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Патент USA US3438709

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April 15'; 1969
' 3,438,704
‘ Filed Oct. 11, '1966
April 15, 1969
Filed Oct? 11; 1966
' 3,438,704 ‘ ’
2 of
April 15;,1969
‘ FilédQct_..fl-1, 1966
FIG‘. 3
FIG. 5
April 15, 1969
méd on. 11. *1966
of 7‘4
FIG. 7
United States Patent Office
Patented Apr. 15, 1969
Another object of this invention is to control the in
tensity of a printing light beam impinging on the surface
of a photoreceptor at a predetermined level.
John J. Schoen, Webster, N.Y., assignor to Xerox Cor
poration, Rochester, N.Y., a corporation of New York
Filed Oct. 11, 1966, Ser. No. 585,908
A further object of the invention is to compensate for
changes in illumination in an optical system more simply
and rapidly than heretofore.
A still further object of the invention is to provide a
novel automatic illumination control system involving
relatively few moving parts and which is reliable in
Int. Cl. G03g 15/08
US. Cl. 355-8
8 Claims
This invention relates in general to electrostatic record
ing and, in particular, to an optical system for projecting
The above objects as well as other features and advan
a line scan image onto a moving photoreceptor, such as,
a xerographic plate, and an illumination control therefor.
In the practice of xerography, as described for exam
tages of the invention are accomplished, generally speak
ing, by positioning a variable aperture slit in a scan type
optical system containing an optical lens primarily cor
rected for aberrations resulting from tangential optical
ray-s. The aperture slit is formed by opaque wall members
ple in US. Patent No. 2,297,691 to Chester F. Carlson,
a xerographic surface comprising a layer of photocon
ductive insulating material a?ixed to a conductive back
arranged for movement toward and away from the cen
ing is used to support electrostatic images. In. the usual
path of the imaging rays in response to a predeter
method of carrying out the process, the xerographic plate
mined change from a reference illumination level that
is electrostatically charged uniformly over its surface and
then exposed to a light pattern of the image being- repro— 20 is established by a control circuit operating in conjunc
tion with a servo control to position the wall members.
duced to thereby discharge the charge in the areas where
For a better understanding of the invention reference
light strikes the layer. The undischarged areas of the layer
is now had to the following detailed description of the
thus form an electrostatic charge pattern in conformity
invention to be read in connection with the accompany
with the con?guration of the original light pattern.
The latent electrostatic image can then be developed 25. ing drawings; wherein:
FIG. 1 illustrates schematically a preferred embodi
by contacting it with a ?nely divided electrostatically at
ment of a xerographic recording apparatus having a line
tractable material such as a powder. The powder is held
scan type optical system with illumination control accord
in image areas by the electrostatic charge on the layer.
ing to the present invention;
Where the charge is greatest, the greatest amount of ma
FIG. 2 is an isometric view of the optical system;
terial is deposited; and where the charge is least, little 30 FIG.
3 is a side elevational view of the slit aperture
or no material is deposited. Thus, a powder image is pro
duced in conformity with the light image of the copy be
FIG. 4 is a cross-sectional view of the slit aperture
ing reproduced. The powder is subsequently transferred
taken along lines 4—4 of FIGS;
to a sheet of paper or other surface and suitably a?ixed
thereto to form a permanent print.
largest single factor effecting exposure latitude, i.e., range
of illumination intensity, is the e?iciency of the developer
system. In other words if the developer system is highly
FIG. 5 and FIG. 6 are left-hand and right-hand end
views of the aperture slit mechanism, respectively;
It can be readily appreciated that the quality of the
print is, in the large part, dependent on the exposure of
the charged xerographic plate to the radiation image. The
' FIG. 7 is a diagrammatic view of a bridge circuit il—
lustrating the relationship‘ of the active and reference sens
ing devices; and,
FIG. 8 is a wiring diagram of the control circuit for
automatically controlling the illumination at the surface
of the xerographic plate.
sensitive so as to develop background or image portions
Referring now to FIG. 1 there is shown schematically
as “grey” areas when in reality these are white, then
high speed automatic xerographic reproduc
illumination control must be commensurately sensitive 45 tion machine incorporating optical scanning appanatus
to provide the proper exposure of the charged xerographic
surface. With modern day improvements to xerographic
developer systems, such as, an electrically biased backing
electrode to enhance solid area development, the desir
ability of maintaining proper illumination becomes in
creasingly apparent.
A uniformly high level of illumination as required for
exacting exposure is complicated by many factors, For
example, variation in lamp output due to changes in am
which includes an automatic illumination control ac
cording to the present invention whereby high quality
reproduction is accomplished.
The automatic xerographic reproducing apparatus de
scribed more fully in US. Patent 3,221,622, comprises
a xerographic plate 20 including a photoconductive layer
on a conductive backing and formed in the shape of a
drum, which is mounted on a shaft journaled in :a frame
to rotate in the direction indicated by the arrow to cause
bient temperature or even age alone is sufficient to cause 55 the drum surface sequentially to pass a plurality of
development of white areas thereby detracting from the
overall quality of the print. Moreover, such things as dust
on the platen and a high density document can affect the
illumination level resulting in white image portions being
xerographic processing stations.
For the purpose of the present disclosure, the several
xerographic processing stations in the path of movement
of the drum surface ‘may be described functionally, as
developed as “grey.”
60 follows:
Now in accordance with the present invention the
A charging station at which a uniform electrostatic
above drawbacks are overcome by an automatic illumi
charge is deposited on the photoconductive layer of the
nation control to maintain illumination at a preselected
level. More than this the illumination control is a linear
system greatly simplifying the operation and maintaining
?xed tolerances throughout the range of operation. Also
the quality of the image is not deleteriously affected as is
xerographic drum;
An exposure station which a light or radiation pattern
65 of copy to be reproduced is projected onto- the 1drum sur
face to dissipate the drum charge
the exposed areas
thereof and thereby form a latent electrostatic image of
the case in an iris shutter mechanism commonly used
the copy to be reproduced;
as an illumination control on cameras.
A developing station at which a xerognaphic developing
It is therefore an object of this invention to improve 70 material including toner particles having an electrostatic
illumination used in high speed automatic reproduction
charge opposite to that of the electrostatic latent image
equipment capable of producing high quality copies.
are cascaded over the drum surface, whereby the toner
particles adhere to the electrostatic latent image to form
a xerographic powder image in the con?guration of the
copy being reproduced;
A transfer station at which the xerographic powder
image is electrostatically transferred from the drum sur
face to a transfer material or support surface; and,
A drum cleaning and discharge station at which the
drum surface is brushed to remove residual toner particles
remaining thereon after image transfer, and at which the
by means of a corona transfer device 51 that is located
at or immediately after the line of contact between the
support material and the rotating drum. In operation, the
electrostatic ?eld created by the corona transfer device is
effective to tack the support material electrostatically to
the drum surface, whereby the support material moves
synchronously with the drum while in contact therewith.
Simultaneously with the tacking action, the electrostatic
?eld is effective to attract the toner particles comprising
drum surface is exposed to a relatively bright light source
the xerographic powder image from the drum surface and
to effect substantially complete discharge of any residual
electrostatic charge remaining thereon.
cause them to adhere electrostatically to the surface of
the support material.
The charging station is preferably located, as indicated
by reference character A. As shown, the charging arrange
ment includes a corona charging device 21 which includes
a corona discharge array of one or more corona dis
Immediately subsequent to the image transfer station,
there is positioned a stripping apparatus to paper pick-off
mechanism 52 for removing the sheets of support material
from the drum surface. This device, which is of the type
charge array of one or more corona discharge electrodes
disclosed in Rutkus et a1. United States Patent 3,062,536,
that extend transversely across the drum surface and are
includes a plurality of small diameter ori?ces supplied
energized from a high potential source and are substan
with pressurized aeriform ?uid by a suitable pulsator or
tially closed within -a shielding member.
20 other device. The pulsator is adapted to force jets of
Next subsequent thereto in the path of motion of the
xerographic drum is an exposure station B. In accordance
with the present invention illumination control, to be de
scribed more fully hereinafter, is accomplished by selec
tively opening and closing an aperture slit mechanism 22
positioned in the path of a ?owing image projected from a
stationary original onto the surface of drum 20‘.
The optical scanning or projection asembly comprises
a setationary oopyboard which consists of a transparent
curved platen member 25 such as, for example, a glass
plate or the like, positioned on the exterior of the cabinet,
which is adapted to support a document to be reproduced,
the document being uniformly illuminated and arranged
in light projecting relation to the moving light-receiving
surface of the xerographic drum. Uniform lighting is
provided by bands of lamps 30 arranged on opposite
sides of the copyboard. Scanning of the document on the
stationary oopyboard is accomplished by means of a rnir
pressurized aeriform ?uid through the outlet ori?ces into
contact with the surface of the xerographic drum slightly
in advance of the sheet of support material to strip the
leading edge of the sheet from the drum surface and to
direct it onto an endless conveyor 55 whereby the sheet
material is carried to a ?xing device 60. At the ?xing de
vice, the transferred xerographic powder image on the
sheet of support material is permanently ?xed or fused
thereto as by heat. After fusing, the reproduction is dis
charged from the apparatus at a suitable point for collec
tion externally of the apparatus by means of the conveyor
The next and ?nal station in the device is a drum clean
ing station E, having positioned therein a corona preclean
device 76, a drum cleaning device 80 adapted to remove
any powder remaining on the xerographic drum after
transfer by means of a rotating brush 81, and a discharge
lamp-83 adapted to ?ood the xerographic drum with light
ror assembly which is oscilliated relative to the copy
to cause dissipation of any residual electrical charge re
board in time-d relation to the movement of the xero 40 maining on the xerographic drum.
graphic drum.
The mirror assembly, which includes an object mirror
31, is mounted below the copyholder to re?ect an image
of the document through a spherical lens 33 onto an
image mirror 35 which, in turn, re?ects the image onto
the xerographic drum.
Adjacent to the exposure station is a development sta
tion C in which there is positioned a developer apparatus
38 including a casing or housing having a lower or sump
portion for accumulating developer material. A bucket
conveyor (not shown) is used to carry the developing ma
terial to the upper part of the developer housing where
it is cascaded over a hopper chute onto the xerographic
drum to effect development.
Positioned next and adjacent to the developing station
is the image transfer station D which includes a sheet
feeding arrangement adapted to feed sheets of support
material, such as paper or the like, successively to the
xerographic drum in coordination with the presentation
of the developed image on the drum surface at the trans
fer station.
The sheet feeding mechanism inicludes a sheet feed
It is believed that the foregoing description is sufficient
for the purposes of this application to show the general
operation of a xerographic reproducing apparatus. For
further details concerning the speci?c construction of the
xerographic apparatus reference is made to U.S. Patent
Refering now to FIGURES 2-6, there is illustrated in
greater detail the automatic illumination control system
according to the present invention. The intensity of illumi
nation is regulated by the opening in slit aperture mecha
nism ‘22 interposed in the optical path adjacent the lens
as best shown in FIG. 2. The illumination level at the
surface of the drum is detected and compared with a ref
erence illumination level in a control circuit described
hereinafter which feeds back a signal to the slit aperture
mechanism to maintain illumination approximately equal
to the preset reference illumination level.
Slit aperture mechanism 22 is positioned so that elon
gated slit opening 101 has its longitudinal axis transverse
to the direction of scan. By this arrangement tangential
light rays pass parallel to the slit opening 101 while sagit
tal light rays pass normal to it. For this reason spherical
device 40 adapted by means of vacuum feeders to feed
lens 33 is corrected for oblique spherical abberation in
the top sheet, of a stack of sheets to roller 42 cooperating
the tangential plane only. The construction of such a lens
with the belts of paper transport 44 for advancing the
is described more fully in copending application Ser. No.
sheet suf?ciently to be held by paper transport 44 which 65 585,936 of David C. Harper, ?led Oct. 11, 1966. It should
in turn, conveys the sheet to a sheet registration device 45
be noted that slit aperture mechanism 22 may be located
positioned adjacent to the xerographic drum. The sheet
on either the image side of lens 23 as illustrated on the
registration device arrests and aligns each individual sheet
object side so long as the slit opening is closed spaced
of material and then in timed relation to the movement of
to the lens so as not to deleteriously affect the quality of
the xerographic drum, advances the sheet material into 70 the image.
contact with the xerographic drum in registration with a
Slit aperture mechanism 22 has a variable slit in a di
previously formed xerographic powder image on the
rection normal to the optical path to thereby increase or
decrease the illumination received at the drum and com
The transfer of the xerographic powder image from the
prises a housing 110 in which ?exible wall members 112
drum surface to the sheets of support material is effected
and 114 are arranged so as to be movably slidable therein.
Wall members 112 and 114 are impervious to light and
made from any suitable material, such as, Mylar dyed
when the light impinging on photocell 170 is less than the
preset value there is a lower voltage. The voltage change
black. Rotatably journaled in the sides‘ of housing 110
must exceed a certain “dead band” to operate class B
are a pair of shafts 122 and 124. On each end of shafts
122 and 124 are mounted sprocket members 128 which
engage apertures 130 formed in wall members 112 and
To move the ?exible wall members in unison there is
provided a reversible drive motor 135 which drivingly
engages counter-rotating spur gears 141 and 143 which 10
ampli?ers 220 and 225 which are normally in the “off”
condition. This “dead band” is determined by the biasing
of transistors Q3 and Q4.
in turn drive ‘gears 145 and 146 mounted on the ends of
drive shafts 122 and 124, respectively. .Also mounted on
Q3 is an NPN transitor and is turned “on” when re
ceiving a positive signal at its base. In similar fashion,
Q4 is a PNP transitor responsive to a negative signal "
exceeding the “dead band” turning the transitor in the
“on” condition. When Q3 is turned “on” this causes
transitors Q5 and Q6 to conduct. Q5 and Q6 serve to
the shafts 122 and 124 are a pair of cams 148 and 149
which serve to actuate limit switches 150 and 151, respec
amplify and invert the signal, respectively. The signal
is a narrow slot 167 extending substantially across the
further ampli?es the signal rendering Q9 conductive.
output from Q5 turns “on” power switch Q7 to provide
tively, located in the rotative path of the cams.
15 a positive voltage level with respect to ground across
A light shield 166 (see FIG. 2) in the form of an open
the terminals of motor 135 driving wall members 112
elongated box is positioned in close proximity to the pe
and 114 further apart to increase the illumination on
ripheral surface of the drum '20. Formed. in the light shield
the drum. In like fashion Q4 will turn “on” Q8 which
length thereof with the center line of'the slot parallel to 20 When Q9 conducts a negative voltage level is supplied
the axis of rotation of the drum.
across the terminals of the motor to drive the wall mem
Light shield 166 houses a photocell 170 and an asso
ciated lamp 172 in the interior thereof outside of the image
area which serve as a part of the control circuit. In com
partment 175 outside of the optical path is another photo
cell 180 and an associated lamp 182 which together also
form a part of the control circuit.
Photocells 170 and 180 serve as leg components in a
bers closer together thereby decreasing illumination avail
able at the surface of the drum.
' To provide a quick stop for wall members 112 and
114 a breaking resistor 250 is connected across the arma
ture terminals of motor 135. Braking resistor 250 pro
vides a low impedance to ground to dissipate energy
stored in the motor. Limit switches 150 and 151 prevent
sensing bridge 185 shown in FIG. 7. The photocells can
the wall members from closing completely or opening
be made from any suitable material, such as, cadmium 30 too far apart as previously discussed.
sulphide. Photocell 170 serves as the “active” cell in the
Above is described an illumination control system
optical illumination path and is positioned to receive il—
wherein an image projected onto a moving photoreceptor
lumination re?ected from a reference strip 190 on the
has a predetermined illumination level irrespective of
platen best seen in FIG. 2. Reference strip 190 is colored
ambient conditions, age of lamps and document density.
to achieve a reference re?ectance, such as, white. Photo 35 Hence when a relatively dense document is to be re
cell 180 is used as a reference in the bridge circuit for
produced, the exposure may be modi?ed by greater illu
comparison with the illumination received by photocell
170. If the illumination received by photocell 170 and 180
mination on the photorecetor as, for example, a xero
graphic drum. As can readily be appreciated such a
is the same there is a balanced condition in the bridge and
system is highly desirable for Xerographic machines hav
no current ?ows. However, if the illumination differs cur 40 mg sensitive development systems.
rent will flow in the bridge which is coupled electrically
to motor 135 as will become apparent. Initially sensing
bridge 185 is set for a predetermined light intensity. This
is accomplished by changing the resistance in variable
resistors ‘210 and 212. Alternatively the intensity of lamps
172 and 182 can be varied to balance the bridge. Upon
depressing the print button on the control panel (not
While the invention has been described with reference
to the structures disclosed herein, it is not con?ned to
the details set forth, and this application is intended to
cover such modi?cations or changes as may come within
the purposes of the improvements or the scope of the
following claims.
What is claimed is:
shown) lamp 172 is ‘dc-energized enabling the preset value
1. In a recording apparatus of the type in which a
of illumination to be compared with the illumination actu
document to be reproduced in projected in line scan
ally received from the optical system. Lamp 172 is ener
gized when the machine is off to maintain the speed of re 50 fashion onto a photoreceptor moved past an exposure
station characterized by an illumination control system
sponse of photocell 170. Hence when the machine is
comprising in combination:
turned on rapid response is attained. Current ?ows when
support means located at the object plane to position
the bridge is unbalanced to provide a polarized signal to
motor 135 causing it to run forward or backward accord
a document to be reproduced,
explained hereinafter.
a source of illumination optically positioned to illumi
nate the document,
a photoreceptor at the image plane to receive a pattern
of light and shadow according to the document to
The operation of the illumination control may best
be understood in connection with the circuit diagram in 60
FIG. 8. The control circuit for actuating motor 135 is
coupled to terminals W, X, Y, and Z of the sensing
an optical system to project a line scan image of the
document onto said photoreceptor, said optical sys
tem including a spherical lens corrected for oblique
ing to whether more or less illumination is required. When 55
the proper illumination is present, the bridge is once more
balanced and motor 135 is dc-ener-gized and braked, as
bridge as shown in FIG. 8. When there is an unbalanced
condition in the bridge a differential amplifer 215 pro
vides a signal to a pair of class -B ampli?ers 220 and
225 connected in push-pull, i.e., when one is “on” the
other is “off.” The output signal from the class B am
pli?ers operates motor 135.
The output signal from the sensing bridge 185 is applied
to the bases of transistors Q1 and Q2 which com-prise 70
differential ampli?er 215. The polarity of the signal pro
duced by the differential ampli?er depends upon whether
the illumination is higher than or less than the preset
value. In the case where it is greater than the preset
value, the voltage would be higher. On the other hand,
be recorded,
spherical aberration in the tangential plane,
light masking means interposed in the optical path in
close proximity to said lens including a pair of
spaced apart wall members impervious to light
adapted for movement transverse to the optical
center line in the sagittal direction to mask out
selected light rays,
drive means operative to position said wall members
toward and away from the optical center line to
control the intensity of illumination at the surface
of said photoreceptor at a predetermined level in
response to discrete bi~polar electrical signals,
circuit means coupled to said drive means to emit
second photosensitive means positioned exterior to the
optical path,
discrete bi-polar electrical signals to actuate said
drive means to move said wall members toward and
a second source of illumination in close proximity to
said second photosensitive means for directing light
of predetermined intensity toward said second photo
away from the optical center line in a sagittal direc
tion to maintain a predetermined level of an illumi
nation on the surface of said photoreceptor ‘with a
sensitive means,
motor driven drive means operative to position said
wall members to control the intensity illumination
at the surface of said xerographic plate at a prede
termined level in response to discrete bi-polar elec
minimum of optical deterioration thereat.
2. Apparatus according to claim 1 wherein said circuit
means includes a sensing bridge having a pair of photo
cells coupled in opposing circuit paths, a one of said
trical signals,
photocells being positioned in the optical path outside
circuit means including a sensing bridge coupling said
?rst and second photosensitive means in opposed
current paths across positive and negative voltage
of the image area, the other of said photocells being
positioned to receive a predetermined level of illumina
tion from a reference source of illumination located
exterior to the optical path.
3. Apparatus according to claim 2 wherein said drive
means includes a reversible motor responsive to bi-polar
signals received from said circuit means, said motor
terminals, a dilferential ampli?er connected to said
sensing bridge to establish a polarized output signal,
a pair of driver ampli?ers connected in push-pull to
receive said polarized output signal from said differ
ential ampli?er, and a motor armature to receive the
being drivingly connected to a pair of shafts mounted for
counterrotation, said shafts being arranged to extend 20
transverse to the optical path in parallel relation in the
tangential plane on opposite sides of the optical center
line, and sprocket members mounted on said shafts to
engage apertures formed in said wall members for ex
output from said driver ampli?ers to actuate said
motor driven drive means in a direction according to
the polarity of said output signal to selectively posi
tion said wall members to maintain illumination at
a predetermined level of intensity at the surface of
erting bi-directional movement thereto upon actuation 25
of said motor.
4. Apparatus according to claim 3 wherein said motor
has a low impedance across the terminals of its armature
said xerographic plate.
6,. Apparatus according to claim 5 wherein said ?rst
photosensitive means is optically aligned with a strip
located on said copyboard adjacent the document and
arranged to be projected therewith by said optical system,
said strip lbeing colored for selective re?ectance in the
whereby stored energy is rapidly dissipated from said
motor to effect dynamic braking of said drive means.
5. Recording apparatus for controlling illumination at
a light receiving surface arranged to receive a ?owing
image of a document to be recorded comprising:
a curved copyboard positioned at the object plane for
supporting a document to be reproduced,
direction of said ?rst photosensitive means.
7. Apparatus according to claim 5 wherein said circuit
:means includes a resistor connected across the terminals
of said motor armature to effect dynamic braking of said
motor driven drive means.
8. Apparatus according to claim 5 wherein said
xerographic plate is a drum mounted for rotating to pass
a ?rst source of illumination arranged to illuminate
the document,
a xerographic plate at the image plane adapted for
a plurality of xerographic processing stations radially dis
placed from the drum axis for recording continuously.
movement to receive a ?owing pattern of light and
shadow according to the document to be recorded, 40
an optical system including a mirror adapted to be
oscillated to project a ?owing image of the document
onto said xerographic plate in synchronization with
the speed thereof, and a spherical lens corrected for
oblique sphrical aberration in the tangential plane,
light masking means interposed in the optical path in
close proximity to said lens including a pair of spaced
apart wall members impervious to light adapted for
References Cited
Mees ______________ __ 88-—24
Shepardson et al. ____ __ 88-24
Ferguson et al. ______ __ 88-24
Lieser _____________ __ 95-——l0
Moss ______________ __ 88—24
NORTON ANSHER, Primary Examiner.
movement transverse to the optical center line in the
sagittal direction to mask out selected light rays,
50 W. A. SIVERTSON, Assistant Examiner.
?rst photosensitive means interposed in the optical
path outside of the image area adjacent the surface
of said xerographic plate,
US. Cl. X.R.
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