JPH0255145A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To enable record in a halftone by generating bubbles by the electrolysis of liquid in a liquid chamber between a pair of electrodes provided in the chamber communicating with a discharge outlet, and then voltage-controlling the volume change of bubbles by a discharge. CONSTITUTION:When a voltage is applied between a first electrode 4 and a second electrode 5 by a driving signal, bubbles 8 are generated. When the bubbles are grown to a predetermined degree, a discharge is generated at a boundary between the bubbles and ink, and the ink is injected from a nozzle by energy at the time of the discharge. In this case, when a current flowing between the electrodes is stopped at a predetermined level, the quantity of ink to be injected from the nozzle can be controlled. For example, when a voltage waveform (b) is used, a driving signal is cut at a level A, a small ink droplet is generated. When a voltage waveform (c) is used, the signal is cut at a level B, and a large ink droplet is formed.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to an inkjet recording device? In particular, the present invention relates to an inkjet recording apparatus capable of halftone recording.

14 Conventionally, as a method for obtaining halftones in recording devices, there is a method for controlling the energization time in thermal printers to obtain halftones, but due to heat accumulation etc., halftone expression is unstable. becomes. In addition, on-demand (bubble jet, piezo type) type inkjet recording devices, etc.
Although halftones are expressed by controlling the number of pulses or the dynamic voltage according to the halftone information, it has been difficult to obtain stable and reliable halftone recording.

Purpose The present invention was made in view of the above-mentioned circumstances, and was made for the purpose of performing halftone recording in an electrolytic discharge type inkjet printer.

Structure In order to achieve the above object, the present invention provides an ejection port for ejecting liquid, a liquid chamber communicating with the ejection port, a pair of electrodes provided in the liquid chamber, and a liquid discharge port between the pair of electrodes. a voltage applying means for applying a voltage to change the volume of the bubbles by electric discharge after generating bubbles in the liquid in the liquid chamber by electrolysis; and a voltage for controlling the change in the volume of the bubbles by the electric discharge. The invention is characterized in that it has a control means. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a sectional view of a nozzle portion of an inkjet head according to an embodiment for explaining the present invention.

In the figure, 1 is a lower plate, 2 is an upper plate, 3 is an injection opening, 4 is a first electrode, 5 is a second electrode, 6 is a drive circuit, 7 is ink, 8 is a bubble, and the first electrode 4 is They are arranged corresponding to the respective injection openings and are each individually connected to a drive circuit. The second electrode 5 is arranged as one common conductor for all the injection openings and is connected to the other side of the drive circuit. here,
Now, when a driving voltage is applied between the first electrode 4 and the second electrode 5 as shown in FIG. 2(a), a current having a waveform as shown in FIG. 2(b) flows. In this case, as shown in FIG. 3(a), if the driving voltage is continued to be applied for a longer time,
As shown in FIG. 3(b), a phenomenon was discovered in which the current waveform shown in FIG. 2(b) repeats at a certain period. This phenomenon can be explained as follows.

Figure 4 is a diagram for explaining the phenomenon shown in Figure 3.
FIG. 4(a) shows the stopped state.

Now, when a driving voltage is applied between the first electrode 4 and the second electrode 5 in FIG. 1, as shown in FIG. 4(b).

Gas (bubbles) 8 begin to be generated around the first electrode 4 due to electrolysis, and gradually increase in size until the electrode surface is covered with gas (FIG. 4(C)), and the current supply is stopped.

As the current stops flowing, the interface between the gas and the ink becomes the same potential as the second electrode 5, the electric field strength between the first electrode 4 and the interface increases, and a discharge phenomenon occurs between the first electrode and the interface. happens.

The gas is expanded by the heat generated by the discharge, and the ink is pushed out from the nozzle surface (FIG. 4(d)).

When the gas expands, the bubbles collapse or shrink, allowing the ink to reach the electrode surface again.
Electrolysis occurs again (Fig. 4(e) to (f)).

The above state occurs repeatedly while the driving voltage is applied.

From this, the repetition period (head structure, applied voltage,
(varies depending on ink physical properties, etc.), by applying a driving voltage for a time that is an integral multiple of this period, it is possible to eject ink i9 proportional to the time applied by the nozzle. Namely.

An image with a density proportional to the time width can be obtained.

FIG. 5 shows an example of a method of applying a pulse with a drive width that is an integral multiple of the discharge period, and shows an interface unit 12 that takes in data from the host machine 11, a control device 131 that controls the entire machine, and the imported printout. A memory part 14 for storing data, a timer part 15 for time management to control printing time. output driving pulses,
I10 section 16 that inputs and outputs other signals; driver section 17 that amplifies drive pulses to the required voltage; It consists of a head 18 and a power supply 19 for driving the head.

FIG. 6 is a flowchart for explaining the operation of FIG. 5. Print data is fetched from the host machine 11 via the interface unit 12 (step 1), and when the fetch is completed (step 2), the control device 13 performs the printing operation. Then, print data is extracted from the imported data (step 3), and the master pulse width is calculated according to the gradation data (step 4).

Calculation of gradation data is as follows: For example, as shown in Table 1, if you have 3-bit data as gradation data, it can represent 7 gradations, and one of these gradation data is a discharge pulse.
If this is to be supported, it is sufficient to set the pulse width to be the number of gradations times the discharge period.

Table 1 (However, IT is one period of discharge.) This calculation data is sent to the timer 15 and (step
5) Issue a command to start outputting drive pulses to the I10 boat 16 (step 6). Timer 15 is
When the time set to cell 1 has elapsed, an interrupt signal is sent to controller 3. When the control device 13 receives this interrupt signal, it issues a command to stop the drive pulses to the machine/○ boards 1 and 16, and finishes printing one dot (step 8).
). All data can be printed by repeating the above operations until there is no more print data (step
p9).

FIG. 7 shows an example of a method for counting the number of discharges and recording halftones. The interface section 22 takes in data from the host machine 21, the control %fa 23 controls the entire machine, and A memory part 24 for storing data, an I10 part 25 for outputting the excitation pulse and input/output of other signals, and a driver part 26 for amplifying the excitation pulse to the required voltage. A detection unit 28 that detects the discharge current t flowing through the head 27, a filter section 29 that averages the high frequency components of the detection signal, and a signal ■ that compares the output signal ◎ of the filter section 29 with a comparison voltage Vref to determine whether or not discharge has occurred. It consists of a comparator 30 that outputs , and a power supply 31 for the head.

FIG. 8 shows each part of FIG. 7, namely, ■, ■'.

The signal waveforms at points ■ and Or■ are shown, respectively. (a) is a print recording signal sent from the control device via l1025.

(a') is a drive signal that is amplified from the recording signal and actually applied to the head.

(b) is an output signal from the current detection section 28 that is proportional to the discharge current.

(e) is a signal from which harmonic components have been removed by passing through a filter part 29 that averages harmonic components caused by discharge contained in the signal (2) from the current detection section 28.

(d) is a signal that is output when the signal ◎ is compared with V ref by the comparator 30 and the signal level of ◎ is higher than V ref.
3 and is used as a count signal for the number of discharges.

Therefore, if the halftone level is 3, (when Φ is output, discharge starts and comparator output ■ is generated. This ■ is counted by the control device 23, and the count number reaches 3. At this point, the output of (2) is stopped.By doing this, a density-modulated image can be obtained on the recording paper.

FIG.
When the import is completed (step 2), the controller 23
enters print cutting and extracts print data from the captured data. step 3) Calculate the number of drive pulses according to the 1st gradation data. For example, as gradation data, 3
If it has data of bits, it can represent seven gradations, and if one of these gradation data corresponds to a discharge pulse, it is sufficient to count the number of pulses that is the number of gradations times the number of discharges (step 6).

Outputs print recording signals for bots 1 to 25.

When the print recording signal is output, a discharge occurs in the head,
This emission generates a signal. This signal (D is counted by the control device and it is determined whether or not the counted number matches the previously calculated gradation data (stcpl)). If they do not match, the print signal continues to be output. On the other hand, if they match, the recording signal is stopped at 1 and printing of one dot is completed (step 8).

All data can be printed by repeating the above operations until there is no more print data (step
9).

The two embodiments have been described above regarding the system controlled by software, but if it is necessary to speed up the process due to issues such as speed, it is also possible to implement these logics in hardware to speed up the process. In addition, not limited to these methods, in short,
It is only necessary to be able to capture the characteristic that electric discharge has periodicity and use this to perform halftone recording.

FIG. 10 is a circuit diagram for explaining another embodiment of the voltage control means for controlling the volume change of bubbles due to discharge based on halftone data. Reference numbers 1 to 7 and 8 in FIG.
The electrode section consisting of is exactly the same as that explained in Fig. 1, and the other circuit parts correspond to the drive circuit 6 in Fig. 1, Q□, Q2 are transistors, R
□~R5 is a resistor, C is a capacitor, Di is a diode,
6a is a control device, 6b is a head folding power source, and 6c is a D/
A converter, 6d is an RS F/F, 6e is a comparator, and 10 is a recording paper.

Now, when a voltage is applied between the electrodes 4 and 5 in the electrode part due to the voltage movement signal, a bubble 8 is generated as described above, and when this bubble has grown to a certain extent, the electrode 4 and the bubble - Electric discharge occurs between the ink and the ink interface, and ink is ejected from the nozzle using the energy generated during this discharge. At this time, the waveform of the current flowing between the electrodes is as shown in Figure 11(a), and it has been found that by stopping this current from flowing at a certain level, it is possible to control the ink droplet ejected from the nozzle. did. Figure 11(b),(c)
are the drive voltage waveforms, respectively. Using the voltage waveform in figure (b), the drive signal can be cut at level A and a small ink droplet is generated, and using the voltage waveform in figure (c), the drive signal can be cut at level B. is cut, creating a larger drop of ink.

In this way, by turning off the discharge current at an appropriate level, the size of the ink droplet can be controlled and halftones can be expressed. Therefore, in FIG. 10, a signal containing halftone data is sent from the print data generating section. The control device 6a sends a coded signal to an n-bit D/A converter 6c to generate a reference voltage (Vref). This D/A converter 6c generates a reference voltage (Vref) based on this coded signal. Also, the control device 6
a is the (12th) set signal for R8F/F6d=
When Figure (a)) is issued, R3F/F6c is set and Q
When the output ■ (FIG. 12(b)) becomes high level, the transistor Q2 is turned off, the transistor Q1 is turned on, and the driving voltage VO is applied between the electrodes 4.5. When a driving voltage Vo is applied to the electrode 4 and a current flows, a voltage Vi (FIG. 12(C)) is generated across the resistor Rs, and this voltage is applied to the positive input side of the comparator 6e. On the other hand, the negative input terminal of the comparator 6e is connected to the D/A converter 6c described above.
Since a reference voltage (Vref), which is the output of d) Output. This signal ◎ resets R8F/F6d, so R8F/F6d is reset.
The output of F6d becomes low level, transistor Q2 is turned on, and transistor Q1 is turned off, so that the voltage Vo (FIG. 12(e)) applied to the electrode disappears and the discharge stops.

By changing the input signal to the D/A converter, the peak value of the flowing current can be changed, thereby modulating the size of the ink droplet and producing halftones.

Effects As is clear from the above explanation, according to the present invention, by utilizing the periodicity of electric discharge, the printing signal can be output while the printing signal is being output.
Halftone recording can be reliably performed by counting the time or the number of discharges, controlling the discharge current, or performing these simultaneously.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a nozzle portion of an inkjet head for explaining an embodiment of the present invention, FIGS. 2 to 4 are diagrams for explaining its operation, and FIG. 5 is an embodiment of the present invention. FIG. 6 is an explanatory diagram of the operation of FIG. 5, FIG. 7 is an overall configuration diagram of another embodiment, and FIGS. 8 and 9 are illustrations of the operation of FIG. 7. 10 is a circuit diagram for explaining another embodiment, and FIGS. 11 and 12 are
FIG. 10 is an explanatory diagram of the operation shown in FIG. 10; 3... Injection opening, 4... First electrode, 5... Second electrode, 6... Drive circuit, 8... Bubbles. Figure f]-1 ■ Figure ■ Figure ■ Atsushi

Claims (1)

[Claims] 1. A discharge port for discharging liquid, a liquid chamber communicating with the discharge port, a pair of electrodes provided within the liquid chamber, and bubbles caused by electrolysis in the liquid in the liquid chamber between the pair of electrodes. An inkjet comprising: a voltage applying means for applying a voltage so as to change the volume of the bubbles due to the discharge after generating the bubbles; and a voltage control means for controlling the change in the volume of the bubbles due to the discharge. Recording device.