JPH07285222A - Ink jet recording device - Google Patents

Abstract

PURPOSE:To provide an ink jet recording device which realizes the output of a high-quality image by discharging microdots by a simple constitution. CONSTITUTION:The ink weight of main dots 2 and that of satellite dots 3, both being caused by a single pressure variation are controlled so that both ink weights are almost the same. Further, the application of dots of smaller size ink droplets is realized by deviating an impact area of each dot, and thus an image of high resolution is output.

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 for a printer or the like in which a pressure is generated in a pressure generating element by an electric signal, and this pressure causes ink droplets to fly to form an ink image on a recording medium such as recording paper. Regarding the device.

[0002]

2. Description of the Related Art Ink jet recording apparatuses have been rapidly popularized in recent years because they are non-impact, have low noise, and are capable of color output by using multicolor inks, and have a simple head structure and can be manufactured at low cost. ing.

An outline of the recording method of this ink jet recording apparatus will be described with reference to FIGS. 5 and 7. FIG. 5 is a structural explanatory view of an inkjet head, which is a main part of an inkjet recording apparatus that ejects ink from a nozzle according to pressure fluctuation of a pressure generating element. Reference numeral 10 shown in FIG. 5 is a nozzle forming substrate on which a plurality of nozzles 1 are formed. The opening area of the nozzle 1 and the thickness of the nozzle forming substrate 10 have a great influence on the ink ejection characteristics. The flow path substrate 11 bonded to the nozzle forming substrate 10 is a member that forms communication ports for the pressure chamber 12, the segment ink supply passage 13, the common ink chamber 14, and the ink supply pipe 15. The pressure chamber 12, the segment ink supply path 13, which are formed in this way,
The common ink chamber 14 is filled with ink. On the other hand, pressure generating elements 17 arranged on the base substrate 16 are bonded to the bottom surface of the flow path substrate 11 so as to correspond to the respective pressure chambers 12. When the segment signal 19 from the drive circuit 21 and the common signal 20 are applied to the pressure generating element 17, the volume of the pressure chamber 12 decreases and the pressure increases,
Ink is ejected from the nozzle 1. FIG. 7 is a diagram showing a state in which the volume of the pressure chamber 12 is contracted (a) and expanded (b) by the pressure fluctuation of the pressure generating element 17.

Here, in addition to the main dots ejected from the nozzles 1, satellite dots are ejected with a time delay after a single pressure change. The satellite dots are mainly due to the natural vibration of the volume velocity of the ink due to the natural vibration (Ta) of the pressure generating element 17 and the natural vibration (Tc) of the pressure chamber 12, and are slightly displaced from the landing position of the main dot. This causes a problem of lowering the output quality. In order to solve such a problem, many techniques for preventing the generation of satellite dots have been proposed. For example, in JP-A-59-133067, residual vibration is suppressed by applying a second pressure fluctuation after the first pressure fluctuation, and in JP-A-61-206662, it is caused by a plurality of pressure fluctuations. Combining a plurality of dots, and Japanese Unexamined Patent Publication
In Japanese Patent Laid-Open No. 192947, there is proposed a technique for preventing the occurrence of satellite dots by driving in accordance with the natural vibration period of the ink volume velocity.

In order to output a good image in ink jet recording, the size of the ejected ink droplet is reduced to improve the resolution, or the ink droplet size is controlled or the ink droplet is ejected within one pixel. It has been proposed that the gradation expression is controlled by controlling the number of. For example, JP-A-4-285
In Japanese Patent Publication No. 47, a technique is proposed in which, in a so-called multi-droplet method in which a plurality of dots are landed in one pixel, a plurality of ink droplets are landed within a certain distance so that high-quality output is performed.

[0006]

However, in the above-mentioned two techniques for preventing the occurrence of satellites, complicated driving conditions are required to cause a plurality of pressure fluctuations, which leads to high cost in the circuit. There are problems such as difficulty in increasing the drive frequency. To reduce the weight of the ink droplets on the main dot to achieve high resolution,
For example, it is possible to deal with the problem by reducing the nozzle diameter, but it is costly to make the nozzle diameter small, and further, there is a problem that the clogging of the nozzle is likely to occur due to the mixing of foreign matters in the ink. Japanese Patent Laid-Open No. 2-19
Even with the technique disclosed in Japanese Patent No. 2947, it is difficult to reduce the weight of the main dots.

Although the multi-droplet type technique can be expected to have high image quality, it still has problems such as a high driving frequency, a load for ejecting fine dots, and a slow recording speed.

The present invention solves these problems.
It is an object of the present invention to provide an ink jet recording apparatus which realizes high quality output by ejecting fine dots with a simple structure.

[0009]

An ink jet recording apparatus of the present invention includes a nozzle for ejecting ink, a pressure chamber communicating with the nozzle, a pressure generating element for generating pressure in the pressure chamber, and a pressure generating element. An ink jet recording apparatus having a voltage applying means for applying a voltage, wherein ink is ejected from a nozzle by pressure fluctuation of the pressure generating element,
It is characterized in that the ink weights of the main dots and the satellite dots caused by the pressure fluctuations are about the same.

Furthermore, the ejection speed of the main dots is Vm (m / m
s), the ejection speed of the satellite dots is Vs (m / s), the ejection time difference between the main dots and the satellite dots is ts (s), the driving frequency is f (Hz), and the distance between the nozzle and the recording medium is G (m). When these are done, these are characterized by satisfying the following relationship.

[0011]

[Equation 2]

Further, one pixel is composed of a main dot and a satellite dot, and the resolution in the main scanning direction is 1/2 of the resolution in the sub scanning direction.

Further, the main dots and the satellite dots ejected from the nozzles are characterized in that the angles with respect to the nozzle surface are different in the main scanning direction.

[0014]

The ink jet recording apparatus of the present invention positively utilizes the ejection characteristics of the main dots and satellite dots generated by one pressure change, and further shifts the landing position of each dot to achieve high dot size. It achieves high resolution and high quality output.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, a control method for ejecting main dots and satellite dots in the same amount will be described.

FIG. 6 is a relational diagram showing a voltage waveform for driving the ink jet head having the structure shown in FIGS. 5 and 7 described in the conventional example and the displacement behavior of the pressure generating element. Further, in FIG. 7, a meniscus 24 is formed in the nozzle 1 by the surface tension of the ink. When a voltage is applied, the pressure generating element 17 expands in the displacement direction of the arrow δ as shown in FIG. 7 (a) to contract the volume of the pressure chamber 12, while in the state where no voltage is applied ( A steady state is reached as shown in b), and the volume of the pressure chamber is relatively increased.

In FIG. 6A, the fall (discharge) time T1 and the rise (charge) time T2 of the voltage waveform 22 are shown.
Is smaller than the natural vibration period Ta of the pressure generating element,
The displacement behavior 23 of the pressure generating element 17 exhibits an excessive vibration behavior. In such a case, residual vibration occurs in the pressure chamber 12, and the meniscus 24 shown in FIG. 7 also vibrates. On the other hand, as shown in FIG. 6B, when the fall time T1 and the rise time T2 of the voltage waveform 22 applied to the pressure generating element 17 are set to be larger than the natural vibration period Ta of the pressure generating element 17, The generating element 17 no longer exhibits an excessive vibration behavior, and the meniscus 24 has a small residual vibration.

Contrary to the pressure generating element 17 shown in FIG. 7,
A pressure generating element having a characteristic of contracting when a voltage is applied to expand the volume of the pressure chamber 12, while being in a steady state when a voltage is not applied and relatively contracting the volume of the pressure chamber 12. When 17 is used, the voltage waveform 22 and the displacement behavior 23 shown in FIG. 6 are inverted vertically, but the essential relationship between T1, T2 and Ta is the same.

The natural vibration period Ta of the pressure generating element 17
Is expressed as in Equation 2.

[0021]

[Equation 3]

Here, L is the pressure generating element 17 shown in FIG.
In the displacement direction, ρ is the density of the pressure generating element 17, E is the Young's modulus of the pressure generating element 17, and λ is the vibration coefficient of the pressure generating element 17 that differs depending on the vibration mode. As shown in FIG. The value is 1.875 in the pressure generating element 17 using the vertical vibration of. In the present invention, the pressure generating element 17 having Ta of about 5 μs is used.

FIG. 8 is a relationship diagram showing the behavior of the voltage waveform 22, the volume change behavior 25 and the meniscus level 26 in the pressure chamber 12 when the ink jet recording apparatus of the present invention is driven. Further, FIG. 9 is an enlarged view of a main part of an inkjet head for explaining an embodiment of the present invention. In FIG. 8, the pressure generating element 17 shown in FIGS. 5 and 7 is shown as a more specific laminated piezoelectric element 18. The laminated piezoelectric element 18 is composed of a segment electrode 28, a piezoelectric material layer 27, and a common electrode 29, and expands in the laminating direction by applying a voltage (d33 effect) and contracts in the laminating direction and orthogonal direction (d31 effect). ) Has characteristics.

A driving method using the d33 effect will be described below with reference to FIGS.

Time t0 to t1 is a steady state. As shown in FIG. 8, since the voltage level is Vh in this state, the laminated piezoelectric element 18 shown in FIG. 9 exhibits the deformation behavior as shown by the broken line A, and the volume change 25 of the pressure chamber 12 is 25. Is at the level of C0 in which the volume of the pressure chamber 12 is relatively contracted. The meniscus level 26 shown in FIG. 8 is maintained at a steady level M0 held by the surface tension of the ink.

Times t1 to t2 are the first step. Figure 8
In this state, the voltage waveform 22 is discharged to the level indicated by VL at the falling time T1 and the volume change 25 of the pressure chamber 12 is changed to the level C1 to expand the volume of the pressure chamber 12 as shown in FIG. The pressure in the chamber 12 is reduced.
At this time, when T1 is 1/2 or less of the natural vibration period Tc of the ink, the volume of the pressure chamber 12 continues to expand even after passing t2. At this time, an inertial flow of ink is generated in the pressure chamber 12 toward the nozzle 1. Following this, the meniscus 24 is pulled inward toward the inside of the pressure chamber 12, and the meniscus level 26 shown in FIG.

The time t2 to t3 is the second step. As shown in FIG. 8, the voltage waveform 22 is VL in this state.
Since the volume is maintained at the level shown in (1), the volume change 25 of the pressure chamber 12 also repeats vibration to return to the level of C1 in which the volume of the pressure chamber is expanded. Further, the meniscus 26 also tries to return to the steady level M0 while repeating vibration.

Times t3 to t4 are the third step. As shown in FIG. 8, the voltage waveform 22 is charged to the level shown by Vh again with a rise time T2 shorter than Tc / 2. At that time, the volume change 25 of the pressure chamber 12 exceeds the level of C0 and further contracts the volume of the pressure chamber 12. As a result, the inside of the pressure chamber 12 is pressurized, so that the meniscus 24 is strongly pushed out in the ink ejection direction, and the ink droplet of the main dot first flies. The ink discharge amount at this time is almost the same as the shaded portion S shown in FIG.
Equivalent to an area of 1. After that, the voltage waveform 22 maintains the steady state of Vh, but the pressure chamber 12 continues to vibrate due to the rapid volume change, and after the main dot is ejected, the meniscus 24 is again pushed out in the ink ejection direction, which corresponds to the area of S2. Eject ink droplets of satellite dots. In FIG. 8, the discharge time difference (t5 to t6) between the main dots and the satellite dots is ts.

Regarding the method of driving the ink jet head using the d31 effect, only the voltage waveform 22 shown in FIG. 8 is inverted up and down, but the essential relationship between T1, T2 and Tc is that when the d33 effect is used. It is the same.

The natural vibration period Tc of the ink with which the pressure chamber 12 is filled is expressed by the equation (3).

[0031]

[Equation 4]

Here, Mn is the inertance of the nozzle 1,
Mi is the inertance of the ink supply path, Ci is the compliance of the ink, and Cc is the compliance of the pressure chamber 12.

Further, Mn, Mi, Ci and Cc are defined by the equations 4 to 7 as follows.

[0034]

[Equation 5]

Here, ρ is the density of the ink, and S (x) is shown in FIG.
The cross-sectional area of the nozzle 1 in the thickness X of the nozzle forming substrate 10 shown in (3), k is a proportional constant in consideration of the unsteady solution determined by the nozzle shape.

[0036]

[Equation 6]

Here, ρ is the density of the ink, S (Lc) is the cross-sectional area of the supply path at the ink supply path length Lc shown in FIG. 9, and k is the unsteady solution determined by the shape of the supply path. And n is the number of supply paths to the nozzle (2 in this embodiment).

[0038]

[Equation 7]

Here, v is the volume of the pressure chamber 12, ρ is the density of ink, and c is the speed of sound of ink.

[0040]

[Equation 8]

Here, ΔV is the deformation volume of the pressure chamber per unit pressure, and P0 is the unit pressure.

Further, the smaller the natural vibration period Tc of the ink determined in this way, the narrower the ink ejection interval can be, and the higher speed printing becomes possible.

Further, the base substrate 16 shown in FIG. 9 is ideally a rigid body, and specifically, it is desirable that the acoustic impedance (Young's modulus × specific gravity) is large. Therefore, as shown in FIG. 9, by holding one end of the laminated piezoelectric element 18 on the base substrate 16 having Young's modulus and specific gravity equal to or higher than Young's modulus and specific gravity of the laminated piezoelectric element 18, the pressure in the pressure chamber 12 is increased. It is possible to efficiently transmit the pressure.

FIGS. 1, 2 and 3 are model diagrams showing the flying states of the main dots 2 and the satellite dots 3 when ink is ejected from the nozzle 1 by changing only the driving conditions based on this embodiment. Each flight state could be realized under the driving conditions shown in Table 1. In these experiments, an inkjet head using the d31 effect was used.
Tc was about 17 μs.

[0045]

[Table 1]

As shown in Table 1 and FIGS. 1, 2 and 3,
By changing the fall time T1, the hold time H, and the rise time T2, the flight states of the main dots 2 and the satellite dots 3 are greatly different. As described above, this is a phenomenon mainly caused by the residual vibration generated by the volume expansion and contraction speed of the pressure chamber 12 and the inertial flow that supplies ink to the pressure chamber 12. Under the conditions shown in FIG. 1, the total weight of the ink droplets including the main dots 2 and the satellite dots 3 is about 0.022 μg, and the weight of each dot is half that. Further, when the respective ejection speeds were measured, the main dot 2 was 9.3 m / s and the satellite dot was 4.7 m / s.

Next, the conditions for accurately landing and recording the main dots 2 and the satellite dots 3 on the recording medium will be described with reference to FIG. FIG. 10 shows a recording medium 3 such as paper.
It is a simple view of a state in which an ink-jet head that sets a distance of G with respect to the surface Y0 of 0 moves on the X0 surface for recording. First, at Xa, the inkjet head ejects the main dots 2 in the direction of the arrow at an ejection speed of Vm. At that time, since the inkjet head is constantly moving in the arrow direction on the X0 surface at the velocity of Vp, the main dots 2 ejected at Xa are landed and recorded on Ya of the recording medium 30. On the other hand, satellite dot 3
Is discharged at Xb due to the time difference of ts, and the speed at that time is V
s. Since the velocity component of Vp works like the main dot, it is landed on Yb. Next, the main dots 2 ejected at Xc after 1 / f time have landed on Yc. Ya to Yc at this time
The distance Lx is the length of the pixel corresponding to the resolution d (dot / inch) in the main scanning direction, and the landing position Yb of the satellite dot 3 must be in the middle of Lx in order to achieve high quality output. . For that purpose, the relationship of the following Expression 8 is required between d, Vp, G, Vm, Vs, and ts.

[0048]

[Equation 9]

At this time, since Vp is represented by f and d, the satellite dot 3 is accurately recorded at the intermediate position of Lx under the condition of Expression 1. It should be noted that in order to achieve high image quality, it is preferable to approach the relationship of Expression 1 as much as possible, but it is possible to maintain high image quality if the satellite dots land within a certain range. Although it depends on the resolution and the characteristics of the recording medium, if the landing accuracy is approximately 30%, an output that is not noticeable to the naked eye can be obtained. If this range is exceeded, an effect such as fluctuations when a uniform pattern is output occurs.

FIG. 4 is a model diagram of the landing state of the main dots 2 and the satellite dots 3 when recording is performed on the recording medium 30 with the distance G changed by actually using the ink jet head which discharges under the conditions of FIG. Show. FIG. 4A shows a landing state when recording is performed by adjusting the distance G so that the relationship of Expression 1 is almost satisfied. The driving frequency f at this time is 4.2 kHz,
The distance G was 1.0 mm. The main dots 2 and the satellite dots 3 are misaligned and landed, and the amount of ink landed per unit area is reduced, which leads to an effect of accelerating the drying speed of the ink. A high-quality recording can be achieved by setting the pixel composed of the main dot 2 and the satellite dot 3 with a small size of the dot to be recorded as one pixel and setting the resolution in the main scanning direction to half the resolution in the sub-scanning direction. It will be possible.
Further, (b) is a landing state when recording is performed with the distance G smaller than that in (a), and the main dots 2 and the satellite dots 3 are formed as one dot on the recording medium. The dot diameter at that time is larger in the sub-scanning direction than in (a). Further, (c) is a landing state when recording is performed with the distance G made larger than that of (a), and the main dots 2 and the satellite dots 3 land too far apart.

Further, by controlling the ejection angles of the main dots 2 and the satellite dots 3 ejected from the nozzles 1 with respect to the main scanning direction, the landing position is optimized even if the relation of the expression 1 is not always satisfied. It is possible to FIG. 11 shows an example of the nozzle forming substrate 1
0 is formed inclined with respect to the main scanning direction. As a result, the ejection angles of the main dots 2 and the satellite dots 3 having different ejection speeds are different as shown in the figure. Also in FIG.
Shows another example. A surface treatment member 31 that exhibits water repellency to ink is formed on the nozzle forming substrate 10, and an ink reservoir 32 is formed so that the surface treatment member 31 becomes non-uniform around the nozzle 1. Due to the action of the surface tension of the ink, the ejection angles of the main dots 2 and the satellite dots 3 during ejection can be different. Therefore, main dot 2
Of the main dots 2 and the satellite dots 3 can be controlled and optimized by optimizing the distance G according to various conditions such as the discharge speed Vm of the satellite dots Vs, the discharge speed Vs of the satellite dots 3 and the respective discharge angles. It will be possible.

FIG. 13 shows a dot landing image when ink droplets are changed to change the resolution. (A)
In contrast to the 300 dpi recording, the (b) recording is performed at 600 dpi, and high-quality output can be obtained, but quadruple time is required unless the drive frequency is changed. Further, (c) is a recording method in which the resolution is increased only in the main scanning direction. In this case, the output time can be doubled, but since the shape of the main dot 2 is a circle, the ink droplets are not evenly landed and the ink droplet is not landed in the sub scanning direction. Easy to make a gap. (D) is a landing image by the ink jet recording apparatus of the present invention, which is capable of obtaining high-quality output with less output time compared to the comparative examples of (a) to (c).

As described above, when the ink jet recording apparatus of the present invention is used, the ejection characteristics of the main dots 2 and the satellite dots 3 produced by one pressure fluctuation are positively utilized, and the landing position of each dot is further utilized. By shifting the dots, it is possible to achieve high resolution by making dots small and to realize high-quality output. Note that the present inkjet recording apparatus has been described using an inkjet recording apparatus that mechanically causes pressure fluctuations, but it is also applicable to a so-called bubble jet type inkjet recording apparatus that ejects ink droplets due to pressure fluctuations due to thermal expansion. Is. The present invention can be applied not only to monochromatic recording but also to color recording.

[0054]

As is apparent from the above description, the ink jet recording apparatus of the present invention controls so that the ink weights of the main dots and the satellite dots generated by one pressure fluctuation become approximately the same, and further, the ink weight of each dot is controlled. By shifting the landing position, it is possible to provide an ink jet recording apparatus that can achieve high resolution by making dots small and realize high-quality output at low cost.

[Brief description of drawings]

FIG. 1 is a model diagram of an ink droplet ejection state showing an embodiment of an inkjet recording apparatus of the present invention.

FIG. 2 is a model diagram of an ink droplet ejection state when the ejection conditions of the embodiment of the inkjet recording apparatus of the present invention are changed.

FIG. 3 is a model diagram of an ink droplet ejection state when the ejection conditions of the embodiment of the inkjet recording apparatus of the present invention are changed.

FIG. 4 is a model diagram showing an ink droplet landing state when the distance between the nozzle and the recording medium is changed in the embodiment of the inkjet recording apparatus of the present invention.

FIG. 5 is a structural explanatory view showing a main part of the head of the inkjet recording apparatus of the present invention.

FIG. 6 is a relationship diagram showing a voltage waveform for driving the head of the inkjet recording apparatus of the present invention and a displacement behavior of the pressure generating element.

FIG. 7 shows an inkjet recording apparatus of the present invention.
(A) is an explanatory view showing a state in which the volume of the pressure chamber is contracted, and (b) is a state in which the volume of the pressure chamber is expanded.

FIG. 8 is a relationship diagram showing a voltage waveform for driving the head of the ink jet recording apparatus of the present invention, volume change behavior in the pressure chamber, and meniscus behavior.

FIG. 9 is a partially enlarged view of the main part of the head showing the embodiment of the present invention.

FIG. 10 is a model diagram for explaining landing positions of main dots and satellite dots by the inkjet recording apparatus of the present invention.

FIG. 11 is a structural explanatory view showing an example for correcting the landing positions of main dots and satellite dots by the inkjet recording apparatus of the present invention.

FIG. 12 is a structural explanatory view showing an example for correcting the landing positions of main dots and satellite dots by the inkjet recording apparatus of the present invention.

FIG. 13 is an explanatory diagram showing landing images of ink drops by the conventional and the inkjet recording apparatuses of the present invention.

[Explanation of symbols]

 1 Nozzle 2 Main Dot 3 Satellite Dot 10 Nozzle Forming Substrate 11 Flow Channel Substrate 12 Pressure Chamber 16 Base Substrate 17 Pressure Generating Element

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B41J 2/075 B41J 3/04 104 A

Claims (4)

[Claims] 1. A nozzle for ejecting ink, a pressure chamber communicating with the nozzle, a pressure generating element for generating a pressure in the pressure chamber, and a voltage applying unit for applying a voltage to the pressure generating element, In an inkjet recording apparatus that ejects ink from a nozzle due to pressure fluctuations of a pressure generating element, a main dot that is a first ejection ink droplet that is generated by one pressure fluctuation and an ejection ink droplet that is generated by residual vibration of pressure fluctuations. An ink jet recording apparatus characterized in that a certain satellite dot has approximately the same ink weight. 2. The discharge speed of the main dots is Vm (m / m
s), the ejection speed of the satellite dots is Vs (m / s), the ejection time difference between the main dots and the satellite dots is ts (s), the driving frequency is f (Hz), and the distance between the nozzle and the recording medium is G (m). The ink jet recording apparatus according to claim 1, wherein the following relationship is satisfied. [Equation 1] 3. The inkjet according to claim 1, wherein a pixel composed of the main dot and the satellite dot is one pixel, and the resolution in the main scanning direction is 1/2 of the resolution in the sub scanning direction. Recording device. 4. The ink jet recording apparatus according to claim 1, wherein the angles of the main dots and the satellite dots ejected from the nozzles with respect to the nozzle surface are different in the main scanning direction.