Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates generally to an area coverage
sensing apparatus and in particular -to energy control for
flash lamp devices by sensing the density of toner images on
copy sheets produced by a copier/duplicator system.
In the xerographic process used for copier/duplicator
systems, a plate, generally comprising a conductive backing
upon which is placed a photoconductive insulating surface,
is uniformly charged and the photocnductive surface then
exposed to a light image of an original to be reproduced.
`; ~he photoconductive surface is caused to become conductive
under the influence of the light image so as to selectively
dissipate the electrostatic charge found thereon to produce
what is developed by means of a variety of pigmented resin
materials specifically made for thij purpose w~ich are known ~ ;,
in the xerograp~ic art as l'toners". The toner material is
electrostatically attracted to the latent image areas on the
plate in proportion to the charge concentration found thereon.
Areas of high charge concentration become areas of high toner
density while correspondingly low charge image areas become
proportionally less dense~ The developed image is transferred
to a final support material, typically paper, and fixed thereto
to form a permanent record or copy of the original.
Many forms of image fixing techniques are known in
the prior art, the most prevalent of which are vapor fixing,
heat fixing, pressure fixing or combination thereof as de-
scribed in U. S. Patent ~o. 3,539,161. Each of ~hese
techni~ues, b~ itself ox in combination sufer from deficiencies
which make their use impractical or difficult for ~pecific
xerographic applications. In general, it has been difficult
to con~truct an entirely satisfactory heat fuser having a
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short warm up time, high efflciency, and each of control.
further problem associated with heat fusers has been their
tendency to burn or scorch the support material. Pressure
fixing methods whether hot or cold have created problem~
with image offsetting~ resolution, degradation and producing
consistently a good class of fix. On the other hand, vapor
fixing, which typically employs a toxic solvent has proven
commercially unfeasible because of the health haæard involved~
Equipment to sufficiently isolate the fuser from the surrounding
ambient air must by its very nature be complex and costly.
With the advent of new materials and new xerographic
processing techniques, it is now feasible to construct auto-
matic xerographic reproducing apparatus capable of producing
copies at an extremely rapid rate. Radiant flash fusing is
one practical method of image fixing that will lend itself
readily to use in a high speed automatic processor as described
~; in U. S. Patent 3,529,129. The main advantage of the flash
fuser over the other known methods is that the energy, which
is propagated in the form of electromagnetic waves, is in-
stanteously available and requires no inter~ening medium
for its propagation. As can be seen, such apparatus does
not require long warm up periods nor does the energy have
to be transferred through a relatively slow conducti~e or
convective heat transfer mechanism.
Although an extremely rapid transfer of energy
between the source and the receiving body is afforded by
the flash fusing process, a major problem with flash fusing
a~ applied to the xerographic fixing art, has been designing
apparatus which can operate at one power level adequate to
fuse all pos~ible copy prints under varying conditions. This
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has led to several problems including a vast over cons~nption o
power and poor negative latitude.
With the present invention the density of toner
images on an individual copy sheet is sensed via its reflectivity
which is then used to regulate the power supply of a flash lamp
system. -
In accordance with one aspect of this invention
there is provided an improved interface system for controlling ~
~; energy to a flash li~mp in response to toner image density on - ~;
copy sheets comprising: means for advancing copy sheets bearing
toner images along a predetermined path, flash lamp means posi- ; ;
tioned in the path Eor processing said copy sheets, area cover- --
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aye sensing means for sensing the densitv of the toner images ;
on said copy sheets advanced and producing spatially concentra-
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ted optical signals thereof and converting the optical signals
into electrical signals proportional thereof, said area coverage
sensing means including first fiber optic means for transmitting ~ ;~
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illumination to a predetermined location in the copy sheet path `
and second fiber optic means for receiving illumination reflect-
ed from said copy sheets and transmitting reflected illumination
-' to a remote location, first circuit means for receiving and
conditioning said electrical signals, variable energy storage ~ ;
means including at least one chargeable capacitor for driving
said flash lamp means, and second circuit means coupled to said
~, energy storage means for receiving the conditioned signals and ~`
j controlling the input to said energy storage means for driving
said flash lamp means in response to the density of toner images '
on said copy sheets. ~;
In accordance with another aspect of this inven-
- 30 tion there is provided a method of controlling the energy to a
flash lamp in xesponse to toner image density on copy sheets
comprising the steps of optically sensing the density of toner
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images on copy sheets advanced along a path, converting the
optically sensed information .into electrical signals proportional
thereto, and transmitting the signals to uni directional switch-
ing means coupled to a variable energy storage device to control
the input to said energy storage device for driving the flash
lamp in response to the densi.ty of toner images on said copy
sheets.
For a better understanding of the invention as well
as further features thereof, reference is had to the following .
description of the invention to be read in conjunction with the
drawings wherein:
Figure 1 illustrates xerographic reproducing
apparatus incorporating a flash fusing system in accordance with
the invention;
Figure 2 i5 a block diagram of the flash fusing
system of the invention; .~
Figure 3 is a schematic view of the copy reflect- - -
ivity sensing apparatus:
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Figure 4 is a circuit fQr the sensor and signal
conditioner shown by a block in Figure ~;
Figure 5 is a circuit for the energy storage power
supply shown by a block in Figure 2.
For a general understanding of the illustrated
copier/reproduction machine, in which the invention may be
incorporated, reference is had to Figure 1 in which the various
system components for the machine are schematically illustrated.
As in all electrostatic systems such as a xerographic machine
of the type illustrated, a light image of a document to be
reproduced is projected onto the sensitized surface of a
xerographic plate to form an electrostatic latent image
thereon. Thereafter, the latent image is developed with an
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oppositely charged develop m g material to form a xerographic ~ -
powder image, corresponding to the latent image on the plate
surface. The powder image is then alectrostatically transferred
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~, to a upport surface to which it is fused in this case by an
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~- improved flash fusing system whereby the powder images are
caused permanently to be affixed to the support surface as
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will be described more fully hereinafter.
In the illustrated machine, an original D to be
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copied i8 placed upon a transparent support platen P ~ixedly
arranged in an illumination assembly generally indicated by
the re~erence numeral 10, arranged at the left end of the
machine. The image rays are projected by means of an optical
~ystem for exposing the photosensitive surface of a xerographic
plate in t7ne form o~ a flexible photoconductive belt 12 which
can be any ~uitable xerographic material such as selenium or
an insulating surface.
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The photoconductive belt 12 is mounted upon the
frame of the machine and is adapted to move in the direction
of the arrow at a constant rate. Duxing this movement of the
belt, the light image of the origina! on the platen i~ flashed
upon the xerographic surface of the belt. The flash exposure
of the belt surface to the light image discharges the photo-
conductive layer in the areas struck by light, whereby there
remains on the belt a latent electrostatic image in image
configuration corresponding to the light image projected
from the original on the supporting platen. Aq the belt
surface continues its movement, the electrostatic image passes
~hrough a developing station B in which there is positioned
a developer assembly generally indicated by the re~erence
numeral 14. The developer a~sembly 14 deposits developing
material to the upper part of the be:Lt where the material is
directed to cascade down over the upwardly moving inclined
belt in order to provide development of the electrostatic
image. As ~he developing material iS cascaded over the xero-
graphic plate, toner particles in the development material
are deposited on the belt surface to form powder images.
The developed electrostatic image is transported
by the belt to a transfer station C where a sheet of copy
paper is moved at a speed in synchronism with the moving belt
in order to accomplish transfer of the developed image. There
is provided at this station a sheet transport mechanism generally
indicated at 16 adapted to transport sheets of paper from a
paper handling mechanism generally indicated by the reference
numeral 18 to the developed image on the belt at the station C.
After the sheet is stripped from the belt 12, it is
conveyed to an improved flash fuser system generally indicated
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by the reference numeral 20 where the developed and transferred
xerographic powder image on the sheet material is permanently
affixed thereto accordin~ to the present invention a3 will ~e
explained hereinafter. A~ter fusing, the finished copy is
di~charged from the apparatus by a belt conveyor 21 to a
suitable point for collection externally of the apparatus.
Suitable drive means may be arranged to drive the
selenium belt 12 in conjunction with timed flash exposure of
an original to be copied, to effect conveying and cascade of
toner material, to separate and feed sheets of paper and to
transport the same across the transfer station C and to convey
the sheet of paper through the ~lash fuser in timed sequence
to produce copies of the original~
It is believed that the foregoing description is
sufficient for the purpose of this application to show the
general operation of an electrostatic copier using an
ill~ination system constructed in accordance with the in-
vention. For further details ~oncerning the specific con-
struction of the electrostatic copier, reference is made to
U. S. Patent ~o. 3,661,452 issued May 3, 1972 in ~he name of
Hewes et al.
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As best depicted in the block diagram of Figure 2,
the mass of toner images I on individual copy sheets S is
sensed via its reflectivity and an input produced by sensor
and ~ignal conditioner 50 is made to an ener~y storage power
supply 52 w~ich supplies an input to one or more flash lamps
40 of the system 20 to produce the desired power level at
optimum energy or ~lashing the lamps. Power ~upply 52
receives another i~put from D.C. voltage sources 54.
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Referring now to Figure 3 there is shown the
sens ing apparatus for sensing the density o~ toner on a copy
sheet to be fused and producing spatially concentrated optical
signals and converting the optical signals into electrical
signals proportional thereto for input as will be discussed
more fully hereinafter. As the lead edge of the copy sheet 5
bearing llose toner images I comes into view of the sensing
apparatus light originating from a light source 60 is conducted
towards the copy sheet S via an array of fiber optic elements
62 such that a uniform line source of illumination is provided
across the sheet S. A second array of fiber opti~ elements 64
receives the reflected illumination which is transmitted to
a localized area 65 and coupled into a photosensor 70.
Shown in Figure 4 is a circuit for the signal
sensor and signal conditioner 50. Photosensor 70 is a photo-
diode whose current is proportional to the incident illumination.
The output of photosensor 70 is amplified by amplifier 75 and :.
integrated by inkegrator 76 providing an output voltage 80 for
controlling the output of the energy storage power supply 52.
t should ~e understood that the ouput voltage 80 from inte-
grator 76 must be reset a~ter each copy sheet S is ~used by
any suitable circuit.
~ he operation of the system can be best understood
by referring to the diagramatic circuit shown in Figure 5. The
output 80 from sensor and conditioner 50 is fed into voltage
sensor 101 which inhibits transistor switch driver 102. The
transistor switch 102 is al80 inhibited by an input from the
minimum current sen~or 105. The peak current sensor 103
provides an enable voltage to driver 102. The driver 102
provides base drive to transistor switches 107 which switches
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curr~nt through the primary winding of transformex 110. The
phasing of primary with respect to the secondary is such that
when the primary is conducting the secondary is not conducting
and vice versa. The energy from the primary winding is coupled
to the secondary winding when said switch is turned off. The
secondary energy is rectified and stored in capacitor C.
Discharging the capacitor which reduces the load impedance
of the secondary to virtua~ly zero allows the primary to
conduct in the normal manner since the primary is not
coupled to the secondaxy load when said switch is on.
The voltage of capacitor C is sensed by and divided
down by resistors Rl and R2 and inputed into voltage sensor
101. The energy stored on capacitor C is delivered as the
input voltage to flash lamps 40 for Eusing the images I on
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copy sheets S. This input voltage supplied to the flash
fusing lamps 40 results in optimum energy to fuse the toner
, imayes onto the copy sheets.
;, Above is described a new and improved area sensing
apparatus which senses the density of toner images and produces
electrical control signals for input to a flash lamp power
supply. It will be appreciated ~hat the sensing apparatus
of the invention produces a spatially concentrated illumination
reflected from copy sheets at a remote location for subsequent
input and control to a copier/duplicator system.
While the invention has been described with reference
to the structure di closed herein it is not confined to the
details set forth in thi~ application but is intended to
cover such modifications or changes as may come with the purpose
of t,he improvement~ or the scope of the fo~lowing claims.
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