JPH0462062A - Image recording device - Google Patents

Abstract

PURPOSE:To permit a high quality image free from density nonuniformity to be obtained by making the read-out range in the direction of a secondary scanning at the time of test pattern read-out longer than the length of the one periodic time of a periodic density nonuniformity caused by the inherent property of the material to be recorded. CONSTITUTION:A conveying belt 8 is made to move at 127mm/S at the time of test pattern recording and brought to a stop when a test pattern recording part thereof reaches directly below a test pattern read-out system. A first scanning is made to store reflection light amount distributing data in a memory. The conveying belt 8 is then moved to move the material 3 to be recorded by 0.5mm. A second scanning is made of the test pattern read-out system. This cyclic action is repeated several times to make the read-out range in a primary scanning direction at least longer than the length of one periodic time of the periodic density nonuniformity caused by the inherent property of the material to be recorded and the results obtained by each scan are stored in a correction memory to correct the driving signal for driving each recording element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image recording apparatus, and more particularly to an image recording apparatus that records an image using a recording head in which a plurality of recording elements are arranged side by side in a predetermined direction.

[Prior Art] Conventionally, for example, in an image recording apparatus such as a multi-nozzle inkjet recording apparatus that records an image using a recording head in which a plurality of recording elements are arranged side by side in a predetermined direction, a test pattern is recorded and the The amount of reflected light when the test pattern is irradiated with light is measured to understand the recording characteristics of the plurality of recording elements described above, and the drive signals for driving each of the recording elements are corrected according to the recording characteristics. The applicant has already proposed an image recording apparatus that prevents variations in the optical density of recorded images (hereinafter referred to as density unevenness) caused by variations in the recording characteristics of each recording element. No. 107744).

That is, the proposed device has a recording head in which a plurality of recording elements are arranged side by side in a predetermined direction (main scanning direction), and the recording head or the recording material is moved in a direction different from the predetermined direction (sub scanning direction). An image recording apparatus that records an image while moving the recording material in a direction), comprising: a pattern generation means for generating a predetermined test pattern; a pattern reading means for reading the reflective optical density of the pattern recorded on the recording material;
The apparatus includes a correction means for correcting a drive signal for driving the plurality of recording elements according to a read signal from the pattern reading means.

FIG. 2 shows an example of a schematic internal configuration when the proposed invention is applied to a multi-nozzle inkjet recording apparatus. In the figure, IC, IM, IY, and IBk (general symbol 1) are multi-nozzle inkjet heads for cyan ink, magenta ink, yellow ink, and black ink, respectively. Each inkjet head 1 has a recording density of 400 DPI (dots/inch), a number of nozzles (ejection ports) of 4,736, and a width of about 300 mm, and the recording material is smaller than a standard A3 size (width in the width direction: 297 mm). (generally paper), for example B4. A4. By selectively discharging ink as the recording material moves (so-called on-demand method),
A multicolor image can be recorded on the entire surface of the recording material by moving the recording material at the same time. Such an inkjet head 1 utilizes a general semiconductor manufacturing process and uses a bubble jet method (an electric pulse is applied to a current-carrying heating resistor, thereby heating and foaming the ink), which can increase the density and increase the length. This can be easily achieved using a bubble jet head that uses the bubbling pressure to eject ink droplets. By using four such bubble jet heads, for example, approximately 3
A very high-speed full-color image recording device such as 0 cpm (7 minute cycle) (30 images are output per minute) is constructed.

2 in FIG. 2 is a cassette in which the recording material 3 is stored. The recording material 3 is picked up by a pickup roller 4, and then transferred to a first roller 5. Guide plate 6. The multi-nozzle ink shed head I is electrostatically attracted to the conveyor belt 8 through the second registration roller 7 and placed on the platen 9.
C, IM, IY.

Inkjet recording is performed using 1Bk.

If the image to be inkjet recorded is a normal recorded image, the test pattern reading system consisting of the lamp light source 1O and the optical sensor 11 does not operate, and the recording material 3 on which the desired image is recorded is not guided. Board 12. Paper ejection roller 13
The paper is then discharged onto the paper discharge tray 14.

On the other hand, if the image to be inkjet recorded is a test pattern for correcting the density unevenness described above, a test pattern reading system consisting of a lamp light source 10 and an optical sensor 11 is activated. That is, at this time, the lamp light source 10 is turned on, the optical sensor 11 receives reflected light from the recorded test pattern, and outputs an electrical signal proportional to the amount of received light. The lamp light source 1O and the optical sensor 11 may be fixed types that are elongated to the same width as the inkjet head 1 or wider, or they may be of a fixed type that is elongated to the same width as the inkjet head 1 or wider, or they may be mounted along a guide rail (not shown) as shown in FIG. It may be of a type that moves and scans in a direction perpendicular to the paper surface to read the recording characteristics of a plurality of recording elements.

Next, an algorithm for correcting density unevenness in a density unevenness correction circuit (not shown) connected to the optical sensor 11 will be briefly described.

First, a test pattern is recorded when all of the recording elements, the number of which corresponds to the transverse width of a standard A3 size, are driven with a uniform drive signal (see FIG. 3(A)!). At this time, it is desirable that the optical density of the test pattern be uniform as shown in Figure 3 CB), but in reality, there are variations that are difficult to avoid in the manufacturing of each recording element and variations that occur due to changes over time. As a result, the density is not uniform as shown in FIG. 3(C), and density unevenness occurs. Therefore,
In this test pattern (Fig. 3 (A)), the lamp light source lO
The reflected light amount distribution is measured via the optical sensor 11, and the light amount-density conversion is performed from the measured reflected light amount distribution data for each recording element, as shown in FIG. 3(C). The overall reflective optical density distribution is calculated and stored.

Here, the recording characteristics of a recording element that performs recording on a portion thinner than the average density surface, such as point A in FIG. The recording element has the characteristic that the density is thinner, and a recording element that records a part with a higher density than the average density OD, such as point B in FIG. 3(C), has a recording density lower than that of other average recording elements. It has a recording characteristic of being dense.

Therefore, when recording normal recorded images such as characters and photographs, the drive signal for a recording element that has recording characteristics such as the recording element that recorded point A, which has a recording characteristic such that the recording density becomes thinner, is changed to a higher density. B
A recording element that has recording characteristics such as a recording element that records dots with a high recording density is driven in a direction that reduces the density (generally, it is sufficient to reduce the level or pulse width of the drive signal). If the signal is corrected and driven, it should be possible in principle to obtain an image to be recorded in an extremely good condition with no density unevenness.

[Problems to be Solved by the Invention] However, when reading a test pattern for understanding the recording density characteristics of each recording element as described above, the reading range in the sub-scanning direction (recording material feeding direction) is short. In fact, the following problem occurred.

In other words, as mentioned above, the cause of uneven density of the test pattern recorded on the recording material by driving each recording element with a uniform drive signal is not only the variation in the recording characteristics of each recording element, but also the actual also includes factors resulting from the unique properties of the recording material. In other words, the recording material such as ink penetrates into the recording material (in some cases, the recording material, especially the fiber structure of the paper, etc.) penetrates into the recording material.
Depending on the characteristics of the
Periodic density unevenness (below) occurs, and if the above reading range in the sub-scanning direction is shorter than the length of one period of this short-period density unevenness, this is originally caused by variations in the recording characteristics of each recording element. The pattern reading signal that should be used to read the density unevenness is noise, but due to the influence of the density unevenness caused by the characteristics inherent to the recording material as described above, the S/N is very low.
This results in a signal with a poor signal-to-noise ratio, resulting in a problem that density unevenness cannot be completely corrected even if the correction described above is performed.

It has been found through experiments that the difference in density caused by variations in the recording characteristics of each recording element is several to ten times larger than the difference in density caused by the inherent properties of the recording material.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an image recording apparatus that improves the accuracy of density unevenness correction by eliminating the influence of disturbance of read data due to the characteristics of a recording material. It is in.

[Means for Solving the Problem] In order to achieve the above object, the present invention provides a recording head in which a plurality of recording elements are arranged in the main scanning direction and a recording material in a sub-scanning direction substantially perpendicular to the main scanning direction. The device records an image while relatively moving in a direction, and includes pattern generating means for generating a predetermined test pattern, and reading the recording density of the test pattern recorded on the recording material by the plurality of recording elements. In an image recording apparatus having a pattern reading means and a correction means for correcting a drive signal for driving the plurality of recording elements based on the density data read by the pattern reading means, When the pattern reading means reads the test pattern, the pattern reading range in the sub-scanning direction is set to be longer than the length of one cycle of periodic density unevenness caused by the inherent properties of the recording material. Features.

[Function] In the present invention, the reading range in the sub-scanning direction when reading a test pattern is longer than the length of one period of periodic density unevenness caused by the inherent properties of the recording material ((more effectively). (longer than the length of several cycles), it is possible to eliminate the influence of periodic density unevenness caused by the inherent properties of the recording material, and therefore the influence of periodic density unevenness caused by variations in the recording characteristics of each recording element can be eliminated. A recorded image in good condition with density unevenness completely corrected can be obtained.

Note that density unevenness caused by variations in the recording characteristics of each recording element becomes stripe-like density unevenness that is very noticeable to the human eye, whereas density unevenness caused by the inherent properties of the recording material is Short period (often 1m)
m or less) Since the density unevenness is like a polka dot pattern, it is not very noticeable to the human eye, and the quality of the recorded image is not deteriorated, so there is no problem. Therefore, by applying the present invention,
It is clear that the image quality can be improved to a point where it is practically satisfactory.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

(mth generation) First, a first embodiment will be described in which the present invention is applied to a multi-nozzle inkjet recording apparatus as shown in FIG. 2 described above.

In this example, the lamp light source JO and the optical sensor 11 are elongated to have the same width as the multi-nozzle inkjet head l. It is assumed that the lamp light source 10 is a halogen lamp, the optical sensor 11 is a CCD (charge coupled device) image sensor, and an optical system such as an imaging lens system is inserted as appropriate. The ink droplet ejection frequency of the multi-nozzle inkjet head 1 is 2 KHz, and the recording density in the sub-scanning direction is the same as that in the main scanning direction < 400 DPI. The length is approximately 1 fiIm when the recording material is a normal recording paper, so the reading range in the sub-scanning direction when reading the test pattern is, for example, 12.7 mm.
By setting it to , it is possible to sufficiently effectively eliminate the influence of density unevenness caused by the inherent properties of the recording material.

As mentioned above, the moving speed of the conveyor belt 8 is 127ml1
/S, in order to set the reading range in the sub-scanning direction when reading the test pattern to 12.7 mm, the test pattern reading system consisting of the light source lamp lO and the optical sensor 11 is controlled by a control system (not shown). 7÷127 = 0
．． All you have to do is activate IS (seconds).

At this time, the density data of the entire reading range read from the optical sensor 11 is added for each recording element in a correction circuit (not shown) and averaged. Density unevenness caused by properties is canceled out by averaging. Therefore, the resulting reflected optical density distribution data (
The average value) properly represents density unevenness caused only by variations in the recording characteristics of each recording element, with the influence of density unevenness caused by the inherent properties of the recording material being eliminated. Therefore, by correcting the input image signal based on this density distribution data, it is possible to obtain a high-quality image in which density unevenness caused by variations in the printing characteristics of each printing element is almost completely eliminated.

Note that the other configurations and operations are the same as those of the prior art example described above, and will therefore be omitted.

(1) Empress In the first embodiment of the present invention described above, the light source lamp lO and the optical sensor 11 are elongated to the same width as the multi-nozzle inkjet head 1. There is a problem that the light source lamp 10 and the optical sensor 11 are expensive.

Therefore, a second embodiment of the present invention using a shorter light source lamp and an optical sensor will be described below.

The overall configuration of the device is the same as that of the first embodiment (as shown in FIG. 2).However, the arrangement of the test pattern reading system 102 consisting of the light source lamp 10 and the optical sensor 11 is the same as that shown in FIG. The structure is as shown in FIG. 1. FIG. 1 is a plan view of the device viewed from above.

In Figure 1, the test pattern reading system (reading head)
A multi-nozzle inkjet head 102 is reciprocated (scanned) along a guide rail 101 in the main scanning direction by a drive system (not shown) such as a motor, and the optical sensor 11 reads the amount of light reflected from the test pattern on the recording material. The recording characteristics of each recording element in No. 1 are ascertained. At this time, the reading range in the sub-scanning direction is 12.7 mm, which is the length of the optical sensor 11 (specifically, the CCD image sensor).

By averaging the read data of each reading element of the optical sensor 11, as described above, the influence of periodic unevenness caused by the inherent properties of the recording material can be eliminated.

The conveyor belt 8 has an ink droplet ejection frequency of 2 KHz and a recording density of 400 DPI in the sub-scanning direction during test pattern recording.
It moves at a speed of = 127 mm/s, stops when the test pattern recording part comes directly under the test pattern reading system 102, and starts moving again after the test pattern reading system 102 finishes reading the test pattern. , conveys the recording material 3 to the paper discharge tray 14.

In this embodiment, it is possible to obtain a high-quality image that is free from density unevenness caused by variations in the recording characteristics of each recording element at a lower manufacturing cost than the first embodiment described above.

■ Summer 1 Next, a third embodiment of the present invention, which is a lower cost version of the second embodiment of the present invention described above, will be described.

The overall device configuration and the arrangement of the test pattern reading system are almost the same as those in the second embodiment, but in order to further reduce the cost, the optical sensor 11 has an aperture of 0.5 mm
A photodiode with a diameter of about 5 mm is used, and a normal tungsten lamp is used as a light source lamp.

In such a configuration, if the test pattern reading system scans in the main scanning direction only once and receives the amount of reflected light, the reading range in the sub-scanning direction at one time is 0.5 mm. The reading range is too short, making it impossible to fully understand the recording characteristics of each recording element. Therefore, in this example, the number of scans of the test pattern reading system is set to multiple times.

To explain in detail, the conveyor belt 8 is moved at a speed of 127 mm/s when recording a test pattern, and is stopped when the test pattern recording portion comes directly below the test pattern reading system. Then, the -th scan is performed, and the reflected light amount distribution data is stored in the memory. Next, by moving the conveyor belt 8, the recording material 3 is moved by 0.5 mm. Then, a second scan of the test pattern reading system is performed.

Repeat the same operation as above several times to make sure that the reading range in the sub-scanning direction is small (longer than one period of the periodic density unevenness caused by the inherent properties of the recording material mentioned above), and The reflected light amount distribution data obtained by scanning is averaged to eliminate the influence of density unevenness caused by the inherent properties of the recording material.The results of this averaging process are stored in a correction memory.

If the drive signal for driving each recording element is corrected in a correction circuit (not shown) based on the test pattern read data averaged in this way, the variation in the recording characteristics of each recording element can be corrected as in the previous embodiment. A high-quality image that eliminates density unevenness can be obtained with a lower cost configuration.

Note that the present invention is of course applicable not only to inkjet printers but also to, for example, thermal transfer printers.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the arrangement of a test pattern reading system according to an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view showing a schematic structure of a multi-nozzle inkjet recording apparatus having a density unevenness correction function to which the present invention can be applied. The top view and FIGS. 3(A), 3(B), and 3(C) are explanatory diagrams for explaining the contents of the density unevenness correction process, respectively. [Effects of the Invention] As explained above, according to the present invention, the reading range in the sub-scanning direction when reading a test pattern is made shorter than the length of one cycle of periodic density unevenness caused by the inherent properties of the recording material. By making the recording characteristics of each recording element longer, it is possible to eliminate the negative effects (noise) due to the inherent properties of the recording material that are included in the test pattern read signal that requires understanding the variation in recording characteristics of each recording element. It is possible to obtain high-quality images without density unevenness caused by variations in recording characteristics. 1...Multi-nozzle inkjet head, 3...
Recording material, 8... Conveyor belt, 9... Platen, 10... Light source lamp, 11... Optical sensor, 14... Paper output tray, 101... Guide rail, 102... Test Pattern reading system.

Claims (1)

[Claims] 1) A device that records an image while relatively moving a recording head in which a plurality of recording elements are arranged in the main scanning direction and a recording material in a sub-scanning direction substantially perpendicular to the main scanning direction, and which performs a predetermined test. pattern generating means for generating a pattern; pattern reading means for reading the recording density of the test pattern recorded on the recording material by the plurality of recording elements;
In the image recording apparatus, the image recording apparatus includes a correction means for correcting a drive signal for driving the plurality of recording elements based on the density data read by the pattern reading means, in which the test pattern recorded on the recording material is The pattern reading range in the sub-scanning direction when the pattern reading means reads,
An image recording apparatus characterized in that the length is set to be longer than one cycle of periodic density unevenness caused by properties specific to the recording material.