JPH0239946A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To obtain a recording image having a large gradation width without damaging resolving power relatively by determining the drive pulse waveform of a recording head corresponding to the dot recording cycle of the pixel pattern selected corresponding to density data. CONSTITUTION:Either one of the 4/4 pattern and 1/4 pattern of a pixel pattern is selected corresponding to the density data OD value of each color. For example, when the OD value is 0.5 or more, the 4/4 pattern is selected and, when the OD value is 0.5 or less, the 1/4 pattern is selected. Further, the OD value of each color is successively inputted to a density/drive pulse voltage converter circuit according to the selected pattern and the OD/voltage converting table stored in a ROM is referred to on the basis of the OD value corresponding to a dot recording cycle and the OD value is converted to drive pulse voltage for recording the dot diameter corresponding to the OD value. An ink droplet is emitted from a head on the basis of said pulse voltage to form a dot on recording paper. The obtained image becomes such a state that high and low density regions are connected smoothly and is excellent in the reproducibility of an extremely low density region.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording method for expressing halftones by changing the dot size.

[Prior Art] Conventionally, as a halftone expression method, there has been a digital method such as a dither method, and an analog method has been, for example, a method of changing the recording dot size in an inkjet recording method.

The dither method expresses a predetermined unit of pixels by a matrix pattern made up of elements of binarized image data, and halftone expression by this method is achieved by changing the number of elements in the matrix.

Furthermore, a method of expressing gradation by changing the dot size has been widely used in on-demand inkjet recording methods. That is, by changing the pulse voltage and pulse width applied to the piezo element or heat generating resistor as the ink ejection energy generating element, the ink ejection amount was changed and the recording dot size was controlled.

[Problems to be Solved by the Invention] However, in the dither method described above, in order to improve gradation, the number of elements in the dither matrix must be increased, and as a result, the resolution of the recorded image is impaired. There was a problem.

Furthermore, this method has the problem that the number of gradations is limited.

Further, in general, in a method for changing the dot size, such as an on-demand inkjet recording method, it is impossible to increase the size range of the dot size, that is, the gradation width, simply by changing the pulse voltage or pulse width.

Therefore, efforts have been made to provide a wide gradation range by providing multiple nozzle diameters and using inks with different densities.

However, with this type of system, the overall size of the device increases,
Not only does this increase complexity, which increases costs, but
Will using small nozzles or dark ink cause nozzle clogging? There was a problem in that images deteriorated over time due to differences in fixability of atR inks on recording paper.

The present invention has been made in view of the above-mentioned problems, and
The purpose is to provide an inkjet recording method that can obtain a recorded image with a large gradation range without compromising resolution by changing the recording dot size and the dot pattern forming pixels.

[Means for Solving the Problems] To this end, the present invention selects one pixel pattern from among a plurality of pixel patterns formed by one or more dots according to the density information of the pixel to be recorded. The driving pulse waveform of the recording head is determined according to the dot recording period of the selected pixel pattern, and recording is performed using the driving pulse waveform determined according to the selected pixel pattern.

[Function] According to the above configuration, it is possible to reproduce a wide range of gradation, that is, a density region, in a recorded image, and in particular, by selecting a predetermined pixel pattern according to the density information, the diameter of the recorded dot can be adjusted. can widen the variable range of
In particular, the reproducibility in the extremely low concentration region is improved.

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

FIGS. 1A and 1B) are conceptual diagrams showing pixel dot patterns in one embodiment of the present invention.

Of these, FIG. 1(A) shows a pattern in which four areas forming one pixel are each filled with dots.
B) shows a pattern in which only one of the four regions is filled with dots, which are herein referred to as a 474 pattern and a 1/4 pattern, respectively.

The recording method of this example uses a 1/4 pattern and a 1/4
The idea is to use different pixels in the pattern and to change the dot diameter.

FIG. 2 is a diagram showing the relationship between the recorded dot diameter and the average reflective optical density of 00 in the recorded image for each of the 1/4 pattern pixel and the 4/4 pattern pixel. As is clear from the figure, when using 4/4 pattern pixels and changing the dot diameter in the range of 100 to 200 μm, 00
Images with values in the range of 0.5 to 1.6 can be realized. Also 1
When /4 pattern pixels are used, it is possible to realize an image with an OD value of 0.5 or less by changing the dot diameter.

As is clear from the above, it is possible to realize an image in a density (gradation) region, especially a low density region, which conventionally could not be obtained only by changing the dot diameter size.

By the way, when recording as in this example, different pixel patterns are mixed, for example, if the recording pattern is as shown in FIG. 10, T is the head drive cycle within the 4/4 pattern. In this case, the head drive cycle within the 1/4 pattern is 2T.

It is generally known that in an inkjet recording head, the longer the drive cycle, the higher the limit ejection performance can be.

Therefore, in the recording method of the present invention, as a result of changing the pixel pattern, the limit driving condition is changed in accordance with the change in the driving cycle, and the maximum performance of the head is brought out. .

In this example, when recording a 1/4 pattern, both the upper and lower limits of the voltage range of the head drive pulse waveform are made wider than when recording a 4/4 pattern, thereby widening the variable range of the recorded dot diameter. conduct.

This is because the upper limit of the head drive pulse voltage is determined so that the refilling time of ink from the ink supply path after ink droplet ejection is shorter than the head drive cycle. This is because it can be made larger, that is, the refill time can be longer, and the maximum dot diameter can be increased.

Furthermore, the lower limit of the head drive pulse voltage is determined by whether the ejection speed of flying ink droplets is above a certain level, and the lower limit of the ejection speed is a value that changes depending on the difference in resolution, that is, the difference in pattern. be. Since the 4/4 pattern has twice the resolution as the 1/4 pattern, it is necessary to record it with higher precision.

In other words, the dot diameter and the ejection speed of the ink droplet are almost proportional, and the slower the ejection speed of the ink droplet, the more the ink droplet becomes 11th.
As shown in figure (A), DI, D2,03 (discharge speed:
DI>02>03) and fly 711 while being deviated in the moving direction of the head. As a result, the ink droplets are placed on the recording paper in the 11th
As shown in Figure (B), the dots land at different positions depending on the difference in dot diameter.

In the 1/4 pattern, 02. in FIG. 11(B). D
Even if the landing position shifts as shown in 3, there is no problem because it will be recorded within the pixel that should be recorded, but if it shifts like this in the 4/4 pattern, the dots that should be adjacent dots will completely overlap. It is also possible to put it away. Therefore, 1/4
With the pattern, it is possible to set the lower limit voltage smaller than with the 4/4 pattern.

FIG. 3 is a perspective view of an on-demand inkjet recording head used in an embodiment of the present invention, and the bottom diameter can be adjusted by changing the voltage or pulse width of the drive pulse waveform applied to the piezoelectric element. change. The recording head 1 includes ejection ports IA corresponding to four colors of ink: cyan, magenta, yellow, and black.

FIG. 4 is a perspective view showing a serial type recording apparatus using the inkjet head 1 shown in FIG. 3. The head 1 performs forward motion parallel to the platen 5 to record the first line, and the dots in the upper half area shown in FIG. is sent vertically. During this time, head 1
returns to its original position by a backward movement, and then the dots in the lower half area shown in FIG. 1 are recorded again by recording the second line.

FIG. 5 is a block diagram of the recorded image data processing circuit according to this embodiment, in which the recorded image data manually inputted with RGB signals is changed into density data by the density conversion circuit 6, and then is properly processed via the masking circuit 7. Color correction is performed, and the density data of each color of cyan, magenta, and yellow, that is, OD
It is input to the pattern selection circuit 8 as a value. Here, either 474 pixel patterns or 1/4 pixel pattern is selected depending on the oD value of each color. For example, as shown in FIG. 2, when the OD value is 0.5 or more, the 4/4 pattern is selected, and when it is less than that, the 1/4 pattern is selected.

Further, according to the selected pattern, the oD value of each color is manually input to the density-driving pulse voltage conversion circuit 9, and based on the OD value corresponding to the dot recording cycle, a 00-voltage conversion table stored in a ROM (not shown) is referred to. Then, it is converted into a driving pulse voltage for recording the dot diameter according to the OD value. This pulse voltage causes ink droplets to be ejected from the head 1, forming dots on the recording paper.

Note that the voltage converted in the concentration-driving pulse voltage conversion circuit 9 is selected from the range shown below.

4/4 hatante is 30 to 70 [v] (dot diameter 1
00~220 [μm1) 25~90[V] for 1/4 pattern (dot diameter 85~
280 [μml] In the image obtained by the recording method described above, the high-density area and the low-density area are smoothly connected, and the reproducibility of the extremely low-density area is excellent.

FIG. 6 shows a pixel pattern according to a second embodiment of the present invention, and shows an example in which the pixel pattern is composed of 272 patterns and 1/2 pattern. When other processing was carried out in the same manner as in the embodiment shown in Fig. 1, the OD value became as shown in Fig. 7, and the high-density area and low-density area of the image were well connected, and the gradation An image with smooth changes was obtained.

FIG. 8 shows a pixel pattern according to a third embodiment of the present invention, and shows an example in which the pixel pattern is composed of 474 patterns, 2/4 patterns, and 1/4 patterns, and other processing is the same as in the above-mentioned embodiments. When I did this, the value of OO was the 9th
As shown in the figure, the high-density, medium-density, and low-density areas of the recorded image are well connected, and it is possible to achieve a wide density area, resulting in images with smooth gradation changes and excellent reproducibility. It was done.

When comparing the image according to the embodiment of the present invention described above and the image according to the conventional example, when an image in a low density area is expressed in 16 gradations using a 4×4 dither matrix with the minimum dot of the conventional method, Not only were the gradations not smooth, but the resolution deteriorated, resulting in extremely poor image quality in highlighted areas.

In addition, when we used an 8 x 8 dither matrix with the smallest dot and expressed it with 64 gradations to express images in low-density areas, the gradations were smooth, but the resolution deteriorated significantly and the highlights were The image quality has become extremely poor.

In the above-described embodiment, one pixel pattern is selected based on the OD value, but if there are multiple patterns corresponding to one OD value, as shown in FIG. 7, the pixel pattern is selected as recording progresses. You may change the pattern.

Further, in the above-described embodiment, the voltage of the drive pulse is changed according to the pixel pattern, that is, the density, but the same effect can be obtained by changing the pulse width.

[Effects of the Invention] As is clear from the above description, according to the present invention, it is possible to reproduce a wide range of gradations, that is, density regions, in a recorded image, and in particular, by selecting a predetermined pixel pattern, it is possible to reproduce a wide range of gradations, that is, density regions, in a recorded image. The variable range of the diameter can be widened, and the reproducibility especially in the extremely low concentration region is improved.

As a result, it has become possible to obtain images of excellent image quality, since particularly low-density regions with relatively poor reproducibility can be expressed with good resolution and single gradation.

[Brief explanation of the drawing]

FIGS. 1(A) and (B) are conceptual diagrams showing the dot pattern of a pixel according to an embodiment of the present invention, and FIG. 2 shows the relationship between the dot diameter and the 00 value according to the embodiment shown in FIG. 3 is a perspective view of a recording head used in an embodiment of the present invention, FIG. 4 is a perspective view of a recording apparatus used in an embodiment of the present invention, and FIG. 5 is a perspective view of a recording head used in an embodiment of the present invention. A block diagram showing an image data signal processing circuit in the recording apparatus used, FIGS. 6 and 8 are conceptual diagrams showing pixel dot patterns according to other embodiments of the present invention, and FIGS. 7 and 9 are A diagram showing the relationship between dot diameter and OD value according to another embodiment of the invention, FIG. 10 is a conceptual diagram for explaining the period of dot recording in the embodiment, and FIGS. 11(A) and (B) are FIG. 2 is a conceptual diagram showing the trajectory of flying droplets. 6... Density conversion circuit, 7... Masking circuit, 8... Pattern selection circuit, 9... Density-drive voltage conversion circuit, 10... Head drive section. 1st 6th figure 7th figure 8th figure 24 dumb sword,) 辷f phrase 10th figure

Claims (1)

[Claims] 1) Selecting one pixel pattern from a plurality of pixel patterns formed by one or more dots according to the density information of the pixel to be recorded; An inkjet recording method, characterized in that a drive pulse waveform of a print head is determined according to a dot recording cycle, and printing is performed using the determined drive pulse waveform according to the selected pixel pattern.