JPH0462063A - Image recording device - Google Patents

Abstract

PURPOSE:To permit a good image with its density nonuniformity corrected to be invariably obtained by a method wherein a judgment is made as to whether or not a corrected value is appropriate when a recording head records a test pattern based on a test pattern read-out signal and threshold to selectively execute the correction processing. CONSTITUTION:A judgment processing part 102 obtains the difference between the maximum and minimum values of a read-out data and judges as to whether or not the value of the difference is less than the threshold preset as reference value for judging the necessity for changing the correction value and, if it is less than the threshold, the normal sequential processing thereof is executed. If the value exceeds the threshold, the read-out data stored in a memory is sent to a correction computation processing part 103, a correction density value is computed for each recording element and the results thus obtained are written in an inner memory of a correction processing part 104 for correcting recording element signal. The density correction is made by this correction processing part 104 and the image with its density nonuniformity corrected is recorded on the material 3 to be recorded.

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.

[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, a test pattern is recorded and light is applied to the test pattern. The amount of reflected light when irradiated with is measured to understand the recording characteristics of the plurality of recording elements, and the drive signal for driving each of the recording elements is corrected according to the recording characteristics. The present applicant has already proposed an image recording apparatus that prevents variations in optical density of recorded images (hereinafter referred to as density unevenness) caused by variations in recording characteristics (Patent Application No. 1-107)
No. 744).

That is, the proposed device is an image recording device that has a recording head in which a plurality of recording elements are arranged side by side, and records an image while moving the recording medium and the recording material relative to each other. A pattern generating means for generating a test pattern, a turn reading means for reading the reflected optical density of the pattern recorded on the recording material, and driving the plurality of recording elements according to the read signal of the pattern reading means. This device is equipped with a correction means for correcting the drive signal.

FIG. 4 shows an example of a schematic internal configuration when the proposed invention is applied to a multi-nozzle inkjet recording apparatus. In the figure, 1 is a multi-nozzle inkjet head. Each inkjet head 1 has a recording density of 400D.
PI (dots per inch).

The number of nozzles (discharge ports) is 4,736, and the width is approximately 300 mm.
97mm) or less (generally paper), such as B
4. A4. By selectively ejecting ink as the recording material moves (so-called on-demand method), it is possible to cover the entire surface of the recording material with a -degree movement of the recording material. Multicolor images can be recorded. 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, a very high-speed image recording device, for example, approximately 30 cpm (7 minute cycle) (outputting 30 images per minute) is constructed.

2 in FIG. 4 is a cassette that stores the recording material 3. As shown in FIG. 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 1 is electrostatically attracted to the conveyor belt 8 through the second registration roller 7 and placed on the platen 9.
Inkjet recording is performed.

If the image to be inkjet recorded is a normal recorded image, mainly the lamp light source lO and the optical sensor 11 are used.
The test pattern reading system consisting of the . The paper is discharged to a paper discharge tray 14 via a paper discharge roller 13.

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 IO is turned on, and 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 10 and the optical sensor 11 may be of a fixed type that is 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 elongated along a guide reflex (not shown) on the paper surface of FIG. 4. It may be of a type that moves and scans in a direction perpendicular to the direction , and reads 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 lateral width of a standard A3 size, are driven with a uniform drive signal (see FIG. 5(A)). At this time, it is desirable that the optical density of the test pattern be uniform as shown in Figure 5 (CB), but in reality, due to variations that are difficult to avoid in manufacturing each recording element, the optical density is uniform as shown in Figure 5 (CB). As shown in C), there are recording heads that do not provide uniform density and cause density unevenness. Therefore, this test pattern (FIG. 5(A)) is irradiated with light from the lamp light source 10, and the amount of reflected light is converted into light amount and density via the optical sensor 11.
Reflection optical density distribution data as shown in FIG. 5(C) is obtained.

Here, the recording characteristics of a recording element that records a portion thinner than the average density OD, such as point A in FIG. It has the characteristic of being thin, and as shown in Figure 5 (point B in CJ, a recording element that records a part with a higher density than the average density OD has a higher recording density than other average recording elements). It has the following recording characteristics.

Therefore, when recording ordinary recorded images such as characters and photographs, the drive signal for a recording element that has a recording characteristic that causes the recording density to become thin, such as the recording element that recorded at point A, is used to increase the density. A recording element that has a recording characteristic that increases the recording density, such as the recording element that recorded point B, is corrected and driven in the direction that makes the density darker. By correcting and driving, it is possible in principle to obtain an image to be recorded in an extremely good condition with no density unevenness.

Furthermore, if the above proposal is implemented, it will be possible to deal with the problem that density unevenness changes over time depending on the usage status of the recording head, etc. by changing the correction value according to changes in density unevenness. I can do it.

[Problems to be Solved by the Invention] However, there are also recording heads that are so light that there is no need to perform density unevenness correction as described above, that is, the degree of density unevenness does not pose a practical problem.

Furthermore, there are recording heads in which even if there is a change in density unevenness, the amount of change is small. On the other hand, in order to perform density unevenness correction as described above, a certain amount of processing time is required, particularly processing time required for calculating correction values, writing correction values, and the like.

However, conventional methods do not have a means for determining whether or not to perform density unevenness correction as described above. There is a problem in that a series of density unevenness correction processes are all performed, resulting in wasted time.

In particular, since density unevenness changes over time depending on the usage status of the recording head, etc., the above-mentioned density unevenness correction process is performed every certain number of sheets, i.e., test pattern recording → test pattern reading → correction value calculation - correction. In the case of an image recording device that uses a sequence that performs value writing processing and rewrites correction values every time a certain number of recordings is made, downtime of approximately several tens of seconds is required for correction value calculation and correction value writing. The increase in the (non-operational time) caused great discomfort to the user, and there was also a particular problem in terms of work efficiency.

Therefore, in view of the above-mentioned problems, an object of the present invention is to
To provide an image recording device capable of preventing density unevenness without wasting processing time by determining whether or not it is necessary to execute density unevenness correction value processing based on a test pattern reading signal. It is in.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a recording head having a plurality of recording elements, a pattern generating means for generating a predetermined test pattern, and a recording head equipped with a plurality of recording elements. A test pattern reading means for reading the recording density of the recorded test pattern, and a drive signal for driving the plurality of recording elements according to the value of the test pattern reading signal read by the test pattern reading means. In an image recording apparatus having a correction means, the value of the test pattern reading signal read by the test pattern reading means is compared with a preset threshold value to determine whether or not to change the correction value of the correction means. The present invention is characterized in that it comprises a determining means for determining, and a control means for canceling the process of changing the correction value of the correcting means based on the determination result of the determining means.

[For Use] In the present invention, it is determined whether or not it is necessary to change the correction value of the recording head based on the read signal read by the test pattern reading means, so that unnecessary processing time is not wasted. It is possible to prevent density unevenness.

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

(1) 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. 4 described above. FIG. 1 schematically shows the main circuit configuration of this embodiment.

Correction of density unevenness in this example is performed for a predetermined number of recording sheets (for example, 500 sheets).
0 sheets) shall be automatically started.

The test pattern recorded on the recording material 3 is read by a test pattern reading system 1 consisting of a lamp light source 10 and an optical sensor 11.
01, and the read data is temporarily held in the memory within the determination processing unit 102.

The determination processing unit 102 calculates the difference between the maximum value and the minimum value of the read data, and determines whether the difference is a certain threshold (8 bits as an example in this embodiment) set in advance as a reference value for determining the necessity of changing the correction value. If it is less than the threshold, the density unevenness correction sequence process is terminated and the process returns to the normal sequence process.

On the other hand, if the difference between the maximum value and the minimum value of the read data is greater than or equal to the certain threshold value, the read data held in the memory is sent to the correction value calculation processing section 103. The correction value calculation processing unit 103 calculates a density correction value for each printing element based on the read data, and writes the result into the internal memory of the printing element drive signal correction processing unit 104.

An image signal sent from a host such as an image reading device, a personal computer, or a word processor is subjected to density correction by the recording element drive signal correction processing section 104.
The corrected recording element drive signal is sent to the recording head 1, and an image whose density unevenness has been corrected is recorded on the recording material 3.

In this way, since the determination processing unit 102 is provided, when there is no need to change the correction value for density unevenness correction, there is no need to perform correction value calculation processing and correction value writing processing, so that downtime can be shortened. With this, density unevenness correction can be automatically performed, and good images with almost no density unevenness can be automatically obtained at all times.

(11) Next, a second embodiment will be described in which the present invention is applied to a full-color multi-nozzle inkjet recording apparatus as shown in FIG. The same reference numerals as in FIG. 4 indicate similar elements.

In Figure 2, IC, LM, IY, and IBk are multi-nozzle inkjet heads for cyan ink, magenta ink, yellow ink, and black ink, respectively, and full-color images are recorded using these four recording heads. do.

An example of the test pattern recorded in this example is shown in FIG. A test pattern as shown in FIG. 3 is recorded, this test pattern is read by the test pattern reading system 101 in the same way as in the first embodiment, and a correction value is determined for each color by the judgment processing unit 102 based on the read data. It is determined whether or not to change. It is desirable to set the threshold value for determination at this time to an optimal value for each color.

As described above, when the present invention is applied to an image recording apparatus having a plurality of recording heads such as a full-color inkjet recording apparatus, it is possible to print a fixed number of sheets (for example, 50 sheets) similar to the first embodiment.
For an apparatus that automatically corrects density unevenness for every 00 sheets), not only the same effect as the first embodiment can be obtained, but also the user can press the density unevenness correction start key at any time of his/her preference. Even for devices where the density unevenness correction is started due to the density unevenness correction, it is possible to correct the density unevenness for the necessary print head without having the user judge which print head is the one whose density unevenness should be corrected. Since the density unevenness can be corrected automatically only when the image is displayed, the density unevenness correction can be completed in a short time without bothering the user, making it easier to produce good images without density unevenness. Obtainable.

■1 and 1 implementation 1 In the first and second embodiments of the present invention described above, the determination processing unit 1
In determining whether or not to change the correction value in 02, the difference between the maximum value and the minimum value of the read data was used as the judgment standard data, but the determination of whether or not to change the correction value will be made more strictly. In order to do this, the following criteria are required, rather than just the difference between the maximum value and the minimum value.

In other words, there is a phenomenon in which when there is a density difference in spatially close parts of a recorded image recorded on the recording material 3, the same density difference is much more noticeable than in spatially distant parts. Therefore, if we consider the case where the correction value is not changed when the difference between the maximum value and the minimum value of the read data is less than 5 levels (8 bits), as in the first embodiment, The correction value is not changed even when the density difference between the read data is 4 levels (8 bits), but when the difference between adjacent read data is 4 levels, it actually makes sense. This is because there are cases where density unevenness becomes noticeable and it is desirable to change the correction value.

Therefore, in the third embodiment of the present invention, the determination processing unit 102 in FIG. After making this determination, further determine whether the density difference between adjacent read data is less than or equal to another threshold value (for example, 3 levels) for those that are less than the threshold value, The correction value is not changed only if it is less than the threshold value. Therefore, in this embodiment, an extremely good recorded image without fine streak-like density unevenness can be automatically obtained.

In the first to third embodiments described above, an inkjet recording device was used as an image recording device, but other types of image recording devices, such as a thermal transfer printer, may also be used.

Of course, the present invention is also applicable to LED line printers and the like.

[Effects of the Invention] As explained above, according to the present invention, the correction value (including the case where there is no correction value) when the recording head records the test pattern based on the test pattern reading signal and the threshold value is Since the correction value update process is selectively executed after determining whether or not it is appropriate, it is possible to automatically produce a good image with density unevenness corrected with minimal downtime and as short a time as possible. There is an effect that allows you to always obtain the following.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing the main circuit configuration of an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view schematically showing the internal structure of an apparatus according to an embodiment of the present invention, and FIG. FIG. 4 is a vertical sectional view showing a schematic internal configuration of an image recording device to which the present invention is applicable; FIGS. 5(A), (B), (C) ) are explanatory diagrams for explaining the contents of density unevenness correction processing. 1...Multi-nozzle head (recording head), 3...
Recording material, 8... Conveyance belt, 9... Platen, 10... Light source lamp, 11... Optical sensor, 14... Paper output tray, 101... Test pattern reading system, 102. . . . Determination processing unit; 103 . . . Correction value calculation processing unit; 104 . . . Recording element drive signal correction processing unit.

Claims (1)

[Scope of Claims] 1) A test for reading the recording density of the test pattern recorded by the plurality of recording elements, including a recording head having a plurality of recording elements, a pattern generating means for generating a predetermined test pattern, and the plurality of recording elements. In an image recording apparatus comprising a pattern reading means and a correction means for correcting a drive signal for driving the plurality of recording elements according to a value of a test pattern reading signal read by the test pattern reading means, the test pattern reading determining means for comparing the value of the test pattern reading signal read by the means with a preset threshold value and determining whether or not to change the correction value of the correcting means; and based on the determination result of the determining means. , and control means for canceling the correction value changing process of the correction means.