JPH02169255A - Liquid droplet generating device - Google Patents

Abstract

PURPOSE:To obtain a liquid droplet generating device capable of accelerating the speed of liquid droplets by providing a pressurizing chamber which applies pressure to a nozzle and liquid and an actuator which drives the pressurizing chamber, and allowing the actuator to resonate so that the drive frequency of the actuator varies with a frequency for liquid droplet generation and a preload is applied to the pressurizing chamber constantly. CONSTITUTION:If an oscillating plate 2 is oscillated by a conversion element 1 after selection of each different resonance point, the displacement of a connecting rod 3 becomes DELTAXb, DELTAXc. However, it is possible to change the displacement to DELTAXb>DELTAXc. Consequently, the preload mode is established in figure (c). In addition, when the phase changes from a preload to liquid protrusion, the oscillating plate generates a residual oscillation due to the effect of an oscillated frequency during preloading for a little time. If a loss is added to the displacement of residual oscillation during liquid protrusion at time for application of a pressure to the pressurizing chamber (points A, B, C), the residual oscillation is offset and the pressing force is increased, thus accelerating the liquid droplets.

Description

[Detailed description of the invention] "Fake" The present invention relates to droplet generators, and more particularly to droplet generators.

The present invention relates to a droplet generating device that converts the displacement of an actuator into pressure fluctuations of recording liquid to generate droplets, and is applicable to on-demand type inkjet recording heads.

1. As a prior art related to the present invention, Japanese Patent Publication No. 1989-8953
There is a publication. This uses a comb-shaped vibrating rod and brings its deformed portion close to the nozzle to increase vibration efficiency.

Further, FIG. 3 shows a conventional droplet generating device, and FIG. 4 shows the driving principle IA of the actuator, and 5(a) shows the case of non-oval movement (no droplet ejection and no preload).

(b) is a diagram showing driving.

In the figure, 1 is an electrical/mechanical conversion element, 2 is a shaking jj plate,
The electromechanical transducer 1 and the diaphragm 2 constitute seven cutuators. 3 is a pressurizing chamber, 4 is a connecting rod connecting the actuator and the pressurizing chamber, and 5 is a nozzle. The force and displacement transmitted to the connecting rod 4 are mainly determined by the rigidity and free length t of the transducer element and the diaphragm 2. In the case of continuous jetting, if the ejection frequency of the droplet is fo2, and the drive frequency of the actuator is fo, then fo=fo. be. Also, if the droplet does not protrude.

fo=0. In this way, conventional on-demand droplet generators have a pressurizing chamber for recording liquid connected to a nozzle.
The system consisted of an actuator that drove a pressurized chamber, and the actuator was driven at the timing when droplets were generated. However, in such cases, the electromechanical conversion cap (hereinafter referred to as conversion element) that constitutes the actuator only transmits the displacement and force generated by this conversion element to the diaphragm, and ultimately Speed is directly dependent on this displacement force. Therefore, if you want to increase the speed of droplets, the main methods are:

The aim was to improve the characteristics of the conversion element, but it was not an efficient method of increasing the size of the conversion element or increasing the applied voltage.

On the other hand, since the droplet speed directly affects print quality, especially in an inkjet recording apparatus, it is preferable that the droplet speed be faster.

L-Road The present invention was made in order to solve the drawbacks mentioned in -, and in the diaphragm and conversion element that constitute the actuator, the conversion element applies a driving frequency as t to the diaphragm. Basically, the resonance of the diaphragm itself causes pressure fluctuations in the pressure chamber, and when droplets are not generated, the vibration mode is changed to give a slight pre-pressure to the pressure chamber. An object of the present invention is to provide a droplet generating device configured to further increase the speed of droplets by exciting the original vibration mode again when a droplet is generated and synchronizing the timing with the residual vibration caused by preload. This was done as a.

In order to achieve the above object, the present invention provides a droplet generator for generating droplets from a nozzle, which includes a nozzle, a pressurizing chamber that pressurizes the liquid, and an actuator that drives the pressurizing chamber. , the gli dynamic frequency fo of the actuator is variable with respect to the droplet generation frequency fo, and when no droplet is generated;
Note fj is different from fo.

At this time, the actuator exhibits a deformation mode different from that during PI & droplet generation, and is characterized by utilizing the resonance of the actuator so as to constantly apply pre-pressure to the pressurizing chamber. Hereinafter, the present invention will be explained based on examples.

Figures 1 (a) to (c) are for explaining an embodiment of the droplet generation device according to the present invention, and Figures 2 (a) to (d) are diagrams showing the driving state of the actuator. , is a diagram of the principle of the phenomenon, and (a) is when the resonant frequency of the diaphragm is fl,
(b) is f2, (c) is fo, (d) is f
In Figure 0 showing case 4, 1 is an electromechanical conversion element, 2 is a diaphragm, and 4 is a connecting rod.

It is generally known that a structure has several resonance points and exhibits a unique deformation moat at each resonance point. Further, its magnitude (displacement) is proportional to the excitation force (in this case, the force generated by the conversion element 1). On the other hand, deformation at the resonance point can be excited even by a small force if the frequency of excitation is close to the resonance point.

Therefore, for example, when using the resonances fo (c) fo and fo (d) in Fig. 2, the displacement of one point P (positional relationship is the same) is f
It can be made larger on the 3 side and smaller on the f4 side. In other words, even if the excitation force is the same for fl and fo, the displacement at one point P can be varied by changing the excitation frequency.

Figure 1 (,) is non-driven (no droplet ejection, no preload), (b
) shows the state of drive (droplet ejection), and (c) shows the state of drive (preload). In figures (b) and (c), when different resonance points are selected and the diaphragm 2 is excited by the conversion element, , the displacement of the connecting rod 4 is Δ×b, Δ×c, but Δxb>ΔXc
Since it is possible to do so, the preload mode is shown in figure (Q).

Further, as shown in FIG. 5, when changing from preload to liquid protrusion, the diaphragm causes residual vibration for a short time due to the influence of the excitation frequency during preload. Therefore, if the displacement of this residual vibration is applied when the liquid protrudes at the timing of pressurizing the pressurizing chamber (points A, B, and C), the residual vibration becomes an offset.
The pressurizing force can be improved and the droplet speed can be further increased.

When applying the present invention to an actual machine, the frequency used for resonance of the diaphragm may be set higher than the highest printing frequency.

In this case, in order to simplify the explanation, the actuator is a cantilever beam, but an actuator as shown in FIG. 6 can also be used. (a) is a case where the beam is supported on both sides, and (b) is a case where the outer periphery is fixed.

As is clear from the explanation above, according to the present invention, since the co-installation of the diaphragm is utilized, a large deformation can be produced with a smaller excitation force than in the conventional method. Therefore, the volume change range of the pressurized chamber is large, and P& and corrosion speed can be improved.

Since preload is always applied and the excitation frequency is changed when necessary, the amount of preload acts as an offset, increasing the amount of volume change in the pressurizing chamber and improving the speed of droplets.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the driving state of an actuator for explaining one embodiment of the droplet generating device according to the present invention, and (a
) is a diagram showing non-DI (no droplet ejection/no preload), (b) is a diagram showing driving (droplet projection), and (c) is a diagram showing driving ('f-pressure) state. Figure 2 shows the phenomenon. 5 principle diagrams to explain
(a) is the resonance frequency of the diaphragm, in the case of fo, (b) in the case of f2, (C) in the case of fo, and (d) in the case of fo. The block diagram of the droplet generator and Figure 4 are diagrams of the principle of its actuator's movement, where (a) is a non-IGKlh (no droplets ejected and no preload), (b) is a diagram showing the driving state, and Figure 4 is a diagram showing the driving state. FIG. 5 is a diagram showing residual vibration of the diaphragm, and FIG. 6 is a diagram showing another embodiment of the actuator.
(a) is a diagram showing a case where the outer periphery is fixed with one beam supported on both sides. 1... Electrical/mechanical conversion element, 2... Vibration plate, 3... Pressure chamber, 4... Connecting rod, 5... Nozzle.

Claims (1)

[Claims] 1. A droplet generator that generates droplets from a nozzle, which includes a nozzle, a pressurizing chamber that pressurizes the liquid, and an actuator that drives the pressurizing chamber, and the drive frequency f_o of the actuator is the droplet generation frequency. It is variable with respect to f_j, and when a droplet is not generated, the above f_o is different from f_j, and at that time, the actuator exhibits a deformation mode different from that when a droplet is generated,
A droplet generating device characterized by utilizing resonance of an actuator so as to constantly apply pre-pressure to a pressurizing chamber.