Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-25
2001-08-07
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S011000
Reexamination Certificate
active
06270179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an on-demand inkjet printing device and an on-demand inkjet printing method for printing characters and/or images for use in a printer, a plotter, a facsimile device, a copying machine or the like.
2. Description of the Prior Art
An on-demand inkjet printhead includes nozzles, pressure chambers, an ink feed system, an ink tank and piezoelectric elements, and injects ink drops via the nozzles by transferring pressures generated by the piezoelectric elements to the corresponding pressure chambers so as to print characters and/or images on a print medium such as a sheet of paper.
The inkjet printing is normally a binary value printing, so that a dithering method, an error diffusion method or the like is used for realizing a halftone printing. In the dithering method, however, the number of dots for forming a unit pixel increases for increasing halftone levels. Thus, a resolution is lowered. On the other hand, in the error diffusion method, a striped pattern of dots largely degrades the quality of an image at a portion with a high brightness. It is possible to remove the foregoing drawbacks in the dithering method or the error diffusion method by enhancing the resolution, which, however, increases the cost of the device.
There is another method of realizing a halftone printing, wherein the darkness of a dot is increased by overprinting the same pixel using a binary value printer. In this event, if an injection amount of one ink drop is set equal to that required in the non-overprinting, the total ink amount per pixel becomes excessive to induce deterioration of the image quality, such as blotting of ink on a print medium. For preventing this, the injection amount of one ink drop is reduced upon overprinting while increasing the number of overprinting times. This, however, lowers the printing speed.
There is another method which realizes a halftone printing by changing amounts of ink drops injected via nozzles of an inkjet printhead. Although it is possible to achieve it by changing diameters of the nozzles of the inkjet printhead, highly precise and costly delicate processing is required for producing such an inkjet printhead.
For solving it, there has been proposed a method, wherein a drive waveform applied to each of piezoelectric elements is controlled to control a pressure in a corresponding pressure chamber so as to controllably change an amount of an ink drop injected from a corresponding nozzle.
There are roughly two methods for applying the drive waveform, i.e. voltage, to the piezoelectric element, in one of which the voltage is constantly applied to the piezoelectric element and in the other of which the voltage is applied to the piezoelectric element only upon injection of an ink drop. In the former method, the stress of the piezoelectric element against the voltage is large so that, for example, an insulation property of the piezoelectric element may be degraded. If the applied voltage is lowered for suppressing the stress, the controllability of the ink injection amount is deteriorated. Further, since the high voltage continues to be applied even in a standby state, the power consumption is also a problem.
When an analog switch is used for feeding the drive waveforms to the piezoelectric elements, such a piezoelectric element that is not used for printing over a long time can not keep a standby state since charges are lost due to discharging. Accordingly, when the printing operation is restarted, the drive waveform rises sharply due to recharging so that the ink may be unwantedly injected or the ink drop injection may become unstable.
On the other hand, for increasing the number of halftone levels, it is effective to increase the number of tone or gradation levels per dot while using the dithering method, the error diffusion method or the like. However, for achieving it, it is necessary to increase the number of drive waveforms to be fed to each of the piezoelectric elements. If a circuit structure as shown in
FIG. 9
is used therefor, drive waveform feed circuits and switching elements are required as many as the number of the gradation levels of the dot. This complicates the circuit structure and increases the cost thereof.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an improved inkjet printing device that can eliminate one or more of the disadvantages inherent in the foregoing conventional techniques.
It is another object of the present invention to provide an improved inkjet printing method that can eliminate one or more of the disadvantages inherent in the foregoing conventional techniques.
For controlling an injection amount of an ink drop, it is necessary to control a pressure in a pressure chamber and a meniscus of ink therein. Specifically, the pressure is first lowered to retreat the meniscus from the tip of a nozzle and then suddenly increased to inject an ink drop via the nozzle. A retreating magnitude of the meniscus, a pressure variation upon increasing the pressure, and a pressure increasing time reflect on injection speed and amount of an ink drop. The pressure variation can be controlled by behavior of a piezoelectric element, i.e. a drive voltage waveform applied to the piezoelectric element. As described above, there are roughly two methods for applying the voltage to the piezoelectric element.
FIG. 10A
shows a case of a printhead wherein a piezoelectric element is contracted when the voltage is applied so that the pressure in a pressure chamber is reduced. In this case, a drive waveform has a triangular shape as shown in FIG.
10
A. On the other hand,
FIG. 10B
shows a case of a printhead wherein a piezoelectric element is expanded when the voltage is applied so that the pressure in a pressure chamber is increased. In this case, a drive waveform has an inverse triangular shape as shown in FIG.
10
B. The present invention deals with the latter case.
According to a first aspect of the present invention, there is provided an inkjet printing device comprising a drive waveform feed device for feeding at least two kinds of drive waveforms; a deform device which deforms according to the drive waveform fed from the drive waveform feed device; and a pressure chamber which is supplied with ink and injects the ink via a nozzle by displacing a meniscus of the ink filled therein due to deformation of the deform device, wherein at least one kind of the drive waveforms fed from the drive waveform feed device has at least two changing points in one drive period thereof.
The drive waveform feed device may be in the form of a specific circuit comprising digital-analog converters etc. or may be realized by a software control so as to feed the drive waveforms. Further, the deform device may be in the form of a piezoelectric element, but is not limited thereto. Specifically, as long as it is subjected to deformation, such as expansion/contraction, shear deformation or bending deformation due to a bimorph effect, in response to applied voltage or the like, there is no particular limitation.
FIG. 1
shows an example of a drive waveform having two changing points in one drive period thereof. As appreciated, the drive waveform of the present invention having at least two changing points in one drive period thereof is not limited thereto. It may be arranged that a standby state is provided per drive period of the drive waveform and the deform device is applied with a given voltage in the standby state, and that a voltage at at least one of the changing points is set lower than the given voltage and a voltage at at least one of the changing points is set higher than the given voltage. When injecting a big ink drop, it is necessary to provide a sufficiently large amplitude of the voltage variation. Accordingly, this structure is particularly effective for injecting the big ink drop.
According to a second aspect of the present invention, there is provided an inkjet printing device comprising a drive waveform feed device for feeding at least t
Armstrong Westerman Hattori McLeland & Naughton LLP
Barlow John
Do An H.
Fujitsu Limited
LandOfFree
Inkjet printing device and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inkjet printing device and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inkjet printing device and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546969