in order from the first line (FIG. 17 ( A)).

However, the method of storing the obtained density data in the memory from the first line in the order in which they were obtained as it is becomes a problem in the following cases. That is, FIG.
When the first index is recorded by the twentieth nozzle, the density data acquired after the first index is not from the twentieth line where the first index exists, but from the first line in the same manner as described above. The data is stored in the memory, and as a result, an erroneous density data profile is created.

In the tenth embodiment, in order to prevent such a problem from occurring, the acquired density data is not stored in the memory from the first line in the order of acquisition, but the 20th line in which the first index exists is stored. As a criterion,
The order in which the density data is stored in the memory is shifted so that the density data obtained after the first index detection is stored in the memory in the order in which they were obtained.

(Appendix) In an image forming apparatus capable of printing a test pattern of a predetermined density level for performing density measurement, a relative movement of the CCD scanner for reading the test pattern, which is performed when the density of the test pattern is measured by the CCD scanner. An image forming apparatus which prints a plurality of index marks for each predetermined dot line along a direction.

2. A plurality of test patterns of different density levels are printed in parallel with respect to the relative reading movement direction of the CCD scanner, and a common index mark is printed on the plurality of test patterns. . 4. The image forming apparatus according to claim 1.

3. 1. The CCD scanner reads the plurality of test patterns and the index pattern simultaneously. 4. The image forming apparatus according to claim 1.

4. The relative amount of the reading movement of the CCD scanner relative to the test pattern, which is performed when the density of the test pattern is measured by the CCD scanner, is a random amount. 4. The image forming apparatus according to claim 1.

[0099]

According to the present invention, it is possible to accurately match the relationship between the measured density data and the recording position even if the transport error of the CCD scanner or the transport error of the paper varies. Become.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an ink jet printer to which an image forming apparatus of the present invention is applied.

FIG. 2 is a diagram for explaining printing of a test pattern.

FIG. 3 is a diagram showing a state in which a black pattern 102 for adjusting the brightness of a CCD and reference lines 103 which are orthogonal to each other and indicate a standby position of the CCD are printed.

FIG. 4 is a diagram for describing reading of a test pattern.

FIG. 5 shows a CCD scanner 11 having a black pattern 102;
FIG. 5 is a diagram showing a state when the display device is positioned at a position facing.

FIG. 6 shows a CCD scanner 11 having a horizontal line 10 of a reference line 103.
It is a figure showing the state where it countered 3-1.

FIG. 7 is a diagram showing a state where the center of the CCD scanner 11 coincides with the intersection of the vertical line 103-2 and the horizontal line 103-1 of the reference line 103.

FIG. 8 is a diagram showing a state in which the image sensors arranged in a line are functionally divided into a test pattern reading element 11-1 and an index reading element 11-3 in the arrangement direction.

FIG. 9 is a diagram showing a density distribution created based on 105 pieces of density data.

FIG. 10 is a diagram for describing a specific example of normalization.

FIG. 11 is a diagram showing a normalized density distribution.

FIG. 12 is a diagram illustrating a third embodiment of the present invention relating to the shape and number of test patterns.

FIG. 13 is a diagram for explaining a fifth embodiment of the present invention relating to types of indexes.

FIG. 14 is a diagram for explaining a modification of the fifth embodiment.

FIG. 15 is a diagram illustrating a modification of the fifth embodiment.

FIG. 16 is a diagram showing test patterns for forward recording and return recording.

FIG. 17 is a diagram for explaining a tenth embodiment of the present invention relating to shifting the order of storing acquired density data in a memory.

FIG. 18 is a diagram (part 1) for describing a conventional technique;

FIG. 19 is a diagram (part 2) for describing the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 CCD scanner 12 Recording head 13 Paper 14 Nip roller 15 Transport roller 16 Platen 17 Nip roller 18 Discharge roller 19 Fan 100 Test pattern 101 (101-1 to 101-6) Index 102 Black pattern 103 Reference line

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Keiji Izumi F-term (reference) 2C056 EB27 EB42 FA10 HA58 5B057 AA12 DA20 DB09 DC22 at 2-34-2 Hatagaya, Shibuya-ku, Tokyo

Claims (3)

[Claims] 1. A print head having a plurality of print elements,
A method of printing a test pattern by providing print data having a predetermined density level, moving a scanner relative to the test pattern, reading an image of the test pattern, and measuring density data of the read image (1) printing a plurality of indices for each predetermined dot line along a test pattern and a relative movement direction of the scanner with respect to the test pattern; and (2) relative to the test pattern and the scanner. (3) intermittently moving and sequentially reading images of test patterns between adjacent indexes; (3) converting the density data of the read image and the number of density data between the adjacent indexes to the number of dot lines between the indexes; Based on the test pattern Concentration measuring method comprising the steps of calculating the density data corresponding to each dot line, in that it consists of. 2. An image forming apparatus capable of printing a test pattern at a predetermined density level for performing density measurement, wherein the relative position of the scanner to the test pattern is measured when the density of the test pattern is measured by the scanner. An image forming apparatus that prints a plurality of index marks for each predetermined dot line along a predetermined reading movement direction. 3. In the relative reading movement direction of the scanner, a first index mark is printed inside the test pattern rather than a leading end of the test pattern, and a last index mark is printed inside the test pattern rather than a trailing end of the test pattern. The image forming apparatus according to claim 2, wherein the image is printed on one side.