JPS627555A - Ink jet recording device - Google Patents

Abstract

PURPOSE:To improve tone characteristics by raising supply energy level when a spacial frequency is high. CONSTITUTION:When a high spacial frequency is detected by a frequency detector 2, a high regional compensation is performed by a high regional compensation circuit 4. When a spacial frequency omega is low, the high regional compensation circuit 4 puts out a linear output against an input density signal. When a spacial frequency omega is high, the circuit further raises the high level of an input density signal. From the above stated constitution, regardless of spacial frequencies, a linear output density characteristics may be obtained against an input. Therefore, a high quality image is made obtainable.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an inkjet recording device, and particularly to an inkjet recording device that can vary the amount of ink ejected.

<Prior Art> In an inkjet recording device, gradation is expressed by varying the dot diameter depending on the amount of ink ejected. Here, ω is the spatial frequency and τ′ is the dot diameter.

When τ is the dot pitch, the output density H(jω) is given by the following equation.

Also, the Nyquist frequency ωN is ωN=π/τ (2) (1
) to find the amplitude characteristics from the equation.

FIG. 1 shows IH(jω)1 when the spatial frequency ω is 0 and ω=ωN as a function of τ′/τ.

As shown in FIG. 1, as the spatial frequency increases, the output density decreases in regions where the ratio of dot diameter to dot pitch is large.

Purpose of the Invention The present invention aims to eliminate the drawbacks of the prior art as described above and provide an inkjet recording device with improved gradation characteristics.

<Embodiment> In FIG. 2 which shows the first embodiment of the present invention, 1 is an input terminal for an input concentration signal, 2 is a frequency detector that detects the frequency of the input concentration signal, and 4 is a frequency detector 2. 6 is an inkjet head drive circuit, and 8 is an inkjet head capable of varying the amount of ink ejected.

When the frequency detector 2 detects that the spatial frequency is high,
High frequency compensation circuit 4 performs high frequency compensation.

The characteristics of the high-frequency compensation circuit 4 are shown in FIG. 3. When the density is high in FIG. 3, the high level of the input density signal is further increased.

With this configuration, an output density characteristic that is linear with respect to the input can be obtained regardless of the spatial frequency.

Next, a second embodiment of the present invention will be described.

In recent years, in order to widen the reproduced gradation range, a recording method has been proposed in which inks of the same color with different densities are used and the dot diameter of each ink is varied.

In such a case, there are problems similar to those described above.

As shown in Fig. 4, when the spatial frequency ω is O, the reproduction range of output density with light ink is A-B, and the range with dark ink is C-D. The reproduction range is continuous.

However, if ω is ωN, it is a light ink.

The reproduction range of each dark ink is A-E', C-ff,
There is a distance between "and C", and the reproduction range of density becomes discontinuous, resulting in a drop in the quality of one image.

Therefore, a signal processing circuit as shown in FIG. 5 is used.
In the figure, the same parts as in FIG. 2 are given the same reference numerals.

3 is a head selection circuit that detects the level of the input density signal and selects whether to use a light ink head or a dark ink head.

4a and 4b are high-frequency compensation circuits for the light ink head and the dark ink head, respectively, and have compensation characteristics as shown in FIG.

That is, as in FIG. 3, when the spatial frequency ω is low, a linear output is produced with respect to the input density signal, and when ω is high, the high level of the input density signal is further increased.

With this configuration, an output density that is linear with respect to the input density signal can be obtained regardless of the spatial frequency, and! Continuity is maintained in the gradation reproduction range of light ink, and high-quality hard copies can be obtained.

Incidentally, in this embodiment, ink having two types of density was used, but three or more types may be used.

Further, although a piezoelectric element is used as the inkjet head, various heads such as a head or a head whose ink ejection amount can be varied depending on the amount of heat of a thermal head can be used.

Effects> As described above, according to the present invention, it is possible to always obtain an output density that is faithful to the density level of the input density signal regardless of the spatial frequency, and to obtain a high-quality image.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in output density characteristics due to differences in spatial frequency, FIG. 2 is a signal processing circuit diagram of the first embodiment, and FIG.
This figure is a compensation characteristic diagram of the high frequency compensation circuit 4 of FIG. 2, and FIG. 4 is a diagram showing output density characteristics when using a dark ink head and a light ink head. Fig. 5 is a signal processing circuit diagram of the second embodiment, and Fig. 6 is a signal processing circuit diagram of the second embodiment.
It is a compensation characteristic diagram of the high frequency compensation circuits 4a and 4b. In the figure, l is an input terminal, 2 is a frequency detection circuit, 3 is a head selection circuit, 4, 4a, 4b are high frequency compensation circuits, 6.
6a and 6b are head drive circuits, 8 is an inkjet head, 8a is a head for light ink, and 8b is a head for dark ink, respectively.

Claims (1)

[Claims] an inkjet head for ejecting ink droplets, a variable means for varying supplied energy to vary the amount of ink ejected from the inkjet head, and a compensation means for increasing the supplied energy level when the spatial frequency of an image to be recorded is high. An inkjet recording device characterized by: