Typewriting machines – Typing by other than type-face or type-die – Thermal
Reexamination Certificate
2001-02-05
2003-03-18
Hirshfeld, Andrew H. (Department: 2854)
Typewriting machines
Typing by other than type-face or type-die
Thermal
C400S120110, C400S062000, C400S073000, C347S023000, C347S188000, C347S191000, C347S195000
Reexamination Certificate
active
06533477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal line printer that prints an image on recording paper in a line sequential fashion, and more particularly to a thermal line printer that reduces unexpected density variations of the printed image caused by thermal deformations of the recording paper.
2. Background Arts
In a color thermosensitive line printer, a thermosensitive color recording paper having thermosensitive coloring layers for yellow, magenta and cyan is heated by a thermal head while being moved relative to the thermal head, to print a full-color image in a three-color frame sequential fashion.
As shown for instance in
FIG. 12
, a thermosensitive color recording paper
43
is moved past a thermal head
44
by conveyer roller pairs
42
, each pair consisting of a capstan roller
40
and a nip roller
41
. The thermal head
44
has a heating element array
46
consisting of a large number of heating elements
45
aligned along a main scan direction that is perpendicular to the conveying direction of the thermosensitive recording paper
43
, as shown in FIG.
13
. The thermal head
44
is driven to record one line of one color at a time on the thermosensitive recording paper
43
, by applying variable heat energies from the heating elements
45
that are determined by coloring characteristics of the individual thermosensitive coloring layers as well as desirable densities or tonal levels of individual pixels designated by image data.
Since the heat energies are applied to the thermosensitive recording paper
43
while the heating elements
45
are pressed onto a surface of the thermosensitive recording paper
43
, the surface of the thermosensitive recording paper
43
is thermally deformed. Especially at a print starting end
48
of an image recording area
47
, that borders a blank margin
49
, the temperature of the thermosensitive recording paper
43
steeply changes, so the deformation of the 10 is the largest. When the deformed portions of the thermosensitive recording paper
43
move past the conveyer roller pairs
42
, conveying speed fluctuates because of the deformation of the thermosensitive recording paper
43
.
As shown for instance in
FIG. 14
, if a convex
50
is formed at the print starting end
48
because of the thermal deformation, load on the conveyer roller pairs
42
is increased as the convex
50
moves past the conveyer roller pairs
42
, so the conveying speed is lowered for that moment. As a result, the thermal head
44
applies more heat energies per unit area of the thermosensitive recording paper
43
than expected, increasing recording densities from designated levels in those lines which are recorded while the convex
50
is moving past the conveyer roller pairs
42
. The lines having the increased recording densities appear as a stripe
51
, as shown for example in FIG.
13
. Such density unevenness, i.e. deviation from unexpected densities, always appears around a distance L
1
from the print starting end
48
, and the distance L
1
is equal to a spacing between the thermal head
43
and the conveyer roller pairs
42
.
The density unevenness or deviation provided in this way is inconspicuous if it is located in an area where a variety of colors and densities are mixed. However, the density deviation becomes so conspicuous if it appears in an area having similar colors or densities, like the sky, the sea or the facial area of a closed-up portrait, especially in an area having the same color and density, that the so-called black strip is apparent with the naked eye.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a thermal line printer and a printing method for the thermal line printer, by which the density deviation as caused by the thermal deformation of the recording paper is made less conspicuous, or reduced.
To achieve the above object in a thermal line printer having a pair of conveyer rollers for nipping and conveying a recording paper along a paper transport path, and a thermal head having an array of heating elements arranged transversely to the paper transport path and pressed onto the recording paper at a constant distance from a nipping position by the conveyer rollers, the thermal head being driven based on image data to record an image frame line by line from a print starting end of an image recording area on the recording paper as the recording paper is conveyed by the conveyer rollers in a direction advancing from the thermal head toward the conveyer rollers, the present invention suggests to provide an image analyzer for calculating a first estimation value representative of conspicuousness of potential density deviation the image frame could have in a first zone including a line that is to be recorded at the constant distance from the print starting end if the image frame is recorded from a top side thereof, and a second estimation value representative of conspicuousness of potential density deviation the image frame could have in a second zone including a line that is to be recorded at the constant distance from the print starting end if the image frame is recorded from a bottom side thereof. The image analyzer calculates the first and second estimation values based on image data of the first and second zones of the image frame respectively. Then, a control device compares the first and second estimation values to each other and controls the thermal head to start recording the image frame either from the top side or from the bottom side depending upon the estimation values such that the potential density deviation becomes less conspicuous.
The estimation values are preferably calculated based on histograms each showing the numbers of pixels contained in each of the zones in relation to tonal levels of the image data, and correction coefficients for correcting the histograms to make the estimation values the larger the more the potential density deviation becomes conspicuous. The numbers of pixels shown in relation to the tonal levels may be called pixel frequencies, and correction coefficients may be called weighting coefficient.
Where the recording paper is a color thermosensitive recording paper having at least three coloring layers for yellow, magenta and cyan, each of the estimation values is calculated by obtaining a density histogram for each color, correcting the histogram with a first kind of correction coefficients determined for each color and with a second kind of correction coefficients that weight the number of those pixels included in a middle density range more than other density ranges, and adding up the histograms for the three colors.
It is preferable to calculate a third estimation value representative of conspicuousness of potential density deviation that the image frame could have in a third zone including a line that is to be recorded at the constant distance from the print starting end if the image frame is recorded from a right side thereof, based on image data of the third zone, and a fourth estimation value representative of conspicuousness of potential density deviation that the image frame could have in a fourth zone including a line that is to be recorded at the constant distance from the print starting end if the image frame is recorded from a left side thereof, based on image data of the fourth zone. The first to fourth estimation values are compared to one another, to decide to start recording the image frame from one of the four sides which corresponds to the smallest estimation value.
According to another aspect of the present invention, a printing method for a thermal line printer wherein an array of heating elements of a thermal head are pressed onto a recording paper and driven in accordance with image data to record an image frame in an image recording area on the recording paper line by line from a print starting end of the image recording area, as the recording paper is conveyed by a pair of conveyer rollers in a direction advancing from the thermal head toward the conveyer roll
Cone Darius N.
Fuji Photo Film Co. , Ltd.
Hirshfeld Andrew H.
LandOfFree
Thermal line printer and printing method therefor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermal line printer and printing method therefor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermal line printer and printing method therefor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3068675