JPS5820461A - Ink jet printer - Google Patents

Abstract

PURPOSE:To achieve early stabilization of an ink jet head with forced discharge of bubble therein by setting the excitation frequency thereof to the value at the resonance frequency thereof for a specified time from the starting of the ink drop injection. CONSTITUTION:With the power source ON, a vibrator 2 of an ink jet head is vibrated with a working frequency f0 applied from an excitation driving circuit 3 and jets an ink pillar which is cut to a specified length lb to become ink drops. For a specific time t1 from the turning on of the power source, the excitation of the vibrator 2 is carried out with the resonance frequency fr to strengthen the pressure wave working on the ink so that bubble in the head can be discharged forcibly as early as possible. This can eliminates instability of the length of the ink pillar due to the bubble and reduces the time required for reaching the prescribed length lb0 in cutting the ink pillar, thereby allowing earlier print starting time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in inkjet printers, and in particular, to exciting an inkjet head to eject ink droplets,
The inkjet printer that performs recording using ink droplets is provided with an excitation drive circuit that sets the excitation frequency for exciting the inkjet head to the resonant frequency of the inkjet head for a predetermined period of time at the start of ink droplet ejection. At the start of droplet ejection, air bubbles within the inkjet head are forcibly ejected to stabilize the head at an early stage.

In an inkjet head, early stabilization at the start of ink droplet ejection is an important issue, and a factor that particularly affects this stabilization is the inclusion of air bubbles in the head. These bubbles are caused by, for example, negative pressure caused by temporary residual pressure inside the inkjet head when a solenoid valve installed in the ink supply system that supplies ink to the inkjet head is shut off when jetting is stopped. This occurs when air is sucked into the inkjet head through the nozzle holes due to pressure, and this air remains in the head as bubbles. Such bubbles are ejected from the nozzle when the inkjet head is driven for a while, but while they remain in the inkjet head,
As is well known, the propagation of vibration from the diaphragm is attenuated by the bubbles, reducing the vibration propagation efficiency, or the bubbles stuck near the nozzle exit disturb the ejecting direction of ink droplets.

In general, these are collectively referred to as poor initial stability of the inkjet head, but in order to improve this initial stability, conventionally, (1) mechanical improvements such as the liquid chamber structure and nozzle structure of the inkjet head have been The structure makes it easy to remove air bubbles, 3)
Countermeasures such as timing the solenoid valve to shut off just when a liquid film forms on the nozzle surface to prevent air from being sucked in from the nozzle due to the liquid film have been proposed.

However, the method (1) has drawbacks such as difficult processing, 1 ton processing, and poor particleization efficiency of the head.
The method (2) had drawbacks such as the timing of liquid film formation being shifted due to external factors such as environmental conditions and impact, resulting in clumping.

The present invention was made in view of the above-mentioned circumstances, and
Air bubbles within the inkjet head are forcibly ejected, thereby achieving early stabilization of the inkjet head.

FIG. 1 is a schematic side sectional view of an inkjet head to which the present invention is applied, in which 1 is the main body of the inkjet spatula 1, 2 is a vibrator, 3 is an excitation drive circuit, 4 is an ink supply port,
5 is an ink column, 6 is an ink droplet, and as is well known, when the power is turned on, an ink supply process (not shown) is activated at the same time.
At the same time, the vibrator 2 of the inkjet head is also marked with a sine wave excitation signal of the operating frequency f0 as shown in FIG.・The ink is transmitted to the nozzle part through the infrastructure in the head, and a column of ink is ejected from the nozzle part,
This ink column is cut at a predetermined length 4b to form ink droplets. Therefore, in the above-mentioned lucky inkjet head, when air bubbles are present inside the head and near the nozzle part, the length of the ink column lb is not stabilized due to the air bubbles.
Printing is not possible.

The present invention has been made to solve the above-mentioned drawbacks, and during a predetermined time t1 when the power is turned on, the excitation of the vibrator 2 is adjusted to the resonance frequency of the inkjet head as shown in FIG. In this way, the vibrator 2 is operated at the resonant frequency of the inkjet head, thereby strengthening the pressure waves acting on the ink inside the head.

The air bubbles existing in the head are quickly discharged.

FIG. 4 is a characteristic diagram showing the time in the trench when the length of the ink column reaches the specified cutting length lbo, where curve A is the characteristic curve according to the prior art and curve B is the characteristic curve according to the present invention, as shown in the figure. Furthermore, according to the present invention, the time required for the length of the ink column to reach the prescribed cutting length lb can be shortened from t3 in the prior art to t2, and the printing start time can be shortened.

As is clear from the above description, according to the present invention, air bubbles in the inkjet head are forcibly ejected using a simple configuration, and the head is stabilized at an early stage, so that the head is ready for printing immediately after the power is turned on. be able to.

[Brief explanation of the drawing]

FIG. 1 is a sectional side view of the main part of an inkjet head to which the present invention is applied, FIG. 2 is a conventional excitation No. 48 waveform diagram, FIG. 3 is an excitation signal waveform diagram according to the present invention, and FIG. 4 is a diagram of the excitation signal waveform according to the present invention. , is a time characteristic diagram of when the ink column reaches the specified cutting length. 1. Inkjet head body, 2. Vibrator, 3.
...Excitation drive circuit, 4--ink supply port, 5--ink column, 6--ink droplet.

Claims (1)

[Claims] In an inkjet printer that excites an inkjet head to eject ink droplets and performs recording using the ink droplets, the excitation frequency for exciting the inkjet head is set to the resonant frequency of the inkjet head for a predetermined time at the start of ink droplet ejection. An inkjet printer characterized by being set to.