Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-11-26
2004-06-15
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S020000
Reexamination Certificate
active
06749279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ejection device that ejects droplets of liquid, and more specifically to an ejection device capable of precisely ejecting droplets at high speed in desired resolutions.
2. Related Art
Japanese Patent-Application Publication No. HEI-11-78013 discloses an inkjet recording device, which is one example of droplet ejection devices. Such an inkjet recording device includes an elongated inkjet recording head formed with a plurality of nozzles aligned equidistance from each other. The nozzle line is angled with respect to a sheet feed direction in which a recording medium is transported. When an energy generating element of each nozzle is applied with a driving voltage based on a recording signal, then a pressure is applied to ink inside an ink chamber, thereby an ink droplet is ejected through an orifice. Thus ejected ink droplet reaches the recording medium and forms a recording dot thereon. Recording operations are performed in this manner. This type of inkjet recording device has a simple configuration and is capable of high speed printing.
FIG.
1
(
a
) shows a piezoelectric-element driver
1420
, which is one example of conventional piezoelectric-element drivers, connected to 128-number of piezoelectric elements
304
. A common power source
202
is connected to a common terminal
304
b
of each piezoelectric element
304
for supplying a 40V direct current to the piezoelectric elements
304
which could be driven by at least 10V electric current. The piezoelectric-element driver
1420
includes 128-number of switches
1203
connected to the corresponding 128-number of piezoelectric elements
304
, a 128-bit latch
204
, a 128-bit shift register
205
, and a rectangular-waveform generating circuit
1206
. A binary ejection signal
207
is input to the shift register
205
and shifts one bit at a time in synchronization with the shift-clock S-CLK. The ejection signal
207
having a value “1” indicates “ejection”, and the ejection signal
207
having a value “0” indicates “non-ejection”. The latch
204
latches 128-bit data from the shift register
205
in synchronization with a pixel-synchronization signal
109
(latch clock L-CLK). The rectangular-waveform generating circuit
1206
generates a common output-enable (OE) signal
206
having a predetermined width in synchronization with the latch clock L-CLK. A logical product of an output from the latch
204
and the common OE signal
206
is input to a switching terminal of each switch
1203
. The switch
1203
connects the individual terminal
304
a
of the piezoelectric element
304
to the ground when a value “1” is applied to the switch terminal, so that a driving waveform Vpzt shown in FIG.
1
(
b
) is applied to the piezoelectric element
304
. On the other hand, the switch
1203
connects the individual terminal
304
a
to the common power source
202
when a value “0” is applied, so that no driving waveform Vpzt is applied to the piezoelectric element
304
.
An example of operations of the piezoelectric-element driver
1420
will be described with reference to the timing chart of FIG.
1
(
b
). In this example, the common OE signal
206
is a well-known rectangular waveform having a driving voltage of 40V and a time-width of 5 &mgr;m to 25 &mgr;m. When the pixel-synchronization signal
109
is received, then the pixel-synchronization signal
109
is input as the latch clock L-CLK to the latch
204
so that the ejection signals
207
that have been stored in the shift register
205
in a previous cycle are stored in the latch
204
at once. Then, the common OE signal
206
that is generated in synchronization with the pixel-synchronization signal
109
is input to the AND circuit. As a result, nozzles whose ejection signals
207
have the value of “1” eject ink droplets, and nozzles whose ejection signals
207
have the value of “0” eject no ink droplets. Then, subsequent ejection signals
207
are input to the shift register
205
in synchronization with the shift-clock S-CLK, and the process waits until the next pixel-synchronization signal
109
is generated.
There have been also provided piezoelectric-element drivers having different configurations. However, these drivers are common in applying an analog voltage to the common terminals of the piezoelectric elements and in switching the connection at the individual terminals. This type of piezoelectric-element driver has a simple configuration and is particularly indispensable in multi-nozzle inkjet recording devices.
Here, in order to form high-quality half toning images like photographical images, multiple level halftoning that creates the appearance of intermediate tones of black, white, and a plurality of gray levels is necessary. There have been known two methods for realizing such multiple tone levels. The one is to control a number of recording dots in a single pixel area, and the other is to change a mass of each droplet by controlling a corresponding driving waveform Vpzt. The latter method is known to be preferable in highly-reliable high-speed inkjet recording devices.
It is conceivable to control an individual driving waveforms Vpzt by providing an individual driving circuit for each one of the nozzles. However, it is not practical to provide so many driving circuits in a multi-nozzle inkjet recording device that includes a great number of nozzles since it greatly increases manufacturing costs of the device. Moreover, in a conventional piezoelectric-element driver such as those shown in FIG.
1
(
a
), it is necessary to change the analog voltage from the power source
202
each time for each nozzle in order to change the driving waveform Vpzt. However, it is difficult to change the analog voltage in such a manner.
A recording resolution is determined by a nozzle density. For example, if the nozzle density is 300 nozzles per inch (npi), then the recording resolution is usually 300 dots per inch (dpi). In order to form a 240 dpi image using a recording device having the nozzle density of 300 dpi, a well-known digital data process, such as enlargement process, high-resolution process, or the like is previously performed to obtain converted data, and then the recording is performed based on thus obtained data.
SUMMARY OF THE INVENTION
However, it is preferable to avoid such a digital data process since the process usually changes or degrades image quality, disabling to provide images desired by users.
In view of forgoing, therefore, it is an object of the present invention to overcome the above problems and also to provide a high-speed ejection device having an elongated head capable of ejecting droplets on precise locations in a designated resolution.
It is also an object of the present invention to provide a multi-nozzle inkjet recording device capable of stably forming high-quality multi-toning images by changing a mass of each ink droplet.
In order to achieve the above and other objects, according to the present invention, there is provided an ejection device including a head formed with a plurality of nozzles arranged in a row for selectively ejecting droplets from the nozzles so as to form dots onto a medium, a transporting means for transporting the medium relative to the head in a first direction, a resolution specifying means for specifying a resolution with respect to the first direction, a preciseness specifying means for specifying preciseness in dot locations on the medium, an angle specifying means for specifying an angle of the head with respect to a second direction perpendicular to the first direction based on the specified resolution, a sub-pixel determining means for determining a size of a sub-pixel with respect to the first direction based on the specified preciseness, a converting means for converting an ejection data to a sub-pixel data based both on the specified resolution and the size of the sub-pixel, and a control means for controlling the head based on the sub-pixel data to selectively ejecting the droplets from the nozzles.
There is also provi
Kida Hitoshi
Kobayashi Shin'ya
Saito Susumu
Satou Kunio
Sekino Takashi
Hitachi Printing Solutions, Ltd.
Nguyen Thinh
Whitham Curtis & Christofferson, PC
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