Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-03-30
2001-10-09
Tran, Huan (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C347S069000
Reexamination Certificate
active
06299271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ink droplet ejection apparatus for ejecting ink to form an image on a recording medium.
2. Description of Related Art
Conventional recorders which are easy of multiple gradation and colorization include ink jet recorders. Of these recorders, ink droplet ejection apparatus of the drop-on-demand type, which eject printing ink, are coming into wide use because of high ejection efficiency and low running costs.
For example, Japanese Patent Application Laid-Open No. 63-247051 discloses ink droplet ejection apparatus of the shear mode type as ink droplet ejection apparatus of the drop-on-demand type. Piezoelectric material is used in the apparatus disclosed in the publication.
FIGS. 23 and 24
of the drawings accompanying this specification show part of a conventional ink droplet ejection apparatus of the shear mode type.
The apparatus shown in
FIGS. 23 and 24
includes a 64-channel multi-nozzle print head
600
, only five channels of which are shown for simplification. The head
600
includes a bottom wall
601
, at top wall
602
and a number of shear mode actuator walls
603
extending between them. Each actuator wall
603
includes an upper part
605
and a lower part
607
which are made of piezoelectric material. The wall parts
605
and
607
are bonded to the walls
602
and
601
, respectively, and polarized oppositely as shown by arrows
609
and
611
, respectively. The actuator walls
603
are arranged in pairs to define channels
613
between them. Spaces
615
are defined between successive pairs of actuator walls
603
.
At one end of the channels
613
is secured a nozzle plate
617
formed with nozzles
618
for the respective channels. The other end of the channels
613
is connected through a manifold
626
to an ink cartridge or another ink supply (not shown). The manifold
626
includes a front wall
627
and a rear wall
628
. The front wall
627
is formed with holes communicating with the respective channels
613
. The rear wall
628
closes the space in the rear of the front wall
627
between the rear ends of the base wall
601
and top wall
602
. Ink can be supplied from the supply to the space between the front wall
627
and rear wall
628
, and then be distributed to the channels
613
.
Electrodes
619
and
621
are disposed on opposite sides of each actuator wall
603
. The electrodes
619
disposed in the channels
613
are connected to a drive circuit
21
. Under the control of a control circuit
22
, the drive circuit
21
can generate or output a voltage and apply it to these electrodes. The electrodes
621
disposed in the spaces
615
and on both sides of the print head
600
are connected to a ground return
623
.
In operation, the voltage applied to the electrodes
619
in each channel
613
causes the actuator walls
603
facing the channel to deform piezoelectrically in such directions that the channel enlarges in volume. For example, if, as shown in
FIG. 25
of the accompanying drawings, a voltage of E volts is applied to the electrodes
619
in one of the channels
613
, electric fields are generated in the actuator walls
603
defining this channel. As shown by arrows
631
and
632
, the fields are normal to the directions
609
and
611
of polarization. This deforms these walls
603
piezoelectrically in such directions that the channel
613
enlarges to reduce the pressure in the channel to a negative pressure.
The voltage applied to the electrodes
619
is held for a period L/V where L is the channel length and V is the sound velocity in the ink in the channel
613
. While the voltage is applied, ink is supplied from the supply to the channel
613
. The period L/V is the one-way propagation delay time T which it takes for the pressure wave in the channel
613
to be propagated one way longitudinally of the channel.
According to the theory of pressure wave propagation, the negative pressure in the channel
613
reverses into a positive pressure when the period L/V passes after the voltage is applied to the electrodes
619
. If the voltage is returned to zero volt when this period passes after the voltage application, the deformed actuator walls
603
return to their original condition shown in
FIGS. 23 and 24
. This applies a positive pressure to the ink in the channel
613
. This pressure is added to the pressure reversed to be positive. As a result, a relatively high pressure develops in that portion of the channel
613
which is near to the associated nozzle
618
, ejecting ink out through the nozzle. The ejected ink sticks to a surface of printing paper or another recording medium to form an image on it.
The present assignee's Japanese Patent Application Laid-Open Nos. 9-29960, 9-29961 and 9-48112 disclose the step of ejecting ink out through a nozzle
618
by generating pressure wave vibration in the ink in the associated channel
613
, and the step of substantially canceling the residual pressure wave vibration of the ink in the channel after the ejection. This cancellation involves generating an additional pulse after the main drive waveform for the ejection. Specifically, the cancellation involves increasing and decreasing the volume of the channel
613
by applying a voltage of E volts to the associated electrodes
619
at a predetermined time after the ejection and by subsequently returning the voltage to 0 volt. The cancellation damps the residual pressure wave vibration in the channel
613
quickly and early. This prevents ink from being ejected or dropped accidentally through the nozzle
618
by the residual pressure wave vibration. Besides, this enables early transition to the process in accordance with the next print command for this channel. It is therefore possible to form a more exact image on a recording medium, and improve the print speed.
The assignee's Japanese Patent Application Laid-Open No. 10-202858 discloses the steps of ejecting ink out through a nozzle
618
in a print cycle, and thereafter canceling the residual pressure wave vibration in the associated channel
613
if there is no print command for this channel for the following cycle, ibut canceling no such vibration if there is a print command therefor. If there is no print command for the following cycle, ;an accidental drop of ink may occur, and therefore the residual pressure wave vibration should be canceled. This results in better image formation not stained or spotted by scattered ink. If there is a print command for the following cycle, the residual pressure wave vibration in the channel
613
should be utilized positively. Specifically, this vibration should be added to the pressure wave vibration generated in accordance with the print command for this cycle. The addition generates greater pressure wave vibration for ejection of a larger ink droplet through the nozzle
618
. Larger ink droplets increase the print density to form a thicker and clearer image.
It is conceivable that it is possible to damp or control ink meniscus vibration more effectively by switching between the execution and no execution of the vibration cancellation for a particular channel in a particular print cycle selectively depending on, not only whether there is a print command for the following cycle for this channel, but also whether there is a print command for the preceding cycle for the channel. This would stabilize the droplet jet velocity and the ejection, and make it possible to obtain an ink droplet of desired volume, thereby improving the print quality.
The viscosity and other characteristics of the ink in an apparatus vary with the temperature and other conditions at or in which the apparatus is used. It is desirable to perform the foregoing switching arbitrarily and easily depending on this variation as well. It has been desirable to generate a stop pulse for the vibration cancellation securely by means of simple structure or construction, depending on the preceding and/or following print data. It has also been desirable to ease the restrictions on the print
Brother Kogyo Kabushiki Kaisha
Dudding Alfred
Oliff & Berridg,e PLC
Tran Huan
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