JPH09193377A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to stably discharge ink droplet in a variable area after the droplet is discharged and to improve the discharge frequency by eliminating the discharge of the ink in an area that the ink droplet volume is abruptly deceased as the droplet discharge timing is lengthened. SOLUTION: The maximum driving frequency fmax is set so that the ink droplet discharge timing is existed in the variable area 7 that the ink droplet volume is increased as the droplet discharge timing is lengthened in the first variable area of the earliest timing in the variation of the ink droplet volume Mj at the droplet discharge timing. Thus, the ink droplet discharge failure scarcely occurs due to the bubble engulfing, the ink droplet discharge can be stably conducted, and stable ink droplet discharge can be conducted under all driving conditions. The change in the meniscus and the ink droplet discharge characteristics are largely related, but the actually driving frequency is driven by 1/n (n is integer) or 1/(n+0.5) of the maximum driving frequency fmax.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly, to an ink jet recording apparatus having one or a plurality of nozzles for ejecting ink droplets, in which the volume of ink droplets fluctuates depending on the difference in droplet ejection timing.

[0002]

2. Description of the Related Art A drop-on-demand (DOD) type ink jet recording apparatus ejects, for example, an ink droplet.
Alternatively, a plurality of nozzles, a liquid chamber communicating with the nozzles, and an actuator (driving source) including an electromechanical conversion element such as a piezoelectric element for pressurizing the liquid chamber or a thermomechanical conversion element such as a thermal resistor are provided. By using an inkjet head, ink droplets are ejected and ejected from nozzles only when a recording signal is input to perform high-speed, high-resolution recording.

By the way, in the DOD type ink jet recording apparatus, the ink droplet ejection characteristics (ink ejection characteristics) are designed to be constant at every droplet ejection timing drive, but the ink droplet ejection characteristics are stabilized. In order to do so, it is necessary to wait until the various vibrations remaining after the droplet ejection are sufficiently attenuated. On the other hand, since it has been waiting until the residual vibration after the droplet ejection is sufficiently attenuated, high-speed printing becomes difficult.

Therefore, conventionally, for example, Japanese Patent Laid-Open No. 63-495 has been used.
As described in Japanese Patent Publication No. 7, the highest drive frequency is set to a frequency that can obtain an ejection speed in a region where the ink droplet ejection velocity fluctuates and in a region where the ejection velocity is stable, Alternatively, as described in Japanese Examined Patent Publication No. 3-42185, it corresponds to each of a plurality of frequency components included in the drive signal formed by dividing only the period of the reference signal of the alternating waveform by 1 / n. It is known that the frequency of the reference signal is set so that the threshold voltages (what the threshold voltage is and what the threshold voltage is) are substantially equal.

[0005]

In the conventional ink jet recording apparatus described above, the liquid ejection timing is advanced by ejecting the liquid in the variable region without waiting for a sufficient stable region after the ink droplet is ejected. It is what However, when the ink droplets are ejected in the variable area after the ink droplets are ejected, the frequency at which the ejection speed equivalent to that in the low frequency drive area is obtained is set to the maximum drive frequency or included in the drive signal as described above. When the frequency of the reference signal (maximum drive frequency) is set so that the threshold voltages corresponding to each of the plurality of generated frequency components become substantially equal, stable ink droplet ejection cannot be performed.

The present invention has been made in view of the above points, and an ink jet that further improves the ink drop ejection frequency by making it possible to stably eject ink drops in a variable region after ink drops are ejected. It is an object to provide a recording device.

[0007]

In order to solve the above-mentioned problems, an ink jet recording apparatus according to a first aspect of the invention has one or a plurality of nozzles for ejecting ink droplets, and the ink droplet volume causes a difference in droplet ejection timing. In an inkjet recording device equipped with an inkjet head that varies depending on
The ink droplets are not ejected in an area where the ink droplet volume fluctuation exceeds a predetermined allowable fluctuation range and in which the ink droplet volume sharply decreases as the droplet ejection timing becomes longer.

An ink jet recording apparatus according to a second aspect of the present invention is an ink jet recording apparatus having an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates depending on a difference in droplet ejection timing. The ink droplets are ejected in an area in which the ink droplet volume fluctuation exceeds a predetermined allowable fluctuation width and the ink droplet volume increases as the droplet ejection timing becomes longer.

An ink jet recording apparatus according to a third aspect of the present invention is an ink jet recording apparatus having an ink jet head having one or a plurality of nozzles for ejecting ink droplets, and the ink droplet volume fluctuating due to a difference in droplet ejection timing. At a region where the ink drop volume fluctuation exceeds a predetermined allowable fluctuation range, the ink drop volume increases as the droplet ejection timing becomes longer, and at a timing when the ink drop volume falls within the allowable fluctuation range. The ink droplets are ejected.

An ink jet recording apparatus according to a fourth aspect is the ink jet recording apparatus according to any one of the first to third aspects, in which the allowable variation range of the ink droplet volume variation is based on the ink droplet volume at a sufficiently slow droplet ejection timing. As ±
Within 20%.

An ink jet recording apparatus according to a fifth aspect is the ink jet recording apparatus according to any one of the first to fourth aspects, in which two or less inflection points are provided in an area where the variation of the ink droplet volume exceeds the allowable variation range. It has a configuration.

An ink jet recording apparatus according to a sixth aspect is the ink jet recording apparatus according to any one of the first to fifth aspects, in which the droplet ejection timing region is faster than twice the droplet ejection timing when driven at the highest driving frequency. In the structure, there is an area exceeding the allowable fluctuation range.

According to a seventh aspect of the present invention, there is provided an ink jet recording apparatus having one or a plurality of nozzles for ejecting ink droplets, the ink jet head having an ink jet head in which the volume of the ink droplets fluctuates due to a difference in droplet ejection timing. The drive frequency exists in the first variation range in which the droplet ejection timing is the earliest in the variation of the ink droplet volume, and in the variation range in which the ink droplet volume increases as the droplet ejection timing becomes longer. Set to frequency.

The ink jet recording apparatus according to claim 8 is the highest ink jet recording apparatus provided with an ink jet head having one or a plurality of nozzles for ejecting ink droplets and in which the ink droplet volume fluctuates depending on the difference in droplet ejection timing. The driving frequency is
In the first fluctuation range with the earliest timing in the fluctuation of the ink droplet volume, and on the slope side where the ink droplet volume increases as the droplet ejection timing becomes longer, at other low frequency driving and the ink droplet volume approximately Are set to a frequency that makes them equal.

According to a ninth aspect of the present invention, there is provided an ink jet recording apparatus having an ink jet head having one or a plurality of nozzles for ejecting ink droplets, and the ink droplet volume fluctuating due to a difference in droplet ejection timing. The droplet ejection timing is in the first fluctuation range with the earliest timing in the fluctuation of the ink drop volume and in the vicinity of the maximum value or the minimum value of the fluctuation of the ink drop volume.

According to a tenth aspect of the present invention, there is provided an ink jet recording apparatus comprising:
The ink jet recording apparatus according to any one of claims 7 to 9, wherein the droplet ejection timing that is 1.5 times or twice as slow as the droplet ejection timing at the highest drive frequency is set to the first
The timing is set so that it does not overlap with the region where the ink droplet volume sharply decreases as the droplet ejection timing in the fluctuation range of 2 becomes longer.

The ink jet recording apparatus according to claim 11 is
In the ink jet recording apparatus according to any one of claims 1 to 10, the actuator for ejecting the ink droplet is composed of a piezoelectric element, and a drive pulse for driving the piezoelectric element by a push drive system is applied.

The ink jet recording apparatus according to claim 12 is
In the ink jet recording apparatus according to the eleventh aspect, the time constant of the falling portion of the drive pulse is made longer than the time constant of the rising portion.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is an external perspective view showing an example of an inkjet head in an inkjet recording apparatus according to the present invention, FIG. 2 is an exploded perspective view of FIG. 1, and FIG.
1 is an enlarged cross-sectional view of the main part taken along the line AA of FIG.
It is a principal part expanded sectional view along a line.

This ink jet head has an actuator unit 1 having a plurality of piezoelectric elements arranged in rows.
And a plurality of pressurized liquid chambers joined to the actuator unit 1 and pressurized by the plurality of piezoelectric elements via the deforming portion, and a plurality of nozzles communicating with the plurality of pressurized liquid chambers. And the liquid chamber unit 2.

The actuator unit 1 has two rows of piezoelectric element rows 4 and 4 in which a plurality of piezoelectric elements are provided in rows on an insulating substrate 3 such as ceramic, and these two rows of piezoelectric element rows 4 and 4. A frame 5 that surrounds the periphery of is bonded by an adhesive 6. The piezoelectric element array 4 includes a plurality of piezoelectric elements (hereinafter referred to as “driving section piezoelectric elements”) 7, 7 ... To which a driving waveform for giving ink droplets and causing the ink to fly is provided, and the driving section piezoelectric elements 7, 7. A plurality of piezoelectric elements (which are referred to as “fixed portion piezoelectric elements”) 8, 8 ... Which are located between and which simply fix the liquid chamber unit 2 to the substrate 3 are alternately arranged.

Here, the substrate 3 of the actuator unit 1 has a thickness of about 0.5 to 5 mm and is made of a material similar to a piezoelectric element, and can be cut together with the piezoelectric element by, for example, a diamond grindstone. Preferably,
In this embodiment, a ceramic substrate is used. An ink supply hole 3a is formed at the end of the substrate 3, and an ink supply pipe 19 is connected to the ink supply hole 3a to supply ink to the liquid chamber in the liquid chamber unit 2. The formation position of the ink supply hole 3a is not limited to the end portion of the substrate 3.

As the driving portion piezoelectric element 7 and the fixed portion piezoelectric element 8 constituting the piezoelectric element array 4, a laminated piezoelectric element having 10 or more layers is used. This laminated piezoelectric element has a thickness of 20 to 50 μm / 1 as shown in FIGS. 7 and 8, for example.
PZT (= Pb (Zr.Ti) O ₃ ) 20 of the layer and a thickness μ
The internal electrodes 21 made of silver / palladium (AgPd) of m / 1 layer are alternately laminated. The drive voltage can be reduced by making the piezoelectric element a stacked type having a thickness of 20 to 50 μm / 1 layer. For example, an electric field strength of 1000 V / mm can be obtained with a pulse voltage of 20 to 50 V.

Then, the internal electrodes 2 of each driving portion piezoelectric element 7
Left and right end face electrodes 22, 2 made of AgPd every other layer
3 (the end faces of the two piezoelectric element arrays 4 and 4 that face each other of the drive portion piezoelectric elements 7 are referred to as end face electrodes 22 and the non-opposed faces are referred to as end face electrodes 23). , 4
The opposite end face electrodes 22 of the piezoelectric elements 7 of the respective driving parts are connected to a common electrode 25 which is an external electrode composed of a Ni / Au vapor deposition pattern via a conductive adhesive 24, while the other two piezoelectric element rows 4, 4 are connected. The end surface electrodes 23 of the respective drive section piezoelectric elements 7 which are not opposed to each other are connected to each drive individual electrode (selection electrode) 27 which is an external electrode having a Ni / Au vapor deposition pattern through the same conductive adhesive 26. An FPC cable 28 is connected to the common electrode 25 and the individual driving electrodes 27. By applying a drive voltage to the drive piezoelectric element 7 via the FPC cable 28, an electric field is generated in the stacking direction, and the drive piezoelectric element 7 is displaced in the extension direction in the stacking direction.

The frame 5 is made of resin, as shown in FIG.
A plate-like member made of ceramics or the like is formed with through holes 5a and 5b corresponding to the piezoelectric element arrays 4 and 4, and the liquid chamber unit 2 is bonded to the periphery of the piezoelectric element arrays 4 and 4. It serves to fix and reduce mutual interference. The frame 5 is provided with an ink supply hole 5c corresponding to the ink supply hole 3a of the substrate 3 (the formation location is not limited).

The material of the frame 5 is preferably one that is excellent in dimensional stability and does not affect the image quality even if the operating environment of the head is shaken within a range of several tens of degrees. For example, resin, ceramics, Although metal or the like can be used, ceramics similar to those used for the driving portion piezoelectric element 7 and the substrate 3 are particularly preferable. When a resin is used as the frame 5, a resin in which a filler that reduces the thermal expansion coefficient is mixed with an engineering plastic resin, such as polyphenylene sulfide, polyether sulfone, polyimide, or epoxy resin, It is preferable to mix a filler such as titanium, alumina, glass filler, carbon or silica. In this way, by using the resin in which the filler that reduces the coefficient of thermal expansion is mixed, the coefficient of thermal expansion can be brought close to that of the driving portion piezoelectric element 7 and the fixed portion piezoelectric element 8 of the piezoelectric element array 4. Moreover, the cost of parts can be reduced.

The liquid chamber unit 2 has two layers (one layer or three layers or more) made of a photosensitive resin film (dry film resist) for forming the pressurized liquid chamber 17 and the like on the vibration plate 12 having the diaphragm portion 11 formed thereon. The liquid chamber flow path forming member 13 having a structure is adhered, and 2 is formed on the liquid chamber flow path forming member 13.
A nozzle plate 16 having a plurality of nozzles 15 formed in a row is bonded. The liquid chamber unit 2 is joined to the actuator unit 1 with high rigidity as a whole by joining required portions of the vibrating plate 12 to the piezoelectric elements 7 and 8 and the frame 5 with the adhesive 18. There is.

The vibrating plate 12 is made of a Ni (nickel) metal plate manufactured by the electron forming method (electroforming). The vibration plate 12 is the liquid chamber flow path forming member 1
The diaphragm portion 12a, the joint region 12b, and the relief region 12c having different thicknesses are formed on the piezoelectric element array 4 side in the direction orthogonal to the channel direction on the third side as a flat surface, and the drive portion piezoelectric element 7 of the piezoelectric element array 4 is formed. , 7 ... are formed with diaphragm portions 11, 11 ...

The diaphragm region 12a has a thickness of 3-1.
It is an elastic portion that is deformed in accordance with the displacement of the driving portion piezoelectric element 7 which is set to about 0 μm. The joint region 12b is the thickest region to be joined to the drive portion piezoelectric element 7, the fixed portion piezoelectric element 8 and the frame 5 of the piezoelectric element array 4, and is formed to have a thickness of, for example, about 20 μm or more. . in this case,
As shown in FIG. 8, in the direction orthogonal to the channel direction,
A portion of each joining region 12b corresponding to the fixed portion piezoelectric element 8 becomes a beam portion 12e for joining the liquid chamber unit 2 to the fixed portion piezoelectric element 8. Further, the escape area 12c is an area having an intermediate thickness and is an escape area for avoiding contact with the driving portion piezoelectric element 7.

The liquid chamber flow path forming member 13 is located between the upper surface of the vibrating plate 12 and the lower surface of the nozzle plate 16 as described above, and forms each pressurized liquid chamber 17 corresponding to each piezoelectric element 7 of the drive section. In addition, common liquid chambers 31 located on both sides of each pressurized liquid chamber 17 for supplying ink to each pressurized liquid chamber 17, and ink supply that communicates both sides of each pressurized liquid chamber 17 with the common liquid chamber 31. The fluid resistance portions 32 and 32, which are the fluid resistance portions that also serve as the paths, are formed. The liquid chamber flow path forming member 13 is
In the manufacturing process, the lower liquid chamber flow path forming layer 33 in which a required liquid chamber pattern is formed on the upper surface of the diaphragm 12 by using a dry film resist (photosensitive resin film) and a required liquid by using the dry film resist. It has a two-layer structure in which the upper liquid chamber flow path forming layer 34 having the chamber pattern is joined.

A large number of nozzles 15 that are fine holes for ejecting ink droplets are formed on the nozzle plate 16, and the diameter of the nozzle 15 is 35 at the ink droplet outlet side.
The nozzle 15 is formed to have a size of less than or equal to μm, and is provided at a position facing the diaphragm portion 11 of the vibrating plate 12 and corresponding to the vicinity of the center of the pressurized liquid chamber 17. This nozzle plate 1
6 also uses a Ni (nickel) metal plate manufactured by the electron forming method (electroforming) similarly to the diaphragm 12, but Si and other metal materials can also be used. Actually, one inkjet head is manufactured with a structure of 64 to 128 in which two nozzles 15 of 32 to 64 are arranged in two rows. However, the quality of the nozzle plate 16 having the nozzles 15 of 128 to 128 is produced. Determines the drop shape and flight characteristics of the ink and has a great influence on the image quality.

This ink jet head having the above-mentioned structure is manufactured by separately assembling the actuator unit 1 and the liquid chamber unit 2 in advance, and then adhesively joining the two units 1 and 2.

The process of assembling and assembling the liquid chamber unit 2 will be described. First, the member in which the lower liquid chamber flow path forming layer 33 is formed on the vibrating plate 12 is manufactured as follows. The vibrating plate 12 made of a Ni (nickel) metal plate by using the electron forming method (electroforming) in advance.
After manufacturing, the negative dry film resist which is a photosensitive resin for forming the lower liquid chamber flow path forming layer 33 is laminated on the flat surface of the vibration plate 12 by heat and pressure. The thickness of this dry film resist is 20-
It is about 50 μm.

Ultraviolet ray (UV light) exposure is performed using a mask corresponding to the flow path pattern to cure the exposed portion. By developing with a solvent capable of removing the unexposed portion to remove the unexposed portion, the lower liquid chamber flow path forming layer 3
3 to form a liquid chamber pattern. Thereby, the liquid chamber patterning on the entire surface can be performed at one time. After rinsing with water and drying, it is fully cured again by exposure to ultraviolet light and heating.

On the other hand, similarly to the vibrating plate 12 side, a member in which the upper liquid chamber flow path forming layer 34 is formed on the nozzle plate 16 side is manufactured. That is, the nozzle 15 made of a Ni (nickel) metal plate is previously formed by using an electron forming method (electroforming).
After the nozzle plate 16 having the above is manufactured, a negative dry film resist, which is a photosensitive resin for forming the upper liquid chamber flow path forming layer 34, is laminated on the flat surface of the nozzle plate 16 by heat and pressure. The thickness of this dry film resist is about 40 to 100 μm.

Ultraviolet (UV) light exposure is performed using a mask corresponding to the flow path pattern to cure the exposed portion. By developing with a solvent capable of removing the unexposed portion and removing the unexposed portion, the upper liquid chamber flow path forming layer 3
4 forms a liquid chamber pattern. Thereby, the liquid chamber patterning on the entire surface can be performed at one time. After rinsing with water and drying, it is fully cured again by exposure to ultraviolet light and heating.

Then, the corresponding surfaces of the lower liquid chamber flow channel forming layer 33 and the upper liquid chamber flow channel forming layer 34 made of the dry film resist formed on the vibrating plate 12 and the nozzle plate 16 as described above To join. This joining is performed using a positioning jig, and pressure and heating at a higher temperature than in the main curing are performed. Actually, in the above steps, assembling is performed using a plate having a head area corresponding to a plurality of heads.

Next, an example of a head drive circuit for driving such an ink jet head will be described with reference to FIGS. This head drive circuit applies a power supply switching circuit 41 that switches a drive voltage Vp in accordance with a print timing signal, and a drive voltage Vp from this power supply switch circuit 41 to each of the piezoelectric elements 4, 4, ... Of the inkjet head H. Fixed charging resistor circuit 42
And a variable discharge resistance circuit 43 and a selection circuit 44 for selecting a piezoelectric element to be driven among the piezoelectric elements 4, 4, ... Of the respective drive units of the ink jet head H in accordance with print data.

As shown in FIG. 6, the power supply switching circuit 41 of the head drive circuit includes a base of a PNP transistor Tr1 for inputting a print timing signal to the base via a buffer B and a base via an inverter I, for example. And an NPN transistor Tr2 for input to
The drive voltage Vp is applied to the emitter of the transistor Tr1 and the emitter of the transistor Tr2 is grounded. The buffer B has a drive voltage Vp when the input is “H”.
A lower predetermined voltage is output, and when the input is "L", the same voltage as the drive voltage Vp is output.

The connection between the emitter of the transistor Tr1 and the collector of the transistor Tr2 is connected to the driving portion piezoelectric element 4 of the ink jet head H through the charging resistance circuit 42 including the diode Da and the charging resistance ra. It is connected to the driving portion piezoelectric element 4 of the inkjet head H via a discharge resistance circuit 41 composed of a diode Db and a discharge resistance rb.

In this head drive circuit, when the print timing signal is applied, the drive voltage V is supplied from the buffer B.
A predetermined voltage lower than p is output and the transistor Tr1
Is turned on, and a driving waveform having a charging time constant determined according to the resistance value of the charging resistor ra is applied to each driving portion piezoelectric element 4 of the inkjet head H. At this time, the transistor Tr2 is in the off state. When the print timing signal is no longer applied, the transistor T
r1 is turned off, transistor Tr2 is turned on, and discharge is performed with a discharge time constant determined according to the resistance value of discharge resistor rb.

Therefore, by decreasing the resistance value of the discharge resistance rb to decrease the discharge time constant, a drive waveform having a sharp fall can be obtained, and the resistance value of the discharge resistance rb can be increased to increase the discharge time constant. As a result, a drive waveform that falls relatively slowly can be obtained.

Therefore, the setting of the ejection timing and the maximum driving frequency in the ink jet recording apparatus having the ink jet head and the head drive circuit configured as described above will be described with reference to FIG. First,
In the on-demand type inkjet recording device,
Generally, the flight characteristics of ink droplets (ink droplet volume Mj, ink droplet velocity Vj) exhibit the behaviors shown in FIGS. 7 and 8, respectively.

That is, the ink drop velocity (flying velocity) Vj
Is influenced by the pressure applied to the ink liquid chamber and the diameter of the nozzle hole for ejecting ink, so that the driving frequency becomes large (higher) as shown in FIG. 7, that is, as the driving timing becomes faster, The residual pressure in the ink liquid chamber has an effect, and a vibration phenomenon as shown in the figure appears. Further, since the ink droplet volume (ink droplet ejection amount) Mj is largely related to the pressure generation timing in the ink liquid chamber and the position of the meniscus of the nozzle hole, in the time band in which the position of the meniscus fluctuates greatly, As shown in FIG. 8, the ejected ink droplet volume Mj also greatly changes.

Therefore, in the general design of ink drop flying performance, as the maximum driving frequency fmax, as shown in FIGS. 7 and 8, the ink drop velocity Vj and the ink drop volume M are set.
The frequency fv having the highest value in the region where j does not show the vibration phenomenon is selected.

On the other hand, in the present invention, the image quality is controlled by controlling the drive cycle characteristics of the ink drop velocity Vj and the ink drop volume Mj as shown in FIGS. 7 and 8 and further adjusting the drive timing. And the printing speed, that is, the ink droplet ejection frequency is improved.

That is, first, the relationship between the ink drop velocity Vj, the ink drop volume Mj, and the meniscus behavior will be described. The particle size characteristic (Vj or Mj) of the ink drop in a sufficiently stable state is the composition of the ink liquid chamber. , Nozzle shape
Although it depends on the size and the driving method, the particle formation characteristics of the ink droplets in the unstable fluctuation region are very much related to the behavior of the meniscus formed in the nozzle.
Therefore, by controlling the meniscus behavior by the head configuration, stable ink droplet ejection in the fluctuation range becomes possible.

The position of the meniscus behaves as shown in FIG. 9A until the stable state is reached after the liquid is discharged. That is, the meniscus is in a position where it is largely drawn in after the ink droplet is ejected, and then returns to the initial meniscus position as ink is refilled (refilled) in the ink liquid chamber. Then, after the meniscus passes through the initial position, it causes a dynping oscillation centering on that position, and gradually shifts to a stable region.

At this time, if the refilling capacity is large, the meniscus returns quickly, but the amplitude of vibration also increases,
As a result, the time required for the vibration to damp to the stable region (damping time) becomes slow. On the contrary, if the refilling ability is small, the vibration of the meniscus is small, but the return of the meniscus is delayed, and as a result, the time to reach the stable region is delayed. Here, since the ink refill ability can be controlled by the liquid chamber configuration, the nozzle shape, etc., the behavior of the meniscus can be controlled by controlling the liquid chamber configuration, the nozzle shape, etc.

The behavior of this meniscus and the ink drop volume Mj
9B, the behavior of the ink droplet volume Mj with respect to the driving timing of the ink droplet ejection is as shown in FIG. 9B, which is almost the same as the behavior of the meniscus in FIG. 9A. . In the meniscus fluctuation region, the position where the value of the ink drop volume Mj is similar to that of the stable region coincides with the timing when the meniscus passes the initial meniscus position, and the meniscus is in the droplet flying direction (direction opposite to the liquid chamber) from the initial meniscus position. The value of the ink drop volume Mj is large in the area projecting to the inside, and conversely, the ink drop volume Mj is in the area retracted from the initial meniscus position toward the liquid chamber.
The value of j becomes smaller.

The behavior of the meniscus and the ink drop velocity V
Looking at the relationship with the fluctuation of j, the behavior of the ink droplet velocity Vj with respect to the driving timing of the ink droplet ejection is as shown in FIG. 7C, while the behavior of the meniscus is shown by the moving velocity in FIG. ), The movement speed of the meniscus and the ink drop speed Vj exhibit almost the same behavior. However, in the fluctuation of the ink drop velocity Vj, vibration which is not in the meniscus position fluctuation appears in the early drive timing region,
This is due to the residual vibration in the ink liquid chamber after the droplet ejection.

As described above, in the high frequency driving region,
It can be seen that the ink drop velocity Vj and the ink drop volume Mj depend on the behavior of the meniscus.

Therefore, the meniscus behavior and the stability of ink droplet ejection will be described. In order to eject ink droplets continuously at a high driving frequency, stable ink droplet ejection is required. Here, factors that make ink liquid ejection unstable are caused by air bubbles mixed in from the nozzle, non-uniformity of the nozzle surface, rise in head temperature, etc., and mechanical movement during printing. There are small disturbances that occur.

Of these factors, the one directly related to the behavior of the meniscus is the inclusion of bubbles from the nozzle. The reason why the bubbles are mixed is that an ink vortex is generated near the nozzle. When air bubbles enter,
If there are adverse effects such as variations in the ejection direction and a decrease in the ink drop velocity Vj, and if a large amount of air bubbles are mixed in, it will become impossible to eject the ink drops.

In the meniscus behavior shown in FIG. 9A, the meniscus is in the direction opposite to the ink droplet ejection direction, and the ink droplet volume Mj increases as the droplet ejection timing becomes longer in the figure.
When the next droplet is ejected at the timing when the ink is moving to the area where the liquid droplet becomes smaller, the moving components of the ink are opposed to each other in the vicinity of the nozzle, and a vortex is generated, and as a result, the liquid ejection becomes unstable. Will be invited.

Actually, the variation of the ink droplet volume Mj is 10 to 10.
In a region where there is a variation of more than 20%, air bubbles are mixed in due to a small external vibration, causing drop ejection failure. It shows no significant instability in the lower vibration region.
That is, it is shown that the region where the variation of the ink droplet volume Mj is suppressed within ± 20%, preferably within ± 10% is in the stable region in fact.

Considering these points, as shown in FIG. 10, in the region where the fluctuation of the ink drop volume Mj exceeds a predetermined allowable fluctuation range, the volume of the ink drop Mj sharply decreases as the droplet ejection timing becomes longer. By not ejecting ink droplets in a region (for example, the region shown in FIG. 6), the direction of ink droplet ejection and the direction of meniscus fluctuation will not be in the opposite direction. Ejection failure is less likely to occur, and ink droplets can be ejected stably.

In addition, in the region where the fluctuation of the ink drop volume Mj exceeds a predetermined allowable fluctuation width, the ink drop is increased in a region where the ink drop volume Mj increases as the droplet ejection timing becomes longer (for example, a region shown in FIG. 6). By doing so, the ink droplet ejection direction and the meniscus fluctuation direction are in the forward direction (the same direction), and therefore ink droplet ejection failure due to entrainment of bubbles is unlikely to occur, and ink droplet ejection is stable. In addition, it is possible to perform stable ink droplet ejection under all driving conditions.

Further, within the area where the fluctuation of the ink drop volume Mj exceeds a predetermined allowable fluctuation range, the ink drop volume increases as the droplet ejection timing becomes longer, and the ink drop volume within the allowable fluctuation range is set. By performing the ink droplet ejection at the timing (the timing within the area shown in the figure), the ink droplet ejection failure due to the entrainment of bubbles is unlikely to occur, and the ink droplet ejection can be stably performed. Moreover, since the ink droplet volume Mj is ejected within the allowable fluctuation range, it is possible to record a high quality image with uniform dot scale.

In these cases, the ink drop volume Mj
The allowable fluctuation range of fluctuation is within ± 20% based on the ink drop volume at a sufficiently slow drop ejection timing, preferably ± 1
By setting the content to be 0% or less, ink droplets can be stably ejected at various driving frequencies, and substantially uniform dots can be formed.

Further, in order to perform more stable droplet ejection than in the steady state, driving is performed at the timing when the meniscus is moving in the forward direction with respect to the ink ejection direction as described above. If the next droplet ejection is performed at the first timing (first area) of returning to the meniscus position and causing overhang, the driving timing becomes the shortest and the driving frequency can be significantly improved.

Therefore, as shown in FIG. 10, the droplet ejection timing is the first variation area with the earliest timing in the variation of the ink droplet volume Mj, and the variation area in which the ink droplet volume increases as the droplet ejection timing becomes longer. (Maximum drive frequency f so that it exists in the area shown by in the figure)
By setting max, it is possible to prevent ink droplet ejection failure due to entrainment of bubbles, etc., to stably perform ink droplet ejection, and to enable stable ink droplet ejection under all driving conditions.

Further, the fluctuation of the meniscus and the ink droplet ejection characteristic are largely related to each other, but the actual driving frequency is 1 / n (n is an integer) or 1 of the maximum driving frequency fmax.
Driving of /(n+0.5) or the like is performed. Therefore, in order to realize stable ink droplet ejection at any drive frequency, it is necessary to damp the meniscus variation early. This is because if long-term fluctuations remain, it becomes very difficult to match the configuration for stable ejection at all drive timings.

Therefore, a meniscus fluctuation, that is, a large fluctuation in which the ink droplet volume Mj deviates from the permissible range width, is one cycle,
More precisely, the inflection points of the fluctuations are set to be two or less as shown by and in FIG. If there are three or more inflection points, the actual (fmax / 2) or (3
When driven at a drive frequency such as fmax / 4), there arises a disadvantage that it overlaps with an unstable region. In this way, by having two or less inflection points in the region where the fluctuation of the ink droplet volume Mj exceeds the allowable fluctuation range, the width for adjusting the driving frequency timing is narrowed, and the driving frequency and the driving frequency are adjusted. The degree of freedom can be given to the selection of pulses and the like.

Further, if the timing of meniscus fluctuation exceeding the allowable range width is set within twice the ejection timing at the maximum driving frequency fmax, the driving timing needs to be adjusted to about one or two points. In other words, the region for adjusting the drive frequency timing is set by making the region in which the ink droplet volume Mj exceeds the allowable fluctuation range only in the timing region that is earlier than twice the ejection timing at the maximum drive frequency fmax. Since the width becomes narrower, more freedom can be given to the selection of the drive frequency and the drive pulse.

As described above, the maximum driving frequency fmax must be set in a certain limited area. by the way,
An important factor required for the inkjet head is the size or position of the dot when the ink droplet reaches the recording medium (paper, OHP sheet, etc.). If the dots are large or small, inconveniences such as insufficient density in solid areas, white stripes, and nonuniform line width occur, and the image quality deteriorates. In addition, if the dot position is incorrect, the image boundary is distorted and the characters, lines, etc. are distorted and the image quality is degraded.

In order to eliminate these inconveniences, the first
Further, in order to make the ink droplet volume Mj uniform at each drive frequency, the drive at the maximum drive frequency fmax is performed at a position that is equivalent to the ink volume Mj at the time of low frequency drive. That is,
The position of the meniscus is low frequency drive and maximum drive frequency f
It means driving at the same position as when driving max.

In other words, the maximum driving frequency fmax is
The droplet ejection timing is in the first variation range where the timing is the earliest in the variation of the ink droplet volume Mj, and on the slope side where the ink droplet volume increases as the droplet ejection timing becomes longer, when the ink droplet is driven at another low frequency and when the ink droplet is ejected. It is set so that the volumes Mj are substantially equal (for example, the timing shown in FIG. 10). As a result, the direction of ink droplet ejection and the direction of meniscus fluctuation are forward directions, ink droplet ejection failure due to air bubble entrainment is less likely to occur, and a high-quality image with a uniform dot diameter can be formed. .

Secondly, in order to make the ink droplet ejection speed uniform, the maximum driving frequency fmax is driven at the timing when the movement speed of the meniscus becomes "0". The moving speed of the meniscus becomes "0" when the meniscus behavior is near the maximum value or the minimum value as shown by'in FIG. Even if this is shown by the ink droplet volume Mj,
It becomes maximum and minimum respectively. Which extreme value location is selected can be selected depending on the ink type, the spreading rate of the ink due to the medium, and the like.

In this way, the droplet ejection timing is set to be in the first fluctuation range having the earliest timing in the fluctuation of the ink drop volume Mj and in the vicinity of the maximum value or the minimum value of the fluctuation of the ink drop volume Mj. As a result, the meniscus fluctuation is moving at a very low speed, so ink droplet ejection failure due to bubble entrainment, etc., is less likely to occur, and the drop speed can be made equivalent to a sufficiently stable drive frequency. It is possible to improve accuracy and form a high quality image.

Although the case where the ink drop velocity Vj and the ink drop volume Mj are controlled has been described here, the ink drop velocity Vj and the ink drop volume Mj are adjusted in consideration of the allowable error. It is also possible to select the highest driving frequency fmax.

As described above, the ink droplet ejection characteristics are greatly related to the meniscus behavior, but this meniscus behavior can be controlled by the head configuration. For example, in the inkjet head shown in FIGS. 1 to 3 described above, the size of the fluid resistance portion 32, which is a fluid resistance portion provided in the ink supply path for supplying ink to the pressurized liquid chamber 17, is changed. By changing the fluid resistance value, the refill ability can be changed and the meniscus behavior can be controlled. The ink drop volume Mj and the ink drop velocity Vj with respect to the ink drop driving cycle are shown in FIG.
1 and fluctuate with the behavior as shown in FIG.

In other words, as shown in FIG. 11, the ink drop volume Mj decreases as the fluid resistance increases in a region where the drive cycle is short. This is because as the driving frequency increases, the number of ink drops increases and the ink flow rate flowing through the fluid resistance units 32 and 32 increases, but as the resistance value increases, the ink supply amount cannot keep up with the result, and as a result, ink drops drop. This is because the volume Mj becomes smaller. Regarding the ink drop velocity Vj, as shown in FIG. 12, as the fluid resistance value increases, a velocity increase phenomenon occurs in a region where the driving cycle is short.

Therefore, by selecting the resistance values of the fluid resistance portions 32, 32, the ink droplet volume M as described above can be obtained.
By controlling the fluctuation of j and selecting the ejection timing and the maximum drive frequency fmax, it is possible to improve the ink droplet ejection frequency while ensuring the stability of ink droplet ejection.

Regarding the relationship with the head drive circuit, when the charge time constant tr is constant and the discharge time constant tf is changed, the fluctuation (behavior) of the ink droplet volume Mj is as shown in FIG.
It changes as shown in FIG. Here, the longer the charging time constant tf, the smaller the fluctuation of the ink droplet volume Mj. However, the longer the charging time constant tf is, the longer the pulse width of the driving pulse (driving waveform) for ejecting one droplet is. The driving frequency fmax is limited. Therefore, it is necessary to adjust to the shortest discharge time constant tf that can suppress the fluctuation of the ink droplet volume Mj.

In this case, since the fluctuation of the pressurized liquid chamber is suppressed by discharging the voltage applied to the piezoelectric element, the driving method of the piezoelectric element is a push drive method capable of adjusting the pressure in the liquid chamber after driving. The ink droplet volume M can be improved by adopting (a method of ejecting ink droplets by the first deformation of the piezoelectric element and then refilling the ink liquid chamber by electric discharge).
It becomes easy to control the amplitude of the fluctuation of j and the inflection point.

In the push drive method, by making the time constant of the falling portion of the drive pulse described above longer than the time constant of the rising portion, sufficient energy for droplet ejection can be ensured, and It is possible to accelerate the pressure attenuation in the ink liquid chamber and control the amplitude and inflection point of the fluctuation of the ink droplet volume Mj to an optimum state.

In the above embodiment, an example in which a piezoelectric element is used as an actuator has been described, but the invention can be similarly applied to an ink jet recording apparatus using a heating element such as a heater.

[0079]

As described above, according to the ink jet recording apparatus of the first aspect, the ink droplet volume is increased as the droplet ejection timing becomes longer in the region where the ink droplet volume variation exceeds the predetermined permissible variation range. Since the ink droplets are not ejected in a region that becomes abruptly small, the direction of ink droplet ejection and the direction of meniscus fluctuation do not become opposite directions, and ink droplet ejection failure due to bubble entrainment or the like is less likely to occur. In addition, the stability of ink droplet ejection can be secured, and the ink droplet ejection frequency can be improved.

According to the ink jet recording apparatus of the second aspect, the ink droplets are ejected in the region where the ink droplet volume becomes larger as the droplet ejection timing becomes longer, in the region where the ink droplet volume fluctuation exceeds the predetermined permissible fluctuation range. Since the ink droplet ejection direction and the meniscus fluctuation direction are in the forward direction, the ink droplet ejection failure due to entrainment of bubbles is unlikely to occur, and the stability of the ink droplet ejection can be ensured. The frequency can be improved, and stable ink droplet ejection is possible under all driving conditions.

According to the ink jet recording apparatus of the third aspect, in the area where the ink droplet volume fluctuation exceeds the predetermined permissible fluctuation width, the ink droplet volume increases as the droplet ejection timing becomes longer, and Since the ink droplets are ejected at the timing when the ink droplet volume is within the fluctuation range, it is difficult to cause ink droplet ejection failure due to entrainment of bubbles, etc., and ink droplets are ejected within the allowable fluctuation range of the ink droplet volume. Thus, a high quality image having a uniform dot diameter can be formed. .

According to the ink jet recording apparatus of the fourth aspect, in the ink jet recording apparatus according to any one of the first to third aspects, the permissible fluctuation range of the fluctuation of the ink droplet volume is set to a sufficiently slow drop ejection timing. Since it is set within ± 20% as a reference, ink droplets can be stably ejected at various drive frequencies, and substantially uniform dots can be formed.

According to the ink jet recording apparatus of the fifth aspect, in the ink jet recording apparatus according to any one of the first to fourth aspects, two or less inflection points are set in an area where the variation of the ink droplet volume exceeds the permissible variation range. Since the configuration is provided, the area for adjusting the timing of the drive frequency is narrowed, and the degree of freedom in selecting the drive frequency and the drive pulse can be provided.

According to the ink jet recording apparatus of the sixth aspect, in the ink jet recording apparatus according to any one of the first to fifth aspects, the droplet ejection earlier than twice the droplet ejection timing when driven at the highest driving frequency is carried out. Since there is a region in the timing region that exceeds the permissible fluctuation range, the region for adjusting the timing of the drive frequency is narrowed, so that the drive frequency and drive pulse can be selected more freely.

According to the ink jet recording apparatus of the seventh aspect, the highest drive frequency is set such that the droplet ejection timing is in the first fluctuation range in which the timing is the earliest in the fluctuation of the ink droplet volume and the droplet ejection timing becomes longer. Since the frequency is set to exist in the fluctuation range where the drop volume increases, the direction of ink drop ejection and the direction of meniscus fluctuation are forward, and it is difficult to cause ink drop ejection failure due to bubble entrainment, etc. Stability can be secured,
The ink droplet ejection frequency can be improved, and stable ink droplet ejection is possible under all driving conditions.

According to the eighth aspect of the ink jet recording apparatus, the highest driving frequency is set such that the droplet ejection timing is in the first variation range where the timing is the earliest in the variation of the ink droplet volume and the droplet ejection timing becomes longer. Since the ink droplet volume is set to a frequency at which the ink droplet volume is almost equal to that at the time of driving at another low frequency on the slope side where the ink droplet volume becomes large, the ink droplet ejection direction and the meniscus fluctuation direction are forward directions.
Ink droplet ejection failure due to air bubble entrapment is less likely to occur, ink droplet ejection stability can be secured, the ink droplet ejection frequency can be improved, and an image with a uniform dot diameter can be formed. Quality is improved.

According to the ink jet recording apparatus of the ninth aspect, the droplet ejection timing is in the first fluctuation range in which the timing is the earliest in the fluctuation of the ink droplet volume, and near or at the maximum value of the fluctuation of the ink droplet volume. Since the configuration is in the vicinity, the meniscus fluctuation is moving at a very low speed, so it is difficult to cause ink droplet ejection failure due to entrainment of bubbles, etc., and the droplet speed should be the same as when driving with a sufficiently stable drive frequency. Therefore, the dot position accuracy can be improved and a high quality image can be formed.

According to the ink jet recording apparatus of the tenth aspect, in the ink jet recording apparatus according to any one of the seventh to ninth aspects, the droplet ejection timing which is 1.5 times and twice as slow as the droplet ejection timing at the highest driving frequency is set. , The timing that does not overlap with the area where the ink droplet volume sharply decreases as the droplet ejection timing in the first fluctuation region becomes longer is set, so the points for adjusting the ejection timing are the maximum drive frequencies fmax, fmax / 2, and 3fmax / It is possible to set only three points of 4, and it is difficult to cause ink droplet ejection failure due to entrainment of bubbles and the like, and the degree of freedom in selection of the drive frequency, the drive pulse, and the like increases.

According to the ink jet recording apparatus of the eleventh aspect, in the ink jet recording apparatus according to any one of the first to tenth aspects, the actuator for ejecting the ink droplet is composed of a piezoelectric element, and the piezoelectric element is push-driven. Since the drive pulse to be driven by the method is applied, it is possible to intentionally change the pressure state of the ink chamber after the droplet is ejected, and it is possible to easily control the amplitude and inflection point of the variation of the ink droplet volume. You can

According to the ink jet recording apparatus of the twelfth aspect, in the ink jet recording apparatus according to the eleventh aspect of the invention, the time constant of the falling portion of the drive pulse is made longer than the time constant of the rising portion. It is possible to accelerate the pressure decay in the ink liquid chamber after the droplet is ejected while sufficiently securing the energy for the purpose, and it is possible to control the amplitude of the variation of the ink droplet volume and the inflection point to an optimum state. .

[Brief description of the drawings]

FIG. 1 is an external perspective view showing an example of an inkjet head in an inkjet recording apparatus according to the present invention.

FIG. 2 is an exploded perspective view of the inkjet head of FIG. 1;

FIG. 3 is an enlarged cross-sectional view of a main part in a direction along the line AA of FIG.

4 is an enlarged cross-sectional view of a main part in a direction along the line BB of FIG.

FIG. 5 is a block diagram showing an example of a head drive circuit.

6 is a circuit diagram showing a specific example of the main part of FIG.

FIG. 7 is a diagram showing a relationship between general driving timing and ink droplet volume fluctuation.

FIG. 8 is a diagram showing the relationship between general driving timing and ink drop velocity.

FIG. 9 is an explanatory diagram for explaining the relationship between meniscus behavior, ink droplet volume, and ink droplet velocity.

FIG. 10 is an explanatory diagram for explaining the fluctuation of the ink droplet volume, the ejection timing, and the setting of the maximum driving frequency.

FIG. 11 is a diagram showing the relationship between drive timing and ink droplet volume when the fluid resistance value is changed.

FIG. 12 is a diagram showing the relationship between drive timing and ink droplet speed when the fluid resistance value is changed.

FIG. 13 is a diagram showing the relationship between the falling time constant of the drive pulse and the fluctuation of the ink droplet volume Mj.

[Explanation of symbols]

1 ... Actuator unit, 2 ... Liquid chamber unit, 3 ...
Substrate, 4 ... Piezoelectric element array, 7 ... Driving portion piezoelectric element, 8 ... Fixed portion piezoelectric element, 12 ... Vibration plate, 13 ... Liquid chamber flow path forming member,
15 ... Nozzle, 16 ... Nozzle plate, 17 ... Pressurized liquid chamber, 22 ... Fluid resistance part, 41 ... Power supply switching circuit,
42 ... Charge resistance circuit, 43 ... Discharge resistance circuit, 44 ... Selection circuit, H ... Inkjet head.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoaki Nakano 1-3-6 Nakamagome, Ota-ku, Tokyo Stock company Ricoh (72) Inventor Shuzo Matsumoto 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Company Ricoh

Claims (12)

[Claims] 1. An ink jet recording apparatus having an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates according to a difference in droplet ejection timing, and the ink droplet volume fluctuation is predetermined. The ink jet recording apparatus is characterized in that the ink droplets are not ejected in an area in which the ink droplet volume sharply decreases as the droplet ejection timing becomes longer in the area exceeding the allowable fluctuation range. 2. An ink jet recording apparatus having an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates depending on the difference in droplet ejection timing, and the ink droplet volume fluctuation is predetermined. The ink jet recording apparatus is characterized in that the ink droplets are ejected in an area in which the ink droplet volume increases as the droplet ejection timing becomes longer in an area exceeding the allowable fluctuation range. 3. An ink jet recording apparatus comprising an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates depending on the difference in droplet ejection timing, and the ink droplet volume fluctuation is predetermined. In a region exceeding the allowable fluctuation range, the ink droplets are ejected in a region where the ink drop volume increases as the droplet ejection timing becomes longer, and at a timing when the ink drop volume falls within the allowable fluctuation range. An ink jet recording apparatus characterized by the above. 4. The ink jet recording apparatus according to claim 1, wherein the allowable fluctuation range of the fluctuation of the ink drop volume is within ± 20% with reference to the ink drop volume at a sufficiently slow drop ejection timing. An inkjet recording device characterized by the above. 5. The ink jet recording apparatus according to claim 1, wherein the ink drop volume has two or less inflection points in a region in which the variation of the ink droplet volume exceeds the allowable variation range. Inkjet recording device. 6. The ink jet recording apparatus according to claim 1, wherein the allowable fluctuation range is set in a droplet ejection timing area that is earlier than twice the droplet ejection timing when driven at the highest driving frequency. An ink jet recording apparatus characterized in that there is a region that exceeds. 7. An ink jet recording apparatus comprising an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates depending on the difference in droplet ejection timing, and the highest driving frequency The timing is set to a frequency in the first fluctuation range having the earliest timing in the fluctuation of the ink drop volume and in the fluctuation range in which the ink drop volume increases as the drop ejection timing becomes longer. Inkjet recording device. 8. An ink jet recording apparatus having an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates depending on a difference in droplet ejection timing. The timing is the first fluctuation range in which the timing is the earliest in the fluctuation of the ink droplet volume, and also on the slope side where the ink droplet volume becomes larger as the droplet ejection timing becomes longer, at the time of driving at another low frequency and the ink. An ink jet recording apparatus, characterized in that a frequency is set so that droplet volumes are substantially equal. 9. An ink jet recording apparatus comprising an ink jet head having one or a plurality of nozzles for ejecting ink droplets, wherein the ink droplet volume fluctuates depending on the difference in droplet ejection timing, wherein the droplet ejection timing is the ink. An ink jet recording apparatus, characterized in that it is in a first fluctuation range with the earliest timing in the fluctuation of the drop volume and in the vicinity of a maximum value or a minimum value of the fluctuation of the ink drop volume. 10. The ink jet recording apparatus according to claim 7, wherein the droplet ejection timing that is 1.5 times and twice as slow as the droplet ejection timing at the highest drive frequency is set to the first variation range. 2. The ink jet recording apparatus, wherein the timing is set so that it does not overlap with the region where the ink droplet volume sharply decreases as the droplet ejection timing becomes longer. 11. The ink jet recording apparatus according to claim 1, wherein the actuator for ejecting the ink droplets is composed of a piezoelectric element, and a drive pulse for driving the piezoelectric element by a push drive method is used. An ink jet recording apparatus characterized by applying a voltage. 12. The ink jet recording apparatus according to claim 11, wherein the time constant of the falling portion of the drive pulse is set longer than the time constant of the rising portion.