Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-09-28
2001-09-18
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06290320
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to plotters, and more specifically to monitoring and controlling the quality of markings on plotting media.
A typical plotter comprises a pen for producing markings on a medium in response to instructions from, for example, a computer. The medium such as paper is movable in a first direction along the X-axis and the pen on a main carriage is movable in a second direction along the Y-axis which is perpendicular to the first direction. Thus, by appropriate control of the drives for the pen and paper movement, any desired graphical representation can be produced on the medium. The writing system also typically comprises a plurality of pens, for example pens of different colors. A pen handling mechanism is provided which permits a pen to move into position on the carriage for plotting on the medium and replaces that pen by another one, for example when a different color is desired.
Writing systems such as the above-mentioned pen plotter are typically used for producing rather complex graphical representations, for example circuit layouts or construction diagrams, which are electronically stored in a computer on which they may also have been created by a user. Once the plotting of those electronically stored drawings has been initiated by a user, the plotting continues automatically and the user only has to take the completed drawing from the plotter. In practice, however, the completed drawings have not always been satisfactory. As a consequence thereof, the entire drawing generally had to be plotted again.
Thus, a considerable amount of time is wasted and the efficiency of the plotting is decreased. Usually these problems are resolved by perfecting the components of the plotter.
Despite such attempts for perfection of the writing components, writing failures may still occur.
More recently, the full color inkjet printer/plotters which have been developed comprise a plurality of inkjet pens of diverse colors. A typical color inkjet printer/plotter has four inkjet pens, one that stores black ink, and three that store colored inks, e.g., magenta, cyan and yellow. The colors from the three color pens are mixed to obtain any particular color.
The pens are typically mounted in stalls within an assembly which is mounted on the carriage of the printer/plotter. The carriage assembly positions the inkjet pens and typically holds the circuitry required for interface to the heater circuits in the inkjet pens.
Full color printing and plotting requires that the colors from the individual pens be precisely applies to the media. This requires precise alignment or the carriage assembly. Unfortunately, mechanical misalignment of the pens in conventional inkjet printer/plotters results in offsets in the X direction (in the media or paper axis) and in the Y direction (in the scan or carriage axis). This misalignment of the carriage assembly manifests as a misregistration of the print images applied by the individual pens. In addition, other misalignments may arise due to the speed of the carriage, the curvature of the platen and/or spray from the nozzles.
However, the integration of the optical and electronic components in the optical sensor, as well as positioning the optical sensor on the carriage have been complicated, expensive and to some extent imprecise in prior printers/plotters. The need for reliability and precision is even greater in recent inkjet printers/plotters which print high resolution color graphics and images, often on very large poster-size printouts.
SUMMARY OF THE INVENTION
It is an object of the invention to solve the aforementioned deficiencies of the prior art, and provide a method and apparatus for assuring that a high degree of reliability is achieved for nonattended plotting.
A related object is to provide a pen verification system that provides predictable performance for different color pens.
A further object is to provide adequate optical sensing of pen lines under varying ambient light conditions.
In accordance with the foregoing objects, the invention provides a method of monitoring and controlling the quality of pen markings on a plotting medium by optically sensing across a sample line drawn on an actual medium.
In another separate and important aspect of the invention, a customized optical sensor is provided for monitoring plotter pen performance by sensing the quality of lines drawn on a medium. An LED emitting a green light beam is angularly directed toward an underlying line so as to reflect into an optical sensor which measures the print contrast ratio of a point on the line. Circuit means amplifies and filters the signal generated by the optical sensor.
Thus, by appropriate selection of the wavelength of the light used for sensing the markings on the medium, it is easily possible to check multi-color drawings for correct quality and colors.
In a presently preferred embodiment of the invention implemented in a color inkjet printer/plotter, a green LED is used for sensing sample patterns printed by each of the black (K), cyan (C) and magenta (M) printheads, while a blue LED is used for sensing sample patterns printed by the yellow (Y) printhead.
Moreover, a light tube on a carriage-mounted optical sensor has inner walls which help direct light from an LED toward an area surrounding a point under the sensor, and outer walls which help block out undesirable external light from being reflected from the area surrounding a point under the sensor into the photocell.
Thus, the invention contemplates optical sensing of different color markings on media using different color lights, whether those markings are vector lines drawn by a pen plotter or raster “lines” (i. e. bars) printed on a pixel grid by an inkjet printer/plotter.
REFERENCES:
patent: 4675696 (1987-06-01), Suzuki
patent: 4812900 (1989-03-01), Kadowaki et al.
patent: 4878063 (1989-10-01), Katerberg
patent: 5975674 (1999-11-01), Beauchamp et al.
patent: 63-153151 (1988-06-01), None
Beauchamp Robert W.
Martos Isidre Rosello
Tarradas Josep
Barlow John
Hallacher Craig A.
Hewlett--Packard Company
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