Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-08-27
2002-10-15
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06464330
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of ink jet printing and more particularly to ink jet printing with a print head capable of depositing multiple drop sizes.
BACKGROUND OF THE INVENTION
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner onto an image recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the recording element to yield the desired image. In one process, known as drop-on-demand ink jet printing, individual ink droplets are projected as needed onto the recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation using heat actuators. With regard to heat actuators, a heater placed at a convenient location within the nozzle or at the nozzle opening heats the ink in selected nozzles and causes a drop to be ejected to the recording medium in those nozzles selected in accordance with image data. With respect to piezoelectro-actuators, piezoelectric material is used which piezoelectric material possesses the property such that when electrical field is applied to the material a mechanical stresse is induced therein reducing the volume of the nozzle and causing a drop to be selectively ejected from the nozzle selected. The image data applied to the print head determines which of the nozzles are selected for ejection of a respective drop from each nozzle at a particular pixel location on a receiver sheet. Some drop-on-demand ink jet printers described in the patent literature use both piezoelectric actuators and heat actuators.
In another process, known as continuous ink jet printing, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the recording element, while unimaged droplets are caught and returned to an ink sump. Ink jet printers have found broad applications across markets ranging from desktop document and pictorial imaging to short run printing and industrial labeling.
A typical ink jet printer reproduces an image by ejecting small drops of ink from a print head containing an array of spaced apart nozzles, where the ink drops land on a receiver medium (typically paper) to form round ink dots. In some printers, all drops are the same size, and therefore, all dots are the same size. Normally, these drops are deposited with their respective dot centers on a rectilinear grid, a raster, with equal spacing, p, in the horizontal and vertical directions. Therefore, to achieve full coverage of the ink it is necessary for the dots, 10, to have at least diameter p*sqrt(2), as shown in FIG.
3
. Some printer designs may allow for even bigger dots in order to compensate for unwanted variations in the placement of the drops.
Modem inkjet printers may also possess the ability to vary (over some range) the amount of ink that is deposited at a given location on the page. Ink jet printers with this capability are referred to as “multitone” or gray scale ink jet printers because they can produce multiple density tones at each pixel location on the page. Some multitone ink jet printers achieve this by varying the volume of the ink drop produced by the nozzle by changing the electrical signals sent to the nozzle or by varying the diameter of the nozzle. See for example U.S. Pat. No. 4,746,935. Other multitone ink jet printers produce a variable number of smaller, fixed size droplets that are ejected by the nozzle (or by plural nozzles during different passes of the nozzle array), all of which are intended to merge and land at the same pixel location on the page. See for example U.S. Pat. No. 5,416,612. These techniques allow the printer to vary the size or optical density of a given ink dot or pixel, which produces a range of density levels at each dot or pixel location, thereby improving the image quality. Thus printing methods that require multiple drop sizes usually depend upon the way the drops are generated by the print head. As noted above some print heads have multiple size nozzle diameters, others have circuitry in which the individual ink chambers acccept changing electrical signals to instruct each chamber how much ink to eject. Still other print heads have nozzles that eject a variable number of small, fixed size droplets that are intended to merge then land in a given image pixel location. Printing methods that deposit more than one drop in a pixel location are typically carried out by multiple printing passes wherein the print head prints a row of pixels pixels multiple times, the image data to the print head changing in accordance with each pass so that the correct number of total droplets deposited at any pixel location is commensurate with the density required by the processed image data.
The exact relationship between drop size and dot size depends on many factors. However, in many cases it can be approximated by the equation
d=a*
v
b
, (Equ 1)
where d is the diameter of the dot, v is the volume of the drop, a is a positive constant whose magnitude depends on the units of d and v, and b is a positive constant in the range 0.0 to 1.0. This means that the ratio of dot size to volume is given by
d/v=a*
v
(b−1)
. (Equ 2)
Therefore, as drop volume goes up the ratio of dot size to drop volume goes down, which generally means that increasing drop volume provides diminishing returns in terms of dot size.
Note, however, to achieve full coverage with a multitone ink jet printer it is still necessary that the largest dot have at least a diameter of p*sqrt(2), and that this largest drop be deposited at each addressable location on the raster.
The time required for an ink jet print to dry can be directly related to the volume of ink deposited on the media. The maximum volume of ink is determined by the dot size required to achieve full coverage. In the case of a binary or multitone printer writing on a raster the dot size per pixel required to achieve full coverage has already been shown in
FIG. 3
to be one dot with diameter p*sqrt(2).
In the field of inkjet printing it is also well known that if ink drops placed at neighboring locations on the page are printed at the same time, then the ink drops tend to flow together on the surface of the page before they soak into the page. This can give the reproduced image an undesirable grainy or noisy appearance often referred to as “coalescence”. It is known that the amount of coalescence present in the printed image is related to the amount of time that elapses between printing adjacent dots. As the time delay between printing adjacent dots increases, the amount of coalescence decreases, thereby improving the image quality. There are many techniques present in the prior art that describe methods of increasing the time delay between printing adjacent dots using methods referred to as “interlacing”, “print masking”, or “multipass printing”. There are also techniques present in the prior art for reducing one-dimensional periodic artifacts or “bands.” This is achieved by advancing the paper by an increment less than the printhead width, so that successive passes or swaths of the printhead overlap. The techniques of print masking and swath overlapping are typically combined. See, for example, U.S. Pat. No. 4,967,203 and 5,992,962. The term “print masking” generically means printing subsets of the image pixels in multiple passes of the printhead relative to a receiver medium.
There is a need for improvement over the prior art in ink jet printing to achieve full coverage with a minimum amount of ink so as to minimize the dry time required for an ink jet print. The prior art utilized large dots with excessive amounts of overlap in order to achieve full coverage. This invention provides a method for achieving full coverage with less dot overlap and with smaller drops, thereby achieving faster dry times.
SUMMARY OF THE INVENTION
An ob
Miller Rodney L.
Newkirk James S.
Nguyen Thinh
Rushefsky Norman
LandOfFree
Ink jet printer with improved dry time does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ink jet printer with improved dry time, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ink jet printer with improved dry time will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2984644