The patent's inventors are Marcus, Michael A. (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfer and fixing. Ink jet printing mechanisms can be categorized by technology as either drop on demand ink jet (DOD) or continuous ink jet (CIJ).
"The first technology, 'drop-on-demand' ink jet printing, provides ink drops that impact upon a recording surface by using a pressurization actuator (thermal, piezoelectric, etc.). One commonly practiced drop-on-demand technology uses thermal actuation to eject ink drops from a nozzle. A heater, located at or near the nozzle, heats the ink sufficiently to boil, forming a vapor bubble that creates enough internal pressure to eject an ink drop. This form of inkjet is commonly termed 'thermal ink jet (TIJ).'
"The second technology commonly referred to as 'continuous' ink jet (CIJ) printing, uses a pressurized ink source to produce a continuous liquid jet stream of ink by forcing ink, under pressure, through a nozzle. The stream of ink may be perturbed in a manner such that the liquid jet breaks up into drops of ink in a predictable manner. Printing occurs through the selective deflecting and catching of undesired ink drops. Various approaches for selectively deflecting drops have been developed including the use of electrostatic deflection, air deflection and thermal deflection mechanisms.
"In a first electrostatic deflection based CIJ approach, the liquid jet stream is perturbed in some fashion causing it to break up into uniformly sized drops at a nominally constant distance, the break-off length, from the nozzle. A charging electrode structure is positioned at the nominally constant break-off location so as to induce an input image data dependent amount of electrical charge on the drop at the moment of break-off. The charged drops are then directed through a fixed electrostatic field region causing each droplet to deflect by an amount dependent upon its charge to mass ratio. The charge levels established at the break-off point cause drops to travel to a specific location on a recording media or to a gutter, commonly called a catcher, for collection and recirculation. This approach is disclosed by
"One known problem with these conventional CIJ printers is variation in the charge on the drops caused by the image data-dependent electrostatic fields from adjacent electrodes associated with neighboring jets. These input image data dependent variations are referred as electrostatic crosstalk. Such electrostatic crosstalk can produce visible artifacts in the printed image. Katerberg disclosed a method to reduce or eliminate the visible artifacts produced by the electrostatic crosstalk interactions by providing guard gutter drops between adjacent print drops across the jet array in U.S. Pat. No. 4,613,871. However, the presence of electrostatic crosstalk from neighboring electrodes limits the minimum spacing between adjacent electrodes and therefore resolution of the printed image.
"Thus, the requirement for individually addressable charge electrodes in traditional electrostatic CIJ printers places limits on the fundamental nozzle spacing and therefore on the resolution of the printing system. A number of alternative methods have been disclosed to overcome the limitation on nozzle spacing by use of an array of individually addressable nozzles in a nozzle array and one or more common charge electrodes at constant potentials. One method uses control of the jet breakoff length as disclosed by Vago et al. in U.S. Pat. No. 6,273,559 issued
"B. Barbet and
"These drop control systems use a charging electrode that is held at a fixed electrical potential relative to the jets in conjunction with image data dependent breakoff lengths. As they employ a charging electrode that is common to the array of nozzles, print drops are not affected by electrostatic crosstalk due to the image dependent voltage on charging electrodes associated with neighboring drops. These drop control systems however do produce print drops that are charged, albeit at a magnitude that is below that of the catch drops. The print drop charge can result in electrostatic interactions between neighboring or nearby print drops which cause alterations of drop trajectories and result in drop placement errors and degraded print quality on the recording media. As the packing density of nozzles in a print head increases to provide higher print resolution, the electrostatic interactions between neighboring or nearby print drops increase causing larger alterations in drop trajectories.
"As such, there is an ongoing need to provide a high print resolution continuous inkjet printing system that prints with selected drops from an array of nozzles without the print defects of these drop control systems."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "It is an object of the invention to minimize drop placement errors in an electrostatic deflection based ink jet printer caused by electrostatic interactions between adjacent print drops. A second object of this invention is to increase the print margin defined as the separation between the print drop and gutter drop trajectories.
"Image data dependent control of drop formation breakoff length at each of the liquid jets in a nozzle array and a common charge electrode having a constant electrical potential are provided by the present invention. Drop formation is controlled to create sequences of one or more print drops having a breakoff length L.sub.p and sequences of one or more non-print drops having a distinct breakoff length L.sub.np in response to the input image data. The nozzle array is made up of a plurality of nozzles being arranged into a first group and a second group of interleaved nozzles. A timing delay device is used to shift the timing of the drop formation waveforms supplied to the drop formation devices of the first group of nozzles relative to the drop formation waveforms supplied to the drop formation devices of the second group of nozzles. This causes print drops formed from nozzles of the first group and the print drops formed from nozzles of the second group to not be aligned relative to each other along the nozzle array direction. The position of the charge electrode relative to the vicinity of the breakoff length L.sub.p and breakoff length L.sub.np result in a difference in electric field strength at the two breakoff lengths thus inducing different amounts of charge on print drops and on non-print drops. As the drops break off from the liquid jets a print drop charge state is produced on the print drops and a non-print drop charge state is produced on the non-print drops which are substantially different from each other. A deflection device is then utilized to separate the paths of print and non-print drops. A catcher then intercepts non-print drops while allowing print drops to travel along a path towards a recording media.
"The present invention improves CIJ printing by increasing the distance between adjacent print drops in neighboring nozzles thereby decreasing drop to drop electrostatic interactions, thus resulting in improved drop placement accuracy over previous CIJ printing systems. The present invention also reduces the complexity of control of signals sent to stimulation devices associated with nozzles of the nozzle array. This helps to reduce the complexity of charge electrode structures and increase spacing between the charge electrode structures and the nozzles. The present invention also allows for longer throw distances by lowering the electrostatic interactions between adjacent print drops.
"According to one aspect of the invention, a method of printing includes providing liquid under pressure sufficient to eject liquid jets through a plurality of nozzles of a liquid chamber. The plurality of nozzles are disposed along a nozzle array direction, The plurality of nozzles are arranged into a first group and second group in which the nozzles of the first group and second group are interleaved such that a nozzle of the first group is positioned between adjacent nozzles of the second group and a nozzle of the second group is positioned between adjacent nozzles of the first group. A drop formation device is associated with each of the plurality of nozzles. Input image data is provided. Each of the drop formation devices is provided with a sequence of drop formation waveforms to modulate the liquid jets to selectively cause portions of the liquid jets to break off into streams of one or more print drops having a jet breakoff length L.sub.p in a print drop breakoff length range R.sub.p and one or more non-print drops having a jet breakoff length L.sub.np in a non-print drop breakoff length range R.sub.np in response to the input image data. A timing delay device is provided to shift the timing of the drop formation waveforms supplied to the drop formation devices of nozzles of one of the first group and the second group so that the print drops formed from nozzles of the first group and the print drops formed from nozzles of the second group are not aligned relative to each other along the nozzle array direction. A charging device includes a first common charge electrode associated with the liquid jets formed from both the nozzles of the first group and the nozzles of the second group and a source of constant electrical potential between the first charge electrode and the liquid jets. The first common charge electrode is positioned relative to the vicinity of the breakoff length L.sub.p and breakoff length L.sub.np such that there is a difference in electric field strength at the two breakoff lengths to produce a print drop charge state on print drops and to produce a non-print drop charge state on non-print drops which is substantially different from the print drop charge state. A deflection device causes print drops having the print drop charge state and non-print drops having the non-print drop charge state to travel along different paths using the deflection device. A catcher intercepts the non-print drops while allowing the print drops to continue to travel along a path toward a recording media."
For the URL and additional information on this patent, see: Marcus, Michael A.; Panchawagh, Hrishikesh V.; Adiga,
Keywords for this news article include: Technology,
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