JPS60151061A - Ink jet recording system - Google Patents

Abstract

PURPOSE:To perform a halftone recording having reproducing capacity from low density to high density without decrease in the resolution by selecting an ink jet head for injecting ink in accordance with a density signal and controlling the volume of ink droplet. CONSTITUTION:A head can inject an ink droplet volume approximately proportional to the pulse length from pulse length tw1 to tw2 of a drive pulse. When th value of input density DI is dense value DIa larger than constant value DT, a high density ink head is selected, ink droplet is injected in pulse length twa corresponding to density level DIa, thereby obtaining corresponding recording density D0a. On the other hand, when the input density level is the value DIb smaller than DT, a low density ink head is selected, ink droplet is injected in pulse length twp corresponding to the density level DIb, thereby obtaining the corresponding recording density Dob. Thus, halftone record from low density DL2 to high density DH1 can be obtained by selecting the head for injecting by the input density level.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inkjet recording system, and particularly to a recording system that enables halftone recording.

(Prior art and its problems) It has been known that in the conventional on-demand type inkjet head, the volume of the ink droplets ejected changes by changing the pulse length and amplitude of the drive pulse. Utilizing this feature, it was possible to perform halftone recording by controlling the drive pulses depending on the gray level of the image to be recorded. However, in an on-demand inkjet head, when the pulse length or amplitude changes, not only the droplet volume but also the droplet volume changes.
Since the flying speed also changes, if we control the speed fluctuation to the extent that a record without a recording type is obtained, the variable range of the droplet volume is not so wide and the volume ratio of the smallest sieve to the largest tube can be obtained at most 3 to 3. It is about 4 times as much. Therefore, when recording is performed at a constant recording density, the halftone reproduction range that can be expressed only by modulating the droplet volume is a reflection density of 0.4 to 1.5 μm, as shown in Figure 1. Although the density can be changed continuously within this range, there is a drawback that the ability to reproduce halftones in bright areas with a density of 0.4 or less is lacking.

Other halftone recording methods include the dither method and the density pattern method. These methods express intermediate tones in a condensed manner by changing the density of dots according to the density. In this pseudo-intermediate reproduction method, in order to increase the number of tones, it is necessary to increase the number of dots in the unit expressing the intermediate tones, which requires a higher recording density, which reduces the recording speed. Put it away. Furthermore, since there is a limit to the miniaturization of ink droplets, there are problems such as limitations in recording resolution.

(Object of the Invention) An object of the present invention is to provide an inkjet recording method that eliminates such conventional drawbacks and realizes halftone recording capable of reproducing from low density to high density without deterioration of resolution. It is in.

(Structure of the Invention) According to the present invention, ink droplets of different concentrations are ejected, and the ink whose volume is controlled by an electric signal is ejected onto a recording medium to determine the dot area. Using a plurality of inkjet heads, each of which performs gradation recording in a predetermined density range by performing modulation recording,
An inkjet recording system is obtained which is characterized by selecting an inkjet head for ejecting ink and controlling the volume of ink droplets according to density signals.

(Detailed Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration. A detailed explanation will be given below using the drawings.

FIG. 2 shows an example of droplet formation characteristics of an inkjet head capable of modulating droplet volume used in the present invention. Such characteristics can be obtained by the head shown in Japanese Patent Application No. 58-159819. This head is capable of ejecting an ink droplet volume approximately proportional to the pulse length over the pulse length twz of the driving pulse from tW1. Here, to simplify the explanation, a case will be described in which halftones are expressed using inks having two types of densities DI+D2. First, by modulating the droplet volume with high-density ink and recording at a constant recording density, gradation recording from the minimum density DL1 to the thickest droplet DH1 can be obtained, as shown in FIG. 3(a). For this high density ink, the density of the low density ink is selected so that the density DHt when printing is performed using the largest cylinder is equal to DLI. Then, as shown in FIG. 3(b), it becomes possible to record from hDL2 to J)DHg using low-density ink, and a wide tone reproduction range from DL2 to Dn+ is obtained as a whole.

When recording using these heads, Fig. 3(c)
), when the value of the input density p1 is a darker value DIa than the constant value DT, a high-density ink head is selected and a thin ink droplet is ejected with a pulse length 'wa corresponding to the density level DIa. and the corresponding recording density. get a. On the other hand, when the input density level is a value DIb thinner than DT,
Select a low-density ink head and set the pulse length t corresponding to the density level DIb.

The ink droplets are ejected and the corresponding recording density is achieved. get b.

By selecting the ejecting head according to the input density level in this manner, halftone recording from low density DLz to high density DI(t) can be obtained.

In the above explanation, an example using two types of density ink was shown, but when using three or more types of ink, the density DL2 at the minimum dot using the low density ink in the previous example can be similarly applied.
On the other hand, inks with lower densities are sequentially selected so that the recording densities DHs of the maximum dots are the same. This makes it possible to widen the recordable density range.

FIG. 4 shows a block diagram for explaining an embodiment of the present invention. In the figure, 41 is an image signal source that outputs a density signal 42 in synchronization with a clock (not shown);
43 is a classification means for comparing the density signal 42 with a preset value, classifying which region includes the density, and outputting the classification signal 44; 45, switching the density signal 42 according to the classification signal 44; distribution means for outputting, 47
Reference numeral 49 indicates an inkjet head, and numeral 49 indicates a driver that outputs a drive signal 48 for ejecting a predetermined amount of ink in accordance with a density signal 46 in synchronization with a clock. Also 47-4
Subscripts 1 to n attached to 9 correspond to inks of different densities, respectively. The ink of each head is modulated by the volume of the droplets of each head so that the maximum and minimum densities when recorded are continuous and do not overlap each other. use. The set value of the sorting means 43 is determined in accordance with the density at the connection point of the recording density by each of these heads.

To explain the operation, first, when a density signal is output from the image signal source 41, the density is discriminated by the discriminating means 43.

The distribution means are controlled according to the density level, and the density signal is input to a driver which records the corresponding density. All outputs other than the output to which the density signal is connected are signals under which ink is not ejected. The driver to which the concentration signal 46 is input forms a drive waveform to eject an ink droplet with a volume corresponding to the concentration signal level,
The ink is output to an inkjet head and droplets are ejected. When using an inkjet head in which the droplet volume changes depending on the pulse length as shown in FIG. A waveform is obtained. With this configuration, the head to which ink is to be ejected is selected according to the density level, and ink is ejected with a controlled volume. Although not shown in this embodiment, ink droplets ejected by each head need to be printed at the same point.

In a recording device, if it is not possible to print at the same point by simultaneous jetting due to constraints on the arrangement of each head, etc., there is a method such as delaying each of the density signals 46-1 to 46-0 according to the positional deviation of each head. to print at the same point.

As described above, according to the present invention, by selecting the size of the printed dot and the ink density, a recording with a wide range of gradation reproduction can be obtained with a single dot, so it is possible to prevent a decrease in resolution. In addition, excellent halftone recording can be realized at a practical recording density.

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[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of gradation reproduction characteristics by conventional droplet volume modulation, FIG. 2 is a diagram showing an example of droplet formation characteristics of an inkjet head used in the present invention, and FIG. ) and (b) are diagrams showing the relationship between the pulse length and recording density using inks of different densities, respectively. Figure 3 (c) is a diagram showing an example of the relationship between the density signal and recording density, and Figure 4. The figure is a block diagram for explaining one embodiment of the present invention. In the figure, 31 and 32 represent the relationship between the input density and the pulse length applied to the high-density ink and low-density ink heads, respectively, and 33 and 34 represent the relationship between the recording density and pulse length by the high-density ink and low-density ink heads, respectively. 41 is an image signal source, 42 is a density signal, 43 is a classification means, 44 is a classification signal, 45 is a distribution means, 46 is a density signal, 47 is a driver, 48 is a drive signal, and 49 is an inkjet head. 0.51 1 dot men

Claims (1)

[Claims] By using ink of different densities, ejecting ink droplets of the respective densities, and ejecting the ink whose volume is controlled by an electric signal onto the recording medium to perform dot area modulation recording, each predetermined amount can be recorded. An inkjet recording method that uses a plurality of inkjet heads that perform gradation recording in a density range, and that selects the inkjet head that ejects ink according to density signals and controls the volume of ink droplets.