Facsimile and static presentation processing – Static presentation processing – Communication
Reexamination Certificate
1999-05-24
2002-12-10
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Communication
C347S005000, C347S009000, C347S010000, C347S073000, C358S003050, C358S001100, C358S001130, C358S001120, C358S003050, C358S003050
Reexamination Certificate
active
06493106
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to digital and print-on-demand printing systems; and more particularly, to a high-speed printer controller system that is configured to control a multitude of print engines simultaneously, and is configured to synchronize the deposition of image pixels and to “lock-step” the transport mechanisms on the multitude of print engines to a single clock source, thereby reducing beat frequency and other errors between the print engines.
An ink jet printing system is an example of a printing system that is notorious for having registration problems and beat frequency errors between various print engines (ink jet printheads) controlled by at least one printer controller. Ink jet printing is a non-impact print method which is based upon controlling the behavior of a fluid ink stream using pressure, ultrasonic vibration and electrostatic forces. A typical ink jet printhead will include a multitude of nozzle orifices, aligned in an array, for emitting a corresponding multitude of fluid ink streams, commonly referred to as an array of ink. Pressure is created by a push rod to force the ink from the ink chamber and through an array of nozzle orifices.
A high frequency ultrasonic vibration (referred to as a “modulation signal”) is applied to the push rod and, in turn, to the ink stored in an ink chamber within the ink jet printhead, to establish a standing wave pattern within the ink. To create the modulation signal, the typical ink jet print head will utilize an internal clock source which is sent to a piezoelectric crystal, typically mounted within the push rod assembly. The piezoelectric crystal will thus vibrate at the frequency of the clock source. The vibrational waves will conduct into the ink chamber, causing the standing wave pattern within the ink. This standing wave pattern in the ink causes the ink to break into individual droplets, corresponding to individual pixels of the printed image, when the ink emerges from the nozzle orifices. The resulting array of ink droplet streams is directed (typically downward) towards the substrate to receive the printed image.
A multitude of electrodes are positioned adjacent to each of the ink droplet streams, near the nozzle orifices. The electrodes, controlled by the ink jet printhead, apply a voltage to the droplets which are not intended to contact the substrate. Below the electrodes, the droplet streams pass through a high voltage field which forces the charged droplets to be deflected into a gutter and which allows the uncharged droplets to pass through the field and onto the substrate, thus forming the printed image.
The nozzle orifices are typically arranged on the ink jet printhead in a row, where each nozzle orifice corresponds to one column of image pixels on the final printed image. The printed image is formed by emitting successive horizontal lines of the ink droplets (referred to as “strokes”) applied to the continuously moving substrate (moving in the vertical direction). Each stroke forms one row of pixels on the final printed image. The electrodes are controlled for each stroke by the ink jet printhead in accordance with the bitmap data sent to the print head by the raster printer controller.
In low-speed printing operations, where the substrate is moved at low speeds under the ink jet printheads, the width of the row of nozzle orifices is not a concern. However, in high-speed printing operations, where the substrate is moved at high speeds under the ink jet printheads (i.e., to print 1000 feet per minute), the size of the row of nozzle orifices becomes a real concern because of the time it takes for the vibrational waves in the chamber to travel from the push rod to the far ends of the printhead. Accordingly, to be able to print detailed, full size images in high speed ink jet print operations, it is necessary to utilize a plurality of the ink jet print heads, where each print head is responsible to print one vertical portion or “swath” of the image. One “swath” of an image corresponds to the number of vertical columns of pixels that one ink jet printhead will be able to print. Typically, the width of each swath can range from approximately 20 to 1024 pixels (i.e., the swath would comprise 20 to 1024 columns of pixels), however the range can vary depending upon the application.
Because the physical width of the ink jet printhead exceeds the width of the swath printed by the ink jet printhead, the multiple ink jet printheads cannot be aligned side by side with respect to each other without experiencing noticeable gaps between the swaths. Therefore, to get a continuous image across the width of the entire printed page, with no noticeable gaps between the swaths, it is necessary to stagger the ink jet print heads vertically with respect to the substrate such that they do not interfere with each other. It is also necessary to simultaneously control the multiple ink jet printheads such that their respective swaths are vertically and horizontally aligned with respect to the substrate. The process of vertically and horizontally aligning these swaths on the substrate to form one image is commonly referred to as “stitching”.
Stitching the multiple ink jet swaths down to the pixel level in order to obtain sub pixel resolution is extremely challenging. Mechanical alignment is the most common method of aligning the printheads to achieve stitching of the swaths. Utilizing micrometer adjustment and measurement devices on the x and y axes, the position of the printheads can be adjusted to approach sub pixel resolution. However, such alignment is only useful for a particular ink viscosity, temperature of the environment, humidity of the environment and print speed. Once any one of these variables changes, i.e., the viscosity of the ink changes, the pixel resolution will again become misaligned. Furthermore, even if the printheads are perfectly aligned, the piezoelectric crystals in each printhead will be driven at a slightly different frequency, thus causing beat frequency drift errors between the printheads which eventually leads to very visible alignment errors between the pixels of the different swaths.
Electronic alignment methods and mechanisms, while more flexible than mechanical alignment systems, also cannot achieve sub pixel resolution because of the piezo beat frequency drift errors, which will eventually cause drift between the printheads, independent of the mechanical and/or electronic methods and systems used for stitching the swaths together.
The problem of beat frequency drift errors is not limited to ink jet engines. As will be appreciated by those of ordinary skill in the art, similar errors may occur in other types of print engines that are linked together to print upon a single substrate or web. For example, magnetographic engines utilize magnetic recording heads to create a latent magnetic image on the surface of a revolving hard metal drum, which is then exposed to magnetic toner particles and transferred/fused to paper. The modulation frequency of the magnetic recording heads is controlled by a clock source, which may be slightly different on each of the print engines. Therefore, if a plurality of the magnetographic print engines are used in series to print a single image, the slight differences in the magnetic recording heads' clock sources may cause slight (but perceptible) registration errors in the printed pixels of the image. Similar beat frequency errors may occur in LED engines, Ion deposition engines, laser engines, magnetographic, xerographic engines and the like.
Accordingly, a need exists for a system and method for simultaneously controlling the plurality of staggered ink jet printheads such that stitching between the swaths generated by the ink jet printheads can be easily accomplished electronically, regardless of the ink viscosity, print speed, temperature and humidity. Furthermore, a need exists for a system and method for synchronizing the piezo clock sources on each of the ink jet printheads to each other such that the stitching can be accomp
Gauthier Forrest P.
Jovic Dimitrije L.
Coles Edward
Ebrahimi Saeid
Taft Stettinius & Hollister LLP
Tesseron Ltd.
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