JPH03164258A - Driving of ink jet recorder - Google Patents

Abstract

PURPOSE:To obtain a uniform jet characteristic by preventing viscosity at a tip part of a nozzle from rising by a method wherein a piezoelectric element is driven by micro-vibration to an extent to wet appropriately the tip part of the nozzle in non-printing. CONSTITUTION:A transistor 9 is always driven at a constant period irrespective of presence of a printing command, and a piezoelectric element 4-1 always repeats micro-vibration. When the printing command of a nozzle to be recorded is given to a transistor 5-1, the piezoelectric element is driven with a resistance 3-1, and jetting of ink is performed. Since micro-vibration is performed commonly to all nozzles, both the transistor 5-1 and the transistor 9 are turned ON. However, since impedance of the transistor 5-1 is extremely small compared with that of the transistor 9 and a resistance 8-1, there is no influence on the jet characteristic. Therefore, when a printing command is applied, jetting of an ink drop is ordinarily performed. When no printing command is applied, micro-vibration is performed, and the ink is supplied to a tip of the nozzle to prevent viscosity of the ink at tip of the nozzle from rising.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for driving an inkjet recording device that performs recording by ejecting ink droplets. An on-demand type inkjet recording apparatus performs recording by selectively driving piezoelectric elements corresponding to each nozzle using a switching element according to a printing pattern of characters or figures to be recorded, and ejecting ink droplets onto a recording medium. Therefore, the frequency of use of each nozzle varies depending on the printing pattern, and some piezoelectric elements may continue to be driven at the highest response frequency, while others may not be driven for a long time. If the non-ejecting state continues for a long time, the viscosity of the ink at the tip of the nozzle changes, causing disturbances in printing during the next ejection. In other words, low-viscosity ink is attached to the tip of a nozzle that has been ejecting ink droplets frequently, and high-viscosity ink is attached to the tip of a nozzle that has stopped ejecting ink for a long time. Another problem is that the wetting state of the nozzle tip differs depending on the driving history of each nozzle, which affects the flight direction and flight speed of the ink droplets during the next jetting, making it impossible to maintain uniform jetting characteristics.

[Problem that the invention seeks to solve]

The present invention eliminates such drawbacks and maintains the ink viscosity at the tip of the nozzle constant in any printing pattern, thereby achieving uniform ink droplet ejection.

[Means for solving problems]

The driving method of the inkjet recording apparatus of the present invention is an on-demand type inkjet that has a plurality of nozzles and performs recording by ejecting ink droplets from the nozzles by applying a driving pulse to a piezoelectric element provided on a part of the wall of an ink chamber. In a recording device, a piezoelectric element is constantly driven at a constant cycle with a voltage that is large enough to prevent ink droplets from being ejected from a nozzle, and the applied voltage is increased only when recording is to be performed to eject ink droplets. It is characterized by That is, during non-printing, the piezoelectric element is driven by minute vibrations that adequately wet the nozzle tip, thereby preventing an increase in viscosity at the nozzle tip and achieving uniform jetting characteristics.

[Effect]

According to the present invention, ink with low viscosity is always supplied to the tip of the nozzle regardless of the driving history of each nozzle.
Ink jetting characteristics are maintained uniformly under any conditions, and uniform printing quality can be obtained.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to embodiments shown in the drawings.

First, the operating principle of the inkjet recording head will be explained.

FIG. 2 is an example of an inkjet recording head that performs recording by applying a drive pulse to a piezoelectric element provided on a wall of a portion of an ink chamber to eject ink droplets from a nozzle. In FIG. 2, 15 is an ink tank, 12 is a pressurizing chamber communicating with the ink tank, 4 is a piezoelectric element, 14 is a diaphragm, 13 is a nozzle, and FIG. 3 is a drive circuit for the ink jet recording head. In Figure 3, resistance 2 (R.) and resistance 3
(R..) and resistance 1 (R.) is the relationship between R. 《Rb＜
(R. What's going on? Figure 4 is a drive timing chart and drive voltage waveform of the inkjet recording head. The operation of the inkjet recording head will be explained with reference to Figures 2, 3, and 4. Before time t in the figure, transistor 7, transistor 6, and transistor 5 are in an off state, and piezoelectric element 4 is charged to approximately voltage VH by resistor 1 and resistor 2. This state is a standby state. When the signal shown in FIG. 4(a) is applied to the terminal a of the transistor 1+ to turn on the transistor 5, the charge in the piezoelectric element 4 is discharged through the resistor 3, and the piezoelectric element 4 gradually bends outward. At the predetermined time T+elapsed dredging time t2, the transistor 5 is turned off and at the same time, as shown in FIG.
By applying the signal b) to the terminal b and turning on the transistor 7, the transistor 6 turns on, the piezoelectric element 4 is rapidly charged, the volume of the pressurizing chamber 12 decreases, and ink droplets are ejected from the nozzle 13. Ru. FIG. 4(C) shows the drive voltage waveform. The falling curve in FIG.
, ), and the rising curve is determined by the capacitance of the piezoelectric element 4, the resistor 2, and the energization time (T2) of the transistor 6, and these determine the actual drive voltage of the piezoelectric element (Fig. 4 (C) ) is determined, and is set so as to obtain the optimum injection characteristics.

FIG. 5 is an example of a multi-nozzle on-demand type inkjet recording apparatus that is equipped with a plurality of the above-mentioned inkjet recording heads and performs recording in a dot matrix by ejecting ink droplets as appropriate according to the print pattern. The figure shows a conventional example of the drive circuit. Figure 6 is the third
This is a multi-nozzle version of the drive circuit shown in the figure, and discharge circuits corresponding to the number of nozzles are configured. However, the charging circuit is common to all nozzles, and only diodes 10-1 to 10-n corresponding to the number of nozzles are added. Terminals a1 to a. in FIG. When a print command is applied to the piezoelectric elements 4-4 to 4-n, the piezoelectric elements 4-4 to 4-n are selectively driven and ink droplets are ejected.

An embodiment of the present invention will be described below. The structure of the inkjet recording head used in the present invention is no different from the conventional one, with only the method of driving the piezoelectric element being improved.

Therefore, the operation regarding ink ejection is exactly the same as described above.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. Resistors 8-1 to 8-n and a transistor 9 are added to the conventional example shown in FIG. Resistors 8-1 (Rd) to 8-n set the drive voltage waveforms of piezoelectric elements 4-1 to 4-n, and R. ((R
The relationship is d. Here, driving of the piezoelectric element 4-1 will be explained. The piezoelectric elements 4-2 to 4-n are driven in exactly the same manner. Terminal a. of the circuit of FIG. Figure 7 (a)
) FIG. 7(c) shows the drive voltage waveform when the signal shown in the timing chart of (b) is applied. When the transistor 5-1 is turned on and driven by discharge through the resistor 3-1 (R.), the voltage applied to the piezoelectric element 4-1 becomes substantially large (as shown in Figure 7). ), the ejection of an ink drop takes place. In addition, terminal C is connected to Fig. 7(a) (
FIG. 7(d) shows the drive voltage waveform when the signal shown in the timing chart b) is applied. transistor 9
In the cantering due to discharge through the resistors 3-1 and 8-1, which turn on the voltage applied to the piezoelectric element 4-1, the voltage applied to the piezoelectric element 4-1 becomes substantially smaller (as shown in FIG. 7 v2). 4
-1 pressure is restricted and ink droplets are not ejected, resulting in minute vibrations. Here, if the resistor 8-1 is set appropriately, it is possible to supply ink to the extent that the nozzle tip is appropriately wetted by this minute vibration. In other words, by constantly driving the nozzle in the non-ejecting state by the resistor 8-1, ink with low viscosity is supplied, and it is possible to prevent disturbances in printing due to an increase in ink viscosity at the tip of the nozzle.

Now, the operation in actual printing will be explained with reference to the timing chart and drive voltage waveform diagram of FIG. Figure 8 (C)
is a print command that is added to the nozzle to be recorded. 8(a), b), and (c) are the terminals C, b, and a of FIG. 1, respectively. is applied to The transistor 9 shown here is always driven at a constant cycle regardless of the presence or absence of a printing command, and the piezoelectric element 4-1 always reciprocates minute vibrations. (Here, the frequency of the microvibration is made to match the response frequency of the inkjet recording head.)
When a print command for the nozzle to be recorded is given to the transistor 5-1, the piezoelectric element is driven by the resistor 3-1 and ink is ejected. At this time, since the micro-vibration is common to all nozzles, both transistor 5-1 and transistor 9 are in the on state, but transistor 5-
Since the impedance of transistor 1 is extremely small compared to transistor 9 and resistor 8-1, there is no effect on the injection characteristics. Therefore, the driving voltage waveform of the piezoelectric element is as shown in Fig. 8(d), and when a printing command is applied, ink droplets are ejected normally, and when there is no printing command, minute vibrations are performed. Ink is flooded to the nozzle tip, preventing the viscosity of the ink at the nozzle tip from increasing. In addition, since microvibration can be performed at the same timing for all nozzles regardless of the presence or absence of a printing command, a common drive structure using one transistor is used to reduce the number of elements. If it is necessary to vary the printing timing depending on the nozzle, the same effect can be obtained by using a number of transistors corresponding to the printing timing system.

〔Effect of the invention〕

As described above, according to the present invention, minute vibrations of the piezoelectric element can be realized with a simple configuration of adding a resistor and a switching element, and this allows the nozzle tip to be always kept in a uniform state, resulting in stable ink droplet ejection characteristics. This makes it possible to provide an inkjet recording device with a high print quality.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a cross-sectional view showing an example of an arrangement of an inkjet recording head, FIG. 3 is a circuit diagram showing one driving method of an inkjet recording head, and FIG. The figure shows the drive timing and drive voltage waveform of the inkjet recording head, Figure 5 shows an example of a Hitotsubashi multi-nozzle on-demand inkjet recording device, and Figure 6 shows the multi-nozzle on-demand inkjet recording device. 7 is a diagram showing the drive timing and drive voltage waveform of an embodiment of the present invention, and FIG. 8 is a diagram showing the cantering timing and drive voltage waveform in the printing state of the same embodiment. Diagram showing. 1, 1-1, 1-2, 1-n...resistance element 2, 2-1
, 2-2, 2-n...resistance element 3, 3-1, 3-2,
3-n...Resistance element 4, 4-1, 4-2, 4-n...
・Piezoelectric elements 5, 5-1, 5-2, 5-n...Transistor 6...Transistor 7...Transistor 8, 8-1, 8-2, 8-n...Resistance element
9...Transistor 10, 10-1, 10-2,
10-n.-=Diode 11... Inkjet recording head 12... Pressure chamber 13, 13-1, 13
-n・Nozzle 14... Vibration plate 15... Ink chamber or above

Claims (1)

[Claims] In an on-demand inkjet recording device that performs recording by applying a drive pulse to a piezoelectric element having a plurality of nozzles and provided on a wall surface of a part of an ink chamber to eject ink droplets from the nozzle, the piezoelectric element is Inkjet recording characterized in that the nozzle is always driven at a constant cycle with a voltage of such a magnitude that no ink droplets are ejected from the nozzle, and the magnitude of the applied voltage is increased only when recording is to be performed to eject ink droplets. How to drive the device.