Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-10-05
2003-05-13
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06561607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to imaging apparatus and methods, and more particularly, to apparatus and a method for maintaining a substantially constant closely spaced working distance between a nozzle plate of a ink jet print head and a surface of a medium or element for receiving liquid or ink droplets as the droplets are being deposited on the receiving medium or element during relative movement of the print head and the medium or element.
BACKGROUND OF THE INVENTION
Ink jet imaging devices use the controlled ejection of small droplets of liquid, to produce an image. Typically, the liquid is ejected through one or more nozzle orifices located in a nozzle plate of a print head. The ejection of the liquid, for instance, ink, through the respective nozzles is effected by a pressure pulse, which in the instance of a piezoelectric print head, is generated by application of an electrical drive waveform to an electromechanical transducer, and in a thermal print head, by application of a waveform to an electrothermal transducer or a resistor.
A problem with known ink jet printing apparatus is that ink droplets ejected from a nozzle orifice may emerge or travel in a direction that varies from the intended direction which is usually perpendicular to the surface of the nozzle plate. Such misdirection can arise from physical causes including a nozzle imperfection or a deposit or deposits on a surface of the nozzle, and can result in an error in the final location of the dot produced by the ink droplet on the receiving medium or element with respect to a desired or intended location of the dot. Such locational errors can result in artifacts in the printed image, such as visible bands and the like.
One contemplated solution for decreasing the severity of such locational errors in dot placement is to reduce the distance between the nozzle plate and the ink receiving medium or element, which is referred to as the working distance. This solution may be beneficial for applications requiring very high image quality and dot placement accuracy, as for example graphic arts printing, in which the spatial frequency of the micro-dots forming the image may be very high: for instance, 1200-2400 dots/inch or higher. In several prior art printing applications, requiring lesser dot placement accuracies, the working distance may be set relatively large, for instance, ink jet printers typically used for home and business applications wherein the working distance is generally 1 to 1 ½ millimeters to accommodate varying paper thicknesses. However, for other applications in which it is desirable to set the working distance to a much smaller value, for example, on the order of 100 to 1000 microns, decreasing the working distance poses the danger of collision or contact between the print head and the receiver, which can result in damage to or destruction of the print head and/or the receiver. Also, the liquid, when ejected from a nozzle typically consists of a liquid droplet having a connected ligament or trailing tail. Some distance of travel from the ejecting nozzle is required for the liquid structure to coalesce into a single or unitary droplet desirable for producing a satisfactory dot. Therefore, the working distance is desired to be small, but not so small as to provide insufficient distance above the receiver surface for coalescence. If the working distance is not sufficiently large to provide the required travel distance, the liquid objects will impinge the surface of the ink receiving medium or element before being completely formed which may result in comet shaped or other undesirable marks on the surface. And, if the working distance is not maintained substantially constant, variations in the printed dots can be present.
To compound the problems in maintaining a substantially constant working distance, typically during ink jet printing, the print head and ink receiving medium or element are moving transversely one relative to the other in at least one direction or along at least one axis. For instance, the ink receiving medium or element will be moved or translated in a direction indicated as y, while the print head maybe moved or scanned across the receiving medium or element in a direction indicated as x. Velocities of movement, for example in the instance of large format printing apparatus, can range up to about 1 meter per second. Such movement can result in variations in the working distance between the print head and the surface of the receiving medium or element due to any of several factors, including, for instance, variances in thickness of the ink receiving medium or element and/or non-flatness of the ink receiving surface thereof, such as a that due to a bow in a platen used for vacuum hold-down of a receiver for printing, or imperfections in the transport or support apparatus for moving the print head and/or the receiving medium or element one relative to the other, for instance, in the case of a cylindrical or roll shaped receiving medium, an eccentricity which results in variations of the working distance when the medium is rotated.
Various methods and apparatus are known for moving and positioning print heads or nozzles for depositing ink and other materials onto surfaces of substrates and other receivers. Reference in this regard, Hirano et al. U.S. Pat. No. 5,468,076 issued Nov. 21, 1995 to Kabushiki Kaisha Tec of Japan which discloses several embodiments of a print gap adjusting device; Petermann U.S. Pat. No. 5,360,276 issued Nov. 1, 1994 to Siemens Nixdorf Informationssysteme Aktiengesellschaft of Germany which discloses a printing device with adjustable printing head gap; and Kotsuzumi et al. U.S. Pat. No. 4,652,153 issued Mar. 24, 1987 which discloses a wire dot-matrix printer. However, all of these devices are directed to the problem of statically sensing the thickness of a receiver or paper placed on a platen, and then adjusting a print head-to-platen gap accordingly, prior to printing. This is in contrast to the present invention, which dynamically senses a print head-to-receiver gap and uses the sensed signal to keep this gap constant, during printing. In addition, all the above cited devices rely either on contact with the paper or other printing receiver or stored data to determine the print gap value to be used. Reliance on contact with the receiver can be a disadvantage in that wear, dirt build-up, and/or marring or other marking of the receiver surface or ink or other material previously deposited on the surface can occur due to the contact. And, reliance on stored gap values may be disadvantageous if the values do not correspond to the actual value required for a particular instance.
Reference also, Tylko U.S. Pat. No. 5,894,036 issued Apr. 13, 1999, which discloses a three dimensional plotter which maintains an ink droplet, or bead, by coordinating the delivery rate of the ink through the dispensing nozzle with the dispensing nozzle height and velocity; and Batcheleder U.S. Pat. No. 5, 303,141, issued Apr. 12, 1994 to International Business Machines Corporation which discloses a model generation system having closed—loop extruding nozzle positioning which includes apparatus for generating a feedback signal that is indicative of at least one characteristic of a most recently extruded portion of material extruded through the nozzle, which apparatus can include, for instance, a visual or infrared emission imaging system, a proximity detecting apparatus such as a capacitive sensor, a tactile sensor, or a pneumatic sensor. However, these disclosures refer to methods for coating a material like a slurry, or adhesive, onto a surface, in which a continuous-pressure pump is used to maintain a contiguous bead of coating material, between the nozzle and the receiver. This is in contrast to the case of the present invention, in which a drop of liquid is broken off from the nozzle by a discontinuous pressure pulse, and travels to the receiver. In addition, these referenced apparatus and methods do not disclose a means for maintaining a s
Freeman Diane C.
Lubinsky Anthony R.
Yandila Simon D.
Nguyen Thinh
Rushefsky Norman
Tran Ly T
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