JP3465523B2 - Ink jet recording device - Google Patents

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 for recording an image by ejecting ink drops.

[0002]

2. Description of the Related Art Conventionally, there has been known a print head of an ink jet printer which uses a piezoelectric element (PZT). In such a print head, a pulse voltage corresponding to image data is applied to the piezoelectric element, and the distortion of the piezoelectric element caused by the application of the pulse voltage pressurizes the ink in a predetermined container (ink channel).
Ink drops fly from the nozzles provided in the ink channels toward the recording sheet. An image based on the image data is recorded on the recording sheet by the flight of these ink drops.

In the above-mentioned ink jet printer, by varying the pulse amplitude of the pulse voltage applied to the piezoelectric element, the piezoelectric element is caused to have strains of different sizes, and the appropriate amount of ink drop to be ejected is adjusted. By adjusting the proper amount of the ink drop, it is possible to obtain a plurality of dot diameters of the ink attached to the recording sheet. Among these plural dot diameters, the one with a large dot diameter expresses the dark part of the image, and the one with a small dot diameter expresses the light part of the image.

[0004]

However, in such a print head, immediately after the piezoelectric element is driven for a certain driving cycle or more to eject a large-diameter ink drop corresponding to a large-diameter dot, When ejecting an ink drop of a small diameter corresponding to a dot of a small diameter,
A dot with a small diameter may be printed in a smaller size than when an ink drop with a large diameter is not ejected.

12 to 14 are views for explaining this. FIG. 12 is for explaining the relationship between the gradation of the image data of the dot printed according to the image data and the size of the dot printed immediately after this dot corresponding to the gradation level 1 of the image data. FIG. The number in the leftmost column in FIG. 12 indicates the gradation of image density. Here, the gradation of the image density to be printed is eight steps from 0 to 7, and the dot A is printed according to these eight steps of gradation. If a dot of gradation level 1 is printed immediately after this dot A, the smallest dot B immediately after printing the dot A is obtained.

As shown in FIG. 12, the minimum dot B printed immediately after printing the dot A from the gradation level 0 to the gradation level 4 has the same size as the dot A of the gradation level 1 The diameter of the minimum dot B printed immediately after the printing of the dot A from level 5 to gradation level 7 becomes smaller as the gradation of the dot A becomes larger. The reason why the diameter of the smallest dot B to be printed immediately after this becomes smaller as the gradation of the dot A becomes larger is presumed as follows.

FIG. 13 shows a large-diameter ink drop corresponding to a large-diameter dot (in FIG. 12, gradation levels 5 to 7).
FIG. 8 is a diagram for explaining the state of the ink in the ink channel when a small-diameter ink drop corresponding to a small-diameter dot is ejected immediately after ejecting (corresponding to FIG. FIG. 13A is a diagram showing a state around the ink channel immediately after the drive voltage (pulse voltage) is applied to the piezoelectric element, and FIG. 13B is a view immediately after the drive voltage to the piezoelectric element is turned off. It is a figure which shows the state of an ink channel periphery, FIG.13 (c) is a figure which shows the state of an ink channel periphery after FIG.13 (b). The same parts as those described later with reference to FIGS. 2 to 4 are denoted by the same reference numerals and will not be described in detail here.

First, when a drive voltage is applied to the piezoelectric element,
As shown in FIG. 13A, strain is generated in the piezoelectric element, and in response to this, pressure 3 is applied toward the inside of the ink channel 306.
54 works. Due to this pressure 354, the partition wall 302 is deformed like a dotted line portion 351, the ink channel 306 is pressurized, and the ink column 352 grows from the nozzle 307. A flying drop 353 separates and flies from the tip of the ink column 352 that has finished growing.

Next, the displacement of the partition wall on which the flying drop 353 has been flown is changed from the dotted line portion 351 in FIG.
It is returned like the solid line part 356 of (b) (Deformation like the dotted line part 357 may occur depending on the case). The ink column 352 is rapidly changed from the state of FIG.
Since the ink is returned to the state shown in (b), the air 355 may be held in the ink channel 306 accordingly.

Thereafter, as shown in FIG. 13 (c), the ink surface 358 vibrates while damping in the orifice and stops after a sufficient time has elapsed.

FIG. 14 shows a small-diameter ink drop corresponding to a small-diameter dot (in FIG. 12, gradation levels 1 to 4).
FIG. 8 is a diagram for explaining the state of the ink in the ink channel when a small-diameter ink drop corresponding to a small-diameter dot is ejected immediately after ejecting (corresponding to FIG. 14 (a) to 14 (c) for explaining the state in the ink channel when ejecting the ink drop of the small diameter.
13 (a) to 13 (c) for explaining the state in the ink channel when ejecting a large-diameter ink drop.
Respectively correspond to.

The process in which the partition wall is displaced by the piezoelectric element to form an ink drop is the same when ejecting a small-diameter ink drop and when ejecting a large-diameter ink drop. However, when a small-diameter ink drop is ejected, the amount of strain of the piezoelectric element caused by the application of the pulse voltage is small at first, and accordingly, according to this, FIG.
The amplitude of the vibration of the ink surface 358 shown in (c) is small and the time until the vibration damps to rest is short. In other words, after ejecting a small-diameter ink drop, after the ejection of a small-diameter ink drop, the vibration of the ink surface in the orifice is attenuated and the ink surface becomes stationary. The ink drop corresponding to the image data can be prepared to fly.

As a result, when the drive frequency of the pulse voltage applied to the piezoelectric element is increased according to the image data, when the small diameter ink drop is ejected immediately after the large diameter ink drop is ejected, the orifice Due to the vibration of the ink surface inside, an ink drop having a smaller diameter may be ejected as compared with the case where the large-diameter ink drop is not ejected immediately after. In the image printed in such a case, the image of the low-density portion printed immediately after the high-density portion (with respect to the scanning direction) becomes lighter than the other portions, and the user's intention On the contrary, an image different from the image data is printed.

The present invention has been made to solve the above problems, and an object thereof is to provide an ink jet recording apparatus capable of recording an image faithfully to image data.

[0015]

According to a first aspect of the present invention, a plurality of ink drops of a plurality of sizes are ejected according to image data, and a plurality of sizes of the ink drops corresponding to the plurality of sizes of the ink drops are ejected. It is an inkjet recording apparatus for recording an image by printing dots on a sheet.

This ink jet recording apparatus uses a drive signal.
Ejection to eject an ink drop by being given
And the size of the ink drop to be ejected on the ejection part
And a control unit that gives different drive signals according to the
For dots of multiple sizes, the first group of dots
Is a dot smaller than the dots included in the first group
A second group of dots, which is
When printing the dots of the second group,
If the dots of the first group were printed immediately before printing,
If the dots of the second group are printed immediately before the dots of the second group are printed,
A larger ink drop than if it had been printed.
Drive signal for ejecting the discharge
The feature is that another control is executed .

According to the invention described in claim 1, the same size
Even if the ink drop is ejected immediately before
Depending on the size of the ejected ink drop,
The drive signal to be changed is changed. That is, when a relatively small dot is printed immediately after a relatively large dot, an ink drop corresponding to a larger dot is ejected than an ink drop ejected corresponding to the relatively small dot in other cases. The control unit to the discharge unit.
The drive signal to be controlled is controlled. As a result, when a small dot is printed immediately after a large dot as in the conventional case, a smaller dot than usual is not printed, and an image can be printed faithfully to image data.
Further, in the inkjet recording apparatus, the control unit is
The smallest dot in the second group of dots is printed.
It is preferable to execute the special control at the time of trace. This
As a result, the small dot immediately after the large dot described above
The image is recorded faithfully to the image data even when printing
Can maximize the effect of being able to
It In the inkjet recording apparatus, the control unit is
Is used to print the dots of the second group.
Immediately before printing the dots in the
If this is done, immediately before printing the dots of the second group,
The number of dots is larger than that when the dots of the second group are printed.
Prints a dot that is one step larger than the other dots
The drive signal given to the discharge section to the discharge section.
Is preferred. In addition, the inkjet recording device is
Printing dots of multiple sizes on a sheet and
By not printing dots on the sheet, there are 8 levels
Printing with adjusted density is possible, and the
3 levels from the highest of the 8 gradation levels
It is preferable to include dots for printing with the gradation density of
Good

[0018]

DETAILED DESCRIPTION OF THE INVENTION An inkjet printer, which is one of the embodiments of the present invention, will be described below with reference to the drawings.

FIG. 1 is a perspective view showing a schematic structure of an ink jet printer 1 which is one of the embodiments of the present invention.

The ink jet printer 1 uses paper or OH
An inkjet head 3 that is an inkjet printhead that prints on a recording sheet 2 that is a recording medium such as a P sheet, a carriage 4 that holds the inkjet head 3, and a carriage 4 that is parallel to the recording surface of the recording sheet 2. Swing shafts 5 and 6 for reciprocating movement, a drive motor 7 that reciprocally drives the carriage 4 along the swing shafts 5 and 6, and an idle pulley for converting rotation of the drive motor 7 into reciprocating motion of the carriage 4. 8 and a timing belt 9 are included.

Further, the ink jet printer 1 includes a platen 10 which also serves as a guide plate for guiding the recording sheet 2 along the conveyance path, and a paper pressing plate 11 for suppressing the floating of the recording sheet 2 between the platen 10 and the platen 10. , Recording sheet 2
A discharge roller 12, a spur roller 13 for discharging
It includes a recovery system 14 for cleaning the nozzle surface of the inkjet head 3 that ejects ink to recover the defective ink ejection to a good state, and a paper feed knob 15 for manually conveying the recording sheet 2.

The recording sheet 2 is sent to a recording unit where the ink jet head 3 and the platen 10 face each other by a sheet feeding device such as a manual feed or a cut sheet feeder (not shown). At this time, the rotation amount of the paper feed roller (not shown) is controlled, and the conveyance to the recording unit is controlled.

In the ink jet head 3, a piezoelectric element (PZT) is used as an energy source for flying ink. A voltage is applied to the piezoelectric element, causing distortion.
This strain changes the volume of the channel filled with ink. Due to the change in the volume of the channel, ink is ejected from the nozzle provided in the channel, and recording on the recording sheet 2 is performed.

The carriage 4 main-scans the recording sheet 2 laterally by the drive motor 7, the idle pulley 8 and the timing belt 9, and the ink jet head 3 mounted on the carriage 4 records an image for one line. 1
Each time the recording of the line is completed, the recording sheet 2 is fed in the vertical direction and is sub-scanned to record the next line.

An image is recorded on the recording sheet 2 in this manner, and the recording sheet 2 that has passed through the recording portion is provided with a discharge roller 12 arranged on the downstream side in the conveying direction and a spur roller which comes into contact with the discharge roller 12 at a constant pressure. And 13 are discharged.

Next, the construction of the ink jet head 3 and its surroundings will be described with reference to FIGS.

2 to 4 are views for explaining the structure of the ink jet head 3. 2 is a plan view of a surface having the nozzle of the inkjet head 3, FIG. 3 is a sectional view taken along line III-III of FIG. 2, and FIG. 4 is IV of FIG.
It is a IV-line sectional view.

The ink jet head 3 has a structure in which a nozzle plate 301, a partition 302, a vibrating plate 303 and a substrate 304 are integrally stacked.

The nozzle plate 301 is made of metal or ceramic, has a nozzle 307, and has a surface 318.
Has an ink repellent layer. A thin film is used for the partition wall 302, and the nozzle plate 301 and the diaphragm 3 are used.
It is fixed between 03 and.

Further, the nozzle plate 301 and the partition 302
A plurality of ink channels 306 that accommodate the ink 305, and an ink inlet 309 that connects each ink channel 306 to the ink supply chamber 308 are formed between and. The ink supply chamber 308 is connected to an ink tank (not shown), and the ink 3 in the ink supply chamber 308
05 is supplied to the ink channel 306.

Each ink channel 3 is provided on the vibrating plate 303.
A plurality of piezoelectric elements 313 corresponding to 06 are included. To process the diaphragm 303, first, the diaphragm 303 is connected to the wiring portion 317.
Is fixed to the substrate 304 having an insulating adhesive, and then
This is performed by forming the separate grooves 315 and 316 by dicing and dividing the diaphragm 303. Further, due to this division, the piezoelectric element 313 corresponding to each ink channel 308, the piezoelectric element column portion 314 located between the adjacent piezoelectric elements 313, and the peripheral wall 310 surrounding them are separated.

The wiring portion 317 on the substrate 304 is individually connected to the common electrode side wiring portion 311 connected to the ground and commonly connected to the piezoelectric element 313 in the inkjet head 3 and each piezoelectric element 313 in the inkjet head 3. The individual electrode side wiring part 312 is provided. The common electrode side wiring portion 311 on the substrate 304 is connected to the common electrode inside the piezoelectric element 313, and the individual electrode side wiring portion 312 is connected to the piezoelectric element 31.
3 to the individual electrodes.

The operation of the ink jet head 3 having such a configuration is controlled by the control unit of the ink jet printer 1. Head ejection drive unit 1 of control unit
From 05 (see FIG. 6), a predetermined voltage, which is a print signal, is applied between the common electrode and the individual electrode provided inside the piezoelectric element 313, and the piezoelectric element is deformed in the direction of pushing the partition wall 302. The deformation of the piezoelectric element 313 is transmitted to the partition wall 302, whereby the ink 30 in the ink channel 306 is discharged.
5 is pressurized, and an ink drop flies toward the recording sheet 2 (see FIG. 1) via the nozzle 307.

FIG. 5 is a perspective view for explaining the structure around the carriage 4. Ink cartridge 40 containing ink and having a vent 404 is provided around the carriage 4.
3, a casing 401 that houses the ink cartridge 403, a casing lid 405, and the ink cartridge 4
03, the ink receiving pin 402 for receiving the ink to the inkjet head 3 while being detachable, and the casing lid 4
Casing lid 405 on casing 401 when 05 is closed.
The biasing clutch 406 and the biasing clutch stop 407 for fixing the ink cartridge 403 together with the casing lid 406 while pushing the ink cartridge 403 in the direction opposite to the direction in which the ink cartridge 403 is stored (the direction of arrow D3). A leaf spring 408 for holding is included. The recording sheet is main-scanned by moving the carriage 4 in the direction of arrow D1 shown in the figure, and ink drops are ejected in the direction of arrow D2.

The ink in the ink cartridge 403 contains 80.9% water as a solvent, 11.0% polyhydric alcohol / diethylene glycol, 2.5% thickener / polyethylene glycol # 400, and a coloring agent. dye/
The one containing 4.6% of Bayer BK-SP, 0.8% of surfactant / Olfin E1010, and 0.2% of pH adjuster / NaHCO3 was used as an additive. The ink 305 having this composition has a surface tension of 36 [dyn / cm] and a viscosity of 2.0 [cp] at 25 [° C.].
As the recording paper (recording sheet 2), Epson Superfine paper is used.

Next, the control section of the ink jet printer 1 will be described. FIG. 6 is a block diagram for explaining the configuration of the control unit of the inkjet printer 1.

The control unit of the ink jet printer 1 is C
PU 101, RAM 102, ROM 103, data receiving unit 104, head ejection drive unit 105, head movement drive unit 106, paper feed motor drive unit 107, recovery system motor drive unit 108, and various sensor units 109. Is included.

The CPU 101, which controls the whole, uses the RAM 102 as necessary to execute the programs stored in the ROM 103. This program includes a head ejection drive unit 105, a head movement drive unit 106, a paper feed motor drive unit, which is connected to a host computer or the like and receives image data to be recorded, based on the image data read from the data receiving unit 104. 107, various sensor units 1
09 for controlling an image on the recording sheet 2 and the recovery system motor drive unit 108 and various sensor units 109 when necessary to restore the nozzle surface of the inkjet head 3 to a good state. And a part for.

Under the control of the CPU 101, the head ejection drive unit 105 controls the piezoelectric element 3 of the ink jet head 3.
13, the head movement drive unit 106 drives the drive motor 7 that moves the carriage 4 that holds the inkjet head 3, and the paper feed motor drive unit 107 drives the paper feed roller. Further, based on the control of the CPU 101, the recovery system motor drive unit 108 drives a motor or the like required to recover the nozzle surface of the inkjet head 3 to a good state.

From the head ejection drive unit 105 to the piezoelectric element 31
The waveform of the pulse voltage applied to No. 3 is shown using FIG. 7 and FIG. FIG. 7 is a diagram for explaining these waveforms.
Here, these waveforms are displayed with the voltage application start time aligned on the coordinate axis with the vertical axis representing voltage and the horizontal axis representing the time from the start of voltage application, and the numbers in the figure correspond to gradations. In the waveforms corresponding to the gradation level 1 and the gradation level 2, the rising is steeper than the risings of the other gradation levels 3 to 7, that is, the flying speed of the small-diameter ink drop and the large-diameter ink drop. Close the difference with the flight speed,
This is to eliminate the deviation of the landing positions of the ink drops having different flight speeds on the recording sheet.

Actually, a pulse voltage having a waveform according to the gradation as shown in FIG. 8 is applied to the piezoelectric element corresponding to the image data. Here, as an example, pulse voltages corresponding to gradation level 7, gradation level 2, and gradation level 1 are shown. By applying the pulse voltage corresponding to these gradations to the piezoelectric element, the dot A shown in FIG. 12 is printed according to each gradation.

Next, the control as shown in FIG.
As a result, the pulse voltage according to the gradation as shown in FIG. 10 is applied.

FIG. 9 is a flow chart showing the procedure of the processing executed by the CPU 101, particularly of the portion related to the present invention.

When applying the pulse voltage to the piezoelectric element, first, the gradation data (gradation level of the image data) is referred to in S1. Based on the referred gradation data, S2
Then, "the gradation data of the dot printed immediately before is 5,
It is either 6 or 7, and the gradation data of the dot to be printed next is 1. " Unless "the gradation data of the dot printed immediately before is 5, 6, or 7, and the gradation data of the dot to be printed next is 1" (NO in S2), In the print sequence of S4, printing of dots corresponding to this gradation data is instructed. If "the gradation data of the dot printed immediately before is any one of 5, 6, and 7, and the gradation data of the dot to be printed next is 1," (YES in S2
In steps S) and S3, 1 is added to the next gradation data, that is, the gradation data is set to 2, and the printing sequence of S4 instructs printing of dots corresponding to this gradation data.

In this way, the gradation data is 5,
Immediately after the dots of 6 and 7, the pulse voltage corresponding to the dot of which the gradation data is 2 is applied corresponding to the dot of which the gradation data is 1.

FIG. 10 is a diagram for explaining an example of pulse voltage application in the ink jet printer 1.

In this example, pulse voltages corresponding to the gradation level 7, the gradation level 2, the gradation level 7, the gradation level 2 and the gradation level 1 with the passage of time (the details are shown in FIG. 7). ) Is applied, these are pulse voltages corresponding to dots of image data corresponding to dots of gradation level 7, gradation level 1, gradation level 7, gradation level 1, gradation level 1. 9 is changed by the control showing the procedure in FIG.

FIG. 11 is a diagram for explaining the effect of dot printing by applying a pulse voltage in the ink jet printer 1.

The relationship 501 in FIG. 11 shows the relationship between the gradation of the image data as shown in FIG. 12 and the dots (dot A in FIG. 12) printed corresponding to the gradation.
The relationship 502 in 1 is a dot printed corresponding to the gradation of the immediately preceding image data and the gradation level 1 of the image data as shown in FIG. 12 in the conventional inkjet printer (FIG. 12).
Shows the relationship with the minimum dot B) printed immediately after the dot A is printed. Further, the relationship 503 in FIG.
The relationship between the gradation of the immediately preceding image data and the dots printed corresponding to the gradation level 1 of the image data, which is obtained by the control unit performing the control shown in FIG. 9, is shown.

In order to obtain these relationships, a pulse voltage shown in FIG. 7 is applied at a driving frequency of 4 [kHz] to a piezoelectric element in which 20 layers of 22 [μm] are laminated for each layer, and each floor is printed on the recording paper. The value obtained by reading and averaging the diameters of the dots adhering to the recording paper when 100 dots are printed for each key is used. The ink and recording paper used are those described with reference to FIG.

Referring to the relationships 502 and 503 shown in FIG. 11, in the conventional ink jet printer, the higher the gradation level of the dot printed immediately before, the smaller the gradation level of the image data corresponding to the gradation level 1. The diameter of the printed dots is improved by using the present invention,
Even if the gradation level of the dot printed immediately before increases, the diameter of the dot printed corresponding to the gradation level 1 of the image data does not decrease. That is, the inkjet printer of the present invention can print an image faithful to the image data.

In this embodiment, the control for correcting the dot diameter is performed only for the smallest dot, but a plurality of dots having a relatively small dot diameter may be used depending on the conditions such as the print head and ink. On the other hand, there is a possibility that the problem described with reference to FIG. 12 in [Problems to be solved by the invention] may occur, and in such a case, a similar correction is performed on a plurality of problematic dots. Can be done.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an inkjet printer 1 which is one of embodiments of the present invention.

FIG. 2 is a plan view of a surface of an inkjet head 3 having a nozzle.

FIG. 3 is a sectional view taken along line III-III in FIG.

4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a perspective view for explaining a configuration around a carriage 4.

FIG. 6 is a block diagram illustrating a configuration of a control unit of the inkjet printer 1.

FIG. 7 is a first diagram for explaining a waveform of a pulse voltage applied from the head ejection drive unit 105 to the piezoelectric element 313.

FIG. 8 is a second diagram for explaining a waveform of a pulse voltage applied from the head ejection drive unit 105 to the piezoelectric element 313.

FIG. 9 is a flowchart showing a procedure of processing executed by the CPU 101, particularly of a portion related to the present invention.

FIG. 10 is a diagram for explaining an example of application of a pulse voltage in the inkjet printer 1.

11 is a diagram for explaining the effect of dot printing by applying a pulse voltage in the inkjet printer 1. FIG.

FIG. 12 is for explaining the relationship between the gradation of the image data of the dot printed according to the image data and the size of the dot printed immediately after this dot corresponding to the gradation level 1 of the image data. FIG.

FIG. 13 is a diagram for explaining a state of ink in an ink channel when a small-diameter ink drop corresponding to a small-diameter dot is ejected immediately after a large-diameter ink drop corresponding to a large-diameter dot is ejected. Is.

FIG. 14 is a diagram for explaining a state of ink in an ink channel when a small-diameter ink drop corresponding to a small-diameter dot is ejected immediately after a small-diameter ink drop corresponding to a small-diameter dot is ejected. .

[Explanation of symbols]

1 inkjet printer 3 inkjet head 105 head ejection drive unit 304 substrate 305 ink 307 nozzles 313 Piezoelectric element

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Claims (4)

(57) [Claims] 1. An image is formed by ejecting ink drops of a plurality of sizes according to image data and printing dots of a plurality of sizes corresponding to each of the ink drops of the plurality of sizes on a sheet. An inkjet recording apparatus for recording, which ejects an ink drop when given a drive signal.
A discharge unit for output, to the discharge unit, response to the size of the ink drops to be ejected
A plurality of dots of the first group,
Every dot smaller than the dots included in the first group
A second group of dots is included, and when the control unit prints the second group of dots,
Immediately before the printing of the dots of the second group, the dots of the first group
Is printed, the printing of the dots of the second group
Than when the dots of the second group were printed immediately before
Drive signal for ejecting a large ink drop
An ink jet recording apparatus characterized by executing special control given to a recording and discharging unit . 2. The controller controls the dots in the second group.
Of the special control when printing the smallest dot of
Ink according to claim 1, characterized in that
Jet recording device. 3. The controller controls the marking of the dots of the second group.
When performing a character, immediately before printing the dots of the second group,
When dots of the first group are printed,
Immediately before printing the dots, the dots in the second group should be printed.
One step out of the dots of multiple sizes than when broken
Driving signal to be given to print large dots
Is given to the discharge part.
The inkjet recording apparatus according to claim 2. 4. The ink jet recording apparatus comprises:
Printing dots of several sizes on the sheet and
8 levels of gradation by not printing dots on the screen
It is possible to print with the density, and the dots of the first group are high in the gradation density of the eight levels.
Dots for printing with three levels of gradation density
Any of claims 1 to 3, characterized in that
An inkjet recording device according to claim 1.