Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-11-14
2003-12-16
Fuller, Benjamin R. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S011000, C347S009000
Reexamination Certificate
active
06663208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a controller for an ink-jet apparatus and, more particularly, to a controller for a piezoelectric type ink-jet apparatus.
2. Description of Related Art
Ink-jet type recording devices are well known in the prior art, and typically used for recording image data outputted from personal computers, facsimile machines, and the like. This type of recording device is superior to other types of recording devices in that it is quiet and capable of recording on sheets of various materials.
FIG. 1
is an exploded perspective view of part of an ink-jet head. Illustrated is the basic construction of an ink-jet head used for a piezoelectric type ink-jet printer. The ink-jet head is formed by stacking a cavity plate
10
, a piezoelectric actuator
20
, and a flexible flat cable
30
in this order from the bottom. The ink-jet head is provided with cavities
16
, a supply hole
19
, for supplying ink to the ink-jet head, and surface electrodes
26
,
27
electrically connected to piezoelectric elements
50
, which will be described later. The cavity plate
10
is formed by stacking five plates.
FIGS. 2A-2C
and
3
A-
3
C are vertical cross-sectional views of the ink-jet head taken along a direction perpendicular to its longitudinal direction when the cavity plate
10
and the piezoelectric actuator
20
are stacked upside down relative to the state shown in FIG.
1
. As shown in
FIG. 2A
, the cavity plate
10
is formed by stacking five plates, namely, a nozzle plate
34
, a first plate
36
a,
a second plate
36
b,
a third plate
36
c,
and a fourth plate
36
d.
A manifold
44
, a restrictor orifice
46
, a cavity
16
, and a communication passage
48
are formed in corresponding plates
36
a
-
36
d.
A nozzle
32
is formed in the nozzle plate
34
and ink in the communication passage
48
is ejected therethrough. The manifold
44
communicates with the supply hole
19
through a passage (not shown). In the ink-jet head,
75
sets of cavities
16
and nozzles
32
are arrayed in a row and another
75
sets of cavities and nozzles, which are bilaterally symmetrical with those shown in
FIGS. 2A-2C
, are arrayed in a row. A total of 150 sets of cavities and nozzles are arrayed in two rows such that 150 nozzles are aligned in a row. The piezoelectric actuator
20
is provided with a plurality of piezoelectric elements
50
, which are placed adjacent to the cavities
16
.
In a state shown in
FIG. 2B
, a voltage is applied to the piezoelectric element
50
to expand the piezoelectric element
50
. When the application of a voltage to the piezoelectric element
50
is stopped, the piezoelectric element
50
contracts, as shown in
FIG. 2C
, and a negative pressure is developed in the cavity
16
. Then, ink flows from the manifold
44
to the cavity
16
. Upon reapplication of a voltage to the piezoelectric element
50
, it expands again, as shown in
FIG. 3A
, and the ink that has flowed in is pressurized and ejected as a main ink droplet I from the nozzle
32
. The above-described operation is repeated a specified number of times, according to a drive waveform supplied from a control circuit to the ink-jet head, to form a dot having the desired density. In short, a plurality of drive pulses are supplied to the ink-jet head in order to form a dot having the desired density.
When two drive pulses are supplied, the second pulse is supplied with such timing as to increase the residual pressure wave vibration in the cavity
16
generated by the first pulse. As a result, the second ink droplet is efficiently ejected.
In this case, however, an extra droplet called a satellite droplet S may be generated in addition to the main ink droplet I, as shown in FIG.
3
B. This may occur when a plurality of droplets are continuously ejected to form a dot. If the pressure wave vibration in the cavity
16
is not reduced sufficiently after the main droplet I has been ejected, such residual pressure wave vibration will cause ejection of extra ink in the form of a satellite droplet. If this occurs, a finished printout may be undesirably altered. This may be especially so if a satellite droplet is ejected when no dot is formed next to the currently formed dot while using the same nozzle
22
. In this event the satellite droplet can be seriously noticeable. Even if such a satellite droplet is not formed, formation of the next dot may become unstable due to the pressure wave vibration. To prevent generation of such an extra ink droplet, a cancel pulse (stabilizing pulse) is conventionally added. For example, when two pulses are supplied as described above, a cancel pulse is supplied following the second drive pulse with such timing as to cancel the residual pressure wave vibration in the cavity
16
. In another conventional method, a first cancel pulse is supplied following the first drive pulse to cancel the residual pressure wave vibration, and a second cancel pulse is also supplied following the second drive pulse.
FIG. 4
shows a timing chart showing generation of a drive waveform having a cancel pulse. Upon generation of a strobe signal that regulates operation of the ink-jet head, dot data including the dot density is inputted to the control circuit of the ink-jet head. Then, the control circuit determines a drive waveform based on the received dot data and clock signals that regulate pulse generation.
A cancel pulse is especially important when no ink is ejected at a print cycle for the next dot. More specifically, when ink is ejected at a print cycle for the next dot, the next ink ejection will be less affected by the residual pressure wave vibration even if it is not attenuated sufficiently. However, when no ink is ejected at a print cycle for the next dot, the above-described satellite droplet will be generated by the residual pressure wave vibration, if it is not attenuated sufficiently.
Whether ink is ejected at each print cycle is determined based on the dot data stored in an image memory.
When the control circuit determines that the current dot data indicates ink ejection and the next dot data indicates no ink ejection, the control circuit selects a drive waveform having a cancel pulse CP to form the current dot. When the piezoelectric element
50
is driven according to the drive waveform having a cancel pulse CP, the pressure wave vibration in the cavity
16
is stabilized, thereby preventing generation of a satellite droplet S or unstable ink ejection, as shown in FIG.
3
C. Although, in
FIG. 4
, a cancel pulse PC is inserted at the end of a drive waveform, it may be inserted in the middle of a drive waveform, or a plurality of cancel pulses may be inserted within a single drive waveform. In the above-described techniques, however, the length of a drive waveform is elongated because a cancel pulse is inserted into an original drive waveform required just for forming a dot. Setting the print cycle based on the elongated drive waveform will reduce the operating speed of the ink-jet head.
Another problem with the case where a plurality of drive pulses are supplied to the ink-jet head to form a dot is that when ink is ejected continuously over two print cycles to form two dots, the time interval between the last drive pulse for the first dot and the first drive pulse for the second dot may become short, depending on the number of drive pulses. As a result, the residual pressure wave vibration in the cavity may not be attenuated in such a short time interval, resulting in unstable ink ejection for the second dot.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved controller for an ink-jet apparatus that can perform high-speed printing and can perform stable ink ejection when ink is ejected continuously over two print cycles.
One aspect of the invention involves a controller for an ink-jet apparatus. The controller includes an ink-jet head that ejects ink from a cavity and a waveform generator that generates a plurality of waveform signals. The waveform signals are issued at predetermined print cycl
Iriguchi Akira
Kojima Masatomo
Suzuki Shigeru
Brother Kogyo Kabushiki Kaisha
Fuller Benjamin R.
Nguyen Lam S
Oliff & Berridg,e PLC
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