JPS6321623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet printer that records images such as desired characters and figures.

In an inkjet printer that applies a pixel signal whose waveform is shaped into a pulse or a sine wave based on a binary image signal to an ink head via an amplifier circuit, the pixel signal is continuously output in response to the pixel signal. When an ink droplet is ejected, its particle size gradually changes from small to large until the ejection operation of the ink droplet reaches a steady state. This particle size variation phenomenon is particularly noticeable in inkjet printers having on-demand ink heads that eject ink droplets as needed.

Fig. 1 shows a typical on-demand ink head disclosed in Japanese Patent Publication No. 53-45698. an inner chamber 1a associated with a piezoelectric vibrator 2 that curves and vibrates in response;
and an outer chamber 1b communicating with the inner chamber 1a via the coupling path 3. Reference numeral 4 denotes an orifice bored from the outer chamber 1b, which causes an ink column 5 to protrude when the piezoelectric vibrator 2 bends and vibrates in a direction that reduces the volume of the inner chamber 1a, and then becomes an ink droplet 6 and flies. do.

Figure 2 shows a block diagram of a basic ink jet printer incorporating an ink head with this structure.
A timing chart of the main parts is shown in Fig. 3.
In Fig. 2, 7 is an AND circuit that samples and synchronizes the transmitted binary image signal a with a sampling signal b of a predetermined period, and 8 is the AND circuit.
An amplifier circuit 9 amplifies the output to a high voltage region, and 9 is an ink head detailed in FIG. As shown in FIG. 4, the above particle size fluctuation phenomenon appears. That is, the particle size of the ink droplet 6 ejected corresponding to each of the unique information periods indicated by periods T ₁ to _{T 3} is the same as that of the corresponding period T ₁
~T ₃ The first one is small and gradually expands. This phenomenon is caused by the fact that the bending vibration of the piezoelectric vibrator 2 is initially small and then vibrates gradually to a larger extent while receiving the inertial force of the previous vibration. Therefore,
After the non-information periods t ₁ and t ₂ continue for a long time, the density of the ejected and recorded image becomes extremely light, and the recorded density becomes uneven as a whole.

The present invention has been developed in view of such uneven recording densities, and one embodiment of the present invention will be described in detail below with reference to FIGS. 5 to 7.

FIG. 5 shows a block diagram of the inkjet printer of the present invention, where 10 is a first AND circuit for sampling the binary image signal a as shown in FIG. 6 with the sampling signal b, and 11 is an inverted signal of the image signal a. a second AND circuit sampling 12
is the AND of the first and second AND circuits 10 and 11 above.
Outputs c and d are connected to third and fourth AND circuits 1, respectively.
3, 14 through the up terminal Up and down terminal
2 ⁿ -ary up/down (U/D) counter input to Do; 15 is a first NAND circuit that NANDs the count output e of the U/D counter 12; 16
is a second NAND circuit that takes the NAND of the inverted count output of the U/D counter 12, which is opposite to the first NAND circuit 15, and these are the first and second NAND circuits.
The NAND outputs of circuits 15 and 16 are the third and fourth
The signals are fed back to AND circuits 13 and 14, respectively. 17 is the above U/D counter 12
18 is an amplifier circuit whose amplification degree is controlled by the analog signal f of the D/A converter 17. The AND output c sampled by the first AND circuit 10 is supplied with power. Reference numeral 19 denotes an on-demand type ink head that ejects ink droplets 20 in response to the pixel signal g amplified by the amplification circuit 18.

Next, a specific operation will be explained using an example in which the U/D counter 12 is a ²⁴ (=16) base counter.

First, in the initial state, the U/D counter 12 is initially cleared by applying a reset signal r to its reset terminal Re. The image signal a transmitted in this state is sampled by the first AND circuit 10, and its AND output c is input to one input terminal of the third AND circuit 13. The other input terminal of this third AND circuit 13 is connected to the U/D counter 12, and its count output e is "0" to
When it is "14", the first AND output c is passed through. The first signal that has passed through this third AND circuit 13
AND output c is the up terminal of U/D counter 12
Up is applied to advance the U/D counter 12 by +1 step. Therefore, the information period in Figure 6
When the first AND output c corresponding to _T1 is added to the U/D counter 12, the U/D counter 12 sequentially counts up from "1" to "6".

A D/A converter 17 connected to the U/D counter 12 converts the inverted signal of the count output e into a D/A converter.
The analog signal f is converted to form an analog signal f. The level of this analog signal f becomes smaller as the count output e becomes larger, and vice versa. More specifically, it reaches a maximum when it is "0", and thereafter decreases stepwise to "15". The analog signal f from the D/A converter 17 is applied to an amplifier circuit 18 to determine the degree of amplification of the circuit 18. Therefore, the first AND output (C ₁₁ ) sampled at the beginning of the information period T ₁ receives the maximum amplification because the count output e of the U/D counter 12 is “0”, and thereafter the U The amplification degree gradually decreases as the /D counter 12 counts up.

In this way, the pixel signal g formed under the amplification effect whose amplification degree gradually decreases is applied to the ink head 19, and first, as described above, in one information period _T1 , the first pixel signal _g11 reaches the maximum level. Therefore, the piezoelectric vibrator 2 of the ink head 19 makes a large curved vibration and ejects ink droplets 20 of the rated particle size. The particle size of the ink droplets 20 that are subsequently ejected is determined by the fact that the piezoelectric vibrator 2 receives the inertial force of the previous vibration, and as the pixel signal g gradually decreases. Nevertheless, the same bending vibration can be obtained, so that the ink droplet has the same diameter as the ink droplet 20, as shown in FIG.

Next, when the no-information period t ₁ arrives, the second AND
The second signal sampled within the period _t1 is sent from the circuit 11 to one input terminal of the fourth AND circuit 14.
AND output b is added. And the fourth AND
A U/D counter 12 is connected to the other input terminal of the circuit 14.
When the NAND of the inverted count output is input and the U/D counter 12 is between "1" and "15",
The second AND output d is applied to the down terminal Do of the U/D counter 12. That is, when the no-information period _t1 arrives, the U/D counter 1 is set to ₁ in the previous information period T1.
2 has counted up to "6", so when the second AND output d is applied to the down terminal Do of the U/D counter 12 via the fourth AND circuit 14, it counts down from "6" to "0". do.

This no-information period _t1 continues and the U/D counter 12
After counting down to “0”, the next information period T ₂
arrives, the U/D counter 13 becomes “0” again.
It works by counting up from. The above information period
If _T2 continues to count up from "0" to "15" for a long period of time, the U/D counter 12 counts up to "15" and then tries to carry back to "0". Count output e is “15”
, the first NAND output becomes logic 0 and the third
The AND circuit 13 is cut off. That is, the count up of the U/D counter 12 is forcibly held at up to "15" without carrying around. Therefore,
The amplification degree of the amplifier circuit 18 decreases by 15 steps from "0" to "14" and becomes constant from 16 steps. This is because when the piezoelectric vibrator 2 undergoes continuous bending vibration to some extent,
This is because the ejected ink droplets 20 stop changing in particle size and return to a normal state, and in this embodiment, the number is set to 16 by using the ^24- digit U/D counter 12. That is, the amplification degree of the amplification circuit 18 is gradually decreased until the particle size of the ink droplets 20 ejected within one information period reaches a substantially steady state, and is kept constant thereafter.

No information period t ₂ after a long information period T ₂ has elapsed
In response, the U/D counter 12 starts a countdown operation from the previous count output "15".

Although the amplification degree of the amplifier circuit 18 increases with this countdown, the pixel signal g is not supplied to the ink head 19 because the first AND output c is logic 0. Then, when the countdown operation reaches “11”, the no-information period t ₂ becomes the information period
Flip to T ₃ . Therefore, the U/D counter 12 starts counting up from the above "11", and the first AND output at the beginning of the information period _T3 .
C ₃₁ receives the pixel signal after amplification corresponding to this “11”
Converted to g ₃₁ .

In this way, for the information period _T3 that arrives after the short-term no information period _t2 , the U/D counter 12
Since it only counts down a little, its amplification degree is suppressed compared to those in other information-bearing periods T ₁ and T ₂ . That is, the first pixel signal _g31 in the no-information period _T3 in FIG. 6 is the corresponding pixel signal in the other periods _T1 and _T2 .
It is suppressed to a lower level than g ₁₁ and g ₂₁ . However, when this pixel signal _g31 is supplied to the ink head 19, the piezoelectric vibrator 2 is affected by the inertial force of the piezoelectric vibrator ₂ during the information period T2 even though the pixel signal _g31 is at a low level. Since it is strongly affected by the pixel signals g 11 and g 21 , the corresponding pixel signals g ₁₁ and g ₂₁ vibrate in a curved manner.
Therefore, ink droplets 20 of the same diameter are ejected from the ink head 19.

As is clear from the above description, in the inkjet printer of the present invention, the amplification degree of the amplification circuit that amplifies the pixel signal that drives the ink head gradually increases within a certain information period until the particle size of the ink droplets reaches a substantially steady state. Since the time is reduced, ink droplets of the same diameter can be obtained over the entire period, and the overall recording density can be made uniform.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a typical on-demand ink head, Figure 2 is a block diagram of a conventional inkjet printer, Figure 3 is a waveform diagram of its main parts, and Figure 4 shows a conventional recording state. Model diagram, 5th
The figure is a block diagram showing the inkjet printer of the present invention, and FIG. 6 is a waveform diagram for explaining its operation.
FIG. 7 is a model diagram showing the recording state of the present invention. 10, 11, 13, 14...1st to 4th
AND circuit, 12...Up-down (U/D) counter, 17...D/A converter, 18...Amplification circuit, 19...Ink head.

Claims (1)

[Claims] 1 In an inkjet printer that records images such as desired characters and figures by ejecting ink droplets as necessary based on a binary image signal, a pixel signal is obtained by sampling the image signal with a sampling signal of a predetermined period. is applied via at least an amplifier circuit to a piezoelectric vibrator of an ink head that ejects the ink droplet, and the amplification degree of the amplification circuit is adjusted within a certain information period in which the ink droplet of the image signal is to be ejected, An inkjet printer characterized in that the particle size of ejected ink droplets is controlled to gradually decrease until it reaches a substantially steady state.