Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-05-04
2001-07-03
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S116000, C347S229000
Reexamination Certificate
active
06256055
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic printer, and more particularly, it relates to an electrophotographic printer which forms an electrostatic latent image on a photosensitive belt.
2. Description of the Prior Art
In this type of the electrophotographic printer, the position of a photosensitive belt shifts in the width direction of the belt according to the rotation of the photosensitive belt, and therefore, previously, steering control has been performed to compensate this shift. The steering control means such a control that a positional shift of the photosensitive belt is detected and inclination of a roller to rotate the belt is changed according to a shifting amount and the belt is set at a fixed position.
A conventional example is shown in FIG.
9
. In FIG.
9
(
a
), a photosensitive belt
51
is hung over a roller
52
with a proper tension. Here, there are a plurality of rollers over which the belt
51
is hung, but part of them are omitted in the figure. Near the photosensitive belt
51
, a laser output section
53
is provided. This laser output section
53
has a function to radiate a laser beam on the surface of the belt
51
and to make this laser beam scan in the width direction of the belt
51
. This laser beam scanned by the laser output section
53
is not only radiated on the surface of the belt
51
, but also radiated on positions apart from the belt
51
at the edge of the scanning range thereof. This laser beam slipping off the belt
51
forms a light spot on a mask
54
according to the scanning position. This mask
54
is provided opposite to the laser output section
53
through the belt
51
. Furthermore, the positioning of each component is made so that the state may gradually change among a state where this laser beam does not come in both the belt
51
and the mask
54
, a state where the laser beam comes in only the mask
54
, a state where the laser beam comes in both the belt
51
and the mask
54
, and a state where the laser beam comes in only the belt
51
in the course of scanning of the laser beam when the belt
51
is arranged in a normal position.
This state will be described referring to FIG.
9
(
b
). FIG.
9
(
b
) is a figure in which the belt
51
and the mask
54
are seen from the laser output section
53
side. Now, when the light spot is scanned in the direction of numeral
56
a
→
56
b
→
56
c
, the light spot does not come in both the belt
51
and the mask
54
in the state of numeral
56
a
. Next, in the state of numeral
56
b
, the state becomes a state where the light spot comes in both the belt
51
and the mask
54
through a state where the laser beam comes in only the mask
54
. Moreover, in the state of numeral
56
c
, the state becomes a state where the light spot comes in only the belt
51
but it does not come in the mask
54
. Accordingly, when a laser beam is scanned by 1 line, the laser beam comes in the mask
54
only for a short time, and since the scanning speed of the laser beam is constant, time of coming-in changes according to the position of the belt
51
. For example, in FIG.
9
(
b
), when the edge of the belt
51
moves from a solid line to a two-dot-chain line as shown by arrows, the time when the laser beam comes in the mask
54
becomes shorter. Therefore, by detecting this light spot coming in the mask
54
by using a photo sensor
55
in FIG.
9
(
a
), the position of the belt
51
can be detected from the time when output of this photo sensor
55
is turned on.
Previously, feedback control of the position in the width direction of the belt
51
has been performed in such a way that a positional shift of the belt
51
is detected by using a position detecting means like this and the roller
52
is inclined according to the shifting amount.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
However, in the above conventional example, it was difficult to accurately converge the position of the belt
51
onto a fixed position, and in some cases, a minute error arose in position in the width direction of the belt on which an electrostatic latent image was formed. Furthermore, even if the roller
52
was inclined, the position of the belt was not immediately compensated, but it gradually approached to a proper position with the rotation of the belt
51
, and therefore, it was impossible to form the electrostatic latent image at a proper position, unless the belt had been rotated several times after the detection of a position of the belt. Accordingly, it was necessary to perform an idle scanning (scanning outputting no image signal) for compensating the position of the belt before the beam scanning for forming an electrostatic latent image.
An object of the present invention is to improve the inconveniences included in such a conventional example, and more particularly, to provide an electrophotographic printer in which the forming position of an electrostatic latent image can be compensated immediately after the detection of the position of a photosensitive belt and furthermore, the electrostatic latent image can be formed at a proper position even in a state where the photosensitive belt is inclined in the width direction.
Summary of the Invention
In order to attain the above object, in the present invention an electrophotographic printer comprises a photosensitive belt on which an electrostatic latent image is formed; a laser output section which scans this photosensitive belt in the width direction to form the electrostatic latent image; and a position sensor section which detects a position in the width direction of the photosensitive belt on the basis of time since a light spot scanned by this laser output section passed a reference position until the light spot passes an edge of the photosensitive belt. Furthermore, it comprises a position control section which controls a forming position of the electrostatic latent image on the photosensitive belt on the basis of a position of the photosensitive belt outputted from this position sensor section and a printer section which develops the electrostatic latent image on a medium and outputs the electrostatic latent image. Then, it employs such a composition that the position control section has a timing compensating function to compensate output timing of the image signal to be outputted when a still more back line is scanned on the basis of a difference between a position of the photosensitive belt which is outputted from the position sensor section when a front line of the electrostatic latent image is scanned and a position of the photosensitive belt which is outputted from the position sensor section when a back line is scanned.
Here, a line to be scanned in advance when forming an electrostatic latent image is called “front line,” a line to be scanned after that is called “back line,” and a line to be scanned further after that is called “still more back line,” and for example, a case where the front line is the n-th line, the back line is the n+1-th line, and the still more back line is the n+2-th line (n=1, 2, 3 . . . ), a case where the front line is the n-th line, the back line is the n+2-th line, and the still more back line is the n+4-th line, and the like are corresponding cases.
In another aspect of the present invention an electrophotographic printer comprises a photosensitive belt on which an electrostatic latent image is formed; four pieces of laser output sections which scan this photosensitive belt in the width direction to form the electrostatic latent image and which respectively correspond to Y, M, C and B; and a position sensor section which detects a position in the width direction of the photosensitive belt for each of Y, M, C, and B on the basis of time since a light spot scanned by these laser output sections passed a reference position until the light spot passes an edge of the photosensitive belt. Furthermore, it comprises a position control section which controls a forming position of the electrostatic latent imag
Foley & Lardner
Le N.
NEC Corporation
Pham Hai C.
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