JPH048571A - Image recorder - Google Patents

Abstract

PURPOSE:To eliminate the variation of a recording image by a method wherein light quantity data is converted to density data on the basis of a conversion parameter corresponding to the type of a recording head, and a correction value is calculated based on the converted density data. CONSTITUTION:After a head of a color requiring the correction of density irregularities is assigned by a correction head assigning part 101, a pattern generator generates a pattern for driving all the recording elements of a recording head on the same drive signal. The test pattern is recorded using the head requiring the correction of density irregularities. A test pattern reading system 104 irradiates the test pattern with light and receives the reflected light. In an A/D conversion part 107, a signal proportional to the quantity of the received light is A/D converted and outputted to a light quantity-density conversion part 103. In the light quantity-density conversion part 103, the signal proportional to the light quantity is converted to a signal proportional to a density using a look-up table for the assigned color. A correction value operation part 105 calculates a correction value. An image signal is corrected with this correction value and drives the recording elements.

Description

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

[Prior Art] Conventionally, in an image recording apparatus such as a multi-noise inkjet recording apparatus that records an image using a plurality of recording heads each having a plurality of recording elements arranged side by side, a test pattern is recorded and the test pattern is The recording characteristics of the plurality of recording elements are determined by measuring the amount of reflected light when the light is irradiated, and the drive signal for driving each of the recording elements is corrected according to the recording characteristics, and the recording of each of the recording elements is performed. The present applicant has proposed an image recording apparatus that prevents variations in optical density of recorded images (hereinafter referred to as density unevenness) caused by variations in characteristics (Japanese Patent Application No. 1-107744).

FIG. 9 shows a schematic configuration diagram when the above proposal is applied to an inkjet recording apparatus.

IC, IM, IY, IBK or each for cyan ink,
This is a multi-nozzle inkjet head for magenta ink, yellow ink, and black ink. The ink jet head has a density of 400 dpi and a number of nozzles of 47.
There are 36 recording materials with a width of about 300 mm and a size smaller than standard A3 size (short side 297 mm), such as B4. A
For recording materials of grade 4, ink is selectively ejected as the recording material moves (so-called ○n dema
nd), an image can be recorded on the entire surface of the recording material by moving the recording material by - degrees.

This type of inkjet head utilizes a semiconductor manufacturing process to produce a high-density, long-length bubble jet head (electric pulses are applied to a current-carrying heating resistor to heat and foam the ink, and the resulting pressure creates ink droplets). This is realized by a bubble jet head (which discharges water). By using four such bubble jet heads, a full-color image recording device with a very high speed of about 300 pm, for example, can be constructed. Reference numeral 2 in FIG. 10 is a cassette containing a recording material 3 (not shown). A recording material 3 (not shown) is picked up by a pickup roller 4, and is moved to a second roller 5. Guide plate 6. It passes through the second registration roller 7, is electrostatically attracted to the conveyor belt 8, and is subjected to inkjet recording on the platen 9.

By the way, when the image on which inkjet recording is performed is a desired 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 moved to the guide plate. 12. Paper ejection roller 1
3, and is 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, the test pattern reading system comprising the lamp light source 1o and the optical sensor 11 is activated.

That is, the lamp light source 1o 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 elongated to have a width equal to or greater than that of the inkjet head 1, or may be elongated in a direction perpendicular to the paper surface of FIG. 9 along a guide rail (not shown). It may also be possible to read the printing characteristics of a plurality of printing elements (in this case, a plurality of ejection nozzles) by scanning.

Next, the algorithm for density unevenness correction proposed above is applied to the 10th algorithm.
A brief explanation will be given with reference to FIGS. 11(a) to 11(c) and FIGS.

First, a test pattern is recorded when all of the plurality of recording elements (discharge nozzles in this case) are driven under the same conditions, that is, with the same drive signal (temporarily S in this case) (see FIG. 10(a)). .

The optical density of the test pattern is not uniform as shown in FIG. This results in uneven density as shown in Figure (C). Therefore, this density unevenness is read and the print head drive signal S is corrected for each printing element in accordance with the read signal to prevent density unevenness.

Specifically, first, the test pattern (FIG. 10(a)
), the reflected light is received, A/D conversion is performed from analog to digital, and the reflected light amount distribution Ei (S
Measure o). i indicates the recording area handled by the first nozzle.

(So) indicates that Ei is a function of S, S=S,
This shows that Ei is when . Perform light amount-density conversion and obtain optical density distribution OD i from reflected light amount distribution Ei (So)
Convert to (S o). Next, the average density 0D(S, ) is calculated, and the inverse ratio of the optical density 0Di(So) of each part to the average density clove (SO) is 0D(So)/○Di(So).
It can be seen that by multiplying the drive signal for driving the i-th recording element by the drive signal for driving the i-th recording element, density unevenness is corrected as shown below, and a uniform image without density unevenness can be obtained.

To briefly explain an example below, it is assumed that the relationship between the drive signal S and the optical density 0Di(S) of the recorded object is proportional. Note that if there is no proportional relationship, the drive signal S may be corrected using a look-up table or the like so that the proportional relationship is maintained.

That is, it is assumed that there is a relationship as shown in FIG. 11(a). The same drive signal S is applied to all recording elements.

Therefore, the optical density differs depending on each recording element (value of 1) as shown in FIG. 11(a). Here, to explain the second recording element i=2 as an example (see FIG. 11(b)), the average density of the entire image is OD(So)=aXS, while the second recording element The optical density of the part where the element is responsible for recording is OD2 (So)
=82×80, which is lighter than the average density.

Therefore, the drive signal for driving the second recording element is multiplied by OD(So)10D2(S,) as described above.
Correct to (So)10D2(So)XSo. U bottom (
so)10D2(so)=(100X So)/(a 2
Since X50)=τ/a 2, the drive signal for driving the second recording element is OD (S o)/○D 2
(S O) X5o=a/azx3o. It will be clear from the following explanation that this correction value is a correct correction value (a correction value that eliminates density unevenness).

As can be seen from Fig. 11(b), △ABC (X: △A
Since it is DE, BC: DE=AC: AE BC:DE=az

So, AE=a/azxso.

The second recording element from FIG. 11(b) is a/azXs
If driven at o, the optical density is aXS.

It can be seen that the density matches the average density, indicating that the unevenness in this area has been corrected. Therefore, the correction value of the drive signal for driving the second recording element is 0D(S 0)10D2(
It was confirmed that (multiplying this value by the drive signal) is sufficient. The same thing can naturally be said for other recording elements, so if the drive signal for driving the i-th recording element is multiplied by 0D10Di as described above, the density unevenness of the recorded image can be uniformly corrected. Recognize. Note that since the SoO value can be any value, all drive signal values S
It is also clear that the density unevenness is corrected and becomes uniform.

To do this, light is irradiated onto a test pattern as shown in FIG. 10(a), the amount of reflected light is measured, the amount of correction is calculated using the calculation described above, and the corrected drive signal is used to drive the recording head. By driving, it is possible to obtain a desired recorded image in a good state in which unevenness in recording density caused by various variations in each recording element is corrected.

[Problem to be solved by the invention] However, for example for cyan as mentioned above.

In an image recording device that has four recording heads, one for magenta, one for yellow, and one for black, and images are recorded using these recording heads, the recording characteristics of each recording head are understood and density unevenness is corrected. To do this, test patterns recorded with each recording head (i.e.
A conversion parameter that converts a signal proportional to the amount of reflected and received light into a signal proportional to the optical density when light is irradiated onto each color (that is, cyan).

magenta, yellow, black), the amount of reflected light received cannot be correctly converted to optical density.
Therefore, there was a problem that density unevenness was not completely corrected.

In addition, test patterns recorded with each recording head (
In other words, when converting into analog digital data proportional to the distribution of the amount of reflected and received light when irradiating light (each with a different color), the analog value that is the standard for A/D conversion is set for cyan, magenta, If it is set constant for each recording head for yellow and black, the resolution of the density unevenness of the yellow, magenta, and cyan recording heads relative to the density of the read data (how small a difference in density can be determined) There was also the problem that the correction accuracy for density unevenness deteriorated.

The present invention eliminates the above-mentioned conventional drawbacks and provides an image recording apparatus that eliminates variations in recorded images due to variations in recording characteristics of recording elements arranged side by side.

[Means for Solving the Problem] In order to solve this problem, the image recording device of the present invention has the following features:
An image recording apparatus that includes a plurality of types of recording heads in which a plurality of recording elements are arranged side by side and records an image using the recording head, the image recording apparatus comprising: A correction means is provided for correcting a drive signal for driving the recording element in accordance with the position of the recording element and the type of the recording head.

Here, the correction means includes a conversion means for converting the read data from light amount data to density data based on a conversion parameter corresponding to the type of the recording head, and a conversion means for converting the read data from light amount data to density data based on the converted density data. and correction value calculation means for calculating the value.

Further, the correction means includes an A/D conversion means for converting the read analog data into the digital light amount data, and a standard for changing a reference level of the A/D conversion means in accordance with the type of the recording head. The apparatus further includes level converting means.

[Function] In this configuration, by varying the conversion parameter for converting light amount data to density data and the reference level serving as a reference for A/D conversion for each recording head,
This leads to improved accuracy in correcting density unevenness for all recording heads.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

The density unevenness correction sequence of this embodiment will be described below with reference to the block diagram shown in FIG. In this embodiment, the recording head is for cyan.

The 9th one is four for magenta, yellow, and black.
An example of a color image recording apparatus as shown in the figure will be explained. Incidentally, similar effects can be obtained in a monochrome image recording apparatus having a head for light black ink and a head for dark black ink.

<Example of light amount-density conversion> FIG. 4 shows a flowchart of the correction procedure of this embodiment.

Density unevenness correction is started by first pressing the density unevenness correction head designation key of the correction head designation section 101, which specifies which color head is to be subjected to density unevenness correction (step Sl). The conversion parameter change instruction unit 102 responds to the designation signal from the correction head designation unit 101 to change the black for cyan, magenta, and yellow as shown in FIG. A signal is output to the light amount-density converter 103 so that the look-up table for the designated hue is used among the four look-up tables for use (step S2).

When the correction head designation unit 101 specifies a head of a color for which density unevenness is to be corrected, a pattern generator (not shown) generates a pattern in which all printing elements of the printing head are driven with the same drive signal. is generated, and a test pattern is recorded using the head for which density unevenness correction is desired (step S3). Test pattern reading system 104
irradiates the test pattern with light, receives the reflected light, and converts a signal proportional to the amount of received light into an A/D converter 107.
/D conversion, output to the light amount-density conversion unit 103 (
Step S4). The light amount-density conversion unit 103 converts a signal proportional to the light amount into a signal proportional to the density using the aforementioned lookup table of the specified hue (step S5). The look-up table shown in FIG. 2 is a look-up table for converting an 8-bit light intensity signal into an 8-bit density signal.

Here, a method for creating this lookup table will be briefly explained with reference to FIG.

First, each gradation pattern of cyan, magenta, 5 yellow, and black is recorded, and a density measuring device (ordinary density measuring device is sufficient, which is close to the density recognition level of the human eye; in the normal case, it is designed for each color of cyan, magenta, and yellow). The density of each gradation is measured for each color of cyan, magenta, yellow, and black. Next, each gradation pattern is read by the test pattern reading system 1 described above.
04 and measure the amount of reflected light.

FIG. 3 is a diagram in which the former is plotted on the horizontal axis and the latter (after A/D conversion) is plotted on the vertical axis. By interchanging the horizontal and vertical axes of Figure 3 obtained in this way, the second
A lookup table like the one shown in the figure is created.

A light amount-to-density conversion unit 103 performs light amount-to-density conversion using the lookup table created in this way, and a correction value calculation unit 105 calculates a correction value as described above in the conventional example.
(Steps S6 to S8). In the recording element drive signal correction unit 106, the correction value calculated for each recording element or for each several recording elements in the correction value calculation unit 105 is stored in the correction value storage unit 106a (step S9), and the correction value is stored in the correction value storage unit 106a (step S9). is corrected with this correction value to drive each recording element. By driving each recording element in this way, density unevenness can be corrected with high precision, regardless of what color the head for which density unevenness correction is to be performed is used.
It is now possible to obtain good images without uneven density.

In the embodiment described above, the head for which density unevenness correction is to be performed is specified, but in this embodiment, an example will be described in which such trouble is omitted.

Density unevenness correction is performed every fixed number of recorded sheets (the number of recorded sheets is counted by a counter, and density unevenness correction is automatically started when the count value reaches a certain value). The test pattern to be recorded is the same as that in the previous embodiment, but as shown in FIG. 5, cyan, magenta, yellow and black patterns are recorded on one sheet of recording material. The test pattern reading system 104 includes a cyan pattern,
The patterns are read in order: magenta pattern, yellow pattern, and black pattern. In synchronization with this, the conversion parameter change instruction section 102 outputs a conversion table change signal to the light amount-density conversion section, and the light amount-density conversion section 103 uses the lookup table for each hue to convert the light amount-density. Conversion takes place. By using such a sequence, it is possible to obtain the same effect as in the embodiment described above without having to specify the head for which density unevenness correction is desired.

Note that this embodiment is obviously applicable to printing apparatuses other than inkjet printing apparatuses. Also,
In this embodiment, when calculating the correction value from the read signal of the test pattern reading means, an example has been described in which the conversion parameters for light intensity-density conversion are changed depending on the color, but other calculation methods are changed depending on the color. You may also do so.

As explained above, according to this embodiment, the light amount-density conversion can be performed accurately regardless of the difference in the recording colors of a plurality of recording heads. It is now possible to correct density unevenness and output good images without density unevenness.

<Example of A/D Conversion> Figure 7 shows the analog data read when the tone patterns recorded by the cyan, magenta, yellow, and black inkjet heads are read by the test pattern reading system. . The horizontal axis of the graph shows the reflected optical density of each gradation of the gradation pattern using a densitometer (ordinary densitometer, which uses color filters for cyan, magenta, and yellow) that is close to the density perception of the human eye. The vertical axis is proportional to the reflected light from each gradation of each gradation pattern received by the test pattern reading system (specifically, it is amplified using an amplifier). ) shows the analog electrical signal value.

The inventors' study has revealed that the appropriate recording duty of the test pattern recorded for density unevenness correction is about 50%. The analog electrical signal value proportional to the amount of reflected light from the -50% test pattern is approximately 0.5V for black and 2V for cyan and magenta.
The value is about V, and the value for yellow is about 4V (see Figure 7).
-, etc.) When converting this analog data to digital data, if A/D conversion is performed, for example, to 8-bit digital data based on a constant reference value regardless of each color, as shown in the above embodiment. The result will be as shown in Figure 3.

Incidentally, the resolution for the concentration is higher as the slope of the curve in FIG. 3 becomes steeper.

This is because the difference in output value with respect to the density difference becomes large. If the slope of the curve in Figure 3 is gentle,
Even if there is a slight difference in density, there will be almost no difference in the output value, and density unevenness due to subtle density differences will not be read.
The accuracy of correction of density unevenness does not become high. Therefore, A/
If the reference value for D conversion is made constant regardless of each color, the correction accuracy will be particularly poor for yellow, magenta, and cyan.

Therefore, as shown in FIG.
The value in the reference level storage unit 108 is changed in accordance with the specification of A/
This changes the reference value during D conversion. In Figure 6, the black “0” is O■, °゛255” is 1■, the cyan and magenta “o” is 1.5■, and the “255” is 2.5■.
, Yellow 0" is 3.5■, '255" is 4.5
A graph similar to that shown in FIG. 3 when set to (2) is shown. As can be seen from this graph, by changing the reference value for A/D conversion for each color, the resolution for density was improved for each color, and the accuracy of correcting density unevenness was actually improved.

Next, an example of a black and white inkjet recording device will be described. An inkjet recording device has been proposed that uses two inkjet heads, one for light black ink and one for light black ink, mainly for binary recording type inkjet recording devices to improve graininess. There is. When correcting density unevenness in such an inkjet recording apparatus, the optical density of a test pattern recorded at 50% duty varies greatly depending on each recording head.
Therefore, the analog output values read by the test pattern reading system also differ greatly between the head for light black ink and the head for light black ink. Therefore, even for such a black and white inkjet recording device, it is very effective to switch the analog value that is the reference for A/D conversion for each recording head, as in the above embodiment, and it is actually Correction of density unevenness has also been greatly improved.

In addition, in the example, an example was described in which so-called shading correction was not performed to correct changes in the light amount of the light source and changes in the output characteristics of the optical sensor. An example of performing shading correction will be described.

When performing this shading correction, - for boat fishing, the analog output value when the test pattern reading system reads the density of the standard whiteboard is "255", and the analog output value when the density of the standard blackboard is read is "O". The two obtained voltage values are converted by an electric circuit as shown in Figure 8, and the converted voltage values are used for A/D conversion. By using this as a reference value, the analog value used as a reference for A/D conversion is changed for each recording head, and the same effect as in each of the embodiments described above is obtained.

With this configuration, it was possible to obtain the same effects as in each of the embodiments described above also in a system that corrects noise such as a change in the light amount of a light source by shading correction.

As explained above, according to this embodiment, the analog value that is the reference for A/D conversion is made variable for each recording head that recorded the test pattern, and is optimized for the test pattern recorded by each recording head. By setting each value to a certain value, the resolution for density is improved, the readable density difference value becomes smaller, and it becomes possible to improve the accuracy of correction of density unevenness.

[Effects of the Invention] According to the present invention, it is possible to provide an image recording apparatus in which variations in recorded images due to variations in recording characteristics of recording elements arranged side by side are accurately eliminated for recording heads of various reliability.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the image recording device of this embodiment, FIG. 2 is a diagram showing a look-up table stored in the light amount-density converter, and FIG. 3 is the same as shown in FIG. FIG. 4 is a flowchart showing the correction procedure of the image recording device of this embodiment. FIG. 5 is a diagram showing a test pattern in another embodiment. The figure shows the light intensity conversion table when the reference value of the A/D converter is changed. Figure 7 shows the relationship between the voltage output when the test pattern reading system reads the gradation pattern and the reflection density. FIG. 8 is a diagram showing an example of changing the reference value of A/D conversion by the A/D conversion reference voltage conversion circuit, and FIG. 9 is an inkjet recording example as an example of a color image recording device to which the present invention can be applied. A schematic cross-sectional view of the apparatus, FIGS. 10(a) to 10(C), and FIGS. 11(a) and 11(b) are explanatory diagrams for explaining the density unevenness correction algorithm. In the figure, 1... recording head, 2... cassette, 4...
・Pickup roller, 5...Second registration roller, 6°12...Guide plate, 7...Second registration roller, 8...
・Transport belt, 9... platen, 10... lamp,
11... Optical sensor, 13... Paper ejection roller, 14.
・・Paper output tray, 101 ・・Correction head specification section, 10
2... Conversion parameter change instruction section, 103... Light amount-density conversion section, 104... Test pattern reading system, 1
05... Correction value calculation section, 106... Recording element drive signal correction section, 07... A/D conversion section, 08... Reference level storage section. Patent Applicant Canon Stock rzma)'s t 7i I♂Pe Figure 9 - Paulownia i + 3'' J to l?: l ( ), , hs each Vw - form O f (1) 3 ku = Kth Figure 8: Wet water bottle Figure 11

Claims (3)

[Claims] (1) An image recording device that has multiple types of recording heads in which multiple recording elements are arranged side by side, and records images using the recording heads, based on read data of test patterns recorded by the recording heads. An image recording apparatus comprising: a correction means for correcting a drive signal for driving the recording element in accordance with the position of the recording element and the type of the recording head. (2) The correction means converts the read data based on a conversion parameter corresponding to the type of the recording head.
2. The image recording apparatus according to claim 1, further comprising a conversion means for converting light amount data into density data, and a correction value calculation means for calculating a correction value based on the converted density data. (3) The correction means includes an A/D conversion means for converting the read analog data into the digital light amount data, and changes a reference level of the A/D conversion means in accordance with the type of the recording head. 3. The image recording apparatus according to claim 2, further comprising reference level converting means.