JPH0226588B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink droplet charging method for an ink jet recording apparatus, and more particularly to an ink droplet charging method for an ink jet recording apparatus capable of performing halftone recording.

Many types of inkjet recording devices have been known in the past. Among these, an ink-on-demand type inkjet recording device using an electroacoustic transducer has advantages such as a simple structure and no need to collect ink because all formed ink droplets are used for recording. Further, by changing the size of the ink droplet using an electric signal applied to the electroacoustic transducer, halftone recording can be performed.

2. Description of the Related Art Conventionally, an apparatus for performing halftone recording is known in which recording paper is wound around a drum and the drum is rotated to perform scanning. However, in such an apparatus, since it is necessary to wind the recording paper around a drum, etc., it is desirable to use a method of scanning by deflecting ink droplets, which facilitates handling of the recording paper.

However, the conventional method for deflecting ink droplets is called the charge-controlled inkjet method, in which droplets of a fixed size are continuously ejected from a nozzle at a fixed cycle, and the droplets are charged in proportion to the amount of deflection. It is known to obtain a desired deflection by bending the ink droplet with a deflection electrode, but this deflection method has the problem that the amount of deflection changes when the size of the ink droplet changes.

Furthermore, in such an ink-on-demand type inkjet device, in order to increase the dynamic range of intermediate tones, by varying the size of ink droplets over a wide range, the viscous resistance received from the air while flying through the air is reduced. Differences occur depending on the size of the droplets, and as the droplets become smaller, the flying speed rapidly slows down, resulting in the disadvantage that the positions at which the ink droplets are struck onto the recording paper become irregular. Furthermore, since the initial velocity of the ink droplets ejected from the nozzle is slower than in other methods, the position of the ink droplets hitting the recording paper tends to be disturbed, making it difficult to increase the distance between the recording paper and the nozzle or increase the recording speed. The problem was that it was difficult.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an ink droplet charging method for an inkjet recording apparatus that can perform halftone recording by changing the size of ink droplets while deflecting the ink droplets.

Another object of the present invention is to provide an ink droplet charging method for an inkjet recording apparatus that can perform halftone recording with less disturbance of the ink droplet placement position on a recording medium by accelerating the ink droplet using an accelerating electric field.

According to the present invention, ink droplets with controlled weights are formed one after another according to an ink droplet formation signal, and each ink droplet is given a predetermined charge by applying a voltage to a charging electrode. In an ink droplet charging method for an inkjet recording device in which recording is performed by injecting an ink droplet into a desired position on a recording medium, the voltage applied to the charging electrode is controlled so as to vary in proportion to the weight of each ink droplet. An ink droplet charging method for an inkjet recording device characterized by the following is obtained.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram for explaining a first embodiment of an inkjet recording apparatus using the ink droplet charging method according to the present invention. The device includes a signal source 8 that outputs an image signal specifying the weight of an ink drop.
, a piezo drive circuit 6 that receives an image signal from this signal source 8 and outputs an electric signal for driving the ink jet head, and an ink jet head that can control the size of ink droplets formed by this electric signal. 1, a charging electrode 5 disposed on the front surface of the nozzle 3, and a charging voltage control means 7 for receiving a signal from the signal source 8 and applying a voltage to the charging electrode 5 that changes depending on the weight of the ink droplet. , an accelerating electrode 9 to which a constant voltage is applied from a power source 10 to accelerate ink droplets, and a recording medium 11 such as paper. The ink jet head 1 shown here includes a nozzle 3 filled with conductive ink supplied from an ink supply system (not shown), and an ink chamber 4.
and a piezo vibrator 2 as an electroacoustic transducer, and is known as an example of an ink-on-demand type. When a voltage panel is applied to the piezoelectric vibrator as an electric signal when forming an ink droplet, the piezoelectric vibrator generates stress in response to the voltage, increases the pressure in the ink chamber, and pushes out ink from the nozzle 3. At this time, the size of the ink droplet formed can be controlled by the amplitude and pulse width of the pulse signal.
Further, in this case, the combination of the amplitude and pulse width of the pulse signal is selected so that the flying speed does not change even if the size of the ink droplet changes. Based on the weight designation information of the image signal, a pulse signal for ejecting an ink droplet of a corresponding weight is selected from this combination and outputted from the piezo drive circuit 6.
The method of charging ink droplets in this device will be explained. First, an image signal specifying the weight of the ink droplet is given to the piezo drive circuit 6 as concentration information from the signal source 8, and as a result, an ink droplet whose size is controlled according to the image signal is ejected from the inkjet head 1. . On the other hand, this image signal is also given to the charging voltage control means 7 at the same time. The charging voltage control means 7 outputs a voltage having a value proportional to the weight of each ink droplet formed, and is applied to the charging electrode 5. Then, the ink droplet ejected from the nozzle is charged by the charging electrode 5 so that q/m becomes constant. Thereafter, it is accelerated by an accelerating electric field between the charging electrode 5 and the accelerating electrode 9. At this time, if the ink droplet charging method shown here is used, even if the weight of the ink droplets differs, the acceleration received by the accelerating electric field will be constant, and all will be accelerated equally. The accelerated ink droplets are ejected onto a recording medium 11 such as paper to perform recording. However, the value of the ratio q/m may have a range within a range that allows variation in speed. Furthermore, the resistance that an ink droplet receives from the air varies depending on its size, and the influence of this air resistance can be large. At this time, by making the force received from the accelerating electric field sufficiently larger than the air resistance, it is possible to prevent velocity unevenness from occurring even if the diameter of the ink droplet changes. Further, even if there is a fluctuation in the initial velocity of the ink droplets, the fluctuation is reduced because the speed is uniformly increased. By using the ink droplet charging method of the present invention as described above,
It becomes possible to uniformly speed up ink droplets having different sizes, and an inkjet recording apparatus capable of performing high-quality recording with little displacement of ink droplets ejected onto a recording medium can be obtained.

Here, the charging voltage control means 7 in this embodiment
For example, there is one that uses digital memory. A digital signal is used as the image signal from the signal source 8, and the address of the digital memory is specified using this signal. Information specifying the voltage value to be applied to the charging electrode is stored as the stored content at that address, and this is read out and used.
As another example, the amplitude of the voltage applied to the charging electrode may be modulated linearly with respect to the weight of the ink droplet based on a signal specifying the weight of the ink droplet.

Next, as a second embodiment, FIG. 2 shows a case where the amount of deflection of an ink droplet is controlled by changing the deflection electric field strength of a deflection electrode. Formation and charging of ink droplets in this embodiment are performed in the same manner as in the first embodiment shown in FIG. In other words, a combination of the amplitude and pulse width of the pulse signal of the on-demand ink jet head is selected so that the flying speed of the ink droplet remains constant even when the droplet volume changes, and this combination is selected based on the weight specification information of the image signal. A pulse signal is selected and driven to eject a droplet of the corresponding weight. Further, the ink droplet is charged in accordance with a signal specifying the weight of the ink droplet from the signal source 8 so that the ratio between the weight of the ink droplet and the amount of charge becomes a constant value. At this time, a change in the value of this ratio results in a change in the amount of deflection, but the ink droplet 12
There is no particular problem even if the value of this ratio fluctuates somewhat as long as the deviation in the position of the implant is not a problem in practice. Ink droplets charged so that the ratio of the weight of the ink droplet to the amount of charge becomes constant are deflected equally by the deflection electrode 14 regardless of the weight of the ink droplet. At this time, by controlling the voltage value applied to the deflection electrode by the deflection amount specifying means 16, the ink droplet can be deflected by the necessary amount.

This embodiment provides an inkjet recording device in which the amount of deflection does not change even if the size of the ink droplets is changed.

Further, in this embodiment, the amplitude and pulse width of the signal given by the piezo drive circuit 6 are adjusted so that the initial velocity of the ink droplets ejected from the nozzle 3 is as constant as possible.

In the above description of the embodiments of the present invention, the formation of ink droplets has been explained using an inkjet head as shown in FIGS. The charging method is not limited to the ink jet head shown here, but can be applied to various types of ink jet heads.

[Brief explanation of drawings]

FIGS. 1 and 2 show the first inkjet recording apparatus using the ink droplet charging method according to the present invention.
FIG. 3 is a schematic diagram for explaining a second embodiment. In the figure, 1 is an inkjet head;
2 is a piezo vibrator, 3 is a nozzle, 4 is an ink chamber,
5 and 13 are charging electrodes, 6 is a piezo drive circuit,
7 is a charging voltage control means, 8 is a signal source, 9 is an accelerating electrode, 10 is a power source, 11 is a recording medium, 12 is an ink droplet, 14 is a deflection electrode, 15 is a deflection voltage generation means, and 16 is a deflection amount specifying means shows.

Claims (1)

[Claims] 1 Apply a voltage pulse as an electric signal to the piezo vibrator according to the ink droplet formation signal to form ink droplets with controlled weight one after another, and apply a voltage to the charging electrode to make each ink droplet have a predetermined shape. In the ink droplet charging method for ink jet head recording devices, which applies a charge and accelerates the charged ink droplets using an electric field, a constant flying speed is determined by an image signal containing information specifying the weight of the ink droplets to be output at predetermined time intervals. and selects a formation signal for ejecting an ink droplet corresponding to the information specifying the weight to form an ink droplet with controlled weight, and at the same time selects a voltage proportional to the weight of the ink droplet to be ejected based on the image signal. A method for charging an ink droplet in an inkjet recording apparatus, characterized in that a voltage is applied to the charging electrode for the predetermined time interval.