U.S. patent number 3,801,197 [Application Number 05/247,477] was granted by the patent office on 1974-04-02 for color electrophotographic copying apparatus capable of color balance adjustment.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Mikio Akiyama, Isao Yoshii.
United States Patent |
3,801,197 |
Akiyama , et al. |
April 2, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
COLOR ELECTROPHOTOGRAPHIC COPYING APPARATUS CAPABLE OF COLOR
BALANCE ADJUSTMENT
Abstract
A color electrophotographic copying apparatus which is capable
of adjusting color balance. With the apparatus, an original image
to be copied is scanned and color-resolved, whereafter one of the
color-resolved radiations is adjusted in color balance by a
corresponding filter. The particular color-resolved radiation is
then converted into an electrical signal, which is corrected and
amplified for further adjustment of the color balance. Thereafter,
the electrical signal is again converted into the form of
radiation, which is scanned to form an electrostatic latent image
on a photosensitive medium. The latent image is developed with a
color toner corresponding thereto, and then transferred and fixed
onto a transfer sheet. Such a cycle of operation is repeated for
each of the resolved colors, and the resultant color images are
superposed one upon another on the transfer sheet to thereby
provide a final copy image with excellent color balance
corresponding to the original image.
Inventors: |
Akiyama; Mikio (Yokohama,
JA), Yoshii; Isao (Tokyo, JA) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JA)
|
Family
ID: |
12269109 |
Appl.
No.: |
05/247,477 |
Filed: |
April 25, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Apr 30, 1971 [JA] |
|
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46-29184 |
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Current U.S.
Class: |
347/118; 355/38;
399/178 |
Current CPC
Class: |
G03G
15/01 (20130101) |
Current International
Class: |
G03G
15/01 (20060101); G03g 013/22 () |
Field of
Search: |
;355/38,4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Horan; John M.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
We claim:
1. A color electrophotographic copying apparatus for forming an
electrostatic latent image on a photosensitive medium having
photoconductivity, said apparatus comprising:
a. means for illuminating an original image;
b. means for scanning said original image to enable radiation
reflected therefrom to be converted into electrical signals, and
means for moving said original image, wherein said means for
scanning the radiation reflected from said original image comprises
a regular polygonal mirror having an axis of rotation extending in
the direction of movement of said original image, said regular
polygonal mirror being rotatable about said axis of rotation
thereof synchronously with the movement of said original image;
c. means including wedge-shaped filter means disposed in the path
of said radiation for color-resolving said radiation reflected from
said scanned original image for providing a plurality of first
separate color-resolved radiations;
d. means for varying the position of said wedge-shaped filter means
to adjust the densities of said color-resolved radiations for the
adjustment of the color balance therebetween;
e. means for converting said color-resolved radiations into
electrical signals and for amplifying such electrical signals and
emitting them again in the form of second radiations for a suitable
image reproduction on a photosensitive medium;
f. means for scanning said second radiations to direct them to a
precharge photosensitive medium to thereby form electrostatic
latent images thereon;
g. developing means for successively imparting color toners to said
electrostatic latent images formed on said photosensitive medium by
said color-resolved radiations, said color toners corresponding to
said electrostatic latent images, respectively;
h. means for transferring said color-developed images to a transfer
sheet;
i. means for cleaning any residual toner on said photosensitive
medium; and
j. means for retaining said transfer sheet until completion of
transferring all the color-resolved images by applying all said
process means for each resolved color.
2. Apparatus according to claim 1 wherein said color-resolving
means further comprises a dichroic mirror for providing said first
separate radiations; and said converting means includes a plurality
of light-receiving elements for generating said electrical signals
representing said resolved colors, and means for successively
selecting said generated signals for coupling to light emitting
means for controlling said light emitting means to provide said
second radiations.
3. Apparatus according to claim 2, wherein said wedge-shaped filter
means comprises a plurality of wedge-shaped filters adjustably
positioned between said dichroic mirror and said light-receiving
elements to vary the transmissibility of said first color-resolved
radiations.
4. Apparatus according to claim 3, wherein an original image having
various primary color tones and a copy thereof are juxtaposed on an
original carriage; means are provided for generating input signals
from said original image and said copy and for comparing said
signals; and means are provided for controlling adjustment of said
wedge-shaped filters in response to said comparison until the
difference between said input signals becomes zero.
5. A color electrophotographic copying apparatus for forming an
electrostatic latent image on a photosensitive medium having
photoconductivity, said apparatus comprising:
a. means for illuminating an original image;
b. means for scanning said original image to enable radiation
reflected therefrom to be converted into electrical signals, and
means for moving said original and said photosensitive medium
synchronously with each other;
c. means including wedge-shaped filter means disposed in the path
of said radiation for color-resolving said radiation reflected from
said scanned original image for providing a plurality of first
separate color-resolved radiations;
d. means for varying the position of said wedge-shaped filter means
to adjust the densities of said color-resolved radiations for the
adjustment of the color balance therebetween;
e. means for converting said color-resolved radiations into
electrical signals and for amplifying such electrical signals and
emitting them again in the form of second radiations for a suitable
image reproduction on a photosensitive medium;
f. means for scanning said second radiations to direct them to a
precharged photosensitive medium to thereby form electrostatic
latent images thereon, wherein said means for scanning the
radiation reflected from said original image and said means for
scanning and directing said color-resolved radiations to said
photosensitive medium are provided by polygonal mirror means
rotatable synchronously with the movement of said original image
and of said photosensitive medium;
g. developing means for successively imparting color toners to said
electrostatic latent images formed on said photosensitive medium by
said color-resolved radiations, said color toners corresponding to
said electrostatic latent images, respectively;
h. means for transferring said color-developed images to a transfer
sheet;
i. means for cleaning any residual toner on said photosensitive
medium; and
j. means for retaining said transfer sheet until completion of
transferring all the color-resolved images by applying all said
process means for each resolved color.
6. Apparatus according to claim 5, wherein said color-resolving
means further comprises a dichroic mirror for providing said
separate radiations and means are provided wherein said electrical
signals representing said resolved colors are successively selected
upon completion of a cycle of operation so that such signals are
successively emitted in the form of radiations of the respective
colors.
7. Apparatus according to claim 6, wherein said wedge-shaped filter
means comprises a plurality of wedge-shaped filters adjustably
positioned perpendicular to the optical paths of said separate
radiations from said dichroic mirror so as to vary the
transmissibility of said color-resolved radiations.
8. Apparatus according to claim 7, wherein an original image having
various primary color tones and a copy thereof are juxtaposed on an
original carriage; means are provided for generating input signals
from said original image and said copy and for comparing said
signals; and means are provided for controlling adjustment of said
wedge-shaped filters in response to said comparison until the
difference between said input signals becomes zero.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrophotographic copying apparatus
for producing colored copies by the use of color resolution, and
particularly to such an apparatus which can automatically carry out
a series of electrophotographic processes repetitively for each of
resolved colors. More particularly, the invention relates to a
copying apparatus which can correct the color balance under optical
and electrical controls to thereby provide colored copies with
excellent color reproducibility.
2. Description of the Prior Art
An electrophotographic technique for providing color copies is
disclosed, for example, in U.S. Pat. No. 2,986,466 to E. K.
Kaprelian issued on May 30, 1961. According to this patent,
photosensitive drums are arranged in response to various colors,
and light from an original picture is passed through filters for
the various colors so as to form latent images on the respective
photosensitive drums. Thereafter, the latent images are developed
with corresponding color toners. From the first to last
photosensitive drums, the developed images are successively
transferred onto a transfer sheet until the image transfer from the
last drum is completed, whereupon there is provided a color copy
image.
Other types of color electrophotography are shown as by U.S. Pat.
No. 2,962,347 to J. Dessauer, issued on Nov. 29, 1960, and U.S.
Pat. No. 3,060,019 to S.W.Johnson, issued on October 23, 1962.
All these prior techniques, however, are unsatisfactory in terms of
the color reproducibility and the size of the apparatus.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a color
copying apparatus which is simple in structure and reliable in
operation.
It is another object of the present invention to provide a color
copying apparatus which can produce copy images with excellent
color balance.
It is still another object of the present invention to provide a
color copying apparatus which permits the use of a photosensitive
medium requiring no panchromatic sensitivity.
It is yet still another object of the present invention to provide
a color copying apparatus which is compact and fully automatic as
well as low in cost.
According to the present invention, an original image to be copied
is scanned for color resolution and optically adjusted in color
balance, whereafter the color-resolved light rays are converted
into electrical signals, which, in turn, are corrected and
amplified in accordance with the characteristics of the
photosensitive medium and other factors. Such electrical signals
are converted again into light rays and projected on the
photosensitive medium to form an electrostatic latent image on the
photosensitive medium. The electrophotographic processes
advantageously available for the present invention may be those
proposed in the applicant's copending applications. The
electrophotographic copying apparatus of the present invention is
based on the process described in copending U.S. Pat. Application
Ser. Nos. 563,899 and 571,538 of the present applicant.
In the process of this invention, fundamentally speaking, the
photosensitive plate comprises a base, a photoconductive layer on
said base, and a translucent insulating layer on said
photoconductive layer. First of all, the surface of the translucent
insulating layer is charged (the primary charge), and by making the
use of the field thereof, the charge layer is strongly trapped
between the photoconductive layer and translucent insulating layer
and in the immediate neighborhood thereof. Next, an alternating
current corona discharge (the secondary corona discharge) of the
polarity opposite to the primary charge, and the illumination of
the original image, and carried out simultaneously. Then, light
rays are uniformly irradiated on the whole surface of the
translucent insulating layer to form the static image of high
contrast in accordance with light and dark patterns of the original
image on the surface of the translucent insulating layer.
Further, in the apparatus of the present invention, various process
means of exposure, charging, development, transfer and cleaning are
all based on those disclosed in U.S. Application, Ser. No. 585,091
filed Oct. 7, 1966 by the applicant which matured into U.S. Pat.
No. 3,438,706 on Apr. 15, 1969.
The original image is illuminated and scanned by a regular
polygonal scanning mirror. This scanning mirror is of the type
commonly used in the art of high-speed cameras, but in the present
invention it is sufficiently small in size to make full use of the
space allotted for an optical system in a conventional copying
apparatus. The reflected light from the original image so scanned
is resolved into three colors by a dichroic mirror. If desired, the
light may be resolved into more colors.
Wedge-shaped filters are movably disposed on the optical path in a
direction perpendicular thereto in order to adjust the color
balance between the respective color-resolved light rays. The
positions of the respective wedge-shaped filters may appropriately
be determined on the paths of the respective color-resolved lights.
The color-resolved lights so adjusted are passed to phototubes,
which convert such lights into electrical signals, which in turn
are suitably corrected and amplified through an amplifier and
thereafter converted again into light rays by a discharge tube. The
extent of such correction and amplification is appropriately
controlled in accordance with the characteristic of the
photosensitive medium, the densities of developing toners, etc. The
light rays thus converted are again scanned and directed to the
photosensitive medium, which thus produces an electrophotographic
latent image thereon. Such electrostatic latent image is developed
with color toner corresponding thereto, and transferred to a
transfer sheet. Thereafter, the photosensitive medium is cleaned.
The above-described operation takes place repetitively for each of
the resolved colors, thus finally providing a color copy of the
original image.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will become fully apparent from the following
detailed description of an embodiment thereof taken in conjunction
with the accompanying drawings, in which:
FIG. 1 is a schematic representation of the optical arrangement in
the apparatus according to an embodiment of the present
invention;
FIG. 2 illustrates the arrangement of various electrophotographic
process systems incorporated in the apparatus of the present
invention; and
FIG. 3 is a perspective view of a regular polygonal scanning mirror
employed in the optical system of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description will now be made of a specific embodiment of the
present copying apparatus in which a color original image is
subjected to color separation and thereafter development is
effected with four color toners such as cyan, magenta, yellow and
black, thereby providing a color copy image.
Referring to FIG. 1 of the drawings, a color original to be copied
is designated by P and which bears an original image facing
downwardly and is movable at a predetermined velocity in a
direction vertical with respect to the plane of the drawing
sheet.
A pair of white light lamps 1 are provided for illuminating the
image-bearing surface of the original P. A regular polygonal mirror
2 is disposed below the original P for rotation about its own
center at a predetermined velocity in the direction as indicated by
an arrow. The regular polygonal mirror is best shown in the
perspective view of FIG. 3. A mirror system is designated by 4. A
dichroic mirror 34 serves to resolve incident light into three
colors. A shaft-mirror 35 is provided to obtain an optical image to
be masked with black toner. Reflective mirrors 36, 37 and 38 are
provided for changing the direction of the light paths
respectively. Filters 3 are provided for color resolution and for
color balance adjustment, the filters 3.sub.1, 3.sub.2, 3.sub.3 and
3.sub.4 corresponding to cyan, magenta, yellow and black,
respectively.
Further provided are slits 5 for cutting scattered light rays,
condenser lenses 6, phototubes 7, a color reproduction correcting
amplifier circuit 8, discharge tube 9, a condenser lens 10, and a
regular polygonal mirror 11 of the same shape as and rotatable
synchronously with the aforesaid polygonal mirror 2. Instead of
using such two similar mirrors 2 and 11, a single such mirror may
be used as a common one. A photosensitive medium 12 is shown as a
rotatable drum type, but alternatively it may take the form of flat
sheet or endless belt.
Referring to FIG. 2, there is shown an arrangement for carrying out
a series of electrophotographic processes with respect to the
photosensitive medium, which has an outermost layer 12' of
dielectric material in accordance with the type of the
electrophotography described previously. The arrangement includes a
primary charger 13, means 14 for effecting exposure and discharge
simultaneously, overall exposure means 15, and developing means 16
for various colors, say, 16.sub.1 for cyan, 16.sub.2 for magenta,
16.sub.3 for yellow and 16.sub.4 for black. The arrangement further
includes an image transfer means 17 having pawl means 17.sub.1 for
retaining a transfer sheet 18 until all color images are
transferred in a manner to be described. Where the toners in use
are of the dry type, heat fixing means 21 may be provided. Cleaning
means is generally designated by numeral 22.
In operation, the color original P is illuminated by the white
light lamps 1 and moved in the aforesaid direction as the
successive portions thereof are scanned laterally thereof (i.e. in
the direction perpendicular to the direction of movement of the
original P) by the successive reflection surface of the regular
polygonal rotatable mirror 2, until the entire surface area of the
original is scanned. During this scanning process, light reflected
from the successive sides of the regular polygonal mirror 2 is
directed to follow a path a so that the light is subjected to color
resolution by the dichroic mirror 34. For further thorough color
resolution and color balance adjustment, the light rays thus
resolved are further passed through filters 3. For example, the
cyan ray is passed through the filter 3.sub.1 for cyan, whereafter
the light ray b resulting from such secondary color resolution is
passed through the slit 5.sub.1 for cutting scattered light and
through the condenser lens 6.sub.1 to the phototube 7.
Thus, the phototube 7 continuously produces a current corresponding
to the intensity of the successive cyan rays resulting from the
color resolution. This current is suitably corrected and amplified
by the color reproduction correcting amplifier circuit 8 in
accordance with various factors such as the reflection factor of
the original, the characteristics of the illuminating lamps,
filters, phototubes, photosensitive medium, toners, the efficiency
of the image transfer, etc. Thereafter, the current is converted
into a radiation c through the phototube 9. The emitted radiation
is scanned by the regular polygonal mirror 11 rotating
synchronously with the regular polygonal mirror 2, and directed to
the surface of the photosensitive medium 12 which is rotating
synchronously with the movement of the original P while the various
electrophotographic process means 13-15 are operative, whereby the
photosensitive medium 12, as it passes the overall exposure means
15, produces an electrostatic latent image corresponding to the
pattern of the cyan component contained in the picture of the color
original P. Subsequently, the electrostatic latent image is
developed by the developing means 16.sub.1 containing a developer
of cyanic color and then transferred onto the transfer sheet 18 at
the transfer means 17.
The described series of processes may be successively repeated with
respect to each of the other resolved colors, i.e. magenta, yellow
and masking black by electrically and mechanically changing over
the respective color resolving filters and developing the
respective latent images with the associated color developing means
(16.sub.2, 16.sub.3 and 16.sub.4 for magenta, yellow and black,
respectively), thus successively providing developed images of the
respective resolved colors on the photosensitive medium 12. These
different color images are then successively transferred onto the
transfer sheet which already carries the cyanic color pattern
thereon, thereby providing a complete color print or copy.
The image transfer means herein used comprises a transfer roller 17
and a pawl 17.sub.1 for retaining a transfer sheet wrapped around
the transfer roller. The transfer roller 17 is rotated in
synchronism with the movement of the original carriage with the
pawl 17.sub.1 retaining the transfer sheet thereto, and when the
four cycles of transfer process have all been completed, the pawl
17.sub.1 releases its retention to allow the transfer sheet to be
discharged through outlet 20.
The heating means 21 serves to heat and fix the toners to the
transfer sheet during each transfer cycle if the toners in use are
dry ones. If the developer in use is in the form of liquid, the
heating means 21 serves to quickly evaporate any carrier liquid and
expedite the fixing and drying of the toner on the transfer
sheet.
Where the photosensitive medium in use is in a continuous form such
as drum or endless belt, more clearly colored copies may be
provided by dividing the image-forming peripheral surface of the
photosensitive medium into sections corresponding to individual
particular colors. More specifically, so long as the illustrated
case, the outer peripheral surface of the drum type photosensitive
medium 12 may be divided into four sections I to IV so as to
correspond to the four colors, i.e. cyan, magenta, yellow and
masking blank, respectively. This will ensure a genuine
monochromatic image to be formed in each divisional surface section
of the photosensitive drum, thus resulting in a highly clear color
copy image with the respective monochromatic images superposed one
upon another.
The operation of the developing means 16.sub.1 - 16.sub.4 with
respect to the corresponding surface sections I - IV of the
photosensitive medium may be accomplished by a cam mechanism. The
cleaning device 22 includes suction type cleaning means 22.sub.1 -
22.sub.4 which are operable with respect to the respective surface
sections I - IV to remove any residual developer of distinct colors
from such surface sections after image transfer.
Further, in the above-described copying apparatus, enhanced color
reproducibility is provided by elaborately designing the various
color-resolving filters. More specifically, as shown, the
color-resolving filters 3.sub.1 - 3.sub.4 are wedge-shaped and
positioned for movement perpendicularly to the optical path to
thereby vary the rate of light transmitting therethrough so as to
adjust the color balance of the resultant copy.
At the outset of a copy operation, a standard two-color test sheet
is first copied and the copy sheet thus obtained is juxtaposed with
the said standard two-color test sheet on the original carriage of
the copying apparatus to electro-optically compare and measure
these two sheets with respect to the difference in color balance
therebetween. Then, the wedge-shaped filters are automatically
adjusted in position in accordance with the output of the measured
difference in color balance until such difference becomes zero.
Thus, the copying apparatus is now ready to continuously produce
copies with high fidelity to the color tones of any color
original.
As noted from the foregoing description, the present invention
enables an operator to obtain electrophotographic color copies
rapidly and automatically on account of a considerably simple and
compact construction, and also enables the resolved color lights of
a color original picture to be temporally converted into electrical
signals which may be suitably corrected and amplified in accordance
with various factors, such as the reflection factor of the
original, the characteristics of the illuminating lamps, filters,
phototubes, photosensitive medium, toners, the image transfer
efficiency, etc., whereby the color balance of the resultant copies
may be readily controlled by an electrical operation to provide
color copies with excellent color reproducibility. Furthermore, the
radiations emitted for scanning the photosensitive medium may be
selected to any suitable wavelength in accordance with the
sensitivity range of the photosensitive medium, and this leads to
an advantage that the photosensitive medium to be used need not
necessarily be panchromatic.
Thus, according to the present invention, the light relfected from
an original image is color-resolved, whereafter the resolved color
lights are automatically adjusted in color balance by the
wedge-shaped filters, then converted into electrical signals and
amplified suitably. This permits the use of a photosensitive medium
having a narrow sensitivity range which has heretofore been
regarded as unsuitable, and also enables the color balance
adjustment to be achieved with much readiness. In these respects,
the color electrophotographic copying apparatus embodying the
present invention is satisfactory for its intended purposes.
Moreover, the copying apparatus of the present invention may find a
usage as a simple printer which can not only copy original images
but also can vary the color balance or equalize the density of the
resultant copies.
It will be apparent to those skilled in the art from the
specification, drawings and appended claims that the apparatus of
the present invention is applicable for other various purposes than
described above.
* * * * *