JPH10305575A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high quality printing of photographic quality level by varying the duration of a second signal for keeping the expanded state of a pressure generation chamber thereby regulating the quantity of a very small ink droplet being jetted through a nozzle opening. SOLUTION: In order to jet a very small ink droplet, a first signal 401 for exciting the meniscus in a nozzle opening abruptly is driven shorter than a period Tc to oscillate the Helmholtz oscillation system of period Tc thus exciting the meniscus abruptly. Thus excited meniscus oscillation of period Tc is temporarily pulled into the nozzle opening and then reset toward the nozzle opening face before a part of meniscus standing up above the nozzle opening face is separated and jetted as a small ink droplet. Since the influence of meniscus push-up force generated by a third signal 403 for contracting the pressure generating chamber is varied when the duration of a second signal 402 402 is varied, the extent and speed of meniscus standing up above the nozzle opening face are varied thus varying the quantity of a small ink droplet being jetted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an ink jet head using an element having piezoelectricity as an actuator, and particularly provides an ink jet recording apparatus for providing high quality printing required for obtaining an image of a photographic quality at a high speed. About.

[0002]

2. Description of the Related Art In an ink jet recording apparatus having an ink jet head for discharging ink droplets by expanding and contracting a pressure generating chamber communicating with a nozzle opening, a very small volume of ink is required to obtain high printing quality. It is necessary to eject droplets.

[0003] Such a method for discharging ink droplets and an ink jet apparatus are described in Japanese Patent Publication No. 4-36071. Figure 12 is a view as described in the above publication, rapidly expanding the pressure generation chamber by T ₁ signal 1201, rapidly draw a meniscus from the nozzle opening. At this time, a protrusion generated near the center on the meniscus is
Separation from the meniscus allows ejection of very small ink droplets.

[0004]

However, in such a method of ejecting ink droplets and an ink jet apparatus, since the size and the displacement speed of the projections generated on the meniscus vary, the ink to be ejected is inconsistent. The amount of the droplet changed, and stable printing quality could not be provided. Also,
In such an ink droplet ejection method and an ink jet apparatus, the T ₂ signal 1202 and the T ₃ signal 1203
But order not to affect the discharge of ink droplets could not be performed subtle drop volume adjustment of ink droplets actively utilizes T ₂ signal 1202 and T ₃ signal 1203.

[0005] Further, such a method of discharging ink droplets,
And in the ink jet apparatus, the amount of ink droplets that greatly changes by changing the viscosity of the ink due to the change in environmental temperature, means to always keep a constant, for example,
There is no means for setting a temperature correction table and adjusting the amount of ink droplets according to a change in environmental temperature. The present invention solves such a problem, and an object of the present invention is to adjust the amount of very small ink droplets by changing the duration of the second signal so as to obtain a photograph. An object of the present invention is to provide an ink jet recording apparatus which realizes high quality printing at a quality level.

[0006]

According to the present invention, there is provided an ink jet recording apparatus comprising: a pressure generating chamber communicating with a common ink chamber via a nozzle opening and an ink supply port and having a Helmholtz resonance frequency of a cycle Tc; An ink jet recording apparatus comprising at least one ink jet head comprising an element for expanding and contracting a pressure generating chamber,
First signal generating means for expanding the pressure generating chamber to rapidly excite a meniscus in a nozzle opening, second signal generating means for maintaining an expanded state of the pressure generating chamber, and the pressure generating chamber A driving means comprising a third signal generating means for contracting the ink, and adjusting the amount of a very small ink droplet ejected from the nozzle opening by changing the duration of the second signal. It is characterized by having.

[0007]

First, in order to eject a very small ink droplet, the first signal is driven to be shorter than Tc to oscillate the Helmholtz oscillation system having the period Tc, thereby rapidly exciting the meniscus. The excited meniscus vibration of the cycle Tc is once drawn into the nozzle opening, then returns toward the nozzle opening surface, and a part of the meniscus rising from the nozzle opening surface is separated and ejected as ink droplets.

According to the first aspect of the present invention, when the duration of the second signal is changed, the amount of influence of the meniscus pushing-up force by the third signal changes, so that the amount and speed of the meniscus rising from the nozzle opening surface change. Therefore, the amount of ink droplets to be ejected can be changed.

According to a second aspect of the present invention, the second signal is set such that the meniscus once drawn into the nozzle opening drives the third signal within a time range toward the nozzle opening surface. The amount of ink droplets to be ejected can be changed.

Further, according to the third aspect of the present invention, by changing the initial value of the second signal among the individual heads, it is possible to prevent variations in the ink droplet amount among the individual heads due to variations in Tc.

According to a fourth aspect of the present invention, stable printing is achieved by changing the second signal in accordance with a change in the environmental temperature, thereby always discharging a constant amount of ink droplets without being affected by the environmental temperature. Can provide quality.

According to a fifth aspect of the present invention, in the flushing, the duration of the second signal is driven to be shorter than the initial value, and the influence of the meniscus pushing-up force by the third signal is increased, so that the vicinity of the nozzle opening is increased. It is possible to forcibly discharge the ink having increased viscosity (hereinafter, referred to as “thickened ink”) to recover a stable ejection state of ink droplets.

According to a sixth aspect of the present invention, in the first ejection of a nozzle having a printing interval for a predetermined time or more immediately after a pause, the duration of the second signal is shorter than the initial value, and the third signal is driven. By increasing the amount of influence of the meniscus pushing-up force due to the ink, the film of the thickened ink near the nozzle opening can be broken, and the ink droplet can be stably ejected.

According to a seventh aspect of the present invention, the driving means of the first aspect and the second driving means for ejecting a large ink droplet by contracting the pressure generating chamber are selected within one printing cycle. , Or by driving in combination, it is possible to eject very small ink droplets to large ink droplets, thereby providing high print quality at a photographic quality level.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

Here, one of the ink jet type recording apparatuses is described.
First, an inkjet printer will be described as an example. However, the ink jet recording apparatus includes not only an ink jet printer but also all devices that can use an ink jet head, such as a copier and a plotter.

1. Configuration of Inkjet Printer FIG. 1 is a functional block diagram of an inkjet printer to which an embodiment of the present invention is applied.

The ink jet printer includes a printer controller 101 and a printer engine 102. The printer controller 101 includes an interface (hereinafter referred to as “I / F”) 103 for receiving print data and the like from a host computer (not shown), a RAM 104 for storing various data, a routine for various data processing, and the like. 105, a control unit 106 including a CPU, etc., an oscillation circuit 107, and a drive signal generation circuit 108 as "drive signal generation means" for generating a drive signal to the inkjet head 110 described later.
And an I / F 109 for transmitting print data and drive signals developed into dot pattern data (bitmap data) to the printer engine 102.

The I / F 103 receives, for example, any one of character code, graphic function, and image data or print data including a plurality of data from a host computer or the like. Also, I / F103
Is a busy signal (BUS) to the host computer.
Y) and an acknowledgment signal (ACK) can be output.

The RAM 104, the receiving buffer 104A, the intermediate buffer 104B, the output buffer 104C, and a work memory (not shown) are used. The print data from the host computer received by the I / F 103 is temporarily stored in the reception buffer 104A. The intermediate buffer 104B stores the intermediate code data converted into the intermediate code by the control unit 106. In the output buffer 104C, the dot pattern data after the gradation data is decoded is developed. ROM1
Reference numeral 05 stores various control routines executed by the control unit 106, font data, graphic functions, various procedures, and the like.

The control unit 106 reads the print data in the reception buffer 104A and converts it into intermediate code data.
This intermediate code data is stored in the intermediate buffer 104B. Next, the control unit 106 analyzes the intermediate code data read from the intermediate buffer 104B, and develops the intermediate code data into dot pattern data with reference to the font data and graphic functions in the ROM 105. The developed dot pattern data is stored in the output buffer 104C after necessary decoration processing is performed.

When dot pattern data corresponding to one line of the ink jet head 110 is obtained, the dot pattern data for one line is serially transferred to the ink jet head 110 via the I / F 109. When one line of dot pattern data is output from the output buffer 104C, the contents of the intermediate buffer 104B are deleted, and the next intermediate code conversion is performed.

The printer engine 102 includes an ink jet head 110, a paper feed mechanism (abbreviated as “paper feed” in the figure) 111, and a carriage mechanism (abbreviated as “carriage” in the figure) 112. The paper feed mechanism 111 includes a paper feed motor, a paper feed roller, and the like, and sequentially feeds a print target such as a recording paper and performs sub-scanning. The carriage mechanism 112 includes a carriage on which the inkjet head 110 is mounted, a carriage motor for moving the carriage via a timing belt or the like, and the like.
The main scanning of the inkjet head 110 is performed.

The ink jet head 110 has a large number of nozzles such as 64 in the sub-scanning direction, and discharges ink droplets from each nozzle at a predetermined timing. Print data expanded to dot pattern data
The data is serially transferred from the I / F 109 to the shift register 113 in synchronization with the clock signal (CK) from the oscillation circuit 107. The print data (S
I) is temporarily latched by the latch circuit 114. The latched print data is boosted by the level shifter 115, which is a voltage amplifier, to a voltage that can drive the switch circuit 116, for example, a predetermined voltage value of about several tens of volts. The print data that has been boosted to a predetermined voltage value is
It is provided to a switch circuit 116 as “switch means”. A drive signal (COM) from the drive signal generation circuit 108 is applied to an input side of the switch circuit 116, and a piezoelectric vibrator 117 as a “pressure generation element” is connected to an output side of the switch circuit 116. ing.

The print data controls the operation of the switch circuit 116. For example, during a period in which the print data applied to the switch circuit 116 is “1”, a drive signal is applied to the piezoelectric vibrator 117, and the piezoelectric vibrator 1
17 expands and contracts. On the other hand, the supply of the drive signal to the piezoelectric vibrator 117 is interrupted while the print data applied to the switch circuit 116 is “0”.

2. Structure of Inkjet Head FIGS. 2 and 3 are views showing the structure of an inkjet head mounted on an inkjet printer according to one embodiment of the present invention.

In the figure, reference numeral 201 denotes a nozzle plate having a nozzle opening 202 formed therein. Further, reference numeral 206 denotes a cavity constituting a flow path, and 207 denotes an elastic plate. The ink plate unit 21 is bonded and sealed with the nozzle plate 201 and the elastic plate 207 so as to sandwich the cavity 206.
1. This ink channel unit 211
A pressure generating chamber 203, a common ink chamber 204, and an ink supply port 205 connecting these are formed, and eject ink droplets or suck ink by extension and contraction of a piezoelectric element 208 described later. .

In the figure, reference numeral 208 denotes a piezoelectric element which is formed by alternately laminating a piezoelectric material and a conductive material in parallel with the extension direction. The piezoelectric element 208 is a so-called longitudinal vibration mode element that contracts in a direction perpendicular to the lamination direction of the conductive layers in a charged state and expands in a direction perpendicular to the conductive layer when the charged state is released. The tip of the piezoelectric element 208 has the elastic plate 2
07, and the other end of the actuator 212 is fixed to the base 209.

The ink flow path unit 211 and the actuator 212 are both in contact with the case head 210 to form a closed circuit dynamically.

The ink jet recording head thus configured has a fluid compliance Ci due to the compressibility of the ink in the pressure generating chamber 203, an elastic plate 207 forming the pressure generating chamber 203, and a nozzle plate. Assuming that the rigidity compliance of the material such as 201 is Cv, the inertance of the nozzle opening 202 is Mn, and the inertance of the ink supply port 205 is Ms, the Helmholtz resonance frequency f of the pressure generating chamber 203 is expressed by the following equation.

[0031]

(Equation 1)

The compliance of the meniscus is C
Assuming that n, the natural oscillation period Tm of the meniscus is expressed by the following equation.

Tm = 2π × {(Mn + Ms) Cn} When the volume of the pressure generating chamber 203 is V, the density of the ink is ρ, and the sound velocity in the ink is c, the fluid compliance Ci is expressed by the following equation. .

Ci = V / ρc ² Further, rigidity compliance Cv of the pressure generating chamber 203
Is equal to the static deformation rate of the pressure generating chamber 203 when a unit pressure is applied to the pressure generating chamber 203.

The cycle Tc of the vibration generated in the meniscus due to the extension and contraction of the piezoelectric element 208 is substantially the same as the cycle obtained by the reciprocal of the Helmholtz resonance frequency f. As a specific example, the fluid compliance Ci is 5 × 10 ^−21.
m ⁵ N ⁻¹ , rigidity compliance Cv is 5 × 10 ⁻²¹ m ⁵
N ⁻¹ , the inertance Mn of the nozzle opening 202 is 1 × 10
⁸ kgm ^-4, Helmholtz resonance frequency f when the inertance Ms of the ink supply port 205 is 1 × 10 ⁸ kgm ^-4
Is 225 kHz, and Tc is 4.4 μs.

3. FIG. 4 is a diagram showing an electric drive pulse according to an embodiment of the present invention. The horizontal axis is the time axis, the vertical axis is the voltage, and reference numeral 401 denotes a first signal, 402 denotes a second signal, and 403 denotes a third signal.
The signal is shown.

Now, when the first signal 401 is applied to the piezoelectric element 208, the piezoelectric element 208 contracts in a direction perpendicular to the elastic plate 207. As a result, the piezoelectric element 208 is
07 is raised to substantially expand the volume of the pressure generating chamber 203. When the volume of the pressure generating chamber 203 increases, a negative pressure is generated in the pressure generating chamber 203, so that the meniscus is drawn from the nozzle opening 202 into the nozzle opening.

If the first signal 401 is shorter than the Helmholtz resonance period Tc, the Tc oscillation system is in an oscillating state, and the oscillation of the period Tc is excited on the meniscus. After that, the Tc vibration generated in the meniscus is caused by the nozzle opening 202
And returns to the outlet of the nozzle, and eventually rises from the nozzle opening surface. The meniscus rising from the nozzle opening surface is
A part of the ink is separated to be ejected as ink droplets. However,
When the driving voltage is low and the meniscus excitation by the first signal 401 is small, the ink droplets may not be ejected because the meniscus is not separated.

Next, when the third signal 403 is applied, the piezoelectric element 208 expands and pushes down the elastic plate 207. As a result, the pressure generating chamber 203 contracts and generates a force in a direction to push the meniscus from the nozzle opening 202. Here, when the duration of the second signal 402 is set so as to drive the third signal 403 within a time range in which the Tc vibration excited by the meniscus in the first signal 401 returns toward the nozzle opening, the nozzle opening 202 The displacement amount and displacement speed of the meniscus which rises from the surface increase. As a result, the mass of the meniscus to be separated increases, so that the amount of ejected ink droplets can be increased. In the ink jet recording apparatus of the present invention, the third signal 403 for pushing up the meniscus
Is adjusted by changing the duration of the second signal 402, and the displacement and displacement speed of the meniscus rising from the nozzle opening 202 are controlled to adjust the ejection ink droplet amount.

In this case, "abruptly" in "abruptly excite the meniscus" of the first aspect means that the second signal 402 and the third signal 403 are excited by the first signal 401 even if they are infinitely long. This means that the ink droplet is ejected by the Tc vibration of the generated meniscus, or that the meniscus is easily oscillated to such an extent that the ink droplet is easily ejected by applying the pushing force of the third signal 403.

Further, the "very small ink droplet" described in claim 1 is an ink droplet which is ejected by a sudden excitation of the meniscus by the first signal 401. (It does not depend on the presence or absence of the influence of the third signal 403.) Since this ink droplet has a smaller amount of ink to be ejected than the ink droplet by the second driving means described in claim 7 described later, such notation is used. Is used.

The method of ejecting ink droplets of the ink jet recording apparatus of the present invention ejects "extremely small ink droplets" utilizing the Tc vibration of the meniscus.
The method is basically different from the method of discharging ink droplets described in Japanese Patent Publication No. 4-36071 in which protrusions generated by a sudden pull-in of a meniscus are separated and discharged.

The present invention modifies the second signal 402 to adjust the amount of influence of the meniscus push-up force by the third signal 403 so as to change the amount of ejected ink droplets or to keep them constant. By doing so, it is possible to provide an ink jet recording apparatus that realizes high printing quality at a photographic quality level.

In this embodiment, the first signal 401 is set to Tc
Meniscus T
The oscillation amount of the c vibration is increased. Also, the second signal 40
By changing the duration of No. 2 within a range of 1/2 or less of Tc, the pushing force by the third signal 403 is effectively applied to the Tc vibration of the meniscus. Furthermore, by setting the third signal 403 that pushes up the meniscus to Tc or a length near Tc or shorter than Tc, the residual vibration of the meniscus after ink droplet ejection is damped, and the peak of the residual vibration is ejected as an ink droplet. Is preventing that.

4. Next, a description will be given based on representative experimental data.

FIG. 5 is an embodiment showing the amount of ink droplet measured by changing the duration of the second signal 402.

The vertical axis in FIG. 5 shows the amount (mass) of the ejected ink droplets, and the horizontal axis shows the duration of the second signal 402. The curve 501 in FIG. 5 is a graph showing the relationship between the ink droplet amount and the second signal 402, and the broken line 502 is the first signal 4
9 is a graph showing the amount of ink droplets ejected only with 01.

In a range where the second signal 402 is short, the pushing up of the meniscus by the third signal 403 affects the ejection of the ink droplet. The influence amount becomes smaller as the second signal 402 becomes longer, so that the longer the second signal 402 is, the smaller the amount of ejected ink droplets becomes. Therefore, the curve 501 in the figure has a downward declining tendency as the second signal 402 becomes longer. However, when the second signal 402 is sufficiently long and the third signal 403 does not affect the ejection of the ink droplet, the amount of the ink droplet is determined only by the oscillation amount of the meniscus by the first signal 401. 2 signals 4
A constant value 502 is obtained regardless of the duration of 02.

In the ink jet recording apparatus according to the present invention, the curve 501 in FIG. 5 has a decreasing tendency, and the range in which the amount of ink droplets ejected by the second signal 402 fluctuates, that is, is indicated by hatching in FIG. The second signal 402 in FIG.
Utilizes a shorter range. Specifically, 5 in FIG.
The duration of the second signal 402, which is 03, is 1 / 2Tc.

5. FIG. 6 is a diagram showing one embodiment of the movement of the meniscus.

In FIG. 6, the horizontal axis is the time axis, the vertical axis is the distance from the nozzle opening surface 603, and the lower side from the nozzle opening surface 603 indicates the inside of the nozzle opening. Also, the curve 60 in FIG.
1, 602 indicates the position of the meniscus, and the hatched portion 60 in the figure.
Areas 7 and 608 indicate the amount of ejected ink droplets.

When the first signal 401 is driven while the meniscus is in a stationary state, and the meniscus is drawn into the nozzle opening, a cosine wave 602 having a period Tc with the center line at the one-dot chain line 604 in the figure is generated in the meniscus. The cosine wave 602 is a damped oscillation, and the meniscus returns to the nozzle opening 202 by its surface tension, so that the center line 604 approaches the nozzle opening surface 603. Here, the second signal 40
When 2 is longer than 1 / 2Tc, the amount of ink droplets to be ejected is determined only by the amount of meniscus oscillation by the first signal 401, and the amount of ink droplets is indicated by a hatched portion 608 in the figure. Also,
When the oscillation of the meniscus due to the first signal 401 is small, 608 in the figure does not exist, that is, the ink droplet may not be ejected.

When the third signal 403 is driven in a range 605 of ＴTc after the first signal 401 where the cosine wave 602 vibrates toward the nozzle opening surface 603, the third signal 40
3 works in the direction of pushing up the meniscus, thereby increasing the amount of ink droplets to be ejected. For example, at time 606, the third signal 403
Is driven, the movement of the meniscus becomes as shown by the curve 601 in the figure, and the amount of the ejected ink drops increases from 608 to 607.

As described above, the ink jet recording apparatus of the present invention can adjust the amount of the ejected ink droplet by changing the second signal 402 within the range of 1 / 2Tc.

6. Printing Method The ink jet recording apparatus of the present invention changes the duration of the second signal 402 every time an ink droplet is ejected. FIG. 7 is a diagram showing an embodiment of printing using such a driving method, in which the horizontal axis represents time and the vertical axis represents voltage. The pulse 701 is an electrical drive pulse when the duration of the second signal 402 is short and the amount of ink droplets is large.
Reference numeral 2 denotes an electric drive pulse when the second signal 402 is long and the amount of ink droplets is small. The dots shown in FIG. 7 indicate the size of the dots formed on the printing target by such an electric drive pulse.

Here, the ink jet recording apparatus of the present invention reduces the amount of ink droplets in a portion where print density is low,
By reducing the diameter of the dots formed on the printing target, the visibility of each dot is reduced, and the printing quality is improved. Further, in response to the difference in print density, the amount of ink droplets is delicately adjusted, and the diameter of dots formed on the print target is changed, thereby improving gradation and improving print quality. For example, as in the case of the pulse 701, a large ink droplet amount is required in a portion where the print density is high. Therefore, the duration of the second signal 402 is shortened to increase the amount of ink droplets to be ejected. As in the case of the pulse 702, the duration of the second signal 402 is extended to eject a small ink droplet.

The change of the second signal 402 can be realized by changing the drive signal from the drive signal generation circuit 108 according to the print density.

7. Initial value of second signal In the inkjet head mounted on the inkjet recording apparatus of the present invention, an initial value of the duration of the second signal 402 is set for each head.

Even if the ink-jet head is driven under the same conditions, if there is a head-to-head difference due to manufacturing variations or parts accuracy variations, the amount of ink droplets to be ejected will not be equal. In particular, when a very small ink droplet is ejected, the print quality greatly changes even with a slight head individual difference, and this head individual difference is a very serious problem.

However, the ink jet recording apparatus of the present invention can change the second signal 402,
By changing the second signal for each ink jet head, the difference between heads can be absorbed, and the same amount of ink droplets can always be ejected even with heads having individual differences.

The initial value of the second signal 402 is set as the initial value by measuring the amount of ink droplets in all the heads at the time of manufacturing and calculating the duration of the second signal 402 for discharging the ink droplet amount as a reference. .

8. Temperature Correction at Ambient Temperature FIG. 8 shows an embodiment in which the change in the ink droplet amount with respect to the duration of the second signal 402 is measured by changing the environmental temperature, similarly to FIG. Curve 801 in FIG. 8 is obtained when the ambient temperature is 40 ° C.
A curve 802 shows the characteristics of the ink droplet amount when the environmental temperature is 10 ° C. A curve 501 is the data of FIG. 5 and is obtained when the environmental temperature is 25 ° C.

In general, the ink used in an ink jet printer has a lower viscosity and a higher fluidity as the temperature is higher.
Conversely, the lower the temperature, the higher the viscosity, and the harder it is to flow. The meniscus formed in the nozzle opening 202 also exhibits similar characteristics depending on the environmental temperature. Therefore, when the temperature is high, the amount of ink droplets ejected by vibrating greatly increases, and when the temperature is low, the vibration decreases and the amount of ink droplets decreases. Become. Therefore, the curve 801 at the environmental temperature of 40 ° C. shifts to the side where the amount of ink drops increases, and the curve 802 at the environmental temperature of 10 ° C. shifts to the side where the amount of ink drops decreases, compared to the curve 501 where the environmental temperature is 25 ° C. ing.

Now, when trying to eject ink droplets having the ink droplet amount 803 in FIG. 8, when the environmental temperature is 25 ° C., the duration of the second signal 402 is set to 804. Similarly, the length may be set to 805 when the environmental temperature is 40 ° C., and to 806 when the environmental temperature is 10 ° C.
Further, when the environmental temperature is higher than 25 ° C. and lower than 40 ° C., a graph indicating the relationship between the duration of the second signal 402 and the ink droplet amount exists between the curve 501 and the curve 801 in FIG. The duration of signal 402 is represented by 804 and 8 in FIG.
05, the same ink droplet volume 803
Can be discharged. Similarly, when the environmental temperature is lower than 25 ° C. and higher than 10 ° C., the second signal is set to 804 and 806.
It may be set between.

The second signal 40 for such an environmental temperature
FIG. 9 shows an embodiment in which the relationship of 2 is obtained from an experiment. FIG.
The horizontal axis represents the environmental temperature, the vertical axis represents the duration of the second signal 402, and the curve 901 represents the relationship between the environmental temperature and the duration of the second signal 402. Using the temperature correction table for the environmental temperature as shown in FIG.
By changing the duration of 02, it is possible to always eject a constant amount of ink droplets without being affected by the environmental temperature.

The ink jet recording apparatus of the present invention has a feature that by changing the duration of the second signal 402 depending on the environmental temperature, it is possible to always provide a constant print quality irrespective of the environmental temperature. . In addition, the present inventor
The experiment was performed in an environment temperature range of from 40 ° C. to 40 ° C., but we are convinced that qualitatively equivalent effects can be obtained outside this temperature range.

9. Reliability The ink jet head mounted on the ink jet type recording apparatus of the present invention has a time during which the nozzle opening 202 is exposed to the air. As a result, a film or an ink thickened portion having an increased ink viscosity is formed.
The ink thickening portion often hinders the ejection of ink droplets, and is a major problem in securing printing reliability.

One method of destroying such an ink thickened portion is to discharge several ink droplets outside the printing area of the printer to discharge the thickened ink (called flushing). In such a method, it is necessary to apply more energy to the meniscus than during printing so that the ink thickened portion can be destroyed.

Therefore, in the ink jet recording apparatus of the present invention, when the ink having the increased viscosity is discharged, the duration of the second signal 402 is shortened, and the influence of the meniscus pushing force by the third signal 403 is reduced. Increase the amount,
It has a function to reliably eject ink with increased viscosity. The inventor of the present invention has conducted experiments by shortening the duration of the second signal 402 during flushing to half the initial value of the head, and confirmed the effect. However, the second signal 4 during flushing
The duration of 02 is not limited to this, since it depends on the specifications of the head to be used, the ink, and the environmental temperature.

In the ink jet recording apparatus of the present invention, the continuation of the second signal 402 is performed only when the first droplet immediately after the pause is ejected from a nozzle that has not ejected an ink droplet for a predetermined time or more. It has a function to shorten the time. This is to shorten the second signal 402 to increase the influence of the third signal 403, and to destroy the ink thickened portion formed on the meniscus during the pause. by the way,
How long the “constant time” according to claim 6 corresponds to a pause time, and how much the second signal 402 is shortened, depend on the specifications of the ink jet head to be used, the ink to be used, and the use of the ink. Therefore, it is necessary to cope with each condition. However, by using this method, the first 1
It is possible to achieve the same ejection of ink droplets as in normal times from the droplets.
The inventor conducted an experiment in the case where there was a printing interval of 1 ms as the fixed time according to claim 6, and confirmed the effect. At this time, the value of the second signal 402 used was の of the initial value set for each head. 10. Combination with another drive means The ink jet recording apparatus of the present invention is characterized in that:
Has a function of performing printing in combination with another driving unit different from the driving unit described in (1).

FIG. 10 is a diagram showing an electric driving pulse of the driving means used in the ink jet recording apparatus of the present invention shown in FIG. 4 and an electric driving pulse of the second driving means according to claim 7. It is. The horizontal axis is a time axis, the vertical axis is a voltage, a pulse 1001 is an electric drive pulse of the driving unit according to claim 1, and a pulse 1002 is a second pulse according to claim 7.
Is an electric driving pulse by the driving means. Reference numeral 1003 in the drawing corresponds to “1 printing cycle”.

In the electric drive pulse of the second drive means, reference numeral 1004 in the figure denotes a fourth signal, 1005 denotes a fifth signal, and 1006 denotes a sixth signal.

As described in claim 7, the fourth signal 10
04 is driven more gently (longer) than the first signal 401, so that even if the fifth signal 1005 and the sixth signal 1006 are made infinitely long, no ink droplet is ejected. The second driving unit 1002 gradually expands the pressure generation chamber 203 to sufficiently fill the pressure generation chamber 203 with ink.
Since the pressure generating chamber 203 is contracted by the sixth signal 1006 to discharge ink droplets, the fourth signal 1004
And the fifth signal 1005 are infinitely long, the sixth signal 1
006 ejects ink droplets. Further, a driving method such as the second driving means discharges ink droplets after sufficiently filling the pressure generating chamber 203 with ink, and is therefore excellent in discharging a relatively large amount of ink droplets.

By the way, in the ink jet recording apparatus, it is necessary to secure a sufficiently high ink density by discharging a very large ink droplet. But,
With the driving means according to the first aspect, it is difficult to eject a very large ink droplet. Therefore, by using in combination with an ink droplet ejection unit such as the second driving unit according to the seventh aspect, it is possible to eject a very small ink droplet to a large ink droplet that can secure a sufficient print density. Printing quality can be improved. FIG.
FIG. 11 is a diagram illustrating combinations that can be realized and sizes of dots formed on a printing target when printing is performed using the electric drive pulse illustrated in FIG. 10. The combination pattern includes a pattern 1101 for ejecting small ink droplets by the driving unit according to claim 1, a pattern 1102 for ejecting ink droplets by the second driving unit according to claim 7,
A pattern 1103 that drives both driving units in one printing cycle 1003 can be considered. The diameter of the dots formed on the print target is determined by the patterns 1101, 110
It becomes larger in the order of 2, 1103. By selecting and implementing such a combination for each nozzle opening 202,
High print quality at the photographic quality level can be realized.

The driving means and the electric driving pulse used in the ink jet recording apparatus of the present invention are shown in FIG.
The driving pulse is not limited to 0 and the driving pulse shown in FIG. 11, but can be combined with many other driving pulses. In this case, it can be easily considered that the combination pattern of the electric drive pulses as shown in FIG. 11 also changes depending on the combined drive pulses.

11. Other Finally, the examples given here have a Tc of 4 μs to illustrate embodiments of the present invention.
To 20 μs, the diameter of the nozzle opening 202 is a representative example of an experiment performed with an inkjet printer equipped with an inkjet head having a diameter of 20 μm to 40 μm,
It is not limited to this.

[0077]

As described above, in the ink jet recording apparatus according to the present invention, in the ejection of a very small ink droplet, the duration of the second signal is changed to reduce the amount of the ink droplet. Adjustment can achieve high print quality at the photographic quality level.

In the ink jet recording apparatus of the present invention, by changing the duration of the second signal in the ejection of very small ink droplets, the ink jet recording apparatus is not affected by individual differences of heads and environmental temperature, and thus always prints. The same amount of ink droplets can be ejected, and stable printing quality can be provided.

In the ink jet recording apparatus of the present invention, by changing the duration of the second signal, the effect of flushing can be enhanced, or stable ejection can be achieved even when ink droplets are ejected immediately after pausing. It can provide reliable and stable printing quality.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of an ink jet printer which is an embodiment of an ink jet recording apparatus of the present invention.

FIG. 2 is a sectional view showing an embodiment of an ink jet head mounted on the ink jet type recording apparatus of the present invention.

FIG. 3 is an assembly diagram showing one embodiment of an ink jet head mounted on the ink jet type recording apparatus of the present invention.

FIG. 4 is a diagram showing an embodiment of an electric drive pulse of an ink jet head mounted on the ink jet type recording apparatus of the present invention.

FIG. 5 is a diagram illustrating an example in which the relationship between the duration of the second signal and the amount of ejected ink droplets is measured by the inkjet head mounted on the inkjet recording apparatus of the present invention.

FIG. 6 is a diagram illustrating an example of meniscus vibration of an ink jet head mounted on the ink jet recording apparatus of the present invention.

FIG. 7 is a diagram showing an embodiment of printing performed by changing an electric drive pulse of an ink jet head mounted on the ink jet type recording apparatus of the present invention.

FIG. 8 is a diagram illustrating an example in which the relationship between the duration of the second signal and the amount of ejected ink droplets is measured by changing the environmental temperature in the inkjet head mounted on the inkjet recording apparatus of the present invention. is there.

FIG. 9 is a diagram showing one embodiment of the temperature correction of the second signal in the ink jet recording apparatus of the present invention.

FIG. 10 is a diagram showing an embodiment of an electric drive pulse of an ink jet head mounted on an ink jet type recording apparatus of the present invention and an electric drive pulse by a second driving means according to claim 7;

FIG. 11 is a diagram showing an embodiment of a combination of an electric drive pulse of the ink jet head mounted on the ink jet recording apparatus of the present invention and an electric drive pulse by the second driving means according to claim 7; .

FIG. 12 is a diagram showing a conventional example of an electric drive pulse used in Japanese Patent Publication No. 4-36071.

[Explanation of symbols]

 201 Nozzle plate 202 Nozzle opening 203 Pressure generating chamber 207 Elastic plate 208 Piezoelectric element 401 First signal 402 Second signal 403 Third signal

Claims (7)

[Claims] 1. An ink jet comprising: a pressure generating chamber communicating with a common ink chamber through a nozzle opening and an ink supply port and having a Helmholtz resonance frequency of a period Tc; and an element for expanding and contracting the pressure generating chamber. In an ink jet recording apparatus provided with at least one or more heads, a first signal generating means for expanding the pressure generating chamber and rapidly exciting a meniscus in a nozzle opening, and an expanded state of the pressure generating chamber. A driving unit including a second signal generation unit for holding and a third signal generation unit for contracting the pressure generation chamber; and changing a duration of the second signal to thereby open the nozzle opening. An ink jet recording apparatus equipped with a function for adjusting the amount of very small ink droplets ejected from a printer. 2. The method according to claim 1, wherein the duration of the second signal is changed within a range in which a larger amount of ink is ejected when the duration of the second signal is sufficiently long. Item 2. An ink jet recording apparatus according to Item 1. 3. The ink jet type according to claim 1, further comprising a function of changing the duration of the second signal for each ink jet head according to the initial value of the second signal set for each ink jet head. Recording device. 4. The ink jet recording apparatus according to claim 1, further comprising a function of changing a duration of the second signal according to an environmental temperature. 5. The ink jet recording apparatus according to claim 1, further comprising a function of driving the duration of the second signal shorter than the initial value in the flushing. 6. The method according to claim 1, wherein the first and second ink droplets are ejected immediately after the nozzles at intervals of printing for a predetermined time or more.
2. The ink jet recording apparatus according to claim 1, further comprising a function of driving the duration of the signal shorter than the initial value. 7. The driving means according to claim 1, further comprising: fourth signal generating means for expanding the pressure generating chamber more slowly than the first signal, and maintaining an expanded state of the pressure generating chamber. And a second signal generating means for contracting the pressure generating chamber and ejecting ink droplets, the second signal generating means comprising: a second signal generating means for contracting the pressure generating chamber and ejecting ink droplets. , The second driving means,
An ink jet recording apparatus having a function of selecting or combining and driving within one printing cycle.