Method for reducing cyclic print errors

Details Method for reducing cyclic print errors Method for reducing cyclic print errors

2000-08-24

2002-03-19

Eickholt, Eugene (Department: 2854)

Typewriting machines

Means auxiliary to typewriting function

Indicator means

C400S070000, C101S486000, C358S504000, C358S505000, C347S019000, C347S037000

Reexamination Certificate

active

06357942

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to printers, and more particularly to a method for reducing cyclic print errors in a printer.
BACKGROUND OF THE INVENTION
Printers include those printers having a print head whose position is determined from its motion across a linear encoder strip. The linear encoder strip has spaced-apart parallel lines (also called bars) and is installed in the printer by being mounted to the body of the printer. Typically, the manufacturer of linear encoder strips uses a laser plotter to make the lines on the linear encoder strip. The print head typically has an LED (light emitting diode)/photodetector mounted on the print head and straddling the linear encoder strip. As the print head moves across the linear encoder strip, light pulses are counted each time the print head moves from over a line on the linear encoder strip (such line blocking the light from the LED from reaching the photodetector) to over a transparent space between the lines on the linear encoder strip (such transparent space permitting the light from the LED to reach the photodetector). The pulse count is used to determine the position of the print head, and the pulse count rate may be used to also determine the velocity of the print head. The position (and velocity, if required) of the print head is used by the printer in deciding when to print and when not to print.
Examination of printed pages from printers sometimes show print errors. Examination of printed pages from printers having a print head whose position is determined from its motion across a linear encoder strip have shown cyclic print errors. Cyclic print errors include a compressed or expanded print space or print image which alone would be practically unnoticeable by a viewer. However, because of the cyclic occurrence of this print error, a pattern of compressed and/or expanded print spaces and/or print images is created. Such pattern, referred to as a cyclic print error, is very noticeable by the viewer. The cause or causes of such cyclic print errors from such printers and a way to reduce such errors have been unknown.
What is needed is a method for reducing cyclic print errors in a printer, wherein the printer has a print head whose position is determined from its motion across a linear encoder strip.
SUMMARY OF THE INVENTION
A first method of the invention is for reducing cyclic print errors in a printer and includes several steps. Step a) includes determining at least one possible consistent line spacing for linear encoder strips. Step b) includes choosing a line spacing from the at least one possible consistent line spacing. Step c) includes obtaining a linear encoder strip having the chosen line spacing. Step d) includes installing the linear encoder strip in the printer.
A second method of the invention is for reducing cyclic print errors in a printer and incudes several steps. Step a) includes determining at least one possible consistent line width for linear encoder strips. Step b) includes choosing a line width from the at least one possible consistent line width. Step c) includes obtaining a linear encoder strip having the chosen line width. Step d) includes installing the linear encoder strip in the printer.
A third method of the invention is for reducing cyclic print errors in a printer and includes several steps. Step a) includes determining at least one possible consistent and equal line spacing and width for linear encoder strips. Step b) includes choosing an equal line spacing and width from the at least one possible consistent and equal line spacing and width. Step c) includes obtaining a linear encoder strip having the chosen equal line spacing and width. Step d) includes installing the linear encoder strip in the printer.
A fourth method of the invention is for reducing cyclic print errors in a printer and includes several steps. Step a) includes choosing an optimal equal line spacing and width from the equation: X
optimal
=round(R*X
ideal
)/R, wherein X
optimal
is the optimal equal line spacing and width, wherein “round” is the mathematical rounding function which rounds a number to the nearest integer using standard mathematical rules for rounding numbers, wherein R is the inverse of the resolution capability of a device which makes/prints linear encoder strips having consistent and equal line spacing and width of the lines on the linear encoder strip, wherein X
ideal
is the ideal consistent and equal line spacing and width, and wherein “*” denotes multiplication and “/” denotes division. Step b) includes obtaining a linear encoder strip having the chosen equal line spacing and width. Step c) includes installing the linear encoder strip in the printer.
Several benefits and advantages are derived from the invention. Applicants discovered that a major source of cyclic print errors was inconsistent line spacing and width of the lines on the linear encoder strip used by the printer to determine the position of the print head. Applicants had ordered from the encoder-strip manufacturer a particular consistent and equal line spacing and width for the linear encoder strip which was the ideal consistent and equal line spacing and width for which Applicants' printer was designed. Although Applicants had specified a particular and equal line spacing and width, Applicants discovered that the manufacturer of linear encoder strips provided strips with inconsistent line spacing and width. Applicants discovered that the encoder-strip manufacturer used a laser plotter to make the lines on the linear encoder strip and that the resolution capability of the plotter was such that it could not match the particular and equal line spacing and width ordered by Applicants. When the plotter of the encoder-strip manufacturer tried to create the particular and equal line spacing and width ordered by Applicants, the plotter performed a rounding-off operation causing round-off errors which led to a cyclic pattern of inconsistent line spacing and width which caused cyclic print errors when the linear encoder strips were used in Applicants' printer. Instead of telling the encoder-strip manufacturer to make a linear encoder strip with a particular and equal line spacing and width, the methods of Applicants' invention choose one of the possible consistent line spacing and/or width of the lines on the linear encoder strip that the manufacture is able to supply. In one example, the chosen line spacing and/or width is the possible consistent line spacing and/or width close or closest to the ideal consistent line spacing and/or width. Applicants found that its printers would operate successfully with the chosen consistent and equal line spacing and width which eliminated the previously-described cyclic print errors. Applicants believe the previously-described cyclic print errors would be reduced if either the line spacing or the line width were consistent. It is noted that a page printed by a printer using Applicants' invention will have a slightly reduced or enlarged print area. However, the slightly reduced or enlarged print area is not objectionable to a viewer of the printed page compared to those objectionable cyclic print areas which are present in the prior art and which are eliminated by use of Applicants' invention.


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