Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-06-17
2001-04-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06217156
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of ink jet print heads in which there is drop ejection apparatus wherein a heater acts on a fluid or fluid meniscus of ink to be ejected.
BACKGROUND OF THE INVENTION
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 transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet.
Great Britain Patent No. 2,007,162, which issued to Endo et al. In 1979, discloses an electrothermal drop on demand ink jet printer which applies a power pulse to an electrothermal heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble which cause drops of ink to be ejected from small apertures along the edge of the heater substrate. This technology is known as Bubblejet™(trademark of Canon K.K. of Japan). U.S. Pat. No. 4,490,728, which issued to Vaught et al. In 1982, discloses an electrothermal drop ejection system which also operates by bubble formation to eject drops in a direction normal to the plane of the heater substrate. Rapid bubble formation provides the momentum for drop ejection.
Commonly assigned U.S. Pat. No. 5,880,759 which issued to Kia Silverbrook on Mar. 9, 1999, discloses a drop on demand liquid printing system wherein drop ejection is effected by selective actuation of a heater acting on the meniscus (the ink-air interface) of ink to be ejected. For this class of printer, the heater element may take the form of a ring or a part of a ring at the top surface of the print head. The top surface through which the orifices open generally defines an “orifice plane.” The placement accuracy of ejected drops is influenced by the line of contact between the meniscus of the ink to be ejected and the top surface of the print head. If the contact line between the ink and the orifice surface is not symmetrically disposed about the orifice, the drops will not necessarily be ejected in a desired direction perpendicular to the orifice plane.
Continuous ink jet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell. Conventional continuous ink jet utilizes electrostatic charging tunnels that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a “catcher”) may be used to intercept the charged drops, while the uncharged drops are free to strike the recording medium. U.S. Pat. No. 3,878,519, which issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
In another class of continuous ink jet printers, such as disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 08/954,317 entitled CONTINUOUS INK JET PRINTER WITH ASYMMETRIC HEATING DROP DEFLECTION filed in the names of Chwalek, Jeanmaire, and Anagnostopoulos on Oct. 17, 1997, an ink jet printer includes a delivery channel for pressurized ink to establish a continuous flow of ink in a stream flowing from a nozzle bore in a direction of propagation related to the orifice plane. A heater having a selectively-actuated section associated with only a portion of the nozzle bore perimeter causes the stream to break up into a plurality of droplets at a position spaced from the heater. Actuation of the heater section produces an asymmetric application of heat to the stream to control the direction of the stream between a print direction and a non-print direction. The placement accuracy of ejected drops is influenced by the line of contact between the meniscus of the ink to be ejected and the surface of the orifice from which the drops are ejected. If the contact line between the ink and the orifice surface is not symmetrically disposed about the orifice, the drops will not necessarily be ejected in a desired direction perpendicular to the orifice plane.
For drop ejection apparatus in which a heater acts on the ink-air interface of ink to be ejected, the need to contact the heater electrically has made it difficult to provide a heater having sufficient symmetry to ensure that drops will be ejected in a direction perpendicular to the orifice plane. An electrical heater surrounds a central bore on a substrate. Electrical leads contact the heater so that the heater can be selectively operated. Ink wicking along the heater leads can distort the shape of the meniscus in the vicinity of the heater and can cause the drops to be ejected at an angle to the orifice plane if the wicking is not symmetrical.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a print head having an ink meniscus heater having sufficient symmetry to ensure that drops are ejected perpendicular to the orifice plane.
Accordingly, it is a feature of the present invention to provide apparatus for controlling an ink jet printer including a substrate; an ink delivery channel below the substrate; and a nozzle bore through the substrate and opening into the ink delivery channel to establish an ink flow path. A resistive heater has an upper surface above the upper surface of the substrate and defines a symmetrical radially-outward heater perimeter edge. Ink tends to form a meniscus on the upper surface of the heater, the meniscus tending to pin at the heater perimeter edge. A plurality of electrodes make contact with the heater at spaced-apart positions below the perimeter edge.
In one embodiment of the invention, the ink flows in a continuous stream from the nozzle bore. The heater defines a plurality of sections, each section having a pair of electrodes. The actuator is adapted to apply the power source across selected pairs of the electrodes such that actuation of only a portion of the heater sections produces an asymmetric application of heat to the stream to control the direction and the amount of deflection of the stream as a function of the activated heater sections.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below.
REFERENCES:
patent: 5812159 (1998-09-01), Anagnostopoulos et al.
patent: 5880759 (1999-03-01), Silverbrook
Anagnostopoulos Constantine N.
Chwalek James M.
Hawkins Gilbert A.
Barlow John
Eastman Kodak Company
Sales Milton S.
Stephens Juanita D.
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