JPS6229232B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive device for a print head for a drop-on-demand type inkjet recording device.

Recently, a drop-on-demand type inkjet recording device has been developed that ejects ink droplets only when necessary. Such inkjet recording devices can be roughly divided into two types: one is a type that pulls ink using electrostatic attraction, and the other is a type that ejects ink using pressure waves from a piezoelectric element. Regarding equipment.

Generally, in a print head for an inkjet recording device using a piezoelectric element, an ink chamber is provided between an ink outlet path leading to an orifice serving as an ink jetting port and an ink supply path leading to an ink tank. A piezoelectric element is provided in the chamber, and ink droplets are ejected from an orifice by applying an electrical signal to the piezoelectric element to change the volume of the ink chamber. There is a phenomenon in which the liquid surface (hereinafter referred to as meniscus) vibration of the ink droplet in the orifice has two resonance frequencies.
Among these, the lower resonant frequency is as described below.
This adversely affects the ink particle velocity, the entry of bubbles into the orifice, residual vibration, etc., and thus reduces the ink ejection efficiency.

However, conventionally, the frequency band of the electric signal applied to the piezoelectric element is wide and includes the above-mentioned low resonance frequency, so there has been a problem that the ink ejection efficiency is low.

An object of the present invention is to improve the ejection efficiency of ink based on the concept of removing in advance low frequency components including the low resonance frequency of the meniscus from the electric signal applied to the piezoelectric element, and to solve the above-mentioned problems. It is in.

The present invention will be explained below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a print head for a typical inkjet recording device. In Figure 1,
1 is an orifice serving as an ink ejection port; 4 is an ink chamber provided between an ink guide path 2 leading to the orifice 1; and an ink supply path 3 leading to an ink tank (not shown); 5 is a volume of the ink chamber 4; It is a piezoelectric element for changing the By applying an electrical signal, such as a rectangular wave signal, to the terminal 6 of the piezoelectric element 5, the volume of the ink chamber 4 is changed, thereby causing an ink droplet to be ejected from the orifice 1.
Such meniscus vibration on the orifice 1 largely depends on the frequency component of the applied electric signal.

FIG. 2 is a graph showing the frequency characteristics of a general meniscus displacement level. As shown in FIG. 2, there are two resonant frequencies f _p1 and f _p2 . Of these, the resonance frequency f _p1 depends on the ink supply path 3 shown in FIG. 1, and the resonance frequency f _p2 depends on the orifice 1 and the ink conduction path 2 shown in FIG.

FIG. 3 is a graph showing a conventional change in meniscus displacement over time, and shows the case where an electrical signal with a rapid impulse waveform is applied to the piezoelectric element 5 of FIG. 1. In FIG. 3, when the meniscus displacement is +, it indicates that the liquid level of the orifice 1 is protruding, and conversely, when the meniscus displacement is -, it indicates that the liquid level of the orifice 1 is depressed. Further, curve A shows the damped vibration due to the resonance frequency f _p1 , curve B shows the damped vibration due to the resonance frequency f _p2 , and curve C shows the damped vibration of the actual meniscus displacement obtained by combining these two damped vibrations. show. In other words, the damped vibration due to the resonance frequency f _p1 (curve A) increases the maximum displacement on the + side of the damped vibration at the resonance frequency f _p2 by l ₁
The maximum displacement on the negative side, −l _{3 ,} is increased to −l ₄ . Incidentally, the formation of ink particles occurs when the initially ejected amount is separated by moving straight due to inertial force, and therefore depends on the maximum displacement l ₂ on the + side of the curve C. The vibrations at the resonant frequency f _p1 tend to reduce the maximum displacement l ₂ , and therefore the vibrations at the resonant frequency f _p1 reduce the ink jetting efficiency. In order to capture this, it is necessary to increase the driving voltage, but this also increases the maximum displacement on the negative side of curve C.
l ₄ increases, leading to air bubbles entering the orifice 1 (FIG. 1). Further, it is preferable to reduce residual vibration after particle formation. As shown in FIG. 3, the damping of vibrations due to the resonance frequency f _p2 (curve B) is fast, but the damping of vibrations due to the resonance frequency f _p1 (curve A) is slow. That is, the residual vibration is large. As described above, the vibration at the resonance frequency f _p1 causes a decrease in the ink particle velocity, a high possibility of bubble expansion into the orifice, a large residual vibration, etc., and therefore reduces the ink ejection efficiency. In the present invention,
In order to prevent vibrations at the resonant frequency f _p1 from occurring in the meniscus displacement, low frequencies including the resonant frequency f _p1 component are removed from the electric signal applied to the piezoelectric element 5 (FIG. 1) in advance.

FIG. 4 is a block circuit diagram of a circuit that generates an electric signal applied to the piezoelectric element 5 of FIG. 1 as an embodiment of the present invention, and FIG. 5a, FIG. 5b, and FIG. 6a and FIG. 6b is a waveform diagram and frequency spectrum diagram of signals "a" and "b" appearing in the circuit of FIG. 4. In FIG. 2, the input signal "a" has its low frequency removed by a low frequency removal filter 41 (high frequency filter), and is then passed through an amplifier 4.
The signal "b" obtained by amplification by 2 is applied to the terminal 6 of the piezoelectric element 5. In this case, the cutoff frequency of the low-pass removal filter 41 is set between the two resonant frequencies f _p1 and f _p2 of the meniscus mentioned above. For example, an impulse signal "a" of pulse width T shown in FIG. 5a (the frequency spectrum of this signal is shown in FIG.
1 and amplifier 42, the signal "b" shown in FIG. 5b (the frequency spectrum of this signal is shown in FIG. 6b) is obtained.

According to experiments, the resonant frequencies f _p1 and f _p2 of the print head shown in Fig. 1 are 2 kHz and 7.5 kHz, respectively. Therefore, the low frequency removal filter 41 shown in Fig. 4 has a cutoff frequency f _c of 3 kHz. A high-pass active filter was used. As a result, as shown by curve C' in FIG. 7 (curve C is based on the conventional type), the maximum displacement of the meniscus on the + side becomes l ₂ ', which increases the ink particle velocity. In this case, the speed was approximately 4.5 m/s (compared to approximately 3 m/s in the past). Further, the maximum displacement on one side of the meniscus is reduced to -l ₄ ', so that it is possible to prevent air bubbles from entering the orifice 1 (FIG. 1). Furthermore,
As can be seen, compared to the conventional curve C, the damping of the curve C' according to the present invention is faster, that is, there are fewer residual vibrations.

As explained above, according to the present invention, compared to the conventional type, the maximum displacement on the + side of the meniscus can be increased, and therefore the ink particle velocity can be increased.
The maximum displacement on one side can be made small, so it is possible to prevent bubbles from entering the orifice, and it is also possible to reduce the residual vibration of the meniscus. Therefore, the ink ejection efficiency can be improved,
This is useful for solving the problems in the conventional type described above.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a print head for a general inkjet recording device, Fig. 2 is a graph showing the frequency characteristics of a general meniscus displacement level, and Fig. 3 is a graph showing the frequency characteristics of a general meniscus displacement level.
FIG. 4 is a block circuit diagram of a circuit that generates an electric signal applied to the piezoelectric element of FIG. 1 as an embodiment of the present invention. FIG. a, FIG. 5b, FIG. 6a, and FIG. 6b are waveform diagrams and frequency spectrum diagrams of signals "a" and "b" appearing in the circuit of FIG. 4, and FIG. 7 is a diagram according to the present invention. It is a graph showing the temporal characteristics of meniscus displacement. 1... Orifice, 2... Ink outlet path, 3...
... Ink supply path, 4 ... Ink chamber, 5 ... Piezoelectric element, 6 ... Terminal, 41 ... Low frequency removal filter, 4
2...Amplifier.

Claims (1)

[Claims] 1 an orifice for ejecting ink droplets;
The ink chamber includes an ink chamber having one end connected to the orifice and the other end connected to the ink supply port, and a piezoelectric element provided in a part of the ink chamber. In a print head for an inkjet recording device in which the ink droplets are ejected from the orifice by changing the volume of the ink chamber, the electrical signal has at least a resonance frequency component f _p1 that depends on the ink supply port side member of the ink chamber. A print for an inkjet recording device, characterized in that the inkjet recording device is applied to the piezoelectric element through a filter that removes and at least passes a resonance frequency component f _p2 (f _p2 > f ₁₀ ) that depends on the orifice side member of the ink chamber. Head drive device.