JPH0465245A - Driving method of ink-jet head - Google Patents

Abstract

PURPOSE:To drive a print head so as to print at a high speed with less influence of changes in the ambient conditions by a method wherein the driving frequency is set at one-third of the natural frequency of the print head so as to perform simple controls at a low cost. CONSTITUTION:Although the liquid surface 12 of ink 11 vibrates and is damped according to the natural frequency (f0) of a print head, the attenuation of the vibration varies depending upon the temperature. Therefore, when the succeeding driving takes place too early after a piezoelectric element 10 has been driven, the vibration to spout ink becomes extremely unstable. On the other hand, when the succeeding driving is delayed more than required for the vibration due to the previous driving to be damped enough, printing at a high speed can not be achieved. In this method, the driving frequency (f) is set at around one-third of the natural frequency f0 of the head. When the driving frequency is set at one-third of the resonance frequency, the driving frequency without an reduction in the frequency characteristic becomes the most efficient value only by correcting the driving voltage or the width of driving pulse corresponding to changes in the viscosity even when the ambient temperature changes in a range of 5-40 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving an inkjet head used in an inkjet printer that performs recording by ejecting ink particles.

Inkjet printers are expected to be used as OA printers in offices because they are quiet, can record high-quality prints on plain paper, and can easily print in color.

3. Detailed Description of the Invention [Summary] This invention relates to a method of driving an inkjet head used in an inkjet printer that performs recording by ejecting ink particles.

The purpose is to provide a method that is stable against changes in environmental temperature and can achieve high-speed printing.

[Conventional technology]

FIG. 3 shows an example of a conventional inkjet head.

What are the heads used in inkjet printers?

There are various types, 8 for example as shown in Figure 3.

The structure is such that pressure can be applied by a piezoelectric element 10 to a pressure chamber into which ink 11 enters.

When a voltage is applied to the piezoelectric element 10 by the piezoelectric element drive circuit 31, the piezoelectric element 10 is distorted, thereby exerting pressure on the wall surface of the pressure chamber to which the piezoelectric element IO is attached, and thereby an ink droplet 30 is ejected from the nozzle. be done.

The head vibrates when the piezoelectric element 10 is driven, and its natural vibration frequency is physically determined by the material and structure of the head.

The magnitude of this vibration largely depends on the viscosity of the ink 11 contained in the pressure chamber.

FIG. 4 shows an example of the temperature dependence of ink.

The viscosity of the ink depends on the temperature, for example, as shown in FIG. 4. The lower the temperature, the higher the viscosity, and the higher the temperature, the lower the viscosity. As described above, ink viscosity increases (changes) depending on temperature, so even if a head whose viscosity is adjusted to its optimal viscosity at room temperature is used, the characteristics will change if the environmental temperature changes.

For this reason, conventional methods have been used to compensate for the temperature, such as installing a heater or changing the driving conditions according to the temperature.

[Problem to be solved by the invention]

However, the method of attaching a heater to keep the temperature constant is expensive, and the method of controlling the driving conditions according to the temperature makes it difficult to select conditions that match one frequency characteristic. The problem was that it also became complicated.

The present invention aims to solve the above-mentioned problems and provides a method that is stable against changes in environmental temperature and can realize high-speed printing.

[Means to solve the problem] FIG. 1 is a diagram illustrating a driving method according to the present invention.

For example, a driving pulse as shown in FIG. 1(B) is applied to the piezoelectric element 10 of an inkjet head as shown in FIG. 1(A). Ink 1 from the nozzle tip
The distance Hx to the liquid level (meniscus) 12 of 1 is shown in Figure 1 (
It vibrates as shown in c).

In FIG. 1(c), the solid line shows the change in the liquid level 12 when the ink viscosity is low at a high temperature.The five-dot line shows the change when the ink viscosity is high at a low temperature.

As shown in FIG. 1, the ink level 12 vibrates and is damped according to the natural vibration frequency f0 of the head.

The damping of this vibration varies depending on the temperature.

Therefore, if the timing between driving the piezoelectric elements 1 and 0 and performing the 5th drive is too early, the variation in ink viscosity due to temperature will increase (it will be affected), and the vibration for jetting the ink will increase. becomes extremely unstable.On the other hand,
If the primary drive timing is delayed more than necessary until the vibrations caused by the first drive are sufficiently attenuated, high-speed printing will not be possible.

In the present invention, the drive frequency f is set to around 1/3 of the natural vibration frequency f of the head. That is, the drive period T of the piezoelectric element 10 is 3/f.

shall be.

The natural vibration frequency f of the head can be determined by conducting a driving test on the print head actually used and observing its resonance point. Its natural vibration frequency f0
From this, the drive frequency f is determined and the clock pulses applied to the piezoelectric element drive circuit etc. are set or adjusted to match the drive frequency f.

[Effect]

In the present invention, by setting the driving frequency f to 1/3 of the print head's natural frequency f0, even if the environmental temperature in which the inkjet printer is used changes, temperature compensation is only performed on the particle velocity, resulting in high print quality. You will gain dignity.

〔Example〕

As shown in Figure 4, the viscosity of ink changes depending on the temperature.9For example, an ink with a viscosity of 2.5 cp at room temperature is
At 5°C, it is approximately 5CP, and at 40°C, it is 1.5cp.

Frequency characteristics of print heads using such ink,
That is, the change in particle velocity with respect to temperature.

It is as shown in Figure 2. In addition, Fig. 2 (a) shows when the temperature is 25°C, and Fig. 2 (b) shows when the temperature is 40°C.
Figure 2 (c) shows the change in particle velocity when the temperature is 5''C, and these changes are caused by changing the pressure with respect to the change in ink viscosity due to temperature. This shows the frequency characteristics when the particle velocity ■ is constant.

Here, fo represents the open vibration frequency determined by the physical conditions of the head shape and material. 2 Particle velocity ■. The speed is extremely high because it resonates with the drive frequency of the head.

Normally, in order to perform good printing, the speed must be varied by about ±20% with respect to the two-particle speed v0. However, if the driving frequency is set to the maximum at room temperature, the speed fluctuation will exceed ±20% when the second temperature reaches 40°C, and the stability of single particle formation will be lost. Also, 5°C
As the viscosity increases, the speed decreases from low frequencies, and in this case as well, the stability of particle formation becomes unstable and the position of the printed dots is misaligned, resulting in a decrease in printing quality.

From the above points, even if the temperature of the environment changes (5 to 40"C)
), the driving frequency that does not cause a drop in the three-frequency characteristics by only compensating only the driving voltage or driving pulse width for changes in viscosity becomes the most efficient value if set to 1/3 of the resonance frequency.

For example, in the example shown in FIG. 2, f0 is 8.2 kHz, and the driving frequency is set to 1/4 of 10.

However, stable printing can be performed at room temperature.

It becomes unstable at 5°C or 40'C. Further, when the driving frequency is set to 1/2 of fo, good printing can be performed up to 5 to 40°C, but the printing speed becomes slow. According to f2, whose driving frequency is set to 1/3 of fo, there is no problem of instability due to temperature as in the case of fI, and it can print faster than f, so it is suitable for temperatures between 5 and 40°C. This makes it possible to perform good printing at the highest frequency.

(Effects of the Invention) As described above, according to the present invention, it is possible to perform a drive that is stable against environmental changes and can print at high speed by simple control at low cost.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a driving method according to the present invention. FIG. 2 is a diagram showing the relationship between temperature and frequency characteristics for explaining an embodiment of the present invention. FIG. 3 is a diagram showing an example of a conventional inkjet head. FIG. 4 is a diagram showing an example of the temperature dependence of ink. In the figure, 10 is the piezoelectric element 711 is the ink, 12 is the liquid level, f
o represents the vibration frequency of the head, f represents the driving frequency, and d represents the driving period.

Claims (1)

[Claims] In a head driving method for an inkjet printer that performs recording by ejecting ink particles, the driving frequency of the inkjet head is set to approximately 1/3 of the natural vibration frequency of the head.
A method for driving an inkjet head, characterized in that it is used as an inkjet head.