[0001] The present invention relates to an ink-jet print head, a driving method thereof
and an ink-jet printer using the same. The present invention relates to, in particular,
a drop-on-demand type ink-jet print head for discharging ink using piezoelectric transducers,
a driving method thereof and an inkjet printer using the same.
[0002] In recent years, it has become prevalent to deal with multi-gradation images such
as picture images even on a personal computer. Accordingly, high-quality gradation
printing is required of an ink-jet type printer serving as a device outputting these
images.
[0003] According to a conventional ink-jet print head of this type, the displacement amount
of a piezoelectric transducer in a pressure chamber provided per nozzle is changed,
the sizes of ink droplets discharged from the nozzle are made variable to thereby
output multi-gradation images at high resolution.
[0004] However, there is a limit to the number of stages in which the sizes of ink droplets
discharged at a time can be stably set. For instance, the dimensions of a pressure
chamber are set small so as to allow stable discharge of small ink droplets. In order
to discharge large ink droplets, meanwhile, it is also necessary to provide a piezoelectric
transducer of large displacement amount to discharge large ink droplets. A normal
single piezoelectric transducer cannot exhibits sufficient displacement amount. Furthermore,
if a multi-layered piezoelectric transducer which can exhibit larger displacement
amount than a single-layered piezoelectric transducer is to be used, it is necessary
to increase the number of layers, which pushes up the cost. Also, it is difficult
to output sufficiently high-quality multi-gradation images in a stable manner.
[0005] To solve the problems, there has been proposed a method of overstriking ink droplets
on a dot a plurality of times using a print head for discharging small ink droplets,
and controlling the overstrike frequency to thereby make gradation control.
[0006] With the method, it is possible to output sufficiently high-quality multi-gradation
images in a stable manner. Nevertheless, the fact that ink is discharged on one dot
a plurality of times causes the reduction of print speed.
[0007] There is also proposed a print method of preparing a low-density ink print head and
a high-density ink print head individually, printing dots of predetermined density
or less using the low-density ink print head and printing dots of predetermined density
or more using the high-density ink print head.
[0008] Since this method requires preparing two different heads, i.e., the low-density ink
print head and the high-density ink print head, the production cost increases accordingly.
[0009] There is yet another method disclosed by Japanese Unexamined Patent Application Publication
No. 8-309971.
[0010] FIG. 13 is a block diagram of ink channels of the ink jet head disclosed therein.
[0011] In the example shown in FIG. 13, each communication hole 51 communicating with a
nozzle 52 is tapered and becomes gradually small toward the direction of the nozzle
52. The hole 51 is provided with two pressure chambers 53 opposite to each other or
offset each other in opposite directions. Side walls constituting the pressure chambers
53 are coupled to the communication holes while they form spirals in the same rotation
direction in the vicinity of the holes 51.
[0012] If ink flows are simultaneously generated from the pressure chambers 53 communicating
with the same communication hole 51 by the piezoelectric transducers, respectively,
then the flows applied with rotation by the side walls turn into eddy flows and run
into the communication hole 51. The flows are superimposed to thereby discharge large
ink droplets from the nozzle 52. The ink droplet volume discharged from the nozzle
is changed by selecting and driving one of or both of the two piezoelectric transducers
installed on the two pressure chambers communicating with the single communication
hole.
[0013] According to the conventional ink-jet head shown in FIG. 13, however, ink is discharged
at right angle with the flow direction of ink generated in the pressure chamber and
pressure chambers are coupled to each other through large openings, respectively.
Due to this, it is difficult to efficiently make use of the energy applied onto the
piezoelectric transducers for purposes of discharging ink.
[0014] Moreover, the side walls of the pressure chambers and the communication holes communicating
therewith have complicated, three-dimensional configurations, which configurations
make manufacturing process difficult and may cause cost increase.
[0015] It is, therefore, an object of the present invention to provide an ink-jet print
head which can be easily manufactured and capable of multistage-varying ink droplets
discharged from a nozzle without causing a reduction in print speed and without using
an expensive layered piezoelectric transducer having great output changes.
[0016] An ink-jet print head according to the present invention includes a plurality of
pressure chamber rows formed by connecting a plurality of pressure chambers in series
through a supply path having a smaller channel area than the pressure chambers; a
plurality of piezoelectric transducers provided in the pressure chambers, respectively
and applied with voltage waveforms independently of one another; an ink pool communicating
with a pressure chamber located on one end of each of the pressure chamber rows; and
a plurality of nozzles each communicating with a pressure chamber located on the other
end of the pressure chamber row.
[0017] In addition, an ink-jet printer according to the present invention includes the above-stated
print head; a voltage applied device selection unit for selecting piezoelectric transducers
applied with voltage wave forms based on ink droplets discharged from the respective
nozzles for every pressure chamber row; and a plurality of voltage waveform application
units for sequentially applying voltage waveforms to the piezoelectric transducers
selected by the voltage applied device selection unit at voltage wave form application
timing, at which voltage waveforms are sequentially applied to piezoelectric transducers
of the first pressure chamber to the second pressure chamber for every pressure chamber
row, the timing delayed in phase by 1/2 of natural periods of pressure waves in pressure
chambers with respect to pressure chambers connected to one another on a ink pool
side.
[0018] According to the present invention, pressure chambers are connected, in series, to
one another between the nozzle and the ink pool and provided With piezoelectric transducers,
respectively. The piezoelectrc transducers are sequentially and selectively driven
with phase differences by 1/2 of natural periods of pressure waves in the respective
pressure chambers given. By doing so, it is possible to discharge ink from the nozzle
at high pressure resulting from combined pressure of the respective piezoelectric
transducers if all of the piezoelectric transducers are driven. On the other hand,
it is possible to discharge ink from the nozzle at low pressure if only one of the
transducers is driven. Thus, the sizes of ink droplets discharged from the nozzle
at a time can be varied in a plurality of stages.
[0019] Further, in another ink-jet print head according to the present invention, the pressure
chamber rows include pressure chambers having different pressure wave natural periods
of the pressure chambers.
[0020] Moreover, another ink-jet printer according to the present invention includes the
above-stated another ink-jet print head; a voltage applied device selection unit for
selecting piezoelectric transducers applied with voltage waveforms and maximum voltages
of the voltage waveforms applied to the piezoelectric transducers; and a plurality
of voltage waveform application units for generating voltage wave forms having maximum
voltages for the piezoelectric transducers selected by the voltage applied device
selection unit and sequentially applying the voltage waveforms to the selected piezoelectric
transducers at voltage waveform application timing, at which voltage waveforms are
sequentially applied to piezoelectric transducers of the pressure chamber connected
to the ink pool to the pressure chamber connected to the nozzle for every pressure
chamber row, the timing delayed in phase by 1/2 of pressure wave natural periods of
pressure chambers with respect to pressure chambers connected to one another on a
ink pool side.
[0021] According to the present invention, piezoelectric transducers applied with voltage
waveforms are selected, voltage waveforms having the selected maximum voltages are
generated for the selected piezoelectric transducers and the generated voltage waveforms
are applied to the selected transducers. By doing so, it is possible to set combinations
of ink droplets discharged from the nozzle in far more stages.
[0022] Now, the embodiments of the present invention will be described in detail with reference
to the accompanying drawings, in which:
FIG. 1 is a perspective cross-sectional view of the print head in the first embodiment
according to the present invention;
FIG. 2 is a block diagram of a drive circuit driving a print head according to the
present invention;
FIG. 3 is a flow chart showing the process of driving the print head by a drive circuit
of FIG. 2;
FIG. 4 shows an example of drive waveforms of piezoelectric transducers in the first
embodiment according to the present invention;
FIG. 5 shows an example of a drive waveform selected in case of discharging small
drops of ink;
FIG. 6 shows an example of a drive waveform selected in case of discharging large
drops of ink;
FIG. 7 is a perspective cross-sectional view of a print head in the second embodiment
according to the present invention;
FIG. 8 is an example of a block diagram of a drive circuit driving the print head
of FIG. 7;
FIG. 9 is a flow chart showing the process of driving the print head by a drive circuit
of FIG. 7
FIG. 10 shows an example of a waveform outputted from a waveform generation circuit
shown in FIG. 8;
FIG. 11 shows an example of a waveform outputted from a drive waveform attenuation
circuit shown in FIG. 8 when the waveform of FIG. 10 is inputted;
FIG. 12 shows an example of waveforms applied to the respective piezoelectric transducers
by the drive circuit shown in FIG. 8; and
FIG. 13 is a block diagram of ink channels for a conventional print head.
[0023] FIG. 1 is a perspective view showing the constitution of a print head in the first
embodiment according to the present invention.
[0024] As shown therein, the print head consists of a nozzle plate 4, a head substrate and
a diaphragm 2 on which a plurality of piezoelectric transducers 1a, 1b and 1c are
provided.
[0025] An ink pool 8 and pressure chambers 6a, 6b, 6c connected to the ink pool 8 through
the supply port 7a, 7b, 7c are formed on the upper surface of the head substrate.
If the head substrate is formed out of a dry film on a base such as an SUS by means
of photolithography, the pressure chambers and supply path can be easily formed into
desired shapes. Alternatively, if the substrate is formed out of ceramic by means
of integral burning, the rigidity of the pressure chambers can increase and pressurizing
energy loss can be reduced.
[0026] Between a nozzle 5 and the ink pool 8, a plurality of pressure chambers 6a, 6b and
6c are substantially aligned in series and connected to the nozzle 5.
[0027] The pressure chambers 6a, 6b and 6c are formed to have a predetermined uniform depth.
If the pressure chambers 6a, 6b and 6c have large areas corresponding to the diaphragm
2 with respect to the heights of the chambers, it is possible to obtain sufficient
pressure even with a single layered piezoelectric transducer with small displacement
amount. In addition, it is preferable that corners R are provided in respective corners
of the pressure chambers so as not to keep bubble remaining in the chambers.
[0028] Supply ports 7a, 7b and 7c each having a predetermined length and a narrower width
are provided in connecting portions between the respective pressure chambers 6a, 6b
and 6c and the ink pool 8, respectively, to maintain pressurizing force within the
chambers.
[0029] The cross-section area and length of a supply port are determined by the relationship
between pressurizing force loss within a pressure chamber and ink refill time after
ink is supplied. Since they contradict against each other, they need to be determined
to obtain desired discharge characteristics.
[0030] The connecting portions between the pressure chambers 6a, 6b, 6c and the supply ports
7a, 7b and 7c are provided with tapered portions or corner R portions as required
so as to prevent cavitations due to the generation of eddy and sharp change of pressure.
It is noted that the tapered or corner R portions may be provided in depth direction.
[0031] Also, tapered or corner portions R may be formed in both thickness and width directions.
[0032] The directions of the supply ports in front or back of the respective pressure chambers
6a, 6b and 6c are oriented in the same direction.
[0033] The shape of the supply ports 7a, 7b, 7c allows pressurizing energy generated within
the respective pressure chamber 6a, 6b and 6c to efficiently act on the discharge
of ink.
[0034] The diaphragm 2 is provided to propagate pressuring force of the piezoelectric transducers
1a, 1b, 1c to ink within pressure chambers. The diaphragm 2 is made of SUS material
or the like having only the portion, to which the piezoelectric transducers 1a, 1b,
1c are attached, formed to be sufficiently thin by means of, for example, electroforming
so as to propagate pressurizing force to ink within the pressure chambers without
preventing the deformation of the piezoelectric transducer 1a.
[0035] The piezoelectric transducers 1a, 1b and 1c for converting electric signals to mechanical
energy corresponding to the respective pressure chamber 6a, 6b and 6c are connected
to the diaphragm 2. In addition, signal lines 9a, 9b, 9c and 10 for transmitting electric
signals to these piezoelectric transducers are formed on the surface of the diaphragm
2.
[0036] Next, description Will be given to the drive circuit for driving the print head according
to the present invention with reference to FIG. 2.
[0037] A waveform generation circuit A 12 which generates waveforms to discharge large ink
droplets, a waveform generation circuit B 13 which generates waveforms to discharge
middle-size ink droplets and a waveform generation circuit C 14 which generates waveforms
to discharge small ink droplets are connected to a switch 15. Output from the selected
circuit by the switch 15 is supplied to the piezoelectric transducer 1c of the pressure
chamber closest to the ink pool 8 through the switch 17. A waveform delayed from a
drive waveform applied to the piezoelectric transducer 1c through a delay circuit
16 for generating a delay by 1/2 of the natural period of pressure wave in the pressure
chambers 6a, 6b, 6c is applied to the piezoelectric transducer 1b closer to the nozzle
than the transducer 1c through the switch 17. The drive waveform outputted from the
delay circuit 16 is further inputted into another delay circuit and delayed. The delayed
drive waveform is then applied to the piezoelectric transducer 1a closest to the nozzle
5. While referring to an ink droplet volume table 19, switches 15 and 17 are selected
by a waveform and device selection circuit 18 so as to drive necessary piezoelectric
transducers with the most suitable drive waveforms for obtaining desired ink droplets.
[0038] The process of driving the piezoelectric transducers in the first embodiment will
be described with reference to FIG. 3.
[0039] Ink is supplied from the ink pool 8 through a plurality of supply paths and pressure
chambers to the nozzle 5 and is filled therein. First, a waveform and device selection
circuit 18 calculates ink droplet volume to be discharged from respective nozzles
connected to respective rows of pressure chambers (step S1). Next, based on respective
ink droplet volume to be discharged, a waveform and device selection circuit 18 selects
waveforms and piezoelectric transducers to apply the drive waveform (step S2). A waveform
and device selection circuit 18 may be connected to, for example, a ink droplet volume
table 19 storing the relations between ink droplet volume to be discharged and waveforms
and piezoelectric transducers to be selected, and select the appropriate drive waveform
and piezoelectric transducer to discharge the ink droplet volume required. The number
N of the pressure chamber to be operated is set to 1 (step S3). A waveform and device
selection circuit 18 judges whether the piezoelectric transducer of the pressure chamber
of No. N is one selected in the step S2 (step S4). If the piezoelectric transducer
is to be selected, a waveform and device selection circuit 18 applies the drive waveform
selected by the switch 15 to the piezoelectric transducer of the pressure chamber
N (step S5). That is to say, a drive waveform selected by the switch 15 is applied,
as a print signal, to the piezoelectric transducer 1c opposite to the pressure chamber
6c in closest proximity of the ink pool 8 through the signal line 9c. The voltage
of the drive waveform, for example, may increase linearly from 0V to a predetermined
drive voltage at predetermined rise time and is held to have a predetermined maximum
drive voltage for a predetermined time period, as shown in FIG. 4. The drive of the
drive waveform linearly may fall from the predetermined voltage to 0V at predetermined
fall time, as shown in FIG. 4.
[0040] In this way, a pressure wave applied through the diaphragm 2 by the piezoelectric
transducer 1c propagates throughout the ink within the pressure chamber 6c. The pressure
wave propagates to the adjacent pressure chamber 6b through the supply port 7b.
[0041] If the piezoelectric transducer of the pressure chamber N is judged to be different
from the one selected in step S4, a waveform and device selection circuit 18 does
not applies the drive waveform selected by the switch 15 to the piezoelectric transducer
of the pressure chamber N.
[0042] Next, a waveform and device selection circuit 18 increments the number N. That is,
the next pressure chamber for the nozzle becomes the object to be operated (step S6).
A waveform and device selection circuit 18 judges whether the piezoelectric transducer
of the pressure chamber N is one selected in the step S2 (step S7) If the piezoelectric
transducer of the pressure chamber N is one selected, a delay circuit 16 forms a waveform
delayed in phase by 1/2 of the natural period of the pressure wave in the pressure
chamber N compared to the drive waveform applied to the pressure chamber N-1 (step
S8). Output from the delay circuit 16 is applied to the piezoelectric transducer of
the pressure chamber N (step S9) That is to say, the piezoelectric transducer 1b opposite
to the pressure chamber 6b next to the pressure chamber 6c is applied with the drive
waveform 11b with phase difference as shown in FIG. 4, for example. If the piezoelectric
transducer of the pressure chamber N is judged to be different from the one selected
in step S7, a waveform and device selection circuit 18 does not applies the drive
waveform selected by the switch 15 to the piezoelectric transducer of he pressure
chamber N.
[0043] A waveform and device selection circuit 18 judges whether the piezoelectric transducer
of the pressure chamber N is last one which connects to the nozzle (step S10). If
the piezoelectric transducer of the pressure chamber N is not last one, a waveform
and device selection circuit 18 increments the number N (step S11) and return to the
step S7.
[0044] It is noted that drive waveforms 11a, 11b and 11c applied to the piezoelectric transducers
1a, 1b and 1c corresponding to the respective pressure chambers may be the same as
shown in FIG. 4. In addition, phase differences given to these drive waveforms are
1/2 time difference of fundamental natural time periods for the pressure waves in
the respective pressure chambers. By sequentially driving the piezoelectric transducers
with different phases given to the waveforms in this way, pressurizing energy generated
within a pressure chamber propagates throughout ink within the pressure chamber from
the supply port. As soon as the pressurizing energy propagates to the supply port
connected to the next pressure chamber, the piezoelectric transducer of the pressure
chamber is driven and provided with pressure energy corresponding to the drive displacement
amount.
[0045] The phase difference given to the drive wave form may be taken as 1/2 time difference
of n-th natural period which is one n-th, where n is an integer, of the basic natural
period for the pressure waves for the respective pressure chambers or as 1/2 time
difference of n-th natural period considering that pressure energy is added almost
in the same manner. It is noted that it is most efficient to use the phase difference
based on the fundamental natural period.
[0046] Lastly, the drive wave form 11a having a phase difference is applied to the piezoelectric
transducer 1a opposite to the pressure chamber 6a connected to the nozzle 5. The pressure
energy within the pressure chamber 6a is added to the pressuring energy propagating
from the pressure chamber 6b. If the combined energy reaches the nozzle 5, an ink
cylinder protrudes from the nozzle 5 and ink is discharged therefrom. The quantity
of ink within the pressure chamber 6a is reduced due to the discharge of ink. Ink
is then supplied from the ink pool 8 through the ink supply paths 7a, 7b, 7c and pressure
chambers 6b, 6c into the pressure chamber by the capillary action of the nozzle 5
and the quantity of ink is recovered to the original level, thus completing a series
of operations.
[0047] Thus, if 3 pressure chambers are included in a respective row, and all of the three
piezoelectric transducers are driven with drive waveforms for largest ink droplets,
pressurizing energy almost three times as large as that in case of a single pressure
chamber is applied to ink. Due to this, ink droplets three times as large as the conventional
largest ink droplet can be discharged. In addition, if only one piezoelectric transducer
is driven under the drive condition that the smallest ink droplets are discharged,
the same quantity of ink droplets as that of the conventional smallest ink droplets
can be discharged. The ink droplets discharged from one nozzle can be stably adjusted
within a wide range.
[0048] Next, the operation of controlling the size of ink droplets discharged from the nozzle
5 by the drive waveforms of the piezoelectric transducers will be described with reference
to FIGS. 5 and 6.
[0049] FIG. 5 shows a waveform in a case where small ink droplets are discharged. FIG. 6
shows a waveform in a case where large ink droplets are discharged.
[0050] Drive displacement amount is set by changing pressure energy, more specifically,
by changing voltage waveforms applied to the piezoelectric transducers. To discharge
small drops of ink, drive voltage is increased, drive time is shortened and rise time
and fall time are shortened as shown in FIG. 5. Conversely, to discharge large drops
of ink, drive voltage is decreased, drive time is lengthened and rise and fall time
are lengthened as shown in FIG. 6.
[0051] Even if the size of an ink droplet is variable, the ink droplet discharge rate should
not be changed between a case where small drops of ink are discharged and a case where
large drops of ink are discharged so as to make the ink droplet position constant.
[0052] In an ink-jet printer employing the ink-jet print head of the present invention,
ink droplets can be adjusted by changing the number and combination of selected piezoelectric
transducers for applying drive waveforms, in a multistage manner stably or without
providing a drive circuit for generating many drive waveform patterns.
[0053] If discharging ink droplets closer to smallest ink droplets, only the piezoelectric
transducer of the pressure chamber closest to the nozzle is applied with a drive waveform
to thereby change the waveform, while the remaining two piezoelectric transducers
are not applied with drive waveforms.
[0054] If discharging ink droplets closer to largest ink droplets, the piezoelectric transducers
of all of the pressure chambers are applied with drive waveforms to thereby change
the waveforms.
[0055] If discharging middle-sized ink droplets, the piezoelectric transducer 1a of the
pressure chamber 6a closest to the nozzle 5 and one of the piezoelectric transducers
of the remaining two pressure chambers are applied with drive waveforms to thereby
change the waveforms. The piezoelectric transducer of the remaining pressure chamber
is not applied with a drive waveform. If the pressure chamber 6c farthest from the
nozzle is selected, energy loss exists since pressure wave passes through the supply
port 7b until pressure wave propagates to the pressure chamber 6a closest to the nozzle.
For that reason, the size of ink droplets applied to the pressure chamber 6a is smaller
than that applied to the pressure chamber 6b even if the same energy is applied to
them.
[0056] If the largest ink droplets in case of applying a drive waveform only to one piezoelectric
transducer are larger than the smallest ink droplets in case of applying drive waveforms
to two piezoelectric transducers, or if the largest ink droplets in case of applying
drive waveforms to two piezoelectric transducers are larger than the smallest ink
droplets in case of applying drive waveforms to three piezoelectric transducers, then
the combination of the number of drive transducers and drive waveforms, by which ink
droplets closest to desired ink droplets are obtained, is selected and the piezoelectric
transducers in accordance with the selected number of the drive transducers are applied
with selected drive waveforms.
[0057] As described above, according to the present invention, a plurality of pressure chambers
necessary to discharge micro-drops and having short natural periods are coupled to
one another. This makes it possible to discharge micro-drops to large drops from a
single nozzle. Owing to this, it is possible to obtain high-speed, inexpensive, high
quality print outputs without the need to overstrike on a dot and use many-valued
density ink to express an image by gradations.
[0058] In this embodiment, the piezoelectric transducers are applied with the same drive
waveforms which are delayed respectively. It is also possible to select different
waveforms and apply them to the piezoelectric transducers. By doing so, far more types
of ink droplets can be discharged.
[0059] In this embodiment, a piezoelectric transducer is used as a transducer for converting
an electric signal for generating pressurizing force in the pressure chamber 6 into
mechanical energy. The piezoelectric transducer may be a single layered piezoelectric
transducer or multi-layered piezoelectric transducer.
[0060] Moreover, in this embodiment, three sets of pressure chambers and supply ports are
connected in series. At least two sets suffice to provide the same advantage.
[0061] Next, the second embodiment of the present invention will be described in detail
with reference to the accompanying drawings.
[0062] FIG. 7 is a perspective cross-sectional view showing the structure of a print head
in the second embodiment according to the present invention. The print head in this
embodiment differs from that in the first embodiment in that three pressure chambers
26a, 26b and 26c coupled to one another through supply ports 7 are formed in different
sizes. For instance, as shown in FIG. 7, unlike the first embodiment, the sizes of
pressure chambers are set smaller so that the natural periods of pressure waves are
made shorter as the pressure chambers are closer to the nozzle 5. In other words,
the sizes of the pressure chambers are set such that the natural period of pressure
wave in the pressure chamber 26b closer to the nozzle 5 than the pressure chamber
26c adjacent to an ink pool 8 is shorter than that in the pressure chamber 26c and
that the pressure wave natural period in the pressure chamber 6a closer to the nozzle
5 than the pressure chamber 26b is shorter than that in the pressure chamber 26b.
The sizes of piezoelectric transducers 21a, 21b and 21c driving the pressure chambers
26a, 26b and 26c, respectively are set according to the sizes of the corresponding
pressure chambers.
[0063] Additionally, a print head drive circuit in the second embodiment according to the
present invention differs from that in the first embodiment in that the piezoelectric
transducers 21a, 21b and 21c are applied with drive waveforms of different maximum
voltages. In this embodiment, as shown in, for instance, FIG. 8, drive waveform attenuation
circuits 32 and 33 for attenuating the maximum voltages of drive waveforms are provided
between switches 17 connected to the piezoelectric transducers 21a, 21b and delay
circuits 16 for delaying the timing of a voltage waveform outputted from a waveform
generation circuit 31, respectively. This print head drive circuit shown in FIG. 8
is also provided with a device and maximum voltage selection circuit 34, which selects
the piezoelectric transducers to apply the voltage waveform among a plurality of piezoelectric
transducers 21a, 21b, 21c and selects maximum voltages of applied drive waveforms
by setting respective attenuation ratios at drive waveform attenuation circuits 32,
33. The waveform generation circuit 31 may have the three waveform generation circuits
described in the first embodiment contained therein and a drive waveform generated
from one of the contained circuits may be selected by a selection circuit which is
not shown. Needless to say, the waveform generation circuit 31 may be structured to
output only one type of waveform.
[0064] Next, the process of driving the piezoelectric transducers in this embodiment will
be described with reference to FIG. 9.
[0065] First, a device and maximum voltage selection circuit 34 calculates ink droplet volume
to be discharged from respective nozzles connected to respective pressure chamber
rows (step S1). Next, based on respective ink droplet volume to be discharged, a device
and maximum voltage selection circuit 34 selects piezoelectric transducers to apply
the drive waveform and maximum voltages of voltage waveform to be applied to these
selected piezoelectric transducers (step S21). The number N of the pressure chamber
to be operated is set to 1 (step S3). A device and maximum voltage selection circuit
34 judges whether the piezoelectric transducer of the pressure chamber of No. N is
one selected in the step S2 (step S4). If the piezoelectric transducer is to be selected,
a device and maximum voltage selection circuit 34 applies the drive waveform having
the selected maximum voltage to the piezoelectric transducer of the pressure chamber
N (step S22).
[0066] If the piezoelectric transducer of the pressure chamber N is judged to be different
from the one selected in step S4, a device and maximum voltage selection circuit 34
does not applies the drive waveform to the piezoelectric transducer of the pressure
chamber N.
[0067] Next, a device and maximum voltage selection circuit 34 increments the number N.
That is, the next pressure chamber for the nozzle becomes the object to be operated
(step S6). A device and maximum voltage selection circuit 34 judges whether the piezoelectric
transducer of the pressure chamber N is one selected in the step S2 (step S7). If
the piezoelectric transducer of the pressure chamber N is to be selected, a delay
circuit 16 forms a waveform having the selected maximum voltage and delayed in phase
by 1/2 of the natural period of the pressure wave in the pressure chamber N with comparison
to the drive waveform applied to the pressure chamber N-1 (step S23). The formed drive
waveform is applied to the piezoelectric transducer of the pressure chamber N (step
S9) If the piezoelectric transducer of the pressure chamber N is judged to be different
from the one selected in step S7, a device and maximum voltage selection circuit 34
does not applies the drive waveform to the piezoelectric transducer of the pressure
chamber N. A device and maximum voltage selection circuit 34 judges whether the piezoelectric
transducer of the pressure chamber N is last one connected to the nozzle (step S10).
If the piezoelectric transducer of the pressure chamber N is not last one, a waveform
and device selection circuit 18 increments the number N (step S11) and return to the
step S7. The waveform generation circuit 31 may include 3 waveform generation circuits
and switch as described in the first embodiment. The waveform generation circuit 31
may output only one waveform, too.
[0068] When a waveform as shown in, for example, FIG. 10 is inputted, the drive waveform
attenuation circuit 32 outputs a waveform which maximum voltage is attenuated while
time from the start of the rise of the inputted waveform until the end of the fall
thereof and rise/fall voltage gradients are not changed.
[0069] The print head drive circuit shown in FIG. 8 respectively applies drive waveforms
41a, 41b and 41c shown in FIG. 12 to the piezoelectric transducers 21a, 21b, 21c.
The drive waveform 41b is delayed by 1/2 of the natural period for the pressure chamber
26b with respect to the drive waveform 41c by the delay circuit 16 and the maximum
voltage of the drive waveform 41b is attenuated by the drive waveform attenuation
circuit 32. The drive waveform 41a is delayed by 1/2 of the natural period for the
pressure chamber 26a with respect to the waveform 41b by the delay circuit 16 and
the maximum voltage of the waveform 41a is attenuated more greatly than the waveform
41b by the drive waveform attenuation circuit 33.
[0070] The maximum voltages of the drive waveforms applied to the piezoelectric transducers
21a and 21b are attenuated more greatly than the maximum voltage of the drive waveform
applied to the piezoelectric transducer 21c. By doing so, the piezoelectric transducers
21a, 21b and 21c corresponding to the respective pressure chambers are applied with
waveforms of different maximum voltages.
[0071] The pressure chambers have different sizes and the settings of maximum voltages of
drive waveforms are different, thereby allowing the combination of the types of ink
droplets to be freely selected.
[0072] As described so far, according to the present invention, plural sets of pressure
chambers and supply ports are arranged to be coupled to one another in series between
the nozzle and the ink pool. In addition, the piezoelectric transducers corresponding
to the respective pressure chambers are arranged. With this structure, it is possible
to drive the selected piezoelectric transducers with selected drive waveforms having
phase differences so as to add driving power in respective pressure chambers. Besides,
if the piezoelectric transducers are selectively driven, it is possible to change
diameters of drops from small drops requiring a pressure chamber having a short natural
period to large drops requiring great changes in the volume of pressure chambers.
[0073] Moreover, by providing a plurality of pressure chambers coupled in series with different
natural periods, or by applying the piezoelectric transducers of the pressure chambers
coupled in series with waveforms of different maximum voltages, it is possible to
arbitrarily set the combination of ink droplets discharged.
1. An ink-jet print head, comprising:
a plurality of pressure chamber rows formed by connecting a plurality of pressure
chambers in series by a plurality of supply paths each having a smaller channel area
than said pressure chamber;
a plurality of piezoelectric transducers provided in the pressure chambers, respectively
and applied with voltage waveforms independently of one another;
an ink pool communicating with a pressure chamber located on one end of each of the
pressure chamber rows; and
a plurality of nozzles each communicating with a pressure chamber located on the other
end of the pressure chamber row.
2. The ink-jet print head according to claim 1, wherein said pressure chamber rows include
pressure chambers having different natural periods of the pressure waves therein.
3. A method for driving an ink-jet print head including a plurality of pressure chamber
rows formed by connecting a plurality of pressure chambers in series by a plurality
of supply paths each having a smaller channel area than sad pressure chamber; a plurality
of piezoelectric transducers provided in the pressure chambers, respectively and applied
with voltage waveforms independently of one another; an ink pool communicating with
a first pressure chamber located on one end of each of the pressure chamber rows;
and a plurality of nozzles each communicating with a second pressure chamber located
on the other end of the pressure chamber row, said driving method comprising:
selecting piezoelectric transducers to be applied with voltage waveforms for every
pressure chamber row;
sequentially generating voltage waveforms for piezoelectric transducers, from said
first pressure chamber to said second pressure chamber, at voltage waveform application
timing delayed in phase from that of other pressure chambers connected to one another
on an ink pool side, by 1/2 of natural periods of pressure wave in pressure chambers;
and
sequentially applying voltage waveforms generated in said generating step to the piezoelectric
transducers selected in said selecting step.
4. The method according to claim 3, wherein said selecting step is further selecting
maximum voltages to be applied to the selected piezoelectric transducers among a plurality
of predetermined voltages.
5. The method according to claim 3, wherein said selecting step is selecting the piezoelectric
transducers based on a combination of piezoelectric transducers capable of providing
ink droplets closest to desired ink droplets while referring to a relationship between
combinations of piezoelectric transducers applied with said voltage waveforms and
the discharged ink droplets.
6. The method according to claim 4, wherein said selecting step is selecting piezoelectric
transducers and maximum voltages based on the piezoelectric transducer driving conditions
capable of providing ink droplets closest to desired ink droplets while referring
to a relationship between the piezoelectric transducer driving conditions and the
ink droplets under the conditions, said conditions including combinations of piezoelectric
transducers to apply voltage waveform and maximum voltages of voltage waveform to
be applied to respective transducers.
7. An ink-jet printer, comprising:
an ink-jet print head including a plurality of pressure chamber rows formed by connecting
a plurality of pressure chambers in series by a plurality of supply paths each having
a smaller channel area than said pressure chamber; a plurality of piezoelectric transducers
provided in the pressure chambers, respectively and applied with voltage waveforms
independently of one another; an ink pool communicating with a pressure chamber located
on one end of each of the pressure chamber rows; and a plurality of nozzles each communicating
with a pressure chamber located on the other end of the pressure chamber row;
voltage applied device selection unit for selecting piezoelectric transducers applied
with voltage waveforms;
voltage waveform generating unit for generating voltage waveforms for piezoelectric
transducers, from said first pressure chamber to said second pressure chamber, at
voltage waveform application timing delayed in phase from that of other pressure chambers
connected to one another on an ink pool side, by 1/2 of natural periods of pressure
wave in pressure chambers; and
voltage waveform application units for sequentially applying voltage waveforms generated
in said voltage waveform generating unit to the piezoelectric transducers selected
in said voltage applied device selection unit.
8. An ink-jet printer, comprising:
an ink-jet print head including a plurality of pressure chamber rows formed by connecting
a plurality of pressure chambers, having different pressure wave natural periods,
in series by a plurality of supply paths each having a smaller channel area than said
pressure chamber; a plurality of piezoelectric transducers provided in the pressure
chambers, respectively and applied with voltage waveforms independently of one another;
an ink pool communicating with a pressure chamber located on one end of each of the
pressure chamber rows; and a plurality of nozzles each communicating with a pressure
chamber located on the other end of the pressure chamber row;
voltage applied device selection unit for selecting piezoelectric transducers applied
with voltage waveforms and maximum voltage of the voltage waveforms applied to the
piezoelectric strain;
voltage waveform generating unit for generating voltage waveforms having said maximum
voltages for piezoelectric transducers, from said first pressure chamber to said second
pressure chamber, at voltage waveform application timing delayed in phase from that
of other pressure chambers connected to one another on an ink pool side, by 1/2 of
natural periods of pressure wave in pressure chambers; and
voltage waveform application units for sequentially applying voltage waveforms generated
in said voltage waveform generating unit to the piezoelectric transducers selected
in said voltage applied device selection unit.