Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
2002-09-27
2004-08-31
Chen, Sophia S. (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C399S125000
Reexamination Certificate
active
06785492
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvement in an image formation apparatus, such as an electrophotographic printer or copier, particularly including a plurality of image formation units disposed along a transfer material transport passage for successively transferring toner images to a transfer material moving on the transfer material transport passage.
Known as a conventional image formation apparatus is an apparatus called tandem type including a plurality of image formation units disposed on a transfer material transport passage extending in a horizontal direction, for example, for successively transferring toner images from the image formation units to a transfer material moving along the transfer material transport passage and forming a color image on the transfer material.
The image formation unit refers to a pair of a photoconductor unit having a photoconductor on which an electrostatic latent image is formed and a developing unit for storing toner supplied to the photoconductor. Already proposed as the transport technique is a transfer roll transport technique wherein each image formation unit is provided with a transfer roll for abutting the photoconductor and paper as a transfer material is transported by the photoconductor and the transfer roll, or a belt transport technique wherein paper is, for example, electrostatically attracted and held on a circulating transport belt.
As for the arrangement structure of the image formation units, already proposed are a landscape orientation type wherein a plurality of image formation units are placed transversely side by side relative to a transfer material transport passage extending in the horizontal direction and a portrait orientation type wherein a plurality of image formation units are placed longitudinally relative to a transfer material transport passage extending in a vertical direction.
However, in this kind of the conventional landscape orientation type, often the image formation units are attached and detached from the direction parallel with the transport face of the transfer material transport member and vertical to the transport direction. In this case, the image formation units are positioned in the apparatus main unit by an image formation unit drive member attached to one side of the apparatus main unit and a positioning member formed on an opposite side of the apparatus main unit with the transport member between.
The image formation unit itself is positioned by a positioning section formed in a support member for supporting the photoconductor without directly positioning the photoconductor as the positioning reference on the configuration. Thus, it is difficult to ensure the positioning accuracy of each image formation unit in the apparatus main unit.
As for the conventional image formation apparatus of the portrait orientation type, each image formation unit can be attached and detached from the direction orthogonal to the transfer material transport passage of roughly vertical portion, so that each image formation unit can be positioned in the apparatus main unit by a unit positioning section formed on both sides of a cabinet and it becomes easy to ensure the positioning accuracy; in contrast, however, a disadvantage occurs in the transfer material transportability.
In the transfer roll transport technique, it the image formation unit spacing is wide to some extent, paper passes through the transfer part of one image formation unit, the pass-through paper portion becomes long, the tip state of the paper becomes easily unstable in such a manner that the tip of the paper curls or remains straight, and the tip position of the paper arriving at the transfer part of the next image formation unit easily varies.
Thus, the write start position of each color component toner image relative to the paper at the transfer part of each image formation unit shifts, causing a color shift or color unevenness phenomenon of a color image.
In the belt transport technique, paper is transported on the paper transport belt and thus the tip entry position of paper in the transfer part of each image formation unit is stable and the color unevenness of a color image relative to the paper transport direction can be suppressed as compared with the transfer roll transport technique. However, as the image formation unit spacing is wider, a walk phenomenon in which when the paper transport belt moves, it meanders in the width direction increases, and color shift or color unevenness of color image worsens in the orthogonal direction (width direction) to the paper transport direction.
SUMMARY OF THE INVENTION
It is therefore a first object of the invention to provide an image formation apparatus for enabling components to be well positioned in an apparatus main unit.
It is a second object of the invention to provide an image formation apparatus for making it possible to suppress a color shift and color unevenness of a color image accompanying transport unevenness of a transfer material and miniaturize the apparatus itself.
Although the solution means of the invention will be described to the specific contents to understand the invention, it is to be understood that the claims are not substantially reduced.
To accomplish the first object, the image formation apparatus of the invention includes the developing unit placed in the apparatus main unit displaceably or in a pressed state, the photoconductor unit placed in the apparatus main unit and is positioned, and the developing unit positioned relative to the positioned photoconductor unit.
To accomplish the second object, the image formation apparatus of the invention includes at least apart of the second photoconductor unit involving the second color positioned so as to overlap the first developing unit involving the first color, placed in the apparatus main unit in the move direction at the placing time.
A supplementary description to the invention to accomplish the second object is given below:
The inventor found out that it is important to miniaturize the apparatus to suppress a color shift and color unevenness of a color image accompanying transport unevenness of a transfer material and obtained the invention.
The process to obtain the invention will be discussed specifically.
Generally, as the color shift, color unevenness amount of color image not perceived as a problem by the user of an image formation apparatus, it is said that the maximum shift amount is 150 &mgr;m in the paper transport direction and is 100 &mgr;m in the orthogonal direction (width direction) to the paper transport direction.
By experiment concerning this point, we found out that the transfer part spacing of each image formation unit needs to be set to 30 mm or less to place within the above-mentioned shift amount.
By the way, in the conventional portrait orientation type, generally the limit of the spacing is 45 mm.
FIG. 15
is a schematic drawing of a conventional color image formation apparatus of the portrait orientation type. It is seen that the occupation space and attachment/detachment space of each image formation unit (
205
a
to
205
d
) govern the image formation unit (
205
a
to
205
d
) spacing.
As the configuration of the image formation unit (
205
a
to
205
d
), the color image formation apparatus is placed in the normal orientation from the viewpoint of ensuring the space of a paper transport passage in the vertical direction and when
FIG. 15
is viewed from the front of the plane of the Figure to the depth, a cleaning member
273
a
, a charging member
236
a
, and light exposure means
253
a
as image formation means are placed in the first quadrant with respect to a photoconductor
234
a
, a developing member is placed in the fourth quadrant, and space of the second and third quadrants is provided as much as possible.
Assuming that the diameter of the photoconductor
234
a
is a, that the height of a developing unit is b, and that the occupation height of the cleaning, charging member is c, the height of the image formation unit becomes about a+(b/2)+c.
If a&e
Kitaoka Yoshitaka
Shimokawa Takuo
Tanizaki Jun-ichi
Chen Sophia S.
Matsushita Electric - Industrial Co., Ltd.
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