JP2000168069A - Method for driving ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To print free from influences by crosstalks without setting a special control circuit, suppress the increase of manufacture cost and improve a printing quality by impressing a dummy voltage to non jet nozzles when a single nozzle or a smaller number than a total number of nozzles are to jet. SOLUTION: A speed of liquid drops is changed by vibrations via an ink or via a piezoelectric element 4 and a piezoelectric element-fixing plate 6 to simultaneously drive adjacent or every one nozzles, as compared with the case where a single nozzle is driven without the vibrations. If there are nozzles not to jet liquid drops, a voltage of a certain level is impressed to the nozzles thereby vibrating the piezoelectric element 4 and an ink meniscus. Accordingly a difference in the speeds between the jetting from the single nozzle and driving a full number of nozzles is reduced. More specifically, nozzles which do not jet liquid drops are driven with a voltage of 50-75% a minimum jet voltage and a maximum driving frequency, and nozzles which jet liquid drops are drive with a constant speed voltage when jetting from the full number of nozzles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an office or industrial ink jet printer, and more particularly to a method for adjusting a head drive.

[0002]

2. Description of the Related Art On-demand type ink jet heads eject ink by a thermal method in which bubbles are generated in ink by an electric heater to eject ink, and a wall of an ink pressurizing chamber using a piezoelectric element. There is a piezoelectric element type in which a part of the element is deformed to eject ink.

In the thermal method, fine processing can be performed by a lithography technique for semiconductor manufacturing.
There is an advantage that it can be reduced to μm or less. However, there are disadvantages that the boiling point of the liquid to be injected is limited to about 100 ° C., and the frequency at the time of continuous injection is limited to about 12 kHz. The restriction of the boiling point restricts the types of inks that can be used, which may hinder industrial applications. In addition, the life of the thin film resistor or the protective film formed to cover the thin film resistor for the purpose of protecting the thin film resistor by electrically heating the thin film resistor is relatively short (less than 100 million dots). Therefore, frequent replacement of the nozzle is required for industrial application.

On the other hand, in the piezoelectric element system, since the displacement of the piezoelectric element is small, it is necessary to increase the surface area of the diaphragm of the ink pressurizing chamber for ink ejection. Therefore, it is difficult to reduce the nozzle pitch to 100 μm or less. It's not easy. However, since the driving frequency depends on the shape of the piezoelectric element,
Hz or higher, which is a method suitable for increasing the printing speed. Also, unlike the thermal method, there is an advantage that the type of ink is not selected, and since the nozzle life is longer than the thermal method by one digit or more, it can be said that it is suitable for industrial application.

[0005]

In an ink jet head, nozzles for ejecting ink are arranged in a row, and the interval between nozzles in one row is generally smaller than the interval between rows. This is one reason for arranging a common ink flow path between rows.

In such a multi-nozzle head,
When all the nozzles are ejected simultaneously when ejecting ink from the nozzles arranged in a line, the droplet speed of the nozzle changes due to the influence of the driving of the adjacent nozzle compared to the droplet speed when driven alone. (Mainly decrease). This was called crosstalk, and was a problem that was not easily solved.

[0007] When crosstalk occurs, the following problem occurs in the print result.

At present, in a general ink jet printer, a head having a plurality of nozzles is mounted on a carriage. The carriage scans in the width direction of the paper, performs printing in the process, and then moves the paper in the longitudinal direction. An image is written on the entire surface of the paper by repeating a cycle of transporting a predetermined amount. When the nozzles are arranged in a line, an image resulting from printing by driving all the nozzles becomes solid or a line perpendicular to the carriage scanning direction. The former is a case where the nozzle is continuously driven, and the latter is a case where the nozzle is intermittently ejected. In the latter case, in particular, if the speed of the ink droplets in one row changes for each nozzle, the position where the ink lands on the paper differs for each nozzle, and the intention of writing a single straight line is originally a curved shape.

A typical example of the latter is shown in FIG.

In this example, of a row of nozzles,
The ink droplet ejected from the center nozzle is greatly affected by the crosstalk, and is shifted downstream in the sheet conveyance direction from the landing position of the ink droplet ejected from the end nozzle. ing. That is, the nozzle at the center has a speed drop due to the influence of crosstalk, whereas the nozzle at the end has a small effect of crosstalk and a relatively small drop in speed. Is an example in which the straight line is curved. Conversely, when a single nozzle or only a small number of nozzles are jetted, the landing position shift is small because the influence of crosstalk is small.

In the above phenomenon, since the driving conditions are determined so that the droplet speeds in the case of single driving of the nozzles become predetermined speeds, the influence of crosstalk is not considered at all. It becomes curved when injected.

On the other hand, as a known example closest to the present application, there is Japanese Patent Application Laid-Open No. Hei 10-119260, which discloses that a cross-talk is reduced by providing a correcting piezoelectric member. However, in this configuration, it is necessary to separately provide a compensating piezoelectric member, and the compensating piezoelectric member is used to drive the compensating drive voltage in synchronism or almost in synchronism with the pressurizing operation and the depressurizing operation of the pressure chamber for ejecting ink. It is necessary to add a control circuit for the piezoelectric member for correction. Therefore, the production cost may increase.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ink-jet head which uses only existing drive control to reduce the manufacturing cost and is free from the effects of crosstalk and which has improved print quality.

[0014]

According to a first aspect of the present invention, there is provided a pressure chamber for storing ink, and a piezoelectric element for generating a pressure fluctuation in the pressure chamber by applying an electric signal. A diaphragm which forms at least a part of a wall surface of the pressurizing chamber and is connected to the piezoelectric element by an elastic material; a restrictor serving as a flow path for supplying ink to the pressurizing chamber; At least one nozzle row composed of a common ink supply path for supplying ink to the reactor, an orifice for ejecting ink droplets from a pressure chamber, and a plurality of nozzles constituted by a piezoelectric element fixing plate for fixing the piezoelectric element. For inkjet heads with more than one row, adjust the droplet speed by increasing or decreasing the drive voltage of each nozzle so that the droplet speed of all nozzles is almost the same when all nozzles in the same row are ejected simultaneously Rutotomoni, when the non-ejection nozzles, not injected there applies a 50% to 75% of the voltage of the minimum voltage that can be ink jet to the non-ejection nozzle at the time of printing,
And driving at the maximum driving frequency.

According to a second method of the present invention, there is provided a pressure chamber for storing ink, a piezoelectric element for generating a pressure fluctuation in the pressure chamber by applying an electric signal, and at least one of a wall surface of the pressure chamber. Forming a portion, a diaphragm connected to the piezoelectric element with an elastic material, a restrictor serving as a flow path for supplying ink to the pressurizing chamber, and a common ink supply path for supplying ink to the restrictor. In an on-demand type multi-nozzle inkjet head having an orifice for ejecting ink droplets from a pressurizing chamber and a plurality of nozzles constituted by a piezoelectric element fixing plate for fixing the piezoelectric element, etc., all nozzles in the same row are simultaneously operated. Adjust the droplet speed by increasing or decreasing the drive voltage of each nozzle so that the droplet speed of all nozzles is almost the same when ejected, and divide all nozzles in the same row into multiple sets When driving is performed by shifting the driving cycle of each set by a value obtained by dividing the driving cycle by the number of sets, and there is a non-ejection nozzle that does not eject at the time of printing, there is a minimum voltage of 50 to 50 to which ink can be ejected to the non-ejection nozzle. It is to drive at a maximum driving frequency by applying a voltage of 75%.

That is, according to the present invention, when determining the driving conditions, the driving state or the pulse width of the nozzles is determined by giving priority to the printing state when all the nozzles are driven, instead of the conventional driving of the nozzles alone. And the non-ejection nozzle is at a voltage of 50 to 75% of the ink ejection minimum voltage,
Moreover, it is driven at the maximum driving frequency.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of the nozzle portion of the multi-nozzle ink jet head used in the present invention.

This head can perform recording by ejecting ink according to an input signal. 1 is an orifice, 2 is a pressure chamber, 3 is a vibration plate, 4 is a piezoelectric element, 5a
And 5b are signal input terminals, 6 is a piezoelectric element fixing plate, 7 is a restrictor that connects the common ink supply path 8 and the pressurizing chamber 2 and controls the flow of ink into the pressurizing chamber 2, and 8 is a common ink supply. 9, an elastic material (for example, silicon adhesive) connecting the diaphragm 3 and the piezoelectric element 4; 10, a restrictor plate forming the restrictor 7; 11, a pressurizing chamber plate forming the pressurizing chamber 2 , 12 are orifice plates forming the orifice 1, 13 is a support plate for reinforcing the vibrating plate 3, 14 and 15 are common ink supply path plates, 16 is a common ink supply path cover, and 17 is a connection between the piezoelectric element and external wiring. The conductive adhesive 18 is a filter.

The diaphragm 3 and the restrictor plate 1
The pressure chamber plate 11 and the support plate 13 are made of, for example, stainless steel, and the orifice plate 12 is made of nickel.

The piezoelectric element fixing plate 6 is made of an insulating material such as ceramics and polyimide.

The ink flows from the upstream to the downstream in the order of the common ink supply path 8, the restrictor 7, the pressurizing chamber 2, and the orifice 1.

The piezoelectric element 4 expands and contracts when a potential difference is applied between the signal input terminals 5a and 5b, and the signal input terminal 5a
It is mounted so as to return to the original state when the potential difference between the terminals 5b and 5b disappears.

FIG. 2 shows a nozzle array of an ink jet head showing an example of the present invention.

In the figure, 32 nozzles are arranged in one row. The total number of nozzle rows is 12 rows.

FIG. 3 is a sectional view taken along line AA of FIG.

In the figure, 4 is a piezoelectric element, and 6 is a piezoelectric element fixing plate for fixing the piezoelectric element.

Hereinafter, a method of driving the ink jet head according to the present invention will be described.

In general, when there is crosstalk, the droplet speed is extremely lower when all the nozzles are driven simultaneously than when only a specific nozzle is driven alone. Conventionally, as a countermeasure, each nozzle is driven independently,
Driving voltage so that each nozzle has a predetermined droplet speed,
The drive pulse width was selected.

On the other hand, in the present invention, in selecting the driving voltage and the driving pulse width, the driving conditions are selected so that the ejection speed from each nozzle becomes a predetermined speed while driving all the nozzles. I do. That is, the driving conditions are determined so that the injection speed becomes the same at the time of all-injection.

In the following, an example will be described in which the driving voltage is set to one and the driving voltage of each nozzle is set in setting the driving conditions.

FIG. 4 shows an example in which the driving voltage is selected as described above.

As a specific adjustment method, there is a method of observing the ink droplets with a microscope or the like while driving all the nozzles with a strobe, and selecting a drive voltage so that the ejection speed from each nozzle becomes a predetermined speed. No.

Alternatively, a straight line is printed by driving all the nozzles, and based on the result, the displacement of the landing position of the ink droplet is measured with a microscope or the like, and the measured displacement amount is used as a driving voltage for each nozzle. There is a way to reflect it.

Further, after a driving voltage to be applied to each nozzle is selected in advance so that a predetermined droplet velocity is obtained when a single nozzle is driven, a change in droplet velocity due to crosstalk when all nozzles are driven is determined. There is a method of adjusting by adjusting the corresponding drive voltage.

As described above, in the present invention, solid coating or linear printing is assumed, and the nozzle (particularly the central portion)
In consideration of the influence of crosstalk, the applied voltage of each nozzle (referred to as the constant speed voltage at the time of all ejections) is determined. And the quality of linear printing has been improved.

Next, a so-called time-division driving in which one column is divided into a plurality of groups and ink is ejected with a time difference will be described. Here, for the sake of convenience, a case will be described in which the nozzles are divided into two groups of even-numbered nozzles and odd-numbered nozzles, but the number of groups to be divided is not limited to this.

For example, in the case of FIG. 2, since there are 32 nozzles in one row, a set of 16 nozzles is provided. Such a driving method is called an even-odd division driving method. When the maximum frequency at the time of driving the printer is given, the driving cycle is obtained by its reciprocal. Then, for example, even nozzles are driven first, and odd nozzles are driven with a delay of a half cycle.

Conventionally, it has been thought that if the nozzles are driven with a time lag as described above, the effect of the nozzle ejected first does not adversely affect the nozzle ejected next. , Crosstalk occurs with a time difference. In other words, the influence of the previously ejected nozzle in the same cycle and the influence of the other nozzles that are driven simultaneously at the same time may spread to the next ejected nozzle, which may cause poor ink ejection and reduced speed. There is.

Therefore, even in such a time-division driving, in selecting the driving voltage, the driving voltage is selected such that the ejection speed from each nozzle becomes a predetermined speed while all the nozzles are time-divisionally driven. Has been selected. The selection method uses the above-described observation with a strobe, and determines the driving conditions such that the ejection speed of all nozzles (even nozzles and odd nozzles) in the same cycle is the same when all nozzles are ejected.

By performing such a driving method, an effect was obtained in the case where all the nozzles were simultaneously driven or the case where all the nozzles were driven in an even-odd manner. And the droplet speed at the time of simultaneous driving of all of them may occur. Therefore, the present invention has taken measures against such a case.

We do not have any vibrations via ink or via a piezoelectric element and a piezoelectric element fixing plate to simultaneously drive adjacent or alternately arranged nozzles. Considering that the droplet speed will change compared to single drive, if there are nozzles that do not eject, apply a certain voltage to those nozzles and vibrate the piezoelectric element and ink meniscus, so that single ejection and 100% drive It was concluded that the difference between the droplet velocities could be reduced with the case of.

Nozzles that do not eject liquid droplets (nozzles without print duty) are 50 to 75% of the minimum ejection voltage.
And the maximum driving frequency (the frequency at which solid printing is performed when used as a printing machine), and the nozzles that eject droplets (nozzles with a printing duty) are determined in the manner described above. It was found that, by driving at a constant speed voltage at the time of 100% ejection, the difference from the droplet speed at the time of simultaneous ejection of all (or time division) nozzles can be reduced even in the case of a nozzle that ejects alone.

Next, a specific method of determining the drive voltage will be described.

First, the minimum injection voltage will be described. When the voltage is increased for each nozzle, the ink starts to be ejected at a certain voltage. This is called the minimum injection voltage.

For a particular nozzle row, this is about 20
V. Therefore, the case where only one nozzle is jetted is taken up, and all the remaining nozzles in the same row (31 nozzles when all the nozzles are 32) are set at 25% of the minimum jetting voltage (5 V in this case). Driving was performed at the maximum drive frequency (dummy driving is not performed because ink is not ejected), and only one ejecting nozzle was driven at a constant speed voltage during all ejections.

Next, the dummy drive voltage is set to the minimum injection voltage of 2
From 5% to 50% to 75%, only one nozzle was driven at a constant drive voltage during all-injection. As a result, when it exceeded 75%, it was found that the orifice surface was wet with the ink, causing liquid dripping or erroneous ejection, which affected print quality.

FIG. 5 shows a summary of such experiments. In this figure, the abscissa represents the dummy voltage, and the ordinate represents the droplet velocity ratio of the nozzles of interest with respect to all the ejections.

When the dummy voltage is low, the speed of the single drive is greater than the speed of the full drive, and
It is not possible to maintain the same head drive environment as in the case of 100% drive, and the effect of crosstalk remains even if the non-ejection nozzles are dummy driven. As the dummy voltage is increased, the speed during single driving approaches the speed during full driving. However, if the dummy voltage is too high, ink will accumulate on the orifice surface, causing erroneous ejection, which may result in no ink ejection at the next print duty. From this figure, it can be seen that the dummy voltage is preferably about 50 to 75% of the minimum injection voltage.

FIG. 7 schematically shows an example of printing in which the driving conditions are determined as described above.

In the drawing, the landed ink droplets (dots) are arranged substantially linearly, and the landing position shift is reduced even when a single nozzle or only a small number of nozzles are ejected.

As described above, according to the present invention, in a head controlled to drive at a constant speed voltage at the time of all-injection, a non-injection nozzle is used when only a small number of nozzles are ejected alone or not all. By applying an appropriate dummy voltage to the above, it is possible to reduce the difference between the droplet speed at the time of single drive and the droplet speed at the time of all-drive.

[0053]

As described above, according to the present invention, it is possible to perform printing without being affected by crosstalk without providing a special control circuit. In addition, it is possible to provide an ink jet head with improved printing quality.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an inkjet head used in the present invention.

FIG. 2 is a plan view showing the arrangement of orifices of the inkjet head used in the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is a graph showing the driving voltage of each nozzle obtained by the method of the present invention and the speed at the time of simultaneous driving.

FIG. 5 is a graph showing a relationship between a dummy drive voltage and a droplet speed in the present invention.

FIG. 6 is a schematic diagram showing a printing result by a conventional driving method.

FIG. 7 is a schematic diagram showing a printing result by the driving method of the present invention.

[Explanation of symbols]

1 is an orifice, 2 is a pressure chamber, 3 is a vibration plate, 4 is a piezoelectric element, 5a and 5b are signal input terminals, 6 is a piezoelectric element fixing plate,
7 is a restrictor, 8 is a common ink supply path, 9 is silicon rubber, 10 is a restrictor plate, 11 is a pressure chamber plate, 12 is an orifice plate, 13 is a support plate, 1
Reference numerals 4 and 15 are a common ink supply path plate, 16 is a common ink supply path cover, 17 is a conductive adhesive, and 18 is a filter.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshitaka Akiyama 1060 Takeda, Hitachinaka-shi, Ibaraki Prefecture Inside Hitachi Koki Co., Ltd. (72) Inventor Masatoshi Sakata 1060 Takeda, Hitachinaka-shi, Ibaraki Prefecture F-term in Hitachi Koki Co. Reference) 2C057 AF42 AG14 AG44 AM18 AM19 BA04 BA14

Claims (2)

[Claims] A pressure chamber for storing ink, a piezoelectric element for generating pressure fluctuation in the pressure chamber by applying an electric signal, and at least a part of a wall surface of the pressure chamber; A diaphragm connected by an elastic material, a restrictor serving as a flow path for supplying ink to the pressurizing chamber, and a common ink supply path for supplying ink to the restrictor;
In an ink jet head having at least one or more nozzle rows composed of a plurality of nozzles constituted by an orifice for ejecting ink droplets from a pressurizing chamber and a piezoelectric element fixing plate for fixing the piezoelectric element, all the nozzles in the same row In addition to adjusting the droplet speed by increasing or decreasing the drive voltage of each nozzle so that the droplet speeds of all the nozzles are almost the same when the nozzles are ejected simultaneously, if there is a non-ejection nozzle that does not eject during printing, A method for driving an ink jet head, comprising applying a voltage of 50 to 75% of a minimum voltage at which ink can be ejected to an ejection nozzle and driving the inkjet nozzle at a maximum drive frequency. 2. A pressure chamber for storing ink, a piezoelectric element for generating pressure fluctuation in the pressure chamber by application of an electric signal, and at least a part of a wall surface of the pressure chamber, A diaphragm connected by an elastic material, a restrictor serving as a flow path for supplying ink to the pressurizing chamber, and a common ink supply path for supplying ink to the restrictor;
In an on-demand type multi-nozzle inkjet head having a plurality of nozzles constituted by an orifice for ejecting ink droplets from a pressurizing chamber and a piezoelectric element fixing plate for fixing the piezoelectric element, etc., all nozzles in the same row are simultaneously ejected. The drive voltage of each nozzle is increased or decreased to adjust the droplet speed so that the droplet speeds of all the nozzles are almost the same when all the nozzles are in the same row, and all the nozzles in the same row are divided into a plurality of groups, and each group is driven. When driving is performed by shifting the period by a value obtained by dividing the cycle by the number of sets, and there is a non-ejection nozzle that does not eject during printing, a voltage of 50 to 75% of the lowest voltage at which ink can be ejected to the non-ejection nozzle And driving at the maximum drive frequency.