JP2001347694A - Ink jet recording head and driving method thereof - Google Patents

Abstract

[PROBLEMS] To provide an ink jet recording head capable of expressing higher gradation and a driving method thereof. SOLUTION: In the ink jet recording head, a piezoelectric element driving section applies a first voltage to a corresponding piezoelectric element for a first time so as to increase the volume of a selected ink chamber, and then the ink chamber Drive pulse generating means for applying a second voltage to the piezoelectric element for a second time so as to reduce the volume of the drive chamber and generating a drive pulse signal for discharging ink from the ink chamber via a nozzle, The drive pulse generation means controls the second time based on the gradation value of the print data input by the print data input means, thereby controlling the size of the ink droplet ejected from the ink chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an ink jet recording head and an ink jet recording head using the driving method, and more particularly to a method of recording a recording dot on a recording medium using recording dots composed of ink droplets. The present invention relates to a method of driving an ink jet recording head for improving tonality and an ink jet recording head using the driving method.

[0002]

2. Description of the Related Art A printer having an ink-jet recording head (hereinafter, referred to as an "ink-jet printer") performs multi-level binarization on an image to be printed and obtains a result of the multi-level binarization. The formation of dots on a recording medium is controlled by each nozzle of the recording head based on the dot on / off signal. In the method of ejecting ink, basically, the ink entering the ink passage reaching the nozzle is pressurized for an extremely short time, and the pressurized ink is ejected as an ink droplet from the tip of the nozzle. There are known a method of generating pressure using an electrostrictive element and a method of applying pressure using generation of bubbles due to heat, depending on a difference in generation mechanism of pressure applied to ink.

In the conventional ink-jet printer, whichever of the above methods is adopted, it is determined whether or not ink droplets are ejected, that is, only the on / off control of dots is performed, and the amount of ejected ink droplets is reduced. It has been extremely difficult to record halftones with continuous control.

[0004] In order to express an intermediate gradation, techniques such as an area gradation method, a dither method, and an error diffusion method have been proposed. In these methods, 1 is recorded on a recording medium.
By forming one pixel with a plurality of dots (ink droplets), printing of intermediate gradation is realized. For example, 4x4
If one pixel is represented by a dot matrix of
The gradation can express the shading, and if the resolution of the pixel is increased, finer gradation expression can be performed.

[0005] However, if the gradation is increased without changing the recording dot diameter, that is, the diameter of one pixel recorded on the recording medium by the ink droplet, the substantial resolution decreases. Also, as the recording dot diameter increases, the roughness of the particles in the low density region on the recording medium becomes noticeable. Therefore, it is necessary to reduce the amount of ink droplets to reduce the recording dot diameter in order not to expose the particle roughness in the area.

On the other hand, when the recording dot diameter is reduced, the recording speed is greatly reduced. For example, when using only small-diameter dots having a dot diameter that is about half the normal recording dot diameter, four times as long as using a normal recording dot diameter is required. In order to prevent such a decrease in the printing speed, it is conceivable to increase the driving frequency for ejecting ink droplets four times or increase the number of nozzles four times, but in each case, the mechanism becomes complicated.

In view of the above, a technique has been proposed in which different amounts of ink droplets are ejected from one nozzle to enable gradation expression. For example, Japanese Patent Application Laid-Open No. Sho 59-133066 discloses that a plurality of the same pulse signals are generated within one recording cycle, thereby generating a plurality of minute ink droplets having the same diameter, and on a recording medium or A technique is disclosed in which a plurality of minute ink droplets are united to form a recording dot of a desired size before the ink droplet lands on a recording medium.

[0008] Japanese Patent No. 280,065 and Japanese Patent Application Laid-Open No. 11-20165 disclose ink droplets of different sizes set in advance within one recording cycle by a pulse signal corresponding to each ink droplet. There has been disclosed a technique for generating recording dots of a desired size by discharging from the same nozzle.

[0009]

According to the techniques described in these publications, recording dots are generated by the number or combination of pulse signals corresponding to ink droplets of a predetermined size, so that the gradation To further increase
Many ink droplets must be ejected within the recording cycle,
There is a problem that the mechanism becomes complicated and one recording cycle becomes longer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an ink jet recording head capable of expressing a higher gradation and a driving method thereof.

[0011]

According to the present invention, a plurality of ink chambers which are separated from each other by partition walls and arranged in series,
A piezoelectric element that forms at least a part of each partition, a piezoelectric element driving unit that applies a voltage to the piezoelectric element to change the volume of an ink chamber selected from a plurality of ink chambers, and is disposed in each ink chamber. And a method for driving an ink jet recording head having a selected ink discharge nozzle, wherein the piezoelectric element driving unit corresponds to the first voltage for a first time so as to increase the volume of the selected ink chamber. Applying to the piezoelectric element, then applying a second voltage to the piezoelectric element for a second time so as to reduce the volume of the ink chamber, ejecting ink from the ink chamber through the nozzle, and A method of driving an ink jet recording head is provided, wherein an amount of ink ejected from the ink chamber is controlled by controlling a second time.

That is, according to the present invention, after increasing the volume of the ink chamber for discharging ink by deforming the partition, the second voltage is applied for a second time so as to reduce the volume of the ink chamber. By controlling the second time when applying to the ink chamber, the amount of ink ejected from the ink chamber can be controlled. Therefore, 1
Within the recording cycle, a plurality of droplet ejection pulses for ejecting different amounts of ink are set in advance, and compared with the conventional method of controlling the amount of ink by selecting these pulses, the number of pulses is one.
It is possible to control the amount of ink ejected without changing the recording cycle, and high-speed printing is possible.

According to the present invention, the piezoelectric element driving section is provided with driving pulse generating means for generating the first and second voltages as first and second driving pulses, and the driving pulse generating means is provided with the first driving pulse. And the second drive pulse are repeatedly generated n times, and a maximum of n ink droplets are ejected from the nozzles of the ink chamber to form one recording dot within a predetermined time, and the pulse width of the second drive pulse is controlled. Thus, a configuration in which the size of each ink droplet ejected as one recording dot is controlled is exemplified. In such a configuration, the time for forming one recording dot, that is, one recording cycle is composed of a plurality of ink droplets, so that the amount of ink that can be ejected in one recording cycle is reduced by the size of the ink droplet and the number of ink droplets Can be configured in multiple stages, and the gradation expression ability is improved. Further, by making one recording cycle constant, printing control becomes easy. Such a gradation expression can be used not only for a monotone gradation expression but also for a color gradation expression. For example, C (cyan) M
Multi-stage gradation expression by color is possible by combining the size of each ink droplet such as (magenta), Y (yellow), K (black) and the number of ink droplets.

The pulse width of the first drive pulse is defined as the time during which a pressure wave generated by driving the piezoelectric element propagates one way in one ink chamber along the partition in the longitudinal direction, and the pulse width of the second drive pulse is defined as By setting the propagation time to twice or less, the ejection speed is maximized, and it is easy to generate small-diameter ink droplets.

According to the present invention, the piezoelectric element driving section provides
A set of at least three chambers including a central ink chamber for discharging ink and an ink chamber that does not discharge ink on both sides thereof is set as a set, and these continuous ink chambers are sequentially shifted one by one when discharging ink. Can transition. This enables, for example, continuous printing in the scanning direction.

According to another aspect of the present invention, a plurality of ink chambers arranged in series separated from each other by a partition, a piezoelectric element constituting at least a part of each partition, and a voltage is applied to the piezoelectric element. A piezoelectric element driving unit that changes the volume of an ink chamber selected from a plurality of ink chambers, an ink discharge nozzle provided in each ink chamber, and a recording pixel that forms an image based on image information. Print data input means for inputting print data having a gradation value, wherein the piezoelectric element drive section responds to the first voltage for a first time so as to increase the volume of the selected ink chamber. A drive pulse signal for applying a second voltage to the piezoelectric element for a second time so as to reduce the volume of the ink chamber and discharging ink from the ink chamber via a nozzle so as to reduce the volume of the ink chamber. generate An ink droplet ejected from the ink chamber by controlling a second time based on a gradation value of the print data input by the print data input means, comprising a dynamic pulse generating means; An ink jet recording head characterized by controlling the size of the ink jet recording head.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a method for driving an ink jet recording head according to the present invention will be described with reference to examples. The present invention is not limited by these examples. FIG. 1 schematically shows the configuration of the ink jet recording head of the present invention. In FIG. 1, a shear mode ink jet recording head 50 mainly includes a plurality of ink chambers 2 separated from each other by a partition wall 1 and a piezoelectric element driving unit 3. The partition walls 1 are erected on the PZT base 21 in parallel and adjacent to each other with the same PZT material, and have a substantially uniform thickness of 70 μm in the horizontal direction in the figure. A cover plate 23 is provided above the partition 1 with an adhesive layer 22 interposed therebetween.

The ink chamber 2 is formed as an ink storage space having a rectangular cross section surrounded on all sides by a partition wall surface 25 of each of the partition walls 1 facing each other and side surfaces (not shown) facing each other in the front-rear direction in the drawing. Is done. In the ink chamber 2, for example,
The height is 300 μm, the width (the interval between the opposing partition walls 25, 25) is 70 μm, and the depth is 1 mm. A nozzle plate (not shown) having nozzles 4 for discharging ink is provided on a side surface (rear side of the paper surface in the drawing) of each ink chamber 2, and an electrode 24 is provided on a partition wall surface 25 of each ink chamber 2 facing the ink plate 2. Will be arranged.
Each electrode 24 is connected to a piezoelectric element driving section 3 described later.

Such an ink chamber 2 is made of, for example, PZT
A plurality of grooves are formed by cutting the base 21 with a diamond plate or the like, and a metal electrode film is formed on the upper half of the opposing partition surface 25 separating the grooves using aluminum or the like by vapor deposition or sputtering. Provided.
Each of the partition walls 1 is connected to an electrode 2 via a piezoelectric element driving unit 3.
4 operates as a piezoelectric element that is distorted by the voltage applied to 4. That is, the PZT forming the partition 1 is polarized in the height direction (the direction of the arrow in the figure), and an electric field is generated perpendicularly to the polarization direction by applying a potential difference to both side surfaces of the partition 1 via the electrodes 24. The partition wall 1 is deformed in the thickness direction (horizontal direction in the figure) due to the piezoelectric shear strain effect.

FIG. 2 is a block diagram showing a schematic configuration for explaining the gradation processing of the printing apparatus 100 using the ink jet recording head 50 of the present invention. Printing device 100
Is a scanner 61 or a keyboard 62 as print data input means for inputting print data having a gradation value for each recording pixel forming an image based on image information, a display 63, a CPU, a ROM, a RAM, and the like. It mainly includes a piezoelectric element driving unit 3 and a printer driving unit 80.

The piezoelectric element driving section 3 has an input interface 71 for inputting an input signal relating to image information from the scanner 61 and the like, and a resolution for converting the resolution of the input image information into a resolution which can be handled by the printer driving section 80. A conversion unit 72, a gradation processing unit 73, and an element driving pulse generation unit 74 (driving pulse generation unit) that generates a pulse signal for performing gradation expression on the image-processed image information on a printing target member And an output interface 75. The printer driving unit 80 has an ink jet recording head 50 composed of the partition walls 1 connected to the electrodes 24 and a power supply, a circuit unit for driving a carriage motor, a paper feed motor (both not shown), and the like.

The piezoelectric element driving section 3 of the printing apparatus 100 shown in FIG.
Will be described. When an input signal related to image information is input from the scanner 61 or the like via the input interface 71, the resolution converter 72 can handle the resolution of the image information by the printer driver 80 based on a predetermined application program. Convert to resolution. The resolution-converted image information is converted into a multi-level signal by a gradation processing unit 73, and further converted into a pulse signal for performing gradation expression on a printing target member by an element driving pulse generation unit 74. The data is output to the inkjet recording head 50 via the output interface 75.

The operation of the partition 1 will be described with reference to FIGS. Shear mode ink jet head 50
In this case, since the ink chambers 2 share the partition wall 1, ink cannot be simultaneously discharged from the adjacent ink chambers 2 in order to prevent the occurrence of crosstalk between the ink chambers 2 and 2. Therefore, as shown in FIG. 1, there are three ink chambers 2 (B) that serve as a central ink chamber and discharge ink, and two adjacent ink chambers 2 (A) and 2 (C) that do not discharge ink. Are set as a set, and the three successive ink chambers 2 are sequentially shifted one by one when ejecting ink. At the time of ink ejection, as shown in FIG. 3, the electrodes 24 of the ink chamber 2 (B) for ejecting ink are used.
b, the same second drive pulse V2 (second voltage) is applied to the ink chambers 2 (A) and 2 (C) that do not discharge ink while applying the first drive pulse V1 (first voltage). ) Is applied. The set of these three continuous ink chambers 2 is shifted one by one, and for example, the ink chambers 2 for ejecting ink are moved from (B) to (C) to (A) to (B) to (C) to
By repeating the transition (A), the ink can be continuously ejected.

The process of discharging ink by the ink jet head 50 will be described with reference to FIGS. 1, 3 and 4. FIG. 4 shows the timings at which the pulse shown in FIG. 3 is given.
(a) to (d) show the movement of the partition wall 1 operating in synchronization with the operation ((a) to (d) in the upper left of the figure correspond to the timings (a) to (d) in FIG. 3). As shown by timings (a) and (d) in FIG.
For convenience, A, B,
As C, a pulse as shown in FIG. 3 is given to these ink chambers A, B, and C.

First, a first drive pulse V1 is applied to the electrode 24b of the ink chamber B for a first predetermined time L / a. The partition walls 13 and 14 in the partition walls 11 to 16 are driven by the first drive pulse V
With the rise of 1, the ink chamber B is deformed so as to increase its volume, as shown in the timing (b) of FIG. As a result, ink is sucked into the ink chamber B via an ink passage (not shown). Then, the first drive pulse V
With the fall of 1, the partitions 13, 14 return to their natural state. Next, at the same time as the fall of the first drive pulse V1, the second drive pulse V2 is applied to the electrode 24a of the ink chamber A and the electrode 24c of the ink chamber C for a second predetermined time of 2 L / a.

The partitions 13 and 14 are deformed with each rising of the second drive pulse V2 so as to reduce the volume of the ink chamber as shown by the timing (c) in FIG. Thus, a predetermined amount of ink sucked into the ink chamber B is discharged from a nozzle (not shown) of the ink chamber B. Thereafter, the state returns to the natural state with each falling of the second drive pulse V2. The first predetermined time L / a, that is, the pulse width of the first drive pulse V1 is such that the pressure wave in the ink chamber 2 is equal to the length L of the ink chamber 2 in the longitudinal direction (vertical direction in FIG. 4). The sound speed a is set to match the propagation time.
By setting the first predetermined time to L / a, the pressure fluctuation can be increased most effectively, and a high discharge speed can be obtained. The reason will be described below.

FIGS. 5 and 6 show the state of pressure fluctuation in the vicinity of the nozzle 4 when the ink is continuously ejected by the ink jet head 50. FIG. The timings (a) to (d) on the horizontal axis in FIGS. 5 and 6 correspond to the timings (a) to (d) in FIGS. FIG. 5 shows the pressure fluctuation under normal discharge conditions. First, as described above, by applying the first drive pulse V1, the ink chamber B is enlarged to generate a negative pressure in the ink chamber B. When this state is maintained, ink is supplied from the common ink chamber into the ink chamber B. Thereafter, the pressure is reversed and the pressure in the ink chamber B becomes positive, and L / a
After time, the positive pressure in the ink chamber B becomes maximum.

The ink chamber B is rapidly reduced in accordance with the timing at which the positive pressure in the ink chamber B is maximized. Is discharged well. The timing for returning the reduced ink chamber B to the natural state is as follows:
It is determined by the pulse width of the second drive pulse V2, and is used for canceling the residual vibration.
/ A.

The present inventors control the timing of returning the reduced ink chamber B to the natural state, that is, by controlling the pulse width of the second drive pulse V2, the volume of the ink to be ejected changes. I found that.
FIG. 6 shows a pressure change when the reduced ink chamber 2 is returned to the natural state at a quick timing, that is, when the pulse width of the second drive pulse V2 is shortened. In this example, after the pressure in the ink chamber B reaches the maximum positive pressure, the ink chamber B is set to the natural state at the timing when the pressure in the ink chamber B turns negative, so that the meniscus of the ink to be ejected can be changed. It is possible to draw into the chamber B, and it is possible to reduce the discharge amount.

FIG. 7 is a graph showing the results obtained by measuring the ejection amount of ink droplets from the ink jet head 50. Here, the horizontal drive axis is created by plotting the pulse width of the second drive pulse V2 and the vertical axis is plotted with the volume of ink droplets to be ejected. The measurement conditions are shown below. Length of ink chamber in longitudinal direction (L): 1 mm (L / a
Discharge frequency: 20 kHz Driving voltage: 25 V As physical properties of the used ink, viscosity: 4.3 cP, surface tension: 25.8 dyne / cm Under the above conditions, shorten the pulse width of the second driving pulse V2. As a result, compared to the ink droplet volume ejected when the pulse width of the second drive pulse V2 is 2 L / a or more,
It was confirmed that about 80% of small ink droplets could be obtained.

FIG. 8 shows an example of ejection when one recording cycle is constituted by a plurality of drive pulses (hereinafter, referred to as a multi-drop method). FIG. 8 shows a drive pulse in one recording cycle and a state of ejection of ink droplets from the nozzle 4 when one recording cycle is configured with a maximum of 7 drops (8 gradations). The ejection frequency of one drop is determined by the pulse width of the first drive pulse, the pulse width of the second drive pulse, and the pause time between each drop.
It is about 5 kHz. At this time, one recording cycle is 1 /
(135 kHz / 7) ≒ 52 μs, and when the ink chambers 2 are driven in groups of three, the driving frequency is 135 kHz / 7/3 ≒ 6.42 kHz.

In the multi-drop system, the number of gradation control stages can be increased by making the pulse width of the second drive pulse V2 variable. For example, one recording cycle is composed of a maximum of three drops, and a second drive pulse (timing in FIG. 5) for obtaining a droplet of a normal size and the small drop (droplet size of 80% of a normal drop) are used. Assuming that two types of obtained second drive pulses (timing in FIG. 6) can be selected, it is possible to obtain the following ten gradation control stages.

[0033]

[Table 1]

FIGS. 9 to 11 show the second drive pulse V
2 shows an ink ejection operation in the ink jet recording head 50 when the pulse width of No. 2 is changed. FIG. 10 shows a drive pulse for changing the pressure of the ink chamber 2 (each A, B, C) shown in FIG. 9, and FIG. 11 shows the second drive pulse V2 in FIG. The state of the ink chamber 2 (each of A, B, and C) when changing to the two drive pulses V21 is shown.
In this example, ink is ejected by basically the same operation as the driving method shown in FIGS. In addition, at the timing (c) in FIGS. 10 and 11, the partition wall 17 on the right side of the ink chamber C1 is displaced in a direction in which the volume of the ink chamber C1 increases, but the pressure fluctuation of the ink chamber A2 is so large that the ink is ejected. Does not grow.

[0035]

According to the present invention, it is possible to control the amount of ink to be ejected without controlling one recording cycle, thereby enabling high-speed printing. Therefore, it is possible to provide an ink jet recording head capable of expressing higher gradation in monochrome and color printing and a driving method thereof.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a shear mode ink jet head.

FIG. 2 is a block diagram showing a schematic configuration for explaining gradation processing of a printing apparatus using the inkjet head of FIG. 1;

FIG. 3 is a diagram illustrating an example of a waveform of a driving voltage of the inkjet head of FIG.

FIG. 4 is a view for explaining the operation of the ink chamber by the drive voltage in FIG. 1;

FIG. 5 is a graph showing pressure fluctuation in the vicinity of a nozzle of the inkjet head of FIG. 1 when a pulse having a normal pulse width is used.

FIG. 6 is a graph showing pressure fluctuation in the vicinity of a nozzle of the inkjet head of FIG. 1 when a pulse having a small pulse width is used.

FIG. 7 is a graph showing the relationship between the pulse width of a second drive pulse and the volume of an ink droplet.

FIG. 8 is an explanatory diagram schematically showing an example of a driving signal of a multi-drop system and an ink droplet ejected from a nozzle by the driving signal.

FIG. 9 is a cross-sectional view of an inkjet head illustrating another embodiment of a multi-drop type driving signal.

FIG. 10 is a diagram illustrating an example of a drive signal applied to the inkjet head of FIG. 9;

FIG. 11 is a view for explaining the operation of the ink chamber by the multi-drop type drive signal of FIG. 10;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Partition wall (piezoelectric element) 2 (A, B, C) ink chamber 3 Piezoelectric element drive part 24 Electrode (piezoelectric element) 25 Partition wall surface 50 Inkjet recording head 100 Printing device V1 First drive pulse (first voltage) V2 First Two drive pulses (second voltage)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 EA01 EC03 EC07 EC37 EC42 EC72 ED01 ED03 FA04 2C057 AF02 AF39 AF40 AG12 AG32 AG39 AG45 AM03 AM15 AM19 AM21 AP03 AP14 AP22 AP25 AP52 AP54 AQ10 AR04 BA03 BA14 CA01 CA04

Claims (5)

[Claims] 1. A plurality of ink chambers arranged in series separated from each other by a partition, a piezoelectric element constituting at least a part of each partition, and a voltage applied to the piezoelectric element to select from the plurality of ink chambers. A method for driving an ink jet recording head having a piezoelectric element driving unit for changing the volume of an ink chamber to be performed and nozzles for ink ejection provided in each ink chamber, wherein the method is selected by the piezoelectric element driving unit. A first voltage is applied to the corresponding piezoelectric element for a first time so as to increase the volume of the ink chamber, and then a second voltage is applied for a second time so as to reduce the volume of the ink chamber. Applying a voltage to a piezoelectric element to discharge ink from the ink chamber through a nozzle, and controlling an amount of ink discharged from the ink chamber by controlling a second time. The driving method of Kujetto recording head. 2. A driving device according to claim 1, further comprising a driving pulse generating means for generating the first and second voltages as first and second driving pulses, wherein the driving pulse generating means generates the first driving pulse and the first driving pulse. By repeatedly generating the two drive pulses n times each, discharging a maximum of n ink droplets from the nozzles of the ink chamber to form one recording dot within a predetermined time, and controlling the pulse width of the second drive pulse. 2. The method according to claim 1, wherein the size of each ink droplet ejected as one recording dot is controlled. 3. The pulse width of the first drive pulse is defined as the time for a pressure wave generated by driving the piezoelectric element to propagate one way in one ink chamber along the partition in the longitudinal direction. 3. The method of driving an ink jet apparatus according to claim 2, wherein the propagation time is set to twice or less. 4. The piezoelectric element driving section discharges ink from a continuous ink chamber as a set of at least three chambers including a central ink chamber for discharging ink and an ink chamber on both sides thereof that does not discharge ink. 4. A method according to claim 1, wherein the transition is performed such that the transition is sequentially made one by one.
5. A method for driving an ink jet recording head according to any one of the above. 5. A plurality of ink chambers arranged in series separated from each other by a partition, a piezoelectric element constituting at least a part of each partition, and a voltage applied to the piezoelectric element to select from the plurality of ink chambers. Element driving unit for changing the volume of the ink chamber to be ejected, nozzles for ink ejection arranged in each ink chamber, and print data having a gradation value for each recording pixel forming an image based on image information. And a print data input unit for inputting the following.The piezoelectric element driving unit applies a first voltage to the corresponding piezoelectric element for a first time so as to increase the volume of the selected ink chamber, and then, Drive pulse generating means for applying a second voltage to the piezoelectric element for a second time so as to reduce the volume of the ink chamber and generating a drive pulse signal for discharging ink from the ink chamber via a nozzle; And The dynamic pulse generating means controls the second time based on the gradation value of the print data input by the print data input means, thereby controlling the size of the ink droplet ejected from the ink chamber. Characteristic inkjet recording head.