Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-07-15
2002-06-25
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S233000, C347S251000
Reexamination Certificate
active
06411322
ABSTRACT:
FIELD OF INVENTION
The field of invention relates generally to the field of printing. More specifically, the invention relates to test patterns used for adjusting spot spacings in multiple beam printheads.
BACKGROUND OF THE INVENTION
Laser printing involves directing a beam of laser light to a photoconducting drum (also referred to simply as a drum). In a typical process, the laser illuminated drum regions electrostatically attract toner particles which are subsequently transferred to a piece of paper. Thus the laser illuminated drum regions typically correspond to the printed matter on the paper.
Multiple beam printhead technology involves simultaneously directing multiple laser beams onto the drum. Currently technology employs four or five laser beams per printhead.
FIG. 1
shows a depiction of the operation a four beam printhead technology.
FIG. 1
is not drawn to scale.
Referring to
FIG. 1
a
, each laser beam has an associated spot location
101
a
-
104
a
(also referred to as spots
101
a
-
104
a
). The size and placement of spots
101
a
-
104
a
are determined by the optical system of the printhead. The printhead also has the ability to sweep the spots
101
a
-
104
a
from left to right across the drum surface
100
. As
FIG. 1
a
shows, the laser beams associated with spots
101
a
and
103
a
are “on” while the laser beams associatedwith spots
102
a
and
104
a
are “off”. The spots spacing between spots
101
a
-
104
a
is constant.
As the spots
101
a
-
104
a
are swept across the drum surface
100
, the regions
105
a
,
106
a
of the drum exposed to the “on” laser beam are electrostatically altered such that toner materials are attracted to them.
FIG. 1
therefore also shows the relationship between the spots
101
a
-
104
a
and the printed end product.
FIG. 1
b
shows the printed matter regions
105
b
,
106
b
if the printhead continues to sweep the spot locations
101
b
-
104
b
from left to right with the same coordination of “on” and “off” laser beams as in
FIG. 1
a
. That is, beams associated
101
a
,
103
a
of
FIG. 1
a
and
101
b
,
103
b
of
FIG. 1
b
remain “on” while beams associated with
102
a
,
104
a
of
FIG. 1
a
and
102
b
,
104
b
of
FIG. 1
b
remain “off”.
FIG. 1
c
shows the printed matter regions
105
c
,
106
c
if the laser beam associated with spot location
103
c
is eventually turned “off” at some point after the situation shown with respect to
FIG. 1
b
and the printhead continues to sweep the spots
101
c
-
104
c
.
FIG. 1
d
shows the printed matter regions
105
d
,
106
d
if the laser beam associated with spot
101
d
is turned off such that edges
108
of the printed matter regions
105
d
,
106
d
“line up”.
FIG. 1
d
also shows the beam associated with spot
102
d
has turned “on” at some later time. Thus regions
105
d
,
106
d
may also be viewed as the printed matter on the page once the printing process is complete.
Ultimately the sweep reaches near the right edge of the drum (which corresponds to the right edge of the finished page). The drum rotates up 4.0 PELS (which corresponds to lowering the spots to a new row just beneath the completed row) and the spots are swept again. Depending on the printing apparatus used, the spots may be swept from right to left during the sweeping of the second row; or, similar to a typewriter, the laser beam writing process may always start from the left. Other printers may always start from the right.
FIG. 2
shows a more detailed view of the printhead's spacing of the spots
201
-
204
.
FIG. 2
shows a slanted angle printhead (also shown in FIG.
1
). 1.0 picture element (PEL) is the “designed for”distance
221
a, b, c
between spot center locations
210
-
213
(also referred to as spot location origins
210
-
213
). The actual spacing between adjacent spot center locations
210
-
213
changes from printer type to printer type. In typical applications, the vertical distance
221
a, b, c
between the spot location origins
210
-
213
is designed to be 1.0 PEL while the horizontal distance
222
a, b, c
is designed to be 40.0 PELs. Printer addressability is typically measured in Dots Per Inch (DPI). A PEL is therefore 1/DPI in the vertical direction. Horizontal distance is the distance along the sweep direction, while vertical distance is the distance perpendicular to the sweep direction.
The quality of images produced by multiple beam printheads is sensitive to the vertical spacings
221
a, b, c
(also referred to as spacings). For example, if the spacings
221
a, b, c
are different than the spacings the image was supposed to be formed with (i.e., something other than 1/DPI of the designed for image), undesirable “bands” (also referred to as banding) may appear in the image. Thus vertical spacings
221
a, b, c
are important to the quality of the printed image. The spacings
221
a,b,c
may be accurately set in a manufacturing environment with sophisticated equipment such as cameras or other alignment tools. However, those involved in field service repairs typically do not have access to such equipment. As such, a test pattern that assists field service personnel in accurate alignment without the use of alignment equipment would improve the optical alignment of field installed or field adjusted printheads.
SUMMARY OF THE INVENTION
A method is described comprising sweeping multiple beams for a plurality of sweeps. The multiple beams are modulated for the plurality of sweeps according to a test pattern. The test pattern has an associated vernier period and the vernier period corresponds to a wavelength. The wavelength is perceptible to the human eye.
An apparatus is described comprising a printhead configured to produce multiple beams where the multiple beams are configured to be modulated according to a stored test pattern. The test pattern has an associated vernier period and the vernier period corresponds to a wavelength. The wavelength is perceptible to the human eye.
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patent: 4796964 (1989-01-01), Connell et al.
patent: 4878063 (1989-10-01), Katerberg
patent: 4978849 (1990-12-01), Goddard et al.
patent: 5255010 (1993-10-01), Mackin
patent: 5323179 (1994-06-01), Sanger et al.
patent: 5508826 (1996-04-01), Lloyd et al.
patent: 5600350 (1997-02-01), Cobbs et al.
patent: 5748223 (1998-05-01), Ito
patent: 5825378 (1998-10-01), Beauchamp
patent: 5835108 (1998-11-01), Beauchamp et al.
patent: 6137592 (2000-10-01), Arquilevich et al.
Carlson, Curtis R., “Economic Display Design,” Information Display, May 1988.
Blakely & Sokoloff, Taylor & Zafman
Pham Hai
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