Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-04-10
2004-04-13
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Fixing
Reexamination Certificate
active
06721531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to flash fixing apparatus for fixing toners on a medium by a flashlight and a printer using the same, and more particularly flash fixing apparatus for fixing a high resolution toner image with reduced non-uniformity of halftone image density and a printer using the same.
2. Description of Related Arts
In a printer for forming a toner image using the electrophotographic method or the like, an image formed of powder toner is produced on a print medium. The image is then fixed by fusing the powder toner. Energy must be applied to the print medium to fix the toner image.
In a high-speed printer, a non-contact type fixing method is employed for applying the fixing energy. The non-contact type fixing method is suitable for fixing a toner image in a high-speed printer because the method enables to apply high fixing energy without affecting a print medium to carry.
As this non-contact type fixing method, there has been employed a flash fixing method using flashlight emitted from a flash lamp. In this flash fixing method, fixing is performed on each predetermined area on the print medium by flashing the flash lamp at predetermined intervals synchronously with carrying the print medium.
In such a flash fixing method, it is efficient to fix toner images on the predetermined area of the print medium by one-time flash. However, because the flash energy distribution of single flashlight is not uniform, it is performed to generally superpose a plurality of flashes in order to obtain uniform flash energy distribution. The fixing characteristic depends on both the light energy distribution and the range of superposition area. There have been proposed various arts to obtain a desired characteristic.
A first prior art is shown in
FIG. 26
, in which a trapezoidal reflection plate
112
is provided around a flash lamp
111
to produce light energy distribution ‘e’ onto a print medium
106
. The produced energy distribution ‘e’ is configured so that 70%-80% of the total irradiation energy is concentrated onto a center zone ‘a’ of the irradiation area A. Providing that the length of the area into which 70% of the total irradiation energy is concentrated is defined as a fixing width W, the relation between moving velocity V of a continuous medium and flash frequency f of the flash lamp
111
is defined by formula (1) shown below.
V/f=W
(1)
In this formula, it has been proposed to set ‘n’ within a range of 1.2-1.8, preferably 1.3-1.7 (for example, as disclosed in the official gazette of Japanese Patent No. 2870705.)
Here, V/f denotes a moving distance of the continuous medium in a time between two flashes (in other words, an area length allotted for one flash.) This distance becomes shorter than the fixing width W by setting ‘n’ to the above-mentioned value. Accordingly, the fixing width is set so that superposition is always existent. This produces the light energy distribution E shown in
FIG. 27
against the continuous medium. Thus prevention of non-uniform fixing is intended.
Now, according to a second prior art, such a reflection plate
112
as shown in FIG.
29
(B) is provided around the flash lamp
111
, so as to obtain a flat flash energy distribution characteristic at the center of the lamp, as shown in FIG.
29
(A). Referring to FIGS.
28
(A),
28
(B), provided that a fixable area L2 is the width of the flash lamp
111
, a half width L1 of the aperture of the reflection plate
112
is defined by the following formula (2), using the relation between moving velocity V of the continuous medium and flash period T of the flash lamp
111
.
V/T≦L
1
≦V/T−L
2/2 (2)
Namely, it has been proposed that the superposition width produced by the superposed flashes is set between the range of L1 (in maximum) and L1−L2/2 (in minimum) (for example, as disclosed in the official gazette of Japanese Unexamined Patent Publication No. Hei-6-308852.)
Such prior arts disclose method for suppress the variation in the flash energy distribution so as to prevent variation of the toner-fixing rate. In other words, the prior arts are based on the concept that the flash energy is more than sufficient for toner-fixing onto the entire area of a continuous medium, and that excess energy is prevented so that toner burst is not produced.
However, in recent years, it has been required to print halftone images, in addition to characters, and to print halftone images with high resolution. Grayscale is represented by the number of black dots in a predetermined area such as an example shown in
FIG. 30
, in which dot printing having alternating one ‘on’ dot and one ‘off’ dot repetitively in the sub scanning direction. In this example, as shown in
FIG. 31
, each dot size is larger in case of lower resolution (for example, 240 dpi), or smaller in case of higher resolution (for example, 600 dpi). Further, when the flash energy is applied, the toners within a dot are fused and the fused toners overflow outside the contour of the dot of interest. The size of the toner-overflowed area depends on the flash energy. That is, the overflowed area is relatively small when the flash energy is small, while the overflowed area is relatively large when the flash energy is large.
The difference of such overflowed areas is not so prominent in case of a relatively low resolution of a large dot in order of 240 dpi. However, in case of high resolution in order of 600 dpi, because a dot size is less than half in dot size compared to 240 dpi, the difference of dot diameter resulting from the difference in the overflowed area in the fixed image becomes prominent. In particular, in case of a halftone image, original halftone images having the identical grayscale look as if these images have different halftones.
In the conventional arts, it is intended to apply flash energy sufficient for fixing toner, and to suppress toner burst in case energy more than required for fixing is applied. There has not been considered non-uniformity of image density possibly produced by the fixing using flash energy.
For example, according to the conventional method for producing a uniform flash energy distribution using superposed flashes, there is obtained the density (by outputs of a densitometer) shown in
FIG. 32
after fixing the print pattern shown in FIG.
30
. As can be seen, the density value varies more than 10, producing a prominent density fluctuation. Especially the output decreases at both the center zone of the fixing and the superposition zone, thus producing stripes (banding).
This is caused by the determination of flash energy distribution, fixing width and superposing width from the viewpoint of preventing non-uniform fixing. There has not been considered variation of flash energy more than the fixing energy. Accordingly, as far as employing conventional superposition theory, it is difficult to prevent non-uniformity of print density under high-resolution printing.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a flash fixing apparatus and a printer using the flash fixing unit for preventing non-uniformity of print density, not only non-uniformity of fixing.
It is another object of the present invention to provide a flash fixing apparatus and a printer using the flash fixing unit capable of high resolution printing reducing non-uniformity of print density.
It is still another object of the present invention to provide a flash fixing apparatus and a printer using the flash fixing unit capable of high resolution printing reducing non-uniformity of print density of a halftone image.
It is still another object of the present invention to provide a flash fixing apparatus and a printer using the flash fixing unit capable of reducing both power consumption and non-uniformity of print density.
To attain the aforementioned objects, a flash fixing apparatus according to the present invention includes a flash fixing unit having a flash lamp and a reflection plate disposed to surround the flas
Akuta Tomakazu
Iwaishi Akira
Kishimoto Teruki
Brase Sandra
Fuji 'Xerox Co., Ltd.
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Flash fixing apparatus and printer using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flash fixing apparatus and printer using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flash fixing apparatus and printer using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3259019