JPH02172755A - Ink jet printer - Google Patents

Abstract

PURPOSE:To easily correct the density of a test pattern during formation thereof by calculating a new image information conversion coefficient to become an ideal density when the density of a detected test pattern is out of the ideal density, and rewriting it. CONSTITUTION:A controller 41 stores a test pattern from a test pattern generator 36 in a frame memory 35, converts image information by using a coefficient stored in advance in a lookup table 37 according to a signal from a color alteration switch 42, and drives a printer head 39 through a line buffer 38 to print it. This printed test pattern density is detected by a sensor 15. When the fact that it is out of an ideal density is determined in LUT operation part 40, a new coefficient is calculated to become an ideal density, the coefficient of the lookup table 37 is updated, and rewritten. Thus, a density correction can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inkjet printer having a function of automatically performing density correction, and more particularly, to an inkjet printer capable of performing the density correction together with the formation of a test pattern. Regarding printers.

BACKGROUND OF THE INVENTION Inkjet printers are widely used in some fields because they are capable of producing highly reproducible color prints.

However, printing with this inkjet printer is easily affected by the quality and color of the paper used for recording, the characteristics of the ink used, and the humidity of the surrounding air.
The drawback is that the density or color characteristics of the print vary slightly due to these influences.

Conventionally, there have been various correction techniques for compensating for the shortcomings of inkjet printers, one of which is as follows.

That is, a test pattern is drawn in advance with an inkjet printer, the density, color, etc. of this test pattern are determined, and based on the data obtained by this measurement, the conversion data used during printing is corrected.
In other words, density correction is performed.

Problems to be Solved by the Invention However, in such conventional inkjet printers, after a test pattern is drawn, the density, color, etc. of this test pattern are determined, and the density correction described above is performed. Therefore, the disadvantage is that it not only takes a lot of effort to correct the problem, but also takes a lot of time. Further, since this density correction cannot be easily performed by the user, there is also the problem that even if the user determines that density correction is necessary, it cannot be performed immediately.

The inkjet printer according to the present invention has been developed in order to eliminate the above-mentioned conventional drawbacks, and is equipped with a function to automatically perform density correction. The purpose is to provide an inkjet printer with

Means for Solving the Problems In order to achieve the above object, the present invention includes a conversion means for converting image information output from an external device into recorded information using a predetermined coefficient, and a conversion means for converting image information outputted from an external device into recorded information using a predetermined coefficient. An image forming means for forming a converted test pattern on a recording medium, a density detecting means for detecting the density of the test pattern being formed by the image forming means, and the test pattern detected by the density detecting means. and correction means for calculating a new coefficient such that the concentration becomes the ideal concentration when the concentration deviates from the ideal concentration, and rewriting the coefficient used in the conversion means with the new coefficient. It is characterized by this.

Operation The inkjet printer of the present invention configured as described above operates as follows.

First, the converting means converts image information outputted from the outside, that is, image information regarding the test pattern, into recorded information using predetermined coefficients possessed by the converting means, and the image forming means converts image information outputted from the outside into recorded information. A test pattern is formed on the recording medium based on the above. On the other hand, the density detection means detects the density of this test pattern that is being formed,
This detected concentration is output to the correction means. and,
If the detected concentration deviates from the ideal concentration, the correction means calculates a new coefficient so that this concentration becomes the ideal concentration, and outputs this coefficient to the conversion means, which changes the current concentration. The coefficient is rewritten with this new coefficient. Then, during the next printing operation, the image information is converted into recorded information using this new coefficient, and an image is formed by the image forming means based on this recorded information.

Embodiments Below, embodiments of an inkjet printer according to the present invention will be described in detail based on the drawings.

FIG. 1 is a schematic configuration diagram of an inkjet printer according to the present invention. In this embodiment, a serial type inkjet printer is exemplified.

As shown in the figure, a drum 2 supports a recording paper 1 as a recording medium and rotates and conveys it in the direction shown.
A drum rotation drive motor 3 is connected to the drum rotation drive motor 3, and the recording paper 1 is rotated and conveyed at high speed in the conveyance direction by the drum rotation drive motor 3. An encoder 4 is connected to the drum rotation drive motor 3, and information regarding the rotational position of the drum 2 is output from the encoder 4. This drum 2
Three image forming means are arranged near the image forming means at a predetermined distance from each other and are capable of individually ejecting ink liquids of three colors: yellow (Y), magenta (M), and cyan (C). A recording head 5 equipped with nozzles 5a, 5b, and 5c is provided, and this recording head 5 is rotated relative to the rotational direction of the drum 2 by a ball screw 8 driven by a head moving pulse motor 7 while being guided by a guide rail 6. It is designed so that it can move in parallel. Further, a density sensor 15 is attached to the side surface of the recording head 5 as a density detection means for detecting the density 1 of the test pattern formed on the recording paper 1, for example, the color density of R, G, and H. Reference numeral 15 is connected to an LUT calculation section which will be described later. This density sensor 15 is installed adjacent to the nozzle 5C that ejects cyan ink liquid, and is installed in this position to detect the density of the test pattern in real time as the test pattern is formed. This is because it is necessary. Note that the amount of feed of the recording head 5 is determined based on information output from the encoder 4. For example, when the encoder 4 detects that the drum 2 has rotated once, the head moving pulse motor 7 rotates by, for example, one pulse to move the recording head 5 by a predetermined amount (one line).

The ink liquid of each color is applied to the recording head 5.
An ink pump 9 pumps the ink to each nozzle 5a, 5b, 5c.
and a high-pressure switch circuit 10 are connected, and the flight of the ink liquid pumped by the ink pump 9 from the recording head 5 to the recording paper 1 is controlled by the high-pressure switch circuit 10.

In other words, control is performed as to whether or not to cause the ink liquid to fly onto the recording paper 1. This high voltage switch circuit 10
A line buffer 12 for temporarily storing one line of image data of the image data stored in the memory 11 is connected to the line buffer 12, and the switching operation for the flight of the ink liquid in the high-pressure switch 10 is performed by the encoder described above. This is performed based on the information regarding the rotational position of the drum 2 output from the drum 4 and the data in the line buffer 12.

Therefore, the recording paper 1 is supported by the drum 2 and rotated at high speed by the drum rotation drive motor 3, and the recording paper 1 is yellow (Y).
, magenta (M), and cyan (C).

When dots 5b and 5c each enter the recording range of the recording paper 1, the high voltage switch circuit 10 controls the flight of each color ink liquid for each dot constituting one line based on the data in the line buffer 12. Then print one line (drum 1
When the rotation (equivalent to rotation) is completed, the head moving pulse motor 7 rotates by a predetermined angle to move the recording head 5 and the density sensor 15.
is advanced by one line, and by this movement, the printing operation for the next line is performed as described above, and this printing operation is performed until each color nozzle goes out of the recording range of the recording paper 1. As a result, a desired image is formed on the recording paper 1. On the other hand, the density sensor 15 repeats the above-described operation to detect the density of the printed test pattern, and outputs the detected data to the LUT calculation section described above.

FIG. 2 is a side sectional view of the inkjet printer shown in FIG. 1.

The drum 2 around which the recording paper 1 is wound has a leading edge clamp 20 that clamps the leading edge of the recording paper 1, and a trailing edge clamp 21 that clamps the rear end of the recording paper 1, and the winding of the recording paper 1 around the drum 2 is as follows: The wrinkle removing roller 22 is used to prevent wrinkles from occurring. Below this drum 2, the recording paper 1 stored in the cassette is placed between a paper feed roller 23° and a transport guide plate 24. A paper feeding device is attached that transports the paper to the drum 2 via a paper feeding roller 25 and a transport guide plate 26. Further, a paper ejection device is attached above the drum 2 to eject the printed recording paper 1 via a paper ejection roller 27, a paper ejection guide plate 28, and a paper ejection roller 29. Furthermore, on the side of the drum 2, a first
A recording head 5 as shown in the figure is provided, and a density sensor 15 is attached to the recording head 5 as shown.

This concentration sensor 15 is attached at a position very close to the drum 21, as shown in the figure. still,
In the figure, a sensor 30 attached to the leading end of the conveyance guide plate 26 is for detecting passage of the leading end of the recording paper 1.

The inkjet printer having the above configuration transports the recording paper 1 and wraps it around the drum 2 or discharges it from the drum 2 in the following manner. That is, the recording paper 1 is sent out in the direction of the conveyance guide plate 24 by the rotation of the paper feed roller 23, and is sent to the conveyance guide plate 26 while being nipped by the paper feed roller 25. When the leading edge of the recording paper 1 sent in this manner is detected by the sensor 30, the leading edge clamp 20 of the drum 2 is opened, and when the leading edge of the recording paper 1 reaches this leading edge clamp 20, the leading edge clamp 20 is opened.
is closed. Next, the drum 2 rotates slowly in the rotational direction in the figure, and the recording paper 1 is pulled by the leading edge clamp 20 and regulated by the wrinkle removing roller 22 so that no wrinkles occur during winding. It is wound around the drum 2. When the winding is completed in this manner, the rear end clamp 21 is closed, and the rear end of the recording paper 1 is clamped by the rear end clamp 21. Next, the drum 2 rotates at high speed, and the printing operation as explained in FIG. Paper 1 is placed on paper ejection roller 27. The paper is ejected by a paper ejection guide plate 28 and a paper ejection roller 29.

FIG. 3 shows an inkjet printer according to the present invention.
FIG. 2 is a schematic configuration diagram of a control section that mainly controls printing operations.

R and G sent from the external interface.

The frame memory 35 that stores the image information of the B signal for one frame, that is, one screen, includes the information shown in FIGS. 5 and 6, which will be described later.
A test pattern generator 36 that outputs image information regarding a test pattern as shown in the figure is connected, and image information regarding the test pattern outputted from the generator 36 is also stored in the frame memory 35 . A look-up table section 37 as a conversion means for storing color conversion information is connected to this frame memory 35, and image information of R, G, and B signals is converted into C and M based on this color conversion information.

It is converted to Y recording information. A line buffer 38 for storing part of the C, M, and Y recording information (for example, one line) is connected to this look-up table section 37, and the nozzles 5a to 5c are connected to this line buffer 38. Printer head 39 based on the recorded information stored in 38
Controlled ink will be ejected. In addition, a concentration sensor 1 provided near the drum 2
5 is connected to an LUT calculation unit 40 as a conversion means for calculating new lookup table information, and this LU
The T calculation unit 40 calculates coefficients to be stored in the lookup table unit 37, that is, color conversion information, based on the detection information from the density sensor 15. In addition, excluding the nozzles 58 to 5C described above (each component includes a controller 41
are connected, and the individual operations and mutual operation timings of each of these components are collectively controlled. Further, a color correction switch 42 is connected to this controller, and the color correction operation described later is started when the color correction switch 42 is turned on and a start switch (not shown) is turned on.

When the inkjet printer of the present invention having the above-described configuration performs a color correction operation, it operates as follows based on the operation flowchart of FIG. 4. Hereinafter, this flowchart will be explained in detail with reference to FIGS. 1 to 3 and 5 to 9.

First, when the color correction switch 42 shown in FIG. 3 is turned on to select the correction mode, and the start switch (not shown) for starting printing is turned on, as described above,
Recording paper 1 is conveyed from the cassette and set on drum 2 (Sl). When this setting is completed, the drum 2 rotates at high speed and the head 5 moves to the print starting position as shown in FIG. Specifically, the nozzle 5a that ejects yellow ink liquid is positioned at the start position of the recording range (S2). The frame memory 35 stores R, R, and R related to the test pattern output from the test pattern generator 36.
Store image information of G and H.

Then, the lookup table section 37 converts this image information into C, M,
This converted recording information is stored in the line buffer 38.

Then, the printer head 39 uses this line buffer 38.
The ejection of each color ink liquid is controlled based on the recording information stored in the . Finally, the fifth
Form a test pattern as shown in the figure. The numbers in the test pattern shown in the figure are the pattern NOs shown in FIG. For example, in the area where the pattern number is 0, as shown in FIG. 6, the R, G, and B gradations are printed at 0, 0° 0, respectively. In other words, this is a portion where the background color of the recording paper 1 on which nothing is printed appears. Further, the portion with pattern number 6 is a portion printed with RlG and B gradations of 6.6.6. In other words, it has gray printing. Further, in the portion with pattern number 15, the R, G, and B gradations are printed at 15.15°15. In other words, it is the part printed in black. still,
In this embodiment, for convenience, an example is shown in which an image can be reproduced in 16 gradations (S3). And concentration sensor 1
5 reaches the printing start position, the R, G,
The concentration of B is detected, and this concentration is stored in the LUT as concentration data.
It is stored in the conversion unit 40.

That is, the concentration sensor 15 detects each concentration of patterns NO2O to 7 of the tester pattern, and then detects each concentration of patterns NO2O to NO7 of the tester pattern.
o, detect each concentration from 8 to 15 and convert these concentrations into L
It will be output to the UT calculation section 40. The density detection for each pattern number is timed based on information regarding the rotational position of the drum 2 output from the encoder 4, and is performed based on this timing (S4).

Next, the LUT calculation unit 40 determines the ideal "gradation-density characteristic" based on the density data for each pattern number detected during this test printing, and the "gradation-density characteristic" detected in step S4.
The difference between the density and gradation characteristics, that is, the color difference, is calculated. For example, the ideal "gradation-density characteristic" stored in the LUT calculation unit 40 is one in which the relationship between gradation and density is linear as shown in FIG. If this color difference is within the specified value, in this case, there is no need to modify the color conversion information existing in the lookup table section 37, so the inkjet printer finishes the printing operation and transfers the recording paper 1 to the drum. 2 through the paper ejection device (85
~S7). On the other hand, as a result of the judgment in S6, if the color difference is larger than the specified value and this is the fourth time that this test pattern has been printed, it means that the three corrections were not carried out normally, and the color difference is larger than the specified value. A correction error is displayed and the process proceeds to S7, where the printing operation is terminated (S8゜S9
). Furthermore, if this test pattern is printed three times or less, the LUT calculation section 40 uses the lookup table section 37 to convert the detected "density-gradation characteristic" into the ideal "gradation-density characteristic". Calculate the coefficients to be stored, that is, the color conversion information.

Specifically, this calculation is performed as follows.

Now, assume that the detected value by the concentration sensor 15 is as follows.

Detection Value RGB Here, the detection value number corresponds to the pattern No. in FIG. 6.

The detected values of R, G, and B densities at each of these input values are respectively Dr (K), Dg (K), and Db (K) (however, in this example, 16 gradations are shown as an example). Therefore, K=0 to 15) These Dr (K), D
Dr, Dg, Db based on the values of g (K) and Db (K)
The approximate formula for the input value is Dr=fr(K) Dg=fg(K) Db=fb(K) OR(0) G(0) B(0)I
R(1) G(1) B
(1) 2 R(2) G(2)
If one of the "density-gradation characteristics" is illustrated as B(2)R(K) G (k) B(k), it will be represented by a characteristic curve as shown in FIG.

Then, if the ideal density-tone characteristic that we want to reproduce with this inkjet printer is Dr=Dg=Db=F (K), then this "/a variation-tone characteristic" is linear as shown in Figure 9. It is expressed as a straight line of a function.

In order to make this detected value have ideal density-gradation characteristics, the color conversion information that should be provided in the lookup table unit 37 is R(K)=fr −1(F (K))G (K)
= f g-' (F (K) IB (K)
= f b−' (F (K) ) (where,
f r"'l, f g-1, f b-' are fr.

It is an inverse function of fg and fb. ) That would be a good thing.

1 of this R(K), G(K), B(K)
If two "density-gradation characteristics" are illustrated, they will be represented by a characteristic curve as shown in FIG.

The LUT calculation unit 40 calculates color conversion information by performing the above calculations (S10). Then, the LUT calculation unit 40 outputs the color conversion information calculated in this way to the lookup table unit 37, and rewrites it to the existing color conversion information (Sll).

Next, the head 5 moves to the second printing start position indicated by the dotted line in FIG. 5, that is, to point A in the figure (S12). Then, the color retouching operation described above is repeated again, and when the color difference falls within the specified value in this retreading operation, the printing operation ends at that point. It should be noted that printing using this color rejuvenation operation will be performed up to three times. As described above, in the color correction operation of the inkjet printer according to the present invention, color correction information is calculated while printing a test pattern. If ideal color correction information cannot be obtained in one color correction operation, this color correction operation is repeated up to three times.

In this embodiment, density correction for a color inkjet printer with 16 gradations is illustrated, but the present invention is not limited to this, and can be applied to density correction of 32 gradations, 64 gradations, etc., for example. Furthermore, it goes without saying that this density correction can be applied not only to color printers but also to monochrome inkjet printers.

Effects of the Invention As is clear from the above explanation, the inkjet printer of the present invention detects the test pattern density that is being formed, and if the detected density deviates from the ideal density, this detection Since a new coefficient is calculated based on the density determined so that the density becomes the ideal density, this coefficient can be calculated during the formation of the test pattern, and the rcuJt correction can be easily performed. Became.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an inkjet printer according to the present invention, FIG. 2 is a side sectional view of the inkjet printer shown in FIG. 1, and FIG. 3 is a schematic diagram of the inkjet printer according to the present invention.
A schematic configuration diagram of the control section that mainly controls the printing operation, FIG. 4 is an operation flowchart of the control section shown in FIG. 3, FIG. 5 is a diagram showing the printing state of the test pattern, and FIG. FIG. 5 is a diagram showing R, G, and B gradations for each pattern number of the test pattern, FIG. 7 is a density-gradation characteristic diagram based on detected density data, and FIG. , a density-gradation characteristic diagram showing the corrected density for the detected density shown in FIG. 7, and FIG. 9 is an ideal density-gradation characteristic diagram. DESCRIPTION OF SYMBOLS 1... Recording paper (recording medium), 5... Head, 5a-5C... Nozzle (image forming means), 15...
Concentration sensor (a degree detection means), 37... Lookup table section (conversion means) 40... LUT calculation section (rehabilitation means). Fig. 1: I will meet you - Evening: Fig. 2: Fig. 7: Fig. 8: Fig. 9: Kawazu 4

Claims (1)

[Claims] Conversion means for converting image information output from the outside into recorded information using predetermined coefficients, and forming a test pattern converted into recorded information by the conversion means on a recording medium. an image forming means; a density detecting means for detecting the density of the test pattern being formed by the image forming means; and, when the density of the test pattern detected by the density detecting means deviates from an ideal density An inkjet printer, comprising: a correction unit that calculates a new coefficient such that the density becomes an ideal density, and rewrites the coefficient used in the conversion unit to the new coefficient.