JPS6233955B2 - - 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.

Conventionally, various types of inkjet recording devices are known. Among these, the ink-on-demand type recording apparatus has advantages such as a simple configuration and, in principle, only forming ink droplets used for recording, so that a system for collecting unnecessary ink is not required. In addition, by changing the diameter of the ink droplets, it is possible to perform medium tone recording. Because of these characteristics, it came to be used in facsimile receivers, etc. Conventionally, scanning in this type of recording apparatus has often been done mechanically by winding the recording paper around a drum and rotating it. However, rather than such mechanical scanning, electrical scanning in which ink droplets are electrostatically deflected is desired in terms of recording speed, reliability, operability, and the like. Conventionally, as a method of electrostatically deflecting ink droplets that vary in size,
A method has been proposed for charging an ink droplet so that the acceleration received from the deflection electric field remains constant even if the weight of the ink droplet changes. This method is very effective under the conditions that the flying speed of the ink droplets hardly changes even if the weight of the ink droplets changes, and the influence of air resistance is small, and the advantage is that the control of charging is not too complicated. be. However, if the weight of the ink droplet is changed significantly to increase the dynamic range of halftones, the initial velocity when ejected from the nozzle and the influence of air resistance may change depending on the size of the ink droplet. As a result, if the variation in the speed of the ink droplet passing through the deflection electrode section increases, a problem arises in that the amount of deflection changes.

The purpose of the present invention is to solve the problems of the prior art,
An object of the present invention is to provide an inkjet recording device capable of performing halftone recording by changing the size of ink droplets while performing deflection.

According to the present invention, there is provided an on-demand type ink jet head capable of ejecting ink droplets of different weights from a nozzle according to a driving waveform, a charging electrode for charging the ink droplets, and a voltage applied to the charging electrode. In the ink droplet charging method of an inkjet recording device, which has a charging voltage control means that generates a waveform and a deflection electrode that generates an electric field whose intensity changes in proportion to the amount of deflection of the charged ink droplets, the ink droplets are output at a predetermined printing cycle. A drive waveform for ejecting an ink droplet having a weight corresponding to the density is selected based on the concentration signal, and the voltage value applied to the charging electrode when the ejected ink droplet is cut off from the nozzle is the ink droplet at the deflection electrode section. After applying the droplet weight, droplet velocity, and drive waveform corresponding to the drive waveform determined in advance to the on-demand type ink jet head so as to be proportional to the product of the square of the flying speed and the ink droplet weight, A waveform to be applied to the charging electrode is selected based on data on the ink droplet cutting time required for the droplet to be cut from the nozzle, and is applied to the charging electrode in synchronization with the concentration signal, and a waveform is applied to the charging electrode in synchronization with the concentration signal. There is obtained an ink droplet charging method for an ink jet recording apparatus characterized in that the driving waveform is applied to the ink jet head at a timing selected based on the data.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram for explaining the ink droplet charging method of the present invention. In the figure, an ink droplet 3 is incident on the deflection electrode 1 from the left side of the figure. A constant voltage is applied to the deflection electrode from a power source 2. At this time, the ink droplet 3 is subjected to a force in the y direction while passing through the deflection electrode portion, and when it leaves the deflection electrode, a velocity component Vy in the y direction is generated as shown in the figure.
As a result, the ink droplet is deflected in the θ direction, and thereafter travels straight and is struck on the recording medium 4 at a position shifted by D from the non-deflection point. At this time, the amount of deflection D
is determined by the size of θ, and D=ltanθ=l・
Vy/Vx. However, Vx is the velocity component in the x-axis direction when exiting the deflection electrode. Also, assuming that the velocity in the x-axis direction of the ink droplet hardly changes while it passes through the deflection electrode, the velocity component in the y-axis direction when it leaves the deflection electrode section will change the charge amount and weight of the ink droplet by q and m, respectively. Then, Vy=qE/m·ld/Vx.
Therefore, the amount of deflection is D=l・Vy/Vx=qE/m・l・l
d/Vx becomes ² .

In order to prevent the deflection amount D from changing even if the weight of the ink droplet is changed, if the deflection electric field E is kept constant, when charging the ink droplet, the weight m of the ink droplet and the x-axis direction immediately after passing through the deflection electrode are The amount of charge on the ink droplet may be determined so that it changes in proportion to the value of the product of the velocity Vx and the square of the velocity Vx. Further, the amount of deflection can be controlled by the intensity of the electric field E.

Next, an embodiment of an inkjet recording apparatus using the ink droplet charge control method according to the present invention will be described. Second
The figure is a schematic diagram for explaining the first embodiment. This device includes a signal source 12 that outputs an image signal specifying the weight of an ink droplet, and a piezo drive circuit 11 that receives the image signal from the signal source 12 and outputs an electric signal for ejecting an ink droplet from an ink jet head. , an ink jet head 5 capable of controlling the size of the ink droplet formed by this electric signal, a charging electrode 9 arranged in front of the nozzle 8, and an ink droplet controlled by the signal from the signal source 12. A charging voltage control means 10 that applies a voltage to the charging electrode, a deflection electrode 13 and a deflection amount specifying means 15, and a power source 14 that applies a voltage proportional to the deflection amount to the deflection electrode 13 according to the specification from the deflection amount specifying means. and a recording medium 17 such as paper. The ink jet head 5 shown here consists of a nozzle 8 filled with conductive ink supplied from an ink supply system (not shown), an ink chamber 7, and a piezo vibrator 6 as an electroacoustic transducer. It is known as an example of ink-on-demand type.
When a voltage pulse 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 expels ink from the nozzle 8. The size and initial velocity of the ink droplet formed can be selected by the amplitude and width of this voltage pulse. Charging control in this device is performed as follows.
First, an image signal specifying the weight of an ink droplet as density information is sent from the signal source 12 to the piezo drive circuit 11.
The voltage is applied to the charging voltage control means 10. Then, an ink droplet having a weight specified by the image signal is ejected from the ink jet head 5. At the same time, the charging voltage control means 10 outputs a voltage proportional to the product of the weight m of the formed ink droplet and the square of the flying speed V of the ink droplet when the ink droplet passes through the deflection electrode 13. is applied to the charging electrode 9. A charge proportional to the voltage applied to the charging electrode is imparted to the ink droplet. As a result, charging as shown in the ink droplet charging method described above is performed, and even if the weight of the ink droplet changes under the same electric field, no difference occurs in the amount of deflection. The ink droplet 16 charged in this way is moved to the deflection electrode 1 to which a voltage proportional to the deflection amount is applied according to an instruction from the deflection amount specifying means 15.
3 and is driven into a predetermined position on the recording medium 17 to perform recording. Here, the flying speed V of the ink droplets when passing through the deflection electrode is measured in advance and given to the charge control means 10 as information on the flying speed with respect to the weight of each ink droplet. An example of the charging voltage control means in this embodiment is one using a digital memory. The address of the digital memory is designated by the image signal from the signal source 8. Information specifying the voltage value to be applied to the charging voltage when forming ink droplets of the corresponding weight is stored at each address. This voltage value is proportional to the product of the weight of the ink droplet and the square of the flying speed. Each time an ink droplet is formed, a predetermined charging can be performed by reading out the contents of the corresponding address from this memory and applying a specified voltage to the charging electrode.

FIG. 3 is a schematic diagram for explaining a second embodiment of the inkjet recording apparatus. This device has an inkjet head 5 that can control the size of ink droplets formed by electrical signals.
, a synchronization signal generation means 21, and a voltage application means 2 that outputs a waveform of a constant period in synchronization with the synchronization signal.
0, a charging electrode 9 arranged in front of the nozzle 8,
A signal source 18, a piezo drive circuit 19 that outputs an inkjet head drive signal according to a synchronization signal from image information from the signal source 18, and a deflection electrode 13.
, a deflection amount specifying means 15, a power source 14 that applies a voltage proportional to the deflection amount to the deflection electrode 13 according to a specification from the deflection amount means, and a recording medium 17 such as paper. The inkjet head 5 shown here is similar to that shown in the first embodiment. In this embodiment, the inkjet head drive signal uses one whose pulse width changes depending on the image signal. This drive signal is applied to the ink jet head, and a predetermined relationship is established between the ink droplet formation time t from the start of ink droplet formation until the ink is cut off from the nozzle, and the ink droplet weight m. let Further, the relationship between the flying speed V of the ink droplet when it passes through the deflection electrode section and the weight m of the ink droplet is determined in advance. The voltage waveform applied to the charging electrode, that is, the output waveform of the voltage applying means, is determined by the relationship m=(t) between the ink droplet formation time and the ink droplet weight, and the relationship V=g(m) between the ink droplet weight and flying speed V. It becomes as follows.

V (kt ₀ +t) = A・m・V ² =A・(t) [g{(t)}] ² (k=0, ±1, ±2,...0≦t<t ₀ A: constant) However, it is assumed that the formation of ink droplets starts at time T=kt ₀ .

When such a waveform is applied to the charging electrode, the voltage value applied to the charging electrode when an ink droplet is formed is proportional to the product of the weight of the ink droplet and the square of the ink droplet velocity at the deflection electrode. The value is as follows. Therefore, the amount of charge on the ink droplet can be adjusted so that the amount of deflection does not change even if the weight of the ink droplet changes. Ink droplet 1 charged in this way
As in the first embodiment, the laser beam 6 is deflected by the deflection electrode 13 and is driven into the recording medium 17 to perform recording.

FIG. 4 is a schematic diagram for explaining a third embodiment of an inkjet recording apparatus according to the present invention.
This apparatus includes an ink jet head 5 that can control the size of ink droplets formed by the amplitude of a signal, a synchronizing signal generating means 26, and a periodic waveform that is synchronized with the synchronizing signal. As an example, voltage application means 25 outputs a sawtooth voltage.
, a charging electrode 9 that applies a charge to the ink droplets ejected from the nozzle 8, a signal source 22 that outputs an electric signal specifying the weight of the ink droplet in synchronization with the sawtooth wave, and an electric signal from this signal source. It consists of a delay means 23 which outputs a signal with a certain time delay depending on the weight of the ink droplet, a deflection electrode 13 which deflects the charged ink droplet, and a recording medium 17 such as paper.
The inkjet head shown here is the first one mentioned above.
and the same as described in the second embodiment. Here, the weight of the ink drop is controlled by the amplitude of the signal input to the ink jet head. Further, as the amount of delay caused by the delay means, the constant waveform voltage applied to the charging electrode is proportional to the product of the square of the velocity of the ink droplet at the deflection electrode section and the weight of the ink droplet, which has been measured in advance. The amount of delay of the delay means is controlled in accordance with the weight of the ink droplet formed at that time so that the ink droplet is cut off from the nozzle when the voltage value is reached. For example, the fifth
In the case of the sawtooth wave shown in Figure a, when the relationship between the weight m of the ink droplet and the flight speed when passing through the deflection electrode is V = g (m), the sawtooth wave as shown in Figure 5b is obtained. The amount of delay α for the rise of the wave is determined by the weight m of the ink droplet: α=L・m・g ² (m)−β−γ L: constant.

β: Pulse width of electrical signal.

γ: Time required for ink droplets to be cut off from the nozzle after the fall of the electrical signal.

is given by The ink droplet is charged in proportion to the voltage V ₁ or V ₂ applied to the charging electrode when it is formed. By using such a charging method, it is possible to adjust the amount of charge of an ink droplet so that it does not change from the amount of deflection even if the weight of the ink droplet changes. The ink droplets charged in this manner are deflected by a deflection electrode and are ejected onto a recording medium to perform recording.

In the second and third embodiments shown here, the voltage waveform applied to the charging electrode does not particularly have to change continuously. For example, if the weight of the ink droplets to be formed is fixed at several values, a staircase wave whose voltage value corresponds to the weight of each ink droplet may be used. As shown in FIG. 6, a continuously changing voltage waveform is indicated by a dotted line. At this time, for example, if the formation of ink droplets is to be fixed in the four cases shown by the arrows, a staircase wave as shown by the solid line can be used.

Further, in the second and third embodiments, even when the ink jet head is a multi-nozzle having a plurality of nozzles, the charging electrode can be shared by each nozzle. That is, by applying a voltage with a constant waveform to this common charging electrode, an electric signal for controlling the weight of the ink droplet can be applied to the piezo vibrator corresponding to each nozzle. In this manner, the present invention is also suitable for multi-use inkjet heads.

Furthermore, in the embodiments of the present invention, the formation of ink droplets was explained using ink jet heads as shown in Figures 2, 3, and 4. There is no limit to this. For example, on-demand type ink jets in which the volume and flying speed of droplets to be ejected are determined by the drive waveform, as shown in the inkjet head described in JP-A-48-9622 and the droplet ejecting device described in JP-A-47-6308. It can be applied to the head.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the ink droplet charging method of the present invention, and FIG. 2, FIG. 3, and FIG. A schematic diagram for explaining the third embodiment, FIG. 5a is an example of the voltage waveform applied to the charging electrode in the third embodiment, and FIG. FIG. 6 is a diagram showing still other signals. In the figure, 1 is a deflection electrode, 2 is a power supply, and 3 is a deflection electrode.
are ink droplets, 4 is a recording medium, 5 is an ink jet head, 6 is a piezo vibrator, 7 is an ink chamber, 8 is a nozzle, 9 is a charging electrode, 10 is a charging voltage control means, 11, 19 and 24 are piezo drives circuit, 1
2, 18 and 22 are signal sources; 13 is a deflection electrode;
14 is a power supply, 15 is a deflection amount specifying means, 16 is an ink droplet, 17 is a recording medium, 20 and 25 are voltage applying means, 21 and 26 are synchronizing signal generating means, 2
3 is a delay means.

Claims (1)

[Claims] 1. An on-demand ink jet head capable of ejecting ink droplets of different weights from a nozzle according to a driving waveform, a charging electrode for charging the ink droplets, and a voltage waveform to be applied to the charging electrode. In the ink droplet charging method for an inkjet recording device that has a charging voltage control means and a deflection electrode that generates an electric field whose intensity changes in proportion to the amount of deflection of charged ink droplets, the density is determined by a density signal output at a predetermined printing cycle. A driving waveform is selected to eject an ink droplet having a weight corresponding to The droplet weight, droplet velocity, and drive waveform corresponding to the drive waveform previously determined for the on-demand type ink jet head are applied so as to be proportional to the product of the square and the ink droplet weight, and then the droplet is released from the nozzle. A waveform to be applied to the charging electrode is selected based on data on the ink droplet cutting time required until cutting, and is applied to the charging electrode in synchronization with the concentration signal, and the data is also applied to the charging waveform. 1. An ink droplet charging method for an inkjet recording apparatus, characterized in that the driving waveform is applied to the inkjet head at a timing selected as follows.