JPH0226591B2 - - 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 according to the electric signal applied to the electroacoustic transducer, halftone recording can be performed. Conventionally, as a device for recording halftones, recording paper is wound around a drum.
There is a known device that performs scanning by rotating a drum. However, in such a device, it is necessary to wrap the recording paper around the drum, so it is desirable to use a method of scanning by deflecting the ink droplets as a method to simplify the handling of the recording paper. There is. However, the conventionally known electrical deflection method has a problem in that the amount of deflection changes when the size of the ink droplet changes.

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 the ink droplet while deflecting the ink droplet.

According to the present invention, an image signal having weight information output at predetermined time intervals causes an on-demand type ink jet head to eject ink droplets of a corresponding weight, and the ink droplets are directed toward the tip of the nozzle of the ink jet head. In the ink droplet charging method of an inkjet recording device, in which printing is performed by charging the ink droplets with arranged charging electrodes and deflecting the charged ink droplets with a deflection electrode with a constant charge, the weight of the ejected droplets is determined by the shape of the drive signal. Using an on-demand type ink jet head with a variable ink jet head, a drive waveform is selected in advance from among the drive waveforms that ejects droplets of a desired weight with a constant flying speed within the range of the ink droplet weight to be used. Then, from among the secured drive waveforms, a drive waveform corresponding to the weight information is selected to eject ink with controlled weight, and at the same time, a voltage proportional to the product of the weight information and the specified deflection amount is selected. Thus, there is obtained a method for charging ink droplets in an inkjet recording device, characterized in that an electric current is applied to the charging electrode during the predetermined time interval.

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. This device is an ink-on-demand type ink cartridge consisting of a nozzle 3 and an ink chamber 4 filled with conductive ink supplied from an ink supply system (not shown), and a piezo vibrator 2 as an electroacoustic transducer. It has a charging electrode 5 disposed in front of an ethead 1 and a nozzle 3, and a deflection electrode 10 to which a constant voltage is applied from a power source 11.

The formation of ink droplets is similar to that of the conventionally known ink-on-demand type inkjet recording apparatus. First, an image signal including density information is applied from the signal source 8 to the piezo drive circuit 6, and a pulse whose amplitude and pulse width are selected according to the density is applied to the piezo vibrator 2. Then, the piezo vibrator deforms according to this input pulse, and the ink chamber 4
The pressure is increased and ink droplets are ejected from the nozzle. At this time, the size of the ink droplet formed can be controlled by the amplitude and pulse width of the pulse signal.

On the other hand, the charging voltage control means 7 is supplied with an image signal from a signal source 8 and a deflection amount designation signal from the deflection amount designation means. The charging voltage control means 7 generates a voltage controlled to vary in proportion to the product of the weight of the ink droplet and the amount of deflection specified by each signal, and applies it to the charging electrode 5.

As a result, the charge amount of the charged ink droplet is q,
If the weight is m, q/m is a value proportional to the specified deflection amount. By controlling the amount of charge on the ink droplets in this way, the accelerations that ink droplets of different weights receive at the deflection electrode 10, that is, qE/m, where E is the deflection electric field strength, become equal, and the ink droplets of different weights The amount of deflection can be made the same for both.

It goes without saying that the above-mentioned relationship between the charging voltage, the weight of the ink droplet, and the amount of deflection is not required to hold strictly. That is, the charging voltage may be varied within a practical range that allows variation in the amount of deflection.

When the deflection amount specified by the signal from the deflection amount specifying means 9 changes, the voltage applied to the charging voltage 5 changes, and as a result, q/m becomes a value proportional to the newly specified deflection amount. . As described above, the ink droplet ejected from the nozzle is controlled in size and charge amount by the image signal and the signal specifying the amount of deflection, and is deflected at the deflection electrode 10 to which a constant voltage is applied, to the specified position on the recording medium 12. Driven. This provides an inkjet recording device capable of performing halftone recording using deflection of ink droplets.

Next, some embodiments of means for controlling the amount of charge on ink droplets will be shown. What is shown in Figure 2 is
First, the density information of the image signal is converted into a digital signal specifying the size of the ink droplet to be formed by an analog/digital converter or the like. Such a digital signal is output from the signal source 13. When this signal is input to the pulse width designation circuit 19, a pulse having a pulse width corresponding to the density information is output. The voltage is then amplified by an amplifier 20 to a voltage necessary to drive a piezoelectric vibrator, and its output 21 is applied to the piezoelectric vibrator to control the size of the ink droplet. Here, instead of the pulse width designation circuit 19, it is also possible to use a pulse amplitude designation circuit that outputs a pulse whose amplitude changes depending on the concentration information.

These are selected depending on the characteristics of the ink jet head, and it is desirable that there be less variation in the speed of the output ink droplets. Furthermore, by changing both the pulse width and pulse amplitude, it is also possible to obtain ink droplets with less variation in velocity. Next, the digital signal from the signal source 13 and the digital signal from the deflection amount specifying means 14 are input to the charging voltage control means 7. As a result, first, the memory 1 is
Address 5 is specified.

A signal specifying the amount of charged charge is stored at each address of the memory 15, and the signal specifying the amount of charged charge at the specified address is read out and converted into an analog signal by the digital-to-analog converter 16. The output of the transducer 16 is amplified by an amplifier 17 and output as the voltage 18 required to charge the ink drop.

In this embodiment, since any value can be set in the memory 15, it is possible to easily perform some kind of compensation in order to prevent a drop in implantation position accuracy due to the shape effect of the deflection electrode, etc., for example.

Next, FIG. 3 shows a second embodiment of means for controlling the amount of charge on an ink droplet. In this example, as in the embodiment shown in FIG. 2, the signal source 13 outputs a digital signal specifying the size of the ink droplet. In accordance with this signal, a pulse width specifying circuit 19 and an amplifier 20 output a driving pulse 21 whose pulse width is modulated according to the density of the image. This drive pulse is applied to the piezo vibrator, and ink droplets with controlled weight are ejected from the nozzle. Further, the digital signal from the signal source 13 is also input to the memory 23.
3. Specify the address. The signal specifying the amount of charged charge stored at the designated address specifies the amount of charged charge required for the weight of the ink droplet.
The signal read from the designated address is converted into an analog signal by the digital-to-analog converter 16, then amplified by the amplifier 24, and output as the voltage 18 necessary to charge the ink droplet.

On the other hand, the amplification degree of this amplifier 24 is variable, and the amplification degree is controlled in accordance with the signal from the deflection amount specifying means 22. Therefore, for example, by controlling the amount of deflection and the degree of amplification so that they are in a proportional relationship, a charging voltage proportional to the weight of the ink droplet and the amount of deflection can be generated.
As a result, the charged ink droplets can be deflected to a desired position.

FIG. 4 shows a third embodiment of the amount of charge on an ink droplet and means for controlling it. In this embodiment, a piezo drive means outputs a piezo drive signal 30 having an amplitude and pulse width necessary to eject an ink droplet of a necessary size in accordance with a signal 26 specifying the size of an ink droplet from a signal source 25. 29 and a signal 26 specifying the size of the ink droplet are converted into an analog signal 28 having an amplitude proportional to the size of the ink droplet by a digital-to-analog converter 27, and this signal is sent to the deflection amount specifying means 22.
The signal is input to an amplifier 24 similar to that used in the embodiment shown in FIG. 3, whose amplification degree changes depending on the signal from the signal. As a result, the ink droplet can be charged so that the ratio of the charge amount to the weight of the ink droplet is always constant for a predetermined deflection amount.

In the first, second and third embodiments of the means for controlling the amount of charge of an ink droplet described above, the signal for charging the ink droplet is transmitted to the charging electrode at least until the ink droplet ejected from the nozzle is cut off from the nozzle. and the nozzle or ink.

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 FIG. The present invention is not limited to the inkjet head shown, and may be applied to, for example, the inkjet head described in JP-A-48-9622 and the inkjet head shown in the liquid ejecting device described in JP-A-47-6308. Can be done.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of the ink droplet charging method according to the present invention, FIGS. 2, 3, and 4.
1A and 1B are diagrams for explaining first, second, and third embodiments of means for controlling the amount of charge of an ink droplet using the ink droplet charging method according to the present invention. In the figure, 1 is the inkjet head, 2
is a piezo vibrator, 3 is a nozzle, 4 is an ink chamber, 5
is a charging electrode, 6 is a piezo drive circuit, 7 is a charging voltage control means, 8 is a signal source, 9, 14 and 22 are:
Deflection amount specifying means, 10 a deflection electrode, 11 a power supply,
12 is a recording medium, 13 and 25 are signal sources, 15
and 23 are digital memories, 16 and 27 are digital-analog converters, 17, 20 and 2
4 is an amplifier, 18 is an output signal, 19 is a pulse width designation circuit, 21 and 30 are piezo drive signals, 26
28 is an analog signal, and 29 is a piezo driving means.

Claims (1)

[Claims] 1. Ink droplets of corresponding weight are ejected from an on-demand type inkjet head based on an image signal having weight information output at predetermined time intervals,
Ink droplet charging in an inkjet recording device in which the ink droplets are charged by a charging electrode placed in front of the nozzle of the inkjet head, and the charged ink droplets are deflected by a deflection electrode having a constant electric field to perform printing. In this method, an on-demand type ink jet head is used in which the weight of the ejected droplets is variable depending on the shape of the drive signal, and the jetting speed is constant within the range of the ink droplet weight to be used from the drive waveform and each desired weight is determined in advance. A drive waveform for ejecting a droplet is selected and secured, and a corresponding drive waveform is selected based on the weight information from among the secured drive waveforms to eject ink whose weight is controlled, and at the same time, the drive waveform specified by the weight information is selected. An ink droplet charging method for an inkjet recording apparatus, characterized in that a voltage proportional to the product of the voltage and the deflection amount is selected and applied to the charging electrode during the predetermined time interval.