Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2003-04-07
2004-12-14
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S012000
Reexamination Certificate
active
06830303
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to a head driving technique of a liquid jet device, which suppresses drive currents of piezoelectric elements provided in correspondence with nozzles used to jet liquid droplets in a jetting head of a liquid jet device, such as an ink-jet type printer.
Currently, while ink-jet type color printers In which several colors of ink droplets are jetted from recording heads have been popularized as output apparatus of computers, these ink-jet type color printers have been widely employed In order to print images processed by computers and the like in multicolor and multi-gradation modes.
For instance, in an ink-jet type printer using piezoelectric elements as driving elements for jetting ink, since a plurality of piezoelectric elements which are provided in correspondence with a plurality of nozzles of a print head are selectively driven, ink droplets are jetted from the nozzles based upon dynamic pressure of the respective piezoelectric elements, and the ink droplets are attached to print paper, so that dots are formed on this print paper so as to perform a printing operation.
In this case, the respective piezoelectric elements are provided in correspondence with nozzles used to jet the ink droplets therefrom, and are driven by drive signals which are supplied from a driver IC (head driving circuit) mounted within the print head so as to jet the ink droplets.
Such a head driving apparatus is arranged as shown in, for example, FIG.
10
. In
FIG. 10
, a head driving apparatus
10
includes piezoelectric elements
11
, a head driving circuit
12
, a current amplifying circuit
13
, and a nozzle selecting switch circuit
14
. The piezoelectric elements
11
are provided in correspondence with a plurality of nozzles of an ink-jet printer. The head driving circuit
12
is employed so as to supply a drive signal with respect to one electrode
11
a
of each of these piezoelectric elements
11
. The current amplifying circuit
13
and the nozzle selecting switch circuit
14
are provided between the head driving circuit
12
and each of the piezoelectric elements
11
.
Each of the piezoelectric element
11
is constructed in such a manner that this piezoelectric element
11
is displaced in response to a voltage applied between both the electrodes
11
a
and
11
b
. The head driving circuit
12
is employed In order to generate a drive signal “COM” for driving the print head of the ink-jet printer, and is arranged, for example, within a main body of the ink-jet printer.
The current amplifying circuit
13
is constructed of two transistors
13
a
and
13
b
. Within these transistors
13
a
and
13
b
, a collector of the first transistor
13
a
is connected to a constant voltage source, a base thereof is connected to one output of the head driving circuit
12
, and an emitter thereof is connected to an input side of the nozzle selecting switch circuit
14
. As a result, this first transistor
13
a
becomes conductive in response to a signal supplied from the head driving circuit
12
, and thus, supplies a drive waveform having a trapezoidal shape via the nozzle selecting switch circuit
14
to the piezoelectric elements
11
.
Also, an emitter of the second transistor
13
b
is connected to an input side of the nozzle selecting switch circuit
14
, a base thereof is connected to a second output of the head driving circuit
12
, and a collector thereof is connected to the ground. As a result, the second transistor
13
b
becomes conductive in response to a signal supplied from the head driving circuit
12
, and thus, discharges the piezoelectric elements
11
via the nozzle selecting switch circuit
14
.
The nozzle selecting switch circuit
14
is turned ON at drive timing of the corresponding piezoelectric element
11
by inputting thereinto a control signal, and then, outputs the drive signal COM to the piezoelectric element
11
. In an actual case, this nozzle selecting switch circuit
14
is arranged as a so-called “transmission gate (TG)” in order to turn ON/OFF the respective piezoelectric elements
11
. In this case, in the head driving apparatus
10
having such an arrangement, the current amplifying circuit
13
may drive all of the piezoelectric elements
11
connected by one set of these transistors
13
a
and
13
b.
As a consequence, since a transistor having such a maximum current capable of supplying a current required when all of the piezoelectric elements
11
are driven at the same time is needed as these transistors
13
a
and
13
b
, the transistors used in the current amplifying circuit
13
are relatively high cost, so that the cost of the resulting head driving apparatus
10
, and thus, the cost of an ink-jet type printer using this head driving apparatus
10
are increased. Also, when the large currents flow through the transistors, waveforms thereof are easily distorted.
Furthermore, in some cases, for instance, plural stages of transistors such as Darlington-connected transistors must be employed so as to supply a large current, so that the cost thereof would be increased and the characteristic thereof would be deteriorated.
On the other hand, in the head driving apparatus
10
, there is a rare case that all of the piezoelectric elements
11
are simultaneously driven during the normal printing operation. In general, a half, or a smaller number of the entire piezoelectric elements
11
are driven at the same time. More specifically, this trend may become conspicuous in such a case that multiple color ink is used in a color printer. For example, in the case of a six-colored ink printer, ⅓, or smaller number of piezoelectric elements are driven at the same time in an average condition. If more than ⅓ of piezoelectric elements are driven at the same time, print paper is excessively wet, so that better printing operation cannot be carried out. To the contrary, there is a very small possibility that all of ink nozzles are locally jetted. In other words, if all of ink nozzles are jetted and thereafter a time period is provided during which all of ink nozzles are not jetted, then all of ink nozzles may be locally jetted in, for example, a six-color ink printer, even when the entire nozzle number is averaged to become approximately ⅓ of the total ink nozzle number.
As a consequence, such a head driving apparatus has been proposed in, for example JP-A-6-115116 and JP-A-1-178456. In this head driving apparatus, when print data is entered by which a predetermined number, or larger numbers of loads are simultaneously driven, since a total number of such loads which are driven at the same time is limited, a transistor having a smaller maximum current is used.
In the head driving apparatus of JP-A-6-115116, the method for processing the print data by the MPU so as to limit the total ON-number of the nozzle selecting switch circuit has been proposed.
Also, in the head driving apparatus of JP-A-1-178455, such a method has been proposed. That is, while the output current of the current amplifying circuit is monitored, when this output current is increased higher than the predetermined value, the total ON-number of the nozzle selecting switch circuit is limited.
However, the above-described methods own the below-mentioned problems. That is, in the case of JP-A-6-115116, since the print data is sequentially processed by the MPU, the data processing speed is restricted, so that the printing speed would be suppressed. Otherwise, since the highspeed-operable MPU must be employed, the cost of the head driving apparatus is increased.
Also, in the case of JP-A-1-178455, when the output current supplied from the power supply actually becomes larger than, or equal to a predetermined current value, a total number of piezoelectric elements which are subsequently driven is restricted. This method has a major object capable of protecting the power supply. Even when a large current having a pulse shape instantaneously flows from the power supply, if the subsequently-driven load is light, then there is no problem as to
Dudding Alfred
Meier Stephen D.
Seiko Epson Corporation
Sughrue & Mion, PLLC
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