Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-02-09
2002-08-06
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06428137
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an on-demand inkjet printing method and an on-demand inkjet printing device 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
Printing devices such as printers are essential in the recent office automation environment, and even personal-use printing devices have been widely spreading. Among them, with respect to the printers, attention has been more paid to inkjet printers as compared with wire printers which perform printing by magnetically driving wires to press them onto a platen via an ink ribbon and a print medium such as a sheet of paper. As appreciated, as compared with the wire printer, the inkjet printer produces less noise and carries out high-speed printing with less printing cost per sheet.
In the inkjet printing, ink drops of different volumes or sizes are injected for forming dots of different sizes on a print medium so as to realize a halftone printing. In this case, the ink drops are jetted successively at constant periods (T[sec]).
Normally, the multi-pass printing is carried out wherein ink drops of the same size are successively jetted on one line, then ink drops of another same size are successively jetted on the same line, which are repeated to jet the ink drops of various sizes without changing the line.
In the foregoing halftone printing, however, there is a serious problem that a disorder of an output image is caused due to the fact that dots are not formed at predetermined positions on the print medium.
Although such a disorder of the output image is prevented in the multi-pass printing, there is a drawback that the printing speed is lowered.
The present inventors tried to seek the reason why the dots are not formed at the predetermined positions on the print medium, and found out that the ink drops hit upon the print medium at positions other than the predetermined positions due to differences in size of the ink drops. Specifically, when the ink drops of different sizes are injected, the flying speed increases as the volume or mass of the ink drop increases. As speed differences among the ink drops increase, the accuracy of the hit positions of the ink drops on the print medium is lowered to degrade the quality of the output image.
SUMMARY OF THE INVENTION
Therefore, it is an 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.
It is another 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.
According to a first aspect of the present invention, there is provided an inkjet printing method wherein ink drops injected from a nozzle one by one to be hit upon a print medium have at least two different sizes, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the size of the ink drop to be injected.
It may be arranged that the ink drop having one of the at least two different sizes is set to be a reference ink drop for determining the injection timing and, when the ink drop to be injected is bigger than the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop having one of the at least two different sizes is set to be a reference ink drop for determining the injection timing and, when the ink drop to be injected is smaller than the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
As the size (volume) of the ink drop increases, the flying speed increases so that the ink drop reaches the print medium earlier. Therefore, if the injection timing is delayed correspondingly, the ink drop hits upon the print medium precisely at a target position. In contrast, as the size of the ink drop decreases, the flying speed decreases so that the ink drop reaches the print medium later. Therefore, if the injection timing is advanced correspondingly, the ink drop hits upon the print medium precisely at a target position. In this fashion, the accuracy of a hit position of the ink drop on the print medium can be enhanced to improve the quality of an output image.
According to a second aspect of the present invention, there is provided an inkjet printing method wherein at least two kinds of drive waveforms having different amplitudes are supplied depending on print data and an ink drop is injected from a nozzle by displacing a meniscus of ink in the nozzle according to each of the drive waveforms, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the amplitude of the corresponding drive waveform.
In the foregoing first aspect of the present invention, the injection timing of the ink drop is determined depending on the size of the ink drop to be injected. Normally, the ink drop is injected by displacing the meniscus of ink in the nozzle so as to first retreat the meniscus from a tip of the nozzle and then suddenly force it forward. In this event, the size of the ink drop to be injected can be adjusted by changing the amplitude of the applied drive waveform to control the backward and forward displacement of the meniscus. Accordingly, the second aspect of the present invention defines the structure in terms of the displacement of the meniscus.
It may be arranged that the ink drop to be injected by the drive waveform having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the drive waveform for the ink drop to be injected is greater than the amplitude of the drive waveform for the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop to be injected by the drive waveform having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the drive waveform for the ink drop to be injected is smaller than the amplitude of the drive waveform for the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
As the amplitude of the applied drive waveform increases, the size of the ink drop increases so that the flying speed increases and thus the ink drop reaches the print medium earlier. Therefore, it is necessary to delay the injection timing correspondingly. In contrast, as the amplitude of the applied drive waveform decreases, the size of the ink drop decreases so that the flying speed decreases and thus the ink drop reaches the print medium later. Therefore, it is necessary to advance the injection timing correspondingly.
According to a third aspect of the present invention, there is provided an inkjet printing method wherein when ink drops are injected from a nozzle one by one, at least two kinds of pressure variations having different amplitudes are applied to ink in the nozzle, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the amplitude of the pressure variation applied to the ink.
When injecting the ink drop by feeding the drive waveform to displace the meniscus of ink, the amplitude of the pressure variation applied to the ink upon injection differs depending on the amplitude of the drive waveform. Accordingly, the third aspect of the present invention defines the structure in terms of the pressure variation applied to the ink.
It may be arranged that the ink drop to be injected by the pressure variation having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the pressure variation for the in
Iwaishi Akira
Kawamura Takumi
Miyaki Akihiko
Ono Masahiro
Armstrong Westerman & Hattori, LLP
Barlow John
Fujitsu Limited
Tran Ly
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