Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-02-24
2001-03-13
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06199971
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to direct electrostatic printing methods in which charged toner particles are transported under control in accordance with an image information from a particle source to form a toner image used in a copier, a printer, a plotter, a facsimile, or the like.
BACKGROUND TO THE INVENTION
According to a direct electrostatic printing method, such as that disclosed in U.S. Pat. No. 5,036,341, a background electric field is produced between a developer sleeve and a back electrode to enable the transport of charged toner particles therebetween. A printhead structure, such as an electrode matrix provided with a plurality of selectable apertures, is interposed in the background electric field and connected to a control unit which converts an image information into a pattern of electrostatic control fields which selectively open or close the apertures, thereby permitting or restricting the transport of toner particles from the developer sleeve. The modulated stream of toner particles allowed to pass through opened apertures impinges upon an information carrier, such as paper, conveyed between the printhead structure and the back electrode, to form a visible image.
According to such a method, each single aperture is utilized to address a specific dot position of the image in a transverse direction, i.e. perpendicular to paper motion. Thus, the transversal print addressability is limited by the density of apertures through the printhead structure. For instance, a print addressability of 300 dpi requires a printhead structure having 300 apertures per inch in a transversal direction.
A new concept of direct electrostatic printing, hereinafter referred to as dot deflection control (DDC), was introduced in U.S. patent application Ser. No. 08/621,074. According to the DDC method each single aperture is used to address several dot positions on an information carrier by controlling not only the transport of toner particles through the aperture, but also their transport trajectory toward a paper, and thereby the location of the obtained dot. The DDC method increases the print addressability without requiring a larger number of apertures in the printhead structure. This is achieved by providing the printhead structure with at least two sets of deflection electrodes connected to variable deflection voltages which, during each print cycle, sequentially modify the symmetry of the electrostatic control fields to deflect the modulated stream of toner particles in predetermined deflection directions.
For instance, a DDC method performing three deflection steps per print cycle, provides a print addressability of 600 dpi utilizing a printhead structure having 200 apertures per inch.
An improved DDC method, disclosed in U.S. patent application Ser. No. 08/759,481, provides a simultaneous dot size and dot position control. This later method utilizes the deflection electrodes to influence the convergence of the modulated stream of toner particles thus controlling the dot size. According to the method, each aperture is surrounded by two deflection electrodes connected to a respective deflection voltage D
1
, D
2
, such that the electrode field generated by the control electrodes remains substantially symmetrical as long as both deflection voltages D
1
, D
2
have the same amplitude. The amplitudes of D
1
and D
2
are modulated to apply converging forces on toner to obtain smaller dots. The dot position is simultaneously controlled by modulating the amplitude difference between D
1
and D
2
. Utilizing this improved method enables 60 &mgr;m dots to be obtained utilizing 160 &mgr;m apertures.
With DDC, in direct electrostatic printing methods, there appears so called dot tailing when the upper limit of the print speed is attained. This is due to insufficient deflection of the last toner particles of a dot. It can thus be considered a drawback of current direct electrostatic printing methods that there is at least to a certain extent a tradeoff between print speed and image quality. Therefore, there seems to still exist a need to improve the current direct electrostatic printing method.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of and device for increasing the print speed of direct electrostatic printing methods.
A further object of the present invention is to provide a method of direct electrostatic printing which increases the print speed without a degradation in print quality.
Still a further object of the present invention is to provide a method of and a device for improving control over dot placement in direct electrostatic printing methods.
Yet a further object of the present invention is to provide a method of and a device for enhancing dot sharpness in direct electrostatic printing methods.
Another object of the present invention is to provide a method of and device for reducing or eliminating dot tailing in direct electrostatic printing methods.
Still another object of the present invention is to provide a method of and a device for trajecting toner particles to predetermined positions in view of an image which is to be printed.
Said objects are achieved according to the invention by providing an image printing device and method for printing an image to an information carrier. The image printing device includes apertures which can be selectively opened or closed to permit or restrict the transport of pigment particles during print sequences, a predetermined number of which print sequences are included in a print cycle, to thereby enable the formation of a pigment image. Further, deflection electrodes are included for, by means of predetermined deflection voltages related to each one of the predetermined number of print sequences, controlling the deflection of pigment particles in transport to thereby be able to deflect pigment particles against predetermined locations in view of the image which is to be printed. To enable a faster print speed, according to the invention, the change of the predetermined deflection voltages of a previous print sequence to the predetermined deflection voltages of a current print sequence is time displaced relative to the beginning of the current print sequence.
Said objects are also achieved according to the invention by an image printing device and method for printing an image onto an information carrier. The direct electrostatic printing device includes a pigment particle source, a voltage source, a printhead structure, a control unit, and an image receiving member. The pigment particle source provides pigment particles. The image receiving member and the printhead structure move relative to each other during printing. The image receiving member has a first face and a second face. The printhead structure is placed inbetween the pigment particle source and the first face of the image receiving member. The voltage source is connected to the pigment particle source and the back electrode to thereby create an electrical field for transport of pigment particles from the pigment particle source toward the first face of the image receiving member. The printhead structure includes control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles during print sequences, a predetermined number of which print sequences are included in a print cycle, to thereby enable the formation of a pigment image on the first face of the image receiving member. According to the invention the printhead structure includes deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport to thereby be able to deflect pigment particles against predetermined locations on the first face of the image receiving member in view of the image which is to be printed by means of predetermined deflection voltages related to each one of the predetermined number of print sequences. And also according to the invention the change of the predetermined deflec
Bern Bengt
Sandberg Agneta
Arrray Printers AB
Barlow John
Gordon Raquel Yvette
Knobbe Martens Olson & Bear LLP
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