Printing method by ink jet and a printing device by ink jet

An amount of ink droplet to form a dot (Ds) that is printed every plural dots (Dn) of normal size is smaller than an amount of ink droplet to form the normal dot (Dn). The special dots (Ds) receive excessive ink from the normal dots (Dn). Deterioration of the print quality, caused by the handing down of ink, is eliminated irrespective of the kind of a material of a print medium.

FIELD OF THE INVENTION 
The present invention relates to a technique for printing an image on a 
print medium by jetting ink droplets through nozzle openings against the 
print medium in accordance with print data. 
DISCUSSION OF THE PRIOR ART 
In printing an image on a print medium by jetting ink droplets through 
nozzle openings against the print medium, an amount of ink droplet is 
controlled so that the adjacent dots are as close as possible to each 
other, in order to improve the print quality. 
There are various kinds of print media. Those print media are different in 
wettabilities to ink and ink absorbing rates. Ink droplets successively 
landing on the print medium attract to each other to form a large ink 
droplet, which in turn moves along fibers of the print medium. This 
phenomenon is frequently observed in the print of ruled lines and graphic 
pattern, which are formed by successively jetting ink droplets. 
Japanese Patent Application Laid-open Nos. Hei. 3-231861 and 4-259566, for 
example, discloses methods for solving those problems inevitable in the 
ink jet printing device. In those methods, ink droplets are shot forth 
every other dot in the main and vertical scan directions in the first 
scan. In the second scan, ink droplets are shot forth against the regions 
where dots were not printed in the first scan. Thus, the time to print one 
dot is made different from the time to print another dot adjacent to the 
former. 
Two scan operations are used for printing a pattern on the region on which 
a pattern can be printed by one scan operation. This remarkably makes the 
printing speed slow. 
There is a proposal to reduce a mixing of color inks in a manner that an 
amount of color ink first used is set to be smaller than a predetermined 
amount of ink (Japanese Patent Application Laid-open No. Hei. 2-253958). 
The proposal requires a fine adjustment of ink amounts. Further, it cannot 
solve the above problem of the monochromatic printing in which one dot is 
printed at one position. 
Accordingly, an object of the present invention is to provide a novel 
printing method by ink jet which can eliminate the handing down of ink and 
ink blot in both monochromatic and color prints, without making the 
printing speed slow. 
Another object of the present invention is to provide a printing method by 
ink jet which can print thin patterns, such as ruled lines, in a 
clearly-delineated fashion. 
Still another object of the present invention is to provide a printing 
method by ink jet which can minimize ink blot in a color print. 
A further object of the present invention is to provide a printing device 
for realizing the printing methods as mentioned above. 
DISCLOSURE OF THE INVENTION 
According to the present invention, there is provided a printing method in 
which dots are formed on a print medium by shooting forth ink droplets 
against the print medium while moving a print head having a plural number 
of nozzle openings in the main scan direction, characterized in that an 
amount of ink used to form a dot that is printed every dots in the main 
scan direction is smaller than an amount of ink used to form each of the 
other dots by a predetermined amount of ink. 
The dots formed by the reduced amount of ink droplets receive excessive 
ink, to thereby eliminate the irregular ink flow along fibers of a print 
medium. 
Elimination of irregular ink blot provides clearly delineated lines and 
images of clear edges. 
When the invention is applied to a color print, the resultant color image 
is clear and sharp since the out-of-register condition of colors caused by 
the ink blot and the handing down of ink are eliminated. 
DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a view showing an embodiment of an ink jet printing device 
incorporating the present invention thereinto. 
FIG. 2 is a view showing an embodiment of an ink jet print head, and 
FIG. 3 is a view showing a pattern of nozzle openings of the print head. 
FIG. 4 is a block diagram showing a print controller according to the 
present invention, 
FIGS. 5(a) to 5(d) show a set of waveforms of drive signals used in the 
print controller, 
FIG. 6 is a flow chart showing the operation of the print controller, and 
FIGS. 7(a) and 7(b) through FIGS. 8(a) and 8(b) show examples of dot 
patterns printed by the printing device. 
FIG. 9 is another flow chart showing the operation of the print controller, 
and 
FIGS. 10(a) and 10(b) show examples of dot patterns printed according to 
the control of the flow chart. 
FIG. 11 is a block diagram showing another print controller according to 
the present invention, and 
FIGS. 12(I) to 12(III) are diagram showing an example of dot pattern 
printed and useful in explaining the operation of the print controller. 
FIG. 13 is a diagram showing nozzle opening patterns of a print head for 
color print to which the present invention may be applied.

BEST MODES OF THE INVENTION 
Embodiments of the present invention will be described with reference to 
the accompanying drawings. 
FIG. 1 shows an embodiment of the present invention. In the figure, 
reference numeral 1 designates a carriage. An ink jet print head 2 which 
faces a print sheet 3 is mounted on the carriage 1. The carriage 1, 
coupled through a timing belt 4 with a drive motor 5, is reciprocatively 
movable along the width of the print sheet 3 (in the directions of arrows 
A and B in the figure), while being guided by a guide member 6. 
The ink jet print head 2 receives ink from an ink tank 8, with its 
connection through an ink supply tube 7 to the ink tank 8. Numeral 9 
designates a sheet transport roller. The sheet transport roller 9, when 
driven by a drive motor (not shown), transports the print sheet 3 in the 
direction (of an arrow C in the figure) perpendicular to the moving 
direction of the carriage 1. 
In FIG. 2 showing an embodiment of the print head. Reference numeral 10 
designates a nozzle plate having nozzle openings 11 formed therein. 
Numeral 12 indicates a fluid path forming plate which includes a through 
hole defining a pressure generating chamber 13, through holes or grooves 
defining ink supply ports 14 and 14 communicatively coupled with both 
sides of the pressure generating chamber 13, and a through hole defining 
two common ink chambers 15 and 15 communicatively coupled with these ink 
supply ports 14 and 14. Numeral 16 represents a vibrating plate 
elastically deformable while being brought into contact with the top of a 
piezoelectric vibrator 17. The nozzle plate 10 and the vibrating plate 16 
are liquid tightly fastened onto the major surfaces of the fluid path 
forming plate 12, respectively, to thereby form a substrate unit 18. 
Reference numeral 19 designates a base including an inner space 20 within 
which the piezoelectric vibrator 17 is placed in a state that it can 
vibrate. More specifically, within the inner space 20, the base part of 
the piezoelectric vibrator 17 is fixed to a fixing member 22, while the 
top of the piezoelectric vibrator 17 is brought into contact with an 
island 16a of the vibrating plate 16 in an opening 21 of the base 19. 
An area of the top of the piezoelectric vibrator 17 may be reduced to be 
extremely small since the piezoelectric vibrator 17 vibrates in a 
longitudinal vibration mode. Therefore, the volume of the pressure 
generating chamber 13 may also be designed to be extremely small. Two 
linear arrays of nozzle openings 11, formed in the nozzle plate 10, are 
arranged parallel to each other and in a zig-zag fashion, as shown in FIG. 
3. 
Black ink, used in the ink jet print head thus constructed, contains 2 wt % 
of carbon black, and color ink used contains 1.5 wt % of pigment, 5 wt % 
of such solvent as diethylene glycol, 15 wt % of such resin emulsion as 
styrene acrylic acid ester copolymer, 7 wt % of maltose, and the remainder 
of pure water. 
The ink thus composed exhibits the following physical properties: viscosity 
is 3 to 5 mPa.multidot.S at normal temperature and surface tension is 30 
to 50 mN/m. The ink jet print head 2 filled with this ink, when driven in 
a normal drive mode, is capable of shooting forth an ink droplet of 0.04 
.mu.g, and forming a dot of 60 .mu.m in diameter on a typical print sheet. 
Therefore, it can draw a continuous line when it shoots forth an ink 
droplet every 1/720 inch of the movement of the print head. 
FIG. 4 shows an arrangement of a print controller for controlling the 
printing operation of the print head. 
The print controller includes an image memory 30 for storing print data 
coming from a host device, specific position determining means 31, edge 
detector means 32 which judges as to whether or not the data to be printed 
is located at the edge, on the basis of data of the image memory 30, 
dot-size select means 33 for determining the size of a dot to be printed 
at a specific position, and dot control means 35 for receiving a signal 
from drive signal generator means 34 and outputting signals to the 
respective piezoelectric vibrators 17 so that the print data from the 
image memory 30 will be printed with a dot of the specified size. 
The specific position determining means 31 includes a column bit counter 40 
for detecting a position of the carriage 1 relative to a print start 
position in the main scan direction in the form of the number of bits, a 
special-dot-position memory 41 for storing data indicative of the position 
where a special dot Ds which are different in size from a normal dot are 
to be printed, and comparator means 42 which produces a signal when the 
contents of the column bit counter 40 are coincident with those of the 
special-dot-position memory 41. 
The drive signal generator means 34 generates a first voltage signal and a 
second voltage signal, as shown in FIG. 5(a). In response to the first 
voltage signal, the piezoelectric vibrator 17 compresses at a fixed rate, 
to thereby cause the ink chamber to suck ink. In response to the second 
voltage signal, the piezoelectric vibrator 17 expands at a fixed rate, to 
thereby cause the ink chamber to shoot forth ink in the form of a droplet 
through the nozzle opening. 
The operation of the dot control means 35 follows. To form a normal dot Dn, 
the dot control means 35 receives the signal (referred to as a normal 
voltage signal) from the drive signal generator means 34, and transfers it 
to the piezoelectric vibrator 17. To form a special dot (different in size 
from the normal dot) at a specific position, the dot control means 35 
selects one of the following three signals from the drive signal generator 
means 34 in accordance with a signal from the dot-size select means 33, 
and transfers the selected one to the piezoelectric vibrator 17. Those 
three signals are: a signal (FIG. 5(b)) (referred to as a first voltage 
signal) whose level is somewhat lower than the signal (FIG. 5(a)), a 
signal (FIG. (c)) (referred to as a second voltage signal) (FIG. 5(c)) 
causing the ink chamber to set forth no ink droplet, and an amplified 
signal (FIG. 5(d)) (referred to as a third voltage signal). 
The operation of the print controller thus arranged will be described with 
reference to a flow chart shown in FIG. 6. 
In response to a print command from a host device (step S01), the print 
controller reads data from the special-dot-position memory 41, to thereby 
determine positions at which special dots Ds are to be printed (step S02). 
In this embodiment, the specific positions of the special dots Ds, as shown 
in FIG. 7(a), are the 4th, 8th, 12th, 16th, . . . columns of the 
odd-numbered main scan line L1, and the 2nd, 6th, 10th, and 14th columns 
on the even-numbered main scan line L2. 
The print data enters the image memory 30, the carriage 1 starts to scan, 
and the ink jet print head 2 reaches a print region. At this time, the 
column bit counter 40 is cleared (step S03), a print operation starts 
(step S04), and the column bit counter 40 starts to count (step S05). 
In this embodiment, the print at the first column C1 is handled. Then, it 
is not coincident with the pattern position (step S06) and no output 
signal is produced from the comparator means 42. Accordingly, the dot 
control means 35 receives a signal (FIG. 5(a)) from the drive signal 
generator means 34, and transfers it to the ink jet print head 2. In turn, 
the ink jet print head 2 shoots forth a preset quantity (0.04 .mu.g in the 
embodiment) of ink against a print medium, to thereby form a dot of the 
normal size (60 .mu.m in diameter in the embodiment) thereon (step S07). 
The column bit counter 40 is incremented every time the print of one column 
is completed (step S05). The comparator means 42 compares the contents of 
the column bit counter 40 with those of the special-dot-position memory 41 
(step S06). 
When the ink jet print head 2 moves to reach the print position of the 2nd 
column C2, the number of the columns of the odd-numbered line L1 is not 
coincident with the contents of the special-dot-position memory 41, but 
the number of the columns of the even-numbered line L2 are equal to a 
value stored in the special-dot-position memory 41. 
Therefore, the dot-size select means 33 receives a first voltage signal 
(FIG. 5(b)) from the drive signal generator means 34, and transfers it to 
the piezoelectric vibrator 17, which is associated with the nozzle opening 
11 aligned with the even-numbered line L2. The same transfers a normal 
voltage signal (FIG. 5(a) that is received from the drive signal generator 
means 34, to the piezoelectric vibrator 17 associated with the nozzle 
opening 11 aligned with the odd-numbered line L1 of the 2nd column C2. 
As a result, a normal dot Dn is printed on the odd-numbered line L1 of the 
2nd column C2 (step S07), and a special dot Ds (smaller than the normal 
dot Dn in the embodiment) is printed on the even-numbered line L2 of the 
same column (step S08). 
Every time the print of one column is thus completed (step S09), the column 
bit counter 40 is incremented (step S05), and the comparator means 42 
compares the contents of the column bit counter 40 with those of the 
special-dot-position memory 41 (step S06). If those are coincident with 
each other, the dot-size select means 33 transfers a first voltage signal 
(FIG. 5(b)) to the piezoelectric vibrator 17, which is associated with the 
nozzle opening aligned with either of the odd- or even-numbered line (step 
S08), and transfers a normal voltage signal (FIG. 5(a)) to other 
piezoelectric vibrators 17 (step S07). 
The thus printed dots are arrayed as shown in FIG. 7(a). As shown, one 
small special dot Ds is located every three normal dots Dn on each line, 
and the special dots Ds on the odd- and even-numbered lines L1 and L2 are 
arranged such that the adjacent special dots Ds are horizontally spaced a 
distance of at least one dot (normal dot Dn). 
Thus, the dots are printed in such a print pattern that one special dot Ds 
is located every three normal dot Dn on each horizontal line, and the 
special dots Ds on the two adjacent lines are not aligned with each other 
in the vertical direction. In the print pattern, a less amount of an ink 
droplet lands on the position of each special dot Ds. An excessive ink at 
the positions of the normal dots Dn on the print medium flows to the 
positions of the special dots Ds. As a result, the special dots Ds 
approach in size to the normal dots Dn, so that one cannot distinguish the 
special dots Ds from the normal dots Dn. The flow of the excessive ink is 
free from the restriction by the fibers of the print medium, for example. 
No irregular blot of ink occurs to the print medium. 
Upon completion of the print of one line (step S09), the print controller 
vertically feeds the print medium at least a distance corresponding to the 
effective print height H (FIG. 3) of the print head. The print controller 
repeats the sequence of the print steps until the print data terminates 
(step S10). 
In the above-mentioned embodiment, the special dot Ds is a small dot. In a 
case where a print sheet of a low ink absorbing rate is used, it is 
preferable to shoot forth no ink droplets to the positions on the print 
sheet which receive the special dots Ds (FIG. 7(b)). That is, the dot-size 
select means 33 sends a second voltage signal (FIG. 5(c)) for causing the 
ink chamber to set forth no ink droplet, to the related piezoelectric 
vibrators 17. Therefore, the excessive ink of the normal dots Dn is 
absorbed to the maximum, to thereby eliminate the hanging down and blot of 
ink perfectly. 
In the pattern of the special dots Ds in the above-mentioned embodiment, 
the special dots Ds on the odd- and even-numbered lines L1 and L2 are 
arranged such that the adjacent special dots Ds are horizontally spaced a 
distance of at least one dot (normal dot Dn). Another pattern of the 
special dots Ds, which may be used, is shown in FIGS. 8(a) and 8(b). As 
shown, the special dots Ds on the odd- and even-numbered lines L1 and L2 
are arranged such that the adjacent special dots Ds have no space 
therebetween, whereby slanted linear arrays of the special dots Ds are 
formed. 
In the above-mentioned embodiment, the special dots Ds are studded in the 
entire dot pattern. To print a line segment of the type in which the 
thickness thereof is particularly thin and the ink blot at the boundaries 
or edges is noticeable, as of ruled lines, the edge detector means 32 is 
operated to print the special dots Ds of small amount of ink only along 
the edges of the line. The resultant line little suffers from ink blot. 
A method of printing the special dots only along the edges of the line, for 
example, will be described with reference to a flow chart of FIG. 9. 
In response to a print command from a host device (step S01), the print 
controller reads data from the special-dot-position memory 41, to thereby 
determine positions at which special dots Ds are to be printed (step S02). 
In this embodiment, the number n (n: integer) of the normal dots Dn is 
designated for the special dot positions. In this embodiment, n is 4. That 
is, data such that the print positions of the special dots Ds on the main 
scan line are 4, 8, 12, and 16 (FIG. 10) is designated. The print data 
enters the image memory 30, the carriage 1 starts to scan, and the ink jet 
print head 2 reaches a print region. In turn, the column bit counter 40 is 
cleared (step S03), and the printing operation starts (step S04). With 
progress of the printing, the column bit counter 40 is incremented (step 
S05). 
The first line L1 corresponds to the edge (step S06). It is not coincident 
with a pattern position stored in the special-dot-position memory 41 since 
the present print is for the first column Cl (step S07). Then, no signal 
is produced from the comparator means 42. 
In this state, the dot control means 35 transfers a normal voltage signal 
(FIG. 5(a)) that is received from the drive signal generator means 34, to 
the print head 2. A preset amount of ink is forcibly discharged through 
the related nozzle opening 11 against the print medium. The result is 
formation of a normal dot Dn on the print medium (step S09). 
The column bit counter 40 is incremented every one column print (step S05). 
The edge detector means 32 checks as to whether or not a pattern to be 
printed is the edge (step S06). In this way, the printing operation 
progresses to reach the print of the fourth column C4. At this time, the 
contents of the column bit counter 40 is equal to a value of the 
special-dot-position memory 41 (step S07). Then, the dot-size select means 
33 transfers a first voltage signal (FIG. 5(b)) that is received from the 
drive signal generator means 34, to the piezoelectric vibrators 17 
associated with the nozzle openings aligned with the first and third lines 
L1 and L3. And the dot-size select means 33 transfers a normal voltage 
signal (FIG. 5(a)) that is received from the drive signal generator means 
34, to the piezoelectric vibrator 17 associated with the nozzle opening 
aligned with the second line L2. 
As a result, the special dots Ds, smaller in size than the normal dot Dn, 
are printed at the fourth column of the first and third lines L1 and L3 
(step S08). The normal dots Dn are printed on the second line L2 (step 
S09). 
In this way, every time the print of one column is completed, the column 
bit counter 40 is incremented (step S05). The lines L1 and L3, which form 
the edges, are compared with the contents of the special-dot-position 
memory 41 (step S07). If the result is the coincidence between them, the 
special dot Ds is printed (step S08). This sequence of the steps is 
repeated. 
The small special dots Ds are regularly printed every three dots on the 
lines L1 and L3 which define the boundaries of a line segment (FIG. 
10(a)). Excessive ink on those lines flows to the special dots Ds, to 
thereby eliminate the irregular blot of ink that otherwise would be caused 
by fibers of the print paper. The resultant line is clearly delineated. 
In the above-mentioned embodiment, the amount of the special dot Ds, which 
is printed on the boundaries of a line segment, is reduced. For some type 
of the print paper, the amount of the special dot Ds may be reduced to 
zero as shown in FIG. 10(b). 
The print of lines is discussed in the above-mentioned embodiments. The 
printing method of the present invention may be applied to a print of the 
type in which a specific area is painted out, such as a graphic print. In 
this case, the peripheral edge of the painted-out area little suffers from 
an irregular blot of ink. In other words, a clearly delineated painted-out 
area is presented. 
FIG. 11 shows an arrangement of a print controller for controlling the 
printing operation of the print head, which is another embodiment of the 
present invention. In the figure, reference numeral 45 designates dot-size 
select means. The dot-size select means 45 determines a print direction on 
the basis of a signal outputted from a print-direction detector means 46. 
In response to a signal representative of a first or forward direction of 
the print, which is produced by the print-direction detector means 46, the 
dot-size select means 33 selects a second voltage signal (FIG. 5(c)), 
which causes the ink chamber to set forth no ink droplet every preset 
number (e.g., four dots) of dots stored in the special-dot-position memory 
41, for the data of the positions which are not arrayed adjacent to each 
other in the vertical scan direction. For other positions than the above 
ones, the dot-size select means 33 selects a normal voltage signal (FIG. 
5(a)) for forming the normal dots Dn, and rids of the designated dots in 
the special-dot-position memory 41. In the print of the second or backward 
direction, the dot-size select means 45 selects a first voltage signal 
(FIG. 5(b)) for forming the special dot Ds of small size at the positions 
of the dots that were removed in the forward print. 
In this embodiment, when color image data enters the image memory 30 from a 
host device, in the forward print mode, the normal dots Dn are printed at 
other column positions other the specific positions, while dots are 
removed every specified position, or four dot columns (FIG. 12(I)). 
Accordingly, excessive ink of the normal dots Dn flows to the empty 
positions formed every plural number of dots, four dots in the embodiment, 
as viewed in the main scan direction. As result, the irregular blot of ink 
does not occur on the paper. 
When the forward print is switched to the backward print, the dot-size 
select means 45 receives a first voltage signal (FIG. 5(b)) from the 
print-direction detector means 46, so that the print head 2 prints a 
special dot Ds at the position at which nothing is printed in the forward 
print mode every time the print head 2 reaches there (FIG. 12(II)). The 
amount of the special dot Ds is smaller than that of the normal dot Dn 
formed or printed in the forward print mode (For example, it is 0.3 times 
as large as the latter). 
A dot pattern formed after the backward print is completed is as indicated 
by the print data and little suffers from the blot of in, as shown in FIG. 
12(III). 
In the above-mentioned embodiments in which empty dots are printed (FIGS. 
7(b), 8(b), and 10(b)), the amount of the normal dot Dn printed is the 
predetermined one. In this case, it may be increased to be 1.2 times as 
large as the predetermined amount of the normal dot Dn. A third voltage 
signal (FIG. 5(d)) whose amplitude is higher than that of the normal 
voltage signal (FIG. 5(a)) for forming the normal dot Dn, is applied to 
the related piezoelectric vibrators 17. The empty dots can satisfactorily 
absorb excessive ink of such large normal dots Dn printed. The resultant 
print has a high density while being free from the hanging down of ink. 
This printing method is suitable for the bold print. 
In the embodiments, the present invention was applied to the monochromatic 
printing. The invention may be applied to a color ink jet print head 
assembly that is constructed as shown in FIG. 13. As shown, the print head 
assembly is provided with four print heads 51, 52, 53 and 54 for black, 
yellow, cyan, and magenta ink. Each print head 51, 52, 53 or 54 has a 
pattern of two, parallel linear arrays of nozzles openings 61, 62, 63 or 
64. In the printing operation, the nozzle opening patterns 61, 62, 63 and 
64 of the print heads 51, 52, 53 and 54 are successively set at the same 
position on the print sheet for printing different color dots there in a 
superimposed fashion. 
Also in the color print head assembly of the invention, the special color 
dot Ds whose ink amount is smaller than the normal color dot Dn is formed 
at a predetermined position on a print medium. Accordingly, the resultant 
color image is free from the dislocation of the dots, the out-of-register 
of colors, and the blot of ink. 
The above-mentioned embodiments each employ the piezoelectric vibrator is 
used for a means for applying a pressure to the pressure generating 
chamber. It is evident that the present invention may be applied to a 
bubble jet print head in which a Joule heat generating element is 
contained in the pressure generating chamber, and the amount of discharged 
ink is controlled by adjusting an electric power fed to the Joule heat 
generating element. 
INDUSTRIAL APPLICATION OF THE INVENTION 
The print head of the present invention can eliminate the irregular ink 
flow which otherwise would be caused by fibers of a print medium, without 
decreasing the print speed, and can make a high quality print on various 
types of the print medium. The print head can eliminate the irregular ink 
blot at the edges of a printed picture. Accordingly, the printed picture 
is clearly delineated, and free from the out-of-register of colors and the 
hanging down of ink.