Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-06-04
2002-12-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S011000
Reexamination Certificate
active
06494555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink ejecting device for forming images on a recording medium, such as paper, by ejecting ink from nozzles in accordance with print commands.
2. Description of the Related Art
Ink jet printers are a type of non-impact printer. They are based on the simplest operation principle and are also easily adapted for both tonal and color printing. Drop-on-demand type ink jet printers, which eject only ink required for printing, have good ejection efficiency and low running costs and so are becoming rapidly more popular. Conventional ink ejection units are described in U.S. Pat. Nos. 4,879,568, 4,887,100, 4,992,808, 5,003,679, and 5,028,936 and in Japanese Patent Application Publication (Kokai) No. SHO-63-247051, which corresponds at least partially to all of these U.S. patents.
Next, an explanation will be provided for an exemplary conventional shear mode type ejection unit that uses piezoelectric material for ejecting ink droplets. The ink ejection unit includes a plurality of ink chambers. Each ink chamber is defined by side walls made from piezoelectric material, and a nozzle plate formed with a nozzle through which ink droplets are ejected from the ink chamber. At the lengthwise end opposite the nozzle plate, the ink chamber is in fluid connection with a manifold through which ink is supplied to the ink chamber.
When an ink droplet is to be ejected from an ink chamber, a voltage is applied to the piezoelectric wells of that chamber, so that the walls of the chamber deform in a direction for increasing volume of the ink chamber and for reducing pressure in the ink chamber. The application of voltage is continued for a time T required for a pressure wave to propagate once from the nozzle plate to the manifold, that is, along the lengthwise direction of the ink chamber. During this time, ink is drawn from into the ink chamber from the manifold. The time T is calculated using the following formula:
T=L/a
where L equals the length of the ink chamber; and
a equals speed of sound through the ink filling the ink chamber.
According to theories on pressure wave propagation, when the time T elapses after start of application of the voltage to the side walls, the pressure in the ink chamber inverts to a positive pressure. At this timing, the voltage applied to the piezoelectric side walls of the ink chamber is switched to zero volts, whereupon the piezoelectric side walls revert to their condition of before deformation, thereby applying pressure to the ink filling the ink chamber. This pressure applied to ink in the ink chamber by the side walls is added to the positive inverted pressure from the pressure wave. As a result, a fairly high pressure is generated near the nozzle of the ink chamber, so that an ink droplet is ejected from the nozzle.
It is well-known that pressure fluctuations, such as those described above, can be used for various purposes. For example, the pressure fluctuations can be used to eject a plurality of ink droplets in succession, in order to increase the surface area where ink clings to the recording medium. That is, when residual pressure wave vibration from a prior ink ejection inverts to a negative pressure, the piezoelectric walls can be applied with a voltage to deform them in the direction for increasing the volume of the ink chamber. When the residual pressure wave vibration inverts back to a positive pressure, then the piezoelectric walls are deformed in the direction for decreasing the volume of the ink chamber. As a result, a plurality of ink droplets are ejected in succession. The plurality of ink droplets either couple together in flight and impinge on the recording medium as a single layer droplet, or impinge on the recording medium separately as a plurality of ink droplets shifted slightly from each other, but in an overlapping condition. In other words, by changing the number of ink droplets ejected in succession, the surface area of ink clinging to the recording medium can be controlled.
Alternatively, the pressure fluctuations can be used to cancel out vibration in the ink in order to prevent undesired ink ejections. In this one, when the residual pressure wave vibration from a prior ejection inverts to a position pressure, the piezoelectric walls are deformed in the direction for increasing the volume in the ink chamber. Afterwards, when the vibration of the residual pressure wave inverts to a negative pressure, the actuator walls are deformed in the direction for decreasing the volume in the ink chamber. As a result, the residual pressure wave vibration is canceled out. The residual pressure wave vibration in the ink chamber undesirably pushes the ink meniscus out of the nozzle or pulls the meniscus into the ink chamber. However, when the residual pressure wave is canceled out in this manner, it has been proven experimentally that undesired ejection of ink from the nozzle can be prevented.
Tonal printing, wherein different tones are achieved by printing in different densities of ink, can be performed using this type of ink ejection unit by changing the number of ink droplets ejected onto the recording medium for each dot's worth of print data. Conventionally, a ROM or other storage device stores separate date for different drive signal types. For example, the ROM or other memory medium stores data for a drive signal for ejecting a single ink droplet for each dot, a drive signal for ejecting two ink droplets for each dot, a drive signal for ejecting three ink droplets for each dot, and the like. Each time a print command is received from an external device, such as a computer, the data for the corresponding drive signal is retrieved from the ROM or other memory medium, and the drive signal is prepared accordingly.
SUMMARY OF THE INVENTION
To properly cancel out residual pressure wave vibration, the signal for canceling out the residual pressure wave vibration must be applied at a fixed timing after a prior ejection signal. Therefore, when a plurality of ink droplets are ejected in succession, the signal for canceling out is added after the plurality of ejection signals. For this reason, the ROM or other memory also stores signals for canceling out the residual pressure wave vibration, separately for each drive signal for ejecting a plurality of ink droplets.
Because data for a variety of different types of drive signal needs to be stored, conventional ink ejection units need to be provided with a memory medium having a relatively large capacity.
It is an objective of the present invention to overcome the above-described problems and to provide an inexpensive ink ejecting device that changes the number of ink droplets ejected in accordance with print data for each dot and that requires only a small capacity memory medium.
According to one aspect of the present invention, an ink ejecting device that prints single dots on a recording medium by ejecting one or more droplets, includes an ink chamber portion, an actuator that applies pressure to the ink in the ink chamber to perform an ink ejection to eject an ink droplet from the nozzle, and a drive unit.
The ink chamber portion is formed with an ink chamber and a nozzle. The ink chamber is filled with ink and the nozzle is in fluid communication with the ink chamber.
The actuator applies pressure to the ink in the ink chamber to perform an ink ejection to eject an ink droplet from the nozzle.
The drive unit applies a drive signal to the actuator to drive the actuator to perform ink ejections. The drive unit includes a generation unit and a correction unit. The generation unit prepares a reference drive signal for driving the actuator to perform a preset maximum number of ink ejections per dot. The correction unit produces a print drive signal for driving the actuator to perform a number of ink ejections required to print a particular single dot. The correction unit produces the print drive signal by removing unnecessary portions from the reference signal, according to the number of ink ejections required
Barlow John
Brother Kogyo Kabushiki Kaisha
Dudding Alfred E
Oliff & Berridg,e PLC
LandOfFree
Ink ejecting device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ink ejecting device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ink ejecting device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2964231