Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-22
2003-05-06
Hsieh, Shih-wen (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06557971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to a method for servicing an inkjet printhead and, more specifically, to a method for recovering against specific failure modes in inkjet devices.
2. Description of the Related Art
Thermal inkjet technology uses heat energy to vaporize a thin layer of ink to form a bubble that expels a small drop of ink through an orifice or nozzle. As the ink leaves the nozzle head, it creates a vacuum that pulls in fresh ink. This process is repeated thousands of times per second. Each nozzle of a typical inkjet printhead is backed by a heater or resistor which heats under control of electronic circuitry. Piezoelectric inkjet printing, another form of drop-on-demand inkjet printing, uses a mechanical mechanism to eject ink.
Thermal inkjet nozzles experience a variety of different failure modes. One of the most typical failure modes is caused by air bubbles which are trapped in the firing chamber. These bubbles can have several sources: air ingested during pen insertion due to a “hard” insertion (pen shock against carriage), very low negative pressure when a pen is running with an almost empty ink supply, and particles blocking an ink entrance and inducing an air bubble.
One solution to this problem is to simply allow the pen to rest long enough for the air bubble to redisolve into the ink. However, such a solution is not always practical or desirable—particularly when end users expect some form of intervention mechanism (user invoked or otherwise) for effecting printhead recovery. Although a printer can be equipped with a positive or negative pressure prime, this will not provide printhead recover in all instances. Also, spitting at one frequency or simply wiping a nozzle is usually not an efficient way to recover from chamber bubbles.
A recent trend in inkjet devices is to reduce the size of the printhead nozzles in order to reduce the volume of the drops fired, thereby increasing perceived image quality. An unfortunate byproduct is this is that smaller sized contaminants which are more difficult to filter can end up leading to malfunctioning nozzles.
Another trend in inkjet devices is to increase the number of nozzles in one printhead to improve print times. However, more nozzles can result in a larger volume of printhead that needs to be free of particles.
A prior approach to solving the problem of internal contaminants is to generate a set of barriers that block the entrance of particles and contaminants to the nozzle chamber but still allow ink to flow through. This is commonly known as particle tolerant architecture (PTA). Usually, the barrier design provides two entrances to each nozzle chamber so that if one is completely blocked, ink can still flow through the other. Examples of particle tolerant architectures can be found in U.S. Pat. No. 5,734,399 to Weber et al., U.S. Pat. No. 5,755,032 to Pan et al., and U.S. Pat. No. 6,007,188 to MacLeod et al.
Although PTA designs are relatively easy to implement and manufacture, they are not without their defects. For example, blockage of one of the entrances usually results in a pressure drop which, in turn, leads to a weak or misdirected nozzle. Also, in particle tolerant architectures, internal contaminants tend to get stuck in the entrances and are difficult to “drag out”.
In designs without PTA, contaminants do not get stuck as easily but they move freely from one nozzle to the other pulled by the negative pressure generated in an adjacent nozzle chamber entrance when that nozzle fires. The end effect is that there are malfunctioning nozzles that “move” along the pen.
Another undesirable effect of internal contaminants is that they can lead to “puddling”. When a particle moves in front of a channel, the nozzle is starved of ink and a chamber bubble forms—effectively shutting down the nozzle. As a result, there is not enough ink available to eject the drop at its normal firing velocity but enough to dump ink out of the nozzle onto the surface of the pen. The external puddle usually ends up growing and knocking out adjacent nozzles which then also contribute to the puddle. This leads to severe banding with some ink drops falling on the media, the puddle being so large that gravity wins against surface tension.
Given the variety of potential failure modes in the printhead operating environment, it would be helpful to have a method for recovering against specific failure modes. In particular, there is a need for a bubble recovery routine which is more efficient and/or effective than conventional servicing spitting. A contaminant purging routine is also needed for non-PTA designs. It would also be helpful to be able to effect a printhead servicing routine in consideration of nozzle health data, diagnostics, or the like to more efficiently and/or effectively address a detected malfunction or condition.
SUMMARY OF THE INVENTION
According to the present invention, a method for servicing an inkjet printhead is provided. In a preferred embodiment, the method for servicing an inkjet printhead effects recovery against a particular printhead failure mode via implementation of a printhead servicing routine including, but not limited to, a bubble recovery routine, a contaminant purging routine, and/or a (standard) printhead servicing routine. In a preferred embodiment, the method for servicing an inkjet printhead takes into consideration nozzle health data, diagnostics, or the like. In a preferred embodiment, a bitmap or mask is employed to control firing of the nozzles during the servicing of the printhead. It is expected that bitmapped or masked spitting will facilitate a wide variety of treatments for printheads in order to restore nozzle performance and combat several failure modes from which conventional spitting does not provide recovery.
A method for servicing an inkjet printhead in accordance with one embodiment of the present invention includes the steps of: providing a printhead for an inkjet printer, the printhead including a plurality of printing nozzles; and firing the printing nozzles in a manner tending to force contaminants at the printing nozzles toward one end of the printhead. In a preferred embodiment, the contaminants are moved by firing consecutive printing nozzles. In a preferred embodiment, the method further includes the step of employing a bitmap to control the firing of the printing nozzles. In a preferred embodiment, the method further includes the step of generating the bitmap to effect recovery against a specific failure mode. In a preferred embodiment, the method further includes the step of generating the bitmap depending upon which of the printing nozzles needs to be serviced. In a preferred embodiment, the method further includes the step of dynamically (or otherwise) generating the bitmap depending upon nozzle health data.
A method for servicing an inkjet printhead in accordance with another embodiment of the present invention includes the steps of: providing a printhead for an inkjet printer, the printhead including a plurality of printing nozzles; selecting a group of the printing nozzles; and firing the group of printing nozzles while varying a firing frequency at which the nozzles are fired. In a preferred embodiment, the firing frequency is selected such that it tends to resonate bubbles which are typically trapped in the printing nozzles. In a preferred embodiment, the firing frequency starts at a low frequency and ends at a high frequency. In a preferred embodiment, the group of printing nozzles includes a malfunctioning nozzle. In a preferred embodiment, the method further includes the step of employing a bitmap or mask to control the firing of the group of printing nozzles.
A method for servicing an inkjet printhead in accordance with another embodiment of the present invention includes the steps of: providing a printhead for an inkjet printer, the printhead including a plurality of printing nozzles and at least one sewage nozzle positioned at an edge of the printhead, the at least one sewage nozzle being larger is size
Bruch Xavier
Girones Xavier
Murcia Antoni
Trueba Kenneth E
Vega Ramon
Hewlett--Packard Company
Hsieh Shih-wen
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