Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-06-29
2002-06-18
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S090000
Reexamination Certificate
active
06406122
ABSTRACT:
FIELD OF THE INVENTION
This present invention relates to methods and system for cleaning ink jet print heads utilized in an ink jet printer system. More particularly, the present invention relates to a method and system for hydrodynamically cleaning ink jet print heads.
BACKGROUND OF THE INVENTION
Modem color printing relies heavily on ink jet printing techniques. The term “ink jet” as utilized herein is intended to include all drop-on-demand or continuous ink jet propulsion systems including, but not limited to, thermal ink jet, piezoelectric, and continuous, which are well known in the printing arts. An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver medium, typically paper, in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In this regard, “continuous” ink jet printers utilize electrostatic charging tunnels that are placed close to the point where ink droplets are ejected in the form of a stream. The electrostatic charging tunnels electrically charge selected ink droplets. The charged ink droplets are then deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter can be utilized to intercept the charged ink droplets, while uncharged ink droplets are free to strike the receiver medium. Ink drops not utilized for printing are transferred to the gutter where they can be recycled. Continuous ink jet systems thus create a continuous stream of ink drops, generated by periodically perturbing an associated print head orifice with, for example, a piezoelectric transducer.
In the case of “on demand” ink jet printers, a pressurization actuator is utilized to produce the ink jet droplet at every orifice. One of two types of actuators, either a heat actuator or piezoelectric actuator, may be utilized to produce the ink jet droplet. In the case of a heat actuator, a heater is placed at a convenient location to heat the ink. A quantity of ink will then phase change into a gaseous steam bubble, thereby raising the internal ink pressure sufficiently to permit an ink droplet to be expelled onto the receiver medium. In the case of piezoelectric actuators, a piezoelectric material possessing piezoelectric properties is utilized to produce an electric field when a mechanical stress is applied. The converse is also true. An applied electric field produces a mechanical stress in the material. Naturally occurring materials possessing such characteristics include quartz and tourmaline. The most commonly produced piezoelectric ceramics include lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
Recently, a new type of continuous ink jet printer was disclosed. U.S. Pat. Nos. 6,079,821 and 6,234,620 to Chwalek et al., which describe a continuous ink jet printer in which on demand asymmetric heating of an ink jet causes selected drops to deflect. In one mode of operation, selected drops are deflected toward an image-receiving medium while the other drops are intercepted in a canopy-type gutter placed in close proximity (e.g., 3 mm) to the ink jet orifice plate.
Inks for high-speed ink jet printers, whether of the “continuous” or “piezoelectric” type, must have a number of special characteristics. For example, the ink should incorporate a nondrying characteristic; so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by the occasional spitting of ink droplets, the cavities and corresponding orifices are kept open. The addition of glycol facilitates free flow of ink through the ink jet chamber.
Of course, the ink jet print head is exposed to the environment where printing occurs. Thus, the aforementioned orifices are exposed to many kinds of air born particulates. Particulate debris may accumulate on surfaces formed around the orifices and in the orifices and chambers themselves. The ink may combine with such particulate debris to form an interference that blocks the orifice or alters surface wetting, thereby inhibiting the proper formation of the ink droplet. The particulate debris should be cleaned from the surface and orifice to restore proper droplet formation. In the prior art, cleaning is commonly accomplished by brushing, wiping, spraying, vacuum suction, and/or spitting of ink through the orifice.
Thus, inks used in ink jet printers can be said to have the following problems: the inks tend to dry-out in and around the orifices resulting in clogging of the orifices; and the wiping of the orifice plate causes wear on the plate and wiper, the wiper itself producing particles that clog the orifice.
Ink jet print head cleaners are known. An ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled “Ink Jet Print Head Face Cleaner” issued Nov. 13, 1990, in the name of James C. Oswald (the '535 Patent). The '535 Patent discloses an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print head face. Air is directed through an inlet into a cavity in the enclosure. The air that enters the cavity is directed past ink jet apertures on the head face and exits via an outlet. A vacuum source is attached to the outlet to create a sub-atmospheric pressure in the cavity. A collection chamber and removable drawer are positioned below the outlet to facilitate disposal of removed ink. The technique uses heated air to remove the ink. Heated air is less effective for cleaning than a liquid solvent and can also damage fragile electronic circuitry that may be present on the print head face.
Other print head cleaning systems attempt to incorporate physical elements to clean debris from ink jet print heads. For example, a skip stroke wiping system is disclosed in U.S. Pat. No. 5,774,140 titled “Skip Stroke Wiping System for Ink Jet Print Heads,” issued Jun. 30, 1998, in the name of Kris M. English (the '140 Patent). The '140 Patent discloses a skip stroke wiping method for cleaning an ink jet print head and involves wiping and scraping steps. While the apparatus and method described in the '140 Patent will remove debris, the harsh scraping and wiping steps can wear down the print head over time, thereby requiring a complicated wiping mechanism that is costly to replace if damaged.
U.S. Pat. No. 6,183,057 to Sharma et al. describes a cleaning assembly involving a removable gutter (not fixed) and a cup that sealingly engages the print head. Cleaning liquid supplied to the cup flows between a septum and the print head surface, thereby creating a zone of high shear. The cleaning liquid then exits via an outlet provided on the opposite side of the septum. This cup and septum arrangement cannot be utilized to clean the printer when the gutter is fixed.
Based on the foregoing, it can be appreciated that what is needed to efficiently clean an ink jet print head is a non-invasive print head cleaning method and system, one that involves the flow of fluids to remove debris and contaminants present on an ink jet print head, without damaging the print head itself. Such a method and system, if implemented, would avoid the aforementioned problems associated with present print head cleaning methods and systems, particularly those that involve heating techniques or complicated wiping mechanisms.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ink jet printer having a cleaning assembly for cleaning a surface of an ink jet print head.
It is another object of the present invention to provide an ink jet printer having a cleaning assembly for cleaning a surface of an ink jet print head having a fixed type gutter.
It is another object of the present invention to provide a method and system for pumping a cleaning liquid across the print head surface to achieve cleaning of the surface and print head orifices.
It is yet anot
Faisst Charles F.
Griffin Todd R.
Sharma Ravi
Barlow John
Eastman Kodak Company
Mouttet Blaise
Stevens Walter S.
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