Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to electrostatic reproduction
machines, and more particularly to an improved charge
control system for use with such machines.
In an electrostatic or xerographic type reproduction
machines or copies, the charge level on the machine photo-
conductive surface or photoreceptor, is critical to satis-
factory operation of the machine. As known to those versed
in the art, the photoconductive surface is first charged,
desirably to a predet charge level, preparatory to imaging.
The level of this initial charge however, is often critical
since too low a charge may result in weak, washed out look-
ing copies whereas too high a charge may result in dark
copies and overloading of the machine cleaning mechanism.
Normally the charge as aforesaid is placed on the
photoconductive surface by a corona generator. Close
control over the corona output of devices of this type is
often difficult, particularly as the machine components
including the corona generator age.
It is therefore an object of an aspect of the present
invention to provide a new and improved charge control for
xerographic type machines.
It is an object of an aspect of the present invention
to provide an improved charge control wherein the initial
charge set down by the corona generator is examined and
changed as necessary to provide the optimum charge desired.
It is an object of an aspect of the present invention
to provide an improved charge control wherein the initial
charge set down by the corona generator is examined and
reduced as necessary by an illuminator whose illumination
intensity is matched to the degree of overcharge.
--1-- -
It is an object of an aspect of the present invention
to provide an improved mechanism for changing the charge on
a photoreceptor surface in response to the existing charge
conditions to provide an optimum photoreceptor charge.
It is an object of an aspect of the present invention to provide a
charge control wherein charges on a photoreceptor are auto-
matically tailored in response to existing photoreceptor
charge conditions to provide an optimized photoreceptor
charge.
Various aspects of the invention are as follows:
In an electrostatic type reproduction machine for
producing copies of an original, the machine having a photo-
receptor, means for charging the photoreceptor in prepara-
tion for imaging, exposure means for exposing the charged
photoreceptor to the original whereby to create a latent
electrostatic image of the original on the photoreceptor,
developing means for developing the latent electrostatic
image on the photoreceptor, and transfer means for trans-
ferring the developed image to a sheet of copy material,
the combination comprising: a. means for generating a
charge level signal reflecting the charge level of said
photoreceptor following charging by said charging means;
b. light means for illuminating said photoreceptor to
reduce the charge level of said photoreceptor, said light
means reducing the charge level on said photoreceptor in
proportion to the intensity of the light produced by said
light means; and c. control means for regulating the
intensity of said light means in response to said charge
level signal.
,
~ 2
The method of controlling the operating charge level
on the photoreceptor of an electrostatic type reproduction
machine for producing copies of an original, comprising
the steps of: generating a charge level signal reflect-
ing the charge level of said photoreceptor followingphotoreceptor charging and illuminating said photoreceptor
with an intensity proportional to said charge level signal
to reduce the charge level of said photoreceptor.
Other objects and advantages will be apparent from
the ensuing description and drawings in which:
Figure 1 is a schematic sectional view of an electro-
static reproduction machine incorporating the charge
control system of the present invention;
Figure 2 is an isometric view showing details of the
ch~rge control apparatus of the present invention; and
~` Figure 3 is a circuit schematic of one embodiment
of the photoreceptor charge control system of the present invention
for reducing or increasing photoreceptor charge.
Figure ~ is a circuit schematic of another embodiment of
.he charge control system of ~he present invention for reducing
~hotoreceptor charge.
Figure 5 ~s a circuit schematic of an alternate
embodiment wherein a fixed light source with liquid crystal
regulator is provided for controlling the intensity of the
light shone upon the photoconductive surface for reducing
photoreceptor charge.
For a general understanding of the invention, an
exemplary copier/reproduction machine in which .he invention
may be incorporated, is shown in Figure 1. The reproduction
or copying machine, is there designated generally by the
numeral 5.
A document 11 to be copied is placed upon a trans-
parent support platen 16 fixedly arranged in an illumination
assembly, generally indicated by the reference numeral 10,
positioned at the left end of the machine 5. Light rays from
an illumination system are flashed upon the document to pro-
duce image rays corresponding to the information~areas. The
_ _ __image rays are projected by means of an optical system onto
the photosensitive surface of a xerographic plate in the form
of a flexible photoconductive belt 12 arranged on a belt
assembly, generally indicated by the reference numeral 9.
The belt 12 comprises a photoconductive layer 15 of
selenium which is the light receiving surface and imaging
medium for the apparatus, on a conductiVe backing. The sur-
face of the photoconductive belt is made photosensitive by
a previous step of uniformly charging the same by means of a
corona generating device 13, which is connected to a power
source 68.
The belt ls journaled for continuous movement upon
three rollers 20, 21 and 22 positioned with their axis in
parrallel. The photoconductlve belt assembly 9 is slidably
mounted upon two support shafts 23 and 24, with the roller
22 rotatably supported on the sha,~. 23 which is secured to
the frame of the apparatus and is rotatably driven by a suit-
able motor and drive assembly (not shown) in the direction of
the arrow at a constant rate. During exposure of the belt 12,
the reflected light image of such original document positioned
on the platen is flashed on the surface 15 of belt 12 to pro-
duce an electrostatic latent image thereon at exposure station
27.
The electrostatic latent image on the moving belt
12 passes through a developing station 28 in which there is
positioned a magnetic brush developing apparatus, generally
indicated by the reference numeral 30, and which provides
development of the electrostatic image by means of multiple
brushes as the same moves through the development zone.
The developed electrostatic image is carried on
belt 12 to transfer station 29 whereat a sheet 6 of copy
paper is fed between transfer roller 7 and belt 12 at a speed
in synchronism with the moving belt to transfer the developed
image to sheet 6 without blurring. A sheet transport mechanism,
generally indicated at 17, brings sheets 6 from paper supply
tray 18 or 18' to the transfer station 29 at the proper time
to match the arrival of the sheet with the arrival of the
developed image on belt 12.
Following transfer, the image bearing sheet is
separated from belt 12 and conveyed to a fuser assembly, gen-
erally indicated by the reference numeral l9, wherein the
developed powder image on the sheet is permanently affixed
thereto. ~fter fusing, the finished copy is discharged from
the apparatus into a suitable collector, i.e. tray 8. Residual
toner particles and any other residue left on belt 12 are
removed by brush 26 at cleaning station 25. Further details
regarding the structure of the belt assembly 9 and its rela-
tionship with the machine and support therefor may be found
_5_ . , . '
s, ~7
in U. S. Patent No. 3,730,623 issued May 1, 1973 and assigned
to the same assignee.
As will be understood by those skilled in the art,
development of the latent electrostatic image formed on belt
12 is dependent upon the voltage differential between the light
image and the developing means. This voltage differential,
which may be described as a xerographic development field,
serves to attract toner to the latent electrostatic image
in accordance with the image outline and density requirements
to faithfully reproduce the original being copied.
Referring now to Figures 2 and 3 of the drawings,
the charge control 50 of the present invention preferably includes
both a supplemental charging section 52 and a charge reducing
section 54. As will appear, supplemental charging section 52
is utilized to automatically increase the charge level on the
photoconductive surface 15 of belt 12 where the original charge
level provided by the corona generating device 13 is found to
be too low while charge reducing section 54 is utilized to auto-
matically reduce the charge on surface 15 where the original
charge is found to be too high. In this way an optimized charge
is provided on the photoconductive surface 15.
Supplemental charging section 52 includes a corona
discharge wire 61 and adjoining shield 63. Shield 63 is formed
from metal and in the arrangement shown, has, when viewed in
cross-section, a ~enerally inverted U-shape with top wall 65,
depending side walls 66, 67, and end walls 62, 64. Corona wlre
61 is strung between end walls 62, 64 of shield 63. To prevent
shorting of corotron wire 61 to metal shield 63, suitable
electrical insulators 69 are provided between wire 61 and the
ends 62, 64 of shield 63. It will be understood that where
corotron shield is composed of an electrical insulating material
such as plastic, insulators 69 and, as will appear conductive
layer 80, may be dispensed ~Jith.
Charge reducing section 54 of charge control device 50
includes a generally rectangular electro-luminescent panel 70,
the length and width dimensions of which are equal to or slightly
less than the corresponding length and width dimensions of shield
63, mounted within the shield interior on the inside surface of
the shield upper wall 65. One suitable electro-luminescent
panel is type 94-0150-1 manufactured by Grimes Manufacturing Co.,
Urbana, Ohio.
To prevent build-up of static electrical charges on
the electro-luminescent panel 70, the exposed or lower surface
71 of panel 70 is covered with a clear conductive material,
preferably a thin layer 80 of NESA glass. Conductive layer 80
is electrically coupled to shield 63 through contact with side
walls 66, 67 of shield 63. It will be understood that where
shield 63 is formed from a non-conductive material, i.e. plastic
conductive layer 80 may be dispensed with.
A preset reference signal, which appears in lead 91,
is developed from a suitable d.c. voltage source shown in
exemplary fashion as battery llO. Battery llO is coupled across
voltage level controller 90, shown as a potentiometer serving to
regulate the voltage level of the reference signal in lead 91 in
accordance with the setting thereof to provide a predet reference
signal. The reEerence signal in lead 91 is applied via resistor 92
to one input of voltage comparator 93.
Powe:r input to cotona discharge wire 61 of supplemental
charging section 52 and electro-luminescent panel 70 of charge
reducing section 54 is derived from viariable d.c. power source
7~, the output of which to either section 52 or section 54 is
regulated in accordance with charge conditions of the photo-
sensitive surface 15 of belt 12 as sensed by a d.c. type electro-
meter 100`. Probe 102 of electrometer 100 is mo~nted in machine
5 in predetermined spaced relationship to .he photoconductive
surrace 15 as will be understood by those skilled in the art.
~n a preferred embodiment, probe 102 is disposed downstream of
the charge control device 50 but before the developing station 30.
Other probe locations, however, may be contemplated.
The d.c. signal output from probe 102, representative
of the charge on the photoconductive surface 15, is inputted
via lead 103 to the main body 106 of of electrometer 100 wherein
the signal is suitably amplified. The signal output of electro-
meter 100 appears in lead 9~ to d.c. power source 74. One type
o' d.c. electrometer that can be employed in both embodiments of
Figures 3 and 4 are described U.S. Patent 3,852,668 issued on
December 3, 1974 in the name of James M. Hardenbrook et al.
Other electxometers including those of the a.c. type may instead
be contemplated.
Power source i4 includes a voltage comparator 93,
which may comprise any suitable circuit effective to compare
voltage levels inpplied thereto and generate an analog signal
proportional to the difference between the input signal voltages.
In the exemplary ci-cuit illustrated, comparator 93 comprises an
operational amplifier, operative to compare the preset control
signal from controller 90 with the signal output of electrometer 100,
tha latter being reprasentative of the charge level on the photo-
conductive surface 15 of belt 12. Variable resistance controls the
gain of comparator 93.
The signal output of comparator 93 is applied via lead
96 to the base electrodes of P~P transistor 97 and ~P~ transistor
98 respactively. The collector of transistor 97 is connected
.`~7
by lead 99 to electro-luminescent panel 70. Lead 101 couples
the emitter of transistor 97 to a suitable source of positive
potential, represented herein by battery 112.
Lead 104 couples the collector of transistor 98 with
the input side of a conventional d.c. to d.c. converter 105. The
output of converter 105, which is used to drive charging section
52 of charge control device 50, is connected by lead 107 with
corona generating wire 61. Lead 108 couples the emitter of
transistor 98 with a suitable source of negative potential
represented herein by battery 109.
D.C. to d.c. converter 105 serves to amplify the
relatively low power variable signal output of transistor 98
to the relatively high power level required to drive charging
section 52. Any suitable commereially available d.e. to d.c.
converter having the neeessary operating speeifieations may be
used for this purpose.
In operation, the optimum eharge level of the photocon-
ductive surface 15 of belt 12 is determined, and the signal out-
put of electrometer 100 corresponding to the optimum charge level
is matched with the reference signal in lead 91. This may be
effected by adjusting the setting of controller 90 until the
ma~ching signal potential is reached. So long as the charge
level on the photoconductive surface 15 remains at the level
desired, the signal inputs in leads 91, 94 to comparator 93
match, and the signal output from comparator ~3 to lead 96
holds transistors 97, 98 in a blocking state. As a result, both
the supplemental charging section 52 and charge reducing section
54 of charge control 50 are inoperative.
Should the charge level on the photoconductive surface
15 rise above the level desired, as represented by the setting
_g_
o~ controller 90, the vol~ag~e potential of the output si~nal
from electrometer 100 in lead 9~ rises. Compar~tor 93 responds
by generating a positive signal output, the potential of which
is proportional to the difference in potential ~etween the input
signals to comparator 93 in leads 91, 9~. Transistor 97 feeds a
proportional amount of power to electro-luminescent panel 70 to
turn panel 70 on and illuminate the photoconductive surface with
an intensity proportional to the streng-th of the signal output
from comparator 93. Light from panel 70 reduces the charge
level on the photoconductive surface 15 to bring the charge
level back to the optimum level desired.
Should the charge level on the photoconductive surface
15 fall below the optimum level desired, the voltage potential
of the output signal from electrometer 100 in lead 94 falls.
Comparator 93 responds by generating a negative signal output,
the potential of which is proportional to the difference in
potential between the signal inputs to comparator 93 in leads
91, 94. Transistor 98 feeds a proportional amount of power,
which is raised to the requisite power level necessary by d.c.
to d.c. converter, to corona discharge wire 61 of supplemental
charging section 52. The resulting corona emissions from w~re
61 add to or supplement the charge previously applied to the
photoconductive surface 15 by corona generating device 13 to
bring the charge level back to the optimum level desired.
While supplemental charging section 52 and charge
reducing section 54 are combined herein to provide a unitary
charge control 50, it will be understood -that supplemental
charging sect:ion 52 and charge reducing section 54 may comprise
separate and discrete entities. In Figure 4, charge reducing
section 54 has been combined with the primary corona generation
device 13 thereby el-minating the need for a separate charge
control 50 as depicted in Figure 1.
--10--
- The corona generaling device 13 includes the corona
discharge wire ol and shield 63. Shield 63 is formed from metal
and in the arrangement shown, has ~hen viewed in cross-section,
a generally inverted U-shape with top wall 65, depending side walls
66, o7, and e~d walls 62, 64. Corona wire 51, which is electrically
coupled to a suitable d.c. power source, represented in exemplary
rashion by battery 68, is strung between end walls 62,6A of shield
63, as shown in Figure 2 shorting of corotron wire 61 to metal
shield 63, suitable electrical insulators 69 would be provided
between wire 61 and the ends 62,6~ of shield 63.
As in ~he case o' the Figure 3 embodiment, charge
control section 54 includes a generally rectangular electro-
luminescent panel 70, the length and width dimensions of which
are equal to or slightly less than the corresponding length and
width dimensions o shield 63, mounted within the shield interior
on the inside surface of the shield upper wall 65. Also, panel
70 is electrically connected to a variable power supply 74 by
lead 98.
To prevent build-up of static electrical charges on
the electro-luminescent panel 70, the ex?osed or lower surface
71 of panel 70 is covered with a clear conductive material,
preferably a thin layer 80 of NESA glass. Conductive layer 80
is electrically coupled to shield 63 through contact with side
walls 66, 67 of shield 63.
Power supply 7a in this e~bodiment is similar to that of
Figure 3 and therefore, like parts have the same referen~e numerals.
A suitable cource of d.c control voltage is provided in the forms of
battery 110. Battery 110 is coupled across voltage level controller
90, which is a potentiometer serving to regulate the control voltage
provided to voltage comparator 93 in accordance with the setting
thereof. The output signal of controller 90 in lead 91 thereof,
which serves a a reference potential, if coupled through resistor
92 with one in~)ut of voltage comparator 93.
--11--
Lead 94 couples the other input of comparator 93 with
a device ~hich generates an output signal indicative of the
charge level on the photoconductive sur~ace 15 o~ belt 12
following charging by corona generating ~evice 13. In the
exemplary arrangement sho~, the charge measuring device com-
prises a d.c. t~pe electrometer 100. Probe 102 of electrometer
100 is mounted in machine 5 in predetermined spaced relationship
to the photoconductive surface 15 as will be understood by
those skilled in the art. In a preferred embodiment, probe
102 is disposed downstream of the corona generating device 13,
but before developing station 30.
The d.c. signal output ~rom probe 102, representative
of the charge on the photoconductive surface 15, is connected by
lead 103 to the main body 106 of electrometer 100, w~erein
~he signal is suitably ampliried. The signal from electrometer
100 is provided to the input gate of comparator 93 through lead 94.
Comparator 93 may comprise any suitable circuit
effective to compare voltage levels supplied thereto and gen-
erate an analog signal proportional to the di~ference between
the input signal voltages. In the exemplary circuit illustrated,
comparator 93 comprises an operational amplifier, operative to
compare the signal outputs of controller 90 and electrometer 100,
the latter signal bring representative of the charge level on the
photoconductive surface 15 of belt 12. The signal output of com-
parator 93 is supplied through lead 96 to the bas2 electrode of
control transistor 79. Lead 99 couples the emitter of transistor
to panel 70 while lead 101 couples the collector of transistor 79
to a suitable power source shown here as battery 112. Control trans-
istor 79 regulates the power input to panel 70 in response to the
output signal ~rom comparator 93 to control the level of illumination
of panel 70. Variable resistor 114 controls the gain of comparator
93.
vi~7
During the operational cycle of reproduction machine
5, the photoconductive surface 15 of belt 12 is charged by the
corona generating device 13 and e~posed at e~posure station
27 to the original 11 being copied to produce a latent electro-
static image of original 11 on the surface 15 of belt 12. The
latent electrostatic image so for~ed is carried past developer
station 28 ~;~ereat the image is develped. The developed image
t'nen passes to transfer station 29 where the developed image is
transferred to a sheet 6 of copy paper brought forward from
supply tray 18 or 18' by transport 17 at the proper time so
as to assure registration of the developed image on belt 12 with
the sheet 6. The copy sheet 6 bearing the developed image is
tnereafter transported to fuser 19 where the image is fixed,
following which the final copy is discharged into tray 8.
Electrometer 100 monitors the charge level on the
portion of the photoconductive surface 15 of belt 12 viewed by
probe 102. The signal ouptut of electrometer 100 is fed to
comparator 93 w~ere the signal from electrometer 100 is com-
pared with the preset reference signal from voltage level con-
troller 90. So long as the voltages of the signal inputs to
comparator 93 are substantially identical, LLd~si~LoL 79 ~oes---n~L
conduct and there is no flow of current to panel 70. As a result,
electro-luminescent panel 70 is not illuminated. ~`~~ ~~~~^~~~-~~~~ ~
Where the signal imputs to comparator 93 are unbal-
anced, reflec~ing charging of the photocinductive surface 15
to a level greater than that represented by the reference ~ol-
tage in lead 91, transistor 79 conducts and provides power to
panel 70 in proportion to the voltage level of the signal on
lead 96 being proportional to the difference in.potential between
the signal on lead 91, and the signal on lead 94. The resulting
current flow in lead 99 to the electro-luminescent panel 70 energizes
panel 70 to produce an illumination whose intensity will be pro-
portional to the power supplied thereto. Illumination from panel
-13-
g7
70 reduces the charge on the photoconductive surface 15
or belt 12 in proportion ~o the amount of illumination.
~ hile the charge generating device 13 and charge
control section 54 mav be combined into one unitary device,
they may comprise se~arate discrete entities as is true in
the arrangement sho~ in Figure 5. There, the cha~ge generating
section comprises a corona generator device 13' while the
charge control section comprises a modified version 54' of
the variable illumination device shown in Figure ~.
Referring now to Figure 5, wherein liXe numerals
refer to like parts, electro-luminescent panel 70 is mounted
within a generally inverted U-shaped shield 165, panel 70 being
disposed against the inside face of the shield upper wall 166.
Shield 165 is supported by suitable means (not shown) in transverse
relationship to belt 12 at some convenient point along the
belt run. In the arrangement illustrated, shield 165 is dis-
posed adjacent to and downstream of corona generator 13'.
~ s will appear, panel 70 serves as the source of
illumination with control o~er the amount of light directed
onto the photoconductive surface 15 of belt 12 being effected
by means of liquid crystal 170 in response to the charge con-
ditions of the photoconductive surface. In this embodiment,
the side of electro-luminescent panel 70 facing the photocon-
ductive surface of belt 12 is overlayed with a liquid crystal
170, crystal 170 preferably being sized and conEigured so as
to cover the entire side of panel 70. Suitable light polarizers
168, 169 such as manufactured by Polaroid Corporation under the
trade name Polaroid sheet are disposed between panel 70 and
liquid crystal :L70, and on the side 171 of cr~stal 170 facing the
photoconductive surface 15.
Liquid crystal 170 comprises any suitable liquid
crystal of the so-called field effect type wherein the light
transmissitivity thereof varies in response to the electric
current applied thereof. A liquid crystal suitable for this
purpose iis manufactured by ~amlin, ~nc., Lake ~ills, Wisc.
In the arrange~ent shown, tne light trans~issitlvity
of liauid crystal 170, and hence the amount of light directed
onto the photoconductive surface, is regulated in response to
the charge conditions of the photoconductive surface 15.
The output of variable T ower source 74, which is representa-
tive of the charge level of the photoconductive surface 15
o_ belt 12 as described heretofore, is applied via lead 98
to liquid crystal 170 to control the light transmissitivity thereof.
Panel 70 in this embodiment serves as the licht source wlth a
constant intensity or illumination and is driven from a suit-
able power source such as battery 172 through lead 173. On/off
switch 174 in lead 173 permits panel 70 to be turned off, as during
periods when machine 5 is not in use.
Corona generator device 13, like device 13 of Figure 1,
comprises any suitable d.c., a.c., or a.c./d.c. type corona charg-
ing device as known to those sXilled in the copier arts. In the
arrangement illustrated, the corona generating device 13' includes
a corona emitting wire 83 supported within shield 84 and coupled
to a suitable source of power, e~emplified by battery 85.
In operation, switch 174 is closed to energize electro-
luminescent panel 70 continuously. The amount of light, if any,
transmitted by liquid crystal 170 onto the photoconductive surface
15 is varied in response to the strength of the signal in output
lead 98 of variable power supply 74, which in turn is represen-
tative of the charge level on the photoconductive surface 15.
Where the charge on surface 15 is at the level desired,
the signal in lead 98 to crystal 170 causes molecular turbulence
which renders crystal 170 opaque with the result that light
from panel 70 to the photoconductive surface 15 is partially
or completely b:Locked. T,~here the signal in lead 98 reflects
overcharging o the photoconductive surface 15, molecular re-
orientation of the molecules within crystal 170 proportional
-15-
y
in degree to the signal strength occurs with the result that
crystal 170 transmits a proportlonal amount of light from
panel 70 therethrough onto the photoconductive surface 15.
The light, thus, reduces the charge level on the photoconductive
surface 15 in proportion to the light intensity.
The corona generating device 13' and c~arge control
5A ~ may be combined as a single unlt. In that event, shield
165 would be dis?ensed with and the liquid crystal 170 would
instead be disposed inside shield 8~ of corona generator 13'.
In the event shield 84 is formed from a conductive material, a
conductive transparent layer, such as the conductive layer 80
shown and described in the Figure 4 embodiment, would preferably
be disposed over the polarizer 169 facing the photoconductive
surface 15.
While the light source has been illustrated and
described as comprising an electro-luminescent panel 70, other
suitable light sources who intensity may be varied can be
contemplated.
.. ..
~16-
' ~ ' ' ' ~, ' , :
