Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1997-06-09
2001-04-17
Royer, William J. (Department: 2852)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06217141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method of driving a piezo-electric type ink jet head for jetting an ink out of a nozzle by making use of a distortion of a piezo-electric element and, more particularly, to a method of driving a piezo-electric type ink jet head for changing a quantity of ink particles jetted out.
2. Description of the Related Art
Ink jet printers are used for apparatuses such as a printer, facsimile and so on. There has been availed a piezo-electric type ink jet printer using a piezo-electric element among those ink jet printers. The piezo-electric type ink jet printer is constructed to jet inks out of a nozzle by making use of a distortion of the piezo-electric element.
In this type of ink jet printer, a print dot diameter is required to be variable to express gradations of a print. For this purpose, changing a quantity of ink particles to be jetted is requested of the above printer.
A method of jetting the inks is classified into a positive polarity drive method of sucking the inks after jetting out the inks, and a negative polarity drive method of jetting out the inks after sucking the inks. According to the negative polarity drive method, a scatter of the ink particles is stable, and a possible-of-getting-particled frequency is broad.
FIGS. 25A-25D
and
FIGS. 26A-26E
are explanatory diagrams showing a first prior art.
A d31-mode is a mode making most of a distortion caused when the piezo-electric element shrinks upon an application of a positive voltage. In this mode, the piezo-electric element is distorted in a perpendicular direction for an electric-field direction. In this d31-mode, when a voltage indicated by a dotted line in
FIG. 25A
is applied to the piezo-electric element, operation of jetting the inks is performed after sucking the inks.
FIGS. 26A-26E
are enlarged views of the nozzle. A meniscus
10
is formed in a nozzle
1
. Herein, a velocity vector the meniscus has is expressed by “V”.
FIG. 26A
shows a state of how the nozzle
1
and the meniscus
10
might be when the piezo-electric element is in an initial state. A surface tension of the meniscus
10
equibrates with a negative within the pressure chamber, and the meniscus
10
exists in an initial position in the vicinity of a nozzle outlet.
FIG. 26B
shows a position. of the meniscus
10
when increasing the negative pressure in the pressure chamber by letting the piezo-electric element shrink in such a direction as to expand the pressure chamber. That is, it shows a case where a positive voltage having a positive inclination is, as indicated by a dotted line in
FIG. 25A
, applied thereto. The negative pressure in the pressure chamber gets larger than the surface tension of the meniscus
10
, and the meniscus
10
is receded toward the pressure chamber.
FIG. 26C
shows a position when the negative pressure in the pressure chamber is reduced due to an influx of the inks from an ink supply port enough to reduce the negative pressure in the pressure chamber and the meniscus
10
is substantially stopped. At this time, the meniscus
10
is forced to move back to the vicinity of the pressure chamber.
FIG. 26D
shows a position of the meniscus
10
when the piezo-electric element is abruptly expanded in such a direction as to contract the pressure chamber. That is, it shows a case where a voltage having a negative inclination is, as indicated by a dotted line in
FIG. 25A
, applied thereto. The meniscus
10
forms a layer flow by dint of a positive pressure within the pressure chamber and the surface tension of the meniscus, and has a larger velocity toward the nozzle outlet. Accordingly, the meniscus
10
quickly moves toward the nozzle outlet.
FIG. 26E
shows a state of the meniscus
10
when the expansion of the piezo-electric element is stopped. The pressure in the pressure chamber becomes a large negative pressure due to a flux of the inks to the ink supply port as well as to the nozzle
1
. Therefore, the inks in the nozzle
1
are abruptly decelerated. The ink liquid outside the nozzle has, however, a velocity enough to scatter out and hence overwhelms the surface tension given from the inks of the nozzle
1
, thereby getting particled. Thereafter, the inks having an insufficient velocity are forced to return inside the nozzle
1
by dint of the surface tension.
The states described above are repeated, thereby forming the ink particles and jetting them out.
Known as a first prior art method of controlling the particle quantity of the ink particles is a method of decreasing a voltage amplitude applied to the piezo-electric element down to V
2
as indicated by a solid line in FIG.
25
A. The particle quantity of the ink particles can be reduced by this method.
FIGS. 25B through 25D
show a state of how the nozzle
1
and the meniscus
10
might be when jetting the small ink particles.
FIG. 25B
shows a state when starting a suction of the inks. The meniscus
10
is moving toward the pressure chamber.
FIG. 25C
shows a state of how the nozzle
1
and the meniscus
10
might be when finishing the suction of the inks and starting the jet-out of the inks. Since an amplitude of the voltage applied to the piezo-electric element is reduced, a recession quantity of the meniscus becomes smaller than in the case of
FIG. 26
c.
FIG. 25D
shows a state of how the nozzle
1
and the meniscus
10
might be when the ink liquid gets particled. As the recession quantity of the meniscus
10
has been decreased, the ink particle quantity also decreases.
A second prior art method of controlling the ink particle quantity will be explained with reference to
FIGS. 27A through 27D
.
According to the second method, the ink particle quantity is reduced by changing a receding velocity of the meniscus. Along with this, a jetting speed is controlled. More specifically, as indicated by a solid line in
FIG. 27A
, a drive voltage for the piezo-electric element remains unchanged, and a rising slope of the drive voltage is made steep. The particle quantity of the ink particles becomes smaller as this slope gets steeper and steeper. Note that the drive waveform in the case of generating a normal quantity of ink particles is shown by the dotted line as in FIG.
25
A.
FIG. 27B
shows a state of how the nozzle
1
and the meniscus
10
might be when starting the suction of the inks. At this time, a higher velocity toward the pressure chamber is given to the meniscus
10
by quickly sucking the inks than in the case of jetting a normal quantity of the ink particles (as indicated by the dotted line in FIG.
27
A). Then, the meniscus
10
is forced to move to the vicinity of the pressure chamber.
FIG. 27C
shows a state of how the nozzle
1
and the meniscus
10
might be when starting the jet-out of the inks upon finishing the suction of the inks. The meniscus
10
is receded to the vicinity of the pressure chamber in the nozzle
1
by the suction of the inks, and therefore the inks can be accelerated enough.
FIG. 27D
shows a state of how the nozzle
1
and the meniscus
10
might be when the ink liquid gets particled. The ink liquid having the sufficient velocity gets particled and thereafter scatter out.
A third prior art method of controlling the ink particle quantity will be described referring to
FIGS. 28A through 28D
.
According to the third method, as indicated by a solid line in
FIG. 28A
, the drive voltage is reduced down to V
2
as in the first prior art method, and the recession quantity of the meniscus when sucking the inks is decreased. Along with this, a voltage changing velocity when jetting the inks is made much higher, thereby preventing the meniscus from decreasing in its velocity when jetting the inks.
FIG. 28B
shows a state of how the nozzle and the meniscus might be when starting the suction of the inks.
FIG. 28C
shows a state of how the nozzle and the meniscus might be when finishing the suction of the inks. The voltage amplitude is reduced, and hence the meniscus
10
is not receded to the vicinity of the pressure chamber. Her
Mikami Tomohisa
Nakamura Shigeyoshi
Nou Hiroshi
Semba Satoshi
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Royer William J.
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