Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-09-17
2001-08-14
Le, Spe N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S246000, C347S116000
Reexamination Certificate
active
06275249
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for evaluating an image formation device, such as a laser printer and a copying machine. More particularly, the invention relates to a method of evaluating characteristics required of a light beam which is emitted from the write unit of an image formation device toward a latent image carrier, such as a photosensitive drum and a photosensitive belt. The invention also relates to a light beam characteristic evaluation apparatus that is employed for evaluating the characteristics, and further relates to an apparatus for adjusting a write unit by employing the evaluation method.
2. Description of the Related Art
Conventionally, an image forming device, such as a laser printer, a copying machine, and a facsimile device, performs writing on the surface of the photosensitive drum (latent image carrier) of an image forming unit by scanning the drum surface in both a horizontal scanning direction (i.e., main scanning direction) and a vertical scanning direction (i.e., sub-scanning direction) with a light beam emitted from a write unit, thereby forming an electrostatic latent image. In order to make the latent image visible and form a toner image, toner is caused to adhere to the surface of the photosensitive drum on which the latent image is formed. The toner image is transferred and fixed onto transfer paper. In this manner, an image is formed on the transfer paper.
The write unit is provided with an optical scanning system for scanning the surface of the photosensitive drum with a beam of light. The surface of the photosensitive drum is scanned in the horizontal scanning direction by the optical scanning system, while the surface is scanned in the vertical scanning direction by rotating the photosensitive drum.
In these image formation devices, incidentally, the characteristics required of the light beam of the write unit are evaluated in performing writing on the surface of the photosensitive drum which is a writing object.
For instance, in a copying machine, the image information on a manuscript is read in sequence and converted to a beam of light. In the case where the light beam writing position on the photosensitive drum surface deviates from a previously designed reference position, there arises a disadvantage that an image corresponding to the image information of a manuscript cannot be formed at the reference position. Particularly, in an image formation device, in which two laser light sources for emitting a beam of light are provided in the write unit and writing is performed on the photosensitive drum surface at two times the normal speed by scanning the photosensitive drum surface in the horizontal scanning direction concurrently with two light beams, if the writing position of one of the two light beams deviates from the writing position of the other light beam in the horizontal scanning direction, the image on a manuscript cannot be reproduced with high fidelity. Therefore, it is required to perform both the evaluation of the writing position of one light beam and the evaluation of the writing position of the other light beam.
In the case of a write unit which performs writing on a photosensitive drum by a single light beam, a writing position is computed for each surface of a polygon mirror constituting an optical scanning system. The object of evaluation in this case is both the position offset in the horizontal scanning direction (pitch fluctuation in the horizontal scanning direction) on each surface of the polygon mirror and the position offset in the vertical scanning direction (pitch fluctuation in the vertical scanning direction) on each surface of the polygon mirror.
In the case of a write unit which performs writing on a photosensitive drum by a plurality of multiplexed light beams, a pitch between light beams is also an object of evaluation in addition to the aforementioned evaluations.
Also, when two points on a manuscript in the horizontal scanning direction are extracted, two points on a copied image on transfer paper corresponding to the two points on the manuscript are extracted, and the distance between the two points on the manuscript is compared with the distance between the two points on the copied image, they must be equal to each other as long as copying is performed with equimagnification. If the distance between two points on a manuscript is not exactly equal to the distance between two points on a copied image, this will result in a magnification error. Since an image cannot be reproduced with high fidelity on transfer paper, performing the evaluation of a magnification error is required. In addition, in the case of enlargement and reduction, a ratio of a copied image formed on transfer paper to an image on a manuscript has to be equal to a desired magnification or demagnification ratio. If these ratio differ from each other, an image cannot be reproduced with high fidelity and therefore the evaluation of a magnification error will also be required.
Additionally, in the case where a left-side point and a right-side point on transfer paper are offset in the vertical scanning direction, it means that the scanning line has a tilt to the left or the right and therefore this scanning line tilt is also an object of evaluation.
Furthermore, assume that three points on a manuscript are extracted from left to right along the horizontal scanning direction and that the middle point is present at equal distances from the remaining two points. If the distance to the corresponding left-side point and the distance to the corresponding right-side point on the transfer paper are not equal with the corresponding middle point on the transfer paper as reference, a copied image will lack the balance between the right side and the left side. Therefore, it is also required to evaluate whether or not a distance from a middle point to a left-side point and a distance from a middle point to a right-side point are equal to each other.
In this case, if the difference between the writing position of the left-side point and the writing position of the middle point is not equal in the vertical scanning direction to the difference between the writing position of the right-side point and the writing position of the middle point, the scanning line will have a curve. Similarly, an image is not reproduced with high fidelity, so that it is also required to evaluate whether or not a scanning line has a curve.
Incidentally, a conventional apparatus for evaluating the characteristics of a light beam in the horizontal scanning direction is shown, for example, in
FIG. 1
(see Japanese Laid-Open Patent Publication No. HEI 5-284293).
In the figure, reference numeral
1
denotes a write unit (optical unit). The write unit
1
is provided with a beam source (laser light source)
2
, a rotatable polygon mirror
3
, and an f &thgr; lens
4
. The beam source (laser light source) consists of a semiconductor laser
2
. The semiconductor laser
2
is modulated and driven by an optical analog modulator
5
. The optical analog modulator
5
modulates the strength of laser light emitted from the semiconductor laser
2
in correspondence to a manuscript image. The laser light emitted from the semiconductor laser
2
is deflected by rotation of the polygon mirror
3
.
A pair of spaced photoelectric conversion elements
7
a
and
7
b
are provided in the horizontal scanning direction on a photosensitive surface
6
equivalent to the surface of a photosensitive drum provided in an image forming unit. In order to enhance received-light position accuracy (writing position accuracy), light intercepting plates
8
a
and
8
b
with a pinhole (circular small hole) are provided directly before the photoelectric conversion elements
7
a
and
7
b
. Let the distance between this pair of pinholes be L.
If the polygon mirror
3
is rotated with the semiconductor laser
2
lit at all times during scanning and if the photosensitive surface
6
is scanned in the horizontal direction Q
1
with the light beam P
1
, the
Abe Katsushi
Ozaki Shin-ichi
Takahashi Nobuhiro
Le Spe N.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pham Hai C.
Ricoh & Company, Ltd.
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