Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-06-01
2001-08-21
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S068000, C310S316030
Reexamination Certificate
active
06276772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric ink recording device, and more particularly to an ink jet recording device that improves precision of where ink droplets impinge on a recording medium.
2. Description of the Related Art
There has been known an ink jet printer with an ink jet head including piezoelectric elements as actuators for ejecting ink droplets.
FIG. 1
shows an example of such an ink jet head. The ink jet head shown in
FIG. 1
is for ejecting hot melt ink, which is solid at room temperature and liquefies when heated. As shown in
FIG. 1
, the ink jet head includes a piezoelectric element
1
, a diaphragm
5
, and a nozzle plate
4
formed with a nozzle
4
a
. The diaphragm
5
is attached to one side of the piezoelectric element
1
. The diaphragm
5
and the nozzle plate
4
define an ink chamber
3
. The nozzle
4
a
is formed in the nozzle plate
4
at a position in confrontation with the diaphragm
5
.
Although not shown in the drawings, the nozzle plate is formed with a plurality of nozzles
4
a
. The nozzles
4
a
are, for example, arranged in 32 columns and 12 rows, wherein the rows extend in the widthwise direction of the recording medium. The nozzle rows are divided into four groups of three rows each, each group being for one of four different colored ink types. That is, three rows each are designated for black, cyan, magenta, and yellow colored inks. An ink chamber
3
and a piezoelectric element
1
are also provided for each one of the plurality of nozzles.
Ink supplied from an ink tank (not shown) is temporarily held in a manifold
7
, and then supplied to the ink chambers
3
through a corresponding ink channel
6
. A heater
11
is provided adjacent to the manifold
7
. The heater
11
heats the manifold
7
and maintains ink in a melted condition. A driver
10
is connected to the piezoelectric element
1
. The driver
10
drives the piezoelectric element
1
in response to print commands from a controller
9
.
FIG. 3
shows a configuration of the driver
10
. The driver
10
is configured from a piezoelectric element driver
24
and a signal generator
25
. A plurality of piezoelectric element drivers
24
are provided in a one-to-one correspondence with the piezoelectric elements
1
a
and
1
b.
When an ink droplet
8
is to be ejected, the signal generator
25
outputs pulse voltage
2
shown in
FIG. 4
having a pulse width W. The pulse voltage
2
is applied to the base of transistors Tr
1
and Tr
2
of the piezoelectric element driver
24
. At this time, DC voltage
18
having a voltage level V is generated from the signal generator
25
and applied to the emitter of the transistor Tr
1
and to resistors R
1
and R
2
. As a result, a pulse voltage
20
having the pulse width W shown in
FIG. 4
is applied to the piezoelectric element
1
a
. The piezoelectric element
1
a
deforms in association with the rising edge of the pulse voltage
20
. The diaphragm
5
bends as indicated by a broken line
5
a
in FIG.
2
. The volume in the ink chamber
3
increases in association with this, so that ink in the manifold
7
is drawn into the ink chamber
3
through the ink channel
6
. Afterwards, the piezoelectric element
1
reverts to its initial shape in association with the falling edge of the pulse voltage
20
. Accordingly, the volume of the ink chamber
3
decreases so that the ink droplet
8
is ejected from the nozzle
4
a
. On the other hand, when an ink droplet
8
is not to be ejected, the signal generator
25
is controlled so as not to generate the pulse voltage
2
.
A laminated type piezoelectric element shown in
FIG. 5
is capable of deforming the diaphragm
5
by a greater amount than other types of piezoelectric elements, so that the piezoelectric element can be driven with good energy efficiency.
However, in the above-described ink jet head, each of the piezoelectric elements has different properties for converting electrical to mechanical power. Also, different piezoelectric elements and corresponding diaphragms are coupled by different amounts and have different positional relationships. Because of these types of variation, the speed at which an ink droplet is ejected can vary depending on the nozzle. When more than one type of variation appears simultaneously in the nozzles, the problem of variation in ejection speed is compounded.
An ink jet head having the above-described variations can not print images with good quality. For example, when such a head is transported at a fixed speed across the width of a recording medium in order to print on the recording medium, the ink droplets can not be impinged at desired locations on the recording medium. The resulting printed image has poor quality. Also, the volume of ink in each ejected droplet can vary. Those nozzle that eject ink droplets with volume outside a certain range can be discarded at the factory in order to reduce variation in amount of ejected ink. However, this reduces the poor of ink jet heads.
The speed at which the ink droplets are ejected from a nozzle can be controlled by controlling a voltage to be applied to the piezoelectric element. Japanese Patent Laid-Open Publications Nos. HEI-4-310747 and HEI-9-39231 disclose methods for controlling charge and discharge currents for the piezoelectric elements. In Japanese Patent Laid-Open Publication No. HEI-4-310747, charge and discharge currents are controlled in the same manner for all of a plurality of nozzles. In Japanese Patent Laid-Open Publication No. HEI-9-39231, a charge pulse with a fixed voltage and a narrow pulse width is repeatedly applied to piezoelectric element circuits having a charge resistor and a discharge resistor. Based on how many narrow pulses produced the optimum printing results for various environments and ink types, a drive waveform for all of the piezoelectric element circuits is determined and stored in a ROM.
The methods disclosed in both of these Japanese Patent Laid-Open Publications uses digitally configured drive waveforms with a pulse width and voltage common for each of the plurality of nozzles. The drive waveform is not controlled differently for each of the nozzles.
SUMMARY OF THE INVENTION
It is an object of the present invention to individually control drive waveform applied to each of a plurality of piezoelectric elements in order to correct for variation in ejection speed of ink droplets ejected from nozzles and improve precision of impinging position of ink droplets on a recording medium.
It is also an object of the present invention to enable modifying waveforms of voltage pulses for individual ejection nozzles of a multi-nozzle ink jet recording device and to improve the yield when manufacturing ink ejection nozzles.
To achieve the above and other objects, there is provided a multi-nozzle type ink jet recording device that ejects ink filling ink chambers from nozzles by using piezoelectric elements to change volume in the ink chambers. The ink jet recording device includes a signal generator, a plurality of charge control circuits, a signal pulse drive circuit, and a plurality of diodes. The signal generator generates a drive signal for driving the piezoelectric elements. The charge control circuits are connected to the signal generator and provided in one-to-one correspondence with the piezoelectric elements. Each charge control circuit is responsive to the drive signal to charge a corresponding piezoelectric element by a predetermined charge amount. The signal pulse drive circuit generates a drive voltage in synchronization with the drive signal. The diodes are also provided in one-to-one correspondence with the piezoelectric elements. Each diode is connected between the signal pulse drive circuit and a corresponding one of the charge control circuits. One connection terminal of each piezoelectric element is connected between an anode terminal of a corresponding diode and a corresponding charge control circuit and another connection terminal of the piezoelectric element is connected to ground.
A pulse from the
Kunimi Keiji
Sakata Masatoshi
Sekino Takashi
Shimizu Kazuo
Barlow John
Dudding Alfred
Hitachi Koki Co,. Ltd.
McGuireWoods LLP
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