Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-05-19
2001-07-17
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S010000, C347S011000
Reexamination Certificate
active
06260959
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink ejector for forming an image on a recording medium such as recording paper by ejecting ink from a number of channels in accordance with print instructions.
2. Description of Related Art
Of all non-impact printers, ink jet printers have simple principles and are easy of multiple gradation and colorization. Drop-on-demand ink jet printers eject only droplets of ink for printing. Ink jet printers of this type are coming rapidly into wide use because of high ejection efficiency and low running costs.
For example, U.S. Pat. Nos. 4,879,568, 4,887,100, 4,992,808, 5,003,679, and 5,028,936, corresponding to Japanese Patent Application Laid-Open No. 63-247051, disclose an ink ejector of the shear mode type for use in a drop-on-demand printer, respectively. Piezoelectric material is used in the disclosed apparatus. The ejector ejects a series of ink droplets through one of nozzles to form a thick and clear image on a recording medium in accordance with the print instruction for one dot.
The viscosity of ink varies with temperature. As the temperature of ink rises, the ink viscosity lowers naturally. This causes ink droplets to be ejected in different manners by the ejector at a predetermined normal temperature (approx. 25 centigrade) and at a higher temperature (approx. 30-45 centigrade). At a higher temperature, ink may be ejected at such a pressure as can cause no ink ejection at a normal temperature, or ink may be spattered or splashed in fine particles. Some of the ink particles may stick to a nozzle plate which defines the nozzle. The surface tension of the ink sticking to the nozzle plate may cause the succeeding ink droplets to be ejected in wrong directions.
The ink temperature may be raised by higher ambient temperature, the heat generated from a controller of the ejector, the heat generated from deformation of the piezoelectric material when ink is ejected, and the heat generated from the carriage motor for moving the ejector relative to a recording paper.
If ink droplets are spattered or ejected in wrong directions, as stated above, excess ink droplets are ejected or ink droplets are ejected onto wrong spots, resulting in poor printing quality.
It has therefore been demanded to provide an ink ejector which can form a clear or sharp image not only at a normal temperature but also at a higher temperature.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an ink ejector for ejecting two or more ink droplets in accordance with the print instruction for one dot and forming a clear or sharp image even at a higher temperature.
In accordance with a first aspect of the invention, an ink ejector is provided which includes and ink jet head for ejecting ink and a controller.
The ink jet head has an ink channel formed therein, which can be filled with ink. The head also has an ink nozzle formed therein and communicating with the channel. The head includes an actuator provided therein for changing the volume of the channel.
The controller controls the actuator to change the channel volume to eject a series of ink droplets from the channel through the nozzle in accordance with the print instruction for one dot. In accordance with the print instruction for one dot, the controller outputs ejection pulses of voltage for driving the actuator to the actuator. The pulses include at least a first pulse and a second pulse which follows the first pulse.
The first pulse has a width between 0.5T and 1.5T where T is the one-way propagation (delay) time during which a pressure wave is propagated one way in the channel. The interval between the first and second pulses, which corresponds to an interval between a falling point (trailing edge) of the first pulse and a rising point (leading edge) of the second pulse, is at least 0.3T. The second pulse has a width which is at least 0.3T. The sum of the pulse interval and the width of the second pulse ranges between 1.3T and 1.7T.
The ejection of the droplets involves increasing the volume of the channel once and decreasing it subsequently. When the volume increases, the pressure in the channel lowers once so that ink flows into it. Subsequently, when the volume decreases, a high pressure develops in the channel to eject an ink droplet. As stated above, the controller outputs at least a first ejection pulse and a second ejection pulse to the actuator in accordance with the print instruction for one dot. This causes the ink jet head to eject at least two consecutive ink droplets in accordance with the print instruction for one dot.
As stated above in connection with the related art, however, the viscosity of ink lowers as the ink temperature rises. Consequently, the ink droplets may be spattered or ejected in wrong directions. As a result of the inventor's studies with the ejector, he discovered that, by setting the widths of the first and second pulses and the interval between the two pulses as stated above, it was possible to form a clear image on a recording medium without spattering ink or ejecting ink in a wrong direction. Specifically, the width of the first pulse should range between 0.5T and 1.5T, and the sum of the width of the second pulse and the pulse interval should range between 1.3T and 1.7T. In addition, the width of the second pulse and the interval should each be 0.3T or longer. As a result, the ejector can form a clear image not only at a predetermined normal temperature but also at a higher temperature.
After the controller outputs the ejection pulses to the actuator, it may output to the actuator a non-ejection pulse of voltage for changing the channel volume to cancel the pressure wave vibration in the channel.
In this case, after the ink droplets are ejected in accordance with the print instruction for one dot, the controller applies the non-ejection pulse to develop pressure in the channel. The pressure changes the channel volume to cancel the pressure wave vibration generated in the channel by the ejection of the droplets. This prevents accidental drops of ink from exiting the nozzle through the channel, and makes it possible to immediately set up for the next ink ejection cycle according to the next print instruction. It is therefore possible to improve the print speed.
The term “vibration cancellation” means not only damping the pressure wave vibration completely, but damping it to such a degree that no ink can be ejected.
The time between the trailing edge of the last ejection pulse and the middle point of the non-ejection pulse may range between 2.25T and 2.75T. Thenon-ejection pulse may have a width between 0.3T and 0.8T. The inventor discovered that it was possible to prevent accidental drops more reliably by limiting the time and the pulse width as stated above. As a result, it is possible to form a clearer image at a higher temperature.
The channel may be defined between side walls made of piezoelectric material. The walls are the actuator. The voltage application to the piezoelectric material deforms it to change the volume of the channel. The actuator of piezoelectric material is simple in structure, durable and cheap. This makes the ejector simple in structure and sufficiently durable, and can make production costs low.
In accordance with a second aspect of the invention, another ink ejector is provided which includes an ink jet head for ejecting ink and a controller.
This ink jet head has an ink channel formed therein, which can be filled with ink. The head also has an ink nozzle formed therein and communicating with the channel. The head includes an actuator provided therein for changing the volume of the channel.
This controller controls the actuator to change the channel volume to eject a series of ink droplets from the channel through the nozzle in accordance with the print instruction for one dot. In accordance with the print instruction for one dot, the controller outputs ejection pulses of voltage to the actuator. The pulses include at least a first pulse and a second pulse which follows the first puls
Brother Kogyo Kabushiki Kaisha
Nguyen Thinh
Oliff & Berridg,e PLC
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